Seamount Subduction Research Articles

Seismic performance of offshore wind turbine in the vicinity of seamount subduction zone

The presence of seamount on the subducting interface of oceanic and continental tectonic plates has potential to alter the characteristics of ground motion due interface earthquakes. In this study, we address the influence of seamount presence on offshore wind turbine response, through a finite element simulation of earthquake and subsequently applying the recorded shaking from earthquake simulation as input to offshore wind turbines. The wind turbine response is computing by incremental dynamic analysis and fragility curves are derived for serviceability and ultimate limits of wind turbines. The effect of hypocenter being above or below the seamount, on the offshore wind turbine fragility is also addressed.

Fluid-rich subducting topography generates anomalous forearc porosity.

The role of subducting topography on the mode of fault slip-particularly whether it hinders or facilitates large megathrust earthquakes-remains a controversial topic in subduction dynamics1-5. Models have illustrated the potential for subducting topography to severely alter the structure, stress state and mechanics of subduction zones4,6; however, direct geophysical imaging of the complex fracture networks proposed and the hydrology of both the subducting topography and the associated upper plate damage zones remains elusive. Here we use passive and controlled-source seafloor electromagnetic data collected at the northern Hikurangi Margin, New Zealand, to constrain electrical resistivity in a region of active seamount subduction. We show that a seamount on the incoming plate contains a thin, low-porosity basaltic cap that traps a conductive matrix of porous volcaniclastics and altered material over a resistive core, which allows 3.2 to 4.7 times more water to subduct, compared with normal, unfaulted oceanic lithosphere. In the forearc, we image a sediment-starved plate interface above a subducting seamount with similar electrical structure to the incoming plate seamount. A sharp resistive peak within the subducting seamount lies directly beneath a prominent upper plate conductive anomaly. The coincidence of this upper plate anomaly with the location of burst-type repeating earthquakes and seismicity associated with a recent slow slip event7 directly links subducting topography to the creation of fluid-rich damage zones in the forearc that alter the effective normal stress at the plate interface by modulating the fluid overpressure. In addition to severely modifying the structure and physical conditions of the upper plate, subducting seamounts represent an underappreciated mechanism for transporting a considerable flux of water to the forearc and deeper mantle.

Long-lived seamount subduction in ancient orogens: Evidence from the Paleozoic South Tianshan

AbstractAlong the present-day circum-Pacific subduction girdle, seamount subduction is known to have significant effects on subduction dynamics including on seismicity and arc magmatism. Because seamount subduction should have occurred throughout much of Earth history, its effects on orogenesis in the overriding plate should be identifiable in ancient orogens. In this study, we investigate the Paleozoic South Tianshan orogen of Central Asia, for which abundant evidence of seamount subduction exists, further bolstered by the continuation of a long-lived plume-induced large igneous province on the subsequently accreted Tarim craton. We find that semi-continuous seamount subduction from ca. 400 to 330 Ma temporarily shut down arc magmatism, and once the seamounts were completely subducted, then arc magmatism resumed and eclogites were quickly exhumed. If such an orogenic fingerprint of seamount subduction can be identified in ancient orogens, a much more complete picture of plume-subduction interaction and its influence on both crustal and mantle processes can be developed.

Geochemistry of subducted metabasites exhumed from the Mariana forearc: Implications for Pacific seamount subduction

