Crustal structure of the Southwest Subbasin,South China Sea,from wide-angle seismic tomography and seismic reflection imaging

The Southwest Subbasin (SWSB) is an abyssal subbasin in the South China Sea (SCS), with many debates on its neotectonic process and crustal structure. Using two-dimensional seismic tomography in the SWSB, we derived a detailed P-wave velocity model of the basin area and the northern margin. The entire profile is approximately 311-km-long and consists of twelve oceanic bottom seismometers (OBSs). The average thickness of the crust beneath the basin is 5.3 km, and the Moho interface is relatively flat (10–12 km). No high velocity bodies are observed, and only two thin high-velocity structures (~7.3 km/s) in the layer 3 are identified beneath the northern continent-ocean transition (COT) and the extinct spreading center. By analyzing the P-wave velocity model, we believe that the crust of the basin is a typical oceanic crust. Combined with the high resolution multi-channel seismic profile (MCS), we conclude that the profile shows asymmetric structural characteristics in the basin area. The continental margin also shows asymmetric crust between the north and south sides, which may be related to the large scale detachment fault that has developed in the southern margin. The magma supply decreased as the expansion of the SWSB from the east to the west.     

An integrated geophysical study of Vestbakken Volcanic Province, western Barents Sea continental margin, and adjacent oceanic crust

This paper describes results from a geophysical study in the Vestbakken Volcanic Province, located on the central parts of the western Barents Sea continental margin, and adjacent oceanic crust in the Norwegian-Greenland Sea. The results are derived mainly from interpretation and modeling of multichannel seismic, ocean bottom seismometer and land station data along a regional seismic profile. The resulting model shows oceanic crust in the western parts of the profile. This crust is buried by a thick Cenozoic sedimentary package. Low velocities in the bottom of this package indicate overpressure. The igneous oceanic crust shows an average thickness of 7.2 km with the thinnest crust (5–6 km) in the southwest and the thickest crust (8–9 km) close to the continent-ocean boundary (COB). The thick oceanic crust is probably related to high mantle temperatures formed by brittle weakening and shear heating along a shear system prior to continental breakup. The COB is interpreted in the central parts of the profile where the velocity structure and Bouguer anomalies change significantly. East of the COB Moho depths increase while the vertical velocity gradient decreases. Below the assumed center for Early Eocene volcanic activity the model shows increased velocities in the crust. These increased crustal velocities are interpreted to represent Early Eocene mafic feeder dykes. East of the zone of volcanoes velocities in the crust decrease and sedimentary velocities are observed at depths of more than 10 km. The amount of crustal intrusions is much lower in this area than farther west. East of the Kn?legga Fault crystalline basement velocities are brought close to the seabed. This fault marks the eastern limit of thick Cenozoic and Mesozoic packages on central parts of the western Barents Sea continental margin.     

Crustal Thinning of the Northern Continental Margin of the South China Sea

Magnetic data suggest that the distribution of the oceanic crust in the northern South China Sea (SCS) may extend to about 21 °N and 118.5 °E. To examine the crustal features of the corresponding continent–ocean transition zone, we have studied the crustal structures of the northern continental margin of the SCS. We have also performed gravity modeling by using a simple four-layer crustal model to understand the geometry of the Moho surface and the crustal thicknesses beneath this transition zone. In general, we can distinguish the crustal structures of the study area into the continental crust, the thinned continental crust, and the oceanic crust. However, some volcanic intrusions or extrusions exist. Our results indicate the existence of oceanic crust in the northernmost SCS as observed by magnetic data. Accordingly, we have moved the continent–ocean boundary (COB) in the northeastern SCS from about 19 °N and 119.5 °E to 21 °N and 118.5 °E. Morphologically, the new COB is located along the base of the continental slope. The southeastward thinning of the continental crust in the study area is prominent. The average value of crustal thinning factor of the thinned continental crust zone is about 1.3–1.5. In the study region, the Moho depths generally vary from ca. 28 km to ca. 12 km and the crustal thicknesses vary from ca. 24 km to ca. 6 km; a regional maximum exists around the Dongsha Island. Our gravity modeling has shown that the oceanic crust in the northern SCS is slightly thicker than normal oceanic crust. This situation could be ascribed to the post-spreading volcanism or underplating in this region.     

