timing of rotational motion of southwest japan inferred from paleomagnetism abstract paleomagnetic field directions for the period younger than 35 ma are obtained from igneous rocks distributed in the san in district inner zone of southwest japan the remanent magnetization of samples between 30 and 35 ma old are fairly well grouped with a mean direction of d 65 9 i 48 6 and 95 6 5 this result establishes that southwest japan rotated clockwise 56 12 during the past 30 m y a declination value of about 60 is observed in the rocks of 28 ma d 52 2 i 33 5 and 21 ma d 69 9 i 49 5 comparing this with results from dacitic rocks with an age of 15 ma in other areas of southwest japan suggests that rotational motion did not occur possibly until 15 ma these results require that the rotation of southwest japan occurred just after the shikoku basin had been created

nd and sr isotopic variations in acidic rocks from japan significance of upper mantle heterogeneity initial nd and sr isotopic ratios have been measured for cretaceous acidic and related intermediate rocks 24 volcanic and two plutonic rocks from the inner zone of southwest japan izswj to investigate the genesis of acidic magmas the initial nd and sr isotopic ratios for these rocks show three interesting features 1 end values for acidic rocks 2 to 9 are negatively correlated with esr values 10 to 90 together with those for intermediate rocks end 3 to 8 esr 0 to 65 2 the end values for silica rich rocks 60 sio2 correlate with the longitude of the sample locality decreasing from west to east in a stepwise fashion four areas characterized by uniform end values are discriminated 3 low silica rocks 60 sio2 in a certain area have distinctly different end values from those of the high silica rocks in the same area

andesites and dacites from daisen volcano japan partial to total remelting of an andesite magma body voluminous andesite and dacite lavas of daisen volcano sw japan contain features suggesting the reverse of normal fractionation anti fractionation in the sense that magma genesis progressed from dacite to andesite accompanied by rises in temperature a positive correlation exists between phenocryst content 0 40 vol and wt sio2 61 67 phenocryst rich dacites contain hornblende and plagioclase that are generally unaltered clear and euhedral however phenocryst poor rocks contain sieve textured plagioclase resorbed plagioclase and opacite in which hornblendes are pseudomorphed some daisen rocks contain two coexisting pyroxenes many orthopyroxene phenocrysts from two pyroxene lavas have high ca overgrowth rims up to 50 mm a feature consistent with crystallization from a higher temperature magma than the core rim compositions are similar from phenocryst to phenocryst in individual samples temperatures of 800 900 c are obtained from the cores whereas temperatures of 1000 1100 c are indicated for the rims lavas ranging from aphyric andesite 61 wt sio2 to phenocryst rich dacite 67 wt sio2 have similar sr sr 0 7045 0 7052 and nd nd 0 5127 0 5128 isotopic variability within daisen volcano is likely to be mantle derived reflecting isotopic variability within the magma source region associated with a single mantle diapir the daisen andesites and dacites have the same trace element signatures as the associated basalts and were probably derived from primary magmas at the same general depth 60 km our interpretation is that mantle derived hydrous magnesian andesite generated in the same mantle diapir as coexisting basalt magma may be parental to the hydrous calc alkaline magmas in daisen volcano we suggest a two stage process involving mid crustal solidification of bodies of this calcalkaline magma followed by varying degrees of partial melting from body to body to produce the magmatic trends and phenocryst zoning patterns observed the heat required for this melting according to our model was supplied by the intermittent rise of subjacent basaltic magma

