Geology of the Canterbury region

On the coast, just southeast of Christchurch, is Banks Peninsula, composed of two large mainly basaltic Miocene volcanoes.

All basement rocks beneath the Canterbury region belong to the Torlesse Composite (Rakaia and Pahau) Terrane.

They are largely composed of greywacke (hardened sandstone and mudstone) that accumulated in a deep marine environment and were accreted to the Gondwana continent before the Tasman Sea opened up in late Cretaceous times (80 Ma).

At the boundary between these two terranes is the Esk Head Belt, an 11 km wide melange of broken and deformed rocks.

The plate boundary is represented by the Alpine Fault, which runs slightly west of the main divide of the Southern Alps.

[1] Volcanic activity occurred around the Mount Somers / Te Kiekie area, and nearby foothills in late Cretaceous times (100–66 Ma).

The Lyttelton / Whakaraupō and Akaroa Harbours correspond to two large overlapping volcanoes, that built Banks Peninsula in late Miocene times (11–6 Ma).