地学前缘 ›› 2014, Vol. 21 ›› Issue (6): 381-401.DOI: 10.13745/j.esf.2014.06.036

• 论文 • 上一篇    

东昆仑夏日哈木铜镍矿镁铁质超镁铁质岩体岩相学、锆石U-Pb年代学、地球化学及其构造意义

王冠，孙丰月，李碧乐，李世金，赵俊伟，奥琮，杨启安   

  1. 1. 吉林大学 地球科学学院, 吉林 长春 130061 2. 青海省地质调查局, 青海 西宁 810001 3. 青海省第五地质矿产勘查院, 青海 西宁 810008
  • 收稿日期:2014-05-20 修回日期:2014-09-02 出版日期:2014-11-15 发布日期:2014-11-15
  • 作者简介:王冠(1984—)，男，博士研究生，主要从事矿床学研究。E-mail：red_moon2002@163.com
  • 基金资助:

    中国地质调查局地质大调查项目(12120111086020)

Petrography, zircon U-Pb geochronology and geochemistry of the maficultramafic intrusion in Xiarihamu Cu-Ni deposit from East Kunlun,with implications for geodynamic setting

  • Received:2014-05-20 Revised:2014-09-02 Online:2014-11-15 Published:2014-11-15

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摘要：

文章报道了东昆仑夏日哈木铜镍矿成矿岩体的岩相学、锆石U-Pb年代学、全岩地球化学以及锆石Hf同位素资料，以确定该岩体的形成时代、岩石成因及其形成的构造环境。夏日哈木Ⅰ号镁铁质超镁铁质岩体位于昆中基底隆起花岗岩带中段，北侧靠近昆北断裂。岩体走向NEE，剖面呈平缓的“岩盆状”，地表出露面积约0.7 km2。该杂岩体主要由辉长苏长岩、斜方辉石岩、橄榄辉石岩、斜长二辉橄榄岩和方辉橄榄岩组成，橄榄岩相和辉石岩相是主要的Cu、Ni赋矿岩相。镁铁质超镁铁质岩体主量元素具有低硅(w(SiO2)=36.68%~52.58%)、低钛(w(TiO2)=0.13%~0.47%)、高镁(w(MgO)=10.91%~35.81%)、贫碱(w(K2O+Na2O)=0.26%~1.95%)的特征，属亚碱性系列岩石，m/f为3.88~6.29，属铁质超基性岩类(m/f=2~6.5)。岩石稀土元素球粒陨石标准化配分模式为轻稀土富集型，(La/Yb)N=1.44~2.98，Eu异常不明显，相似的稀土元素配分模式说明岩体的同源性。岩石富集大离子亲石元素(Rb、Th、U、K)，相对亏损高场强元素(Nb、Ta)。岩体中存在新元古代花岗岩的捕虏体以及La/Yb、Ce/Yb、Th/Yb、Nb/La、La/Sm比值显示岩体经历了有限的地壳混染。辉长苏长岩锆石的LA-MCICPMS、U-Pb年代学研究表明，岩体形成年龄为(423±1) Ma，MSWD=0.14，属晚志留世。锆石的176Hf/177Hf比值为0.282 628~0.282 833，相应的εHf(t)均为正值(4.0~10.9)，Lu-Hf的单阶段模式年龄(tDM1)为610~875 Ma，平均值为788 Ma，大于锆石U-Pb年龄。研究认为，岩体的岩浆源区主要为亏损地幔，可能有早期流体交代的富集岩石圈地幔组分的加入和地壳物质的混染。结合区域构造演化，文章认为岩体形成于碰撞后伸展的构造环境，可能与俯冲板片的断离作用有关。岩浆演化过程中橄榄石和斜方辉石的分离结晶作用和地壳中硫的加入可能是促使岩浆体系达到硫饱和的主要机制。

关键词: 夏日哈木Cu-Ni矿床, 镁铁质超镁铁质岩, 锆石U-Pb年龄, 岩石地球化学, 构造环境, 东昆仑

Abstract:

In this paper, we present petrographical, zircon U-Pb dating and geochemical data for the maficultramafic intrusion in Xiarihamu CuNi deposit to constrain its formation time, petrogenesis and the tectonic setting. Xiarihamu No.1 maficultramafic intrusion locates in the middle of the Eastern Kunlun middle uplifted basement and granitic belt, south of the North Kunlun Fault. The intrusion covers an area of 0.7 km2, in shape of a flat lopolith, with the strikes of NEE. The intrusion is mainly composed of gabbronorite, orthopyroxenite, olivine pyroxenites, plagiolherzolite and orthopyroxene peridotite. Pyroxenite and peridotite are the main host rocks for the Cu-Ni ores. Major element contents of Xiarihamu complex show subalkalic series and are characterized by low SiO2 contents (SiO2 36.68%52.58%), low TiO2 contents (TiO2 0.13%0.47%) and alkali contents (Na2O+K2O 0.26%1.95%), but high MgO contents (MgO 10.91%35.81%). The m/f values of the rocks range from 3.88 to 6.29, falling into the range of ferrousultramafic rocks. Similar LREErich pattern ((La/Yb)N=1.442.98) and no Eu anomaly indicate that Xiarihamu complex have the same magma source. Trace elements are enriched in LILE (Rb, Th, U, K) and relatively depleted in HFSE (Nb and Ta). The presence of Neoproterozoic granite relicts and the La/Yb, Ce/Yb, Th/Yb, Nb/La, and La/Sm values suggest the limited crustal contamination during the rise of the magma. Zircon LA-MC-ICPMS、U-Pb dating of gabbronorite yielded 423±1 Ma, MSWD=0.14, i.e., the Late Silurian. Zircon 176Hf/177Hf values are in the range of 0.2826280.282833 with corresponding εHf(t) values of 4.010.9. Lu-Hf singlestage modal ages (tDM1) vary from 610 to 875 Ma and mean age (788 Ma) , which is older than U-Pb age. We suggest that the primary magma derived from a depleted mantle, and may have been added metasomatic enriched lithospheric mantle components, and contaminated by crustal material. Combined with regional tectonic evolution, we believe that the intrusion formed in the post-collisional extension setting, perhaps triggered by slab break-off. The fractional crystallization of olivine and orthopyroxene and addition of crustal S appear to be directly related to trigger S saturation.

 

Key words:  Xiarihamu Cu-Ni deposit, maficultramafic intrusion, zircon U-Pb age, geochemistry, tectonics setting, East Kunlun

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