proterozoic accretionary tectonics at the southern margin of the archean wyoming craton the proterozoic cheyenne belt at the southern margin of the archean wyoming craton consists of strongly deformed lithotectonic blocks bound by major mylonite zones from north to south and structurally lowest to highest these blocks include 1 archean crystalline basement and associated early proterozoic miogeoclinal rocks 2 an amphibolite grade orthogneiss terrane of unknown age containing probable rift related mafic intrusive rocks 3 a 1750 1790 ma marginal basin succession consisting of upper amphibolite grade pelitic and volcano genie schist associated peraluminous granite and minor ultramafic rocks and 4 a 1750 1790 ma intermediate to mafic plutonic metamorphic complex interpreted as the deep roots of an island arc system the earliest deformation d1 produced a synmetamorphic penetrative horizontal transposition foliation and associated recumbent folds tectonic blocks were juxtaposed along major mylonite zones during d2 macroscopic anil microscopic structures associated with d2 indicate northward thrusting along low angle mylonite zones of successively deeper crustal blocks over supracrustal rocks of the wyoming craton at about 1750 ma thrusting occurred at minimum temperatures of 475 c and produced an inverted metamorphic gradient in pelitic rocks north of the belt mylonite zones were subsequently steepened and reactivated under greenschist facies conditions during a period of dextral strike slip d3 between 1750 and 1400 ma cataclasis d4 and brecciation associated with the laramide orogeny d5 locally overprint earlier structures oblique convergence between an island arc and the archean continental nucleus may explain accretion crustal shortening and subsequent strike slip the phanerozoic accretionary events of eastern and western north america provide an analog for this model presence of similar lithologies and shear zones south of the cheyenne belt suggest that the southern margin of the wyoming craton may have been a long lived zone of crustal accretion

geodynamic framework of large unique uranium orebelts in southeast russia and east mongolia abstract some of the largest uranium orebelts and deposits of asia occur in southeast russia and east mongolia in russia the elkon and streltsovka belts are located in the aldan south yakutia and urulyungui southeast trans baikal area districts covering a distance of more than 1200 km the superlarge dornod deposit occurs in the north choibalsan district of east mongolia ca 300 km to the southwest of streltsovka these uranium occurrences are distributed in the central aldan and kerulen argun cratonic domains separated by the selenga stanovoi yenisei trans baikal and mongol okhotsk orogenic belts a synthesis of the characteristics and the timing of mineralization suggest that all of these occurrences were generated synchronously seismic tomography data show that these deposits are mostly located above the frontal part of a stagnant oceanic slab we envisage that slab dehydration and influx of fluids into the asthenospheric mantle and their subsequent interaction with the lithosphere aided the localization of these unique scale uranium concentrations

sulfur isotopes and hydrochemical variations in spring waters of southern indiana u s a abstract water chemistry and 34 s so 4 studies suggest two flow systems in the karst terrane of southern indiana 1 a shallow flow system exists which is dominated by surface water entering the ground through fractures and 2 a deeper regional groundwater flow system recharged by diffuse flow the chemistry of the water in the regional system may be dominated by the solution of gypsum in the lower st louis limestone sulfur isotope studies suggest two flow systems and show that the high so 2 4 concentrations in local waters result from solution of gypsum reported 34 s so 4 for upper mississippian evaporites and fresh water range from 14 to 19 to 8 to 12 respectively isotope analysis of gypsum cores from the lower st louis limestone evaporite unit shows 34 s values between 14 10 and 15 13 in the study area groundwater chemistry studies show a direct linear relationship between so 2 4 concentrations and 34 s values groundwater varies in so 2 4 concentrations between 20 and 1970 mg l 1 the 34 s values range from 10 61 for a conduit spring to 18 57 for a diffuse spring the waters with high so 2 4 concentrations have 34 s so 4 values higher than the local gypsum deposits analysed and contain h 2 s suggesting a deeper flow system in which fractionation by bacterial reduction of so 2 4 is occurring waters with low so 2 4 concentrations have 34 s so 4 values in the range of local fresh water indicating a shallow flow system

paleovolcanic necks and extrusions indicators of large uranium orebelts in the territories joining russia mongolia and china abstract the large ore clusters and uranium deposits detected in southeast russia eastern transbaikal region eastern mongolia and northern china constitutes a large area specialised in u with a wide range of geological and mineral ore types amongst various types of uranium ore hydrothermal deposits related to volcanic rocks infiltration deposits of uranium sandstone and polygenous mineralisation in leucogranites represent main commercial interest large uranium clusters are located on the outer side and peripheral parts of the great xing an volcano plutonic belt as well as in the framing taphrogenic depressions the clusters formation timed to late mesozoic i k geodynamic processes deep geodynamics allowed the fluid flows of asthenosphere which were concentrating around the periphery of the slab stagnated in the transition mantle zone to penetrate into the above lithosphere and earth s crust with formation of pockets of magma and ore bearing volcano tectonic depressions eventually therefore the presence of igneous stocks extrusions and volcanic necks within the volcano plutonic belts and depressions can be indicative of mineral potential of the area

high closure temperatures of the u pb system in large apatites from the tin mountain pegmatite black hills south dakota usa abstract the cores of several large 1 2 cm apatites from the early proterozoic tin mountain pegmatite black hills south dakota have concordant u pb ages the age uncertainties of these samples are less than 5 ma the lead isotopic compositions of muscovite and k feldspar coexisting with the apatites were used for initial lead isotopic corrections the resulting u pb concordia ages agree well with u pb and pb pb isochron ages based solely on multiple fragments from single apatites this agreement justifies the use of coexisting muscovite and k feldspar for initial lead corrections the precision of these u pb ages is comparable to those of the u pb systems of more commonly analyzed minerals such as zircon monazite and sphene the estimated u pb closure temperature t c of these apatites is about 620 c this t c is in close agreement with the t c calculated for 0 5 cm diffusion radii and published data for diffusivity and activation energy of lead diffusion in apatite apatite can therefore yield high precision u pb ages that are close to its crystallization age in igneous rocks

