西菲律宾海盆的构造沉积特征及对海盆演化的指示--来自地球物理大断面的证据

TECTONIC AND SEDIMENTARY FEATURES OF THE WEST PHILIPPINE BASIN AND ITS IMPLICATION TO THE BASIN EVOLUTION——EVIDENCE FROM A SEISMIC TRANSECTION

菲律宾海发育了全球最典型的沟弧盆体系,新老俯冲系统众多,是研究大洋板块扩张过程的理想场所。本文主要利用2015年中科院海洋所在西菲律宾海采集的1400km地球物理大断面,并结合最新的重力数据,对比、分析了西菲律宾海内部古扩张中心(中央海盆裂谷)和残留弧(九州-帕劳海脊)的沉积地貌和地壳结构特征。研究表明:(1)中央海盆裂谷内部发育远洋沉积为主的沉积物,沉积层序分布不均,局部盆地内沉积物厚度可达300m。九州-帕劳海脊附近发育与火山碎屑物源有关的厚层沉积物;(2)以129°30′E处的转换断层为界,裂谷东西部洋壳结构分别体现"慢速"和"快速"扩张特征,东部洋壳岩浆供应较少,厚度较小,断裂较为发育,其附近可能发生水岩作用;西部洋壳岩浆供应较多,厚度较大,结构相对均一;盆地西部的小规模地幔柱可能控制了裂谷东西部不同洋壳结构的发育;(3)九州-帕劳海脊内的角度不整合面代表岛弧裂解事件,张裂与挤压构造共同发育反映了裂解过程的复杂性。

The Philippine Sea features a typical trench-arc-basin system in the world, and numerous intricate new or old subduction systems. It is an ideal area to study the process of oceanic plate expansion. In this study, we used data especially the latest gravity data acquired in a 1400 km-long seismic transection survey conducted by the Institute of Oceanology, China Academy of Sciences in Philippine Sea in 2015. We interpreted and analyzed the sedimentary geomorphology and oceanic structure of fossil spreading center（Central Basin Fault） and remnant arc（Kyushu-Palau Ridge） in the West Philippine Basin on multi-channel seismic profiles. Three conclusions have been drawn. First, the pelagic sediment developed in the Central Basin Fault and the sediment thickness is non-uniform; in local nodal basins, it can reach as thick as 300 m in Kyushu-Palau Ridge, being mainly volcanic debris. Second, the oceanic crust displays ＂slow＂ and ＂fast＂ spreading features in the east and west of Central Basin Fault respectively, divided by the transform fault at 129°30′E. In the eastern region, poor magma supply made the thinner crust with many faults, resulting in extensive water-rock interaction. On the contrast, rich magma supply in the western region caused relatively thicker and evener structure. Small mantle plumes in the western basin may controlled the formation of different oceanic crusts. Thirdly, the angular unconformity in Kyushu-Palau Ridge represents an internal rifting event. Extensional and compressional structures co-development during the event indicates a complex rifting process in the Kyushu-Palau Ridge.