pedogenic origin of dolomite in a basaltic weathering profile kohala peninsula hawaii we document stoichiometric dolomite occurring in a nonsaline quaternary soil on the kohala peninsula northwestern hawaii geologic constraints and geochemical and isotopic data confirm that this dolomite is not the result of marine influence or wind blown dust the strontium isotopic composition of the dolomite 87sr 87sr 0 7045 0 7048 is indicative of its derivation primarily from the weathering of basaltic parent material rather than from meteoric water or seawater infiltration of soil waters with elevated mg ca 1 derived from alteration of ferromagnesian minerals such as olivine likely led to dolomitization of early precipitated soil calcite and or to direct dolomite precipitation in the profile this demonstrates that well ordered dolomite can form in a nonmarine environment at temperatures 100 c without undergoing burial diagenesis

chemical weathering rates of silicate dominated lithological classes and associated liberation rates of phosphorus on the japanese archipelago implications for global scale analysis abstract lithology is an important characteristic of the terrestrial surface whose properties influence chemical weathering rates specifically non silicate minerals may contribute significantly to the weathering derived fluxes from silicate dominated lithological classes the japanese archipelago consists of predominantly silicate dominated lithologies with a high proportion of volcanics however the spatially explicit representation of chemical weathering rates remains difficult for such a large region because many controlling factors on chemical weathering rates are correlated with each other due to the spatial heterogeneity of lithology a multi lithological model approach to estimate spatially explicit chemical weathering rates for unmonitored areas is applied here to achieve this hydrochemical data of 381 catchments are used to train a set of models recognizing the contribution of a variety of proposed factors influencing chemical silicate rock weathering rates csrwr cations plus dissolved silica flux the monitored catchments cover 44 of the japanese archipelago cation chemical weathering rates excluding si are linearly correlated with csrwr and show outliers if basic volcanics or pyroclastic flows are present due to increased silica release rates lithology and runoff are identified as the strongest predictors for chemical weathering rates temperature and gradient of slope are of less relevance for the regional scale prediction while further proposed factors like soil properties or land cover are not identified as major predictors latter findings are partly attributed to geodata quality low variability of parameter values as well as spatial correlations of proposed controlling factors with lithology or runoff the calculated average csrwr of the archipelago is 25 t km 2 a 1 and ranges from 5 9 to 107 t km 2 a 1 in monitored catchments weathering rates per lithological class as a function of runoff can be grouped into three classes a pyroclastic flows showing the highest chemical weathering rates b alluvial deposits mixed sediments and basic to intermediate volcanics with medium rates and c metamorphics siliciclastic sediments acid volcanics acid plutonics and unconsolidated sediments other than alluvial deposits showing the lowest rates the recognition of lithogenic sulfur would add 9 7 to csrwr of considered catchments results suggest that the lithological classes acid volcanics and unconsolidated sediments contribute above average to the sulfur fluxes possible biases of this observation are discussed the contribution of ca fluxes from non silicate calcic minerals named ca excess ca fluxes in addition to silicate ca fluxes is about 10 of the csrwr on average and is attributed by a wide value range the calculated ratio ca excess to total ca fluxes from chemical weathering averages around 62 75 56 83 and 84 for the lithological classes acid plutonics metamorphics siliciclastic sediments mixed sediments and acid volcanics respectively this suggests a major ca contribution from non silicate calcic minerals for these lithological classes phosphorus release from rocks due to chemical weathering is estimated to be between 1 kg p km 2 a 1 and 390 kg p km 2 a 1 the p release patterns in dependence of runoff per lithological class are different from csrwrs due to differences of applied p content in rocks the identified spatial p release patterns suggest that the consideration of dynamic and spatially resolved p release rates by chemical weathering might improve ecosystem studies later findings may be of importance for analysing the influence of p release from rocks on the climate system via ecosystem functioning on geological time scales a first application of the p release model to the global scale suggests an annual release of 1 6 mt p 13 8 kg p km 1 a 1 by chemical weathering of silicate dominated lithological classes excluding carbonate sedimentary rocks

posteruptive impacts of pyroclastic deposits from basaltic andesite stratovolcanoes on surface water composition volcanic ash deposition following explosive eruptions can pose significant hazards for water quality human health agriculture and infrastructure functionality many studies have examined how fresh ash deposition may lower the ph of and introduce a range of potentially toxic elements into exposed surface waters however no study has yet determined the effects on water composition as a result of mechanical pyroclast disaggregation and production of new fresh particle surfaces and increasingly fine grained particles such disaggregation could result from natural posteruptive processes such as debris avalanches lahars or fluvial aeolian transport and human activities such as cleanup efforts or mining of pyroclastic deposits the posteruption time scales of pyroclast disaggregation may vary from months in moist tropical or temperate environments to years or decades in arid settings here we show for the first time in experimental studies that mechanical milling of pyroclasts will introduce a range of elements into exposed waters including al which can be toxic at elevated levels and na which increases the electrical conductivity of solutions the ph of leaching solutions also increases by several log units such dramatic changes on the experimental scale may have implications for surface water composition in posteruptive settings necessitating longer term risk assessments for ecosystem health and consideration of the role of pyroclastic deposits in element cycling in volcanically active regions

the mass balance of soil evolution on late quaternary marine terraces northern california mass balance interpretation of a soil chronosequence provides a means of quantifying elemental addition removal and transformation that occur in soils from a flight of marine terraces in northern california six soil profiles that range in age from several to 240 000 yr are developed in unconsolidated sandy marine and eolian parent material deposited on bedrock marine platforms soil evolution is dominated by 1 open system depletion of si ca mg k and na 2 open system enrichment of p in surface soil horizons 3 relative immobility of fe and al and 4 transformation of fe si and al in the parent material to secondary clay minerals and sesquioxides net mass losses of bases and si are generally uniform with depth and substantial in some cases approaching 100 however the rate of loss of each element differs markedly causing the ranking of each by relative abundance to shift with time loss of si from the sand fraction by dissolution and particle size diminution from 100 to 80 to 90 to 10 concurrently with an increase of ai in the organic sesquioxide and clay phases to 10 and 50 respectively while only minor increases occur in the nonorganic sesquioxide phases

high resolution record of environmental changes and tephrochronological markers of the last glacial holocene transition at lake lautrey jura france this paper presents the results of a multiproxy investigation including volume magnetic susceptibility mineral and pollen analyses of late glacial sediments from lake lautrey jura france small scale lithological variations have been identified with high stratigraphic resolution in order to establish lithostratigraphic correlations between cores measurements combined with mineralogical analyses provide information on past sedimentary processes this combined approach reflects major changes in terrestrial habitats and soil processes which may relate to the climatic events characterising the late glacial climatic warming and cooling phases during warm intervals the record indicates increased lake productivity via carbonate precipitation and decreased input of detrital material in contrast cooler intervals show reduced lake productivity catchment area instability and increased detrital inputs several short interruptions in reforestation and in soil stabilisation can be identified and linked with abrupt colder events occurring through the bolling a general trend of warming is recorded from the coldest part of the younger dryas three tephra layers were also detected the mineral composition analyses show that the upper tephra layer corresponds to the laacher see eruption eifel germany while the lower ones may relate to the volcanic activity of the chaine des puys massif central france around 13 000 cal yr bp these two events recognised for the first time outside the massif central region may provide additional chronostratigraphic markers for the late glacial sedimentary records of the jura mountains and northern alps copyright 2004 john wiley sons ltd

40ar 39ar constraints on a temporal link between gold mineralization magmatism and continental margin transtension in the jiaodong gold province eastern china abstract the jiaodong gold province is the largest gold repository in china both mineralization and granitoid hosts are spatially related to the crustal scale tan lu strike slip fault system which developed along the mesozoic continental margin in eastern china a series of 40ar 39ar laser incremental heating analyses of hydrothermal sericite muscovite from three major gold deposits jiaojia xincheng and wangershan and igneous biotite from the granodiorite hosts were performed to establish a possible temporal link between gold mineralization magmatism and movement along the tan lu fault zone magmatic biotite crystals yield well defined and concordant plateau ages between documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewco

constancy of silicate mineral weathering rate ratios between natural and experimental weathering implications for hydrologic control of differences in absolute rates abstract inverse models which apportion watershed effluxes geochemical mass balance over estimated mineral surface area give weathering rates for individual silicate minerals e g feldspar 1 3 orders of magnitude slower than laboratory rates comparisons of rates calculated from several recent watershed geochemical mass balance studies with experimentally determined rates reveal that the ratio of mineral weathering rates for a given silicate mineral pair determined in an internally consistent field study equals the ratio of rates for the same minerals in any internally consistent set of laboratory experimental data thus the coefficient which corrects the weathering rate for any mineral from a laboratory data set to a field setting is identical to the corresponding coefficient for any other mineral in the same data sets the correction factor linking experimental and natural rates must be independent of composition physical e g hydrologic controls rather than compositional or chemical controls cause the difference between weathering rates in nature and the laboratory because flow in natural weathering profiles is spatially heterogeneous not all of the potentially available surface in natural systems actually participates in reactions with pore fluids

