帕里西维拉海盆南端的地质构造特征及成因分析

The geological and structural characteristics of the southern Parece Vela Basin and their genetic mechanisms

帕里西维拉海盆是西太平洋地区最大、最典型的弧后盆地,根据帕里西维拉海盆的形态特征,将帕里西维拉海盆分为帕里西维拉海盆主盆地和帕里西维拉海盆南端。本文利用国际公开的重力数据和实测的多波束、浅地层剖面数据研究了帕里西维拉海盆南端的重力异常特征和海底地形特征,并进一步探讨了该区域的特殊性及成因机制。海底地形与地球物理特征研究表明,帕里西维拉海盆南端可划分为A、B、C、D、E5个区域,分别代表海盆NE-SW向扩张形成的NW-SE向扩张构造、海盆E-W向扩张形成的N-S向扩张构造、海盆旋转过程中由北向南传播的扩张中心与海盆最南端的裂谷系统相互作用形成的NEE-SWW向构造、与帕里西维拉海盆同期形成的海山区以及裂谷系统相互作用形成的深渊区。海盆南端表现出明显的东西不对称性,海盆只存在扩张中心以西的部分,推测受卡罗琳海脊碰撞影响,帕里西维拉海盆南端东半部一部分逆冲至雅浦岛弧之上,还有一部分被推离至现今西马里亚纳海脊以西,随着洋壳持续的逆冲和迁移,最南端逐渐暴露的帕里西维拉海盆扩张中心与雅浦海沟合并,形成现今的雅浦海沟,最终造成了现今帕里西维拉海盆南端缺失东半部的构造形态。

Parece Vela Basin(PVB),the most typical and largest back-arc basin in the western Pacific,is divided into the main PVB and the southern PVB based on its morphological distribution.In this study,the gravity anom-alies and seafloor topographic features of the southern PVB are analyzed based on the open source gravity data,the measured swath bathymetry data and the sub-bottom profile data,and the particularity of this region and its genetic mechanism are further discussed.According to the seafloor topographic and geophysical characteristics,the south-ern PVB is mainly divided into five regions,namely,A,B,C,D,and E,which represent that the NW-SE seafloor fabrics formed during the NE-SW spreading,that the N-S spreading fabrics formed during the stage of E-W spreading of the PVB,that the NEE-SWW fabrics formed by the interaction between N-S trending spreading axis propagated from the north and the southernmost rift system during the rotation of the basin,that the seamounts formed at the same time as the PVB,and that the deeps formed by the interaction of the rift systems,respectively.The southern PVB shows obvious east-west asymmetry,that is,only the part west of the spreading center exists in the basin.We speculate that a part of the eastern half of the southern PVB thrusted over the Yap Arc,and another part was offset by a transform fault and the region now lies west of the West Mariana Ridge affected by the colli-sion of the Caroline Ridge.With the continuous thrusting and migration of the oceanic crust,the gradually exposed spreading center of the southern PVB merged with the Yap Trench to form the present Yap Trench,and finally res-ulting in the absence of the eastern counterpart of the southern PVB.