Australo-Antarctica in the supercontinent cycle

• Main Author: Maritati, A
• Format: Thesis
• Language: English
• Published: 2020
• Subjects: East Antarctica; supercontinent; geochronology; tectonics; Antarctic; Beardmore; Bunger Hills; Pacific; Transantarctic Mountains; Wilkes Land; Antarc*; Antarctica
• Online Access: https://eprints.utas.edu.au/36003/; https://eprints.utas.edu.au/36003/1/Maritati_whole_thesis.pdf; https://eprints.utas.edu.au/36003/7/Maritati%2036003%20Supplementary%20Material.zip

The large-scale continental domains that make up East Antarctica are important to global plate reconstructions. A key piece in this continental jigsaw puzzle is the AustraloAntarctic domain that formed part of the Gondwana–Pangea (0.5–0.3 Ga), Rodinia (1.0 Ga), and Nuna (1.7 Ga) supercontinents. Its vast underexplored bedrock can inform tectonic and paleogeographic reconstructions through deep time. The central aim of this thesis is to constrain the poorly-known continental evolution of Australo-Antarctica in the context of supercontinent cycles. This aim is addressed by examining the geological record of frontier regions of Australo-Antarctica and the conjugate southern Australian region using a combination of regional geophysical data and rock- and sediment-based geological analysis in a plate reconstruction framework. The first research chapter explores the poorly known age, composition and tectonic affinity of Precambrian basement and sedimentary cover of interior Wilkes Land. Zircon U–Pb–Hf isotopic data from isolated coastal outcrops are combined with regional aeromagnetic data to map Mesoproterozoic (c. 1600–1300 Ma) basement provinces across southern Australia and East Antarctica. This new analysis provides a revised basement architecture shaped through orogenic cycles associated with the Nuna and Rodinia supercontinents. Into the interior, the enigmatic subglacial Sabrina Basin mapped previously from geophysics, is here sampled for the first time via sandstone erratics deposited at the coast. Coupled in situ authigenic monazite and detrital zircon isotopic data reveal that these sandstones were deposited during the Neoproterozoic (before c. 633 Ma). Similarities in age and provenance between these Sabrina Basin samples and other Neoproterozoic strata in the Transantarctic Mountains (Beardmore Group) and southern Australia (Officer Basin) suggest that Neoproterozoic sedimentary rocks likely covered a large sector of the Australo-Antarctic domain, forming an extensive platform basin on the proto-Pacific rifting margin of Rodinia. The second research chapter of this thesis examines the Phanerozoic tectonic history of Australo-Antarctica, with a focus on the age and tectonic origin of onshore sedimentary basins. (U–Th)/He thermochronology data from basement rocks in the Bunger Hills region is used to investigate the timing of extensional tectonism of the inaccessible Knox Rift. Inverse modelling of thermochronology data support ~2–4 km of exhumation of local basement in the Late Paleozoic–Triassic during extension in the Knox Rift. These new results are combined with existing low-temperature (<300ºC) thermochronology constraints from East Antarctic basement rocks to propose widespread basement exhumation in the Late Paleozoic–Triassic driven by intraplate extension during the earliest stages of Pangea rifting. This phase of tectonic activity is responsible for the formation of large basins across Pangea including the Knox Rift as well as the Aurora, Vincennes and Wilkes subglacial basins further east across Australo-Antarctica. Paleozoic–Mesozoic km-scale exhumation of East Antarctic basement generated a significant volume of clastic material that filled basins across East Gondwana. The third research chapter focuses on refining sediment dispersal patterns using International Ocean Discovery Program (IODP) cores from Mesozoic strata in the frontier Mentelle Basin of southwestern Australia. Provenance of these sedimentary rocks is explored using detrital zircon and monazite isotopic data and is compared with the provenance record of other Antarctic and Australian Paleozoic–Mesozoic strata. The results provide the first record of a transcontinental sediment pathway connecting basement regions within the Gondwanaforming Kuunga Orogen (0.7–0.5 Ga) with the Tethys Ocean via a series of intraGondwanan rift basins. Together with other proposed large-scale sediment pathways, this was one of the principal modes of siliciclastic sediment delivery to Paleozoic–Mesozoic sedimentary basins in East Antarctica and Australia. The results presented in this thesis reveal plate-scale processes in Australo-Antarctica in unprecedented detail, and in doing so more clearly frame its continental evolution into current plate tectonic models. This body of work will inform both future regional studies and global tectonic reconstructions.