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

weathering rates and 87sr 86sr ratios an isotopic approach the 87sr 86sr ratios of precipitation throughfall groundwater streamwater and mineral matter were analyzed precipitation strontium ratios are around 0 71 throughfall which is affected by strontium from the mineral soil has ratios of 0 72 0 73 and shallow groundwater in a drug well and runoff have ratios around 0 73 0 74 there is a tendency for this relationship to be reversed for discharge higher ratios are associated with lower discharges water from a fracture zone gave the highest value 0 78 approaching the value of the bedrock around 0 85 a calcium budget which reflects the mean conditions over a few years has been calculated this budget indicates that weathering should be of the order of 8 kg ca ha 1yr 1 to maintain the pool of exchangeable calcium at a constant level the major anion in the runoff is suphate which has entered the system in the form of acid rain sulphur deposition has been rather constant over the last two decades if acidification had an effect on weathering of silicates this would have shown up in a tendency of the strontium isotope ratios toward higher values in the soil pool and in runoff water thus its seems from the observed ratios that at least a major portion of the excess calcium export resulting from sulphur deposition is taken from the soil pool resulting in a gradual acidification of the soil

the age isotopic signature and significance of the youngest mesozoic granitoids in the jiaodong terrane shandong province north china craton abstract most cretaceous granitoids in the jiaodong terrane of shandong province north china craton were intruded between 130 and 122 ma however four granitoid batholiths are significantly younger with an average zircon u pb shrimp emplacement age of 116 2 ma these are the sanfoshan batholith 118 1 ma the aishan batholith 116 1 ma the yashan pluton 113 2 ma and the laoshan batholith 115 2 ma these granitoids post date proposed delamination that occurred prior to 125 ma in the eastern ncc and their geochemistry thus provides information about the nature of the continental crust at this time the rocks are mostly monzogranites and syenogranites of i type affinity with local alkali feldspar granite of a type affinity in addition a monzogranite sample from the aishan batholith records an age of 125 3 ma indicating a direct association with the slightly older granitoids in the area indeed they all contain inherited zircons with ages of 125 120 ma indicating interaction with these earlier granitoids most samples are metaluminous enriched in light rare earth elements and depleted in high field strength elements paleo to neoarchean t dm2 model ages ranging from 3900 ma to 2491 ma and negative e hf t values imply the involvement of archean basement and older recycled continental crustal material in the magma source region they were likely derived from partial melting of the lower or middle crust due to mafic magma underplating followed by various degrees of interaction between mantle derived mafic magma and felsic crustal magma accompanied by fractional crystallization we propose that lithospheric thinning and extension in the early cretaceous due to roll back of the pacific plate beneath the eastern north china craton led to asthenospheric upwelling and basaltic magmatism this underplating in turn led to crustal melting and evolution of the granitic intrusions described here

gold hosting high ba sr granitoids in the xincheng gold deposit jiaodong peninsula east china petrogenesis and tectonic setting abstract the xincheng deposit is the only large gold deposit with a proven reserve of 200 t gold hosted by the early cretaceous granitoids in northwest jiaodong peninsula east china the granitoids hosting this ore deposit comprise an inner medium to fine grained quartz monzonite and an outer medium to coarse grained monzogranite with distinctive k feldspar megacrysts la icp ms zircon dating yields u pb ages of 128 1 to 132 1 ma and 127 2 to 129 1 ma for the quartz monzonite and the monzogranite respectively the early cretaceous ages obtained in our study are comparable with the 126 130 ma age range reported for the guojialing granitic suite the monzogranites typical high ba sr granites possess high sio2 70 89 73 35 k2o 3 85 4 32 total alkalis k2o na2o 8 08 8 68 sr 634 888 ppm ba 1395 2111 ppm and lree 59 43 145 88 with low hree and hfse contents and insignificant eu anomalies the rocks display markedly high sr y 114 297 and la yb n 20 79 ratios they have low mgo 0 23 0 62 cr 0 4 8 33 ppm and ni 0 47 2 92 ppm contents the typical high ba sr signatures of the outer acidic monzogranites are also shared by the inner intermediate acidic quartz monzonites with a relatively higher abundance of these elements the plagioclases in the quartz monzonites and monzogranites are oligoclase andesine with an contents of 11 7 44 5 and oligoclase with an contents of 12 9 29 3 respectively which both show the reverse zoning texture the quartz monzonites have zircon ehf t values of 21 3 to 13 9 average 18 7 which are less negative and show larger variations than those of the monzogranites ehf t 24 7 to 18 1 average 19 5 detailed elemental mineralogical and isotopic data suggest that the high ba sr quartz monzonites and monzogranites were most likely generated by partial melting of the basement rocks of the jiaobei terrane accompanied by crustal assimilation with minor addition of the intermediate magma derived from the partial melting of juvenile mafic lower crust formed by the earlier underplating of mantle magma and the quartz monzonites may represent the path of intermediate magma inputting into felsic magma in combination with previous investigations we suggest subduction of the paleo pacific slab beneath the north china craton ncc and associated asthenosphere upwelling were most likely the mechanism associated with the generation of the high ba sr granites

what controls gold distribution in archean terranes despite intensive efforts determination of a predictable pattern of gold distribution to enhance process understanding and simplify exploration has remained elusive the pattern of gold distribution along the archean boulder lefroy shear zone in the yilgarn craton of western australia provides insights into gold distribution in one of the world s richest provinces four world class gold deposits including the giant golden mile at kalgoorlie are regularly spaced along the shear zone providing a window into understanding large scale archean hydrothermal systems relationships among gold endowment shear zone trend and geologic complexity as measured by fractal dimensions indicate that 1 ore fluids were focused into those parts of the shear zone with greatest misorientation from the regional trend which define dilational sites during shearing and became the sites of world class gold deposits and 2 the degree of complexity contrast along the shear zone modulated gold endowment

nature age and tectonic setting of granitoid hosted orogenic gold deposits of the jiaodong peninsula eastern north china craton china the jiaodong gold province along the southeastern margin of the north china craton has combined production and resources of 900 tonnes of gold more than 95 of the gold in this province is hosted in mesozoic granitoids which intruded late archean metamorphic basement rocks episodically at ca 160 150 and 130 126 ma the deposits of the jiaodong peninsula form one of the largest provinces of granitoid hosted lode gold deposits in the world the jiaodong gold deposits occur as massive auriferous quartz veins hosted in subsidiary second or third order faults and as disseminated and stockwork style mineralization hosted in alteration zones along major regional scale faults mineralization took place during brittle reactivation d3 of pre existing d2 ductile shear zones wall rock alteration is dominated by k feldspar and sericite with also sulfide minerals and extensive silicification closest to the orebodies the alteration was accompanied by the introduction of volatiles fe mg k rb ag as au bi and sb enrichment of base metals in the gold lodes is generally low although locally significant gold deposition took place at temperatures of 250 to 350 c for most gold deposits and the ore fluids are co2 bearing and have calculated salinities of 6 13 wt nacl equiv deposits from the zhao ye xixia and muping rushan belts have similar if not identical structural controls alteration patterns ore mineral assemblages and stable isotope signatures lead isotope data indicate that the ore stage leads were buffered by their host rocks the granitoid hosted gold deposits in the zhao ye belt are most radiogenic the greenstone hosted deposits in the xixia belt is the least radiogenic and the granitoid hosted deposits in the muping rushan belt have intermediate compositions gold mineralization in the zhao ye xixia and muping rushan belts in the jiaodong gold province appears to be broadly contemporaneously at ca 130 120 ma as constrained by shrimp u pb zircon dating on host rocks and a post gold dike as well as by ar ar rb sr and k ar dating of hydrothermal alteration minerals and ores this early cretaceous age is about 100 million years younger than the peak of ultra high pressure metamorphism in the qinling dabie sulu orogen between the north china and yangtze cratons and about 500 km south of the gold province however it overlaps with the extension and exhumation stage of the collisional orogeny and the subduction of the pacific plate beneath the eurasian continental crust whereas the majority of the jiaodong gold deposits occur on the margin of the north china craton some also occur in the suture zone between the two cratons they are significantly landward relative to the subduction zone of the pacific plate compared with typical orogenic lode gold deposits globally lode gold deposits of ca 130 120 ma occurred on both sides of the tan lu fault zone available data favor a temporal link of gold mineralization with pacific plate subduction

some exact solutions to the nonlinear shallow water wave equations these exact solutions correspond to time dependent motions in parabolic basins a characteristic feature is that the shoreline is not fixed it is free to move and must be determined as part of the solution in general the motion is oscillatory and has the appropriate small amplitude limit for the case in which the parabolic basin reduces to a flat plane there is a solution for a flood wave these solutions provide a valuable test for numerical models of inundating storm tides

the granny smith gold deposit the role of heterogeneous stress distribution at an irregular granitoid contact in a greenschist facies terrane the granny smith gold deposits formed late in the structural history of the yilgarn block at a high crustal level in a largely brittle structural regime gold mineralisation is located along a n s striking fault which wraps around the contact of a small granitoid intrusion in different sections of the fault mineralisation may be developed in the granitoid in the adjacent sedimentary sequence and or along the contact between them in the granitoid gold mineralisation is in conjugate networks of thin carbonate quartz veins and their alteration halos small displacements along veins are common in contrast veins and faults in the sedimentary rocks are subparallel to bedding spatial variations in the conjugate vein orientations indicate that the local stress field was heterogeneous and controlled by the shape of the granitoid contact the greatest variations in vein and implied stress orientations occur in zones where the contact is most irregular these are also the areas of richest mineralisation fluid flow was thus focused in a regional scale low mean stress region created by the geometry of the granitoid intrusion its irregular contact caused deposit scale variations in fluid flow and resulted in heterogeneous gold grades along the contact zone

chemical weathering in two adirondack watersheds past and present day rates rates of chemical weathering in two forested adirondack watersheds were determined from mineral and elemental depletion trends in soil profiles and from input output budgets based on precipitation and surface water chemistry long term rates of weathering have averaged about 500 to 600 eq ha yr for both watersheds since the glaciers retreated from the region about 14 000 yr ago present day denudation rates average 1679 eq ha yr in the panther lake watershed and only 198 eq ha yr in the woods lake watershed mineral weathering reactions in both watersheds involve primarily the dissolution of plagioclase potassium feldspar and hornblende mass balance calculations however indicate that hornblende weathers in disproportionately large amounts in the panther lake watershed relative to its abundance in soils and till cation exchange in the glacial till mantling the panther lake watershed may also play an important role in controlling surface water chemistry in the basin in the panther lake watershed the current rate of weathering which is about a factor of 3 greater than the long term average may reflect a recent adjustment for higher hydrogen ion fluxes brought about by acid deposition the capacity of the thick till deposits in the panther lake watershed to neutralize acidity is ultimately reflected by the circum neutrality of panther lake in the woods lake watershed the soils and thin till deposits cannot effectively neutralize current acid loadings and therefore woods lake is acidic with a ph below 5

