Ultrafast plate and trench motions reveal weak mantle below the NW Pacific

Ultrafast plate and trench motions reveal weak mantle below the NW Pacific | 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 Physical Sciences - Article Ultrafast plate and trench motions reveal weak mantle below the NW Pacific Daniel Pastor-Galán, Bram Vaes, Lydian Boschman, Arwen Deuss, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9503143/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Tectonic plate motions reflect a balance of driving and resisting forces and typical velocities of <10 cm/yr. Episodes of unusually rapid plate motion provide insights on the processes that reduce this resistance 1–4 . Here, we show that an ancient island arc now exposed in Hokkaido (Japan), together with its associated subduction system, migrated across the mantle beneath the NW Pacific region at ~25 cm/yr between 85 and 50 Ma, based on new paleomagnetic data. Such exceptional rates require an unusually weak upper mantle. There is no evidence for past or present thermal anomalies that, elsewhere, have been proposed to explain anomalous velocities 2,3 . Instead, seismological data show surprisingly high upper‑mantle seismic attenuation in the NW Pacific, signaling reduced grain size and/or elevated water content that likely reflect water and sediment input into the mantle from past intra‑oceanic subduction, which both could cause major mantle weakening. Seismic tomography shows that intra-oceanic subduction also occurred in the NW Pacific before 85 Ma 5–7 , possibly preconditioning the NW Pacific mantle for anomalously high plate rates. Together with emerging evidence of geochemically heterogeneous mantle provinces 8 that preserve relics of ancient subduction or plume activity 9–13 , our findings demonstrate that the distribution, composition, and rheology of mantle heterogeneities record that stem from past geodynamic processes may exert first‑order control on past and present plate motions. Earth and environmental sciences/Solid Earth sciences/Geodynamics Earth and environmental sciences/Solid Earth sciences/Tectonics Earth and environmental sciences/Solid Earth sciences/Palaeomagnetism Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction The rate of tectonic plate motion reflects the balance between driving forces (slab pull, ridge push 14 ) and resisting forces (shear at subduction interfaces, and shear between plate and mantle known as mantle drag 15,16 ). Plates typically move between 2 and 9 cm/yr relative to the mantle. Plates with continents typically move slower than oceans because they have continental keels into the underlying mantle that increase mantle drag 17 . Although plate speeds rarely exceed these ranges, plate reconstructions reveal that transient episodes of ultra‑fast motion have occurred in the geological past. A classic example is the Indian Plate that moved northward toward Eurasia and accelerated at ~65 Ma, reaching >20 cm yr⁻¹, and then rapidly decelerating after 50 Ma 3,18 . Because subduction geometry remained largely unchanged, the ultra‑fast India Plate rates are best explained by a reduction in resistance to plate motion. The correspondence between the arrival of the Deccan mantle plume below the Indian plate ~66 Ma 19 and the plate acceleration led to hypotheses of thermal weakening or continental root erosion, which decreased drag or briefly enhanced mantle flow increasing push as possible drivers of plate acceleration 2,3 . Increased resistance at the plate contact during continental collision may later have caused the deceleration 3 . Recent plate reconstructions suggest that now-fully subducted plates in the northwest Pacific, such as the Izanagi and Olyutorsky plates, may have reached velocities of up to ~25 cm/yr between ~100 and 50 Ma 20,21 . These high rates affected not only plates moving over the mantle but also a subduction zone whose slab was rolling back through the mantle 20,22 . If these rates are correct, such ultra-fast plate and trench motions offer a unique natural laboratory for understanding mantle weakening mechanisms and plate-mantle coupling. As there is no geological record of plume activity in this region since the Late Cretaceous, the high plate rates here cannot be readily attributed to a mantle plume. However, plate reconstructions in the NW Pacific region are far less certain than those for India because magnetic anomaly records have subducted. Therefore, we first test with new paleomagnetic data whether the previously inferred ultra‑fast motions are robust. Ultrafast NW Pacific plate motions Magnetic anomalies preserved on the Pacific Plate reveal that a conjugate oceanic plate once existed in the NW Pacific region that has now been fully subducted: the Izanagi Plate 26 , 27 . The youngest unsubducted ocean floor in the NW Pacific that formed at the Pacific–Izanagi ridge and escaped subduction is ~100 Ma old. Plate reconstructions place that ridge >5000 km southeast of the Japan Trench 23 . Geological evidence shows that this ridge subducted at the Japan subduction zone at ~55-50 Ma 21,24 . Assuming constant spreading rates between ~100 Ma and 55 Ma, the Izanagi plate would have subducted below Japan at high rates (15 to 25 cm/yr) 25 . The Izanagi plate is known only from accreted, deformed and commonly metamorphosed fragments 26 , which do not permit independent verification of its spreading rates. Hokkaido (northern Japan), Sakhalin, and Kamchatka (far‑eastern Russia) preserve the geological record of an intra‑oceanic subduction-related arc, known as Nemuro-Olyutorsky or “paleo‑Kuril” arc (Nemuro hereafter). This arc was ~2500 km wide (Fig. 1) and formed between ~85 and 50 Ma within the NW Paleo‑Pacific 20,22,27,28 . The modern tectonic architecture of Kamchatka indicates that Eurasia was the downgoing plate relative to the Olyutorsky arc, which developed above a south‑ to southeast‑dipping subduction zone that rolled back north‑ to northwestward until its collision with Eurasia at~50 Ma 20,22,27–31 . Subduction may have started at the original Izanagi-Pacific Ridge, implying that Olyutorsky arc motion and rollback rates were similar to the high velocities of the Izanagi plate 20 . Alternatively, subduction may have started within the Izanagi Plate 24 which would yield lower rates. Paleomagnetic analysis of the geological record of the Nemuro arc enables reconstruction of arc and subduction‑zone motion. Paleomagnetic measurements unveil the direction and inclination of Earth’s magnetic field preserved in rocks, allowing determination of their formation latitude. Changes in paleolatitude quantify the north–south component of paleo-plate motion. Previous paleomagnetic studies showed low inclinations for the Nemuro arc suggesting it formed far south of its present position (Extended Data File 7). However, substantial uncertainties in these datasets, many of which are derived from sedimentary rocks uncorrected for inclination shallowing and therefore prone to underestimating paleolatitudes, allowed two competing interpretations. One assumes strong distortion of the sedimentary magnetic record, implying that true paleolatitudes were much higher than measured and that the Nemuro arc experienced only limited and slow motion between ~80 and 50 Ma. In this scenario, the Nemuro arc may have been part of the Pacific Plate, moving with a rate of ~8 cm/yr 22 . Alternatively, the low inclinations may accurately reflect paleolaltitude, which requires that the Nemuro Arc traveled much faster than the Pacific Plate 27,30 . It must then have been part of a plate that spread away from the Pacific Plate, the Olyutorsky Plate 20 , which would have moved ≥ 20 cm/yr. To distinguish between these scenarios, we collected a large paleomagnetic dataset from the Nemuro Arc of Hokkaido, Japan. Sampling included two well‑dated volcano‑sedimentary formations with abundant pillow lavas of Campanian–Maastrichtian age (71 ± 1 Ma, 40 Ar/ 39 Ar bulk rock age; the Nokkamappu and Otamura formations; Fig. 2, Extended Data Files. 1–2) 28,32 , as well as Paleocene adakitic lavas and sills from Nosappu Cape (62.4 ± 1 Ma, 40 Ar/ 39 Ar bulk rock age) 33 (Fig. 2). For the Campanian-Maastrichtian section we applied an inclination‑shallowing correction for the volcano-sedimentary rocks and found that corrected sedimentary directions are statistically indistinguishable from the time-equivalent lavas (Extended Data File 5). We computed a grand mean paleomagnetic pole based on N = 237 paleomagnetic directions, which is located at 52.7° N and 68.8° E, with a bootstrapped 95% cone of confidence (P 95 34 ) of 4.9° (Extended data Fig. 6) and a paleolatitude of 40 ± 5°. This pole passes common paleomagnetic reliability tests (reversal test, conglomerate test) and adheres to statistical criteria that show that the known behavior of the paleomagnetic field is represented by the dataset (see Methods). The Paleocene adakites yielded a paleomagnetic pole based on 40 paleomagnetic directions, located at 64.8º N, 108.1 E, with a parametric 95% cone of confidence A 95 = 6.3° and a paleolatitude of 55 ± 6°. Our dataset provides robust estimates on paleolatitudes and after incorporating age uncertainties, we estimate that the Nemuro arc moved northward at 19.5 cm/yr between 71 and 62 Ma, with bootstrapped 95% confidence limits of 9.2 and 30.2 cm/yr (Extended data Fig. 6). This value represents the minimum plate velocity relative to the Earth’s spin axis, because paleomagnetism only constrains the latitudinal motion, therefore any longitudinal component is not included. Our ~62 Ma pole places the arc close to the final obduction latitude around 55-50 Ma (Fig. 1). The ultra-high rates that we reconstructed between 71 and 62 Ma support the large and fast displacement scenario based on paleomagnetic data from Kamchatka and Sakhalin 20 , which suggests that the entire preserved length of the arc (>2,500 km) migrated northward on the same plate. Plate reconstructions indicate northwestward motion of the Olyutorsky plate, implying that its plate-motion rate exceeded its paleolatitudinal velocity. Since the Nemuro arc occupied the upper plate above a northwestward‑retreating slab, these plate-motion rates provide a first-order proxy for slab rollback. To estimate these rates, we updated the kinematic reconstruction of the Olyutorsky Plate 20 and evaluated motions using models that place plates relative to the mantle 35,36 , to eliminate the effects of the common rotation of plates and mantle together relative to the Earth's spin axis (i.e, true polar wander 38,40 ). This reveals rollback rates of 17 cm/yr with a 95% uncertainty between 7 and 28 cm/yr. These rollback rates for the Olyutorsky subduction zone are the fastest ever reconstructed. Such values greatly exceed typical rollback velocities observed today, which normally rarely exceed a few cm/yr for large, long slabs the size of the Olyutorsky plate 37 . Such unprecedented