OFFSHORE-ONSHORE CORRELATION OF PLEISTOCENE RHYOLITIC ERUPTIONS FROM NEW ZEALAND: IMPLICATIONS FOR TVZ ERUPTIVE HISTORY AND PALEOENVIRONMENTAL CONSTRUCTION

Deep-sea cores retrieved from Ocean Drilling Program sites 1123 and 1124, located east of New Zealand, have provided an unpreceded 12 m.y. record of major rhyolitic eruptions from the Coromandel (CVZ) and Taupo Volcanic Zones (TVZ). A total of 197 macroscopic tephras have been dated by a combination of magnetostratigraphy, orbitally tuned stable-isotope data and isothermal plateau fission track ages. The widespread occurrence of ash offshore to the east of New Zealand is favoured by the small size of New Zealand, the explosivity of the mainly plinian and ignimbritic eruptions and vigorous prevailing westerly winds.

In cores 1124 and 1123, c. 100 tephra beds are recognised post-dating the Plio-Pleistocene boundary at 1.81 Ma. Though some tephras can be directly attributed to known TVZ eruptions, there are many more tephras represented with the ODP-cores that have yet to be recognised in near-source sequences. This can be attributed to proximal source area erosion and/or deep burial as well as the adverse effect of vapour phase alteration and devitrification within near-source welded ignimbrites. Despite these difficulties, a number of key deep-sea tephras can be reliably correlated to equivalent-aged tephra exposed in uplifted marine back arc successions of Wanganui Basin where an excellent chronology also exists based on magnetostratigraphy, orbitally tuned stable-isotope data and isothermal plateau fission track ages. Significant Pleistocene tephra markers include: Kawakawa, Rangitawa, Onepuhi, Kupe, Kaukatea, Potaka, Ridge, Pakihikura, Birdgrove, Ototoka, Table Flat and Vinegar Hill Tephras.

The identification of these Pleistocene TVZ-sourced tephras within the ODP-cores, and their correlation to Wanganui Basin is a significant advance for two reasons. Firstly, it provides an even higher-resolution history of the TVZ than can be currently achieved from the near-source record and secondly, it yields a detailed and reliable tephrochronologic framework essential for future paleoenvironmental reconstructions.