on the geologic structure at the epicenter of the 1886 charleston south carolina earthquake the study focuses on evidence of cenozoic faulting in the epicentral area of the 1886 charleston south carolina earthquake and its connection with mesozoic structure the seismic data consist of several reflection profiles collected near summerville south carolina in the period 1975 1983 reprocessing of the data reveals an extensive early mesozoic extensional basin approximately 20 km in width between summerville and charleston the basin is delineated by the geometry of reflections that image early mesozoic volcanic and sedimentary rocks and by positive magnetic and gravity anomalies cenozoic compressional reactivation of mesozoic extensional faults is imaged in the interior of the basin the northwestern boundary of the basin is marked by a sharp gradient in the magnetic field folded cretaceous and tertiary atlantic coastal plain sediments in association with diffractions and truncated reflections from the early mesozoic section at four locations along this magnetic gradient indicate that the northwestern basin boundary is faulted instrumentally located earthquakes are clustered at the location of the faults imaged in the interior of the basin and in proximity to the northwestern basin margin modeling of magnetic and gravity data indicates that the upper crust beneath the seismically imaged structural basin is composed largely of mafic rocks to a depth of at least 4 km we propose that the charleston earthquake occurred due to compressional reactivation of a mesozoic fault in a localized zone of intense early mesozoic continental rifting

germanium silicon fractionation in the weathering environment abstract we present a detailed study of germanium behavior in the soil weathering environment as an important step toward using the ge si system as a tracer of silicate weathering processes in both modern and ancient environments intensely weathered soils developed on hawaiian basalts have bulk soil ge si ratios 2 to 10 times higher than fresh basalt e g 10 to 25 mol mol vs 2 5 mol mol soil ge concentrations increase with si and decrease with fe suggesting that ge sequestration is related to accumulation of secondary soil silicates rather than retention in soil fe oxy hydroxides sequential extractions of these soils suggest that ge si fractionation takes place by ge sequestration during the initial precipitation of secondary soil aluminosilicates principally allophane further si loss and changes in mineralogy as these soils age result in little additional ge si fractionation ge si ratios in granitic soils and saprolites are strongly influenced by relative weathering rates of primary minerals kaolinite has a ge si ratio 5 9 mol mol higher than the plagioclase from which it forms 3 1 mol mol whereas accumulation of primary quartz ge si 0 5 mol mol prevents granitic soils from attaining high ge si ratios laboratory synthesis of allophane confirms that ge is preferentially partitioned into the solid phase upon precipitation of secondary aluminosilicates from solution

spirit mars rover mission to the columbia hills gusev crater mission overview and selected results from the cumberland ridge to home plate this paper summarizes the spirit rover operations in the columbia hills of gusev crater from sols 513 to 1476 and provides an overview of selected findings that focus on synergistic use of the athena payload and comparisons to orbital data results include discovery of outcrops voltaire on husband hill that are interpreted to be altered impact melt deposits that incorporated local materials during emplacement evidence for extensive volcanic activity and aqueous alteration in the inner basin is also detailed including discovery and characterization of accretionary lapilli and formation of sulfate silica and hematite rich deposits use of spirit s data to understand the range of spectral signatures observed over the columbia hills by the mars reconnaissance orbiter s compact reconnaissance imaging spectrometer crism hyperspectral imager 0 4 4 m is summarized we show that crism spectra are controlled by the proportion of ferric rich dust to ferrous bearing igneous minerals exposed in ripples and other wind blown deposits the evidence for aqueous alteration derived from spirit s data is associated with outcrops that are too small to be detected from orbital observations or with materials exposed from the shallow subsurface during rover activities although orbital observations show many other locations on mars with evidence for minerals formed or altered in an aqueous environment spirit s data imply that the older crust of mars has been altered even more extensively than evident from orbital data this result greatly increases the potential that the surface or shallow subsurface was once a habitable regime

diagenetic fractionation of ge and si in reducing sediments the missing ge sink and a possible mechanism to cause glacial interglacial variations in oceanic ge si the average ge si ratio in the ocean is determined by the budgets for each of these elements previous budget formulations have assumed that the only important sink for both elements is burial as opal based on studies of the si cycle and the close oceanic coupling observed between inorganic ge and si distributions however these budgets implied two paradoxes 1 hydrothermal flow through ocean ridges is smaller than predicted by other tracers and 2 the lower ge si ratio of opal deposited during glacial times compared to that deposited during interglacial times required enhanced weathering during cooler drier climates both paradoxes could be resolved if a significant sedimentary sink for ge other than opal burial could be identified and the objective of this study was to search for one two pore water profiles collected in equatorial pacific sediments show that ge and si behave similarly in the upper 10 cm of sediment indicating no evidence for a significant non opal sink for ge in oxic sediments by contrast profiles in several cores from the california margin demonstrate that in reducing sediments ge diagenesis is poorly coupled to si diagenesis significant ge removal is evident both downcore and sometimes in the near surface benthic flux chamber measurements at three continental slope stations all with an oxic layer less than 1 cm thick and large iron gradients in near surface pore waters showed that 55 9 of the ge released by opal dissolution is sequestered however at two locations with anoxic sediments but little pore water fe 2 in the upper 2 cm flux measurements indicated little fractionation from the oceanic ratio during diagenesis implicating the importance of iron for fractionating ge from si during diagenesis if the ge sequestration observed in the iron rich ca margin sediments is typical of all slope sediments using a depth range of 200 1000 m then the ge sink is sufficient to bring the hydrothermal budget based on ge into concurrence with that based on other tracers the temporal variation in oceanic ge si could be explained if ge and si inputs remain constant and the effective diagenetic fractionation of ge increases by a factor of 2 3 during glacial times increased fractionation would require that glacial periods are characterized by increased opal dissolution in iron rich reducing sediments this could be caused by 1 thinning of the oxygenated sediment layer in response to decreased bottom water oxygen concentrations or increased rain of organics to the sea floor 2 increased rain of iron rich detrital sediments in areas receiving high opal rain 3 increased rain of opal to sediments in margin areas if the oceanic ge si ratio reflects increased rain of diatom opal or organic carbon in margin areas during glacial periods it may indicate an increase in the efficiency of the biological pump for co2 during glacial times

effects of black shale weathering on the mobility of rhenium and platinum group elements radiogenic os from the continents dominates the late cenozoic marine os budget a variety of proposed radiogenic sources includes organic rich sediments precambrian shields and re rich sulfides identifying the dominant sources of radiogenic os to the oceans has a strong impact on past climate models because weathering of silicates acts as a net sink of co 2 whereas weathering of organic matter acts as a source here we investigate the effects of black shale weathering on the integrity of the re os isotope system and release of re and platinum group elements time correlative pairs of fresh drill core and weathered outcrop black shales of late ordovician age utica shale magnafacies quebec were analyzed for re os ir pt and pd as well as total s n and c as c carb and c org the results indicate that 25 64 of the initial re budget 45 90 of the os budget 14 65 of the ir budget 60 77 of the pt budget 69 86 of the pd budget and 44 96 of the c org budget are lost during weathering we use positive correlations of os pt and pd with c org and n to calculate the respective platinum group element concentrations in the unweathered organic matter end member as 3 ng g os 9 ng g pt and 11 24 ng g pd although black shales make up

germanium geochemistry in the southern california borderlands abstract concentrations of ge oh 4 denoted as ge i or inorganic germanium and si oh 4 were measured in water column and pore water samples from san pedro and san nicolas basins in the southern california borderlands there is a characteristic linear relationship between ge i and si in the water column which implies that the distributions of germanium and silica are controlled by similar processes in contrast the pore water chemistry of germanium appears to differ from that of silica particularly in the reducing organic rich sediments of san pedro basin silica concentrations in san pedro basin pore water asymptotically increase to 480 m at 35 40 cm depth ge i concentrations in the topmost 2 cm of pore water from san pedro basin are an order of magnitude greater than bottom water concentrations below 2 cm ge i concentrations decrease exponentially with a half distance of about 8 cm cycling of ferric oxyhydroxides at a redox boundary is the most likely cause of the ge i enrichment in san pedro basin pore water while authigenic pyrite formation with the concomitant inclusion of germanium is a probable but undocumented cause of the downcore decrease in ge i pore water ge i and silica concentrations in sediments of san nicolas basin are generally greater than bottom water concentrations but vary irregularly with depth probably due to irrigation

germanium isotopic variations in igneous rocks and marine sediments a new technique for the precise and accurate determination of ge stable isotope compositions has been developed and applied to silicate rocks and biogenic opal the analyses were performed using a continuous flow hydride generation system coupled to a mc icpms samples have been purified through anion and cation exchange resins to separate ge from matrix elements and eliminate potential isobaric interferences variations of 74ge 70ge ratios are expressed as 74ge values relative to our internal standard and the long term external reproducibility of the data is better than 0 2 for sample size as low as 15 ng of ge data are presented for igneous and sedimentary rocks and the overall variation is 2 4 in 74ge representing 12 times the uncertainty of the measurements and demonstrating that the terrestrial isotopic composition of ge is not unique co variations of 74ge 70ge 73ge 70ge and 72ge 70ge ratios follow a mass dependent behaviour and imply natural isotopic fractionation of ge by physicochemical processes the range of 74ge in igneous rocks is only 0 25 without systematic differences among continental crust oceanic crust or mantle material on this basis a bulk silicate earth reservoir with a 74ge of 1 3 0 2 can be defined in contrast modern biogenic opal such as marine sponges and authigenic glauconite displayed higher 74ge values between 2 0 and 3 0 this suggests that biogenic opal may be significantly enriched in light isotopes with respect to seawater and places a lower bound on the 74ge of the seawater to 3 0 this suggests that seawater is isotopically heavy relative to bulk silicate earth and that biogenic opal may be significantly fractionated with respect to seawater deep sea sediments are within the range of the bulk silicate earth while mesozoic deep sea cherts opal and quartz have 74ge values ranging from 0 7 to 2 0 the variable values of the cherts cannot be explained by binary mixing between a biogenic component and a detrital component and are suggestive of enrichment in the light isotope of diagenetic quartz further work is now required to determine ge isotope fractionation by siliceous organisms and to investigate the effect of diagenetic processes during chert lithification

