Reconstruction of the evolution and deformation history of an active fault – implications from the Atera fault, Central Japan

doi:10.21203/rs.3.rs-3222381/v1

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Reconstruction of the evolution and deformation history of an active fault – implications from the Atera fault, Central Japan

https://doi.org/10.21203/rs.3.rs-3222381/v1

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Atera fault clay gouges were collected for age dating near Kawaue, Nakatsugawa city, central Japan and the results integrated within its complex geological history. The results 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. The Atera illite age data complete recently obtained limited, illite fault gouge age data from underground exposure in the Toki granite, and the data are identical within error. The age of the heterogenous welded tuff breccia zone (Atera 1) ranges from 40.6 ± 1.0 Ma to 60.0 ± 1.4 Ma whereas ages of the fault core gouge sample (Atera 2) range from 41.8 ± 1.0 Ma to 52.7 ± 1.2 Ma. The finest < 0.1 µm fraction for the fault breccia and fault core gouge yield ages around 41 Ma, identical within error. The obtained data indicate brittle faulting and a subsequent geothermal event occurring in the Paleogene–Eocene, similar to the nearby Toki granite. The brittle deformation and thermal event were synchronous with the post-intrusive exhumation of the pluton. The Atera fault illite age data provide additional insights into an integrated, regional-scale record of tectonic displacement of central Japan, and can be linked to the large scale tectonic processes such as the Emperor sea mount kink around 55 to 46 Ma with fault initiation around 50 Ma and brittle fault cessation or reactivation around 40 Ma in the Eocene.

Clay fault gouges are present in active brittle faults formed under near surface conditions (e.g., Scholz 2002). Geological processes in active fault zones might comprise of: fragmentation of host rocks, grain-size reduction and authigenesis of clay minerals (illite, smectite, chlorite) and muscovite; secondary heating and melting of host rocks by frictional deformation (pseudotachelytes), and/or mineral vein formation caused by fault related fluid flow (e.g., Holdsworth et al., 1997; Tagami 2012). If authigenic illite is present, gouges can reliably constrain the timing of fault activity by K-Ar, ⁴⁰Ar/³⁹Ar and Rb-Sr dating (see summaries in Vrolijk et al., 2018; Tsukamoto et al., 2020). Despite more than 50 years of research, the timing of slip on brittle faults in the Earth’s upper crust is difficult to constrain, and direct radiometric dating of fault-generated materials remains challenging. Over the last decade, K-Ar data of authigenic illite formed in brittle fault zones are integrated with fission track data (AFTA, ZFTA), as the frictional heating caused by fault motion can partially or totally reset the “clock” of the dating methods (Zwingmann and Mancktelow 2004; Tagami, 2005; Zwingmann et al. 2010a, 2010b, Tagami 2012, Yamasaki et al. 2013). Timing of fault formation and its corresponding geofluid sources can be investigated through the robust isotopic memory of neo-crystallized authigenic clay minerals as its crystal structure includes H (as OH) and K, enabling constraint of fluid sources through H isotope analysis and timing through Argon dating (e.g., Hetzel et al., 2013; Mancktelow et al., 2015; 2016; Lynch and van der Pluijm, 2016; Heinecke et al., 2019). Limited studies apply a whole range of dating methods such as K–Ar, ⁴⁰Ar/³⁹Ar, and Rb–Sr dating of syntectonic fault related illite (e.g., Middleton et., 2014; Uysal et al., 2020). Carbonate U-Pb geochronology can provide direct timing constraints for geological processes including: diagenesis, fluid flow, brittle faulting via carbonate slickenfibers and vein related tectonic processes (e.g., Mottram et al., 2020), but was applied prior to in situ U-Pb dating of low-U fault-related carbonate (e.g., Nuriel et al., 2017; Roberts et al., 2020). However, some fault gouge lack calcite and quartz veins developed by fluid interaction and therefore cannot be investigated by in situ U-Pb geochronology (i.e. Kemp et al., 2019). Most studies focus on the thermal effect on clay gouge during brittle deformation, as fault zones might reactivate numerous times over their complex geological history, from formation to last slip event and subsequent grain size reductions during multiple faulting events might affect its isotopic signature (e.g., Zwingmann et al., 2019). In this study, samples of clay fault gouge associated with the Atera fault were collected for K–Ar dating from a well exposed river section near Kawaue, Nakatsugawa city, central Japan (Fig. 1).

Active inland faults are widespread in Japan and investigations are important for earthquake forecasting and seismic hazard assessments (Toda, 2016). Comprehensive geological summaries of fault zones in Japan and the Geology of Japan, including the study area, can be found elsewhere (Moreno et al., 2016). The study area is located in Central Japan approximately 70 km NE of Nagoya (Fig. 1). The Atera fault is one of several major left-lateral, strike–slip active faults in Central Japan and extends for ca. 55 km from Nakatsugawa city to Gero city in Gifu Prefecture in a general NW to SE trend (Takagi et al., 2005). The outcrop consists of fault breccia, clay-rich fault gouge, and cataclasite (Niwa et al., 2009) and cover, in a cross-section, significant asymmetry due to different protolith lithology, and record several stages of deformation. The architectural evolution of the Atera fault zone is based on a field-based and microstructural study (Niwa et al., 2009). The last recent displacement occurred along the Atera Fault during a major earthquake in 1586 (Toda et al., 1996).

