新疆圪塔山口含铜镍岩体锆石SHRIMPU-Pb年龄、岩石地球化学特征及其地质意义

圪塔山口含铜镍镁铁-超镁铁质岩体位于东天山黄山–镜儿泉–图拉尔根铜镍矿带东段。岩体由I-1,I-2,I-3,I-4四个小岩体组成,主要岩石类型为辉石橄榄岩、橄榄辉石岩、辉长岩和闪长岩,主要赋矿岩相为辉石橄榄岩。I-2号含矿岩体锆石SHRIMP U-Pb年龄为275.0±3.6 Ma,与东天山地区含铜镍矿镁铁–超镁铁岩体形成时代相近,I-4号不含矿岩体锆石SHRIMP U-Pb年龄为364.2±3.9 Ma,明显早于含矿岩体。样品的主量元素组成显示岩浆演化过程主要发生了橄榄石和少量辉石的分离结晶/堆晶作用;稀土元素球粒陨石标准化配分曲线呈轻稀土略富集的右倾型,Eu异常不明显;微量元素特征显示相对富集大离子亲石元素(Cs、Sr、Ba),适度亏损高场强元素(Nb、Ta、Ti)。岩石地球化学特征表明岩浆演化过程中遭受了较弱的中–下地壳物质混染。U/Th-Th/Zr、Ba/Th-Th/Yb图解,La/Nb、La/Ba和Ba/Nb比值表明岩浆源区遭受了明显的俯冲流体交代作用。综合含矿岩体年代学、岩石地球化学特征及区域演化历史,认为圪塔山口含矿岩体形成于碰撞后伸展背景,可能同时叠加了塔里木地幔柱活动的影响。

Geochronological and Geochemical Characteristics of Getashankou Cu-Ni Bearing Intrusion in Eastern Tianshan,Xinjiang and its Geological Significance

The Cu-Ni mineralized Getashankou mafic-ultramafic complex is located at the eastern section of the Huangshan-Jingerquan-Tulaergen Cu-Ni Ore Belt,eastern Xinjiang.The Getashankou complex is composed of four small intrusions,named I-l,I-2,I-3,I-4 intrusions,respectively.The I-2 intrusion mainly consists of diorite,gabbro,olivine pyroxenite and wehrlite,while the wehrlite is the main ore-bearing rock type.Zircon U-Pb SHRIMP age of I-2 and I-4 intrusions are 275±3.6 Ma and 364.2±3.9 Ma,respectively,therefore the I-4 intrusion emplaced later than the I-2 Cu-Ni bearing complex.The geological characteristics of the I-1,I-2 and I-3 intrusions are of comagmatic.Chondrite normalized REE patterns of the rocks show slight enrichment of LREE and insignificant Eu anomalies.The rocks are enriched in LILEs (Cs,Sr,Ba) and depleted in HFSEs (Nb,Ta,Ti).The magma experienced olivine and pyroxenes fractionation crystallization/accumulation,and weak contamination of the middle-lower crust during ascending.La/Nb,La/Ba,and Ba/Nb ratios suggest that the mantle source was metasomatized by subduction-related fluid.The chronological and geochemical characteristics,together with regional evolution history of the Eastern Tianshan area indicate that the Getashankou Cu-Ni ore-bearing complex might be related to the post-collision extension and mantle plume activities.