variable parent magmas and recharge regimes of the parinacota magma system n chile revealed by fe mg and sr zoning in plagioclase abstract zoning patterns of an content and fe mg and sr concentrations in plagioclase phenocrysts in andesites from parinacota volcano n chile reflect alternating recharge events with two chemically distinct mafic magmas these magmas are characterized by low and high sr contents similar to two recent mafic flank eruptions one end member basaltic andesite shows large sr enrichment and heavy rare earth depletions and thus equilibrated with lower crustal rocks at depth where plagioclase high sr is unstable and garnet high hree y is stable a second end member magma is lower in sr ba contents and has ree patterns typical for parent magmas elsewhere in the central andes the number of recorded recharge events increases after a catastrophic sector collapse and during the subsequent rebuilding of the stratocone variations of an fe and mg contents and morphology of zones suggest also changes in water pressure including decompression under water under saturated and water saturated conditions evidence for decompression is more present in post collapse samples suggesting that the change in the volcano dynamics involves changes in magma chamber location this shows the importance of the cone collapse event in the volcano s magmatic evolution we propose that both end members are only seen at the surface of parinacota volcano because of the particular dynamics of this volcanic system and that similar processes might occur in other volcanic centres of the central volcanic zone

radiative transfer modeling of near infrared reflectance of lunar highland and mare soils 1 with near infrared hyperspectral data sets returned from kaguya selene and chandrayaan 1 s moon mineralogic mapper m3 accurate evaluation and interpretation of lunar data sets with higher spectral resolution has never been more critical here we test a new radiative transfer spectral modeling algorithm to determine composition from hyperspectral reflectance spectra of lunar soils data for 19 lunar mare and highland soil samples previously characterized by the lunar soil characterization consortium are used for validation spectral fits are made using a goodness of fit metric considering spectral shape spectral contrast spectral slope and iron abundance high precision fits are achieved for nearly every soil with this algorithm using a plot of spectral shape relative to the ratio mg i e molar mg mg fe 100 determines the winning model and composition mg is determined with an average difference of 11 15 and 3 8 units before and after a correction is applied respectively mineralogy is determined with an average difference of 5 15 vol depending upon the mineral constituent

effect of mantle compressibility on the thermal and flow structures of the subduction zones 1 the heat generated by viscous dissipation is consistently evaluated using a 2 d compressible subduction model with variations of mantle rheology constant as well as pressure and temperature dependent viscosity dip age and velocity of the subducting slab for comparison we also conduct 2 d incompressible subduction calculations with the same conditions and parameters used in the compressible formulation the effect of compressibility on the thermal and flow structures of the subduction zones is relatively small and concentrated along the base of the mantle wedge with temperature differences 100 c and differences in kinematic energy of the mantle wedge 1 between compressible and incompressible models mantle rheology has a stronger effect on thermal and flow structures than mantle compressibility as well as the variations of dip age and velocity of the subducting slab the heat from viscous dissipation in the compressible model increases the slab temperatures over the incompressible model 70 c as a result of additional conduction across the slab surface constant viscosity and thinning of the thermal boundary layer caused by viscosity reduction pressure and temperature dependent viscosity

radiative transfer mixing models of meteoritic assemblages 1 a spectral mixing model for the expected conditions on asteroid surfaces based on hapke s radiative transfer theory for intimate mixtures is presented this model calculates the visible near infrared reflectance spectrum of an intimate mixture incorporating the modal mineralogy the mineral chemistry the particle size and the degree of space weathering as factors and includes an improved treatment for the spectral effects of coarse grained fe ni metal this model can reproduce the spectra of geologically plausible mixtures of silicate components and meteorites with known mineral abundances chemistry and particle sizes we compare the model spectral effects of the coarse grained fe ni metal naturally present on asteroid surfaces to the spectral effects of submicroscopic iron produced by lunar style space weathering the model spectral effects of large asteroid surface concentrations of coarse grained fe ni metal are similar to the spectral effects of smfe in some cases we model the composition of asteroid 4 vesta and find it to be consistent with a minimally space weathered eucritic composition finally we predict the spectral properties of some example of ordinary chondrite parent bodies when modeled with particle sizes matching the optically dominant particle size of the lunar surface and minimal abundances of smfe these model ordinary chondrite parent bodies plot outside the s iv asteroid field on a band area ratio versus band i center plot we find that a combination of larger particle sizes and increased smfe abundances is the most effective way to move these models into the s iv field

discriminating assimilants and decoupling deep vs shallow level crystal records at mount adams using 238u 230th disequilibria and os isotopes article a suite of 23 basaltic to dacitic lavas erupted over the last 350 kyr from the mount adams volcanic field has been analyzed for u th isotope compositions to evaluate the roles of mantle versus crustal components during magma genesis all of the lavas have 230 th 238 u n1 and span a large range in 230 th 232 th ratios

internal heating and thermal constraints on the mantle we have carried out numerical simulations to study the average temperature and thermal structure of an internally heated mantle it is found that in an incompressible mantle the hottest parts are localized in regions of slow flow in the middle and upper mantle whereas in a compressible mantle they occur over laterally extensive regions near the core mantle boundary cmb for chondritic concentrations of heat producing elements hpe s the average thermal conductivity in the mantle must be high to avoid heating the core and the temperature of the cmb tcmb is low to avoid large scale melting the mantle may have been extensively molten in the archaean

