Hida Metamorphic Belt Research Articles

飛騨外縁帯の地質構造発達史―日本列島地質体最古の太平洋型造山運動の復元―

The geotectonic evolution of the 450-270 Ma old serpentinite melange of the Itoigawa–Omi area of the Hida marginal belt has been reexamined from the viewpoint of reconstructing the oldest Pacific–type orogenic belt of Japan from a recently collected data set. Initiation of subduction to form a juvenile island arc followed by the accretionary complex of Southwest Japan took place at ca. 520 Ma as indicated by U–Pb zircon ages from metasomatic jadeitite formed by subduction zone fluids. Also, the 520 Ma zircons are indentified from volcaniclastic sediments of the eastern Hida marginal belt. Continued subduction proceeded with serpentinization and amphibolitization of the newly formed mantle wedge peridotite and crust, respectively, and high–P/T type metamorphism reaching eclogite facies older than ca. 380 Ma, as indicated by the EC unit of the Itoigawa–Omi area. This prolonged subduction zone metamorphism since the Cambrian formed essential members of the Oheyama–Renge belt of the Pacific–type orogenic belt of Japan, leading to tectonic erosion by subducting the oceanic plate, thereby the position of the subduction zone remained unchanged. The ca. 300 Ma Renge schists of the greenschist through epidote–amphibolite facies to eclogite facies of the Itoigawa–Omi area resulted from recrystallization probably by a subducting oceanic ridge. This ridge subduction caused exhumation of the Oheyama–Renge belt as a serpentinite belt including various hanging wall rocks with pre–existing subduction zone metamorphic rocks at a later stage. Remobilization of serpentinite melange of the Hida marginal belt continued to act as a lubricant zone at the past Benioff thrust after the Permian, and defined the structure of the Hida marginal belt up to the present. The Itoigawa–Omi area is a type locality of the oldest Pacific–type orogenic belt of Japan. The Hida marginal belt is thus redefined as a composite tectonic belt including the Oheyama–Renge, and Akiyoshi and Maizuru belts, along with Paleozoic fore–arc basin deposits such as the Hitoegane formation of ca. 500 Ma. Note that the Unazuki metamorphic rocks are not members of the Hida marginal belt developed at the periphery of South China plate, but the Hida metamorphic belt as a collision zone between the North and South China plates.

Eoarchean–Paleoproterozoic zircon inheritance in Japanese Permo-Triassic granites (Unazuki area, Hida Metamorphic Complex): Unearthing more old crust and identifying source terrranes

U–Pb zircon geochronology of two Permo-Triassic granites (samples OT-52 and OT-272 with ages of 229 ± 8 Ma and 256 ± 2 Ma, respectively) in the Unazuki area, Hida Metamorphic Belt, southwest Japan, revealed the presence of Eoarchean to Paleoproterozoic inheritance. Inheritance is consistent with both samples showing low zircon saturation temperatures for their bulk compositions. In OT-52, dark in CL, low Th/U zircon domains have a mean 207Pb/ 206Pb age of 1940 ± 17 Ma, which is consistent with an age of 1937 ± 6 Ma for anatexis in the Precambrian Busan gneiss complex in Korea. Eoarchaean inherited zircons with 207Pb/ 206Pb ages from ca. 3750 to 3550 Ma are common in OT-272 but are few in OT-52, suggesting a source from rocks with affinities to those in the Anshan area in the northeast China part of the North China Craton. On the other hand, a Hida Metamorphic Belt metasedimentary gneiss into which the granites were intruded contains ca. 1840, 1130, 580, 360, 285 and 250 Ma zircons ( Sano et al., 2000). These ages suggest that the Unazuki Mesozoic granites did not originate from proximal Hida Metamorphic Complex rocks, but instead from unrelated rocks obscured at depth. The predominance of Eoarchean to Paleoproterozoic age components, and the marked lack of 900–700 Ma components suggest that the source was the (extended?) fringe of the North China Craton, rather than from Yangtze Craton crust. The Mesozoic evolution of Japan and its linkages to northeast Asia are discussed in the context of these results.

