x ray microanalysis of fluid inclusions and its application to the geochemical modeling of evaporite basins direct access to brines trapped in halite is possible by freezing and breaking halite crystals on a cooling stage inside a scanning electron microscope quantitative analyses of major solutes na mg k ca cl and so4 in natural brines were obtained by means of x ray microanalysis of the frozen fluid inclusions using frozen droplets of brines with known composition as standards precision errors were estimated to be lower than 10 and detection limits vary from below 0 02 mol l for ca k and so4 to 0 55 mol l for na analyses of several inclusions of sizes larger than 20 m were performed for each cross section of halite the composition of primary fluid inclusions in halites from a drill core in the messinian basin of lorca se spain were used to constrain the parameters of a geochemical model of the evolution of the basin a computer program to simulate evaporation paths was developed using thermodynamic equilibrium and mass balance as constraints the halite sequence was interpreted as resulting from the evaporation of initial seawater in a hydrologically open basin with seawater replacing the evaporated water and a small fraction of basinal brine leaking out in the middle of the sampled sequence the basin was closed to the sea and only continental water flowed into the basin reworking part of the halite deposited in the margins in contrast with these results only very poor information would have been obtained from the mineralogical record alone consisting mainly of halite and minor gypsum

retreat of glaciar tyndall patagonia over the last half century we report measurements of ice surface elevation ice thickness and surface area for glaciar tyndall patagonia made in 1999 2002 the measurements together with previously published observations show acceleration over the last few decades of the rates of thinning and retreat of the main calving front the acceleration of shrinkage appears to be driven by a combination of climate and feedback processes the dominant feedback being increased melting associated with lowering of the glacier surface elevation feedback the melting capacity in the main terminus lake is now too small to be a major factor accelerating the retreat the glacier bed has low slope and remains below the elevation of the lake spillway for 14 km upstream from the 2000 calving front indicating the potential for extensive retreat under the influence of strong elevation feedback and increasing interaction with the lake as it enlarges

analysis techniques for coherent airborne radar sounding application to west antarctic ice streams 1 analysis of coherent radar sounding echoes from polar ice sheets can provide information suitable for classifying the subglacial environment echoes from a general interface consist of both specularly reflected and diffusely scattered contributions specular reflection results from smooth uniform interfaces whereas diffuse scattering results from rough nonuniform interfaces and inhomogeneous media this article discusses how these phenomena are important to the acquisition and analysis of coherent radar sounding data reflection results are presented from airborne surveys conducted in 1987 over the downstream portions of whillans ice stream and ice stream c west antarctica additionally reflection and scattering analyses along with new results are presented for repeat profiles flown in 2001 over ice stream c analysis methods include using echo amplitudes to compute reflection coefficients which are used for inferring the dielectric properties of the subglacial material echo phase analysis provides the locations of dominant scattering centers which relate to reflection or scattering from the interface as well as provide interface roughness estimates comparison of low and high resolution imaging obtained from synthetic aperture radar techniques indicates a reflecting and or scattering interface combining the results from these independent analyses provides classification of the subglacial environment classified regions include smooth seawater smooth saturated sediments accreted marine ice rough bottom crevasses mixed conditions with partial subglacial water and dry frozen conditions

geochemistry of the fluids related to epigenetic carbonate hosted zn pb deposits in the maestrat basin eastern spain fluid inclusion and isotope cl c o s sr evidence epigenetic zn pb deposits in the maestrat basin eastern spain are hosted by dolostones that replace aptian limestones the deposits have morphologies ranging from mineralized breccias to stratiform massive replacements sphalerite and galena cementing breccias precipitated as well formed crystals whereas the stratiform replacements are characterized by textures such as colloform and skeletal or dendritic growths two mineralized areas are found valdelinares and mas de la mina cedraman the highest ore grades up to 11 zn and largest deposits ca 30 000 t of sulfides occur as stratiform deposits in the valdelinares area resurreccion and restauracion mines in the valdelinares area microthermometry of fluid inclusions reveals that ore stage minerals precipitated by the mixing of two distinct fluids fluid a a high salinity brine with salinity greater than 26 wt percent nacl equiv and temperatures above120oc and fluid b a low salinity fluid with less than 15 wt nacl equiv and temperatures around 40oc fluid a dominated brines are found in mineralized breccias located in the vicinity of major fracture zones whereas more dilute fluids are typical of massive ores in the mas de la mina area the presence of two fluids is less evident although the ranges in both temperature and salinity also point to mixing na k li cl br systematics of the inclusion fluids indicates that fluids a and b were evaporated seawater that did not significantly interact with k and li rich sediments the most diluted mixtures fluid b are characterized by relatively heavy cl 37 cl 1 11 and 1 19 compared to fluid a dominated brines which have 37 cl values close to seawater 0 the sulfur isotope compositions range from 10 5 to 13 4 per mil for sulfides and between 16 and 17 8 per mil for barite such values are consistent with mixing of a metal rich brine with small amounts of 32 s enriched sulfur and a sulfur rich fluid with a 34 s close to the marine sulfate of late cretaceous to early paleocene age the c and o isotope compositions of ore stage calcite 13 c from 0 6 to 7 8 18 o from 17 2 to 20 9 are also explained by the precipitation from different mixtures of fluids a and b from the geochemical data it is inferred that fluid mixing played a key role in the formation of the zn pb deposits in the maestrat basin ore precipitation occurred in places where brines ascending through faults interacted with a dilute sulfur rich fluid deposits with the highest ore grade and size are related to areas where the most extensive mixing occurred

