evidence of a shallow water submarine hydrothermal field off zannone island from morphological and geochemical characterization implications for tyrrhenian sea quaternary volcanism discoveries from multibeam bathymetry and geochemical surveys performed off zannone island western pontine archipelago tyrrhenian sea provide evidence of an undocumented hydrothermal field characterized by ongoing fluid emissions and morphologically complex giant depressions located in shallow water 250 m that host pockmarks mounds small cones and active fluid vents and which are interpreted as complex fluid escape features developed both through vigorous explosive events and steady seepage their spatial distribution suggests that the ne sw trending faults bounding the ponza zannone structural high and the shallow fractured basement are favorable conditions for the upward migration of hydrothermal fluids moreover we performed a detailed geochemical study to investigate the source of the hydrothermal fluids the geochemical signature of the collected fluids provides information of active co2 dominated degassing with a significant contribution of mantle volatiles with measured 3he 4he values 3 0 ra that are similar to those recorded at stromboli and panarea volcanoes the hydrothermal system produces volatiles that may originate from residual magma batches similar to the pleistocene trachytes cropping out in the se sector of ponza island that were probably intruded in the shallow crustal levels and never erupted the discovery of the zannone hydrothermal field updates the record of active hydrothermal areas of the mediterranean sea moreover the recognition of several giant hydrothermal depressions characterized by a complex morphology is peculiar for the mediterranean sea

geochemistry of hydrothermal fluids from the eastern sector of the sabatini volcanic district central italy abstract this study reports a complete geochemical dataset of 215 water and 9 gas samples collected in 2015 from thermal and cold discharges located in the eastern sector of the sabatini volcanic district svd italy based on these data two main aquifers were recognized as follows 1 a cold ca hco3 to ca na hco3 aquifer related to a shallow circuit within pliocene pleistocene volcanic and sedimentary formations and 2 a deep co2 pressurized aquifer hosted in mesozoic carbonate evaporitic rocks characterized by a ca hco3 so4 to na ca hco3 cl composition a thick sequence of low permeability formations represents a physical barrier between the two reservoirs interaction of the co2 rich gas phase with the shallow aquifer locally producing high tds and low ph cold waters is controlled by fractures and faults related to buried horst graben structures the 18o h2o and d h2o values indicate meteoric water as the main source for both the shallow and deep reservoirs carbon dioxide which is characterized by 13c co2 values ranging from 4 7 to 1 0 v pdb is mostly produced by thermo metamorphic decarbonation involving mesozoic rock formations masking possible co2 contribution from mantle degassing the relatively low r ra values 0 07 1 04 indicate dominant crustal he with a minor mantle he contribution the co2 3he ratios up to 6 1012 support a dominant crustal source for these two gases the 34s h2s values from 9 3 to 11 3 v cdt suggests that h2s is mainly related to thermogenic reduction of triassic anhydrites the 13c ch4 and d ch4 values from 33 4 to 24 9 v pdb and from 168 to 140 v smow respectively and the relatively low c1 c2 ratios

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

origin of the ore forming fluids of the tongchang porphyry cu mo deposit in the jinshajiang red river alkaline igneous belt sw china constraints from he ar and s isotopes abstract the jinshajiang red river alkaline igneous belt with abundant cu mo au mineralization in the eastern indian asian collision zone is an important cenozoic magmatic belt formed under an intra continental strike slip system in southwestern sw china the tongchang deposit is a representative porphyry cu mo deposit in southern segment of the jinshajiang red river alkaline igneous belt with 8621 t cu 1 24 wt and 17 060 t mo 0 218 wt in this study he ar and s isotopic compositions of the tongchang deposit were determined he and ar isotopic compositions suggest that the ore forming fluids with 3he 4he ratios varying from 0 17 to 1 50 ra and 40ar 36ar ratios from 299 1 to 347 3 for the deposit are a mixture between a crust derived fluid masw with near atmospheric ar and crustal he and a mantle derived fluid however the 34s values of the hydrothermal pyrite samples ranging from 1 0 to 1 5 with an average of 1 2 indicate that the sulfur in the ore forming fluids of the tongchang deposit was primarily derived from the magma or indirectly mantle derived without assimilation of crustal sulfur in combination with previously published he and ar isotopic data of the yulong and machangqing deposits in northern and central segments of the jinshajiang red river alkaline igneous belt respectively the ore forming fluids of the yulong and machangqing deposits are obviously richer in 3he and 40ar and poorer in 36ar in comparison with the tongchang deposit implying that more mantle derived fluids were involved in the ore forming fluids of the yulong and machangqing deposits than those for the tongchang deposit this might be one of the most important factors producing larger scales of mineralization in the yulong and machangqing deposits than the tongchang deposit

mantle derived noble gases in ore forming fluids of the granite related yaogangxian tungsten deposit southeastern china more than 90 of the tungsten resources of china are in the nanling region of south china and the yaogangxian vein deposit is the largest tungsten deposit in this region the tungsten deposits have ages of 150 160 ma and are spatially temporally and genetically related to granites which were previously believed to be produced by crustal anatexis this paper provides he and ar isotope data of fluid inclusions in pyrite and arsenopyrite from the yaogangxian w veins 3he 4he ratios range from 0 41 to 3 03 ra where ra is the 3he 4he ratio of air 1 39 10 6 and 40ar 36ar ratios from 328 to 1 191 moreover there are excellent correlations between he and ar isotopic compositions the results suggest that the ore forming fluids are a mixture between a crustal fluid containing atmospheric ar and crustal 4he and a fluid containing mantle components it is likely that the former is a low temperature meteoric fluid and the later is a fluid exsolved from the w associated granitic magma which formed by crustal melting induced by intrusion of a mantle derived magma

isotopic evolution of mauna loa volcano abstract in an effort to understand the temporal helium isotopic variations in mauna loa volcano we have measured helium strontium and lead isotopes in a suite of mauna loa lavas that span most of the subaerial eruptive history of the volcano the lavas range in age from historical flows to ninole basalt which are thought to be several hundred thousand years old most of the samples younger than 30 ka in age kau basalt are radiocarbon dated flows while the samples older than 30 ka are stratigraphically controlled kahuku and ninole basalt the data reveal a striking change in the geochemistry of the lavas approximately 10 ka before present the lavas older than 10 ka are characterized by high 3 he 4 he 16 20 times atmospheric higher 206 pb 204 pb 18 2 and lower 87 sr 86 sr 0 70365 ratios than the younger kau samples having he pb and sr ratios of approximately 8 5 atmospheric 18 1 and 0 70390 respectively the historical lavas are distinct in having intermediate sr and pb isotopic compositions with 3 he 4 he ratios similar to the other young kau basalt 8 5 atmospheric the isotopic variations are on a shorter time scale 100 to 10 000 years than has previously been observed for hawaiian volcanoes and demonstrate the importance of geochronology and stratigraphy to geochemical studies the data show consistency between all three isotope systems which suggests that the variations are not related to magma chamber degassing processes and that helium is not decoupled from the other isotopes however the complex temporal evolution suggests that three distinct mantle sources are required to explain the isotopic data most of the mauna loa isotopic variations could be explained by mixing between a plume type source similar to loihi and an asthenospheric source with helium isotopic composition close to morb and elevated sr isotopic values an asthenospheric source or variation within the plume source is considered more likely than lithospheric sources due to the elevated 87 sr 86 sr ratios in the recent kau basalts however the distinct isotopic characteristics of the historical lavas are inferred to be related to lithospheric involvement in the latest stages of shield building volcanism

concurrent evolution of 3he 4he ratio in the earth s mantle reservoirs for the first 2 ga the differences in 3he 4he ratios between mid oceanic ridge basalts morbs and ocean island basalts oibs require the existence of at least two distinct mantle reservoirs that have been preserved over long periods of the earth s history however it is unclear how the 3he 4he ratios have evolved in the mantle over time and when these reservoirs acquired their present day signatures here we report the results of our model calculation for helium evolution in the mantle and show that from the time of the earth s formation to the late archean 2 ga the 3he 4he ratios in both the morb and oib mantle reservoirs evolved in a rather homogeneous fashion in contrast to previous models our model suggests that the distinction in 3he 4he ratios between the morb type source and the plume type source is a relatively recent characteristic of the earth s mantle

volatile fluxes through the big bend section of the san andreas fault california helium and carbon dioxide systematics abstract to investigate the source of volatiles and their relationship to the san andreas fault system safs 18 groundwater samples were collected from wells near the big bend section of the safs in southern california and analyzed for helium and carbon abundance and isotopes concentrations of 4 he corrected for air bubble entrainment vary from 4 15 to 62 7 10 8 cm 3 stp g 1 h 2 o 3 he 4 he ratios vary from 0 09 to 3 52 r a where r a air 3 he 4 he consistent with up to 44 mantle helium in samples a subset of 10 samples was analyzed for the major volatile phase co 2 the hypothesized carrier phase of the helium in the mantle crust system co 2 3 he ratios vary from 0 614 to 142 10 11 and 13 c co 2 values vary from 21 5 to 11 9 vs pdb 3 he 4 he ratios and co 2 concentrations are highest in the wells located in the mil potrero and cuddy valleys adjacent to the safs the elevated 3 he 4 he ratios are interpreted to be a consequence of a mantle volatile flux though the safs diluted by radiogenic he produced in the crust samples with the highest 3 he 4 he ratios also had the lowest co 2 3 he ratios the combined helium isotope he co 2 elemental relationships and 13 c co 2 values of the groundwater volatiles reveal a mixture of mantle and deep crustal metamorphic fluid origins the flux of fluids into the seismogenic zone at high hydrostatic pressure may cause fault rupture and transfer volatiles into the shallow crust we calculate an upward fluid flow rate of 147 mm a 1 along the safs up to 37 times higher than previous estimates kennedy et al 1997 however using newly identified characteristics of the safs we calculate a total flux of 3 he along the safs of 7 4 10 3 cm 3 stp a 1 0 33 mol 3 he a 1 and a co 2 flux of 1 5 10 13 cm 3 stp a 1 6 6 10 8 mol a 1 1 of previous estimates lower fluxes along the big bend section of the safs suggest that the flux of mantle volatiles alone is insufficient to cause the super hydrostatic pressure in the seismogenic zone however results identify crustal metamorphic fluids as a major component of the co 2 volatile budget which may represent the additional flux necessary for fault weakening pressure in the safs

he ar and s isotopic constraints on the relationship between a type granites and tin mineralization a case study of tin deposits in the tengchong lianghe tin belt southwest china abstract the tengchong lianghe tin belt in western yunnan province southwest china is the most important tin mineralization belt in the sanjiang tethyan metallogenic domain stmd there are two large tin deposits in this belt the paleogene lailishan and the late cretaceous xiaolonghe deposits the two deposits are spatially and temporally associated with the lailishan and xiaolonghe granitic plutons respectively recent studies suggest that the lailishan and xiaolonghe granitic plutons exhibit most of the mineralogical and geochemical characteristics of a type granites in this study we discuss the he ar and s isotopes of pyrite samples from the two large tin deposits to trace ore forming fluids and elements we also review the relationship between a type granites and tin deposits from a new perspective the 34scdt values of the lailishan tin deposit range from 4 9 to 6 7 with an average value of 5 53 the 34scdt values of the xiaolonghe tin deposit range from 5 0 to 8 1 with an average value of 6 33 these values are slightly higher than those of the granites 0 to 5 7 in the tengchong lianghe area indicating mainly magmatic sources for the sulfur of ore forming fluids with a small amount of s from the wall rocks the lailishan tin deposit has 3he 4he values of 1 57 3 46 ra with an average value of 2 078 ra and 40ar 36ar values of 382 00 622 99 with an average value of 459 67 the xiaolonghe tin deposit has 3he 4he values of 0 53 0 88 ra with an average value of 0 686 ra and 40ar 36ar values of 301 06 348 43 with an average value of 322 04 these values suggest that ore forming fluids of the lailishan and xiaolonghe tin deposits have mixed crustal mantle and a small volume of meteoric water sources in different proportions the mantle 4he values and 3he 4he values of the lailihsan tin deposit 26 44 1 57 3 46 ra are markedly higher than those of the xiaolonghe tin deposit 8 15 0 53 0 88 ra implying increased crust mantle interaction in the paleogene relative to the late cretaceous in western yunnan this interaction may be attributed to the upwelling of the asthenosphere through the break off of the neo tethyan slab during the main collisional period 65 41 ma of india asia

the primordial noble gases in the earth a key constraint on earth evolution models abstract we made an extensive compilation of noble gas data obtained from morb oceanic island basalts oib and diamonds on the basis of this data base we discuss the primordial noble gases in the earth and its implications on mantle evolution we conclude that in the contrary to a common assumption the primordial ne ar kr and xe in the earth are distinctly different from the solar noble gases the primordial noble gases were derived from the solar noble gas through rayleigh distillation like mass dependent fractionation the primordial ar kr xe are identical with the atmospheric components but ne observed in the mantle derived materials differs significantly from the atmospheric ne we suggest that ne was further fractionated in the atmosphere while the abundances of ar kr and xe in the mantle derived materials are well correlated to each other he and ne in morb is totally uncorrelated with the heavier noble gases this indicates that he and ne in morb is decoupled from the heavier noble gases in the mantle source he ne ar systematics indicate that he was open to the morb and oib mantle sources and ne in the morb mantle source while he is excess in the morb mantle source it is deficient in the oib mantle source relative to the closed system values however it is not known whether this apparent complementary characteristic corresponds to some fundamental mantle dynamics or accidental coincidence

he and sr isotopic constraints on subduction contributions to woodlark basin volcanism solomon islands in order to assess the nature and spatial extent of subduction contributions to arc volcanism sr and he isotopic compositions are measured for dredged volcanic rocks from the woodlark basin in the western pacific sup 87 sr sup 86 sr ratios increase geographically from ocean ridge values 7025 7029 at the woodlark spreading center to island arc ratios 7035 7039 in the solomon islands forearc with intermediate values near the triple junction where the woodlark spreading center subducts beneath the solomon islands sup 3 he sup 4 he ratios are also more radiogenic in the forearc 6 9 plus minus 2 r sub a at active kavachi volcano than along the spreading center where values typical of major ocean ridges were found 8 2 9 3 r sub a very low sup 3 he sup 4 he ratios occur in many triple junction rocks 1 to 5 r sub a but consideration of he isotopic differences between crushing and melting analyses suggests that the low ratios were caused by atmospheric 1 r sub a and radiogenic approx 0 2 r sub a helium addition after eruption variations in unaltered magnetic sup 3 he sup 4 he and sup 87 sr sup 86 sr ratios are best explained by subduction related fluid or silicate melt contributions to the magma source region perhaps from ancient pacific lithosphere however more mantle volatiles dominate the generation of woodlark basin rocks despite extensive subduction in the region less

