Terminal suturing of Gondwana and the onset of the Ross–Delamerian Orogeny: the cause and effect of an Early Cambrian reconfiguration of plate motions

Abstract

A review of U–Pb age data from intrusive and volcanic rocks for Antarctica and Australia has highlighted the remarkable synchronicity in the shift from passive margin or continental arc tectonism, to convergent orogenesis along the Pacific margin of Gondwana. This event, the Ross–Delamerian Orogeny, marks a distinct and rapid shift in the style of deformation, rate of uplift, volume of magmatism and syn-orogenic sedimentation along the entire 4000+ km length of the orogen. The Ross–Delamerian Orogeny is constrained to have begun at 515±5 Ma, an interval that also encompasses the youngest collisional events that lead to the suturing of Gondwana. We propose that these geographically separate events are intimately linked and represent the cause and effect of a major tectonic reorganisation in the motion of the Earth’s plates. We suggest the mechanism controlling this Early to Middle Cambrian plate reorganisation was the rapid reduction in relative motion, driven by continental collision, between the final two components of Gondwana. Due to the need to maintain a zero sum for all plate motions, the change in the rate of convergence at this boundary resulted in compensatory changes elsewhere in the global plate circuit. One such change was an increase in the rate and perhaps direction of convergence along the Pacific margin of Gondwana.