comparison of granite related uranium deposits in the beaverlodge district canada and south china a common control of mineralization by coupled shallow and deep seated geologic processes in an extensional setting abstract many uranium deposits are related to granitic rocks but the mineralization ages are much younger thus excluding a direct magmatic hydrothermal link between the mineralization and the granites two such examples are the proterozoic vein type uranium deposits in the beaverlodge district in canada and the mesozoic granite related uranium deposits in south china both areas have been extensively studied but the critical factors that control the mineralization remain unclear the uranium mineralization in the beaverlodge district occurs in quartz carbonate albite veins and breccias developed within and near major deformation zones and are mainly hosted by ca 2 33 1 90 ga granitic rocks and ca 2 33 ga murmac bay group amphibolite these rocks are unconformably overlain by the martin lake basin which was formed during a period of regional extension in the later stage of the trans hudson orogeny and is filled with red beds a ca 1820 ma mafic magmatic event is manifested as volcanic rocks occurring within the martin lake basin and as dikes crosscutting the basement rocks and lower martin group strata uraninite u pb and pb pb ages range from ca 2290 ma to the granite related uranium mineralization in south china occurs mainly as quartz carbonate fluorite veins and as disseminations in the host rocks adjacent to fracture zones the deposits are hosted by or occur adjacent to granitic rocks and are spatially close to cretaceous tertiary red bed basins that were formed in a basin and range like tectonic setting related to roll back of the pacific plate these red bed basins contain intervals of bimodal volcanic rocks and are crosscut by coeval mafic dikes uraninite u pb ages dominantly range from 100 to 50 ma which is much younger than the host granites 145 ma and broadly contemporaneous with development of the red bed basins and mafic magmatism comparison of the two study areas reveals striking similarities in geologic attributes related to uranium mineralization specifically the development of large volumes of granitic rocks that are relatively enriched in uranium and the development of red bed basins with accompanying coeval mafic magmatism in extensional tectonic settings it is proposed that oxidizing basinal fluids from the red bed basins circulated into the underlying fertile granitic rocks along high permeability structural zones acquired uranium in the path through fluid rock interaction and precipitated the uranium where they encountered reducing agents elevated geothermal gradients associated with the mantle derived magmatism greatly enhanced the mineralization by facilitating the uranium extraction and transport processes thus it is the coupling of shallow red bed basin and oxidizing basinal fluid development and deep seated mantle derived magmatism and related thermal activity processes together with the pre enrichment of uranium in basement rocks particularly granitic rocks and pre existing deformation zones that controlled the formation of the granite related uranium deposits in both beaverlodge and south china and perhaps elsewhere in the world with similar geologic setting

fluid compositions and p t conditions of vein type uranium mineralization in the beaverlodge uranium district northern saskatchewan canada the beaverlodge district in northern saskatchewan is known for vein type uranium mineralization most of the uranium deposits are spatially related to major structures and hosted by ca 3 2 1 9 ga granitic rocks and albitite derived from them and by ca 2 33 ga murmac bay group amphibolite all of which are unconformably overlain locally by deformed but unmetamorphosed redbeds of the ca 1 82 ga martin group and by the flat lying ca 1 75 1 5 ga athabasca group the uranium mineralization is mainly hosted in fault rocks breccias and carbonate quartz albite veins referred to as breccia style and vein style mineralization respectively with the latter being the focus of this study most of the mineralized veins occur in the basement rocks although some crosscut the martin group this study examines the field petrographic fluid inclusion and c o isotope characteristics of mineralized and non mineralized veins from 19 deposits occurrences as well as from the martin group with an aim to better understand the mineralizing environment and processes the coexistence of liquid dominated l v vapour dominated v l and vapour only v fluid inclusions within individual fluid inclusion assemblages fias in the veins suggests fluid immiscibility and heterogeneous trapping the l v inclusions with the lowest homogenization temperatures th within individual fias are interpreted to represent homogeneous trapping of the liquid phase which yield th values from 78 to 330 c mainly 100 to 250 c and salinities from 0 2 to 30 8 wt nacl equivalent mass spectrometric analysis of bulk fluid inclusions shows that the volatiles are dominated by h2o average 97 2 mol with minor amounts of co2 ch4 h2 o2 n2 ar and he fluid pressures were estimated to be 200 bars based on the inference of fluid immiscibility fluid temperatures of 100 to 250 c and low concentrations of non aqueous volatiles 3 mol the 18ovpdb and 13cvpdb of carbonate minerals associated with mineralization range from 20 5 to 8 9 and 10 1 to 0 9 respectively the 18ovsmow values of the parent fluids calculated using the th values range from 9 6 to 17 0 with the majority from 0 to 5 0 o isotopes of paired equilibrium quartz and calcite analyzed by secondary ion mass spectrometry sims yield temperatures from 161 to 248 c which are consistent with the fluid inclusion data the new fluid inclusion and stable isotope data are inconsistent with a metamorphic or magmatic hydrothermal model as proposed in some previous studies for breccia style and vein style mineralization but rather support a model in which the vein type uranium mineralization took place at relatively low temperature 100 to 250 c and shallow 2 km conditions with fluid pressure fluctuating between hydrostatic and sub hydrostatic regimes possibly related to episodic faulting the mineralizing fluids were mainly sourced from the martin lake basin and uraninite was precipitated as a result of mixing between this basin derived fluid and fluids carrying reducing agents fe2 ch4 derived from the basement although fluid rock reactions and fluid immiscibility may have also played a role

alteration mineralogy and stable isotope geochemistry of paleoproterozoic basement hosted unconformity type uranium deposits in the athabasca basin canada unconformity type uranium deposits are characterized by mineralization developed along the contact between younger sandstone cover and underlying crystalline basement rocks mineralization may extend up to 400 m into the underlying basement rocks whereas sandstone hosted unconformity type deposits have been well studied deposits hosted primarily in the basement have not this study examines the deposits at rabbit lake dawn lake and mcarthur river in the athabasca basin of canada which are hosted by the metamorphic archean and early paleoproterozoic rocks forming the basement to younger late paleoproterozoic sandstones alteration is similar in the three deposits and is characterized by three distinct paragenetic stages 1 preore alteration involving illitization of plagioclase and amphibole followed by chloritization of biotite and illite which formed at ca 230 c 2 ore stage alteration characterized by uraninite and coarse grained illite which formed at ca 240 c 3 postore alteration comprising spherulitic dravite vein chlorite quartz calcite and fe cu co and pb sulfides which formed at ca 135 c fluid circulation associated with emplacement of later mackenzie dikes initiated partial recrystallization of uraninite a later stage of alteration includes kaolinite and iron hydroxide precipitation formed at much lower temperatures of ca 50 c stable isotope compositions of the alteration minerals in conjunction with their paragenesis indicate that oxidized basinal fluids d 43 to 21 18o 3 8 were derived primarily from evolved seawater and leached uranium from the overlying sandstones of the athabasca formation and transported it into the basement via infiltration along fracture zones associated with reverse faults graphitic units in the basement and preore alteration served as both physical fractured zones and chemical reductants traps for the uranium mineralization the basinal fluids were responsible for the preore illite chlorite synore uraninite illite and the early postore alteration events this differs from many other sandstone hosted deposits where both oxidized basinal and reduced basement derived fluids were responsible for uranium precipitation

soil genesis and mineralogy across a volcanic lithosequence abstract lithology is a principle state factor of soil formation interacting with climate organisms topography and time to define pedogenesis a lithosequence of extrusive igneous lithologies rhyolite obsidian dacite andesite and basalt was identified in the clear lake volcanic field in the coast range of northern california to determine the effects of lithology on pedogenesis clay mineralogy and soil physiochemical properties based on regional landscape erosion rates 0 2 0 5 mm yr 1 the soil residence times for the investigated pedons 150 cm deep were of the order of 3000 to 7500 years indicating that the soils developed under the relatively stable holocene mesic xeric climate regime soils from all lithologies developed to a similar xeralf taxonomy with remarkably consistent physiochemical properties although total fet and dithionite citrate extractable fed iron concentrations diverged across lithologies the degree of weathering as assessed by the fed fet ratio was similar across the lithosequence in spite of large differences in silica content of the parent materials the clay mineralogical assemblage of all lithologies was dominated by kaolin minerals kaolinite and or halloysite all pedons displayed an increase in halloysite and the degree of halloysite hydration with increasing depth except the basalt pedon which was dominated by kaolinite with only trace halloysite we attribute this lack of halloysite in the basalt pedon to the lower silica activities associated with this silica poor lithology there was a lack of nanocrystalline minerals across all lithologies as inferred from selective dissolution the dominance of crystalline materials is a function of the xeric soil moisture regime whereby summer soil profile desiccation promotes dehydration and crystallization of metastable nanocrystalline precursors further the pronounced summer dry period results in dehydration of halloysite 1 0 nm to halloysite 0 7 nm also referred to as meta halloysite in some literature together with transformation to kaolinite in the upper soil profile in spite of the relatively young soil residence times of these soils holocene age the effects of lithology persisted only in differences in fe oxide concentrations fed as well as a lack of significant halloysite in basalt pedons the overwhelming effect of climate in these highly weatherable parent materials narrowed the trajectory of pedogenesis resulting in soils from contrasting lithologies converging on kaolin mineralogy a lack of nanocrystalline constituents and similar soil physiochemical properties

influences of forested and grassland vegetation on late quaternary ecosystem development as recorded in lacustrine sediments geosphere biosphere interactions are ubiquitous features of the earth surface yet the development of interactions between newly exposed lithologic surfaces and colonizing plants during primary succession after glaciation are lacking temporal detail to assess the nature rate and magnitude of vegetation influence on parent material and sediment delivery we analyzed ecosystem and geochemical proxies from lacustrine sediment cores at a grassland site and a forested site in the northern united states over time terrigenous inputs declined at both sites with increasing amounts of organic inputs toward present the similarities between sites were striking given that the grassland sequence began in the early holocene and the forested sequence began after the last glacial maximum multiple mechanisms of chemical weathering hydrologic transport and changes in source material potentially contribute to this pattern although there were strong links between vegetation composition and nitrogen cycling at each site it appears that changes in forest type or from oak woodland to grassland did not exert a large influence on elemental k ti si ca fe mn and s abundance in the sedimentary sequences rather other factors in the catchment lake system determined the temporal sequence of elemental abundance

origin of nodules in mixed siliciclastic carbonate sandstones the lower eocene roda sandstone member southern pyrenees spain abstract calcite cement is heterogeneously distributed in the eocene roda sandstone member strongly cemented nodules and layers intercalated within less well lithified sandstones are common the nodules yield valuable information about the factors that controlled the onset and the degree of cementation all nodules are associated with abandonment surfaces formed when sedimentation ceased for a variable length of time the nodules represent a first stage in the development of continuous hardgrounds the initiation of early cementation was dependent on a combination of several parameters such as grain sorting and the presence and amount of carbonate nucleation centers early cementation began at distinct points now manifested by nodules aggrading into layers in cases where sedimentation had ceased for a sufficient length of time the resulting variability in the amount of cement determines the present day difference in weathering behaviour between nodules and the adjacent less well cemented sandstones

watershed averaged denudation rates from cosmogenic 36cl in detrital magnetite abstract quartz is widely used as a target mineral for determining watershed averaged denudation rates because it is resistant to chemical weathering geologically widespread and has a well constrained 10be production rate however quartz is not available in many landscapes developed on mafic to intermediate igneous rocks this creates a need to develop new target minerals that are applicable in these environments magnetite is a common accessory mineral in many rock types without quartz and like quartz is resistant to chemical weathering here we evaluate magnetite s suitability as a target mineral by comparing denudation rates inferred from 36cl in magnetite to 10be in quartz at 12 watersheds in the sierra nevada region of california we find that magnetite and quartz produce denudation rates that are in broad agreement validating the use of magnetite the reproducibility between the two minerals is comparable to the reproducibility of measurements of 10be from repeat samples of quartz from a single catchment this level of variance is likely attributable to the stochastic nature of erosion and sediment supply in small mountainous watersheds

