Ca-rich carbonates associated with ultrabasic-ultramafic melts: Carbonatite or limestone xenoliths? A case study from the late Miocene Morron de Villamayor volcano (Calatrava Volcanic Field, central Spain)

The volcanic products of the late Miocene Morron de Villamayor volcano (Calatrava Volcanic Field, central Spain) are known for being one of the few outcrops of leucitites in the entire circum-Mediterranean area. These rocks are important because aragonite of mantle origin has been reported as inclusion in olivine macrocrysts. We use petrographic observations, mineral compositions, as well as oxygen and carbon isotope ratios coupled with experimental petrology to understand the origin of carbonate phase in these olivine-phyric rocks. Groundmass and macrocryst olivines range from delta O-18(VSMOW) of + 4.8 parts per thousand, typical of mantle olivine values, to + 7.4 parts per thousand, indicating contamination by sedimentary carbonate. Carbonates are characterized by heavy oxygen isotope compositions (delta O-18(VSMOW) >+ 24 parts per thousand), and relatively light carbon isotopes (delta(CPDB)-C-13 < -11 parts per thousand), resembling skarn values, and distinct from typical mantle carbonatite compositions.