西藏东喜马拉雅错那地区亚马荣淡色花岗岩的年代学、地球化学与岩石成因

摘要

本文通过对东喜马拉雅错那地区亚马荣岩体的地球化学、锆石U-Pb年代学和Hf同位素研究,试图探索亚马荣岩体的形成机制,解释地壳深熔作用过程.锆石U-Pb定年获得两期年龄,分别为14.4Ma和17Ma,结合前人已有结果,本文认为错那地区的深熔作用至少持续5 Myr时间.亚马荣岩体具有较高SiO2 (71.85％ ～72.91％)、Al2O3 (15.30％ ～ 15.67％)含量,较低的Fe2O3T(0.58％ ～0.90％)、CaO(0.72％ ～ 1.05％)含量,铝饱和指数(A/CNK)为1.08～1.22;锆石Ti温度计、εHf(t)的变化以及大离子亲石元素Rb/Sr比值和Ba含量之间的协变关系都说明,错那淡色花岗岩形成过程中存在多种熔融方式,经历了脱水熔融和水致熔融的转变,发生熔融反应的转变可能与藏南东-西向伸展构造的启动有关.%Leucogranite is very important to reveal the dynamics of deep crust.We study the geochemistry,zircon U-Pb chronology and in-suit Hf isotopes on leucogranites from Tsona area,Eastern Himalaya,explore the formation mechanism of the Yamarong leucogranites,and to further explain related problems of continental crustal anatexis.The zircon U-Pb dating displayed two ages of magmatism,14.4Ma and 17Ma respectively.Combined with the published data,the time of anatexis in Tsona area had lasted for more than 5Myr.The Yamarong leucogranites have high SiO2 (71.85％ ～ 72.91％),Al2O3 (15.30％ ～ 15.67％),but low Fe2O3T (0.58％ ～0.90％),CaO (0.72％ ～ 1.05％),with the A/CNK ratios ranging from 1.08 to 1.22.The zircon titanium thermometry,εHf(t) value and the covariant relation of Rb/Sr and Ba show that Tsona leucogranties originated from more than one melting reactions.They had experienced the change from dehydration melting to fluid fluxed melting,and the reason of this transformation may be the start of the E-W extension in Southern Tibet.