Geosites are sites of scientific interest based on geology or geomorphology that can serve various purposes such as research, conservation, education, tourism, and sustainable development. Quantifying their value to potential visitors and researchers is widely recognized as a useful tool for the effective development and management and for the protection of geological heritage of a certain area. Although many quantitative evaluation schemes have been proposed for various types of sites in Europe, over the past two decades, the schemes can give widely variable results for the same sites due to differences in needs and expectations, which can present difficulties for inter-site comparison for management purposes. It therefore remains necessary to develop a uniform evaluation scheme with low overall complexity to assist with prioritization and management. This study presents a new evaluation scheme based on the most commonly used attributes for quantifying geosites as applied to geomorphological landscapes and geological processes with natural and/or cultural heritage. The utility of the evaluation scheme is demonstrated through application to selected geosites in Japan, Germany, and Poland. The results clearly show the present condition of geosites, identify their promotional advantages and disadvantages, and provide a widely applicable reference for planning and development of such sites for geotourism.

The stress conditions of the ductile-to-brittle regime have been assessed along the Asuke Shear Zone (ASZ), which strikes NE-SW in the Cretaceous Ryoke granite terrain in SW Japan. Along the ASZ, pseudotachylyte and mylonitized pseudotachylyte are locally developed together with cataclasite. The simultaneous operation of dislocation creep and grain-size-sensitive creep, as indicated by the coexistence of the Z-maximum and relatively random c-axis lattice preferred orientations as well as the sizes of dynamically recrystallized quartz grains (6.40-7.79 mu m) in the mylonitized pseudotachylyte, suggest differential stresses of 110-130 MPa at similar to 300 degrees C. The e-twin morphology, twinning ratio, and distribution of the glide direction on the e-twin plane of the twinned calcite in the amygdules of the pseudotachylyte suggest the stress conditions of the sigma(1) and sigma(3) axes trend 228 degrees and 320 degrees and plunge 55 degrees and 1 degrees, respectively, and indicate differential stresses of 40-80 MPa at 150-200 degrees C. Based on kinematic indicators in the fault rocks, the stress conditions estimated from calcite twins, and the cooling history of the granitic protolith, the ASZ is inferred to have been activated under a stress state that caused sinistral normal movements before and after pseudotachylyte formation at 70-50 Ma. (C) 2016 Elsevier Ltd. All rights reserved.

Crystallographic orientations of minerals were determined by electron backscatter diffraction (EBSD) under a scanning electron microscope. In this study, we introduce a technique for vibratory polishing of rock samples using colloidal silica (CS), for EBSD analysis of quartz in granite and calcite in limestone. Evaluation of the surface state consisted of a band contrast (BC) measure to represent the surface state, a hit rate to represent the success rate of indexing, and a mean angular deviation (MAD) to represent the accuracy of indexing. The factor that most affected the BC and the hit rate was the total amount of displacement of the sample. However, the BC and hit rate also showed a dependency on the crystallographic orientation. When eight Kikuchi bands were detected, the value of the MAD was < 1°, and the MAD was independent of the BC. The BC measure showed that the optimal CS polishing times for quartz and calcite were 3 hours and 1 hour, respectively. When preparing a sample with for the first time, CS polishing for 3 hours and detection of the eight Kikuchi bands provide the most effective method for determining crystallographic orientations.

We investigated the petrology and geochronology of Pre-Neogene basement core samples obtained at Kukizaki (southern Tsukuba observatory well) in 2006 by the National Research Institute for Earth Science and Disaster Prevention (NIED). The depths of the excavated core samples of the basement rocks were 801-804 m, 944-947 m, 1,111-1,114 m, and 1,114-1,117 m. The basement rocks consisted mainly of mylonitized hornblende biotite tonalite (shallower cores) and hornblende gabbro (deeper cores). In the 944-947-m core, the mylonitic foliation dips northward at low to high angles (average dip, ~40°), as determined from an oriented sample. The thickness of the mylonite zone is at least 200 m. Kinematic indicators within the oriented mylonite sample indicate a top-to-the-southwest thrust/sinistral shear sense. The K-Ar hornblende age obtained on the gabbro (depth, 1,115 m)is 66.1±1.1 Ma, and the SHRIMP U-Pb zircon age of tonalite (depth, 803 m) is 86.3±0.6 Ma. Initial ⁸⁷Sr/⁸⁶Sr ratios (SrI), calculated using the U-Pb ages of whole-rock samples of both tonalite (depth, 803 m) and gabbro (depth, 1,115 m), are 0.7067 and 0.7073, respectively. These isotopic ages and SrI values of rocks from the Kukizaki core are concordant with those of the Ryoke granitic rocks, including the Iwatsuki mylonite obtained at a depth of 3506.6 m in the Kanto Plain, whereas the ages are discordant with the Tsukuba granitic rocks, which are younger in age (ca. 60 Ma) and show higher SrIs (>0.711). However, zircon fission-track age dating of the tonalite sample (depth, 803 m) yielded an age of 16.9±0.6 Ma (Miocene), which is discordant with the U-Pb age but is similar to the K-Ar biotite age of 17.65±0.29 Ma of the Iwatsuki quartz porphyry (depth, 3346-2864 m), suggesting that thermal effects of the acidic intrusion at Iwatsuki extend eastward to Kukizaki. Considering the isotopic data and the sinistral/thrust shear sense in the Kukizaki core, we infer that the mylonite zone in the Kukizaki core is the northeastern extension of the mylonite zone observed in the Ryoke belt along the Median Tectonic Line in the Kanto region.