hydrothermal origin of syndepositional chert bands and nodules in the mesoproterozoic wumishan formation implications for the evolution of mesoproterozoic cratonic basin north china abstract abundant chert bands and nodules are discovered throughout the mesoproterozoic wumishan formation 1 5 ga in the north china block the middle part of the wumishan formation consists of cyclic deposition of calcareous shale massive microbial dolostone thrombolites and stromatolites and laminated dolostone chert bands occur most abundantly in the laminated dolostone although they are also found with lower abundance in other lithologies chert bands are normally parallel to the bedding plane and show soft deformation structures suggesting early silicification at or near the water sediment interface the wumishan chert is composed of two types of silica fabric the microcrystalline and cryptocrystalline quartz that derives from the replacement of host dolomitic rock and the mosaic chalcedonic quartz representing typical void filling precipitation we measured the germanium silica ratios ge si and the ree compositions of the chert bands nodules collected from a 60 m interval in the middle part of the wumishan formation in the mopanyu section ge si ratios of the buck samples measured by icp ms range from 13 6 to 35 6 mol mol additional la icp ms analyses allow the measurements of individual silica fabric providing more detailed information about the geochemistry of chert nodules and bands ge si ratios of the replacive chert vary between 10 and 20 mol mol while the mosaic chalcedonic quartz has wider range of variation 1 1 93 2 mol mol these values are 1 order of magnitude higher than the modern seawater value 0 72 mol mol but is within the range of hydrothermal fluids 3 4 51 3 mol mol average 13 mol mol n 101 suggesting hydrothermal fluid as an important si source this conclusion is consistent with the positive eu anomaly in the ree pattern a mass balance calculation indicates that hydrothermal fluid would account for 10 15 20 25 40 55 and 75 of si for the fluid temperature of 100 c 150 c 200 c and 250 c respectively although large igneous provinces are not discovered in the north china block during the deposition of the wumishan formation the studied wumishan cherts have significant contribution from hydrothermal fluid which might be related to the early rifting activities in the north china block before the breakup of supercontinent nuna

87sr 86sr ca sr and ge si ratios as tracers of solute sources and biogeochemical cycling at a temperate forested shale catchment central pennsylvania usa plant uptake and biological cycling processes are commonly the largest flux of nutrients in terrestrial ecosystems hydrologic and other losses are offset by inputs from atmospheric deposition and weathering this multi tracer study investigates these effects using 87sr 86sr ca sr and ge si ratios from solid soil profiles and bedrock biological leaves and sap waters and water pore ground stream waters samples to study ca sr ge and si sources and cycling in a forest catchment underlying gray shale in the temperate climate of central pennsylvania leaves and sap waters were found to have similar ge si ratios 1 mol mol which is consistent with biological fractionation occurring at the root soil water interface ge si ratios in soil porewaters were higher near the surface and increased over the growing season suggesting plant preferential uptake of si over ge ca sr ratios in oak leaves 1360 40 mol mol were significantly higher than those in maple leaves 650 20 mol mol ca sr ratios were also generally higher in leaves than in sap waters which are consistent with preferential sr adsorption or sr uptake during transpiration 87sr 86sr ratios in both leaves and sap waters were similar for a given site implying that trees access similar pools of sr and ca although there are site to site differences additionally 87sr 86sr ratios in plant tissues were most similar to shallow pore waters 0 50 cm suggesting that mineral nutrients are obtained by trees from the near sub surface 87sr 86sr ratios in soil solutions from ridgetop and swale sites are best explained by mixing sr derived from shale and atmospheric deposition valley bottom soil reservoirs and stream and groundwater samples include sr and ca derived from dissolution of two isotopically distinct generations of carbonates a preliminary estimate of the sr and ca stream fluxes and isotopic mass balances imply propagation of a carbonate weathering front of ca 300 m myr 1 a value larger than previously reported for regolith weathering advance rates calculated based on cosmogenic nuclides and u series isotopes the data for ca sr si and ge in soil soil solutions and stream waters reflect the interaction of slower weathering processes with rapid biologically driven cycling between soils and biomass

cenozoic faulting in the vicinity of the charleston south carolina 1886 earthquake multichannel seismic reflection profiles in the meizoseismal area of the 1886 charleston earthquake and nearby offshore area show evidence of cenozoic faulting deformation observed on two land profiles defines a northeast striking reverse fault zone named the cooke fault a jurassic age basalt layer at 750 m depth has 50 m vertical displacement southeast side down overlying upper cretaceous and cenozoic beds have decreasing displacement with decreasing depth these displacements coupled with larger 190 m displacements of reflectors below the basalt indicate continuing cenozoic movement of a post basalt flow pre late cretaceous fault into eocene time or later the fault extends into a cluster of 1973 1978 epicenters this suggests a possible causal relationship with seismicity marine multichannel seismic reflection data combined with single channel high resolution reflection profiles reveal cenozoic faulting beneath the continental shelf near charleston a reverse fault 12 km offshore named the helena banks fault extends for at least 30 km and is observed as shallow as 10 m below the sea bottom with the most recent movement in post miocene or pliocene time there is no known seismicity in the area of this fault the reverse movement on the helena banks and cooke faults is consistent with a northwest southeast compressional stress regime elucidation of the relation if any between reactivated triassic or older structures and or a decollement defined by diffractions at 11 4 1 5 km depth on the one hand and seismicity on the other will be important in assessing earthquake risk in many areas of similar tectonic setting outside of the charleston region in the atlantic coastal and continental margin area

germanium silicon fractionation in a tropical granitic weathering environment abstract germanium silicon ge si ratios were determined on quartz diorite bedrock saprolite soil primary and secondary minerals phytolith soil and saprolite pore waters and spring water and stream waters in an effort to understand ge si fractionation during weathering of quartz diorite in the rio icacos watershed puerto rico the ge si ratio of the bedrock is 2 mol mol with individual primary mineral phases ranging between 0 5 and 7 mol mol the ratios in the bulk saprolite are higher 3 mol mol than values measured in the bedrock the major saprolite secondary mineral kaolinite has ge si ratios ranging between 4 8 and 6 1 mol mol the high ge si ratios in the saprolite are consistent with preferential incorporation of ge during the precipitation of kaolinite bulk shallow soils have lower ratios 1 1 1 6 mol mol primarily due to the residual accumulation of ge poor quartz ge si ratios measured on saprolite and soil pore waters reflect reactions that take place during mineral transformations at discrete depths spring water and baseflow stream waters have the lowest ge si ratios 0 27 0 47 mol mol reflecting deep initial weathering reactions resulting in the precipitation of ge enriched kaolinite at the saprolite bedrock interface mass balance calculations on saprolite require significant loss of si and al even within 1 m above the saprolite bedrock interface higher pore water ge si ratios 1 2 mol mol are consistent with partial dissolution of this ge enriched kaolinite pore water ge si ratios increase up through the saprolite and into the overlying soil but never reach the high values predicted by mass balance perhaps reflecting the influence of phytolith recycling in the shallow soil

a possible link between the seawater osmium isotope record and weathering of ancient sedimentary organic matter the os isotopic composition of leachable os from a north pacific pelagic clay sequence pegram et al 1992 and bulk sediment samples of metalliferous carbonates deposited near the east pacific rise ravizza 1993 display similar patterns of temporal variation fig 1 this similarity indicates that the composite record of t87os 186os ratio variations reflects changes in the os isotopic composition of seawater temporal changes in the sr isotopic composition of seawater record changes in the relative rates of continental weathering and oceanic crustal alteration the os isotopic composition of seawater should be influenced by similar processes in both the rb sr and re os systems the continental crust is characterized by large time integrated parent daughter ratios compared to the deep earth imparting relatively radiogenic sr and os signatures to continental material however the seawater sr and os records are decoupled from one another over the past 27 ma from 27 to 15 ma 87sr 86sr increased rapidly while the 18vos 186os ratio of seawater remained nearly constant at 15 ma the 87os ts6os ratio of seawater began to increase rapidly but the rate

chemical weathering in a tropical watershed luquillo mountains puerto rico ii rate and mechanism of biotite weathering abstract samples of soil saprolite bedrock and porewater from a lower montane wet forest the luquillo experimental forest lef in puerto rico were studied to investigate the rates and mechanisms of biotite weathering the soil profile at the top of a ridge in the rio icacos watershed consists of a 50 100 cm thick layer of unstructured soil above a 600 800 cm thick saprolite developed on quartz diorite the only minerals present in significant concentration within the soil and saprolite are biotite quartz kaolinite and iron oxides biotite is the only primary silicate releasing significant k and mg to porewaters although biotite in samples of the quartz diorite bedrock is extensively chloritized chlorite is almost entirely absent in the saprolite phyllosilicates phyllosilicate grains are present as 200 1000 m wide books below about 50 cm depth x ray diffraction xrd and electron microprobe analyses indicate that the phyllosilicate grains contain a core of biotite surrounded by variable amounts of kaolinite lattice fringe images under transmission electron microscope tem show single layers of biotite altering to two layers of kaolinite suggesting dissolution of biotite and precipitation of kaolinite at discrete boundaries some single 14 a layers are also observed in the biotite under tem the degree of kaolinitization of individual phyllosilicate grains as observed by tem decreases with depth in the saprolite this tem work is the first such microstructural evidence of epitaxial growth of kaolinite onto biotite during alteration in low temperature environments the rate of release of mg in the profile calculated as a flux through the soil normalized per watershed land area is approximately 500 mol hectare 1 yr 1 1 6 10 9 molmg msoil 2 s 1 this rate is similar to the flux estimated from mg discharge out the rio icacos 1000 mol hectare 1 yr 1 or 3 5 10 9 molmg msoil 2 s 1 indicating that scaling up from the soil to the watershed is possible for mg release the rate of mg release from biotite normalized to brunauer emmett teller bet surface area is calculated using a mass balance equation which includes the density and volume of phyllosilicate grains porewater chemistry and flux and soil porosity the mean rates of biotite weathering calculated from k and mg release rates are approximately 6 and 11 10 16 molbiotite mbiotite 2 s 1 respectively significantly slower than laboratory rates 10 12 to 10 11 molbiotite mbiotite 2 s 1 the discrepancy in scaling down from the soil to the laboratory is probably explained by 1 differences in weathering mechanism between the two environments 2 higher solute concentrations in soil porewaters 3 loss of reactive surface area of biotite in the saprolite due to kaolinite and iron oxide coatings and or 4 unaccounted for heterogeneities in flow path through the soil

