Quaternary Tectonics of New Zealand

Abstract

The New Zealand landmass exists because it straddles the active obliquely convergent Pacific-Australia plate boundary, which comprises the opposite-dipping Hikurangi and Fiordland subduction systems linked by the Alpine Fault transform. Changes in the form of the plate boundary along New Zealand are accompanied by variations in the tectonics, sedimentary basins, crustal structure and topography. Quaternary deformation is constrained by structure mapping, growth strata, thermochronology, shallow crustal seismicity, GPS velocities and principal shortening axes, and uplift patterns. The majority of the relative plate motion through New Zealand (>70 %) is accommodated by the Hikurangi subduction thrust, Marlborough Fault System and Alpine Fault. Additional faulting (strike slip, reverse and normal), folding and vertical-axis rotations produce deformation across a plate boundary zone that is 150–450 km wide. The Cenozoic plate boundary formed at least 20 Myr ago, although margin-wide observations suggest that the present rates and kinematics of deformation commenced during the Quaternary. Topography is positively related to rock uplift rates which mainly reflect a combination of geodynamic processes (e.g., collision, subducted sediment under-plating and mantle flow) and fault slip during earthquakes. Contemporary regional-scale topography within the plate boundary zone, where rates of vertical motion are highest, mainly formed in the Quaternary, while elsewhere it may be as old as Late Miocene in age.