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

migration of brines in the basement rocks of the athabasca basin through microfracture networks p patch u deposit canada abstract the unconformity type uranium deposits of the athabasca basin saskatchewan canada are hosted near the unconformity between a middle proterozoic intracratonic sedimentary basin and an archean to paleo proterozoic metamorphic and plutonic basement these deposits which are considered to be the richest u deposits in the world are the result of massive basinal fluid migrations in the basement rocks this study shows that basinal brines have strongly penetrated into the basement not only through faults and major pathways but also by way of dense networks of microfractures which favoured the percolation of fluids down to considerable depths hundred metres below the unconformity and their chemical modification salinity increase by interaction with basement lithologies these processes are one of the major causes of uranium mobility within the basement rocks and the formation of unconformity type mineralization microfracture networks which opened during the basinal brine stage ca 1600 1400 ma are interpreted as sets of mode i cracks corresponding to a specific stage of deformation and occur as fluid inclusion planes after healing the stress field at that stage 1 n130 150 e subvertical partly reopened the earlier microcrack networks 1 n80 110 e and n130 150 e subvertical issued from the trans hudson orogeny late retrograde metamorphic stage ca 1795 1720 ma the circulation of the two types of fluids carbonic and brines occurs thus at two distinct events trans hudson orogeny late retrograde metamorphism for carbonic fluids and maximal burial diagenesis for brines but the same main microfissure geometry was used by the fluids this demonstrates the existence of a similar stress field direction acting before and after the basin formation moreover the brine circulations in the basement acted in a wider volume than the clay rich alteration halo surrounding the u ores generally considered as the main envelope of fluid percolation outside the fault systems the data on the chemistry of the fluids and on the geometry of their migration at various scales emphasise the fundamental role of the basement in the chemical evolution of highly saline brines linked to unconformity related uranium mineralization in the athabasca basin

oxidation of methane at the ch4 h2o co2 transition zone in the external part of the central alps switzerland evidence from stable isotope investigations abstract with the aim of understanding the mechanisms that control the metamorphic transition from the ch 4 to the h 2 o co 2 dominated fluid zone in the helvetic domain of the central alps of switzerland fluid inclusions in quartz illite crystallinity index vitrinite reflectance and the stable isotope compositions of vein and whole rock minerals and fluids trapped in quartz were investigated along four cross sections increasing temperature during prograde metamorphism led to the formation of dry gas by hydrocarbon cracking in the ch 4 zone fluid immiscibility in the h 2 o ch 4 co 2 nacl system resulted in cogenetic ch 4 and h 2 o dominated fluid inclusions in the ch 4 zone fluids were trapped at temperatures 270 5 c the end of the ch 4 zone is marked by a sudden increase of co 2 content in the gas phase of fluid inclusions at temperatures 270 5 c in the h 2 o zone the total amount of volatiles within the fluid decreased below 1 mol with no immiscibility this resulted in total homogenization temperatures of h 2 o co 2 ch 4 nacl inclusions below 180 c hydrogen isotope compositions of methane in fluid inclusion have d values of less than 100 in the ch 4 zone typical for an origin through cracking of higher hydrocarbons but where the methane has not equilibrated with the pore water d values of fluid inclusion water are around 40 in isotopic equilibrium with phyllosilicates of the whole rocks within the ch 4 to h 2 o co 2 transition zone d h 2 o values in fluid inclusions decrease to 130 interpreted to reflect the contribution of deuterium depleted water from methane oxidation in the h 2 o zone d h 2 o values increase again towards an average of 30 which is again consistent with isotopic equilibrium with host rock phyllosilicates 13 c values of methane in fluid inclusions from the ch 4 zone are around 27 in isotopic equilibrium with calcite in veins and whole rocks the 13 c ch 4 values decrease to less than 35 at the transition to the h 2 o zone and are no longer in equilibrium with the carbonates in the whole rocks 13 c values of co 2 are variable but too low to be in equilibrium with the wall rock fluids compatible with a contribution of co 2 from closed system oxidation of methane differences in isotopic composition between host rock and alpine fissure carbonate are generally small suggesting that the amount of co 2 produced by oxidation of methane was small compared to the c budget in the rocks and local pore fluids were buffered by the wall rocks during precipitation of calcite within the fissures