Central Japan has a long and complex deformation history that has continued to the present-day and is reflected in a strong interrelationship between topography, erosion and neotectonics. Good surface exposures make the region attractive for the study of fault gouges which are otherwise poorly preserved due to extended weathering. The ages of the basement and host rocks are well constrained and supplemented with a large set of regional thermochronological data. However, there have been few studies specifically on localized retrograde authigenic clay mineral formation in discrete fault zones in Japan, although such brittle faults are widespread and similar to studies reported within the European Alps (Zwingmann and Mancktelow 2004, Zwingmann et al., 2010a). The fault outcrops investigated in this study are located in Kawaue, Nakatsugawa City (Fig. 1c; Niwa et al. 2009; 2015). The Kawaue basement comprises: the Inagawa granite, the Gero Ash-Flow sheet of the Nohi rhyolite, the Naegi–Agematsu granite, the Toki Sand and Gravel Bed, and the Ueno basaltic rocks (Fig. 2). The Inagawa granite is part of the widespread Ryoke granites, which intruded into the southwestern Japanese Islands during the Cretaceous. The Inagawa granite age was constrained by CHIME analyses in two localities with ages of 82.6 ± 1.8 Ma and 81.9 ± 1.4 Ma (2s) which are identical within error (Suzuki and Adachi, 1998). The Gero Ash-Flow Sheet, a welded tuff, yielded a younger 75.2 ± 6.2 Ma (1s) Rb–Sr whole-rock isochron age (Shirahase 2005; Yamada and Koido, 2005), and is part of the Late Cretaceous Nohi rhyolite composite volcanism in Central Japan (Yamada et al., 2005). The Naegi–Agematsu granite, which intrudes both the Inagawa Granite and the Gero Ash-Flow Sheet, was dated at 67.2 ± 3.2 Ma (CHIME, 2s) (Suzuki et al. 1994) and 71.3 ± 1.6 Ma (SHRIMP, 2s) (Nakajima et al. 1993). The terrestrial Toki Sand and Gravel Beds are of upper Miocene to lower Pleistocene age (Editorial Committee of CHUBU II 1988). The Ueno Basaltic Rocks are extrusive rocks from a late Pliocene to early Pleistocene volcano group above the Toki Sand and Gravel Bed. K–Ar ages of the Ueno Basaltic Rocks at Sakashita ranges from: 1.41 ± 0.12 Ma (Uto and Yamada, 1985), 1.68 ± 0.11 Ma (Shimizu et al., 1988), 1.64 ± 0.08 Ma to 1.54 ± 0.08 Ma (Ujike et al., 1992) with an overall average of 1.57 ± 0.05 Ma (2s) based on error propagation. The Atera fault in the Kawaue area separates the welded tuff of the Gero Ash- Flow Sheet from the Naegi–Agematsu granite (Fig. 2a). The studied outcrop rocks include welded tuff of the Gero Ash-Flow Sheet and granite of the Naegi–Agematsu granite (Fig. 2b). The welded tuff is rhyolitic and phenocryst-rich, with phenocrysts of quartz, plagioclase, K-feldspar, and biotite in a glassy groundmass accompanied by quartz and chlorite. Remaining feldspars are highly sericitized. Clay minerals and calcite occur as secondary minerals caused by groundmass alteration.

The Naegi–Agematsu granite is composed of: quartz, plagioclase, K-feldspar, and biotite, showing micrographic texture with minor sutured structure. Biotite is partly chloritized, needle-shaped, and fine-grained (Niwa et al., 2009; 2015).

The Atera fault outcrops consist of an ~ 42 m wide fault zone, subdivided into paired damage zones derived from welded tuff and granite, and a 1.2 m wide fault core (Fig. 2). The welded tuff damage zone, which is dominant in the western part of the fault zone, is composed of a 10 m wide zone of welded tuff with a high fracture density and a 14 m wide fault breccia. The granite damage zone in the eastern part of the Atera fault is composed of a 12 m wide zone of granite with a high fracture density and a 5 m wide granite cataclasite.

The 1.2 m wide fault core is clay-rich and contains fragments of welded tuff, granite, and basalt. The fragments in the 1.2 m wide fault core are friable and are associated with fractures. The basalt fragments can be correlated with the neighboring volcanic rocks of the Ueno Basaltic Rocks (Niwa et al., 2009). This observation places a constraint on the maximum age of fault core formation. The fault core trends NW-SE to NNW-SSE with a subvertical dip. Slickenline plunging gently south is developed along the border of the fault core (Fig. 2c). Some rounded fragments have been rotated and display asymmetric tails indicating a sinistral sense of shear. These structural features of the fault core are consistent with the general structure of the Atera fault.

Aside from the 1.2 m-wide fault core, a 30 cm-wide fault overprints the granite cataclasite (Fig. 2c). The fault gouge is clay-rich and includes granite fragments. The trend of the gouge is subparallel to the 1.2 m wide fault core, i.e. NW-SE to NNW-SSE strike, and a subvertical dip and slickenlines on the gouge plunge gently south (Niwa et al., 2015).

Sampling

Three clay rich gouge samples were obtained from the main outcrop shown in Fig. 2c and selected based on the host rock mineralogy. An undeformed host rock sample from the Gero Ash-Flow Sheet of the Nohi rhyolite was collected about 3 km to the west (Fig. 1c). Sample Atera 1 (3369) originates from the welded tuff fault breccia, sample Atera 2 (3370) from the center of the 1.2-m-wide fault core and sample Kawaue (3367) from the 30 cm-wide fault gouge within the granite cataclasite. The location of the outcrop is shown in Fig. 1c and GPS location data summarized in Table 1. The procedures applied in this study are based on Zwingmann et al. (2010a). Approximately 100 g of fresh gouge and cataclastically ground rock material was collected from each sample site. Samples were gently disaggregated using a repetitive freezing and heating technique to avoid artificial reduction of rock components with K-bearing minerals, such as micas or K-feldspars (Liewig et al. 1987). Grain size fractions < 2, 2–6 and 6–10 µm were separated in distilled water according to Stokes’ law and < 0.1 µm fractions were separated using a high-speed centrifuge but only limited amount could be obtained. For whole-rock host rock analysis a small amount of sample material was crushed in an agate mortar by hand. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

Table 1. GPS outcrop location

Fault gouges: N35°36'21" / E137°29'49"

Host rock: N35°35'58" / E137°27'51"

XRD

The mineralogy of the size fractions was determined by XRD on randomly oriented powder samples. Results for the < 0.1 µm fractions could not be obtained due to very limited sample amount and these fractions were mainly investigated by TEM (see below). Diffractograms of the samples were obtained and analyzed using a Rigaku Ultima IV with a two-axis goniometer, CuKα radiation, a Kβ filter, and a one-dimensional X-ray detector (D/teX Ultra) at 40 kV and 30 mA, with 0.5° and 10 mm divergence slits, and an 8 mm anti-scattering slit. The samples were scanned over the range 2θ = 3–70° with a scan rate of 1° min^− 1 and a step size of 0.01°. The XRD results are listed in Table 2.

