Fault gouge analyses: K–Ar illite dating, clay mineralogy and tectonic significance—a study from the Sierras Pampeanas, Argentina

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

“…This can indeed be observed for all analysed samples ( Fig. 14; Tables 1-3, see also Bense et al, 2014).…”

“…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.…”

“…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. Following this idea, the interpretation of K-Ar illite ages is constrained by evaluation of several independent parameters, e.g., illite crystallinity, illite polytype quantification, illite grain-size, clay mineralogical observations, K-Ar muscovite and biotite host-rock cooling ages, as well as low-temperature thermochronological data derived from, e.g., fission track or the (U-Th)/He dating.…”

“…This allows a better error evaluation of individual methods by highlighting concordant data in multi-methodological datasets, as well as an easier combination of all observations into a consistent regional evolution model. For a detailed discussion of methodological, interpretation and analytical issues, the reader is referred to Bense et al (2014). Further details on data interpretation and analytical procedures are given in the Appendix.…”

“…In turn, the complementary 2M 1 end-member age may represent a) the oldest generation of neoformed illite, under retrograde (cooling) conditions (see Bense et al, 2014) and/or b) the age of "detrital" muscovite, meaning crushed muscovite from the host rock (Fig. 13).…”