A seismic refraction study of cretaceous oceanic lithosphere in the Northwest Pacific Basin

A seismic refraction study on old (110 Myr) lithosphere in the northwest Pacific Basin has placed constraints on crustal and uppermantle seismic structure of old oceanic lithosphere, and lithospheric aging processes. No significant lateral variation in structure other than azimuthally anisotropic mantle velocities was found, allowing the application of powerful amplitude modeling techniques. The anisotropy observed is in an opposite sense to that expected, suggesting the tectonic setting of the area may be more complex than originally thought. Upper crustal velocities are generally larger than for younger crust, supporting current theories of decreased porosity with crustal aging. However, there is no evidence for significant thickening of the oceanic crust with age, nor is there any evidence of a lower crustal layer of high or low velocity relative to the velocity of the rest of Layer 3. The compressional and shear wave velocities rule out a large component of serpentinization of mantle materials. The only evidence for a basal crustal layer of olivine gabbro cumulates is a 1.5 km thick Moho transition zone. In the slow direction of anisotropy, upper mantle velocities increase from 8.0 km s^-1 to 8.35 km s^-1 in the upper 15 km below the Moho. This increase is inconsistent with an homogeneous upper mantle and suggests that compositinal or phase changes occur near the Moho.     

东海莫霍面起伏与地壳减薄特征初步分析

收集、整理大量由地震剖面提供的沉积层厚度资料,得到东海沉积层等厚图。对完全布格重力异常进行沉积层重力效应改正后,得到剩余重力异常,利用地震资料揭示的莫霍面深度值来约束界面反演得到东海莫霍面埋深。结果表明,东海陆架盆地莫霍面深度在25～28 km之间平缓变化,地壳厚度为14～26 km,西厚东薄;冲绳海槽盆地莫霍面深度为16～26 km,地壳厚度为12～22 km,北厚南薄。东海陆架盆地东部与冲绳海槽盆地南部地壳减薄明显,拉张因子分别达到2.6和3。初步分析认为冲绳海槽地壳以过渡壳为主,并未形成洋壳。     

Oceanic crust thickens approaching the Clipperton Fracture Zone

A multi-channel seismic reflection image shows the reflection Moho dipping toward the Clipperton Fracture Zone in crust 1.4 my old. This seismic line crosses the fracture zone at its eastern intersection with the East Pacific Rise. The seismic observations are made in travel time, not depth. To establish constraints on crustal structure despite the absence of direct velocity determinations in this region, the possible effects of temperature, tectonism, and anomalous lithospheric structure have been considered. Conductive, advective, and frictional heating of the old crust proximal to the ridge-transform intersection can explain <20% of the observed travel-time increase. Heating has a negligible effect on crustal seismic velocity beyond ~10 km from the ridge tip. The transform tectonized zone extends only 6 km from the ridge tip. Serpentinization is unlikely to have thickened the seafloor-to-reflection Moho section in this case. It is concluded that, contrary to conventional wisdom, the 1.4 my old Cocos Plate crust thickens approaching the eastern Clipperton Ridge-Transform Intersection. Increase in thickness must be at least 0.9 km between 22 and 3 km from the fracture zone.     

Lithospheric structure below the eastern Arabian Sea and adjoining West Coast of India based on integrated analysis of gravity and seismic data

Four uniformly spaced regional gravity traverses and the available seismic data across the western continental margin of India, starting from the western Indian shield extending into the deep oceanic areas of the eastern Arabian Sea, have been utilized to delineate the lithospheric structure. The seismically constrained gravity models along these four traverses suggest that the crustal structure below the northern part of the margin within the Deccan Volcanic Province (DVP) is significantly different from the margin outside the DVP. The lithosphere thickness, in general, varies from 110–120 km in the central and southern part of the margin to as much as 85–90 km below the Deccan Plateau and Cambay rift basin in the north. The Eastern basin is characterised by thinned rift stage continental crust which extends as far as Laxmi basin in the north and the Laccadive ridge in the south. At the ocean–continent transition (OCT), crustal density differences between the Laxmi ridge and the Laxmi basin are not sufficient to distinguish continental as against an oceanic crust through gravity modeling. However, 5-6 km thick oceanic crust below the Laxmi basin is a consistent gravity option. Significantly, the models indicate the presence of a high density layer of 3.0 g/cm³ in the lower crust in almost whole of the northern part of the region between the Laxmi ridge and the pericontinental northwest shield region in the DVP, and also below Laccadive ridge in the southern part. The Laxmi ridge is underlain by continental crust upto a depth of 11 km and a thick high density material (3.0 g/cm³) between 11–26 km. The Pratap ridge is indicated as a shallow basement high in the upper part of the crust formed during rifting. The 15 –17 km thick oceanic crust below Laccadive ridge is seen further thickened by high density underplated material down to Moho depths of 24–25 km which indicate formation of the ridge along Reunion hotspot trace.     