tracing silicon cycling in the okavango delta a sub tropical flood pulse wetland using silicon isotopes chemical weathering of silicate minerals releases elements into solution whereas the neoformation of secondary minerals works in the opposite direction potentially confounding estimates of silicate weathering rates silicon isotopes d30si may be a useful tool to investigate these processes here we present 82 d30si measurements from surface waters pore waters biogenic silica bsi clays sand and vegetation from the okavango delta botswana a freshwater sub tropical flood pulse wetland hydrologically the okavango is dominated by evapotranspiration water losses to the atmosphere it receives an annual pulse of water that inundates seasonal floodplains while river baseflow is sufficient to maintain a permanent floodplain d30si in dissolved silica dsi in surface waters along a 300 km transect at near peak flood show a limited range 0 36 1 19 imply ing the delta is well buffered by a balance of processes adding and removing dsi from the surface water a key control on dsi concentrations is the uptake production of bsi and recycling of si by aquatic vegetation although the net isotopic effect is necessarily small since all bsi re dissolves on short timescales in the sediments bsi d30si n 30 ranges from less

diagenetic ge si fractionation in continental margin environments further evidence for a nonopal ge sink we present data for dissolved germanic and silicic acids from several settings sediment pore water profiles collected from the peru chile continental margin fluxes measured with in situ benthic flux chambers and shipboard whole core incubations and water column profiles from the california continental margin collectively these data show that ge and si are fractionated in these continental margin sedimentary environments during diagenesis with 50 of the ge released by opal dissolution being sequestered within the sediments the areal extent of this diagenetic fractionation covers station depths from 100 m to 1000 m sediments from these sites typically have high pore water fe2 present in the upper 2 cm at sites with low fe2 concentrations in the upper pore waters the ge si benthic regeneration ratio indicates little or no fractionation during diatom dissolution consistent with the sedimentary fractionation water column dissolved ge si ratios along the continental margin are on average lower 0 66 mol mol than the global average ratio 0 72 mol mol mortlock and froelich 1996 this lower average ratio is driven by two distinct ge si data trends having similar slopes but different intercepts data from the upper 150 m has a ge si slope of 0 74 0 04 mol mol 2 and an intercept of 0 5 0 4 whereas below 550 m the slope is 0 70 0 06 mol mol but the intercept is 5 0 8 0 assuming that the sediments sampled here are representative of all reducing marine environments an assumption requiring further testing our calculations indicate that sequestration of ge into a nonopal phase throughout the global ocean in the depth range 0 2 1 km is sufficient to balance the ge budget thus we tentatively conclude that sequestering of ge in reducing continental margin sediments is the missing ge sink

the os isotopic composition of himalayan river bedloads and bedrocks importance of black shales re os data are presented for bedrocks and bedloads of selected rivers from the himalayan range in central nepal and bangladesh these data demonstrate that the os isotopic composition of most of the bedrocks is similar to that of the average continental crust notable exceptions to this are the black shales from the lesser himalaya lh which contain large quantities of radiogenic osmium in the black shales the os is not concentrated in the sulfides and may instead be associated with organic matter bedloads collected from rivers which include lh black shales in their catchment basins have notably high os ratios 187os 188os 3 this radiogenic signature persists into the ganga river in contrast the brahmaputra river is less radiogenic suggesting an ophiolite input in the headwater region simple physical mixtures of lh black shales with eroded products from the high range require unreasonably high proportions of black shale to explain the high os ratios observed at the outflow of the range assuming that our bedrock and bedload samples are representative of the source region and the eroded mixture respectively this observation suggests that erosion may not be occurring at steady state in addition mass balance calculations indicate that about 20 of the os and 60 of the re are carried in dissolved form implying that chemical erosion plays an important role in the osmium budget finally the contrast in os isotope ratio between ganga bedloads and bulk sediments in the bengal fan suggests that radiogenic os carried by particulate matter and later remobilized may significantly influence the os composition of seawater

germanium incorporation into sponge spicules development of a proxy for reconstructing inorganic germanium and silicon concentrations in seawater abstract measurements of germanium ge in deep sea sponge skeletons are presented for sponges collected by dredge and for spicules isolated from a range of deep sea sediment cores germanium to silicon si ratios ge si sp for sponge silica ranged between 0 075 and 0 380 mol mol which are much lower than the present day seawater ge si ratio of 0 7 mol mol a plot of ge si sp versus estimated seawater ge and si concentration produced a linear relationship with the ge content of spicules increasing with seawater ge concentration plots of ge si sp versus depth for both dredged sponges and sediment bound spicules produced oceanic profiles similar to those of dissolved ge and si concentration to explain the fractionation seen in the sponge ge si sp data two models are presented the first model used to interpret the data assumes that sponges only respond to the ge content of the ambient seawater implying that ge incorporation into sponge silica is independent of the seawater ge si ratio up to a si concentration of about 100 mol l this model is consistent with the 68 ge uptake results of davie et al e i davie t l simpson r garonne experimental germanium incorporation into siliceous sponge spicules biol cell 48 1983 191 202 for cultured spicules their results showed that the incorporation of ge in sponge silica is only dependent on the ge concentration of the water in which a sponge is growing the second model used to explain the data assumes that ge si sp fractionation results from subtle differences in the uptake kinetics of ge and si while the assumptions used by each model to describe the data are different it is possible to use sponge ge si sp data to reconstruct palaeo ge concentrations using model i and to reconstruct palaeo si concentrations using both models palaeo si concentrations estimated using both models are in good agreement

mesozoic and cenozoic faulting imaged at the epicenter of the 1886 charleston south carolina earthquake a seismic reflection profile collected in 1981 southeast of summerville south carolina was reprocessed to investigate the recent observation of unusual features the reprocessing included geometrical spreading and attenuation correction minimum phase filtering and spiking deconvolution which led to improved velocity analysis and residual static correction the result gives an improved image of the shallow crust in the epicentral area of the 1886 charleston earthquake there is clear evidence of a down to the east steeply dipping fault with approximately 200 m of vertical offset displacing lower mesozoic sedimentary and volcanic rocks diffraction from fault edges is responsible for the observation of unusual events with abnormal move out which led to the discovery of the faulting the overlying cretaceous and tertiary sedimentary section shows approximately 10 m of reverse up to the east displacement resolved by the data to within 100 m of the ground surface two other near vertical faults with down to the east offset of lower mesozoic units are inferred from the data immediately to the northwest of the major fault the locality is on the north side of the ashley river near the place known as gregg s landing and it coincides with the epicenters of modern seismic activity and maximum shaking effects documented in 1886 the charleston earthquake was very likely associated with this faulting

ge and si isotope signatures in rivers a quantitative multi proxy approach abstract solutes derived from the dissolution of silicate minerals play a key role in earth s climate via the carbon and other biogeochemical cycles silicon si is a unique constituent of silicate minerals and a biologically important nutrient so tracing its behavior in near surface environments may provide important insights into weathering processes however si released by weathering is variably incorporated into secondary mineral phases and biota obscuring signals derived from primary weathering processes due to chemical similarities germanium ge may help better understand the si cycle and its relationship to chemical weathering with this aim we report new measurements of the concentration and isotopic composition of ge for both the dissolved and particulate phases of a variety of global rivers these measurements are combined with analyses of concentration and isotopic ratio of si on the exact same sample set in order to make direct comparisons of the behavior of these two elements in natural river systems with this dataset we develop a new modeling framework describing the full elemental and isotopic systems of these solutes in rivers i e ge si 74 ge and 30 si this multi proxy approach allows us to ascertain the relative importance of biological versus mineral uptake in modulating the fluxes of these elements delivered to the modern ocean dissolved 74 ge composition of rivers studied thus far range from 0 9 to 5 5 with a discharge weighted global average of 2 6 0 5 the ge isotope composition of riverine suspended and bedload sediments is indistinguishable from silicate source rocks which is consistent with mass balance expectations the multi proxy modeling suggests that among the watersheds studied here the isotopic fractionation of si during secondary mineral phase precipitation 30 si s e c ranges from 2 7 to 0 2 which removes between 19 79 of the initial dissolved si while between 12 54 is incorporated by biota for ge modeling indicates that 79 98 of the dissolved load is incorporated into secondary mineral phases with a 74 ge s e c ranging from 4 9 to 0 3 the fractionation induced by biological uptake is calculated to range from 2 6 to 1 3 for 30 si b i o and 0 7 0 7 for 74 ge b i o in addition to improving our understanding of the coupled ge and si cycles our study provides a framework for using multiple isotopic tracers to elucidate the chemical behavior of solutes in natural waters

germanium enrichment in supergene settings evidence from the cristal nonsulfide zn prospect bongara district northern peru supergene nonsulfide ores form from the weathering of sulfide mineralization given the geochemical affinity of ge to si4 and fe3 weathering of ge bearing sulfides could potentially lead to ge enrichments in silicate and fe oxy hydroxide minerals although bulk rock ge concentrations in supergene nonsulfide deposits are rarely reported here we present the results of an investigation into ge concentrations and deportment in the cristal supergene zn nonsulfide prospect bongara northern peru which formed from the weathering of a preexisting mississippi valley type mvt sulfide deposit material examined in this study originates from drillcore recovered from oxidized zn rich bodies 15 20 m thick containing 5 45 wt zn and ge concentrations 100 ppm microanalysis and laser ablation icp ms show that precursor sphalerite is rich in both fe mean fe 8 19 wt and ge mean ge 142 ppm using the mineral geothermometer ggimfis geothermometer for ga ge in mn and fe in sphalerite proposed by frenzel et al ore geol rev 76 52 78 2016 sphalerite trace element data from the cristal prospect suggest a possible formation temperature tggimfis of 225 50 c anomalously high for a mvt deposit germanium concentrations measured in both goethite mean values 100 to 229 ppm max 511 ppm and hemimorphite mean values 39 to 137 ppm max 258 ppm are similar to concentrations measured in hypogene sphalerite additionally the ge concentrations recorded in bulk rock analyses of sphalerite bearing and oxidized samples are also similar a persistent warm humid climate is interpreted for the region resulting in the development of an oxidation zone favoring the formation of abundant zn hydrosilicates and fe hydroxides both able to incorporate ge in their crystal structure in this scenario ge has been prevented from dispersion during the weathering of the ge bearing sulfide bodies and remains in the resultant nonsulfide ore

