西南日本夜久野(Yakuno)蛇绿混杂岩锆石U-Pb定年及其对晚古生代-早中生代华南大地构造演化的指示  

Zircon U-Pb Dating of Yakuno Ophiolitic Complex in Southwest Japan and its Indications for the Late Paleozoic to Early Mesozoic Tectonic Evolution of South China

作　　者：洪文涛[1,2] 余明刚[2] 赵希林[2] 褚平利[2] HONG Wentao;YU Minggang;ZHAO Xilin;CHU Pingli(State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210093,Jiangsu,China;Nanjing Center,China Geological Survey,Nanjing 210016,Jiangsu,China)

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学与工程学院,江苏南京210093 [2]中国地质调查局南京地质调查中心,江苏南京210016

出　　处：《大地构造与成矿学》2022年第4期728-743,共16页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(41702061);中国地质调查局项目(DD20190361、DD20190373)联合资助。

摘　　要：晚古生代-早中生代的构造运动在华南大地构造演化过程中意义重大,但对其动力学机制却存在两种截然不同的认识,即与特提斯洋闭合有关的碰撞造山以及与华南东缘大洋俯冲相关的增生造山。后一种认识备受争议的主要原因是华南地区缺少晚古生代与俯冲直接相关的增生杂岩、高压变质岩等记录,而这些记录在西南日本保存完整。本文通过对西南日本内带朝来地区晚古生代夜久野(Yakuno)蛇绿混杂岩的锆石U-Pb定年,结合区域构造-地层分析,探讨西南日本晚古生代-早中生代构造演化过程。LA-ICP-MS锆石U-Pb定年结果表明,朝来地区夜久野蛇绿混杂岩中-上部辉长岩形成于早二叠世(281.8±1.8 Ma);而斜长角闪岩的变质年龄为231.0±5.8 Ma,与西南日本广泛分布的周防带(Suo belt)高压变质时间一致,表明西南日本主要的造山事件发生在印支期。综合夜久野蛇绿混杂岩内不同类型火成岩的年代学及岩石地球化学组成,以及区域构造-地层特征,将该蛇绿岩的构造演化归结为三个阶段:(1)晚石炭世大洋(泛大洋或古太平洋)扩张阶段;(2)早二叠世洋内弧-弧后盆地阶段,夜久野蛇绿混杂岩主体即形成于弧后盆地;(3)早二叠世末期(约280~272Ma),弧后盆地闭合,岛弧-洋岛海山地体与华南大陆东缘碰撞形成新的陆缘弧,这一弧-陆拼贴过程控制着东南沿海地区中二叠世的古地理格局转变。考虑到西南日本晚古生代俯冲增生作用一直持续至中三叠世末期,中三叠世西南日本以及华南东缘的印支造山可能主要受控于泛大洋(或古太平洋)板块的俯冲作用。Late Paleozoic to Early Mesozoic orogeny is the key to understand the Phanerozoic tectonic evolution of South China.Two distinct models have been proposed for the dynamic mechanism of the orogeny,that is,collision orogeny related to the closure of the Tethys Ocean and the accretionary orogeny,which was controlled by the subduction of Panthalassa(or Paleo-Pacific)plate in the western South China.The latter model has long been controversial due to the lack of Late Paleozoic ophiolite,high-pressure metamorphic rocks and arc magmatism in the mainland of South China.Unlike South China,the subduction-related rocks are well preserved in Southwest Japan and can be used to infer the Late Paleozoic to the Early Mesozoic tectonic evolution of South China.In this paper,based on zircon U-Pb dating of the gabbro and amphibolite in the Late Paleozoic Yakuno ophiolitic complex,combined with regional stratigraphic characteristics of Southwest Japan,we summarize the Late Paleozoic to the Early Mesozoic tectonic evolution of Southwest Japan and further propose a new Late Paleozoic to Early Mesozoic tectonic evolution model for South China.Zircon LA-ICP-MS U-Pb dating results show that the gabbro in the middle to upper unit of the Yakuno ophiolitic complex in the Asago region formed in Early Permian(281.8±1.8 Ma),while the metamorphic age of the amphibolite is 231.0±5.8 Ma,which is consistent with the Suo belt high-pressure metamorphic rocks widely distributed in Southwest Japan.Based on chronology,geochemistry and stratigraphic evidence of the study region,the geotectonic history of the Yakuno opiolitie can be summarized as follows:(1)oceanic(Panthalassa or Paleo-Pacific)crust formation in the Early Carboniferous;(2)the Yakuno ophiolitic complex formed in the back arc basin behind the island arc during the Early Permian;(3)the back-arc basin closure,while the island-arc and seamount accreted to the eastern margin of South China continent in the end of the Early Permian.The collision resulted in the transition of the eastern margi

关 键 词：西南日本 夜久野蛇绿混杂岩 晚古生代 华南 印支造山 

分 类 号：P597[天文地球—地球化学]