Control of slab tears and slab flat wedging on volcanism in the Alaska subduction zone

Control of slab tears and slab flat wedging on volcanism in the Alaska subduction zone | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Control of slab tears and slab flat wedging on volcanism in the Alaska subduction zone ZHI WANG, Yaping Hu, Cunxi Liu, Feiyu Zhao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4457707/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Oct, 2024 Read the published version in Scientific Reports → Version 1 posted 14 You are reading this latest preprint version Abstract Multistage plate subduction plays a crucial role in magmatism; however, the mechanisms by which deep geodynamic processes govern volcanism in the Alaska subduction zone remain controversial. In this study, we revealed that the Pacific Plate transitioned from oblique subduction along the Aleutian volcano chain to lower-angle subduction beneath the Pacific-Yakutat Plate interaction zone, forming two slab tears that enhance hot asthenosphere materials upwelling. The partial melting of the mantle wedge induced by Pacific slab dehydration and, the concurrent upwelling of mantle materials, jointly drove volcanism in the transition zone. However, the flat subduction of the Yakutat slab into the mantle wedge overlying the Pacific slab effectively hindered the upwelling of hot hybrid materials, cooling the Pacific mantle wedge. This process produced a non-volcanic gap beneath Denali, reducing volcanic degassing. The findings provide novel perspectives on understanding the volcanic activities in Alaska and their influence on the carbon cycle. joint seismic tomography slab tearing plate subduction geometries volcanism plate interaction Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction The subduction of tectonic plates is commonly accompanied by various geological phenomena, such as volcanic eruptions, slab tearing, and plate interaction. Investigating the correlation between arc magmatism and subduction dynamics can provide valuable insights into the migration of fluids and mantle volatiles during subduction 1 , enhancing our comprehension of the relevant carbon cycle associated with volcanic degassing (e.g., CO 2 ) processes in subduction zones. The Alaska subduction zone (ASZ), characterized by its distinctive "corner-shape" geometry 2 , offers an exceptional opportunity for investigating volcanic formation dynamics and mantle flow patterns 3 . In the western ASZ, the Pacific Plate is undergoing a north-northwestward movement towards the North American Plate at an approximate rate of 55 mm/yr 4 (Fig. 1 a). This tectonic process has led to significant volcanic activities, including the formation of the Alaska island arc and Aleutian volcanic chain. In contrast, in the eastern ASZ, intricate volcanic activity and subduction morphology are influenced by collisional processes and accretion between the Yakutat Terrane and Pacific Plate 2,5 . The Yakutat Terrane was formed at approximately 50 Ma along the western coast of the North American plate 6–8 . At approximately 35 Ma, the Yakutat Plate underwent northward subduction at an approximate rate of 50 mm/yr, resulting in a collision event between the Yakutat Terrane and the southern boundary of Alaska 9 . This tectonic event led to distinctive geological processes, including partial or complete plate interactions 10–12 , rapid mountain uplift, and diverse volcanic activity in southern Alaska 5,13–15 . The ongoing collision and subduction of the Pacific Plate with the Yakutat slab beneath the North American Plate have resulted in a complex and distinctive arc volcanic framework along the northeastern Pacific Rim (Fig. 1 a). The distribution of volcanoes in the ASZ is characterized by unevenness across three primary regions: the Aleutian volcano arc in the west, exhibiting irregular spacing; the Buzzard Creek-Jumbo Dome volcano situated in the middle; and the concentrated Wrangell volcanos located in the east (Fig. 1 b). The areas between the Aleutian volcano chain and Buzzard Creek-Jumbo Dome volcano, commonly referred to as the Denali Volcanic Gap (DVG), show no discernible volcanic activity 16 . In contrast to the Aleutian volcano chain, the Buzzard Creek-Jumbo Dome volcano exhibits a relatively smaller scale 17 . These observed features of volcanism can be attributed to deep plate tectonics, which influences fluid and causes varying degrees of melting and migration within the mantle wedge. As a result, arc volcanism in the ASZ exhibits diverse characteristics 1,18–22 . Numerous studies have utilized a variety of geophysical data and methods to gain insights into the crust and upper mantle structures in the ASZ, aiming to investigate the volcanism characteristics associated with plate subduction 1–3,23−30 . However, the distribution patterns of volcanoes, including discontinuities and regional concentrations, as well as variations in volcanic activities among adjacent volcanic groups 1 , continue to present perplexing challenges. Given the unique geographical location and complex tectonic environment of this region, obtaining high-resolution seismic structures for both P- and S-waves in the crust and upper mantle of the ASZ is crucial. Thus, we employed a joint inversion tomographic method 31,32 to determine fine three-dimensional (3-D) P- and S-wave velocity structures (𝑉𝑝 and 𝑉𝑠) in the crust and upper mantle. This was achieved by an extensive dataset consisting of travel times recorded by dense arrays of seismic stations from the Alaska Transportable Array (USArray), the Alaska Regional Network, and the International Seismological Center (ISC) (Fig. 2 ). Our high-resolution tomographic models provided new seismic evidence that identified the phenomenon of Pacific slab tearing and the Yakutat slab flat wedging process, thereby providing fresh insights into the magma sources, migration pathways of volcanoes, and their spatial distribution. The findings significantly enhanced our comprehension of the influence of these dynamic processes on volcanic activity, improving our understanding of the regional carbon cycle associated with volcanic degassing. Results Tomographic results. The map views of 𝑉𝑝 and 𝑉𝑠 images in the crust and upper mantle are illustrated in Figs. 3 and 4 , respectively, with a 5-km-thickness of earthquakes bound to each depth. Figures 5 and 6 present multiple vertical profiles perpendicular (Fig. 5 ) and parallel (Fig. 6 ) to the trench, providing insights into the lateral variations of the deep velocity structures. The tomographic images of 𝑉𝑝 and 𝑉𝑠 have good consistency at all depths (Figs. 3 – 6 ). The synthetic results of checkerboard resolution (Supplementary Fig. 1) and amplitude recovery tests (Supplementary Fig. 2) demonstrated satisfactory resolutions in both checkerboard patterns and amplitude anomalies within the target regions, indicating that the inverted seismic models exhibited reliable features rather than artificial artifacts. Our tomographic findings revealed significant lateral heterogeneity in the velocity structures of the crust and upper mantle beneath the ASZ, which could potentially be attributed to intricate surface geological features resulting from long-term tectonic processes associated with plate subduction 27 . In the crust (Figs. 3 a-d and 4 a-d), low-velocity (low-V) anomalies become increasingly prominent with depth along the Aleutian volcanic chain, suggesting the presence of magma chambers beneath the volcanoes. This velocity change feature exhibits similarities to previous body wave imaging findings 33 ; however, our tomographic results revealed the absence of a northward extension for the low-V body. Beneath the southern region of Spurr volcano, low-V anomalies that extended from the crust to the upper mantle were observed. The Cook Inlet basin displayed distinct and robust low-V anomalies that agree with prior seismic tomographic studies 2,23,27,28,34 and geological investigations 13 . These were believed to be associated with thick Cenozoic sedimentary basins. In contrast, the western region of the Cook Inlet basin exhibiting prominent high-V anomalies could be attributed to extensive plutonism during the Late Cretaceous-Early Tertiary period, as indicated by previous tomographic images 2,28 . The presence of predominantly high-V anomalies beneath the Kenai Mountains suggests a composition of turbidites, granitic plutons, and oceanic volcanic rocks 2,35 . The profiles (Fig. 5 ) perpendicular to the trench reveal a prominent northwest-dipping high-V anomaly in the upper mantle beneath the ASZ, agreeing with numerous regional and global tomographic findings 5,27,28,36,37 and, aligning with the upper boundary isobath of the Slab 2.0 model. This observation was interpreted as the subducting Pacific slab. The seismicity clearly demonstrated the morphological changes of the subducting Pacific lithosphere along the strike of the trench, transitioning from oblique subduction along the Aleutian Island Arc in the western region (Fig. 5 e-l) to a lower angle of subduction beneath the central Yakutat slab (Fig. 5 a-d). The subducting Pacific slab exhibited a dipping angle of approximately 15° to a depth of approximately 80 km, gradually steepening to 40˚ at greater depths. Previous tomographic studies have illustrated similar morphological variations observed in the subducting Pacific Plate 2,24,27,28,33,36 . The presence of a northwest-southeast laterally-oriented planar high-velocity anomaly was observed, overriding the northeastern region of the Pacific mantle wedge (Fig. 5 a-f). This observation preliminarily aligned with numerous tomographic findings 2,7,38–40 . Progressing eastward along the Yakutat Terrane, the dip angle of the high-V lateral zone progressively increased at greater depths beneath the Aleutian volcanic chain (Fig. 5 e-i). This observation provided evidence for the existence of the Yakutat slab lithosphere. The uppermost section of the Pacific Plate displayed a partial low-V anomaly, which was potentially linked to dehydration processes occurring within the upper oceanic crust of the plate, whereas its underlying high-V layer corresponded to its lower crust and mantle lithosphere. A pronounced low-V anomaly proximal to the mantle wedge indicated the existence of magmatic fluids linked to Pacific slab subduction. Prominent high-V anomalies observed between the Moho and 100 km depth along SW-NE vertical profiles potentially indicated the presence of lower-angle subducting segments of the Yakutat plate (Fig. 6 a-f). Additionally, a discernible low-V anomaly in the upper mantle interrupted the otherwise high-V feature associated with the Pacific Plate (Fig. 6 a, b). Our findings challenged those of previous studies 27,41 and provided new evidence for a slab-tearing event within the Pacific Plate 42 . Tearing of the subducting Pacific slab. The slab tearing of the subducting Pacific Plate in the ASZ has consistently ignited debates within the scientific community. Several tomographic studies have revealed evidence of tears or gaps within the Pacific slab 1,27,42 ; however, other studies unveil a continuous high-V zone associated with the subducting Pacific slab in the Alaska region 33,36 . A previous study proposed that the absence of high-velocity anomalies near 61°N provided evidence for the separation between the Pacific Plate and Yakutat slab, whereas low-velocity anomalies within