【摘要】 黑云母是花岗岩中常见的造岩矿物,其化学成分可以用于判断岩体形成时的物理化学条件、岩石成因类型及构造环境。本文利用电子探针（EMPA）对武当隆起西段牌楼花岗岩中的黑云母进行了成分分析,结果发现这些黑云母Al^Ⅵ原子数较低（0.128～0.395）,而Ti原子数适中（0.236～0.267）,属于铁叶云母,并且均具富Fe贫Mg的特征,Fe²⁺/(Fe²⁺+Mg)值为0.985～0.989。岩相学观察和化学成分分析结果显示,牌楼二长花岗岩中的黑云母为岩浆成因,结晶温度为640～710℃,寄主岩体的固结压力为0.9～1.7 GPa,log f_O2变化于-18.1～-17.4之间,指示其形成于低氧逸度环境中。岩浆的氧逸度较低可能是导致牌楼岩体不能形成Cu、Au和Mo矿化的决定因素,而缺乏Sn矿化可能与熔体温度较低有关。综合黑云母化学成分和岩石地球化学特征,认为牌楼似斑状二长花岗岩为A型花岗岩,侵位于非造山的伸展构造背景。更多还原

【Abstract】 Biotite is an important rock-forming mineral in most of granites,and its mineral chemistry can reveal the crystallization conditions,petrogenesis and tectonic setting in the magma system.In this study,the authors utilized electron microprobe analysis（EMPA）to determine the mineral composition of biotite grains hosted in the Pailou granite.The EMPA data show that the biotite is poor in Al^Ⅵ（0.128 to 0.395）atomic number and moderate in Ti（0.236 to 0.267）atomic number,and shows siderophyllite affinity.In addition,the biotite is rich in iron and poor in magnesium,with Fe²⁺/(Fe²⁺+Mg)values from 0.985 to 0.989.Petrography and mineral chemistry indicate that the biotite grains are of magmatic origin.Based on calculation of the EMPA data,the crystallization temperature and pressure of biotite are 640～710℃ and 0.9～1.7 GPa,respectively.Besides,it was formed under the condition of low oxygen fugacity,with the log f_O2values from -18.1 to -17.4.The low oxygen fugacity of magmas can explain the lack of Cu,Au and Mo mineralization,whereas the lack of Sn mineralization may be attributed to the low temperature of magmas.Combined with the study of mineral chemistry of biotite and geochemical features of hosted rocks,the authors hold that the Pailou monzogranite is of A-type and was formed in the nonorogenic tectonic setting.更多还原