a framework for karst ecohydrology ecohydrology can be defined as the science of integrating hydrological and biological processes over varied spatial and temporal scales there exists in karst a strong and direct interaction between the circulation and storage of groundwater and surface water these fluxes in turn affect the spatial distribution of organisms in these habitats because of the fact that the appearance storage and circulation of water in karstified areas is significantly different from other more homogenous and isotropic terrains karst ecohydrology should develop original methods and approaches at the same time traditional approaches are also very useful large karst underground geomorphological patterns occur in many sizes and varieties ranging from a few meters long or deep to very large the deepest being deeper than 1km and longer than hundreds of kilometres in this article special attention is paid to ecohydrological functions of karst underground features caves pits conduits etc which play a crucial dual role in 1 hydrology and hydrogeology of water circulation and storage and 2 ecology of many rare and endangered species differences in morphology hydrology hydrogeology and climate have resulted in a range of different environments which provide the opportunity for the coexistence of different species the role of the epikarst and vadose zones as well as caves in ecohydrological processes is discussed the importance of the flood factor in karst ecology is analysed the aim of this article is to move forward the discussion among different disciplines to promote and develop a conceptual framework for karst ecohydrology

structural setting and age of the partridge island block southern new brunswick canada a link to the cobequid highlands of northern mainland nova scotia the partridge island block is a newly identified tectonic element in the saint john area of southern new brunswick located south of and in faulted contact with proterozoic and cambrian rocks of the ganderian brookville and avalonian caledonia terranes it includes the lorneville group and tiner point complex the lorneville group consists of interbedded volcanic and sedimentary rocks subdivided into the taylors island formation west of saint john harbour and west beach formation east of saint john harbour a sample from thin rhyolite layers interbedded with basaltic flows of the taylors island formation at sheldon point yielded a late devonian early carboniferous u pb zircon age of 358 9 6 5 ma petrological similarities indicate that all of the basaltic rocks of the taylors island and west beach formations are of similar age and formed in a continental within plate tectonic setting west of saint john harbour basaltic and sedimentary rocks of the taylors island formation are increasingly deformed and mylonitic to the south and in part tectonically interlayered with mylonitic granitoid rocks and minor metasedimentary rocks of the tiner point complex based on magnetic signatures the deformed rocks of the tiner point complex can be traced through partridge island to the eastern side of saint john harbour where together with the west beach formation they occupy a thrust sheet above a redbed sequence of the mid carboniferous balls lake formation the tiner point complex includes leucotonalite and aegirine bearing alkali feldspar granite with a type chemical affinity and early carboniferous u pb zircon ages of 353 6 5 7 and 346 4 0 7 ma respectively based on similarities in age petrological characteristics alteration iron oxide copper gold iocg type mineralization and deformation style the partridge island block is correlated with late devonian early carboniferous volcanic sedimentary plutonic rocks of the cobequid highlands in northern mainland nova scotia deformation was likely a result of dextral transpression along the cobequid chedabucto fault zone during juxtaposition of the meguma terrane

40ar 39ar whole rock phyllite ages from late precambrian rocks of the avalon composite terrane new brunswick evidence of silurian devonian thermal rejuvenation several variably deformed and metamorphosed late precambrian volcanic sedimentary successions have been recognized within the avalon composite terrane exposed in the caledonian highlands of southern new brunswick whole rock samples of metasedimentary phyllite and phyllitic metatuff from the oldest ca 600 635 ma avalonian succession display similar internally discordant 40ar 39ar age and apparent k ca spectra intermediate temperature gas fractions were experimentally evolved solely from very fine grained cleavage aligned white micas these yield apparent ages between ca 430 and 410 ma and are interpreted to closely date a static late silurian early devonian thermal rejuvenation evidence for a silurian devonian thermal event has not been previously documented in avalonian rocks of the caledonian highlands caledonia assemblage however a thermal overprint of similar age ca 400 ma is recorded by metamorphic muscovite in high grade gneisses and platformal metasedimentary rocks brookville a

late proterozoic high pressure granulite facies meta morphism in the north east ox inlier north west ireland high pressure granulite facies gneisses in the ne ox inlier in nw ireland have undergone extensive caledonian retrogression in the local area of slishwood however reworking was negligible and the gneisses psammites semipelites pelites metabasites and ultramafites preserve evidence of p t changes at high grade which mainly post date pre caledonian polyphase deformation temperatures reached 850 900 c based on garnet clinopyroxene geothermometry and the presence of mesoperthite during and after decompression from earlier eclogite facies conditions inferred from textural evidence of plagioclase release in sieve textured augite subsequent cooling at high pressure is inferred from the unequivocal replacement of sillimanite by kyanite a sm nd mineral isochron gt cpx plag wr of 605 37 ma is taken to date a point on the cooling path and confirms the hitherto suspected pre caledonian age of the high grade metamorphism geochemical and sm nd isotopic data indicate that the protoliths were probably late proterozoic arkosic sediments and tholeiites following metamorphism they apparently came to reside near the base of the crust where they slowly cooled the eventual exhumation of these gneisses is attributed to caledonian crustal imbrication followed by rapid isostatic recovery

nd isotope systematics of coarse and fine grained sediments examples from the middle proterozoic belt purcell supergroup sm nd isotopic compositions are reported for 20 fine and 5 coarse grained samples of the belt purcell supergroup of western north america varepsilon nd and sm nd ratios for fine grained belt purcell sediments are remarkably uniform indicating crustal residence ages ranging only from 1 6 to 2 1 ga varepsilon nd and sm nd ratios for coarse grained sediments however are much more varied and contain evidence of sm nd fractionation during sedimentary recycling assuming that this ree fractionation occurred between the time source areas were eroded and when sediment was deposited a new method of calculating crustal residence age intervals is derived for the coarse grained samples which serves to place constraints on the average time since source materials were extracted from the mantle the nd data from both sample groups provide an average age estimate of 2 0 pm 0 3 ga for the middle proterozoic crust from which most of the belt purcell supergroup was derived the isotopic data toge

the genesis of gold mineralisation hosted by orogenic belts a lead isotope investigation of irish gold deposits abstract lead isotope analyses have been performed on 109 gold and 23 sulphide samples from 34 irish gold occurrences including 27 placers and used to shed light on the sources of mineralising fluids and metals associated with gold mineralisation hosted by orogenic belts the pb isotope ratios of lode and placer gold range from 206pb 204pb 17 287 18 679 207pb 204pb 15 382 15 661 and 208pb 204pb 37 517 38 635 consistent with the pb isotopic data on previously reported irish sulphide mineralisation there is no evidence that gold mineralisation is associated with distinctive source regions and it appears to have been derived from similar sources to those responsible for the widespread sulphide mineralisation in ireland it is inferred that the principal controls on the au mineralisation are structural and not related to the distribution of au in their source rocks the range of pb isotope ratios favours the interaction of multiple source reservoirs predominantly during the caledonian orogeny c 475 380 ma underlying basement was the primary control on two key sources of pb gold occurrences located to the south east of the iapetus suture are characterised by pb compositions that derive predominantly from the late proterozoic crustal basement or overlying lower palaeozoic sediments whilst those located north west of the iapetus suture are characterised by less radiogenic pb signatures derived predominantly from late proterozoic or older crustal basement a third source relatively enriched in radiogenic pb also played a role in the formation of a number of irish gold occurrences and may have been associated with syn to post orogenic intrusives magmatic processes may therefore have played an important role in the formation of some orogenic gold occurrences

ndsr isotopic study of proterozoic to triassic sediments from southeastern british columbia abstract sedimentary rocks from the southeastern canadian cordillera varying in age from mid proterozoic to triassic have been analysed for their nd isotopic composition e nd t values range from 1 5 to 17 2 and nd model ages t dm nd vary from 1 00 to 2 32 ga much in excess over their stratigraphic ages the difference between the two ages ranges from 0 43 to 1 93 ga decreasing as the sediments become stratigraphically older nd isotopic compositions of sediments suggest that there are two distinct continental sources of sediments in the cordilleran miogeocline a an older source e nd 0 from 20 3 to 23 8 with apparent crustal residence ages of 2 26 2 32 ga and b a younger source average e nd 0 14 0 with the crustal residence age of about 1 8 ga the older residence ages are interpreted to be due to mixtures of materials from the archean and proterozoic crusts sediments belonging to the laib formation lower cambrian and lower clastic part of the milford group namurian appear to have derived from an archean continental segment with some admixture of sediments from the early proterozoic source the younger crustal source which seems to be the principal supplier of sediments for most of the stratigraphic units aldridge formation middle proterozoic horsethief creek group upper proterozoic hamill and lardeau groups lower cambrian nelway formation middle cambrian active formation ordovician and part of milford group is not the archean canadian shield immediately to the east recent subsurface mapping of the alberta basement beneath the phanerozoic sedimentary cover using u pb zircon dating of igneous lithologies 1 has established the extensive archean and early proterozoic crustal provinces it is proposed here that the early proterozoic province of west central alberta is the most likely source of the easterly derived sedimentary rocks of the cordilleran miogeocline with t cr ages from 1 94 to 1 50 ga on the basis of sedimentologic tectonic and isotopic evidence we suggest that the younger sediments could be to some extent recycled older sediments for the triassic slocan and ymir groups eastern part of quesnel terrane sedimentologic lithologic tectonic and isotopic evidence suggest the source was a western one with about 1 8 ga crustal residence age comparison of the crustal residence ages with stratigraphic ages shows the best fit nd evolution curve for the cordilleran miogeocline approximately coincides with the continental growth curve deduced for the north atlantic province and similar to the growth curve for gondwana during the phanerozoic this curve also passes through the north american composite the levelling off of crustal residence ages for the mid proterozoic to triassic sediments at about 1 8 ga supports the idea of negligible crustal growth since at least 1 7 ga the average crustal residence age of the modern miogeoclinal and cratonic sediments

provenance of pliocene sediments and paleoenvironmental changes in the southern north sea region using samarium neodymium sm nd provenance ages and clay mineralogy abstract an 800 m thick sedimentary succession from the late pliocene north sea has been investigated on the provenance of the sediments and on changes of the source regions related to transport processes and climate changes the lower zanclean to piacenzian part of the succession from 1250 to 1050 m depth and the middle early gelasian part from 1100 to 700 m depth belong to one distributory system with at least two contributing source areas provenance ages calculated on basis of sm nd content indicate one old archean and one young