the PYCP zone indicated an internal tear of the Yakutat lithosphere 1 . Similarly, extensive anisotropic Pn tomography has identified a prominent gap near 60°N 42 . Our tomographic analysis clearly illustrated the presence of a high-V belt along the trajectory of Slab 2.0, as depicted in Figs. 3 – 6 . The slab continuity in the upper mantle was disrupted by a low-velocity anomalous body, spanning 62–64˚N (referred to as ST1 in Figs. 3 and 4 ). Our investigation confirmed the presence of the high-V zone, providing compelling evidence for the northward extension of the Pacific slab (Fig. 5 ). The high-V zone observed in cross-sections A and B (Fig. 5 a-d) also mirrored the horizontally inclined subduction process occurring within the PYCP zone associated with the Pacific Plate. Therefore, we propose that these low-V anomalies indicated internal deformation within the Pacific Plate rather than being attributed to deformations within the Yakutat slab, offering a plausible explanation for the spatial distribution of intraplate earthquakes along this tectonic plate. Moreover, we have identified an additional low-V zone situated between latitudes 60–61˚N (referred as ST2 in Figs. 3 – 6 ), which has also been proposed by previous studies 1,42 . This low-V zone was another representation of internal weakening within the Pacific Plate rather than a separation between the Pacific and Yakutat plates. We conducted model recovery tests to verify the credibility of high-V anomalies inferred from the Yakutat slab and Pacific Plate and low-V anomalies inferred from slab tearing. The results demonstrated an excellent restoration of the output model (Supplementary Fig. 2). In this study, a schematic model was constructed to provide a comprehensive understanding of the subduction process and occurrence of slab tears within the Pacific Plate (Fig. 7 ). Our findings provide compelling evidence for the phenomenon known as slab tearing occurring within subducting plates. The observed occurrences of two distinct instances of slab tearing beneath ASZ could be attributed to spatial variations in subduction angles across different regions along this plate boundary. These identified slab tearings played a crucial role in facilitating the upward movement and transport of asthenosphere materials. Discussion Diverse magma evolution under the ASZ. The complex origin of volcanoes in the ASZ region, including the continuous Aleutian arc and isolated Buzzard Creek-Jumbo Dome volcanoes, suggested the involvement of multiple magmatic processes (Fig. 1 ). Magma generation in volcanic areas is typically associated with subducting slab dehydration and upwelling hot mantle materials 1,22 . In this framework, the descending plate undergoes a series of progressive geochemical reactions or physical transformations, such as plate dehydration, serpentinization, and hydrated peridotite melting. At shallower depths of the forearc region beneath the Aleutian volcanic chain, low-V anomalies indicated Pacific slab dehydration (Fig. 5 e-j). The presence of a fluid-rich forearc, coupled with an approximately 15° inclined subduction slab and pronounced seismic activity, is characterized by a typical subduction zone of the Pacific Plate in the Aleutian volcanic chain 1,43 . The increasing subduction depth resulted in a progressive elevation of temperature and pressure, leading to the release of fluids into the overriding mantle wedge. Consequently, this process initiated melting or partial melting in the mantle wedge 22,44,45 . Our tomographic findings unveiled regions of low-V within the mantle wedge, indicating partial melting of garnet-peridotite materials initiated by fluids released from dehydration of the subducting Pacific slab. In addition, discernible low-V anomalies were observed in the upper crust of the subducting Pacific slab (Fig. 5 g-l), suggesting that slab melting of the subducting oceanic crust occurred, facilitating water infiltration into the overlying mantle wedge 22 . These mechanisms collectively contributed to volcanic activity via magmatic processes arising from the partial melting of peridotites in the mantle wedge 22,46 . Furthermore, a distinct low-V body was observed within the high-V anomalous belt at 60–61˚N (Figs. 3 and 4 ). This low-V body was interpreted as a result of upwelling asthenosphere materials driven by dehydration of the descending Pacific slab and facilitated by slab tearing, which serves as a conduit for these materials to enter the mantle wedge (Fig. 8 a). The relatively low seismic activity near the low-V area could be attributed to contrasting physical properties between slab tearing and its surroundings. Dehydration reactions occurring in the upper crust of the Pacific Plate altered rock stress states, leading to fracturing and subsequently causing high seismicity within the Pacific slab. Conversely, seismic activity in the slab tearing was impeded by the plastic nature of upwelling mantle materials, leading to a low earthquake frequency (Figs. 5 a, b; 5 i, j; 6 c, d). Previous studies 1 have also identified significant trench mantle flow induced by robust thermal anomalies in the back-arc region, which could potentially supply additional magma to sustain Aleutian arc volcanoes. However, these studies did not clarify how magma is transported from the back-arc region to these volcanoes owing to the considerable distance between the observed back-arc low-V zone above the Pacific Plate and the Aleutian arc. Our findings provided a plausible explanation for understanding how upwelling mantle materials are connected with magma within the mantle wedge. The Buzzard Creek-Jumbo Dome volcano is situated 320 km northeast of the Hayes volcano on the eastern side of the Aleutian arc (Fig. 1 ). Its tectonic affiliation with the Aleutian subduction zone remains enigmatic 47 . The presence of a mantle low-V anomaly beneath the Buzzard Creek‐Jumbo Dome volcano suggests potential contributions from either corner flow or asthenosphere upwelling to its volcanic activity 1,48 . The presence of an uppermost mantle high-V zone suggests the existence of oceanic lithosphere associated with flat subduction, which is hypothesized to result in limited or absent magmatism beneath the DVG 1,49 . The presence of this high-V body may hinder the generation of a significant amount of active crustal magma in the wedge, as well as impede the ascent of corner material or asthenosphere upwelling that contributes to the formation of surface volcanoes. This observation is similar to that of a previous study, which demonstrated the influence of the Philippine Sea slab on the spatial distribution of surface volcanoes in the central Japan subduction zone, where it is inserted into the Pacific slab mantle wedge 50 . Our tomographic images indicated both low-V and high-V anomalies in the southwestern region of the Buzzard Creek‐Jumbo Dome volcano within the upper mantle and crust, respectively (Fig. 6 c, d). This was compelling evidence for the upwelling of asthenosphere material along the flat subducting Yakutat slab, providing partial magma for volcanic activities at Buzzard Creek‐Jumbo Dome volcano (Fig. 7 ). Although low-V anomalies may indicate the presence of melting or partial melting that has contributed to the formation of Buzzard Creek Jumbo Dome volcano, the high-V anomalies interpreted as flat subduction of the Yakutat slab likely impeded magma upwelling, resulting in a smaller-scale eruption compared to other volcanoes in the arc region. Based on our findings, we propose models to identify the diverse magmatic processes along the ASZ (Fig. 8 ). Within the Aleutian volcanic chain region, partial melting occurred in the quartz-eclogite oceanic crust of the subducting Pacific slab owing to elevated temperatures prevailing in the upper mantle. These molten materials subsequently ascended and integrated with the mantle wedge, contributing to magma generation 22,51 . The dehydration of the subducting Pacific slab crust resulted in fluid release into the mantle wedge, inducing peridotite melting within the upper mantle. Previous studies have emphasized the significance of hydrous peridotite melting in generating magma within the mantle wedge associated with volcanic activity 22,45,52 . Moreover, a low-V anomalous gap associated with slab tearing at a depth of approximately 80 km at 60–61˚N within the Pacific slab likely served as a conduit for the upwelling of hot mantle material (Fig. 8 a). This type of slab tearing was not limited to the Aleutian arc but has also been observed in other regions of the Pacific Plate, such as the Wrangell Volcanic field 27,53 and northeast China 54 . Therefore, the combination of partial melting of subducting oceanic crust, mantle wedge melting induced by plate dehydration, and upwelling of asthenosphere materials through a torn slab collectively contributed crucial magma for volcanic activities within the Aleutian volcanic chain. In the DVG region, the slab tearing provided a conduit for the upwelling of mantle materials, potentially facilitating volcano formation; however, the presence of the flat Yakutat slab overlying the mantle wedge hindered this magma upwelling (Fig. 8 b). This obstruction restricted the ascent of mantle material, causing it to primarily expand and flow along the lower boundary of the Yakutat slab (Fig. 7 ), impeding volcano evolution in the DVG. Regarding the origin of the Buzzard Creek-Jumbo Dome volcano, we propose that upwelling mantle materials contribute to its volcanic activity. Nevertheless, several factors constrained the scale of volcanic activity in this area. First, the presence of a flat subducting Yakutat slab hindered the direct ascent of mantle materials, causing them to flow along the lower boundary of the Yakutat slab and potentially reducing magma influx beneath the Buzzard Creek‐Jumbo Dome volcano. Second, the diminished prominence of plate dehydration and mantle wedge melting in this region led to a solitary magma source, resulting in attenuated volcanic activity. These combined factors contributed to the relatively smaller size of Buzzard Creek‐Jumbo Dome volcano compared to those within the Aleutian Arc 47 . Formation of the Denali Volcanic Gap. The absence of volcanic activity in the DVG region is believed to be closely linked to the flat subduction of the Yakutat slab, as suggested by previous studies 8,42 . However, considerable controversy remains surrounding the specific mechanisms through which the Yakutat slab influences the cessation of volcanism, primarily due to significant variations in velocity structure images beneath the DVG. The issue regarding DVG and volcanic activity includes two key aspects: whether magma exists beneath the DVG and how melt ascent is hindered if melting materials are associated with magmatism under the DVG. Earlier studies have identified a high-V anomaly within the mantle wedge, interpreted as an absence of melt accumulation beneath the DVG resulting in a lack of volcanism 1,8,16,26,53,55 . The flat subduction of the Yakutat Plate at shallow depth effectively regulates thermal conditions within the mantle wedge beneath the DVG, leading to a suppression of partial melting and consequent lack of surface volcanism 16,41 . An alternative hypothesis suggests that predominant dehydration processes occurring in the upper crust of a horizontally subducting Yakutat slab hinder fluid release and suppress partial melt