integrated 3d density modelling and segmentation of the dead sea transform a 3d interpretation of the newly compiled bouguer anomaly in the area of the dead sea rift is presented a high resolution 3d model constrained with the seismic results reveals the crustal thickness and density distribution beneath the arava araba valley av the region between the dead sea and the gulf of aqaba elat the bouguer anomalies along the axial portion of the av as deduced from the modelling results are mainly caused by deep seated sedimentary basins d 10 km an inferred zone of intrusion coincides with the maximum gravity anomaly on the eastern flank of the av the intrusion is displaced at different sectors along the nnw sse direction the zone of maximum crustal thinning depth 30 km is attained in the western sector at the mediterranean the southeastern plateau on the other hand shows by far the largest crustal thickness of the region 38 42 km linked to the left lateral movement of approx 105 km at the boundary between the african and arabian plate and constrained with recent seismic data a small asymmetric topography of the moho beneath the dead sea transform dst was modelled the thickness and density of the crust suggest that the av is underlain by continental crust the deep basins the relatively large intrusion and the asymmetric topography of the moho lead to the conclusion that a small scale asthenospheric upwelling could be responsible for the thinning of the crust and subsequent creation of the dead sea basin during the left lateral movement a clear segmentation along the strike of the dst was obtained by curvature analysis the northern part in the neighbourhood of the dead sea is characterised by high curvature of the residual gravity field flexural rigidity calculations result in very low values of effective elastic lithospheric thickness te 5 km this points to decoupling of crust in the dead sea area in the central av the curvature is less pronounced and te increases to approximately 10 km curvature is high again in the southernmost part near the aqaba region solutions of euler deconvolution were visualised together with modelled density bodies and fit very well into the density model structures

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

3 d density modelling of underground structures and spatial distribution of salt diapirism in the dead sea basin a new compilation of bouguer gravity data stemming from airborne shipborne and terrestrial data set in the entire dead sea basin dsb was reinterpreted by applying 3 d density modelling that incorporated independent information on other geophysical researches allowing for regional and residual filtering in the gravity field carrying out curvature analysis and euler deconvolution of the combined gravity field 3 d density modelling enables us to detailed resolution of upper crustal structures from the southern to the northern subbasin below the saline dead sea 3 d gravity modelling led to the identification of three salt structures which are found beneath the sedom area the lisan peninsula and the dead sea in the vicinity of the western margin of the dead sea a salt diapir segment with a thickness of about 4 km has been identified at a top depth of about 2 km which has not been recognised by any other geophysical interpretations the thickness of the sedimentary infill overlying the basement in the dsb decreases from 14 km in the vicinity of the lisan peninsula to 8 km in the northern and the southern subbasins large negative gravity anomalies lower than 100 x 10 5 m s 2 observed in the dsb correspond with the spatial distribution of salt diapirism with an average density of 2 100 kg m 3 the shallower microearthquakes registered in the dsb are related to the movement of salt diapir in the dsb

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

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

crustal structure along the strike of the offshore santa maria basin california abstract the geology of the central california offshore region contains the record of the early miocene transition of the western north american continental margin from a site of subduction to one of transform motion the fundamental elements of crustal structure and composition within the margin are defined by the seismic reflection image on the marine profile pge b 10 12 km of franciscan basement rocks c a 7 10 km thickness of oceanic crust seismic sequence analysis provides a foundation for interpreting the evolution of the offshore santa maria basin results indicate that the basin fill is predominantly miocene to pliocene in age and that subsidence began in early miocene times a late miocene to early pliocene shortening event led to faulting and folding of basin strata and to uplift of basement blocks the franciscan complex an accretionary wedge assemblage which floors the basin reveals little internal seismic structure however reflections from the franciscan oceanic crust boundary at 12 15 km depth supply evidence for the existence of an antiform with 2 3 km relief within the oceanic crustal layer this antiform probably formed during early miocene shortening of the oceanic crust alternatively the antiform could represent primary oceanic crustal topography such as seamounts or a fracture zone

