Persisting influence of continental inheritance on early oceanic spreading

Persisting influence of continental inheritance on early oceanic spreading | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Persisting influence of continental inheritance on early oceanic spreading ADRIEN MOULIN, Sigurjon Jonsson This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3862377/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 25 Mar, 2025 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract Formation of new lithosphere at mid-oceanic ridges occurs through magmatic crustal accretion and cooling of the asthenosphere, and is essentially controlled by the spreading-rate, ridge segmentation, and eventual arrival of deeply-sourced hot mantle plumes. Its dependence on long-term inheritance is supposedly weak, except in cases where ridge segmentation is preconditioned by the reactivation of continental weak zones during the rifting phase. Here, we provide the first evidence that pre-rift lithospheric thickness variations constitute another forcing that may transmit influence from past Wilson cycles beyond the stage of continental break-up. This long-term control involves differential redistribution of heat/melt sources along young laterally-confined plume-assisted rifts. This is demonstrated here in the case of the Red Sea from the correlation between on-axis volcano-tectonic patterns, distribution of onshore volcanism, and lithospheric thickness variations of the rifted margins. Earth and environmental sciences/Solid earth sciences/Geodynamics Earth and environmental sciences/Solid earth sciences/Tectonics Earth and environmental sciences/Solid earth sciences/Volcanology Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Where and how continents rift is a long-lasting and still debated question 1 . According to the Wilson cycle theory, the closure and opening of oceans repeatedly occur along persistent zones of weakness, such that passive margins initially develop from inherited suture zones 1 , 2 . An underlying consequence is that along-strike variations in the lithospheric structure and tectonic architecture of plate boundaries (tectonic style, crustal and lithospheric thickness, etc.) are being alternatively passed from one stage of the cycle to the other, and modulate their subsequent evolution 3 , 4 , 5 . In between these two stages, the sensitivity of the oceanic spreading phase to lithospheric inheritance is supposedly weak, as it is accommodated by continuous formation of new lithosphere from the asthenosphere, through cooling and magmatic crustal accretion. Instead, the mode of oceanic spreading is thought to be dominantly controlled by how much of the plate divergence is accommodated magmatically 6 , 7 , which in turn essentially depends on the local thermal structure. Critical parameters in that case include the spreading rate 6 , the subsidiary arrival of hot deeply-sourced mantle plume material at the ridge axis 8 , and the along-strike segmentation of the spreading ridge 9 . It is generally considered that significant contribution from long-term lithospheric inheritance may only exist for the latter of these parameters, for example when rift segmentation develops along pre-existing zones of weakness which later evolve as oceanic transform faults 4 . Numerical models however indicate that lateral spreading of mantle plumes is strongly controlled by the topography of the lithosphere-asthenosphere boundary (LAB) 10 , 11 , 12 , making possible that the early mode of oceanic spreading be modulated by the inherited LAB topography of continental margins through the subridge concentration versus escape of hot plume material. This hypothesis remains so far untested, mainly because it requires detailed information about the mechanisms of accommodation of plate separation during the early stages of sea-floor spreading. At global scale, early oceanic lithosphere is generally old, and hence buried beneath large amounts of post-rift clastic sediments derived from the erosion of the passive margin. The Red Sea represents a somewhat unique prototype in that view, as it meets the basic requirement of a young spreading ridge cutting at high angle across major crustal and lithospheric fabrics, itself inherited from the Proterozoic accretion of distinctive terranes that formed the Arabo-Nubian Shield (ANS) 13 . On the Arabian side of the rift, both the LAB mapped from Sp-receiver functions 14 (Fig. 1 b) and crustal density models derived from combined gravity and seismic data 15 indeed show that the constitutive terranes of the ANS preserve unique lithospheric characters (Fig. 1 b), providing a natural laboratory to evaluate the influence of these inherited fabrics on the mechanisms of early sea-floor spreading. Geological background The NNW-SSE-trending Red Sea Rift developed over the last 23Ma 16 as a result of the ~ 0.39°/Ma counter-clockwise rotation of the Arabia Plate relative to Nubia about a pole located in the southeastern Mediterranean (the pole used in this study is 24.22°E, 31.61°N, yielding opening rates that increase from ~ 7 mm/yr in the NNW to 16 mm/yr in the SSE) 17 , 18 , 19 (Fig. 1 a). Towards the SSW, the Arabia/Nubia plate boundary splays into two branches that isolate the Danakil microplate 18 , 19 , 20 before linking to the Gulf of Aden and Ethiopian rifts to form a rift-rift-rift triple junction (Fig. 1 a). This triple junction is closely associated with the Afar mantle plume 21 , whose initiation preceded rifting and relative to which the Nubia plate moves NW at ~ 15 mm/yr 22 . From the stable ANS to the plate boundary, the Red Sea rift (Fig. 1 a) is composed of 1) a coastal plain bounded by the external rift escarpments and underlain by tilted blocks and their accompanying syn-rift sediments 16 , 2) a smooth offshore shelf marked by a gradually increasing elevation toward the SSE 18 , and whose basement is blanketed by more than 1 km of Miocene evaporites 23 , 24 , 25 , and 3) a discontinuous 15-70-km-wide axial trough, essentially restricted to the Southern and Central Red Sea, where the oceanic crust and its rugged volcano-tectonic sea-floor are exposed except at the so-called “inter-trough zones” occupied by allochtonous salt flows 26 , 27 , 28 , 29 . The weak penetration of geophysical surveys across the Miocene evaporites led to ambiguities about the nature of the offshore shelves 18 . In particular, forward modeling of gravity anomalies and the absence of a clear magnetic signature have led some authors to conclude that the axial trough approximately captures the whole extent of the oceanic lithosphere (proximal OCT end-member: oceanic spreading < 5 Ma and diachronous along axis) 23 , 29 , 30 . Conversely, seismic reflection data and segmentation trails inferred from vertical gravity gradient patterns have been used by others to place the ocean-continent transition (OCT) at the outer edge of the shelves (distal OCT end-member: oceanic spreading ~ 13-14-Ma-old and synchronous) 18 , 31 . Whereas most debate about the recent evolution of the Red Sea Rift has focused on the position of the OCT, little attention has comparatively been paid to the along-axis variability of oceanic spreading mode 27 . Here, we combine GEBCO 2021 (GEBCO Compilation Group, 2021) and high-resolution bathymetry with satellite free air gravity anomalies (see Methods) to characterize the topographic, gravity, and volcano-tectonic signatures of the axial trough North of its intersection with the Danakil microplate (Figs. 2 and 3 ) and identify long- and short-wavelength along-axis gradients. These gradients are then compared to primary characteristics of the continental margin (lithospheric thickness and distribution of volcanism, Fig. 1 b), and integrated into a kinematically-constrained numerical model of plume-assisted rifting. Along-axis topography, gravity, and volcano-tectonic patterns Long-wavelength along-axis topography of the Red Sea Ridge features a relatively stable axial depth of ~ 2000 m.b.s.l. in the Northern and Central Red Sea (N-RS and C-RS labelled on top of Fig. 3 ; reference to specific location of Fig. 3 will be hereafter given in kilometers from the Arabia/Nubia pole, and denoted as K##), followed by a gradual shallowing up to ~ 1100 m.b.s.l. when approaching the Afar plume in the Southern Red Sea (Fig. 3 a). To a first order, variations of the axial Mantle Bouguer Anomaly (MBA; see Methods and Supplementary Fig. 1 for calculation procedure) occur symmetrically to this topographic trend (Fig. 3 a). Superimposed on the long-wavelength topographic signal are short-wavelength undulations characterized by peak-to-peak distances that apparently decrease from ~ 250 km South of K2000 to 60–100 km farther North (Fig. 3 b). The positive anomalies show no clear relation with the inter-trough zones, but instead correlate with large axial volcanoes. The negative anomalies generally correspond to the Red Sea “Deeps” 26 and exhibit a bi-modal distribution with vertical residuals scattering around − 250 m and − 600 m. In general, these anomalies leave no or very little MBA signature (Fig. 3 a and 3 b). The slope distribution of the flanks of the axial trough also displays large lateral variability (Fig. 3 c). Nevertheless, the similarity between NE flank and SW flank distributions clearly indicates that the axial trough is highly symmetric in cross-section. The 5% threshold used in constructing Fig. 3 c is intended to capture the extent of the axial trough (see Methods). Its outer (and so vertical) extension is thus visualized by the shallowest terrains plotted in Fig. 3 c, and shows that the top of the axial trough records a long wavelength topographic signal similar to that of the axial ridge. Antithetic slopes (i.e., opposite to the average flank slope) are locally observed in association with large axial volcanoes NW of K2000 and become widespread farther South (Fig. 3 c). Two ridge segments (Nereus around K1570 and Suakin around K1960, also located in Fig. 1 ) display unusually steep flanks relative to other sections (Fig. 3 c), and correlate with the two most negative anomalies (~-600m) of residual topography evidenced in Fig. 3 b. Both flanks of the axial trough are also characterized by a similar pattern of normal faulting (Fig. 3 d), which again attests to the symmetric nature of the spreading centers. In general, fault spacing and fault offset apparently increase away from the axial volcanic ridge, which might reflect a resolution and/or preservation bias (see Methods). As for the topographic analysis, the Nereus and Suakin segments exhibit a distinctive pattern, with wider fault spacing and larger fault offsets (Fig. 3 d and 4 ). The maximum fault offset along most of the axial trough is around 600–700 m, but increases to ~ 1300 m at the Nereus and Suakin segments. The magmatic contribution to plate opening (M: sense of (ref. 6)) determined from this faulting pattern (Methods) displays a very subtle decrease from SSE to NNW (~ 0.92 to ~ 0.85), which locally becomes much stronger at the Nereus and Suakin segments (Fig. 3 d). The analysis of the sea-floor morphology is hampered by both the variable width of the stripe covered by high-resolution bathymetry, and the presence of large portions of terrains occupied by allochtonous evaporites 26 (Fig. 2 ). Since the maximum possible proportion of volcanic terrains includes areas that are unclassified in Fig. 3 f, it is visualized from this Figure as the sum of the red-tone envelopes (see Methods). Accordingly, the Nereus and Suakin segments appear as the most magma-poor ridge segments, with less than 20% of volcanic sea-floor. Although topographic, tectonic, and volcanic metrics vary continuously along the Red Sea axial trough, the Nereus and Suakin segments appear to share prominent anomalies, characterized by a deeper less volcanic spreading ridge flanked by more spaced larger displacement normal faults. These “anomalous segments” occur along the less oblique and less segmented sections of the Red Sea Ridge (Fig. 3 e). On the other hand, they seem to align with major geophysical and geological structures of the Arabian margin. In particular, Nereus and Suakin occur next to the Lunayyir and Tufail onshore volcanic fields (located in Fig. 1 b), which have the largest seaward