magma evolution and ascent at volcanic arcs constraining petrogenetic processes through rates and chronologies large 226 ra excesses in a number of mafic arc magmas and geophysical observations of earthquake hypocenters locations indicate that mafic melts can get transferred from source to surface within days to 1 kyr decreasing 226 ra 230 th disequilibria with increasing sio2 in co magmatic suites of individual arc volcanoes suggest that magma differentiation often occurs on timescales of a few thousand years in closed systems or less in open systems however the rapid decrease of global 238 u 230 th disequilibria with increasing sio2 within basaltic andesite compositions suggests that rapid closed system differentiation does not typically produce more evolved compositions from mafic parental magmas with large 238 u excesses in the case of rapid magmatic evolution open system processes are frequently involved in the production of andesites and dacites and the data imply that the open system component is close to 238 u 230 th secular equilibrium melts modeling of magma evolution at santorini in the aegean arc provides corroborating evidence from an individual well studied arc volcano that closed system fractional crystallization fails to produce the more evolved compositions and increasing 87 sr 86 sr ratios with increasing sio2 from andesites to rhyolites suggests assimilation of old crust is involved these observations can be conceptualized through thermal modeling of basaltic sill injections into the lower and upper crust melt production in deep crustal hot zones provides an explanation for low 238 u 230 th disequilibria of the evolved magmatic component as significant accumulation of evolved melts through partial re melting of previously intruded basalts requires n100 kyr incubation time at typical magmatic flux rates thermal modeling also provides a framework for understanding assimilation of old upper crustal rocks in more mature magmatic systems further insights into magmatic evolution can be gained from dating of minerals from mafic intermediate and felsic arc magmas a many u th mineral isochrons in mafic arc magmas yield ages significantly older than those

thermal expansion measurements at very high pressure systematics and a case for a chemically homogeneous mantle new data on thermal expansivity of iron to over 400 kbar in laser and electrically heated diamond anvil cells and on mgo and forsterite from spectroscopic data to over 200 kbar and previously measured adiabats boehler 1982 imply that at high pressure may be described by a constant value of 1n 1nv t 5 5 0 5 this behavior is supported by previous measurements at lower pressures on a large variety of materials densities of magnesio wustite and silicate perovskite in a pyrolitic ratio calculated at lower mantle conditions using a finite strain equation and at high pressures using the above systematics match those in prem through the entire lower mantle making a strong case for a uniform mantle

shallow and deep crustal control on differentiation of calc alkaline and tholeiitic magma article u 230 th isotopes 87 sr 86 sr lower crust assimilation the role of changing crustal interaction and plumbing geometry in modulating calc alkaline vs tholeiitic magma affinity is well illustrated by the influence of 70 km thick crust beneath volcan parinacota changes in petrologic affinity correlate with periods of cone building sector collapse and rebuilding of the volcano over the last 52 ka and are well explained by changes in magma recharge regime with increasing recharge and magma output lavas transition from low fe strongly calc alkaline phenocryst rich silicic compositions to medium fe near tholeiitic mafic and aphanitic characteristics strontium isotope data show that the change in magma regime did not affect all parts of the system simultaneously these are characterized by distinctive 87 sr 86 sr ratios which suggest an initially compartmentalized system relatively high 230 th 232 th activity ratios of 0 72 in early erupted calc alkaline lavas are consistent with interaction with high u upper crust low 230 th 232 th activity ratios of 0 55 and up to 33 th excess in younger near tholeiitic lavas correlate with steep ree patterns indicating lower crustal interaction thorium excesses at the time of eruption approach the maximum that can be generated via small degree garnet residual melting in the lower crust or mantle and imply that transit time through the crustal column for the most tholeiitic magmas had to be short on the order of b2 10 4 yr in contrast lavas with greatest calc alkalinity are also at or near secular

radiative transfer modeling of the effect of mineralogy on some empirical methods for estimating iron concentration from multispectral imaging of the moon 1 several empirical models for deriving feo concentration from multispectral imaging of the moon are tested using model spectra of lunar soil the spectra are computed from a radiative transfer model based on the work of bruce hapke and cover the system plagioclase orthopyroxene clinopyroxene olivine ilmenite and vary the mg number and maturity over lunar relevant ranges the high degree of correlation between measured and spectrally estimated feo when applied to lunar soils returned by apollo provides constraints on the abundance of certain rock types and these constraints are consistent with geochemical mixing models good feo estimates are yielded for mixtures of plagioclase clinopyroxene and ilmenite by all the algorithms it is found that all spectral algorithms show large errors in the presence of significant olivine and significant errors in the presence of ferroan orthopyroxene the best performance is shown by the lemouelic et al 2002 algorithm that is also insensitive to topographic shading in the absence of ilmenite previously noted differences between spectrally derived feo and that derived by other techniques are all consistent with reported mineralogical differences

space weathering on airless bodies resolving a mystery with lunar samples using new techniques to examine the products of space weathering of lunar soils we demonstrate that nanophase reduced iron npfe0 is produced on the surface of grains by a combination of vapor deposition and irradiation effects the optical properties of soils both measured and modeled are shown to be highly dependent on the cumulative amount of npfe0 which varies with different starting materials and the energetics of different parts of the solar system the measured properties of intermediate albedo asteroids the abundant s type asteroids in particular are shown to directly mimic the effects predicted for small amounts of npfe0 on grains of an ordinary chondrite regolith this measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids

rheological models and interpretation of postglacial uplift accepted 1989 february 1 received 1989 january 28 in original form 1988 september 26 summary paper investigates four generalized maxwebl bodies gmbs and the classical maxwell body cmb with respect to their potential to explain postglacial uplift the gmbs are the lomnitz body defined by a logarithmic creep law the q power law body defined by a power law dependence of the quality factor on frequency the caputo body defined by a special stress strain relation with memory and the burgers body the burgers body is a 4 parameter model the other gmbs have 3 and the cmb has only 2 parameters theoretical uplift curves are calculated for simple space time models of the canadian and fennoscandian deglaciations and hedgehog inversion yields the successful model parameters the gmbs explain the data better than the cmb the parameters of the burgers body are only rather weakly constrained because of trade offs among them from the success of the gmbs we conclude that long time scale transient creep is a possible rheological behaviour of mantle rocks viscosity extrapolation from the time constant of postglacial uplift about 10 ka to the time constant of mantle convection roughly 100 ma is made with the effective viscosity and yields approximately ld2 pas q power law body loz3 pas caputo body and loz5 pas lomnitz body hence postglacial uplift does not strongly constrain the long time scale mantle viscosity it provides only a lower bound about loz1 pas this value follows from data interpretation with the cmb model in which steady state creep is present alone rayleigh number estimates for whole mantle convection are clearly supercritical for the cmb the q power law body and the caputo body but only about critical or even subcritical for the lomnitz body both postglacial uplift and mantle convection is satisfactorily explained by the cmb the q power law body and the caputo body

