estimating groundwater exchange with lakes 1 the stable isotope mass balance method groundwater inflow and outflow contributions to the hydrologic budget of lakes can be determined using a stable isotope 18o 16o mass balance method the stable isotope method provides a way of integrating the spatial and temporal complexities of the flow field around a lake thereby offering an appealing alternative to the traditional time and labor intensive methods using seepage meters and an extensive piezometer network in this paper the method is applied to a lake in northern wisconsin demonstrating that it can be successfully applied to lakes in the upper midwest where thousands of similar lakes exist inflow and outflow rates calculated for the wisconsin lake using the isotope mass balance method are 29 and 54 cm yr respectively which compare well to estimates derived independently using a three dimensional groundwater flow and solute transport model of 20 and 50 cm yr such a favorable comparison lends confidence to the use of the stable isotope method to estimate groundwater exchange with lakes in addition utilization of stable isotopes in studies of groundwater lake systems lends insight into mixing processes occurring in the unsaturated zone and in the aquifer surrounding the lake and verifies assumed flow paths based on head measurements in piezometers

effect of anisotropy and groundwater system geometry on seepage through lakebeds 1 analog and dimensional analysis abstract distribution of seepage through lakebeds is controlled partly by geometric configuration of the lake and of the groundwater system interacting with the lake to evaluate the effect of these factors conductive paper electric analog models were used to analyze a number of lake and groundwater settings having different geometric configurations most settings analyzed are of lakes that do not penetrate the groundwater system the width ratio the ratio of half the lake width to thickness of the groundwater system is the principal geometric characteristic used in this study because the distribution of groundwater seepage into a lake is not uniform across the lakebed the concept of a streamlinecrowding factor is developed and is used to determine seepage patterns from geometric characteristics of the lake and its contiguous groundwater system analysis of fourteen different width ratios of lake and groundwater systems indicates that lakes can be defined by three general groups of seepage patterns which include flow patterns volumes and rates 1 lakes having width ratios less than 0 6 show relatively uniform distribution of seepage across the lakebed 2 lakes having width ratios of 0 6 to 2 0 change in absolute and relative streamline crowding in the near shore region and 3 lakes having width ratios greater than 2 0 show stable flow patterns near shore however with increasing lake width the relative streamline crowding increases relative to that width for deep lakes and those in anisotropic media the crowding effect is decreased resulting in more uniform seepage across the lakebed

alpine tectonics in the calabrian peloritan belt southern italy new 40ar 39ar data in the aspromonte massif area this study provides new ar 40 ar 39 geochronological constraints on the age of the alpine tectonics in the aspromonte massif southern part of the calabrian peloritan belt this massif exposes the upper units of the calabride complex which originated from the european continental margin the calabride complex was incorporated in the alpine orogenic wedge and then integrated into the apennines and maghrebides fold and thrust belts throughout the calabride complex there is evidence for a two stage tectonic history which remains however rather poorly dated alpine nappe stacking is followed by extensional reworking along the former thrust contacts or along new detachment surfaces our new ages suggest that exhumation of the uppermost units which accompanied nappe stacking probably started at 45 ma and that the deepest units were almost completely exhumed at 33 ma this kinematics probably corresponds to syn orogenic extension while the end of exhumation is clearly related to the extensional tectonics dated at 28 6 ma along detachment structures our geochronological data reveal a very short lag time between accretional and extensional processes in this part of the mediterranean alpine orogenic belt the direction of extension when the units are restored to their initial position i e before the opening of the western mediterranean basins and the bending of the arc is nne ssw such a direction does not fit with the eastward slab retreat model generally put forward to explain extension in the western mediterranean in contrast we provide evidence for roughly n s middle oligocene extension in the accretionary prism not previously described in this part of the mediterranean domain