the geochemistry of inorganic germanium in natural waters we present the initial results from a survey of the distribution of dissolved inorganic germanium in rivers in the oceans and in hydrothermal vents and plumes in the ocean germanium cycling mimics that of silica since siliceous organisms incorporate ge as a trace constituent in biogenic opal the vertical and horizontal distributions of ge concentrations in seawater are thus identical to those of silica ge si 0 7 10 6 and reflect uptake into and dissolution from the frustules of siliceous organisms germanium enters the ocean via dissolution of continental and seafloor silicates the naturally weathered flux from continents to oceans carries a dissolved ge si atom ratio in rivers of about 0 7 10 6 which reflects the ratio in average continental granites rivers draining industrial regions with significant coal combustion are contaminated with ge leached from fly ash particles resulting in ge si ratios up to tenfold above the naturally weathered background the flux to the oceans via high temperature alteration of seafloor basalts hot springs produces a ge anomaly in hydrothermal plumes over the east pacific rise crest 20 s combining the observed ge and 3he anomalies in plumes with 3he si observations in hot springs suggests that the ge si hydrothermal flux to the oceans is about 4 10 6 near the ratio for average oceanic basalts 2 6 10 6 vent effluents from the galapagos hot springs measured directly display ge si ratios of 16 10 6 suggesting that the ratio is variable between vent fields metalliferous sediments accumulating on the epr crest 17 s are enriched in germanium suggesting that a fraction of the hydrothermal germanium source on the rise crest is scavenged into these rapidly accumulating iron and manganese hydroxyoxide phases

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

germanium silicon fractionation in a river influenced continental margin the northern gulf of mexico abstract in this study we have sampled the water column and sediments of the gulf of mexico to investigate the effects of high riverine terrigenous load and sediment redox conditions on the cycling of ge and si water column ge si ratios across the gulf of mexico continental shelf range from 1 9 to 25 mol mol which is elevated compared to the global ocean value of 0 7 mol mol the ge enrichment in the gulf of mexico seawater is primarily due to anthropogenic contamination of the mississippi river which is the main ge and si source to the area and to a smaller extent due to discrimination against ge during biogenic silica bsi production ge si 1 2 1 8 mol mol especially by radiolarians and siliceous sponges ge si 0 6 1 1 mol mol most sediment pore waters ge si 0 3 4 5 mol mol and sediment incubation experiments benthic flux ge si 0 9 1 2 mol mol indicate precipitation of authigenic phases that sequester ge from pore waters non opal sink this process appears to be independent of oxidation reduction reactions and suggests that authigenic aluminosilicate formation reverse weathering may be the dominant ge sink in marine sediments compilation of previously published data shows that in continental margins non opal ge burial flux is controlled by bsi supply while in open ocean sediments it is 10 100 times lower and most likely limited by the supply of lithogenic material we provide a measurement based estimate of the global non opal ge burial flux as 4 32 mmol yr 1 encompassing the 2 16 mmol yr 1 needed to keep the global marine ge cycle at steady state

early diagenesis of germanium in sediments of the antarctic south atlantic in search of the missing ge sink pore water and solid phase geochemistry profiles were obtained from several cores between 41 degree s and 53 degree s in the atlantic sector of the southern ocean pore water nitrate manganese and iron profiles delineate standard redox zones in these sediments and help characterize those with classic vs burn down behaviors pore water si and ge profiles demonstrate that ge released during opal dissolution is removed pervasively throughout the uppermost interval of silicate release and also downwards into the suboxic zone by as yet unidentified precipitation mechanisms these results indicate that early diagenesis of ge is uncoupled from that of opal solid phase extractions fe mn u mo ge cu ni co v and cd in a few cores suggest that anthigenic ge removal in the suboxic zone is not associated with peaks in authigenic mn cycling mno sub 2 and related metals but rather with processes deeper in the sediments perhaps fe or u diagenesis below the interval of ge removal pre water ge increases linearly with depth by over two orders of magnitude indicating a deep below recovery source of large magnitude the fraction of opal derived ge precipitated authigenically in these sediments ranges from approximately 1 to 96 and correlates strongly with the detrital fraction asmore well as the detrital to opal ratio both of which generally decrease from north to south the ge sink observed in these sediments would need to be globally representative to account for the entire missing ge sink in today s oceanic ge balance which seems unlikely benthic fluxes of ge and si estimated from these pore water profiles and from measurements in three benthic flux chamber experiments at high carbon rain continental margin sites demonstrate that the ge si rate released from the seafloor in locations with high benthic silicate and carbon fluxes is congruent with holocene opal dissolution ge si approximately 0 7 x 10 sup minus 6 in contrast ge si flux ratios in areas with low silicate fluxes are ge depleted ge si 0 5 x 10 sup minus 6 the authors speculate that glacial interglacial changes in oceanic ge si as recorded in diatoms may be due in part to variations in this authigenic ge sink perhaps related to shifts in siliceous productivity from open ocean antarctic siliceous oozes during interglacials to areas of higher detrital input sub antarctic continental margins and possibly also to generally more reducing conditions in sediments during glacials less

gemas source distribution patterns and geochemical behaviour of ge in agricultural and grazing land soils at european continental scale abstract agricultural soil ap horizon 0 20 cm and grazing land soil gr horizon 0 10 cm samples were collected from a large part of europe 33 countries 5 6 million km 2 as part of the gemas geochemical mapping of agricultural and grazing land soil soil mapping project gemas soil data have been used to provide a general view of element mobility and source rocks at the continental scale either by reference to average crustal abundances or to normalized patterns of element mobility during weathering processes the survey area includes a diverse group of soil parent materials with varying geological history a wide range of climate zones and landscapes the concentrations of ge in european soil were determined by icp ms after an aqua extraction and their spatial distribution patterns generated by means of a gis software the median values of ge and its spatial distribution in ap and gr soils are almost the same 0 037 vs 0 034 mg kg respectively the majority of ge anomalies is related to the type of soil parent material namely lithology of the bedrock and minor influence of soil parameters such as ph toc and clay content metallogenic belts with sulphide mineralisation provide the primary source of ge in soil in several regions in europe e g in scandinavia germany france spain and balkan countries comparison with total ge concentrations obtained from the baltic soil survey shows that aqua regia is a very selective method with rather low efficiency and cannot provide a complete explanation for ge geochemical behaviour in soil additionally large differences in ge distribution are to be expected when different soil depth horizons are analysed

biogenic and pedogenic controls on si distributions and cycling in grasslands of the santa cruz soil chronosequence california abstract biogenic and pedogenic processes control silica cycling in grasslands growing on a soil chronosequence and dominated by strong seasonal variabilities of a mediterranean climate shallow pore water si in spite of significant annual uptake and release by plant growth and dieback exhibits only moderate seasonal fluctuations reflecting strong buffering from labile biogenic si dominated by phytoliths and by secondary pedogenic silicates long phytolith residence times 340 900 yrs reflect the seasonally dry climate and high solute si concentrations water extractable si is closely associated with al indicating seasonal precipitation and dissolution of a highly labile 1 1 hydroxyaluminosilicate has probably allophane which transforms in deeper soil into fine grained poorly crystalline kaolinite shallow plant roots extract greater proportions of biogenic si and deeper plant roots larger amounts pedogenic si high pore water ge si in late winter and spring reflects the reinforcing effects of plant fractionation and concurrent dissolution of ge enriched has the same processes produce pore waters with depleted 30 si 28 si in the summer and fall ge si declines and 30 si 28 si increases reflecting the cessation of plant uptake continued dissolution of soil phytoliths and re precipitation of less soluble has si inputs from weathering 2 90 mmol m 2 yr 1 and losses from pore water discharge 18 68 mm m 2 yr 1 are comparable for individual soils decline with soil age and are significantly less than amounts of si annual cycled through the vegetation 42 171 mm m 2 yr 1 mobile si is generally balanced in the soils with upward bio pumping by the shallow rooted grasses efficiently competing against downward leaching and pore water discharge small net annual increases in si in the present day soils could not have been maintained over the time scale represented by the chronosequence 65 225 yrs implying past changes in environmental conditions

trace element and textural evidence favoring lunar not terrestrial origin of the mini granite in apollo sample 14321 abstract the 14321 lunar granite 14321g has recently been reinterpreted bellucci et al 2019 as a piece of the hadean earth impact transported to the moon in principle samples of such derivation may afford important insights into the nature of earth s hadean crust we have tested the terrestrial provenance hypothesis by comparing trace element data from 14321g versus other lunar evolved rocks and a large data base for terrestrial granites volatile trace metals zn ga and ge are depleted in 14321g below the terrestrial granite ranges and relative to the terrestrial granite averages by factors of 27 2 0 and 18 respectively evidence from shocked chondrites martian meteorites and impact shock studies in general indicates that such major depletions are unlikely to develop without near complete shock melting which clearly did not occur in the mostly still crystalline 14321g moreover other aspects of compositional disparity between 14321g and terrestrial granites involve exclusively refractory trace elements compared to terrestrial granites of similarly high ba content 14321 is enriched in ta by a factor of 10 and the few terrestrial granites that are as ta rich as 14321 have 10 times lower ba the refractory element ratio lu sm is also close to 10 times higher in 14321g than in terrestrial granites of similarly high ba content other highly evolved lunar rocks felsites strongly resemble 14321g in all these respects we conclude that 14321g is probably of wholly lunar derivation this finding stands in contradiction to a recent inference from ti in quartz modeling bellucci et al 2019 that 14321g crystallized at a pressure of 0 69 gpa the geodynamically limited moon was presumably never capable of forming or burying such a highly granitic material 100 km below the base of its crust nor of excavating material from such a depth to the surface

