high 3he emanations from the source regions of recent large earthquakes central japan 1 recently two shallow mw 6 6 inland earthquakes the 2004 mid niigata prefecture earthquake and the 2007 niigataken chuetsu oki earthquake occurred in the niigata sedimentary basin near the boundary between the eurasian and the north american plates in order to elucidate the geographic distribution of the 3he 4he ratios in and around the seismic source regions new helium isotope data from hot spring gases and water samples from much denser sampling than in previous studies were determined although temporal changes in the 3he 4he ratios obtained from each well were unknown before and after the earthquakes higher 3he 4he ratios were observed in the earthquake source regions compared to other regions geochemical evidence for the presence of hot spring gases and natural gases with anomalously high 3he 4he ratios 3 8 ra indicates infiltration of mantle fluids derived from the subcrustal lithosphere a plausible source of mantle helium can be attributed to upward mobilization of aqueous fluids generated by dehydration of the subducting pacific plate slab resulting in the acquisition of primordial helium from a mantle wedge as the fluids into the crust in addition aqueous fluids may raise the earth s surface along permeable conduits leading to the reactivation of high angle inverted normal faults and the triggering of recent earthquakes

highly evolved juvenile granites with tetrad ree patterns the woduhe and baerzhe granites from the great xing an mountains in ne china abstract in ne china voluminous granitoids were emplaced in late paleozoic and mesozoic times we report here sr nd o isotopic and elemental abundance data for two highly evolved granitic plutons woduhe and baerzhe from the great xing an mountains they show a rather juvenile sr nd isotopic signature and a spectacular tetrad effect in their ree distribution patterns as well as non charac charge and radius controlled trace element behavior the emplacement ages are constrained at 130 4 ma for the woduhe and 122 5 ma for the baerzhe granites by rb sr and sm nd isotope analyses both granites are also characterized by low but imprecise initial 87sr 86sr ratios of about 0 703 the nd sr isotope data argue for their generation by melting of dominantly juvenile mantle component with subordinate recycled ancient crust this is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt the parental magmas for both the woduhe and baerzhe granites have undergone extensive magmatic differentiation during which intense interaction of the residual melts with aqueous hydrothermal fluids probably rich in f and cl resulted in the non charac trace element behavior and the tetrad effect of ree distribution both the woduhe and baerzhe granites show the characteristic trace element patterns of rare metal granites but their absolute abundances differ by as much as two orders of magnitude the oxygen isotope compositions of the two granites have been severely disturbed significant 18o depletion in feldspar but not so much in quartz suggests that the hydrothermal alteration took place in a temperature condition of 300 500 c this subsolidus hydrothermal alteration is decoupled from the late stage magma fluid interaction at higher temperatures despite the two distinct and intense events of water rock interaction the rb sr and sm nd geochronological systems seem to have maintained closed hence suggesting that the two events occurred shortly after the plutonic emplacements

p wave tomographic imaging of the crust and upper mantle beneath the japan islands more than 50 000 high accuracy arrival times from 1200 shallow and deep earthquakes selected from the japan university network earthquake catalog are used to investigate the three dimensional 3 d seismic velocity structure beneath japan travel times and ray paths are accurately calculated by using an efficient 3 d ray tracing technique p wave tomographic images of the crust and upper mantle to a depth of 500 km beneath the japan islands are determined with spatial resolutions of 25 50 km the obtained p wave velocity in the crust and uppermost mantle is slightly higher and relatively homogeneous in western japan in contrast with an average lower velocity and a large heterogeneity in eastern japan where many active volcanoes exist this feature correlates well with the distributions of heat flow and gravity anomalies low velocity low v zones are imaged in the crust and uppermost mantle beneath active volcanoes the low v zones in the mantle wedge dip toward the west and extend continuously to a depth of about 200 km a high velocity high v zone corresponding to the subducted pacific plate is delineated the thickness of the high v zone is estimated to be 80 90 km in southwestern japan the descending philippine sea plate is also delineated its thickness is estimated to be 30 km

toward an understanding of the metallogeny of the tasman fold belt system the tasman fold belt system which makes up the eastern third of the australian continent is a composite of five paleozoic orogenic belts the major mineral provinces of the tasman fold belt system include provinces of volcanic hosted massive sulfide deposits porphyry granitoid associated cu au and au deposits and granitoid associated sn and w deposits as well as provinces of structurally controlled au and cu pb zn deposits the localization of these provinces is discussed in terms of the nature of the magmatism which is a source of heat and in many cases of fluids and metals the fracture systems which facilitate the transfer of heat magmas and or aqueous fluids through the crust and the timing and nature of the stress regimes that permit these fracture systems to be open to fluid flow the available data indicate that the magmatism of the cu au province of central west new south wales originated in the mantle magma systems linked with the deposits of the volcanic hosted massive sulfide province of western tasmania the sn w provinces of the tasman fold belt system and the porphyry associated au deposits of north queensland had their roots in crust mantle interactions crystal fractionation was an important process in the magma systems related to the development of these provinces a feature of the tasman fold belt system is the prevalence of major north south trending fault systems more subtle west northwest structural trends can be appreciated at the continent scale and these proterozoic structural trends appear to have exerted a significant control on the distribution of major mineral provinces within the tasman fold belt system extension reactivation of basement structures late in tectonic cycles was a major mechanism for creating permeable domains in the upper crust and focusing fluid flow and hydrothermal mineralization it is suggested that the permo carboniferous au and sn provinces of north queensland developed

building robust models to forecast the induced seismicity related to geothermal reservoir enhancement abstract near real time seismicity forecasting is critically important for decision making during the reservoir creation phase of enhanced geothermal systems egs to compute within a probabilistic framework the seismic hazard and risk posed by induced seismicity it is necessary to calibrate robust forecast models quantitatively assess their reliability and capture the uncertainty of the process here we test the performance of three model classes each forecasting the induced seismicity observed during the failed 2006 2007 egs reservoir creation underneath basel switzerland each model class represents a logic tree branch that captures the epistemic uncertainty of the process the aleatory variability is accounted for by bootstrapping of the observed seismicity we calibrate each model using a range of updating strategies and quantitatively test the performances of the models using likelihood tests we then define a combined model based on akaike weights and show that the combined model outperforms in our pseudoprospective testing environment all of the individual models we also show that seismicity recorded during the initial one to three days of seismicity several days before the onset of felt seismicity is sufficient for deciding with confidence that the prescribed injection regime will eventually lead to unacceptably high levels of seismicity

the influence of magnitude range on empirical ground motion prediction a key issue in the assessment of seismic hazard in regions of low to moderate seismicity is the extent to which accelerograms obtained from small magnitude earthquakes can be used as the basis for predicting ground motions due to the larger magnitude events considered in seismic hazard analysis in essence the question is whether empirical ground motion prediction equations can be applied outside their strict range of applicability as defined by the magnitude and distance ranges covered by the datasets from which they are derived this question is explored by deriving new spectral prediction equations using an extended strong motion da taset from europe and the middle east covering the magnitude range mw 3 0 7 6 and comparing the predictions with previous equations derived using data from only mw 5 0 and above events the comparisons show that despite their complex func tional form including quadratic magnitude dependence and magnitude dependent attenuation the equations derived from larger magnitude events should not be extra polated to predict ground motions from earthquakes of small magnitude moreover the results suggest not only that ground motion prediction equations cannot be used outside the ranges of their underlying datasets but also that their applicability at the limits of these ranges may be questionable although only tested for smaller magni tudes the results could be interpreted to suggest that predictive equations also cannot be reliably extrapolated to higher magnitudes than those represented in the dataset from which they are derived a finding that has important implications for seismic hazard analysis the conclusion of the study is that empirical derivation of ground motion pre diction equations should be based on datasets extending at least one unit below the lower limit of magnitude considered in seismic hazard calculations the inclusion of small magnitude recordings results in a significant increase in the aleatory varia bility of the equations although it is yet to be established whether this is due to greater uncertainty in the associated metadata or whether ground motion variability is gen uinely dependent on earthquake magnitude

