Terrane and core complex architecture of the Otago Schist in the Dunstan and Cairnmuir Mountains, New Zealand, from U-Pb and (U-Th)/He zircon dating
Department or Administrative Unit
We report ten new zircon (U-Th)/He ages from psammitic greyschists collected in a southwest-northeast profile in the Otago Schist across the Dunstan and Cairnmuir Mountains, New Zealand. Six of the samples have accompanying new detrital zircon U-Pb ages. In this part of the Otago Schist, a broad antiformal core of garnet-biotite-albite zone schist defines a range-scale footwall block to the gently northeast-dipping Thomsons Gorge Fault and the gently southwest-dipping Cromwell Gorge faults. Hanging wall blocks above the faults comprise lower-grade chlorite zone schists. Nine schist samples from footwall and hanging wall blocks close to the low-angle faults exhibit a weighted mean (U-Th)/He age of 82 ± 3 Ma. We interpret that both low-angle fault systems were active prior to c. 82 Ma and confirm that they were extensional. We interpret the antiformal schist core as the late Early Cretaceous (c. < 122–109 Ma) ductile extensional lower plate of a metamorphic core complex. The lower plate (footwall) core was juxtaposed against the upper plate (hanging wall) schists by the low-angle normal decollement faults. Detrital zircon U-Pb ages indicate Carboniferous, Permo-Triassic, Jurassic and Cretaceous maximum depositional ages of schist protoliths which demand more complex terrane and metamorphic interpretations for the Otago Schist than previously recognised.
Mortimer, N., Lee, J., & Stockli, D. F. (2023). Terrane and core complex architecture of the otago schist in the dunstan and cairnmuir mountains, new zealand, from u-pb and (U-th)/he zircon dating. New Zealand Journal of Geology and Geophysics, ahead of print. https://doi.org/10.1080/00288306.2023.2176892
New Zealand Journal of Geology and Geophysics
This article was originally published in New Zealand Journal of Geology and Geophysics. The full-text article from the publisher can be found here.
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