release of ni from birnessite during transformation of birnessite to todorokite implications for ni cycling in marine sediments abstract the phyllomanganate birnessite is the main mn bearing phase in oxic marine sediments where it exerts a primary control on the concentration of micronutrient trace metals in seawater however during sediment diagenesis and under mild hydrothermal conditions birnessite transforms into the tectomanganate todorokite we have recently shown that the transformation of birnessite to todorokite proceeds via a four stage nucleation and growth mechanism beginning with todorokite nucleation then crystal growth from solution to form todorokite primary particles followed by their self assembly and oriented growth via oriented attachment to form crystalline todorokite laths culminating in traditional crystal ripening atkins et al 2014 here we determine the fate and mobility of ni sorbed by birnessite during this transformation process specifically in our recent work we predict that the presence of ni within the phyllomanganate matrix will disrupt the formation of todorokite primary particles as such contrary to current understanding we suggest that ni sorbed by birnessite will slow the transformation of birnessite to todorokite and or be released to marine porewaters during sediment diagenesis here we transform a synthetic poorly crystalline ni sorbed 1 wt ni hexagonal birnessite analogous to marine birnessite into todorokite under a mild reflux procedure developed to mimic marine diagenesis and mild hydrothermal conditions we characterise our birnessite and reflux products as a time series including x ray diffraction xrd high resolution transmission electron microscopy hr tem and extended x ray absorption fine structure exafs spectroscopy in addition we determine ni speciation and mineral phase associations in a suite of natural marine ferromanganese precipitates containing intermixed phyllomanganate and todorokite our work shows for the first time that ni significantly slows the transformation of birnessite to todorokite and reduces the crystallinity of the neo formed todorokite phase but does not alter the mechanism and pathway of todorokite formation compared to a ni free system furthermore in systems tending towards todorokite as the final diagenetic product we see that up to 50 of the ni originally sequestered by birnessite is released to solution during the transformation our work indicates that the transformation of birnessite to todorokite in oxic marine sediments likely provides a significant source of ni to marine sedimentary porewaters and potentially a hitherto unrecognized benthic flux of ni to seawater

population wide garnet growth zoning revealed by la icp ms mapping implications for trace element equilibration and syn kinematic deformation during crystallisation the strong partitioning of many trace elements into garnet and their slow diffusivities in both garnet and the rock matrix means that their distribution may record valuable petrogenetic information not documented by major elements in metamorphic rocks complex trace element growth zoning in garnet porphyroblasts from a garnet grade metapelite from the barrovian sequence of the sikkim himalaya is assessed using quantified la icp ms raster mapping coupled with x ray micro computed tomography the data document systematic changes in the zoning patterns from early to late nucleated crystals and also suggest that the ree y chemistry incorporated into garnet is dependent on persistent disequilibrium in the rock volume there is evidence for hree y diffusion haloes surrounding growing garnets and a heterogeneous hree y distribution in the rock matrix annuli superimposed on oscillatory zoning are not consistent with formation during some rock wide event but are dependent on the spatial disposition of the garnet annuli are interpreted to reflect an integrated history of varying growth rates and the incorporation of pre existing heterogeneities due to relatively slow matrix diffusivities conversely smooth zoning of many transition metals indicate that their distribution in garnet may be controlled by equilibrium partitioning between garnet and the rock matrix significant rotation of garnet porphyroblasts during growth is revealed due to immobility of cr over the duration of the crystallisation interval and overprinting of the heterogenous precursor cr distribution strain rate estimates derived from this zoning are on the order of 10 11 10 12 hbox s 1

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

geochemical features of fe mn micronodules in deep sea sediments of the western north pacific ocean potential for co product metal extraction from rey rich mud abstract rare earth element and yttrium rey rich mud around minamitorishima island japan in the western north pacific ocean has received significant attention as a novel rey resource in rey rich muds industrially critical metals such as co ni and mo occur in relatively high concentrations we show that fe mn micronodules separated from rey rich muds are significantly enriched in these elements we measured co contents of almost 3000 ppm and ni contents that exceed 39 000 ppm through experiments we demonstrated that reductive chemical leaching can be used to extract major portions generally 80 of the metals associated with fe mn oxyhydr oxides from rey rich muds the fe mn micronodules were of an oxic diagenetic origin a simple mass balance calculation indicated that the contribution of the fe mn micronodules to the bulk fe mn oxyhydr oxides in the sediment can amount to 8 50 median 18 the other metals associated with fe mn oxyhydr oxides seem to be hosted in mn microparticles probably of a hydrogenetic origin we estimate that the most promising site for rey rich mud development contains 9 3 0 6 102 t 1 6 0 1 103 t and 2 8 0 2 102 t of leachable co ni and mo respectively in 1 km2 0 10 m below seafloor these amounts account for 0 66 0 04 0 061 0 004 and 0 097 0 007 of present annual global productions of co ni and mo respectively the feasibility of extracting these metals as co products during rey rich mud development depends on the cost efficiency of the recovery process which ultimately depends on their market price in the near future

determining the significance of high grade shear zones by using temperature time paths with examples from the grenville orogen ductile shear zones preserve essential information on processes that are active in orogenic roots but the significance of these zones is often difficult to interpret structural petrologic and geochronologic data from shear zones yield elements of the history that are not necessarily synchronous however by combining these data with temperature time t t paths insights are obtained into the nature of shear zones the relation between bounding blocks and orogenic evolution of the deep crust this procedure is illustrated with two examples from the mid proterozoic grenville orogen t t paths from 1160 to 900 ma are based on u pb dating of metamorphic minerals including garnet closure temperature t c 800 c monazite t c 725 c sphene t c 600 c and rutile t c 400 c and 40 ar 39 ar hornblende ages t c 480 c comparison of t t paths from adjacent blocks allows predictions about the significance kinematics and timing of displacement of shear zones in the grenville orogen t t paths can distinguish between major terrane boundaries e g the carthage colton shear zone and within terrane shear zones e g the bancroft shear zone thus these data can also be used to identify individual tectonic terranes in the deep crust this integrated approach to analysis of shear zones provides constraints needed to determine the nature and rate of deep orogenic processes in areas that are complicated by high metamorphic grades

ferromanganese nodules and micro hardgrounds associated with the cadiz contourite channel ne atlantic palaeoenvironmental records of fluid venting and bottom currents abstract ferromanganese nodule fields and hardgrounds have recently been discovered in the cadiz contourite channel in the gulf of cadiz 850 1000 m this channel is part of a large contourite depositional system generated by the mediterranean outflow water ferromanganese deposits linked to contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals we present a complete characterisation of these deposits based on submarine photographs and geophysical petrographic mineralogical and geochemical data the genesis and growth of ferromanganese deposits strongly enriched in fe vs mn av 39 vs 6 in this contourite depositional system result from the combination of hydrogenetic and diagenetic processes the interaction of the mediterranean outflow water with the continental margin has led to the formation of late pleistocene holocene ferromanganese mineral deposits in parallel to the evolution of the contourite depositional system triggered by climatic and tectonic events the diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons 13 c pdb 20 to 37 and organic matter within the channel floor sediments promoting the formation of fe mn carbonate nodules high 87 sr 86 sr isotopic values up to 0 70993 0 00025 observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep seated fluid venting across the fault systems in the diapirs below the cadiz contourite channel erosive action of the mediterranean outflow water undercurrent could have exhumed the fe mn carbonate nodules especially in the glacial periods when the lower core of the undercurrent was more active in the study area the growth rate determined by 230 th excess 232 th was 113 11 mm ma supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka ca rich layers in the nodules could point to the interaction between the mediterranean outflow water and the north atlantic deep water during the heinrich events siderite rhodochrosite nodules exposed to the oxidising sea bottom waters were replaced by fe mn oxyhydroxides slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds which show imprints of the mediterranean outflow water with low 87 sr 86 sr isotopic values down to 0 70693 0 00081 we propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents we also compare and discuss the generation of ferromanganese deposits in the cadiz contourite channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting

pb isotopic evidence for an early enriched crust on mars abstract martian meteorite nwa 7533 is a regolith breccia that compositionally resembles the martian surface measured by orbiters and landers nwa 7533 contains monzonitic clasts that have zircon with u pb ages of 4 428 ga the pb isotopic compositions of plagioclase and alkali feldspars as well as u pb isotopic compositions of chlorapatite in the monzonitic clasts of nwa 7533 have been measured by secondary ion mass spectrometry sims the u pb isotopic compositions measured from the chlorapatite in nwa 7533 yield an age of 1 357 81 ga 2 the least radiogenic pb isotopic compositions measured in plagioclase and k feldspar lie within error of the 4 428 ga geochron these data indicate that the monzonitic clasts in nwa 7533 are a product of a differentiation history that includes residence in a reservoir that formed prior to 4 428 ga with a value 238 u 204 pb of at least 13 4 1 7 2 and a value 232 th 238 u of 4 3 this value is more than three times higher than any other documented martian reservoir these results indicate either the martian mantle is significantly more heterogeneous than previously thought value of 1 14 vs 1 5 and or the monzonitic clasts formed by the melting of martian crust with a value of at least 13 4 therefore nwa 7533 may contain the first isotopic evidence for an enriched differentiated crust on mars

a seismic based cross section of the grenville orogen in southern ontario and western quebec a schematic crustal cross section is presented for the southwestern grenville province based on reprocessed lithoprobe near vertical incidence seismic reflection data and compiled seismic refraction wide angle velocity models interpreted with geological constraints the schematic crustal architecture of the southwest grenville province from southeast to northwest comprises allochthonous crustal elements frontenac adirondack belt and composite arc belt that were assembled prior to ca 1160 ma and then deformed and transported northwest over reworked rocks of pre grenvillian laurentia and the laurentian margin primarily between 1120 and 980 ma reworked pre grenvillian laurentia and laurentian margin rocks are interpreted to extend at least 350 km southeast of the grenville front beneath all of the composite arc belt three major structural boundary zones the grenville front and adjacent grenville front tectonic zone the central metasedimentary belt boundary thrust zone and the elzevir frontenac bou