an introduction to the geology and metallic ore deposits of tasmania the major operating metallic ore deposits of tasmania are a volcanic hosted massive sulfide deposits at que river rosebery and hercules fe zn pb cu type mt lyell fe cu type and savage river fe oxide type b tin tungsten deposits in veins at aberfoyle lutwych storys creek and mt oakleigh c tin deposits of carbonate replacement type at renison and cleveland and d scheelite skarn deposits at king island and kara the massive sulfide deposits are cambrian and occur in calc alkaline volcanics the magnetite deposits at savage river are proterozoic and occur in basaltic volcanics and the tin and tungsten deposits are related to devonian granitoids of various types tasmania has in the past been also a producer of osmiridium nickel sulfide ore in cambrian mafic ultramafic rocks and gold in early paleozoic mudstone graywacke successions

three dimensional structure of vp vs and vp vs beneath northeastern japan implications for arc magmatism and fluids we estimated both p v p and s wave velocity v s structures beneath northeastern japan by applying a tomographic method to 169 712 p and 103 993 s wave arrival time data from 4338 local events the average value of v p v s ratio is 1 69 in the upper crust 1 75 in the lower crust and 1 77 in the uppermost mantle these differences in v p v s ratio may mainly reflect the lithological variations with depth low v p low v s and high v p v s zones are extensively distributed along the volcanic front in the uppermost mantle and are downward to the back arc side in the mantle wedge here the low v p low v s and high v p v s values are interpreted because of partial melting materials which imply the presence of a vast amount of melt in the uppermost mantle in the lower crust low v p low v s and high v p v s zones are not continuously visible along the volcanic front but are confined to individual volcanic areas which suggests that melting of lower crustal materials occurs just beneath each active volcano in contrast the upper crust beneath active volcanoes exhibits low v p low v s and low v p v s these results suggest that the partial melting zones under northeastern japan spread out from the uppermost mantle along the volcanic front up to the midcrust right beneath active volcanoes the low v p low v s and low v p v s features in the upper crust suggest the existence of h 2 o rather than melt right beneath active volcanoes

a seismological model for earthquakes induced by fluid extraction from a subsurface reservoir a seismological model is developed for earthquakes induced by subsurface reservoir volume changes the approach is based on the work of kostrov 1974 and mcgarr 1976 linking total strain to the summed seismic moment in an earthquake catalog we refer to the fraction of the total strain expressed as seismic moment as the strain partitioning function a probability distribution for total seismic moment as a function of time is derived from an evolving earthquake catalog the moment distribution is taken to be a pareto sum distribution with confidence bounds estimated using approximations given by zaliapin et al 2005 in this way available seismic moment is expressed in terms of reservoir volume change and hence compaction in the case of a depleting reservoir the pareto sum distribution for moment and the pareto distribution underpinning the gutenberg richter law are sampled using monte carlo methods to simulate synthetic earthquake catalogs for subsequent estimation of seismic ground motion hazard we demonstrate the method by applying it to the groningen gas field a compaction model for the field calibrated using various geodetic data allows reservoir strain due to gas extraction to be expressed as a function of both spatial position and time since the start of production fitting with a generalized logistic function gives an empirical expression for the dependence of on reservoir compaction probability density maps for earthquake event locations can then be calculated from the compaction maps predicted seismic moment is shown to be strongly dependent on planned gas production

helium isotopes as a tool for detecting concealed active faults 1 a magnitude mj 7 3 crustal earthquake occurred in the western tottori area southwest japan on 6 october 2000 however there was no obvious prefaulting indication at surface of a fault corresponding to the western tottori earthquake in 2000 this study was undertaken to elucidate the geographic distribution of 3he 4he ratios around the seismic source region using helium isotope data obtained from groundwater samples from drinking water wells the maximum 3he 4he ratio observed was from the water well nearest to the epicenter of the main shock in addition there appears to be a clear trend of decreasing 3he 4he ratios with distance away from the main trace of the probable fault segments the observations provide significant evidence that the source fault of the earthquake in 2000 is associated with leakage of mantle volatiles through the crust to the earth s surface we suggest that helium isotopes can be regarded as a tool for investigating and or mapping concealed active faults with no surface expression

radiogenic 87sr its mobility and the interpretation of rbsr fractionation trends in rare element granitic pegmatites abstract the extent of fractionation of rb and sr is routinely used in petrogenetic modelling of igneous processes including internal fractionation of individual pegmatites as well as large scale evolution of pegmatite groups and fields however highly evolved granitic pegmatites may contain as much as 14000 ppm rb and less than 150 ppm sr the total sr in k feldspar and micas from geologically old and rb rich pegmatites may consist predominantly of radiogenic 87 sr which obscures the original relationship of rb to common sr at the time of crystallization a subtraction of radiogenic 87 sr calculated from the rb content and age of emplacement is possible but it commonly results in negative concentrations of sr the relative immobility of rb analytically determined isotopic composition of sr apparent ages of the rb sr bearing minerals high concentration of 87 sr in coexisting rb poor phases and experimental evidence indicate that post crystallization migration of radiogenic 87 sr is significant where isotopic data are not available rb sr trends in geologically old and highly fractionated pegmatites are misleading and cannot be used for geochemical interpretation of pegmatite derivation or evolution

plate convergence and long term crustal deformation in central japan surveys by continuous global positioning system in and around japan revealed that the amurian plate collides with the north american plate in central japan by 2 cm yr long term crustal deformation seems to be influenced mainly by this collision although subduction of oceanic plates governs short term elastic deformation over the arc here we study the long term deformation field by carefully removing the short term signals inferred from a priori plate convergence vectors and coupling strengths predicted by a thermal model the obtained field shows that the change in velocities occurs along the longitude 135 137 and there exist a relatively rigid block and zones accommodating strains characteristic compressional deformation is found northwest of izu due possibly to the collision of the izu bonin arc with honshu plate convergence rate along the nankai suruga trough is considerably smaller in eastern parts due partly to the transition from the amurian to the north american plate of the landward side and partly to the motion of the izu microplate relative to the philippine sea plate this accounts for longer recurrence intervals of interplate earthquakes in the suruga trough where the tokai earthquake is anticipated to occur

the role of the mantle in the genesis of tin deposits and tin provinces of eastern australia initial nd isotope data for the four granites related to the ardlethan sn deposit in the wagga sn belt of the central lachlan fold belt of eastern australia range from 11 6 to 2 1 increasing with increasing fractionation the four granites beneath the renison tin mine in western tasmania range from 6 1 to 3 9 the data clearly establish the presence of light rare earths of mantle origin in the fractionated granites associated with the ardlethan porphyry sn deposits and hint at the same relationship for the renison granites though in this case the mineralizing pluton is probably yet to be discovered sulfur and carbon isotope data from the ardlethan and renison ores and from similar deposits in tasmania suggest that mantle volatiles played a significant role in the genesis of sn granites and deposits mantle input may have occurred either by mixing of crustal and mantle melts or metasomatism by mantle derived fluids

