甘肃北山红柳沟铜镍矿化基性-超基性岩体SHRIMP锆石U-Pb年龄及其地质意义

摘要

The Hongliugou copper-nickel mineralized mafic-ultramafic rock is located in the Beishan rift belt on the northern mar-gin of the Tarim plate. There are two regional deep fracture zones in the rock on both sides, i.e., Dashantou-Gangliunaozi and Fang-shankou-Miaomiaojing-Shuangyingshan. Rock mass was emplaced in the the Dunhuang rock group, copper-nickel mineralization usually occurs in lherzolite, whereas olivine two-pyroxene monzonite and olivine norite-gabbro. SHRIMP U-Pb dating of zircon from the olivine hornblende gabbro norite yielded an age of (396.7±3.8) Ma, which suggests that both the intrusion of the ore-bear-ing complex and the mineralization occurred in middle Devonian. Combined with the age of Heishan and Guaishishan copper-nick-el ore-bearing rock, it is revealed that Beishan area of Gansu was in a continental margin rift extensional environment in the mid-dle-Late Devonian.%红柳沟铜镍矿化基性-超基性岩体位于塔里木板块北缘北山裂谷带,岩体两侧分别为大山头—岗流脑子、方山口—庙庙井—双鹰山2条区域性深大断裂带。岩体侵位于敦煌岩群,铜镍矿化通常赋存于杂岩体中二辉橄榄岩、橄榄二辉辉长岩、橄榄苏长辉长岩等基性程度较高的岩石内。通过SHRIMP锆石U-Pb定年,首次获得红柳沟矿化橄榄角闪辉长苏长岩锆石的U-Pb年龄为(396.7±3.8) Ma,表明该含矿杂岩体的侵位及矿化作用均发生于中泥盆世,结合区内已知黑山和怪石山等铜镍含矿岩体年龄,从而揭示出甘肃北山地区在中—晚泥盆世一直处于陆缘裂谷拉张环境。