This paper describes newly discovered pseudotachylyte along the Atotsugawa Fault at the Magawa outcrop, where this fault divides Quaternary deposits in the SW from Triassic Hida granitic rocks to the NE. Within several meters of the fault surface, pseudotachylyte veins are found with a thickness of less than 10cm, but are displaced by fault brecciation. Zircon fission track dating of pseudotachylyte samples yields ages of 48.6-50.2 Ma (sample AT-A), 55.1 Ma (AT-A'-1) and 60.9 Ma (AT-D-1); the latter is similar to the fission track ages of 56.1-60.1 Ma for granitic protoliths. The results of fission track length analyses in zircon suggest that pseudotachylytes (AT-A and AT-D-1) and protolith granite are mostly annealed. Consequently, the pseudotachylyte (AT-A) reached the highest temperature during 48.6-50.2 Ma, thereby resetting the fission track system totally in zircon during faulting. Another pseudotachylyte (AT-A'-1) and its wall rock granite contain shortened tracks within zircon grains suggesting partial annealing. The age distribution pattern of the former also contains decomposed age after the normality test (Shapiro-Wilk test) in which the major age yields 52.5 Ma. Accordingly, these pseudotachylytes yield a peak age of about 50 Ma, whereas the peak ages of one pseudotachylyte (AT-D-1) and the protolith Hida granitic rocks are about 60 Ma, representing the thermal effects not caused by frictional heating but by intrusions of Late Cretaceous to Paleogene granitoids that are probably concealed below the exposed Triassic Hida granitic rocks. Such thermal effects did not affect the K-Ar muscovite age (149 Ma) for the protolith granite because of the higher closure temperature of this system. Using the new geochronological data, we can elucidate the cooling history of the Hida granitic rocks, and constrain the timing of the main pulse of pseudotachylyte generation along the Atotsugawa Fault at about 50 Ma.

Measurements of temporal changes in the three-dimensional (3D) orientation and density of intracrystalline healed and sealed (open) microcracks in quartz grains have enabled the reconstruction of paleostress fields and determination of the history of microcracking in the Late Cretaceous Nojima Granodiorite of northern Awaji Island. This in turn has allowed the determination of the relationship between these features and the Nojima Fault, which was seismically reactivated during the 1995 Kobe Earthquake. The 3D orientations of healed microcracks (HC) indicate that σ₃ stress directions had N–S orientations at almost all locations, whereas sealed microcracks (SC) preserve evidence of NW–SE and N–S σ₃ orientations. K–Ar biotite ages for the Nojima Granodiorite and fluid inclusion formation temperatures (c. 320–370°C) suggest that the healed microcracks formed at around 80 Ma. Fission-track ages of associated pseudotachylytes indicate that initial movements on the Nojima Fault probably occurred at around 56 Ma, with spatial variations in microcrack density indicating that initial faulting occurred after HC formation but before SC formation. This indicates a NW–SE σ₃ orientation during HC formation (after restoration incorporating the clockwise rotation of SW Japan at c. 15 Ma), with the subsequent formation of NE–SW and E–W trending high-angle SCs filled with limonite or iron oxides. These SCs probably formed at shallower crustal depths than the HCs. The fact that the σ_Hmax SC orientation is not consistent with the current NW–SE or WNW–ESE regional stress field means that SC formation must have ceased by the Quaternary. In addition, the HC σ₃ orientation is nearly normal to the general trend of the Median Tectonic Line, suggesting the existence of a significant NW–SE extensional stress field prior to the clockwise rotation of SW Japan, rather than a NW–SE regional compressive field that would be conformable with oceanic plate movement directions during the Late Cretaceous.

We estimated the thickness of the fault damage zone in granitoid along the linan transect at the Median Tectonic Line (MTL) and along the Magawa transect at the Atotsugawa Fault, southwest Japan, based on the density of penetrative mesocracks, and on analyses of intracrystalline strain in pulverized quartz using X-ray line broadening (beta) and the crystallinity index (Cl). The mesocrack density and intracrystalline strain show an increase toward the MTL, from similar to 400 m from the fault. High amounts of intracrystalline strain in quartz, characterized by large beta and low CI. reflect the presence of dense, heterogeneous tangles of short dislocations. For the Atotsugawa Fault, in contrast, we observed no increase in intracrystalline strain within quartz, even within highly fractured rock showing high mesocrack density located close to the fault (similar to 10 m). This difference in the intensity of intracrystalline strain close to the fault between the MTL and the Atotsugawa Fault suggests that dislocation substructures did not accumulate at shallower levels in the brittle regime, but accumulated at deeper levels. Accordingly, analyses of intracrystalline strain in pulverized quartz, using X-ray line broadening and CI are useful in evaluating the degree of cataclasis of quartz-bearing rocks at deeper levels of the brittle regime. (C) 2011 Elsevier Ltd. All rights reserved.

To constrain the thermal and its spatial conditions of pseudotachylyte formation and cooling, we dated zircons from a pseudotachylyte in the Ryoke belt obtained about 100 m north from the Median Tectonic Line in the Taki area, southwest Japan, and its host rock, the Hatai Tonalite, by the (U-Th)/He method. The ages obtained are 60.3 +/- 2.7 and 55.5 +/- 4.5 (1SE) Ma, respectively, which are essentially the same within the error. This is the first (U-Th)/He age directly measured for a pseudotachylyte. The coincidence between these ages indicates that the pseudotachylyte formed at ca. 60 Ma under the ambient temperature of about 180 degrees C, the closure temperature of zircon (U-Th)/He method. The Fish Canyon Tuff zircon, one of the most well-known geological age standards, was also dated to confirm the validity of our analyses, which yielded the weighted mean age of 29.6 +/- 1.5 (1SE) Ma, consistent with other reported ages. The average cooling rates and denudation rates of the host rock were calculated based on these ages, reported zircon fission-track ages (ca. 70 Ma) and apatite fission-track ages (ca. 40 Ma) as about 12 degrees C/Myr and about 0.6 mm/yr from 70 to 60 Ma, and about 4 degrees C/Myr and about 0.2 mm/yr from 60 to 40 Ma, respectively, assuming that the closure temperatures of zircon and apatite FT methods are 300 degrees C and 110 degrees C, respectively, and a geothermal gradient of 20 degrees C/km. One possible reason of this slow down of denudation rates is the decrease of convergent rate and change in the movement direction of the Pacific Plate relative to the Eurasian Plate along the southwest Japan in the Paleogene. (C) 2011 Elsevier Ltd. All rights reserved.

