We review the properties of the Neoarchean Ventersdorp Supergroup and provide new trace element concentrations and the first combined Sr-Nd-Hf isotopic compositions for the mafic magmatic products. These sequences contain the remnants of some of the world's oldest Large Igneous Provinces (total preserved volume = 0.659 × 10 km). Ventersdorp rocks have been divided into three major units, separated by prominent unconformities: the basal Klipriviersberg Group (∼2.78 Ga), the medial Platberg Group (2.72 Ga) and the upper Pniel Sequence (2.68 Ga). The base of the Klipriviersberg Group is the Westonaria Formation, composed almost entirely of picrites (12–18 wt% MgO) and komatiites (>18 wt% MgO). All other formations of the Klipriviersberg Group contain mainly basaltic (<12 wt% MgO, 45–57 wt% SiO) and andesitic rocks (57–63 wt% SiO). The Platberg Group is composed of bimodal mafic lavas (Goedgenoeg and Rietgat Formations) and crustally derived dacites and rhyolites (Makwassie Formation); we did not study the crustally derived sequences. The Pniel Sequence contains basaltic lavas in the Allanridge Formation (<7.8 wt% MgO). Strontium isotopes have been modified by extensive low-grade hydrothermal alteration processes and cannot be used to make inferences about magmatic processes. Initial ε and ε values are highest for Westonaria picrites and komatiites (maximum ε = +2.16; ε = +3.60), and match Neoarchean depleted, asthenospheric mantle, implying derivation from large degree partial melting in a plume head. Klipriviersberg basaltic-komatiitic lavas have the largest volume (0.145 × 10 km), qualifying this as a Large Igneous Province in its own right; Platberg and Allanridge basalts and basaltic andesites have unradiogenic ε and ε (ε = −2.45 to −4.01; ε = −2.73 to −10.12), and lower volumes (Platberg = 0.022 × 10 km; Allanridge = 0.042 × 10 km), too small to represent LIPs. Although Westonaria picrites and komatiites were likely sourced from the hot, central portions of a flattened plume head, the other magmatic Formations in the Ventersdorp Supergroup may have been derived from cooler, compositionally different, marginal parts of the plume head, or possibly the plume tail. The three Ventersdorp magmatic components can be interpreted in terms of a single, long-lasting plume, with the spatial overlap having been caused by a stationary African plate over a time interval of >100 million years. Trace element ratios and isotopic compositions suggest that fractional crystallization and crustal assimilation were minor to absent in Ventersdorp basaltic magmas. Negative NbTa anomalies are present in all magmatic rocks except those of the Westonaria Formation, suggesting that the lithospheric mantle component bears a subduction signature; this component probably represents deeply subducted oceanic lithosphere that was entrained in the deep mantle by an ascending plume. Volume and compositional relations preclude derivation of the basaltic lavas from subcontinental lithospheric mantle or small, enriched domains in the SCLM. Zn/Fe relations can be interpreted in terms of heterogeneous sub-lithospheric mantle sources, with Klipriviersberg Group lavas having been derived dominantly from peridotitic sources, whereas Platberg and Allanridge mafic lavas were derived from a source richer in pyroxenitic components. Our new Nd isotopic data coupled with lithostratigraphic differences indicate that correlations between the Ventersdorp (South Africa) and the coeval (2.77–2.71 Ga) Fortescue (Australia) sequences are more complex than is currently understood, possibly reflecting differences in basin structure and evolution. More data are needed to constrain the Vaalbara hypothesis, which postulates that the Kaapvaal and Pilbara Cratons were adjoined in the late Archean.

中文翻译：

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南非文特斯多普大火成岩省的新太古代熔岩：Sr-Nd-Hf同位素和微量元素证据证明静止的非洲大陆下方存在长期存在的羽流

我们回顾了新太古代文特斯多普超群的性质，并提供了新的微量元素浓度和镁铁质岩浆产物的第一个组合 Sr-Nd-Hf 同位素组成。这些序列包含一些世界上最古老的大型火成岩省的遗迹（总保存体积 = 0.659 × 10 km）。文特斯多普岩石被分为三个主要单元，由显着的不整合面隔开：基底 Klipriviersberg 群（∼2.78 Ga）、内侧 Platberg 群（2.72 Ga）和上部 Pniel 层序（2.68 Ga）。 Klipriviersberg 群的底部是 Westonaria 地层，几乎完全由苦味石（12-18 wt% MgO）和科马提岩（>18 wt% MgO）组成。 Klipriviersberg 群的所有其他地层主要含有玄武岩（<12 wt% MgO、45–57 wt% SiO）和安山岩（57–63 wt% SiO）。 Platberg 群由双峰式镁铁质熔岩（Goedgenoeg 和 Rietgat 组）和地壳衍生的英安岩和流纹岩（Makwassie 组）组成；我们没有研究地壳衍生的序列。 Pniel 层序包含 Allanridge 地层中的玄武岩熔岩（<7.8 wt% MgO）。锶同位素已被广泛的低品位热液蚀变过程所改变，不能用于推断岩浆过程。 Westonaria 苦味岩和科马提岩的初始 ε 和 ε 值最高（最大值 ε = +2.16；ε = +3.60），与新太古代贫化的软流圈地幔相匹配，这意味着源自羽流头部的大规模部分熔融。 Klipriviersberg 玄武岩-科马提岩熔岩体积最大（0.145 × 10 km），使其本身就具有大型火成岩省的资格； Platberg 和 Allanridge 玄武岩以及玄武安山岩具有非放射性 ε 和 ε (ε = -2.45 至 -4.01; ε = -2.73 至 -10.12)，并且体积也较低 (Platberg = 0.022 × 10 km; Allanridge = 0.042 × 10 km)小代表 LIP。尽管韦斯托尼亚苦味岩和科马提岩很可能源自扁平羽流头部的炎热中央部分，但文特斯多普超群中的其他岩浆岩层可能源自羽流头部较冷、成分不同的边缘部分，或者可能来自羽流尾部。文特斯多普的三个岩浆成分可以用单一的、持久的羽流来解释，其空间重叠是由静止的非洲板块在超过 1 亿年的时间间隔内造成的。微量元素比率和同位素组成表明，文特斯多普玄武岩浆中的分步结晶和地壳同化作用很小甚至不存在。除 Westonaria 组外，所有岩浆岩中均存在 NbTa 负异常，表明岩石圈地幔成分具有俯冲特征；这个部分可能代表了深俯冲的海洋岩石圈，它被上升的地幔柱夹带在深部地幔中。体积和成分关系排除了玄武岩熔岩源自次大陆岩石圈地幔或 SCLM 中小型富集区域的可能性。 Zn/Fe 关系可以用异质亚岩石圈地幔源来解释，Klipriviersberg 群熔岩主要源自橄榄岩源，而 Platberg 和 Allanridge 镁铁质熔岩则源自富含辉石岩成分的源。我们的新 Nd 同位素数据加上岩石地层差异表明，文特斯多普（南非）和同时期（2.77-2.71 Ga）福蒂斯丘（澳大利亚）序列之间的相关性比目前理解的更为复杂，可能反映了盆地结构和演化的差异。需要更多数据来约束瓦尔巴拉假说，该假说假设卡普瓦尔克拉通和皮尔巴拉克拉通在太古代晚期毗邻。