Australia: The Land Where Time Began

A biography of the Australian continent 

Australia - Effects of the Collision of East and West Gondwana

The Mozambique Orogenic Belt, and an orthogonal belt through Prydz Bay and Cape Leeuwin, with distributed thrusting and associated metamorphism throughout Australia, originated when the Mozambique Ocean closed about 650-580 Ma. The resulting collision between East and West Gondwana, and the pan-African contraction that continued until 500 Ma, together with the beginnings of the palaeo-Pacific Plate along eastern Australia about 560 Ma, as well as its oblique subduction beneath Antarctica, beginning at about 550 Ma, were the beginning of Phanerozoic Australia.

600-550 Ma Late Neoproterozoic Australia

Deformation-metamorphism and magmatism continued in the Mozambique and Pridz-Leeuwin Belts, following the closure of the Mozambique Ocean, as the final collision between West and East Gondwana occurred at about 580 Ma. From 580-560 Ma the Beardmore Orogeny interrupted the long-lasting turbidite deposition along the line where the Transantarctic Mountains would rise. It has been suggested this resulted from the docking of the Beardmore Microcontinent (Veevers, 2001). At about 600 Ma, widespread rifting and Marinoan glacial deposition was taking place in the Adelaide Rift Complex and the Centralian Superbasin.

Rift volcanics were erupted to the east of the Adelaide Rift Complex, along a trend that developed into the continental margin of a back-arc basin of the Pacific Ocean, at about 560 Ma. In the New England Fold Belt it is represented by ophiolites from that time. In the western Tasmania Terrane a similar volcanic rift formed. The interior was flooded by the basalt from the Antrim Plateau and Table Hill. Alongside the Darling Fault, the Yilgarn Block was intruded by the Boyagin dyke swarm. It was possibly at this time that mafic flows erupted in Central Australia. At Mt Crofton and Samphire Marsh, about 630-600 Ma, granite intruded the area that was deformed 560-540 Ma in the formation of the Paterson Fold Belt. This occurred on the same trend as the Petermann Fold Belt, of 570-530 Ma. The King Leopold Fold Belt developed with the Halls Creek Fold Belt, that was orthogonal sinistral, to the north at about 560-530 Ma. A postulated regional dextral shear has been suggested to resolve the coeval contraction and extension, the north-trending structures being extended, and east-trending structures being contracted. When the ocean was finally closed in the Mozambique Orogenic Belt, the oblique coupled subduction beneath Antarctica subjected East Gondwana to sinistral shear. Australia was deformed by the regional dextral shear system that was transmitted to Australia by this oblique stress.

550-530 Ma Latest Neoproterozoic-earliest Cambrian

The opening of the Kanmantoo Marginal Basin, between the Tasman Surface and the Victorian Microcontinent, and the Gnalta Microcontinent dating to 560-530 Ma is overlapped by the contraction of the fold belts over the same period of time, 560-530 Ma. To the east of the Tasman Surface and north of the transform fault, intra-ocean (Mariana type) subduction drove back-arc spreading. An accretionary wedge, close to the Tasman Surface in North Queensland, initially involving the Anakie metamorphics, suggests a change to an oceanic-continental (Chilean-type) subduction in the north. The Anakie protolith, dated to about 540 Ma, and deformed at about 500 ma, has been compared to Molar Formation of 520 Ma, in an accretionary wedge, North Victoria Land, that was deformed during the Ross Orogeny about 500 Ma. The Granite Harbour Intrusives, along a Chilean magmatic margin that formed behind an obliquely (sinistral) subducting Pacific Plate indicate the Molar wedge accumulated in front of the magmatic arc. The Philippine Plate, that is a 4000 km-long plate between Korea and New Guinea is an example from the present of a Mariana-type subduction between to sections of subduction that are of the Chilean type. It is double the length of the Australian example, which is 2000 Km long.

530-510 Ma Early to Middle Cambrian

The Uluru Shelf of Australia extended in a northwesterly direction to link with the the North China Shelf. Northeastward subduction under the Stavely Volcanic Arc began the closing of the Kanmantoo Marginal Basin. Sediment from Antarctica, as well as from the lateral  fold belt that was rising, was deposited along the axis of the Kanmantoo Marginal Basin. The Glasgow Volcanics were generated by the northeastward subduction in Australia as it passed southward in North Victoria Land. To the west, the Molar wedge formed above the westward-subducting limb, which continued to generate synorogenic magmas, including marine volcanics, along the line from which the Transantarctic Mountains arose. Penultimate magmatism-metamorphism occurred in parts of the Mozambique Belt and the Prydz-Leeuwin Belt.

510-490 Ma  Late Cambrian Climax

A line of granites, beginning in the Antarctic Peninsula, passing through Marie Byrd Land, along the Transantarctic Mountains (Ross), extended to Tasmania, a distance of 4500 km. A 700 km-long offset passes westward to the Delamerian granites that had been generated as the Kanmantoo Zone closed. In New Zealand, a line of single occurrences of granites and volcanics is believe to have possibly been generated by subduction that was relocated to the east of New Zealand as the marginal basin in North Victoria Land closed. The Chilean-type subduction, in a trench off the Transantarctic Mountains, was offset to 80oS to east of New Zealand, where granites and volcanics were generated by the subduction slab. During the collision between the Robertson Bay Terrane and the Wilson Terrane, the subduction beneath North Victoria Land ended. To the north, the trench off New Zealand  was part of a Mariana-type subduction zone, the north Queensland section becoming part of Chilean-type margin, a wide accretionary prism, that was metamorphosed, and at 500 Ma, was intruded by plutons. Evidence has not been found of activity at about 600-500 Ma on the far side of the East Antarctic coast, in the Mozambique Belt and the Prydz-Leeuwin Belt, granite emplacement and metamorphism declined. Fans of Tumblagooda Sandstone were formed in the nascent Perth-Carnarvon Basin from material being shed as uplift occurred along the Darling Fault. The King Leopold Fold Belt, to the northeast, is terminally metamorphosed and thrusted. The Kimberley Block has been uplifted and stripped. A new developmental phase was begun by the ending of the thermal event that occurred throughout Gondwana 600-500 Ma.

 

Sources & Further reading

  1. Scheibner, E, in Veevers, J. J  (ed.), 2000, Billion-year earth history of Australia and neighbours in Gondwanaland, GEMOC Press Sydney.
  2. Veevers, J.J., 2001, Atlas of Billion-year earth history of Australia and neighbours in Gondwanaland, GEMOC Press Sydney.

 

Author: M. H. Monroe
Email:  admin@austhrutime.com
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading