中亚造山带东段古元古代结晶基底:来自中蒙边境花岗岩和沉积地层的证据  

Paleoproterozoic basement in eastern Central Asia Orogenic Belt: Evidence from granite and sedimentary strata in Sino-Mongolia border area

作　　者：苏茂荣[1] 李英雷 刘汇川 邵永旭[1] 张青[1] 周飞 曹磊 孙景浩 SU Maorong;LI Yinglei;LIU Huichuan;SHAO Yongxu;ZHANG Qing;ZHOU Fei;CAO Lei;SUN Jinghao(Inner Mongolia Key Laboratory of Magmatic Mineralization and Ore-Prospecting,Geological Survey Institute of Inner Mongolia,Hohhot 010020,Inner Mongolia,China;Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum(Beijing),Beijing 102249,China;College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China)

机构地区：[1]内蒙古自治区地质调查院,内蒙古自治区岩浆活动成矿与找矿重点实验室,内蒙古呼和浩特010020 [2]中国地质科学院矿产资源研究所,北京100037 [3]北京大学地球与空间科学学院,北京100871 [4]中国石油大学油气资源与探测国家重点实验室,北京102249 [5]中国石油大学地球科学学院,北京102249

出　　处：《中国地质》2020年第4期1186-1203,共18页Geology in China

基　　金：中国地质调查局项目(DD2016041-17);国家自然科学基金项目(41502210)联合资助。

摘　　要：中亚造山带东段多个地块内鲜有古老结晶基底物质报道,严重制约了我们对其早期属性的认识。本研究在内蒙古北部与蒙古国接壤的乌力吉特敖包地区,发现了被中下泥盆统泥鳅河组不整合覆盖的古元古代细粒二长花岗岩和沉积地层(乌兰敖包组)。对二长花岗岩开展的LA-ICM-MS锆石U-Pb定年显示其结晶年龄为(1686±10) Ma,说明形成于古元古代。乌力吉特敖包二长花岗岩高钾钙碱性,过铝质(A/CNK=1.08~1.11),且含有大量白云母,属S-型花岗岩。不同于常见的显生宙以来的S-型花岗岩,乌力吉特敖包古元古代花岗岩具有正的εHf(t)值(+2.9^+6.7),但εHf(t)值远低于1.7 Ga地壳演化趋势线,且锆石原位Hf同位素二阶段模式年龄为2.0~2.3 Ga,因此其应该来源于古老变泥质岩部分熔融。乌力吉特敖包古元古代花岗岩形成于陆陆同碰撞的构造环境。在古元古代乌兰敖包组变质泥岩获得了一个显著的碎屑锆石峰值年龄(1698 Ma),且该地层被元古宙花岗岩侵入。本研究发现的乌力吉特敖包古元古代末期花岗岩和乌兰敖包组沉积地层说明:中亚造山带东缘各地块内存在古老的结晶基底物质。这为我们认识这些地块早期演化历史提供了重要地质证据。There are few reports of Archean crystalline basement in the eastern part of the Central Asian Orogenic Belt, which impedes researchers’ understanding of ancient tectonic evolution of this area. In this study, the authors discovered Paleoproterozoic fine-grained adamellite and sedimentary rocks(Wulanaobao Formation) unconformably covered by the Niqiuhe Formation of Middle Lower Devonian in the Ulikit Obo area along central China-Mongolia border area. The zircon U-Pb dating results(LAICP-MS) show that the crystallization age of monzogranite is 1686 ± 10 Ma, formed in Paleoproterozoic. The Ulikit Obo granites are high-K calc-alkaline, peraluminous(A/CNK=1.08-1.11). In combination with the existence of muscovite, the Ulikit Obo granites could be classified as S-type granites. They have positive εHf(t) value(+ 2.9-+ 6.7),which is located lower than the 1.7 Ga crustal evolution trend line;besides, the in-situ Hf isotope two-stage model age of zircon is 2.0-2.3 Ga, so the zircon should be derived from partial melting of pelites in syn-collisional tectonic settings. The Wulanaobao Formation was intruded by the Paleoproterozoic Ulikit Obo granites and their detrital zircons yielded a youngest age peak of ca. 1698 Ma. The discovery of Paleoproterozoic Ulikit Obo granites and Wulanaobao Formation indicates the existence of Paleoproterozoic crystalline basement for the microcontinental massifs in the eastern section of the Central Asian orogenic belt.

关 键 词：中亚造山带 古元古代 S型花岗岩 中蒙边境 结晶基底 地质调查工程 

分 类 号：P548[天文地球—构造地质学] P597[天文地球—地质学]