中祁连西段盐池湾地区大青沟杂岩体中侵入岩与火山岩的岩石成因关系研究  

The connection of volcanic-plutonic rocks of the Daqinggou complex pluton in the central Qilian belt,NW China

作　　者：刘柯 王超[1] 张吉衡 李雪 孙晓奎 郝江波 喻遵谱 Liu Ke;Wang Chao;Zhang Jiheng;Li Xue;Sun Xiaokui;Hao Jiangbo;Yu Zunpu(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an 710069;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049)

机构地区：[1]西北大学地质学系,大陆动力学国家重点实验室,西安710069 [2]中国科学院大学地球与行星科学学院,北京100049

出　　处：《地质科学》2024年第4期870-888,共19页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金项目(编号:42272054,42030307);科技部大陆动力学国家重点实验室课题项目资助。

摘　　要：研究大型硅质岩浆体系中的侵入岩与火山岩之间的成因关系对揭示岩浆动力学过程以及大陆地壳的成分演化具有重要意义。中祁连西段盐池湾地区的大青沟火山-侵入杂岩体为理解侵入岩与火山岩之间的成因联系提供了一个新窗口。本文以大青沟火山岩及其下伏的侵入岩作为研究对象,通过野外地质、岩石地球化学、锆石U‐Pb定年、锆石Hf同位素及锆石微量元素分析,获得大青沟火山-侵入杂岩体中的流纹岩、二长花岗岩和花岗闪长岩的形成时代分别为456±2 Ma、454±3 Ma和455±4 Ma,三者具有一致的形成时代。锆石Hf同位素组成相对一致,ε_(Hf)(t)值为-5.2~+0.3。地球化学分析结果表明,大青沟火山-侵入杂岩具有高硅、富K的特征,富集大离子亲石元素、亏损高场强元素,具有明显的Eu负异常。研究表明,三者可能来源于同一岩浆储库,是岩浆房晶体-熔体持续分离的产物。流纹岩与二长花岗岩分异程度较高,流纹岩是先存晶粥活化、分异而喷出地表的产物,而二长花岗岩是岩浆分异后未喷发而侵入地下的产物;花岗闪长岩分异程度较低,代表了晶粥的产物。Investigating the genetic relationship between intrusive and volcanic rocks in large silicic magma systems can provide insights in revealing magma dynamics processes and the compositional evolution of continental crust.The Daqinggou intrusive‐volcanic complex from the Yanchiwan area in the central Qilian belt provides a best opportunity for the genesis of intrusive rocks and volcanic rocks.This paper focuses on the Daqinggou volcanic rocks and related intrusive rocks.Field geology,geochemical,zircon U‐Pb dating,zircon Hf isotope combined with zircon trace element analysis indicate the formation ages of rhyolite,monzogranite and granodiorite in the Daqinggou volcanic‐intrusive complex were 456±2 Ma,454±3 Ma and 455±4 Ma,respectively.These intrusive and volcanic rocks share similar zircon Hf isotopic composition with theε_(Hf)(t)value ranging from-5.2 to 0.3.Geochemical analyses indicate that the Daqinggou intrusive‐volcanic complex is enriched in Si and K,and it exhibits enrichment in LILE sand depletion in HFSE as well as pronounced Eu‐negative anomalies.Integrated analyses suggest these three types of intrusive‐volcanic rocks are derived from the same magma reservoir and formed by continuous crystal‐melt crystal fractionation in the magma chamber.The rhyolite is the product of the activation and fractionation of pre‐existing crystal mush,while the monzogranite is the intrusive fractioned magmas without eruption and the granodiorite represents the product of crystal mush with low degree of fractionation.

关 键 词：大青沟杂岩体 火山-侵入杂岩 晶粥模型 结晶分异 岩浆补给 

分 类 号：P588.14[天文地球—岩石学]