Detrital chromites are commonly reported within Archean metasedimentary rocks, but have thus far garnered little attention for use in provenance studies. Systematic variations of Cr–Fe spinel mineral chemistry with changing tectonic setting have resulted in the extensive use of chromite as a petrogenetic indicator, and so detrital chromites represent good candidates to investigate the petrogenesis of eroded Archean mafic and ultramafic crust. Here, we report the compositions of detrital chromites within fuchsitic (Cr-muscovite rich) metasedimentary rocks from the Jack Hills, situated within the Narryer Terrane, Yilgarn Craton, Western Australia, which are geologically renowned for hosting Hadean (>4000 Ma) zircons. We highlight signatures of metamorphism, including highly elevated ZnO and MnO, coupled with lowered Mg# in comparison with magmatic chromites, development of pitted domains, and replacement of primary inclusions by phases that are part of the metamorphic assemblages within host metasedimentary rocks. Oxygen isotope compositions of detrital chromites record variable exchange with host metasedimentary rocks. The variability of metamorphic signatures between chromites sampled only meters apart further indicates that modification occurred in situ by interaction of detrital chromites with metamorphic fluids and secondary mineral assemblages. Alteration probably occurred during upper greenschist to lower amphibolite facies metamorphism and deformation of host metasedimentary rocks at ∼2650 Ma. Regardless of metamorphic signatures, sampling location or grain shape, chromite cores yield a consistent range in Cr#. Although other key petrogenetic indices, such as Fe2O3 and TiO2 contents, are complicated in Jack Hills chromites by mineral non-stoichiometry and secondary mobility within metasedimentary rocks, we demonstrate that the Cr# of chromite yields significant insights into their provenance. Importantly, moderate Cr# (typically 55–70) precludes a komatiitic origin for the bulk of chromites, reflecting a dearth of komatiites and intrusive equivalents within the erosional catchment of the Jack Hills metasedimentary units. We suggest that the Cr# of Jack Hills chromite fits well with chromites derived from layered intrusions, and that a single layered intrusion may account for the observed chemical compositions of Jack Hills detrital chromites. Where detailed characterization of key metamorphic signatures is undertaken, detrital chromites preserved within Archean metasedimentary rocks may therefore yield valuable information on the petrogenesis and geodynamic setting of poorly preserved mafic and ultramafic crust.

中文翻译：

---

来自西澳大利亚杰克希尔斯的碎屑铬铁矿：变质作用的特征和来源的限制

碎屑铬铁矿通常在太古宙变沉积岩中被报道，但迄今为止在物源研究中很少受到关注。Cr-Fe尖晶石矿物化学随构造环境变化的系统变化导致铬铁矿被广泛用作岩石成因指示剂，因此碎屑铬铁矿是研究侵蚀的太古代镁铁质和超镁铁质地壳岩石成因的良好候选者。在这里，我们报告了位于西澳大利亚州伊尔加恩克拉通的 Narryer 地块内的 Jack Hills 的褐铁矿（富含 Cr-白云母）变沉积岩中的碎屑铬铁矿的组成，该地块在地质上以拥有 Hadean（>4000 Ma）锆石而闻名. 我们强调变质作用的特征，包括高度升高的 ZnO 和 MnO，再加上与岩浆铬铁矿相比降低的 Mg#、坑状域的发育以及原生包裹体被作为宿主变质沉积岩中变质组合的一部分的相替代。碎屑铬铁矿的氧同位素组成记录了与宿主变沉积岩的可变交换。相距仅数米采样的铬铁矿之间变质特征的可变性进一步表明，通过碎屑铬铁矿与变质流体和次生矿物组合的相互作用，就地发生了改性。蚀变可能发生在上绿片岩到下角闪岩相变质作用和宿主变沉积岩变形过程中~2650 Ma。无论变质特征、取样位置或晶粒形状如何，铬铁矿岩心产生的 Cr# 范围是一致的。尽管杰克希尔斯铬铁矿的其他关键岩石成因指数（如 Fe2O3 和 TiO2 含量）因矿物非化学计量和变沉积岩内的二次流动性而变得复杂，但我们证明铬铁矿的 Cr# 对它们的来源产生了重要的见解。重要的是，中等 Cr#（通常为 55-70）排除了大部分铬铁矿的科马提岩起源，这反映了杰克山变沉积单元的侵蚀集水区内缺乏科马提岩和侵入性等效物。我们认为 Jack Hills 铬铁矿的 Cr# 与来自层状侵入体的铬铁矿非常吻合，并且单层侵入体可能解释了观察到的 Jack Hills 碎屑铬铁矿的化学成分。在对关键变质特征进行详细表征的情况下，