snow cover simulations in mountainous regions based on general circulation model outputs a meteorological analysis procedure allowing simulation of the snow cover in mountainous regions where the general circulation model orography differs from thc real orography is described this proccdure uscs modcl outputs to estimate the data needed to forcc a snow modcl tcmpcrature and prccipitation deduccd from threc five year runs were comparcd to thc snow climatology of the french alps the snow covcr simulations are very sensitive to temperature at middle elevations at high elevations the altitude of the equilibrium line is simulated well

sector trilling in cordierite and equilibrium overstepping in metamorphism the origin of sector trilling in cordierite is due to the hexagonal orthorhombic al si ordering transformation which under non equilibrium conditions proceeds via a short range ordered modulated structure the growth of these distortion waves associated with progressive ordering produces a strain field which is minimized by a cyclic distribution of symmetrically equivalent modulations sector and complexly trilled cordierites in metamorphic rocks grew as the hexagonal polymorph with a considerable degree of al si disorder the enthalpy and entropy of disorder are evaluated from recent experimental work the implication is that in metamorphic rocks substantial overstepping of stable equilibrium phase boundaries is required to nucleate hexagonal cordierite moreover its composition coexisting with other phases will also be significantly different from that of the stable ordered form

hydrogen and oxygen stable isotope signatures of goethite hydration waters by thermogravimetry enabled laser spectroscopy abstract the hydrogen and oxygen stable isotope composition 2h and 18o values of mineral hydration waters can give information on the environment of mineral formation here we present and validate an approach for the stable isotope analysis of mineral hydration waters based on coupling a thermogravimetric analyzer with a laser based isotope ratio infrared spectroscopy instrument picarro l 2130i which we abbreviate as tga iris tga iris generates 2h and 18o values of liquid water samples with precision for 2h of 1 2 and for 18o of 0 17 for hydration waters in goethite precision for 2h ranges from 0 3 to 1 6 and for 18o ranges from 0 17 to 0 27 the ability of tga iris to generate detailed water yield data and 2h and 18o values of water at varying temperatures allows for the differentiation of water in varying states of binding on mineral surfaces and within the mineral matrix tga iris analyses of hydrogen isotopes in goethite yields 2h values that reflect the hydrogen of the oh phase in the mineral and are comparable to that made by irms and found in the literature in contrast 18o values on goethite reflect the oxygen in oh groups bound to fe fe oh group and not the oxygen bound only to fe fe o group in the mineral crystal lattice and may not be comparable to literature 18o values made by irms that reflect the total o in the mineral tga iris presents the possibility to isotopically differentiate the various oxygen reservoirs in goethite which may allow the mineral to be used as a single mineral geothermometer tga iris measurements of hydration waters are likely to open new avenues and possibilities for research on hydrated minerals

formation of sapphirine and corundum in scapolitised and mg metasomatised gabbro terra nova 22 166 171 2010 abstract sapphirine mg3 41fe0 11al4 45 al4 55si1 45 o20 and corundum are found as inclusions 0 2 mm in cl rich scapolite me24 25 and plagioclase an20 24 in the metasomatised parts of the odegarden gabbro bamble sector south norway microtextural relationships suggest that the overall reaction plagioclase mg cl sapphirine corundum scapolite ca fe took place in two stages possibly related to infiltration of two metasomatic fronts gresen analyses support that the scapolitisation was combined with a strong mg metasomatism and removal of fe and ca on a whole rock scale the ferromagnesian minerals associated with sapphirine in the scapolite metagabbro have especially high mg ratios orthopyroxene mg 0 96 phlogopite mg 0 95 amphibole mg 0 81 0 87 clinopyroxene mg 0 95 this is much higher than in biotite mg 0 60 and clinopyroxene mg 0 78 0 81 in the unscapolitised parts of the gabbro and comparable with that found in sapphirine bearing orthoamphibole cordierite schists in the region suggesting that they also formed by metasomatism a metasomatic origin for the sapphirine has consequences for models of crustal growth and metamorphic history

environmental memory and a possible seasonal bias in the stable isotope composition of u th he dated goethite from the canadian arctic abstract goethite ax 2 from axel heiberg island 80 n on the margin of the arctic ocean is the dominant mineral in a sample of petrified eocene wood but u th and he measurements suggest that the goethite feooh crystallized in the latest miocene pliocene ca 5 5 to 2 8 ma measured d and 18 o values of ax 2 are 221 6 and 9 6 0 5 respectively the inferred d and 18 o values of the ancient water were about 139 and 18 6 respectively with a calculated temperature of crystallization of 3 5 c which compares with the modern summer j j a temperature of 3 c and contrasts with a modern mat of 19 c published results from various biological proxies on nearby ellesmere island indicate a pliocene 4 ma mat of either 6 or 0 4 c and corresponding seasonal amplitudes of about 18 or 13 c a conductive heat flow model suggests that a temperature of 3 c could represent goethite crystallization at depths of 100 200 cm for mat 6 c or 250 450 cm for mat 0 4 c over seasonally restricted intervals of time the 18 o value of the ax 2 water 18 6 is more positive than the modern j j a precipitation 22 in combination the paleotemperatures and 18 o values of ancient waters from ax 2 and published results from three eocene or pliocene proxy sites on axel heiberg and ellesmere islands are consistent with a warm season bias in those isotopic proxies the results are also consistent with higher proportions of j j a precipitation in the annual total if so this emphasizes the importance of seasonality at high latitudes even in times of warmer global climates and suggests that the arctic hydrologic cycle as expressed in the seasonal distribution and isotopic composition of precipitation perhaps modified by a warmer arctic ocean differed from modern the 13 c value of the fe co 3 oh component in the ax 2 goethite is 6 6 which is much more positive than expected if crystallizing goethite incorporated co 2 derived primarily from oxidation of relict eocene wood with 13 c values of about 24 this apparent paradox may be resolved if the goethite is a product of oxidation of 13 c rich siderite which had previously replaced wood in an eocene methanogenic burial environment thus the goethite retains a carbon isotope memory of a diagenetic eocene event but a d and 18 o record of the latest miocene pliocene arctic climate

oxygen and hydrogen isotope variations among goethites α feooh and the determination of paleotemperatures abstract a plot of d vs 18o values from a diverse group of natural goethites defines a data array which is approximately parallel to the meteoric water line the 18o values range from 9 5 to 4 4 per mil while the corresponding d values vary from 202 to 94 per mil there is considerable scatter in the d vs 18o array which can be attributed primarily to different temperatures of mineral formation as determined previously yapp and pedley 1985 and confirmed in this study the goethite water d h fractionation factor is essentially independent of temperature over the range from 25 c to 145 c however the goethitewater 18 o 16 o fractionation factor does vary with temperature as indicated by initial goethite synthesis experiments conducted at 25 c 44 c and 62 c the synthetic goethite 18 g w values suggest that the natural goethites in this study formed at temperatures that may range from about 8 c to 66 c support for the validity of these approximate calculated temperatures is provided by a natural goethite sample from the atlantis ii deep in the red sea these results suggest that goethite can be used as a single mineral low temperature geothermometer perhaps more importantly goethite can be used in low temperature oxygen isotope mineral pair geothermometers such as chert goethite calcite goethite phosphate goethite etc

