Geology of Torlesse and Waipapa terrane basement rocks encountered during the Tongariro Power Development project, North Island, New Zealand

Abstract Greywacke-type basement rocks from tunnels and other excavations along the western part of the Kaimanawa Range (eastern diversions) and in a buried sequence cut by the Whakapapa-Tawhitikuri tunnel (western diversions) comprise mainly sandstone, siltstone, and argillite, but chert and minor basaltic rock and limestone are also present in the Kaimanawa Range. Rocks of the latter are comparable with Torlesse terrane sequences elsewhere, whereas the Whakapapa-Tawhitikuri tunnel rocks have contrasting petrography and structural style and belong to the younger Waipapa terrane, forming part of the Morrinsville facies. Petrographic, modal, and chemical data show that the Torlesse rocks are more siliceous and contain abundant granitic debris; the Waipapa terrane rocks are considerably less siliceous, and typical sandstones have a high content of intermediate volcanic clasts. Among the Kaimanawa Range rocks, complexly intermixed units, involving sandstone, siltstone, argillite, and chert, approach typical ...