ka band backscattering from water surface at small incidence a wind wave tank study we report on an experiment conducted at the large pytheas wind wave facility in marseille to characterize the ka band radar return from water surfaces when observed at small incidence simultaneous measurements of capillary gravity to gravity wave height and slopes and normalized radar cross section nrcs were carried out for various wind speeds and scattering angles from this data set we construct an empirical two dimensional wave number spectrum accounting for the surface current to describe water surface motions from decimeter to millimeter scales some consistency tests are proposed to validate the surface wave spectrum which is then incorporated into simple analytical scattering models the resulting directional nrcs is found in overall good agreement with the experimental values comparisons are performed with oceanic models as well as in situ measurements over different types of natural surfaces the applicability of the present findings to oceanic as well as continental surfaces is discussed

stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

importance of peakedness in sea surface slope measurements and applications we recall the simple statistical concept that non gaussian distribution peakedness results from the compounding of random processes this idea is applied to observations and analysis of sea surface slopes as inferred using optical and microwave scattering measurements our study emphasizes the importance of identifying and quantifying the distribution variance and kurtosis from observations data are shown to indicate consistently non gaussian peakedness to indicate the need to report at least two parameters in an even order analysis and to indicate near equivalence between radar and optical data physical interpretation for observed infrequent steep slopes is given via compounding statistical processes where normally distributed short scale waves are modulated because of random fluctuations mainly associated with the underlying long wave field implications of non gaussian peakedness are provided for altimeter backscatter theory and for modeling wave breaking probability

uplift and erosional history of the deccan traps india evidence from laterites and drainage patterns of the western ghats and konkan coast abstract the western ghats escarpment in the western coastal region of peninsular india is locally capped by plateau remnants on which a regional high level laterite carapace is preserved geochemical fingerprinting studies show that the laterite has been developed from a protolith of panhala formation basalts the youngest known formation of the deccan sequence the high level laterite is in detail structurally concordant with its underlying basalts and hence it is concluded that it represents the original top of the lava pile a younger low level laterite carapace is developed on the konkan plain below the escarpment where it lies discordantly on basalts of the ambenali and poladpur formations from which it developed in situ the low level laterite rises topographically northwards in response to differential uplift probably at a maximum in the nasik region the main structures of the ghats region excluding the coastal monocline are the nasik dome and the mahabaleshwar anticline these have no effect on regional drainage patterns and it is argued that they are largely secondary features developing in response to post volcanic uplift

lead isotope study of zn pb ore deposits associated with the basque cantabrian basin and paleozoic basement northern spain a total of forty three galena samples from syngenetic and epigenetic pb zn mineralizations emplaced in the lower cretaceous basque cantabrian basin and paleozoic basement of the cinco villas massif in the western pyrenees have been analyzed for pb isotopic composition galena from sedex mineralizations hosted in carboniferous clastic rocks in the cinco villas massif display an homogeneous lead isotopic signature 206pb 2044pb 18 43 207pb 204pb 15 66 208pb 204pb 38 69 suggesting a single lead reservoir these values are slightly more radiogenic than lead from other european hercynian deposits possibly reflecting the influence of a more evolved upper crustal source underlying paleozoic sediments are proposed as lead source for the cinco villas massif ores analyses from twenty six galena samples from the four strata bound ore districts hosted in mesozoic rocks reveal the existence of two populations regarding their lead isotopic composition galena from the western santander districts e g reocin is characterized by more radiogenic isotope values 206pb 204pb 18 74 207pb 204pb 15 67 208pb 204pb 38 73 than those from the central and eastern districts troya legorreta central and western vizcaya 206pb 204pb 18 59 207pb 204pb 15 66 208pb 204pb 38 73 in all districts the most likely source for these mineralizations was the thick sequence of lower cretaceous clastic sediments the existence of two separate lead isotopic populations could be the result of regional difference in the composition of the basement rocks and the clastic sediments derived of it or different evolution histories in both sub basins isotopic ratios indicate an increase in crustal influence as the age of the ores decreases

40ar 39ar dating of mineral separates and whole rocks from the western ghats lava pile further constraints on duration and age of the deccan traps abstract there has been an ongoing debate for almost two decades on the age and duration of deccan trap volcanism some of the best available ages have been determined using the 40 ar 39 ar method but differences in sample location laboratory procedure type of analyzed material and ages of monitors may have been responsible for much of the apparent spread in the data we have collected and analyzed samples from close to the bottom and top of the main lava pile in the western ghats near bombay we confirm previous findings that alteration and ar recoil strongly affect these rocks particularly measurements made on whole rocks when mineral separates mostly plagioclase are analyzed the spread is much reduced we find a mean age of 65 4 0 7 ma for five flows near the base of the section jahwar and igatpuri formations and 65 2 0 4 ma for a dyke cross cutting the poladpur formation below the topmost mahabaleshwar formation this implies that at least 1800 m out of the 2500 m composite trap section were erupted in a short interval less than 1 ma long and close to 65 5 ma i e close to the cretaceous tertiary boundary we find that older ages near 67 ma found by several authors are essentially based on whole rock samples which display disturbed spectra when this can be checked i e when the spectra are published

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

measuring sea surface mean square slope with a 36 ghz scanning radar altimeter values of sea surface mean square slope mss computed from the backscattered power falloff with incidence angle measured by an airborne 36 ghz scanning radar altimeter are presented when the mss values are plotted against the 10 m wind speed extrapolated from the 46 to 110 m aircraft height for wind speeds up to 7 m s 1 the values scatter about a curve which is scaled from that obtained by wu 1990 by a factor of 0 85 wu s result was a reanalysis of the optical measurements of cox and munk 1954 the offset between the microwave and optical curves is reasonable because one would expect the surface to appear smoother to the microwave wavelength than to the optical this is unlike the mss values inferred from absolute power measurements at nadir by 14 ghz satellite altimeters which indicate a higher mss under light wind conditions than the optical measurements indicate for wind speeds below 7 m s 1 the peak of the backscattered power distribution is observed at nadir but for higher speeds the peak shifts off nadir in the downwind direction

the source of lead in the osen sandstone lead deposit on the baltic shield norway the sandstone hosted lead deposits on the baltic shield occur in marine late precambrian to early cambrian sedimentary rocks a ground water model in which the basement is postulated as the metal source has been proposed for these deposits to test this model the osen deposit was selected because it lies directly on a homogeneous granite basement on the basis of u th pb whole rock isotopic analyses for three samples of unweathered basement granite trysil granite a basement age of 1 598 m y was established the lead isotopic compositions of four out of five specimens of galena from the osen deposit plot between isochrons calculated for the granite at 500 m y and 540 m y this is strong support for the hypothesis that the lead source was basement granite and suggests that mineralization took place soon after sedimentation a basement source for the lead is further substantiated by the regional pattern of lead isotopic compositions of sandstone lead deposits which reflects the character of adjacent basement terranes

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

stratigraphy structure and volcanology of the se deccan continental flood basalt province implications for eruptive extent and volumes the deccan volcanic province is one of the world9s largest continental flood basalt provinces and derives additional importance because its eruptions 64 67 ma straddle the cretaceous tertiary boundary to better assess the environmental impact of deccan volcanism and its possible effect upon cretaceous tertiary boundary biota it is necessary to document the stratigraphy chronology and volume of the eruptions new chemostratigraphical data permit mapping of the se deccan these data strengthen the likelihood that the rajahmundry traps of eastern india were originally fed by long distance flows and are an extension of the main deccan volcanic province an east west cross section reveals a depression or moat around the se periphery of the deccan volcanic province this provided a site in which shallow lakes initially formed and along which later lava eruptions became channelled and confined published palaeomagnetic data indicate that the lavas of the se deccan were erupted during chron 29r coeval with the cretaceous tertiary boundary and the chemostratigraphic data place the associated lake sediments i e lameta group beneath and within lavas of the wai subgroup finally these new map data are combined with previous work to provide a quantitative estimate for the original deccan volcanic province eruptive volume of c 1 3 10 6 km 3

origin of the deccan trap flows at mahabaleshwar inferred from nd and sr isotopic and chemical evidence abstract the deccan flows at mahabaleshwar are divisible into a lower and an upper group based on nd and sr isotopic ratios which define two correlated trends this distinction is supported by incompatible element ratios and bulk compositions the data reflect contamination in a dynamic system of magmas from an lil depleted e juv 8 mantle by two different negative e juv endmembers one undoubtedly continental crust the other either continental crust or enriched mantle the depleted mantle source anomalously high in 87 sr 86 sr may have been in the subcontinental lithosphere or a region of rising indian ocean morb mantle

ocean wave slope observations using radar backscatter and laser altimeters abstract combination of laser and radar aboard an aircraft is used to directly measure long gravity wave surface tilting simultaneously with nadir viewing microwave backscatter from the sea surface the presented dataset is extensive encompassing varied wind conditions over coastal and open ocean wave regimes laser derived slope statistics and ka band 36 ghz radar backscatter are detailed separately to document their respective variations versus near surface wind speed the slope statistics measured for 1 2 m show good agreement with cox and munk s oil slickened sea measurements a notable exception is elevated distribution peakedness and an observed wind dependence in this likely proxy for nonlinear wave wave interactions aircraft ka band radar data nearly mimic ku band satellite altimeter observations in their mean wind dependence the present calibrated radar data along with relevant observational and theoretical studies suggest a large 5 db bias in previous ka band results next wave

lead isotope behaviour in a polyphased pb zn ore deposit les malines cevennes france les malines mine cevennes france provides an example of pb zn ore bodies that underwent a polyphased evolution on the pb pb diagram experimental points of the les malines ore types always plot in the central part of the field defined for the cevennes metallogenic province this homogeneity the similarities with the pb isotopic compositions of the surrounding rocks and the comparison with pb isotopes evolution of whole rocks and minerals of the neighbouring continental lands which emerged during triassic and liassic times rule out the participation of extraneous pb during the successive concentration stages and agree with an initial metal stock transformed and mobilized in a pb closed system hercynian k feldspars are the main source of the pb preconcentrated during triassic times most of the cevennes pb zn ore bodies could derive from this triassic metal stock nevertheless local pb isotopic anomalies suggest hydrothermal sources for some pb zn ore bodies located along the cevennes fault

