Systematic meteorite searches have been conducted around the Sør Rondane Mountains in Antarctica by the 51st Japanese Antarctic Research Expedition in 2010. A total of 635 meteorite specimens, including one iron and two ureilites, have been successfully found. The meteorites will be termed the Asuka 09 meteorites.

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CaAl2O4-phases in an unusual Ca-Al-Fe-rich inclusion in the Vigarano CV3 chondrite have been investigated by SEM-EBSD and TEM. The grains of CaAl2O4 phase are smaller than 400 micron in size and chemically homogeneous. In EBSD analyses, the CaAl2O4 phase showed Kikuchi patterns of the high-pressure phase with space group P21/c. On the other hand, SAED patterns of a CaAl2O4 grain could be indexed only by low-pressure phase with space group P21/n. The CaAl2O4 phase would have been crystallized from Ca-Al-Fe-rich melt as the P21/n phase together with grossite and hercynite in the solar nebula. Subsequently, the P21/n phase would have been mostly transformed into the P21/c by shock metamorphism in the Vigarano parent body.

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In the present study, we report microstructure of the isotopically anomalous material COS in the carbonaceous chondrite Acfer 094 using transmission electron microscopy. The TEM observations shows that COS grain consists of magnetite + pyrrhotite (+ minor pentlandite) with a symplectitic texture in tens nm scale. The grain boundaries between magnetite and pyrrhotite are smoothly rounded, and both phases are directly contacted without amorphous regions. Such a nanometer scale inter-growth texture may suggest the simultaneous and rapid crystal growth of the constituent minerals at the time of formation.

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In primitive solar materials spherical organic matters with hollow called organic nanoglobules were discovered. It is suggested that they were formed from photochemical reaction to ice particles at molecular clouds or outer protosolar disk or aqueous alteration of organic matters. If they are true, hollow regions might be filled with H₂O-rich ices or fluids. However they have not been detected because they had been lost during destructive observations. In the present study, we have tried to determine the existence of fluids non-destructively using synchrotron radiation-based X-ray microtomography. We succeeded to identify many spherical objects that are the candidates of organic nanoglobules in the CT images. Then, we microtomed some samples and observed the samples under a TEM. Comparison between the CT and the TEM images showed that at least some objects are actually the organic nanoglobules.

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CH chondrites are unusual carbonaceous chondrites, and are characterized by abundant Fe-Ni metal, small chondrule size distribution, and so on. Here we report the bulk chemical compositions of chondrules in CH chondrites, in comparison with those in CO, EH and H3 chondrites. Cryptocrystalline chondrules experienced complete melting and rapid cooling. They were also subjected to fractionation of refractory and volatile elements, along with Mg/Si fractionation, resulting in the depletion of olivine. On the other hand, porphyritic chondrules are depleted in Na, in comparison with those in other chondrites, and are more magnesian than those in CO and H3. Their precursor materials formed under higher temperatures and more reducing conditions than chondrules from other chondrite groups.

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We studied 103 micrometeorites (MMs) bearing relicts of olivines and low-Ca pyroxenes focusing on the relationship with chemical groups of chondrites. As a result, we found that 53 MMs are similar to carbonaceous chondrites, 31 to ordinary chondrites, and the remains (19 MMs) to others. MMs bearing low-Ca pyroxenes are dominant of unmelted MMs. Four unmelted MMs show poikilitic textures that droplet kamacites are enclosed in low-Ca pyroxenes. They are rounded with one hundred micron meter, similar to CO3 chondrules. A MM similar to shock-melted H chondrite was also identified.

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We report our finding of a highly hydrated clast in a CV3 chondrite. This clast provides evidence that the CV parent body had a very wet region where intensive aqueous alteration occurred. This clast supports our proposal that the chondrules/rims are actually clasts transported from a wet region on the meteorite parent body different from where the host meteorite was lithified.