the role of the subcutaneous zone in karst hydrology abstract the subcutaneous zone is the upper weathered layer of rock beneath the soil but above the permanently saturated phreatic zone it is of particular hydrological importance in karst because of its high secondary permeability arising from the considerable chemical solution in this zone however corrosional enlargement of fissures diminishes with depth thus permeability decreases in the same direction with the result that percolation is inhibited except down widened master joints and faults storage of water consequently occurs in this zone particularly after storms the upper surface of this suspended saturated layer in the subcutaneous zone is defined by a perched water table which slopes towards points of rapid vertical percolation the potential induces lateral water movement converging on the most permeable areas such as beneath dolines leakage from the subcutaneous store sustains slow percolation in the vadose zone cross correlation of rainfall with percolation rates in caves in new mexico u s a and new zealand reveal response lags of 2 14 weeks with no apparent relationship to depth below the surface other percolation sites show no correlation with rainfall interpreted as being a consequence of considerable friction in tight fissure networks the recognition of storage and rapid as well as very slow percolation from the subcutaneous zone requires re interpretation of the components of hydrographs from karst springs and of some conceptual models of karst aquifers the importance of subcutaneous storage in sustaining baseflow discharge at some sites must be recognised as must the contribution of subcutaneous water to flood hydrographs methods of estimating the volumes of subcutaneous and phreatic components of karst spring flood hydrographs are presented the paper concludes with a discussion of the significance of subcutaneous hydrologic processes for an understanding of karst geomorphology the desirability of explaining karst landform evolution in terms of hydrologic processes is stressed

geological and land use control on δ34s and δ18o of river dissolved sulfate the moselle river basin france abstract the upper part of the moselle river basin northeastern france shows contrasting lithology and topography granitic formations upstream in the vosges mountains and carbonate platform downstream on the lorraine plateau we measured concentration and isotopic composition of dissolved so 4 in the moselle river and its main tributaries in order to identify the sources of sulfate rainwater lichens s fertilizers and natural gypsum were also analyzed as potential sulfate sources along the moselle river dissolved so 4 concentrations and s o isotopes display relationships which suggest two major sources of sulfates 1 a low concentration and low delta values 34 s of 6 9 and 18 o of 6 9 component upstream and 2 a high concentration and high delta values 34 s of up to 17 and 18 o of up to 13 these are likely 1 atmospheric s input with some retention time in forest soils as carbon bonded sulfur and 2 sulfates from the dissolution of evaporites from the muschelkalk and keuper formations of the lorraine plateau the madon tributary drains a basin largely used for agriculture 35 of the land surface and formed by carbonate and evaporite rocks deviation from the general 34 s 18 o trend for dissolved so 4 was found to be seasonal and related to land use and agricultural practices and are interpreted as a significant input of sulfates from fertilizers used in the area isotope mixing models indicate that between 1 1 10 7 and 1 9 10 7 mol of anthropogenic so 4 are annually exported through the madon river these values compared well with the expected annual fertilizer spreading rates in the area and demonstrate the powerful source tracing done by using s isotopes in dissolved sulfates this implies that combining isotopic fingerprinting approach to knowledge of the catchment i e land use agricultural practices river flow would provide key information for decision makers in the context of river basin management

identifying water sources in a karst aquifer using thermal signatures using thermal data a unique approach to delineate flow components in a karsts aquifer was conducted thermal signatures from seven wells and six springs were analyzed to determine potential relationships among different storage reservoirs and the air temperature the temperature signatures revealed three distinct reservoirs epikarst shallow groundwater and deep groundwater the reservoirs have different thermal signatures and relationships with the air temperature during a wetter period the epikarst water temperatures more closely follow the air temperature trend and are closer in value but during drier conditions the shallow groundwater temperatures are more similar in value to air temperature deep groundwater temperatures show no relationship to variations in surface air temperature using the water temperatures from the three reservoirs the sources of water at two major springs copperhead and langle were delineated during the wetter period the shallow groundwater and the epikarst were the primary contributors of water to the springs as conditions became drier a transition occurred the deep groundwater became the major source of water to the springs variation in temperatures of waters at copperhead and langle spring is a result of the epikarst and the shallow groundwater which represents ineffective thermal reservoirs

seasonal fluctuation in δ15n of groundwater nitrate in a mantled karst aquifer due to macropore transport of fertilizer derived nitrate twenty wells were sampled and analyzed for nitrate content and nitrogen isotopes during late september 1986 the groundwater nitrate 15n values ranged from 6 8 to 17 6 with a mean of 10 3 eleven samples had 15n values greater than 9 5 indicating an animal waste origin septic tanks are probably the predominant source of waste derived nitrate macropores draining septic tank filter fields may provide a nearly continuous flow of effluent to the aquifer the 15n values of the other nine samples ranged from 6 8 to 8 4 suggesting a possible mixing of waste derived nitrate and that derived from isotopically lighter cultivation sources i e inorganic fertilizer and or mineralized soil organic nitrogen the twenty wells were resampled during late may 1987 shortly after inorganic fertilizers had been applied to the corpland throughout the study area the groundwater nitrate 15n values ranged from 3 6 to 14 7 with a mean of 8 3 nineteen of the wells showed a shift towards the lighter 15n values expected from the fertilizer derived nitrate the 15n decreases ranged from 0 6 to 4 8 with a mean of 2 2 despite the apparent influx of fertilizer derived nitrate eleven samples with 15n 8 0 to 14 7 still were composed of predominantly waste derived nitrate only nine samples with 15n 3 0 to 5 8 may have had fertilizer derived component approaching in magnitude that of waste derived nitrate regional groundwater nitrate concentration did not substantially increase macropore cracks root channels etc flow appears to contribute significantly to the recharge of the aquifer rapid response of the groundwater nitrate 15n values to fertilization demonstrates the ability of macropore flow to transport fertilizer derived nitrate which has been flushed from the tilled soil layer other agriculture chemicals pesticides and herbicides may also be transported to the aquifer in this manner