mechanisms and rates of plagioclase carbonation reactions abstract plagioclase is one of the most abundant sources of calcium in the earth s crust and it may play an important role for co2 storage this study address the carbonation of anorthite rich plagioclase an67 an73 in a system with fluid transport and under stagnant conditions a combined approach of flow through column and batch experiments has been used experimental conditions ranging from 100 to 250 c and 20 to 120 bar and different preparations of the starting material were applied the overall carbonation reaction consists of plagioclase dissolution coupled to a number of precipitation reactions the flow through column experiments at 250 c showed stoichiometric dissolution of the plagioclase al hydroxide proto al hydroxide nucleated on the plagioclase as the first phase to precipitate a secondary porosity developed between the shrinking plagioclase and the enclosing proto al hydroxide calcite as the second phase to precipitate filled the primary pore space a reaction front was developed separating the zone at the inlet where all the plagioclase had dissolved and the less reacted outlet of the column redissolution of the calcite and formation of euhedral boehmite crystals occurred when a sufficient amount of plagioclase had dissolved clay minerals were not precipitated in the column experiments between 11 and 30 of the plagioclase was dissolved within 72 168 h of reaction a much higher extent of plagioclase dissolution was observed in the high pressure experiments compared to the low pressure however a smaller share of the released ca was trapped as calcite in the high pressure experiments both observations are consistent with a more rapid progression of the dissolution front at high pressure the batch experiments showed conversion of the plagioclase to a mixture of al hydroxide possibly gibbsite clays and calcite a range in conversion from below the detection limit to 91 was observed within reaction periods of 24 72 h crystallinity of the feldspar was the most important factor contributing to increased reaction rates a general positive effect of increasing temperature on the conversion is observed for all materials whereas pressure and the addition of cacl2 did not have any effect the carbonation of plagioclase at stagnant conditions is slow compared to olivine at temperatures around 200 c however industrial operations involving high fluid flows of co2 water mixtures induce gradients in ph or solute concentrations which may lead to increased reaction rates and changes in porosity permeability

implications of trace element geochemistry for the origin of cordierite orthoamphibole rocks from orijarvi sw finland we present the first comprehensive geochemical data major elements and 31 trace elements by xrf and inaa for the metamorphic cordierite orthoamphibole anthophyllite gedrite rocks cor that occur in the early proterozoic 1 85 ga svecofennian supracrustal rocks at orijarvi finland eight samples and associated cummingtonite biotite plagioclase gneisses five samples cor 57 3 76 9 wt sio are distinguished from 50 4 61 7 wt sio by lower sc cr and co and by higher zr hf nb tth and u cor have enriched and fractionated lree 45 105x chondrites flat hree 10 21x and prominent negative eu anomalies display highly variable lree 10 90x chondrites flat hree 4 20x and mostly positive eu anomalies four of five samples for all samples concentrations of sr 18 304 ppm correlate strongly with cao 0 1 9 4 wt cor and have low concentrations of cu 10 90 ppm and moderate concentrations of zn 50 400 ppm several elemental parameters la th sc and th hf co proportions z

mg metasomatism of metagranitoids from the alps genesis and possible tectonic scenarios terra nova 24 423 436 2012 abstract mg metasomatic rocks e g whiteschists leucophyllites derived from post variscan granitoids are common in the alps previously reported field petrological geochemical and fluid inclusion data are combined to trace the genetic processes and the associated tectonic scenarios many common features can be recognised in all of the continental mg metasomatic rocks indicating that the genetic process is likely common in the entire range of the alps this process assumes highly channelised fluids derived from ultramafic rocks previously interacting with seawater that infiltrated the continental crust along strain zones and produced chromatographic fractionation of major and trace elements three tectonic scenarios involving distinct mantle sources are proposed rift related ocean continent transition continental subduction and continent continent collision all these data suggest that the mg metasomatism was diachronous and occurred at different structural levels during the alpine history

cordierite formation during the experimental reaction of plagioclase with mg rich aqueous solutions the reaction between plagioclase labradorite and oligoclase and mg rich aqueous solutions was studied experimentally at hydrothermal conditions 600 700 c 2 kbar during the experiments plagioclase grains were readily converted to cordierite and quartz within 4 days the cordierite crystals had well developed polyhedral shapes but showed skeletal internal morphologies suggesting that the initial growth occurred fast under high driving force conditions in pure mgcl2 solutions 0 5 5 m plagioclase dissolution and cordierite precipitation were spatially uncoupled indicating that al was to some extent mobile in the fluid cordierite crystals formed at 700 c showed orthorhombic symmetry whereas those formed at 600 c dominantly persisted in the metastable hexagonal form suggesting a strong increase in al si ordering speed between 600 and 700 c the thermodynamic evolution of the fluid solid system ultimately resulted in stabilization of ca rich plagioclase as demonstrated by partial anorthitization of unreacted plagioclase grains cordierite was also observed to form when mg was added to a potentially albitizing na silicate bearing solution in that case cordierite precipitation appeared to be more closely coupled to plagioclase dissolution and secondary alteration of remnant plagioclase grains did not occur most likely due to armoring of the plagioclase by the cordierite overgrowth the fast reaction rates observed in our experimental study have potential implications for mg metasomatism as a rock forming process

oxygen and hydrogen isotope compositions in clay minerals a potential single mineral geothermometer the opposite slopes of the isotopic fractionation of hydrogen and oxygen in the clay water system and the well known relationship between d and 18o in meteoric waters allow the isotopic composition of clay minerals to be used as a single mineral geothermometer equations can be derived which are valid for continental systems where meteoric waters are common the following equation was derived for smectite 3 54 106t 2 18osm 0 125 dsm 8 95 0 150 this equation was used to determine the isotopic composition and temperature of the waters involved in the transformation of volcanic rock to bentonite at the cortijo de archidona southeastern spain site the values obtained 6 t 21 c i e environmental temperatures confirm the reliability of this equation

carbonate clumped isotope bond reordering and geospeedometry carbonate clumped isotope thermometry is based on the preference of 13c and 18o to form bonds with each other at elevated temperatures such bond ordering is susceptible to resetting by diffusion of c and o through the solid mineral lattice this type of bond reordering has the potential to obscure primary paleoclimate information but could also provide a basis for reconstructing shallow crustal temperatures and cooling rates we determined arrhenius parameters for solid state reordering of c o bonds in two different calcites through a series of laboratory heating experiments we find that the calcites have different susceptibilities to solid state reordering reaction progress follows a first order rate law in both calcites but only after an initial period of non first order reaction that we suggest relates to annealing of nonequilibrium defects when the calcites are first heated to experimental temperature we show that the apparent equilibrium temperature equations or closure temperature equations for carbonate clumped isotope reordering are analogous dodson s equations for first order loss of daughter isotopes for each calcite the sensitivity of apparent equilibrium temperature to cooling rate is sufficiently high for inference of cooling rates within a factor of 5 or better for cooling rates ranging from tens of degrees per day to a few degrees per million years however because the calcites have different susceptibilities to reordering each calcite defines its own cooling rate apparent equilibrium temperature relationship the cooling rates of carrara marble inferred from carbonate clumped isotope geospeedometry are 10 6 10 3 degrees per annum and are in broad agreement with rates inferred from thermochronometric methods cooling rates for 13c depleted calcites from the late neoproterozoic doushantou cap carbonates in south china are on the order of 102 104 degrees per annum consistent with rapid cooling following formation of these calcites by a short lived hydrothermal event bristow et al 2011 nature v 474 p 68 71 most of the uncertainty in these estimates relates to uncertainty in arrhenius parameters for different calcites thus while the carbonate clumped isotope geospeedometer shows promise for recording cooling rates in settings and lithologies where other geospeedometers may not be applicable the uncertainty in cooling rate will be large without independent knowledge of the reordering kinetics of each study material thus the full potential of the method will only be realized if reordering kinetics can be accurately determined for each study material or predicted on the basis of mineral composition texture or other observable parameters

rusty relics of earth history iron iii oxides isotopes and surficial environments abstract the two most common low temperature iron iii oxides on earth are goethite feooh and hematite fe2o3 the 18o values of natural goethites range from 15 5 to 3 3 whereas 18o values of low temperature hematites range from 16 7 to 4 7 plots of d against 18o for continental goethites are approximately parallel to the meteoric water line of craig h craig 1961 science 133 1702 3 this suggests that goethite water fractionation factors are systematic over a wide range of surficial environments and may indicate that isotopic equilibrium is commonly attained or closely approached several experimental or calculated mineral water oxygen isotope fractionation curves have been determined for both goethite and hematite although there is not yet a consensus on which of these curves best approximates isotopic fractionation in natural samples oxygen isotope measurements of both goethite and hematite have provided evidence of significant continental climate change on time scales that

