燕山褶断带下板城盆地杏石口组沉积特征及其构造意义  

Sedimentation feature and its tectonic significances of Xingshikou formation in Xiabancheng basin,Yanshan fold-and-thrust belt.

作　　者：刘健[1] 赵越[1] 柳小明[2] 刘晓文[3] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]西北大学大陆动力学重点实验室,西安710069 [3]国土资源部实物资料中心,河北三河燕郊065201

出　　处：《岩石学报》2007年第3期639-654,共16页Acta Petrologica Sinica

基　　金：国家重点基础研究973项目(2006CB403501);国家自然科学基金重点项目(40132020);国土资源大调查项目(200013000168)

摘　　要：本文通过对燕山褶断带下板城盆地杏石口组沉积物的成分、古水流及其底部砾岩的砂质充填物中碎屑锆石和砾岩中部出露的花岗岩、花岗片麻岩砾石中锆石LA-ICP-MS U-Pb测年分析结果,并结合来源区的构造与岩浆作用的调查,揭示了杏石口组沉积时环境的剧变。三叠纪时期刘家沟组至二马营组均为河流相沉积,其古流向自东向西,而杏石口组沉积期变为快速堆积的山麓冲积扇相砾岩,古流向自北-北西向南-南东。杏石口组一段至二段的沉积特征记录了该时期内蒙古隆起的构造抬升及剥露过程。杏石口组中碎屑锆石和花岗岩、花岗片麻岩砾石中锆石U-Pb年龄范围可分为3组:2025～2565Ma、1659～1888Ma和193～691Ma。其中,最年轻的碎屑锆石的加权平均年龄为197±6Ma,表明杏石口组的砂砾岩沉积时代应晚于197±6Ma,即其沉积时代应为早侏罗世。笔者曾获得下板城盆地北侧王土房杂岩体中不同单元花岗岩的锆石U-Pb年龄为191±1Ma和207±1Ma,其与本文获得杏石口组中最年轻的碎屑锆石及两枚花岗岩砾石中锆石的加权平均年龄197±6Ma和206±2Ma、207±2Ma在误差范围内一致,表明与王土房杂岩体同期侵位的岩体在杏石口期发生了快速抬升剥露。暗示了内蒙古隆起在早侏罗世发生了快速抬升及剥露的构造过程。结合前人研究,燕山褶断带前180Ma构造幕发生时代应在197～180Ma期间。Based on the component of sediment,paleocurrent of Xingshikou formation, and the zircon LA-ICP-MS datas from detrital zircons of sandy fillings, granite and granite gneiss gravel preserved in the middle segment of Xingshikou formation in the Xiabancheng basin, Yanshan fold-and-thrust belt, combined with the research of tectonics and magmatism of provenance, this paper studies dramatic transformation of the depositional environment during Early Mesozoic. The Liujiagou formation and Ermaying formation were fluvial environment in Triassic, its paleocurrent was west to east. However, the sedimentary features of Xingshikou formation indicated the environment was piedmont alluvial fan, and its paleocurrent was north-northwest to south-southeast. The lower and middle segments of Xingshikou formation recorded the process of uplift and denudation of the Mongolian paleo-uplift. Zircons from detrial zircons to gravel of granite and granite gneiss are characterized by three major groups of U-Pb ages： 2025-2565Ma, 1659-1888Ma and 193-691Ma. Ages of the youngest detrital zircons weighted mean were 197 ± 6Ma. It indicates sedimentation age of the Xingshikou formation was posterior to 197±6Ma. Therefore, Xingshikou formation formed in Early Jurassic. The zircon U-Pb ages of different unit granite in rock complex of the Wangtufang , the northern Xiabancheng basin, author had obtained are 191± 1 and 207±1Ma. These ages of the granite are the same as detrital zircons and gravel of granite of Xingshikou formation in error limit. It shows the contemporary magmatic body emplacement with the Wangtufang complex rock and the Mongolian paleo-uplift experienced quick uplift and denudation in the Xingshikou period. Integrated with findings of the predecessor, this paper considers the age of before -180Ma tectonic phase in the Yanshan fold-and-thrust belt was 197 - 180Ma.

关 键 词：燕山褶断带 杏石口组 碎屑锆石 剥露过程 锆石LA-ICP-MS U-Pb定年 

分 类 号：P542.2[天文地球—构造地质学] P588.21[天文地球—地质学]