Crustal seismic reflection measurements across the northern extension of the Taupo Volcanic Zone, North Island, New Zealand

Abstract

A crustal seismic reflection profile across the offshore Taupo Volcanic Zone (OTVZ) has been reprocessed to improve the lower crust–upper mantle image. The OTVZ is underlain by several strong sub-horizontal crustal reflections that may correspond to shear zones or mafic sills. A reflector interpreted to correspond to Moho lies at a depth of about 8–8.5 s twt (seconds two-way-traveltime) – about 20 km – under the western margin of the Raukumara Peninsula and rises to a depth of about 6 s twt (about 16 km) under the active, eastern part of the OTVZ and can be traced at about this depth across most of the OTVZ. Underlying this inferred Moho are two diffuse zones of discontinuous reflectivity, one underlying the active eastern OTVZ and a less well defined one underlying the landward extension of the Havre Trough. They extend from about 15 to 35 km depth, within the mantle wedge, and are inferred to be imaging a zone of depleted upper mantle associated with crustal extension. A localised zone of deep (30–50 km) reflectivity and seismicity occurs under the eastern OTVZ margin and may relate to fluid flow from the Hikurangi plateau being subducted further east.