search for the mantle nitrogen in the ultramafic xenoliths from san carlos arizona abstract mineral separates olivine ol clinopyroxene cp and orthopyroxene op of ultramafic xenoliths from san carlos have been analyzed for nitrogen and noble gases in an effort to evaluate the isotopic signatures for the sub continental mantle the concentrations of noble gases are generally small but in one clinopyroxene separate cp1 they are about an order of magnitude higher the gases seem mostly to be sited in fluid inclusions elevated isotopic ratios of 20 ne 22 ne 40 ar 36 ar 129 134 136 xe 132 xe with respect to air clearly show the presence of mantle noble gas components in san carlos xenoliths isotopic ratios of xe and ar show that the noble gas systematics in san carlos xenoliths can be explained as a mixture of morb and air like components nitrogen contents in these separates range from 0 1 to 1 5 ppm the 15 n varying from 2 to 5 in totals and from 9 to 10 in the temperature fractions the nitrogen data can be explained by the presence of at least three components a a light nitrogen component 15 n 9 of mantle origin b a heavy nitrogen component 15 n 15 from recycled materials and c an air like nitrogen component 15 n 0 which is incorporated during the emplacement of the host magma while the noble gas isotopic ratios cannot clearly distinguish between an atmospheric and a recycled component 15 n clearly resolves these two using the noble gas and nitrogen isotopic systematics and the end member values from the literature a contribution of 30 to 60 recycled nitrogen component has been estimated in the mantle source region of san carlos xenoliths

a noble gas study of a granulite sample from the nilgiri hills southern india implications for granulite formation the he and ar isotopic composition of several mineral separates from a 2 5 ga old enderbite sample from the nilgiri hills southern india were analyzed the sample contains abundant high density carbonic fluid inclusions which have been well characterized in previous studies 1 2 on this particular sample garnet contains synmetamorphic primary fluid inclusions while quartz and plagioclase contain re equilibrated secondary inclusions the noble gases were extracted by crushing or heating of the minerals all measured 3he 4he ratios are above the typical value of old crustal rocks which is about 0 01 0 02 times the atmospheric ratio ra fluid inclusions from the crushed garnet sample contain helium with the highest 3he 4he ratio of 2 34 0 36 ra the he excess is mantle derived and cannot be explained by a cosmogenic or nucleogenic 3he rich component the elemental and isotopic ratios of he ne and ar in all minerals can be explained by a combination of elemental fractionation during diffusional loss of noble gases production of radiogenic nucleogenic4he 21ne 22ne and40ar and atmospheric contamination depending on the assumptions made for the evolution of the he trapped in the garnet fluid inclusions we obtain mixing ratios between mantle derived he and crustal he ranging from 1 5 5 to essentially pure mantle he however probably pure mantle he was trapped in the minerals 2 5 ga ago these data suggest that the enderbite sample represents a former mantle derived tonalitic magma which exsolved its volatiles upon crystallization in the lower crust liberation of a huge amount of co2 by similar intrusions together with the heat provided by them might be responsible for the dehydration of the former amphibolite facies rocks to the north bordering the nilgiri hills

multiple isotope composition s pb h o he and ar and genetic implications for gold deposits in the jiapigou gold belt northeast china the jiapigou gold belt 150 t au one of the most important gold producing districts in china is located at the northeastern margin of the north china craton it is composed of 17 gold deposits with an average grade around 10 g t au the deposits are hosted in archean gneiss and ttg rocks and are all in shear zones or fractures of varying orientations and magnitudes the 34s values of sulfide from ores are mainly between 2 7 and 10 the pb isotope characteristics of ore sulfides are different from those of the archean metamorphic rocks and mesozoic granites and dikes and indicate that they have different lead sources the sulfur and lead isotope compositions imply that the ore forming materials might originate from multiple mainly deep sources fluid inclusions in pyrite have 3he 4he ratios of 0 6 to 2 5 ra whereas their 40ar 36ar ratios range from 1 444 to 9 805 indicating a dominantly mantle fluid with a negligible crustal component 18o values calculated from hydrothermal quartz are between 0 2 and 5 9 and d values of the fluids in the fluid inclusions in quartz are from 70 to 96 these ranges suggest dominantly magmatic water with a minor meteoric component the noble gas isotopic data along with the stable isotopic data suggest that the ore forming fluids have a dominantly mantle source with minor crustal addition

hydrothermal evolution and ore precipitation of the no 2 porphyry cu au deposit in the xiongcun district tibet evidence from cathodoluminescence fluid inclusions and isotopes abstract the no 2 porphyry cu au deposit in the xiongcun district forms part of the gangdese porphyry copper belt of tibet this study clarifies the fluid evolution and ore precipitation mechanisms of the magmatic hydrothermal system that formed the deposit by combining the results of fluid inclusion petrography microthermometry scanning electron microscope cathodoluminescence imaging and stable isotope analyses of multiple quartz dominated veins four distinct sets of quartz dominated veins and eight generations of quartz q1 q8 within the veins were identified namely from early to late early barren quartz veins v1 comprised of equigranular cl bright q1 quartz quartz pyrite chalcopyrite magnetite veins v2 containing early equigranular cl bright q1 quartz and later cl gray or cl dark q2 3 q2 q3 quartz grains intergrown with cu fe sulfides quartz molybdenite pyrite chalcopyrite veins v3 comprised of quartz grains q4 q6 characterized by subhedral comb like textures with well developed oscillatory growth zoning and late quartz veins v4 containing cl gray q7 quartz with euhedral growth zones and later cl dark q8 quartz fluid inclusions in these veins can be classified into six types b40 b40h b80 b15h b15h and b15 the b40 and b40h inclusions b80 inclusions and b15 b15h and b15h inclusions contain vapor bubbles occupying 30 60 vol 70 vol and 5 25 vol respectively in addition b15h b15h and b40h inclusions contain transparent daughter minerals halite and in some cases sylvite raman spectra showed that co2 is only present in b40 and b80 inclusions in the q1 quartz in v1 and v2 veins the dominant type of inclusions is b40 which have homogenization temperatures th of 278 c 389 c peaking at 310 c 330 c and salinities of 2 0 12 8 wt nacl equiv in q2 3 quartz in v2 veins all inclusion types were observed these were trapped at temperatures of approximately 325 c 340 c and had salinities of 1 8 69 7 wt nacl equiv in v3 veins only b15h and b15 inclusions were observed which had th values of 171 c 320 c peaking at 240 c 260 c and 173 c 317 c peaking at 210 c 230 c and salinities of 28 7 33 9 wt nacl equiv and 5 6 23 1 wt nacl equiv respectively in v4 veins only b15 inclusions were observed primary b15 inclusions in v4 veins yielded th values of 166 c 229 c peaking at 170 c 200 c and salinities of 5 1 17 1 wt nacl equiv the 3he 4he and 40ar 36ar ratios of the fluid inclusions exhibited the ranges of 0 08 0 84 ra and 451 3 1567 8 respectively and the 18ofluid and dfluid values varied from 3 2 to 5 8 and 92 8 to 80 3 respectively by integrating all results from the fluid inclusion cathodoluminescence and isotopic analyses we conclude that the initial ore forming fluids of the no 2 deposit were low salinity co2 rich single phase fluids of magmatic origin subsequently fluid immiscibility developed in the initial ore forming fluids generating hypersaline liquid and low salinity vapor phases and leading to the separation of a co2 phase plus chalcopyrite precipitation from the fluids as meteoric water was injected into the hydrothermal system the ore forming fluids gradually evolved to become meteoric water dominated low temperature low salinity and co2 poor in addition fluid cooling due to the meteoric water input resulted in molybdenite precipitation

evidence for a mantle component shown by rare gases c and n isotopes in polycrystalline diamonds from orapa botswana in an attempt to constrain the origin of polycrystalline diamond combined analyses of rare gases and carbon and nitrogen isotopes were performed on six such diamonds from orapa botswana helium shows radiogenic isotopic ratios of r ra 0 14 1 29 while the neon ratios 21 ne 22 ne of up to 0 0534 reflect a component from mantle nucleogenic and atmospheric sources 40 ar 36 ar ratios of between 477 and 6056 are consistent with this interpretation the 129 xe 130 xe isotopic ratios range between 6 54 and 6 91 and the lower values indicate an atmospheric component the he ne ar and xe isotopic compositions and the xe isotopic pattern are clear evidence for a mantle component rather than a crustal one in the source of the polycrystalline diamonds from orapa they 13 c and y 15 n isotopic values of 1 04 to9 79xand 4 5 to 15 5x respectively lie within the range of values obtained from the monocrystalline diamonds at that mine additionally this work reveals that polycrystalline diamonds may not be the most appropriate samples to study if the aim is to consider the compositional evolution of rare gases through time our data shows that after crystallization the polycrystalline diamonds undergo both gas loss that is more significant for the lighter rare gases such as he and ne and secondary processes such as radiogenic nucleogenic and fissiogenic as well as atmospheric contamination finally if polycrystalline diamonds sampled an old mantle 1 3 2 ga the determined xe isotopic signatures which are similar to present morb mantle no fissiogenic xe from fission of 238 u being detectable imply either that xe isotopic ratios have not evolved within the convective mantle since diamond crystallization or that these diamonds are actually much younger d 2005 elsevier b v all rights reserved

a geochemical traverse along the sperchios basin e evoikos gulf graben central greece origin and evolution of the emitted fluids the studied area is a 130 km long fast spreading graben in central greece its complex geodynamical setting includes both the presence of a subduction slab at depth responsible for the recent quaternary volcanic activity in the area and the western termination of a tectonic lineament of regional importance the north anatolian fault a high geothermal gradient is made evident by the presence of many thermal springs with temperatures from 19 to 82 c that discharge along the normal faults bordering the graben in the period 2004 2012 58 gas and 69 water samples were collected and their chemical and isotopic analysis revealed a wide range of compositions two main groups of thermal waters can be distinguished on the basis of their chemical composition the first represented by dilute waters e c 0 6 ms cm of the westernmost sites is characterised by the presence of ch4 rich and mixed n2 ch4 gases the second displays higher salinities e c from 12 to 56 ms cm due to mixing with a modified marine component reservoir temperatures of 150 160 c were estimated with cationic geothermometers at the easternmost sites along the graben from west to east the gas composition changes from ch4 to co2 dominated through mixed n2 ch4 and n2 co2 compositions while at the same time the he isotopic composition goes from typical crustal values 0 1 r ra up to 0 87 r ra showing in the easternmost sites a small 3 11 but significant mantle input the 13c values of the co2 rich samples suggest a mixed origin mantle and marine carbonates

fluid geochemical transect in the northern apennines central northern italy fluid genesis and migration and tectonic implications chemical and isotopic characteristics of natural gas and thermal water discharges from the western back arc tyrrhenian sea across the apennine thrust belt to the po valley and adriatic coast foredeep basins in the northern apennines central northern italy reveal a large scale fluid motion in the upper crust both vertically and horizontally on the basis of gas compositions two different domains of rising fluids have been distinguished 1 co2 rich he poor 3he 4he high domain in the western peri tyrrhenian extensional sector 2 ch4 rich he rich 3he 4he low domain in the eastern adriatic compressional sector such gases rising from various depths are crossed by a huge lateral n2 rich water flow in the peri tyrrhenian sector of ca so4 hco3 meteoric derived waters that move in a regional wide aquifer hosted in a quite thick mesozoic carbonate series morphologically the co2 vents consist of mud basins with high gas rate emission where the rising fluids move upwards through diatremes on the other hand ch4 emissions seep out from typical mud volcanoes with a reduced gas flow rate where the fluid motion is likely related to saline diapir extrusions and the methane is mostly carried to the surface by the associated mud the two rising mechanisms described locate southwest and northeast of the apennine watershed respectively from a seismic point of view the ch4 domain in the thrust belt and foredeep areas is characterized by a large number of earthquakes indirectly pointing to a different rheological behavior of the terrains with respect to the more internal peri tyrrhenian area owing to the quite high thermal gradient of the latter the boundary of the brittle ductile crust in the peri tyrrhenian sector can be located at a 10 km shallow depth although the presence of several post orogenic basins would suggest widespread extensional tectonics in all areas west of the apennine watershed those located in the easternmost part display gas vents with typical crustal 3he 4he ratios as this ratio is very sensitive to deep fluids rising from the mantle we hypothesize that such basins at the foot of the apennines are not due to tensive stress as suggested by their morphological shape they are piggy back thrust top basins developed and evolved in a still acting compressive tectonic regime

submarine gas burst at panarea island southern italy on 3 november 2002 a magmatic versus hydrothermal episode 1 on 3 november 2002 fishermen observed the sudden appearance at the sea surface of three large whitish plumes 3 km offshore of panarea island aeolian islands southern italy caused by the uprising from the seafloor of huge columns of gas bubbles mixed with sediments and colloidal sulfur the degassing event partly superimposed an already existing gentle degassing fumarolic field since 12 november 2002 a discontinuous geochemical monitoring program of these new discharging fluids have been carried out the submarine emissions collected on november 2002 were an emulsion made by a co2 dominated continuous gas phase with suspended sediments colloidal sulfur and water condensate microdroplets acidified by dissolution of compounds such as so2 hcl and hf in the gas phase light unsaturated hydrocarbons also occurred possibly related to relatively high temperature and oxidizing conditions due to local input of magmatic fluids at depth whose occurrence was also supported by the relative high values of 3he 4he isotopic ratio r rair 4 62 with respect to previously measured values r rair 4 2 the flux of the submarine emissions significantly decreased in a couple of months together with the almost complete disappearance of the magmatic chemical markers and the decrease of the helium isotopic ratio thus the most striking feature of the temporal and spatial evolution in the chemical and isotopic compositions of the submarine fumaroles was the relatively rapid restoration since january 2003 of the precrisis conditions i e typical of a stationary hydrothermal system

a noble gas study of cubic diamonds from zaire constraints on their mantle source cubic diamonds are known to contain fluid in submicrometer inclusions which are thought to originate from the mantle beneath the continental crust noble gas elemental and isotopic compositions of sixteen cubic diamonds from zaire are noticeably different from those in morb the 3he 4he ratios observed in the diamonds are 5 12 10 6 and lower than the typical morb value of 1 10 5 the 20ne 22ne ratios 11 and the 21ne 22ne ratios 0 06 show a rough linear correlation and have a slope that is lower than that defined for morb the excess 21ne responsible for the shallower slope may be produced by nuclear reactions either in the source mantle or in the fluid trapped in the diamonds a nucleogenic origin for excess 21ne in the cubic diamonds relative to morb is consistent with their lower 3he 4he ratios positively correlated excesses of 129xe and 131 136xe of up to 10 relative to the atmospheric xe ratios are also observed they are attributed to the decay of extinct 129i and to spontaneous fission of extinct 244pu and or extant 238u respectively xenon isotopic data for the cubic diamonds lie on the same correlation line as that defined for morb in the three isotope diagram of 136xe 130xe vs 129xe 130xe very high 40ar 36ar ratios of up to 35000 are found and are similar to the expected value for the morb source mantle from the 3he 4he and 40ar 36ar ratios some constraints can be made on the origin of cubic diamonds the observed ratios can be explained if the cubic diamonds crystallized in a fluid which separated from a mantle source previously enriched in incompatible elements this is consistent with the previously suggested model for the origin of fluid bearing diamonds the 38ar 36ar ratios in the cubic diamonds are slightly but significantly higher than the atmospheric ratio this high 38ar 36ar ratio may represent the primordial isotopic ratio preserved in the mantle alternatively the observed excess 38ar may be attributed to the nuclear reaction 35cl p 38ar in the fluid phase if the production rate of nucleogenic 38ar is about ten times higher than the previously reported value and the age of the fluid inclusions is quite old 109 yr

