Thermochronological investigation of fault zones

Abstract

The timing of faulting episodes can be constrained by radiometric dating of fault-zone rocks. Fault-zone material suitable for dating is produced by tectonic processes, such as (1) fragmentation of host rocks, followed by grain-size reduction and recrystallization to form mica and clay minerals, (2) secondary heating/melting of host rocks by frictional fault motions, and (3) mineral vein formation as a result of fluid advection associated with the fault motions. The thermal regime of fault zones consists primarily of the

Tectonothermal history of an exhumed thrust‐sheet‐top basin: An example from the south Pyrenean thrust belt

“…Temperature increase related to deformation (shear‐heating) is also unlikely as (i) the high temperatures found in the lower turbidites are not specifically related to fault zones, (ii) the inferred mean strain rates in the wedge are low (see above), and (iii) the east‐west temperature variations (e.g., between OR14 and TUR3; Figure ) do not correlate to detectable differences of macroscopic deformation. By contrast, large amounts of fluids can flow across sedimentary wedges and hot fluids migrating over a relatively short time span can noticeably modify the local geothermal gradient and affect the thermometry and thermochronology systems [e.g., McCulloch , ; O'Brien et al ., ; Arehart and Donelick , ; Tagami , ]. In such cases, the behavior of the thermometry and low‐temperature thermochronology systems is largely controlled by their kinetics, i.e., their capacity to react rapidly to temperature changes: the vitrinite system equilibrates very quickly [e.g., Galushkin , ; Huang , ; Le Bayon et al ., ] while the AFT system has a much slower kinetics.…”

Structural and temporal evolution of a reactivated brittle–ductile fault – Part II: Timing of fault initiation and reactivation by K–Ar dating of synkinematic illite/muscovite

“…Along the northeastern margin of the shield a phase of orogenic deformation and metamorphism known as the Timanian took place in the Late Vendian to early Cambrian (Roberts and Siedlecka, 2002). Although the arguments in favor of the Finnmarkian phase by Sturt et al (1978) are no longer considered valid (Corfu et al, 2007), K-Ar, 40 Ar/ 39 Ar and Rb-Sr dating of slates in the lower grade nappes east of the RTW suggests that metamorphism and cleavage development did indeed take place as early as c. 520-470 Ma (Sturt et al, 1978;Taylor and Pickering, 1981;Dallmeyer et al, 1989;Rice and Frank, 2003;Sundvoll and Roberts, 2003;Kirkland et al, 2008). Although the arguments in favor of the Finnmarkian phase by Sturt et al (1978) are no longer considered valid (Corfu et al, 2007), K-Ar, 40 Ar/ 39 Ar and Rb-Sr dating of slates in the lower grade nappes east of the RTW suggests that metamorphism and cleavage development did indeed take place as early as c. 520-470 Ma (Sturt et al, 1978;Taylor and Pickering, 1981;Dallmeyer et al, 1989;Rice and Frank, 2003;Sundvoll and Roberts, 2003;Kirkland et al, 2008).…”

Complete 40Ar resetting in an ultracataclasite by reactivation of a fossil seismogenic fault along the subducting plate interface in the Mugi Mélange of the Shimanto accretionary complex, southwest Japan

“…Fault rocks in the brittle regime often contain clay minerals with KeAr or AreAr ages that differ from those of the host rocks (e.g., Kralik et al, 1987). This age difference occurs because new clay minerals have grown in the fault rocks (Vrolijk and van der Pluijm, 1999), or because the KeAr system has been reset by argon diffusion (e.g., Tagami, 2012). Regardless of the resetting processes, KeAr or AreAr dating of clay minerals in fault rocks can be used to determine the youngest age at which fault activity occurred (Kralik et al, 1987;van der Pluijm et al, 2001;Clauer et al, 2012).…”