西太平洋中段沉积盆地新生代构造－沉积演化特征

摘要

The middle Western Pacific is characterized by the trench-arc-basin system,because it is located in the junction area of the Euro-Asia Plate,the Pacific Plate and the India Plate.Three different types of basins developed in this area,including fore-arc basins,back-arc basins and continental margin basins.Based on the comprehensive study of tectonic environment,formation and evolution of the basins, and sedimentary characteristics of the seventeen basins in this area,we made the following conclusions. (1 ) All types of basins have experienced four stages of tectonic-sedimentary evolution.The tectonic-sedi-mentarg evolution of fore-arc basins and back-arc basins can be divided into subduction stage (K2 -E), basin-forming stage (N 1 1 -N 1 3 ),subsidence stage (N 1 4 -N 1 5 ) and compression stage (N 2 -Q):Vol-canic rocks and metamorphic basement mainly developed in the subduction stage,with marine clastic rocks deposited in local areas.Marine sediments took dominance in the basin-forming stage,accompanied by volcanic activities and some local continental sediment.Marine facies and delta facies mainly developed in the subsidence stage and compression stage while local areas also developed fluvial and lacustrine facies in the latter stage.Meanwhile,that of continental margin basins can be divided into pre-rift stage (K2 -E 1 ),rift stage (E 2 -E 3 1 ),depression stage (E 3 2 -N 1 3 ) and subsidence stage (N 1 4 -Q):The conti-nental alluvial fan-fluvial-lacustrine sedimentary system primarily developed in the pre-rift stage and rift stage,with intense volcanic activities.Depression stage is characterized by the evolution from continental facies to transitional facies.Marine facies and transitional facies both developed in the subsidence stage. (2) Different types of basins possess different features of tectonic-sedimentary evolution.The fore-arc ba-sins are 3.6 kmmeters thick on average,and their evolution were primarily controlled by compression and plate subduction,which experienced an evolution of marine-continental sedimentation -continental sedi-mentation.The back-arc basins are 4.8 kmmeters thick on average,and their tectonic environments are controlled by subduction retreat and back-arc oceanic crust expansion which experienced an evolution of marine sedimentation-marine-continental sedimentation.The continental rift basins are more than 1 0 km thick on average with double fault structure,which experienced an evolution of continental sedimentation-marine sedimentation.%西太平洋中段位于欧亚板块、太平洋板块和印度洋板块的交汇处，是全球沟弧盆体系最为发育的地区，主要发育弧后盆地、弧前盆地和陆架边缘盆地。文中通过综合研究西太平洋中段17个盆地的大地构造背景、盆地的形成与演化和沉积特征后认为：（1）各类盆地的构造－沉积演化均经历4个期次。弧前盆地和弧后盆地的构造－沉积演化可分为俯冲期（K2－E）、盆地发育期（N 11－N 13）、沉降期（N 14－N 15）和挤压期（N 2－Q）：俯冲期发育火山岩和变质岩基底，局部为海相碎屑岩；盆地发育期以海相沉积为主，伴有火山活动，局部发育陆相沉积；沉降期以海相和三角洲相沉积为主；挤压期以三角洲相和海相沉积为主，局部发育河湖相沉积。陆架边缘盆地的构造－沉积演化也分为4期，分别为前裂陷期（K2－E 1）、裂陷期（E 2－E 31）、拗陷期（E 32－N 13）和沉降期（N 14－Q）：前裂陷期和裂陷期主要发育冲积扇—河流—湖泊沉积体系，火山活动强烈；拗陷期沉积环境由陆相向海陆过渡相演化；沉降期以海相和海陆过渡相沉积为主。（2）不同类型盆地的构造－沉积演化特征各不相同：弧前盆地构造以挤压和板块俯冲为主，平均沉积厚度为3.6km，总体由海陆过渡相向陆相演化；弧后盆地构造受板块俯冲后撤和弧后洋壳扩张作用控制，平均沉积厚度为4.8km，总体由海相向海陆过渡相演化；陆架边缘盆地构造呈下断上拗双层结构，平均沉积厚度超过10km，总体由陆相演化为海相。