Anatexis of meta-marls generates (silico-)carbonatites in orogenic settings

The genesis of anatectic carbonatites – i.e., rocks crystallized from carbonate melts generated by partial melting of metasediments – remains unclear, though essential to elucidate their occurrence. Reports of anatectic carbonatites are increasing, but their origin from marly metasediments has never been proved. Here we present mesostructural, microstructural and geochemical evidence documenting the origin of anatectic carbonatites through in situ incongruent melting of meta-marls in an orogenic setting. The presence of silicate vs calc-silicate assemblages (K-feldspar vs calcite ± scapolite) interstitially crystallized in distinct domains of the migmatitic meta-marl leucosome indicates late-stage immiscibility between silicate and (silico-)carbonate liquids, preceded by fractional crystallization. The carbonate/silicate melt partition coefficients estimated for major elements are consistent with those experimentally determined for water-bearing silica-rich potassic systems. Our results introduce a new perspective on carbonatite genesis by proposing a viable process for generating carbonate melts in the orogenic crust, challenging the prevailing view that most carbonatites are mantle-derived.