Isotopic and geochemical constraints on Proterozoic crustal growth from the Mt Painter Inlier

Abstract

The Mt Painter Inlier comprises sequences of Palaeo-Mesoproterozoic metasediments, granitoids and granites. The igneous suites are geochemically similar to penecontemporaneous Australian I- and A-type granites, and contain elevated immobile element concentrations relative to Phanerozoic analogues. The metasedimentary sequences indicate shallow water, intracontinental depositional environments and isotope studies suggest short transport distance and local provenance. Nd depleted mantle model ages for the oldest granitoids and metasediments are clustered around 2.1-2.4 Ga, with the younger granitic units returning older model ages of 2.9-3.3 Ga. The 2.1-2.4 Ga event is correlated with events of similar age from other Australian terrain, and is interpreted to represent a period of major continental crustal growth in Australia. The Archaean model ages for the younger granite sites are older than those of the neighbouring Gawler Craton, and may represent the juxtaposition of hitherto undocumented Archaean terrain prior to ~1700 Ma. Proterozoic tectonic processes must therefore be responsible for the relative movement of stable cratonic nucleii on large scales in order to produce allochthonous juxtaposition. The Mt Painter Inlier therefore records an active tectonic evolution throughout the Proterozoic, incorporating continental crustal growth periods between 2.1-2.4 and ~3 Ga. Tectonic activity continues to the present day, with both the Delamerian Orogeny and ongoing Tertiary thrusting processes being responsible for the current morphology of the inlier.