An ultra-high-pressure metamorphic condition and isothermal decompression path obtained from a garnet-pyroxenite in the Horní Bory granulite of the Bohemian Massif

Abstract

An ultra -high -pressure metamorphic condition (~ 140 km) at ~ 950 °C is identified from a garnet -pyroxenite, containing primary supersilicic clinopyroxene, as a part of the mafic -ultramafic lenses enclosed in the Gföhl granulite at the Horní Bory quarry of the Bohemian Massif, Czech Republic. Petrological data indicate that the garnet -pyroxenite was isothermally (~ 900 °C) exhumed from the upper mantle (~ 140 km) to the lower crust (~ 50 km), and the supersilicic clinopyroxene was decomposed to sodic augite and quartz during the exhumation. This ultra -high -pressure metamorphic evidence is the first to be derived from the mafic rock directly enclosed within the Horní Bory granulite in the Moldanubian zone of the Bohemian Massif.