Clay quantification and Ar–Ar dating of synthetic and natural gouge: Application to the Miocene Sierra Mazatán detachment fault, Sonora, Mexico

Variations in the Illite to Muscovite Transition Related to Metamorphic Conditions and Detrital Muscovite Content: Insight from the Paleozoic Passive Margin of the Southwestern United States

“…Randompowder mounts were prepared for !2-mm-size fractions that had been reacted with weak acetic acid to remove trace amounts of adhered carbonate. The mounts were scanned from 16Њ to 44Њ2v, and the resulting XRD patterns were compared with "endmember" patterns from two standards, the Cambrian Silver Hill Formation from Montana, which contains 0% 2M 1 and 100% 1Md illite, and Owl Creek muscovite, which contains 100% 2M 1 illite/ muscovite (Haines and van der Pluijm 2008), as well as synthetic intermediate patterns generated by linearly mixing the end-member patterns. Polytype compositions were estimated by visually choosing the linearly mixed pattern that best matched the pattern of the unknown.…”

Post-Caledonian brittle deformation in the Bergen area, West Norway: results from K–Ar illite fault gouge dating

“…Illite is one of these newly grown minerals, and since illite fixes potassium in its crystal structure and can retain the radiogenic daughter product argon over many millions of years, it is amenable to radiometric dating by the K-Ar or Ar-Ar method (e.g., review by Clauer, 2013). Depending on the mineralogy of the host rock and availability and chemistry of fluids, illite can grow by illitisation of smectite or dissolution and reprecipitation of pre-existing clays (in clay-bearing host rocks; e.g., Vrolijk & van der Pluijm, 1999;Solum et al, 2005;Haines & van der Pluijm, 2008), by retrograde hydration reactions of feldspar and mica (mainly in crystalline host rocks; e.g., Zwingmann & Mancktelow, 2004;Siebel et al, 2010;Zwingmann et al, 2010b) or even by direct neocrystallisation from a fluid phase. The growth of illite during fault activity is promoted by a number of factors, including temperature (frictional heating and advective heating by hydrothermal fluids), grain comminution (increased surface area), strain (increase of crystal defects) and changes in fluid composition (mainly availability of potassium) and fluid/rock ratio (Vrolijk & van der Pluijm, 1999;Yan et al, 2001).…”

“…Whether the two low-temperature 1M d and 1M polytypes are really distinct polytypes or endmembers of a single polytype is still controversial (e.g., Haines & van der Pluijm, 2008) and they are here summarised as a single 1M/1M d polytype. 1M/1M d is the only polytype that can grow in the diagenetic zone, and at increasing temperatures it is irreversibly converted into 2M 1 illite, which is the only polytype stable in the epizone (e.g., Merriman & Peacor, 1999).…”

Exhumation history and landscape evolution of the Sierra de San Luis (Sierras Pampeanas, Argentina) - new insights from low - temperature thermochronological data

“…In these localized fault zones, the increased area/volume ratio of rock fragments together with fluid circulation favors high chemical reactivity, allowing retrograde processes to produce fault gouges composed of authigenic hydrosilicates such as illite. Thus, the formation time of the authigenic illite in a fault gouge, can be correlated with periods of motion along the fault and thus constrains the timing of faulting where favorable conditions for illite formation are present (e.g., Lyons and Snellenberg, 1971;Kralik et al, 1987;Wemmer, 1991;Solum et al, 2005;Haines et al, 2008;Zwingmann et al, 2010;Surace et al, 2011;Wolff et al, 2012;Bense et al, 2014). Bense et al (2014) suggested a concept to evaluate the timing of brittle deformation based on K-Ar illite fine-fraction ages from fault gouges, which are developed in non-sedimentary host rocks during retrograde cooling.…”