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

sea level and turbidity controls on mangrove soil surface elevation change increases in sea level are a threat to seaward fringing mangrove forests if levels of inundation exceed the physiological tolerance of the trees however tidal wetlands can keep pace with sea level rise if soil surface elevations can increase at the same pace as sea level rise sediment accretion on the soil surface and belowground production of roots are proposed to increase with increasing sea level enabling intertidal habitats to maintain their position relative to mean sea level but there are few tests of these predictions in mangrove forests here we used variation in sea level and the availability of sediments caused by seasonal and inter annual variation in the intensity of la nina el nino to assess the effects of increasing sea level on surface elevation gains and contributing processes accretion on the surface subsidence and root growth in mangrove forests we found that soil surface elevation increased with mean sea level which varied over 250 mm during the study and with turbidity at sites where fine sediment in the water column is abundant in contrast where sediments were sandy rates of surface elevation gain were high but not significantly related to variation in turbidity and were likely to be influenced by other factors that deliver sand to the mangrove forest root growth was not linked to soil surface elevation gains although it was associated with reduced shallow subsidence and therefore may contribute to the capacity of mangroves to keep pace with sea level rise our results indicate both surface sedimentation and subsurface root growth processes can influence mangrove capacity to keep pace with sea level rise within the same geographic location and that current models of tidal marsh responses to sea level rise capture the major feature of the response of mangroves where fine but not coarse sediments are abundant

geochronology of unconformity related uranium deposits in the athabasca basin saskatchewan canada and their integration in the evolution of the basin the importance of geochronology in the study of mineral deposits in general and of unconformity type uranium deposits in particular resides in the possibility to situate the critical ore related processes in the context of the evolution of the physical and chemical conditions in the studied area the present paper gives the results of laser step heating 40ar 39ar dating of metamorphic host rock minerals pre ore and syn ore alteration clay minerals and laser ablation inductively coupled plasma mass spectrometer la icp ms u pb dating of uraninite from a number of basement and sediment hosted unconformity related deposits in the athabasca basin canada post peak metamorphic cooling during the trans hudson orogen of rocks from the basement occurred at ca 1 750 ma and gives a maximum age for the formation of the overlying athabasca basin pre ore alteration occurred simultaneously in both basement and sandstone hosted mineralizations at ca 1 675 ma as indicated by the 40ar 39ar dating of pre ore alteration illite and chlorite the uranium mineralization age is ca 1 590 ma given by la icp ms u pb dating of uraninite and 40ar 39ar dating of syn ore illite and is the same throughout the basin and in both basement and sandstone hosted deposits the mineralization event older than previously proposed as well as several fluid circulation events that subsequently affected all minerals studied probably correspond to far field continent wide tectonic events such as the metamorphic events in wyoming and the mazatzal orogeny ca 1 6 to 1 5 ga the berthoud orogeny ca 1 4 ga the emplacement of the mckenzie mafic dyke swarms ca 1 27 ga the grenville orogeny ca 1 15 to 1 ga and the assemblage and break up of rodinia ca 1 to 0 85 ga the results of the present work underline the importance of basin evolution between ca 1 75 ga basin formation and ca 1 59 ga ore deposition for understanding the conditions necessary for the formation of unconformity type uranium deposits

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

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

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

evaluating deep subsidence in a rapidly accreting mangrove forest using gps monitoring of surface elevation benchmarks and sedimentary records abstract ultimately the fate of mangrove forests depends on substrate elevation gains keeping pace with relative sea level rise rslr some of the world s largest mangrove forests occur on tectonically active margins river deltas and sedimentary basins where sea level trends are largely controlled by vertical land motion i e subsidence so that rslr can be markedly higher than sea level rise induced by climate warming the rod surface elevation table marker horizon rset mh method has been applied globally to evaluate coastal wetland resilience to slr by quantifying net rates of elevation change relative to a benchmark a limitation of the rset method is that the stability of the benchmark i e vertical trend is unknown and rslr in wetlands is typically inferred from regional tide gauge records in the present study we evaluate rslr in a rapidly subsiding avicenna marina mangrove forest with a large terrigenous sediment supply firth of thames new zealand using independent and complimentary methods 1 campaign gps surveys of the stability of three rset benchmarks driven 18 m into unconsolidated sediment a tide gauge some 10 km distant and a reference station located on basement rock 2007 2016 that are tied to a network of satellite based geodetic sites and 2 137cs validated 210pb sediment accumulation rates sar measured in cores as a proxy for rslr the similarity of deep subsidence rates at the rset benchmarks located several hundred metres apart 7 7 0 5 to 9 4 0 5 mm yr 1 provides confidence in these results these subsidence rates are two to five fold higher than recorded at the nearby tide gauge 3 6 0 7 mm yr 1 and reference station 1 6 0 5 mm yr 1 weighted average 210pb sar of 9 9 mm and 9 3 mm yr 1 yield similar estimates of deep subsidence i e 8 4 and 6 9 mm yr 1 slr adjusted for vertical land motion indicating that this geological process is the major driver of the long term sea level trend in the mangrove forest our findings suggest that regional tide gauge records may not provide reliable estimates of rslr for all coastal wetlands due to local subsidence associated with natural processes and human activities subsidence rates and rslr within coastal wetlands can be evaluated using campaign gps surveys of rset benchmarks and independently from longer term sedimentary records finally evaluations of the resilience of coastal wetlands to rising sea levels over the coming decades must be based on measurements of rslr from these systems themselves