a newly dated cretaceous hydrothermal event in the iberian ranges eastern spain and its significance within the mesozoic thermal history in the iberian peninsula abstract the iberian peninsula hosts the world class hg mining district of almaden besides pre hercynian ore bodies alpine cycle hg bearing veins are also present in the eastern iberian ranges espadan deposits we present both the first absolute ages 84 4 and 85 3 ma for a post hercynian hg deposit in spain obtained from primary muscovites and a complete compilation of published mesozoic radiometric absolute ages of the iberian peninsula we deduce that there are three main thermal episodes that affected the iberian peninsula which have been revealed after the comparison among the magmatic metamorphic and hydrothermal ages moreover the espadan hydrothermal system was active when both the cretaceous alkalic magmatism took place in southern portugal and in the pyrenees and during the opening of the bay of biscay

an improved coherent radar depth sounder the university of kansas developed a coherent radar depth sounder during the 1980s this system was originally developed for glacial ice thickness measurements in the antarctic during the field tests in the antarctic and greenland we found the system performance to be less than optimum the field tests in greenland were performed in 1993 as a part of the nasa program for arctic climate assessment parca we redesigned and rebuilt this system to improve the performance the radar uses pulse compression and coherent signal processing to obtain high sensitivity and fine along track resolution it operates at a center frequency of 150 mhz with a radio frequency bandwidth of about 17 mhz which gives a range resolution of about 5 m in ice we have been operating it from a nasa p 3 aircraft for collecting ice thickness data in conjunction with laser surface elevation measurements over the greenland ice sheet during the last 4 years we have demonstrated that this radar can measure the thickness of more than 3 km of cold ice and can obtain ice thickness information over outlet glaciers and ice margins in this paper we provide a brief survey of radar sounding of glacial ice followed by a description of the system and subsystem design and performance we also show sample results from the field experiments over the greenland ice sheet and its outlet glacicrs

pbzn mineralization associated with diapirism fluid inclusion and stable isotope h c o evidence for the origin and evolution of the fluids at fedj el adoum tunisia pb zn mineralizations occur in the contact zone to a saliferous diapir and its surrounding cretaceous limestonerich sediments the diapir of triassic formations was initially intruded hot from a depth of 3 7 km during the cretaceous three principal types of mineralization occur bedded vein and massive combined microthermometric and stable isotope h c o studies have characterized three principal thermal events before cool meteoric waters entered the system 1 1 hot 170 250 c saline 22 33 eq wt nacl fluids of probable deep formation water origin with d 43 and 18o 20 precipitated calcite with 13c 8 and celestite in the inner part of the contact zone with the diapir 2 2 hot 100 130 c saline 18 23 eq wt nacl fluids with d 60 and 18o 13 containing co2 n2 and hydrocarbons precipitated sphalerite calcite 13c 9 quartz and minor galena as banded mineralization in the outer part of the contact zone more galena rich vein mineralizations in the contact zone were deposited at similar temperatures from comparable fluids mineralizing solutions are interpreted to be formation waters with the carbonate carbon being derived from organic carbon the colloform textures in the banded mineralization suggest that the nearby sedimentary basin underwent episodic dewatering 3 3 warm 70 90 c saline 16 22 eq wt nacl fluids with d 110 and 18o 10 precipitated calcite with 13c 16 galena rich ore in the massive mineralizations and vein mineralizations in the cenomanian turonian limestones and essentially sulphide free calcite in the banded and contact vein mineralizations a locally derived organic water origin is proposed where both hydrogen and carbon were derived from organic constituents such as petroleum during bacterial sulphate reduction reactions variable d and salinity values suggest mixing processes between the d depleted organic water and a more d rich formation or meteoric water 4 4 low temperature 50 c meteoric waters with d 15 to 25 introduced a second generation of calcite with the carbonate largely coming from the sedimentary carbonates in the massive and turonian vein mineralizations anhydrite was probably converted to gypsum at about this time and before fedj el adoum arrived at its present altitude

