40 r139 r and k ar age constraints on shear zone evolution southern taltson magmatic zone northeastern alberta1 new 40ar 39ar analyses of hornblende muscovite biotite and k feldspar constrain the timing of deformation and cooling of the southern taltson magmatic zone which underwent lower granulite to upper amphibolite grade deformation in part synchronous with voluminous 1 99 1 92 ga magmatism new data are combined with existing k ar dates into a regional cooling framework to provide thermotemporal constraints on the deformational history 40ar 39ar hornblende ages of ca 1900 ma are interpreted to record relatively rapid cooling following ductile thrusting on the andrew lake shear zone and younger anatectic magmatism these data with published k ar and u pb data support relatively rapid cooling of the taltson magmatic zone from monazite closure temperature of 725 c at ca 1930 ma to 525 c at ca 1900 ma cooling rate estimates are about 7 c ma which suggests moderate exhumation rates during the high grade part of the deformational history a muscovite 40 r 39ar plateau age of 1803 f 11 ma is consistent with the mean muscovite k ar age of 1792 ma indicating regional cooling through about 350 c at ca 1800 ma 40ar 39ar ages from magmatic biotite of 1856 and 1799 ma also suggest slow cooling during greenschist grade deformation which can be no older than ca 1860 ma a k feldspar 40ar 39ar age of 1681 ma provides a lower limit for the time of greenschist grade deformation cooling rate estimates during amphibolite to greenschist grade deformation are 1 75 2 25 cima

particle transport of 234u 238u in the kalix river and in the baltic sea the role of particles for u isotope transport was investigated in the kalix river watershed a particle poor fe mn rich river in northern sweden and in the baltic sea estuary particles 0 45 m are strongly enriched in u and contain 20 50 of the total riverine uranium budget and 1 of the total u in brackish waters 3 7 psu the particles have high 234 u which is close to that of dissolved u in the associated water indicating that u on particles is dominantly nondetrital and isotopically exchanges rapidly with the ambient dissolved u particles at the river mouth are dominated by nondetrital fe mn oxyhydroxides uranium and fe are strongly correlated clearly demonstrating that secondary fe oxyhydroxide is the major carrier of u in river water there is no evidence for significant association of u with mn oxyhydroxide apparent u distribution coefficients k d fe were calculated for u between the authigenic fe on particles and the solution these values appear to be relatively constant throughout the year this suggests an equilibrium between fe in solution and authigenic fe oxyhydroxides on detrital particles high values of k d fe calculated for one summer as well as high u concentrations in brackish waters can be explained by u scavenging by biogenic phases with low authigenic fe content

major and trace element abundances and strontium isotopes in the nyong basin rivers cameroon constraints on chemical weathering processes and elements transport mechanisms in humid tropical environments this paper aims to improve our understanding of chemical weathering processes and element transport mechanisms in the humid tropical environments we studied the nyong river basin 27 800 km2 located on the northwestern part ntem complex of the congo craton central africa the dissolved concentrations i e 0 20 m of major and trace elements dissolved organic carbon doc and the 87sr 86sr ratios have been measured in more than 20 rivers draining watersheds with various surface areas 1 to 28 000 km2 all these rivers exhibit low major cations concentrations i e na mg k ca but high concentrations of some trace elements al fe th zr y ree silica and doc the total dissolved load tds is low 20 mg l 1 and dominated by silica and organic matter the comparison of different watersheds shows us that chemical weathering is more efficient in the small unit watersheds all the sampled rivers exhibit a wide range of 87sr 86sr ratios and high ca na ratio that can be explained by the heterogeneity of the crystalline rock constituting the cratonic basement four selected rivers mengong awout soo and nyong having different drainage areas and hydrological parameters were sampled over a 2 year period collected data show that all these rivers present the same monthly seasonal variations with higher concentrations during rainy season and lower concentrations during dry season this implies that the weathering and transport mechanisms of small watersheds can be extended to the whole nyong basin in the small unit watersheds chemical weathering mainly occurs in swamp zones where mineral dissolution is enhanced by humic substances these swamp zones constitute a pool of organic rich water which can be quickly mobilized during rain seasons in these waters doc and insoluble element concentrations e g al fe and th were strongly correlated which show the key role of organic colloidal matter in the transport of some insoluble elements some other relationships al vs fe ree vs al were also examined in order to get information about chemical weathering or element transport based on these data it has been concluded that the chemical composition of these river waters is controlled by geomorphic and historic factors e g thick cation poor soil in contrast the present day climatic parameters high rainfall and temperature play a minor role in water chemistry regulation even though they are likely to enhance mineral dissolution even if organic matter favors mineral dissolution chemical weathering in this area is low compared to other world regions which suggest on a global scale a relatively small effect of these environments on the co2 consumption

first cycle quartz arenites in the orinoco river basin venezuela and colombia modern first cycle quartz arenites are forming in the orinoco drainage basin by at least two distinct mechanisms common to both mechanisms is an environment of intense chemical weathering and extended time over which weathering can occur in the llanos andean foreland basin extended time is provided by temporary storage of orogenically derived sediments on extensive alluvial plains in lowland portions of the guayana shield long soil mineral residence times are produced by very low erosion and transport rates resulting from low relief and tectonic quiescence both weathering intensity and the duration of weathering are important in the modification of sand composition first cycle quartz arenites are produced in diverse tectonic settings and cannot be used by themselves to infer paleotectonic settings of ancient sequences furthermore although tectonic setting is of great importance in determining sand composition modifications during transport and deposition can overprint the effects of the tecto

cycling of iron manganese silica phosphorus calcium and potassium in two stratified basins of shagawa lake minnesota geochemical studies of fe mn si p ca and k were made in two basins of shagawa lake minnesota during summers 1977 1979 within the metalimnion upward and laterally diffusing fe ii oxidizes and co precipitates a large fraction of soluble p nevertheless the soluble fep ratio decreases while progressing upward through the oxidation zone the mean paniculate fesi ratio is 3 0 0 5 in the thermocline but because of the stoichiometric excess of dissolved si over fe and preferential associations between fe and p the oxidation of fe has a negligible effect on the dissolved sio2 profiles the lake sediments are net sources of ca k and p during summer stratification these elements are transported upward through the thermocline and exported from the lake despite the very active sediment release of dissolved sio2 and upward transport through the thermocline the lake acts as a net sink for biogenic opal in summer the prominent soluble mn maxima in the thermocline of the east basin result from antecedent sediment release mn2 and vertical transport primarily in the west basin followed by dispersion and oxidation in the epilimnion and finally downward settling and dissolution within the east basin thermocline rhodochrosite solubility does not influence mn2 profile development very large percentage increases in epilimnetic fe mn si and p occur simultaneously during episodes of wind activated entrainment of metalimnion water these increases are in stoichiometric agreement with the entrained water mass provided account is also taken of the preformed slurries overlying the metalimnetic shelf sediments in mid summer the bathylimnetic soluble fep ratio remains low since the cultural inputs of p were terminated in early 1973 this geochemical stability is explained by the large reserves of potentially mobile p in the upper post cultural sediments phosphorus release from these sediments and transport phenomena account for the persistent eutrophic condition of the lake during mid late summer despite the 80 reduction in external p loading

development of late paleozoic volcanic arcs in the canadian cordillera an example from the klinkit group northern british columbia and southern yukon the late paleozoic volcanic rocks of the northern canadian cordillera lying between ancestral north america to the east and the accreted terranes of the omineca belt to the west record early arc and rift magmatism along the paleo pacific margin of the north american craton the mississippian to permian volcano sedimentary klinkit group extends discontinuously over 250 km in northern british columbia and southern yukon the two stratotype areas are as follows 1 in the englishman range southern yukon the english creek limestone is conformably overlain by the volcano sedimentary mount mccleary formation lower clastic member alkali basalt member and volcaniclastic member and 2 in the stikine ranges northern british columbia the screw creek limestone is conformably overlain by the volcano sedimentary butsih formation volcaniclastic member and upper clastic member the calc alkali nature of the basaltic volcaniclastic members of the klinkit group indicates a volcanic arc setting la yb n 2 77

variable eocene miocene sedimentation processes and bottom water redox conditions in the central arctic ocean iodp expedition 302 abstract in 2004 integrated ocean drilling program expedition 302 arctic coring expedition acex to the lomonosov ridge drilled the first central arctic ocean sediment record reaching the uppermost cretaceous 430 m composite depth while the neogene part of the record is characterized by grayish yellowish siliciclastic material the paleogene part is dominated by biosiliceous black shale type sediments the lithological transition between paleogene and neogene deposits was initially interpreted as a single sedimentological unconformity hiatus of 26 ma duration separating eocene from miocene strata more recently however continuous sedimentation on lomonosov ridge throughout the cenozoic was proclaimed questioning the existence of a hiatus in this context we studied the elemental and mineralogical sediment composition around the paleogene neogene transition at high resolution to reconstruct variations in the depositional regime e g wave current activity detrital provenance and bottom water redox conditions already below the hiatus mineralogical and geochemical proxies imply drastic changes in sediment provenance and or weathering intensity in the hinterland and point to the existence of another earlier gap in the sediment record the sediments directly overlying the hiatus the zebra interval are characterized by pronounced and abrupt compositional changes that suggest repeated erosion and re deposition of material regarding redox conditions euxinic bottom waters prevailed at the eocene lomonosov ridge and became even more severe directly before the hiatus with detrital sedimentation rates decreasing authigenic trace metals were highly enriched in the sediment this continuous authigenic trace metal enrichment under persistent euxinia implies that the arctic trace metal pool was renewed continuously by water mass exchange with the world ocean so the eocene arctic ocean was not fully restricted above the hiatus extreme positive ce anomalies are clear signs of a periodically well oxygenated water column but redox conditions were highly variable during deposition of the zebra interval significant mn enrichments only occur above the zebra interval documenting the miocene establishment of stable oxic conditions in the arctic ocean in summary extreme and abrupt changes in geochemistry and mineralogy across the studied sediment section do not suggest continuous sedimentation at the lomonosov ridge around the eocene miocene transition but imply repeated periods of very low sedimentation rates and or erosion

