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首页> 外文期刊>South African Journal of Geology: Being the Transaction of the Geological Society of South African: Syndie die Verhandelinge van die Geologiese Vereniging van Suid-Afrika >Origin of discordant ultramafic pegmatites in the Bushveld Complex from externally-derived magmas
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Origin of discordant ultramafic pegmatites in the Bushveld Complex from externally-derived magmas

机译：来自外部衍生的岩浆的Bushveld复合体中不间断的Ultramafic Pegmatites的起源

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Coarse-grained, discordant, mainly ultramafic, bodies cut the layered succession of the Bushveld Complex. Previous models have subdivided them into magnesian dunite, considered to have been emplaced upward, and more ironrich wehrlite (± oxides), referred to as iron-rich ultramafic pegmatites (IRUP), emplaced downward. We have studied a number of these IRUP bodies in an open pit on Marikana Mining Operations platinum mines property, near Rustenburg, as well as other samples from different levels in the intrusion. A compilation of our and previously published compositions for olivine and clinopyroxene suggests that there are not two discrete suites and processes, but that all bodies originated from multiple magmas with a similar source, resulting in formation of magnesian olivine followed by progressively more iron-rich olivine and clinopyroxene in a fractionating system. In fact, more evolved compositions of discordant pegmatitic gabbro mineralogy exist that have been largely ignored in the past, but are considered here to be cogenetic with the ultramafic bodies. These rocks are all cumulates, based on their simple mineralogy and extreme deficiency in incompatible trace elements in whole-rock compositions. We question the previous models. The first involved fluid replacement. We question from where the high TiO_2 content of these bodies originated and to where the high Al_2O_3 (from the replaced plagioclase) went, noting that TiO_2 and Al_2O_3 are typically the most refractory of oxides. The second involved highly evolved or immiscible liquids or products of disequilibrium melting, generated within the intrusion, considered to have penetrated downward (kms) displacing a succession of cumulate rocks. We question the mechanism by which a downward penetrating magma could displace pre-existing cumulates, presumably returning them back up the same conduit without any interaction between the two. We suggest that initial upward penetration of magmas, not generated within t
机译：粗粒度，不和谐，主要是超铜，尸体切割了丛林电流复杂的层次连续。以前的模型将它们细分为氧化镁DUNITE，被认为已经向上施加，并且更多的Ironrich Wehrlite（±氧化物），称为富含铁的超空地Pegmatites（IRUP），向下施加。我们研究了在Marikana Mining作业的露天坑中研究了许多这些IRUP尸体，铂金矿业属性，靠近Restenburg，以及来自侵入中不同水平的其他样品。汇编我们和以前公布的Olivine和Clinoceoxene的组合物表明，没有两个离散的套件和过程，但所有的身体来自多个岩浆，具有类似的来源，导致形成氧化镁橄榄石，然后逐渐形成铁富含铁的橄榄石和临床在分馏系统中。事实上，在过去的存在中存在不间断的卵鼠植物矿物学的更加流变的组合物，但在此被认为是用utermafiC体的泌尿动态。这些岩石都是全部累积，基于整个岩石组合物中的简单矿物学和极端缺陷。我们质疑以前的模型。第一个涉及的流体更换。我们根据这些身体的高TiO_2含量起源于高Al_2O_3（来自替换的Plagioclase）的位置，注意到TiO_2和Al_2O_3通常是最难由的氧化物。第二种涉及高度进化或不混溶的液体或不含不平衡熔化的产物，在入侵中产生，被认为已经穿透地渗透（KMS），其次取代累积岩石。我们质疑向下穿透岩浆可以取代预先存在的累积的机制，大概将它们返回相同的导管，而不会在两者之间的任何相互作用。我们建议岩浆初步向上渗透，而不是在t中产生

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