40ar 39ar ages for minerals from the amphibolite dynamothermal aureole mont albert gaspe quebec new 40ar 39ar ages are presented for two hornblendes and one biotite from the dynamothermal aureole that is situated at the base of the mont albeit ophiolite analysis by the incremental release technique reveals a small component of excess 40ar in one hornblende though both exhibit plateau type spectra the biotite was analyzed by the total fusion technique all apparent ages are concordant and average 456 3 ma dynamothermal aureoles form during the obduction process which juxtaposes ophiolites and amphibolite protoliths during a compressional tectonic event at a plate margin in this instance thrusting of the mont albert ophiolite over rocks of the shickshock group the concordance of biotite and hornblende ages indicates rapid postmetamorphic cooling and firmly dates obduction at 456 3 ma ago an age younger than any of the other northern appalachian ophiolites the high pressure metamorphism of the amphibolite is inconsistent with the present high structural level of the composite mont albert

a geodynamic perspective of world class gold deposits in east asia abstract the world class gold ore districts of south east russia and north east china are located above the frontal and peripheral regions of subducted oceanic lithosphere accumulated as stagnant slabs in the mantle transition zone generated by paleo pacific plate subduction the highly productive ore systems of the aldan south yakutiya baley transbaikalia and zhao ye jiaodong metallogenic belts which are widely separated in space but formed at the same time are associated with similar mechanisms of huge magma flare ups in the middle jurassic early cretaceous driven by deep mantle processes their common features and crust mantle interaction signature offer important clues to mantle dynamics rooted along the periphery of the subducted slabs in a mega convergent zone in east asia

mesozoic metallogeny in east china and corresponding geodynamic settings an introduction to the special issue abstract the giant east china mesozoic metallogenic province hosts some of the world s largest resources of tungsten tin molybdenum antimony and bismuth ores of gold silver mercury lead zinc copper uranium and iron are also of major importance the province and its constituent metallogenic belts or regions south china middle lower yangtze river valley east qinling dabie interior of north china craton yan liao and north east china are the products of several pulses of igneous activity and mineralisation between 240 and 80 ma each successive stage has produced a distinctive suite of deposits that can be readily related to the geodynamic evolution of the region during the mesozoic this geodynamic evolution is linked to a complex series of tectonic events involving far field subduction plate collisions crustal thickening post collision collapse and rifting

the crystal chemical basis for ar retention in micas inferences from interlayer partitioning and implications for geochronology cation partitioning data for coexisting muscovite and biotite are shown to be useful indicators of relative interlayer bond length strength in these minerals these data therefore provide a useful crystal chemical perspective on relative mass transfer kinetics of radiogenic isotopes and account for the observation that biotite is generally less retentive of 40ar and 87sr than coexisting muscovite partitioning behavior of trace elements underscores three reasons why overall interlayer bonding in biotite is weaker than in muscovite first the preferences of large rb cs in biotite and of small la3 and na in muscovite indicate a relatively spacious interlayer volume in biotite suggesting a longer mean k o bond second the preference of interlayer vacancies in biotite with some all possibly h2o h3o filled suggests that its adjacent 2 1 sheets are connected by fewer interlayer bonds per unit cell than those of muscovite third the relative exclusion of large ba2 from biotite despite its large interlayer sites is attributed to o h bonds pointing into the interlayer cavity sub normal to 001 k ba2 h repulsion thereby induced by the bare proton both destabilizes ba2 and weakens k o bonds in contrast muscovite offers a more favorable electrostatic environment for ba2 substitution since its o h bonds are directed into the vacant m1 octahedral site sub parallel to 001 this hypothesis is supported by the observation that progressive f oh 1 exchange enhances ba2 partitioning into biotite phlogopite relative to coexisting muscovite these crystal chemical differences between biotite and muscovite are mirrored in calculated values of ionic porosity z i defined here as the percentage of their interlayer unit cell volume not occupied by ions a monitor of ionic packing density and geometry z i is inversely correlated with k o bond strength which appears to be the rate determining kinetic common denominator for a variety of processes affecting micas including those responsible for loss of radiogenic isotopes in biotite and muscovite accordingly the relatively longer weaker k o bonds of biotite are envisioned as being more easily stretched during volume diffusion or broken during recrystallization or retrograde alteration this in turn accounts for common observations of enhanced radiogenic ar sr loss and younger 40ar 39ar and rb sr ages in natural biotite high z i relative to coexisting muscovite lower z i significantly this pattern may arise irrespective of isotopic loss mechanism diffusion or recrystallization etc and it follows that any age discordance observed between muscovite and biotite cannot be ascribed uniquely to one mechanism or the other without appropriate field petrographic and petrologic constraints extension of this partitioning porosity based synthesis leads to prediction of corollary age retentivity composition effects among chemically diverse trioctahedral and dioctahedral micas which are best field tested in terranes that cooled slowly under dry static conditions pressure effects on argon retention are also inferred from the porosity model

40ar 39ar age gradients in micas from a high temperature low pressure metamorphic terrain evidence for very slow cooling and implications for the interpretation of age spectra estimates of the time temperature history of geologic samples are often based on 40 ar 39 ar ages obtained through incremental heating experiments on minerals with different ar retentivities laser incre mental heating of single crystals of muscovite and biotite from an 1700 ma monzogranite from a low pressure high temperature metamorphic terrain in central arizona suggested an essentially uniform distribution of radiogenic 40 ar in each crystal and yielded ages of 1412 5 ma for the muscovite and 1410 10 ma for the biotite the similarity in these ages implies rapid 25 k m y cooling of the monzogranite after a reheating episode slightly before 1412 ma in contrast detailed age mapping of single crystals from the same samples with the laser microprobe revealed large radiogenic 40 ar gradients indicative of very slow 400 m y evidence for such low cooling rates has important implications for the longevity of high thermal gradients in the early middle proterozoic lithosphere in addition inconsistency between the laser mapping and incremental heating results for these micas suggests caution when interpreting incremental heating data for slowly cooled samples