weathering processes and the composition of inorganic material transported through the orinoco river system venezuela and colombia abstract the composition of river borne material in the orinoco river system is related primarily to erosion regime which in turn is related to tectonic setting especially notable is the contrast between material derived from tectonically active mountain belts and that from stable cratonic regions for a particular morpho tectonic region the compositional suites of suspended sediment bed material overback deposits and dissolved phases are fairly uniform are are typically distinct from whose of other regions for each region a consistent set of chemical weathering reactions can be formulated to explain the composition of dissolved and solid loads in developing these formulations erosion on slopes and storage of solids in soils and alluvial sediments are important considerations compositionally verymature sediment is derived from areas of thick soils where erosion is transport limited and from areas where sediments are stored for extended periods of time in alluvial deposits compositionally immature sediments are derived from tectonically active mountain belts where erosion is weathering limited weathering limited erosion also is important in the elevated parts of the guayana shield within areas of sleep topography compared to the mountain belts sediments derived from elevated parts of the shield are more mature a greater degree of chemical weathering seems to be needed to erode the rock types typical of the shield the major element chemistry and mineral composition of sediment delivered by the orinoco river to the ocean are controlled by rivers that have their headwaters in mountain belts and cross the llanos a region of alluvial plains within the foreland basin the composition of sediments in rivers that drain the shield seems to be established primarily at the site of soil formation whereas for rivers that drain the mountain belts additional weathering occurs during s episodes of storage on alluvial plains as sediments are transported across the llanos to the main stem of the orinoco after mixing into the main stem there seems to be little subsequent alteration of sediment

strontium dissolved and particulate loads in fresh and brackish waters the baltic sea and mississippi delta a study was conducted of the isotopic composition and concentration of sr and of major elements in dissolved and suspended loads of fresh and brackish waters the purpose was to establish the contributions of different parent rocks and minerals to sr during weathering and transport and to identify the role of fe mn oxyhydroxides in the redistribution of sr in the water column during the sedimentary cycle studies were conducted on a profile across an oxic anoxic boundary in the baltic and on rivers covering behavior over an annual cycle in general the 87sr 86sr ratios differ between particulate and dissolved loads with more radiogenic sr in the particulate loads these differences are attributed to differential weathering of minerals where high rb sr minerals dominate the particulate load and low rb sr the dissolved load there is broad correlation of 87 sr 86 sr with k al in the suspended load the differences in 87 sr 86 sr between suspended and dissolved load are highly variable and are related to the fe or mn concentration on the particulates in samples with high fe al the difference becomes small a good correlation was found between sr al and fe al or mn al in the particulates both in brackish and fresh waters sr is removed from solution both in rivers and in the baltic sea whenever there is formation of fe mn oxyhydroxide particulates this precipitation greatly diminishes the difference in isotopic composition of the dissolved and suspended loads as the particles containing fe mn oxyhydroxides settle they dissolve in anoxic zones and release sr this provides a mechanism for sr redistribution in the water column sr is thus only quasi conservative in environments where fe mn oxyhydroxides form or dissolve from consideration of the isotopic differences in sr between dissolved and suspended loads it follows that the net sr input depends upon weathering characteristics of the contributing mineral phases changes in weathering mechanisms due to climate change may cause sr isotopic shifts in the marine environment

colloidal rare earth elements in a boreal river changing sources and distributions during the spring flood abstract variations in the physico chemical speciation of the rare earth elements ree have been investigated in a subarctic boreal river during an intense spring flood event using prefiltered

tectonic affinity of nisutlin and anvil assemblage strata from the teslin tectonic zone northern canadian cordillera constraints from neodymium isotope and geochemical evidence we present geochemical and isotopic data for nisutlin assemblage metasedimentary rocks and anvil assemblage greenstones from the teslin tectonic zone of the northern canadian cordillera this study aims to establish the tectonic setting of formation for the sedimentary and basaltic protoliths of these highly deformed and metamorphosed rocks and thereby place constraints on the origin of these enigmatic rocks for which differing tectonic models have been proposed for the nisutlin assemblage metasedimentary rocks the geochemical and isotopic data show that two widely different source regions contributed detritus to the original sediments one source region was felsic upper crustal material with nd isotopic compositions compatible with ultimate derivation from the north american continent depleted mantle model age tdm 2 5 2 8 ga the second source region is deduced to be chemically primitive crust basaltic andesitic with a short crustal residence history 0 9 ga for the anvil assemblage greenstones immobile trace element abundances are dissimilar to within plate oceanic arc and normal mid ocean ridge basalts and similar to calc alkaline basalts in active continental margin settings we interpret the paleosetting for the nisutlin assemblage to be at the outermost margin of the ancestral north american continent in an area which received detrital input from the distal north american craton in the early paleozoic however this area also received detritus from a chemically and isotopically juvenile magmatic arc source a source type not known from paleozoic metasedimentary rocks from the miogeoclinal sequence on the basis of similar nd isotopic relationships recorded elsewhere in deformed paleozoic rocks of the orogen we infer that these geochemical signals reflect tectonic processes of regional extent the trace element geochemistry of the anvil assemblage greenstones does not support a correclation with known paleozoic greenstones of the slide mountain terrane which some tectonic models have advocated

the importance of colloids and mires for the transport of uranium isotopes through the kalix river watershed and baltic sea the importance of colloids and organic deposits for the transport of uranium isotopes from continental source regions and through the estuarine environment was investigated in the mire rich kalix river drainage basin in northern sweden and the baltic sea ultrafiltration techniques were used to separate uranium and other elements associated with colloids 10 kd and 3 kd from solute uranium and provided consistent results and high recovery rates for uranium as well as for other elements from large volume samples uranium concentrations in 0 45 m filtered kalix river water samples increased by a factor of 3 from near the headwaters in the caledonides to the river mouth while major cation concentrations were relatively constant 234 u 238 u ratios were high 234 u 770 1500 throughout the basin without showing any simple pattern and required a supply of 234 u rich water throughout the kalix river a large fraction 30 90 of the uranium is carried by 10 kd colloids which is compatible with uranium complexation with humic acids no isotopic differences were found between colloid associated and solute uranium within the baltic sea about half of the uranium is removed at low salinities the proportion that is lost is equivalent to that of river derived colloid bound uranium suggesting that while solute uranium behaves conservatively during estuarine mixing colloid bound uranium is lost due to rapid flocculation of colloidal material the association of uranium with colloids therefore may be an important parameter in determining uranium estuarine behavior mire peats in the kalix river highly concentrate uranium and are potentially a significant source of recoil 234 u to the mirewaters and river waters however mirewater data clearly demonstrate that only small 234 u 238 u shifts are generated relative to inflowing groundwater a simple box model of uranium accumulation in peat and transport through the mire that is compatible with the mire data demonstrates that with efficient removal of uranium from solution only small shifts in 234 u 238 u ratios can be generated in mirewater uranium the measurements and model calculations show that mirewaters are not the primary source of the uranium in the river bedrock groundwaters with high 234 u 238 u ratios and uranium concentrations must be the dominant source of riverine uranium

the behavior of u and th series nuclides in the estuarine environment rivers carry the products of continental weathering and continuously supply the oceans with a broad range of chemical constituents this erosional signature is however uniquely moderated by biogeochemical processing within estuaries estuaries are commonly described as complex filters at land sea margins where significant transformations can occur due to strong physico chemical gradients these changes differ for different classes of elements and can vary widely depending on the geographic location u and th series nuclides include a range of elements with vastly different characteristics and behaviors within such environments and the isotopic systematics provide methods for investigating the transport of these nuclides and other analog species across estuaries and into the coastal ocean there are numerous types and definitions of estuaries see dyer 1973 in this paper it is simply considered to be a region where freshwater and seawater mix to emphasize the chemical focus of the issues involved here this region can either be contained within a river channel or extend onto the shelf with effects often extending well into an adjoining ocean basin fairbridge 1980 these are complex ecological biogeochemical and hydrodynamic systems with strong gradients in the concentrations and composition of micro and macro particulate matter as well as dissolved organic and inorganic species particle reactive radionuclides and trace elements being transported across estuaries are subject to partitioning between the dissolved colloidal and particulate phases the variable chemical nature of the u and th series radionuclides is evident in their distributions in an estuarine environment such radionuclides can effectively serve as tracers to identify the sources fate and transport of particles and colloids as well as other pollutants that behave similarly to these nuclides these nuclides also have a wide range of half lives that can be used to examine processes over various time scales for example th and ra daughter isotopes have

deep electrical structure of northern alberta canada implications for diamond exploration geophysical studies of upper mantle structure can provide constraints on diamond formation teleseismic and magnetotelluric data can be used in diamond exploration by mapping the depth of the lithosphere asthenosphere boundary studies in the central slave craton and at fort a la corne have detected conductors in the lithospheric mantle close to or beneath diamondiferous kimberlites graphite can potentially explain the enhanced conductivity and may imply the presence of diamonds at greater depth petrologic arguments suggest that the shallow lithospheric mantle may be too oxidized to contain graphite other diamond bearing regions show no upper mantle conductor suggesting that the correlation with diamondiferous kimberlites is not universal the buffalo head hills in alberta host diamondiferous kimberlites in a proterozoic terrane and may have formed in a subduction zone setting long period magnetotelluric data were used to investigate the upper mantle resistivity structure of this region magnetotell

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

nd isotopic evidence for crustal recycling in the ca 2 0 ga subsurface of western canada sm nd isotopic data are presented for 23 drill core samples from five aeromagnetically and geochronologically u pb zircon distinct domains of the precambrian basement of northern alberta the domains in question are the taltson 1 96 1 94 ga buffalo head 2 32 1 99 ga chinchaga 2 19 2 09 ga ksituan 1 99 1 90 ga and nova 2 81 ga these domains are truncated to the north and south by the great slave lake shear zone and the snowbird tectonic zone respectively initial end values are 5 0 to 9 7 for the taltson 0 2 to 6 3 for the buffalo head 0 6 to 1 8 for the chinchaga 1 8 to 2 1 for the ksituan and 5 6 for the nova crustal residence model ages fall in the 2 5 2 8 ga range the nd isotopic signatures may be viewed in terms of mixing a minimum of 10 archean continental crust with a depleted mantle component speculations on the tectonic history of the basement domains in question involve the assembly of archean crustal nuclei to form the buffalo head chinchaga composite domain a

taltson basement gneissic rocks upb and nd isotopic constraints on the basement to the paleoproterozoic taltson magmatic zone northeastern alberta the taltson magmatic zone is a 300 km long northerly trending belt of archean to paleoproterozoic granitic basement gneiss amphibolite supracrustal gneissic rocks and voluminous paleoproterozoi

