滇西香格里拉阿热岩体岩相学与矿物化学特征及意义  

Petrography, Mineral Chemistry and Implications of the A're Porphyry of Shangri-La, Western Yunnan

作　　者：董毅[1] 刘显凡[1] 邓江红[1] 任科法[1] 李春辉[1] 赵甫峰[1] 

机构地区：[1]成都理工大学地球科学学院,成都610059

出　　处：《地质学报》2013年第4期498-514,共17页Acta Geologica Sinica

基　　金：中国地调局地调项目(编号212011120587);国家公益性行业科研专项项目--系统矿物学研究(编号:201011005-5);矿物学岩石学矿床学国家重点(培育)学科建设项目(编号SZD0407)共同资助的成果

摘　　要：阿热岩体呈NNE方向展布于义敦岛弧带中甸弧南端,与相邻格咱断裂方向一致。岩体主要发育有角闪闪长玢岩、辉石闪长玢岩、含辉石角闪闪长玢岩及石英闪长玢岩。本文根据岩体内斑晶分布特征,选择角闪闪长玢岩、辉石闪长玢岩及含辉石角闪闪长玢岩及其析离体中的角闪石和单斜辉石进行岩相学及矿物化学研究。其结果显示岩体中角闪石及单斜辉石均分为高Mg#及低Mg#两类,角闪石及辉石均发育与岩浆混合作用相关的不平衡结构,存在同源异相岩浆混合作用,分异结晶作用不明显;成岩岩浆与三叠纪俯冲的甘孜-理塘洋壳板片有关,俯冲过程中板片脱水形成的流体及部分熔融形成的熔体与地幔楔交代是其岩浆形成的重要机制,其岩浆过程主要受构造应力控制,由不富水或局部富水岩浆向富水岩浆演化,具高MgO及SiO2/Al2O3向低MgO及SiO2/Al2O3演化的特点;角闪石温度压力估算结果显示先形成的低Mg#角闪石结晶压力远大于高Mg#角闪石。根据岩浆侵位的构造、压力环境及其动力学背景,我们认为甘孜-理塘洋壳向西俯冲过程中由于中咱地块西侧的羌塘地块于中三叠时期(～230Ma)开始向东挤压碰撞,在此过程中洋壳板片可能发生断离,导致该区背景构造挤压应力在228～219Ma期间先增大后变小。The A're porphyry is located at the north end of the Zhongdian Arc, which is consistent with the direction of the Geza Fault (NNE). It is composed mainly of amphibole diorite porphyry, clinopyroxene diorite porphyry, clinopyroxene amphibole diorite porphyry and qaurtz diorite porphyry. According to the distribution features of phenocrysts in the A're porphyry, we studied the petrography and mineral chemistry of the amphibole diorite porphyry, clinopyroxene diorite porphyry, clinopyroxene amphibole diorite porphyry and the schlieren. The results show that both amphibole and clinopyroxene can be divided into two types: high Mg# and low Mg#. The disequilibrium textures related to magmatic mixing are found to occur in amphibole and pyroxene, suggesting mixing of homologous heterogeneous magma (without obvious crystallization fraction). Diagenetic magmas might be related to the subducting Ganze-Litang ocean slab of Late Triassic. Metasomatism of fluid derived from dehydration due to plate subduction and melt from partial melting with the mantle wedge is the important mechanism for formation of magma. The magma process was controlled by tectonic stress and magma was changing from poor in water or local water to water rich magmas, characterized by high MgO and SiO2/Al2O3 ratio to the low MgO and SiO2/Al2O3. The results from estimation of amphibole geothermobarometry exhibits low Mg #amphiboles formed at much higher pressure than high Mg# amphibole did. Based on the structure, stress and dynamic backgrounds of magma emplacement, it can be concluded that during the westward subduction of the Ganze-Litang Ocean slab, the ocean slab might break-off due to eastward extrusion of the Qiangtang Block to the south of the Zongzai Block in ~230Ma, and thus the tectonic stress in the research area decreased after short increasing during 228~219Ma.

关 键 词：滇西阿热岩体 岩相学 矿物化学 地质温压计 构造背景 

分 类 号：P586[天文地球—岩石学] P57[天文地球—地质学]