numerical model to determine the composition of h2o nacl cacl2 fluid inclusions based on microthermometric and microanalytical data natural fluids approximated by the h2o nacl cacl2 system are common in a wide range of geologic environments including sedimentary basins associated with hydrocarbon occurrences and mvt deposits submarine hydrothermal systems and other metamorphic magmatic and hydrothermal environments we present a comprehensive numerical model and microsoft excel based computer program to determine the compositions of fluid inclusions in the h2o nacl cacl2 system based on microthermometric and microanalytical data the model consists of six polynomial correlation equations that describe liquid salinity as a function of nacl cacl2 ratio and melting temperature on each of the ice hydrohalite halite antarcticite cacl2 4h2o and cacl2 2h2o vapor saturated liquidus surfaces the cotectic and peritectic boundaries are determined from the intersections of the liquidus surfaces the model is implicitly internally consistent and topologically correct the model expands upon the compositional range of applicability and the data types that can be used for compositional determination it reproduces experimental data for all compositions that lie within the h2o nacl cacl2 4h2o compositional triangle in the h2o nacl cacl2 system and yields accurate reproductions of the h2o nacl and h2o cacl2 binaries furthermore in comparison to previously published models the one presented here eliminates systematic errors wavy isotherms and cotectic and peritectic curves with local bumps

estimating millennial scale rates of dust incorporation into eroding hillslope regolith using cosmogenic nuclides and immobile weathering tracers 1 dust fluxes are of wide interest because of the effects of dust on climate oceanic primary productivity terrestrial biogeochemical cycles and regolith composition estimating long term dust deposition rates however can be difficult especially in steep eroding terrain here we present a geochemical mass balance method for estimating long term average rates of dust incorporation into regolith on steadily eroding hillslopes this method requires measurements of the local regolith production rate and the concentrations of two immobile elements in the regolith its parent rock and dust dust incorporation rates inferred with this method are averaged over the long timescale of regolith residence on the hillslope typically 103 105 years and thus may serve as long term averages against which modern day dust fluxes may be compared we apply this model to 17 field sites in the south fork of the salmon river in the idaho batholith where rock and regolith compositions imply that mafic rich material has been added to the otherwise granitic regolith we suggest that the most likely source of this mafic material is dust sourced from the same glacial outburst flood sediments that generated the palouse loess on the columbia plateau and we use the published composition of these sediments to infer dust incorporation rates of 3 13 t km 2 yr 1 at these sites comparable to modern day dust fluxes elsewhere in the western united states

calcium carbonate cementation of sand a method for producing artificially cemented samples for geotechnical testing and a comparison with natural cementation processes abstract the experience of dutch dredging companies is that cemented layers in holocene calcareous sands are much more frequent than expected in an effort to alleviate this problem a method for producing slightly calcium carbonate cemented sand is presented these samples being used to better constrain the geotechnical parameters of slightly cemented carbonate sands when assessing dredging conditions the most important environments where early marine cementation mainly by high magnesian calcite and aragonite occur are intertidal beaches and tidal flats subtidal sandflats and reefs each environment has its typical occurrence and dimension of cemented layers and a characteristic form and distribution of cementing materials within the sandstone it is therefore expected that sandstones from each environment will have a distinct set of geotechnical properties important factors controlling calcium carbonate cementation are the chemistry of the seawater the source of the cementing material the physical conditions in terms of hydraulic energy sedimentary parameters such as permeability texture and composition of the sand and an initially stabilizer of the loose sediment all these factors and the way in which they relate to each other explain large variability in marine cement forms and the variability of the geotechnical properties of the cemented calcareous sediments the factors controlling early cementation in the shallow marine environment are discussed in order to evaluate the boundary conditions for a laboratory model used to produce artificially cemented and by simulating natural subtidal cementation processes the resulting cemented sands are shown to be comparable with natural sandstones and to exhibit similar behaviour during strain tests for the purposes of assessing dredging conditions these artificial samples have advantages over natural samples

clay mineralogy and isotope geochemistry of the alteration halo at the cigar lake uranium deposit the clay size fraction of the alteration halo associated with the cigar lake uranium deposit consists of illite with subordinate kaolinite sudoite al chlorite fe chlorite hematite and traces of an illite chlorite mixed layer mineral the kubler index of illite crystallinity ranges from 2 0 to 6 7 the most altered samples average 4 0 these data indicate that high grade diagenetic to anchizonal conditions have been reached within the alteration halo intensity ratios of the 002 and 001 illite reflections i 002 i 001 are generally greater than 0 4 the phengite muscovite boundary reflecting aluminum rich illites illite composition approaches hydromuscovite whereas 1m and 2m polytypes prevail regionally the presence of 3t and 2m polytypes in the alteration halo suggests that locally higher temperatures have been attained than the regional estimates of 180 220 c k ar dates for illite rich samples from 1255 to 1148 ma could reflect variable resetting of the k ar system during hydrothermal f

giant uranium deposits formed from exceptionally uranium rich acidic brines the athabasca basin canada is home to some of the world s largest uranium deposits analysis of preserved ore forming fluids and experimental measurement of uranium solubility in analogous solutions show that the giant deposits could have formed relatively rapidly from extremely uranium rich brines under acidic conditions

the effective elastic thickness of the continental lithosphere comparison between rheological and inverse approaches 1 following the release of global continental effective elastic thickness te maps obtained using different approaches we now have the opportunity to provide better constraints on te we improve previous estimates of te derived from thermo rheological models of lithospheric strength or ter using new equations that consider variations of the young s modulus in the lithosphere these new values are quantitatively compared with those obtained from an inverse approach or tei based on a comparison of the spectral coherence between topography and gravity anomalies with the flexural response of an equivalent elastic plate to loading the two models show in general a good agreement having equal means at the 95 significance level in about half of the continental areas in other regions tei exceeds ter in about 65 of the data points showing that tei provides an upper bound on te the two data sets have a similar range but demonstrate different distributions ter has a bimodal distribution with the two peaks representative of the cratons and of the areas outside of them in contrast tei has more uniform distribution without predominant peaks our models show higher similarities in the meso cenozoic orogens than in the archaean and proterozoic shields and platforms due to the methods employed for the regions with the most robust determinations of ter and tei the relationship between them is close to linear the results of this work can be used for further studies on the mechanical properties of the lithosphere

climate driven processes of hillslope weathering climate controls erosion and weathering on soil mantled landscapes through diverse processes that have remained diffi cult to disentangle due to their complex interactions we quantify denudation soil and saprolite weathering and soil transport near the base and crest of the western slope of the sierra nevada to examine how large differences in climate affect these processes depth profi les of fallout radionuclides and fi eld observations show relative differences in erosion and weathering processes at these two climatically diverse sites and our data suggest fundamentally different patterns of soil production and transport mechanisms biotically driven soil transport at low elevation and surface erosion driven by overland fl ow at high elevation soil production rates from cosmogenic 10 be decrease from 31 3 to 13 6 m ma with increasing soil depth at low elevation but show uncertain depth dependence at the high elevation site our data also show a positive correlation between physical erosion and saprolite weathering at both sites highly weathered saprolites are overlain by weakly weathered and rapidly eroding soils while chemically less depleted saprolites are overlain by slowly eroding more weathered soils our data are among the fi rst to quantify the critical role of saprolite weathering in the evolution of actively eroding upland landscapes and our results provide quantitative constraints on how different climates can shape hillslopes by driving processes of erosion and weathering

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

influence of parent material on the aluminium fractions in acidic soils under pinus pinaster in galicia nw spain abstract study of the influence of the parent rock on al fractionation in acidic soils that are rich in organic matter can provide useful information related to forest productivity in areas of high geological diversity we studied how parent material affects several chemical parameters mainly focusing on the total soluble aluminium and aluminium forms in solid fractions in different acidic soils in galicia nw spain the soils were developed over slate biotitic schist mica schist and granite and all were under pinus pinaster six soil samples three samples of rhizospheric and three samples of non rhizospheric soil were collected in each study plot aluminium was extracted from the solid phase with the following solutions ammonium oxalate al o sodium pyrophosphate al p copper chloride al cu lanthanum chloride al la and ammonium chloride al nh4 the total al in the liquid phase al t was also determined there was no significant difference in any parameter between rhizospheric and non rhizospheric soils in all soils organo aluminium complexes predominated over inorganic compounds of low crystallinity al p always represented more than 96 of the al o overall the parent material had a significant effect on chemical soil parameters in the soil over biotitic schist characterised by low acidity ph water 5 4 and organic matter with relatively high evolution c n 12 7 the concentrations of al o and al p were higher and tended to form highly stable organic aluminium complexes whereas the concentrations of exchangeable al nh4 and al t were significantly lower than in the other soils nevertheless in soils developed from slate the higher acidity ph 4 7 and the organic matter with relatively low evolution c n 20 7 favoured the formation of moderate and low stability organic aluminium complexes al cu al la and higher concentrations of exchangeable al and al in solution the characteristics of the soils over granite and mica schist were intermediate in more acidic conditions the destabilisation of organo aluminium complexes and the release of al to the soil solution seem the most likely mechanisms of ph buffering

tabular fracture clusters dynamic fracturing produced by volatile expulsion sierra nevada batholith california abstract an undocumented type of fracture system tabular fracture clusters tfcs occurs in the cathedral peak granodiorite sierra nevada batholith ca tfcs are linear zones of sub parallel densely spaced fractures approximately 4 40 cm wide and 3 100 m long tfcs occur in highest density adjacent to the johnson granite porphyry which intruded the cathedral peak granodiorite individual fractures in tfcs exhibit only opening mode displacement microstructural analysis indicates that tfc fractures contain micro breccia of angular clasts of host rock fine grained zeolite and quartz are observed along many of the fractures within tfcs all of which are absent in the host rock the characteristics of tfcs suggest that they differ from previously documented fracture systems in the sierra nevada batholith the dense spacing nature of the fractures and association of tfcs with miarolitic cavities provide compelling evidence that tfcs formed in response to volatile overpressure from the adjacent johnson granite porphyry we attribute the formation of tfcs to dynamic fracturing based on the clustered nature of the extension fractures and the geometric similarities of tfcs to other dynamic fracturing arrays

chemical weathering mass loss and dust inputs across a climate by time matrix in the hawaiian islands we determined the total mass loss and rate of chemical weathering from three minimally eroded hawaiian lava flows that are 10 170 and 350 ka old using a backhoe we sampled the entire weathering zone at 28 sites and measured the depletion or enrichment of each major element in each soil horizon relative to parent material we were able to assess the influence of both climate and substrate age on chemical weathering because each flow crosses a precipitation gradient from 600 to 2500 mm yr 1 mass loss rates were highest for the 0 10 ka interval under the wettest climatic conditions 54 t km 2 yr 1 and decreased to near zero in the wet sites during the 10 170 and 170 350 ka intervals not surprisingly weathering rates were lower in drier sites 24 t km 2 yr 1 from 0 10 ka to b 2tk m 2 yr 1 thereafter however the effects of precipitation were non linear there was a precipitation threshold below which mass loss was relatively small and above which mass loss was substantial but insensitive to increased rainfall chemical weathering rates depend on tectonic uplift erosion climate rock type or some combination thereof by working on stable uneroded surfaces of a single rock type across a well constrained precipitation gradient we were able to identify another potential driver the rate of dust deposition although hawai i is one of the least dusty places in the northern hemisphere dust inputs reached 82 of the total mass loss from the weathering zone at some sites and averaged 30 on the 170 ka flow this highlights the potential importance of dust as a component of observed weathering fluxes from catchments worldwide

boron and magnesium rich marine brines at the origin of giant unconformity related uranium deposits δ11b evidence from mg tourmalines in giant unconformity related u deposits from the athabasca basin canada the origin of the ore fluids and the source of elements typically associated with u ore such as mg and b are highly controversial this paper presents a petrographic and boron isotopic study of mg tourmalines dravites coeval with u oxides and of primary tourmalines from basement rocks the heavy b isotopic compositions of dravites 11 b 19 6 36 5 contrast with the light composition of basement tourmalines 11 b 8 1 3 3 and clearly show that most of the b was brought to the ore system by basinal brines of marine origin because the latter are also typically mg rich a similar origin for mg is proposed these results support the idea that marine derived brines were the only fluids involved in the formation of the deposits and therefore challenge the previous models in which the b and mg were leached from sedimentary and or basement rocks or carried by a basement derived fluid