k metasomatism and detachment related mineralization harcuvar mountains arizona the bullard detachment fault a regional low angle normal fault exposed in the harcuvar mountains of west central arizona separates lower plate mylonitic rocks and chloritic breccia from upper plate volcanic and sedimentary rocks areally extensive k metasomatism has converted upper plate mafic flows and felsic ash flow tuffs into rocks with 8 to 12 wt k 2 o 2 o and a simple k feldspar hematite quartz mineralogy the secondary k feldspar is very pure or 95 to 99 5 monoclinic and structurally similar to orthoclase differences in 18 o values between secondary k feldspar replacing sanidine phenocrysts 9 to 11 and k feldspar replacing groundmass 11 to 14 in the tuffs imply differential o exchange with migrating fluids whole rock 18 o values for tuffs 10 to 14 and mafic flows 6 to 9 do not therefore represent primary igneous values the rocks apparently became k metasomatized and 18 o enriched while interacting with low to moderate temperature neutral to alkaline oxidizing brines that accumulated in an extensional basin above the detachment fault cu au ag mineralization is concentrated in faults and fissures in metasomatized mafic flows above the detachment fault fluid inclusion studies show that mineralizing fluids had minimum temperatures of 290 to 330 c along the detachment fault 240 to 290 c in mafic flows above the detachment fault and 100 to 130 c in barite calcite mn oxide veins farther from the detachment fault the predominant mineralizing fluids near the detachment fault and in the mafic flows were saline brines with 13 to 17 equivalent wt naci more dilute brines with 6 to 12 equivalent wt naci formed the barite calcite mn oxide veins inferred 18 o values of the mineralizing fluids range from 3 for high temperature quartz sulfide veins to 5 for lower temperature barite calcite mn oxide veins the high salinities oxygen isotope compositions and geologic setting indicate that the mineralizing fluids were basinal brines the mineralizing fluids apparently evolved from early deep level reducing basin brines to a later stage marked by the influx of higher level oxidizing basin brines relatively minor amounts of less evolved lower 18 o meteoric water entered the system during the very late stages of mineralization paragenetic relations and geochemical and isotopic data indicate that mineralization was superimposed on previously k metasomatized rocks mineralization and k metasomatism may be indirectly linked however because both occurred during detachment faulting and both involved basinal brines specifically k metasomatism of upper plate units liberated elements such as cu pb zn mn sr and na that were incorporated into the mineralizing basin brines multiple fluid regimes during detachment faulting are indicated because basin brine dominated mineralization overprinted lower plate mylonitic rocks and breccia that had probably previously equilibrated with igneous or metamorphic fluids at deeper levels of the detachment system

mg metasomatism and formation conditions of mg chlorite muscovite quartzphyllites leucophyllites of the eastern alps w hungary and their relations to alpine whiteschists the lower austroalpine orthogneiss micachist complex of the sopron fertorakos area of w hungary contains mg chlorite muscovite quartzphyllites leuco phyllite and mg chlorite bearing kyanite quartzites whose chemical compositions differ greatly from their surrounding rocks formation of leucophyllites took place in shear zones and was associated with depletion in alkalies and iron and enrichment of magnesium and h2o mg zonation of relict igneous muscovites of leucophyllites and changes in the whole rock chemical compositions suggest mg metasomatism material gains and losses have been assessed using the composition volume relationship approach proceeding from metagranite through transition rocks to leucophyllites mgo h2o feo and alkalies show continuously increasing dispersion in isocon plots with mg enrichment even in sheared gneiss not in contact with leucophyllite the metasomatic processes that formed the mg rich rocks may be similar to those responsible for the formation of high pressure whiteschists in the central and western alps the geochemical characteristics of the dora maira whiteschists italy and their country gneisses are very similar to those of the sopron leucophyllites supporting the theory that mg metasomatism produced the whiteschist chemistry on the basis of oxygen isotope compositions of relict igneous muscovites the precursor granitic rock had a 18o value around 13 proving its crustal anatectic origin the leucophyllites have whole rock oxygen isotope compositions around 8 5 which is in conflict with the theory of an mg rich sedimentary protolith rather the low 18o values reflect fluid rock interaction with a low 18o fluid quartz mineral oxygen isotope fractionations yield a metamorphic temperature of 560 30 c which agrees with earlier estimates from mineral stabilities silicon contents of phengites correspond to a metamorphic pressure of 13 gpa at this temperature indicating eclogite facies metamorphism the fluids in equilibrium with leucophyllites had oxygen isotope compositions around 7 9 similar to those calculated for the ultrahigh pressure dora maira whiteschists 7 6 further supporting the genetic link between the leucophyllites and whiteschists hydrogen isotope compositions of mixed white mica chlorite samples from leucophyllites range from 40 to 35 correlating with chlorite contents the calculated endmember chlorite and white mica have d values of 30 and 40 respectively the similar d values of the white micas in leucophyllites gneisses and metagranites suggest an overall equilibration with respect to h isotopes the calculated d value of the fluid is approximately 0 suggesting a seawater origin this conclusion was also reached for the dora maira whiteschists a possible fluid source that satisfies both metasomatic and isotopic data is dehydration of hydrothermally altered oceanic crust the mafic ultramafic complex of the alpine penninic unit underlying the austroalpine nappes is a likely candidate the subduction and subsequent dehydration of the ophiolite series would supply the mg rich fluids whose migration brought about the metasomatic alteration of the overlying gneiss micaschist complexes

geochemistry and origin of cordierite orthoamphibole gneiss and associated rocks at an archaean volcanogenic massive sulphide camp manitouwadge ontario canada abstract cordierite orthoamphibole gneiss amphibolites quartz biotite schist and calc silicate rocks occur in spatial association with archaean metamorphosed volcanogenic massive sulphide vms deposits at manitouwadge ontario trace element characteristics particularly those of the high field strength elements hfse support field relationships that most of the cordierite orthoamphibole gneisses represent metamorphosed equivalents of chlorite rich rocks that were derived hydrothermally from tholeiitic basalts as an integral part of the syngenetic ore forming processes on the archaean seafloor however a garnet rich cordierite orthoamphibole dike that is characterized by low tio2 content and high concentrations of zr y nb and ree and has single zircon pb evaporation 207 pb 206 pb ages of 2715 2743 ma may have been derived from a synvolcanic felsic dike evidently the seafloor hydrothermal alteration at manitouwadge resulted in similar alteration products from contrasting protoliths and therefore was a fluid dominant system the amphibolite lenses within the cordierite orthoamphibole gneiss also have been affected by the seafloor hydrothermal alteration and some of them most likely represent metamorphosed equivalents of calcsilicate alteration products formed on the seafloor mass balance calculations indicate that hfse and ree were mobilized during the seafloor hydrothermal alteration the mobility of hfse and ree was controlled by both their host minerals and the hydrothermal fluids in particular a significant portion of igneous zircon in the garnet rich dike has survived the seafloor hydrothermal alteration and the subsequent high grade regional metamorphism the regional metamorphism did not change the bulk rock ree characteristics but was important in redefining the mineralogy of ree trace element geochemistry of mafic metavolcanic rocks at manitouwadge are similar to those of the adjacent schreiber hemlo greenstone belt and are consistent with a volcanic island arc setting however further work is required to determine whether the manitouwadge and adjacent greenstone belts of the wawa subprovince were originally a larger continuous terrane

intracrystalline site preference of oxygen isotopes in goethite a single mineral paleothermometer abstract the crystal structure of goethite feo oh has two distinct oxygen sites one with exclusively fe o bonds the other with bonds to both iron and hydrogen we developed a method to assess the oxygen isotope contrast between these sites by measuring both the bulk goethite and the oxygen released in the conversion of goethite to hematite the method involves collecting the water released by dehydroxylation fluorinating that population of extracted atoms and measuring the resulting oxygen isotope composition extracted o 18 then on a separate aliquot all structural oxygen is fluorinated and measured bulk o 18 using synthetic goethite precipitates grown under controlled environmental conditions we found significant temperature dependent fractionation e bulk extracted 5 51 0 26 10 6 t 2 44 5 2 8 t in kelvin this intracrystalline fractionation forms the basis of a single phase paleothermometer with an estimated uncertainty of 2 3 c the temperature dependence appears to be independent of the isotopic composition of the parent fluid from which the goethite formed and the ph of that fluid this intracrystalline thermometer can be used to simultaneously determine the formation temperature of a goethite and the isotopic composition of the water from which it formed natural goethites analyzed with this technique yield geologically reasonable formation temperatures of between 15 and 41 c

