noble gases and nitrogen mixing and temporal evolution in the fumarolic fluids of vulcano italy abstract since 1979 noble gases he ne ar and n 2 in the medium temperature fumaroles of vulcano crater have been analyzed repeatedly during these 10 years of surveillance variations have been noticed in fluid composition until 1986 40 ar 36 ar ratios up to 2000 were found n 2 ar was 1600 and he ar was 1 9 indicating the presence of a deep component as the result of a mixing between mantle and crustal fluids since 1987 the atmospheric component has increased and the fluid composition has evolved towards an air saturated groundwater asw this change is considered to be the result of mixing between magmatic fluids and meteoric waters that release their atmospheric gases on entering the volcanic system these gases thus mask the magmatic component which has remained more or less constant in the last decade

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

model for the evolution of the avalonian cadomian belt the inception and termination of the ca 670 550 ma avalonian cadomian orogenic cycle are interpreted in terms of the amalgamation and breakup of a late precambrian supercontinent synorogenic arc related volcano sedimentary and granitoid rocks are attributed to oblique southward directed subduction along the margin of the supercontinent after its amalgamation breakup of the supercontinent and inception of the iapetus cycle led to termination of subduction and its replacement by transform activity the resulting closure of late precambrian arc related basins and the development of early cambrian platform successions with acado baltic fauna accompanied the formation of iapetus but took place on the active margin of a preexisting ocean and do not record the evolution of its rifted european flank

a precise late neoproterozoic u pb zircon age for the syntectonic perelle quartz diorite guernsey channel islands uk a precise u pb zircon age of 611 4 2 0 1 1 ma has been determined for the foliated quartz diorite at perelle bay guernsey uk channel islands the age is based on the analysis of single zircons half of a single grain and groups of two and three zircons the age is nearly 100 ma younger than that suggested by other workers based on 207 pb 206 pb dates of large multi grain fractions of zircon and thus rules out this intrusion as the earliest marker of the onset of cadomian magmatism in the north armorican massif a 611 ma crystallization age for the perelle quartz diorite is consistent with previous detailed fabric development studies that suggested magmatic fabrics within the pluton are largely overprinted by similarly oriented solid state deformation fabrics resulting from syntectonic emplacement during cadomian orogenesis the u pb age is approximately 8 15 ma older than 40 ar 39 ar hornblende dates for the pluton consistent with the emplacement of the intrusion followed by slow cooling in a region of moderate to high ambient crustal temperatures these new data emphasize the fact that periods of pluton emplacement are considerably briefer than periods of deformation and thus syntectonic intrusions do not date regional deformational events but only mark events within a period of regional tectonism the ability to analyse single zircons and selected portions of single zircons using ultra low blank u pb analytical techniques documents the feasibility of determining precise emplacement ages of other neoproterozoic granitoids that contain a significant percentage of xenocrystic zircon

mantle helium flux from the bottom of lake mashu japan abstract most of the 52 water samples from lake mashu hokkaido japan show large anomalies in their3he 4he ratios up to 4 6 times the atmospheric ratio and4he 20ne ratios indicating continuous injection of mantle he due to hot spring activity at the lake bottom the3he 4he ratio of the injected mantle he is estimated at3he 4he 9 43 0 17 10 6 which is close to the highest value reported for volcanic gases from the japanese islands accumulation of mantle he in the near bottom water can be reasonably explained by a diffusion process with a constant he flux from the lake bottom off4he 9 2 107 atoms cm2 s andf3he 8 7 102 atoms cm2 s the heat 3he ratio 1 7 10 7j atom falls in the range of values reported for submarine hydrothermal systems 0 4 26 10 7 j atom whereas the c3he ratio 1 8 1011 is about two orders of magnitude higher than the morb average 2 109 the mantle he injected from the lake bottom has a fairly short mean residence time in the lake water and is estimated at about 2 4 years overturn of the lake water which occurs twice a year probably plays an important role in the rapid transportation of the mantle he from the bottom to the surface

age of amphibolitic metamorphism in the ophiolitic unit of the morais allochthon portugal implications for early hercynian orogenesis in the iberian massif structurally lower portions of the allochthonous morais complex are comprised of an ophiolitic unit exposed in two contrasting structural units separated by a ductile thrust fault the lower unit is dominated by variably foliated amphibolite whereas the upper unit is largely comprised of metaperidotite and metagabbro most of the ophiolitic unit has recrystallized synkinematically under amphibolite facies metamorphic conditions c 500 c and 5 kbar amphiboles formed during this metamorphism are typically magnesio hornblende an amphibole concentrate from the lower structural unit records a 39 ar 40 ar plateau age of 397 3 4 ma an amphibole concentrate from the upper structural unit displays an internally discordant 39 ar 40 ar age spectrum corresponding to a total gas age of 431 1 27 3 ma gas fractions evolved from each amphibole concentrate at intermediate and high experimental temperatures are characterized by similar apparent k ca ratios and yield well defined 36 ar 40 ar v 39 ar 40 ar isotope correlations which result in similar ages of 384 2 5 2 and 392 4 7 3 ma these are considered to be more reliable than the plateau ages and are interpreted as dating the last cooling through those temperatures required for intracrystalline retention of argon within constituent amphibole grains the associated tectonothermal event represented a first stage of hercynian orogenesis in the iberian massif it was probably related to oceanic closure and associated obduction of granulitic eclogitic massifs which at present structurally overlie the ophiolitic unit

helium isotopes as geochemical indicators of a serpentinized fore arc mantle wedge new helium isotope data from hot springs on eastern kyushu island were obtained in order to elucidate the geographic distribution of 3 he 4 he ratios in the fore arc regions of southwest japan systematic regional variations in 3 he 4 he ratios are clearly distinguished across the fore arc from kyushu island 0 093 0 79 r a where r a denotes the atmospheric 3 he 4 he ratio of 1 4 x 10 6 to shikoku island 0 17 3 6 r a and to the kii peninsula 0 24 7 4 r a the distribution of mantle helium relative to total helium reveals a close association with the geophysical evidence of a serpentinized fore arc mantle wedge including the occurrence of deep nonvolcanic low frequency tremors lfts believed to be caused by upwardly mobile aqueous fluids derived from slab dehydration flux of mantle helium carried by aqueous fluids via a non serpentinized fore arc mantle wedge is very low on kyushu island where lfts have not been detected and 3 he 4 he ratios are lower than the atmospheric ratio on the other hand hot springs above the regions where lfts occur in the kii peninsula and northern shikoku island have high 3 he 4 he ratios indicating a significant contribution of mantle helium carried by aqueous fluids via a serpentinized fore arc mantle wedge the helium isotopes in hot and natural spring gases may be a useful geochemical indicator of a serpentinized fore arc mantle wedge especially in areas with sparse seismic station coverage

anti atlas morocco role in neoproterozoic western gondwana reconstruction abstract reconstruction of latest neoproterozoic gondwana hinges on the interpretation of the subduction and collision kinematics of pan african orogenic belts that rim the west african craton the anti atlas suture zone of southern morocco has presented an enigma in this reconstruction as the inferred subduction zone polarity and age of suturing appear to be incongruous with better known west african orogens to the west mauretanian bassaride and rokelide and transaharan orogens to the east ougarta tuareg gourma and dahomeyan contrary to previous interpretations new data from the anti atlas indicate a history of late neoproterozoic 750 600 north dipping subduction culminating in the 600 ma collision of the saghro magmatic arc to the north with the north facing rifted margin of the west african craton thus the anti atlas suture links a 6000 km long chain of pan african suture zones that essentially encircle the west african craton the suture zones demarcate the former position of subduction zones that in all cases dipped away from the west african craton the anti atlas suture links the western and eastern segments of the pan african orogenic belts associated with the amalgamation of western gondwana

the eastern tibetan plateau geothermal belt western china geology geophysics genesis and hydrothermal system abstract the eastern tibetan plateau geothermal belt etgb which is located in 98 102 e 28 32 n belongs to the eastern part of the mediterranean himalayan geothermal belt recently about 248 natural hot springs have been found in the etgb 60 of these springs have temperatures of 40 c and 11 springs have temperature above the local water boiling point using the helium isotopic data gravity magnetic and seismic data we analyzed the thermal structure and the relationship between hydrothermal activity and geothermal dynamics of the etgb results show that 1 the 248 springs can be divided into three geothermal fields kangding luhuo geothermal field kgf litang ganzi geothermal field lgf and batang xiangcheng geothermal field bgf the bgf and lgf have hot crust and warm mantle and are characterized by the higher heat flux 66 26 mw m2 and higher ratios of crust derived heat flux to total flux 47 46 60 62 the kgf has cool crust and hot mantle and is characterized by the higher heat flux and lower qc qm 2 there is a relatively 4 6 m higher gravimetric geoid anomaly dome which is corresponding with the etgb and in hydrothermal activity areas of the bgf and lgf there is a northwest southeast trending tensile stress area and the upper middle crust uplift area 3 an abnormal layer exists in the middle lower crust at a depth of 13 30 km beneath the etgb and this layer is 8 10 km thick and is characterized by lower velocity vp 2 5 high conductivity 10 m and high temperature 850 1000 c finally based on the heat source and geological and geophysical background we propose kangding type and batang type hydrothermal system models in the etgb