Deep structure of the US East Coast passive margin from large aperture seismic experiments (LASE)

Multiple ship multichannel seismic measurements in the Baltimore Canyon Trough reveal a deep crustal layer with p-wave velocity of 7.2 km s⁻¹. It apparently continues into oceanic layer 3 from beneath the inner shelf where it presumably underlies the continental basement. The layer may be plutonically solidified mantle melt. Its continuity from continental shelf to deep ocean basin may reflect a continuous progression between plutonic emplacement into the continental crust and plutonic construction of the lower oceanic crust. The deep magmatic expression of late stage continental rifting and early seafloor spreading may be very similar and blur the structural expression of the continent-ocean boundary.     

Characteristics of seismic reflections in central region of the South China Sea and their geological significance

I~IOXThe speCiality in gootectonic position and complicity in origin and evolution of the sleuth China Sea (SCS) has aroused particular attention of the geoscientists at home and abroad. The central region, which consists of continental slope, island slope and a deep-sea basin, is an importantarea for the study of the mechanism of origin and evolution of the SCS. In addition to the surveysof bathemetry, gravity and magnetism, seismic surveys have been carried out by domestic andforeign in…     

Møre Margin: Crustal structure from analysis of Expanded Spread Profiles

Analysis in both the x—t and —p domains of high-quality Expanded Spread Profiles across the Møre Margin show that many arrivals may be enhanced be selective ray tracing and velocity filtering combined with conventional data reduction techniques. In terms of crustal structure the margin can be divided into four main areas: 1) a thicker than normal oceanic crust in the eastern Norway Basin; 2) expanded crust with a Moho depth of 22 km beneath the huge extrusive complex constructed during early Tertiary breakup; 3) the Møre Basin where up to 13–14 km of sediments overlie a strongly extended outer part with a Moho depth at 20 km west of the Ona High; and 4) a region with a 25–27 km Moho depth between the high and the Norwegian coast. The velocity data restricts the continent-ocean boundary to a 15–30 km wide zone beneath the seaward dipping reflector wedges. The crust west of the landward edge of the inner flow is classified as transitional. This region as well as the adjacent oceanic crust is soled by a 7.2–7.4 km s^–1 lower crustal body which may extend beneath the entire region that experienced early Tertiary crustal extension. At the landward end of the transect a 8.5 km s^–1 layer near the base of the crust is recognized. A possible relationship with large positive gravity anomalies and early Tertiary alkaline intrusions is noted.     

Deep crustal structure of the conjugate margins of the SW South China Sea from wide-angle refraction seismic data

The South China Sea is the largest marginal basin of SE Asia, yet its mechanism of formation is still debated. A 1000-km long wide-angle refraction seismic profile was recently acquired along the conjugate margins of the SW sub-basin of the South China Sea, over the longest extended continental crust. A joint reflection and refraction seismic travel time inversion is performed to derive a 2-D velocity model of the crustal structure and upper mantle. Based on this new tomographic model, northern and southern margins are genetically linked since they share common structural characteristics. Most of the continental crust deforms in a brittle manner. Two scales of deformation are imaged and correlate well with seismic reflection observations. Small-scale normal faults (grabens, horsts and rotated faults blocks) are often associated with a tilt of the velocity isocontours affecting the upper crust. The mid-crust shows high lateral velocity variation defining low velocity bodies bounded by large-scale normal faults recognized in seismic reflection profiles. Major sedimentary basins are located above low velocity bodies interpreted as hanging-wall blocks. Along the northern margin, spacing between these velocity bodies decreases from 90 to 45 km as the total crust thins toward the Continent–Ocean Transition. The Continent–Ocean Transitions are narrow and slightly asymmetric – 60 km on the northern side and no more than 30 km on the southern side – indicating little space for significant hyper-stretched crust. Although we have no direct indication for mantle exhumation, shallow high velocities are observed at the Continent–Ocean Transition. The Moho interface remains rather flat over the extended domain, and remains undisturbed by the large-scale normal faults. The main décollement is thus within the ductile lower crust.     