a cenozoic terrestrial paleoclimate record from he dating and stable isotope geochemistry of goethites from western australia supergene goethites from the hamersley region of western australia were analyzed for 18 o and the results combined with both new and previously published u th he ages to assess the paleoenvironmental signal recorded by surficial goethite in a long term continental archive 18 o goe values increase monotonically by 3 between 71 ma and 5 ma and appear little affected by changes in temperature or other characteristics of depositional environment the temporal trend likely reflects the isotopic composition of meteoric water from which the goethite formed which varied as australia migrated 3000 km northward over the cenozoic translating age to paleolatitude reveals that the 18 o goe data are consistent with a latitudinal gradient in the 18 o precip that throughout the cenozoic remained largely unchanged from the modern gradient there is a 5 offset between the latitudinal trends of 18 o goe and modern precipitation approximately as expected from the water goethite fractionation factor temporal variation in the 18 o of local meteoric water arising from changes in moisture source or pathway are not evident in the goethites at least in part because topography is subdued and has evolved little in this tectonically quiescent landscape our results provide evidence that the efficiency of water transport from equator to pole that governs the latitudinal 18 o gradient of precipitation has been roughly constant over southern temperate latitudes for the entirety of the cenozoic

plagioclase and epidote buffering of cation ratios in mid ocean ridge hydrothermal fluids experimental results in and near the supercritical region abstract experiments have been performed with na ca k cl fluids of seawater chlorinity and diabase basalt and plagioclase bearing mineral mixtures at 350 425 c and 250 400 bars to help constrain hydrothermal alteration processes at mid ocean ridges dissolved ca na and ph for all experiments responded systematically to differences in dissolved sio2 concentrations and the compositions of plagioclase reactants diabase alteration at low fluid rock mass ratios 0 5 to 1 produces fluids undersaturated with respect to quartz during hydration of primary olivine and orthopyroxene whereas basalt alteration under similar conditions yields fluids slightly supersaturated with respect to quartz during breakdown of glass to smectite and amphibole fluid chemistry in all experiments appears to approach a partial equilibrium state with the albite and anorthite components in plagioclase and approaches a ph consistent with plagioclase alteration to epidote trace element data from vent fluids specifically b and sr together with major element chemistry ca na sio2 ph provides evidence that the reaction zone for black smoker fluids at mid ocean ridges is composed of only slightly altered diabase and is characterized by small amounts of epidote nearly fresh plagioclase and clinopyroxene and partially to completely hydrated olivine and orthopyroxene fluids reacting with this rock may be undersaturated with respect to quartz so pressure estimates based on the quartz geobarometer should be regarded as minimums using equilibrium between plagioclase the dominant reactant and epidote the dominant reaction product in experiments we estimate that temperatures in reaction zones are in excess of 375 c for most vent systems these temperatures are higher than measured vent temperatures suggesting that hotspring fluids commonly loose heat during ascent to the seafloor

weathering geochronology by u th he dating of goethite nine samples of supergene goethite feooh from brazil and australia were selected to test the suitability of this mineral for u th he dating measured he ages ranged from 61 to 8 ma and were reproducible to better than a few percent despite very large variations in u and th in all samples with internal stratigraphy or independent age constraints the he ages corroborated the expected relationships these data demonstrate that internally consistent he ages can be obtained on goethite but do not prove quantitative 4he retention to assess possible diffusive he loss stepped heating experiments were performed on two goethite samples that were subjected to proton irradiation to produce a homogeneous distribution of spallogenic 3he the 3he release pattern indicates the presence of at least two diffusion domains one with high helium retentivity and the other with very low retentivity at earth surface conditions the low retentivity domain which accounts for 5 of 3he contains no natural 4he and may represent poorly crystalline or intergranular material which has lost all radiogenic 4he by diffusion in nature diffusive loss of 3he from the high retentivity domain is independent of the macroscopic dimensions of the analyzed polycrystalline aggregate so probably represents diffusion from individual micrometer size goethite crystals the 4he 3he evolution during the incremental heating experiments shows that the high retentivity domain has retained 90 95 of its radiogenic helium this degree of retentivity is in excellent agreement with that independently predicted from the helium diffusion coefficients extrapolated to earth surface temperature and held for the appropriate duration considering both the high and low retentivity domains these data indicate that one of the samples retained 90 of its radiogenic 4he over 47 5 ma and the other retained 86 over 12 3 ma thus while diffusive loss corrections to supergene goethite he ages are required these initial results indicate that the corrections are not extremely large and can be rigorously quantified using the proton irradiation 4he 3he method

metasomatic albitites and related biotite rich schists from a low pressure polymetamorphic terrane snake creek anticline mount isa inlier north eastern australia microstructures and p t d paths rocks of the snake creek anticline are mainly pelitic schists psammitic schists and quartzites that were metamorphosed during multiple high t low p events extending from d1 to d5 with the metamorphic peak occurring late to post d3 albitites are widespread but are concentrated in five areas they are typically fine to medium grained and consist of albite with or without combinations of quartz biotite staurolite cordierite garnet andalusite sillimanite kyanite gedrite and tourmaline from the presence or absence of albite inclusions in porphyroblasts the albitites are interpreted as forming early in the d3 event as a result of infiltration of external fluids psammitic schists and quartzites were preferentially altered but pelitic schists were also albitized in localities where the alteration was more extreme with the replacement of muscovite total and the replacement of quartz and biotite variable structural controls on albitization include fracturing and syn d3 shear zones in fold hinges biotite schists with abundant porphyroblasts combinations of staurolite garnet andalusite and cordierite occur adjacent to albitites and it is argued that they formed by the addition of fe and mg sourced from the albitites in several albitite rich areas cordierite grew early in d3 and was partly or entirely replaced during or after d3 by combinations of biotite andalusite tourmaline staurolite and sillimanite a postulated p t d path involved an increase in pressure with or without a decrease in temperature subsequent to early d3 albitization followed by an increase in temperature up to the metamorphic peak late d3 to early d4 the metamorphism was contemporary in part with the emplacement of the williams batholith c 1550 1500 ma which probably supplied the na rich fluids

evidence for 5 ma paleo exposure of an eocene miocene paleosol of the bohnerz formation switzerland we obtained u th he formation ages and cosmogenic 3he concentrations for pisoliths from a paleosol of the bohnerz formation siderolithic of central europe the paleosol is exposed in the almenbuhl quarry near lohn canton schaffhausen switzerland the paleosol consists of red clay of 3 4 m thickness developed on deeply weathered jurassic limestone and overlain by early miocene conglomerates the u th he formation ages of the pisoliths are between 50 ma and 8 ma with most ages being older than 17 ma there is a sharp decline in the frequency of ages at the time of burial of the paleosol at 17 ma these ages are inconsistent with the previous assumption that the bohnerz formation formed in a cretaceous to early eocene laterite in a tropical climate we propose that the bohnerz formation more closely resembles terra rossa soils which do not require a tropical climate to form the 3he concentration in the pisoliths is roughly constant with depth throughout the paleosol at 300 matoms g we interpret this as the result of soil convection during cosmic ray exposure the minimum exposure duration at the surface of the paleosol is 5 ma a simple model of soil convection shows that the true exposure duration of the paleosol is approximately 10 20 ma these results indicate that the clay soils of the bohnerz formation were continuously exposed at the surface for millions of years since the paleosol was covered by conglomerate since 17 ma the 3he measured here was produced by cosmic ray exposure before burial cosmogenic 3he concentrations measured in fine grained soil iron oxides 1 m are similar to those measured in pisoliths this might indicate that fine grained iron oxides are retentive to helium and might be used for studying the formation and cosmic ray exposure of modern soils and paleosols

