an electron microprobe study of the u th pb systematics of metamorphosed monazite the role of pb diffusion versus overgrowth and recrystallization abstract an electron microprobe emp was used to obtain u th pb chemical ages from monazite that underwent an amphibolite facies metamorphic overprint in the monashee complex southern canadian cordillera u pb isotope dilution dating of single grains yielded discordant ages that plot in linear arrays on a concordia diagram upper intercepts of the arrays indicate primary growth in the proterozoic and cretaceous and lower intercepts are coeval with a tertiary metamorphic event the microprobe s high spatial resolution 2 m and ability to quickly differentiate between domains with greatly contrasting u th and pb concentrations made it the ideal tool for investigating the cause of the u pb isotopic discordance the microprobe dating shows that proterozoic monazite lies directly adjacent to generally small

spatiotemporal variations of jurassic cretaceous magmatism in eastern asia tan lu fault to sw japan evidence for flat slab subduction and slab rollback here we examine spatiotemporal variations of jurassic cretaceous magmatism along a c 1000 km transect across eastern asia including sw japan the korean jiaodong and liaodong peninsulas and eastern jilin province integration of tectonic regime data with age data from igneous rocks in eastern asia from the tan lu fault to sw japan suggests a shallowing of the subduction angle and subsequent flat slab subduction during the jurassic and slab rollback during the early cretaceous the combination of a subducting plateau and root enhanced suction provides the best explanation for the flat slab subduction in the final stage albian of slab rollback the geotectonic setting changed from subduction accretion to a continental arc in the area close to the ancient trench i e the inner zone of sw japan

the elastic properties of hcp fe alloys under the conditions of the earth s inner core abstract geophysical and cosmochemical constraints suggest the inner core is mainly composed of iron with a few percent of light elements however despite extensive studies over many years no single alloying light element has been found that is able to simultaneously match the observed inner core density and both seismic velocities this has motivated a number of suggestions of other mechanism to lower velocities such as anelasticity or premelting however an unexplored possibility is that a combination of two or more light elements might produce the desired reduction in velocities and densities of the inner core in order to test this we use ab initio molecular dynamics calculations to map the elastic property space of hcp fe alloyed with s si and c at 360 gpa up to the melting temperature based on a mixing solid solution model together with direct simulations on the ternaries we found a number of compositions which are able to match the observed properties of the inner core this is the first time that the density v p v s and the poisson s ratio of the inner core have been matched directly with an hcp fe alloy

th u pb monazite geochronology of the luliang and wutai complexes constraints on the tectonothermal evolution of the trans north china orogen abstract recent lithological metamorphic and geochronological studies show that the basement of the north china craton ncc formed by collision of two discrete archean to paleoproterozoic blocks eastern and western blocks along a paleoproterozoic orogen named the trans north china orogen however the timing of the collision is controversial and post collisional exhumation has not been precisely dated this study applies the electron microprobe th u pb monazite dating technique to determine the ages of the peak metamorphic event and subsequent exhumation of the low to medium grade luliang and wutai complexes in the trans north china orogen electron microprobe th u pb monazite data for the luliang complex reveal five tho 2 pbo age ranges 1 1940 1938 ma 2 1880 1847 ma 3 1795 1755 ma 4 1720 1703 ma and 5 1648 ma of these age ranges the first four have also been recorded in the wutai complex which yields tho 2 pbo ages of 1 1930 ma 2 1838 1822 ma 3 1793 ma and 4 1719 ma the oldest age range of 1940 1930 ma is interpreted to record the widespread emplacement of mafic dikes in rocks of the luliang and wutai complexes the age range of 1882 1822 ma is in accord with the shrimp u pb ages of metamorphic zircons and mineral sm nd and 40 ar 39 ar ages obtained for other complexes in the orogen and is interpreted as the age of the major metamorphic event caused by amalgamation between the eastern and the western blocks the age range of 1795 1755 ma is consistent with emplacement of large scale unmetamorphosed mafic swarms at 1800 1765 ma interpreted as the time of post orogenic extension the 1720 1703 ma and 1648 ma ages are considered to date later multiple stages of hydrothermal alteration since monazites with such young ages only occur along fractures in older monazite grains and at the rims these new monazite tho 2 pbo ages support the tectonic model for the evolution of the north china craton that envisages discrete eastern and western blocks colliding along the trans north china orogen at 1 85 ga and then undergoing post collisional extension in the period 1795 1755 ma

an improved u th pb age calculation for electron microprobe dating of monazite abstract determination of u th pb ages using the electron probe microanalyser epma is an inexpensive alternative method for dating monazite the method is rapid and reliable both for simple monogenenetic monazite and for complex polygenetic monazite having undergone metamorphic events involving fluid interaction and recrystallization the main limitation of the method is its rather poor precision i e 45 to 120 ma for ages ranging from 300 to 3000 ma calculated on each spot the precision is limited by pb content and by counting statistics which cannot give precision better than 2 for individual determinations on u th and pb even at high levels a procedure that uses the new th pb vs u pb diagram to improve the calculated precision on u th pb ages gives results to within 5 to 15 ma for ages ranging from 300 to 3000 ma with complex polygenetic monazite in which either the points show large scattering indicated by a large mswd or the regression line exhibits a slope very different from neighbour theoretical isochrons the procedure must be applied separately on homogeneous domains only this makes it possible to distinguish between events separated by a gap of 20 to 60 ma according to the range of ages concerned i e 300 to 3000 ma several examples are given to illustrate these systematics

development of migmatites and the role of viscous segregation in high t metamorphic complexes example from the ryoke metamorphic complex mikawa plateau central japan abstract the ryoke metamorphic complex of the mikawa plateau central japan contains well preserved geological and thermal structures formed during cretaceous high temperature high t metamorphism these structures can be explained by a pervasive melt migration model however the estimated flux of melt is much higher than that expected for compaction flow of felsic melt an additional tectonic force and or melt segregation to network of veins or layers is therefore required this paper presents the results of numerical modeling of the structural evolution of immiscible viscous fluids under simple shear deformation and discusses the role of viscous segregation in enabling pervasive melt flow in hot crust the results of numerical modeling of simple shear deformation of immiscible viscous fluids reveal that low viscosity fluids segregate into lenses and layers this segregation is a type of viscous segregation that takes place to minimize the dissipation of energy in the system the rate of energy dissipation is proportional to viscosity therefore this process is expected to occur universally in immiscible viscous fluids with large viscosity contrasts and is an important process in focusing melt in partially melted rocks the structures produced by the numerical simulation are similar to those of migmatites the simulation results suggest that melts distributed randomly in partially melted rock will segregate into lenses or layers with progressive simple shear deformation during deformation enhanced segregation a melt network will form dynamically if this process occurs at small to large scales in the hot crust melts will be effectively transported upward due to buoyancy forces it is possible that pervasive migmatites at low structural levels within high t metamorphic complexes may represent fossil melt pathways formed by crustal scale viscous segregation

on the resolution of density within the earth roughly 30 years have passed since the last publication of a linear resolution calculation of density inside the earth since that time the data set of free oscillation degnerate frequencies has been completely re estimated taking into account the biassing effects of splitting and coupling due to 3d structure this paper presents a new resolution analysis based on the new data and focuses on two particular issues 1 the density jump at the inner core boundary which is important in discussions of the maintenance of the geodynamo and 2 a possible density excess in the lowermost mantle which might be indicative of a hot abyssal layer we find that the density jump at the inner core boundary is 0 82 0 18 mg m 3 which is significantly larger than previously thought we also find little support for an excess density in the lowermost mantle though an increase

timing of the late cretaceous ignimbrite flare up at the eastern margin of the eurasian plate new zircon u pb ages from the aioi arima koto region of sw japan abstract the kinki district in the inner zone of southwest japan is characterized by late cretaceous volcanic rocks of the aioi and arima groups and the koto rhyolites from west to east these rocks are dominated by pyroclastic flow deposits related to caldera forming events here we present new laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb ages for the aioi group four isolated caldera filling deposits the lower middle and upper parts of the arima group and one intrusive rock the kashihara quartz gabbro and the lower and upper parts of the koto rhyolites including the oldest volcanic unit within these rhyolites these analyses yielded ages of ca 86 82 ma for the aioi group ca 83 81 ma for the arima group 78 6 ma for the kashihara quartz gabbro and ca 74 73 ma for the koto rhyolites the aioi group represents a cluster of calderas and the ages obtained for individual units in this group differ from the ages of adjacent units the arima group and the koto rhyolites both consist of pyroclastic flow deposits associated with caldera forming events and the ages of these rocks are all the same within error this suggests that the aioi group represents a series of individual caldera forming eruptions that are distinct from the arima group and the koto rhyolites which formed during a single stage of caldera formation the u pb ages presented here indicate that the late cretaceous caldera forming eruptions in the study area occurred at intervals of 1 myr and represent individual events that lasted for

hydrothermal chloritization processes from biotite in the toki granite central japan temporal variations of of the compositions of hydrothermal fluids associated with chloritization this paper describes the biotite chloritization process with a focus on mass transfer in the toki granitic pluton central japan and also depicts the temporal variations in chemical characteristics of hydrothermal fluid associated with chloritization during the sub solidus cooling of the pluton singular value decomposition svd analysis results in chloritization reaction equations for eight mineral assemblages leading to the quantitative assessment of mass transfer between the reactant and product minerals and inflow and outflow of components through the hydrothermal fluid the matrices for svd analysis consist of arbitrary combinations of molar volume and closure component in the reactant and product minerals the eight reactions represent the temporal variations of chemical characteristics of the hydrothermal fluid associated with chloritization the progress of chloritization results in gradual increase of silicon potassium and chlorine and gradual decrease of calcium and sodium in the hydrothermal fluid with temperature decrease the biotite chloritization involves two essential formation mechanisms chlorite formation cf mechanism 1 small volume decrease from biotite to chlorite and large inflow of metallic ions such as al3 fe2 mn2 and mg2 from the hydrothermal fluid and cf mechanism 2 large volume decrease and large outflow of the metallic ions into hydrothermal fluid chlorite produced with cf mechanism 1 dominates over that of cf mechanism 2 resulting in the gradual decrease of the metallic components in the hydrothermal fluid with chloritization progress the chloritization reactions also give the temporal variations in physicochemical parameter of the hydrothermal fluid a gradual decrease of ph and a gradual increase of redox potential in the hydrothermal fluid as chloritization proceeds the combination of continuous reactions based on compositional variations in chlorite together with corresponding continuous aliv variations gives an indication of the temporal variations in rates of decreasing and increasing concentration of chemical components in the hydrothermal fluid associated with chloritization the biotite chloritization and resultant temporal variations of chemical and physicochemical characteristics in hydrothermal fluid act as a trigger for the successive dissolution precipitation process of a granitic rock

possible manifestations of slab window magmatisms in cretaceous southwest japan abstract the slab window system related to ridge subduction is studied to explain the conspicuous activity and the along arc migration of the magmatisms in the eastern margin of eurasian continent in the late mesozoic the trend of the granite ages is scrutinized with systems approach and analyzed by the statistical method in cretaceous southwest japan a reference field of the eurasian eastern margin the magmatic distribution of simultaneous activity was determined to be the v shape of the slab window excluding dating errors from the located age data the slab window magmatism has the most dominant zone of the acidic rocks at or near the centerline of the window the spreading center of two plates and also has the subdominant zone of the acidic to intermediate rocks on either side of the window as the slab window opens due to the plate motions the upwelling current is adiabatically induced in the asthenosphere to fill the window gap the partial melt is generated in the upwelling flux and transports heat to the lower crust to make greater granitic magma chambers by heat conduction to and assimilation with the crustal matter the younger and hotter slabs outside the window also play a role in partial slab melting and or dehydration to the asthenosphere and generate the subdominant granodioritic and adakitic and or high magnesian andesitic magmatisms as the pre and post activities of the main granite genesis the slab window formed by the subducted ridge between the kula and pacific plates was the strong heat source of the active magmatisms and migrated at the rate of 2 8 cm year from southwest to northeast about 8000 km along the continental margin the growth of the continent associated with the active acidic to intermediate magmatisms including the adakitic and or high magnesian andesitic activities is modeled by the slab window system