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Mineralogical characteristics of CK chondrites reflect the complex metamorphic history of this group. We here present the mineralogical features of plagioclase in LEW87009. Our goal is to reveal the thermal and shock history of CK chondrites. Shock melt veins are observed in LEW87009, and plagioclase near the largest shock vein is partially vitrified. Pervasive fractures are omnipresent in crystal regions, but glass regions are smooth and lack fractures. It suggests that plagioclase glass was formed by shock-induced melting and subsequent quenching. Thermal metamorphism is so progressed in LEW87009, but plagioclase glass near shock vein is not recrystallized. It suggests that the shock event was occurred following thermal metamorphism, and then thermal metamorphism was not progressed.

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We performed a mineralogical study of Almahata Sitta which was the first recovered asteroid fall (2008TC3) in history and found that it was composed of both coarse-grained and fine-grained lithic clasts of ureilites. The olivine and pyroxene mineralogy gave the cooling rate of 0.2-5 oC/hour, which is in agreement with the general thermal history of the ureilite parent body with the quenching episode due to the impact break-up of the parent body while it was still hot. The asteroid 2008TC3 implies an origin from the loosely-packed brecciated surface of the re-accreted body composed of fragments with different degrees of quenched thermal history that were produced by the impact break-up of the original ureilite parent body.

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We studied thermal history of diogenites to better understand the formation processes of the crust of the parent body, asteroid 4 Vesta. We found diogenites that preserve chemical zoning in pyroxene. These diogenites cooled rapidly from the melt near the surface. The fact argues against the idea that diogenites were plutonic rocks from the lower crust. We suggest that parent magmas of diogenites intruded into the early-formed eucritic crust, and some of which cooled rapidly near the surface. This model is consistent with the geochemical evidence that parent magmas of some diogenites were interacted with eucrites.

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NWA1950 is a typical lherzolitic shergottite similar to other samples of this Martian meteorite group. However olivine in NWA1950 shows strong dark color in thin sections and dark parts consist of crystallographically-controlled dark stripes present in colorless olivine crystal. Parallel stripes of 200-500 nm width were observed under TEM that are corresponding to dark stripes under optical microscope. Stripes are consist of tens-nanometer-sized minute crystals although they are inside of a single crystal. Dislocations are present in the surrounding host crystal, but not in stripes. Fe-rich nano-particles are concentrated in stripes. Nano-particles are usually 10-20 nm in diameter and do not contain Ni. The FFT patterns of these nano-particles are consistent with hematite.

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Shergottite is the largest group of Martian meteorites. In this study, we investigated the formation sequence and relationship of enriched shergottites with MELTS calculation by using their estimated melt compositions. We used nine enriched shergottites for sample and these four samples are non-cumulate rocks.We employed bulk composition of two non-cumulate Olivine-Phyric samples as the starting melt composition of enriched shergottites. The results of MELTS calculation suggested that a similar composition to the bulk compositions of Los Angeles and Dhofar 378 (Basaltic and non-cumulate samples) could be produced at 1110 and 1040 degrees Celsius. This study demonstrates that these nine enriched shergottites may have been formed by the same magmatic event as they show similar crystallization and exposure ages.

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Anorthositic crust of the Moon and eucritic crust of the Asteroid 4 Vesta preserve the records of their formation from some magma oceans. Pyroxenes from the HED achondrites, which are proposed to come from Vesta keep the records of the crust formation and the subsequent cooling histories. An inverted pigeonite in a cumulate eucrite shows textures indicative of exsolution and inversion to orthopyroxene. Two lunar meterorite groups of the farside origin have been reported. Although low Th and FeO concentrations are common features, pyroxene fragments similar to those of so-called Mg-suite rocks of the nearside are dominant in the matrices of the Y-86032 group, but more olivine fragments and rare magnesian exsolved pigeonites are found in the matrices of the Dhofar 489 group.

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The next Japanese lunar exploration project: SELENE-2 is planned as a follow-on mission of Kaguya (SELENE). The spacecraft is to be launched around the middle of 2010's. In order to select the landing site candidates which maximize the scientific gain of the project, SELENE-2 Landing Site Research Board started in March, 2010. The working group has discussed the various scientific proposals and the landing site candidates in cooperation with domestic researchers who were interested in lunar science, and now proposes several model missions which execute the scientific exploration of the highest priority today. In our presentation, the present landing site candidates, the grounds of the selection, and the process of further selection of the landing site in the future would be shown.