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

a 3 800 million year isotopic record of life from carbon in sedimentary rocks an increased ratio of 12c to 13c an indicator of the principal carbon fixing reaction of photosynthesis is found in sedimentary organic matter dating back to almost four thousand million years ago a sign of prolific microbial life not long after the earth s formation partial biological control of the terrestrial carbon cycle must have been established very early and was in full operation when the oldest sediments were formed

high surface elevation gains and prediction of mangrove responses to sea level rise based on dynamic surface elevation changes at dongzhaigang bay china abstract mangrove forest responses to sea level rise slr are likely misestimated in many studies because current assessment methods often assume a constant rate of surface elevation change along the intertidal profile most studies also neglect the ecogeomorphic feedback process known to accelerate soil building with slr here an empirical dynamic model that accounts for the above processes is constructed for the intertidal zone of a mangrove bay in hainan china the model allows us to explore the response of a tide dominated mangrove forest to different rates of slr rod surface elevation table marker horizon rset mh data 2015 2018 indicate rather high rates of surface accretion 13 3 57 9 mm yr 1 and surface elevation changes 7 9 35 5 mm yr 1 surface accretion and surface elevation change decreased exponentially with increasing ground elevation our model showed that slr at rates of 4 and 16 mm yr 1 would not lead to the loss of mangrove cover but that it could alter mangrove species zonation along the intertidal profile by 2100 due to a rich sediment supply and ecogeomorphic feedback importantly rapid slr and landward barriers can pose a considerable threat to the high intertidal community by causing increased inundation of the high intertidal zone subsequent shifts in species zones and the loss of mangrove biological and structural diversity along the intertidal profile overall this study predicts probabilities of habitat suitability for mangrove species under slr and expands our current understanding of the impacts of slr on tide dominated mangrove forests in sediment rich systems incorporation of extensive long term rset data into this kind of dynamic model could contribute to the better prediction of mangrove responses to slr at large scales in the future

a fluid inclusion study of syntectonic zn pb ag mineralization at dugald river northwest queensland australia petrographic microthermometric and laser raman microprobe analyses of fluid inclusions from the zn pb ag sulfide deposit at dugald river northwest queensland indicate that fluids with a wide range of compositions in the co 2 ch 4 h 2 o nacl system were involved in the formation of the deposit early primary inclusions are characterized by higher homogenization temperatures centered on 360 degrees c an average salinity of 13 wt percent nacl equiv and they tend to be relatively co 2 rich such a fluid migrating through the thick sequence of the middle proterozoic metasediments of the corella formation would acquire metals and reduced sulfur as well as ch 4 due to its interaction with the country rocks at deep levels ore deposition is interpreted to have resulted from syntectonic boiling of ch 4 rich volatile and aqueous chloride solutions and consequent filling and replacement of brecciated and foliated black slate by metal bearing hydrothermal fluids the pressure and temperature conditions of mineralization show a narrow pressure range of 1 1 to 1 5 kbar and a wide temperature range of 315 degrees to

