Molybdenum isotopes (reported as δ⁹⁸Mo relative to NIST-3134) show resolvable isotope differences in igneous rocks with the continental crust being markedly heavier in isotope composition than mid-ocean ridge lavas, lunar basalts or the Earth’s mantle. The tholeiitic differentiation series at the intra-plate Hekla volcano (Iceland) shows no resolvable Mo isotope differences from basaltic to rhyolitic compositions. In contrast, convergent margin lavas show a transition from isotopically lighter mantle to heavy continental crust, suggesting that subduction processes drive continental crust towards heavier values. Archean komatiitic lavas, presumed probes of the Archean mantle, have Mo isotope values identical to modern depleted mantle, raising the questions if and how the Mo isotope crust-mantle disparity developed so early in Earth’s history. Here we present new Mo isotope data for a set of cumulate rocks from the Upper Zone of late Archean (2.8 Ga) Windimurra Igneous Complex, a mafic/ultramafic layered intrusion. The intrusion is not subduction related and contains no apparent primary hydrous minerals. We tested the effect of crystal fractionation on Mo isotopes in relatively dry melt along a tholeiitic liquid line of descent by using the cumulate effect of normally anhydrous minerals in the layered intrusion. Near mono-mineralic olivine-pyroxene-rich, feldspar-rich and Fe-Ti-rich oxides show small variations (~0.15‰) in Mo isotope signatures. This is consequently to predominantly isotopically light Fe-Ti-oxide-rich and isotopically heavier feldspar-rich rocks, respectively. This is suggesting minor Mo isotope fractionation, even in dry, tholeiitic systems, which however, counterbalance each other and thus potentially remain undetected. On average, the Windimurra mantle source is indistinguishable, or slightly isotopically lighter than the Mo isotope signature of komatiites. This is reinforcing an isotopically light Mo isotope signature of Archean mantle sources of high-degree mantle melts and is extending these signatures to predominantly mafic Archean crust. It remains to be tested if Archean felsic crust resembles modern continental crust in its heavy isotope values and to which extend the mantle was already isotopically depleted in Mo isotopes at Mesoarchean time.

钼同位素（报告为δ ⁹⁸Mo（相对于NIST-3134）表现出火成岩中可分辨的同位素差异，其中大陆壳的同位素组成明显比中海脊熔岩，月球玄武岩或地球地幔重。板内赫克拉火山（冰岛）的生烃作用分化系列显示，从玄武质到流纹岩成分没有可分辨的Mo同位素差异。相比之下，会聚的边缘熔岩显示出从同位素更轻的地幔到沉重的大陆壳的过渡，这表明俯冲过程使大陆壳趋向于更重的值。太古代的科玛特质熔岩是太古代的地幔的推测，其钼同位素值与现代贫化地幔相同，这引发了这样的问题：钼同位素地幔视差是否以及如何在地球历史的早期发展。在这里，我们介绍了来自晚太古代（2.8 Ga）Windimurra火成岩复合体（镁铁质/超镁铁质层状侵入体）上部地区的一组堆积岩石的新Mo同位素数据。入侵与俯冲无关，并且不含明显的主要含水矿物。我们通过使用层状侵入体中正常无水矿物的累积效应，测试了沿相对液态液相线下降的相对干燥熔体中晶体分馏对Mo同位素的影响。接近单矿物的富含橄榄石-茂铁，富含长石和富含Fe-Ti的氧化物在Mo同位素特征上显示出很小的变化（〜0.15‰）。因此，这分别主要是同位素较轻的富铁钛氧化物和同位素较重的长石富集岩石。这表明即使在干燥的高脂体系中，Mo同位素的分馏程度也较小，但是，彼此抵消，因此潜在地未被发现。平均而言，温迪莫拉地幔源与科马铁矿的Mo同位素特征没有区别，或者同位素上的同位素稍轻。这加强了高地幔熔体的太古宙地幔源的同位素轻钼同位素特征，并将这些特征扩展到以镁铁质太古宙地壳为主。太古宙的长英质地壳在重同位素值方面是否与现代大陆壳类似，并且地幔延伸至同位素阶段在Mesoarchean时代已经同位素耗尽，尚待检验。这加强了高地幔熔体的太古宙地幔源的同位素轻钼同位素特征，并将这些特征扩展到以镁铁质太古宙地壳为主。太古宙的长英质地壳在重同位素值方面是否与现代大陆壳类似，并且地幔延伸至同位素阶段在Mesoarchean时代已经同位素耗尽，尚待检验。这加强了高地幔熔体的太古宙地幔源的同位素轻钼同位素特征，并将这些特征扩展到以镁铁质太古宙地壳为主。太古宙的长英质地壳在重同位素值方面是否与现代大陆壳类似，并且地幔延伸至同位素阶段在Mesoarchean时代已经同位素耗尽，尚待检验。