generation within the mantle wedge 8 . In contrast, previous studies have reported the presence of extensive high 𝑉𝑝/𝑉𝑠 and low-V zones beneath the DVG, indicating potential magma generation that has not yet reached the surface 42,53,56 . Alternatively, it is plausible that enhanced crustal compression between the megathrust and Denali fault system may impede mantle material ascent, thereby hindering melt migration to the surface 56 . Our study has observed a low-V anomaly in the upper mantle beneath the DVG (Figs. 5 – 8 ), indicating favorable conditions for magma generation without reaching the Earth's surface to form volcanoes. The presence of low- and high-V anomalous bodies beneath the DVG is interpreted as indicative of a torn Pacific slab and a flat subducting Yakutat slab, respectively (Figs. 3 – 6 ), suggesting their association with this phenomenon. We attributed this low-V anomaly in the mantle wedge to asthenosphere upwelling rather than the molten material 56 . Despite the presence of a torn Pacific slab that facilitated the upwelling of hot asthenosphere material that, acted as a primary source for volcanic magma in volcanic arc regions (Fig. 7 ), the ascent and dispersion of these upwellings along the base of the Yakutat slab were impeded because of its flat subduction, hindering magma accumulation (Fig. 7 ). Moreover, the subduction of the flat Yakutat slab resulted in mantle wedge cooling beneath the DVG, leading to reduced melt production and impeding magma generation and extraction processes. Furthermore, our study uncovered an intriguing partially coupled relationship between the Pacific and Yakutat plates within this composite area-a phenomenon rarely encountered in volcanic arc regions (Fig. 5 ). The Yakutat slab was directly underlying and in contact with the Pacific Plate beneath the PYCP area (Fig. 7 ). The contact region between the slab and the plate corresponds to the contours of the upper surface of the Pacific Plate, determined using the Slab 2.0 model (Fig. 6 a, b). The Yakutat slab overlapped the subducting Pacific slab in deeper regions. This overlay impeded temperature increase within the Pacific Plate caused by heating from the upper hot mantle wedge, significantly delaying the phase transition associated with dehydration reactions occurring within its crust. Furthermore, the flat subduction of the Yakutat slab was primarily driven by the subduction process of the Pacific Plate, resulting in a comparatively slower rate of subduction within the PYCP area when compared to that observed in the volcanic arc region (Fig. 1 ). This accounted for the absence of surface volcanic activity under Denali (Fig. 8 b), aligning with the report by Rondenay et al. 16 . Therefore, the absence of volcanic activity beneath the DVG could primarily be attributed to the presence of the flatly subducting Yakutat slab, which was inserted into the Pacific mantle wedge. Implication for the carbon cycle. The subduction processes of the Pacific and Yakutat slabs have influenced the transfer of volatile elements among the Alaska mantle, crust, and atmosphere. The carbon within a subducted zone is derived from trench-fill (terrigenous) and incoming (typically marine) sediments, as well as the altered oceanic crust 57 . Carbon recycled to arc volcanoes originates from various sources, including degassing of the subducted slab and CO 2 released during volcanic activity. Significant variations in volcanic gases along the Aleutian subduction zone are observed owing to differential efficiencies in carbon recycling from subducting materials to the atmosphere through multiple pathways, with arc volcanism being a prominent mechanism 57 . Our study has revealed that the ASZ system exhibited distinctive features, including slab tears, flat slab wedging, and slab interaction. These revealed new tectonic processes contribute to a slow and warm subduction regime, facilitating forearc sediment removal and resulting in the release of 6–9% of altered oceanic crust carbon into the atmosphere through western Aleutian volcanic degassing. As documented by Lopez et al. 57 , this phenomenon leads to reduced volcanic degassing from the deep mantle compared to rapidly cooling subduction zones, which typically release approximately 43–61% of sediment-derived organic carbon into the atmosphere via volcanic degassing from both the mantle wedge and deep mantle reservoirs. Consequently, carbon flux emissions induced by volcanic eruption in the Alaska subduction zone may be lower than previously estimated owing to the presence of slab tears and flat slab wedging. Methods Data Processing. To simultaneously acquire 3-D seismic 𝑉𝑝 and 𝑉𝑠 velocities in the crust and upper mantle, we carefully gathered a substantial amount of P- and S-wave arrival time data from numerous earthquakes within the study region (154˚W ~ 146˚W, 58˚N ~ 64.2˚N) (Fig. 1 ), while strictly adhering to stringent data selection criteria to ensure the inclusion of high-quality seismic travel time data during the inversion process. This involved: ( 1 ) identifying local seismic events recorded by the seismic networks; ( 2 ) selecting earthquakes with magnitudes greater than M2.0 within the specified region; ( 3 ) ensuring each earthquake has a minimum of eight observed travel times of P- and S-waves; ( 4 ) choosing earthquakes with an epicenter's latitude and longitude uncertainty ≤ 7 km and focal depth error ≤ 10 km; and ( 5 ) limiting the focal depth to less than 200 km. During the inversion process, we employed the double-difference positioning method for relocating seismic events, following Waldhauser & Ellsworth 58 , and Wang & Zhao 59 . For those not processed using double-difference repositioning, we relocated those not processed using double-difference repositioning using the conventional relocation method described by Zhao et al. 31 . In this study, a total of 288 seismic stations were utilized, comprising 41 stations affiliated with the EarthScope USArray project and 247 stations from the Alaska Regional Network and the International Seismological Center (ISC) bulletins (Fig. 2 a). Our dataset encompassed an extensive collection of seismic travel times, including 551,856 P-wave and 186,204 S-wave measurements (Fig. 2 c), derived from 13,473 local earthquakes that occurred from 1985 to 2016. Joint tomographic inversion. In this study, we employed the joint tomographic method proposed by Zhao et al. 31,32 to invert the P- and S-wave travel time data separately for determining the 3-D seismic velocities (𝑉𝑝, 𝑉𝑠) in the crust and upper mantle. A pseudo-3-D ray-tracing technique was utilized to compute theoretical travel time and ray paths. The ray tracing algorithm selects paths with the minimum travel time while considering possible multiple paths within the epicenter distance 32 . The application of this pseudo-ray-tracing method effectively enhanced the accuracy of 3-D ray tracing and reduced errors caused by velocity discontinuity surfaces such as Conard and Moho discontinuities. Furthermore, this algorithm demonstrated commendable efficiency. The inversion process involved the joint inversion of source and velocity parameters, utilizing the Sparse Equations and Least Squares (LSQR) algorithm method 60 with damping and smoothing regularizations to solve the coefficient matrix for linear inversion. This approach effectively associated travel time data with unknown 3D velocity and local seismic source parameters, facilitating the generation of 3-D seismic velocity models that encompass continuously changing velocity structures alongside complex discontinuities. Parameter initialization. We constructed a 3D grid with a lateral grid interval of 0.25˚ in both latitude and longitude, as well as a vertical grid spacing ranging from 10 to 30 km, to accurately depict the 3-D velocity structure (Fig. 2 a) while considering the impact of station, seismic data, and ray coverage density on imaging resolution in the ASZ. Throughout the inversion process, we employed the 3-D grid points to portray the spatial distribution of subsurface velocities within our model. The velocity values for each point in the model space were determined using linear interpolation based on data from eight surrounding points. Furthermore, we incorporated lateral variations in depth for the Conrad and Moho discontinuities from the Crust1.0 model 61 into our model setup and ray tracing procedures. To establish an initial one-dimensional velocity model for joint tomographic inversion (Fig. 2 b), we calculated the average depths of these discontinuities within our study area using data from the Crust1.0 model for crustal regions while applying the IASP91 model 62 for upper mantle regions. After calculating the theoretical travel times of P and S waves based on a 1-D initial velocity model, we determined the residuals by subtracting the observed data from the theoretical results. Figure 2 c illustrates the statistically normal distribution of relative travel time residuals within ± 3.0 and ± 4.0 s for P- and S-waves, respectively. Both distributions converged towards a model that effectively captures the observed anomalies after conducting local earthquake inversions. To mitigate the influence of velocity anomalies beyond our study area, we incorporated relative travel time residuals obtained by subtracting the mean residual for each event from the raw data during the final joint tomographic inversion. Following Dueker et al. 63 , the average residual for each event represented a consistent time shift accumulated by all rays traveling along identical paths through the mantle outside of the receiver region. Supplementary Fig. S3 displays the variations in travel-time residuals of P- and S-waves before and after tomographic inversions, demonstrating a more concentrated and symmetrical focus compared to the pre-inversion. Resolution tests for seismic tomography. As part of our seismic tomographic analysis, we conducted comprehensive checkerboard resolution tests (CRTs) 32 to evaluate the resolving capability of the selected seismic data and the appropriateness of parameter initialization employed in seismic tomography. The input parameters, including the initial velocity model, grid-spacing settings, damping, iterations, and data sets, remained consistent between the CRTs and final seismic tomography. We introduced positive and negative velocity perturbations of 6% to adjacent grid nodes and then conducted forward modeling to calculate synthetic travel times. In general, CRT synthetic inversions can be easily evaluated for resolution results because the velocities (𝑉𝑝 and 𝑉𝑠) were inverted using synthetic data to estimate their extent restored by estimating amplitudes and patterns of inverted values. Considering the spatial distributions of sources and stations across the entire study region, we tested the same grid as the final seismic tomography with a lateral grid interval of 0.25˚ in both latitude and longitude while maintaining a vertical grid spacing ranging from 10–30 km at different depths for CRTs (Fig. 2 a). The CRT results demonstrate a strong coherence between P- and S-velocities, with the amplitudes of 𝑉𝑝 and 𝑉𝑠 effectively restored in the crust and uppermost mantle in the target region (Supplementary Fig. 1). The high-resolution area gradually diminished with increasing depth, particularly in the southeastern region of the study area, where fewer stations and earthquakes are present compared to other regions, resulting in inadequate coverage of low-resolution areas by radiation (Supplementary Fig. 1). Nevertheless, our seismic data-derived velocity model and initial parameter selection successfully restored the resolution of the main research area in the crust and uppermost mantle. Furthermore, high ray-path coverages of P- and S-waves were observed in the crust and upper mantle (Supplementary Fig. 4), indicating the robustness of our seismic data. These findings suggest that the velocity models inverted from the seismic data were reliable and credible. Declarations Data availability The travel time data utilized in this study were sourced from both the Transportable Array Deployment to Alaska (www.usarray.org/Alaska) and the International Seismological Center (ISC) bulletins (www.isc.ac.uk). The final 3D seismic models can be accessed through the Open database at https://doi.org/10.5281/zenodo.10272868. Code availability All figures presented herein were generated using Generic Mapping Tools 64 . The analysis codes used in the main text and supplementary information are available from the corresponding author upon reasonable request. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments We express our sincere gratitude to Prof. D. Zhao from Tohoku University of Japan for generously providing us with the seismic tomographic code essential for determining the seismic structure in this study. This study was funded by the National Natural Science Foundation of China (Grant No. 92058210, 42074047, 42241206) and supported by the Open Fund from the Engineering Research Center for Seismic Disaster Prevention and Engineering Geological Disaster Detection of Jiangxi Province (Grant No. SDGD202208). Author contributions Yaping Hu : Writing – review & editing, Writing – original draft, Investigation, Visualization, Conceptualization. Zhi Wang: Writing – review & editing, Supervision, Project administration, Investigation, Funding acquisition, Visualization, Validation, Investigation, Data curation, Conceptualization. Cunxi Liu: Writing – review & editing, Software, Resources, Visualization, Methodology, Validation, Investigation. Feiyu Zhao: Writing – review & editing, Data curation. Y. H. and Z.W. contributed equally to this work and all authors approved the final version. Competing interests The authors declare no competing interests. Supplementary information The online version contains supplementary material available at Figures and f igure captions References Yang, X. & Gao, H. Segmentation of the Aleutian‐Alaska subduction zone revealed by full‐wave ambient noise tomography: Implications for the along‐strike variation of volcanism. J. Geophys. Res. Solid Earth , 125 , e2020JB019677; https://doi.org/10.1029/2020JB019677 (2020). Eberhart-Phillips, D. et al. Imaging the transition from Aleutian subduction to Yakutat collision in central Alaska, with local earthquakes and active source data. J. Geophys. Res. , 111 , B11303; https://doi.org/10.1029/2005JB004240 (2006). Venereau, C. M. A., Martin-Short, R., Bastow, I. D., Allen, R. M., & Kounoudis, R. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4457707","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":309394155,"identity":"c8528369-5c00-4274-89f1-de6066686af2","order_by":0,"name":"ZHI WANG","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1UlEQVRIiWNgGAWjYDACCcYGECUHIg6QpMWYFC0QKrGBaHfJz25uk/i5ozZ9fvvxhwc+MNjJM7CfxW8b45yDbZK9Z47nbjiTY3BwBkOyYQNPXgJeLcwSiW03eNuO5W6Q4GE4zMPAnMAgwWOAVwsbUMvNv23H0uVnsD8AaqknrIUHqOU2b1tNAsMNBgOglsOEtUhIJLb/lm07YAjxi8FxwzaeHPxa5GekPzZ821YnL99+/PGHDxXV8vzsZ/BrgYLDUBqomI0Y9UBQR6S6UTAKRsEoGJEAACueQwsVOt/kAAAAAElFTkSuQmCC","orcid":"","institution":"South China Sea Institute of Oceanlogy of Chinese Academy of Sciences","correspondingAuthor":true,"prefix":"","firstName":"ZHI","middleName":"","lastName":"WANG","suffix":""},{"id":309394156,"identity":"44a8cb88-9bcc-4096-89be-57add406a470","order_by":1,"name":"Yaping Hu","email":"","orcid":"","institution":"East China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yaping","middleName":"","lastName":"Hu","suffix":""},{"id":309394157,"identity":"a9ed0789-177b-43dd-a85b-35eb3ae52c5d","order_by":2,"name":"Cunxi Liu","email":"","orcid":"","institution":"Yalong River Hydropower Development Company","correspondingAuthor":false,"prefix":"","firstName":"Cunxi","middleName":"","lastName":"Liu","suffix":""},{"id":309394158,"identity":"0d6bc7c4-ceab-4d24-b0ad-b0073451a407","order_by":3,"name":"Feiyu Zhao","email":"","orcid":"","institution":"East China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Feiyu","middleName":"","lastName":"Zhao","suffix":""}],"badges":[],"createdAt":"2024-05-22 02:32:53","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4457707/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4457707/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-024-76595-4","type":"published","date":"2024-10-28T16:20:27+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":57755125,"identity":"2cac6fc5-c520-42ca-b743-461999d06037","added_by":"auto","created_at":"2024-06-05 08:14:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1380638,"visible":true,"origin":"","legend":"\u003cp\u003eTectonic\u0026nbsp;background and topography\u0026nbsp;of southern Alaska (a) and the Alaska subduction zone (b). The blue dashed line represents the outline of the Yakutat-Pacific composite plate (YPCP)\u003csup\u003e2\u003c/sup\u003e. The black solid and dashed line donate the Quaternary faults from the USGS (United States Geological Survey) (https://www.usgs.gov/-programs/earthquakehazards/faults) and contours of Slab 2.0\u003csup\u003e65\u003c/sup\u003e, respectively. Volcano signs indicate\u0026nbsp;the locations of volcanos from Athey et al.\u003csup\u003e17\u003c/sup\u003e. BD-JG, Buzzard Creek‐Jumbo Dome volcano; DG, Double Glacier volcano. The plate motion\u0026nbsp;rate\u0026nbsp;in Figure (a) is\u0026nbsp;based on\u0026nbsp;Elliott et al.\u003csup\u003e9\u003c/sup\u003e\u0026nbsp;for\u0026nbsp;YPCP\u0026nbsp;and Plattner et al.\u003csup\u003e4\u003c/sup\u003e\u0026nbsp;for the Pacific plate.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4457707/v1/188b3dc09a4dbaae351b37b9.png"},{"id":57755126,"identity":"0766000c-9df4-444f-a4ee-55c7785df67a","added_by":"auto","created_at":"2024-06-05 08:14:24","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1308487,"visible":true,"origin":"","legend":"\u003cp\u003eSpatial distribution of earthquakes, 3-D grid model, seismic stations (a), 1-D velocity model (b), and seismic arrival time phases (c). (a) Blue and purple squares denote selected stations from USArray and ISC, respectively. Color dots present earthquakes used in this study. (b) Initial and calculated 1-D velocity models. Dashed red lines indicate the initial velocity models and solid black lines show the calculated optimal velocity models. (c) Collected P- and S-wave travel time phases used in this study. The travel-time residuals for P and S phases are ± 3.0 s and ± 4.0 s, respectively.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4457707/v1/6f438b01849168c6dcde9432.png"},{"id":57755625,"identity":"c7dd4966-1d6b-4e3d-88d5-62c6687599e2","added_by":"auto","created_at":"2024-06-05 08:22:24","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":993415,"visible":true,"origin":"","legend":"\u003cp\u003eHorizontal slices of P-wave velocity images at each depth. The black dots show the locations of earthquakes within 5 km along each depth. The slow and fast scale of velocity perturbations are revealed by red and blue colors at the right of The slow and fast scale of velocity perturbations are revealed by red and blue colors at the right of the figure, respectively. Blue and black dashed lines show the outline of the subducted YPCP from Eberhart-Phillips et al. (2, 2006) and the contours of Slab 2.0\u003csup\u003e65\u003c/sup\u003e, respectively. The red volcano icons denote volcanic locations. The black lines in (a) represent the coastline in the ASZ. White lines show the active faults. YS, Yakutat slab; PP, Pacifica plate; ST1, Slab tearing 1; ST2, Slab tearing 2.\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4457707/v1/70b180cb4eb7a7b7640afc1a.png"},{"id":57755127,"identity":"3eb025bd-0e08-4626-a8cf-28b2f481fa05","added_by":"auto","created_at":"2024-06-05 08:14:24","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":886098,"visible":true,"origin":"","legend":"\u003cp\u003eHorizontal slices of S-wave velocity images at each depth.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4457707/v1/4c5ba802dc869f48f9888615.png"},{"id":57755131,"identity":"1d72abfd-ca68-49aa-962f-e289bc3b269c","added_by":"auto","created_at":"2024-06-05 08:14:24","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1493676,"visible":true,"origin":"","legend":"\u003cp\u003eVertical cross sections of P- and S-wave velocity images across the subduction slabs. The black dots denote earthquake hypocenters within 5 km from each profile. Black dashed lines show the Conrad and the Moho discontinuities. The positions of the structure profiles are indicated in the lower-right corner. Slow and fast scale of velocity perturbations are revealed by red and blue colors at the right of figure, respectively. The surface topography is shown on top of each section.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4457707/v1/be7952939e982674cff75392.png"},{"id":57755132,"identity":"bcce80c8-6f06-4b27-b16a-5ba3dd732b1e","added_by":"auto","created_at":"2024-06-05 08:14:24","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1733774,"visible":true,"origin":"","legend":"\u003cp\u003eVertical profiles of Vp and Vs along the lines parallel to the Pacific slab. The remaining symbols are identical to those depicted in Figure 6. The locations of the structural profiles are indicated in the lower-right corner.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4457707/v1/ab6f59ce782a17b5fa78e08c.png"},{"id":57755626,"identity":"48275970-8a02-4a5e-8418-8fd8c941d143","added_by":"auto","created_at":"2024-06-05 08:22:24","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":460001,"visible":true,"origin":"","legend":"\u003cp\u003eA schematic model showing the structure beneath the ASZ influenced by the subduction of the Pacific plate and the wedged Yakutat slab.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-4457707/v1/e338201f4b81dc3b9b8c3221.png"},{"id":57755134,"identity":"f9bb8adf-e876-473d-9527-b2213094a7ec","added_by":"auto","created_at":"2024-06-05 08:14:24","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":761940,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic models illustrating the diverse magma evolution along the ASZ based on the calculated seismic structures.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-4457707/v1/48bcdb20806936778e408875.png"},{"id":68207308,"identity":"2eae22c4-8fbf-43d2-8805-a86308e37bca","added_by":"auto","created_at":"2024-11-04 16:36:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":11359421,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4457707/v1/58e80721-a0c6-43b1-9c3f-99fe1dfbaf5e.pdf"},{"id":57755130,"identity":"787b7a84-ba66-45f2-92a3-4aedb94faf71","added_by":"auto","created_at":"2024-06-05 08:14:24","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1688999,"visible":true,"origin":"","legend":"","description":"","filename":"20240522SISR.