reaction of plagioclase feldspars with co2 under hydrothermal conditions abstract geological storage of co 2 in plagioclase bearing sediments granitic rocks and fractured basalts is expected to have a variety of geochemical and geomechanical effects including mineral trapping and porosity permeability changes the amount of co 2 trapped by mineralisation and the extent of any changes in host rock transport or mechanical properties depend on rock composition to date studies of mineralisation have mainly been based on dissolution and precipitation experiments performed at ambient surface conditions or at slightly elevated temperature and pressure however the reactions that occur under in situ conditions are poorly constrained in an attempt to determine the secondary phases formed in the plagioclase co 2 water system under such conditions we performed a set of batch experiments at temperatures in the range 200 300 c using carbon dioxide pressures from 0 4 to 15 mpa we investigated reaction of anorthite and albite which are expected to precipitate calcite and kaolinite and dawsonite and quartz respectively however in most of our experiments reactions precipitating clays kaolinite and smectite or illite boehmite and a mg ni fe hydrotalcite like phase dominated the nickel being derived from the reaction vessel little or no carbonate and no dawsonite were detected additional feldspar free control experiments employing mg rich brine showed that carbonates would be preserved in our feldspar experiments if formed but that a carbonate substrate is needed to promote precipitation since the secondary phases formed in our plagioclase experiments are stable under a wide range of conditions we expect that they will also form under co 2 storage systems with suitable fluid rock composition from our results we conclude that clay precipitation can proceed or accompany carbonate precipitation depending on the availability of carbonate substrate though an artefact in our experiments in the context of subsurface alkaline waste injection hydrotalcite may play a positive role here by immobilising heavy metals while carbonates will mineralise the co 2

climate changes caused by degassing of sediments during the emplacement of large igneous provinces most mass extinctions during the last 500 m y coincide with eruptions of large igneous provinces lips the cretaceous tertiary extinction was synchronous with the deccan flood volcanism the permian triassic extinction with the eruption of the enormous siberian traps and the end guadalupian extinction with the emeishan volcanic province the causal link remains disputed however and many lips apparently had no significant impact on the biosphere here we show that a key control on the destructive consequences of lip emplacement is the type of sedimentary rock in basins beneath the flood basalts contact metamorphism around intrusions in dolomite evaporite coal or organic rich shale generates large quantities of greenhouse and toxic gases co 2 ch 4 so 2 which subsequently vent to the atmosphere and cause global warming and mass extinctions the release of sediment derived gases had a far greater impact on the environment than the emission of magmatic gases

40ar 39ar and u th he 4he 3he geochronology of landscape evolution and channel iron deposit genesis at lynn peak western australia u th he geochronology of authigenic goethite cements from the lynn peak channel iron deposit cid hamersley province western australia reveals a history of mineral precipitation ranging from ca 33 to 14 ma massive goethites from nearby weathering profiles at roy hill north a possible source of detrital material during the aggradation of the lynn peak channels yield u th he results as old as ca 64 ma the combination of u th he geochronology with incremental outgassing 4he 3he studies on proton irradiated samples reveals that lynn peak goethites host radiogenic 4he in low retentivity lrd and high retentivity hrd domains and that the hrds account for most of the sample mass and have lost very little of their original 4he over geologic time such high retentivity is especially notable given the goethites were collected from the surface where they were subject to significant heating by solar irradiation minor contamination by detrital fragments of potentially 4he rich primary phases e g rutile ilmenite zircon occurs in some samples fortunately the 4he 3he method permits characterization of this extraneous 4he component which is small 10 wt of the total 4he in the goethite and can be corrected out in estimating the goethite formation age these results indicate that the lynn peak channel was already aggraded and undergoing goethite cementation by ca 33 ma the history of aggradation and channel cementation independently measured through 40 ar 39 ar geochronology is consistent with that obtained from the u th he and 4he 3he record laser incremental heating 40 ar 39 ar geochronology of detrital and authigenic mn oxides primarily cryptomelane kmn 8o 16 xh 2o from the same locality in the lynn peak channel reveals that detrital oxides are older than ca 44 ma and as old as ca 65 ma and authigenic oxides are younger than ca 35 ma and as young as ca 16 ma authigenic cryptomelane precipitation and channel cementation occurred throughout the miocene with a particularly strong period at around 20 ma the 40 ar 39 ar geochronological results suggest that regional weathering profiles developed before 44 ma and possibly as early as ca 65 ma were incised and partially eroded in the 44 35 ma interval semi arid conditions promoted the transport of large volumes of sediments aggrading the regional drainage system metasomatic reactions in the aggraded channels caused the ferruginization and in some places manganese replacement of the cids goethite and k mn oxide cementation continued throughout the oligocene and miocene post miocene aridification contributed to the preservation of the cemented channel sediments forming some of the largest readily mineable iron ore deposits on earth

paleoenvironment and the oxygen isotope geochemistry of ironstone of the upper ordovician neda formation wisconsin usa geological evidence suggests that the goethite dominated oolitic ironstone of the upper ordovician neda formation in the north central united states was subaerially weathered in the late ordovician the oxygen isotope ratios of the goethites in the open quotes hard close quotes and open quotes soft close quotes ores of this deposit are rather uniform with a delta sup 18 o value of about minus 1 0 per thousand this delta sup 18 o value indicates the presence of meteoric water at the time of goethite formation and supports the idea that the goethites in hard and soft ores were formed in the same chemical weathering environment 440 million years ago the delta sup 18 o value of accessory phosphate in some soft ore goethite rich ooids was measured and combined with the goethite delta sup 18 o value to calculate a temperature of formation of about 23 degrees c the corresponding delta sup 18 o value of the ancient water was calculated to have been minus 7 3 per thousand the relatively open quotes cool close quotes temperature calculated for the low altitude tropical site occupied by the neda ironstone in the late ordovician is consistent with published evidence from fossil marine invertebrates for global cooling at that time the delta sup 18 o value of minus 7 3 per thousand for the ancient tropical precipitation could indicate intense rainfall ofmore a seasonal perhaps monsoonal character 27 refs 7 figs 3 tabs less

d h of late miocene meteoric waters in western australia paleoenvironmental conditions inferred from the δd of u th he dated cid goethite abstract nineteen u th he ages were determined for eight samples from a core drilled in an ore grade channel iron deposit cid of the robe pisolite robe formation of mesa j in western australia with one exception uncorrected ages of the analyzed aliquots range from 6 7 0 4 ma to 30 2 3 1 ma while molar ratios of th u range from 0 42 to 5 06 the exception is an aliquot with an apparent age of 2 7 ma and th u of 5 70 a three component mixing model involving one generation of goethite and two generations of hematite suggests that the age of crystallization of the oolitic goethites is 7 1 ma if so the goethites have effectively been closed systems for 7 million years and should preserve a stable hydrogen isotope record of late miocene rainfall in the vicinity of mesa j cenozoic movement of the australian continent had placed mesa j and environs in the subtropics at a paleolatitude of about 29 s during the late miocene al adjusted d values of oolitic goethite in the eight cid samples range from 153 to 146 and imply that the d of the late miocene meteoric waters ranged from 61 to 53 with an average of 56 these relatively negative d values might indicate that near coastal late miocene rain was derived primarily from summer season tropical cyclones with storm tracks that extended into the subtropics of western australia the postulated late miocene tropical cyclones would have occurred more often and or exhibited greater intensity at a paleolatitude of 29 s than is the case for modern sites at approximately 30 s on the west coast of australia e g perth higher fluxes of meteoric water in the miocene summers would have facilitated dissolution and removal of bif sourced silica with concomitant enrichment in oxidized fe moreover wetter late miocene summers could have promoted multiple cycles of microbially mediated dissolution and recrystallization of fe iii oxides in the aerobic systems the oolitic textures may be indicative of such recycling however the oolitic goethites of mesa j were closed systems after 7 ma therefore the climate in the vicinity of mesa j seems to have changed in the late miocene to conditions that did not favor widespread recycling of fe iii oxides perhaps changing from seasonally wet to the modern dry climate

