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Australia: The Land Where Time Began |
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Alice Springs Orogeny The Alice Springs Orogeny had its beginnings in the Late Ordovician, continuing during the Silurian and Devonian, and by the Carboniferous the folding of the sedimentary deposits of the central Australian basins had produced the mountainous terrain of the MacDonnell Ranges area. These ranges being the eroded remnants of the once high mountains produced by this folding between about 450 and 300 million years ago. According to Chris Klootwijk, a northward excursion in the Early Carboniferous, of about 30o, ending in the middle-late Visean, is indicated by palaeomagnetic results from the ignimbrite-rich Carboniferous succession of the Tamworth Belt, Southern New England Orogen (SNEO) in eastern Australia. The Australian Craton and the Tasman Orogenic System have also produced evidence, in the form of palaeomagnetic data, of the excursion that could possibly have begun in the Early Devonian. The promontory of the Australian Craton in central New Guinea had reached as far as 30-40o N by the middle-late Visean, putting it well inside the range of the Central Asian Orogen Belt (CAOB) of what was then southern Laurasia. Australia was on the northeastern margin of Gondwana when that part of the supercontinent converged with, and then collided with the Central Asian Orogenic Belt in the Devonian-Carboniferous. This is proposed by Klootwijk to be the cause of variscan tectonism along the northern and southern margins of the Palaeopacific Ocean, as well as in the hinterland, that was contemporaneous with the convergence and collision, within the Central Asian Orogenic Belt and in Australia, the Alice Springs, Kanimblan and Quilpie Orogenies. A "compression box", an area to which compressional deformation associated with convergence was essentially confined to in Australia, extending the the central New Guinean cratonic promontory, was bounded in the west by the Lasseter Shear Zone, and in the east by the future East Australian Rift System (Fig. 1A, source 1). The conditions of Variscan Australia-Asia were comparable to those of the Indian-Asian of the Cainozoic indentation and extrusion process, included north-south compression that was driven by convergence, in the Larapintine graben weak heated crust, and in the Tasman Orogenic System (TOS), oceanic basement (Fig. 1B, source 1), and the "free" oceanic boundary of the Palaeopacific (Royden et al., 2008; Burchfield et al., 2008). According to Klootwijk (2000), the Thompson Orogen (mainly) and the Northern New England Orogen (NNEO) were displaced to the east by the tectonic extrusion of ductile lower crust and partial melt from the Larapintine graben that is believed to have possibly been associated with the slab rollback of subduction in the Palaeopacific. The Diamantina River Lineament-Clarke River Fault Zone guided upper crustal displacement in the north, and in the south it was the Darling River/Cobar-Inglewood Lineaments and the Caro Fracture Zone, as well as the Lake Blanche-Olepoloko Fault Zones and Lachlan Transverse Zone (Fig. 1B, source 1). Klootwijk claims the tectonic extrusion hypothesis allows new ways of interpreting some aspects of the geological evolution of the Australian continent of the Late Palaeozoic.
Texas is a town in southern Queensland near the New South Wales border. Links |
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |