智利三联点相关的板块相对运动及其地球动力学意义  

Relative motion of plates related to the Chile triple junction and geodynamic significance

作　　者：贾鸿瑞 魏东平[1,2] JIA HongRui;WEI DongPing(Key Laboratory of Computational Geodynamics,Chinese Academy of Sciences,Beijing 100049,China;College of Earth and Planetary Science,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院计算地球动力学重点实验室,北京100049 [2]中国科学院大学地球与行星科学学院,北京100049

出　　处：《地球物理学报》2021年第10期3567-3575,共9页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41874115)资助.

摘　　要：智利三联点作为典型的RTT型三联点,伴随智利洋脊俯冲到南美大陆板块下方,通过建立纳兹卡—南极—南美—太平洋四板块系统,并基于GPS、地震滑移矢量、洋中脊扩展速率及转换断层方位角等观测资料,给出了前三个板块相对于太平洋板块的欧拉矢量,据此进一步得到了各板块两两之间的相对欧拉运动矢量.结果显示,整个智利海沟处,三联点以北表现为纳兹卡板块相对南美板块的约83.0 mm·a^(-1)的近东向俯冲,快速下降到三联点以南的南极板块相对南美板块的约22.0 mm·a^(-1)的东偏南俯冲,由于洋脊俯冲效应,智利三联点自5.3Ma以来,整体由南向北作迁移运动,同时因为智利洋脊被转换断层切割成多个小段,导致智利三联点的性质在RTT型与FTT型间不断转变,当智利三联点为FTT型时,其运动方向改变为反向自北向南迁移,使得部分地区会经历多段洋脊的重复俯冲,从而导致洋壳玄武岩多次经历800~900℃的温度条件和低压(10~20 km深度)下的部分熔融,使熔体与残留物从第一次相平衡后形成的中性岩石,在经历又一次的部分熔融后形成酸性岩,这也是我们在三联点交替向北向南迁移的位置,多处发现弧前酸性岩存在的重要原因.At the Chile triple junction(CTJ),a representative RTT-type structure,the Chile ridge is currently subducting under the South America plate.Here we show the relative Euler vectors among the Nazca,Antarctica and South America plates by constructing the Nazca-Antarctica-South America-Pacific plate system based on GPS observations,seismic sliding vectors,mid-ocean ridge spreading rates and the azimuth of transform faults.The results reveal distinct subduction characteristics of the Nazca plate(eastward,~83.0 mm·a^(-1))and the Antarctic plate(southeastward,~22.0 mm·a^(-1))beneath the South America plate on either side of the CTJ.The CTJ moves northward since 5.3 Ma due to the subduction of the ocean ridge,with the nature of CTJ changing between RTT-type and FTT-type in response to the modification of the Chile ridge by the transform faults.The repeated subduction of the ocean ridge induced by the southward movement of the FTT-type CTJ causes the repeated partial melting of basalts under high T(800~900℃)and low P(10~20 km)conditions.The intermediate rocks formed in the initial phase equilibrium are transformed into acid rocks during the following partial melting processes,which is responsible for the pre-arc acid rock outcrops at the crossover location of the CTJ movement.

关 键 词：智利三联点 欧拉矢量 板块相对运动 洋脊俯冲 弧前酸性岩 

分 类 号：P315[天文地球—地震学] P541[天文地球—固体地球物理学]