Tectonic controls on the evolution of the Clutha River catchment, New Zealand

Abstract

• A synthesis of published information on mountain uplift and river capture in Otago suggests that the Clutha River catchment has evolved westwards and expanded since the Pliocene. River capture events that facilitated catchment expansion are indicated by sediment provenance, drainage geometry and freshwater fish genetics. The catchment has been partly confined by NW-trending ranges and the Southern Alps to the west, and drainage geometry was disrupted by subsequent growth of NE-trending ranges. Examination of crustal-scale deformation via an established numerical model, which portrays the Otago Schist basement as rheologically weak compared to adjacent greywacke-dominated structural blocks, suggests that uplift geometry was controlled by the inherited Cretaceous boundary between these crustal blocks. Pre-existing faults had relatively minor effects on uplift geometry. A low-relief corridor between Canterbury and Southland permitted genetic connections of freshwater fish populations through to <1 Ma, to the west of the developing Clutha catchment.