Although geological comparisons between Australia and North America have provided a basis for various Neoproterozoic Rodinia reconstructions, quantitative support from precisely dated palaeomagnetic poles has so far been lacking. We report U–Pb ages and palaeomagnetic results for two suites of mafic sills within the intracratonic Bangemall Basin of Western Australia, one of which is dated at 1070 ± 6 Ma and carries a high‐stability palaeomagnetic remanence. Comparison of the Bangemall palaeopole with Laurentian data suggests that previous reconstructions of eastern Australia against either western Canada (SWEAT) or the western United States (AUSWUS) are not viable at 1070 Ma. This implies that the Pacific Ocean did not form by separation of Australia–Antarctica from Laurentia, and that up to 10 000 km of late Neoproterozoic passive margins need to be matched with other continental blocks within any proposed Rodinia supercontinent. Our results permit a reconstruction (AUSMEX) that closely aligns late Mesoproterozoic orogenic belts in north‐east Australia and southernmost Laurentia.
Research Article| December 01, 2007 Zircon geochronology and partial structural re-interpretation of the late Archaean Mashaba Igneous Complex, south-central Zimbabwe M.D. Prendergast; M.D. Prendergast Guesachan, Shielhill Road, Kirriemuir, Angus DD8 4PA, Scotland, United Kingdom, e-mail: marprend@hotmail.com Search for other works by this author on: GSW Google Scholar M.T.D. Wingate M.T.D. Wingate Geological Survey of Western Australia, 100 Plain St., East Perth, WA 6004, Australia, and Tectonics Special Research Centre, School of Earth and Geographical Sciences, University of Western Australia, WA 6004, Australia, e-mail: michael.wingate@doir.wa.gov.au Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2007) 110 (4): 585–596. https://doi.org/10.2113/gssajg.110.4.585 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M.D. Prendergast, M.T.D. Wingate; Zircon geochronology and partial structural re-interpretation of the late Archaean Mashaba Igneous Complex, south-central Zimbabwe. South African Journal of Geology 2007;; 110 (4): 585–596. doi: https://doi.org/10.2113/gssajg.110.4.585 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract Ion microprobe (SHRIMP) U-Pb zircon dating has determined the age of a gabbroic enclave within the supraregional intrusive komatiitic Mashaba Igneous Complex (MIC) to be 2743 ± 11 Ma and that of an interpreted comagmatic thick differentiated komatiitic flow within the adjacent Mashava-Masvingo greenstone belt to be 2754 ± 13 Ma. Recent geological observations support a revised structural interpretation of the MIC as an assemblage of three separate horizontal layered sills emplaced almost coevally at two different crustal depths: the chromititiferous Prince Sill intruded concordantly, and prior to regional folding, into the basal sedimentary rocks of the late Archaean Upper Bulawayan Supergroup, the relatively thin and evolved West Sill within early Archaean greenstone and gneissic basement, and the major Northwest Arm-Main Sill mainly within adjacent basement gneiss. The sill assemblage was vertically linked via ultramafic dykes and, as previously proposed, was fed through the dyke-like Northeast Arm, whose overlying layered rocks are here interpreted as correlatives of the Northwest Arm-Main Sill. The new precise age for the MIC is 50 Ma years older than the former geological estimate of ~2.7 Ga. The comparable date for the volcanic phase supports the interpretation of both as component phases of a putative Masvingo W komatiitic sill-flow complex but is incompatible with interpretation of the late Archaean lithostratigraphy of the Mashava-Masvingo belt as a thrust-stacked package of unrelated continental and oceanic rocks. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The post-Mesoproterozoic tectonometamorphic history of the Musgrave Province, central Australia, has previously been solely attributed to intracontinental compressional deformation during the 580–520 Ma Petermann Orogeny. However, our new structurally controlled multi-mineral geochronology results, from two north-trending transects, indicate protracted reactivation of the Australian continental interior over ca. 715 million years. The earliest events are identified in the hinterland of the orogen along the western transect. The first tectonothermal event, at ca. 715 Ma, is indicated by 40Ar/39Ar muscovite and U–Pb titanite ages. Another previously unrecognised tectonometamorphic event is dated at ca. 630 Ma by U–Pb analyses of metamorphic zircon rims. This event was followed by continuous cooling and exhumation of the hinterland and core of the orogen along numerous faults, including the Woodroffe Thrust, from ca. 625 Ma to 565 Ma as indicated by muscovite, biotite, and hornblende 40Ar/39Ar cooling ages. We therefore propose that the Petermann Orogeny commenced as early as ca. 630 Ma. Along the eastern transect, 40Ar/39Ar muscovite and zircon (U–Th)/He data indicate exhumation of the foreland fold and thrust system to shallow crustal levels between ca. 550 Ma and 520 Ma, while the core of the orogen was undergoing exhumation to mid-crustal levels and cooling below 600–660 °C. Subsequent cooling to 150–220 °C of the core of the orogen occurred between ca. 480 Ma and 400 Ma (zircon [U–Th]/He data) during reactivation of the Woodroffe Thrust, coincident with the 450–300 Ma Alice Springs Orogeny. Exhumation of the footwall of the Woodroffe Thrust to shallow depths occurred at ca. 200 Ma. More recent tectonic activity is also evident as on the 21 May, 2016 (Sydney date), a magnitude 6.1 earthquake occurred, and the resolved focal mechanism indicates that compressive stress and exhumation along the Woodroffe Thrust is continuing to the present day. Overall, these results demonstrate repeated amagmatic reactivation of the continental interior of Australia for ca. 715 million years, including at least 600 million years of reactivation along the Woodroffe Thrust alone. Estimated cooling rates agree with previously reported rates and suggest slow cooling of 0.9–7.0 °C/Ma in the core of the Petermann Orogen between ca. 570 Ma and 400 Ma. The long-lived, amagmatic, intracontinental reactivation of central Australia is a remarkable example of stress transmission, strain localization and cratonization-hindering processes that highlights the complexity of Continental Tectonics with regards to the rigid-plate paradigm of Plate Tectonics.
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