noble gas isotopic systematics of fe ti v oxide ore related mafic ultramafic layered intrusions in the panxi area china the role of recycled oceanic crust in their petrogenesis olivine and clinopyroxene grains have been separated from four large fe ti v oxide ore bearing intrusions panzhihua hongge baima and taihe in the panxi area emeishan large igneous province southwest china for he and ar isotope studies the samples examined revealed extremely low 3 he 4 he ratios 0 078 4 34 ra with the mean value 0 78 ra for gases extracted by stepwise heating this feature combined with low 40 ar 36 ar ratios can be interpreted as due to addition of subduction related fluids and melts that had been stored in the lithospheric mantle for long periods considering the regional geologic history such addition can be attributed to the paleo subduction that occurred along the western margin of the yangtze block during the neoproterozoic the subducted oceanic crust beneath the panxi area underwent eclogite facies metamorphism and subsequent exhumation the infiltration of subduction related melts and fluids into the lithospheric mantle led to enriched isotopic signatures from that of the slightly depleted asthenopheric mantle which has been suggested by the sr nd and pb isotopic data of the emeishan basalts and picrites in addition considerable amounts of eclogitic melts produced by partial melting of eclogite facies oceanic crust extensively contaminated the lithospheric mantle during the late permian partial melting of an upwelling mantle plume that contained an eclogite or pyroxenite component generated the parental fe rich magma that supplied the ore bearing intrusions the combination of these factors may have been the crucial reason that many world class fe ti v oxides deposits are clustered in the panxi area

compositional spatial zonation and 2005 2013 temporal evolution of the hydrothermal magmatic fluids from the submarine fumarolic field at panarea island aeolian archipelago southern italy abstract the november 2002 submarine gas blast at panarea island sicily southern italy was an unexpected reactivation event able to locally affect this hydrothermal magmatic system whose the youngest eruptive products were dated at 20 000 2000 years bp the presence of magmatic gases so 2 and hf in the fumarolic gas discharges after the violent exhalative event was indicative of a magmatic input that temporary displaced the hydrothermal system a few months later these acidic gases were indeed not detected in any of the studied fumaroles nevertheless new geochemical data obtained by periodical sampling up to june 2013 suggest that the chemical physical conditions of the hydrothermal magmatic system at panarea were not completely restored with respect to the geochemical data obtained in the early nineties thus the 2002 gas burst has unequivocally caused a permanent modification to the fluid circulation system feeding the submarine fumaroles in addition strong compositional differences were observed by the 46 gases collected in 2012 2013 from submarine fumaroles located in different sites of the studied area allowing to distinguish three different groups of fumaroles a h 2 and co rich gases which also show relatively low ar concentrations b h 2 s rich gases having variable co ch 4 ratios and c ar rich gases having relatively low h 2 concentrations gases from group a are distributed along nw and ne trending fault systems whereas those of groups b and c discharge at increasing distance from the intersection of the two fault systems indicating a spatial and compositional control by the local tectonic setting the h 2 co ratios of groups a and b gases are significantly lower than those measured prior to 2012 this would imply an increase of gas pressure at depth possibly caused by continuous addition of gas and energy from the magmatic source to the hydrothermal reservoir continuation of this process may lead to the occurrence of gas burst events in the next future a hypothesis that is supported by the strong ongoing degassing activity at the surface notwithstanding a decrease of temperatures at depth a geochemical seismological and ground deformation monitoring of the panarea submarine fumarolic field is highly recommended to obtain precursory signals of new strong degassing phenomena

the early cretaceous yangzhaiyu lode gold deposit north china craton a link between craton reactivation and gold veining the yangzhaiyu gold deposit is one of numerous lode gold deposits in the xiaoqinling district southern margin of the north china craton gold mineralization is hosted in neoarchean to early paleoproterozoic amphibolite facies metamorphic rocks and consists of auriferous quartz veins and subordinate disseminated ores in the vein proximal alteration zone ore related hydrothermal alteration is dominated by sericite quartz sulfide assemblages close to gold veins and biotite quartz pyrite chlorite epidote alteration generally distal from mineralization pyrite is the predominant sulfide mineral locally coexisting with minor amounts of chalcopyrite sphalerite and galena gold occurs mostly as free gold enclosed in or filling microfractures of pyrite and quartz and is also present in equilibrium with au bearing tellurides mainly petzite and calaverite coexisting with hessite tellurobismuthite and altaite fluid inclusion studies suggest that gold veins were deposited at intermediate temperatures 175 313 c from aqueous or aqueous carbonic fluids with moderate salinity 5 14 wt nacl equiv 34s values of sulfide minerals range mainly from 2 0 to 4 4 whereas auriferous quartz vein samples have 18o values of 12 4 to 9 6 with calculated 18oh2o values of 6 0 to 3 2 gold related pyrite grains yield elevated 3he 4he ratios 1 51 0 32 ra relative to crustal reservoirs and mantle like 20ne 22ne and 21ne 22ne ratios 9 90 9 68 and 0 029 respectively the stable and noble gas isotopes thus suggest deep seated most likely magmatic and mantle derived sources for the ore fluids sulfur and by inference other components in the ore system 40ar 39ar dating of ore related sericite and biotite separates indicates two episodes of gold genesis at 134 5 to 132 3 and 124 3 to 123 7 ma the mineralization ages overlap zircon u pb ages of 141 0 1 6 to 125 8 1 4 ma 2 for the wenyu and niangniangshan monzogranite plutons and a number of mafic to intermediate dikes intruding these plutons all being proximal to the yangzhaiyu gold deposit the synchronism of gold genesis and magmatism provides additional weights of evidence for a magmatic derivation of ore fluids and sulfur the geochronologic data also suggest that gold veining took place billions of years after the stabilization of the north china craton and associated metamorphism in the late archean to early paleoproterozoic this contrasts sharply to lode gold deposits in other precambrian cratons that formed predominantly in late archean to paleoproterozoic temporarily and genetically related to regional high grade metamorphism and compressional or transpressional tectonism available data have demonstrated that the north china craton was reactivated in the late mesozoic as marked by voluminous igneous rocks faulted basin formation high crustal heat flow and widespread metamorphic core complexes in the eastern part of the craton it is thus suggested that the yangzhaiyu gold deposit together with other deposits of similar ages in the xiaoqinling district were products of this craton reactivation event lithospheric extension and extensive magmatism related to the craton reactivation may have provided sufficient heat energy fluid and sulfur required for the formation of the gold deposits

helium and argon isotope geochemistry of alkaline intrusion associated gold and copper deposits along the red river jinshajiang fault belt sw china abstract the red river jinshajiang strike slip fault zone on the eastern margin of the tibetan plateau was originally produced by the india eurasia collision 60 70 myr ago numerous post collisional mantle derived alkaline igneous rocks with ages of 40 30 ma have been intruded along this fault zone in recent years several copper and gold deposits associated with the alkaline intrusions of this region were discovered such as the yao an and beiya gold deposits and the yulong and machangqing copper deposits studied in this paper the mineralised intrusions are felsic with sio 2 ranging from 61 4 to 67 7 wt k 2 o na 2 o from 8 1 to 11 5 wt and k 2 o na 2 o 1 the deposits are located at both the exo and endo contact zones of the intrusions the mineral deposits are of hydrothermal origin with the ore forming temperatures mainly in the range 150 450 c this paper presents he and ar isotope analyses of these four deposits the concentrations of 4 he trapped in fluid inclusions of pyrites from the ores are 0 7 54 1 10 6 cm 3 stp g 1 and those of 40 ar are 0 6 7 3 10 6 cm 3 stp g 1 3 he 4 he ratios are 0 3 2 5 ra ra represents the 3 he 4 he ratio of air 1 39 10 6 40 ar 36 ar ratios are 316 1736 and 3 he 36 ar ratios are 0 2 11 2 10 3 generally the 3 he 4 he 40 ar 36 ar and 3 he 36 ar ratios for the gold deposits are higher than those for the copper deposits we suggest that the ore forming fluids of both gold and copper deposits were differentiated from the mantle derived alkaline magmas but were diluted by modified air saturated water masw that experienced intensive interaction with crustal rocks however the magmatic fluids responsible for the gold deposits were less extensively diluted by masw resulting in higher 3 he 4 he 40 ar 36 ar and 3 he 36 ar ratios than the copper deposits

helium neon and argon systematics of the european subcontinental mantle implications for its geochemical evolution in this study we present a comprehensive noble gas study of mantle xenoliths from various european cenozoic volcanic provinces the main body of samples is from the massif central france and the eifel germany smaller subsets of samples are from spitsbergen and the graz basin austria in all the helium neon and argon isotopic abundances of a total of forty five mantle xenoliths phenocrysts and xenocrysts were determined the 3he 4he ratios within each volcanic province are very uniform irrespective of the diverse lithologies and p t conditions which are represented by our sample suite mean 3he 4he ratios of the massif central eifel spitsbergen and kapfenstein are 6 53 25 6 03 14 6 65 25 and 6 1 7 1 times the atmospheric ratio ra respectively the strontium and neodymium isotopic composition of some of the cpx separates are highly variable and therefore in contrast to the uniform he signature we thus conclude that he and probably also the other noble gases in the xenoliths are effectively decoupled from the non volatile elements therefore the he signature that is preserved in the xenoliths is actually that of their host magmas published strontium neodymium and lead isotope data of the unevolved host magmas of the xenoliths correlate well with our xenolith he data the position of the fields of the investigated volcanic provinces in hesr hend and hepb variation diagrams depict ternary mixtures between dmm em himu endmembers as the source the host magmas and their volatiles the neon isotopic composition of the gases released from the xenoliths is in most cases atmospheric and probably reflects atmospheric contamination only a few samples reveal indications for morb type ne or evidence of mass fractionation the 40ar 36ar ratios of the xenoliths are mostly radiogenic with the highest ratio being 17 000 however all samples have suffered a certain degree of atmospheric contamination we calculate that the uncontaminated 40ar 36ar ratio of the european subcontinental mantle is 30 000 the4he 40ar ratios have been fractionated since with values around 0 25 they are below both the current production ratio and the morb ratio they cannot be explained by atmospheric contamination as the samples with high 40ar 36ar ratios also have low 4he 40ar ratios helium and ar were probably fractionated during initial closed system degassing of the host magma we calculate the original unfractionated 4he 40ar ratios of the massif central and eifel magma source which are 2 56 18 and 2 71 17 respectively the noble gas systematics are compatible with the notion that addition of crustal material has modified a former morb source signature we use our mean 3he 4 he ratios and reconstructed 4he 40ar ratios to model the time and degree of contamination of a morb like source with crustal material combining our model with evidence from published oxygen strontium neodymium and lead isotope data we judge that the source of the massif central and eifel magmas became enriched in k u and th shortly prior or during the variscan orogeny pre collisional collisional in this case the enrichment in these elements is therefore most probably related to subduction of crustal material in a destructive continental margin setting

geochemical evolution in crustal magma reservoirs trace element and srndo isotopic variations in two continental intraplate series at monts dore massif central france both silica saturated and undersaturated series lavas occur at mont dore french massif central a large stratovolcano whose activity began at 3 ma with a caldera collapse which produced rhyolitic pyroclastics rhyolitic lavas and heterogeneous trachyandesites then were erupted until 1 4 ma with a short tephritic and phonolitic episode at 2 ma after erosion and basaltic eruptions major volcanic activity resumed with trachytic pyroclastics and abundant heterogeneous trachyandesites from 1 0 to 0 25 ma major and trace element data for both series are roughly indistinguishable below 55 wt sio2 but well separated above 58 wt sio2 compatible and incompatible element variations reflect the fractionation of olivine clinopyroxene plagioclase amphibole and feldspars as well as accessory phases such as sphene zircon and apatite in the more differentiated lavas trachytes rhyolites and phonolites for the silica saturated series sr and nd isotope variations are well correlated with sio2 contents and 18o values these isotopic variations are interpreted to be a product of afc processes within the upper crust and emphasize the role of continental crust in the saturated series magma evolution for the undersaturated series tephrites and phonolites display slightly higher 87sr86sr ratios than basanites probably due in part to secondary hydrothermal or alteration processes as indicated by 18o values however their 143nd144nd ratios are identical to those of basanites suggesting that either no crustal contamination occurred in the undersaturated series or that the contaminant was crust of less distinct radiogenic isotope composition the genesis of rhyolites via an afc process is related to the development of a shallow magmatic reservoir this began as a dense network of anastomosed dykes having variable width in relation with the tectonic state of the granitic basement in the first 5 km once formed the reservoirs expanded through the crust with successive pulses of basic magma and were periodically refilled providing heterogeneous and less contaminated trachyandesite magmas for the silica undersaturated series fractional crystallization may have occurred either at great depth or in ancient inactive reservoirs of the saturated series after exhaustion of the potential upper crustal contaminants by the saturated magmas or may have been accompanied by an afc process that involved young igneous crust of similar radiogenic isotope compositions

reduced fluids in porphyry copper gold systems reflect the occurrence of the wall rock thermogenic process an example from the no 1 deposit in the xiongcun district tibet china abstract high fo2 conditions characterize the majority of global porphyry copper deposits and contain highly oxidized minerals such as magnetite and anhydrite in contrast the no 1 porphyry cu au deposit in the xiongcun district tibet china has abundant pyrrhotite reduced fluids ch4 co2 and a relative lack of highly oxidized minerals which are indicative of low fo2 conditions scanning electron microscopy fluid inclusion c h o he ar isotopes and whole rock organic carbon contents and isotope analysis were used to constrain the evolution of ore forming fluid the origin of ch4 and metal deposition mechanisms for the no 1 deposit the he ar isotopic compositions 3he 4he 0 11 0 96 ra 40ar 36ar 418 7 2920 2 suggest that the ore forming fluids predominantly derived from crust source with minor mantle input the h o isotopic analysis results 18oh2o 1 8 to 5 2 d 106 to 89 9 indicate that the ore forming fluids were derived from a magmatic source that mixed with some meteoric waters the element compositions of zircons and fluid melt inclusions from the mineralized middle jurassic quartz diorite porphyry reveal that the primary magma was characterized by high log fo2 nno conditions the quartz diorite porphyry intruded into the carbon bearing wall rocks produced abundant ch4 by thermal decomposition of organic matter 13cch4 26 3 to 28 5 which changed the redox state of the porphyry copper system from oxidized to reduced condition ore elements were deposited via fluid boiling as a consequence of the rapid decrease in temperature and pressure