rollback rates require a substantial reduction in upper‑mantle resistance beneath the NW Pacific. We evaluate this prediction using seismological observations. A weak NW Pacific upper mantle Seismology provides a means to estimate properties of the present-day mantle below the NW Pacific. Seismic attenuation (or damping) is the loss of seismic‑wave energy to heat as waves travel through the Earth. In combination with seismic velocity variations, it may be used as a proxy for viscosity variations in Earth’s mantle. In the NW Pacific, a recent global model of seismic attenuation shows high attenuation 38 , both in the global attenuation model, as well as in more detailed splitting function measurement for upper mantle-sensitive normal modes (Fig. 2). Older upper mantle attenuation models made with seismic surface waves, also showed this anomaly 39,40 . Even though it is a robust feature, it has remained largely uninterpreted, because the region does not have anomalously-low seismic velocity, typical for mid-ocean ridges of mantle plumes/hotspots that would explain high attenuation if temperature were the only control 38 . Instead, the combination of high attenuation with normal mantle velocity may alternatively be explained by either reduced grain sizes and/or elevated water contents, each of which reduces effective viscosity and provides a possible physical origin for an anomalously weak upper mantle anomaly beneath the NW Pacific. Subduction-induced mantle weakening Reduced grain size or elevated water content of upper mantle rock are both features that could be explained by mantle modification due to subduction processes. During subduction, slab dehydration and/or melting will expel SiO 2 -rich fluids. Flushing the mantle with such fluids will trigger chemical reactions that generate heterogeneous mixtures of olivine, pyroxene, and hydrous phases (e.g., amphibole and chlorite at depths <100 km, and phlogopite ~200 km), or under some circumstances, trigger partial melting of the mantle due to down-temperature shifting of the wet peridotite solidus 41 . Si-(re)addition can introduce mineralogical heterogeneities even in mantle provinces that have experienced prior chemical depletion, as is common in mantle wedges above subducting plates 42 . Well-mixed, heterogeneous mantle phase assemblages are known to exhibit smaller grain sizes on average than monophase aggregates, because grain growth is inhibited due to ‘pinning’ of grain and phase boundaries 43 . Whereas a dry upper mantle viscosity at ~200 km may span ~10 22-24 Pa-s, a fine-grained, ‘wet’, and/or low-volume melt-bearing upper mantle at similar depths may exhibit extreme viscosity reduction to as low as ~10 18 Pa-s 44,45 . If the present-day NW Pacific upper mantle retains chemical or mineralogical remnants of ancient subduction, conditioning by subduction-derived fluids is a strong candidate for the rheological weakening that enabled ultrafast motion. If this weak mantle was restricted to the NW Pacific, as seismology suggests, it would have affected Izanagi and Olyutorsky plate motions that were both restricted to this region much more than the much larger Pacific plate. However, the modern anomaly may partly reflect the late Cretaceous intra‑oceanic subduction history beneath the Nemuro arc. Invoking this mechanism requires evidence that mantle‑viscosity reduction was already established before ~85 Ma and persisted throughout the subsequent interval of rapid plate and trench motion. Seismic tomographic images below the NW Pacific region (Fig. 3) image the subducted slab that is linked to subduction below the Nemuro Arc as a flat-lying anomaly around 1400-1200 km depth that in the north southward with a top at ~600–800 km depth (the Agattu slab 46 ). However, below the Agattu slab are deeper anomalies in the same region that have been interpreted as older subducted slabs. This indicates that widespread subduction also occurred > 85 Ma, likely during Jurassic to Early Cretaceous time 5,6,47 . This shows that it is feasible that subduction-modified mantle may have been present in the NW Pacific before the high plate motions and rollback rates of the Olyutorsky Plate and overlying Nemuro arc. A geophysical measure to evaluate whether there may have been lateral variation in upper mantle viscosity and plate-mantle coupling during ultrahigh Olyutorsky plate motion is the net rotation of lithosphere - the average rotation of the entire lithosphere relative to the underlying mantle obtained by integrating all absolute plate‑motion vectors over Earth’s surface 48,49 . If mantle viscosity would be spatially uniform, net rotation of the lithosphere would approach zero; in contrast, lateral differences in viscous coupling result in positive values 43 . For instance, with the current assumptions of viscosity differences of the upper mantle underneath oceanic and continental plates, net lithosphere rotation values are estimated at ~0.1-0.2°/Myr, but during the ultrahigh plate motion rates of the Indian Plate between 65 and 50 Ma they were raised to ~0.3°/Myr 49 , indicating departures from typical upper‑mantle strength caused by localized upper mantle weak zones 50 . Incorporating our ultrafast NW Pacific plate motions into a global plate model 51 and computing net lithosphere rotation using a minimum-continent-motion reference frame leads to net rotation values of up to 0.35°/Myr for the whole 80-50 Ma interval. This supports the hypothesis that already at the time of Olyutorsky and Izanagi plate motion there must have been regional variations in viscosity and thus plate mantle coupling. Geological history of the upper mantle The long-term preservation of compositional anomalies in the upper mantle may be surprising in light of the common assumption that the upper mantle is vigorously convecting and well-mixed 47 . However, there is a growing evidence that there is geochemical upper mantle “provinciality” 8 : regions of the mantle with characteristic chemical, seismological, or thermal features some of which may have formed 150 Myr ago or more. For example, upper mantle geochemical anomalies were inferred below the Gakkel and South-Atlantic ridges revealing traces of subduction that are (still?) located above deep-mantle slabs that subducted as much as 150-200 Ma ago 11,12 . Additionally, in young Galápagos and Easter Island hotspot volcanoes zircon xenocrysts were found that have with plume-related chemistry but with ages up to 170 Ma older than the volcanoes or underlying crust. These suggest that the remains of earlier parts of the plumes did not mix or flow away in the upper mantle for at least 170 Ma 9,10 . Populations of even older zircons are found in intraplate volcanoes and on mid-ocean ridges with continental crustal compositions, showing a spread of ages from the Archean to the Mesozoic 9,10 . These are interpreted as xenocrysts of sand grains introduced into the mantle by former subduction zones 7,52 . These findings demonstrate that compositional heterogeneity in the upper mantle may be preserved for hundreds of millions of years in the region where it was generated. Our results open new opportunities to explain anomalous plate motion. The example from the NW Pacific highlights that the composition of the upper mantle may exert a first-order control on mantle drag. Other proposed explanations for enhanced plate motion include the push exerted by mantle plume heads 3 . The absence of a late Cretaceous-Paleocene plume record associated with the Olyutorsky plate, together with widespread lower‑mantle slabs beneath the region that would hamper plume rise, makes this mechanism unlikely. Major lower mantle upwellings around the Pacific LLSVP and associated rapid whole-mantle convection 4 also cannot account for the observations: reconstructed plate and trench rates are five times faster than even generous numerical models of whole-mantle convection processes 4 . Moreover, slab remnants of the late Cretaceous-Paleocene intra-oceanic subduction zones of the NW Pacific sank at ~1.2-1.6 cm/yr 20,22 , on par with globally reconstructed rates 46 . This is over an order of magnitude slower than the reconstructed plate and trench motions suggesting that the high plate motion rates did not involve anomalously high lower mantle convection rates. We thus conclude that the anomalously high plate motion rates in the NW Pacific had a compositional rather than a thermal origin. The key difference is that the former implies that the geological history of the upper mantle, over time scales of at least 100-200 Myr, is a key ingredient to understand present‑day geodynamics. Predictive dynamic models of plate motions at any given time thus not only require understanding the driving forces from slab pull, ridge push, and convection, but also the preceding geological history that preconditioned the upper mantle composition and resulting viscosity structure. Methods Paleomagnetism Paleomagnetic samples with a standard diameter of 25 mm were collected with a water-cooled, petrol-powered drill during a field campaign in July 2017. The orientation of the samples was measured using a magnetic compass with an inclinometer attached. The Nemuro arc contains an up to 3000 m thick Campanian–Paleocene marine sedimentary sequence (Nemuro Group), interpreted to be deposited in a forearc basin environment and subdivided in several informal formations (EDF-1B) 31,32 . In this study, we have sampled the two lowermost (volcano-)sedimentary formations: the Nokkamappu and Otamura Formations (Fig. 2, Figs. EDF-1B and EDF-2). The Nokkamappu Formation comsists of tuff breccias, volcanic conglomerates, sandstones, siltstones, and pillow lavas of basaltic and andesitic composition with intraoceanic arc signatures 33 . Biostratigraphic ages constrained the age of the formation to 77 to 70.6 Ma and the fossil content indicates a shallow marine depositional environment 31,33 . The Otamura Formation is mainly composed of hemipelagic mudstone and thinly bedded turbiditic sandstone (with negligible quartz) with a few lavas (olivine and clinopyroxene basalts). Both formations are intruded by shoshonitic sills of 70.99 ± 0.87 and 71.9 ± 1.1 Ma and adakites with ages of 62.4 ± 1 Ma (bulk rock Ar-Ar) 33 . In each sedimentary rock sequence, we sampled a clastic sedimentary succession with >90 sites to allow robust correction for inclination shallowing 53,54 . We carried out the paleomagnetic measurements at the paleomagnetic laboratory of Fort Hoofddijk, Utrecht University (Utrecht, The Netherlands). Samples were either demagnetized using stepwise alternating field (AF) demagnetization in a robotized setup 55 or stepwise thermal (TH) demagnetization. The magnetization was measured on a 2G DC-SQUID magnetometer. Throughout the demagnetization process, samples were kept in a magnetically shielded room. We interpreted the analyzed the paleomagnetic measurements and interpretated the data using the