recognition of the shimanto hp metamorphic belt within the traditional sanbagawa hp metamorphic belt new perspectives of the cretaceous paleogene tectonics in japan abstract the sanbagawa metamorphic belt in sw japan has been traditionally referred as a typical subduction related high pressure hp metamorphic belt this belt extends e w direction for more than 800 km from the kanto mountains to kyushu island in part protoliths of many hp metamorphic rocks formed as an accretionary complex after ca 90 80 ma and suffered a blueschist facies metamorphism at 66 61 ma this metamorphic event clearly postdates the sanbagawa metamorphism of 120 110 ma this newly recognized hp rocks occur extensively in the traditional sanbagawa hp metamorphic belt throughout shikoku kii peninsula and kanto mountains thus it was named as the shimanto hp metamorphic rocks thus the traditional sanbagawa metamorphic belt comprises two distinct hp metamorphic belts and the sanbagawa metamorphic rocks cover less than half of the areas for the traditional sanbagawa metamorphic belt importantly the metamorphic grade of the shimanto metamorphic rocks ranges from the pumpellyite actinolite to epidote amphibolite facies just like many sanbagawa metamorphic rocks the similarity between metamorphic rocks of these two belts in spatial distribution metamorphic grades and metamorphic facies series was the main reason why these two belts had not previously been differentiated a pacific type orogenic belt in general comprises a belt of accretionary complex and hp metamorphic belt on the ocean side plus a fore arc basin and a granite batholith belt on the continent side in sw japan the sanbagawa metamorphic belt is chronologically accompanied with the accretionary complex southern chichibu belt lower cretaceous fore arc sediments and the ca 120 70 ma sanyo batholith belt with ryoke low pressure metamorphic rocks likewise the shimanto hp metamorphic belt is accompanied with an upper cretaceous accretionary complex northern shimanto belt campanian to maastrichtian fore arc sediments and the san in batholith belt the opening of a back arc basin japan sea at ca 20 ma extensively modified the primary spatial arrangements of the two cretaceous paleogene orogenic belts in particular the southward thrusting of the ryoke sanyo granitic batholith belt over the sanbagawa metamorphic belt formed the present structural superposition of the ryoke above the sanbagawa and shimanto metamorphic belts

nd and sr isotope systematics of miocene to holocene volcanic rocks from southwest japan volcanism since the opening of the japan sea isotope nd and sr and geochemical data for twelve volcanic rocks from the shimane oki san in region of southwest japan give some insight into the miocene recent volcanic history of southern japan since rifting from the asian mainland the oldest rocks examined dolerites and ushikiri formation were erupted during the opening of the japan sea at about 15 ma and comprise arc tholeiites derived from a depleted source end 0 esr 0 interpreted in terms of a depleted mantle source modified by a slab derived fluid volcanics of oki dozen island in the japan sea are alkalic derived from an enriched mantle plume isotopically distinct from nearly oki dogo island eruption of the calc alkaline wakurayama andesite early pliocene and both arc and within plate type basalts 1 ma show that magmas were tapped from a variety of sources taking into account plate tectonics and seismic data the subduction influence until the quaternary was the pacific plate with philippines sea plate subduction affecting quaternary and younger volcanics

combined neutralization adsorption system for the disposal of hydrothermally altered excavated rock producing acidic leachate with hazardous elements abstract hydrothermally altered rock excavated in a tunnel project produces acidic leachate containing hazardous elements that include arsenic as lead pb copper cu and zinc zn to mitigate this problem this paper evaluated a combined neutralization adsorption system that used readily available and cheap reagents like calcium carbonate caco3 and partly weathered volcanic ash batch neutralization experiments showed that caco3 was effective in raising the ph of the leachate around neutral while the batch adsorption experiments illustrated that the volcanic ash sample collected near the tunnel project area was highly capable of adsorbing arsenate as v pb cu and zn under column conditions the amount of hazardous elements released from the rock increased by several folds and their breakthrough curves had flushing out trends the mechanisms of as and heavy metals release probably include the dissolution of soluble phases and pyrite oxidation addition of caco3 in the column experiments based on estimates from the batch results underestimated the amount of neutralizer needed to adjust the effluent ph to around 8 resulting only in slight increase of the ph nevertheless the presence of caco3 drastically reduced the amount of hazardous elements released from the altered rock especially during the initial stages of the column experiments combining neutralization and adsorption effectively reduced the amount of as and heavy metals in the effluent throughout the duration of the column experiments which is attributed to the slight neutralizing effect of volcanic ash that raised the ph around circumneutral as well as its rich al and fe oxyhydroxide oxide contents the combined system immobilized the hazardous elements through a combination of co precipitation and adsorption reactions and showed potential as an alternative method for the disposal of altered rocks producing acidic leachate

