The Mesozoic terrane boundary beneath the Taupo Volcanic Zone, New Zealand, and potential controls on geothermal system characteristics

The Taupo Volcanic Zone (TVZ) in the central North Island of New Zealand lies across the boundary formed in the late Mesozoic between two major basement regions: the Waipapa and Torlesse composite terranes. However, the precise location of this terrane contact within the TVZ is not well constrained because it is buried beneath Pleistocene volcanic and volcaniclastic sequences locally >3 km thick. Here we report new U-Pb zircon detrital age spectra from basement sandstones and younger Waikora Formation greywacke gravel from five geothermal well core samples and one surface sample. We combine these new data with existing TVZ zircon xenocryst and xenolith age spectra from volcanic host rocks, to correlate these materials with each basement terrane and constrain the likely spatial location and uncertainty of the terrane boundary under the TVZ. Its position with respect to surficial geothermal systems suggests that, at depth, the terrane boundary may have been reactivated by Quaternary extension in the evolving Taupo Rift. Put another way, the past and current position of the Taupo Rift fundamentally may have been controlled by the terrane boundary, which may ultimately be partly responsible for providing enhanced fracture permeability for deep-seated geothermal fluids.