statistical characterization of short wind waves from stereo images of the sea surface we propose a methodology to extract short scale statistical characteristics of the sea surface topography by means of stereo image reconstruction the possibilities and limitations of the technique are discussed and tested on a data set acquired from an oceanographic platform at the black sea a validation is made with simultaneous it in situ measurements as well as results from the literature we show that one and two point properties of the short scale roughness can be well estimated without resorting to an interpolation procedure or an underlying surface model we obtain the first cumulants of the probability distribution of small scale elevations and slopes as well as related structure functions we derive an empirical parametrization for the skewness function which is of primary importance in analytical scattering models from the sea surface

lead isotope and pb pb model age determinations of ores from central europe and their metallogenetic interpretation the paper presents lead isotope data from 211 samples from phanerozoic lead bearing ore occurrences in central europe particularly from the southern part of the former german democratic republic the data are interpreted in terms of amov s dynamic model of continuous lead isotope evolution the relationships between thoro genic and urano genic model ages and the source of lead in different regional units are discussed we observed differences in lead isotope evolution in the hercynian internides and externides within the moldanubian and saxothuringian zones we distinguish five main lead bearing ore associations 1 cambrian stratiform base metal hermsdorf waldsassen 206pb 204pb 17 50 17 70 2 devonian vein type sb bearing metamorphogene neumuhle hartmannsdorf 17 80 18 00 3 upper carboniferous permian polymetallic including tin vein type kutna hora freiberg altenberg 18 00 18 20 4 triassic jurassic pb ba vein type st ibro halsbrucke 18 20 18 60 5 cenozoic polymetallic vein type riftogene roztoky banska stiavnica 18 80 19 10 pb isotope characteristics from ores of the montagne noire and the brioude massiac district correspond to this subdivision ore associations from the rheno hercynian zone display higher 207pb 204pb ratios which can be explained by more evolved and less metamorphosed source rocks mineralizations of the eastern harz strasberg neudorf belong to the permian association those from the western harz clausthal bad grund to the triassic jurassic because of pb isotope agreement the stratabound rammelsberg and the vein bound ramsbeck i mineralization are presumed to be isogenetic pb isotope identity of distinct mineralizations in the basement zone halsbrucke bad grund and in the triassic sediments gorny slask mechernich bleiglanzbanke suggests a strong genetic coherence pb isotope conformity between the upper carboniferous permian triassic ore associations and hercynian postkinematic granitoids and lamprophyric rocks also favours a close relationship pb isotope and other data indicate crustal sources as the age of the ore associations decreases crustal influences generally increase apart from the roztoky mineralization

geological context and plumbotectonic evolution of the giant almaden mercury deposit abstract the almaden mine has been the largest among several mercury deposits that represent the biggest mercury concentration in the world the deposits form a mining district which is located in a 30 km long and up to 15 km wide wnw ese oriented syncline where a thick lower ordovician upper devonian siliciclastic sedimentary sequence outcrops most of the deposits are located in the south subvertical syncline flank which has an opposite vergence to the rest of the region of special note is the presence of important nw se to wnw ese crustal structures that played a major role at several times during the regional geological history and controlled the sedimentary unit distribution volcanism and deformation one of these structures seems to have played an important role in the almaden area probably having been responsible for the anomalous syncline geometry this structure acted during the e w variscan shortening as a ductile fragile sinistral shear zone that resulted in a subvertical attitude of the southern almaden syncline flank affecting the sedimentary sequence longitudinally the hg deposits in the region correspond to two types stratabound and stockworks the former are hosted in well defined criadero quartzite orthoquartzite levels of ordovician silurian age these deposits were folded and sheared during the variscan deformation the stockwork deposits filled fractures and veins and partially replaced the volcanic rocks affected by the variscan shear zones the replacement process took place at the end of the e w variscan shortening the almaden deposit belongs to the stratabound type and has three mineralized levels one located in the lower part and the other two in the upper part of the criadero quartzite of minor relevance other small stockwork bodies replacing a volcanic breccia tuff known as frailesca rock have also been exploited this rock formed massive lenticular bodies that have been interpreted as pre variscan diatremes on the basis of field criteria we conclude that the frailesca rock emplacement took place later than cinnabar mineralization after the frailesca rock was formed it was cut by sills of quartz diabase that resulted from a new magmatic event both volcanic materials affect the mercury ore developing small aureoles of contact metamorphism and volatilizing the cinnabar the deposit shows three sectors separated by two straight dextral faults which cut the sinistral wnw ese shears bands the latter affect the mercury ore mostly in its western area lead isotopes from almaden cinnabar deposits show a broad range of values higher than those predicted for the stacey and kramers and cumming and richards crustal pb evolution models but largely tallying with the sardinia evolution line for this sector of the variscan basement quite well the data set plotted along the sardinia curve in several well defined clusters that could be interpreted as a lead extraction by means of large scale convective hydrothermal systems from a lead reservoir located in the upper crust at a time indicated by the sardinia curve the estimated ages for this lead model evolution indicate lead extraction as having occurred during the late silurian devonian 420 375 ma late variscan 300 ma permian triassic 290 220 ma late jurassic early cretaceous 200 150 ma and eocene oligocene 50 25 ma and are coincident with the main extensional tectonic episodes from late ordovician to devonian permian to triassic and late jurassic to early cretaceous this shows that cinnabar is likely to have been mostly remobilized crystallized during the regional extensional tectonic events capturing lead from the host sedimentary sequence this lead was mobilized by large scale long term hydrothermal convective cells at various times constituting a complex geotectonic history for the ore forming processes

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

diagenetic evolution of the carnian wetterstein platforms of the eastern alps the carbonate platforms of the wetterstein formation of the eastern alps drau range and northern calcareous alps show a distinct facies zonation of reefs and lagoons while some lagoonal areas were episodically emerged and formed lagoonal islands others remained permanently flooded the scale of near surface meteoric or marine diagenesis was related to this lagoonal topography at shallow burial depth cementation was dominated by altered marine solutions which additionally caused recrystallization of metastable constituents of the sediment and earlier marine cements high magnesian calcite aragonite connected with a carbon and oxygen isotopic change to more negative values deeper burial cementation shows a succession with two types of saddle dolomite and three types of blocky calcite carbon and oxygen isotopic values of these cements show a trend towards more negative values from the first to the last generation in the following succession clear saddle dolomite zoned blocky calcite cloudy saddle dolomite post corrosion blocky calcite replacive blocky calcite fluid inclusion studies of the carbonate cements are interpreted to indicate a deeper burial temperature development that first increases from 175 to 317 c followed by a temperature decrease to 163 260 c and subsequent increase up to 316 c whereby the samples of the drau range always show the lowest values calculations of the isotopic composition of the water from which the carbonate cements were precipitated yielded positive 18o values from 6 66 to 17 81 o smow which are characteristic for formation and or metamorphic waters also the isotopic compositions of the palaeofluids probably changed during deeper burial diagenesis following the temperature development

sulfur and chlorine in late cretaceous deccan magmas and eruptive gas release large volume p hoehoe lava flows erupted 67 to 65 million years ago forming the deccan traps india the impact of these flood basalt eruptions on the global atmosphere and the coeval end cretaceous mass extinction has been uncertain to assess the potential gas release from this volcanism we measured sulfur and chlorine concentrations in rare glass inclusions inside crystals and on glassy selvages preserved within lavas concentrations range from 1400 parts per million of s and 900 parts per million of cl in inclusions down to a few hundred parts per million in the lava these data indicate that eruptions of deccan lavas could have released at most 0 103 weight of s yielding up to 5 4 teragrams of so2 per cubic kilometer of lava a more conservative estimate is 0 07 weight of s and 0 04 weight of cl yielding 3 5 teragrams of so2 and 1 teragram of hcl for every cubic kilometer of lava erupted the flows were very large in volume and these results imply that huge amounts of s and cl gases were released the environmental impact from even individual eruptions during past flood basalt activity was probably severe

pb isotope evidence for the origin of lead in strata bound pb zn deposits in triassic carbonates of the eastern and southern alps a comparison of ore lead isotope ratios of pb zn deposits hosted in triassic carbonates of the eastern and southern alps with the isotopic composition of trace leads of their host rocks of triassic volcanics and of the underlying clastic sediments shows that these rocks could have supplied only part of the ore lead the isotopic signature of feldspar lead from crystalline basement rocks however reveals that they must have contributed a significant amount of metal to these deposits the presence of barite and of thallium is also indicative that feldspars were the main source of lead arsenic is one of the few important trace elements in these deposits and is known to occur in some areas of lower paleozoic metasediments in unusually high concentrations any model explaining the origin of these deposits must consider the extensive leaching of the basement and to some extent of the overlying clastic sediments as well how the metal bearing solutions entered the lagoonal back reef areas is still open to question as feeder channels have not yet been positively identified the results further demonstrate that the basement also acted as a metal source for galena bearing deposits hosted in permian sediments vein type deposits in permian volcanics and probably the barite fluorite polymetallic deposits along a devonian erosional surface in the carnic alps as well

peakedness effects in near nadir radar observations of the sea surface the simulation and interpretation of microwave sea radar return in the near nadir region are still issues in view of the limitations of the geometrical optics approximation and the multiscale and non gaussian nature of the surface we show that an unambiguous and fully consistent physical approach can be reached in the framework of the physical optics the model is developed on the basis of various satellite and airborne c ku and ka band measurements using different reference surface roughness spectra as found the introduction of a peakedness correction based upon the excess kurtosis of slopes is necessary to obtain consistent analysis across the microwave frequency range the model yields accurate simulations for the omnidirectional near nadir normalized radar cross section in different frequency bands provided the spectrum satisfies some a priori constraints on the distribution of the total and filtered slopes

