the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

an ion microprobe study of the intra crystalline behavior of ree and selected trace elements in pyroxene from mare basalts with different cooling and crystallization histories abstract to study the effects of crystallization sequence and rate on trace element zoning characteristics of pyroxenes we used combined electron microprobe ion microprobe techniques on four nearly isochemical apollo 12 and 15 pigeonite basalts with different cooling rates and crystallization histories major and minor element zoning characteristics are nearly identical to those reported in the literature all the pyroxenes have similar chondrite normalized ree patterns negative eu anomalies positive slopes as defined by yb ce and slopes of ree patterns from ce to sm much steeper than from gd to yb the characteristics of the ree patterns of pigeonite and augite can be rationalized in terms of ree size and charge and m2 site characteristics numerous ree and other trace element v sr zr na sc cr zoning characteristics can be correlated with quadrilateral composition the total ree abundances increase with increasing ca in the m2 site and indicate that the distribution coefficients of ree between pyroxene and melt vary systematically with the wo component the total ree abundances also increase with decreasing mg mg fe and increasing al prior to plagioclase crystallization the eu anomaly in pyroxene is not substantially affected by plagioclase crystallization because eu3 is effectively partitioned into pyroxene relative to eu2 eu 2 eu 3 03 in pigeonite and the plagioclase effect is diluted by the low eu distribution coefficient for the more abundant pyroxene the cr and v components behave similarly in that cr and v decrease with increasing ti al in basalt sample 15058 and decrease with crystallization and at similar ti al na and sc increase in abundance from pigeonite to augite with similar ti al in both 15058 and 15499 in 15058 na decreases coherently with increasing ti al whereas sc shows a limited variability sr and zr in 15058 are somewhat more enriched in the augite with low ti al relative to pigeonite the augite does not become enriched in zr or sr until the pyroxene has high ti al and low mg mg fe in 15499 sr and zr show slight enrichment in augite relative to pigeonite these trace element zoning characteristics in pyroxene and the partitioning of trace elements between pyroxene and the melt are intimately related to the interplay among the efficiency of the crystallization process the kinetics at the crystal melt interface the kinetics of plagioclase nucleation and the characteristics of the crystal chemical substitutions within both the pyroxene and the associated crystallizing phases i e plagioclase

the upper critical zone of the eastern bushveld complex precursor of the merensky reef the upper critical zone in the central sector of the eastern bushveld complex consists predominantly of norites although bronzitites anorthosites chromitites and other chromitic rocks appear at intervals in the sequence gabbronorites appear near the middle of the zone the rock sequence is divided into 14 principal units plus the series from the base of the merensky reef to the top of the bastard reef mineralogical compositions of successive units have been determined from modal analyses and compositions of bronzite and plagioclase in the various rock units have been determined by microprobe analysis the results indicate that although parts of the zone show normal fractionation the zone as a whole is not the product of progressive fractionation of a magma crystal settling appears to have played a relatively minor role in evolution of the zone successive pulses of parent magma into the chamber may account for some of the mineralogical and chemical variations but features of certain thick norite units suggest stratification of the magma in the chamber the study suggests that the merensky reef registers a sudden event in the bushveld magma chamber an event that altered the chemistry of the system and triggered precipitation of sulfides and platinoid minerals the alternative hypothesis that the reef is the culmination of a long period of magma fractionation is not supported by the evidence presented chromite occurs in a variety of associations with plagioclase and bronzite the associations are consistent with phase relations in the system mg 2 sio 4 iron oxide caal 2 si 2 o 8 sio 2 at elevated pressure