eight phase alkali feldspars low temperature cryptoperthite peristerite and multiple replacement reactions in the klokken intrusion eight feldspar phases have been distinguished within individual alkali feldspar primocrysts in laminated syenite members of the layered syenite series of the klokken intrusion the processes leading to the formation of the first four phases have been described previously the feldspars crystallized as homogeneous sodian sanidine and exsolved by spinodal decomposition between 750 and 600 c depending on bulk composition to give fully coherent strain controlled braid cryptoperthites with sub m periodicities below 500 c in the microcline field these underwent a process of partial mutual replacement in a deuteric fluid producing coarse up to mm scale turbid incoherent patch perthites we here describe exsolution and replacement processes that occurred after patch perthite formation both or and ab rich patches underwent a new phase of coherent exsolution by volume diffusion or rich patches began to exsolve albite lamellae by coherent nucleation in the range 460 340 c depending on patch composition leading to film perthite with 1 m periodicities below 300 c misfit dislocation loops formed which were subsequently enlarged to nanotunnels ab rich patches bulk composition ab91or1an8 in one sample exsolved giving peristerite with one strong modulation with a periodicity of 17 nm and a pervasive tweed microtexture the ab rich patches formed with metastable disorder below the peristerite solvus and intersected the peristerite conditional spinodal at 450 c this is the first time peristerite has been imaged using tem within any perthite and the first time peristerite has been found in a relatively rapidly cooled geological environment the lamellar periodicities of film perthite and peristerite are consistent with experimentally determined diffusion coefficients and a calculated cooling history of the intrusion all the preceding textures were in places affected by a phase of replacement correlating with regions of extreme optical turbidity we term this material ultra porous late feldspar uplf it is composed predominantly of regions of microporous very or rich feldspar mean ab2 5or97 4an0 1 associated with very pure porous albite ab97 0or1 6an1 4 implying replacement below 170 90 c depending on degree of order in tem uplf has complex irregular diffraction contrast similar to that previously associated with low temperature albitization and diagenetic overgrowths replacement by uplf seems to have been piecemeal in character ghost like textural pseudomorphs of both braid and film parents occur formation of patch perthite film perthite and peristerite occurred 104 105 year after emplacement but there are no microtextural constraints on the age of uplf formation

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

felsic mineral crystallization trends in differentiating alkaline basic magmas mineral compositional relationships have been studied in a variety of alkaline basic rocks from small highlevel intrusions these small intrusions must have cooled quickly as the phases are all zoned especially those forming the matrix of some of the rocks which seem to have formed under conditions of almost perfect fractional crystallization

mechanical twinning of plagioclase in a deformed meta anorthosite the production of m twinning mechanical twins on both the albite and pericline laws are well developed on an optical scale in basic plagioclase from the harris meta anorthosite where the rock is affected by closely spaced shear fractures associated with pseudotachylite formation in some cases the twinning is accompanied by kinking or intracrystalline fractures the twins may be periodic and form a ladder structure and sometimes appear to intersect on an optical scale showing structures which very closely resemble those seen in microcline both albite and pericline twins are lenticular as observed by tem but isolated twin tips were rarely seen no dislocations are associated with the twin tips the twins in the optically observed ladder structure when thicker than 2 m have themselves a very fine secondary ladder structure consisting of periodic 200 600 nm lenticular twins which impinge on the perpendicular twin wall intersecting twins were also observed and where two sets of equally thick twins intersect m twinning develops as shown by selected area diffraction the twin formation is analyzed in terms of the plagioclase structure and a coherent model for twin nucleation proposed true twins can develop in plagioclase only if the al si distribution is unchanged or nearly so after deformation mechanical twinning is quite easy in low plagio clases between an100 and about an30 which have p 1 or i 1 lattices or domains with i 1 type structures only one kind of nucleus can develop coherently in a single crystal but it may grow to give either an albite or a pericline twin periodic nucleation and growth give complex textures the qualitative variation of the twin energy as a function of the obliquity is given for different twin shapes and degrees of al si order m twinning arises mechanically by coherent growth and interference of the strain fields

