哀牢山构造带新安寨晚二叠世末期过铝质花岗岩锆石U-Pb年代学及Hf同位素组成研究  

Zircon U-Pb Geochronology and Hf Isotopic Composition of the Xin′anzhai Granite along the Ailaoshan Tectonic Zone in West Yunnan Province

作　　者：刘汇川[1,2] 王岳军[1] 蔡永丰[1,2] 马莉燕[1,2] 邢晓婉[1,2] 范蔚茗[1] 

机构地区：[1]中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640 [2]中国科学院大学,北京100049

出　　处：《大地构造与成矿学》2013年第1期87-98,共12页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(批准号:40825009;41190073和40830319);中国科学院135项目(编号:GIGCAS-135-Y234151001)联合资助

摘　　要：对采自云南元阳新安寨花岗岩体东、西两侧的高钾过铝质黑云母二长花岗岩中的锆石进行了LA-ICP-MSU-Pb年龄测试,分别得到了251.9±1.4Ma和251.2±1.4Ma的206Pb/238U加权平均年龄,说明新安寨花岗岩并非原先认为的形成于燕山期或者晚三叠世,而是晚二叠世-早三叠世的产物。样品的锆石εHf(t)分别介于-9.8～-6.2和-11.1～-3.1间,平均为-7.6和-6.9,其二阶段模式年龄tDM2分别为1.67～1.90Ga和1.47～2.00Ga,平均为1.76Ga和1.72Ga,推测源岩可能是元古宙哀牢山群变质杂砂岩。结合前人研究成果,认为新安寨花岗岩体形成于岛弧向陆陆碰撞转换或者同碰撞的构造环境,指示了哀牢山带的古特提斯支洋盆或弧后盆地在二叠纪和三叠纪之交(251.6Ma)可能已经基本闭合。A set of zircon U-Pb geochronogical and in-stiu Hf isotopic data was presented for the Xin＇anzhai granite along the Ailaoshan tectonic zone in west Yunnan province. Our dating results show that zircon grains separated from the two samples （lOHH-43B and 10HH--45B） from the Xin＇anzhai granite yield weighted mean ^206pb/^238U ages of 251.9 - 1.4 Ma and 251.2 - 1.4 Ma, respectively, which are interpreted as the crystallization age of the Xin＇anzhai pluton. This indicates that the Xin＇anzhai pluton emplaced at P-T boundary rather than during the Yan- shanian period or late Triassic previously perceived of. Their ear（t） values range from -9.8 - -6.2 for 10HH- 43B and - 11.1 - -3.1 for 10HH-45B with mean values of -7.6 and -6.9, respectively. The corresponding two-stage Hf model ages range from 1.67 - 1.90 Ga and 1.47 N 2.00 Ga. These data together with other observa- tions indicate that the Xin＇anzhai peraluminous biotite monzonitic granite originated from the metagreywacke in the Proterozoic Ailaoshan metamorphic complex and formed in the syn-collisional setting in response to the assemblage of the Yangtze with Simao-Indochina Blocks.

关 键 词：红河-哀牢山构造带 同碰撞花岗岩 新安寨花岗岩体 锆石U—Pb年代学 HF同位素 

分 类 号：P597[天文地球—地球化学]