reply to comment by paul a hwang on a study of the slope probability density function of the ocean waves from radar observations by d hauser et al in response to the comment of hwang 2009 this paper presents an addendum to the study published by hauser et al 2008 on the mean square slopes mss derived from radar observations at c band and incidence angles between 7 and 21

sulphur isotope distribution in the pb zn deposit bleiberg carinthia austria the sulphur isotope composition of 233 sulphides and 40 sulphates has been investigated and evaluated in combination with 29 earlier published data the total variation of 34s values for the sulphides and the sulphates ranges from 40 up to 1 and from 7 up to 20 respectively for the mineral species the variations are with number of samples in brackets galena 96 32 up to 2 sphalerite 141 30 up to 4 marcasite 16 27 up to 1 pyrite 10 26 up to 13 molybedenite 3 40 up to 29 anhydrite and gypsum 8 15 up to 20 coelestine 1 19 and barite 33 7 up to 18 the frequency distribution of the 34s values corresponds with the complexity of the ore forming processes which resulted in six strata bound ore mineralizations the sulphate values clearly show that the sulphate sulphur originates from sea water sulphate the sulphides are formed by bacteriogeneric processes from seawater sulphate and their sulphur isotope composition depends on the lithofacies of the sediments as well as on the following diagenetic processes

lead isotopic composition of hercynian granitic k feldspars constrains continental genesis lead isotope compositions have been determined in many k feldspars from granitic rocks emplaced during the variscan hercynian orogeny sensu lato around 300 myr in various parts of europe and the eastern us the ratios show a regular geographical pattern with contours arched around southern france and parallel to the atlantic coast of the us this distribution parallels predriftpalaeogeographical zones during the palaeozoic the lead isotope pattern of variscan granitic rocks is similar to that of some orogenic volcanic suites but is better explained by crustal melting than by an hercynian mantle crust material mixing the continental crust from these areas must be older than 3 000 myr large scale fluid circulation in the crust during orogenic processes apparently explains the observed geographical patterns of lead isotopes

variations of sulfur isotopes trace element compositions and cathodoluminescence of mississippi valley type pb zn ores from the drau range eastern alps slovenia austria implications for ore deposition on a regional versus microscale the sulfur isotope composition of sulfide ore minerals of the drau range varies considerably down to centimeter scale variations both on a regional and a local scale broadly scattering 34s values ranging between 2 and 25 per mil with a mean around 17 per mil are probably related to both local bacteriogenic and thermal reduction of late triassic marine sulfate the 34s is typically more depleted in ore deposited in subtidal carbonate rocks than in the economic zn and pb ore preferably deposited within intratidal carbonate host rock the 34s 32s ratio increases on the order of fes2 pbs zns which reflects disequilibrium and low temperature formation the strong depletion of 34s in botryoidal sphalerite ranging between 24 and 32 per mil appears to be correlated with the crystal mode wurtzite sphalerite fibers and the enrichment of the trace elements fe as tl and ge sphalerite generations of specific cathodoluminescense color and closely related trace element composition are correlated district wide a decrease of the trace elements fe as tl and ge in the sphalerite generations is coeval with a minor depletion of 34s in the range of 3 and 12 per mil for 34s values in several hand specimens variations in 34s values and trace element zonation on a regional to local scale indicates mixing of local sulfur sources with a regional metal rich brine however distinct peaks in some ore deposits and more positive 34s values of between 5 and 10 per mil are also compatible with derivation of the sulfur from basement rocks the enrichment of the trace element cu in orange luminescing sphalerite negatively correlated with fe as tl and ge and therefore strongly suggests leaching of copper from late permian to early triassic continental red beds frequent evaporites in this stratigraphic section might have supplied sulfur of relatively heavy isotopic composition to the brine hence some sulfur may also have been transported with a metal rich brine

the southern ocean waves experiment part iii sea surface slope statistics and near nadir remote sensing abstract during the southern ocean waves experiment sowex registered ocean wave topography and backscattered power data at ka band 36 ghz were collected with the nasa scanning radar altimeter sra off the coast of tasmania under a wide range of wind and sea conditions from quiescent to gale force winds with 9 m significant wave height collection altitude varied from 35 m to over 1 km allowing determination of the sea surface mean square slope mss the directional wave spectrum and the detailed variation of backscattered power with incidence angle which deviated from a simple gaussian scattering model the non gaussian characteristics of the backscatter increased systematically with the mss suggesting that a global model to characterize ka band radar backscatter from the sea surface within 25 of nadir might be possible

the timing of crustal extension and the eruption of continental flood basalts the association between mantle plumes continental flood basalt eruption and the extension and rifting of the crust is well recognized1 3 but there has always been controversy as to whether the plume or the rifting was the initiating factor4 5 was rifting triggered by doming above the thermal plume2 3 6 or was rifting the driving force preceding the associated volcanicity7 8 here i show that recent flow by flow mapping of two continental flood basalt provinces the columbia river basalt group and the deccan basalt group allows one to infer the relative timing of volcanicity and crustal extension in both provinces eruption of the main tholeiitic phase preceded significant extension and crustal thinning this suggests that the primary event in the formation of these provinces was the upwelling of a mantle plume and that the subsequent crustal extension rifting and decompression was in part a consequence of the initiation of that plume

main deccan volcanism phase ends near the k t boundary evidence from the krishna godavari basin se india abstract recent studies indicate that the bulk 80 of the deccan trap eruptions occurred over less than 0 8 m y in magnetic polarity c29r spanning the cretaceous tertiary k t boundary determining where within this major eruptive phase the k t mass extinction occurred has remained problematic for this reason models estimating the biotic and environmental consequences have generally underestimated the rate and quantity of deccan gas emissions by orders of magnitude leading to conclusions that volcanism could not have been one of the major causes for the k t mass extinction in this study we report that the most massive deccan trap eruption occurred near the k t mass extinction these results are based on sedimentologic microfacies and biostratigraphic data of 4 9 m thick intertrappean sediments in four quarry outcrops in the rajahmundry area of the krishna godavari basin of southeastern india in this area two deccan basalt flows known as the rajahmundry traps mark the longest lava flows extending 1500 km across the indian continent and into the bay of bengal the sediments directly overlying the lower rajahmundry trap contain early danian planktic foraminiferal assemblages of zone p1a which mark the evolution in the aftermath of the k t mass extinction the upper rajahmundry trap was deposited in magnetic polarity c29n preceding full biotic recovery these results suggest that volcanism may have played critical roles in both the k t mass extinction and the delayed biotic recovery

regional uplift associated with continental large igneous provinces the roles of mantle plumes and the lithosphere the timing and duration of surface uplift associated with large igneous provinces provide important constraints on mantle convection processes here we review geological indicators of surface uplift associated with five continent based magmatic provinces emeishan traps 260 million years ago ma siberian traps 251 ma deccan traps 65 ma north atlantic phase 1 61 ma and phase 2 55 ma and yellowstone 16 ma to recent all five magmatic provinces were associated with surface uplift surface uplift can be measured directly from sedimentary indicators of sea level in the north atlantic and from geomorpholocial indicators of relative uplift and tilting in yellowstone in the other provinces surface uplift is inferred from the record of erosion in the deccan north atlantic and emeishan provinces transient uplift that results from variations in thermal structure of the lithosphere and underlying mantle can be distinguished from permanent uplift that results from the extraction and emplacement of magma transient surface uplift is more useful in constraining mantle convection since models of melt generation and emplacement are not required for its interpretation observations of the spatial and temporal relationships between surface uplift rifting and magmatism are also important in constraining models of lip formation onset of surface uplift preceded magmatism in all five of the provinces biostratigraphic constraints on timing of uplift and erosion are best for the north atlantic and emeishan provinces where the time interval between significant uplift and first magmatism is less than 1 million years and 2 5 million years respectively rifting post dates the earliest magmatism in the case of the north atlantic phase 1 and possibly in the case of siberia the relative age of onset of offshore rifting is not well constrained for the deccan and the importance of rifting in controlling magmatism is disputed in the emeishan and yellowstone provinces in these examples rifting is not a requirement for onset of lip magmatism but melting rates are significantly increased when rifting occurs models that attempt to explain emplacement of these five lips without hot mantle supplied by mantle plumes often have difficulties in explaining the observations of surface uplift rifting and magmatism for example small scale convection related to craton or rift boundaries edge driven convection cannot easily explain widespread 1000 km scale transient surface uplift emeishan deccan north atlantic and upper mantle convection initiated by differential incubation beneath cratons the hotcell