bedrock composition regulates mountain ecosystems and landscape evolution earth s land surface teems with life although the distribution of ecosystems is largely explained by temperature and precipitation vegetation can vary markedly with little variation in climate here we explore the role of bedrock in governing the distribution of forest cover across the sierra nevada batholith california our sites span a narrow range of elevations and thus a narrow range in climate however land cover varies from giant sequoia sequoiadendron giganteum the largest trees on earth to vegetation free swaths that are visible from space meanwhile underlying bedrock spans nearly the entire compositional range of granitic bedrock in the western north american cordillera we explored connections between lithology and vegetation using measurements of bedrock geochemistry and forest productivity tree canopy cover a proxy for forest productivity varies by more than an order of magnitude across our sites changing abruptly at mapped contacts between plutons and correlating with bedrock concentrations of major and minor elements including the plant essential nutrient phosphorus nutrient poor areas that lack vegetation and soil are eroding more than two times slower on average than surrounding more nutrient rich soil mantled bedrock this suggests that bedrock geochemistry can influence landscape evolution through an intrinsic limitation on primary productivity our results are consistent with widespread bottom up lithologic control on the distribution and diversity of vegetation in mountainous terrain

metal rich fluid inclusions provide new insights into unconformity related u deposits athabasca basin and basement canada the paleoproterozoic athabasca basin canada hosts numerous giant unconformity related uranium deposits the scope of this study is to establish the pressure temperature and composition p t x conditions of the brines that circulated at the base of the athabasca basin and in its crystalline basement before during and after uo2 deposition these brines are commonly sampled as fluid inclusions in quartz and dolomite cementing veins and breccias associated with alteration and u mineralization microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms data from five deposits rabbit lake p patch eagle point millennium and shea creek complement previously published data for the mcarthur river deposit in all of the deposits investigated fluid inclusion salinity is between 25 and 40 wt nacl equiv with compositions displaying a continuum between a nacl rich brine end member cl na ca mg k and a cacl2 rich brine end member cl ca mg na k the cacl2 rich brine has the highest salinity and shows evidence for halite saturation at the time of trapping the continuum of compositions between the nacl rich brine and the cacl2 rich brine end members combined with p t reconstructions suggest anisothermal mixing of the two brines nacl rich brine 180 30 c and 800 400 bars cacl2 rich brine 120 30 c and 600 300 bars that occurred under fluctuating pressure conditions hydrostatic to supra hydrostatic however because the two brines were u bearing and therefore oxidized brine mixing was probably not the driving force for uo2 deposition several scenarios are put forward to account for the cl na ca mg k composition of the brines involving combinations of seawater evaporation halite dissolution mixing with a halite dissolution brine mg ca exchange by dolomitization na ca exchange by albitization of plagioclase na k exchange by albitization of k feldspar and mg loss by mg rich alteration finally the metal concentrations in the nacl rich and cacl2 rich brines are among the highest recorded compared to present day sedimentary formation waters and fluid inclusions from basin hosted base metal deposits up to 600 ppm u 3000 ppm mn 4000 ppm zn 6000 ppm cu 8000 ppm pb and 10 000 ppm fe the cacl2 rich brine carries up to one order of magnitude more metal than the nacl rich brine though the exact origin of major cations and metals of the two brines remains uncertain their contrasting compositions indicate that the two brines had distinct flow paths and fluid rock interactions large scale circulation of the brines in the athabasca basin and basement was therefore a key parameter for metal mobility including u and formation of unconformity related u deposits

quantifying quartz enrichment and its consequences for cosmogenic measurements of erosion rates from alluvial sediment and regolith abstract in situ cosmogenic 26 al and 10 be record the residence time of quartz grains near the earth s surface and thus can be used to measure whole catchment erosion rates averaged over millennial time scales quartz is enriched in hillslope regolith by the dissolution of more soluble minerals thus its residence time will be longer than the regolith average it has been noted that this introduces a bias into erosion rate estimates derived from cosmogenic nuclide concentrations in regolith or alluvium geomorphology 27 1999 131 but the magnitude of this bias has not previously been measured the enrichment of quartz in regolith and the resulting bias in cosmogenic erosion rate estimates can be quantified using concentrations of immobile elements such as zirconium in bedrock and regolith here we show that the erosion rate bias introduced by regolith dissolution is less than 12 across 22 granitic catchments that span a wide range of temperate climates except in extreme weathering environments biases due to regolith dissolution will be a small component of the overall uncertainty in cosmogenic erosion rate measurements

post taltson sedimentary and intrusive history of the southern rae province along the northern margin of the athabasca basin western canadian shield abstract the southern rae province of the western canadian shield underwent extensive reworking during paleoproterozoic time widespread granitic plutonism and poorly defined metamorphism resulting from the ca 2 5 to 2 3 ga arrowsmith orogen was followed by more intense thermotectonic overprints attributed to the 1 99 1 92 ga taltson orogen in the west and ca 1 91 1 90 ga tectonic activity associated with the snowbird tectonic zone in the east the thluicho lake group is a fining upwards conglomerate arkose argillite succession deposited in an intermontane setting towards the end of the taltson orogen following deposition the thluicho lake group underwent two phases of regional folding and greenschist facies metamorphism marking the latest taltson and snowbird overprints respectively prior to the emplacement of extensive 1 82 ga mafic dykes these depositional constraints support correlation of the thluicho lake group with the lithologically similar nonacho group in the northwest territories whereas petrological similarities and coeval emplacement ages indicate that the mafic dykes represent a southeastward extension of the sparrow dykes mafic volcanic rocks geochemically linked to the dykes are intercalated within the martin group a continental redbed succession deposited in trans tensional basin settings indicating that deposition was ongoing at 1 82 ga similarities in age lithological association and depositional setting suggest that the martin group is broadly correlative with the baker lake group of the lower dubawnt supergroup in nunavut widespread lamprophyre dykes of the type that fed minette volcanic rocks of the christopher island formation in the baker lake group are also spatially associated with the martin group the broadly coeval hudson granites which extend over much of the same ground as the lamprophyres in nunavut also appear to have analogs in the southern rae province the formation of widespread trans tensional basins together with extensive dyke emplacement implies a period of intense brittle to brittle ductile deformation throughout the western churchill province at about 1 83 1 82 ga this deformation is attributed to a broadly east west stress regime imposed by accretion of the nahanni fort simpson terrane to the west combined with terminal collision in the trans hudson orogen to the east

erosional equilibrium and disequilibrium in the sierra nevada inferred from cosmogenic 26al and 10be in alluvial sediment we used cosmogenic 26 al and 10 be in stream sediment to measure landscape scale erosion rates for topographically diverse catchments at seven sierra nevada sites at three sites erosion rates and hillslope gradients are strongly correlated increasing with proximity to fault scarps and river canyons which appear to have accelerated local base level lowering rates and thus increased catchment erosion rates by up to 15 fold at four other sites far from fault scarps and river canyons erosion rates are much more uniform and less sensitive to average hillslope gradient our measurements show that contrasts in landscape erosion rates cannot be inferred from hillslope gradients alone because landscapes can evolve toward a state of erosional equilibrium in which steep and gentle slopes erode at similar rates

fluid p t x characteristics and evidence for boiling in the formation of the phoenix uranium deposit athabasca basin canada implications for unconformity related uranium mineralization mechanisms abstract the phoenix uranium deposit in the southeastern athabasca basin canada is a typical unconformity contact hosted uranium deposit characterized by an association with reactivated basement faults graphite rich rocks in the underlying basement and a pervasive clay alteration halo surrounding the mineralized zones petrographic results suggest that the mineralizing hydrothermal system was characterized by alternating desilicification and silicification events uraninite and clay size minerals tourmaline kaolinite illite and minor chlorite mainly precipitated in the desilicification periods whereas hydrothermal quartz mainly drusy quartz formed during the silicification periods primary fluid inclusions in the hydrothermal quartz are inferred to represent the ore forming fluids even though quartz did not co precipitate with uraninite the coexistence of multiple types of fluid inclusions liquid dominated biphase vapor dominated biphase vapor only and halite bearing triphase within individual fluid inclusion assemblages is interpreted to indicate fluid boiling and heterogeneous trapping bulk fluid inclusion volatile analysis by mass spectrometry indicates h2o as the dominant species with less than 1 mol non aqueous volatiles that show a compositional trend typical of fluid boiling microthermometric and cryogenic raman spectroscopic analyses indicate that the mineralizing fluids are of h2o nacl cacl2 mgcl2 composition with salinities ranging mainly from 23 4 to 31 1 wt the liquid dominated biphase inclusions excluding those interpreted to have resulted from heterogeneous trapping have homogenization temperatures from 90 to 157 c these data are generally consistent with the classical diagenetic hydrothermal model in which basinal brines that extracted uranium from the basin or the basement were channeled along reactivated basement faults and precipitated uraninite near the unconformity through reaction with reducing agents however the relatively low fluid inclusion homogenization temperatures documented in this paper together with fluid boiling inferred from fluid inclusion assemblages suggest that the deposit may have formed in a shallower environment 2 5 km than assumed in the conventional diagenetic hydrothermal model 5 km abrupt fluid pressure drops during episodic faulting may have resulted in fluid boiling flash vaporization changing the fluid ph and promoting uraninite precipitation with the alternating liquid vapor conjugates of the boiling system resulting in alternating precipitation of quartz and uraninite respectively

isotopic systematics o h c sr nd of superimposed barren and u bearing hydrothermal systems in a hercynian granite massif central france abstract the hercynian 325 ma granitic complex of saint sylvestre experienced two hydrothermal episodes the first one leading to the formation of a typical alteration facies called episyenite mainly characterized by the dissolution of granitic quartz the second one leading to the deposition at 280 ma of a major u deposit the present study documents the isotopic characteristics of these hydrothermal events 18 o 16 o d h and 13 c 12 c systematics demonstrate that barren episyenites were generated during hydrothermal interaction of large amounts of mainly meteoric water with the granite the ore depositing fluid equilibrated in a sedimentary formation before entering the granite episyenitization was dated at 301 2 ma which is 25 ma later than the granite emplacement the rb sr isochron relationship implies isotopic equilibrium within the fluid phase and between the fluid and the host rocks which confirms the high water rock ratio inferred from o h isotope systematics a coupled nd and sr isotope investigation demonstrates that at least nd was reworked from the granite in the episyenite genesis but sr and possibly nd had an exotic origin consistent with the inferred sedimentary origin during the ore forming stage the present study emphasizes the fact that spatially superimposed hydrothermal events in a granitic environment can be 1 disconnected from the magmatic history of the granite itself and 2 mutually disconnected from chronological and chemical points of view

the effect of land plants on weathering rates of silicate minerals abstract land plants and their associated microbiota directly affect silicate mineral weathering in several ways by generation of chelating ligands by modifying ph through production of co2 or organic acids and by altering the physical properties of a soil particularly the exposed surface areas of minerals and the residence time of water in laboratory experiments far from equilibrium 1 mm oxalate a strong chelator of al has a negligible effect on the dissolution rate of alkali feldspars but some effect on calcic feldspars and olivine by analogy to oxalate the overall effect of organic ligands on the weathering rate of silicate minerals in nature is likely to be small except perhaps in microenvironments adjacent to roots and fungal hyphae the effect of ph on silicate mineral dissolution rate depends on ph below ph 4 5 the rate increases with decreasing ph in the circumneutral region the rate is ph independent and at ph values above around 8 the rate increases with increasing ph vegetation should thus cause an increase in weathering rate through the ph effect only where the ph is below 4 5 as an overall generalization the effect of plants on weathering rate through changes in soil solution chemistry is probably small for granitic rocks it may be greater for more mafic rocks it is the release of ca and mg from mafic rocks that has the greatest influence on the global co2 budget the effect of changes in soil physical properties on weathering rate can be major by binding fine particles plants can greatly increase weathering rates in areas of high physical erosion where erosion rates are lower the effect of plants is less clear on long timescales plants may decrease chemical weathering by binding secondary products and isolating unweathered minerals from meteoric water a major unknown in estimating the effect of the advent of land plants on weathering rates is the nature thickness particle size distribution permeability of the regolith on the pre silurian continents the indirect effect of vegetation through changing the regional distribution of precipitation may be as important as the direct effects

