摘要
西藏曲水碰撞花岗岩地处冈底斯构造-岩浆带中部,呈东西向平行雅鲁藏布缝合带分布。该岩体以花岗闪长岩、石英闪长岩为主,其次为石英二长闪长岩。岩体内普遍发育微粒镁铁质包体。对花岗闪长岩、石英闪长岩及微粒镁铁质包体的成因矿物学研究结果显示:(1)斜长石发育环带且边缘和核部偏基性,幔部酸性;(2)斜长石斑晶边缘常含有角闪石、黑云母等暗色矿物包体;(3)钾长石X射线结构分析显示自核部向边缘温度呈现逐渐升高的特点;(4)长石矿物中普遍含有较高的Cr、Ni、Co元素,明显不同于壳熔花岗岩;(5)角闪石、黑云母矿物MgO含量高于典型壳熔花岗岩;(6)包体中发育针状磷灰石和角闪石,显示为岩浆淬冷的结果。上述特征不可能用正常岩浆分异作用来解释,而更可能是壳-幔岩浆混合作用的结果。采用矿物温压计所得到的结果也符合混合后的岩浆演化特征。
The Qushui collisional granitoids in Tibet is located in the middle part of the southern Gangdis Mts. , extending west to east parallel to the Yarlung Zangbo Suture. The granitoids mainly consist of mid-coarse-grained granediorite and quartz diorite with abundant mafic microgranular enclaves （MMEs）. Genetic mineralogical and petrographical studies suggest that the Qushui granodiorite and MMEs were generated by magma mixing and could not be evolved magma by FC （AFC） which is excluded by evidences as follows ： （ 1 ） Oscillatory zoning of plagioclase with basic core and rim, but felsic mantle; （2）Amphiboles and biotites as inclusions in the rim of the feldspars, but seldom in the core;（3）Temperature increased from the core to rim of K-feldspar phenocryst; （4）Relatively high content of the Cr, Ni, Co elements in feldspars than those of the crust granitoids ; （5） Contents of MgO in both amphiboles and biotites indicating their crustmantle sources;（6）Needle shape of the apatites and amphiboles in MMEs implying the process of fast cooling. Pressure and temperature estimated with mineral Geothermo-barometers further support magma mixing is the main process of the Qushui granitoids and enclaves due to different emplacement depth between the host rocks and their enclaves, but approximately the same forming temperature,
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第4期884-894,共11页
Acta Petrologica Sinica
基金
国家重点基础研究发展规划项目(2002CB412603)
国家自然科学基金项目(40073012)
中国地质调查局项目(200313000068)资助.
关键词
西藏
曲水
碰撞花岗岩
岩浆混合
成因矿物学
Collisional granitoids, Magma mixing, Genetic mineralogy, Qushui, Tibet