40k 40ar dating of the main deccan large igneous province further evidence of ktb age and short duration most mass extinctions coincide in time with outpourings of continental flood basalts cfb some 20 years ago it was shown courtillot v besse j vandamme d montigny r jaeger j j cappetta h 1986 deccan flood basalts at the cretaceous tertiary boundary earth planet sci lett 80 361 374 courtillot v feraud g maluski h vandamme d moreau m g besse j 1988 deccan flood basalts and the cretaceous tertiary boundary nature 333 843 846 duncan r a pyle d g 1988 rapid eruption of the deccan flood basalts at the cretaceous tertiary boundary nature 333 841 843 that the age of the deccan traps was close to the cretaceous tertiary kt boundary and its duration under 1 myr we have undertaken a new geochronological study using the unconventional 40k 40ar cassignol gillot technique which is particularly well suited to the potassium poor deccan lavas the mean of 4 determinations from the topmost ambenali and mahabaleshwar formations is 64 5 0 6 ma they straddle the c29r c29n reversal boundary for which they provide a new constraint the mean age of 3 determinations from the oldest jawhar formation is 64 8 0 6 ma the difference in age between top and bottom of a 3500 m composite section probably comprising 80 of the total deccan volume is statistically insignificant with the overall mean age being 64 7 0 6 ma n 7 our results are consistent with the most recent 40ar 39ar determinations knight k b renne p r halkett a white n 2003 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps earth planet sci lett 208 85 99 knight k b renne p r baker j waight t white n 2005 reply to 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps discussion by a k baksi earth planet sci lett 239 374 382 confirming that there should be no systematic difference between the two methods when they are used in an optimal way an earlier smaller but significant pulse of volcanism between 68 and 67 ma extending over at least 500 km in latitude in the northern part of the deccan cfb has also been identified after 2 to 3 ma of quiescence the second major phase of volcanism occurred near 65 ma expanding over most of the area covered by the first pulse and another 500 km to the south consistent with drift of india by 300 to 450 km at not vert similar 150 mm yr during the quiescence period new paleontological data from the remote rajahmundry section keller g adatte t gardin s bartolini a bajpai s humler e in prep the cretaceous tertiary boundary in deccan traps of the krishna godavari basin of southeastern india epsl to be submitted suggest that this second pulse can itself be divided into two major pulses one starting in c29r and ending at the kt boundary the second starting in the upper part of c29r and ending within c29n

the 3d facies architecture of flood basalt provinces and their internal heterogeneity examples from the palaeogene skye lava field quantifying the facies architecture of flood basalt provinces is important as it can be used to understand the physical volcanology and rock property variations throughout the lava sequence the 3d facies architecture and internal heterogeneity of the skye lava field for example provides important insights into the evolution of the british tertiary igneous province and valuable information to aid in the exploration of potential offshore reservoirs underlying significant flood lavas along the north atlantic margin the volcanic stratigraphy of the talisker bay area of skye comprises 1 lower compound braided lavas flow lobes 3 the transitional sequence 7 4 km 3 and the upper sequence 17 0 km 3 the lower sequence lavas formed on the flanks of a shield volcano and were sourced from the ne volcanological features such as lava feeder tubes pahoehoe textures and lobes indicate a scale of volcanism similar to that of present day hawaii the within flow heterogeneity of the basalts is characterized using an intrafacies scheme allowing comparison of variations in lithofacies with characteristic geophysical rock properties of compressional wave velocity and density

plumbotectonic evolution of the ossa morena zone iberian peninsula tracing the influence of mantle crust interaction in ore forming processes the ossa morena zone in the variscan belt of the iberian peninsula is characterized by a complex geotec tonic evolution it hosts a neoproterozoic paleozoic sequence that records the existence of two orogenic events cadomian and variscan separated by rift and stable platform stages middle cambrian to late devonian volcanogenic and sediment hosted massive sulfides skarns magmatic ni cu deposits synmetamorphic and intragranitic and perigranitic veins and replacement bodies are related to different magmatic hydrothermal systems ranging in age from 650 ma to about 250 ma the lead isotope signatures from 26 different mineral deposits show variable ratios of 206pb 204pb 17 49 18 44 207pb 204pb 15 47 15 67 and 208pb 204pb 37 37 38 78 that have low average values 9 7 but high values 38 3 as a whole the lead isotope data define an irregular cluster that plots around the stacey and kramers 1975 growth curve but clearly marks the existence of two main ore forming events during cadomian and variscan times the most radiogenic samples are from some minor zn pb stratiform sedimentary exhalative mineralization they are interpreted as having a dominantly crustal derivation 10 1 in which most of the lead was leached from a pre cadomian continental basement with a long crustal history this basement has strong geochemical affinities with the oldest rocks of the iberian terrane however most of the ore samples investigated plot below the stacey and kramers 1975 reference curve indicating polyphase but variable mixing of lead from upper crustal and mantle lead reservoirs at the terrane scale clear mixing lines between the two end member reser voirs are evident only in the oldest volcanic rock and sedimentary rock hosted massive sulfide deposits related to the cadomian late neoproterozoic early cambrian magmatic arc in the other deposit types lead isotopes have more restricted values the crustal lead is interpreted as having been derived from ancient crust 2 1 2 5 ga and the derived shales montemolin formation that predated the cadomian orogeny the mantle derived lead may have been derived from three different sources neoproterozoic tholeiitic orthoamphibolite syn cadomian calc alkaline andesite or calc alkaline metaluminous plutonic rocks intruded during the variscan orogeny the first two sources probably controlled the lead isotope signatures of the cadomian massive sulfide deposits and the variscan synmetamorphic veins the input of primitive lead is especially significant during variscan times 350 300 ma and is interpreted as having been related to the existence of a large primitive reservoir that controlled the variscan magmatic metallogenic and hydrothermal evolution of the ossa morena zone this primitive lead is recognized in most of the magmatic hydrothermal deposits including the typically crust derived w and pb bearing perigranitic hydrothermal systems likewise associated plutonic rocks have more primitive lead isotope signatures than their counterparts in other iberian terranes the lead isotope evolution of the region is consistent with recent geophysical data that suggest that a deep large mafic sill was intruded below the ossa morena zone during variscan times this sill was a likely key factor in the different pb isotope evolution of the ossa morena zone compared with the nearby iberian terranes and the entire western mediterranean province which are char acterized by lengthy crustal histories with very little input of primitive lead the extensive mantle crust inter action probably explains the wide variety and the unusual metallogenic features of the ossa morena zone

sediment geochemistry and base metal sulphide mineralisation in the quidong area southeastern new south wales australia geochemically anomalous pyritic sediments occur directly above a mid silurian unconformity in the quidong area of southeastern new south wales the composition of these sediments reflects derivation from a mixture of a feldspar and mica depleted detritus reworked from underlying quartz rich flysch b mg rich clay or chlorite precipitated from hydrothermal exhalations and c pyrite formed by reaction of iron in clays or oxides with reduced sulphur derived largely from sea water sulphate and possibly a magmatic source three types of base metal sulphide mineralisation occur at quidong including a weak syngenetic concentrations in the pyritic sediments b stratabound and fault controlled bodies of massive sulphides hosted by the pyritic sediments and containing higher grade pb zn and cu and c small vein and cavity fillings of galena barite and other minor sulphides in overlying limestones all types of mineralisation are related to hydrothermal activity which occurred during and after deposition of the pyritic facies the geochemistry of the immediately underlying basement rocks and pb isotope data indicate that the source of the metal bearing fluids was deeper in the crust and probably related to widespread partial melting and magmatic processes the sulphidic sediments and stratabound sulphide deposits represent syngenetic epigenetic sediment hosted mineralisation developed in a shallow marine environment distal from major volcanic centers this style of mineralisation has not previously been described from the region it has some similarities to the irish alpine type spectrum of deposits best known in europe

structural control and geological significance of the zn pb ores formed in the benasque pass area central pyrenees during the post late ordovician extensional event of the gondwana margin abstract the benasque pass area central pyrenees is located in the eastern part of the variscan lys caillaouas massif where cambro ordovician rocks of the hesperian massif crop out in the area several zn pb deposits are located in variscan structures lead isotopes indicate a late ordovician early devonian model age for the deposits in the region an unconformity between pre late ordovician and late ordovician rocks has been defined by several authors and has been identified in the study area the first structures observed in the benasque pass area consist of a pre variscan cleavage which only affects the pre late ordovician rocks in the study area the main structures correspond to two variscan generations i e w trending north verging folds which are associated with the main foliation s 1 d 1 ii e w trending upright folds and associated small south directed thrusts d 2 d 2 structures are the ones hosting the zinc lead ore in the benasque pass area d 1 and d 2 variscan structures have developed under low grade metamorphic conditions some faults observed in the north and the south of the study area may have alpine movement in the benasque pass area the strongly silicified and brecciated zinc lead ore is mainly developed in the d 1 short limb of the mina peak syncline within which s 1 foliation is intensely folded and cross thrust by d 2 structures taking into account their model age all these zinc lead deposits seem to be stratiform stratabound or filling open spaces in origin and related to the pre variscan extension described for the central pyrenees however the zinc lead ore is hosted in strongly silicified and brecciated variscan structures the 34 s isotopic composition of sulfides indicates that the metamorphism and deformation did not completely obliterate the original isotopic composition suggesting that sulfur in the benasque pass has mainly come from the reduction of marine sulfate extracted from the rocks of the metasedimentary sequence in the benasque pass area the lead isotope ratios are homogeneous and have a pre variscan model age which is also the age of the host rocks in the case of the benasque pass the deposits occurred in variscan structures making it impossible to recognize their original pre variscan characteristics indicated by lead isotopes model age the correlation between the pb isotope data for deposits from the benasque pass and aran valley also located in the central pyrenees and those for other deposits from the southern european gondwana is evident and the isotopic data set closely fits the two stage pb evolution model for sardinia terrane the coherence of the pb isotope trends in all the deposits suggests that pb was extracted at various times from sources with similar time averaged u pb th pb and th u values through a process of leaching of the basement rocks by large volumes of hydrothermal fluids in the case of the pyrenees central and eastern the lead and other metals present in the deposit were extracted by hydrothermal fluids from the upper crust rocks during the post late ordovician extensional event of the gondwana margin

