东南大陆边缘早侏罗世火成岩特征及其构造意义

Characteristics of Early Jurassic igneous rocks on the continental margin of southeastern China and their tectonic significance

东南大陆边缘早侏罗世火成岩主要呈双峰式火山岩、基性超基性杂岩体及A型花岗岩等形态产出。本文运用岩石学探针技术,通过早侏罗世火成岩岩石学与地球化学研究,并与晚中生代火成岩作对比,提出早侏罗世火成岩的形成与南岭东段近EW向张性断裂活动有关,标志着印支挤压造山的结束;之后东南大陆进入晚中生代NE向活动大陆边缘俯冲造山阶段,经历了挤压造山—剪切拉张过程,并在晚白垩世末期进入又一轮后造山拉张裂解阶段,即中生代时东南大陆边缘经历了早中生代(三叠纪—早侏罗世)和晚中生代(中侏罗世—晚白垩世)两期造山事件,其中早侏罗世的区域拉张作用是特提斯构造域向滨太平洋构造域转换的前奏,构造域转换可能始于中侏罗世(165Ma)。

Early Jurassic igneous rocks on the continental margin of southeastern China are mainly present as bimodal volcanic rocks,basic-ultrabasic complexes and A-type granites.By using the petrological probe analysis,the paper studies the petrological and geochemical characteristics of the Early Jurassic igneous rocks and discusses their comparison with Late Mesozoic igneous rocks,and on that basis the paper proposes that the formation of the Early Jurassic igneous rocks is related to the nearly E-W-trending active continental-margin tensional faulting in the eastern segment of the Nanling Mountains and marks the end of Indosinian compressional orogeny.Afterward southeastern China entered the stage of Late Mesozoic NE-trending ac-tive continental-margin subduction orogeny,experienced the process of compressional orogeny-shear exten-sion and entered the stage of postorogenic extensional breakup at the end of the Late Cretaceous.During the Cenozoic,southeastern China became the passive continental margin where only intracontinental exten-sional breakup took place.In other words,in the Mesozoic,the continental margin of southeastern China underwent the Early Mesozoic(Triassic-Early Jurassic)and Late Mesozoic(Middle Jurassic-Late Creta-ceous )orogenic events.The Early Jurassic extension was a prelude of transformation from the Tethys tec-tonic domain to the Paleo-Pacific tectonic domain.This transformation may have started in the Middle Jurassic(165Ma BP)and it was a dynamic process that progressed from south to north.