Provenance analysis using conglomerate clast lithologies: a case study from the Pahau terrane of New Zealand

• Published in: Sedimentary Geology
• Main Authors: Wandres, Anekant, Bradshaw, John D., Weaver, Steve, Maas, Roland, Eby, Nelson, Ireland, Trevor
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier
• Subjects: Keywords: accretionary prism; conglomerate; provenance; sediment transport; terrane; Australasia; New Zealand Amundsen Province; Antarctica; Conglomerate clast; Geochronology; Isotope chemistry; Marie Byrd Land; Median Tectonic Zone; New Zealand; Pahau terrane; Rakaia terrane; Pacific; Byrd; Campbell Plateau; Antarc*
• Online Access: http://hdl.handle.net/1885/86292; https://doi.org/10.1016/j.sedgeo.2004.02.002; https://openresearch-repository.anu.edu.au/bitstream/1885/86292/7/01_Wandres_Provenance_analysis_using_2004.pdf.jpg

The field of provenance analysis has undergone a revolution with the development of single-crystal isotope dating techniques using mainly silt to sand sized single minerals. This study focuses on coarser-grained rocks, notably conglomerates, which involve much shorter transport distances and therefore may be used to trace proximal sources. 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. Geochronology, geochemistry and Sr-Nd isotopes of igneous clasts from Pahau terrane conglomerates identify the Median Tectonic Zone (s.l.) as a major contributor of detritus to the Pahau depositional basin. SHRIMP U-Pb zircon ages of igneous clasts range from 128 to 123 Ma and from 147 to 135 Ma. Calc-alkaline clasts of the latter range are indistinguishable in age, chemical composition, and petrogenesis from the calc-alkaline granitoids of the Darran Suite, whereas alkaline clasts correlate with the Electric Granite, both parts of the Median Tectonic Zone. An Early Jurassic calc-alkaline rhyolite clast from Kekerengu (188 ± 3 Ma) correlates with the Bounty Island Granite, Campbell Plateau. The petrography and geochemistry of Pahau terrane sandstone clasts indicate the recycling of Permian to early Late Triassic older Rakaia terrane rocks. This is further supported by the detrital zircon age data. Igneous conglomerate clasts are capable of placing exceptionally tight constraints on Pahau provenance and on its Mesozoic tectonic setting within the Southwest Pacific margin of Gondwana. They provide the best evidence yet that the Pahau terrane is locally derived.