Provenance study of the Torlesse Terranes and implications for the origin of the continental crust of eastern New Zealand.

• Main Author: Wandres, Marcel Charles Anekant
• Format: Other/Unknown Material
• Language: English
• Published: University of Canterbury. Geological Sciences 2002
• Subjects: Antarctic; New Zealand; Antarc*
• Online Access: http://hdl.handle.net/10092/5730; https://doi.org/10.26021/6759

The Torlesse terranes - part of the New Zealand Eastern Province - are accretionary complexes that comprise an enormous volume of quartzofeldspathic sandstones and mudstones with subsidiary conglomerates plus minor oceanic assemblages. Two terranes are recognised in the South Island, the Permian to Late Triassic Rakaia terrane and the Late Jurassic to Early Cretaceous Pahau terrane. Recent studies in detrital petrology and geochemistry have been important in establishing the broad type of source for these two terranes. All studies point to a continental arc/cratonic provenance and various source areas have been proposed. This thesis provides the best evidence yet that the Pahau terrane is locally derived and that an Antarctic source for the Rakaia sediments must be (re)considered. A detailed sampling program and geochronological, geochemical and Sr-Nd isotope analyses of igneous clasts from seven Torlesse terrane conglomerates, in conjunction with SHRIMP U-Pb detrital zircon ages from three Torlesse sandstones, have helped to broadly characterise the igneous protosources for the Pahau and Rakaia terranes. The conglomerate locations were chosen to represent the full stratigraphic range of both terranes, and the geographical distribution of the conglomerates mimics an approximate inboard to outboard transect of the two terranes with respect to the Panthalassan margin of Gondwana. Igneous clasts from the Aptian (Mount Saul and Ethelton) and Albian (Kekerengu) Pahau terrane conglomerates are predominantly volcanic and hypersolvus, calc-alkaline, metaluminous to weakly peraluminous and display a general geochemical concordance that suggests a similar petrogenesis. SHRIMP U-Pb zircon ages of these clasts range from 128-123 Ma and from 147-135 Ma. These clasts are indistinguishable in age (except for the younger group), chemical composition, and petrogenesis from the felsic members of the calc-alkaline I-type granitoids of the Darran Suite, whereas alkaline rhyolitic clasts correlate best with the Electric Granite. The ...