Two-sided accretion and polyphase metamorphism in the Haast Schist belt, New Zealand: Constraints from detrital zircon geochronology

Research Article| March 28, 2018 Two-sided accretion and polyphase metamorphism in the Haast Schist belt, New Zealand: Constraints from detrital zircon geochronology Alan F. Cooper; Alan F. Cooper † 1Geology Department, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand †alan.cooper@otago.ac.nz Search for other works by this author on: GSW Google Scholar J. Michael Palin J. Michael Palin 1Geology Department, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand Search for other works by this author on: GSW Google Scholar GSA Bulletin (2018) 130 (9-10): 1501–1518. https://doi.org/10.1130/B31826.1 Article history received: 10 Apr 2017 rev-recd: 08 Oct 2017 accepted: 10 Feb 2018 first online: 28 Mar 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alan F. Cooper, J. Michael Palin; Two-sided accretion and polyphase metamorphism in the Haast Schist belt, New Zealand: Constraints from detrital zircon geochronology. GSA Bulletin 2018;; 130 (9-10): 1501–1518. doi: https://doi.org/10.1130/B31826.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Haast Schist of South Island, New Zealand, consisting of the Otago, Alpine, and Marlborough Schist components, is the most deeply buried and strongly metamorphosed part of an accretionary complex above a westward-dipping subduction zone on the eastern margin of Gondwana. Conventional wisdom is that the schist formed in the Jurassic (ca. 170 Ma) by collision between Carboniferous to Triassic graywacke sequences of the exotic eastern Torlesse composite terrane and the western Caples terrane. However, extensive areas of Alpine Schist in the west, rich in metabasite, and in part overlying a metamorphosed ophiolitic sequence, have anomalously young, mid-Cretaceous, ca. 108 Ma, detrital zircon ages. Their deposition and subsequent deformation occurred approximately synchronous with the cessation of westward-directed subduction in the Eastern Province of New Zealand, the onset of regional extension, and deposition of terrestrial and volcanic sediments on the exhumed erosion surface of the eastern schist basement. These Cretaceous schist protoliths are interpreted to form the exotic Pounamu terrane, accreted and interfolded with Otago Schist on the western margin of the Haast Schist. The Alpine Schist metamorphism is dated from zircon overgrowths on detrital grains at ca. 70 Ma (although over an extended period, 98–64 Ma, regionally). This thermal event is unknown further east. The Haast Schist is therefore a polygenetic unit formed by the amalgamation of metamorphic components accreted from both the east and west sides of the SE Zealandia microplate. Existence of the Pounamu terrane requires a major revision to the Cretaceous tectonic history of southern New Zealand. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.