ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    中部非洲淡色花岗岩(约1.0 Ga)的年代学、岩石地球化学特征、构造背景及其与成矿的关系

    Geochronology, Petrogeochemical Characteristics, Tectonic Setting of the Leucogranites (~1.0 Ga) in Central Africa and Its Relationship with Mineralization

    • 摘要: 中部非洲的传统中元古代基巴拉造山带内发育大量与花岗岩−伟晶岩体系相关的金属矿产,尤其是以标志性的稀有金属(Nb−Ta−Li)、钨、锡和金等成矿作用为特色,成矿地质过程往往和罗迪尼亚超大陆聚合事件相对应。通常 认为,与成矿直接密切相关的花岗岩是新元古代早期的一套淡色花岗岩(G4花岗岩),即含Sn花岗岩。G4花岗岩过去通常被视作成矿母岩,长期以来受到广泛关注,但是前人的研究表明基巴拉带不同地区的G4花岗岩在野外判别标志、形成时限、地球化学特征等方面存在一定差异,导致对岩石类型、岩石成因及其产出的构造背景的认识还不统一。因此,笔者在系统收集、整理前人资料的基础上,详细总结G4花岗岩的野外岩石类型、年代学研究、全岩地球化学数据及同位素等方面特征,初步探讨成岩成矿过程。结果显示,G4花岗岩的源区物质以变泥质岩为主,岩浆形成方式主要是局部的部分熔融或深熔作用,并不像过去认为的那样来源于一个深部较大岩浆房的长期分异演化,而G4花岗岩的演化则与区域成矿作用存在直接关联。结合区域构造演化研究,推测G4花岗岩可能形成于基巴拉造山作用的同碰撞‒后碰撞阶段。

       

      Abstract: A large number of mineral resources related to granite−pegmatite system that are found in the traditional Mesoproterozoic Kibaran belt in Central Africa, especially characterized by the distinctive mineralization of rare metals (Nb−Ta−Li), tungsten, tin and gold. The metallogenic events can be associated with the process of Rodinia amalgamation. Most of these mineral occurrences are linked to the early Neoproterozoic G4 leucogranitic intrusions, also termed “tin (−bearing) granites”. G4 granites have been extensively scrutinised because they are considered as the parental rocks to the ore mineralization in the region. The field identification criteria, timing, geochemical characteristics for G4 granites in different parts of Kibaran belt, however, have been shown to vary in previous studies. As a result, the type of rock, the petrogenesis of these parental granites and the geodynamic context is still a matter of debate. Combined with the disparate nature of datasets in the literature (e.g. field outcrops, petrography, geochronology, geochemistry and isotopes), the results show that the derivation of G4 granite is consistent with a meta−pelitic source, and these leucocratic granites could be considered more like anatectic migmatites rather than actual highly fractionated granites formed by fractionation out of large magma chambers. It has been largely established via the research of diagenetic and metallogenic processes that the protracted differentiation of G4 granites is the primary driver of diverse mineralization in the Kibaran belt. It’s hypothesized that the G4 granite was probably emplaced in the syncollisional to post−collisional stage of Kibaran orogeny when considering the regional tectonic background.

       

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