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

paleosol stratigraphy of the eskridge formation early permian pedogenesis and climate in southeastern nebraska abstract at least five aridisol and vertisol like paleosols are developed within the eskridge formation lower permian in richardson county nebraska these soils are recognized by their prominent soil structure peds nodules and filled cracks micromorphology oriented clay fabrics and iron cutans and well developed carbonate enriched horizons eskridge paleosols represent significant decreases or cessations in terrestrial sedimentation during long term subaerial exposure direct evidence for drowning of three out of the five paleosols by subsequent marine transgressions indicates strong marine influence on the duration of pedogenesis stratigraphic fluctuations in the 13c and 18o values of eskridge pedogenic micrites are potentially compatible with climatic fluctuations between wetter and drier conditions during the permian based on comparisons with isotope values from cenozoic paleosols occurrence of fossil plants and coals along with evaporites as well as the different paleosol types tends to support an interpretation of varying climate recognition of paleosols within the eskridge improves the understanding of cyclic sedimentation and sea level change by recording several episodes of low terrestrial sedimentation and geomorphic stability these episodes probably correspond to peak marine regressions

chemostratigraphic age model for the tornillo group a possible link between fluvial stratigraphy and climate abstract the expression of global climate trends 10 6 to 10 7 years and events 10 5 years in terrestrial sedimentary sections can only be assessed from long continuous continental records such records are rare due to the paucity of well dated terrestrial deposits covering millions of years this study uses isotope chemostratigraphy to develop an age model for fluvial sedimentary rocks of the tornillo group tornillo basin tx and to decipher the potential expression of global climate variations in this sub tropical paleo fluvial system the carbon isotope ratio 13 c of tornillo group pedogenic carbonate correlates well with 13 c variations from benthic foraminifera and suggests deposition between 69 ma and 52 ma for the studied stratigraphic interval higher sediment accumulation rates occurred in the greenhouse period of the early eocene than during the cooler middle paleocene carbon isotope excursions associated with eocene hyperthermals were not identified but their predicted stratigraphic positions coincide with thick sand bodies we interpret the long term sediment accumulation rates and rapid shifts in facies distribution as reflecting change in sediment supply in the basin possibly driven by fluctuations in precipitation seasonality and intensity driven associated with global temperature changes carbon and oxygen isotope ratios from pedogenic carbonates display a strong correlation throughout the section interpreted as an expression of coupling between the hydrological cycle and soil processes those observations suggest that global climate variations along with tectonic and eustatic sea level changes may be an important control of stratigraphic variations of the tornillo group at multiple timescales

nucleation and growth of todorokite from birnessite implications for trace metal cycling in marine sediments the phyllomanganate birnessite is the main mn bearing phase in oxic marine sediments and through coupled sorption and redox exerts a strong control on the oceanic concentration of micronutrient trace metals however under diagenesis and mild hydrothermal conditions birnessite undergoes transformation to the tectomanganate todorokite the mechanistic details of this transformation are important for the speciation and mobility of metals sequestered by birnessite and are necessary in order to quantify the role of marine sediments in global trace element cycles here we transform a synthetic poorly crystalline hexagonal birnessite analogous to marine birnessite into todorokite under a mild reflux procedure developed to mimic marine diagenesis and mild hydrothermal conditions we characterize our birnessite and reflux products as a time series employing x ray diffraction xrd fourier transform infrared spectroscopy ftir bet surface area analysis scanning electron microscopy sem high resolution transmission electron microscopy hr tem and extended x ray absorption fine structure spectroscopy exafs we provide new insight into the crystallization pathway and mechanism of todorokite formation from birnessite under conditions analogous to those found in marine diagenetic and hydrothermal settings specifically we propose a new four stage process for the transformation of birnessite to todorokite beginning with todorokite nucleation then crystal growth from solution to form todorokite primary particles followed by their self assembly and oriented growth via oriented attachment to form crystalline todorokite laths culminating in traditional crystal ripening we suggest that contrary to current understanding trace metals like ni might retard the transformation of birnessite to todorokite and be released to marine sedimentary pore waters during this diagenetic process thus potentially providing a benthic flux of these micronutrients to seawater

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

u pb geochronology of the mazinaw terrane an imbricate segment of the central metasedimentary belt grenville province ontario the mazinaw terrane in the central metasedimentary belt of the grenville province comprises volcanic sedimentary and plutonic rocks that were intensely folded and faulted and metamorphosed to as high as upper amphibolite facies u pb geochronology establishes an early period of magmatism and sedimentation at about 1280 1240 ma probably in a marginal basin setting and a multistage rhetamorphic evolution in the period between 1100 and 980 ma which was probably related to crustal thickening by imbrication during compression and wedging of the terrane some of the earliest magmatism formed calc alkalic volcanic rocks of kashwakamak formation at 1276 2 ma an associated sedimentary assemblage was intruded by the helena trondhjemite stock at 1267 5 ma a younger succession formed between 1250 and 1240 ma includes the bimodal volcanic mazinaw lake formation alaskitic granites of the norway lake and abinger plutons and a granodioritic gneiss phase of the cross lake pluton these units were covered

carbon isotopic evidence for organic matter oxidation in soils of the old red sandstone silurian to devonian south wales uk petrographic and calcrete carbon isotope data from seasonally waterlogged upper silurian p idoli to lower devonian pragian palaeo vertisols of the old red sandstone south wales uk are presented the 13 c values mostly range from 9 to 12 vpdb suggesting that the soils were inhabited by abundant vegetation that when oxidized perhaps with microbial assistance resulted in co 2 rich soils such soils would favour calcrete precipitation through equilibration of soil zone co 2 with the relatively lower atmospheric p co 2 however reliably estimating palaeoatmospheric p co 2 using these carbon isotope data is a challenge supplementary material detailed information on stable isotope measurement methods descriptions of the samples and carbon and oxygen isotope data are available at www geolsoc org uk sup18754

geochronology of the belmont lake metavolcanic complex and implications for crustal development in the central metasedimentary belt grenville province ontario u pb analyses of zircon and titanite were carried out on eight rocks from the belmont lake metavolcanic complex a volcano sedimentary sequence in the central metasedimentary belt of the grenville province of southeastern ontario the ages of concordant supracrustal rocks within the complex do not accord with stratigraphic position the youngest volcanic age is from a rhyolite near the base of the sequence the oldest age is from a dacite in the middle this is overlain by a rhyolite in age a rhyolite at the top of the sequence appears to contain zircon inherited from a source about 1870 ma old the complex is therefore interpreted as comprising a lithotectonic sequence composed of structurally interleaved segments of contrasting age tectonic emplacement of these segments was most likely along previously unrecognized thrust faults the supracrustal rocks were subjected to at least two major deformational events as well as a late metamorphism the earliest event was probably associated with thrusting t

geochronology and geochemistry of precambrian gneisses metabasites and pegmatite from the tobacco root mountains northwestern wyoming craton montanathis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh t e krogh deceased april 2008 the middle mountain metamorphic domain of the montana metasedimentary terrane northwestern wyoming craton within the northwestern tobacco root mountains mainly comprises migmatized tonalitic gneiss interlayered with amphibolitic hornblende gneiss both of which are cut by metamorphosed mafic rocks together these gneisses are defined as middle mountain gneiss archean tonalitic gneiss from west of and amphibolitic gneiss from east of the bismark fault give from chemically and air abraded zircon grains u pb id tims ages of 3325 5 1 7 and 3340 ma respectively these results reflect primary magmatic ages and show that the middle mountain gneiss extends into the northern area of the central fault block between the bismark and mammoth faults older crustal processes in the tonalitic gneiss are evidenced by inherited grains the oldest of which is 3460 ma a metabasite hosted in tonalitic gneiss in the bismark fault selvage zone yields a zircon age of 2468 ma which is interpreted as the time of

use of carbon isotopes in paleosols as an indicator of the p co2 of the paleoatmosphere measurements of carbon isotopic composition of coexisting paleosol organic matter and carbonate results in improved estimates of the paleo p co2 content of the paleoatmosphere measurements from tertiary paleosols indicate that the levels of co2 in the early eocene middle and late miocene and pliocene were less than 1000 ppmv early cretaceous levels of p co2 were significantly higher of the order of 1500 to 3000 ppmv