extension at the scale of the entire Red Sea (Fig. 3 g), and are markedly younger (last ~ 1 Ma and last ~ 3.5 Ma 32 , 33 compared to last ~ 12 Ma). They also occur next to the Proterozoic Hijaz and Asir terranes of the Arabian margin 13 , whose bounding suture zones are intimately associated with strong density variations at Moho depth inferred from the joint inversion of seismic and gravity data 15 , and strong gradients in lithospheric thickness as mapped from Sp-receiver functions 14 (Fig. 1 b). In between, the Jeddah terrane exhibits a denser crust 15 and thicker lithosphere (Fig. 1 b). Variability of oceanic spreading mode Thermo-mechanical models of spreading ridges predict that the fraction of plate separation accommodated magmatically (M) exerts a primary control on the pattern of normal faulting, such that increasing M will be recorded on the sea-floor by smaller and less spaced normal fault scarps 6 , 7 . It is worth noting that an accurate estimation of M from bathymetry data requires tectonic displacements to be readily reflected in the sea-floor topography. It is known that this assumption may become unverified when M becomes so little that spreading switches to a detachment mode 34 . In that case, the progressive flexure of detachment faults will lead tectonic displacements to be poorly reflected in the bathymetry 35 , 36 . The sea-floor topography of the Red Sea axial trough documented above and by (ref. 4 and 5) however lacks typical characteristics of a detachment mode of spreading, such as domal corrugated surfaces, across-ridge topographic asymmetry, or gently dipping fault surfaces 1 , 2 , 6 (Figs. 3 and 4 ). Instead, a negative relation between the slope of the axial trough flanks and the proportion of volcanic terrains seems to be the general rule along the Red Sea axis (Fig. 3 c and 3 f). This is at odds with the gentler scarps that would be otherwise expected along the less volcanic segments if spreading switched to a detachment mode. More generally, there is no avolcanic segment along the Red Sea Ridge (at least where the basement is exposed) despite the slow- to ultra-slow opening. These observations support the estimation of M from observed normal fault scarps, as well as its relevance for tracking lateral variations of the magmatic contribution along the Red Sea Ridge. Lateral variations of the faulting pattern, as encapsulated into M, display two superposed signals. A subtle long-wavelength decrease of M (from ~ 0.92 to ~ 0.85) is observed towards the NNW, except around K1700 where it increases along with the apparent magma focusing signed by the large Hatiba Mons volcano 27 (see the large positive anomaly around K1700 in Fig. 3 b). Superposed onto this signal are larger drops near the Nereus and Suakin segments (M ~ 0.3–0.4) (Fig. 3 d). These latter are also accompanied by a local doubling of the maximum fault offset (passing from an average of 600–700 m to ~ 1300 m), that goes along with a decrease of the number of overlapping faults (Fig. 3 d). These two signals point to a slight regional northward decrease of the proportion of plate separation accommodated magmatically, and a more pronounced local decrease at the Suakin and Nereus segments. This interpretation is consistent with the locally lower proportion of exposed volcanic sea-floor (Fig. 3 f). On the other hand, the few high-resolution bathymetric data available SE of K2000 (Fig. 2 ) show that the axial volcanic ridges are generally wider and more continuous than farther NNW 26 , 27 . Flank antithetic-slopes, interpreted as large tectonically-splitted volcanoes, also become more abundant along this section (Fig. 3 c), which might be indicative of a magmatically more robust character of the spreading ridge. The data therefore show that plate opening is less and less accommodated magmatically when moving towards the NNW, and that this trend is locally amplified at the Suakin and Nereus segments. Whereas the regional trend could easily be explained by a combination of decreasing spreading-rate and increasing distance from the Afar plume towards the NW (Fig. 1 a and 3 ), the anomalous character of the Suakin and Nereus segments appears more enigmatic. In particular, there is no evidence that the local decrease of M is controlled by the segmentation of the ridge (Fig. 3 ), as observed along other slow-spreading ridges 9 . Instead, the Suakin and Nereus segments are located along the less oblique and less segmented sections of the Red Sea Ridge (Fig. 3 e). Moreover, along-axis variations of the MBA surprisingly show an absence of typical bull-eye patterns centered on segment centers 35 , 38 . The MBA also gradually increases from the Suakin segment towards the SSE (Fig. 3 a), which is contrary to what would be expected from an increasing crustal thickness. In general, MBA varies symmetrically with the mean axial depth at long wavelengths (Fig. 3 a), which suggests that the axial ridge is not isostatically compensated. These observations converge to suggest that the expected gravity signature is hidden by a dynamic topographic support, as proposed for example by (ref. 37) along the Reykjanes Ridge. Differential focusing of plume-related heat by the thickness of the marginal lithosphere Lateral spreading of the hot and buoyant Afar plume into the laterally-confined Red Sea Rift has been already documented from the 4 He/ 3 He signature of axial basalts 39 and the density structure of the upper-mantle beneath the Red Sea Ridge 15 , and thus constitutes a natural candidate for this dynamic support (Fig. 1 a). We think it constitutes the primary cause of the shallow axial depth of the Southern Red Sea, but also of the western termination of the Gulf of Aden (Fig. 1 a). Although it does not exclude the hypothesis of a flexural lifting induced by enhanced erosion of the Arabian margin as recently advocated by (ref. 40), this latter should translate into an ENE-WSW cross-sectional bathymetric asymmetry, which is not specifically observed (Fig. 1 a). We suggest that the narrowness of the Red Sea basin is the key condition for focusing buoyant plume material beneath the spreading ridge, and that this condition exerts primary thermal and gravitational controls on the regional trend observed in Fig. 3 . Accordingly, we argue that the anomalous character of the Nereus and Suakin segments most likely records a locally decreased focusing. Specifically, we propose that the spatial correspondence between these two segments, the onshore Lunayyir and Tufail volcanic fields, and the shallower LAB of the Hijaz and Asir terranes (Fig. 1 b and 3 ) is best explained by an outboard deflection of the heat source where it becomes less laterally confined due to shallowing of the marginal lithosphere. This is demonstrated using a modified version of the numerical model of (ref. 41), which is appropriate to track the effect of LAB topography variations on the lateral spreading of low-density ponded material (see Methods). Our simulations are kinematically constrained to fit with both the rotational opening and lithospheric thinning of the Red Sea and Gulf of Aden, and the coeval motion of the Afar hotspot relative to the lithospheric plates, and account for the shallower pre-rift LAB of the Hijaz and Asir terranes in the form of two rift-oblique sub-lithospheric channels (Fig. 5 ) (see Methods). These simulations show that channeling of plume material beneath the tectonically thinned rift is accompanied at the intersections with these sub-lithospheric channels by the development of on-axis plume thickness anomalies and outboard viscous fingering during the continental rifting phase (Fig. 5 a and S3). Following the onset of oceanic spreading, the on-axis anomalies are dissipated through along-axis diverging flow of the buoyant material and continuing viscous fingering towards the continental margins (Fig. 5 b). These primary features account for the coeval development of comparatively less magmatic segments at Nereus and Suakin and onshore volcanism of Lunayyir and Tufail. We also emphasize that the only uplifted Arabian marine terraces are precisely located at the suspected onshore outlet of the Nereus/Lunayyir deflected flow along a 20-km-long coast-line section (Supplementary Fig. 2), which might consistently indicate dynamic uplift. The simulation shown in Fig. 5 prescribes a synchronous onset of oceanic spreading (see Methods) consistent with the distal OCT end-member 18 , 31 , and for which the on-axis divergence of plume material lasts ~ 1 Ma. Sensitivity tests show that models prescribing a northward propagating onset of spreading (in line with the proximal OCT end-member 42 ) differ only in terms of the response time, with the dissipation of the on-axis anomaly taking up to ~ 8 Ma (Supplementary Fig. 3). We therefore suggest that additional chronologic constraints on the proximal onshore volcanism might provide indirect insights about the rhythm of propagation of sea-floor spreading in the Red Sea. On the other hand, onshore volcanism is highly asymmetric at rift scale (Fig. 1 ). In the context of our model, this could be explained if syn-rift lithospheric thinning was also asymmetric as previously proposed by (ref. 43), and/or if the pre-rift lithospheric structure of the Hijaz and Asir terranes on the Nubian margin (for now poorly constrained 14 , 15 ) lacked the shallow LAB features seen on the Arabian conjugate. The mechanism advocated here is similar to that proposed by (ref. 12) to account for the distribution of syn-rift volcanism in Iceland and the North Atlantic region. Our study shows from in-situ observations that this mechanism may persist beyond the stage of continental break-up, and points to the decisive role played by pre-rift lithospheric inheritance on the mode of early sea-floor spreading in plume-assisted rift settings. By differentially focusing thermal lithospheric thinning, this mechanism might also determine the final geometry of the associated oceanic basins. Methods Analyzed datasets and data projection To map the seafloor, we used high-resolution multibeam bathymetric data sets, where available 26 , 28 , and the 15-arc-second GEBCO 2021 data set (GEBCO Compilation Group, 2021). The analyzed metrics are plotted in Fig. 3 against the distance from the Arabia/Nubia rotation pole, the inversion of which yielding similar results over geological (post-5Ma) and decadal (GPS) timescales 17 , 19 . This projection allows the influence of the spreading rate to be easily tracked (spreading rate is proportional to the distance from the rotation pole) and is a prerequisite for the calculation of the magmatic contribution (M), estimation of cross-axis symmetry, and calculation of cumulative fault offsets. Given the average linearity of the Red Sea and the small magnitude of transform or non-transform offsets, this choice does not affect the evaluation of Afar plume influence. Fault offsets and magmatic contribution We measured fault offsets using an approach similar to that employed by (ref. 47 and 48) along the Kenya rift. For each fault, both the footwall and corresponding hangingwall cut-offs were mapped from the bathymetric surface. We then extracted (x,y,z) coordinates along the cut-off lines and converted (x,y) into rotation-pole-centered coordinates (RPC system). Fault offsets were finally quantified by associating each point of the footwall cut-off to its hanging-wall counter-part (defined as the closest point in terms of co-latitude in the RPC system, hereafter referred to as θ RPCS ), and computing the vertical separation between them. We ascribed an ordering index to each fault (incrementally increasing from 1 away from the ridge axis) using a θ RPCS scanning window of 0.005° (~ 555m) (i.e., the ordering of a given fault is k if there are (k-1) faults closest to the ridge axis within an along-axis distance of 0.005°). We then computed the cumulative offset of fault k as the summed fault offsets of faults 1 to k. The selected width of the scanning window was set to a value slightly higher than the grid cells to ensure that any fault crossing the window is effectively captured. In practice, each fault was thus sampled once or twice (the averaged was taken in the latter case). Given the low resolution of the GEBCO grid, it is possible that some fault scarps mapped