Palaeoprotrozoic high-T, low-P metamorphism and dehydration melting in metapelites from the Mopunga Range, Arunta Inlier, central Australia

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Authors:Scrimgeour, I.; Smith, J. B.; Raith, J. G.
Author Affiliations:Primary:
University of Leoben, Institute of Geosciences, Leoben, Austria
Northern Territory Geological Survey, Australia
Australian Geological Survey Organisation, Australia
Volume Title:Journal of Metamorphic Geology
Source:Journal of Metamorphic Geology, 19(6), p.739-757. Publisher: Blackwell, Oxford, United Kingdom. ISSN: 0263-4929
Publication Date:2001
Note:In English. 84 refs.; illus., incl. 6 tables, geol. sketch map
Summary:A sequence of psammitic and pelitic metasedimentary rocks from the Mopunga Range region of the Arunta Inlier, central Australia, preserves evidence for unusually low P (∼ 3 kbar), regional-scale, upper-amphibolite and granulite-facies metamorphism and partial melting. Upper amphibolite facies metapelites of the Cackleberry Metamorphics are characterized by cordierite-andalusite-K-feldspar assemblages and cordierite-bearing leucosomes with biotite-andalusite selvages, reflecting P-T conditions of ∼ 3 kbar and ∼ 650-680°C. Late development of a sillimanite fabric reflects either an anticlockwise, or a later independent higher-P thermal event. Coexistence of andalusite with sillimanite in these rocks appears to reflect the sluggish kinematics of the Al2SiO5 polymorphic inversion. In the Deep Bore Metamorphics, 20 km to the E, dehydration melting reactions in granulite-facies metapelites have produced migmatites with quartz-absent sillimanite-spinel-cordierite melanosomes, whilst in semipelitic migmatites discontinuous leucosomes enclose cordierite-spinel intergrowths. Metapsammitic rocks are not migmatized, and contain garnet-orthoyroxene-cordierite-biotite-quartz assemblages. Reaction textures in the Deep Bore Metamorphics are consistent with a near-isobaric heating-cooling path, with peak metamorphism occurring at 2.6-4.0 kbar and ∼ 750-800°C. SHRIMP U-Pb dating of metamorphic zircon rims in a cordierite-orthopyroxene migmatite from the Deep Bore Metamorphics yielded an age of 1730 ± 7 m.y., whilst detrital zircon cores define a homogeneous population at 1805 ± 7 m.y. The 1730 m.y. age is interpreted to reflect the timing of high-T, low-P metamorphism, synchronous with the regional late Strangways event, whereas the 1805 m.y. age provides a maximum age for deposition of the sedimentary precursor. The Mopunga Range region forms part of a more extensive low-P metamorphic terrain in which lateral T gradients are likely to have been induced by localized advection of heat by granitic and mafic intrusions. The near-isobaric Palaeoproterozoic P-T-t evolution of the Mopunga Range region is consistent with a relatively transient thermal event, due to advective processes that occurred synchronous with the regional late Strangways tectonothermal event. [P.J.T.]
Subsections:Metamorphism: regional, dynamic
Subjects:Dehydration; Facies; Granulite facies; High temperature; Low pressure; Melting; Metamorphic rocks; Metamorphism; Metapelite; Metasedimentary rocks; P-T conditions; Paleoproterozoic; Partial melting; Petrography; Precambrian; Pressure; Proterozoic; Temperature; Upper Precambrian; Arunta Block; Australasia; Australia; Northern Territory Australia; Central Australia; Mopunga Range
Coordinates:S224000 S224000 E1352000 E1352000
Abstract Numbers:02M/3626
Record ID:2002007606
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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