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4457707/v1/35735f118a5d061ff0eaa1b9.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Control of slab tears and slab flat wedging on volcanism in the Alaska subduction zone","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe subduction of tectonic plates is commonly accompanied by various geological phenomena, such as volcanic eruptions, slab tearing, and plate interaction. Investigating the correlation between arc magmatism and subduction dynamics can provide valuable insights into the migration of fluids and mantle volatiles during subduction\u003csup\u003e1\u003c/sup\u003e, enhancing our comprehension of the relevant carbon cycle associated with volcanic degassing (e.g., CO\u003csub\u003e2\u003c/sub\u003e) processes in subduction zones. The Alaska subduction zone (ASZ), characterized by its distinctive \"corner-shape\" geometry\u003csup\u003e2\u003c/sup\u003e, offers an exceptional opportunity for investigating volcanic formation dynamics and mantle flow patterns\u003csup\u003e3\u003c/sup\u003e. In the western ASZ, the Pacific Plate is undergoing a north-northwestward movement towards the North American Plate at an approximate rate of 55 mm/yr\u003csup\u003e4\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). This tectonic process has led to significant volcanic activities, including the formation of the Alaska island arc and Aleutian volcanic chain. In contrast, in the eastern ASZ, intricate volcanic activity and subduction morphology are influenced by collisional processes and accretion between the Yakutat Terrane and Pacific Plate\u003csup\u003e2,5\u003c/sup\u003e. The Yakutat Terrane was formed at approximately 50 Ma along the western coast of the North American plate\u003csup\u003e6\u0026ndash;8\u003c/sup\u003e. At approximately 35 Ma, the Yakutat Plate underwent northward subduction at an approximate rate of 50 mm/yr, resulting in a collision event between the Yakutat Terrane and the southern boundary of Alaska\u003csup\u003e9\u003c/sup\u003e. This tectonic event led to distinctive geological processes, including partial or complete plate interactions\u003csup\u003e10\u0026ndash;12\u003c/sup\u003e, rapid mountain uplift, and diverse volcanic activity in southern Alaska\u003csup\u003e5,13\u0026ndash;15\u003c/sup\u003e. The ongoing collision and subduction of the Pacific Plate with the Yakutat slab beneath the North American Plate have resulted in a complex and distinctive arc volcanic framework along the northeastern Pacific Rim (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe distribution of volcanoes in the ASZ is characterized by unevenness across three primary regions: the Aleutian volcano arc in the west, exhibiting irregular spacing; the Buzzard Creek-Jumbo Dome volcano situated in the middle; and the concentrated Wrangell volcanos located in the east (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The areas between the Aleutian volcano chain and Buzzard Creek-Jumbo Dome volcano, commonly referred to as the Denali Volcanic Gap (DVG), show no discernible volcanic activity\u003csup\u003e16\u003c/sup\u003e. In contrast to the Aleutian volcano chain, the Buzzard Creek-Jumbo Dome volcano exhibits a relatively smaller scale\u003csup\u003e17\u003c/sup\u003e. These observed features of volcanism can be attributed to deep plate tectonics, which influences fluid and causes varying degrees of melting and migration within the mantle wedge. As a result, arc volcanism in the ASZ exhibits diverse characteristics\u003csup\u003e1,18\u0026ndash;22\u003c/sup\u003e. Numerous studies have utilized a variety of geophysical data and methods to gain insights into the crust and upper mantle structures in the ASZ, aiming to investigate the volcanism characteristics associated with plate subduction\u003csup\u003e1\u0026ndash;3,23\u0026minus;30\u003c/sup\u003e. However, the distribution patterns of volcanoes, including discontinuities and regional concentrations, as well as variations in volcanic activities among adjacent volcanic groups\u003csup\u003e1\u003c/sup\u003e, continue to present perplexing challenges.\u003c/p\u003e \u003cp\u003eGiven the unique geographical location and complex tectonic environment of this region, obtaining high-resolution seismic structures for both P- and S-waves in the crust and upper mantle of the ASZ is crucial. Thus, we employed a joint inversion tomographic method\u003csup\u003e31,32\u003c/sup\u003e to determine fine three-dimensional (3-D) P- and S-wave velocity structures (\u0026#119881;\u0026#119901; and \u0026#119881;\u0026#119904;) in the crust and upper mantle. This was achieved by an extensive dataset consisting of travel times recorded by dense arrays of seismic stations from the Alaska Transportable Array (USArray), the Alaska Regional Network, and the International Seismological Center (ISC) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Our high-resolution tomographic models provided new seismic evidence that identified the phenomenon of Pacific slab tearing and the Yakutat slab flat wedging process, thereby providing fresh insights into the magma sources, migration pathways of volcanoes, and their spatial distribution. The findings significantly enhanced our comprehension of the influence of these dynamic processes on volcanic activity, improving our understanding of the regional carbon cycle associated with volcanic degassing.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e \u003cb\u003eTomographic results.\u003c/b\u003e The map views of 𝑉𝑝 and 𝑉𝑠 images in the crust and upper mantle are illustrated in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, respectively, with a 5-km-thickness of earthquakes bound to each depth. Figures\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e present multiple vertical profiles perpendicular (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) and parallel (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) to the trench, providing insights into the lateral variations of the deep velocity structures. The tomographic images of 𝑉𝑝 and 𝑉𝑠 have good consistency at all depths (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e–\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The synthetic results of checkerboard resolution (Supplementary Fig.\u0026nbsp;1) and amplitude recovery tests (Supplementary Fig.\u0026nbsp;2) demonstrated satisfactory resolutions in both checkerboard patterns and amplitude anomalies within the target regions, indicating that the inverted seismic models exhibited reliable features rather than artificial artifacts. Our tomographic findings revealed significant lateral heterogeneity in the velocity structures of the crust and upper mantle beneath the ASZ, which could potentially be attributed to intricate surface geological features resulting from long-term tectonic processes associated with plate subduction\u003csup\u003e27\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the crust (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-d and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea-d), low-velocity (low-V) anomalies become increasingly prominent with depth along the Aleutian volcanic chain, suggesting the presence of magma chambers beneath the volcanoes. This velocity change feature exhibits similarities to previous body wave imaging findings\u003csup\u003e33\u003c/sup\u003e; however, our tomographic results revealed the absence of a northward extension for the low-V body. Beneath the southern region of Spurr volcano, low-V anomalies that extended from the crust to the upper mantle were observed. The Cook Inlet basin displayed distinct and robust low-V anomalies that agree with prior seismic tomographic studies\u003csup\u003e2,23,27,28,34\u003c/sup\u003e and geological investigations\u003csup\u003e13\u003c/sup\u003e. These were believed to be associated with thick Cenozoic sedimentary basins. In contrast, the western region of the Cook Inlet basin exhibiting prominent high-V anomalies could be attributed to extensive plutonism during the Late Cretaceous-Early Tertiary period, as indicated by previous tomographic images\u003csup\u003e2,28\u003c/sup\u003e. The presence of predominantly high-V anomalies beneath the Kenai Mountains suggests a composition of turbidites, granitic plutons, and oceanic volcanic rocks\u003csup\u003e2,35\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe profiles (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) perpendicular to the trench reveal a prominent northwest-dipping high-V anomaly in the upper mantle beneath the ASZ, agreeing with numerous regional and global tomographic findings\u003csup\u003e5,27,28,36,37\u003c/sup\u003e and, aligning with the upper boundary isobath of the Slab 2.0 model. This observation was interpreted as the subducting Pacific slab. The seismicity clearly demonstrated the morphological changes of the subducting Pacific lithosphere along the strike of the trench, transitioning from oblique subduction along the Aleutian Island Arc in the western region (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee-l) to a lower angle of subduction beneath the central Yakutat slab (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-d). The subducting Pacific slab exhibited a dipping angle of approximately 15° to a depth of approximately 80 km, gradually steepening to 40˚ at greater depths. Previous tomographic studies have illustrated similar morphological variations observed in the subducting Pacific Plate\u003csup\u003e2,24,27,28,33,36\u003c/sup\u003e. The presence of a northwest-southeast laterally-oriented planar high-velocity anomaly was observed, overriding the northeastern region of the Pacific mantle wedge (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-f). This observation preliminarily aligned with numerous tomographic findings\u003csup\u003e2,7,38–40\u003c/sup\u003e. Progressing eastward along the Yakutat Terrane, the dip angle of the high-V lateral zone progressively increased at greater depths beneath the Aleutian volcanic chain (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee-i). This observation provided evidence for the existence of the Yakutat slab lithosphere.\u003c/p\u003e \u003cp\u003eThe uppermost section of the Pacific Plate displayed a partial low-V anomaly, which was potentially linked to dehydration processes occurring within the upper oceanic crust of the plate, whereas its underlying high-V layer corresponded to its lower crust and mantle lithosphere. A pronounced low-V anomaly proximal to the mantle wedge indicated the existence of magmatic fluids linked to Pacific slab subduction. Prominent high-V anomalies observed between the Moho and 100 km depth along SW-NE vertical profiles potentially indicated the presence of lower-angle subducting segments of the Yakutat plate (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea-f). Additionally, a discernible low-V anomaly in the upper mantle interrupted the otherwise high-V feature associated with the Pacific Plate (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, b). Our findings challenged those of previous studies\u003csup\u003e27,41\u003c/sup\u003e and provided new evidence for a slab-tearing event within the Pacific Plate\u003csup\u003e42\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cb\u003eTearing of the subducting Pacific slab.