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

spectral behavior of sulfides in simulated daytime surface conditions of mercury supporting past messenger and future missions bepicolombo abstract to detect the mineral diversity of a planet s surface it is essential to study the spectral variations over a broad wavelength range at relevant simulated laboratory conditions the messenger mercury surface space environment geochemistry and ranging mission to mercury discovered that irrespective of its formation closest to the sun mercury is richer in volatiles than previously expected this is especially true for sulfur s with an average abundance of 4 wt it has been proposed that sulfur in the interior of mercury can be brought to the surface through volcanic activity in the form of sulfides as slag deposits in mercury hollows and pyroclastic deposits however comprehensive spectral library of sulfide minerals measured under vacuum conditions in a wide spectral range 0 2 100 m was lacking this affects the detectability and understanding of the distribution abundance and type of sulfides on mercury using remote sensing spectral observations in the case of mercury the effect of thermal weathering affecting the spectral behavior of these sulfides must be studied carefully for their effective detection in this study we present a spectral library of synthetic sulfides including mgs fes cas crs tis nas and mns for each sample we performed emissivity measurements in the thermal infrared range tir 7 14 m for sample temperatures from 100 c 500 c covering the daytime temperature cycle on mercury s surface in addition for each sample we measured the spectral reflectance of fresh and thermally processed sulfides over a wide spectral range 0 2 100 m and at four different phase angles 26 40 60 80 this spectral library facilitates the detection of sulfides by past and future missions to mercury by any optical spectrometer of any spectral range specifically the emissivity measurements in this study will support the mercury radiometer and thermal imaging spectrometer mertis instrument on the esa jaxa bepicolombo mission which will study the surface mineralogy over a wavelength range of 7 14 m at a spatial resolution of 500 m pixel the measured reflectance of these sulfides in 0 2 100 m at various phase angles will support the interpretation of measurements from past mdis mascs on messenger and future missions simbio sys on bepicolombo

the copper isotope geochemistry of rivers and the oceans abstract we present the first extensive dataset for copper cu isotopes in rivers as well as preliminary data for estuaries and seawater rivers exhibit a range in dissolved 65 cu relative to nist srm 976 of 0 02 to 1 45 per mil the discharge weighted average dissolved 65 cu and cu concentration for the studied rivers representing around 25 of the global riverine water discharge are 0 68 and 18 8 nmol kg 1 respectively isotopic data for the dissolved phase in two small estuaries in se england exhibit relatively minor variation through the salinity gradient 0 42 to 0 94 and are close to both the data for the rivers upstream from the estuaries and a measurement of the coastal sea at their mouths analyses of the particulate phase in the estuaries reveal a complementary light pool 0 24 to 1 02 the isotopic composition of the total cu inventory is however close to that of the crustal source these data along with published constraints suggest that the isotopically heavy dissolved phase of all the rivers originates in an isotopic partitioning of the weathered pool of cu between a light fraction adsorbed to particulates and a heavy dissolved fraction dominated by cu bound to strong organic complexes open ocean seawater samples generally exhibit even heavier dissolved cu isotopic compositions than the riverine input 65 cu 0 9 to 1 5 the heavy isotopic composition of seawater is inferred to originate from intra oceanic processes the small dataset presented here is most consistent with further isotopic partitioning between an isotopically light pool adsorbed to particulates and a heavy dissolved pool strongly bound to organic ligands scavenging appears to have greatest impact in the surface ocean and least in both the oxygen minimum zone and the ocean bottom perhaps reflecting the relative importance of scavenging and thus the sequestration of light cu to particulate material at different depths

formation of freshwater fe mn coatings on gravel and the behavior of 60co 90sr and 137cs in a small watershed iron and manganese oxide coatings are actively forming on stream substrates in the white oak creek watershed in east tennessee although oxidizing conditions are required for fe mn oxide precipitation coatings accumulate only if dissolved iron and manganese exceed 50 g l below this coatings are lost by abrasion as fast as or faster than they form annual rates of formation of 3 mg g on substrate gravel were observed manganese is dissolved from coatings between eh values of 100 to 300 mv and below 1 mg l dissolved o2 at ph 6 5 to 7 5 iron oxides can be precipitated under these conditions uncontaminated gravels with oxide coatings composed of illite quartz and feldspar adsorbed radionuclides rapidly from waters below mpc maximum permissible concentration levels contaminated gravels placed in uncontaminated waters lost 60co by abrasion in oxidizing conditions and by dissolution of manganese coatings in reducing conditions exchangeable 90sr was completely lost after one month whereas nonexchangeable 90sr was lost more slowly 137cs was totally retained by the gravels gravels such as these can be used to monitor the radionuclide content of waters in the environment

weathering rinds and rock coatings from an arctic alpine environment northern scandinavia coarse rock debris exposed in the subaerial environment of northern sweden displays the development of a wide variety of surface coatings these include weathering rinds as well as a great diversity of geochemical coatings including those dominated by ca fe si and al each of these types of rock coatings displays a high degree of geochemical complexity the weathering rinds exhibit both geochemical and morphologic changes to the parent rock cores including extensive dissolution oxidation and hydration as well as disaggregation fracturing and cementation by secondary geochemical coatings chemical breakdown of the rock to form weathering rinds includes loss of k si mg and ca and buildup of fe weathering rinds are fundamentally the result of dissolution as no clay minerals were identified in the rinds rock coatings are distinguished from rinds by their clear accretionary nature despite the distinction made between weathering rinds and rock coatings it is important to note that often the two are intimately related the presence of rock coatings as well as weathering rinds on rock surfaces amplifies the important role played by geochemical processes in the arctic alpine climate of northern sweden in particular as well as its significance in landscape evolution in such environments in general

chemical weathering in granitic environments abstract factors controlling chemical weathering in granitic environments are deduced using an extensive database from the literature based on a transition state theory model we evaluated the effects on chemical weathering of runoff temperature and ph the dependence between temperature and runoff and chemical weathering is complicated by other factors such as the presence depth of soil cover soil cover favors chemical weathering when it is thin and rich in weatherable minerals in contrast it reduces chemical weathering when is thick and poor in primary minerals processes that increase the contact time and the surface of the water rock interactions such as physical denudation increase chemical weathering rates in granitic environments the effect of temperature can be quantified assuming an apparent activation energy value of 48 7 kj mol to describe chemical weathering of silica in granitic crystalline environment under high runoff conditions

geochemistry of manganese in the kalix river northern sweden dissolved and suspended mn in the kalix river northern sweden were measured weekly over a period of eighteen months during the same period four lakes in the kalix catchment were sampled at their outlets and in vertical profiles within the lakes together with a stream draining a series of mires with shallow lakes snow melting in mid may increased the dissolved mn concentration in the river tenfold compared with a concentration of 5 g l 1 during the winter discharge january to april we suggest that the increase was caused by mn rich mire water mixing with melting snow and being transported to the river large concentrations of dissolved mn built up in the hypolimnion of the lakes studied during the icecovered period break up of the ice and spring overturn in june increased the dissolved mn concentration tenfold in lake discharge and a concomitant peak in the dissolved mn concentration was observed in the river lake derived mn was the dominant source for mn in the river during this time suspended mn in the river was hosted mainly in detrital particles during flood in may in mid june non detrital suspended mn started to accumulate and reached a maximum in late july and early august the mnal ratio was 25 times higher during this period than during flood in may suggesting the precipitation of an mn oxyhydroxide phase the precipitation of the non detrital mn rich phase was correlated in time with increased temperature increased ph and increased concentration of suspended biogenic particles the precipitation of dissolved mn was biologically mediated sedimentation and mineralisation of the non detrital mn phase in river and lake sediments resulted in a steady increase of the dissolved mn concentration in the river water during autumn

temporal variations in the fractionation of the rare earth elements in a boreal river the role of colloidal particles rare earth element ree data from weekly sampling of the filtered 0 45 m and suspended particulate phase during 18 months in the kalix river northern sweden are presented together with data on colloidal particles and the solution fraction 3 kda the filtered ree concentration show large seasonal and temporal variations in the river lanthanum varied between approximately 300 and 2100 pm high ree concentration in the filter passing fraction is related to increased water discharge and there is a strong correlation between the ree concentration organic carbon al and fe physical erosion of detrital particles plays a minor role for the yearly transport of particulate ree in this boreal river system the suspended particulate fraction which is dominated by non detrital fractions accounted for only 35 of the yearly total transport of la in the river approximately 10 of the ree were transported in detrital particles during winter at spring flood in may about 30 of the lree and up to 60 of the hree where hosted in detrital particles ultrafiltration of river water during spring flood shows that colloidal particles dominate the transport of filter passing ree less than 5 of the filtered ree are found in the fraction smaller than 3 kda the colloidal fraction shows a flat to slightly lree enriched pattern whereas the solution fraction 3 kda show an hree enriched pattern compared with till in the catchment suspended particles show a lree enriched pattern data indicate that the ree are associated with two phases in the colloidal and particulate fraction an organic rich phase with associated al fe and an fe rich fe oxyhydroxide inorganic phase the ce anomaly in the suspended particulate fraction in the river shows systematic variations and can be used to interpret fractionation processes of the ree during weathering and transport there was no anomaly at maximum spring flood but during the ice covered period the anomaly became more and more negative the temporal and seasonal variations of the ce anomaly in the suspended particulate phase reflect transport of ree c al fe enriched colloids from the upper section of the till and or from mires to the river at storm events