Seamounts on the drifting oceanic crust are inevitably carried by plate motions and eventually accreted or subducted. However, the geochemical signatures of the subducted seamounts and the significance of seamount subduction are not well constrained. Hundreds of seamounts have subducted beneath the Philippine Sea Plate following the westward subduction of the Pacific Plate since the Eocene (~52 Ma). The subducted oceanic crust and seamount materials can be exhumed from the mantle depth to the seafloor in the Mariana forearc region by serpentinite mud volcanoes, providing exceptional opportunities to directly study the subducted oceanic crust and seamounts. The International Ocean Discovery Program (IODP) expedition 366 has recovered a few metamorphosed mafic clasts exhumed from the Mariana forearc serpentinite mud volcanoes, e.g., the Fantangisña and Asùt Tesoru seamounts. These mafic clasts have tholeiitic to alkaline affinities with distinct trace elements and Nd-Hf isotopes characteristics, suggesting different provenances and mantle sources. The tholeiites from the Fantangisña Seamount have trace element characteristics typical of mid-ocean ridge basalt. The Pacific-type Hf-Nd isotopic compositions, combined with the greenschist metamorphism of these tholeiites further suggest that they came from the subducted Pacific oceanic crust. The alkali basalts-dolerites from the Fantangisña and Asùt Tesoru seamounts show ocean island basalt (OIB)-like geochemical characteristics. The OIB-like geochemical signatures and the low-grade metamorphism of these alkali basalts-dolerites suggest they came from subducted seamounts that originally formed in an intraplate setting on the Pacific Plate. The Pacific Plate origin of these metabasites suggests they were formed in the Early Cretaceous or earlier.Two types of OIBs have been recognized from alkali metabasites, one of which is geochemically similar to the HIMU-EMI-type OIBs from the West Pacific Seamount Province, and another is similar to the EMII-type OIBs from the Samoa Island in southern Pacific, with negative Nb-Ta-Ti anomalies and enriched Nd-Hf isotopes. Generally, these alkali metabasites are sourced from the heterogeneous mantle sources that are similar to the present South Pacific Isotopic and Thermal Anomaly. This study provides direct evidence for seamount subduction in the Mariana convergent margins. We suggest seamount subduction is significant to element cycling, mantle heterogeneity, and mantle oxidation in subduction zones.

Effect on Subduction of Deeply Buried Seamounts Offshore of Kodiak Island

AbstractSeamounts are ubiquitous on the oceanic plate; those situated near convergent margins will eventually undergo subduction. Using six prestack depth migrated MCS profiles transecting the Aleutian Trench, we investigate deeply buried seamounts offshore Kodiak Island, within 145–155°W and 55–58°N. A distinct sedimentary horizon exists in all six seismic profiles, at or above the average height of seamounts, which appears to be the preferred structural detachment zone. Where drilled, this horizon contains gravel‐sized debris interpreted to be ice rafted and marks the onset of intensification of Northern Hemisphere glaciation at ~2.7 Ma. Beneath this horizon, sediments prior to the Surveyor Fan development were deposited, all or the majority of these sediments will eventually be subducted. Despite the subducted seamounts being deeply buried, these features cause enhanced surface slope of the accretionary prism. Our observations lead us to propose a model for the stages of subduction for deeply buried seamounts. These stages include the following: (1) Prior to subduction, the protothrust zone undergoes enhanced shortening, (2) frontal thrust steepening and enhanced backthrusting occurs during subduction with a potential décollement step down seaward and a steeping outward of the deformation front to the limit of the protothrust zone, and (3) further subduction results in a pattern of uplift farther into the wedge resulting in enhanced out‐of‐sequence thrusting and persistence of the more seaward deformation front position. This pattern is distinct from the dominance of embayments and effective removal of prism material during seamount subduction described along margins with less deeply buried edifices.

Seafloor morphology along the active margin in Guerrero, Mexico: Probable earthquake implications

Submarine geomorphic features on the active margin along the Mexican Pacific coast are the result of subduction process. We analyze bathymetric data and present an overview of the continental slope geomorphology in the Guerrero seismic gap. For the first time we identify and describe submarine landforms in this area, including small-scale forearc basins, trench basin segmentation, narrow accretionary wedge and seamounts. We propose that the presence and formation of forearc basins are related to seamount subduction as well as the origin of higher relief above subducted seamounts. Here, forearc basins and trench sediments are sourced from submarine canyons. Notably, the thickness of sediments along the trench changes due to the presence of seamounts. Some parts of the trench seem to contain little sedimentary fill, which may increase friction along these segments of the subduction zone.

