Over the past 25 million years or so, tectonic deformation caused by the collision of the Australian and Pacific plates has resulted in uplift of the Southern Alps and the ranges of northern Canterbury and Marlborough, including the
Canterbury foothills. Much of the cover rocks have been eroded away in the foothills, exposing the basement rock
(Figure A5.1).
Figure A5.1 Geology is from the GNS Science QMAP digital database (Cox & Barrell, 2007; Forsyth et al., 2008). Faults related to the 2010-2011 earthquake sequence include the ground-surface rupture marked by the Greendale Fault
(Barrell et al., 2011; Quigley et al., 2012), and subsurface faults defined by geodetic modelling (Beavan et al., 2012) and by clusters of epicentres within the aftershock pattern (J.R. Pettinga, personal communication, May 2012).
The Pleistocene Epoch, which began at ~2.6 Ma, was characterised by ice ages, in which episodes of cooler climate were interspersed with phases of warmer interglacial climate, such as the past ~12,000 years of the present
Holocene Epoch. Large volumes of sediment generated during cycles of glaciation in the Southern Alps were carried eastwards via the river systems and deposited on the Canterbury Plains. Beneath the plains and offshore, the basement rocks are still overlain by cover rocks, but the cover rocks (including the flanks of the Banks Peninsula volcanoes) are blanketed by mid- to Late Pleistocene and Holocene sediments that in places are up to several hundred metres thick (Jongens et al., 2012).
In summary:
Following tectonic uplift that created the mountains and steep hills of inland Canterbury over the past 25 million years, the
Canterbury Plains were formed from quaternary moraine gravels which were erdoded in the areas of high relief, transported by glaciers and deposited during glacial periods in the late Pleistocene approximately 3 million years to 10,000 years ago.