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Textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand

Textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand
Textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand
Graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization. We examine processes of graphitic carbon emplacement and deformation in the active Alpine Fault Zone, New Zealand by analysing samples obtained from Deep Fault Drilling Project (DFDP) boreholes. Optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain. Raman spectroscopy allowed interpretation of the degree of graphite crystallinity, which reflects both thermal and mechanical processes. In the amphibolite-facies Alpine Schist, highly crystalline graphite, indicating peak metamorphic temperatures up to 6408C, occurs mainly on grain boundaries within quartzo-feldspathic domains. The subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions (500-6008C), resulting in clustered (in protomylonites) and foliation-aligned graphite (in mylonites). In cataclasites, derived from the mylonitized schists, graphite is most abundant (,50% as opposed to ,10% elsewhere), and has two different habits: inherited mylonitic graphite and less mature patches of potentially hydrothermal graphitic carbon. Tectonic–hydrothermal fluid flow was probably important in graphite deposition throughout the examined rock sequences. The increasing abundance of graphite towards the fault zone core may be a significant source of strain localization, allowing fault weakening.
Geological Society of London
Kirilova, Martina
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Toy, Virginia G.
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Timms, Nick
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Halfpenny, Angela
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Menzies, Catriona
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Craw, Dave
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Beyssac, Olivier
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Rupert, Sutherland
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Townend, John
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Boulton, Carolyn
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Carpenter, Brett
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Cooper, Alan
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Grieve, Jason
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Little, Tim
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Morales, Luiz
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Morgan, Chance
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Mori, Hiroshi
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Sauer, Katrina
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Schleicher, Anja
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Williams, Jack
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Craw, Lisa
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Sorjonen-Ward, Peter
Blenkinsop, Tom
Gessner, Klaus
Kirilova, Martina
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Toy, Virginia G.
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Timms, Nick
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Halfpenny, Angela
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Menzies, Catriona
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Craw, Dave
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Beyssac, Olivier
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Rupert, Sutherland
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Townend, John
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Boulton, Carolyn
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Carpenter, Brett
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Cooper, Alan
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Grieve, Jason
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Little, Tim
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Morales, Luiz
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Morgan, Chance
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Mori, Hiroshi
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Sauer, Katrina
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Schleicher, Anja
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Williams, Jack
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Craw, Lisa
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Sorjonen-Ward, Peter
Blenkinsop, Tom
Gessner, Klaus

Kirilova, Martina, Toy, Virginia G., Timms, Nick, Halfpenny, Angela, Menzies, Catriona, Craw, Dave, Beyssac, Olivier, Rupert, Sutherland, Townend, John, Boulton, Carolyn, Carpenter, Brett, Cooper, Alan, Grieve, Jason, Little, Tim, Morales, Luiz, Morgan, Chance, Mori, Hiroshi, Sauer, Katrina, Schleicher, Anja, Williams, Jack and Craw, Lisa (2017) Textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand. In, Sorjonen-Ward, Peter, Blenkinsop, Tom and Gessner, Klaus (eds.) Advances in the Characterization of Ore-Forming Systems From Geological, Geochemical and Geophysical data. (Geological Society of London Special Publications) London. Geological Society of London. (In Press)

Record type: Book Section

Abstract

Graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization. We examine processes of graphitic carbon emplacement and deformation in the active Alpine Fault Zone, New Zealand by analysing samples obtained from Deep Fault Drilling Project (DFDP) boreholes. Optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain. Raman spectroscopy allowed interpretation of the degree of graphite crystallinity, which reflects both thermal and mechanical processes. In the amphibolite-facies Alpine Schist, highly crystalline graphite, indicating peak metamorphic temperatures up to 6408C, occurs mainly on grain boundaries within quartzo-feldspathic domains. The subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions (500-6008C), resulting in clustered (in protomylonites) and foliation-aligned graphite (in mylonites). In cataclasites, derived from the mylonitized schists, graphite is most abundant (,50% as opposed to ,10% elsewhere), and has two different habits: inherited mylonitic graphite and less mature patches of potentially hydrothermal graphitic carbon. Tectonic–hydrothermal fluid flow was probably important in graphite deposition throughout the examined rock sequences. The increasing abundance of graphite towards the fault zone core may be a significant source of strain localization, allowing fault weakening.

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Accepted/In Press date: 31 August 2017

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Local EPrints ID: 415098
URI: http://eprints.soton.ac.uk/id/eprint/415098
PURE UUID: 8eb0534c-ab91-4186-9a37-8a7bf99c21d4

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Date deposited: 27 Oct 2017 16:30
Last modified: 24 Jan 2020 17:32

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Contributors

Author: Martina Kirilova
Author: Virginia G. Toy
Author: Nick Timms
Author: Angela Halfpenny
Author: Catriona Menzies
Author: Dave Craw
Author: Olivier Beyssac
Author: Sutherland Rupert
Author: John Townend
Author: Carolyn Boulton
Author: Brett Carpenter
Author: Alan Cooper
Author: Jason Grieve
Author: Tim Little
Author: Luiz Morales
Author: Chance Morgan
Author: Hiroshi Mori
Author: Katrina Sauer
Author: Anja Schleicher
Author: Jack Williams
Author: Lisa Craw
Editor: Peter Sorjonen-Ward
Editor: Tom Blenkinsop
Editor: Klaus Gessner

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