initial tectonothermal evolution within the scandinavian caledonide accretionary prism constraints from40ar 39ar mineral ages within the seve nappe complex sarek mountains sweden in the caledonide orogen of northern sweden the seve nappe complex is dominated by rift facies sedimentary and mafic rocks derived from the late proterozoic baltoscandian miogeocline and offshore continent iapetus transition metamorphic breaks and structural inversions characterize the nappe complex within the sarek mountains the sarektjakka nappe is composed of c 600 ma old dolerites with subordinate screens of sedimentary rocks these lithological elements preserve parageneses which record contact metamorphism at shallow crustal levels the sarektjakka nappe is situated between eclogite bearing nappes mikka and tsakkok nappes which underwent high p metamorphism at c 500 ma during westward subduction of the baltoscandian margin 40ar 39ar mineral ages of c 520 500 ma are recorded by hornblende within variably foliated amphibolite derived from mafic dyke protoliths within the sarektjakka nappe plateau ages of 500 ma are displayed by muscovite within the basal thrust of the nappe and are consistent with metamorphic evidence which indicates that the nappe escaped crustal depression as a result of detachment at an early stage of subduction cooling ages recorded by hornblende from variably retrogressed eclogites in the entire region are in the range of c 510 490 ma and suggest that imbrication of the subducting miogeocline was followed by differential exhumation of the various imbricate sheets hornblende cooling ages of 470 460 ma are recorded from massive dyke protoliths within the sarektjakka nappe these are similar to ages reported from the seve nappe complex in the central scandinavian caledonides probably these date imbrication and uplift related to early ordovician arrival of outboard terranes e g island arc sequences represented by structurally lower horizons of the koli nappes metamorphic contrasts and the distinct grouping of mineral cooling ages suggest that the various seve structural units are themselves internally imbricated and were individually tectonically uplifted through argon closure temperatures during assembly of the seve nappe complex the cooling ages of 520 500 ma recorded within seve terranes and along terrane boundaries of the sarek mountains provide evidence of significant accretionary activity in the northern scandinavian caledonides in the late cambrian early ordovician

metamorphic consequences of thrust emplacement fall mountain new hampshire metamorphic pressure temperature p t paths from the upper and lower plates of the fall mountain nappe southwest new hampshire reveal different thermal histories in the two structural levels upper plate rocks experienced early low p high t contact metamorphism to peak p t conditions of 700 750 c 3 4 5 kbar these p t conditions were followed by loading to approximately 5 6 kbar and then by nearly isobaric cooling to approximately 500 c 4 5 kbar upper plate rocks then experienced minor heating with unloading and finally cooling the lower plate rocks also experienced early low p high t contact metamorphism but only to p t conditions of 480 510 c 2 3 5 kbar nappe emplacement resulted in nearly isothermal loading to 500 c 5 6 kbar which was followed by either heating or cooling depending on the proximity of the sample to the upper plate the early pressures recorded in both the upper and lower plate rocks suggest a depth of approximately 10 km for origination of the nappe the post nappe pressures 5 6 kbar imply a total tectonic thickness of approximately 20 km or a doubling of the overburden thickness diffusion calculations suggest that the emplacement of the nappe took less than approximately 10 m y and u pb chronology on zircon suggests that it occurred between 400 and 410 ma 4o ar 39 ar cooling ages on micas indicate that the terrane was cooled to approximately 300 c by 340 ma

a comparison of shear and buoyancy driven planetary boundary layer flows abstract planetary boundary layer pbl flows are known to exhibit fundamental differences depending on the relative combination of wind shear and buoyancy forces these differences are not unexpected in that shear instabilities occur locally while buoyancy force sets up vigorous thermals which result in nonlocal transport of heat and momentum at the same time these two forces can act together to modify the flow field in this study four large eddy simulations less spanning the shear and buoyancy flow regimes were generated two correspond to the extreme cases of shear and buoyancy driven pbls while the other two represent intermediate pbls where both forces are important the extreme cases are used to highlight and quantify the basic differences between shear and convective pbls in 1 flow structures 2 overall statistics and 3 turbulent kinetic energy tke budget distributions results from the two intermediate les cases are used to develop and verify a velocity scaling and a tke budget mode

evidence of multiple halogen sources in scapolites from iron oxide copper gold iocg deposits and regional nacl metasomatic alteration norrbotten county sweden abstract scapolites from barren regional na cl metasomatic assemblages rm iron oxide copper gold deposits iocg scapolite altered metabasic rocks iocg m and from iocg proximal alteration na skarns iocg ps from norrbotten county in northern sweden have been analysed for halogen content and cl stable isotope composition the aim of the study was to constrain the source of halogens within alteration assemblages and to investigate the possible fractionation of cl isotopes between scapolite and the hydrothermal fluid scapolite separates were analysed for cl br and major oxide concentrations using electron probe micro analysis epma and micro x ray fluorescence xrfm spectrometry chlorine was extracted from the scapolite separates via pyrohydrolysis and then analysed for their stable cl isotope compositions by isotope ratio mass spectrometry irms all samples of scapolite investigated in this study are marialitic in composition one of the scapolites from the gruvberget deposit iocg ps had a cl br molar ratio of 2363 which is the highest amongst all scapolites reported in the literature to date cl br molar ratios lower than seawater 650 were identified in two iocg ps scapolite samples cl br 554 and 271 as well as in two iocg m scapolites cl br 393 and 565 three rm scapolites had cl br molar ratios very close to or slightly higher than seawater values 639 to 770 samples with cl br molar ratios less than seawater are inferred to have halogens derived from evaporative residual brines whereas samples with molar ratios higher than seawater may have halogens derived from fluids that have dissolved halite and or are from magmatic systems considering the wide variation of the cl br molar ratios in the iocg ps and iocg m scapolites compared to the restricted composition of the regional alteration rm it is proposed that the hydrothermal fluids interacted with several different protoliths to generate the iocg alteration rm alteration scapolites had 37 cl values from 0 1 to 0 3 two iocg m scapolites had values of 0 2 and iocg ps scapolites had 37 cl values from 0 1 to 1 0 using a previously published 37 cl value from fluid inclusion leachates 1 7 from the iocg m mineralisation at pahtohavare and the 37 cl value of co existing scapolite measured in this study 0 2 an empirical fluid scapolite fractionation factor was calculated to be 1 9 this large fractionation factor is not supported by previous predictions for monovalent chlorides and assuming equilibrium indicates that 37 cl was preferentially accommodated in the a site of the scapolite structure this indicates that either the stable cl isotope partitioning between the cacl 2 rich brine and the scapolite may differ from currently available estimates for nacl brines in equilibrium with silicate minerals or that the scapolite and brine are not in isotopic equilibrium overall the data in this study suggest that halogens in early scapolites were derived from residual brines and halite during metamorphism of evaporites linked to the rm alteration later in the history of the norrbotten district components of the rm alteration were recycled and mixed during magmatic and local metasomatic events to varying extents resulting in the brines associated with iocg alteration

signature of ongoing brine reinjection on noble gas isotopes and fluid chemistry at las tres virgenes geothermal field mexico abstract a geochemical survey of the las tres virgenes geothermal field ltvgf baja california sur mexico was carried out to determine the origin and evolution of its fluids along with the influence of injection of local brines and inhibitors intended to manage carbonate scaling issues major and minor cations cl br sr o h and noble gas he ne ar kr and xe isotopes were measured in fluids collected from four production wells two injection wells and one fumarole el azufre in 2016 and 2018 variations in the stable isotopes of water d and 18o and halogens 37cl 81br over the years suggest that local brine reinjection might have started to modify the pristine chemistry of the fluids however relevant information on the original geothermal fluids has been preserved the na br and cl br ratios suggest that ltvgf brines are seawater having leached evaporite deposits halite these deposits are absent in the area but were likely present during the miocene prior to the breakup of the gulf of california suggesting that the saline fluid end member at the ltvgf could be several million years old measured 3he 4he ratios r normalized to the atmospheric ratio ra 1 384 10 6 plotted against the 4he 20ne ratios suggest mixing between a mantle fluid with a r ra of 6 19 typical of the sub continental lithospheric mantle and an atmospheric helium component the r ra versus the 132xe 36ar ratio normalized to air suggests mixing between a mantle rich pre production fluid and air the source of air appears to be linked to local gravity controlled flow reinjection which causes the entrapment of air bubbles leading to a fluid supersaturated in atmospheric noble gases this pattern suggests that reinjection fluids are impacting the production area

hydrochemical and isotopic δ18o δ2h 87sr 86sr δ37cl and δ81br evidence for the origin of saline formation water in a gas reservoir abstract the permo triassic kangan gasfield in southern iran is composed of an aquifer the kangan aquifer ka and an overlying gas reservoir it is located in the kangan and dalan formations and consists predominantly of limestone and dolomite the kangan gasfield is exploited from 36 wells at depths from 2300 to 2860 m the quality of the produced formation waters pfw varies from fresh to saline with salinities of up to 60 000 mg l the present study aims to identify the origin of the salinity of the pfws the concentration of major ions li sr and br as well as 18o d 87sr 86sr 37cl and 81br isotope compositions of the ka water and pfw samples a fresh and a brine spring and the persian gulf water were all measured the suite of isotopic 37cl and 81br and hydrochemical data li cl and br concentrations and cf index in this study indicates that the salinity origin of the pfws is evaporated seawater which could be either the ka water or the intergranular saturated brine in the kangan gas reservoir kgr both derived from permo triassic evaporated seawater 18o and 87sr 86sr data exclude the ka water as the source of the saline pfw leaving the intergranular brine of the kgr as the most likely source although further isotopic and geochemical tests are needed to verify this this work also proposes for the first time the use of a li cl versus br cl diagram to distinguish between evaporate formation water water modified by halite dissolution and fresh water it is recommended to apply these comprehensive methods to deep brine aquifers especially related to gasfields

an observational study of the evolution of horizontal convective rolls abstract a comprehensive observational dataset encompassing the entire temporal evolution of horizontal convective rolls was obtained for the first time florida illinois and kansas measurements from preroll conditions through the development of well defined rolls to their dissipation were utilized to determine the factors influencing roll evolution when the buoyancy flux reached a critical value of 35 50 w m 2 the first form of boundary layer convection resolved by radar was rolls it was noted that two dimensional convective rolls can evolve in a convective boundary layer in the absence of significant wind speed and shear in fact the value of wind speed or shear in itself did not seem to determine when or if rolls would form although it did influence roll evolution well defined two dimensional rolls only occurred while zi l where zi is the convective boundary layer depth and l is the monin obukhov length was less than 25 which is consistent with previous studies as zi l increased through

chlorine isotopic compositions of high temperature hydrothermal vent fluids over ridge axes abstract we present chlorine stable isotope compositions of high temperature hydrothermal vent fluids from two mid oceanic ridges the six hydrothermal fluids come from sites along the slow spreading mid atlantic ridge menez gwen at 37 50 n lucky strike at 37 17 n and rainbow at 36 14 n and the ultrafast spreading east pacific rise from three contiguous segments centered respectively at 17 25 s 18 15 s and 18 26 s these samples exhibit a large range in temperature ph chlorinity and mg content reflecting various geological settings and substrata nature basaltic or ultramafic although showing a large range of chlorinity from 251 to 821 mmol kg the fluids display homogeneous chlorine isotope signatures 37 cl smoc 0 03 0 06 indistinguishable from that of seawater this homogeneity contrasts with the large range of 37 cl previously observed in continental or off axis oceanic fluids this study explores possible processes that may change cl concentration during fluid genesis and discusses their theoretical isotopic effects the 37 cl homogeneity implies that at the p t conditions of the ridge axis the process of phase separation at sub or super critical conditions that explains most of chlorinity variations does not significantly fractionate chlorine isotopes this study shows that the physical and chemical processes that likely alter cl concentrations in ridge axis systems i e transport processes mixing or water rock interaction contribute to minimize the range of 37 cl around the seawater 37 cl value

an integrated modelling approach to reconstruct complex solute transport mechanisms cl and δ37cl in pore water of sediments from a former brackish lagoon in the netherlands abstract a one dimensional transport model was developed to reconstruct historical conservative transport of chloride and 37 cl in pore water of sediments from a former brackish lagoon in the netherlands an area now covered by the freshwater lakes ijssel and marken knowledge of the mechanism of historical solute transport in the sediments and environmental conditions during transport is critical in understanding observed pore water chemistry and will form a basis for simulating effects of changing environmental climate change conditions the model synthesizes present knowledge of geology and historical information on storm surges in the area and takes into account processes such as erosion of sediments mixing of pore water sedimentation and diffusion emsd the chemistry of pore water from one particular boring in the area was found to be mainly controlled by alternating seawater and freshwater diffusion models with a constant averaged porosity 0 55 and tortuosity factor 0 3 showed similar results as models incorporating the measured bulk porosity variations 0 4 0 8 and variable tortuosity factors calculated with archie s law the relatively small tortuosity factor either results from anion exclusion or from the heterogeneous build up of the profile in which a peaty layer in the middle part may obstruct diffusion diffusion of 35 cl was found to be 1 0017 times faster than of 37 cl seawater diffusion into the sediments started at least 400 years ago and refreshening took place since the lagoon was isolated from the sea by a dam in 1932

