Abstract - Evolution of slab geometry beneath the North Island, New Zealand,
has been investigated using a combination of published arc-type volcanic ages and earthquake
locations in the subducting Pacific plate. Arc-front volcanoes migrated SE by 150km in the
last 8myr subparallel to the present active arc. Migration of the arc is interpreted to mainly
reflect slab rollback along the Tonga–Kermadec subduction system changing to fixed hinge
slab steepening beneath the central North Island. The strike of the Pacific plate beneath the North Island, imaged
by Benioff zone seismicity (50–200 km) and positive mantle velocity anomalies (200–600 km), is parallel to the
NE–SW trend of arc-front volcanism. Arc parallelism since 16Ma indicates that the strike of the subducting plate
beneath the North Island was constant over this time interval, in contrast to clockwise vertical-axis rotations of
more than 50° of the overriding plate over the same period along the eastern and southern Hikurangi margin. Acceleration
of arc-front migration rates (from c. 4 to c. 18mm per year), eruption of high-Mg# andesites, increasing eruption
frequency and size, and uplift of the overriding plate indicate an increase in the hydration, temperature and size
of the mantle wedge beneath the central North Island from c. 7Ma.
Journal of the Geological Society, Longon, 171, 131-143, 2014.