sm nd isotope characteristics of late cadomian granite magmatism in northern france and the channel islands sm nd isotopic studies of granites within the late precambrian cadomian orogenic belt of the north armorican massif northwestern france and channel islands reveal differences between arc related granite magmatism in outboard terranes and intracrustal granite magmatism in inboard terranes late cadomian c 570 ma arc related granitoids exhibit a range of e nd 2 to 6 and nd model ages t dm 1 0 1 3 ga reflecting variable contamination between late precambrian mantle derived magmas and ancient c 2 0 ga continental crust the contamination did not involve exposed granitic icartian basement to anygreat degree a more likely contaminant being unexposed lower crust of intermediate to acidic granulitic composition or early cadomian plutons which were themselves contaminated by lower crust voluminous granites of the mancellian region c 550 540 ma share common isotopic characteristics e nd 4 to 7 t dm 1 5 1 7 ga with migmatites and anatectic granites produced by partial melting of metasedimentary sequences within the st malo region consistent with a common source

the cadomian orogeny in the north armorican massif a brief review the north armorican massif nam of nw france is the type locality of the late precambrian cadomian orogenic belt the nam largely escaped reworking during the upper palaeozoic variscan cycle with the result that earlier geological relationships are commonly preserved intact a large part of the cadomian belt of the nam comprises variably deformed and metamorphosed supracrustal rocks of the brioverian succession barrois 1895 1896 1908 graindor 1957 cogne 1962 le corre 1977 rabu et al 1982 1983 chantraine et al 1982 the cadomian orogeny which takes its name from cadomus caen in normandy was defined by bertrand 1921 as the late precambrian orogeny which in the nam resulted in the folding and uplift of the brioverian succession prior to the deposition of lower palaeozoic red bed sequences events which have been ascribed to the cadomian orogeny span the period c 700 425 ma during which time the brioverian was heterogeneously deformed and metamorphosed and intruded by calc alkaline igneous complexes the evolution of the belt has been interpreted in terms of the gradual cratonization of calc alkaline arc complexes and syn orogenic sediments in an andean type continental margin brown et al 1990 dupret et al 1990 this contribution reviews briefly the geology of the cadomian belt of the nam fig 1 and outlines some of the more controversial debates concerning the distribution and status of precadomian basement the stratigraphy of the brioverian succession the nature of cadomian magmatism the kinematic significance of major structures and the geotectonic setting of the component parts of the belt

39ar recoil artifacts in chloritized biotite biotite separates from the metamorphosed granitic rocks of eastern taiwan yield disturbed 40ar39ar age spectra their disturbed profiles become more pronounced with increasing degree of chloritization and are attributed to mixed release of argon from sub micron scale biotite and chlorite intercalations 39ar internal recoil best explains the discordance of the age spectra chlorite is randomly intercalated with biotite at scales ranging from 10 a to several tens of microns both 40ar and k were evidently lost during the chloritization reaction during the neutron irradiation 39ar atoms recoil into the chlorite from the adjacent biotite intercalations the recoil and chloritization combine to produce a variable 40ar39ar spatial distribution in the intercalated biotite chlorite during 40ar39ar step heating analyses argon in biotite is released in two pulses centered at 650 c and 950 1050 c which represent two stages of dehydroxylation of the biotite chlorite out gasses in two pulses centered at 550 c and 700 900 c during dehydroxylation and then decomposes this differential thermal release of argon from each mineral phase with variable 40ar39ar ratios yields discordant incremental heating age spectra

effect of the volcanic front migration on helium nitrogen argon and carbon geochemistry of hydrothermal magmatic fluids from hokkaido volcanoes japan abstract active volcanoes from hokkaido are distributed along the sw ne trending volcanic front where the subducting pacific plate changes direction from n s to wsw ese one exception is the tokachi volcano which is located approximately 50 km to the north west of the current volcanic front the tokachi oki slab cracking zone represents the transitional zone between the honshu and kurile trenches this change is responsible for the rapid lateral variation of the subduction angle and slab shape we investigate the consequence of this change on the chemical and isotopic compositions from hydrothermal magmatic fluids and mineral separates collected from three volcanoes of hokkaido northern japan namely tarumae tokachi and meakan our data show that these volcanoes have a distinct range of he n and c isotopic compositions meakan fumaroles have a 3he 4he ratio that ranges from 4 46ra to 6 88ra 15n from 2 2 to 3 5 and 13c co2 from 8 47 to 9 81 consistent with subducted sediment contribution tarumae fumaroles have a particularly low 3he 4he ratio 3 08ra in comparison with their hot springs up to 5 24ra and are associated with high co2 3he ratios 2 2 5 3 1011 hydrothermal crustal interactions from the dome or from a deeper hydrothermal system are the main mechanisms that control the 3he 4he and co2 3he ratios in tarumae fumaroles the 15n and 13c co2 values for tarumae volcano range from 0 6 to 3 1 and from 6 34 to 6 43 respectively tokachi fumaroles are characterized by high 3he 4he up to 7 38ra low 15n 2 4 0 1 and low 13c co2 up to 5 32 consistent with mantle contribution and minor subducted sediment contribution the limestone sediment mantle ratio shows a decreasing contribution from subducted sediments starting from tokachi 1 9 to meakan 3 4 and finally tarumae 5 3 this change of isotopic compositions from the sw ne of hokkaido is the result of the tokachi oki slab cracking zone slab dehydration under tokachi occurs at a deeper level 150 200 km than in other hokkaido volcanoes 100 km which produces the migration of the volcanic front therefore we argue that the isotopic signature of tokachi is the result of i a lower sediment contribution from the slab ii a deeper dehydration of the slab and iii a lower degree of partial melting

widespread distribution of ascending fluids transporting mantle helium in the fore arc region and their upwelling processes noble gas and major element composition of deep groundwater in the kii peninsula southwest japan abstract chemical and isotopic studies including analyses of noble gases were comprehensively conducted on the groundwater of the entire kii peninsula which is located in the fore arc region of southwest japan groundwater of na cl hco3 na hco3 cl and na cl types was shown to be distributed across the whole area groundwater in the inland central part of the peninsula shows relatively low salinity whereas groundwater from the area along the ene trending median tectonic line mtl on the north side of the peninsula shows high salinity up to 18 800 mg l of cl and the presence of unusual heavy oxygen isotopes this trend is similar to that documented in saline waters from the arima region the so called arima type thermal water high 3he 4he ratios relative to the atmospheric value up to 6 7 ra were recorded throughout the kii peninsula covering a wider area than documented previously the saline groundwater is also strongly depleted in 20ne and heavy noble gases from the wide distribution of high 3he 4he values and the associated 20ne and cl concentrations we infer that aqueous fluids derived from dehydration of the subducting slab are present at depth beneath almost the entire kii peninsula these aqueous fluids may ascend along the major north dipping boundary faults the isotopic composition of groundwater from the southern part of the peninsula suggests that the contribution from these dehydration derived fluids is relatively small in this region however volatile components e g noble gases and co2 in the groundwater of this area may originate from the dehydration derived fluids upwelling of arima type thermal water of the na cl hco3 type is expected to undergo a phase separation of volatile species due to decompression as the fluid ascends the variety of water types documented may be due to this water gas separation and the subsequent incorporation of gaseous species into shallow meteoric groundwater the observed high 3he 4he ratios in the absence of a mantle wedge below the southern part of the kii peninsula may reflect the oblique ascent of these fluids along north dipping boundary faults

variable variscan thermal rejuvenation in the st malo region cadomian orogen france evidence from 40ar 39ar mineral ages abstract the st malo region in north west france contains migmatites and anatectic granites derived by partial melting of metasedimentary protoliths during cadomian orogenesis at c 540 ma previously reported rb sr model ages for muscovite and biotite range from c 550 to c 300 ma and suggest variable resetting of mineral isotopic systems these rocks display microscopic evidence for variably intense cadomian intracrystalline plastic strain but record no obvious evidence of penetrative palaeozoic regional deformation 40ar 39ar mineral ages have been determined to evaluate better the extent timing and significance of palaeozoic overprinting eleven muscovite concentrates and one whole rock phyllite have been prepared from various units exposed in the st malo and adjacent mancellian regions in the mancellian region muscovite from two facies of the bonnemain granite complex record 40ar 39ar plateau ages of c 527 and 521 ma an internally discordant 40ar 39ar release spectrum characterizes muscovite from protomylonitic granite within the cadomian alexain deux evailles ize granite complex and probably records the effects of variscan displacement along the north armorican shear zone muscovite concentrates from anatectic granite and from cadomian mylonites along ductile shear zones within the north western sector of the st malo region exhibit internally discordant 40ar 39ar release spectra which suggest variable and partial late palaeozoic rejuvenation by contrast muscovite concentrates from samples of variably mylonitic brioverian metasedimentary rocks exposed within the south eastern sector of the st malo region display internally concordant apparent age spectra which define plateaux of 326 320 ma a whole rock phyllite sample from brioverian metasedimentary rocks exposed along the eastern boundary of the st malo region displays an internally discordant argon release pattern which is interpreted to reflect the effects of a partial late palaeozoic thermal overprint muscovite from the plelan granite part of the variscan plelan bobital granite complex yields a 40ar 39ar plateau age of c 307 ma the 40ar 39ar results indicate that cadomian rocks of the st malo region have undergone a widespread and variable palaeozoic carboniferous rejuvenation of intracrystalline argon systems which apparently did not affect the mancellian region this rejuvenation was not accompanied by penetrative regional deformation and was probably of a static thermal hydrothermal origin the heat source for rejuvenation was probably either the result of heating during variscan extension or advection from variscan granites which are argued to underlie the st malo region

short paper cadomian terrane tectonics and magmatism in the armorican massif the north armorican composite terrane nw france is a collage of displaced terranes which result from the amalgamation of cadomian continental arcs and marginal basin complexes by sinistral transpression along a continental margin above a subduction zone early cadomian arc activity occurred at c 700 650 ma but terrane accretion did not occur until c 540 ma and post tectonic magmatism persisted well into the palaeozoic cadomian events thus span a considerably greater period than previously supposed