thrust tectonics in the south central pyrenees abstract surface structural data and published stratigraphies are combined to construct two balanced and restored sections through the nogueras zone of the south central pyrenees the allochthonous nogueras zone units are interpreted as the foreland dipping margin of a major antiformal stack in the palaeozoic rocks of the pyrenean axial zone their structural evolution is summarized in a hangingwall sequence diagram this reinterpretation of the nogueras zone is incorporated into a new n s balanced and restored section from the centre of the pyrenean axial zone to the ebro basin a classical rocky mountains piggy back thrust model is employed and the resulting section is a significant departure from those previously published it is argued that gravity gliding has never been an important mechanism in the alpine pyrenees section restoration casts doubt on the correlation of the surface expression of the north pyrenean fault and the seismically detected moho step beneath it

bedrock fracture density controls on hillslope erodibility in steep rocky landscapes with patchy soil cover southern california usa abstract although many steep landscapes comprise a patchwork of soil mantled and bare bedrock hillslopes models typically assume hillslopes are entirely soil mantled or bare bedrock making it challenging to predict how rock properties influence hillslope erodibility and landscape evolution here we study headwater catchments across the san gabriel mountains sgm and northern san jacinto mountains nsjm in southern california two steep landscapes with similar climate and lithology but with distinctly different bedrock fracture densities 5 higher in the sgm we combine new and published detrital in situ cosmogenic 10be derived erosion rates with analysis of high resolution imagery and topography to quantify how the morphology and abundance of bare bedrock and soil mantled hillslopes vary with erosion rate within and between the two landscapes for similar mean hillslope angles 35 46 catchments in the nsjm erode at rates of 0 1 0 6 m kyr 1 compared to 0 2 2 2 m kyr 1 in the sgm in both landscapes bare bedrock hillslopes increase in abundance with increasing erosion rate however more and steeper bedrock is exposed in the nsjm indicating that wider bedrock fracture spacing reduces soil production efficiency and supports steeper cliffs additionally higher erosion rates in the sgm require a 3 higher soil transport efficiency reflecting an indirect control of bedrock fracture density on the size of sediment armoring hillslopes our data highlight how hillslope morphodynamics in steep landscapes depend on the strength of soil and bedrock and the efficiency of soil production and transport all of which are variably sensitive to rock properties and influence the partitioning of soil and bare bedrock on hillslopes

petrography and environmental controls on the formation of phanerozoic marine carbonate hardgrounds early marine seafloor lithification of carbonate sediments leads to the formation of hardgrounds and is known from rocks as old as the proterozoic hardground surfaces however are more commonly recorded in the phanerozoic sedimentological archive while ecological studies of hardground biota abound the environmental and physico chemical parameters leading to the development of seafloor lithification remain in many cases poorly understood and documented this paper reviews published evidence on the petrography mineralogy and geochemistry of phanerozoic carbonate hardgrounds within a process oriented context of their environmental controls hardgrounds typically develop in warm and shallow agitated tropical waters that are saturated with respect to caco3 but are also reported from hemi pelagic to bathyal realms and from cool water temperate settings a range of early marine cement types are documented from present day hardgrounds whereas preserved cement fabrics and related mineralogies are less diverse in early phanerozoic hardgrounds carbonate hardgrounds are widespread during calcite sea periods e g ordovician and cretaceous as opposed to some preservation bias ancient aragonite seas e g permian and triassic obviously the relation between seawater chemistry and hardground abundance and attributes is not an easy one here the concept of aragonite versus calcite seas serves as a first order template for the sake of a structured discussion whereas modern aragonite mode oceans document a significant diversity in spatial and bathymetric seawater properties this spatio temporal complexity is perhaps reflected in the scarce record of calcite sea hardgrounds from the devonian or paleogene rock record contrasted by the abundance in aragonite holocene and recent seas holocene hardgrounds allow for the direct assessment of rates of and reasons for early subaquatic lithification and in most cases escaped subsequent non marine diagenetic overprint conversely studies of ancient hardgrounds are often biased by early biological and mechanical erosion the degree of diagenetic overprint and tectonic to orogenic processes the formation distribution and physical properties of hardgrounds depend on the global climatic context greenhouse icehouse modes on sea level changes on ocean stratification on the spatial extent of epicontinental seas and carbonate depositional environments and on the spatially different mineralogies and rates of carbonate production the fabrics and mineralogies of early hardgrounds cement seem to substantially hinge on variations in atmospheric co2 thus the application of lessons from modern to ancient hardground case examples is not straightforward a holistic model explaining the full variability of controls on submarine hardground formation and their cement petrography throughout the phanerozoic is as yet lacking a more critical view on secular changes in hardground formation patterns is clearly needed future work should rely on the combination of sedimentological stratigraphic palaeoecological petrographic and geochemical approaches specific emphasis should be given to time intervals triassic carboniferous cambrian etc where the bulk of reported case studies is at best scarce

mineral chemistry and oxygen isotopic analyses of uraninite pitchblende and uranium alteration minerals from the cigar lake deposit saskatchewan canada abstract the cigar lake unconformity type u deposit is one of the largest and highest grade u deposits in the proterozoic athabasca basin northern saskatchewan canada cigar lake has recently been the focus of an international 3 a collaborative program in which this u deposit was studied as a natural analogue for a spent nuclear fuel repository the deposit is located near the eastern margin of the athabasca basin 430 m below the surface at the intersection between hudsonian age faults and the unconformity between athabasca group sandstones and aphebian metasediments three stages of u mineralization have been identified based on cross cutting relationships and textures observed in thin section and back scattered electron bse images o isotope data and chemical compositions all stages of u mineralization have been variably altered to ca rich u hydrate minerals or uranyl oxide hydrate minerals and coffinite u pb chemical ages of the 3 stages of u mineralization from cigar lake coincide with the 3 major fluid events that precipitated clay and silicate minerals at 1500 ma 950 ma and 300 ma throughout the entire athabasca basin stage 1 and 2 uraninite and pitchblende have the lowest 18o values that range from 30 1 to 15 2 whereas stage 3 uraninite has 18o values ranging from 10 0 to 3 4 uranyl oxide hydrate minerals have 18o values that range from 11 3 to 8 2 whereas uranyl minerals have much higher 18o values based on u pb chemical ages 18o values and petrographic relationships of u alteration minerals associated with primary u mineralization the cigar lake u ore is similar to u ore from other unconformity type u deposits in the athabasca basin therefore the cigar lake ore deposit although surrounded by clay and sandstone barriers has been effected by the same fluid events that have altered other unconformity type u deposits in the athabasca basin the 3 stages of ore formation and associated alteration minerals permit the detailed study of fluids responsible for u deposition and alteration this information provides the necessary context for the evaluation of the cigar lake deposit as a natural analogue for the disposal of spent nuclear fuel in underground vaults in rocks of the canadian shield

quantifying effects of deep and near surface chemical erosion on cosmogenic nuclides in soils saprolite and sediment cosmogenic nuclides in rock soil and sediment are routinely used to measure denudation rates of catchments and hillslopes although it has been shown that these measurements are prone to biases due to chemical erosion in regolith most studies of cosmogenic nuclides have ignored this potential source of error here we quantify the extent to which overlooking effects of chemical erosion introduces bias in interpreting denudation rates from cosmogenic nuclides we consider two end member effects one due to weathering near the surface and the other due to weathering at depth near the surface chemical erosion influences nuclide concentrations in host minerals by enriching or depleting them relative to other more or less soluble minerals this increases or decreases their residence times relative to the regolith as a whole at depth where minerals are shielded from cosmic radiation chemical erosion causes denudation without influencing cosmogenic nuclide buildup if this effect is ignored denudation rates inferred from cosmogenic nuclides will be too low we derive a general expression termed the chemical erosion factor or cef which corrects for biases introduced by both deep and near surface chemical erosion in regolith the cef differs from the quartz enrichment factor of previous work in that it can also be applied to relatively soluble minerals such as olivine using data from diverse climatic settings we calculate cefs ranging from 1 03 to 1 87 for cosmogenic nuclides in quartz this implies that ignoring chemical erosion can lead to errors of close to 100 in intensely weathered regolith cef is strongly correlated with mean annual precipitation across our sites reflecting climatic influence on chemical weathering our results indicate that quantifying cefs is crucial in cosmogenic nuclide studies of landscapes where chemical erosion accounts for a significant fraction of the overall denudation copyright 2012 john wiley sons ltd

the archean murmac bay group evidence for a giant archean rift in the rae province canada abstract the lower amphibolite to granulite facies archean murmac bay group of the southwestern rae province canada formed during continental extension rifting of an underlying granitoid basement complex that includes the 3060 40 ma lodge bay granite and the 2999 7 ma cornwall bay granite the contact between the murmac bay group and the basement complex is an unconformity that is locally marked by polymictic conglomerate overlying the conglomerate is basal quartzite of the murmac bay group that contains a laterally extensive 10 km intraformational oligomictic quartzite pebble conglomerate that may have formed by uplift during rifting distinctive medium to coarse grained gabbro dykes and sills that cut both the basement complex and the basal quartzite are interpreted as feeders to stratigraphically overlying tholeiitic basalt flows that have geochemical signatures consistent with formation in a continental rift setting the quartzite basalt contact exhibits rare stratigraphic interlayering and is a horizon along which oxide and silicate facies iron formation dolostone and pelite locally occur ultramafic rocks with komatiitic compositions also intrude these lower stratigraphic units the upper murmac bay group is dominated by pelitic to psammitic rocks that may represent deepening of the sedimentary basin during continued extension ancient approximately 3 62 and 3 7 ga grains dominate the detrital zircon population of the murmac bay group sediments but deposition occurred after approximately 2 77 ga the youngest detrital zircon in our study the age of the murmac bay group is thus constrained as younger than approximately 2 77 ga and older than the crosscutting 2631 12 ma dead man and donaldson lake granites the gross lithological and stratigraphic make up of the murmac bay group closely resembles that of the prince albert woodburn lake and mary river groups of the northern rae province all three of which have been interpreted as approximately 2 7 ga continental rift successions we propose that the murmac bay group is correlative with these successions if correct the total length of this neoarchean rift is at least 2000 km extending from baffin island to northwestern saskatchewan canada the supracrustal rocks of the rift record the break up of a large paleo to early neoarchean continent nunavutia which experienced magmatic events at approximately 3 0 3 62 and 3 7 ga

pressure fluctuations phase separation and gold precipitation during seismic fracture propagation gold mineralization at croagh patrick western ireland occurs in quartz veins associated with three synchronous oblique tensile shear systems the veins evolved by progressive thickening of isolated en echelon lensoid tensile fractures that show a power law relation between their length and thickness a change in power law exponent marks the linking of the en echelon arrays by large oblique tensile veins fluid inclusion data show that gold was deposited due to unmixing of an h 2 o co 2 nacl fluid at 320 240 c and 160 30 mpa primarily due to decreases in fluid pressure evidence for phase separation is only observed in the large linking veins and is abundant close to intersections of the vein arrays these sites are where high gold grades occur the distribution of gold is believed to reflect both spatial and temporal variations in fluid pressure fluctuation during seismic fracture propagation controlled by the vein growth mechanism and zones of maximum dilation

ecosystem development following deglaciation a new sedimentary record from devils lake wisconsin usa abstract processes and rates of ecosystem development can be reconstructed using lacustrine sedimentary sequences but this approach often requires records that contain the start of primary succession most lakes in the upper midwestern u s were formed by glaciers at the end of the last ice age approximately 11 700 cal yr bp devils lake wisconsin is a rare example of a lake from this region whose sediments extend into the pleistocene and may include the last glacial maximum sediment magnetic geochemical pollen and charcoal records were generated from a 10 m core whose basal sediments may be 28 000 years old together with a previously published pollen record these proxies combine to reveal a history of long term climatic vegetative and geologic change during the late pleistocene to holocene we identify six sedimentary units that indicate a series of consecutive events rather than a predictable trajectory of ecosystem development at the site productivity in the lake was low during the late pleistocene and increased during the holocene as reflected by the sediment lithology which shows a sudden shift from glacial vivianite rich and organic poor clastic dominated sediments to holocene diatomaceous sapropels several important processes initiated around 17 000 cal yr bp including the onset of organic matter accumulation and fire in the terrestrial ecosystem however the post glacial landscape was not devoid of vegetation because pollen assemblages indicate that terrestrial vegetation likely a spruce tundra survived near the site a switch to a hardwood forest period during the holocene also led to a change in the fire regime with increased frequency of burning aquatic ecosystem productivity lagged terrestrial ecosystem productivity throughout the record nutrient cycling as recorded by sedimentary 15n was variable but not directional and appeared to be correlated with climate conditions early in the record and terrestrial ecosystem processes later in the record throughout the holocene magnetic mineral concentration decreased as productivity increased and the source of magnetic material shifted from almost exclusively lithogenic to approximately 50 derived from soil or biogenic sources magnetic grain size ambrosia pollen percentages and charcoal concentration increased and 15n decreased in the most recent part of the record due to anthropogenic influence in the region including agricultural activities