origin of methane rich natural gas in japan formation of gas fields due to large scale submarine volcanism eighty seven samples of ch4 rich natural gas were collected from commercial gas and oil wells in japan the3he 4he and4he 20ne ratios chemical composition of major minor and trace components ch4 c2h6 c3h8 co2 n2 o2 ar he ne and h2 and the c isotope composition of ch4 are reported most3he 4he ratios of natural gases in the forearc regions are as low as 1 4 10 7 and are comparable to those from large gas reservoirs in other parts of the world suggesting that the ch4 has a biogenic origin in contrast the3he 4he ratios of samples from gas reservoirs in the green tuff region along the japan sea vary considerably high ratios are observed for gases from volcaniclastic reservoirs in the deeper zone and low ratios are found in shallow reservoirs of sedimentary rocks the highest3he 4he ratio 9 37 0 34 10 6 is equivalent to the highest value in the subduction zone the high4he 20ne ratios observed in most samples suggest that there is no significant atmospheric contamination an overall regularity between3he 4he ratios and 13cch4 values is observed for japanese natural gases the 13cch4 value of gas with a high3he 4he ratio reaches about 35 and that of gas with a low ratio is about 75 total c to3he ratios c 3he vary over a wide range 6 108 9 1012 but those of gases in volcaniclastic reservoirs are in a rather narrow range with a value of 2 109 coinciding with that of a mantle reservoir the relation between the observed3he 4he ratios and 13cch4 values of gases together with their c 3he ratios suggests that ch4 rich gases in volcaniclastic reservoirs are a mixture of gases from two sources magmatic and biogenic the formation of gas reservoirs with high3he 4he ratios may be attributed to large scale submarine volcanism that occurred in the middle miocene gas separation from volcaniclastic rocks is expected to have occurred during the process of sea water rock interaction at a high temperature over a long period in a submarine environment the middle miocene volcanic episode which occurred under extensional stress was quite different from the present arc volcanism and is thought to have been closely related to the opening of the japan sea

u pb rb sr and sm nd chronology of granitic basement hydrothermal albitites and uranium mineralization lagoa real south bahia brazil the granites orthogneisses hydrothermal albitities and rocks which have suffered uranium mineralization from the lagoa real district south state of bahia brazil have been investigated by u pb rb sr and sm nd techniques u pb values on zircons from the granitic protolith give an age of 1725 ma u pb on u mineralization dates the primary mineralization at 1395 ma and indicates a reworking at 480 ma which may represent the age of the thrusting of the lagoa real complex over espinhaco metasediments during the brazilian orogeny these two dates are given by rb sr on albitites but from sparse information and are not supported by unequivocal arguments the uranium deposition and sodium metasomatism however cannot be linked either with the thermal history of the granite or with brazilian thrusting sm nd gives scattered results which are suggestive of autochtonous reworkings of rees these results lead to the following suggestions 1 magmatic activity of subalkaline affinity existed within the sao francisco craton at about 1 7 ga 2 such subalkaline plutons are likely sources for u mineralization 3 at about 1 4 ga an unknown event caused hydrothermal activity leading to u deposition at lagoa real 4 brazilian overthrusting at about 480 ma did not play any genetic role in the hydrothermal activity

magmatic and hydrothermal history of the porphyry style deposits of the ardlethan tin field new south wales australia the cassiterite sulfide deposits of the ardlethan tin field are classified as porphyry style sn deposits on the basis of the intimate spatial and temporal relationships of the breccia pipes and sn deposits with the ardlethan granite and in particular the mine porphyry the continuum of salinity and temperature conditions from high temperature and high salinity fluids in the ardlethan granite to lower temperature and less saline fluids in the breccia pipes in the mine granite and the isotopic character of the ore fluids which is consistent with a magmatic fluid source characterized by primitive isotopic signatures for carbon and sulfur the deposits occur in breccia pipes in the siluro devonian mine granite 417 or 2 5 ma close to its contacts with the ardlethan granite 410 or 2 5 ma and ordovician metasediments the ardlethan granite and related phases are moderately to strongly fractionated and enriched in rb th u nb y li as ta w f and sn tourmaline nodules occur within the ardlethan granite and halite bearing fluid inclusions found in quartz from the nodules homogenized between 250 degrees and 485 degrees c one of the most fractionated phases of the ardlethan granite the mine porphyry was emplaced into the major breccia pipe of the mine granite following the onset of brecciation brecciation and mineralization are linked to the release of magmatic volatiles and saline brines from the ardlethan granite the vug filling minerals in all the deposits show a paragenetic sequence from cassiterite wolframite arsenopyrite milky quartz and tourmaline to pyrite chalcopyrite sphalerite galena tourmaline and clear quartz to late stage toothy quartz fluorite and cookeite fluid inclusion data from quartz show that the deposition of milky quartz and cassiterite occurred between 300 degrees and 370 degrees c sulfide and clear quartz between 210 degrees and 2800c and toothy quartz fluorite and cookeite between 105 degrees and 245 degrees c fluid salinities ranged

neodymium and strontium isotope study of the blue tier batholith ne tasmania and its bearing on the origin of tin bearing alkali feldspar granites the middle to late devonian plutons of the blue tier and eddystone batholiths of ne tasmania intrude quartz wacke and mudstone of the ordovician devonian mathinna beds four granitoid types are recognized hornblende biotite granodiorite biotite granite biotite cordierite garnet granite and alkali feldspar granite afg minor diorite bodies and dolerite dykes are also present tin w mineralisation is genetically associated with the afg major granitoid types other than afg of the blue tier and eddystone batholiths all have similar 143nd 144nd initial ratios nd 5 0 to 6 5 at ma more fractionated felsic samples within individual plutons have lower nd values suggesting progressive involvement up to about 5 of the sedimentary country rocks which have nd of about 11 at 370 ma the source rock model age for all granitoids except afg based on a depleted mantle evolution model tdm is about 1 6 ga on the basis of geochemical data 87sr 86sr initial ratios 0 707 0 713 oxygen isotope ratios 180 9 to 12 and rb sr and k ar isotopic age dates 368 to 388 ma the major plutons were interpreted to have been generated independently from heterogeneous crustal sources geochemical variation within each major granitoid type with the possible exception of the afg is due to fractional crystallisation accompanied by some country rock assimilation integrated nd sr and o isotopic systematics of the blue tier batholith of the bassian terrain are different from granite batholiths in the mainland of the lachlan fold belt similarity of isotopic systematics of the blue tier batholith to those of devonian granites in central victoria reinforces the geological correlation between western tasmania and south australia in the early paleozoic two competing hypotheses for the generation of sn w mineralized afg have been proposed on the basis of geological relationships chemical and mineralogical trends and stable and radiogenic isotopes the first hypothesis groves et al 1977 higgins et al 1985 higgins 1990 links the afg with the country rock more mafic poimena granite through processes of fractional crystallisation and subsequent metasomatic modification the second hypothesis suggests that these afg are unrelated to the poimena granite they are specialised granites derived from a different parent with distinctive chemical isotopic systematics sun et al 1986 mackenzie 1986 mackenzie et al 1988 1990 according to the first hypothesis the afg exhibit a range in nd initial values from 5 9 to 2 2 however there is no known isotopic mechanism which can produce this range within the geological time frame of intrusion and solidification at this time the authors favour the second hypothesis because of chemical and isotopic correlations on the basis of a distinct discontinuity between poimena and afg on a y versus ga al plot there is also a clear grouping of initial nd for the poimena granite around 6 and the afg 2 4 it is argued that those few afg having much lower nd than 2 4 are either samples of altered poimena granite two samples with nd 6 8 and 9 1 or a result of extensive metasomatic modification one sample nd 5 9 involving circulation of fluids in equilibrium with the country rocks poimena granite initial nd 6 and mathinna beds 11 hydrothermal minerals from the anchor tin deposit show a range in initial nd and 87sr 86sr correlated with paragenesis apatite formed during albitisation of the lottah granite has nd and sr isotopic compositions intermediate between those of the lottah and poimena granites greisen fluorites have initial nd between 4 0 and 4 6 closer to the lottah average composition while initial 87sr 86sr approaches that of the metasedimentary country rock 0 729 fluorites formed during sericitic alteration have lower nd compositions 0 721 these data support an origin of tin mineralisation through mixing of an afg derived magmatic fluid with a externally derived meteoric groundwater dominated fluid