Table 2

XRD data. Semiquantification was based on integrated intensity ratio using reference of corundum, WR whole rock.
Sample	ID #	Fraction	Smectite	Illite	Chlorite	Quartz	Plagioclase	K-feldspar
		(µm)	(%)	(%)	(%)	(%)	(%)	(%)
Atera 1	3369	< 2	44	27	0	10	14	5
		2–6	22	20	0	21	31	6
		6–10	13	12	0	31	35	8
Atera 2	3370	< 2	57	30	0	5	5	3
		2–6	43	17	0	18	18	4
Kawaue	3367	< 2	9	33	0	20	28	11
Host rock		WR	-	-	6	39	51	5

Petrography

The Atera 1 and 2 fault gouge and the host rock samples were investigated by thin section petrography. Petrographic information about sample Kawaue (3367) from the 30-cm wide fault gouge within the granite cataclasite can be found in Niwa et al. (2009).

The fault rock samples were impregnated with low-viscosity epoxy (Struers Epofix) before cutting. Due to water-sensitive clay minerals in the fault rocks, synthetic hydrocarbon oil (ENEOS METAL WORK S) was used throughout thin section preparation including cutting and grinding. Petropoxy 154 was used to mount the sample chips to glass slides and the mounted sections and reduced to ~ 35 µm thickness and subsequently polished.

For SEM investigations, freshly broken surfaces of sample chips were carbon-coated and examined in secondary electron mode using a HITACHI TD-1000 SEM equipped with an energy dispersive system X-ray analyzer (EDS; Horiba EMAX) at the JAEA Tono Geoscience Center, Japan. A JEOL F200 (CF-HR) TEM operating at 200KV equipped with a Gatan OneView camera was used for detailed, grain-by-grain morphological characterization of selected < 0.1 µm clay fractions, and to investigate the grain-size distribution within the fractions at the CMCA, UWA, Perth, Australia. For TEM investigation, samples were prepared by placing one drop of clay solution on a Cu TEM grid with a thin, amorphous carbon support film and drying in air. The composition of individual particles was investigated with a JEOL SD100WL 100 mm2 SDD EDS detector run through Oxford Instruments’ AZtec software.

K-Ar dating

K–Ar dating was performed at CSIRO Energy, Perth, Australia, and follows standard methods given in detail by Dalrymple and Lanphere (1969). Ar isotopic determinations were performed using a procedure similar to that described by Bonhomme et al. (1975). Potassium content was determined by ICP-OES (Agilent Technologies 725 ICP-OES). Approximately 20 mg of sample was dissolved with HF and HNO₃. The samples once in solution were diluted to 10–50 ppm K for the ICP-OES analysis. The pooled error of K determination of all samples and standards is better than 2%. Argon was extracted from the separated mineral fraction by fusing the sample within a vacuum line serviced by an online ³⁸Ar spike pipette. The isotopic composition of the spiked Ar was measured with an online VG3600 mass spectrometer. The ³⁸Ar was calibrated against standard biotite GA1550 (McDougall and Roksandic, 1974). Due to the hygroscopic nature of clays, special care was taken in the preparation of both K and Ar sample splits. For Ar analysis by noble gas spectrometry, sample splits were loaded into clean Mo-foil (Goodfellow molybdenum foil, thickness 0.025 mm, purity 99.9%), weighed and subsequently preheated to 80°C overnight to remove moisture, and re-weighted using a Mettler AT20 balance and the measured dry weight used in the K-Ar age calculation. Samples were stored in a desiccator before loading into the Ar purification line. Blanks for the extraction line and mass spectrometer were systematically determined, and the mass discrimination factor was determined regularly by airshots (small amounts of air for ⁴⁰Ar/³⁶Ar ratio measurements). During the study, 5 international standards (3 HD-B1, 2 LP-6) and 4 airshots were analyzed (Table 3). The error for the ⁴⁰Ar/³⁶Ar value of the airshot yielded 295.63 ± 0.21 (1σ). The general error for argon analyses is below 1.0% (2σ) based on the long-term precision of measurements of international Argon standards. The K–Ar age was calculated using ⁴⁰K abundance and decay constants recommended by Steiger and Jäger (1977). The age uncertainties consider the errors during sample weighing, ³⁸Ar/³⁶Ar and ⁴⁰Ar/³⁸Ar measurements, and K analysis. Ages are reported to the timescale of Cohen et al. (2013).

Table 3

K-Ar standards and airshot data. References HD-B1 (Hess and Lippolt, 1994), LP6 (Odin et al., 1982), airshot (Steiger and Jäger, 1977).
CSIRO ID	K	Rad. 40Ar	Rad. 40Ar	Age*	Error	Remark
standard	(%)	(mol/g)	(%)	(Ma)	(Ma)	% error to references
HD-B1-154	7.96	3.4055E-10	92.16	24.51	0.33	1.24
HD-B1-157	7.96	3.3524E-10	90.12	24.13	0.32	-0.33
HD-B1-156	7.96	3.4037E-10	91.30	24.50	1.38	1.20
LP6-171	8.37	1.9222E-09	97.12	127.77	1.64	-0.10
LP6-170	8.37	1.9144E-09	97.00	127.27	1.31	-0.49

Airshot ID	⁴⁰Ar/³⁶Ar	+/-
AS148-AirS-2	295.95	0.18
AS148-AirS-2	295.74	0.22
AS150-AirS-1	295.41	0.27
AS151-AirS-2	295.40	0.16

XRD

The fault clay gouge mineralogy was obtained by XRD analysis. The representative XRD spectra of the < 2 µm fractions and the host rock powder are summarized in Fig. 3. The fault gouge sample mineralogy comprises smectite, illite, quartz, K-feldspar and plagioclase (Table 2). Amounts of smectite and illite increase with decreasing particle size and amounts of quartz, K-feldspar and plagioclase decrease with decreasing particle size. For sample Atera 1, the < 2 µm fraction contains the highest amount of illite with 27%, decreasing to 20% in the 2–6 µm and 12% in the coarsest 6–10 µm fraction. This trend is similar for the Atera 2 sample with illite enriched in the < 2 µm fraction with 30% decreasing to 17% in the 2–6 µm fraction. The smectite content of both samples is decreasing in a similar manner for both fault gouge samples from 44% in the < 2 µm fraction, 22% in the 2–6 µm fraction to 13% in the coarse 6–10 µm fraction for Atera 1 and, 57% for the < 2 µm fraction to 43% in the 2–6 µm fraction for the Atera 2 sample, respectively. In both samples the K-feldspar content increases with grainsize from 5 to 8% for Atera 1 fractions whereas, for the Atera 2 fractions, K-feldspar content is homogenous ~ 3 to 4%. The Kawaue sample contains a high amount of illite at 33%, a low amount of smectite at 9% and a significant K-feldspar content of 11%. The Nohi Rhyolite host rock is rich in quartz, plagioclase, K-feldspar, and chlorite with no illite present. Illite polytype analysis results are inconclusive due to low amounts of sample and mixture of illite and feldspar in the < 2 µm and coarser fractions.