\u003c/b\u003e The slab tearing of the subducting Pacific Plate in the ASZ has consistently ignited debates within the scientific community. Several tomographic studies have revealed evidence of tears or gaps within the Pacific slab\u003csup\u003e1,27,42\u003c/sup\u003e; however, other studies unveil a continuous high-V zone associated with the subducting Pacific slab in the Alaska region\u003csup\u003e33,36\u003c/sup\u003e. A previous study proposed that the absence of high-velocity anomalies near 61°N provided evidence for the separation between the Pacific Plate and Yakutat slab, whereas low-velocity anomalies within the PYCP zone indicated an internal tear of the Yakutat lithosphere\u003csup\u003e1\u003c/sup\u003e. Similarly, extensive anisotropic Pn tomography has identified a prominent gap near 60°N\u003csup\u003e42\u003c/sup\u003e. Our tomographic analysis clearly illustrated the presence of a high-V belt along the trajectory of Slab 2.0, as depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e–\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The slab continuity in the upper mantle was disrupted by a low-velocity anomalous body, spanning 62–64˚N (referred to as ST1 in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Our investigation confirmed the presence of the high-V zone, providing compelling evidence for the northward extension of the Pacific slab (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The high-V zone observed in cross-sections A and B (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-d) also mirrored the horizontally inclined subduction process occurring within the PYCP zone associated with the Pacific Plate. Therefore, we propose that these low-V anomalies indicated internal deformation within the Pacific Plate rather than being attributed to deformations within the Yakutat slab, offering a plausible explanation for the spatial distribution of intraplate earthquakes along this tectonic plate. Moreover, we have identified an additional low-V zone situated between latitudes 60–61˚N (referred as ST2 in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e–\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), which has also been proposed by previous studies\u003csup\u003e1,42\u003c/sup\u003e. This low-V zone was another representation of internal weakening within the Pacific Plate rather than a separation between the Pacific and Yakutat plates. We conducted model recovery tests to verify the credibility of high-V anomalies inferred from the Yakutat slab and Pacific Plate and low-V anomalies inferred from slab tearing. The results demonstrated an excellent restoration of the output model (Supplementary Fig.\u0026nbsp;2). In this study, a schematic model was constructed to provide a comprehensive understanding of the subduction process and occurrence of slab tears within the Pacific Plate (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Our findings provide compelling evidence for the phenomenon known as slab tearing occurring within subducting plates. The observed occurrences of two distinct instances of slab tearing beneath ASZ could be attributed to spatial variations in subduction angles across different regions along this plate boundary. These identified slab tearings played a crucial role in facilitating the upward movement and transport of asthenosphere materials.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003e \u003cb\u003eDiverse magma evolution under the ASZ.\u003c/b\u003e The complex origin of volcanoes in the ASZ region, including the continuous Aleutian arc and isolated Buzzard Creek-Jumbo Dome volcanoes, suggested the involvement of multiple magmatic processes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Magma generation in volcanic areas is typically associated with subducting slab dehydration and upwelling hot mantle materials\u003csup\u003e1,22\u003c/sup\u003e. In this framework, the descending plate undergoes a series of progressive geochemical reactions or physical transformations, such as plate dehydration, serpentinization, and hydrated peridotite melting. At shallower depths of the forearc region beneath the Aleutian volcanic chain, low-V anomalies indicated Pacific slab dehydration (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee-j). The presence of a fluid-rich forearc, coupled with an approximately 15° inclined subduction slab and pronounced seismic activity, is characterized by a typical subduction zone of the Pacific Plate in the Aleutian volcanic chain\u003csup\u003e1,43\u003c/sup\u003e. The increasing subduction depth resulted in a progressive elevation of temperature and pressure, leading to the release of fluids into the overriding mantle wedge. Consequently, this process initiated melting or partial melting in the mantle wedge\u003csup\u003e22,44,45\u003c/sup\u003e. Our tomographic findings unveiled regions of low-V within the mantle wedge, indicating partial melting of garnet-peridotite materials initiated by fluids released from dehydration of the subducting Pacific slab. In addition, discernible low-V anomalies were observed in the upper crust of the subducting Pacific slab (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg-l), suggesting that slab melting of the subducting oceanic crust occurred, facilitating water infiltration into the overlying mantle wedge\u003csup\u003e22\u003c/sup\u003e. These mechanisms collectively contributed to volcanic activity via magmatic processes arising from the partial melting of peridotites in the mantle wedge\u003csup\u003e22,46\u003c/sup\u003e. Furthermore, a distinct low-V body was observed within the high-V anomalous belt at 60–61˚N (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). This low-V body was interpreted as a result of upwelling asthenosphere materials driven by dehydration of the descending Pacific slab and facilitated by slab tearing, which serves as a conduit for these materials to enter the mantle wedge (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea). The relatively low seismic activity near the low-V area could be attributed to contrasting physical properties between slab tearing and its surroundings. Dehydration reactions occurring in the upper crust of the Pacific Plate altered rock stress states, leading to fracturing and subsequently causing high seismicity within the Pacific slab. Conversely, seismic activity in the slab tearing was impeded by the plastic nature of upwelling mantle materials, leading to a low earthquake frequency (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, b; \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ei, j; \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec, d). Previous studies\u003csup\u003e1\u003c/sup\u003e have also identified significant trench mantle flow induced by robust thermal anomalies in the back-arc region, which could potentially supply additional magma to sustain Aleutian arc volcanoes. However, these studies did not clarify how magma is transported from the back-arc region to these volcanoes owing to the considerable distance between the observed back-arc low-V zone above the Pacific Plate and the Aleutian arc. Our findings provided a plausible explanation for understanding how upwelling mantle materials are connected with magma within the mantle wedge.\u003c/p\u003e\u003cp\u003eThe Buzzard Creek-Jumbo Dome volcano is situated 320 km northeast of the Hayes volcano on the eastern side of the Aleutian arc (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Its tectonic affiliation with the Aleutian subduction zone remains enigmatic\u003csup\u003e47\u003c/sup\u003e. The presence of a mantle low-V anomaly beneath the Buzzard Creek‐Jumbo Dome volcano suggests potential contributions from either corner flow or asthenosphere upwelling to its volcanic activity\u003csup\u003e1,48\u003c/sup\u003e. The presence of an uppermost mantle high-V zone suggests the existence of oceanic lithosphere associated with flat subduction, which is hypothesized to result in limited or absent magmatism beneath the DVG\u003csup\u003e1,49\u003c/sup\u003e. The presence of this high-V body may hinder the generation of a significant amount of active crustal magma in the wedge, as well as impede the ascent of corner material or asthenosphere upwelling that contributes to the formation of surface volcanoes. This observation is similar to that of a previous study, which demonstrated the influence of the Philippine Sea slab on the spatial distribution of surface volcanoes in the central Japan subduction zone, where it is inserted into the Pacific slab mantle wedge\u003csup\u003e50\u003c/sup\u003e. Our tomographic images indicated both low-V and high-V anomalies in the southwestern region of the Buzzard Creek‐Jumbo Dome volcano within the upper mantle and crust, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec, d). This was compelling evidence for the upwelling of asthenosphere material along the flat subducting Yakutat slab, providing partial magma for volcanic activities at Buzzard Creek‐Jumbo Dome volcano (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Although low-V anomalies may indicate the presence of melting or partial melting that has contributed to the formation of Buzzard Creek Jumbo Dome volcano, the high-V anomalies interpreted as flat subduction of the Yakutat slab likely impeded magma upwelling, resulting in a smaller-scale eruption compared to other volcanoes in the arc region.\u003c/p\u003e\u003cp\u003eBased on our findings, we propose models to identify the diverse magmatic processes along the ASZ (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Within the Aleutian volcanic chain region, partial melting occurred in the quartz-eclogite oceanic crust of the subducting Pacific slab owing to elevated temperatures prevailing in the upper mantle. These molten materials subsequently ascended and integrated with the mantle wedge, contributing to magma generation\u003csup\u003e22,51\u003c/sup\u003e. The dehydration of the subducting Pacific slab crust resulted in fluid release into the mantle wedge, inducing peridotite melting within the upper mantle. Previous studies have emphasized the significance of hydrous peridotite melting in generating magma within the mantle wedge associated with volcanic activity\u003csup\u003e22,45,52\u003c/sup\u003e. Moreover, a low-V anomalous gap associated with slab tearing at a depth of approximately 80 km at 60–61˚N within the Pacific slab likely served as a conduit for the upwelling of hot mantle material (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea). This type of slab tearing was not limited to the Aleutian arc but has also been observed in other regions of the Pacific Plate, such as the Wrangell Volcanic field\u003csup\u003e27,53\u003c/sup\u003e and northeast China\u003csup\u003e54\u003c/sup\u003e. Therefore, the combination of partial melting of subducting oceanic crust, mantle wedge melting induced by plate dehydration, and upwelling of asthenosphere materials through a torn slab collectively contributed crucial magma for volcanic activities within the Aleutian volcanic chain. In the DVG region, the slab tearing provided a conduit for the upwelling of mantle materials, potentially facilitating volcano formation; however, the presence of the flat Yakutat slab overlying the mantle wedge hindered this magma upwelling (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb). This obstruction restricted the ascent of mantle material, causing it to primarily expand and flow along the lower boundary of the Yakutat slab (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e), impeding volcano evolution in the DVG. Regarding the origin of the Buzzard Creek-Jumbo Dome volcano, we propose that upwelling mantle materials contribute to its volcanic activity. Nevertheless, several factors constrained the scale of volcanic activity in this area. First, the presence of a flat subducting Yakutat slab hindered the direct ascent of mantle materials, causing them to flow along the lower boundary of the Yakutat slab and potentially reducing magma influx beneath the Buzzard Creek‐Jumbo Dome volcano. Second, the diminished prominence of plate dehydration and mantle wedge melting in this region led to a solitary magma source, resulting in attenuated volcanic activity. These combined factors contributed to the relatively smaller size of Buzzard Creek‐Jumbo Dome volcano compared to those within the Aleutian Arc\u003csup\u003e47\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e \u003cb\u003eFormation of the Denali Volcanic Gap.