Incursion of meteoric waters into the ductile regime in an active orogen

Catriona D. Menzies (Corresponding Author), Damon A. H. Teagle, Dave Craw, Simon C. Cox, Adrian J. Boyce, Craig D. Barrie, Stephen Roberts

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Abstract

Rapid tectonic uplift on the Alpine Fault, New Zealand, elevates topography, regional geothermal gradients, and the depth to the brittle ductile transition, and drives fluid flow that influences deformation and mineralisation within the orogen. Oxygen and hydrogen stable isotopes, fluid inclusion and Fourier Transform Infrared (FT-IR) analyses of quartz from veins which formed at a wide range of depths, temperatures and deformation regimes identify fluid sources and the depth of penetration of meteoric waters. Most veins formed under brittle conditions and with isotope signatures (δ18OH2O = −9.0 to +8.7 per cent VSMOW and δD = −73 to −45 per cent VSMOW) indicative of progressively rock-equilibrated meteoric waters. Two generations of quartz veins that post-date mylonitic foliation but endured further ductile deformation, and hence formation below the brittle to ductile transition zone (>6–8 km depth), preserve included hydrothermal fluids with δD values between −84 and −52 per cent, indicating formation from meteoric waters. FT-IR analyses of these veins show no evidence of structural hydrogen release, precluding this as a source of low δD values. In contrast, the oxygen isotopic signal of these fluids has almost completely equilibrated with host rocks (δ18OH2O = +2.3 to +8.7 per cent). These data show that meteoric waters dominate the fluid phase in the rocks, and there is no stable isotopic requirement for the presence of metamorphic fluids during the precipitation of ductilely deformed quartz veins. This requires the penetration during orogenesis of meteoric waters into and possibly below the brittle to ductile transition zone.
Original languageEnglish
Pages (from-to)1-13
Number of pages13
JournalEarth and Planetary Science Letters
Volume399
Early online date20 May 2014
DOIs
Publication statusPublished - 1 Aug 2014

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Keywords

  • fluid flow
  • stable isotopes
  • Alpine Fault
  • meteoric water
  • fluid inclusions
  • Southern Alps

Cite this

Menzies, C. D., Teagle, D. A. H., Craw, D., Cox, S. C., Boyce, A. J., Barrie, C. D., & Roberts, S. (2014). Incursion of meteoric waters into the ductile regime in an active orogen. Earth and Planetary Science Letters, 399, 1-13. https://doi.org/10.1016/j.epsl.2014.04.046