the timing of uplift volcanism and rifting peripheral to the red sea a case for passive rifting prior to the formation of the red sea the northeastern afro arabian continent had low relief and was largely below sea level from the late cretaceous to the early oligocene the events leading to the formation of the red sea followed the sequence 1 alkaline volcanism and rifting beginning about 30 32 ma affecting a narrow linear zone in the continent 2 rotational block faulting and detachment faulting well underway by 25 ma 3 gabbro and diorite magmatism andesite to rhyolite volcanism and fine grained nonmarine sedimentation in the rift between 20 and 25 ma 4 fine grained marine sedimentation in the rift as the early shelves started to subside in the middle miocene and 5 uplift of the adjacent continents about 3 km and subsidence of the shelves about 4 km between 13 8 and 5 ma the youth of the uplift is suggested by 44 fission track dates on apatites from rocks of the proterozoic arabian shield that range in age from 13 8 to 568 ma the youngest of these ages coupled with the present high relief along the arabian escarpment and published heat flow measurements indicate that 2 5 4 km uplift has occurred in the last 13 8 m y the sequence volcanism rifting followed by uplift leads to our adoption of a passive mantle model for rift origin models that require uplift to create the rift are rejected because of the late uplift we advocate a model of lithospheric extension caused by two dimensional plate stress over those requiring tractional drag at the base of the lithosphere caused by vigorous flow in the asthenosphere it is acknowledged that traction models could explain the observed data but they imply a rigid static lithosphere and seem to require a link between the direction of flow in the asthenosphere and plate motions neither requirement is necessary in the extension model the rift starts with mechanical extension in a narrow zone of lithosphere between 25 32 ma in our model the thinned lithosphere is replaced by upwelling asthenosphere and by rocks from the adjacent deep continental lithosphere which flow into the rift ductile flow of the deep continental lithosphere is accelerated by partial melting as rocks flow upward toward the rift axis once partially melted rocks formerly part of the continental lithosphere join the upwelling asthenosphere resulting in a rapid erosion of the lithospheric mantle beneath the continent near the rift edge the resulting density decrease explains the uplift we think that the red sea began as a consequence of changing plate geometries resulting from the collision of india and eurasia after the collision the segment of the owens fracture zone north of the carlsberg ridge became locked forcing the northeast corner of afro arabia to rotate with the indian plate away from the rest of africa

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

lithospheric composition and thermal structure of the arabian shield in jordan abstract in this paper a unique set of samples from the uppermost crust down to the lithospheric mantle of jordan is analyzed for composition and petrophysical properties density thermal conductivity radiogenic heat production these data covering a vertical section of almost 65 km are used in conjunction with surface heat flow to generate a detailed and comprehensive lithospheric thermal model that reflects the conditions of the arabian shield as prior to the post oligocene onset of lithosphere thinning and voluminous basaltic volcanism the pre miocene model geotherms based on conductive surface heat flows of 55 and 60 mw m 2 a meet the range of lithosphere asthenosphere boundary depths of 110 160 km known from seismology b conform to results of thermomechanical models on the origin of the dead sea basin that started in miocene time and c are consistent with typical xenolith derived geotherms for terranes of similar age and lithospheric thickness moho temperatures at depths between 35 and 40 km of the as in pre miocene times were most likely in the order of 530 650 c with mantle heat flows averaging between 24 and 29 mw m 2 results contradict former views of the late proterozoic early cambrian stabilized as being an anomalously cold terrane a cold thermal structure inferred from previously measured low surface heat flows generally 45 mw m 2 is inconsistent with the thickness composition and petrophysical properties of the stable lithosphere of the shield

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

lower crustal strength under the dead sea basin from local earthquake data and rheological modeling we studied the local seismicity of the dead sea basin for the period 1984 1997 sixty percent of well constrained microearthquakes ml 3 2 nucleated at depths of 20 32 km and more than 40 occurred below the depth of peak seismicity situated at 20 km with the moho at 32 km the upper mantle appeared to be aseismic during the 14 year data period a relocation procedure involving the simultaneous use of three regional velocity models reveals that the distribution of focal depths in the dead sea basin is stable lower crustal seismicity is not an artifact created by strong lateral velocity variations or data related problems an upper bound depth uncertainty of 5 km is estimated below 20 km but for most earthquakes depth mislocations should not exceed 2 km a lithospheric strength profile has been calculated based on a surface heat flow of 40 mw m 2 and a quartz depleted lower crust a narrow brittle to ductile transition might occur in the crust around 380 c at a depth of 31 km for the upper mantle the brittle to ductile transition occurs in the model at 490 c and at 44 km depth the absence of micro seismicity in the upper mantle remains difficult to explain