nd and sr isotopic systematics of central australian granulites chronology of crustal development and constraints on the evolution of lower continental crust nd and sr isotopic data are reported for a granulite terrain in the proterozoic arunta block of central australia sm nd data from a wide range of rock types define a crust formation age of 2 070 125 ma and provide further evidence for voluminous crustal growth in the proterozoic an nd value of 1 5 0 8 indicates a depleted mantle source for this crustal segment and there is no evidence for a large component of significantly older sialic crust field relationships geochemistry and rb sr data for mafic and felsic granulites indicate that intracrustal differentiation and polyphase deformation were followed by granulite facies metamorphism rb depletion at 1 800 ma rb sr data for strongly retrogressed granulites define an age of 1 700 ma which is interpreted as the time of retrograde biotite growth partial melting at the presently exposed crustal level and anatexis at deeper crustal levels were broadly coeval with the retrograde metamorphism sm nd and rb sr isotopic systematics of minerals indicate that the terrain cooled slowly did not experience significant uplift until 1 000 ma and remained at temperatures above 320 c until the late palaeozoic the mineral data are consistent with geological relationships and petrological evidence for a prolonged period of isobaric cooling followed by uplift late in the metamorphic evolution of the terrain the granulite protoliths appear to have formed in a rift which closed within 280 ma of initial separation deformation and granulite facies metamorphism at 1 800 ma are interpreted to be a consequence of collision between the continental blocks which defined the rift regional retrogression and granitoid magmatism at 1 700 ma are attributed to underthrusting of the granulites by lower grade rocks in the final stages of collision subsequent events in the cooling and uplift history appear to have been controlled by the presence of long lived major faults in the crust and a prolonged history of episodic compression in the continental lithosphere the results of this study suggest that granulite terrains in general cannot be equated with lower continental crust but instead represent assemblages of mainly supracrustal rocks which in some instances have been involved in major collision events

neodymium isotopic composition of ordovician conodonts as a seawater proxy testing paleogeography 1 to evaluate recent ordovician paleogeographic reconstructions end values were determined in conodonts as a proxy for the isotopic variations in ancient seawater using samples from the major cratons and microplates isotopic variations reveal the existence of distinct oceanic masses and epeiric seas that constrain the position of plates and terranes relative to these water masses and hence constrain models of regional and global paleogeography the isotopic patterns show a consistent picture of the changes in the ordovician oceans the end values for water masses associated with laurentia are strongly negative 28 to 18 in the early ordovician evolving over time to higher values in the range 13 to 5 the early ordovician signature of laurentia is in marked contrast to other cratons and microplates which have a range of values from 10 to 5 samples from south china show interesting signals that reflect a greater similarity to laurentia than other peri gondwana terranes the isotopic variations are a function of both regional geology and global tectonic processes the most obvious being the taconic orogeny and onset of the closure of the iapetus ocean regional and global models of paleogeography are considered in light of these proxy signals this study also reveals that conodonts are powerful geochemical tools for obtaining information on ancient water masses the use of the nd isotopic signatures from conodonts provides a method independent of paleomagnetism and biogeography to test paleogeographic models by integrating such information a more multidisciplinary approach is possible

the isotopic and structural age of the aberdeen granite new uranium lead isotope data from monazites yield an emplacement age of 470 1 ma for the 9s9 type aberdeen granite emplacement of this intrusion was late tectonic with respect to the grampian early caledonian orogeny and followed closely on the upper amphibolite facies meta morphic climax in the dalradian country rocks the field relations of the associated vein complexes suggest that this isotopic age also dates the local d3 deformation of the dalradian supergroup previously published isotope data indicate that the granite originated largely by melting of metasediments with a minimum crustal residence time of c 1 2 to 1 8 ga rocks with comparable isotopic characteristics form the migmatitic country rock envelope to the granite and we advocate extensive contemporaneous melting of such rocks at shallow depths below the level of emplacement then 17 20 km

petrology and age of the mechanic settlement pluton avalon terrane southern new brunswick the mechanic settlement pluton located at the northern margin of the caledonian highlands in southern new brunswick is composed of rocks ranging from ultramafic lherzolite plagioclase bearing lherzolite through mafic mainly olivine gabbronorite and gabbro to intermediate quartz diorite and monzodiorite spatial distribution of these lithologies textural features and geochemistry are consistent with evolution of a tholeiitic mafic parent magma by crystal fractionation processes with some evidence for magma mingling between evolved gabbroic and quartz dioritic magmas the dioritic rocks form most of the southwestern upper part of the pluton whereas the varied gabbroic rocks with ultramafic layers form the northeastern part u pb zircon dating of a quartz diorite sample from the southwestern part of the pluton indicates crystallization at 557 3 ma amphibole and phlogopite in two lherzolite samples from the northeastern part of the pluton gave 40ar 39ar dates of 550 5 and 539 5 ma re

little river revisited thirty five years after hack and goodlett abstract in possibly the first detailed study to relate geomorphology vegetation and hydrology at a watershed scale hack and goodlett 1960 documented variation in the eastern forest with topograhic positions of cove side slope and nose runoff identified as convergent parallel or divergent supported forest types respectively of northern hardwood oak and yellow pine the study conducted in the little river basin of northwestern virginia also described effects on landforms and vegetation of a catastrophic flood that occurred in june 1949 field investigations conducted nearly 4 decades later review selected parts of the study by hack and goodlett 1960 replicate data provide a basis to evaluate interpretations of hack and goodlett to document geomorphic change within the little river basin since the 1949 flood and to identify vegetation change in uplands and bottomlands results suggest that change to hillslope landforms has been minor since 1949 but that changes have occurred to the little river and its tributaries seemingly during flow events of 1952 1955 and 1985 change in areal extent of forest types was not detected change in the relative abundances of dominant species may have resulted from 20th century fire suppression

detrital zircon ages from the loch maree group lewisian complex nw scotland confirmation of a palaeoproterozoic laurentia fennoscandia connection ion microprobe u pb zircon ages of detrital zircons from a metasediment of the loch maree group lewisian complex nw scotland show striking similarities to those in coeval palaeoproterozoic belts of laurentia and fennoscandia and confirm previous suggestions of a connection between them late archaean zircons 3 06 2 48 gyr old represent derivation from lewisian quartzofeldspathic gneisses andlor a contemporaneous terrane palaeoproterozoic zircons 2 2 2 0 gyrold place a maximum age constraint upon deposition an appropriate quartzofeldspathic source for these latter zircons is not presently known either in the lewisian or the wider laurentia fennoscandia region although its requirement would be consistent with a development of the loch maree group together with juvenile magmatic arc rocks at an active margin which was probably removed by lateral tectonics comparisons are made with contemporaneous supracrustal sequences throughout the laurentia fennoscandia region which exhibit marked similarities in source region age characteristics lithologies and inferred depositional environment

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

the water on a small karst island the island of korcula croatia as an example the island of korcula which has an area of 271 47 km2 is located along the north eastern coast of the adriatic sea due to the mediterranean climate size and karst geology its water resources are very scarce this paper describes the natural features of the island air temperature precipitation geology hydrogeology and groundwater which are important for the water appearance and its distribution in time and space the water supply of the island has been managed in the following ways through a pipeline from the mainland by drawing groundwater and by rain harvesting tourism causes high seasonal water needs which are barely met by the existing water supply system therefore present water resource management on the island must be improved the paper also presents mathematical programming scheme to get optimal costs and benefits of water exploitation on the island besides economic aspect linear programming is applied to social and ecological objectives as well this study suggests that island s water management should be primarily based on wisely using its proper water resources

crustal reworking in southern africa constraints from sr nd isotope studies in archaean to pan african terrains abstract isotopic data for crustal rocks from southern africa indicate that significant crustal growth occurred prior to 2 5 ga and crustal growth since 1 0 ga was negligible orogenic events since about 2 0 ga appear to have reworked progressively larger proportions of pre existing crustal material and the last major orogenic event the damara of namibia resulted in no detectable increase in crustal mass model age ratios dm nd t dm sr refect intracrustal fractionation of rb sr relative to sm nd and so constrain models for intracrustal reworking data from sedimentary rocks suggest that rb sr ratios are increased at average rates of between 1 2 and 2 2 per billion years by processes of erosion and sedimentation metamorphism and intracrustal melting in the continuously reworked upper crust these inferred rates of rb sr fractionation can account for the present day 87 sr 86 sr ratios in modern river particulates and the restricted range of depositional 87 sr 86 sr ratios in upper proterozoic sediments

impact of intensive groundwater exploitation on an unprotected covered karst aquifer a case study in kermanshah province western iran islam abad region located in the southwestern of kermanshah province is a karst region where over exploitation from the deep karst water resources has directly affected the water balance of the whole area using a combination of geophysical investigations and analysis of well log data and other relevant hydrogeological studies we looked for the actual relationship between over exploitation from deep water wells penetrated into the covered karst aquifer and the drying out of some of the main karst springs throughout the study area in total 20 piezometric wells and 4 main karst springs have been chosen for groundwater monitoring network by integrating gis processing system and a classical water balance method together with hydrogeology and hydrogeochemical spatial maps critical zones of human impacts on groundwater resources made by water extraction for agricultural demand were identified results show that water balance in the islam abad basin is in clear disequilibrium since 2 15 mcm of water depletes from the main aquifers of the study area annually this volume of water shortage has resulted in a 7 m groundwater level decline in the last decade which caused both drying out and reduction in discharge rate of some of the main karst springs throughout the study area depths of penetration of deep water wells into the covered karst aquifer vary from 1 to 93 m hydrogeochemical evaluations including ion relations and hydrogeochemical diagrams show interactions between karst and alluvium aquifers results showed a broad connection between these two resources and therefore any pressure on alluvium aquifer will affect the karst aquifer especially by excessive deep water wells drilling in mutual alluvial and covered karst aquifers

geochemistry petrogenesis and tectonic significance of the early proterozoic loch maree group amphibolites of the lewisian complex nw scotland

proposal for a terrane based nomenclature for the lewisian gneiss complex of nw scotland the current nomenclature for the lewisian gneiss complex has evolved from lithological and structural correlations made prior to any dating initial flawed geochronological studies gave some names an apparent chronological standing but as work advanced fitting events into a coherent regional framework became increasingly difficult modern dating studies have shown that the lewisian gneiss complex was progressively assembled from disparate blocks of archaean continental crust and juvenile proterozoic arcs which satisfy the definition of terranes each terrane had its own separate accretionary and metamorphic history followed by a common history once juxtaposed against other terranes based on a new compilation of modern geochronology allied to the many detailed structural and metamorphic studies this paper proposes a new systematic terminology for the lewisian gneiss complex that is more applicable to this new tectonic framework

