New constraints on the origin and evolution of the Thomson Orogen and links with central Australia from isotopic studies of detrital zircons

Interpretation of the Thomson Orogen and its context within the Tasmanides of eastern Australia is hampered by vast areas of deep sedimentary cover which also mask potential relationships between central and eastern Australia. Within covered areas, basement drill cores offer the only direct geological information. This study presents new detrital zircon isotopic data from these drill cores and poorly understood outcropping units to provide new age and provenance information for sedimentary rocks from the Thomson Orogen. Two distinct detrital zircon signatures are revealed. One is dominated by Grenvillian-aged (1300-900 Ma) zircons with a significant peak at similar to 1180 Ma and lesser peak at similar to 1070 Ma. These age peaks, along with Lu-Hf isotopic compositions (median cHf(t) = +1.5), dominantly mantle-like 6180 values (median = 5.53 parts per thousand.) and model ages of similar to 1.89 Ga, support a Musgrave Province (central Australia) source. The dominance of Grenvillian-aged material additionally points to deposition during the Petermann Orogeny (570-530 Ma) when the Musgrave Province was uplifted, shedding abundant material to the Centralian Superbasin. Comparable age spectra suggest that parts of the Thomson Orogen were connected to the Centralian Superbasin during this period. We use the term 'SynPetermann' to describe this signature which is observed in two drill cores adjacent to the North Australian Craton and scattered units in the outcropping Thomson Orogen. The second signature marks a significant provenance shift and is remarkably consistent throughout the Thomson Orogen. Age spectra exhibit dominant peaks at 600-560 Ma, lesser 1300-900 Ma populations and maximum depositional ages of similar to 495 Ma. This pattern is termed the 'Pacific Gondwana' detrital zircon signature and is recognised throughout eastern Australia, Antarctica and central Australia. Lu-Hf isotope data for Thomson Orogen rocks with this signature are highly variable with cHf(t) values between -49 and +10 and dominantly supracrustal delta O-18 values suggesting input from different and more diverse source regions relative to those exhibiting the Syn-Petermann signature. Crown Copyright (C) 2016 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. All rights reserved.