Seismic stratigraphy and structure adjacent to an evolving plate boundary, western Chatham Rise, New Zealand ( DSDP, Leg 90).

Abstract

Seismic profiles obtained from the E side of New Zealand, in transit to and from Site 594, illustrate the evolution of the W end of the Chatham Rise and the S extremity of the Hikurangi Trough. They show several unconformities and several major changes in tectonic and depositional regime. Tectonism is exemplified by a Late Cretaceous phase of block faulting, heralding the rift from Gondwanaland, and by Plio-Pleistocene normal faulting on the N flank of the rise antithetic to the oblique-collision plate boundary in the S Hikurangi Trough. This active normal faulting may iondicate that the NW corner of Chatham Rise continental crust is being dragged down with the subducting slab to the N. The depositional regime has changed from Late Cretaceous infilling of fault-angle depressions, through an early Tertiary transgression and mid-Tertiary carbonate drape, to a late Miocene-Recent sequence recording repeated glacial-interglacial events. This upper stratified unit onlaps a late Miocene erosion/phosphatization unconformity toward the crest of the rise. It is locally truncated by a slope-parallel erosion surface, with downslope buildup, which may indicate either current scour and deposition or mass movement.-from Authors