The 1370 Ma Gifford Creek Carbonatite Complex (GCCC) comprises a diverse suite of alkaline dyke and sill complexes that cover an area of ~ 250 km 2 in the Gascoyne Province, Western Australia. Most carbonatite types are interpreted to be related products of fractional crystallisation, with calcite carbonatites representing cumulate rocks and dolomite carbonatites representing crystallised products of the derivative liquids. Genetic relationships between these carbonatites and other alkaline igneous units are less clear. The ankerite–siderite carbonatites and magnetite-biotite dykes are likely of related magmatic origin as both have distinctly high LREE and low HFSE contents. The ankerite–siderite carbonatites have mantle-like δ 13 C isotope values of − 6.1 to − 7.1‰ and similar geochemistry to other known magmatic ferrocarbonatites. Silica-rich alkaline veins found near the centre of the complex have trace element signatures that are antithetic to the magnetite–biotite dykes, so these veins are interpreted to represent products of alkali- and F-rich magmatic-hydrothermal fluids exsolved from the magnetite–biotite dykes during their emplacement. Carbon, O, Sr, and Nd isotope data are consistent with an enriched mantle source for the origin of the GCCC, with mantle enrichment likely caused by plate convergence processes associated with the c. 2.0 Ga Glenburgh Orogeny. There is no evidence to link mantle plume activity with formation of the GCCC; rather, alkaline magmatism is interpreted to result from low degree melting of the metasomatised mantle during reactivation of the crustal suture zone at 1370 Ma. The carbonatitic magmas utilised the Lyons River Fault to traverse the crust to be emplaced as the GCCC. Post magmatic alteration has variably modified the O and Sr isotope compositions of carbonates from these rocks. We therefore appeal for careful evaluation of isotopic data from ancient carbonatites, as isotopic resetting may be more common than currently recognised.

中文翻译：

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西澳大利亚吉福德溪碳酸岩复合体的岩石成因

1370 Ma Gifford Creek Carbonatite Complex (GCCC) 包括一套多样化的碱性岩脉和窗台复合体，覆盖西澳大利亚加斯科因省约 250 平方公里的区域。大多数碳酸岩类型被解释为分步结晶的相关产物，方解石碳酸岩代表堆积岩，白云石碳酸岩代表衍生液体的结晶产物。这些碳酸盐岩和其他碱性火成岩单元之间的成因关系不太清楚。铁橄榄石-菱铁矿碳酸盐岩和磁铁矿-黑云母岩脉可能具有相关的岩浆成因，因为两者都具有明显高的 LREE 和低 HFSE 含量。铁橄榄石-菱铁矿碳酸盐岩具有类似地幔的 δ 13 C 同位素值为 - 6.1 至 - 7.1‰，地球化学性质与其他已知的岩浆碳酸铁岩相似。在复合体中心附近发现的富含二氧化硅的碱性矿脉具有与磁铁矿-黑云母岩脉对立的微量元素特征，因此这些矿脉被解释为代表从磁铁矿中溶出的富含碱性和 F 的岩浆热液的产物——就位期间的黑云母岩脉。碳、O、Sr 和 Nd 同位素数据与 GCCC 起源的富集地幔源一致，地幔富集可能是由与 c. 2.0 Ga 格伦堡造山运动。没有证据表明地幔柱活动与 GCCC 的形成有关；相反，碱性岩浆作用被解释为地壳缝合带在 1370 Ma 重新激活期间交代地幔的低度熔化造成的。碳酸岩岩浆利用里昂河断层横穿地壳，形成GCCC。岩浆蚀变改变了这些岩石中碳酸盐的 O 和 Sr 同位素组成。因此，我们呼吁对古代碳酸岩的同位素数据进行仔细评估，因为同位素重置可能比目前认识的更常见。