plate tectonics and crustal deformation around the japanese islands we analyze over a century of geodetic data to study crustal deformation and plate motion around the japanese islands using the block fault model for crustal deformation developed by matsu ura et al 1986 in this model crustal deformation corresponds to the sum of relative movement among designated blocks and displacement due to dislocations along the locked parts of designated faults we model the area including the japanese islands with 19 crustal blocks and 104 faults based on the distribution of active faults and seismicity three kinds of data are used rates of change of angles and lengths and average velocities of very long baseline interferometry stations with the inversion of these geodetic data we obtain block motions and average slip rates of faults this geodetic model predicts that the pacific plate moves n69 2 w at about 80 3 mm yr relative to the eurasian plate which is much lower than that predicted in geologic models substantial aseismic slip occurs on the subduction boundaries the block containing the izu peninsula may be separated from the rigid part of the philippine sea plate the faults on the coast of japan sea and the western part of the median tectonic line have slip rates exceeding 4 mm yr while the fossa magna does not play an important role in the tectonics of the central japan the geodetic model requires the division of northeastern japan contrary to the hypothesis that northeastern japan is a part of the north american plate owing to rapid convergence the seismic risk in the nankai trough may be larger than that of the tokai gap

determination of radiogenic isotopes rbsr smnd and pbpb in fluid inclusion waters an example from the bluebell pb zn deposit british columbia canada abstract rb sr pb nd and sm isotopes were determined in fluid inclusion waters extracted from quartz samples of the bluebell pb zn deposit british columbia the results demonstrate that radiogenic isotopes in fluid inclusion waters can constitute useful geochronological and genetic tools when applied in conjunction with geological geochemical and other geochronological studies rb sr isotopes of fluid inclusion waters and of mineralized marbles hosting the deposit indicate a tertiary mineralization age of 19 2 5 9 ma and an initial 87 sr 86 sr ratio of 0 7143 this rb sr date is in general agreement with a cenozoic age suggested by geologic field relations described by irvine 1957 and fyles 1967 pb isotope data suggest two isotopically distinct fluids one less radiogenic and similar to values measured on galenas and the other more radiogenic this is in agreement with ohmoto and rye s 1970 hypothesis of two meteoric hydrothermal fluids and lecouteur s 1973 convection cell model nd and sm isotope also suggest mixing of fluids both pb pb and nd sm data suggest very old lower and upper crustal materials as possible source of the metals

zircon u pb ages and sr nd hf isotopes of the highly fractionated granite with tetrad ree patterns in the shamai tungsten deposit in eastern inner mongolia china implications for the timing of mineralization and ore genesis abstract the shamai tungsten deposit is located in the eastern part of the central asian orogenic belt caob tungsten mineralization is closely related to the emplacement of fine to medium grained biotite monzogranite g1 and porphyritic biotite monzogranite g2 in the shamai granite nw trending joints and faults host orebodies in the shamai granite and devonian hornfels the mineralization is characterized by a basal veinlet zone progressing upwards to a thick vein zone followed by a mixed zone a veinlet zone and a thread vein zone at the top the ore related alteration typically consists of muscovite greisen and hornfels in order to constrain the timing of the shamai mineralization and discuss the ore genesis muscovite ar ar molybdenite re os and zircon u pb geochronological geochemical and sr nd hf isotopic studies were completed on the deposit the u pb zircon dating yielded weighted mean ages of 153 1 ma for g1 and 146 1 ma for g2 muscovite from a wolframite bearing quartz vein yielded an ar ar plateau age of 140 1 ma whereas two molybdenite samples yielded identical re os model ages of 137 2 ma these two ages are younger than the two monzogranites suggesting a prolonged magmatic hydrothermal interaction during tungsten mineralization major and trace element geochemistry shows that both g1 and g2 are characterized by high sio2 and k2o contents high a cnk values 1 08 1 40 a spectacular tetrad effect in their ree distribution patterns and non charac charge and radius controlled trace element behavior this suggests that both g1 and g2 are highly differentiated peraluminous rocks with strong hydrothermal interaction the nd hf isotope data for the shamai granite end t between 1 9 and 7 4 hf t from 5 2 to 12 8 are largely compatible with the general scenario for much of the phanerozoic granite emplaced in the caob it is here suggested that the shamai granite originated from partial melting of a juvenile lower crust with minor input of upper crustal material caused by the underplating of mafic magma in an extensional setting it can also be concluded that the prolonged fractional crystallization and magmatic hydrothermal interactions have contributed to the formation of the shamai tungsten deposit

are discontinuous chondrite normalized ree patterns in pegmatitic granite systems the results of monazite fractionation abstract all 14 stable rare earth elements rees in biotite muscovite granite and tourmaline rich granite of the harney peak granite black hills south dakota usa have been analyzed using inductively coupled plasma mass spectrometry chrondrite normalized ree patterns of the tourmaline rich granites are discontinuous between nd and sm the discontinuity was modeled successfully by the fractional crystallization of monazite from a biotite muscovite granite initial composition this explanation may also apply to the development of such discontinuous patterns in other highly evolved rocks

geographical distribution of 3he 4he ratios in japan implications for arc tectonics and incipient magmatism the 3he 4he and 4he 20ne ratios of 115 natural gas samples including various types of gases from volcanoes hot springs mineral springs water wells petroleum fields and natural gas fields were measured using a mass spectrometer the observed 3he 4he and 4he 20ne ratios range from 7 47 10 8 to 9 65 10 6 and from 0 26 to 1100 respectively the 3he 4he ratios reflect well the geotectonic structure of the japanese islands in northeastern ne japan there is a clear geographical difference in the 3he 4he ratios between the frontal arc forearc and volcanic arc back arc regions lower ratios were found in the trench side region and higher ratios in the back arc side this result suggests that the mantle derived helium in the volcanic arc region is associated with the diapiric uprise of a magma lower 3he 4he ratios in the frontal arc region may be due to radiogenic he produced by radioactive decay of u and th in the crustal and sedimentary rocks in southwestern sw japan there is no clear geographical contrast in the 3he 4he ratios some samples in the frontal arc region show quite high 3he 4he ratios the tendency of the 3he 4he ratios agrees with the distribution of terrestrial heat flow data and reflects geotectonic structures different from ne japan the high 3he 4he ratios observed in the frontal arc region in sw japan may be indicative of renewed or incipient magmatism due to a descending young and warm slab

mineralogical sources of the buffer capacity in a granite catchment determined by strontium isotopes abstract the role of different minerals in base cation release and thus the increase of buffering capacity of groundwater against acid deposition is controversially discussed in the literature the 87sr 86sr ratios and base cation concentration were investigated in whole rock leachates mineral separates precipitation soil solution groundwater and stream water samples in the lehstenbach catchment germany to identify the weathering sequence of the granite bedrock three different approaches were followed in parallel it was assumed that the contribution of different minerals to base cation supply of the groundwater with increasing weathering intensity would be observed by investigating 1 unweathered rock leachates deep groundwater and shallow groundwater 2 groundwater samples from new groundwater wells reflecting the initial weathering of the drilled bedrock and groundwater from wells that were drilled in 1988 3 stream water during baseflow dominated by deep groundwater and stream water during high flow being predominantly shallow groundwater whereas the first approach yielded consistent patterns there was some evidence that groundwater from the new wells initially reflected contamination by the filter gravel rather than cation release in an initial stage of weathering time series samples of stream water and groundwater solute concentrations and isotope ratios turned out to reflect varying fractions of soil water and precipitation water at baseflow and high flow conditions rather than varying contributions of different minerals that prevail at different stages of granite weathering the early phase of weathering was clearly dominated by base cation release from biotite weathering and to a lesser extent by apatite dissolution feldspars contributed to base cation release as well but could not be regarded as endmembers of the mixing diagram there was no clear evidence for a contribution from calcite correspondingly base cation input by atmospheric deposition and liming had only minor effects on groundwater buffer capacity