detrital muscovite 40ar 39ar ages from carboniferous sandstones of the british isles provenance and implications for the uplift history of orogenic belts major progradations of clastic sediments are recorded in the sedimentary record of the famennian and the visean namurian of the united kingdom and surrounding waters we have determined 40ar 39ar ages of 162 detrital muscovites from 11 coarse sandstones which were deposited between 370 and 465 ma spanning both progradations detrital mica ages are dominated by a peak at 415 ma with minor peaks at 440 ma and 390 ma the 415 ma muscovites are derived from the unroofing of the scandian nappes during the compressional phase of the caledonian orogeny in scandinavia the 440 ma muscovites record pre scandian orogenic activity which is rarely preserved in the orogenic record thermochronological evidence suggests that episodic postorogenic uplift and exhumation events kept the scandian orogen a major topographic feature and likely a sediment source for over 100 million years after nappe emplacement and implicates tectonic rather than climatic control on the clastic sediment progradations the near total absence of detrital muscovites with ages 415 ma suggests that the scandian nappes had not been entirely eroded despite repeated uplift during the postorogenic extension the river s which supplied the sediments probably ran parallel to the strike of the major scandian thrusts along the length of the caledonian orogen in a manner analogous to the major river systems of contemporary orogenic highlands

eclogites and polyphase p t cycling in the caledonian uppermost allochthon in troms northern norway eclogites in the tromso area northern norway are intimately associated with meta supracrustals within the uppermost allochthon of the scandinavian caledonides the tromso nappe complex the whole sequence which includes pelitic to semipelitic schists and gneisses marbles and calc silicate rocks quartzofeldspathic gneisses metabasites and ultramafites has undergone three main deformational metamorphic events d1 m1 d2 m2 and d3 m3 detailed structural microtextural and mineral chemical studies have made it possible to construct separate p t paths for these three events chemically zoned late syn to post d1 garnets with inclusions of bt pl and qtz in ky bearing metapelites indicate a prograde evolution from 636 c 12 48 kbar to c 720 c 14 15 kbar this latter result is in agreement with grt cpx geothermometry and grt cpx pl qtz geobarometry on eclogites and trondhjemitic to dioritic gneisses maximum pressures at c 675 c probably reached 17 18 kbar based on cpx pl qtz inclusions in eclogitic garnets and grt ky pl qtz and jd ab qtz in trondhjemitic gneisses post d1 pre d2 decompressional breakdown of the high p assemblages indicates a substantial drop in pressure at this stage inclusions and chemical zoning in syn to post d2 garnets from metapelites record a second episode of prograde metamorphism from 552 c 7 95 kbar passing through a maximum pressure of 10 64 kbar at 644 c with final equilibration at c 665 c 9 10 kbar the corresponding apparently co facial paragenesis grt cpx pl qtz in metabasites yields c 635 c 8 10 kbar in the metapelites post d3 grt in apparent equilibrium with bt phe and pl yield c 630 c 9 kbar the d1 m1 and d2 m2 episodes are exclusively recorded in the tromso nappe complex and must thus pre date the emplacement of this allochthonous unit on top of the underlying lyngen nappe while the d3 m3 episode is common for the two units a previously published sm nd mineral isochron grt cpx am on a partly retrograded and recrystallized ecologite of 598 107 ma represents either the timing of formation of the eclogites or the post eclogite pre d2 decompression stage while a rb sr whole rock isochron of an apparently post d1 pre d2 granite of 433 11 ma is consistent with a k ar age of post d1 pre d2 amphiboles from a retrograded eclogite of 437 16 ma which most likely record cooling below the 475 500 c isotherm after the m3 metamorphism

exhumation of the high pressure tsakkok lens swedish caledonides insights from the structural and white mica 40ar 39ar geochronological record

mantle fragments in the scandinavian caledonides abstract mantle fragments of ultramafic composition are widespread in the scandinavian caledonides sc lenses and boudins of alpine type peridotites in the scandinavian caledonides represent parts of dismembered ophiolite sequences and fragments of sub continental upper mantle metaperidotites of nappes in internal positions are generally isofacial with the metamorphic envelope usually caledonian metasediments but in places also precambrian metagranitoids forming the basement cores of the nappes caledonian metamorphism strongly modified the texture and mineralogy of the peridotites and resulted in a systematic metamorphic pattern which is consistent with the pattern observed in the envelope metaperidotites of the external massifs display at least a two stage metamorphic history an early caledonian high pressure high temperature phase related to early crustal stacking and a late caledonian regional metamorphic overprint which produced a regular barrovian type metamorphic pattern of in situ metamorphism metaperidotites from nappes in intermediate positions iapetus ocean ophiolites and ultramafic rocks from island arc environments show strongly diverging histories metaperidotites from internal ophiolites oceanic ophiolites koli lack any evidence of subduction metamorphism are serpentinized to various degrees show abundant primary mantle relic mineralogies and the caledonian metamorphic overprint is low metaperidotites from external island arc ophiolites and other associations seve often show relic high pressure metamorphism related to the finnmarkian phase of the caledonian orogeny the seve metaperidotites are occasionally associated with eclogites and show a weak overprint of late caledonian regional metamorphism alpine type peridotites are absent in the foreland of the baltic shield and in the innermost nappes lofoten the metamorphic characteristics and evolution recorded by the metaperidotites in the scandinavian caledonides allow a general reconstruction of the dynamics of collision belt formation

sources of fluids and gases expelled at cold seeps offshore georgia eastern black sea four seep sites located within an 20 km2 area offshore georgia batumi seep area pechori mound iberia mound and colkheti seep show characteristic differences with respect to element concentrations and oxygen hydrogen strontium and chlorine isotope signatures in pore waters as well as impregnation of sediments with petroleum and hydrocarbon potential all seep sites have active gas seepage near surface authigenic carbonates and gas hydrates cokheti seep iberia mound and pechori mound are characterized by oil stained sediments and gas seepage decoupled from deep fluid advection and bottom water intrusion induced by gas bubble release pechori mound is further characterized by deep fluid advection of lower salinity pore fluids the pechori mound pore fluids are altered by mineral water reactions at elevated temperatures between 60 and 110 c indicated by heavier oxygen and lighter chlorine isotope values distinct li and b enrichment and k depletion strontium isotope ratios indicate that fluids originate from late oligocene strata this finding is supported by the occurrence of hydrocarbon impregnations within the sediments furthermore light hydrocarbons and high molecular weight impregnates indicate a predominant thermogenic origin for the gas and oil at pechori mound iberia mound and colkheti seep c15 hydrocarbons at the oil seeps are allochtonous whereas those at the batumi seep area are autochthonous the presence of oleanane an angiosperm biomarker suggests that the hydrocarbon source rocks belong to the maikopian formation in summary all investigated seep sites show a high hydrocarbon potential and hydrocarbons of iberia mound colkheti seep and pechori mound are predominantly of thermogenic origin however only at the latter seep site advection of deep pore fluids is indicated

extensional deformation along the late precambrian cambrian baltoscandian passive margin the sarektjakka nappe swedish caledonides the structural evolution of a part of the late precambrian baltoscandian passive margin just before the inception of seafloor spreading is described recording the change from deformation by faulting to dominantly magmatic extension of the crust the allochthon of the scandinavian caledonides contains the imbricated passive margin of continental baltica overlain by various exotic terranes the sarektjakka nappe in the seve nappe complex which contains the outer parts of baltica s passive margin consists of sedimentary rocks occurring as screens between vendian 573 74 ma diabase dykes these dykes constitute 70 80 of the nappe and locally form sheeted dyke complexes the sarektjakka nappe largely escaped penetrative caledonian deformation and preserves igneous metamorphic and structural elements that are linked to the evolution of a pre caledonian rift to a passive continental margin extensional deformation before dyke emplacement is recorded by normal faults pull apart structures and folds unconformities dykes affected by brittle deformation and fluidization of sediments during dyke emplacement indicate close relations between the deposition of sediments extensional deformation and dyke emplacement the sarektjakka nappe is compared with other parts of the baltica s passive margin and its tectonic evolution is discussed

chlorine isotopic composition in seafloor serpentinites and high pressure metaperidotites insights into oceanic serpentinization and subduction processes bulk rock chlorine content and isotopic composition 37 cl were determined in oceanic serpentinites high pressure metaperidotites and metasediments in order to gain constraints on the global chlorine cycle associated with hydrothermal alteration and subduction of oceanic lithosphere the distribution of insoluble chlorine in oceanic serpentinites was also investigated by electron microprobe the hydrothermally altered ultramafic samples were dredged along the south west indian ridge and the mid atlantic ridge the high pressure metamorphic samples were collected in the western alps metaperidotites in the erro tobbio unit and metasediments in the schistes lustres nappe oceanic serpentinites show relatively large variations of bulk rock cl contents and 37 cl values with mean values of 1105 596 ppm and 0 7 0 4 o respectively n 8 1 serpentines formed after olivine meshes show lower cl content than those formed after orthopyroxene bastites in bastites of two different samples cl is positively correlated with al 2 o 3 and negatively correlated with sio 2 these relationships are interpreted as reflecting preferential cl incorporation into the bastite structure distorted by al substituted for si rather than different alteration conditions between olivine and orthopyroxene minerals high pressure metaperidotites display relatively homogeneous cl contents and 37 cl values with mean values of 467 88 ppm and 1 4 0 1 respectively n 7 1 a macroscopic high pressure olivine bearing vein formed from partial devolatilization of serpentinites at 2 5 gpa and 500 600 c shows a cl content and a 37 cl value of 603 ppm and 1 6 o respectively metasediments n 2 show low whole rock cl contents 15 ppm cl that did not allow cl isotope analyses to be obtained the range of negative 37 cl values observed in oceanic serpentinites is likely to result from water rock interaction with fluids that have negative 37 cl values the homogeneity of 37 cl values from the high pressure olivine bearing vein and the metaperidotite samples implies that progressive loss of cl inherited from oceanic alteration throughout subduction did not significantly fractionate cl isotopes chlorine recycled in subduction zones via metaperidotites should thus show a range of 37 cl values similar to the range found in oceanic serpentinized peridotites

chlorine isotope residual salt analysis a new tool to investigate formation waters from core analyses this article presents the first results of chlorine residual salt analysis cl rsa a new technique that allows investigation of the isotopic composition of chlorine in oil field waters from core analysis as water evaporates the residual salts precipitate in the pores of a core unlike the routinely used strontium isotope residual salt analysis sr rsa technique which determines the composition of a trace element strontium the cl rsa technique allows the determination of the isotopic composition and origin of one of the most abundant anions in natural waters the results show that combining the 37cl of two successive leachates of a core sample leads to an isotopic composition that is representative of pore water the reproducibility of the method applied to sandstone samples is considered to be 0 05 the cl rsa technique was tested on two wells from the elgin area north sea united kingdom the 37cl results in formation waters range from 1 03 to 0 57 with an overall increase with depth these results have been compared to the 87sr 86sr ratios of pore waters determined in the same wells using the sr rsa technique the similarity of form between the 37cl and 87sr 86sr profiles with depth confirms that residual salts permit a reliable investigation of the chlorine isotopic composition from core analysis as with the sr rsa technique cl rsa could be used to test the isotopic homogeneity of a sample and to assess the compartmentalization of oil fields and reservoirs this technique could provide key information regarding the origin of the salinity and its evolution during the reservoirs filling as well as help in the monitoring during field production

the stable isotopic composition 37cl 35cl of dissolved chloride in rainwater abstract the stable isotopic composition of dissolved cl in rainwater was measured from a coastal and an interior location in eastern canada at the interior bonner lake ontario site the 37cl values of dissolved cl in precipitation ranged from 3 5 to 1 2 smoc with an amount weighted annual average of 2 3 at the coastal site bay d espoir newfoundland 37cl values of dissolved cl values ranged from 3 1 to 0 0 with an amount weighted annual average of 1 3 these negative 37cl values provide evidence that atmospheric hcl is 37cl depleted presumably from acidification of sea salt aerosols accordingly dissolved cl in the headwaters of two montane rivers in western canada had similarly depleted 37cl values these results have implications to the interpretation of the isotopic compositions of dissolved cl in surface waters formation fluids and groundwaters

modelling convectively induced secondary circulations in the terra incognita with terrsysmp advances in high performance computing have led to kilometre and even sub kilometre scale regional simulations with numerical weather prediction models this range of grid resolution also termed terra incognita approaches the length scale of the most energetic eddies of the convective atmospheric boundary layer abl which accordingly can only be inadequately resolved this dilemma becomes particularly obvious when simulating convectively induced secondary circulations ciscs in the terra incognita because the modelled cisc like circulations also termed m ciscs are poorly resolved and exhibit a grid resolution dependence previous studies have pointed out this problem using different modelling platforms and also suggested options for attenuating poorly resolved m ciscs with methods specific to the applied abl schemes this study examines m ciscs at horizontal grid resolutions of o 1km using the terrestrial systems modeling platform terrsysmp for idealised and real case studies the analysis of simulations using different surface heterogeneity and grid resolutions of o 1km shows that the presence of a super adiabatic layer near the surface and the increase of the horizontal grid resolution allow the critical rayleigh number to be exceeded generating poorly resolved m ciscs whose amplitudes are strongly dependent on the horizontal grid resolution we show that the asymptotic turbulent mixing length scale in the used abl scheme can be tuned in a way that m ciscs are attenuated while the non resolved turbulence dealt with by the abl scheme effectively propagates the surface fluxes into the abl and sustains reasonable abl profiles

empirical garnet muscovite geothermometry in metapelites abstract two empirical garnet muscovite geothermometers assuming no ferric iron model a and 50 ferric iron model b in muscovite respectively were calibrated under the physical conditions of p 3 0 14 0 kbar and t 530 700 c the input temperatures and pressures were determined by simultaneously applying the garnet biotite thermometer am mineral 85 2000 881 and the gasp geobarometer am mineral 86 2001 1117 to natural metapelites to confirm internal thermodynamic consistency holdaway s am mineral 85 2000 881 garnet mixing properties were adopted muscovite was treated as a symmetric fe mg al vi ternary solid solution and its margules parameters were derived in this work the resulting two formulae reproduced the input garnet biotite temperatures well within 50 c and gave identical results for a great body of natural samples moreover they successfully distinguished the systematic changes of temperatures of different grade rocks from a prograde sequence inverted metamorphic zone and thermal contact aureole pressure estimation has almost no effect on the two formalisms of the garnet muscovite geothermometer assuming analytical error of 5 for the relevant components of both garnet and muscovite the total random uncertainty of the two formulations will generally be within 5 c the two thermometers derived in this work may be used as practical tools to metamorphic pelites under the conditions of 480 to 700 c low to high pressure in the composition ranges xalm 0 51 0 82 xpyr 0 04 0 22 and xgros 0 03 0 24 in garnet and fe tot 0 03 0 17 and mg 0 04 0 14 atoms p f u in muscovite