integration of geochemical mass balance with sediment transport to calculate rates of soil chemical weathering and transport on hillslopes 1 we developed a process oriented hillslope soil mass balance model that integrates chemical and physical processes within hillslope soils the model explicitly factors that soil chemical weathering at any hillslope position is related to the flux of soil eroded from upslope as well as soil production from underlying bedrock the model was merged with measurements of soil elemental chemistry and cosmogenic radionuclide based saprolite to soil conversion rates along a 50 m transect of a semiarid granodiorite hillslope in the southeastern australian highlands inverse modeling results in the simultaneous quantification of the rates of soil chemical weathering and soil transport as a function of hillslope position soil chemical weathering rates per land surface area systematically varied along the transect from losses of 0 035 kg m 2 yr 1 on the ridge to gains of 0 035 kg m 2 yr 1 at the lowest slope position the mass loss via soil chemical weathering would have been overestimated by 40 if the impact of soil transport on soil chemistry was ignored the chemical mobility of elements combined with biological nutrient demand controlled the spatial redistribution of individual elements p and ca were preferentially retained relative to si al and fe within the hillslope base the calculated soil transport rate is linearly related to the product of soil thickness and slope gradient instead of slope alone soil residence time was determined by calculating the time length for a 3 dimensional box volume 1 m2 surface area soil thickness to be entirely removed by mass flux of soil transport 4 ka on the ridge to 0 9 ka at the hillslope base these soil residence times combined with soil chemical weathering rates indicate that a 1 m2 area of soil loses 1 800 kg via chemical weathering while passing through the upslope portion of the hillslope but that it regains 90 kg probably via clay precipitation and biological retention of cations during its passage through the lower segments of the transect this study provides a previously unrecognized linkage between physical soil transport and soil chemical weathering that have implications for hillslope evolution as well as biogeochemistry

petrography fluid inclusion analysis and geochronology of the end uranium deposit kiggavik nunavut canada the end deposit is one of several uranium deposits in the kiggavik area near the proterozoic thelon basin which is geologically similar to the athabasca basin known for its unconformity related uranium deposits the mineralization occurs as uraninite and coffinite in quartz veins and wall rocks psammopelitic gneisses in the sub thelon basement and is associated with clay and hematite altered fault zones fluid inclusions were studied in quartz cementing unmineralized breccias formed before mineralization q2 quartz veins that were formed before mineralization but spatially associated with uranite q4 and calcite veins that were formed after mineralization four types of fluid inclusions were recognized namely liquid dominated biphase liquid vapor vapor dominated biphase vapor liquid monophase vapor only and triphase liquid vapor halite inclusions the first three types were found in q2 whereas all four types were found in q4 and calcite the coexistence of these different types of inclusions within individual fluid inclusion assemblages is interpreted to indicate fluid immiscibility and heterogeneous trapping based on microthermometry the fluids associated with q2 are characterized by low salinities 0 4 to 6 6 wt and moderate temperatures from 148 to 261 c and the fluids associated with calcite show high salinities 26 8 to 29 3 wt and relatively low temperatures from 146 to 205 c whereas the fluids associated with q4 have a wide range of salinities from 0 7 to 38 8 wt and temperatures from 80 to 332 c microthermometric and cryogenic raman spectroscopic studies indicate that the high salinity fluids in q4 and calcite belong to the h2o nacl cacl2 mgcl2 system with some dominated by nacl and others by cacl2 the fluid inclusions in q2 are interpreted to be unrelated to mineralization whereas those in q4 and calcite reflect the mineralizing fluids the fluid inclusion data are consistent with a genetic link of mineralization with basinal brines derived from the thelon basin however unlike the conventional deep burial 5 km diagenetic hydrothermal model proposed for the unconformity related uranium deposits the uranium mineralization in the end deposit is inferred to have formed in a shallow environment probably 2 km based on fluid immiscibility and low fluid pressures obtained in this study the u pb age of uraninite 1295 12 ma is interpreted to reflect isotopic resetting after the primary mineralization

hillslope soils and vegetation abstract assessing how vegetation controls hillslope soil processes is a challenging problem as few abiotic landscapes exist as observational controls here we identify five avenues to examine how actively eroding hillslope soils and processes would differ without vegetation and we explore some potential feedbacks that may result in landscape resilience on vegetated hillslopes the various approaches suggest that a plant free world would be characterized by largely soil free hillslopes that plants may control the maximum thickness of soils on slopes that vegetated landforms erode at rates about one order of magnitude faster than plant free outcrops in comparable settings and that vegetated hillslope soils generally maintain long residence times such that both n and p sufficiency for ecosystems is the norm we conclude that quantitatively parameterizing biota within process based hillslope models needs to be a priority in order to project how human activity may further impact the soil mantle

structural development during flysch basin collapse the fencemaker allochthon east range nevada abstract during mesozoic deformation in north central nevada a thick succession of triassic siliciclastic and hemipelagic carbonate strata that were deposited in a deep water basin shortened against and overrode penecontemporaneous shallow water carbonates and interbedded siliciclastics at the eastern margin of the basin initial rheologic contrasts developed between lithologic units during shallow pretectonic burial localized displacements within fine grained poorly cemented units and along lithologic boundaries changes in theology during low pressure and low temperature deformation led to more brittle conditions possibly due to fluid expulsion and subsequent displacements truncated bedding structures in triassic strata suggest that the w facing slope of the shelf to basin transition localized thrusting collapse of the basinal strata against strata of the basin margin and formation of a thrust at the shelf to basin transition demonstrate the ability of stratigraphic declivities and associated rheologic contrasts to buttress deformation and localize thrusting

facies analysis and high resolution sequence stratigraphy of the lower eocene shallow marine ametlla formation spanish pyrenees the lower eocene ametlla formation of the ager basin spanish pyrenees is a rapidly deposited shallow marine unit formed in a setting characterized by syn sedimentary tectonic activity mapping of the formation over a distance of 25 km was conducted according to sequence stratigraphical principles with emphasis on facies analysis twelve facies grouped in five facies associations have been recognized in the ametlla formation the studied succession records a vertical transition from deltaic systems prograding onto a sediment starved shelf via estuarine deposits associated with incised valleys to sandbar complexes in a tidal seaway in terms of sequence stratigraphy three scales of genetic sedimentary units were recognized 1 at the regional scale elements of two 3rd order composite sequences sensu exxon have been recognized these include a 3rd order highstand sequence set encompassing the lowermost part of the ametlla formation and the underlying passarella formation and a 3rd order transgressive sequence set that constitutes the middle parts of the ametlla formation the sequence sets are separated by an unconformity with up to 35 m of incision that is interpreted as a major sequence boundary it is argued that the incised valleys associated with this unconformity were infilled during landward stepping of the shelfal depositional system basinwards the unconformable surface becomes subhorizontal and is overlain by a 2 m thick oyster bed formed in a sediment starved setting subsequent to flooding of the incised valleys which still acted as sediment conduits sandstones dominate the transgressive sequence set whereas the highstand sequence set is dominated by siltstones particularly in the lower part in the transgressive sequence set an upward increase in sand content and calibre is observed relatable to punctuations of the transgressive trend by high frequency sea level fluctuations and to downslope redistribution of sand 2 at the subregional scale detailed mapping indicates the presence of five 4th order sequences the 4th order sequence boundaries are associated with sediment bypassing and minimal erosional relief and were created by forced regressions during periods of relative sea level fall sharp based sandstones overlying these unconformities are believed to have accumulated during subsequent rise of relative sea level where 4th order maximum flooding surfaces can be recognized the sequences may be subdivided into a sandstone dominated transgressive systems tract and a siltstone dominated highstand systems tract 3 at the local scale 2 9 5th order parasequences are present within the 4th order sequences superimposed parasequences are separated by flooding surfaces characterized by bioclastic accumulations pervasive burrowing and extensive calcite cementation the parasequences are commonly stacked in a landward stepping manner

composition age and origin of granitoid rocks in the davin lake area rottenstone domain trans hudson orogen northern saskatchewan the rottenstone domain of the trans hudson orogen is a 25 km wide granitic migmatitic belt lying between the la ronge volcanic plutonic island arc 1890 1830 ma to the southeast and the ensialic wathaman batholith 1855 ma to the northwest the rottenstone domain consists of three lithotectonic belts parallel to the orogen i southeast gently folded migmatized quartzo feldspathic metasedimentary and mafic metavolcanic rocks intruded by small concordant and discordant white tonalite monzogranite bodies ii central intensely folded and migmatized metasedimentary rocks and minor metavolcanic rocks intruded by largely discordant xenolith rich pink aplite pegmatite monzogranite bodies and iii northwest steeply folded migmatized metasedimentary rocks cut by subvertical white tonalite monzogranite sheets emplacement of granitoid rocks consists predominantly of contiguous orogen parallel steeply dipping syntectonic and post tectonic sheets with prominent magmatic schlieren bands overprinted by parallel solid state deformation features the white granitoid rocks have a cnk mol al2o3 mol cao na2 o k 2o 1 14 1 22 k rb 500 ree sum of rare earth elements 1 87 sr 86 sri 0 7032 and endi 2 the pink monzogranites have a cnk 1 11 1 16 k rb 500 ree 90 ppm eu eu 1 87 sr 86 sri 0 7031 and endi 2 the white granitoid rocks show a wider compositional range and more compositional scatter than the pink monzogranites reflecting some combination of smaller volume melts less homogenization and less control by crystal melt equilibria all metavolcanic metasedimentary and granitic rocks in the rottenstone domain have the distinctive geochemical signatures of an arc environment new sensitive high resolution ion microprobe shrimp u pb geochronology on the rottenstone granitoid rocks reveals complex growth histories for monazite and zircon variably controlled by inheritance magmatism and high grade meta morphism monazite ages for the granitoid bodies and migmatites cluster at 1834 and 1814 ma whereas zircon ages range from 2480 ma rare cores to 1900 1830 ma cores and mantles but also 1818 1814 ma for low th u recrystallized rims overgrowths and rare discrete euhedral prisms these results demonstrate that at least some source material for the granitic magmas included earliest paleoproterozoic crust sask craton or its derived sediments and that rottenstone granitic magmatism postdated plutonism in the bounding la ronge arc and wathaman batholith we estimate the age of terminal metamorphism in the davin lake area to be 1815 ma petrogenetically the rottenstone migmatites and granitoid rocks appear for the most part locally derived from their metasedimentary and metavolcanic host rocks shed from the la ronge arc sask craton and possibly the hearne craton the rottenstone domain was the least competent member in the overthrust stack and probably underwent a combination of fluid present melting and fluid absent decompression melting resulting in largely syntectonic granitoid magmatism 1835 1815 ma analogous to granite production in the high himalayan gneiss belt

arrested development erosional equilibrium in the southern sierra nevada california maintained by feedbacks between channel incision and hillslope sediment production tributary creeks of the southern sierra nevada have pronounced knickpoints that separate the landscape into an alternating sequence of gently sloped treads and steeply sloped risers these knickpoints and the surrounding stepped topography suggest that the landscape is still responding to pleistocene changes in base level on main stem rivers we tested this hypothesis using cosmogenic nuclides and uranium isotopes measured in stream sediment from widely distributed locations catchment scale erosion rates from the cosmogenic nuclides suggest that the treads are relict surfaces that have adjusted to a previous base level nevertheless erosion rates of relict interfluves are similar to canyon incision rates implying that relief is unchanging in the lower kings and san joaquin rivers in addition our results suggest that much of the southern sierra nevada is in a state of arrested development the landscape is not fully adjusted to and moreover is not responding to changes in base level lowering in the canyons we propose that this can be explained by a paucity of coarse sediment supply which fails to provide sufficient tools for bedrock channel incision at knickpoints we hypothesize that the lack of coarse sediment in channels is driven by intense weathering of the local granitic bedrock which reduces the size of sediment supplied from hillslopes to the channels our analysis highlights a feedback in which sediment size reduction due to weathering on hillslopes and transport in channels is both a key response to and control of bedrock channel incision and landscape adjustment to base level change

