magnetism and transmission electron microscopy of fe ti oxides and pyroxenes in a granulite from lofoten norway granulites from southwest lofoten norway often carry intense and stable components of natural remanent magnetization nrm coercivities in excess of 100 mt and blocking temperatures up to 580 645 c are common several phases in these rocks can carry stable components of nrm clinopyroxenes augite with exsolved pigeonite and orthopyroxene usually contain abundant fe ti oxides the majority of which are too small to be studied conclusively with visible light additionally these rocks typically contain coarse grained 100 1000 m exsolution intergrowths of rhombohedral fe ti oxides and coarse grained magnetite we have studied the magnetism and mineralogy of the titanohematite and the inclusion bearing augites in one granulite sample using transmission electron microscopy tem and magnetic experiments to understand better the remanence properties of naturally occurring fe ti oxides and their relationships to silicate minerals the coarse grained titanohematite has a coercivity of 350 mt and a laboratory saturation remanence that unblocks at 570 600 c the hysteresis characteristics of this titanohematite are typical of much smaller 10 m sized single domains which apparently reflects the presence of exsolved ilmenite lamellae as small as 10 nm in thickness these lamellae presumably inhibit 1 domain wall nucleation and 2 movement of walls that manage to nucleate the inclusions in the augites serve as carriers of lower coercivity remanence with blocking temperatures less than about 560 c magnetite hematite and ilmenite are present in the augite and intergrowth of the rhombohedral phases revealed by tem persists down to the 20 nm scale the distribution of the magnetite inclusions in the augite appears to be unrelated to any silicate microstructure while that of the rhombohedral fe ti oxides is strongly controlled by silicate microstructure with intergrowths of these oxides commonly decorating lamellae of pigeonite orthopyroxene and clinoamphibole within the augite the nrm of this sample possibly dates from the amphibolite facies metamorphism that the region experienced about 1000 m y ago paleomagnetic studies of these rocks could readily recover virtual geomagnetic poles dating from this event in addition to the included oxides the augites display a number of unusual features that probably result from the protracted polymetamorphic history of these granulites pigeonite lamellae are not parallel to the b crystallographic axis pigeonite lamellae cut across those of orthopyroxene and numerous included minerals occur rare earth elements are concentrated within inclusions that reside in the augite

geochemistry of thermal fluids in nw honduras new perspectives for exploitation of geothermal areas in the southern sula graben abstract the results of a geochemical survey on thermal waters and for the first time for this site gas discharges in five geothermal sites azacualpa la cueva rio ulua rio gualcarque el olivar and laguna de agua caliente in nw honduras are here presented and discussed el olivar and laguna de agua caliente in the southern part of the sula graben are very close to a quaternary basaltic field whereas azacualpa la cueva rio ulua and rio gualcarque located to the southwest of the yojoa lake direcly emerge from the cretaceous limestone deposits the measured temperatures range between 37 5 and 104 8 c mature alkaline na so 4 thermal waters discharge from azacualpa la cueva while those from el olivar and laguna de agua caliente are immature and show a na hco 3 composition chemical equilibria of waters and gases from the azacualpa la cueva thermal springs indicate temperatures ranging from 150 to 200 c conversely gas discharges from el olivar and laguna de agua caliente have attained a partial chemical equilibrium in the liquid phase at slightly higher temperatures 200 250 c although gas gas faster reactions involving co seem to be adjusted in an isothermally separated vapor phase unlike azacualpa sio 2 geothermometer at el olivar and laguna de agua caliente indicates equilibrium temperatures for the liquid phase much lower than those calculated for the gas phase 120 c we conclude that thermal waters from the azacualpa area likely represent the direct emergence of a water dominated reservoir having temperatures 150 200 c by contrast at el olivar and laguna de agua caliente hot springs are supplied by a boiling shallow aquifer fed by a vapor phase rising from a steam dominated zone the above geochemical model is consistent with a geothermal reservoir hosted within the cretaceous carbonate sequences of the yojoa group in the whole investigated sites the reservoir extensively crops out in the azacualpa area whereas the geothermal sites of the southern sula graben laguna de agua caliente and el olivar are covered by the oligocene miocene volcano sedimentary sequences of the matagalpa formation possibly acting as efficient impermeable cap rocks these results significantly differ from those reported by previous studies and emphasize that the southern sula graben in particular the el olivar area can represent among the investigated thermal springs the most promising site for the exploitation of a high enthalpy geothermal field

magnetic fabric of granitoids from southern corsica and northern sardinia and implications for late hercynian tectonic setting anisotropy of magnetic susceptibility ams data 180 sites from hercynian granitoids from southern corsica france and northern sardinia italy provide a high density net of structural information for this part of the european hercynian belt two main groups of granitoids defined according to petrography and relative chronology provide contrasting ams results for both groups shallowly dipping magnetic foliations and lineations suggest that these granitoids were emplaced as large scale shallowly dipping sheets or open funnel shaped structures at a high structural level in non leucocratic granitoids 305 300 ma foliation and lineation trajectory maps reveal antiforms and synforms with a n130 axial trace intersection of the foliation planes indicates a n120 low plunging fold axis revealing a n120 maximum stretching direction slightly younger leucocratic granitoids 295 285 ma bounded by late hercynian faults display n50 lineations parallel to the elongated shapes of these intrusions this structural pattern is undisturbed by the faults and suggests an intrusion in decakilometre scale tensional fractures indicating a n140 instantaneous stretching direction compatible with the stretching direction evidenced in non leucocratic granitoids a younger c n20 oriented permian dyke swarm confirms the permanence of this stretching direction over at least 35 ma and indicates a coaxial strain regime to integrate these new data within a broader context in the hercynian belt corsica has to be back rotated clockwise by 70 to its permian position which indicates a north to n30 stretching direction for the 305 285 ma interval compatible with the post collisional strain and stress fields of the french massif central at about the same period

thermal structure beneath tohoku northeast japan combined with geophysical observations and petrological considerations we have studied the thermal models of the tohoku northeast japan subduction zone the temperature of the deeper part of the mantle wedge is constrained by the petrological requirements that demand a high temperature region 1400 c beneath the volcanic zone to satisfy this condition namely to explain the arc volcanism in the tohoku subduction zone a high temperature upper mantle beneath the japan sea possibly 1400 c at the depth shallower than 100 km is required heat flow distribution which constrains the temperature structure at shallower depth shows that low heat flow values ranging from 20 to 50 mw m2 are distributed between the trench and aseismic front and consistently high heat flow values 80 120 mw m2 prevail in the area landward of the volcanic front including the japan sea recent heat flow measurements indicate that the transition from low to high heat flow occurs between the aseismic front and volcanic front this heat flow distribution restricts the form of the flow in the mantle wedge and shear stress acting at the plate boundary a rigid non moving triangular region bounded by the subducting slab and the vertical plane beneath the aseismic front is necessary to explain the low heat flow zone between the trench and aseismic front shear stress of about 500 to 1000 bar is supposed to act at the interface between the subducting slab and rigid triangular mantle we also suggest that to explain the peak of heat flow near the volcanic front 120 mw m2 magma migration rate of about 0 05 cm3 cm 2 year 1 is necessary a comparison of the thermal structure of the tohoku subduction zone with that of the central south america which was preliminary calculated by the similar scheme shows that the temperature in the mantle wedge of the central south america is probably lower than that of the tohoku subduction zone this difference may result in that of the nature of volcanic rocks

tracing the migration of mantle co2 in gas fields and mineral water springs in south east australia using noble gas and stable isotopes abstract geochemical monitoring of co2 storage requires understanding of both innate and introduced fluids in the crust as well as the subsurface processes that can change the geochemical fingerprint of co2 during injection storage and any subsequent migration here we analyse a natural analogue of co2 storage migration and leakage to the atmosphere using noble gas and stable isotopes to constrain the effect of these processes on the geochemical fingerprint of the co2 we present the most comprehensive evidence to date for mantle sourced co2 in south east australia including well gas and co2 rich mineral spring samples from the otway basin and central victorian highlands cvh 3he 4he ratios in well gases and co2 springs range from 1 21 to 3 07 ra and 1 23 3 65 rc ra respectively we present chemical fractionation models to explain the observed range of 3he 4he ratios he ne ar kr xe concentrations and 13c co2 values in the springs and the well gases the variability of 3he 4he in the well gases is controlled by the gas residence time in the reservoir and associated radiogenic 4he accumulation 3he 4he in co2 springs decrease away from the main mantle fluid supply conduit we identify one main pathway for co2 supply to the surface in the cvh located near a major fault zone solubility fractionation during phase separation is proposed to explain the range in noble gas concentrations and 13c co2 values measured in the mineral spring samples this process is also responsible for low 3he concentrations and associated high co2 3he which are commonly interpreted as evidence for mixing with crustal co2 the elevated co2 3he can be explained solely by solubility fractionation without the need to invoke other co2 sources the noble gases in the springs and well gases can be traced back to a single end member which has suffered varying degrees of radiogenic helium accumulation and late stage degassing this work shows that combined stable and noble gas isotopes in natural gases provide a robust tool for identifying the migration of injected co2 to the shallow subsurface

molecular and isotopic compositions and origin of natural gases from cambrian and carboniferous lower permian reservoirs of the onshore polish baltic region natural gases from middle cambrian and carboniferous lower permian reservoirs of the onshore polish baltic region were studied for their molecular and stable isotope compositions the following gas species were analysed 12 13c in ch4 c2h6 c3h8 n c4h10 i c4h10 and co2 1 2h in ch4 14 15n in n2 and stable isotopes of all noble gases due to significantly different geological settings and genetic types of source rocks of eastern and western pomerania the molecular and isotopic compositions of natural gases of these two regions exhibit distinct differences hydrocarbon gases associated with oil accumulated in the middle cambrian reservoir of eastern pomerania were generated during low temperature thermogenic processes from a single source rock containing type ii kerogen at one phase of petroleum generation non associated hydrocarbon gases accumulated in the carboniferous mississippian and pennsylvanian lower permian rotliegend reservoirs of western pomerania originated during at least two phases of gas generation by thermogenic processes from mainly type iii kerogen and a small component of mixed type iii ii kerogen noble gases are in general heavily enriched in radiogenic and nucleogenic isotopes such as 4he 40ar and 21ne accumulated in the reservoirs weak contributions of mantle derived he and ne are observed radiogenic 4he 40ar ratios are higher than the average production rate ratio of about 5 for radiogenic 4he 40ar in crustal materials which might have been caused by a selective supply of 4he that is lighter than 40ar from crustal rocks or u th k ratio might be higher than the average in crustal block carbon dioxide from gases of both the western and eastern pomerania were mainly generated during thermogenic processes of transformation of organic matter although gases of western pomerania can contain an endogenic component molecular nitrogen from the eastern pomeranian natural gases was mainly generated during low temperature thermal transformation of organic matter and derived from nh3 and nh4 of crustal fluid whereas molecular nitrogen from western pomeranian natural gases contains a significant component from the destruction of organic matter at a higher maturity level which may have been caused by a high heat flux from the volcanic activity during late pennsylvanian early rotliegend ages and has a bigger component release from nh4 rich illites

release of mantle helium from forearc region of the southwest japan arc abstract shikoku japan is an island located on the forearc region of the western sector of the southwest sw japan arc that was formed by subduction of the philippine sea plate beneath the eurasian plate noble gas isotope analyses were carried out for 30 bubbling gas samples and spring water samples collected in shikoku in addition chemical and carbon isotope analyses were conducted for six gas samples observed 3 he 4 he ratios were 0 17 r r a to 3 56 r r a showing that several samples contain mantle helium components although some samples contain helium of crustal origin geographical distributions of 3 he 4 he ratios show that high 3 he 4 he ratios originate mainly from two areas one along the median tectonic line mtl a major active fault in japan the other coinciding with a region in which non volcanic long period tremors occur about 30 km deep obara k 2002 nonvolcanic deep tremor associated with subduction in southwest japan science 296 1679 1681 this fact indicates that fluids liberated from the slab in the forearc region cause deep tremors and fracturing within the crust thereby easing the transfer of fluids to the surface that are mixed with mantle helium to the surface an active fault system can also provide an efficient path for mantle helium transfer

