南海东北部陆缘地壳结构特征及下地壳高速层成因

doi:10.3969/j.issn.1001-909X.2019.02.005

摘要/Abstract

摘要： 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V_p/V_s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。

关键词: 南海东北部, 地壳厚度, 极端减薄, 吕宋-琉球转换板块边界, 下地壳高速层

Abstract: Abundant information about tectonic evolution in the northeastern South China Sea margin is essentially important for understanding the evolution of the South China Sea. The deep reflection seismic profiles and wide-angle reflection seismic profiles across the northeastern South China Sea were collected, and the crustal thickness and high-velocity lower crustal thickness were extracted respectively. Combining with geological and geophysical information such as bathymetry, gravity and magnetic anomalies, and lithospheric rheology, the crustal thinning of the northeastern South China Sea, nature of the Luzon-Ryukyu Transform Plate Boundary and distribution of the high-velocity lower crust and its origins were discussed. The northeastern crust is unevenly thin in lateral and vertical, dominated with lower crust thinning, like in the Taixinan Basin. There are similar extremely thinned crusts in the Baiyun Sag, Xisha Trough and Zhongjiannan Basin. They are always conjugated with or adjacent to rigid blocks. We agree that lower crust flow and mantle upwell caused by the existence of rigid blocks during initiated breakup are responsible for locally extreme thinning of the crust. Both sides of the Luzon-Ryukyu Transform Plate Boundary are different in the bathymetry, Cenozoic reflections, gravity and magnetic anomalies. The LRTPB intersected high magnetic anomaly zone caused by Mesozoic with a large-angle, indicating the Luzon-Ryukyu Transform Plate Boundary may be a boundary fault converted from the Mesozoic Paleo-Tethys tectonic domain to the Pacific tectonic domain. The distribution range of the extensive HVLC in the northeastern margin consistent with post-rift igneous. Combining with distribution interval of ratios V_p/V_s of the high-velocity lower crust, It is suggested that the high-velocity lower crust primarily consists of mafic rock caused by multiple-epoch underplating.

Key words: the northeastern South China Sea, crustal thickness, extremely thinning, Luzon-Ryukyu Transform Plate Boundary, high-velocity lower crust

中图分类号:

P736.1

李海龙, 吴招才, 许明炬. 南海东北部陆缘地壳结构特征及下地壳高速层成因[J]. 海洋学研究, 2019, 37(2): 44-56.

LI Hai-long, WU Zhao-cai, XU ming-ju. Crustal structure features and origins of high-velocity lower crust in the northeastern South China Sea[J]. Journal of Marine Sciences, 2019, 37(2): 44-56.

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