日本列島の誕生場―古太平洋の沈み込み開始を示す飛騨外縁帯の５２０Ｍａの熱水活動―

This paper examines the early stage of the geotectonic history of the Japanese Islands on the basis of finding hydrothermal jadeitite including zircons of ca. 520 Ma in serpentinite mélange of the Itoigawa-Omi area of the Hida-Gaien belt, Central Japan. Hydrothermal jadeitite contains euhedral jadeite in natrolite veins and patches, and consists of jadeite-albite and jadeite-natrolite without quartz. These minerals were crystallized from an aqueous fluid phase at the low-pressure and high-temperature side of the reaction boundary of albite = jadeite + quartz in the system NaAlSiO4-SiO2-H2O. The occurrence of rounded relict hornblende mantled by omphacite rimmed by fine-grained aggregates of jadeite in the matrix of jadeite and albite suggests a pervasive hydrothermal fluid flow, through which metabasite was extensively replaced by jadeitite. This rather high-temperature hydrothermal activity of ca. 520 Ma did not occur in an ordinary subduction zone but in a newly-formed mantle wedge suffering severe hydration from a subducting slab. Recently accumulated U-Pb ages of zircon of ca. 450-500 Ma from paleozoic sediments and granitic rocks of the Hida-Gaien belt were due to initiation of subduction followed by subduction zone magmatism. Protolith of serpentinite in the Hida-Gaien belt includes highly depleted harzburgite, thus requiring tectonic setting of a high-temperature-rift zone rather than a low-temperature-slow spreading ridge. Subduction was initiated at ca. 520 Ma along the boundary between low-density harzburgitic rift zone peridotite and lherzolitic spreading ridge peridotite with a slightly higher density, resulting in the common occurrence of harzburgitic serpentinite in the oldest part of the accretionary complex of Southwest Japan. An area including the Japanese Islands was born around the Yangtze block by the breaking up of the Rodinia supercontinent, because the oldest K-Ar age of biotite actinolit rock of 672 Ma (Matsumoto et al., 1981) and the subduction initiation of ca. 520 Ma are in accord with the paleogeographic history of the Yangtze block, and because ca. 300 Ma Renge schists of the Hida-Gaien belt did not suffer the ca. 280-200 Ma collision-type metamorphism of the Hida metamorphic belt that is an eastern extension of the suture between the Sino-Korea and Yangtze blocks.

Geological structure of the Hida metamorphic belt and mineralization of the Kamioka-type ore deposits:Studies on regional geology and mineralization in the Kamioka district, No. 1.

Geological structure of the Hida metamorphic belt and mineralization of the Kamioka-type ore deposits:Studies on regional geology and mineralization in the Kamioka district, No. 1.

Fission-track analysis of the Atotsugawa Fault (Hida Metamorphic Belt, central Japan): fault-related thermal anomaly and activation history

Abstract Fission-track (FT) thermochronology was applied to the Atotsugawa Fault in the Hida Metamorphic Belt, central Japan, to detect any ancient thermal anomaly associated with fault displacements. Apatite and zircon grains from gouges ( c . 2 cm wide) and fractured rocks ( c . 10 cm) at six fracture zones within a 15 m-wide fault zone were dated. Most of the zircon (120–150 Ma) and apatite (44–60 Ma) ages agree well with emplacement ages for the granites that intrude the Hida Belt. The discordance in zircon and apatite FT ages is interpreted to reflect cooling due to regional uplift and associated erosion. A thermal anomaly was identified at one of the gouge zones that showed an exceptionally young apatite age ( c . 32 Ma) with an unimodal FT length distribution. It presumably indicates secondary heating induced by frictional slip during an earthquake, possibly giving a younger limit of the initiation of the activity in the Hida Belt.

