IODP Borehole Constraints on Timing of Eocene Compressional Plate Failure During Subduction Initiation, Northern Zealandia, Southwestern Pacific.

Abstract:

A total of 3600 m of sediment was cored on IODP Expedition 371: Tasman Frontier Subduction Initiation and Paleogene Climate, at six borehole sites across northern Zealandia. The tectonic goal of the expedition was to date deformation that can be temporally linked to the evolution of the Tonga-Kermadec subduction system. The marine depositional setting of northern Zealandia during the Cainozoic was a good recorder of deformation events that can be linked to the evolving plate boundary. Deformation events in these sediments document a shortening event that lasted up to 20 myrs and acted over distances up to ~1000 km inboard of the evolving plate margin. The position of the rotation pole during the shortening event indicates that convergence rates were low, and subduction may not have reached a self-sustaining state. Multichannel data tied to our new borehole sites show that the shortening occurred predominantly in the middle to late Eocene with some deformation related to slope failure on the margins of the New Caledonia Trough continuing into the Oligocene. The termination of shortening is linked to opening of the backarc basins of the south west Pacific and the migration of the subduction trench to the east which removed the structural evidence of the Eocene plate margin behind the basins. We link these deformation events to the change from subduction initiation to propagation of the established Tonga-Kermadec subduction system south-eastwards across northern Zealandia in the Eocene.