Granitoid-greenstone relationships in the eastern Kaapvaal craton and implications for early crustal evolution

在我们的项目中，已经研究了斯威士兰的古片麻岩杂岩（AGC）和西格陵兰南部的Itsaq片麻岩杂岩（IGC）的早白垩世大陆地壳历史，我们现在集中于巴伯顿绿岩带最低地层单位的镁铁质和超镁铁质岩石的地球化学，约1000年。3.53南非Ga Theespruit和Sandspruit地层，以及斯威士兰古代片麻岩杂岩中的绿岩内层。我们的第一个项目阶段的初步结果暗示，在长英质基底以上的绿岩序列和旧的大陆地壳，现在暴露在AGC。镁铁质-超镁铁质火山岩的化学特征可能是地壳污染，可以跟踪使用的主要和微量元素和铪-钕同位素组成的组合。此外，我们计划进行不同的岩石类型（片麻岩，斜长角闪岩）的古片麻岩杂岩和巴伯顿绿岩带的岩性的142 Nd分析，以调查是否最古老的岩石Kaapvaal克拉通早期分化的历史，可能开始于冥古宙，当灭绝的核素系统仍然活跃。我们将调查是否可能的142 Nd异常可能已经减少了幼年地壳的贡献，随着时间的推移，或是否持续在年轻的岩浆岩。

Following up on our project, where the early Archaean continental crustal histories of the Ancient Gneiss Complex (AGC),of Swaziland and the Itsaq Gneiss Complex (IGC) of southern West Greenland) have been studied, we now focus on the geochemistry of mafic and ultramafic rocks of the lowermost stratigraphic units of the Barberton Greenstone Belt, the ca. 3.53 Ga Theespruit and Sandspruit Formations, South Africa, as well as on greenstone inliers in the Ancient Gneiss Complex of Swaziland. The preliminary results of our first project phase hint at a felsic basement to the above greenstone sequences and older continental crust as now exposed in the AGC. Chemical signatures of mafic-ultramafic volcanic rocks possible crustal contamination may be traced using a combination of major and trace elements and Hafnium-Neodymium isotope compositions. Moreover, we plan to carry out 142Nd analyses on different rock types (gneisses, amphibolites) of the Ancient Gneiss Complex and the lithologies of the Barberton Greenstone Belt to investigate whether the oldest rocks of the Kaapvaal craton had an early differentiation history that possibly began in the Hadean, when the extinct nuclide system was still active. We shall investigate whether a possible 142Nd anomaly may have been diminished by juvenile crustal contributions with time or whether it sustained in younger magmatic rocks.