freely-available tools on Paleomagnetism.org 56,57 . All our data is available in the Paleomagnetism.org database as well as the MagIC database 57,58 . Demagnetization diagrams were plotted as orthogonal vector diagrams 59 and principal component analysis was used to the determine each of the components 60 . We used Fisher 61 statistics on virtual geomagnetic poles following statistical procedures described in Deenen et al. 62 to calculate site mean directions. We only interpreted as a component when specimens delivered at least five consecutive demagnetization steps in a line. AF steps affected by gyroremanent magnetization 63 were not used for any component interpretation. Where two components unblocked simultaneously and successive demagnetization steps did not trend towards the origin, we used great circle interpretation 64 . We note that we have not used any of the great circles interpreted for the five paleomagnetic poles presented in the results of this study. For comparison, we show the results with and without remagnetization circles in supplementary table ST1. We favor the interpretation of components without them being anchored to the origin, and only forced the vector through the originwhen demagnetization results were noisy. We did not consider any ChRM direction that showed a maximun deviation angle (MAD) > 15º, despite a recent study by Gerritsen et al. 65 that showed that this makes little or no difference for the precision or position of the final paleomagnetic pole. Finally, we applied a 45° cutoff 66 to eliminate outliers that may represent transitional directions or short-term excursions of the past magnetic field. We discarded localities and group of samples that do not properly average paleosecular variation following Deenen et al.’s criteria 62 . We used the elongation-inclination (E/I) method 67 to quantify and correct for inclination shallowing in the sampled sedimentary sequences. The Nokkamappu formation yielded well-defined normal and reverse polarities, passing the conglomerate test (Fig. EDF-3). The application of the elongation-inclination (E/I) correction 67 yielded a flattening factor of f=0.49, increasing the original inclination from 41.1º ± 5.6º to 59.4º +9-11 (Fig. EDF-4). The Otamura formation has a single normal polarity component with a corrected inclination of 53.2º +14-3 (original: 50.4º ± 3.2º) (Fig. 2). For the shoshonitic rocks, we sampled a 71 ± 1 Ma sill intruding the Otamura formation and pillow lavas atop the Nokkamappu formation (Fig. EDF-1). The sill shows two nearly antipodal components (Fig. EDF-5), with a combined normal polarity pointing NW and an inclination of 59.3º ± 5.2º (paleolatitude 40.1º). The pillow lavas yield directions with only reversed polarity that provide a statistically identical mean inclination of -59.2º ± 4.2º (corresponding to a paleolatitude of 40º). Finally, adakitic lavas and sills at Nosappu Cape (62.4 ± 1.1 Ma) 33 exhibit normal polarity with a significantly higher inclination of 70.8º ± 4.5º, corresponding to a paleolatitude of 53.3º (Fig. EDF-5). We estimated a grand mean paleopole from the four Late Cretaceous datasets (ca. 71 Ma) by using a bootstrap approach. We obtained bootstrap samples by re-sampling (with replacement) the VGPs of the igneous datasets, i.e. the data from Nokkamappu pillow basalts (N=53) and the Otamura sills (N=21). For both the sediment-derived datasets, we re-sample the paleomagnetic directions with replacement and compute a flattening factor for this directional dataset using the elongation versus inclination curve predicted by the TK03.GAD model of Tauxe & Kent. After unflattening these re-sampled directions with the obtained flattening factor, we compute convert these directions to VGPs. This yields a sample of N=237 VGPs, from which we compute a single estimate of the mean paleomagnetic pole. By repeating this procedure 5000 times, we obtained a cloud of 5000 paleomagnetic poles. The grand mean paleopole is then computed at the Fisher mean of these poles, with a 95% confidence ellipse (P95) computed from the circle that contains 95% of the bootstrapped poles. This pole passes common paleomagnetic reliability tests (reversal test, conglomerate test) and adheres to statistical criteria that show that the known behavior of the paleomagnetic field is represented by the dataset 62,68 Net lithosphere rotation Net lithosphere rotation is computed by integrating all surface velocity vectors over the surface of the Earth 49 , from which it logically follows that the motions of oceanic plates, having large surfaces and high velocities, predominantly determine net lithosphere rotation. Higher rates of net lithosphere rotation are therefore generally related to rapid oceanic plate motion and may signal deviations from the assumed strength in upper mantle viscosity resulting from local weak zones 50 . Pacific hotspot frames generally record higher rates of net lithosphere rotation up to 0.44°/Ma 72 , because they include faster Pacific plate motion to fit hotspots. While this is usually explained by errors in reconstruction and hotspot motion, Wagenaar et al. 36 recently showed a similar peak up to ~0.45±0.05°/Ma at 85 Ma using a mantle reference frame based on minimal continent motion, thus independent of hotspot motion or oceanic plate motion. The peak in net lithosphere rotation can be traced to the rapid motion of the Izanagi plate (>20 cm/a) in the continent frame of Wagenaar et al. 36 , along with the Pacific plate moving in the same direction as the Izanagi plate, seemingly pulled along over the ridge, following the cessation of subduction under Antarctica. However, different reconstructions of the NW-Pacific, specifically with intra-oceanic subduction zones 20 may dampen the peak in net rotation. We therefore evaluate the robustness of the net lithosphere rotation peak by considering alternative reconstructions. We integrate the reconstruction of the NW-Pacific by Vaes et al. 20 into the global plate model of Merdith et al. 51 , specifically the intra-oceanic subduction zone at the IZA-PAC ridge producing the Olyutorsky arc. Using the continent frame by Wagenaar et al. 36 , we calculate net lithosphere rotation following the method outlined in Torsvik et al. 49 over the optimal 5 Ma time interval as suggested by Atkins and Coltice 50 , including an estimate of the error caused by age uncertainties of plate tectonic features. The altered reconstruction causes a slight decrease in net lithosphere rotation of ~0.05°/Ma at most, reducing the peak at 85 Ma to 0.35°/Ma. This shows differences in reconstruction do influence net lithosphere rotation, as expected, but the presence of the peak remains robust when accounting for the possibility of intra-oceanic subduction. Data Availability Paleomagnetic raw data associated to this manuscript is stored in the zenodo repository under the DOI: 10.5281/zenodo.19704051. The dataset will be uploaded to MagIC and paleomagnetism.org databases upon acceptance. Declarations Author Contribution Daniel Pastor Galán conceived the study, acquired and curated the paleomagnetic data, secured funding, performed formal analyses and interpretations, prepared most of the visualizations and all supplementary material, and co-wrote the first draft of the manuscript. Bram Vaes contributed to methodological development providing pole calculations, conducted formal analyses, prepared visualizations, and wrote sections of the first draft. Lydian M. Boschman conceived the study and acquired the paleomagnetic data, performed the laboratory analyses, and participated in writing through review and editing. Arwen F. Deuss contributed to seismology with methodological development, carried out formal analyses, prepared visualizations, and contributed to manuscript review and editing. Stefania D.M. Wagenaar performed formal analyses and contributed to writing a section in the first draft. Alissa J. Kotowski contributed formal analyses and participated in a section of the first draft and reviewed and edited the manuscript. Naoto Hirano acquired and curated paleomagnetic data, secured funding, and contributed to writing through review and editing. Douwe J.J. van Hinsbergen secured funding, contributed to conceptualization, supervised the project, validated results, and co-wrote original draft of the manuscript. References Behr, W. M. & Becker, T. W. Sediment control on subduction plate speeds. 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Paleomagnetism of a Late Cretaceous island arc complex from South Sakhalin, East Asia: Convergent boundaries far away from the Asian continental margin? Journal of Geophysical Research: Solid Earth 106 , 19193–19205 (2001). Katagiri, T., Naruse, H., Ishikawa, N. & Hirata, T. Collisional bending of the western Paleo-Kuril Arc deduced from paleomagnetic analysis and U–Pb age determination. Island Arc 29 , e12329 (2020). Additional Declarations There is NO Competing Interest. Supplementary Files EDF1.pdf Extended Data Figure 1: Detailed sampling locations within the Nemuro arc. (A) Present-day tectonic map showing the Nemuro-Terpeniya-Olyutorsky and Kronotsky arcs, with the sampling area marked by a red square. (B) Geological map of the Nemuro Peninsula, Hokkaido Island, Japan, with sampling localities in the original field coding highlighted in red. EDF2.pdf Extended Data Figure 2: Demagnetization vector endpoint (Zijderveld) diagrams. Selected examples of Zijderveld diagrams from samples in the Nemuro Peninsula, representing all lithologies and demagnetization techniques applied, including both alternating field (AF) and thermal demagnetization. EDF3.pdf Extended Data Figure 3: Results from Nokkamappu-Otamura formations (sedimentary) Nokkamappu Formation show double polarity results that show a common mean direction in (A) geographic and (B) tectonic coordinates. In addition to pass a reversal test, the Nokkamappu formation passes a conglomerate test. The clasts are distributed close to randomly (C) in contrast to the beds and matrix (A and B). EDF4.pdf Extended Data Figure 4: Results of inclination shallowing analysis from sedimentary formations using the E/I method (Tauxe and Kent, 2003). (A-1) Otamura Formation shows slight flattening; the original inclination falls within the bootstrap limits (B-1), so we use the unflattened directions for better fit. (A-2) Nokkamappu Formation exhibits significant shallowing, with results outside the bootstrap limits (B-2). EDF5.pdf Extended Data Figure 5: Paleomagnetic results by lithology. Summary of locality-specific paleomagnetic results in tectonic coordinates, including associated statistical parameters for each lithology. EDF6.pdf Extended Data Figure 6: Paleolatitudes and paleolatitudinal motion of the Nemuro arc. Distribution of paleolatitude estimates from the grand mean paleopole and adakites data. The upper panel shows 10000 predictions of the paleolatitude based on parametric re-sampling of the paleomagnetic