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Mesozoic subduction-accretion zone in northeastern south{1. {2. inferred from geophysical interpretations

Science china Earth {1. 2006年第5期49卷 471-482页

作者： zhou di1, wang wanyin2. wang jialin3, pang xiong4. cai dongsheng5 & sun zhen1 1. key laboratory of marginal sea Geology, south china sea institute of oceanology, chinese academy of sciences, guang- zhou 510301, china 2. College of Geological and Topographical Engineering, Chang’an University, Xi’an 710054, china 3. key laboratory of Marine Geology, Tongji University, Shanghai 200092, china 4. china National Offshore Oil Co. Limited – Shenzhen Branch, Shenzhen 518067, china 5. china National Offshore Oil Co. Limited – Research Center, Beijing 100027, china 1. key {1. of marginal sea Geology South China Sea Institute of Oceanology Chinese Academy of Sciences Guangzhou 510301 China 2. College of Geological and Topographical Engineering Chang’an University Xi’an 710054 China 3. key {1. of Marine Geology Tongji University Shanghai 200092 China 4. china National Offshore Oil Co. Limited — Shen{1. Branch Shenzhen 518067 China 5. china National Offshore Oil Co. Limited — Re{1.rch Center Beijing 100027 China

A segment of Mesozoic subduction-accretion zone was inferred across thenortheastern south{1. {2. at approximately NE450 orientation. Basic evidence includes thefollowing: A belt of peek gross horizontal Bouguer gravity gradient (PGHGBA) is comparable in sizeand intensity to that of the Manila subduction-accretion zone. A belt of high positive magneticanomalies appears to the north and sub-parallel to the PGHGBA, representing the volcanic arcassociated to the subduction zone. The PGHGBA crosses obliquely both Cenozoic structures and present{2.floor topography, indicating a pre-Cenozoic age. The segment is offset left-laterally byNW-running strike-slip faults, in concord with the Mesozoic stress field of south{1.. Inaddition, the existence of the subduction zone is supported by wide-angle seismic data obtained indifferent years by different institutions. At approximate localities, a north-dipping ramp of Mohosurface is indicated by records of ocean-bottom seismometers, and a strong reflector about 8 kmbeneath the Moho reflector is indicated by both OBS and long-cable seismic records. Theidentification of a segment of Mesozoic subduction zone in NE south{1. {2. fills nicely the gapof the Great Late Mesozoic Circum SE Asia Subduction-acrretion Zone, which extended from Sumatra,Java, SE Kalimantan to N Palawan, and from Taiwan, Ryukyu to SW Japan.

关键词： Mesozoic, subduction zone, SE Asia, NE south china sea, geophysics.

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Stretching characteristics and its dynamic significance of the northern continental margin of south{1. {2.

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Science china Earth {1. 2008年第3期51卷 422-430页

作者： ZHANG YunFan sun {1. {2. di GUO XingWei SHI XiaoBin WU XiangJie pang xiong CAS key {1. of {2. sea Geology South China Sea Institute of OceanologyChinese Academy of SciencesGuang-zhou 510301China Graduate University Chinese Academy of SciencesBeijing 100049China Qingdao institute of Marine Geology China Geological SurveyQingdao 266071China china National Offshore Oil Corp.china Limited Shen{2. Guangzhou 510240China

To investigate the thinning of the whole crust, and the contribution of the upper versus lower crust to the stretching since Cenozoic, we calculated the stretching factor of the northern margin of south{1. {2. with data such as whole crustal thickness, depth of Cenozoic sedimentary basement and the horizontal displacement of faults. An isometric line drawing on whole crustal stretching factor is then obtained. Along the seismic Line 1.30 in Baiyun sag, we also calculated the stretching factors of the upper and lower crust. The results suggest that the whole crustal thickness decreases {2.ward while the whole crustal stretching factor increases from shelf to slope. The Moho upwells highest beneath where the crust is thinned most. The value of the whole crustal stretching factor ranges from 1.5 to 6. Two areas were thinned intensely: the center of Yinggehai Basin, and the Baiyun sag in the Pearl River Mouth Basin. The calculation of the upper and lower crustal stretching factors from DSP1.30 in Baiyun sag shows that the original crust of Baiyun sag should be thinned before deformation. Its pre-Cenozoic evolution as well as tectonic position during Cenozoic might be responsible for that.

关键词： stretching factor the northern continental margin of south china sea upper crust lower crust original hot thinned crust Baiyun sag

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Dynamics Analysis of the Baiyun Sag in the Pearl River Mouth Basin,North of the south{1. {2.

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Acta Geologica Sinica(English Edition) 2008年第1期82卷 73-83页

作者： sun {1. ZHONG Zhihong {2. di pang xiong HUANG Chunju CHEN Changmin HE Min XU Hehua CAS key {1. of {2. sea Geology South China Sea Institute of Oceanology Guangzhou Guangdong 510301 Department of Technology Shenzhen Branch of CNOOC Guangzhou Guangdong 510240

The Baiyun sag is a deep one developing on the slope of the Pearl River Mouth Basin. It occurs as a composite graben horizontally, and is composed of two sub-sags versus one low uplift. Vertically, the sedimentary architecture could be divided into three layers, i.e. the faulted layer on the bottom, the faulted-ductile stretching layer in the middle and the draping layer on the top. The main rifting stage of the sag is supposed to be characterized by ductile extension and thinning of the crust. The special deformation pattern is probably attributed to the fact that the Baiyun sag is located in the transfer zone of the pre-existing weak zone, which made the sag a strongly deformed area, characterized by the greatly thinned lithosphere and active magmatism. The highly rising mantle under the Baiyun sag should be an important mechanism responsible for the ductile deformation, which caused partial melting of the upper mantle. Upweiling to the upper crust and the sedimentary layers, the partial melting materials accommodated extensional strain and caused non-faulted vertical subsidence. Magma was collected under the transfer zone after the first stage of rifting, and transferred laterally in a direction perpendicular to the extension to the ENE and WSW parts of the sag and upwelled along the NW-trending basal faults, where WNW-trending shear faults developed in swarms. The faulting activity and sedimentation history of the Baiyun sag may have been affected by the ocean ridge jump around 2. Ma and the cessation of sea floor spreading around 1. Ma.

关键词： Baiyun sag dynamics analysis transfer zone ductile extension

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