班公湖-怒江成矿带西段阿翁错地区早白垩世花岗闪长岩的成因及构造背景--来自斜长石和黑云母化学成分的约束  

Origin and Tectonic Setting of the Early Cretaceous Granodiorites in Awengcuo Area,Western Bangong Co-Nujiang Metallogenic Belt:Constraints from Mineral Chemistry of Plagioclase and Biotite

作　　者：雷传扬[1,2,3] 宋元宝 唐菊兴[2] 王波[1] 吴建亮[1] 刘文[1] 范敏[1] 张伟[1] LEI Chuanyang;SONG Yuanbao;TANG Juxing;WANG Bo;WU Jianliang;LIU Wen;FAN Min;ZHANG Wei(Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resource Key Laboratory of Sichuan Province,Sichuan Geological Survey,Chengdu 610081,Sichuan,China;MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,CAGS,Beijing 100037,China;405 Geological Team,Sichuan Bureau of Geology and Mineral Resources,Dujiangyan 611830,Sichuan,China)

机构地区：[1]四川省地质调查院,稀有稀土战略资源评价与利用四川省重点实验室,四川成都610081 [2]自然资源部深地资源成矿作用与资源预测重点实验室,中国地质科学院矿产资源研究所,北京100037 [3]四川省地矿局四〇五地质队,四川都江堰611830

出　　处：《大地构造与成矿学》2023年第1期193-213,共21页Geotectonica et Metallogenia

基　　金：国家重点研发计划项目(2022YFC2905001);国家自然科学基金项目(42230813、42272093);中国地质科学院矿产资源研究所基本科研业务费(KJ2102、KK2116、KK2017);中国地质调查局项目(DD20221684)联合资助。

摘　　要：阿翁错地区早白垩世花岗闪长岩位于班公湖-怒江成矿带西段,广泛发育暗色微粒包体,是研究岩浆混合作用的理想对象。本文从地质学、岩相学和矿物化学等方面对花岗闪长岩开展了详细研究。包体形态多样,与寄主岩呈渐变或截然型接触关系,包体与寄主岩之间相互穿插,接触带发育冷凝边,包体从寄主岩中捕获了大量捕虏晶矿物,包体和寄主岩中均见针状磷灰石。电子探针结果显示:具正环带特征的寄主岩斜长石An值变化范围不大,在48.16~59.05之间,具致密韵律环带特征,可能代表镁铁质岩浆注入长英质岩浆房前结晶的斜长石;具反环带特征斜长石的An值变化范围较大,核部An值为29.86,往外An值陡增至51.09,整体呈逐渐增大趋势,暗示存在富钙基性岩浆的加入;具正-反环带特征的寄主岩斜长石核部至中间区域An值变化相对复杂,具稀疏韵律环带结构特征,反映斜长石结晶过程中因岩浆混合作用岩浆房环境发生突变,随着混合作用持续进行,岩浆逐渐冷却,斜长石在静态环境下继续结晶形成干净的正环带边部;包体斜长石虽然存在正环带,但其An值变化范围较大,在28.63~62.40之间,核部An值高,边部An值骤然降低,可能是镁铁质岩浆与长英质岩浆混合的结果;具反环带和正-反环带特征的包体斜长石核部遭受了弱的熔融作用,但An值变化范围相对较小,具致密韵律环带特征,核部熔蚀作用可能是镁铁质岩浆上升过程中压力快速降低引起的,形成于静态岩浆房环境。寄主岩黑云母和包体黑云母为原生岩浆黑云母,二者的Al^(Ⅵ)值分别为0~0.16 apfu和0~0.04 apfu,氧化系数分别为0.11~0.63和0.16~1.66,镁质率分别为0.40~0.47和0.42~0.46,表明寄主岩和包体均为钙碱性Ⅰ型花岗岩,具壳幔混源成因,其形成与岛弧的俯冲消减作用有关。结合区域构造背景,本文认为阿翁错地区早白垩世花岗闪长岩形成于狮泉河-�Located at the western part of the Bangong Co-Nujiang metallogenic belt,the Early Cretaceous granodiorites from the Awengcuo area are characterized by the widely developed mafic microgranular enclaves(MMEs)and obvious magma mixing.Plagioclase and biotite,as the main rock-forming minerals,record the material composition and physicochemical conditions of the magmatic system,which are ideal objects for studying the petrogenesis,magmatic evolution and tectonic setting.This paper focuses on the granodiorites(host rock)and MMEs from the aspects of geology,petrography and mineral chemistry.The MMEs are in various shapes and have sharp or transitional contact boundaries with the host rocks.The enclaves often contain back vein.The MMEs and host rocks are commonly interpenetrated with each other,and chilled borders with width of 1-2 mm on the enclaves’side can be observed occasionally.Many phenocrysts in the enclaves are captured from the host rocks,and acicular apatite formed by quenching is found in both the MMEs and host rocks.The above characteristics suggest that the MMEs are the products of magma mixing and mingling,and material interchanges are common.The results show that the plagioclases in the host rocks have intensive oscillatory normal zoning features with narrow An value range of 48.16 to 59.05,which may represent the plagioclase crystallized before the injection of mafic magma.The An values of the plagioclase with normal zoning features vary widely,with a core An value of 29.86 and a sudden increase to 51.09 outward,showing an overall gradual increase,indicating the addition of calcium-rich magma.Plagioclases of the host rocks show normal and reverse zoning features,with relatively complex core to mantle variations of An values and wide oscillatory zonation.Formation of the wide core to mantle oscillatory zonation of the plagioclase may due to the abrupt changes triggered by magma mixing.With the continuous mixing and gradual cooling of the magma,the plagioclase continued to crystallize in the static enviro

关 键 词：岩相学 矿物化学 岩石成因 构造背景 阿翁错花岗闪长岩 狮泉河-纳木错特提斯洋 青藏高原中北部 

分 类 号：P581[天文地球—岩石学] P575[天文地球—地质学]