Abstract: Plate Boundary Reorganization as a Requisite Mechanism for Terrane Accretion: An Example from the Late Cenozoic of Northern New Guinea

John D. Pigott, Andrew B. Cullen

Dynamic plate interactions can lead to the growth or destruction of plates. With respect to buoyant crust, terrane accretion at the edges of collisional orogens is the principal mechanism for bringing plate fragments together and allowing the lateral growth of continental plates. For the accretionary process to come to completion and welding to occur, the fragments must be preserved from the continuation of destructive processes at collisional orogens: pure shear with resultant shortening, uplift, and erosion and/or simple shear with the lateral dismemberment of plate fragments. For relative plate motions to diminish and the juxtaposed plates to permanently weld, plate boundaries must be reorganized. Collisional plate-boundary reorganization can occur by either of two processes: (1) a justment, i.e., lateral shifting of plate boundaries, or (2) reconfiguration, i.e., the formation of entirely new plate boundaries.

A southeast Asian example of plate-boundary reorganization that follows terrane accretion is provided by a plate kinematic study of the New Guinea region. Neogene collision of the Finisterre terrane with the Marinumi Arc subduction zone in northeastern New Guinea led to a major reorganization of the area's tectonic setting. Reversal in subduction zone polarity coupled with increasingly oblique sinistral convergence between Indo-Australian and Pacific plates led to the initiation of sea-floor spreading in the Bismarck Sea and the formation of an entirely new plate, the Bismarck plate. Holocene dextral convergence (S 3°E, 9.1 cm/a) along the newly formed Indo-Australian and Bismarck plate boundary represents a major change both from the sinistral convergence that characterized the egion prior to the terrane accretion and which still is occurring along the modern Indo-Australian plate boundary west of the Bismarck plate. The present-day kinematics, a direct product of this plate-boundary reorganization, favor the eventual welding of the Finisterre Terrane to the Indo-Australian plate, rather than its dismemberment by the left lateral north New Guinea fault zone along the Indo-Australian/Pacific boundary to the west.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994