soil development along an elevational transect in the western sierra nevada california soil development along an elevational transect on the western slopes of the the central sierra nevada was investigated to assess the effects of climate on soil properties and processes the transect of seven soils formed in granitic residuum spans elevations from 198 to 2865 m with mean annual temperature and precipitation differences of 13 c 3 9 16 7 and 94 cm 33 127 respectively soil ph decreased by about two units and base saturation decreased from 90 to 10 with increasing elevation concentrations of organic c in the solum increased with elevation with the largest single increase occurring between the oak woodland 5 6 kg c m2 and mixed conifer sites 10 15 kg c m2 clay mineralogy showed a general trend of desilication and hydroxy al interlayering of 2 1 layer silicates with increasing elevation the degree of chemical weathering based on clay and secondary fe oxide concentration in the solum showed a maximum clay 536 kg m2 and fe oxides 24 kg m2 at mid elevations having intermediate levels of precipitation and temperature while some soil properties show a continuous progression e g organic carbon base saturation clay mineralogy with elevation other properties e g ph soil color clay and secondary fe oxide concentrations show a pronounced change threshold type step over a short distance at about 1600 m the explanation for the abrupt nature of this shift is not known however it coincides with the approximate elevation of the present day average effective winter snow line

controls on stratigraphic architecture in contemporaneous delta systems from the eocene roda sandstone tremp graus basin northern spain abstract the eocene roda sandstone of the spanish pyrenees is comprised of two coeval coarse grained delta systems which share correlatable surfaces but show a markedly different internal facies architecture the two deltas developed contemporaneously with the differences in internal architecture attributed to basin morphology and the role of two distinct sediment sources while the correlatability of the larger scale packages indicates an external allocyclic control as such the roda sandstone provides the possibility to address the relative roles of different parameters known to interact and control stratal architecture the roda sandstone crops out at the ne margin of the tremp graus basin a piggyback basin initiated in palaeogene times in the foreland of the southern pyrenees the study area 30 km2 is composed of the well understood and well exposed parts of the roda sandstone cropping out along the isabena valley and the less worked and less exposed outcrops to the north along barranco de ricans and barranco de codoneras data for this study include a combination of conventional sedimentology data coupled with analyses of 3d virtual outcrop models based on these methods 8 different facies associations have been distinguished their distribution suggests that the roda sandstone is composed of two different but coeval delta systems and their linked subenvironments a gilbert type delta outcropping along isabena valley and a shoal water fan delta along barranco de ricans and barranco de codoneras along the isabena valley the outcrops of the gilbert type deltaic system are composed of at least 6 distinct packages roda u z characterized by texturally mature delta front sandstones separated by offshore mudstones the stacked basinward stepping architecture of the roda u y units here represents a minimum of 3 major phases of sw directed progradation capped by hardground horizons formed during the subsequent flooding phases tidally modified delta front deposits found in the distal exposures of roda y represent the redistribution of the delta toeset by w nw directed ebb tidal currents active during advanced stages of progradation of the gilbert type delta the more gentle sloping shoal water fan delta system found in barranco de ricans and barranco de codoneras is characterized by progradational to aggradational stacking of texturally immature wave modified mouth bar sandstone packages separated by offshore mudstones the zone of interference between the gilbert type and shoal water delta is dominated by wave reworked sediments deposited as shoreface barrier and spit deposits biostratigraphic dating suggests that the roda sandstone was deposited during a 3rd order relative sea level cycle as a shelf margin systems tract however the stacking of the individual roda u y units demarcated by offshore mudstones both within the gilbert type and the shoal water deltaic systems suggest that 4th order fluctuations occurred these 4th order units are physically correlatable between the two deltaic systems which implies that both deltas responded synchronously to a combination of regional subsidence and eustatic sea level fluctuations the differing internal architecture such as the steeply dipping textural mature foreset beds of the gilbert type delta versus the more gentle sloping textural immature mouth bars of the shoal water fan delta are controlled by different hinterland characteristics and intrabasinal topography

early diagenetic alteration of shallow marine mixed sandstones an example from the lower eocene roda sandstone member tremp graus basin spain abstract a lower eocene shallow marine sandstone complex composed of calcareous quartzose arkoses was modified partly by diagenesis relatively shortly after deposition the sandstone complex forms the lower member of the roda formation which represents part of the palaeogene fill of the tremp graus basin in the southern pyrenees spain early diagenesis comprised the introduction of matrix into the sandstone framework through mechanical infiltration and bioturbation and the precipitation of a mainly aragonitic rim cement this early diagenetic modification occurred in the uppermost parts of sandstone bodies beneath abandonment surfaces the early cement stabilized the sandstone framework and counteracted mechanical compaction in sandstones lacking this early cement on the other hand mechanical compaction severely reduced the primary porosity during a first burial phase causing the development of a thightly compacted fabric mechanical compaction was highly effective because of a high content of ductile grains afterwards two major erosional phases truncated the sandstone complex in the northern part of the area studied probably through the introduction of meteoric water unstable carbonate phases such as aragonite and high mg calcite were replaced by low mg calcite whereas a contemporaneous second calcite cement generation was precipitated after the erosional phases the sandstones were buried once again until recent uplift and denudation brought them to the surface

the search for a topographic signature of life landscapes are shaped by the uplift deformation and breakdown of bedrock and the erosion transport and deposition of sediment life is important in all of these processes over short timescales the impact of life is quite apparent rock weathering soil formation and erosion slope stability and river dynamics are directly influenced by biotic processes that mediate chemical reactions dilate soil disrupt the ground surface and add strength with a weave of roots over geologic time biotic effects are less obvious but equally important biota affect climate and climatic conditions dictate the mechanisms and rates of erosion that control topographic evolution apart from the obvious influence of humans does the resulting landscape bear an unmistakable stamp of life the influence of life on topography is a topic that has remained largely unexplored erosion laws that explicitly include biotic effects are needed to explore how intrinsically small scale biotic processes can influence the form of entire landscapes and to determine whether these processes create a distinctive topography

insights into the genesis of orogenic gold deposits from the zhengchong gold field northeastern hunan province china abstract the zhengchong gold deposit is located in the central jiangnan orogen belt where gold ore occurs mainly as quartz veins altered slates and minor breccias hosted by shear zones in the lengjiaxi group based on its vein crosscutting relationships mineral assemblages and paragenetic sequences mineralization in this deposit is divided into four stages stage 1 quartz q1 pyrite stage stage 2 quartz q2 pyrite arsenopyrite stage stage 3 quartz q3 pyrite polymetallic sulfide mineral stage and stage 4 quartz q4 carbonate stage two types of fluid inclusions have been recognized in the quartz grains co2 bearing fluid inclusions c type and aqueous fluid inclusions w type fluid inclusions in hydrothermal quartz yield homogeneous temperatures and salinities of 312 406 c and 4 65 9 21 wt naclequiv stage 1 252 324 c and 2 20 8 10 wt naclequiv stage 2 193 296 c and 2 24 14 04 wt naclequiv stage 3 and 127 209 c and 2 57 6 59 wt naclequiv stage 4 the co occurrence of these inclusion types despite their variable fluid salinities can be explained by fluid boiling during stages 2 and 3 of mineralization possibly as a result of episodic pressure decreases linked to fault valve activity laser raman spectroscopic analysis results reveal that small quantities of ch4 and n2 are present in the stage 2 3 fluid inclusions fluid inclusion data and microthermometric results show that the ore fluids were low salinity and co2 rich yielding both co2 inclusions c type and aqueous inclusions w type the trapping pressures estimated from the c type inclusions are 80 180 mpa for stages 2 and 3 yielding gold mineralization depths of 7 8 km the mineralizing fluids had calculated 18oh2o values ranging from 3 7 to 8 2 and d values from 75 2 to 61 8 indicating derivation mainly from metamorphic fluids the sulfide minerals yield 34s values of 8 9 to 0 1 and 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 17 83 18 12 15 67 15 76 and 38 03 38 62 respectively which differ significantly from the isotopic composition of the granodiorite 34s 2 4 to 1 0 206pb 204pb 18 57 19 28 207pb 204pb 15 69 15 76 208pb 204pb 38 97 40 34 however the s pb isotopic compositions of the sulfide minerals are similar to those of slates of the lengjiaxi group in the study area the zhengchong gold deposit probably originated from a metamorphic fluid system characterized by low salinity low density and co2 enrichment with limited admixture of magmatic fluids based on similarities to other orogenic gold deposits we infer that the zhengchong orebody represents an orogenic gold deposit formed during the late ordovician jiangnan orogeny caused by collision of the yangtze and cathaysia blocks

nucleation growth and structural development of mylonitic shear zones in granitic rock abstract well exposed shear zones in granitic rock of the sierra nevada are preserved in various degrees of development facilitating interpretation of the mechanisms of shear zone nucleation and growth field relations suggest that these shear zones formed by shear localization within pre existing aplite dikes that served as tabular zones of inherent weakness crossing dikes provide a measure of the offset at several points along the shear zones apparently the shear zones grew in width as they accumulated offset and propagated longitudinally by end to end linkage of approximately coplanar aplite dike segments propagation caused discontinuous dikes or dike segments to be joined giving the shear zones a forked or eye shaped trace pattern some shear zones have developed opening fractures at their tips analogous to the splay fractures that form near the tips of small faults these shear zones provide an excellent opportunity to study the processes involved in natural shear zone formation in granitic rocks where shear is localized along pre existing zones of inherent weakness they may serve as useful analogs for the growth and development of larger scale faults that involve ductile shearing

selective crystallization and precipitation of authigenic pyrite during diagenesis in uranium reservoir sandbodies in ordos basin abstract the occurrence characteristics of authigenic pyrite during diagenesis in uranium reservoir sandbodies of zhiluo formation in ordos basin are investigated based on outcrop area investigations and drilled cores observations the pyrite is closely related to carbonaceous debris microscopically the host components for pyrite consist of carbonaceous debris clay minerals biotite the earlier pyrite and ilmenite by emphasizing on 34s values via la icp ms as well as observing through optical microscope and scanning electron microscope equipped with energy dispersive spectroscope three kinds of distribution pattern of pyrite are classified as i periphery ii infilling iii the combined form of the above two in situ micrometer scale sulfur isotope analyses of pyrite demonstrated that broad scale isotopes are heterogeneous from 52 5 to 35 4 of 34s and sulfur is derived from more than a single source significant differences of host components effects on authigenic pyrite formation are discussed the carbonaceous debris can supply the energy for the bacterial sulfate reduction process and the biotite can provide the source of iron for pyrite precipitation the ferrous ion can be adsorbed on the surface of the clay minerals meanwhile the authigenic pyrite is distributed in or around the earlier pyrite and ilmenite by the indirect adsorption of ferrous ion and the ilmenite may also provide the source of iron futhermore the uranium minerals are mainly associated with the authigenic pyrite relevant to carbonaceous debris and clay minerals which indicates there exists constraints of authigenic pyrite during diagenesis on the uranium mineralization

transgression of an estuarine channel and tidal flat complex the lower triassic of barles alpes de haute provence france the lower triassic succession of barles alpes de haute provence france comprises an unconformable quartz arenite sand body of 90m thickness the succession may be informally divided into i lower channellized cross bedded member overlain by ii an upper fining upward member the lower member comprises vertically stacked subtidal channel units separated into five major sand bodies by thin developments of fine grained channel margin and shoal deposits subtidal channel fill deposits are dominated by varying scales of cross bedding these scales vary systematically from the base to the top of the member with large scale planar sets dominating the lowest channel sand body sand body 1 medium scale planar and trough cross bedding characterizing sand bodies 2 4 the largest scale planar sets in the highest sand body sand body 5 this upward change in cross bedding scale is concomitant with a decrease in both the relief of major channel sand body erosion surfaces and the proportion of preserved interchannel shoal deposits the succeeding fining upward member comprises small scale tidal channel units overlain by channel shoal and tidal flat deposits tidal flat sequences are characterized by parallel laminated wave and current rippled sandstones separated by bioturbated fine grained siltstones and mudstones the vertical variation in facies of the lower triassic succession suggests two main periods of deposition the lower member is considered to preserve successively more seaward components of a transgressive estuarine complex the overlying upper member records the seaward progradation of tidal channel shoal and tidal flat environments the unconformity bounded nature of the lower member combined with its systematic variation in facies suggests it may represent an incised valley estuarine fill developed in response to an early triassic relative sea level fall and subsequent rise succeeding tidal channel and tidal flat deposits forming the upper fining upward member reflect a change in sediment supply and or rate of relative sea level rise comparable with a progradational shoreline it is unclear whether this final depositional episode represents a period of highstand progradation or a later lowstand shoreline system developed following a further period of relative sea level fall and rise