outside the coverage of high-resolution bathymetric data (Fig. 2 ) are actually composed of several closely stacked scarps that cannot be discriminated individually within the available resolution. This might account for the apparent increase in fault spacing away from the ridge axis (Fig. 3 d). Fault offsets determined from GEBCO data should thus be considered as maximum values. However, the maximum fault offsets determined along the Suakin and Nereus segments were all quantified from high-resolution bathymetric data, such that this potential does not impact the interpretation of the present study. We computed the magmatic contribution (M) as follows. The cumulative offset recorded by the fault farthest from the ridge axis was extracted using the same scanning window, and converted into divergence (D obs ) by assuming a uniform fault dip of 60°. For each of these cumulative fault offsets, the model opening (D mod ) was calculated as the distance of that fault from the ridge axis along the corresponding Arabia/Nubia small circle (D mod = [λ RPCS(fault) -λ RPCS(axis) ]*R*cos(π/2-θ RPCS ), where λ RPCS is the longitude in the RPC system and R is the Earth’s radius). M was then calculated as 1-D obs /D mod . Terrains We classified terrain types into 4 categories using a resolution of 50 m: unclassified (lack of high-resolution bathymetric data), volcanic (hummocky terrains, and (eventually splitted) volcanic edifices), sedimented (low gradient and low internal relief surfaces, as well as non-volcanic fault scarps), and salt-covered (no constraint on whether salt seals volcanic or sedimented terrains). We analyzed the terrain type distribution within the post-0.7Ma axis-centered stripe. The use of a synchronous stripe allows removing marine sedimentation effects (the proportion of volcanic terrains classified as sedimented terrains because of burial by marine sediments should be the same within a synchronous stripe, provided that sedimentation rate is invariant along axis). The choice of the 0.7 Ma isochron was constrained by the availability of high-resolution bathymetric data from which terrains can be classified (compromise between maximizing the covered area and minimizing the amount of unclassified terrains). Offshore volcanic fields The distribution of offshore volcanic fields was taken from (ref. 44). For the fields closest to the Red Sea, we carefully removed the lava tongues that grade down along the rift escarpment, as they would artificially bias the results shown in Fig. 3 g. This essentially concerned the lava flows that were channeled from the Rahat volcanic field (broadly coinciding with the Jeddah terrane in Fig. 1 b) along SW-directed valleys, and are now preserved as interfluves 44 . The restoration of the volcanic fields to 13 Ma (Fig. 3 g) configuration was performed by assuming they remained part of rigid Arabia over the entire time period. Axial depth filtering and residual topography We extracted the (x,y,z) coordinates of exposed oceanic crust within 3 km from the mapped axis from the bathymetric grid. We then calculated the averaged axial depth over a 0.02°-wide (~ 2.2km) sliding window using sliding increments of 0.01°. We then applied a Savitsky-Golay filter to the data in order to obtain the long-wavelength undulation of the axial depth. To do so, we used the ‘sgolay’ method of the Matlab function ‘smooth’ to fit the data by a polynomial of degree 6 across a span of θ RPCS = 0.7°. The residual topography was then calculated as the difference between filtered depth and observed depth, to highlight local bathymetric perturbations. The topographic grid around the Suakin segment was also processed specifically to depict the elevation above the mean axial depth in 3D (Fig. 4 ). The procedure was as follows: 1) we extracted the bathymetric data located less than 2 km away from the mapped axial volcanic ridge, 2) we calculated the mean axial depth using a 1-km-wide scanning window, 3) we interpolated the mean axial depth as a function of θ RPCS , and 4) we calculated the mean axial depth for every cell of the initial grid using this interpolant. Flank slope We smoothed the bathymetric grid using a 2D gaussian-weighted 10 km low-pass filter, and used it to compute the first derivative of topography (slope) in the average predicted direction of extension. We applied a slope cut-off of 5% to the resulting data, a value appropriate to discriminate between the axial trough and the nearby offshore shelves. Mantle Bouguer Anomaly The Mantle Bouguer Anomaly (MBA) is widely used to evaluate sources of gravity variations at mid-ocean ridges, and involves the removal of seafloor and Moho gravity effects from the free-air anomaly 37 . As MBA calculations usually assume a constant crustal thickness, MBA anomalies are often used to detect possible crustal thickness variations 37 , 38 . We calculated the MBA using the GEBCO global bathymetric grid, and the satellite-derived free air gravity anomaly grid, version 30.1 46 . The bathymetric grid was re-gridded at the same resolution as the gravity data (3.5 km) before carrying out the calculation. Sediment grids were prepared as follows. The allochtonous salt flows that locally bury the axial trough were assumed to linearly thicken from zero to a range of realistic values as a linear function of the distance from the flow edges. The preferred maximum thickness of intra-trough salt was set to 500 m following (ref. 26), but we carried out alternative calculations using maximum thicknesses of 250 m and 1000 m (the corresponding sediment thickness maps are provided in Supplementary Fig. 1). On the other hand, salt thickness is poorly constrained outside the axial trough, which is why we have restricted the discussion of the MBA to the axial region. Nevertheless, we have assumed that axis-normal geometry of the salt layer is equivalent to a ~ 100-km-long lens that reaches a maximum thickness of 2000 m halfway, and thins towards both the continental margin and the axial trough, following interpretative seismic sections of (ref. 18) (Supplementary Fig. 1). Calculations carried out with different geometries leaves the axial MBA unchanged however. Data processing and gravity calculation was carried out using GMT software version 6.3.0 49 , and using densities of 1030 kg/m 3 (seawater), 2100 kg/m 3 (sediment), 2730 kg/m 3 (crust), and 3330 kg/m 3 (mantle) (detailed procedure described in (ref. 37)). Plume spreading Modeling The plume spreading models were conducted using a modified version of the code presented in (ref. 41). This code is particularly adapted to simulate in a simple way the influence of topographic variations of the LAB on the lateral sub-lithospheric propagation of buoyant plume material 50 . Our model is a 4600 km × 4600 km grid, with cells of 60 km. Each node of the 2D grid is composed of 3 layers (lithosphere, plume material, and normal asthenosphere) of uniform density and viscosity. Employed viscosities are 10 19 Pa⋅s for the asthenosphere and 10 18 Pa⋅s for the plume material, and the density contrast between plume and asthenosphere is set to 20 kg/m 3 . Plume material is sourced at the 5 central nodes, with a flux appropriate (given the employed viscosities and density contrast) for it to spread up to the model Northern Red Sea at the end of the simulations. Flux is kept constant during the pre-rift and continental rifting phases, and is ceased at the onset of the oceanic spreading phase to better evaluate the influence of LAB topographic fabrics. Flow of plume material is driven by plate tectonics drag (V drag caused by motion of the overlying lithosphere), buoyancy (V B caused by lateral variations of the base of the plume material), and pressure gradients (V press caused by the excess pressure developed from local divergence/convergence of material). Analytical solutions of the shear traction terms (see governing equations in (ref. 41)) are found locally by assuming that V drag is equal to the plate velocity at the LAB, that V B and V press are equal to zero at the LAB, and that the three components are all zero at the base of the asthenosphere. Excess pressure is updated at each time step by solving a system of linear equations using the conjugate gradient method. Like in the model presented by (ref. 41), most of the flow in our models is driven by the V B component. Separated from this kinematic step, each time increment contains a thermal step where heat exchanges occur between the three layers, and allow further thickness variations. Isostatic and dynamic adjustments of the base of the lithosphere and plume material are also explicitly treated, whereas the base of the asthenosphere is kept at 230 km depth. The lithosphere is imposed to move at a background rate of 15 mm/yr to the NW relative to the source of plume material, in accordance with reconstructions of the Afar plume track of (ref. 22). At 16 Ma in our model, a rifting-related component simulating the rotation of Arabia relative to Nubia is added to this background plate kinematics. We did not simulate the Somalia Plate, so the opening of the Red Sea and Gulf of Aden are both governed by a unique rotation pole. Initial lithospheric thickness is set to 140 km, except along two 150-km-wide sub-lithospheric channel trending obliquely relative to the rift axis. Initial lithospheric thickness is decreased from 140 km at the edges of these channels to 90 km at their axes in a pattern governed by the error function. Rifting-induced variations in lithospheric thickness are calculated by assuming that the zone of active extension keeps a fixed width of 160 km and remains centered on the rift axis (which simulates the progressive inward migration of the deformation), and that instantaneous lithospheric thinning is homogeneous within this zone. For the model presented in Fig. 5 , the phase of oceanic spreading is initiated at 26 Ma, 10Ma after the onset of continental rifting, and is assumed to be synchronous along the entire length of the rift (consistent with the distal OCT end-member of (ref. 18 and 31)). Declarations Acknowledgements This work benefited from discussion with Mathilde Cannat and Ran Issachar. Margherita Fittipaldi and Matthieu Ribot are acknowledged for their contribution in mapping the coral marine terraces. This research was supported by King Abdullah University of Science and Technology (KAUST) under the Award Number OSR-CRG2019-4076. Author contributions: A.M. designed the study, performed the data analysis and modeling, wrote the first draft and prepared the Figures. S.J. provided guidance with the Methods and edited the manuscript. S.J. acquired the funding and resources. Data availability statement Global bathymetry and gravity datasets can be accessed from the GEBCO (https://www.gebco.net/data_and_products/gridded_bathymetry_data/) and University of San Diego (https://topex.ucsd.edu/grav_outreach/#grid) websites. High-resolution bathymetry data are from Mitchell et al. (2010) (https://doi.org/10.1130/B26518.1) and Augustin et al. (2014) (https://doi.org/10.1016/j.epsl.2014.03.047). Competing Interests Statement The authors declare no competing interests. References Brune, S., Kolawole, F., Olive, J. A., Stamps, D. S., Buck, W. R., Buiter, S. J., … Shillington, D. J. (2023). 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Petrunin, A. G., Kaban, M. K., El Khrepy, S., & Al-Arifi, N. (2020). Mantle convection patterns reveal the mechanism of the Red Sea rifting. Tectonics, 39 (2), e2019TC005829. de Gouveia, S. V., Besse, J., de Lamotte, D. F., Greff-Lefftz, M., Lescanne, M., Gueydan, F., & Leparmentier, F. (2018). Evidence of hotspot paths below Arabia and the Horn of Africa and consequences on the Red Sea opening. Earth and Planetary Science Letters, 487 , 210–220. Bosworth, W., & Burke, K. (2005). Evolution of the Red Sea—Gulf of Aden rift system. Mitchell, N. C., Ligi, M., Feldens, P., & Hübscher, C. (2017). Deformation of a young salt giant: regional topography of the Red Sea Miocene evaporites. Basin Research, 29 , 352–369. Mitchell, N. C., Shi, W., Izzeldin, A. Y., & Stewart, I. C. (2021). Reconstructing the level of the central Red Sea evaporites at the end of the Miocene. Basin Research, 33 (2), 1266–1292. Augustin, N., Devey, C. W., Van der Zwan, F. M., Feldens, P., Tominaga, M., Bantan, R. A., & Kwasnitschka, T. (2014). The rifting to spreading transition in the Red Sea. Earth and Planetary Science Letters, 395 , 217–230. Augustin, N., van der Zwan, F. M., Devey, C. W., Ligi, M., Kwasnitschka, T., Feldens,P., … Basaham, A. S. (2016). Geomorphology of the central Red Sea Rift: Determining spreading processes. Geomorphology , 274 , 162–179. Mitchell, N. C., Ligi, M., Ferrante, V., Bonatti, E., & Rutter, E. (2010). Submarine salt flows in the central Red Sea. Bulletin, 122 (5–6), 701–713. Ligi, M., Bonatti, E., Bortoluzzi, G., Cipriani, A., Cocchi, L., Caratori Tontini,F., … Schettino, A. (2012). Birth of an ocean in the Red Sea: initial pangs. Geochemistry, Geophysics, Geosystems , 13 (8). Issachar, R., Gómez-García, Á. M., & Ebbing, J. (2023). Lithospheric structure of the Red Sea based on 3D density modeling: A contrasting rift architecture. Journal of Geophysical Research: Solid Earth, e2022JB025458. Augustin, N., Van der Zwan, F. M., Devey, C. W., & Brandsdóttir, B. (2021). 