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1.
Nelta David Matsinhe Yong Tang Chun-Feng Li Jiabiao Li Estev?o Stefane Mahanjane He Li Yinxia Fang 《海洋学报(英文版)》2021,40(7):170-182
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. 相似文献
2.
南海东北部陆缘构造演化信息丰富,对于理解南海的演化过程至关重要。本文收集了南海东北部的深反射地震和海底广角地震成果剖面,提取地壳和下地壳高速层的厚度结果,并结合水深、重磁异常和岩石圈的流变学等地质地球物理资料,对南海东北部的地壳减薄特征、吕宋-琉球转换板块边界的性质和下地壳高速层的分布及成因进行了分析和讨论。南海东北部的地壳减薄在横向和垂向上都存在不均匀性,以下地壳减薄为主,在台西南盆地存在极端减薄地壳;南海北缘的白云凹陷、西沙海槽和西缘的中建南盆地也存在类似的极端减薄地壳,且都与刚性地块共轭或邻近,推测刚性地块的存在导致地壳初始破裂时下地壳流动和地幔上隆是局部出现地壳极端减薄的主要原因。吕宋-琉球转换板块边界两侧在海底地形、新生代反射和重磁异常等方面均存在差异,与中生代岛弧引起的高磁异常大角度相交,其可能是中生代古特提斯构造域向太平洋构造域转换的边界断裂。下地壳高速层在南海东北部广泛发育,结合其分布特征和波速比Vp/Vs的分布区间,认为其是多期次岩浆底侵形成的铁镁质基性岩。 相似文献
3.
The Sardinia Channel dataset was collected as part of the European Geotraverse (EGT)—a 4000 km seismic refraction line running from Northern Norway to the Sahara, designed to investigate the structure of the lithosphere beneath Europe. Wideangle seismic data recorded by ocean bottom seismometers deployed in the Sardinia Channel as part of the Southern Segment of the EGT, together with gravity data, were used to constrain the final crustal model. In the centre of the Channel the crust is identified as thinned continental in nature, with a crystalline thickness of 10 km overlain by 4 km of sediments and 2.5 km of water in the most extended region. High velocities in the lower crust in the central region are thought to represent an area of underplating or intrusion by igneous material caused by extension related to the opening of the Tyrrhenian Sea. The crust overlies an anomalously low velocity upper mantle. 相似文献
4.
2-D and 3-D modelling of wide-angle seismic data: an example from the Vøring volcanic passive margin
Stéphane Rouzo Frauke Klingelhöfer Hélène Jonquet-Kolstø Ridvan Karpuz Karl Kravik Rolf Mjelde Yoshio Murai Thomas Raum Hideki Shimamura Paul Williamson Louis Géli 《Marine Geophysical Researches》2006,27(3):181-199
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. 相似文献
5.
南海区域岩石圈的壳-幔耦合关系和纵向演化 总被引:11,自引:2,他引:11
南海区域岩石圈由地壳层和上地幔固结层两部分组成。具典型大洋型地壳结构的南海海盆区莫霍面深度为9~13km,并向四周经陆坡、陆架至陆区逐渐加深;陆缘区莫霍面一般为15~28km,局部区段深达30~32km,总体呈与水深变化反相关的梯度带;东南沿海莫霍面深约28~30km,往西北方向逐渐增厚,最大逾36km。南海区域上地幔天然地震面波速度结构明显存在横向分块和纵向分层特征。岩石圈底界深度变化与地幔速度变化正相关;地幔岩石圈厚度与地壳厚度呈互补性变化,莫霍面和岩石圈底界呈立交桥式结构,具有陆区厚壳薄幔—洋区薄壳厚幔的岩石圈壳-幔耦合模式。南海区域白垩纪末以来的岩石圈演化主要表现为陆缘裂离—海底扩张—区域沉降的过程,现存的壳-幔耦合模式显然为岩石圈纵向演化产物,其过程大致可分为白垩纪末至中始新世的陆缘裂离、中始新世晚期至中新世早期的海底扩张和中新世晚期以来的区域沉降等三个阶段。 相似文献
6.