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

geodynamics of late mesozoic pge au and u mineralization in the aldan shield north asian craton abstract late mesozoic pge au and u mineralization in the precambrian aldan shield constitutes important ore deposits on the southern margin of the siberian craton here we provide an overview of the salient characteristics of these ore deposits and evaluate their regional geodynamic setting geological geophysical and geochronological data on the distribution and timing of the ultramafic and alkaline magmatism in the aldan shield and the associated late jurassic early cretaceous pge au and u mineralization correlate with the convergence in the asia pacific zone during the late mesozoic the multistage magmatism and ore formation can be traced along the perimeter of the subducted slab now stagnant at the mantle transition zone the flanks of which coincide with paleo transform faults slab dehydration is considered to have transferred source metals through plume conduits resulting in the formation of productive ore magmatic systems

syncontractional crustal anatexis and deformation during emplacement of 1435 ma plutons western needle mountains colorado mesoproterozoic deformation and biomodal magmatism in southwest colorado offer important insight into the nature and tectonic regime of 1 4 ga magmatism in the western united states we document syncontractional emplacement of coeval gabbroic and granitic plutons in the middle crust at 1435 ma in the western needle mountains this is incompatible with extension dominated anorogenic models proposed for the generation of 1 4 ga plutonic rocks in the southwest but lends further support for synkinematic intracontinental magmatism in response to regional tectonic strains created by transpressive or compressive plate margin interactions between 1500 1300 ma intrustion of the 1435 ma electra lake gabbro and eolus granite into paleoproterozoic rocks caused local crustal anatexis and extensive thermal metamorphism in the needle mountains deformation of paleoproterozoic country rocks at 1435 ma is widespread but is concentrated in pluton aureoles where thermally softened crust accommodated the strain we int

gold deposits and gold metallogeny of far east russia abstract the russian far east or far east russia fer is host to a huge gold endowment and has produced more than 6500 t of gold since the 1860s much of this gold has come from several mining districts aldan upper amur lower amur okhotsk allakh yun yana kolyma priokhotie omolon and chukotka these districts include several gold deposits mostly of orogenic and epithermal nature as well as large and very large alluvial placer deposits the main gold districts are of late mesozoic age but there are also three districts aldan omolon and southern primorie with pre mesozoic gold ores and three districts kamchatka sakhalin south kurile and lower amur with gold ores of cenozoic age this review paper attempts to marshal on the regional scale all available data aiming to provide a framework for generating and testing new ideas on the gold deposits of fer the focus is on 1 gold metallogeny 2 details of key gold deposits and 3 relationship between gold ore forming processes metamorphic processes and granitoid intrusions in different geodynamic settings the largest gold metallogenic belts in fer were formed in the late mesozoic namely in the late jurassic yana kolyma early cretaceous eastern flank of mongol okhotsk aldan oloy chukotka okhotsk koryak and late cretaceous sikhote alin the mesozoic era was also the time when most of the gold hosting orogens were formed paleozoic mesozoic and cenozoic orogens resulted from the interaction between the pacific oceanic plates with the siberian craton and the north china craton these orogens are products of diverse geodynamic settings and can be divided into four types 1 collisional e g yana kolyma 2 accretionary or uncompleted collisional e g okhotsk koryak or kamchatka 3 combined collisional and transform margin mongol okhotsk and 4 active transform margin sikhote alin the first two types are typical of north east russia whereas the third and fourth types are in the southern part of fer the late cretaceous okhotsk chukotka and east sikhote alin gold provinces are associated with continental margin magmatic arcs and are post accretionary post orogenic comparison of lode gold deposits from different geodynamic settings reveals specific features in metallogeny of the late mesozoic orogens at the southern and eastern margins of the siberian craton yana kolyma collisional orogen okhotsk koryak accretionary orogen and mongol okhotsk transform margin orogen these orogens possess different metal associations the yana kolyma belt contains au sn w and cu pb zn lode deposits the late jurassic transbaikalian sector of the mongol okhotsk orogen contains au mo pb zn sn ta nb w hg sb lode deposits whereas early cretaceous au cu mo hg sb lode deposits are present in the amur sector finally the okhotsk koryak orogen hosts au cu mo cu w bi ag co bi as and be sn li w deposits of early cretaceous age epithermal gold deposits occur in two different geodynamic settings 1 island arcs kamchatka kurile islands and magmatic belts at active continental margins omolon okhotsk chukotka and eastern sikhote alin and 2 rift related magmatism linked with orogenic events and strike slip kinematics such as transform like continental margin settings aldan and upper amur in the mongol okhotsk orogen mineralogic geochemical and isotope systematics indicate a metamorphic magmatic origin of hydrothermal plutonic systems in collisional settings yana kolyma okhotsk koryak and oloy chukotka orogens and active continental margin okhotsk chukotka and east sikhote alin settings with source contributions from the lower crust and mantle the mongol okhotsk and sikhote alin orogens are of transform fault related origin and suggest a source of the ore forming fluids mostly from the mantle