isotope geochemistry of pantelleria volcanic fluids sicily channel rift a mantle volatile end member for volcanism in southern europe chemical and isotopic ratio he c h and o analysis of hydrothermal manifestations on pantelleria island the southernmost active volcano in italy provides us with the first data upon mantle degassing through the sicily channel rift zone south of the african european collision plate boundary we find that pantelleria fluids contain a co2 he rich gas component of mantle magmatic derivation which at shallow depth variably interacts with a main thermal 100 c aquifer of mixed marine meteoric water the measured 3he 4he ratios and 13c of both the free gases 4 5 7 3 ra and 5 8 to 4 2 respectively and dissolved helium and carbon in waters 1 0 6 3 ra and 7 1 to 0 9 together with their covariation with the he co2 ratio constrain a 3he 4he ratio of 7 3 0 1 ra and a 13c of ca 4 for the magmatic end member these latter are best preserved in fluids emanating inside the active caldera of pantelleria in agreement with a higher heat flow across this structure and other indications of an underlying crustal magma reservoir outside the caldera the magmatic component is more affected by air dilution and at a few sites by mixing with either organic carbon and or radiogenic 4he leached from the u th rich trachytic host rocks of the aquifer pantelleria magmatic end member is richer in 3he and has a lower closer to morb 13c than all fluids yet analyzed in volcanic regions of italy and southern europe including mt etna in sicily 6 9 0 2 ra 13c 3 1 this observation is consistent with a south to north increasing imprint of subducted crustal material in the products of italian volcanoes whose he and c but also o and sr isotopic ratios gradually evolve towards crustal values northward of the african eurasian plate collision boundary our results for pantelleria extend this regional isotopic pattern further south and suggest the presence of a slightly most pristine or less contaminated 3he richer mantle source beneath the sicily channel rift zone the lower than morb 3he 4he ratio but higher than morb co2 3he ratio of pantelleria volatile end member are compatible with petro geochemical evidence that this mantle source includes an upwelling himu em1 type asthenospheric plume component whose origin according to recent seismic data may be in the lower mantle

fluid mixing in carbonate aquifers near rapolano central italy chemical and isotopic constraints chemical major and trace elements and isotopic compositions dd and d 18 o in waters and d 13 ci n co 2 and 3 he 4 he in gases of natural thermal 11 and cold 39 fluids spring waters and gases discharging from a tectonic window of mesozoic limestones in central italy have proved to be the result of mixing processes inside the limestone formations the limestones provide a preferential route for subsurface fluid migration and they gather both descending cold ca hco3 b depleted groundwaters and rising convective ca so4 hco3 co2 saturated b rich thermal waters atmospherically derived descending gas components n2 ne he dissolved in rainfall that infiltrates the limestone system mix with n2 ne he depleted hot rising waters boron in the liquid phase and n2 and ne in the gas phase are the most useful elements to trace the mixing process the deeper gas samples recognised in the area are associated with the hotter waters emerging in the area in spite of being depleted in ne and he and light hydrocarbons they have the higher measured 3 he 4 he ratios suggesting a contribution of mantle 3 he to the gas phase this contrasts with deep circulation in the crust which would lead to increased concentration of 4 he in the deeper gases paradoxically there is more relative concentration of 4 he in the more air contaminated gas samples than in the deeper gas samples a similar paradox exists when the d 13 co f co 2 in the deeper gas samples is considered the shallower air contaminated gas samples although they should be affected by the addition of soil 13 c depleted organic c have d 13 ci n co 2 more positive than the deeper gas samples recognized since any deep hydrothermal source of co2 should generate co2 with more positive values of d 13 c than those measured at surface a multiple single calcite precipitation process from hydrothermal solutions with c isotopic fractionation along the rising path inside the mesozoic limestone formations is proposed 2002 elsevier science ltd all rights reserved

helium isotopes in paleofluids and present day fluids of the larderello geothermal field constraints on the heat source 1 the he isotope composition of paleofluids entrapped in fluid inclusions of hydrothermal minerals is compared with the present day fluid composition of the larderello geothermal field almost constant values of 3he 4he m 3he 4he air r ra over time indicate that no important changes have occurred in the deep source of gases at least during the last 3 8 million years on a regional scale a correlation has been found between the r ra spatial distribution heat flow and bouguer gravity anomaly high values of r ra and heat flow and low bouguer anomaly values indicate that the larderello field is an area of preferential escape for mantle derived fluids a positive correlation has also been found between the r ra spatial distribution and a major seismic reflector named the k horizon a deep magma source refilled by periodic gas input from the mantle is the most likely source of 3he enriched fluids and the anomalously high heat flow the nearly constant value of r ra clearly indicates that input of fresh mantle material has occurred up to recent times clear evidence of mixing between mantle and crustal fluids indicates that the high r ra is the lower limit of the actual mantle value which is suggested to be similar to the subcontinental european mantle the decrease of r ra over time in the peripheral part of the larderello field indicates that important changes in the feeding fracture system and or cooling rate have occurred in these areas

geochemistry of dissolved gases from the eastern carpathians transylvanian basin boundary abstract we show the results of a study on the volatiles dissolved in mineral waters discharged over a 200 km long transect along the rodna b rg u area and c limani gurghiu harghita volcanic chain eastern carpathians romania all of the collected mineral water samples carry dissolved gas with carbon dioxide content up to 1 99 cm 3 stp gh 2 o and helium content up to 2 3 10 5 cm 3 stp gh 2 o carbon 13 c tdic total dissolved inorganic carbon ranging from 15 6 to 5 32 vs vpdb he systematics he isotopes in the range of 0 38 0 99 ra ra air normalized 3 he 4 he ratio and co 2 3 he ratio spanning over four orders of magnitude from morb like values of 2 92 10 9 to crustal type values of 3 02 10 13 coherently indicate the presence of fluids from different crustal sources e g sediments hydrocarbon reservoirs besides minor but detectable contributions of mantle magmatic derived fluids up to 16 45 our investigations show that the wide range of chemical and isotopic composition can be explained in terms of mixings among different gas sources feeding the groundwater and the contemporary occurrence of gas water interactions like degassing and deposition of carbonates affecting the circulating waters after their infiltration

mantle derived gaseous components in ore forming fluids of the xiangshan uranium deposit jiangxi province china evidence from he ar and c isotopes abstract the xiangshan u deposit the largest hydrothermal u deposit in china is hosted in late jurassic felsic volcanic rocks although the u mineralization post dates the volcanics by at least 20 ma the mineralization coincides with intrusion of local mantle derived mafic dykes formed during cretaceous crustal extension in south china ore forming fluids are rich in co 2 and u in the fluid is thought to have been dissolved in the form of uo 2 co 3 2 2 and uo 2 co 3 3 4 complexes this paper provides he and ar isotope data of fluid inclusions in pyrites and c isotope data of calcites associated with u mineralization pitchblende in the xiangshan u deposit he isotopic compositions range between 0 1 and 2 0ra where ra is the 3 he 4 he ratio of air 1 39 10 6 and correlates with 40 ar 36 ar although there is potential for significant 3 he production via 6 li n 3 h 3 he reactions in a u deposit due to abundant neutrons nucleogenic production cannot account for either the 3 he concentration in these fluids nor the correlations between he and ar isotopic compositions it is more likely that the high 3 he 4 he ratios represent trapped mantle derived gases a mantle origin for the volatiles of xiangshan is consistent with the 13 c values of calcites which vary from 3 5 to 7 7 overlapping the range of mantle co 2 the he ar and co 2 characteristics of the ore forming fluids responsible for the deposit are consistent with mixing between 3 he and co 2 rich mantle derived fluids and co 2 poor meteoric fluids these fluids were likely produced during cretaceous extension and dyke intrusion which permitted mantle derived co 2 to migrate upward and remobilize u from the acid volcanic source rocks resulting in the formation of the u deposit subsequent decay of u within the fluid inclusions has reduced the 3 he 4 he ratio and variations in u 3 he result in the range in 3 he 4 he observed with u 3 he ratios in the range 5 17 10 3 likely corresponding to u concentrations in the fluids

a geochemical traverse across the eastern carpathians romania constraints on the origin and evolution of the mineral water and gas discharges abstract the inner sector of the eastern carpathians displays a large number of na hco 3 co 2 rich meteoric originated cold springs soda springs and bore wells as well as dry mofettes they border the southern part of the pliocene quaternary calimani gurghiu harghita cgh calc alkaline volcanic chain both volcanic rocks and co 2 rich emissions are situated between the eastern part of the transylvanian basin and the main east carpathian range where active compression tectonics caused diapiric intrusions of miocene halite deposits and associated saline co 2 rich waters along active faults the regional patterns of the distribution of co 2 in spring waters as calculated p co 2 and the distribution pattern of the 3 he 4 he ratio in the free gas phases up to 4 5 r m r a show their maximum values in coincidence with both the maximum heat flow measurements and the more recent volcanic edifices moving towards the eastern external foredeep areas where oil fields and associated brines are present natural gas emissions become ch 4 dominated such a change in the composition of gas emissions at surface is also recorded by the 3 he 4 he ratios that in this area assume typical crustal values r m r a 0 02 in spite of the fact that thermal springs are rare in the harghita volcanic area and that equilibrium temperature estimates based on geothermometric techniques on gas and liquid phases at surface do not suggest the presence of shallow active hydrothermal systems a large circulation of fluids gases is likely triggered by the presence of mantle magmas stored inside the crust if total 3 he comes from the mantle or from the degassing of magmas stored in the crust co 2 might be associated to both volcanic degassing and thermometamorphism of recently subducted limestones

a primitive alkali basaltic stratovolcano and associated eruptive centres northwestern spitsbergen volcanology and tectonic significance abstract three quaternary volcanic centres sverrefjell sigurdfjell and halvdanpiggen in northwestern spitsbergen formed by off ridge alkali basaltic volcanism associated with nearby ocean floor spreading and subsequent tectonism the sverrefjell volcano is a unique stratovolcano constructed of primitive alkali basaltic pyroclastics with subordinate lavas about 15 20 vol of this volcanic and the other centres comprises a wide variety of upper mantle and lower crustal xenoliths a new estimate of the age of the sverrefjell volcano places the time of formation at a minimum of 100 000 250 000 years ago earlier than previous estimates the occurrence of interbedded pillow lavas and pahoehoe flows at all levels of sverrefjell suggests that the volcano grew concurrently with the rise of the surrounding glaciers basaltic sequences occurring as nearby mountain cappings represent earlier volcanism 2 5 11 5 ma also probably a result of thermal disturbance related to nearby ocean floor spreading geothermobarometry calculations on xenoliths from the three quaternary localities define a very high geotherm consistent with their location near the yermak hot spot and provide a good datum point for the geothermal gradient adjacent to such a thermal anomaly

geochemical characteristics and origins of natural gas in the zhu iii sub basin pearl river mouth basin china abstract the zhu iii sub basin is an important petroliferous region in the south china sea where hydrocarbon distribution shows strong heterogeneity with oil primary produced from the wenchang b depression and gases from the wenchang a depression however a mixture of oil and gases are produced from the surrounding qionghai and shenhu uplifts the origin generation history and migration pathway of oil have been intensively studied but no study have been done directly on the gas which restricts future petroleum exploration in this study natural gas molecular compositions were measured on 46 samples stable carbon isotopic composition were measured on 39 samples and light hydrocarbon composition were measured on 30 samples results indicate that natural gases in the zhu iii sub basin are mainly composed of hydrocarbon gases with abundant co2 and n2 the hydrocarbon gases are all thermogenic gases which are mainly derived from the oligocene enping formation e3e 35 30 ma the contribution of the eocene wenchang formation e2w 56 35 ma to natural gases increases from the wenchang a depression to the south boundary fault sbf and surrounding uplifts this is caused by the early generated natural gases with more contribution from the e2w and dissolved in oils that migrated to the surrounding qionghai and shenhu uplifts natural gases and oil in the surrounding uplifts and near the sbf therefore avoided secondary cracking due to the high gas migration rate through the sbf and lateral sandstone carrier beds whereas natural gases in the wenchang a depression mainly originated from the secondary cracking of oil the equivalent vitrinite reflectance values of source rocks when the natural gases were generated varied from 0 6 to 1 5 based on carbon isotope differences between hydrocarbons indicating mature to high mature stage co2 with abundance less than 10 mainly originated from organic matter decomposition co2 with abundance more than 15 was sourced from the deep mantle and crust and mainly concentrated in the deep layers near the sbf which cuts into the basement n2 is probably the product of in situ reservoir alteration such as biodegradation in shallower layers our study on the geochemical characteristics and origins of the natural gas will enable a better understanding of petroleum system in the zhu iii sub basin and provide theoretical basis for optimizing future petroleum exploration strategy detailed study on shallow layers in the qionghai and shenhu uplifts and deep layers near the sbf are needed because exploration risks are relatively high in these plays

he ar o sr and nd isotope constraints on the origin and evolution of mount etna magmatism abstract the 0 5 ma history of the origin and evolution of mount etna sicily has been investigated by analysing the isotopic composition of he ar o sr and nd in 21 selected lava samples the near constancy of the isotopic compositions of oxygen 18 o 5 4 0 3 and of helium trapped in olivine phenocrysts 6 7 0 4 ra is interpreted as evidence of a single mantle source despite drastic petrological changes during the volcano s history he analyses performed by crushing cogenetic pyroxene and olivine phenocrysts show a tendency to lower 3 he 4 he ratios in pyroxenes this is best explained by crystallization of pyroxenes at a depth shallower than that of olivines and or by exchange of helium trapped in pyroxenes with atmospheric or radiogenic he before eruption 87 sr 86 sr ratios of recent lavas tend to increase with time and to correlate with rb th ratios and for historical lavas these variations are tentatively attributed to shallow selective contamination from underlying sediments based on the similarity of the 3 he 4 he ratios at etna to those of european mantle xenoliths 1 we propose that the baseline geochemical signature of isotopic tracers at etna reflects the composition of the subcontinental mantle comparison to other southern italian active volcanoes etna vulcano ischia campi flegrei vesuvius shows gradual dilution of the predominantly mantle etnean end member by more radiogenic sr and he and material with higher 18o and c 3 he which is reasonably explained by the progressively important influence of subducted continental crust

the yermak plateau formed at a triple junction the yermak plateau is an arcuate marginal plateau located seaward of northwestern spitsbergen the plateau is divided into two zones based on bathymetric trends and magnetic characteristics that have roughly coincident boundaries north of latitude 82 n where the bathymetric contours trend ne the magnetic amplitudes are large whereas the southern portion strikes nnw and exhibits a subdued magnetic signature beneath the northern section of the plateau crustal refraction velocities of 5 0 km s 1 underlain by 7 2 km s 1 are recorded while farther south velocities of 4 3 6 0 and 8 0 km s 1 are measured the 6 0 km s 1 velocity is similar to ones reported on the continental shelf south of spitsbergen dredged material gravity heat flow and seismic reflection and refraction data indicate the northern region of the plateau is oceanic and formed in conjunction with the morris jesup rise in contrast the southern section is thinned continental crust formed by the initial rifting process at a triple junction north of greenland plate reconstructions for anomalies 24 and 13 are consistent with this interpretation little space is required for the yermak plateau at anomaly 24 because it is composed of oceanic and thinned continental crust the development of the yermak plateau and the morris jesup rise paired aseismic ridges took place when the north american eurasian and greenland plates were moving independently

