Paper No. 8
Presentation Time: 10:45 AM
PROVENANCE AND PALEOGEOGRAPHIC RECONSTRUCTION OF A PROGRADATIONAL DEEP-WATER SLOPE SUCCESSION IN THE LATE MIOCENE TARANAKI BASIN, NORTH ISLAND, NEW ZEALAND
Combined new zircon U-Pb age spectra from deep-water slope sediments, zircon U-Pb ages from ash layers, stratigraphic analysis, and sedimentologic interpretation from a late Miocene Taranaki Basin coastal outcrop provide constraints on provenance, sedimentation, erosion, and uplift rates in the North Island, New Zealand. Late Miocene Taranaki Basin depocenters existed in a complicated tectonic setting flanked to the north and west by arc-related volcanism, to the east and south by a fold-and-thrust belt, and to the south by the evolving transpressional plate boundary. Deep-water slope deposits of the Urenui and Kiore formations formed part of an extensive progradational wedge of sediment within this hybrid tectonic setting with both passive and active margin characteristics. Results for seven detrital samples from the slope deposits (total 675 single-grain ages) are visually and statistically compared to New Zealand basement rocks to evaluate potential source terranes. Taranaki samples contain multiple age peaks 100-2,600 Ma, with most grains 100-700 Ma. All grains were >10 My older than the depositional age of the sediments (8.98±0.22 Ma) established from volcanic ash zircon U-Pb ages. Based on statistically indistinguishable detrital zircon age spectra, Torlesse sub-terranes in the North Island axial ranges are interpreted to have provided a consistent source for detrital zircon to Taranaki slope deposits. New zircon ages from ash layers within the Taranaki outcrop are in close agreement with biostratigraphic data and suggest a rapid overall sedimentation rate in the slope deposits of ~900-2100 m/Ma (not accounting for compaction). Interpretation of sedimentary provenance and sedimentation rates implies that the ancestral axial ranges were uplifting, eroding, and providing sediments by the late Miocene, possibly at rates comparable to modern values. Late Miocene transport of sediments occurred via a westward draining fluvial system that did not intersect contemporary rhyolitic volcanism, in contrast to modern drainages and sediment dispersal systems.