effect of anisotropy and groundwater system geometry on seepage through lakebeds 2 numerical simulation analysis abstract the interaction of lakes and groundwater is controlled partly by the geologic framework through which the water flows two interrelated geometric factors of the groundwater system that affect flow are overall geometry of the system and anisotropy of the porous media within the system numerical simulation analysis was made for variations in the coefficient of anisotropy for each of several lake and groundwater settings having different geometric configurations these analyses indicate that for a given geometric setting as the anisotropy of geologic materials decreases seepage from a lake decreases and depth of the local groundwater flow system associated with the lake increases transformation of scale of groundwater systems that have anisotropic media to isotropic equivalents results in a change in the overall geometry because of the different slopes of the water table and lakebed resulting from the scale transformations a series of numerical experiments were made for various geometric configurations for a given anisotropy these analyses indicate that as thickness of the groundwater system decreases relative depth of the local flow system increases and seepage from the lake decreases

regional tree ring based chronology of landslides in the outer western carpathians abstract landslides are a type of mass wasting and denote any downslope movement of soil and rock under the influence of gravity as such they can represent a dangerous natural hazard process especially in case that they affect inhabited areas or transport infrastructure because the occurrence of landslides is typically favoured by terrain and lithological conditions the process is frequently concentrated in relatively small isolated regions exhibiting suitable initial conditions of terrain instability extensive regional assessments of landslide activity have been used in the past to uncover common triggers and process patterns mostly in the aftermath of large regional disasters by contrast however regional reconstructions of past landslide activity have not been realized with dendrogeomorphic techniques and with the aim to date past landslide histories over extended time periods and with annual dating precision this study therefore aims at disentangling landslide dynamics at the regional scale covering ca 600 km2 by using growth ring records of trees that grow on active landslides the studied area of the host nsko vsetinska hornatina mts central europe is well known for its high landslide activity but has so far been lacking a detailed chronology of past events to this end we dated past activity on 26 landslide bodies using tree ring series from 1322 disturbed trees to reconstruct 327 landslide reactivations during the last century the reconstructed landslide database allowed correlations between landslide types and their frequencies or occurrence as well as inferences between selected morphometric parameters with landslide frequency and magnitude we also observe periods of increased landslide activity 1940s 1960s 1980s and 1990s and events of regional importance e g 1961 1985 and 1997 as well as a significant decrease in landsliding during the last two decades

carbonate deposition pyramid lake subbasin nevada 4 comparison of the stable isotope values of carbonate deposits tufas and the lahontan lake level record abstract in this paper the fundamental importance of changes in hydrologic balance and hydrologic state on the 18o and 13c values of water and dissolved inorganic carbon dic in lakes of the lahontan basin is illustrated abrupt changes in 18o and 13c values of carbonate deposits tufas from the pyramid lake subbasin nevada coincide with abrupt changes in lake level and hydrologic state minima in lake level at 26 000 15 500 and 12 000 yr b p are associated with relatively heavy 18o and 13c values maxima in the lake level record at 14 000 and 10 500 yr b p are associated with relatively light 18o and 13c values we believe that the correlation between maxima and minima in the lake level and 18o records reflect the fundamental effect of lake level dynamics on the 18o value of lake water evaporation increases the 18o value of lake water whereas streamflow discharge and on lake precipitation decrease the 18o value variation in the 18o value of lake water therefore indicates change in the hydrologic balance increases in 18o accompany decreases in lake volume and decreases in 18o accompany increases in lake volume covariance of 13c and 18o indicates that change in 13c values of dic also accompany change in lake volume we offer the hypothesis first put forward by j a mckenzie that change in the productivity photosynthesis respiration balance is responsible for much of the observed variation in 13c most great basin lakes including lake lahontan experienced changes in hydrologic state during the late wisconsin when a lake becomes hydrologically open the residence time of water decreases the greater the rate of spill the greater the volume of evaporated 18o enriched water removed from the spilling lake and the more negative the 18o value of water remaining in the spilling lake the concentration of dic as well as the concentrations of photosynthesis limiting nutrients e g phosphorus nitrogen silica molybdenum decrease as spill increases increasing rates of spill therefore lead to overall decreases in photosynthetic rates relative to respiration rates and as a consequence the 13c values of dic become more negative