Petrography

Optical microscope petrography

Optical microscopic observation reveals that all Atera fault gouge samples are clay-rich with distinct foliation defined by a preferred alignment of minerals (Fig. 4). The Atera 1 welded tuff fault breccia gouge sample shows significant development of microfractures in lithic fragments of welded tuff and mineral fragments of quartz and feldspar. Clay minerals are unevenly distributed and concentrated in larger fractures.

The Atera 2 sample originates from the main fault core and contains polymineralic fragments of welded tuff, granite, and andesite/basalt, and monomineralic fragments of quartz, plagioclase, and K-feldspar in a clayey matrix. The fragments are subangular to subrounded. The matrix clay is composed of fine fragments of well aligned phyllosilicates and quartz. Additional petrographic information of the Atrea fault zone can be found in Niwa et al. (2009).

Contrary to the Atera fault samples, the thin section petrography of the Nohi Rhyolite host rock indicates no foliation and few microfractures. The host rock sample contains large ~ 1–3 mm quartz and plagioclase minerals as well as chloritized mafic minerals. The fine-grained groundmass is mainly composed of quartz and plagioclase. The quartz phenocrysts are often corroded and plagioclase mostly sericitized.

SEM results

SEM investigations reveal that illite/smectite minerals in the fault gouge zones have a preferred orientation and shows regular, euhedral grain boundaries, typical of an authigenic and synkinematic origin, compared to host rock samples as shown in Fig. 5 (Clauer and Chaudhuri, 1995). However, no direct anastomosing foliation defined by illite/scmetite (I/S) wrapping around clasts of host rock can be observed. The preferred orientation suggests that the gouge minerals are of synkinematic origin. Irregular remaining host rock grains are surrounded by a finer grained matrix, both of which appear to have developed by mechanical comminution rather than the well-crystallized, fibrous, lath-shaped or platelet forms more typical of authigenic clay minerals (Inoue et al., 1988; Pevear, 1999). The petrographic observations are similar to a study focusing on retrograde faults from the Swiss Alps (Mancktelow et al., 2015). Features revealed by the SEM are different between the fault gouge and Nohi Rhyolite host rock. Euhedral mineral grains mostly composed of quartz and feldspar are filled tightly, without fragmentation. The particles investigated by SEM contain: Al, Si, O, K and Fe as determined by EDS, and correspond to illite/smectite minerals as identified by XRD.

TEM results

TEM investigations of the selected < 0.1 µm clay fractions indicate distinct idiomorphic platy illite flakes, with well crystallized edges (Fig. 6), and some detrital, electron dense dark particles with diffuse and irregular edges (Fig. 6). The separated clay mineral particles have a platelet form, generally with straight, idiomorphic, euhedral edges (Fig. 6). The particles investigated by TEM EDS contain mainly Al, Si, O, K and Fe and correspond to illite/smectite minerals as identified by SEM and XRD. Detrital clay particles are often volumetrically larger than neoformed illite particles and are characterized by different morphological shapes. Detrital illite normally shows irregular edges, while neoformed illite particles have sharp, and well-defined edges (Clauer and Chaudhuri, 1995). The platy idiomorphic shapes of the illite identified by TEM in the fault gouge suggest an in situ neoformation.

K-Ar data

Nine new K–Ar analyses comprising of one whole rock sample and eight clay fractions from < 0.1 to 6–10 µm, were obtained in this study (Table 4). The whole rock analysis of an undeformed host rock yields an age of 54.9 ± 1.3 Ma (Paleogene-Eocene-Ypresian) and the Atera fault gouges clay ages range from 40.6 to 60.0 Ma (Paleogene-Eocene-Bartonian to Paleogene-Paleocene-Selandian). As reported in numerous studies involving clay-size fractions, there is a consistent decrease in age with decreasing grain size (Fig. 7) (see summaries in Vrolijk et al., 2018; Tsukamoto et al., 2020). The ages of the < 2 µm fractions from the three fault gouge samples vary significantly from 50.2 ± 1.2 Ma for Atera 1, to 47.0 ± 1.1 Ma for Kawaue to 44.1 ± 1.0 Ma for sample Atera 2. Ages of the Atera 1 sample originating within the welded tuff breccia range from 40.6 ± 1.0 Ma for the finest < 0.1 µm fraction to 60.0 ± 1.4 Ma for the coarsest 6–10 µm fraction. Ages of the Atera 2 samples originating from the fault core yield an age of 41.8 ± 1.0 Ma for the finest < 0.1 µm fraction, (identical within error of the Atera 1 < 0.1 µm sample) and a significantly younger age of 52.7 ± 1.2 Ma for the coarser 2–6 µm fraction. K concentration ranges from 2.74 to 4.98% and radiogenic ⁴⁰Ar content from 78.9 to 95.7% indicating no significant contamination with atmospheric ⁴⁰Ar.

Table 4. K-Ar age data. WR whole rock, timescale Cohen et al. (2013).

Sample	CSIRO ID	K	Rad. 40Ar	Rad. ⁴⁰Ar	Age	Error	Timescale
	(µm)	(%)	(mol/g)	(%)	(Ma)	(Ma)	Period-Epoch-Stage
Atera 1(welded tuff breccia)	3369 < 0.1	3.56	2.5354E-10	78.9	40.6	1.0	Paleogene-Eocene-Bartonian
	3369 < 2	4.44	3.9201E-10	93.7	50.2	1.2	Paleogene-Eocene-Ypresian
	3369 2–6	4.00	4.1703E-10	94.9	59.1	1.4	Paleogene-Paleocene-Thanetian
	3369 6–10	3.92	4.1464E-10	95.7	60.0	1.4	Paleogene-Paleocene-Selandian
Atera 2Atera 2 (fault core)	3370 < 0.1	2.74	2.0091E-10	89.5	41.8	1.0	Paleogene-Eocene-Lutetian
	3370 < 2	2.80	2.1694E-10	88.3	44.1	1.0	Paleogene-Eocene-Lutetian
	3370 2–6	3.18	2.9515E-10	92.6	52.7	1.2	Paleogene-Eocene-Ypresian
Kawaue (granite cataclasite)	3367 < 2	4.98	4.1180E-10	92.9	47.1	1.1	Paleogene-Eocene-Lutetian
Tsukechi River (host rock	3510 WR	1.57	1.5170E-10	81.6	54.9	1.3	Paleogene-Eocene-Ypresian