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

transitions in boundary layer meso γ convective structures an observational case study boundary layer rolls over lake michigan have been observed in wintertime conditions predicted by many past studies to favor nonroll convective structures such as disorganized convection or cellular convection this study examines mechanisms that gave rise to transitions between boundary layer rolls and more cellular convective structures observed during a lake effect snow event over lake michigan on 17 december 1983 the purposes of this study are to better understand roll formation in marine boundary layers strongly heated from below and examine the evolution of snowfall rate and mass overturning rate within the boundary layer during periods of convective transition a method of quantifying the uniformity of convection along the roll axes based on dual doppler radar derived vertical motions was developed to quantify changes in boundary layer convective structure roll formation was found to occur after within 1 h increases in low level wind speeds and speed shear primarily below about 0 3zi with little change in directional shear within the convective boundary layer roll convective patterns appeared to initiate upstream of the sample region rather than form locally near the downwind shore of lake michigan these findings suggest that either rolls developed over the upwind half of lake michigan or that the convection had a delayed response to changes in the atmospheric surface and wind forcing mass overturning rates at midlevels in the boundary layer peaked when rolls were dominant and gradually decreased when cellular convection became more prevalent radar estimated aerial mean snowfall rates showed little relationship with changes in convective structure however when rolls were dominant the heaviest snow was more concentrated in updraft regions than during more cellular time periods

thermal history of thrust sheets in an orogenic wedge 40ar 39ar data from the polymetamorphic seve nappe complex northern swedish caledonides the seve nappe complex in the scandinavian caledonides contains the fragmented late precambrian continent ocean transition between baltica and the iapetus ocean this passive margin was fragmented and thrust eastwards over the baltic shield during caledonian orogenesis the individual thrust sheets in the seve nappe complex went through different p t t evolutions resulting in dramatic metamorphic contrasts eclogite bearing nappes are juxtaposed with nappes showing no evidence of caledonian deformation or metamorphism in their interiors strain localization to the marginal parts of the thrust sheets left records of both pre orogenic rift and early orogenic subduction and subsequent uplift processes in the thrust sheets of the seve nappe complex even though it has been transported several hundred kilometres only the margins of the eastern part of the sarektjakka nappe are affected by penetrative caledonian deformation this part of the sarektjakka nappe is dominated by pristine tholeiitic dykes and cross bedded sandstones the dykes are 608 1 ma old and make up 70 80 of the nappe widely spaced thin shear zones of the ruopsok fault system represent the only caledonian penetrative deformation in the interior of the nappe previously published ar ar dates indicate cooling below the closure temperature of hornblende at c 470 ma but numerous ages have been recorded ar dating of biotite and muscovite from a cross laminated metapsammite in the sarektjakka nappe gave well defined ages of 428 5 3 6 and 432 4 3 8 ma respectively muscovite from a shear zone in the ruopsok fault system gave 428 2 4 0 ma whereas hornblende from the same locality did not yield interpretable data the results indicate that these rocks were completely degassed at some unknown time presumably at the emplacement of the dyke swarm no subsequent excess argon contamination can be detected a likely candidate for the degassing event is the emplacement of the dykes at 608 ma the interior of the nappe and thus the entire nappe complex cooled below 350 c at around 430 ma cooling from more than 500 c at c 470 ma to 350 c at c 430 ma suggests an average cooling rate of 4 c ma a prolonged period of slow cooling exhumation following the initial rapid uplift of the eclogite bearing nappes and early ordovician construction of the seve nappe complex is suggested

protracted shearing at midcrustal conditions during large scale thrusting in the scandinavian caledonides during continental collision large tracts of crust are mobilised along major shear zones the metamorphic conditions at which these zones operate the duration of thrusting and the deformation processes that facilitated hundreds of km of tectonic transport are still unclear in the scandinavian caledonides the lower seve nappe displays a main mylonitic foliation with thickness of 1 km this foliation is overprinted by a brittle to ductile deformation pattern localized in c and c type shear bands proximal to the tectonic contact with the underlying sarv nappe thermobarometry of amphibolites and micaschists suggest a first high pressure stage at 400 500 c and 1 1 3 gpa recorded in mineral relics the main mylonitic foliation developed under epidote amphibolite facies conditions along the retrograde path from 600 c and 1 gpa to 500 c and 0 5 gpa age dating of synkinematic titanite grains in the amphibolites indicates that this mylonitic fabric formed at around 417 9 ma but older ages spanning 460 430 ma could represent earlier stages of mylonitization the shear bands developed at lower metamorphic conditions of 300 400 c and 0 3 gpa in the micaschists the recrystallized grain size of quartz decreases towards the shear bands monomineralic quartz layers are eventually dismembered to form polyphase aggregates deforming by dominant grain size sensitive creep accompanied by slip in muscovite and chlorite plagioclase zoning truncations suggest that the shear bands originated by fracturing followed by ductile deformation the results suggest protracted and long lasting shearing under amphibolite to greenschist facies conditions during the juxtaposition stacking and exhumation of the lower seve nappe

early ordovician u pb metamorphic ages of the eclogite bearing seve nappes northern scandinavian caledonides eclogite grade metamorphism of the seve nappe complex snc in norrbotten sweden records the attempted subduction of the baltic continental margin during the early palaeozoic evolution of the iapetus ocean metamorphic titanite sampled from several calcsilicate gneisses of the snc in norrbotten occurs as part of a prograde eclogite facies metamorphic mineral assemblage and yields concordant to nearly concordant u pb ages of 500 475 ma later structural disruption of these rocks occurred during the siluro devonian scandian phase of the caledonide orogeny but the u pb systematics show no evidence of a second generation metamorphic or recrystallized of titanite or of post early ordovician disturbance through pb loss hence the u pb ages are believed to record the time of prograde mineral growth during eclogite facies metamorphism of the snc these results support earlier sm nd and 40ar 39ar studies indicating an early ordovician metamorphic age for the eclogitic norrbotten snc and confirm the early ordovician destruction of at least this segment of the palaeozoic passive margin of baltica these results indicate that the snc in the northern scandinavian caledonides was subducted and metamorphosed to high grade some 50 70 myr prior to the high grade metamorphism of the snc in the central scandinavian caledonides this result requires significantly different early palaeozoic tectonic histories for rocks mapped as snc in the northern caledonides and those in the central caledonides despite a seemingly similar tectonostratigraphic position and broadly similar high grade metamorphism

the caledonian heilhornet pluton north central norway geological setting radiometric age and implications for the scandinavian caledonides the heilhornet pluton is a medium sized c 50 km 2 sub circular discordant intrusion which penetrates the thrust zone separating the helgeland nappe complex from paragneisses in the vestranden region north central norway the intrusion consists of biotite hornblende granite and ranges in composition from 61 5 to 72 5 wt si0 2 the initial sr ratio c 0 7070 shows that crustal sources have been involved in the petrogenesis of the granite a u pb zircon age of 444 11 ma for the pluton indicates that juxtaposition of the nappe complex with metasedimentary rocks in vestranden took place prior to or during the late ordovician a consequence of this is that the general correlation of the metasedimentary rocks in vestranden with the seve nappes must be revised final eastward thrusting of the complex together with a yet unknown part of the vestranden supracrustal sequence probably took place during the middle silurian to early devonian scandian orogenic event

microdiamond on areskutan confirms regional uhp metamorphism in the seve nappe complex of the scandinavian caledonides metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust here we present a new occurrence of diamond within the seve nappe complex snc of the scandinavian caledonides on areskutan in jamtland county sweden microdiamond is found in situ as single and composite diamond carbonate inclusions within garnet in kyanite bearing paragneisses the rocks preserve the primary peak pressure assemblage of ca mg rich garnet phengite kyanite rutile with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite calculated p t conditions for this stage are 830 840 c and 4 1 4 2 gpa in the diamond stability field the ultrahigh pressure uhp assemblage has been variably overprinted under granulite facies conditions of 850 860 c and 1 0 1 1 gpa leading to formation of ca mg poor garnet biotite plagioclase k feldspar sillimanite ilmenite quartz this overprint was the result of nearly isothermal decompression which is corroborated by ti in quartz thermometry chemical th u pb dating of monazite yields ages between 445 and 435 ma which are interpreted to record post uhp exhumation of the diamond bearing rocks the new discovery of microdiamond on areskutan together with other evidence of ultrahigh pressure metamorphism uhpm within gneisses eclogites and peridotites elsewhere in the snc provide compelling arguments for regional at least 200 km along strike of the unit uhpm of substantial parts of this far travelled allochthon the occurrence of uhpm in both rheologically weak gneisses and strong lithologies eclogites peridotites speaks against the presence of large tectonic overpressure during metamorphism

chlorine isotope and cl br fractionation in fluids of poas volcano costa rica insight into an active volcanic hydrothermal system abstract halogen rich volcanic fluids issued at the surface carry information on properties and processes operating in shallow hydrothermal systems this paper reports a long term record of cl br concentrations and 37cl signatures of lake water and fumaroles from the active crater of poas volcano costa rica where surface expressions of magmatic hydrothermal activity have shown substantial periodic changes over the last decades both the hyperacid water of its crater lake laguna caliente and subaerial fumaroles show significant temporal variability in cl br concentrations br cl ratios and 37cl reflecting variations in the mode and magnitude of volatile transfer the 37cl signatures of the lake covering the period 1985 2012 show fluctuations between 0 02 0 06 and 1 15 0 09 condensate samples from adjacent fumaroles on the southern shore collected during the interval 2010 2012 with strong changes in gas temperature 107 763 c display a much larger range from 0 43 0 09 to 14 09 0 08 most of the variations in cl isotope br cl and concentration signals can be attributed to interaction between magma derived gas and liquid water in the volcanic hydrothermal system below the crater the 37cl were lowest and closest to magmatic values in 1 fumarolic gas that experienced little or no interaction with subsurface water and followed a relatively dry pathway and 2 water that captured the bulk of magmatic halogen output so that no phase separation could induce fractionation in contrast elevated 37cl can be explained by partial scavenging and fractionation during subsurface gas liquid interaction hence strong cl isotope fractionation leading to very high 37cl in poas fumaroles indicates that they followed a wet pathway highest 37cl values in the lake water were found mostly in periods when it received a significant input from subaqueous fumaroles or when high temperatures and low ph caused hcl evaporation it is concluded that combined monitoring of 37cl and br cl in laguna caliente and adjacent fumaroles provides valuable information on activity in the subsurface hydrothermal system with significant relevance for volcanic surveillance of poas

seamless stratocumulus simulation across the turbulent gray zone abstracta pragmatic approach for representing partially resolved turbulence in numerical weather prediction models is introduced and tested the method blends a conventional boundary layer parameterization suitable for large grid lengths with a subgrid turbulence scheme suitable for large eddy simulation the key parameter for blending the schemes is the ratio of grid length to boundary layer depth the new parameterization is combined with a scale aware microphysical parameterization and tested on a case study forecast of stratocumulus evolution simulations at a range of model grid lengths between 1 km and 100 m are compared to aircraft observations the improved microphysical representation removes the correlation between precipitation rate and model grid length while the new turbulence parameterization improves the transition from unresolved to resolved turbulence as grid length is reduced

