青海东昆仑埃达克岩的构造环境及成矿意义

Tectonic Environment of Adakite in Eastern Kunlun Area,Qinghai,and Its Ore-Forming Significance

东昆仑地区沿昆中深大断裂分布的一些晚三叠世火山岩和花岗岩,具有高Al2O3、Sr、Sr/Y、(La/Yb)N和低Y、Yb含量,弱负至正Eu异常,表现出与埃达克岩(Adakite)相似的地球化学特征,与岩浆混合作用形成的花岗岩(简称浆混杂岩体)时空伴生,其稀土、微量元素特征和同位素组成与底侵作用形成的基性岩有亲缘性。研究表明:东昆仑地区的埃达克质花岗岩和火山岩不是由俯冲的洋壳熔融形成,而是由晚三叠世幔源岩浆的底侵作用形成,该埃达克质火成岩的物质来源与底侵作用形成的基性岩相似,都为富集地幔Ⅱ。埃达克质岩的发现标志着昆中深大断裂向东延入鄂拉山构造带的南端,揭示了昆中深大断裂独特的动力学背景及成矿意义。在埃达克(质)岩的发育地段,多形成了东昆仑最具魅力的矿产集中区,进一步分析初步认为其中的赛什塘铜矿与埃达克质岩及其共生岩石成矿关系密切,有明显斑岩矿床特点,具进一步找矿潜力。

Some late Triassic volcanic rock and granite distributed along the deep fault in the central section of eastern Kunlun area, is characterized by high Al2O3, Sr, Sr/Y, （La/Yb）N and low Y and Yb, with weak negative-postive Eu anmolies, all of which are similar to those of adakite. They also coexist with granite formed by mixing with magma spatially and temporally, and their rare element and trace elements, and isotopic composition indicate a genetic relationship to basic rocks resulted from diapirism. Study shows that the adakitic granite and volcanic rock in the eastern Kunlun area were not formed by melted oceanic crust during subduction but the late Triassic mantle-derived magma through the diapirism. Material source of the adikitic volcanic rock is similar to that of the basic rock, all coming from the enriched mantle Ⅱ. The finding of the adikitic rock marks that the deep fault in the central Kunlun area extends eastward to the southern end of the Elashan Mountain tectonic belt, revealing its unique geodynamic setting and oreforming significance. The sections where the adikitic rock is distributed set up a mineral-intensive area. The further analysis believes that the Saishentang Cu deposit with porphyritic feature is closely related to the cogenetic adikitic rock, and of a great potential for further exploration.