中祁连西段野马南山埃达克质花岗岩的地球化学特征及成因  

Geochemical characteristics and genesis of adakite-like granites at Yema Nanshan in the western segment of the Central Qilian Mountains

作　　者：苏建平[1,2] 张新虎[3] 胡能高[4] 付国民[4] 张海峰[3] 

机构地区：[1]中国科学院寒区旱区环境与工程研究所 [2]甘肃省地质调查院,甘肃兰州730000 [3]甘肃省地质调查院 [4]长安大学地球科学与国土资源学院

出　　处：《中国地质》2004年第4期365-371,共7页Geology in China

基　　金：国家自然科学基金重大项目(90102003);中国地质调查局地质大调查项目(DK0002019)资助。

摘　　要：祁连西段野马南山一带发育大量的加里东期花岗岩,其中大部分花岗岩具有与adakite岩相似的地球化学特征,SiO2≥56%,Al2O3≥15.0%,低MgO(平均2.04%),高Sr(257～889μg/g,平均值546.42μg/g),低Y(7.1～25.3μg/g,平均16.67μg/g),Sr/Y平均为35.89μg/g,Eu无明显负异常,Sr正异常,Adakite岩石类型有石英闪长岩、石英二长闪长岩、石英二长岩、角闪花岗岩、二长花岗岩,岩石中普遍含有角闪石,属I型花岗岩,地球化学图解反映该花岗岩形成环境为板块碰撞前的岛弧型,锆石U-Pb同位素年龄为444+38/-33Ma,处在祁连造山带板块俯冲收缩阶段,因此可以推断野马南山埃达克质Adakite花岗岩是俯冲板片部分融熔和壳幔岩浆混合形成的。这一发现对于丰富中国埃达克岩的研究和对祁连造山带演化、地球动力学以及成矿作用的研究具有重大意义。Calidonian granites are widely developed in the Yema Nanshan area in the western segment of the Qilian orogenic belt. The geochemical characteristics of most of the granites are similar to those of adakites: SiO2≥56%, Al2O3≥15.0%, low MgO (average 2.04%), high Sr (257-889μg/g, average 546.42μg/g), low Y (7.1-25.3μg/g,average 16.67μg/g), average Sr/Y=5.89, no pronounced Eu anomaly and Sr positive anomaly. Adakites in this area have five rock types, quartz diorite, quartz monzodiorite, quartz monzonite, monzogrannite and hornblende granite. These rocks commonly contain hornblende, belonging to I-type granites. The geochemical diagram indicates that the granites formed in a pre-collision island-arc environment, with a zircon U-Pb age of 444±33 Ma, in a plate suduction convergence stage of the Qilian orogenic belt. Therefore, it may be inferred that adakite-like granites of Yema Nanshan formed by partial melting of the subducted slab and crust-mantle magma mixing. This discovery has enriched the study of adakite in China and has great significance for the study of the evolution, geodynamics and metallogenesis of the Qilian orogen.

关 键 词：花岗岩 地球化学特征 造山带 闪长岩 埃达克岩 PB同位素 加里东期 中国 平均 南山 

分 类 号：P588.1[天文地球—岩石学] P595[天文地球—地质学]