suspended sediment transport under seiches in circular and elliptical basins abstract enclosed bodies of water such as lakes or harbours often experience large scale oscillatory motions seiching as a simple model of such flow we investigate exact solutions to the shallow water equations which represent oscillatory flow in an elliptical basin with parabolic cross section specifically we consider two fundamental modes of oscillation in one of which the flow is parallel to the axis of the ellipse while in the other it is radial we obtain periodic analytical solutions for sediment transport including erosion deposition and advection under either mode of oscillation and present a method for obtaining such solutions for a more general class of flow fields and sediment transport models our solutions provide estimates of the morphodynamical importance of seiching motions and also reveal a characteristic pattern of net erosion and deposition associated with each mode in particular we find that a net flux of suspended sediment can be transported from the deeper to the shallower regions of the basin these transport patterns which are driven essentially by settling lag are highly robust to the formulation of the sediment transport relation and appear not to be substantially affected by the omission of frictional terms in the hydrodynamics they should thus provide considerable insight into sediment transport in less idealised systems

nitrogen release from rock and soil under simulated field conditions abstract a laboratory study was performed to simulate field weathering and nitrogen release from bedrock in a setting where geologic nitrogen has been suspected to be a large local source of nitrate two rock types containing nitrogen slate 1370 mg n kg 1 and greenstone 480 mg n kg 1 were used along with saprolite and bc horizon sand from soils derived from these rock types the fresh rock and weathered material were used in batch reactors that were leached every 30 days over 6 months to simulate a single wet season nitrogen was released from rock and soil materials at rates between 10 20 and 10 19 mol n cm 2 s 1 results from the laboratory dissolution experiments were compared to in situ soil solutions and available mineral nitrogen pools from the bc horizon of both soils concentrations of mineral nitrogen no 3 nh 4 in soil solutions reached the highest levels at the beginning of the rainy season and progressively decreased with increased leaching this seasonal pattern was repeated for the available mineral nitrogen pool that was extracted using a kcl solution estimates based on these laboratory release rates bracket stream water no 3 n fluxes and changes in the available mineral nitrogen pool over the active leaching period these results confirm that geologic nitrogen when present may be a large and reactive pool that may contribute as a non point source of nitrate contamination to surface and ground waters

tectonics granitoids and mesozoic gold deposits in east shandong china abstract mesozoic granitoids in east shandong 1 contain some 30 moz gold making east shandong the largest granitoid hosted gold province in the world the gold province is located along the northern boundary of the suture zone between the north china and south china cratons according to their mineralogical geochemical and geochronological characteristics two groups of mesozoic granitoids are recognised in east shandong namely the middle yanshanian my ca 160 150 130 ma and the late yanshanian ly ca 117 85 ma granitoids the first group of granitoids only occur to the north of the suture zone whereas the second group of granitoids occur on both sides of the suture zone these characteristics suggest that the two groups of granitoids were associated with different tectonic events a tectonic analysis suggests that the my granitoids are the result of collision and suturing of the north and south china cratons during the triassic to jurassic whereas formation of the ly granitoids is attributed to the distal inland influence of subduction of the pacific izanagi plate underneath the eurasian continent during the cretaceous the major gold deposits are spatially associated with the my granitoids in east shandong most of the gold occurs either as quartz veins in the granitoids or disseminated in altered shear zones along the boundary of the granitoids and archaean metamorphic rocks the major gold mineralization and alteration generally display the characteristics of gold only provinces namely co 2 rich low salinity and reduced fluids and proximal mica and sulfide alteration these characteristics are different from those of phanerozoic granitoid related skarn porphyry systems accordingly the gold mineralization may be more tectonically and structurally controlled rather than have a direct genetic relationship with the granitoid itself according to the relationships between tectonics granitoids distribution of gold deposits and fluid geochemistry the major gold in east shandong may have been formed during the subsequent exhumation stage after the collision of the north and south china cratons

pedogenesis and weathering rates of a histic andosol in iceland field and experimental soil solution study abstract it is important to study the rate determining processes of chemical weathering and soil formation in volcanic islands since a significant part of the carbon fixed by chemical weathering of silicates on earth is fixed at the surface of volcanic islands these soils are fertile and much of the river suspended matter delivered to the ocean stems from these islands this study determines the factors that drive the pedogenesis of a histic andosol in western iceland soil solutions were extracted from the profile in the field from undisturbed ex situ mesocosms and from repacked laboratory microcosms concentrations of measured and calculated inorganic species in the field and experimental soil solutions were used for thermodynamic and kinetic interpretation and to calculate the weathering rates the main primary rock constituent of the 205 cm thick soil profile was basaltic glass allophane content ranged from 2 to 22 and the soil carbon content ranged from 11 to 42 mean soil solution ph value ranged from 4 to 6 with the lowest value at 80 cm depth and highest between 150 to 205 cm the high solute concentrations in soil solutions in the beginning of the microcosm weathering experiment declined faster for anions than cations under field conditions inorganic anions were supplied by marine and anthropogenic rather than pedogenic sources and hence these anions were subsequently leached out during the experimental duration when there was a limited input of anions through experimental precipitation the factor which defined the rate at which each ion was depleted from the exchange complex of the soil decreased down the soil profile the release sequence at 50 cm depth was cl na so 4 f si the si and base cations experimental weathering rate when normalized to geographical surface area are similar to or lower than those measured from river catchments in southwestern iceland the dissolved al flux was much higher from the soil when compared to the river catchments field and experimental soil solutions were all highly undersaturated with respect to basaltic glass field and mesocosm samples were supersaturated with respect to secondary allophane and imogolite while samples from the microcosms were often undersaturated with respect to allophane and imogolite predicted dissolution rate was dictated by the soil solution a h 3 a al 3 activity ratio but slowed down by up to 20 and 30 by decreasing undersaturation in field and mesocosms respectively predicted dissolution rates according to the a h 3 a al 3 activity ratio increased up to factor of 7 30 and 37 by speciating al 3 with oxalate in field mesocosms and microcosms respectively speciation with oxalate which represents the maximum effect of the dissolved organic carbon doc on dissolution rates generally had more effect near the surface than at deep levels in the soil profile this study shows that at fixed temperature reactive surface area and composition of the volcanic glass in the soil the chemical weathering rates of andosols are dictated by 1 aeolian deposition rates and drainage which affect the saturation state and the a h 3 a al 3 activity ratio 2 the production of organic anions within the soil and 3 external supply of anions capable of complexing al 3

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

the coolgardie goldfied western australia district scale controls on an archaean gold camp in an amphibolite facies terrane archaean lode gold deposits in the coolgardie goldfield western australia occur in mafic and ultramafic rocks which have been metamorphosed to the amphibolite facies mineralisation was broadly synchronous with peak metamorphism the main phase of granitoid emplacement and regional deformation several different structural styles are represented by the deposits of the coolgardie goldfield mineralisation occurs along sheared felsic porphyry ultramafic rock contacts in gabbro hosted quartz vein sets in fault bounded quartzvein sets and in laminated quartz reefs sited in brittleductile shear zones the structures hosting mineralisation formed in response to a progressive deformation event related to granitoid emplacement in an east west compressional far field stress regime but with local heterogeneous stress orientations this occurred after an earlier period of thrust stacking with probable north south directed tectonic transport two contrasting styles of goldrelated wallrock alteration are associated with the auriferous lodes of the coolgardie goldfield a high temperature assemblage formation temperature 500 c characterised by the proximal alteration assemblage garnet hornblende plagioclase pyrrhotite contrasts with a medium temperature assemblage formation temperature 500 c consisting of calcic amphibole biotite plagioclase calcite arsenopyrite pyrrhotite the distribution of the two styles of gold related alteration is controlled by distance from voluminous syntectonic granitoids located to the west of the coolgardie goldfield with the high temperature style of alteration more proximal to the granitoid greenstone contact than the medium temperature style the occurrence of gold deposits that formed under amphibolite facies conditions throughout the coolgardie goldfield supports a crustal continuum model for archaean lode gold deposits which proposes that gold is deposited in metamorphic environments that range from the sub greenschist to granulite facies in addition the data from coolgardie suggest that syntectonic synmineralisation granitic plutons may play a significant role in controlling the style of gold associated wallrock alteration at deep crustal levels

weathering reactions and hyporheic exchange controls on stream water chemistry in a glacial meltwater stream in the mcmurdo dry valleys 1 in the mcmurdo dry valleys antarctica dilute glacial meltwater flows down wellestablished streambeds to closed basin lakes during the austral summer during the 6 12 week flow season a hyporheic zone develops in the saturated sediment adjacent to the streams longer dry valley streams have higher concentrations of major ions than shorter streams the longitudinal increases in si and k suggest that primary weathering contributes to the downstream solute increase the hypothesis that weathering reactions in the hyporheiczonecontrolstreamchemistrywastestedbymodelingthedownstreamincreasein solute concentration in von guerard stream in taylor valley the average rates of solute supplied from these sources over the 5 2 km length of the stream were 6 1 10 9 mol si l 1 m 1 and 3 7 10 9 mol k l 1 m 1 yielding annual dissolved si loads of 0 02 1 30 mol si m 2 of watershed land surface silicate minerals in streambed sediment were analyzed to determine the representative surface area of minerals in the hyporheic zone subject to primary weathering two strategies were evaluated to compute sediment surface area normalized weathering rates the first applies a best linear fit to synoptic data in order to calculate a constant downstream solute concentration gradient dc dx constant weathering rate contribution crc method the second uses a transient storage model to simulate dc dx representing both hyporheic exchange and chemical weathering hydrologic exchange he method geometric surface area normalized dissolution rates of the silicate minerals in the stream ranged from 0 6 10 12 mol si m 2 s 1 to 4 5 10 12 mol si m 2 s 1 and 0 4 10 12 mol k m 2 s 1 to 1 9 10 12 mol k m 2 s 1 these values are an order of magnitude lower than geometric surface area normalized weathering rates determined in laboratory studies and are an order of magnitude greater than geometric surface area normalized weathering rates determined in a warmer wetter setting in temperate basins despite the cold temperatures lack of precipitation and lack of organic material these results suggest that the continuous saturation and rapid flushing of the sediment due to hyporheic exchange facilitates weathering in dry valley streams index terms 1045 geochemistry low temperature geochemistry 1806 hydrology chemistry of fresh water 1625 global change geomorphology and weathering 1824 1886 1890 hydrology wetlands keywords hyporheic zone chemical weathering flow path antarctica stream

