Eocene to Miocene Subduction Initiation Recorded in Stratigraphy of Reinga Basin, Northwest New Zealand

Abstract

AbstractReinga Basin, northwest of New Zealand, contains deformed Cretaceous and Cenozoic strata, flat unconformities interpreted as sea level‐modulated erosion surfaces, and volcanics. Marine conditions since the Late Cretaceous resulted in deposition of thick sequences of fossil‐rich sediments. We present a seismic stratigraphic analysis that is tied to dredged rock samples and International Ocean Discovery Program Site U1508. The Cenozoic tectonic evolution of Reinga Basin comprises four phases. (1) Folding was accompanied by uplift from lower bathyal water depths at 56–43 Ma along West Norfolk Ridge, where wave ravinement surfaces were cut. (2) Basin‐wide compression and reverse faulting at 39–34 Ma exposed Eocene and older strata along the northeastern basin margin and farther south in western New Zealand. (3) Emplacement of South Maria Allochthon at 34–28 Ma along the northeast margin postdated thick‐skinned reverse faulting and folding, was broadly synchronous with the onset of basin volcanism, and immediately predated wave ravinement of nearby ridges. Normal faulting disrupted the western basin margin at this time. (4) During the final phase of the Reinga Basin deformation, South Maria Ridge subsided ∼1,000–2,000 m from the middle shelf to bathyal depths after 23–19 Ma, and the deformation migrated southeastwards. The Northland Allochthon was emplaced at 23–20 Ma, and Northland volcanism with confirmed arc character occurred at 23–12 Ma. The early Eocene onset of tectonic activity recorded by deformation in Reinga Basin is shown to be older than previously recognized and broadly synchronous with other events related to subduction initiation and plate motion change elsewhere in the western Pacific.