Crustal structure and mantle transition zone thickness beneath a hydrothermal vent at the ultra-slow spreading Southwest Indian Ridge (49°39′E): a supplementary study based on passive seismic receiver functions

As a supplementary study, we used passive seismic data recorded by one ocean bottom seismometer (OBS) station (49°41.8′E) close to a hydrothermal vent (49°39′E) at the Southwest Indian Ridge to invert the crustal structure and mantle transition zone (MTZ) thickness by P-to-S receiver functions to investigate previous active seismic tomographic crustal models and determine the influence of the deep mantle thermal anomaly on seafloor hydrothermal venting at an ultra-slow spreading ridge. The new passive seismic S-wave model shows that the crust has a low velocity layer (2.6 km/s) from 4.0 to 6.0 km below the sea floor, which is interpreted as partial melting. We suggest that the Moho discontinuity at ~9.0 km is the bottom of a layer (2–3 km thick); the Moho (at depth of ~6–7 km), defined by active seismic P-wave models, is interpreted as a serpentinized front. The velocity spectrum stacking plot made from passive seismic data shows that the 410 discontinuity is depressed by ~15 km, the 660 discontinuity is elevated by ~18 km, and a positive thermal anomaly between 182 and 237 K is inferred.     

The crustal nature of the northern Mozambique Ridge,Southwest Indian Ocean

The Mozambique Ridge (MOZR) is one of the basement high structures located in the Southwest Indian Ocean, parallel to the Southeast African continental margin. It was formed as a result of the tectono-magmatic evolution of the Gondwana breakup. The origin of the MOZR has been highly debated, with models suggesting either continental or oceanic origin. With new free-air gravity anomaly and multichannel seismic (MCS) reflection data, we present results of 2D density modeling along two seismic profiles acquired by R/V Xiangyanghong 10 at the northern Mozambique Ridge (N-MOZR) between 26°S and 28°S. We observed high free-air gravity anomaly and strong positive magnetic anomaly related to the emplaced seaward dipping reflectors (SDR) and high density lower crustal body (HDLCB), and high Bouguer gravity anomaly associated with the thinning of the continental crust underneath the N-MOZR over a distance of ~82 km. This suggests a thinned and intruded continental crust bound by the Mozambique Fracture Zone (MFZ) that is characterized by gravity low and negative magnetic anomaly. This fracture zone marks the continent-ocean boundary (COB) while the N-MOZR is the transform margin high, i.e., marks the continent-ocean transition (COT) of the Southern Mozambique margin, following the definition of transform margins. We suggest that the N-MOZR was formed by continental extension and subsequent breakup of the MFZ, accompanied by massive volcanism during the southward movement of the Antarctica block. The presence of SDR, HDLCB, and relatively thick oceanic crust indicates the volcanic nature of this transform margin.     

2-D and 3-D modelling of wide-angle seismic data: an example from the Vøring volcanic passive margin

This study presents the modelling of 2-D and 3-D wide-angle seismic data acquired on the complex, volcanic passive margin of the Vøring Plateau, off Norway. Three wide-angle seismic profiles were shot and recorded simultaneously by 21 Ocean Bottom Seismometers, yielding a comprehensive 3-D data set, in addition to the three in-line profiles. Coincident multi-channel seismic profiles are used to better constrain the modelling, but the Mesozoic and deeper structures are poorly imaged due to the presence of flood basalts and sills. Velocity modelling reveals an unexpectedly large 30 km basement high hidden below the flood basalt. When interpreted as a 2-D structure, this basement high produces a modelled gravity anomaly in disagreement with the observed gravity. However, both the gravity and the seismic data suggest that the structure varies in all three directions. The modelling of the entire 3-D set of travel times leads to a coherent velocity structure that confirms the basement high; it also shows that the abrupt transition to the slower Cretaceous basin coincides in position and orientation with the fault system forming the Rån Ridge. The positive gravity anomaly over the Rån Ridge originates from the focussed and coincident elevation of the high velocity lower crust and pre-Cretaceous basement. Although the Moho is not constrained by the seismic data, the gravity modelled from the 3-D velocity model shows a better fit along the profiles. This study illustrates the interest of a 3-D acquisition of wide-angle seismic over complex structures and the benefit of the subsequent integrated interpretation of the seismic and gravity data.     