compositional variations of the lunar crust results from radiative transfer modeling of central peak spectra 1 we present model mineralogy of impact crater central peaks combined with crustal thickness and crater central peak depth of origin models to report multiple perspectives of lunar crustal composition with depth here we report the analyses of 55 impact crater central peaks and how their compositions directly relate to the lunar highlands sample suite a radiative transfer model is used to analyze clementine visible plus near infrared spectra to place compositional constraints on these central peak materials central peaks analyzed are dominantly magnesian and plagioclase poor strong compositional similarities to lunar mg suite materials are evident relative to crustal thickness estimates central peak mineralogy becomes more plagioclase rich as the crust thickens relative to the crust mantle boundary the origin of peaks with dominantly mafic mineralogy are confined to the lower crust and primarily within the south pole aitken and procellarum kreep terranes pkt additionally central peaks with anorthositic mineralogy 60 vol plagioclase are transported to the surface from all depths in the crustal column and confined to the feldspathic highlands terrane fht the discovery of mafic and magnesian materials consistent with mg suite rocks of the sample collection in all lunar terranes suggests that the process and sources that give rise to these types of rocks is not unique to the pkt and not necessarily dependent on incompatible elements for formation the identification of ferroan and magnesian anorthositic material near the crust mantle boundary of the fht is also inconsistent with an increasing mafic feldspar ratio and mg with depth in the crust

viscoelastic responses of a hard transition zone effects on postglacial uplifts and rotational signatures abstract recent studies from laboratory s karato 1989 and monte carlo inversion y ricard et al 1989 have argued that the transition zone between 400 and 670 km depth may be stiffer than the lower mantle and the upper mantle above it using a five layer viscoelastic spherical model we have calculated the transient displacements of postglacial rebound the induced polar motions and the temporal variations of the geopotential up to degree eight of the zonal coefficients we have compared two models a one with two viscoelastic layers separated at 670 km and b the other with three layers in which a hard garnet layer lies between the upper and lower mantle forward modelling shows that it may be possible to discern the presence of a hard garnet layer with a viscosity of at least ten times greater than the upper mantle on the basis of uplift data near the center of the former laurentide ice sheet and from polar wander and j 2 data temporal variations of higher gravity harmonics such as j 6 and j 8 can potentially place even tighter constraints on the rheological properties of the hard transition zone a lower mantle viscosity between 2 and 4 10 22 pa s is generally preferred in models with a garnet layer which may be as large as 50 times more viscous than the upper mantle

model near infrared optical constants of olivine and pyroxene as a function of iron content the imaginary coefficients of the complex index of refraction of olivine low ca orthopyroxene and high ca clinopyroxene are derived as a function of iron content and wavelength over the spectral region 0 4 to 2 5 m from reflectance spectra of powders and hapke radiative transfer theory reflectance spectra as a function of composition and grain size are computed and compared i find that while spectral effects of variations in these parameters are similar they are distinguishable variations in iron content do not explain all the observed spectral variations in the spectra of the samples investigated

u series evidence for crustal involvement and magma residence times in the petrogenesis of parinacota volcano chile in this study we present th u disequilibria as well as radiogenic and trace element data for recent volcanic rocks from the nevados de payachata volcano which erupted through 70 km of continental crust in the central volcanic zone of the andes 18 s 69 w both lavas and mineral separates were analyzed by mass spectrometry for 238u 230th disequilibria the lavas are characterized either by 230th enrichment or depletion relative to its parent nuclide 238u mineral separates are used to derive u th isochron ages and these ages compare favorably with inferred stratigraphic ages or k ar ages although in one case the u th age is significantly older than the stratigraphic age despite relatively constant sr nd and pb isotope ratios the lavas display inverse trends in 230th 238u versus ce yb or ba hf diagrams these trends cannot be interpreted by simple two component mixing rather there must be three and perhaps four components involved in the genesis of the parinacota lavas a mantle wedge a slab fluid and a lower crustal component can be identified a sediment component is more difficult to detect as it is difficult to decipher its signature because of the strong crustal influence the existence of binary arrays can be explained by variable amounts of crustal material the process of crust mantle interaction must have been short enough to preserve u th disequilibrium 300 ka

effects on post glacial rebound from the hard rheology in the transition zone summary we analyse the influences of a viscosity increase in the transition zone between 420 and 670 km on the geophysical signatures induced by post glacial rebound ranging from the perturbations in the earth s rotation to the short wavelength features associated with the migration of the peripheral bulge a self gravitating model is adopted consisting of an elastic lithosphere a three layer viscoelastic mantle and an inviscid core the horizontal displacements and velocities and the stress pattern are extremely sensitive to the viscosity increase and to the chemical stratification of the transition zone the hardening of the upper and the chemical density jumps in mantle below the 420 discontinuity induces a channel effect which contaminates the horizontal deformation both in the near field and in the far field from the ice sheets these findings indicate that intraplate geodetic data can be used to put bounds on the viscosity increase in the transition zone and on the amount of chemical stratification in the mantle the stress field induced in the lithosphere by the pleistocenic ice sheet disintegration is a very sensitive function of mantle viscosity stratification the existence of seismic activity along passive continental margins of previously glaciated areas requires a substantial viscosity increase in the mantle with the viscosity of the transition zone acting as a controlling parameter a viscously stratified mantle is responsible for a delayed upward migration of stress in the lithosphere which can account for the seismicity today