Publisher Correction: Mechanical and hydrological effects of seamount subduction on megathrust stress and slip

Publisher Correction: Mechanical and hydrological effects of seamount subduction on megathrust stress and slip

Mechanical and hydrological effects of seamount subduction on megathrust stress and slip

Subduction of rough seafloor and seamounts is thought to impact a broad range of geodynamic processes, including megathrust slip behaviour, forearc fluid flow and long-term structural evolution in the overriding plate. Although there are many conceptual models describing the effects of seamount subduction, our quantitative and mechanistic understanding of the underlying deformation and fluid processes remains incomplete. Here we investigate the interplay between sediment consolidation, faulting and the evolution of stress and pore fluid pressure in response to seamount subduction, using a numerical model that couples mechanical and hydrological processes and is constrained by laboratory and field observations. Our results show that subducting topography drives marked spatial variations in tectonic loading, sediment consolidation and megathrust stress state. Downdip of a subducting seamount on its leading flank, enhanced compression and drainage lead to large fault-normal stress and overconsolidated wall rocks. A stress shadow in the seamount’s wake leads to anomalously high sediment porosity. These variations help explain observed patterns of megathrust slip, with earthquakes and microseismicity favoured at the downdip edge of seamounts and aseismic or slow slip in the updip stress shadow. Changing stresses and pore fluid pressures during subduction of seamounts, as simulated with a numerical model that couples mechanical and hydrological processes, help explain observed patterns of megathrust slip.

Conjugate strike-slip faulting across a subduction front driven by incipient seamount subduction

Abstract The initial stages of seamount subduction and associated deformation in an overriding accretionary wedge is rarely documented. Initial subduction of Bennett Knoll seamount and faulting of the overlying strata along the Hikurangi subduction margin, New Zealand, are here studied using multibeam swath bathymetry, subbottom profiles, and regional seismic reflection lines. Our results provide new insights into the earliest stages of seamount collision at sediment-rich margins. Differential shortening along the subduction front induced by seamount subduction is initially accommodated in the accretionary wedge by conjugate strike-slip faults that straddle the buried flanks of the seamount and offset the frontal thrusts by as much as 5 km. The geometries of the strike-slip faults are controlled by the seamount’s dimensions and aspect, the obliquity of plate convergence, pore-fluid pressure, and the thickness and rheology of the incoming sedimentary section. Strike-slip faults in such settings are ephemeral and overprinted by the formation of new structures as seamount subduction advances.

Mariana serpentinite mud volcanism exhumes subducted seamount materials: implications for the origin of life.

The subduction of seamounts and ridge features at convergent plate boundaries plays an important role in the deformation of the overriding plate and influences geochemical cycling and associated biological processes. Active serpentinization of forearc mantle and serpentinite mud volcanism on the Mariana forearc (between the trench and active volcanic arc) provides windows on subduction processes. Here, we present (1) the first observation of an extensive exposure of an undeformed Cretaceous seamount currently being subducted at the Mariana Trench inner slope; (2) vertical deformation of the forearc region related to subduction of Pacific Plate seamounts and thickened crust; (3) recovered Ocean Drilling Program and International Ocean Discovery Program cores of serpentinite mudflows that confirm exhumation of various Pacific Plate lithologies, including subducted reef limestone; (4) petrologic, geochemical and paleontological data from the cores that show that Pacific Plate seamount exhumation covers greater spatial and temporal extents; (5) the inference that microbial communities associated with serpentinite mud volcanism may also be exhumed from the subducted plate seafloor and/or seamounts; and (6) the implications for effects of these processes with regard to evolution of life.This article is part of a discussion meeting issue ‘Serpentine in the Earth system’.