data. The mean and 95% confidence limits are indicated with the solid and dashed lines, respectively. The bottom panel shows the distribution of paleolatitudinal motion estimates derived from the 10000 re-sampled paleolatitudes. The mean (19.5 cm/yr) and 95% confidence limits are again indicated by the solid and dashed lines. EDF7.pdf Extended Data Figure 7: Distribution of studied paleopoles and comparison with literature. (A) Geographic projection showing studied poles and literature results 20,73,74 , with the latter exhibiting consistently shallower inclinations due to uncorrected inclination shallowing in sedimentary rocks. Our ~71 Ma poles (A and B) display consistent paleolatitudes, even with potential inclination shallowing. However, declinations vary widely (A and C) due to large-scale differential vertical-axis rotations and oroclinal bending 75 . Supplementaryinfo.docx Supplementary text TableST1.xlsx Supplementary Table 1: Statistical results per sampled locality Statistical synthesis of the sampled localities following the original field coding (see Extended Data Figure. Sites have been divided in Normal (N) and Reverserd (R) components when both occurred. TableST2.xlsx Supplementary Table 2: Statistical results per formation groups Statistical synthesis of the different groups of localities. Results have been scaffolded (for example the Nokkamappu formation shows the conglomerate blocks results as sepparate). We mark in red results that are unreliable. For example (1) the second locality of the Otamura formation seems to be a spot reading of the magnetic field; or (2) Nokkamappu formation without 45 cut-off show too large of a scatter. Cite Share Download PDF Status: Posted Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-9503143","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":634947425,"identity":"77520af3-c7d6-44c2-8dd1-c186ec8e63f0","order_by":0,"name":"Daniel Pastor-Galán","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7ElEQVRIiWNgGAWjYDCCAzAGOxB/YGDgIU4LWBszAwPjDJK1MBOhnoGB73bz488fKu7Z9TczP3tsU1Mnw9/AfPgDPi2Sd46ZSRw4U5w84zCbuXHOscM8EgfY0iTwaTG4kWDGcLAtIZnhMIOZdG7DAR4DBh4zvA4zuJH++QNIi/xh9m/Slg11QC38n/E6zOBGjoEEUIudwWEeM2nGBmaQLQx4HSZ550yZxJkzCQmGh3nKJHtAfjnMZoZXC9/t9s0fKioS7OWOt2+T+FFTZ8/f3vwYr8NgbkhsgIsw41WP0GJPSN0oGAWjYBSMYAAAAj1JlUPKOxQAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-0226-2739","institution":"CSIC","correspondingAuthor":true,"prefix":"","firstName":"Daniel","middleName":"","lastName":"Pastor-Galán","suffix":""},{"id":634947426,"identity":"5f76cf84-9f18-4beb-a9e7-18f1e5990237","order_by":1,"name":"Bram Vaes","email":"","orcid":"","institution":"Università degli Studi di Milano-Bicocca","correspondingAuthor":false,"prefix":"","firstName":"Bram","middleName":"","lastName":"Vaes","suffix":""},{"id":634947427,"identity":"6ff5a24f-3669-439c-ac18-0111e98d180b","order_by":2,"name":"Lydian Boschman","email":"","orcid":"https://orcid.org/0000-0002-1802-0187","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Lydian","middleName":"","lastName":"Boschman","suffix":""},{"id":634947428,"identity":"56efed67-d0df-40d0-9d90-380d2fe45c85","order_by":3,"name":"Arwen Deuss","email":"","orcid":"","institution":"Utrecht University","correspondingAuthor":false,"prefix":"","firstName":"Arwen","middleName":"","lastName":"Deuss","suffix":""},{"id":634947429,"identity":"a9b044d1-043b-40cc-ab88-536bc2efef49","order_by":4,"name":"Stefania Wagenaar","email":"","orcid":"","institution":"University of Postdam","correspondingAuthor":false,"prefix":"","firstName":"Stefania","middleName":"","lastName":"Wagenaar","suffix":""},{"id":634947430,"identity":"4b145aef-6d99-4790-a5be-ada679235718","order_by":5,"name":"Alissa Kotowski","email":"","orcid":"https://orcid.org/0000-0002-1257-4402","institution":"Utrecht University","correspondingAuthor":false,"prefix":"","firstName":"Alissa","middleName":"","lastName":"Kotowski","suffix":""},{"id":634947431,"identity":"d54f480c-ee87-4049-9b2e-9d1bff6ed84b","order_by":6,"name":"Naoto Hirano","email":"","orcid":"https://orcid.org/0000-0003-0980-3929","institution":"Tohoku University","correspondingAuthor":false,"prefix":"","firstName":"Naoto","middleName":"","lastName":"Hirano","suffix":""},{"id":634947432,"identity":"a1ea725a-fb49-4591-be7c-5261a66ba0a0","order_by":7,"name":"Douwe van Hinsbergen","email":"","orcid":"https://orcid.org/0000-0003-3410-0344","institution":"Utrecht University","correspondingAuthor":false,"prefix":"","firstName":"Douwe","middleName":"van","lastName":"Hinsbergen","suffix":""}],"badges":[],"createdAt":"2026-04-23 06:54:45","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9503143/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9503143/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108957100,"identity":"68dac5ed-0096-42ad-bf57-8249706ea77d","added_by":"auto","created_at":"2026-05-11 08:16:42","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":134130,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePaleolatitudinal northward motion of the Nemuro arc.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe upper panel illustrates Paleolatitudes and associated uncertainties inferred from paleomagnetic data, plotted in present‑day geographic coordinates and compared with the apparent polar wander paths of the Eurasia, Pacific, and Okhotsk plates after Vaes et al.\u003csup\u003e20\u003c/sup\u003e B1 denotes the Grand Mean Pole (71 Ma) from the Nemuro arc, whereas B2 corresponds to the pole derived from the 62 Ma adakites. The lower panel shows Four snapshots of a tentative reconstruction of Okhotsk plate motion and ultrafast trench‑rollback rates from ~70 Ma to the present day. The sampling area is indicated.\u003c/p\u003e","description":"","filename":"Binder11.png","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/d0d4525ef96a0f8518082d6c.png"},{"id":108957135,"identity":"a8249b74-77be-40da-9c61-312707df8628","added_by":"auto","created_at":"2026-05-11 08:16:55","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":660779,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eNormal‑mode splitting function for mantle elastic and anelastic structure.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNormal mode splitting function measurement for normal mode 2S12\u003csup\u003e38\u003c/sup\u003e, which averages mantle structure in the top 800 km of the map, showing (top) elastic structure, i.e. dominantly shear wave velocity and (bottom) anelastic structure, i.e. shear attenuation. In most places, strong attenuation (red colors in bottom panel) correlate with low wave speed anomalies (red colours in top panel) that in turn correlate with spreading ridges. There, elevated temperature may explain both observations.\u0026nbsp; In the NW Pacific, however, strong attenuation is not linked to high temperature and requires an alternative explanation\u003csup\u003e38\u003c/sup\u003e. Red line on the map indicates the P-wave tomographic cross section of Figure 3.\u003c/p\u003e","description":"","filename":"Binder12.png","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/3cbcd4480799d4637d1e02c2.png"},{"id":108957169,"identity":"8cc8a393-0b11-4b91-83cd-564dac0fe632","added_by":"auto","created_at":"2026-05-11 08:17:04","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":466679,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSeismic tomographic cross‑section through the NW Pacific mantle.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSeismic tomographic cross section through the NW Pacific mantle based on the UUP07 tomographic model\u003csup\u003e46\u003c/sup\u003e through the enigmatic zone of strong attenuation imaged by normal mode splitting function measurements (Figure 2). The Agattu slab, obliquely cut here, has a southward dip component and is correlated to the southeastward intra-oceanic subduction zone below the Olyutorsky Plate and Nemuro Arc\u003csup\u003e20,22,46\u003c/sup\u003e. The Aleutian slab is to the east connected to the actively subducting Pacific plate below the Aleutian arc\u003csup\u003e46\u003c/sup\u003e, but in this section is decoupled from the surface because the SW Aleutian plate boundary is a transform. The anomaly may also contain slab remnants of the Bower's Ridge subduction zone\u003csup\u003e20\u003c/sup\u003e. Both slabs are Cenozoic in age. Deeper anomalies reflect earlier Mesozoic intra-oceanic subduction in the NW Pacific realm\u003csup\u003e21\u003c/sup\u003e, below the region of anomalously strong attenuation in the upper mantle (Figure 2).\u003c/p\u003e","description":"","filename":"Binder13.png","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/8003b0cdb08ce551cd0e7efb.png"},{"id":108957137,"identity":"aef4fab4-45e7-4a29-a706-61cbd0ce0a7a","added_by":"auto","created_at":"2026-05-11 08:16:55","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":63036,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eConceptual model for the mantle‑dynamical evolution of the NW Pacific.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSchematic illustration summarizing the proposed mantle evolution beneath the NW Pacific. Left panels show cross‑sections through the upper mantle; right panels present perspective views of intra‑oceanic subduction dynamics.\u003c/p\u003e\n\u003cp\u003eA) Subduction of an Early–Mesozoic slab triggers chemical reactions that weaken portions of the upper mantle.\u003c/p\u003e\n\u003cp\u003eB) The Early Mesozoic slab penetrates the mantle transition zone, while a new phase of intra‑oceanic subduction initiates—likely associated with the Izanagi–Pacific plate boundary. A mechanically weakened mantle domain, inherited from the earlier subduction episode, persists.\u003c/p\u003e\n\u003cp\u003eC) This pre‑existing weak mantle promotes ultrafast slab rollback, consistent with paleomagnetic constraints and seismic observations. The Agattu slab forms during this stage, further contributing to compositional weakening of the upper mantle.\u003c/p\u003e\n\u003cp\u003eD) Present‑day configuration. Both Early and Late Mesozoic slabs are imaged in mantle tomography (Figure 3), while the weakened upper mantle is inferred from strong seismic attenuation (Figure 2).\u003c/p\u003e","description":"","filename":"Binder14.png","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/89cf5ce1f1b94d40784ae7fc.png"},{"id":108977811,"identity":"8caddbf6-7034-43c0-ab83-297459777406","added_by":"auto","created_at":"2026-05-11 11:33:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1581951,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/1479a9d0-2017-48c3-85c1-2cac1a4361cf.pdf"},{"id":108957087,"identity":"3c47fd71-d77b-4cf7-a89c-530db7e5e059","added_by":"auto","created_at":"2026-05-11 08:16:41","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":770276,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExtended Data Figure 1: Detailed sampling locations within the Nemuro arc.