Age and isotopic characterisation of metasedimentary rocks from the Torlesse Supergroup and Waipapa Group in the central North Island, New Zealand

C. J. Adams*, N. Mortimer, H. J. Campbell, Bill Griffin

*Corresponding author for this work

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    70 Citations (Scopus)

    Abstract

    Detrital zircon U-Pb ages in greywackes and initial (87)Sr/(86)Sr ratios are reported for low-grade metasedimentary rocks from Torlesse Supergroup, Waipapa Group, and Kaimanawa Schist in the central North Island, New Zealand. The data reveal the presence of a hitherto unsuspected, areally extensive, Jurassic part of the Torlesse composite terrane in the Kaimanawa, Kaweka, and Ruahine Ranges, which we name the Kaweka Terrane. Kaweka rocks have initial (87)Sr/(86)Sr ratios (at metamorphism) and detrital zircon patterns that in part are transitional between Rakaia and Pahau Terrane rocks and in part similar to Waipapa Terrane rocks. Combined detrital zircon age data for all Torlesse and Waipapa Terrane data reveal an essential unity, with a long persistence (260-120 Ma) of predominant Permian-Triassic sources in the form of a major Cordilleran-style batholith, a decline in major early Paleozoic-Precambrian sources between 260 and 220 Ma, and presence of minor Early Carboniferous to Late Devonian sources between 180 and 120 Ma. Rb-Sr and K-Ar ages indicate latest Triassic to Early Cretaceous metamorphism in an evolving accretionary wedge.

    Original languageEnglish
    Pages (from-to)149-170
    Number of pages22
    JournalNew Zealand Journal of Geology and Geophysics
    Volume52
    Issue number2
    DOIs
    Publication statusPublished - Jun 2009

    Keywords

    • New Zealand
    • Torlesse Supergroup
    • Waipapa Group
    • Torlesse Terrane
    • Waipapa Terrane
    • Kaweka Terrane
    • U-Pb dating
    • Rb-Sr dating
    • Sr isotopes
    • detrital zircon
    • petrographic modes
    • new structural name
    • K-AR GEOCHRONOLOGY
    • U-PB ZIRCON
    • RB-SR AGE
    • SOUTH-ISLAND
    • ACCRETIONARY WEDGE
    • MARLBOROUGH SCHIST
    • FOSSIL LOCALITIES
    • DETRITAL ZIRCONS
    • BASEMENT ROCKS
    • LOW-GRADE

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