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首页> 外文期刊>Contributions to Mineralogy and Petrology >On the relationships between the Bushveld Complex and its felsic roof rocks, part 1: petrogenesis of Rooiberg and related felsites
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On the relationships between the Bushveld Complex and its felsic roof rocks, part 1: petrogenesis of Rooiberg and related felsites

机译：关于布什维尔德情结与其长岩屋顶岩石之间的关系，第1部分：Rooiberg及其相关长岩的成岩作用

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A major question concerning the Bushveld Complex is the relationship between the layered mafic rocks and the overlying Rooiberg Group felsites and related granophyres. Here, we assemble bulk-rock analyses to gain insight into this question and investigate the petrogenesis of the felsic rocks. The data indicate that the Rooiberg Group consists of distinctive magnesian and ferroan lavas. The former dominates the basalts to rhyolites of the basal Dullstroom Formation, while nearly all the dacites to rhyolites of the overlying Damwal, Kwaggasnek, and Schrikkloof Formations are ferroan. The ferroan rocks also include the Stavoren Granophyre, which exists regionally as a several-hundred-meter-thick concordant sheet between the Bushveld Complex and Rooiberg lavas. The compositions of the magnesian lavas are similar to calc-alkaline granitoids found in convergent margins, suggesting that the lavas could have originated in a mantle affected by previous Archean subduction events that are recorded by xenoliths and inclusions in diamonds from most Kaapvaal kimberlites. In contrast, the compositions of the ferroan lavas indicate formation by fractional crystallization of basaltic liquids and are essentially identical to ferroan rhyolites associated with mafic rocks from other settings. The hypothesis that these rocks are fractional crystallization products of Bushveld mafic liquids is consistent with published radiogenic and stable isotope data and known age relations. Based on compositional characteristics and geologic relations, the Stavoren Granophyre is the most likely candidate for the residual liquid that escaped from the top of the Bushveld Complex. Whether the bulk of the Bushveld Province ferroan rhyolites formed in the chamber of the extant layered mafic sequence or in a deeper, hidden crustal magma reservoir remains unclear.
机译：关于布什维尔德复合体的一个主要问题是层状镁铁质岩石与上覆的鲁伊贝格群长石质和相关的花岗石之间的关系。在这里，我们进行块岩分析，以深入了解该问题并研究长英质岩石的成岩作用。数据表明，鲁伊伯格群由独特的镁质和二茂铁熔岩组成。前者在基底Dullstroom层的流纹岩中占主导地位，而上层的Damwal，Kwaggasnek和Schrikkloof层的流纹岩中几乎所有的衰变因子都是二茂铁。这些铁岩石还包括Stavoren Granophyre，它在Bushveld Complex和Rooiberg熔岩之间以数百米厚的一致片状存在于该地区。镁质熔岩的成分类似于在会聚边缘发现的钙碱性花岗岩，这表明熔岩可能起源于先前的太古宙俯冲事件所影响的地幔，该异常曾被异质岩和大多数Kaapvaal金伯利岩的钻石包裹体记录。相反，亚铁熔岩的成分表明是通过玄武质液体的分步结晶形成的，并且与与来自其他地方的镁铁质岩石相关的亚铁流纹岩基本相同。这些岩石是布什维尔德镁铁质液体的分步结晶产物的假说与已发表的放射成因和稳定同位素数据以及已知的年龄关系一致。基于成分特征和地质关系，Stavoren Granophyre是从Bushveld配合物顶部逸出的残留液体的最有可能的候选者。尚不清楚在现成的层状镁铁质层序的腔室中，还是在更深的，隐蔽的地壳岩浆储层中形成的大部分布什维尔德省的铁氧流纹岩。

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