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Present-day tectonic map showing the Nemuro-Terpeniya-Olyutorsky and Kronotsky arcs, with the sampling area marked by a red square.\u003c/p\u003e\n\u003cp\u003e(B) Geological map of the Nemuro Peninsula, Hokkaido Island, Japan, with sampling localities in the original field coding highlighted in red.\u003c/p\u003e","description":"","filename":"EDF1.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/71e30cd48b3e9302ae89ca6c.pdf"},{"id":108957082,"identity":"3850fd75-cc3a-4051-821e-3b26e9bf3cec","added_by":"auto","created_at":"2026-05-11 08:16:40","extension":"pdf","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":125522,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExtended Data Figure 2: Demagnetization vector endpoint (Zijderveld) diagrams.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSelected examples of Zijderveld diagrams from samples in the Nemuro Peninsula, representing all lithologies and demagnetization techniques applied, including both alternating field (AF) and thermal demagnetization.\u003c/p\u003e","description":"","filename":"EDF2.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/5b235891b376b2bb4cf9d4a3.pdf"},{"id":108957076,"identity":"068a0f79-e904-4450-b300-a1ea244ee463","added_by":"auto","created_at":"2026-05-11 08:16:39","extension":"pdf","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":355689,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExtended Data Figure 3: Results from Nokkamappu-Otamura formations (sedimentary)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNokkamappu Formation show double polarity results that show a common mean direction in (A) geographic and (B) tectonic coordinates. In addition to pass a reversal test, the Nokkamappu formation passes a conglomerate test. The clasts are distributed close to randomly (C) in contrast to the beds and matrix (A and B).\u003c/p\u003e","description":"","filename":"EDF3.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/2459eca892fd5bb5849e6f39.pdf"},{"id":108957131,"identity":"b6a79fbd-8813-497d-8ce1-e1e20b86539b","added_by":"auto","created_at":"2026-05-11 08:16:53","extension":"pdf","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":279178,"visible":true,"origin":"","legend":"\u003cp\u003eExtended Data Figure 4: Results of inclination shallowing analysis from sedimentary formations using the E/I method (Tauxe and Kent, 2003).\u003c/p\u003e\n\u003cp\u003e(A-1) Otamura Formation shows slight flattening; the original inclination falls within the bootstrap limits (B-1), so we use the unflattened directions for better fit.\u003c/p\u003e\n\u003cp\u003e(A-2) Nokkamappu Formation exhibits significant shallowing, with results outside the bootstrap limits (B-2).\u003c/p\u003e","description":"","filename":"EDF4.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/c73ef1d3748738725a861351.pdf"},{"id":108957078,"identity":"bdcae638-e8ab-4475-8184-53e0fdbcf167","added_by":"auto","created_at":"2026-05-11 08:16:40","extension":"pdf","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":214665,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExtended Data Figure 5: Paleomagnetic results by lithology.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSummary of locality-specific paleomagnetic results in tectonic coordinates, including associated statistical parameters for each lithology.\u003c/p\u003e","description":"","filename":"EDF5.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/9ad9588088d6e125dd83c204.pdf"},{"id":108957134,"identity":"43fd72a3-1d8a-4923-8bf7-606504aecc2c","added_by":"auto","created_at":"2026-05-11 08:16:54","extension":"pdf","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":147928,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExtended Data Figure 6: Paleolatitudes and paleolatitudinal motion of the Nemuro arc.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDistribution of paleolatitude estimates from the grand mean paleopole and adakites data. The upper panel shows 10000 predictions of the paleolatitude based on parametric re-sampling of the paleomagnetic data. The mean and 95% confidence limits are indicated with the solid and dashed lines, respectively. The bottom panel shows the distribution of paleolatitudinal motion estimates derived from the 10000 re-sampled paleolatitudes. The mean (19.5 cm/yr) and 95% confidence limits are again indicated by the solid and dashed lines.\u003c/p\u003e","description":"","filename":"EDF6.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/90bd2acff8497a8a15eb998f.pdf"},{"id":108957171,"identity":"eb3b055e-ca3c-42ec-a864-7f82e3a92632","added_by":"auto","created_at":"2026-05-11 08:17:05","extension":"pdf","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":2752955,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExtended Data Figure 7: Distribution of studied paleopoles and comparison with literature.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(A) Geographic projection showing studied poles and literature results\u003csup\u003e20,73,74\u003c/sup\u003e, with the latter exhibiting consistently shallower inclinations due to uncorrected inclination shallowing in sedimentary rocks. Our ~71 Ma poles (A and B) display consistent paleolatitudes, even with potential inclination shallowing. However, declinations vary widely (A and C) due to large-scale differential vertical-axis rotations and oroclinal bending\u003csup\u003e75\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"EDF7.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/966b5ed0ed65a09a655c4e31.pdf"},{"id":108957162,"identity":"b88671e3-4084-41e2-8f51-f407efae397c","added_by":"auto","created_at":"2026-05-11 08:16:59","extension":"docx","order_by":8,"title":"","display":"","copyAsset":false,"role":"supplement","size":34920,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary text\u003c/p\u003e","description":"","filename":"Supplementaryinfo.docx","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/509770adecf6cafbcc4f3219.docx"},{"id":108957138,"identity":"9018049f-ae5e-4d59-b0aa-93bce1560baa","added_by":"auto","created_at":"2026-05-11 08:16:55","extension":"xlsx","order_by":9,"title":"","display":"","copyAsset":false,"role":"supplement","size":19919,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSupplementary Table 1: Statistical results per sampled locality\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStatistical synthesis of the sampled localities following the original field coding (see Extended Data Figure. Sites have been divided in Normal (N) and Reverserd (R) components when both occurred.\u003c/p\u003e","description":"","filename":"TableST1.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/ac684cdf9fb323ae47acb14c.xlsx"},{"id":108957172,"identity":"de5db070-04a0-4657-848d-8bc4975c7dff","added_by":"auto","created_at":"2026-05-11 08:17:05","extension":"xlsx","order_by":10,"title":"","display":"","copyAsset":false,"role":"supplement","size":14906,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSupplementary Table 2: Statistical results per formation groups\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStatistical synthesis of the different groups of localities. Results have been scaffolded (for example the Nokkamappu formation shows the conglomerate blocks results as sepparate). We mark in red results that are unreliable. For example (1) the second locality of the Otamura formation seems to be a spot reading of the magnetic field; or (2) Nokkamappu formation without 45 cut-off show too large of a scatter.\u003c/p\u003e","description":"","filename":"TableST2.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-9503143/v1/41fa26d65fdccbeb5c4f861c.xlsx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Ultrafast plate and trench motions reveal weak mantle below the NW Pacific","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe rate of tectonic plate motion reflects the balance between driving forces (slab pull, ridge push\u003csup\u003e14\u003c/sup\u003e) and resisting forces (shear at subduction interfaces, and shear between plate and mantle known as mantle drag\u003csup\u003e15,16\u003c/sup\u003e). Plates typically move between 2 and 9 cm/yr relative to the mantle. Plates with continents typically move slower than oceans because they have continental keels into the underlying mantle that increase mantle drag\u003csup\u003e17\u003c/sup\u003e. Although plate speeds rarely exceed these ranges, plate reconstructions reveal that transient episodes of ultra‑fast motion have occurred in the geological past. A classic example is the Indian Plate that moved northward toward Eurasia and accelerated at ~65 Ma, reaching \u0026gt;20 cm yr⁻¹, and then rapidly decelerating after 50 Ma\u003csup\u003e3,18\u003c/sup\u003e. Because subduction geometry remained largely unchanged, the ultra‑fast India Plate rates are best explained by a reduction in resistance to plate motion. The correspondence between the arrival of the Deccan mantle plume below the Indian plate ~66 Ma\u003csup\u003e19\u003c/sup\u003e and the plate acceleration led to hypotheses of thermal weakening or continental root erosion, which decreased drag or briefly enhanced mantle flow increasing push as possible drivers of plate acceleration\u003csup\u003e2,3\u003c/sup\u003e. Increased resistance at the plate contact during continental collision may later have caused the deceleration\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Recent plate reconstructions suggest that now-fully subducted plates in the northwest Pacific, such as the Izanagi and Olyutorsky plates, may have reached velocities of up to ~25 cm/yr between ~100 and 50 Ma\u003csup\u003e20,21\u003c/sup\u003e. These high rates affected not only plates moving over the mantle but also a subduction zone whose slab was rolling back through the mantle\u003csup\u003e20,22\u003c/sup\u003e. If these rates are correct, such ultra-fast plate and trench motions offer a unique natural laboratory for understanding mantle weakening mechanisms and plate-mantle coupling. As there is no geological record of plume activity in this region since the Late Cretaceous, the high plate rates here cannot be readily attributed to a mantle plume. However, plate reconstructions in the NW Pacific region are far less certain than those for India because magnetic anomaly records have subducted. Therefore, we first test with new paleomagnetic data whether the previously inferred ultra‑fast motions are robust.