fingerprinting feldspar phenocrysts using crystal isotopic composition stratigraphy implications for crystal transfer and magma mingling in s type granites microsampling of cm scale feldspar crystals within an s type granite from the lachlan fold belt of southeastern australia has revealed complex internal sr and nd isotopic variations the observed isotopic zonations are in part interpreted as recording feldspar crystallisation in a dynamically mixing magma system the isotopic composition of which was varying in response to the influx of more mafic and isotopically more mantle like magmas the latter stages of which are now represented in modified form by microgranular enclaves similar core to rim isotopic variations in feldspar megacrysts from a microgranular enclave and the adjacent host granite strongly suggest megacrysts in the enclave were transferred from the granitic magma during crystallisation feldspar rims have higher 87sr 86sri and lower nd i than adjacent whole rock analyses but match those of mineral separates from the surrounding enclave matrix this suggests that the final stages of megacryst growth occurred in the presence of a component that had previously interacted with a high 87sr 86sr low nd i component such as metasedimentary wall rocks isotopic heterogeneities are also presererved within different mineral phases in the enclave matrix suggesting that differing phases grew at differing stages of equilibration between the enclave magma and its host granitic magma our results reveal major isotopic heterogeneities on a single crystal and also inter mineral scale in a pluton which shows well constrained evidence for magma mingling these results indicate the suitability of feldspars as recorders of isotopic change in magmatic systems even those which have cooled slowly in the plutonic environment and suggest that much heterogeneity in plutonic systems may be overlooked on a whole rock scale

relationship between 3he 4he ratios and subduction of the philippine sea plate beneath southwest japan 1 regional and local variations in mantle helium provide insight into the coupling of mantle crust tectonics and heat and or mass transfer from the earth s interior in order to further elucidate the geographic distribution of3he 4he ratios in southwest japan the data from a total of 924 sites were compiled and synthesized these include data from 48 additional hot spring and drinking water well sites on the northern kyushu island and in the northern chugoku region there appears to be good correlation between variations in helium isotope ratios and the geophysical evidence used to determine the configuration of the subducting philippine sea plate phs seismological studies reveal that the leading edge of the aseismic slab does not extend to the northern chugoku region nor to the osaka bay area where gas samples with significantly elevated 3he 4he ratios occur this is consistent with a mantle derived helium in these areas from melts and or mantle fluids ascribed to upwelling asthenosphere without being hindered by the descending phs slab in contrast gas samples in the regions where the overriding crust comes into direct contact with the subducting phs are dominated by radiogenic helium derived from the crust because of the absence of a mantle wedge the most plausible source of mantle helium owing to the abrupt changes in the seismicity and focal mechanisms of intraplate earthquakes the phs is considered to have slab tears beneath the kii channel and or the eastern kii peninsula oriented in a nw se direction however the lenear alignment of anomalously high3he 4he ratios does not appear to be nw se trending along the assumed slab tears but rather forms an broad ene wsw trending zone between the tears where low frequency events occur the emanation of gas with elevated3he 4he ratios in the central peninsula can be explained by the upward mobilization of mantle volatiles derived from the mantle wedge above the phs and or transferred from the hydrated slab mantle through the n s trending fractured medium within the phs accordingly the helium isotopes observed on the earth s surface may be efficient geochemical indicators of the configuration of a relatively younger warm aseismic slab and be especially useful in seismically inactive areas

la icp ms u pb zircon columbite tantalite and 40ar 39ar muscovite age constraints for the rare element pegmatite dykes in the altai orogenic belt nw china the chinese altai is renowned for its rich rare element resources nine representative rare element rel pegmatites were dated using la icp ms and 40ar 39ar methods the columbite grains yield a weighted mean 206pb 238u age of 239 6 3 8 ma for the dakalasu be nb ta pegmatite and concordia u pb ages of 258 1 3 1 ma and 262 3 2 5 ma for the xiaokalasu li nb ta pegmatite the zircons display a weighted mean 206pb 238u age of 198 5 2 5 ma for the husite be pegmatite and concordia u pb ages of 194 3 1 6 ma and 248 2 2 2 ma for the qunkuer be and taerlang barren pegmatites the muscovite 40ar 39ar dating gives plateau ages of 286 4 1 6 ma 297 0 2 6 ma 265 2 1 5 ma 178 8 1 0 ma 162 2 0 9 ma 237 7 1 3 ma 237 4 1 2 ma and 231 9 1 2 ma for the talate li be nb ta baicheng nb ta kangmunagong barren husite be qunkuer be nb ta xiaokalasu li nb ta weizigou be and taerlang barren pegmatites respectively these new ages coupled with previous geochronological work suggest that the rel pegmatites in the chinese altai formed during early permain late jurassic time the rel pegmatites located in the central altaishan terrane are younger than those in the qiongkuer abagong terrane showing a correlation with the coeval and adjacent granites the formation of the rel pegmatites and these granites indicates frequent and strong magmatic activity in the post orogenic and anorogenic setting the spatial and temporal distribution of pegmatites and granites reveals a magmatism path from the se of age early middle permian to the nw middle permian middle triassic and finally to the central part middle triassic jurassic of the chinese altai

deaggregation of probabilistic ground motions in the central and eastern united states abstract probabilistic seismic hazard analysis psha is a technique for estimating the annual rate of exceedance of a specified ground motion at a site due to known and suspected earthquake sources the relative contributions of the various sources to the total seismic hazard are determined as a function of their occurrence rates and their ground motion potential the separation of the exceedance contributions into bins whose base dimensions are magnitude and distance is called deaggregation we have deaggregated the hazard analyses for the new usgs national probabilistic ground motion hazard maps frankel et al 1996 for points on a 0 2 grid in the central and eastern united states ceus we show color maps of the geographical variation of mean and modal magnitudes m m and distances d d for ground motions having a 2 chance of exceedance in 50 years these maps are displayed for peak horizontal acceleration and for spectral response accelerations of 0 2 0 3 and 1 0 sec we tabulate m d m and d for 49 ceus cities for 0 2 and 1 0 sec response thus these maps and tables are psha derived estimates of the potential earthquakes that dominate seismic hazard at short and intermediate periods in the ceus the contribution to hazard of the new madrid and charleston sources dominates over much of the ceus for 0 2 sec response over 40 of the area for 1 0 sec response over 80 of the area for 0 2 sec response d ranges from 20 to 200 km for 1 0 sec 30 to 600 km for sites influenced by new madrid or charleston d is less than the distance to these sources and m is less than the characteristic magnitude of these sources because averaging takes into account the effect of smaller magnitude and closer sources on the other hand d is directly the distance to new madrid or charleston and m for 0 2 and 1 0 sec response corresponds to the dominating source over much of the ceus for some cities in the north atlantic states short period seismic hazard is apt to be controlled by local seismicity whereas intermediate period 1 0 sec hazard is commonly controlled by regional seismicity such as that of the charlevoix seismic zone