sensitivity of the sediment trapping capacity of an estuarine mangrove forest intertidal mangrove forests exist in a dynamic coastal environment that is increasingly impacted by human interference leading to habitat fragmentation reduced habitat quality and changing hydrodynamic and geomorphological conditions biophysical feedback mechanisms are essential to maintain mangrove ecosystems under such changing conditions for example by facilitating sediment deposition during periods of tidal flooding to allow for long term coastal accretion however human interferences affect these biophysical interactions this study investigated the consequences of two widespread anthropogenic intervention scenarios on biophysical interactions in mangroves sediment starvation reduced sediment supply and coastal squeeze limited landward accommodation space field observations of hydrodynamics and sediment dynamics were conducted in mandai mangrove fringing the sheltered northern shore of singapore a process based numerical model delft3d of this field site was set up providing accurate approximations of the observed flow velocities and deposition rates this model was used for a scenario analysis of the initial response of the sediment trapping capacity in the mangrove system to instantaneous changes related to anthropogenic interventions this analysis showed increased deposition rates in major parts of the mangrove when sediment supplies increased up to three times more deposition after 1 tide or when the landward accommodation space of the mangrove was extended 17 deposition a comparison of the outcomes of these scenarios with the current state of the mangrove underlined a lack of short term sediment trapping capacity affecting the longer term adaptive capacity of the system thus at present mandai mangrove is potentially affected by reduced sediment supply and limited landward accommodation space importantly actions to reduce this anthropogenic influence could enhance mangroves sediment trapping capacity facilitating increased resilience to future projected changes such as sea level rise understanding this influence of anthropogenic interventions on mangrove resilience is essential if we are aiming to maintain coastal ecosystem stability especially along rapidly changing and urbanizing tropical shorelines

biophysical controls on accretion and elevation change in caribbean mangrove ecosystems abstract habitat stability of coastal ecosystems such as marshes and mangroves depends on maintenance of soil elevations relative to sea level many such systems are characterized by limited mineral sedimentation and or rapid subsidence and are consequently dependent upon accumulation of organic matter to maintain elevations however little field information exists regarding the contribution of specific biological processes to vertical accretion and elevation change this study used biogenic mangrove systems in carbonate settings in belize bz and southwest florida fl to examine biophysical controls on elevation change rates of elevation change vertical accretion benthic mat formation and belowground root accumulation were measured in fringe basin scrub and dwarf forest types plus a restored forest elevation change rates mm yr 1 measured with surface elevation tables varied widely bz dwarf 3 7 bz scrub 1 1 fl fringe 0 6 fl basin 2 1 bz fringe 4 1 and fl restored 9 9 root mass accumulation varied across sites 82 739 g m 2 yr 1 and was positively correlated with elevation change root volumetric contribution to vertical change mm yr 1 was lowest in bz dwarf 1 2 and fl fringe 2 4 intermediate in fl basin 4 1 and bz scrub 4 3 and highest in bz fringe 8 8 and fl restored 11 8 sites surface growth of turf forming algae microbial mats or accumulation of leaf litter and detritus also made significant contributions to vertical accretion turf algal mats in fringe and scrub forests accreted faster 2 7 mm yr 1 than leaf litter mats in basin forests 1 9 mm yr 1 but similarly to microbial mats in dwarf forests 2 1 mm yr 1 surface accretion of mineral material accounted for only 0 2 3 3 of total vertical change those sites with high root contributions and or rapid growth of living mats exhibited an elevation surplus 2 to 8 mm yr 1 whereas those with low root inputs and low or non living mat accumulation showed an elevation deficit 1 to 5 7 mm yr 1 this study indicates that biotic processes of root production and benthic mat formation are important controls on accretion and elevation change in mangrove ecosystems common to the caribbean region quantification of specific biological controls on elevation provides better insight into how sustainability of such systems might be influenced by global e g climate atmospheric co2 and local e g nutrients disturbance factors affecting organic matter accumulation in addition to relative sea level rise

high precision measurements of wetland sediment elevation ii the rod surface elevation table abstract a new high precision device for measuring sediment elevation in emergent and shallow water wetland systems is described the rod surface elevation table rset is a balanced lightweight mechanical leveling device that attaches to both shallow 1 m in order to be stable the pipe is driven to refusal but typically to a depth shallower than the rod bench mark because of greater surface resistance of the pipe thus the rset makes it possible to partition change in sediment elevation over shallower e g the root zone and deeper depths of the sediment profile than is possible with the set the confidence intervals for the height of an individual pin measured by two different operators with the rset under laboratory conditions were 1 0 and 1 5 mm under field conditions confidence intervals for the measured height of an individual pin ranged from 1 3 mm in a mangrove forest up to 4 3 mm in a salt marsh