the history of a continent from upb ages of zircons from orinoco river sand and smnd isotopes in orinoco basin river sediments abstract we report shrimp u pb ages of 49 zircons from a sand sample from the lower orinoco river venezuela and nd model ages of the fine sediment load from the main river and tributaries the u pb ages reflect individual magmatic or metamorphic events the sm nd model ages reflect average crustal residence ages of the sediment sources together they allow delineation of the crust formation history of the basement precursors of the sediments the u pb ages range from 2 83 to 0 15 ga and most are concordant or nearly so discrete age groupings occur at 2 8 2 1 and 1 1 ga the oldest group contains only three samples but is isolated from its closest neighbors by a 600 ma age gap larger age groupings at 2 1 and 1 1 ga make up about a third and a quarter of the total number of analyses respectively the remaining analyses scatter along concordia and most are younger than 1 6 ga the 2 8 and 2 1 ga ages correspond to periods of crust formation of the imataca and trans amazonian provinces of the guyana shield respectively and record intervals of short but intensive continental growth these ages coincide with 2 9 and 2 1 ga nd model ages of sediments from tributaries draining the archean and proterozoic provinces of the guyana shield respectively indicating that the u pb ages record the geological history of the crystalline basement of the orinoco basin zircons with ages corresponding to the major orogenies of the north atlantic continents the superior at 2 7 ga and hudsonian at 1 7 1 9 ga were not found in the orinoco sample the age distribution may indicate that south and north america were separated throughout their history nd model ages of sediments from the lower orinoco river and andean tributaries are 1 9 ga broadly within the range displayed by major rivers and dusts this age does not coincide with known thermal events in the region and reflects mixing of sources with different crust formation ages the igneous and metamorphic history of these sources as recorded by the detrital zircons is that of the orinoco basin basement this implies that despite evidence of fast sedimentary recycling global similarities in nd crustal residence ages and the probability of cross continent mixing through continental drift the sedimentary material carried by individual rivers is mainly derived from the crystalline basement in the basin the global semblance in nd isotope ratios in major river sediments and atmospheric dusts results from the averaging effect of large scale sampling of the continents which are heterogeneous in age on smaller regional scales a large portion of the continental crust in the orinoco basin formed during the trans amazonian orogeny at 2 0 2 1 ga and smaller portions formed both earlier at 2 8 ga and later after 1 6 ga these observations which are consistent with the relative sizes of crustal age provinces in the orinoco basin indicate that sediments from the lower orinoco and andean tributaries contain 25 35 of material added to the crust since trans amazonian times nd model ages of these sediments underestimate the average crust formation age of the basement of the orinoco basin by only about 10 if this relationship holds in other river basins then nd model ages of major rivers and wind blown particulates indicate that the mean age of the continental crust is 1 9 2 ga

sm nd studies of archaean metasediments and metavolcanics from west greenland and their implications for the earth s early history metasedimentary and metavolcanic rocks from the archaean of west greenland have been examined for evidence of crustal components greater than 3 8 ga in age and for their compatibility with the presently adopted bulk earth sm nd parameters sm nd isotopic data have been obtained for the garbenschiefer metagabbro unit metasediments from the isua supracrustal belt gneisses interior to the isua belt and metasediments from the malene supracrustal belt using estimates of emplacement age t of between 3 77 and 3 67 ga for the parental volcanics to the garbenschiefer unit initial143nd 144nd ratios yield positiveendt values between 1 0 and 3 1 relative to the chur parameters for seven out of eight samples model sm nd ages for the isua gneisses and metasediments are only compatible with their estimated stratigraphic ages if their sources were ca 2end relative to chur at those times similarly model sm nd ages for the malene samples are only compatible with stratigraphic age constraints when based on a source evolution with positiveendt implications of these results for the early development of the earth s mantle are discussed

u pb rb sr and sm nd chronology of granitic basement hydrothermal albitites and uranium mineralization lagoa real south bahia brazil the granites orthogneisses hydrothermal albitities and rocks which have suffered uranium mineralization from the lagoa real district south state of bahia brazil have been investigated by u pb rb sr and sm nd techniques u pb values on zircons from the granitic protolith give an age of 1725 ma u pb on u mineralization dates the primary mineralization at 1395 ma and indicates a reworking at 480 ma which may represent the age of the thrusting of the lagoa real complex over espinhaco metasediments during the brazilian orogeny these two dates are given by rb sr on albitites but from sparse information and are not supported by unequivocal arguments the uranium deposition and sodium metasomatism however cannot be linked either with the thermal history of the granite or with brazilian thrusting sm nd gives scattered results which are suggestive of autochtonous reworkings of rees these results lead to the following suggestions 1 magmatic activity of subalkaline affinity existed within the sao francisco craton at about 1 7 ga 2 such subalkaline plutons are likely sources for u mineralization 3 at about 1 4 ga an unknown event caused hydrothermal activity leading to u deposition at lagoa real 4 brazilian overthrusting at about 480 ma did not play any genetic role in the hydrothermal activity

hydraulic properties of karst fractures filled with soils and regolith materials implication for their ecohydrological functions abstract in regions with shallow soils underlain by fractured bedrock hydrological processes of substrate are no longer only limited to soil layers however ecohydrological functions of bedrock fractures especially those filled with different soil and regolith materials have not been fully understood in this study we aimed to evaluate water transport and supplying capacities of the filled fractures through investigating hydraulic properties and explore their dominant influencing factors three typical fractures a vertical one filled with fine textured soil vsf a vertical one filled with soil and regolith materials vsrf and a non vertical one filled with coarse textured soil nsf were selected from a large newly excavated trench on a karst hillslope of southwest china stratified samples of fracture fillings were collected to measure saturated hydraulic conductivity k s water retention curves and basic physicochemical properties additionally twenty soil profiles in different topographic locations in the same study area were also analyzed in order to support the results derived from the filled fractures all fractures exhibited extremely high k s 87 149 mm h 1 in surface soil 0 10 cm which allowed rapid infiltration of rainwater into subsurface subsurface water transport was smooth when underlying fracture fillings were loamy with relatively high k s about 10 mm h 1 like in nsf but was blocked when they were clayey with low k s 1 like in vsf and vsrf all fracture fillings had abilities to hold water and available water was the most in nsf which provided an extra water source for plant growth in shallow soil regions the ecohydrological functions of the filled fractures often depend on the properties and layering of fracture fillings which was supported by those obtained from the twenty soil profiles these results are helpful for better understanding of the ecohydrological processes and functions of fractures filled with different materials in karst regions

crustal evolution of the hercynian belt of western europe evidence from lower crustal granulitic xenoliths french massif central abstract granulite facies lower crustal xenoliths scavenged by the tertiary basaltic pipes of bournac and roche pointue massif central france have been analysed for major and trace elements and radiogenic sr nd isotope ratios they display wide variations in major elements rare earth elements and isotopes 87 sr 86 sr 0 7041 0 7216 nd 11 9 to 1 5 which tend to correlate with the three different rock types encountered basic and acidic meta igneous and metasediments the basic liquids are of calc alkaline affinity and cumulates are abundant there is a gap in silica content between the basic and acid meta igneous xenoliths the isotopic compositions suggest mixing of old pre existing continental crust represented by the metasediments and mantle derived basic melts which represent juvenile addition to the crust during the hercynian orogeny the basic meta igneous rocks have been contaminated during their emplacement into the crust whereas the surrounding metasediments have suffered partial fusion and contamination by the same liquid producing the hercynian granitoids which have nd and sr initial ratios identical to those of the lower crustal xenoliths the residue from melting may be represented by the acid meta igneous rocks some of which have positive eu anomalies these results indicate that an important basaltic underplating event occurred during the evolution of hercynian orogenic belt although the exact timing of the underplating requires further constraint

dissolved oxygen fluctuations in karst spring flow and implications for endemic species barton springs edwards aquifer texas usa summary karst aquifers and springs provide the dissolved oxygen critical for survival of endemic stygophiles worldwide but little is known about fluctuations of dissolved oxygen concentrations do and factors that control those concentrations we investigated temporal variation in do at barton springs austin texas usa during 2006 2012 do fluctuated by as much as a factor of 2 and at some periods decreased to concentrations that adversely affect the barton springs salamander eurycea sorosum 4 4 mg l a federally listed endangered species endemic to barton springs do was lowest 4 4 mg l when discharge was low 1 m 3 s and spring water temperature was 21 c although not at a maximum the minimum do recorded was 4 0 mg l relatively low do 3 s and maximum t 22 2 c a four segment linear regression model with daily data for discharge and spring water temperature as explanatory variables provided an excellent fit for mean daily do nash sutcliffe coefficient for the validation period of 0 90 do also fluctuated at short term timescales in response to storms and do measured at 15 min intervals could be simulated with a combination of discharge spring temperature and specific conductance as explanatory variables on the basis of the daily data regression model we hypothesize that more frequent low do corresponding to salamander mortality could result from i lower discharge from barton springs resulting from increased groundwater withdrawals or decreased recharge as a result of climate change and or ii higher groundwater temperature as a result of climate change

neodymium isotopes as tracers in marine sediments and aerosols north atlantic nd and sm concentrations and nd isotopic compositions were measured on the detrital fraction of deep sea surface sediments and on aerosols sampled over the north atlantic and mediterranean sea the data expressed asend 0 and as model ages ranged from 14 5 end 0 4 9 and from 0 01 to 2 21 ga respectively two areas where the sediments contain relatively less radiogenic nd are to the west off north africa and eastward of the canadian shield this distribution is consistent with other tracers in suggesting that a significant fraction of the sediments are derived from aeolian material transported by major wind systems saharan dust transported in the equatorial trade winds belt and north american soil material transported in the latitudes of the westerlies between these aeolian dominated belts along an axis from the azores to gibraltar and the mediterranean lies a zone of more radiogenicend 0 values in sediments and aerosols influenced by the recent volcanism of this region previously reported distributions of nd isotopes in bottom formed iron manganese crusts and coatings are similar to distributions of nd isotope values in detrital sediments and aerosols this suggests that the detrital fraction has undergone partial dissolution and desorption in the water column and or in the pore waters of near surface sediments and that a significant proportion of nd in the authigenic ferromanganese phases is derived from this source and may therefore not represent strictly dissolved seawater nd isotope ratios useful as watermass tracers

geochemical and isotopic characteristics of blueschist facies rocks from the ile de groix armorican massif northwest france abstract nine samples of blueschist facies metabasic rocks and four samples of associated metasedimentary lithologies were analysed for ree contents and nd isotopic composition sampling includes the main rock types exposed on groix concentrating on those metabasic rocks with least dispersed rb sr systems the ree abundance patterns appear not to have suffered significant alteration since emplacement of the protolith magma despite subsequent blueschist facies metamorphism the data when integrated into a wider geochemical data base allow the identification and characterization of both tholeiitic and alkaline magma types in the original igneous suite which was differentiated from depleted mantle sources the basalts probably originated in an oceanic context some sediments are predominantly volcaniclastic in which a continental crustal component may be recognized other sediments are closer in composition to continental crust with variable additions of tholeiitic or alkali basalt debris the volcanic sedimentary assemblage on groix is suggestive of ocean island magmatic activity associated with a sedimentary sequence derived from a nearby continent