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

tectonothermal chronology of early cadomian arc development in guernsey and sark channel islands the cadomian orogen exposed in nw france and the channel islands comprises a collage of variably displaced terranes which record the late proterozoic evolution of a continental margin within a complex subduction zone on the islands of guernsey and sark calc alkaline quartz diorite stocks were emplaced during early stages of the cadomian orogeny zircons from two stocks of deformed quartz diorite display evidence of inheritance in larger and more magnetic fractions upper intercept ages for these discordant concentrates are c 1300 ma sm nd whole rock model ages t dm suggest older ages of c 2000 ma conversely the smallest and least magnetic zircons exhibit a distinct lead loss pattern suggesting that the 207 pb 206 pb dates of c 700 ma correspond to the time of crystallization of the stocks and provide a lower age constraint for initiation of subduction related magmatism in the cadomian orogen hornblende concentrates from deformed quartz diorite stocks exposed on guernsey and sark display discordant 40 ar 39 ar age spectra five samples record well defined isotope correlation ages ranging between 596 ma and 606 ma a hornblende concentrate from host orthogneiss sark yields a plateau age of 608 ma the hornblende ages are interpreted as dating post metamorphic cooling following late proterozoic deformation and metamorphism within the arc system both magmatic and cooling ages from this early cadomian arc contrast with those of younger initial tectonothermal activity c 570 ma and c 540 ma in other cadomian terrane elements and suggest palinspastic separation until very late stages of the orogeny the polyphase nature of this late proterozoic activity is similar to that of related orogens which probably occupied similar tectonic settings along the margin of gondwana e g sw iberia west africa

helium isotope systematics at nevado del ruiz volcano colombia implications for the volcanic hydrothermal system abstract we have collected 14 water and gas samples from 9 thermal springs and gas vents near nevado del ruiz volcano colombia the 3 he 4 he and 4 he 20 ne ratios vary significantly from 0 98 r atm where r atm is the atmospheric 3 he 4 he ratio of 1 4 10 6 to 6 30 r atm and from 0 37 to 7 0 respectively the 3 he 4 he ratio corrected for air contamination decreases with increasing distance from the central crater of the volcano to the sampling site the trend is very similar to that observed at ontake volcano japan a hydrodynamic porous media dispersion model can explain the 3 he 4 he trend the temporal variations in the 3 he 4 he ratio at four sites provide useful information on the apparent velocity of the magmatic fluid flow brought on by a volcanic eruption the estimated value of several tens m day 1 agrees well with the inferred velocity of flow in oshima volcano japan and is comparable to the largest rate of groundwater movement in a deep sedimentary basin

the isotopic composition of radiogenic helium and its use to study groundwater movement in confined aquifers abstract the 3 he 4 he ratio for radiogenic he is shown to be primarily determined by the abundance of li and neutron absorbing elements in the host formations and is almost independent of the radioelement abundance the 3 he 4 he ratios have been computed for various li contents in rock matrices with average abundances of other elements the 3 he 4 he ratio is specific for each formation and may therefore be used to study crustal diffusion of he it is shown however that both the 3he and 4he contents of continental basements are likely to exceed those of the mantle so that diffusion of mantle he through continental crust is not likely to occur changes in the 3 he 4 he ratio for dissolved he have potential for studying groundwater movement and mixing processes atmospheric he which was dissolved at recharge is progressively diluted by radiogenic he with an isotopic ratio characteristic of the aquifer as the groundwater migrates down dip mixing proportions for formation he and atmospheric he in aquifers for which there is admixture of fracture borne water and interstitially stored water can also be estimated from isotopic measurements these processes are discussed in relation to two aquifers in eastern england

carbon and noble gases in archean chert abstract in order to study the origin and evolution of volatiles trapped in archean and early proterozoic cherts we have measured contents and isotopic compositions of carbon and noble gases using step heating and mass spectrometry the observed negative correlation between the 13c value and nitrogen carbon ratio in the samples suggests that trapped carbon in archean cherts is a mixture of carbonate sedimentary organic matter and an atmospheric component elemental abundance patterns of noble gases show a slight depletion of 20ne and excess of 132xe relative to air which is explained by atmospheric noble gases dissolved in water at relatively low temperature the 3 he 4 he ratios indicate an apparent crustal value of 1 3 10 3 consistent with the in situ radiogenic production ratio significant excess 21ne 131xe and 132 136xe as well as slight enrichment of 38ar and 86kr relative to atmosphere are found in the onverwacht chert at the 800 and 1200 c steps similar but small isotope anomalies are detected in the frere formation chert at the 1800 c step excess 21ne shows positive correlations with 38ar 86kr and 132xe 136xe enrichments while excess 131xe has no relation with the other isotope anomalies the 21ne anomaly can be attributable to the nuclear reaction 18o n 21ne the enrichments of 86kr and 132xe 136xe are derived from spontaneous fission of 238u in the cherts the slight excess 38ar may be due to the 35cl p 38ar reaction based on the positive correlation between 21 ne 22 ne and 38 ar 36 ar ratios but should be verified in future work

erratum for closure to assessment of the liquefaction susceptibility of fine grained soils by jonathan d bray and rodolfo b sancio

variations in the 3he 4he ratios of hot springs on shikoku island southwest japan new helium isotopic data from hot springs on shikoku island were obtained from a larger number of sampling points than previous studies in order to elucidate the geographical distribution of 3he 4he ratios in the fore arc regions of southwest japan systematic regional variations in 3he 4he ratios were observed on both shikoku island and the kii peninsula the hot springs on shikoku island have 3he 4he ratios between 0 21 ra and 2 5 ra on the other hand the majority of hot springs in the kii peninsula have significantly higher 3he 4he ratios than those on shikoku island it has been suggested that the anomalously high 3he 4he ratios in the fore arc region of southwest japan are related to the migration of morb type helium with aqueous fluids generated by dehydration of the subducting philippine sea plate and mixing with terrestrial waters e g matsumoto et al 2003 according to recent seismological observations of crustal microearthquakes and their focal mechanisms the geotectonic environment beneath shikoku island is subject to a stress field with no normal faulting and with extremely low crustal seismicity this argues against migration of aqueous fluids from the subcrustal lithosphere resulting in a relatively small influence of mantle derived helium at the surface as a consequence the regional variation in 3he 4he ratios of hot springs on shikoku island is interpreted as a three component mixture of mantle derived helium associated with magmatism of middle miocene of age 3 4 ra crustal radiogenic helium and atmospheric helium

helium isotopes and tectonics in southern italy geodynamic evolution of southern italy can be understood within the framework of the mediterranean alpine system subduction of a plate along the sicily calabrian forearc under the tyrrhenian sea has been suggested by many geophysicists although it is not yet confirmed and remains somewhat controversial helium isotope ratios provide useful information on the geotectonic structure of the region the authors report here the sup 3 h sup 4 he ratios of terrestrial gas samples from southern italy the observed sup 3 he sup 4 he ratios are relatively high in the eolian volcanic arc region and low in the other areas dichotomous explanations are presented firstly volcanic arc forearc hypothesis suggests the subduction along the sicily calabrian forearc secondly horizontal transport hypothesis is described based on the relationship between the ratios and radial distance from the recent spreading basin in southern tyrrhenian sea

behaviour of rb sr whole rock and u pb zircon systems during partial melting as shown in migmatitic gneisses from the st malo massif ne brittany france the age of regional metamorphism and partial melting in the late proterozoic succession of the st malo area has been established at around 540 ma whole rock homogenization of the sr isotope systems has been achieved only in the anatectic granites whereas the associated metatexitic and diatexitic gneisses remain highly heterogeneous at lower grade than the sillimanite isograd metasedimentary gneisses contain detrital zircons which record the regional metamorphic event as a u pb lower intercept age 536 14 ma in the sillimanite zone u pb zircon lower intercept ages are around 500 10 ma and suggest a recent loss of radiogenic pb from the observed overgrowths zircons from the anatectic granites do not yield u pb intercept ages due to the presence of inherited radiogenic pb but the finer fractions define a discordant array whose upper intercept on concordia yields 555 13 ma an age significantly older than the partial melting event indicated by the lower grade zircon ages the lower intercept defined by the fine grained anatectic zircons yields a date in the future negative ordinate value in their regional context the st malo migmatites can be considered as resulting from late stage crustal melting in the cadomian orogenic belt following genesis of calc alkaline magma at an active margin around 600 ma ago an age of 540 ma for partial melting in the st malo migmatites places the end of the cadomian orogeny near the precambrian cambrian boundary

isotopes of the light noble gases in mineral waters in the eastern part of the balkan peninsula bulgaria the concentration and isotopic composition for the light noble gases in spontaneous gas from mineral waters in the eastern part of balkan peninsula are presented in this paper the isotopic ratio 3he4he in dissolved gases varies within the range 0 15 1 1 10 6 and the concentration of helium in these gases is between 0 002 and 3 14 vol it is determined that 86 7 98 8 0 4 9 2 and 1 of 4he is derived from the crust mantle and atmosphere respectively the main source of 3he is the earth s mantle the isotopic composition of neon is nearly the same as that in the atmosphere several samples show a slight excess of light isotopes probably due to the mass fractionation of atmospheric neon the isotopic composition of argon is also quite near to that in the atmosphere in three cases argon contains 18 1 12 3 and 7 9 of the radiogenic component the arn2 a ratios as a rule vary between 0 012 air and 0 027 dissolved air so that n2 in most of the samples is also assumed to be of atmospheric origin the ratio c3he in many sites is as low as 107 but this fact cannot be used to reveal unambiguously the origin of c containing gases