This report describes the subsurface geology, based on the petrography of rock cuttings taken from bore holes at spa sites, at Shimohara, Tsukuba City, Ibaraki Prefecture, and at Hanai, Noda City, Chiba Prefecture, both upon the Kanto Plain. The cutting samples from Tsukuba (four samples from 1241–1210 m depth) are hornfels, biotite-muscovite schist, and sillimanite-andalusite gneisses that resemble the Tsukuba metamorphic rocks. A single cutting sample from Noda (1295–1300 m depth) is mylonitized biotite granite that is similar in lithology to the Late Cretaceous Name Granite in the Shimonita area, Gunma Prefecture. These results provide new information on the eastern extension of the Ryoke Metamorphic Belt and the southern extension of the Tsukuba Metamorphic Belt. The occurrence of mylonite from Noda also provides important information in terms of constraining the eastern extension of the Median Tectonic Line.

We report a distinct garnet-bearing pumiceous tephra in Lower Pleistocene (following the geological time scale in ISC chart 2009) sediments (Kazusa Group) from outcrops in Choshi (Na-G), Kamakura (KGP), and Aikawa-cho (Kanagawa, Mk19), and from a spot core sample (depth: 1217 m) at Koto (Tokyo, KT1217) in the Southern Kanto region. To correlate these garnet-bearing tephras and discuss their possible source, we examined their petrography and performed EPMA and grain-size analyses of constituent garnets, as well as considering their stratigraphic context.<br>The garnet-bearing tephras contain sponge- and fiber-shaped glass shards, abundant garnet grains that contain ilmenite inclusions, minor amphibole (orthoamphibole and hornblende), minor biotite, and rare ortho- and clinopyroxenes and cordierite. They also contain rock fragments of green schist and minor granitic rocks. The range of chemical compositions of garnet is X_Fe=0.50−0.59, X_Mn=0.18−0.26, X_Mg=0.14−0.17, and X_Ca=0.07−0.11, similar to that of garnet phenocrysts from rhyolite (c. 2.5 Ma) in the Nakagawa area, southern Tanzawa Mountains. This garnet composition is markedly different from that of garnet phenocrysts from other Neogene-Quaternary tephras and volcanic rocks in central Japan. The age of the studied garnet tephras is estimated at about 2.5 Ma, based on the stratigraphic horizons at the CN12b-CN12c zone (Okada and Bukry, 1980), the NPD9 zone (Yanagisawa and Akiba, 1998), and the N.21 zone (Yanagisawa, 2006), as well as the magnetostratigraphy of the lower part of the Matuyama Chron.<br>The results indicate that the garnet tephras at the four locations are clearly correlatives, representing the newly defined Tanzawa garnet pumice (Tn-GP). The likely source of Tn-GP is located west of Aikawa-cho, in the Tanzawa Mountains, given the westward increase in garnet grain size, the existence of green schist fragments that correlate with the Tanzawa Group, and the existence of ∼2.5 Ma garnet-bearing rhyolite that intrudes into the Tanzawa Group. Tn-GP is likely to play an important role in terms of constraining the P/P boundary in the new geological time scale, the age of the Kurotaki Unconformity, and the subsurface geology of the Kanto Plain.

The deformation of serpentinites along the Sashu Fault, Saganoseki Peninsula, SW Japan, involved both mylonitization and brecciation. The brecciation was accompanied by metasomatism, and the metasomatized rocks record additional ductile deformation. Serpentinite mylonite is composed mainly of antigorite, with minor magnetite and Cr-spinel. Foliation and lineation in this rock type are defined by the shape preferred orientation of antigorite and the alignment of fine-grained magnetite and carbonate minerals. The antigorite also shows a lattice preferred orientation (LPO), as measured with a universal stage, with c axes oriented near-perpendicular to the foliation and b axes oriented parallel to the lineation. Brecciation is concentrated in the reaction zone along the boundary between serpentinites and surrounding country rocks. Talc and chlorite schists developed in this zone as a result of associated metasomatism and deformation; consequently, they contain composite planar fabrics and drag folds. The breccias themselves are composed of serpentinite fragments cut by veins of calcite and talc. Analyses of fluid inclusions in calcite from the breccia indicate that brecciation occurred at 200-300 degrees C at depths of 3.8-11.8 km. Metasomatic reactions, particularly the formation of talc, contributed to weakening of this serpentinite-bearing fault zone. (C) 2010 Elsevier Ltd. All rights reserved.

This paper discusses the paleostress field and its history in the Tanzawa tonalite body in the Izu arc-Honshu arc collision zone, as determined from the 3-D orientation of healed and sealed intracrystalline microcracks in quartz grains, in conjunction with microthermometry of fluid inclusions in healed microcracks. Crosscutting relationships indicate that the healed microcracks formed prior to the formation of sealed (and possibly open) microcracks. Both healed and sealed microcracks strike NNE-SSW and dip vertically. It is estimated that healed microcracks were formed at a pressure range of 0.20-0.29 GPa and a temperature range of 275-410°C, based on isochores inferred from microthermometry of the fluid inclusions and with reference to the geothermal gradient (30-50°C/km). The formation temperature of the healed microcracks can be correlated with the closure temperature of the biotite K-Ar system, considering that the Azegamaru and Yushin plutons of the Tanzawa tonalite body yield K-Ar biotite ages of 5-4 Ma. The healed microcracks probably formed in the early Pliocene during collision of the Tanzawa block against the Honshu arc. Because the dominantly NNE-SSW trending microcracks were rotated clockwise by 10° during the collision of the Izu block against the Honshu arc at about 1 Ma, as deduced from reported paleomagnetic data, the orientation of maximum horizontal stress (σ_Hmax) in the Tanzawa tonalite body during and after its collision is inferred to have trended nearly N-S. Recently reported in situ stress measurements in the Tanzawa tonalite body indicate that σ_Hmax trends NNE-SSW. Accordingly, the N-S to NNE-SSW trends in σ_Hmax have not changed greatly during or after the formation of healed microcracks in the Tanzawa tonalite body, which occurred at about 5-4 Ma.