contribution of the patagonia icefields of south america to sea level rise digital elevation models of the northern and southern patagonia icefields of south america generated from the 2000 shuttle radar topography mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers during the period 1968 1975 2000 these glaciers lost ice at a rate equivalent to a sea level rise of 0 042 0 002 millimeters per year in the more recent years 1995 2000 average ice thinning rates have more than doubled to an equivalent sea level rise of 0 105 0 011 millimeters per year the glaciers are thinning more quickly than can be explained by warmer air temperatures and decreased precipitation and their contribution to sea level per unit area is larger than that of alaska glaciers

cl br and i in igneous standard rocks abstract radiochemical neutron activation analysis rnaa and isotope dilution mass spectrometry idms are applied to the determination of cl br and i in igneous standard rocks seventeen different standard samples of igneous rocks distributed by the geological survey of japan gsj and by the association national de la recherche technique anrt in france were investigated the cl contents range from 10 to 1000 ppm br from 0 05 to 2 5 ppm and i from 5 to 100 ppb in this study four standard samples for cl eight for br and six for i were newly determined the analytical results between rnaa and idms are in good agreement within one standard deviation the halogen contents are found to be well correlated for cl and br but less clearly for i halogens generally are enriched in rhyolites in the volcanic rock series while they are depleted in plutonic rock series especially in granite

mapping subglacial surfaces of temperate valley glaciers by two pass migration of a radio echo sounding survey high resolution maps of the glacier bed are developed through a pseudo three dimensional migration of dense array of radio echo sounding profiles resolution of three dimensional maps of subglacial surfaces is determined by the radio echo sounding wavelength data spacing in the field and migration based on synthetic radio echo sounding profile experiments the maximum resolution of the final map cannot exceed one half wavelength a methodology of field and processing techniques is outlined to develop a maximum resolution map of the glacier bed the field and processing techniques are used to develop a map of the glacier bed below part of worthington glacier a temperate valley glacier in south central alaska the field techniques and the processing steps used on the glacier result in a map of 20 m 20 m resolution

origin of vein hydrothermal carbonates in triassic limestones of the espadan ranges iberian chain e spain dolomitization and hg bearing veins in the lower triassic limestones of the espadan ranges iberian chain e of spain

a low frequency ice penetrating radar system adapted for use from an airplane test results from bering and malaspina glaciers alaska usa ice thickness measurements are needed to calculate fluxes through fast flowing outlet glaciers in greenland alaska patagonia and antarctica however relatively high attenuation of radio waves by dielectric absorption and volume scattering from englacial water hampers detection of the bed through warm deep ice in the past we have had success measuring ice thickness of temperate glaciers using a ground based monopulse radar system operating at low frequencies 2 mhz here we adapt the same system to operate from an airplane test flights over bering glacier alaska usa detected the bed through ice up to 1250 m thick flights across the seward malaspina glacier system alaska resolved the ice thickness of malaspina glacier but strong hyperbolic shaped returns obscured the bed echo through the seward throat it is likely that this clutter in the signal was caused by off nadir returns from chaotic surface crevasses that are ubiquitous in the throat region

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

fluid inclusions in pre ore minerals from the carbonate hosted mercury deposits in the espadan ranges eastern spain abstract the fluids associated with pre ore minerals in the carbonate hosted mercury veins from the espadan ranges eastern spain have been studied using microthermometry cryo sem eds raman spectroscopy and crush leach analyses in order to determine their origin and the processes responsible for mineralization three primary fluid inclusion types have been found in quartz and dolomite 1 type s composed of liquid vapour mainly co 2 halite 2 type s v composed of liquid high density co 2 double bubble halite and 3 type v composed of high density co 2 n 2 mixtures type s fluid inclusions are preferentially trapped in betxi type veins characterized by the presence of hydrothermal dolomite whereas type v fluid inclusions are trapped almost exclusively in eslida type veins which were without dolomite from these data two different fluids can be inferred to occur during the period of formation of the veins 1 a complex polysaline brine of nacl kcl cacl 2 mgcl 2 so 4 2 h 2 o composition with a salinity of up to 33 eq wt nacl and a 2 co 2 n 2 rich fluid the brine halogen composition points to its secondary origin caused by the dissolution of underlying marine evaporites it is thought that these deposits were formed during jurassic or cretaceous rifting periods as a consequence of fluid mixing between a high salinity secondary brine and connate waters the generation of a co 2 n 2 rich phase caused the pressure increase of the fluids that favoured the hydraulic fracturing of the enclosing rock dolostone the origin of this volatile rich phase probably occurred due to the oxidation and thermochemical breakdown of the organic matter contained in the host rock this event is recorded by the coetaneous trapping of both aqueous and carbonic fluids in quartz crystals the formation conditions for the hypogene sulphide paragenesis are obscure but the coincidence between the preferential trapping of type v fluid inclusions the absence of hydrothermal dolomite and the major abundance of mercury in eslida type veins is thought to be linked to a mercury fractionation event to the vapour phase during the release of the volatiles

