The Cambrian arc complex of the Takaka Terrane, New Zealand: An integrated stratigraphical, paleontological and geochemical approach

Abstract

The Cambrian succession of the Takaka Terrane represents a volcano‐sedimentary arc complex, which was once part of the Pacific margin of Gondwana. The succession has been folded and disrupted by faulting during at least four tectonic events, bringing together at least 12 fault slices with dissimilar stratigraphy. A revised stratigraphy and regional models for lithofacies relationships, magmatic history, and tectonic setting are proposed. They are based on analysis of the lithostratigraphy, biostratigraphy, petrology, geochemistry, geochronology, and field relationships. Volcanic rock formations recognised are Benson Volcanics (arc), Mataki Volcanics (back‐arc), and Cobb Igneous Complex (boninites), which are all grouped in the Devil River Volcanics Group. Petrography and trace element geochemistry enable discrimination of the volcanic units of the Devil River Volcanics. Rocks of the Benson Volcanics are by far the most voluminous and are subdivided into nine (informal) volcanic suites. Arc activity lasted from middle Mid Cambrian (Undillan) to Late Cambrian ( Mindyallan or younger), about 20 m.y., constrained by ages based on trilobites, brachiopods, and conodonts in mterbedded sediments and U‐Pb and Ar‐Ar dates. This period of arc activity is different from those in Tasmania and southeast Australia, where post‐collisional volcanism commenced in the late Mid Cambrian. A separate igneous unit in the Takaka Terrane is the rift‐related Gendarme Dolerite of latest Cambrian to early Ordovician age. Sedimentary formations recognised are Tasman Formation, Mount Benson Sandstone (new), Ruby Saddle Formation (new), Lake Peel Formation (new), Lockett Conglomerate, Christmas Conglomerate, Salisbury Conglomerate, and Heath Creek beds, all comprising the Haupiri Group, and the Junction Formation (group unassigned). Rocks of the Haupiri Group were deposited in a back‐arc or intra‐arc setting.