germanium silicon ratios in the copper river basin alaska weathering and partitioning in periglacial versus glacial environments 1 glacial to interglacial variation in the germanium to silicon ratio ge si of biogenic opal in oceanic sediment cores has been proposed to record terrestrial silicate weathering intensity however data connecting ge si ratios to weathering are sparse especially for cold regions to characterize ge si of the dissolved loads of rivers draining modern glacial and periglacial regions we measured ge and major element chemistry of more than 30 streams in the copper river basin of south alaska we measured significantly higher ge si in rivers with greater than 15 glacial cover in their basins than in rivers draining areas with less glacial cover which we attribute to preferencial subglacial weathering of biotite we also ran laboratory experiments to investigate the role of differential sorption of ge and si on hydrous iron oxides in moderating the ge si ratio of rivers in recently deglaciated basins these experiments indicate that ge is preferentially adsorbed over si by hydrous iron oxides over a wide range of ph values and support differential sorption as a potentially significant fractionation process our measured high ge si in glaciated basins is in striking contrast to the low ge si in the oceanic record during glacial periods the glacial to interglacial changes in marine ge si cannot simply reflect changes in glacier cover on land as the mineralogy of silicates weathered and processes partitioning ge in soils must also strongly influence the fluvial ge and si inputs to the ocean

germanium geochemistry and mineralogy abstract germanium is enriched in the following geologic environments 1 1 iron meteorites and terrestrial iron nickel 2 2 sulfide ore deposits particularly those hosted by sedimentary rocks 3 3 iron oxide deposits 4 4 oxidized zones of ge bearing sulfide deposits 5 5 pegmatites greisens and skarns and 6 6 coal and lignitized wood in silicate melts ge is highly siderophile in the presence of native iron nickel otherwise it is highly lithophile among silicate minerals ge is concentrated in those having less polymerized silicate tetrahedra such as olivine and topaz in deposits formed from hydrothermal solutions ge tends to be enriched mostly in either sulfides or in fluorine bearing phases it is thus concentrated both in some hydrothermal sulfide deposits and in pegmatites greisens and skarns in sulfide deposits that formed from solutions having low to moderate sulfur activity ge is concentrated in sphalerite in amounts up to 3000 ppm sulfide deposits that formed from solutions having higher sulfur activity allowed ge to either form its own sulfides particularly with cu or to substitute for as sn or other metals in sulfosalts the ge in hydrothermal fluids probably derives from enrichment during the fractional crystallization of igneous fluids or is due to the incorporation of ge from the country rocks particularly from those containing organic material germanium bonds to lignin derivative organic compounds that are found in peat and lignite accounting for its common concentration in coals and related organic material germanium is precipitated from water together with iron hydroxide accounting for its concentration in some sedimentary and supergene iron oxide deposits it also is able to substitute for fe in magnetite in a variety of geologic environments in the oxidized zone of ge bearing sulfide deposits ge is concentrated in oxides hydroxides and hydroxy sulfates sometimes forming its own minerals it is particularly enriched in some iron and manganese bearing oxides and hydroxides including goethite up to 5300 ppm and hematite up to 7000 ppm

germanium silica ratios in diagenetic chert nodules from the ediacaran doushantuo formation south china abstract germanium silica ge si ratios of dolostone and mudstone hosted chert nodules from the ediacaran 635 542 ma doushantuo formation in the yangtze gorges area south china are reported these chert nodules typically have a calcite rim a pyrite rim and a silica core the latter sometimes containing disseminated pyrite the silica core was precipitated by early diagenetic replacement of carbonate and silty muddy sediments two types of chert nodules are identified based on their mineralogy and geochemistry type 1 chert nodules are poor in disseminated pyrite in the silica core they also have low al and show a strong positive correlation between al contents and ge si with a near zero or negative intercept in contrast type 2 chert nodules contain abundant disseminated pyrite in the silica core and show a weakly positive correlation between ge si ratios and al contents with a large positive intercept on the ge si axis the ge si of doushantuo nodules are greater than those of cretaceous deep sea cherts suggesting that the ge si ratio of ediacaran seawater porewater was greater than the cretaceous due to the more effective discrimination against ge by inorganic opal precipitation relative to biogenic opal precipitation the positive correlation between ge si and al can be interpreted using a mixing model with a pure chert characterized by a low ge si ratio and an al rich endmember characterized by a high ge si ratio the latter is most likely represented by a clay component but the model based estimate of the ge si ratio inferred for the al rich clay endmember is much higher than that of phanerozoic clay minerals these high ge si ratios for the clay endmember may be related to the generally high ge si ratio of ediacaran seawater but could also be related to clay organic matter interactions organic matter absorbed to clays could provide an additional source of ge because certain organic molecules are known to have a high affinity for ge due to their strong metal ion chelating properties the high ge si ratio of the al rich endmember in type 1 chert nodules suggests that ge in porewaters from which these cherts precipitated may have been dominated by ge organic complexes the low ge si ratio inferred for the al rich endmember in type 2 chert nodules is therefore taken to indicate that ge was released from organic matter perhaps due to anaerobic degradation of organic matter accompanied by the formation of pyrite and was redistributed between clay organic endmembers and pure chert resulting in a non zero intercept in the ge si vs al 2 o 3 plots these observations suggest that a strong terrestrial influence in a restricted sedimentary basin or a high content of dissolved organic carbon in ediacaran seawater and porewater may have contributed to the dominance of ge organic complexes in the doushantuo basin in the yangtze gorges area

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

chemical weathering of phosphate and germanium in glacial meltwater streams effects of subglacial pyrite oxidation data from three glacial meltwater streams draining mt tronador in the southern argentine andes 72 w 4 1 s show that subglacial pyrite oxidation and the subsequent precipitation of iron oxides strongly influence dissolved phosphate concentrations but do not appear to affect dissolved germanium concentrations total fe tfe and total p tp concentrations are high in all three glacial streams but the ratios of soluble reactive phosphate srp to tp are very different the upper manso stream that drains the manso glacier has relatively low srp 0 01 0 23 pm representing a small fraction of its tp o l 5 the srp of the two streams draining smaller side glaciers 0 124 69 pm represents a much larger portion of their tp 20 32 tfe dissolved sulfate and 634s data suggest that pyrite oxidation is the most likely weathering reaction contributing sulfate to the upper manso stream but not to the two smaller glacialfed streams in which atmospheric inputs can account for all of the sulfate dissolved ge appears to show no preferential sorption relative to dissolved silica in contrast to the speculation that ge preferentially sorbs on fresh iron hydroxyoxide surfaces

a global ge isotope budget we present measurements of ge isotope composition and ancillary data for samples of river water low and high temperature hydrothermal fluids and seawater the dissolved 74ge composition of analyzed rivers ranges from 2 0 to 5 6 which is significantly heavier than previously determined values for silicate rocks 74ge 0 4 0 7 escoube et al geostand geoanal res 36 2 2012 from which dissolved ge is primarily derived an observed negative correlation between riverine ge si and 74ge signatures suggests that the primary 74ge fractionation mechanism during rock weathering is the preferential incorporation of light isotopes into secondary weathering products high temperature 150 c hydrothermal fluids analyzed in this study have 74ge of 0 7 1 6 most likely fractionated during fluid equilibration with quartz in the reaction zone low temperature 25 63 c hydrothermal fluids are heavier 74ge between 2 9 and 4 1 and most likely fractionated during ge precipitation with hydrothermal clays seawater from the open ocean has a 74gesw value of 3 2 0 4 and is indistinguishable among the different ocean basins at the current level of precision this value should be regulated over time by the isotopic balance of ge sources and sinks and a new compilation of these fluxes is presented along with their estimated isotopic compositions assuming steady state non opal ge sequestration during sediment authigenesis likely involves isotopic fractionation 74gesolid solution that is 0 6 1 8

desilication in archean weathering processes traced by silicon isotopes and ge si ratios abstract the influence of continental weathering on oceanic seawater compositions in the precambrian is poorly understood here we combine si isotopes and ge si ratios of a mesoarchean paleosol 2 95 ga and overlying shales as proxies for weathering processes and si mass transfer at the early earth s surface results show that as with modern soils neoformation of secondary clay minerals in the paleosol was associated with the fractionation of si isotopes and ge si ratios in response to chemical weathering and soil desilication furthermore the loss of fe bearing minerals most likely fe bearing smectites produced additional controls on si and ge mobility through the coupled dissolution and re precipitation of clay minerals under reductive conditions opposite fractionation behaviors are observed neoformed secondary clay minerals acted as a 28 si and ge sink whereas the leaching of fe bearing minerals released 28 si and ge into soil solutions an attempt to estimate 30 si and ge si signatures of released dissolved elements into soil solution provided 30 si and ge si signatures of about 0 1 and 1 4 mol mol respectively furthermore shales deposited shortly after paleosol formation display 30 si and ge si compositions that may be explained as mixtures of the recognized paleosol components the shale record suggests that weathering induced desilication and leaching of fe bearing minerals to a lesser extent might have been widely effective during the mesoarchean for the transfer of si from the continents to the hydrosphere comparison of si isotopes recorded in detrital sediments and chemical precipitates over time might thus provide a useful supplementary tool to decipher the impact of putative increases in continental weathering and desilication relative to changes in hydrothermal and continent derived solute inputs to ocean and ocean cooling

biogenic silica a neglected component of the coupled global continental biogeochemical cycles of carbon and silicon on geological time scales 106 years the global geochemical cycles of carbon and silicon are coupled by the drawdown of atmospheric co2 through chemical weathering of ca and mg silicate minerals in continental rocks rivers transport the soluble products of weathering cations alkalinity and silicic acid to the oceans where they are utilized by marine ecosystems on decadal to glacial interglacial time scales however large biotic fluxes and storages of si within terrestrial and freshwater ecosystems need to be taken into account recent studies have emphasized the importance of si accumulating plants which deposit significant amounts of amorphous hydrated silica in their tissues as opal phytoliths these include grasses sedges palms some temperate deciduous trees and conifers and many tropical hardwoods landscapes dominated by accumulator plants such as tropical rainforests grasslands herbaceous wetlands and bamboo forests act as silica factories important silica bioengineers in freshwater ecosystems comprise diatoms sponges and chrysophytes this paper reviews the biological role of si in higher plants the impact of vegetation on rates of chemical weathering the fluxes of si through catchment ecosystems lakes and rivers and the potential contribution of new geochemical and isotopic tracers to si biogeochemistry multiproxy investigations of lake sediments will provide novel insights into past variations in si biocycling from terrestrial to aquatic realms on 10 106 year time scales copyright 2008 john wiley sons ltd