complexity in the behavior and recrystallization of monazite during high t metamorphism and fluid infiltration abstract a detailed study of monazite grains in silica undersaturated and quartz bearing mg al metapelite from the oygarden group of islands east antarctica reveals a complex history of growth and recrystallization during two separate events in the neoproterozoic and earliest cambrian monazite grains from garnet poor and garnet rich metapelite preserve core domains that have ages corresponding to growth and or recrystallization at granulite facies p 9 1 0 gpa t 850 900 c conditions during the rayner structural episode between 930 and 890 ma high th rims 22 wt tho 2 that are in textural equilibrium with sapphirine orthopyroxene symplectites formed after garnet during late rayner decompression occur on monazite grains in garnet rich assemblages and give electron microprobe ages 883 18 ma within error of core domains 903 14 ma these high th rim domains are interpreted to have formed through recrystallization of liberated inclusions via a process dominated by coupled dissolution reprecipitation reactions facilitated by transient fluid films on the large surface areas in the symplectite and not by new growth in garnet poor metapelite monazite grains that have grain boundaries in textural equilibrium with the granulite facies assemblage also show alteration to higher th compositions on rims and along vein like fractures this compositional shift is accompanied by partial to complete resetting of ages to 500 ma along with minor modification of core domain ages textures and patterns of chemical age resetting are interpreted to also be the result of a coupled dissolution reprecipitation reaction process but in contrast to garnet bearing assemblages this alteration occurred during a fluid influx at lower temperatures during regional pan african tectonism this study highlights the susceptibility of monazite to resetting with fluid present conditions dramatically increasing the potential for recrystallization

epma u th pb monazite and shrimp u pb zircon geochronology of high pressure pelitic granulites in the jiaobei massif of the north china craton the jiaobei massif constitutes the southern segment of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton and contains high pressure hp mafic and pelitic granulites the hp pelitic granulites contain four distinct mineral assemblages garnet kyanite biotite muscovite rutile m1 garnet kyanite ternary feldspar biotite muscovite rutile m2 garnet sillimanite biotite perthite anti perthite m3 and biotite muscovite sillimanite plagioclase m4 of which m2 is a typical hp pelitic assemblage the origin of these hp granulites is important for understanding the tectonic evolution of the jiao liao ji belt but the timing of the hp event still remains unknown this study applied the epma u th pb monazite and shrimp u pb zircon dating techniques to determine the metamorphic ages of the hp pelitic granulites in the jiaobei massif cl images and th u ratios show that all monazite and zircon grains in the analyzed samples are of metamorphic origin eighty two epma analyses on 16 monazite grains from two samples yielded three age groups at 1895 to 1882 ma 1814 to 1813 ma and 1706 to 1692 ma and the ages of 16 shrimp analyses on 14 zircon grains from one sample range from 1864 to 1803 ma the oldest ages of 1895 to 1882 ma were yielded from high y monazite grains enclosed in garnet and sillimanite pseudomorph after kyanite and thus interpreted as the time of the hp m2 granulite facies metamorphism the epma monazite ages of 1814 to 1813 ma and shrimp zircon ages of 1864 to 1803 ma are interpreted as the approximate ages of the post hp granulite facies metamorphism m3 most probably resulting from the exhumation of the hp granulites to the medium pressure granulite facies levels the youngest age group of 1706 to 1692 ma obtained from low y monazite grains in the matrix can be interpreted as the age of late cooling and retrograde metamorphism m4 that occurred when the hp pelitic granulites were exhumed to the upper crust the presence of paleoproterozoic hp mafic and pelitic granulites in the southern segment of the jiao liao ji belt suggests that the evolution of the jiao liao ji belt in the eastern block of the north china craton must have been involved in subduction or collision related tectonic processes

thermal event records in se china coastal areas constraints from monazite ages of beach sands from two sides of the taiwan strait abstract chime ages of 460 detrital monazites from beach sands from se china chinmen island and w taiwan were determined in order to deduce the major tectonothermal events affecting the coastal areas of se china additional 360 monazites from estuarine sediments of the minjiang river eastern china metamorphic rocks from chinmen island and sedimentary rocks from w taiwan were also dated ages of the chinmen beach monazites 245 80 ma reveal that they are derived from adjacent gneisses and mixed with sediment from the jiulongjiang river se china some large euhedral monazites contain older cores 220 ma and younger rims 137 124 ma demonstrating that overgrowth on inherited indosinian grains occurred at the time of gneiss formation 137 ma monazites of w taiwan fall into two age groups one in the paleoproterozoic 1900 1650 ma and the other spanning the phanerozoic 530 120 ma based on similar ages of phanerozoic monazites from the minjiang river and w taiwan monazites of the latter group are inferred to be derived mainly from this river hence the paleoproterozoic monazites are most probably derived from cathaysia basement exposed in the drainage basin of the wuyishan nw fujian along with monazite ages of the two mica schist sediments from the uplifted changle nanao shear zone cnsz constitute only a minor component of deposits in w taiwan the age frequency distribution of phanerozoic monazites from w taiwan which shows peaks at 450 430 360 350 275 and 245 ma suggests the existence of caledonian hercynian and indosinian crust beneath the immense yanshanian cover of the se china coastal area

geological characterisation of the active atera fault in central japan implications for defining fault exclusion criteria in crystalline rocks around radioactive waste repositories abstract in the orogenic field of the japanese archipelago faults are inevitably distributed in all types of potential host rocks for high level radioactive waste hlw repositories these faults could have an adverse impact on a repository if they were to provide a short circuit to the biosphere so allowing any radionuclides released from the repository a more rapid transport pathway to the surface than would be the case otherwise associated with many faults is a damage zone with fault gouge and crushed rock developed in and alongside the main fault plane the specific characteristics of a damage zone are considered to be a reflection of the process of faulting and may be used to understand the influence of fault movement on the surrounding host rocks in order to clarify the geological characteristics by which potentially transmissive features of faults can be avoided when siting a radioactive waste repository for hlw in a crystalline host rock the active atera fault which is located in central japan has been studied relationships between the morphological features of the fault its associated damage zone and the fracture frequency have been investigated detailed mapping of the damage zone shows that the fractures formed by later faulting activity can be distinguished from the early fractures developed in the rock by using the microscopic textures and the differences between fracture filling minerals in particular a network of shortly transected fractures filled by carbonate and iron oxyhydroxide minerals was preferentially formed in the damage zone along the atera fault probably by recent fault movement the density of fractures also suggests that the mechanical damage zone formed by faulting extends for up to ca 200 m on each side of the main fault plane however the geochemically influenced zone has been spatially restricted by geochemical buffering reactions involving crushed fracture filling materials along the fault the results provide a basis for defining exclusion zones around faults that might be identified in a future crystalline repository host rock the methodology is applicable to site characterization and the appropriate allocation of repository panels and deposition holes for waste canisters

holocene break up and reestablishment of the petermann ice tongue northwest greenland abstract over the last decade two major calving events of the petermann ice tongue in northwest greenland have led to speculation on its future stability and contribution to further greenland ice sheet mass loss however it has been unclear if these events are anomalous or typical within the context of limited historical observations we extend the historical record of the floating ice tongue using the stratigraphy of petermann fjord sediments to provide a longer term perspective computed tomography ct scans x ray fluorescence xrf scans ice rafted debris ird counts and the magnetic properties of specific particle size fractions constrain changes in depositional processes and sediment sources at our core sites allowing for reconstructions of past behavior of the petermann ice tongue radiocarbon dating of foraminifera 210pb and paleomagnetic secular variation psv provide age control and help to address uncertainties in radiocarbon reservoir ages a floating ice tongue in petermann fjord formed in late glacial time as petermann glacier retreated from an advanced grounded position this paleo ice tongue broke up during the early holocene when high northern latitude summer insolation was higher than present after gradual regrowth of the ice tongue associated with regional cooling the ice tongue reached its historical extent only within the last millennium little or no ice tongue was present for nearly 5000 years during the middle holocene when decadal mean regional temperatures are estimated to be 0 8 2 9 c higher than preindustrial 1750 ce and seasonal sea ice in the lincoln sea was reduced this pre historical behavior shows that recent anthropogenic warming may already be in the range of ice tongue instability and future projected warming increases the risk of ice tongue break up by the mid 21st century

viscous flow and deformation of regional metamorphic belts at convergent plate boundaries 1 viscous flow and deformation of a newtonian fluid between rigid boundaries have been modeled for investigating deformation of a forearc wedge and a regional metamorphic belt as a weak deforming zone between the plates at convergent boundaries three types of analytic formulations together with numerical formulations for a newtonian fluid with a constant viscosity are used for investigating various flows and deformation 1 flows induced by squeezing between two parallel boundaries 2 flows induced by squeezing and heterogeneous mass influx in the wedge between two oblique boundaries e g accretionary wedge over the subducting plate with the continental plate as a backstop and 3 flows induced by dragging along the boundaries and by homogeneous mass influx in the wedge as in type 2 all cases include strike slip movements of the boundaries which allows us to investigate three dimensional 3 d deformation e g 3 d corner flow the corresponding flow deformation of infinitesimal and finite elements and the timescale of flow are calculated for each configuration with various mechanical boundary conditions the model results show that configuration and mechanism of the flow can be inferred from the spatial variation of finite deformation e g deformed radiolarians as a strain marker and geometry of folding as finite deformation of a large block in particular prolate strain nearly parallel to the strike of subduction zone together with a large scale folding can be a good indicator for deformation in the forearc wedge associated with 3 d corner flow induced by oblique subduction deformation observed in the cretaceous regional metamorphic belts in southwest japan can be explained by this mechanism

nondestructive chemical dating of young monazite using xrf 1 design of a mini probe age data for samples from the central alps and comparison to u pb tims data the analytical capabilities of an improved mini xrf instrument for trace element analysis are explored to obtain u th pb ages for single monazite grains as small as 50 m the detection limits for u th and pb with counting times of 10 min are 10 ppm counts collected for 40 min are sufficient to date single monazite grains as young as 15 ma the precision of the age data depends essentially on the counting statistics of the main x ray peak npb l 1 2 used to analyze for lead the age uncertainty is proportional to the age of the grain the total contents of th and u and the squared integration time the reliability of the chemical dating method is tested using monazite separates from amphibolite facies metamorphic monazite samples from the central alps for which the chemical ages are compared to mass spectrometric u pb tims ages we show that populations of analyses obtained using the new instrument on single grains as young as 25 30 ma agree within error with the tims data for monazite separates with complex age patterns such as polymetamorphic samples yielding discordant isotopic ages the statistical analysis of chemical age data obtained from populations of 26 50 grains is advantageous in that it may provide additional insight into the reasons for the discordancy chemical th u pb dating of monazite by the xrf method offers considerably improved accuracy and precision compared with chemical dating by electron microprobe which typically becomes impractical for samples less than 100 200 ma in age conversely the minimum grain size required for the new instrument 50 m is well above the spatial resolution of the electron microprobe 2 m a companion paper scherrer et al this volume describes further developments towards microanalysis by xrf with improved spatial resolution

chlorite and biotite weathering fe2 rich corrensite formation and fe behavior under low po2 conditions and their implication for precambrian weathering fresh and weathered granite from drill cores in tono gifu japan was examined to understand weathering products and the mechanisms of chlorite and biotite weathering under low p o 2 conditions a fresh sample from 365 m depth a slightly weathered light green sample from 367 m depth and a nearly fresh sample from 369 m depth but with brown stains on fractures were investigated the xrd sem empa and tem analysis of green grains present within chlorite biotite and plagioclase grains and in veins was found to be fe 2 rich corrensite about 40 wt feo with fe fe mg 0 94 the corrensite is interpreted to have formed from chlorite and biotite via a dissolution precipitation mechanism the 2 fe value of 0 69 which when combined with the presence of amorphous fe 3 hydr oxides confirmed by tem indicates that the fe 2 fe value of corrensite is 0 69 these results indicate that on dissolution of chlorite and biotite fe 2 was transported as fe 2 and precipitated as fe 2 rich corrensite and a part of the dissolved fe 2 was oxidized to amorphous fe 3 hydr oxides under low p o 2 conditions the formation of fe 2 rich corrensite and that of fe 2 rich smectite or vermiculite in the laboratory at 1 atm of p co 2 and 3 10 5 atm of p o 2 murakami et al 2004 suggest that a possible fe 2 bearing product during precambrian weathering is fe 2 rich sheet silicates but not siderite

sound velocity measurements in dhcp feh up to 70 gpa with inelastic x ray scattering implications for the composition of the earth s core abstract we have determined the density evolution of the sound velocity of dhcp fehx x 1 up to 70 gpa at room temperature by inelastic x ray scattering and by x ray diffraction we find that the variation of vp with density is different for the ferromagnetic and nonmagnetic dhcp fehx and that only nonmagnetic dhcp fehx follows birch s law combining our results with birch s law for iron and assuming an ideal two component mixing model we obtain an upper bound of the hydrogen content in the earth s inner core 0 23 6 wt h corresponding to feh0 13 3 the iron alloy with 0 23 6 wt h can satisfy the density and compressional and shear sound velocities of the prem inner core assuming that there are no other light elements in the inner core

