Composite basement along the southern margin of the North Australian Craton: Evidence from in-situ zircon U-Pb-O-Hf and whole-rock Nd isotopic compositions

Abstract

Hafnium-isotope compositions of emplacement-age zircon grains are integrated with zircon δ18O and whole-rock Nd-isotope data in order to characterise the age and composition of the sources of Paleoproterozoic granites along the southern margin of the North Australian Craton. The petrogenesis of the granitic rocks is interpreted in terms of partial melting of distinct crustal components with variable crustal residence ages, at different crustal levels, reflecting the local Paleoproterozoic crustal architecture. This finding implies a composite nature of the unexposed deep crust, which comprises Paleoproterozoic supracrustals and subordinate, discontinuous and local Neoarchean meta-igneous components. The limited lateral extension of Neoarchean deep crust does not support tectonic models for the Paleoproterozoic amalgamation of the craton that consider intracratonic and/or continent-continent collision settings. The composite nature of the basement and the presence of cryptic boundaries are consistent with the accretion of Paleoproterozoic supracrustal elements, as back-arc and island-arc, to a Neoarchean proto-craton. The dominant Paleoproterozoic reworking of Archean-derived supracrustal materials indicates that accretionary orogenesis was an important setting for crustal reworking and craton stabilisation in the Paleoproterozoic.