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Lunar carbon is discussed in Ca-rich plagioclases and nano-textures of expected nano-diamonds and chained iron-oxides. Calculated vacancies of lunar Ca-plagioclases which are calculated from the EPMA data found higher in lunar breccias are consistent with higher storages of light elements of carbon etc. in the breccias, which indicate information of lunar formation with impact processes followed volcanism. Nano-textures formed by shock-wave explosions on the Moon are expected to find nano-diamonds and carbon-bearing iron-oxides on the airless-Moon when there are carbon sources (by meteoroids impacts and giant impact with carbon air planets of primordial Earth).

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Meteorite carbon is discussed in expected carbon-bearing grains in the Itokawa asteroid, by comparing with the stony meteorites reported, Antarctic and Tagish Lake meteorites. Stony meteorites are assemblages of Fe-core metals and impact-generated iron oxides with carbon and Ca contents. Carbon-bearing micro-grains with 100nm in size are observed in the Antarctic and Tagish Lake chondrites by FE-ASEM. Expected micro-grain from the Itokawa Asteroids are two types of stony coliisons and gas-fixed solids during its formation.

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Anomalous Ca-Al-Fe-rich spherical inclusion (CAFI) is found from the Vigarano CV3 chondrite. The CAFI has an igneous texture, and occupied by large amounts of end-member and coarse-grained hercynite grains. The CAFI includes refractory phases such as grossite and perovskite. However melilite and Mg-spinel, that are common phases in the normal CAI, are very rare. Another unique characteristic of the CAFI is the presence of dmitryivanovite in its core, which has been formed by shock metamorphism of a low-pressure form of CaAl2O4 that was originally crystallized from the molten droplet. The Ca-Al-Fe-rich characteristic of the CAFI may suggest that its precursor has a genetic link with CH/CB chondrites which contain abundant Fe-metal and grossite-rich CAIs.

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So far, electron microprobe has been used to study two dimensional distributions of elements in earth and planetary materials. However, the analytical sensitivity of the method for trace elements was low. On the other hand, synchrotron X-ray fluorescence imaging had high sensitivity, however microprobe analysis of trace heavy elements was difficult. In this study LA-ICP-MS method was adopted to analyze two dimensional distributions of trace heavy elements in meteorites. As a result, the distributions of platinum group and rare-earth elements in chondrite were revealed clearly. Since the LA-ICP-MS imaging provide information of trace element distributions of light and heavy elements, it is expected that this method becomes a powerful analytical tool for earth and planetary materials.

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The Onodani area in the Besshi district, Sambagawa metamorphic belt, is located about 1 km west of the Sebadani area, and a western extension of the Seba eclogitic basic schists. The Onodani area consists mainly of basic, pelitic and siliceous schists. Eclogites within the Seba basic schists are usually found as lenticular bodies or layers ranging from centimeters to a few meters in thickness. These eclogites experienced three different metamorphic episodes during multiple burial and exhumation cycles.

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Three metamorphic events are distinguished in the eclogites occurring in the Besshi district, Sambagawa metamorphic belt, southwest Japan. They are, 1) precursor metamorphism before high P/T eclogitic metamorphism (granulite-amphibolite facies) , 2) multiple eclogite facies metamorphism, and 3) epidote amphibolite metamorphism. The eclogites in the Besshi district experienced some of these metamorphic events.

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Three types of zoning structure of garnet were identified from a glaucophane (Gln) bearing eclogite from the Kotsu area in the Sambagawa belt. Type 1 is characterized as a fine grained euhedral crystal (about 100μm) showing Mn bell shape pattern with dusty inclusions in its core. Type 2 is a coarse grained euhedral crystal (about 1,000μm) showing Mn bell shape pattern with omphacite (Omp) inclusions in its rim. Type 3 is a coarse grained anhedral crystal (about 1,000μm) with almost homogeneous composition which is identical with rim compositions of type 1 & 2. Type 3 contains Omp inclusions through the grain. Type 1 & 2 has a nearly symmetrical chemical profile of a grain passing through its geometrical center each other, although they have distinct grain size. The host rock is composed of rusty colored layer and perse one. Type 1 is predominant in the rusty layer along with quartz, the others occur in perse one along with Omp and Gln. These data suggest that the Mn-rich core of type 1 & 2 nucleated at relatively low temperature conditions, whereas the nucleation and growth of type 3 delayed until the peak stage of eclogite facies metamorphism.