p t t evolution of sapphirine bearing semipelitic granulites from vadkampatti in eastern madurai domain southern india insights from petrography pseudosection modelling and in situ monazite geochronology abstract migmatitic semipelitic granulites from the eastern madurai domain of southern india preserves reaction textures indicating a clockwise p t evolution with near isothermal decompression the prograde history is recorded by included phases within porphyroblastic garnet and orthopyroxene development of high xmg garnet up to 0 69 orthopyroxene al2o3 up to 9 6 wt assemblage indicates attainment of ultrahigh temperature uht condition at the peak stage subsequent formation of a series of symplectic assemblages opx2 spr2 sil2 pl2 and opx2 crd2 with aluminous orthopyroxene al2o3 up to 9 5 wt at the expense of garnet indicates decompression at ultrahigh temperatures conventional thermobarometry and feldspar thermometry indicate peak metamorphic p t conditions of 970 30 c 10 3 0 4 kbar and formation of symplectites at 960 20 c 9 2 0 3 kbar for opx2 spr2 sil2 and at 890 40 c 7 3 0 6 kbar for opx2 crd2 obtained p t conditions are in agreement with the p t estimates from pseudosection modelling texturally controlled in situ monazite dating shows that the th poor and extremely hree depleted dark cores of matrix monazite with a weighted age of 586 8 ma formed simultaneously with garnet growth during the prograde evolution on the other hand th rich and hree depleted bright rims with a weighted age of 532 7 ma formed from the dissolution reprecipitation due to melt crystallization at or near t max dating the peak of metamorphism the compositionally homogeneous hree y enriched monazite in the symplectite with a weighted age of 475 12 ma formed along with the symplectites during garnet breakdown our results are suggestive of a late neoproterozoic to cambrian long lived ca 55 million years hot orogenic plateau in the madurai block uht conditions were likely achieved by conductive heating before being rapidly uplifted to shallower crustal depth during late cambrian to early ordovician 475 12 ma this is consistent with the hot orogen model for the attainment of uht conditions which demonstrates that crusts that are moderately rich in heat producing elements can reach temperatures 900 c when the duration of orogeny is sufficiently long i e slow erosion rates to allow conductive heating through radioactive decay

outer core compositional layering and constraints on core liquid transport properties a variety of studies of the earth s outer core report wave speeds near the top of the core slightly lower than reference models for core properties one interpretation of the slower wavespeed profile is that it could represent a change in the core s light element concentration with depth in the core i explore the consequences of this idea by interpreting the velocity profile as arising from diffusion gradients imposed in the outer core by various mechanisms in order to estimate relative diffusion rates for light elements in liquid iron i also examine theories for transport properties of high pressure metallic liquids that are based on hard sphere models from the seismic wavespeed profile an effective diffusivity may be obtained which ranges from 0 1 to 10 10 7 m2s 1 depending on the particular boundary condition or initial condition chosen the upper bound of the range is higher than expected from high pressure experiments and models of diffusivity in liquid metals for all elements except h the lower bound is within the uncertainty of theoretical predictions and experimental determinations given the range of expected outer core temperatures if diffusion involves low z elements plausible agreement arises from a class of models that represent diffusion out of a compositionally different layer existing from the time of the formation of the earth if the wavespeed profile in the core is diffusive in nature the data suggest that it is an original feature of the core

numerical modeling of thermal structure circulation of h2o and magmatism metamorphism in subduction zones implications for evolution of arcs abstract numerical models on thermal structure convective flow of solid generation and transportation of h2o rich fluid in subduction zones are consolidated to have a comprehensive view of the subduction zone processes heat balance circulation of h2o magmatism metamorphism growth of arcs and continental margins a large scale convection model with steady subduction of a cold old slab 130 myr old predicts rapid 100 myr cooling of subduction zones resulting in cessation of magmatism the model also predicts that the mantle temperature beneath arcs and continental margins is greatly affected by the effective temperature of the subducting slab i e the age of the subducting slab if subduction of a young hot slab including ridge subduction occurs every 60 to 120 myr as is suggested for eastern asia the average temperature beneath arcs is increased by about 300 c which may explain the long lasting magmatism in eastern asia associated with subduction of young slabs and ridges thermal structure and circulation of h2o are greatly modified to cause a transition from 1 normal arc magmatism 2 forearc mantle melting to 3 slab melting to produce a significant amount 100 km3 of granitic melts associated with both high p t and low p t type metamorphism the last stage of 3 can result in formation of a granitic batholith belt and a paired metamorphic belts synthesis of the numerical models and observations suggest that episodic subduction of young slabs and ridges can explain heat source for generating a large amount of granitic magmas of batholiths synchronous formation of batholith and regional metamorphic belts and p t conditions of the paired metamorphism even the high p t metamorphism requires an elevated geothermal structure in the forearc region associated with ridge subduction although the emplacement of the batholiths and the regional metamorphic belts and the mass balance in subduction zones are not well constrained at present the episodic event associated with ridge subduction is thought to be essential for net growth of arcs and continental margins as well as for the long term heat balance in subduction zones

determination of the stress conditions of the ductile to brittle regime along the asuke shear zone sw japan abstract the stress conditions of the ductile to brittle regime have been assessed along the asuke shear zone asz which strikes ne sw in the cretaceous ryoke granite terrain in sw japan along the asz pseudotachylyte and mylonitized pseudotachylyte are locally developed together with cataclasite the simultaneous operation of dislocation creep and grain size sensitive creep as indicated by the coexistence of the z maximum and relatively random c axis lattice preferred orientations as well as the sizes of dynamically recrystallized quartz grains 6 40 7 79 m in the mylonitized pseudotachylyte suggest differential stresses of 110 130 mpa at 300 c the e twin morphology twinning ratio and distribution of the glide direction on the e twin plane of the twinned calcite in the amygdules of the pseudotachylyte suggest the stress conditions of the 1 and 3 axes trend 228 and 320 and plunge 55 and 1 respectively and indicate differential stresses of 40 80 mpa at 150 200 c based on kinematic indicators in the fault rocks the stress conditions estimated from calcite twins and the cooling history of the granitic protolith the asz is inferred to have been activated under a stress state that caused sinistral normal movements before and after pseudotachylyte formation at 70 50 ma

format and philosophy for collecting compiling and reporting microprobe monazite ages microprobe monazite dating has been increasingly used to constrain the timing of deformation and metamorphism because of the potential to date very small monazite domains down to 5 m or less in structural and petrologic context this paper presents an analytical strategy presentation format and error considerations for microprobe monazite dating the strategy involves high resolution compositional mapping to delineate compositional domains within monazite crystals then for each compositional domain a series of th u and pb analyses are made and a single date and error are calculated the number of analyses in each domain is determined by the desired statistical precision of the date results from several monazite grains are typically combined and along with textural relationships are used to build an argument that the dates constrain the age of a deformation or metamorphic event the total error involves three components short term random error dominated by counting statistical uncertainty short term systematic error uncertainty in background correction conductive coating variation and calibration and long term systematic error uncertainty in standard composition mass absorption factors decay constants etc in homogeneous compositional domains short term random errors 2 of less than 10 m y can be obtained from five to ten analyses however short term systematic error mainly background estimation uncertainty would typically result in a doubling of the magnitude of random error microprobe dates are presented as a single gaussian probability distribution for each domain along with representative compositional maps it is recommended that a consistency standard be analyzed during each analytical session and the results be reported along with those from the unknown this proposed strategy and format are compatible with those of other geochronological techniques they incorporate analytical limitations associated with trace as opposed to major element microprobe analysis and will allow better comparisons to be made between labs and between different geochronological techniques

provenance implications of th u pb electron microprobe ages from detrital monazite in the carboniferous upper silesia coal basin poland abstract this paper reports the results of chime chemical th u pb isochron method dating of detrital monazites from carboniferous sandstones in the upper silesia coal basin uscb a total of 4739 spots on 863 monazite grains were analyzed from samples of sandstone derived from six stratigraphic units in the sedimentary sequence age distributions were identified in detrital monazites from the uscb sequence and correlated with specific dated domains in potential source areas most monazites in all samples yielded ca 300 320 ma variscan ages however eo variscan caledonian and cadomian ages were also obtained the predominant ages are comparable to reported ages of certain tectonostratigraphic domains in the polyorogenic bohemian massif bm which suggests that various crystalline lithologies in the bm were the dominant sources of uscb sediments

dissolution and precipitation processes in deformed amphibolites an example from the ductile shear zone of the ryoke metamorphic belt sw japan the granitic mylonite zone in the cretaceous ryoke metamorphic belt contains deformed amphibolites as thin layers the amphibolite layers do not exhibit pinch and swell or boudinage structures even when contained in a high strain granitic mylonite this mode of occurrence suggests that they were deformed as much as the surrounding granite mylonite in the highly deformed zone strongly foliated amphibolites contain ti rich brown amphibole porphyroclasts rimmed by ti poor green amphibole titanite and chlorite these porphyroclasts are elongated forming shear surfaces defined by preferential distribution of the chlorite and titanite porphyroclastic plagioclase in the strongly foliated amphibolites consists of two components an anorthite rich core and an anorthite poor rim based on these observations the mass balanced reaction occurring during deformation is defined as as the reaction products form a weak interconnected matrix the strain rate of the amphibolites may be controlled by the rate of dissolution precipitation through fluids weakly foliated amphibolites in the low strain zone exhibit cataclastic microstructures whereas the strongly foliated amphibolites do not exhibit such features these microstructural and chemical changes suggest that high strain amphibolites were initially deformed by cataclasis followed by deformation through metamorphic reactions during the metamorphism deformation old plagioclase grains with high xan were not stable and dissolved and new plagioclase grains with low xan crystallized at the old plagioclase rim dissolution of old plagioclase and precipitation of new plagioclase occurred normal to and parallel to the foliation respectively reflecting incongruent pressure solution due to differential stress and changes in p t h2o conditions the development of incongruent pressure solution is attributed to increased fluid flux in the strongly foliated amphibolites as evidenced by the greater abundance of hydration reaction products in the strongly foliated amphibolites than in the weakly foliated ones

proterozoic polymetamorphism in the quanji block northwestern china evidence from microtextures garnet compositions and monazite chime ages abstract the quanji block situated close to the triple junction of three major precambrian terranes in china i e the north china craton the yangtze block and the tarim block is composed of precambrian metamorphic crystalline basement and an unmetamorphosed mesozoic paleozoic sedimentary cover it has been interpreted as a remnant continental fragment microtextural relationships garnet trace element compositions and monazite chime ages in paragneisses schists and granitic leucosomes show two episodes of regional metamorphism in the quanji block basement the first regional metamorphism and accompaning anatexis took place at 1 93 ga the second regional metamorphism occurred between 1 75 and 1 71 ga mineral compositions of the first metamorphism including those of monazite were significantly disturbed by the second event these two regional metamorphic episodes were most likely linked to assembly and breakup of the supercontinent columbia respectively

elemental and sr nd isotopic geochemistry of cretaceous to early paleogene granites and volcanic rocks in the sikhote alin orogenic belt russian far east implications for the regional tectonic evolution abstract the sikhote alin orogenic belt in russian far east is an important late mesozoic to early cenozoic accretionary orogen related to the subduction of the paleo pacific plate this belt was generated by successive accretion of terranes made of accretionary prisms turbidite basins and island arcs to the continental margin of northeastern asia represented by the bureya jiamusi khanka block from jurassic to late cretaceous in order to study the tectonic and crustal evolution of this orogenic belt we carried out zircon u pb dating and whole rock elemental and sr nd isotopic analyses on granites and volcanic rocks from the primorye region of southern sikhote alin zircon dating revealed three episodes of granitoid emplacement permian early cretaceous and late cretaceous to early paleogene felsic volcanic rocks mainly rhyolite dacite and ignimbrite that overlay all tectonostratigraphic terranes were erupted during 80 57 ma postdating the accretionary process in the sikhote alin belt the cretaceous paleogene magmatism represents the most intense tectonothermal event in the sikhote alin belt whole rock major and trace elemental data show arc like affinity for granitoids and volcanic rocks indicating that they were likely generated in a supra subduction setting their initial 87sr 86sr ratios range from 0 7048 to 0 7114 and end t values vary from 1 7 to 3 8 mostly