\u003c/b\u003e The absence of volcanic activity in the DVG region is believed to be closely linked to the flat subduction of the Yakutat slab, as suggested by previous studies\u003csup\u003e8,42\u003c/sup\u003e. However, considerable controversy remains surrounding the specific mechanisms through which the Yakutat slab influences the cessation of volcanism, primarily due to significant variations in velocity structure images beneath the DVG. The issue regarding DVG and volcanic activity includes two key aspects: whether magma exists beneath the DVG and how melt ascent is hindered if melting materials are associated with magmatism under the DVG. Earlier studies have identified a high-V anomaly within the mantle wedge, interpreted as an absence of melt accumulation beneath the DVG resulting in a lack of volcanism\u003csup\u003e1,8,16,26,53,55\u003c/sup\u003e. The flat subduction of the Yakutat Plate at shallow depth effectively regulates thermal conditions within the mantle wedge beneath the DVG, leading to a suppression of partial melting and consequent lack of surface volcanism\u003csup\u003e16,41\u003c/sup\u003e. An alternative hypothesis suggests that predominant dehydration processes occurring in the upper crust of a horizontally subducting Yakutat slab hinder fluid release and suppress partial melt generation within the mantle wedge\u003csup\u003e8\u003c/sup\u003e. In contrast, previous studies have reported the presence of extensive high 𝑉𝑝/𝑉𝑠 and low-V zones beneath the DVG, indicating potential magma generation that has not yet reached the surface\u003csup\u003e42,53,56\u003c/sup\u003e. Alternatively, it is plausible that enhanced crustal compression between the megathrust and Denali fault system may impede mantle material ascent, thereby hindering melt migration to the surface\u003csup\u003e56\u003c/sup\u003e. Our study has observed a low-V anomaly in the upper mantle beneath the DVG (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e–\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e), indicating favorable conditions for magma generation without reaching the Earth's surface to form volcanoes. The presence of low- and high-V anomalous bodies beneath the DVG is interpreted as indicative of a torn Pacific slab and a flat subducting Yakutat slab, respectively (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e–\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), suggesting their association with this phenomenon. We attributed this low-V anomaly in the mantle wedge to asthenosphere upwelling rather than the molten material\u003csup\u003e56\u003c/sup\u003e. Despite the presence of a torn Pacific slab that facilitated the upwelling of hot asthenosphere material that, acted as a primary source for volcanic magma in volcanic arc regions (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e), the ascent and dispersion of these upwellings along the base of the Yakutat slab were impeded because of its flat subduction, hindering magma accumulation (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eMoreover, the subduction of the flat Yakutat slab resulted in mantle wedge cooling beneath the DVG, leading to reduced melt production and impeding magma generation and extraction processes. Furthermore, our study uncovered an intriguing partially coupled relationship between the Pacific and Yakutat plates within this composite area-a phenomenon rarely encountered in volcanic arc regions (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The Yakutat slab was directly underlying and in contact with the Pacific Plate beneath the PYCP area (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The contact region between the slab and the plate corresponds to the contours of the upper surface of the Pacific Plate, determined using the Slab 2.0 model (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, b). The Yakutat slab overlapped the subducting Pacific slab in deeper regions. This overlay impeded temperature increase within the Pacific Plate caused by heating from the upper hot mantle wedge, significantly delaying the phase transition associated with dehydration reactions occurring within its crust. Furthermore, the flat subduction of the Yakutat slab was primarily driven by the subduction process of the Pacific Plate, resulting in a comparatively slower rate of subduction within the PYCP area when compared to that observed in the volcanic arc region (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This accounted for the absence of surface volcanic activity under Denali (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb), aligning with the report by Rondenay et al.\u003csup\u003e16\u003c/sup\u003e. Therefore, the absence of volcanic activity beneath the DVG could primarily be attributed to the presence of the flatly subducting Yakutat slab, which was inserted into the Pacific mantle wedge.\u003c/p\u003e\u003cp\u003e \u003cb\u003eImplication for the carbon cycle.\u003c/b\u003e The subduction processes of the Pacific and Yakutat slabs have influenced the transfer of volatile elements among the Alaska mantle, crust, and atmosphere. The carbon within a subducted zone is derived from trench-fill (terrigenous) and incoming (typically marine) sediments, as well as the altered oceanic crust\u003csup\u003e57\u003c/sup\u003e. Carbon recycled to arc volcanoes originates from various sources, including degassing of the subducted slab and CO\u003csub\u003e2\u003c/sub\u003e released during volcanic activity. Significant variations in volcanic gases along the Aleutian subduction zone are observed owing to differential efficiencies in carbon recycling from subducting materials to the atmosphere through multiple pathways, with arc volcanism being a prominent mechanism\u003csup\u003e57\u003c/sup\u003e. Our study has revealed that the ASZ system exhibited distinctive features, including slab tears, flat slab wedging, and slab interaction. These revealed new tectonic processes contribute to a slow and warm subduction regime, facilitating forearc sediment removal and resulting in the release of 6–9% of altered oceanic crust carbon into the atmosphere through western Aleutian volcanic degassing. As documented by Lopez et al.\u003csup\u003e57\u003c/sup\u003e, this phenomenon leads to reduced volcanic degassing from the deep mantle compared to rapidly cooling subduction zones, which typically release approximately 43–61% of sediment-derived organic carbon into the atmosphere via volcanic degassing from both the mantle wedge and deep mantle reservoirs. Consequently, carbon flux emissions induced by volcanic eruption in the Alaska subduction zone may be lower than previously estimated owing to the presence of slab tears and flat slab wedging.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eData Processing.\u003c/b\u003e To simultaneously acquire 3-D seismic 𝑉𝑝 and 𝑉𝑠 velocities in the crust and upper mantle, we carefully gathered a substantial amount of P- and S-wave arrival time data from numerous earthquakes within the study region (154˚W ~ 146˚W, 58˚N ~ 64.2˚N) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), while strictly adhering to stringent data selection criteria to ensure the inclusion of high-quality seismic travel time data during the inversion process. This involved: (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) identifying local seismic events recorded by the seismic networks; (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) selecting earthquakes with magnitudes greater than M2.0 within the specified region; (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) ensuring each earthquake has a minimum of eight observed travel times of P- and S-waves; (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e) choosing earthquakes with an epicenter's latitude and longitude uncertainty ≤ 7 km and focal depth error ≤ 10 km; and (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e) limiting the focal depth to less than 200 km. During the inversion process, we employed the double-difference positioning method for relocating seismic events, following Waldhauser \u0026amp; Ellsworth\u003csup\u003e58\u003c/sup\u003e, and Wang \u0026amp; Zhao\u003csup\u003e59\u003c/sup\u003e. For those not processed using double-difference repositioning, we relocated those not processed using double-difference repositioning using the conventional relocation method described by Zhao et al.\u003csup\u003e31\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn this study, a total of 288 seismic stations were utilized, comprising 41 stations affiliated with the EarthScope USArray project and 247 stations from the Alaska Regional Network and the International Seismological Center (ISC) bulletins (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Our dataset encompassed an extensive collection of seismic travel times, including 551,856 P-wave and 186,204 S-wave measurements (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec), derived from 13,473 local earthquakes that occurred from 1985 to 2016.\u003c/p\u003e \u003cp\u003e \u003cb\u003eJoint tomographic inversion.\u003c/b\u003e In this study, we employed the joint tomographic method proposed by Zhao et al.\u003csup\u003e31,32\u003c/sup\u003e to invert the P- and S-wave travel time data separately for determining the 3-D seismic velocities (𝑉𝑝, 𝑉𝑠) in the crust and upper mantle. A pseudo-3-D ray-tracing technique was utilized to compute theoretical travel time and ray paths. The ray tracing algorithm selects paths with the minimum travel time while considering possible multiple paths within the epicenter distance\u003csup\u003e32\u003c/sup\u003e. The application of this pseudo-ray-tracing method effectively enhanced the accuracy of 3-D ray tracing and reduced errors caused by velocity discontinuity surfaces such as Conard and Moho discontinuities. Furthermore, this algorithm demonstrated commendable efficiency. The inversion process involved the joint inversion of source and velocity parameters, utilizing the Sparse Equations and Least Squares (LSQR) algorithm method\u003csup\u003e60\u003c/sup\u003e with damping and smoothing regularizations to solve the coefficient matrix for linear inversion. This approach effectively associated travel time data with unknown 3D velocity and local seismic source parameters, facilitating the generation of 3-D seismic velocity models that encompass continuously changing velocity structures alongside complex discontinuities.