monazite u th pb geochronology of the central metasedimentary belt boundary zone cmbbz grenville province ontario canada the central metasedimentary belt boundary zone cmbbz is a crustal scale shear zone that juxtaposes the central gneiss belt and the central metasedimentary belt of the grenville province geochronological work on the timing of deformation and metamorphism in the cmbbz is ambiguous and the questions that motivate our study are how many episodes of shear zone activity did the cmbbz experience and what is the tectonic significance of each episode we present electron microprobe data from monazite the u th pb chemical method to directly date deformation and metamorphism recorded in five garnet biotite gneiss samples collected from three localities of the cmbbz of ontario west guilford fishtail lake and killaloe all three localities yield youngest monazite dates ca 1045 ma most of the monazite domains that yield these dates are high y rims in comparison with this common late ottawan history the earlier history of the three cmbbz localities is less clearly shared the west guilford samples have m

extension in the central metasedimentary belt of the ontario grenville timing and tectonic significance a laterally extensive zone of southeast dipping marble mylonites in the central metasedimentary belt cmb of the southern ontario grenville the bancroft shear zone records southeast directed extension and a displacement of about 10 12 km calcite graphite carbon isotope thermometry indicates that the maximum temperature at which shearing occurred was ca 450 c in contrast carbon isotope fractionations 13 c cc gr within the marble protolith consistently give temperatures of 650 700 c the bancroft shear zone postdates 1060 ma and older high grade shear zones in the central gneiss belt and the cmb that are associated with northwest directed thrusting comparison of the temperature data from the retrograde marble mylonites with cooling curves for the cmb gives a late grenvillian age range of 935 1010 ma for the extensional event the geometric relation between thrusting and normal faulting in the cmb is comparable to that in parts of the himalayas and southern tibet and similarly we interpret late normal faulting in the cmb to be a result of gravitational collapse of a thrust thickened crust in contrast to the himalaya tibet region however accretion in the grenville becomes older in the direction of regional thrusting

trace element mapping by la icp ms assessing geochemical mobility in garnet a persistent problem in the study of garnet geochemistry is that the consideration of major elements alone excludes a wealth of information preserved by trace elements particularly the rare earth elements rees this is despite the fact that trace elements are generally less vulnerable to diffusive resetting and are sensitive to a broader spectrum of geochemical interactions involving the entire mineral assemblage including the growth and or dissolution of accessory minerals we outline a technique for the routine acquisition of high resolution 2d trace element maps by la icp ms and introduce an extension of the software package xmaptools for rapid processing of la icp ms data to visualise and interpret compositional zoning patterns these methods form the basis for investigating the mechanisms controlling geochemical mobility in garnet which are argued to be largely dependent on the interplay between element fractionation mineral reactions and partitioning and the length scales of intergranular transport samples from the peaked hill shear zone reynolds range central australia exhibit contrasting trace element distributions that can be linked to a detailed sequence of growth and dissolution events trace element mapping is thus employed to place garnet evolution in a specific paragenetic context and derive absolute age information by integration with existing u pb monazite and sm nd garnet geochronology ultimately the remarkable preservation of original growth zoning and its subtle modification by subsequent re equilibration is used to see through multiple superimposed events thereby revealing a previously obscure petrological and temporal record of metamorphism metasomatism and deformation

stable isotopic composition of calcic paleosols of the early cretaceous hasandong formation southeastern korea abundant pedogenic carbonate nodules are present in the cretaceous non marine hasandong formation southeastern korea the oxygen isotope compositions of these pedogenic carbonates range from 14 2 to 18 0 pdb the meteoric water composition estimated from the oxygen isotope composition of the soil water in equilibrium with the carbonates is much depleted compared with the previous estimate this suggests that the oxygen isotope compositions of the hasandong pedogenic carbonates were modified during diagenesis the carbon isotopic compositions of the hasandong carbonates range from 2 4 to 9 3 pdb with an average of 5 6 pdb suggesting carbonate formation in soils dominated by c3 type of vegetation the estimated average composition of the vegetation is about 6 pdb enriched compared with the present day c3 vegetation this is probably due to atmospheric influence contributing about 35 of the total co2 in the soil an analysis of this contribution using the model of cerling 1991 indicates that the partial pressure of co2 in the early cretaceous hasandong atmosphere was about 2300 ppmv

1 1 ga k rich alkaline plutonism in the sw grenville province u pb zircon and baddeleyite dating of six syenitic stocks establishes that the ultrapotassic potassic alkaline and shoshonitic magmatism with island arc affinities in the central metasedimentary belt cmb of the southwestern grenville province canada took place between 1089 and 1076 ma along a 400 km long northeast trending plutonic belt these ages indicate that ultrapotassic rocks with arc affinities are not unique to the phanerozoic west to east emplacement ages along a northern and southern cross section of this belt range from 1083 2 ma kensington through 1081 2 ma lac rouge to 1076 1 3 ma loranger in the north and from 1089 3 4 ma loon lake and 1088 2 ma calabogie to 1076 2 ma westport in the south although closely spaced in time in detail these ages suggest a slight younging of this magmatic activity to the southeast integration of the geochronological data with the spatial extent and potassic character of the plutons shows that the k rich alkaline suite is distinct from the nepheline syenite belt of the bancroft terrane and from the syenite monzonite suite of the frontenac terrane of the cmb and it is considered to be a magmatic episode unique to the elzevir terrane and its gatineau segment the timing and the postmetamorphic emplacement of these plutons indicate that the regional greenschist to granulite facies metamorphism of the country rock precise age unknown is older than 1089 ma throughout the entire elzevir terrane the potassic magmatism is interpreted as the initiation of the 1090 1050 ma ottawan orogeny in the elzevir terrane thus the regional metamorphism in this terrane previously assigned to the ottawan orogeny is an earlier event the contemporaneous emplacement of this postmetamorphic plutonic belt with keweenawan volcanism is at variance with current tectonic models which consider the keweenawan rift to be formed at the same time as regional metamorphism in the cmb

age of the cretaceous alkaline magmatism in northeast iberia implications for the alpine cycle in the pyrenees cretaceous magmatism in northeast iberia is related to the opening of the bay of biscay and counterclockwise rotation of iberia with respect to europe and predates the collision between iberia and europe that resulted in the formation of the pyrenees to better constrain the age of this magmatism we have undertaken a ar ar study on samples from the pyrenees and the catalonian coastal ranges in the basque cantabrian basin and the north pyrenean basins we have obtained albian ages ca 102 ma in the northern catalonian coastal ranges we have obtained campanian ages ca 79 ma we integrate our data with a review of previously published ages and discuss our results in terms of their geodynamic significance the cretaceous magmatism in the pyrenees is albian santonian mostly occurring between 105 to 85 ma and was emplaced in a tectonically unclear context after the opening of the bay of biscay and rotation of iberia the magmatism in the catalonian coastal ranges is well constrained to ca 79 ma and could mark the onset of alpine shortening in the pyrenean realm in northeasternmost iberia finally we describe a late triassic ca 232 ma early jurassic ca 180 ma phase of magmatism in the central pyrenees previously considered to be cretaceous that widens temporally and geographically the extent of the rift related alkaline magmatism in southwestern europe at that time key points new ar ar data update the age of the cretaceous magmatism in ne iberia magmatism in the pyrenees postdates the rotation of iberia magmatism in the catalonian coastal ranges could mark the onset of alpine shortening

stable isotope geochemistry of vertisols formed on marine limestone and implications for deep time paleoenvironmental reconstructions abstract carbon and oxygen isotope compositions of pedogenic carbonate preserved in paleosols have been used extensively to reconstruct ancient environmental conditions one concern is that pedogenic carbonate precipitated in association with a limestone parent material may include a contribution from inherited detrital lithogenic marine calcite thus compromising interpretations of stable isotope compositions to investigate the impact of lithogenic calcite on environmental interpretations using paleosols we measured stable isotope ratios in pedogenic carbonates and coexisting soil organic matter som in modern vertisols fine smectitic thermic udic haplusterts from riesel texas heiden series and zabcikville texas houston black series forming on cretaceous chalk deposits the pedogenic and lithogenic components in the heiden series soil at riesel were identified using micromorphology and cathodoluminescence cl which showed incorporation of luminescent marine allochems i e foraminifera mollusks into hard nodules and soft powdery pedogenic masses additionally micromorphology showed evidence of meteoric recrystallization of the allochems despite the presence of these inherited carbonates into hard nodules and soft powdery masses the stable isotope compositions recorded a partial pedogenic signal recrystallization of the marine allochems resulted in overprinting of primary marine isotope ratios with ratios that are more similar to those expected for pedogenic carbonates in these soils this study demonstrates that incorporation of parent material into pedogenic carbonates does not necessarily compromise the pedogenic signal that is useful for paleoenvironmental reconstructions however overprinting of marine allochems if present can be important and needs to be identified using micromorphology and cathodoluminescence before using stable isotope ratios of pedogenic carbonates for paleoenvironmental reconstructions

