西藏冈底斯确角弄岩体年代学、地球化学及成矿意义

发布时间：2018-02-10 15:07

  本文关键词： 冈底斯 早白垩世岩浆作用 岩石成因 地球化学 成矿意义　出处：《地质学报》2017年04期 　论文类型：期刊论文

【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,(~(87)Sr/~(86)Sr)_i值高(0.70926~0.71424),负全岩ε_(Nd)(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Ce~(4+)/Ce~(3+)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]:The Meso-Cenozoic magmatic activity is widely developed in the central Gangdis, Tibet, and its petrogenesis and magmatic source are still disputed. The early Cretaceous magmatism is the key element in exploring the large-scale magmatic mineralization in the Gangdese belt. In this paper, the early Cretaceous granitic granitic bodies in the Qiaojiaonong area of the Middle Gangdis belt are taken as the objects, and the LA-ICP-MS zircon U-Pb geochronology is carried out in detail. The main rock types of granitic bodies are biotite granodiorite, followed by quartz monzonite, syenite, etc. It belongs to type I metamorphic high-potassium calc-alkaline granitoids. The emplacement age of biotite granodiorite is 127 卤1.6 Ma-1. The age of biotite granodiorite is 127 卤1.6 Ma. The age of biotite granodiorite is 127 卤1.6 Ma. The Sr / P ~ (86) T ~ (-1) value is 0.70926 ~ (0.71424), and the negative whole rock 蔚 ~ (-1) is -7.0 ~ (-1) ~ (-1) ~ (-1) ~ (-1). The trace elements are characterized by the enrichment of large ion lithophile elements in subduction zone and the depletion of high field strength elements. The magmatic source mainly comes from the partial remelting of the ancient basement rocks and may involve a small amount of mantle material. The genesis of the rocks may be related to the plate fragments that occurred during the southward subduction of the Bangonghu-Nujiang oceanic lithosphere during the early Cretaceous. The Keijiaonong rock body is a belt of the Middle Cretaceous early Cretaceous. The magmatic eruption continued in the central part of the country. A strong hydrothermal alteration occurred in the contact zone between the rock mass and the surrounding rock. It has a very high anomalous value of ferro-tungsten geophysical and geochemical prospecting. Magnetite mineralization points have been found locally. The zircon of the ore-forming rock mass has a high Ce~(4 / ce ~ (3) ratio of 450 ~ 769 ~ (9), and the Ti saturation temperature of zircon is about 776 鈩，

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