compositional control of magnetic anisotropy in the thomson formation east central minnesota abstract anisotropy of magnetic low field susceptibility ams and anisotropy of anhysteretic susceptibility aas of the middle precambrian thomson formation east central minnesota generally record structural features but orientations and axial ratios of the susceptibility ellipsoids depend on local magnetic mineralogy the northern structural zone of the thomson formation is characterized by an upright east west slaty cleavage the susceptibility ellipsoids plot in the flattening field of a flinn diagram with minimum axes normal to the cleavage aas ellipsoids are coaxial with ams ellipsoids but are generally more prolate anisotropy increases with mean susceptibility at one outcrop interpreted as mixing of weakly anisotropic paramagnetic chlorite with more strongly anisotropic magnetite a second outcrop shows the opposite pattern anisotropy decreases with increasing mean susceptibility suggesting that here the magnetite may be relatively isotropic or possibly post deformational the southern structural zone of the thomson formation is characterized by a subhorizontal foliation s 1 and an upright crenulation cleavage s 2 here the magnetic susceptibility minima are coincident with poles to s 1 and maxima are parallel to the s 1 s 2 intersection correlation between directional susceptibilities and mean susceptibility technique of henry and daly 1983 suggests that paramagnetic minima are poles to the early foliation while possibly interdeformational magnetite minima record the second deformation this interpretation however is not supported by the aas fabric by thin section observations or by high field measurements of paramagnetic susceptibility alternatively both directional and mean susceptibilities may be controlled by syndeformational chlorite

evidence for subduction related components in the subcontinental mantle from low 3he 4he and 40ar 36ar ratio in mantle xenoliths from far eastern russia abstract by applying both vacuum crushing and stepwise heating methods for the extraction of the noble gases we have discovered 3he 4he ratios much lower than the atmospheric ratio 0 3 ra ra is the atmospheric 3he 4he ratio of 1 4 10 6 and relatively low 40ar 36ar ratios spectroscopic and petrographic observations confirm that there are at least two compositionally distinct fluids in these xenoliths liquid co2 inclusions and melt inclusions with shrinkage bubbles based on the crushing experiments it is inferred that the inclusions of liquid co2 have a 3he 4he ratio similar to that of morb and the component with the low 3he 4he ratio is derived from the shrinkage bubbles in the melt inclusions for the present samples the 40ar 36ar ratios obtained by crushing were less than 1000 suggesting incorporation of atmospheric components in the source materials since low 40ar 36ar ratios were observed irrespective of the occurrence of the liquid co2 inclusions the atmospheric component exists in the melt inclusions ne and xe isotopes are also consistent with incorporation of atmospheric components since the far eastern russia area was located at a subduction zone in the jurassic early cretaceous period it is most likely that the melt inclusions displaying atmospheric noble gas characteristics together with low 3he 4he ratios have been derived from the jurassic cretaceous subducted slab although we cannot exclude the possibility that low 3he 4he ratios are due to the existence of minor u bearing minerals in the lithospheric continental mantle caused by metasomatism we have no petrographical evidence for such minerals in this area on the other hand 3he 4he ratios observed in the liquid co2 inclusions which are similar to the morb like value might reflect the general character of the upper mantle the far eastern russian mantle may therefore be a morb like source that has been partly infiltrated by subduction related fluids

genesis of the shangxu orogenic gold deposit bangong nujiang suture belt central tibet china constraints from h o c si he and ar isotopes abstract shangxu is an orogenic gold deposit in the bangong nujiang suture zone central tibet china formed in the early cretaceous orogene related to convergence and collision between the qiangtang and lhasa terranes the mineralization at shangxu is hosted by jurassic turbidite sedimentary rocks of the mugagangri group and is associated with a regional fault system hydrothermal minerals develop muscovite carbonate sulfides and chlorite hydrothermal fluids record three main hydrothermal stages based on mineral paragenesis the earliest is barren quartz stage h1 which is pre ore during the early mineralization quartz pyrite stage h2a defined by massive quartz veins with minor euhedral pyrite and gold hydrothermal fluids had a 18ofluid of 6 1 6 4 d of 74 to 116 13cco2 of 5 4 to 7 6 and 30si of 0 1 in the quartz pyrite sulfides stage h2b characterized by abundant quartz granular pyrite muscovite with minor chalcopyrite galena sphalerite and gold fluids had a 18ofluid of 7 8 2 d of 109 to 120 13cco2 of 9 6 and 30si of 0 1 to 0 2 during the ankerite sulfide stage h3a distinguished by abundant ankerite muscovite sulfides with minor quartz and chlorite hydrothermal system had a fluid with 18ofluid of 4 9 5 3 d of 125 3 30si of 0 1 13cco2 of 12 4 in quartz inclusion fluid and 13cco2 of 2 7 in ankerite the calcite sulfide stage h3b is characterized by calcite sulfides with minor quartz and chlorite quartz formed earlier than calcite from a fluid having a 18ofluid of 6 4 d of 112 6 30si of 0 1 and 13cco2 of 7 4 after which calcite precipitated from a hydrothermal fluid with 18ofluid of 5 5 9 13cco2 of 0 5 to 2 8 hydrothermal fluids in h2b pyrite have 3he 4he ratios of 0 27 0 42ra and 40ar 36ar ratios of 313 372 the stable isotope composition of hydrothermal fluids from the shangxu gold deposit is similar to that of typical orogenic gold deposits the early stage h1 methane bearing fluids were probably sourced from the basin sediments leading to precipitation of early barren quartz veins and siderite alteration from the quartz sulfide stage h2 to carbonate sulfide stage h3 hydrothermal fluids were likely derived from dissolution of the marine carbonate cement from sedimentary host rocks during metamorphism at depth the decreasing d and 13c of the ore forming fluids from early to late suggests mixing with 13c depleted oxidized graphite in sedimentary rocks meteoric waters or reation between d depleted organic matters generally these fluids were likely generated at depth through prograde metamorphic devolatilization of hydrous minerals in the deeper equivalents of the sedimentary rocks of the mugagangri group sulfur and gold by inference likely originated from sedimentary diagenetic pyrite or the metasedimentary rocks between the greenschist and amphibolite facies and migrated with the metamorphic fluids during transportation to the site of deposition gold bearing fluids variably reacted with country rocks

evidence for ascending upper mantle derived melt beneath the cheb basin central europe 1 we present new 3he 4he data of co2 rich gas exhalations of three presently nonvolcanic areas in europe the 3he 4he ratios from the cheb basin czech republic are clearly higher than data obtained ten years ago whereas the 3he 4he ratios from the other areas laacher see germany and marianske lazn cr have remained nearly constant no other locality showing such high 3he 4he ratios in free gases supplied by continental mantle degassing is known in the european cenozoic rift system at the northeastern edge of the cheb basin swarm earthquakes repeatedly occur in the context of contemporaneous periods of seismicity the increased 3he 4he ratios are interpreted as the first geochemical evidence for ascending mantle derived melt beneath the cheb basin which is related to the triggering of earthquake swarms

origin of ore forming fluids of the haigou gold deposit in the eastern central asian orogenic belt ne china constraints from h o he ar isotopes abstract the haigou lode deposit contains 40 t of gold at an average grade of 3 5 g t and is one of the largest deposits in the jiapigou gold belt located along the eastern segment of the northern margin of the north china craton the deposit comprises 15 gold bearing quartz veins hosted in a carboniferous monzonite monzogranite stock cretaceous dikes consisting of diorite diabase and granodiorite porphyries are well developed in the deposit the diorite porphyry dikes 130 4 6 3 ma occur together with gold bearing quartz veins in nne and ne striking faults gold bearing quartz veins crosscut the diorite porphyry dikes and the veins are in turn crosscut by e w striking 124 6 2 2 ma granodiorite porphyry dikes the mineralization mainly occurs as auriferous quartz veins with minor amounts of sulfide minerals including pyrite galena chalcopyrite and molybdenite gold occurs as either native gold or calaverite common gangue minerals in the deposit include quartz sericite and calcite the deposit is characterized by various types of hydrothermal alteration including silicification sericitization chloritization potassic alteration and carbonatization three stages of hydrothermal activity have been recognized in the deposit 1 a barren quartz stage 2 a polymetallic sulfide gold stage 3 a calcite stage fluid inclusions in hydrothermal pyrites have 3he 4he ratios of 0 3 to 3 3 ra and 40ar 36ar ratios of 351 to 1353 indicating mixing of fluids of mantle and crustal origin hydrothermal quartz yielded 18o values of 1 3 to 7 2 and d values of fluid inclusions in the quartz vary between 80 and 104 these stable isotope data also suggest mixing of magmatic and meteoric fluids noble gas and stable isotopic data suggest that the ore fluids have a predominant mantle source with a significant crustal component based on the spatial association of gold bearing quartz veins with early cretaceous intrusions and the h o he ar isotopic data from the deposit and intrusions we propose that gold mineralization in the haigou deposit was formed in an extensional setting and was related to the early cretaceous mantle derived intrusions

he sr and nd isotopes in xenoliths from hawaii and other oceanic islands abstract isotopic analyses on he whole rock and sr nd separated clinopyroxenes are reported for ultramafic and gabbroic xenoliths from the hawaiian islands canary islands kerguelen gough and madeira the he isotopic compositions in samples of varied petrologic type from hawaii show a remarkably narrow range r ra 8 2 9 5 are within the previously reported range for hawaiian xenoliths and are indistinguishable from the range of 3he 4he ratios seen in morb in contrast sr and nd isotopic compositions show a significant range samples from the canary islands kerguelen gough and madeira considered as a group show a similar trend with a restricted range in 3he 4he 5 2 7 ra contrasted by sr and nd isotopic compositions extending over almost the entire range of oceanic basalts the relationship between he and sr nd isotopes of ocean island xenoliths are strikingly similar to that observed for continental ultramafic xenoliths by porcelli et al 1986 1 these systematics suggest metasomatic introduction of lithophile sr and nd and volatile he elements into the lithosphere beneath ocean islands overprinting depleted mantle isotopic characteristics the addition of volatiles must be accomplished by a different process to that of lithophiles probably due to selective transport most likely migration of a lithophile poor co2 h2o fluid consideration of he sr data for oceanic basalts suggests that similar fluid related processes may operate prior to or during mantle melting if so the interpretation of he sr relationships of oceanic basalts in terms of simple mixing between isotopically well defined sources is likely to be invalid

noble gas isotopic variations and geological implication of longmaxi shale gas in sichuan basin china the large difference in carbon isotopic compositions of shale gases from the lower silurian longmaxi formation marine organic rich shales between changning and weiyuan areas in sichuan basin china is a still debate issue in this study 30 produced shale gas samples were collected during 3 years production period and analyzed for noble gas he ne and ar abundances and isotopic compositions to reveal the origin and variation causes of shale gases the results show that the longmaxi shale gases show low 3he 4he and 20ne 22ne and varied but high 21ne 22ne and 40ar 36ar ratios the weiyuan shale gases are characterized by low 3he 4he high 40ar 36ar ratios and varied 4he and 40ar abundances and a large increase in 40ar contents and a slight decrease in 40ar 36ar ratios display during 3 years shale gas production period from jan 2014 to jun 2016 whereas the changning shale gases are characterized by low and varied 3he 4he ratios and high 4he and 40ar abundances and small fluctuations in 40ar contents and 40ar 36ar ratios exhibit during 3 years production period in addition the shale gases produced from horizontal wells in the weiyuan area possessed higher 40ar and 40ar 36ar ratio than that those from vertical wells at same well site the noble gas isotopic compositions and variation of longmaxi shale gases suggested that they are originated mainly from crust air saturated fluid asf and radiogenic accumulation the variation of 40ar and 4he contents during shale gas production mainly reflects the degree of shale gas source supply from mineral matrix to fracture network and the greater increases in 40ar and 4he contents with production time show less abundant shale gas supply therefore the increase trend of 40ar contents with shale gas production time in the weiyuan area during 3 years production period possibly suggests less adequate shale gas supply in contrast the uniform or nearly constant of 40ar content through production time in the changing area indicates abundant supply of shale gas sources from mineral matrix resulting in less production decline variation in 4he and 40ar contents through shale gas production time could be sensitive indicators of abundant or depleted shale gas source supply

remobilization of metasomatized mantle lithosphere a new model for the jiaodong gold province eastern china the 120 ma jiaodong province in the north china craton composed of abundant mesozoic granites that intrude precambrian metamorphic basement is bordered by the sulu orogenic belt which formed through the collision between the north china and yangtze cratons in the triassic insights on the geodynamic setting and source of gold and fluids in the jiaodong gold province are based on a detailed study of the sanshandao deposit the 13cpdb and 18o values of hydrothermal calcite from this deposit range from 4 3 to 6 5 and 11 4 to 15 1 respectively which are compatible with a mantle source pre ore mafic dykes in the deposit show typical arc like geochemical features suggesting that the mantle source was metasomatized prior to the basic magmatism the 34s values of gold related pyrite from sanshandao and other large deposits in the province range from 10 9 to 11 5 and are higher than those of the country rocks but consistent with the signature of orogenic gold deposits sourced from a neoproterozoic sedimentary reservoir these high positive 34s values are interpreted to be inherited from auriferous neoproterozoic sedimentary rocks of the northern yangtze craton which were subducted into the mantle lithosphere beneath the north china craton during the formation of eclogite in the adjacent sulu orogenic belt in the triassic the syn ore lower cretaceous mafic dykes display oceanic island basalt like geochemical features suggesting that asthenosphere upwelling triggered the release of gold and sulfur from an enriched and fertilized mantle lithosphere contributing to the auriferous fluid which formed the widespread gold mineralization in the jiaodong province at ca 120 ma

quantification of gas fluxes from the subcontinental mantle the example of laacher see a maar lake in germany abstract vertical and horizontal distributions of helium and neon isotopes were measured in the water of laacher see a maar lake in the east eifel volcanic field in germany neon is in approximate atmospheric equilibrium throughout the lake but the concentrations of both helium isotopes increase with depth and reach values of up to 10 4 he and 50 3 he times the atmospheric equilibrium concentration the isotopic ratio of the helium excess r ex 3 he ex 4 he ex is 7 42 0 03 10 6 i e r ex r a 5 36 0 02 where r a 1 384 10 6 is the isotopic ratio in air this indicates the presence of mantle derived helium laacher see is thermally stratified during the summer it acts as an almost perfect trap for injected gases the helium concentration in the hypolimnion deep water approximately doubled from may to september 1991 yielding a mean 4 he flux of 10 2 10 12 atoms m 2 s 1 this value is 30 times smaller than in lake nyos cameroon but 20 times larger than in crater lake usa release of bubbles of nearly pure co 2 99 observable in shallow waters at the eastern shore as well as detected by divers in about 30 m depth was identified as an important source of the helium excess in the lake if carefully sampled by divers to avoid air contamination the bubbles exhibit mantle influenced isotopic signatures not only for helium but also for neon and argon 20 ne 22 ne 9 92 0 03 40 ar 36 ar 391 4 based on the elemental ratios of carbon neon and argon to 3 he the fluxes of volatiles from the mantle into laacher see are determined as 7 4 10 7 atoms m 2 s 1 for 3 he 13 10 7 atoms m 2 s 1 for 20 ne 26 10 7 atoms m 2 s 1 for 361 ar and 6 4 10 17 molecules m 2 s 1 for co 2 non atmospheric neon was also found in the well wallenborn in the west eifel volcanic field with a 20 ne 22 ne ratio as high as 11 21 0 06

