Extensional fault kinematics within the Taupo Volcanic Zone, New Zealand: soft-linked segmentation of a continental rift system

The Taupo Volcanic Zone (TVZ) is a young (less than or equal to2 Ma) arc-backarc system in continental crust at the southern end of the Havre Trough characterised by intense volcanism and geothermal activity. An extensional fault belt (known locally as the Taupo Fault Belt) can be traced semicontinuously within the TVZ from Ruapehu in the southwest to the Bay of Plenty coast in the northeast. Contained within the belt are numerous active volcanic centres (andesitic, basaltic, rhyolitic) and geothermal systems. Kinematic studies demonstrate that normal faulting predominates within the fault belt, which we interpret as a distributed rift system (here termed the Ruaumoko Rift System), within which rift axes are locally defined by crudely symmetric dispositions of northwest- and southeast-dipping faults. The entire fault belt is partitioned along-strike into offset rift segments defined by association with discrete rift axes. Fault dips, where measurable, are generally steep (delta > 60 degrees). Systematic fracture sets occur in all rock types in the TVZ and generally show a strong northeast-southwest trend, indicating a component of extensional strain distributed throughout the rock mass. Extension is predominantly orthogonal to the rift axes except in accommodation zones where interaction between offset rifting segments perturbs the stress field, locally enhancing permeability. The varying trends of extensional structures lie perpendicular to least principal stress trajectories in a locally heterogeneous stress field with normal dip-slip as the predominant fault mechanism.