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

timing of mantle upwelling evidence for a passive origin for the red sea rift mantle xenoliths from western saudi arabia some 220 km east of the red sea margin indicate temperatures as high as 900 c in the mantle at about 40 km depth beneath an area of the arabian shield where surface heat flow is lower than the world average this suggests that there has been a large increase in the mantle temperature that has not had time to equilibrate at the surface the amount of uplift and the difference between the observed xenolith temperature and that obtained by projecting the surface heat flow to depth suggests that the lithosphere has been thinned by 30 to 100 km to its present calculated thickness of about 80 km calculations of the time necessary for thermal reequilibration indicate that the lithospheric thinning probably occurred less than 20 m y ago so it postdates rifting which started about 30 ma if there was a prolonged upwelling of deep mantle material resulting in a thinner lithosphere prior to rifting there should have been enough time for some reequilibration at the surface and the observed heat flow should be higher over the broad area of uplift adjacent to the red sea our calculations are consistent with a postrift age of uplift adjacent to the red sea as determined from regional geologic evidence and fission track ages on apatites from shield rocks the red sea appears to have begun with alkaline volcanism on the arabian shield followed by rifting uplift and lithospheric thinning adjacent to the red sea rift began 5 10 m y after rifting this suggests that the red sea is a passive rift that formed because of two dimensional plate motions rather than as a consequence of mantle upwelling a possible cause for the stress in the plates might have been the change of plate motions in the indian ocean that resulted from the collision of india with eurasia

the mantle beneath the red sea margin xenoliths from western saudi arabia abstract xenoliths from alkali basalts in western saudi arabia provide the opportunity to study the composition and rheology of the mantle beneath the red sea rift margins characteristics of mantle xenolith suites from each of three localities in western saudi arabia can be related to locality position relative to the rift axis and to crustal thickness and heat flow at each locality mantle xenoliths from harrat al birk nearest the rift axis are dominantly websterites spinel plagioclase amphibole olivine garnet clinopyroxenite and two pyroxene gabbro olivine peridotite xenoliths are rare garnet clinopyroxenites contain zoned clinopyroxene with fe al rich rims and reaction rims on garnet formed by breakdown of garnet to orthopyroxene clinopyroxene spinel plagioclase zoning and reaction rims are interpreted as forming under conditions of increasing temperature thermobarometry on harrat al birk garnet bearing xenoliths yield high temperatures 1015 1040 c at about 12 kbar the abundance of plagioclase bearing assemblages may be related to a relatively shallow upper mantle which extends up into stability fields for plagioclase bearing pyroxenite and peridotite harrat al kishb and harrat hutaymah are farther from the red sea axis on the flanks of the rift the mantle xenolith suites of al kishb and hutaymah are similar consisting of abundant spinel peridotite and spinel pyroxenite xenoliths and minor garnet pyroxenites plagioclase bearing xenoliths are extremely rare the harrat hutaymah suite includes wehrlite and amphibole bearing peridotite lithologies not found at al kishb variation of peridotite composition may reflect varying degrees of partial melt extraction igneous textures of some pyroxenite xenoliths and structural relationships in composite peridotite pyroxenite nodules suggest that pyroxenites formed by crystallization of magmas within mantle veins abundant pyroxenites and fragments of amphibole veins reflect the activity of magmas and hydrous fluids within the mantle thermobarometry of al kishb and hutaymah garnet bearing nodules yield temperatures of 1000 1050 c at pressures of about 13 5 16 0 kbar mineral zoning and exsolution features indicate decreasing temperature conditions in the mantle at the flanks of the red sea rift