SHRIMP U-Pb dating of detrital zircons in paragneiss from Oki-Dogo Island, western Japan

We obtained the radiometric ages of detrital zircons from two samples of paragneiss from Oki-Dogo Island, Japan, from the 238U/206Pb ratio and isotopic composition of Pb determined using a Sensitive High-Resolution Ion MicroProbe (SHRIMP II). The zircons show two main age clusters around 2200 Ma and 1800 Ma, with some discordant ages. One zircon grain has a rim with a concordant age of 236 ± 3 Ma, which is consistent with the age of peak metamorphism in the Hida Metamorphic Belt. The modal proportions of zircon ages from Oki-Dogo Island are clearly different from those for paragneiss of the Hida Terrane. This indicates that the Oki Gneiss is derived from an Early Proterozoic rock and is different from the Hida Gneiss in terms of provenance and/or the depositional age of the parent sediment.

Ion microprobe U-Pb zircon geochronology of the Hida gneiss. Finding of the oldest minerals in Japan.

We have measured U concentrations, and elemental ratio of 238 U/ 206 Pb, and isotopic compositions of Pb in thirteen zircons extracted from a volcaniclastic rock of the Kamiaso conglomerate in the Mino terrane and sixty three analyses in fifty zircons from the Amo gneiss, a metamorphic rock originated from an intermediate volcanic rock in the Hida terrane of central Japan by means of an ion microprobe. Zircons from the Kamiaso were first analyzed in Australian National University (ANU) and then measured again by Hiroshima University (HU) Sensitive High Resolution Ion MicroProbe. Both radiometric ages of 238 U/ 206 Pb* and 207 Pb*/ 206 Pb* obtained by the ANU instrument agree well with those by HU except for one sample. There are six geochronological episodes in the Kamiaso sample; about 2550 Ma, 2000 Ma, 1300 Ma, 920 Ma, 250 and 220 Ma. U-Pb zircon geochronology of the Amo sample indicates that there are six concordant zircon episodes and three concordia intercept episodes; about 3420 Ma, 2560 Ma, 1840 Ma, 1130 Ma, 580 Ma, 400 Ma, 360 Ma, 285 Ma, and 250 Ma. The 3420 Ma is the oldest age so far reported in Japan. The 2560 Ma event may have a relation to the period of the evolution of the Sino-Korean craton between 2.7‐2.5 Ga. The third age peak of about 1840 Ma suggests that the zircons were derived from the Ryongnam massif in South Korea with the similar formation age. The younger ages of 1130 Ma, 580 Ma, 400 Ma, 360 Ma and 285 Ma may be minor events recorded in the Hida metamorphic belt. The latest age of 250 Ma may be the most important metamorphic event in Hida terrane. Rare earth element abundance patterns of the Amo zircons show progressive increase with atomic number together with positive Ce anomaly, which is a typical zircon signature. Small negative anomaly of Eu is found in zircons with the age of 2560 Ma and 250 Ma while zircons with intermediate ages show large anomaly. There is no correlation between Ce and Eu anomaly, suggesting that both anomalies may not have been simply controlled by the oxidation state during zircon crystallization.

Incipient Stage of Ore Formation Process of the Kamioka Zn‐Pb Ore Deposit in the Hida Metamorphic Belt, Central Japan: Leaching and Precipitation of Clinopyroxene