u th he geochronology of goethite and the origin and evolution of cangas abstract u th he geochronology of 147 grains of goethite cements extracted from ferruginous duricrusts cangas developed on banded iron formations from the quadrilatero ferrifero region minas gerais brazil records a history of protracted mineral dissolution reprecipitation that started at ca 48 1 4 8 ma and continues intermittently until the present a large majority of the samples more than 30 are younger than 2 ma revealing active mineral dissolution reprecipitation in the recent past within cangas goethite cements are younger near the surface and become progressively older towards the bottom of the weathering profile indicating that iron is more effectively cycled in the parts of the weathering profile more strongly affected by biogenic activity u th he geochronology of 14 goethite grains from saprolites in the same profiles yield results ranging from 55 3 5 5 to 25 7 2 6 ma for a single weathering profile goethite cements from cangas are invariably younger than goethite grains from the underlying saprolite indicating that the duricrust and the saprolite behave as independent and separate systems responding to different environmental controls thorium shows conservative behaviour during goethite dissolution reprecipitation and it is enriched towards the surface of the weathering profile uranium on the other hand is preferentially leached from the surface into the saprolite or out of the weathering profile recurrent goethite dissolution reprecipitation lends great textural complexities to cangas but it is also responsible for its capacity to reheal when physically disrupted this self healing property accounts for canga s role in armoring banded iron formation landscapes

a numerical model to simulate snow cover stratigraphy for operational avalanche forecasting laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature density and liquid water profiles of snow cover as a function of weather conditions to establish these laws the authors have summarized previous studies on temperature gradient and on wet snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh snow samples an original formalism was developed to allow a description of snow with parameters evolving continuously throughout time the introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow covered albedo which depend on the simulated stratigraphy i e the type and size of snow grains of different layers of the snow cover the model was tested during a whole winter season without any re initialization comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail the model proved itself to be very efficient in simulating accurately the evolution of the snow cover stratigraphy throughout the whole winter season

high elevation of the nevadaplano during the late cretaceous during the late cretaceous central nevada may have been a high elevation plateau the nevadaplano some geodynamic models of the western us require thickened crust and high elevations during the mesozoic to drive the subsequent tectonic events of the cenozoic while other models do not to test the hypothesis of high elevations during the late mesozoic we used carbonate clumped isotope thermometry to determine the temperature contrast between late cretaceous to paleocene carbonates atop the putative plateau in nevada versus carbonates from relatively low paleoelevation central utah site lacustrine carbonates from the nevada site preserve summer temperatures 13 c cooler than summer temperatures from paleosol carbonates from the utah site after correcting for 1 2 c of secular climatic cooling between the times of carbonate deposition at the two sites this 13 c temperature difference implies an elevation difference between the two sites of 2 2 3 1 km including uncertainties from age estimation and climate change broadens this estimate to 2 km our findings support crustal thickness estimates and cenozoic tectonic models that imply thickened crust and high elevation in nevada during the mesozoic

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

mass transfer and porosity evolution during low temperature water rock interaction in gneisses of the simano nappe arvigo val calanca swiss alps late alpine fissures and fractures in amphibolite facies basement gneisses at arvigo val calanca swiss alps show distinct cm sized reaction selvages parallel to the fracture walls that composed of subgreenschist facies assemblages produced by the interaction of water present in the fracture porosity with the old high grade gneiss assemblages the process of selvage or reaction vein formation occurred in the brittle deformation regime and at temperatures characteristic of first the prehnite pumpellyite facies and then later of the zeolite facies the vein formation occurred during uplift and cooling at very late stages of the alpine orogeny the reaction veins are composed of a selvage of altered gneiss on both sides of the central fracture and a central zone with fissure minerals that have been growing in the open fracture pore space the central zone of the arvigo veins contains an early assemblage with epidote prehnite and chlorite and a late succession sequence of various species of zeolite the veins of the arvigo quarry are convincing evidence that fracture fluids in gneiss and granite have the potential to precipitate ca zeolite this is an important find because many fluids recovered from deep continental drill holes and from geothermal energy exploration are found to be oversaturated in respect to a number of ca zeolite species vein formation during late uplift and cooling of the alps occurred at continuously decreasing t and at hydrostatic pressure 1 coexisting prehnite epidote records temperatures of 330 380 c 2 chlorite formation at temperature of 333 32 c and 3 formation of zeolites 250 c in the selvages the prime reaction is the replacement of plagioclase by albite along a sharp reaction front that separates the selvage from unaltered gneiss in addition to albitisation chloritisation of biotite is the second important reaction in the alteration process the reactions release components for the formation of ca al silicates the water rock interaction is associated with a depletion of al si ca fe and k in the altered wall rock the overall reaction is associated with an increase in porosity of up to 14 2 2 2 in the selvage zone altered wall rock caused by the volume decrease during albitisation and the removal of biotite the propagation of the sharp reaction front through the gneiss matrix occurred via a dissolution reprecipitation mechanism zeolite formation is tied to the plagioclase alteration reaction in the rock matrix which releases components for zeolite formation to a co2 poor aqueous liquid

dating paleochannel iron ore by u th he analysis of supergene goethite hamersley province australia u th he dating of late stage authigenic goethite combined with corrections for diffusive loss of he 4 by the he 4 he 3 methodology reveals strong correlation between a sample s age and its depth in ferruginized channel sediments from the yandicoogina deposit western australia corrected ages ranging from ca 18 ma near the surface to ca 5 ma at the bottom of the profile indicate that ferruginization of the aggraded channels becomes progressively younger with depth this trend is consistent with goethite precipitation at the groundwater atmosphere interface during water table drawdown driven by the aridification of western australia during the neogene the results demonstrate that the u th he system is ideal for dating goethite if diffusive loss corrections are applied the approach is suitable for dating weathering reactions on earth and should also be suitable for dating fe oxyhydroxides in the martian regolith

atmospheric carbon dioxide linked with mesozoic and early cenozoic climate change carbon isotopes of fossil plants and model simulations suggest that atmospheric carbon dioxide levels were variable during the period 200 to 60 million years ago the large decreases in the partial pressure of co2 coincide with glaciations providing evidence against climate co2 decoupling during the mesozoic

cretaceous and early tertiary climates of antarctica evidence from fossil wood abstract fossil wood is abundant in cretaceous and early tertiary sediments of the northern antarctic peninsula region the wood represents the remains of vegetation that once grew in high palaeolatitudes when the polar regions were warmer during former greenhouse climates fossil wood is a unique data store of palaeoclimate information analyses of growth rings and anatomical characters in fossil wood provide important information about temperature rainfall seasonality and climate trends for this time period in antarctica climate signals from fossil wood supported by sedimentary and geochemical evidence indicate a trend of cool climates during the early cretaceous followed by peak warmth during the coniacian to early campanian narrower growth rings suggest that the climate cooled during the maastrichtian and palaeocene cool wet and possibly seasonal climates prevailed at this time with tentatively estimated mean annual temperatures mats falling from 7 c to 4 8 c respectively determined from dicotyledonous dicot wood anatomy the late palaeocene early eocene was once again warm with estimated mats of 7 15 c from dicot wood analysis but conditions subsequently deteriorated through the latter part of the eocene when cold seasonal climates developed ultimately leading to the onset of cenozoic ice sheets and the elimination of vegetation from most of antarctica

isotopic evidence for holocene climate change in the northern rockies from a goethite rich ferricrete chronosequence abstract climate proxy records often show regional heterogeneity due to the complex interplay of large scale atmospheric circulation patterns and local topographic features this is especially prevalent in the mountainous regions of the western united states where the interaction of two seasonally distinct weather systems can result in locally abrupt climate boundaries here we establish oxygen isotope ratios of goethite from ferricrete chronosequences formed by natural acid rock drainage as a new source of spatially small scale holocene climate information systematic study of these deposits may prove useful in understanding regional variations in response to global holocene climate change oxygen isotope ratios of goethites from the mountainous northeastern yellowstone region show an increase of 3 over the past 9000 years we attribute this isotopic change to a local increase of isotopically heavier summer precipitation since the early holocene possibly augmented by seasonal temperature differences brought on by orbitally forced insolation changes over the past 9000 years our interpretation is compatible with palynology studies as well as holocene climate simulations which indicate a decrease in monsoon intensity from 9000 years b p to the present unlike the southwestern united states this change may have resulted in wetter summers in our study area

