西秦岭造山带早白垩世大陆裂谷存在的依据——青海同仁地区麦秀山群新建的意义  

The evidence for the existence of Early Cretaceous continental riftin West Qinling orogenic belt: the significance of the newly built Maixiushan Group in Tongren area of Qinghai Province

作　　者：祁生胜[1,2,3] 邓晋福[1] 赵呈祥 胡旭丽 史连昌[2,3] 陈健[2,3] 

机构地区：[1]中国地质大学(北京),北京100083 [2]青海省地质调查院,青海西宁810012 [3]青海省青藏高原北部地质过程与矿产资源重点实验室,青海西宁810012 [4]青海省地质矿产勘查开发局,青海西宁810012 [5]青海省第三地质矿产勘查院,青海西宁810012

出　　处：《地质通报》2011年第11期1706-1715,共10页Geological Bulletin of China

基　　金：中国地质调查局项目<青海1:25万贵南县-河南蒙古族自治县幅区域地质调查>(编号:1212010510408)

摘　　要：青海省唯一的一套早白垩世陆相火山岩地层分布在青海省黄南州同仁县—泽库县之间的麦秀山一带,位于西秦岭地层区泽库地层分区。根据剖面研究和区域地层对比,将这套地层新命名为早白垩世麦秀山群(K1M),下部的紫红—灰紫色中基性火山岩夹砂砾岩新建为多禾茂组(K1d),为一套典型的陆相裂隙式喷发的碱性玄武岩+陆相红层沉积建造,上部的紫红色砂砾岩组合延用万秀组(K1w),为一套冲积扇相陆相红层的类磨拉石建造,二者之间为明显的整合接触关系。根据麦秀山群与上下地层之间的角度不整合接触关系,以及多禾茂组火山岩中的同位素年龄和万秀组的昆虫、叶肢介、植物化石,可确定麦秀山群的形成时代为早白垩世。麦秀山群沿近南北向张裂带分布,是在早白垩世陆内环境下产生并在陆内环境下消亡的陆内裂谷相沉积,它的形成标志着西秦岭地区在早白垩世进入区域性伸展阶段。The only Early Cretaceous continental volcanic strata in Qinghai Province are distributed in Maixiushan area between Tongren County and Zeku County in Huangnan Prefecture of Qinghai Province and lie in Zeku subunit of West Qinling stratigraphic unit. Based on profile study and regional stratigraphic correlation,the authors newly named this suite of strata Early Cretaceous Maixiushan Group（K1M）.The purplish red-grayish purple intermediate-basic volcanic rocks intercalated with sandy conglomerate in its lower part constitute the newly-built Duohemao Formation（K1d）,which is a suite of typical continental fissure eruption alkaline basalt and continental red bed formation.The purplish red sandy conglomerate assemblage in the upper part of the Maixiushan Group remains called Wanxiu Formation（K1w）,which is a suite of alluvial fan facies continental molasses formation.The two parts are obviously in conformable contact.According to the angular unconformity between Maixiushan Group and its overlying and underlying strata, the isotopic ages of volcanic rocks of Duohemao Formation and the insects,estherites and plant fossils in Wanxiu Formation,the authors hold that the Maixiushan Group was formed in Early Cretaceous.Distributed along the nearly NS-trending tensional faulting belt,the Maixiushan Group is of the intracontinental rift facies sedimentation which was produced in Early Cretaceous intracontinental environment and withered away in the same environment,and the formation of the Maixiushan Group indicated that the the West Qinling area entered into a regional extension stage in Early Cretaceous period.

关 键 词：西秦岭造山带 早白垩世 麦秀山群陆内裂谷伸展环境 

分 类 号：P542.4[天文地球—构造地质学] P534.53[天文地球—地质学]