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.