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

Abstract

Mineral textures, coupled with thermodynamic modelling in the MnO-Na 2 O-CaO-K 2 O-FeO-MgOAl 2 O 3 -SiO 2 -H 2 O (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°C 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.

Timing of Proterozoic metamorphism in the southern Curnamona Province: implications for tectonic models and continental reconstructions ∗

“…Clearly, such widespread compressional tectonics and high-grade metamorphism along the eastern margin of the North Australia Craton during this time interval was a response to major tectonic processes. Previous tectonic reconstruction models interpret tectonism at ca 1550 Ma recorded in the Mt Isa and Georgetown Inliers to be a response to accretion of the Georgetown crustal block with the eastern margin of the North Australia Craton at ca 1550 Ma (Boger & Hansen 2004) and/or Laurentia with the eastern margin of the North Australia Craton .…”

U – Pb zircon ages from leucogneiss in the Etheridge Group and their significance for the early history of the Georgetown region, north Queensland

“…In most models for the Palaeoproterozoic evolution of the Australian Craton (Laing 1996;Betts et al 2002;Giles et al 2004), Georgetown is considered (albeit, usually in passing references) to be a part of the craton. However, Boger and Hansen (2004) have recently speculated that the metamorphic evolution of the Georgetown region, and some of its other geological characteristics, suggest it was accreted to the North Australian Craton during the construction of Rodinia, rather than having always been part of it.…”

Petrologic modeling of chloritoid–glaucophane schists from the NW Iberian Massif

“…However, the comparison between both phase diagrams is useful for visualizing the influence of Ca and Mn, small amounts of which can strongly influence garnet stability (Spear and Cheney, 1989;Symmes and Ferry, 1992;Mahar et aL, 1997), The effect of adding these components generally results in a dramatic widening of the garnet stability field (see e,g, Tinkham et aL, 2003;Proyer, 2003;Boger and Hansen, 2004;Zuluaga et aL, 2005 ), The most useful aspect of this pseudosection is in the ability to plot isopleths for silica content in phengite in the different stability fields (dashed lines in Fig, 9), which provides an accurate barometer (e,g, Massone and Schreyer, 1987) that is essentially in agreement with the pressure values obtained from average P-T calculations at the same temperatures,…”