A major debris flow, the Trig Point Hill flow, originating from Kerimasi volcano (Tanzania) contains numerous blocks of extrusive/pyroclastic carbonatites similar to those exposed at the rim of the currently inactive crater. The blocks of calcite carbonatite consist of: (1) large clasts of corroded and altered coarse grained calcite; (2) primary prismatic inclusion bearing phenocrystal calcite; and (3) a matrix consisting primarily of fine-grained prismatic calcite. The large clasts are inclusion free and exhibit a ‘corduroy-like’ texture resulting from solution along cleavage planes. The resulting voids are filled by brown Fe–Mn hydroxides/oxides and secondary calcite. The prismatic or lath-shaped phenocrystal calcite is not altered and contains melt inclusions consisting principally of primary Na–Ca carbonates which contain earlier-formed crystals of monticellite, periclase, apatite, Mn–Mg-magnetite, Mn–Fe-sphalerite and Nb-perovskite. Individual Na–Ca carbonate inclusions are of uniform composition, and the overall range of all inclusions analysed (wt.%) is from 28.7 to 35.9 CaO; 16.7–23.6 Na2O; 0.5–2.8 K2O, with minor SO3 (1.1–2.2) and SrO (0.34–1.0). The Na–Ca carbonate compositions are similar to that of shortite, although this phase is not present. The Na–Ca carbonates are considered to be primary deuteric phases and not secondary minerals formed after nyerereite. Monticellite shows limited compositional variation and contains 2–4 wt.% MnO and 12 wt.% FeO and is Mn-poor relative to monticellite in Oldoinyo Lengai natrocarbonatite. Periclase is Fe-bearing with up to 13 wt.% FeO. Spinels are Cr-free, Mn-poor and belong to the magnetite–magnesioferrite series in contrast to Mn-rich spinels of the magnetite–jacobsite series occurring in Oldoinyo Lengai natrocarbonatite. The matrix in which the ‘corduroy’ clasts and phenocrystal calcite are set consists of closely packed small prisms of calcite lacking melt inclusions, with interstitial fine-grained apatite, baryte, strontianite and minor fluorite. Pore spaces are filled with secondary Mn–Fe hydroxides/oxides, anhydrite and gypsum. The hypothesis that flow-aligned calcite in volcanic calciocarbonatites from Kerimasi, Tinderet, Homa and Catanda is altered nyerereite is discussed and it is considered that these calcite are either primary phases or altered melilite. The nyerereite alteration hypothesis is discussed with respect to the volumetric and compositional aspects of pseudomorphism by dissolution–precipitation replacement mechanisms. This study concludes that none of the volcanic calciocarbonatites containing flow-aligned calcite phenocrysts are altered natrocarbonatite.

源自 Kerimasi 火山（坦桑尼亚）的主要泥石流 Trig Point Hill 流包含许多喷出/火山碎屑碳酸盐岩块，类似于暴露在当前不活动火山口边缘的那些。方解石碳酸岩块由：（1）腐蚀和蚀变粗粒方解石的大碎屑；(2)含物晶方解石的原生棱柱状包裹体；(3) 主要由细粒棱柱方解石组成的基质。大的碎屑不含内含物，并呈现出“灯芯绒般”的质地，这是由沿着解理面的溶液产生的。由此产生的空隙被棕色的 Fe-Mn 氢氧化物/氧化物和二次方解石填充。棱柱状或板条状表晶方解石未发生蚀变，含有主要由原生 Na-Ca 碳酸盐组成的熔体包裹体，其中包含早期形成的蒙脱石、方镁石、磷灰石、Mn-Mg-磁铁矿、Mn-Fe-闪锌矿和 Nb-钙钛矿。单个 Na-Ca 碳酸盐夹杂物成分均匀，分析的所有夹杂物的总体范围 (wt.%) 为 28.7 至 35.9 CaO；16.7–23.6 钠2 O; 0.5–2.8 K 2 O，含少量 SO 3(1.1–2.2) 和 SrO (0.34–1.0)。Na-Ca 碳酸盐组成与短铁矿相似，尽管该相不存在。Na-Ca 碳酸盐被认为是主要的氘相，而不是在镍铁矿之后形成的次生矿物。蒙脱石显示出有限的成分变化，包含 2-4 wt.% MnO 和 12 wt.% FeO，相对于 Oldoinyo Lengai natrocarbonatite 中的蒙脱石，锰含量较低。方镁石是含铁的，含有高达 13 wt.% 的 FeO。尖晶石不含铬、锰含量低，属于磁铁矿-镁铁氧体系列，而富锰尖晶石是产于 Oldoinyo Lengai natrocarbonatite 的磁铁矿-雅克文系列的富锰尖晶石。“灯芯绒”碎屑和表晶方解石所在的基质由紧密堆积的方解石小棱柱组成，没有熔体包裹体，间质细粒磷灰石、重晶石、菱锶矿和少量萤石。孔隙空间充满了二次 Mn-Fe 氢氧化物/氧化物、硬石膏和石膏。讨论了来自 Kerimasi、Tinderet、Homa 和 Catanda 的火山钙碳酸盐岩中的流动排列方解石是蚀变尼雷石的假设，并认为这些方解石要么是初级相，要么是蚀变黄长石。关于通过溶解-沉淀置换机制产生的假晶现象的体积和组成方面讨论了尼雷石蚀变假说。该研究得出的结论是，含有流动排列的方解石斑晶的火山钙碳酸盐岩都不是蚀变的碳酸盐岩。讨论了来自 Kerimasi、Tinderet、Homa 和 Catanda 的火山钙碳酸盐岩中的流动排列方解石是蚀变尼雷石的假设，并认为这些方解石要么是初级相，要么是蚀变黄长石。关于通过溶解-沉淀置换机制产生的假晶现象的体积和组成方面讨论了尼雷石蚀变假说。该研究得出的结论是，含有流动排列的方解石斑晶的火山钙碳酸盐岩都不是蚀变的碳酸盐岩。讨论了来自 Kerimasi、Tinderet、Homa 和 Catanda 的火山钙碳酸盐岩中的流动排列方解石是蚀变尼雷石的假设，并认为这些方解石要么是初级相，要么是蚀变黄长石。关于通过溶解-沉淀置换机制产生的假晶现象的体积和组成方面讨论了尼雷石蚀变假说。该研究得出的结论是，含有流动排列的方解石斑晶的火山钙碳酸盐岩都不是蚀变的碳酸盐岩。关于通过溶解-沉淀置换机制产生的假晶现象的体积和组成方面讨论了尼雷石蚀变假说。该研究得出的结论是，含有流动排列的方解石斑晶的火山钙碳酸盐岩都不是蚀变的碳酸盐岩。关于通过溶解-沉淀置换机制产生的假晶现象的体积和组成方面讨论了尼雷石蚀变假说。该研究得出的结论是，含有流动排列的方解石斑晶的火山钙碳酸盐岩都不是蚀变的碳酸盐岩。