13 million years of seafloor spreading throughout the Red Sea Basin. Nature communications, 12 (1), 2427. Duncan, R. A., & Al-Amri, A. M. (2013). Timing and composition of volcanic activity at Harrat Lunayyir, western Saudi Arabia. Journal of Volcanology and Geothermal Research, 260 , 103–116. Pallister, J. S. (1986). Red-Sea rift magmatism near Al lith, kingdom of Saudi Arabia (p. 41). US Department of the Interior, Geological Survey. Sauter, D., Cannat, M., Rouméjon, S., Andreani, M., Birot, D., Bronner, A., … Searle,R. (2013). Continuous exhumation of mantle-derived rocks at the Southwest Indian Ridge for 11 million years. Nature Geoscience , 6 (4), 314–320. Cannat, M., Sauter, D., Lavier, L., Bickert, M., Momoh, E., & Leroy, S. (2019). On spreading modes and magma supply at slow and ultraslow mid-ocean ridges. Earth and Planetary Science Letters, 519 , 223–233. Reston, T. (2018). Flipping detachments: The kinematics of ultraslow spreading ridges. Earth and Planetary Science Letters, 503 , 144–157. Martinez, F., & Hey, R. (2022). Mantle melting, lithospheric strength and transform fault stability: Insights from the North Atlantic. Earth and Planetary Science Letters, 579 , 117351. Cannat, M., Rommevaux-Jestin, C., Sauter, D., Deplus, C., & Mendel, V. (1999). Formation of the axial relief at the very slow spreading Southwest Indian Ridge (49 to 69 E). Journal of Geophysical Research: Solid Earth, 104 (B10), 22825–22843. Moreira, M., Valbracht, P. J., Staudacher, T., & Allègre, C. J. (1996). Rare gas systematics in Red Sea ridge basalts. Geophysical research letters, 23 (18), 2453–2456. Stüwe, K., Robl, J., Turab, S. A., Sternai, P., & Stuart, F. M. (2022). Feedbacks between sea-floor spreading, trade winds and precipitation in the Southern Red Sea. Nature Communications, 13 (1), 5405. Sleep, N. H. (1996). Lateral flow of hot plume material ponded at sublithospheric depths. Journal of Geophysical Research: Solid Earth, 101 (B12), 28065–28083. Bosworth, W. (2015). Geological evolution of the Red Sea: historical background, review, and synthesis. The Red Sea: The formation, morphology, oceanography and environment of a young ocean basin , 45–78. Dixon, T. H., Ivins, E. R., & Franklin, B. J. (1989). Topographic and volcanic asymmetry around the Red Sea: Constraints on rift models. Tectonics, 8 (6), 1193–1216. Coleman, R. G., Gregory, R. T., & Brown, G. F. (1983). Cenozoic volcanic rocks of Saudi Arabia (Vol. 83, No. 788). US Department of the Interior, Geological Survey. Bosworth, W., & Stockli, D. F. (2016). Early magmatism in the greater Red Sea rift: timing and significance. Canadian Journal of Earth Sciences, 53 (11), 1158–1176. Sandwell, D. T., Müller, R. D., Smith, W. H., Garcia, E., & Francis, R. (2014). New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure. science, 346 (6205), 65–67. Riedl, S., Melnick, D., Njue, L., Sudo, M., & Strecker, M. R. (2022). Mid-Pleistocene to Recent Crustal Extension in the Inner Graben of the Northern Kenya Rift. Geochemistry, Geophysics, Geosystems , 23 (3), e2021GC010123. Shmela, A. K., Paton, D. A., Collier, R. E., & Bell, R. E. (2021). Normal fault growth in continental rifting: Insights from changes in displacement and length fault populations due to increasing extension in the Central Kenya Rift. Tectonophysics, 814 , 228964. Wessel, P., Luis, J. F., Uieda, L., Scharroo, R., Wobbe, F., Smith, W. H., & Tian, D. (2019). The generic mapping tools version 6. Geochemistry, Geophysics, Geosystems, 20 (11), 5556–5564. Ebinger, C. J., & Sleep, N. H. (1998). Cenozoic magmatism throughout east Africa resulting from impact of a single plume. Nature, 395 (6704), 788–791. Additional Declarations No competing interests reported. Supplementary Files MoulinandJonssonSupplementaryInformation.docx Cite Share Download PDF Status: Published Journal Publication published 25 Mar, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 02 Apr, 2024 Reviews received at journal 18 Mar, 2024 Reviews received at journal 14 Feb, 2024 Reviewers agreed at journal 29 Jan, 2024 Reviewers agreed at journal 29 Jan, 2024 Reviewers invited by journal 17 Jan, 2024 Editor assigned by journal 15 Jan, 2024 Editor invited by journal 15 Jan, 2024 Submission checks completed at journal 15 Jan, 2024 First submitted to journal 14 Jan, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3862377","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":267243453,"identity":"8941ec6e-7357-4b80-bba5-300273f07af3","order_by":0,"name":"ADRIEN MOULIN","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABD0lEQVRIie3QsUrDQADG8e840CWha6bmFa6zSh/EJeEgLs3gUjI4xCVdWrM2ID5DpuJ44UCX0Kw3NouuFRcdCr1gLQhn7ehwfzi4O+7HcQfYbP+yAOJrQlOBJNjtnhxFiCZ1R+jfBN8EJDuC9CZxK94ecdnzwlt5/RD5rGkE1mMJfyKMxKtfWVXUiIt5mMpiMRqUioPMlxKsDowEKoJ0M8Sl0sRdJKRUFNTNNIGZ+B3Z7Ml9MiwbCbrRxM9XRsI6QvYkHYWl4KBEEyjzLYP6BdUs8+Ji2qbSeYp4oTirpssrhynzLf3niK4/s/M4P+Xy3bnhF3dN1a4+xmd9P//l+buP+7kUejiHzttsNpvtcFvOF2qS7PIeWgAAAABJRU5ErkJggg==","orcid":"","institution":"King Abdullah University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"ADRIEN","middleName":"","lastName":"MOULIN","suffix":""},{"id":267243454,"identity":"566ede65-39fd-47ca-bcd2-f535a96d244b","order_by":1,"name":"Sigurjon Jonsson","email":"","orcid":"","institution":"King Abdullah University of Science and Technology (KAUST)","correspondingAuthor":false,"prefix":"","firstName":"Sigurjon","middleName":"","lastName":"Jonsson","suffix":""}],"badges":[],"createdAt":"2024-01-14 06:29:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3862377/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3862377/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-93942-1","type":"published","date":"2025-03-25T15:57:10+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":49767677,"identity":"f340e0f8-ae56-4032-bdaa-4c12f99faa9e","added_by":"auto","created_at":"2024-01-17 17:18:04","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":19702308,"visible":true,"origin":"","legend":"\u003cp\u003eTopography over the Red Sea region and estimated depth of the Lithosphere-Asthenosphere boundary (LAB). (a) Topography with spreading centers and Dead Sea Transform fault as thick solid lines (where high-resolution topographic data are available), inferred spreading centers as thin solid lines (where the ridge axis is only covered by GEBCO bathymetry), and other inferred plate boundary locations as dashed lines (where the oceanic crust is not exposed or absent). Small circles indicating the Arabia-Nubia relative motion are from (ref. 17 and 19) and onshore volcanic fields compiled from (ref. 44 and 45). (b) Estimated depth of the LAB from the Sp-receiver functions mapping of (ref. 14), and the limits of accreted Proterozoic terranes and the Arabo-Nubian Shield\u003csup\u003e13\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"Fig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3862377/v1/482f54257dab2ea3fe627e57.jpg"},{"id":49767676,"identity":"27b40950-b2fd-4b4f-b813-e7e63a9b0e11","added_by":"auto","created_at":"2024-01-17 17:18:04","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":6110725,"visible":true,"origin":"","legend":"\u003cp\u003eVolcano-structural mapping of the Red Sea ridge axis. The seafloor mapping in between the 5.3 Ma isochrons was achieved from the analysis of available high-resolution bathymetric data\u003csup\u003e26,28\u003c/sup\u003e, shown here as shaded relief map, and GEBCO bathymetry. No high-resolution bathymetric data is available within white areas. Coordinates apply only to the high-resolution shaded relief map, with the mapping shifted by 100 km to the East.\u003c/p\u003e","description":"","filename":"Fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3862377/v1/29819195678e17aa864623ff.jpg"},{"id":49767673,"identity":"6bbd33ce-d928-4b4f-b738-c8a5ca034d4e","added_by":"auto","created_at":"2024-01-17 17:18:03","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":10154876,"visible":true,"origin":"","legend":"\u003cp\u003eVariations of topographic, gravity, tectonic and volcanic metrics along the axial trough of the Red Sea (UTM Northing interval is ~1900-2850 km). (a) Observed and filtered (filter parameters specified in (b)) axial bathymetry extracted from GEBCO 2021 and free-air gravity anomaly\u003csup\u003e46\u003c/sup\u003e, used together to compute the Mantle Bouguer Anomaly (see Methods), whose range of variations depends on sediment corrections (Methods and Supplementary Fig. 1) and is included within the red curve except where the axial trough is covered by salt flows, then it is depicted as a transparent red envelope. Note that the large negative anomaly around K1400-K1500 results from unconstrained sediment thickness (Supplementary Fig. 1). (b) Residual topography computed as the difference between the observed and filtered topography shown in (a). (c) Gray envelopes depict the average axial depth (2s) computed across a 50-km-wide moving window; the flanks of the axial trough above this envelope are color-coded as a function of the local average slope with antithetic-slopes depicted in black (see Methods). (d) Black dots depict cumulative throw of individual faults (sum of all throws from the ridge axis to this fault: see Methods); color-coded envelopes represent the maximum fault throw recorded across a 1.1-km-wide moving window; blue dots show the magmatic contribution assuming a constant fault dip angle of 60° (see Methods) and its 5-km-scanning-window average depicted as black lines. (e) Fault azimuth of individual strands is plotted as their deviation from the normal to the predicted opening direction (rotated clockwise when \u0026gt;0); the cumulative transform offset of the axial volcanic ridge (in red; starting from the SE edge) is computed along the small circles predicted by model Arabia-Nubia rotation parameters (see Methods). (f) Relative proportion of terrain type in between the 0.7 Ma isochrons (see Methods). (g) Distance of onshore Arabian volcanic fields relative to the ridge axis (computed along small circles) in their current position and at 13 Ma (see Methods). Red arrows point to the maximum seaward extension of volcanism at Lunayyir and Tufail. Gray bands in all sub-figures correspond to inter-trough zones (sea-floor covered by allochtonous salt flows).\u003c/p\u003e","description":"","filename":"Fig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3862377/v1/0ec435ac20b0f3e430e41d8e.jpg"},{"id":49767674,"identity":"722fccee-1ff6-4920-9650-d7b8db7e029b","added_by":"auto","created_at":"2024-01-17 17:18:04","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":5271067,"visible":true,"origin":"","legend":"\u003cp\u003e3D view of the Red Sea axial trough around the Suakin segment looking NW. The bathymetry visualized here is the elevation above the mean axial depth (see Methods for calculation, and note that it generated subtle artefacts visible in the image in the form of axis-normal fabrics mostly outside the limit of high-resolution bathymetric data) and allows capturing the increased cumulative fault throw at the Suakin segment (white sections of the upper shelf in the middle of the image). Note the larger than average normal fault offsets shown by the black arrows and the coincident reduction of the axial volcanic ridge. The dotted line depicts the limit of high-resolution bathymetric data. The thick black line represents the 5.3 Ma isochrons.