Carbonic fluid inclusions in a garnet-pyroxene granulite from austhovde in the lützow-holm complex, East Antarctica: Implications for a decompressional P-T path

Abstract

A garnet-pyroxene granulite from Austhovde in the Lützow-Holm Complex, East Antarctica, contains two types of fluid inclusions: A small number of primary inclusions in garnet and quartz, and dominant secondary inclusions in garnet and plagioclase. The melting temperatures of the trapped fluids lie in a range of-57.2 to -56.4 °C, which are close to the triple-point temperature of pure CO2. The primary inclusions are homogenized at +1.8 to +12.6 °C, which correspond to densities of 0.842-0.917 g/cm3. However, the estimated pressure conditions (3-5 kbar at 850 °C) from the fluid densities of the primary inclusions are not consistent with the peak P-T conditions recorded in the rock (840-860 °C and 8.3-8.7 kbar). Homogenization of the secondary inclusions into the liquid phase occurs within a range of +11.5 to +25.2 °C, which correspond to low CO2 densities of 0.708 to 0.851 g/cm3. The results imply that fluid density decreased by partial leakage of the trapped fluid in the primary inclusions during post-peak exhumation stage, and the process is consistent with the occurrence of orthopyroxene + hornblende + plagioclase symplectite around garnet, suggesting post-peak rapid decompression.