temporal variations in dissolved and suspended iron and manganese in the kalix river northern sweden abstract particulate and dissolved fe and mn were measured once a week from may to september 1982 in the kalix river north sweden during winter baseflow the dissolved fe concentration was 450 g l 1 early snow melt discharge increased the concentration slightly but during springflood maximum the concentration decreased to a minimum value of 60 g l 1 in mid july particulate matter in the kalix river is dominated by fe which ranges between 14 and 38 of the ashed suspended load 70 80 of the total fe load being retained by 0 45 m filters approximately 10 of particulate fe can be accounted for by a detrital phase the particulate fe al ratio showed a mean value of 6 5 which is more than ten times the ratio in mean world river particulate fe showed a peak during early snowmelt and decreased during maximum discharge similar to dissolved fe dissolved mn concentrations ranged from 1 1 to 53 4 m l 1 with a mean value of 11 2 12 4 g l 1 whereas particulate mn ranged from 3 1 ti 18 2 g l 1 with a mean concentration of 10 6 4 9 g l 1 during may and june most mn was transported in the dissolved phase whereas in july and august the particulate fraction dominated there was a drastic increase in non detrital particulate mn with a concomitant decrease in the dissolved fraction in early july with peak values in mid july and early august the decrease in dissolved mn and increase of particulate mn is probably the consequence of two processes namely addition of non detrital particulate mn to the river possibly from lakes and transformation of dissolved mn to a particulate phase within the river a combination of increased ph temperature and particulate mn triggered the precipitation of dissolved mn although the significance of each factor can not be evaluated from this study

laboratory studies on the 3 μm spectral features of mg rich phyllosilicates with temperature variations in support of the interpretation of small asteroid surface spectra abstract recent orbital data revealed the presence of hydrated minerals on the surfaces of asteroids mainly through the identification and the study of the 3 m spectral absorption band hamilton et al 2019 kitazato et al 2019 the presence of an absorption feature around 3 m on planetary bodies surfaces is indicative of the presence of oh bearing minerals this band has been widely detected on carbonaceous chondrites but its appearance and its shape are diverse indicating different composition and or the occurrence of subsequent alteration events in this work we present the results of laboratory experiments performed at the planetary spectroscopy laboratory psl of the german aerospace center dlr to study the spectral behaviour of the 3 m spectral features in the mg oh minerals with thermal variation it has been suggested that thermal alteration processes can darken the surfaces of carbonaceous chondrites thus decreasing the appearance and visibility of the spectral features around 3 m thermal alteration processes are consistent with the scenario currently proposed to explain the formation of 162173 ryugu asteroid sugita et al 2019 the near infrared spectrometer nirs3 on the hayabusa2 mission detected a weak and narrow absorption feature centred at 2 72 m across the entire observed surface of the c type asteroid kitazato et al 2019 however the collected spectra from the ryugu surface show no other absorption features in the 3 m region to investigate this point further and analyze the variation of the spectral features around 3 m with thermal alteration we studied the mg rich phyllosilicates serpentine and saponite in two different situations 1 thermal alteration at increasing temperature the samples were heated at steps of 100 c starting from 100 c up to 700 c for 4 hours each 2 long time heating at constant temperature samples were kept constantly at 250 c for 1 month 1st step then cooled down and measured in reflectance this long heating process has been repeated at the same temperature of 250 c for 2 months 2nd step the results obtained show an important variation of phyllosilicates spectral bands with temperature and provide useful data for the interpretation of past and future mission small bodies collected surface spectra

binding and transport of rare earth elements by organic and iron rich nanocolloids in alaskan rivers as revealed by field flow fractionation and icp ms abstract water samples were collected from six small rivers in the yukon river basin in central alaska to examine the role of nanocolloids 0 5 40 nm in the dynamics and transport of rare earth elements rees in northern high latitude watersheds influenced by permafrost total dissolved 40 nm colloids in a river sampled at higher altitude the

regional mapping of precambrian basement beneath phanerozoic cover in southeastern trans hudson orogen manitoba and saskatchewan the northern edge of phanerozoic platformal rocks of the western canada sedimentary basin overlies the flin flon belt trans hudson orogen in manitoba and saskatchewan a program of regional mapping of the phanerozoic covered basement has been undertaken involving the integration of high resolution aeromagnetic and gravity data with extensive drill core information several major domains are recognized in the buried basement each with a distinct lithotectonic character and potential field anomaly pattern three lithotectonic domains in the buried basement clearwater athapapuskow and amisk lake domains are characterized by northerly trending positive gravity and aeromagnetic anomalies and correlate with the 1 92 1 83 ga volcanic and plutonic rocks of the exposed flin flon belt amisk collage and snow lake assemblage an upper amphibolite grade orthogneiss complex namew gneiss complex containing calc alkaline intrusive rocks ranging in age from 1 88 to 1 83 ga and screens derived from the older v

olivine thermal emissivity under extreme temperature ranges implication for mercury surface abstract the work shows for the first time experimentally and numerically how the thermal emissivity spectra of a mg rich olivine i e mg 1 84 fe 0 16 sio 4 fo 92 fa 8 with fo mg 2 sio 4 and fa fe 2 sio 4 significantly change as a function of temperature thermal infrared spectra at two different temperatures between about 350 and 770 k were collected in order to simulate the typical diurnal equatorial temperature variation of the surface of mercury such temperature increase i e 420 k modifies the olivine spectrum shifting in wavelength its emissivity features simulating the spectrum of an olivine strongly enriched in iron a fa abundance increase from 8 to 23 this chameleon like behavior indicates that the spectroscopic investigations of the surface of mercury must take into account the local solar time dependency to properly infer the compositions of planetary materials by remote sensing acquisition of future space missions although previous works already investigated the effect of temperature on ir olivine spectra none of them definitively pointed out the reasons of the above mentioned spectral changes

manganese rich brown layers in arctic ocean sediments composition formation mechanisms and diagenetic overprint we present inorganic geochemical analyses of pore waters and sediments of two late quaternary sediment cores from the western arctic ocean southern mendeleev ridge rv polarstern expedition ark xxiii 3 focussing on the composition and origin of distinct brown colored mn rich sediment layers carbonate enrichments occur in association with these layers as peaks in ca al mg al sr al and sr mg suggesting enhanced input of both ice rafted and biogenic carbonate for the first time we show that the mn rich layers layers are also consistently enriched in the scavenged trace metals co cu mo and ni distinct bioturbation patterns specifically well defined brown burrows into the underlying sediments suggest these metal enrichments formed close to the sediment water interface the geochemical signature of these metal and carbonate rich layers most probably documents formation under warmer climate conditions with an intensified continental hydrological cycle and only seasonal sea ice cover both rivers and sea ice delivered trace metals to the arctic ocean while enhanced seasonal productivity exported reactive organic matter to the sea floor the coeval deposition of organic matter mn oxyhydr oxides and trace metals triggered intense diagenetic mn cycling at the sediment water interface these processes resulted in the formation of mn and trace metal enrichments and the degradation of labile organic matter with the onset of cooler conditions reduced riverine runoff and or a solid sea ice cover terminated the input of riverine trace metal and fresh organic matter resulting in deposition of grayish yellowish metal poor sediments oxygen depletion of arctic bottom waters under these cooler conditions is not supported by our data and did not cause the sedimentary mn distribution while the original composition and texture of the brown layers resulted from specific climatic conditions and corresponding diagenetic processes pore water data show that diagenetic mn redistribution is still affecting the organic poor deeper sediments given persistent steady state conditions purely authigenic mn rich brown layers may form while others may be partly or completely dissolved the degree of diagenetic mn redistribution largely depends on the depositional environment the mn and organic matter availability and apparently affected the co mo ratios of mn rich layers thus brown arctic layers are not necessarily synchronous features and should not be correlated across the arctic ocean without additional age control

proterozoic tectonic accretion and growth of western laurentia results from lithoprobe studies in northern alberta the western canadian shield of northern alberta is composed of a series of continental slivers that were accreted to the margin of the archean rae hinterland ca 1 9 2 0 ga preserving a unique record of continental evolution for the interval 2 1 2 3 ga this part of laurentia owes its preservation to the accretionary style of tectonic assembly south of the great slave lake shear zone which contrasts with indentation escape processes that dominate the paleoproterozoic record farther north the buffalo head and chinchaga domains form the central core of this region comprising a collage of ca 2325 2045 ma crustal elements formed on an archean microcontinental edifice and similar age crust is preserved as basement to the taltson magmatic zone the distribution of magmatic ages and inferred collision and subduction zone polarity are used to indicate closure of intervening oceanic basins that led to magmatism and emplacement of continental margin arc and collisional belts that formed from ca 1998 to1900

the effect of organic matter on chemical weathering study of a small tropical watershed nsimi zoetele site cameroon abstract the effect of organic matter during soil water interaction is still a debated issue on the controls of chemical weathering in a tropical environment in order to study this effect in detail we focused on the weathering processes occurring in a small tropical watershed nsimi zoetele south cameroon this site offers an unique opportunity to study weathering mechanisms in a lateritic system within a small basin by coupling soil and water chemistry the lateritic cover in this site can reach up to 40 m in depth and show two pedological distinct zones unsaturated slope soils on the hills and or elevated areas and water saturated soils in the swamp zone which represent 20 of the basin surface the study present chemical analysis performed on water samples collected monthly from different localities between 1994 1997 and on soil samples taken during a well drilling in december 1997 the results suggest the existence of chemical and spatial heterogeneities of waters in the basin colored waters flooding the swamp zone have much higher concentrations of both organic matter i e doc and inorganic ions e g ca mg al fe th zr than those from springs and groundwater from the hills nevertheless these organic rich waters present cation concentrations na ca mg k which are among the lowest compared to that of most world rivers the main minerals in the soils are secondary kaolinite iron oxi hydroxides quartz and accessory minerals e g zircon rutile we mainly focused on the mineralogical and geochemical study of the swamp zone soils and showed through sem observations the textural characterization of weathered minerals such as kaolinite zircon rutile and the secondary recrystallization of kaolinite microcrystals within the soil profile water chemistry and mineralogical observations suggest that hydromorphic soils of the swamp zone are responsible for almost all chemical weathering in the basin thus in order to explain the increase of element concentration in the organic rich waters we suggest that organic acids enhance dissolution of minerals such as kaolinite goethite and zircon and also favors the transport of insoluble elements such as al fe ti zr and ree by chemical complexation sio2 aq concentrations in these waters are above saturation with respect to quartz dissolution of phytholithes amorphous silica may be responsible for this relatively high sio2 aq concentration al mg ratios obtained for the soil and the mengong river waters show that a significant amount of al does not leave the system due to kaolinite recrystallisation in the swamp zone soils geochemical data obtained for this watershed show the important contribution of vegetation and organic matter on chemical weathering in the swamp zone quantitatively we propose that the increasing amount in total dissolved solid tds due to organic matter and vegetation effect is about 35 in summary this interaction between soils and waters occurs mostly in soils that are very depleted in soluble elements thus the low concentration of major elements in these water is a direct consequence of the depleted nature of the soils

