Thirty-nine garnet harzburgites from Kimberley in the Kaapvaal Craton (South Africa) were studied to constrain the origin, age and evolution of sub-cratonic lithospheric mantle (SCLM). In order to avoid chemical overprinting by recent metasomatism, only garnet harzburgites that appeared clinopyroxene-free to the naked eye were sampled. The majority of garnets were, however, in equilibrium with clinopyroxene (24 of 39). Whole rock and mineral major–trace element geochemistry and garnet Sr–Nd–Hf isotope data are presented. Equilibration pressures range from 3.8–6.1 GPa, indicating the harzburgites were derived from a large portion of the SCLM (~115–185 km). High olivine Mg# (~93.4, n = 39) and low whole rock heavy rare earth elements (HREE) contents are consistent with large degrees of partial melting (>45%) and garnet exhaustion leaving a dunitic residue with olivine ≥90%, orthopyroxene ≤10% and HREE <0.01 times chondrite. Mineral modes, whole rock Al₂O₃ (0.5–3.2 wt%) and SiO₂ (43.1–49.1 wt%), however, indicate heterogeneous re-introduction of garnet (≤13%) and orthopyroxene (≤50%). Harzburgites with high garnet and relatively low orthopyroxene modes (mostly ~7–13% and ~ 9–30%; n = 6) are characterised by mildly sinusoidal garnet REE patterns (Tb->Dy minimum and high HREE) and Archaean depleted Hf T_DM ages (2.7–3.3 Ga; ε_Hfe: +190 to +709). In contrast, harzburgites with high orthopyroxene and relatively low garnet and modes (~1.5–7.5% and ~ 25–50%; n = 19) are characterised by highly sinuous REE patterns (Ho->Yb minimum and low HREE) and Proterozoic enriched Hf T_DM ages (0.7–1.6 Ga; ε_Hfe: −16 to +6). It is inferred that Archaean G10 garnet re-introduction caused a significant increase in HREE, making melt depletion models based on HREE inaccurate. Orthopyroxene addition, a few hundred million years later, most likely at ~2.7 Ga and associated with Ventersdorp magmatic activity, caused partial consumption of garnet and olivine, and changed garnet compositions leading to: 1) Cr/Al ratio increase; 2) HREE decrease; 3) more sinusoidal REE patterns; and 4) un-radiogenic ¹⁷⁶Hf/¹⁷⁷Hf. Garnets define a Lu->Hf isochron age of 2702 ± 64 Ma (ε_Hfi = +44, n = 31), which is interpreted as a consequence of partial isotopic equilibrium within the SCLM and mixing of the garnet- and orthopyroxene-rich metasomatic components. The low LILE contents and absence of Nb->Ta anomalies are consistent with modal metasomatism caused by intra-plate magmatism. In addition, the REE signatures of metasomatic agents in equilibrium with the garnets suggest that carbonatitic melts and SiO₂-rich hydrous melts were responsible for re-introduction of garnet and orthopyroxene, respectively. Sr->Nd isotope systematics were disrupted associated with kimberlite magmatism (Nd isochron: 217 ± 58 Ma, ε_Ndi = +4; n = 34), consistent with recent G10 garnet transformation into G9 garnets (Ca + Fe-enriched). This event may have caused garnet addition (up to 1%), suggesting that garnet was formed or destroyed in at least 4 different events: i) initial extensive polybaric melting, ii) asthenospheric melts re-introducing the bulk of the garnet, iii) orthopyroxene addition and garnet loss, all in the Archaean, and iv) minor garnet addition possibly related to recent kimberlite magmatism prior to eruption.

研究了来自Kaapvaal Craton（南非）的金伯利的三十九个石榴石harzburgites，以限制亚克拉通岩石圈地幔（SCLM）的起源，年龄和演化。为了避免由于最近的交代作用而造成化学叠印，仅对肉眼观察不到无斜环的石榴石harzburgite进行采样。然而，大多数石榴石都与斜比茂（39个中的24个）处于平衡状态。介绍了整个岩石和矿物的主要微量元素地球化学和石榴石Sr-Nd-Hf同位素数据。平衡压力范围为3.8–6.1 GPa，这表明哈兹伯格岩是从SCLM的很大一部分（〜115–185 km）中获得的。高橄榄石Mg＃（〜93.4，n= 39）且低全岩重稀土元素（HREE）含量与较大程度的部分熔融（> 45％）和石榴石耗尽相符，留下橄榄岩≥90％，邻二甲苯≤10％和HREE <0.01倍的二元残渣球粒陨石。矿物模式，即整个岩石中的Al ₂ O ₃（0.5–3.2 wt％）和SiO ₂（43.1–49.1 wt％），表明石榴石（≤13％）和邻二甲苯（≤50％）的异质再引入。石榴石含量高而邻苯二酚模式相对较低的Harzburgites（主要为〜7–13％和〜9–30％；n = 6）的特征是轻度正弦形石榴石REE模式（Tb-> Dy最小和高HREE）和古生的贫化Hf T_糖尿病年龄（2.7–3.3 Ga; _εHfe：+190至+709）。相比之下，具有高邻苯二茂基和相对较低石榴石和模态（〜1.5–7.5％和〜25–50％；n = 19）的哈茨堡石的特征是高度曲折的REE模式（Ho-> Yb最小值和低HREE）和元古代富集HFŤ _DM年龄（0.7-1.6 GA;ε _HFE：-16至+6）。可以推断，重新引入古细菌G10石榴石会导致HREE显着增加，从而使基于HREE的熔体耗尽模型不准确。几亿年后添加的邻二甲苯，最有可能在〜2.7 Ga时发生，并与Ventersdorp岩浆活动有关，引起石榴石和橄榄石的部分消耗，并改变了石榴石成分，导致：1）Cr / Al比增加；2）HREE减少；3）更多的正弦REE模式；和4）不辐射¹⁷⁶ f / ¹⁷⁷ f。石榴石定义的Lu-> Hf等时年龄为2702±64 Ma（_εHfi = +44，n = 31），这被解释为SCLM中部分同位素平衡以及富含石榴石和富含邻苯二茂基的交代物混合的结果成分。低LILE含量和Nb-> Ta异常的缺失与板内岩浆作用引起的模态交代作用是一致的。此外，与石榴石平衡的交代剂的REE特征表明，碳酸盐熔体和富含SiO _2的含水熔体分别负责重新引入石榴石和邻二甲苯。与金伯利岩岩浆作用有关的Sr-> Nd同位素系统被破坏（Nd等时线：217±58 Ma，_εNdi= +4; n = 34），这与最近的G10石榴石转化为G9石榴石（富含Ca + Fe）相一致。此事件可能导致了石榴石的添加（高达1％），表明石榴石是在至少4种不同的事件中形成或破坏的：i）最初的广泛多巴的融化，ii）软流圈熔体重新引入了大量的石榴石，iii）邻苯二甲醚的添加和石榴石的流失，都在古生菌中，以及iv）少量的石榴石添加可能与喷发前最近的金伯利岩岩浆作用有关。