orogen parallel tectonic transport in the variscan belt of northeastern sardinia italy implications for the exhumation of medium pressure metamorphic rocks a transpressive crustal scale dextral shear zone is documented in the variscan basement of northeastern sardinia it indicates the presence of a shear deformation parallel to the belt overprinting previous d1 structures related to nappe stacking and top to the s and sw thrusting the l2 stretch ing lineation points to an orogen parallel stretching and to a general change in the tectonic transport from d1 to d2 phase d1 developed during initial frontal collision whereas the d2 deformation was characterized by dextral shearing during the increasing curvature of the ibero armorican arc transpressional deformation developed in a regime of decreasing pressure it caused telescoping of the barrovian isograds and the exhumation of the low to medium grade metamorphic rocks in this sector of the variscan belt exhumation is due to continuing compression with an increasing compo nent of horizontal displacement the overall change of the shortening direction in a large sector of an orogenic belt with the occurrence of increasing orogen parallel displacement may be regarded as a general mechanism affecting the exhumation of rocks and preventing the thickened collisional crust from undergoing a generalized gravitational collapse

nitrogen sources and recycling at subduction zones insights from the izu bonin mariana arc 1 we report new chemical and nitrogen isotopic data from 29 volcanic and hydrothermal gas samples covering eight centers in the izu bonin mariana ibm arc to investigate the sources flux and mass balance of nitrogen at a cool convergent margin the majority of samples have high n2 he 1217 17 300 and low co2 n2 exc 78 937 implying addition of nitrogen from the subducting slab this inference is supported by positive i e sediment like 15n values up to 5 5 in most samples the exception to these trends is agrigan in the mariana arc with low n2 he 200 high co2 n2 exc 1500 and negative 15n mixing calculations suggest an average of 34 of the nitrogen in our samples is derived from subducted sediment or 75 after correction for atmospheric contamination sediment derived n2 fluxes estimated by three different methods range from 0 25 108 to 1 11 108 mol yr 1 n2 representing 4 17 of the total nitrogen input flux or 11 51 of the sedimentary nitrogen input flux the altered oceanic crust is identified as an important contributor to the arc nitrogen budget and the 15n of the residual nitrogen subducted into the mantle is estimated at approximately 1 9 despite similarities in gas chemistry and 15n values our conclusions regarding nitrogen recycling for ibm are markedly different than those for the nicaraguan segment of the central american arc and we suggest that thermal regime is the major control on nitrogen recycling within subduction zones the global nitrogen cycle is estimated to be in steady state suggesting either that subducted sediments are an unlikely source for heavy nitrogen in plume related rocks or secular variation in the isotopic composition of subducted sediments better constraints on nitrogen recycling at other arcs are required to test these conclusions

geochemical and isotopic evidences of magmatic inputs in the hydrothermal reservoir feeding the fumarolic discharges of tacora volcano northern chile abstract tacora volcano is a nearly unknown and understudied 5980 m high volcano located on the northernmost border between chile and peru tacora is characterized by intense fumarolic activity with extensive white colored hydrothermal areas along the nw and w flanks of the volcanic structure the chemical and isotopic features of gas emissions indicate that the hydrothermal reservoir is significantly affected by contributions from magmatic degassing despite relatively low outlet temperatures 82 93 c water and gas isotopic signatures stem from degassing of andesitic magmas produced from the sediment poor subducting slab isotopic data suggests ch 4 co 2 isotopic equilibration occurs at 400 c likely in the deepest portion of the hydrothermal magmatic fluid reservoir the h 2 h 2 o co co 2 h 2 ar ch 4 co 2 and c 2 c 3 alkenes alkanes pairs tend to approach a chemical equilibrium at temperatures between 200 and 320 c when redox conditions are more oxidizing than those determined by the typical feo feo 1 5 rock buffer system boiling occurs at shallow depth at 85 c within a discontinuous thin aquifer enough as thermal buffer but not able to scrub the uprising magmatic related acidic gases

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

zircon coronas around fe ti oxides a physical reference frame for metamorphic and metasomatic reactions ilmenite in coronitic gabbros from the bamble and kongsberg sectors southern norway is surrounded by zircons ranging in diameters from a fraction of a micrometer to 10 m across the zircons are inert during subsequent metamorphism amphibolite to pumpellyite prehnite facies and metasomatism scapolitization and albitization and can be found as trails in silicates phlogopite talc chlorite amphibole albite and tourmaline in the altered rocks the trails link up to form polygons outlining the former oxide grain boundary this 3 dimensional framework of zircons is used to a recognize metasomatic origin of rocks b quantify the mobility of elements during mineral replacement c establish the growth direction of reaction fronts and to identify the reaction mechanism as dissolution reprecipitation zircon coronas on fe ti oxides have been described from a number of terrains and appear to be common in mafic rocks gabbros and granulites providing a tool for a better understanding of metasomatic and metamorphic reactions

effects of climatic change and bog development on holocene tufa formation in the lorze valley central switzerland a massive tufa complex in the lower lorze valley 550 m a s l north central switzerland formed between 9000 and 5000 cal yr bp in the plain 4 km southeast of the complex lies neugrundmoor 830 m a s l a mire in the hydrologic recharge area of the springs responsible for the tufa formation here we address an earlier untested hypothesis that the transition of neugrundmoor from fen to raised bog caused the end of the tufa formation by means of pollen and testate amoebae analyses on a peat section the chronology of the section is based on ten ams c 14 dates of terrestrial plant macrofossils our results suggest that until 7100 cal yr bp the plain had shallow ponds which gradually developed into fens starting 5350 cal yr bp large raised bogs developed in the fens in a few centuries this agrees with the hypothesis that the end of tufa formation coincided with the transition from fen to raised bog it also coincided with the end of the mid holocene temperature optimum when climate became cooler and wetter we suggest that the main factor causing the end of tufa formation at 5500 5000 cal yr bp was declining air temperatures which on the one hand led to diminished calcium precipitation on the other to enhanced bog formation peat has a low hydraulic conductivity so we suggest that less water became available for tufa formation because of increased thickness of peat layers exacerbating the direct effect of cooling on calcium precipitation noticeable human influence in the surroundings did presumably not start before c 3500 cal yr bp and was then very weak so this was not responsible for the end of the tufa formation extrapolation of our results suggests that climatic cooling alone is sufficient to explain the widespread termination of tufa formation after the mid holocene

hydrothermal venting and mineralization in the crater of kick em jenny submarine volcano grenada lesser antilles kick em jenny is a frequently erupting shallow submarine volcano located 7 5 km off the northern coast of grenada in the lesser antilles subduction zone focused and diffuse hydrothermal venting is taking place mainly within a small 70 110 m depression within the 300 m diameter crater of the volcano at depths of about 265 m much of the crater is blanketed with a layer of fine grained tephra that has undergone hydrothermal alteration clear fluids and gas are being discharged near the center of the depression from mound like vents at a maximum temperature of 180 c the gas consists of 93 96 co2 with trace amounts of methane and hydrogen gas flux measurements of individual bubble streams range from 10 to 100 kg of co2 per day diffuse venting with temperatures 5 35 c above ambient occurs throughout the depression and over large areas of the main crater these zones are colonized by reddish yellow bacteria with the production of fe oxyhydroxides as surface coatings fragile spires up to several meters in height and elongated mounds up to tens of centimeters thick a high resolution photomosaic of the inner crater depression shows fluid flow patterns descending the sides of the depression toward the crater floor we suggest that the negatively buoyant fluid flow is the result of phase separation of hydrothermal fluids at kick em jenny generating a dense saline component that does not rise despite its elevated temperature

water rock interaction in the magmatic hydrothermal system of nisyros island greece abstract in this work we investigated the water rock interaction processes taking place in the hydrothermal reservoir of nisyros through both 1 a review of the hydrothermal mineralogy encountered in the deep geothermal borehole nisyros 2 and 2 a comparison of the analytically derived redox potentials and acidities of fumarolic related liquids with those controlled by redox buffers and ph buffers involving hydrothermal mineral phases the propylitic zone met in the deep geothermal borehole nisyros 2 from 950 to 1547 m total depth is characterised by abundant well crystallised epidote adularia albite quartz pyrite chlorite and sericite muscovite accompanied by less abundant anhydrite stilpnomelane wairakite garnet tremolite and pyroxene these hydrothermal minerals were produced in a comparatively wide temperature range from 230 to 300 c approximately hydrothermal assemblages are well developed from 950 to 1360 m whereas they are less developed below this depth probably due to low permeability based on the r h values calculated for fumarolic gases and for the deep geothermal fluids of nisyros 1 and nisyros 2 wells redox equilibrium with the feo feo 1 5 rock buffer appears to be closely attained throughout the hydrothermal reservoir of nisyros this conclusion may be easily reconciled with the nearly ubiquitous occurrence of anhydrite and pyrite since r h values controlled by coexistence of anhydrite and pyrite can be achieved by gas separation the ph of the liquids feeding the fumarolic vents of stephanos and polybote micros craters was computed by means of the eq3 code based on the cl d relationship which is constrained by the seawater magmatic water mixing occurring at depth in the hydrothermal magmatic system of nisyros the temperature dependence of analytically derived ph values for the reservoir liquids feeding the fumarolic vents of stephanos and polybote micros craters suggests that some unspecified ph buffer fixes the acidity of these reservoir liquids at values of 4 72 4 85 and 4 88 5 23 respectively many of these ph values are lower than those expected for the full equilibrium condition although they are close to those of the reservoir liquids of nisyros 1 5 16 and nisyros 2 4 87 it is likely that this excess of acidity producing species chiefly co 2 promotes release of fe ii and fe iii to the reservoir liquids through rock dissolution permitting the attainment of redox equilibrium with the feo feo 1 5 rock buffer as already suggested by the late werner giggenbach

magmatic helium in subduction zone natural gases abstract he isotope ratios provide important constraints on the input of magmatic gases into crustal systems natural gas associated with active continental margins from taiwan r o c new zealand the philippines indonesia thailand and alaska u s a contain a magmatic he component based on measured 3 he 4 he ratios r ranging from 0 5 to 3 8 times the atmospheric value ra the methane helium results can be interpreted as the result of a mixture between a low 3 he 4 he 0 01r a high ch 4 3 he crustal end member and a high 3 he 4 he 0 6 3 9r a low ch 4 3 he 6 magmatic component the presence of mantle he does not require significant amounts of mantle methane a better fit to the data is obtained using a zero methane magmatic end member the worldwide association of 3he and magmatic activity suggests that volcanism plays a role in methane generation by supplying the heat needed to convert organic matter to methane thermogenically only gases from the accretionary prism of barbados west indies appear totally devoid of magmatic he 3 he 4 he ratio 0 02ra the he is completely of crustal origin there is no evidence that faults within the accretionary prism of this fore arc act as conduits for the migration of mantle he many of the gases studied contain significant quantities of co2 which appear to result from two processes 3 he 4 he high co 2 3 he gases 0 01ra 1011 possibly result from decarbonation reactions in the crust while the high 3 he 4 he low co 2 3 he gases 2 4ra

ca distribution between almandine rich garnet and plagioclase in pelitic and psammitic schists from the metamorphic basement of north eastern sardinia garnet and plagioclase pairs from fourteen selected samples from garnet to sillimanite zones collected along a ns traverse throughout the metamorphic basement of ne sardinia have been analyzed by microprobe