alkali feldspar microtextures as provenance indicators in siliciclastic rocks and their role in feldspar dissolution during transport and diagenesis abstract alkali feldspars usually exhibit optical or sub optical intergrowths of albite and k feldspar known generically as perthite which have morphologies and crystallographic characteristics that are distinctive of the igneous or metamorphic environment in which they grew and cooled to surface temperatures we review the current terminology and understanding of how the microtextures form and discuss their role in feldspar dissolution during weathering transport and diagenesis we show how microtextures can be used as provenance indicators in arkosic siliciclastic rocks using examples from the fulmar formation a reservoir rock in the upper jurassic humber group in the central north sea in which feldspar dissolution is a major source of secondary porosity we describe the most effective techniques for routine characterization of which the most practical is back scattered electron imaging in a scanning electron microscope often coupled with cathodoluminescence we provide an atlas of the main types of perthitic intergrowth likely to be encountered in igneous and metamorphic rocks worldwide and show how many of the microtextures can be matched in clastic grains in the fulmar formation grains which are preferentially preserved have microtextures that make them relatively unreactive in aqueous fluids at low temperatures and we conclude that provenance has a major impact on reservoir quality detrital grains in the fulmar exhibit authigenic albitization k feldspar overgrowths and replacement and we discuss how diagenetic features can be distinguished from replacive features developed in the protolith

a tem and microprobe study of a two perthite alkali gabbro implications for the ternary feldspar system an unusual magmatic three feldspar syenogabbro occurs 3 m inside the contact of the klokken gabbro syenite stock it contains plagioclase mesoperthite and cryptoperthite together with a low temperature symplectite intergrowth textural relationships have been investigated by cathodoluminescence bulk chemistry by microprobe and exsolution microtextures and intracrystalline boundaries by tem the mesoperthite has a bulk composition around or26ab52an22 well outside accepted limits of ternary feldspar solid solution it is a mainly coherent lamellar intergrowth of sodic andesine and orthoclase with incipient mtwinning the cryptoperthite bulk composition around or61ab33an6 is a coherent lamellar intergrowth of orthoclase and sodic low oligoclase the compositions of the exsolved phases have been estimated the meso and cryptoperthite crystals have sharp boundaries with each other

authigenic calcium carbonate flux in groundwater controlled lakes implications for lacustrine paleoclimate records groundwater dominated lakes are an important feature of many landscapes their sediments are a particularly valuable source of paleoenvironmental information in semiarid regions where perennial lakes may otherwise be scarce where groundwater and lake composition are favorable carbonate mineral precipitation evaporative concentration of lake water and microbial processes can combine to strongly deplete dissolved ca relative to influent groundwaters the authigenic carbonate flux acf can then become limited by water column cation availability and thereby be coupled to groundwater inflow rates and aquifer recharge here we analyze sedimentary records from two marl producing groundwater controlled lakes and demonstrate a link between one dimensional acf and the palmer drought severity index pdsi a measure of land surface wetness in a restricted outflow lake with high carbonate alkalinity acf is enhanced during historically wet climatic periods in response to increased aquifer recharge rates acf in this lake declines during droughts a neighboring dilute lake with a high rate of groundwater outflow shows comparatively weak coupling between acf and pdsi history ionic chemistry carbonate mineral equilibria and 13 c patterns of dissolved inorganic carbon show that the sensitivity of the acf signal depends on the degree of evaporative evolution of lake water and the mineral saturation state of the water column under conditions of stratification and ice cover copyright 2005 elsevier ltd

cryptoperthites and cooling rate in a layered syenite pluton a chemical and tem study alkali feldspars in the klokken layered syenite south greenland are optically either coarse turbid deuteric patch perthites or clear unaltered fine braid microor cryptoperthites irregular clear volumes can be found in most turbid grains electron microscopy shows that all clear crystals or volumes are cryptoperthites in which the periodicity of the exsolution lamellae increases systematically with distance from the roof of the intrusion from 40 nm to 300nm they are composed of low albite and diagonally associated maximum microcline a secondary coarsening is responsible for optically visible braid microperthites the layered series consists of interleaved granular syenites and coarser grained laminated syenites with mineral layering microprobe analyses show a downward decrease in ca and ba in the granular syenite feldspars consistent with chilling from the roof inwards most laminated syenite feldspars contain 1 an increasing to 5 in mafic layers the periodicity of the exsolution lamellae in the laminated syenite feldspars is consistently up to twice that in adjacent granular syenites periodicity is not influenced by ab or or an content but high an feldspars have continuous zig zag intergrowths while others are more lozengeshaped lamellar periodicities largely reflect cooling rate in the pluton cooling times in the exsolution interval were probably about 103 104 years at the top of the series whereas existing experimental data suggest that the periodicities would be reached in a few days or years the periodicities at the top of the granular series are only slightly greater than experimentally determined initial wavelengths for spinodal decomposition suggesting that little or no coarsening occurred despite the long cooling times coarsening did occur lower in the pile framework ordering and twinning must slow or stop coarsening the difference in periodicity between the granular and laminated syenite series may be caused by differences in amount of water incorporated in the feldspar structure from the magma the exsolution of this water at low temperatures could be the cause of the deuteric unmixed patch perthites small volumes of cryptoperthite which have escaped deuteric unmixing may be common in igneous rocks in general and may be useful relative indicators of cooling rate

