Deformation style and history of the eketahuna region, hikurangi forearc, New zealand, from shallow seismic reflection data

Abstract

A shallow seismic reflection survey across the Eketahuna region, located at the inboard edge of the obliquely convergent Hikurangi subduction margin, New Zealand, records deformation of a Miocene‐Pliocene forearc basin sequence and underlying greywacke basement. A suite of northeast‐trending strike‐slip and reverse faults deforms the region into northwest‐tilted blocks. Southeast‐verging folding associated with the faults includes open hanging‐wall anticlines and footwall synclines, and fault propagation folds above non‐emergent fault tips. Secondary faults commonly disrupt synclinal cores. Faults emerge from the greywacke basement at near‐vertical (strike‐slip faults) or 35–70° (reverse faults) dips. Faults in the L'ketahuna and adjacent Dannevirke and Wairarapa Basins are shown from seismic reflection data to have been active, at least in part, contemporaneously with submarine deposition of Miocene‐Pliocene sediments in the forearc basin. In the southern part of the basin, widespread Pleistocene uplift and erosion of greywacke basement caused an influx of coarse detritus into the basin. Still later, emergence of the forearc region occurred. Whereas uplift of the forearc is considered to be due to large scale processes (such as underplating, subduction of thick, buoyant oceanic crust, or an influx of sediments to the Hikurangi trough), widespread and closely spaced disruption of the forearc basin may be due to encroachment of the Hikurangi margin on the continental crust of the Chatham Rise causing increased coupling across the subduction interface. © 1995 The Royal Society of New Zealand.