the late miocene quaternary antofalla volcanic complex southern puna nw argentina protracted history diverse petrology and economic potential abstract the antofalla volcanic complex avc is located on the southern puna plateau of nw argentina 100 km east of the main axis of the cordillera occidental volcanic arc it lies on the nw se archibarca lineament one of several transverse structures that cut across the andes from chile and divert arc magmatism in se trending fingers across the puna 40ar 39ar dating of volcanic products from the avc reveals a protracted magmatic history from 10 9 to 1 6 ma initial volcanism was characterized by eruption of voluminous rhyolitic ignimbrites deposited directly onto exposed crystalline basement and supracrustal sedimentary rocks these rhyolites record significant geochemical evidence for crustal contamination or derivation by crustal melting which decreases upwards through the pyroclastic sequence they were followed by extrusion of potassic lavas of the shoshonite latite trachydacite suite from 10 1 to 9 5 ma subsequent magmatism 9 1 1 6 ma was of basaltic andesite andesite dacite composition with localized smaller volume dacitic and rhyolitic ignimbrites monogenetic basaltic andesite cinder cones and lava flows were erupted in the quaternary in response to a change to transtensional tectonics in the puna the volcanic sequence is interpreted to record the early development of a lower crustal mash zone at 11 ma where mantle derived arc magmas interacted extensively with felsic lower crustal rocks to produce evolved shoshonitic compositions and crustal melts that erupted to form rhyolitic ignimbrites common at this time throughout the puna after establishment of a steady state mash zone by 9 ma subsequent basaltic andesite andesite magmas show less evidence of felsic crustal contamination and may have developed largely by interaction with previous ultramafic mafic fractionates of early magmas in the lower crust more felsic dacitic magmas appear to have evolved largely by fractional crystallization from basaltic andesites and andesites with widespread evidence of mixing and mingling between magmas of different degrees of differentiation some contamination by upper crustal components is also evident in these dacites but is shown more clearly by small volume rhyolites some of which may again represent predominantly crustal melts epithermal deposits of au and pb zn ag occur within the avc apparently associated with the formation of rhyolite domes the mineralization style is typical of other andean volcanic centres and may be underlain by deeper seated porphyry styles of mineralization extensive blanketing by younger lavas and limited erosion restricts exposure of these altered and mineralized sequences however although the potential for further discoveries beneath cover or at depth in this system appears high

rapid magma ascent and generation of 230 th excesses in the lower crust at puyehue cordon caulle southern volcanic zone chile basaltic to rhyolitic lavas and tephras erupted over the last 70 kyr at the puyehue cordon caulle volcanic complex in the andean southern volcanic zone svz were analyzed for major and trace element sr isotope and u th isotope compositions to constrain the timescales of magmatic processes and identify the subducted and crustal components involved in magma genesis internal u th mineral isochrons from five lavas and three tephra fall deposits are indistinguishable from their eruption ages indicating a short period b1000 yr of crystal residence in the magma prior to eruption the 230 th 232 th ratios define a narrow range 0 80 0 83 compared to that of all svz lavas 0 72 0 97 suggesting that puyehue basalt was derived from a relatively uniform mantle source dacites and rhyolites have the largest u excesses and likely evolved via fractional crystallization of a plagioclase dominated mineral assemblage in contrast basalts have 1 to 6 230 th excesses a characteristic not previously observed in frontal arc stratovolcanoes of the andean svz the 230 th excesses are interpreted to reflect a relatively small degree of fluid flux melting coupled with assimilation and melting of the lower crust lower crustal processes therefore have dampened the 238 u excesses that were generated during fluid addition to the mantle wedge although prior 238 u 230 th 226 ra studies of lavas from other southern svz stratovolcanoes 36 to 41 s have inferred that slab additions and the extent of mantle melting were nearly constant along strike of the arc our results suggest that mash processes envisioned by hildreth and moorbath w hildreth s moorbath crustal contributions to arc magmatism in the andes of central chile contrib mineral petrol 98 1988 455 489 in the northern svz also occur in the southern svz where the crust is relatively thin

imaging spectroscopy earth and planetary remote sensing with the usgs tetracorder and expert systems 1 imaging spectroscopy is a tool that can be used to spectrally identify and spatially map materials based on their specific chemical bonds spectroscopic analysis requires significantly more sophistication than has been employed in conventional broadband remote sensing analysis we describe a new system that is effective at material identification and mapping a set of algorithms within an expert system decision making framework that we call tetracorder the expertise in the system has been derived from scientific knowledge of spectral identification the expert system rules are implemented in a decision tree where multiple algorithms are applied to spectral analysis additional expert rules and algorithms can be applied based on initial results and more decisions are made until spectral analysis is complete because certain spectral features are indicative of specific chemical bonds in materials the system can accurately identify and map those materials in this paper we describe the framework of the decision making process used for spectral identification describe specific spectral feature analysis algorithms and give examples of what analyses and types of maps are possible with imaging spectroscopy data we also present the expert system rules that describe which diagnostic spectral features are used in the decision making process for a set of spectra of minerals and other common materials we demonstrate the applications of tetracorder to identify and map surface minerals to detect sources of acid rock drainage and to map vegetation species ice melting snow water and water pollution all with one set of expert system rules mineral mapping can aid in geologic mapping and fault detection and can provide a better understanding of weathering mineralization hydrothermal alteration and other geologic processes environmental site assessment such as mapping source areas of acid mine drainage has resulted in the acceleration of site cleanup saving millions of dollars and years in cleanup time imaging spectroscopy data and tetracorder analysis can be used to study both terrestrial and planetary science problems imaging spectroscopy can be used to probe planetary systems including their atmospheres oceans and land surfaces

