Peridotite xenoliths from the Kaapvaal cratonic lithosphere are characterized by high modal orthopyroxene (Opx), which is inconsistent with the mineralogy of residues of partial melting of primitive mantle. The high orthopyroxene content has been explained by the reaction between Opx-poor peridotite and silica-rich melts. To assess and further constrain this model, we conducted a series of experiments on the interaction of Si-rich melt with Opx-poor harzburgite at 1.5 GPa and 1100 to 1250 °C. Orthopyroxene is enriched in all experiments. In the low temperature run at 1100 °C, melt is consumed and phlogopite is precipitated with the generation of orthopyroxene. Mg# (atomic 100*Mg/(Mg+Fe)) values in olivines also exhibit a decrease compared with the starting olivines. At temperatures of ≥1200 °C, phlogopite is absent as the temperatures are higher than its upper stability field. The residues are composed of high modal orthopyroxene and high Mg# olivine. Only the residues in the high temperature runs are consistent with Kaapvaal cratonic mantle xenoliths. Combined our experiments with the distribution, geochronological and geochemical data of the xenoliths, we propose a two-stage ‘metasomatism-depletion’ model to explain the generation of Opx-rich xenoliths in Kaapvaal craton. In the early Archean, high-degree melting of primitive mantle produced a highly depleted lithospheric mantle, which was Opx-poor. Subsequently, Si-rich melts/fluids were released from the subducting oceanic slabs to interact with the Opx-poor mantle, generating an Opx-rich, but hydrous and fertile mantle. The metasomatic mantle is similar to the result of the run at 1100 °C. In the late Archean, the metasomatic mantle was re-melted in post-collisional extensional environments, which produced voluminous lavas with residues of highly depleted, Opx-rich peridotites. The Opx-rich residual peridotites are consistent with the runs at ≥1200 °C. Thus, Opx enrichment in the Kaapvaal craton lithospheric mantle can be well explained by the two-stage ‘metasomatism-depletion’ model.

来自Kaapvaal克拉通岩石圈的橄榄岩异岩为特征的高模态邻苯二酚（Opx），这与原始地幔部分熔融的残余物的矿物学特征不一致。高邻位邻苯二酚的含量可以通过贫Opx橄榄岩和富二氧化硅熔体之间的反应来解释。为了评估并进一步约束该模型，我们在1.5 GPa和1100至1250°C的温度下对富硅熔体与Opx贫哈氏体的相互作用进行了一系列实验。在所有实验中邻苯二酚均富集。在1100°C的低温下，熔体被消耗，金云母沉淀，并生成邻苯二甲ene。与起始橄榄石相比，橄榄石中的Mg＃（原子100 * Mg /（Mg + Fe））值也显示出降低。在≥1200°C的温度下，由于温度高于其上部稳定性场，因此不存在金云母。残留物由高峰态邻苯二甲酚和高Mg＃橄榄石组成。仅高温运行中的残留物与Kaapvaal克拉通地幔异种岩一致。将我们的实验与异种岩的分布，地质年代和地球化学数据相结合，我们提出了一个两阶段的“变质耗竭”模型来解释在Kaapvaal克拉通中富含Opx的异种岩的产生。在太古宙早期，原始地幔的高度融化产生了贫瘠的岩石圈地幔，这是Opx贫瘠的。随后，从俯冲的大洋板中释放出富含硅的熔体/流体，与贫Opx的地幔相互作用，生成富Opx但含水且肥沃的地幔。交代地幔类似于在1100°C下运行的结果。在太古宙晚期，变质作用地幔在碰撞后的伸展环境中重新融化，产生了大量熔岩，残留着高度贫化，富含Opx的橄榄岩。富含Opx的残余橄榄岩与≥1200°C时的结果一致。因此，Kaapvaal克拉通岩石圈地幔中的Opx富集可以通过两阶段的“变质-耗竭”模型很好地解释。