geology geochemistry and genesis of axi a paleozoic low sulfidation type epithermal gold deposit in xinjiang china abstract axi is a low sulfidation type epithermal gold deposit hosted in paleozoic subaerial volcanic rocks in the western tianshan orogenic belt xinjiang china the resource is more than 50 t gold at an average grade of 4 4 ppm the deposit occurs in the tulasu volcanic fault basin in the paleozoic active continental margin on the northern side of the yili central tianshan plate the host rocks are andesitic volcaniclastic rocks of the paleozoic dahalajunshan formation and the orebodies occur as veins in annular faults of a paleocaldera mineralization at axi can be subdivided into five stages quartz and or chalcedony vein quartz vein quartz carbonate vein sulfide vein and carbonate vein there are two types of ore host quartz vein and altered rocks ore minerals are native gold electrum pyrite marcasite arsenopyrite hematite limonite and trace amounts of pyrargyrite polybasite naumannite cerargyrite sphalerite chalcopyrite tetrahedrite galena pyrrhotite and clausthalite gangue minerals are mainly quartz chalcedony illite calcite siderite dolomite adularia and laumontite the main wall rock alteration is silicification and phyllic alteration carbonatization and propylitization the deposit is characterized by an enrichment relative to crustal abundance of au ag as sb bi hg se te and mo depletion in base metals cu pb and zn and a low ag au ratio 0 5 3 7 three types of fluid inclusions were recognized in quartz from the major mineralization stages liquid aqueous inclusions liquid rich two phase inclusions and small amounts of vapor rich two phase inclusions microthermometric measurements indicate that the final ice melting temperatures are 0 3 to 4 4 c corresponding to salinities of 0 5 6 9 wt nacl equiv 2 2 wt nacl equiv in average the peak temperatures of ice melting varies from 0 4 to 1 9 c corresponding to salinities of 0 7 3 1 wt nacl equiv homogenization temperatures range mainly between 120 and 240 c with an average of 190 c and a maximum of 335 c the fluid density is 0 73 to 0 95 g cm 3 and thus the estimated maximum mineralization depth is about 700 m hydrogen and oxygen isotopic compositions of the ore fluids lie within a narrow range d h2o is 98 to 116 and 18 o h2o 1 8 to 0 4 3 he 4 he ranges from 0 0218 to 0 138 ra with an average of 0 044 ra indicating that he derived predominantly from crust with negligible mantle he in the ore fluids by contrast the 40 ar 36 ar ranges from 317 7 to 866 0 suggesting that crust derived radioactive 40 ar accounts for 7 0 to 66 and atmospheric 40 ar about 43 to 93 in the ore fluids hydrogen oxygen carbon sulfur and noble gas isotopes indicate that the ore forming fluids of the axi gold deposit consisted predominantly of circulating meteoric water ore forming metals may have derived mainly from the host volcaniclastic rocks of the dahalajunshan formation and basement rocks the occurrence of adularia platy calcite and quartz or sulfide aggregates as pseudomorphs after bladed calcite in ore veins and occurrence of aqueous liquid and liquid rich and vapor rich two phase inclusions indicates that boiling of the ore forming fluid have occurred leading to supersaturation of the hydrothermal solution and deposition of ore metals this is the main mineralization mechanism for quartz vein type ores in axi the ore forming fluid was buffered to a near neutral ph in a reduced environment during mineralization the preservation of this paleozoic axi deposit and its discovery required a rapid accumulation of sediments in the basin after formation of the deposit and minimal amount of erosion after late cenozoic uplift

the corrosion of basaltic dykes in evaporites ar sr nd isotope and rare earth elements evidence abstract the corrosion of basaltic dykes from central germany which intruded during the tertiary into rock and potash salts of upper permian age zechstein has been studied the corrosion behavior of these glassy basalts can serve as a natural analogue for the long term corrosion expected for nuclear waste glasses in a salt repository our data demonstrate mobility and fractionation of the rare earth elements ree during a postintrusive circulation of salt brines the processes controlling this behavior of the ree were dissolution and reprecipitation of phosphates the k ar data document the synintrusive assimilation of a salt phase followed by a postintrusive fluid circulation in the peripheral parts this circulation removed the assimilated salt and imported highly radiogenic salt ar which was integrated into newly formed sheet silicates the central part of the dyke was not affected by this circulation and could retain a mantle gas phase the sr isotope data document a synintrusive assimilation of salt sr and a strong exchange with salt fluids during the postintrusive corrosion which was strongest in a zone next to the chilled dyke margins this locally stronger alteration is probably due to different cooling and shrinking rates of the basalt at the margins and in the core of the dyke which led to the formation of a highly permeable fractured zone

deriving inertial wave characteristics from surface drifter velocities frequency variability in the tropical pacific two techniques have been developed for estimating statistics of inertial oscillations from satellite tracked drifters these techniques overcome the difficulties inherent in estimating such statistics from data dependent upon space coordinates that are a function of time application of these techniques to tropical surface drifter data collected during the norpax epocs and toga programs reveals a latitude dependent statistically significant blue shift of inertial wave frequency the latitudinal dependence of the blue shift is similar to predictions based on global internal wave spectral models with a superposition of frequency shifting due to modification of the effective local inertial frequency by the presence of strongly sheared zonal mean currents within 12 of the equator

origin of the ore forming fluids and metals of the bangpu porphyry mo cu deposit of tibet china constraints from he ar h o s and pb isotopes abstract the bangpu porphyry mo cu deposit is a representative mo dominated deposit besides the sharang porphyry mo deposit in the gangdese metallogenic belt the mo cu mineralization has a close relationship with the monzogranite porphyry and diorite porphyrite we identify three stages during the ore formation a pre ore stage a main ore stage with mo cu deposited dominantly and a post ore stage in this study he ar h o s and pb isotopic compositions of the bangpu deposit were determined based on these determinations integrated isotope geochemistry studies were performed to constrain the possible sources of the ore forming fluids and metals the 3 he 4 he and 40 ar 36 ar ratios of fluid inclusions exhibit a range of 0 12209 0 36370 ra and 275 6 346 1 respectively the 4 he and 40 ar concentrations vary from 1 51 to 3 57 10 7 cm 3 stp g 1 and 0 49 to 9 31 10 7 cm 3 stp g 1 respectively he ar isotopic compositions suggest dominantly crustal derived fluid with minor amount of meteoric water in the main ore stage the 18 o fluid and d fluid values vary from 1 3 to 3 9 and 140 5 to 73 7 respectively indicating that magma fluids mixed with meteoric water the average 34 s value of the sulfides 0 3 in the main ore stage is close to the ore forming porphyries indicating a magmatic source the lead isotopic components of ore sulfides exhibit restricted ranges with 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 18 450 18 728 15 602 5 672 and 38 715 39 211 respectively and values in the range of and 9 46 9 58 indicating ore forming metals of primarily an upper crust source with a small amount of mantle materials compared to the bangpu deposit the ore metals derived from mantle are even greater in the jiama and qulong deposits which leads to cu being the dominant mineralization in the jiama and qulong deposit

metallogeny of the sarsuk polymetallic au deposit in the ashele basin altay orogenic belt xinjiang nw china constraints from mineralogy fluid inclusions and he ar isotopes the sarsuk polymetallic au deposit is located in the devonian volcano sedimentary ashele basin of the altay orogenic belt aob xinjiang mineralization in the deposit is confined to an area of 400 m long and 50 120 m wide and occurs as dense massive banded disseminated stockwork and veinlet ore structures exhalative sedimentary subvolcanic hydrothermal and supergene periods have been distinguished although syn depositional ores can be found the main orebodies from this period have been eroded thus the orebodies being mined are hosted mainly in a rhyolite porphyry subvolcanic intrusion within the volcanic conduit of a hydrothermal system electron microprobe analysis of the main ore minerals indicates that pyrite is the main au bearing mineral the au occurs mainly as either inclusions or in fissures in the form of tellurides and is closely associated with ag zn fe ratios of sphalerite vary from 11 37 to 251 36 with an average of 96 65 and the formation temperatures of chlorites are 155 206 c with an average of 175 c the compositions of sphalerite and chlorite indicate that the main mineralization occurred in a low to moderate temperature environment homogenization temperatures of fluid inclusions from ores of the main mineralization stage vary generally from 130 c to 390 c with peaks at 140 c 190 c and 310 c their corresponding salinities range from 3 0 to 10 0 wt nacl equivalent with densities from 0 56 to 1 03 g cm3 the main mineralizing fluid of the deposit is characterized by high low temperatures moderate low salinities and moderate low densities the 3he 4he ratios of fluid inclusions in pyrite are 0 02 to 0 44 ra and the percentage of mantle derived he ranges from 0 06 to 7 45 40ar 36ar ratios range from 319 6 to 458 5 and the percentage of 40ar varies from 7 53 to 35 55 both fluid characteristics and he and ar isotope compositions suggest that the ore forming fluids were a mixture of magmatic fluid and seawater the co2 rich fluids in the ores suggest that boiling occurred the mixing of a high temperature and high pressure magmatic fluid with deeply circulating seawater caused a decrease in temperature and phase separation in the ore forming fluids thus the precipitation of the most economically important ore materials was the result of this mixing process

fluid origin and structural enhancement during mineralization of the jinshan orogenic gold deposit south china the jinshan orogenic gold deposit is a world class deposit hosted by a ductile shear zone caused by a transpressional terrane collision during neoproterozoic time ore bodies at the deposit include laminated quartz veins and disseminated pyrite bearing mylonite most quartz veins in the shear zone with and without gold mineralization were boudinaged during progressive shear deformation with three generations of boudinage structures produced at different stages of progressive deformation observations of ore controlling structures at various scales indicate syn deformational mineralization fluid inclusions from pyrite intergrown with auriferous quartz have 3he 4he ratios of 0 15 0 24 ra and 40ar 36ar ratios 575 3 060 18ofluid values calculated from quartz are 5 5 8 4 and d values of fluid inclusions contained in quartz range between 61 and 75 the 13c values of ankerite range from 5 0 to 4 2 and ankerite 18o values from 4 4 to 8 0 the noble gas and stable isotope data suggest a predominant crustal source of ore fluids with less than 5 mantle component data also show that in situ fluids were generated locally by pervasive pressure solution and that widespread dissolution seams acted as pathways of fluid flow migration and precipitation the in situ fluids and fluids derived from deeper levels of the crust were focused by deformation and deformation structures at various scales through solution dissolution creep crack seal slip and cyclic fault valve mechanisms during progressively localized deformation and gold mineralization

source of ore forming fluids of the yangshan gold field western qinling orogen china evidence from microthermometry noble gas isotopes and in situ sulfur isotopes of au carrying pyrite abstract the yangshan gold ore belt contains a series of sediment hosted disseminated gold deposits in the southern subzone of the western qinling orogen the ore deposits formed in the middle devonian carbonaceous clastic carbonate sequences that underwent strong deformation and low greenschist facies regional metamorphism the shapes and distribution of the ore bodies are strictly confined by the e w trending anchanghe guanyinba thrust fault zone pyrite and arsenopyrite are the major au carrying minerals microthermometric results show that the ore forming fluids are co2 rich aqueous solutions the homogenization temperatures range from 221 to 303 5 c and salinities range from 2 0 to 7 2 wt nacl equiv these characteristics are consistent with orogenic gold deposit noble gas isotopic measurement shows that 3he 4he ratios of pyrite and quartz grains inherited from the mineralized carbonaceous phyllite ranging from 0 033 to 0 081 ra implying that the origins of ore fluids are restricted within the crustal regime the 40ar 36ar ratios range from 434 to 863 indicating 34 to 68 crust derived radiogenic 40ar in the ore fluids based on the backscattered electron bse maps of pyrite three generations i e core mantle rim are distinguished pre ore pyrite including framboidal pyrites and the cores of zoned pyrites both in the phyllite and plagiogranite dikes ore stage pyrites including the middle zones of the three zoned pyrites in the granitic dikes and the outer zones of the zoned pyrites in the phyllite post ore pyrites i e the outermost rims of the zoned pyrites in the dikes the arsenopyrite in the phyllite has similar texture to the pyrite and is regarded as the peak of the mineralization due to its highest au concentrations high spatial resolution nanosims multi elemental maps of the pyrites reveal that i gold is distributed heterogeneously as lattice bounded au in the zoned pyrites with higher au as in the middle zones and lower au as in the inner and outermost zones no nano particles of native gold was identified in pyrite ii gold mineralization occurred in a single event instead of multistage ore formation iii gold precipitation event is followed by an overgrown zone with low au and as concentrations in situ sulfur isotopes of au bearing pyrite identified two types of sulfur sources one is framboidal pyrite and the barren core of pyrite in the carbonaceous phyllite which have very negative 34s values combining au concentrations with the corresponding 34s values in the pyrites reveals that the zones with high au have lower 34s values and vice versa this coupling relation between au and s isotope has been also identified in other orogenic and carlin type gold deposits the oxidation of ore fluid is taken as the key for gold precipitation during formation of orogenic gold deposit however the oxidation of ore fluids accompanied by the escape of reduced gas e g h2s should result in high au coupled with high 34s therefore we propose that the yangshan gold deposit forms through partitioning aqueous vapor with high au as and lower 34s from a deep magma chamber under the ore field which leads to overgrowth of the pre existing pyrites based on the geological features texture of pyrite and sulfur isotopic characteristics we suggested that the yangshan gold deposits have the characteristics between carlin type and orogenic gold deposits they are the product of the western qinling orogeny during the late triassic