deformation of the core mantle boundary induced by spherical shell compressible convection we derive the single mode mean field equations for spherical shell convection with variable viscosity and compressibility included core mantle boundary cmb topography produced by whole mantle convection is computed for various rheologies and different thermal boundary conditions at cmb results for long wavelength undulations show the extreme sensitivity of these signatures to rheological and equation of state parameters in order to obtain excess ellipticity of about 1 km the activation energy and volume in the lower mantle should be low and the temperatures at cmb around 4 500 k in accord with recent experimental findings

lower mantle viscosity constrained by seismicity around deglaciated regions knowledge of the viscosity structure of the earth s mantle is important for constraining models of mantle convection and isostatic rebound here we show that seismicity around the margins of deglaciated areas provides a constraint on the viscosity of the lower mantle in addition to those previously proposed1 2 calculations using a spherical viscoelastic earth model show that the present day magnitude of the stress fields induced in the lithosphere beneath the now disappeared laurentide and fennoscandian ice sheets is very sensitive to the value of the lower mantle viscosity stresses of 100 bar sufficient to cause seismicity can still remain in the lithosphere for lower mantle viscosities greater than 1022 pa s for lower mantle viscosities of 1021 pa s only a few tens of bars of stress persist in the lithosphere today this influence of lower mantle viscosity on the state of stress in the lithosphere also has implications for the migration of stress from earthquakes and hence for earthquake recurrence times

dynamical influences from thermal chemical instabilities at the core mantle boundary two dimensional time dependent calculations show that the thermal and flow structures can be influenced by the lower mantle thermal chemical instabilities the style of the core mantle boundary cmb deformation in thermal chemical convection is different from that obtained in thermal convection the amplitude of cmb hills is reduced greatly from the depth dependence of thermal expansivity found in recent high pressure experiments

neogene to quaternary broken foreland formation and sedimentation dynamics in the andes of nw argentina 25 s 1 the northwest argentine andes constitute a premier natural laboratory to assess the complex interactions between isolated uplifts orographic precipitation gradients and related erosion and sedimentation patterns here we present new stratigraphic observations and age information from intermontane basin sediments to elucidate the neogene to quaternary shortening history and associated sediment dynamics of the broken salta foreland this part of the andean orogen which comprises an array of basement cored range uplifts is located at 25 s and lies to the east of the arid intraorogenic altiplano puna plateau in the salta foreland spatially and temporally disparate range uplift along steeply dipping inherited faults has resulted in foreland compartmentalization with steep basin to basin precipitation gradients sediment architecture and facies associations record a three phase 10 5 and 2 ma east directed yet unsystematic evolution of shortening foreland fragmentation and ensuing changes in precipitation and sediment transport the provenance signatures of these deposits reflect the trapping of sediments in the intermontane basins of the andean hinterland as well as the evolution of a severed fluvial network present day moisture supply to the hinterland is determined by range relief and basin elevation the conspiring effects of range uplift and low rainfall help the entrapment and long term storage of sediments ultimately raising basin elevation in the hinterland which may amplify aridification in the orogen interior

x ray digital imaging petrography technique development for lunar mare soils remote sensing studies are the primary means of solar system exploration in particular spectral reflectance measurements involve determinations of the nature and compositions of other worlds through analysis of absorption features characteristic of the surface chemistry and mineralogy these studies are particularly applicable to airless solar system bodies e g the moon because atmospheres such as on earth tend to interfere with the reflectance spectrum the precision of the spectral measurements is greatly increased by calibration with actual lunar soils in the past these calibrations were done using particle counting data collected for the study of soil formation processes soil classification and provenance determination these particle counting data while valuable in those areas of study neither identify the true volume percentages of soil particles nor give the true modal values for the various phases i e minerals and glasses which make up the soil grains these data are paramount for accurate spectral reflectance calibrations therefore in this paper a new technique is presented that involves x ray digital imaging of lunar soils using an energy dispersive spectrometer eds on an electron microprobe in contrast to particle counting with an optical microscope the digital imaging method allows precise volume percentages of soil grains to be determined including absolute modal abundances of the various phases locked within the particles as well as their chemistry in order to validate this method for characterization of lunar soils the technique was applied to four apollo 17 soils that were previously described by heiken and mckay 1974 via particle counts with an optical microscope and similar results were obtained in addition to verifying the x ray digital imaging technique the obtained data were applied in order to better understand the lunar soil formational process specifically the variation of particle types with maturity

re examination of crystal ages in recent mount st helens lavas implications for magma reservoir processes u series data for recent mount st helens lavas suggest that crystallization preceded eruption by more than 0 5 ka but are complicated by possible evidence of crystal recycling and or addition of radium to the liquid after crystallization we report new ion and electron microprobe trace and major element data for plagioclase and pyroxene in these recent mount st helens lavas and use these data to reassess 226ra 230th crystal ages by taking into account differences in the partitioning behavior of radium and barium and the effects of impurities in mineral separates revised 226ra 230th model crystallization ages are 2 4 ka for plagioclase with the exception of the 1982 dacite and 0 15 5 7 ka for pyroxene in contrast to previous interpretations no late stage addition of ra to the liquid after precipitation of the minerals is required the variability of ba concentrations measured in plagioclase is too large to be consistent with progressive crystallization from the same liquid or with diffusive re equilibration of xenocrysts with a new host liquid ba heterogeneity limits the residence time of the crystals in a magma at high temperatures and also suggests that in most cases ra th ages have not been significantly modified by ra diffusion into or out of the crystals high 226ra ba in plagioclase in the 1982 dacite relative to the host liquid likely reflects crystallization processes that precluded bulk crystal liquid chemical equilibrium one possibility is that of growth entrapment of surface enrichments during rapid crystallization which could lead to less discrimination between ra and ba than predicted by calculated bulk partition coefficients 226ra 230th crystal ages for the castle creek andesite and basalt that are younger than 230th 238u ages of the same crystals could be explained by mixing of crystals into melts with different 230th 232th ratios by combinations of older and younger crystal growth within the same magma or for the basalt by diffusion of ra into crystals at high magmatic temperatures average plagioclase ages in most of the samples of 2 ka imply that some significant mass fraction of the crystals in each flow was present simultaneously beneath the volcano this observation could be consistent either with simultaneous storage of physically distinct magma batches or with incorporation of a population of similarly aged crystals into each successive magma batch