hydrocarbon biomarkers in the topla mežica zinc lead deposits northern karavanke drau range slovenia paleoenvironment at the site of ore formation the mississippi valley type zinc and lead deposits at topla 250 150 metric tons t of ore grading 10 wt zn and 3 3 wt pb and me ica 19 million metric tons mt of ore grading 5 3 wt pb and 2 7 wt zn occur within the middle to upper triassic platform carbonate rocks of the northern karavanke drau range geotectonic units of the eastern alps slovenia the ore and host rocks of these deposits have been investigated by a combination of inorganic and organic geochemical methods to determine major trace and rare earth element ree concentrations hydrocarbon distribution and stable isotope ratios of carbonates kerogen extractable organic matter and individual hydrocarbons these data combined with sedimentological evidence provide insight into the paleoenvironmental conditions at the site of ore formation the carbonate isotope composition the ree patterns and the distribution of hydrocarbon biomarkers normal alkanes and steranes suggest a marine depositional environment at topla a relatively high concentration of redox sensitive trace elements v mo u in the host dolostones and ree patterns parallel to that of the north american shale composite suggest that sediments were deposited in a reducing environment anoxic conditions enhanced the preservation of organic matter and resulted in relatively higher total organic carbon contents up to 0 4 wt the isotopic composition of the kerogen 13 c kerogen 29 4 to 25 0 15 n kerogen 13 6 to 6 8 suggests that marine algae and or bacteria were the main source of organic carbon with a very minor contribution from detrital continental plants and a varying degree of alteration extractable organic matter from topla ore is generally depleted in 13 c compared to the associated kerogen which is consistent with an indigenous source of the bitumens the mineralization correlates with 15 n kerogen values around 0 per mil 13c depleted kerogen 13c enriched n heptadecane and relatively high concentrations of bacterial hydrocarbon biomarkers indicating a high cyanobacterial biomass at the site of ore formation abundant dissimilatory sulfate reducing bacteria feeding on the cyanobacterial remains led to accumulation of biogenic h 2 s in the pore water of the sediments this biogenic h 2 s was mainly incorporated into sedimentary organic matter and diagenetic pyrite higher bacterial activity at the ore site also is indicated by specific concentration ratios of hydrocarbons which are roughly correlated with total pb plus zn contents this correlation is consistent with mixing of hydrothermal metal rich fluids and local bacteriogenic sulfide sulfur the new geochemical data provide supporting evidence that topla is a low temperature mississippi valley type deposit formed in an anoxic supratidal saline to hypersaline environment a laminated cyanobacterial mat with abundant sulfate reducing bacteria was the main site of sulfate reduction

implications of the infra and inter trappean biota from the deccan india for the role of volcanism in cretaceous tertiary boundary extinctions the fossil record shows a remarkable similarity between the biota that existed before and after the initiation of deccan volcanic activity virtually all the available palaeontological evidence such as the fauna and flora of the freshwater infra and inter trappean beds and the planktonic foraminifera from the subsurface infra and inter trappean beds of the southeastern coast do not favour the initiation of deccan volcanism as the cause of mass extinctions at the cretaceous tertiary k t boundary instead a combination of events such as an extended period of volcanism changes in sea level and related climatic changes and certain local factors may have played a significant role in selectively eliminating various groups of organisms this view is further reinforced by the biotic changes across the k t iridium layer in the um sohryngkew river section of meghalaya northeastern india

geochemistry and genesis of the lengenbach pb zn as tl ba mineralisation binn valley switzerland the lengenbach pb zn as tl ba mineralisation is located in triassic dolostones of the penninic zone in the swiss alps where alpine metamorphism reached upper greenschist to lower amphibolite grade geochemical data are used to constrain the origin of this unique occurrence two metamorphic redox environments are present the as iii rich zone is controlled by barite pyrite while the reduced zone contains graphite or pyrrhotitepyrite and formally zerovalent as the as iii rich zone is characterised by a mineral assemblage consistent withfo2 in the stability field of barite pyrite an as pb tl rich sulphide melt coexisted with a hydrothermal fluid at 300 c in this zone mineralised dolostones are anomalous in as pb ag tl hg zn ba cd fe cu mo u v b ga cr and possibly sri and au in order of decreasing enrichment as pb and zn are present in the 0 1 to 1 range tl and ag reach several hundred ppm uraninite is concentrated in silicate rich bands and yields a late alpine u pb age of 18 5 0 5 ma pb and s isotopic variations are interpreted by metamorphic overprinting and re equilibration within an isochemically metamorphosed mineralisation hydrothermal sulphides are more strongly affected by uranogenic pb than massive pb as sulphides representing a former sulphide melt the least overprinted mineralisation is characterised by206pb 204pb 18 44 18 56 207pb 204pb 15 60 15 75 208pb 204pb 38 44 38 84 and 34s sulphide 25 2 s isotopic variations are largely a result of sulphide sulphate re equilibration yielding temperatures of 450 30 c 87sr 86sr ratios of mineralised samples are lower than or equal to host dolostones precluding major infiltration of basement derived fluids during alpine metamorphism the sr source 87sr 86sr close to 0 708 probably was seawater with a radiogenic detrital mineral component the genesis of the unique lengenbach mineralisation is interpreted as the result of isochemical metamorphic overprinting of a carbonate hosted stratiform sulphide mineralisation well crystallised sulphide minerals in fissures and druses formed during retrograde cooling of a sulphide melt in equilibrium with a hydrothermal fluid the primary mineralisation was probably formed at or close below the sea floor and fed by sulphide poor hydrothermal fluids sulphide was largely derived from seawater by open system bacterial sulphate reduction u v and mo may be seawater derived

does large igneous province volcanism always perturb the mercury cycle comparing the records of oceanic anoxic event 2 and the end cretaceous to other mesozoic events mercury hg is increasingly being used as a sedimentary tracer of large igneous province lip volcanism and supports hypotheses of a coincidence between the formation of several lips and episodes of mass extinction and major environmental perturbation however numerous important questions remain to be answered before hg can be claimed as an unequivocal fingerprint of lip volcanism as well as an understanding of why some sedimentary records document clear hg enrichment signals whilst others do not of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle as well as the role played by depositional processes in recording global hg cycle perturbations here new mercury records of cretaceous oceanic anoxic event 2 oae 2 94 ma and the latest cretaceous 67 66 0 ma are presented oae 2 is associated with the emplacement of multiple predominantly submarine lips the latest cretaceous with subaerial volcanism of the deccan traps both of these connections are strongly supported by previously published trends towards unradiogenic osmium os isotope values in globally distributed sedimentary records hg data from both events show considerable variation between different locations attributed to the effectiveness of different sediment types in registering the hg signal with lithologically homogeneous records documenting more clear hg enrichments than sections with major changes in lithology such as limestones to claystones or organic rich shales crucially there is no geographically consistent signal of sedimentary hg enrichment in stratigraphic records of either oae 2 or the latest cretaceous that matches os isotope evidence for lip emplacement indicating that volcanism did not cause a global hg perturbation throughout the entire eruptive history of the lips formed at those times it is suggested that the discrepancy between os isotope and hg trends in records of oae 2 is caused by the limited dispersal range of hg emitted from submarine volcanoes compared to the global scale distribution of os a similar lack of correlation between these two proxies in uppermost cretaceous strata indicates that although subaerial volcanism can perturb the global hg cycle not all subaerial eruptions will do so these results highlight the variable impact of different volcanogenic processes on the efficiency of hg dispersal across the globe factors that could influence the impact of lip eruptions on the global mercury cycle include submarine versus subaerial volcanism volcanic intensity or explosivity and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic rich sediments

plumbotectonic aspects of polymetallic vein mineralization in paleozoic sediments and proterozoic basement of moravia czech republic a regional isotopic study of pb and s in hydrothermal galenas and u pb and s in potential source rocks was carried out for part of moravia czech republic two major generations of veins syn variscan and post variscan are defined based on the pb isotope system together with structural constraints local structures and regional trends the pb isotopic compositions of galena plot in two distinct populations with outliers in 206pb 204pb 207pb 204pb space galena from veins hosted in greywackes provides a cluster with the lowest pb pb ratios 206pb 204pb 18 15 18 27 207pb 204pb 15 59 15 61 208pb 204pb 38 11 38 23 those hosted in both limestones and greywackes provide the second cluster 206pb 204pb 18 37 18 44 207pb 204pb 15 60 15 63 208pb 204pb 38 14 38 32 these clusters suggest model pb ages as early carboniferous and triassic jurassic the latter associated with mvt like deposits two samples from veins hosted in proterozoic rocks lie outside the two clusters in metagranitoid 206pb 204pb 18 55 207pb 204pb 15 64 208pb 204pb 38 29 and in orthogneiss 206pb 204pb 18 79 207pb 204pb 15 73 208pb 204pb 38 54 the results from these two samples suggest an interaction of mineralizing fluids with the radiogenic pb rich source basement the values of 34s suggest the paleozoic host rocks mostly 6 7 to 5 2 cdt as the source of s for hydrothermal sulfides mostly 4 8 to 2 5 cdt u pb data and pb isotope evolutionary curves indicate that late devonian and early carboniferous sediments especially siliciclastics are the general dominant contributor of pb for galena mineralization developed in sedimentary rocks plumbotectonic mixing occurred it is deduced only between the lower and the upper crust the latter involving proterozoic basement containing heterogeneous radiogenic pb without any significant input from the mantle it is concluded that in the moravo silesian and rhenohercynian zones including proximal districts in poland lead and sulfur have been mobilized from the adjacent rocks during multiple hydrothermal events in processes that are remarkably comparable in timing geochemistry of fluids and nature of sources

simulation of l band bistatic returns from the ocean surface a facet approach with application to ocean gnss reflectometry we present the implementation of a facet based simulator to investigate the forward scattering of l band signals from realistic sea surfaces and its application to spaceborne ocean global navigation satellite system gnss reflectometry this approach provides a new flexible tool to assess the influence of the ocean surface roughness on scattered gnss signals the motivation stems from the study by clarizia which revealed significant differences between delay doppler maps ddms obtained from uk dmc satellite data and ddms simulated with the zavorotny voronovich z v model here the scattered power and polarization ratio pr are computed for explicit 3 d ocean wave fields using a novel implementation of the kirchhoff approximation ka which we call the facet approach fa we find that the fa is consistent with the full ka and the geometrical optics go used in the z v model while being less computationally expensive than the ka and able to represent polarization effects not captured by the go instantaneous maps of the bistatic normalized radar cross section computed with the fa show clear patterns associated with the underlying waves the wave field is particularly visible in the pr indicating that the scattering is generally dominated by the hh component particularly from ocean wave troughs polarization effects show for the first time a strong correlation to the explicit sea surface from which the scattering originated ddms of the scattered power computed with the fa reveal patchy patterns and power distributions that differ from those obtained with z v and show closer similarities with observed ddms from uk dmc

