Eclogite xenoliths, together with garnet pyroxenites and some mafic garnet granulites, found in kimberlites located along the southern margin of the Kaapvaal craton in southern Africa have been analysed by electron microprobe and mass spectrometry techniques to determine their geochemical characteristics. The majority of eclogites are bimineralic with garnet and omphacitic clinopyroxene in subequal proportions, with rutile as the main accessory phase; a few contain kyanite. Based on K₂O in clinopyroxene and Na₂O in garnet, the eclogites can be classified as Group II eclogites, and the majority are high-Ca in character. Garnet pyroxenites comprise garnet clinopyroxenites and garnet websterites.Major and trace element concentrations and isotope ratios of reconstituted bulk rock compositions of the eclogites and garnet pyroxenites allow constraints to be placed on depth of origin and likely protolith history. Calculated Fe-Mg exchange equilibration temperatures for the eclogites range from 815 to 1000 °C, at pressures of 1.7±0.4 GPa as determined by REE partitioning, indicating that they were sampled from depths of 50-55 km; i.e. within the lower crust of the Namaqua-Natal Belt. The garnet pyroxenites show slightly lower temperatures (686-835 °C) at similar pressures of equilibration. Initial ¹⁴³Nd/¹⁴⁴Nd and ⁸⁷Sr/⁸⁶Sr ratios (calculated to time of kimberlite emplacement) of both lithologies overlap the field for lower crustal samples from the Namaqua-Natal Belt. Further evidence for a crustal origin is found in the similar REE patterns shown by many of the associated garnet granulite xenoliths. Garnet pyroxenites are interpreted to have a similar origin as the associated eclogites but with the mafic protolith having insufficient Na (i.e. low modal plagioclase) to allow for development of omphacitic pyroxene. Metamorphism of the mafic protoliths to these eclogites and garnet pyroxenites is inferred to have occurred during crustal shortening and thickening associated with the collision of the Namaqua-Natal Belt with the Kaapvaal craton at 1-1.2 Ga.

中文翻译：

---

来自金伯利岩的榴辉榴辉岩和石榴石辉绿岩异岩沿非洲南部Kaapvaal克拉通的南缘放置：地幔或下部地壳碎片？

通过电子探针和质谱技术分析了位于非洲南部Kaapvaal克拉通南部边缘的金伯利岩中的榴辉岩异岩，石榴石辉绿岩和一些镁铁石榴石颗粒，并通过电子探针和质谱技术对其进行了分析，以确定其地球化学特征。大部分榴辉岩是双矿物的，石榴石和全斜晶石的亚辉石的比例均等，金红石为主要的辅助相。一些含有蓝晶石。基于斜发py中的K ₂ O和Na ₂石榴石中的O可以将榴辉岩归为II组榴辉岩，且大多数为高钙钙岩。石榴石辉石岩包括石榴石斜辉石岩和石榴石韦氏石岩。榴辉岩和石榴石辉石岩的重整块岩石成分的主要元素和痕量元素浓度以及同位素比使得可以限制成矿深度和可能的原石历史。稀土元素计算得出的榴辉岩的Fe-Mg交换平衡温度范围为815至1000°C，压力为1.7±0.4 GPa，表明它们是从50-55 km深度取样的。即在纳马夸-纳塔尔带的下地壳内。石榴石辉绿岩在相似的平衡压力下表现出稍低的温度（686-835°C）。初始¹⁴³ Nd / ¹⁴⁴两种岩性的Nd和⁸⁷ Sr / ⁸⁶ Sr之比（按金伯利岩侵位时间计算）与来自Namaqua-Natal带的下地壳样品的场重叠。在许多相关的石榴石粒状异种岩显示的相似的REE模式中发现了地壳起源的进一步证据。石榴石辉绿岩的来源与相关榴辉岩相似，但镁铁质原石的Na含量不足（即低模数斜长石），无法发育全相辉石。据推测，镁铁质原生质岩向这些榴辉岩和石榴石辉绿岩的变质发生在地壳缩短和增厚的过程中，这与Namaqua-Natal带与Kaapvaal克拉通在1-1.2 Ga的碰撞有关。