mantle convection with internal heating and pressure dependent thermal expansivity recent laboratory work 1 suggests that the thermal expansivity of the mantle decreases strongly with pressure determines the buoyancy of plumes and the rate at which plumes lose their thermal signature as they rise and so may be expected to have a strong influence on the temperature and velocity structure of the mantle numerical simulations were conducted on convection in an internally heated compressible mantle including constant and pressure dependent and thermal conductivityk they show that a pressure dependent allows the existence of thermal plumes rising from the core mantle boundary cmb however the plumes are weak and dissipate higher in the mantle

space weathering from mercury to the asteroid belt the variety of evidence bearing on the nature of space weathering is reviewed the effects of space weathering include spectral darkening reddening and subdued absorption bands and the distinctive magnetic electron spin resonance caused by single domain metallic iron particles ever since the apollo missions two paradigms have dominated the thinking of the planetary science community concerning space weathering 1 the optical effects are caused by impact vitrified glass in agglutinates and 2 the submicroscopic metallic iron results from the reduction of ferrous iron by the impact melting of minerals whose surfaces have been saturated with hydrogen from the solar wind however studies carried out since the apollo program showed that both of these paradigms are invalid a hypothesis first suggested by the author and his colleagues 26 years ago but not generally accepted at that time now appears to be essentially correct both the optical and magnetic effects are caused by metallic iron particles smaller than the wavelength in ubiquitous vapor deposited coatings on soil particle surfaces and inside agglutinates the vapor is generated by both solar wind sputtering and micrometeorite impact vaporization and injected preferentially downward into the porous regolith the iron is reduced by a physical process the selective loss of oxygen that occurs during deposition of the vapor and does not require heating melting or a reducing environment a mathematical theory that describes the optical effects of the submicroscopic iron quantitatively is derived and applied to the regoliths of the moon mercury and an s asteroid

rapid remobilization of magmatic crystals kept in cold storage we lack thermal histories for magma reservoirs but here the magma under mount hood oregon usa is shown to have been too cold to mobilize for most of the time it has been stored which implies that magma mobilizes at which point it can be imaged geophysically very quickly prior to eruption this paper presents a novel approach to constraining the thermal history of the subsurface magma bodies that feed eruptions by combining temporal information from a variety of sources kari cooper and adam kent combine timescales derived from uranium series disequilibria textural information and trace element zoning in crystals they show that at mount hood oregon only a small fraction of the total storage duration has been spent at temperatures above the critical crystallinity the point at which magma is easily mobilized they conclude that largely liquid bodies that could be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption the processes involved in the formation and storage of magma within the earth s upper crust are of fundamental importance to volcanology many volcanic eruptions including some of the largest result from the eruption of components stored for tens to hundreds of thousands of years before eruption1 2 3 although the physical conditions of magma storage and remobilization are of paramount importance for understanding volcanic processes they remain relatively poorly known4 5 eruptions of crystal rich magma are often suggested to require the mobilization of magma stored at near solidus conditions6 7 8 however accumulation of significant eruptible magma volumes has also been argued to require extended storage of magma at higher temperatures7 8 9 what has been lacking in this debate is clear observational evidence linking the thermal and therefore physical conditions within a magma reservoir to timescales of storage that is thermal histories here we present a method of constraining such thermal histories by combining timescales derived from uranium series disequilibria crystal sizes and trace element zoning in crystals at mount hood oregon usa only a small fraction of the total magma storage duration at most 12 per cent and probably much less than 1 per cent has been spent at temperatures above the critical crystallinity 40 50 per cent at which magma is easily mobilized partial data sets for other volcanoes also suggest that similar conditions of magma storage are widespread and therefore that rapid mobilization of magmas stored at near solidus temperatures is common magma storage at low temperatures indicates that although thermobarometry calculations based on mineral compositions may record the conditions of crystallization they are unlikely to reflect the conditions of most of the time that the magma is stored our results also suggest that largely liquid magma bodies that can be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption

moon near infrared spectral reflectance a first good look a positive identification of the minerals olivine plagioclase and several types of pyroxenes were made at several locations on the lunar surface by using remote measurements for example the crater aristarchus is found to have an average pyroxene composition of augite and plagioclase is obviously present a dark mantle deposit in the crater j herschel is at least partly composed of a mixture of 70o7o olivine and 30o7o pyroxene these determinations were possible because the reflectance spectra for 10 20 km diameter lunar areas have been measured for the first time in the ir spectral region 0 65 2 5 m with sufficient spectral resolution and photometric precision to define mineral electronic absorption bands the reflectance for all lunar regions observed over 100 to present continues to increase toward longer wavelengths to at least 2 5 m and several mineral absorption bands appear the telescopic spectra are of similar quality and contain features similar to laboratory spectra of lunar samples the absorption features in several spectra have been quantitatively analyzed using newly developed computer processing techniques including thermal flux removal and absorption band fitting to produce these mineral identifications detection and quantitative analysis of these absorptions provide a much improved basis for remotely determining and mapping surface mineralogy quantitatively from the ground or using airborne or spacecraft platforms

compressible convection in the earth s mantle a comparison of different approaches numerical models of mantle convection using the boussinesq extended bousinessq and anelastic liquid approximation are compared for steady state solutions there is good quantitative agreement between the results if they are scaled in a proper way time dependent extended boussinesq and anelastic liquid flows show only qualitative agreement the main difference being a distortion of timescale compressibility induces an asymmetry in the structure of upper and lower boundary layers that cannot be observed in boussinesq fluids

