Evidence for low-pressure incongruent melting of limestone containing up to 40 wt% of silicate minerals (marly limestone) is reported from the Khamaryn–Khural–Khiid Combustion Metamorphic (CM) complex in East Mongolia. Marly limestone exposed to high-temperature metamorphism during wild coal fires has acquired a mineral assemblage consisting of gehlenitic melilite and Al-diopside-to-kushiroite-dominant clinopyroxene as main phases and rare phases of celsian, spinel, perovskite, geikielite, etc. Melting of silicate minerals and calcite produced silicate melts of different compositions and stoichiometric calcitic (CaCO₃) or non-stoichiometric carbonatite-like (CaCO₃ + CaO) melts. Coalescence of silicate melt drops was followed by the formation of silica-undersaturated Ca-rich and Na-bearing paralava melts. Melilite-nepheline paralavas discovered in the Khamaryn–Khural–Khiid and Nyalga CM complexes in Mongolia have exceptional features of mineralogy and chemistry due to a rare combination of P–T conditions associated with wild coal fires and combustion metamorphism: a high temperature (> 1250 °C) and fluid pressure above 4 MPa that prevented decomposition of calcite. Such paralavas from the two CM complexes are composed of similar mineral assemblages made up of melilite, clinopyroxene, plagioclase, nepheline, Fe–Ca olivines (Ca-fayalite and kirschsteinite), K-Ba feldspars (celsian and hyalophane), spinel-group minerals, and rhönite-kuratite, with broad composition variations. Paralavas of this kind have never been reported before from anywhere. Their local mineralogical and geochemical specificity may be due to variations in the composition of carbonate protolith and in physicochemical conditions above the coal fire foci (T, P, gas composition, oxygen fugacity, and melt cooling rate). Low-pressure melting of calcite and the formation of carbonate (calcitic or carbonatite-like) melts have implications for phase relations in carbonate rocks altered by high-temperature metamorphism and metasomatism, as well to the origin of carbonatites. Calcite in carbonate sediments exposed to low pressures and high temperatures (above the invariant point Q₁ in the CaCO₃ phase diagram) does not decompose and can melt. Correspondingly, metamorphic decarbonation reactions do not produce CaO required for the crystallization of many Ca-rich index minerals of spurrite–merwinite facies. The melting point of calcite decreases markedly with increasing H₂O content in the H₂O–CO₂ fluid, which may lead to melting of calcite in carbonate sediments and to formation of calcite-rich carbonatites at P–T crustal conditions.

据报道，蒙古东部的Khamaryn-Khural-Khiid燃烧变质（CM）复杂地证实了含40％（重量）以上硅酸盐矿物（石灰灰岩）的石灰石的低压不均匀熔融。在野火中暴露于高温变质作用的马来灰岩已获得一种矿物组合，其中包括风化闪锌矿和铝-透辉石-风铁矿为主的斜辉石为主，而硅藻土，尖晶石，钙钛矿，geikielite等为主要相和稀有相。硅酸盐矿物和不同的组合物和化学计量的方解石（碳酸钙的方解石产生硅酸盐熔体的₃）或非化学计量的碳酸盐类（碳酸钙₃ + CaO）熔化。硅酸盐熔体滴的聚结之后，形成了二氧化硅含量不足的富钙和含钠的巴拉瓦熔体。在蒙古的Khamaryn–Khural–Khiid和Nyalga CM配合物中发现的美长石-霞石巴拉瓦斯矿物具有独特的矿物学和化学特征，这是由于P–T的罕见结合与野火和燃烧变质相关的条件：高温（> 1250°C）和高于4 MPa的流体压力可防止方解石分解。来自两个CM配合物的这类巴拉瓦由相似的矿物组合组成，该组合由以下组成：陨石，斜辉石，斜长石，霞石，Fe-Ca橄榄石（Ca-铁橄榄石和Kirschsteinite），K-Ba长石（硅藻土和透明石），尖晶石族矿物，以及rhönite-kuratite，具有广泛的成分差异。从未有过这样的巴拉瓦火山报道。它们的局部矿物学和地球化学特异性可能是由于碳酸盐原生岩的组成变化以及煤火震源上方的理化条件（T，P，气体组成，氧气逸度和熔体冷却速率）。方解石的低压熔融和碳酸盐（方解石或类碳酸盐样）熔体的形成对高温变质作用和交代作用所改变的碳酸盐岩的相关系以及碳酸盐的成因都具有重要意义。暴露于低压和高温下（在CaCO ₃相图中不变点Q ₁以上）的碳酸盐沉积物中的方解石不会分解并且会熔化。相应地，变质脱碳反应不产生钙铁矿–闪锌矿相的许多富含钙的指数矿物的结晶所需的CaO。随着H ₂ O–CO中H ₂ O含量的增加，方解石的熔点显着降低₂流体，这可能导致在碳酸盐沉积物和在形成富方解石碳酸盐的方解石的熔化对-叔地壳条件。