@article{SchuckJanssenSchleicheretal.2018, author = {Schuck, Bernhard and Janssen, C. and Schleicher, Anja Maria and Toy, Virginia G. and Dresen, Georg}, title = {Microstructures imply cataclasis and authigenic mineral formation}, series = {Journal of structural geology}, volume = {110}, journal = {Journal of structural geology}, publisher = {Elsevier}, address = {Oxford}, issn = {0191-8141}, doi = {10.1016/j.jsg.2018.03.001}, pages = {172 -- 186}, year = {2018}, abstract = {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.}, language = {en} } @article{ToySutherlandTownendetal.2017, author = {Toy, Virginia Gail and Sutherland, Rupert and Townend, John and Allen, Michael J. and Becroft, Leeza and Boles, Austin and Boulton, Carolyn and Carpenter, Brett and Cooper, Alan and Cox, Simon C. and Daube, Christopher and Faulkner, D. R. and Halfpenny, Angela and Kato, Naoki and Keys, Stephen and Kirilova, Martina and Kometani, Yusuke and Little, Timothy and Mariani, Elisabetta and Melosh, Benjamin and Menzies, Catriona D. and Morales, Luiz and Morgan, Chance and Mori, Hiroshi and Niemeijer, Andre and Norris, Richard and Prior, David and Sauer, Katrina and Schleicher, Anja Maria and Shigematsu, Norio and Teagle, Damon A. H. and Tobin, Harold and Valdez, Robert and Williams, Jack and Yeo, Samantha and Baratin, Laura-May and Barth, Nicolas and Benson, Adrian and Boese, Carolin and C{\´e}l{\´e}rier, Bernard and Chamberlain, Calum J. and Conze, Ronald and Coussens, Jamie and Craw, Lisa and Doan, Mai-Linh and Eccles, Jennifer and Grieve, Jason and Grochowski, Julia and Gulley, Anton and Howarth, Jamie and Jacobs, Katrina and Janku-Capova, Lucie and Jeppson, Tamara and Langridge, Robert and Mallyon, Deirdre and Marx, Ray and Massiot, C{\´e}cile and Mathewson, Loren and Moore, Josephine and Nishikawa, Osamu and Pooley, Brent and Pyne, Alex and Savage, Martha K. and Schmitt, Doug and Taylor-Offord, Sam and Upton, Phaedra and Weaver, Konrad C. and Wiersberg, Thomas and Zimmer, Martin}, title = {Bedrock geology of DFDP-2B, central Alpine Fault, New Zealand}, series = {New Zealand journal of geology and geophysics : an international journal of the geoscience of New Zealand, the Pacific Rim, and Antarctica ; NZJG}, volume = {60}, journal = {New Zealand journal of geology and geophysics : an international journal of the geoscience of New Zealand, the Pacific Rim, and Antarctica ; NZJG}, number = {4}, publisher = {Taylor \& Francis}, address = {Abingdon}, organization = {DFDP-2 Sci Team}, issn = {0028-8306}, doi = {10.1080/00288306.2017.1375533}, pages = {497 -- 518}, year = {2017}, abstract = {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.}, language = {en} }