trace element diffusion in jadeite and diopside melts at high pressures and its geochemical implication abstract diffusivities of geochemically important trace elements eleven rare earth elements ree rb sr ba and y in jadeite and diopside melts and those of zr nb th and u in jadeite melt have been measured at pressures between 7 5 and 20 kbar and at temperatures 50 200 above the liquidus using diffusion couples and ion microprobe analysis the concentrations of these elements in the experimental charges are close to those in natural igneous rocks in the jadeite melt which is nearly fully polymerized nbo t 0 1 diffusivities of ree increase with increasing ionic radii 2 diffusivities of tri and tetravalent elements increase with increasing pressure at constant temperature whereas those of mono and divalent elements do not change significantly with pressure and 3 diffusivities of these elements decrease with increasing their ionic charge at constant pressure and temperature in the diopside melt which is considerably less polymerized nbo t 2 1 diffusivities of these trace elements depend mainly on their ionic radii rather than ionic charges the diffusivities of mono and divalent ions decrease with increasing ionic radii at constant pressure and temperature and 2 diffusivities of ree are nearly the same as that of ca and decrease with increasing pressure at constant temperature the behavior of these trace elements is correlated with that of major elements in the jadeite melt tri and tetravalent elements behave similarly to network forming cations al and si whereas mono and divalent elements behave as network modifying cations similarly to na in the diopside melt the diffusion behavior of all these trace elements is similar to that of network modifying cations ca and mg the results of the present experiments suggest that the abundance of some trace elements in igneous rocks may have been affected by diffusion process at the magmatic stage in the case of ree for example if two different magmas with high and low ree concentrations become in contact one another by multiple intrusion and a zoned magma chamber is formed diffusion begins to take place between them and near the interface the ree enriched magma will become more light ree depleted whereas ree depleted magma will become more light ree enriched and in addition if magmas are reduced the former will show a negative eu anomaly whereas the latter will show a positive eu anomaly

carbon and oxygen isotopic signatures in albian danian limestones of cauvery basin southeastern india abstract the albian danian limestones of cauvery basin show a wide range of d13c and d18o values 13 2 to 1 1 and 9 0 to 2 5 respectively the cement samples show negative carbon and oxygen isotope values 18 9 to 3 9 and 9 0 to 4 3 respectively the petrographic study reveals the presence of algae molluscs bryozoans foraminifers and ostracods as major framework constituents the limestones have microspar and equant sparry calcite cements the pore spaces and vugs are filled with sparry calcite cement the bivariate plot of d13c and d18o suggests that most of the samples fall in the freshwater limestone and meteoric field while few samples fall in the marine limestone and soil calcite fields the presence of sparry calcite cement together with negative carbon and oxygen isotope values indicates that these limestones have undergone meteoric diagenesis

geothermometry from 40ar39ar dating experiments abstract we have selected a variety of minerals from three basic intrusions within the high grade metamorphic terrane near haliburton ontario for k ar dating by application of 40 ar 39 ar incremental heating experiments we conclude that the discordant k ar mineral dates can best be explained by a slow cooling history from the stepwise heating experiments we calculated isotopic closure temperatures using dodson s theory for slow cooling and from these constructed a cooling curve this curve was then compared to independent constraints to test the overall validity of our procedures and assumptions the results are geologically reasonable insofar as 1 a the maximum calculated temperatures from hornblendes of 700 c are consistent with independent approximate metamorphic grid arguments 2 b the ar closure temperatures for biotites 350 400 c are consistent with independent evidence and 3 c minerals with older k ar dates have higher calculated closure temperatures the resultant geological cooling curve implies that a maximum temperature of 700 c was reached before 1000 ma ago and thereafter the temperature decreased via changes in uplift and cooling rates to below 200 c by 700 ma ago we have discovered that plutonic plagioclases are very sensitive indicators comparable to k felds pars of ar loss and therefore can usefully extend the range of application of the 40 ar 39 ar stepwise heating method we also describe experiments in which we have tested the effects on the ar systematics of acid leaching of plagioclases

calcium phosphate control of rey patterns of siliceous ooze rich deep sea sediments from the central equatorial pacific abstract rare earth elements and yttrium rey are often used as proxies for paleo environmental conditions and for the reconstruction of element sources and transport pathways many geological systems are well described with respect to the behavior of rey but deep sea sediments with their manifold processes impacting the sediment during early diagenesis leave some questions about the origin and development of the shale normalized rey reysn patterns unanswered here we report rey data for sediment solid phase and pore water from the upper 10 m of deep sea sediments from the clarion clipperton zone ccz in the central equatorial pacific the solid phase rey profiles show highest concentrations at depth below 5 8 m the reysn patterns show an enrichment in middle rey mrey lasn gdsn between 0 35 and 0 60 gdsn ybsn between 1 19 and 1 47 and either no or negative cesn and ysn anomalies i e chondritic to sub chondritic y ho ratios between 24 7 and 28 7 based on correlation analyses of bulk sediment element concentrations and sequential extractions we suggest that a ca phosphate phase controls the distribution and the patterns of rey in these silty clay pelagic sediments rich in siliceous ooze the mrey enrichment develops at the sediment water interface and intensifies systematically with depth the negative cesn anomaly intensifies with depth possibly because ce is mostly bound to mn and fe oxyhydr oxides therefore ce concentrations remain relatively constant throughout the sediment core while its trivalent rey neighbors are mostly hosted by the ca phosphate phase that continuously incorporates rey from ambient pore waters the non redox sensitive trivalent rey concentrations increase with depth producing or enhancing a negative cesn anomaly through coupled substitution of rey3 and na for ca2 the solid phase reysn pattern is therefore determined by the pore water reysn pattern and not suitable for paleoceanographic interpretation the similarity of the pore water and solid phase reysn patterns suggests however that only minor fractionation occurs during rey incorporation into the ca phosphate crystal structure

magmatic and tectonic emplacement of the pukaskwa batholith superior province ontario canadathis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh the neoarchean pukaskwa batholith consists of pre syn and post tectonic phases emplaced over an interval of 50 million years pre tectonic phases are broadly synvolcanic and have a high al tonalite trondhjemite granodiorite ttg affinity interpreted to reflect derivation by partial melting of basaltic crust at lower crustal or upper mantle depths minor syn tectonic phases slightly post date volcanism and have geochemical characteristics suggesting some involvement or interaction with an ultramafic mantle source component magmatic emplacement of pre and syn tectonic phases occurred in the midcrust at paleopressures of 550 600 mpa and these components of the batholith are thought to be representative of the midcrust underlying greenstone belts during their development subsequent to emplacement of the syntectonic phases and likely at approximately 2680 ma the pukaskwa batholith was uplifted as a structural dome relative to flanking greenstone belts synchronously with ongoing regional sinistral t

proterozoic subduction and terrane amalgamation in the southwestern grenville province canada evidence from ultrapotassic to shoshonitic plutonism a late grenvillian 1089 1076 ma subduction regime followed by terrane amalgamation is postulated as the paleoenvironment of a 400 km long belt of potassium rich alkaline and shoshonitic plutons in the central metasedimentary belt of the southwestern grenville province canada emplacement of the plutons postdates the regional metamorphism in the country rock but predates major shear zones that form a structural boundary for the plutonic belt the extent timing and magmatic affinities of the suite delineate the gatineau domain within the current mont laurier terrane of quebec and are compelling evidence for the allochthonous nature of the elzevir terrane and its extension eastward to rideau lake in ontario and northward into the gatineau domain the belt trends northeast the emplacement ages are younger to the southeast and the magmatic affinities are those of island arc ultrapotassic to shoshonitic rocks this is interpreted to reflect the existence of a southeast dipping northeast trending subduction zone beneath the combined elzevir gatineau terrane between 1089 and 1076 ma subsequent to subduction amalgamation of the elzevir terrane to the other terranes formed the central metasedimentary belt which then accreted and collided with the allochthonous polycyclic belt these events provide evidence that the ottawan orogeny commenced at ca 1090 ma in the central metasedimentary belt a modern analogue of this plutonism and its tectonic setting may have been the magmatism and arc continent collision and subduction setting of the sunda are indonesia

antiphase hydrogen and oxygen isotope periodicity in chert nodules abstract oxygen and hydrogen isotope analyses were made of jurassic age chert nodules from the holy cross mountains se poland along radial transects at high spatial resolution there is a radial sigmoidal periodicity for both isotope ratios but the two are out of phase with high d values corresponding to low 18 o values periodicity for a 100 to 120 mm diameter nodule is approximately 16 mm increasing slightly toward the rim with amplitudes approaching 20 and 3 0 for hydrogen and oxygen respectively the combined hydrogen oxygen isotope data for one nodule fall on a published curve for chert forming in equilibrium with seawater knauth and epstein 1976 the range of delta values corresponds to temperature variations of 10 c data for a second chert fall on a subparallel d 18 o line with d values that are almost 50 lower the d 18 o patterns for the nodules cannot be explained by periodic mixing of meteoric and ocean water because the hydrogen and oxygen isotope data are out of phase two possible explanations for the antiphase periodicity are a cyclical temperature variations perhaps related to an unstable convection system e g bolton et al 1999 and b self organizing catalytic precipitation e g wang and merino 1990 the systematic isotopic variations are difficult to explain by diagenesis and strongly suggest that primary isotopic compositions are preserved the isotopic data provide important information on the thermal history of the sedimentary basin if temperature variations are the cause of the isotopic periodicity

