Geochronological constraints for a two-stage history of the Albany-Fraser Orogen, Western Australia

Based on structural, petrographic and geochronological work (SHRIMP zircon, monazite and rutile), the Mesoproterozoic Albany-Fraser Orogeny is divided into two discrete thermo-tectonic stages, between c. 1345 and 1260 Ma (Sta ge I) and c. 1214 and 1140 Ma (Stage II). The existence of a two-stage hist ory is confirmed by the discovery of 1321 +/- 24 Ma detrital zircons and 11 54 +/- 15 Ma metamorphic rutiles in metasedimentary rocks from Mount Ragged . The detrital zircons demonstrate that the Mount Ragged metasedimentary ro cks unconformably overly, and were derived from, Stage I basement. Metamorp hic rutile formed as a consequence of overthrusting by high-grade early-Sta ge II rocks along an inferred NE-SW striking structure (the Rodona Fault). This interpretation is supported by zircon geochronology, which demonstrate s that granulite facies metamorphism on the northwestern side of the struct ure predates that on the southeastern side by similar to 100 Ma. Rocks to t he northwest record a low-grade imprint relating to the younger (Stage II) event. The two-stage thermo-tectonic history of the Albany-Fraser Orogen co rrelates with adjacent Grenville-age orogenic belts in Australia and East A ntarctica, implying that Mesoproterozoic Australia assembled in two stages subsequent to the amalgamation of the North Australian and West Australian cratons. Initial collision between the combined West Australian-North Austr alian craton and the South Australian-East Antarctic continent at c. 1300 M a was followed by intracratonic reactivation affecting basement and cover a t c. 1200 Ma. Two comparable and contemporaneous compressional orogenies co ntrolled the formation of the Kibaran Belt in Africa and the Grenville Belt in Canada, suggesting that tectonic events in Mesoproterozoic Australia fo llow a similar pattern to that recognised for Rodinia amalgamation world-wi de. (C) 2000 Elsevier Science B.V. All rights reserved.