dynamic topography and gravity anomalies for fluid layers whose viscosity varies exponentially with depth summary we have derived analytic integral relations between boundary topography and temperature as a function of wavenumber for a fluid layer whose viscosity varies exponentially with depth similar relations between gravity and temperature are also derived it is found that when the viscosity changes little over the depth of the layer less than an order of magnitude the topography kernels for both the surface and bottom boundaries are similar to those for the isoviscous case the differences being more pronounced at intermediate wavelengths twice the layer depth at these wavelengths the extrema of the gravity kernel can be altered by as much as 30 per cent for a factor of two increase or decrease in viscosity over the depth of the layer at wavelengths less than the layer depth there are dependences on both the rate of growth of viscosity and the surface boundary condition the latter dependency vanishing in the isoviscous case for greater viscosity variation several orders of magnitude topography and gravity kernels at all wavelengths are strongly affected viscosity increasing rapidly with depth can approximate a rigid lower boundary condition causing gravity kernels calculated with a free lower boundary condition to be negative for a significant range of source depths for very rapidly varying viscosity the sign of the perturbation pressure near the layer boundaries can be reversed from the isoviscous case resulting in topography kernels that are negative for some source depths

u th pa ra study of the kamchatka arc new constraints on the genesis of arc lavas abstract the 238u 230th 226ra and 235u 231pa disequilibria have been measured by mass spectrometry in historic lavas from the kamchatka arc the samples come from three closely located volcanoes in the central kamchatka depression ckd the most active region of subducted related volcanism in the world the large excesses of 226ra over 230th found in the ckd lavas are believed to be linked to slab dehydration moreover the samples show the uncommon feature of 230th 238u activity ratios both lower and higher than 1 the u series disequilibria are characterized by binary trends between activity ratios with 231pa 235u ratios all 1 it is shown that these correlations cannot be explained by a simple process involving a combination of slab dehydration and melting we suggest that they are more likely to reflect mixing between two end members a high magnesia basalt hmb end member with a clear slab fluid signature and a high alumina andesite haa end member reflecting the contribution of a slab derived melt the u th ra characteristics of the hmb end member can be explained either by a two step fluid addition with a time lag of 150 ka between each event or by continuous dehydration the inferred composition for the dehydrating slab is a phengite bearing eclogite equilibrium transport or dynamic melting can both account for 231pa excess over 235u in hmb end member nevertheless dynamic melting is preferred as equilibrium transport melting requires unrealistically high upwelling velocities to preserve fluid derived 226ra 230th a continuous flux melting model is also tested in this model 231pa 235u is quickly dominated by fluid addition and for realistic extents of melting this process cannot account for 231pa 235u ratios as high as 1 6 as observed in the hmb end member the involvement of a melt derived from the subducted oceanic crust is more likely for explaining the haa end member compositions than crustal assimilation melting of the oceanic crust is believed to occur in presence of residual phengite and rutile resulting in no 226ra 230th disequilibrium and low 231pa excess over 235u in the high alumina andesites consequently it appears that high alumina andesites and high magnesia basalts have distinct origins the former being derived from melting of the subducted oceanic crust and the latter from hydrated mantle it seems that there is no genetic link between these two magma types in contrast with what was previously believed

the extent of u series disequilibria produced during partial melting of the lower crust with implications for the formation of the mount st helens dacites the extent to which u series disequilibria can be produced during partial melting of mafic lower crust is quantified using a simple batch melting model and both experimental and theoretical partition coefficients for u th and ra we show that partial melting of mafic lower crust can only produce small disequilibria between 238u 230th and 226ra crystallisation of basalt and mixing between young basalt and crustal derived melts will have a similar or smaller effect consequently u series disequilibrium in arc andesites and dacites can generally only be an inherited feature derived from a mantle parent unless the timescales of silicic magma production within the crust are short compared to the half life of 226ra our results have profound implications for several recent models of silicic magma production by thermal incubation and partial melting of the lower crust we show that the 226ra excess observed in most arc andesites and dacites requires extremely rapid differentiation and or the involvement of mantle derived basalts less than a few thousand years old application to mount st helens suggests that crystallisation of young mantle derived magma is likely to be the dominant process in the formation of these dacites

radiative transfer modeling of lunar highlands spectral classes and relationship to lunar samples 1 tompkins and pieters 1999 identified eleven spectral classes present on the surface of the moon here we model these spectral classes to determine the compositions that define them we do this by mathematically matching spectral classes to radiative transfer computed spectra using spectral shape contrast and excursion parameters as defining characteristics model spectra are based upon known mineralogies mafic mineral mg s molar mg mg fe 100 and maturities we compare these compositional results to a compilation of 100 apollo samples to determine plausible representative samples for these spectra results indicate that unique mineralogic solutions for several spectral classes can be determined unambiguously however classes previously interpreted to be pyroxene rich are compositionally ambiguous results suggest these ambiguous mineral assemblages are not random but correlate with variations in absolute reflectance these data further suggest absolute reflectance is a compositionally diagnostic spectral parameter that should be used in conjunction with relative reflectance analysis to constrain mineralogy although absolute reflectance for the eleven spectral classes is not available to constrain their composition we detail mineral chemical i e mg and absolute reflectance variations of matching model relative reflectance spectra to narrow the possibilities this information is used in a pilot study of bullialdus crater for which clementine absolute reflectance is known results indicate bullialdus s central peak consists of tompkins and pieters spectral classes an agn and n bullialdus s spectra that match class n are roughly consistent with previous compositional interpretations however matches to classes an and agn indicate more mafic assemblages typical of mg suite norite gabbronorite rocks