fluid rock interactions and the role of late hercynian aplite intrusion in the genesis of the castromil gold deposit northern portugal abstract castromil northern portugal is one of several important orogenic gold deposits located within the central iberian geotectonic zone of northwest iberia the deposit occurs at the margin of a variscan syn to late d3 biotite granite and is spatially associated with a small tourmaline aplite body that intrudes the granite at its contact with a secondary anticline of palaeozoic arenaceous and argillaceous metasediments of the valongo belt identification of the ore fluids and their pathways and the reconstruction of the p t x conditions during mineralisation were obtained by combining the geometric characteristics of veins and microstructures together with a detailed study of the inclusion fluids several stages of fluid percolation following contact metamorphism can be recognised at each stage the contact zone characterised by intrusive aplites related faults and fractures appears to have focused the hydrothermal flow and acted as a structural conduit for deeper sourced hydrothermal fluids the earliest fluid stage stage i is characterised by aqueous carbonic fluids dominated by co2 and ch4 that were probably generated by high temperature fluid rock interaction 400 500 c with graphitic schists interbedded with the metasediments these fluids were responsible for significant alteration greisenisation of the aplite and its host granite and the formation of silicified flat lying structures that can be traced along the strike length of the deposit at temperatures between 400 and 500 c fluid pressure ranges from 230 to 300 mpa which is equivalent to a depth of 10 1 5 km the second stage of mineralisation stage ii as ore stage is also characterised by aqueous carbonic fluids and represents the main phase of quartz arsenopyrite pyrite deposition the third stage of mineralisation stage iii au ore stage was accompanied by intense microfracturing of the preexisting quartz veins and the preferential deposition of gold along microfractures in the sulphides the introduction of gold corresponds to the percolation and mixing of two distinctive aqueous fluids of contrasting salinity at relatively low temperatures 150 275 c based on compositional and temperature data it is suggested that during the main phase of uplift shallow waters penetrated deep into the basement allowing gold to be leached from potential source rocks most probably the palaeozoic metasediments and deposited in structural and geochemical traps formed during earlier stages of the hydrothermal system the decrease in pressure during the as ore stage corresponds to a significant tectonic uplift around 5 6 km and probably marks the transition from lithostatic to hydrostatic pressure conditions furthermore if uplift had already been initiated during aplite emplacement the prevailing sub isothermal high temperature conditions provide an explanation for the presence of decrepitated aqueous carbonic inclusions in metamorphic quartz lenses and veins in the surrounding metasediments to conclude localised heat flows linked to late hercynian magmatism at deeper structural levels appears to be the main cause of fluid circulation at castromil evidence suggests that contact zones related to faulting along a secondary anticline of the valongo belt controlled both aplite intrusion and subsequent long lived hydrothermal fluid circulation the proposed genetic model differs from orogenic gold deposit models in emphasising the role of late stage aqueous fluids in the development of economic grade 10 15 g t gold ores

identification of fluid inclusions in relation to their host microstructural domains in quartz by cathodoluminescence abstract the geometry of fluid trapping in relation to microfracture healing or filling was investigated using massive quartz vein samples characterized by multistage deformation and fluid trapping the multidisciplinary approach used in this study includes 1 mapping of oriented thin sections of quartz using the cathodoluminescence cl mode of a scanning electron microscope sem sem cl images display areas of different intensities from dark to white which correspond to the intensity of the cl and are caused by trace elements present in the quartz microfracture healing by newly formed quartz crystallization may occur under physical chemical conditions different from those which characterized the early quartz matrix formation thus evidences of linear cathodoluminescent markers have been searched and identified by paralleling sem cl images and transmitted light microphotographs data show that cathodoluminescence makes clearly visible the healed crack networks which are only detected in part by transmitted light microscopy the technique is essential to establish the microcrack chronology and to estimate the width affected by healing along a fluid inclusion trail such data are useful for the estimation of the microfracture permeability changes throughout the history of fluid migration 2 systematic and statistical analysis of the microstructural markers in horizontal and oriented planes using an interactive videographic analyzer which gives the geometry of the paleofluid pathways orientation dip and width of the veinlets fluid inclusion trails and cathodoluminescent microdomains 3 microthermometric and raman analyses of fluid inclusions in selected fluid inclusions for the determination of the p v t x conditions of fluid migration in a specific microcrack network studied quartz samples come from au mineralized quartz veins from the french massif central and some quartz samples from the cassiar mountains in british columbia have been observed for comparison in all samples the quartz matrix exhibits intense microfracturing suggesting strong brittle deformation which postdates the main stage of quartz lens formation the quartz veins are characterized by multistage quartz crystallization healed microfractures clear quartz bands as well as quartz comb veinlets were studied as functions of the physicochemical conditions in relation to stages of deformation and ore deposition this study shows that systematic measurements of microstructural marker orientations together with detailed fluid inclusion and mineral petrography and microthermometry may lead to a precise determination of ore fluid pathways and chronology