mantle derived helium in two peruvian hydrothermal ore deposits strong differences exist between the helium isotopic compositions of mantle derived magmas1 8 axial vent hotspring fluids9 14 subduction related magmas15 20 and many associated hot springs21 24 and the atmospheric and crustal values fig 1 here we report helium isotope ratios for two late tertiary fossil hydrothermal systems responsible for precious metal base metal and tungsten mineralization and compare them to those of circum pacific hot spring emanations the 3he 4he ratios of inclusion fluids hosted by gangue and sulphide minerals from casapalca and pasto bueno peru all lie between two and three times the atmospheric value indicating the presence of a dilute component of mantle helium consistent with previously reported stable isotope evidence for the presence of magmatic fluids during mineralization25 27 although post trapping modification of the helium isotope composition is possible we suggest that these apparently low values represent the composition of helium inherited from contributing magmas as a tracer of magmatic fluids in hydrothermal systems helium isotopes are decoupled from the factors that govern other stable isotope signatures

helium 3 emission from nevado del ruiz volcano colombia high helium 3 helium 4 ratios up to 6 6ratm 6 6 times the atmospheric ratio of 1 40 10 6 were observed in nine samples of gases and hot waters from seven sites located around the volcano nevado del ruiz colombia the values of the ratio decrease with distance from the crater such a tendency coincides well with the pattern first reported from the volcano ontake central japan and suggests a general signature of helium isotope ratios around individual volcanoes the corrected helium 3 helium 4 ratios at one gas vent sampled twice over six months increased this is interpreted to mean that the mantle contribution of helium may have increased with time

helium 3 emission related to volcanic activity the helium 3 helium 4 ratio in bubbling gases from ten hot springs located around mount ontake an active volcano in central japan ranges from 1 71 r sub atm 1 71 times the atmospheric ratio of 1 40 x 10 sup 6 to 6 15 r sub atm the value of the ratio decreases with distance from the central cone of the volcano such a tendency may be a characteristic of helium 3 emission in volcanic areas and suggests more primitive helium 3 is carried with fluid flowing through a conduit during volcanic activity 6 references 1 figure 1 table

natural gas association with water and oil as depicted by atmospheric noble gases case studies from the southeastern mediterranean coastal plain a model for the equilibrium distribution of atmospheric noble gases ang between natural gas and water phases was extended to include the gas oil relationship the basic assumption is that the ang are introduced into hydrocarbon systems via recharge or seawater theoretical ang patterns of natural gas at equilibrium with water fall between the air pattern and that of air saturated water theoretical ang patterns of natural gas degassed from oil which had previously equilibrated with a water phase cover a wide range including the range calculated for gas water equilibration ang patterns in natural gas which fall outside the overlapping range may thus indicate association of the gas with oil the model was tested in the case of hydrocarbon systems of the southeastern mediterranean coastal plain other geochemical evidence indicates that the ashdod sadot shallow gas wells are not related to oil the relative ang abundances in gas samples from these wells lie within the range predicted for gas water association the relative ang abundances in samples degassed from oils of the helez kokhav oilfield are similar to specific patterns predicted for the degassing of oil which was previously associated with water published and new analyses of methane dominated natural gas samples from california japan and northern israel also reveal ang patterns of the type predicted by the model the results of the case studies support our hypothesis that water is responsible for transport of atmospheric noble gases into subsurface hydrocarbon systems this forms the basis for identification of oil associated natural gases via ang study

u pb geochronological constraints on the timing of plutonism volcanism and sedimentation jersey channel islands uk uranium lead dates for single and small multiple grain zircon separates are presented for the main geological units from jersey british channel islands a turbiditic sandstone from the jersey shale formation brioverian supergroup contains detrital zircons of a variety of ages ranging from c 2 6 to 0 6 ga the youngest zircons yielded nearly concordant u pb dates of 586 7 3 0 ma and 587 1 2 7 ma providing a maximum depositional age for the unit zircons from overlying volcanic rocks anne port rhyolite give an upper intercept date of 582 8 3 2 7 ma considered to be the age of eruption the undeformed sw jersey granite which intrudes and locally thermally metamorphoses the folded jersey shale formation is dated at 580 2 3 1 6 ma these dates constrain tightly the timing of deposition of the jersey shale formation and the age of deformation on jersey and indicate a dynamic arc environment during the late neoproterozoic zircons from the nw jersey granite define an upper intercept date of 482 7 1 6 ma similar to the previously reported 40 ar 39 ar hornblende date of c 473 ma confirming a renewed pulse of magmatism during the ordovician in this sector of cadomia

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

helium isotope evidence for magmatic gases in lake nyos cameroon we have measured he 4he and 4he 20ne ratios of gas samples collected at lake nyos where a toxic gas disaster occurred on august 21 1986 and at lake monoun in cameroon west africa the he 4he ratios corrected for air contamination are 5 39 5 75 ratm where ratm is the atmospheric ratio of 1 40 10 6 for lake nyos and 3 56 ratm for lake monoun the data suggest a significant contribution of mantle derived helium in these cameroon volcanic crater lakes the origin of co2 gas erupted during lake nyos disaster is inferred to be of magmatic origin based on the high he 4he ratio

rare gas isotopic compositions in natural gases of japan isotopic and elemental compositions of rare gases in various types of gas samples collected in the japanese islands were investigated excess3he was found in most samples many samples showed a regionally uniform high3he 4he ratio of about 7 times the atmospheric ratio the he concentrations varied from 0 6 to 1800 ppm and they were low in co2 rich gases and high in n2 rich gases ne isotopic deviations from the atmospheric ne were detected in most volcanic gases the deviations and the elemental abundance patterns in volcanic gases can be explained by a mixing between two components one is mass fractionated rare gases and the other is isotopically atmospheric and is enriched in heavy rare gas elements ar was a mixture of mass fractionated ar atmospheric ar and radiogenic ar and the contribution of radiogenic40ar was small in all samples except for he elemental abundance patterns were progressively enriched in the heavier rare gases relative to the atmosphere several samples were highly enriched in kr and xe relative to the abundance pattern of dissolution equilibrium of atmospheric rare gases in water the component which is highly enriched in heavy rare gases may be released from sedimentary materials in the crust

palaeozoic terrane amalgamation in central europe a ree and sm nd isotope study of the pre variscan basement ne bohemian massif

polyphase late paleozoic tectonothermal evolution of the southwestern meguma terrane nova scotia evidence from 40ar 39ar mineral ages 40ar 39ar incremental release ages of hornblende muscovite and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late paleozoic tectonothermal evolution for the southwestern meguma terrane regional d1 folding with cleavage formation under greenschist lower amphibolite facies m1 metamorphic conditions occurred at ca 400 410 ma and was followed by emplacement of a series of granitic stocks ranging in age between ca 375 and 315 ma these were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade these are locally superposed on m1 regional metamorphic assemblages and result in a complex isograd pattern 40ar 39ar mineral ages suggest episodes of contact metamorphism occurred at 1 360 375 ma possibly related to emplacement of the south mountain batholith or temporal equivalents 2 350 356 ma around the port mouton pluton and northeastern shelburne pluton 3 ca 315 325 ma near the wedgeport pluton and in

geographical distribution of 3he 4he ratios in north kyushu japan geophysical implications for the occurrence of mantle derived fluids at deep crustal levels abstract we measured 3he 4he ratios in hot spring gases collected from sites in north kyushu japan that represent an island arc setting associated with the subduction of the philippine sea plate beneath the eurasian plate our results revealed relatively high 3he 4he ratios about 4 to 8 ra in the beppu shimabara graben a continuation of the okinawa trough and relatively low ratios about 0 1 to 2 ra in areas located to the north and south of the graben slightly elevated ratios about 3 to 4 ra were observed in areas further north of the graben north kyushu hosts unusual he isotopic signatures considering that its backarc location would predict higher 3he 4he ratios than the low ratios observed here instead of reflecting a regional tectonic signature the geographic distribution of 3he 4he ratios appears to vary with seismic velocity perturbations as detected at 20 30 km depth the correspondence between these two parameters suggests that 3he 4he ratios in this case relate to the spatial distribution of fluids at the base of the crust

variations in thermal state revealed by the geochemistry of fumarolic gases and hot spring waters of the tateyama volcanic hydrothermal system japan this study reports the chemical and isotopic compositions of hot spring waters and fumarolic gases sampled in the jigokudani valley of tateyama volcano central japan in 2015 and 2016 to reveal the state of the underlying hydrothermal system we discuss the cause of temporal variations in geochemical data in terms of temperature change in the hydrothermal system and clarify the relationship between hot spring waters and fumarolic gases the volcanic gas supplied from deep seated magma was separated into liquid and vapor phases when it reached a shallow depth each phase formed the following three types of hot spring water 1 high anion concentrations and isotopic compositions similar to magmatic water 2 lower isotopic compositions compared to type 1 waters and large variations in cl so42 and 3 low cl and total anion concentrations the formation of type 1 and type 2 hot springs was influenced by magmatic components such as hcl and so2 we consider that type 1 hot springs are derived from the liquid phase while type 2 hot springs are derived from the vapor phase of the two phase zone the temporal variations in cl so42 are considered to result from temperature changes in the reservoir where liquid and vapor separated as the hcl partitioning coefficient between the vapor and liquid phases is strongly dependent on temperature type 3 hot springs are derived from the vapor phase which is depleted in hcl and so2 we propose that the cl concentration of type 2 hot springs could be a measure of volcanic activity because it reflects the thermal state of the shallow two phase zone where phreatic eruptions occur

