Further evidence for ∼8 kbar amphibolite facies metamorphism in the Marymia Inlier, Western Australia

Pressure estimates for amphibolite-facies metamorphism at Plutonic Gold Mine (Plutonic), Marymia Inlier, Western Australia, were recently revised significantly upwards from similar to 4 +/- 2 kbar/550-600 degrees C to >= 8 kbar/similar to 600 degrees C, based on the calculated stability fields for mineral assemblages in garnet-free mafic rocks. These conditions are anomalous in the context of the Yilgarn Craton. Here, we present new mineral equilibria calculations for rare garnet-bearing rock types from Plutonic that confirm those higher pressure estimates, and provide confidence that the determinations of metamorphic conditions based only on results from metamorphosed mafic rocks are robust and reliable. Taken together, the new estimates (7.3-8.2 kbar/580-590 degrees C) from the garnet-bearing rocks, and the existing results from the mafic rocks, provide evidence that, most probably during the late Archean, rocks now exposed along the northern margin of the Yilgarn Craton underwent substantial increases in pressure, which was likely followed by rapid exhumation.