87sr 86sr compositional linkage between geological and biological materials a case study from the toyota granite region of japan abstract the strontium isotope value 87sr 86sr is often used to identify the origins of agricultural products and the movements of ancient people maps delineating the distribution of 87sr 86sr values can therefore be of great use previous 87sr 86sr distribution maps of stream sediments covering small areas of japan largely reflect the 87sr 86sr values of underlying bedrock it remains unclear however whether the 87sr 86sr values of stream sediments may also reflect the 87sr 86sr values of the nearby vegetation and fauna we sought to resolve this question by investigating the relationship between 87sr 86sr values in biological samples and in geological samples from the sites from which the biological samples grew the geological samples consisted of soil samples from 2 paddy fields and 13 bed sediment samples grain size in the geological samples the 87sr 86sr values of water extracted sr water soluble sr and ammonium acetate extracted sr exchangeable sr fractions in paddy soils were almost the same as each other 0 7098 0 7100 and slightly lower than the 87sr 86sr values of bulk sr fractions 0 7099 0 7106 the 87sr 86sr values of biological samples 0 7098 0 7100 were also similar to those of the water soluble sr and exchangeable sr fractions in paddy soils though they varied among the parts of plants analyzed this indicates that exchangeable sr is absorbed by plants from soils through nutrients and water and ingested by herbivorous animals from soils through plants and water the 87sr 86sr values of bulk sr in paddy soils ranged somewhat widely while those from stream sediments collected around paddy fields were less variable 0 7099 0 7100 the difference in 87sr 86sr values between the paddy soils and stream sediments samples similarly derived from inagawa granite bedrock may be related to the variable degree of weathering and ultimately to the mineral composition of the samples this difference however was smaller than the range of 87sr 86sr values observed in the watershed geology we therefore propose that in a silicate dominated geology of the type typical of japan an 87sr 86sr spatial distribution map using both exchangeable sr and bulk sr fractions in stream sediments can provide useful guidance for identifying the geographic origins of food or for serving other related purposes

fe feo and fe fe 3 c melting relations at earth s core mantle boundary conditions implications for a volatile rich or oxygen rich core eutectic melting temperatures in the fe feo and fe fe3c systems have been determined up to 150 gpa melting criteria include observation of a diffuse scattering signal by in situ x ray diffraction and textural characterisation of recovered samples in addition compositions of eutectic liquids have been established by combining in situ rietveld analyses with ex situ chemical analyses gathering these new results together with previous reports on fe s and fe si systems allow us to discuss the specific effect of each light element si s o c on the melting properties of the outer core crystallization temperatures of si rich core compositional models are too high to be compatible with the absence of extensive mantle melting at the core mantle boundary cmb and significant amounts of volatile elements such as s and or c 5 at corresponding to 2 wt or a large amount of o 15 at corresponding to 5 wt are required to reduce the crystallisation temperature of the core material below that of a peridotitic lower mantle

tourmaline breakdown in the migmatite zone of the ryoke metamorphic belt sw japan a sharp line delimitating the distribution of tourmaline termed as a tourmaline out isograd is defined in the migmatite zone of the ryoke metamorphic belt japan the trend of the tourmaline out isograd closely matches that of the isograds formed through the regional metamorphism suggesting that it represents the breakdown front of tourmaline during regional metamorphism this is confirmed by the presence of the reaction textures of tourmaline to sillimanite and cordierite near the tourmaline out isograd the breakdown of tourmaline would release boron into associated melts or fluids and be an important factor in controlling the behaviour of boron in tourmaline bearing high temperature metamorphic rocks near the tourmaline out isograd large tourmaline crystals occur in the centre of interboudin partitions containing leucosome in the melanosome of the intervening matrix reaction textures involving tourmaline are locally observed these observations imply that tourmaline breakdown is related to a melting reaction and that the boron in the leucosome is derived from the breakdown of tourmaline in the melanosome during prograde metamorphism boron released by tourmaline breakdown lowers both the solidus temperature of the rock and the viscosity of any associated melt considering that the tourmaline out isograd lies close to the schist migmatite boundary these effects might have enhanced melt generation and segregation in the migmatite zone of the ryoke belt the evidence for the breakdown of tourmaline and the almost complete absence of any borosilicates throughout the migmatite zone suggest that boron was effectively removed from this region by the movement of melt and or fluid this implies that the tourmaline out isograd can reflect a significant amount of mass transfer in the anatectic zones

proton microprobe for chemical dating of monazite abstract although quantitative chemical analysis by proton microprobe has become an established technique it has been rarely applied to problems in the earth sciences the method having lower detection limit better than 10 ppm for u th and pb and higher spatial resolution than electron microprobe typically 1 m vs 3 m can be successfully used in geology here we present a procedure for the chemical dating of monazite ree po4 by proton microprobe the procedure is compared with electron probe microanalysis technique epma

redox front penetration in the fractured toki granite central japan an analogue for redox reactions and redox buffering in fractured crystalline host rocks for repositories of long lived radioactive waste abstract redox buffering is one important factor to be considered when assessing the barrier function of potential host rocks for a deep geological repository for long lived radioactive waste if such a repository is to be sited in fractured crystalline host rock it must be demonstrated that waste will be emplaced deeper than the maximum depth to which oxidizing waters can penetrate from the earth s surface via fractures during the assessment timeframe typically 1 ma an analogue for penetration of such oxidizing water occurs in the cretaceous toki granite of central japan here a deep redox front is developed along water conducting fractures at a depth of 210 m below the ground surface detailed petrographical studies and geochemical analyses were carried out on drill core specimens of this redox front the aim was to determine the buffering processes and behavior of major and minor elements including rare earth elements rees during redox front development the results are compared with analytical data from an oxidized zone found along shallow fractures up to 20 m from the surface in the same granitic rock in order to understand differences in elemental migration according to the depth below the ground surface of redox front formation geochemical analyses by xrf and icp ms of the oxidized zone at 210 m depth reveal clear changes in fe iii fe ii ratios and ca depletion across the front while fe concentrations vary little in contrast the redox front identified along shallow fractures shows strong enrichments of fe mn and trace elements in the oxidized zone compared with the fresh rock matrix the difference can be ascribed to the changing eh and ph of groundwater as it flows downwards in the granite due to reactions with rock forming minerals in particular feldspar dissolution these observations give important insights into the processes that control the rates of redox front penetration in fractured crystalline rock the findings of the study can be used to help build confidence among stakeholders that radioactive waste would be emplaced in such rocks at greater depth than that to which oxidizing water is likely to penetrate in future

palaeomagnetism of middle triassic red bedded cherts from southwest japan equatorial palaeolatitude of primary magnetization and widespread secondary magnetization summary middle triassic anisian red bedded cherts were collected from the ajiro area in kyushu island southwest japan for a palaeomagnetic study thermal demagnetization showed five distinct remanent magnetization components from the cherts the lowest temperature component below 200 c component a is a present day viscous overprint the second up to 420 c component b and third demagnetized up to 580 c component c components are secondary magnetizations of thermoviscous and chemical origin respectively both of which reside in magnetite the fourth removed component component d was demagnetized at 630 c and is a secondary magnetization carried by haematite components b and c are considered to be a result of widespread remagnetization in southwest japan during the cretaceous the basis of this consideration is that red chert remagnetizations from an area about 600 km away from the present study area are of the same origins with unblocking spectra similar to those observed in this study the last removed component during thermal demagnetization up to 695 c component e is a primary magnetization carried by haematite the directions of this component after correction for the inclination flattening yielded a mean palaeolatitude of 2 s at the time of deposition in the middle triassic the ajiro cherts accreted as part of an accretionary complex to the eastern margin of the south china block during the middle jurassic and were then translated northwards from the continental margin to their present position through a margin parallel translation process owing to the oblique convergence of the oceanic plate

dating pseudotachylyte of the asuke shear zone using zircon fission track and u pb methods abstract zircon fission track ft and u pb analyses were performed on zircon extracted from a pseudotachylyte zone and surrounding rocks of the asuke shear zone asz aichi prefecture japan the u pb ages of all four samples are 67 76 ma which is interpreted as the formation age of ryoke granitic rocks along the asz the mean zircon ft age of host rock is 73 7 2 ma suggesting a time of initial cooling through the zircon closure temperature the pseudotachylyte zone however yielded a zircon ft age of 53 9 2 ma statistically different from the age of the host rock zircon fts showed reduced mean lengths and intermediate ages for samples adjacent to the pseudotachylyte zone coupled with the new zircon u pb ages and previous heat conduction modeling the present ft data are best interpreted as reflecting paleothermal effects of the frictional heating of the fault the age for the pseudotachylyte coincides with the change in direction of rotation of the pacific plate from nw to n which can be considered to initialize the nne ssw trending sinistral extensional asz before the miocene clockwise rotation of sw japan the present study demonstrates that a history of fault motions in seismically active regions can be reconstructed by dating pseudotachylytes using zircon ft thermochronology

chemical th u total pb dating by electron microprobe analysis of monazite xenotime and zircon from the archean napier complex east antarctica evidence for ultra high temperature metamorphism at 2400 ma abstract the chemical th u total pb isochron method chime of dating was carried out on monazite xenotime zircon and polycrase in six samples of ultra high temperature uht granulites and one of pegmatite from five localities in the napier complex enderby land east antarctica despite the chronological heterogeneity in many grains the chime ages overall show strong evidence for a major event near 2420 ma analyzed monazite and xenotime grains except monazite from mt riiser larsen have a narrow range of chime ages 2412 42 ma from beaver island and 2429 36 2421 18 and 2431 22 ma from reference peak these ages are indistinguishable from chime ages on zircon 2436 17 and 2420 20 ma and on central older domains of monazite 2404 54 ma from mt riiser larsen and on a zircon rim 2430 15 ma from mt cronus we conclude that the ca 2420 ma ages relate to the uht metamorphism but we do not exclude the possibility that lead loss has lowered the ages by some 50 ma this interpretation is consistent with a preponderance of ages obtained by other methods on the napier complex particularly the ca 2475 25 ma age for a generation of pegmatites coeval with the uht event and containing the uht mineral assemblage beryllian sapphirine khmaralite quartz events prior to 2500 ma and after 2420 ma have also left their imprint on the chime ages for example a 3646 ma chime age suggests that a zircon core is inherited whereas ca 2200 and 2000 ma chime ages in zoned monazite could be due to further lead loss during post uht activity the much younger chime age of 1094 67 ma for monazite from a pegmatite at zircon point casey bay confirms 1000 1100 ma lead loss ages reported for this region and could result from fluid activity in an outlier of rayner activity near the boundary between the rayner and napier complexes approximately 2500 ma ages have been reported from granulite facies but not uht rocks in the madras and nilgiri blocks in south india these blocks and the napier complex could have constituted a single structural unit by late archean time

heterogeneity of initial 87sr 86sr ratios within a single pluton evidence from apatite strontium isotopic study abstract magmatic apatite in samples of the unmetamorphosed undeformed cretaceous pluton of the habu granodiorite southwestern japan was examined to determine its viability as an indicator of initial 87sr 86sr heterogeneity in magmatic bodies the habu granodiorite is a zoned pluton in the ryoke metamorphic belt of southwestern japan a published rb sr whole rock isochron age of 124 2 10 8 ma is significantly older than th u total pb monazite ages of ca 86 ma a rb sr mineral isochron of 90 0 2 5 ma for a sample of granodiorite from the margin of the pluton has an initial 87sr 86sr sri of 0 7056 0 0001 similar to a 87sr 86sr of 0 70539 for coexisting euhedral apatite similarly a rb sr mineral isochron of 91 4 2 5 ma for a sample of adamellite from the center of the pluton has an sri of 0 7068 0 0001 corresponding to a 87sr 86sr ratio of 0 70673 0 70684 for three fractions of coexisting euhedral apatite the uniformity of 87sr 86sr values of apatite in individual samples and accordance of 87sr 86sr values of apatite and sri from the mineral isochron suggest that magmatic apatite can be considered as a reliable indicator of sri in granitic rocks the sr isotopic compositions of euhedral apatite coupled with those determined through the mineral isochrons and whole rock data indicate that sri varies between samples from 0 7054 to 0 7074 this provides direct evidence of sri heterogeneity within a compositionally zoned pluton such heterogeneity can produce spurious whole rock age estimates in granitic plutons even where the true age of a pluton is uniform within measurable error assimilation cannot account for chemical differences between granodiorite and adamellite as well as sr isotopic heterogeneity it is likely that the heterogeneity of sri is caused by magma source materials

high poisson s ratio of earth s inner core explained by carbon alloying earth s core exhibits similar elastic properties to rubber experiments show that a high pressure phase of iron carbide modifies iron s elastic properties under inner core conditions suggesting that carbon is the light element in the core

microprobe monazite geochronology understanding geologic processes by integrating composition and chronology abstractmonazite is a light rare earth element lree bearing phosphate mineral that is present in a wide variety of rock types has an extremely variable composition reflecting host rock conditions and is a robust geochronometer that can preserve crystallization ages through a long history of geological events monazite crystals typically contain distinct compositional domains that represent successive generations of monazite which in turn can provide a detailed record of the geologic history of its host rocks the electron microprobe can be used to characterize the geometry of compositional domains analyze the composition of each domain and when carefully configured determine the u th total pb age for domains as small as 5 m in width these data allow the monazite to be linked with and place timing constraints on silicate processes in the host rocks current applications span a broad range of geologic processes in igneous metamorphic hydrothermal and sedimentary rocks