the pb sr nd isotope geochemistry of some recent circum mediterranean granites pb sr and nd isotopic compositions have been analyzed in recent granites from northern africa northern italy and greece lead isotope compositions of k feldspars are rather homogeneous and cluster close to the modern lead of stacey and kramers 1975 but with slightly higher207pb 204pb and208pb 204pb ratios the cyclades samples however have higher206pb 204pb ratios addition of mantle derived lead was probably very limited which supports a quasi closed system evolution of this element in the continental crust the sr nd data fall in the enriched part of the143nd 144nd vs 87sr 86sr diagram and define a smooth hyperbolic mixing curve over a wide area straddling different orogens most granites may be accounted for by a binary mixture between a recycled crustal component and a depleted mantle like component no correlation is observed between either pb and sr or nd isotopic ratios or any isotopic ratio and major element contents quantitative modelling suggests that two cases fit the sr and nd characteristics of these granites they both require anatexis of the crust on a scale large enough to average the isotopic properties of heterogeneous terranes in the first case the mantle derived component may be represented by differentiated island arc type magmas and the granites result from mixing these magmas with anatectic melts in the second case mantle derived igneous rocks such as obducted ophiolites are part of the crustal source and their variable involvement in the anatectic process causes isotopic variations

characterization of the main karst aquifers of the tezbent plateau tebessa region northeast of algeria based on hydrogeochemical and isotopic data chemical properties and hydrogeological characterization of water resources were studied in the hammemt plain which is located in the northwest of the tezbent mountain range city of tebessa northeast of algeria which drains carbonate aquifers through various large karst springs the physical and chemical characteristics of spring and well water samples were studied for 2 years in order to assess the origin of groundwater and determine the factors driving its geochemical composition the ionic speciation and mineral dissolution precipitation were calculated where we found that water wells characterizing groundwater circulation at shallow depths are moderate to highly mineralized waters of the na hco3 type in contrast to the shallow environment the co2 rich deeper waters are of the ca hco3 type and undergo significant changes in their baseline chemistry along flow lines with increasing residence time the main factors controlling the groundwater composition and its seasonal variations are geology because of the presence of different carbonate formations additionally elevation and the rate of karst development supersaturation with respect to calcite indicates co2 degasing occurs either inside the aquifer in open conduits or at the outlet in reservoirs undersaturation with respect to calcite shows the existence of fast flow and short residence time conditions inside the aquifer the main springs and wells of the tazbent mountain have been studied by means of stable isotope measurement where the values are varied in 18o between 8 2 and 7 76 for spring samples and from 8 26 to 7 15 for well samples and in 2h between 52 92 and 49 11 for spring samples and from 55 47 to 47 44 for well samples showing that the groundwater recharge is of meteoric origin and suggests the absence of the evaporation effect on the isotopic composition

geochemistry and tectonic setting of late precambrian volcanic and plutonic rocks in southeastern cape breton island nova scotia late precambrian volcanic sedimentary belts in the mira avalon terrane of southeastern cape breton island display differences in rock types petrochemistry and age showing that they did not form contemporaneously above a single northwest dipping subduction zone as proposed in earlier models the oldest rocks are 680 ma mafic and felsic flows and tuffs and abundant mainly tuffaceous sedimentary rocks in the stirling belt they are interpreted to have formed in a trough within or peripheral to a volcanic arc complex northwest of the stirling belt the east bay hills coxheath hills and sporting mountain belts consist of ca 620 ma mafic to felsic subaerial pyroclastic rocks and flows and contemporaneous dioritic to granitic plutons both volcanic and plutonic rocks are calc alkalic to high k calc alkalic suites formed in a continental margin volcanic arc a correlative 620 ma plutonic suite intruded the western margin of the stirling belt suggesting that subduction may have been toward the prese

investigations of the spatial and temporal variations of sr and nd isotopes in sediments from two indian rivers implications to source identification radiogenic isotopes of sr and nd provide crucial information on chemical and physical erosion processes therefore used as tracers for fingerprinting the sources of fluvial sediments moreover elemental geochemistry 87sr 86sr and 143nd 144nd signatures in silicate fractions of sediments primarily reflect intricate controls of characteristics and provenance of sediment a suite of sediment samples collected from two rivers of india narmada large and netravati small were analyzed for elemental concentrations 87sr 86sr and 143nd 144nd in silicate as well as acid leachable fractions 87sr 86sr in acid leachable sediment fractions from both the rivers 0 7094 0 0002 for narmada and 0 7158 0 003 for netravati showed more radiogenic 87sr 86sr in netravati compared to narmada indicating influence of source rocks in their watersheds weak correlation of sedimentary 87sr 86sr and 143nd 144nd with al and chemical index of alteration cia in silicate fraction indicate that isotopic compositions are primarily controlled by their sources and not by chemical weathering in both the rivers provenance of sediments in narmada is dominated by their supply from deccan deposits with secondary supply from mid late proterozoic vindhyan along with mesoproterozoic to mesoarchean tdmnd ages sediments from netravati reflected signatures of peninsular gneisses dominant with gneisses schists and granodiorite along with paleoarchean tdmnd ages based on variability of 87sr 86sr and 143nd 144nd present study highlight that sediment supplies from tributaries to the mainstream in narmada is inadequate as compared to that in netravati 87sr 86sr and 143nd 144nd signatures in narmada and netravati are comparable with global rivers this article is protected by copyright all rights reserved

deep circulation changes in the labrador sea since the last glacial maximum new constraints from sm nd data on sediments sm nd concentrations and nd isotopes were investigated in the fine fraction of two labrador sea cores to reconstruct the deep circulation patterns through changes in sedimentary supply since the last glacial stage three sources are involved the north american shield palaeozoic rocks from northeastern greenland and mid atlantic volcanism the variable input of these sources provides constraints on the relative sedimentary supply in conjunction with inception of deep currents during the last glacial stage a persistent but sluggish current occurred inside the labrador basin an increasing discharge of volcanic material driven by the north east atlantic deep water is documented since 14 3 kyr signaling the setup of a modern like deep circulation pattern throughout the labrador irminger and iceland basins during the last deglacial stage the isotopic record was punctually influenced by erosion processes related mainly to ice sheet instabilities especially 11 4 10 2 and 9 2 kyr ago

effects of juniper removal and rainfall variation on tree transpiration in a semi arid karst evidence of complex water storage dynamics brush removal is widely practiced as a tool for increasing groundwater recharge but its efficacy depends greatly on the way in which the removed species interact with the hydrological system relative to the vegetation replacing it we examined the effects of ashe juniper removal in the recharge zone of the edwards aquifer texas usa a karst aquifer the study was conducted in an ashe juniper juniperus ashei live oak quercus fusiformis woodland on a hill slope composed of rocky shallow soils over fractured limestone bedrock ashe juniper is a native species that has been encroaching grasslands and savannas over the past century in september 2008 a plot was cleared of 90 of its juniper trees tree transpiration predawn water potentials and vegetation cover across the cleared plot and an adjacent reference site were measured from may 2009 to december 2011 stand level tree transpiration from may 2009 to march 2010 was diminished by a severe summer drought in 2009 from which trees were slow to recover subsequently tree transpiration was 5 10 higher in the woodland compared to the clearing for all of 2011 also a drought year tree transpiration in the woodland exceeded precipitation inputs indicating a high capacity for water storage at the study site however site differences for oak trees were generally larger than for juniper trees while juniper removal accounted for a 431 mm year 1 difference in tree transpiration between sites vegetation cover in the clearing increased from 42 to 90 over two years suggesting that understory growth was increasingly compensating for the loss of juniper transpiration we conclude that the removal of a relatively shallow rooted tree when replaced with herbaceous vegetation and low shrubs has little effect on deep recharge by contrast successive years of precipitation extremes may be more effective increasing recharge by lowering the water transport capacity of trees in the aftermath of severe drought copyright 2016 john wiley sons ltd

some aspects of the geochemistry provenance and palaeoclimatology of the torridonian of nw scotland geochemical data mostly from mudstones are used in an attempt to investigate some aspects of the palaeoclimatology and provenance of the torridonian succession in nw scotland the basal part of the stoer group which has been interpreted as glaciogenic is thought to have formed in a warm arid setting the presence of oscillation ripples and desiccation cracks in mudstones containing isolated clasts is thought to preclude their interpretation as ice rafted debris some aspects of the major element geochemistry of the stoer group mudstones suggest deposition in an environment with little weathering but chemical weathering is inhibited in both frigid and arid settings and sedimentological evidence favours the latter the stoer group mudstones are enriched in mg ca and na relative to the torridon group samples which are much closer in composition to an average shale estimate paas the cr and ni contents of the stoer mudstones are significantly higher than those of the torridon group samples there is however no evidence that enrichment in these elements was due to contamination with volcanic material like that of the stac fada member the scourian basement appears to be an adequate source of the ni and cr in the stoer group sediments th sc ratios are higher in the torridon than in the stoer mudstones this difference is interpreted as indicating that the stoer mudstones were largely derived from local archaean sources but that the torridon group mudstones incorporated materials from a much wider provenance including younger and recycled materials evidence from rare earth elements also provides evidence for different source terrains for the stoer and torridon groups the torridon group mudstones are more weathered have a higher ree content and display a more prominent eu anomaly lower value for eu eu than do the stoer samples these results support evidence from th sc ratios that the torridon group was derived from a more varied recycled and granite rich terrain than the stoer much of which appears to have relatively local provenance the geochemistry of mudstones can shed considerable light on problems of provenance and palaeoclimatology because many useful trace elements tend to be concentrated in such fine grained rocks and some aspects of their major element chemistry may be related to climatic factors

