Coeval basin formation, plutonism and metamorphism in the Northern Tasmanides: extensional Cambro-Ordovician tectonism of the Charters Towers Province

Henderson, R.A., Fergusson, C.L., and Withnall, I.W. (2020) Coeval basin formation, plutonism and metamorphism in the Northern Tasmanides: extensional Cambro-Ordovician tectonism of the Charters Towers Province. Australian Journal of Earth Sciences, 67 (5). pp. 663-680.

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The Charters Towers Province, of the northern Thomson Orogen, records conversion from a Neoproterozoic passive margin to a Cambrian active margin, as characteristic of the Tasmanides. The passive margin succession includes a thick metasedimentary unit derived from Mesoproterozoic rocks. The Cambrian active margin is represented by upper Cambrian-Lower Ordovician (500-460 Ma) basinal development (Seventy Mile Range Group), plutonism and metamorphism resulting from an enduring episode of arc-backarc crustal extension. Detrital zircon age spectra indicate that parts of the metamorphic basement of the Charters Towers Province (elements of the Argentine Metamorphics and Charters Towers Metamorphics) overlap in protolith age with the basal part of the Seventy Mile Range Group and thus were associated with extensional basin development. Detrital zircon age data from the extensional basin succession indicate it was derived from a far-field (Pacific-Gondwana) primary source. However, a young cluster (<510 Ma) is interpreted as reflecting a local igneous source related to active margin tectonism. Relict zircon in a tonalite phase of the Fat Hen Creek Complex suggests that active margin plutonism may have extended back to ca 530 Ma. Syntectonic plutonism in the western Charters Towers Province is dated at ca 485-480 Ma, close to timing of metamorphism (477-467 Ma) and plutonism more generally (508-455 Ma). The dominant structures in the metamorphic basement formed with gentle to subhorizontal dips and are inferred to have formed by extensional ductile deformation, while normal faulting developed at shallower depths, associated with heat advection by plutonism. Lower Silurian (Benambran) shortening, which affected metamorphic basement and extensional basin units, resulted in the dominant east-west-structural trends of the province. We consider that these trends reflect localised north-south shortening rather than rotation of the province as is consistent with the north-south paleogeographic alignment of extensional basin successions.

Item ID: 63093
Item Type: Article (Research - C1)
ISSN: 1440-0952
Keywords: extensional tectonism, Tasmanides, Thomson Orogen, Charters Towers Province, extensional basin, magmatic arc, extensional metamorphism
Copyright Information: © 2020 Geological Society of Australia
Date Deposited: 13 May 2020 07:30
FoR Codes: 37 EARTH SCIENCES > 3705 Geology > 370511 Structural geology and tectonics @ 70%
37 EARTH SCIENCES > 3705 Geology > 370502 Geochronology @ 30%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8499 Other Mineral Resources (excl. Energy Resources) > 849999 Mineral Resources (excl. Energy Resources) not elsewhere classified @ 50%
97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 50%
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