mesozoic episodic magmatism in south korea and its tectonic implication 1 ne trending granitoid batholiths in south korea are part of the huge phanerozoic granitoid belt in east asia the crystallization ages of granitoid plutons show three episodes of mesozoic magmatism in south korea triassic 248 210 ma jurassic 197 158 ma and late cretaceous early tertiary 110 50 ma with a late jurassic early cretaceous 50 m y hiatus the granitoid ages and kinematic analyses of the mesozoic structures in south korea suggest that the middle jurassic 180 170 ma dextral strike slip ductile shear zones formed by the northwest orthogonal subduction of the izanagi plate whereas the cretaceous sinistral faults formed by the northward oblique subduction of the same plate which generally agree with proposed reconstruction of plate motions albeit uncertain around east asia among the models proposed to explain magmatic lull in a continental arc shallow angle subduction associated with high convergence rate and subduction of oceanic plateaus might be the probable cause for the magmatic hiatus in south korea and japan the huge width 500 km of the east asian granitoid belt may be explained by oceanward retreat of subduction zone in the cretaceous in association with change in the movement direction of the subducting plate

interaction between felsic and mafic magmas in the salmas intrusive complex northwestern iran constraints from petrography and geochemistry abstract the salmas plutonic complex in the northernmost part of sanandaj sirjan zone of iran provides evidence for magma interaction processes the complex contains mafic intermediate hybrid and felsic rocks which intruded into the paleozoic metamorphic complex they show typical relationships described in many mafic felsic mingling and mixing zones worldwide such as mafic microgranular enclaves in felsic and hybrid rocks mafic sheets and hybrid rocks the mafic microgranular enclaves mmes are characterized by fine grained equigranular and hypidiomorphic texture and some special types of microscopic textures e g quartz xenocrysts oscillatory zoned plagioclase small lath shaped plagioclase in large plagioclase spike zones in plagioclase and spongy cellular plagioclase textures rounded plagioclase megacrysts blade shaped biotite acicular apatite the mafic sheets and mmes in granites mme gr which indicated magma mingling structures show isr values and end i similar to diorites the hybrid rocks and their mafic enclaves mme h show isotope signatures similar to each other granites have isotope signatures higher 87sr 86sr i 0 70788 0 71075 and lower end i 2 4 to 4 2 distinct to those of the all rock types and mmes major trace and ree modeling show that hybrid rocks are generated via 40 60 mixing of mafic dioritic and felsic granitic end members all the geochemical data suggest that underplating of dioritic magma which has been produced by fractional crystallization of gabbros under the lower crust caused its melting to make felsic granitic magma injection of dioritic magma into the base of the felsic magma chamber and a limited mixing of two end members the lower crust derived magma and mantle derived melts formed hybrid magma and their enclaves injections of new mafic magma pulses into hybrid magma generated mafic enclaves into them the injections of denser dioritic magma pulses into a felsic magma chamber and spreading of it at the level of rheological contrast have been formed mafic sheets and mmes in granites

provenance of paleozoic mesozoic sedimentary rocks in the inner zone of southwest japan an evaluation based on nd model ages abstract nd model ages using depleted mantle tdm values for the sedimentary rocks in the inner zone of the sw japan and western area of tanakura tectonic line in the ne japan allow classification into five categories 2 6 2 45 2 3 2 05 1 9 1 55 1 45 1 25 and 1 2 0 85 ga the provenance of each terrane belt district is interpreted on the basis of the tdms 147sm 144nd vs 143nd 144nd relation nd isotopic evolution of the source rocks in east china and u pb zircon ages the provenance of 2 6 1 8 ga rocks which are reported from hida oki and renge belts and kamiaso conglomerates is inferred to be the sino korean craton skc the 2 3 1 55 ga rocks mostly from ryoke mino and ashio belts are originally related with the skc and or yangtze craton yc the provenances of the sedimentary rocks with 1 45 0 85 ga from the suo belt higo and some districts in the mino and ashio belts are different from the skc and yc especially the higo with 1 2 0 85 ga is considered as a fragment of collision zone in east china akiyoshi belt probably belongs to the youngest age category of 1 2 0 85 ga some metasedimentary rocks from the ryoke belt have extremely high 147sm 144nd and 143nd 144nd ratios whose main components are probably derived from mafic igneous rocks within the ryoke belt itself and from the adjacent tamba belt