Crustal structure of the Co^te d’Ivoire–Ghana marginal ridge and its transition with oceanic lithosphere are deduced from
multichannel seismic reflection, wide-angle seismic, and gravity data. The CIGMR is cut into rotated blocks and displays a
crustal structure quite similar to that of the nearby northern Ivorian extensional basin. These results strongly support that
the CIGMR represents an uplifted fragment of continental crust. Transition with the oceanic crust appears sharp; continental
crustal thinning occurs over less than 5 km. We did not find evidence for underplating and/or contamination as anticipated
from such a sharp contact between continental and oceanic crust.
Received: 12 March 1995/Revision received: 2 July 1996 相似文献
7.
Geology of the Continental Margin of Enderby and Mac. Robertson Lands, East Antarctica: Insights from a Regional Data Set 总被引:1,自引:0,他引:1
H. M. J. Stagg J. B. Colwel N. G. Direen P. E. O’Brien G. Bernardel I. Borissova B. J. Brown T. Ishirara 《Marine Geophysical Researches》2004,25(3-4):183-219
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. 相似文献
8.
Berndt C. Mjelde R. Planke S. Shimamura H. Faleide J.I. 《Marine Geophysical Researches》2001,22(3):133-152
Ocean bottom seismograph (OBS), multichannel seismic and potential field data reveal the structure of the Vøring Transform Margin (VTM). This transform margin is located at the landward extension of the Jan Mayen Fracture Zone along the southern edge of the Vøring Plateau. The margin consists of two distinctive segments. The northwestern segment is characterized by large amounts of volcanic material. The new OBS data reveal a 30–40 km wide and 17 km thick high-velocity body between underplated continental crust to the northeast and normal oceanic crust in the southwest. The southeastern segment of the mar is similar to transform margins elsewhere. It is characterized by a 20–30 km wide transform margin high and a narrow continent-ocean transition. The volcanic sequences along this margin segment are less than 1 km thick. We conclude from the spatial correspondence of decreased volcanism and the location of the fracture zone, that the amount of volcanism was influenced by the tectonic setting. We propose that (1) lateral heat transport from the oceanic lithosphere to the adjacent continental lithosphere decreased the ambient mantle temperature and melt production along the entire transform margin and (2) that right-stepping of the left-lateral shear zone at the northwestern margin segment caused lithospheric thinning and increased volcanism. The investigated data show no evidence that the breakup volcanism influenced the tectonic development of the southeastern VTM. 相似文献
9.
The structure of the oceanic crust adjacent to the Côte d’Ivoire–Ghana transform margin is deduced from multichannel seismic reflection and seismic wide-angle data, showing crustal heterogeneities within oceanic basement; the oceanic crust adjacent to the transform margin is half as thick as standard Atlantic oceanic crust. Refraction data indicate a gradual velocity transition towards typical mantle velocities. Such an abnormal oceanic crustal structure appears quite similar to crustal structures known along transform faults. This crustal thinning may be related to thermal effects of the nearby continental crust, on the oceanic accretion processes. We did not find geophysical evidence for oceanic crust contamination by continental lithosphere. 相似文献
10.
Compilation of currently-available gravity data permits the construction of a free-air anomaly contour map of the continental margin west of Ireland (51–54 N). Major elements in the structure of the margin, previously delineated on the basis of seismic reflection and magnetic surveys, are clearly seen on the FAA contour map, notably the Porcupine Seabight Trough, and Porcupine Ridge. However, contrary to earlier ideas, the gravity data imply that the Seabight Trough extends northwards onto the Slyne Ridge; and the Slyne Trough, formerly regarded as northeasterly prolongation of the Seabight Trough, appears to be a discrete, fault-bounded, feature separated from the latter by a basement ridge. East-west gravity profiles are modelled in terms of thinned crust with the Moho at a minimum depth of 15 km beneath the axis of the Seabight Trough. The models tend to support hypotheses invoking formation of the Seabight Trough by simple westward translation of Porcupine Ridge with respect to the Irish Mainland. 相似文献
11.