geochemistry of pelitic and psammopelitic precambrian metasediments from southwestern sri lanka implications for two contrasting source terrains and tectonic settings most of the pelitic and psammopelitic metasediments of southwestern sri lanka are compositionally transitional between shales and greywackes and are of two isotopically distinct types metasediments of the northern part have nd model ages of 1 5 ga and belong to the relatively younger nd model age province of wanni complex wc model ages of two southerly located samples are 2 8 ga being compatible with those of the highland complex hc in accordance with mostly mesoproterozoic to late archaean crustal residence ages cr ni la th and ree data also suggest that the sources of these metasediments are plagioclase fractionated post archaean upper crustal material crustal differentiation of source terrains corresponding to the hc and the wc probably occurred at distinctly different time intervals significant differences exist between the major and trace element chemistry of the metapelites from the wc north and the hc south suggesting derivation from two different source terrains metasediments of the south are slightlymmore siliceous low in sc and v and highly enriched in lree 220 ppm their sources have been chemically evolved felsic igneous rocks and or recycled sediments relatively high v sc feo mgo tio2 and slightly low sio2 in the rocks of the wc indicate contribution of more basic sources cia chemical index of alteration estimates and comparative alkali alkaline earth element patterns suggest relatively fresh source material the o isotope data indicate that the pre metamorphic isotope signatures are preserved and the clay component of the original sediments mainly consisted of illite typifying continental weathering conditions sediments of the south hc were probably deposited in a passive continental margin continental rift environment while those of the northern part wc were probably formed at an andean type active continental margin the two units were tectonically juxtaposed prior to pan african granulite metamorphism

a model for continental crust genesis by arc accretion rare earth element evidence from the irish caledonides abstract the formation of continental crust is a complex problem with a paradox at its center continental material is believed to form by arc magmatism a model that does not reconcile the bulk mafic and light rare earth element lree depleted composition of intra oceanic arcs with the andesitic lree enriched composition of continents we present evidence supporting an arc origin for continental crust by demonstrating significant changes in magmatic chemistry during arc continent collision we use as an example the connemara region of the western irish caledonides where metamorphism and orogenesis of dalradian sedimentary sequences record the collision of the oceanic lough nafooey arc with the passive margin of laurentia at 475 ma arenig this arc was mafic and lree depleted during its oceanic activity during collision rhyolites more lree enriched than the surrounding continental crust were erupted while the mid crust was intruded by similarly lree enriched gabbro and diorite crystal fractionation caused lree enrichment to exceed that expected by assimilation of continental crust alone we propose that subsequent loss of the corresponding lower crustal cumulates into the mantle removed this lree depleted material from the net crust added to the continent the combined processes of crystal fractionation and lower crustal loss during arc continent collision drive the average bulk arc composition toward that of average continental crust

impact of grout curtains on karst groundwater behaviour an example from the dinaric karst grout curtains are vertical grout walls installed in the ground in karst terrains their construction is primarily connected with dams and reservoirs their main role is to increase watertightness and prevent progressive erosion blocking possible seepage paths along karst fissures and conduits in this paper changes in the behaviour of the groundwater level gwl and the water temperature in nine deep piezometers which were caused by the construction of a grout curtain at the ale reservoir on the cetina river croatia were analysed the total length of the grout curtain is 3 966 m it spreads 120 m below the dam the most of analysed data is from the period after the dam had been built only few data and figures concern the comparison between pre and post dam periods the hourly data of the gwl and the water temperature were analysed for the period between 1 sep 2008 at 02 h to 31 dec 2009 at 23 h 11 687 hours total in six deep piezometers marked in the text and figures as 1 2 3 4 5 and 6 for three piezometers marked in the text and figures as a b and c some discontinuous measurements of the gwl and the water temperature were available for analysis the construction of the grout curtain made strong sudden and possibly dangerous changes to the characteristics of the aquifer and the circulation of groundwater in the local area special attention is paid to analyses of the behaviour of the hourly gwl data measured in the piezometers pairs two neighbouring piezometers one inside and the other outside of the grout curtain during more than 80 of the analysed period the gwl was higher in the piezometer inside the grout curtain than the one outside of it the intensity and range of the dynamics of gwl was higher in piezometer outside the grout curtain than the inside ones after the construction of the grout curtain the maximum measured hydrostatic pressure on some parts of the grout curtain was about 40 m it changes quickly in both time and direction the water temperature was found to be similar in all of the measured piezometers and it varies between 10 2 and 15 7 oc with an average value of 12 7 oc

geochronology and petrogenesis of shoshonitic igneous rocks luzong volcanic basin middle and lower yangtze river reaches china abstract the luzong volcanic basin has a unique tectonic background being located at the northeastern margin of the yangtze craton and the foreland of the dabie sulu orogen near the intersection of the renowned tanlu and yangtze river faults the volcanic and subvolcanic rocks in the basin are characterized by high potassium contents and are rich in alkali elements and belong to a typical shoshonite series geochemically these rocks are depleted in high field strength elements such as nb and ta and enriched in highly incompatible elements such as rb th u k and light rare earth elements nd and sr isotope compositions combined with elemental geochemical characteristics indicate that the parental magmas were formed mainly by partial melting of enriched subcontinental lithospheric mantle the magmas underwent minor or negligible contamination by upper crustal rocks or fractional crystallization at low pressures i e 1 5 gpa dominated by the removal of clinopyroxene and fe ti oxides the volcanic rocks of the luzong basin can be divided into four formations which from early to late are the longmenyuan zhuanqiao shuangmiao and fushan formations each separated by clear gaps in eruptive activity in this study we obtained zircon u pb shrimp ages from two subvolcanic samples from the longmenyuan and zhuanqiao formations which yield emplacement ages of 132 1 ma and 131 1 ma these data combined with ages reported by other workers show that the duration of volcanism in the luzong basin and the whole middle and lower yangtze river reaches was very short 8 ma we consider that in the early cretaceous the foreland area of the dabie orogenic belt was under extension influenced by the relative motion of the pacific and eurasian plates and by sinistral displacement along the tanlu fault at this time rapid mechanical delamination of thickened lithosphere caused lithospheric thinning and resultant asthenospheric upwelling in the middle and lower yangtze river region and the dabie orogenic belt these deep geological and tectonic events in turn produced the shoshonite volcanic rocks in the luzong basin

nd and sr isotopic characterization of the wrangellia terrane and implications for crustal growth of the canadian cordillera nd and sr isotopic data are reported from samples of most of the major lithologic units of the wrangellia terrane exposed on vancouver island and the queen charlotte islands initial epsilon nd values range from 1 0 to 7 3 and initial 87 sr 86 sr ratios range from 0 70323 to 0 70481 these ratios are similar to those of modern island arcs and demonstrate the unevolved juvenile nature of this terrane these data indicate that wrangellia probably resided in an intra oceanic environment until its accretion to north america nd crustal residence ages for clastic sedimentary rocks of wrangellia mean t cr 0 77 pm 0 33 ga t dm 0 57 pm 0 35 ga are much closer to their stratigraphic ages than is the case for the ages of many other phanerozoic sedimentary rocks thus providing strong evidence for phanerozoic crustal addition to north america early proterozoic crustal components cannot comprise more than about 6 of wrangellia therefore the terrane consists of 94 new mantle d

samarium neodymium isotope stratigraphy of the lunde and statfjord formations of snorre oil field northern north sea two sequences of fluviatile sediments from snorre oil field are investigated by the sm nd isotopic method the results illustrate distinctly different source areas for the upper triassic upper member of the lunde formation and for the lower jurassic statfjord formation the lunde formation has sm nd provenance ages mainly in the range 1500 to 1700 ma which is not diagnostic of a specific source area the statfjord formation has provenance ages in the range 1700 to 2150 ma this is old within the context of source areas in the hinterland of the northern north sea and provenance partly from the archaean lewisian shield to the northwest is suggested intensive sampling through the statfjord formation in one well illustrates that the provenance ages evolve systematically with time the pattern provides a detailed record of how source areas evolved during deposition of these strata the possibility is recognized of correlating changes or trends in provenance between wells the data also suggest that sm nd ratios and isotopic compositions of these rocks are not significantly fractionated between fine and coarse grained sediments by mechanical or diagenetic processes

neodymium and strontium isotopic dating of diagenesis and low grade metamorphism of argillaceous sediments the behaviour of the rb sr and sm nd isotopic systems with increasing degree of hercynian metamorphic overprint was studied along a transect in cambrian shales of northwestern morocco clay fractions of 0 2 to 2 6 m size from five samples were investigated representing a range from nonmetamorphic to epizonal metamorphic conditions the samples were washed in cold l n hc1 prior to digestion to separate soluble exchangeable rb sr sm and nd from amounts of these elements fixed in the crystallographic sites of the minerals and to analyze both components separately the results reveal that the rb sr isotopic system is dominated by sr hosted by clay mineral phases both detrital and authigenic illite and chlorite and carbonate hosted soluble sr isotopic homogenization of sr occurred during hercynian metamorphism yielding ages between 309 and 349 ma the sm nd isotopic system on the other hand is dominated by cogenetic apatite and fe oxide hydroxide both having high contents of leachable rees the leachates yield a sm nd isochron age of 523 72 ma indicating diagenetic equilibrium between apatite and fe oxide hydroxide fine grained clay fractions of 0 2 m show inheritance of a detrital nd component the study demonstrates that the diagenesis of the investigated argillaceous sediments can be dated by the sm nd chronometer in authigenic cement phases the isotopic system of these minerals apatite fe hydroxide oxide was homogenized during authigenic mineral growth in a sediment that was flushed by diagenetic fluids and had abundant primary or secondary interconnected pore space the hercynian metamorphic overprint caused partial isotopic rehomogenization of the adsorbed and clay hosted portion of the sr as well as of the carbonate hosted sr the sm nd system in the cement phases survived this metamorphism this results in decoupling of the two isotopic systems and allows the dating of diagenesis on the one hand sm nd and metamorphism on the other hand rb sr

tectonic setting of avalonian volcanic and plutonic rocks in the caledonian highlands southern new brunswick canada the caledonian highlands of southern new brunswick consist of late proterozoic to cambrian rocks generally considered typical of the avalon terrane of the northern appalachian orogen mainly tuffaceous volcanic and sedimentary rocks of the broad river group and cogenetic dioritic to granitic plutons with ages ca 620 ma form most of the eastern caledonian highlands they have petrological features indicative of origin in a continental margin subduction zone significantly younger ca 560 550 ma dacitic to rhyolitic lapilli tuffs and flows laminated tuffaceous siltstone basaltic and rhyolitic flows and clastic sedimentary rocks of the coldbrook group form most of the western highlands and occur locally throughout the highlands the mainly tuffaceous lower part of the group has been intruded by gabbroic and syenogranitic plutons that are interpreted to be cogenetic with basaltic and rhyolitic flows in the upper part of the group this voluminous subaerial magmatism may have formed during postorogenic ex

