拉萨地块西北部阿翁错复式岩体岩浆混合作用:岩相学和矿物学约束  

Magma mixing and mingling in Awengcuo composite pluton in the northwesternpart of the Lhasa Block:Constraints from petrography and mineral chemistry

作　　者：雷传扬 杨宗耀 唐菊兴[2] 文辉 王静 杨显华 罗海金 LEI ChuanYang;YANG ZongYao;TANG JuXing;WEN Hui;WANG Jing;YANG XianHua;LUO HaiJin(Sichuan Geological Big Data Center,Chengdu 610072,China;Institute of Mineral Resources,CAGS,MNR Key Laboratory of Metallogeny and Mineral Assessment,Beijing 100037,China)

机构地区：[1]四川省地质大数据中心,成都610072 [2]自然资源部成矿作用与矿产评价重点实验室,中国地质科学院矿产资源研究所,北京100037

出　　处：《岩石学报》2025年第5期1606-1625,共20页Acta Petrologica Sinica

基　　金：中国地质调查局项目(DD20230054、DD20230358、DD20230286)资助详细信息。

摘　　要：阿翁错复式岩体位于班公湖-怒江成矿带西段, 复式岩体中暗色微粒包体广泛发育, 岩浆混合作用特征明显, 是开展岩浆混合作用研究的理想场所。本次研究选择复式岩体中花岗闪长岩及其中发育的暗色微粒包体为研究对象, 着重从岩相学和矿物化学等方面对其进行详细研究。包体和寄主岩中见大量不平衡结构, 如嵌晶结构、环斑结构、石英眼斑结构, 包体中见针状角闪石、磷灰石等。寄主岩斜长石普遍发育复杂的韵律环带, An值为32~65, 以中长石和拉长石为主, 少量奥长石, An值多呈振荡变化, 边部具致密韵律环带结构特征, 是结晶晚期阶段岩浆房静态环境下快速结晶的产物, 幔部区域具有稀疏韵律环带结构特征, An值为44~65, 属于岩浆混合作用的产物, 从核部→幔部→边部整体呈现出正环带→反环带→正环带或正环带→反环带→正环带→反环带→正环带的变化趋势;包体中斜长石捕虏晶形态多样, 但仍具有与寄主岩斜长石相似的形态特征, 与寄主岩斜长石的差异表现在斜长石捕虏晶An值为10~68, 整体偏低, 具清晰的核-边结构, 从核部→幔部→边部整体呈现出反环带→正环带或反环带→正环带→反环带→正环带的变化趋势;包体基质斜长石粒径明显偏小, 核部存在弱的熔蚀作用, 见少量具正环带结构的斜长石, An值为26~62, 代表镁铁质岩浆注入长英质岩浆房前结晶的斜长石, 但大多数包体基质斜长石具明显的核-边结构, 发育正-反环带, An值为32~77。与寄主岩相比, 包体基质斜长石核部An值明显偏低, 两者可能来自不同的岩浆体系。矿物温压计研究表明, 寄主岩形成于216~304MPa压力和632~718℃温度环境, 而包体形成于279~463MPa压力和722~768℃温度环境。结合区域构造背景, 认为阿翁错复式岩体与早白垩世晚期狮泉河-纳木错特提斯洋盆持续向北俯冲诱发镁铁质岩浆底The Awengcuo composite pluton is located in the western segment of the Bangong Co-Nujiang metallogenic belt. This pluton is characterized by the widespread development of dark microgranular enclaves and evident magma mixing, making it an ideal site for studying magma mixing processes. This study focuses on the granodiorite within the composite pluton and the dark microgranular enclaves it contains, and conducted detailed investigations on their petrographic and mineral chemical perspectives. Both the enclaves and the host rock exhibit numerous disequilibrium textures, such as poikilitic, rapakivi and quartz eye textures. Within the enclaves, acicular amphibole and apatite are commonly observed. Plagioclase in the host rock typically displays complex rhythmic zoning, with An values ranging from 32 to 65, predominantly composed of andesine and labradorite with minor oligoclase. The An values often show oscillatory variations, with dense rhythmic zoning at the edges, indicative of rapid crystallization in a static magma chamber during the late stages of crystallization. In contrast, the mantle regions exhibit sparse rhythmic zoning, with An values ranging from 44 to 65, suggesting they are products of magma mixing. From the core to the mantle and then to the rim, the zoning patterns generally transition from normal→reverse→normal or normal→reverse→normal→reverse→normal zoning. Plagioclase xenocrysts within the enclaves exhibit diverse morphologies but retain characteristics similar to those of the host rock plagioclase. However, they differ in their An values, which range from 10 to 68, i.e., generally lower, and display clear core-rim structures. From the core to the mantle and then to the rim, the zoning patterns typically transition from reverse→normal or reverse→normal→reverse→normal zoning. The matrix plagioclase in the enclaves is notably finer-grained, with weak corrosion observed in the cores. A small proportion of plagioclase exhibits normal zoning, with An values ranging from 26 to 62,

关 键 词：岩相学 矿物化学 岩浆混合作用 阿翁错复式岩体 狮泉河-纳木错 特提斯洋 西藏 

分 类 号：P575.1[天文地球—矿物学] P588.122[天文地球—地质学]