the study of hydrodynamic behaviour of a complex karst system under low flow conditions using natural and artificial tracers the catchment of the unica river sw slovenia in this study a multi tracer test with fluorescent tracers was combined with time series analyses of natural tracers to characterize the dynamics of the solute transport through different recharge pathways and to study hydraulic behaviour of a binary karst system under low flow conditions fluorescent tracer testing included the introduction of uranine amidorhodamine g or naphthionate at three injection points sampling and monitoring took place at two karst springs malenscica unica and at two underground rivers pivka rak recharging the unica river at the polje of planina sw slovenia other monitored parameters included precipitation spring or underground river discharge water temperature and electrical conductivity water samples were collected and analyzed for total organic carbon mg2 so42 and no3 in the laboratory in the study area results of the tracer test suggest that contaminant transport in karst may be retarded for several weeks during low flow conditions followed by increases in contaminant concentrations after subsequent rainfall events based on interpretation of tracer concentration breakthrough curves low apparent dominant flow velocities i e between 5 8 and 22 8 m h through the well developed karst conduits and 3 6 m h through the prevailing vadose zone with a dominant influence of a diffuse recharge were obtained together with analyses of hydro chemographs the artificial tracing identified different origins of water recharging the studied aquifer during prolonged low water conditions the malenscica spring is mainly recharged from the karst aquifer and the unica spring by the sinking pivka river after more intensive rainfall events allogenic recharge from cerknica prevails in the malenscica spring while the unica spring drains mainly the allogenic water from the pivka valley these findings of alternating hydraulic connections and drainage areas due to respective hydrological conditions are important and should be considered when monitoring water quality implementing groundwater protection measures and optimizing future water exploitation

insights from the salinity origins and interconnections of aquifers in a regional scale sedimentary aquifer system adour garonne district sw france contributions of δ34s and δ18o from dissolved sulfates and the 87sr 86sr ratio abstract the multi layered eocene aquifer is a regional scale sedimentary aquifer system occupying 120 000 km 2 within the adour garonne district france local authorities have recently identified the aquifer as being at risk from extensive irrigation abstractions threatening the sustainability of this key resource because large water abstractions for human activities can significantly influence the natural functioning of such aquifer systems e g with leakage between aquifer layers which can lead to water quality degradation the characterization of such large systems constitutes a key point to protect and prevent further deterioration of aquatic ecosystems this study provides further insight on this large aquifer through a geochemical approach which addresses the limited number of groundwater wells where sampling is possible for that purpose a geochemical analysis combining two isotope systems 34 s so4 18 o so4 and 87 sr 86 sr has been applied the eocene sedimentary aquifer system detrital to carbonate deposits is made up of four aquifer layers eocene infra molassic sand early eocene middle eocene and late eocene and has a mineralized area north of the aquitaine basin where groundwater shows strong mineralization and anomalous levels of critical substances so 4 f etc increasing the difficulty of resource exploitation the extreme heterogeneity of the geochemical composition of the groundwater between the aquifers and within a single aquifer is discussed in terms of the lithological control induced by the lateral variation of facies and interconnections between aquifer layers geochemical tools especially the 34 s and 18 o from dissolved sulfates and the 87 sr 86 sr ratio suggest that evaporite dissolution both sulfate and halite is the main process controlling the high salinity levels observed in the groundwater explaining the spatial variations observed at the aquifer system scale isotopic tools also provide new information regarding the interconnections between aquifer layers supporting the hypothesis that the eocene aquifer system integrates groundwater from the oligocene miocene aquifer through leakage effects these new insights will likely help decision makers adjust their choices when managing quality problems in particular in the mineralized area of the entre deux mers where targeted groundwater wells used for drinking water display anomalous levels of critical substances

the generation and crystallization conditions of the proterozoic harney peak leucogranite black hills south dakota usa petrologic and geochemical constraints the mineralogy petrology and geochemistry of the proterozoic harney peak granite black hills south dakota were examined in view of experimentally determined phase equilibria applicable to granitic systems in order to place constraints on the progenesis of peraluminous leucogranites and commonly associated rare element pegmatites the granite was emplaced at 3 4 kbar as multiple sills and dikes into quartz mica schists at the culmination of a regional high temperature low pressure metamorphic event principally along the periphery of the main pluton and in satellite intrusions the sills segregated into granite pegmatite couplets the major minerals include quartz k feldspar sodic plagioclase and muscovite biotite mg no molar mgo mgo feo 0 32 0 38 is the predominant ferromagnesian mineral in the granite s core whereas at the periphery of the main pluton and in the satellite intrusions tourmaline mg no 0 18 0 48 is the dominant ferromagnesian phase almandine spessartine garnet is also found in the outer intrusions there is virtually a complete overlap in the wide concentration ranges of sio2 cao mgo feo sr zr w of the biotite and tourmaline bearing granite suites with no discernable differentiation trends on harker diagrams precluding the derivation of one suite from the other by differentiation following emplacement this is consistent with the oxygen isotope compositions which are 11 5 0 6 for the biotite granites and 13 2 0 8 for the tourmaline granites suggesting derivation from different sources the concentrations of tio2 and possibly ba are higher and of mno and b are lower in the biotite granites the normative orthoclase albite ratio is extremely variable ranging from 0 26 to 1 65 in the biotite granites to 0 01 1 75 in the tourmaline granites very few sample compositions fall near the high pressure watersaturated haplogranite minima eutectic trend indicating that the granites for the most part are not minimum melts generated under conditions with a text h text 2 text o 1 instead most biotite granites are more potassic than the water saturated minima and eutectics and in analogy with experimentally produced granitic melts they are best explained by melting at 6 kbar a text h text 2 text o 1 and temperatures 800 c such high temperatures are also indicated by oxygen isotope equilibration among the constituent minerals nabelek et al 1992 several of the tourmaline granite samples contain virtually no k feldspar and have oxygen isotope equilibration temperatures 716 775 c therefore they must represent high temperature accumulations of liquidus minerals crystallized under equilibrium conditions from melts more sodic than the water saturated haplogranite minima or during fractionation of intruded melts into granite pegmatite couplets accompanied by volatile aided differentiation of the alkali elements the indicated high temperatures a text h text 2 text o 1 the relatively high tio2 and ba concentrations and the relatively low partial 18 text o values of the biotite granites suggest that they were generated by high extent biotite dehydration melting of an immature archean metasedimentary source the ascent of the hot melts may have triggered low extent muscovite dehydration melting of schists higher in the crust producing the high b low ti melts comprising the periphery of the main pluton and the satellite intrusions alternatively the different granite types may be the result of melting of a vertical section of the crust in response to the ascent of a thermal pulse with the low partial 18 text o biotite granites generated at a deeper hotter region and the high partial 18 text o tourmaline granites at a higher cooler region of the crust the low ti and high b concentrations in the high partial 18 text o melts resulted in the crystallization of tourmaline rather than biotite which promoted the observed differentiation of the melts into the granitic and pegmatitic layers found along the periphery of the main pluton and the satellite intrusions