a review of the metallogeny and tectonics of the lachlan orogen future mineral exploration within eastern australia will be enhanced by resolving the tectonic evolution of the lachlan orogen to establish the spatial and temporal terrane distribution of the various mineral deposits the lachlan orogen from north eastern tasmania through to central and eastern new south wales is host to a number of major mineral deposit styles including orogenic gold e g stawell ballarat bendigo volcanic hosted massive sulphide e g woodlawn currawong sediment hosted cu au e g cobar basin deposits porphyry au cu e g cadia parkes cowal and granite related sn e g ardlethan beechworth each of these mineral deposit styles is a sensitive and diagnostic indicator of the prevalent tectonic environment during their formation in this review we briefly summarise the deposit to large scale factors that define the diverse metallogenic evolution of the lachlan orogen this overview is intended to set the scene for subsequent specialist papers published in this thematic issue on the metallogeny and tectonics of the lachlan orogen in south east australia

observations on regional variability in ground motion amplitudes for small to moderate earthquakes in north america abstract the regional variability in earthquake ground motion amplitudes for a given magnitude and distance in western north american environments was examined using shakemap data from small to moderate events the abundance of data for small to moderate events in california allows average ground motion levels as a function of magnitude and distance to be resolved with a high level of confidence ground motion amplitudes in northern california are lower on average than those for southern california for events of the same magnitude at distances in the range from 120 to 250 km over all frequencies the observed regional variations could be indicative of regional differences in attenuation effects or site effects an unexpected result of the study is the finding that ground motions for events of m m m m

reply to n c higgins comment on origin of alkali feldspar granites an example from the poimena granite northeastern tasmania australia this paper acts as a rebuttal to comments made by other scientists regarding the origin of the poimena granite as discussed in an earlier paper by these authors the lottah granite and the enclosing poimena granite of northeastern tasmania represent one of the best documented and most intensely li f rich alkali feldspar granite and its much more voluminous biotite granite host the issue under debate is which of the two most generally supported models for the origin of li f sn granites magmatic or metasomatic hydrothermal best explains the data obtained from the lottah and poimena granites it is not the authors intent to imply that alkali feldspar granites cannot be generated from granites similar to the poimena granite by fractional crystallization the st austell granite is an excellent example of such a relationship nor do the authors intend to imply that metasomatic and hydrothermal processes have not operated at all in the lottah granite they seek rather to demonstrate that magmatic processes alone are capable of generating alkali feldspar granites enriched in sn li rb f etc and that such granites need not be genetically linked to spatially associated normal granites some of the arguments and data are subsequently presented in this paper

the petrogenesis of an i type volcanic plutonic suite the st marys porphyrite tasmania the devonian i type st marys porphyrite 388 1ma comprises two petrographically similar units an 800 m thick pyroclastic sheet compositionally dacite and rhyolite and a subvolcanic feeder dyke the pyroclastics are crystal rich and contain in order of decreasing abundance plagioclase quartz biotite augite hypersthene and sanidine phenocrysts in an aphanitic groundmass

comment on origin of alkali feldspar granites an example from the poimena granite northeastern tasmania australia in the last decade much research into the origin and evolution of tin granites and rare metal pegmatites has concentrated on understanding the processes of their emplacement crystallization chemical and fluid evolution and mineralization in this regard the granites of eastern australia and particularly the blue tier batholith btb of eastern tasmania have been important in contributing to our knowledge of these complex systems since highly differentiated tin granites and pegmatites are commonly the last phase of intrusion in complex batholiths the age difference between them and earlier phases is extremely important in assessing rival models for the evolution of the tin granites in the blue tier batholith and in general elsewhere if the lottah granite is 10 ma younger than the poimena granite then they must be separate unrelated melts if the data are inconclusive regarding an age difference then alternative explanations for the genesis of the afg cannot be discounted a re appraisal of the data of mackenzie et al 1988 does not lend support to their conclusion that there is an age difference and this combined with a balanced assessment of the chemical and mineralogical data suggests that an earlier model for the evolution of the lottah andmore other afg of the btb is more appropriate higgins et al 1985 less

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

high strain rate zone in central honshu resulting from the viscosity heterogeneities in the crust and mantle abstract a linear zone with high strain rates along the backarc side of central honshu the so called niigata kobe tectonic zone has been revealed by the dense gps array geonet operated by the geographical survey institute of japan in order to explore the origin of this zone we examine rheological heterogeneities in the crust or mantle above a subducting slab which possibly contribute to the high strain rates we calculate velocity profiles at the surface of the upper plate due to loading and unloading of the subducting philippine sea plate using a 2 dimensional finite element method from the numerical experiments we find that the high strain rates can be reproduced by viscosity heterogeneities either in the crust or the mantle if viscosity heterogeneity in the crust is an origin the conditions to be satisfied are i an effective elastic thickness of 5 km for short term loading 10 2 10 3 yr ii a low viscosity 19 pa s in the lower crust beneath the zone with a normal viscosity 10 21 pa s in the ambient lower crust and iii a uniform viscosity of 10 19 pa s in the upper mantle on the other hand if viscosity heterogeneity in the mantle is an origin the conditions to be satisfied are i an effective elastic thickness of 30 km for short term loading ii a low viscosity 10 18 pa s at least down to a depth of 60 km in the zone and to a depth of 10 km further seaward below the moho depth and iii a viscosity of 10 20 pa s in the ambient mantle the crust heterogeneity model contradicts the 15 km cut off depth of intraplate seismicity and the 20 km effective elastic thickness previously inferred from gravity and topography in central honshu the fact that quaternary active faults and intraplate earthquakes are not particularly concentrated in the zone also favours the mantle viscosity heterogeneity model thus we prefer the mantle heterogeneity model we suggest that upward movement of water dehydrated from the subducting philippine sea and pacific plates partial melting of the mantle above the pacific plate and serpentinization in the wedge mantle above the philippine sea plate are possible origins of the low viscous upper mantle possible low viscosities in the upper mantle wedge presented in this study seem to provide important constraints for subduction processes of oceanic plates and strain accumulation processes in the upper plate

a jurassic garnet bearing granitic pluton from ne china showing tetrad ree patterns abstract ne china is characterized by the massive distribution of phanerozoic granitoids most of them are of i and a type granites whereas s type granites are rarely documented the present work deals with the dongqing pluton a small granitic body emplaced in the southern zhangguangcai range the pluton comprises a two mica garnet granite and a garnet bearing muscovite granite the latter occurs as veins in the former the pluton shows a gradational contact with the surrounding host granites rb sr and sm nd isotope analyses on whole rocks and minerals reveal that the two types of granites were emplaced synchronously at about 160 ma the pluton was emplaced coeval with the surrounding i type granitic pluton and had a rapid cooling history it is characterized by an initial sr isotopic ratio of 0 706 slightly negative end t values 0 5 to 1 9 and young depleted mantle model ages 970 1090 ma this suggests that the parent magma originated from partial melting of relatively juvenile crust which is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt geochemically the granites of the dongqing pluton are peraluminous with a shand index molar ratio a cnk of 1 0 1 1 for the two mica granites and 1 2 1 3 for the garnet bearing granites all the garnet bearing granites and some of the two mica granites show tetrad ree patterns tetrad group whereas most two mica granites show normal granitic ree patterns normal group the normal group granites exhibit depletion in nb ta p and ti in spidergrams and generally weak positive eu anomalies in ree patterns by contrast the tetrad group granites manifest depletion in ba nb ta sr p and ti and significant negative eu anomalies the trace element data constrain the parental magmas to having undergone extensive magmatic differentiation during their late stage magmatic evolution intense interaction of residual melts with aqueous hydrothermal fluids resulted in the non charac charge and radius controlled trace element behavior and the tetrad effect in ree distribution patterns this in turn leads to the invalidation of the commonly used tectonic discrimination criteria derived from trace element abundances of normal granites in view of this and previous studies we conclude that there were probably no s type granites produced in ne china during the phanerozoic consequently weathered sedimentary material did not play an important role in the genesis of the strongly peraluminous granites in the zhangguangcai range