lithospheric memory state of stress and rheology neotectonic controls on europe s intraplate continental topography abstract to date research on neotectonics and related continental topography development has mostly focused on active plate boundaries characterized by generally high deformation rates the intraplate sedimentary basins and rifts of the northern alpine foreland are associated with a much higher level of neotectonic activity than hitherto assumed seismicity and stress indicator data combined with geodetic and geomorphologic observations demonstrate that europe s intraplate lithosphere is being actively deformed this has major implications for the assessment of its natural hazards and environmental degradation the lithosphere of the northern alpine foreland has undergone a polyphase evolution with an intense interplay between upper mantle thermal perturbations and stress induced intraplate deformation that points to the importance of lithospheric folding of the thermally weakened lithosphere in this paper we address relationships between deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland with special emphasis on tectonically induced topography the objectives are to quantify the effects of ongoing alpine collision and atlantic ridge push on the intraplate deformation in europe and its impact on topography evolution and related natural hazards this paper reviews the four dimensional topographic evolution of the european lithosphere through a multi disciplinary approach linking geology geophysics and geotechnology until now research on neotectonics and related topography development of intraplate regions has received little attention our study examines a number of selected natural laboratories in continental europe from orogen through platform to continental margin these natural laboratories include the carpathians pannonian system the northwest european platform iberia and the atlantic continental margin we focus on lithosphere memory and neotectonics with special attention to the thermo mechanical structure of the lithosphere mechanisms of large scale intraplate deformation late neogene anomalies in subsidence and uplift and links with surface processes and topography evolution

helium and argon isotope systematics of the central lau basin and valu fa ridge evidence of crust mantle interactions in a back arc basin abstract we report helium and argon isotope analyses of fresh lau basin volcanic glasses from six sites within the central basin 18 s six localities along the valu fa ridge 21 22 4 s and a single site from the northeastern basin 15 s central basin basalts have 3 he 4 he ratios r between 8 2 8 5 r a r a air 3 he 4 he 40 ar 36 ar ratios significantly greater than atmosphere up to 4900 and 4he contents from 3 5 9 4 10 6cm3 stp g similar to n morbs worldwide these results are consistent with trace element and other radiogenic isotope data on these samples which indicate derivation from a depleted mantle source region in contrast evolved lavas from the valu fa ridge all have r r a and show evidence of mixing with a component rich in radiogenic helium there is a clear relationship between the 3 he 4 he ratios of these samples and their chemistry basaltic andesites have 6 02 r c r a andesites have lower ratios 2 37 2 65 ra and a dacite has the lowest value of the entire sample suite 1 19 ra all lavas have 40 ar 36 ar ratios similar to the atmospheric value and low helium concentrations from 3 11 10 8cm3 stp g or between 30 and 300 times less than the central basin basalts although the helium isotope results of the valu fa lavas mirror the shift to more radiogenic values of other isotope systems e g 206 pb 204 pb 87 sr 86 sr which indicate addition of subducted sediment to these magma sources we find no evidence that the radiogenic helium has a mantle or slab derivation or is in any way coupled to these other tracers instead the most plausible mechanism to explain its incorporation into the valu fa lavas is by assimilation of old lau crust in the near surface environment by previously degassed magma we argue that this mechanism has general applicability and can explain a number of hitherto apparently paradoxical geochemical features of some back arc and ocean ridge lavas such as their high volatile and lil element contents with low rare gas concentrations and their mantle 3 he 4 he ratios with hydrated oceanic crustal d h values the realisation that the helium and argon systematics of the valu fa lavas are controlled by crust mantle interactions has important implications for distinguishing between a number of models proposed for the formation of such evolved lavas and we show that fractional crystallisation processes can most readily account for the low concentrations of and systematic trends in the mantle derived helium and argon component of these lavas in addition because pre existing crust in the lau basin must be old and or altered enough to supply the radiogenic helium and atmospheric like 40 ar 36 ar component to the valu fa lavas the occurrence of crust mantle interactions implies that old forearc crust may have been trapped within the lau basin such a scenario has a clear bearing on ideas of the tectonic development of the basin finally because of the potential of crust mantle interactions to modify 3 he 4 he and 40 ar 36 ar ratios of mantle derived melts we assess the implications for using he and ar tracers to characterise mantle sources in arcs back arcs and spreading ridges and consider the consequences for the combined use of rare gases with other radiogenic isotopic tracers of magma provenance at such settings the basaltic andesite from the northeastern basin may also be influenced by the same kind of crustal interaction as the valu fa lavas as it falls within the 3 he 4 he range 6 9ra of the other basaltic andesites interestingly other helium isotope studies indicate that this part of the basin is characterised by a wide range in 3 he 4 he ratios from morb values up to 22ra the low 3 he 4 he ratio of the basaltic andesite therefore serves to illustrate the possible effects of magma chamber processes on the rare gas and other volatile characteristics of hotspot lavas an observation which is important not only for this part of the lau basin but for other localities worldwide

geochronological and sulfur isotopic evidence for the genesis of the post magmatic deeply sourced and anomalously gold rich daliuhang orogenic deposit jiaodong china the daliuhang gold deposit 20 t gold is located in the central penglai qixia belt of the giant jiaodong gold province eastern china the ore hosting guojialing granodiorite and pegmatite were formed at 129 0 0 6 ma and 126 2 0 6 ma respectively syn ore monazite with a u pb age of 120 5 1 7 ma represents the timing of gold mineralization given at least 5 m y between magmatism and mineralization a genetic relationship to magmatic hydrothermal activity is negated noble gas isotopes of pyrite have crust mantle mixed 3he 4he 1 13 to 1 50 ra and air like 40ar 36ar 327 574 together with the broadly positive correlation between 3he and 36ar it is inferred that the initial ore forming fluids were deeply sourced from the sedimentary wedge overlying the subducted plate and overlying mantle during early cretaceous paleo pacific plate subduction the pre ore and post ore pyrites have low 34s values 3 7 5 6 and 5 3 6 4 respectively whereas ore related pyrites have higher 34s values especially in as au rich domains 7 8 8 3 these positive 34s values also suggest that the initial ore fluid and some of the sulfur component were derived via subduction related devolatilization the elevated 34s values of the ore related pyrite are partly ascribed to mass fractionation and partly to a contribution from sulfur leached from crustal host rocks this interpretation is also supported by neodymium isotope ratios of monazite end 120 ma 13 7 to 11 6 which correlate well with the ore hosting guojialing granodiorite this study highlights the combined roles of deeply derived fluids and intense interaction with upper crustal rocks in the formation of jiaodong gold deposits

partition of noble gases between olivine and basalt melt abstract the distribution coefficients ki of noble gases were determined for synthesized olivine basalt melt pairs seven samples bh series were synthesized at 1370 1300 c under a one atmospheric pressure 105 pa noble gas mixture and four samples hpp and hpg series at 1360 1050 c at high pressures 0 2 1 5 gpa the two different experiments gave consistent results with each other some bh series olivine samples were apparently contaminated with gas rich inclusions or the glass phase and the effects of such interferences on the calculated distribution coefficients were evaluated the possible ranges of the distribution coefficients of noble gases thus obtained are khe 0 07 kne 0 006 0 08 kar 0 05 0 15 kkr 0 15 and kxe 0 3 these show remarkable features compared to solid element distribution coefficients the distribution coefficients of noble gases are rather insensitive to or even positively correlated with the atomic size of noble gases the striking contrast between the partition of noble gases and that of solid elements may be attributed to the electrical neutrality of noble gases and the increasing electronic polarizability from he to xe

origin and interactions of fluids circulating over the amik basin hatay turkey and relationships with the hydrologic geologic and tectonic settings abstract we investigated the geochemical features of the fluids circulating over the amik basin se turkey syria border which is crossed by the northern extension of the dsf dead sea fault and represents the boundary area of three tectonic plates anatolian arabian and african plates we collected 34 water samples thermal and cold from natural springs and boreholes as well as 8 gas samples bubbling and gas seepage besides the gases dissolved in the sampled waters the results show that the dissolved gas phase is a mixture of shallow atmospheric and deep components either of mantle and crustal origin coherently the sampled waters are variable mixtures of shallow and deep ground waters the latter being characterised by higher salinity and longer residence times the deep groundwaters from boreholes deeper than 1000 m have a ch 4 dominated dissolved gas phase related to the presence of hydrocarbon reservoirs the very unique tectonic setting of the area includes the presence of an ophiolitic block outcropping in the westernmost area on the african plate as well as basalts located to the north and east on the arabic plate the diffuse presence of co 2 enriched gases although diluted by the huge groundwater circulation testifies a regional degassing activity fluids circulating over the ophiolitic block are marked by h 2 dominated gases with abiogenic methane and high ph waters the measured 3 he 4 he isotopic ratios display contributions from both crustal and mantle derived sources over both sides of the dsf although the serpentinization process is generally independent from mantle type contribution the recorded helium isotopic ratios highlight variable contents of mantle derived fluids due to the absence of recent volcanism over the western side of the basin african plate we argue that co 2 rich volatiles carrying mantle type helium and enriched in heavy carbon are degassed by deep rooted regional faults rather than from volcanic sources

cenozoic normal faulting and regional doming in the southern hangay region central mongolia implications for the origin of the baikal rift province abstract the hangay dome in central mongolia is a mountainous region covering more than 200 000 km2 with numerous flat topped peaks over 3000 m that preserve a late cretaceous paleogene erosion surface doming began in the middle oligocene producing more than 2000 m of regional topographic uplift the range represents an important kinematic link between the baikal rift province to the north and altai transpressional ranges to the south and west structural field investigations of major faults visible on satellite imagery indicate that the southern hangay dome region is dominated by late cenozoic normal faults that bound small half graben most faults are ne striking and faults at the highest elevations are the most recently active most graben appear to be isolated systems that constitute small sediment sinks perched on the flanks and crests of the dome the first order feature is the dome itself and most sediment eroded off of the dome is deposited in the mongolian valley of lakes or is carried northwards by the selenga river and its extensive tributaries the basement of the dome is a precambrian craton although the shape and dimensions of the craton are poorly constrained to the north and east late cenozoic uplift of the southern dome region appears to be confined to the area underlain by cratonic basement whereas the altai region to the south and west is underlain by mechanically weaker palaeozoic arc and accretionary belts with respect to the regional northeast directed shmax the hangay craton appears to have acted as a rigid passive indentor focusing late cenozoic transpressional deformation around its west and southern margins models invoking a late cenozoic plume as the driving force for doming and widespread alkaline volcanism on the dome are not strongly supported by geochemical and isotopic data on neogene recent volcanics and the spatial correlation between areas that are domed and older cratonic crust appears too coincidental to be ignored convective removal of an overthickened lithospheric root leading to adiabatically decompressed asthenosphere could explain regional doming and volcanism however major crustal thickening last occurred in the permian in the southern hangay region and the time lag between thickening and postulated root removal and plateau uplift 200 myr appears too long an alternative model is explored based on speculated lithospheric mantle flow patterns driven by india s continued northeastward indentation it is suggested that lithospheric mantle flow diversion around the overthickened hangay craton crustal keel could cause lithospheric thinning beneath the craton and passive asthenospheric upwarp leading to regional topographic uplift and decompression melting alkali volcanism in general the angular relationship between precambrian craton boundaries and the prevailing northeasterly shmax appears to control the kinematics of late cenozoic deformation throughout the hangay altai sayan and baikal regions

mantle crustal and atmospheric noble gases in ailaoshan gold deposits yunnan province china abstract helium and argon isotopic and elemental compositions of fluids released by crushing pyrite grains are reported from the ailaoshan gold province china the province is a series of gold deposits hosted on a 200 km segment of a major normal fault formed during eocene extension the deposits have been well characterised using conventional geochemical and microthermometric techniques the results of which are consistent with a predominantly high temperature magmatic fluid present in the ore minerals in contrast analyses of noble gases from three gold deposits demonstrate the palaeofluids were a mixture between a mantle derived magmatic fluid and two different low temperature fluids similar to modern groundwaters the specific isotopic and abundance characteristics of helium and argon allow unequivocal identification of both a mantle derived component and a surface derived component to these fluids the magmatic fluid dominates deposits from the northern end of the fault the second groundwater is present only in deposits in the south of the province by assuming fluid inclusion homogenisation temperatures in coexisting quartz are representative of fluid temperature 3he heat ratios can be estimated the 3he heat ratios vary systematically along the fault from 30 10 12 cm3 stp j 1 in the northern deposits to

ndsr isotope and ree geochemistry of alkali basalts from the massif central france abstract nd and sr isotopic compositions as well as trace element concentrations have been determined on a suite of alkali basalts from the massif central in france samples show a typical enrichment in incompatible elements in particular the ree patterns exhibit a strong fractionation characterized by a la yb n ratio of about 20 the ybn content is about 10 times chondrite the 143 nd 144 nd ratios exhibit a range from 0 512775 to 0 512989 values quite comparable to those from oceanic island basalts the 87 sr 86 sr ratios vary between 0 70338 and 0 70458 and are anti correlated with the nd isotopic ratio the isotopic and the trace element in particular ree data have been used in order to quantitatively model the genesis of the alkali basalts among the several types of models tested here the most likely one appears to be the model of mantle metasomatism a semi quantitative approach shows that the source of alkali basalts from the massif central was metasomatized prior to melting in such a model the basalts could be produced by rather high degrees of partial melting such as 10 or 15 of the metasomatically enriched mantle

the isotope systematics of a juvenile intraplate volcano pb nd and sr isotope ratios of basalts from loihi seamount hawaii abstract sr nd and pb isotope ratios for a representative suite of 15 basanites alkali basalts transitional basalts and tholeiites from loihi seamount hawaii display unusually large variations for a single volcano but lie within known ranges for hawaiian basalts nd isotope ratios in alkali basalts show the largest relative variation 0 51291 0 51305 and include the nearly constant tholeiite value 0 51297 pb isotope ratios show similarly large ranges for tholeiites and alkali basalts and continue tatsumoto s 31 loa trend towards higher 206pb 204pb ratios resulting in a substantial overlap with the kea trend 206pb 204pb ratios for loihi and other volcanoes along the loa and kea trends 31 are observed to correlate with the age of the underlying lithosphere suggesting lithosphere involvement in the formation of hawaiian tholeiites loihi lavas display no correlation of nd sr or pb isotope ratios with major element compositions or eruptive age in contrast with observations of some other hawaiian volcanoes 38 isotope data for loihi as well as average values for hawaiian volcanoes are not adequately explained by previously proposed two end member models new models for the origin and the development of hawaiian volcanoes must include mixing of at least three geochemically distinct source regions and allow for the involvement of heterogeneous oceanic lithosphere

accumulation of mantle gases in a permanently stratified volcanic lake lac pavin france abstract lac pavin is a volcanic crater lake in the massif central france characterized by a permanent vertical density stratification resulting from a strong and persistent chemocline between about 60 and 70 m depth the deep water below the chemocline forms the monimolimnion in which most dissolved ions as well as helium carbon dioxide and methane are strongly enriched the 3he 4he isotope ratio of the excess helium is 9 09 0 01 10 6 or 6 57 0 01 ra these findings clearly indicate a flux of mantle derived magmatic gases into the monimolimnion in order to derive the fluxes of magmatic volatiles into lac pavin it is essential to understand the hydrologic characteristics of the lake previously published two box models have assumed groundwater input at the lake bottom a short residence time in the monimolimnion and biogenic origin of the co2 we propose an alternative model with a flux of magmatic gases but not of water into the monimolimnion and a weak diffusive coupling between the monimolimnion and the overlying mixolimnion which leads to a long deep water residence time 70 yr we reassess the carbon budget of the lake and conclude that the major part of the accumulated co2 in the monimolimnion is of magmatic origin from the model derived water exchange rates we calculated a mantle 4he flux of 6 2 1011 atoms m 2 s 1 this value lies near the lower end of the range found in comparable volcanic lakes the flux of magmatic co2 is estimated as 1 2 0 4 10 7 mol m 2 s 1 which is also comparatively low the monimolimnion appears to be in steady state with respect to these fluxes therefore no further potentially hazardous accumulation of co2 takes place