An anisotropy of magnetic susceptibility (AMS) analysis was conducted for a typical S-C mylonite in a small-scale ductile shear zone derived from Late Cretaceous magnetite-free granite in the Ryoke Belt, Teshima Island, southwest Japan. In such mylonites, paramagnetic minerals such as biotite and hornblende, which define foliations, are assumed to control the AMS. Accordingly, we attempted to measure the orientations of both minerals to correlate the S-C-C&apos; fabric to the AMS using techniques of microscopic and back-scattered electron (BSE) image analyses. A measured magnetic fabric of the S-C mylonite that is expressed by a K(min) normal plane (K(max)-K(int) plane) approximated S foliation, K(max) orientation coincided well with the orientations of mean resultant vectors for long axes of biotite and minor hornblende, whereas K(max) did not coincide well with those of the mean resultant vectors for long axes of the brighter domain (aggregates of biotite and minor hornblende) from the binary BSE image. These results show that the magnetic fabric fairly reflects the shape preferred orientation of individual grains of paramagnetic monoclinic minerals, especially biotite, which forms the S-C-C fabric. (C) 2009 Elsevier Ltd. All rights reserved.

Fission-track (FT) dating of pseudotachylyte (PST) associated with the Median Tectonic Line (MTL) in the Taki area, Mie Prefecture, SW Japan, provides new constraints on the timing of movement upon this fault. A PST vein with a thickness of about 5 cm yields a zircon FT age of 60.0 ± 3.5 Ma (1σ). In contrast, a weighted average of zircon FT ages obtained for protolith samples (cataclastic mylonitized Hatai Tonalite) collected 10 cm and 15 m from the PST vein boundary is 69.8 ± 1.2 Ma, which is significantly older than the age of the PST. Decomposition of feldspars in the PST suggests that the temperature exceeded 1100°C, which is sufficient to completely erase previous fission tracks in zircon within several seconds. The distribution of fission-track lengths in zircon from the PST vein also supports the interpretation that the zircon FT age was completely reset during frictional fusion of the PST vein. Considering an apatite FT age of 38.0 ± 1.5 Ma for the host rock, the age of the PST indicates that the frictional fusion was occurred during cooling of the Ryoke granite at temperatures between 250°C (closure temperature of the zircon FT system) and 100°C (closure temperature of the apatite FT system). This PST age is comparable with the oldest K-Ar age obtained for fine fractions of MTL fault gouge derived from both the Sanbagawa pelitic schist and the Izumi Group in Shikoku, indicating that the initiation of brittle fault movement associated with formation of the PST and/or fault gouges along the MTL had occurred by 60 Ma.

The exhumation of high-P/T metamorphic rocks plays a key role in the rearrangement of the geotectonic framework in arc-trench systems. The deposition of clasts of exhumed rocks constrains the timing of exhumation and the denudation history. We obtained the K-Ar ages of clasts from the Miocene Aoiwa Conglomerate, Hiki Hills, eastern Kanto Mountains. The Aoiwa Conglomerate is an unsorted breccia (maximum clast diameter up to ca. 3 m) composed of clasts of high-P/T metamorphic rocks (greenstones and crystalline schists), granitic rocks, low-P/T metamorphic rocks (mafic to felsic plutono-metamorphic rocks), and sedimentary rocks.<br>The clasts of high-P/T metamorphic rocks were previously considered to have been derived from the Sanbagawa metamorphic rocks, which have been exposed nearby since the Miocene. However, schist clasts yield K-Ar phengite ages of 127.2-121.0 and 98.4-80.7 Ma, significantly older than ages obtained for the Sanbagawa metamorphic rocks in the Kanto Mountains, although the mineral assemblage and metamorphic grade of clasts are similar.<br>Clasts of granitic rocks and low-P/T metamorphic rocks yield K-Ar hornblende ages of 131.5-114.0 Ma and phengite ages of 97.8-88.9 Ma, significantly older than ages obtained for Ryoke granites in the Kanto Mountains. In addition, a tonalite mylonite clast yields a lower ⁸⁷Sr/⁸⁶Sr initial ratio (0.70510-0.70520 or 0.70498-0.70505) than that of the Ryoke granites.<br>Based on the results of K-Ar dating and a detailed petrologic study of the clasts, we conclude that the schist clasts were derived from an older unit within the Sanbagawa metamorphic rocks and that granitic and mafic metamorphic clasts were derived from the paleo-Ryoke terrane, which previously overlaid the Sanbagawa metamorphic rocks and today occurs only as sporadic allochthonous rocks. The Aoiwa Conglomerate was probably deposited in association with denudation of the paleo-Ryoke and uppermost Sanbagawa terranes. Deposition was accelerated during exhumation of Sanbagawa metamorphic rocks during the Middle Miocene.

Based on the 3-D orientations of intracrystalline healed, sealed and open extension microcracks in quartz grains in the Late Cretaceous Toki Granite, we discuss the paleostress field and the history of microcracking combining the microthermometry of fluid inclusions in healed microcracks and sealing material identification in sealed microcracks. Twenty one oriented samples are collected from the DH-15 core (240-1000 mabh) drilled by Japan Atomic Energy Agency (JAEA) and additionally five oriented samples from outcrops in the Tono region. 3-D orientations of healed microcracks indicate the σ_<Hmax> orientation of N-S to NW-SE in almost all sites, whereas those of sealed and open microcracks indicate the dominant σ_<Hmax> orientation of E-W. Two or three orthogonal sets of microcracks are common in both healed and sealed (+ open) microcracks. The formation of these sets can be attributed to the switch of principal stress axis due to stress release just after the crack formation. Healed microcracks probably reflect more regional paleostress field because of consistency of the orientations than the case of sealed and open microcracks that show rather scattering orientations. N-S to NW-SE trending healed microcracks are formed around 60 Ma on the basis of K-Ar biotite ages of the Toki Granite and formation temperature (c. 300-400℃) of fluid inclusions estimated from microthermometry in the case of intrusion depth (3.5 km = 100 MPa) of the Toki Granite. Thus the σ_<Hmax> orientation trended NW-SE after the restoration of clockwise rotation of SW Japan at c. 15 Ma. Following the healed microcrack formation, E-W trending high-angle sealed microcracks filled with carbonate mineral are formed. Open microcracks presumably formed at near-surface at the last stage of sealed microcrack formation after c. 20 Ma when the Mizunami Group deposited unconformably on the granite.

