摘要
位于藏南特提斯喜马拉雅带中段的康巴穹窿,其核部出露有形成于渐新世时期的淡色花岗岩,主要造岩矿物为石英、钾长石、斜长石和白云母,常见石榴子石,偶见少量黑云母和电气石.岩相学观察表明,该花岗岩中的矿物大都形成于多个世代,各种交代结构十分发育.晶体形态和化学成分特点指示,部分锆石在富Hf流体的参与下发生了重结晶作用.全岩地球化学分析结果显示,康巴淡色花岗岩富硅(74.4 wt.%~76.6 wt.%),过铝(A/CNK=1.14~1.28),贫钙、铁、镁、钛,具有高FeO*/MgO和(K2O+Na2O)/CaO比值以及高岩石分异指数(D.I.>93),微量元素组成表现出不受价态和离子半径约束的地球化学行为特点.上述特征表明,康巴淡色花岗岩是经历了强烈结晶分异作用的高演化岩浆结晶而成,并在成岩过程中发生过强烈的热液出溶.根据岩石的Sr-Nd-Hf同位素的组成特点可以推断,在热液流体作用过程中该岩浆体系的各同位素发生过不同程度的迁移,特别是Sr同位素组成,还明显受到来自围岩的混染.
The Kampa dome is located in the middle section of the Tethyan Himalaya belt,with a Oligocene leucogranite emplacement in its core.This leucogranite is mainly composed of quartz,K-feldspar,plagioclase,muscovite,garnet,and occasionally a small amount of biotite and tourmaline.Most of the rock-forming minerals have multiple generations,and various metasomatic structures are observed in this granite.Textural characteristics and elemental compositions indicate that some zircons have dissoved and reprecipitated with participation of Hf-enriched hydrothermal fluid.The Kamba leucogranite is strongly peraluminous with A/CNK values of 1.14~1.28,and it has high content of SiO2 but low levels of CaO,TiO2,MgO,and FeO*,with elevated FeO*/MgO and(K2O+Na2O)/CaO ratios and differentiation index(D.I.).It shows non-CHARAC(Charge-And-Radius-Controlled)trace element behavior.These features together suggest that the Kamba leucogranite has experienced highly crystal fractionation and exsolved fluid phase at the latest stage.The Rb-Sr,Sm-Nd,and Lu-Hf isotopic analyses showed that these isotopes have migrated in different degrees during the hydrothermal process,especially the Sr isotope.
作者
刘志超
刘小驰
俞良军
王建刚
Liu Zhichao;Liu Xiaochi;Yu Liangjun;Wang Jian'gang(School of Earth Sciences and Engineering,Sun Yat-sen University,Guangzhou,510275,China;Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing,100029,China)
出处
《南京大学学报（自然科学版）》
CAS
CSCD
北大核心
2020年第6期800-814,共15页
Journal of Nanjing University（Natural Science）
基金
国家自然科学基金(41672055)
第二次青藏高原综合科学考察研究(2019QZKK0802)。
关键词
喜马拉雅
康巴穹窿
淡色花岗岩
高分异
热液流体
Himalaya
Kampa dome
leucogranite
highly fractionated granite
hydrothermal fluid