geologic control of sr and major element chemistry in himalayan rivers nepal our study of the seti river in far western nepal shows that the solute chemistry of the river and its tributaries is strongly controlled by geology the seti flows through four distinct terranes starting with the tethyan sedimentary series tss and greater himalayan series ghs tss ghs waters display 87 sr 86 sr ratios of 0 73 and high sr and ca consistent with the composition of limestone and marble common in these terranes the 87 sr 86 sr ratio and mg increase markedly as the river passes into the lesser himalayan series lhs where tributaries have 87 sr 86 sr ratios from 0 75 to 1 02 and high sr ca and mg the high mg in lhs waters correlate with high 87 sr 86 sr ratios which we attribute to weathering of highly radiogenic 0 71 0 82 dolostones tributaries to the seti river draining the largely carbonate free dadeldhura thrust sheet dts have ratios near 0 74 but low sr ca and mg and therefore have little impact on seti mainstem chemistry mass balance calculations and camg weathering indices show that carbonate weathering accounts for 70 of total dissolved solids to the seti river sr ca ratios of river waters provide a minimum estimate of the carbonate weathering contribution to sr due to partitioning of sr and ca during incongruent dissolution and reprecipitation of calcite overall we attribute high 87 sr 86 sr ratios in the seti river and its tributaries to the weathering of metacarbonates especially dolostones in the upper nawakhot group which have exchanged sr with silicates during metamorphism our modeling of sr fluxes in the seti river indicates that the tss ghs accounts for 36 39 of the sr the lhs for 40 53 and 8 23 for the dts prior to exposure of lhs rocks at 12 ma tss and ghs carbonates with low 87 sr 86 sr ratios dominated himalayan rivers we attribute the elevated 87 sr 86 sr ratios of himalayan paleorivers during the late miocene and pliocene to exposure and weathering of lhs metacarbonates copyright 2000 elsevier science ltd

refractory element mobility in volcanic soils refractory trace element concentrations in strongly weathered hawaiian soils ranging in age from 20 to 4100 ka are highly elevated over parent rock values due to extensive mass loss of more soluble major elements during pedogenesis nb and ta exhibit virtually no mobility soil nb ta ratios are within the range of fresh bedrock even when soil nb concentrations are residually enriched by a factor of 10 in contrast al zr and hf are depleted relative to nb in surface soil horizons but are enriched at depth clearly indicating mobility of these elements variations in th nb ratios in soil profiles indicate significant th mobility within the soil column however mass balance calculations require that accretion of th enriched asian dust has resulted in a net increase in th in some soils soils developed on a 150 ka rainfall gradient show that the mobility and loss of zr increase with mean annual precipitation

germanium silicon as a flow path tracer application to the rio icacos watershed 1 we use dissolved silicon together with its geochemical twin germanium for the first time as a hydrologic tracer to study water delivery to the stream during storm events in the rio icacos watershed puerto rico ge and si were measured on base flow stormflow springwater and soil water samples compositions of all of these waters appear to reflect varying contributions from three components which we attribute to solutes released from bedrock weathering groundwater from short term soil water interaction quick soil water and longer term soil water interaction matrix soil water base flow stream waters have high si and moderate ge ge si ratio 0 29 mol mol consistent with a predominantly bedrock weathering source as indicated by their similarity with water sampled from springs emerging from the saprolite bedrock boundary on a hillslope landslide scar during storm events there is a shift toward more dilute compositions but higher ge si ratios similar to those measured on water samples from temporary depression storage and overland flow quick soil water geochemical mass balance shows that 80 90 of the stream chemistry can be explained by mixing groundwater with this quick soil water composition which we infer to reflect new water traveling as shallow throughflow stream water 18o values decrease to more negative values typical of precipitation supporting rapid delivery of rainwater to the stream channel during stormflow the third component with a ge rich composition characteristic of soil matrix water sampled by tension lysimeters is required to explain higher stream water ge si ratios measured during hydrograph recession we infer from this an additional slower and less dominant pathway for delivery of soil water to the stream channel

silicon isotopes record dissolution and re precipitation of pedogenic clay minerals in a podzolic soil chronosequence by providing the largest part of the reactive surface area of soils secondary minerals play a major role in terrestrial biogeochemical processes the understanding of the mechanisms governing neo trans formation of pedogenic clay minerals in soils is therefore of the utmost importance to learn how soils evolve and impact the chemistry of elements in terrestrial environments soil forming processes governing the evolution of secondary aluminosilicates in podzols are however still not fully understood the evolution of silicon si isotope signature in the clay fraction of a podzolic soil chronosequence can provide new insight into these processes enabling to trace the source of si in secondary aluminosilicates during podzol forming processes characterized by the mobilization transport and precipitation of carbon metals and si the si isotope compositions in the clay fraction comprised of primary and secondary minerals document an increasing light 28 si enrichment and depletion with soil age respectively in illuvial b horizons and eluvial e horizon the mass balance approach demonstrates that secondary minerals in the topsoil eluvial e horizons are isotopically heavier with 30 si values increasing from 0 39 to 0 64 in c a 200years while secondary minerals in the illuvial bhs horizon are isotopically lighter 30 si 2 31 compared to the original unweathered secondary minerals in bc horizon 30 si 1 40 the evolution of si isotope signatures is explained by the dissolution of pedogenic clay minerals in the topsoil which is a source of light 28 si for the re precipitation of new clay minerals in the subsoil this provides consistent evidence that in strong weathering environment such as encountered in podzols si released from secondary minerals is partially used to form tertiary clay minerals over very short time scales ca 300years our dataset demonstrates the usefulness to measure si isotope signatures in the clay fraction to discern clay mineral changes e g neoformation versus solid state transformation during soil evolution this offers new opportunity to better understand clay mineral genesis under environmental changes and the short term impact of the dissolution and re precipitation of pedogenic clay minerals on soil fertility soil carbon budget and elemental cycles in soil plant systems 2014 elsevier b v

accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances hawaiian soils contain a mixture of material derived from in situ weathering of parent material plus atmospheric inputs including sea salt aerosols and asian dust we use soil mineralogy and radiogenic isotope geochemistry sr and nd to evaluate the impact of asian dust on a chronosequence of hawaiian soils dust becomes an important constituent of soils 20 ky and older near surface 50 cm depth horizons contain as much as 30 quartz a mineral absent from local parent material basaltic sr and nd isotope signatures in these horizons have been completely overprinted by asian dust signatures with 87sr 86sr ratios as high as 0 723 and end values as low as 7 ree patterns in these soils are indistinguishable from that of average upper continental crust quartz abundance and nd isotopes provide two independent tracers of long term dust additions to the chronosequence soils the two tracers indicate a minimum long term average dust accretion rate of 125 mg cm 2 ky 1 at the 150 ka chronosequence site roughly a factor of three higher than holocene dust accumulation rates estimated from north pacific sediment cores we find that the mass of dust preserved in these soil profiles does not increase with age in soils 150 ka and older requiring a loss mechanism for accreted dust on the basis of the geomorphic stability of these sites observed preferential loss of dust derived mica relative to quartz and estimates of soil si leaching rates we argue that chemical weathering is the dominant loss mechanism for dust from these soils dust has a profound effect on the budgets of elements that are susceptible to leaching losses dust becomes the dominant source of soil nutrients si and p in the oldest most intensely weathered soils we calculate a dust derived p input flux of 0 8 mg cm 2 ky 1 and a dust derived si input flux of 35 mg cm 2 ky 1 si leaching fluxes are high 1400 mg cm 2 ky 1 in the youngest 2 ka soils and drop systematically with soil age to a value that closely balances the dust derived si input flux by 4100 ka extremely refractory elements such as nb which are concentrated in soils by residual enrichment processes are much less readily impacted by dust addition although dust has had a pronounced impact on sr and nd isotopic budgets and on soil mineral composition at the 150 ka site dust cannot have contributed 4 of the total nb contained in this soil profile

germanium sequestration by soil targeting the roles of secondary clays and fe oxyhydroxides abstract germanium is a trace element that behaves similarly to silicon and shows promise as a tracer of silicate weathering processes sequestration of ge by clay minerals is thought to be the dominant mechanism responsible for ge si fractionation during weathering in some environments ge may be sequestered by iron oxyhydroxides we examine ge behavior in soils along a well characterized climate gradient on the hawaiian island of maui to clarify the relationship between fe geochemistry and soil ge si ratios all of the sites are developed on basaltic lavas and tephras approximately 400 ky old are highly si depleted and have ge si ratios higher than parent material sites experiencing less than 3300 mm rain yr host oxidized highly weathered basaltic soils in which fe is present as secondary fe oxyhydroxide minerals in contrast the wetter sites 3340 mm yr show extensive fe reduction mobilization and loss we show that ge sequestration is independent of fe redox behavior along the gradient and thus precipitation of fe oxyhydroxides is not a major factor contributing to ge si fractionation during weathering instead elevated soil ge si ratios reflect partitioning of ge into secondary clay minerals plus additional retention of ge by refractory non silicates