\u003c/p\u003e\n\u003cp\u003eUltrafast NW Pacific plate motions\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Magnetic anomalies preserved on the Pacific Plate reveal that a conjugate oceanic plate once existed in the NW Pacific region that has now been fully subducted: the Izanagi Plate\u003csup\u003e26\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e27\u003c/sup\u003e. The youngest unsubducted ocean floor in the NW Pacific that formed at the Pacific–Izanagi ridge and escaped subduction is ~100 Ma old. Plate reconstructions place that ridge \u0026gt;5000 km southeast of the Japan Trench\u003csup\u003e23\u003c/sup\u003e. Geological evidence shows that this ridge subducted at the Japan subduction zone at ~55-50 Ma\u003csup\u003e21,24\u003c/sup\u003e. Assuming constant spreading rates between ~100 Ma and 55 Ma, the Izanagi plate would have subducted below Japan at high rates (15 to 25 cm/yr)\u003csup\u003e25\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;The Izanagi plate is known only from accreted, deformed and commonly metamorphosed fragments\u003csup\u003e26\u003c/sup\u003e, which do not permit independent verification of its spreading rates. Hokkaido (northern Japan), Sakhalin, and Kamchatka (far‑eastern Russia) preserve the geological record of an intra‑oceanic subduction-related arc, known as Nemuro-Olyutorsky or “paleo‑Kuril” arc (Nemuro hereafter). This arc was ~2500 km wide (Fig. 1) and formed between ~85 and 50 Ma within the NW Paleo‑Pacific\u003csup\u003e20,22,27,28\u003c/sup\u003e. The modern tectonic architecture of Kamchatka indicates that Eurasia was the downgoing plate relative to the Olyutorsky arc, which developed above a south‑ to southeast‑dipping subduction zone that rolled back north‑ to northwestward until its collision with Eurasia at~50 Ma\u003csup\u003e20,22,27–31\u003c/sup\u003e. Subduction may have started at the original Izanagi-Pacific Ridge, implying that Olyutorsky arc motion and rollback rates were similar to the high velocities of the Izanagi plate\u003csup\u003e20\u003c/sup\u003e. Alternatively, subduction may have started within the Izanagi Plate\u003csup\u003e24\u003c/sup\u003e which would yield lower rates.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Paleomagnetic analysis of the geological record of the Nemuro arc enables reconstruction of arc and subduction‑zone motion. Paleomagnetic measurements unveil the direction and inclination of Earth’s magnetic field preserved in rocks, allowing determination of their formation latitude. Changes in paleolatitude quantify the north–south component of paleo-plate motion. Previous paleomagnetic studies showed low inclinations for the Nemuro arc suggesting it formed far south of its present position (Extended Data File 7). However, substantial uncertainties in these datasets, many of which are derived from sedimentary rocks uncorrected for inclination shallowing and therefore prone to underestimating paleolatitudes, allowed two competing interpretations. One assumes strong distortion of the sedimentary magnetic record, implying that true paleolatitudes were much higher than measured and that the Nemuro arc experienced only limited and slow motion between ~80 and 50 Ma. In this scenario, the Nemuro arc may have been part of the Pacific Plate, moving with a rate of ~8 cm/yr\u003csup\u003e22\u003c/sup\u003e. Alternatively, the low inclinations may accurately reflect paleolaltitude, which requires that the Nemuro Arc traveled much faster than the Pacific Plate\u003csup\u003e27,30\u003c/sup\u003e. It must then have been part of a plate that spread away from the Pacific Plate, the Olyutorsky Plate\u003csup\u003e20\u003c/sup\u003e, which would have moved ≥ 20 cm/yr.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;To distinguish between these scenarios, we collected a large paleomagnetic dataset from the Nemuro Arc of Hokkaido, Japan. Sampling included two well‑dated volcano‑sedimentary formations with abundant pillow lavas of Campanian–Maastrichtian age (71 ± 1 Ma, \u003csup\u003e40\u003c/sup\u003eAr/\u003csup\u003e39\u003c/sup\u003eAr bulk rock age; the Nokkamappu and Otamura formations; Fig. 2, Extended Data Files. 1–2)\u003csup\u003e28,32\u003c/sup\u003e, as well as Paleocene adakitic lavas and sills from Nosappu Cape (62.4 ± 1 Ma, \u003csup\u003e40\u003c/sup\u003eAr/\u003csup\u003e39\u003c/sup\u003eAr bulk rock age)\u003csup\u003e33\u003c/sup\u003e (Fig. 2). For the Campanian-Maastrichtian section we applied an inclination‑shallowing correction for the volcano-sedimentary rocks and found that corrected sedimentary directions are statistically indistinguishable from the time-equivalent lavas (Extended Data File 5). We computed a grand mean paleomagnetic pole based on N = 237 paleomagnetic directions, which is located at 52.7° N and 68.8° E, with a bootstrapped 95% cone of confidence (P\u003csub\u003e95\u003c/sub\u003e\u003csup\u003e34\u003c/sup\u003e) of 4.9° (Extended data Fig. 6) and a paleolatitude of 40 ± 5°. This pole passes common paleomagnetic reliability tests (reversal test, conglomerate test) and adheres to statistical criteria that show that the known behavior of the paleomagnetic field is represented by the dataset (see Methods). The Paleocene adakites yielded a paleomagnetic pole based on 40 paleomagnetic directions, located at 64.8º N, 108.1 E, with a parametric 95% cone of confidence A\u003csub\u003e95\u003c/sub\u003e = 6.3° and a paleolatitude of 55 ± 6°.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Our dataset provides robust estimates on paleolatitudes and after incorporating age uncertainties, we estimate that the Nemuro arc moved northward at 19.5 cm/yr between 71 and 62 Ma, with bootstrapped 95% confidence limits of 9.2 and 30.2 cm/yr (Extended data Fig. 6). This value represents the minimum plate velocity relative to the Earth’s spin axis, because paleomagnetism only constrains the latitudinal motion, therefore any longitudinal component is not included. Our ~62 Ma pole places the arc close to the final obduction latitude around 55-50 Ma (Fig. 1). The ultra-high rates that we reconstructed between 71 and 62 Ma support the large and fast displacement scenario based on paleomagnetic data from Kamchatka and Sakhalin\u003csup\u003e20\u003c/sup\u003e, which suggests that the entire preserved length of the arc (\u0026gt;2,500 km) migrated northward on the same plate.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Plate reconstructions indicate northwestward motion of the Olyutorsky plate, implying that its plate-motion rate exceeded its paleolatitudinal velocity. Since the Nemuro arc occupied the upper plate above a northwestward‑retreating slab, these plate-motion rates provide a first-order proxy for slab rollback. To estimate these rates, we updated the kinematic reconstruction of the Olyutorsky Plate\u003csup\u003e20\u003c/sup\u003e and evaluated motions using models that place plates relative to the mantle\u003csup\u003e35,36\u003c/sup\u003e, to eliminate the effects of the common rotation of plates and mantle together relative to the Earth's spin axis (i.e, true polar wander\u003csup\u003e38,40\u003c/sup\u003e). This reveals rollback rates of 17 cm/yr with a 95% uncertainty between 7 and 28 cm/yr. These rollback rates for the Olyutorsky subduction zone are the fastest ever reconstructed. Such values greatly exceed typical rollback velocities observed today, which normally rarely exceed a few cm/yr for large, long slabs the size of the Olyutorsky plate\u003csup\u003e37\u003c/sup\u003e. Such unprecedented rollback rates require a substantial reduction in upper‑mantle resistance beneath the NW Pacific. We evaluate this prediction using seismological observations.\u003c/p\u003e\n\u003cp\u003eA weak NW Pacific upper mantle\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Seismology provides a means to estimate properties of the present-day mantle below the NW Pacific. Seismic attenuation (or damping) is the loss of seismic‑wave energy to heat as waves travel through the Earth. In combination with seismic velocity variations, it may be used as a proxy for viscosity variations in Earth’s mantle. In the NW Pacific, a recent global model of seismic attenuation shows high attenuation\u003csup\u003e38\u003c/sup\u003e, both in the global attenuation model, as well as in more detailed splitting function measurement for upper mantle-sensitive normal modes (Fig. 2). Older upper mantle attenuation models made with seismic surface waves, also showed this anomaly\u003csup\u003e39,40\u003c/sup\u003e. Even though it is a robust feature, it has remained largely uninterpreted, because the region does not have anomalously-low seismic velocity, typical for mid-ocean ridges of mantle plumes/hotspots that would explain high attenuation if temperature were the only control\u003csup\u003e38\u003c/sup\u003e. Instead, the combination of high attenuation with normal mantle velocity may alternatively be explained by either reduced grain sizes and/or elevated water contents, each of which reduces effective viscosity and provides a possible physical origin for an anomalously weak upper\u0026nbsp;mantle anomaly beneath the NW Pacific.\u003c/p\u003e\n\u003cp\u003eSubduction-induced mantle weakening\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Reduced grain size or elevated water content of upper mantle rock are both features that could be explained by mantle modification due to subduction processes. During subduction, slab dehydration and/or melting will expel SiO\u003csub\u003e2\u003c/sub\u003e-rich fluids. Flushing the mantle with such fluids will trigger chemical reactions that generate heterogeneous mixtures of olivine, pyroxene, and hydrous phases (e.g., amphibole and chlorite at depths \u0026lt;100 km, and phlogopite ~200 km), or under some circumstances, trigger partial melting of the mantle due to down-temperature shifting of the wet peridotite solidus\u003csup\u003e41\u003c/sup\u003e. Si-(re)addition can introduce mineralogical heterogeneities even in mantle provinces that have experienced prior chemical depletion, as is common in mantle wedges above subducting plates\u003csup\u003e42\u003c/sup\u003e. Well-mixed, heterogeneous mantle phase assemblages are known to exhibit smaller grain sizes on average than monophase aggregates, because grain growth is inhibited due to ‘pinning’ of grain and phase boundaries\u003csup\u003e43\u003c/sup\u003e. Whereas a dry upper mantle viscosity at ~200 km may span ~10\u003csup\u003e22-24\u003c/sup\u003e Pa-s, a fine-grained, ‘wet’, and/or low-volume melt-bearing upper mantle at similar depths may exhibit extreme viscosity reduction to as low as ~10\u003csup\u003e18\u003c/sup\u003e Pa-s\u003csup\u003e44,45\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;If the present-day NW Pacific upper mantle retains chemical or mineralogical remnants of ancient subduction, conditioning by subduction-derived fluids is a strong candidate for the rheological weakening that enabled ultrafast motion. If this weak mantle was restricted to the NW Pacific, as seismology suggests, it would have affected Izanagi and Olyutorsky plate motions that were both restricted to this region much more than the much larger Pacific plate. However, the modern anomaly may partly reflect the late Cretaceous intra‑oceanic subduction history beneath the Nemuro arc. Invoking this mechanism requires evidence that mantle‑viscosity reduction was already established before ~85 Ma and persisted throughout the subsequent interval of rapid plate and trench motion.