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

multiple lines of evidence for crustal magma storage beneath the mesozoic crystalline iide mountains northeast japan 1 it has been recognized that the iide mountains consisting of mesozoic sedimentary rocks and late cretaceous to paleogene granitic rocks northeast japan are unique although they occur in a nonvolcanic region hot springs in the iide mountains have anomalously high heat discharge values similar to those from hot springs in volcanic regions in order to provide geochemical constraints on the heat source for the hydrothermal activity the chemical and isotopic compositions of 10 gas and water samples were determined the 3he 4he ratios determined range from 0 22 to 7 9 ra and the highest ratio is similar to morb type helium indicating a significant contribution of primordial mantle helium considering the relationship between the magnitude of the 3he 4he ratios and the distance of the sample locations from the kitamata dake the peak in the iide mountains where the largest ratio occurs it is apparent that there is a sharp decrease in 3he 4he ratios laterally away from the peak furthermore the peak is also the location where geophysical anomalies such as an anomalous conductive body and zones with low vp and low vs have been detected in the middle lower crust these high helium ratios are considered to indicate the likelihood of mantle derived materials supplying morb type helium beneath the kitamata dake and the possibility that mantle derived helium has been diluted by atmospheric and or crustal components with lower helium ratios away from the peak in order to examine whether or not ancient magma of middle miocene age is a possible source of the high 3he 4he ratios of the hot spring gases we calculated the evolution in 3he 4he ratios of the ancient magma with time as a result it is concluded that the anomaly beneath the iide mountains is due to newly ascending magmas in the present day subduction system rather than hydrothermal fluids related to late remnant magmatism of middle miocene age

subduction of the philippine sea plate beneath southwestern japan slab geometry and its relationship to arc magmatism 1 we carry out high resolution three dimensional seismic tomography of the crust and upper mantle beneath southwestern sw japan using arrival time data obtained from the nationwide seismograph network the tomographic images provide new insights into the configuration of the philippine sea slab and arc magmatism the results confirm the existence of an aseismic portion of the philippine sea slab at greater depths beyond the seismic portion the philippine sea slab is subducting aseismically down to at least a depth of 200 km in chubu 60 80 km in kinki and 60 km in chugoku and is subducting seismically to depths of 150 200 km in kyushu in the chubu district it is subducting seismically at a shallow dip and then bends downward beneath the volcanic area whereas in the kinki district it is subducting subhorizontally as far as the japan sea the differences in the slab geometry between adjacent regions correlate with the differences in volcanic activity suggesting the importance of the geometry of the philippine sea slab on arc magmatism our tomographic images further imply subduction of the philippine sea slab down to a depth of around 70 km northwest of the izu peninsula the philippine sea slab in that region might have split into western and eastern parts separated by a slab tear and collided with the pacific slab at depths of 150 200 km

a monte carlo method for probabilistic hazard assessment of induced seismicity due to conventional natural gas production abstract a monte carlo approach to probabilistic seismic hazard analysis is developed for a case of induced seismicity associated with a compacting gas reservoir the geomechanical foundation for the method is the work of kostrov 1974 and mcgarr 1976 linking total strain to summed seismic moment in an earthquake catalog our monte carlo method simulates future seismic hazard consistent with historical seismic and compaction datasets by sampling probability distributions for total seismic moment event locations and magnitudes and resulting ground motions ground motions are aggregated over an ensemble of simulated catalogs to give a probabilistic representation of the ground motion hazard this approach is particularly well suited to the specific nature of the time dependent induced seismicity considered we demonstrate the method by applying it to seismicity induced by reservoir compaction following gas production from the groningen gas field a new ground motion prediction equation gmpe tailored to the groningen field has been derived by calibrating an existing gmpe with local strong motion data for 2013 2023 we find a 2 chance of exceeding a peak ground acceleration of 0 57 g and a 2 chance of exceeding a peak ground velocity of 22 cm s above the area of maximum compaction disaggregation shows that earthquakes of m w 4 5 at the shortest hypocentral distances of 3 km and ground motions two standard deviations above the median make the largest contributions to this hazard uncertainty in the hazard is primarily due to uncertainty about the future fraction of induced strains that will be seismogenic and how ground motion and its variability will scale to larger magnitudes

spatial variations in 3he 4he ratios along a high strain rate zone central japan abstract a linear zone with high strain rates along the japan sea coast the niigata kobe tectonic zone nktz is considered to be associated with rheological heterogeneities in the lower crust and or upper mantle helium isotope variations along the nktz reveal a close association with the geophysical evidence for rheological heterogeneities in the crust and mantle in the southern nktz the 3 he 4 he ratios lower than 3 4 ra ra denotes the atmospheric 3 he 4 he ratio of 1 4 10 6 could be interpreted as a two component mixture of helium stored in aqueous fluids driven off the subducting oceanic crust and radiogenic crustal helium higher 3 he 4 he ratios are observed in the central nktz where quaternary volcanoes and high temperature hot springs are concentrated suggesting that the 3 he emanation manifest in the central nktz results from the effective transfer of mantle helium by intrusion and degassing of mantle derived magma in the crust in the northern nktz where two large inland earthquakes occurred recently there appears to be many samples with 3 he 4 he ratios significantly higher than those observed in the fore arc side of northeast japan a plausible source of mantle helium could be attributed to upward mobilization of aqueous fluids generated by dehydration of the subducting pacific plate slab

the slip distribution of the 1946 nankai earthquake estimated from tsunami inversion using a new plate model abstract a new model for the shape of the philippine sea plate psp subducting beneath southwest japan was constructed by combining marine seismic survey results and seismicity data this resulted in a plate model that is generally 3 5 km shallower than previous estimates and contains new details of plate boundary structure near the nankai trough axis we estimated the slip distribution of the 1946 nankai earthquake by inverting tsunami waveforms using the new plate boundary model and found that the large slip off cape muroto and seismic moment were reduced by about 10 from the previous estimate of tanioka and satake 2001a however we also found reason to suspect the tide gauge closest to the epicenter at shimotsu and this resulted in a much more substantial reduction in the amount of slip in the eastern segment of the rupture area we also find that our new rupture model correlates well with features of the subducting plate boundary such as a large subducting seamount off cape muroto kodaira et al 2000a this suggests that such features have an important effect on either earthquake rupture propagation or the interseismic accumulation of elastic strain energy or both

three dimensional seismic velocity structure and configuration of the philippine sea slab in southwestern japan estimated by double difference tomography 1 three dimensional seismic velocity structure in and around the philippine sea plate subducting beneath southwestern sw japan is determined by applying double difference tomography method to arrival time data for earthquakes obtained by a dense nationwide seismic network in japan a region of low s wave velocity and high vp vs of several kilometers in thickness is recognized immediately above the region of intraslab seismicity in a wide area from tokai to kyushu this characteristic layer dips shallowly in the direction of slab subduction compared with the upper surface of the philippine sea slab based on seismic reflection and refraction surveys on seven survey lines we interpret that the low vs and high vp vs layer corresponds to the oceanic crust of the philippine sea slab on the basis of the position of the low vs and high vp vs layer and the precisely relocated hypocenter distribution of intraslab earthquakes the upper surface of the philippine sea slab is reliably determined for the entire area of sw japan nonvolcanic deep low frequency earthquakes that occurred associated with the subduction of the philippine sea slab are distributed along the isodepth contour of 30 km in sw japan except for the tokai district where the depth of deep low frequency earthquakes becomes gradually deeper toward northeast