numerical simulations of crystallization processes of plagioclase in complex melts the origin of major and oscillatory zoning in plagioclase numerical simulations of the growth of a large crystal face of plagioclase in response to an instantaneous undercooling below the equilibrium temperature are presented for model granodiorite and basalt melts with varying water contents the simulations suggest that the anorthite content of plagioclase decreases uniformly from the composition in equilibrium with the bulk melt as undercooling is increased and that the water content in the melt has little influence on this result comparison of the simulations with sharp compositional changes in natural profiles suggests that undercoolings of tens of degrees c can be rapidly imposed on plutonic phenocrysts large changes of undercooling most likely result from chilling of the magma and local convection around growing crystals the observation in experiments that growth rate does not increase rapidly with increasing water content in the starting melting composition can be attributed to the concentration of water at the crystal face during growth the action of water to reduce liquidus temperature and undercooling has a greater effect on growth rate than its action to increase transport rates even at large undercooling there is no significant increase in temperature at the interface caused by the release of heat of crystallization

trough structures in the western syenite of kungnât s greenland mineralogy and mechanism of formation in the western layered syenite stock of the kungn t complex close to the intrusion wall there are two groups of regularly spaced horizontally aligned stacks of infilled troughs these features resemble to some extent the trough layering within the uza trough zone of the gabbroic skaergaard1 intrusion such features have never before been described in syenitic rocks the lower group comprises six stacks of infilled troughs the upper group comprises seven the two groups are vertically separated by about 10 m of sparsely layered syenite the infilled troughs in the upper group are stacked vertically those in the lower group gradually shift laterally and appear to converge over an antiformal structure it is not possible to measure the plunge of the troughs due to outcrop geometry troughs are up to about 80 cm deep the material filling the troughs is more melanocratic than the syenite that surrounds them individual troughs exhibit normal grading the syenite within the troughs contains large amphibole and biotite oikocrysts faintly layered syenite occurs laterally between stacks minerals in the host syenite are more ferroan than those in the troughs this is thought to represent re equilibration with residual melt feldspar textures irregular pyroxene and apatite zoning and the presence of irregular shaped amphibole patches within pyroxene grains all imply alteration by a pervasive deuteric fluid in both troughs and host syenite we suggest the following hypothesis for the formation of the troughs a mafic crystal sheath which grows on the walls of the magma chamber becomes detached and flows downwards the descending slurry forms a series of regularly spaced streams which erode trough shaped channels into the crystal pile at the base of the chamber uneroded crystal material separates the channels crystals are deposited from these streams successive streams flow over each other to generate stacks of troughs