did changes in late last glacial and early holocene atmospheric co2 concentrations control rates of tufa precipitation gases trapped within arctic antarctic and greenland ice cores document a dramatic increase in atmospheric co2 levels by almost 100 in the period between the last glacial maximum and the late holocene the authors note an apparent correlation between increases in levels of atmospheric co2 during this period and an episode of mass deposition of freshwater carbonate tufas and travertines as changes in atmospheric co2 levels are likely to affect carbonate deposition tucker and wright 1990 we propose the hypothesis that a relationship exists between increasing atmospheric co2 levels and tufa deposition

mid holocene erosive episodes in tufa deposits from trabaque canyon central spain as a result of abrupt arid climate transitions during the holocene a series of tufa sediments were deposited from a karstic spring along the trabaque canyon central spain a long term lowering of the water table caused the location of the spring to be displaced from the upper sector of the canyon during the early holocene to the lower sector in the late holocene this progressive shift was in response to decreased precipitation in the region the depositional environments and their geomorphologic relationships were characterized thus five morphosedimentary units msus were identified within the holocene tufa deposits erosive episodes were recognized between msus and as most of the msus partially overlap the older ones are perched in relation to the younger ones the chronology of the msus is based on 14c dates and stable isotopes and total organic carbon content provided environmental information during the period of tufa sedimentation the successive dissection episodes in the trabaque canyon tufa deposits took place during transitioning climate conditions from the relatively wet early holocene to the more arid late holocene during this transitional period in the mid holocene wet phases alternated with more arid conditions causing the largest hydrological regime gradients in the holocene thus the four erosive episodes causing tufa dissection in trabaque during the holocene are interpreted as the result of abrupt transitional periods towards arid conditions

carbon dioxide emissions from soils at hakkoda north japan 1 a soil gas and co2 efflux survey was carried out at hakkoda north japan to investigate the spatial distribution and origin of the gas which caused the accidental death of three japanese soldiers on 12 july 1997 in the study area no fumarolic and or thermal activity is observed chemical composition of the gas from areas with high co2 effluxes 5 000 g m 2 d 1 and high co2 contents 15 vol indicate a strong deep sourced contribution for co2 whereas air and or air saturated water is suggested for the rest of the discharged gases which are mainly released from a shallow aquifer isotopic analysis of soil gas and hot spring discharges suggests a combination of magmatic degassing and thermal decarbonation with magmatic degassing being the main contributior to the high co2 emission approximately 74 t d 1 of deep seated magmatic plus thermal decarbonation origin co2 were estimated to contribute to the total output of co2 from this area

transformation of cumulate mafic rocks to granulite and re equilibration in amphibolite and greenschist facies in ne sardinia italy abstract the ultramafic amphibolites hosted in the hercynian migmatite of ne sardinia consist of three main compositional layers a b c from a few metres to a few decametres thick layer a is made up of coarse grained olivine chlorite amphibole spinel minor pyroxene garnet and rarely plagioclase layer b is made up of coarse grained plagioclase olivine pyroxene spinel garnet and amphibole layer c consists mainly of porphyroblastic garnet pyroxene large amphibole grains up to 5 cm and minor plagioclase on the basis of mineral assemblages and microstructures three stages of mineralogical re equilibration can be recognised granulite amphibolite and greenschist primary igneous olivine and anorthite reacted under granulite conditions to produce coronas consisting of orthopyroxene clinopyroxene green spinel and garnet the amphibolite stage is characterised by the formation of brown and green clinoamphiboles between pyroxene and corona garnet anthophyllite talc mg rich chlorite plagioclase and cr bearing spinel greenschist stage minerals mostly replacing the mafic minerals consist of tremolite fayalite epidote albite calcite dolomite and serpentine the history of the ultramafic amphibolites started with igneous crystallisation and continued through granulite t 700 740 c p 8 10 kbar amphibolite t 580 640 c p 4 6 kbar and greenschist facies t 330 400 c p evaluation of p t conditions indicated a p t path from the protolith to granulite stage characterised by an increase in pressure and temperature and then from the granulite facies through amphibolite to the greenschist stage characterised by a decrease in pressure and temperature the petrological evolution of the ultramafic amphibolites and the p t time path is discussed in the context of the hercynian orogeny in sardinia

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

petrophysical data and opaque mineralogy of high grade and retrogressed lithologies implications for the interpretation of aeromagnetic anomalies in northern vestranden central norway abstract a regional aeromagnetic anomaly centred around roan northern vestranden western gneiss region central norway is caused by the presence of high grade orthogneisses and metabasites with 1 2 vol magnetite granulites are surrounded and partly covered by amphibolite facies rocks which consist of reworked retrogressed granulite facies orthogneisses and bands of metasediments prograde metamorphism from amphibolite to granulite facies led to production of magnetite as a result of the breakdown of hydrous fe mg al silicates the magnetite occurs as 0 5 1 mm amoeboid grains surrounded by plagioclase and k feldspar this magnetite is nearly pure with only a negligible content of ulvospinel fetio4 in solid solution early retrogression at low ph2o conditions is characterized by breakdown of garnet producing fine grained magnetite in almandine rich varieties this secondary magnetite is common in basic rocks where it can be the dominant type grains smaller than 10 m are associated with high coercivities and this magnetite may be the carrier of remanence in such lithologies a probably contemporaneous development of magnetite can be seen in clinopyroxenes where it occurs as 0 1 mm long needles or rods within crystallographic planes clinopyroxene that crystallized at high pressure can hold an excess of fe in the lattice but upon decompression will release this fe producing fe ti oxides late retrogression at high ph2o leads to reduction of the magnetite content due to replacement of magnetite by silicates mainly hornblende and sphene also leucoxene magnetite is still stable into the upper amphibolite facies the close correlation between petrophysical data aeromagnetic anomalies and geological units allows mapping of these units in the offshore areas metasedimentary rocks that are downfolded in the orthogneisses show low magnetic susceptibility values and can be traced as zones of lowest magnetization level

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

helium carbon relationships in geothermal fluids of western anatolia turkey abstract we investigate the helium carbon and oxygen hydrogen isotopic systematics and co2 3he ratios of 8 water and 6 gas samples collected from 12 geothermal fields in western anatolia turkey 3he 4he ratios of the samples r normalized to the atmospheric 3he 4he ratio ra 1 39 10 6 range from 0 27 to 1 67 and are significantly higher than the crustal production value of 0 05 fluids with relatively high r ra values are generally found in areas of significant heat potential kizildere and tuzla fields co2 3he ratios of the samples ranging from 1 6 109 to 2 3 1014 display significant variation and are mostly higher than values typical of an upper mantle source 2 109 the 13c co2 and 13c ch4 values of all fluids vary from 8 04 to 0 35 and 25 80 to 23 92 vs pdb respectively stable isotope values 18o d of the geothermal waters are conformable with the mediterranean meteoric water line and indicate a meteoric origin the temperatures calculated by gas geothermometry are significantly higher than estimates from chemical geothermometers implying that either equilibrium has not been attained for the isotope exchange reaction or that isotopic equilibration was disturbed due to gas additions en route to the surface evaluation of he co2 abundances indicates that hydrothermal degassing and calcite precipitation controlled probably by adiabatic cooling due to degassing significantly fractionate the elemental ratio co2 3he in geothermal waters such processes do not affect gas phase samples to anywhere near the same extent for the gas samples mixing between mantle and various crustal sources appears to be the main control on the observed he c systematics however crustal inputs dominate the co2 inventory considering that limestone is the main source of carbon 70 to 97 of the total carbon inventory the carbon flux from the crust is found to be at least 20 times that from the mantle as to the he inventory the mantle derived component is found to vary up to 21 of the total he content and is probably transferred to the crust by fluids degassed from deep mantle melts generated in association with the elevated geotherm and adiabatic melting accompanying current extension the range of 3he enthalpy ratios 0 000032 to 0 19 10 12 cm3 stp j of fluids in western anatolia is consistent with the release of both helium and heat from contemporary additions of mantle derived magmas to the crust the deep faults appear to have facilitated the deep circulation of the fluids and the transport of mantle volatiles and heat to the surface

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

post earthquake anomalies in he co2 isotope and relative abundance systematics of thermal waters the case of the 2011 van earthquake eastern anatolia turkey abstract we report the helium and carbon isotope 3 he 4 he 13 c and relative abundance co 2 3 he characteristics of hydrothermal gases from eastern anatolia sampled 1 month after the october 23 2011 van earthquake mw 7 2 focal depth 19 km seven sites were sampled which comprise three localities along the caldiran fault zone at a distance of 58 66 km to the epicenter group i two localities north of the caldiran fault about 90 113 km from the epicenter group ii and two localities in the vicinity of the historically active nemrut caldera at a distance of 110 126 km from the epicenter group iii all sites were previously sampled for their he co 2 systematics in 2009 mutlu et al 2012 facilitating direct comparison with the post earthquake dataset the post earthquake values cover a wide range of 3 he 4 he 13 c and co 2 3 he ratios from 0 84 to 6 37 r a where r a air 3 he 4 he 5 30 to 0 49 vs vpdb and 4 9 10 10 to 6 85 10 13 respectively group i samples show a consistent post earthquake increase in 3 he 4 he whereas both group ii localities decreased in 3 he 4 he no change was recorded for the two group iii localities he isotope variations are consistent with simple changes in the proportions of mantle and crustal volatiles with all group i sites showing an increase in the mantle he contribution we hypothesize that the enhanced mantle he signal is derived from asthenospheric melts intruded into the crust with seismic perturbations responsible for bubble formation and growth leading to overpressure and gas loss the strike slip caldiran fault zone provides the permeable pathway for the liberated volatiles to reach hydrothermal systems at shallow levels of the crust and the surface release of crustal he dominates the he mass balance of group ii samples as locations are further from the earthquake epicenter group iii samples are even further away from the earthquake and show no perturbations in he isotopes whereas binary mixing dominates the he isotope systematics co 2 shows additional effects involving the hydrothermal system consequently changes in the balance between mantle and crustal co 2 are masked and more difficult to discern the results emphasize the sensitivity of he isotopes to seismic perturbations in the crust and illustrate how location of sampling sites on permeable segments of faults and distance from seismic events influence resulting changes involving gas chemistry

active deposition of calcareous tufa in wessex uk and its implications for the late holocene tufa decline recent publications have suggested that deposition of calcareous tufa and travertine in the british isles has declined since the mid holocene several causal mechanisms have been postulated which include changes in both palaeoenvironmental and palaeoecological conditions results presented here for actively depositing tufa in the wessex region of southwest england suggest that there has been significant under reporting of contemporary tufa deposition this factor must be taken into consideration in any investigation of a possible tufa decline in the late holocene geochemical and environmental conditions at 26 tufa deposition sites are reported in order better to elucidate the climatic and environmental factors which constrain contempor ary tufa deposition and to achieve a better understanding of the controls on holocene deposition

geochemical characterisation of gases along the dead sea rift evidences of mantle co2 degassing abstract the dead sea transform dst fault system where a lateral displacement between the african and arabian plates occurs is characterised by anomalous heat flux in the israeli area close to the border with syria and jordan the concentration of he and co2 and isotopic composition of he and total dissolved inorganic carbon were studied in cold and thermal waters collected along the dst in order to investigate the source of volatiles and their relationship with the tectonic framework of the dst the waters with higher temperature up to 57 2 c are characterised by higher amounts of co2 and helium up to 55 72 and 1 91 10 2 cc l 1 respectively helium isotopic data r ra from 0 11 to 2 14 and 4he 20ne ratios 0 41 106 86 show the presence of deep deriving fluids consisting of a variable mixture of mantle and crust end members with the former reaching up to 35 carbon isotope signature of total dissolved carbon from hot waters falls within the range of magmatic values suggesting the delivery of deep seated co2 the geographical distribution of helium isotopic data and isotopic carbon co2 values coupled with co2 3he ratios indicate a larger contribution of mantle derived fluids affecting the northern part of the investigated area where the waters reach the highest temperature these evidences suggest the occurrence of a favourable tectonic framework including a moho discontinuity up rise and or the presence of a deep fault system coupled with the recent magmatic activity recognised in the northern part of israel

the late holocene tufa decline in europe over much of europe it has been postulated that in the late holocene since c 2500 bp there was a marked decline in the deposition of tufa there has been considerable debate about the causes of this phenomenon with some authors postulating the importance of natural climatic changes and others asserting that miscellaneous human influences have been crucial this article discusses the role that various changes both natural and anthropogenic may have played and suggests ways in which the large number of possible hypotheses can be tested

