甘蒙北山地区下石炭统绿条山组时代修正及其构造意义  

Chronology of the Lütiaoshan Formation in the Beishan Area and Its Tectonic Significances

作　　者：牛亚卓[1] 卢进才[1] 魏建设[1] 陈高潮[1] 史冀忠[1] 吴俊[2] 

机构地区：[1]中国地质调查局西安地质调查中心,西安710054 [2]中国地质调查局武汉地质调查中心,武汉430205

出　　处：《地质论评》2014年第3期567-576,共10页Geological Review

基　　金：中国地质调查局矿产资源调查评价专项(编号1212011120962;12120114083001)资助成果

摘　　要：甘肃—内蒙古北山地区位于中亚造山带中段,其晚古生代洋盆最终闭合时间倍受关注且久有争议。早石炭世是该区洋陆转换的关键时期之一,下石炭统下部绿条山组与下伏的下、中泥盆统之间的角度不整合被认为是该区构造隆升的主要证据之一。但由于研究程度限制,绿条山组的时代尚有争议,一定程度上制约了该区构造演化的深入分析。北山北部甜水井北与碎石山剖面绿条山组火山岩的LA-ICP-MS锆石U-Pb年龄分别为296.8±3.5Ma与311.1±3.2Ma,产出晚石炭世巴什基尔期(Bashkirian)菊石Gastrioceras和Branneroceras,时代应修订为晚石炭世—早二叠世早期。研究区下泥盆统—上石炭统沉积充填及生物群落特征表明该区可能在晚石炭世由大陆边缘浅海演化至裂谷盆地,上石炭统与下、中泥盆统之间的角度不整合代表洋陆转化造成的长时间隆升剥蚀。The timing of closure of the Paleoasian Ocean is hotly debated in Beishan area, which is located in the middle part of the Central Asian orogenic belt. The Early Carboniferous is one of the key periods when tectonic plates changed drastically. The unconformity between the Lower Carboniferous Ltitiaoshan Formation and the Lower or Middle Devonian has been considered as an important evidence of the Late Paleozoic tectonic uplift. However, the age of the Lütiaoshan Formation is controversial and therefore limits the further discussion of the tectonic evolution. This paper proposes an Early Carboniferous to earlier Early Permian age of the Lütiaoshan Formation based on ammonites Gastrioceras and Branrteroceras from the Suishishan section, as well as two LA-ICP-MS zircon U-Pb ages of volcanic rocks from the Tianshuijingbei and Suishishan sections, which are respectively 296. 8 ±3.5Ma and 311.1 ±3.2Ma. The Beishan area translated from ocean to rift basin from the Early Devonian to Late Carboniferous. The unconformity between the Upper Carboniferous and the Lower or Middle Devonian implies the tectonic uplift caused by ocean—land transition.

关 键 词：甘肃 内蒙古 北山 早石炭世 绿条山组 年代学 洋陆转化 

分 类 号：P534.45[天文地球—古生物学与地层学]