中国海—西太平洋典型剖面(南幅)揭示的微陆块-窄洋盆构造格局

Tectonic framework of miniature continental block—narrow oceanic basin revealed by the southern typical profile in the China seas—Western Pacific Ocean

基于编制最新地学成果图件的需要,我们整合了最新地质、地球物理资料成果,运用最新的技术方法,开展了中国海—西太平洋地区典型剖面的编制工作.典型剖面(南幅)主要集成了南海地区近年来获得的广角地震探测资料,运用重-磁-震联合反演方法,结合拖网、钻井、地热、地质剖面等,以块体构造学说为编图思想编制而成.典型剖面(南幅)从华南以NNW-SSE向直抵苏拉威西海,穿过了多个构造单元,包括3个陆缘-离散地块区(华南块体—南海北部陆缘、中沙地块、礼乐—北巴拉望地块)、4个海盆区(西北次海盆、中央海盆、苏禄海盆、苏拉威西海盆)、2个俯冲-岛弧区(卡加延脊、苏禄脊),这些构造单元一起构成了西太平洋边缘独特的“微陆块-窄洋盆”构造格局.自古特提斯向欧亚大陆之下俯冲以来,该区域经历了复杂的构造演化过程.在形成这种构造格局的过程中,地壳处在不断消亡和生成的动态循环之中,同时构造应力也处在动态变化之中.通过对区域地球动力学的综合分析,认为这种微陆块-窄洋盆构造格局的形成,很大程度上是由于其位于三大板块交接的独特区域,以及受区域内复杂而丰富的俯冲作用的影响和制约.通过典型剖面编制工作,推动了中国海—西太平洋区域内大地构造和地球物理特征研究,为“跳出南海看南海”提供了良好的研究范例,同时启发我们未来加强对邻区研究空白区域的探索.

Due to the need of compiling the newest maps of geological and geophysical results,we integrated the latest geological and geophysical data,and used advanced methods to compile the southern typical profile across the China seas and the western Pacific Ocean area.The compilation is mainly based on wide-angle seismic survey data collected in the South China Sea in recent years,using joint inversion of gravity-magnetic-seismic data,supplemented by dredging,drilling,geothermal data and geological sections,and under the guidance of the theory of Block Tectonics.The southern typical profile trends in NNW-SSE,and starts from the Southern China's Mainland to the Sulawesi Sea,spanning multiple tectonic units,including three continental margin—discrete continental blocks,e.g.,South China block—northern South China Sea margin(crustal thickness of^26-32 km),Zhongsha Block(crustal thickness of^14-25 km),Liyue—north Palawan Block(crustal thickness of^19-23 km);four oceanic basins,e.g.,Northwest Sub-basin(crustal thickness of^6-8 km),Central Sub-basin(crustal thickness of^5-6 km),Sulu Sea(crustal thickness of^6-20 km),Sulawesi Sea(crustal thickness of^7-8 km);and two subduction—arc zone,e.g.,Cagayan Ridge(crustal thickness of^8 km),and Sulu Ridge(crustal thickness of^15 km).The results of the joint geophysical inversion reveal the crustal nature beneath the miniature continental blocks,the narrow oceanic basins,and the volcanic arcs distributed alternatively.They constitute the unique tectonic framework“Miniature Continental Block—Narrow Oceanic Basin”in the western Pacific margin.This tectonic framework is confined by strike-slip boundaries in the east and the west,and a subduction boundary in the south.Since the ancient-Tethys subducted into the Eurasia plate,this region has undergone a complex tectonic evolution process.The crust is in the dynamic cycle of the constant extinction and formation,and the tectonic stress also changed dynamically.Based on the comprehensive analysis of regional geodynamics,it is concluded that the formation of the Miniature Continental Block—Narrow Oceanic Basin tectonic framework is largely by reason of its unique location where three plates meet together and the effect from complex and abundant subduction in the region.Such a compilation of the typical profiles has advanced the study of tectonic and geophysical characteristics in the China seas—western Pacific Ocean area,providing a good research example for“Look into the South China Sea from outside”.At the same time,it inspires us to strengthen the exploration of the adjacent research blank areas in the future.