Abstract: Boundaries between the cpx Zn‐Pb ores of the Kamioka ore deposit and host clinopyroxene granitoid in the Hida metamorphic belt were examined to decipher the incipient stage of ore formation process. The boundaries are characterized by the compositional zoning of relic clinopyroxene with outward increase of XMg from 0. 5 to 0. 75 in the host rocks, and by the incline of XMg towards the ores, passing through the boundaries, reaching up to 0. 95. In the ores, relic clinopyroxene is rimmed by hedenbergite. Both clinopyroxenes show compositional zoning with outward decrease and increase of XMg and MnO, down to 0. 02 and to 3. 2 wt%, respectively. The presence of high magnesian clinopyroxene can be explained if hydrothermal fluid flow had leached hedenbergite component of relic clinopyroxene. The incline of XMg of clinopyroxene toward the ores was attributed to the degree of dissolution of clinopyroxene, and thus the total amounts of fluid to have passed. The outward decrease of XMg of clinopyroxenes in the ores was due to crystal‐fluid fractionation during precipitation.These mineralogical changes at the boundaries indicate the time‐integrated phenomena of hydrothermal ore forming process. Firstly, leaching of ore components by infiltrating fluid proceeded in host rocks, and enhanced the formation of a fluid channel. The condition of fluid changes through the fluid channel in P‐T space, and hence ore forming minerals precipitate at a remote place from the leaching one. This in turn caused the physicochemical change of fluid condition anyhow, and accelerated the precipitation of the minerals. This leaching‐precipitation sequence appears a basic process of hydrothermal ore‐forming system, and characterizes the incipient stage of ore formation process of the Kamioka Zn‐Pb ore deposit. Compositional zoning of clinopyroxenes defines Z‐shaped compositional trend in the Di–Hd–Jo diagram, each arm of which corresponds to the leaching and the precipitation stages, and the secondary dissolution of precipitated clinopyroxene.

Timescales and mechanisms of fluid infiltration in a marble: an ion microprobe study

Using a recently developed ion microprobe technique, a detailed oxygen isotope map of calcite grains in a coarse-grained marble has been constructed, supported by trace element (Mn, Sr, Fe) analysis and cathodoluminescence (CL) imaging, in order to constrain scales of oxygen isotope equilibrium, timescales and mechanisms of metamorphic fluid infiltration, and fluid sources and pathways. Results are compared with a previous study of this sample (Wada 1988) carried out using a cryo-microtome technique and conventional oxygen isotope analysis. The marble, from the high temperature/low pressure Hida metamorphic belt in north-central Japan, underwent granulite facies followed by amphibolite facies metamorphic events, the latter associated with regional granite intrusion. The CL imaging indicates two types of calcite, a yellow luminescing (YLC) and a purple luminescing (PLC) variety. The YLC, which occupies grain boundaries, fractures, replacement patches, and most of the abundant deformation twin lamellae, post-dates the dominant PLC calcite and maps out fluid pathways. Systematic relationships were established between oxygen isotope and trace element composition, calcite type and texture, based on 74 18O/16O and 17 trace element analyses with 20–30 μ m spatial resolution. The YLC is enriched in Mn and Fe, and depleted in 18O and Sr compared to PLC, and is much more 18O depleted than is indicated from conventional analyses. Results are interpreted to indicate infiltration of 18O-depleted (metamorphic or magmatic) fluid (initial δ18O = 9‰–10.5‰) along grain boundaries, fractures and deformation twin lamellae, depleting calcite grains in Sr and enriching them in Mn and Fe. The sample is characterised by gross isotopic and elemental disequilibrium, with important implications for the application of chromatographic theory to constrain fluid fluxes in metacarbonate rocks.

飛騨変成帯東漆山に産出する変複合貫入岩体

飛騨変成帯東漆山に産出する変複合貫入岩体

Stable isotope analysis of small amount of carbon dioxide and its application to the microscale isotopic zoning of graphite crystals in metamorphic rocks.

A conventional dynamic mass spectrometer with an inlet system specially modified for microscale samples was used to measure carbon isotopic ratio of subsamples within individual graphite crystals collected from Hida metamorphic belt, central Japan. The graphite crystals with three different occurrences i.e., in pelitic gneiss, skarn deposit, and crystalline limestone were examined for their isotopic zonation. Single graphite crystals collected from pelitic gneiss and hedenbergite skarn deposit has homogeneous isotopic distribution, whereas composite graphites of marble show complicated zonation which may imply the evolution of the metamorphic fluid during metamorphism.

