东昆仑东段加鲁河中基性岩体环石英捕虏晶角闪石和黑云母矿物学特征及其对岩浆混合过程的约束

Mineralogical features of the amphiboles and biotites on the quartz xenocrysts rim of Jialuhe intermediate-basic pluton,eastern East Kunlun Orogen:constraints on the magma mixing and mingling process

加鲁河中基性岩体位于东昆仑造山带东段,岩体边部岩浆混合作用明显,富含暗色环边石英,是研究岩浆混合作用的理想地质体。本文在详细岩石学研究基础上,对寄主岩(香加南山花岗岩基)-包体-包体捕虏晶-暗色环边石英的矿物(黑云母和角闪石)进行电子探针成分分析。研究表明,不同类型黑云母的Fe^(2+)/(Fe^(2+)+Mg)比值基本一致,介于0.53~0.59,寄主岩黑云母的MgO含量较低(8.06%~8.29%),包体捕虏晶-暗色环边的黑云母MgO含量较高(分别为9.38%~9.45%和9.25%~9.52%);不同类型角闪石的(Ca+AlⅣ)较高,大于0.5,寄主岩角闪石具有较高的FeO^T含量(20.27%~21.01%)和较低Mg#值(45~47);包体-包体捕虏晶-暗色环边的角闪石具有较低的FeO^T含量(分别为18.31%~19.49%、18.11%~18.90%和18.01%~18.43%)和较高的Mg#值(分别为50~54、52~53和55~60)。寄主岩的角闪石(为铁浅闪石)和黑云母(为铁质黑云母)具壳型特征;包体-包体捕虏晶-暗色环边的角闪石(为镁角闪石)和包体-暗色环边的黑云母(为镁质黑云母)具壳幔型特征。寄主岩和包体捕虏晶的角闪石具有近似的成分和结晶环境,显示包体与寄主岩间存在成分交换。早期富水岩浆有利于磁铁矿和钛铁矿结晶,使晚期结晶的暗色环边矿物(黑云母和角闪石)具有较高的MgO含量和较低的FeO^T含量,以及最低的结晶温度和压力。

The Jialuhe intermediate-basic pluton, which is located in the eastern part of the East Kunlun Orogen, has undergone obvious magma mixing and mingling in the pluton boundary with lots of quartz xenocrysts wrapped by dark rims, and is one of the ideal geological body for studying the magma mixing and mingling. Based on detailed petrological study, the paper has analyzed the chemical composition of mineral from the host rock （Xiangjiananshan granitic batholith）-mafic microgranular enclaves （MMEs）-xenocrysts in MMEs-dark rims （biotite and amphibole） around quartz xenocrysts by means of electron microprobe analyses. The results show that the biotites have stable Fe2＋/（Fe2＋ ＋Mg） ratios ranging from 0. 53 to 0. 59. They have low MgO contents （8. 06%- 8.29%） in host rocks, but have high MgO contents in the xenocrysts and dark rims around quartz xenocrysts （9. 38%- 9. 45% and 9. 25%- 9. 52%, respectively）. The amphiboles have high Ca＋A1Ⅳ contents （〉0. 5）. The amphiboles in host rock have high FeOr contents （20. 27%- 21.01%） and low Mg# ratios （45 - 47）. The amphiboles in the MMEs, the xenocrysts in MMEs and the dark rims around quartz xenocrysts consistently have low FeOr contents （18. 31%- 19. 49%, 18. 11~/00- 18. 90% and 18. 01%-18. 43%, respectively）, and high Mg# ratios （50- 54, 52 - 53 and 55 - 60, respectively）. The amphiboles （irony amphiboles） and biotites （irony biotites） in host rocks have crust-type features. The amphiboles （magnesian amphiboles） in MMEs, xenocrysts in the MMEs and the dark rims around quartz xenocrysts have the features of crust-mantle mixture type, so as the biotites （magnesian biotites） in MMEs and the dark rims around quartz xenoerysts. The amphiboles in host rocks have the similar component and crystallization environments as the amphiboles in the xenocrysts of the MMEs, which shows that there were component exchanges between host rock and the MMEs. The water-rich magma avails the magnetite and ilmenite to crystallize in the early stage, which made the dark rim minerals （biotite and amphibole） have higher MgO contents, low FeOT contents and the lowest crystallization temperature and pressure.