origin and fate of hydrothermal fluids at piton des neiges volcano reunion island a geochemical and isotopic o h c sr li cl study of thermal springs abstract as many ocean basaltic volcanoes worldwide piton des neiges reunion island hosts a hydrothermal system that represents a potential geothermal resource despite several prospection campaigns over the past decades this potential has never been confirmed because many aspects of fluid supply and circulation remain unclear to track the origin and fate of hydrothermal fluids we analyzed the geochemistry of thermal springs water and gas by combining conventional tracers major trace elements and o h c sr li isotopes with cl isotopes a geochemical tool under development added to literature data our new results allow us to compare the composition of thermal springs with cold waters rocks gas and fumarolic deposits from la reunion and elsewhere and to untwine the complex history of fluid mixing that constitutes the geothermal system of piton des neiges 18oh2o and dh2o values of springs 8 67 to 4 9 and 56 3 to 23 5 vsmow respectively are positioned close to the local meteoric water line showing that thermal waters are of meteoric origin however their depletion in heavy isotopes relative to cold waters suggests a recharge strongly influenced by cyclones with a possible contribution from high altitude 2000 m rainfalls their absence of 18o enrichment relative to the local meteoric water line indicates that the isotopic exchange between rocks and water is very limited and therefore suggests that their deep temperatures are relatively low and or the water rock ratios are high 13c values in thermal waters 8 0 to 3 2 pdb and gases 6 7 to 5 3 pdb confirm that carbon is essentially of magmatic origin which we interpret as supplied by regional degassing of la reunion hotspot major trace elements and 87sr 86sr 0 704142 to 0 704336 7li 2 and 34 8 lsvec and 37cl 0 35 and 0 40 smoc compositions show that three additional processes contribute to the mineralization of thermal waters 1 interaction with basalt at temperatures 50 c 2 very limited seawater contamination the geothermal system of piton des neiges is thus the result of meteoric water interaction with a trachytic heat source as a solidified intrusion or a magma pocket unrelated to the co2 flux we also emphasize that thermal waters at piton des neiges are exceptionally isolated from seawater compared to other geothermal systems in ocean island volcanoes worldwide which implies a heat source located above the seawater freshwater interface these inferences are of critical importance for the future geothermal exploration on the island as they suggest that the geothermal resource is within reach of relatively shallow drilling depths 1000 m

a cross calibration of chlorine isotopic measurements and suitability of seawater as the international reference material abstract a collection of 24 seawaters from various worldwide locations and differing depth was culled to measure their chlorine isotopic composition 37cl these samples cover all the oceans and large seas atlantic pacific indian and antarctic oceans mediterranean and red seas this collection includes nine seawaters from three depth profiles down to 4560 mbsl the standard deviation 2 of the 37cl of this collection is 0 08 which is in fact as large as our precision of measurement 0 10 thus within error oceanic waters seem to be an homogeneous reservoir according to our results any seawater could be representative of standard mean ocean chloride smoc and could be used as a reference standard an extended international cross calibration over a large range of 37cl has been completed for this purpose 13 geological fluid samples of various chemical compositions and a manufactured ch3cl gas sample with 37cl from about 6 to 6 have been compared data were collected by gas source isotope ratio mass spectrometry irms at the paris reading and utrecht laboratories and by thermal ionization mass spectrometry tims at the leeds laboratory comparison of irms values over the range 5 3 to 1 4 plots on the y x line showing a very good agreement between the three laboratories on 11 samples the trend line between paris and reading universities is 37clreading 1 007 0 009 37clparis 0 040 0 025 with a correlation coefficient r2 0 999 tims values from leeds university have been compared to irms values from paris university over the range 3 0 to 6 0 on six samples the agreement between these two laboratories using different techniques is good 37clleeds 1 052 0 038 37clparis 0 058 0 099 with a correlation coefficient r2 0 995 the present study completes a previous cross calibration between the leeds and reading laboratories to compare tims and irms results anal chem 72 2000 2261 both studies allow a comparison of irms and tims techniques between 37cl values from 4 4 to 6 0 and show a good agreement 37cltims 1 039 0 023 37clirms 0 059 0 056 with a correlation coefficient r2 0 996 our study shows that for fluid samples if chlorine isotopic compositions are near 0 their measurements either by irms or tims will give comparable results within less than 0 10 while for 37cl values as far as 10 either positive or negative from smoc both techniques will agree within less than 0 30

a comparison of roll and nonroll convection and the subsequent deepening moist convection an lem case study based on scms data abstract rolls observed during the small cumulus microphysical study scms field campaign are simulated using a large eddy model lem the simulated boundary layer properties were in a good agreement with sounding profiles and aircraft observations and the observed boundary layer rolls were reproduced by the model rolls started to decay when zi l exceeded a threshold with a value between 5 and 45 here zi and l refer to the height of the top of convective boundary layer and the monin obukhov length respectively this value was found to depend on a nondimensional combination of the low level wind shear the height of the cbl and the eddy velocity scale larger surface buoyancy fluxes and smaller shears gave higher thresholds for the case modeled rolls persisted for surface buoyancy fluxes less than 110 w m 2 and formed for boundary layer wind shears greater than 5 10 3 s 1 which is consistent with previous studies the simulated roll convection was compared with a nonroll simulation which wa

chlorine isotopes in fluid inclusions determination of the origins of salinity in magmatic fluids abstract thermal ionisation mass spectrometry tims of the cs 2 cl ion has been used to determine the 37 cl value of paleofluids trapped in fluid inclusions modifications to the existing published method have lowered the precision by a factor of 2 0 09 1 thereby allowing real differences to be measured with greater certainty the method has been applied to determine 37 cl of two sets of magmatic fluids trapped in fluid inclusions samples were studied from the capitan pluton in new mexico and the sw england batholith both of which have high temperature fluids whose d and 18 o signatures are distinctly magmatic relative to standard mean ocean chloride smoc the 37 cl values of the capitan samples cluster around 0 whereas those from sw england cluster around 1 8 the br cl ratios of the capitan fluid inclusions are low indicative of halite dissolution and are comparable to local high salinity waters derived from leaching permian evaporites the br cl ratios of the sw england fluid inclusions are much higher and within the range of values normally considered to be magmatic we conclude that the 37 cl value of the capitan magmatic fluids confirms the evidence from br cl ratios that cl was derived from an evaporite source whereas the 37 cl value of the sw england fluids appears to be more representative of a deep magmatic source

isotopic tracing of perchlorate sources in groundwater from pomona california abstract the groundwater of pomona california is contaminated with perchlorate clo 4 this water is treated to reduce the clo 4 concentration to less than 6 g l 1 for compliance with california department of public health drinking water regulations a study of the isotopic composition of oxygen and chlorine in clo 4 has been conducted to determine the source of the contamination isotopic compositions were measured for clo 4 samples extracted from 14 wells yielding ranges of 18 o values from 10 8 to 8 0 17 o values from 4 6 to 7 5 and 37 cl values from 12 8 to 8 9 evaluation of mixing proportions using published isotopic data for three clo 4 end members synthetic atacama and indigenous natural clo 4 indicates that contamination is dominantly 85 89 atacama clo 4 derived from past use of imported chilean nitrate fertilizer in citrus cultivation this interpretation is consistent with 1 aerial photography archives showing extensive citrus fields surrounding pomona in the early to mid 20th century 2 mass balance estimates for clo 4 and 3 numerical hydrologic models yielding travel times for clo 4 from fields to wells that are in the range of 15 to 100 years the hydrologic models predict that clo 4 contamination of pomona groundwater will persist for decades into the future

the origin of continental carbonates in andean salars a multi tracer geochemical approach in laguna pastos grandes bolivia abstract in continental volcanic settings abundant carbonate precipitation can occur with atypical facies compared to marine settings the bio chemical processes responsible for their development and early diagenesis are typically complex and not fully understood in the bolivian altiplano laguna pastos grandes hosts a 40 km2 carbonate platform with a great diversity of facies and provides an ideal natural laboratory to understand the processes responsible for the precipitation of carbonates in a continental province dominated by volcanism in order to trace the origin of both water and solutes in the lagoon the major element and stable isotope compositions 2h 18o 37cl 7li 11b and 87sr 86sr of the spring and stream waters were characterized as well as the stable isotope compositions 13c 15n and noble gas isotope ratios of hydrothermal gases associated with spring waters the results show that thermal springs discharging on the carbonate platform are close to saturation with calcite phreeqc modeling together with fluid geochemistry and temperature estimated from a combination of geothermometers indicate that ca in these springs is inherited from the alteration of the volcanic bedrock by aqueous fluids heated at 225 c and enriched in magmatic mantle derived co2 our results clearly show that the main driver for the precipitation of modern carbonates in laguna pastos grandes is the deeply sourced co2 which boosts the alteration of volcanic rocks at depth

absolute timing of caledonian orogenic wedge assembly central sweden constrained by rb sr multi mineral isochron data abstract multi mineral rb sr isochron ages for mylonites of the caledonian nappe pile jamtland sweden constrain the orogenic evolution of the central scandinavian caledonides an age of 437 8 3 9 ma from a metamorphic leucosome in the central nappe stack dates crystallization of migmatized gneiss thirteen isotopic ages derived from mylonites across all structural levels are between 434 6 6 9 ma and 426 3 3 1 ma these results complemented by a dense network of kinematic field data are interpreted to reflect the timing of protracted top to the ese general shear under decreasing amphibolite to upper greenschist facies conditions across all nappes three samples derived from the top middle and bottom of the nappe pile yield additional deformation ages between 416 0 3 6 ma and 410 1 3 0 ma these ages are interpreted to represent post assembly imbrication of the nappe stack under decreasing metamorphic conditions the new tectonochronologic data are consistent with a tectonic model that explains nappe stacking in jamtland by three stages of ese directed in and out of sequence thrusting in the first stage postdating earlier subduction exhumation of the high grade metamorphic seve nappe complex the latter was emplaced in sequence in the lower mid crust above nappes in its footwall foreland at c 430 ma this event is related to the collision of baltica with an island arc concurrently at c 430 ma determined by paleogeography and structurally unrelated to the first stage second stage out of sequence thrusting emplaced the koli nappe complex atop the developing nappe stack during final baltica laurentia collision eventually imbrication and exhumation of the composite jamtland nappe stack in the uppermost middle crust during the third stage at c 414 ma was caused by continuous underthrusting of baltica beneath laurentia this three stage thrust model reflects the complex interactions of baltica arc laurentia collisions that were accommodated by two merging subduction zones

p t paths in the handl area central scandinavia record of caledonian accretion of outboard rocks to the baltoscandian margin the seve koli nappe complex is widespread in the scandinavian caledonides and is composed of units representing parts of the baltoscandian margin seve nappes now overlain by magmatic sedimentary rocks koli nappes derived from west of this margin the metamorphic evolution of koli and seve units has been studied in the handol area central scandinavian caledonides where a fragmented ophiolite with cover sequence in the lower koli units is thrust over the higher grade seve units thermobarometry constrains metamorphic conditions to 490 570 c 950 600 mpa with a slight downwards increase in grade for the lower koli bunnerviken lens 520 620 c 1000 600 mpa for the upper seve taljstensvalen complex 630 740 c 750 650 mpa for the middle seve snasahogarna nappe and 480 600 c 1150 1000 mpa for the lower seve blahammarfjallet nappe p t paths during garnet growth have been constructed for all units except the highest grade middle seve these paths record heating at the base of the koli and cooling in the underlying seve units pressure increase during garnet growth is indicated for all units leading to anticlockwise p t paths in the seve the results imply thermal convergence with time for all units and spatial convergence in metamorphic grade in the koli it is suggested that the contrasting metamorphic histories on either side of the seve koli boundary resulted from the emplacement of relatively colder koli rocks on top of relatively hotter seve rocks and that emplacement of structurally higher units contributed to the increase in pressure

a high resolution simulation of convective roll clouds during a cold air outbreak 1 a ubiquitous feature of the high latitude ocean is the occurrence of convective clouds that are organized into two dimensional structures known as roll clouds or cloud streets in this paper we present a simulation of these structures that was performed in a domain large enough to simulate numerous roll clouds and their downstream evolution at a resolution sufficient to resolve the individual convective clouds the simulations were initialized and validated using observations of roll clouds over the labrador sea the model results indicate that the secondary flow associated with the roll clouds results in significant differences in the temperature humidity and momentum fields between the updrafts and downdrafts the model was also able to reproduce the observed downstream evolution of the clouds as the organization of the convection changed from two dimensional rolls to three dimensional closed cells