coupling spatial geochemical and lithological information to distinguish silicate and non silicate chemical weathering fluxes lithological maps have been proved to be a useful tool to evaluate regional and global matter fluxes from chemical weathering however lithological classes provide aggregated information of mineralogical geochemical sedimentary or diagenetic properties thus using a limited number of lithological classes introduces by their definition a bias to the analysis of weathering fluxes specifically in the case of multilithological catchments here it is shown that the coupling of geochemical with lithological information may help to better identify the sources of the weathering fluxes using the example of dissolved ca to better distinguish weathering rates of silicate and non silicate minerals

climate dependent chemical weathering of volcanic soils in iceland abstract the major element mobility within soil profiles of brown to gleyic andosols that developed under diverse climatic conditions in iceland is assessed the volcanic soils were selected from areas with good monitoring of annual temperature and precipitation and the degree of weathering and elemental behavior is compared icelandic soils are subject to high fluxes of aeolian dust and at times to tephra ejecta from volcanic eruptions the source of dust input is assessed for each profile based on comparison of the chemical signatures found in the less weathered upper horizons with those of volcanic systems supplying material to source areas results show that tio 2 al 2 o 3 and fe 2 o 3 t and mno are the least mobile species and generally found enriched within more mature horizons the mobile base cations mgo cao and na 2 o are depleted in these horizons as a result of chemical weathering during pedogenesis soils developed in colder climatic conditions with mean annual temperature mat 1 c give values for the chemical index of weathering ciw of 37 45 that reflect only weak chemical weathering soils developed in milder climates mat 2 4 c are more strongly affected by weathering ciw 50 77 the parent material has ciw values of 37 temperature is demonstrated as the dominant variable exerting control on the extent of weathering with only minor mobilization following the incipient near surface weathering stage a robust linear relationship is found between ciw and model mat mat 0 21ciw 8 93 r 2 0 81 this climofunction can deliver proxy climate estimations from volcanic soils and paleosols of basaltic origin in cool to subarctic conditions 2 to 6 c

chemical weathering of a soil chronosequence on granitoid alluvium ii mineralogic and isotopic constraints on the behavior of strontium the use of strontium isotopes to evaluate mineral weathering and identify sources of base cations in catchment waters requires an understanding of the behavior of sr in the soil environment as a function of time our approach is to model the temporal evolution of 87sr 86sr of the cation exchange pool in a soil chronosequence developed on alluvium derived from central sierra nevada granitoids during the past 3 ma with increasing soil age 87sr 86sr of ammonium acetate extractable sr initially decreases from values typical of k feldspar to those of plagioclase and hornblende and then remains constant even though plagioclase and hornblende are absent from the soils after approximately 1 ma of weathering the temporal variation of 87sr 86sr of exchangeable sr is modeled by progressively equilibrating sr derived from mineral weathering and atmospheric deposition with sr on exchange sites as waters infiltrate a soil column observed decreases in quartz normalized modal abundances of plagioclase hornblende and k feldspar with time and the distinct87sr 86sr values of these minerals can be used to calculate sr flux from weathering reactions hydrobiotites in the soils have nearly constant modal abundances chemistry and 87sr 86sr over the chronosequence and provide negligible sr input to weathering solutions the model requires time and soil horizon dependent changes in the amount of exchangeable sr and the efficiency of sr exchange as well as a biologic cycling term the model predicts that exchangeable sr initially has 87sr 86sr identical to that of k feldspar and thus could be dominated by sr leached from k feldspar following deposition of the alluvium the maximum value of 87sr 86sr observed in dilute stream waters associated with granitoids of the yosemite region is likewise similar to that of the k feldspars suggesting that k feldspar and not biotite may be the dominant source of radiogenic sr in the streams this study reveals that when attempting to use strontium isotopes to identify sources of base cations in catchment waters and biomass both preferential leaching of sr from minerals during incipient soil development and changing sr exchange efficiency must be considered along with chemical contributions due to mineral dissolution

correlation between mineralization intensity and fluid rock reaction in the xinli gold deposit jiaodong peninsula china constraints from petrographic and statistical approaches abstract the jiaodong peninsula the most productive gold province in china is dominated by jiaojia type gold deposits that formed at ca 120 ma the deposits are characterized by widespread alteration and mineralization resulted from fluid rock reactions in the footwall of regional faults it is known that the interrupted appearance of continuous mineralization zones and barren zones along regional faults is controlled by changes in the dip direction and dip angle of these faults which can cause local dilational sense in the continuous mineralization zone intensive fluid rock reactions occurred yet whether and how the fluid rock reaction impacted on the mineralization intensity are not well constrained in this study we selected the xinli jiaojia type gold deposit associated sanshandao cangshang fault located on the northwest margin of the jiaodong peninsula to examine in detail the distribution of orebody parameters and to observe the mineralization occurrences we applied the number size fractal model and the lacunarity method to quantify the distribution of gold concentration along drifts with the goal of clarifying the ambiguities noted above the drifts in continuous mineralization zones can be divided into stable and unstable types according to lateral changes in the dip direction and dip angle of the sanshandao cangshang fault stable and unstable drifts share several common features 1 statistical results show that changes in the dip direction and dip angle of this fault bear almost no relationship to the thickness or grade thickness of the orebody 2 mineralization along drifts is most intense at some distance from the fault plane rather than at locations immediately adjacent to the fault plane where fracturing is most extensive and according to fluid infiltration theory would be the most likely regions of intense mineralization 3 gold bearing sulfide pods and veinlets in the alteration zone commonly possess irregular and corroded boundaries that are considered to be an indicator of fluid rock reactions 4 the threshold the gold concentration that divides a segment with a lower fractal dimension in a lower concentration range from one with a higher fractal dimension in a higher concentration range and the lacunarity the parameter that evaluates the evenness of high gold concentration distribution show positive and negative relationships respectively to the thickness and grade thickness of a drift we thereby argue on the basis of these features that fluid rock reactions were an important factor responsible for the mineralization upgrade in continuous mineralization zones an increase in the threshold and a decrease in the lacunarity indicate that fluid rock reactions causing gold precipitation are more intensive and more evenly distributed throughout the footwall for better mineralization these phenomena suggest that fluid rock reactions responsible for the gold precipitation possibly own the characteristics of spatial self organization mechanism which is widely developed in various geological fluid rock reaction processes

fault fracture density and mineralization a contouring method for targeting in gold exploration abstract a widely observed correlation between high fracture density and mineralization throughout terranes and geological time indicates a fundamental underlying ore forming process in archaean greenstone hosted deposits high density fracturing was accompanied by enhanced fluid flow during fault fracture network development producing regional scale fluid pressure gradients that focussed hydrothermal fluids into preferentially fractured areas fracture density is both increased and decreased during faulting and fault healing and fracture density accumulates over time in zones of high palaeo fluid flow localised zones where the density of fracturing is increased by deformation become permeability nodes for migrating hydrothermal fluids leading to large zones of alteration and gold precipitation the ora banda mining centre in western australia contains significant gold deposits that appear to demonstrate a close association between high density fracturing and gold precipitation fracture density in the ora banda mines was enhanced by fault fault intersections fault contact intersections and changes in fault geometry the mine scale relationships between fracture density and gold mineralization are repeated at smaller and larger scales hence these relationships may be used in targeting for gold exploration contouring the density of fracturing in a region provides a semi quantitative way to rank areas for exploration and uses data from mapping drilling and high quality geophysical data as a basis for analyses fracture density contouring is complementary to other prospectivity analysis methods

1822 earthquake triggered homogenite in lake le bourget nw alps high resolution textural signatures of an earthquake induced historical homogenite layer are presented as well as its 3d distribution this homogeneous deposit is correlated with the ad 1822 event vii viii msk intensity the main historical earthquake of the french outer alps using 210pb dating and historical chronicles during this earthquake a violent lake water oscillation was reported seiche effect in the present study we discuss the influence of lake water oscillations during earthquake induced subaqueous slide through a pluridisciplinary analysis of subbottom sediments including high resolution seismic sidescan sonar and short gravity coring

direct effects of co2 and temperature on silicate weathering possible implications for climate control a critical uncertainty in models of the global carbon cycle and climate is the combined effect of organic activity temperature and atmospheric co2 on silicate weathering here we present new dissolution rates of anorthite and augite which indicate that silicate weathering in organic rich solutions is not directly affected by soil co2 but is very sensitive to temperature apparently co2 accelerates silicate weathering indirectly by fertilizing organic activity and the production of corrosive organic acids the weathering dependencies highlight the ability of silicate weathering to act as a global thermostat and damp out climate change when used as input in steady state carbon cycle and climate models

on fine sediment transport by long waves in the swash zone of a plane beach we calculate suspended sediment transport erosion and deposition under reflected long waves on a plane beach our method employs the shallow water equations and is based on the calculation of the concentration field in lagrangian coordinates this allows results to be obtained readily throughout the whole domain including the often troublesome shoreline region these results suggest that the tendency of wave dominated muddy shores to export sediment and erode over long time scales is not due to wave forcing at infragravity frequencies since the sediment transport under such waves is localized close to the shoreline and is principally directed shorewards they also provide easily reproduced test cases against which to validate the numerical methods used in more detailed studies of coastal sediment transport and morphodynamics