noble gases in mafic phenocrysts and xenoliths from new zealand we have determined the elemental and isotopic compositions of noble gases in young subduction related phenocrystic olivine and clinopyroxene samples from the taupo volcanic zone central north island new zealand and in behind arc intraplate phenocrystic and xenolithic olivine samples from the northland and auckland volcanic provinces northern north island new zealand helium isotopic ratios range from morb like 3he4he values of about 11 10 6 to lower values of about 6 10 6 consistent with previous measurements of helium isotopic ratios in subduction related samples 40ar36ar and 21ne22ne ratios range from atmosphere like compositions to maximum values of about 700 and 0 033 respectively in contrast most of the 21ne22neratios are generally indistinguishable from atmospheric values the variations in helium neon and argon isotopic ratios are interpreted as resulting from mixing of 1 a a primordial 3he rich component derived from the upper mantle and characterised by morb like 3he4he ratios of about 12 10 6 2 b a radiogenic 4he rich component derived from crustal materials and characterised by a 3he4he ratio of less than 2 10 7 and 3 c a helium poor atmosphere derived component which dominates the heavier noble gases by combining the helium and argon isotopic results it is possible to estimate the relative contribution of each of these three components to the total 40ar observed in each sample based on the present understanding of the origin and evolution of arc magmas a simple qualitative model of the mechanisms which introduce noble gases to the parent magmas of the samples is developed however it remains uncertain whether the atmospheric and crustal derived noble gas components are introduced to the mantle source regions of the magmas by subduction or alternatively are introduced by interactions between the ascending parent magmas and the overlying crust

the geothermal system of wairakei new zealand physical processes and age estimates inferred from noble gases abstract atmospheric and non atmospheric noble gases were identified by their isotopic composition in 31 samples from geothermal features from the wairakei tauhara and mokai geothermal fields north island new zealand in the fumaroles atmospheric noble gases ang were found in concentrations that exceed the values in air saturated recharge water asw by a factor of up to 14 significant concentrations of non atmospheric na 4 he he na and 40 ar ar na were observed up to 4 3 10 4 and up to2 9 10 4 cm 3 stp g fluid respectively in contrast the hot spring waters revealed significant depletions in ang as low as 0 02 of the asw concentrations and low but recognizable concentrations of he na and ar na in geothermal wells a wide spectrum of ang concentrations was observed from 0 02 to 30 times the concentrations in asw 4 he na and 40 ar na varied accordingly these observations lead to the simplified boiling model meteoric water penetrated into the geothermal compartment where it was heated and enriched by 4 he na and 40 ar na of mantle and crustal origins boiling of ascending fluid due to pressure decrease results in formation of a noble gas enriched steam phase issuing as fumaroles and drowned fumaroles and a noble gas depleted residual liquid the latter may cause secondary boiling of shallow groundwater emerging in hot springs geothermal wells tap fluids at various degrees of steam separation the depth of recharge of meteoric water into the geothermal system exceeds the depth of boiling which is 600 m at the studied area the ang patterns along with he na ang ratios are applied to identify the following physical processes a mixing of early separated steam with residual liquid b mixing of a few per cent groundwater with residual liquid c addition of air d addition of excess ne and e encroachment of recent groundwater due to pressure decrease retention enrichment values of the ang were applied to reconstruct non atmospheric initial nai concentrations of he nai ar nai and the initial co 2 in the geothermal water literature data on 3 he 4 he were used to separate the 4 he nai concentrations into crustal and mantle derived components the crustal radiogenic 4 he concentration calculated for the initial water was applied to derive an age estimate of the geothermal water assuming storage in rhyolitic rocks effective ages of 2 10 4 1 10 5 and2 10 5 a were obtained for the initial liquids feeding the wairakei wells fumaroles and mokai wells respectively crustal ar na concentrations were estimated from those of crustal he and from the rhyolitic 4 he 40 ar production ratio the calculated crustal 40 ar is 0 1 of 40 ar na and 4 he 40 ar contribution is found at wairakei to be 0 5 within the range of values measured by other workers in mantle derived rocks

time span of plutonism fabric development and cooling in a neoproterozoic magmatic arc segment u pb age constraints from syn tectonic plutons sark channel islands uk abstract new u pb zircon and titanite dates from syn tectonic plutons on the british channel island of sark constrain the time span of plutonism fabric development and cooling in this part of the neoproterozoic cadomian magmatic arc the tintageu leucogneiss is a mylonitic unit that was dated previously at 615 6 4 2 2 3 ma the port du moulin quartz diorite which intruded the tintageu unit contains a high strain solid state deformation fabric that is less intense than but parallel to fabrics in the leucogneiss and yields a u pb zircon date of 613 5 2 3 1 5 ma the little sark quartz diorite also displays solid state deformation fabrics in addition to relict magmatic textures and yields a u pb zircon date of 611 4 2 1 1 3 ma the north sark granodiorite is largely penetratively undeformed exhibits mainly magmatic fabrics and textures and has a u pb zircon date of 608 7 1 1 1 0 ma two fractions of titanite from each intrusion are essentially concordant and are identical within error with mean dates of 606 5 0 4 ma port du moulin quartz diorite 606 2 0 6 ma little sark quartz diorite 606 4 0 6 ma north sark granodiorite the new u pb data in combination with previous u pb and 40 ar 39 ar data and previous field studies confirm the syn tectonic nature of the sark plutons and quantify the time span ca 7 m y required for intrusion and sufficient crystallization of each body to record incremental strain during waning deformation titanite u pb and hornblende 40 ar 39 ar dates mark final cooling about 2 m y after intrusion of the last pluton

significance of a hiatus in down temperature fabric development within syn tectonic quartz diorite complexes channel islands uk detailed fabric development histories have been deduced for neoproterozoic foliated quartz diorite complexes of the channel islands uk the plutons were emplaced during regional d2 deformation magmatic fabrics formed at low crystal contents pre rheologically critical melt percent are only locally preserved due to overprinting by solid state deformation which occurred at moderate temperatures 400 550 c this is demonstrated by brittle microcracking of plagioclase and amphibole with only local ductile bending and dynamic recrystallization marginal recrystallization and myrmekite development on alkali feldspar ductile deformation of quartz to form types 2 3 ribbons quartz recrystallization by sub grain rotation associated with a slip but not c slip biotite recrystallization within micro shears and variable amphibole recrystallization the deformation histories display a distinct division between magmatic state and moderate temperature solid state deformation features with little evidence for intervening high temperature solid state fabrics this contrasts with criteria widely considered diagnostic of syn tectonic plutons which envisage development of a continuum of magmatic through high temperature solid state deformation fabrics however we consider the plutons syn tectonic and attribute the hiatus to contrasting strain and pluton cooling rates length and nature of deformation events and host rock ambient temperatures intermediate magmas emplaced at moderate to shallow levels in the crust may be more prone to develop such apparently punctuated deformation histories than sio 2 richer granitoids

infrared microthermometric and noble gas isotope study of fluid inclusions in ore minerals at the woxi orogenic au sb w deposit western hunan south china abstract the woxi au sb w deposit hosted by the neoproterozoic low grade metamorphic clastic rocks is located in a brittle ductile shear zone within the xuefengshan range south china orebodies are predominantly banded quartz veins which are strictly controlled by bedding faults and display significant vertical extents up to 2 km without obvious vertical metal zoning fluid inclusions hosted in quartz scheelite and stibnite from quartz scheelite and quartz sulfide gold veins have been studied using conventional and infrared microscopy respectively four types of fluid inclusions were identified based on petrography including type i two phase liquid rich aqueous inclusions type ii two or three phase co 2 rich inclusions type iii two phase vapour rich aqueous inclusions and type iv single phase aqueous inclusions the fluid inclusions in ore minerals scheelite and stibnite and their coexisting quartz largely share similar characteristics in terms of their types homogenization temperatures and salinities this is consistent with the fact that these ore minerals are always intergrown with quartz microthermometric and laser raman data indicate a low to moderate temperature 140 240 c low salinity 2 rich n 2 bearing aqueous ore forming fluid such fluid is further identified as a deeply non magmatic crustal fluid rather than a mantle source fluid by the significantly low 3 he 4 he ratios 0 002 0 281 ra and a small amount of meteoric water or host rock buffered fluid could be involved w ore precipitation was probably associated with mixing between a deeply originated crustal fluid and host rock buffered fluid based on the fluid inclusion features in scheelite and quartz i however au and sb ore deposition probably resulted from boiling which was caused by the marked pressure drop geological features such as banded structure and crack sealing structure also indicate that fluid pressure fluctuation induced by fault valve mechanism occurred during ore precipitation these characteristics of the ore forming fluids in the woxi deposit are in good agreement with the definition of orogenic gold deposits and the woxi au sb w deposit is probably an atypical orogenic gold deposit for its unique ore forming element association

