Proterozoic cooling and exhumation of the northern central Halls Creek Orogen, Western Australia: constraints from a reconnaissance 40 Ar/ 39 Ar study

Authors: Bodorkos, S.¹; Reddy, S. M.²

Source: Australian Journal of Earth Sciences, Volume 51, Number 4, August 2004 , pp. 591-609(19)

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Abstract:

The Palaeoproterozoic Halls Creek Orogen preserves the most complete record of Barramundi (1880–1820 Ma) tectonism in northern Australia, but appears unaffected by the 1750–1500 Ma tectonomagmatic activity that pervades other parts of the North Australian Craton. However, reliable geochronological data in the Halls Creek Orogen are largely restricted to U–Pb zircon and monazite determinations, and the history of post-tectonic cooling in the crystalline basement remains poorly understood. A reconnaissance 40 Ar/ 39 Ar study has been undertaken in the northern central part of the orogen, where 1850–1845 Ma high-grade metamorphism pre-dated 1835–1825 Ma emplacement of the Mabel Downs Tonalite, and the subsequent development of the Highway Shear Zone under greenschist-facies conditions. Hornblende and biotite 40 Ar/ 39 Ar results from the Mabel Downs Tonalite yield plateau ages of 1705 ± 5 Ma and 1546 ± 19 Ma, respectively, interpreted to record cooling through the temperatures 540 ± 40°C and 315 ± 45°C, respectively. These values yield slow time-averaged cooling rates of 1.5 ± 0.5°C/10 6 years (1845–1705 Ma) and 1.4 ± 0.4°C/10 6 years (1705–1545 Ma). Variably discordant muscovite and biotite 40 Ar/ 39 Ar analyses from sheared leucogneiss and retrogressed pelitic migmatite in the Highway Shear Zone are difficult to interpret, although none record Palaeoproterozoic isotopic closure and most preserve evidence for resetting during Neoproterozoic (900–800 Ma) recrystallisation. In the absence of a reliable minimum age for the Yampi Orogeny (previously published pre- 1000 Ma K–;Ar ages may be affected by unrecognised excess argon), the present 40 Ar/ 39 Ar data may reflect deformation associated with reactivation of the Highway Shear Zone during this event.

Keywords: argon-argon dating; cooling rate; Halls Creek Orogen; Palaeoproterozoic

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1400-0952.2004.01077.x

Affiliations: 1: School of Earth Sciences, University of Melbourne, Vic. 3010, Australia 2: Tectonics Special Research Centre, Department of Applied Geology, Curtin University of Technology, Perth, WA 6845, Australia

Publication date: 2004-08-01

Proterozoic cooling and exhumation of the northern central Halls Creek Orogen, Western Australia: constraints from a reconnaissance 40 Ar/ 39 Ar study

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