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U-Pb ages of detrital zircons and white mica K-Ar ages are obtained from two psammitic schists from the Sanbagawa Belt, Tenryu area. The youngest zircon ages and white mica ages of the sample from Western Unit yield 94 and 70 Ma, respectively. On the othe hand, the ages of the sample from Eastern Unit yield 73 and 55 Ma, respectively. Western Unit had been already at the metamorphism stage when the Eastern Unit, was still at the depositional stage. The present results may induce the development of a model that a metamorphic belt is subdivided into some units formed at different stages. And "120 Ma metamorphic belt" is not identified in the Tenryu area.

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We report petrography and bulk chemical compositions of Kurosegawa blueschists from Kyushu, Shikoku and Kii peninsula, and discuss their origin. Blueschists from Yaeyama metamorphic complex will also be discussed.

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We found possible prograde deserpentinized peridotites from the Happo complex central Japan. High-P and low-P prograde peridotites show differences in their field relation and mineral assemblage. The high-P prograde peridotites have a mineral assemblage, Opx + Olv + Tlc + rare edenite and phlogopite. Olivine has low Fo91, in contrast to olivine in the low-P deserpentinized peridotites from the talc zone, due to a reducing environment. Their bulk chemistry confirms serpentinites as a protolith. The low-P, high-T peridotites metamorphosed by Cretaceous granitic intrusion from the talc zone are composed of prograde tremolite, metamorphic olivine, antigorite and talc. Prograde tremolite is very low in Al2O3,Na2O,Cr2O3,Li,La,Ce,Sr,Ti,Yb,Sc,and V, but is high in SiO2 and Mg# relative to retrograde tremolite. This depletion of mobile elements is due to their mobility during deserpentinization process, whereas immobile-element depletion is related to the parental source. Olivine containing opaque inclusions is high in Fo, 93.5 to 96.4. It is enriched in B,Sc,Ti,Y,Zr,Nb and Ni relative to mantle olivines because of its opaque inclusions.

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Three types of high-P/T metamorphic rocks, i.e. garnet-barroisite schists, glaucophane aegirine-augite scishts and epidote-glaucophane schists, from the Heilongjiang Complex in the western margin of the Jiamusi Massif have been petrologically investigated. The peak metamorphic conditions obtained here for the high-P/T type rocks of the Heilongjiang Complex vary in different lithologies and areas, from the epidote blueschist facies to the epidote amphibolite facies. The petrological and geochronological characteristics of the high-P/T Heilongjiang metamorphism may be compared to those high-P/T metamorphic rocks in the Suo belt, SW Japan, suggesting the Suo metamorphic belt is a possible southern extension of the Heilongjiang Complex at the time before Japan Sea opened.

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The decompressional P-T path was estimated for UHP eclogite from Taohang area of the Sulu region, eastern China. Application of geothermobarometers to the cores of garnet and omphacite gave P-T conditions of about 700degreeC and 3.4 GPa. On the other hand, applying a geothermometer to pairs of garnet rims and their adjacent omphacite rims, temperatures of 566 +/- 54degreeC were obtained at 1.5 GPa. Thus, these P-T estimations indicate that temperatures should have significantly declined during the early decompression stage of this eclogite. In other areas of the Sulu region, isothermal decompression paths were proposed, and it was concluded that the UHP rocks were exhumed as a large mass to avoid thermal effects from the surroundings. However, the newly identified decompression path accompanying the significant cooling may indicates that the Taohang outcrop was located at the margin of the Sulu UHP terrane.

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The occurrence of complete and atoll-shaped garnets in garnet amphibolites in the Aktyuz complex, northern Kyrgyz Tien-Shan has been described. Based on the mineral textures and chemical compositions of minerals, the possible mechanism of formation of atoll garnets has been discussed. It is suggested that the atoll garnets were formed by breakdown of pre-existing inclusion-rich, Ca- and Mn-rich garnet core (incipient of garnet resorption from the core) by infiltration of fluids along fractures during the prograde HP-HT metamorphism.