timing and nature of fluid flow and alteration during mesoproterozoic shear zone formation olary domain south australia the development of shear zones at mid crustal levels in the proterozoic willyama supergroup was synchronous with widespread fluid flow resulting in albitization and calcsilicate alteration monazite dating of shear zone fabrics reveal that they formed at 1582 22 ma at the end of the olarian d3 deformational event and immediately prior to the emplacement of regional s type granites two stages of fluid flow are identified in the area first an albitizing event which involved the addition of na and loss of si k and fe and a second phase of calcsilicate alteration with additions of ca fe mg and si and removal of na fluid fluxes calculated for albitization and calcsilicate alteration were 5 56 109 to 1 02 1010 mol m 2 and 2 57 108 5 20 109 mol m 2 respectively these fluxes are consistent with estimates for fluid flow through mid crustal shear zones in other terranes the fluids associated with shearing and alteration are calculated to have 18o and d values ranging between 8 and 11 and 33 and 42 respectively and nd values between 2 24 and 8 11 our results indicate that fluids were derived from metamorphic dehydration of the willyama supergroup metasediments fluid generation occurred during prograde metamorphism of deeper crustal rocks at or near peak pressure conditions shear zones acted as conduits for major crustal fluid flow to shallow levels where peak metamorphic conditions had been attained earlier leading to the apparent retrograde fluid flow event thus the peak metamorphism conditions at upper and lower crustal levels were achieved at differing times prior to regional granite formation during the same orogenic cycle leading to the formation of retrograde mineral assemblages during shearing

climate and tectonic influences on continental erosion of tropical south america 0 13 ma is tectonic uplift or climate change the primary driving force behind continent scale erosion here we examine these two hypotheses for tropical south america by comparing a high resolution record of terrigenous sediment accumulation rates from the western tropical atlantic ocean with continental tectonic reconstructions and both low latitude and high latitude climate indices that span the past 13 m y over the full record terrigenous sedimentation rates most closely follow lowland aridity as recorded by abundance ratios of terrigenous oxide minerals an indication that basin integrated climate is an important control of erosion step like transitions in the flux and composition of terrigenous material near 8 and 4 5 ma however follow dated tectonic events which suggests progressive expansion of the drainage basin into less humid or less vegetated regions that were more prone to erosion on long time scales high latitude climate variability and sea level as recorded by 1 8 o do not closely track terrigenous sedimentation we conclude that regional climate change provides a mechanism for long term erosion of tropical south america tectonics plays a significant but secondary role in this area perhaps by shaping the drainage basin to include regions in which the climate is more favorable to erosion

35 ma old ultrahigh pressure metamorphism and evidence for very rapid exhumation in the dora maira massif western alps abstract ion microprobe shrimp data on zircons from various rock types of an ultrahigh pressure uhp metamorphic whiteschist type pyrope quartzite lens of the dora maira massif dmm consistently show domains giving a late eocene age of 35 4 1 0 ma which is taken as the age of uhp metamorphism these domains partially replace the older oscillatory zoning pattern of the zircons formed during primary magmatic crystallization at about 275 ma zircons of a metagranitic country rock next to the uhp metamorphic lens have these primary features best preserved all zircons measured also yield intermediate ages between 275 and 35 ma with a statistical concentration between 260 and 210 ma thus the uniformity of the initial zircon population both in the lens and the country rock evidences a common protolith that is a granite intruded during the late herynian while the intermediate ages are at least partly due to incomplete resetting of the zircons during uhp metamorphism those in the 260 210 ma range may be related to rifting episodes in the permotriassic the mg rich chemistry of the whiteschist lenses is due to local metasomatic alterations of the granite perhaps by fluids derived from evaporitic sediments dating as early as the permotriassic as well the more pervasive resetting of zircon ages during uhp metamorphism in the pyrope quartzite lenses is explained by the ubiquity of fluids and or melts produced during subduction by a series of dehydration reactions that occurred only in the more hydrous mg rich protoliths and not in their drier granitic neighborhood fission track ages determined partly on the same zircon samples yielding 29 9 1 4 ma mark the time when the uhpm unit had reached about 290 c at a shallow location within the crust thus exhumation over a vertical distance of about 120 km must have occurred within about 5 6 ma indicating an average uplift rate of about 20 24 km ma and an average cooling rate of about 85 100 c ma the radiometric data obtained do not lend any support to an eo alpine cretaceous subduction event so that deep subduction and immediately following exhumation all took place during early to mid tertiary time this scenario seems to apply to large portions of the western and central alps as well calling for drastic geodynamic reinterpretations of these parts of the alps

microstructural evolution during experimental albitization of k rich alkali feldspar crystals of k feldspar c2 m in contact with highly concentrated aqueous nacl solutions at 500 c and 200 mpa are pseudomorphically replaced by high albite c bar 1 as a result of an interface coupled dissolution reprecipitation process the reaction occurs at an extremely sharp reaction front 10 nm and involves the complete breakdown of the initial framework structure this results in the release of tetrahedrally incorporated elements such as fe3 and ti4 and a significant increase in si al disorder across the reaction interface the evolving microstructure is controlled by crystallographic relations between the phases this leads to highly anisotropic sawtooth shaped intergrowths of albite and initial k feldspar resulting in the least structural misfit between the two framework structures as a result the newly formed interfaces appear to be semicoherent and cracks across the reaction fronts even indicate elastic strain the reaction produces 2 distinctive albite types albite 1 and albite 2 both are polycrystalline with albite 2 showing significantly larger subgrain sizes this indicates a secondary coarsening step driven by the reduction in interfacial energy within the polycrystalline replacement product the reaction also produces a highly porous rim however the porosity is not evenly distributed resulting in a porous albite 1 and a non porous albite 2 that mostly surrounds large euhedral pores despite the substantial volume fraction of porosity in albite 1 no significant 3d interconnectivity could be detected making the presence of a pervasive porosity unlikely however the result of coarsening is the continuous modification of the 3d porosity distribution this could potentially provide a mechanism for fluid transport through the replacement rim until textural and chemical equilibration is achieved

whiteschists and orthoamphibole cordierite rocks and the p t t path of the modum complex south norway abstract this paper describes the second known occurrence of whiteschist from norway whiteschists and orthoamphibole cordierite rocks which can both be described in the m f ash system are found in the modum complex together with albitites in contact zones between metagabbros and supracrustals they are formed due to extensive hydrothermal activity bulk rock and mineral chemistry define a bimodal fe mg distribution talc kyanite schists and fe poor orthoamphibole cordierite rocks form a leucocratic group and fe rich orthoamphibole cordierite rocks a melanocratic group the break down of an early orthoamphibole cordierite paragenesis to a later talc kyanite paragenesis indicates a cooling path at isobaric conditions or under increasing pressure the temperature pressure regime is of the order of 600 750 c and 6 8 kb reaction textures with talc albite kyanite forming pseudomorphs after gedrite indicate excess albite these nonisochemical reactions indicate the presence of an active na bearing fluid at deep levels in the crust

the replacement of plagioclase feldspars by albite observations from hydrothermal experiments oligoclase and labradorite crystals have been experimentally replaced by albite in an aqueous sodium silicate solution at 600 c and 2 kbars the replacement is pseudomorphic and is characterised by a sharp chemical interface which progresses through the feldspar while preserving the crystallographic orientation reaction rims of albite up to 50 m thick can be readily achieved within 14 days re equilibration of plagioclase in an 18o enriched sodium and silica bearing solution results in oxygen isotope redistribution within the feldspar framework structure the observed characteristics of the reaction products are similar to naturally albitised plagioclase and are indicative of an interface coupled dissolution reprecipitation mechanism chemical analyses demonstrate that the albitisation is accompanied by the mobilisation of major minor and trace elements also including elements such as al and ti which are commonly regarded as immobile during hydrothermal alteration the results contribute to developing our understanding of the close association between large scale albitisation and secondary ore mineralisation which is common in nature

