THE OBLIQUELY-CONVERGENT PLATE BOUNDARY IN THE SOUTH ISLAND OF NEW-ZEALAND - IMPLICATIONS FOR ANCIENT COLLISION ZONES

The Alpine Fault of New Zealand forms the western boundary of a zone of distributed deformation formed by the oblique convergence of continental crust belonging to the Pacific and Australian plates. Structural and geodetic data from the Alpine Fault show that a large proportion of the total plate displacement is accommodated by rapid oblique slip on the fault. The remaining displacement is distributed over a 200 km wide zone to the east. The collision may be modelled as a two-sided deforming orogen, with the partitioning of deformation being controlled by erosional differences between the narrow high-strain inboard and broad low-strain outboard sides. In ancient collision zones, little evidence may remain of the nature and amount of displacement on the inboard side. Partitioning of deformation among pre-existing structures complicates interpretation of the outboard zone. Radiometric ages may post-date collision by several tens of millions of years and indicate slow isostatic uplift and unroofing. Collision ages, if preserved, may be recognized by high uplift rates calculated from muscovite-biotite pairs. © 1990.