Australia: The Land Where Time Began

A biography of the Australian continent 

Largest impact zone in the World believed Uncovered in Central Australia by ANU Researchers¹

It is said by team leader Dr. Andrew Glikson from the ANU that 2 ancient craters they found in Central Australia were believed to have been caused by a single meteorite that broke in half, each appearing to be about 200 km in diameter, which would make them the largest meteorite known of that hit the Earth. As the age of the impact is still to be determined it is not known if they could have caused a mass extinction. The material from both sites seems to be identical, which is the basis for the belief that they are probably from the same meteorite. The twin craters were revealed by geothermal drilling in an area that includes parts of South Australia, the Northern Territory and Queensland, though the visible signs of the crater have been eroded to the point at which they are no longer obvious on the surface. Further research, possibly including a deep crust seismic traverse, will hopefully find more evidence of the impact event.

According to Dr Glikson they don’t yet have the evidence required from beneath the Cooper Basin and the Warburton Basin, their seismic information covering to a depth of 5 km, and some other data that includes seismic tomography and magnetic data. Beneath the site the mantle has been up-domed, suggests a major impact event.

As to whether the twin asteroid impact could have affected life on Earth will only be known when the age of the impact has been determined, as it may then be possible to correlate the impact with known large mass extinction events, which occurred at the end of specific eras.

Geophysical anomalies and quartz deformation of the Warburton West structure, central Australia²

Major geophysical anomalies are featured in the Eastern Warburton Basin, northeast South Australia, which include a magnetic high of near -20 nT centred on a magnetic low that is ~25 km wide (<100 nT), which has been interpreted as a magnetic body below a depth of 6 km. In this paper Glikson et al., suggest a distinct seismic tomographic low velocity anomaly may reflect its thick sedimentary section, 9.5 km, as well as high temperatures and the possibility of deep fracturing. Microbreccia veins that consist of micron-scale particles injected into resorbed quartz grains have been resolved by an analysis using a scanning electron microscope (SEM). Occurring in granites, volcanics and sediments of the >30,000 km-large Eastern Warburton Basin are planar and sub-planar elements in quartz grains (Qz/PE). Multiple intersecting planar to curved sub-planar elements with relic lamellae less than 2 μm wide and spacing of 4-5 μm are included in the Qz/PE grains. Qz/PE are commonly re-deformed, displaying patterns that are bent and wavy accompanied with fluid inclusions. Of a total of 243 planar sets in 157 grains U-stage measurements indicate dominance of Π{10-12}, ω{10-13} and subsidiary §{11-22}, {22-41}, m{10-11} and x{51-61} planes. Relic narrow lamellae, ≤ 1-μm-wide, and relic non-sub grain boundaries where optical continuity is maintained by crystal segments. Hydrothermal alteration to a depth of ~500 m below the unconformity overlying the Qz/PE-bearing Warburton Basin terrain is suggested by extensive alteration of feldspar. The data are discussed in terms of :

(A) Tectonic-metamorphic deformation and

(B)  Impact shock metamorphism that produces planar deformation features (Qz/PE).

Deformed Qz/PE was compared to re-deformed Qz/PE in the Sudbury, Vredefort, Manicouagan and Charlevoix impact structures. At the Big Lake Granite Suite an uplift of 4-5 km is consistent with missing Upper Ordovician to Devonian strata and possible impact rebound. Below the east Warburton Basin the occurrence of circular seismic tomography anomalies, the Poolowana Basin and the Woodleigh impact structure signifies a potential diagnostic nature of circular tomographic anomalies.

Sources & Further reading

1. Clarissa Thorpe, 2015, World’s largest impact zone believed uncovered by ANU researchers in central Australia, abc.net.au

2. Glikson, A. Y., A. J. Meixner, B. Radke, I. T. Uysal, E. Saygin, J. Vickers and T. P. Mernagh (2015). "Geophysical anomalies and quartz deformation of the Warburton West structure, central Australia." Tectonophysics 643(0): 55-72.