\u003c/p\u003e","description":"","filename":"Fig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3862377/v1/b9942451623bcac2479cfeec.jpg"},{"id":49769224,"identity":"1cccebcd-4470-45e9-b15a-a502aa91a25e","added_by":"auto","created_at":"2024-01-17 17:26:03","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":3886176,"visible":true,"origin":"","legend":"\u003cp\u003eNumerical simulations of the lateral spreading of low-density plume material from rifting to spreading. (a) Plume thickness after 16 Ma of lateral propagation followed by 10 Ma of continental rifting along 2 arms during which the lithosphere is homogeneously thinned across a 160-km-wide symmetric zone of active extension (see Methods). The vector field depicts plate motion relative to the Afar hotspot (15 mm/yr SW of the rift, and 15 mm/yr + model rotation of Arabia relative to Nubia NE of the rift). The blue star denotes the hotspot position. The dashed blue line represents the axis of a pre-rift 150-km-wide sub-lithospheric channel along which the initial lithospheric thickness is reduced to 90 km (versus 140 km over the rest of the grid). Note the enhanced accumulation of plume material at the intersection between the rift and the sub-lithospheric channel. (b) Cumulative accumulation of plume material (relative to stage in (a)) after 4 Ma of oceanic spreading. Note the accumulation deficit at the intersection between the rift and the sub-lithospheric channel. This deficit grows during the first ~1 Ma in our model, after which sub-axis flow remains similar to nearby sections. Also note the lateral escape flow NE of this intersection, which lasts up to 4-5 Ma in our model. The second sub-lithospheric channel (not yet reached by plume material in (a)) is also depicted with a dashed blue line. Note that inflow of plume material is set to zero from the onset of oceanic spreading, such that NNW-directed redistribution of plume material along the rift occurs to achieve gravitational stability.\u003c/p\u003e","description":"","filename":"Fig.5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3862377/v1/eecc50802d5cd63e3ed56789.jpg"},{"id":79605139,"identity":"6e66428e-9014-4c8f-b1e8-73ada57ecef3","added_by":"auto","created_at":"2025-03-31 16:10:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":45813846,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3862377/v1/d0a8c980-6c70-47f0-89f2-aeba1494d890.pdf"},{"id":49767671,"identity":"e108f936-89c3-4b0d-a49e-e23bdd6bc277","added_by":"auto","created_at":"2024-01-17 17:18:03","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1243903,"visible":true,"origin":"","legend":"","description":"","filename":"MoulinandJonssonSupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-3862377/v1/df97407362323996c3a72ce8.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Persisting influence of continental inheritance on early oceanic spreading","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWhere and how continents rift is a long-lasting and still debated question\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. According to the Wilson cycle theory, the closure and opening of oceans repeatedly occur along persistent zones of weakness, such that passive margins initially develop from inherited suture zones\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. An underlying consequence is that along-strike variations in the lithospheric structure and tectonic architecture of plate boundaries (tectonic style, crustal and lithospheric thickness, etc.) are being alternatively passed from one stage of the cycle to the other, and modulate their subsequent evolution\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn between these two stages, the sensitivity of the oceanic spreading phase to lithospheric inheritance is supposedly weak, as it is accommodated by continuous formation of new lithosphere from the asthenosphere, through cooling and magmatic crustal accretion. Instead, the mode of oceanic spreading is thought to be dominantly controlled by how much of the plate divergence is accommodated magmatically\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e, which in turn essentially depends on the local thermal structure. Critical parameters in that case include the spreading rate\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, the subsidiary arrival of hot deeply-sourced mantle plume material at the ridge axis\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e, and the along-strike segmentation of the spreading ridge\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. It is generally considered that significant contribution from long-term lithospheric inheritance may only exist for the latter of these parameters, for example when rift segmentation develops along pre-existing zones of weakness which later evolve as oceanic transform faults\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eNumerical models however indicate that lateral spreading of mantle plumes is strongly controlled by the topography of the lithosphere-asthenosphere boundary (LAB)\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e, making possible that the early mode of oceanic spreading be modulated by the inherited LAB topography of continental margins through the subridge concentration versus escape of hot plume material. This hypothesis remains so far untested, mainly because it requires detailed information about the mechanisms of accommodation of plate separation during the early stages of sea-floor spreading. At global scale, early oceanic lithosphere is generally old, and hence buried beneath large amounts of post-rift clastic sediments derived from the erosion of the passive margin.\u003c/p\u003e \u003cp\u003eThe Red Sea represents a somewhat unique prototype in that view, as it meets the basic requirement of a young spreading ridge cutting at high angle across major crustal and lithospheric fabrics, itself inherited from the Proterozoic accretion of distinctive terranes that formed the Arabo-Nubian Shield (ANS)\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. On the Arabian side of the rift, both the LAB mapped from Sp-receiver functions\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) and crustal density models derived from combined gravity and seismic data\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e indeed show that the constitutive terranes of the ANS preserve unique lithospheric characters (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), providing a natural laboratory to evaluate the influence of these inherited fabrics on the mechanisms of early sea-floor spreading.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Geological background","content":"\u003cp\u003eThe NNW-SSE-trending Red Sea Rift developed over the last 23Ma\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e as a result of the ~\u0026thinsp;0.39\u0026deg;/Ma counter-clockwise rotation of the Arabia Plate relative to Nubia about a pole located in the southeastern Mediterranean (the pole used in this study is 24.22\u0026deg;E, 31.61\u0026deg;N, yielding opening rates that increase from ~\u0026thinsp;7 mm/yr in the NNW to 16 mm/yr in the SSE)\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Towards the SSW, the Arabia/Nubia plate boundary splays into two branches that isolate the Danakil microplate\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e before linking to the Gulf of Aden and Ethiopian rifts to form a rift-rift-rift triple junction (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). This triple junction is closely associated with the Afar mantle plume\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, whose initiation preceded rifting and relative to which the Nubia plate moves NW at ~\u0026thinsp;15 mm/yr\u003csup\u003e22\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eFrom the stable ANS to the plate boundary, the Red Sea rift (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) is composed of 1) a coastal plain bounded by the external rift escarpments and underlain by tilted blocks and their accompanying syn-rift sediments\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, 2) a smooth offshore shelf marked by a gradually increasing elevation toward the SSE\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, and whose basement is blanketed by more than 1 km of Miocene evaporites\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e, and 3) a discontinuous 15-70-km-wide axial trough, essentially restricted to the Southern and Central Red Sea, where the oceanic crust and its rugged volcano-tectonic sea-floor are exposed except at the so-called \u0026ldquo;inter-trough zones\u0026rdquo; occupied by allochtonous salt flows\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe weak penetration of geophysical surveys across the Miocene evaporites led to ambiguities about the nature of the offshore shelves\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. In particular, forward modeling of gravity anomalies and the absence of a clear magnetic signature have led some authors to conclude that the axial trough approximately captures the whole extent of the oceanic lithosphere (proximal OCT end-member: oceanic spreading\u0026thinsp;\u0026lt;\u0026thinsp;5 Ma and diachronous along axis)\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. Conversely, seismic reflection data and segmentation trails inferred from vertical gravity gradient patterns have been used by others to place the ocean-continent transition (OCT) at the outer edge of the shelves (distal OCT end-member: oceanic spreading\u0026thinsp;~\u0026thinsp;13-14-Ma-old and synchronous)\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eWhereas most debate about the recent evolution of the Red Sea Rift has focused on the position of the OCT, little attention has comparatively been paid to the along-axis variability of oceanic spreading mode\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. Here, we combine GEBCO 2021 (GEBCO Compilation Group, 2021) and high-resolution bathymetry with satellite free air gravity anomalies (see Methods) to characterize the topographic, gravity, and volcano-tectonic signatures of the axial trough North of its intersection with the Danakil microplate (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) and identify long- and short-wavelength along-axis gradients. These gradients are then compared to primary characteristics of the continental margin (lithospheric thickness and distribution of volcanism, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), and integrated into a kinematically-constrained numerical model of plume-assisted rifting.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eAlong-axis topography, gravity, and volcano-tectonic patterns\u003c/h2\u003e \u003cp\u003eLong-wavelength along-axis topography of the Red Sea Ridge features a relatively stable axial depth of ~\u0026thinsp;2000 m.b.s.l. in the Northern and Central Red Sea (N-RS and C-RS labelled on top of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e; reference to specific location of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e will be hereafter given in kilometers from the Arabia/Nubia pole, and denoted as K##), followed by a gradual shallowing up to ~\u0026thinsp;1100 m.b.s.l. when approaching the Afar plume in the Southern Red Sea (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). To a first order, variations of the axial Mantle Bouguer Anomaly (MBA; see Methods and Supplementary Fig.