Textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand
Posted on 2017-10-24 - 11:39
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.
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Kirilova, Martina; Toy, Virginia G.; Timms, Nick; Halfpenny, Angela; Menzies, Catriona; Craw, Dave; et al. (2017). Textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand. Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.3911797.v1
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AUTHORS (21)
MK
Martina Kirilova
VT
Virginia G. Toy
NT
Nick Timms
AH
Angela Halfpenny
CM
Catriona Menzies
DC
Dave Craw
OB
Olivier Beyssac
RS
Rupert Sutherland
JT
John Townend
CB
Carolyn Boulton
BC
Brett M. Carpenter
AC
Alan Cooper
JG
Jason Grieve
TL
Timothy Little
LM
Luiz Morales
CM
Chance Morgan
HM
Hiroshi Mori
KS
Katrina M. Sauer
AS
Anja M. Schleicher
JW
Jack Williams
CATEGORIES
KEYWORDS
hydrothermal graphitic carbonrock sequencesgraphitic carbonDeep Fault Drilling Projectamphibolite-facies Alpine Schistfault zone coreNew ZealandAlpine FaultTextural changesquartzo-feldspathic domainsshear strainmicrotextural recordanalysing samplesRaman spectroscopyorogenic gold mineralizationDFDPmylonitic graphitegraphite depositiongrain boundariesfault zoneshydrothermal processesmylonitized schistsscanning electron microscopygraphitic carbon emplacementplate boundary fault zonestrain localizationAlpine Fault Zonegraphite crystallinityNew Zealand Graphitizationmylonitization processgraphite mobilizationfoliation-aligned graphiteGeology