Stable isotopic evidence for migration of metamorphic fluids along grain boundaries of marbles.

In order to elucidate carbon and oxygen isotopic systematic in metamorphosed limestone and isotopic behavior during metamorphism, microscale carbon and oxygen isotopic compositions of graphite and calcite in crystalline limestone were determined for the contact metamorphic aureole of the polymetamorphosed Hida metamorphic belt, central Japan. In this area granulite facies metamorphic rocks were overprinted by contact metamorphism related to a granitic intrusion. Carbon isotopic fractionation between individual crystalline graphites and the cores of coexisting calcite grains gives a constant value independent of the sampling localities. Graphites armored by silicates have the same δ13C as other graphites in calcite. These indicate that carbon isotopic equilibrium between graphite and calcite was completely attained during granulite facies metamorphism. Values of δ18O in the cores of individual calcite grains vary over about 2‰ near the granite contact, and the range of variation tends to become smaller with increasing distances from the contact. In calcite grains near the granite contact, δ18O values sharply decrease by up to 7‰ within 200∼300 μm wide zones toward grain boundaries, whereas δ13C remain almost constant. This δ18O trough at the grain boundaries is less pronounced with increasing distance from the granite contact and is almost no longer seen at distance about 1.3 km. Oxygen isotopic zonation of calcite at grain boundaries strongly suggests partial isotopic exchange with water-rich metamorphic fluids that migrated along grain boundaries. This fluid-rock interaction occurred preferentially in the grain boundaries with very limited scale at distances up to 1.3 km from the granite contact, although the contact aureole defined by the mineralogical paragenesis is limited to within several tens of meters of the contact. Skeletal graphites growing over the substrata of large hexagonal graphite grains have lower δ13C values than those of the host graphite. It is considered that the fine-grained graphite crystals were formed in isotopic equilibrium with low δ13C carbon in the metamorphic fluids.

Microscale isotopic zoning in calcite and graphite crystals in marble

Chemical and isotopic zoning in minerals is a clear indication of disequilibrium and provides an important key for elucidating metamorphic processes. Here I present carbon and oxygen isotope data from calcite and graphite crystals in a marble from the Hida metamorphic belt, central Japan, showing isotopic zoning within individual crystals. Within 100μm of the calcite–graphite grain boundary the 13C contents gradually decrease from the constant values of the crystal core to values ˜1‰ lower; 18O contents in calcite decrease by up to 7‰ within 200–300 (Jim of the boundary. At a calcite–calcite grain boundary, similar patterns of 13C and 18O depletions were found, whereas the 13C contents of graphites remained constant except in a narrow zone at the calcite contact. These isotopic patterns are interpreted as reflecting isotopic exchange with metamorphic fluids that were relatively depleted in 13C and 18O. These results strongly suggest that the most accurate geothermometry will be obtained if only the cores of crystals are used, and that isotopic zoning may provide another way to elucidate polymetamorphic processes.

The obliquity of K-feldspar from schists, gneisses, and granites in the north-eastern part of the Hida metamorphic belt, central Japan

AbstractMost of 325 K-feldspars from the Hida metamorphic belt are characterized by diffuse 131 and 11 reflections. These K-feldspars are classified into eight obliquity types on the basis of the width of the 131 peak or the ratio of mean height of two outer peaks (131 and 11) to that of the middle composite peak. From the distribution of obliquity types and the microscopic characteristics of K-feldspars, this area is divisible into six zones.The feature of each zone is shown by the frequency distribution of eight obliquity types in each zone, which reflects the strength of later retrogressive effects. The frequency distribution of Δ values in each of the types IV-VIII provides further information on later events.The result of the K-feldspar study possibly indicates that the inversion of monoclinic to triclinic K-feldspar, characterized by the development of perthitic texture or crosshatched twinning, is sensitive to the degree of later retrogressive events. Some data on 2θ values of 04, 060 and 01 reflections in each types are presented.

