新疆东天山磁海铁矿区侵入岩年龄及其对矿床形成时代的制约

Geochronology of intrusive rocks and their constraint on formation age of Cihai iron deposit, Eastern Tianshan Mountains, Xinjiang

新疆东天山是中国重要铁铜多金属成矿带之一，磁海大型铁矿床位于该成矿带南缘的北山裂谷带内。铁矿体赋存于早期辉绿岩和矽卡岩中，呈透镜状、脉状近平行排列，后期辉绿岩脉穿切早期辉绿岩和矿体。在野外地质调查的基础上，文章对早期辉绿岩和成矿期后辉绿岩脉进行了年代学研究。锆石LAMC-ICPMSU—Pb测年结果表明，赋矿辉绿岩的形成时代为（286．5±1.8）Ma和（284．8±1．3）／Via，辉绿岩脉形成于（275．8±2．2）Ma，由此限定磁海铁矿床的形成年龄在286--275Ma，属于早二叠世成矿。结合区域岩浆和构造活动研究成果认为，磁海铁矿床成矿作用与东天山地区早二叠世大规模镁铁质一超镁铁质岩浆作用密切相关，形成于碰撞后伸展构造环境中。

The eastern Tianshan metallogenic belt is one of the most important iron-copper polymetallic belts in China, and the large-size Cihai iron deposit is hosted in Beishan rift of the southern part of the eastern Tianshan metallogenic belt. The direct wall rocks of iron orebodies are diabase and skarn, and the major iron orebodies are banded and nearly parallel in form. The iron orebodies are hosted in the early diabase and skarn, and there are some diabase veins cutting through the early formed iron orebodies and diabase. The diabase as host rock of iron orebodies and the diabase veins formed after the ore deposit were chosen as the study objects. The LA-MC-ICP MS zircon U-Pb dating of these two samples yielded ages of（286.5±1.8） Ma and （284.8 ±1.3） Ma for ore-hosting diabase while the diabase vein cutting through the former diabase and iron orebodies gave an age of （275.8 ± 2.2）, indicating that the ore-forming age of the Cihai deposit is between 286 and 275 Ma in Early Permian. It is held that the mineralization of the Cihai iron ore deposit was closely related to the massive mafic-ultramafic magmatism of eastern Tianshan region in the Early Permian and occurred in a post-collisional extensional tectonic environment.