TY  - JOUR
A1  - Schuck, Bernhard
A1  - Janssen, C.
A1  - Schleicher, Anja Maria
A1  - Toy, Virginia G.
A1  - Dresen, Georg
T1  - Microstructures imply cataclasis and authigenic mineral formation
JF  - Journal of structural geology
N2  - The Alpine Fault is capable of generating large (MW > 8) earthquakes and is the main geohazard on South Island, NZ, and late in its 250–291-year seismic cycle. To minimize its hazard potential, it is indispensable to identify and understand the processes influencing the geomechanical behavior and strength-evolution of the fault. High-resolution microstructural, mineralogical and geochemical analyses of the Alpine Fault's core demonstrate wall rock fragmentation, assisted by mineral dissolution, and cementation resulting in the formation of a fine-grained principal slip zone (PSZ). A complex network of anastomosing and mutually cross-cutting calcite veins implies that faulting occurred during episodes of dilation, slip and sealing. Fluid-assisted dilatancy leads to a significant volume increase accommodated by vein formation in the fault core. Undeformed euhedral chlorite crystals and calcite veins that have cut footwall gravels demonstrate that these processes occurred very close to the Earth's surface. Microstructural evidence indicates that cataclastic processes dominate the deformation and we suggest that powder lubrication and grain rolling, particularly influenced by abundant nanoparticles, play a key role in the fault core's velocity-weakening behavior rather than frictional sliding. This is further supported by the absence of smectite, which is reasonable given recently measured geothermal gradients of more than 120 °C km−1 and the impermeable nature of the PSZ, which both limit the growth of this phase and restrict its stability to shallow depths. Our observations demonstrate that high-temperature fluids can influence authigenic mineral formation and thus control the fault's geomechanical behavior and the cyclic evolution of its strength.
KW  - Alpine Fault
KW  - Fluid-rock interaction
KW  - Fault-rock microstructures
KW  - Fault healing
KW  - Authigenic mineral formation
KW  - Brittle deformation
Y1  - 2018
U6  - https://doi.org/10.1016/j.jsg.2018.03.001
SN  - 0191-8141
VL  - 110
SP  - 172
EP  - 186
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Toy, Virginia Gail
A1  - Sutherland, Rupert
A1  - Townend, John
A1  - Allen, Michael J.
A1  - Becroft, Leeza
A1  - Boles, Austin
A1  - Boulton, Carolyn
A1  - Carpenter, Brett
A1  - Cooper, Alan
A1  - Cox, Simon C.
A1  - Daube, Christopher
A1  - Faulkner, D. R.
A1  - Halfpenny, Angela
A1  - Kato, Naoki
A1  - Keys, Stephen
A1  - Kirilova, Martina
A1  - Kometani, Yusuke
A1  - Little, Timothy
A1  - Mariani, Elisabetta
A1  - Melosh, Benjamin
A1  - Menzies, Catriona D.
A1  - Morales, Luiz
A1  - Morgan, Chance
A1  - Mori, Hiroshi
A1  - Niemeijer, Andre
A1  - Norris, Richard
A1  - Prior, David
A1  - Sauer, Katrina
A1  - Schleicher, Anja Maria
A1  - Shigematsu, Norio
A1  - Teagle, Damon A. H.
A1  - Tobin, Harold
A1  - Valdez, Robert
A1  - Williams, Jack
A1  - Yeo, Samantha
A1  - Baratin, Laura-May
A1  - Barth, Nicolas
A1  - Benson, Adrian
A1  - Boese, Carolin
A1  - Célérier, Bernard
A1  - Chamberlain, Calum J.
A1  - Conze, Ronald
A1  - Coussens, Jamie
A1  - Craw, Lisa
A1  - Doan, Mai-Linh
A1  - Eccles, Jennifer
A1  - Grieve, Jason
A1  - Grochowski, Julia
A1  - Gulley, Anton
A1  - Howarth, Jamie
A1  - Jacobs, Katrina
A1  - Janku-Capova, Lucie
A1  - Jeppson, Tamara
A1  - Langridge, Robert
A1  - Mallyon, Deirdre
A1  - Marx, Ray
A1  - Massiot, Cécile
A1  - Mathewson, Loren
A1  - Moore, Josephine
A1  - Nishikawa, Osamu
A1  - Pooley, Brent
A1  - Pyne, Alex
A1  - Savage, Martha K.
A1  - Schmitt, Doug
A1  - Taylor-Offord, Sam
A1  - Upton, Phaedra
A1  - Weaver, Konrad C.
A1  - Wiersberg, Thomas
A1  - Zimmer, Martin
T1  - Bedrock geology of DFDP-2B, central Alpine Fault, New Zealand
JF  - New Zealand journal of geology and geophysics : an international journal of the geoscience of New Zealand, the Pacific Rim, and Antarctica ; NZJG
N2  - During the second phase of the Alpine Fault, Deep Fault Drilling Project (DFDP) in the Whataroa River, South Westland, New Zealand, bedrock was encountered in the DFDP-2B borehole from 238.5–893.2 m Measured Depth (MD). Continuous sampling and meso- to microscale characterisation of whole rock cuttings established that, in sequence, the borehole sampled amphibolite facies, Torlesse Composite Terrane-derived schists, protomylonites and mylonites, terminating 200–400 m above an Alpine Fault Principal Slip Zone (PSZ) with a maximum dip of 62°. The most diagnostic structural features of increasing PSZ proximity were the occurrence of shear bands and reduction in mean quartz grain sizes. A change in composition to greater mica:quartz + feldspar, most markedly below c. 700 m MD, is inferred to result from either heterogeneous sampling or a change in lithology related to alteration. Major oxide variations suggest the fault-proximal Alpine Fault alteration zone, as previously defined in DFDP-1 core, was not sampled.
KW  - Alpine Fault
KW  - New Zealand
KW  - scientific drilling
KW  - mylonite
KW  - cataclasite
Y1  - 2017
U6  - https://doi.org/10.1080/00288306.2017.1375533
SN  - 0028-8306
SN  - 1175-8791
VL  - 60
IS  - 4
SP  - 497
EP  - 518
PB  - Taylor & Francis
CY  - Abingdon
ER  -