Understanding the exhumation process of deep-seated material within subduction zones is important in comprehending the tectonic evolution of active margins. The deformation and slip history of superficial nappe pile emplaced upon high-P/T type metamorphic rocks can reveal the intimate relationship between deformation and transitions in paleo-stress that most likely arose from changes in the direction of plate convergence and exhumation of the metamorphic terrane. The Kinshozan-Atokura nappe pile emplaced upon the high-P/T type Sanbagawa (=Sambagawa) metamorphic rocks is the remnant of a pre-existing terrane located between paired metamorphic terranes along the Median Tectonic Line (MTL) of central Japan. Intra- and inter-nappe structures record the state of paleo-stress during metamorphism and exhumation of the Sanbagawa terrane. The following tectonic evolution of the nappes is inferred from a combined structural analysis of the basal fault of the nappes and their internal structures. The relative slip direction along the hanging wall rotated clockwise by 180 degrees, from S to N, in association with a series of major tectonic changes from MTL-normal contraction to MTL-parallel strike-slip and finally MTL-normal extension. This clockwise rotation of the slip direction can be attributed to changes in the plate-induced regional stress state and associated exhumation of the deep-seated Sanbagawa terrane from the Late Cretaceous (Coniacian) to the Middle Miocene. (C) 2007 International Association for Gondwana Research. Published by Elsevier B.V All rights reserved.

Aso-4 pyroclastic flow is one of the largest volcanic activities in Japan and formed huge caldera of the Aso volcano at about 90,000 years b.p.. This pyroclastic flow brought about accidental clasts of granitic mylonite in the Aso-4 pyroclastic deposit in northern area of the caldera. These granitic mylonite clasts were investigated petrologically and geochronologically, and compared with the Nioki Granite in the Asaji area to the east of the volcano. The Aso-4 granitic clasts are characterized by garnet-muscovite bearing adamelite-granite, and all of them are moderately to strongly mylonitized and show porphyroclastic texture. Their SiO_2 content ranges 71-74 wt.%. The range of garnet composition of the Aso-4 granitic clasts is Alm_<69〜78>, Sps_<14〜27>, Pyr_<0.2〜3.3>, Grs_<1.0〜9.3>. These mineral and chemical compositions are quite similar to those of the Nioki Granite. The K-Ar muscovite age for Aso-4 granitic clasts is 98.4±2.1 Ma, whereas Nioki Granite is 98.8±2.1 Ma. The heat of magma of the volcano did not affect the K-Ar closure system for muscovite when the pyroclastic flow took place, because heating has not fundamentally shortened the fission tracks within zircon grains in the dated clast. Accordingly, the Aso-4 granitic mylonite clasts are correlative with the Nioki Granite, which is also weakly to moderately mylonitized. The intrusive age of the Nioki Granite is also determined using CHIME monazite dating, and the result is 106±4 Ma. This suggests that subsurface ductile mylonite zone initiated around 100 Ma of the major fault extends from Asaji area to the Aso volcano. This fault coincides with the Oita-Kumamoto Tectonic Line, along which the active fault segment has been known. The occurrence of EW extending mylonite zone is also significant evidence in considering the western extension of the Median Tectonic Line in Kyushu.

The Median Tectonic Line (MTL) is Japan's largest onshore fault and has been active since the mid-Cretaceous. Foliated cataclastic fault rocks are exceptionally well exposed in the fault core at Anko, Nagano Prefecture. Following an early phase of mylonitization and exhumation during left-lateral shearing, brittle fracture and cataclasis occurred leading to the development of centimeter- to submillimeter-spaced, fault zone parallel fracture systems. These fracture systems established an initial architectural hierarchy that influenced the subsequent development of foliated cataclasites and gouge. Initially, fracture systems coalesced to form interconnected zones of fine-grained ultracataclasite. Fluid influx at the onset of grain-scale brittle deformation led to precipitation of fibrous chlorite within the ultracataclasites, ultimately leading to the development of an interconnected network of foliated, phyllosilicate-rich cataclasites and gouges in the core of the MTL. The brittle reduction of grain size and ingress of a chemically active fluid phase simultaneously promoted reaction softening and diffusive mass transfer in the foliated ultracataclasites, leading to rate-dependent "frictional-viscous" flow at sub-Byerlee friction values. Associated weakening is indicated by the preferential localization of deformation within the ultracataclasites. A protracted sequence of carbonate mineralization and cementation events is also recognized during the fault rock evolution and suggests episodic periods of fluid overpressuring. A crustal-scale fault zone model is proposed, suggesting that the foliated cataclasites/gouges are weak in the long term and represent shallower crustal equivalents of phyllonitic fault rocks exposed in more deeply exhumed fault zones, including other parts of the MTL.

Zircon fission-track (FT) and U-Pb analyses were performed on zircon extracted from a pseudotachylyte zone and surrounding rocks of the Asuke Shear Zone (ASZ), Aichi Prefecture, Japan. The U-Pb ages of all four samples are similar to 67-76 Ma, which is interpreted as the formation age of Ryoke granitic rocks along the ASZ. The mean zircon FT age of host rock is 73 +/- 7 (2 sigma) Ma, suggesting a time of initial cooling through the zircon closure temperature. The pseudotachylyte zone however, yielded a zircon FT age of 53 +/- 9 (2 sigma) Ma, statistically different from the age of the host rock. Zircon FTs showed reduced mean lengths and intermediate ages for samples adjacent to the pseudotachylyte zone. Coupled with the new zircon U-Pb ages and previous heat conduction modeling, the present FT data are best interpreted as reflecting paleothermal effects of the frictional heating of the fault. The age for the pseudotachylyte coincides with the change in direction of rotation of the Pacific plate from NW to N which can be considered to initialize the NNE-SSW trending sinistral-extensional ASZ before the Miocene clockwise rotation of SW Japan. The present study demonstrates that a history of fault motions in seismically active regions can be reconstructed by dating pseudotachylytes using zircon FT thermochronology. (c) 2006 Elsevier B.V. All rights reserved.

