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

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.