sm nd dating of seve eclogites norrbotten sweden evidence for early caledonian 505 ma subduction the seve nappes consist of long transported thrust sheets belonging to the upper allochthon within the scandinavian caledonides eclogites from two different megalenses within the seve nappe complex in norrbotten northern sweden have been dated with the sm nd method the two eclogite bearing megalenses have been subjected to different pressure and temperature conditions during the high pressure metamorphism garnet omphacite whole rock from ts2 within the tsakkok lens give an age of 505 18 ma 2 i 0 512231 0 000024 mswd 0 10 garnet and whole rock from ts5 and whole rock ts3 also fall on the above isochron the composite isochron gives an age of 503 18 ma 2 these results are interpreted to date the peak of the high pressure metamorphism 500 630 c and 12 15 kbars for the tsakkok lens the eclogites in the vaimok lens at grapesvarre were subjected to higher pressure and temperature conditions and more extensive reequilibration during the early cooling stages retrograde breakdown reactions accompanied by retrograde zoning of relict garnet seems to be associated with disturbance of the sm nd isotopic systems in contrast a sample with unzoned garnet and well preserved high pressure mineralogy from grapesvarre gives a sm nd garnet omphacite age of 503 14 ma 2 i 0 512010 0 000038 2 the ages for the seve eclogites are significantly older than the sm nd eclogite dates from the western gneiss region of norway wgr suggesting the existence of at least two eclogite forming events in the caledonide orogen the younger event has been related to the main continent continent collision stage of the caledonian orogeny while the older event that led to the production of the norrbotten eclogites must have taken place several hundred kilometres to the north and in a different tectonic setting more oceanward to the wgr it appears that the older event ca 505 ma was restricted to the subduction of dyke intruded sedimentary cover rocks which are thought to represent the rifted edge of the baltic continent

evaluation of biotite garnet geothermometers application to the english river subprovince ontario in recent years there have been numerous calibrations of the biotite garnet fe mg exchange geothermometer the eastern lac seul region of the english river subprovince ontario provides an excellent field area in which to compare these calibrations

origin and evolution of fluids from mud volcanoes in the barbados accretionary complex a large collection of fluids 54 interstitial fluids and four expelled fluids were sampled at the manon site at the outer edge of the barbados accretionary complex these warm fluids up to 20 c are expelled by sub marine 5000 mbsl mud volcanoes consisting of diapirs unchanneled flow and diatremes channeled chlorine stable isotope ratios of these fluids were measured by irms with a reproducibility of 0 05 1 versus smoc standard mean ocean chloride a large range of 37cl between 5 3 and 0 1 is observed data from each volcanic structure describe a mixing between seawater and a low 37cl fluid the whole set of data is interpreted as the result of a mixing between two deep components and seawater the two deep fluids are chemically distinct e g in ca mg k li sr and br contents and br cl ratio they display low and significantly different 87sr 86sr ratios 0 707790 and 0 707892 respectively and 37cl values 4 51 and 5 24 respectively physicochemical processes such as mineralogical transformation diffusion compaction or ion filtration are known to fractionate chlorine stable isotopes and can produce fluids with negative 37cl values ion filtration due to sediment compaction appears to be the more likely process to explain the negative 37cl values observed at the manon site a model for the generation of these signatures is proposed where a residual negative 37cl fluid reservoir is created at the bottom of the prism or the sediment pile further compaction fracturing and or dewatering of the slab may flush out these fluids and focus them towards the decollement zone mixing between the fluids and ultimately with seawater and water released during gas hydrate destabilizations may explain the data set within the individual cores and between the different structures

polyorogenic 40ar 39ar mineral age record within the kalak nappe complex northern scandinavian caledonides the kalak nappe complex is composed of variably retrogressed middle proterozoic basement and imbricated polydeformed metasedimentary cover successions which at least in part appear to have originated within the late proterozoic early palaeozoic baltoscandian miogeocline mafic alkaline plutons seiland igneous suite occur within uppermost structural units of the nappe complex 40 ar 39 ar incremental release mineral ages suggest local differences in tectonothermal evolution within the kalak nappe complex post metamorphic cooling dates of c 490 ma are locally recorded by hornblende within the structurally highest tectonic unit suggesting significant orogenic activity occurred during and or immediately prior to the arenig a distinctly later metamorphic overprint occurred in the silurian and was of sufficient magnitude to everywhere rejuvenate ar systems in muscovite and nepheline and locally in hornblende this was followed by relatively rapid post metamorphic cooling through hornblende and muscovite ar closure temperatures between c 425 and 415 ma the complex tectonic history suggested for the kalak nappe complex is generally similar to that previously outlined for the central swedish caledonides together 40 ar 39 ar mineral ages from these widely separated areas indicate that significant tectonothermal activity occurred along the baltoscandian margin prior to the silurian this activity appears at least in part to have been associated with formation of a late cambrian early ordovician accretionary wedge over a westward dipping subduction zone during initial closure of the iapetus ocean

chlorine isotope variations along the central american volcanic front and back arc volcanic outputs ash tephra and lava samples of 23 volcanic centers from the volcanic front secondary front and back arc in central america were analyzed for their 37cl values with the goal of using chlorine isotopes as a tracer of fluids sourced from the subducting cocos slab 37cl values range from 2 6 to 3 0 with systematic variations along the length of the front values from the northernmost guatemala and el salvador and southernmost costa rica ends of the front have mantle like signatures in contrast 37cl values are both positive and negative in the center of the front nicaragua implying a sediment and or serpentinite derived component geophysical observations are consistent with extensive hydration of the cocos plate offshore of nicaragua in support of a serpentinite derived fluid source fluids from dehydrating serpentinites may also incorporate cl from overlying sediments resulting in a multiple source chlorine signature

convectively induced secondary circulations in fine grid mesoscale numerical weather prediction models abstractmesoscale numerical weather prediction models using fine grid o 1 km meshes for weather forecasting environmental assessment and other applications capture aspects of larger than grid mesh size convectively induced secondary circulations ciscs such as cells and rolls that occur in the convective planetary boundary layer pbl however 1 km grid spacing is too large for the simulation of the interaction of ciscs with smaller scale turbulence the existence of ciscs also violates the neglect of horizontal gradients of turbulent quantities in current pbl schemes both aspects poorly resolved ciscs and a violation of the assumptions behind pbl schemes are examples of what occurs in wyngaard s terra incognita where horizontal grid spacing is comparable to the scale of the simulated motions thus model ciscs m ciscs cannot be simulated reliably this paper describes how the superadiabatic layer in the lower convective pbl together with increased horizontal resolution allow the critical ra

microbial perchlorate reduction a precise laboratory determination of the chlorine isotope fractionation and its possible biochemical basis abstract perchlorate reducing bacteria fractionate chlorine stable isotopes giving a powerful approach to monitor the extent of microbial consumption of perchlorate in contaminated sites undergoing remediation or natural perchlorate containing sites this study reports the full experimental data and methodology used to re evaluate the chlorine isotope fractionation of perchlorate reduction in duplicate culture experiments of azospira suillum strain ps at 37 c 37 cl cl clo 4 previously reported without a supporting data set by coleman et al coleman m l ader m chaudhuri s coates j d 2003 microbial isotopic fractionation of perchlorate chlorine appl environ microbiol 69 4997 5000 in a reconnaissance study with the goal of increasing the accuracy and precision of the isotopic fractionation determination the method fully described here for the first time allows the determination of a higher precision 37 cl cl clo 4 value either from accumulated chloride content and isotopic composition or from the residual perchlorate content and isotopic composition the result sets agree perfectly within error giving average 37 cl cl clo 4 14 94 0 15 complementary use of chloride and perchlorate data allowed the identification and rejection of poor quality data by applying mass and isotopic balance checks this precise 37 cl cl clo 4 value can serve as a reference point for comparison with future in situ or microcosm studies but we also note its similarity to the theoretical equilibrium isotopic fractionation between a hypothetical chlorine species of redox state 6 and perchlorate at 37 c and suggest that the first electron transfer during perchlorate reduction may occur at isotopic equilibrium between an enzyme bound chlorine and perchlorate

deep water circulation at the northern pyrenean thrust implication of high temperature water rock interaction process on the mineralization of major spring water in an overthrust area abstract in an overthrust context of the northern pyrenean area groundwater is affected by high mineralization sources a multi isotopic approach was used to track the origin of mineralization in a complex multilayer aquifer system through the study of a major regional spring the oeillal spring water osw which shows a not yet investigated geochemical singularity the aims of this study are to understand the hydrogeochemical evolution and the mineralization mechanisms of groundwater in a large scale aquifer extending over the northern pyrenean overthrust oriental corbieres based on an adequate set of geochemical and isotopic tracers including cosmogenic stable and radiogenic isotopes we have revealed complex hydrogeochemical processes that cannot be tracked with traditional hydrochemical and isotopic tracers the high 87 sr 86 sr ratios of the osw associated with relatively high concentrations in trace elements cs rb sr b li suggest the influence of brine from the triassic deposits containing saliferous clay orsaline fluids from the fractured basement the basement hypothesis may be considered regarding the hydro geochemical fingerprint of the paleozoic basement as demonstrated in previous study and further data would be required to validate the contribution of basement fluids contrasting with marine primary brine and current seawater the relatively high 37 cl 0 22 and 0 39 of osw attests the non marine origin of the chloride ion 36 cl cl shows that the osw is issued from a mixing process between recently recharged water lightly mineralized and significantly marked in 36 cl by the thermonuclear bomb pulse and a saline deep end member at secular equilibrium this indicates that cl in these springs is primarily derived from subsurface non meteoric sources the osw s low br cl molar ratio suggests the influence of simple dissolution of halite and or the contribution of more complex secondary brine the deep saline water may results from meteoric infiltration into the lower jurassic aquifer in contact with triassic deposits or deeper high temperature promotes water rock interaction enhancing leaching of mg k rich saliferous clay this is supported by environmental scanning electron microscopy esem analyses showing that i cl is found in accessory minerals from the kcl mgcl 2 h 2 o system of the triassic deposits and ii cs rb molar ratio is similar to that of osw ranging between 0 13 and 0 7 and from 0 13 to 0 4 respectively laboratory experiments carried out on triassic material show that high temperature water rock interaction is suitable to explain the relatively high 87 sr 86 sr observed in groundwater such process can be investigated to confirm the deep origin of the osw and to explain the signature of deep brines in contact with the triassic deposits under high temperature conditions basement fluid contribution may also be considered regarding the hydro geochemical fingerprint of the paleozoic basement as shown in previous studies further data would be required to validate this hypothesis

accretion and lateral extension in an orogenic wedge evidence from a segment of the seve ko li terrane boundary central scandinavian caledonides abstract the seve ko li boundary in the central scandinavian caledonides represents the transition from baltica continental margin related rocks seve to outboard westerly derived terranes ko li in this study we present and discuss structural and kinematic data recording the syn and post accretionary evolution of this boundary in west central sweden amphibolite facies thrusting mylonitization imbrication and folding occurred before and during the establishment of the seve ko li boundary subsequent asymmetric lateral extension considerably modified earlier structures and the boundary at lower grade contractional ramps and extensional synforms developed and translation continued during progressive deformation kinematic analysis indicates dominant movement towards the east or southeast local movement in the opposite direction may be due to stretching and rotation in the hanging wall above extensional shear zones a pattern of minor shear zones and shear bands demonstrate stretching in an approximately e w direction the presence of extensional structures developed during top to the east movement suggests alternative mechanisms for the formation of some characteristic caledonian structures e g late synforms and thin lenticular tectonic units these features may be due to asymmetric extension during scandian top to the east motion of the nappe pile contemporaneously basement antiforms may have been stacked at lower tectonic levels

chlorine isotope constraints on fluid rock interactions during subduction and exhumation of the zermatt saas ophiolite 1 chlorine isotope compositions of high pressure 2 3 gpa serpentinite rodingite and hydrothermally altered oceanic crust aoc differ significantly from high and ultrahigh pressure 3 2 gpa metasedimentary rocks in the aosta region italy texturally early serpentinites rodingites and aoc have bulk 37cl values indistinguishable from those of modern seafloor analogues 37cl 1 0 to 1 0 in contrast serpentinites and aoc samples that recrystallized during exhumation have low 37cl values 2 7 to 0 5 37cl depletion correlates with progressive changes in bulk chemistry hp uhp metasediments have low 37cl values median 2 5 that differ statistically from modern marine sediments median 0 6 cl in metasedimentary rocks is concentrated in texturally early minerals indicating modification of seafloor compositions early in the subduction history the data constrain fluid sources during both subduction and exhumation related phases of fluid rock interaction 1 marine sediments at the top of the downgoing plate likely interacted with isotopically light pore fluids from the accretionary wedge in the early stages of subduction 2 no pervasive interaction with externally derived fluid occurred during subsequent subduction to the maximum depths of burial 3 localized mixing between serpentinites and fluids released by previously isotopically modified metasediments occurred during exhumation in the subduction channel most samples however preserved protolith signatures during subduction to near arc depths