seasonal bias in the formation and stable isotopic composition of pedogenic carbonate in modern soils from central new mexico usa in order to better calibrate pedogenic carbonate as a proxy for past environments we compared the stable isotopic composition of soil co 2 soil water and pedogenic carbonate in young soils from central new mexico usa seasonal changes in the 13 c value of soil co 2 the 18 o value of soil water and the soil temperature were monitored to establish the timing of isotopic equilibrium with the carbonate calcite solubility was calculated from measured temperatures and co 2 concentrations in the soil this approach allowed us to determine the conditions associated with pedogenic carbonate formation carbon isotope equilibrium oxygen isotope equilibrium and minimum calcite solubility all occurred simultaneously during warm dry conditions in may 2008 when soil co 2 concentrations were low it is therefore concluded that pedogenic carbonate forms during warm dry periods and does not record mean growing season conditions as typically assumed the seasonal bias in pedogenic carbonate formation may explain the occurrence of pedogenic carbonate in monsoon climates and its absence in regions where annual precipitation is more uniformly distributed the implications of the seasonal bias for stable isotope based paleoenvironmental reconstructions are that paleoelevations may have been previously over or underestimated paleoatmospheric co 2 concentrations likely have been signifi cantly overestimated and pedogenic carbonate provides a c 4 biased record of paleovegetation especially in dry soils

calcium and sodium exchange during hydrothermal alteration of calcic plagioclase at 400 c and 400 bars a series of experiments were conducted to measure the effect of plagioclase composition on the composition of coexisting cl dominated hydrothermal fluids assemblages containing quartz and natural plagioclase with a composition of either an60 or an82 were reacted with na ca cl fluids at 400 c and 400 bars using flexible cell hydrothermal facilities plagioclase remained homogeneous during these experiments despite the fact that homogeneous solid solutions with intermediate compositions are likely metastable with respect to mechanical mixtures at these conditions it was found that ca and na exchange between fluids and minerals appears to be reversible and highly dependent on plagioclase composition but mca m2na ratios remained constant with increasing cl for a given plagioclase composition in fact a solid solution model which approaches ideal behavior appears to account best for the chemistry of fluids coexisting with an60 and an82 plagioclase these data may have a direct bearing on hydrothermal alteration processes responsible for the chemistry of hot spring fluids at mid ocean ridges which appear to have equilibrated with metastable plagioclase solid solutions of composition an60 to an70

rapid short term cooling following the chicxulub impact at the cretaceous paleogene boundary the mass extinction at the cretaceous paleogene boundary 66 ma is thought to be caused by the impact of an asteroid at chicxulub present day mexico although the precise mechanisms that led to this mass extinction remain enigmatic most postulated scenarios involve a short lived global cooling a so called impact winter phase here we document a major decline in sea surface temperature during the first months to decades following the impact event using tex86 paleothermometry of sediments from the brazos river section texas we interpret this cold spell to reflect to our knowledge the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere blocking incoming solar radiation this impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis

protocols for in situ measurement of oxygen isotopes in goethite by ion microprobe abstract we present protocols for high spatial resolution measurement of oxygen isotope ratios of goethite feooh with the sensitive high mass resolution ion microprobe stable isotopes shrimp si and propose a natural sample as a potential goethite reference material rm for ion microprobe analysis we assess the effects of goethite chemical composition crystallographic orientation and texture on the accuracy and repeatability of shrimp si 18o 18osims results synthetic goethites evaluated as potential 18osims rm are powdery porous and finely crystalline they do not yield repeatable results a dense colloform goethite from the capao topaz mine minas gerais brazil fulfills major prerequisites it is stoichiometrically relatively pure yields repeatable oxygen isotope results and occurs in abundance to produce a rm for long term use we use an average laser fluorination 18olf vsmow value of 17 3 0 3 1sd obtained for five aliquots of this rm to normalize all 18osims measurements multiple 18osims analyses of a large fragment of the capao l4 cl4 rm analyzed in three different runs yield an overall repeatability of 17 3 0 5 2sd n 294 for all three runs combined natural variability and crystal orientation effects are the main reasons for the excess spread of the 18osims results compared to the spot internal precision ca 0 2 all 18osims analyses n 1027 in various aliquots of cl4 randomly oriented and analyzed in 26 sessions during eight distinct runs yield an overall repeatability of 17 3 0 7 2sd confirming that cl4 is a suitable sims rm after ascertaining its suitability as a rm we used cl4 to standardize analyses of other natural goethite samples with the shrimp si and compared 18osims and laser fluorination results to test the relationship between natural properties e g porosity minor elements substituting for fe preparation procedures e g polish and relief instrument conditions and the overall precision and accuracy of the sims analyses samples containing minor elements substituting for fe e g al mn cu zn etc or as contaminants e g si p require significant matrix corrections because we could not find homogenous natural goethite samples showing a large range in metal concentrations we extrapolate our calibration curves beyond the composition of our calibration goethite samples 18osims results corrected for instrument mass fractionation using cl4 and compositionally dependent matrix effects using several calibration goethites of known elemental composition are less precise but statistically indistinguishable from their laser fluorination results however porous samples are unsuitable for shrimp si 18o analysis dense colloform samples yield repeatable results for individual growth bands showing that the high spatial resolution moderate precision and speed of analysis of the shrimp si can resolve variations in oxygen isotope composition acquired during sample growth u th he geochronology of equivalent aliquots from the same goethite samples reveal that the combination of the two methods permits the extraction of temporal variation in the isotopic compositions of meteoric solutions in the geological past

age and evolution of diachronous erosion surfaces in the amazon combining u th he and cosmogenic 3he records u th he geochronology of two weathered plateaus in the carajas mountains para brazil reveals a history of weathering spanning from ca 80 ma to the present for this high elevation 720 m land surface cosmogenic 3he measurements of hematite pebbles and blocks cemented onto the plateaus at two sites n1 and s11d yield erosion rates as low as 0 09 and 0 08 m ma 1 respectively thus these results confirm that the plateau surfaces are nearly immune to physical erosion for tens of millions of years u th he geochronology of ferruginous duricrusts blanketing the low elevation 250 100 m plains surrounding the carajas mountains yield results consistently younger than 10 ma the geochronology results also reveal that the low elevation plain is diachronous becoming progressively younger towards the receding plateaus the spatial distribution of u th he ages permits reconstruction of the history of scarp retreat for the carajas landscape showing that scarp retreat along major river valleys may have been as fast as 20 km ma 1 during tectonically active and humid periods in the cenozoic the cessation of scarp retreat at some sites suggests that metamorphosed banded iron formations and quartzites provide effective barriers to retreating escarpments helping to preserve some of the oldest continuously exposed land surfaces on earth

partial eclogitisation of gabbroic rocks in a late precambrian subduction zone zambia prograde metamorphism triggered by fluid infiltration gabbros and eclogites occur closely associated in a 200 km long and up to 40 km wide area of the zambezi belt in central zambia this area is interpreted to represent part of a late precambrian suture zone with the mafic rocks being relics of subducted oceanic crust gradual stages of prograde transformation from gabbro to eclogite are preserved by disequilibrium textures of incomplete reactions this resulted in kyanite omphacite bearing assemblages for eclogites that have al poor bulk compositions undeformed eclogites typically preserve features of a former gabbroic texture reflected by replacements of plagioclase and magmatic pyroxene by eclogite facies minerals textures of deformed eclogites range from sheared porphyroclastic to porphyroblastic relics of magmatic pyroxene are common and complete eclogitisation occurred only in millimetre to centimetre scale domains in most of the rocks no evidence for prograde blueschist or amphibolite facies mineral assemblages was found in eclogites in contrast the fine grained intergrowth of omphacite garnet kyanite and quartz which replace former plagioclase or was formed in the pressure shadow of magmatic pyroxene relics indicates that eclogitisation might have affected the gabbroic protoliths directly without any significant intervening metamorphic reactions eclogitisation took place under p t conditions of 630 690 degreesc and 26 28 kbar suggesting a large overstepping 10 kbar of reaction boundaries eclogitisation was initialised and accompanied by a channelised fluid flow resulting in veins with large subhedral grains of omphacite kyanite and garnet the gabbro to eclogite transformation was enhanced by a fluid which allowed the necessary material transport for the dissolution precipitation mechanism that characterises the metamorphic mineral replacements the process of eclogitisation was limited by reaction kinetics and dissolution precipitation rates rather than by the metamorphic p t conditions even though ductile deformation occurred and equilibrium phase boundaries were overstepped the infiltration of fluids was necessary for triggering the gabbro to eclogite transformation