Tectonic and geomorphic controls on the distribution of submarine landslides across active and passive margins, eastern New Zealand

Abstract Submarine landslides occur on continental margins globally and can have devastating consequences for marine habitats, offshore infrastructure and coastal communities due to potential tsunamigenesis. Therefore, understanding landslide magnitude and distribution is central to marine and coastal hazard planning. We present the first submarine landslide database for the eastern margin of New Zealand comprising >2200 landslides occurring in water depths from c. 300–4000 m. Landslides are more prevalent and, on average, larger on the active margin compared with the passive margin. We attribute higher concentrations of landslides on the active margin to tectonic processes including uplift and oversteepening, faulting and seamount subduction. Submarine landslide scars are concentrated around canyon systems and close to canyon thalwegs. This suggests that not only does mass wasting play a major role in canyon evolution, but also that canyon-forming processes may provide preconditioning factors for slope failure. Results of this study offer unique insights into the spatial distribution, magnitude and morphology of submarine landslides across different geological settings, providing a better understanding of the causative factors for mass wasting in New Zealand and around the world.

Long-term non-erosive nature of the south Costa Rican margin supported by arc-derived sediments accreted in the Osa Mélange

Understanding the erosive and accretionary nature of convergent margins is significant to understand tectonics and the crustal mass balance at subduction zones. The Costa Rican margin is commonly regarded as an archetypal example of an erosive margin, where subduction of sediments and basal removal of the upper plate in the subduction zone have occurred for most of the Cainozoic. This view is supported by structural constraints from 3D seismic reflection data in the outer forearc, as well as periods of forearc subsidence at ODP/DSDP/IODP drill sites. However, determining the origin of the Upper Eocene-Miocene Osa Mélange that is exposed in south Costa Rica only 10–30 km from today's trench offers another opportunity to constrain the long-term erosive, accretionary, and/or non-erosive evolution of the margin. Existing models for formation of the mélange propose that it resulted from (i) accretion of arc-derived trench-fill sediments, (ii) punctual accretion of the clastic apron of an ocean islands system, (iii) local dismemberment of the margin due to tectonic erosion, or (iv) in-situ deformation of a forearc sedimentary cover. To test the validity of these models and provide new constraints on the accretionary and/or erosive nature of the margin we studied the provenance of volcaniclastic material in the Upper Eocene San Pedrillo Unit of the Osa Mélange using geochemical analysis of detrital pyroxenes, amphiboles and igneous rocks. This innovative approach to determine the origin(s) of dismembered sedimentary sequences reveals that the volcaniclastic fraction of the mélange is, without ambiguity, predominantly composed of forearc material that preserves an assemblage of arc basement, proto-arc and arc sequences of the pre-Oligocene Costa Rican margin. This result and previous geological constraints show that the Osa Mélange formed through accretion of arc-derived trench-fill deposits in the Late Eocene to Miocene, with possibly minor tectonic incorporation of intra-oceanic material (ocean floor and seamount sequences). Therefore, consistently with recent seismic observations in south Costa Rica that document a phase of accretion within the past ∼5 m.yr., preservation of arc-derived sediments in the Osa Mélange shows that the margin was predominantly non-erosive over the past ∼35 m.yr. Cycles of subsidence and uplift in the south Costa Rican forearc during this period could represent a tectonic response to episodic subduction of seamounts formed at the Galapagos Hotspot, without causal link to short-term subduction erosion or accretion. Fundamentally, new results from the Osa Mélange show that large (10 km-thick) accretionary complexes can form durably due to local sedimentary recycling of the forearc in seamount collisional settings. The recycled component of the NW Osa Mélange exemplifies that quantifying the extent of local recycling vs net crustal addition through accretion of intra-oceanic sequences or net crustal loss due to tectonic erosion poses a serious challenge to determine the crustal mass balance at subduction zones.

