Late Neoproterozoic/Cambrian high-pressure mafic granulites from the Grove Mountains, East Antarctica: P–T–t path, collisional orogeny and implications for assembly of East Gondwana

The Grove Mountains are an inland continuation of the Late Neoproterozoic/Cambrian Prydz Belt of East Antarctica. In this paper we report high-pressure (HP) mafic granulites that occur in glacial moraines from this area. Petrographical textures, mineral compositions and P–T pseudosection calculations in the system NCFMASHTO (Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3) suggest that the HP mafic granulites record peak P–T conditions of 11.8–14.0 kbar and 770–840 °C. The post-peak evolution of these rocks involved near-isothermal decompression of ca. 6 kbar followed by a greenschist facies overprint. SHRIMP U-Pb zircon dating, coupled with the identification of mineral inclusion assemblage in zircons, reveals HP metamorphism occurred at ca. 545 Ma and subsequent retrograde reactions involving near-isothermal decompression at ca. 530 Ma. Garnet-clinopyroxene-whole-rock Sm-Nd isotopic analyses also yield Cambrian ‘isochron’ ages. This reflects collision at a convergent plate margin followed by extensional exhumation as the orogen collapsed during Late Neoproterozoic/Cambrian orogeny. Therefore, the occurrence of HP mafic granulites from the Grove Mountains provides evidence for a collisional tectonic setting for the Prydz Belt, which supports the notion that East Gondwana was not finally assembled until the Cambrian.