emplacement ages geochemical and sr nd hf isotopic characterization of mesozoic to early cenozoic granitoids of the sikhote alin orogenic belt russian far east crustal growth and regional tectonic evolution abstract the sikhote alin range of the russian far east is an important accretionary orogen of the western pacific orogenic belt in order to study the formation and tectonic evolution of the orogen we performed zircon u pb dating as well as geochemical and sr nd hf isotopic analyses on 24 granitoid samples from various massifs in the primorye and khabarovsk regions the zircon dating revealed that the granitoids were emplaced from 131 to 56 ma cretaceous to paleogene in the primorye region granitoids in the coastal sikhote alin intruded the cretaceous taukha accretionary terrane from ca 90 to 56 ma whereas those along the central sikhote alin fault zone intruded the jurassic samarka accretionary terrane during ca 110 75 ma the oldest monzogranite 131 ma was emplaced in the lermontovka area of the nw primorye region granitoid massifs along the central sikhote alin fault zone in the khabarovsk region formed from 109 to 58 ma thus the most important tectonothermal events in the sikhote alin orogen took place in the cretaceous geochemical analysis indicates that most samples are i type granitoids they have initial 87sr 86sr ratios ranging from 0 7040 to 0 7083 and initial nd isotopic ratios expressed as end t values from 3 0 to 5 0 mostly 0 to 5 the data suggest that the granitoid magmas were generated by partial melting of sources with mixed lithologies including the subducted accretionary complex hidden paleozoic proterozoic basement rocks based on whole rock nd isotopic data we estimated variable proportions 36 77 of juvenile component mantle derived basaltic rocks in the generation of the granitic magmas furthermore zircon hf isotopic data ehf t 0 to 15 indicate that the zircon grains crystallized from melts of mixed sources and that crustal assimilation occurred during magmatic differentiation the quasi continuous magmatism in the sikhote alin orogen suggests that the paleo pacific plate subduction was very active in the late cretaceous the apparently regular progression of granitic intrusion ages from 80 to 56 ma in the taukha terrane may reflect oblique underflow of the paleo pacific plate beneath the eurasian continental margin subduction was not only manifested by granitic intrusion but also by abundant silicic volcanism the late cretaceous paleo pacific plate motion probably changed from parallel or sub parallel to oblique relative to the continental margin of the sikhote alin leading to the change of magmatic source region and geochemical characteristics of the derived igneous rocks late cretaceous rapid sea floor spreading at ca 100 ma induced highly active subduction and led to voluminous magmatism in the entire circum pacific realm finally the present age and isotopic study lends support to the hypothesis of geologic and tectonic correlation between sikhote alin and sw japan

mullions in the high ardenne slate belt belgium numerical model and parameter sensitivity analysis in the high ardenne slate belt belgium pre existing layer perpendicular quartz veins in psammite layers acted as mechanical boundaries due to the difference in competence between vein quartz and psammite this caused the formation of mullions during layer parallel shortening in this paper the process of mullion formation is modelled using finite element techniques a parameter sensitivity analysis of the mullion model demonstrates that the stress exponent of psammite the total horizontal shortening of the psammite layers the initial aspect ratio of the psammite segments between the veins and the competence contrast between psammite and vein quartz are the controlling parameters for the shape of the mullions our results suggest that the morphology of the mullions can be used to constrain the rheology of psammite deforming in the middle crust moreover the parameter sensitivity analysis illustrates the range of layer parallel shortening extension structures associated with layer perpendicular quartz veins that can be expected in nature e g dogbones inverted mullions and creates future perspective for the use of the model as a paleorheological gauge for these structures

