Petrology and phase equilibrium modeling of spinel-sapphirine-bearing mafic granulite from Akarui Point, Lützow-Holm Complex, East Antarctica: Implications for the P-T path

摘要

We report new petrological and P -T data for spinel-sapphirine-bearing mafic granulite from Akarui Point in the upper amphibolite- to granulite-facies transitional zone of the Lützow-Holm Complex (LHC), East Antarctica, and provide unequivocal evidence for extreme crustal metamorphism possibly associated with the collisional orogeny during the Neoproterozoic. The reaction microstructures in the rock suggest the stability of the prograde pargasite + garnet + orthopyroxene + plagioclase + hematite assemblage followed by the formation of plagioclase + orthopyroxene + spinel + sapphirine symplectite after garnet. The application of mineral equilibrium modeling on the mafic granulite in the system NCFMASHTO yields a prograde condition of 11-12 kbar and ～ 900 °C, followed by decompression to the peak stage (Pgs + Pl + Opx + Spl ± H_(2)O) of 5-6 kbar and 900-920 °C, and subsequent cooling to less than 890 °C, possibly along a clockwise P -T path. The high-temperature and possibly ultrahigh-temperature condition observed at Akarui Point might reflect an effect of a local thermal event or the presence of an exotic crustal block within the LHC, which are essentially associated with the complex collisional evolution of this region during the assembly of Gondwana.