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Seismic tomographic images below the NW Pacific region (Fig. 3) image the subducted slab that is linked to subduction below the Nemuro Arc as a flat-lying anomaly around 1400-1200 km depth that in the north southward with a top at ~600–800 km depth (the Agattu slab\u003csup\u003e46\u003c/sup\u003e). However, below the Agattu slab are deeper anomalies in the same region that have been interpreted as older subducted slabs. This indicates that widespread subduction also occurred \u0026gt; 85 Ma, likely during Jurassic to Early Cretaceous time\u003csup\u003e5,6,47\u003c/sup\u003e. This shows that it is feasible that subduction-modified mantle may have been present in the NW Pacific before the high plate motions and rollback rates of the Olyutorsky Plate and overlying Nemuro arc.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;A geophysical measure to evaluate whether there may have been lateral variation in upper mantle viscosity and plate-mantle coupling during ultrahigh Olyutorsky plate motion is the net rotation of lithosphere - the average rotation of the entire lithosphere relative to the underlying mantle obtained by integrating all absolute plate‑motion vectors over Earth’s surface\u003csup\u003e48,49\u003c/sup\u003e. If mantle viscosity would be spatially uniform, net rotation of the lithosphere would approach zero; in contrast, lateral differences in viscous coupling result in positive values\u003csup\u003e43\u003c/sup\u003e. For instance, with the current assumptions of viscosity differences of the upper mantle underneath oceanic and continental plates, net lithosphere rotation values are estimated at ~0.1-0.2°/Myr, but during the ultrahigh plate motion rates of the Indian Plate between 65 and 50 Ma they were raised to ~0.3°/Myr\u003csup\u003e49\u003c/sup\u003e, indicating departures from typical upper‑mantle strength caused by localized upper mantle weak zones\u003csup\u003e50\u003c/sup\u003e. Incorporating our ultrafast NW Pacific plate motions into a global plate model\u003csup\u003e51\u003c/sup\u003e and computing net lithosphere rotation using a minimum-continent-motion reference frame leads to net rotation values of up to 0.35°/Myr for the whole 80-50 Ma interval. This supports the hypothesis that already at the time of Olyutorsky and Izanagi plate motion there must have been regional variations in viscosity and thus plate mantle coupling.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Geological history of the upper mantle\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;The long-term preservation of compositional anomalies in the upper mantle may be surprising in light of the common assumption that the upper mantle is vigorously convecting and well-mixed\u003csup\u003e47\u003c/sup\u003e. However, there is a growing evidence that there is geochemical upper mantle “provinciality”\u003csup\u003e8\u003c/sup\u003e: regions of the mantle with characteristic chemical, seismological, or thermal features some of which may have formed 150 Myr ago or more. For example, upper mantle geochemical anomalies were inferred below the Gakkel and South-Atlantic ridges revealing traces of subduction that are (still?) located above deep-mantle slabs that subducted as much as 150-200 Ma ago\u003csup\u003e11,12\u003c/sup\u003e. Additionally, in young Galápagos and Easter Island hotspot volcanoes zircon xenocrysts were found that have with plume-related chemistry but with ages up to 170 Ma older than the volcanoes or underlying crust. These suggest that the remains of earlier parts of the plumes did not mix or flow away in the upper mantle for at least 170 Ma\u003csup\u003e9,10\u003c/sup\u003e. Populations of even older zircons are found in intraplate volcanoes and on mid-ocean ridges with continental crustal compositions, showing a spread of ages from the Archean to the Mesozoic\u003csup\u003e9,10\u003c/sup\u003e. These are interpreted as xenocrysts of sand grains introduced into the mantle by former subduction zones\u003csup\u003e7,52\u003c/sup\u003e. These findings demonstrate that compositional heterogeneity in the upper mantle may be preserved for hundreds of millions of years in the region where it was generated.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Our results open new opportunities to explain anomalous plate motion. The example from the NW Pacific highlights that the composition of the upper mantle may exert a first-order control on mantle drag. Other proposed explanations for enhanced plate motion include the push exerted by mantle plume heads\u003csup\u003e3\u003c/sup\u003e. The absence of a late Cretaceous-Paleocene plume record associated with the Olyutorsky plate, together with widespread lower‑mantle slabs beneath the region that would hamper plume rise, makes this mechanism unlikely. Major lower mantle upwellings around the Pacific LLSVP and associated rapid whole-mantle convection\u003csup\u003e4\u003c/sup\u003e also cannot account for the observations: reconstructed plate and trench rates are five times faster than even generous numerical models of whole-mantle convection processes\u003csup\u003e4\u003c/sup\u003e. Moreover, slab remnants of the late Cretaceous-Paleocene intra-oceanic subduction zones of the NW Pacific sank at \u0026nbsp;~1.2-1.6 cm/yr\u003csup\u003e20,22\u003c/sup\u003e, on par with globally reconstructed rates\u003csup\u003e46\u003c/sup\u003e. This is over an order of magnitude slower than the reconstructed plate and trench motions suggesting that the high plate motion rates did not involve anomalously high lower mantle convection rates.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;We thus conclude that the anomalously high plate motion rates in the NW Pacific had a compositional rather than a thermal origin. The key difference is that the former implies that the geological history of the upper mantle, over time scales of at least 100-200 Myr, is a key ingredient to understand present‑day geodynamics. Predictive dynamic models of plate motions at any given time thus not only require understanding the driving forces from slab pull, ridge push, and convection, but also the preceding geological history that preconditioned the upper mantle composition and resulting viscosity structure.\u003c/p\u003e"},{"header":"Methods","content":"\u003ch2\u003ePaleomagnetism\u003c/h2\u003e\n\u003cp\u003ePaleomagnetic samples with a standard diameter of 25 mm were collected with a water-cooled, petrol-powered drill during a field campaign in July 2017. The orientation of the samples was measured using a magnetic compass with an inclinometer attached.\u003c/p\u003e\n\u003cp\u003eThe Nemuro arc contains an up to 3000 m thick Campanian\u0026ndash;Paleocene marine sedimentary sequence (Nemuro Group), interpreted to be deposited in a forearc basin environment and subdivided in several informal formations (EDF-1B)\u003csup\u003e31,32\u003c/sup\u003e. In this study, we have sampled the two lowermost (volcano-)sedimentary formations: the Nokkamappu and Otamura Formations (Fig. 2, Figs. EDF-1B and EDF-2). The Nokkamappu Formation comsists of tuff breccias, volcanic conglomerates, sandstones, siltstones, and pillow lavas of basaltic and andesitic composition with intraoceanic arc signatures\u003csup\u003e33\u003c/sup\u003e. Biostratigraphic ages constrained the age of the formation to 77 to 70.6 Ma and the fossil content indicates a shallow marine depositional environment\u003csup\u003e31,33\u003c/sup\u003e. The Otamura Formation \u0026nbsp;is mainly composed of hemipelagic mudstone and thinly bedded turbiditic sandstone (with negligible quartz) with a few lavas (olivine and clinopyroxene basalts). Both formations are intruded by shoshonitic sills of 70.99 \u0026plusmn; 0.87 and 71.9 \u0026plusmn; 1.1 Ma and adakites with ages of 62.4 \u0026plusmn; 1 Ma (bulk rock Ar-Ar)\u003csup\u003e33\u003c/sup\u003e. In each sedimentary rock sequence, we sampled a clastic sedimentary succession with \u0026gt;90 sites to allow robust correction for inclination shallowing\u003csup\u003e53,54\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eWe carried out the paleomagnetic measurements at the paleomagnetic laboratory of Fort Hoofddijk, Utrecht University (Utrecht, The Netherlands). Samples were either demagnetized using stepwise alternating field (AF) demagnetization in a robotized setup\u003csup\u003e55\u003c/sup\u003e or stepwise thermal (TH) demagnetization. The magnetization was measured on a 2G DC-SQUID magnetometer. Throughout the demagnetization process, samples were kept in a magnetically shielded room.\u003c/p\u003e\n\u003cp\u003eWe interpreted the analyzed the paleomagnetic measurements \u0026nbsp;and interpretated the data using the freely-available tools on Paleomagnetism.org\u003csup\u003e56,57\u003c/sup\u003e. All our data is available in the Paleomagnetism.org database as well as the MagIC database\u003csup\u003e57,58\u003c/sup\u003e. Demagnetization diagrams were plotted as orthogonal vector diagrams\u003csup\u003e59\u003c/sup\u003e and principal component analysis was used to the determine each of the components\u003csup\u003e60\u003c/sup\u003e. We used Fisher\u003csup\u003e61\u003c/sup\u003e statistics on virtual geomagnetic poles following statistical procedures described in Deenen et al.\u003csup\u003e62\u003c/sup\u003e to calculate site mean directions. We only interpreted as a component when specimens delivered at least five consecutive demagnetization steps in a line. AF steps affected by gyroremanent magnetization\u003csup\u003e63\u003c/sup\u003e were not used for any component interpretation. Where two components unblocked simultaneously and successive demagnetization steps did not trend towards the origin, we used great circle interpretation\u003csup\u003e64\u003c/sup\u003e. We note that we have not used any of the great circles interpreted for the five paleomagnetic poles presented in the results of this study. For comparison, we show the results with and without remagnetization circles in supplementary table ST1. We favor the interpretation of components without them being anchored to the origin, and only forced the vector through the originwhen demagnetization results were noisy. We did not consider any ChRM direction that showed a maximun deviation angle (MAD) \u0026gt; 15\u0026ordm;, despite a recent study by Gerritsen et al.\u003csup\u003e65\u003c/sup\u003e that showed that this makes little or no difference for the precision or position of the final paleomagnetic pole. Finally, we applied a 45\u0026deg; cutoff\u003csup\u003e66\u003c/sup\u003e to eliminate outliers that may represent transitional directions or short-term excursions of the past magnetic field. We discarded localities and group of samples that do not properly average paleosecular variation following Deenen et al.