geochemistry of the mercur gold deposit utah u s a abstract the mercur gold deposits of west central utah are disseminated carlin type deposits which are hosted by the upper portion of the topliff member of the mississippian great blue limestone strata bound alteration and mineralization are related to sedimentary lithologies over a 60 80 m section of the topliff member hydrothermal alteration at mercur can be separated into replacement and vein alteration assemblages two replacement assemblages are recognized jasperoid facies consists of replacement of massive limestone by silica and minor sericite and kaolinite argillic facies alteration is characterized by decarbonation of silty limestones fluids which formed the argillic facies became progressively more reduced and acidic through reaction with carbonaceous argillaceous pyritiferous limestones three vein assemblages are recognized at mercur 1 pyrite orpiment organics marcasite 2 calcite realgar and 3 halloysite barite calcite considerable temporal and spatial overlap exists among all hydrothermal assemblages varying degrees of au mineralization are associated with most styles of alteration fluid inclusion studies show that jasperoid facies rocks were formed at temperatures of 220 270 c hydrothermal calcite at 150 190 c and barite at 150 300 c salinities throughout the paragenesis remained relatively constant at 5 8 eq wt nacl a geochemical model based on fluid inclusion data microprobe data and mineral solubilities allows constraints to be placed on the chemical characteristics of the mercur ore forming fluids jasperoid facies rocks were formed by fluids at ph 3 6 p co 2 f o 2 34 to 32 the argillic facies vein assemblages were formed at a ph of 4 0 p co 2 of 100 bar log f o 2 of 40 4 to 39 6 and log f h 2 s of 3 1 to 2 7 the available data indicate oreforming solutions are near a au solubility minimum but do not allow an exact determination of the mechanism of au deposition

rapid changes in ice discharge from greenland outlet glaciers using satellite derived surface elevation and velocity data we found major short term variations in recent ice discharge and mass loss at two of greenland s largest outlet glaciers their combined rate of mass loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates likely as a result of fast re equilibration of calving front geometry after retreat total mass loss is a fraction of concurrent gravity derived estimates pointing to an alternative source of loss and the need for high resolution observations of outlet dynamics and glacier geometry for sea level rise predictions

saddle dolomite as a by product of chemical compaction and thermochemical sulfate reduction petrographic stable and radiogenic isotope trace element and fluid inclusion data from the devonian nisku reef trend in the subsurface of alberta canada suggest that saddle dolomite was a by product of chemical compaction and thermochemical sulfate reduction in subsiding dolomitized rocks furthermore thermochemical sulfate reduction may be representative of other processes that increase the amount of saddle dolomite via an increase in carbonate alkalinity the data also confirm that saddle dolomite is most likely to form at elevated temperatures from hypersaline brines