uplift and denudation history of the eastern dead sea rift flank sw jordan evidence from apatite fission track thermochronometry 1 the dead sea rift dsr developed along the dead sea transform plate boundary is characterized by salient flanks and morphotectonic asymmetry apatite fission track thermochronology aft along 1200 m high vertical profiles in neoproterozoic basement and overlying cambrian sandstone in southwestern jordan is used to reconstruct timing magnitude and rate of uplift and denudation of the eastern dsr flank and examine its relationship to rift development and its flank landscape time temperature models based on aft data suggest three major phanerozoic heating and cooling episodes late paleozoic early cretaceous and oligocene the latest episode on which this study focuses indicates uplift of 3 8 0 3 km under a moderate paleogeothermal gradient about 40 of the uplift was tectonically driven with the remainder attributed to isostatic rebound in response to denudation and erosion models suggest that uplift commenced in the oligocene with a considerable part occurring prior to development of the dsr despite being 200 km from the red sea gulf of suez rift margin uplift is probably part of a regional rearrangement along the western arabian platform margin occurring at the time of red sea rift initiation transition from primarily sedimentary layer stripping most likely by scarp retreat to one of dominantly incision of the underlying crystalline basement occurred in late miocene pliocene time following enhanced subsidence and development of a low base level in the dsr consequently the magnitude of uplift by isostatic rebound due to incision exceeded lowering by surface truncation and increased summit elevation and riftward flexing of the flank

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

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

thermo mechanical model of the dead sea transform abstract we employ finite element thermo mechanical modelling to study the dynamics of a continental transform boundary between the arabian and african plates marked by the dead sea transform dst that accommodated ca 105 km of relative transform displacement during the last 20 myr we show that in the initially cold lithosphere expected at the dst shear deformation localizes in a 20 40 km wide zone where temperature controlled mantle strength is minimal the resulting mechanically weak decoupling zone extends sub vertically through the entire lithosphere one or two major faults at the top of this zone take up most of the transform displacement these and other modelling results are consistent with geological observations and lithospheric structures imaged along the desert seismic line suggesting that the arava valley segment of the dst is an almost pure strike slip plate boundary with less than 3 km of transform perpendicular extension modelling suggests that the location of the arava valley segment of the dst has been controlled by the minimum in lithospheric strength possibly associated with margin of the arabian shield lithosphere and or by regionally increased crustal thickness models also show that heating of the arabian shield mantle adjacent to the dst inferred independently by petrological and seismological studies is required to explain asymmetric late cenozoic uplift in the area

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

thickness of the lithosphere east of the dead sea transform summary we use the s receiver function method to study the lithosphere at the dead sea transform dst a temporary network of 22 seismic broad band stations was operated on both sides of the dst from 2000 to 2001 as part of the desert project we also used data from six additional permanent broad band seismic stations at the dst and in the surrounding area that is in turkey saudi arabia egypt and cyprus clear s to p converted phases from the crust mantle boundary moho and a deeper discontinuity which we interpret as lithosphere asthenosphere boundary lab have been observed the moho depth 30 38 km obtained from s receiver functions agrees well with the results from p receiver functions and other geophysical data we observe thinning of the lithosphere on the eastern side of the dst from 80 km in the north of the dead sea to about 65 km at the gulf of aqaba on the western side of the dst the few data indicate a thin lab of about 65 km for comparison we found a 90 km thick lithosphere in eastern turkey and a 160 km thick lithosphere under the arabian shield respectively these observations support previous suggestions based on xenolith data heat flow observations regional uplift history and geodynamic modelling that the lithosphere around dst has been significantly thinned in the late cenozoic likely following rifting and spreading of the red sea

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

estimates of virgin rock temperature derived from bht measurements bias and error virgin rock temperatures are important to hydrocarbon exploration as these temperatures are necessary for the computation of source rock temperatures and for hydrocarbon generation computations several methods have been developed for determination of virgin rock temperatures from maximum temperatures recorded during logging in the past decades this paper describes an investigation where the calculated virgin rock temperatures from several different methods were examined for bias and accuracy using 18 different measurement series at the oseberg field the temperatures were corrected for different depths of burial and then compared with each other and with drill stem test dst measurements to investigate the inaccuracy of the methods the most advanced methods gave values close to the dst temperatures on average but with standard deviations as high as 9 degrees c the less advanced models like the horner plot method have systematically too low virgin rock temperatures by about 8 degrees c for the oseberg field with standard deviations of 8 degrees c the errors in calculated virgin rock temperatures are large enough to completely alter predictions of hydrocarbon generation in an area the large errors are attributed to poor quality data and to physical effects that are not properly taken into account in the temperature calculations improved sampling of temperature data can probably reduce the errors to some extent

