A Forearc Stratigraphic Response to Cretaceous Plateau Collision and Slab Detachment, South Island, New Zealand

Sedimentary successions deposited within arc-trench gaps (forearcs) record topographic oscillations related to subduction tectonism. The collision of oceanic plateaus can inhibit normal subduction and induce detachment of the subducted oceanic lithosphere (slab), leading to subduction translation or shut-down. Such second-order subduction processes complicate the stratigraphic record making discrete events difficult to resolve, as preserved examples are rare and typically overprinted by deformation. We compiled and averaged (stacked) top subduction wedge (Pahau Terrane) subsidence and paleo-water depth curves from 30 locations containing mid-Cretaceous forearc successions in Marlborough, New Zealand. Subsidence curve stacking proved effective in removing deformation due to normal subduction, allowing for resolution of higher order plate-margin events. The stacked curves reveal a synchronous topographic oscillation affecting over 100 km of the paleo-coastline between 110 and 95 Ma, which penetrated almost 250 km into the forearc hinterland and created up to 3 km of accommodation space. Topographic drawdown and highstand deposition from 110 Ma were followed by rebound and volcanism by 98 Ma, a response to regional tectonism that was compared to theoretical predictions for ridge and plateau collision. We conclude that plate flexure, and slab extension and tearing reasonably account for the synchronous topographic oscillation observed, which we attribute to Hikurangi Plateau collision. We postulate that collision began east of Marlborough along the present day Chatham Rise from 110 Ma, producing topographic upheaval and disruption of adjacent sedimentary systems. Sediments deposited contemporaneously along the margin preserve a record of these events and provide a rare insight into evolving mid-Cretaceous plate dynamics.