geochemistry and origin of ferromanganese concretions in the gulf of bothnia abstract ferromanganese concretions cover large areas of the gulf of bothnia they are flat to well rounded the rounded ones being richer in oxyhydroxides of iron and manganese rounded and ellipsoidal nodules particularly those in the northern gulf of bothnia are richest in mn ni ba and cu which probably coexist in a mn oxyhydroxide phase flat nodules are enriched in fe p rare earths and as probably associated with an fe oxy hydroxide component aluminum v cr and ti occur in still another phase the sediments of the gulf generally consist of a 10 50 mm thick layer of oxidized surface sediment enriched in mn ba p and ni lying on top of reduced sediments which are diagenetically depleted in these elements the remobilized elements have redeposited in the nodules but this process cannot explain the origin of all the nodular material some released mn ba and ni furthermore enter into suspended phases which eventually leave the baltic sea the economic value of the nodules in the gulf of bothnia is probably limited at present

fluvial geochemistry of the eastern slope of the northeastern andes and its foredeep in the drainage of the orinoco in colombia and venezuela abstract the fluvial geochemistry of the tributaries of the orinoco draining the eastern branch of the northern andes in colombia and venezuela is determined by lithology and ranges from rivers dominated by aluminosilicate weathering mainly of shales and mafic rocks to those bearing the signatures of dissolution of marine limestones and evaporites and of continental playa deposits these left bank tributaries of the orinoco provide the overwhelming proportion of the suspended and dissolved loads transported by the main stem although feeding only half the discharge however due to the extreme severity of weathering on the guayana shield the right bank tributaries supply about half the silica and 40 of the k carried by the orinoco there is a similar partitioning between the andes and the lowlands in the amazon drainage in contrast the mackenzie which drains the northern extremity of the continental arc of the western americas is completely dominated by the weathering of limestones and evaporites and transports very little silica this again appears to be a reflection of lithology since the yukon in similar latitudes and terrain has silica concentrations comparable to the tropical systems in addition a conservative deconvolution of the data gives estimates of the net consumption of atmospheric co 2 by aluminosilicate weathering that follows the same pattern thus the available evidence from the western americas indicates that exposure and lithology rather than the climatic variables temperature and runoff dominate the weathering yields in active orogenic belts these observations contradict the conventional view of weathering processes and their controls and are at complete variance with the assumptions parameterised in most models of the geochemical cycle

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

a cretaceous back arc basin in the coast belt of the northern canadian cordillera evidence from geochemical and neodymium isotope characteristics of the kluane metamorphic assemblage southwest yukon the coast belt of the northern cordillera in canada is the locus of the boundary between accreted and ancient north american margin rocks the largest exposure of metasedimentary rocks in the coast belt is the kluane metamorphic assemblage kma a northwest striking belt 160 km long of graphitic mica quartz schist and gneiss with minor interfoliated olivine serpentinite the kma does not appear to correlate with other sedimentary or metamorphic rock assemblages in the canadian cordillera to determine its tectonic setting and protolith provenance we analyzed trace element rare earth elements and neodymium isotope compositions of the kma of the adjacent pericratonic aishihik metamorphic suite ams of the yukon tanana terrane and of adjacent slates of the dezadeash formation df filling a late jurassic early cretaceous flysch basin the end 0 values of analyzed kma samples range from 1 4 to 5 6 and depleted mantle model ages t dm range from 1 16 to 1 45 ga kma samples are intermediate between more evolved ams samples average end 0 25 t dm 2 6 ga and more juvenile df samples end 0 1 9 t dm 0 95 ga the intermediate characteristics of the kma samples cannot be linked to a known source region and are interpreted to reflect homogeneous mixing from predominantly juvenile and minor evolved sedimentary sources a compatible tectonic setting is a back arc basin within influence of a continental source eastward subduction of the kma beneath ancient north america collapsed the back arc basin by latest cretaceous time

2 8 1 7 ga history of the jiao liao ji belt of the north china craton from the geochronology and geochemistry of mafic liaohe meta igneous rocks abstract the assembly and long term evolution of the eastern block of the north china craton are poorly constrained here we use bulk rock geochronological and geochemical data from mafic meta igneous rocks hornblendites amphibolites and a metagabbro of the liaohe group to reconstruct the neoarchean to paleoproterozoic history of the jiao liao ji belt located between the longgang and nangrim blocks that together form the eastern block of the north china craton the mafic ultramafic meta igneous rocks have intrusive or tectonic contacts with the liaoji granitic rocks 2 2 2 0 ga which form the basement of the jiao liao ji belt the major and trace element data indicate that the protoliths had calc alkaline composition and formed along an active continental margin subduction zone the mafic rocks form a whole rock 176lu 177hf isochron with an age of 2 25 0 31 ga overlapping with u pb zircon ages for mafic and granitic rocks from the jiao liao ji belt and consistent with being the emplacement age of the mafic protoliths along the active continental margin in contrast the whole rock 147sm 144nd isochron age of 2 83 0 18 ga is likely to reflect the average age of the lithospheric mantle source from which the mafic ultramafic protoliths were extracted together with geological evidence we propose that the southwestern portion of the longgang block was an active continental margin since at least the early paleoproteorozic literature age data from metamorphic zircons show that peak granulite metamorphism took place at 1 96 1 88 ga resulting from the collisional event that fused the longgang and nangrim blocks into the eastern block of the north china craton our bulk rock 207pb 206pb age of 1824 19 ma and our 87rb 86sr age of 1671 58 ma reflect retrograde cooling stages during the exhumation of the jiao liao ji belt after the orogenesis

sulfur solubility in reduced mafic silicate melts implications for the speciation and distribution of sulfur on mercury abstract chemical data from the messenger spacecraft revealed that surface rocks on mercury are unusually enriched in sulfur compared to samples from other terrestrial planets in order to understand the speciation and distribution of sulfur on mercury we performed high temperature 1200 1750 c low to high pressure 1 bar to 4 gpa experiments on compositions representative of mercurian lavas and on the silicate composition of an enstatite chondrite we equilibrated silicate melts with sulfide and metallic melts under highly reducing conditions iw 1 5 to iw 9 4 iw iron wustite oxygen fugacity buffer under these oxygen fugacity conditions sulfur dissolves in the silicate melt as s 2 and forms complexes with fe 2 mg 2 and ca 2 the sulfur concentration in silicate melts at sulfide saturation scss increases with increasing reducing conditions from 10 wt s at iw 8 and with increasing temperature metallic melts have a low sulfur content which decreases from 3 wt at iw 2 to 0 wt at iw 9 we developed an empirical parameterization to predict scss in mercurian magmas as a function of oxygen fugacity f o 2 temperature pressure and silicate melt composition scss being not strictly a redox reaction our expression is fully valid for magmatic systems containing a metal phase using physical constraints of the mercurian mantle and magmas as well as our experimental results we suggest that basalts on mercury were free of sulfide globules when they erupted the high sulfur contents revealed by messenger result from the high sulfur solubility in silicate melt at reducing conditions we make the realistic assumption that the oxygen fugacity of mantle rocks was set during equilibration of the magma ocean with the core and or that the mantle contains a minor metal phase and combine our parameterization of scss with chemical data from messenger to constrain the oxygen fugacity of mercury s interior to iw 5 4 0 4 we also calculate that the mantle of mercury contains 7 11 wt s and that the metallic core of the planet has little sulfur

climate controlled variability of iron deposition in the central arctic ocean southern mendeleev ridge over the last 130 000 years abstract distinct brown coloured mn rich layers are common features in quaternary sediments of the central arctic ocean but their paleoenvironmental significance is disputed glacial interglacial changes in bottom water ventilation variable riverine input and diagenetic processes have all been suggested to cause the cyclicity in optical and geochemical parameters in these deposits to better assess the nature and origin of these sediment intervals and their implications for nutrient cycles we applied bulk geochemical analyses and a sequential fe extraction scheme to a sediment record covering the last 130 ka on the southern mendeleev ridge all brown layers in this core are enriched in mn but also in fe oxyhydr oxides e g ferrihydrite lepidocrocite goethite that contribute to the characteristic sediment colour phosphorus and several trace metals as co cu mo ni are also enriched indicating that both mn and fe oxyhydr oxides adsorbed p and trace metals from the water column the metal enrichments are most probably caused by a combination of enhanced mn and fe input from arctic rivers and or the erosion of shelf deposits coupled with early diagenetic processes leading to precipitation of authigenic mn and fe oxyhydr oxides close to the sediment water interface both primary supply and diagenetic recycling of metals should have been enhanced by a more intense hydrological cycle under warmer climate conditions combined with seasonal increases in productivity and reactive organic matter export during ice free conditions in the central arctic ocean consequently the studied metal oxyhydr oxide rich layers were formed under interglacial interstadial climatic conditions in contrast sheet silicate bound fe e g chlorite a second major fe pool in these sediments 15 35 of total fe is enriched between the oxide rich layers thus the delivery of fe rich sheet silicates from the east siberian hinterland or the bering sea and subsequent deposition on the mendeleev ridge was enhanced by more intense physical weathering during glacial stadial periods these contrasts in fe speciation between the brown layers and the adjacent sediments document the direct response of biogeochemical element cycles to glacial interglacial variations in river input weathering regime and sea level in the arctic ocean