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

fluid geochemistry and geothermometry in the western sector of the sabatini volcanic district and the tolfa mountains central italy abstract a geochemical survey of 197 fluid discharges cold and thermal waters and bubbling pools and 15 gas emissions from the western sector of the sabatini volcanic district and the tolfa mountains latium central italy was carried out in 2007 2008 the chemical and isotopic compositions of the fluid discharges indicate the occurrence of two main sources 1 relatively shallow aquifers with ca na k hco 3 and ca mg hco 3 compositions when trapped in volcanic and sedimentary formations respectively and 2 a deep reservoir which is hosted in the mesozoic carbonate sequence rich in co 2 and having a ca so 4 hco 3 composition dissolution of a co 2 rich gas phase into the shallow aquifers produces high tds and high pco 2 cold waters while oxidation of deep derived h 2 s to so 4 2 generates low ph the 13 c co 2 values for gas emissions from 2 8 to 2 7 vs vpdb suggest that the origin of co 2 associated with the deep fluids is mainly related to thermo metamorphic reactions within the carbonate reservoir although significant mantle contribution may also occur however r r a values 0 37 0 62 indicate that he is mainly produced by a crustal source with a minor component from a crust contaminated mantle on the basis of the 13 c ch 4 and d ch 4 values from 25 7 to 19 5 vs vpdb and from 152 to 93 4 vs vsmow respectively ch 4 production is associated with thermogenic processes possibly related to abiogenic co 2 reduction within the carbonate reservoir the 34 s h 2 s values from 9 3 to 10 4 vs vcdt are consistent with the hypothesis of a sedimentary source of sulfur from thermogenic reduction of triassic sulfates geothermometric evaluations based on chemical equilibria co 2 ch 4 and separately h 2 s suggest that the reservoir equilibrium temperature is up to 300 c the d and 18 o data indicate that water recharging both the shallow and deep aquifers has a meteoric origin fluid geochemistry coupled with gravimetric data and tectonic lineaments supports the idea that significant contributions from a deep seated geothermal brine are present in the stigliano thermal fluid discharges exploration surveys investigated this area during 70 s 90 s for geothermal purposes nevertheless presently the area is still under exploited the presence of thermal waters and anomalous heat flow together with the demographic growth of the last years makes this site a suitable location for direct applications of the geothermal resource

the hydrothermal system of volcan purace colombia this paper presents chemical and isotopic data for thermal waters gases and s deposits from volcan purace summit elevation 4600 m in sw colombia hot gas discharges from fumaroles in and around the summit crater and thermal waters discharge from three areas on its flanks the waters from all areas have d values of 75 1 indicating a single recharge area at high elevation on the volcano aircorrected values of3he 4he in thermal waters range from 3 8 to 6 7 ra and approach those for crater fumarole gas 6 1 7 1 ra indicating widespread addition of magmatic volatiles an economic s deposit el vinagre is being mined in the rio vinagre fault zone at 3600 m elevation sulfur isotopic data are consistent with a magmatic origin for s species in thermal waters and gases and for the s ore deposit isotopic equilibration between s species may have occurred at 220 40 c which overlaps possible equilibration temperatures 170 40 c determined by a variety of other geothermometers for neutral thermal waters apparent ch4 co2 equilibration temperatures for gases from thermal springs 400 50 c and crater fumaroles 520 60 c reflect higher temperatures deeper in the system hot magmatic gas ascending through the rio vinagre fault zone is though to have precipitated s and generated thermal waters by interaction with descending meteoric waters

aeromagnetic anomalies magnetic petrology and rock magnetism of hemo ilmenite and magnetite rich cumulate rocks from the sokndal region south rogaland norway aeromagnetic maps of the egersund mid proterozoic igneous province show a spectacular range of positive and negative magnetic anomalies with a contrast up to 15 600 nt the positive magnetic anomalies are over magnetite norites and overlying mangerites and quartz mangerites of the bjerkreim sokndal layered intrusion these rocks are dominated by multi domain md magnetite the negative magnetic anomalies are over ilmenite rich norites of the bjerkreim sokndal layered intrusion the tellnes ilmenite norite ore deposit and massif anorthosites these rocks are dominated by hemo ilmenite and or by silicates containing fine grained oxide exsolution lamellae electron microprobe analyzes of coexisting fe ti oxides in the layered intrusion confirm earlier observations that oxides in early magmatic rocks are dominated by hemo ilmenite with minor end member magnetite followed by more reduced oxides dominated by titanomagnetite with minor near end member ilmenite what is not fully understood is the property of ilmenite with hematite exsolution lamellae or even more striking hematite with ilmenite lamellae to produce strong remanent magnetization of high coercivity and with a neel temperature equal to or above the curie temperature of magnetite this property makes the rhombohedral oxides an important candidate to explain some high amplitude deep crustal anomalies on earth or strong remanent magnetization on other planets a remarkable feature in the egersund province is that primitive magmas produced rocks rich in hemo ilmenite causing negative magnetic anomalies related to magnetic remanence and more evolved magmas produced rocks rich in magnetite related to positive induced magnetic anomalies all in the course of crystallization differentiation

gas geochemistry of hot springs at the tengchong field southwest china controlled by the spatial distribution of magmatic chamber abstract the tengchong volcanic field located at the collision zone between the indian and eurasian plates is well known for its large scale holocene volcanic eruptions and extensive hydrothermal activities bubbling gases from eight geothermal springs at the tengchong field were collected and analyzed for their chemical and isotopic compositions 3he 4he 20ne n2 ar 13cch4 and 13cco2 the results show that the gas samples could be categorized into a group i dominated by n2 and a group ii with co2 as major component the air corrected 3he 4he ratios ranged from 0 17 ra to 4 76 ra and the calculated mantle contributions dramatically varied from 1 9 to 77 9 for group ii by contrast an invariant air corrected 3he 4he ratio of about 0 30 ra and a relatively constant mantle contribution of 4 0 to 5 0 was obtained for group i the sampling sites just on top of the magma chamber received significant mantle derived helium and magmatic gas components at the proximal site of the magma chamber 95 magmatic gas contributions the calculated n2 ar ratio of the hydrothermal endmember for group ii sample sites close to the magma chamber was 61 7 66 2 suggesting that the reaction zone temperature is between 223 c and 252 c the influence of the magma chamber decreases with increasing distance of the sampling sites from the chamber apex the sampling sites group i at the marginal area discharge gases with relatively low 3he 4he ratios and magmatic contributions 19 24 the temperature of the reaction zone for this group was estimated to be 74 c based on the n2 ar ratio of 42 this study provided important constraints to relate hydrothermal gas geochemistry directly with the spatial distribution of the underlying magma chamber plain language summary geochemical characteristics of gases discharged from hydrothermal systems are usually affected by deep magmatic processes shallow hot fluids circulation and water rock interactions in the reaction zone in this study we analyzed the gas abundances and isotopic compositions of hydrothermal gas discharged from the yunnan tibet geothermal belt we used a gas mixing model to quantify the contributions of mantle derived magmatic endmember and hydrothermal endmember the 3he 4he ratios magmatic contribution and temperature of the reaction zone decreased significantly with increasing distance from the magma chamber underneath the tengchong field highlighting the intimate relationships between gas transport hydrothermal circulation and the extent of the magma chamber

helium isotopes in geothermal and volcanic gases of the western united states ii long valley caldera abstract systematic trends in helium isotope ratios and gas compositions in long valley caldera hot spring and fumarole gases reflect subsurface processes and conditions in the hydrothermal system high 3 he 4 he ratios to 6 5 atmospheric indicate a magmatic helium source diluted to varying degrees by crustal radiogenic helium as observed in western united states geothermal systems in general helium isotope ratios increase eastward across the caldera which we interpret as an input of magmatic helium to the hydrothermal fluid as it flows eastward over the caldera decreasing he condensible gas he co2 ratios accompanying this trend suggest that co2 addition and or preferential helium loss due to boiling are also occurring although near surface ph related co2 hco3 equilibria obscure the nature of this effect substantial changes in 3 he 4 he ratios were observed in long valley gases between 1978 and 1985 helium isotope ratios increased by 15 in the hot creek thermal vent with maximum ratios achieved in 1983 helium isotope ratios subsequently decreased in this and other hot vents in the caldera these observations indicate that substantial changes in the mixing ratio of radiogenic and magmatic helium may occur over relatively short periods of time in magmatically active systems

gas geochemistry and co2 output estimation at the island of milos greece abstract twenty gas samples have been collected from the natural gas manifestations of milos island the majority of which is found underwater along its coast furthermore three anomalous degassing fumarolic areas kalamos paleochori and adamas have been recognized on land almost all the gases are co2 dominated with co2 ranging from 88 to 99 vol for the samples taken underwater while the on land manifestations show a wider range 15 98 due to air contamination methane reaches up to 1 0 vol h2 up to 3 2 vol and h2s up to 3 5 vol indicating a hydrothermal origin of the gases the isotope composition of he points out to mantle contributions up to 45 while the c isotope composition of co2 from 1 9 to 1 3 vs v pdb with most of the values around 0 5 suggests a prevailing limestone origin isotope composition of ch4 ranging from 18 4 to 5 0 vs v pdb for c and from 295 to 7 vs v smow for h points to a geothermal origin with sometimes evident secondary oxidation processes additionally co2 flux measurements showed high values in the three fumarolic areas up to 1100 1500 and 8000 g m2 d at kalamos paleochori and adamas respectively with the highest co2 flux values up to about 23 000 g m2 d being measured in the sea at kanavas with a floating chamber the south western part of the island was covered with a lower density prospection revealing only few anomalous co2 flux values up to 650 g m2 d the total output of the island 30 5 t d is typical of quiescent closed conduit volcanoes and comparable to the other volcanic geothermal systems of the south aegean active volcanic arc nisyros kos nea kameni methana and sousaki

magnetic petrology of variably retrogressed eclogites and amphibolites a case study from the hercynian basement of northern sardinia italy 1 this study constitutes the first attempt to integrate rock magnetism and metamorphic petrology in the hercynian basement of northern sardinia the investigation focused on the magnetic petrology of variably retrogressed eclogites and amphibolites from two suites of basic meta igneous rocks which occur along a major tectonic line posada asinara line within a medium grade mg and a high grade hg metamorphic complex consistent with petromagnetic results hg metabasites contain variable amounts of monoclinic pyrrhotite intergrown with rutile and titanomagnetite occurring as inclusions in garnet abundant ilmenite associated to secondary hornblende and with sphene low ti magnetite rims and rutile both as inclusions in ilmenite and as discrete grains in mg metabasites pyrrhotite is restricted to amphibolites of the posada valley area where it occurs as rare inclusions in garnet all samples are characterized by variable amounts of ilmenite rutile and sphene which show the same microstructural features described in hg rocks microstructural evidence and geothermobarometric data indicate that 1 pyrrhotite and titanomagnetite likely formed prior to and remained stable during the eclogite facies metamorphic peak and 2 the growth of ilmenite and sphene can be attributed to the amphibolite facies retrogression mainly due to model reactions such as garnet omphacite rutile h2o hornblende plagioclase ilmenite and amphibole ilmenite o2 sphene magnetite quartz h2o the results from our combined petrological and petromagnetic study corroborate the hypothesis that significant volumes of mafic ultramafic rocks similar to some of the investigated outcrops may account for the magnetic anomalies flanking the northeastern part of the posada asinara line