timing of post tectonic cadomian magmatism on guernsey channel islands evidence from 40ar 39ar mineral ages the channel island of guernsey exposes pre and post tectonic calc alkaline plutonic rocks attributed to late precambrian cadomian subduction activity 40 ar 39 ar mineral cooling ages presented here clarify the age and time span of post tectonic intrusions amphibole from the bon repos meladiorite yields an isotope correlation age of 605 3 4 6 ma indicating emplacement during late stages of the tectonothermal event recorded within its host rocks igneous hornblendes from the northern igneous complex record consistent isotope correlation ages st peter port gabbro 570 2 1 1 ma bordeaux diorite complex 569 0 1 1 and 565 3 2 2 ma and a comagmatic enclave within cobo granite 570 2 1 5 ma hornblende and biotite from contact metamorphosed host rocks adjacent to the cobo granite yield isotope correlation ages of 569 6 1 1 and 563 8 3 3 ma respectively these ages together with field data demonstrate that the various members of the northern igneous complex were emplaced contemporaneously at c 570 ma significantly earlier than a c 500 ma rb sr whole rock isochron age previously reported for the cobo granite the 40 ar 39 ar ages indicate that post tectonic magmatism on guernsey was broadly coeval with post metamorphic cooling around the baie de st brieuc on the adjacent french mainland and occurred c 30 ma prior to peak cadomian deformation and metamorphism in the st malo area

aqueous fluids derived from a subducting slab observed high 3he emanation and conductive anomaly in a non volcanic region kii peninsula southwest japan abstract it has long been recognized that the kii peninsula in the southwest japan arc is peculiar in a non volcanic region indicated by the presence of high temperature hot springs high terrestrial heat flow and high 3 he content in hot spring gases geophysical and geochemical studies were carried out to understand the geotectonic environment in the southern part of the kii peninsula most of the measured 3 he 4 he ratios are similar or higher than air indicating wide spread incorporation of mantle derived helium into meteoric water a region with rather high 3 he 4 he ratios 4 r a on the west side of the omine mountains coincides with the occurrence of high temperature hot springs a deep crustal resistivity structure across the omine mountains was imaged by wide band magnetotelluric soundings a 2 d inversion with n s strike using both tm and te modes reveals two conductors one in the upper 3 7 km depth and the other in lower crust 25 35 km depth to the west of the omine mountains the distribution of microearthquakes and low frequency tremors and the existence of seismic reflectors indicate that the large conductor in the lower crust is related to aqueous fluids derived from the philippine sea plate the upper crustal conductive zone may also reflect the aqueous fluids trapped in the upper crust which are presumably derived from the subducting slab considering the occurrence of seismic events in the subducting slab beneath the southern kii peninsula the aqueous fluids generated by dehydration of the slab mantle could plausibly include morb type helium derived from the residual lithospheric mantle therefore the high temperature hot springs and high 3 he emanations in hot spring gases and other geotectonic events in the southern kii peninsula may be due to heat flux and mantle derived helium discharged from aqueous fluid in the upper crust

strontium isotopic composition of hot spring and mineral spring waters japan abstract in japan hot springs and mineral springs are distributed in quaternary and neogene volcanic regions as well as in granitic sedimentary and metamorphic regions lacking in recent volcanic activity the87sr 86sr ratio was determined in hot spring and mineral spring waters obtained from 47 sites the ratios of waters from quaternary and neogene volcanic regions were in the range 0 703 0 712 which is lower than that from granitic sedimentary and metamorphic regions 0 706 0 712 the geographical distribution of the ratios coincides with the bedrock geology and particularly the ratios of the waters in quaternary volcanic regions correlate with those of surrounding volcanic rocks these features suggest that subsurface materials control the87sr 86sr ratios of soluble components in the hot spring and mineral spring waters

co2 gas pools in jiyang sag china abstract the co2 gas pools of jiyang sag are located along the gaoqing pingnan fault within a region of alkaline basalts the concentration of co2 in the gas pools is in the range of 68 85 96 99 all of the geochemical tracers for the co2 gas pools support the suggestion that co2 was mainly derived from mantle degassing the 13c values of co2 in the gas pools are in the range of 5 67 3 41 which are higher than those of organogenic co2 and near to those of abiogenic co2 their 3he 4he ratios are 2 80 4 47 106 i e the r ra ratios are 2 00 3 19 showing that the jiyang sag had undergone strong mantle degassing co2 3he ratios are 0 59 0 89 109 which are identical to those for n morb indicating that co2 in these co2 gas pools was mainly derived from the mantle accompanying the intrusion of mantle derived magma the mantle derived co2 migrated upwards along deep faults and was trapped in advantageous structures forming gas pools

fluid kinematics fluid residence times and rock degassing in oceanic crust determined from noble gas contents of deep sea drilling project pore waters the 3he 4he ne and ar in sedimentary pore fluids extracted in situ were measured on samples from deep sea drilling project dsdp sites 398 410 419 420 424 436 and 438 earlier results from dsdp leg 15 are also discussed where regional sediment cover prevents direct penetration of seawater into basement rocks at sites 149 436 and 438 he concentration profiles indicate slow vertical and or horizontal advection of sedimentary pore fluids suggesting that fluids can ventilate through the sediment cover either in diffuse bulk flow or in aquifers confined to regions of relatively high permeability such as ash beds sand silt layers or fracture channels in lithified sediments at site 410 where basement outcrops are prevalent no advection was detectable in the sediments however the basement was well flushed by seawater on 1 5 108 years apparent age in sediments on the active continental margin off ne japan

mantle derived noble gases in natural gases from songliao basin china abstract abundances and isotopic compositions of noble gases have been measured in six natural gas samples co 2 and ch 4 rich from the songliao basin jilin province in northeastern china the samples contain noble gases of mantle origin the 3 he 4 he ratio reaches 5 0 times the atmospheric ratio in a three isotope plot of neon the 20 ne 22 ne up to 10 9 and 21 ne 22 ne up to 0 051 ratios make a positive correlation array together with natural gases from other continental areas compared with a correlation band for morb the natural gases have a lower slope with more nucleogenic 21 ne the natural gas samples contain radiogenic argon with 40 ar 36 ar ratios up to 7700 a positive correlation between 40 ar 36 ar and 20 ne 22 ne ratios indicates occurrence of mantle derived ar slight excess of 38 ar can be attributed to a nuclear reaction like 35 c1 p 38 ar apparent excesses of 129 2 xe 132 136 xe are recognized in four samples the excess of 129 xe up to 3 can be attributed to a decay of extinct 129 i excess 132 136 xe is not large enough to determine if the origin of the excess is 238 u or 244 pu anomaly in 129 xe 130 xe ratio is correlated with that of 136 xe 130 xe the isotopic features of the natural gases with radiogenic 4 he and nucleogenic 21 ne can be produced within the crust alternatively they may reflect the geochemical features of the subcontinental mantle which has been enriched in u th we can not distinguish the two possibilities however a natural gas from another basin in eastern china with a different reservoir age contains mantle derived neon which falls on the neon correlation line formed by the samples from the songliao basin this consistency suggests that the isotopic features of the natural gases aren t necessarily ascribable to surface contamination of radiogenic and nucleogenic isotopes

neoproterozoic shear zone tectonics within the icartian basement of guernsey and sark channel islands the channel islands of guernsey and sark are amongst the few localities within the neoproterozoic cadomian orogenic belt where palaeoproterozoic basement is exposed basement units collectively referred to as icartian comprise orthogneisses e g the c 2000 ma icart granite gneiss metasediments and amphibolites on guernsey the protolith to the icart granite gneiss was intruded into metasediments already deformed during a d 1 deformation event both were variably deformed during a d 2 event within an approximately north south trending steeply dipping oblique dextral shear zone on sark metasediments and amphibolites carry a d 1 fabric not necessarily correlatable with that on guernsey which was deformed during d 2 to form recumbent gently inclined folds and tectonic fabrics which locally carry top to the south kinematic indicators early cadomian quartz diorites which intruded the icartian basement carry variably developed magmatic and moderate temperature 400 550 c ls solid state fabrics which are similarly oriented to d 2 basement structures this indicates that the quartz diorites were emplaced and deformed during a protracted d 2 event published 40 ar 39 ar amphibole cooling ages of c 600 ma from guernsey and sark quartz diorites and a host icartian amphibolite are consistent with reworking of basement units during the cadomian orogeny the contrasting kinematic pattern during cadomian deformation implies that a flat lying shear zone on sark may have accommodated oblique dextral strike slip movement on guernsey with an overall southerly direction of tectonic transport deformation most likely occurred in the hanging wall of a major south dipping neoproterozoic subduction zone

chronology of cadomian tectonothermal activity in the baie de saint brieuc north brittany france evidence from 40ar 39ar mineral ages the late precambrian cadomian orogen exposed in the north armorican massif northwest france is a collage of displaced terranes that in part developed during amalgamation of continental arc and marginal basin complexes 40ar 39ar mineral ages reported here place new constraints on the timing of cadomian tectonothermal activity in the southern part of the st brieuc terrane in the baie de saint brieuc area brioverian supracrustal units were deformed metamorphosed and intruded by calc alkaline plutonic complexes metamorphic hornblende from a metabasic amphibolite sheet within brioverian rocks records an isotope correlation age of 568 4 2 6 ma interpreted to date postmetamorphic cooling through appropriate argon closure temperatures similar isotope correlation cooling ages are recorded by metamorphic hornblende within both an amphibolite sheet intrusive into the penthievre complex 567 5 1 2 ma and the la croix gibat amphibolite 574 8 2 1 ma igneous hornblende from the late tectonic to pos

magnetotelluric imaging of crustal magma storage beneath the mesozoic crystalline mountains in a nonvolcanic region northeast japan mesozoic crystalline mountains iide mountains in a nonvolcanic region of the northeast japan arc were imaged by wide band magnetotelluric soundings a two dimensional model shows that an anomalous conductive body 10 m is clearly visible beneath the iide mountains the conductor widens with increasing depth and extends from the near surface down to the base of the crust and perhaps into the upper mantle the location of the conductive body correlates with high temperature hot springs with high 3he 4he ratio thinning of the brittle seismogenic layer and anomalies of low seismic velocity we conclude that the conductor reflects the presence of partial melts in the crust related to renewed magmatism in the present day subduction system