paragenesis elemental distribution and stable isotopes at the pena colorada iron skarn colima mexico the pena colorada iron skarn is located in the southern part of the guerrero terrane it contains 150 million metric tons mt with a grade of 36 percent magnetite the deposit occurs at the contact of a 68 ma equigranular diorite with mid cretaceous volcano sedimentary rocks of the tepalcatepec formation volcanic units within this formation have tholeiitic affinity and ree patterns that are compatible with a primitive arc setting the pena colorada diorite and associated voluminous aplitic phases are part of a late cretaceous calc alkaline continental arc that subsequently intruded this basin northeast vergent deformation affected the region in the late cretaceous north south and east west reverse and northwest and northeast strike slip faults localize the mineralization the alteration halo around the diorite intrusion is 500 m wide within an inner 200 m halo the volcano sedimentary section was affected by an early metamorphic event with discontinuous bands of pyroxene di 68 hd 29 jo 3 hornfels and garnet gr 61 am 36 ad 3 disseminations metasomatic pyroxene garnet and plagioclase cut the early metamorphic event preferentially replacing carbonate and volcanic units up to and including a 35 m thick marl located 200 m above the intrusion metasomatic pyroxene and garnet have average compositions of di 77 hd 21 jo 2 and ad 76 gr 20 am 2 sp 1 py 1 respectively pyroxene compositions reach di 94 hd 5 jo 1 whereas garnet exhibits intragrain compositional zoning from ad 49 gr 46 in the core to ad 100 gr 0 in the rim albitization of preexisting protoliths modified igneous plagioclase compositions from ab 67 an 32 or 1 up to ab 96 an 3 or 1 albitization is followed by abundant fracture controlled fe epidote and cl bearing chlorite cha 84 cli 14 pen 2 that extend from the marl unit outward some 300 m this association is cut by a later assemblage of epidote chlorite prehnite that affects the entire 500 m width of the alteration halo and part of the intrusion chlorite cha 54 cli 45 pen 1 from this later event is richer in mg than that from the previous association igneous hornblende in the intrusion is altered to actinolite a potassic alteration event related to a hydrothermal breccia and aplitic dikes overprints the pre existing calc silicate associations alteration minerals in the breccia and the 200 m potassic halo around it evolve from early k feldspar biotite quartz to late jasperoid fluorapatite calcite veins mg rich biotite phl 77 ann 23 and ree rich apatite contain f cl oh ratios of 1 0 3 and 1 0 0 respectively massive magnetite 36 specular hematite 7 sulfide o c s and h stable isotope determinations on minerals from the calc silicate association are consistent with an igneous source for the initial fluids which mixed outward with an increasing component of trapped seawater or evaporite however water in equilibrium with magnetite exhibits unusually enriched 18 o values relative to other coexisting mineral derived fluids a solution that equilibrated with limestone at relatively high temperature is required to explain these heavy values

oxygen isotope study of the kamioka zn pb skarn deposits central japan the kamioka zn pb deposits consist of clinopyroxene rich skarns replacing limestone lenses in hida gneissose rocks paleozoic metabasite early jurassic funatsu granitic rocks and late cretaceous porphyritic dikes and stocks are the known igneous rocks in the mining area oxygen isotopic compositions of eight separates each of clinopyroxene and quartz from the deposits table 1 and some minerals and rocks from the major rock units around the deposits table 2 have been analyzed the estimated oxygen isotopic ratios of the fluids responsible for the formation of the deposits range as low as 4 to 3 smow these values are considerably lower than expected from magmatic waters and demonstrate that none of the igneous rocks in the area could be a direct source of the skarn and ore forming fluids the data instead show that the deposits are formed by a huge convective circulation of solutions of meteoric water origin promoted by a hidden batholithic intrusion at the time of the late cretaceous

the effect of streambed topography on surface subsurface water exchange in mountain catchments a numerical hydrological simulation suggested that water exchange between stream channels and adjacent aquifers is enhanced by convexities and concavities in streambed topography at st kevin gulch an effluent stream in the rocky mountains of colorado subsurface hydraulic gradients and movement of ionic tracers indicated that stream water was locally recharged into well defined flow paths through the alluvium stream water filled flow paths in the alluvium referred to as substream flow paths returned to the stream a short distance downstream 1 to 10 m recharge to the substream flow paths occurred where stream water slope increased at the transition from pools 1 to steeper channel units 5 20 return of substream flow paths to the stream occurred where stream water slope decreased at the transition from steeper channel units to pools a net water flux calculation is typically used to characterize water and solute fluxes between surface and subsurface zones of catchments along our study reach at st kevin gulch the net inflow of water from subsurface to stream 1 6 ml s 1 m 1 underestimated the gross inflow 2 7 ml s 1 m 1 by 40 the influence of streambed topography is to enhance hydrological fluxes between stream water and subsurface zones and to prolong water sediment contact times these effects could have important consequences for solute transport retention and transformation in catchments