paleoproterozoic structural evolution of the southern segment of the jiao liao ji belt north china craton abstract the paleoproterozoic jiao liao ji belt separates the eastern block of the north china craton into two small sub blocks the northern longgang and the southern rangrim blocks however it still remains unknown or controversial about the subduction polarity collisional deformation and kinematics between two sub blocks the southern segment of the belt consists of the paleoproterozoic fenzishan and jingshan groups and paleoproterozoic high pressure mafic granulites and serpentinites blocks which are located in the jiaodong complex all of which are separated from the jiaodong complex of neoarchean ttg gneisses by stz1 ductile shear zones structural analysis in this study indicates that most of the rocks in all the units of the southern segment of the jiao liao ji belt underwent three distinct episodes of folding d1 to d3 and two stage of ductile thrust shearing stz1 coeval to d1 and d2 stz2 between d2 and d3 the d1 deformation formed penetrative axial planar foliations s1 bedding parallel ductile shear zone mineral stretching lineations l1 and rarely preserved small isoclinal d1 folds in the jingshan and fenzishan groups in the jingshan group however penetrative deformational transposition resulted in stacking of sedimentary compositional layers which are separated by bedding parallel ductile shear zones stz1 at a period of about 1956 ma to 1914 ma the kinematic indicators of stz1 in the jingshan group with resultant prograde peak metamorphism up to granulite facies grade and the fenzishan group with peak metamorphism up to amphibolite facies grade indicate nw directed compression d2 resulted in crustal thickening with retrograded medium pressure granulite facies grade at about 1914 1893 ma the d2 deformation produced nw verging asymmetric and recumbent folds interpreted to have resulted from basement involved thicken skin structures the jiaodong complex was also involved into the development of wnw verging asymmetric tight folds associated with d2 in the jingshan and the fenzishan groups ongoing collision led to the development of transpressional ductile shearing stz2 forming the transpressional taipingzhuang dextral ductile shear zone between the jingshan group and the southern archean complex and the transpressional tading xiadian sinistral ductile shear zone between the jingshan group and the northern archean complex all three lithotectonic units were superposed during the late d3 deformation with amphibolite facies metamorphism the d3 deformation developed wnw trending open to tight upright folds at about 1893 1875 ma the structural pattern resulting from superimposition of d2 and d3 is a composite synform in the fenzishan and jingshan groups the structural events of d1 and stz1 and d2 and stz2 deformation were possibly responsible for fast syn collisional exhumation of the high pressure mafic granulites the structural patterns and deformational history of the fenzishan and jingshan groups suggest a southeastward directed oblique subduction beneath the northwestern margin of the rangrim block and that the final scissor shaped closure of the rift led to collision between the two blocks to form the coherent basement of the eastern block of the north china craton

chemical trends in a perhumid soil catena on the turrialba volcano costa rica abstract the variation in chemical composition of soil samples xrfs data from a soil catena of 14 soil profiles on the northern slope and foot slope of the andesitic turrialba volcano 3300 m has been analysed to test the two hypotheses which underlie our interpretation that this catena is a weathering sequence the first hypothesis is that all parent material is chemically homogeneous and the second hypothesis is that development of chemical variation is the net result of progression of weathering and of diversity of weathering which both depend on altitude via gradients in temperature and precipitation the aim of this purely chemical approach is to find out if trace elements are significant tracers for different weathering paths leading to different amorphous or crystalline products for example imogolite allophane halloysite gibbsite and ferrihydrite the results show that volcanic ash is sufficiently homogeneous to detect the well known dominance of a general weathering trend with relative depletion of mobile elements mg k si etc and relative enrichment of less mobile elements ti fe al ce cr v zr etc the least mobile elements were ti v and zr from their contents a weathering index for all samples has been derived that describes 95 of their total variance hypothesis 1 in addition to this general trend ti v and zr showed systematic deviations that could be defined as a chemical differentiation factor in combination with the general weathering trend this explained 99 of the total variation of ti v and zr hypothesis 2 the contents of other major minor and trace elements used can only partially be described by the ti v zr derived weathering index and chemical differentiation the level of explanation decreases roughly with increasing mobility of the chemical element in the system triangular plots of element ratios suggest that contents of mobile elements are influenced by too many weathering processes trace elements did not show a more specific chemical differentiation than major and minor oxides the leaching pattern of mg indicates the presence of three different processes 1 short term preferential leaching of basic cations at high altitude 2 subsequent allophane formation between 660 and 1220 m altitude and 3 long term loss of basic oxides and not of silica upon ageing of fluvio volcanic sediments in the foot plain below 240 m fe shows anomalous depletion redistribution due to oxidation and reduction and al shows extra depletion in two of the allophanic profiles

geology and timing of mineralization at the cangshang gold deposit north western jiaodong peninsula china the cangshang gold deposit of the north western jiaodong peninsula contains reserves of greater than 50 tonnes t and is developed by the largest open pit gold mine in china this deposit is a jiaojia style i e disseminated and veinlet deposit it is controlled by the san cang fault zone which trends 040 and dips 40 75 se at the mine site the main no 1 orebody lies between a hanging wall of precambrian metamorphic rocks mainly amphibolite of the fenzishan group and a footwall composed of the mesozoic linglong granitoid the ore zone is mainly composed of pyritized sericitized and silicified granitoid which has undergone variable degrees of cataclasis shrimp u pb dating of zircon indicates that the protolith of the hanging wall amphibolite was formed at 2530 17 ma and underwent metamorphism at 1852 37 ma the footwall granodiorite has been dated at 166 4 ma whereas zircons from the ore zone yield a younger age of 154 5 ma cathodoluminescence images of zircons from the granodiorite and ore zone show oscillatory zonation indicative of an igneous origin for both and the ages of these zircons therefore are all interpreted to be representative of magmatic crystallization dating of sericite by 40ar 39ar has been used to directly determine the timing of formation of the cangshang deposit providing the first time absolute age on formation of the jiaojia style gold deposits the well defined age of 121 3 0 2 ma provides the precise timing of gold mineralization at the cangshang deposit this age is consistent with those of linglong style vein type gold mineralization also from the north western jiaodong peninsula at between 126 and 120 ma therefore our work indicates that both styles of gold deposits in the jiaodong peninsula were formed during the same mineralization event

cretaceous cenozoic tectonic history of the jiaojia fault and gold mineralization in the jiaodong peninsula china constraints from zircon u pb illite k ar and apatite fission track thermochronometry the jiaojia fault jjf in the jiaodong area of eastern china is an important nne trending structure that is subsidiary to the regional tancheng lujiang tan lu fault zone and hosts 1200 t of gold reserves contained in disseminated and stockwork ore dominantly in the footwall of the fault we present new zircon u pb apatite fission track and illite k ar data along the jjf and have delineated its tectonic history focusing on its formation and reactivation zircon u pb dating shows that the shangzhuang granite is a composite body with ages between 132 1 and 127 1 ma illite k ar ages for the fault s gouge range from 83 2 to 68 2 ma and the measured apatite fission track ages for ores are between 55 and 21 ma previous zircon u pb geochronology and structural studies suggest that the jjf was originally activated in the jurassic during 160 150 ma as a sinistral fault the jjf was a normal fault in the early cretaceous due to nw se orientated tension and ne sw compression which lasted from 135 to 120 ma this was followed by sinistral strike slip faulting due to nw se compression and ne sw tension during 120 110 ma and it changed to normal displacement at ca 110 ma our apatite fission track data analysis and thermal modeling of representative samples suggest that there was a subsequent dextral reactivation of the fault at ca 55 ma previous age data of ca 130 110 ma for gold mineralization along the jjf coincides with the early cretaceous magmatism and is coeval with the transition from normal faulting to sinistral strike slip faulting of the jjf in early cretaceous which is interpreted to be due to changing direction of the subducting pacific plate

atmospheric co2 consumption by chemical weathering in north america abstract co 2 consumption by chemical weathering is an integral part of the boundless carbon cycle whose spatial patterns and controlling factors on continental scale are still not fully understood a dataset of 338 river catchments throughout north america was used to empirically identify predictors of bicarbonate fluxes by chemical weathering and interpret the underlying controlling factors detailed analysis of major ion ratios enables distinction of the contributions of silicate and carbonate weathering and thus quantifying co 2 consumption extrapolation of the identified empirical model equations to north america allows the analysis of the spatial patterns of the co 2 consumption by chemical weathering runoff lithology and land cover were identified as the major predictors of the riverine bicarbonate fluxes and the associated co 2 consumption other influence factors e g temperature could not be established in the models of the distinguished land cover classes artificial surfaces dominated by urban areas increase bicarbonate fluxes most followed by shrubs grasslands managed lands and forests the extrapolation results in an average specific bicarbonate flux of 0 3 mmol km 2 a 1 by chemical weathering in north america of which 64 originates from atmospheric co 2 and 36 from carbonate mineral dissolution chemical weathering in north america thus consumes 50 mt atmospheric co 2 c per year about half of that originates from 10 of the area of north america the estimated strength of individual predictors differs from previous studies this highlights the need for a globally representative set of regionally calibrated models of co 2 consumption by chemical weathering which apply very detailed spatial data to resolve the heterogeneity of earth surface processes

an efficient solver for nearshore flows based on the waf method abstract we describe an efficient and robust flow solver for the integration of the classic nonlinear shallow water equations nswe on a beach of arbitrary topography on the basis of the shock capturing weighted average flux waf method a numerical code is implemented which employs a space splitting technique to integrate the nswe over a horizontally two dimensional domain 2dh special care is put in handling the moving shoreline and a new efficient formulation of the shoreline boundary conditions is presented this is based on the hydrodynamic equivalent of the cavitation condition used in gas dynamics model capabilities are illustrated by means of a number of tests both 1dh and 2dh these reveal that though primarily conceived for modelling nearshore hydrodynamics the solver can be successfully adopted even for studying the run up of large tsunami waves