Ductile to brittle fault rocks including pseudotachylyte are narrowly distributed along the NE-SW trending Asuke Shear Zone in the Inagawa granite bodies of the Ryoke Belt, Chubu region, SW Japan. The Asuke Shear Zone is composed of many small-scale shear zones with left-stepping en echelon arrangement (P shear orientation for sinistral shear zone). Kinematic indicators and stretching lineations in mylonite and foliated pseudotachylyte of the small-scale shear zones indicate sinistral - extensional shear. These lines of evidence suggest that the Asuke Shear Zone has thicken under transtensional tectonic regime. The existence of mylonitized pseudotachylyte and mylonitized cataclasite, and fractured mylonite suggests that the major deformation along the shear zone took place in cataclastic-plastic transition regime. Pseudotachylyte fault veins tend to generate along the P shear whereas cataclasite along the Y and R_1 shear surfaces. This result is explained by that frictional fusion preferentially occurs along mesoscopically transpressional fault surface where the rate of heat production per unit area is relatively high.

The Tanakura Shear Zone is a NNW-SSE trending major fault which divides pre-Neogene basement rocks into NE and SW Japan. Within the study area, the fracture zone is 3 to 4km in width, and consists of various kinds of fault rocks derived from the Jurassic accretionary complex of the Yamizo Belt, together with metamorphic and granitic rocks derived from the Abukuma Belt. Distribution patterns of brittle faults, fabric patterns and shear senses of fault gouge within the fault zone are described to interpret kinematics of the Tanakura Shear Zone during the Late Cenozoic. Based on paleo stress fields estimated from shear senses of fault gouge by multiple inverse methods (a technique to separate stresses based on heterogeneous fault-slip data), two brittle deformation stages (D_1 and D_2) are identified. During the Paleogene, a sinistral brittle fault set was originally generated. During exhumation of the shear zone, the fault kinematics inverted from a sinistral (D_1: 17Ma) to a dextral movement (D_2: 15Ma). Therefore, from Paleogene to the mid-Miocene, fault gouges within the Tanakura Shear Zone were reactivated under switched stress fields.

Fission-track dating was carried but on zircon grains from pseudotachylyte associated with a Late Pleistocene landslide (Tsergo Ri landslide) in Langtang Himal, Nepal. Zircon grains were separated from an injection pipe of glassy and vesicular pseudotachylyte about 10 cm in diameter. The resulting age of 51 +/- 13 Ka lies between the two subpeaks (70 and 20 Ka) of the Wurm glacial period, and is concordant with the previous age estimate from geomorphological evidence (i.e. older than 25-30 Ka). This is the first reliable isotopic age for a landslide-generated pseudotachylyte excluding the possibility of contamination by an inherited age. (c) 2006 Elsevier Ltd. All rights reserved.

Fault gouges were mapped and collected along the Atotsugawa fault, one of the major active faults in Japan, and along the Mozumi-Sukenobu fault, branching off from the Atotsugawa fault. Most of the fault gouge samples contain mica clay minerals, chlorite, smectite, and quartz. To constrain the timing of faulting, K-Ar and x-ray diffraction analyses (XRD) were carried out on mica clay minerals separated from the gouge samples. Each gouge sample was divided into four grain-size fractions of 5-2, 2-1, 1-0.35, and 0.35-0.05 μm. Kübier illite crystallinity indices for the finer grain-size fractions (0.05-1 μm
illite crystallinity = 0.4-0.8) were found to be higher than those for the coarser fractions (1-5 μm
illite crystallinity = 0.3-0.6), indicating the relatively higher concentration of authigenic mica clay minerals. The genesis of the clay minerals was probably related to hydrothermal alteration events associated with fault activity in the finer fractions. K-Ar ages were younger for the finer fractions of all samples. One sample from the Atotsugawa fault yields the youngest age of 61 Ma for the finer two fractions, which probably dates the thermal activity associated with the fault because of a similar age for the finer two fractions. This also suggests that the contamination of protolith mica is negligible for these samples. The finest fraction of the Mozumi-Sukenobu fault gouge derived from the interbedded sandstone and mudstone of the Tetori Group (Upper Jurassic-Lower Cretaceous) gives a K-Ar age of 45 Ma. Although this gouge sample is derived from mudstone and sandstone and, thus, the contamination of protolith illite cannot be identified by illite crystallinity, the age probably approximates that of a hydrothermal alteration event associated with the fault activity, because the age is significantly younger than the sedimentary age of the protolith Tetori Group. These K-Ar ages from the Atotsugawa and Mozumi-Sukenobu faults are compared with previous K-Ar ages of fault gouges from major active faults in Japan, including the Median Tectonic Line in Shikoku-Kinki and the Atera fault. The K-Ar data from these faults indicate that the major active faults in the Inner Zone of Southwest Japan were initiated at 60-50 Ma. Heterogeneity in and around the Late Cretaceous granitic terrane, especially the boundary of rigid granitic body and soft accretionary complex, seems to be the preferred sites for fault initiation. Copyright © 2005 by The American Association of Petroleum Geologists.