南海西北部与红河地区地球物理场及其地壳深部结构特征

分析了南海西北部与红河地区地球物理场特征，计算了研究区重、磁资料的一阶小波细节变换、四阶小波逼近变换。根据重力场资料以及南海北部盆地钻井取样的测试结果，同时参考在研究区进行的地震勘探结果，对研究区的地壳结构进行了反演计算。结果表明，研究区域地壳结构较为复杂，地壳厚度在17—38km之间，总的趋势由陆向洋地壳厚度逐渐减薄，反映出该区域地壳具有陆壳、过渡壳的性质，同时存在上地幔隆起区及凹陷区。用地震层折成像结果与重力资料计算出的地壳分布趋势进行了对比验证。根据地幔对流结果探讨了研究区深部地球动力学特征及其与深部地壳结构的关系。     

Geology of the Continental Margin of Enderby and Mac. Robertson Lands, East Antarctica: Insights from a Regional Data Set

In 2001 and 2002, Australia acquired an integrated geophysical data set over the deep-water continental margin of East Antarctica from west of Enderby Land to offshore from Prydz Bay. The data include approximately 7700 km of high-quality, deep-seismic data with coincident gravity, magnetic and bathymetry data, and 37 non-reversed refraction stations using expendable sonobuoys. Integration of these data with similar quality data recorded by Japan in 1999 allows a new regional interpretation of this sector of the Antarctic margin. This part of the Antarctic continental margin formed during the breakup of the eastern margin of India and East Antarctica, which culminated with the onset of seafloor spreading in the Valanginian. The geology of the Antarctic margin and the adjacent oceanic crust can be divided into distinct east and west sectors by an interpreted crustal boundary at approximately 58° E. Across this boundary, the continent–ocean boundary (COB), defined as the inboard edge of unequivocal oceanic crust, steps outboard from west to east by about 100 km. Structure in the sector west of 58° E is largely controlled by the mixed rift-transform setting. The edge of the onshore Archaean–Proterozoic Napier Complex is downfaulted oceanwards near the shelf edge by at least 6 km and these rocks are interpreted to underlie a rift basin beneath the continental slope. The thickness of rift and pre-rift rocks cannot be accurately determined with the available data, but they appear to be relatively thin. The margin is overlain by a blanket of post-rift sedimentary rocks that are up to 6 km thick beneath the lower continental slope. The COB in this sector is interpreted from the seismic reflection data and potential field modelling to coincide with the base of a basement depression at 8.0–8.5 s two-way time, approximately 170 km oceanwards of the shelf-edge bounding fault system. Oceanic crust in this sector is highly variable in character, from rugged with a relief of more than 1 km over distances of 10–20 km, to rugose with low-amplitude relief set on a long-wavelength undulating basement. The crustal velocity profile appears unusual, with velocities of 7.6–7.95 km s⁻¹ being recorded at several stations at a depth that gives a thickness of crust of only 4 km. If these velocities are from mantle, then the thin crust may be due to the presence of fracture zones. Alternatively, the velocities may be coming from a lower crust that has been heavily altered by the intrusion of mantle rocks. The sector east of 58° E has formed in a normal rifted margin setting, with complexities in the east from the underlying structure of the N–S trending Palaeozoic Lambert Graben. The Napier Complex is downfaulted to depths of 8–10 km beneath the upper continental slope, and the margin rift basin is more than 300 km wide. As in the western sector, the rift-stage rocks are probably relatively thin. This part of the margin is blanketed by post-rift sediments that are up to about 8 km thick. The interpreted COB in the eastern sector is the most prominent boundary in deep water, and typically coincides with a prominent oceanwards step-up in the basement level of up to 1 km. As in the west, the interpretation of this boundary is supported by potential field modelling. The oceanic crust adjacent to the COB in this sector has a highly distinctive character, commonly with (1) a smooth upper surface underlain by short, seaward-dipping flows; (2) a transparent upper crustal layer; (3) a lower crust dominated by dipping high-amplitude reflections that probably reflect intruded or altered shears; (4) a strong reflection Moho, confirmed by seismic refraction modelling; and (5) prominent landward-dipping upper mantle reflections on several adjacent lines. A similar style of oceanic crust is also found in contemporaneous ocean basins that developed between Greater India and Australia–Antarctica west of Bruce Rise on the Antarctic margin, and along the Cuvier margin of northwest Australia.     