fluid mixing and recycling during pyrenean thrusting evidence from fluid inclusion halogen ratios abstract syntectonic fluids have been sampled through fluid inclusion microthermometry and crush leach analyses cations and halogens from a 50 km n s transect through the central southern pyrenees the fluid inclusions are contained in syntectonic quartz veins in triassic redbeds cretaceous carbonates and hercynian basement rocks with some calcite and dolomite data from limestones and evaporites in more external parts of the belt the main datasets come from 1 alpine shear zones cutting the neouvielle granodiorite in the hercynian axial zone at the north end of the transect 2 an imbricate zone beneath the alpine gavarnie thrust at the pic de port vieux 3 several localities in the footwall and hangingwall of the gavarnie thrust on the southern margin of the axial zone the inclusion fluids generally decrease in salinity from 27 35 at the northern end of the transect to 7 22 on the southern margin of the axial zone the majority of the inclusions have cl br ratios lower than seawater and are interpreted as relict fluids after seawater evaporation and halite precipitation in the upper trias this interpretation is supported by cl br na systematics which are consistent with a change from halite to halite sylvite precipitation with progressive evaporation fluids in the basement shear zones are interpreted to have essentially the same evaporitic origin as those still contained in sedimentary formations although it is possible that final concentration of brines in the neouvielle massif involved retrograde hydration reactions with removal of water by precipitation of hydrous minerals the fluids are also very similar in salinity and halogen chemistry to those found in veins associated with mesozoic pb zn f deposits which predate the thrusting the lower salinities seen at the southern margin of the axial zone are interpreted to reflect mixing of the brines with a higher level fluid connate or meteoric water circulating within the mesozoic carbonates of the higher thrust sheets at one locality where triassic evaporites are still present high cl br ratios at relatively low salinities are present in inclusions within the underlying triassic redbeds but low cl br ratios at higher salinities are seen lower in the sequence this is consistent with dissolution of halite by a dilute fluid but with limited penetration downwards we suggest that the fluid history of the pyrenees evolved through a series of stages 1 upper triassic evaporite formation with sinking of brines into underlying redbeds and fractured basement rocks 2 circulation of brines with formation of pb zn deposits along faults at some time between the triassic and the upper cretaceous 3 renewed extension with erosion of triassic rocks in many areas and further drawing down of triassic brines into the basement 4 deposition of u cretaceous and palaeocene carbonates containing connate waters of marine origin 5 formation of the pyrenean thrust belt with overpressuring and expulsion of the brines along shear zones and faults 6 creation of topography with a high level circulation system in the mesozoic thrust sheets driven largely by topography at the southern margin of the axial zone there was limited mixing of the deeper overpressured brines with these more dilute hydrostatically pressured fluids an important point is that because of their density hypersaline brines are difficult to expel from the upper crust and may be involved in a succession of alteration and mineralisation events in the same general area over hundreds of millions of years

origin of the atrevida vein catalonian coastal ranges spain mineralogic fluid inclusion and stable isotope study atrevida is a ba f base metal vein located in the catalonian coastal ranges of spain about 100 km southwest of barcelona the vein cuts paleozoic metasediments and granites of the hercynian basement and triassic red beds at the base of an overlying transgressive sequence the atrevida vein can be divided into three parts on the basis of mineralogy the lower level contains sugarlike quartz fluorite minor barite the middle level contains a breccia of banded barite basement rocks cemented by a complex sulfide arsenide assemblage with galena ni sulfide ag sulfosalt and native silver veinlets the upper level contains symmetrical bands of white barite late calcite and marcasite are found in geodes the only alteration observed is quartz sericite chlorite after k feldspar and biotite where the vein cuts granite host rocks fluid inclusions in fluorite homogenize at 110 degrees c and have salinities of 21 wt percent nacl equiv inclusions in sphalerite homogenize at 90 degrees c and have salinities of 22 wt percent nacl equiv eutectic results in both minerals are as low as 59 degrees c indicating that the trapped fluids are complex cacl 2 bearing polysaline brines fluid inclusions in late calcite homogenize at 0 3 degrees c indicating that low salinity waters invaded the vein system during calcite deposition sulfur and oxygen isotope analyses reveal that vein barites have delta 34 s values of 14 to 17 9 per mil cdt and delta 18 o values of 9 5 to 12 2 per mil smow barite also occurs as cement in the triassic red beds with delta 34 s 15 3 per mil and delta 18 o 10 6 per mil both the sulfur and the oxygen isotope compositions are within the ranges reported for lower triassic to lower jurassic age evaporites banded galena from the middle level of the vein has delta 34 s values between 6 3 and 8 9 per mil and rimming anglesite has delta 34 s values of 21 to 30 9 per mil galena from the central breccia has delta 34 s values of 14 9 to 16 1 per mil and coexisting sphalerite is about 10 per mil quartz in the lower level of the vein has delta 18 o in the range 20 7 to 22 7 per mil we infer that sulfate in the vein was derived directly from seawater or from a solution which dissolved evaporites as it descended through the triassic section along the fault zone barite and sulfides were precipitated where the sulfate bearing solution mixed with an ascending ba rich brine the reduced sulfur found in the vein may have been carried by the ascending brine banded galena and may also have been produced by bacterial reduction of sulfate from a surficial source galena in breccia oxidizing nonmarine waters were introduced into the hydrothermal system giving rise to anglesite rims on galena mineralization took place in the late triassic during an extensional tectonic regime characterized by a high geothermal gradient atrevida and similar barite veins found throughout the catalonian coastal ranges formed along basin margin faults near a paleosurface formed on hercynian basement on a broader scale low temperature veins are known to occur throughout western europe and northern africa if atrevida is representative of the group then the formation of these veins may be linked to mesozoic extensional tectonics