archean rocks of the black hills south dakota reworked basement from the southern extension of the trans hudson orogen the little elk and the bear mountain terranes on the margin of the precambrian core of the black hills provide the only known exposures of archean rocks between the archean wyoming and superior provinces the little elk terrane consists of a supracrustal sequence dominated by biotite feldspar gneiss meta arkose or metatuff that is intruded by the slightly metaluminous to peraluminous calc alkaline little elk granite which has a u pb intercept age of 2 549 11 m y a biotite plagioclase schist metagraywacke dominates the bear mountain terrane and is intruded subparallel to foliation by the peraluminous granite at bear mountain an isochron calculated from six severely discordant u pb zircon analyses yields an age of 2 393 230 m y the archean terranes participated in the trans hudson orogenic event suggested by a published rb sr age for the little elk granite 1 850 m y 1 87 1 97 gaigneous activity in the black hills and the similarity in orientation of the proterozoic deformational fabric with geophysical anomalies interpreted to be associated with the trans hudson orogen the metamorphic conditions estimated for the archean rocks may be the result of a thermal event that produced the proterozoic harney peak granite and thermal high northeast of lead south dakota the unexposed precambrian basement is probably dominated by granites similar to the little elk granite and supracrustal rocks consisting of continental margin deposits based on the ree contents of the archean schists and on the heavy mineral assemblages in the uraniferous nature of and the metasedimentary clasts in the lower proterozoic box elder creek formation the ages and the relatively long lived crustal sources for these archean granites and the similarity of the inferred basement characteristics to those of rocks in the wyoming province suggest that the black hills archean rocks may be the easternmost exposures of this province the probable trans hudsonian reworking of the black hills proterozoic rocks and their similarity to those in northern saskatchewan imply that the black hills occupies a tectonic position comparable to that of rocks described from the cree lake zone of saskatchewan

the cheyenne belt analysis of a proterozoic suture in southern wyoming abstract the cheyenne belt of southeastern wyoming is a major shear zone which separates archean rocks of the wyoming province to the north from 1800 1600 ma old eugeoclinal gneisses to the south miogeoclinal rocks 2500 2000 ma old unconformably overlie archean basement immediately north of the shear zone and were deposited under transgressive conditions along a rift formed continental margin intrusive tholeiitic sills and dikes are interpreted as rift related intrusions and a date of 2000 ma on a felsic differentiate of these intrusions gives the approximate age of rifting there are no known post 2000 ma felsic intrusions north of the cheyenne belt volcanogenic gneisses and abundant syntectonic calc alkaline plutons of the southern terrane are interpreted as island are volcanic and plutonic rocks the volcanics are a bimodal basalt rhyolite assemblage plutons include large gabbroic complexes and quartz diorite 1780 ma syntectonic granitoids 1730 1630 ma and post tectonic anorthosite and granite 1400 ma there is no evidence for archean crust south of the cheyenne belt structural data thrusts in the miogeoclinal rocks vertical stretching lineations and the same fold geometries north and south of the shear zone suggest that juxtaposition of the two terranes took place by thrusting of the southern terrane island arc over the northern terrane craton and miogeocline probably as a continuation of the south dipping subduction which generated calc alkaline plutons of the southern terrane a metamorphic discontinuity across the shear zone with greenschist facies rocks to the north and upper amphibolite facies rocks and migmatites to the south also suggests thrusting of the southern terrane deeper crustal levels over the northern terrane shallower levels the cheyenne belt may be a deeply eroded master decollement perhaps analogous to a ramp in the master decollement in the southern appalachians this interpretation of the cheyenne belt as a proterozoic suture zone provides an explanation for the geologic geochronologic geophysical metallogenic and metamorphic discontinuities across the shear zone

core complex model proposed for gneiss dome development during collapse of the paleoproterozoic penokean orogen minnesota gneiss domes preserved throughout the paleoproterozoic 1870 1820 ma penokean orogenic belt are commonly viewed as collisional features however 1700 ma mica 40ar 39ar ages from archean rocks of the mcgrath gneiss dome minnesota are in marked contrast with 1750 1760 ma mica ages obtained everywhere outside the dome suggesting the dome may have formed well after compression had ceased we hypothesize that the bimodal age pattern is a result of crustal excision between archean basement and paleoproterozoic cover during extensional collapse of the overthickened orogen removal of structural section and progressive unroofing may have led to the development of a domed basement cover shear zone in this respect the mcgrath gneiss dome would represent one of the oldest analogues of a metamorphic core complex postorogenic collapse of the penokean orogen was apparently long lived with significant pulses occurring at 1755 ma and at 1700 ma the sudden and widespread crustal fusion at 1770 1760 ma that preceded the proposed collapse suggests that rapid subcrustal lithospheric thinning may have triggered collapse as has been proposed recently for several phanerozoic collapsed orogens

stagnant slab a review a stagnant slab is a subducted slab of oceanic lithosphere subhorizontally deflected above across or below the 660 km discontinuity this phenomenon has now been widely recognized beneath subduction zones around the circum pacific and in the mediterranean collaboration of seismic and electromagnetic observations mineral physics measurements and geodynamic modeling has begun to provide a consistent picture of stagnant slab

