Other
Scientific paper
Jul 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976esrv...12..161r&link_type=abstract
Earth Science Reviews, Volume 12, Issue 2-3, p. 161-196.
Other
24
Scientific paper
Three main basement provinces can be recognized in Australia, viz. Tasman (Late Precambrian-Phanerozoic), Arunta-Gawler (Early and Middle Proterozoic), Pilbara-Yilgarn (Archaean). The Tasman Province records a history of mobile-belt evolution, east of a craton represented by pre-Adelaidean basement rocks. Orogenic activity shifted episodically away from the craton, causing the stabilization (‘cratonization’) of successive sub-provinces, in the principal phases.The Late Precambrian Penguin orogeny in the orthotectonic mobile belt and the associated Cambro-Ordovician Delamerian orogeny in the paratectonic zone adjacent to the craton.The Devonian ‘Tabberabberan’ orogeny (Lachlan sub-province).The Permian Hunter-Bowen orogeny (New England sub-province). The regressive orogeny represented in these three sub-provinces does not necessarily indicate a corresponding lateral continental accretion. The three sub-provinces are quite different in sedimentary facies. A major volcanic chain of Andeantype, presumably subduction controlled, was apparently virtually fixed in position, during the Devonian and Carboniferous, between the Lachlan and New England sub-provinces. It was probably of less importance, but not greatly different in position, during the Lower Palaeozoic. Thus the main deformation and plutonism of the Lachlan sub-province took place behind the volcanic chain while that of the New England sub-province took place in front. In neither case, therefore, does the plutonism represent the roots of the pre-existing volcanic arc and alternative interpretations are discussed. The stabilization of the New England Province caused a restriction of tectonic activity to more easterly areas (e.g. New Zealand and New Caledonia) which have since been rifted from the Australian continent. If large-scale accretion has occurred, it must be essentially by ensimatic back-arc accretion in former marginal basins, but the evidence for this is not compelling. The northern (Arunta) and southern (Gawler) sub-provinces of the Arunta-Gawler Province are separated in central Australia by the Amadeus Transverse Zone. A remarkable feature of this intracontinental zone is the presence of conjugate dislocations of the crust which have produced thrusting towards the Amadeus Basin from both sides. These were initiated as major mylonitic zones, which have brought up granulite facies rocks, prior to 1100 m.y., and they were re-juvenated in the late Precambrian (Petermann Ranges orogeny) and Upper Palaeozoic (Alice Springs orogeny). The Arunta sub-province, like the Lachlan sub-province, is largely non-volcanogenic. One major plutonic episode (ca. 1700 1850 m.y.) and associated compressional deformation can be recognized right across the province. However, no major calc-alkaline volcanic chain has been recognized and it must be inferred that any active continental margin lay east of the province as at present exposed. In the Gawler sub-province the existence of extensive areas of high-grade metamorphism in regions of relatively thin and mature earlier Proterozoic sedimentation are not yet satisfactorily explained. Neither the absolute, nor relative ages of the Archaean greenstone sequences in the Pilbara and Yilgarn sub-provinces are firmly established but the presence of older ‘granites’ (ca. 3100 m.y.) and a different tectonic style suggest that the Pilbara sub-province is older. Actualistic island-arc or ocean-floor models are unsatisfactory in explaining development of the Yilgarn sequences in shallow water, simultaneously over wide areas. Development on a proto-continental crust, not necessarily ‘granitic’, with a high geothermal gradient appears to be required. As in the Arunta and Lachlan sub-provinces the main plutonic episode (ca. 2650 m.y.) is closely associated with the relatively short-lived terminal compressional deformation.
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