摘要
后碰撞阶段花岗质岩浆的源区多较为复杂,需要从多方面开展同位素的研究来加以识别,阿拉玛斯花岗质岩体位于西昆仑造山带东段。先前的研究表明阿拉玛斯岩体是后碰撞阶段下地壳部分熔融。为进一步研究阿拉玛斯花岗岩类的源区特征,本文对阿拉玛斯花岗岩类进一步进行Pb-Hf同位素的测定。结果显示:阿拉玛斯岩体具低的锆石εHf(t)值为-9.5^-3.2(平均值为-5.6),二阶段模式年龄为1633~2028 Ma,反映了岩浆来源于较老的下地壳部分熔融。阿拉玛斯岩体的206Pb/204Pb范围为18.382~19.333,平均值为18.784,207Pb/204Pb范围为15.589~15.642,平均值为15.614,208Pb/204Pb范围为38.585~39.080,平均值为38.800,μ值范围为9.45~9.48,平均值为9.46,ω值的范围33.80~38.14,平均值为36.16。在岩体源区判别图解上,样品主要落在上地壳的范围内,反映了阿拉玛斯岩体源区具有高Pb的同位素特征,说明岩浆源区有少量高Pb物质(沉积物)的混入,从而说明后碰撞阶段形成岩体的物质来源具有多样性。
The source of granitic magma was complex in the post collision stage and needs to be further studied by using various isotope methods. The Alamas granitoids is distributed in the eastern section of the West Kunlun orogenic belt and of important significance for understanding the continental growth evolution after the closure of the Proto Tethys. Previous studies have shown that the Alamas granitoids was the product of partial melting of an ancient, deep crustal source in the post collision stage. In order to understand the source characteristic of the Alamas granitoids, Pb Hf isotopic compositions of the granitoids were analyzed. The results show that the ε-Hf（t） values range from -9.5 to -3.2 （averaging -5.6） and the two stage Hf model ages range from 1633Ma to 2028 Ma, indicating that the Alamas pluton likely sourced from the partial melting of an ancient, deep crust. The granitoids have ^206Pb/^204Pb values between 18.382 and 19.333 （averaging 18.784）,^207Pb/^204Pb values between 15.589 and 15.642 （averaging 15.614）, ^208Pb/^204Pb values between 38.585 and 39080 （averaging 38.800）, μ values from 9.45 to 9.48 （averaging 9.46）, and ω values from 33.80 to 38.14 （averaging 36.16）. In the discrimination diagram, these samples are plotted mostly in the field of the upper crust rocks, indicating that the source area of the Alamas pluton is characteristic of high Pb isotope. Therefore, addition of a minor amount of high Pb isotopic material （sediments） into magmatic source resulted in diversity of material source for formation o f the Alamas pluton in the post collision stage.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2017年第12期2667-2678,共12页
Acta Geologica Sinica
基金
中国地质科学院中央级公益性基本业务费专项基金(编号:YWF201601)
中国地质调查局国土资源大调查研究项目(编号:DD20160004
DD20160083-1
12120115000801
121201101000150014)资助成果