mesoscale shallow convection in the atmosphere this paper is a review of the observational experimental theoretical and numerical studies of mesoscale shallow convection msc in the atmosphere typically msc is 1 to 2 km deep has a horizontal length scale of a few to a few tens of kilometers and takes distinctive planforms linear and hexagonal the former is called a cloud street roll or band while the latter is called mesoscale cellular convection mcc comprising three dimensional cells msc is characterized by its shape horizontal extent convective depth and aspect ratio the latter is the ratio of the horizontal extent to that in the vertical for cells the horizontal extent is their diameter whereas for rolls it is their spacing rolls usually align along or at angles of up to 10 from the mean horizontal wind of the convective layer with lengths from 20 to 200 km widths from 2 to 10 km and convective depths from 2 to 3 km the typical value of aspect ratio ranges from 2 to 20 rolls may occur over both water surface and land surfaces mesoscale convective cells may be divided into two types open and closed open cell circulation has downward motion and clear sky in the cell center surrounded by cloud associated with upward motion closed cells have the opposite circulation both types of cell have diameters ranging from 10 to 40 km and aspect ratios of 5 to 50 and both occur in a convective layer with a depth of about 1 to 3 km both the magnitude and direction of horizontal wind in the convective layer change little with height msc results from a complex and incompletely understood mix of processes these processes are outlined and their interplay is examined through a review of theoretical and laboratory analyses and numerical modeling of msc

chlorine isotopes of thermal springs in arc volcanoes for tracing shallow magmatic activity the evaluation of the status of shallow magma body i e from the final intrusion stage to quiescence and back to activity one of the key parameters that trigger and sustain volcanic eruptions has been challenging in modern volcanology among volatile tracers chlorine cl uniquely exsolves at shallow depths and is highly hydrophilic consequently cl enrichment in volcanic gases and thermal springs has been proposed as a sign for shallow magmatic activities however such enrichment could also result from numerous other processes e g water evaporation dissolution of old chloride mineral deposits seawater contamination that are unrelated to magmatic activity here based on stable isotope compositions of chloride and dissolved inorganic carbon as well as previous published 3he 4he data obtained in thermal springs from two recently erupted volcanoes la soufriere in guadeloupe and montagne pelee in martinique in the lesser antilles arc we show that the magmatic cl efficiently trapped in thermal springs displays negative 37cl values 0 65 0 65 consistent with a slab derived origin but distinct from the isotope compositions of chloride in surface reservoirs e g seawater local meteoric waters rivers and cold springs displaying common 37cl values of around 0 using this 37cl difference as an index of magmatic cl we further examined thermal spring samples including a 30 year archive from two thermal springs in guadeloupe covering samples from its last eruption in 1976 1977 to 2008 and an island wide sampling event in martinique in 2008 to trace the evolution of magmatic cl in the volcanic hydrothermal systems over time the results show that magmatic cl can be rapidly flushed out of the hydrothermal systems within 30 to 80 years after the eruption much quicker than other volatile tracers such as co2 and noble gases which can exsolve at greater depths and constantly migrate to the surface because arc volcanoes often have well developed hydrothermal systems where magmatic cl is easily transferred to the surface following its exsolution from shallow magma body we suggest that 37cl has great potential to be a unique proxy to monitor the cessation and revival of infrequent arc volcanoes particularly at centennial time scales

chlorine transfer out of a very low permeability clay sequence paris basin france 35cl and 37cl evidence abstract the marine callovo oxfordian clay formation is found at a depth around 410m in the eastern part of the paris basin france it is a very low permeability formation investigated by the french agency for nuclear waste management andra to study the feasibility of a radioactive waste disposal examining hydrogeological and geochemical characteristics of the clay sequence may test confinement properties of this formation this study uses chlorine isotopes to investigate long term transport processes which may carry chemical elements out of the clay layer to the surrounding rocks detailed chlorine concentration and 37cl depth profiles are examined using pore waters and aquifer waters sampled in the clay formation and its surrounding aquifers the dogger at the bottom and the oxfordian kimmeridgian tithonian unit at the top they are discussed in terms of chlorine budget and hydrogeological processes clay pore waters and aquifer waters show strong chlorine concentration depletion a steep cl concentration gradient from the dogger at 500m in depth 2500 mg l to the oxfordian kimmeridgian tithonian aquifer near the surface 10 mg l is associated to a v shaped profile of the 37cl values modelling cl transport shows that a hydrodynamic dispersion process explains cl concentration and 37cl profiles in oxfordian limestone this process implies a mean upward flux of chloride in the 2 6 10 8 8 2 10 8 mole m2 yr range from the clay formation towards upper limestones where a westward advective flow disperses the chloride the modelling and knowledge of underground water transfer suggest a maximum effective cl hydrodynamic vertical dispersion coefficient vertical cl transport coefficient of 7 6 10 10 m2 s chlorine transfer through the callovo oxfordian clay since deposition 160my ago can be mainly described by the interplay of an early dilution and a later hydrodynamic dispersion event which has apparently erased most of the isotopic effects of diagenetic events such as early diffusion ion filtration etc

cl br ratios and stable chlorine isotope analysis of magmatic hydrothermal fluid inclusions from butte montana and bingham canyon utah a bulk geochemical study has been carried out on fluid inclusion leachates extracted from quartz veins from porphyry cu deposits in butte montana usa and bingham canyon utah usa the leachates mostly represent low salinity magmatic hydrothermal fluid inclusions their halogen ratios br cl of fluid inclusion leachates were determined by ion chromatography and 37cl values of the leachates were measured by continuous flow isotope ratio mass spectrometry br cl ratios from early pre main stage and later main stage veins at butte range from 0 60 to 1 88 10 3 m ratios are similar in pre main stage veins with sericite bearing selvages and main stage samples ranging from 0 81 to 1 08 10 3 and from 0 92 to 1 88 10 3 m respectively clustering below seawater 1 54 10 3 m and overlapping mantle values 1 2 10 3 m two samples associated with early pre main stage potassic alteration yield distinctly lower br cl ratios of 0 60 and 0 64 10 3 m butte 37cl values range from 0 8 to 2 3 with no significant difference between pre main stage and main stage samples br cl ratios for quartz veins from bingham canyon range from 0 18 to 3 68 10 3 m br cl ratios from bingham range above and below previously reported for porphyry copper deposits in contrast to butte 37cl values for bingham are lower ranging from 0 9 to 4 1 in the absence of any processes which can significantly fractionate chlorine isotopes at high temperatures we suggest that the porphyry system at bingham and to a lesser extent at butte have inherited negative chlorine isotopic signatures from the subducting slab generated at low temperatures

extraction and analysis of hydrosoluble chlorine and its stable isotopic composition in soil using thermal ionization mass spectrometry abstract chlorine is an essential micronutrient for high plant growth the uptake of chlorine by plants is controlled by the hydrosoluble chlorine in soil which can lead to the cycle change of chlorine isotopes in surficial processes in this study a novel method using water extraction coupled with concatenated ion exchange chromatography for the extraction of hydrosoluble chlorine in soil samples is established for the determination of chorine isotopes by thermal ionization mass spectrometry the results show that no loss of cl ion and the fractionation of chlorine isotopes occur in the extraction with recoveries ranging from 96 4 to 106 4 the variations of 37cl values in soil samples range from 2 40 to 1 31 with an average of 0 44 at a standard deviation of 1 08 stepwise linear regression analysis reveals a positive linear relationship between 37cl values and cl amount in ht soil profile which indicates that the diffusion of cl ion along with soil water flow controls the chlorine isotope in the range of less than 2 in soils the correlation in wf soils shows that except the seawater invasion the 37cl value variation is attributable to the mixing of different sources including anthropogenic activities

establishing constraints on groundwater ages with 36cl 14c 3h and noble gases a case study in the eastern paris basin france abstract groundwaters from the tithonian kimmeridgian oxfordian and upper dogger aquifers within the eastern part of the paris basin france were characterised using 3 h 14 c and 36 cl and noble gases tracers to evaluate their residence times and determine their recharge period this information is an important prerequisite to evaluating the confinement properties of the callovo oxfordian clay formation sandwiched between the oxfordian aquifer and the dogger aquifer currently being investigated by the french nuclear waste management agency andra for radioactive waste disposal data presented in this paper are used to test 4 hypotheses 1 the oxfordian limestone is isolated from the overlying tithonian kimmeridgian surface aquifer this first hypothesis is supported by the presence of measurable 3 h activities in groundwaters from the surface aquifer 6 11 tu and by its absence in groundwaters derived from deeper aquifers 2 the callovo oxfordian clay sequence in the vicinity of the url serves as an effective barrier to advective flow and transport between the underlying upper dogger aquifer and the overlying oxfordian limestone aquifer this second hypothesis is supported by relatively low concentrations of cl 3 5 78 mg l 1 na 15 145 mg l 1 br 0 08 0 4 mg l 1 and 4 he rad 0 2 2 3 ccstp g 1 and slightly higher 36 cl cl ratios 2 7 59 10 15 at at 1 in groundwaters from the oxfordian aquifer compared to those from the upper dogger aquifer 345 4027 mgcl l 1 402 2390 mgna l 1 1 8 22 2 mgbr l 1 1 6 37 2 ccstp he g 1 1 5 10 15 at 36 cl at 1 cl 3 groundwaters from the oxfordian aquifer in the vicinity of url are pre holocene with residence times exceeding 10 ka geochemical and isotopic lines of evidence for this hypothesis include a 13 c values measured on oxfordian aquifer waters that are close to 13 c of the aquifer matrix reflecting strong isotopic exchange over several thousand years b noble gas temperatures that indicate recharge temperatures between 3 and 8 6 c lower by 2 7 c than the modern average temperature in this area c radiogenic 4 he concentrations between 0 16 10 5 and 2 3 10 5 ccstp g 1 of water about 2 3 orders of magnitude greater than the 4 he concentration of air equilibrated water 4 groundwater residence time for the upper dogger aquifer in the vicinity of the url probably exceed several hundred thousand years such long residence times are indicated by the accumulation of radiogenic he up to 37 10 5 ccstp g 1 assuming a closed system primary contributors to uncertainties in interpretation of the data presented in this paper are the lack of well defined 36 cl cl input ratio knowledge about the 4 he rad sources for oxfordian and dogger aquifers knowledge about transport processes occurring through the dogger aquifer and the extensive dilution of initial 14 c activities by dissolution exchange with aquifer matrix overall however although the data presented in this paper remain semi quantitative due to inevitable intrinsic limitations of the methods none contradict the hypotheses of long residence times and aquifer isolation in the vicinity of the url

an evaporated seawater origin for the ore forming brines in unconformity related uranium deposits athabasca basin canada cl br and δ37cl analysis of fluid inclusions abstract analyses of halogen concentration and stable chlorine isotope composition of fluid inclusions from hydrothermal quartz and carbonate veins spatially and temporally associated with giant unconformity related uranium deposits from the paleoproterozoic athabasca basin canada were performed in order to determine the origin of chloride in the ore forming brines microthermometric analyses show that samples contain variable amounts of a nacl rich brine cl concentration between 120 000 and 180 000 ppm and a cacl2 rich brine cl concentration between 160 000 and 220 000 ppm molar cl br ratios of fluid inclusion leachates range from 100 to 900 with most values between 150 and 350 cl br ratios below 650 seawater value indicate that the high salinities were acquired by evaporation of seawater most 37cl values are between 0 6 and 0 seawater value which is also compatible with a common evaporated seawater origin for both nacl and cacl2 rich brines slight discrepancies between the cl concentration cl br 37cl data and seawater evaporation trends indicate that the evaporated seawater underwent secondary minor modification of its composition by i mixing with a minor amount of halite dissolution brine or re equilibration with halite during burial ii dilution in a maximum of 30 of connate and or formation waters during its migration towards the base of the athabasca sandstones iii leaching of chloride from biotites within basement rocks and iv water loss by hydration reactions in alteration haloes linked to uranium deposition the chloride in uranium ore forming brines of the athabasca basin has an unambiguous dominantly marine origin and has required large scale seawater evaporation and evaporite deposition although the direct evidence for evaporative environments in the athabasca basin are lacking due to the erosion of 80 of the sedimentary pile cl br ratios and 37cl values of brines have behaved conservatively at the basin scale and throughout basin history

chlorine isotopes unravel conditions of formation of the neoproterozoic rock salts from the salt range formation pakistan during the late neoproterozoic the salt range in pakistan was one of the regions where the tethys truncated and marine strata developed the numerous transgressions and regressions that occurred d

halogens of bushveld complex south africa δ37cl and cl f evidence for hydration melting of the source region in a back arc setting abstract the bushveld complex is one of only a few layered intrusions anomalously enriched in chlorine this study presents the first chlorine stable isotope analyses of bushveld and associated rocks designed to constrain the source of bushveld cl most samples overlap the range of values for pristine morb and altered seafloor samples 37 cl 4 relative to sea water this contrasts with distal metasedimentary floor rocks 37 cl 0 with little evidence of contamination away from the marginal rocks the cl isotope composition and high cl f ratio is therefore a fundamental characteristic of the lower and critical zone magmas and not derived from infiltration from the country rock these results the high cl f ratio and the boninitic arc like character of bushveld magma are consistent with hydration partial melting of a depleted source in a subduction related setting with cl supplied either by the dehydration of a subducted slab with a heavy cl signature or an overridden wet mantle hotspot

polyorogenic 40 ar 39 ar mineral age record in the seve and koli nappes of the gaddede area northwestern jamtland central scandinavian caledonides in the scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica contrasting tectonothermal histories are recorded in seve and koli nappes exposed in the gad dede area northern jamtland county sweden eclogite bearing seve rocks underwent an initial amphibolite grade regional metamorphism smi with different structural units experiencing contrasting high to intermediate pressure conditions subsequent ductile imbrication sm2 of high and intermediate pressure structural units occurred prior to 460 470 ma cooling through temperatures required for intracrystalline retention of argon in hornblende a later thermal overprint sm3 everywhere rejuvenated seve biotite and muscovite and locally hornblende argon systems at 430 pm 5 ma 40 ar 39 ar plate