geochronology and geochemistry of metamorphic rocks in the jiaobei terrane constraints on its tectonic affinity in the sulu orogen abstract tectonic affinity of tectono lithological units close to ultrahigh pressure metamorphic belt is a key issue for understanding the geodynamics of continental collision this is particularly so for the jiaobei terrane northeast of the dabie sulu orogenic belt in china new data from la icpms zircon u pb dating whole rock elements and nd sr isotopes and mineral o isotopes are presented for metamorphic rocks from this terrane the results place geochronological and geochemical constraints on their protolith nature and metamorphic timing and thus on its tectonic affinity to one of the two triassic collided continents the north and the south china blocks protolith ages for ttg gneiss amphibolite and mafic granulite are 2 7 2 5 and 2 4 ga respectively regional metamorphism took place extensively at 1 76 ga protolith of the ttg gneiss was generated by partial melting of mantle derived rocks at the root of a thickened crust protolith of the amphibolite was probably a product of arc like magmatism protolith of the mafic granulite was derived from a depleted mantle source both of them were locally contaminated by supracrustal materials protoliths of paragneiss and schist in the fenzishan group were mostly derived from supracrustal sources but protolith of amphibolite in the fenzishan group is of mantle derived signature unlike the uhp metaigneous rocks in the dabie sulu orogenic belt that show unusual 18 o depletion the jiaobei metamorphic rocks have basically preserved their original mantle like o isotope compositions in general the nature and timing of geological events recorded in the metamorphic rocks from the jiaobei terrane are comparable with those from the north china block rather than the south china block thus the jiaobei terrane is concluded to have tectonic affinity to the former but behave like a micro continent during the triassic continental collision the 1 76 ga regional metamorphism in the jiaobei terrane is likely related to reworking of the arc continent collisional orogen in the periphery of the north china block rather than the 1 85 ga collision event between the eastern and western north china blocks the present study lends support to the common assumption that the suture boundary between the north and south china blocks in the sulu orogen is located along the wulian yantai fault tectonic mingling along the wulian yantai fault is probably related to subduction erosion during the continental collision

the immediate environmental effects of tephra emission the earth s history is punctuated by large explosive eruptions that eject large quantities of magma and silicate rock fragments into the atmosphere these tephra particles can sometimes be dispersed across millions of square kilometres or even entire continents the interaction of tephra with or in receiving environments may induce an array of physical chemical and biological effects the consequences for affected systems and any dependent communities may be chronic and localised in the event of frequent small eruptions while larger and rarer events may have acute regional scale impacts it is therefore necessary to document the range of possible impacts that tephra may induce in receiving environments and any resulting effects in interconnected systems we collate results from many studies to offer a detailed multidisciplinary and interdisciplinary review of the immediate post eruptive effects of tephra emission into the atmosphere onto vegetation soil or ice snow surfaces and in aquatic systems we further consider the repercussions that may be induced in the weeks to years afterwards in the atmosphere tephra can influence cloud properties and air chemistry by acting as ice nuclei in or by offering sites for heterogeneous reactions respectively tephra on vegetation causes physical damage and sustained coverage may elicit longer term physiological responses tephra deposits on soils may alter their capacity to exchange gas water and heat with the atmosphere or may have a specific chemical effect such as nutrient input or acidification on sensitive soils tephra deposition onto snow or ice may affect ablation rates rivers and lakes may experience turbidity increases and changes in their morphology as a result of fallout and prolonged months or years erosion from the tephra covered catchment in the first weeks after deposition tephra leaching may affect river chemistry the abundance and speciation of phytoplankton populations in lakes may be altered by tephra induced changes in water chemistry or sediment water nutrient cycling in the oceans tephra deposition may fertilise fe limited waters with potential impacts on the global carbon cycle embracing the full complexity of environmental effects caused by tephra fall demands a renewed investigative effort drawing on interdisciplinary field and laboratory studies combined with consideration of the interconnectivity of induced impacts within and between different receiving environments

the intraplate character of supercontinent tectonics abstract for several decades geoscientists have recognised intraplate tectonic activity far from plate margins both from modern and ancient examples this apparent disconnect with the drivers of plate tectonics does not necessarily imply unconnected processes but rather an uncertainty in understanding exactly how these systems operate are the driving forces derived locally or do they propagate from plate margins how do these forces interact with a complex tectonic inheritance to generate the observed tectonism furthermore what novel approaches have been applied to understand these processes here we review the general literature and the contents of this special issue to develop some partial answers to these questions key observations include the critical importance of local lithospheric heterogeneities as a control on the mode of orogenesis and also the role of locally derived forces from mantle upwelling or from depositing thick piles of magmatic or sedimentary rocks these processes happen within the overarching tectonic setting provided by far field plate margins which show intimate links in both time and observed processes with many intraplate regions these insights would not be possible without a growing arsenal of geological geophysical and numerical methods that can be applied to intraplate regions and this is reflected in the varied approaches within the issue we envisage that this special issue will provide a stimulus for further progress in understanding intraplate tectonics

40ar 39ar geochronological constraints on the formation of the dayingezhuang gold deposit new implications for timing and duration of hydrothermal activity in the jiaodong gold province china abstract china s largest gold resource is located in the highly endowed northwestern part of the jiaodong gold province most gold deposits in this area are associated with the ne to nne trending shear zones on the margins of the 130 126 ma guojialing granite these deposits collectively formed at ca 120 5 ma during rapid uplift of the granite the dayingezhuang deposit is a large 120 t au orogenic gold deposit in the same area but located along the eastern margin of the late jurassic linglong metamorphic core complex new 40ar 39ar geochronology on hydrothermal sericite and muscovite from the dayingezhuang deposit indicate the gold event is related to evolution of the core complex at 130 4 ma and is the earliest important gold event that is well documented in the province the dayingezhuang deposit occurs along the linglong detachment fault which defines the eastern edge of the ca 160 150 ma linglong granite granodiorite massif the anatectic rocks of the massif were rapidly uplifted at rates of at least 1 km m y from depths of 25 30 km to form the metamorphic core complex the detachment fault with precambrian metamorphic basement rocks in the hangingwall and the linglong granitoids and migmatites in the footwall is characterized by early mylonitization and a local brittle overprinting in the footwall gold is associated with quartz sericite pyrite k feldspar altered footwall cataclasites at the southernmost area of the brittle deformation along the detachment fault our results indicate that there were two successive yet distinct gold forming tectonic episodes in northwestern jiaodong one event first reactivated the detachment fault along the edge of the linglong massif between 134 and 126 ma and then a second reactivated the shears along the margins of the guojialing granite both events may relate to a component of northwest compression after a middle early cretaceous shift from regional nw se extension to a ne sw extensional regime

characterization of the reaction and transport properties of porous rhyolite and its application to the quantitative understanding of the chemical weathering rate abstract the chemical weathering of porous rhyolite from kozushima japan was studied and the factors controlling the weathering rate including advection diffusion and dissolution were characterized using laboratory experiments the results were used to analyze the reaction and transport rates and the relationship between the weathering rates obtained in the laboratory and field was evaluated a flow through dissolution experiment using a rhyolite core demonstrated that the dissolution rate r mol cm 2 s 1 in deionized water depends on time t days according to the relationship r 2 9 10 16 t 0 65 the dissolution rate was also dependent on the concentration of dissolved si according to the relationship r 1 n where c ceq ceq 230 mol l 1 and n 1 0 or 0 33 the hydraulic conductivity and diffusion coefficients were measured under water saturated and unsaturated conditions the saturated hydraulic conductivity was 10 times greater than the unsaturated conductivity and the saturated effective diffusion coefficient of dissolved si was 5 times greater than the unsaturated diffusion coefficient previous studies on the weathering of the rhyolites from kozushima have shown that the field dissolution rate over 52 000 years was 3 10 19 6 10 19 mol si cm 2 s 1 these values are 12 1000 times lower than the dissolution rates obtained in the laboratory over a reaction time of 277 days reactive transport analysis demonstrated that the effect of on the dissolution rate is enhanced as the water saturation decreases the rate decreasing effect of was large in the early stages of weathering and then gradually decreased with time the 52 000 year weathering period is inferred to have occurred following a decrease in the dissolution rate to a value close to the field rate during an early weathering stage and subsequent further decrease in the rate owing to the effect of

volcanic ash leachates a review and recommendations for sampling methods tephra in plumes can scavenge and thereby rapidly deposit volatiles including sulphur halogen and metal species these may then be leached e g by rainfall potentially releasing heavy loadings to soils and water bodies several eruptions have resulted in contamination of pasture sometimes with serious impacts on livestock water quality has also been an issue in some areas affected by tephra fall this work synthesises the literature on volcanic ash leachates and considers the controls on volatile adsorption general trends emerge for basaltic intermediate and silicic tephra as well as for variable particle size and transport distance the applications of ash leachate data to plume gas geochemistry calculation of volatile budgets and environmental impact assessment are evaluated comparisons for different eruptions are hampered by disparities in leachate analysis techniques a standardised methodology is therefore proposed to facilitate future health impact assessment and volcanological interpretation of results from different sites

a case for chemical weathering in soils of hurd peninsula livingston island south shetland islands antarctica abstract the soils of the south shetland islands antarctica are considered weakly developed chemical weathering processes are generally considered to be negligible except in areas that receive large additions of seabird guano in this paper we describe and analyze 19 soils on hurd peninsula livingston island in the south shetland island archipelago the soils were classified according to us soil taxonomy and were generally weakly developed gelorthents humigelepts and haplorthels however b horizon formation rubification and increases in extractable fe and al were observed on toposequences of raised beaches the deposition of tephra and or guano is likely responsible for the chemically driven processes guano deposits contain phosphates and oxalic acid causing phosphatization and or dissolution of silicates input of tephra with easily weatherable minerals may account for metastable mineral formation tephra deposition in the oldest raised beaches has formed a fine textured mantle overlying the coarser textured subsoils highly weatherable tephra as opposed to guano deposition appears to influence soil formation at hurd peninsula

