The West Coast region of the South Island is situated astride the Pacific -
Australian plate boundary zone. The most significant component of this zone is
the Alpine Fault. A variety of reconstructions of the pre-Alpine Fault plate
tectonic configuration of the New Zealand continental area have been attempted
over the past 25 years or so. Most of these have not been closely constrained by
a regional compilation of field data related to the age and horizontal
displacement history of the Alpine Fault.
A model in which the Alpine Fault was initiated no earlier than the interval
18 - 16.5 Ma (B.P.) is proposed, a significantly younger age of inception than
has been widely accepted as the onset of dextral displacement along the plate
boundary through the South Island. A subsequent history of displacement is
presented consistent with the West Coast basin stratigraphy.
The alluvial gold content of some parts of the Miocene to Pleistocene
conglomerate sequences is also discussed.