evolution of a gneiss in the seve nappe complex of central sweden hints at an early caledonian medium pressure metamorphism abstract ultrahigh pressure uhp metamorphism has recently been reported from various crustal rocks in the seve nappe complex snc in which microdiamonds were found we studied a gneiss from the areskutan nappe in central sweden this nappe of the snc was recently interpreted to have experienced uhp metamorphism the studied medium grained and well foliated gneiss contains quartz biotite garnet k feldspar plagioclase and potassic white mica with accessory kyanite sillimanite rutile ilmenite and monazite pressure p temperature t pseudosections were mainly used to decipher the metamorphic evolution of the gneiss according to polyphase inclusions such as biotite chlorite potassic white mica in the garnet core the prograde p t conditions were approximately 600 c and 8 8 5 kbar an isobaric heating to 700 c followed constrained by homogenous garnet with xca 0 03 and xmg 0 295 the highest si content of 3 15 per formula unit in potassic white mica and zr in rutile thermometry a late migmatitic stage occurred at about 725 c and 6 5 kbar u th pb dating of monazite included in garnet with the electron microprobe yielded two populations at 463 12 2 ma y2o3 2 0 wt and 458 7 2 ma y2o3

the effect of post growth thermal events on growth zoned garnet implications for metamorphic p t history calculations we present a simple diffusion model for investigation of the effect of a post growth thermal history on growth zoned minerals the model treats the mineral as a chemically closed system our treatment incorporates the effects of any thermal history into one essential parameter we then demonstrate that the usability of zoned minerals in metamorphic p t history calculations depends on the mineral grain size and the post growth thermal history using garnet as an example we show that while large garnets 1 mm are safe to use garnets smaller than that that have experienced temperatures characteristic of upper greenschist or lower amphibolite facies metamorphism will yield seriously misleading information the deviation of the calculated growth history from the true growth history can be greater than 100 c and is the greatest for the early part of the garnet history

the convective boundary layer in the terra incognita numerical simulations of a convective boundary layer cbl are performed to investigate model behavior in the terra incognita also known as the gray zone the terra incognita of the cbl refers to a range of model grid spacing that is comparable to the size of the most energetic convective eddies which are on the order of the boundary layer depth using the rayleigh benard thermal instability as reference a set of idealized simulationsisused toshow that grayzone modelingisnot onlya numericalchallenge but also poses dynamical difficulties when the grid spacing falls within the cbl gray zone grid dependent convection can occur the size of the initial instability structures is set by the grid spacing rather than the natural state of the flow this changes higher order flow statistics and poses fundamental difficulties for gray zone modeling applications

thrust related metamorphism in basement windows of the central scandinavian caledonides the late caledonian metamorphic evolution of the basement beneath the caledonian allochthons of the central scandes has been determined by studying mafic schists and phyllonites of the crystalline basement and the overlying vendian and or cambrian sedimentary rocks the studied rocks occur along the caledonian front and in tectonic windows within the scandinavian caledonides a gradual westwards increase in metamorphic grade is recorded which varies from upper diagenetic conditions in the autochthonous rocks along the eastern thrust front of the caledonides to middle amphibolite facies in the western parts of the nasafjall and tomeras windows locally strain related deviations from this pattern occur further west the grade of caledonian metamorphism of the basement increases and reaches the eclogite and granulite facies the scandian metamorphic conditions in the basement rocks studied prevailed in the mid to late silurian at pressures of 8 2 kbar and temperatures of 550 50 c in the tommeras window and 7 2 kbar at 550 50 c in the nasafjall window uplift and cooling followed thereafter continuing into the devonian the final retrograde metamorphism was characterized by temperatures of 450 50 c at pressures of about 3 kbar in the nasafjall and tommeras windows the occurence of syn schistosity amphibolite facies assemblages implies heating of the basement rocks during nappe emplacement available time constraints suggest that this was a relatively rapid process in late silurian to early devonian the prograde phase was followed by uplift and erosion the metamorphic evolution also demonstrates that early devonian thrust movements were associated with a decrease in the thickness of the nappe pile

stable cl isotopes and origin of high cl magmas of the stillwater complex montana the first cl isotopic determinations on biotite from the ultramafic series and from the j m reef of the lower banded series of the stillwater complex montana have 37 cl values normalized to seawater 95 confidence limit error is 0 2 ranging from 0 27 to 0 93 the average is 0 18 assuming minimal fractionation on incorporation into biotite these data imply an ultimate crustal source for the cl however field petrographic and isotopic evidence suggests that high cl fluids did not infiltrate from the country rocks after emplacement of the stillwater magma nor was the cl isotopic signature the result of assimilation of cl rich crustal rocks stillwater parent magmas have boninitic affinities and can be modeled as second stage melts from a metasomatically enriched depleted mantle we propose that the early melt extraction event depleted the mantle in f and cl subsequent metasomatism by a cl rich agent with a crustal cl isotopic signature probably a fluid produced a source rock with a high cl f ratio in modern magmas high cl f weight ratios are associated with high overall volatile contents suggesting that the stillwater complex and other high cl layered intrusions crystallized from magmas that may have contained in excess of 1 wt water

the interglacial glacial cycle and geochemical evolution of canadian and fennoscandian shield groundwaters abstract results from cryogenic column experiments are compared with the geochemical data collected in the canadian and fennoscandian shields over the past 25 years to investigate the relative influence of the glacial interglacial cycle specifically the impact of continental glaciers permafrost and methane hydrate on the evolution of groundwater from crystalline shield environments several different geochemical indicators of freezing processes either glacial or permafrost related were utilized comparisons of na cl and br cl ratios 18 o and 2 h values and 18 o values and cl concentration during freezing fluids with different dominant cations follow distinctly different linear trends when na cl and br cl ratios are compared significantly none of the freezing trends follows the trend hypothesized by herut et al 1990 for the evolution of seawater chemistry during freezing intrusion of glacial meltwater and in situ freezing i e permafrost formation result in a similar end member when comparing 18 o values and cl concentration the geochemical influence of a freezing process on fresh brackish and some saline fluids was identified at some but not all canadian shield sites regardless of site location with respect to modern day permafrost appreciably physical and geochemical data do not support the formation of brines through any freezing process in the canadian and fennoscandian shields as hypothesized by starinsky and katz 2003 rather on all diagnostic freezing plots brines are an end member indicating a different evolutionary pathway significant depletions in 18 o with respect to modern precipitation an indication of either glacial meltwater or a freezing process were identified at depths of up to 1 km at some sites in the canadian shield and to shallower depths in the fennoscandian shield the potential of this fluid to reach such depths could be attributable to artificial gradients and mixing glacial recharge permafrost or paleo permafrost formation or methane hydrate or paleo methane hydrate formation at most locations it was not possible to distinguish between the different scenarios using the current geochemical database

influence of deformation on pressure temperature paths of metamorphism pressure temperature p t paths in structural terranes dominated by folds and thrust faults can be complex and can vary widely within a single metamorphic belt the complexity and variability of p t paths result from the advection of heat by folding and thrusting conductive heat transfer during and after deformation and the relatively short times for thermal relaxation within folds and thrusts in fold terranes contrasting p t paths are observed between anticlines and adjacent synclines cooling paths are observed within anticlines whereas heating paths are observed within synclines these different p t paths result from the folding of isotherms during deformation and the subsequent relaxation of isotherms after deformation in polydeformed fold terranes noncoaxial folding results in complex p t paths over small distances less than 15 km within a metamorphic belt because of the repetition of the process of folding and relaxation of isotherms during each folding event in structural terranes dominated by thrust faults p t paths differ between major thrust sheets because heat is transferred from the hotter overriding sheet to the cooler lower plate during deformation heat transfer during thrusting causes the upper plate to cool and the lower plate to heat in terranes with multiple thrust sheets p t paths can be complex and will depend upon the relative timing of thrust development and the rate at which heat can be transferred from one thrust sheet to the next the p t paths observed in both the fold and thrust terranes discussed here record relatively short time intervals of 10 5 or 10 6 yr because the mineral equilibria respond to small scale thermal perturbations there may be a wide variability in p t paths over a small distance in a metamorphic belt therefore before p t paths are used to reconstruct tectonic histories both structural and petrologic investigations must be carried out

halogen element and stable chlorine isotope fractionation caused by fluid rock interaction bamble sector se norway pervasive interaction between rock and fluid produces regional scale alteration and or metasomatism of rock units the middle and upper crustal rocks from the bamble sector se norway show a complex history of metamorphic and metasomatic events accompanied by ore deposit formation which provides an excellent context for investigation of regional scale fluid rock interaction halogens are important agents of rock alteration and ore metal transportation in such hydrothermal regimes here we use f cl br and i concentrations and stable chlorine isotope ratios d 37 cl to trace the metasomatic evolution of two gabbroic bodies and understand the interplay between localized and pervasive fluid flow in the upper crust an alteration sequence was sampled from pristine gabbro to an amphibolitic shear zone showing progressive amphibolitization and scapolitization caused by pervasive fluid ingress halogen concentrations and ratios suggest the evolution of a single fluid causing enrichment of cl br and i in samples nearest the shear zone owing to the differences in fluid mineral distribution coefficients fluid mineral interaction resulted in either enrichment or depletion of halogens in the fluid as it reacted pervasively with the gabbro although scapolite formation leads to progressive desalination of the fluid near the shear zone increasing cl concentrations in amphibole near the gabbro reflect an increase in salinity towards the unaltered gabbro owing to desiccation of the fluid the formation of alteration minerals mainly governs changes in the halogen chemistry of the fluid showing that halogens do not behave fully conservatively during fluid rock interaction nevertheless the evolving fluid has a feedback on the stability of alteration minerals such as scapolite and biotite which form only close to the shear zone the br cl and i cl ratios of the most highly altered samples are 3 10 3 and 25 10 6 respectively and overlap with the range of ratios measured for marine pore fluids remobilization of evaporites would have produced distinctly lower halogen ratios and can be ruled out as a fluid source the unaltered gabbro has d 37 cl values near 0 and a similar value is inferred for the infiltrating fluid minimally altered samples noted by the presence of 20 vol amphibole have negative d 37 cl values average 0 6 6 0 1 the d 37 cl values increase up to 1 nearest the shear zone with increasing evidence of fluid rock interaction towards the shear zone mixing of different cl reservoirs i e gabbro and fluid cannot explain the observed changes in the d 37 cl values instead isotopic fractionation owing to rayleigh distillation with a fractionation factor of 1 0010 can explain the observed negative d 37 cl values of the alteration sequence by the evolution of a single fluid

isotopic and hydrochemical data as indicators of recharge areas flow paths and water rock interaction in the caldas da rainha quinta das janelas thermomineral carbonate rock aquifer central portugal summary an updated conceptual circulation model for the caldas da rainha and quinta das janelas thermomineral waters was developed these thermomineral waters t 33 c are related to a huge syncline ascribed to the regional flow paths two diapiric structures were responsible for the uplift and subsequent folding of regional jurassic carbonate rocks environmental isotopic 2h and 18o data indicates that the main recharge area of the thermomineral system is linked to the jurassic limestones candeeiros mountains e border of the syncline the thermomineral waters belong to the cl na sulphurous type with a total mineralization of about 3000 mg l the thermomineral aquifer system seems to be isolated from anthropogenic contamination which is typical for the local shallow groundwater systems due to the existence of impermeable layers composed of a series of loamy and detritic rocks of the upper jurassic the presence of 3h in some thermomineral borehole waters not accompanied by an increase in so 4 2 and no 3 could be ascribed to different underground flow paths and different mean residence time the 34s so4 and 18o so4 values of dissolved sulphate of groundwaters of the caldas da rainha spas indicate that the sulphate is the result of water rock interaction with evaporitic rocks e g gypsum and anhydrite ascribed to the regional synclinal structure

mineral age record of a polyorogenic evolution within the seve and koli nappes trondelag norway abstract in the central scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica hornblende within amphibolite at one locality within westernmost exposures of seve nappe units in trandelag norway displays an internally discordant 40 ar 39 ar age spectrum which suggests a polyphase thermal evolution including 1 1 initial post metamorphic cooling through argon retention temperatures at c 475 480 ma 2 2 partial rejuvenation during a silurian c 400 425 ma thermal overprint muscovite within the exposure was more extensively rejuvenated during the silurian overprint at twelve other trandelag sample locations hornblende muscovite and biotite within both the seve and koli nappe complexes record post metamorphic cooling ages between 420 and 435 ma and display no direct evidence of a pre silurian thermal record however the widespread occurrence of intracrystalline extraneous argon components and textural complexities clearly point toward a pre silurian tectonothermal history comparison with 40 ar 39 ar mineral ages reported elsewhere in the central scandinavian caledonides suggests a polyorogenic evolution consisting of 1 1 variable high pressure metamorphism of distal baltoscandian miogeoclinal sequences during entrainment in an accretionary wedge which developed in the late cambrian early ordovician over a west dipping subduction zone related arc volcanic activity occurred in more outboard western sectors 2 2 ductile imbrication of high and intermediate pressure sequences within the accretionary wedge diachronous cooling and or chronologically distinct tectonic episodes are indicated throughout the early and middle ordovician 3 3 ultimate accretion of a variety of eugeoclinal terranes along the baltica continental margin 4 4 imbrication and metamorphism of the eugeoclinal terranes and previously deformed portions of the miogeocline during eastward translation onto the baltoscandian platform in the silurian crystalline baltica basement and overlying structural cover units were depressed to significant crustal depths during eastward nappe transport with resultant formation of high temperature eclogues previously reported crystallization ages of c 425 ma suggest that the eclogites formed at approximately the same time as minerals within the superencumbent nappe units cooled through argon closure temperatures following eastward nappe transport the basement experienced rapid uplift and resultant adiabatic decompression this was followed by rapid cooling through argon retention temperatures at 390 400 ma