geology and tectonics of japanese islands a review the key to understanding the geology of asia abstract the age of the major geological units in japan ranges from cambrian to quaternary precambrian basement is however expected as the provenance of by detrital clasts of conglomerate detrital zircons of metamorphic and sedimentary rocks and as metamorphic rocks intruded by 500 ma granites although rocks of paleozoic age are not widely distributed rocks and formations of late mesozoic to cenozoic can be found easily throughout japan rocks of jurassic age occur mainly in the jurassic accretionary complexes which comprise the backbone of the japanese archipelago the western part of japan is composed mainly of cretaceous to paleogene felsic volcanic and plutonic rocks and accretionary complexes the eastern part of the country is covered extensively by neogene sedimentary and volcanic rocks during the quaternary volcanoes erupted in various parts of japan and alluvial plains were formed along the coastlines of the japanese islands these geological units are divided by age and origin i e paleozoic continental margin paleozoic island arc paleozoic accretionary complexes mesozoic to paleogene accretionary complexes and cenozoic island arcs these are further subdivided into the following tectonic units e g hida oki unazuki hida gaien higo hitachi kurosegawa south kitakami nagato renge nedamo akiyoshi ultra tamba suo maizuru mino tamba chichibu chizu ryoke sanbagawa and shimanto belts the geological history of japan commenced with the breakup of the rodinia super continent at about 750 ma at about 500 ma the paleo pacific oceanic plate began to be subducted beneath the continental margin of the south china block since then proto japan has been located on the convergent margin of east asia for about 500 ma in this tectonic setting the most significant tectonic events recorded in the geology of japan are subduction accretion paired metamorphism arc volcanism back arc spreading and arc arc collision the major accretionary complexes in the japanese islands are of permian jurassic and cretaceous paleogene age these accretionary complexes became altered locally to low temperature and high pressure metamorphic or high temperature and low pressure metamorphic rocks medium pressure metamorphic rocks are limited to the unazuki and higo belts major plutonism occurred in paleozoic mesozoic and cenozoic time early paleozoic cambrian igneous activity is recorded as granites in the south kitakami belt late paleozoic igneous activity is recognized in the hida belt during cretaceous to paleogene time extensive igneous activity occurred in japan the youngest granite in japan is the takidani granite intruded at about 1 2 ma during cenozoic time the most important geologic events are back arc opening and arc arc collision the major back arc basins are the sea of japan and the shikoku and chishima basins arc arc collision occurred between the honshu and izu bonin arcs and the honshu and chishima arcs

plate margin processes and paired metamorphic belts in japan comment on thermal effects of ridge subduction and its implications for the origin of granitic batholith and paired metamorphic belts by h iwamori abstract the traditional view of paired metamorphic belts forming adjacent to each other in a common arc trench subduction system is challenged and it is suggested that an alternative view based on terrane tectonics is more consistent with the geological evidence for the low p t ratio ryoke metamorphic belt of southwest japan an origin by ridge subduction is consistent with the geological evidence and results of numerical modeling by iwamori however the parallel high p t ratio sanbagawa metamorphic belt most likely was translated northeast after the ryoke ridge subduction event and was juxtaposed against the low p t ratio metamorphic belt during the late cretaceous causing progressive southwest to northeast exhumation and diachronous cooling of the low p t ratio metamorphic rocks similarly accretion by underplating in the shimanto belt likely caused exhumation and cooling of the high p t ratio metamorphic rocks of the sanbagawa and northern chichibu belts concurrently with exhumation and cooling of the ryoke belt as a result the prograde metamorphic evolution of the ryoke and sanbagawa belts cannot be modeled as a pair that formed in situ the application of results of numerical models to the origin of plate margin metamorphic belts must be based on an understanding of the geology in the model presented by iwamori the low p t ratio metamorphism and high p t ratio metamorphism are ascribed to the same ridge subduction event in a common trench system although such a scenario may produce lower p to higher p metamorphism in the inboard direction it cannot generate a high p t ratio belt outboard of a low p t ratio belt

formation of monazite via prograde metamorphic reactions among common silicates implications for age determinations three lines of evidence from schists of the great smoky mountains nc indicate that isogradic monazite growth occurred at the staurolite in isograd at 600 c 1 monazite is virtually absent below the staurolite in isograd but is ubiquitous several hundred grains per thin section in staurolite and kyanite grade rocks 2 many monazite grains are spatially associated with biotite coronas around garnets formed via the reaction garnet chlorite muscovite biotite plagioclase staurolite h2o 3 garnets contain high y annuli that result from prograde dissolution of garnet via the staurolite in reaction followed by regrowth and rare monazite inclusions occur immediately outside the annulus and in the matrix but not in the garnet core larger monazite grains also exhibit quasi continuous th zoning with high th cores and low th rims consistent with monazite growth via a single reaction and fractional crystallization during prograde growth common silicates may host sufficient p and lrees that reactions among them can produce observable lree phosphate specifically phosphorus contents of garnet and plagioclase are hundreds of parts per million and dissolution of garnet and recrystallization of plagioclase could form thousands of phosphate grains several micrometers in diameter per thin section lrees may be more limiting but sheet silicates and plagioclase can contain tens to 100 ppm lree so recrystallization of these silicates to lower lree contents could produce hundreds of grains of monazite per thin section monazite ages determined via electron and ion microprobes are 400 ma directly linking prograde barrovian metamorphism of the western blue ridge with the acadian orogeny in contrast to previous interpretations that metamorphism was taconian 450 ma interpretation of ages from metamorphic monazite grains will require prior chemical characterization and identification of relevant monazite forming reactions including reactions previously viewed as involving solely common silicates

electron microprobe monazite geochronological constraints on the late palaeozoic tectonothermal evolution in the chinese tianshan electron microprobe monazite data from the early palaeozoic granitoid gneisses in the central tianshan tectonic zone provide two main ages 1 an age of 355 12 ma obtained on the chemically complex grains which is good agreement with the high pressure metamorphic age obtained on eclogite and blueschist rocks from the south tianshan tectonic zone 2 an age of 323 7 ma obtained on the complex and the monogenetic grains which is also closely consistent with the age for a major episode of cooling recrystallization of these high pressure rocks monazite from the schist of the xingxingxia complex yields a younger th pb u pb centroid age of 282 9 ma this younger age is interpreted as being linked to a magmatic episode possibly related to underplating extension and or shear activities these data provide timing constraints on the episodes of metamorphism and high pressure metamorphism and evidence for transition from compression to extension during the carboniferous to early permian for the chinese tianshan region moreover this study shows that electron microprobe dating of monazite together with recent statistical treatment can provide a reliable method to reveal a sequence of events within an orogenic cycle

thermal effects of ridge subduction and its implications for the origin of granitic batholith and paired metamorphic belts distribution of temperature and h2o in subduction zones during the course of ridge subduction are investigated numerically in order to constrain the timing and extent of metamorphism and melting within the subducting oceanic crust and the overlying arc crust the model assumes that after ridge subduction the two plates move together without creating a slab window the results suggest that before ridge subduction temperature along the subducting slab starts to rise when the slab is younger than 10 myr a drastic thermal impact occurs associated with subduction of the ridge crest followed by a diffusion stage of the impact the temperature elevation is limited within a few tens of kilometers from the slab crust interface and within 30 myr after ridge subduction although it will last for a longer period if a slab window is formed during the peak stage slab melting occurs and generates a significant amount of granitic melt mainly at depths shallower than 40 km at p t conditions corresponding to low p t metamorphism high p t metamorphism with a significant water flux is also achieved near the interface when a subducting slab is less than 10 myr old before ridge subduction or 20 myr old after ridge subduction consequently the low and high p t metamorphism accompanied by a significant amount of granitic melt is associated closely in time and space with the ridge subduction this model can explain the observed characteristics of the granitic batholith and the paired metamorphic belts through these processes arcs and continents can grow within the short period of time associated with the episodic subduction of ridges

mid crustal horizontal shear zone in the forearc region of the mid cretaceous sw japan arc inferred from strain analysis of rocks within the ryoke metamorphic belt abstract the strain geometry of a cretaceous low p high t metamorphosed accretionary complex in sw japan is one of the key geological constraints in understanding the cretaceous tectonics of the forearc region at the eastern margin of eurasia we studied the strain geometry of upper greenschist to lower amphibolite facies metamorphic rocks from the mid cretaceous low p high t ryoke metamorphic belt which during the mid cretaceous were located at mid crustal depths close to the volcanic front strain analysis focused on deformed radiolarian fossils in metachert and sandstone chert clasts within metapelite the maximum stretching direction x direction of the strain ellipsoid of the schistosity forming deformation at the peak metamorphism is oriented e w and the xy plane of the strain ellipsoid developed parallel to schistosity the metachert and metapelite exhibit plane strain to general flattening strain that probably largely resulted from the schistosity forming deformation based on the results of the previous strain analyses and this study it reveals that the schistosity forming deformation occurred under bedding normal shortening resulting in general flattening strain throughout the ryoke metamorphic belt the x direction of the strain ellipsoid of the schistosity forming deformation is oriented parallel to the length of the ryoke metamorphic belt throughout the sw japan arc the schistosity formed parallel to bedding planes that developed horizontally in non metamorphosed accretionary complexes of sw japan indicating horizontal xy plane of the strain ellipsoid these observations indicate the occurrence of horizontal shear deformation within the middle crust 15 km depth at the time of the low p high t metamorphism the deep seated horizontal shear zone and the shallower incipient median tectonic line mtl fault system could result in a crustal scale detachment fault in the forearc region of the mid cretaceous sw japan arc after the formation of the detachment the left lateral pull apart forearc basins onogawa izumi group distributed on the north side of the mtl and the southern marginal mylonite zone might be formed by the sinistral movement along the detachment fault

monazite behaviour and age significance in poly metamorphic high grade terrains a case study from the western musgrave block central australia abstract integrated in situ textural chemical and electron microprobe age analysis of monazite grains in a migmatitic metapelitic gneiss from the western musgrave block central australia has identified evidence for multiple events of growth and recrystallisation during poly metamorphism in the mesoproterozoic garnet sillimanite bearing metapelite underwent partial melting and segregation to palaeosome and leucosome during metamorphism between 1330 and 1296 ma with monazite grains in leucosome recording crystallisation at 1300 ma monazite breakdown during melting is inferred to have occurred in the palaeosome during a subsequent granulite facies event at 1200 ma deformation and metamorphism of leucosome and palaeosome resulted in partial disturbance of ages and potential minor growth on 1300 ma monazite in leucosome growth of new high y hree monazite in palaeosome domains occurred during garnet breakdown in the presence of sillimanite to cordierite and spinel as a result of post peak isothermal decompression diffusive enrichment of resorbed garnet rims in y hree suggests garnet breakdown occurred slower than volume diffusion of ree monazite in both palaeosome and leucosome were subsequently partially to penetratively recrystallised during a retrogression event that is suggested to have occurred at 1150 1130 ma the intensity of recrystallisation and disturbance of ages appears linked to proximity to retrogressed garnet porphyroblasts and their occurrence in the relatively reactive or fertile local environments provided by the palaeosome mesosome volumes which caused localised changes in retrogressive fluids towards compositions more aggressive to monazite like reaction textures it is apparent that domainal equilibrium and reaction may control or at least strongly influence monazite ree and u th pb chemistry and hence ages

isotope geochronology geochemistry and mineral chemistry of the u bearing and barren granites from the zhuguangshan complex south china implications for petrogenesis and uranium mineralization abstract the zhuguangshan complex carries some of the most important granite hosted uranium deposits in south china here we investigate the changjiang and jiufeng granites which represent typical u bearing and barren granites in the complex using zircon u pb ages whole rock geochemistry sr nd isotopic and zircon hf isotopic data and mineral chemistry to constrain the petrogenesis and uranium mineralization la icp ms zircon u pb dating shows that both the changjiang and jiufeng granites were emplaced ca 160 ma these rocks show high silica weakly to strongly peraluminous compositions enrichment in rb th and u and depletion in ba nb sr p and ti these features coupled with the high initial 87 sr 86 sr ratios negative end t values and ehf t values and the paleoproterozoic two stage model ages of these two granites suggest that the two granites belong to s type granites and the parental magmas of the two granites were derived from the paleoproterozoic metasedimentary rocks however the granitoids show different mineralogical characteristics the biotite in the changjiang granite belongs to siderophyllite marking higher degree of chloritization whereas the biotite in the jiufeng granite is ferribiotite characterized by only slight chloritization compared with the jiufeng granite the biotite in the changjiang granite has lower crystallization temperature and oxygen fugacity but higher f content and the uraninite has higher uo 2 content but lower tho 2 content and stronger corrosion the chemical ages of uraninites from both granites are within error consistent with the zircon u pb ages and are considered to represent the emplacement ages of granites chemical ages of pitchblende in the changjiang granite yield 118 8 ma 87 4 ma and 68 6 ma representing multiple episodes of hydrothermal events that are responsible for the precipitation of u ores in the changjiang uranium ore field our study suggests that the degree of magma differentiation and physicochemical conditions of the magmatic hydrothermal system are the key factors that control the different u contents of these two granites the mineralogical characteristics of uraninite and biotite can be used to distinguish between u bearing and barren granites and serve as a potential tool for prospecting granite hosted uranium deposits