infiltration metasomatism in layered intrusions an example from the stillwater complex montana abstract the contact between anorthosite zone ii an ii and the overlying troctolite of olivine bearing zone v ob v of the stillwater complex is characterized by a 5 m thick adcumulate anorthosite this adcumulate anorthosite separates rocks of an ii characterized by the apparent crystallization sequence plagioclase followed by orthopyroxene clinopyroxene quartz fe ti oxide assemblages from those of ob v where the apparent crystallization sequence is olivine plagioclase followed by orthopyroxene the grain size and compositional zoning of plagioclase in this transition zone is similar to that in the overlying troctolite and distinct from the coarser complexly zoned plagioclase that makes up the underlying anorthosite in contrast the minor interstitial pyroxene in the transition zone compositionally overlaps that in the underlying anorthosite and both have a lower molar mg mg fe ratio than the pyroxene of the troctolite these relationships suggest that the intercumulus liquids of an ii and ob v were compositionally distinct model phase diagram considerations suggest that infiltration of any plagioclase saturated liquids into a troctolite assemblage will result in the assimilation of olivine and depending on the actual composition of the anorthositic liquid will also either assimilate or crystallize plagioclase as well hence the monomineralic anorthosite zone at the top of an ii can be attributed to infiltration of interstitial liquids from an ii that were displaced upward into the troctolite during compaction of an ii this reaction can be either exothermic or endothermic depending on the actual composition of the infiltrating liquid and the bulk solids composition numerical models of the thermal effects of infiltration suggest that heat of reaction can significantly affect the liquid solid ratio away from the infiltration boundary

alluvial characteristics groundwater surface water exchange and hydrological retention in headwater streams conservative solute injections were conducted in three first order montane streams of different geological composition to assess the influence of parent lithology and alluvial characteristics on the hydrological retention of nutrients three study sites were established 1 aspen creek in a sandstone siltstone catchment with a fine grained alluvium of low hydraulic conductivity 1 3 10 4 cm s 2 rio calaveras which flows through volcanic tuff with alluvium of intermediate grain size and hydraulic conductivity 1 2 10 3 cm s and 3 gallina creek located in a granite gneiss catchment of coarse poorly sorted alluvium with high hydraulic conductivity 4 1 10 3 cm s all sites were instrumented with networks of shallow groundwater wells to monitor interstitial solute transport the rate and extent of groundwater surface water exchange determined by the solute response in wells increased with increasing hydraulic conductivity the direction of surface water groundwater interaction within a stream was related to local variation in vertical and horizontal hydraulic gradients experimental tracer responses in the surface stream were simulated with a one dimensional solute transport model with inflow and storage components otis model derived measures of hydrological retention showed a corresponding increase with increasing hydraulic conductivity to assess the temporal variability of hydrological retention solute injection experiments were conducted in gallina creek under four seasonal flow regimes during which surface discharge ranged from baseflow 0 75 l s in october to high 75 l s during spring snowmelt model derived hydrological retention decreased with increasing discharge the results of our intersite comparison suggest that hydrological retention is strongly influenced by the geologic setting and alluvial characteristics of the stream catchment temporal variation in hydrological retention at gallina creek is related to seasonal changes in discharge highlighting the need for temporal resolution in studies of the dynamics of surface water groundwater interactions in stream ecosystems 1997 by john wiley sons ltd

transient storage as a function of geomorphology discharge and permafrost active layer conditions in arctic tundra streams 1 transient storage of solutes in hyporheic zones or other slow moving stream waters plays an important role in the biogeochemical processes of streams while numerous studies have reported a wide range of parameter values from simulations of transient storage little field work has been done to investigate the correlations between these parameters and shifts in surface and subsurface flow conditions in this investigation we use the stream properties of the arctic namely highly varied discharges channel morphologies and subchannel permafrost conditions to isolate the effects of discharge channel morphology and potential size of the hyporheic zone on transient storage we repeated stream tracer experiments in five morphologically diverse tundra streams in arctic alaska during the thaw season may august of 2004 to assess transient storage and hydrologic characteristics we compared transient storage model parameters to discharge q the darcy weisbach friction factor f and unit stream power across all studied streams permafrost active layer depths i e the potential extent of the hyporheic zone increased throughout the thaw season and discharges and velocities varied dramatically with minimum ranges of eight fold and four fold respectively in all reaches the mean storage residence time tstor decreased exponentially with increasing q but did not clearly relate to permafrost active layer depths furthermore we found that modeled transient storage metrics i e tstor storage zone exchange rate otis and hydraulic retention rh correlated better with channel hydraulic descriptors such as f and than they did with q or channel slope our results indicate that q is the first order control on transient storage dynamics of these streams and that f and are two relatively simple measures of channel hydraulics that may be important metrics for predicting the response of transient storage to perturbations in discharge and morphology in a given stream