upper mantle reflectivity beneath the williston basin phase change moho and the origin of intracratonic basins cocorp consortium for continental reflection profiling deep reflection profiles crossing the northern williston basin show 1 dipping reflections within the crust of the underlying trans hudson orogen that extend downward into the upper mantle and 2 no clearly defined reflection moho in contrast lithoprobe canada9s national geoscience project profiles crossing the trans hudson orogen north of the basin show dipping reflections within the crust that terminate at a sharply defined subhorizontal reflection moho a reflection character typical of the interior of collapsed phanerozoic orogens we suggest that a crustal root produced during hudsonian collision was incompletely removed by normal postorogenic extension in the region now underlain by the williston basin this remnant crustal keel much later underwent eclogite facies metamorphism which overprinted a new nonreflective moho across the root and induced the subsidence of the williston basin

delineating the karstic flow system in the upper lost river drainage basin south central indiana using sulphate and δ34sso4 as tracers abstract a karstic flow system in the upper lost river drainage basin in south central indiana usa was investigated using so4 concentration and 34sso4 as tracers the flow system was characterized as vadose flow and phreatic diffuse flow vadose flow samples were collected from 7 epikarstic outlets after storm events phreatic diffuse flow samples were collected from the orangeville rise the major emergence point for the drainage basin during the base flow periods discharge from the orangeville rise was constant during the base flow periods but showed large variations in flow rate 0 3 11 7 m3 s so4 concentration 11 220 mg l and 34sso4 5 2 to 15 0 after storm events due to the mixing of rain vadose flow and phreatic diffuse flow in the conduits that feed the orangeville rise sulphate concentrations and 34sso4 were unique in vadose flow sso4 13 24 mg l 34sso4 1 9 to 3 8 and phreatic diffuse flow so4 220 mg l 34sso4 15 0 mean so4 concentration of rainwater in the study area was measured as 1 8 mg l using a 3 component mixing model for water in the karstic conduits the mixing ratios of rain 16 5 vadose flow 58 5 and phreatic diffuse flow 25 0 components were calculated in the orangeville rise discharge these mixing ratios attained using so4 concentration as a tracer indicated the important role of the vadose zone as a water storage area in karst aquifers

a four component mixing model for water in a karst terrain in south central indiana usa using solute concentration and stable isotopes as tracers the study area lies in a highly karstified carbonate terrain in south central indiana sinkholes conduits and caves form large secondary pathways for the subsurface flow as a result the discharge from a main emergence point for the subsurface flow system the orangeville rise quickly responds to the storm events and shows wide variations in flow rate water chemistry and stable isotopic compositions these responses are attributed to the mixing of water in secondary pathways in the study area recharge occurs through the thick mantled karst plain and the sinkhole plains and the role of soil layer and epikarst in the recharge process is of great importance rain dic 2 hco3 mg l 13cdic 7 soil water dic 544 hco3 mg l 13cdic 14 7 epikarstic water dic 224 hco3 mg l 13cdic 13 6 and phreatic diffuse flow water dic 299 hco3 mg l 13cdic 11 8 generally showed unique and constant dissolved inorganic carbon dic and 13cdic values over time using dic and 13cdic as tracers a four component mixing model was established for the karstic flow system by constructing the discharge hydrograph separation curves the mixing ratio of each component rain 10 6 soil 3 1 epikarstic 52 3 and phreatic 34 0 water was determined for the orangeville rise discharge over the testing period of 104 h after the storm event of 10 4 90 vadose water occupied 55 4 of spring discharge and this demonstrates the importance of the unsaturated zone especially the epikarst in the karstic flow systems

seismic image and origin of the changbai intraplate volcano in east asia role of big mantle wedge above the stagnant pacific slab abstract we determined p wave tomography of the crust and upper mantle under the changbai volcanic area in northeast asia by using 289 318 arrival time data from 4802 local earthquakes and 9599 teleseismic events a prominent low velocity anomaly is clearly imaged in the crust and upper mantle down to about 410 km depth beneath the changbai volcano a broad high velocity anomaly is revealed in the mantle transition zone and deep earthquakes occurred actively there suggesting that the subducting pacific slab is stagnating in the mantle transition zone under east asia our results suggest that the formation of the changbai and other intraplate volcanoes in northeast asia is related to the upwelling of hot and wet asthenospheric materials in the big mantle wedge above the stagnant pacific slab hence the active intraplate volcanoes in northeast asia are not hotspots related to deep mantle plumes but are caused by plate tectonic processes in the upper mantle

infiltration mechanisms related to agricultural waste transport through the soil mantle to karst aquifers of southern indiana usa abstract a hydrogeological study was conducted during the 1991 1992 water year in the clay soil mantled portion of a limestone terrain in southern indiana the purpose of the study was to investigate the modes of soil water infiltration contributing to rapid transport of nitrate to the saturated zone the 1 year cycle profiles of nitrate concentration vs time show a consistent increase of nitrate at various depths in the unsaturated zone during the period of investigation the increase of nitrate in soil water is attributed to the rapid flushing of the inorganic fertilizers from the fields after the area received sufficient rainfall in late fall the investigation also showed a major movement of nitrate in quick pulses through the unsaturated zone rather than a slow uniform recharge immediately after a major storm event the asymmetric profiles of nitrate concentration vs depth point to the existence of preferential flow through macropores in the clay soil mantle above the bedrock soil water transport between storm events is by matrix type flow nitrogen isotopes were analyzed for representative groundwater samples collected before and immediately after fertilization of fields in the summer 1991 the 615n values of the samples did not show any major shift in nitrate sources between the sampling periods the summer of 1991 was extremely dry prohibiting vertical transport of nitrate from the fields to the groundwater system any change in nitrate concentration in groundwater during this time is attributed to the mixing through lateral flow within the aquifer