paleomagnetic results from the southeastern margin of the ebro basin northeastern spain evidence for a tertiary clockwise rotation abstract triassic rocks underlying the paleogene deposits of the ebro basin are exposed along its se margin about 200 samples of middle triassic and paleogene rocks from this margin have been demagnetized and analysed the middle triassic red beds contain one or two secondary components of magnetization the high unblocking temperature component has a mean direction of d 1 and i 6 the eocene red beds display a very stable magnetization nevertheless some samples have a high temperature component with the present day field direction the eocene mean direction is d 22 and i 51 the paleomagnetic results show a systematic 20 clockwise rotation relative to the data from the pyrenean and cantabrian ranges and the western and sw part of iberia to explain these results two hypotheses are presented one implies the rotation of the ne part of iberia whereas the other refers to a rigid block rotation mechanism along the catalan coastal range

influence of wind stress wind stress curl and bottom friction on the transport of a model antarctic circumpolar current abstracteddy permitting simulations of a wind driven quasigeostrophic model in an idealized southern ocean setting are used to attempt to describe what sets the wind driven circumpolar transport of the antarctic circumpolar current acc for weak forcing the transport is well described as a linear sum of channel and basin components the authors main focus is on stronger forcing in this regime an eddy driven recirculation appears in the abyssal layer and all time mean circumpolar streamlines are found to stem from a sverdrup like interior the sverdrup flux into drake passage latitudes can then be thought of as the sum of one part that feeds the circumpolar current and another that is associated with the recirculation the relative fractions of this partitioning depend on the bottom drag the midchannel wind stress and the wind stress curl increasing the strength of the bottom drag reduces the recirculation and increases circumpolar transport increasing a zero curl eastward wind stress reduces th

na cl br systematics of mineralizing brines in mississippi valley type deposits new and published analyses of fluid inclusion leachates from mississippi valley type mvt deposits can be divided into two groups on the basis of na br and cl br ratios mvt leachates from the illinois kentucky and cincinnati arch districts and from cubic galena in the viburnum trend have na br and cl br ratios that extend to values significantly above that of seawater which are characteristic of evaporite dissolution brines mvt leachates from polaris and octahedral galena in the viburnum trend have na br and cl br ratios that plot below seawater and along the compositional trend formed by evaporation solubility volume constraints require that brines formed by seawater evaporation had high dissolved metal contents preliminary correlation of leachate compositions allows delineation of two brine provinces in the midcontinent united states 1 an early high br province found only in southeastern missouri and 2 a later low br province of probable permian age that extended from the cincinnati arch to the tri state district these observations along with na cl br data for modern brines from the illinois basin argue against models for single stage midcontinent mvt brine flow based on recharge from late paleozoic arkoma foreland basins to the south

velocity of radio waves in glaciers as an indicator of their hydrothermal state structure and regime the results of measurements of radio wave velocities rwv by wide angle reflection war methods in the temperate abramov glacier in the alai mountain ridge and the two layered sub polar fridtjovbreen and hansbreen on svalbard using a low frequency 2 13 mhz radar are considered and discussed the experimental data obtained and the data from the literature show that the values of rwv could be a good indicator of the hydrothermal state of glaciers as such these data enable the identification of cold temperate and transitional two layered glaciers and can be used for estimation of the water content in glaciers and changes in the hydrothermal state

paleogeographical significance of the rot anisian triassic facies marines clays muds and marls fm in the iberian ranges eastern spain abstract the marines clays muds and marls formation consists of fine grained sediments recording the transition from distal fluvial facies to shallow marine sediments representing the onset of the first marine transgression of the tethys sea in the iberian basin muds show irregular parallel lamination of possible cryptalgal origin wave ripples linsen bedding mud cracks vertical burrows and halite pseudomorphs and contain anisian palynomorphs the carbonate content increases towards the se the deposition of the marines formation took place in a rift the iberian basin during a period of distensive tectonics and probably during a marine transgression of eustatic origin but the relative importance of the tectonic and eustatic factor is a matter of speculation in the area up to now

