西南三江甘孜-理塘洋晚古生代构造演化:来自理塘蛇绿混杂岩堆晶辉长岩U-Pb年龄的约束  

Late Paleozoic tectonic evolution of Ganzi-Litang Ocean in Sanjiang region,Southwest China:Constraints from U-Pb geochronology of cumulate gabbro in Litang ophiolitic mélange belt

作　　者：喻光明 毛世东 周振菊[3] 谢亘 黄豪擎 YU Guangming;MAO Shidong;ZHOU Zhenju;XIE Gen;HUANG Haoqing(Natural Resources Comprehensive Survey Command Center,China Geological Survey,Beijing 100055,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;Institute of Geomechanics,Chinese Academy of Geological Science,Beijing 100081,China;Center for Geophysical Survey Center,China Geological Survey,Langfang 065000,Hebei,China)

机构地区：[1]中国地质调查局自然资源综合调查指挥中心,北京100055 [2]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [3]中国地质科学院地质力学研究所,北京100081 [4]中国地质调查局地球物理调查中心,河北廊坊065000

出　　处：《地质通报》2024年第1期61-75,共15页Geological Bulletin of China

基　　金：国家自然科学基金项目《西南天山境内外造山型金矿构造变形-成矿作用特征对比研究》(批准号:42172093)和《西南天山阿沙哇义造山型金矿构造-流体控矿作用研究》(批准号:41772085);中国地质调查局项目《全国自然资源调查项目组织实施费》(编号:DD20220851)和《四川甘孜州金沟、大河边幅1:50 000区域地质矿产调查》(编号:12120113071700)。

摘　　要：理塘县高城镇西北的擦岗隆洼岩组是一套以玄武岩为基质的蛇绿混杂岩,通过该蛇绿混杂岩中堆晶辉长岩的LA-ICP-MS锆石U-Pb定年,显示其年龄范围介于349~274 Ma之间,形成2个年龄组:第一组斜锆石^(206)Pb/^(238)U年龄加权平均值为346±17Ma,代表堆晶辉长岩早期岩浆活动的时代;第二组斜锆石^(206)Pb/^(238)U年龄加权平均值为286.2±5.1 Ma,代表了堆晶辉长岩晚期岩浆活动的结晶年龄。擦岗隆洼岩组的超基性—基性岩具有N-MORB(正常洋中脊玄武岩)和E-MORB(富集型洋中脊玄武岩)组合特征,指示这些岩石可能形成于洋中脊环境,岩浆物质源自N-MORB所代表的亏损上地幔源区受地幔柱交代混染后而形成的混合源区。研究认为,甘孜-理塘洋最早可能在中泥盆世,受区域地幔柱活动影响开始拉张,导致中咱地块从扬子陆块西缘裂离,并在早石炭世发育形成洋盆。在中晚三叠世甘孜-理塘洋壳开始向西俯冲,并于晚三叠世末闭合,区域进入弧陆碰撞造山阶段。Located in the northwest of Gaocheng Town,Litang County,the Caganglongwa rock Formation is a set of ophiolitic mélange with basalt as the matrix.LA-ICP-MS zircon U-Pb dating of the cumulate gabbro in the ophiolitic mélange shows an age distribution range from 274 Ma to 349 Ma,indicating two age groups.The first group of baddeleyite ^(206)Pb/^(238)U has a weighted average age of 346±17 Ma,which represents the age of early magmatism of cumulate gabbro;the second group of baddeleyite ^(206)Pb/^(238)U has a weighted average age of 286.2±5.1 Ma,which represents the crystallization age for late magmatism of cumulate gabbro.The ultrabasic and basic rocks in the Caganglongwa rock Formation display combined characteristics of N-MORB and E-MORB,indicating that these rocks may be formed in the mid-ocean ridge environment,and the magma material comes from a mixed source region formed by depleted upper mantle source region represented by N-MORB and metasomatically contaminated by the mantle plume.The research finds that the Ganzi-Litang Ocean may begin to stretch as early as the Middle Devonian due to the regional mantle plume activity,resulting in the split of the Zhongza block from the western margin of the Yangtze block and the Formation of an ocean basin in the Early Carboniferous.By the Mid-Late Triassic,the Ganzi-Litang oceanic crust was subducted westward and closed at the end of the Late Triassic,and the region entered the arc-continent collision orogeny stage.

关 键 词：斜锆石U-Pb年龄 堆晶辉长岩 擦岗隆洼岩组 甘孜-理塘蛇绿混杂岩带 

分 类 号：P534.4[天文地球—古生物学与地层学] P579.3[天文地球—地质学]