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Zwingmann, H.*; Niwa, Masakazu; Todd, A.*; Saunders, M.*
Earth, Planets and Space (Internet), 76, p.27_1 - 27_16, 2024/02
Times Cited Count：0 Percentile：0.02(Geosciences, Multidisciplinary)Atera fault zone clay gouges were collected for age dating from a river section near Kawaue, Nakatsugawa city, central Japan and the results integrated within its complex geological history. The results from the Atera Fault form an internally consistent data set with constraints from existing geochronological data (AFTA, ZFTA, CHIME) and demonstrate the application of gouge dating in providing new data to constrain timing of brittle deformation in Central Japan.
Yamasaki, Seiko; Zwingmann, H.*; Todd, A.*; Yamada, Kunimi; Umeda, Koji; Tagami, Takahiro*
no journal, ,
Early studies highlighted the potential for determining the timing of brittle fault deformation using isotopic dating of authigenic illites in fault gouge. However, it has remained difficult owing to the possibility of contamination of detrital material. In recent years, precise size separation combined with mineral characterization of the gouge samples has demonstrated the suitability of illite K-Ar dating for constraining the timing of brittle deformation, but further investigation on various geological setting is needed. In this study, we present K-Ar age data from two gouge samples collected from the fault in the Cretaceous Toki granite, central Japan. The gouge samples were separated into four grain-size fractions and characterized by XRD, SEM, and TEM. The fine fractions give younger K-Ar ages, suggesting enrichment in more recently grown authigenic illites. The K-Ar ages of the fractions with no detectable contamination from detrital K-bearing minerals on XRD analysis range from 53 to 43 Ma. This age is consistent with the stability field of illite and the main temperature field of brittle deformation within the cooling history of Toki granite body, which was evaluated by the ages from the hostrock.
Zwingmann, H.*; Niwa, Masakazu; Yamaguchi, Asuka*; Fujimoto, Koichiro*; Todd, A.*
no journal, ,
Studies of the thermal, mechanical and hydrothermal effects of Nobeoka drilling core samples indicate distinctive changes in the Illite crystallinity between the footwall, main fault zone and hanging wall. Detailed illite crystallinity investigations of the core samples provide a unique framework to constrain timing of authigenic illite formation within an ancient tectonic boundary thrust system. This pilot study investigates timing of thrust formation by dating of authigenic illite (
2 micron fractions) separated from 2 fresh non- weathered fault core, 3 footwall and 2 hanging wall core samples from the Nobeoka drilling core collected over a depths range of 80 to 30 m below ground surface. The obtained K-Ar ages will be discussed within the geological background of an ancient tectonic boundary thrust system.
Zwingmann, H.*; Niwa, Masakazu; Todd, A.*
no journal, ,
Active inland faults are widespread in Japan and investigations are important for earthquake forecasting and seismic hazard assessments. We describe authigenic illite fault gouge age dating results from a unique outcrop of the active Atera Fault, central Japan. This study investigates the timing of fault formation by K-Ar dating of authigenic illite separated from 3 fresh, non-weathered samples from the outcrop. Prior to age dating, extensive mineral characterization was carried out comprising petrography (TS, SEM, TEM) and XRD clay analyses. An undeformed host rock yields an age of 55 Ma (Paleogene-Eocene) and the Atera fault gouges clay ages range from 40 to 60 Ma (Paleogene-Eocene to Paleocene) and will be discussed within the geochronological and thermochronological background of the study area.