observation of tetravalent cerium in zircon and its reduction by radiation effect 1 the oxidation state of ce in zircons of the cretaceous habu and yamanaka granodiorite from southwest japan was measured by ce liii edge x ray absorption near edge structure xanes the results confirmed that tetravalent ce is incorporated in zircon as estimated from the positive ce anomaly in the ree pattern of zircons however the ceiv percentage in yamanaka zircon is much smaller than expected from the degree of its ce anomaly the irradiation experiments suggest that the decrease of ceiv can be well explained by the reductive reaction of ceiv to ceiii by the radiation effect due to u and th in the zircon this suggests that it is possible to date zircon by the amount of ce reduced after sample formation as shown in this it is possible to deduce geochemical information by comparing the ceiv percentage at present given by xanes and the initial ceiv percentage estimated from ce anomaly

discovery of a c 370 ma granitic gneiss clast from the hwanggangri pebble bearing phyllite in the okcheon metamorphic belt korea abstract the chemical th u total pb isochron method chime of dating was carried out on accessory minerals in samples from the okcheon metamorphic belt in korea dated minerals include xenotime and monazite with overgrown mantles in a granitic gneiss clast from the hwanggangri formation metamorphic allanite in garnet bearing muscovite chlorite schist of the munjuri formation and polycrase and monazite in post tectonic granite from the hwanggangri area overgrowth of mantles took place at 369 10 ma on c 1750 ma cores of xenotime and monazite in the granitic gneiss allanite occurring in textural equilibrium with peak metamorphic minerals yields a chime age of 246 15 ma that is discriminably older than the polycrase 170 6 ma and monazite 170 3 ma ages of the post tectonic granite these chronological data suggest that some of the metasedimentary rocks in the belt formed through a single stage of metamorphism at c 250 ma from post 370 ma sediments late permian age signatures have also been reported from the precambrian gyeonggi and yeongnam massifs that border the okcheon metamorphic belt and indicate that parts of the basement massifs and the metamorphic belt were affected by the same regional metamorphic event

contrasting ages between isotopic chronometers in granulites monazite dating and metamorphism in the higo complex japan abstract the higo complex of west central kyushu western japan is a 25 km long body of metasedimentary and metabasic lithologies that increase in metamorphic grade from schist in the north to migmatitic granulite in the south where granitoids are emplaced along the southern margin the timing of granulite metamorphism has been extensively investigated and debated previously published sm nd mineral isochrons for garnet bearing metapelite yielded ca 220 280 ma ages suggesting high grade equilibration older than the lower grade schist to the north which yielded ca 180 ma k ar muscovite ages ion and electron microprobe analyses on zircon have yielded detrital grains with rim ages of ca 250 ma and ca 110 ma electron microprobe ages from monazite and xenotime are consistently 110 130 ma two models have been proposed 1 high grade metamorphism and tectonism at ca 115 ma with older ages attributed to inheritance and 2 high grade metamorphism at ca 250 ma with resetting of isotopic systems by contact metamorphism at ca 105 ma during the intrusion of granodiorite these models are evaluated through petrographic investigation and electron microprobe th u total pb dating of monazite in metapelitic migmatites and associated lithologies in situ investigation of monazite reveals growth and dissolution features associated with prograde and retrograde stages of progressive metamorphism and deformation monazite th u pb isochrons from metapelite diatexite and late deformational felsic dykes consistently yield ca 110 120 ma ages earlier and later stages of monazite growth cannot be temporally resolved the preservation of petrogenetic relationships coupled with the low diffusion rate of pb at

high ductility of k feldspar and development of granitic banded ultramylonite in the ryoke metamorphic belt sw japan granitic mylonites from an upper greenschist facies mylonite zone in the ryoke metamorphic belt sw japan show three types of microstructure with increasing mylonitization 1 mylonite 2 banded mylonite and 3 banded ultramylonite the banded mylonites and ultramylonites include bands of quartz biotite k feldspar plagioclase k feldspar quartz biotite and k feldspar plagioclase quartz the inequality sign indicates abundance in modal proportion within a band microstructural and textural investigations by cathodoluminescence cl scanning electron microscopy sem and electron back scatter diffraction ebsd show that the microstructural changes from mylonites to banded ultramylonites have occurred through fracturing of plagioclase porphyroclasts k feldspar replacement by myrmekite k feldspar precipitation in fractures and tails and dislocation creep of quartz and k feldspar development of the banded structure was promoted by high mobility via solution transfer of k feldspar clear spatial distribution of constituent minerals in polyphase feldspar rich bands instead of homogeneous mixing of them indicates that the grain boundary sliding was not the dominant deformation process

origin and mechanical significance of foliated cataclastic rocks in the cores of crustal scale faults examples from the median tectonic line japan 1 the median tectonic line mtl is japan s largest onshore fault and has been active since the mid cretaceous foliated cataclastic fault rocks are exceptionally well exposed in the fault core at anko nagano prefecture following an early phase of mylonitization and exhumation during left lateral shearing brittle fracture and cataclasis occurred leading to the development of centimeter to submillimeter spaced fault zone parallel fracture systems these fracture systems established an initial architectural hierarchy that influenced the subsequent development of foliated cataclasites and gouge initially fracture systems coalesced to form interconnected zones of fine grained ultracataclasite fluid influx at the onset of grain scale brittle deformation led to precipitation of fibrous chlorite within the ultracataclasites ultimately leading to the development of an interconnected network of foliated phyllosilicate rich cataclasites and gouges in the core of the mtl the brittle reduction of grain size and ingress of a chemically active fluid phase simultaneously promoted reaction softening and diffusive mass transfer in the foliated ultracataclasites leading to rate dependent frictional viscous flow at sub byerlee friction values associated weakening is indicated by the preferential localization of deformation within the ultracataclasites a protracted sequence of carbonate mineralization and cementation events is also recognized during the fault rock evolution and suggests episodic periods of fluid overpressuring a crustal scale fault zone model is proposed suggesting that the foliated cataclasites gouges are weak in the long term and represent shallower crustal equivalents of phyllonitic fault rocks exposed in more deeply exhumed fault zones including other parts of the mtl

thermal degradation and polymerization of carbonaceous materials in a metapelite granitoid magma system in the ryoke metamorphic belt sw japan abstract some granitoid magmas in subduction zones are closely related to sedimentary rocks due to partial melting or assimilation during generation and ascent in the ryoke high temperature t low pressure p metamorphic belt of sw japan syngenetic carbonaceous material containing organic matter occurs in granodiorite which interacted with pelitic rocks under middle crust t and p conditions solid state carbonaceous materials in metapelites injection gneiss and granodiorite consist of graphite and organic matter x ray mapping by epma shows that granular carbonaceous material a few tens of microns in diameter consisting of c with or without n cl and s occurs as inclusions in quartz feldspar biotite and garnet micro laser raman spectro analysis shows that some carbonaceous inclusions in injection gneiss and metapelite are graphite peaks characteristic of phenyl h alkyl ch3 ch2 c o and c c stretching vibrations are present in ft ir spectra of biotite flakes indicating that hydrocarbon compounds are uniformly distributed in the crystal structure and or along cleavages of that mineral particulate carbonaceous materials in minerals in the granodiorite contain long aliphatic hydrocarbon bonds oxygen bearing organic compounds and aromatic fragments the distribution of these organic groups differs among feldspar quartz and biotite carbon isotopic ratios in the granodiorite are lighter than those of graphite and amorphous carbon in the metapelite suggesting an origin from low molecular weight hydrocarbons released from the metapelite carbonaceous materials probably formed by hydrocarbon polymerization and solidification of gaseous hydrocarbons were trapped in the highly viscous granodiorite magma during crystallization and cooling and under differing oxidation conditions the presence of such organic matter in granitoids is important for the understanding of the behavior and circulation of volatile components in arc systems during subduction accretion and magmatism

epma and pixe dating of monazite in granulites from stary gieraltow ne bohemian massif poland abstract chemical th u total pb chime dating of monazite by electron probe microanalyzer epma and proton microprobe pixe was carried out on felsic granulites from stary gieraltow poland which represent part of the orlica nieznik dome in the ne bohemian massif analyzed monazite is characterized by mosaic zoning rather than simple core to rim growth and strontium contents of up to 750ppm an isochron age of 347 13ma represents timing of amphibolite facies metamorphism in agreement with previously published estimates

some remarks on deformation and p t conditions of the cretaceous regional metamorphic belts in southwest japan reply to comment by m brown on thermal effects of ridge subduction and its implications for the origin of granitic batholith and paired metamorphic belts abstract deformation and p t conditions of the cretaceous ryoke sambagawa metamorphic belts have been analyzed based on recent numerical modeling of plastic flow at convergent plate boundaries the analyses suggest that a three dimensional corner flow in the forearc wedge associated with subduction with moderate obliquity more than 45 for the angle between the subduction direction and the trench can explain the observed prolate strain a large strain more than 10 with the angle of 10 30 between the elongation axis and the strike of the regional metamorphic belts is attributed to a combination of 1 stretching in the subduction direction above the subducting plate and 2 stretching and rotation towards the along trench direction at the wedge corner therefore the observed large strain is not a consequence of a significant lateral displacement of the two plates based on the analyses the contemporaneous ryoke low p t sambagawa high p t metamorphic belts are suggested to have been formed within a single trench forearc system by a series of events not by accidental amalgamation of two distinct terranes the contrasting low and high p t metamorphic conditions are demonstrated to be simultaneously achieved in the forearc region during the dynamic flow associated with ridge subduction where a large temperature gradient is produced

eutectic melting of fe 3 at si 4 at c up to 200 gpa and implications for the earth s core abstract properties of the fe si and fe c binary systems have been shown unable to satisfy the geophysical and petrological constraints of the earth s core i e velocities densities melting temperature if only si or c were to be incorporated as light element recent ab initio calculations suggest on the contrary that density compressional and shear sound velocities as well as the poisson s ratio of the inner core could be matched by an hcp fe alloy containing si and c the combined effect of the two elements in a ternary fe si c system has never been experimentally investigated under high pressure we thus studied the melting curve and the phase relations of the ternary iron silicon carbon system by in situ x ray diffraction at high pressures and high temperatures starting with a low light element content 4 at c 3 at si a stable assemblage made of hcp fe si c and fe3c is observed up to 200 gpa fe can incorporate both si and c in its hexagonal structure with the latter strongly affecting the volume and the melting temperature while the presence of a third light element is likely necessary we here document that the effect of c in lowering the melting temperature of fe si is large enough to possibly keep the core mantle boundary temperature below the solidus of the mantle silicates

restoration of exotic terranes along the median tectonic line japanese islands overview abstract this paper reviews recent progress on the geotectonic evolution of exotic paleozoic terranes in southwest japan namely the paleo ryoke and kurosegawa terranes the paleo ryoke terrane is composed mainly of permian granitic rocks with hornfels mid cretaceous high grade metamorphic rocks associated with granitic rocks and upper cretaceous sedimentary cover they form nappe structures on the sambagawa metamorphic rocks the permian granitic rocks are correlative with granitic clasts in permian conglomerates in the south kitakami terrane whereas the mid cretaceous rocks are correlative with those in the abukuma terrane this correlation suggests that the elements of northeast japan to the northeast of the tanakura tectonic line were connected in between the paired metamorphic belt along the median tectonic line southwest japan the kurosegawa terrane is composed of various paleozoic rocks with serpentinite and occurs as disrupted bodies bounded by faults in the middle part of the jurassic chichibu terrane accretionary complex it is correlated with the south kitakami terrane in northeast japan the constituents of both terranes are considered to have been originally distributed more closely and overlay the jurassic accretionary terrane as nappes the current sporadic occurrence of these terranes can possibly be attributed to the difference in erosion level and later stage depression or transtension along strike slip faults the constituents of both exotic terranes especially the ordovician granite in the kurosegawa south kitakami terrane and the permian granite in the paleo ryoke terrane provide a significant key to reconstructing these exotic terranes by correlating them with paleozoic granitoids in the eastern asia continent

crystallization processes of quartz in a granitic magma cathodoluminescence zonation pattern controlled by temperature and titanium diffusivity abstract quartz from a granitic pluton is found to have formed through sequential growth events under different mechanisms and crystallization temperatures which can provide new insights into magmatic processes of granitic magmas that were eventually consolidified into plutons the events were identified using 1 the description of crystal shape and occurrence 2 the study of the internal structure with cathodoluminescence cl and 3 derivation of the crystallization temperatures based on titaniq thermometry the magmatic quartz crystals from the toki granite central japan are characterized as having the following internal structures oscillatory zonation no oscillatory zonation with luminescence gradation gradational zonation and heterogeneous cl the quartz crystals with oscillatory zonation were formed in the temperature range of about 800 c to below 700 c which is referred to as oscillatory zoning temperature ozt conditions the cl zonation pattern was controlled by the temperature conditions and titanium diffusivity in the melt magma the crystallization process of quartz within the toki granite reveals the cooling processes of the granitic pluton the lithofacies with a high frequency of oscillatory zoned quartz underwent slower cooling under the ozt conditions than those in other lithofacies