the age and origin of the barite fluorite pbzn veins of the sierra del guadarrama spanish central system spain a radiogenic nd sr and stable isotope study fluorite and barite rich veins sulphides of the sierra del guadarrama spanish central system are usually hosted by hercynian granitoids zoned fluorites from one of these veins have a sm nd age of 145 18 ma this age is similar to the k ar ages obtained in other hydrothermal rocks of the spanish central system 156 152 ma and confirms the existence of an important hydrothermal event during the late jurassic probably related to extensional fracturing accompanying the opening of the north atlantic ocean the 87sr 86sr ratio found in fluorite and barite 0 7154 0 7207 is in most cases lower than that found in the host granitoids 0 7194 and 0 7209 suggesting more than one source of strontium this in turn supports previous models that involve mixing of two fluids during mineralization an ascending hot 300 c and low salinity fluid and a shallow cooler 100 c and more saline brine the ascending fluid probably reacted to a variable extent with the host granitoids and the most likely source for the shallow fluid derived from a marine evaporitic environment with a low 87sr 86sr ratio 0 7069 in the late jurassic the calculated end composition of the fluorites 8 8 to 7 6 as well as the 147sm 144nd variation found in this mineral 0 153 0 405 do not conflict with the mixing model although they can be largely explained by interaction of the ascending fluid with the host granitoids sulphur isotopic compositions of sulphides range between 3 4 and 0 8 and those of barites from 15 5 to 15 8 the near 34s value of the sulphides suggests that their sulphur was derived from the hydrothermal leaching of the granitoids by the ascending fluid the 34s value of barite is consistent with upper jurassic marine sulphate as the source of sulphate in the shallow fluid the absence of equilibrium between reduced and oxidized sulphur species can be easily interpreted as a consequence of the short residence time of the mixed fluid in the open fractures at temperatures between 250 and loo c although no pre cretaceous sediments are found on this part of the iberian hercynian basement the data presented here support the existence of a shallow platform joining central spain with the iberian or the subbetic realm in late jurassic times

reactivity of dolomitizing fluids and mg source evaluation of fault controlled dolomitization at the benicassim outcrop analogue maestrat basin e spain abstract the mechanisms responsible for the formation of huge volumes of dolomitized rocks associated with faults are not well understood we present a case study for high temperature dolomitization of an early cretaceous aptian albian ramp in benicassim maestrat basin e spain in this area seismic scale fault controlled stratabound dolostone bodies extend over several kilometres away from large scale faults this work aims at evaluating different mg sources for dolomitization estimating the reactivity of dolomitizing fluids at variable temperature and quantifying the required versus available fluid volumes to account for the benicassim dolostones field relationships stable 13 c and 18 o isotopes as well as radiogenic 87 sr 86 sr isotopes indicate that dolomitization at benicassim was produced by a high temperature fluid 80 c 13 c and 18 o isotopic compositions for dolomite vary from 0 5 to 2 9 v pdb and from 21 1 to 24 3 v smow respectively a mg source analysis reveals that the most likely dolomitizing fluid was seawater derived brine that interacted with underlying triassic red beds and the paleozoic basement geochemical models suggest that evolved seawater can be considerably more reactive than high salinity brines and the maximum reactivity occurs at about 100 c mass balance calculations indicate that interstitial fluids with high pressure and or high temperature relative to the normal geothermal gradient cannot account for the volume of dolomite at benicassim instead a pervasive fluid circulation mechanism like thermal convection is required to provide a sufficient volume of dolomitizing fluid which most likely occurred during the late cretaceous post rift stage of the maestrat basin this study illustrates the importance of fluid budget quantification to critically evaluate genetic models for dolomitization and other diagenetic processes

kar ages of clay size concentrates from the mineralisation of the pedroches batholith spain and evidence for mesozoic hydrothermal activity associated with the break up of pangaea abstract the k ar ages of 32 clay concentrates extracted from samples of ore gangue and wallrock associated with mineralisation in the pedroches batholith lie in the range 119 285 ma although some of the mineralisation is of permian age more than half of the ages lie between 210 and 230 ma and indicate a hydrothermal event at this triassic time a comparison with age data for mineralisation and certain anorogenic magmatism in other areas of the north atlantic reveals a consistent pattern of a major event at ca 210 230 ma and a minor event at ca 160 ma with little cretaceous or tertiary activity it is proposed that the ca 210 230 ma event was related to an initial rapid fracturing of the crust associated with the break up of pangaea which was related with an increase in the geothermal gradient and penetration of the deep crust by surface waters which returned via both new and rejuvenated fissure systems

