新疆菁布拉克含铜镍矿杂岩体形成时代与地球化学特征
Chronology and Geochemistry of Jingbulake Complex Containing Cu-Ni Mineralization, West Tianshan Mountain, NW China
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摘要: 西天山菁布拉克含铜镍矿杂岩体处于伊犁微板块南部边缘隆起活动带内.通过LA-ICP-MS获得辉石闪长岩锆石U-Pb加权平均年龄为(414.8±0.9)Ma.地球化学特征上,岩体的稀土总量总体变化较小,岩体中各样品的La/Sm值介于1.07～2.61,球粒陨石标准化配分曲线表现为平缓型到轻稀土元素低度富集型.总体上富集大离子亲石元素(Rb、Ba、Sr等),相对亏损高场强元素(Nb、Ta、Zr、Hf、Ti等),尤其明显亏损Nb、Ti和Ta.岩体εNd(t)为+3.8～+6.3,表明岩浆源区为亏损地幔.研究认为菁布拉克含矿杂岩体的形成与早古生代南天山洋向中天山板块下的俯冲作用有关,沉积物脱水产生流体交代地幔楔导致地幔部分熔融,分离结晶及微弱的同化混染作用导致成岩成矿.Abstract: The Jingbulake complex containing Cu-Ni Mineralization in west Tianshan Mountain is located in the south of Yili block.The pyroxene diorite has a LA-ICP-MS zircon U-Pb isotope age of (414.8±0.9)Ma.The contents of REE has little change in all rocks,which have flat chondrite-normalized rare element or slight LREE enrichment pattern and that of La/Sm(1.07-2.62) and Mg#(0.59-0.85).They are enriched in large ion lithophile elements,such as Cs,Ba,Sr,and show negative Nb-Ta 、Zr、Hf and Ti anomalies on mantle-normalized trace element diagrams.They have positive εNd values(+3.8-+6.3),which indicated a depleted mantle source.The genesis of the Jingbulake complex suggests subduction of the South Tianshan oceanic lithosphere beneath the YIli-Central Tianshan block.The subduction-related fluids triggered the melting of the mantle.The genesis of the rocks and mineralization caused by magmatic differentiation and slight crustal contamination.
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