an isotopic study of paleosol carbonates from olduvai gorge the isotopic composition of paleosol carbonates from olduvai gorge can be used to give estimates of the paleoclimatic history of east africa during the plio pleistocene oxygen isotopes are indicative of major changes in the isotopic composition of meteoric water while carbon isotopes are indicative of major changes in the fraction of biomass using the hatch slack c4 photosynthetic pathway three major periods of climatic change in this terrestrial setting occurred at about 1 67 1 3 and 0 6 myr these involved major changes in flora as well as major changes in the isotopic composition of meteoric water overall the climate has become warmer and more arid over the past 2 2 myr

plants and the palaeoatmosphere the effects of the development of terrestrial vegetation during devonian and carboniferous times is considered and it is concluded that the maximum possible global biomass in carboniferous times was equivalent to about 1 148 10 15 g c which is in excess of the current earth9s biomass 560 860 10 i5 g c global primary productivity however estimated at about 73 10 15 g c a 1 is of the same order as that of the present day the amount of carbon actually becoming stored as 9fossil fuel9 was a very small proportion of this productivity estimated here at only 0 00002 over 65 10 6 a thus the vegetation of carboniferous times cannot be regarded as a significant carbon sink the atmosphere of the mesozoic is discussed in relation to the evolution of angiosperms in particular the photosynthetic modifications in so called c 4 and cam plants are considered in relation to atmospheric and other environmental stresses taxonomic evidence indicates that the c 3 system is primitive in the angiosperms and that the modified systems have a polyphyletic origin physiological considerations suggest that their development relates more clearly to the demands of water balance rather than to lowered atmospheric co 2 or high atmospheric levels of oxygen it is not considered likely that the evolution of these mechanisms or of the angiosperms in general has had any profound effect upon the carbon content of the atmosphere

enrichment of rare earth elements in siliceous sediments under slow deposition a case study of the central north pacific abstract as an important submarine rare earth elements ree exploration target the ree rich deep sea mud in the pacific ocean has recently attracted much research attention yet its metallogenic mechanism has not been sufficiently addressed in this study we conducted detailed grain size analysis mineral identification and geochemical measurement for the mg026 sediment core in the central north pacific the 63 m fraction of the samples mainly contains siliceous bioclastics phillipsite accretions fish teeth and bones and ferromanganese micro nodules the 4 63 m fraction mainly contains the abovementioned biological detritus together with ilmenite quartz and zeolite the

geologic transect across the grenville orogen of ontario and new york revised cross sections of the western grenville province incorporate new geologic results and reprocessed seismic reflection data the geology is presented in terms of three tectonic elements 1 pre grenvillian laurentia and its margin with ca 1740 and 1450 ma continental arc plutons and associated supracrustal rocks 2 composite arc belt of allochthonous 1300 1250 ma volcanic arcs and sedimentary rocks and 3 frontenac adirondack belt characterized by supracrustal and granitoid rocks and anorthosites of uncertain affinity that may represent a distinctive part of the composite arc belt or an offshore micro continent rocks of the composite arc and frontenac adirondack belts were amalgamated with each other by ca 1160 ma were then thrust over laurentia during ca 1080 1035 ma and ca 1010 980 ma phases of convergence and were dissected and exhumed by 1040 ma normal faults penetrative deformation was restricted to that part of the pre grenvillian laurentian margin that lies to the southeast of the grenville front and parts of the accreted composite arc and frontenac adirondack belts the laurentian rocks in the grenville province are bounded to the northwest and southeast by southeast dipping ductile thrust and or normal shear zones the composite arc and frontenac adirondack belts to the southeast are bounded by ductile and brittle ductile thrust and or normal faults that separate domains with contrasting cooling histories despite a long pre grenvillian tectonic and plutonic history the present crustal architecture and much of the seismic reflectivity were acquired during 1080 980 ma phases of compression and extension

a complete holocene climate and environment record for the western carpathians slovakia derived from a tufa deposit calcareous tufas are great archives of geochemical information for the reconstruction of past climate their importance increases in the regions where other proxies are rare such as western carpathians here we present the first whole holocene palaeoclimatic reconstruction for this region based on geochemical proxies we analysed o 18 c 13 and mg ca ratio on tufa calcite of the mituchovci site white carpathian mountains w slovakia and compared these with pollen plant macrofossil and mollusc data according to o 18 two distinct thermal maxima occurred in the region around 11 4 ka and between 7 3 and 6 9 ka bp according to c 13 and mg ca ratio a steep increase in moisture and rainfall took place around 8 5 ka cal bp preceded by a cold and dry event these events are well reflected in the biotic proxies and are suggested also by other palaeoenvironmental studies from the carpathians we found some later fluctuations with dry and warm bronze age ca 3 6 ka cal bp cold and wet urnfield period ca 2 8 ka cal bp warm roman period ca 2 ka cal bp and cold but humid migration period ca 1 5 ka cal bp we observed extreme abruptness and amplitude of the variation in all geochemical proxies in the last 500 years when biotic proxies imply a very intense human deforestation land use changes may have altered both the temperature regime in the studied fen and the carbon cycle in the recharge area

u mo and ree mineralization in late tectonic granitic pegmatites southwestern grenville province canada abstract late tectonic granitic pegmatites occur throughout most of the southwestern grenville province of ontario and quebec these vary from mineralogically simple 3 4 major phases to complex 4 major phases pegmatites the latter are variably enriched in u th mo and rare earth elements ree and zr and nb the mineralogical and whole rock geochemical data obtained from simple pegmatites suggest crystallization from low temperature h 2 o undersaturated partial melts generated in amphibolite to granulite grade felsic paragneisses and orthogneisses that have undergone an earlier stage of melting these magmas coalesced and fractionated during ascent to mid crustal levels the mineralogical complexity and increase in abundance of ferromagnesian silicates in individual pegmatites arises from interaction with the host rocks hybridization skarnification previous research has shown that there is an empirical relationship between ferromagnesian silicate content and u th and ree enrichment although this phenomena has not been investigated petrogenetically interaction with the host rocks hybridization produced compositional changes in the pegmatites through bimetasomatic two way exchange processes that modified normal fractional crystallization processes high concentrations of ca fe mg and possibly ti depending on the host rock are interpreted to indicate bimetasomatic exchange resulting in a mineralogical modification of the pegmatitic magma for instance the introduction of ca into the pegmatite magma may lead to local saturation of titanite and or allanite high concentrations of u th ree and nb in these titanites suggests that elemental distribution coefficients are affected within the pegmatite melts by the appearance of hybrid titanite the role of a fluid phase in the hybridization skarnification process is two fold 1 the fluid phase will enhance bimetasomatic diffusive exchange of constituents between the host rocks e g ca fe mg ti and the pegmatite si al k na fe u th ree nb zr h 2 o f cl over that of normal melt solid diffusivities and 2 the fluid may be enriched in certain constituents that become saturated during metasomatic interaction between the pegmatite and host rocks

an isotopic study of a fluvial lacustrine sequence the plio pleistocene koobi fora sequence east africa stable isotopic analyses of plio pleistocene and modern sediments in the fluvial lacustrine system occupying the turkana basin east africa provide constraints on the paleoenvironmental and diagenetic histories of the pliocene through the recent sediments in the basin the 13c values for carbonates in lacustrine sediments range from 15 to 22 relative to pdb depending on the varying proportions of co2 from the atmospheric reservoir and from various metabolic sources the 18o values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10 from the pliocene to the present the 13c values for pedogenic carbonates record paleoccologic variations and suggest that c4 plants did not become well established in the preserved depositional parts of the basin until about 1 8 myr ago the 18o values pedogenic carbonates suggest a range of over 10 for the isotopic composition of soil water during this interval they also suggest a period of major climatic instability from about 3 4 to 3 1 myr and at about 1 8 myr together the 13c and 18o values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these plio pleistocene sediments

stable isotope signatures associated with palaeosols pennsylvanian holder formation new mexico the holder formation pennsylvanian virgilian of southern new mexico usa consists of limestones interbedded with siliciclastics it was deposited during times of glacio eustatic sea level change and was exposed subaerially during multiple sea level lowstands microcomponents and whole rock samples of limestones were analysed for 13c and 18o values to examine the method of whole rock isotopic analysis for detecting subaerial exposure events and to determine the diagenetic processes acting during subaerial exposure whole rock isotopic shifts are not consistently present across petrographically identified subaerial exposure surfaces apparently whole rock isotopic shifts do not result from wholesale replacement of the host sediment during soil formation however the isotopic shifts are present in calcareous soil precipitated microcomponents such as rhizoliths laminated crusts and soil precipitated cements the components are heterogeneous in isotopic composition but converge on a meteoric calcite line at about 18o 5 5 these microcomponents are heterogeneous in distribution and may either dominate or be a minor constituent of the whole rock at a single stratigraphic horizon without petrographic selection of palaeosol components the detection of whole rock isotopic shifts may depend on the selection or chance sampling of a rock containing abundant microcomponents precipitated in a soil environment only minor whole rock isotopic shifts come from those rocks bearing no evidence of exposure and bearing lithological characteristics suggesting subaerial exposure was unlikely