initial generation of sand across climate zones of the mojave sierra nevada and klamath batholiths in california u s a the generation of modern plutoniclastic sediment across california varies with climate resulting in significant mineralogical and geochemical differences between parent rock weathering profile material and low order stream sand with average precipitation of 15 cm yr in the arid zones and 120 cm yr in the temperate zones feldspar is relatively decreased in stream sand compared to parent rock by 2 and 20 respectively potassium feldspar is more resistant to weathering than plagioclase but is less stable than quartz in temperate climates hornblende and biotite are more easily weathered in temperate than arid climates although their occurrence in medium grained stream sands is affected by hydraulic sorting and comminution during transport temperate climate sands have lower concentrations of cao and na2o compared to k2o and al2o3 reflective of the expected faster loss of plagioclase than potassium feldspar during weathering with the exception of biotite the mineralogy of medium grained stream sand reflects that of medium grained weathering profile material in both climates confirming the findings from constant climate case studies that the composition of proximal sand is largely achieved within weathering profiles and during initial erosion we encourage continued attention to climate as a control on sand composition in provenance and paleoclimate studies where a moderate precipitation shift is capable of producing a significant loss of feldspar the differential response of common minerals to chemical weathering should be considered for studies and modeling related to bedrock erodibility sediment supply and landscape evolution

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

experimental exsolution textures in the system bornite chalcopyrite genetic implications concerning natural ores textural interpretation of ore mineral assemblages such as bornite chalcopyrite bn cpy intergrowths should be based on definite experimentation appropriate exsolution and coarsening experiments were performed using sealed evacuated silicaglass tubes synthetic bn cpy solid solutions were annealed between 100 and 350 c for times of 20 min to 10 weeks early formed textures develop through nucleation and growth and depend on the initial degree of supersaturation and the metal diffusivities final textures due to additional growth and coarsening are very sensitive to temperature and may serve as geothermometers mutual boundary textures which form above 250 c can originate by 1 simultaneous precipitation 2 exsolution during slow cooling from above the solvus and 3 metamorphism to temperatures above about 250 c widmanstatten textures are not compatible with slow cooling but indicate 1 low temperature replacement of bn or 2 exsolution of cpy lamellae from anomalous bn heated to around 200 250 c during mild metamorphism

restoring dense vegetation can slow mountain erosion to near natural benchmark levels tropical mountain areas may undergo rapid land degradation as demographic growth and intensified agriculture cause more people to migrate to fragile ecosystems to assess the extent of the resulting damage an erosion rate benchmark against which changes in erosion can be evaluated is required benchmarks reflecting natural erosion rates are usually not provided by conventional sediment fluxes which are often biased due to modern land use change and also miss large episodic events within the measuring period to overcome this we combined three independent assessment tools in the southern ecuadorian andes an area that is severely affected by soil erosion first denudation rates from cosmogenic nuclides in river sediment average over time periods of 1 100 k y and establish a natural benchmark of only 150 100 t km 2 yr 1 second we find that land use practices have increased modern sediment yields as derived from reservoir sedimentation rates which average over periods of 10 100 yr to as much as 15 10 3 t km 2 yr 1 third our land cover analysis has shown us that vegetation cover exerts first order control over present day erosion rates at the catchment scale areas with high vegetation density erode at rates that are characteristically similar to those of the natural benchmark regardless of whether the type of vegetation is native or anthropogenic therefore our data suggest that even in steep mountain environments sediment fluxes can slow to near their natural benchmark levels with suitable revegetation programs a set of techniques is now in place to evaluate the effectiveness of erosion mitigation strategies

sedimentary basins formed and carried piggyback on active thrust sheets small sedimentary basins that formed on the apennine southern margin of the po basin complex northern italy have been studied using borehole and seismic reflection information and their evolution can be dated using the largely marine biostratigraphy of the miocene to quaternary sediments these studies show that the basins formed and were filled while being carried on moving thrust sheets and they are therefore named piggyback basins each of these basins corresponds to the active phase of a different thrust front ramp on the pyrenean northern margin of the ebro basin complex northern spain similar piggyback basins formed between eocene and mid miocene time they have since been uplifted and eroded and may therefore be studied in outcrop in northern spain much of the basin fill sediment was deposited in nonmarine environments

cosmogenic 10be derived denudation rates of the eastern and southern european alps denudation rates from cosmogenic 10be measured in quartz from recent river sediment have previously been used in the central alps to argue that rock uplift occurs through isostatic response to erosion in the absence of ongoing convergence we present new basin averaged denudation rates from large rivers in the eastern and southern european alps together with a detailed topographic analysis in order to infer the forces driving erosion denudation rates in the eastern and southern alps of 170 1 400 mm ky 1 are within a similar range to those in the central alps for similar lithologies however these denudation rates vary considerably with lithology and their variability generally increases with steeper landscapes where correlations with topographic metrics also become poorer tertiary igneous rocks are associated with steep hillslopes and channels and low denudation rates whereas pre alpine gneisses usually exhibit steep hillslopes and higher denudation rates molasse flysch and schists display lower mean basin slopes and channel gradients and despite their high erodibility low erosion rates exceptionally low denudation rates are also measured in permian rhyolite which has high mean basin slopes we invoke geomorphic inheritance as a major factor controlling erosion such that large erosive glaciers in the late quaternary cold periods were more effective in priming landscapes in the central alps for erosion than in the interior eastern alps however the difference in tectonic evolution of the eastern and central alps potentially adds to differences in their geomorphic response their deep structures differ significantly and unlike the central alps the eastern alps are affected by ongoing tectonic influx due to the slow motion and rotation of adria the result is a complex pattern of high mountain erosion in the eastern alps which has evolved from one confined to the narrow belt of the tauern window in late tertiary time to one affecting the entire underthrust basement orogenic lid and parts of the southern alps today

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

the critical role of climate and saprolite weathering in landscape evolution landscapes evolve in response to external forces such as tectonics and climate that influence surface processes of erosion and weathering internal feedbacks between erosion and weathering also play an integral role in regulating the landscapes response our understanding of these internal and external feedbacks is limited to a handful of field based studies only a few of which have explicitly examined saprolite weathering here we report rates of erosion and weathering in saprolite and soil to quantify how climate influences denudation by focusing on an elevation transect in the western sierra nevada mountains california we use an adapted mass balance approach and couple soil production rates from the cosmogenic radionuclide crn 10be with zirconium concentrations in rock saprolite and soil our approach includes deep saprolite weathering and suggests that previous studies may have underestimated denudation rates across similar landscapes along the studied climate gradient chemical weathering rates peak at middle elevations 1200 2000 m averaging 112 3 9 7 t km 2 y 1 compared to high and low elevation sites 46 8 5 2 t km 2 y 1 measured weathering rates follow similar patterns with climate as those of predicted silica fluxes modeled using an arrhenius temperature relationship and a linear relationship between flux and precipitation furthermore chemical weathering and erosion are tightly correlated across our sites and physical erosion rates increase with both saprolite weathering rates and intensity unexpectedly saprolite and soil weathering intensities are inversely related such that more weathered saprolites are overlain by weakly weathered soils these data quantify exciting links between climate weathering and erosion and together suggest that climate controls chemical weathering via temperature and moisture control on chemical reaction rates our results also suggest that saprolite weathering reduces bedrock coherence leading to faster rates of soil transport that in turn decrease material residence times in the soil column and limit soil weathering copyright 2009 john wiley sons ltd

the role of magnesite spatial distribution patterns in determining dissolution rates when do they matter we systematically explore the role of magnesite distribution patterns in dictating its dissolution rates under an array of flow velocity and permeability contrast conditions using flow through column experiments and reactive transport modeling columns were packed with magnesite distributed within quartz matrix in different spatial patterns the mixed column has uniformly distributed magnesite while the zonation columns contain magnesite in different number of zones parallel to the main flow dissolution rates are highest under conditions that maximize water flowing through the magnesite zone this occurs under fast flow and high permeability or uniformly distributed magnesite zones under high flow and low permeability magnesite conditions dissolution only occurs at the magnesite quartz interface leading to rates an order of magnitude lower in the one zone columns than those in the mixed columns spatial patterns do not make a difference under low flow conditions when the system approaches equilibrium v 0 36 m d or under conditions where magnesite zones have higher permeability than quartz zone the bulk column scale rate depends on ae through rmgco3 b mol s 10 9 60 ae where ae is the surface area that effectively dissolves with iap keq 0 1 the rate constant of 10 9 60 is very close to 10 10 0 mol m 2 s under well mixed conditions suggesting the potential resolution of laboratory field rate discrepancy when ae instead of the total bet surface area at i s used the ae values are 1 3 orders of magnitude lower than at the effectively dissolving magnesite quartz interface areas vary between 60 and 100 of ae pointing the importance of reactive interfaces in heterogeneous porous media this work quantifies the significance of magnesite spatial distribution patterns it has important implications in understanding biogeochemical processes in the critical zone and in the deep subsurface where spatial variations in mineral properties prevail

mixing of sodic and calcic brines and uranium deposition at mcarthur river saskatchewan canada a raman and laser induced breakdown spectroscopic study of fluid inclusions the richest u deposit in saskatchewan canada occurs in the mcarthur river area in the vicinity of the unconformity between the athabasaca sandstones and an archean to lower proterozoic basement paleofluids related to the silicification of the sandstones and the formation of pre and postore cements in breccias were studied using microthermometry raman microspectroscopy and laser induced breakdown spectroscopy libs on individual fluid inclusions a detailed reconstruction of the fluid composition in the system na ca mg cl shows that two types of brines are responsible for the main quartz cements an nacl rich brine 25 wt nacl up to 14 wt cacl 2 and up to 1 wt mgcl 2 which is interpreted as a primary formation water that was expelled from bedded evaporites and a cacl 2 rich brine 5 8 wt nacl 20 wt cacl 2 and up to 11 wt mgcl 2 which is considered to have formed during the interaction between the nacl rich brine and ca rich minerals in the basement and was introduced into the fault system and mixed with the nacl rich brine during the critical stage of u deposition the pressure temperature conditions of formation of the quartz cements are estimated to be 1 200 to1 400 bars and 190 to 235 c for the silicification events during the preore stage and 500 to 900 bars after a pressure decrease from lithostatic conditions and slightly lower temperatures due to the mixing of the nacl rich brine with the cooler approx 140 c cacl 2 rich brine during the main stage of breccia sealing temperature and pressure drops combined with the effects of brine mixing appear to be key factors for the main stages of quartz cementation and u deposition at the mcarthur deposit

modulation of erosion on steep granitic slopes by boulder armoring as revealed by cosmogenic 26al and 10be cosmogenic 26 al and 10 be in quartz from boulders bedrock and sandy sediment from 21 small watersheds in the diamond mountains batholith ca usa and two small watersheds from the nearby fort sage mountains confirm that exposed granitic bedrock and boulders erode more slowly than the catchments in which they are found exposed bedrock and boulders are more abundant on steep slopes and may play an important role in regulating mountain erosion rates rapid transport of fine sediment on steep slopes exhumes resistant corestones which accumulate on the surface the resulting boulder lag apparently shields the underlying soil and bedrock from erosion even when the bedrock is deeply weathered and friable where steep slopes have an abundant boulder lag they erode as slowly as gentler slopes nearby in contrast steep slopes lacking a boulder lag erode much more quickly than gentle slopes boulder armoring can modulate hillslope erosion such that erosion rates of summits steep mountain flanks and gentle footslopes are indistinguishable thus permitting local relief and steep mountain slopes to persist for long periods of time fl 2001 elsevier science b v all rights reserved