F. J. Davey 《Marine Geophysical Researches》1972,1(4):428-435
Gravity measurements in the South Atlantic Ocean over Burdwood Bank show a large negative gravity anomaly extending along its northern edge. An interpretation of the gravity data has been made based on the seismic refraction measurements of Ludwig et al. (1968) and shows that the negative gravity anomaly can be largely attributed to a basin containing low density sediments about 8 km thick. The crustal sections constructed also indicate that the crust increases in thickness from about 20 km under Burdwood Bank to about 30 km under the Falkland Islands platform. 相似文献
12.
白云凹陷地球物理场及深部结构特征 总被引:13,自引:2,他引:13
珠江口盆地白云凹陷是南海最具代表性的第三系深水陆坡沉积区。以穿过白云凹陷中部的一条深反射地震剖面(14s)为研究基础,采用综合地球物理研究方法分析了该区地球物理场特征,根据重力异常平面等值线勾画了白云凹陷的形态,并提取该测线相对应的重磁剖面数据,利用重磁资料和地震剖面进行了综合反演。以深剖面地震资料建立了地质模型,利用所得的重力数据进行了研究深部结构的正演拟合,实测与计算值拟合较好,支持中生代俯冲洋壳存在的观点;同时结合地震资料对深部结构进行了分析,该区莫霍面由陆向海抬升,呈阶梯状变化,地壳厚度逐渐减薄,具有大陆边缘陆壳向洋壳过渡的特征。根据地质模型还进行了变密度综合反演拟合来分析基底岩性特征,该区基底主要为中酸性岩浆岩,部分为变质岩和基性火山岩,岩石密度由陆向洋逐渐减小,磁性体分布不均。 相似文献
13.
Lithospheric structure below the eastern Arabian Sea and adjoining West Coast of India based on integrated analysis of gravity and seismic data 总被引:1,自引:0,他引:1
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. 相似文献
14.
The present-day basement depth of the seafloor in the absence of sediment loading was inferred along a traverse crossing the
Southern Tyrrhenian Basin. A correction for sediment loading was proposed on the basis of density, seismic velocity and porosity
data from selected deep boreholes. The empirical relation between sediment correction and seismic two-way travel time was
extrapolated downward by applying the Nafe–Drake curve and a specific porosity–depth relation. The sediment loading response
of the basement calculated for flexural isostasy is on average about one hundred meters lower than results for local isostasy.
A pure lithosphere extensional model was then used to predict quantitatively the basement subsidence pattern on the margins
of the basin. The basement depth is consistent with uniform extension model predictions only in some parts of the margins.
The observed variability in the region of greatest thinning (transition from continental to oceanic crust) is attributable
to the weakening effect caused by diffuse igneous intrusions. Subsidence of the volcanic Calabrian–Sicilian margin is partly
accounted for by magmatic underplating. The comparison of the calculated subsidence with an oceanic lithosphere cooling model
shows that subsidence is variable in some areas, particularly in the Marsili Basin. This argues for a typical back-arc origin
for the Tyrrhenian Basin, as a result of subduction processes. By taking into account the geodynamic setting, stratigraphic
data from the deepest hole and the terrestrial heat flow, we reconstructed the paleotemperatures of cover sediments. The results
suggest that low temperatures generally have prevailed during sediment deposition and that the degree of maturation is expected
not to be sufficient for oil generation processes. 相似文献
15.