\u003c/p\u003e \u003cp\u003e \u003cb\u003eParameter initialization.\u003c/b\u003e We constructed a 3D grid with a lateral grid interval of 0.25˚ in both latitude and longitude, as well as a vertical grid spacing ranging from 10 to 30 km, to accurately depict the 3-D velocity structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) while considering the impact of station, seismic data, and ray coverage density on imaging resolution in the ASZ. Throughout the inversion process, we employed the 3-D grid points to portray the spatial distribution of subsurface velocities within our model. The velocity values for each point in the model space were determined using linear interpolation based on data from eight surrounding points. Furthermore, we incorporated lateral variations in depth for the Conrad and Moho discontinuities from the Crust1.0 model\u003csup\u003e61\u003c/sup\u003e into our model setup and ray tracing procedures. To establish an initial one-dimensional velocity model for joint tomographic inversion (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb), we calculated the average depths of these discontinuities within our study area using data from the Crust1.0 model for crustal regions while applying the IASP91 model\u003csup\u003e62\u003c/sup\u003e for upper mantle regions.\u003c/p\u003e \u003cp\u003eAfter calculating the theoretical travel times of P and S waves based on a 1-D initial velocity model, we determined the residuals by subtracting the observed data from the theoretical results. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec illustrates the statistically normal distribution of relative travel time residuals within ± 3.0 and ± 4.0 s for P- and S-waves, respectively. Both distributions converged towards a model that effectively captures the observed anomalies after conducting local earthquake inversions. To mitigate the influence of velocity anomalies beyond our study area, we incorporated relative travel time residuals obtained by subtracting the mean residual for each event from the raw data during the final joint tomographic inversion. Following Dueker et al.\u003csup\u003e63\u003c/sup\u003e, the average residual for each event represented a consistent time shift accumulated by all rays traveling along identical paths through the mantle outside of the receiver region. Supplementary Fig. S3 displays the variations in travel-time residuals of P- and S-waves before and after tomographic inversions, demonstrating a more concentrated and symmetrical focus compared to the pre-inversion.\u003c/p\u003e \u003cp\u003e \u003cb\u003eResolution tests for seismic tomography.\u003c/b\u003e As part of our seismic tomographic analysis, we conducted comprehensive checkerboard resolution tests (CRTs)\u003csup\u003e32\u003c/sup\u003e to evaluate the resolving capability of the selected seismic data and the appropriateness of parameter initialization employed in seismic tomography. The input parameters, including the initial velocity model, grid-spacing settings, damping, iterations, and data sets, remained consistent between the CRTs and final seismic tomography. We introduced positive and negative velocity perturbations of 6% to adjacent grid nodes and then conducted forward modeling to calculate synthetic travel times. In general, CRT synthetic inversions can be easily evaluated for resolution results because the velocities (𝑉𝑝 and 𝑉𝑠) were inverted using synthetic data to estimate their extent restored by estimating amplitudes and patterns of inverted values. Considering the spatial distributions of sources and stations across the entire study region, we tested the same grid as the final seismic tomography with a lateral grid interval of 0.25˚ in both latitude and longitude while maintaining a vertical grid spacing ranging from 10–30 km at different depths for CRTs (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). The CRT results demonstrate a strong coherence between P- and S-velocities, with the amplitudes of 𝑉𝑝 and 𝑉𝑠 effectively restored in the crust and uppermost mantle in the target region (Supplementary Fig.\u0026nbsp;1). The high-resolution area gradually diminished with increasing depth, particularly in the southeastern region of the study area, where fewer stations and earthquakes are present compared to other regions, resulting in inadequate coverage of low-resolution areas by radiation (Supplementary Fig.\u0026nbsp;1). Nevertheless, our seismic data-derived velocity model and initial parameter selection successfully restored the resolution of the main research area in the crust and uppermost mantle. Furthermore, high ray-path coverages of P- and S-waves were observed in the crust and upper mantle (Supplementary Fig.\u0026nbsp;4), indicating the robustness of our seismic data. These findings suggest that the velocity models inverted from the seismic data were reliable and credible.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe travel time data utilized in this study were sourced from both the Transportable Array Deployment to Alaska (www.usarray.org/Alaska) and the International Seismological Center (ISC) bulletins (www.isc.ac.uk). The final 3D seismic models can be accessed through the Open database at https://doi.org/10.5281/zenodo.10272868.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll figures presented herein were generated using Generic Mapping Tools\u003csup\u003e64\u003c/sup\u003e. The analysis codes used in the main text and supplementary information are available from the corresponding author upon reasonable request.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe express our sincere gratitude to Prof. D. Zhao from Tohoku University of Japan for generously providing us with the seismic tomographic code essential for determining the seismic structure in this study. This study was funded by the National Natural Science Foundation of China (Grant No. 92058210, 42074047, 42241206) and supported by the Open Fund from the Engineering Research Center for Seismic Disaster Prevention and Engineering Geological Disaster Detection of Jiangxi Province (Grant No.\u0026nbsp;SDGD202208).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eYaping Hu\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e Writing \u0026ndash; review \u0026amp; editing, Writing \u0026ndash; original draft, Investigation, Visualization, Conceptualization. \u003cstrong\u003eZhi Wang:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; review \u0026amp; editing, Supervision, Project administration, Investigation, Funding acquisition,\u0026nbsp;Visualization, Validation, Investigation,\u0026nbsp;Data curation, Conceptualization.\u003cstrong\u003e\u0026nbsp;Cunxi Liu:\u003c/strong\u003e Writing \u0026ndash; review \u0026amp; editing, Software, Resources, Visualization, Methodology, Validation, Investigation. \u003cstrong\u003eFeiyu Zhao:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; review \u0026amp; editing, Data curation.\u0026nbsp;Y.\u0026nbsp;H. and Z.W.\u0026nbsp;contributed equally to this work and all authors approved the final version.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eSupplementary information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe online version contains supplementary material available at\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigures and\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ef\u003c/strong\u003e\u003cstrong\u003eigure captions\u003c/strong\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eYang, X. \u0026amp; Gao, H. 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Slab2, a comprehensive subduction zone geometry model. \u003cem\u003eScience\u003c/em\u003e, \u003cstrong\u003e362\u003c/strong\u003e(6410), 58\u0026ndash;61; DOI: 10.1126/science.aat4723 (2018).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"joint seismic tomography, slab tearing, plate subduction geometries, volcanism, plate interaction","lastPublishedDoi":"10.21203/rs.3.rs-4457707/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4457707/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMultistage plate subduction plays a crucial role in magmatism; however, the mechanisms by which deep geodynamic processes govern volcanism in the Alaska subduction zone remain controversial. In this study, we revealed that the Pacific Plate transitioned from oblique subduction along the Aleutian volcano chain to lower-angle subduction beneath the Pacific-Yakutat Plate interaction zone, forming two slab tears that enhance hot asthenosphere materials upwelling. The partial melting of the mantle wedge induced by Pacific slab dehydration and, the concurrent upwelling of mantle materials, jointly drove volcanism in the transition zone. However, the flat subduction of the Yakutat slab into the mantle wedge overlying the Pacific slab effectively hindered the upwelling of hot hybrid materials, cooling the Pacific mantle wedge. This process produced a non-volcanic gap beneath Denali, reducing volcanic degassing. The findings provide novel perspectives on understanding the volcanic activities in Alaska and their influence on the carbon cycle.\u003c/p\u003e","manuscriptTitle":"Control of slab tears and slab flat wedging on volcanism in the Alaska subduction zone","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-05 08:14:19","doi":"10.21203/rs.3.rs-4457707/v1","editorialEvents":[{"type":"communityComments","content":2},{"type":"decision","content":"Revision requested","date":"2024-09-05T06:57:56+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-05T01:54:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"321050537045205292474486291980179493257","date":"2024-08-30T12:28:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"340110979057130386318025665513272319832","date":"2024-07-23T09:23:44+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-17T09:39:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"192981962252290140689592023085656462348","date":"2024-07-12T07:38:23+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-18T16:48:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"104579070648940341059995341503579530327","date":"2024-06-10T02:09:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"110931336235825784580534789395321648420","date":"2024-06-08T09:53:19+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-27T11:58:40+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-27T11:57:13+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-05-27T10:41:38+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-05-24T03:47:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-05-22T02:31:39+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ed3ee4c4-ed25-4ee4-9d42-d0c708624bca","owner":[],"postedDate":"June 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-11-04T16:27:59+00:00","versionOfRecord":{"articleIdentity":"rs-4457707","link":"https://doi.org/10.1038/s41598-024-76595-4","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2024-10-28 16:20:27","publishedOnDateReadable":"October 28th, 2024"},"versionCreatedAt":"2024-06-05 08:14:19","video":"","vorDoi":"10.1038/s41598-024-76595-4","vorDoiUrl":"https://doi.org/10.1038/s41598-024-76595-4","workflowStages":[]},"version":"v1","identity":"rs-4457707","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4457707","identity":"rs-4457707","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}