Oblique back arc rifting of Taupo Volcanic Zone, New Zealand

摘要

Taupo Volcanic Zone (TVZ) is a back arc rift in North Island, New Zealand. Its geometry and kinematics are investigated using shaded relief images, field examination of faults and offset stream channels. The results show that TVZ trends NNE, is ～250 km long by ～20 km wide and consists of five segments. Extension is principally manifest as steeply dipping (60°-90°) normal faults parallel to TVZ; these, in the last 300 kyr, have experienced a component of dextral shear. TVZ is therefore an oblique back arc rift. The dextral shear is ～37% of the total displacement, which, for previously estimated spreading rates ～7 mm/yr, corresponds to ～2.6 mm/yr. This value is similar to previous estimates of the dextral shear from the back arc to the forearc domains in the North Island. Distributed dextral shear across TVZ thus suggests that strain partitioning across the plate boundary at latitudes of TVZ is less significant than previously thought.