a late middle pleistocene temperate periglacial temperate sequence oxygen isotope stages 7 5e near marsworth buckinghamshire uk abstract river channel and colluvial deposits near marsworth buckinghamshire record a temperate periglacial temperate sequence during the late middle pleistocene the deposits of a lower channel contain tufa clasts bearing leaf impressions that include acer sp and sorbus aucuparia and containing temperate arboreal pollen attributed to ash dominated woodland the tufa probably formed at the mouth of a limestone spring before being redeposited in a small river whose deposits contain plant remains mollusca coleoptera ostracoda and vertebrate bones of temperate affinities the sediments sedimentary structures and limited biological remains above the lower channel deposits indicate that fluvial deposition preceded climatic cooling into periglacial conditions fluvial deposition recurred during a later temperate episode as shown by the mammalian bone assemblage in stratigraphically higher channel deposits the upper channel deposits are confidently attributed to oxygen isotope sub stage 5e ipswichian on the basis of their vertebrate remains however the age of the lower channel deposits is less clear the mammalian and coleopteran remains in the lower channel strongly suggest correlation with oxygen isotope stage 7 on the basis of their similarities to other sites whose stratigraphy is better known and the clear difference of the lower channel assemblage from well established faunas of ipswichian or any other age by contrast u th dating of the tufa clasts suggests an age post 160 ka bp while aile ile ratios on mollusca point to an ipswichian age and younger four ways of interpreting this age discrepancy are considered the preferred one correlating the lower channel deposits with oxygen isotope stage 7

a new hydrothermal scenario for the 2006 lusi eruption indonesia insights from gas geochemistry abstract the 29th of may 2006 gas and mud eruptions suddenly appeared along the watukosek fault in the north east of java indonesia within a few weeks several villages were submerged by boiling mud the most prominent eruption site was named lusi to date november 2011 lusi is still active and a 7 km2 area is covered by the burst mud breccia the mechanisms responsible for this devastating eruption remain elusive while there is consensus about the origin of the erupted mud the source of water is uncertain the origin of the gas is unknown and the trigger of the eruption is still debated in order to shed light on these unknowns we acquired a wide set of data of molecular and isotopic composition of gas sampled in several lusi vents in the surrounding mud volcanoes in the closest natural gas field wunut and in the hydrothermal vents at the neighbouring volcanic complex in the period 2006 2011 the boiling fluids erupted in the crater zone are apparently co2 dominated while colder ch4 dominated and c2 c3 bearing fluids are identified at several sites around the crater zone gas genetic diagrams maturity plots and gas generation modelling suggest that the hydrocarbons are thermogenic 13c1 up to 35 13c2 up to 20 deriving from marine kerogen with maturity of at least 1 5 ro for instance in the 4400 m deep ngimbang source rocks co2 released from the crater and surrounding seeps is also thermogenic 13c from 15 to 24 related to kerogen decarboxylation or thermal ch4 oxidation in deep rocks although three vents just outside the crater showed an apparent inorganic signature 7 5 4000 m magmatic intrusions and hydrothermal fluids responsible for the enhanced heat that altered source rocks and or gas reservoirs the neighbouring magmatic arjuno complex and its fluid pressure system combined with high seismic activity could have played a key role in the lusi genesis and evolution within this new model framework lusi is better understood as a sediment hosted hydrothermal system rather than a mud volcano

diffuse co2 efflux from iwojima volcano izu ogasawara arc japan abstract iwojima volcano located on the southernmost part of the izu ogasawara arc is characterized by the extrusion of trachyte or trachy andesite lavas and pyroclastic rocks of holocene and surface thermal manifestations small phreatic explosions have been recorded frequently during the last 100 years with the most recent in 1999 and 2001 in order to elucidate the behavior of volcanic volatiles and to assess the potential activity of this volcano diffuse co 2 efflux co 2 content and 13 c co 2 in soil gas and soil temperature at 30 cm depth were measured at 272 sites in march 2000 112 sites in december 2000 and 40 sites in december 2001 we found that high co 2 efflux values of more than 100 g m 2 day 1 occurred at several locations on motoyama volcano corresponding with high soil temperatures more than 60 c at 30 cm depth region and with areas where co 2 with magmatic 13 c was observed here the magmatic 13 c determined for fumarolic co 2 data ranged from 2 to 3 which is clearly higher than magmatic gas values 8 to 2 typically found in island arc settings around the world however this can be explained in terms of carbon isotope fractionation between calcite and co 2 under subsurface temperature and pressure conditions at iwojima a total efflux of co 2 for iwojima volcano is estimated to be 760 t day 1 with a magmatic contribution of about 450 t day 1 this value is rather high compared with other volcanoes in island arc settings since iwojima has no visible plume almost all volcanic co 2 is released as diffuse efflux through the volcanic edifice

structural architecture releasing deep sourced carbon dioxide diffuse degassing at the caviahue copahue volcanic complex abstract the link between carbon dioxide diffuse degassing and its structural control was examined in the caviahue copahue volcanic complex over an area of approximately 10 km2 that encompasses five hydrothermal sites namely anfiteatro copahue town las maquinitas i las maquinitas ii and las maquinas both geochemical and structural approaches were applied in order to investigate the structural scenario releasing hydrothermal fluids in this area also the first isotopic analysis of soil co2 degassing in the andean region is presented the geochemical analysis shows well defined co2 diffuse degassing structures in copahue town las maquinitas i las maquinitas ii and las maquinas hydrothermal sites soil diffuse co2 is fed by multiple sources a deep magmatic hydrothermal source a biogenic source and a mixed source the structural analysis indicates the presence of an extensional regime that gives place to three structural trends consisting of ne sw trending normal faults nw se sinistral strike slip faults and ene wsw right lateral strike slip faults the comparison between diffuse degassing structures directions and faults directions suggests that there is a structural control on diffuse degassing diffuse co2 is released through an early extensional setting and it is emitted through normal faults strike slip faults and through areas with higher structural damage such as relay areas between fault segments and terminations of individual fault segments

spatial and temporal variations of gas geochemistry at mt ontake japan abstract this report describes spatial and temporal variations of helium carbon and nitrogen isotopes measured in co2 rich bubbling gases from natural springs associated with mt ontake central honshu japan from november 1981 through september 2015 during the entire period the 3he 4he ratio decreased concomitantly with increasing distance of the sampling site from the central cone in contrast the co2 3he ratios and the 13c values of co2 increased with distance these spatial trends became more pronounced after the september 27 2014 ontake eruption suggesting reactivation of the volcano plumbing system with enhanced emission of magmatic volatiles although the spatial trend of nitrogen isotopes disappeared the 3he 4he ratios of the most proximal site to the central cone remained constant until 2000 apparently increasing from june 2003 through october 2014 they became constant soon after the eruption until september 2015 the ten year 3he enhancement might have been a precursor of the 2014 ontake eruption in contrast 13c values of co2 at the same site remained constant through this period the lack of 13c anomaly might be attributable to 1 negligibly small amounts of magmatic co2 introduced into the source of hot springs compared to ambient co2 in the air saturated aquifer or 2 close resemblance of the carbon signature of magmatic co2 to that of ambient co2 therefore its addition cannot change the overall 13c value of the sampled hot springs at distal sampling sites no measurable change of helium carbon or nitrogen isotopes was observed in relation to the 2014 ontake eruption suggesting that the effect of this eruption on the ontake hydrothermal system was geographically localized

carbon release from submarine seeps at the costa rica fore arc implications for the volatile cycle at the central america convergent margin 1 we report total dissolved inorganic carbon dic abundances and isotope ratios as well as helium isotope ratios 3he 4he of cold seep fluids sampled at the costa rica fore arc in order to evaluate the extent of carbon loss from the submarine segment of the central america convergent margin seep fluids were collected over a 12 month period at mound 11 mound 12 and jaco scar using copper tubing attached to submarine flux meters operating in continuous pumping mode the fluids show minimum 3he 4he ratios of 1 3 ra where ra is air 3he 4he consistent with a small but discernable contribution of mantle derived helium at mound 11 13c co2 values between 23 9 and 11 6 indicate that dic is predominantly derived from deep methanogenesis and is carried to the surface by fluids derived from sediments of the subducting slab in contrast at mound 12 most of the ascending dissolved methane is oxidized due to lower flow rates giving extremely low 13c co2 values ranging from 68 2 to 60 3 we estimate that the carbon flux co2 plus methane through submarine fluid venting at the outer fore arc is 8 0 105 g c km 1 yr 1 which is virtually negligible compared to the total sedimentary carbon input to the margin and the output at the volcanic front unless there is a significant but hitherto unidentified carbon flux at the inner fore arc the implication is that most of the carbon being subducted in costa rica must be transferred to the deeper mantle i e beyond the depth of arc magma generation

the effects of volatile recycling degassing and crustal contamination on the helium and carbon geochemistry of hydrothermal fluids from the southern volcanic zone of chile abstract we report new helium and carbon isotope 3he 4he 13c and relative abundance co2 3he characteristics of a suite of hydrothermal gases and fluids fumaroles hot springs geothermal wells from 18 localities in the central southern volcanic zone csvz of chile the csvz is characterized by a wide range of 3he 4he ratios from 1 50 to 6 47 ra where ra air 3he 4he 13c co2 values from 2 9 to 17 7 vs pdb and co2 3he ratios which vary over 5 orders of magnitude 3 1 105 to 2 3 1011 one hydrothermal locality aguas calientes has combined he co2 characteristics remarkably similar to other arc related systems worldwide implying that the underlying subduction zone complex and mantle wedge supplies volatiles to the volcanic front with little or no modification en route to the surface the mechanism controlling helium isotope ratios of other hydrothermal systems appears to be mixing between mantle derived helium and a radiogenic component derived from 4he rich country rock the variable he co2 elemental relationships and 13c co2 values at these localities are consistent with gas separation gas samples or temperature dependent calcite precipitation water samples in shallow level hydrothermal systems both processes result in co2 loss which exacerbates the effects of contamination by crustal gases whereas the aguas calientes locality is useful for understanding the role of the underlying mantle wedge and subducting slab in supplying volatiles to the andean volcanic front the value of the majority of hydrothermal samples in the present study lies with discerning the potentially complicating effects of degassing and or crustal contamination on the resulting he co2 record

hydrothermal systems of the karymsky volcanic centre kamchatka geochemistry time evolution and solute fluxes abstract karymsky volcanic centre kvc at the middle of the frontal volcanic chain of the kamchatka arc consists of two joined calderas akademii nauk and karymsky volcano and hosts two hydrothermal systems akademii nauk an and karymsky k the an is a typical boiling system with na cl waters tds 1 g l low gas content co2 n2 with deep calculated temperatures of 200 c in contrast springs of the k system have lower temperatures up to 42 c strong gas bubbling tds 2 5 g l and are enriched in hco3 and so42 with mg2 as the main cation there are two intriguing characteristics of the k field i their co2 rich gas 97 mol has the highest 3he 4he ratios ever measured for hydrothermal systems in kamchatka of 8 ra where ra 1 4 10 6 and ii their thermal waters have an unusual cation composition mg na ca after the 1996 sublimnic eruption within an caldera new hot springs appeared close to the eruption site in this paper we synthesize all published and new geochemical data sets the karymsky lake and post 1996 new thermal springs demonstrate exponential decreases in their main dissolved species with a characteristic time of 5 to 8 years the chemistry of an and k springs did not change after the eruption however the concentration of chloride in the lake water approached 35 mg l compared with a background of 8 11 mg l revealing a possible new source of hot water within the karymsky lake all thermal fields of the kvc are drained by the karymsky river with an outflow rate at the source of 2 m3 s flowing out from karymsky lake and at the exit from the karymsky caldera of 4 5 m3 s using the measured solute fluxes at the source an springs and at the exit an k springs the natural heat flux from the two systems can be estimated as 67 mw and 120 mw respectively and 20 t d for the chloride output from both systems