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The Akdjon Group is divided into the structurally lower Makbal Formation and the upper Neldy Formation. Coesite and quartz pseudomorphs after coesite included in the garnets have been found in the garnet-talc-chloritoid schists and meta-quartzites in the Makbal Formation. Eclogite blocks across occur as lenses within the meta-quartzite, garnet-talc-chloritoid schists, marbles and pelitic schists in the Makbal Formation. The Neldy Formation is composed mainly of pelitic schists (garnet-phengite-quartz-albite schists), chlorite-carbonate rocks with minor amounts of marble and meta-quartzite. Eclogites are preserved in the central parts of the garnet-amphibolite bodies are intercalated in the pelitic schists of the Neldy Formation. The metamorphism of the Neldy eclogites is divided into three events, (1) precursor metamorphic event (amphibolite facies), (2) first high-P (eclogite facies) metamorphic event, (3) second high-P (epidote amphibolite facies) events.

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Pelitic metamorphic rocks from Pranburi have mineral assemblage of Grt+Sil+/-Crd+Bt with rare andalusite. The presence of tourmaline showing two growth stages and retrograde dumortierite suggest that intrusion of the tourmaline-bearing leucogranite that crosscut the foliation of metamorphic rocks may have caused the retrograde metamorphism by infiltration of boron-bearing fluid. Metagranite from Hua Hin has Grt+Sil+Bt assemblage. The peak metamorphic condition of these two areas probably exceeded the stability limit of Ms+Qtz. The metamorphic grade increases from Hub Kapong at the NW, where Bt+Ms assemblage is found, to Pranburi at the SE. Because of the strong retrograde metamorphism, age determination utilizing zircon and monazite would be important to constrain the timing of metamorphism.

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Our Cr-spinel data together with the previous studies provide evidence for existence of two independent northward subduction systems in Cretaceous in the Ladakh Himalaya. One is the Shyok oceanic plate subduction underneath the Karakoram block. The other is the Neo-Tethys oceanic plate subduction underneath the Ladakh arc. Both type of subduction systems produced the Andean-type calc-alkaline magmatism to form Ladakh island arc and Karakoram continental arc.

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Recently the Dronning Maud Land region including the Sør Rondane (SR) Mountains attracts attentions for their tectonic and metamorphic evolutions through the Gondwana Super continent evolution and construction. The region is considered as the main portion of the East-West Gondwana collision during the East Africa-Antarctica Orogen (EAAO: e.g. Jacobs and Thomas, 2004). We suggest that the western and the eastern blocks would be belonging to the EAAO and E-Gondwana, respectively. The final collision boundary between them would have formed during the Pa-African time of 530-550 Ma.

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High-pressure experiments carried out on the Ti solubility in quartz coexisting with rutile at pressures 1 atm to 20 kbar and temperatures 800-1500 °C. Experimental results shows that Ti in quartz changes following equation: RTlnX=-8504-4.975T-39.7P, where X is the cationin mole fraction of TiO₂ in quartz. The equation indicates the pressure dependence of Ti solubility is very small. Wark & Watson's (2006) Ti-in-Qtz geothermometer resulted about 200 °C higher in a retrograde temperature than those of present experimental results.

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Peak metamorphic temperature condition using calcite-graphite carbon isotope thermometry in marble layers from a regionally rehydrated high-grade terrain of Sor Rondane Mountains. Carbon isotope fractionation between calcite/dolomite and graphite range between 2.2 to 3.8, correspond to metamorphic temperatures between 1000 and 680 C were estimated for the marbles.

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Some volcanic rocks have experienced mass fractionation from the atmospheric argon isotopes. We propose a model when, where and how the mass fractionation from the atmospheric argon isotopes takes place during processes from the magmatism to the volcanism.

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The conventional K-Ar method assumes that the initial argon isotopic ratio is equal to the atmospheric ratio. Argon analyses of historical lavas (free in radiogenic argon) revealed that the initial isotopic ratios of rocks have experienced mass fractionation from the atmospheric argon isotopic ratio, requiring the peak comparison method for dating volcanic rocks. We analyzed using the peak comparison method; intra plate volcanic rocks from New Zealand, island arc volcanic rocks from Bali Island and dredge samples from deep-sea volcano in Mariana. The results give more reliable ages in comparison with the reported ages.

