藏南错那洞淡色花岗岩成因:来自全岩地球化学和锆石U-Pb年龄的约束  

Petrogenesis of the Cuonadong leucogranite in South Tibet:constraints from bulk-rock geochemistry and zircon U-Pb dating

作　　者：黄春梅[1,2] 李光明 张志[2] 梁维[2] 黄勇[2] 张林奎[2] 付建刚[2] HUANG Chunmei;LI Guangming;ZHANG Zhi;LIANG Wei;HUANG Yong;ZHANG Linkui;FU Jiangang(School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China;Chengdu Center of Geological Survey,China Geological Survey,Chengdu 610081,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地质调查局成都地质调查中心,四川成都610081

出　　处：《地学前缘》2018年第6期182-195,共14页Earth Science Frontiers

基　　金：国家重点研发计划项目“深地资源勘查开采”(2018YFC0604103;2016YFC0600308);中国地质调查局项目“冈底斯—喜马拉雅铜矿资源基地调查”(DD20160015)

摘　　要：藏南错那洞穹隆位于喜马拉雅造山带东部,淡色花岗岩是其核部组成部分之一.对其中的弱定向二云母花岗岩和含石榴子石二云母花岗岩进行LA-ICP-MS锆石U-Pb定年,显示其结晶年龄分别为(20.6±0.3) Ma和(16.7±0.2) Ma,属于喜马拉雅中新世淡色花岗岩.错那洞含石榴子石二云母花岗岩和弱定向二云母花岗岩均具有富硅(w(SiO2)为71.6 %~74.6%)、富铝(w(Al2O3)为14.5%~16.1%)、富钾(w(K2O)为4%~4.7%)及高铝饱和指数(A/CNK=1.16~1.22)的特征,属高钾钙碱性系列的强过铝质花岗岩,并且两类花岗岩都富集Rb、U、K、Pb,相对亏损Nb、Ta、Zr、Ti.但含石榴子石淡色花岗岩具有明显的Eu负异常(Eu/Eu*=0.29~0.46),而弱定向二云母花岗岩Eu的负异常相对较弱(Eu/Eu*=0.58~0.80).弱定向二云母花岗岩的Rb/Sr值为2.4~3.5,Ba含量为(200~253)×10-6,TiO2含量相对较低,表明错那洞弱定向二云母花岗岩是在无水条件下由变泥质岩中的白云母脱水熔融而形成,并且弱定向二云母花岗岩的产生可能与藏南拆离系(STDS)启动造成的构造减压有关.含石榴子石二云母花岗岩的K/Rb、Zr/Hf、Nb/Ta、WHo值呈现出非球粒陨石异常,稀土四分组效应和异常高的Rb/Sr值(18.6~22.2)表明错那洞含石榴子石二云母花岗岩是经过岩浆高度演化而形成的.高度演化的岩浆有利于W、Sn、Be等稀有金属成矿.错那洞含石榴子石二云母花岗岩与错那洞穹隆的W-Sn-Be矿具有相邻的空间位置,两者之间可能存在一定的成因联系;而错那洞弱定向二云母花岗岩与扎西康Pb-Zn矿床在时间上和空间上都具有一致性,两者之间很可能也存在一定的成因联系.Leucogranite is one of the mineral components of the Cuonadong dome core located in the eastern part of the Himalayan orogenic belt.LA-ICP-MS zircon U-Pb dating yielded crystallization ages of 20.6±0.3 Ma and 16.7±0.2 Ma for two-mica and garnet-bearing muscovite granites,respectively,in accordance with the Miocene Himalayan leucogranites.The characteristics of both leucogranites feature high SiO2(71.6%-74.6%),Al2O3(14.5%-16.1%),and K2O(4%-4.7%)contents with A/CNK of 1.16-1.22,suggesting the leucogranites belong to high-K calc-alkaline and strongly peraluminous granites that are enriched in Rb,U,K,and Pb and relative depleted in Nb,Ta,Zr and Ti.Garnet-bearing muscovite granites have strong negative Eu anomalies(Eu/Eu*between 0.29 and 0.46),while relatively weak negative Eu anomalies(Eu/Eu* between 0.58 and 0.80)were found in two-mica granites.Two-mica granites have Rb/Sr ratios of 2.4-3.5,Ba contents of(200-253)×10-6,and relatively low TiO2 contents,likely formed from muscovite dehydration melting of metapelites under the decompression condition caused by the movement of the STDS.Garnet-bearing muscovite granites,on the other hand,show non-chondritic anomalies in K/Rb,Zr/Hf,Nb/Ta and Y/Ho ratios,REE tetrad effects,and abnormally high Rb/Sr ratios(18.6-22.2)—all features of highly evolved granites favoring mineralization of rare metal elements such as W,Sn,Be,etc.Meanwhile,garnet-bearing muscovite granite pluton is adjacent to the W-Sn-Be ore deposits within the Cuonadong dome,raising the likelihood that the occurrence of the garnet-bearing muscovite granite might contribute to W-SnBe mineralization.Likewise,common spatiotemporal patterns are shared by two-mica granites and Zhaxikang Pb-Zn deposits,an indication that a genesis relationship may exist between the two.

关 键 词：藏南错那洞淡色花岗岩 岩石成因 高分异花岗岩 白云母脱水熔融 扎西康Pb-Zn矿床 

分 类 号：P588.121[天文地球—岩石学] P581[天文地球—地质学]