Seismic constraints on a remnant Mesozoic forearc basin in the northeastern South China Sea
Seismic constraints on a remnant Mesozoic forearc basin in the northeastern South China Sea
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DOI：
10.1016/j.gr.2020.10.006
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发表时间：
2020-10
影响因子：
6.1
通讯作者：
C. Fan;S. Xia;Jinghe Cao;F. Zhao;K. Wan
中科院分区：
文献类型：
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作者：
C. Fan;S. Xia;Jinghe Cao;F. Zhao;K. Wan
南海东北部经历了从中生代汇聚型陆缘到新生代扩张型陆缘的构造反转。火山弧和弧前盆地等与俯冲有关的残余构造可能为揭示这一构造反转的动力学机制提供了重要线索。利用海底地震仪（OBS）资料，结合多道地震、重力、钻井和岩石学观测资料，揭示了东沙盆地的地球物理和构造特征。中生代地层具有厚度大（1-8 km）、纵波速度较高（3.5- 5.5km/s）、密度高（2.55- 2.65g/cm ~ 3）、褶皱交错、逆冲断层发育等特点，与新生代地层有明显区别。东沙盆地西北侧为中生代花岗岩弧，东南侧为古太平洋俯冲带，处于中生代弧前区。考虑到在南海南缘发现的相似中生代地层和在巴拉望大陆地体中发现的同生增生杂岩露头，我们认为这两个地区的中生代地层起源于一个共同的中生代弧前盆地，该盆地被弧前裂谷作用破坏，随后又被新生代南海的扩张作用分隔开。据此，重建了一个包括弧-弧前-增生楔构造序列在内的连续的古太平洋俯冲体系。综合全球弧前裂谷作用机制和华南陆侧火山弧退缩机制，推测古太平洋俯冲板片的回退可能是弧前裂谷作用和南海初始伸展的原因之一。
The northeastern of the South China Sea (SCS) has undergone tectonic inversion from a Mesozoic convergent continental margin to a Cenozoic divergent continental margin. The remnant subduction-related structures, such as volcanic arc and forearc basin, likely preserve key clues to reveal the dynamic mechanism of this tectonic inversion. We applied ocean bottom seismometers (OBS) data, combining with multi-channel seismic data, gravity data, drilling data, and petrologic observations, to reveal geophysical and structural features of the Dongsha Basin, a Mesozoic basin in the northeastern SCS. The Mesozoic strata are characterized by large thickness (~1–8 km), relatively highP-wave velocities (3.5–5.5 km/s), high densities (2.55–2.65 g/cm3), alternating folds, and thrust faults, which are significantly different from the features of Cenozoic strata. The Dongsha Basin is flanked by a Mesozoic granitic arc to the northwest and an inferred Palaeo-Pacific subduction zone to the southeast, indicating that it is geographically located in the Mesozoic forearc region. Considering the similar Mesozoic strata detected in the southern margin of the SCS and the contemporaneous accretionary complex outcrops observed in the Palawan Continental Terrane, we propose that the Mesozoic strata in these two regions originated from a common Mesozoic forearc basin, which was broken by the forearc rifting and subsequently separated by the spreading of Cenozoic SCS. Accordingly, a continuous Palaeo-Pacific subduction system is reconstructed, including the “arc-forearc-accretionary wedge” tectonic sequences. Reviewing the mechanisms of forearc rifting globally and the retreat of volcanic arcs onshore South China, we speculate that rollback of the Palaeo-Pacific subduction slab might be one of the causes for the forearc rifting and the initial extension of the SCS.