The ca. 1740–1710 Ma Leichhardt Event: Inversion of a continental rift and revision of the tectonic evolution of the North Australian Craton

Abstract

Interpretation and modelling of high resolution regional geophysical data of the central Leichhardt River Fault Trough in the Mount Isa Inlier are used to determine the timing of a major basin inversion event following the development of the ca.1780–1740 Ma Leichhardt Superbasin. Inversion of the Leichhardt Superbasin formed the regional north-south trending Leichhardt Anticline during east-west shortening. The limbs of the anticline are overprinted by several east-west trending wedge-shaped, non-magnetic sub-basins filled with ca.1710 Ma Calvert and Isa superbasin successions. These relationships suggest inversion of the Leichhardt Superbasin occurred between ca.1740 and 1710 Ma. The event is also known to have affected the northern and eastern North Australian Craton. The scale of the inversion suggests it was a significant event that we have defined as the Leichhardt Event. This event requires a major tectonic driver to the east of the North Australian Craton, possibly the accretion of a micro-continental ribbon to the east of the Mount Isa Inlier. The results of this study have implication for paleogeographic reconstruction of the Australian continent during the formation of Nuna because eastern North Australian Craton faced an ocean at ca.1740–1720 Ma. The results also challenge the significance and intensity of crustal shortening associated with the ca.1600–1500 Ma Isan Orogeny throughout the western Mount Isa Inlier.