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

platinum group element mineralization in the critical zone of the western bushveld complex i sulfide poor chromitites below the ug 2 primary stratiform platinum group element pge mineralizations associated with chromitites in the critical zone of the bushveld complex south africa are confined to cumulate layers that are regionally persistent over tens of kilometers four categories ofchromitite are recognized layers at the bases of cycles in the lower critical zone type i layers at the bases of cycles in the upper critical zone type ii thin layers in the intermediate parts of cycles type iii and stringers associated with orthopyroxene pegmatoids type iv these latter may not be of primary magmatic origin nevertheless probably each type of chromitite contains anomalous concentrations of pge chromitites at the bases of cycles comprising the lower group lg middle group mg and upper group ug are further categorized into types ia lg 1 lg 4 ib lg 5 mg 1 iia mg 2 ug 1 and iib ug 2 and above on the basis of lithostratigraphy chromite and pge chemistry and sulfide content type iib chromitites contain significant quantities of sulfides and are not investigated here new whole rock and electron microprobe chemical analyses of the sulfide poor type ia ib and iia chromitites cu contents 1 8 low pge contents 2 type ib chromitites occur in pyroxenite cycles and form an intermediate group these regular variations with increased height are interpreted as a differentiation trend pge are concentrated in sulfide poor chromitites as a result of chromitite control a process not fully understood but thought to involve a combination of direct nucleation of platinum group minerals and localized s saturation it is the crystallization of copious quantities of chromite from hybridized melts close to the crystal liquid interface that triggers this process but magma mixing essential to drive the melt into the chromite field is the overall cause replenishment of the magma chamber was from a single magma batch because the chromitites below the ug 2 are not associated with major isotopic inflections huge volumes of dense hot magma were fed as basal flows along the crystal liquid interface the magma chamber was compartmentalized at an early stage possibly in response to basement tectonics and lateral mixing over distances of 150 km is an alternative mechanism for achieving sufficiently high r values repeated replenishment of the magma chamber resulted in mixing with resident liquid that became increasingly differentiated with height type ia chromitites are ascribed to replenishment and mixing with the relatively primitive lower zone residue type ib crystallized as a result of mixing with lower critical zone resident liquid and type iia due to mixing with more evolved upper critical zone resident liquid differentiation of pge with height is a critical part of the process which culminates in the occurrence of higher grade pge mineralization in sulfide bearing chromitites ug 2 merensky reef in the uppermost part of the upper critical zone

the distribution of chalcophile and platinum group elements in the ug 2 chromitite layer of the bushveld complex a ug 2 chromitite sample contains two sequences in which the concentrations of cu ni s pt pd rh ru and ir conform to a process of fractionation according to the rayleigh law both of these sequences are followed by others in which the trends are almost horizontal from the sequences that conform to the rayleigh law one can calculate the relations between the possible thicknesses of the magma column that gave rise to the ug 2 layer the bulk distribution coefficients and the original concentrations of the elements involved it appears that the elements were withdrawn from a surprisingly thin layer of magma between the first and the second cycles certain elements have been depleted and others enriched which indicates a heave of new magma rather than the recirculation of old partly depleted magma by a process like convective overturn the fact that s and the chalcophile elements cu and ni were concentrated in the same way and at the same time as the platinum group elements shows that the same collector was probably involved therefore sulfide could not have acted as a collector for the platinum group elements it is thought that chromite or a precursor of chromite was involved in some way with the collection process

