Structure and origin of Australian ring and dome features with reference to the search for asteroid impact events

Abstract

Ring, dome and crater features on the Australian continent and shelf include (A) 38 structures of confirmed or probable asteroid and meteorite impact origin and (B) numerous buried and exposed ring, dome and crater features of undefined origin. A large number of the latter include structural and geophysical elements consistent with impact structures, pending test by field investigations and/or drilling. This paper documents and briefly describes 43 ring and dome features with the aim of appraising their similarities and differences from those of impact structures. Discrimination between impact structures and igneous plugs, volcanic caldera and salt domes require field work and/or drilling. Where crater-like morphological patterns intersect pre-existing linear structural features and contain central morphological highs and unique thrust and fault patterns an impact connection needs to tested in the field. Hints of potential buried impact structures may be furnished by single or multi-ring TMI patterns, circular TMI quiet zones, corresponding gravity patterns, low velocity and non-reflective seismic zones. A. Examples of crater-form and dome-form features containing elements consistent with an impact origin, though unproven, include Auvergne, Delamere, Fiery Creek, Monte Christo, Mount Moffatt, Tanami East, Youngerina, and Tingha.

B. Examples of buried multi-ring features of possible to probable impact origin include Augathella, Balfour Downs, Calvert Hills, Camooweal, Green Swamp Well, Herbert, Ikybon River, Ilkurka, Lennis, McLarty Hills, Mount Davies, Mulkara; Neale; Sheridan Creek, Oodjuongari and Renehan.

C. Examples of igneous plugs unrelated to impacts include the Monto gabbro and numerous circular granitoid plugs such as Windinie Hills granite and Yataga granodiorite.

D. Large circular structures such as Mount Ashmore and Gnargoo are considered to have convincing structural deformation features warranting classification as probable impact structures.

The origin of very large circular TMI and gravity patterns such as of the Diamantina River drainage feature, Coonamona anomaly and the multiple TMI ring pattern of the Deniliquin-Booligal remain unresolved. The advent of ~ 40 m TMI grid coverage promises to further uncover ring and dome features, such as the McLarty Hills multi-ring feature, potentially increasing the inventory of ring structures on the Australian continent. Compared with frequency distribution patterns of extra-terrestrial impact structures worldwide, the Australian record displays a relatively common occurrence of large impact structures and relative depletion in small impact structures and craters. This is explained by the better preservation of large structures at deep crustal zones as compared to the erosion of small craters.