the quaternary travertine deposits of europe and asia minor abstract a summary is provided of the published information relating to all aspects of quaternary travertine formation in europe west of the ural mountains the deposits have been divided into two broad groups the meteogene travertines which result primarily from the degassing of soil borne aqueous co 2 and thermogene deposits resulting from the degassing of thermally generated co 2 meteogene deposits are rare above latitude 58 n and in regions where the mean annual air temperature is below 5 c a significant positive correlation exists between mean air temperature and travertine deposit thickness the combined effects of temperature and rainfall are used to provide a zoned map showing the travertine forming potential of limestones within the region information from 14 c dating indicates that deposition reached a maximum in the period 5 10 ka bp and is currently limited by land and water management practices in the populated areas thermogene deposits occur in regions of high co 2 discharge resulting from tectonic activity such as italy and turkey where there is much vulcanism these travertines are frequently more massive and less readily weathered than meteogene deposits fully referenced information is provided for 320 important mostly well studied sites 227 meteogene 93 thermogene of which 156 are currently active

are current models of tufa sedimentary environments applicable to tropical systems a case study from the gregory river abstract tufa formation in the gregory river tropical northern australia is strongly influenced by high evaporation rates perennially warm water temperatures construction behaviour of aquatic insect larvae and regular high magnitude floods these conditions contrast with those of the cool temperate tufa depositing streams for which sedimentary models have already been developed gregory river tufas occur as multiple series of dams separated by waterholes indicating that under all climatic conditions there is a persistence of hydraulic factors in controlling the dam pool sequence in fluvial tufa systems however at the scale of individual tufa deposits and facies the gregory river system displays a deviation away from current models tufa domes upstream dipping ramps calcite rafts and larval facies are all common and important features in both modern and fossil tufas of the gregory river but they are not included in current tufa models thus specific sedimentary models need to be developed for seasonally humid tropical tufa systems to understand their formation and interpret them correctly in the rock record

co2 outgassing and calcite precipitation in falling spring creek virginia u s a abstract chemical and physical observations are presented to explain the evolution of stream water chemistry along the flow path in warm river cave and falling spring creek mixing of two chemically and thermally distinct waters in the cave defines the initial stream water chemistry all along the flow path the observed composition is influenced by outgassing of co2 the water is supersaturated with respect to co2 both in the subsurface and at the surface of the earth but outgassing is greatest in turbulent stretches of the stream above and at the waterfalls the loss of co2 drives the solution to high degrees of supersaturation with respect to calcite physical evidence for calcite precipitation exists in the rimstone dams observed inside the cave and in the travertine deposits above and below the falls along falling spring creek travertine precipitation in the streambed consumes ca2 and hco 3 with most of the precipitation occurring where the stream experiences the most rapid co2 loss the stream water maintains a significant level of supersaturation with respect to calcite over the entire length of the flow path studied

carbon and helium isotopic ratios at kusatsu shirane volcano japan abstract we have measured the chemical compositions he ne ratios he and c isotopes of 14 gas samples collected from the crater lake fumaroles and hot springs associated with kusatsu shirane volcano japan the 3 he 4 he ratio decreases with increasing distance from the central crater of the volcano to the sampling site whereas the 13 c value of co 2 increases with the distance this tendency suggests that high 3 he 4 he low 13 c magmatic gas is mixed with and or diluted by low 3 he 4 he high 13 c crustal gas with increasing distance from the crater alternatively the variation of 13 c values may be the result of isotope fractionation during migration since the isotope shift is relatively small based on the apparent mixing trend in a 3 he 4 he 13 c diagram the magmatic he and co 2 in the volcano may have a 3 he 4 he ratio of 8 r atm and a 13 c value of 3 2 respectively the co 2 3 he ratios show a positive correlation with temperature of fumaroles or hot springs which may be caused by a difference of temperature dependencies of the solubilities between co 2 and he

methane clumped isotopes in the songliao basin china new insights into abiotic vs biotic hydrocarbon formation abiotic hydrocarbon gas typically generated in serpentinized ultramafic rocks and crystalline shields has important implications for the deep biosphere petroleum systems the carbon cycle and astrobiology distinguishing abiotic gas produced by chemical reactions like sabatier synthesis from biotic gas produced from degradation of organic matter or microbial activity is sometimes challenging because their isotopic and molecular composition may overlap abiotic gas has been recognized in numerous locations on the earth although there are no confirmed instances where it is the dominant source of commercially valuable quantities in reservoir rocks the deep hydrocarbon reservoirs of the xujiaweizi depression in the songliao basin china have been considered to host significant amounts of abiotic methane here we report methane clumped isotope values 18 and the isotopic composition of c 1 c 3 alkanes co 2 and helium of five gas samples collected from those xujiaweizi deep reservoirs some geochemical features of these samples resemble previously suggested identifiers of abiotic gas 13 c enriched ch 4 decrease in 13 c 12 c ratio with increasing carbon number for the c1 c4 alkanes abundant apparently non biogenic co 2 and mantle derived helium however combining these constraints with new measurements of the clumped isotope composition of methane and careful consideration of the geological context suggests that the xujiaweizi depression gas is dominantly if not exclusively thermogenic and derived from over mature source rocks i e from catagenesis of buried organic matter at high temperatures methane formation temperatures suggested by clumped isotopes 167 213 c are lower than magmatic gas generation processes and consistent with the maturity of local source rocks also there are no geological conditions e g serpentinized ultramafic rocks that may lead to high production of h 2 and thus abiotic production of ch 4 via co 2 reduction we propose that the songliao gas is representative of an atypical type of thermogenic gas that can be mistaken for abiotic gas such gases may be encountered more frequently in future exploration of deep or over mature petroleum systems

tracing deep thermal water circulation systems in the e w trending buyuk menderes graben western turkey abstract we present information on the spatial variation of helium isotope ratios and several conservative geochemical constituents that serve as natural tracers to identify thermal water flow systems along the e w trending buyuk menderes graben the air normalized r r a ratios where r sample 3 he 4 he and r a air 3 he 4 he of geothermal fluids in the graben range from 3 69 to 0 2 r r a ratios of the high temperature fluids display regular variation along the graben from high mantle values in the east to low crustal values in the west the highest r r a ratios showing significant mantle he signatures occur at the eastern segment of the graben in the central section r r a ratios are lower and vary between 1 82 and 1 14 the lowest ratio of 0 20 r a indicating a value of high crustal helium up to 98 was observed in the germencik field where one of the highest temperatures recorded was 232 c at the western segment of the graben a regional variation is also apparent in the co 2 he systematics mantle derived carbon proportions were found to be generally less than 2 but similar to the r r a ratios the higher mantle carbon proportions occur at the eastern segment of the graben the spatial distribution of all the data points over the entire extent of the graben shows a regularly decreasing trend of mantle derived he and co 2 contributions toward the west these results were interpreted as a progressive dilution process of mantle volatiles resulting from the systematic addition of 3 he depleted crustal co 2 components finally because the r r a ratios of geothermal fluids in the graben decrease continuously in e to w direction we propose a continuous dilution process involving the addition of crustal radiogenic 4 he associated with deep circulating fluid flow this conclusion is compatible with the b and cl concentrations of the thermal waters that show a westward increasing trend this trend appears to be controlled by water rock interaction and may be linked to a possible thermal water circulation system trending from e to w toward the aegean sea

estimating peak currents at ground lightning impacts using remanent magnetization 1 the impact of lightning is permanently recorded in struck material by a secondary magnetization called lightning induced remanent magnetization lirm we introduce an original rock magnetic method based on alternating field demagnetization to define both the geometry and the intensity of the peak lightning magnetic field it also provides positive evidence than a material has effectively been struck on a schoolyard tree struck by lightning we were able to locate the impact to within a few centimeters to prove that it was a vertical negative current and to estimate a peak current intensity of 99 7 ka this value is 14 ka higher than the one provided by meteorage lightning detection network and offers an independent calibration

secular variations of helium and carbon isotopes at galeras volcano colombia copyright c 1997 elsevier science b v all rights reserved we have measured 3 he 4 he 4 he 20 ne and co 2 4 he ratios and d 13 c values of co 2 in eighteen samples from crater fumaroles of galeras volcano colombia and seven samples of bubbling gases of the pandiaco mineral spring located about 8 km east of the volcano from april 1988 to july 1995 the 3 he 4 he ratios of crater fumaroles corrected for atmospheric contamination increased significantly from 5 47 r atm in december 1989 to 7 93 r atm in august 1990 and reached a maximum of 8 84 r atm in may 1992 the ratio then decreased gradually until july 1995 overall variation of helium isotopes appears to be related to the current activity of the volcano the 3 he 4 he ratios of pandiaco mineral spring were constant between april 1988 and november 1991 and increased in april 1993 although experimental error is large the d 13 c values of co 2 of crater fumaroles show negative correlation to the helium isotopes while those of pandiaco are relatively constant based on the d 13 c values and co 2 3 he ratios it is possible to estimate fractions of upper mantle carbon in these samples calculated mantle fractions are 3 10 in crater fumaroles while those in pandiaco spring are negligibly small

he ar n and c isotope compositions in tatun volcanic group tvg taiwan evidence for an important contribution of pelagic carbonates in the magmatic source abstract the tatun volcanic group tvg northeastern taiwan is considered to be the extension of the ryukyu arc and belongs to the post collisional collapse okinawa trough strong hydrothermal activity is concentrated along the chinshan fault and da you keng dyk represents the main fumarolic area where the most primitive isotopic and chemical composition is observed in this study we present chemical and he ar c and n isotopic compositions of fumaroles bubbling gas and water from hot springs sampled in 2012 and 2013 high 3 he 4 he ratios from dyk fumaroles 6 5 ra show a typical arc like setting whereas other sampling areas show a strong dependence of 3 he 4 he and ch 4 3 he ratios with the distance from the main active hydrothermal area dyk this could mean strong crustal contamination and thermal decomposition of organic matter from local sediments carbon isotope compositions of dyk range from 6 67 to 5 85 and indicate that carbon contribution comes mainly from pelagic carbonates from the slab limestone mantle and sediment contributions are 63 19 and 18 respectively this is consistent with the negative 15 n values 1 4 0 5 observed for dyk implying a strong nitrogen mantle contribution and an absence of contribution from nitrogen pelagic carbonates these results have important consequences related to the ryukyu subducted slab in fact the ryukyu margin presents little in off scraping the sedimentary cover to the subducting plate that does not permit any nitrogen contribution in magma from tvg

mineral solubility and aqueous speciation under hydrothermal conditions to 300 c the carbonate system as an example carbon is a major element in the earth s system and plays an important role in many geochemical processes including metamorphism volcanism oceanic systems and atmospheric evolution knowledge and understanding of chemical speciation mineral solubility and reactivity involving carbon are very important in order to qualitatively and quantitatively understand these processes indeed dissolved inorganic carbon is among the major components of natural geothermal fluids it originates from various sources including magmatic degassing rock dissolution and organic matter degradation e g giggenbach 1992 giggenbach et al 1993 simmons and cristenson 1994 sanoa and marty 1995 dissolved co2 is the most common form of dissolved inorganic carbon in these systems though other forms exist like ch4 and co but usually in much lower concentrations than co2 e g chiodini and marini 1998 stefansson and arnorsson 2002 the concentrations of dissolved inorganic carbon dic in geothermal fluids from active geothermal systems throughout the world are shown in figure 1a together with the ph of the fluids in general the dic concentration increases in geothermal fluids with increasing temperature from a few mmol per kg up to half a mole per kg of fluid this increase is accompanied by a decrease in the fluid ph fig 1b higher concentrations not shown are observed in fumarole fluids discharging volcanic gases e g chiodini et al 1996 at earth s surface co2 also degasses through the soils in active geothermal systems e g chiodini et al 1998 the chemistry and transport of dic in natural geothermal systems is influenced by many processes including magma degassing water rock interaction and partitioning of co2 between liquid and vapor phases upon boiling and phase separation it has been concluded that the concentration of dic and all other major elements besides incompatible elements such as cl are

