北秦岭翠华山-库峪一带晚中生代花岗岩黑云母地球化学特征及成因意义

北秦岭造山带晚中生代岩浆作用的成因机制复杂多样,为了探讨北秦岭造山带晚中生代岩浆成因,本文以北秦岭中段翠华山、大峪及库峪地区晚中生代二长花岗岩为研究对象,利用电子探针技术对其中的黑云母进行地球化学分析。结果显示,所采样品中的黑云母主体属于镁质黑云母,其成因类型为原生黑云母。矿物化学数据计算结果显示,翠华山、大峪及库峪二长花岗岩样品中黑云母的结晶压力均值分别为205MPa、202MPa、211MPa,结晶深度均值分别为7.8 km、7.6 km、8.0 km,结晶温度均值分别为711℃、653℃、657℃,氧逸度均值分别为-16.45、-18.40、-18.27。基于上述结果分析,揭示研究区二长花岗岩源区中仅有少量幔源物质加入,翠华山、大峪及库峪二长花岗岩具有I型花岗岩亲缘性,均属于造山带钙碱性花岗岩系。

Geochemical characteristics and genetic significance of biotites from Late Mesozoic granites in the Cuihuashan-Kuyu area, North Qinling

The genetic mechanism of the Late Mesozoic magmatism in the North Qinling orogenic belt is complex and diverse. In order to discuss the genesis of the Late Mesozoic magmatism in the North Qinling orogenic belt, this paper takes the Late Mesozoic monzogranite in Cuihuashan, Dayu and Kuyu areas in the middle part of the North Qinling as the research object, and uses the electron probe technology to make geochemical analysis of the biotite in the monzogranite. The results show that the main body of biotite in the samples belongs to magnesian biotite, and its genetic type is primary biotite. The calculated mineral chemistry data show that the average crystallization pressure of biotite in Cuihuashan, Dayu and Kuyu monzogranite samples is 205 MPa, 202 MPa and 211 MPa, the average crystallization depth is 7.8 km, 7.6 km and 8.0 km, and the average crystallization temperature is 711 ℃, 653 ℃ and 657 ℃, respectively. The mean values of oxygen fugacity were -16.45, -18.40 and -18.27, respectively. Based on the above results, it is revealed that there is only a small amount of mantle-derived material in the source area of the monzogranite in the study area, and the monzogranites in Cuihuashan, Dayu and Kuyu have I-type granite affinity, belonging to the calc-alkaline granite series of the orogenic belt.