A geodynamic model of subduction evolution and slab detachment to explain Australian plate acceleration and deceleration during the latest Cretaceous–early Cenozoic

Abstract

During the latest Cretaceous-early Cenozoic, the northern margin of the Australian plate was characterized by a large (4000 km wide) northto northeast-dipping subduction zone (New Guinea-Pocklington subduction zone) consuming a marginal basin. Geological and geophysical data imply that the subduction zone was active ca. 71-50 Ma, and suggest that it was responsible for plate acceleration from ~1.0 to ~7.3 cm/yr ca. 64-59 Ma, and plate deceleration from ~7.3 to ~0.3 cm/yr at 52-49 Ma. This paper presents a numerical model of buoyancy-driven subduction to test if the rates of Australian plate acceleration and deceleration can be ascribed to the progressive evolution of a subducting slab. The geodynamic model reproduces the first-order plate velocity evolution of the Australian plate, with a transient ~5 m.y. period of acceleration from 2 to 8 cm/yr during upper mantle slab lengthening, an ~5 m.y. period of rapid plate motion (~5-8 cm/yr), and a short, 3.9 m.y., period of plate deceleration, starting with a 2 cm/yr velocity drop during 3.1 m.y. of continental subduction and followed by ~0.8 m.y. of rapid deceleration (4 cm/yr velocity drop) during slab detachment. The geodynamic model demonstrates that plate velocity increases or decreases of ~4-6 cm/yr can occur over a period lasting < 1 m.y. to a few million years, comparable to what is observed for the latest Cretaceous-early Cenozoic evolution of the Australian plate. Such rates of plate acceleration and deceleration could be tested against plate kinematic data for other subduction settings on Earth.