Rb-Sr ages of the gneiss and metamorphosed intrusive rocks of the Hida metamorphic belt in the Urushiyama area, Gifu Prefecture, central Japan.

Metamorphosed intrusive rocks (metagabbro and metatonalite), and nonmetamorphosed aplite dyke, all of which intrude into the coarse-grained biotite-hornblende gneiss, are exposed in the Urushiyama area along the Takahara River, the main part of the Hida metamorphic belt. RbSr mineral isochron ages of 216±10 Ma and 222±2 Ma are given for the coarse-grained biotitehornblende gneiss and metagabbro, respectively. On the contrary, the whole rock isochrons of the metagabbro and metatonalite show 415±144 Ma and 332±74 Ma, respectively. These whole rock ages correspond to the ages of intrusion of the gabbro and tonalite and they were re-equilibrated with respect to the Rb-Sr system approximately 220 Ma by the regional metamorphism. Whole rock samples of aplite dyke yield an isochron age of 172±7 Ma. The Hida gneiss in the Urushiyarna area seems to have been formed by the main stage of metamorphism and the deformation having been already finished before the intrusion of gabbro.

Geological structure and lithofacies in the central part of the Hida metamorphic belt

Geological structure and lithofacies in the central part of the Hida metamorphic belt

富山県南東部和田川地域の泥質片麻岩中の逆累帯ざくろ石

The Wada-gawa area, central part of the Hida metamorphic belt, consists of diverse gneisses of the upper amphibolite facies, which were later intruded by several small granitic bodies. Garnet porphyroblasts in pelitic gneisses are replaced by biotite along their rims and cracks, and are separated into smaller parts by biotites films. The replacement proceeds more remarkably in the neighbourhood of the small granitic bodies, suggesting that the replacement is closely related to the granitic intrusion. Each of the separated parts of the garnet shows a reverse zoning in which Fe and Mn contents increase and Mg content decreases from the core to the rim, although the core of some larger garnet is homogeneous. The compositional contour of the reverse zoning is concordant with irregular outline of the resorbed garnet. The mode of occurrence and the zoning pattern of garnet suggest that the reverse zoning of garnet was formed by volume diffusion in garnet crystal during the retrogression of garnet which was closely associated with the intrusion of small granitic bodies.

Metamorphism of calc-siliceous rocks in the Momose-Mizunashi district, Hidametamorphic belt, central Japan

Metamorphism of calc-siliceous rocks in the Momose-Mizunashi district, Hidametamorphic belt, central Japan

飛だ変成帯の角せん石のＫ‐Ａｒ年代

K-Ar ages have been determined on hornblendes from seven metamorphic rocks and two Funatsu Granitic Rocks from the Hida Metamorphic Belt. The ages of metamorphic rocks range from 174 to 223 m.y., and grouped into two: about 220 m. y. and 175-195m.y. The former ages represent the time of the main metamorphism in the Hida Metamorphic Belt, whereas the latter may have resulted from rejuvenation by the intrusion of the Funatsu Granitic Rocks or from slow cooling. An age or 180m.y. is obtained on hornblende from the Shimonomoto type of the Funatsu Granitic Rocks, and it confirms the time of intrusion for the Funatsu Granitic Rocks. Hornblende from augen gneiss, gives an age of 213m.y., which is similar to that of hornblendes from the Hida Metamorphic Rocks, thus suggesting that the augen gneiss is genetically different from the typical Funatsu Granitic Rocks. It is interpreted that hornblendes dated here contain no excess argon.

Geological study of the Hida metamorphic belt in the eastern Part of Toyama Prefecture, central Japan (Part 2):Structure of the Hida metamorphic rocks and the plutonic rocks of the Funatsu stage

Geological study of the Hida metamorphic belt in the eastern Part of Toyama Prefecture, central Japan (Part 2):Structure of the Hida metamorphic rocks and the plutonic rocks of the Funatsu stage