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

geothermal measurements in a deep well at regina saskatchewan abstract the university of regina geothermal project was designed to demonstrate the use of moderate temperature geothermal resources from sedimentary aquifers in heating large buildings the first well was drilled on the campus of the university of regina in the winter of 1979 hydraulic potentials show that individual aquifers of the basal clastic unit are not in direct hydraulic connection and temperature measurements show that flow is occurring in the open hole apparent terrestrial heat flow varies vertically in the upper clastic unit showing either cross formational water flow or errors in the measurement of thermal conductivity of shales a reasonably uniform heat flow of 51 mw m 2 in the carbonate evaporite unit may represent the terrestrial heat flow from the basement but this cannot be demonstrated with certainty

basal heat flow and hydrothermal regime at the golan ajloun hydrological basins summary a shallow heat anomaly in the form of heated groundwater is detected in the lower yarmouk gorge lyg at northern israel and jordan results of 2 d numerical simulations of groundwater flow and heat transfer conducted for the golan ajloun area indicate that satisfying the thermal field observations requires a existence of an exceptional source of geothermal heat below the golan heights gh b existence of a deep flow path 3 km of several mcm yr of the total 45 5 mcm yr forced convection flow component originating at hermon ridge and discharging at the lyg outlets said flow component serves as fundamental heat convection component which transports heat from a great depth and vast area and significantly affects the geothermal pattern this deep circulation is causing a considerable part of the basin s elevated heat to be transported to the lyg outlets preventing shallow thermal expression at the gh model results indicate that regional mean basal heat flow value of the gh is 100 mw m 2 and that the shallow thermal anomaly of the lyg is an expression of a deep crust geothermal anomaly additional possible hydrothermal configurations involve an eastern exceptional heat source or alternatively deep convection that is larger by area magnitude 3600 km 2 and under standard regional basal heat flow 50 mw m 2

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

the uplift history of the arabian plateau as inferred from geomorphologic analysis of its northwestern edge abstract the arabian plateau ap is an oligocene sub horizontal regional planation surface extending throughout the western half of the arabian peninsula its present elevation of about 1 km required a prominent uplift since the late eocene in order to reconstruct the uplift history we documented abundant abrasive and fluvial terraces that were left along and across the raised judea mountains jm which comprised the nw edge of the ap using the ages of those terraces and the differences in height between them we found that the jm was uplifted in three major phases a few hundred meters during the late eocene early oligocene 500 m during the early miocene early middle miocene and 350 m during the late pliocene the two earliest uplift phases predate the formation of the dead sea transform dst which today separates the jm from the ap meaning that these two phases affected the continuous rigid lithosphere extending southeastwards to the ap interiors moreover restoration of the paleogeography predating the lateral offset along the dst eliminates the main height differences across it and suggests that the dst does not play a major role in the vertical position of its bordering plates but rather forms a relatively narrow deformation strip within the ap those two early phases of uplift can be corroborated by previous thermochronology studies which exhibit similar ages around the red sea but may reflect the uplift age of the entire region the present sub horizontal morphology of the ap is in contrast to the presumed original northeastward drainage and may suggest a subsequent long wave moderate tilting to the sw three possible mechanisms were suggested for the uplift of the ap a long wavelength flexure of the arabian plate during early stages of the uplift and lithospheric thinning or dynamic topography during later stages of the uplift

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

the shallow p velocity structure of the southern dead sea basin derived from near vertical incidence reflection seismic data in project desire summary as a part of the dead sea integrated research desire project a near vertical incidence reflection nvr experiment with a profile length of 122 km was completed in spring 2006 the profile crossed the southern dead sea basin dsb a pull apart basin due to the strike slip motion along the dead sea transform dst the dst with a total displacement of 107 km since about 18 ma is part of a left lateral fault system which connects the spreading centre in the red sea with the taurus collision zone in turkey over a distance of about 1100 km the seismic experiment comprises 972 source locations and 1045 receiver locations each source was recorded by 180 active receivers and a field data set with 175 000 traces was created from this data set 124 444 p wave first break traveltimes have been picked with these traveltimes a tomographic inversion was carried out resulting in a 2 d p wave velocity model with a rms error of 20 9 ms this model is dominated by a low velocity region associated with the dsb within the dsb the model shows clearly the position of the lisan salt diapir identified by a high velocity zone a further feature is an unexpected laterally low velocity zone with p velocities of 3 km s 1 embedded in regions with 4 km s 1 in the shallow part on the west side of the dsb another observation is an anticlinal structure west of the dsb interpretated to the related syrian arc fold belt