geochemical and mineralogical studies of ca 12 ma hydrothermal manganese rich rocks in the hokuroku district in japan abstract geological and geochemical studies were performed on ca 12 ma mn rich rocks in the hokuroku district in japan to constrain the origin of mn rich hydrothermal fluids and precipitation pathways of mn oxides mn rich rocks occur in hyaloclastites of rhyolite lavas in the studied areas colloform textures of mn oxides were common in those mn rich rocks carbonaceous layers uniquely alternate with mn oxides in the colloform textures the mn oxides layers in the colloform textures were composed of aggregates of nano scale todorokite birnessite and pyrolusite the carbonaceous layers also host apatite nano crystals these findings imply that the carbonaceous layers most likely represent fossilized microbial mats of mn oxidizing bacteria the close association of nano scale mn oxides with organic matter clay and silica minerals suggests that mn oxides initially precipitated near venting areas of low temperature hydrothermal fluids the early mn oxides were trapped in the hyaloclastites and experienced diagenetic modifications combined with hydrothermal alteration seawater penetration and microbial activities in the hyaloclastites such secondary processes further enriched mn in the hyaloclastites forming various mn silicates e g pennantite and shirozulite and veins made of mn ii and iii silicate and oxide silicate e g rhodonite and braunite later hydrothermal fluids also brecciated the massive mn rich rocks rhodochrosite and rhodonite occurred in such brecciated mn rich rocks or sheared hyaloclastites preferentially the carbon isotope compositions of rhodochrosite ranged from 26 7 to 20 8 vpdb the mudstone and early colloform textures in the hyaloclastites contained appreciable amounts of organic matter such organic matter was degraded by microbial processes under the influence of the later hydrothermal activities followed by the formation of rhodochrosite these findings contribute not only to understanding the formation mechanisms of hydrothermal mn rich rocks but also to future exploration of mn deposits

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

oxygen isotope study of metamorphosed manganese deposits of the noda tamagawa mine northeast japan manganese ores of the noda tamagawa mine are metamorphosed equivalents of bedded type sedimentary manganese deposits the ore lenses are typically zoned with a central pyrochroite hausmannite zone an outer tephroite zone and an outermost rhodonite zone closest to the wall rock chert the 18 o vsmow values of 65 tephroite 32 rhodonite and eight quartz samples from the manganese ores and chert are in the ranges of 9 9 to 20 0 11 7 to 20 3 and 23 0 to 23 9 per mil respectively the overall order of 18 o enrichment corresponds to the order of equilibrium fractionation among these minerals however the temperatures calculated from quartz rhodonite and rhodonite tephroite pairs from neighboring ore zones are not consistent with those estimated from the mineral assemblages in the wall rocks the 18 o values for mnco 3 the most probable candidate of the precursor manganese mineral were calculated from the oxygen isotope mass balance among manganese silicates silica and co 2 to be 19 2 to 23 4 per mil if the mnco 3 initially precipitated from fluids of 18 o 0 0 to 2 5 per mil the temperatures of precipitation can be calculated to be between 62 and 111 c consistent with the primary mnco 3 having been precipitated by low temperature submarine hydrothermal solutions

thermodynamics and lattice vibrations of minerals 5 applications to phase equilibria isotopic fractionation and high pressure thermodynamic properties in previous papers in this series a model that uses available elastic structural and spectroscopic data on minerals has been used to predict the thermodynamic functions cv heat capacity s entropy e internal energy and f helmholtz free energy in this paper four applications to problems of current geochemical and geophysical interest are presented 1 interpretation of complex trends of calorimetric data 2 calculation of phase equilibria 3 calculation of oxygen isotopic fractionation factors and 4 estimation of the effect of pressure on thermodynamic functions the model demonstrates that trends in high temperature thermodynamic properties of silicates are determined by the position and relative numbers of high frequency modes generally antisymmetric si al o stretching modes the position of these modes varies systematically with degree of polymerization of tetrahedra and therefore high temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition trends at low frequency are much more complex because the low frequency optic modes that most strongly influence the low temperature thermodynamic functions depend in a complex way on the size coordination and mass of cations and various polyhedra in the minerals the heat capacity curves of kyanite andalusite and sillimanite and of quartz coesite and stishovite show crossovers that cannot be explained by debye theory which accounts only for acoustic mode behavior but can be explained by the model spectra proposed because proper account is taken of the changing low and high frequency optic modes upon polymorphic transformations the proposed model is sufficiently accurate that phase equilibrium problems can be addressed the quartz coesite stishovite equilibrium curves the kyanite andalusite sillimanite triple point and the breakdown of albite to jadeite plus quartz are cited as specific examples for each example predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally the calculated slopes are sensitive to spectroscopic parameters particularly to the distribution of optic modes in the far infrared this sensitivity is discussed in detail for the albite breakdown reaction the model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated a simple set of rules for generating hypothetical spectra of 18o minerals from measured spectra of the 16o forms is given reduced partition functions are calculated for 13 minerals at 298 k the model values of reduced partition function 1000 ln of these minerals decrease in the order quartz calcite albite muscovite clinoenstatite anorthite diopside pyrope grossular zircon forsterite andradite rutile in good agreement with experimental data at 1000 k the first six minerals show small crossovers so that the order becomes calcite muscovite albite quartz anorthite and clinoenstatite the differences in 1000 ln at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends the model clearly defines the region in which the fractionation factors do not follow a 1 t trend and should be useful for extrapolation of experimental data to low temperatures finally a modified gruneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression and thermodynamic properties to 1000 kbar 1000 k are given for nine minerals at 1 mbar the predicted decrease in entropy at 298 k ranges from 54 of the 1 bar value for periclase to 25 for stishovite