The fundamental assumptions and limitations of K-Ar illite fault gouge dating are discussed elsewhere (Vrolijk et al., 2018; Tsukamoto et al., 2020). K-Ar dating of authigenic clays and illite in general requires careful investigations and is discussed by Clauer et al. (2012) and Meunier and Velde (2004), in some detail. The obtained ages are interpreted as maximum ages as the authigenic illite within the finest separated particle size represents the most recently grown illite. We interpret the grain-size fractions of the separated authigenic illite as mixtures of illite particles formed at different times during growth and this growth history is usually investigated by dating a range of different grainsize fractions. Illite in fault gouge is formed in a low-temperature retrograde environment where mineral reactions are governed by kinetics rather than equilibrium thermodynamics (e.g., Vrolijk and van der Pluijm, 1999; Zwingmann and Mancktelow, 2004).

The relationship of increasing K-Ar age with increasing grain size is illustrated in Figs. 7 and 8 consistent with increased contamination in the coarse fractions relative to the finer fractions as confirmed by XRD data (Table 2 ). The Atera 1 gouge sample originates from a heterogenous welded tuff breccia zone and the finest < 0.1 µm fraction yields an age of 40.6 ± 1.0 Ma and increases significantly by about 10 Ma to 50.2 ± 1.2 Ma for the coarser < 2 µm fraction. For the coarser, 2–6 µm and 6–10 µm fraction, the ages increase again by a steep 10 Ma to 59.1 ± 1.4 Ma and 60.0 ± 1.4 Ma respectively. A similar but less severe age increase can be observed for the Atera 2 gouge sample originating from the fault core with the finest < 0.1 µm fraction yielding an age of 41.8 ± 1.0 Ma and increases by about 2 Ma to 44.1 ± 1.0 Ma for the coarser < 2 µm fraction. For the coarser 2–6 µm and fraction the age increases again by a significant 10 Ma to 52.7 ± 1.2 Ma compared to the < 0.1 µm fraction. For the Kawaue gouge sample (3367) obtained from within the granite cataclasite zone, only a < 2 µm fraction was analyzed which yielded an age of 47.0 ± 1.1 Ma. This age is intermediate between the Atera 1 and 2, < 2 µm ages. The obtained whole rock host rock age is similar to the coarser 2–6 and 6–10 µm fractions from the fault zone samples (Fig. 7) and, suggests that a thermal overprint or hydrothermal overprint might be associated with the fault initiation around 41.2 Ma and, might have partially influenced and reset the isotopic signatures of the Nohi rhyolite host rock.

The increase in ages of both fault gouge samples can be explained by increasing contamination (Table 2) and highlights that the most reliable isotopic ages for neoformed illite are obtained from the finest size fractions (< 0.1 µm) of gouge rock samples, due to minimal contamination as discussed by Zwingmann et al. (2010a), Torgersen et al. (2015) and Viola et al. (2016). The average age of the two < 0.1 µm Atera gouge fractions yields a mean of 41.2 ± 0.7 Ma, which is significantly younger than the < 2 µm fraction ages of 47.2 ± 0.8 Ma, and correspond, within error, to the age obtained from the gouge sample within the granite cataclasite zone (Kawaue, 3367). The ages of all size fractions are quite heterogenous indicating that: (1) different contamination sources are present in the fault gouge samples or, (2) the fault core sample experienced a more severe last faulting event suggesting the effect of mechanical comminution increases toward the fault core (Fukuchi et al., 2014).

Implications for geology of Central Japan

As discussed by Zwingmann and Mancktelow (2004) and Yamasaki et al. (2013) the K–Ar ages of gouge samples are bracketed by the zircon and apatite fission-track ages from host rocks (Fig. 8). Brittle faulting and authigenic illite growth occur under thermal conditions bracketed by the partial annealing zones of apatite in the lower 60–120°C temperature range (e.g., Laslett et al., 1987; Green and Duddy, 1989; Corrigan, 1993) and in the higher 170–390°C temperature range for zircon, (Yamada et al., 1995) with a tendency to be closer to that of apatite. Similar to the limited illite brittle fault age data from the Toki granite, (Yamasaki et al., 2013) the obtained age of main illite formation within the Atera fault of ~ 47.1 Ma is younger than age data results from the Nojima fault ca. 250 km to the SW (Zwingmann et al., 2010b). However, Paleogene–Early Eocene ages are widely reported in Japan, ranging from the Median Tectonic Line (Shikoku and Kinki location ca. 200–350 km to the SW) and the Mozumi–Sukenobu fault ca. 100 km to the N (e.g., Yamasaki et al., 2013). Major active faults are distributed mainly in or around the margin of the Cretaceous granitic terrane and also in Jurassic accretionary complexes in the Inner Zone of SW Japan (Takagi et al., 2005). Major hydrothermal events are associated with faults in SW Japan, occurring at ~ 60–50 Ma and, once clay gouge is formed, subsequent hydrothermal fluid circulation has limited permeation into the fault core thus unable to form new clay minerals during fault reactivation. In our study, the age difference between the Nohi Rhyolite breccia zone sample (Atera 1), and the fault core sample (Atera 2), might indicate a later reactivation. This is similar to gouge samples from the Nojima fault, Japan and the Deokpori thrust in Korea which highlights some age variation of fine-grained clay fractions with decreasing ages in grain size and might indicate illite formation during potential fault reactivation (Zwingmann et al., 2010b, 2011). Data for the nearby Toki granite reported by Yamasaki et al. (2013) suggest that in the brittle faults, formed in relation to a subsequent geothermal event under the condition of illite formation (i.e. 100–200°C), occurred at approximately 54 to 43 Ma, and no further hydrothermal fluid event is documented by illite ages after 43 Ma (Paleogene–Middle Eocene).