the apure river geochemistry of major and selected trace elements in an orinoco river tributary coming from the andes venezuela the analysis of physicochemical variables and selected dissolved elements was performed on the apure river waters for 15 months the variables ph alkalinity dissolved o2 conductivity and na ca mg and cd concentrations showed maximum values during low water whereas k si fe al mn zn cu cr and dissolved organic carbon doc showed maximum concentrations during rising and high water five important factors were found to control the amount and temporal variability of the dissolved elements lithology hydrology vegetation floodplain processes redox conditions and organic complexation weathering of silicates carbonates and evaporites in the andes provides most of the proportion of na ca mg and hco3 to waters the temporal variability of these ions is controlled by a dilution process although si can be taken up by the biomass si and k can be leached from the floodplain by weathering of clays microbial decay of the submerged plants in the floodplain during the inundation periods provides doc and k to river waters and changes the redox conditions in water the changing redox conditions control the solubility of mn zn and fe dissolved mn is a function of ph dependent redox process whereas zn solubility is controlled by scavenging of zn during the oxidation of mn2 to mno2 positive relationships between al fe cu cr and doc suggest that these elements are complexed by organic colloids generated in the floodplain moreover the binding capacity of fe with doc increases under reducing conditions although cd seems to be provided by weathering in the andes several processes can affect the mobility of cd during transport copyright 2010 john wiley sons ltd

dissolved suspended and colloidal fluxes of organic carbon major and trace elements in the severnaya dvina river and its tributary abstract the chemical status of major and trace elements te and organic carbon oc has been studied in the severnaya dvina and pinega rivers draining granitic moraine carbonate and sedimentary deposits of the arkhangelsk region nw russia the white sea basin of the arctic ocean sampling was performed during winter and summer baseflow seasons and during the spring flood 2007 2008 size separation procedure included on site filtration through 5 m 0 22 m 100 10 and 1 kda and dialysis through 1 kda and 10 kda pore size membranes the organic carbon concentration in truly dissolved form trace and major element concentrations in the suspended matter of the river severnaya dvina were measured during different seasons over three years of observation based on collected data we evaluate here for the first time the seasonal fluxes of major and trace elements in the suspended 0 22 m total dissolved

nd isotopic evolution of the taltson magmatic zone northwest territories canada insights into early proterozoic accretion along the western margin of the churchill province the taltson magmatic zone is a north trending belt of early proterozoic granitoids exposed over an area exceeding 18 000 km 2 in the northwest territories of canada three petrologically and geochronologically discrete intrusive suites comprise the taltson zone these are the 1986 ma deskenatlata suite the 1955 to 1925 ma slave suite and the 1935 ma konth suite the deskenatlata suite is composed of biotite hornblende diorite to granite and displays a more mafic geochemical character relative to the other two intrusive suites initial epsilon nd values for the deskenatlata suite range from 2 7 to 3 6 the slave and konth suites are compositionally heterogeneous to homogeneous leucocratic granitoids that contain numerous xenoliths of dominantly pelitic high grade paragneiss and display a peraluminous granite mineralogy and geochemistry initial epsilon nd values for the konth suite cluster within 4 7 and 5 5 and are completely overlapped by the 4 1 to 6 0 range of the pelitic xe

temporal variability of selected dissolved elements in the lower orinoco river venezuela monthly analyses of ph conductance alkalinity total suspended solids dissolved major cations na k ca and mg and selected dissolved trace elements fe al mn cu zn and cr were conducted on waters of the lower orinoco river from february 2004 to may 2006 the data show strong seasonal variability major cations had maximum concentrations at low water and were correlated with ph conductance and alkalinity because of the tributaries coming from the andean zones where the weathering of evaporites and carbonate shales controls water chemistry k concentrations did not show any relation with evaporite weathering probably because large amounts of k come from the guayana shield rivers as a consequence of feldspar weathering the concentrations of dissolved fe mn and cu were highest during the high water stage concentrations of the elements k cr zn and cu are correlated with each other but not with dissolved fe and al which probably are complexed with humic and fulvic substances mn concentrations did not show relationships with other variables inter annual variability of dissolved elements is explained by temporal changes in precipitation copyright 2008 john wiley sons ltd

correlation of mid cretaceous granites with source terranes in the northern canadian cordillera this study presents a broad geochemical and isotopic synthesis of mid cretaceous granites in the southern yukon as well as a comparative data set for granites sourced from and hosted by accreted

geochemical and nd pb o isotope systematics of granites from the taltson magmatic zone ne alberta implications for early proterozoic tectonics in western laurentia the early proterozoic taltson magmatic zone tmz comprises the southern part of the taltson thelon orogenic belt of northwestern canada the tmz is dominated by 1 96 1 99 ga i type and 1 93 1 95 ga s type suites of granitoids previous workers attributed the formation of the i type granitoids to subduction of oceanic crust beneath the churchill craton in an andean type setting and generation of the s type granitoids to subsequent collision between the churchill craton and the buffalo head terrane to test this hypothesis we carried out a geochemical and isotopic nd pb and o study of granitoids and associated metasedimentary rocks and basement gneisses from the southern part of the tmz both i and s type suites of granitoids are characterized by relatively high sio2 content with the great majority of samples containing more than 64 wt sio2 the two suites also have strongly crustal end t values of 3 8 to 9 8 and an average tdm of 2 8 ga the initial pb isotope composition of the granitoids as determined from leached feldspar mineral separates forms a linear array that is bracketed by the isotopic compositions of basement orthogneisses and metasediments similarly 18o values of the granitoids overlap those of the orthogneisses and metasediments these isotopic data are consistent with derivation of the granitoids from a mixture of metaigneous and metasedimentary source rocks similar to those presently exposed in the tmz importantly the data suggest that both i and s type granitoids of the southern tmz had an exclusively intra crustal origin unlike phanerozoic examples of subduction related magmatism where a significant mantle contribution is easily recognized therefore we argue that the existing andean type model for early tmz magmatism is not viable the tmz granitoids show geochemical and isotopic similarities to the cordilleran interior granitoids of western north america which formed in response to crustal thickening in the distant hinterland of a convergent plate margin we propose that these hinterland granitoids are a more appropriate analogue for tmz magmatism than are the granitoids of plate margins the tectonic implication of this proposal is that the taltson thelon orogenic belt does not mark the location of the plate boundary in western laurentia at 1 9 2 0 ga rather the tectonic setting of the tmz at that time may have been more akin to the present day intra continental mountain belts of central asia e g tian shan mountains where compressional tectonism and crustal thickening are occurring well inboard from a convergent plate margin

major and trace elements in river borne materials from the cuyuni basin southern venezuela evidence for organo colloidal control on the dissolved load and element redistribution between the suspended and dissolved load abstract the cuyuni basin is a metallogenic rich area located in southern venezuela in the precambrian guyana shield it comprises two geologically distinct zones one with granite domes and intercalated greenstone belts in the northern and western part of the basin and the other with stratified arenaceous deposits in the south the suspended dissolved and total load of the rivers draining these contrasting zones show similar characteristics to those observed in other major tropical rivers such as the congo and amazon and vary in composition between the different source areas although the river borne material in this basin varies in composition from one river to another and contains highly variable proportions of dissolved constituents the ratio between the suspended and the dissolved load msusp mdiss appears related to the ratio of suspended to dissolved organic carbon contents ss doc according to the relationship m susp m diss k i ss doc the coefficient of proportionality ki in this equation varies from one element to another this relationship leads us to recognize a the important role of organo colloidal phases in controlling the elements in solution b the occurrence of a re distribution of elements between the suspended and dissolved load in the river environment according to this analysis coefficients ki appear to represent partition coefficients between two phases the suspended load and the organic rich colloidal fraction of the dissolved load these coefficients estimated from analysis of the total dissolved load versus ss doc diagrams yield values which classify in an order similar to that classically proposed for the relative capacity of the elements to form organic ligands or their adsorption capacity the coefficients actually vary as a function of the hydrolysis constants of the respective elements theoretical considerations show that equilibrium processes between the surfaces of suspended material and those of colloidal type species in solution are able to explain the observed relationship we show that such surface equilibria can be extended to the whole products in conditions which may prevail in tropical river waters that is suspended matter primarily consisting of phases for which surface complexation is important as is the case of clays or iron manganese oxides produced by the present day weathering of tropical soils finally we analyse the specific behaviour of the ree in rivers of the cuyuni basin

the oceanic mass balance of copper and zinc isotopes investigated by analysis of their inputs and outputs to ferromanganese oxide sediments abstract the oceanic biogeochemical cycles of the transition metals have been eliciting considerable attention for some time many of them have isotope systems that are fractionated by key biological and chemical processes so that significant information about such processes may be gleaned from them however for many of these nascent isotopic systems we currently know too little of their modern oceanic mass balance making the application of such systems to the past speculative at best here we investigate the biogeochemical cycling of copper cu and zinc zn isotopes in the ocean we present estimates for the isotopic composition of cu and zn inputs to the oceans based on new data presented here and published data the bulk isotopic composition of dissolved cu and zn in the oceans 65cu 0 9 66zn 0 5 is in both cases heavier than their respective inputs at around 65cu 0 6 and 66zn 0 3 respectively implying a marine process that fractionates them and a resulting isotopically light sedimentary output for the better known molybdenum isotope system this is achieved by sorption to fe mn oxides and this light isotopic composition is recorded in fe mn crusts hence we present isotopic data for cu and zn in three fe mn crusts from the major ocean basins which yield 65cu 0 44 0 23 mean and 2sd and 66zn 1 04 0 21 thus for cu isotopes output to particulate fe mn oxides can explain the heavy isotopic composition of the oceans while for zn it cannot the heavy zn in fe mn crusts and in all other authigenic marine sediments measured so far implies that a missing light sink is still to be located these observations are some of the first to place constraints on the modern oceanic mass balance of cu and zn isotopes