structure of crust and upper mantle beneath the ordos block and the yinshan mountains revealed by receiver function analysis a temporary seismological network of broadband three component stations has been deployed n s to investigate the crust and upper mantle structure across the ordos block and the yinshan mountains p wave receiver functions reveal the moho depth to be about 41 km beneath the central ordos block and down to 45 km beneath the northern ordos block a slight uplifting to 42 43 km beneath the hetao graben increasing to 47 48 km beneath the yinshan mountains and then decreasing to 44 km beneath the northern yinshan mountains along the profile in the ordos block the crustal vp vs ratio about 1 80 south to the hetao graben differs from that about 1 75 beneath the center ordos block the crustal vp vs ratio is significantly lower about 1 65 1 70 beneath the yinshan mountains the p wave receiver function migration imaging suggests relatively flat discontinuities at 410 and 660 km indicating the lack of a strong thermal anomaly beneath this profile at these depths and a low s wave velocity anomaly in the upper mantle beneath the hetao graben we suggest that the low s wave velocity anomaly may be attributable to heat and that the thermal softening advances the evolution of the hetao graben while the lower crustal ductile flows transfer from the hetao graben to the northern ordos block resulting in crustal thickening

ge si in hamersley bif as tracer of hydrothermal si and ge inputs to the paleoproterozoic ocean abstract ge si and ge fe ratios have been measured by laser ablation icp ms in selected sections of the hamersley banded iron formation bif including chert siderite bands i e carbonate and silicate facies bif the major ge carriers are magnetite and hematite in the oxide facies and the fe rich silicates greenalite minnesotaite and stilpnomelane in chert siderite bands while quartz has the lowest ge si ratios 0 15 0 7 mol mol in accord with discrimination against ge in quartz the homogeneous si fe ratio of 1 25 for dales gorge oxide facies bif is consistent with si ferrihydrite as precursor phase this si concentration is sufficiently high for formation of iron free silica clusters at the surface of ferrihydrite so that only a minor fractionation of the ge si ratio should result from preferential ge adsorption relative to si hematite chert bands that have been minimally altered by metamorphic reactions and or fluid metasomatism are the preferred material to determine the sources of silica in hamersley bif variations of fe si and ge si ratios in chert mesobands are interpreted as the result of diagenetic mineral segregation a consistent ge si 3 mol mol is then derived by extrapolation of measured ge si ratios to the average fe si composition of dales gorge bif simple mass balance calculations indicate hydrothermal inputs to the ocean of the order of 25 for si and 90 for ge assuming ge si 10 mol mol for high temperature hydrothermal fluids the high si concentration in siderite chert bands si fe 4 demands only a small amount of si ferrihydrite precursor and some excess silica likely precipitated in pore water oversaturated with regard to amorphous silica the average ge si 0 80 0 1 mol mol for bulk chert siderite samples including some stilpnomelane rich cherts is within the compositional range of modern riverine and aeolian inputs pointing to a continental si source during their deposition

upper mantle anisotropy and transition zone thickness beneath southeastern north america and implications for mantle dynamics a variety of models for mantle flow beneath southeastern north america have been proposed including those that invoke westward driven return flow from the sinking farallon slab small scale convective downwelling at the edge of the continental root or the upward advective transport of volatiles from the deep slab through the upper mantle we use shear wave splitting observations and receiver function analysis at broadband seismic stations in the southeastern united states to test several of these proposed mantle flow geometries near the coast stations exhibit well resolved null no splitting behavior for sks phases over a range of back azimuths consistent with either isotropic upper mantle or with a vertical axis of anisotropic symmetry farther inland we identify splitting with mainly ne sw fast directions consistent with asthenospheric shear due to absolute plate motion apm lithospheric anisotropy aligned with appalachian tectonic structure or a combination of these phase weighted stacking of individual receiver functions allows us to place constraints on the timing of arrivals from the 410 and 660 km discontinuities and on average transition zone thickness beneath individual stations at most stations we find transition zone thicknesses that are consistent with the global average 240 km with two stations showing evidence for a slightly thickened transition zone 250 km our results are relevant for testing different models for mantle dynamics beneath the southeastern united states but due to the sparse station coverage we are unable to uniquely constrain the pattern of mantle flow beneath the region our sks splitting observations support a model in which mantle flow is primarily vertical either upwelling or downwelling beneath the southeastern edge of the north american continent in contrast to the likely horizontal apm driven flow beneath the continental interior however our receiver function analysis does not provide unequivocal support either for widespread hydration of the transition zone or for widespread thickening due to the downwelling of relatively cold mantle material we expect that the necessary data to constrain such models more tightly can be obtained from the operation of denser seismic networks including the transportable array and flexible array components of usarray

variations of δ30si and ge si with weathering and biogenic input in tropical basaltic ash soils under monoculture in soils silicon released by mineral weathering can be retrieved from soil solution through clay formation si adsorption onto secondary oxides and plant uptake thereby impacting the si isotopic signature and ge si ratio of dissolved si dsi exported to rivers here we use these proxies to study the contribution of biogenic si bsi in a soil plant system involving basaltic ash soils differing in weathering degree under intensive banana cropping delta si 30 and ge si ratios were determined in bulk soils 2 mm sand 50 2000 mu m silt 2 50 mu m amorphous si asi 2 50 mu m and clay 2 mu m fractions delta si 30 by mc icp ms nu plasma in medium resolution operating in dry plasma with mg doping delta si 30 vs nbs28 0 12 parts per thousand 2 sigma sd ge si computed after determination of ge and si concentrations by hr icp ms and icp aes respectively components of the asi fraction were quantified by microscopic counting phytoliths diatoms ashes compared to fresh ash delta si 30 0 38 parts per thousand ge si 2 21 mu mol mol 1 soil clay fractions 2 mu m were enriched in light si isotopes and ge with increasing weathering degree delta si 30 decreased from 1 19 to 2 37 parts per thousand and ge si increased from 4 10 to 5 25 mu mol mol 1 sand and silt fractions displayed delta si 30 values close to fresh ash 0 33 parts per thousand or higher due to saharian dust quartz deposition whose contribution was evaluated by isotopic mass balance calculation si isotopic signatures of bulk soils 2 mm were strongly governed by the relative proportions of primary and secondary minerals the bulk soil si isotopic budget could be closed indicating that all the phases involved were identified microscopic counting highlighted a surface accumulation of banana phytoliths and a stable phytolith pool from previous forested vegetation delta si 30 and ge si values of clay fractions in poorly developed volcanic soils isotopically heavier and ge depleted in surface horizons support the occurrence of a dsi source from banana phytolith dissolution available for si sequestration in clay sized secondary minerals clay minerals formation and si adsorption onto fe oxide in the soil plant system delta si 30 and ge si are thus highly relevant to trace weathering and input of dsi from phytoliths in secondary minerals although not quantifying the net input of bsi to dsi c 2009 elsevier ltd all rights reserved

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

ge si ratios indicating hydrothermal and sulfide weathering input to rivers of the eastern tibetan plateau and mt baekdu abstract concentrations of dissolved silicon in river waters reflect a complex interplay among chemical weathering of primary silicate minerals formation and weathering of secondary clay minerals hydrothermal input and biological cycling formation and dissolution of opal phytoliths and growth of diatoms we applied the ge si ratio to assess the different sources of dissolved si in rivers hailing from the eastern tibetan plateau the salween mekong chang jiang yangtze hong red and huang he yellow and from mt baekdu the duman elevated riverine ge si ratios were observed in arid regions with high geothermal activity in the salween chang jiang and mt baekdu streams in the huang he and hong river basins geothermal influence was not as pronounced but weathering of sulfide and coal bearing minerals may be responsible for the high ge si ratios in rivers where inputs from hydrothermal and sulfide weathering are minimal our data mostly fall in the weathering limited regime of high riverine si concentrations and low ge si ratios

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

the isotope composition of inorganic germanium in seawater and deep sea sponges abstract although dissolved concentrations of germanium ge and silicon si in modern seawater are tightly correlated uncertainties still exist in the modern marine ge cycle germanium stable isotope systematics in marine systems should provide additional constraints on marine ge sources and sinks however the low concentration of ge in seawater presents an analytical challenge for isotopic measurement here we present a new method of pre concentration of inorganic ge from seawater which was applied to measure three ge isotope profiles in the southern ocean and deep seawater from the atlantic and pacific oceans germanium isotopic measurements were performed on ge amounts as low as 2 6 ng using a double spike approach and a hydride generation system coupled to a mc icp ms germanium was co precipitated with iron hydroxide and then purified through anion exchange chromatography results for the deep i e 1000 m depth pacific ocean off hawaii nearby loihi seamount and the deep atlantic off bermuda bats station showed nearly identical 74 70ge values at 3 19 0 31 2sd n 9 and 2 93 0 10 2sd n 2 respectively vertical distributions of ge concentration and isotope composition in the deep southern ocean for water depth 1300 m yielded an average 74 70ge 3 13 0 25 2sd n 14 and ge si 0 80 0 09 mol mol 2sd n 12 significant variations in 74 70ge from 2 62 to 3 71 were measured in the first 1000 m in one station of the southern ocean near sars seamount in the drake passage with the heaviest values measured in surface waters isotope fractionation by diatoms during opal biomineralization may explain the enrichment in heavy isotopes for both ge and si in surface seawater however examination of both oceanographic parameters and 74 70ge values suggest also that water mass mixing and potential contribution of shelf derived ge also could contribute to the variations combining these results with new ge isotope data for deep sea sponges sampled nearby allowed us to determine a ge isotope fractionation factor of 0 87 0 37 2sd n 12 during ge uptake by sponges although ge has long been considered as a geochemical twin of si this work underpins fundamental differences in their isotopic behaviors both during biomineralization processes and in their oceanic distributions this suggests that combined with si isotopes ge isotopes hold significant promise as a complementary proxy for delineating biological versus source effects in the evolution of the marine silicon cycle through time