3 he 4 he ratios in ch 4 rich natural gases suggest magmatic origin natural gas and oil fields commercially exploited since the 1950s are distributed in the zonal area facing the sea of japan in north east japan we report here measurements of the 3he 4he ratios in 27 ch4 rich natural gases obtained from commercial oil and gas wells in the area we observed extraordinarily high 3he 4he ratios up to 8 65 10 6 in gases from wells drilled into deep reservoirs in volcaniclastic rock formations the so called green tuff fig 1 these values are almost identical to those of volcanic fumaroles in the japanese islands in contrast gases in shallower sedimentary rock reservoirs have low 3he 4he ratios with a minimum value of 0 3 10 6 these low values are similar to those of natural gases originating from biological materials this suggests that the formation of natural gas reservoirs in the volcaniclastic rock may be attributed to large scale magmatic activities which occurred in the middle miocene

geochemical evidence for triassic rifting in southwestern florida abstract mesozoic rhyolites and basalts from three drillholes penetrating the pre cretaceous basement of southwestern florida were analyzed for their trace element and sr and nd isotopic compositions major and trace element abundances suggest the suite was erupted in an extensional environment and isotopic data indicate derivation primarily from aged enriched precambrian continental lithosphere combined to varying degrees with an asthenospheric component nd model ages show no significant difference in the age of the lithosphere from which these rocks and volcanic rocks of paleozoic age from north florida were derived arguing against major displacement across the peninsula including along proposed extensions of the jay fault and or bahamas fracture zone we suggest that the geophysically inferred boundary across the peninsula if a fault may have had a strong normal component consistent with the greater depth to basement south of the boundary in this view the southwestern florida mesozoic volcanic province sfmv may represent a part of a major triassic rift basin associated with the breakup of pangaea

tritiogenic3he in groundwater in takaoka 3he 4he ratios up to 3 5 times the ratio of atmospheric he were found in groundwater samples the3he enrichment can be attributed to radiogenic3he produced by in situ beta decay of3h this shows that tritiogenic3he is accumulating in confined waters from tritiogenic3he and3h concentrations ages of groundwaters can be calculated detection of tritiogenic3he gives a tool to trace a tritium contamination which occurred in the past and cannot be assessed only by the3h counting method

heat source for an amagmatic hydrothermal system noto peninsula central japan 1 although there is no evidence of volcanism in the noto peninsula since the late miocene the peninsula has long been known to be unusual and atypical of non volcanic regions as indicated by high temperature hot springs and a geothermal gradient greater than 50 k km in order to provide geochemical constraints on the heat source for amagmatic hydrothermal activity the chemical and isotopic compositions of 14 gas and water samples from hot springs were measured the observed 3he 4he ratios of most hot spring gases range from 0 03 to 1 2 ra ra denotes the atmospheric 3he 4he ratio of 1 4 10 6 in these samples mantle helium composes less than 10 of the total helium indicating an insignificant contribution of mantle derived volatiles from for example newly ascending magma and or aqueous fluid generated by dehydration of the subducting slab the noto peninsula mainly consists of neogene volcaniclastic and sedimentary rocks overlying paleozoic to mesozoic basement rocks associated with uranium bearing granite pegmatite containing elevated concentrations of heat generating elements such as uranium thorium and potassium a plausible heat source for the amagmatic hydrothermal activity can be attributed to this distinctive geological environment where high heat producing granitic rocks are buried under neogene sedimentary rocks with low thermal conductivities that act as thermal blankets most noto peninsula hot springs are found in areas of active faulting where stress concentrations since the late miocene could open an existing fault pathway because the fluid pressure is close to the lithostatic pressure meteoric waters circulating through hot basement rock come to the surface along these permeable conduits with minimal mixing with shallow groundwater resulting in emanation of high temperature hot springs with low 3he 4he ratio gases along active fault zones

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

precise u pb zircon ages from alderney channel islands growing evidence for discrete neoproterozoic magmatic episodes in northern cadomia the northernmost exposures of rocks formed during the late neoproterozoic cadomian orogeny in the channel islands northern france region occur on alderney the island mainly comprises foliated quartz diorite once considered to be 2 ga pre cadomian basement and an undeformed basic to intermediate plutonic complex a precise age of 610 2 ma based on u pb analyses of single and small groups of zircons for the foliated fort tourgis quartz diorite demonstrates that the oldest rocks were emplaced and deformed during a cadomian magmatic event the age is virtually identical to ages from similar foliated syntectonic quartz diorite bodies on the islands of guernsey and sark and at la hague north normandy indicating that this magmatic and deformational event was regional in extent discordant zircon xenocrysts define an upper intercept age of c 2 ga indicating the presence of palaeoproterozoic basement at depth single zircons from the undeformed bibette head granodiorite give a precise u pb age of 572 1 ma this age is closely similar to that for the emplacement of the northern igneous complex of guernsey the emerging data indicate that cadomian magmatism in the northern channel islands region was not a protracted continuum but occurred during two distinct short lived events separated by c 30 40 my

real time drill mud gas logging at the usdp 4 drilling unzen volcano japan abstract during the unzen conduit drilling project usdp 4 the gas phase dissolved in the drill mud was continuously analyzed starting from the volcano s north flank an almost complete gas profile was achieved to the final depth of 1995 75 m in july 2004 limitations were given due to the extremely difficult drilling conditions the highly fractured rock formation led to loss of drill mud circulation in the shallow parts of the drill hole significant fluid inflow horizons did not occur above 800 m drill string length starting from that depth on invading fluids were detected with the real time gas monitoring system major variations in the mud gas composition occurred only below a depth of 1000 m of major importance are fluid inflow zones with high 3he 4he at depths of 1555 m 7 3 ra 1755 5 m 7 48 ra and 1977 4 m 6 21 ra these values indicate a significant influence of fluids with mantle signature furthermore enhanced methane radon and helium concentrations were also detected at specific depth these detected major fluid and gas inflow horizons may be able to explain magmatic degassing processes related to the unzen s eruption mechanism this is generally true for the main fluid inflow zones and especially for the detected inflows at 1555 m 1755 5 m and 1977 4 m furthermore a correlation between lithology and gas composition was observed higher h2s concentrations were detected while drilling in pyrite rich rocks cracks and fissures as well as lithological changes are often correlated with increasing amounts of gas trends with depth from a minor to a more magmatic influenced regime were observed together with a change in hydrothermal alteration of the surrounding rock this corresponds with the magmatic conduit zone which was penetrated at a depth of 1600 m and supports the model of a high influence of hydrothermal fluid accelerating cooling and mineral alteration

island arc tectonics of new zealand manifested in helium isotope ratios abstract thirty gas samples of various types volcanic gas geothermal gas ch4 rich natural gas and petroleum gas were collected in and around the north island new zealand 3 he 4 he and 4 he 20 ne ratios were measured using a mass spectrometer the observed 3 he 4 he and 4 he 20 ne ratios of the samples varied from 0 08 10 6to 8 75 10 6 and from 4 8 to 2100 respectively based on a 3 he 4 he 4 he 20 ne diagram he in the samples can be explained by mixing of a subduction type magmatic a radiogenic and an air component the geographical distribution of 3 he 4 he ratios over the island indicates a clear contrast between forearc and volcanic arc regions high in the former and low in the latter a he boundary can be drawn from the taupo volcanic zone to egmont volcano in terms of the 3 he 4 he profile this boundary agrees well with that of high q lowq in the upper mantle as well as with the geographical distribution of terrestrial heat flow values the high 3 he 4 he ratios in the volcanic arc region are attributed to subduction type he associated with an uprising magma from the upper mantle and the lower ratios in the forearc region to radiogenic he derived from u and th in basement and sedimentary rocks this tendency is very similar to that found in northeast japan and is understood to be a general signature of the he isotope ratio in an island arc system

behavior of a fine grained soil during the loma prieta earthquake results of an investigation into the behavior of a fine grained clayey soil at moss landing during the 1989 loma prieta earthquake are presented a deposit of this soil underlies portions of the mo

the noble gas isotope record of hydrocarbon field formation time scales abstract noble gases may be considered as the most prominent tracers of natural fluids including hydrocarbons the atmosphere is the only source of 20ne 36ar 84kr 130xe in subsurface environments and their concentrations in pore waters after recharge are known from the solubility data this allows modelling of noble gas partitioning between coexisting gas oil and water phases in the course of hydrocarbon formation migration and storage radiogenic isotopes 4he 21ne 40ar 136xe after being released from source rocks are mixed with air derived noble gases already present in the pore space concentrations of radiogenic species in the pore space of typical hydrocarbon fields are generally so high that they can hardly be accumulated in situ and thus indicate noble gas transfer from ground waters the time bearing ratios 4he 20ne 21ne 20ne 4he 40arair 40ar 40arair in hydrocarbon fields are thus proportional to the time interval between the ground water recharge and noble gases partitioning into the hydrocarbon phase s the recharge partition interval the largest available data set allows the recharge partition intervals to be constrained for a large number of hydrocarbon fields situated in different tectonic settings ancient plates young plates mobile belts these intervals increase systematically with the ages of hydrocarbon source and trap lithologies and are comparable with these ages this important feature valid in general for different hydrocarbon fields implies i local sources of radiogenic noble gas isotopes in ground waters ii relatively recent formation of hydrocarbon fields and iii their short formation time scales in some cases the duration of formation of a hydrocarbon field can be constrained for example nearly constant 21ne 20ne 40ar 40arair ratios measured in samples from the magnus oil field north sea give an accumulation time scale 10 ma it should be emphasized that the above noble gas isotope ratios give the time estimates which are independent of geological reconstructions sometimes the noble gas inventory in a hydrocarbon field and ground waters allows characterization of the source rock volume involved in formation of the field generally this volume exceeds that of the hydrocarbon field rocks by orders of magnitude

