Crustal seismic study of an ensialic back-arc basin (Bay of Plenty, New Zealand)

Tbc Central Volcanic Region of North Island (New Zealand) bas been a zone of back-are extension and are volcanism, associated with the subduetion of the Pacific plate under the Australian plate along tbc Hikurangi margin, for tbc past 4 Ma. Present activity (< 0.6 Ma) is concentrated on tbc 40 km wide Taupo Voleanie Zone along its eastern margin. Marine crustal seismic reflection measurements have been carried out across the Central Volcanic Region, providing new insight into tbc structure of this intracontinental back-are basin. A broad, block faulted extensional basin is identified containing up to 2.5 seconds two way time of sediments of presumed voleanogenie origin. Faulting is more intense along the eastern margin of the basin. Sedimentary structures are complex and two phases of sedimentation Can be identified in some areas. In the presendy active Taupo Voleanic Zone, sediment thickness increases towards its centre where a deep basement ridge occurs but cannot be unequivocally interpreted to be of volcanic origin. However, strong inid and lower crustal reflectors occur under tbc central part of Taupo Volcanie Zone and are interpreted to be associated with magma or voleanic siRs. The deepest reflector is close to tbc refraction Moho.