zoned ternary feldspars in the klokken intrusion exsolution microtextures and mechanisms the microtextures developed during relatively slow cooling as a function of bulk composition in zoned ternary feldspars from syenodiorites and syenites in the klokken intrusion described in the preceding paper were determined by tem and their origin and evolution deduced the feldspars normally have a plagioclase core and an alkali feldspar rim cores become smaller and rims larger and the an content of both decrease with distance from the contact of the intrusion the following microtextural sequence was observed the inner plagioclase cores are homogeneous oligoclase andesine with albite growth twins only but are crypto antiperthitic towards the outer core at first small platelets of low sanidine a few nanometres thick and up to 10 nm long occur sporadically only on albite twin composition planes with further increase in bulk or they are homogeneously distributed in the plagioclase thicker through going plates in platelet free areas are found which induce albite twins in the surrounding plagioclase the microtextures in the rims are regular cryptomesoperthitic with 601 lenses or lamellae depending on the bulk or content of low sanidine in albite twinned low oligoclase andesine albite and pericline twins in plagioclase in an m twin relationship together with lenticular low sanidine were found in only one small area the overall diffraction symmetry of the mesoperthites is monoclinic showing that exsolution started in a monoclinic feldspar whereas that of the antiperthites is triclinic the intermediate zone between the core and rim is more complex and microtextures vary over distances of a few micrometres the cryptomesoperthites are very regular where or rich and probably arose by spinodal decomposition the platelets in the outer cores arose by heterogeneous nucleation on twin composition planes and by homogeneous nucleation elsewhere near the intermediate zone they coarsened to give larger plates which induced albite twins in the plagioclase because of the zoning microtextures that were initiated in areas of given composition can propagate laterally into zones of different composition a diagram is given showing the relationship between ternary bulk composition and the microtexture developed in coherent perthitic alkali feldspars and plagioclases from slowly cooled rocks

high temperature fluid rock interactions in a layered syenite pluton variation in mineral composition with stratigraphie height in layered igneous intrusions is generally taken to indicate progressive fractional crystallization and following pioneering work on the skaergaard complex1 petrologists have used this variation in modelling the evolution of magma bodies in cooling plutons however major chemical changes may occur in circulating deuteric fluids2 3 in the klokken south greenland layered syenite we have discovered that mineral compositions vary both along and normal to the strike of individual layers and we argue that major chemical changes have occurred in a circulating aqueous fluid constrained to move along relatively permeable high temperature aquifers in the layered series

ground water processes controlling a prairie lake s response to middle holocene drought lake response to climate forcing is commonly regarded as being controlled by within lake processes we present a case from the northern great plains in which holocene drought response recorded in lake sediments was determined by changes in chemical characteristics of source ground water middle holocene ostracode assemblages were dominated by halophylic limnocythere staplini indicating increased lake water salinity yet the oxygen isotope values in this period decreased by 2 to 3 contrary to expectations of evaporative dominance we infer from these proxy records and ground water flow model results that the paleoclimatic record in the lake was mediated by changes in ground water catchment area and by reduction in evapotranspiration accompanying desiccation of peripheral lake basins

a hydrous ca bearing magnesium carbonate from playa lake sediments salines lake spain sediments of playa lake salines se spain contain a carbonate mineral characterized by x ray diffraction peaks very similar to but systematically shifted from those of pure magnesite analyses sem ir and raman spectroscopy dta tga and icp indicate the mineral is a hydrous ca bearing magnesium carbonate with the chemical formula mg sub 0 92 ca sub 0 08 co 3 3h 2 o thermal characteristics of the mineral are similar to those of other known hydrated magnesium carbonates x ray and electron diffraction data suggests a monoclinic system p21 n space group with unit cell parameters of a 6 063 6 b 10 668 5 and c 6 014 4 aa and beta 107 28 degrees

the interaction of lakes with variably saturated porous media numerical simulation of variably saturated porous media indicates that groundwater recharge is variable in time and space depending on the thickness of the unsaturated zone through which infiltrating water must move the resulting complex transient groundwater flow systems have significant impact on contiguous surface water in very permeable media small local closed groundwater flow systems can develop and dissipate within a few weeks to several months after major recharge these have a direct effect on contiguous surface water by alternately causing seepage to and seepage from the surface water the transient nature of these flow systems indicates that reversals of the direction of groundwater flow may be common in less permeable media the same complex flow systems may occur but the time for development and dissipation is much greater for example it is conceivable that small local flow systems may exist for many months or years as a result of major recharge therefore directions of flow in such systems are more stable and the effect on contiguous surface water also is more stable the findings of this study indicate that wells and groundwater quality sampling sites need to be carefully located to define accurately water table configuration groundwater recharge direction of seepage through the beds of surface water bodies and complex geochemical processes related to changing directions of groundwater flow

