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

TY - JOUR

T1 - Textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand

AU - Kirilova, Martina

AU - Toy, Virginia G.

AU - Timms, Nick

AU - Halfpenny, Angela

AU - Menzies, Catriona Dorothy

AU - Craw, Dave

AU - Beyssac, Olivier

AU - Sutherland, Rupert

AU - Townend, John

AU - Boulton, Carolyn

AU - Carpenter, Brett M.

AU - Cooper, Alan

AU - Grieve, Jason

AU - Little, Timothy

AU - Morales, Luiz

AU - Morgan, Chance

AU - Mori, Hiroshi

AU - Sauer, Katrina

AU - Schleicher, Anja M.

AU - Williams, Jack

AU - Craw, Lisa

N1 - Raman spectra of graphite from the Alpine Fault rocks is available at https://doi.org/10.6084/m9.figshare.c.3911797 We gratefully acknowledge the contribution of all members of DFDP-1 and DFDP-2 Science Teams, as described in GNS Science Report 2011/48 and GNS Science Report 2015/50. DFDP drilling projects were funded by: the International Continental Scientific Drilling Program (ICDP); GNS Science; Victoria University of Wellington; the University of Otago; the University of Auckland; the University of Canterbury; Deutsche Forschungsgemeinschaft; the University of Bremen; the University of Liverpool; the Marsden Fund of the Royal Society of New Zealand; New Zealand Ministry for Business Innovation and Employment; and Natural Environment Research Council (NERC) grants. The current research was funded by the University of Otago. The authors acknowledge the use of Curtin University’s Microscopy & Microanalysis Facility, whose instrumentation has been partially funded by the University, State and Commonwealth Governments of Australia. We also wish to thank our colleague Olivier Beyssac for generously offering use of Raman microspectrometer laboratory facilities at IMPMC, Paris, France, and for valuable discussions and helpful comments during the acquisition, processing and interpretation of Raman data. From: Gessner, K., Blenkinsop, T. G. & Sorjonen-Ward, P. (eds) Characterization of Ore-Forming Systems from Geological, Geochemical and Geophysical Studies. Geological Society, London,

PY - 2018

Y1 - 2018

N2 - 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.

AB - 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.

KW - graphite

KW - hydrothermal

KW - tectonic

KW - fault

KW - cataclasite

KW - Raman

KW - Alpine Fault

KW - Deep Fault Drilling Project (DFDP)

UR - https://eprints.soton.ac.uk/415098/

U2 - 10.1144/SP453.13

DO - 10.1144/SP453.13

M3 - Article

VL - 453

SP - 205

EP - 233

JO - Geological Society Special Publications

JF - Geological Society Special Publications

SN - 0305-8719

ER -