investigation of azimuthal variations from x band medium grazing angle sea clutter the ingara x band fully polarimetric medium grazing angle sea clutter data set was collected in the australian maritime environment over an angular range of 360 in azimuth and from 15 to 45 in grazing this paper reports further analysis of this data set focusing on understanding the azimuth variation to enable improved simulation accuracy and extraction of relevant geophysical parameters this includes some original properties of the co and cross polarized normalized radar cross section as a function of the scattering geometry and sea surface parameters we also assess the performances and limitations of recent sea surface scattering models in the light of this rich data set

comment on a study of the slope probability density function of the ocean waves from radar observations by d hauser et al 1 intermediate scale waves isw about 0 02 to 6 m long are the main contributor of the ocean surface roughness relevant to passive and active microwave remote sensing of the ocean while wind speed is the most important parameter determining the spectral composition of the ocean surface roughness analysis of field measurements indicates that the wave spectrum of isw is strongly modified by background waves the mean square slope derived from the wave spectrum is therefore also modified by the background wave condition investigation of ocean surface roughness without taking into account the sea state parameter can lead to incorrect conclusions 2 the paper by hauser et al 2008 hereinafter referred to as hcgm08 presented very interesting results on the properties of ocean surface roughness derived from c band 5 35 ghz radar observations they compared the filtered mean square slope obtained under the assumption of gaussian probability density function pdf of surface slopes with three published spectral models their interpretation of the empirical spectral model of hwang 2005 hereinafter referred to as h05 is inaccurate as a result they attributed the disagreement between their data with h05 to the discontinuity in the h05 spectrum caused by matching the empirically parameterized intermediate scale wave isw spectrum and an assumed equilibrium spectrum for the longer waves the issue of matching will be further discussed in section 2 their description on the comparison with h05 was verbal hcgm08 p 9 the result is shown in figure 1 here the analyses of hcgm08 produced two sets of mean square slope mss as a function of wind speed based on the assumption of gaussian shown in their figure 6d and nongaussian their figure 11b surface slope pdf they have noticed the large difference between the two sets of mss but no further comment or explanation was offered derivation of ocean surface roughness from radar backscattering cross section is a complex topic extensive discussions on the subject have been given in earlier publications e g jackson et al 1992 walsh et al 1998 results of mss computation using essentially the same approach of hcgm08 by jackson et al 1992 for ku band 14 ghz andwalsh et al 1998 for ka band 36 ghz are also shown in figure 1 together with the sun glitter data of cox and munk 1954 and the filtered mss of h05 spectral model integrated to an upper cutoff wave number kc suggested by jackson et al 1992 this cutoff wave number corresponds to surface wavelength about 4 7 times the radar wavelength the cutoff wave number used by hcgm08 is much higher corresponding to surface wavelength about 2 2 times the radar wavelength for their c band radar frequency 5 35 ghz kc is 24 rad m on the basis of the criterion of jackson et al 1992 and 51 rad m on the basis of hcgm08 also shown in their figure 1 are the filtered mean square slope derived from direct inversion of the backscattering cross section of ka band radar reported by vandemark et al 2004 further discussion of these data is deferred to section 3 3 after a close examination of their experimental conditions it becomes clear that the source of disagreement is quite different from that suggested by hauser et al and the hint was in fact given in h05 that is the mean square slope of the ocean surface is significantly modified by background waves hcgm08 did not provide too much information about the wind and wave conditions of their experiment however on the basis of the tabulated data presented in an earlier paper of the same experiment mouche et al 2005 the wavefields are strongly influenced by swell not related to the local wind condition in contrast the database used in constructing the h05 spectrum is wind sea dominant with mild swell presence section3 because radar remote sensingplays an increasingly more important role in oceanographic research and environmental monitoring and that an accurate interpretation of the remote sensing measurement requires a correct understanding of the ocean surface roughness in response to various geophysical parameters of interest such as wind air sea stability condition waves of various scales and currents of various sources a clarification of the properties of the ocean surface roughness spectrum is important i hope this note serves to correct the misinterpretation given by hauser et al 2008 regarding the ocean surface roughness spectrum and to call attention the important role of a missing parameter the background wave condition in their analysis

the origin of a mississippi valley type deposit in the viburnum trend southeast missouri petrologic and isotopic studies of the base metal sulfide mineralization in the buick mine have established the following paragenesis an early stage of fine grained pyrite and marcasite replaced the dolostone host rock the iron disulfides and dolostone were replaced by sphalerite during the main stage of sphalerite precipitation delta 34 s sp 16 5 to 19 0ppm following the sphalerite two main stages of galena were precipitated a cuboctahedral stage delta 34 s gn 21 3 to 10 0ppm during which galena replaced dolostone and sphalerite and grew in vugs in the dolostone and in the sphalerite and a cubic stage delta 34 s gn 10 5 to 0 9ppm the two stages of galena precipitation were separated by a period during which the main stage of sphalerite and the cuboctahedral galena were partially dissolved and bladed marcasite delta 34 s mc 2 3 to 4 1ppm was precipitated and followed by a period of mild etching of the cubic galena minor amounts of pale sphalerite delta 34 s sp 14 0 to 16 5ppm were then precipitated white and colorless rhombs of dolomite were precipitated at the same time as some of the main stage of sphalerite the cubic galena and the pale sphalerite after the pale sphalerite was precipitated chalcopyrite quartz and siegenite were precipitated followed by calcite and finally kaolinite the paragenetic and textural data for both galena and sphalerite in the buick mine strongly suggest that these minerals were precipitated and dissolved repetitively during ore formation similar textural evidence for galena reported by other workers for different mines in the viburnum trend implies that repetitive precipitation and dissolution of galena was probably an important process during the formation of the entire viburnum trend fluid inclusions in late quartz crystals coprecipitated with chalcopyrite have filling and freezing temperatures within the ranges reported for sphalerite from other parts of the viburnum trend demonstrating that the ore forming solutions in the viburnum trend were probably at temperatures in the range 105 degrees to 141 degrees c assuming a maximum pressure correction of about 11 degrees c and were extremely saline containing about 4 0 to 5 0 molal chloride consideration of typical chemical analyses of fluid inclusions from other mississippi valley type deposits suggests that the maximum likely concentration of dissolved co 2 in the ore forming solutions was about 0 05 molal at these concentrations the ore forming solutions that travelled to the site of deposition could have had ph9s about two units less than neutral and still have been in equilibrium with dolomite or calcite the ranges of sulfur and lead isotopic compositions of galena from the buick mine are very similar to those established by earlier studies of the old lead belt and adjacent subdistricts however the correlation of isotopically lighter sulfur with more radiogenic lead is much stronger for the viburnum trend suggesting that galena was precipitated from many solutions each of which carried lead and sulfur together and had different lead and overall sulfur isotopic compositions the textural paragenetic and isotopic data for the buick mine cannot be easily explained either by a sulfate reduction model in which sulfate was reduced by organic matter or methane or mixing models in which base metals and reduced sulfur were transported separately to the site of deposition instead the data strongly support a reduced sulfur model for ore formation according to which the base metals were transported together with reduced sulfur as h 2 s in the same solutions to the sites of deposition the reduced sulfur model is also supported by a theoretical calculation of the solubilities of galena and sphalerite which demonstrate that low but economically significant concentrations of lead or zinc could have been transported as chloride complexes together with equivalent concentrations of reduced sulfur at temperatures of 100 degrees to 150 degrees c and ph9s of one to two units less than neutral and could have been precipitated by ph increases cooling or dilution at the sites of deposition

microbial sphalerite formation in carbonate hosted zn pb ores bleiberg austria micro to nanotextural and sulfur isotope evidence microglobular sphalerite 90 180 m is a major form of sphalerite in the abandoned triassic carbonate hosted zn pb deposit at bleiberg austria it is common in ores from the crest horizon and the first cardita horizon which contain about 0 5 to 3 mm thick and up to 5 cm long wavy discontinuous sphalerite rich bands composed of agglomerations of microglobular sphalerite based on comparisons with modern environments these textures are interpreted as peloids and probably represent fossil microbial mats these are inter layered with carbonate and marcasite rich as well as finely banded sphalerite layers fibrous galena and relics of oxysulfides resulting in the characteristic rhythmically banded macrotexture of these zn dominated ores microbial nanotextures made visible by field emission scanning electron microscopy fesem after etching include sphalerite nanospheres 10 90 nm and bacterial filaments the sphalerite nanospheres are identical to those previously reported for mixed calcite sphalerite peloids from bleiberg and are very similar to nanotextures observed in recent bacterial biofilms made by desulfobacteriaceae the observed sphalerite nanospheres are interpreted as in situ metabolic products of sulfate reducing bacteria micro and nanotextures suggest that the larger m sized sphalerite globules formed by agglomeration of sphalerite nanospheres as well as by replacement of peloids representing former bacterial colonies the latter are now composed of zn calcite cores surounded by serrated sphalerite rims most samples studied evidence recrystallization of sphalerite that is broadly coeval with formation of fluorite involvement of sulfate reducing bacteria in the formation of this early sphalerite mineralization is supported by sulfur isotope data sphalerite is generally characterized by isotopic light sulfur with 34 s per mil values ranging from 30 5 to 20 3 per mil the most negative sulfur isotope values are recorded from sphalerite 30 5 30 2 and galena with unusual fibrous to dendritic morphology 31 9 31 8 both are associated with oxysulfides microglobular sphalerite with well preserved sphalerite globules has a 34 s value of 28 8 to 28 2 per mil colloform sphalerite schalenblende ranges from 29 0 to 25 0 per mil microglobular sphalerite associated with fine grained fluorite and euhedral sphalerite formed through recrystallization processes show a trend to less negative values i e 26 3 to 22 2 per mil and 22 9 to 20 3 per mil respectively we suggest that the combined biogenic nano to macrotextures and sulfur isotope data are evidence that microbes played a key role in formation of alpine carbonate hosted zn pb deposits results of this study contradict the mvt model suggested for alpine pb zn deposits which calls for formation of pb zn mineralization during late diagenetic burial in the late triassic early jurassic