ray path interpretation of the crustal structure beneath saudi arabia abstract interpretation of a long range seismic refraction line in saudi arabia has shown that beneath the arabian shield velocity generally increases with depth from about 6 km s 1 at the surface to about 7 km s 1 at the top of the crust mantle transition zone the base of this transition zone moho occurs at 37 44 km in depth intracrustal discontinuities can also be recognized the most important being in the 10 20 km depth range and separating the upper from the lower crust laterally the variations in the intracrustal discontinuities and the total crustal thickness can be correlated with previously defined tectonic regions beneath the red sea shelf and coastal plain the crust including 4 km of sediments is only 15 17 5 km thick with the aid of both seismic and gravity data an abrupt steeply dipping transition from the crust of the red sea shelf and coastal plain to that of the arabian shield has been derived with a jump of more than 20 km in moho depth this appears to be the major discontinuity between the red sea depression and the arabian continental shield

lithosphere structure across the dead sea transform as constrained by rayleigh waves observed during the desert experiment summary the interdisciplinary dead sea rift transect desert project that was conducted in israel the palestine territories and jordan has provided a rich palette of data sets to examine the crust and uppermost mantle beneath one of earth s most prominent fault systems the dead sea transform dst as part of the passive seismic component thirty broad band sensors were deployed in 2000 across the dst for roughly one year during this deployment we recorded 115 teleseismic earthquakes that are suitable for a fundamental mode rayleigh wave analysis at intermediate periods 35 150 s our initial analysis reveals overall shear velocities that are reduced by up to 4 per cent with respect to reference earth model prem to the west of the dst we find a seismically relatively fast but thin lid that is about 80 km thick towards the east shallow seismic velocities are low while a deeper low velocity zone is not detected this contradicts the currently favoured thermomechanical model for the dst that predicts lithospheric thinning through mechanical erosion by an intruding plume from the red sea on the other hand our current results are somewhat inconclusive regarding asthenosphere velocities east of the dst due to the band limitation of the recording equipment in jordan

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

what controls thickness of sediments and lithospheric deformation at a pull apart basin we present a simplified three dimensional thermomechanical model of a pull apart basin formed at an overstepping of an active continental transform fault the modeling shows that for a given strike slip displacement and friction on the faults the major parameter that controls basin length thickness of sediments and deformation pattern beneath the basin is the thickness of the brittle layer the unusually large length and sediment thickness of the dead sea basin the classical pull apart basin associated with the dead sea transform can be explained by 100 km of strike slip motion and a thick 20 22 km up to 27 km locally brittle part of the cold lithosphere beneath the basin the thinner sedimentary cover in the gulf of aqaba basin located at the southernmost part of the dead sea transform close to the red sea rift is probably due to a thinner brittle part 15 km of the warmer lithosphere the modeling also suggests no more than 3 km of moho uplift beneath narrow 10 15 km pull apart basins formed in cold lithosphere such as the dead sea basin we also infer that a pull apart basin may only form if a several kilometer thick ductile detachment zone exists between the brittle crust and upper mantle modeling shows that this would not be the case for the dead sea basin if the surface heat flow there were indeed as low as 40 mw m 2 as previously reported we consider this result as an indication that the surface heat flow at the dead sea might have been underestimated

a global analysis of heat flow from precambrian terrains implications for the thermal structure of archean and proterozoic lithosphere previous studies of heat flow from precambrian terrains have yielded two different relationships a global temporal relationship between heat flow and tectonic age and a regional spatial relationship between heat flow and the proximity of archean cratons we analyze heat flow from tectonically stable precambrian terrains worldwide to address questions associated with these two heat flow patterns 1 is the spatial relationship a global pattern 2 do the two heat flow relationships have a common underpinning in answer to the first question our data analysis reveals a widespread spatial pattern between heat flow and the proximity of archean cratons which is characterized by low heat flow in archean cratons and proterozoic terrains adjacent to cratonic margins and higher heat flow in proterozoic terrains that are more than a few hundred kilometers from a craton to address the second question we examine three previous interpretative models of precambrian heat flow 1 simple cooling of a thermal boundary layer 2 thicker lithosphere in archean terrains than in proterozoic and 3 greater heat production in proterozoic crust than in archean model 1 predicts essentially no change in heat flow in terrains older than 1 5 ga and therefore does not likely provide a common underpinning for the precambrian heat flow patterns models 2 and 3 when combined with the special structural configuration of sutures can independently yield both the spatial and temporal heat flow distributions and thus alone or together may be considered candidates to explain the precambrian heat flow patterns however thermal models of the lithosphere in which the heat flow patterns are explained entirely by variations in crustal heat production cannot satisfy constraints on upper mantle temperatures beneath archean cratons derived from xenolith thermobarometry the thermobarometry constraints can be satisfied by models in which differences in lithospheric thickness are the principal factor controlling the surface heat flow distributions if the heat flow patterns result primarily from variations in lithospheric thickness then a different temporal heat flow relationship for precambrian terrains can be proposed one in which heat flow varies inversely with the age of stabilization of the lithosphere