behavior of sm and nd in a lateritic soil profile a study of lateritic soils and samples of ground and river waters was carried out in the nsimi zoetele a tropical watershed in the southern cameroon the nd isotopic compositions and concentrations of nd and sm were determined it was found that the nd isotopic composition of the river waters was much more radiogenic than the parent rocks and that the nd in the waters is not homogeneous but is carried by different dissolved and complexed components that are not isotopically homogenized the soil profile shows a regular increase in e nd going from the parent rock e nd 36 to e nd 18 near the top of the profile the nd transported in the river is thus not representative of the parent rock but reflects the results of differential weathering of constituent minerals and the redeposition of ree in phosphates and a significant contribution of radiogenic nd from dust the concentration of nd in the river water is far above that found in temperate climate rivers and thus this type of tropical river may play a dominant role in the marine nd and ree budget it is suggested that the correlation of ree with doc is related to doc fixing some dissolved ree but that the ree in solution is governed by other mechanisms no major shifts were found in sm nd however a regular progression from the parent rock through the lateritic profile was found the upper laterite profile shows large almost uniform depletions in all ree below tb and enrichment above complementary behavior was found in the lower part of the section the concentration of nd relative to the immobile elements zr and ti in the laterite is depleted by a factor of 10 th nd and sm are enriched in the lowest zone sampled and must reflect redeposition of ree from the upper part of the weathering section and is associated with phosphate formation it is concluded that the soil evolution involves both differential dissolution of primary phases from the parent rock significant to major input of ree from atmospheric dust from other regions and the formation of diagenetic phases particularly phosphates

water geochemical characteristic variations in and around a karst dominated natural reserve area southwestern china this paper reports original data on the physical and chemical parameters of precipitation river water and groundwater in and around the longhushan nature reserve area located in southwestern china karst region and provides a preliminary characterization of the hydrogeochemical process governing the natural water evolution in this area the rainfall and river water mainly pertain to the hco3 ca2 type and groundwater mainly pertain to the hco3 ca2 mg2 type the hco3 was the predominant anion and ca2 was the predominant cation in all waters respectively the gibbs boomerang envelop model the 1 1 relationship of na plus k versus cl as well as the 1 1 relationship of ca2 plus mg2 versus hco3 all suggested geochemical weathering is the main controlling factor for the geochemical compositions of this natural water in surface water the mg2 ca2 ratios ranged from 0 32 to 0 42 and the na ca2 varied between 0 04 and 0 05 in the groundwater the mg2 ca2 ratios varied from 0 37 to 0 62 and were below the ideal ratio of 0 8 these ratios showed the presence of a dolomite source analysis of trace elements showed that as b pb se sr v and zn elements were abundant in the natural water during summer in this region

nd and sr isotopic study of volcanic rocks from japan two older granitic rocks and some selected quaternary volcanic rocks from the japanese islands were analyzed in a reconnaissance study for the purpose of examining the relationships between nd and sr isotopic abundances and the megatectonic structure around the japanese islands model ages of 0 9 ae were determined by the nd and sr methods on a paleozoic gneiss which confirms that a relatively ancient acidic basement exists in the japanese islands the nd and sr isotopic data show that the cretaceous granodiorite is the result of partial melting of older crust the nd of tholeiitic rocks from the izu arc gives e nd ranging from 8 3 to 9 3 and with the corresponding e sr from 14 5 to 18 5 these results are identical to those found for the mariana arc these values are distinctly lower than typical morb by around 1 2 eu this difference in e nd between arcs and morb is attributed to the contribution of oceanic sediments to the partial melts produced during subduction of oceanic crust the hakone volcano is clearly confirmed as belonging to an oceanic source by nd isotopic results e sr e nd values of the volcanics from a section along the fossa magna show a clear indication that they are a blend of oceanic mantle material and continental crustal material the crustal component clearly increases in going from south to north volcanics across the northeast japan arc also show a distinct correlation of e sr e nd related to the position relative to the active subduction zone but with the opposite trend these relationships of the present isotopic pattern and the zonal arrangement relative to the subduction zone suggest the former existence of a local spreading center in the japan sea in general there appear to be regular isotopic relationships between the izu mariana oceanic island arc and the continental island arc of japan which indicates that partially melted or assimilated older continental basement is admixed with young rising oceanic arc magmas

evolution of cambrian and early ordovician arcs in the kyrgyz north tianshan insights from u pb zircon ages and geochemical data abstract geochronological geochemical and structural studies of magmatic and metamorphic complexes within the kyrgyz north tianshan nts revealed an extensive area of early palaeozoic magmatism with an age range of 540 475 ma during the first episode at 540 510 ma magmatism likely occurred in an intraplate setting within the nts microcontinent and in an oceanic arc setting within the kyrgyz terskey zone in the south during the second episode at 500 475 ma the entire nts represented an arc system these two phases of magmatism were separated by an episode of accretionary tectonics of uncertain nature which led to obduction of ophiolites from the kyrgyz terskey zone onto the microcontinent the occurrence of zircon xenocrysts and predominantly negative whole rock nd t values and hf t values of magmatic zircons suggest a continental setting and melting of precambrian continental sources with minor contributions of palaeozoic juvenile melts in the generation of the magmatic rocks the late cambrian to early ordovician 500 475 ma arc evolved mainly on mesoproterozoic continental crust in the north and partly on oceanic crust in the south arc magmatism was accompanied by spreading in a back arc basin in the south where supra subduction ophiolitic gabbros yielded ages of 496 to 479 ma the relative position of the arc and active back arc basin implies that the subduction zone was located north of the arc dipping to the south variably intense metamorphism and deformation in the nts reflect an early ordovician orogenic event at 480 475 ma resulting from closure of the djalair naiman ophiolite trough and collision of the djel tau microcontinent with the northern margin of nts comparison of geological patterns and episodes of arc magmatism in the nts and chinese central tianshan indicate that these crustal units constituted a single early palaeozoic arc and were separated from the tarim craton by an oceanic basin since the neoproterozoic

disturbances in the sm nd isotope system of the acasta gneiss complex implications for the nd isotope record of the early earth abstract the whole rock 143nd isotope record of the acasta gneiss complex agc has been used to argue for the development of both depleted mantle and enriched crustal reservoirs during the hadean the 147sm 143nd isotope compositions of rocks from agc however fall on an array with an errorchron date of 3 3 ga despite the majority of samples yielding substantially older zircon u pb ages this has led to the suggestion of a major sm nd resetting event at this time in the agc to better understand the sm nd bulk rock systematics of the agc we investigate the u pb age and sm nd isotope compositions of apatite and titanite from the agc using the laser ablation split stream lass method apatite from all samples yield broadly similar u pb dates of 1 89 to 1 83 ga in agreement with resetting during the 1 9 ga wopmay orogen the sm nd isotope compositions of the apatite however lie off the wr errorchron and show a high degree of initial nd isotope heterogeneity conversely titanite sm nd systematics are consistent with the 3 3 ga whole rock errorchron further supporting sm nd modification at 3 3 ga taken together these show that the oldest rocks in the agc underwent at least two post crystallization events at 3 3 and 1 9 ga that modified the sm nd isotope system these results also demonstrate the relative mobility of the sm nd isotope system during orogenic events which may compromise the ability to determine robust bulk rock 143nd isotope signatures

geology and geochemistry of the late precambrian coldbrook group near saint john new brunswick the late precambrian coldbrook group comprises basal basaltic flows and pyroclastic rocks fragmental andesitic to rhyolitic rocks and minor capping sedimentary strata all deformed and metamorpho

paleoproterozoic crustal history of the southwestern grenville province evidence from nd isotopic mapping nd isotopic mapping in the north bay area of the central gneiss belt southwestern grenville province has revealed the precise trend of a tdm model age line developed between the uplifted southern margin of the archean superior craton tdm 2 7 ga and a paleoproterozoic allochthon tdm 1 9 ga separating these two crustal blocks is a narrow zone of gneisses with intermediate tdm ages these transitional gneisses are interpreted to reflect a remnant fault or ductile shear zone of uncertain age along which crustal material from both blocks mechanically mixed during their juxtaposition accordingly the nature of the tdm line in the north bay area is interpreted to be tectonic in the temiscaming area widespread exposures of mature metasedimentary gneisses are shown by their tdm ages to be dominantly of paleoproterozoic provenance these results are consistent with the existing detrital zircon geochronology inferring a maximum depositional age of 1 7 ga the anorogenic chemistry of the north bay o

the erosion of the alps nd isotopic and geochemical constraints on the sources of the peri alpine molasse sediments abstract sm nd data from molasse sedimentary deposits from eastern france and switzerland are used to quantify the erosion of the alps during the oligocene and miocene the average present day nd value of the continental sedimentary deposits increases from 11 for cretaceous and eocene substratum to 9 for the first oligocene molasse sediments this increase requires the erosion of mesozoic marine sediments to explain the average nd value 9 1 of the rupelian and lower chattian sediments then the average nd value 9 7 and the chemical compositions of the upper chattian and aquitanian sediments are consistent with the erosion of granitic rocks of the variscan crust this change in source allows us to define a second cycle in the peri alpine molasse which began at 24 5 ma with the deposition of the calcaires et dolomies this basin wide unit represents the sedimentary record of a halt in the input of alpine detritus in the western part of the molasse basin and we suggest that the limit between lower and upper chattian sediments at 24 5 ma corresponds to a major tectonic event in the alps a further increase of 1 nd unit recorded by the burdigalian marine sandstones average of 8 defines a third molasse cycle which resulted from the erosion of late variscan alkaline granites having high nd values between 1 8 and 5 2 this study concludes that the erosion of the alps increased the nd values of the sedimentary mass in two stages 1 during the rupelian and lower chattian by recycling of marine chemical sediments having nd values similar to that of tethys seawater nd 8 and which represent 90 of the eroded materials and 2 during the burdigalian by the erosion of a variscan crust representing at least 20 of the eroded material half of this variscan material was composed of alkaline granites with high nd values suggesting the addition of mantle derived material to the crust during late variscan events

non linearities in drip water hydrology an example from stump cross caverns yorkshire drip rate data have been collected at 15 min intervals at six locations in stump cross caverns n england since 1998 the different drip sites cover a wide range of drip rates from 2 drips s to 2 drips h and in general the variability of drip rate increases with mean drip rate in our continuous data sampling we observe rapid discharge increases which appear to be synchronous between drips sites and which can be explained by flow switching of the water overlying the cave during times of high infiltration rate such as intense rain storms or rapid snowmelt a test for non linearity white test in the drip series provides very strong evidence that many of the drip sequences are non linear we conclude that at our drip sites there is a non linear input weather and non linearities within the karst system leading to non linear dripping which is independent of drip rate our results have implications for stalagmite palaeoclimatology where such widespread non linearities have not been taken account of

