东昆仑埃坑德勒斯特二长花岗岩岩石地球化学特征及岩石成因
Geochemistry and Genesis of Monzonitic Granite from Aikengdelesite Area in East Kunlun, Qinghai
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摘要: 埃坑德勒斯特铜（钼）矿是近年来在东昆仑地区发现的斑岩型铜（钼）矿，矿区位于东昆南复合拼贴带内，花岗斑岩及外围碎裂的二长花岗岩是主要的赋矿围岩。对二长花岗岩进行了岩石地球化学和Sr-Nd同位素研究，讨论了岩浆来源、岩石成因和构造背景。研究表明，岩石富硅，相对富钠贫钙和镁，属钙碱性过铝质系列岩石。岩石明显富集大离子亲石元素（K、Ba、Rb）和活泼的不相容元素（如Th、U），相对亏损高场强元素（Nb、Ta、P、Ti）。样品的ISr值为0.707 05~0.707 37，εNd（t）为-2.2~-1.6，Rb/Sr为0.17~0.32，反映岩浆来源具壳幔混合特点。根据Y+Nb-Rb、La/Nb-Ba/Nb等判别图解及与俯冲有关的蛇绿岩带发育特征，表明该岩体形成于安第斯型活动大陆边缘环境。俯冲作用导致俯冲板片的流体降低熔点和直接交代地幔，使地幔部分熔融形成基性岩浆。幔源岩浆底侵作用提供热能，使基性下地壳物质部分熔融形成花岗质岩浆，其中混入了少量幔源岩浆。Abstract: The Aikengdelesite Cu-Mo deposit is a newly discovered porphyry deposit in the southern compound margin of East Kunlun.The ore bodies are found in granite porphyry and broken monzonitic granite.Based on the studies of geochemistry and Sr-Nd isotope, this paper mainly discusses the petrogenesis, magma source, tectonic setting of the monzonitic granite.The results show that the monzonitic granite is characterized by high SiO2and Na2O, low MgO and CaO contents, belonging to calc-alkaline and peraluminous series groups.The trace elements show the enrichment in LILE (such as K, Ba and Rb)and mobile incompatible elements (such as Th, U), but they are relatively depleted in HFSE (such as Nb, Ta, P, Ti).The results of ISr ratios range from 0.707 05 to 0.707 37, and εNd(t)values vary from -2.2 to -1.6, as well as Rb/Sr ratios from 0.17 to 0.32, indicating that the monzonitic granite was derived with crust-mantle mixed magma.After analyzing the Y+Nb-Rb and La/Nb-Ba/Nbdiagrams, and the Ophiolite belt occurred with ocean subduction, it is suggested that the monzonitic granite was formed in Andean-type active continental margin.Subduction leaded to the subducting slab fluids lower the melting point and directly replace mantle, and then the mantle occur the partial melting to form the basic magma.The basic magma underplated and provided thermo-power.The Aikengdelesite monzonitic granite was finally formed by the partial melting of basic lower crust, which was mixed a small amount of mantle-derived magma.
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Key words:
- geochemistry /
- Sr-Nd isotopes /
- monzonitic granite /
- Aikengdelesite /
- East Kunlun
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