[S-GL23] 地球年代学・同位体地球科学

[SGL23-P01] Flash heating of clay gouge – implications for fault zone dating

*Horst Zwingmann¹、Andrew Todd²、Christoph Schrank³、Venice Akker⁴、Alfons Berger⁴、Marco Herwegh⁴ (1.Kyoto University、2.CSIRO Energy, Perth, Australia、3.QUT, Brisbane, Australia、4.Bern University, Switzerland)

キーワード：Fault zones, authigenic illite, shear heating experiments, geochronology

Fault slip and heating processes influence the isotopic signatures of authigenic clay in fault zones. The processes remain poorly understood and have not been widely studied. Identifying the effects of fault processes at sub-seismic slip velocities during earthquake nucleation, and further deformation and shear heating during earthquake propagation, is a fundamental prerequisite for dating fault motion by noble gas methods, which assume no inheritance of radiogenic 40Ar in K-Ar dating (Zwingmann et al., 2019). We report flash heating experimental data (4-32 micron, 300 to 1000°C; 30 secs, air) on a well characterized and dated fault sample from the Glarus Alps (Akker et al., 2021). The radiogenic 40Ar loss of the heterogenous fault gauge fraction is compared to the monomineralic GLO standard (Odin et al., 1982) at each temperature step. For example, a 30 sec. 800°C experiment reduces the radiogenic 40Ar concentration by 48%. Supplementary Argon diffusion modelling enables a direct comparison with the fractional radiogenic 40Ar loss measured in the laboratory experiments. The combination of experimental data with Argon diffusion modelling might assist to constrain the effects of short shear heating events on the isotopic signatures of fault clay gouge material and thus the reliability of fault gouge age data.

References
Akker et al., 2021. Tectonophysics, 800, doi.org/10.1016/j.tectp.2020.228708
Odin, G.S., 35 collaborators, 1982. In: Odin, G.S. (Ed.), Numerical Dating in Stratigraphy. Part 1. John Wiley and Sons, Chichester, pp. 123–148.
Zwingmann et al., 2019. Chem. Geol. 51, doi.org/10.1016/j.chemgeo.2019.03.034