Gravity and multichannel seismic reflection constraints on the lithospheric structure of the Canary Swell

Deep penetrating multichannel seismic reflection and gravity data have been used to study the lithospheric structure of the Canary Swell. The seismic reflection data show the transition from undisturbed Jurassic oceanic crust, away from the Canary Islands, to an area of ocean crust strongly modified by the Canary volcanism (ACV). Outside the ACV the seismic records image a well layered sedimentary cover, underlined by a bright reflection from the top of the igneous basement and also relatively continuous reflections from the base of the crust. In the ACV the definition of the boundary between sedimentary cover and igneous basement and the crust-mantle boundary remains very loose. Two-dimensional gravity modelling in the area outside the influence of the Canary volcanism, where the reflection data constrain the structure of the ocean crust, suggests a thinning of the lithosphere. The base of the lithosphere rises from 100 km, about 400 km west of the ACV, to 80 km at the outer limit of the ACV. In addition, depth conversion of the seismic reflection data and unloading of the sediments indicate the presence of a regional depth anomaly of an extension similar to the lithospheric thinning inferred from gravity modelling. The depth anomaly associated with the swell, after correction for sediment weight, is about 500 m. We interpret the lithospheric thinning as an indication of reheating of old Mesozoic lithosphere beneath the Canary Basin and along with the depth anomaly as indicating a thermal rejuvenation of the lithosphere. We suggest that the most likely origin for the Canary Islands is a hot spot.     

南海中部地震反射波特征及其地质解释

20世纪70年代以来,在南海中部海区开展了各种地震调查,为研究盖层和基底发育、断裂和岩浆活动、海盆成生演化提供了重要依据。在对南海中部海区4112km48道反射地震资料解释的基础上,识别出了T₁,T₂,T₄,T₆,T_g等五个反射界面;识别出了I～V五套地震反射层组,推测时代分别为上新世-第四纪、中新世晚期、中新世早-中期、渐新世和前渐新世。层组I～Ⅱ全区广布。在陆坡、岛坡区,层组Ⅲ以下层组主要见于断陷中;在深海盆,层组Ⅲ分布仍较广,除了在深海盆北段见到层组Ⅳ外,在西南次海盆剖面两缘也见到该层组。在东部次海盆剖面中还不同程度见到了双程反射时间为8.4～8.7s的莫霍面反射,埋深为10～12km,地壳厚度为6～8km.西南次海盆水深和新生界基底埋深均比深海盆北段除外的东部次海盆深,分别为4000-4300和5200～5500m.根据年龄和基底深度关系经验公式,计算西南次海盆基底年龄为距今51～39Ma.地震反射层组解释和年龄一基底深度关系计算表明,西南次海盆形成并非晚于东部次海盆,而是同时或早于东部次海盆。     

The Crustal Structure Character of East China Sea

This paper presents actuality of investigation and study of the crustal structure characters of East China Sea at home and abroad. Based on lots of investigation and study achievements and the difference of the crustal velocity structure from west to east, the East China Sea is divided into three parts - East China Sea shelf zone, Okinawa Trough zone and Ryukyu arc-trench zone. The East China Sea shelf zone mostly has three velocity layers, i.e., the sediment blanket layer （the velocity is 5.8-5.9 km/s）, the basement layer （the velocity is 6.0-6.3 km/s）, and the lower crustal layer （the velocity is 6.8-7.6 km/s）. So the East China Sea shelf zone belongs to the typical continental crust. The Okinawa Trough zone is located at the transitional belt between the continental crust and the oceanic crust. It still has the structural characters of the continental crust, and no formation of the oceanic crust, but the crust of the central trough has become to thinning down. The Ryukyu arc-trench zone belongs to the transitional type crust as a whole, but the ocean side of the trench already belongs to the oceanic crust. And the northwest Philippine Basin to the east of the Ryukyu Trench absolutely belongs to the typical oceanic crust.     

伊豆−博宁−马里亚纳岛弧地壳厚度分布及其对岩浆活动的指示

数值模拟研究认为洋底高原/洋脊俯冲和弧后扩张能够有效影响俯冲带岩浆活动和岛弧地壳增生。本文以伊豆?博宁?马里亚纳(IBM)俯冲带为实例,论证该结论的有效性。以卫星测高反演重力异常为基础,通过构建地球不同圈层密度模型,反演得到IBM俯冲带莫霍面埋深。本文的莫霍面埋深反演结果与地震解释结果具有一致的分布趋势。结合开源水深和沉积层厚度数据,给出了IBM俯冲带地壳厚度分布。IBM岛弧地壳体积沿走向的分布特征表明:①小笠原洋底高原和相对较小规模达顿洋脊的俯冲,都能够使得相应位置的岛弧变窄、地壳变厚、体积增大;②马里亚纳海槽扩张显著降低了岛弧地壳体积的增生量。