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Synchrotron XRF analysis was conducted to know an effect of (Na, K)Cl on the elemental distribution between aqueous fluids and high Mg andesite under high-pressure and high-temperature conditions. We found increases of partitioning of Cs and Ba to the (Na, K)Cl rich fluids at 1.5 GPa.

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Crystal settling is an important process for magmatic differentiation. To clarify the effect of crystal settling, it is necessary to distinguish between initial phenocrysts and newly-formed crystals, but it is difficult to do so in plutonic rocks. To solve the problem, we investigated the occurrence and chemical variation of chrome spinel from the Murotomisaki Gabbro. In consequence, we found that chrome spinel inclusions in plutonic olivine and plagioclase crystals were useful markers to identify the zone of phenocryst accumulation.

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Diffusion of P in feldspars is considered to be sluggish, and thus can preserve the information on its formation. Utilizing this characteristic, the formation process of Bt+Pl intergrowth after Grt is studied. In between the intergrowth and the matrix feldspars, two textures are found: (i) A single grain feldspar possessing the adjoining perthitic and anti-perthitic parts. (ii) Serrate projections of Bt developed against the Or lamellas in Afs. Texture (i) formed under 750-825°C, and texture (ii) formed under lower-T than (i), both of these by consuming K in feldspars to grow Bt. From the viewpoint of diffusion distance, the intergrowth possibly formed at higher-T than 750-825°C, before the formation of texture (i), by the reaction between Grt and melt. Feldspars in the matrix has P-poor core and the rim as rich in P as Pl in the intergrowth. This P-rich part possibly crystallized simultaneously with Pl from the melt.

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Late Miocene to Pliocene Wakurayama dacite is distributed within a 5km radius in Matsue city, Sanin district, southwest Japan. We clarified the Bulk rock chemical compositions and Sr-Nd-Pb isotopic ratios of Wakurayma dacite. It has been understood that the chemical compositions of all Wakurayama dacite is extremely similar to the adakite. And it is also similar to chemical compositions of Quaternary Daisen volcano of Sanin district. In addition, a lot of Quaternary adakitic rocks are reported to the Sanin district. It may be explained that the adakitic magma source is exist in the Subducted Philippine Sea plate, and Wakurayama dacite might have been a beginning activity of adakite at 5Ma in the Sanin district.

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Cretaceous granitic rocks, Inner Zone of southwest Japan, intruded along the continental margin and played an important role for the formation of continental crust. The granitic rocks from the central to north Kyushu and the Ryoke belt are divided into two stages in terms of their intrusive order. Geological investigation reveals that the two-stage crustal melting would be triggered by mantle derived basaltic magma in each stage. Isotopic differences of the granitic rocks from both regions can be explained by degree of assimilation rate of crustal materials in their source regions.

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In western Marie Byrd Land of the West Antarctica, a diorite pluton and widely distributed mafic dykes occur in the Fosdick migmatite-granite complex, which is interpreted to represent middle-to-lower crustal rocks of the paleo-Pacific Gondwana margin. New U-Pb geochronology of magmatic zircon in these rocks yields mid-Cretaceous crystallization ages. These mafic intrusive rocks are medium- to high-K-series calc-alkaline rocks with basic-intermediate composition. They have trace element patterns characterized by LIL-element enrichments and negative Nb anomalies indicating their origin from a hydrous mantle source metasomatized by slab-derived components. Their Sr-Nd isotope data are consistent with derivation from an enriched mantle source. The results of this study are more consistent with melting of metasomatized sub-arc mantle sources during back-arc extension than melting associated with a mantle plume.

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Magnetic petrological investigations for the pyroclastic deposits of the Tenmei eruption of the Asama-Maekake volcano are carried out. Magnetic properties of the pumice deposits suggest that magmatic/volcanic process or eruptive style changed during a sequence of the Tenmei eruption.