effects of tephra addition on soil processes in spodosols in the cascade range washington u s a abstract a study was conducted in the cascade range of washington state u s a to examine the effects of tephra additions on soil processes occurring in spodosols unleached tephra from the 18 may 1980 mt st helens eruption was applied in 5 or 15 cm depths to soils that had escaped airfall tephra deposition in 1980 but had received periodic additions of tephra during the holocene soil solutions were collected from the major genetic horizons of tephra treated and non treated profiles interpretation of soil solution composition provided an instantaneous record of the response of soil processes to the added tephra soluble salts composed of basic cations ca2 na mg2 k and so42 were initially leached from the tephra basic cations in the leachate displaced h and al3 from the exchange sites in the original upper horizons the soluble salts and al3 migrated through the soil profile where their concentrations were greatly attenuated by interaction with the solid phase calcium k al3 and so42 were strongly retained in the b horizons whereas na mg2 and cl showed little affinity for the solid phase biological uptake anion adsorption exchange reactions and neoformation of minerals may all be responsible for the differential movement of solutes through the soil profile no enhancement of elemental leaching was measured from the c horizon during the first four months of monitoring podzolization the prevailing process in these mountains was relatively unaffected by the addition of tephra

relative roles of formation and preservation on gold endowment along the sanshandao gold belt in the jiaodong gold province china importance for province to district scale gold exploration the 13 km long sanshandao gold belt along the nne trending sanshandao fault has highly variable orogenic gold endowment along strike new thermochronological data from the small cangshang gold deposit demonstrate similar degrees of uplift and exhumation rates as for larger deposits negating selective preservation as the prime gold endowment factor the haiyu sanshandao xiling and cangshang deposits of variable gold endowment lie adjacent to ne ene trending jogs similar to those at jiaojia and linglong so these structures cannot be the prime control on gold mineralization ore zones show a broad gentle northeast plunge with the southwestern cangshang and xinli deposits being closest to the ground surface and the northeastern haiyu deposit being the deepest thus preferential erosion of the shallower southwestern orebodies could be a factor affecting endowment another variable is the depth of drilling at haiyu sanshandao gold mineralization is better developed on more gently dipping fault segments consistent with a thrust component of oblique slip along them relative to the northeastern deposits the cangshang and xinli deposits are located in areas where relatively shallow drilling has intersected ore zones on steeply dipping fault segments indicating the potential for deeper drilling to intersect gold ore along deeper more gently dipping segments heterogeneous gold endowment is thus largely a formational factor related to the plunge of orebodies combined with the variable depth of drilling along the sanshandao fault over the entire jiaodong gold province there are equivalent age mesozonal to epizonal orebodies implicating their preservation at different crustal levels and thus increasing the province scale gold endowment potential and probability of further exploration discoveries

leaching experiments in recent tephra deposits from talang volcano west sumatra indonesia abstract tephra deposits are prone to leaching because of their high contents of easily weatherable primary minerals rapid weathering of pristine tephra results in soil solutions becoming saturated with soluble cations such as calcium magnesium and potassium which are major nutrient elements essential for plant growth determining cations and phosphate leached from tephra deposits is important for understanding the geochemical weathering of the volcanic materials mt talang erupted on april 12 2005 depositing basalto andesitic ash over portions of the solok district in west sumatra indonesia a leaching study was conducted to examine the chemical fluxes of cations from these tephra deposits in closed batch reaction vessels the tephra samples were leached with de ionized water organic citric and oxalic and inorganic nitric and sulfuric acids for 60 days in the laboratory at temperatures of 10 27 and 40 c respectively the leachates were collected after 24 h and after 10 30 and 60 days up to 30 days leaching of the tephra samples with water decreased leachate ph from 6 75 to 4 51 leachate ph was also noticed to decrease from 3 85 to 3 11 3 25 to 2 71 3 20 to 2 71 and 3 03 to 2 39 due to leaching with citric acid oxalic acid nitric acid and sulfuric acid respectively after 60 days leaching with water has decreased the ph by 0 9 2 9 units whereas that with citric and sulfuric acids by 0 06 0 24 units however leaching with oxalic and nitric acids has increased the ph by 0 16 1 38 units the release of cations from the mt talang tephra was in the decreasing order of ca mg k na the rate of initially dissolved calcium was very high in contrast the amount of dissolved k and na were low in the beginning but increased sharply after 10 days over the next 2 months there was a distinct decrease in the concentration of ca and mg the amount of p released by water citric nitric sulfuric and oxalic acid after 24 h was 237 349 681 964 and 1057 mg of p 2 o 5 kg 1 respectively at the low temperature of 10 c but the values tended to increase with increasing temperature it was noticed that the amount of dissolved p decreased exponentially with time of leaching which was highly correlated when using oxalic and sulfuric acid at the end of the incubation period dissolved p accounted for less than 36 mg of p 2 o 5 kg 1 higher amounts of total dissolved p were obtained when using inorganic sulfuric and nitric acids compared with those of organic oxalic and citric acids

fluxes of high versus low temperature water rock interactions in aerial volcanic areas example from the kamchatka peninsula russia abstract volcanic areas play a key role in the input of elements into the ocean and in the regulation of the geological carbon cycle the aim of this study is to investigate the budget of silicate weathering in an active volcanic area we compared the fluxes of the two major weathering regimes occurring at low temperature in soils and at high temperature in the active volcanic arc of kamchatka respectively the volcanic activity by inducing geothermal circulation and releasing gases to the surface produces extreme conditions in which intense water rock interactions occur and may have a strong impact on the weathering budgets our results show that the chemical composition of the kamchatka river water is controlled by surface low temperature weathering atmospheric input and in some limited cases strongly imprinted by high temperature water rock reactions we have determined the contribution of each source and calculated the rates of co 2 consumption and chemical weathering resulting from low and high temperature water rock interactions the weathering rates between 7 and 13 7 t km 2 yr for cations only and atmospheric co 2 consumption rates 0 33 0 46 10 6 mol km 2 yr for kamchatka river due to rock weathering in soils low temperature are entirely consistent with the previously published global weathering laws relating weathering rates of basalts with runoff and temperature in the kamchatka river co 2 consumption derived from hydrothermal activity represents about 11 of the total hco 3 flux exported by the river the high temperature weathering process explains 25 of the total cationic weathering rate in the kamchatka river although in the rivers non affected by hydrothermal activity the main weathering agent is carbonic acid reflected in the abundance of hco 3 in rivers in the region most impacted by hydrothermalism the protons responsible for minerals dissolution are provided not only by carbonic acid but also by sulphuric and hydrochloric acid a clear increase of weathering rates in rivers impacted by sulphuric acid can be observed in the kamchatka river 19 of cations are released by hydrothermal acids or the oxidative weathering of sulphur minerals our results emphasise the important impact of both low and high temperature weathering of volcanic rocks on global weathering fluxes to the ocean our results also show that besides carbonic acid derived from atmospheric co 2 hydrochloric acid and especially sulphuric acid are important weathering agents clearly sulphuric acid with hydrothermal activity are key parameters that cause first order increases of the chemical weathering rates in volcanic areas in these areas accurate determination of weathering budgets in volcanic area will require to better quantify sulphuric acid impact

shear zones fault networks and archean gold conjugate ductile shear zones developed mostly on granite greenstone margins are a dominant structural feature of the yilgarn craton these greenstone belt scale shear zones lack both gold deposits and gold related alteration previous interpretations of the shear zones as part of a linked system as craton scale terrane boundaries or as crustal scale pathways for gold mineralizing fluids all appear equivocal instead gold mineralizing fluids in the yilgarn craton illustrated here by the gold rich yandal belt were focused by a network of middle to upper crustal brittle faults in the late archean the faults are 040 to 060 trending dextral and 090 to 120 trending sinistral the maximum compression direction is about 075 gold mineralization occurs in laminated and other schistosity parallel quartz veins where brittle faults refract along earlier subsidiary within greenstone ductile shear zones and in quartz veins within late archean faults

a field based estimate of the zircon fission track closure temperature abstract a field based estimate of the zircon fission track closure temperature is proposed from 13 zircon fission track cooling ages of the gold butte block se nevada using previously published and new thermochronological data the thermal history of the gold butte block is re evaluated resulting in a geothermal gradient estimate of 20 3 c km and a slow cooling rate of 0 55 0 02 c m y from the late jurassic to the early miocene before onset of rapid miocene cooling the rapidly cooled part of the gold butte block provides a slip rate of 10 5 km m y of the hanging wall that caused the miocene exhumation of this crustal section assuming these thermal conditions are correct the closure temperature of the zircon fission track system is determined at 205 18 c which is in good agreement with previous field based estimates because of the variation in zircon fission track annealing behavior with radiation damage field studies are a suitable way to calibrate the closure temperature of the zircon fission track system

on the transport of suspended sediment by a swash event on a plane beach we develop solutions for the transport of suspended sediment by a single swash event following the collapse of a bore on a plane beach and we investigate the morphodynamical role that such transport may play although the intrinsic asymmetry between uprush and backwash velocities tends to encourage the export of sediment we find that swash events may be effective in distributing across the swash zone much or all of the sediment mobilised by bore collapse additionally settling lag effects may promote a weak onshore movement of sediment we quantify both effects in terms of the properties of the sediment and of the swash event and comment on the relationship between our findings and recent field studies of swash zone sediment transport

metamorphic core complexes vs synkinematic plutons in continental extension setting insights from key structures shandong province eastern china abstract continental extension is an important geodynamical process mostly diagnostic of a peculiar behaviour of the crust accommodated by geological structures that highlight these specific conditions in the crust though a metamorphic core complex mcc reveals a much stronger crustal extension than a synkinematic pluton the nature of those two structures implies different implications in terms of crustal extension mechanisms and geodynamic significations in eastern asia a major continental extensional event occurred during mesozoic and early cenozoic times the resulting various extensional events described in previous studies consist in large intracontinental basins important volcanism emplacement of plutons in the upper crust and exhumation of mccs an efficient description of mccs and plutons in eastern asia is essential to discriminate important differences of those two structures in terms of strain amount undergone by continental crust and geodynamic significations in that way an integrated structural and geophysical study has been realized to precisely discriminate the structure in the jiaodong peninsula shandong province eastern china previously regarded as simple sheared plutons a succession of three main stages have been identified all pertaining to a nw se extensional setting 1 the exhumation of the late jurassic early cretaceous linglong mcc below the se dipping linglong detachment fault 2 the emplacement of the guojialing syntectonic pluton below the n dipping extensional guojialing intracrustal shear zone 130 124 ma and 3 a penetrative brittle normal faulting associated with gold mineralizations 120 ma as a result the maximum amount of extension in jiaodong peninsula characterized by partially melted lower to middle crust upward into the linglong mcc should be revised to late jurassic early cretaceous period