D. Franke U. BarckhausenN. Baristeas M. EngelsS. Ladage R. LutzJ. Montano N. PellejeraE.G. Ramos M. Schnabel 《Marine and Petroleum Geology》2011,28(6):1187-1204
The South China Sea formed by magma-poor, or intermediate volcanic rifting in the Paleogene. We investigate the structure of the continent-ocean transition (COT) at its southern margin, off NW Palawan between the continental blocks of Reed Bank and the islands of Palawan and Calamian. Several surveys, recorded by the BGR from 1979 to 2008, established a comprehensive database of regional seismic lines, accompanied with magnetic and gravity profiles.We interpret two major rifted basins, extending in the NE direction across the shelf and slope, separated by a structural high of non volcanic origin.The continent-ocean transition is interpreted at the seaward limit of the continental crust, when magnetic spreading anomalies terminate some 80-100 km farther north. The area in between displays extensive volcanism - as manifest by extrusions that occasionally reach and cut the seafloor, by dykes, and by presumed basaltic lava flows - occurring after break-up.The COT is highly variable along the NW Palawan slope: One type shows a distinct outer ridge at the COT with a steep modern seafloor relief. The other type is characterised by rotated fault blocks, bounded by listric normal faults ramping down to a common detachment surface. Half-grabens developed above a strongly eroded pre-rift basement. The seafloor relief is smooth across this other type of COT.We suggest the pre-rift lithospheric configuration had major influence on the formation of the COT, besides transfer zones. Volcanic domains, confined to the north of competent crustal blocks correlate with the style of the COT.Gravity modelling revealed an extremely thinned crust across the shelf. We propose a depth-dependent extension model with crust being decoupled from mantle lithosphere, explaining the discrepancy of subsidence observed across the South China Sea region. 相似文献
16.
Ching-Hui Tsai Shu-Kun Hsu Yi-Ching Yeh Chao-Shing Lee Kanyuan Xia 《Marine Geophysical Researches》2004,25(1-2):63-78
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. 相似文献
17.
Wojciech Czuba 《Marine Geophysical Researches》2007,28(3):213-233
Deep seismic sounding measurements were performed in the continent-ocean transition zone of the northern Svalbard continental
margin in 1985 and 1999. Data from seismic profile AWI-99200 and from additional crossing profiles were used to model the
seismic crustal structure of the study area. Seismic energy (airgun and TNT shots) was recorded by land (onshore) seismic
stations, ocean bottom seismometers (OBS), and hydrophone systems (OBH). 3-D tomographic inversion methods were applied to
test the previous 2-D modelling results. The results are similar to the earlier 2-D modelling, supplemented by new off-line
information. The continental crust thins to the west and north. A minimum depth of about 6 km to the Moho discontinuity was
found east of the Molloy Deep. The continent-ocean transition zone to the east is characterized by a complex seismic velocity
structure according to the 2-D model and consists of several different crustal blocks. The zone is covered by deep sedimentary
basins. Sediment thicknesses reach a maximum of 5 km. The Moho interface deepens to 28 km depth beneath the continental crust
of Svalbard. 相似文献
18.
Two long seismic refraction lines along the crest of the Iceland-Faeroe Ridge reveal a layered crust resembling the crust beneath Iceland but differing from normal continental or oceanic crust. The Moho was recognised at the south-eastern end of the lines at an apparent depth of 16–18 km. A refraction line in deeper water west of the ridge and south of Iceland indicates a thin oceanic type crust underlain by a 7.1 km/s layer which may be anomalous upper mantle.An extensive gravity survey of the ridge shows that it is in approximate isostatic equilibrium; the steep gravity gradient between the Norwegian Sea and the ridge indicates that the ridge is supported by a crust thickened to about 20 km rather than by anomalous low density rocks in the underlying upper mantle, in agreement with the seismic results. An increase in Bouguer anomaly of about 140 mgal between the centre of Iceland and the ridge is attributed to lateral variation in upper mantle density from an anomalous low value beneath Iceland to a more normal value beneath the ridge. Local gravity anomalies of medium amplitude which are characteristic of the ridge are caused by sediment troughs and by lateral variations in the upper crust beneath the sediments. A steep drop in Bouguer anomaly of about 80 mgal between the ridge and the Faeroe block is attributed partly to lateral change in crustal density and partly to slight thickening of the crust towards the Faeroe Islands; this crustal boundary may represent an anomalous type of continental margin formed when Greenland started to separate from the Faeroe Islands about 60 million years ago.We conclude that the Iceland-Faeroe Ridge formed during ocean floor spreading by an anomalous hot spot type of differentiation from the upper mantle such as is still active beneath Iceland. This suggests that the ridge may have stood some 2 km higher than at present when it was being formed in the early Tertiary, and that it has subsequently subsided as the spreading centre moved away and the underlying mantle became more normal; this interpretation is supported by recognition of a V-shaped sediment filled trough across the south-eastern end of the ridge, which may be a swamped sub-aerial valley. 相似文献
19.
