Metamorphic evolution of the Georgetown Inlier, northeast Queensland, Australia; evidence for an accreted Palaeoproterozoic terrane?

Mineral textures, coupled with thermodynamic modelling in the MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O (MnNCKFMASH) model system, of mid-amphibolite facies metapelites from the Georgetown Inlier, northeast Australia, point to the recording of two separate and unrelated metamorphic events. The first occurred contemporaneously with Palaeo- to Mesoproterozoic orogenesis and involved heating and burial to temperatures and pressures of approximately 600-650 degreesC and 6.0-7.0 kbar. Textural evidence for the up-temperature (and pressure) prograde part of this path is inferred from the inclusion of garnet in biotite and staurolite. The second metamorphic event resulted in a low-pressure thermal overprint that is equated with the advective addition of heat to the terrane via the emplacement of the Forsayth Batholith (c. 1550 Ma). This event is inferred from subsequent growth of andalusite and randomly orientated fibrolitic sillimanite after garnet, biotite and staurolite. This two stage metamorphic evolution, when coupled with a number of other distinct geological characteristics, suggests that the Georgetown Inlier is dissimilar to the other Australian Palaeoproterozoic terranes with which it is commonly correlated.