Structure and metamorphism of a subducted seamount (Zagros suture, Southern Iran)

Abstract Millions of seamounts on modern and past seafloor end up being subducted, and only small pieces are recovered in suture zones. How they are metamorphosed and deformed is, however, critical to understand how seamount subduction can impact subduction zone geometry, fluid circulation or seismogenic conditions, and more generally to trace physical conditions along the subduction boundary. Since geophysical studies mostly reach the shallowest subducted seamounts and miss internal structures due to low resolution, there is a high need for fossil seamount exposures. We herein report on a fully exposed, 3D example of seamount that we discovered in the Siah Kuh massif, Southern Iran. Through a series of sections across the whole massif and the combination of magmatic-metamorphic-sedimentary petrological data, we document several distinct stages associated with seamount build-up on the seafloor and with subduction. In particular, we constrain different stages of metamorphism and associated mineralogy, with precise conditions for subduction-related metamorphism around 250 °C and 0.7 GPa, in the middle of the seismogenic zone. Extensive examination of the seismogenic potential of the Siah Kuh seamount reveals that it was not a large earthquake asperity (despite the report of a rare example of cm-scale, high-pressure pseudotachylyte in this study), and that it possibly behaved as a barrier to earthquake propagation. Finally, we discuss the nature of high-pressure fluid circulation preserved in this seamount.

Late Quaternary sea-level history of Saipan, Commonwealth of the Northern Mariana Islands, USA: A test of tectonic uplift and glacial isostatic adjustment models

Abstract In 1979, S. Uyeda and H. Kanamori proposed a tectonic model with two end members of a subduction-boundary continuum: the “Chilean” type (shallow dip of the subducting plate, great thrust events, compression, and uplift of the overriding plate) and a “Mariana” type (steep dip of the subducting plate, no great thrust events, tension, and no uplift). This concept has been used to explain variable rates of Quaternary uplift around the Pacific Rim, yet no uplift rates have been determined for the Mariana Islands themselves, one of the end members in this model. We studied the late Quaternary Tanapag Limestone, which rims much of the eastern and southern coasts of Saipan, Northern Mariana Islands, with elevations of ∼13 m to ∼30 m. Samples from 12 well-preserved corals (Acropora, Porites, and Goniastrea) yielded U-series ages ranging from ca. 134 ka to ca. 126 ka. These ages correlate the emergent reef of the Tanapag Limestone with the last interglacial period, when sea level was several meters above present. Ages and measured reef elevations from the Tanapag Limestone, along with paleo–sea-level data, yield relatively low late Quaternary uplift rates of 0.002–0.19 m/k.y., consistent with the Uyeda-Kanamori model. A review of data from other localities near subduction zones around the Pacific Basin, however, indicates that many coastlines do not fit the model. Uplift rates along the Chilean coast are predicted to be relatively high, but field studies indicate they are low. On some coastlines, relatively high uplift rates are better explained by subduction of seamounts or submarine ridges rather than subduction zone geometry. Despite the low long-term uplift rate on Saipan, the island also hosts an emergent, low-elevation (+3.9–4.0 m) reef with corals in growth position below a notch (+4.2 m). The corals are dated to 3.9–3.1 ka. The occurrence of this young, emergent reef is likely not due to tectonic uplift; instead, it is interpreted to be the result of glacial isostatic adjustment processes after the end of the last glacial period. Our findings are consistent with similar observations on tectonically stable or slowly uplifting islands elsewhere in the equatorial Pacific Ocean and agree with numerical models of a higher-than-present Holocene sea level in this region due to glacial isostatic adjustment processes.

Plio‐Quaternary Outer Forearc Deformation and Mass Balance of the Southern Costa Rica Convergent Margin