sedimentary features of the nunarssuit and klokken syenites s greenland summary the sediment like features of two layered syenites are described and reviewed in the light of recent suggestions that layering in gabbros maybe produced by in situ crystal growth in a near rigid medium in the nunarssuit syenite igneous layering is normally graded sharp mafic bases becoming more feldspathic upwards and channel structures some with breccias and extreme concentrations of mafic phases are evidence of magmatic currents contorted bedding provides evidence of c 15 m of crystal mush in the chemically similar klokken laminated syenite the layers are inversely graded with well sorted horizons of hedenbergite or fayalite at the top of graded units current bedding and rare channels are superimposed o n this inverse grading and striking load structures occur at junctions with interbedded horizons of granular syenite demonstrating the presence of 3 m of crystal mush the klokken laminated syenites are slightly more fractionated than nunarssuit and approach the water rich termination of fractionation of olivine clinopyroxene and ternary feldspar cumulus phases in nunarssuit layers are chemically less fractionated than those in normal rock and occur with cumulus chevkinite and zircon consistent with separation of suspended crystals from melt but cumulus minerals at klokken do not show this type of chemical contrast calculated magma densities and viscosities show that crystal settling of all phases was feasible in both complexes if the magmas were hydrous druses at klokken suggest that the intercumulus liquid was water saturated during load structure formation sorting of locally derived crystals by currents accounts for the nunarssuit layering but at klokken the crystal supply was controlled by order of nucleation and growth rate effects although crystal settling occurred

sidewall crystallization in the klokken intrusion zoned ternary feldspars and coexisting minerals the syenitic layered series in the klokken intrusion is surrounded by a zone 500 m thick of nearly structureless unlaminated syenite followed outwards by a zone of vertically banded gabbro 200 m thick at the outer rim the unlaminated syenite is intrusive into the gabbro and develops a thin 2 m transition zone of syenodiorite at the contact a traverse across the vertical transition zone and inwards towards the layered series was sampled with a portable drill mafic silicates olivine clinopyroxene biotite show inward evolution in fe fe mg across the syenodiorite unlaminated syenite zones feldspars change rapidly across the syenodiorite zone from rocks dominated by plagioclase in some cases together with two alkali feldspars one a mesoperthite or cryptomesoperthite the other a cryptoperthite to rocks in which plagioclase is seen only rarely as cores to cryptomesoperthitic alkali feldspar crystals plagioclase is absent from the layered series

climate driven hydrologic transients in lake sediment records calibration of groundwater conditions using 20th century drought abstract the effect of 20th century drought on groundwater and lakes in a climatically sensitive area of the northern great plains grant county western minnesota was investigated by analysis of lake sediments and historical air photos in conjunction with groundwater flow simulations drought caused an observed 4 0 to 5 1 m lake head decline between 1923 and 1938 all but three either dried completely or declined to 210 pb dated sediment core was analyzed for ostracode species distribution and geochemistry of c rawsoni shells 18 o 13 c mg ca sr ca mg ca and 13 c increased during drought at the same time that salinity tolerant ostracodes thrived suggesting increasing salinity however 18 o decreased during drought anti correlative with mg ca a numerical model for transient response of groundwater flow to drought modeled after that of 1923 38 was constrained by drought end recessional strand lines observed on air photos of one lake with strand line elevations inferred from bathymetry simulated lake water level declines in the first 15 drought years were consistent with strand line elevations the rate of decline was exponential at drought onset slowing as water in lakes and wetlands receded to below land surface and lake evaporation declined a near steady state was attained between 40 and 50 simulation years after onset of drought with the water table from 1 5 m below the level of dry lakebeds and only the two deepest lakes still holding water they were however greatly constricted in area and depth simulated evaporation fluxes were reduced by over 50 within 15 years despite increased et rates due to lake area constriction and water table declines both relate to land surface morphology beneath and around lakes model results suggest that lake bed elevations exert control on the rate and ultimate level to which groundwater is depressed by drought the deepest lakes in any region will tend to become the focus of groundwater flow during sustained drought once lakes around it dry out the unexpected finding of decreasing shell 18 o in response to drought is interpreted as some combination of source and or evaporation reduction effects such as seasonality of recharge precipitation or reduced et flux from wetlands that seep back into lakes

