Two collisions, two sutures: Punctuated pre-1950 Ma assembly of the West Australian Craton during the Ophthalmian and Glenburgh Orogenies

Abstract

The Gascoyne Province lies at the western end of the Capricorn Orogen, and includes a range of Neoarchean to Paleoproterozoic gneisses and metasedimentary basins (the Glenburgh Terrane) that record the amalgamation of the Archean Pilbara and Yilgarn Cratons to form the West Australian Craton. New Lu–Hf zircon data, integrated with the existing framework of U–Pb zircon and monazite data, provide direct evidence for the punctuated assembly of the West Australian Craton as a result of two discrete pre-1950 Ma collision/accretion events. First, 2555–2430 Ma granitic gneisses of the Glenburgh Terrane, interpreted as being exotic to both the Pilbara and Yilgarn Cratons, collided with (or were accreted to) the southern margin of the Pilbara Craton during the 2215–2145 Ma Ophthalmian Orogeny. The predominantly psammitic protoliths to the Moogie Metamorphics were deposited in a pro-foreland basin across the Glenburgh Terrane in response to this collision, with detrital zircon Lu–Hf signatures indicating significant Pilbara-type crust in the source region. The Lu–Hf isotopic signatures of magmatic zircons from granitic gneisses and granites of the 2005–1970 Ma Dalgaringa Supersuite, and of detrital zircon from 2000 to 1955 Ma-aged fore-arc deposits (Quartpot Pelite of the Camel Hills Metamorphics), indicate that the magmatic rocks formed in a continental margin arc, by the mixing of juvenile, mantle-derived material with older continental crust. The isotopic signature of this older crustal material is similar to that of the Glenburgh Terrane, suggesting that oceanic plate subduction occurred toward the north, under the southern, leading edge, of the Glenburgh Terrane. Although the arc was initiated at c. 2080 Ma, the older parts (pre-2005 Ma) are no longer exposed. Ocean basin closure and collision between a combined Pilbara Craton–Glenburgh Terrane and the Yilgarn Craton occurred during the latter part of the Glenburgh Orogeny between c. 1965 and c. 1950 Ma.