rare earth elements and yttrium in seawater icp ms determinations in the east caroline coral sea and south fiji basins of the western south pacific ocean abstract using inductively coupled plasma mass spectrometry icp ms vertical profiles of yttrium and all the rare earth elements rees in seawater were obtained at three locations in the western south pacific the east caroline coral sea and south fiji basins based on the data we have analyzed the inter ree iii relationships and found that ree iii s heavier than dy and particularly close neighbors show strong coherencies in their oceanic behavior considering that the heavy ree iii s are less particle reactive than the light and middle ree iii s and that they have very tight correlations with regressions passing almost through the origin the neighboring element ratios of the heavy ree iii s behave virtually conservatively and are suitable as tracers of water masses the dy ho er system is practically good because its dynamic range signal to noise ratio is large in the ocean the highest ho dy ratios 0 31 are found in intermediate and deep waters throughout the western south pacific which overlie the antarctic bottom water with a low ho dy ratio 0 27 these high ho dy waters are probably formed in the polar and subantarctic frontal zone and advect northward ree iii data provide better insights into the deep water recirculation in the south pacific than those discussed based upon the regular oceanographic properties alone

raman spectral elemental crystallinity and oxygen isotope variations in conodont apatite during diagenesis abstract conodont apatite has long been used in paleoenvironmental studies often with minimal evaluation of the influence of diagenesis on measured elemental and isotopic signals in this study we evaluate diagenetic influences on conodonts using an integrated set of analytical techniques a total of 92 points in 19 coniform conodonts from ordovician marine units of south china were analyzed by micro laser raman spectroscopy m lrs laser ablation inductively coupled plasma mass spectrometry la icp ms high resolution x ray microdiffraction hxrd and secondary ion mass spectrometry sims each conodont element was analyzed along its full length including the albid crown hyaline crown and basal body in either a whole specimen i e reflecting the composition of its outer layer or a split specimen i e reflecting the composition of its interior in the conodonts of this study the outer surfaces consist of hydroxyfluorapatite and the interiors of strontian hydroxyfluorapatite ionic substitutions resulted in characteristic raman spectral shifts in the position ss1 and width ss2 of the 1 po43 stretching band although multiple elements were enriched sr2 mg2 and depleted fe3 mn2 ca2 during diagenesis geochemical modeling constraints and known raman spectral patterns suggest that sr uptake was the dominant influence on diagenetic redshifts of ss1 all study specimens show lower ss2 values than modern bioapatite and synthetic apatite suggesting that band width decreases with time in ancient bioapatite possibly through an annealing process that produces larger more uniform crystal domains most specimens consist mainly of amorphous or poorly crystalline apatite which is inferred to represent the original microstructure of conodonts in a subset of specimens some tissues especially albid crown exhibit an increased degree of crystallinity developed through aggrading neomorphism however no systematic relationship was observed between crystallinity and raman spectral or elemental parameters oxygen isotopes show substantial variation within the conodont study specimens albid crown is on average 0 28 0 32 more depleted in 18o equivalent to 1 2 1 4 c higher temperatures than hyaline crown and basal body and the interiors of conodont elements are 1 08 0 37 more depleted in 18o equivalent to 3 0 6 4 c higher temperatures relative to their outer layers although albid crown is widely regarded as better preserved than other conodont tissue types its 18o depleted composition and greater development of secondary crystallinity suggest that in fact it may be the most strongly altered tissue type we conclude that raman spectral la elemental and hxrd microstructural data can provide useful information about the extent of diagenetic alteration of conodont elements and that such information should be taken into consideration in using conodont elemental and oxygen isotope data in paleoenvironmental studies

the age and origin of grenville province uraniferous granites and pegmatites uranium mineralization in pegmatites and granites occurs widely in the grenville province but is especially important near bancroft ontario and north of mont laurier and johan beetz in quebec most investigators have concluded that these rocks were produced by anatexis of a uranium enriched sedimentary protolith we have used rb sr isotopic methods to test this and other hypotheses and have reexamined the petrologic and structural features that led to these hypotheses rb sr whole rock isochron ages from all three areas range from 937 to 980 ma some 150 ma younger than the age of the peak of grenville metamorphism as inferred from numerous ages from syntectonic intrusive rocks and high grade metasediments the ages of the pegmatites are similar to or just slightly greater than k ar ages from this region the initial 87sr 86sr ratios range from 0 7028 to 0 7054 plus one poorly defined value of 0 709 excluding this last one these values are only slightly greater than mantle ratios and calculations show

sharbot lake terrane and its relationships to frontenac terrane central metasedimentary belt grenville province new insights from u pb geochronology the sharbot lake terrane of the central metasedimentary belt in ontario comprises marbles minor tholeiitic basalts and siliciclastic rocks metamorphosed at low to moderate degrees and is intruded by several suites of mafic to felsic plutons gabbroic and associated monzogranitic phases of the lavant complex in northwestern parts of the terrane yield ages of 1224 2 ma for zircon and monazite and 1221 1211 ma for titanite the wolf grove structure a gneissic domain in the northeastern part of the area was migmatized and intruded by granites at 1168 ma prior to its tectonic juxtaposition on amphibolites and marbles of the sharbot lake terrane correlative events recorded by gneiss quartzite and marble from carleton place farther east stress the strong affinity of the wolf grove structure with rocks of the frontenac terrane the 1156 2 ma posttectonic maberly stock intrudes rocks near the boundary zone between the frontenac and sharbot lake terranes suggesting that the two terranes were linked by

carbon dioxide in the paleozoic atmosphere evidence from carbon isotope compositions of pedogenic carbonate stable carbon isotope compositions of pedogenic carbonate occurring in three clay rich vertic paleosols within paleozoic red bed successions in central pennsylvania provide a record of past pedogenic environments and can be used to estimate co sub 2 pressure p sub co sub 2 of the paleozoic atmosphere the delta sup 13 c values of carbonate nodules from paleosols in the deltaic lower bloomsburg formation upper silurian reflect the contribution of carbon from marine groundwater or fossils coupled with low biological activity the delta sup 13 c values of carbonate rhizocretions from stratigraphically high paleosols in the bloomsburg formation and in the alluvial catskill upper devonian and mauch chunk upper mississippian formations suggest an extensive c sub 3 flora and significant contribution of atmospheric co sub 2 paleozoic atmospheric co sub 2 levels inferred from delta sup 13 c of pedogenic carbonate are significantly higher than present levels

understanding crystal populations and their significance through the magma plumbing system crystals are rarely composed of a single crystal population that have grown solely from the batch of magma in which they are resident on emplacement either by eruption or shallow intrusion close investigation of the majority of crystal populations reveal that they comprise up to four main components phenocrysts crystals co genetic with their magmatic host xenocrysts crystals wholly or in part foreign to the magmatic host and magma system antecrysts crystals which are recycled one or several times before inclusion in the host magma but have an origin within the magmatic system and microlites which represent small co genetic crystals which nucleate and grow rapidly on decompression and eruption textural analysis techniques are employed to quantify key aspects of the crystal population including crystal shape crystal size distributions spatial distribution patterns and textural modification using dihedral angles santorini provides a case study of an active volcanic system where a combined textural analysis study has been developed highlighting how the crystal population is being continuously modified by a series of replenishment and mixing events developing textural and microgeochemical techniques provides the next stage in the interrogation of crystal populations linking textures to isotopic heterogeneities and providing fingerprints of where crystals are sourced and re cycled

u pb geochronology of the raglan gabbro belt central metasedimentary belt ontario implications for an ensialic marginal basin in the grenville orogen the raglan gabbro belt of the ontario grenville orogen is coincident with the top of the central metasedimentary belt boundary thrust zone a major mid crustal shear zone separating the central gneiss belt in the footwall from the central metasedimentary belt in the hanging wall it has been suggested that the gabbros making up the belt are coeval that they formed in a marginal basin within the central metasedimentary belt and that they formed a horizon of theologically stiff material that controlled the localization of the top of the boundary thrust zone during its initiation as the marginal basin closed at ca 1190 ma u pb zircon dating of plutons within the raglan gabbro belt was undertaken to test the coeval nature of intrusions in the belt magmatic crystallization ages for three of the gabbros fall in the range 1246 1227 ma and a fourth yields a minimum age of ca 1175 ma the results are permissive of a common origin for the gabbros and allow that the raglan gabbro belt may have been related to