The Asaji metamorphic rocks have previously been considered as a member of the Ryoke belt. However, the occurrence of ultramafic bodies interlayered in the Chokai Unit and the Hikata Unit has led to an alternative suggestion for the correlation of the Asaji metamorphic rocks with other terranes, such as the Sambagawa terrane or the Kurosegawa terrane. To discuss these possibilities, we examined the petrological characteristics of the ultramafic rocks and chemical compositions of chromian spinel. The ultramafic body is composed mainly of pyroxenites and serpentinite. Spinel in the serpentinite has high Cr# (Cr/(Cr+Al) atomic ratio) of 0.7-0.9 and very low TiO_2content (<0.5 wt%). Although the ultramafic body suffered weak contact metamorphism, chemical composition of chromian spinel has preserved those in the peridotite stage. The spinel chemistry suggests that the original peridotite is a refractory residue after the extraction of basaltic magma. The pyroxenites are subdivided into clinopyroxenite, olivine-clinopyroxenite and olivine-websterite. Compositions of clinopyroxene from the pyroxenites are similar to those of arc comulates. It suggests that the peridotites (now completely serpentinitized) and pyroxenites were formed in a subduction zone. Chemical compositions of spinel in the serpentinites from the Saganoseki area (the Sambagawa metamorphic belt), the Sashu Fault on the southern margin of the Sambagawa metamorphic belt, and the Miemachi and Usuki area (the Kurosegawa belt) exposed near the Asaji metamorphic rocks were analyzed for comparison. Spinels from the Saganoseki area are clearly different in Cr# and TiO_2, content from those from the Asaji area and also from the Sashu Fault. On the other hand, the chemical compositions of spinels from the Miemachi and Usuki area (the Kurosegawa belt) resemble to those from the Asaji area, suggesting a similar tectonic setting for the formation of those ultramafic rocks.

This paper reviews recent progress on the geotectonic evolution of exotic Paleozoic terranes in Southwest Japan, namely the Palco-Ryoke and Kurosegawa terranes. The Palco-Ryoke Terrane is composed mainly of Permian granitic rocks with hornfels, mid-Cretaceous high-grade metamorphic rocks associated with granitic rocks, and Upper Cretaceous sedimentary cover. They form nappe structures on the Sambagawa metamorphic rocks. The Permian granitic rocks are correlative with granitic clasts in Permian conglomerates in the South Kitakami Terrane, whereas the mid-Cretaceous rocks are correlative with those in the Abukuma Terrane. This correlation suggests that the elements of Northeast Japan to the northeast of the Tanakura Tectonic Line were connected in between the paired metamorphic belt along the Median Tectonic Line, Southwest Japan. The Kurosegawa Terrane is composed of various Paleozoic rocks with serpentinite and occurs as disrupted bodies bounded by faults in the middle part of the Jurassic Chichibu Terrane accretionary complex. It is correlated with the South Kitakami Terrane in Northeast Japan. The constituents of both terranes are considered to have been originally distributed more closely and overlay the Jurassic accretionary terrane as nappes. The current sporadic occurrence of these terranes can possibly be attributed to the difference in erosion level and later stage depression or transtension along strike-slip faults. The constituents of both exotic terranes, especially the Ordovician granite in the Kurosegawa-South Kitakami Terrane and the Permian granite in the Paleo-Ryoke Terrane provide a significant key to reconstructing these exotic terranes by correlating them with Paleozoic granitoids in the eastern Asia continent.

This paper describes for the first time evidence for a northeastward brittle extensional movement of the Main Central Thrust (MCT) zone overprinting the southward ductile thrust movement. The MCT zone is the major tectonic boundary between the Lesser Himalayan metasedimentary sequence (LHS) and Higher Himalayan. crystalline sequence (HHS) and contributes to the kinematic and tectonic evidence of continent-continent collision in the Neogene. The Langtang area, 50 km north of Kathmandu, is a matter of interest in considering the movement of the Kathmandu Nappe because the general trend of foliation of the HHS and the underlying MCT zone is turned from WNW-ESE to N-S or NNE-SSW. The major tectono-lithostratigraphic units of the MCT zone in the study area are divided into three: the lower and middle units included in the LHS and the upper unit even included in the HHS. Characteristic mesoscopic quartz lenses are developed in the schists of the Lower unit forming asymmetric boudins. This asymmetry indicates an extensional (top-to-the-NE) shear sense. However, a thrust sense of top-to-the-SW is also preserved in microscopic ductile shear bands and mica fish. The extensional shear movement in the Lower unit took place after the major thrust movement in the MCT zone as a negative inversion. The Middle unit contains Ulleri-type augen gneiss (Syabru Bensi augen gneiss) which is widely distributed in the MCT zone in the other parts of the Nepalese Himalaya. Asymmetric clast-tails (or clast-pressure shadows) and asymmetric boudins observed in the Syabru Bensi augen gneiss give a dextral-thrust oblique sense of shear. This dextral component is regarded as movement of a N-S-trending lateral ramp during the overthrusting of the Kathmandu Nappe. The Upper unit above the MCT is commonly made up of kyanite-bearing medium pressure type amphibolite-facies pelitic gneiss. Asymmetric deformational features such as mica fish and shear bands in the pelitic gneisses commonly show a thrust (top-to-the-W) sense of movement.
After the emplacement of the Kathmandu Nappe (similar to 9-6 Ma), brittle extensional shear occurred only in the crystalline schists of the Lower unit presumably associated with layer-parallel slip. This extensional movement in the Lower unit is probably caused by the change in strike of foliations, e.g., from a general trend of E-W in the other areas to N-S as seen in the study area. This is because N-S contraction during continued continent-continent collision produced E-W extension normal to the contraction axis (N-S), thus the relative east-directed movement on normal faults took place only in the N-S trending domain of the MCT zone. Another possibility for the extensional movement is squeezing of the upper part of the LHS between the MCT above and an out-of-sequence thrust or the Main Detachment Fault below. (C) 2003 Elsevier Science B.V. All rights reserved.