geology and thermotectonic evolution of the western margin of the trans hudson orogen evidence from the eastern sub athabasca basement saskatchewan in the cree lake zone of northern saskatchewan reworked archean orthogneisses are overlain by a highly deformed supracrustal sequence the paleoproterozoic wollaston group this package of rocks was deformed and metamorphosed during the ca 1 8 ga continent continent collision of the trans hudson orogen tho forming the wollaston fold thrust belt that underlies the eastern athabasca basin the hudsonian structural metamorphic and magmatic evolution of the wollaston fold thrust belt in the eastern athabasca area involved six major stages 1 early collisional stage dp1 at 1860 1835 ma involved burial of wollaston group metasediments from surface to depths equivalent to 3 5vkbar 1 kbar 100 mpa by thrust pile stacking or imbrication tectonics prograde metamorphism with garnet growth and development of early leucosomes and emplacement of ca 1840 ma grey granite suite 2 collisional stage dp2a at 1835 1820 ma involved continued deeper burial of wollaston group metasediments along a prograde

exhumation of the ultrahigh pressure tso morari unit in eastern ladakh nw himalaya a case study exhumation processes of the ultra high pressure uhp tso morari dome nw himalaya are investigated using structural petrological and geochronological data the uhp tso morari unit is bounded by the low grade metamorphic indus suture zone to the ne and mata unit to the sw three deformation phases d1 d2 and d3 are observed only d3 is common to the uhp unit and the surrounding units in the uhp unit the first deformation phase d1 produced upright folds under eclogitic conditions 20 kbar 580 60 c d1 is overprinted by d2 structures related to a nw se trending open anticline this phase is characterized by blueschist mineral associations and corresponds to the quasi isothermal decompression from a depth of 90 km eclogitic conditions up to 30 40 km the final exhumation phase of the tso morari unit is dominated by tectonic denudation and erosion d3 associated with a slight temperature increase radiochronological analyses indicate that the uhp exhumation process began during the eocene exhumation was fast during d1 d2 and slowed down through d3 in oligocene time the change in the deformation style from d1 d2 to d3 in the tso morari unit coincides with changes in the exhumation rates and in the metamorphic conditions these changes may reflect the transition from an exhumation along the subduction plane in a serpentinized wedge to the vertical uplift of the tso morari unit across the upper crust

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

c o h n fluids circulations and graphite precipitation in reactivated hudsonian shear zones during basement uplift of the wollaston mudjatik transition zone example of the cigar lake u deposit abstract graphitic shear zones are spatially associated with unconformity related uranium deposits that are located around the unconformity between the strata of the paleo to mesoproterozoic athabasca basin saskatchewan canada and its underlying archean to paleoproterozoic basement the present study focuses on basement hosted ductile brittle graphitic shear zones near the cigar lake u deposit one of the largest unconformity related u deposits the goal of the study is to decipher the pre athabasca basin fluid migration history recorded within such structures and its potential role on the formation of such exceptional deposit dominantly c o h n metamorphic fluids have been trapped in fluid inclusion planes fips in magmatic quartz within ductile brittle graphitic shear zones active during retrograde metamorphism associated with the formation of the wollaston mudjatik transition zone wmtz between ca 1805 and 1720 ma such fluids show a compositional evolution along the retrograde path from a dense and pure co2 fluid during the earliest stages through a lower density co2 ch4 n2 h2o fluid and finally to a very low density ch4 n2 fluid statistical study of the orientation distribution proportion and chemical characterization of the fips shows that i co2 13cco2 around 9 pdb from decarbonation reactions and or partial water metamorphic graphite equilibrium initially migrated regionally and pervasively under lithostatic conditions at about 500 to 800 c and 150 to 300 mpa such p t conditions attest to a high geothermal gradient of around 60 to 90 c km probably related to rapid exhumation of the basement or a large scale heat source ii later brittle reactivation of the shear zone at around 450 c and 25 50 mpa favored circulation of co2 ch4 n2 h2o fluids in equilibrium with metamorphic graphite 13cco2 around 14 under hydrostatic conditions and only within the shear zones cooling of these fluids and the water uptake linked to fluid basement rock reactions led to the precipitation at around 450 c of poorly crystallized hydrothermal graphite this graphite presents isotopic 13c 30 to 26 pdb and morphological differences from the high t metamorphic graphite 600 c 29 to 20 13c derived from metamorphism of c rich sedimentary material the brittle structural reactivation and the related fluid migration and graphite precipitation were specifically focused within the shear zones and related damage zones the brittle reactivation produced major changes in the petro physical mineralogical and chemical characteristics of the structures and their damage zones it especially increased the fracture paleoporosity and rock weakness toward the fault cores these major late metamorphic modifications of the graphitic shear zones were likely key parameters favoring the enhanced reactivity of these basement zones under tectonic stress following deposition of the athabasca basin and so controlled basinal brine movement at the basin basement interface related to the formation of the unconformity related uranium deposits this relationship consequently readily explains the specific spatial relationships between unconformity related u deposits and the ductile brittle graphitic shear zones