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

preferential eruption of andesitic magmas through recharge filtering at subduction zones andesite lavas erupt in greater abundance than the individual magmas that mix to produce them textural and geochemical analyses of andesites from mount hood oregon reveal that injection and mixing of iron and magnesium rich magma in the magma chamber can initiate the volcanic eruption andesitic volcanic rocks are common in subduction zones and are argued to play an important role in the formation and evolution of the continental crust at convergent margins1 2 3 4 andesite formation is dominated by mixing between iron and magnesium rich mafic magmas and silica rich felsic magmas1 2 4 the abundance of andesites in many subduction zones suggests they erupt in preference to the magmas that mix to produce them4 however the reasons for this remain unclear here we use textural and geochemical analyses of andesites from mount hood oregon to show that eruptions are closely linked with episodes of mafic recharge the intrusion of mafic magma into a shallow felsic magma reservoir the felsic and mafic magmas involved rarely erupt by themselves probably because the former are too viscous and the latter too dense mafic recharge overcomes these barriers to eruption and as it also promotes efficient mixing results in preferential eruption of mixed andesitic magmas the abundance of andesites therefore relates to local crustal conditions and the ability of magmas to erupt we suggest that volcanoes such as mount hood that erupt homogeneous andesitic compositions through time are those that are the most reliant on mafic recharge to initiate eruptions

mineralogy and crystal chemistry of mn fe co ni and cu in a deep sea pacific polymetallic nodule minor element concentrations in marine ferromanganese nodules are primarily controlled by the mineralogy which itself depends on redox conditions at the sediment water interface results are presented for the first in depth x ray microstructural and microspectroscopic investigation of a mixed hydrogenetic diagenetic nodule which is representative of ferromanganese deposits on abyssal plains the measurements were conducted by micro x ray diffraction and x ray absorption spectroscopy both xanes and exafs on hydrogeneous and diagenetic regions of the nodule the hydrogenetic diagenetic interface was imaged by x ray microfluorescence after which regions of interest were chosen to represent mineralogical and chemical transformations that occurred at the early stage of suboxic diagenesis in the hydrogenetic nodule oxic environment mn is speciated as fe vernadite a nanocomposite material composed of intergrown feroxyhite feooh and monodispersed phyllomanganate layers having no interlayer mn vernadite in the diagenetic nodule suboxic environment mn is speciated dominantly as mg rich 10 a vernadite which consists of a random intergrowth of vernadite and its transformation product todorokite the authigenic 10 a vernadite precipitated from the components of vernadite in fe vernadite that were dissolved in suboxic microenvironments of the sediment direct evidence supporting a redox driven dissolution reaction is provided by the valence composition of mn as measured by micro xanes which is 0 69mn4 0 24mn3 0 07mn2 average 3 62 0 04 v u for fe vernadite and 0 61mn4 0 23mn3 0 16mn2 average 3 28 0 04 v u for 10 a vernadite ni and cu derived mainly from dissolved vernadite and oxidized organic matter replace structural mn3 4 in both the mno2 layer and todorokite domains of 10 a vernadite pure todorokite in highly diagenetic regions of the nodule has an average formula of mg2 0 167 mn4 0 783 mn3 0 099co3 0 002ni2 0 076cu2 0 040 o2 n h2o with an atomic ratio of cu ni co mn 0 13 which is slightly lower than 0 167 1 6 the maximum metal uptake capacity reported for marine nodules by analogy with synthetic todorokites we infer that mg2 which has a hydrated diameter close to that of the 3 3 tunnel size of todorokite and mn3 and cu2 which prefer jahn teller distorted octahedra play a crucial role in templating the topotactic transformation of 10 a vernadite to todorokite and stabilizing todorokite in suboxic marine sediments

u pb geochronology of the grenville orogen of ontario and new york constraints on ancient crustal tectonics based on lithological structural and geophysi cal characteristics the proterozoic grenville orogen of southern ontario and new york has been divided into domains that are separated from each other by ductile shear zones in order to constrain the timing of meta morphism u pb ages were determined on metamorphic and igneous sphenes from marbles calc silicate gneisses amphibolites granitoids skarns and pegmatites in addi tion u pb ages were obtained for monazites from meta pelites and for a rutile from an amphibolite these mineral ages constrain the timing of mineral growth the duration of metamorphism and the cooling history of the different domains that make up the southern part of the exposed grenville orogen based on the ages from metamorphic minerals regional and contact metamorphism occurred in the following intervals central granulite terrane

stable isotopic composition of pedogenic carbonates of the early cretaceous shimonoseki subgroup western honshu japan abstract abundant pedogenic carbonate nodules are present in the shimonoseki subgroup in the kanmon basin of kyushu and honshu japan the oxygen isotope compositions of these pedogenic carbonates range from 20 1 to 22 8 pdb which is 7 lower than those of the septarian crystallaria in the carbonate nodules the meteoric water composition estimated from the oxygen isotope composition of the soil water in equilibrium with the carbonates is much depleted compared with the estimate from other sources this suggests that the oxygen isotope compositions of the shimonoseki pedogenic carbonates were modified during diagenesis the carbon isotopic compositions of the shimonoseki carbonates range from 5 4 to 7 0 pdb with an average of 6 7 pdb suggesting carbonate formation in soils dominated by c 3 type of vegetation an analysis of these values using cerling s model cerling t e wright v p vanstone s d 1992 further comments on using carbon isotopes in paleosols to estimate the co 2 content of the palaeo atmosphere j geol soc london 148 1991 945 947 149 673 676 indicates that the partial pressure of co 2 in the early cretaceous shimonoseki atmosphere was about 1700 3200 ppmv

deep sea mud in the pacific ocean as a potential resource for rare earth elements world demand for rare earth elements and the metal yttrium is rapidly increasing an analysis of more than 2 000 seafloor sediment samples suggests that deep sea mud constitutes a highly promising giant resource for these elements

iron mineral structure reactivity and isotopic composition in a south pacific gyre ferromanganese nodule over 4ma abstract deep sea ferromanganese nodules accumulate trace elements from seawater and underlying sediment porewaters during the growth of concentric mineral layers over millions of years these trace elements have the potential to record past ocean geochemical conditions the goal of this study was to determine whether fe mineral alteration occurs and how the speciation of trace elements responds to alteration over 3 7 ma of marine ferromanganese nodule mfn formation a timeline constrained by estimates from 9be 10be concentrations in the nodule material we determined fe bearing phases and fe isotope composition in a south pacific gyre spg nodule specifically the distribution patterns and speciation of trace element uptake by these fe phases were investigated the time interval covered by the growth of our sample of the nodule was derived from 9be 10be accelerator mass spectrometry ams the composition and distribution of major and trace elements were mapped at various spatial scales using micro x ray fluorescence xrf electron microprobe analysis empa and inductively coupled plasma mass spectrometry icp ms fe phases were characterized by micro extended x ray absorption fine structure exafs spectroscopy and micro x ray diffraction xrd speciation of ti and v associated with fe was measured using micro x ray absorption near edge structure xanes spectroscopy iron isotope composition 56 54fe in subsamples of 1 3 mm increments along the radius of the nodule was determined with multiple collector icp ms mc icp ms the spg nodule formed through primarily hydrogeneous inputs at a rate of 4 0 0 4 mm ma the nodule exhibited a high diversity of fe mineral phases feroxyhite feooh goethite feooh lepidocrocite feooh and poorly ordered ferrihydrite like phases these findings provide evidence that fe oxyhydroxides within the nodule undergo alteration to more stable phases over millions of years trace ti and v were spatially correlated with fe and found to be adsorbed to fe bearing minerals ti fe and v fe ratios and ti and v speciation did not vary along the nodule radius the 56 54fe values when averaged over sample increments representing 0 25 0 75 ma were homogeneous within uncertainty along the nodule radius at 0 12 0 07 2sd n 10 our results indicate that the fe isotope composition of the nodule remained constant during nodule growth and that mineral alteration did not affect the primary fe isotope composition of the nodule furthermore the average 56 54fe value of 0 12 we find is consistent with fe sourced from continental eolian particles dust despite mineral alteration the trace element partitioning of ti and v and fe isotope composition do not appear to change within the sensitivity of our measurements these findings suggest that fe oxyhydroxides within hydrogenetic ferromanganese nodules are out of geochemical contact with seawater once they are covered by subsequent concentric mineral layers even though fe bearing minerals are altered trace element ratios speciation and fe isotope composition are preserved within the nodule

high resolution la icp ms mapping of deep sea polymetallic micronodules and its implications on element mobility abstract enrichments of rey rare earth yttrium and other trace metals co and ni in deep sea ferromanganese fe mn micronodules have received increasing attention in both deep sea research and mineral exploration due to the presence of multiple easily crushed and poorly crystallized phases in micronodules the genesis of micronodules and their adsorption of various trace elements are poorly understood to address this gap we examined the spatial distributions of elements in cross sections of micronodules from the western tropical north pacific ocean using high resolution hr la icp ms raster mapping coupled with laser raman and x ray photoelectron spectroscopy xps the ferromanganese micronodules we studied are dominated by fe and mn oxides with minor carbonate minerals such as siderite rhodochrosite and calcite la icp ms maps show that these micronodules consist of a mn rich core and a fe rich rim the fe enriched rim is enriched in as and surrounds a mg mn cu co and ni concreted core laser raman maps show that the micronodule core contains more birnessite an important scavenger of trace metals in deep sea sediments than the rim the birnessite filled core of these micronodules does not have elevated rey indeed birnessite line channels may feed metal rich fluid containing rey to adjacent minerals including well crystallized bio apatite and zeolite as high ce and y levels are spatially correlated with these minerals the observed element profiles and xps observations showing the coexistence of multiple oxidation states of mn 2 3 and 4 fe 2 and 3 and ce 3 4 demonstrate that the fe mn phases of these micronodules are of a diagenetic origin and that they are sites of redox driven metal enrichment in deep sea sediment