epigenetic dolomitization and the origin of xenotopic dolomite texture abstract xenotopic texture which is commonly observed in pre cenozoic rocks is defined here as a mosaic of anhedral crystals with irregular or curved intercrystalline boundaries and usually undulatory extinction xenotopic dolomite texture is similar in appearance to neomorphic limestone textures idiotopic dolomite texture euhedral to subhedral crystals with straight intercrystalline boundaries contrasts with xenotopic texture and is commonly observed in both cenozoic and more ancient dolomites texture may be controlled by the temperature at which crystals grow crystal growth theory predicts that at low temperature a smooth crystal surface is energetically favored and atoms are added to crystal faces layer by layer with dislocations acting as nucleation sites this results in faceted crystals and euhedral to subhedral crystal mosaics above a critical roughening temperature crt a rough surface is energetically favored surface nucleation does not require dislocations and atoms are randomly added to the crystal surface resulting in nonfaceted growth and an anhedral crystal mosaic it is hypothesized that a critical roughening temperature exists for dolomite above 50 c xenotopic dolomites are produced by dolomitization of limestone and or neomorphic recrystallization of dolomite at elevated temperature above the crt after burial idiotopic dolomites are produced below the crt by near surface processes and are occasionally produced above crt if growth inhibiting effects of the solution or impurities stabilize crystal faces calcite has a crt below 25 c and therefore develops anhedral crystal mosaics characteristic of neomorphic texture both at near surface and at elevated temperatures synthetic xenotopic dolomite was produced in the laboratory at 250 c and 300 c by dolomitization of aragonite and calcite skeletal fragments and by recrystallization neomorphism of nonstoichiometric cenozoic dolomites xenotopic dolomite resulted from the metamorphic recrystallization of the idiotopic hueco dolomite permian texas near the marble canyon intrusion at temperatures between 350 c and 600 c hydrothermal dolomitization of periclase calcite marble near the intrusion also resulted in a xenotopic texture xenotopic dolomite in the galena group ordovician wisconsin was produced by neomorphism of a preexisting dolomite during the emplacement of lead zinc sulfides at temperatures between 80 c and 227 c in the trenton limestone ordovician michig n xenotopic dolomite replaced limestone during the migration of hot 50 c fluids along fracture systems xenotopic dolomite was not observed in cenozoic dolomites that were subjected to temperatures near surface values only

airborne radar stratigraphy and electrical structure of temperate firn bagley ice field alaska u s a helicopter borne 135 mhz short pulse radar profiles of the bagley ice field southern alaska u s a have been analyzed to determine the nature of radio wave propagation through crevassed stratified wet and draining firn diffractions characterize the firn horizons along the trunk and reflections characterize those of overlying snow fields dynamic stacking was used to form and determine firn depths and unstacked diffraction analysis to determine firn layer properties refractive indices range from 4 1 to 4 5 for the near surface from 1 7 to 2 1 at about 13 17 m depth along the main trunk and to 2 6 to 58 m depth within a snowfield average trunk values correspond with volumetric water contents of about 0 09 which agree with values measured for other glaciers the analysis of the airborne recorded diffractions is confirmed by deriving the approximate refractive index of water from a supraglacial lake bottom diffraction the lack of snowfield diffractions suggests that crevassing and not firn structure caused the trunk diffractions the reasonable values of the indices imply that the diffractions originated from single points or edges orthogonal to the profile transect and they predict low interlayer transmission losses the snowfield penetration suggests that several hundred meters might be penetrated in uncrevassed accumulation zones with improved system design

fluorite deposits at encantada buenavista mexico products of mississippi valley type processes ore geol rev 23 2003 107 124 a reply we very much appreciate the comments of dr spirakis regarding the fluorite deposits of la encan tada buenavista the contribution by gonza lez par tida et al 2003 represents a partial report of thework we are carrying out on the fluorite deposits ofnorthern coahuila state mexico we have subse quently conducted further work on the deposit inorder to complement the information already pub lished addressing controls on the distribution of themineralized bodies and halogen studies of fluid inclu sions we discuss here in light of our new results theproblem of fluorine transport and precipitation at laencantada buenavista new developments in the mine showed that there isa strong structural control on the distribution offluorite bodies the latter are found at the intersectionof low permeability barriers with low angle faults layer parallel slip developed at stratification bound aries with abundant clayey materials precipitation offluorite is preceded by a dramatic increase in perme ability due to the hydraulic fracturing of the host rock enclosing rock fragments included in the newlydeveloped breccias are usually recrystallized andslightly corroded but are also rapidly covered byfluorite the precipitation of which appears to precludethe continuance of carbonate replacement a thincalcite blanket typically a few centimeters to deci meters thick is found at the boundary of the fluoritebody smoothly passing to the slightly recrystallizedenclosing limestone fluorite appears as white tocolorless corrosion free crystals indicative of passivemineral precipitation late cavities are filled up byidiomorphic cubic zoned fluorite crystals with adeep purple color in their outer zones minor idiomor phic calcite scalenoedrons and extremely rare crystalsof barite

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100