西藏冈底斯确角弄岩体年代学、地球化学及成矿意义
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Geochronology and Geochemistry of the Quejiaonong Pluton in Middle Section of Gangdese, Tibet and its Mineralization Significance
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    摘要:

    西藏冈底斯中部广泛发育中新生代岩浆活动,而其岩石成因及岩浆源区仍存争议。早白垩世岩浆作用既是探究冈底斯带大规模的岩浆成矿作用的关键要素,又是认识其地球动力学过程的关键窗口。本文以中冈底斯带确角弄地区出露的早白垩世花岗质岩体为对象,进行了详细的LAICPMS锆石UPb年代学、全岩地球化学和SrNd同位素研究。花岗质岩体岩石类型以黑云母花岗闪长岩为主,其次为石英二长岩、正长花岗岩等,属I型偏铝质高钾钙碱性系列花岗岩。确角弄岩体黑云母花岗闪长岩侵位年龄为127±1.6Ma,(87Sr/86Sr)i值高(0.70926~0.71424),负全岩εNd(t)值 (-7.0~-9.1),微量元素表现出消减带富集大离子亲石元素、亏损高场强元素的特征,显示岛弧花岗岩的亲缘性。岩浆源区主要来自古老基底岩石的部分重熔并可能有少量幔源物质的参与,经历了强烈分离结晶作用。岩石成因可能与早白垩世时受到班公湖-怒江洋壳岩石圈向南俯冲过程中发生的板片断离有关。确角弄岩体是中冈底斯早白垩世带状岩浆大爆发事件在中部的延续。岩体与围岩接触带发生了强烈的热液蚀变,具有很高的铁钨物化探异常值,局部地方发现了磁铁矿矿化点,成矿岩体锆石都具较高的Ce4+/Ce3+比值(450~769),锆石Ti饱和温度较高为776℃左右,显示成矿岩浆为高温岩浆热液体系并具有高氧逸度特征,化探趋势剩余异常的空间展布受地层岩性、断裂构造、岩浆岩控制明显,指示了良好的铁钨找矿前景。

    Abstract:

    Magmatic activities were very active in the middle section of the Gangdise during Mesozoic to Cenozoic periods, but petrogenesis and magma source of this area is still in dispute. The Early Cretaceous magmatism is not only key element for understanding magmatismrelated mineralization temporally concentrated in the Gangdise,but also a window for probing geodynamic process. With the Early Cretaceous granite complex in the Quejiaonong area as an example, we conducted an integrated study of petrology, zircon UPb age, and elemental geochemistry and SrNd isotopes. Lithological assemblages of granitoid rock are dominated by biotite granodiorite with minor quartz monzonite and rare Kfeldspar granite, and belong to highK calcalkaline and I type granitoids. Zircon UPb dating indicates that the biotite granodiorite rocks were emplaced at 127±1.6Ma and are characterized by high (87Sr/86Sri) ratio (0.70926-0.71424), negative wholerock εNd(t) value (-7.0~-9.1),enrichment in large ion lithophile elements and depletion in high field strength elements, displaying an affinity of volcanic arc granite. The magma was sourced from antexis of ancient lower crust materials and minor mixed mantlederived melts, experienced significant fractional crystallization. Lithogenesis of the pluton was likely related to the slab breakoff during southward subduction of BangongNujiang Tethys oceanic crust during the Early Cretaceous. The Quejiaonong pluton was a continuation of eruption event of strip magma in the middle Gangdese in Early Cretaceous, resulting in strong alteration between the pluton and country rocks. High geophycial anomalous values indicate iron and tungsten mineralization with locally mineralized prospects of magnetite. Oreforming plutons have high Ce4+/Ce3+ ratios (450769) and temperature calculated by Tiinzircon thermometeris was ca. 776℃, indicating that the orebearing magma was characterized by a relatively high oxygen fugacity and high diagenetic temperature. Spatial distribution of geochemical trend residual anomalies is controlled by geochemical anomalies is controlled by strata, fault structure and magmatic rocks, suggesting a promising outlook for iron and tungsten exploration in this area.

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王力圆,高顺宝,郑有业,李伟良,毛荣威,黄亮亮.2017.西藏冈底斯确角弄岩体年代学、地球化学及成矿意义[J].地质学报,91(4):822-835.
WANG Liyuan, GAO Shunbao, ZHENG Youye, LI Weiliang, MAO Rongwei, HUANG Liangliang.2017. Geochronology and Geochemistry of the Quejiaonong Pluton in Middle Section of Gangdese, Tibet and its Mineralization Significance[J]. Acta Geologica Sinica,91(4):822-835.

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  • 在线发布日期: 2017-04-25
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