AbstractIdentifying the processes that control the rates, magnitudes, and longevity of outer forearc deformation is fundamental to our understanding of how mass is distributed within subduction zone systems. The margin of southern Costa Rica has been the target of numerous onland field studies, geophysical surveys, and the Costa Rica Seismogenesis Project (CRISP) drilling expedition. Despite these extensive data sets, the relative roles that subduction erosion, shortening, and seamount subduction play in shaping the behavior and evolution of the outer forearc remain debated. Here we analyze new and existing geomorphic, geologic, stratigraphic, and geochronologic data sets across the entire forearc‐arc‐backarc system near the Costa Rica Seismogenesis Project transect to test several conceptual models for outer forearc deformation in southern Costa Rica. The results from the compilation agree with a model where recent arcward retreat of the trench (movement of the trench in the direction of the arc) occurs due to underthrusting of the outer forearc beneath the inner forearc, and outer forearc deformation occurs primarily by transient rapid vertical tectonism due to the subduction of bathymetric relief. These results lead to a new conceptual model for Plio‐Quaternary outer forearc deformation in southern Costa Rica that does not require large amounts of net mass loss within the upper plate.

Kazakhstan Orocline bending in response to seamounts subduction

Oroclines are map‐view deformation of Earth's crust resulting from bending of quasi‐linear elements. The Central Asian Orogenic Belt (CAOB) is one of the largest and long‐lived accretionary orogens in the world and mainly consists of the Kazakhstan and Tuva–Mongolian oroclines. However, the mechanism of the oroclines is still in debate. Therefore, in this paper, we combine some investigation of high bathymetric relief resistance to subduction, review oroclinal bending models of the Kazakhstan Orocline, and propose a tentative model that involves asymmetric rollback in response to seamounts subduction and accretion, followed by bending associated with the convergence of the Siberian and Tarim cratons. Moreover, the role of pinning due to seamount and ridge subduction is probably more important than the convergence of continents in the CAOB. This model is compatible with the occurrence of seamounts, the spatial migration of intra‐oceanic arcs, and the development of multiple rollback processes during amalgamation of Eurasia. However, only geochemical and geochronological data will enable definition of the seamounts in CAOB so far, without much matching structural data. So we need more work to understand seamounts subduction and accretion as well as orocline bending in CAOB.

An overview of oceanic island basalts in accretionary complexes and seamounts accretion in the western Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) is one of the largest and long-lived accretionary collages worldwide, and provides an ideal opportunity to address the fundamental geological processes and continental growth of accretionary orogens. However, the tectonic history of the CAOB is still controversial. Previous studies mainly focused on the process and model of accretion and subduction, but did not pay much attention to oceanic intraplate volcanoes. In this paper, we provide an overview of the salient features of twelve OIB-hosting accretionary complexes with ages from Late Neoproterozoic to Early Carboniferous in western the CAOB, and distinguish rock association of typical seamounts from accretionary complexes and shear zones, including pillow basalt, volcanic breccia, limestone, olistostromes and terrestrial clastic rocks. Combined with unique structural features of seamount, the stratigraphic framework of seamount was preliminarily reconstructed in Paleo-Asian Ocean, but the distribution and scale of seamounts is still not clear. Geochemically, volcanic rocks from seamounts are mainly alkaline basalts with litte tholeiitic basalts. The alkaline basalts are characterized by LREE enrichment and HREE depletion, and no obvious Nb, Ta and Ti negative anomalies, suggesting typical OIB affinity. The Nd, Sr and Pb isotopic features indicate that magma sources have enriched components and show fluid metasomatism. In short, this is consistent with geochemical features of Louisville, Ontong Java and Hawaiian seamounts which are related to mantle plumes, but do not contain high-Mg picrite and komatitic basalt. Based on our observations, and in combination with previous work, we present an innovative model in which the CAOB was involved multiple intra-oceanic arc with seamounts subduction and accretion, which is similar to the present-day Pacific and can better explain the tectonic evolution of the CAOB. However, further studies are needed to document the distribution, scale and mantle dynamics of seamounts in the CAOB.