\u0026nbsp;1 for calculation procedure) occur symmetrically to this topographic trend (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Superimposed on the long-wavelength topographic signal are short-wavelength undulations characterized by peak-to-peak distances that apparently decrease from ~\u0026thinsp;250 km South of K2000 to 60\u0026ndash;100 km farther North (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The positive anomalies show no clear relation with the inter-trough zones, but instead correlate with large axial volcanoes. The negative anomalies generally correspond to the Red Sea \u0026ldquo;Deeps\u0026rdquo;\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e and exhibit a bi-modal distribution with vertical residuals scattering around \u0026minus;\u0026thinsp;250 m and \u0026minus;\u0026thinsp;600 m. In general, these anomalies leave no or very little MBA signature (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003eThe slope distribution of the flanks of the axial trough also displays large lateral variability (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Nevertheless, the similarity between NE flank and SW flank distributions clearly indicates that the axial trough is highly symmetric in cross-section. The 5% threshold used in constructing Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec is intended to capture the extent of the axial trough (see Methods). Its outer (and so vertical) extension is thus visualized by the shallowest terrains plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, and shows that the top of the axial trough records a long wavelength topographic signal similar to that of the axial ridge. Antithetic slopes (i.e., opposite to the average flank slope) are locally observed in association with large axial volcanoes NW of K2000 and become widespread farther South (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Two ridge segments (Nereus around K1570 and Suakin around K1960, also located in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) display unusually steep flanks relative to other sections (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), and correlate with the two most negative anomalies (~-600m) of residual topography evidenced in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb.\u003c/p\u003e \u003cp\u003eBoth flanks of the axial trough are also characterized by a similar pattern of normal faulting (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed), which again attests to the symmetric nature of the spreading centers. In general, fault spacing and fault offset apparently increase away from the axial volcanic ridge, which might reflect a resolution and/or preservation bias (see Methods). As for the topographic analysis, the Nereus and Suakin segments exhibit a distinctive pattern, with wider fault spacing and larger fault offsets (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The maximum fault offset along most of the axial trough is around 600\u0026ndash;700 m, but increases to ~\u0026thinsp;1300 m at the Nereus and Suakin segments. The magmatic contribution to plate opening (M: sense of (ref. 6)) determined from this faulting pattern (Methods) displays a very subtle decrease from SSE to NNW (~\u0026thinsp;0.92 to ~\u0026thinsp;0.85), which locally becomes much stronger at the Nereus and Suakin segments (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe analysis of the sea-floor morphology is hampered by both the variable width of the stripe covered by high-resolution bathymetry, and the presence of large portions of terrains occupied by allochtonous evaporites\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Since the maximum possible proportion of volcanic terrains includes areas that are unclassified in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef, it is visualized from this Figure as the sum of the red-tone envelopes (see Methods). Accordingly, the Nereus and Suakin segments appear as the most magma-poor ridge segments, with less than 20% of volcanic sea-floor.\u003c/p\u003e \u003cp\u003eAlthough topographic, tectonic, and volcanic metrics vary continuously along the Red Sea axial trough, the Nereus and Suakin segments appear to share prominent anomalies, characterized by a deeper less volcanic spreading ridge flanked by more spaced larger displacement normal faults. These \u0026ldquo;anomalous segments\u0026rdquo; occur along the less oblique and less segmented sections of the Red Sea Ridge (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). On the other hand, they seem to align with major geophysical and geological structures of the Arabian margin. In particular, Nereus and Suakin occur next to the Lunayyir and Tufail onshore volcanic fields (located in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), which have the largest seaward extension at the scale of the entire Red Sea (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg), and are markedly younger (last\u0026thinsp;~\u0026thinsp;1 Ma and last\u0026thinsp;~\u0026thinsp;3.5 Ma\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e compared to last\u0026thinsp;~\u0026thinsp;12 Ma). They also occur next to the Proterozoic Hijaz and Asir terranes of the Arabian margin\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e, whose bounding suture zones are intimately associated with strong density variations at Moho depth inferred from the joint inversion of seismic and gravity data\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, and strong gradients in lithospheric thickness as mapped from Sp-receiver functions\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). In between, the Jeddah terrane exhibits a denser crust\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e and thicker lithosphere (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eVariability of oceanic spreading mode\u003c/h2\u003e \u003cp\u003eThermo-mechanical models of spreading ridges predict that the fraction of plate separation accommodated magmatically (M) exerts a primary control on the pattern of normal faulting, such that increasing M will be recorded on the sea-floor by smaller and less spaced normal fault scarps\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. It is worth noting that an accurate estimation of M from bathymetry data requires tectonic displacements to be readily reflected in the sea-floor topography. It is known that this assumption may become unverified when M becomes so little that spreading switches to a detachment mode\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. In that case, the progressive flexure of detachment faults will lead tectonic displacements to be poorly reflected in the bathymetry\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. The sea-floor topography of the Red Sea axial trough documented above and by (ref. 4 and 5) however lacks typical characteristics of a detachment mode of spreading, such as domal corrugated surfaces, across-ridge topographic asymmetry, or gently dipping fault surfaces\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Instead, a negative relation between the slope of the axial trough flanks and the proportion of volcanic terrains seems to be the general rule along the Red Sea axis (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). This is at odds with the gentler scarps that would be otherwise expected along the less volcanic segments if spreading switched to a detachment mode. More generally, there is no avolcanic segment along the Red Sea Ridge (at least where the basement is exposed) despite the slow- to ultra-slow opening. These observations support the estimation of M from observed normal fault scarps, as well as its relevance for tracking lateral variations of the magmatic contribution along the Red Sea Ridge.\u003c/p\u003e \u003cp\u003eLateral variations of the faulting pattern, as encapsulated into M, display two superposed signals. A subtle long-wavelength decrease of M (from ~\u0026thinsp;0.92 to ~\u0026thinsp;0.85) is observed towards the NNW, except around K1700 where it increases along with the apparent magma focusing signed by the large Hatiba Mons volcano\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e (see the large positive anomaly around K1700 in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Superposed onto this signal are larger drops near the Nereus and Suakin segments (M\u0026thinsp;~\u0026thinsp;0.3\u0026ndash;0.4) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). These latter are also accompanied by a local doubling of the maximum fault offset (passing from an average of 600\u0026ndash;700 m to ~\u0026thinsp;1300 m), that goes along with a decrease of the number of overlapping faults (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). These two signals point to a slight regional northward decrease of the proportion of plate separation accommodated magmatically, and a more pronounced local decrease at the Suakin and Nereus segments. This interpretation is consistent with the locally lower proportion of exposed volcanic sea-floor (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef).\u003c/p\u003e \u003cp\u003eOn the other hand, the few high-resolution bathymetric data available SE of K2000 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) show that the axial volcanic ridges are generally wider and more continuous than farther NNW\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. Flank antithetic-slopes, interpreted as large tectonically-splitted volcanoes, also become more abundant along this section (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), which might be indicative of a magmatically more robust character of the spreading ridge. The data therefore show that plate opening is less and less accommodated magmatically when moving towards the NNW, and that this trend is locally amplified at the Suakin and Nereus segments.\u003c/p\u003e \u003cp\u003eWhereas the regional trend could easily be explained by a combination of decreasing spreading-rate and increasing distance from the Afar plume towards the NW (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), the anomalous character of the Suakin and Nereus segments appears more enigmatic. In particular, there is no evidence that the local decrease of M is controlled by the segmentation of the ridge (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), as observed along other slow-spreading ridges\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. Instead, the Suakin and Nereus segments are located along the less oblique and less segmented sections of the Red Sea Ridge (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee).\u003c/p\u003e \u003cp\u003eMoreover, along-axis variations of the MBA surprisingly show an absence of typical bull-eye patterns centered on segment centers\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. The MBA also gradually increases from the Suakin segment towards the SSE (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea), which is contrary to what would be expected from an increasing crustal thickness. In general, MBA varies symmetrically with the mean axial depth at long wavelengths (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea), which suggests that the axial ridge is not isostatically compensated. These observations converge to suggest that the expected gravity signature is hidden by a dynamic topographic support, as proposed for example by (ref. 37) along the Reykjanes Ridge.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eDifferential focusing of plume-related heat by the thickness of the marginal lithosphere\u003c/h2\u003e \u003cp\u003eLateral spreading of the hot and buoyant Afar plume into the laterally-confined Red Sea Rift has been already documented from the \u003csup\u003e4\u003c/sup\u003eHe/\u003csup\u003e3\u003c/sup\u003eHe signature of axial basalts\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e and the density structure of the upper-mantle beneath the Red Sea Ridge\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, and thus constitutes a natural candidate for this dynamic support (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). We think it constitutes the primary cause of the shallow axial depth of the Southern Red Sea, but also of the western termination of the Gulf of Aden (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Although it does not exclude the hypothesis of a flexural lifting induced by enhanced erosion of the Arabian margin as recently advocated by (ref. 40), this latter should translate into an ENE-WSW cross-sectional bathymetric asymmetry, which is not specifically observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003eWe suggest that the narrowness of the Red Sea basin is the key condition for focusing buoyant plume material beneath the spreading ridge, and that this condition exerts primary thermal and gravitational controls on the regional trend observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Accordingly, we argue that the anomalous character of the Nereus and Suakin segments most likely records a locally decreased focusing. Specifically, we propose that the spatial correspondence between these two segments, the onshore Lunayyir and Tufail volcanic fields, and the shallower LAB of the Hijaz and Asir terranes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) is best explained by an outboard deflection of the heat source where it becomes less laterally confined due to shallowing of the marginal lithosphere.