on the biogeochemical response of a glacierized high arctic watershed to climate change revealing patterns processes and heterogeneity among micro catchments our novel study examines landscape biogeochemical evolution following deglaciation and permafrost change in svalbard by looking at the productivity of various micro catchments existing within one watershed it also sheds light on how moraine talus and soil environments contribute to solute export from the entire watershed into the downstream marine ecosystem we find that solute dynamics in different micro catchments are sensitive to abiotic factors such as runoff volume water temperature geology geomorphological controls upon hydrological flowpaths and landscape evolution following sea level and glacial changes biotic factors influence the anionic composition of runoff because of the importance of microbial so42 and no3 production the legacy of glaciation and its impact upon sea level changes is shown to influence local hydrochemistry allowing cl to be used as a tracer of thawing permafrost that has marine origins however we show that a glacial signal dominates solute export from the watershed therefore although climatically driven change in the proglacial area has an influence on local ecosystems the biogeochemical response of the entire watershed is dominated by glacially derived products of rapid chemical weathering consequently only the study of micro catchments existing within watersheds can uncover the landscape response to contemporary climate change

hyporheic zone hydrologic science a historical account of its emergence and a prospectus the hyporheic zone defined by shallow subsurface pathways through river beds and banks beginning and ending at the river is an integral and unique component of fluvial systems it hosts myriad hydrologically controlled processes that are potentially coupled in complex ways understanding these processes and the connections between them is critical since these processes are not only important locally but integrate to impact increasingly larger scale biogeochemical functioning of the river corridor up to the river network scale thus the hyporheic zone continues to be a growing research focus for many hydrologists for more than half the history of water resources research this manuscript partly summarizes the historical development of hyporheic zone hydrologic science as gleaned from papers published in water resources research from the birth of the concept of the hyporheic zone as a hydrologic black box sometimes referred to as transient storage zone to its adolescent years of being torn between occasionally competing research perspectives of interrogating the hyporheic zone from a surface or subsurface view to its mature emergence as an interdisciplinary research field that employs the wide array of state of the art tools available to the modern hydrologist the field is vibrant and moving in the right direction of addressing critical fundamental and applied questions with no clear end in sight in its growth there are exciting opportunities for scientists that are able to tightly link the allied fields of geology geomorphology hydrology geochemistry and ecology to tackle the many open problems in hyporheic zone science

simulating unsteady flow anabranching and hyporheic dynamics in a glacial meltwater stream using a coupled surface water routing and groundwater flow model 1 flooding affects ecosystems by transporting water and solutes across aquatic terrestrial interfaces removing nutrient and organic substrate limitations and spurring biogeochemical activity few studies have considered the influence of flooding on surface water groundwater interactions this research examines the temporally variable water storage and exchange in a stream in the mcmurdo dry valleys mdv of antarctica where diel flood pulses occur due to glacial melt several mdv streams display truncated discharge peaks suggesting water storage between the source glacier and the gauging station we tested the hypothesis that stream braids and subsurface water storage contribute to the difference between glacial melt and stream outflow hydrographs by constructing a coupled surface water routing and subsurface water flow model this model routes water into stream braids at high flows and allows this water to infiltrate and return to the stream via subsurface flow paths as flows recede our simulation demonstrates the importance of surface subsurface water interactions in controlling the hydrograph shape maximum simulated discharge was sensitive to storage parameters including aquifer depth and the flooding threshold while minimum discharge was sensitive to hydraulic conductivity subsurface storage volume varied by 38 over a diel cycle and stream subsurface exchange rates varied from 0 to 0 19 m3 h 1 m 1 with exchange from the stream to the subsurface during high flows and vice versa at low flows these results underscore how unsteady flow can increase hyporheic interactions and ecosystem productivity and provide support for maintaining natural stream morphology and flow regimes