zircon u pb age and nd isotope geochemistry of latest neoproterozoic to early paleozoic oeyama ophiolite evidence for oldest morb type oceanic crust in japanese accretionary system and its tectonic implications abstract the oeyama ophiolite is considered as one of the major ophiolites in the japanese islands that forms a part of the circum pacific phanerozoic multiple ophiolite belts in this study zircon u pb age and their ree geochemistry and nd sr isotope geochemistry are presented for the gabbroic rocks of the oeyama ophiolite to determine the precise crystallization age and characterize the proper tectonic setting of this ancient oceanic crust the zircon grains of the two studied gabbroic samples yield 206pb 238u ages of 545 4 2 6 ma and 532 4 3 1 ma from five gabbroic rocks a comparable 566 95 ma sm nd whole rock isochron age is obtained the time corrected etnd values t 545 ma for each sample are ranging from 7 2 to 7 7 that suggest their normal mid oceanic basalt n morb affinity discrimination diagrams using zircon u yb versus hf and y also indicate their oceanic crustal origin this is so far known the oldest date of ophiolite in the japanese accretionary system on the basis of the present dataset we have offered a scenario of the potential tectonic development highlighting the journey of this group of oceanic crustal rocks from the mid oceanic region till their final accretion to the japanese islands the present tectonic model envisages an initial oceanward subduction at ca 530 ma switched over to the present continentward subduction at ca 400 ma moreover the three different units of the oeyama ophiolite have been re classified based on the present age dataset and the formation and evolution of these units constituting the typical lower part of the ocean plate are explained

k ar age and geochemistry of the sw japan paleogene cauldron cluster implications for eocene oligocene thermo tectonic reactivation abstract systematic k ar dating and geochemical analyses of paleogene cauldrons in the sanin belt of sw japan have been made to explore the relationship between the timing of their formation and the paleogene subduction history of sw japan documented in the shimanto accretionary complex we also examine the magma sources and tectonics beneath the backarc region of sw japan at the eastern plate boundary of eurasia fifty eight new k ar ages and 19 previously reported radiometric age data show that the cauldrons formed during middle eocene to early oligocene time 43 30 ma following a period of magmatic hiatus from 52 to 43 ma the hiatus coincides with absence of an accretionary prism in the shimanto belt resumption of the magmatism that formed the cauldron cluster in the backarc was concurrent with voluminous influx of terrigenous detritus to the trench as a common tectono thermal event within a subduction system the cauldrons are composed of medium k calc alkaline basalts to rhyolites and their plutonic equivalents these rocks are characterized by lower concentrations of large ion lithophile elements lile including k2o ba rb th u and li lower la yb n ratios lower initial sr isotopic ratios 0 7037 0 7052 and higher end t values 0 5 to 3 5 relative to late cretaceous to early paleogene equivalents there are clear trends from enriched to depleted signatures with decreasing age from the late cretaceous to the paleogene the same isotopic shift is also confirmed in lower crust derived xenoliths and is interpreted as mobilization of pre existing enriched lithospheric mantle by upwelling depleted asthenosphere relatively elevated geothermal gradients are presumed to have prevailed over wide areas of the backarc and forearc of the sw japan arc trench system during the eocene to oligocene newly identified late eocene low silica adakites and high mg andesites in the sanin belt and early eocene a type granites in the sw korea peninsula probably formed due to upwelling of hot asthenosphere and subduction of a young plate the backarc region was an extensional tectonic setting and some paleogene rift basins and sanin belt cauldrons occur in linear arrays the eocene oligocene sanin se korea continental arc lies on the ne extension of the east china sea basin the initial stage of which probably formed by continental arc rifting this rifting may have been triggered by upwelling of hot asthenosphere into the wedge space created by rollback of the subducted slab in response to decreased convergence rate between the pacific and eurasian plates

