Isotopic test of a thermally driven intraplate orogenic model, Australia

Abstract

A recently proposed model for intraplate orogenesis couples long-term self-heating of basement rocks by radioactive decay with thermal blanketing by overlying sedimentary deposits. This model has been tested in one of the type areas in central Australia, the Proterozoic Musgrave Complex, which was reworked in an Early Cambrian orogeny. We have determined the source of the pre orogenic and postorogenic sediments in the Amadeus basin immediately to the north of the reworked basement, including the fan deposits associated with uplift, comprising Uluru (Ayers Rock) and Kata Tjuta (Olgas). Detrital-zircon age populations indicate that all basin sediments were derived from the Musgrave Complex, which was therefore emergent rather than covered by sediments as required by the model. In the basement, the preservation of Mesoproterozoic mica ages during transpressive burial to depths of ∼40 km ca. 550 Ma indicates that the associated thermal pulse was short-lived, not long-lived as envisaged in the model. We conclude therefore that the thermal-blanketing model is inconsistent with the isotopic data and that the localization of deformation in intracratonic settings is associated with regions of contrasting strengths; in central Australia, these are along the margins of the Amadeus basin with the Musgrave Complex and Arunta inlier.