zinc and germanium in the sedimentary rocks of gale crater on mars indicate hydrothermal enrichment followed by diagenetic fractionation zinc and germanium enrichments have been discovered in sedimentary rocks in gale crater mars by the alpha particle x ray spectrometer on the rover curiosity concentrations of zn 910 840 ppm and ge 65 58 ppm are tens to hundreds of times greater than in martian meteorites and estimates for average silicate mars enrichments occur in diverse rocks including minimally to extensively altered basaltic and alkalic sedimentary rocks the magnitude of the enrichments indicates hydrothermal fluids but curiosity has not discovered unambiguous hydrothermal mineral assemblages we propose that zn and ge rich hydrothermal deposits in the source region were dispersed in siliciclastic sediments during transport into the crater subsequent diagenetic mobilization and fractionation of zn and ge is evident in a zn rich sandstone windjana zn 4000 ppm ge 85 ppm and associated cl rich vein stephen zn 8000 ppm ge 60 ppm in ge rich veins garden city zn 2200 ppm ge 650 ppm and in silica rich alteration haloes leached of zn 30 200 ppm in moderately to highly altered silica rich rocks ge remained immobile relative to leached elements fe mn mg and ca consistent with fluid interaction at ph 7 in contrast crosscutting ge rich veins at garden city suggest aqueous mobilization as ge f complexes at ph 2 5 multiple jarosite detections by the chemin x ray diffractometer and variable zn concentrations indicate diagenesis of lower mount sharp bedrock under acidic conditions the enrichment and fractionation of zn and ge constrains fluid events affecting gale sediments and can aid in unraveling fluid histories as curiosity s traverse continues

river fluxes of dissolved silica to the ocean were higher during glacials ge si in diatoms rivers and oceans two centric marine diatom species thalassiosira oceanica and thalassiosira antarctica were grown in batch cultures to determine the incorporation of germanium ge and silicon si into siliceous shells opal the results were modeled as ge si isotope fractionation during exponential growth diatoms take up and incorporate ge si from solution without major discrimination against ge during stationary phase growth near silica limitation the antarctic species t antarctica discriminates slightly against ge but integrated ge si opal produced over the latter portion of the growth cycle is indistinguishable from the initial solution ratio these results confirm experiments using radioactive 68ge that showed absence of fractionation during diatom silica uptake azam and volcani 1981 in contrast to two box ocean models that invoke 50 ge discrimination by diatoms to explain the observed excess surface ocean germanium concentration murnane and stallard 1988 froelich et al 1989 and late pleistocene ocean sediment ge si opal records mortlock et al 1991 runs of a 10 box ocean ge and si model pandora with 50 discrimination reproduce the excess surface ocean ge but introduces curvature into the deep ocean ge versus si relationship that is not observed in the oceans thus 50 fractionation is not supported by either cultures or models if diatoms do not fractionate ge si then late pleistocene ge si opal variations in piston cores are caused not by changes in local biosiliceous production and silica utilization mortlock et al 1991 but rather by whole ocean changes in ge si seawater the marine ge si opal record of the last 450 kyr can be modeled as transient oceanic responses to instantaneous continental climate transitions consistent with the chemical weathering model of murnane and stallard 1990 glacial periods are characterized by lower continental weathering intensity lower ge si riv and two fold higher dissolved silica river fluxes marine ge si opal records thus contain a history of ocean silica chemistry that reflect rapid global changes in continental weathering

the potential role of ridge flank hydrothermal systems on oceanic germanium and silicon balances abstract sediment pore water samples and warm spring fluids from three ridge flank hydrothermal systems 40 75 c were analyzed for ge si and mg to quantify the contribution of these systems to oceanic ge and si balances these warm hydrothermal fluids have elevated concentrations of ge and si relative to bottom seawater indicating that these systems are net sources of ge and si to the oceans end member ge si molar ratios range from 12 to 34 mol mol which is similar to but elevated relative to the average ratio from high temperature 350 c midocean ridge hydrothermal systems the source for this ge and si is suggested to be a combination of seawater reaction with basalt and diffusive exchange with overlying basal pore waters which are in pseudo equilibrium with amorphous silica because the ge si molar ratio in both basalt and sediment is much less than those measured in the dissolved phase a net preferential removal of si relative to ge must occur within basaltic basement as suggested for high temperature hydrothermal systems we suggest that this removal mechanism is likely a consequence of quartz precipitation and the formation of secondary clays i e smectite we estimate that ridge flank hydrothermal systems likely provide 10 of the ge and si fluxes to the oceans

modern seismicity and the fault responsible for the 1886 charleston south carolina earthquake abstract an eight station seismic network was installed in august 2011 in the epicentral area of the 1886 charleston south carolina earthquake within and near the town of summerville the network operated for one year and located 134 earthquakes with duration magnitudes ranging from 1 8 to 2 6 the earthquakes occurred in a tabular zone striking n186 e with dip of about 43 to the west the focal depths range from 13 km to the top of the early mesozoic section at a depth 1 km the dimensions of the seismic zone are 23 km along strike and 15 km down dip many of the earthquakes are concentrated in the 2 6 5 km depth range near shallow faults imaged on seismic reflection profiles adjacent to the ashley river our hypocenter relocations of 228 earthquakes occurring in the period 1977 2005 are consistent with the results obtained from the recent one year station deployment the 48 well constrained focal mechanisms derived from the one year deployment are predominantly reverse motion and 30 exhibit north south trending nodal planes consistent with the orientation of the seismic zone the seismicity near summerville has characteristics in common with the aftershock sequence of the 23 august 2011 mineral virginia earthquake we interpret these results to indicate that the modern seismicity is the lingering aftershock sequence of the 1886 shock and that the mainshock occurred on a south striking west dipping fault plane with predominantly reverse motion possibly with a component of right lateral strike slip most moment release probably occurred at depths greater than 6 km online material tables listing hypocenters and focal mechanisms and an animation showing hypocenter profiles oriented along different azimuths

quartz control of high germanium silicon ratios in geothermal waters germanium silicon ge si ratios in himalayan hot spring fluids show a wide range 4 1000 mmol mol equilibrium calculations with an ideal solid solution model of germanium in quartz yield ge sifluid ratios consistent with data from high temperature reservoirs but do not fit lower temperature observations in part because of kinetic constraints a model of progressive si loss via precipitation of ge poor quartz rayleigh distillation can produce the extreme ge sifluid ratios observed in the himalayan and other systems small variations in si loss mixing with surface waters and or disequilibrium can produce the observed variability in ge sifluid within a given hydrothermal system the high level of si loss 95 required to reach extreme ge sifluid ratios is consistent with reaction path calculations for the evolution of a geothermal fluid from its reservoir to surface temperatures and implies that ge si ratios can be a useful tracer of silica dynamics in hydrothermal systems

coupled ge si and ge isotope ratios as geochemical tracers of seafloor hydrothermal systems case studies at loihi seamount and east pacific rise 9 50 n germanium ge and silicon si exhibit similar geochemical behavior in marine environments but are variably enriched in seafloor hydrothermal fluids relative to seawater in this study ge isotope and ge si ratio systematics were investigated in low temperature hydrothermal vents from loihi seamount pacific ocean 18 54 n 155 15 w and results were compared to high temperature vents from the east pacific rise epr at 9 50 n loihi offers the opportunity to understand contrasting ge and si behavior in low temperature seafloor hydrothermal systems characterized by abundant fe oxyhydroxide deposition at the seafloor the results show that both ge si and 74 70ge in hydrothermal fluids are fractionated relative to the basaltic host rocks the enrichment in ge vs si relative to fresh basalts together with ge isotope fractionation 74 70gefluid basalt up to 1 15 at epr 9 50 n and 1 64 at loihi are best explained by the precipitation of minerals e g quartz and fe sulfides during higher temperature seawater rock reactions in the subsurface the study of fe rich hydrothermal deposits at loihi largely composed of fe oxyhydroxides shows that ge isotopes are also fractionated upon mineral precipitation at the seafloor we obtained an average ge isotope fractionation factor between fe oxyhydroxide ferrihydrite and dissolved ge in the fluid of 2 0 0 6 2sd and a maximum value of 3 6 0 6 2sd which is consistent with recent theoretical and experimental studies the study of a hydrothermal chimney at bio 9 vent at epr 9 50 n also demonstrates that ge isotopes are fractionated by approximately 5 6 0 6 2sd during precipitation of metal sulfides under hydrothermal conditions using combined ge si and estimated ge isotope signatures of ge sinks and sources in seawater we propose a preliminary oceanic budget of ge which reveals that an important sink referred as the missing ge sink may correspond to ge sequestration into authigenic fe oxyhydroxides in marine sediments this study shows that combining ge si and 74 70ge systematics provides a useful tool to trace hydrothermal ge and si sources in marine environments and to understand formation processes of seafloor hydrothermal deposits

germanium silicon of the ediacaran cambrian laobao cherts implications for the bedded chert formation and paleoenvironment interpretations sedimentary strata of the terminal ediacaran 635 542 ma to early cambrian 542 488 ma laobao liuchapo bedded cherts in the south china block include the ediacaran oxidation event and the cambrian explosion understanding the origin and depositional environment of the bedded cherts may provide insight into how the earth s surface environment changed between the proterozoic and phanerozoic we measured major and trace element compositions and ge si ratios of the laobao cherts from northern guangxi province the laobao cherts were deposited in the deep basinal environment of the south china block we show that the composition of the laobao cherts is determined by a mixture of four components quartz clay carbonate and pyrite iron oxide the quartz component is the dominant component of the laobao cherts the maximum estimated ge si of the quartz component is between 0 4 and 0 5 mol mol which is close to the ge si of modern seawater and biogenic silica but 1 order of magnitude lower than that of hydrothermal fluids these ge si systematics suggest that normal seawater rather than mid ocean ridge hydrothermal fluids is the primary si source for the laobao cherts the ge si of the clay component varies between 1 and 10 mol mol which is comparable to the ge si of typical marine clays but 10 100 times lower than that of chert nodules from early ediacaran beds the doushantuo formation predating the terminal ediacaran laobao cherts studied here our observations indicate that the clay component ge si ratio decreased from the early ediacaran to the late ediacaran we speculate that high ge si ratios in clays reflect the preferential chelation of ge by dissolved organic compounds adsorbed onto clays if so this suggests that the decrease in ge si ratio of the clay component in the ediacaran signifies a decrease in the total dissolved organic carbon content of seawater toward the ediacaran cambrian transition consistent with oxidation of the oceans during the late ediacaran finally the seawater origin of the laobao cherts also suggests that replacement of carbonate may not be the primary cause for bedded chert formation instead direct precipitation from seawater or early diagenetic silicification of calcareous sediments perhaps due to the emergence of si accumulation bacteria may have been responsible for the bedded laobao liuchapo chert formation in south china block