spatial variations of sr and nd isotope ratios of cretaceous paleogene granitoid rocks southwest japan arc cretaceous paleogene granitoid rocks and contemporaneous volcanic rocks are widely distributed in the inner zone of southwest japan this intense intermediate to felsic magmatism is considered to have taken place on the eastern margin of the eurasian continent before the southwest japan arc drifted away from the continent in the middle miocene resulting in the opening of the japan sea the granitoid rocks show regional variations in terms of their radiometric age petrography sr nd and o isotope ratios based on sr and nd isotope ratios granitoid rocks can be divided into three zones south transitional and north between the median tectonic line and the japan sea granitoid rocks and associated gabbros of the north zone have low initial sr isotope ratios 0 7048 to 0 7068 and high initial end values 3 to 2 2 whereas granitoid rocks and gabbros from the south zone have high initial sr isotope ratios 0 7070 to 0 7088 and low initial end values 3 0to 8 0 most granitoid rocks from the transitional zone have sr and nd isotope ratios that lie between those of the north and south zones although there is some overlap contamination of magmas by upper crust cannot explain this geographical variation in sr and nd isotopes instead the regional variation is attributed to compositionally different magma sources probably upper mantle and lower crust beneath the north and south zones this is supported by the sr and nd isotopic ratios of upper mantle and lower crustal xenoliths included in cenozoic volcanic rocks in the north and south zones these ratios are similar to those of the granitoid rocks in the respective zones it is suggested that a micro continent or island arc consisting of continental crust was underthrust beneath the south zone before or during the cretaceous resulting in compositionally distinct sources for granitoid rocks of the north and south zones the large variation observed in sr and nd isotope ratios for transitional zone granitoid rocks is explained by variable proportions of the two different crustal and upper mantle components

the late jurassic oblique collisional orogen of sw japan new structural data and synthesis the structural configuration of sw japan mainly reflects a late jurassic early cretaceous orogeny the region is divided into an inner belt and an outer belt on the japan sea and pacific ocean sides respectively by a strike slip fault the median tectonic line mtl both consist of a series of stacked nappes the inner belt is divided into a jurassic olistostrome known as the tanba zone and a hinterland area comprising continental triassic jurassic sediments the tanba zone is sliced into two units a lower one with late jurassic matrix and triassic early jurassic radiolarite olistoliths tectonically overthrust by an upper unit comprising an olistostrome with middle jurassic matrix and blocks which include late paleozoic limestone basic lava and radiolarite the tanba zone is overthrust by a paleozoic nappe complex derived from the hinterland the basal sole of the nappe corresponds to a peculiar unit called the ultra tanba zone in the chugoku area the hinterland is divided into an upper nappe the oga nappe formed by permo carboniferous limestone and permian clastic rocks and a lower one the sangun maizuru nappe formed by paleozoic high pressure hp metamorphics the sangun schists the permian maizuru olistostrome and the dismembered paleozoic yakuno ophiolites in the northern part of sw japan the tanba zone is in faulted contact with the circum hida and the hida zones the former is interpreted as the equivalent of the oga and sangun maizuru nappes of the chugoku domain crushed by post cretaceous tectonics the latter consists of paleozoic high temperature ht metamorphic rocks and late triassic early jurassic granite locally mylonitized and covered by early jurassic sandstone the outer belt is formed by a superficial nappe similar to the tanba zone thrust upon a deep domain characterized by a synmetamorphic ductile deformation the deep domain is divided into a lower unit the oboke unit formed by continental derived arenites and a green schist nappe consisting of oceanic sediments and resedimented ophiolites the green schist nappe overthrusts the oboke unit under synmetamorphic conditions with an eastward displacement the two belts are separated by the ryoke zone which corresponds to the southern part of the tanba zone affected by a cretaceous ht metamorphism and sharply cut by the mtl a geodynamic model is proposed for the jurassic orogeny of sw japan assuming that the evolution of the inner and outer belts are linked in the late triassic early jurassic sw japan is an active plate margin the upper plate or south china block consisted of the hinterland and the tanba belt a forearc basin the lower plate consisted of an oceanic area and the south japan continent the basic mechanism of the orogeny is ascribed to the oblique subduction and collision of the south japan continent

