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Metamorphic rocks
Published in W.S. MacKenzie, A.E. Adams, K.H. Brodie, Rocks and Minerals in Thin Section, 2017
W.S. MacKenzie, A.E. Adams, K.H. Brodie
A cataclasite is a rock intensely deformed at low temperature by processes involving brittle fracturing and frictional sliding between the fragments. Cataclasis is often localized into fault zones but can be widely distributed. The rock can be cohesive, with a poorly developed or absent schistosity or foliation, or can be incohesive, characterised by generally angular porphyroclasts and rock fragments in a finer-grained matrix of similar composition. Cohesive cataclasites are usually held together either by a cement phase deposited from solution or by clay minerals if present in sufficient proportions. Cataclasites in fault zones are commonly termed fault gouge and are often quite well foliated or banded. Coarse grained cataclasites are often called a breccia.
A many-body disk model of slip phenomena: an implication to earthquake faulting
Published in H. Ogasawara, T. Yanagidani, M. Ando, Seismogenic Process Monitoring, 2017
Takayuki Hirata, Tatsuaki Yoshimura, Atsushi Ogawa, Yoshifumi Harada
Large earthquakes are the biggest stick-slip phenomena observed in the earth. Recently, stick-slip phenomena have been attracting a great deal of attention from not only seismologist but also physicists (Thompson & Robbins 1990, Yoshizawa et al. 1993, Drda & Wang 1995, Radjai & Roux 1995, Radjai et al. 1995, Demirel & Granick 1996, Nasuno et al. 1997, Persson 1998). A fault gouge lies between slip surfaces of earthquake faults (Fig. 1), and plays an important role in fault sliding.
Structure and topology of a brittle-ductile fault swarm at Crawford Knob, Franz Josef, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2023
Susan Ellis, Matthew Hill, Timothy A. Little
The transition from pressure-dependent frictional behaviour in the upper, brittle part of the crust to strongly temperature- and rate-dependent behaviour at greater depths is marked by changes in rock structure, rheology, and fluid activity that are closely tied to the seismic cycle (e.g. Sibson 1983; Evans et al. 1990; Kohlstedt et al. 1995; Huc et al. 1998; Rolandone et al. 2004; Ellis and Stöckhert 2004; Handy et al. 2007; Nüchter and Stöckhert 2008; Hirth and Beeler 2015; Marchesini et al. 2019). Observations of hypocentre depths and variations in slip stability in fault gouge suggest that earthquakes often nucleate just above the brittle-ductile transition, near where brittle strength reaches its maximum (Sibson 1983; Scholz 1988; Van Dinther et al. 2013; Mitchell et al. 2016; Niemeijer et al. 2016). Outcrops containing crustal rocks only recently exhumed from the mid-crust that preserve the imprint of the brittle-ductile region are rare but can provide important clues about these processes. This study summarises three-dimensional (3-D) structural mapping and analysis of one such example in New Zealand, an outcrop at Crawford Knob in the Southern Alps that has been exhumed from mid-crustal depths during the past several million years.
K-Ar fault-gouge dating in the Lower Buller gorge constrains the formation of the Paparoa Trough, West Coast, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2021
Uwe Ring, Ibrahim Tonguc Uysal, Kui Tong, Andrew Todd
Fault gouge generated in upper-crustal, brittle fault zones contains crushed rock fragments including metamorphic mica derived from the protoliths with variable amounts of newly-grown authigenic illite, which can be distinguished from each other by the type of crystallographic stacking, called polytypism (Verma and Krishna 1966). The 1M/Md polytype is diagnostic of fault-related authigenic illite and commonly grows during the development of clay-rich gouge at temperatures less than 200°C (Grathoff et al. 2001). Fault gouge also contains higher temperature (>280°C) illite/muscovite, which is mechanically introduced into the gouge from the host rock and typically occurs as the 2M1 polytype (Srodon and Eberl 1984). The 2M1 polytype is indicative for metamorphic or magmatic muscovite. The 1M/Md polytype usually occurs as very fine-grained crystallites and is distinctly smaller than the detrital illite/muscovite 2M1 polytype. Therefore, the 1M/Md polytype indicates in-situ growth in the gouge and is not an inherited phase (Vrolijk and van der Pluijm 1999; van der Pluijm et al. 2001). Radiogenic Ar is locked in the illite lattice as long as later fluid circulations or thermal events have not affected the samples at sufficiently high temperatures (close or higher than the illite formation temperature) assumed to cause partial or complete Ar loss (Clauer and Chaudhuri 1995; Lerman et al. 2007).
The Listafjorden–Drangedal Fault Complex of the Agder–Telemark Lineament Zone, southern Norway. A structural analysis based on remote sensing and potential field data
Published in GFF, 2019
Roy H. Gabrielsen, Odleiv Olesen, Alvar Braathen, Jan Inge Faleide, Vikas Chand Baranwal, Conrad Lindholm
The Listafjord–Drangedal Fault Complex is one of the several major fault complexes onshore southern Norway that contributes to a interlinking system of N-S and NE-SW- to ENE-WSW-trending lineament zones (e.g., Gabrielsen et al. 2018). The NE-SW-trending Listafjord–Drangedal Fault Complex itself includes several distinct segments and isolated, internal mega-scale shear lenses. It is part of the Agder–Telemark (lineament) Zone and is associated with splay faults of regional significance (e.g., the Lygne–Porsgrunn Fault Complex). Separate segments of the fault complex are characterized by contrasting fault attitudes and styles of deformation from fracture lineaments to full-fledged faults containing several generations of fault rock including mylonite, cataclasite, fault gouge and pseudotachylite. The fault mode is also variable in that some segments are steeply dipping and containing numerous strike-parallel fault lenses with mylonitic and cataclastic fault rocks, indicative of strike-slip (the Fedafjord segment; Segment 2 and the Selandsdalen segment; Segment 5), whereas other segments are characterized by gently dipping (ca. 40°) extensional faults with many metres thick zones of fault gouge, overprinting plastic and brittle cohesive fault rocks. Indications of an offshore continuation of the Listafjord–Drangedal Fault Complex are found in the digital bathymetrical and potential field data (Segment 1), except for a linear gravity field contrast probably reflecting the basin margin of the Varnes Basin. The strongest offshore anomalies occur with angles of 10–20° to the regional strike of the segment, or are situated outside, but parallel to it. We take this as an indication that the Listafjord–Drangedal Fault Complex continues at basement level at the shelf close to the mainland, but that it is covered by (Late) Palaeozoic-Cenozoic metasediments and that it has not become significantly reactivated in post-Caledonian times. It is also noted that the northeastern margin of Segment 7 is characterized by a major open imbricate fan (horse-tail fault splay) that is commonly taken as an indication of fault growth during strike-slip (e.g., Freund 1974; Twiss & Moores 2007; Lopes Cardozo et al. 2002).