\u003c/p\u003e \u003cp\u003eThis is demonstrated using a modified version of the numerical model of (ref. 41), which is appropriate to track the effect of LAB topography variations on the lateral spreading of low-density ponded material (see Methods). Our simulations are kinematically constrained to fit with both the rotational opening and lithospheric thinning of the Red Sea and Gulf of Aden, and the coeval motion of the Afar hotspot relative to the lithospheric plates, and account for the shallower pre-rift LAB of the Hijaz and Asir terranes in the form of two rift-oblique sub-lithospheric channels (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) (see Methods). These simulations show that channeling of plume material beneath the tectonically thinned rift is accompanied at the intersections with these sub-lithospheric channels by the development of on-axis plume thickness anomalies and outboard viscous fingering during the continental rifting phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and S3).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFollowing the onset of oceanic spreading, the on-axis anomalies are dissipated through along-axis diverging flow of the buoyant material and continuing viscous fingering towards the continental margins (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). These primary features account for the coeval development of comparatively less magmatic segments at Nereus and Suakin and onshore volcanism of Lunayyir and Tufail. We also emphasize that the only uplifted Arabian marine terraces are precisely located at the suspected onshore outlet of the Nereus/Lunayyir deflected flow along a 20-km-long coast-line section (Supplementary Fig.\u0026nbsp;2), which might consistently indicate dynamic uplift.\u003c/p\u003e \u003cp\u003eThe simulation shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e prescribes a synchronous onset of oceanic spreading (see Methods) consistent with the distal OCT end-member\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e, and for which the on-axis divergence of plume material lasts\u0026thinsp;~\u0026thinsp;1 Ma. Sensitivity tests show that models prescribing a northward propagating onset of spreading (in line with the proximal OCT end-member\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e) differ only in terms of the response time, with the dissipation of the on-axis anomaly taking up to ~\u0026thinsp;8 Ma (Supplementary Fig.\u0026nbsp;3). We therefore suggest that additional chronologic constraints on the proximal onshore volcanism might provide indirect insights about the rhythm of propagation of sea-floor spreading in the Red Sea.\u003c/p\u003e \u003cp\u003eOn the other hand, onshore volcanism is highly asymmetric at rift scale (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In the context of our model, this could be explained if syn-rift lithospheric thinning was also asymmetric as previously proposed by (ref. 43), and/or if the pre-rift lithospheric structure of the Hijaz and Asir terranes on the Nubian margin (for now poorly constrained\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e) lacked the shallow LAB features seen on the Arabian conjugate.\u003c/p\u003e \u003cp\u003eThe mechanism advocated here is similar to that proposed by (ref. 12) to account for the distribution of syn-rift volcanism in Iceland and the North Atlantic region. Our study shows from in-situ observations that this mechanism may persist beyond the stage of continental break-up, and points to the decisive role played by pre-rift lithospheric inheritance on the mode of early sea-floor spreading in plume-assisted rift settings. By differentially focusing thermal lithospheric thinning, this mechanism might also determine the final geometry of the associated oceanic basins.\u003c/p\u003e \u003c/div\u003e "},{"header":"Methods","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003eAnalyzed datasets and data projection\u003c/h2\u003e \u003cp\u003eTo map the seafloor, we used high-resolution multibeam bathymetric data sets, where available\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e, and the 15-arc-second GEBCO 2021 data set (GEBCO Compilation Group, 2021). The analyzed metrics are plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e against the distance from the Arabia/Nubia rotation pole, the inversion of which yielding similar results over geological (post-5Ma) and decadal (GPS) timescales\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. This projection allows the influence of the spreading rate to be easily tracked (spreading rate is proportional to the distance from the rotation pole) and is a prerequisite for the calculation of the magmatic contribution (M), estimation of cross-axis symmetry, and calculation of cumulative fault offsets. Given the average linearity of the Red Sea and the small magnitude of transform or non-transform offsets, this choice does not affect the evaluation of Afar plume influence.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eFault offsets and magmatic contribution\u003c/h3\u003e\n\u003cp\u003eWe measured fault offsets using an approach similar to that employed by (ref. 47 and 48) along the Kenya rift. For each fault, both the footwall and corresponding hangingwall cut-offs were mapped from the bathymetric surface. We then extracted (x,y,z) coordinates along the cut-off lines and converted (x,y) into rotation-pole-centered coordinates (RPC system). Fault offsets were finally quantified by associating each point of the footwall cut-off to its hanging-wall counter-part (defined as the closest point in terms of co-latitude in the RPC system, hereafter referred to as θ\u003csub\u003eRPCS\u003c/sub\u003e), and computing the vertical separation between them.\u003c/p\u003e \u003cp\u003eWe ascribed an ordering index to each fault (incrementally increasing from 1 away from the ridge axis) using a θ\u003csub\u003eRPCS\u003c/sub\u003e scanning window of 0.005\u0026deg; (~\u0026thinsp;555m) (i.e., the ordering of a given fault is k if there are (k-1) faults closest to the ridge axis within an along-axis distance of 0.005\u0026deg;). We then computed the cumulative offset of fault k as the summed fault offsets of faults 1 to k. The selected width of the scanning window was set to a value slightly higher than the grid cells to ensure that any fault crossing the window is effectively captured. In practice, each fault was thus sampled once or twice (the averaged was taken in the latter case).\u003c/p\u003e \u003cp\u003eGiven the low resolution of the GEBCO grid, it is possible that some fault scarps mapped outside the coverage of high-resolution bathymetric data (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) are actually composed of several closely stacked scarps that cannot be discriminated individually within the available resolution. This might account for the apparent increase in fault spacing away from the ridge axis (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Fault offsets determined from GEBCO data should thus be considered as maximum values. However, the maximum fault offsets determined along the Suakin and Nereus segments were all quantified from high-resolution bathymetric data, such that this potential does not impact the interpretation of the present study.\u003c/p\u003e \u003cp\u003eWe computed the magmatic contribution (M) as follows. The cumulative offset recorded by the fault farthest from the ridge axis was extracted using the same scanning window, and converted into divergence (D\u003csub\u003eobs\u003c/sub\u003e) by assuming a uniform fault dip of 60\u0026deg;. For each of these cumulative fault offsets, the model opening (D\u003csub\u003emod\u003c/sub\u003e) was calculated as the distance of that fault from the ridge axis along the corresponding Arabia/Nubia small circle (D\u003csub\u003emod\u003c/sub\u003e = [λ\u003csub\u003eRPCS(fault)\u003c/sub\u003e-λ\u003csub\u003eRPCS(axis)\u003c/sub\u003e]*R*cos(π/2-θ\u003csub\u003eRPCS\u003c/sub\u003e), where λ\u003csub\u003eRPCS\u003c/sub\u003e is the longitude in the RPC system and R is the Earth\u0026rsquo;s radius). M was then calculated as 1-D\u003csub\u003eobs\u003c/sub\u003e/D\u003csub\u003emod\u003c/sub\u003e.\u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eTerrains\u003c/h2\u003e \u003cp\u003eWe classified terrain types into 4 categories using a resolution of 50 m: unclassified (lack of high-resolution bathymetric data), volcanic (hummocky terrains, and (eventually splitted) volcanic edifices), sedimented (low gradient and low internal relief surfaces, as well as non-volcanic fault scarps), and salt-covered (no constraint on whether salt seals volcanic or sedimented terrains). We analyzed the terrain type distribution within the post-0.7Ma axis-centered stripe. The use of a synchronous stripe allows removing marine sedimentation effects (the proportion of volcanic terrains classified as sedimented terrains because of burial by marine sediments should be the same within a synchronous stripe, provided that sedimentation rate is invariant along axis). The choice of the 0.7 Ma isochron was constrained by the availability of high-resolution bathymetric data from which terrains can be classified (compromise between maximizing the covered area and minimizing the amount of unclassified terrains).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eOffshore volcanic fields\u003c/h2\u003e \u003cp\u003eThe distribution of offshore volcanic fields was taken from (ref. 44). For the fields closest to the Red Sea, we carefully removed the lava tongues that grade down along the rift escarpment, as they would artificially bias the results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg. This essentially concerned the lava flows that were channeled from the Rahat volcanic field (broadly coinciding with the Jeddah terrane in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) along SW-directed valleys, and are now preserved as interfluves\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. The restoration of the volcanic fields to 13 Ma (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg) configuration was performed by assuming they remained part of rigid Arabia over the entire time period.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eAxial depth filtering and residual topography\u003c/h2\u003e \u003cp\u003eWe extracted the (x,y,z) coordinates of exposed oceanic crust within 3 km from the mapped axis from the bathymetric grid. We then calculated the averaged axial depth over a 0.02\u0026deg;-wide (~\u0026thinsp;2.2km) sliding window using sliding increments of 0.01\u0026deg;. We then applied a Savitsky-Golay filter to the data in order to obtain the long-wavelength undulation of the axial depth. To do so, we used the \u0026lsquo;sgolay\u0026rsquo; method of the Matlab function \u0026lsquo;smooth\u0026rsquo; to fit the data by a polynomial of degree 6 across a span of θ\u003csub\u003eRPCS\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.7\u0026deg;. The residual topography was then calculated as the difference between filtered depth and observed depth, to highlight local bathymetric perturbations.\u003c/p\u003e \u003cp\u003eThe topographic grid around the Suakin segment was also processed specifically to depict the elevation above the mean axial depth in 3D (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The procedure was as follows: 1) we extracted the bathymetric data located less than 2 km away from the mapped axial volcanic ridge, 2) we calculated the mean axial depth using a 1-km-wide scanning window, 3) we interpolated the mean axial depth as a function of θ\u003csub\u003eRPCS\u003c/sub\u003e, and 4) we calculated the mean axial depth for every cell of the initial grid using this interpolant.