Aillikites are carbonate-rich ultramafic lamprophyres often associated with carbonatites. Despite their common field relationships, the petrogenetic links, if any, between aillikites and carbonatites remain controversial. To address this question, this study reports the results of a detailed geochemical and isotopic examination of the Permian Wajilitag aillikites in the northwestern Tarim large igneous province, including bulk-rock major- and trace-element and Sr–Nd isotope compositions, olivine major- and trace-element and (in situ secondary ion mass spectrometry) oxygen isotope compositions, oxygen isotope data for clinopyroxene separates, and bulk-carbonate C–O isotopic analyses. Olivine in the aillikites occurs in two textural types: (1) microcrysts, 0·3–5 mm; (2) macrocrysts, 0·5–2·5 cm. The microcrysts exhibit well-defined linear correlations between Fo (79–89) and minor and trace elements (e.g. Ni = 1304–3764 μg g–1 and Mn = 1363–3042 μg g–1). In contrast, the olivine macrocrysts show low Fo (79–81), Ni (5·3–442 μg g–1) and Ca (477–1018 μg g–1) and very high Mn (3418–5123 μg g–1) contents, and are displaced from the compositional trend of the microcrysts. The microcrysts are phenocrysts crystallized from the host aillikite magmas. Conversely, the lack of mantle-derived xenoliths in these aillikites suggests that the macrocrysts probably represent cognate crystals (i.e. antecrysts) that formed from earlier, evolved aillikite melts. Olivine phenocrysts in the more primitive aillikite dykes (Dyke 1) have relatively higher Fo (Fo82–89) and mantle-like oxygen isotope values, whereas those in the more evolved dykes (Dykes 2 and 3) exhibit lower Fo (Fo79–86) and oxygen isotope values that trend toward lower than mantle δ18O values. The decreasing δ13C values of carbonate from Dyke 1 to Dykes 2 and 3, coupled with the indistinguishable Sr–Nd isotopes of these dykes, suggest that the low δ18O values of olivine phenocrysts in Dykes 2 and 3 resulted from carbonate melt/fluid exsolution from a common progenitor melt. These lines of evidence combined with the overlapping emplacement ages and Sr–Nd isotope compositions of the aillikites and carbonatites in this area suggest that these exsolved carbonate melts probably contributed to the formation of the Tarim carbonatites, thus supporting a close petrogenetic relationship between aillikites and carbonatites.

中文翻译：

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塔里木大火成岩省埃利基岩与碳酸岩成岩联系的地球化学和O-C-Sr-Nd同位素约束

Aillikite 是富含碳酸盐的超镁铁质灯石，通常与碳酸盐岩有关。尽管它们有共同的领域关系，但 aillikite 和碳酸盐岩之间的成岩联系（如果有的话）仍然存在争议。为了解决这个问题，本研究报告了对塔里木西北部大型火成岩省二叠纪瓦吉里塔格埃利基岩的详细地球化学和同位素检查结果，包括块状岩石主要元素和微量元素以及 Sr-Nd 同位素组成、橄榄石主要-和微量元素和（原位二次离子质谱）氧同位素组成，单斜辉石分离的氧同位素数据，以及本体碳酸盐 C-O 同位素分析。橄榄石中的橄榄石有两种质地类型：（1）微晶，0·3-5 mm；(2) 大晶体，0·5–2·5 cm。微晶在 Fo (79-89) 与微量元素和微量元素（例如 Ni = 1304-3764 μg g-1 和 Mn = 1363-3042 μg g-1）之间表现出明确的线性相关性。相比之下，橄榄石大晶的 Fo (79-81)、Ni (5·3-442 μg g-1) 和 Ca (477-1018 μg g-1) 和非常高的 Mn (3418-5123 μg g-1) ) 含量，并且偏离了微晶的成分趋势。微晶是从宿主埃利沸石岩浆中结晶出来的斑晶。相反，在这些埃利基岩中缺乏源自地幔的捕虏体表明，这些大晶体可能代表了由早期演化的埃利基岩熔体形成的同源晶体（即前晶）。更原始的埃利基岩脉（Dyke 1）中的橄榄石斑晶具有相对较高的 Fo（Fo82-89）和类似地幔的氧同位素值，而那些在更进化的岩脉（Dykes 2 和 3）中表现出较低的 Fo（Fo79-86）和氧同位素值，趋向于低于地幔 δ18O 值。从 Dyke 1 到 Dykes 2 和 Dykes 3，碳酸盐的 δ13C 值降低，再加上这些 Dykes 的 Sr-Nd 同位素难以区分，表明 Dykes 2 和 Dykes 3 中橄榄石斑晶的低 δ18O 值是由于碳酸盐熔体/流体从一个共同祖先融化。这些证据与该地区埃利克岩和碳酸盐岩的重叠侵位年龄和Sr-Nd同位素组成表明，这些溶出的碳酸盐熔体可能促成了塔里木碳酸盐岩的形成，从而支持了埃利克岩和碳酸盐岩之间密切的岩石成因关系。 .