volatile fluxes during flood basalt eruptions and potential effects on the global environment a deccan perspective abstract we examine the role that flood basalt eruptions may have played during times of mass extinction through the release of volcanic gases continental flood basalt provinces have formed by numerous eruptions over a short period of geologic time characteristically a few million years within this period a short lived climactic phase that lasts about 1 ma typically emplaces a large proportion of the lava volume this phase consists of a series of huge eruptions each yielding 10 3 10 4 km 3 of magma each eruption lasted on the order of a decade or more and built an immense p hoehoe dominated lava flow field by eruptive activity along fissures tens to hundreds of km long high fire fountains emanating from vents along the fissures at times sustained eruption columns that lofted gas and ash into the upper troposphere and lower stratosphere while the lava flows covered huge areas the combination of large eruption magnitudes maintained high effusion rates during eruptions and the repeated nature of the characteristic large scale eruptive activity occurs in earth history only during periods of flood basalt volcanism based on recent analogs and determination of volatile contents of ancient flood basalt lavas we estimate that individual eruptions were capable of releasing 10 000 tg of so 2 resulting in atmospheric loadings of 1000 tg a 1 during a sustained decade long eruptive event we apply this model of flood basalt volcanism to estimate the potential mass of co 2 and so 2 released during formation of the 65 ma deccan province the deccan lava pile contains the record of hundreds of enormous p hoehoe flow fields erupted within a period of about 1 ma consequently atmospheric perturbations associated with so 2 emissions from just one of these long lasting eruptions were likely to have been severe and constantly augmented over a decade or longer by contrast the amounts of co 2 released would have been small compared with the mass already present in the atmosphere and thus much more limited in effect individual eruptions were followed by hiatuses of hundreds to thousands of years during which the gas contributions to the atmosphere would be recycled it is clear that the nature and potential atmospheric impact of a series of huge volume repeated long term degassing events requires further investigation in conjunction with appropriate climate models

a novel combined approach for compositional and pb isotope data of leaded copper based alloys bronze coinage in magna graecia and rome 5th to 2nd centuries bce abstract lead is a ubiquitous and ambiguous component of ancient copper based artefacts as it can be a residue of the ore or could have been deliberately added in this study we present compositional and pb isotope data of a set of roman syracusan and south italian indigenous bronze coins from the 5th to 2nd centuries bce we describe an approach that considers the pb content and its potential implications for provenance and technology as a variable alongside pb isotope source characteristics by combining elemental with isotopic data of lead and in a subsequent step with trace element signatures this method allows to identify endmembers of natural and or anthropogenic mixing and to outline their possible provenance in a wider context our results show how the existing bronze currencies transform parallel to the changing political situation and how rome s bronze monetary instruments develop from a combination of local tradition and greek practices into a coinage in its own right

multiple factors in the origin of the cretaceous tertiary boundary the role of environmental stress and deccan trap volcanism a review of the scenarios for the cretaceous tertiary k t boundary event is presented and a coherent hypothesis for the origin of the event is formulated many scientists now accept that the event was caused by a meteorite impact at chicxulub in the yucatan peninsula mexico our investigations show that the oceans were already stressed by the end of the late cretaceous as a result of the long term drop in atmospheric co2 the long term drop in sea level and the frequent development of oceanic anoxia extinction of some marine species was already occurring several million years prior to the k t boundary the biota were therefore susceptible to change the eruption of the deccan traps which began at 66 2 ma coincides with the k t boundary events it erupted huge quantities of h2so4 hcl co2 dust and soot into the atmosphere and led to a significant drop in sea level and marked changes in ocean temperature the result was a major reduction in oceanic productivity and the creation of an almost dead ocean the volcanism lasted almost 0 7 m y extinction of biological species was graded and appeared to correlate with the main eruptive events elements such as ir were incorporated into the volcanic ash possibly on soot particles this horizon accumulated under anoxic conditions in local depressions and became the marker horizon for the k t boundary an oxidation front penetrated this horizon leading to the redistribution of elements the eruption of the deccan traps is the largest volcanic event since the permian triassic event at 245 ma it followed a period of 36 m y in which the earth s magnetic field failed to reverse instabilities in the mantle are thought to be responsible for this eruption and therefore for the k t event we therefore believe that the k t event can be explained in terms of the effects of the deccan volcanism on an already stressed biosphere the meteorite impact at chicxulub took place after the onset of deccan volcanism it probably played a regional rather than a global role in the k t extinctions

the deccan traps an interpretation in terms of progressive lithospheric flexure in response to a migrating load abstract structural and geochemical data from the western ghats india have been used to construct an accurate north south section of the volcanic stratigraphy of the southwest part of the deccan province the characteristic style of the section is one of southerly dip reversing in the extreme south southward overstep of higher units onto pre deccan rocks and down dip thinning of individual formations in contrast an east west section shows continuity of essentially horizontal stratigraphic units without overstepping relationships previous authors have interpreted these data in terms of the progressive southward migration of the volcanic source as india drifted northwards over a hot spot now centered beneath reunion we have compared the observed stratigraphy to the predictions of a geophysical model based on the flexural response of the continental lithosphere to a migrating volcanic load the best fit to the observed section is for the structurally lowest part of the modelled sections with an elastic thickness of the lithosphere of 100 km this value explains the present day width of the traps in peninsula india but requires that up to 5 5 km of the upper part of the flank section has been removed by erosion the origin of the erosion is not clear but it may be related to flexural rebound following removal of the cone loads that formed along the trace of the plume the model cannot explain the subsidence of the traps beneath the shelf off bombay or the rim uplift of the traps in the western ghats we attribute these modifications of the stratigraphy to vertical movements uplift and subsidence that followed rifting of india from the mascarene plateau during the eocene

scattering of gps signals from the ocean with wind remote sensing application a theoretical model that describes the power of a scattered global positioning system gps signal as a function of geometrical and environmental parameters has been developed this model is based on a bistatic radar equation derived using the geometric optics limit of the kirchhoff approximation the waveform i e the time delayed power obtained in the delay mapping technique depends on a wave slope probability density function which in turn depends on wind waveforms obtained for aircraft altitudes and velocities indicate that altitudes within the interval 5 15 km are the best for inferring wind speed in some regimes an analytical solution for the bistatic radar equation is possible this solution allows converting trailing edges of waveforms into a set of straight lines which could be convenient for wind retrieval a transition to satellite altitudes together with satellite velocities makes the peak power reduction and the doppler spreading effect a significant problem for wind retrieval based on the delay mapping technique at the same time different time delays and different doppler shifts of the scattered gps signal could form relatively small spatial cells on sea surface suggesting mapping of the wave slope probability distribution in a synthetic aperture radar sar fashion this may allow more accurate measurements of wind velocity and wind direction

paleomagnetic constraints on the structure of the deccan traps abstract new paleomagnetic results from two widely separated areas of the deccan traps allow one to test the simple normal reversed normal nrn magnetostratigraphic model previously proposed the new data from the mandla region to the northeast of the main outcrop of the deccan traps together with earlier apparently conflicting results are all compatible with the nrn stratigraphy provided the flows are not strictly horizontal but have a synform antiform structure with 500 m amplitude and 150 km wavelength the structure parallels the paleozoic narmada son rift system with slopes never exceeding 0 5 sampling in rajahmundry a remote southeastern outlier of the deccan with well constrained age allowed identification of the rn boundary in an area where only normal polarities had been reported it has also been possible to correlate the detailed geochemical stratigraphy in the western ghats with the nrn magnetic stratigraphy a compilation of 35 magnetic studies together with the above findings confirms the general applicability of the nrn model and reveals the large scale topography of the rn boundary which is an isochron over most of the deccan the rn isochron surface displays a boomerang shape with topography ranging from sea level to above 1600 m this observed topography is consistent with a simple model in which doming and renewed rifting and dyke intrusion resulted from impingement 70 65 ma ago of the reunion plume under the indian lithosphere the narmada son rift was rejuvenated and a continental rift system with minor extension with a triple junction in the cambay graben resulted and was subsequently covered by the deccan flows although in places tectonic faulting and volcanism continued to interfere the rajahmundry outcrops constrain the original extent and southeastward dip away from the triple junction of much of the traps a significant part of which has now been removed by erosion and rifting away of the seychelles

a geological map of the southern deccan traps india and its structural implications a geological map of an area of over 125 000 km 2 within the southern deccan traps india is presented which is based upon variations in the basalt geochemistry it represents a synthesis of new data and earlier work the use of large data sets has allowed stratigraphic boundaries to be established with greater accuracy over a much larger area than before the geochemical sections demonstrate that the southward overstepping stratigraphic style encountered along the ghats ridge has an essentially north to south polarity and that there appears to be detectable overstep in an east to west sense however the stratigraphy defines a pronounced coastward dipping monoclinal flexure across the western ghats ridge between 16 n and 18 n the data are consistent with two models of eruption the first considers the deccan eruptive focus to have been fixed throughout the volcanic episode producing an essentially annular flow pattern the second considers the flow pattern to have been generated from a southerly migrating eruptive centre resulting from the northerly drift of india over a fixed hotspot both hypotheses are consistent with recent quantitative models which suggest that rapid and voluminous flood basalt eruptions are the result of continental rifting events associated with plume generated thermal 9highs9 until a causal link between established plume hotspot trails and impact sites can be satisfactorily demonstrated we find it unnecessary to invoke a cataclysmic impact event as an explanation for the deccan eruptions

