狼山发现蛇绿混杂岩--华北克拉通与中亚造山带碰撞边界的关键证据  

Ophiolitic Mélanges Found in Mount Langshan as the Crucial Evidence of Collisional Margin between North China Craton and Central Asian Orogenic Belt

作　　者：吕洪波 冯雪东 王俊[2] 朱晓青[3] 董晓朋[4] 张海春[5] 章雨旭[7] LU Hongbo;FENG Xuedong;WANG Jun;ZHU Xiaoqing;DONG Xiaopeng;ZHANG Haichun;ZHANG Yuxu(School of Geosciences,China University of Petroleum,Qingdao,Shandong,266580;Department of Earth Sciences,University of Hong Kong,Hang Kong;Qingdao Institute of Marine Geology,Qingdao,Shandong,266071;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing,100081;Nanjing Institute of Geology and Paleontology,Chinese Academy of Sciences,Nanjing,210008;Wujiahe Station,Earthquake Agency of Inner Mongolia Autonomous Region,Bayannur,Inner Mongolia,015331;Chinese Academy of Geological Sciences,Beijing,100037)

机构地区：[1]中国石油大学地球科学与技术学院,山东青岛266580 [2]香港大学地球科学系,中国香港 [3]青岛海洋地质研究所,山东青岛266071 [4]中国地质科学院地质力学研究所,北京100081 [5]中国科学院南京地质古生物研究所,南京210008 [6]内蒙古地震局乌加河地震台,内蒙古巴彦淖尔市乌拉特中旗015331 [7]中国地质科学院,北京100037

出　　处：《地质论评》2018年第4期777-805,共29页Geological Review

基　　金：中陕核工业集团委托项目“测老庙地区区域地质研究与铀矿有利区带预测”和国家自然科学基金资助项目(编号：41072074)的成果.

摘　　要：通过对内蒙古西部狼山地区进行野外调查,笔者等在狼山南缘的一系列构造逆冲片露头中发现了蛇绿混杂岩。根据野外观测、岩石薄片鉴定、岩石地球化学分析和锆石U-Pb定年等综合研究,确定了蛇绿混杂岩的基质为绿泥石片岩,而混杂岩块包括:紫红色硅质岩、石英角斑岩、玄武岩、蚀变辉绿岩和变质辉长岩等。其中,绿泥石片岩、玄武岩、蚀变辉绿岩中年轻的岩浆锆石年龄将岩浆喷发时代锁定在早白垩世晚期到晚白垩世早期,而且该三种岩石都具有高铝(Al_2O_3>17%)玄武岩的特征,指示了本区白垩纪与俯冲带相关的构造环境。依据狼山白垩纪蛇绿混杂岩的发现笔者等尝试重新厘定华北克拉通与中亚造山带之间的碰撞时间和边界:作为华北克拉通西北重要组成部分的鄂尔多斯地块在晚白垩世向北俯冲并最终与中亚造山带碰撞拼合,从而造成了阴山造山带西段狼山的隆起。根据构造地貌相似性原理,华北克拉通北部边界可能要从白云鄂博至西拉木伦河一带向南移到阴山—燕山一带,而最后的碰撞时间则由晚古生代推迟到晚白垩世。华北克拉通与西伯利亚克拉通之间的中亚造山带的宽度也进一步向南加宽为整个蒙古南部与内蒙古高原区,构成新的中亚造山带。这一认识为华北克拉通和中亚造山带中新生代构造演化研究以及重要成矿带成因机制探讨提供了新的大地构造模型,也为促进华北克拉通中生代破坏理论的改进提供新的信息和思路。Objective： Mount Langshan is the western section of Yinshan Mountain in the southern Inner Mongolia, north of China. Yinshan Mountain, being treated as a typical intra plate orogenic belt, has been regarded as the northern margin within the North China Craton by former geologists. However, our new discovery in Mount Langshan has attributed it to collisional orogeny. Our study indicates that Yinshan Mountain should be the Late Cretacous collision margin between North China Craton （NCC） and Central Asian Orogenic Belt （CAOB）.Methods： We found the outcrop of ophiolitic mélanges in Mount Langshan, west of Inner Mongolia, in a geologic expedition in 2015. To confirm our discovery we conducted more field investigation in 2016 and collected ample rock samples for laboratory tests. We examined the textures and mineral compositions of major ophiolitic mélanges through microscopic petrology, analyzed the chemical compositions （major oxides and trace elements） of key rock types, dated the geological times of important igneous rocks through U Pb zircon ages.Results： Geological fieldwork reveals that there are a series of thrust sheets in the southern flank of Mount Langshan. All the thrust sheets incline northward, and the ophiolitic mélanges are enclosed within one thrust sheet. The high Aluminum basalts and related igneous rocks （Al2O3〉17%） indicate that the major ophiolitic mélanges were originated in the subduction setting, representing the relics of the oceanic crust. The youngest ages of basalts and diabases imply their cooling time in the Late Cretaceous.Discussion and Conclusion： The authors of this article found the outcrops of ophiolitic mélanges in the southern piedmont of Mount Langshan, western part of Inner Mongolia. Our study reveals the following achievements： The ophiolitic mélanges are enclosed in a large thrust sheet of more than 500m in width and 3km in length. The thrust sheet extended in east-west direction and inclined northward, and there are many thrust sheets of

关 键 词：内蒙古 狼山 蛇绿混杂岩 华北克拉通 中亚造山带 碰撞边界 晚白垩世 

分 类 号：P542[天文地球—构造地质学] P587[天文地球—地质学]