南冲绳海槽岩石圈构造动力作用机制探讨

PROBING INTO LITHOSPHERIC TECTONIC MECHANICS OF SOUTHERN OKINAWA TROUGH

由最新获得的重磁、地震和多波束地形数据 ,结合多尺度的地幔流动力分析 ,展示了南冲绳海槽岩石圈构造动力的多样性特征和其内在的联系。从上新世开始的三幕张性断陷活动是在以前的压性断裂构造的基础上发展起来的 ,向岛弧侧迁移 ,岩浆、火山活动主要集中在正断层与平移断层的交汇处。深部动力源可归结为上地幔对流产生的菲律宾海板块俯冲 ,引起岛弧岩石圈挤压褶皱而向海沟旋张掀斜 ,产生弧后岩石圈的张性构造 ;进一步引起弧后软流圈挤压隆起 ,岩石圈与软流圈耦合作用导致海槽断陷张裂、岩浆活动。冲绳海槽仍是一个软流圈在汇聚的弧后盆地。全球性左旋压扭滑移背景 ,琉球海沟南段俯冲受阻小、强度大 ,台湾—吕宋的北向挤压 ,使海槽表现为剪张性 ,由平移断层调控使张性断裂左旋雁行排列 ,整个海槽张性构造由北往南推进 ,张应力方向由NW过渡到NNW。

On the basis of recently acquired gravity, magnetics, seismic and multibeam data, complemented with multi scale stress fields of mantle flow, the diversity and relation of tectonic characteristics of the southern Okinawa Trough lithosphere are displayed. Three phases of rifting depression after the Miocene are developed upon the original compressive belts migrating toward Ryukyu Islands. Volcanic and magmatic activities are closely distributed at crosses of the normal and strike slip faults. Deep tectonic origin can be attributed to subduction of the Philippine Sea plate driven by its upper mantle convection flow, which makes lithosphere rotate, tilt toward the trench along the island arc and extend, causing sink behind the arc, and also makes asthenosphere converge, causing uplift behind the arc. Interaction between lithosphere and asthenosphere causes magmatic intrusion with the trough rifting depression. The Okinawa Trough is a back arc basin still driven by the converging asthenosphere. The large scale background of sinistral compresso shear, intense subduction at the south and northward advance of the Taiwan Luzon block are all coherent with the shear opening feature around the northern end of Taiwan, which leads to the sinistral en echelon normal faults adjusted by strike slip faults. The shear opening advancing from the north towards the south makes the trough rifting trend change from NW to NNW.