Seismic reflection provides detail on Australia's formation

11 July 2011

The boundary between the Arunta Region and Amadeus Basin

The boundary between the Arunta
Region and Amadeus Basin.
© Geoscience Australia

New deep seismic information has provided fresh insights into how the Australian continent may have formed during the Archean Era and Proterozoic Era by the amalgamation of many smaller crustal blocks over at least, and possibly much longer than, 800 million years.

The information follows the interpretation under Geoscience Australia's Onshore Energy Geodynamic Framework Project of data from several deep seismic surveys, together with data from magnetotelluric, airborne electromagnetic and gravity surveys, which were carried out as part of the Onshore Energy Security program.

The surveys reveal a number of previously unknown geological features, including structures extending beyond the current Moho, or Mohorovicic discontinuity, which marks the geophysical boundary between the Earth's crust and the mantle.

Geoscience Australia scientist, Dr Russell Korsch, says the data have helped to develop a better understanding of how and when the crustal blocks which form the core of Australia's continent came together.

Dr Korsch says there is evidence of major crustal boundaries which can be interpreted as features where the continent has come together to form a suture, or welding together of cratons, which are part of the old, stable and strong continental core onto which younger rocks have accumulated.

"A deep seismic survey imaged a major Paleoproterozoic Era or older crustal boundary in north Queensland, which is interpreted as a suture separating relatively thick crust in the west from thinner, two layered crust to the east." Dr Korsch said.

"As well, seismic profiles in a transect from Broken Hill to the Gawler Craton in southeast Australia imaged at least four distinct blocks in the middle to lower crust, which are bounded by crustal-penetrating fault zones that extend to the Moho. These domains are estimated to be older that the upper crustal rocks above them, most of which are Archean to Mesoproterozoic in age," he said.

Another survey in northern South Australia and the Northern Territory provided an image of the entire crust through a region containing five crustal blocks which were joined during the Paleoproterozoic Era to early Mesoproterozoic Era.

In the Tanami Region on the border of the Northern Territory and Western Australia, a boundary which extends from the near surface to the Moho, also appears to be a suture boundary formed during the Mesoproterozoic Era.

Dr Korsch said that the improved understanding of how the continent was formed would assist with the provision of pre-competitive data for energy and mineral exploration by identifying and assessing possible geological similarities revealed by the newly acquired data with those in known energy and mineral provinces.

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