Abstract
The Blue Lake Fault Zone occurs at a major crustal boundary between Otago Schist and Torlesse greywacke. This zone has been active since the middle Cretaceous (c. 112 Ma), when extensional exhumation of the Otago Schist belt was initiated. The Blue Lake Fault Zone is dominated by a set of normal faults that have caused juxtaposition of rocks of different metamorphic grade, from prehnite-pumpellyite facies turbidites to pervasively recrystallised greenschist facies schists. This metamorphic transition has been thinned from c. 15 km to c. 2 km by normal fault motion on the scale of kilometres. This condensed section is the narrowest such section on the Otago Schist margin. The faults in this condensed section are defined by gouge zones that are hundreds of metres wide and constitute about 30% of the section. Gouge zones were locally reactivated as thin Late Cenozoic reverse faults on the centimetre to metre scale.