three dimensional seismic reflection investigation of the upper crustal winagami sill complex of northwestern alberta canada summary using a 3 d seismic reflection data set recorded by the canadian petroleum exploration industry to 5 1 s two way traveltime 15 km depth in northwestern alberta the winagami reflection sequence wrs an interpreted sill complex previously identified on lithoprobe 2 d multichannel seismic reflection lines is investigated to determine its 3 d geometry and reflective characteristics clear evidence of the top of the wrs emerges from the data set data sections outline a 3 d reflective sheet dipping to the southeast from polarity comparisons with reflections from the sedimentary sequence the reflective signature of the deep body is inferred to result from higher impedance material than the surrounding host rocks thus reinforcing earlier interpretations that the deep reflections result from doleritic sills intruded into gneissic crystalline basement simple 1 d forward modelling reveals that the thickness of the sheet is on the order of 100 m throughout the survey region from 3 d kirchhoff forward modelling a model of the reflective sheet is constrained between 11 and 16 km depth along the northwestern edge of the survey area the absence of the winagami reflections and basement reflectivity in general in the southeast of the survey region coincides with a positive aeromagnetic anomaly inferred to be caused by magmatic rocks the presence of the magmatic rocks may have either influenced the geometry of the intrusion of the sills overprinted their reflective signature or been co magmatic dependent upon the relative timing of emplacement of the two features the winagami sill complex appears to have been intruded horizontally into the crust during a period of tectonic compression the emplacement of such deep precambrian sills represents an under appreciated mode of magmatic addition into the crystalline crust

chemical weathering in the drainage basin of a tropical watershed nsimi zoetele site cameroon comparison between organic poor and organic rich waters abstract this study deals with the weathering processes operating at the scale of a small catchment nsimi zoetele cameroon and is focused on the role of organic colloids on mineral weathering and transport of elements in natural waters samples of river spring and groundwaters from nsimi zoetele were filtered through membranes of decreasing pore size 0 22 m 0 025 m or 300 000 da 5000 da to separate colloidal fractions from the truly dissolved one major and trace elements and dissolved organic carbon doc were analysed in each fraction two kinds of waters can be distinguished in the catchment clear and coloured waters clear waters exhibit low concentrations of major and trace elements and doc elements are carried in these solutions in a true dissolved form except al and rare earth elements rees by contrast the higher abundances of al fe and trace elements in coloured waters are controlled by the colloidal fraction thermodynamic equilibrium calculations show that clear waters are in equilibrium with kaolinite and iron oxi hydroxide which are major minerals in the weathered soil for coloured waters the aqueous speciation of ca mg cu fe al la and th was calculated taking into account the complexes with humic acids speciation calculations for cu fe al la th show a strong complexation with humic acids in good agreement with the results of the filtration experiments by contrast although filtration experiments show a strong control of major cations by organic matter for example 75 for ca speciation calculations reveal that their complexes with humic ligands do not exceed a few percent of total dissolved elements this discrepancy is explained as an artefact induced by the organic colloids and occurring during the filtration procedure finally both filtration experiments and speciation calculations show that organic matter plays an important role in natural doc rich waters organic acids increase significantly the dissolution rates of silicates and oxi hydroxides and thus the amounts of solutes and of complexed elements leaving the catchment

tectonic setting of the taltson magmatic zone at 1 92 0 ga a granitoid based perspective the paleoproterozoic taltson magmatic zone is one of the key tectonic features of western laurentia the existing tectonic model for the belt envisions its formation by subduction of oceanic crust beneath a continental margin followed by direct collision between formerly separate crustal blocks we tested this model by comparing the large geochemical and isotopic database available for taltson magmatic zone granitoids with similar databases for phanerozoic granitoid suites from different tectonic environments the comparison reveals that the early granitoid suite of the taltson magmatic zone which had been ascribed to the subduction phase of orogenesis lacks the mantle signature apparent in granitoids of phanerozoic continental margin arc settings instead both early and late suites appear to have an intracrustal origin similar to mesozoic and cenozoic granitoids of the cordilleran interior of western north america which formed in the distant hinterland of a convergent plate margin in light of thes

origin and environment of manganese rich sediments within black shale basins abstract sediments with unusually high manganese contents occur in anoxic basins of the central baltic sea we present a new model for the enrichment of manganese which is based on sedimentological and geochemical analyses of holocene sediments from the gotland deep and on published hydrographic data due to salinity stratification and high primary production bottom waters of the central baltic sea are anoxic and rich in dissolved mn 2 episodically bottom waters become oxygenated by inflows of denser water from the north sea mixing results in oxidation of mn 2 to fine grained particulate oxides which accumulate in the deepest parts of the basins where currents are mostly absent here anoxic conditions are re established within a few months or years and manganese oxides are again dissolved causing high concentrations of mn 2 in the near bottom layer alkalinity is high as a consequence of bacterial reduction of manganese oxides and sulphate under these conditions manganese is reprecipitated and forms a layer of ca rich rhodochrosite on the top of laminated sapropels occasionally periods of such extremely and rapidly changing redox conditions are followed by long term oxygenation of bottom waters in that case a layer rich in manganese oxides forms on the top of a bioturbated layer due to dissolution of rhodochrosite and oxidation of manganese in the near surface sediment return of anoxic conditions results again in the transformation of manganese oxides into rhodochrosite varying rhodochrosite contents in the basinal sediments therefore record a detailed history of redox conditions in bottom waters the manganese rich sediments of the baltic sea share many features with some occurrences of lower jurassic and lower carboniferous manganese ores in western and central europe we therefore suggest that these manganese enrichments were formed by similar processes

plant decay as a major control of river dissolved potassium a first estimate abstract living plants which acquire significant amounts of k primarily from weathered silicate materials may be considered as an intermediate storage for part of k that is ultimately of the origin of silicate mineral weathering part of this plant k is transferred to streams and rivers as dead vegetation on the ground surface and within the soil beneath the surface becomes decomposed and leached by surface and ground waters with the remaining k being recycled to new growth of plants the plant k transferred to rivers was never included in any previous budget model that assessed the sources and pathways of k in global river a popularly current view claims that nearly 87 of the total k in global river water comes from weathered silicate source relative to 5 from evaporite deposits 1 from atmospheric salt cycling and 7 from fertilizers in fact some fraction of this silicate material derived k in global river should belong to plant source k derived from leaching of dead vegetation on the surface and in the soils by surface and ground waters the importance of decay of vegetation on the surface and in soils as being a source of k in global river was assessed by using a mass balance equation that expresses the k rb weight ratio of global river in terms of fractional contributions of k from various sources to global river water and the k rb ratios of the contributing sources considering a wide range of values for the k rb ratio of each source of k in global river water calculations have shown that of the proposed 87 silicate derived k in global river water nearly 70 to 30 can be attributed to leaching of dead vegetation on the surface and in soils by surface and ground waters whereas the remaining 17 to 57 can be assigned to leaching of the weathered silicate materials by surface and ground waters a more realistic estimate can be based on taking into account the average crustal silicate k rb ratio of about 250 300 by this measure the k derived from leaching of decayed plant by surface and ground waters is at least as important as the k derived from leaching of weathered silicate materials by surface and ground waters 43 44 each and may be even more important than the k derived from leaching of the weathered silicate materials 70 72 for the plant source k in contrast to 15 17 for the silicate source k as a control of the dissolved k in global river water we have also estimated that nearly 97 98 of k released from dead vegetation on the surface and in the soils is cycled back each year to newly grown plants

visible and near infrared reflectance spectra of thermally processed synthetic sulfides as a potential analog for the hollow forming materials on mercury abstract we have obtained reflectance spectra in the visible spectral range of magnesium calcium and manganese sulfides before and after thermal processing at mercury dayside temperatures in vacuum conditions all measurements were made at the planetary emissivity laboratory pel at dlr these experiments are motivated by the recent findings of the mercury surface space environment geochemistry and ranging messenger mission of hollows on mercury and the notion that sulfides might be a candidate material for their formation from these new measurements we infer that all sulfides studied here display a diagnostic feature at or near 0 6 m the spectral contrast of this diagnostic feature can be strongly affected by heating of the samples to mercury daytime temperatures of approximately 500 c in a vacuum environment both the spectral slope and the color observed before and after thermal processing showed significant changes the laboratory work also indicates that sulfides can be thermally decomposed at temperature below 500 c well below their melting point our results are consistent with models explaining hollows on mercury s surface by the thermal decomposition of sulfides

strontium and its isotopes in canadian rivers fluxes and global implications systematic sampling of the 39 largest canadian rivers shows that the weighted average 87sr86sr ratio in the dissolved load is 0 7111 similar to previous measurements on such large rivers as the amazon and mississippi consequently we believe that the above estimate is likely representative of the global average this imposes a limit of 6 5 1011g yr 1 on the amount of sr exchanged with basalts in hydrothermal cells on mid oceanic ridges evaluation of geological information suggests that sr from silicate sources is of considerable importance for all but the largest canadian rivers the latter have chemical and isotopic composition consistent with 4 1 carbonate vs silicate derivation of sr but such interpretation is not unique in terms of their water discharge the 39 canadian rivers studied account for 4 2 of the world total and their weighted average concentrations for other dissolved solutes are tds 176 ppm ca 18 ppm cl 6 8 ppm and sr 84 ppb

the emissivity of a fine grained labradorite sample at typical mercury dayside temperatures abstract analyzing the surface composition of mercury s regolith from remote sensing measurements is a challenging task in support of the national aeronautics and space agency s mercury surface space environment geochemistry and ranging messenger mission and especially in preparation for the mercury radiometer and thermal infrared spectrometer mertis instrument on the bepicolombo mission of the european space agency and the japan aerospace exploration agency we are developing a planetary emissivity laboratory at deutsches zentrum fur luft und rahmfahrt dlr in berlin here we present the first measurements of labradorite as a mercury surface analog obtained with a test setup at a temperature of 420 c appropriate for the dayside of mercury because of limitations on the current test apparatus we present here data only for mid infrared wavelengths the spectra show strong indications of significant changes in spectral features in the mid infrared with changing temperature this result introduces an additional complication to the analysis of spectra obtained from the surface of mercury as the surface temperature and the thermal history of an observed area must be taken into account in the interpretation of the spectra this inference implies that the latitude and possibly also the time of day must be considered when analyzing a spectrum in particular the surface at the equator might exhibit different spectral characteristics than the surface at high latitudes even for the same composition these observations while still preliminary underscore strongly the need for temperature dependent measurements of emissivity of candidate planetary surface materials