kiglapait mineralogy v feldspars in a hot dry magma the lithology of the 1 305 ga kiglapait intrusion is dominated by a lower zone of troctolite succeeded by an upper zone of olivine gabbro ferrodiorite and syenite with olivine composition of pure fayalite the feldspar composition of the intrusion varies from an 68 to an 9 over a thickness of 8 4 km from the base to a sandwich horizon under an upper border zone the anhydrous nature of the kiglapait syenites is shown by their high temperature by the loss of minor biotite up stratigraphy in the intrusion and the absence of amphibole the end stage feldspar of the kiglapait syenites is that of a solidus embedded in a solvus in a 3 kbar eutectic at 1000 c the end member assemblage at temperature and pressure is invariant the final bulk composition is relatively an rich an 11 with a composition of x or 1 3 when projected to the ab or sideline the experimental feldspar solvus when corrected for the effects of an and ba and referred to 3 kbar penetrates the solidus and fits the experimental tie lines these conditions precede a stage of local coarsening under subsolidus conditions that is found in colloform symplectites invading mesoperthite the oligoclase orthoclase symplectites are iso compositional with their host mesoperthites the coarsening is assumed to be related to a plausibly f rich vapor phase that is locally consumed with time the observed phase compositions indicate the end of exsolution at 800 c at 3 kbar on the binodal solvus

calorimetric and phase diagram approaches to two feldspar geothermometry a critique two feldspar geothermometers based on the thermodynamic properties of the limiting binaries ab an and ab or are unsatisfactory because the ternary nature of the feldspar pairs cannot be accounted for and critical points are not generated ternary mixing data are mandatory there are also serious shortcomings in the experimental ternary phase relation data available at present and even ambiguities in the interpretation of the thermodynamic properties of the binaries which preclude development of a practical geothermometer recent work on feldspar zoning patterns in rocks allows some deductions to be made concerning the geometry of the ternary system but there are dilliculties in the interpretation of natural feldspar pairs framework order disorder presents problems which may be insuperable

estimating groundwater exchange with lakes 2 calibration of a three dimensional solute transport model to a stable isotope plume a three dimensional groundwater flow and solute transport model was calibrated to a plume of water described by measurements of 18o and used to calculate groundwater inflow and outflow rates at a lake in northern wisconsin the flow model was calibrated to observed hydraulic gradients and estimated recharge rates calibration of the solute transport submodel to the configuration of a stable isotope 18o plume in the contiguous aquifer on the downgradient side of the lake provides additional data to constrain the model a good match between observed and simulated temporal variations in plume configuration indicates that the model closely simulated the dynamics of the real system the model provides information on natural variations of rates of groundwater inflow lake water outflow and recharge to the water table inflow and outflow estimates compare favorably with estimates derived by the isotope mass balance method krabbenhoft et al this issue model simulations agree with field observations that show groundwater inflow rates are more sensitive to seasonal variations in recharge than outflow

spatial variability of late quaternary paleoclimates in the western united states abstract paleoclimatic interpretation of proxy data is complicated sometimes by the appearance of heterogeneous patterns of climatic responses across networks of sites modern climate analogues for the western united states similar to those patterns of atmospheric circulation of 18 000 and 9000 yr b p were examined in order to explain such patterns of spatial heterogeneity modern analogues were defined by comparing modern atmospheric circulation patterns with those simulated by general circulation models maps of temperature and precipitation anomalies of the modern analogues reveal patterns of spatial heterogeneity which resemble the patterns of effective moisture compiled from paleoclimatic data january 1957 was found to be a reasonable 18 000 yr b p analogue and it features isolated areas of increased wetness in the northern great basin and increased dryness in the northwest interior analogues for 9000 yr b p from a composite of 11 augusts display patterns of spatial heterogeneity of effective moisture over most of the mountainous areas the analogues suggest that spatial heterogeneity of climate is the rule rather than the exception over much of the western united states with the climatic anomalies at any particular time representing the outcome of the mediation of large scale atmospheric circulation controls by smaller scale topographic features