new palaeomagnetic data from the mahabaleshwar plateau deccan flood basalt province india implications for the volcanostratigraphic architecture of continental flood basalt provinces abstract new magnetostratigraphic data from seven western ghats sections in the deccan volcanic province are presented these are combined with an established geochemically defined stratigraphy and volcanological logs to provide a correlated chronological eruptive framework we identify two magnetic polarities in five of the sections and these are assigned to chrons 29r and 29n importantly the reversal boundary represents an identifiable isochronous surface within the volcanic pile this surface occurs at different elevations as does the altitude of the geochemically defined formation boundary i e ambenali mahabaleshwar fms which defines a second isochronous surface inspection reveals significant differences in the number and thickness of lava units preserved between these two surfaces this indicates that there was significant local topography c 80 m across deccan volcanic province lava fields during their development an interpretation consistent with topographies observed across modern and historical examples e g hawaii iceland these data also indicate that the geochemical stratigraphies of continental flood basalt provinces can mask local and sub regional detail in lava stacking patterns when applied at smaller spatial scales 2 10 4 m finally transitional r n directions preserved in some eruptive units place constraints upon the rates of eruption and indicate c 2 ka periods of volcanic repose

constraints on the sources of ore metals in mississippi valley type deposits in central and east tennessee usa using pb isotopes abstract the mississippi valley type mvt central and east tennessee tn districts contain lead zinc deposits that occur in the early ordovician carbonates of the knox group although both districts share similar host rock have similar temperatures of formation and typically fill open spaces of collapse breccias or replace their host carbonates previous studies may suggest that these ores did not form from the same mineralizing fluids and may have different pb sources nu plasma mc icp ms pb isotopic analyses on sulfides from central and east tn were conducted and the metal sources evaluated pb isotope ratios from the young mine in the east tn district plot within ranges defined by other east tn district samples from previous studies generally pb isotope ratios or ores from the elmwood mine in the central tn district are more radiogenic and plot between samples from the southern appalachians and illinois kentucky districts it appears that the thick black metal rich shales of the appalachian basin have been the source of the pb zn and ore fluids of mvt deposits that formed the east tn deposits when east tn pb data from this study are compared to central tn pb data central tn pb is commonly more radiogenic suggestive of a mineralizing fluid with different compositions lead isotopic signature of central tn ores may imply potential mixing between end member sources originating from the southern appalachians and illinois basins lead isotopes in mvt and carbonate hosted base metal deposits in us south america and europe display two basic types of pb isotopic signatures the classic mvt deposits in the mid continent us se and central missouri illinois kentucky and upper mississippi valley districts have highly radiogenic pb isotopic compositions and they generally display linear pb isotopic arrays in contrast deposits from europe irish type silesian type alpine type and cevennes region the appalachians and andean type deposits have lower pb isotopic values the european deposits except for the irish type have a restricted range of isotopic ratios which suggest a single mineralizing event of relatively short duration it appears that basement rocks or sedimentary rocks derived from the basement contributed pb to many mvt and carbonate hosted base metal deposits worldwide hydrothermal leaching of radiogenic pb from the crystalline basement rocks may have occurred during formation of these ore deposits high 238u 204pb values for several districts also suggest a supracrustal origin of pb

pre hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the schwarzwald crystalline sw germany ii lead isotope evolution of the european hercynides

quasi gaussian probability density function of sea wave slopes from near nadir ku band radar observations abstract although in most circumstances sea wave slope probability density function pdf is expressed as gaussian distribution there is evidence that it follows quasi gaussian distribution which can be represented by gram charlier series to fourth order all the statistical parameters of slope pdf have previously been derived by using optical methods in specular conditions and values and relationships with surface parameters have been presented in the literature however they may not be relevant at microwave wavelengths due to diffraction effects up to now sea surface slope pdf consistent with ocean microwave remote sensing is not known yet so it is important to establish the parameter models of quasi gaussian slope pdf compatible with radar application in this paper based on the backscattering coefficients from the ku band space borne radar precipitation radar pr data all the parameters of the quasi gaussian slope pdf are inverted using a so called go4 boisot et al 2015 model with a two dimensional 2 d non linear least square fit on the backscattering coefficients we also establish the empirical formulae relating the statistical parameters of the quasi gaussian sea slope pdf with wind speed which may be used for ocean ku band radar application the proposed empirical formulae are compared to the cox and munk 1954 cm slope parameter model the results confirm that the slope variance in upwind and crosswind directions as well as the skewness coefficients exhibit intermediate values between the cm slope parameters of clean surface and slick surface cases the coefficients of peakedness are just in the range of the cm slope peakedness parameter values the impacts of wave conditions swell or wind sea on slope pdf parameters are also studied the results show that in most wind speed conditions the presence of swell increases the skewness coefficients while it decreases the peakedness coefficients

pre hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the schwarzwald crystalline sw germany lead isotopes of k feldspars from five granites of the se schwarzwald and from metamorphites are positively correlated in 207 204 as well as 208 204 vs 206 204 diagrams

lead isotope models for the genesis of carbonate hosted zn pb shale hosted ba zn pb and silver rich deposits in the northern canadian cordillera isotope analyses of galena from syngenetic barite zinc lead and epigenetic zn pb and ag rich deposits from the northern canadian cordillera are subdivided into four distinct fields and lines on 207 pb 204 pb and 208 pb 204 pb vs 206 pb 204 pb plots these lines used in conjunction with constraints imposed by stratigraphy by k ar isotopic dates and by minor element analyses in sphalerite define three metallogenic events dating about 0 52 0 37 and 0 09 b y which are summarized as follows 1 old carbonate hosted zn pb deposits formed in the lower cambrian about 0 52 b y ago define closely a maximum source age of 1 9 b y this is the first lead isotopic indication of hudsonian basement in the northern canadian cordillera spatial association of these deposits to unconformities and generation of lead in an upper crustal but generally uranium poor environment supports a karstic model for their origin 2 shale hosted ba zn pb mineralization from upper devonian to lower mississippian about 0 37 b y old rocks is indistinguishable in lead isotope composition from the majority of post lower ordovician to devonian young carbonate hosted zinc lead deposits these deposits formed near 0 37 b y ago from brines dewatered from the selwyn shale basin where solutions were guided by faults either within the basin e g shale hosted ba zn pb deposits formed along grabens near hinge lines close to the margin of the basin or peripheral to and away from the basin e g carbonate hosted zn pb deposits lead for these deposits evolved in an upper crustal uranium rich carbonaceous shale basin environment from which lead relatively rich in radiogenic component was extracted 8 although most ag rich deposits occur as veins not directly associated with plutons some veins occur within or are directly associated with cretaceous plutons indicating a general age of mineralization of 0 09 b y an apparent hudsonian source is indicated some highly radiogenic leads characteristic of the silver deposits were probably formed by preferential leaching of lead from uranium rich minerals

a post k t boundary early palaeocene age for deccan type feeder dykes goa india basaltic dykes exposed along the coast of goa represent the youngest phase of a number of different mafic suites intruding the complex precambrian terrain that forms the pre deccan basement of peninsular india these dykes crop out 50 80 km beyond the southern limits of the deccan continental flood basalt cfb province four of seven sampled dykes were dated using the whole rock 40ar 39ar step heating technique three 40ar 39ar determinations yield palaeocene plateau and isochron ages that clearly indicate an early post cretaceous i e danian age and as a weighted mean average of all four samples yields an age of 62 8 0 2 ma these intrusions are clearly significantly younger than the current estimates for the age range of deccan traps volcanism 65 69 ma the trace element signatures rare earth element patterns and 87sr 86sr ratios of these dykes are consistent with those of the nearby deccan basalts more specifically their geochemical signatures are similar to those of the basalt flows composing the volumetrically important ambenali mahabaleshwar formations which form the uppermost succession wai subgroup of the sw deccan these geochemical and age data demonstrate that deccan type magmatism continued to affect western india for at least 1 2 my after the k t boundary 65 0 0 1 ma and therefore their emplacement places important constraints upon the timing duration and evolution of this much debated cfb province the importance of these dykes is examined within the context of the deccan eruptions and the associated rifting of the western indian margin

response cretaceous extinctions the letters by archibald et al keller et al and courtillot and fluteau question our conclusion that the cretaceous paleogene mass extinction was caused by the asteroid impact at chicxulub all three letters stress that deccan flood basalt volcanism played a major role in the extinction keller

comparison of model predictions with measurements of ku and ka band near nadir normalized radar cross sections of the sea surface from the genesis and rapid intensification processes experiment a comparison of model predictions with measurements of near nadir normalized radar cross sections nrcss of the sea surface at ku and ka bands is reported measurements of airborne precipitation radar second generation apr 2 from near nadir to 25 incidence angle along with simultaneous wind truth from dropsonde observations are compared with predictions of the cutoff invariant two scale model of sea scattering with the overall goal of assessing the model for possible future use in the apr 2 calibration process the performance of the model as a function of wind speed and incidence angle is therefore emphasized the measured data set acquired primarily during the 2010 genesis and rapid intensification processes grip experiment includes wind speeds from approximately 5 to 45 m s model comparisons are limited by uncertainties in the wind fields due to limited dropsonde coverage the data set is separated into more reliable containing wind speeds of 5 20 m s and less reliable wind speeds of 5 45 m s wind truth categories accordingly because a model of the sea spectrum is required for cutoff invariant model predictions comparisons with measured data are performed for three differing sea spectrum descriptions it is found that a bias of less than 1 db over the wind speed range 5 40 m s and a standard deviation less than 1 db over the wind speed range 10 40 m s can be achieved when using the unified sea spectrum description of elfouhaily the model also provides error levels that are near uniform with respect to both incidence angle and wind speed