liquefaction and soil failure during 1994 northridge earthquake the 1994 northridge california earthquake caused widespread permanent ground deformation on the gently sloping alluvial fan surface of the san fernando valley the ground cracks and distributed deformation damaged both pipelines and surface structures to evaluate the mechanism of soil failure detailed subsurface investigations were conducted at four sites three sites are underlain by saturated sandy silts with low standard penetration test and cone penetration test values these soils are similar to those that liquefied during the 1971 san fernando earthquake and are shown by widely used empirical relationships to be susceptible to liquefaction the remaining site is underlain by saturated clay whose undrained shear strength is approximately half the value of the earthquake induced shear stress at this location this study demonstrates that the heterogeneous nature of alluvial fan sediments in combination with variations in the groundwater table can be responsible for complex patterns of permanent ground deformation it may also help to explain some of the spatial variability of strong ground motion observed during the 1994 earthquake

u pb geochronology and sm nd isotopic composition of proterozoic gneisses channel islands uk gneissic units of the channel islands united kingdom have traditionally been considered to be palaeoproterozoic basement to the late neoproterozoic cadomia terrane based on lithological correlations and imprecise or ambiguous isotopic data a new precise u pb date of 2061 2 ma based on analyses of single zircons for the icart granitic orthogneiss of guernsey confirms a palaeoproterozoic age of its igneous protolith the nd depleted mantle model age t dm of this gneiss is 2220 ma only slightly older than its crystallization age indicating that it represents juvenile crust other gneisses from guernsey have similar t dm ages ranging from 2210 to 2370 ma suggesting that they are also exposures of juvenile palaeoproterozoic crust a component from a penetratively deformed orthogneiss from sark previously correlated with icartian gneisses on guernsey yields a u pb zircon date of 616 4 2 ma this crystallization age demonstrates that the protolith was a cadomian intrusion and that penetrative deformation and amphibolite facies metamorphism in the northern channel islands were cadomian in age the use of gneissic features as a means of invoking the antiquity of many other undated gneissic units in the region is thus considered unreliable the presence of 2170 7 ma zircon xenocrysts within the sark orthogneiss combined with its initial e nd 615 9 5 are strong evidence that pre cadomian basement was a significant source component and that documenting the extent and age of pre cadomian basement may be possible by indirect geochemical methods

formation processes of thermal waters in green tuff a geochemical study in the hokuriku district central japan abstract thermal waters from green tuff region in the hokuriku district central japan were investigated to reveal formation process of water based on the chemical and isotopic compositions of water and dissolved gases in water the thermal waters of local meteoric origin are typical green tuff type water na ca cl so 4 type or na cl so 4 type which well reacted by water rock interaction and is found to be saturated with calcite and undersaturated with gypsum the green tuff type waters have relatively high 3 he 4 he ratio indicating high contribution of mantle derived helium and have extremely low total carbon 3 he ct 3 he ratio compared with the ratio of morb due to removal of carbon species from waters caused by calcite deposition in contrast a mineral spring water close to an active fault is found to be an immature water with less water rock interaction containing a large amount of gaseous co 2 and is undersaturated with both calcite and gypsum this water has high 3 he 4 he ratio and ct 3 he ratio indicating the high contribution of mantle derived helium and deep seated co 2 and likely provided through the fault we proposed a chemical evolution model considering existence of both chemically immature co 2 gas rich water and mature carbon poor water which well reacted with rocks deep seated co 2 and mantle derived helium are upwelling via faults and are supplied to the groundwater of local meteoric origin and an immature water containing high content of co 2 and mantle derived helium is formed during the circulation of this immature water in the green tuff layers water rock interaction such as ion exchanges with minerals dissolution of gypsum and deposition of calcite occurred at the interaction with rocks deposition of calcite occurs and results in a loss of ca 2 and decrease of ca 2 brings dissolution of gypsum and more calcite deposition consequently almost all the supplied co 2 is eliminated from the water furthermore we made a quantitative evaluation of the chemical evolution of green tuff type water using geochemical modeling code phreeqc taking account of addition of gas components and found the good agreement with observational results this study reveals that the supply of large amounts of co 2 and subsequent water rock interaction are necessary for the formation of green tuff type water with high 3 he 4 he ratio and extremely low ct 3 he ratio

the cadomian active margin north armorican massif france a segment of the north atlantic panafrican belt abstract within the european variscan belt the armorican massif northwestern france contains an isolated fragment of the north atlantic panafrican belt the cadomian block mostly unaffected by variscan deformation this block is composed of neoproterozoic rocks ranging in age from 620 to 540 ma brioverian locally overlying a composite basement of icartian 2000 ma or pentevrian 750 ma age the cadomian tectonics the last magmatic manifestations of which are dated at around 540 ma were sealed by a cover of early cambrian rocks in normandy and early ordovician rocks in brittany five units are distinguished in this cadomian block tregor saint brieuc guingamp saint malo and fougeres although the units are bound by major faults the overall coherence of their different protolithic characteristics suggests that they can be fitted into a simple geodynamic model the tregor unit represented by the north tregor batholith of crustal affinity and its icartian host rock probably reflects an early cadomian evolution the saint brieuc unit essentially made up of magmatic rocks of juvenile affinity includes two assemblages juxtaposed by the cadomian tectonics 1 a volcanosedimentary succession formed in a typical island arc setting reflecting subduction around 610 ma and 2 a volcanic plutonic complex emplaced around 590 ma in an extensional active continental margin of pentevrian age the guingamp unit predominantly migmatitic includes a tectonic slice of deep origin the extrusion of which accompanied the exhumation of the migmatites it may represent the trace of a possible suture the saint malo unit is composed of brioverian detrital rocks the significance of which is uncertain passive continental margin or accretionary prism it is structured around a late migmatitic dome 540 ma the fougeres unit corresponds to the outer domain of the cadomian orogeny it was only weakly deformed by cadomian tectonics and is intruded by the large mancellian batholith of crustal origin dated at 540 ma together the structural units are interpreted in the framework of an evolving active margin juxtaposing continental margin marginal basin and volcanic arc before being shortened during the cadomian convergent tectonics

tectonomagmatism in continental arcs evidence from the sark arc complex abstract the island of sark channel islands uk exposes syntectonic plutons and country rock gneisses within a precambrian cadomian continental arc this sark arc complex records sequential pulses of magmatism over a period of 7 ma ca 616 609 ma the earliest intrusion ca 616 ma was a composite sill that shows an ultramafic base overlain by a magma mingled net vein complex subsequently deformed at near solidus temperatures into the amphibolitic and tonalitic tintageu banded gneisses the deformation was synchronous with d 2 deformation of the paragneissic envelope with both intrusion and country rock showing flat top to the south ls fabrics later plutonism injected three homogeneous quartz diorite granodiorite sheets the creux moulin pluton 150 250 m ca 614 ma the little sark pluton 700 m 611 ma and the northern pluton 500 m 609 ma similar but thinner sheets in the south derrible hogsback dixcart and west port es saies brecqhou are interpreted as offshoots from the creux moulin pluton and little sark pluton respectively all these plutons show the same ls fabric seen in the older gneisses with rare magmatic fabrics and common solid state fabrics recording syntectonic crystallisation and cooling the cooling rate increased rapidly with decreasing crystallisation age 9 ma for the oldest intrusion to cool to lower amphibolite conditions 7 8 ma for the creux moulin pluton 5 6 ma for the little sark pluton and 2 the initiation of the d 2 event is suggested to have been a response to the intrusion of the tintageu magma which promoted a rapid increase in strain rate 10 14 s 1 that focussed extensional deformation into the sark area the increased rates of extension allowed ingress of the subsequent quartz diorite granodiorite sheets although strain rate slowly declined as the whole complex cooled during exhumation the regional architecture of syntectonic cadomian arc complexes includes flat lying sark type and steep guernsey type domains produced synchronously in shear zone networks induced by oblique subduction a pattern seen in other continental arcs such as that running from alaska to california

noble gas constraints on the layered structure of the mantle several chemical models of mantle structure have been proposed1 6 based on isotopic data such as sr nd hf and pb in volcanic rocks from both oceanic and continental areas the most popular of these are two chemical models of the vertically layered mantle 1 that it is a depleted mantle from which mid oceanic ridge basalt morb is derived and 2 that it is a fertile mantle from which a mantle plume may arise1 5 however these models are almost always based on solid elements such as sr nd hf and pb isotopes and do not fully reflect the noble gas data because noble gases are liable to be lost from the solid earth when a mantle differentiation occurs on a global scale in the upper mantle the data on noble gas isotopes could give constraints on the structure of the mantle that differ from those by solid element isotopes based on a consideration 3he 4he and 40ar 36ar ratios of recent samples i argue here that the observed data suggest that mixing occurs between the source materials of a mantle plume and of morb the data seem to favour the model which assumes that the source of a typical mantle plume is deeper than that of morb