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    中昆仑耸石山地区晚古生代花岗岩地球化学特征、成岩作用与构造环境研究

    Geochemical characteristics, rock-forming processes and tectonic setting of Late Paleozoic granites in the Songshishan area, Central Kunlun Mountains

    • 摘要: 提要:昆仑山中段耸石山地区发育晚古生代花岗岩,由石英闪长岩、英云闪长岩、花岗闪长岩和二长花岗岩等4类岩石组成。岩石低硅、低钾、贫碱、富钠,SiO2和K2O含量分别为56.42%~73.70%和1.70%~3.56%,Na2O+K2O平均6.13%,Na2O平均3.49%,K2O/Na2O比值0.51~0.99;富铝,Al2O3平均为14.90%。总体属镁质、准铝质—弱过铝质钙性—钙碱性花岗岩。Ba、U、Nb、Ta、Sr、P、Ti等表现为较明显但并不强烈的相对亏损,Rb、Th、K、La、Nd、(Zr+Hf+Sm)、(Y+Yb)等则相对富集。ΣREE平均105μg/g;轻稀土富集,(La/Yb)N值平均13.91;Eu弱亏损或无亏损,δEu值平均0.85。石英闪长岩在主要氧化物Harker图解中显著偏离演化线,且δEu值最低;二长花岗岩δEu值最高;岩石在C/MF-A/MF图解中落入不同区域;多种同分母的氧化物比值相关图中未一致显示线性相关,也未构成双曲线趋势;在La/Sm—La图解中4类花岗岩未构成分异演化趋势;花岗岩中发育岩浆混合成因镁铁质微粒包体等,说明花岗岩源岩和岩浆具多源性,岩浆形成过程中具岩浆混合作用。微量元素蛛网图特征,氧化物与微量元素构造环境判别图解以及区域构造格局等,表明花岗岩形成于岛弧环境。

       

      Abstract: Abstract:The Late Paleozoic granites occurring in the Songshishan area, Central Kunlun Mountains are composed of quartz diorite, tonalite, granodiorite and monzogranite. The rocks have low contents of SiO2 (56.42%-73.70%) and K2O (1.70%-3.56%) and are poor in alkalis with Na2O+K2O=6.13% on average and rich in sodium with Na2O=3.49% on average and K2O/Na2O= 0.51-0.99 and aluminium with Al2O3=14.90% on average. The granites as a whole are of magnesian, sub-aluminous-weakly peraluminous calc-calc-alkaline series. Ba, U, Nb, Ta, Sr, P and Ti are pronounced but not strongly depleted, while Rb, Th, K, La, Nd, (Zr+Hf+Sm) and (Y+Yb) are comparatively concentrated. ΣREE values average 105μg/g and LREE values are enriched with (La/Yb)N=13.91 on average. δEu values are weakly depleted or show no depletion, with δEu=0.85 on average. Quartz diorite is notably deviated from the evolution line in the Harker diagram of main oxides and has the lowest δEu values, monzogranite has the highest δEu values, the data points of the rocks fall in different fields of the C/MF-A/MF diagram, the oxide variation curves neither show straight lines nor form hyperbolas on the syn-denominator diagrams, the 4 types of granites do not show the trend of differentiation in the La/Sm-La diagram, and there are mafic microgranular enclaves of magma mingling origin in granites—all these suggest that the parent rocks and magma of the granites have multiple sources and that magma mixing occurred during the formation of the magma. The characteristics of the trace element spidergram, various oxide and trace element diagrams for tectonic environment discrimination and regional tectonic framework reveal that the rocks were formed in an island-arc environment.

       

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