the jiaodong type gold deposits characteristics origin and prospecting abstract the jiaodong type comprises a unique class of gold mineralisation which includes the linglong type quartz vein hosted and the jiaojia type fracture disseminated style deposits although the type area is in the jiaodong peninsula in ne china where some of the world s richest gold reserves occur we identify similar occurrences in other parts of china and elsewhere in the world under this category the ore fluids migrated upwards forming quartz vein type of gold ore linglong type wherever the ore controlling fractures are at high angles fluid infiltration into the surrounding wall rocks and generation of the jiaojia type disseminated style deposits resulted where the ore bearing fluids encountered low angle fractures on a regional scale the jiaodong type gold mineralisation occurs along the margins of reactivated cratons within the interior of cratons along paleosuture zones or along the junctions of micro blocks and is distinctly different from the classic orogenic gold in terms of their tectonic setting ore characteristics and genetic history unlike skarn and porphyry type of deposits the jiaodong type gold deposits do not always show close spatial relationship with magmatic intrusives and some of the deposits occur distal to plutons 10 km in this paper we evaluate the salient geological geochronological geochemical and isotopic features of the jiaodong type gold deposits and propose some general guidelines for gold prospecting based on case studies we predict that the gold lodes in the jiaodong type mineralised zones might extent vertically up to 3000 m with only minor mineralogical and geochemical variations

geochemical characterization and dating of r tephra a postglacial marker bed in mount rainier national park washington usa the oldest postglacial lapilli ash tephra recognized in sedimentary records surrounding mount rainier washington state usa is r tephra a very early holocene deposit that acts as an important stratigraphic and geochronologic marker bed this multidisciplinary study incorporates tephrostratigraphy radiocarbon dating petrography and electron microprobe analysis to characterize r tephra tephra samples were collected from tipsoo lake and a stream cut exposure in the cowlitz divide area of mount rainier national park field evidence from 25 new sites suggests that r tephra locally contains internal bedding and has a wider distribution than previously reported herein we provide the first robust suite of geochemical data that characterize the tephra glass compositions are heterogeneous predominantly ranging from andesite to rhyolite in ash to lapilli sized clasts the mineral assemblage consists of plagioclase orthopyroxene clinopyroxene and magnetite with trace apatite and ilmenite subaerial r t

towards a weathering model of mount lamington ash papua new guinea abstract the mount lamington ash halo has been studied at six sites both close to and distant from the volcano negligible alumina occurs in the seepage waters from the ash and so alumina is assumed constant during weathering in andesitic ashes weathering to allophane an approximation to a first order reaction was found in 1968 and is confirmed here with given infiltration and silica concentration the weathering rate constant decreases with increasing content of weathering minerals and increasing thickness of ash being weathered the rate constant also increased with increasing infiltration and decreasing median size of the ash the total weathering rate is the product of the thickness percentage of ash being weathered and the weathering rate constant the total weathering rate is the same for thick less weathered proximal ashes as it is for the thin more weathered distal ashes first order kinetics imply a high rate of leaching decreasing with time but continual burial under new ash at a nearly constant rate leads to linear leaching of the upper part of the profile the leaching rate decreases exponentially with depth and appears to ignore buried topsoil barriers it is possible to construct weathering models exploring the rate constant and to link it with leaching rates two thirds of the loss on weathering is silica and there is a total leaching rate of 3 4 mg sio 2 cm 2 year 1 as on basalt in hawaii and on andesite in st vincent water analyses show silica concentrations in the ash of 17 35 ppm and in draining streamlets of 9 20 ppm measured concentrations agree with calculated concentrations from the weathering data silica concentrations are similar in other humid tropical rivers

summary of pre 1980 tephra fall deposits erupted from mount st helens washington state usa mount st helens has been a prolific source of tephra fall deposits for about 40 000 years these tephra deposits 1 record numerous explosive eruptions 2 form important regional time stratigraphic marker beds and 3 record repeated changes in composition within and between eruptive periods

field weathering rates of mt st helens tephra the initial stages of chemical weathering in tephra were examined under field conditions in a cool and humid forest ecosystem in the cascade mountains of washington unleached tephra from the 1980 eruption of mt st helens was applied in 5 cm and 15 cm depths to simulate natural tephra deposition leachate solutions from the tephra were then collected and analyzed over a 4 year period concentrations of dissolved elements were combined with the water fluxes to determine elemental fluxes from tephra and to estimate chemical weathering rates solutions leached from the tephra layer indicate incongruent dissolution resulting in formation of a cation depleted silica rich leached layer on glass and mineral surfaces measured weathering rates were 1 3 orders of magnitude less than comparable rates reported in the literature for laboratory dissolution studies but considerably greater than those measured for entire watersheds in field studies dissociation of carbonic acid originating primarily from upward transport of carbon dioxide from the buried soil was the dominant source of protons for weathering reactions weathering rates in the 5 cm treatment were approximately twice those of the 15 cm treatment a greater flux of co2 per unit volume of tephra in the 5 cm treatment is believed to be responsible for the differential weathering rates

fast microscale controlled weathering of rhyolitic obsidian to quartz and alunite abstract six year experiments of volcanic glass reacting with waters of different chemistry two freshwaters seawater and brine at 22 c have produced the thorough transformation of mm size glass chips into quartz with minor alunite and calcite these results contradict the current thinking about glass weathering and quartz formation the reaction from glass to quartz took place at an estimated velocity ranging from 300 2000 times to 10 6 times faster than the accepted values for quartz precipitation depending on how rates were assessed the most likely process taking place is the rapid transformation of cation depleted glass into quartz in addition alunite formed very efficiently from low s glass 40 15 ppm such effective reaction in the absence of the accepted conditions for alunite formation is attributed to the high al and k content combined with the generation of low ph conditions at the microscale local low ph conditions may arise due to proton for na substitution at the earliest stage followed by liberation of the protons as glass later corroded the surprising results show a new pathway of glass weathering and point towards reactions controlled by microscale conditions producing high activities locally such conditions may be common in the mineral fluid interface with saline waters immobile waters or systems with low water rock ratios the rapid precipitation of quartz at low temperature is relevant to the origin of quartz and the silica budget in a variety of sedimentary environments and prompts their reconsideration

swash overtopping a truncated plane beach swash on a plane beach is modelled by using a solution of the shallow water equations due to shen meyer 1963 the equations are used in a form appropriate for a plane at a finite angle to the horizontal the beach is cut off at a level below that of the maximum run up and the water is taken to fall freely over the end of the beach an explicit solution is found which permits evaluation of the overtopping flow and total volume for one swash event

ore forming fluids associated with granite hosted gold mineralization at the sanshandao deposit jiaodong gold province china the sanshandao gold deposit with total resources of more than 60 t of gold is located in the jiaodong gold province the most important gold province of china the deposit is a typical highly fractured and altered disseminated gold system with high grade quartz sulphide vein veinlet stockworks that cut mesozoic granodiorite there are four stages of veins that developed in the following sequence 1 quartz k feldspar sericite 2 quartz pyrite arsenopyrite 3 quartz base metal sulfide and 4 quartz carbonate fluid inclusions in quartz and calcite in vein veinlet stockworks contain c o h fluids of three main types the first type consists of dilute co2 h2o fluids coeval with the early vein stage molar volumes of these co2 h2o fluid inclusions ranging from 50 60 cm3 mol yield estimated minimum trapping pressures of 3 kbar homogenization temperatures obtained mainly from co2 h2o inclusions with lower co2 concentration range from 267 375 c the second inclusion type with a co2 h2o ch4 composition was trapped during the main mineralizing stages these fluids may reflect the co2 h2o fluids that were modified by fluid rock reactions with altered wallrocks isochores for co2 h2o ch4 inclusions with homogenization temperatures ranging from 204 325 c and molar volumes from 55 to 70 cm3 mol provide an estimated minimum trapping pressure of 1 2 kbar the third inclusion type aqueous inclusions trapped in cross cutting microfractures in quartz and randomly in calcite are post mineralization and have homogenization temperatures between 143 228 c and salinities from 0 71 7 86 wt nacl equiv stable isotope data show that the metamorphic fluid contribution is minimal and that ore fluids are of magmatic origin most likely sourced from 120 126 ma mafic to intermediate dikes this is consistent with the carbonic nature of the fluid and the cross cutting nature of those deposits relative to the host mesozoic granitoid

lacustrine responses to tephra deposition examples from mexico one of the major problems with palaeoclimate investigations in volcanic regions is that tephra inputs to lakes can cause changes in proxies analogous to those of climate forcing we review the range of impacts thought to be associated with tephra deposition distinguishing between direct effects on lake ecosystems and indirect changes to catchment nutrient cycles to achieve better understanding of these complex responses we have used high resolution diatom analysis from around 17 tephra layers in three mexican lakes a positive response to the tephra inputs has been identified for over half of these layers the most common response was for diatom concentrations to increase after tephra deposition also in plankton dominated systems fragilaria spp replaced stephanodiscus spp and aulacoseira spp an increase in the supply of silica to the lakes through their catchments is probably the cause of the diatom changes in the lakes studied direct effects of the tephra inputs to these lakes can be excluded as they would not generate changes of sufficient longevity the impact of these tephras which lasted for several decades was insufficient to perturb the underlying long term climate forcing of these lake systems c 2004 elsevier ltd all rights reserved