behavior of zircon in the upper amphibolite to granulite facies schist migmatite transition ryoke metamorphic belt sw japan constraints from the melt inclusions in zircon behavior of zircon at the schist migmatite transition is investigated syn metamorphic overgrowth is rare in zircon in schists whereas zircon in migmatites has rims with low th u that give 90 3 2 2 ma u pb concordia age between inherited core and the metamorphic rim a thin dark cl annulus containing melt inclusion is commonly developed suggesting that it formed contemporaneous with the rim in the presence of melt in diatexites the annulus is further truncated by the brighter cl overgrowth suggesting the resorption and regrowth of the zircon after near peak metamorphism part of the zircon rim crystallized during the solidification of the melt in migmatites preservation of angular shaped inherited core of 5 10 m in zircon included in garnet suggests that zircon of this size did not experience resorption but developed overgrowths during near peak metamorphism the ostwald ripening process consuming zircon less than 5 10 m is required to form new overgrowths curved crystal size distribution pattern for fine grained zircons in a diatexite sample may indicate the contribution of this process zircon less than 20 m is confirmed to be an important sink of zr in metatexites and ca 35 m zircon without detrital core are common in diatexites supporting new nucleation of zircon in migmatites in the ryoke metamorphic belt at the aoyama area monazite from migmatites records the prograde growth age of 96 5 1 9 ma using the difference of growth timing of monazite and zircon the duration of metamorphism higher than the amphibolite facies grade is estimated to be ca 6 myr

tectonic evolution of the cretaceous gyeongsang back arc basin se korea transition from sinistral transtension to strike slip kinematics abstract the gyeongsang basin the largest cretaceous nonmarine sedimentary basin in korea formed as a continental back arc basin related to nnw directed subduction of the proto pacific plate underneath the eurasia plate the basin can be divided into an earlier formed western back arc depression and a later formed eastern volcanic arc platform we investigated the basin evolution and the associated tectonic settings largely based on an analysis of structures individuated in the field in the back arc region from 127 ma the basin initiated as a nne trending narrow depression bordered by nne striking sinistral faults and then progressively expanded under a transtensional kinematics induced by progressive trench roll back sinistral shearing of inherited nne striking structures played an important role in basin subsidence and secondary wnw to nw striking transverse faults acted as normal faults the nne striking principal displacement zone in the west of the basin runs along the western marginal area of the jinju and daegu domains and passes through the uiseong domain from south to north but most of this zone is now preserved as deep structures volcanic activity starting at ca 115 ma was characterized mainly by episodic basaltic eruptions occurring contemporaneously with back arc deposition of a sedimentary sequence after ca 90 ma a transtensional kinematics changed to a strike slip one and the basin expansion and sedimentation in the back arc region terminated during the strike slip event rhyolitic dacitic volcanism increased in intensity as a large ne trending volcanic arc developed close to subduction zone and its loading caused the stratal flexure in the back arc region and the orientations of the shortening and stretching axes remained nw se and ne sw respectively additionally continuing sinistral shear generated local depressions along the faults located in the west of the back arc region and within the volcanic arc

how the development of magma chambers affects collapse calderas insights from an overview here we review the studies of pluton emplacement and caldera collapse proposing a model linking the two processes the shallow rise of magma occurs by dyking and its emplacement occurs along major anisotropies many plutons are emplaced at subhorizontal discontinuities forming sills these will eventually grow forming laccoliths the most common mechanism to store shallow magma calderas are a surface expression of these reservoirs and can be approximated by a piston cylinder which sinks due to 1 underpressure in the reservoir producing outward dipping reverse faults 2 overpressure within a silllike chamber undergoing doming and 3 overpressure within a laccolith generating apical tensile stresses in the latter two cases inward dipping normal faults form we suggest that collapse calderas are the surface expression of pressure variations within laccoliths or tabular intrusions their geometric relationships depend on the shape and aspect ratio of the intrusion and its pressure conditions tabular intrusions generating ring faults mainly at their tips form calderas with a similar width to the intrusion laccoliths may generate ring faults along the intrusion roof forming calderas narrower than the intrusion the outward or inward dip of the caldera faults results from the underpressure or overpressure conditions within the

extending the applicability of the raman carbonaceous material geothermometer using data from contact metamorphic rocks the degree of graphitization of carbonaceous material cm has been widely used as an indicator of metamorphic grade previous work has demonstrated that peak metamorphic temperature t o f regional metamorphic rocks can be estimated by an area ratio r2 of peaks recognized in raman spectra of cm the applicability of this method to low pressure 50 that adequately reflects the range of sample heterogeneity using this procedure with 532 nm laser and adapting our new calibration the errors of the raman cm geothermometer for contact metamorphic rocks decrease to 30 c

analytical perils and progress in electron microprobe trace element analysis applied to geochronology background acquisition interferences and beam irradiation effects electron probe microanalysis epma of accessory minerals such as monazite xenotime and thorite for minor and trace element concentrations and geochronology requires consideration of beam irradiation effects increasing heat and charge as higher current densities and lengthy counting times are employed and requires careful detailed assessment of background intensities and interferences a carbon coat 250 a thickness is generally inadequate for prevention of absorbed current s uctuation and beam damage when using the high current densities applied for high precision e g 200 na focused beam beam irradiation effects include element mobility in monazite resulting in p loss relative to ree coating materials of higher electrical and thermal conductivity are indicated and use of gold 100 a is strongly suggested systematic compositional and therefore age variability can result simply from analytical effects requiring evaluation of all aspects of data acquisition the spectra relevant to measurement of y th pb and u are complex especially in ree bearing minerals acquisition of detailed spectral wavelength scans allows recognition of background and peak interferences as well as curvature background intensities can be extracted directly from scan data by regression x ray mapping allows delineation of domains guiding background acquisition and detailed quantitative analysis minor substitution or s uorescence of unexpected elements can compromise analyses one documented effect being the s uorescence of k in monazite adjacent to or hosted by k feldspar or micas this effect clearly evident within 10 micrometers from k feldspar can result in erroneous u concentrations leading to misinterpretation of rim ages as younger overgrowths absorption edges associated with th also become relevant to the measurement of u at high th concentrations because background intensity is sensitive to variation in average atomic number backgrounds must be acquired from each identi ed domain with particular attention being paid to th variation misapplication of background intensities can result in large age discrepancies for example application of backgrounds obtained from a high th domain in monazite to measurement of a low th domain 1 3 of the amount in the high th domain results in an overestimation of the um background intensity of 0 008 cps na and an overall increase in age of 70 m y

the earth s core composition from high pressure density measurements of liquid iron alloys abstract high pressure high temperature in situ x ray diffraction has been measured in liquid iron alloys fe 5 wt ni 12 wt s and fe 5 wt ni 15 wt si up to 94 gpa and 3200 k in laser heated diamond anvil cells from the analysis of the x ray diffuse scattering signal of the metallic liquids we determined density and bulk modulus of the two liquid alloys comparison with a reference earth model indicates that a core composition containing 6 of sulfur and 2 of silicon by weight would best match the geophysical data models with 2 5 of sulfur and 4 5 of silicon are still consistent with geophysical constraints whereas silicon only compositions are not these results suggest only moderate depletion of sulfur in the bulk earth

electron microprobe dating of monazite the story abstract this paper is a testimony of how electron microprobe dating of monazite was developed in the early days of this technique in the 90 s five contributions have been collected from nagoya clermont ferrand orleans salzburg and amherst the technique was designed in nagoya by professor suzuki using an old jxa 5a jeol electron microprobe the first results were published in 1991 with great difficulty professor suzuki also created the isochron like pb th diagram to present the data progressive improvement of the method finally allowed the nagoya team to date cenozoic monazite the technique was re discovered in clermont ferrand using a cameca camebax microprobe this team demonstrated the accuracy of the method and proposed statistical tools to improve the precision and to handle multimodal populations the first results were published in 1993 in orleans the french geological survey brgm developed the method with a cameca sx50 to support mapping projects they developed a new method for calculating the age and showed that this technique was very efficient for dating monazite in migmatites in salzburg the first results were obtained in 1996 using a jeol jx 8600 it proved to be very efficient in the alps to distinguish cadomian ordovician variscan and alpine events it allowed this team to directly date a monazite allanite reaction they described for the first time finally the amherst team investigated in detail the technical issues of electron microprobe monazite dating they showed that the best analytical procedures must include at least detailed chemical mapping several interference corrections and special care for background measurements with the help of cameca they designed a specific microprobe for dating named ultrachron with this machine high precision ages can be obtained on well characterized individual grains in thin section giving birth to a new era in geochronology of complex metamorphic rocks

the first u th he thermochronology of pseudotachylyte from the median tectonic line southwest japan abstract to constrain the thermal and its spatial conditions of pseudotachylyte formation and cooling we dated zircons from a pseudotachylyte in the ryoke belt obtained about 100 m north from the median tectonic line in the taki area southwest japan and its host rock the hatai tonalite by the u th he method the ages obtained are 60 3 2 7 and 55 5 4 5 1se ma respectively which are essentially the same within the error this is the first u th he age directly measured for a pseudotachylyte the coincidence between these ages indicates that the pseudotachylyte formed at ca 60 ma under the ambient temperature of about 180 c the closure temperature of zircon u th he method the fish canyon tuff zircon one of the most well known geological age standards was also dated to confirm the validity of our analyses which yielded the weighted mean age of 29 6 1 5 1se ma consistent with other reported ages the average cooling rates and denudation rates of the host rock were calculated based on these ages reported zircon fission track ages ca 70 ma and apatite fission track ages ca 40 ma as about 12 c myr and about 0 6 mm yr from 70 to 60 ma and about 4 c myr and about 0 2 mm yr from 60 to 40 ma respectively assuming that the closure temperatures of zircon and apatite ft methods are 300 c and 110 c respectively and a geothermal gradient of 20 c km one possible reason of this slow down of denudation rates is the decrease of convergent rate and change in the movement direction of the pacific plate relative to the eurasian plate along the southwest japan in the paleogene

high pressure melting experiments on fe si alloys and implications for silicon as a light element in the core abstract we carried out melting experiments on fe si alloys to 127 gpa in a laser heated diamond anvil cell dac on the basis of textural and chemical characterizations of samples recovered from a dac a change in eutectic liquid composition in the fe fesi binary system was examined with increasing pressure the chemical compositions of coexisting liquid and solid phases were quantitatively determined with field emission type electron microprobes the results demonstrate that silicon content in the eutectic liquid decreases with increasing pressure to less than 1 5 0 1 wt si at 127 gpa if silicon is a single light element in the core 4 5 to 12 wt si is required in the outer core in order to account for its density deficit from pure iron however such a liquid core whose composition is on the si rich side of the eutectic point crystallizes less dense solid cscl b2 type phase at the inner core boundary icb our data also show that the difference in silicon concentration between coexisting solid and liquid is too small to account for the observed density contrast across the icb these indicate that silicon cannot be the sole light element in the core previous geochemical and cosmochemical arguments however strongly require 6 wt si in the core it is possible that the earth s core originally included 6 wt si but then became depleted in silicon by crystallizing sio2 or mgsio3

phase relations in the fe fesi system at high pressures and temperatures the earth s core is comprised mostly of iron and nickel but it also contains several weight percent of one or more unknown light elements which may include silicon therefore it is important to understand the high pressure high temperature properties and behavior of alloys in the fe fesi system such as their phase diagrams we determined melting temperatures and subsolidus phase relations of fe 9 wt si and stoichiometric fesi using synchrotron x ray diffraction at high pressures and temperatures up to 200 gpa and 145 gpa respectively combining this data with that of previous studies we generated phase diagrams in pressure temperature temperature composition and pressure composition space we find the b2 crystal structure in fe 9si where previous studies reported the less ordered bcc structure and a shallower slope for the hcp b2 to fcc b2 boundary than previously reported in stoichiometric fesi we report a wide b2 b20 two phase field with complete conversion to the b2 structure at 42 gpa the minimum temperature of an fe si outer core is 4380 k based on the eutectic melting point of fe 9si and silicon is shown to be less efficient at depressing the melting point of iron at core conditions than oxygen or sulfur at the highest pressures reached onlymore the hcp and b2 structures are seen in the fe fesi system we predict that alloys containing more than 4 8 wt silicon will convert to an hcp b2 mixture and later to the hcp structure with increasing pressure and that an iron silicon alloy in the earth s inner core would most likely be a mixture of hcp and b2 phases less

