During the latest Cretaceous–early Cenozoic, the northern margin of the Australian plate was characterized by a large (4000 km wide) north- to 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.

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