Bonaparte rift basin: effects of axial doming and crustal spreading

Abstract

The Bonaparte Basin of Northwestern Australia commenced development as a Devonian rift which underwent a pivot-type opening about a pole at its southern end. By the cessation of the opening process in the Mid Carboniferous, the bounding faults at the northern end of the rift were separated by 250+ km and crustal splitting had occurred on the floor of the rift, allowing the emplacement of a 100+ km expanse of oceanic crust. In contrast, the bounding faults at the southern end of the rift are only 80 km apart and the intervening crust is entirely continental. A key element in the rift development was the intrusion of a large axial dyke of dense magnetic upper mantle material whose emplacement was an immediate precursor to the crustal splitting process. This dyke reached progressively higher levels as rift widening and crustal thinning progressed, until at the northern end of the rift crustal splitting occurred along the axis of the intrusion. Doming of the rift-fill sediments by the axial intrusion controlled erosion and sedimentation within the rift during the final stages of its development. With the termination of crustal spreading the Bonaparte Basin underwent a long period of subsidence and associated burial. Bonaparte rift structures were preserved in their attitudes existing at the end of the spreading process, and their geometry is reflected by drapes in the subsidence phase sediments.