new experimental approach to understanding igneous texture thin sections containing a magma like mixture of three crystalline ammonium compounds and intercrystalline melt can be prepared and observed microscopically during crystallization melting and deformation the aim of such observations is to establish links between active processes in the crystal melt mixture and the textural signatures of the processes the hope is to improve the basis for process interpretation of textures in rocks although the value of the experimental system in this regard is still unknown three unexpected processes are seen creation of growth centers for later blocky grains by isothermal decomposition of early dendritic grains migration of grain boundaries early in the crystallization history and growth of porphyroblast like grains by phase boundary migration with abundant melt nearby textural metamorphism begins in this material well before its melt present history is complete

precipitation of gold in a low sulfidation epithermal gold deposit insights from a submillimeter scale oxygen isotope analysis of vein quartz sir we welcome the opportunity to respond to bogie and lawless discussion of our paper on the submillimeter scale oxygen isotope variation of vein quartz from the low sulfidation style gold deposit at the hishikari mine the disputed point is whether or not the bladed and fine grained quartz precipitated initially as chalcedony and recrystallized to quartz in a subsequent stage similarity of texture between chalcedony e g typically found in agate and flaky or acicular bladed quartz suggests that there is some truth in bogie and lawless idea the texture of bladed quartz suggests rapid crystallization from solutions supersaturated with respect to quartz however it is difficult to define only from the texture whether

measuring thaw depth beneath peat lined arctic streams using ground penetrating radar in arctic streams depth of thaw beneath the stream channel is likely a significant parameter controlling hyporheic zone hydrology and biogeochemical cycling as part of an interdisciplinary study of this system we conducted a field investigation to test the effectiveness of imaging substream permafrost using ground penetrating radar gpr we investigated three sites characterized by low energy water flow organic material lining the streambeds and water depths ranging from 0 2 to 2 m we acquired data using a 200 mhz pulsed radar system with the antennas mounted in the bottom of a small rubber boat that was pulled across the stream while triggering the radar at a constant rate we achieved excellent results at all three sites with a clear continuous image of the permafrost boundary both peripheral to and beneath the stream our results demonstrate that gpr can be an effective tool for measuring substream thaw depth copyright 2005 john wiley sons ltd

substrate size and heterogeneity control anomalous transport in small streams in alluvial systems substrate characteristics play a critical role in slowing downstream transport of both water and solutes we present results from solute injection experiments testing the influence of sediment size pea gravel versus coarse gravel and heterogeneity alternating sections versus well mixed reaches on solute transport dynamics in four experimental streams at the notre dame linked experimental ecosystem facility the stream with pea gravel resulted in more long term retention than the stream with coarse gravel whereas both streams with heterogeneous substrate alternated and mixed fell between with similar late time scaling inverse modeling of solute breakthrough curves suggested that residence times were distributed according to a truncated power law while conservative solute transport in all four streams was anomalous truncation times were influenced by sediment size with the smaller pea gravel exhibiting a later truncation time than the coarse gravel and the two streams with heterogeneous substrate having an intermediate cutoff these results uniquely associate transport scaling with substrate characteristics in fluvial systems revealing truncation time scales that had been previously predicted but not observed and quantified in field conditions because both benthic i e substrate water interface and subsurface hyporheic regions are known biogeochemical hot spots relating physical characteristics to the macroscopic transport behavior could be crucial to improve our estimates of solute export from fluvial systems