iron and manganese layering in recent sediments in the gulf of bothnia abstract the oxidized surface layer of recent soft sediments in the gulf of bothnia northern part of the baltic sea has been investigated distinct stratification of fe and mn is observed with up to five different horizons in well developed profiles these layered top sediments although not previously noticed occur extensively in the gulf of bothnia there is a close association of mn and ni ba zn and cu whereas p ca and sr are associated with fe high dissolved fe and mn contents coupled with a strong redox gradient are recorded in the interstitial waters formation of these layers is linked to varying redox conditions fe and mn tend to be dissolved under reducing conditions to migrate upwards and to reprecipitate as oxyhydroxides along favourable redox horizons reaching oxidizing conditions fe precipitates prior to mn and is always found below the mnrich strata the character of the oxidized zone is quite different in the two sub basins of the gulf of bothnia mn rich horizons together with spherical mn rich nodules are frequently found in the bothnian bay while in the bothnian sea mostly fe rich layers are present together with abundant fe rich flat concretions this difference is interpreted as being due to a lower redox level in the bothnian sea

variations in the isotopic composition of molybdenum in freshwater lake systems variations in molybdenum isotopic composition spanning the range of similar to 2 3 parts per thousand in the terms of mo 97 mo 95 ratio have been measured in sediment cores from three lakes in northern sweden and north western russia these variations have been produced by both isotopically variable input of mo into the lakes due to mo isotopic heterogeneity of bedrock in the drainage basins and fractionation in the lake systems due to temporal variations in limnological conditions mo isotope abundances of bedrock in the lake drainage basins have been documented by analysis of mo isotope ratios of a suite of molybdenite occurrences collected in the studied area and of detrital fractions of the lake sediment cores the median delta mo 97 value of the investigated molybdenites is 0 26 parts per thousand with standard deviation of 0 43 parts per thousand n 19 whereas the median delta mo 97 value of detrital sediment fractions from two lakes is 0 40 parts per thousand with standard deviation of 0 36 parts per thousand n 15 the isotopic compositiori of mo in the sediment cores has been found to be dependent on redox conditions of the water columns and the dominant type of scavenging phases hydrous fe oxides have been shown to be an efficient scavenger of mo from porewater under oxic conditions oxidative precipitation of fe ii in the sediments resulted in co precipitation of mo and significant authigenic enrichment at the redox boundary in spite of a pronounced increase in mo concentration associated with fe oxides at the redox boundary the isotopic composition of mo in this zone varies insignificantly suggesting little or no isotope fractionation during scavenging of mo by hydrous fe oxides in a lake with anoxic bottom water a chironomid inferred reconstruction of o 2 conditions in the bottom water through the holocene indicates that increased o 2 concentrations are generally associated with low delta mo 97 mo 95 values of the sediments whereas lowered o 2 contents of the bottom water are accompanied by relatively high delta mo 97 mo 95 values thus confirming the potential of mo isotope data to be a proxy for redox conditions of overlying waters however it is pointed out that other processes including input of isotopically heterogeneous mo and mn cycling in the redox stratified water column can be a primary cause of variations in mo isotopic compositions of lake sediments less

sequence stratigraphy provenance c and o isotopic composition and correlation of the late paleoproterozoic early mesoproterozoic upper hornby bay and lower dismal lakes groups nwt and nunavut abstract late paleoproterozoic basins of canada s north including the thelon athabasca and hornby bay basins can be broadly correlated based on similarities in age sequence stratigraphy paleocurrents and detrital zircon provenance but their detailed evolution is poorly understood and their age and lateral equivalencies are poorly constrained this study contributes to the understanding of sedimentary basins during a critical interval of time representing the latest stages of amalgamation of the supercontinent laurentia nuna through a detailed study of the hornby bay basin the hornby bay basin strata have been divided into four unconformity bounded subsequences a1 a2 a3 a4 that belong to the first of three unconformity bounded post hudsonian proterozoic stratigraphic packages in northwestern canada subsequences a2 1600 ma and a3 analysis of sm nd isotopes on mudrocks yielded isotopic compositions in the range 8 2 to 2 3 nd 1600 ma in subsequence a2 and 9 8 to 5 0 nd 1400 ma in subsequence a3 an nd versus time graph illustrates two distinct groupings that plot within known isotopic evolution fields of the taltson thelon tectonic zone and the great bear magmatic zone sediment provenance was strongly influenced by the paleoproterozoic forward orogeny but there are no significant changes in sedimentary provenance across the a2 a3 sequence boundary stable isotope analyses of c and o in the dolomitic east river formation of subsequence a2 reveal a relatively monotonous signal with an average of 0 5 13 c and 8 76 18 o which is consistent with global values of other late paleoproterozoic carbonate successions enriched mn values and depleted sr values however suggest that the east river carbonate rocks experienced some degree of meteoric alteration it is unknown how much this alteration affected stable isotope compositions based on similarities in sedimentary provenance age and sequence stratigraphy subsequence a2 of the hornby bay group is correlated with the wernecke supergroup yukon the latter is interpreted to represent the deep water distal equivalent of the upper hornby bay group in a westward deepening basin deposition of subsequence a2 is recorded across north america and is mirrored by deep water sedimentation along the eastern margin of the north australian craton the tectonic evolution of subsequence a2 in laurentia is therefore remarkably similar to that of the north australian craton up to 1600 ma the age of the forward orogeny and this has implications for interpretation of the latest stages of accretion of the supercontinent nuna

trace element geochemistry in the upper amazon drainage basin bolivia abstract the distribution of trace elements sr mo ba rb u mn ni cu zn and cd was investigated in surface waters and associated particulates in two upper amazonian basins mamore and beni dissolved sr ba mo rb u and to a lesser extent zn and cd correlate with major ions and appear to be predominantly derived from soluble rocks carbonates evaporites or sulfides essentially contained in shales these elements are conservative in waters except in highly alkaline or sulfate rich waters where calcite and barite can precipitate the concentrations of transition element are generally not correlated with major ion chemistry their behaviour can be largely explained by equilibrium reactions in solution and solid liquid exchanges additionally the distribution of mn and cu reflects also the lithological differences between the mamore and beni basins the occurrence of mineralisation in the beni basin explains the high zn cd as well as the concentrations of cu in some rivers of the beni basin the higher content of mn in the mamore basin may reflects the predominance of carbonate rocks the fractionation of trace elements in spm has been attributed to the sorting of feldspars during transport in water and to the mixing between clay minerals and quartz these minerals refractory to weathering and introduced in water rivers by mechanical erosion have not contributed to the dissolved load

spatial characteristics and controlling factors of chemical weathering of loess in the dry season in the middle loess plateau china hydrochemistry methods were used to decipher the weathering and geochemical processes controlling solute acquisition of river waters in the dry season in the middle loess plateau mlp one of the most severely eroded areas and turbid riverine systems in the world river waters were neutral to slightly alkaline with ph varying from 7 6 to 9 6 the total dissolved solids decreased from northwest to southeast with a mean value of 804 mg l much higher than the global average and other large rivers in china ternary diagram showed that river waters were dominated by na hco3 and cl with the main water type of hco3 cl na saturation index values mg2 ca2 and hco3 analyses indicated the preferential ca2 removal by calcite precipitation gibbs plots and stoichiometry plots indicated that the dissolved solutes were mainly derived from rock weathering with minor anthropogenic and atmospheric inputs samples in the northwestern basin are also influenced by evaporation a forward model of mass budget calculation showed that owing to high soluble characteristics evaporite dissolution was a major feature of river waters and contributed 41 to the total dissolved cations on average while carbonate and silicate weathering contributed 28 and 25 on average respectively besides evaporite dissolution cation exchange is also responsible for the high concentrations of na in river water spatial variations showed that evaporite dissolution and silicate weathering were higher in the northern basin whereas carbonate weathering was higher in the southern basin different from most rivers in the world the physical erosion rates varying from 117 7 to 4116 6 t km2y are much higher than the chemical weathering rates varying from 3 54 to 6 76 t km2y in the mlp because of the loose structure of loess and poor vegetation in the basin in the future studies on comparison of water geochemistry in different seasons and on influence of different types of land use and soil salinization on water geochemistry denudation rates and water quality should be strengthened in the mlp these results shed some lights on processes responsible for modern loess weathering and also indicate the importance of time series sampling strategy for river water chemistry copyright 2016 john wiley sons ltd

heavy nickel isotope compositions in rivers and the oceans abstract nickel is a biologically active trace metal whose dissolved concentration depth profiles in the ocean show nutrient like behaviour if the pronounced removal of nickel from the dissolved phase in the surface ocean and its return in the deep is associated with an isotopic fractionation nickel isotopes may be able to yield constraints on the precise biogeochemical processes involved here we present the first nickel isotope data for seawater along with data for the dissolved phase of rivers one of the principal sources of nickel to the oceans the dissolved phase of rivers exhibits substantial variability in both ni concentration and 60 ni from 2 2 to 35 nmol kg 1 and 0 29 to 1 34 respectively the most striking result from the nickel isotope analyses of rivers is that they are substantially heavier by up to 1 for 60 ni than the range for silicate rocks on the continents a finding that is analogous to that for other transition metal isotope systems if the data presented here are close to representative of the global riverine flux they suggest an annual input of ni to the oceans of 3 6 10 8 moles and a discharge and concentration weighted 60 ni average of 0 80 the relationship between ni isotopes and concentrations shows similarities with those for other transition metal isotope systems where the main control has been suggested to be isotopic partitioning between the dissolved phase and particulates either in the weathering environment or during transport in stark contrast to the rivers the dataset for seawater is very homogeneous with 2sd of the entire dataset being only twice the analytical reproducibility the second main feature is that seawater is distinctly heavier in ni isotopes than rivers the average 60 ni is 1 44 0 15 2sd and only 2 of the 29 seawater analyses have a ni isotopic composition that is lighter than the heaviest river the lack of an isotopic shift associated with the drawdown of nickel concentrations in the surface ocean suggests that the cycling of nickel between the surface and deep ocean is not associated with a pronounced isotopic fractionation the isotopic data also present a mass balance problem the main output of nickel from the oceans sorption to fe mn oxides appears to be similar in isotopic composition to the dissolved phase yet the riverine input is lighter than the dissolved pool this observation either requires other inputs that are isotopically heavy or an output that is isotopically light further large inputs over and above the dissolved riverine source appear to be required by what we know of the elemental budget but the isotopic mass balance suggests that such an input needs to be isotopically much heavier than both the riverine dissolved load and the lithogenic isotopic composition of nickel