proterozoic collisional tectonism in the trans hudson orogen saskatchewan isotopic and structural data from the juvenile reindeer zone of the trans hudson orogen northern saskatchewan indicate a pre 1 85 ga thermotectonic event possibly reflecting arc continent collision followed by a more extensive nappe forming ca 1 83 1 80 ga thermotectonism during terminal continent continent collision preliminary data from the adjacent ensialic cree lake zone suggest high grade reworking of archean crust by the pre 1 85 ga event in the rae province to the west high grade metamorphism and reworking of archean crust occurred about 2 0 ga and may be related to the formation of the coeval taltson magmatic zone

distribution of porphyry deposits in the eurasian continent and their corresponding tectonic settings in the eurasian continent there are three huge metallogenic belts of cu and mo porphyry deposits comprising the paleozoic central asian ore belt in the north the tethyan eurasian ore belt of jurassic to cenozoic age in the southwest and the east margin ore belt of the eurasian continent of jurassic to cretaceous age in the east the latter is considered to be part of the vast circum pacific ore belt some of the main features of the spatial temporal distribution of cu and mo porphyry systems and related geodynamic processes of the three metallogenic belts are described in particular the key role of postsubduction related porphyry ore systems is emphasized comprising collisional and post collisional cu mo porphyry deposits during the geological history of the eurasian continent the recurrent feature of these ore systems and related felsic rocks is their derivation from partial melting of stagnant or residual oceanic slabs and mixing with a variable amount of crustal material during magma ascent to shallower levels 2013 published by elsevier ltd

40ar 39ar evidence for middle proterozoic 1300 1500 ma slow cooling of the southern black hills south dakota midcontinent north america implications for early proterozoic p t evolution and posttectonic magmatism 40ar 39ar total gas and plateau dates from moscovite and biotite in the southern black hills south dakota provide evidence for a period of middle proterozoic slow cooling early proterozoic 1600 1650 ma mica dates were obtained from metasedimentary rocks located in a synformal structure between the harney peak and bear mountain domes and also south of bear mountain metamorphic rocks from the dome areas and undeformed samples of the 1710 ma harney peak granite hpg yield middle proterozoic mica dates 1270 1500 ma two samples collected between the synform and bear mountain dome yield intermediate total gas mica dates of 1550 ma we suggest two end member interpretations to explain the map pattern of cooling ages 1 subhorizontal slow cooling of an area which exhibits variation in mica ar retention intervals or 2 mild folding of a middle proterozoic 1500 ma 300 c isotherm according to the second interpretation the preservation of older dates between the domes may reflect reactivation of a preexisting synformal structure and downwarping of relatively cold rocks during a period of approximately east west contraction and slow uplift during the middle proterozoic the mica data together with hornblende data from the black hills published elsewhere indicate that the ambient country rock temperature at the 3 4 kbar depth of emplacement of the hpg was between 350 c and 500 c suggesting that the average upper crustal geothermal gradient was 25 40 c km prior to intrusion the thermochronologic data suggest hpg emplacement was followed by a 200 m y period of stability and tectonic quiescence with little uplift we propose that crust thickened during the early proterozoic was uplifted and erosionally thinned prior to 1710 ma and that the hpg magma was emplaced into isostatically stable crust of relatively normal thickness we speculate that uplift and crustal thinning prior to hpg intrusion was the result of differential thinning of the subcrustal lithosphere beneath the black hills if so this process would have also caused an increase in mantle heat flux across the moho and triggered vapor absent melting of biotite to produce the hpg magma this scenario for posttectonic granite generation is supported in part by the fact that in the whole of the black hills the hpg is spatially associated with the deepest exposed early proterozoic country rock

structure of the upper mantle and transition zone beneath southeast asia from traveltime tomography 1 tomographic images of the mantle beneath east asia were obtained from the inversion of traveltime data from global and regional seismograph networks and from temporary arrays on and around the tibetan plateau our results are consistent with previous studies but the unprecedented resolution of mantle heterogeneity provides new insight into the large scale tectonic framework of the continental india asia collision in the western part of the study region and subduction of the oceanic lithosphere in the east in the realm of continental collision west of 100 e a relatively slow p wave speed characterizes the upper mantle beneath much of the tibetan plateau but the wave speed is high beneath cratonic india the southern and western part of the tibetan plateau hindu kush and the tian shan in the subduction realm east of 110 e the main structures are i pronounced low wave speed anomalies at a depth of between 100 and 400 km beneath asia s southeastern seaboard and the back arc regions of ongoing subduction ii narrow fast anomalies in the upper mantle beneath major subduction zones and iii widespread fast anomalies at a depth of 500 700 km beneath the sea of japan the northern part of the philippine sea plate and southeastern china if the latter anomalies represent stagnant slabs their fragmented nature and large lateral extent suggest that they are produced by different episodes of subduction beneath western pacific island arcs along the old se margin of asia or during the mesozoic collision of cratonic units in southeast asia attribution to ancient subduction systems implies that slab fragments can reside in the transition zone for at least several tens of millions of years shallow slow anomalies beneath the red river fault region connect to deep anomalies beneath the south china fold belt and south china sea suggesting a causal relationship between the evolution of the continental lithosphere of sw china and deeper mantle processes between the collision and the subduction realms tomography reveals high wave speed continental roots beneath the western part of the north china craton ordos block and the south china or yangtze craton sichuan basin to a depth of 300 km

pressure temperature time path related to the thermotectonic evolution of an early proterozoic metamorphic terrane black hills south dakota a pressure temperature time path determined from zoned garnet and associated minerals in a metapelite from a dome in the western part of the black hills south dakota precambrian core shows two clockwise loops that link the previously postulated thermal and tectonic events affecting early proterozoic age rocks between ca 1 850 and 1 715 ga the shape of the loops indicates that two distinctly different styles of tectonic processes occurred during this time period the first loop established from the garnet core is correlated with crustal thickening by thrusting and nappe development followed by a period of erosional uplift the second loop from the garnet rim resulted from homogeneous thickening represented by north northwest trending isoclinal folds the peak conditions of this event are interpreted to be associated with anatexis doming and intrusion of harney peak s type granite 1 715 ga