Tectonostratigraphic terranes of the Croissilles Harbour region, South Island, New Zealand

Abstract

The boundary between Hokonui and Te Anau assemblages is flanked by a broad (10-20 km) zone of imbricated slabs of late Paleozoic and Mesozoic lithostratigraphic terranes. Five terranes are mapped, three of predominantly sedimentary character (Dun Mountain-Maitai, Rai, Pelorus) are separated by two consisting of ophiolitic melange (Patuki, Croisilles). A regional stratigraphy is mapped within the Late Permain Maitai Group, but formational subdivision of Rai and Pelorus rocks is not attempted because of degree of deformation and the more monotonous aspect of these greywacke-dominated suites. Sandstone petrography and petrochemistry indicate provenance of sands mainly from dissected and undissected arc sources. Each of the three sedimentary belts possesses its own lithic character and we can see no evidence for original stratigraphic interrelations. The two ophiolitic melanges are similar, but not identical. They probably formed through tectonic disruption of the Dun Mountain ophiolite. Correlation seems more likely for these but must await further evidence. Each terrane possesses distinctive structural style, metamorphic grade, and probably metamorphic timing. The Croisilles area represents a complex zone of rocks formed under both convergent and divergent conditions; their evolution began early in the Permian and continued until achieving the present relationship, probably by middle Mesozoic time. Original relations between the five terranes remain equivocal and they should be regarded as suspect terranes until further constraints are available.