天山古生代洋盆开启、闭合时限的岩石学约束——来自震旦纪、石炭纪火山岩的证据

Constraints on the timing of opening and closing of the Tianshan Pa leozoic oceanic basin:Evidence from Sinian and Carboniferous vol canic rocks

天山及邻区各微地块上分布有震旦纪—早寒武世火山-沉积岩系,寒武系底部均发育含磷层,震旦系中见2～3层大致可对比的冰碛岩,暗示各微地块当时可能是一个统一大陆块的组成部分。震旦纪—早寒武世大陆拉伸→大陆裂谷火山活动是天山古生代洋盆开启的前兆,意味着早寒武世为天山古生代洋盆开启时限的下限。中天山巴仑台微地块中的下石炭统马鞍桥组底部的粗碎屑岩,是碰撞造山中晚期的地质记录。它意味着天山古生代洋盆已经闭合。石炭纪时,天山造山带已进入新的造山后裂谷拉伸阶段,发育有大规模大陆裂谷双峰式火山活动和花岗质岩浆活动。早石炭世是天山古生代洋盆闭合时限的上限。

Sinian and Early Cambrian volcano -sedimentary series is distributed in various Precambrian mi-croblocks in the Tianshan Mountains and their neighboring areas.Phosphatic rocks are commonly developed at the bottom of the Cambrian and two or three roughly comparable tillite beds are observed in the Sini-an.This suggests that the various microblocks may have been the component parts of a unifying large con-tinental block.The Sinian and Early Cambrian continental extension-continental rift volcanism were the precursor of the opening of the Tianshan Paleozoic oceanic basin.It implies that the Early Cambrian is the lower limit of the opening stage of the Tianshan Paleozoic oceanic basin.The coarse clastic rocks at the bottom of Lower Carboniferous Ma'anqiao Formation in the Baluntay microblock of the central Tianshan Mountains are the geologic record of the collisional orogen.It implies that the paleozoic ocean basin of Tianshan had closed at that time.InCarboniferous ,the Tianshan orogenic belt entered the post-orogenic rift-extensional stage,accompanied by extensive continental rift bimodal volcanism and granitic magmatism.The Early Carboniferous is the upper limit of the closing stage of the Tianshan Paleozoic oceanic basin.