The paragenesis of carbonates in the Cold Bokkeveld CM chondrite is determined from a detailed petrographic, chemical, spectroscopic, and isotopic study of nine associations of carbonates (aragonite, calcite, and dolomite) with other secondary minerals that occur within the meteorite. Our study reveals the existence of carbonates displaying petrographic features that are distinct from those of type 1 and type 2 carbonates commonly observed in CM2 meteorites. These include carbonates interstitial to octahedral magnetite crystals, for which a new designation of “type 1c” is suggested. The O isotopic values of dolomite (δ¹⁸O ranging from +21.1 to +25.8‰ and Δ¹⁷O from −4.9 to −4.0‰) are similar to those measured in dolomites from other CM chondrites. The presence of complex carbonates with a CaCO₃ core and Mg-enriched rim implies several generations of fluids and/or their evolving composition on the CM parent body(ies). Petrographic characteristics indicate at least six stages of potentially overlapping carbonate and phyllosilicate formation events. We show that type 1 and type 2 calcite have distinct Raman spectral characteristics. Type 1 calcite is characterized by very broad peaks, whereas type 2 calcite displays narrow peaks similar to those of typical abiotic terrestrial calcite, suggesting high crystallinity. A carbonate Raman spectrum showing features characteristic of both aragonite and calcite likely documents an aragonite-calcite phase transition. Raman spectroscopy also reveals the presence of organic matter in the majority of carbonates. This indicates that organic carbon was mobilized by aqueous fluids for extended periods.

中文翻译：

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Cold Bokkeveld CM 球粒陨石中的碳酸盐组合揭示了复杂的母体演化

Cold Bokkeveld CM 球粒陨石中碳酸盐的共生作用是根据对碳酸盐（文石、方解石和白云石）与陨石中其他次生矿物的九种组合的详细岩相学、化学、光谱和同位素研究确定的。我们的研究揭示了碳酸盐的存在，其岩相特征不同于 CM2 陨石中常见的 1 型和 2 型碳酸盐。这些包括填隙到八面体磁铁矿晶体的碳酸盐，建议将其命名为“1c 型”。白云岩的O同位素值（δ ¹⁸ O 范围从+21.1到+25.8‰和Δ ¹⁷O 从 -4.9 到 -4.0‰) 与在来自其他 CM 球粒陨石的白云岩中测得的值相似。具有 CaCO ₃的复合碳酸盐的存在核心和富含镁的边缘意味着在 CM 母体上存在几代流体和/或它们的演化成分。岩相特征表明至少有六个阶段的碳酸盐和页硅酸盐地层事件可能重叠。我们表明 1 型和 2 型方解石具有明显的拉曼光谱特征。1 型方解石的特点是峰很宽，而 2 型方解石的峰很窄，类似于典型的非生物陆生方解石，表明结晶度高。显示文石和方解石特征的碳酸盐拉曼光谱可能记录了文石-方解石相变。拉曼光谱还揭示了大多数碳酸盐中有机物的存在。这表明有机碳在较长时间内被水性流体流动。