assessing the carbon dioxide content of ancient atmospheres using palaeocalcretes theoretical and empirical contraints recent suggestions that the 13 c composition of calcretes can be used to determine the p co 2 of ancient atmospheres is critically evaluated the problem of differentiating pedogenic calcretes from groundwater ones which could not be used for p co 2 determinations is considered a critical problem a basic tenet of the use of calcretes for assessing p co 2 is that plants using c 4 or cras sulacean acid metabolism photosynthetic pathways were unimportant until the miocene this view is questioned and evidence is presented from carboniferous calcified root mats that non c 3 plants were probably present at this time confirming speculations by palaeobotanists that crassulacean acid metabolism or c 4 photosynthesis may have arisen numerous times during the evolution of higher plants

harvey cardiff domain and its relationship to the composite arc belt grenville province insights from u pb geochronology and geochemistrythis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh combined mapping u pb isotope dilution thermal ionization mass spectrometry id tims geochronology and geochemical studies in harvey cardiff domain in the western composite arc belt reveal the presence of a long lived magmatic metamorphic history between 1290 and 1030 ma following intrusion of gneissic tonalite of the anstruther and burleigh gneiss complexes at ca 1290 ma diorite of the salmon burn intrusive complex was emplaced at 1242 1 1 1 ma a potassium feldspar megacrystic monzogranite in the salerno creek deformation zone that forms the boundary between harvey cardiff domain and bancroft terrane was emplaced at 1211 3 1 5 ma similar to the 1220 1 6 ma old junction pluton and a previously reported age of ca 1229 ma from another methuen suite granite in the domain all three ages are 20 to 30 million years younger than methuen suite ages elsewhere in the composite arc belt 1250 1240 ma deformation along the salerno creek deformation zone is constrained between 1211 ma the age of th

new insights into nanostructure and geochemistry of bioapatite in ree rich deep sea sediments la icp ms tem and z contrast imaging studies abstract rare earth elements ree and yttrium y termed as rey are recently found to be extremely enriched in some pelagic sediments which could be an important resource for rey in the future however their enrichment mechanism remains controversial because biogenetic apatite is one of the most important rey carriers in rey rich deep sea sediment it is critical to identify its mineralogical and geochemical characteristics by using combined methods of in situ chemical analysis and atomic resolution chemical imaging scanning electron microscope and transmission electron microscopy studies reveal that bioapatite fossils mainly consist of aligned hydroxyapatite nano plates laser ablation inductively coupled plasma mass spectrometry analyses show that the rey are not uniformly distributed within the studied bioapatite fossils concentration profiles from the measurements and modeling analyses indicate that the major rey should be incorporated into the bioapatite fossil from seawater as well as the pore water during the early stage of diagenesis z contrast imaging results reveal the following two possible coupled substitutions in the apatite ree3 na 2ca2 and or ree3 si4 ca2 p5 which is distinguished from those ion absorption type ree deposits on land our study indicates that bioapatite fossils are prone to undergo alteration during diagenesis and thus cautious examination should be taken when applying ree signal of bioapatite as a proxy for palaeo ocean environmental reconstruction

a new discrimination scheme for oceanic ferromanganese deposits using high field strength and rare earth elements abstract ferromanganese fe mn deposits constitute a ubiquitous mineral type in oceanic settings with metal cu ni zn co pt and rare earth element ree enrichments of potential economic interest routine analysis of trace elements by icp ms has advanced our understanding of the impact of hydrogenetic diagenetic and hydrothermal processes on the mobility and interaction of high field strength elements hfse zr and ti and ree and yttrium rey with fe mn oxyhydroxides recent discoveries in the french exclusive economic zone eez of wallis and futuna southwest pacific ocean have brought new insight into the formation of low temperature lt hydrothermal mn deposits and lead us to reconsider the classification and discrimination diagrams for fe mn deposits and ore forming processes using a suite of lt hydrothermal fe mn crusts from wallis and futuna we investigate how contrasting genetic processes influence the distribution of metals mn fe cu ni and co hfse and rey in hydrogenetic diagenetic hydrothermal and mixed type deposits from different environments in the global ocean the interaction of the different metal oxide forming processes indicates that i enrichment of co hfse and rey is favored by hydrogenetic precipitation ii diagenetic processes produce higher mn cu and ni concentrations with oxic remobilization in the sedimentary column while suboxic conditions promote greater mn and fe remobilization that competes with the incorporation of cu and ni ions in nodules hfse and rey derived from seawater are usually low in diagenetic precipitates which discriminate between hydrogenetic and diagenetic inputs within nodules iii hydrothermal fe mn deposits show strong depletion in hfse and rey due to rapid formation and high contents of either fe or mn oxides we present a new discrimination scheme for the genetic types of fe mn deposits using a 10 cu ni co 100 zr y ce fe mn 4 ternary diagram the use of hfse and rey in the classification allows for a more robust discrimination of i each ore forming process with well delimited fields without overlap of metal rich hydrothermal samples and hydrogenetic samples ii oxic and suboxic diagenesis within nodules iii trends between hydrogenetic and diagenetic end members forming a continuum and iv mixed genetic types such as the presence of hydrothermal particles within hydrogenetic crust layers alternatives are also explored to adapt our discriminative diagram to elements measurable by on board instruments to aid in exploration at sea

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

diffusion coupling between trace and major elements and a model for calculation of magma residence times using plagioclase residence times of plagioclase crystals in magma reservoirs can be determined by modeling the compositional zoning of trace elements in these crystals we present a formulation to model diffusion of trace elements in plagioclase paying special attention to certain thermodynamic and kinetic aspects in particular we account for the compositional dependence on anorthite content of the chemical potential and diffusion coefficients of trace elements e g mg the choice of suitable boundary conditions and potential effects of diffusion in more than one dimension we show that contrary to intuition diffusive fluxes of trace elements may be coupled to major element concentration gradients and ignoring such coupling can lead to incorrect estimates of timescales we illustrate application of the model using plagioclase crystals from a suite of gabbroic xenoliths from a holocene dacitic lava flow of volcan san pedro chilean andes 36 s the inferred timescale for metasomatism of the xenoliths by evolved liquids is on the order of 100 30 to 148 yr and serves to illustrate how trace element zoning in plagioclase provides a window into timescales of magmatic processes inaccessible by isotopic or other methods

high resolution la icp ms trace element mapping of igneous minerals in search of magma histories we report experiments on optimisation of la icp ms mapping as a tool for visualising and quantifying internal structure of trace element concentration in igneous minerals the experimental design was refined with maps on clinopyroxene and amphibole macrocrysts mainly antecrysts from a porphyritic lamprophyre in ne spain as well as on a high precision metal wire grid in terms of spatial resolution we demonstrate with scanning electron microscope and white light interferometry that a full ablation removes between 0 4 and 0 7 mu m of material depending on ablation parameters maps were produced with square laser beam spots of 12 and 24 mu m it was found that complexities can be resolved in the sample even though they are smaller than the beam diameter e g 7 10 mu m discontinuities using 12 mu m laser beam resolution in x and y was found to be identical probably reflecting the fast washout of the two volume ablation cell and the short total dwell time of the analyte menu selected due to the excellent stage reproducibility and the limited ablation depth it is feasible to re ablate the identical map area many times employing different instrument parameters or analyte menus on the magmatic crystals la icp ms maps define very sharp compositional zoning in trace elements highlighting complex crystallisation histories where normal magmatic fractionation is not the only process events of mafic recharge are easily recognised as zones enriched in compatible metals such as cr ni or sc further trace element maps reveal complexities in mineral zoning previously undetectable with petrography or major element data these include resorbed primitive cores and oscillatory zoning within apparently homogeneous mineral zones therefore la icp ms mapping opens a new window of opportunity for analysis of magmatic histories the wide combination of instrumental parameters such as laser beam size scan speed and repetition rate make it possible to carry out experiments at different levels of detail we recommend a two step approach to mapping the initial step involves rapid maps to gain an overview of potential complexities in the sample this enhances representativeness of the analysed materials as a large number of crystals and trace elements can be tested in little time subsequently detailed maps can be carried out on areas of interest an additional functionality is to create 1d profiles from 2d maps the potential of the technique to unveil compositional complexities efficiently and at greater detail than traditional microanalysis will help to improve our understanding of processes in the magmatic environment and beyond c 2015 elsevier b v all rights reserved