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

Incursion of meteoric waters into the ductile regime in an active orogen
Incursion of meteoric waters into the ductile regime in an active orogen
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 (?18OH2O = ?9.0 to +8.7‰VSMOW and ?D=?73 to ?45‰VSMOW?D=?73 to ?45‰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>6–8 km depth), preserve included hydrothermal fluids with ?D?D values between ?84 and ?52‰?52‰, 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 ?D?D values. In contrast, the oxygen isotopic signal of these fluids has almost completely equilibrated with host rocks (?18OH2O = +2.3 to +8.7‰). 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.
fluid flow, stable isotopes, alpine fault, fluid inclusions, southern alps, meteoric water
0012-821X
1-13
Menzies, Catriona D.
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Teagle, Damon A.H.
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Craw, Dave
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Cox, Simon C.
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Boyce, Adrian J.
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Barrie, Craig D.
6c728ef8-3b87-462d-9e6c-772b153c6bed
Roberts, Stephen
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Menzies, Catriona D.
04bc2a62-064d-4911-9c45-17b47f3005de
Teagle, Damon A.H.
396539c5-acbe-4dfa-bb9b-94af878fe286
Craw, Dave
c5701ce3-cff8-41c0-916a-5479e18b9bfc
Cox, Simon C.
662059ba-abb6-44a0-aa48-82818ef0e278
Boyce, Adrian J.
e21e60d3-a9ab-4cad-9bd8-f6680f3dbd7f
Barrie, Craig D.
6c728ef8-3b87-462d-9e6c-772b153c6bed
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856

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

Record type: Article

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 (?18OH2O = ?9.0 to +8.7‰VSMOW and ?D=?73 to ?45‰VSMOW?D=?73 to ?45‰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>6–8 km depth), preserve included hydrothermal fluids with ?D?D values between ?84 and ?52‰?52‰, 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 ?D?D values. In contrast, the oxygen isotopic signal of these fluids has almost completely equilibrated with host rocks (?18OH2O = +2.3 to +8.7‰). 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.

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Accepted/In Press date: 29 April 2014
e-pub ahead of print date: 20 May 2014
Published date: 1 August 2014
Keywords: fluid flow, stable isotopes, alpine fault, fluid inclusions, southern alps, meteoric water
Organisations: Geochemistry

Identifiers

Local EPrints ID: 365127
URI: http://eprints.soton.ac.uk/id/eprint/365127
ISSN: 0012-821X
PURE UUID: 4eb1863d-6235-4e68-b1f5-f55db521d04c
ORCID for Damon A.H. Teagle: ORCID iD orcid.org/0000-0002-4416-8409
ORCID for Stephen Roberts: ORCID iD orcid.org/0000-0003-4755-6703

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Date deposited: 21 May 2014 14:18
Last modified: 15 Mar 2024 03:05

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Contributors

Author: Catriona D. Menzies
Author: Dave Craw
Author: Simon C. Cox
Author: Adrian J. Boyce
Author: Craig D. Barrie
Author: Stephen Roberts ORCID iD

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