Subducted seamount diverts shallow slow slip to the forearc of the northern Hikurangi subduction zone, New Zealand

Fluid migration and pore fluid pressure have been implicated in generating the transitional fault zone properties thought to be important for slow slip events (SSEs) in subduction zones. At the northern Hikurangi margin, New Zealand, overpressurized sediments spatially correlated with shallow SSEs are imaged downdip of subducted seamounts, providing an excellent environment to study the relationship between subducted oceanic relief, fluids, shallow SSEs, and related microseismicity. Using data from ocean-bottom seismometers, we detect “burst-type” repeating earthquakes coincident with tremor on an upper-plate fracture network above a subducted seamount. This activity occurred at the edge of a large, shallow SSE recorded offshore of Gisborne, New Zealand, in September–October 2014, but began days to weeks after the SSE and continued for nearly two months. We propose that during the large plate-boundary SSE, fluids migrated from the downdip overpressurized sediments into the fracture network, diverting aseismic slip to multiple faults in the upper plate. Thus, seamount subduction appears to play a key role in controlling the mechanics of shallow slow slip and microseismicity at the northern Hikurangi margin.

Geochemistry and Geochronology of the Accreted Mafic Rocks From the Hengchun Peninsula, Southern Taiwan: Origin and Tectonic Implications

AbstractThe accretionary prism of the Hengchun Peninsula at the southernmost tip of the active Taiwan orogen has newly emerged due to the transition from a subduction zone to an arc‐continent collision zone. The mafic rocks within the Hengchun accretionary prism, whose provenance has long been controversial, are highly indicative of the mantle nature and tectonic evolution around the northern Manila Trench. Based on geochemical analyses, the accreted basalts are classified as normal and enriched mid‐ocean ridge basalts (N‐MORB and E‐MORB) and alkaline ocean island basalts. The N‐MORBs, which exhibit geochemical signatures indicative of virtually unmetasomatized depleted MORB mantle and yield zircon U‐Pb ages of 22.8 ± 0.3 and 24.2 ± 1.1 Ma, were off‐scraped from the subducted oceanic crust of the South China Sea (SCS). The alkaline ocean island basalts are considered fragments of subducted seamount due to their geochemical similarity with seamount basalts from the SCS. The Hf‐Nd isotopic compositions of basalts from the north SCS may represent the contributions of recycled oceanic crust and the upwelling Hainan Plume. The E‐MORBs, which exhibit similar geochemical compositions as rocks from the Huatung Basin and yield an 40Ar/39Ar age of 135.0 ± 5.6 Ma, were removed from the overriding plate due to the excessive shear stress between the converging plates and were laterally transported by strike‐slip movement; alternatively, they were off‐scraped from the subducted Luzon forearc slices. The temporary uplift and collapse of the accretionary prism caused by seamount subduction may have been responsible for the genesis of the lenticular Shihmen Conglomerate.

Subduction Erosion, Crustal Structure, and an Evolutionary Model of the Northern Yap Subduction Zone: New Observations From the Latest Geophysical Survey

AbstractThe Yap subduction zone is a distinctive erosive margin with an extremely slow convergence rate. The high relief of the subducting plate, generated by horst and graben structures and seamounts, leads to attenuation of the crust. In this study, we present the latest geophysical data, collected by the Chinese research vessel Kexue, to investigate subduction erosion at the Yap subduction zone and develop subduction models for Yap subduction zone structures. We show an anomalous distance between the Yap Trench and the adjacent volcanic arc, the steep slope of the trench arcward, a frontal prism, and rare sediment in the trench, all typical features of erosive margins. We propose that the high‐relief subducting plate has led to erosion of the overlying plate and that different subduction processes, controlled locally by the topography of the subducting plate, have modified the Yap subduction zone. Numerous normal faults increase the relief of the seafloor entering the trench, and an anomalously large slope angle along the trench reflects uplift of the fore‐arc high via seamount subduction. In addition, the thin crust of the subducted horst and graben structures, along with the normal faults, might have eroded the fore‐arc crust and subsequently eroded the Yap arc crust during subduction. These subduction erosional processes at the Yap Trench provide one of the best cases of an erosive margin in the world, particularly for a subduction zone with an extremely slow convergence rate.