progradation of the yellow huanghe river delta in response to the implementation of a basin scale water regulation program the water and sediment supply to the lower reach and estuary of the yellow huanghe river have been altered to a very significant degree by the construction of numerous small to large reservoirs and the progressive implementation of water and soil conservation measures across the entire drainage basin since the late 1950s followed by a basin scale water regulation program since 2002 there is an urgent need to know how progradation of the yellow river delta yrd an area on which people live and farm has continued and will continue to respond to these controls this study examines the changing patterns of water and sediment supply to the yrd over the period of 1950 2013 and using remote sensing it evaluates the morphological changes of the delta during 1976 2013 although both water and sediment input to the delta have been described as declining significantly since the mid 1960s we show that since 2005 the supply of water has remained at around 20 billion m 3 yr 1 and that for sediment at about 0 13 billion t yr 1 water input has been even slightly increasing the dynamics of extension shrinking and avulsion in river mouth channels and accretion erosion of shorelines is an integrated response to the complex variations in both sediment and water supply this study develops a quantitative relationship between water and sediment supply and the area of land accretion and it predicts the critical condition for land accretion in the yrd to ensure that delta land will not be lost care is needed in the future implementation of the basin scale water regulation program c 2015 elsevier b v all rights reserved

terrace formation and river valley development along the lower taohe river in central china abstract a flight of nine river terraces has been well developed and preserved along the course of the lower taohe river based on optically stimulated luminescence osl electron spin resonance esr paleomagnetic and loess paleosol stratigraphic analyses we found that the accumulation ages of the gravel layers of terraces t9 t1 correspond to the loess layers l13 l9 l8 l6 l5 l4 l3 l2 l1 4 and l1 1 respectively the chronologic results indicate that the formation and development of the modern river valley in this area occurred between 1 4 and 1 14 ma the topographic fluctuation caused by the kunhuang movement appears to have been the main reason for the reorganization of the river system and valley development in the area in the context of this tectonic uplift fluvial processes were coupled with the regional climate on a geomorphic equilibrium scale i e over a glacial interglacial cycle that is river aggradation appears principally to have occurred during glacial periods while a graded state existed during interglacial periods in addition rapid river downcutting in response to climate change occurred during the transition periods from glacial to interglacial climates

differential rates of vertical accretion and elevation change among aerial root types in micronesian mangrove forests abstract root systems in mangrove swamps have captured the attention of scientists for decades among the postulated roles of root structures include a contribution to the geomorphological stability of mangrove soils through sediment trapping and binding in this study we used feldspar marker horizons and sediment pins to investigate the influence of three different functional root types prop roots in rhizophora spp root knees in bruguiera gymnorrhiza and pneumatophores in sonneratia alba on vertical accretion and elevation change in three mangrove forests in the federated states of micronesia prop roots facilitated vertical accretion 11 0 mm year 1 more than pneumatophores or bare soil controls mean 8 3 mm year 1 sediment elevation on the other hand increased at an average rate of only 1 3 mm year 1 across all root types with rate differences by root type ranging from 0 2 to 3 4 mm year 1 being detected within river basins this investigation demonstrates that prop roots can assist in the settling of suspended sediments from estuarine waters yet prop root structures are not as successful as pneumatophores in maintaining sediment elevation over 2 5 years as root densities increase over time an increase in turbulence induced erosion and in shallow subsidence as organic peat layers form is expected in micronesian mangrove forests