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eFlank slope\u003c/h2\u003e \u003cp\u003eWe smoothed the bathymetric grid using a 2D gaussian-weighted 10 km low-pass filter, and used it to compute the first derivative of topography (slope) in the average predicted direction of extension. We applied a slope cut-off of 5% to the resulting data, a value appropriate to discriminate between the axial trough and the nearby offshore shelves.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eMantle Bouguer Anomaly\u003c/h2\u003e \u003cp\u003eThe Mantle Bouguer Anomaly (MBA) is widely used to evaluate sources of gravity variations at mid-ocean ridges, and involves the removal of seafloor and Moho gravity effects from the free-air anomaly\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. As MBA calculations usually assume a constant crustal thickness, MBA anomalies are often used to detect possible crustal thickness variations\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. We calculated the MBA using the GEBCO global bathymetric grid, and the satellite-derived free air gravity anomaly grid, version 30.1\u003csup\u003e46\u003c/sup\u003e. The bathymetric grid was re-gridded at the same resolution as the gravity data (3.5 km) before carrying out the calculation. Sediment grids were prepared as follows.\u003c/p\u003e \u003cp\u003eThe allochtonous salt flows that locally bury the axial trough were assumed to linearly thicken from zero to a range of realistic values as a linear function of the distance from the flow edges. The preferred maximum thickness of intra-trough salt was set to 500 m following (ref. 26), but we carried out alternative calculations using maximum thicknesses of 250 m and 1000 m (the corresponding sediment thickness maps are provided in Supplementary Fig.\u0026nbsp;1). On the other hand, salt thickness is poorly constrained outside the axial trough, which is why we have restricted the discussion of the MBA to the axial region. Nevertheless, we have assumed that axis-normal geometry of the salt layer is equivalent to a\u0026thinsp;~\u0026thinsp;100-km-long lens that reaches a maximum thickness of 2000 m halfway, and thins towards both the continental margin and the axial trough, following interpretative seismic sections of (ref. 18) (Supplementary Fig.\u0026nbsp;1). Calculations carried out with different geometries leaves the axial MBA unchanged however.\u003c/p\u003e \u003cp\u003eData processing and gravity calculation was carried out using GMT software version 6.3.0\u003csup\u003e49\u003c/sup\u003e, and using densities of 1030 kg/m\u003csup\u003e3\u003c/sup\u003e (seawater), 2100 kg/m\u003csup\u003e3\u003c/sup\u003e (sediment), 2730 kg/m\u003csup\u003e3\u003c/sup\u003e (crust), and 3330 kg/m\u003csup\u003e3\u003c/sup\u003e (mantle) (detailed procedure described in (ref. 37)).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003ePlume spreading Modeling\u003c/h2\u003e \u003cp\u003eThe plume spreading models were conducted using a modified version of the code presented in (ref. 41). This code is particularly adapted to simulate in a simple way the influence of topographic variations of the LAB on the lateral sub-lithospheric propagation of buoyant plume material\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eOur model is a 4600 km \u0026times; 4600 km grid, with cells of 60 km. Each node of the 2D grid is composed of 3 layers (lithosphere, plume material, and normal asthenosphere) of uniform density and viscosity. Employed viscosities are 10\u003csup\u003e19\u003c/sup\u003e Pa\u0026sdot;s for the asthenosphere and 10\u003csup\u003e18\u003c/sup\u003e Pa\u0026sdot;s for the plume material, and the density contrast between plume and asthenosphere is set to 20 kg/m\u003csup\u003e3\u003c/sup\u003e. Plume material is sourced at the 5 central nodes, with a flux appropriate (given the employed viscosities and density contrast) for it to spread up to the model Northern Red Sea at the end of the simulations. Flux is kept constant during the pre-rift and continental rifting phases, and is ceased at the onset of the oceanic spreading phase to better evaluate the influence of LAB topographic fabrics.\u003c/p\u003e \u003cp\u003eFlow of plume material is driven by plate tectonics drag (V\u003csub\u003edrag\u003c/sub\u003e caused by motion of the overlying lithosphere), buoyancy (V\u003csub\u003eB\u003c/sub\u003e caused by lateral variations of the base of the plume material), and pressure gradients (V\u003csub\u003epress\u003c/sub\u003e caused by the excess pressure developed from local divergence/convergence of material). Analytical solutions of the shear traction terms (see governing equations in (ref. 41)) are found locally by assuming that V\u003csub\u003edrag\u003c/sub\u003e is equal to the plate velocity at the LAB, that V\u003csub\u003eB\u003c/sub\u003e and V\u003csub\u003epress\u003c/sub\u003e are equal to zero at the LAB, and that the three components are all zero at the base of the asthenosphere. Excess pressure is updated at each time step by solving a system of linear equations using the conjugate gradient method. Like in the model presented by (ref. 41), most of the flow in our models is driven by the V\u003csub\u003eB\u003c/sub\u003e component.\u003c/p\u003e \u003cp\u003eSeparated from this kinematic step, each time increment contains a thermal step where heat exchanges occur between the three layers, and allow further thickness variations. Isostatic and dynamic adjustments of the base of the lithosphere and plume material are also explicitly treated, whereas the base of the asthenosphere is kept at 230 km depth.\u003c/p\u003e \u003cp\u003eThe lithosphere is imposed to move at a background rate of 15 mm/yr to the NW relative to the source of plume material, in accordance with reconstructions of the Afar plume track of (ref. 22). At 16 Ma in our model, a rifting-related component simulating the rotation of Arabia relative to Nubia is added to this background plate kinematics. We did not simulate the Somalia Plate, so the opening of the Red Sea and Gulf of Aden are both governed by a unique rotation pole.\u003c/p\u003e \u003cp\u003eInitial lithospheric thickness is set to 140 km, except along two 150-km-wide sub-lithospheric channel trending obliquely relative to the rift axis. Initial lithospheric thickness is decreased from 140 km at the edges of these channels to 90 km at their axes in a pattern governed by the error function.\u003c/p\u003e \u003cp\u003eRifting-induced variations in lithospheric thickness are calculated by assuming that the zone of active extension keeps a fixed width of 160 km and remains centered on the rift axis (which simulates the progressive inward migration of the deformation), and that instantaneous lithospheric thinning is homogeneous within this zone. For the model presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the phase of oceanic spreading is initiated at 26 Ma, 10Ma after the onset of continental rifting, and is assumed to be synchronous along the entire length of the rift (consistent with the distal OCT end-member of (ref. 18 and 31)).\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work benefited from discussion with Mathilde Cannat and Ran Issachar. Margherita Fittipaldi and Matthieu Ribot are acknowledged for their contribution in mapping the coral marine terraces. This research was supported by King Abdullah University of Science and Technology (KAUST) under the Award Number OSR-CRG2019-4076.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA.M. designed the study, performed the data analysis and modeling, wrote the first draft and prepared the Figures. S.J. provided guidance with the Methods and edited the manuscript. S.J. acquired the funding and resources.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGlobal bathymetry and gravity datasets can be accessed from the GEBCO (https://www.gebco.net/data_and_products/gridded_bathymetry_data/) and University of San Diego (https://topex.ucsd.edu/grav_outreach/#grid) websites. High-resolution bathymetry data are from Mitchell et al. (2010) (https://doi.org/10.1130/B26518.1) and Augustin et al. (2014) (https://doi.org/10.1016/j.epsl.2014.03.047).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBrune, S., Kolawole, F., Olive, J. A., Stamps, D. S., Buck, W. R., Buiter, S. J., \u0026hellip; Shillington, D. J. (2023). Geodynamics of continental rift initiation and evolution. Nature Reviews Earth \u0026amp; Environment, \u003cem\u003e4\u003c/em\u003e(4), 235\u0026ndash;253.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBuiter, S. J., \u0026amp; Torsvik, T. H. (2014). A review of Wilson Cycle plate margins: A role for mantle plumes in continental break-up along sutures?. Gondwana Research, \u003cem\u003e26\u003c/em\u003e(2), 627\u0026ndash;653.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDewey, J. F., \u0026amp; Burke, K. C. (1973). 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Cenozoic magmatism throughout east Africa resulting from impact of a single plume. Nature, \u003cem\u003e395\u003c/em\u003e(6704), 788\u0026ndash;791.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-3862377/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3862377/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Formation of new lithosphere at mid-oceanic ridges occurs through magmatic crustal accretion and cooling of the asthenosphere, and is essentially controlled by the spreading-rate, ridge segmentation, and eventual arrival of deeply-sourced hot mantle plumes. Its dependence on long-term inheritance is supposedly weak, except in cases where ridge segmentation is preconditioned by the reactivation of continental weak zones during the rifting phase. Here, we provide the first evidence that pre-rift lithospheric thickness variations constitute another forcing that may transmit influence from past Wilson cycles beyond the stage of continental break-up. This long-term control involves differential redistribution of heat/melt sources along young laterally-confined plume-assisted rifts. This is demonstrated here in the case of the Red Sea from the correlation between on-axis volcano-tectonic patterns, distribution of onshore volcanism, and lithospheric thickness variations of the rifted margins.","manuscriptTitle":"Persisting influence of continental inheritance on early oceanic spreading","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-17 17:17:58","doi":"10.21203/rs.3.rs-3862377/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-04-02T09:26:05+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-03-18T09:22:24+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-02-14T22:12:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"8514c788-7972-48cc-a48f-193550beef8d","date":"2024-01-29T19:43:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"14db860d-8a15-4f25-bf6c-dffed8f47c45","date":"2024-01-29T09:40:33+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-01-17T18:42:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-01-15T16:03:19+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-01-15T13:21:54+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-01-15T13:16:57+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-01-14T06:16:37+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f19db7ee-0adb-4b58-8fee-23caa3d8d79e","owner":[],"postedDate":"January 17th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":28154226,"name":"Earth and environmental sciences/Solid earth sciences/Geodynamics"},{"id":28154227,"name":"Earth and environmental sciences/Solid earth sciences/Tectonics"},{"id":28154228,"name":"Earth and environmental sciences/Solid earth sciences/Volcanology"}],"tags":[],"updatedAt":"2025-03-31T16:06:52+00:00","versionOfRecord":{"articleIdentity":"rs-3862377","link":"https://doi.org/10.1038/s41598-025-93942-1","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-03-25 15:57:10","publishedOnDateReadable":"March 25th, 2025"},"versionCreatedAt":"2024-01-17 17:17:58","video":"","vorDoi":"10.1038/s41598-025-93942-1","vorDoiUrl":"https://doi.org/10.1038/s41598-025-93942-1","workflowStages":[]},"version":"v1","identity":"rs-3862377","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3862377","identity":"rs-3862377","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}