\u0026rsquo;s criteria\u003csup\u003e62\u003c/sup\u003e. We used the elongation-inclination (E/I) method\u003csup\u003e67\u003c/sup\u003e to quantify and correct for inclination shallowing in the sampled sedimentary sequences.\u003c/p\u003e\n\u003cp\u003eThe Nokkamappu formation yielded well-defined normal and reverse polarities, passing the conglomerate test (Fig. EDF-3). The application of the elongation-inclination (E/I) correction\u003csup\u003e67\u003c/sup\u003e yielded a flattening factor of f=0.49, increasing the original inclination from 41.1\u0026ordm; \u0026plusmn; 5.6\u0026ordm; to 59.4\u0026ordm; +9-11 (Fig. EDF-4). The Otamura formation has a single normal polarity component with a corrected inclination of 53.2\u0026ordm; +14-3 (original: 50.4\u0026ordm; \u0026plusmn; 3.2\u0026ordm;) (Fig. 2).\u003c/p\u003e\n\u003cp\u003eFor the shoshonitic rocks, we sampled a 71 \u0026plusmn; 1 Ma sill intruding the Otamura formation and pillow lavas atop the Nokkamappu formation (Fig. EDF-1). The sill shows two nearly antipodal components (Fig. EDF-5), with a combined normal polarity pointing NW and an inclination of 59.3\u0026ordm; \u0026plusmn; 5.2\u0026ordm; (paleolatitude 40.1\u0026ordm;). The pillow lavas yield directions with only reversed polarity that provide a statistically identical mean inclination of -59.2\u0026ordm; \u0026plusmn; 4.2\u0026ordm; (corresponding to a paleolatitude of 40\u0026ordm;). Finally, adakitic lavas and sills at Nosappu Cape (62.4 \u0026plusmn; 1.1 Ma)\u003csup\u003e33\u003c/sup\u003e exhibit normal polarity with a significantly higher inclination of 70.8\u0026ordm; \u0026plusmn; 4.5\u0026ordm;, corresponding to a paleolatitude of 53.3\u0026ordm; (Fig. EDF-5).\u003c/p\u003e\n\u003cp\u003eWe estimated a grand mean paleopole from the four Late Cretaceous datasets (ca. 71 Ma) by using a bootstrap approach. We obtained bootstrap samples by re-sampling (with replacement) the VGPs of the igneous datasets, i.e. the data from Nokkamappu pillow basalts (N=53) and the Otamura sills (N=21). For both the sediment-derived datasets, we re-sample the paleomagnetic directions with replacement and compute a flattening factor for this directional dataset using the elongation versus inclination curve predicted by the TK03.GAD model of Tauxe \u0026amp; Kent. After unflattening these re-sampled directions with the obtained flattening factor, we compute convert these directions to VGPs. This yields a sample of N=237 VGPs, from which we compute a single estimate of the mean paleomagnetic pole. By repeating this procedure 5000 times, we obtained a cloud of 5000 paleomagnetic poles. The grand mean paleopole is then computed at the Fisher mean of these poles, with a 95% confidence ellipse (P95) computed from the circle that contains 95% of the bootstrapped poles.\u003c/p\u003e\n\u003cp\u003eThis pole passes common paleomagnetic reliability tests (reversal test, conglomerate test) and adheres to statistical criteria that show that the known behavior of the paleomagnetic field is represented by the dataset\u003csup\u003e62,68\u003c/sup\u003e\u003c/p\u003e\n\u003ch2\u003eNet lithosphere rotation\u003c/h2\u003e\n\u003cp\u003e\u0026nbsp;Net lithosphere rotation is computed by integrating all surface velocity vectors over the surface of the Earth\u003csup\u003e49\u003c/sup\u003e, from which it logically follows that the motions of oceanic plates, having large surfaces and high velocities, predominantly determine net lithosphere rotation. Higher rates of net lithosphere rotation are therefore generally related to rapid oceanic plate motion and may signal deviations from the assumed strength in upper mantle viscosity resulting from local weak zones\u003csup\u003e50\u003c/sup\u003e. Pacific hotspot frames generally record higher rates of net lithosphere rotation up to 0.44\u0026deg;/Ma\u003csup\u003e72\u003c/sup\u003e, because they include faster Pacific plate motion to fit hotspots. While this is usually explained by errors in reconstruction and hotspot motion, Wagenaar et al.\u003csup\u003e36\u003c/sup\u003e recently showed a similar peak up to ~0.45\u0026plusmn;0.05\u0026deg;/Ma at 85 Ma using a mantle reference frame based on minimal continent motion, thus independent of hotspot motion or oceanic plate motion. The peak in net lithosphere rotation can be traced to the rapid motion of the Izanagi plate (\u0026gt;20 cm/a) in the continent frame of Wagenaar et al.\u003csup\u003e36\u003c/sup\u003e, along with the Pacific plate moving in the same direction as the Izanagi plate, seemingly pulled along over the ridge, following the cessation of subduction under Antarctica.\u003c/p\u003e\n\u003cp\u003eHowever, different reconstructions of the NW-Pacific, specifically with intra-oceanic subduction zones\u003csup\u003e20\u003c/sup\u003e may dampen the peak in net rotation. We therefore evaluate the robustness of the net lithosphere rotation peak by considering alternative reconstructions. We integrate the reconstruction of the NW-Pacific by Vaes et al.\u003csup\u003e20\u003c/sup\u003e into the global plate model of Merdith et al.\u003csup\u003e51\u003c/sup\u003e, specifically the intra-oceanic subduction zone at the IZA-PAC ridge producing the Olyutorsky arc. Using the continent frame by Wagenaar et al.\u003csup\u003e36\u003c/sup\u003e, we calculate net lithosphere rotation following the method outlined in Torsvik et al.\u003csup\u003e49\u003c/sup\u003e over the optimal 5 Ma time interval as suggested by Atkins and Coltice\u003csup\u003e50\u003c/sup\u003e, including an estimate of the error caused by age uncertainties of plate tectonic features.\u003c/p\u003e\n\u003cp\u003eThe altered reconstruction causes a slight decrease in net lithosphere rotation of ~0.05\u0026deg;/Ma at most, reducing the peak at 85 Ma to 0.35\u0026deg;/Ma. This shows differences in reconstruction do influence net lithosphere rotation, as expected, but the presence of the peak remains robust when accounting for the possibility of intra-oceanic subduction.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003ePaleomagnetic raw data associated to this manuscript is stored in the zenodo repository under the DOI: 10.5281/zenodo.19704051. The dataset will be uploaded to MagIC and paleomagnetism.org databases upon acceptance.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDaniel Pastor Galán conceived the study, acquired and curated the paleomagnetic data, secured funding, performed formal analyses and interpretations, prepared most of the visualizations and all supplementary material, and co-wrote the first draft of the manuscript. Bram Vaes contributed to methodological development providing pole calculations, conducted formal analyses, prepared visualizations, and wrote sections of the first draft. Lydian M. Boschman conceived the study and acquired the paleomagnetic data, performed the laboratory analyses, and participated in writing through review and editing. Arwen F. Deuss contributed to seismology with methodological development, carried out formal analyses, prepared visualizations, and contributed to manuscript review and editing. Stefania D.M. Wagenaar performed formal analyses and contributed to writing a section in the first draft. Alissa J. Kotowski contributed formal analyses and participated in a section of the first draft and reviewed and edited the manuscript. Naoto Hirano acquired and curated paleomagnetic data, secured funding, and contributed to writing through review and editing. Douwe J.J. van Hinsbergen secured funding, contributed to conceptualization, supervised the project, validated results, and co-wrote original draft of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eBehr, W. M. \u0026amp; Becker, T. W. 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Collisional bending of the western Paleo-Kuril Arc deduced from paleomagnetic analysis and U\u0026ndash;Pb age determination. \u003cem\u003eIsland Arc\u003c/em\u003e \u003cstrong\u003e29\u003c/strong\u003e, e12329 (2020).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-9503143/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9503143/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eTectonic plate motions reflect a balance of driving and resisting forces and typical velocities of \u0026lt;10 cm/yr. Episodes of unusually rapid plate motion provide insights on the processes that reduce this resistance\u003c/strong\u003e\u003csup\u003e1–4\u003c/sup\u003e\u003cstrong\u003e. Here, we show that an ancient island arc now exposed in Hokkaido (Japan), together with its associated subduction system, migrated across the mantle beneath the NW Pacific region at ~25 cm/yr between 85 and 50 Ma, based on new paleomagnetic data. Such exceptional rates require an unusually weak upper mantle. There is no evidence for past or present thermal anomalies that, elsewhere, have been proposed to explain anomalous velocities\u003c/strong\u003e\u003csup\u003e2,3\u003c/sup\u003e\u003cstrong\u003e. Instead, seismological data show surprisingly high upper‑mantle seismic attenuation in the NW Pacific, signaling reduced grain size and/or elevated water content that likely reflect water and sediment input into the mantle from past intra‑oceanic subduction, which both could cause major mantle weakening. Seismic tomography shows that intra-oceanic subduction also occurred in the NW Pacific before 85 Ma\u003c/strong\u003e\u003csup\u003e5–7\u003c/sup\u003e\u003cstrong\u003e, possibly preconditioning the NW Pacific mantle for anomalously high plate rates. Together with emerging evidence of geochemically heterogeneous mantle provinces\u003c/strong\u003e\u003csup\u003e8\u003c/sup\u003e\u003cstrong\u003e that preserve relics of ancient subduction or plume activity\u003c/strong\u003e\u003csup\u003e9–13\u003c/sup\u003e\u003cstrong\u003e, our findings demonstrate that the distribution, composition, and rheology of mantle heterogeneities record that stem from past geodynamic processes may exert first‑order control on past and present plate motions.\u003c/strong\u003e\u003c/p\u003e","manuscriptTitle":"Ultrafast plate and trench motions reveal weak mantle below the NW Pacific","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-11 08:15:54","doi":"10.21203/rs.3.rs-9503143/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d350417f-d18c-44db-902b-02bb6e0b303f","owner":[],"postedDate":"May 11th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":67577208,"name":"Earth and environmental sciences/Solid Earth sciences/Geodynamics"},{"id":67577209,"name":"Earth and environmental sciences/Solid Earth sciences/Tectonics"},{"id":67577210,"name":"Earth and environmental sciences/Solid Earth sciences/Palaeomagnetism"}],"tags":[],"updatedAt":"2026-05-11T08:15:54+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-11 08:15:54","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9503143","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9503143","identity":"rs-9503143","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}