u pb age constraints on the stratigraphy and tectonic history of the avalon terrane new brunswick canada six new u pb ages for avalonian plutonic and volcanic rocks from the eastern caledonia highlands southern new brunswick indicate that magmatic activity occurred between 625 600 ma ago with another probably separate major episode at ca 550 ma this gap in igneous activity is consistent with differences in the metamorphic and deformational character of rocks from the two episodes the 625 600 ma activity was calc alkalic and probably occurred in an andean type magmatic arc it correlates with most volcanism and plutonism in the type avalon terrane of newfoundland the ca 550 ma activity formed bimodal volcanic rocks and high level plutons probably in an extensional setting u pb ages of xenocrystic zircons from avalonian igneous rocks indicate both archean and proterozoic components at depth in avalonian basement an observation consistent with pb isotopic signatures which suggest an old radiogenic crustal source the african craton for the magmatic products

nd and sr isotope systematics of clastic metasediments from isua west greenland identification of pre 3 8 ga differentiated crustal components recent field work on the isua metasediments has established that there are two lithological sequences a and b which are divided into a number of distinct formations each clastic metasedimentary unit has a relatively unique trace element signature the depleted mantle sm nd model ages of samples from all major units range from 3 59 to 3 98 ga whereas rb sr model ages cover a very wide range 1 9 4 6 ga the samples from the sequence a felsic gneiss formation a6 yield a relatively good rb sr isochron age of t 3 71 0 07 ga the sequence b samples do not yield a rb sr isochron however some of the samples plot close to the a6 rb sr isochron and sequences a and b appear to have essentially the same deposition age the sm nd data for both sequences yield initial end values in the range 1 to 3 for a deposition age tstrat 3 64 ga if tstrat 3 81 ga the range is 0 4 this range appears to reflect real variability of initial end values corresponding to the time of deposition data trends in end versus 1 nd diagrams suggest at least three distinct components in each of sequences a and b model age calculations suggest that some of these components must be derived from continental crustal sources that predate the time of deposition of these sediments by as much as 0 4 b y other components appear to be derived from volcanic sources that are roughly coeval with sediment deposition the very high initial end values implied for early depleted mantle sources 2 to 4 suggest a very large pre 3 8 ga continental crust alternatively these high values could reflect an early terrestrial mantle with highly fractionated cumulate layers that formed in a 4 5 ga magma ocean

episodic growth of the gondwana supercontinent from hafnium and oxygen isotopes in zircon it is thought that continental crust existed as early as 150 million years after planetary accretion but assessing the rates and processes of subsequent crustal growth requires linking the apparently contradictory information from the igneous and sedimentary rock records for example the striking global peaks in juvenile igneous activity 2 7 1 9 and 1 2 gyr ago imply rapid crustal generation in response to the emplacement of mantle super plumes rather than by the continuous process of subduction yet uncertainties persist over whether these age peaks are artefacts of selective preservation and over how to reconcile episodic crust formation with the smooth crustal evolution curves inferred from neodymium isotope variations of sedimentary rocks detrital zircons encapsulate a more representative record of igneous events than the exposed geology and their hafnium isotope ratios reflect the time since the source of the parental magmas separated from the mantle these model ages are only meaningful if the host magma lacked a mixed or sedimentary source component but the latter can be diagnosed by oxygen isotopes which are strongly fractionated by rock hydrosphere interactions here we report the first study that integrates hafnium and oxygen isotopes all measured in situ on the same precisely dated detrital zircon grains the data reveal that crust generation in part of gondwana was limited to major pulses at 1 9 and 3 3 gyr ago and that the zircons crystallized during repeated reworking of crust formed at these times the implication is that the mechanisms of crust formation differed from those of crustal differentiation in ancient orogenic belts

effects of partial and full pipe flow on hydrochemographs of logsdon river mammoth cave kentucky usa summary logsdon river within kentucky s mammoth cave system drains the 25 km2 cave city groundwater basin temperature specific conductance stage and velocity were measured at the river s downstream end within the cave with 2 min resolution for one year beginning on may 5 1995 new interpretation of these data show relationships to the conduit s geometry and fluid transport behavior the 37 observed storm hydrographs chemographs are classified into two groups open channel flow and pipe flow conduit filled in the 16 pipe flow events logsdon river exceeded the capacity of its conduit raising the water table above the conduit ceiling with some storm water thus temporarily stored within the aquifer adjacent to the conduit pipe flow events were characterized by depression of specific conductance spc before peak discharge a peak in spc at peak discharge and a second depression in spc after peak discharge the first spc minimum represents the maximum concentration of passing storm water and the second is interpreted as the result of recent storm water draining back into the conduit having been temporarily stored in the aquifer adjacent to the conduit mean velocity decreases in the transition from partial to full pipe flow due to increased head loss at full pipe flow compared to nearly full pipe flow each of the open channel flow cases shows a depression in spc either coincident with or after peak discharge while the hydrochemographs of pipe flow are mainly controlled by the aquifer conduit network geometry in open channel cases they are mainly controlled by external recharge conditions including behavior of sinking streams

rare earth elements and neodymium isotopes in ferromanganese oxide coatings of cenozoic foraminifera from the atlantic ocean abstract an evaluation has been made of the method of establishing the ree contents and patterns and nd isotopic compositions of sea water over cenozoic time from their record in the femn oxide coatings of foraminiferal calcite using 0 60 ma samples from the rio grande rise dsdp site 357 it has been established that the ree contents of the coatings are generally similar to those of recent samples however in the cenozoic samples the surface coatings have been diagenetically modified under suboxic conditions resulting in a distinctly different ree pattern although the original 143 nd 144 nd ratios appear to have been preserved the nd isotopic curve for cenozoic sea water in the s atlantic shows clear temporal trends although these are not so extreme as to show 143 nd 144 nd ratios outside the range observed in modem sea water with the principal exception of the oldest samples there is an approximate inverse relationship between the nd and sr isotopic compositions of the foraminifera it is suggested that the changes reflect both global changes in the relative proportions of nd and sr derived from continental input and from the weathering of volcanic debris together with short term and local variations to which the sr curve is insensitive reflecting the different response times of the two elements to changes in oceanic input functions the nd isotope curve appears to be a potentially useful tracer of ocean palaeochemistry

karst geomorphology of carbonatic conglomerates in the folded molasse zone of the northern alps austria germany abstract the folded molasse zone of the northern alps consists of clastic sedimentary rocks that are usually not considered to be karstifiable however large areas within this zone are composed of carbonatic conglomerates numerous karst landforms have recently been discovered but are not recorded on official maps and in the literature therefore a research programme was initiated at the hochgrat site austria germany that included geomorphological mapping and characterisation of the karst phenomena both fracture controlled and hydrodynamically controlled karren were observed on conglomerate outcrops the predominant karst landforms dolines are typically circular funnel shaped most often 2 to 9 m in diameter 1 to 6 m deep and frequently act as swallow holes poljes that are atypically small 1 ha occur in either glacial cirques or syncline depressions are flat floored and lined with sediment and soil and drain underground via swallow holes short caves springs with marked discharge variations and estavelles are further evidence for karst development karstic landforms are widespread in carbonatic conglomerate terrains but their dimensions are smaller than in typical limestone karst the practical implications of these findings are also briefly mentioned in this paper

hydrology of cave drip waters at varying bedrock depths from a karst system in southeastern australia the study of how cave drip water discharge responds to recharge events is fundamental to evaluating the potential of actively forming speleothems as high resolution climate archives most previous research has focused on caves of the northern hemisphere middle latitudes where recharge is strongly seasonal few studies have explored drip water behaviour from regions where the expected seasonal rainfall pattern is significantly perturbed on an irregular basis by changing regional atmospheric circulation patterns here we report the results of a 4 year study of cave drip water climate relationships from two caves in eastern australia the discharge of 10 drip sites located beneath bedrock thicknesses of 12 22 and 45 m was monitored either continuously using automated infrared sensors or at discrete approximately monthly intervals and compared with local rainfall and water balance data the study period traversed two major droughts including the severe 2002 2003 el nino drips at 12 and 22 m depths responded almost simultaneously to individual recharge events although the time lag between individual events varied according to the volume of recharge and pre event storage overall a steady decline in discharge is evident through the moisture deficit period with increased flows through phases of positive water balance speleothems growing at these and similar shallow chamber sites have potential for reconstructing palaeo rainfall trends at high resolution although the highly variable nature of year to year recharge would make it difficult to obtain data on a calendrical time scale drips at 45 m depth did not respond consistently to individual recharge events and displayed hydrological behaviour markedly dissimilar to one another and to the near surface drip sites indicating great complexity in karst architecture and the absence of fissure flow although speleothems at this depth may well preserve information on longer term rainfall trends their potential to encode a palaeo rainfall variability signal at interannual resolution is poor copyright 2007 john wiley sons ltd

recognising different sediment provenances within a passive margin setting towards characterising a sediment source to the west of the british late carboniferous sedimentary basins to investigate whether sediments with subtly different provenances could be recognised within a passive margin setting samples were taken from westphalian sedimentary rocks of the pennine basin south wales coalfield culm basin of britain and from northern ireland although previous work has shown that 3 major source areas were responsible for the infill of the pennine basin this study is restricted to sediments believed to have been derived from the west their nominally similar western provenance was confirmed using sm nd isotope techniques and their deposition in a passive margin setting was established using elemental discrimination diagrams while the overall sediment provenance may have been from the west the trace element geochemistry indicates that at least two major sediment pathways can be distinguished plots of eu eu gdn ybn along with ternary plots of cr v ti zr gdn ybn or sc cr suggest different source areas for the culm basin and the south wales coalfield in the culm basin the cr v ratio generally exceeds 1 25 with a small eu anomaly and a low gdn ybn ratio the cr v ratio is less than 1 25 in the south wales with a larger eu ratio and a higher gdn ybn than the culm basin significant separation of the culm basin and the south wales coalfield during the early westphalian by the bristol channel bray fault may have been a factor contributing to the provenance differences late carboniferous dextral displacement along this fault brought these basins into close juxtaposition and it is unlikely that the bristol channel landmass formed a common source area for these two basins

coupled sm nd and u pb systematics in late caledonian granites and the basement under northern britain the british late caledonian granites display a close correspondence between inherited u pb systematics in zircons and initial end indicating that both were controlled by the age of a major component of continental crust the data confirm and refine previous models of a basement comprising young crust in the south which includes arc and oceanic crust scrapings and progressively older continental crust northwestwards across scotland

