LATE ARCHEAN AND EARLY PROTEROZOIC CRUSTAL EVOLUTION OF THE MOUNT-ISABLOCK, NORTHWEST QUEENSLAND, AUSTRALIA

Recognition of Late Archean and Early Proterozoic tonalite-trondhjemit e-granodiorite crust in the Mount Isa block, northwest Queensland, Aus tralia, has important implications for Proterozoic crustal evolutionar y models in the North Australian craton, Protoliths of the Black Angel Gneiss Complex formed 2.42-2.50 Ga (Black Angel Gneisses) and 1.97-2. 00 Ga (Pothole Creek Gneisses), Both groups have Nd model ages of 2.42 to 2.58 Ga. Supracrustal components within the gneiss complex have Nd model ages of 2.75 to 2.83 Ga, These data, and inherited components i n zircons, indicate the presence of even older Archean crust, Crystall ization of 1.81-1.87 Ga rims record a thermal event during a subsequen t period of granitic (Kalkadoon-Leichhardt) magmatism, Both the Black Angel Gneiss Complex and Kalkadoon-Leichhardt magmatic suite have stro ng are geochemical signatures and have components that are composition ally similar to Archean tonalite-trondhjemite-granodiorite lithologies , A seismically defined, crustal-scale, west-dipping feature in the Mo unt Isa block may be a Proterozoic cryptic suture, Subduction-zone mag matism may be related to this feature, Late Archean and Early Proteroz oic crust formation in this segment of the North Australian craton was subduction driven, involving assembly of microcontinental terranes si milar to other Early Proterozoic belts, This observation is significan t, because paleomagnetic data indicate that the North Australian crato n and Laurentia were juxtaposed during Early to Middle Proterozoic tim e.