variation in noble gas isotopic composition of gas samples from the aegean arc greece abstract in contrast to most other arcs with oceanic plate subduction the aegean arc is characterized by continent continent subduction noble gas abundances and isotopic compositions of 45 gas samples have been determined from 6 volcanoes along the arc 2 islands in the back arc region and 7 sites in the surrounding areas the 3he 4he ratios of the samples ranged from 0 027ra to 6 2ra ra denotes the atmospheric 3he 4he ratio of 1 4 10 6 demonstrating that even the maximum 3he 4he ratio in the region is significantly lower than the maximum ratios of most oceanic subduction systems which are equal to the morb value of 8 1 ra regional variations in the 3he 4he ratio were observed both along and across the arc the maximum 3he 4he ratio was obtained from nisyros volcano located in the eastern end of the arc and the ratio decreased westward possibly reflecting the difference in potential degree of crustal assimilation or the present magmatic activity in each volcano across the volcanic arc the 3he 4he ratio decreased with an increasing distance from the arc front reaching a low ratio of 0 063ra in macedonia which suggested a major contribution of radiogenic helium derived from the continental crust at nisyros a temporal increase in 3he 4he ratio due to ascending subsurface magma was observed after the seismic crisis of 1995 1998 and mantle neon was possibly detected the maximum 3he 4he ratio 6 2ra in the aegean region which is significantly lower than the morb value is not probably due to crustal assimilation at shallow depth or addition of slab derived helium to morb like mantle wedge but inherent characteristics of the subcontinental lithospheric mantle sclm beneath the aegean arc

he sr and nd isotopes of mantle derived xenoliths in volcanic rocks of ne china abstract abundances and isotopic ratios of he and isotopic ratios of sr and nd have been measured for 18 mantle derived xenoliths from three cenozoic volcanic provinces in ne china the xenoliths are characterized by low he concentrations 2 3 10 9 2 5 10 7 cm3 stp g 1 and large variations of 3he 4he ratios 1 6 10 7 15 8 10 6 or r ra 0 1 11 3he 4he 87sr 86sr and 143nd 144nd ratios in xenoliths from kuandian holocene volcanic provinces are consistent with those observed in mid oceanic ridge basalt morb indicating that the source of he sr nd in the lithospheric mantle is chemically and isotopically identical to that of morb reservoir however xenoliths in huinan pleisteocene holocene volcanic province are characterized by slightly low 3he 4he ratios r ra 4 3 6 5 and more radiogenic sr and nd the age corrected 3he 4he ratios suggest that their time integrated ratio of u th 3he is slightly elevated compared to the depleted upper mantle the hannuoba xenoliths in the miocene volcanic province show much lower and wider variable 3he 4he ratios which is most likely caused by in situ radiogenic 4he accumulation since it erupted on to the surface the he sr nd results suggest chemical and isotopical heterogeneity in the subcontinental mantle beneath ne china

resolving mantle and crustal contributions to ancient hydrothermal fluids hear isotopes in fluid inclusions from dae hwa wmo mineralisation south korea abstract helium and argon isotopes from fluid inclusions in individual colour zones b c d and e of a large scheelite crystal from the 88 ma dae hwa w mo deposit south korea trace the source and history of the ore fluids a gradual decrease of the fluid 3 he 4 he 3 he 36 ar and 40 ar 36 ar from the core to the edge of the scheelite reflects the progressive dilution of a magmatic fluid by meteoric water and is consistent with the previously observed decrease of 18oh2o and fluid inclusion homogenisation temperatures th shelton et al 1987 the covariation of fluid inclusion he ar isotope systematics with 18o and th defines a magmatic component with 3 he 4 he 1 2 10 6 3 he 36 ar 0 01 and 40 ar 36 ar 1000 anomalously high helium and argon isotope ratios in zone d fluids represents undiluted magmatic noble gases this may reflect local variation in the magmatic gas flux or gas loss due to boiling of the hydrothermal fluids prior to mixing with magmatic gas helium and argon isotope systematics constrain mantle and crustal components in the hydrothermal fluids 40 ar 3 he 4 5 104 are close to the mid ocean ridge basalt value implying that 40ar is mantle in origin radiogenic isotope ratios of the mantle endmember 40 ar 4 he 0 69 0 06 are similar to contemporary geothermal fluids the coincidence of mantle derived he and ar in the fluids is strong evidence that mantle melting during late cretaceous subduction triggered the crystal melting responsible for granite formation 40 ar 4 he of the meteoric fluid 0 007 0 001 is far lower than the crystal production ratio 0 2 implying an origin in crust below 200 c

auriferous pyrite re os geochronology and he ar isotopic compositions of the jinchangyu au deposit in the northern margin of the north china craton abstract the jinchangyu au deposit is the largest quartz vein gold deposit in eastern hebei province china in the northern margin of the north china craton nmncc three mineralization stages are identified based on crosscutting relationships and mineral assemblages with au occurring mainly in pyrites in quartz sulphide veinlets and quartz albite veins five low level highly radiogenic pyrite samples in the quartz sulphide veinlets yielded a re os isochron age of 223 5 6 0 ma auriferous pyrite he ar isotopic analyses indicate that the ore forming fluid was a mixture of mantle derived and crustal fluids 3he 4he ratios are in the range 1 72 3 92 ra corresponding to 22 50 mantle he contribution these high 3he 4he ratios are related to lithospheric thinning in the nmncc during the middle late triassic with initial thinning during that period being supported by the wide distribution of indosinian au deposits and the regional tectonic and magmatic evolution the mineralization of the jinchangyu deposit and of other similar triassic deposits was a response to post orogenic to intraplate lithospheric extension after collision between the ncc and the southern margin of the siberian plate

the quartz diorites of limousin elemental and isotopic evidence for devono carboniferous subduction in the hercynian belt of the french massif central a chain of late devonian early carboniferous intrusions on the western margin of the french massif central the limousin tonalite belt consists of quartz diorites which are unusual among french hercynian granitoids in their low silica contents 53 68 wt sio2 and abundant hornblende they represent the earliest and most primitive plutonism post dating the main phase of hercynian metamorphism and have chemical characteristics strongly resembling andesitic lavas of calc alkaline affinity they differ from other massif central hercynian granitoids in their low 87sr86sr360 0 7047 0 7059 and high nd360 0 7 to 1 8 their initial pb composition was rather homogeneous 206pb204pb360 18 15 18 38 207pb204pb360 15 57 15 62 208pb204pb360 38 06 38 26 and their 207pb204pbi values are significantly lower than those of other hercynian granitoids the limousin quartz diorites are considered to have originated from an enriched mantle with characteristics modified by subduction of oceanic crust and terrigenous sediments the primitive quartz dioritic magmas were then contaminated in the lower continental crust by an afc process involving acid metaigneous or metasedimentary lithologies the occurrence of such plutons in the earliest phase of hercynian plutonism in the massif central is probably related to minor subduction at an active continental margin

origin of ore fluids in the muruntau gold system constraints from noble gas carbon isotope and halogen data abstract hydrothermal vein minerals directly associated with native gold mineralization in the muruntau vein system uzbekistan have been studied for noble gas carbon isotope and halogen chemistry of the trapped ore related fluids helium trapped in early arsenopyrite 1 which has preserved the original fluid signature better than associated scheelite and quartz indicates a small input from a mantle source 5 of total he however the overwhelming majority of the he in the fluid 95 is from crustal sources the noble gases ne kr and xe in the sample fluids are dominated by gases of atmospheric origin the carbon isotope 13 c 2 1 to 5 3 and halogen characteristics of the fluids log br cl 2 64 to 3 23 lend further support for the activity of juvenile fluids during the main ore stage the high proportion of crustal components in the ore forming fluids may be explained by intense fluid rock interaction and is also supported by previous nd and sr isotope studies the involvement of a juvenile fluid component during the main stage of hydrothermal activity at muruntau 275 ma can be linked to the emplacement of lamprophyric dikes at muruntau due to apparently overlapping ages for high temperature alteration related ore vein formation and intrusion of the dikes the input of mantle derived fluids possibly related to the hercynian collisional event in the western tien shan stimulated intense fluid rock interaction in the crust in this context the mantle derived fluid should be considered as one possible carrier of metals significant amounts of external meteoric fluids circulating in fracture systems are interpreted to have modified the noble gas signature of fluid in quartz mostly during late low temperature fluid circulation

intraplate deformation and 3d rheological structure of the rhine rift system and adjacent areas of the northern alpine foreland the lithosphere of the northern alpine foreland has undergone a polyphase evolution during which interacting stress induced intraplate deformation and upper mantle thermal perturbations controlled folding of the thermally weakened lithosphere in this paper we address relationships among deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland with special emphasis on tectonically induced topography we focus on lithosphere memory and neotectonics paying special attention to the thermo mechanical structure of the rhine graben system and adjacent areas of the northern alpine foreland lithosphere we discuss implications for mechanisms of large scale intraplate deformation and links with surface processes and topography evolution

he pb and s isotopic constraints on the relationship between the a type qitianling granite and the furong tin deposit hunan province china abstract the furong tin deposit located in southern hunan province china is a large newly discovered deposit with an estimated sn reserve of about 700 000 tons the deposit is spatially and temporally associated with the a type qitianling granite the 3he 4he ratios of fluid inclusions trapped in sulfides from the deposit range from 0 13 to 2 95 ra indicating a mixed crust mantle source similar to that of the qitianling granite complex lead isotopes in feldspars of the granite mostly in the range of 206pb 204pb 18 547 19 180 207pb 204pb 15 598 15 825 208pb 204pb 37 912 39 068 and in sulfide minerals 206pb 204pb 18 467 18 836 207pb 204pb 15 503 15 772 208pb 204pb 38 607 39 099 are essentially the same indicating that the lead in both was derived mainly from the upper crust with a small mantle component the sulfur isotopic values of the ore minerals vary widely ranging from 26 1 to 10 4 but are mainly within the range of 0 2 to 10 4 implying that the s in the hydrothermal fluids was derived mainly from magmatic fluids with minor contributions from the mantle sedimentary rocks and biogenic material the he pb and s isotopes all confirm that the ore forming fluids of the furong deposit were magmatic in origin derived from the melts that produced the qitianling a type granite the tin mineralization occurs within or along the margins of the qitianling granite complex and the timing of the mineralization coincides with the intrusive age of the granite the available data suggest that the emplacement of the granites and the mineralization was related to mantle upwelling and extension of the lithosphere in south china during the mesozoic

noble gases their carrier phases and argon chronology of upper mantle rocks from zabargad island red sea abstract three ultramafic bodies on zabargad island contain fresh peridotites with mostly unfractionated primitive bulk major and trace element abundances and mostly monomineralic vein rocks pyroxenites olivinites homblendites etc we analyzed a set of coarse grained vein rocks with the 40ar 39ar technique applying high resolution stepheating neutron induced argon isotopes derived from ca k and cl and the specific degassing behaviour of major and accessory minerals enabled us to separate and identify different trapped and radiogenic argon components and their hosts within two clinopyroxenites trapped argon is present in 1 low temperature low 40 ar 36 ar phases serpentine and or fluid inclusions 2 pyroxene related cl rich carriers pyroxene and or associated microinclusions and 3 amphiboles which are intimately and nonseparably intergrown with pyroxene the amphiboles which can texturally chemically and isotopically be divided into different generations formed by interaction of spinels and pyroxenes with mantle fluids during different stages of diapiric uplift agrinier et al 1993 formation of these amphiboles and microinclusions in pyroxenes along with incorporation of isotopically distinct ar with 40 ar 36 ar ratios up to 8000 can be related to recent mantle metasomatism also evident in arabian xenoliths henjes kunst et al 1990 and must have been induced by a variety of mantle fluids for a homblendite in situ radiogenic and excess argon components could be separated the plateau age of 18 7 1 3 ma is in perfect agreement with a zircon pb pb age of 18 4 1 0 ma oberli et al 1987 interpreted as the age of crustal intrusion obviously the formation of the hornblendite occurred during the final stage of uplift most probably by interaction with seawater as suggested by strontium oxygen and hydrogen isotopic data agrinier et al 1993 and the low 40 ar 36 ar ratio 305 of the trapped argon 4he 20ne 40ar and 36ar were measured in the orthopyroxenite vein rock z31 by stepwise crushing and subsequent total fusion isotopic ratios show a well defined correlation with crushing step that indicates the presence of two different types or generations of inclusions which were subjected to different degrees of contamination by atmosphere type noble gases as inclusions were trapped before tje main deformation of the peridotite complex kurat et al 1993 argon with relatively low 40 ar 36 ar ratios 1500 was trapped in the mantle which requires an admixture of argon of atmospheric composition to the source region of the peridotites radiogenic isotopes 4he 40ar are dominated by the mantle source however the 4 he 40 ar ratio 0 16 is much lower than expected from long term decay of radioactive parent nuclides u th and k such low ratios which have previously been observed also in mantle xenoliths obviously reflect the indigenous peridotitic source and are most probably due to fractionation processes in the mantle

the beiminghe skarn iron deposit eastern china geochronology isotope geochemistry and implications for the destruction of the north china craton article i nfo the beiminghe bmh iron ore in the southern part of the taihang mountain tm hebei province is one of the largest skarn iron deposits in china here we report phlogopite 40 ar 39 ar and zircon u pb age data as well as sulfur lead and he ar isotope geochemistry of pyrite from the ores and skarnitized rocks in the deposit in an attempt to constrain the timing and mechanism of formation of the mineralization the phlogopite 40 ar 39 ar and la icp ms zircon u pb data show markedly consistent ages constraining the timing of ore formation as 136 137 ma the presence of several inherited zircons with late archean or paleoproterozoic ages indicates the participation of the basement rocks during the ore forming process the 34 sv alues of pyrite from the ores range from 12 2 to 16 5 with 206 he 0 036 0 421 the mesozoic magmatism and metallogeny in the bmh correlate well with the peak event of lithospheric thinning and destruction of the north china craton during this process the early precambrian lower crustal rocks in the region were re melted through underplating of mantle magmas leading to the forma tion of the beiminghe monzodioritic pluton minor mantle input occurred during the evolution of the monzodiorite magma which scavenged the ore forming materials from the lower crust interaction of the magmas and fluids with the surrounding rocks resulted in the formation of the beiminghe skarn iron deposits the magmatism and metallogeny in the taihang mountain are signatures of the extensive craton destruction and lithospheric thinning in the eastern part of the north china craton during mesozoic probably associated with pacific slab subduction