藏东察雅县察拉地区中生代花岗岩LA-ICP-MS锆石U-Pb年龄和构造环境  

LA-ICP-MS zircon U-Pb age and tectonic setting of Mesozoic granite in Chala area,Caiya County,eastern Tibet

作　　者：李彬[1,2] 向树元[2] 冯德新 罗拉次旺 噶桑顿珠 周渝 

机构地区：[1]湖南省地质调查院,湖南长沙410116 [2]中国地质大学,湖北武汉430074 [3]西藏地勘局地热地质大队,西藏拉萨851400 [4]江西省地质调查院,江西南昌330043

出　　处：《地质通报》2012年第5期696-706,共11页Geological Bulletin of China

基　　金：中国地质调查局青藏专项<西藏邦达地区1:5万地质矿产调查>(编号:1212010918028)

摘　　要：藏东察拉地区广泛发育中生代侵入岩体,沿澜沧江结合带呈带状展布,以复式岩基、岩枝和透镜体产出,侵入于早石炭世卡贡岩卡组和吉塘群变质岩系中,主要岩性有二长花岗岩、花岗闪长岩及少量闪长岩。目前该区研究程度较低,报道较少,构造意义不明确。本次在察拉地区获得4个岩体样品的LA-ICP-MS锆石U-Pb年龄数据,时代为中—晚三叠世,其中1件样品测试结果为219.8Ma±2.4Ma,代表澜沧江结合带闭合期的年龄,其余3件测试结果相近,分别为239.2Ma±1.7Ma、241.5Ma±2.3Ma和242.5 Ma±1.6Ma,为俯冲消减期的年龄。岩石地球化学特征表明,区内岩体具有从同碰撞一直到碰撞后板内花岗岩的特点,经历了从造山运动的碰撞前期至造山运动最后阶段的构造体制转变过程,总体为"后造山"构造环境,为澜沧江洋板块向东与昌都微陆块碰撞之后地壳伸展、快速隆升背景下地壳深熔的结果。There are Mesozoic intrusive rocks along the Lancang River in Chala area of eastern Tibet,which mainly occur as complex batholiths and apophyses and lenticular granite that intruded in Early Carboniferous Kagongyanka Formation and Jitang Group metamorphic rocks.The intrusive rocks are mainly composed of monzonitic granite and granodiorite with a little diorite.So far,the genesis of these rocks,including their formation age and tectonic significance,has been poorly studied.In this paper,four granite samples were used for LA-ICP-MS U-Pb dating,and the dating results show that the age of a sample is 219.8Ma±2.4Ma,and the ages of the other three samples are 239.2 Ma±1.7 Ma,241.5 Ma±2.3Ma and 242.5 Ma±1.6Ma respectively,suggesting similar formation ages in Middle-Late Triassic period.Geochemical studies indicate that these granites were formed in intraplate syncollisional to post-collisional tectonic setting which underwent the evolution from early collision to the last stage of orogeny.The environment was a tectonic regime of the transformation stage regarded as a ＂post-orogenic＂ tectonic environment which was produced by crust anatectic melting as a result of crust extension and rapid uplift after the collision between the eastward Lancangjiang plate and the Changdu micro-plate.

关 键 词：藏东 澜沧江结合带 花岗岩 LA-ICP-MS锆石U-PB年龄 构造环境 

分 类 号：P597.3[天文地球—地球化学]