The thermochronological history and cooling curve of the study area for the nearby Toki granite was summarized by Yamasaki et at. (2013) (Fig. 9A). Based on this study we adapted and approximated the thermochronological history and well-defined cooling curve for the Nohi rhyolite and Naegi Agematsu granite (Fig. 9B). Ages are plotted from high closing to low closing temperature of minerals based on Suzuki and Adachi (1998), Shirahase (2005), Yamada and Koido (2005), Suzuki et al. (1994) and Nakajima et al. (1993). The age data of the whole rock Rb–Sr, monazite CHIME, hornblende, biotite K–Ar, and zircon fission-track for host rocks from the Nohi rhyolite and Naegi–Agematsu granite are similar to the Toki granite. The data support a model of Yamasaki et al. (2013) suggesting that the pluton intruded at around 70 Ma and cooled rapidly to ~ 300°C. As outlined for the Toki granite, the Naegi–Agematsu granite experienced an initial rapid cooling after the intrusion and cooled slowly, associated with subsequent exhumation between the closure temperatures of zircon (~ 300°C) and apatite (~ 100°C) fission-track ages, at a cooling rate of ~ 7–9°C/m.y. (Yamasaki and Umeda, 2012). The newly obtained K-Ar illite ages ranging from 40 to 60 Ma for the Atera 1 sample fraction and 41 to 53 Ma for Atera 2 fractions, plot on the 100–200°C temperature range of this cooling curve similar to the Toki granite fault gouge deformation (Fig. 9A). The < 0.1 µm fractions of both Atera fault gouge samples yield ages identical within error around 40 Ma, whereas the < 2 µm ages vary by 5 Ma from 50 to 44 Ma which might be caused by variable K-feldspar contamination. As the Kawaue < 2 µm fraction contains the highest amount of K-feldspar contamination of ~ 11% but yields an intermediate age of 47 Ma, the overall impact of contamination might be negligible as the K-feldspar might be partially reset (Zwingmann et al., 2010a). The new Atera fault gouge illite age data confirm that brittle deformation and continuous thermal events are synchronous with the post-intrusive uplifting in this part of central Japan.

Complex fault cores and brittle fault rocks are rarely preserved in outcrops in Japan due to weathering, erosion and vegetation cover. River outcrops and fresh exposures therefore provide important opportunities to investigate the fault zones and architecture of regionally important tectonic frameworks. The results presented here from the Atera Fault in Central Japan form an internally consistent data set, with constraints from existing geochronological data (AFTA, ZFTA, CHIME), that demonstrates the application of gouge dating in providing new data for constraining timing of brittle deformation in Central Japan. The new illite age data from the well-exposed Atera fault complete recently obtained, limited fault illite gouge age data from the Toki granite (Yamasaki et al., 2013), and are, within error, identical. The age of the heterogenous welded tuff breccia zone (Atera 1) ranges from 40.6 ± 1.0 Ma to 60.0 ± 1.4 Ma (Eocence Bartonian to Paleocene Selandian). The age of the fault core gouge sample (Atera 2) ranges from 41.8 ± 1.0 Ma to 52.7 ± 1.2 Ma (Eocence Lutetian - Ypresian). The finest < 0.1 µm fraction for the fault breccia and fault core gouge yield within error identical ages of around 41 Ma (Eocence Bartonian). Similar to the nearby Toki granite, the obtained data indicate brittle faulting and a subsequent geothermal event occurring in the Paleogene–Eocene. The brittle deformation and continuous thermal event were synchronous with the post-intrusive exhumation of the Toki granitic pluton. The obtained illite ages are comparable with results obtained from other faults in the Inner Zone of southwest Japan, comprising: the Nojima fault, the Median Tectonic Line, the Atera fault and the Mozumi–Sukenobu fault (Shibata et al., 1989; Yamada et al., 1992; Takagi et al., 2005; Zwingmann et al., 2010b). The Atera fault illite age data provide important new insights into an integrated regional-scale record of tectonic displacement in central Japan and can be linked to the large-scale tectonic processes such as the Emperor sea mount kink around 50 to 46 Ma (Murakami and Tagami, 2005) with fault initiation around 55 Ma and brittle fault cessation or reactivation around 40 Ma in the Eocene.

Data availability statement

All data in this study can be obtained in the figures, tables and references. All data will be uploaded into KURENAI, Kyoto University's institutional repository via a DOI (to be obtained if manuscripts is accepted for publication).

Acknowledgements

This study was funded by METI, Japan as part of its R&D supporting program titled “Establishment of Advanced Technology for Evaluating the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste (JPJ007597) (Fiscal Years 2018-2022)”. The authors acknowledge the facilities, and the scientific and technical assistance of Microscopy Australia at the Centre for Microscopy, Characterisation & Analysis, The University of Western Australia, a facility funded by the University, State and Commonwealth Governments.

Competing interests

The authors declare no competing interests.

Author contributions

The main idea was developed by H.Z. and N.M. and all authors contributed to writing of the text. XRD, SEM and thin section analyses were conducted by N.M. and H.Z. K-Ar geochronology was established by H.Z. and A.T. TEM data were provided by M.S. in collaboration with H.Z. All authors discussed the results and commented on the manuscript.

