青海沱沱河地区赛多浦岗日二长花岗岩中黑云母化学成分特征及地质意义

Chemical composition and geological significance of biotites from monzonitic granite in Tuotuohe Saiduopugangri area in Qinghai

电子探针分析结果表明,沱沱河地区赛多浦岗日二长花岗岩中黑云母具有富MgO、SiO_2、(Na_2O+K_2O),相对贫Al_2O_3、FeO^t的特征;镁质率(M=0.60~0.65)高,∑Al值(1.30~1.39)偏低,中等Fe/(Mg+Fe)(0.42~0.44)比值,为镁质黑云母;估算其结晶温度为580℃~645℃,且岩浆体系具有较高的氧逸度。黑云母的成分特征显示其寄主岩体为造山背景下形成的钙碱性花岗岩,其源区具有壳-幔混源的特征。

Electron microprobe analyses（ EMPA） demonstrate that biotites from the Saiduopugangri monzonitic granite in Tuotuohe area,Qinghai Province,are enriched in MgO,SiO_2,（Na_2O ＋ K_2O）,but relatively depleted in Al_2O_3 and FeO^t,with the characteristics of high M（0. 60 ~ 0. 65）,low ∑Al（1. 30 ~ 1. 39） and medium Fe/（Mg ＋ Fe）（0. 42 ~ 0. 44）,suggesting that they are Mg-biotites. The biotites crystallized at the temperature of580℃ to 645℃ with high oxygen fugacity in the magmatic system. The compositions of biotites revel that the calcalkaline granite formed in the orogenic background and the magma was from crust-mantle mixed source.