40 ar 39 ar mineral age record of early caledonian tectonothermal activity in the baltoscandian miogeocline central scandinavia in central portions of the scandinavian caledonides greenschist facies volcanosedimentary successions within the koeli nappe complex have been thrust several hundred kilometers eastward onto the baltoscandian platform these were derived from eugeoclinal terranes situated outboard west of the baltica continent during the early paleozoic the koeli nappe complex is tectonically underlain by higher grade units within the seve nappe complex these are composed of amphibolite and granulite facies rocks and locally contain eclogites the seve nappes tectonically separate koeli units from structurally lower allochthons derived from more inboard environments along the baltoscandian miogeocline previous mineral isotopic age determinations from seve and koeli units have been in the 430 to 390 ma range and have been interpreted to presumably date cooling following scandian middle silurian to early devonian metamorphism however incremental release sup 40 ar sup 39 ar dates recorded by minerals within some of the koeli and seve nappes exposed in jaemtland sweden taennforsen and are districts provide evidence of earlier tectonothermal activity hornblendes from the seve and koeli nappe complexes display variably discordant age spectra as a result of low temperature experimental evolution of loosely bound extraneous argon components however in most analyses plateau ages of 510 to 475 ma koeli and 465 to 455more ma seve are defined in contrast muscovite and biotite from all tectonic units record scandian cooling ages between 245 and 410 ma the older events recorded by hornblende within these seve and koeli units are evidence of early caledonian tectonothermal activity and subsequent diachronous cooling during the early middle ordovician less

chlorine stable isotopic composition of basement fluids of the eastern flank of the juan de fuca ridge odp leg 168 abstract this paper presents chlorine stable isotope compositions 37cl of sediment pore waters collected by squeezing sediment cores from the sediment basement interface along an east west transect through the eastern flank of the juan de fuca ridge odp leg 168 these near basement fluids nbf are generally thought to be representative of low temperature fluids circulating in the off axis basaltic crust the 37cl value of the fluid directly sampled from a flow at the base of site 1026 wstp1026 is also reported nbf display 37cl values between 2 09 and 0 12 relative to the standard mean ocean chloride smoc defined as 0 and small variations in chlorinity 4 these data contrast with the homogeneity of 37cl values associated with highly variable chlorinities observed in high temperature on axis fluids m bonifacie j l charlou n jendrzejewski p agrinier j p donval chlorine isotopic compositions of ridge axis high temperature hydrothermal vent fluids chem geol 221 2005 279 288 the nbf 37cl values show a general decreasing trend with distance from the ridge axis except for two fluids when plotted against 18o values the 37cl of the nbf show two different trends this paper discusses the possible contributions on nbf 37cl values of fluid mixing water rock interactions and transport processes diffusion ion membrane filtration that can occur in the igneous basement however as none of these processes can fully explain the observed 37cl variations the potential effect of the sediment cover is also investigated at site 1026 the interstitial pore fluid displays a 37cl signature significantly lower than that of the fluid discharge sample 1 90 and 0 28 respectively this difference demonstrated here cannot be an artifact of the sampling method rather indicates the influence of the sediment cover on nbf 37cl values the potential contributions of physical processes associated with transport compaction e g diffusion ion membrane filtration adsorption ion exchange on nbf 37cl values are qualitatively discussed here but require additional studies for further insights however this study indicates that near basement fluids nbf are not at least for cl isotopic compositions necessarily as representative of fluids circulating in the basaltic crust as initially thought these results add new constraints on cl geodynamics and show that cl isotopes fractionate during low temperature circulation of fluids in off axis and off margin flow contexts but not to the extent observed for active margins fluids circulating at low temperature in the magmatic and or the sedimentary part of the oceanic crust might have played a major role on the 37cl evolution of seawater over geologic time

the middle to late devonian hoybakken detachment central norway 40ar 39ar evidence for prolonged late post scandian extension and uplift the regionally significant 0 5 2 km thick hoybakken detachment in central norway bounds the southern margin of the central norway basement window and exhibits a well developed top to the wsw fabric characteristic of late scandian devonian ductile extension 40 ar 39 ar data obtained from hornblende mica and k feldspar mineral separates of rocks collected in a transect through the hoybakken detachment yield well defined plateau and isochron mineral ages early devonian exhumation and cooling of the hoybakken detachment footwall is recorded by hornblende ages of 400 ma and mica ages of 390 ma the mylonitic fabric overlying the footwall records younger middle devonian mica crystallization ages of 384 381 ma that are among the youngest extensional ductile fabrics dated in the caledonides and suggest prolonged extensional activity on the hoybakken detachment after inferred cessation of ductile extension at 381 ma the rate of uplift and cooling was reduced and the footwall records late devonian to early carboniferous k feldspar ages of 371 356 ma prolonged extensional activity at hoybakken is compatible with recent u pb ages of deformed titanite crystals and established rb sr ages of white mica in shear related pegmatites both from the southwestern part of the fosen peninsula and 40 ar 39 ar ages of syn tectonic mica overgrowth from the adjacent hitra snasa fault together these ages suggest the onset of ductile extension soon after 401 ma and with the middle devonian crystallization ages determined here suggest that ductile extension on the hoybakken detachment had a duration of 11 20 ma the youngest age of 320 ma was obtained from a k feldspar in a cataclastic granite of the hoybakken detachment s hangingwall and is considered to date a phase of post scandian brittle deformation that overprinted the mylonitic shear fabric

strong impact of ion filtration on the isotopic composition of chlorine in young clay rich oceanic sediment pore fluids abstract a collection of 34 pore fluids from young clay rich sedimentary piles of the shikoku basin on the philippine oceanic plate at the front of the nankai subduction zone southeast of japan were analyzed for their chloride content and chlorine stable isotope composition 35cl and 37cl reported as 37cl these pore fluids are samples from iodp sites c0011 and c0012 which penetrate deeper than 500 meters below the seafloor at both sites the 37cl values display a regular decrease with depth from about 0 seawater value at the seafloor to 8 5 and 6 5 respectively in hydrogeologically isolated low permeability sediment levels at some depths local deviations of up to 6 in 37cl interrupt the overall decreasing trends they may be interpreted as the injection of external fluids into the sedimentary piles as a result of sedimentary levels with higher permeability at the bottom of the sedimentary piles the injected fluids probably originating from the altered oceanic crust systematically have 37cl values closer to seawater literature data indicate the display of downward trends of decreasing 37cl values of the pore fluids in many other young clay rich sedimentary piles nankai trough and the japan trench accretionary prisms black ridge and juan de fuca ridge flank here we use conservation equations to demonstrate that these 37cl depth profiles can be modeled using the effect of the compaction of growing clay rich sedimentary piles on the water and chlorides including 35cl and 37cl isotopes this modeling shows that a small isotope fractionation of chlorine isotopes 37cl 35clexpulsed fluid residual fluid in the range of 1 006 to 1 001 may explain the observed negative 37cl chlorides at the bottom of the sedimentary piles the complementary positive 37cl chlorides must accumulate at the top but are very likely erased by dilution with seawater chlorides across the seafloor interface this range of chlorine isotope fractionation values is in agreement with the theory of ion filtration of phillips and bentley 1987 in which the mobility of chlorides through semi permeable clay membrane is determined by ion repulsion based on this study we show that young pore fluids in clay rich sediments of the oceanic crust are 37cl depleted chloride reservoirs they might be the source of 37cl depleted chloride fluids advected at mud volcanoes on the seafloor but do not seem to contribute largely to subduction zone magmatic tectonic metamorphic products where no such 37cl depleted chlorine is documented this in turn is a strong argument to propose that most of the clay rich sediment s pore waters are released back into the ocean rather than subducted

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

a chlorine isotope study of dsdp odp serpentinized ultramafic rocks insights into the serpentinization process abstract eight dsdp odp cores were analyzed for major ion concentrations and 37cl values of water soluble chloride 37clwsc and structurally bound chloride 37clsbc in serpentinized ultramafic rocks this diverse set of cores spans a wide range in age temperature of serpentinization tectonic setting and geographic location of drilled serpentinized oceanic crust three of the cores were sampled at closely spaced intervals to investigate downhole variation in cl concentration and chlorine isotope composition the average total cl content of all 86 samples is 0 26 0 16 wt 0 19 0 10 wt as water soluble cl xwsc and 0 09 0 09 wt as structurally bound cl xsbc structurally bound cl concentration nearly doubles with depth in all cores there is no consistent trend in water soluble cl content among the cores chlorine isotope fractionation between the structurally bound cl site and the water soluble cl site varies from 1 08 to 1 16 averaging to 0 21 samples with negative fractionations may be related to reequilibration of the water soluble chloride with seawater post serpentinite formation six of the cores have positive bulk 37cl values 0 05 to 0 36 the other two cores 173 1068a leg hole and 84 570 have negative bulk 37cl values 1 26 and 0 54 the cores with negative 37cl values also have variable cl so42 ratios in contrast to all other cores the isotopically positive cores 153 920d and 147 895e show no isotopic variation with depth the isotopically negative core 173 1068a decreases by 1 with depth for both the water soluble and structurally bound cl fractions non zero bulk 37cl values indicate cl in serpentinites was incorporated during original hydration and is not an artifact of seawater infiltration during drilling cores with positive 37cl values are most likely explained by open system fractionation during hydrothermal alteration with preferential incorporation of 37cl from seawater into the serpentinite and loss of residual light cl back to the ocean fluid rock ratios were probably low as evidenced by the presence of water soluble salts the two isotopically negative cores are characterized by a thick overlying sedimentary package that was in place prior to serpentinization we believe the low 37cl values of these cores are a result of hydration of ultramafic rock by infiltrating aqueous pore fluids from the overlying sediments the resulting serpentinites inherit the characteristic negative 37cl values of the pore waters chlorine stable isotopes can be used to identify the source of the serpentinizing fluid and ultimately discern chemical and tectonic processes involved in serpentinization

circulation and seasonal evolution of polar waters south of australia implications for iron fertilization of the southern ocean abstract the southern ocean iron release experiment soiree was carried out in late summer february 1999 south of australia 61 s 140 e this region of the southern antarctic zone az s between the southern branch of the polar front pf and the southern front of the antarctic circumpolar current saacf is characterized by weak currents and is remote from the influence of sea ice or coastal waters the soiree site exhibits high nutrient concentrations year round phosphate nitrate and silicate remain above 10 m low chlorophyll accumulations

the sources and evolution of mineralising fluids in iron oxide copper gold systems norrbotten sweden constraints from br cl ratios and stable cl isotopes of fluid inclusion leachates we have analysed the halogen concentrations and chlorine stable isotope composition of fluid inclusion leachates from three spatially associated fe oxide cu au mineralising systems in norrbotten sweden fluid inclusions in late stage veins in fe oxide apatite deposits contain saline brines and have a wide range of br cl molar ratios from 0 2 to 1 1 10 3 and 37cl values from 3 1 to 1 0 leachates from saline fluid inclusions from the greenstone and porphyry hosted cu au prospects have br cl ratios that range from 0 2 to 0 5 10 3 and 37cl values from 5 6 to 1 3 finally the cu au deposits hosted by the nautanen deformation zone ndz have br cl molar ratios from 0 4 to 1 1 10 3 and 37cl values that range from 2 4 to 0 5 although the bulk of the data fall within 0 0 5 the br cl ratios of leachates are consistent with the derivation of salinity from magmatic sources or from the dissolution of halite most of the isotopic data from the fe oxide apatite and greenstone deposits are consistent with a mantle derived source of the chlorine with the exception of the four samples with the most negative values the origin of the low 37cl values in these samples is unknown but we suggest that there may have been some modification of the cl isotope signature due to fractionation between the mineralising fluids and cl rich silicate assemblages found in the alteration haloes around the deposits if such a process has occurred then a modified crustal source of the chlorine for all the samples cannot be ruled out although the amount of fractionation necessary to generate the low 37cl values would be significantly larger the source of cl in the ndz deposits has a crustal signature which suggests the cl in this system may be derived from meta evaporites or from input from crustal melts such as granitic pegmatites of the lina suite