Bonhomme MG, Thuizat R, Pinault Y, Clauer N, Wendling R, Winkler R (1975) Methodé de Datation Potassium-Argon: Appareillage et Technique, 53 edn. pp., Cent. de Geochem. de la Surface, Univ. Louis Pasteur, Strasbourg, France
Clauer N, Zwingmann H, Liewig N, Wendling R (2012) Comparative ⁴⁰Ar/³⁹Ar and K-Ar dating of illite-type clay minerals: a tentative explanation for age identities and differences. Earth-Sci Rev 115:76–96. https://doi.org/10.1016/j.earscirev.2012.07.003
Clauer N, Chaudhuri S (1995) Clays and Crustal Cycles. Springer, Heidelberg
Cohen KM, Finney SC, Gibbard PL, Fan J-X (2013) updated The ICS International Chronostratigraphic Cart. Episodes 36:199–204 Updated v2019/05 www. stratigraphy.org/ICSchart/ChronostratChart2019-05.pdf
Dalrymple GB, Lanphere MA (1969) Potassium-Argon Dating: Principles, Techniques and Applications to Geochronology, 258 edn. pp., W. H. Freeman, San Francisco, Calif
Editorial committee of Chubu II (1988) Regional Geology of Japan Part 5 CHUBU II. Kyoritsu Shuppan Co., Ltd., Tokyo. (in Japanese)
Fukuchi R, Fujimoto K, Kameda J, Hamahashi M, Yamaguchi A, Kimura G, Hamada Y, Hashimoto Y, Kitamura Y, Saito S (2014) Changes in illite crystallinity within an ancient tectonic boundary thrust caused by thermal, mechanical, and hydrothermal effects: an example from the Nobeoka Thrust, southwest Japan. Earth Planets and Space 66:116. https://doi.org/10.1186/1880-5981-66-116
Heineke C, Hetzel R, Nilius N-P, Zwingmann H, Todd A, Mulch A, Wölfler A, Glotzbach C, Akal C, Dunkl I, Hampel A (2019) Timing of detachment faulting in a symmetric core complex from K-Ar dating of fault gouge. J Struct Geol 127. https://doi.org/10.1016/j.jsg.2019.103865
Hess JC, Lippolt HJ (1994) Compilation of K-Ar measurements on HD-B1 standard biotite, in Phanerozoic Time Scale, Bull. Liaison Inf., vol. 12, pp. 19–23, edited by G. S. Odin, IUGS Subcomm. Geochronology, Paris
Hetzel R, Zwingmann H, Mulch A, Gessner K, Akal C, Hampel A, Güngör T, Petschick R, Mikes T, Wedin F (2013) Spatio-temporal evolution of brittle normal faulting and fluid infiltration in detachment fault systems - a case study from the Menderes Massif, western Turkey. Tectonics 32:1–13. https://doi.org/10.1002/tect.20031
Inoue A, Velde B, Meunier A, Touchard G (1988) Mechanism of illite formation during smectite-to-illite conversion in a hydrothermal system. Am Mineral 73:1325–1334
Kemp SJ, Gillespie MR, Leslie GA, Zwingmann H, Diarmad S, Campbell G (2019) Clay mineral dating of displacement on the Sronlairig Fault: implications for Mesozoic and Cenozoic tectonic evolution in northern Scotland. Clay Miner 54:181–196. https://doi.org/10.1180/clm.2019.25
Liewig N, Clauer N, Sommer F (1987) Rb–Sr and K–Ar dating of clay diagenesis in Jurassic sandstone oil reservoirs, North Sea, vol 71. American Association of Petroleum Geologists Bulletin, pp 1467–1474
Lynch EA, van der Pluijm B (2017) Meteoric fluid infiltration in the Argentine Precordillera fold-and-thrust belt: Evidence from H isotopic studies of neoformed clay minerals. Lithosphere 9:134–145. https://doi.org/10.1130/L568.1
Mancktelow N, Zwingmann H, Campani M, Fügenschuh B, Mulch A (2015) Timing and conditions of brittle faulting on the Silltal-Brenner Fault Zone, Eastern Alps (Austria). Swiss J Geosci 108:305–326. https://doi.org/10.1007/s00015-015-0179-y
Mancktelow N, Zwingmann H, Mulch A (2016) Dating of fault gouge from the Naxos detachment (Cyclades, Greece). Tectonics 35:2334–2344. https://doi.org/10.1002/2016TC004251
Middleton AW, Uysal IT, Bryan SE, Hall CM, Golding SD (2014) Integrating ⁴⁰Ar–³⁹Ar, ⁸⁷Rb–⁸⁷Sr and ¹⁴⁷Sm–¹⁴³Nd geochronology of authigenic illite to evaluate tectonic reactivation in an intraplate setting, central Australia. Geochim Cosmochim Acta 134:155–174. https://doi.org/10.1016/j.gca.2014.02.048
McDougall I, Roksandic Z (1974) Total fusion ⁴⁰Ar/³⁹Ar ages using HIFAR reactor. J Geol Soc Aust 21:81–89. https://doi.org/10.1080/00167617408728836
Meunier A, Velde B (2004) Illite: Origins, Evolution and Metamorphism, 286 edn. pp., Springer, Berlin
Moreno T, Wallis S, Kojima T, Gibbson W (eds) (2016) The Geology of Japan, 522 edn. pp., Geological Society, London
Mottram CM, Kellett D, Baressi T, Zwingmann H, Friend M, Todd A, Percival JB (2020) Syncing fault rock clocks: Direct comparison of U-Pb carbonate and K-Ar illite fault dating methods. Geology 48:1179–1183. https://doi.org/10.1130/G47778.1
Nakajima T, Williams IS, Watanabe T (1993) SHRIMP U-Pb ages of the Ryoke and Sanyo granitioids in Southwest Japan. Abstract of the 100th Annual Meeting of the Geological Society of Japan, 358. https://doi.org/10.14863/geosocabst.1993.0_584
Niwa M, Mizuochi Y, Tanase A (2009) Reconstructing the evolution of fault zone architecture: Field-based study of the core region of the Atera Fault, Central Japan. Isl Arc 18:577–598. https://doi.org/10.1111/j.1440-1738.2009.00674.x
Niwa M, Mizuochi Y, Tanase A (2015) Changes in chemical composition caused by water–rock interactions across a strike-slip fault zone: case study of the Atera Fault, Central Japan. Geofluids 15:387–409. https://doi.org/10.1111/gfl.12096
Nuriel P, Weinberger R, Kylander-Clark ARC, Hacker BR, Craddock JP (2017) The onset of the Dead Sea transform based on carbonate age-strain analyses. Geology 45:587–590. https://doi.org/10.1130/G38903.1
Odin GS, 35 collaborators (1982) Interlaboratory standards for dating purposes, in Numerical Dating in Stratigraphy, vol. 1, edited by G. S. Odin, pp. 123–148, John Wiley, Chichester, U. K
Pevear DR (1999) Illite and hydrocarbon exploration. Proceedings of the National Academy of Sciences, 96, 3440–3446
Roberts NMW et al (2020) Laser ablation inductively coupled plasma mass spectrometry (LA- ICP-MS) U-Pb carbonate geochronology: Strategies, progress, and limitations. Geochronology 2:33–61. https://doi.org/10.5194/gchron-2-33-2020
Scholz CH (2002) The Mechanics of Earthquakes and Faulting, 471 pp., 2nd edition. Cambridge University Press, Cambridge, UK