Crustal seismic structures beneath the West Philippine Sea are determined by using explosive sources (0.5–108.6 kg) and ocean bottom seismometers to measure refracted compressional waves. Total crustal thicknesses are shown to be thinner in the eastern part of the ocean basin, approaching only 3.5 km. Crustal thinning toward the east is consistent with the Palau Kyushu Ridge being a remnant transform fault connecting the Central Basin Ridge and the Kula Pacific Ridge in the past. A velocity-depth inversion from the westernmost refraction profile indicates the upper transitional crust layer to have strong velocity gradients which gradually decrease with depth; the lower crust is characterized by a nearly constant velocity gradient. The western part of the ocean basin is also shown to have more typical oceanic thicknesses, as is found in deep ocean basins of the Pacific. Spectral energy models using WKBJ synthetic seismograms suggest that there is a sharp seismic discontinuity between the crust and moho in the western part of the basin. Predicted water depths for the West Philippine Basin using an age-depth relation and corrected for an isostatic response to the measured crustal thicknesses, are still 300 meters shallower than observed depths. The depth anomaly can not be fully reconciled by thinner crust in the eastern part of the basin. This observation implies that a deeper seated anomaly is present beneath the West Philippine Basin. 相似文献
20.
Chun-Feng Li Zuyi Zhou Jiabiao Li Bing Chen Jianhua Geng 《Marine Geophysical Researches》2008,29(4):223-238
We made a systematic investigation on major structures and tectonic units in the South China Sea basin based on a large magnetic
and seismic data set. For enhanced magnetic data interpretation, we carried out various data reduction procedures, including
upward continuation, reduction to the pole, 3D analytic signal and power spectrum analyses, and magnetic depth estimation.
Magnetic data suggest that the South China Sea basin can be divided into five magnetic zones, each with a unique magnetic
pattern. Zone A corresponds roughly to the area between Taiwan Island and a relict transform fault, zone B is roughly a circular
feature between the relict transform fault and the northwest sub-basin, and zones C, D, and E are the northwest sub-basin,
the east sub-basin, and the southwest sub-basin, respectively. This complexity in basement magnetization suggests that the
South China Sea evolved from multiple stages of opening under different tectonic settings. Magnetic reduction also fosters
improved interpretation on continental margin structures, such as Mesozoic and Cenozoic sedimentary basins and the offshore
south China magnetic anomaly. We also present, for the first time, interpretations of three new 2D reflection seismic traverses,
which are of ~2,000 km in total length and across all five magnetic zones. Integration of magnetic and seismic data enables
us to gain a better 3D mapping on the basin structures. It is shown that the transition from the southwest sub-basin to the
east sub-basin is characterized by a major ridge formed probably along a pre-existing fracture zone, and by a group of primarily
west-dipping faults forming an exact magnetic boundary between zones D and E. The northwest sub-basin has the deepest basement
among the three main sub-basins (i.e., the northwest sub-basin, the southwest sub-basin, and the east sub-basin). Our seismic
data also reveal a strongly faulted continent–ocean transition zone of about 100 km wide, which may become wider and dominated
with magmatism or transit to an oceanic crust further to the northeast. 相似文献