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引用本文:康欢,李大鹏,陈岳龙,胡国强,邓伟兵. 康定杂岩成因和构造意义——来自Hf同位素的证据[J]. 中国地质, 2017, 44(6): 1175-1189.
KANG Huan,LI Dapeng,CHEN Yuelong,HU Guoqiang,DENG Weibing. Origin and tectonic implications of Kangding intrusive complexes in Sichuan Province: Evidence from zircon Hf isotope[J]. Geology in China, 2017, 44(6): 1175-1189(in Chinese with English abstract).
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康定杂岩成因和构造意义——来自Hf同位素的证据
康欢1, 李大鹏1,2, 陈岳龙1, 胡国强3, 邓伟兵4
1.中国地质大学(北京) 地球科学与资源学院, 北京 100083;2.中国地质科学院地质研究所 北京离子探针中心, 北京 100037;3.江西省地质矿产开发研究中心, 江西 南昌 33002;4.核工业金华工程勘察院湖州分院, 浙江 湖州 313000
摘要:
康定杂岩位于扬子地块西缘,通过对四川康定—冕宁—攀枝花—云南元谋地区出露的康定杂岩中基性、中性、酸性岩岩石学、锆石Lu-Hf同位素等多方面系统研究,确定这套岩石形成于岛弧环境。分析表明:康定杂岩中镁铁质侵入体锆石εHft)变化范围-4.2~+11.0,Hf模式年龄742~2386 Ma;长英质侵入体锆石εHft)变化范围-4.9~+9.4,Hf模式年龄为967~2707 Ma;暗示康定杂岩体复杂的构造成因。锆石Hf同位素分析表明其岩浆锆石具有与扬子地块西缘同时代镁铁质/长英质侵入体相似的Hf同位素组成,暗示其相似的岩浆起源。研究表明,康定杂岩为大洋俯冲背景下的产物,镁铁质侵入体来源于较为亏损地幔源区,长英质侵入体为新生陆壳与古老地壳物质相互作用形成的产物。锆石Hf同位素数据表明,康定侵入体杂岩中锆石Hf-全岩Nd解耦,为“锆石效应”与少量地壳物质加入共同作用结果。结合岩石学、地层学、构造及地球化学证据综合表明,新元古代时期,扬子地块可能位于Gondwana超大陆的边缘,而不是澳大利亚与北美Laurentia古陆之间的连接部分。
关键词:  康定侵入体杂岩  新元古代岩浆作用  Hf同位素  Hf-Nd解耦  活动边缘
DOI:10.12029/gc20170610
分类号:P534.3;P597
基金项目:国家自然科学基金项目(41502212、41473015)、基本科研业务费优秀教师项目(2652015013)及国家科技基础条件平台北京离子探针中心开放基金课题(DD12-118)联合资助。
Origin and tectonic implications of Kangding intrusive complexes in Sichuan Province: Evidence from zircon Hf isotope
KANG Huan1, LI Dapeng1,2, CHEN Yuelong1, HU Guoqiang3, DENG Weibing4
1.Schoolof Earth Science and Resources, China University of Geosciences, Beijing 100083, China;2.Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3.The Development Research Center of Geology and Mineral Resources in Jiangxi Province, Nanchang 330002, Jiangxi, China;4.Nuclear Industry Jinhua Engineering Investigation Institute Huzhou Branch, Huzhou 313000, Zhejiang, China
Abstract:
Kangding metamorphosed intrusions in Kangding, Mianning and Panzhihua areas of Sichuan Province and Yuanmou area of Yunnan Province were formed in the island arc setting, as shown by the integrated study of petrogenesis and Hf isotopic geochemistry of plutonic rocks ranging from acid to basic ones. Zircons from the mafic plutons have εHf(t) values ranging from -4.2 to +11.0, with their Hf model ages ranging from 742 to 2386 Ma. The felsic plutons have εHf(t) values ranging from -4.9 to +9.4, with their Hf model ages ranging from 967 to 2707 Ma. Magmatic zircons from the Kangding intrusive complexes show similar Hf isotope compositions to those from coeval felsic intrusions on the west margin of the Yangtze Craton, implying their similar magmatic origins. The Kangding intrusive complexes were formed in an oceanic subduction setting, the mafic plutons were derived from depleted mantle sources, whereas the felsic plutons were formed by melting of ancient crustal materials and juvenility crustal materials. According to the Nd isotopic data of the whole rock and the Hf isotopic data of the corresponding zircons in this area, the Hf-Nd decoupling must have resulted from the "zircon effect" and crustal material interaction. Petrology, stratigraphic correlations, tectonic analysis and geochemical evidence suggest that the Yangtze block of South China was located along the margin of the Neoproterozic supercontinent Gondwana rather than at the connection between Australia and Laurentia old land in North America.
Key words:  Kangding-Yuanmou complex  Neoproterozoic magmatism  zircon Hf isotope  Hf-Nd decoupling  active margin