Shimizu S, Yamazaki M, Itaya T (1988) K-Ar ages of Plio-Pleistocene volcanic rocks in the Ryohaku- Hida mountains area, Japan. Bull Hiruzen Res Inst 14:1–36 (in Japanese with English abstract)
Shirahase T (2005) Rb-Sr whole-rock isochron ages and Sr isotopic ratios of the Nohi Rhyolite. Monogr Association Geol Collab Japan 53:119–127 (in Japanese with English abstract)
Suzuki K, Adachi M (1998) Denudation history of the high T/P Ryoke metamorphic belt, southwest Japan: Constraints from CHIME monazite ages of gneisses and granitoids. J Metamorph Geol 16:23–37
Suzuki K, Morishita T, Kajizuka I, Nakai Y, Adachi M, Shibata K (1994) CHIME ages of monazites from the Ryoke metamorphic rocks and some granitoids in the Mikawa-Tono area, central Japan. Bull Nagoya Univ Furukawa Museum 10:17–38 (in Japanese with English abstract)
Steiger RH, Jäger E (1977) Subcommission on geochronology: convention on the use of decay constants in geo-and cosmochronology. Earth Planet Sci Lett 36:359–362
Tagami T (2012) Thermochronological investigation of fault zones. Tectonophysics 538–540. https://doi.org/10.1016/j.tecto.2012.01.032
Takagi H, Iwamura A, Awaji D, Itaya T, Okada T (2005) Dating of fault gouges from the major active faults in southwest Japan; constraints from integrated K/Ar and XRD analyses. - in Faults, fluid flow and petroleum traps, American Association of Petroleum Geologists Memoir, 85, edited by R. Sorkhabi and Y. Tsuji, 287–301. https://doi.org/10.1306/1033729M853139
Toda S (2016) Crustal earthquakes. In The Geology of Japan, edited by Moreno, T., Wallis, S., Kojima, T. and Gibbson, pp. 371–408, Geological Society, London
Toda S, Inoue D, Miyakoshi K (1996) Paleoseismicity of the Atera Fault System, Central Japan, during the Holocene (Part 1) – Fault activity of the central to southern part and timing of the most recent faulting. Civil Engineering Laboratory Reports, Central Research Institute of Electric Power Industry. (in Japanese with English abstract)
Torgersen E, Viola G, Zwingmann H, Henderson ICH (2015) Inclined illite K-Ar age spectra in brittle fault gouges. Terra Nova 27:106–113. https://doi.org/10.1111/ter.12136
Tsukamoto S, Tagami T, Zwingmann H (2020) Direct dating of fault movement, in Understanding Faults, Elsevier, edited by D. Tanner and C. Brandes, 257–282. https://doi.org/10.1016/B978-0-12-815985-9.00007-2
Ujike O, Iizuka Y, Nakano S (1992) K-Ar ages of the Ueno basaltic rocks. J Mineralogy Petrol Economic Geol 87:102–106 (in Japanese with English abstract)
Uto K, Yamada N (1985) K-Ar age of Ueno basalt, Sakashita-cho and a basalt lava south of Takayama- shi, Gifu Prefecture, central. Japan Bull Geol Surv Japan 36:47–52 (in Japanese with English abstract)
Uysal T, Delle Piane C, Todd A, Zwingmann H (2020) Precambrian faulting episodes and insights into the tectonothermal history of North Australia: Microstructural evidence and K–Ar, ⁴⁰Ar–³⁹Ar, and Rb–Sr dating of syntectonic illite the intracratonic Millungera Basin. - Solid Earth 11:1653–1679. https://doi.org/10.5194/se-11-1653-2020
Viola G, Zwingmann H, Mattila J, Kapyaho A (2013) K-Ar illite age constraints on the Proterozoic formation and reactivation history of a brittle fault in Fennoscandia. Terra Nova 25:236–244. https://doi.org/10.1111/ter.12031
Viola G, Scheiber T, Fredin O, Zwingmann H, Margreth A, Knies J (2016) Deconvoluting complex structural histories archived in brittle fault zones. Nat Commun 7:13448. https://doi.org/10.1038/ncomms13448
Vrolijk P, van der Pluijm BA (1999) Clay gouge. J Struct Geol 21:1039–1048. https://doi.org/10.1016/S0191-8141(99)00103-0
Vrolijk P, Pevear D, Covey M, LaRiviere A (2018) Fault gouge dating: history and evolution. Clay Miner 53:305–324. https://doi.org/10.1180/clm.2018.22
Yamada N, Koido Y (2005) Nohi Rhyolite: Distribution, basement rocks, ages and lithologic features. Monogr Association Geol Collab Japan 53:15–28 (in Japanese with English abstract)
Yamada N, Koido Y, Harayama S (2005) Volcanostratigraphy of the Nohi Rhyolite. Monogr Association Geol Collab Japan 53:29–69 (in Japanese with English abstract)
Yamasaki S, Zwingmann H, Yamada K, Tagami T, Umeda K (2013) Constraining timing of brittle deformation and faulting in the Toki granite, central Japan. Chem Geol 351:168–174. https://doi.org/10.1016/j.chemgeo.2013.05.005
Zwingmann H, Mancktelow N (2004) Timing of Alpine fault gouges. Earth Planet Sci Lett 223:415–425. https://doi.org/10.1016/j.epsl.2004.04.041
Zwingmann H, Offler R, Wilson T, Cox S (2004) K-Ar dating of fault gouge in the northern Sydney basin, Australia – implications for the breakup of Gondwana. J Struct Geol 26:2285–2295. https://doi.org/10.1016/j.jsg.2004.03.007
Zwingmann H, Mancktelow N, Antognini M, Lucchini R (2010a) Dating of shallow faults – new constraints from the AlpTransit tunnel site (Switzerland). Geology 38:487–490. https://doi.org/10.1130/G30785.1
Zwingmann H, Yamada K, Tagami T (2010b) Timing of brittle faulting within the Nojima fault zone, Japan. Chem Geol 275:176–185. https://doi.org/10.1016/j.chemgeo.2010.05.006
Zwingmann H, Han R, Ree JH (2011) Cretaceous reactivation of the Deokpori Thrust, Taebaeksan Basin, South Korea, constrained by K-Ar dating of clayey fault gouge. Tectonics 30:TC5015. https://doi.org/10.1029/2010TC002829
Zwingmann H, den Hartog SA, Todd A (2019) The effect of sub-seismic fault slip processes on the isotopic signature of clay minerals–Implications for K-Ar dating of fault zones. Chem Geol 514:112–121. https://doi.org/10.1016/j.chemgeo.2019.03.034

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Reconstruction of the evolution and deformation history of an active fault – implications from the Atera fault, Central Japan

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K-Ar data

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Implications for geology of Central Japan

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