regional and temporal variations in co2 3he 3he 4he and δ13c along the north anatolian fault zone turkey abstract new he and c relative abundance isotope and concentration results from nine geothermal locations situated along an 800 km transect of the north anatolian fault zone nafz turkey that were monitored during the period november 2001 november 2004 are reported the geothermal waters were collected every 3 6 months to study possible links between temporal geochemical variations and seismic activity along the nafz at the nine sample locations the he isotope ratios range from 0 24 to 2 3 r a 13 c values range from 4 5 to 5 8 and co 2 3 he ratios range from 5 10 9 to 5 10 14 the following geochemical observations are noted 1 the highest 3 he 4 he ratios are found near the galatean volcanic region in the central section of the nafz 2 at each of the nine sample locations the 3 he 4 he ratios are generally constant however co 2 3 he ratios and he contents both show one order of magnitude variability and 13 c values show up to 4 variability and 3 at all locations except resadiye 13 c values show positive correlations with co 2 contents the results indicate that at least three processes are necessary to account for the geochemical variations 1 binary mixing between crustal and mantle derived volatiles can explain the general characteristics of 3 he 4 he ratios 13 c values and co 2 3 he ratios at the nine sample locations 2 preferential degassing of he from the geothermal waters is responsible for variations in co 2 3 he values and he contents at each sample location and 3 co 2 dissolution followed by calcite precipitation is responsible for variations in co 2 contents and 13 c values at most locations for each of the geochemical parameters anomalies are defined in the temporal record by values that fall outside two standard deviations of average values at each specific location geochemical anomalies that may be related to seismic activity are recorded on june 28 2004 at yalova where a m 4 2 earthquake occurred 43 days earlier at 15 km distance from the sample location and on april 7 2003 at efteni where a m 4 0 earthquake occurred 44 days later at a distance of 12 km at both locations the sampling periods containing geochemical anomalies were preceded by an increase in m 3 earthquakes occurring within 60 days and less than 40 km distance

magnetic petrology of deep crustal rocks ivrea zone italy magnetic petrology is an extension of petrology integrating magnetic property studies with conventional petrology for the purpose of understanding the development and modification of the magnetization in rocks the magnetic properties of a suite of samples from the ivrea zone northern italy are described with the aim of developing a magnetic petrology for deep crustal rocks samples studied include a variety of metamorphosed mafic granulites granofelses plagioklasfelse amphibolite pyriclasite and pelitic quartzo feldspathic rocks acid granulites stronalite and kinzigite gneisses schists and representative ultramafic rocks phlogopite peridotite pyroxenite hornblendite ilmenite is the chief oxide mineral in a majority of the samples but in a few mafic rocks magnetite is the principal oxide constituent cr al spinel is common in ultramafic samples and rutile is present in some metapelites sulfides are generally subordinate in abundance to oxide minerals the mafic rocks in the ivrea section have the broadest range of magnetic properties and include the most strongly magnetic samples the ivrea ultramafic rocks are moderately magnetic the magnetite present appears to be secondary and is associated with crustal alterations while pelitic and quartzo feldspathic lithologies are dominantly paramagnetic or only weakly magnetic the main ferromagnetic mineral in all strongly magnetic samples is magnetite that is nearly pure fe3o4 in composition consequently curie temperatures are 565 580 c for these rocks pyrrhotite contributes to the magnetism in several ultramafic and mafic rocks and it is the sole ferromagnetic mineral in the pelitic and quartzo feldspathic samples the results of our study indicate that certain mafic rock types amphibolites mafic granulites pyriclasites are the most likely source of the ivrea zone s regional scale magnetic anomalies if the ivrea zone represents a tectonically exposed cross section of continental crust the geographic distribution of these rock types suggests the presence of multiple and variably thick strongly magnetic layers with magnetite curie temperatures in the deep crust petrographic evidence suggests however that the magnetic mineralogy of the sampled ivrea rocks might have been changed subsequent to peak metamorphic conditions therefore considerable care must be taken in evaluating the magnetic record in these crustal cross sections particularly if they are to be used to model the magnetic characteristics of the lower crust

geochemistry of gas and water discharge from the magmatic hydrothermal system of guallatiri volcano northern chile this work presents the first chemical and isotopic 13c co2 13c ch4 3he 4he 20ne 40ar 36ar 18o and d data for fluid discharges from guallatiri volcano a remote and massive stratovolcano which is considered as the second most active volcano of the central volcanic zone cvz in northern chile fumarolic gases had outlet temperatures of between 80 2 and 265 c and showed a significant magmatic fluid contribution marked by the occurrence of so2 hcl and hf that are partially scrubbed by a hydrothermal aquifer the helium isotope ratios 3 2 were relatively low compared to those of other active volcanoes in cvz possibly due to contamination of the magmatic source by 4he rich crust and or crustal fluid addition to the hydrothermal reservoir geothermometry in the h2o co2 co h2 ch4 system suggests equilibrium temperatures of up to 320 c attained in a vapor phase at redox conditions intermediate between those typical of hydrothermal and magmatic environments thermal springs located 12 km northwest of the volcano s summit had outlet temperatures of up to 50 1 c neutral to slightly basic ph and a sodium bicarbonate composition typical of distal fluid discharges in volcanic systems cold springs at the base of the volcanic edifice showing a calcium sulfate composition were likely produced by interaction of shallow meteoric water with co2 and h2s rich gases a geochemical conceptual model was constructed to graphically represent these results which can be used as an indication for future geochemical monitoring and volcanic hazard assessment

the na ca amphibole albite chlorite epidote quartz geothermobarometer in the system s a f m c n h2o 1 an empirical calibration the proposed geothermobarometer is based on an empirical calibration which takes account of two equilibria involving the tremolite edenite pargasite and hastingsite components in amphiboles it has applications to assemblages found in metabasic rocks of widely different chemical compositions magnesian to fe rich metabasalts and for metamorphism ranging from lower greenschist to highest amphibolite facies knowing the si t1 aliv alvi fe3 fe2 mg ca nam4 naa and a vacancy in an amphibole and the al3 and xmg in coexisting epidote and chlorite it is possible to calculate two values of in kd for this assemblage these equilibria involve edenite tremolite and pargasite hastingsite tremolite end members in amphibole the calculation program is given for these equilibria the isopleths iso values of kd have been calculated for 0 27 xmg 0 75 and 0 xfe3 fe3 fe3 alvi 0 8 it is then possible to determine pressure and temperature directly when xmg xfe3 in kd for tremoliteedenite and in kd for pargasite hastingsite tremolite are known application of this geothermobarometer is limited to ca free plagioclase assemblages and complete p t paths can be drawn only if all the minerals are considered together phase relations at successive stages of crystallization can be constrained by studying the relationships between the coexisting minerals their zoning and the metamorphic fabrics

fluid geochemistry of the cuopu high temperature geothermal system in the eastern himalayan syntaxis with implication on its genesis abstract high temperature geothermal fluids dissolve constituents pertinent to water rock interaction and magmatic volatile absorption resulting in high total dissolved solid tds values however this study focuses on the hydrochemical evolution of the low salinity hco3 na type high temperature geothermal fluid in cuopu eastern himalayas the geothermal water is recharged by local precipitation and glacier water from surrounding mountains the tds values are below 834 mg l and the constituents are mainly products of the water carbon dioxide rock interactions lacking magmatic volatile dissolved in the fluid the geothermal water reaches an almost complete chemical equilibrium with the feldspar or plagioclase enriched reservoir rock in a reducing condition the reservoir temperature is between 175 c 200 c while the temperature could reach up to 400 c in the deep crustas indicated by the carbon isotopic exchange equilibrium between co2 and ch4 the infiltrated glacier water was heated during its circulation within the hot thickened crust and continued dissolving the crustal metamorphic gas such as radiogenic helium and limestone metamorphic co2 until the junction of the two sets of faults provided an ascending channel for it upon rising along the conduit the geothermal water mixed with cold groundwater to different degrees approximately 0 015 mol l co2 escaped from the geothermal fluid when it scattered as bubbling hot springs on the surface of the anisotropic porous quaternary sediments such kind ofhydrochemical evolution of lowsalinity alkaline hco3 na type water represents a typical formation mechanism of the high temperature geothermal systems along the himalayas

origin of hydrocarbon and noble gases carbon dioxide and molecular nitrogen in devonian pennsylvanian and miocene strata of the polish lublin and ukrainian lviv basins southern part of the upper silesian coal basin and western part of the carpathian foredeep poland abstract sixteen natural gas samples were collected from devonian pennsylvanian and miocene strata of the polish lublin and ukrainian lviv basins from the southern area of the upper silesian coal basin uscb and western part of the carpathian foredeep cf in poland the samples were analysed for the molecular composition and stable isotope compositions of gaseous hydrocarbons ch4 c2h6 and c3h8 and co2 n2 and noble gases he ne ar kr and xe in order to reveal the origin and migration pathways of these gases hydrocarbon gases and the majority of the of co2 were generated during two stages of thermogenic processes from type ii and ii iii kerogens in the lublin basin and during both thermogenic and microbial processes in the lviv basin the thermogenic component was generated from type ii kerogen coal bed hydrocarbon gases accumulated in the pennsylvanian strata of the southern part of the uscb originated from both thermogenic and microbial processes isotopically light microbial methane may have migrated from miocene upper badenian skawina formation of the cf to carboniferous coal bearing strata and or might result from diffusion and adsorption desorption processes during the migration of thermogenic gases from deeper lying coal seams through the microporous coal structure hydrocarbon gases and carbon dioxide which accumulated in the sandstone reservoirs of upper badenian skawina formation of the western part of the cf most probably were generated from dispersed organic matter within the claystones and mudstones of these strata and at least partly migrated from the carboniferous coal bearing strata of the uscb n2 could have been produced as a result of various biogenic and abiogenic processes and contributed to the atmospheric component characteristic radiogenic 4he composition of the analysed gases suggest the accumulation of particles formed from u and th radioactive decay in the crustal gas reservoirs radiogenic 40ar and nucleogenic 21ne with abundance ratios characteristic of crustal reservoirs were also observed addition of mantle derived he to the gases from miocene strata is evident from elevated 3he 4he ratios ranging between 0 2 and 1 6 10 6 a small contribution of ne from the mantle along with he is also suggested by the slightly elevated 20ne 22ne ratios relative to atmosphere the mantle component is most likely to have migrated from the upper mantle to the gas reservoirs through the deep seated bzie czechowice fault zone

magnetism at depth a view from an ancient continental subduction and collision zone recent sophisticated global data compilations and magnetic surveys have been used to investigate the nature of magnetization in the lower crust and upper mantle two approaches to constraining magnetizations are developed providing minimum 0 01 si and maximum 0 04 si susceptibility estimates given some assumed thickness 15 km here these values are higher than are found in many continental rocks are there rocks deeper in the crust or upper mantle that are more magnetic than expected or are the model assumptions incomplete what is the magnetic behavior of deep crustal and upper mantle rocks when slightly cooler than the curie or neel temperatures of their magnetic minerals after being exhumed from locations of high grade metamorphism at greater depth different sets of equilibrium metamorphic minerals can be considered that would form under different conditions results on 1501 samples from the western gneiss region wgr norway mainly from mafic and ultramafic bodies subducted to depths of 60 200 km and temperatures of 750 up to 950 c at the very highest pressures show that rocks did not fully equilibrate to the dominant metamorphic facies conditions there is a large variation in petrophysical properties oxide minerals and mineral assemblages in wgr samples though they cannot explain the broad high amplitude deep seated anomalies measured in this region the presence of magnetite and exsolved titanohematite and hemo ilmenite in samples shows those magnetic phases are preserved even at eclogite facies conditions in part because complete eclogite facies equilibrium was rarely achieved

