南中国海成因:右行拉分作用与左行转换挤压作用交替

Genesis of South China Sea: Intervening of dextralpull-apart and sinistral transpression

总结分析了南中国海各次级盆地及其周缘有关盆地的裂谷作用序列 ,认为它们的裂谷作用序列是相似的 ,虽然存在局部差异。古近纪 (—早中新世 )和新近纪分别为一级裂谷阶段和后裂谷阶段 ,并可进一步划分次一级裂谷和后裂谷阶段。南中国海总体几何学特征及其次级盆地和周缘盆地的几何学特征表明 ,它们的裂谷作用是以近南北向主断裂为主剪切的右行拉分作用。在右行拉分过程中 ,东越南断裂的南延 (翼他陆架部分 )可能没有发生巨大脆性平移而表现为巨大的右行韧性牵引 ;印支—苏门答腊地块是被东越南断裂、东安达曼海断裂、红河断裂和苏门答腊断裂等四条断裂围限的呈菱形的右行走滑双重构造。深海盆的洋壳在许多方面与概念化大洋洋壳不同 ,相互矛盾的各种磁异常条带年龄并不可信。它的洋壳是右行拉分作用形成的洋壳。它们的后裂谷作用是以近南北向主断裂为主剪切的左行转换挤压反转变形为特征。联系到裂谷作用序列 ,南中国海成因具有右行拉分作用、裂谷作用和左行转换挤压作用交替出现的特征 ,表现了具有转换性质的“开”与“合”

This paper proposes that the subsidiary-basins of South China Sea(SCS) and its adjacent basins shared similar rifting sequence during the Cenozoic on the basis of synthetic analysis of the published data, though there are some local differences. The sequence can generally be divided into two first-order phases: Paleogene(-Early Miocene) rifting and Neogene post rifting, and can further be subdivided into sub-order rifting and post rifting periods, as evidenced by many unconformities developed in the basins. Overall geometry of SCS and geometry of its subsidiary-basins as well as geometry of its adjacent basins, compared with geometry of analogue modeling of dextral transtensional basins, clearly indicate that the rifting resulted from dextral pull-apart along its east and west principal boundary faults of about NS-trending. During the rifting period: the southward extending segment of East Vietnam Fault exhibits dextral ductile drag accommodating its large dextral strike-slip displacement; the Indochina-Sumatra block, delimited by East Vietnam Fault, East Andaman sea Fault, Red River Fault and Sumatra Fault, appears as a lozenge-shaped dextral strike-slip duplex. Oceanic crust of the East- SW-, NW- and NE-subsidiary-basins of SCS are different from conceptual major oceanic crust in many aspects, and the self-contradictory ages determined for the striped pattern of magnetic anomalies are not convincing. Its oceanic crust possibly formed from multi-episodic dextral pull-apart and its earliest age might be the late Mesozoic or the mid-Eocene. Its post-rifting deformations were characteristic of sinistral transpression as shown by structures and geodynamic setting. Clearly, the dextral pull-apart and the sinistral transpresion were intervening, exhibiting an alternation of transformational “Open-Close Tectonics”.