Geochronology and geochemistry of the Devonian Gumbardo Formation (Adavale Basin): evidence for cratonisation of the Central Thomson Orogen by the Early Devonian |
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| Authors: | P Asmussen S E Bryan C M Allen D J Purdy |
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| Institution: | 1. School of Earth Systems, Queensland University of Technology, 2 George Street, GPO Box 2434, Brisbane, QLD, 4001, Australia;2. pascal.asmussen@hdr.qut.edu.au https://orcid.org/0000-0002-8337-378X;4. Central Analytical Research Facility, Queensland University of Technology, 2 George Street, GPO Box 2434, Brisbane, QLD, 4001, Australia;5. Department of Natural Resources and Mines, Geological Survey of Queensland, PO Box 15216, City East, QLD, 4002, Australia |
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| Abstract: | AbstractThe Devonian subsurface Adavale Basin occupies a central position in the Paleozoic central Thomson Orogen of eastern Australia and records its tectonic setting during this time interval. Here, we have focussed on the basal volcanics of the Gumbardo Formation to clarify the tectonic setting of the basin. The approach has been to undertake stratigraphic logging, LA-ICP-MS U–Pb zircon geochronology and whole-rock geochemical analysis. The data indicate that basin initiation was rapid occurring at ca 401?Ma. The volcanic rocks are dominated by K-feldspar phyric rhyodacitic ignimbrites. The whole-rock geochemical data indicate little evidence for extensive fractional crystallisation, with the volcanic suite resembling the composition of the upper continental crust and exhibiting transitional I- to A-type tectonomagmatic affinities. One new U–Pb zircon age revealed an Early Ordovician emplacement age for a volcanic rock previously interpreted to be part of the Early Devonian Gumbardo Formation, and older basement age is consistent with seismic interpretations of uplifted basement in this region of the western Adavale Basin. Five ignimbrites dated from different stratigraphic levels within the formation yield similar emplacement ages with a pooled weighted age of 398.2?±?1.9?Ma (mean square weighted deviation?=?0.94, n?=?93). Significant zircon inheritance in the volcanic rocks records reworking of Ordovician and Silurian silicic igneous basement from the Thomson Orogen and provides insight into the crustal make-up of the Thomson Orogen. Collectively, the new data presented here suggest the Adavale Basin is a cover-type basin that developed on a stabilised Thomson Orogen after the major Bindian deformation event in the late Silurian. |
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| Keywords: | Thomson Orogen Adavale Basin Gumbardo Formation Devonian rift volcanics zircon dating zircon inheritance geochemistry Queensland Tasmanides |
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https://orcid.org/0000-0002-8337-378X;4. Central Analytical Research Facility, Queensland University of Technology, 2 George Street, GPO Box 2434, Brisbane, QLD, 4001, Australia;5. Department of Natural Resources and Mines, Geological Survey of Queensland, PO Box 15216, City East, QLD, 4002, Australia