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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

By
Martina Kirilova
Martina Kirilova
Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
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Virginia G. Toy
Virginia G. Toy
Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
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Nick Timms
Nick Timms
Department of Applied Geology, Western Australian School of Mines, Curtin University of Technology, Bentley, WA 6102, Australia
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Angela Halfpenny
Angela Halfpenny
Microscopy and Microanalysis Facility, John de Laeter Centre, Curtin University, Perth, WA 6854, Australia
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Catriona Menzies
Catriona Menzies
Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton SO14 3ZH, UK
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Dave Craw
Dave Craw
Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
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Olivier Beyssac
Olivier Beyssac
Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, CNRS–UMP, 4 Place Jussieu, 75005 Paris, France
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Rupert Sutherland
Rupert Sutherland
School of Geography, Environment, and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand
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John Townend
John Townend
School of Geography, Environment, and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand
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Carolyn Boulton
Carolyn Boulton
Department of Earth and Ocean Sciences, University of Liverpool, 4 Brownlow Street, Liverpool L69 3GP, UK
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Brett M. Carpenter
Brett M. Carpenter
School of Geology & Geophysics, University of Oklahoma, Norman, OK 73019, USA
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Alan Cooper
Alan Cooper
Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
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Jason Grieve
Jason Grieve
Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
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Timothy Little
Timothy Little
School of Geography, Environment, and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand
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Luiz Morales
Luiz Morales
ScopeM – ETH Zürich, HPT D 9, Auguste-Piccard-Hof 1, 8093 Zurich, Switzerland
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Chance Morgan
Chance Morgan
School of Geology & Geophysics, University of Oklahoma, Norman, OK 73019, USA
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Hiroshi Mori
Hiroshi Mori
Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano, 390-8621, Japan
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Katrina M. Sauer
Katrina M. Sauer
Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
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Anja M. Schleicher
Anja M. Schleicher
Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany
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Jack Williams
Jack Williams
Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
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Lisa Craw
Lisa Craw
Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
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Published:
January 01, 2018

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 640°C, occurs mainly on grain boundaries within quartzo-feldspathic domains. The subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions (500–600°C), 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.

Supplementary material: Raman spectra of graphite from the Alpine Fault rocks is available at https://doi.org/10.6084/m9.figshare.c.3911797

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Contents

Geological Society, London, Special Publications

Characterization of Ore-Forming Systems from Geological, Geochemical and Geophysical Studies

K. Gessner
K. Gessner
Geological Survey of Western Australia, Australia
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T.G. Blenkinsop
T.G. Blenkinsop
Cardiff University, UK
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P. Sorjonen-Ward
P. Sorjonen-Ward
Geological Survey of Finland, Finland
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Geological Society of London
Volume
453
ISBN electronic:
9781786203342
Publication date:
January 01, 2018

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