coastal wetlands sea level and the dimensions of geomorphic resilience abstract geomorphic system resilience is often perceived as an intrinsic property of system structure and interactions but is also related to idiosyncratic place and history factors the importance of geographical and historical circumstances makes it difficult to generate categorical statements about geomorphic resilience however network based analyses of system structure can be used to determine the dynamical stability resilience based on generally applicable relationships and to determine scenarios of stability or instability these provide guidelines for assessing place and history factors to assess resilience a model of coastal wetlands is analyzed based on interactions among relative sea level wetland surface elevation hydroperiod vegetation and sedimentation the system is generally but not always dynamically unstable and non resilient because of gradients of environmental factors and patchy distributions of microtopography and vegetation a coastal wetland landscape may have extensive local variations in stability resilience and in the key relationships that trigger instabilities this is illustrated by a case study where dynamically unstable fragmentation is found in two nearby coastal wetlands in north carolina s neuse river estuary otter creek mouth and anderson creek neither is keeping pace with relative sea level rise and both show unstable state transitions within the wetland system but locally stable relationships exist within the wetland systems

vein graphite deposits geological settings origin and economic significance graphite deposits result from the metamorphism of sedimentary rocks rich in carbonaceous matter or from precipitation from carbon bearing fluids or melts the latter process forms vein deposits which are structurally controlled and usually occur in granulites or igneous rocks the origin of carbon the mechanisms of transport and the factors controlling graphite deposition are discussed in relation to their geological settings carbon in granulite hosted graphite veins derives from sublithospheric sources or from decarbonation reactions of carbonate bearing lithologies and it is transported mainly in co2 rich fluids from which it can precipitate graphite precipitation can occur by cooling water removal by retrograde hydration reactions or reduction when the co2 rich fluid passes through relatively low fo2 rocks in igneous settings carbon is derived from assimilation of crustal materials rich in organic matter which causes immiscibility and the formation of carbon rich fluids or melts carbon in these igneous hosted deposits is transported as co2 and or ch4 and eventually precipitates as graphite by cooling and or by hydration reactions affecting the host rock independently of the geological setting vein graphite is characterized by its high purity and crystallinity which are required for applications in advanced technologies in addition recent discovery of highly crystalline graphite precipitation from carbon bearing fluids at moderate temperatures in vein deposits might provide an alternative method for the manufacture of synthetic graphite suitable for these new applications

sediment dynamics and morphological stability of estuarine mangrove swamps in sherbro bay west africa abstract the relationship between the circulation of fine suspensions in a mangrove colonised estuarine complex short term mangrove substrate accretion and medium term mangrove swamp geomorphic evolution was studied in sherbro bay an infilling microtidal to mesotidal embayment in southern sierra leone formed behind holocene sandy beach ridge barriers the estuarine reaches of streams debouching into the bay have relatively high suspension concentrations sc of silts and clays that ranged during the survey period in 1991 from 0 8 to 40 g l 1 in association with the constitution of turbidity maxima 5 50 g l 1 at the interface between freshwater drainage and the saltwater intrusion however the surveyed mangrove swamp plots showed much lower suspension concentrations 0 09 0 6 g l 1 and low albeit minimum rates of accretion 1 1 3 mm a 1 monitored between 1980 and 1989 these low rates are attributed mainly to the short duration of tidal flooding due to a high substrate elevation within the tidal range and to the low settling potential of the very fine grained suspensions circulating over the swamps a comparison of two sets of aerial photographs 1954 1960 and 1976 showed that these swamps and their channel networks are also characterised by a remarkable medium term morphodynamic stability this stability and the low accretion suggest that the swamps and their channel networks are largely in equilibrium with the hydrology notably flooding duration and sediment loads settling out of mud from the turbidity zones contributes to higher accretion rates up to 12 mm a 1 not taking into account the effects of shallow subsidence on parts of the mudflats fronting the mangroves which are flooded for longer periods some of the mud is deposited over sandy channel bars in the main bay channel and the rest exported seaward it is tentatively suggested that an increase in the duration of tidal flooding generated by global sea level rise at the presently predicted rates could lead to higher sedimentation in the mangrove swamps thus enhancing accretion and the chances of mangrove survival