melt instabilities in an intraplate lithosphere and implications for volcanism in the harrat ash shaam volcanic field nw arabia we investigate melt generation in a slowly extending lithosphere with the aim of understanding the spatial and temporal relationships between magmatism and preexisting rift systems we present numerical models that consider feedback between melt generation and lithospheric deformation and we incorporate three different damage mechanisms brittle damage creep damage and melt damage melt conditions are calculated with a helmholtz free energy minimization method and the energy equation is solved self consistently for latent heat and shear heating effects using a case of a slowly extending 1 1 5mm yr continental lithosphere with a relatively low surface heat flow similar to 50mw m 2 we show that melt rich shear bands are nucleated at the bottom of the lithosphere as a result of shear heating and damage mechanisms upon further deformation melt zones intersect creep damage zones thus forming channels that may be used for the melt to migrate upward if a preexisting structure resides only in the brittle crust it does not control the path of melt migration to the surface and melt filled channels propagate from the bottom upwards independently of upper crustal structures in contrast a preexisting weak structure that reaches a critical depth of 20km allows fast similar to 2ma propagation of melt filled channels that link melt damage from the bottom of the lithosphere to near surface structures our model results may explain the short time scale volume and magma extraction from the asthenosphere through a low surface heat flow lithosphere such as observed for example in the harrat ash shaam volcanic field northwestern arabia which developed in the arabian plate and is spatially linked to the azraq sirhan graben

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

the surface heat flow of the arabian shield in jordan abstract surface heat flow in southern jordan western part of the arabian plate was determined in a dense cluster of five up to 900 m deep boreholes that have encountered sedimentary rocks of paleozoic ordovician and silurian age these rocks are underlain by an igneous and metamorphic basement which has been studied for its radiogenic heat production along the eastern margin of the dead sea transform dst fault system the heat flow calculated from continuous temperature logs and laboratory measured thermal conductivity of drillcores and surface samples averages to 60 3 3 4 mw m 2 and contrasts the common view of the late proterozoic consolidated arabian shield constituting a low heat flow province of 45 mw m 2 although only characterizing an area of about 300 km 2 this average is unlikely representing a positive local anomaly caused by voluminous hhp granites rhyolites at shallow depths instead a heat flow of 60 mw m 2 is considered a robust estimate of the phanerozoic conductive surface heat flow not only for jordan but for the arabian shield in areas unaffected by younger reactivation the large variation in conductive heat flow 36 88 mw m 2 previously observed in jordan southern syria and saudi arabia is irreconcilable with their broad similarity in lithosphere structure and composition and rather reflects a combination of factors including low quality temperature data and insufficient knowledge on thermal rock properties

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

the thermal structure of israel and the dead sea fault abstract in this paper we analyze temperature data from all the available oil and water wells in israel and compare the results with seismicity depth and with heat flux estimation from xenoliths we show that the average heat flux in israel is 40 45 mw m 2 consistent with measurements of the arabian shield a heat flux anomaly exists in northern israel and jordan this could be attributed to groundwater flow or young magmatic activity 100 000 years that is common in this area a higher heat flux exists in southern israel and jordan probably reflecting the opening of the red sea and the gulf of eilat gulf of aqaba and does not represent the average value present in the arabian shield the temperature gradient at the dead sea basin is relatively low resulting in low heat flux 2 and a relatively deep seismicity extending to lower crustal depths in agreement with earthquake depths 2 and at the gulf of eilat 65 mw m 2 results with shallower seismicity 80 mw m 2 could be the result of local heating by magmas or by lithospheric necking and shear heating