Timing of pegmatite emplacement and skarn formation in the Malyovitsa Unit, NW Rila: evidence from zonal grossular crystals

Contact Ca-skarns are formed in the marbles of the Malyovitsa Lithotectonic Unit as a result of emplacement of crosscutting pegmatite injections in the area of the Dzhendemski Ezera, NW Rila Mt. Large (up to 4 cm), well-shaped garnet crystals dominate the mineral association with additional vesuvianite, diopside, scapolite and zoisite. Garnets were selected for mineralogical, geochemical and U-Pb geochronological study. Their crystals show clear zonal pattern due to variation in the octahedral position (Fe3+/Al3+), although the overall composition defines grossular predominance (72–95 mol.% grossular; 4–24% andradite). Trace-element signatures reveal constant isomorphic incorporation of P, V, Zn, Ga, Ge and Y, REE, HFSE, U. Results from the in-situ U-Pb dating of the studied skarn materials suggest the timing of pegmatite intrusion onto the metamorphic rocks and marble-hosted skarn formation at 58.37±0.70 Ma.