九州-帕劳海脊中段及两侧盆地构造沉积特征及俯冲起始:多道反射地震综合研究

Tectono-sedimentary characteristics and subduction initiation in the middle Kyushu-Palau Ridge and adjacent basins:A comprehensive study of multichannel seismic reflection profiles

九州-帕劳海脊及两侧的盆地是研究边缘海形成演化和板块俯冲起始机制的理想区域。利用最新采集的深反射地震数据并结合钻孔数据,研究了九州-帕劳海脊及其东西两侧盆地的构造沉积特征及地壳结构,探讨了西菲律宾海的起源及沿古伊豆-博宁-马里亚纳弧的俯冲起始机制。地震剖面和钻孔岩心揭示西菲律宾海盆发育上、下两套不同来源的沉积物盖层,其中下部地层厚度差别大,多为火山物质,来源于九州-帕劳海脊的岛弧火山作用,表现为向海脊方向的持续增厚,靠近海脊的山脚下发育火山碎屑岩裙;上部地层厚度较为稳定,为一套大洋的深水细粒沉积物。西菲律宾海盆和帕里西维拉海盆的地壳厚度约为6~8 km,接近全球平均洋壳厚度;西菲律宾海盆的莫霍面呈宽缓的褶皱状,与沉积物之下的洋壳基底基本同步起伏。西菲律宾海盆在中生代可能位于南半球澳大利亚的北缘,是在陆缘弧(包含部分大陆碎片)的基础上,因古近纪弧间伸展和海底扩张而逐步发展起来的。西菲律宾海盆的地震剖面和钻井均揭示了始新世时期的构造挤压事件,沿古伊豆-博宁-马里亚纳弧的俯冲起始可能是印亚碰撞的远场效应引起的诱导俯冲,俯冲过程伴随着侧向传播和持续的挤压应力场,直到约30 Ma开始岛弧裂离。该研究对揭示东南亚板块构造演化过程和板块俯冲起始机制具有一定的理论意义。

The Kyushu Palau Ridge and the basins on the both sides are ideal areas for understanding the formation and evolution of marginal seas and the initiation mechanism of plate subduction.We studied the tectonic sedimentary characteristics and crustal structure of the KyushuPalau Ridge(KPR) and adjacent basins using newly collected deep reflection seismic data combined with the borehole data,and discussed the origin and subduction initiation mechanism of the West Philippines Sea.Seismic profiles and drill cores revealed that two sets of sediment caprocks are developed from different sources in the Western Philippines Basin.The thickness of the lower set is very different,and most of them are volcanic materials that derived from island arc volcanos of KPR,showing continuous thickening towards KPR,and volcanoclastic rock skirts are developed near the foot of KPR.The thickness of the upper set is relatively stable,being composed of deep-water fine-grained sediments.The crust thickness of the western Philippines Basin and Parece Vela Basin is 6-8km,which is similar to the global average oceanic crust thickness.The Moho surface of the Western Philippines Basin is in a wide-gentle fold shape,and fluctuates synchronously with the ocean crust basement beneath sediments.The Western Philippines Basin might be located in the northern margin of Australia in the southern hemisphere in the Mesozoic,and was gradually developed on a continental margin arc(including some continental fragments) due to inter-arc extension and submarine spreading in the Paleogene.Seismic profiles and drilling in the Western Philippines Basin have revealed tectonic compression events during the Eocene.The subduction along the paleo-IBM(Izu-Bonin-Mariana) might be induced by the remote effect of the Indo-Asian collision.The subduction process was accompanied by lateral propagation and persistent compressive stress field,which consequently resulted in the island arc broke up in about 30Ma.This study has certain theoretical significance for studying the plate tectonic evolution and subduction initiation mechanism in Southeast Asia.