effect of time dependence on probabilistic seismic hazard maps and deaggregation for the central apennines italy abstract we produce probabilistic seismic hazard assessments for the central apennines italy using time dependent models that are characterized using a brownian passage time recurrence model using aperiodicity parameters of 0 3 0 5 and 0 7 we examine the sensitivity of the probabilistic ground motion and its deaggregation to these parameters for the seismic source model we incorporate both smoothed historical seismicity over the area and geological information on faults we use the maximum magnitude model for the fault sources together with a uniform probability of rupture along the fault floating fault model to model fictitious faults to account for earthquakes that cannot be correlated with known geologic structural segmentation we show maps for peak ground acceleration pga and 1 0 hz spectral acceleration sa 1 on rock having 10 probability of exceedence in 50 yr we produce maps to compare the separate contributions of smoothed seismicity and fault components in addition we construct maps that show sensitivity of the hazard for different parameters and the poisson model for the poisson model the addition of fault sources to the smoothed seismicity raises the hazard by 50 at locations where the smoothed seismicity contributes the highest hazard and up to 100 at locations where the hazard from smoothed seismicity is low for the strongest aperiodicity parameter smallest the hazard may further increase 60 80 or more or may decrease by as much as 20 depending on the recency of the last event on the fault that dominates the hazard at a given site in order to present the most likely earthquake magnitude and or the most likely source site distance for scenario studies we deaggregate the seismic hazard for sa 1 and pga for two important cities rome and l aquila for pga both locations show the predominance of local sources having magnitudes of about 5 3 and 6 5 respectively for sa 1 at a site in rome there is significant contribution from local smoothed seismicity and an additional contribution from the more distant apennine faults having magnitude around 6 8 for l aquila the predominant sources remain local in order to show the variety of impact of different values we also obtained deaggregations for another three sites in general as decreases periodicity increases the deaggregation indicates that the hazard is highest near faults with the highest earthquakes rates this effect is strongest for the long period 1 sec ground motions

partitioning of lithophile trace elements between h 2 o and h 2 o co 2 fluids and topaz rhyolite melt experiments have been conducted with h 2 o and h 2 o co 2 bearing fluids and melts of a cl f and lithophile trace element enriched vitrophyre associated with topaz rhyolite from spor mountain utah the starting material is mildly peraluminous and contains 1 25 wt percent f and 1 500 ppm cl the experiments were conducted with f sub o 2 controlled near ni nio at pressures of 0 5 to 4 kbars and at temperatures of 770 degrees to 950 degrees c fluid melt trace element distribution coefficients d i were calculated for li be b rb sr y zr nb cs ba ce th and u after ion microprobe analysis of starting material and run product glasses the concentration of element i in the fluid was calculated by mass balance and the fluid melt distribution coefficient d i was calculated as ppm by weight of i in fluid ppm by weight of i in melt the partitioning of li rb sr y nb cs and ce between aqueous fluids and melts of topaz rhyolite composition depends strongly on temperature and pressure at 0 5 kbars li rb sr y nb cs and ce concentrate in the fluid at temperatures or 900 degrees c at 2 kbars this same group of lithophile elements except for sr concentrate in the fluid at t or 900 degrees c be b and ba partition in favor of the melt at 0 5 and 2 kbars and at all temperatures of this study in the presence of co 2 free aqueous fluids at 4 kbars and at temperatures of 770 degrees to 950 degrees c all lithophile elements partition in favor of the melt this behavior for lithophile elements mimics that of published data on the partitioning of pb and zn between rhyolitic melts and cl bearing fluids previous studies have demonstrated an equivalent effect of pressure on the distribution of chalcophile trace elements between granitic melts and cl bearing aqueous fluids fluid melt distribution coefficients for the lithophile trace elements are significantly smaller for topaz rhyolite melts in equilibrium with mixed co 2 h 2 o fluids than for topaz rhyolite melts plus co 2 free aqueous fluids there is no evidence for co 2 complexing with the lithophile trace elements at pressures 6 m the data imply that the alkali elements m dissolve into the fluid as mcl 0 complexes and that ce dissolves into the fluid as a cecl 0 3 complex water saturated magmas of topaz rhyolite composition may become differentiated with respect to li cs and rb or ce y and nb if an aqueous fluid phase is evolved and moves through the magma under the influence of a temperature gradient that has a maximum temperature of at least 850 degrees to 900 degrees c

geochemistry of the rare metal bearing pegmatite no 3 vein and related granites in the keketuohai region altay mountains northwest china abstract the chemical composition of a barren biotite granite a two mica granite and a rare metal bearing pegmatite the no 3 vein in keketuohai altay mountains northwest china along with mineral separates of apatite and mica were analyzed and compared in the present work bulk chemistries of biotite granite two mica granite and pegmatite rim are consistent with fractional crystallization trend from granites toward pegmatite changes in pegmatite composition can be explained mainly by fractional crystallization of biotite rb sr isochrons yield 248 8 7 5 ma for the biotite granite 247 8 6 3 ma for the two mica granite and 218 4 5 8 ma for the pegmatite rim similar geochemical characteristics including initial e nd t values ranging from 0 76 to 3 04 for apatites similar initial e nd t values for whole rock samples of studied granites and pegmatite ranged from 1 40 to 3 21 and for biotites from granites ranged from 2 75 to 3 15 suggest that these rocks were derived from a common magma source old continental crust may have played a significant role in magma generation based on these data we interpret the evolution of the keketuohai granite pegmatite by magma differentiation from a common source biotite granite was the first to crystallize followed by two mica granites the residual melt was probably stored in a granitic batholith the pegmatite veins were injected 30 m y later during another episodic tectono magmatic event in the altay mountains

heightened odds of large earthquakes near istanbul an interaction based probability calculation we calculate the probability of strong shaking in istanbul an urban center of 10 million people from the description of earthquakes on the north anatolian fault system in the marmara sea during the past 500 years and test the resulting catalog against the frequency of damage in istanbul during the preceding millennium departing from current practice we include the time dependent effect of stress transferred by the 1999 moment magnitude m 7 4 izmit earthquake to faults nearer to istanbul we find a 62 15 probability one standard deviation of strong shaking during the next 30 years and 32 12 during the next decade

seismic images of the source area of the 2004 mid niigata prefecture earthquake in northeast japan to better understand the generation mechanism of the 23 october 2004 mid niigata prefecture earthquake m 6 8 we used 120 352 p wave and 95 391 s wave high quality arrival times from 5013 earthquakes to determine the three dimensional seismic velocity vp vs and poisson s ratio structures in and around the source area the hypocenter locations of the aftershocks are relocated accurately by using absolute and relative travel time double difference data our results demonstrate that the seismic velocity and poisson s ratio vary markedly around the source area most active faults are located along the margins of low velocity and high velocity zones an obvious change in seismic velocity and poisson s ratio occurs between the northwest and southeast parts of the study area and this boundary zone reflects the spatial distribution of active faults being well consistent with the surface geological features most of the large historic crustal earthquakes are located in or around the low seismic velocity zones the mainshock hypocenter is located near the margin of low velocity high poisson s ratio and high velocity low poisson s ratio anomalies along the active fault zone a zone with pronounced low velocity and high poisson s ratio is clearly imaged in the lower crust under the source area reflecting the existence of fluids that are released due to the dehydration of the subducting pacific slab such fluids might have reduced the mechanical strength of the fault zone and thus initiated the mid niigata prefecture earthquake