isotopic mapping of age provinces in precambrian high grade terrains sri lanka nd model ages of amphibolite and granulite grade rocks in sri lanka form a simple regional pattern that broadly correlates with mappable geological units and is in effect an isotopic map of the island s basement the granulite grade units of the highland group and southwest group have model ages of 2 2 3 0 ga indicating derivation mainly from late archean sources they are bounded to the east and west by late proterozoic gneisses of the vijayan complex with model ages of 1 1 2 0 ga the isotopic data identify three distinct crustal provinces and are not consistent with earlier suggestions that the vijayan gneisses are retrograde equivalents of the highland granulites sri lanka is not a direct continuation of the archean dharwar craton of southern india identification of vijayan type juvenile crustal terrains in other gondwana fragments may play a key role in determining the precise attachment of southern india sri lanka in eastern gondwana

samarium neodymium elemental and isotopic systematics in sedimentary rocks abstract trace element sm nd th sc and nd isotopic data for sedimentary rocks are examined in order to evaluate 1 1 possible secular trends in the composition of the sedimentary mass and upper continental crust 2 2 the role of tectonic setting in controlling the chemical and nd isotopic composition of the sedimentary mass when plotted against either sedimentation age or average provenance age determined mainly from nd model ages sm nd in sedimentary rocks decreases abruptly from about 0 21 to 0 19 at the archean proterozoic transition consistent with a change towards a more felsic upper crustal composition the change is only somewhat less pronounced for turbidite sediments than for those of continental affinity a trend toward increasing sm nd approaching or exceeding archean values is observed for phanerozoic turbidites this latter change is interpreted as indicating undifferentiated young crust as a component in the sediment which has been lost from the older post archean record due to sedimentary and igneous intracrustal recycling processes when plotted against sedimentation age th sc ratios exhibit a trend directly comparable to that of sm nd in this case th sc increases abruptly at the archean proterozoic boundary from about 0 5 to 1 0 and then decreases to about 0 7 during the phanerozoic nd isotopic composition of modern sediments is affected by tectonic association with those deposited at active margin settings tending to have higher nd reflecting younger provenance and higher and more scattered sm nd reflecting less homogenized and differentiated provenance it is likely that these distinctions can be traced back for about 1 2 ga but with the current data base are not readily resolved in older sedimentary rocks the degree to which the preserved sedimentary mass is open to new additions from the mantle either through replacement during sedimentary recycling or sediment mass growth is highly variable but averages about 15 25 during the phanerozoic

the provenance and crustal residence ages of british sediments in relation to palaeogeographic reconstructions 24 smnd isotope analyses of fine grained phanerozoic and modern clastic sediments from britain and quebec are presented in combination with published data they have been used to calculate crustal residence ages tcr and to assess the provenance of the british sedimentary mass sediments now preserved on either side of the suture formed by the closure of the iapetus ocean ca 400 ma ago were derived from isotopically distinct source regions sediments north of the suture are characterised by1 7 tcr 2 8 ga whereas those to the south exhibit a smaller range and an average value of 1 6 ga the northern and southern source regions were most probably laurentia and gondwana respectively it seems likely that a third source perhaps baltica provided the lower palaeozoic southern uplands succession sediments deposited in southern britain after the closure of iapetus were derived mainly from the recycling of older sediments the tectonic rearrangements which occurred during the phanerozoic are not reflected in the smnd isotopic structure of the southern british sedimentary mass suggesting that the caledonian and hercynian orogenies and even the grenville orogeny involved minimal accretion of new mantle derived material into the british and adjacent continental crust smnd analyses of fine grained clastic sediments provide a powerful sedimentological tool for elucidating palaeogeography clastic source areas sediment recycling and maturity and some aspects of sediment transport

evolution of carbonate and karst critical zones abstract carbonate terrains ct underlie one fifth of terrestrial ice free land and are an important supply of potable water to the world s population and yet processes endemic to ct critical zones cz and responses of these processes to climatic and anthropogenic pressures are not well understood given the rapid dissolution rates and ability to generate well developed networks of secondary porosity these landscapes can be highly sensitive to impacts from climate change e g modifications of temperature precipitation sea level and human disturbance e g water withdrawal diversions changes in land use land cover this special issue includes 16 papers focused on ct cz processes and potential responses to climatic and human perturbations five major themes emerge from these papers namely 1 anthropogenic climate and land use changes alter ct cz weathering rate and diagenesis 2 metal and carbon fluxes in ct cz will respond to increasing hydrologic variance caused by climate change 3 endogenous and exogenous processes operating over short time periods

submerged caves of croatia distribution classification and origin presently 235 submerged caves and pits have been recorded along the croatian coast and islands partly or completely submerged by sea water contrary to the inland situation recorded submerged features are predominantly horizontal 60 though there are indications that the real situation is similar to that of the continental part where 69 are vertical pits completely marine conditions are established in 126 caves and the rest are anchihaline caves and submarine springs speleothems are found in more than 140 caves by their origin the investigated caves are all continental features formed in mesozoic and palaeogene carbonates subsequently submerged owing to sea transgression due to the relatively low wave energy rapid sea level rise and maturity of the host rock they do not fit into concepts of a sea cave or a flank margin cave development but they fulfil several conditions for being the blue holes since the term blue hole is mainly associated with the bahamian karst our attempt is only to show the possible similarities with no intention of ascribing that term to the croatian caves beside karstological issues croatian submerged caves are unique environmental archaeological and tourism assets

sm nd isotopic characteristics of sedimentary provenance the windermere supergroup of nw england nd model ages of windermere supergroup sediments increase from the upper ashgill to the upper ludlow below the lower llandovery increasing t dm reflects mixing between the underlying borrowdale volcanic group and hemipelagic detritus possibly sourced from the lauren tian margin the ongoing rise of t dm into the upper ludlow probably reflects the growing influence of sediment sourced from the scandian orogen a poiadoli drop in t dm is interpreted as recording the re establishment of supply from the local laurentian margin north to south sediment dispersal indicating the effective demise of the iapetus ocean as a barrier to sediment dispersal

chemical and isotopic systematics of the caledonian intrusions of scotland and northern england a guide to magma source region and magma crust interaction chemical and 0 sr nd and pb isotope relations for the british caledonian granitoids exhibit systematic variations that are attributed to derivation from both mantle and crustal sources the older more than ca 470 ma pre and syn tectonic granites were the product of local anatectic melting of late proterozoic metasedimentary upper crust 6180 i 8 to 14 87sr 86sr 0 710 206pb 204pb w 18 1 19 2 during the peak thermal conditions of the grampian orogeny the younger less than ca 440 ma post tectonic granitoids have a complex origin which in individual cases involved at least four different source regions i the upper mantle or subducted oceanic crust 6180 5 7 to 7 0 o 87sr 86sr w 0 7035 0 7040 206pb 204pb 17 9 to 18 1 and ii lower palaeozoic geosynclinal sedimentary upper crust 6180 11 to 14 o 87sr 6sr w 0 705 0 711 206pb 204pb 18 4 within the paratectonic caledonides in the scottish midland valley and southern uplands and in northern england or iii middle proterozoic mafic to intermediate granulitic lower crust 6180 w 8 to 10 o 87sr 86sr w 0 705 0 707 206pb 20pb 16 5 17 0 and iv middle to late proterozoic metasedimentary upper crust 6180 8 to 14 87sr 86sr 0 710 206pb 207pb w 18 1 19 2 in the scottish highlands mantle derived magmas or their direct derivatives were likely involved in the development of all of the younger granitoids either as end member components or as the source for a substantial part of the heat required for crustal melting and assimilation although the lower palaeozoic was a time during which a large amount of igneous material was introduced into the upper crust in britain it was not a major crust forming period because the caledonian granitoids are dominated by recycled continental crust

intracrustal recycling and upper crustal evolution a case study from the pan african damara mobile belt central namibia abstract clastic sediments from the pan african damara mobile belt show a wide range in depositional nd nd 0 18 to 1 and several key trace element ratios notably th nd and la sm increase from 0 2 to 0 7 and 4 0 to 8 0 respectively with decreasing nd 0 such trace element ratio nd 0 data arrays are attributed to binary mixing within the sedimentary mass and the data array defined by the damara sediments is consistent with data from other regions the low nd 0 end member is characterised by high th nd th y la sm and hf zr ratios and reflects highly differentiated upper crust dominated by granitoids pb isotope data suggest that the low nd 0 end member also had relatively high time integrated th u 4 by contrast the high nd 0 end member reflects juvenile upper crust but this end member has la sm th nd and hf zr ratios 4 0 0 2 and 0 02 respectively slightly lower than those of taylor and mclennan s preferred model for bulk crust and significantly lower than those of the andesite model intracrustal differentiation is discussed in terms of bulk crust present day average upper crust post archaean shale and a highly differentiated low nd 0 end member trace element ratios which are not significantly fractionated during erosion and sedimentation e g th nd th y and la sm show relatively smooth increases between these reservoirs whereas other trace element ratios which are fractionated both by sedimentary and magmatic processes e g rb sr and rb zr increase dramatically in the more differentiated crustal reservoirs

epikarst communities biodiversity hotspots and potential water tracers there is an exceptionally rich aquatic fauna in the epikarst the skin of karst high species richness in the epikarst coupled with its special vulnerability as the first point of entry of nearly all toxic spills makes its protection especially important the epikarst fauna may also be an useful tool in tracing the potential route of pollutants copepods in epikarst have extremely local distributions and their body size is such that they are largely at the mercy of directional flows in a series of caves in southwest slovenia and west virginia a significant fraction of the copepod species occur in less than 100 m of linear extent this suggests a pattern of highly restricted lateral flow under normal conditions and the distribution of copepods could potentially be used to trace water movement under high flow conditions as would often be the case with toxic spill mounding of water may increase the lateral radius of flow nevertheless copepods may be useful tracers

a nd isotope investigation of sediments related to crustal development in the british isles the times of original fractionation of the sm and nd component of clastic sediments from a mantle source crustal residence age have been estimated from sm nd model ages calculated relative to a depleted mantle evolution in this way the provenance and evolution of selected precambrian and phanerozoic sediments and metasediments from the british isles have been examined whereas some archaean and early proterozoic sediments have sm nd model ages that are close to their stratigraphic age the phanerozoic sediments analysed have model ages as much as 2 0 ga in excess of their stratigraphic age a more detailed study of lower palaeozoic sediments deposited on the northern margin of the iapetus ocean provides evidence for a marked change of provenance in the ordovician after the deposition of the dalradian supergroup a component with comparatively high143nd 144nd and sm nd ratio presumably basaltic is present in the sediments throughout the accretionary prism crustal residence age estimates average about 1 5 ga for both these lower palaeozoic sediments and modern pelagic clays and collectively fail to provide any evidence for significant continental growth during the phanerozoic