东天山土屋-延东斑岩铜矿围岩的同位素年代和地球化学研究

Geochronological and geochemical study on the wallrock of Tuwu-Yandong porphyry copper deposits,eastern Tianshan mountains.

东天山土屋-延东大型斑岩铜矿的成岩成矿时代及其构造背景还存在很大争议。本文报道了铜矿远矿围岩—企鹅山群的同位素年代和地球化学研究结果。研究表明,企鹅山群安山岩中锆石 SHRIMP U-Pb 谐和年龄值336.5±6.6Ma,玄武岩的透辉石、斜长石和全岩 Sm-Nd 内部等时线年龄值334±36Ma,两个结果一致地表明企鹅山群形成于早石炭世。元素地球化学研究表明,企鹅山群玄武岩样品属于岛弧拉斑玄武岩系列,其稀土元素配分模式显示轻稀土相对富集,重稀土相对亏损的右倾模式,与洋中脊玄武岩相比,具有大离子亲石元素相对富集、高场强元素相对亏损的特征,具有俯冲带岛弧火山岩的典型特征。构造环境判别图解也指示企鹅山群形成于俯冲带环境。本研究对土屋-延东大型斑岩铜矿的成岩成矿作用时代及其构造背景问题提供了重要制约。

This paper reports the isotopic age of Qi＇eshan Group, the wallrock of Tuwu-Yandong porphyry copper deposits in eastern Tianshan mountains. The analyses by SHRIMP shows that the zircon crystals separated from the andesite within Qi＇eshan Group have the concordant U-Pb age of 336.5 - 6.6 Ma, and the Sm-Nd isochronic age of the basalt and its constituent minerals, diopside and plagioclase, collected from the same group is 334 -36 Ma. These results conformably demonstrate that Qi＇eshan Group was formed in early Carboniferous epoch. The basahs of Qi＇eshan Group are of island arc tholeiite series, and are characterized by moderate enrichment of the LREE relative to the HREE. They all show significant enrichment of large ion lithophile elements and relative depletion in high strength field elements relative to N-MORB, indicating that Qi＇eshan Group was formed at a subduction zone setting, in accordance with the tectonic discrimination diagram. The geochronological determination of Qi＇eshan Group provides important constraints for the petrogenetic and metallogenic age of the deposits and its tectonic setting, which were much controversial issues before.