[S-GL23] Geochronology and Isotope Geology

[SGL23-01] Constraining complex isotopic signatures in brittle fault zones

★Invited Papers

*Horst Zwingmann¹ (1.Kyoto University)

Keywords:Brittle fault zones, clay minerals, authigenic illite, geochronology

Radiometric dating of fault gouges has become a widely used method in tectonics studies and understanding of fault and earthquake processes. Displacement on the fault planes can results to fault gouge composed of rock fragments and authigenic clay illite. Numerous studies over the last 30 years focussing on faults formed within Neoproterozoic to Neogene host rocks have demonstrated that the absolute timing of complex brittle fault histories recorded in the isotopic signatures in of authigenic clay minerals can be constrained by using isotopic dating techniques (see summaries in Vrolijk et al., 2018; Tsukamoto et al., 2020). Fault gouge illite age data from studies in Europe, Australia and Asia including Japan (MTL, ATL, Nojima) will be presented to discuss the history and evolution of the brittle fault dating and tracing approach. Illite ages generally decrease with grain size, are consistent with the cooling history of host rocks and bracketed by AFTA and ZFTA ages. Clay gouges are formed within the stability field of illite and the main temperature field of brittle deformation (<300°C). The internal consistency of the K-Ar ages of fault gouges, as well as consistency with constraints from field relationships and existing geochronological data demonstrate a powerful approach to constraint absolute timing of brittle deformation processes.

References
Tsukamoto, S. et al., 2020. Direct dating of fault movement. https://doi.org/10.1016/B978-0-12- 815985-9.00007-2.
Vrolijk et al., 2018. Fault gouge dating: history and evolution. https://doi.org/10.1180/clm.2018.22.