CRUSTAL CARBONATITES: DEFINITION, GEOLOGY, MINERALOGY, AND GEOCHEMISTRY

This is a synopsis of the available data on crustal carbonatites, including their temporal and spatial distribution, mineralogy, geochemistry, and stable isotope (δ 18 O and δ 13 C) patterns. Crustal carbonatites are intrusive rocks containing >50 vol. % carbonate minerals and ≤20 wt. % SiO 2 , which crystallize from partial melts of primary sedimentary carbonate rocks in the lower crust. They commonly occur as dykes in high-grade metamorphic complexes, bear silicate minerals typical of metasomatic environments, show isotopic and geochemical signatures of carbonate sediments or transitional varieties to mantle-derived carbonatites, and are emplaced during tectonic activity in strike-slip, rifting, or postcollisional extension settings. Partial melting of carbonate material in the crust and intrusion of melt batches to shallower crust levels is possible provided that primary carbonate sediments are present in the lower crust while the melting region is heated up by underplated mantle mafic magma and is fluxed sufficiently with H 2 O-rich fluids.