This paper aims to document the principal features of the ductile shear deformation of the Sambagawa metamorphic rocks in the Ogawa-Ayukawa area, Kanto Mountains by integrating geological, petrological, microstructural and kinematic data. Metamorphic zones change northward from chlorite in the south to garnet, biotite and again garnet. Lithologic layering and metamorphic zone boundaries are generally parallel.A penetrative horizontal stretching lineation trending WNW-ESE is well developed, and is almost parallel to the trend of the Sambagawa Belt. Convincing shear sense determination using shear bands, oblique shape and c-axis fabrics of quartz grains in XZ thin sections was possible for about 14% of all samples collected. Top-to-the-west sense of shear is dominant in the study area, but minor domains with opposite sense of but shear (top-to-the-east) also occur particularly in the northern and southern areas. Quartz shape fabric and shear bands in opposite limbs of small-scale recumbent fold (F_1) indicate the same sense of shear. This suggests that the shearing postdates or was synchronous with the recumbent folding. The distribution of metamorphic zoning has been interpreted as the result of a macroscopic recumbent fold with northward vergence, however, studies of the distribution of lithology, mineral assemblages and shear-sense indicators gave no evidence in support of a large-scale recumbent fold in the area. Domains showing opposite oblique quartz shape fabrics and related interference colors with the gypsum plate inserted are observed in some quartz schists. The boundaries of the domains showing inverted sense of shear indicator are subparallel to the schistosity. Quartz c-axis fabrics have cleft girdle patterns suggesting uniaxial stretching deformation. The shortest axis of each quartz grain is parallel to Y or subsidiary to Z, suggesting that not only Z-parallel shortening but also Y-parallel shortening is dominant. Minor folds (crenulation) are commonly observed in YZ sections. These lines of evidence suggest that the bulk shear flow (fundamentally westward flow) was partitioned into the domains with opposite sense of shear and that X-parallel stretching is dominant.These features suggest the dominant deformation in the area is a ductile flow with partitioning into kinematically distinct domains and associated with overall uniaxial extension. This ductile flow is probably related to a tectonic framework such as oblique subduction of oceanic plate relative to continental plate during and after the peak metamorphism of the Sambagawa Belt. No evidence of dip-slip ductile to brittle shear which support the extrusion model of the high-P metamorphic rocks has been found in the study area.

Fault-generated pseudotachylytes showing reddish, greenish and grayish color have recently been found from the mylonitized Ryoke Granites along the Median Tectonic Line (MTL). These pseudotachylytes are suggested to have a melt origin on the basis of petrographic observations of typical melt-quenched microstructures such as microlites and amygdales. Preferential melting of low melting point minerals is the most probable melting process. The absence of lithic fragments of hornblende and biotite, and systematic decrease of bulk SiO_2 contents in the pseudotachylytes compared with their host rocks support this interpretation. These pseudotachylytes were formed after mylonitization and were post-dated by weak cataclasis resulting from movement of the MTL. Similar orientation of the MTL, fault veins of pseudotachylytes, and mylonitic foliation indicate that the deformation sequence of mylonite, pseudotachylyte, and cataclasite formation probably progressed under a single tectonic stress field. These pseudotachylytes are examples of the remnants of ancient faulting with frictional melting indicating seismic activity of the MTL.

Small-scale ultramylonite and cataclasite bands, millimeters to tens of centimeters thick, are developed in granitic rocks west of the Hatagawa Fault Zone (HFZ) in the Abukuma Belt, northeast Japan. They occur as single or paired bands with sharp planar boundaries trending NNE-SSW, and often form networks and conjugate sets. The very small S-C angle and the high displacement/thickness ratio of the bands suggest that the shear strain is high. The ultramylonite bands are commonly associated with cataclasite bands and mineral veins, and rarely with pseudotachylyte. Some cataclasite bands contain mylonitized layers in which quartz fragments are strongly deformed and dynamically recrystallized. On the other hand, some ultramylonites are fractured producing fragments that have rotated during later cataclasis.
The major element content of the ultramylonite bands is similar to that of the surrounding granitic rocks, strongly suggesting that the ultramylonite bands have formed through in-situ deformation of the granitic protolith without significant mass transfer. Mineralogy and microstructures of some ultramylonites suggest the strong possibility that they are derived from pseudotachylyte. The ultramylonite bands are interpreted as forming in the 10-15-km-deep cataclastic-plastic transition zone under greenschist facies conditions where co-seismic fracturing and aseismic plastic flow have alternated. (C) 2000 Elsevier Science Ltd. All rights reserved.

K-Ar and Rb-Sr age determinations were carried out on the Usukigawa quartzdiorite and associated metamorphic rocks along the Usuki-Yatsushiro Tectonic Line in eastern Kyushu, Southwest Japan. The Usukigawa quartzdiorite is composed of hornblende-biotite quartzdiorite to tonalite, and those in the western area of the body are strongly mylonitized. K-Ar hornblende ages of four samples of the Usukigawa quartzdiorite range from 252 to 272 Ma. Rb-Sr whole-rock isochron for four quartzdioritic rocks and three aplitic rocks gives an age of 275 ± 56 Ma with an initial 87Sr/86Sr ratio of 0.7040. On the other hand, K-Ar hornblende age of amphibolite which is intercalated as a small lenticular body along the northern boundary fault of the quartzdiorite is 124 Ma. The results of age and initial Sr isotope ratio of the Usukigawa quartzdiorite suggest that this Permian granitoid is correlative to the Kinshozan quartzdiorite which forms a nappe structure on the Mikabu green rocks in the Kanto Range, and is also correlative to the granitic clasts in the Usuginu-type conglomerate in South Kitakami belt. On the other hand, the K-Ar hornblende age of amphibolite and lithology of pelitic gneiss which is intercalated along the southern boundary fault of the quartzdiorite suggest that these high-grade metamorphic rocks are correlative to the Oshima metamorphic rocks in the Maana belt in western Shikoku and the Yorii metamorphic rocks in Kanto Range, and also correlative to the Takanuki metamorphic rocks in the Abukuma belt. The correlation of rocks mentioned above and close association and occurrence of three rock types
Permian granitoid Early Cretaceous high-grade metamorphic rocks and Late Cretaceous terrigenous sediments strongly suggest that the rocks of South Kitakami and Abukuma belts remain as a nappe on the Sambagawa metamorphic rocks in both Kanto and eastern Kyushu.

The closure temperature for zircon in the fission-track dating has been poorly estimated because of interpolation between minerals with very different closure temperatures. We find that K-Ar ages and fission-track ages of coexisting K-feldspars and zircons in Cretaceous granitic rocks from Japan are concordant within the experimental errors, with the exception of a few cataclastically deformed samples near the Median Tectonic Line. The concordance between the two systems suggests that the closure temperature for zircon in the fission-track system may be lower than 200-degrees-C.