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In this study, occurrences and chemistry of magnetite crystals in Cenozoic alkali basaltic lavas from the Fukuoka district, SW Japan, were described and their relative timing of crystallization was examined. The lavas are ferrobasaltic and have characteristic phenocryst mineral assemblage: magnetite coexists with olivine and plagioclase phenocryst is absent in the lavas. Magnetite crystals occur not only as discrete phenocrysts but also as inclusions partially or fully surrounded by olivine. EPMA analyses of magnetite inclusions and their host olivine showed that Mg, Al and Cr contents decrease and Ti content increases in magnetite as Mg# of olivine decreases. These indicate that magnetite inclusions in olivine were primocrysts and hence early saturation of magnetite occurred in the magma. We will also discuss about the physicochemical conditions for early saturation of magnetite in the basaltic magma.

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Quartz diorite, tonalite, and leucogranite are widely distributed in Obara area, San-in zone, SW Japan. The quartz diorite is mingled with the tonalite, and the both is intruded by the leucogranite. In this paper, we report their data of geology, petrography, and Rb-Sr whole rock ages.

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The Cretaceous granitic rocks in the Yanai district, the eastern part of Yamaguchi Prefecture, are divided into three groups: Older Ryoke granites, Younger Ryoke granites and Sanyo granites. The Kibe pluton belongs to Younger Ryoke granites. The pluton consists mainly of biotite-granite including euhedral K-feldspar as phenocrysts. Field occurrence, peterography and geochemical studies reveal that lithological variation of the Kibe pluton can be explained by assimilation and fractionation model.

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The metamorphic rocks accompanied by serpentinite melange in the Tenzan area. Saga Prefecture consists of low-P/T type metamorphic rocks lacking high-P/T type metamorphic rocks. On the other hand, serpentinite melange from the Nagato Tectonic belt in Yamaguchi Prefecture contains high-P/T type metamorphic rocks and meta-trondhjemite as blocks in the serpentinite matrix. The metamorphic rocks from the Tenzan area and the Nagato Tectonic belt have been considered as a member of the Sangun belt. Considering of geochemistry of metamorphic rocks and compositions of chromite in serpentinite, the metamorphic rocks of the Tenzan area can be correlated with those of the Higo metamorphic terrane.

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Mafic and ultramafic Complex in Yamaga district, Kumamto Prefecture have ophiolitic rock assemblage with depleted in HFS elements. Felsic rock with quartz-plagioclase dominant have zircon with 489 Ma U-Pb zircon age. This age probably shows the original age of Yamaga gabbro complex.

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The early-Paleozoic (500-400Ma) amphibolites occur in the Kitomyo, the Fuko pass, the Wakazakura area of SW Japan, and the Kiroko and the Motai area of NE Japan. These metamorphic rocks have a similar petrological feature, and provide a petrotectonic constraint on the earliest subduction event in the Japanese orogen. In this study, analytical results of these amphobolite and its related rocks are reported to clarify the tectonic development during the earliest stages of orogenic growth of Japanese island.

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The Iwakuni area, western part of Yamaguchi prefecture is dominated by the unmetamorphosed Kuga group in north and the low-grade part of Ryoke belt in south. The Kuga group conformably overlays the Ryoke belt without any structural gaps. According to the degree of graphitization, the metamorphic grade progressively increases from the Kuga group to the Ryoke belt regardless of any deformational features. The Kuga group was formed as the accretionary complex followed by undergoing the low-pressure type of the Ryoke metamorphism. Therefore, the main deformational events occurred to be prior to the Ryoke metamorphism.

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Metamorphic rocks from the east and west of Onikobe-Yuzawa mylonite zone are compared to those in the Kitakami and Abkuma Mountains of NE Japan. In the east, southern Mt.Yakeishi, amphibolites and serpentinites are exposed. In the west, Shirakawa area of the Kamuro Mountains, biotite gneisses and amphibolites are exposed. Chemical compositions of amphiboles from the southern Mt. Yakeishi are similar to the Ohachimori amphibolites in the Matugadaira-Motai metamorphic belt in Kitakami Mts. Spinel compositions are similar to ultramafic rocks form Mt. Hayachine in the South Kitakami belt. Amphiboles and garnets compositions from Shirakawa are close to those from the Abukuma metamorphic rocks. Yakeishi and Shirakawa compare to the Matugadaira-Motai and Abukuma metamorphic belts, respectively.

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