carbon sources in arc volcanism with implications for the carbon cycle new co2 3 he data from the east sunda arc indonesia confirm earlier observations that arc volcanic gases have higher co2 3 he ratios than mor environments on average 80 of arc volcanic co2 is recycled exogene carbon addition of a few percent of carbonate bearing sediments to the mantle wedge explains much of the carbon abundance andcarbon isotopic data of arc gases but can not explain the he isotope observations the co2 3he in arc volcanoes is not strongly dependent on the composition of modem trough sediments e g deep sea clays vs carbonate rich sequences and calcite veins in the hydrothermally altered subducted slab may provide a contribution to the recycled carbon flux of arcs the sum of globally deep subducted sediment and slab carbon exceeds the estimated arc co2 flux and approximately 3 5 teramole of carbon may return annually to the mantle in convergent zones the modem combined processes of mor volcanism slab alteration and subduction volcanism do not produce a substantial carbon flux into the exosphere and rate changes in ocean floor spreading are unlikely to cause major changes in atmospheric co2 as a result of changes in the volcanic co2 fluxes intense pulses of flood basalt volcanism however may alter the co2 contents of the atmosphere over the course of a millenium or so and influence global climate

magnetic petrology of high fe ti eclogites from the ccsd main hole implications for subduction zone magnetism 1 the high fe ti eclogites with exsolved lamellar in 530 600 m depths from the chinese continental scientific drilling ccsd main hole in the sulu ultra high pressure uhp metamorphic belt eastern china record an anomalously high susceptibility natural remanent magnetization nrm and koenigsberger ratio q nrm ji ji is induced magnetization this provides us with a good opportunity to study the effects of magnetic minerals and exsolution lamellae on the magnetic properties of deep rocks in this paper we have measured systematically magnetic properties and mineral assemblage and structure for three special samples no 83 no 86 and no 89 results show that these fe ti rich eclogites are the result of the fine grained titano magnetite exsolution in pyroxene and lamellar structure consisting of finely interlayered ilmenite and hematite in exsolved hemo ilmenite we found that the dominant fe bearing oxide minerals in samples studied are ilmenite hematite hem ilm up to 25 little titano magnetite and pyrite the ferromagnetic susceptibility is mainly controlled by fine grained titano magnetite and nrm is closely related to the exsolved lamellar structure we hence propose that the anomalous magnetism of these eclogites observed in our samples is the result of exsolution from homogenous pyroxene and ilmeno hematite during cooling and decompression processes these fe ti rich eclogites might be one of the sources of high magnetic anomalies observed in the sulu subduction zone eastern china

major and rare gases at white island volcano new zealand origin and flux of volatiles analyses of fumarolic gases at white island new zealand are reported with special emphasis on rare gases he ne ar kr and xe normalization of major species to rare gases have lead to the identification of several sources air saturated meteoric or marine water a magma body the crust and or sediments when compared to mid ocean ridge discharges the white island gas discharge represents about 3 0 7 0 1 and 0 05 of the global water carbon sulfur and helium 3 discharges respectively this balance shows that except for 3he which derives from the mantle practically all rare gases water and carbon and part of sulfur derive from originally superficial sources

wasp waisted hysteresis loops mineral magnetic characteristics and discrimination of components in mixed magnetic systems rock magnetic studies of complex systems that contain mixtures of magnetic minerals or mixed grain size distributions have demonstrated the need for a better method of distinguishing between different magnetic components in geological materials hysteresis loops that are constricted in the middle section but are wider above and below the middle section are commonly observed in mixed magnetic assemblages such wasp waisted hysteresis loops have been widely documented particularly with respect to rare earth permanent magnets basaltic lava flows remagnetized paleozoic carbonate rocks and an increasingly wide range of other rocks our modelling combined with a review of previous work indicates that there are several conditions that give rise to as well as magnetic properties that are characteristic of wasp waisted hysteresis loops first at least two magnetic components with strongly contrasting coercivities must coexist this condition can arise from either mixtures of grain sizes of a single magnetic mineral or a combination of magnetic minerals with contrasting cocrcivities or a combination of these two situations second materials that give rise to wasp waisted hysteresis loops will have relatively high ratios of the coercivity of remanence to coercive force b cr b c because b0 is controlled by the soft low coercivity component whereas bcris controlled by the hard high coercivity component third values of b cr b c 10 usually only occur for strongly wasp waisted loops when the low coercivity component comprises an overwhelmingly large fraction of the total volume of magnetic grains fourth a given mixture of superparamagnetic and single domain sd grains is more likely to give rise to wasp waisted hysteresis loops than an equivalent mixture of sd and multidomain grains fifth our results provide empirical confirmation that the total magnetization of a material is the sum of the weighted contributions of each component in the absence of significant magnetic interaction between particles thus to contribute significantly to wasp waisted behavior a mineral magnetic component must give rise to a significant portion of the total magnetization of the rock as a result minerals with weak magnetic moments such as hematite need to occur in large concentrations to cause wasp waistedness in materials that also contain ferrimagnetic minerals we outline a method for determining the magnetic components that can give rise to wasp waisted hysteresis loops this method is based on high and low temperature magnetic measurements that are used to identify the dominant remanence bearing mineral s and on mineral magnetic techniques that are used to discriminate between different magnetic domain states the method is illustrated with several examples from archaeological geological and synthetic materials

the 2012 2016 eruptive cycle at copahue volcano argentina versus the peripheral gas manifestations hints from the chemical and isotopic features of fumarolic fluids this study presents the chemical and isotopic compositions of hydrothermal gases from fumaroles discharging around copahue volcano argentina gas samples including those from two fumaroles at the active summit crater were collected during 13 surveys carried out by different research teams from 1976 to february 2016 the time series of h2 co and light hydrocarbons showed episodic increases related to the main events of the last eruptive cycle that started on 19 july 2012 concentration peaks were likely caused by enhanced input of hot magmatic fluids affecting the hydrothermal reservoir these data contrast with the temporal variations shown by rc ra and 13c co2 values in 2012 2014 which indicated an increasing input from a crustal fluid source in 2015 2016 however these isotopic parameters showed opposite trends their composition became closer to that of the two summit fumaroles which possibly corresponds to that of the deep magmatic related end member the delayed and reduced compositional changes in the peripheral hydrothermal fluid discharge in response to the 2012 2016 eruptive events suggest that geochemical surveys of these emissions are unlikely to provide premonitory signals of volcanic unrest if the volcanic activity remains centered in the main crater instead an instrument which is able to provide measurements of volcanic gases in the air e g multigas may be used to detect changes at the summit crater otherwise monitoring of seismic activity and ground deformation as well as the periodic measurement of the chemistry of the water in the rio agrio which is fed by thermal discharge from the summit crater seem to represent the most reliable means of monitoring at copahue however the relative compositional stability of the hydrothermal reservoir is a great advantage in terms of geothermal resource exploitation and could encourage new investments in the copahue geothermal project which was abandoned in the 1990s

he n and c isotopes and fluxes in aira caldera comparative study of hydrothermal activity in sakurajima volcano and wakamiko crater kyushu japan abstract we investigate the degassing activity of an active submarine crater wakamiko and an active sub aerial volcano sakurajima both located in aira caldera southern kyushu japan we provide 3he 4he 13c co2 and 15n data for 15 hot springs wells and bubbling gas from sakurajima volcano along with 3he 4he from seawater at four different sites for both kagoshima bay and wakamiko crater we find a common magmatic 3he 4he ratio for sakurajima and wakamiko 7 2 0 8 ra which is consistent with 1 a mixing between air saturated water asw and morb type he and 2 a common magmatic source located in the center of aira caldera corrected 3he 4he 13c co2 and ch4 3he data for sakurajima are correlated with the distance from the volcanic vent showa crater which we attribute to crustal contamination and biogenic reaction the low 13c co2 values 10 1 0 2 to 13 7 0 3 observed at sakurajima may result from the addition of carbon from organic matter from basement rocks in magmatic source after correction for air derived nitrogen we find 15nc values range between 1 7 and 4 3 which indicates that magmatic n is dominated by a sedimentary derived component up to 65 8 we calculate wakamiko fluxes of 4he 975 228 mol y 3he 0 011 0 003 mol y co2 184 43 t d and heat 195 22 mw our helium and heat fluxes are the first in situ fluxes ever reported for wakamiko crater all these wakamiko fluxes are at least one order of magnitude lower than those observed for sakurajima co2 1800 t d 3he 0 71 mol y heat 2100 mw degassing at sakurajima volcano is much stronger than that at wakamiko crater the variation of sakurajima co2 flux with time source minamidake or showa crater and eruptive activity appears not to significantly affect the co2 flux at wakamiko crater which is much more stable 132 307 t d during the last 30 years this indicates that there is no link between sakurajima and wakamiko degassing activity despite having the same magmatic source

origins of methane discharging from volcanic hydrothermal geothermal and cold emissions in italy abstract we have addressed the origins of methane in fumarolic thermal and cold emissions discharging from a diversity of geological settings spread all over the italian peninsula and at panarea and pantelleria islands fluid discharges from the main geothermal systems of the peri tyrrhenian area including mt amiata larderello latera and manziana show 13c ch4 and d ch4 values 28 v pdb and 160 v smow respectively and c1 c2 concentration ratios 1000 these patterns suggest that ch4 discharged from these systems is primarily generated by abiogenic reduction of co2 and or co methane seems to have at least partially a different origin than the higher hydrocarbons that might be entirely related to the thermal decomposition of organic matter or alternatively to methane polymerization fumaroles from the volcanic systems of solfatara vesuvio panarea and pantelleria have c1 c2 concentration ratios in a wide range from 17 to 4300 but 13c ch4 and d ch4 values 21 v pdb and 120 v smow respectively such isotopic values are very similar to those reported for ch4 discharging from ultramafic hydrothermal systems in agreement with recent evidence provided for solfatara and pantelleria we therefore infer that the ch4 in the volcanic fumaroles is mainly abiogenic too the 13c ch4 from 21 6 to 36 9 v pdb and d ch4 from 113 to 164 v smow values as well as the c1 c2 concentration ratios from 19 to 2240 in the co2 rich fluid discharges located between the geothermal volcanic systems and the apennine sedimentary chain tend to decrease eastwards as the temperatures of the fluid reservoirs progressively diminish suggesting that the ch4 production is mainly related to thermogenic processes according to this general trend the ch4 dominated fluids from mud volcanoes located eastwards of the co2 rich emissions are fed by an almost pure thermogenic source the easternmost fluid discharges from the po valley and the adriatic coast where organic matter evolves at relatively shallow depths in the presence of a low geothermal gradient record the lowest 13c ch4 and d ch4 values i e as low as 69 v pdb and

key factors controlling massive graphite deposition in volcanic settings an example of a self organized critical system massive graphite deposition resulting in volumetrically large occurrences in volcanic environments is usually hindered by the low carbon contents of magmas and by the degassing processes occurring during and after magma emplacement in spite of this two graphite deposits are known worldwide associated with volcanic settings at borrowdale uk and huelma spain as inferred from the borrowdale deposit graphite mineralization resulted from the complex interaction of several factors so it can be considered as an example of self organized critical systems these factors in turn could be used as potential guides for exploration the key factors influencing graphite mineralization in volcanic settings are as follows 1 an unusually high carbon content of the magmas as a result of the assimilation of carbonaceous metasedimentary rocks 2 the absence of significant degassing related to the presence of sub volcanic rocks or hypabyssal intrusions acting as barriers to flow 3 the exsolution of a carbon bearing aqueous fluid phase 4 the local structural heterogeneity represented at borrowdale by the deep seated burtness comb fault 5 the structural control on the deposits implying an overpressured fluid rich regime favouring a focused fluid flow 6 the temperature changes associated with fluid flow and hydration reactions resulting in carbon supersaturation in the fluid and leading to disequilibrium in the system this disequilibrium is regarded as the driving force for massive graphite precipitation through irreversible mass transfer reactions therefore the formation of volcanic hosted graphite deposits can be explained in terms of a self organized critical system