climatic control of denudation in the deglaciated landscape of the washington cascades erosion in the washington cascades mountains was dominated by glacier activity until the end of the last glacial maximum when fluvial incision and mass wasting became the dominant drivers an analysis of millennial scale rates of denudation in the range suggest erosion is sensitive both to spatial variations in precipitation and inherited topography

fossiliferous intervals and sequence boundaries in shallow marine fan deltaic deposits early eocene southern pyrenees spain abstract carbonate rich fossiliferous intervals are commonly intercalated in shallow marine siliciclastic successions in a sequence stratigraphic approach to basin modelling such layers tend to be used for interpretation in terms of sea level changes as reflecting maximum flooding events however in this paper it will be demonstrated that such interpretation may not be generally applicable during the eocene a fan delta system developed in the tectonically active tremp graus basin a southern pyrenean foreland basin in spain fan delta lobes prograded rapidly during periods of active sediment supply fossiliferous calcareous intervals were formed during local abandonment of individual fan delta lobes and distributary channel mouthbars and occur on top of the depositional lobes on their foreslopes and on their more distal toes calcareous intervals originated as a consequence of the local development of an in situ macrofauna association during periods of clastic abandonment the macrofauna typically reflects environmental conditions ranging from shallow high energy conditions to somewhat deeper water and more tranquil conditions two laterally equivalent faunal associations dominate a high energy and shallow water fauna typified by mytilus spondylus cardiacea and a low energy and somewhat deeper water fauna characterized by turritella corbulidae each calcareous horizon is related to a pause in clastic sedimentation as a result of autocyclic lateral shifting of the local depocentre differences in faunal associations and substrate conditions are related to water depth which is largely defined by clastic sediment accumulation although each calcareous interval was caused by local starvation of clastic sediment supply the macrofauna associated with abandonment surfaces indicates that relatively little time was involved in their development suggesting that such surfaces do not mark regional discontinuities in a sequence stratigraphic frame the in situ macrofauna associations can be used for estimating the significance of hardground like layers

hydrothermal rare earth element xenotime mineralization at maw zone athabasca basin canada and its relationship to unconformity related uranium deposits a reply

sea level fluctuations and the geometric variability of tide dominated sandbodies abstract this paper presents examples of various large tidal sandbodies from the eocene roda sandstone in the southern pyrenees and the late pleistocene and early holocene in the east china sea an attempt is made to summarize the geometric variability of these large tidal sandbodies in relation to the sediment supply and tidal discharge of the depositional system transverse sand bars were developed in low sinuosity high gradient channels with high influxes of coarse sediments and water from fluvial systems tidal point bars were formed in meandering low gradient estuarine channel where tidal influence was stronger and sediment was finer than those of the transverse sand bar a tidal delta complex was built up at the estuary mouth with an abundant sediment supply and an increased tidal discharge tidal sand ridges were formed when relict fluvial or deltaic sands were eroded and reworked by strong tidal currents during subsequent sea level rise since the sediment supply and the tidal discharge of the depositional system were closely related to the eustatic sea level change and basin subsidence i e the relative sea level change special attention will be given to the relationship between geometric variability of tidal sandbodies and the sequence stratigraphic framework in which various sandbodies occurred three orders of eustatic sea level fluctuations can be recognized the third order eustatic sea level cycle together with basin subsidence controlled the development of systems tracts and the occurrence of different tidal sandbodies such as estuary and tidal flat facies during the late stage of a lsw systems tract type 1 sequence or a sm systems tract type 2 sequence tidal point bar facies tidal delta facies or tidal sand ridge facies during a tr systems tract estuary facies during an early hs systems tract and fluvial sand bar facies in a late hs systems tract and the early stage of a sm or lsw systems tract there are also the fourth order and fifth order eustatic fluctuations which are superimposed on the third order eustatic changes and have important control on the build up abandonment and preservation of composite and single tidal sandbodies respectively since the deposition of tidal sandbodies is very sensitive to eustatic sea level changes recognition of various tidal sandbodies is important in sequence stratigraphy analyses of sedimentary basins and in the facies prediction of clastic sediments in basin modelling

calcite cementation in shallow marine eocene sandstones and constraints of early diagenesis the lower eocene shallow marine roda sandstone member forms part of the paleogene fill of the tremp graus basin in the southern spanish pyrenees it is composed of mixed siliciclastic carbonate sandstones that were severely modified in composition and texture shortly after deposition during pauses in sedimentation moreover part of the sand was lithified by an early marine fringe cement this early diagenetic cement stabilized the sandstone framework and prevented mechanical compaction where early cement was absent mechanical compaction severely reduced the primary porosity during a first burial phase ductile grains were squeezed between rigid grains obstructing pore connections this caused the development of distinct porosity patterns in the sandstone bodies after the first burial phase two major phases of uplift and erosion resulted in the truncation of the roda sandstone member in the northern part of the area studied after the erosional phases the sandstones were buried again recharge of the sandstone bodies with fresh water caused replacement of aragonite and high magnesian calcite by low magnesian calcite simultaneously a second generation of sparry calcite cement was precipitated replacement and cementation were completed first in the most porous and permeable levels represented by those parts of the sandstone that contained the early cement the intervals compacted during the first burial were cemented later or cementation was completed later

differential early diagenetic low mg calcite cementation and rhythmic hardground development in campanian maastrichtian chalk abstract the campanian maastrichtian limestones in the south of the netherlands are well sorted fine grained mudstones and silt to fine sand sized bioclastic grainstones these limestones show a distinct lithological cyclicity manifested by fining upward grain size cycles with calcite cemented layers or hardgrounds capping each cycle in the lower part of the succession the cyclicity is further enhanced by nodular chert layers these fining upward cycles are caused by fair weather or storm wave related energy fluctuations and consequently changing rates of deposition differences in composition and texture and differences in the degree of early diagenesis cemented layers and hardgrounds are the result of differential early marine calcite cementation in these limestones early calcite cementation cannot be explained by the supply of cementing materials from saturated seawater an alternative model for early marine calcite cementation is proposed in which early calcite cementation occurred within the sediment at some distance below the seafloor as a result of organic matter degradation and internal redistribution of bioclastic carbonate bacterial organic matter degradation caused dissolution of relatively unstable high mg calcite and or aragonite in the oxic zone followed by precipitation of calcite cement as a consequence of bacterial iron reduction duringperiods with a lower sedimentation rate any significant early cementation and replacement of high mg calcite occurred when younger oxic burrows dissected older burrowed sediment with a more advanced stage of organic matter degradation in particular iron reduction cementation also occurred when redox boundaries repeatedly moved through the same layers during periods with low nett sedimentation and increased storm activity and erosion the differences in the degree of early diagenetic calcite cementation were further enhanced during paleocene karstification and development of secondary porosity by dissolution of remaining unstable carbonate grains and by associated meteoric water calcite cementation

predictive modeling of bedrock outcrops and associated shallow soil in upland glaciated landscapes abstract identifying the areal extent of bedrock outcrops and shallow soils has important implications for understanding spatial patterns in vegetation composition and productivity stream chemistry gradients and hydrologic and soil properties of landscapes manual methods of delineating bedrock outcrops and associated shallow soils are still commonly employed but they are expensive to implement over broad areas and often limited by representation of polygon units few studies have automated the delineation of bedrock outcrops these focused on delineation approaches in landscapes with rapidly eroding hillslopes and sparse vegetation the objectives of this study were to assess the accuracy of visually interpreting high resolution relief maps for locating bedrock outcrops and associated shallow soil boss

a statistical evaluation of the origin of cypress domes in florida two competing explanations exist for the origin of one type of karstic landform found in florida called the cypress dome one explanation relies on complex ecological feedbacks stemming from nutrient cycling suggesting biota contribute more significantly to processes of landscape evolution in florida than anywhere else in the world the second explanation is that the landforms are sinkholes that completely preclude the biological explanation while fitting more parsimoniously with the surrounding geological narrative this work puts forward geostatistical analyses and a model linking the landforms to sinkholes thus bolstering the geological explanation for origin of the landform satellite imagery of sinkholes occurring in limestone from locations spanning the planet was analyzed measurements of globally distributed limestone sinkhole surface areas are best characterized by an exponential distribution indicating sinkhole formation is robust to starting conditions i e climate tectonics this observation is supported by an analysis of sinkhole geometry and geospatial dispersion this demonstrates the geospatial parameters space for globally distributed groups of sinkholes forming in limestone are statistically indistinguishable despite sinkhole formation in different climates tectonic regimes and at different times employing this observation as a tool sinkholes are directly compared to the cypress domes in florida and are found to be statistically indistinguishable from the striking similarity in spatial parameter spaces in conjunction with the geologic history of the area it is interpreted that these landforms originate through geologic not biologic processes

bedrock fracture control of glacial erosion processes and rates the importance of rock type and tectonic history on rates of glacial erosion and the relative roles of glacial quarrying and abrasion are poorly understood we use concentrations of cosmogenic 10be in glacial polish and measurements of bedrock fracture spacing to explore the relationship between erosion rates and rock fracturing at 23 sites along tuolumne river valley and five sites in tenaya canyon in yosemite national park california usa most sites yield 10be concentrations that can be best explained as reflecting solely postglacial nuclide accumulation six sites however display anomalously high concentrations implying incomplete removal of the pre glacial nuclide inventory during the last glaciation these require that erosion in the last glacial cycle was 2 3 m these low erosion sites occur preferentially in massive units of the cathedral peak granodiorite and the el capitan granite fractures in high erosion sites are more closely spaced than in low erosion sites with spacings that average 1 1 0 03 m and 3 3 0 1 m respectively our data suggest that the distance between fractures in the rock dictated in part by the original spacing in a particular pluton and in part by the specific tectonic history of the sierra nevada governs the pace of glacial erosion in yosemite

formation of joints in cooling plutons abstract the geometry age and mineralogy of steeply dipping joints in the lake edison granodiorite of california indicate that thermal stresses played a key role in the formation of the joints joint traces curve to approach the pluton boundary at high angles at both large and small scales and they generally terminate at or near the contact with an older pluton radiometric dates and the epidote and chlorite fillings of the joints tie jointing to the initial cooling of the pluton a thermo mechanical stress analysis assuming two dimensional conductive cooling predicts thermal stresses of several tens of mpa the same order of magnitude as plausible fluid pressures regional stresses and lateral normal stresses associated with the overburden the orientation of the joints can be accounted for rather well by the stress field formed by superposing a uniform regional stress field on the predicted thermal stresses the large scale pattern of the early joints in many plutons should be predictable based on a pluton s geometry its age relative to the adjacent rock and knowledge of the regional stress at the time of initial cooling these findings bear on issues pertinent to mining petroleum recovery nuclear waste repository siting and ground water flow

petrography and geochemistry of granitoids from the samphire pluton south australia implications for uranium mineralisation in overlying sediments abstract the blackbush uranium deposit jorc inferred resource 12 580 tonnes u located on the north eastern eyre peninsula is currently the only sediment hosted u deposit investigated in detail in the gawler craton uranium is hosted within eocene sandstone of the kanaka beds overlying mesoproterozoic granites of the samphire pluton affiliated with the hiltaba intrusive suite 1 6 ga these are considered the most probable source rocks for uranium mineralisation by constraining the petrography and mineralogy of the granites insights into the post emplacement evolution can be gained which may provide an exploration indicator for other sediment hosted uranium systems three geochemically distinct granite types were identified in the samphire pluton and correspond to domains interpreted from geophysical data all granites show complex alteration overprints and textures with increasing intensity closer to the deposit as well as crosscutting veining alkali feldspar has been replaced by porous k feldspar and albite and plagioclase is overprinted by an assemblage of porous albite sericite calc silicates prehnite pumpellyite and epidote this style of feldspar alteration is regionally widespread and known from hiltaba aged granites associated with iron oxide copper gold mineralisation at olympic dam and in the moonta wallaroo region in two granite types biotite is replaced by calcic garnet calc silicates are indicative of ca metasomatism sourced from the anorthite component of altered plagioclase minor clay alteration of feldspars is present in all samples mineral assemblages in veins include quartz hematite hematite coffinite fluorite quartz and clay minerals minor chlorite and sericite are found in all vein types all granite types are anomalously rich in u concentrations between 10 and 81 ppm highly variable th u ratios as well as hydrothermal u minerals mostly coffinite in granites and veins are clear evidence for u mobility uranium may have been preconcentrated in veins in the upper parts of the pluton and was subsequently leached after deposition of the sediment