3:30 PM - 5:00 PM
[SCG54-P01] Constraining timing of the Hakumaisan fault, Ichishi basin, southwest Japan
★Invited Papers
Keywords:Median Tecctonic Line, Miocene, transtensional basin
Opening of the Japan Sea back arc basin involves widespread extensional tectonics in the SW Japan arc. Numerous Early Miocene grabens in the arc, especially in central SW Japan, suggest multi-directional rifting involving strike-slip components of some basin-margin faults. A detailed field survey in the Early Miocene Ichishi basin on the northern side of the Median Tectonic Line, central SW Japan by Kinoshita and Yamaji (2021) revealed such transtensional deformations.
This pilot study investigates timing of deformation of the Hakumaisan fault—the southern marginal fault of the Ichishi basin—by K-Ar dating of fault gauge. Structural analyses of the slickenside striations and fault rocks of this fault indicate multiple tectonic events with different slip directions (Kinoshita and Yamaji, 2021). We dated authigenic illite (< 0.1, < 2 and 2–6 micron fractions) separated from 2 fresh and non-weathered samples from outcrops along the fault. Extensive mineral characterization was carried out comprising petrography (TS, SEM, TEM) and XRD clay analyses prior to K-Ar age dating (e.g. Zwingmann et al., 2010).
The Hakumaisan fault gouges clay ages range from ~10 to 36 Ma (late Miocene to Eocene) and will be discussed within the geochronological and complex transtensional tectonic framework of the study area. The age data suggest fault initiation ~ 20 Ma in the Early Miocene and a potential reactivation ~10 Ma in the late Miocene documented in the finest < 0.1 micron fraction. The age data might constrain timing of the graben formation and subsequent reactivation of the fault associated with the resumed or accelerated subduction of the Philippine plate.
Kinoshita and Yamaji, 2021. Island Arc. 2021;30:e12418; doi.org/10.1111/iar.12418
Zwingmann et al., 2010. Geology, 38, 6, 487-490; doi10.1130/G30785.1
This pilot study investigates timing of deformation of the Hakumaisan fault—the southern marginal fault of the Ichishi basin—by K-Ar dating of fault gauge. Structural analyses of the slickenside striations and fault rocks of this fault indicate multiple tectonic events with different slip directions (Kinoshita and Yamaji, 2021). We dated authigenic illite (< 0.1, < 2 and 2–6 micron fractions) separated from 2 fresh and non-weathered samples from outcrops along the fault. Extensive mineral characterization was carried out comprising petrography (TS, SEM, TEM) and XRD clay analyses prior to K-Ar age dating (e.g. Zwingmann et al., 2010).
The Hakumaisan fault gouges clay ages range from ~10 to 36 Ma (late Miocene to Eocene) and will be discussed within the geochronological and complex transtensional tectonic framework of the study area. The age data suggest fault initiation ~ 20 Ma in the Early Miocene and a potential reactivation ~10 Ma in the late Miocene documented in the finest < 0.1 micron fraction. The age data might constrain timing of the graben formation and subsequent reactivation of the fault associated with the resumed or accelerated subduction of the Philippine plate.
Kinoshita and Yamaji, 2021. Island Arc. 2021;30:e12418; doi.org/10.1111/iar.12418
Zwingmann et al., 2010. Geology, 38, 6, 487-490; doi10.1130/G30785.1