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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 >Geochemistry and petrogenesis of South African transitional kimberlites located on and off the Kaapvaal Craton
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Geochemistry and petrogenesis of South African transitional kimberlites located on and off the Kaapvaal Craton

机译：位于Kaapvaal Craton上下的南非过渡金伯利岩的地球化学和岩石成因

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摘要

Eight Jurassic to Cretaceous transitional kimberlites located on and off the Kaapvaal craton have been analysed in order to evaluate their petrogenesis and relationship to typical Group I and Group II southern African kimberlites. The transitional kimberlites tend to show intermediate petrographic and geochemical characteristics to Group I and II kimberlites for some parameters (e.g. variable phlogopite, TiO2, La/Nb, Ba/Nb and Th/Nb) and especially in their 143Nd/144Nd and 87Sr/86Sr ratios. For other parameters (e.g. MgO, Ni), they span the ranges shown by Group I and Group II kimberlites. These characteristics are interpreted to suggest that transitional kimberlites are derived from source regions with mixed Group I/Group II kimberlite source characteristics. The off-craton transitional kimberlites show greater petrographic and geochemical affinity to Group II kimberlites, and have similar emplacement ages, whereas the on-craton transitional kimberlites are petrographically and geochemically more similar to Group I kimberlites and also have similar emplacement ages. Although derived from a mixed source having both Group I and Group II geochemical signatures, the mantle source giving rise to off-craton transitional kimberlites is interpreted to have stronger Group II kimberlite-like characteristics, whereas that giving rise to on-craton transitional kimberlites had stronger Group I kimberlite-like characteristics.
机译：为了评估它们的成岩作用以及与典型的I组和II组南部非洲金伯利岩的关系，对位于Kaapvaal克拉通上和下的8个侏罗纪至白垩纪过渡金伯利岩进行了分析。对于某些参数（例如可变金云母，TiO2，La / Nb，Ba / Nb和Th / Nb），尤其是在143Nd / 144Nd和87Sr / 86Sr中，过渡金伯利岩倾向于表现出I和II类金伯利岩的中间岩石学和地球化学特征。比率。对于其他参数（例如MgO，Ni），它们的范围跨越第I组和第II组金伯利岩。这些特征被解释为表明过渡金伯利岩是从具有I / II类金伯利岩混合源特征的源区中获得的。克拉通外过渡金伯利岩与第二类金伯利岩表现出更大的岩石学和地球化学亲和力，并且具有相似的沉积年龄，而克拉通过渡金伯利岩在岩石学和地球化学上与第一类金伯利岩更相似，并且具有相似的沉积年龄。尽管来自具有第一和第二组地球化学特征的混合源，但产生地幔外过渡金伯利岩的地幔源被解释为具有更强的类似于第二组金伯利岩的特征，而引起克拉通过渡金伯利岩的地幔源具有我组具有更强的金伯利岩样特征。

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