origin of the granodiorite in the forearc region of southwest japan melting of the shimanto accretionary prism abstract in the forearc region of southwest japan felsic to intermediate volcano plutonic complexes of middle miocene age intruded into the shimanto accretionary complex possibly in association with megatectonic events such as the opening of the japan sea and resultant underthrusting of the newly borne shikoku basin philippine sea plate beneath the southwest japan arc activities of mantle derived magmas are also distinct in the forearc of middle miocene southwest japan tholeftic basalts are closely related to igneous activity of the shikoku basin and high mg andesites probably formed under anomalously high temperature conditions caused by the opening of japan sea two plutons uwajima and miuchi were chosen for understanding the origin of felsic magmas in the forearc region of southwest japan all granitic rocks of the plutons show enriched isotopic characteristics with higher 87 sr 86 sr and lower 143 nd 144 nd tha bulk earth which suggests that the contribution of crustal materials has a magma source however they have lower 87 sr 86 sr and higher 143 nd 144 nd than shimanto sediments and hence an additional component with lower 87 sr 86 sr and higher 143 nd 144 nd than granitic rocks must be required possible candidates for such components are coeval mantle derived magmas mass balance modelling between mantle derived magmas and shimanto sediments on the basis of their sr nd isotopic compositions suggested that mixing of anatectic melt of the shimanto sediments and porphyritic andesite magma evolved from high mg andesite as a possible mechanism of the origin of the granodiorites of the uwajima pluton injection of high mg andesite into the shimanto accretionary prism may triggered the melting of sediments calculated composition of anatectic melt of the shimanto sediment and p t condition of the gneissose enclave in the granodiorite suggest that the melting of sediments may have occurred at higher temperature conditions than those of the melting reactions involving biotite breakdown

compositional variation of the late cretaceous paleogene plutons from southwest japan and its implication for ore genesis and continental growth abstract during the late cretaceous paleogene period the fluids liberated from the subducting slab along japanese arc subduction zone could have triggered the partial melting of the mantle wedge whose composition was similar to the fertile primitive mantle underplating of the produced basaltic magmas beneath the continental crust could further facilitate the partial melting of the lower continental crusts the primary magmas produced by the mixing of resultant partial melts underwent various degrees of fractional crystallization processes to produce the late cretaceous paleogene plutons in southwest japan and have contributed to the growth of continental crust with new non recycled materials during the phanerozoic the factor analysis of chemical data from ore barren ryoke and w sn ore rich sanyo plutonic rocks identifies three major groups of elements the mafic group al fe mg mn ca sr zn co v p cu ni and cr the felsic group si k rb cs tl pb y nb ta hf ge sn w th u and hree and the lree zr group ba la ce pr nd eu zr and hf mafic group and felsic group elements are inversely correlated the concentrations of lree zr group elements increase first then decrease with increasing sio2 content therefore the high silica samples of the ryoke sanyo belts are low in lree zr group elements in the ryoke samples mo behaves like zr which results in the lowest mo content in the ryoke samples with high silica the high mo and si contents in some sanyo samples suggest that the zircon compatible mo4 may be converted to incompatible mo6 under a relatively high oxygen fugacity condition at the late stage of magmatic differentiation w and sn behave as the felsic group elements in the ryoke sanyo samples thus their concentrations are high in the high silica granitoids especially rock samples from the sanyo belt which are often associated with w sn ores the factor analysis of the sanin plutonic samples indicates that w still belongs to the felsic group but sn no longer correlates with w and behaves more like zr due to the conversion of incompatible sn2 to zircon compatible sn4 under a relatively high oxygen fugacity condition in the sanin belt therefore sn content is low in high silica granitoids from sanin belt the high silica sanin samples are often enriched in mo again suggesting the conversion of zircon compatible mo4 into incompatible mo6 in the magmas of those samples the high mo granitoids from the sanin belt are probable source rocks for the associated mo ores in the area

an adakitic pluton on kyushu island southwest japan arc abstract an adakitic pluton is designated the shiraishino granodiorite ca 15 km2 in outcrop area on kyushu island southwestern japanese arc sr y and rare earth element concentrations and crystallization characteristics of the pluton are similar to those of adakites geochemical and tectonic considerations show that the pluton was derived from partial melting of a subducted slab with minor contamination of high 87sr 86sr material and subsequent fractional crystallization of plagioclase hornblende compiled sr and y data indicate that most cretaceous granitic rocks of southwestern japan generated by partial melting of mafic lower crust adakitic plutons derived by slab melting occur rarely and have older ages it is concluded that plutonism in the southwestern japanese arc during cretaceous time was began with the emplacement of small adakitic intrusions and progressed to more abandant granitic rocks of the type derived from the mafic lower crust