melting experiments on the fe c binary system up to 255 gpa constraints on the carbon content in the earth s core abstract phase relations including the eutectic liquid composition in the fe c binary system remain unclear under the core pressure range which makes estimating the carbon budget in the earth s core difficult to explore this issue we have conducted melting and subsolidus experiments on fe c alloys in a diamond anvil cell up to 255 gpa textural and compositional characterizations of quenched samples show that carbon concentration in the eutectic liquid slightly decreases with increasing pressure and is about 3 wt at the inner core boundary icb pressure the solubility of carbon in solid fe is found to be almost constant at 1 0 wt in situ x ray diffraction data indicate that fe forms eutectic melting with fe3c to 203 gpa and with fe7c3 at 255 gpa previous studies on liquid fe c alloys suggested that the density of the outer core is explained by liquid fe containing 1 8 to 4 2 wt c if the liquid core includes

boron in metapelites controlled by the breakdown of tourmaline and retrograde formation of borosilicates in the yanai area ryoke metamorphic belt sw japan tourmaline out isograd formed by the breakdown of tourmaline is defined in the upper amphibolite facies metapelites in the yanai area ryoke metamorphic belt sw japan the rim composition of tourmaline progressively becomes aluminous with ascending metamorphic grade and the chemical zoning of tourmaline is controlled by x alna 1mg 1 and mgtiyal 2 vectors in low to medium grade zones where muscovite is stable whereas it is controlled by mg oh yal 1o 1 camgox 1 yal 1 oh 1 and mgtiyal 2 vectors in further higher grade muscovite unstable zones the size of tourmaline increases drastically where breakdown of muscovite quartz takes place probably due to the growth of tourmaline during breakdown of muscovite on the high temperature side of the tourmaline out isograd depletion of whole rock boron is observed escape of boron bearing melt or the fluid evolved from the melt during its crystallization probably caused this depletion although locally trapped boron bearing melt or fluid formed irregularly shaped tourmaline and dumortierite during retrograde metamorphism

an unrecognized major collision of the okhotomorsk block with east asia during the late cretaceous constraints on the plate reorganization of the northwest pacific abstract interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions however the traditional tectonic model for the east asian margin during the mesozoic invoking successive episodes of paleo pacific oceanic subduction does not provide an adequate context for important late cretaceous dynamics across east asia including continental scale orogenic processes significant sinistral strike slip faulting and several others the integration of numerous documented field relations requires a new tectonic model as proposed here the okhotomorsk continental block currently residing below the okhotsk sea in northeast asia was located in the interior of the izanagi plate before the late cretaceous it moved northwestward with the izanagi plate and collided with the south china block at about 100 ma the indentation of the okhotomorsk block within east asia resulted in the formation of a sinistral strike slip fault system in south china formation of a dextral strike slip fault system in north china and regional northwest southeast shortening and orogenic uplift in east asia northeast striking mountain belts over 500 km wide extended from southeast china to southwest japan and south korea the peak metamorphism at about 89 ma of the sanbagawa high pressure metamorphic belt in southwest japan was probably related to the continental subduction of the okhotomorsk block beneath the east asian margin subsequently the north northwestward change of motion direction of the izanagi plate led to the northward movement of the okhotomorsk block along the east asian margin forming a significant sinistral continental transform boundary similar to the san andreas fault system in california sanbagawa metamorphic rocks in southwest japan were rapidly exhumed through the several kilometer wide ductile shear zone at the lower crust and upper mantle level accretionary complexes successively accumulated along the east asian margin during the jurassic early cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike slip fault system the departure of the okhotomorsk block from the northeast striking asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin in the campanian the block collided with the siberian margin in northeast asia at about 77 ma a new oceanic subduction occurred to the south of the okhotomorsk block ending its long distance northward motion based on the new tectonic model the abundant late archean to early proterozoic detrital zircons in the cretaceous sandstones in kamchatka southwest japan and taiwan are interpreted to have been sourced from the okhotomorsk block basement which possibly formed during the late archean and early proterozoic the new model suggests a rapidly northward moving okhotomorsk block at an average speed of 22 5 cm yr during 89 77 ma it is hypothesized that the okhotomorsk east asia collision during 100 89 ma slowed down the northwestward motion of the izanagi plate while slab pull forces produced from the subducting izanagi plate beneath the siberian margin redirected the plate from northwestward to north northwestward motion at about 90 89 ma

melting experiments on fe fe3s system to 254 gpa abstract melting experiments were performed on the fe fe 3 s system at high pressures between 34 and 254 gpa in a laser heated diamond anvil cell dac using starting materials of fine grained homogeneous mixtures of fe and fes 5 7 0 3 wt s coexisted with both solid fe 3 s and fe containing 3 9 0 4 wt s at 254 gpa and 3550 k the eutectic liquid at inner core boundary icb pressure includes less sulfur than is required to account for the density deficit of the outer core 10 wt s furthermore the difference in sulfur concentration between coexisting liquid and solid is not sufficient to account for the observed density jump across the icb these indicate that sulfur cannot be a predominant light element in the core

experimental determination of stability relations between monazite fluorapatite allanite and ree epidote as a function of pressure temperature and fluid composition the experimental alteration of monazite to allanite ree epidote fluorapatite and or fluorapatite britholite was investigated at 450 to 610 mpa and 450 to 500 c experiments involved monazite albite k feldspar muscovite biotite sio 2 caf 2 and variety of fluids including h 2 o kcl h 2 o nacl h 2 o cacl 2 h 2 o na 2 si 2 o 5 h 2 o 1 m hcl 2 m naoh 2 m koh 1 m ca oh 2 2 m ca oh 2 and caco 3 h 2 o the reaction products or lack thereof clearly show that the stability relations between monazite fluorapatite and allanite or ree epidote are more dependent on the fluid composition and the ratio of silicate minerals than on the p t conditions a high ca content in the fluid promotes monazite dissolution and the formation of fluorapatite and allanite or ree epidote lowering the ca content and raising the na content in the fluid decreases the solubility of monazite but promotes the formation of allanite replacing na with k in the same fluid causes fluorapatite with a britholite component to form from the monazite however allanite and ree epidote are not formed monazite is stable in the presence of nacl brines in kcl brine monazite shows a very limited reaction to fluorapatite when the fluid is na 2 si 2 o 5 h 2 o strong dissolution of monazite occurs resulting in the mobilization of rees and actinides to form fluorapatite britholite and turkestanite these experimental results are consistent with natural observations of the partial to total replacement of monazite by fluorapatite ree epidote and allanite in fluid aided reactions involving the anorthite component in plagioclase at mid to high grade metamorphic conditions in contrast an alkali bearing environment with excess na prevents the growth of allanite and eventually promotes the precipitation of secondary monazite the results from this study provide implications for geochronology and for deducing fluid compositions in metamorphic rocks

denudation history of the high t p ryoke metamorphic belt southwest japan constraints from chime monazite ages of gneisses and granitoids chime chemical th u total pb isochron method monazite ages were determined for gneisses and granitoids from the eastern and western parts of the ryoke belt separated by about 500 km the monazite ages for the gneisses are concentrated between 102 and 98 ma and are interpreted as the time of monazite formation under lower amphibolite facies conditions the peak metamorphism seems to be contemporaneous with the emplacement of the geologically oldest plutons that are dated at c 95 ma in both the eastern and western parts in the eastern part plutonism continued from c 95 ma to c 68 ma at intervals of 2 10 ma whereas in the western part it ceased at c 85 ma the chime monazite ages agree well with the relative age of granitoids derived from intrusive relationships of granitoids in both parts these lines of evidence are incompatible with a current view that the plutonometamorphism in the ryoke belt becomes younger towards the east the chime monazite ages coupled with available data on the depth at which the ryoke metamorphism took place and the emplacement of individual plutons show that the western part was eroded more rapidly about 1 5 mm year 1 than the eastern part about 0 8 mm year 1 over the time span from 91 to 85 ma the denudation rates agree well with those in active orogenic belts like the alps and himalayas

position by position cooling paths within the toki granite central japan constraints and the relation with fracture population in a pluton abstract understanding the locational differences of time temperature t t paths within the granite contributes to clarifying the detailed formation history especially the thermal evolution of the entire pluton after the incipient intrusion of the granitic magma into the shallow crust the position by position t t paths of fifteen samples of the toki granitic pluton central japan are reconstructed from thermochronological data including zircon u pb biotite k ar zircon fission track zft and apatite fission track aft ages ft length characterization and ft inverse calculation in case of sample no 1 the t t path consists of zircon u pb ages 74 0 1 1 ma and 72 6 1 7 ma a biotite k ar age 73 0 1 8 ma a zft age 57 2 2 3 ma an aft age 41 5 2 7 ma and the ft inverse calculation the t t paths show position specific characteristics that reflect the history of the pluton after the incipient intrusion of the granitic magma into the shallow crust shallow parts of the western and northeastern margins of the pluton show rapid cooling from the intrusion stage to the zft partial annealing zone paz and thus represent position specific characteristics in relation to crustal assimilation in the intrusion emplacement processes the cooling behavior around the condition of aft paz was interpreted as a reflection of regional tectonic exhumation of the pluton this study also presents useful knowledge to evaluate fracture populations in a granitic pluton the relationship between the position specific t t path and fracture frequency fracture number per unit interval provides a criterion for evaluating the fracture population of the granitic pluton called thermochronological evaluation which is a key insight to investigating fluid flow and mass transfer in the rock mass the t t path shows whether cooling was slow or rapid from thermal conditions of solidification crystallization to the biotite k ar closure temperature parts of the pluton that cooled slowly correspond to parts with high frequencies of fractures and vice versa the absolute value for duration between the zircon u pb age evaluated from the oscillatory zoned area oz age and biotite k ar age shows high correlation with fracture frequency r2 0 89 and thus gives a quantitative indicator for evaluating fracture frequency longer duration accompanies higher frequency a combination of thermochronological evaluation the local cooling indicator and the lithofacies effect can be applied as potential diagnostic tools for detailed evaluation of the fracture population

w and m type tetrad effects in ree patterns for water rock systems in the tono uranium deposit central japan abstract abundances of rare earth elements plus y ree were determined for granitic rocks tertiary sedimentary rocks and related groundwater in the tono area central japan tetrad effects concave curves in ree patterns were found for these rocks and groundwater samples conjugate m and w types of tetrad effects were simultaneously observed in these specimens which constitute the water rock system the granitic rocks show the m type tetrad effects while the groundwater and the sedimentary rocks exhibit the w type tetrad effects non chondritic y ho ratios were found especially in the groundwater y ho ratios showed larger values than the chondritic value for the samples showing w type tetrad effects and vice versa these results suggest that 1 preference of the groundwater for a w type tetrad effect and larger y ho ratio than chondrite produces an m type tetrad effects and lower y ho ratios in the granitic rocks during weathering processes 2 the w type tetrad effect and larger y ho ratio for the sedimentary rocks is brought about by the fixation of groundwater ree onto the sedimentary rocks the variation of the tetrad effect and y ho ratio was confirmed by laboratory experiments on the leaching of ree from the granitic rocks the w type tetrad effect and large y ho ratio in the u mineralization zone in the sedimentary rocks were also found by sims analysis which is consistent with the w type tetrad effect and larger y ho ratio in the whole rock abundances of the sedimentary rocks disequilibrium of the u series 234 u 238 u analyzed by sims in the u mineralization zone suggests that the u bearing minerals were formed through precipitation from groundwater as it became reducing these results suggest that the ree in the sedimentary rocks were transported by the groundwater from the granitic rocks in the tono area based on this study it is implied that the degree of the tetrad effects and the variation of y ho ratio can be valuable tools to investigate the migration of ree during water rock interactions in natural systems

the use of apatite as a record of initial 87sr 86sr ratios and indicator of magma processes in the inagawa pluton ryoke belt japan abstract sr isotopic analysis of apatite in the extensive inagawa pluton of southwestern japan reveals the spatial distribution of initial 87sr 86sr sri within this body with an unprecedented resolution while the sri values in older units show the largest variation 0 7093 0 7107 the younger ones have relatively homogeneous sri values around 0 7096 the older units also contain numerous mafic microgranular enclaves which are absent in the younger units combining these results with bulk rock analyses and field observations suggests the wide variation in petrology and bulk chemistry in the inagawa pluton is not solely due to fractional crystallization as previously thought mixing between mafic and felsic melts has also played a significant role the lack of enclaves and homogeneous sri values in the younger units suggest that mixing was complete by this time

constraining the timing of brittle deformation and faulting in the toki granite central japan abstract constraining of the timing of fault zone formation is of fundamental geotectonic importance to understand structural evolution and brittle fault processes here we present authigenic illite k ar age data from brittle fault zones comprising two gouges within the toki granite central japan the gouge samples were collected at depths of 252 9 and 403 7 m from a shaft at the mizunami underground research laboratory and were separated into five grain size fractions