天宇铜镍矿床的岩相学、锆石U-Pb年代学、地球化学特征:对东疆镁铁-超镁铁质岩体源区和成因的制约  

Lithological, chronological and geochemical characteristics of Tianyu Cu-Ni deposit: Constraints on source and genesis of mafic-ultramafic intrusions in eastern Xinjiang.

作　　者：唐冬梅[1,2] 秦克章[1] 孙赫[1,2] 苏本勋[1,2] 肖庆华[1,2] 程松林[3] 李军[3] 

机构地区：[1]中国科学院矿产资源研究重点实验室,中国科学院地质与地球物理研究所,北京100029 [2]中国科学院研究生院,北京100049 [3]新疆维吾尔自治区地质矿产勘查开发局第六地质大队,哈密839000

出　　处：《岩石学报》2009年第4期817-831,共15页Acta Petrologica Sinica

基　　金：中国科学院知识创新工程重要方向项目(KZCX2-YW-107);国家“十一五”科技支撑计划新疆305项目东天山铜镍矿专题 (2006BAB07B03-01)资助

摘　　要：天宇镁铁-超镁铁质岩体位于新疆中天山地块与觉罗塔格构造带的分界断裂——沙泉子深大断裂的南侧约5km。岩体呈向北陡倾的岩墙状,地袁出露面积约0.056km^2。该杂岩体主要由辉长岩、辉石岩、辉橄岩和橄榄岩相组成,橄辉岩、辉橄岩和橄榄岩是主要的Cu、Ni赋矿岩相。镁铁-超镁铁岩的主量元素含量显示,天宇岩体属拉斑玄武岩成因系列,m/f为1.44～3.61,平均值为2.25,为铁质超基性岩(m/f=2～6.5)。稀土元素标准化配分模式为轻稀土富集型,Eu弱负异常或无异常,相似的稀土元素配分模式说明岩体的同源性。富集大离子亲石元素,亏损高场强元素Nb、Ta,说明源区可能有陆壳物质的混染。Nb/Hf、Ce/Pb、Nb/U、La/Sm、Th/Nb比值显示岩体可能经受上地壳物质的混染。锆石的LA-ICP-MS U-Pb年代学研究表明,岩体形成年龄为290.2±3.4Ma,与东天山地区镁铁-超镁铁质杂岩体的形成时间一致。锆石的Lu/Hf比值比较均一,且(^(176)Hf/^(177)Hf)_i变化很小,说明源区性质比较单一。锆石的(^(176)Hf/^(177)Hf)_i值为0.282625～0.282770,相应的ε_(Hf)(t)均为正值 (1.10～6.06),Lu-Hf的单阶段模式年龄(t_(DM1))为674～884.7Ma,平均年龄为799Ma,比岩体的U-Pb年龄大,显示岩浆来源于亏损地幔或者源区有壳源物质的加入。上述岩石地球化学、年代学特征,为晚古生代古亚洲洋向南俯冲提供了佐证。Tianyu mafic-ultramafic intrusions are located in the south of the Shaquanzi deep-seated fault. Shaquanzi fault is the boundary between the Central Tianshan Massif and Jueluotage tectonic belt. It covers an area of 0.056 km(2) in shape of dyke pitched to the north. The intrusions consist of gabbro, pyroxenite, olivine pyroxenite, pyroxene peridotite and peridotite. Olivine pyroxenite, pyroxene peridotite and peridotite are the main host rocks for the Cu-Ni ores. Major-element contents of Tianyu complex show tholeiitic evolution trend and m/f values range from 1.44 to 3.61 with 2.25 on average, falling into the range of ferrous-ultramafic rocks. Similar LREE-rich pattern and negative or no Eu anomaly indicate that Tianyu complex have the same magma source. Trace elements show LILE-rich and HFSE-depleted pattern. The depletion of Nb, Ta implies the contamination of continental material. Nb/Hf, Ce/Pb, Nb/U, La/Sm, Th/Nb values suggest the contamination of upper crust during upward of magma. Zircon LA-ICP-MS U-Pb dates yield 290.2 +/- 3.4Ma which is consistent with the age of other mafic-ultramafic complex in East Tianshan. Uniform Lu/Hf values and the ((176)Hf/(177)Hf)(i) reveal that the characteristics of source are simple. Th, ((176)Hf/(177)Hf)(i) are in the range of 0.282625 similar to 0.282770 with corresponding epsilon(Hf)(t) values of 1.10 similar to 6.06. Lu-Hf single-stage modal ages (t(DMI)) vary from 674.0 to 884.7Ma, mean age(799Ma) is older than U-Pb age. These characteristics indicate that the parental magma derived from depleted mantle or had been contaminated by crustal material. These geochemical and chronological characteristics also constrain the southern subduction of Paleo-Asia Ocean in Paleozoic.

关 键 词：天宇Cu-Ni矿床 岩石地球化学 锆石LA-ICP-Pb定年 LU-HF同位素 地壳混杂 东疆 

分 类 号：P618.41[天文地球—矿床学] P618.63[天文地球—地质学] P597.3