甘新蒙北山地区古生代构造演化研究——北山古生代洋盆开启、闭合时限最新进展

北山及邻区各微地块上分布有震旦纪—早寒武世沉积岩系,寒武系底部发育含磷层,震旦系中见大致可对比的冰碛岩(3层),暗示各微地块当时可能是一个统一大陆块的组成部分。下寒武统双鹰山组薄层状大理岩、灰岩为浅海或滨海相环境产物;中上寒武统西双鹰山组青灰色硅质岩夹有薄层状灰岩,为深海相化学沉积产物,意味着早寒武世为北山古生代洋盆开启时限下限。泥盆纪三个井组不整合于寒武、奥陶纪之上,三个井组显示前陆盆地特征,花岗岩"线-面-点"产出形态可能代表俯冲-碰撞-碰撞后造山期地质记录。因此,早泥盆世为北山古生代洋盆闭合时限上限。

Evolution of the Geological Structure in Beishan Area Across Gansu Province,Xinjiang Autonomous Region and Inner Mongolia Autonomous Region-Constraints on the Timing of Opening and Closing of the Beishan Paleozoic Oceanic Basin

Sinian and Early Cambrian sedimentary series is distributed in various Precambrian microblocks in the Beishan 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 Sinian.This suggest that the various microblocks may have been the component parts of a unifying large continental block.Marble and Limestone of Early Cambrian Shuangyingshan groups are products of Shallow phase or binhai phase environment;Caesious siliceous rocks and thin layer limestone of mid-late Cambrian Xishuangyingshan groups are products of Deep-sea phase chemical deposition environment.It implies that the Early Cambrian is the lower limit of the opening stage of the Beishan Paleozoic oceanic basin.Devonian Sangejing groups unconformity on the Cambrian and Ordovician,Sangejing groups showed obvious foreland basin characteristics,Granite shows "line-surface-point" feature may represent subduction-collide-after collision orogenic stage geologic record.These characteristics implies that the Early Devonian is the upper limit of the closing stage of the Beishan Paleozoic oceanic basin.