divergence and flow direction as indicators of subsurface heterogeneity and stage dependent storage in alluvial floodplains assuming homogeneity in alluvial aquifers is convenient but limits our ability to accurately predict stream aquifer interactions research is needed on i identifying the presence of focused as opposed to diffuse groundwater discharge recharge to streams and ii the magnitude and role of large scale bank and transient storage in alluvial floodplains relative to changes in stream stage the objective of this research was to document and quantify the effect of stage dependent aquifer heterogeneity and bank storage relative to changes in stream stage using groundwater flow divergence and direction monitoring was performed in alluvial floodplains adjacent to the barren fork creek and honey creek in northeastern oklahoma based on results from subsurface electrical resistivity mapping observation wells were installed in high and low electrical resistivity subsoils water levels in the wells were recorded real time using pressure transducers august to october 2009 divergence was used to quantify heterogeneity i e variation in hydraulic conductivity porosity and or aquifer thickness and flow direction was used to assess the potential for large scale 100 m bank or transient storage areas of localized heterogeneity appeared to act as divergence zones allowing stream water to quickly enter the groundwater system or as flow convergence zones draining a large groundwater area maximum divergence or convergence occurred with maximum rates of change in flow rates or stream stage flow directions in the groundwater changed considerably between base and high flows suggesting that the floodplains acted as large scale bank storage zones rapidly storing and releasing water during passage of a storm hydrograph during storm events at both sites the average groundwater direction changed by at least 90 from the average groundwater direction during baseflow aquifer heterogeneity in floodplains yields hyporheic flows that are more responsive and spatially and temporally complex than would be expected compared to more common assumptions of homogeneity copyright 2012 john wiley sons ltd

stage dependent transient storage of phosphorus in alluvial floodplains models for contaminant transport in streams commonly idealize transient storage as a well mixed but immobile system these transient storage models capture rapid near stream hyporheic storage and transport but do not account for large scale stage dependent interaction with the alluvial aquifer the objective of this research was to document transient storage of phosphorus p in coarse gravel alluvium potentially influenced by large scale stage dependent preferential flow pathways pfps long term monitoring was performed at floodplain sites adjacent to the barren fork creek and honey creek in northeastern oklahoma based on results from subsurface electrical resistivity mapping which was correlated to hydraulic conductivity data observation wells were installed both in higher hydraulic conductivity and lower hydraulic conductivity subsoils water levels in the wells were monitored over time and water samples were obtained from the observation wells and the stream to document p concentrations at multiple times during high flow events contour plots indicating direction of flow were developed using water table elevation data contour plots of total p concentrations showed the alluvial aquifer acting as a transient storage zone with p laden stream water heterogeneously entering the aquifer during the passage of a storm pulse and subsequently re entering the stream during baseflow conditions some groundwater in the alluvial floodplains had total p concentrations that mirrored the streams total p concentrations a detailed analysis of p forms indicated that particulate p i e p attached to particulates greater than 0 45 m was a significant portion of the p transport this research suggests the need for more controlled studies on stage dependent transient storage in alluvial systems copyright 2011 john wiley sons ltd

manganese formations in the accretionary belts of japan implications for subduction accretion process in an active convergent margin abstract in the accretionary complexes of japan many bedded manganese and iron manganese ore deposits occur especially in the jurassic complexes such as the chichibu tamba mino ashio and northern kitakami belts the manganese ores in these jurassic accretionary complexes probably formed from manganese nodule crust bearing siliceous sediments on deep sea floor and were subsequently converted to the manganese ores by metamorphism during the subduction accretion process some of the deposits also show the signatures of younger granitic intrusions the manganese formations now incorporated within these belts are marker beds of accretionary tectonics associated with plate tectonic processes in convergent margins

the ug2 merensky reef interval of the bushveld complex northwest of pretoria northwest of pretoria the ug2 merensky reef interval overlies a critical zone lower zone sequence that contains numerous large blocks of floor material nevertheless individual layers can be correlated with equivalent units at crocodile river mine the rustenburg impala union and amandelbult sections concentrations of platinum group elements in two borehole intersections of the ug2 chromitite are 4 ppm over 1 2 m and 2 4 ppm over 2 2 m therefore bulk pge levels appear to be only moderately lower than those at western platinum mine this renders models explaining pge enrichment by upward percolating melt or fluids problematic the merensky reef although containing sulphides is only weakly mineralized with pge 0 6 ppm the ug2 pyroxenite is separated from the ug2 chromitite by a 15 m noritic layer the introduction of feldspathic cumulates between two units that elsewhere directly overly each other may be explained by the more evolved composition of resident magma in those parts of the chamber distally located with regard to a major feeder zone at union section it also suggests that the ug2 unit is a multiple rather than a single cyclic unit