calculating iron contents of lunar highland materials surrounding tycho crater from integrated clementine uv visible and near infrared data 1 optical properties of lunar surface materials are modified by exposure to the space environment including bombardment by solar wind particles and micrometeorites one of the main problems in the interpretation of lunar spectral observations is to separate the effects of exposure space weathering and those due to the composition of the soils mainly iron and titanium content here we use clementine near infrared nir data to investigate this problem for highland type soils in the tycho crater area our approach is based on the methods developed for an analysis of a mare region near aristarchus plateau le mouelic et al 2000 we show that the systematic relationships between spectral parameters 1 m band depth and continuum slope which were previously observed in a mare area with varying maturity degree are also valid for highland type soils this technique aimed at evaluating the iron content of the surface materials from clementine uv visible uvvis and near infrared data can therefore be applied globally this approach complements the widely used method of lucey and coworkers which relies on the uv visible bands only the proposed method relies mostly on band ratios the iron map produced from this method is therefore less dependent on topography than the iron estimates obtained with uv visible data alone where brightness is one of the controlling parameters therefore the proposed approach should be particularly useful at middle to high latitudes where local topography generates large variations in brightness and therefore hampers the interpretation of iron maps produced from uv visible bands only

post glacial relaxation of a viscously stratified compressible mantle summary we investigate the post glacial relaxation phenomenon of a viscously compressible non self gravitating spherical shell model we have developed analytical solutions to an exponentially depth dependent viscosity with various types of compressible density models such as those with an exponential dependence of the radius and an algebraic root dependence of the radius the solutions of a viscously compressible multilayered model with constant thermodynamic properties and viscosity are developed by the propagator matrix method our results show that inferences of deep mantle viscosity from post glacial rebound would be hampered by mantle compressibility for long wavelength harmonics because of the smaller excitation of compressible eigenfunctions in the lower mantle the relaxation times and velocity fields are more sensitive to higher viscosity contrast for the exponentially varying viscosity than for models with discrete jumps in the viscosity structure stress fields associated with deglaciation are extremely sensitive to the underlying mantle viscosity structure large stresses o 102 bar can still remain at the deglaciated region if the lower mantle viscosity is o 1023p the presence of a hard garnet layer in the transition zone will induce a smaller viscosity in the lower mantle in the viscosity trade off with the standard two layer model

timescales of crustal magma reservoir processes insights from u series crystal ages the dynamic processes operating within crustal magma reservoirs control many aspects of the chemical composition of erupted magmas and crystals in volcanic rocks provide a temporally constrained archive of these changing environments in this review i compile 238 u 230 th ages of accessory phases and 238 u 230 th 226 ra ages of bulk mineral separates of major phases these data document that crystals in individual samples can have ages spanning most of the history of a volcanic centre age populations for accessory phases show protracted pre eruptive crystal residence times but few crystals predate magmatic activity at a given centre these data have been interpreted in the context of residence times of the host magmas or timescales of the storage of crystals within a largely crystalline portion of the reservoir system in contrast less than half of the bulk separate 238 u 230 th 226 ra ages for major phases are more than 10 kyr older than the eruption many of these apparently conflicting observations of ages of major and accessory phases can be reconciled within the context of a model where a crystal mush was remobilized during processes leading to eruption overall the compiled data show that crystals contain rich archives of magmatic processes in crustal reservoirs especially when combined with other crystal scale geochemical data

the nature and origin of rims on lunar soil grains abstract space weathering processes that operate in the lunar regolith modify the surfaces of lunar soil grains transmission electron microscope analysis of the lunar soil grains from the fine size fraction of several lunar soils show that most grains are surrounded by thin 60 200 nm thick rims the microstructure and chemical compositions of the rims can be used to classify rims into four broad categories amorphous inclusion rich multiple and vesicular amorphous rims are noncrystalline generally lack crystalline inclusions show evidence for preferential sputtering of cations and are produced largely by solar wind irradiation damage inclusion rich rims contain abundant nanometer sized grains of fe metal as randomly dispersed inclusions or as distinct layers embedded in an amorphous silica rich matrix inclusion rich rims are compositionally distinct from their host grains and typically contain accumulations of elements that are not indigenous to the host inclusion rich rims are formed largely by the deposition of impact generated vapors with a contribution from the deposition of sputtered ions a continuum in the chemical and microstructural properties exists between typical amorphous rims and typical inclusion rich rims multiple rims consist of a distinct radiation damaged layer up to 50 nm thick that is overlain by vapor deposited material of comparable thickness vesicular rims are compositionally similar to their hosts and are characterized by an abundance of small the formation of rims on lunar soils is complex and involves several processes whose effects may be superimposed from this study it is shown that one process does not dominate and that the relative importance of vapor deposition is comparable to radiation damage in the formation of rims on lunar silicate grains the presence of rims on lunar soil grains particularly those with nanometer sized fe metal inclusions may have a major influence on the optical and magnetic properties of lunar soils

sr isotope zoning in plagioclase from parinacota volcano northern chile quantifying magma mixing and crustal contamination we present analyses of sr isotope zoning by microdrilling and thermal ionization mass spectrometry in plagioclase crystals from parinacota volcano central volcanic zone northern chile which were analysed for major and minor element zoning in a previous study although the isotopic range of the bulk rock samples is small at this volcano 0 7067 0 7070 except for one flow of mafic andesite at 0 7061 significant variations are seen 0 70649 0 70700 within and between plagioclase crystals a general negative correlation is observed between sr isotope composition and sr concentration in the liquid in equilibrium with each plagioclase zone as calculated from chemical zoning data and partition coefficients additional scatter is superimposed on this general trend indicating a decoupling between isotopic and chemical variations for sr in one dacite sample a detailed isotopic profile shows increasing contamination during crystal growth except for an abrupt decrease correlated with a dissolution surface and interpreted as a recharge event we apply energy constrained recharge assimilation and fractional crystallization modelling to the melt evolution recorded in the chemical and isotopic zoning in this crystal results suggest 20 assimilation of the local wall rock gneiss at high initial temperatures the isotopic data confirm the involvement of two contrasting mafic magmas which are sampled at flank cinder cone vents one lower ajata has a low sr content with high 87sr 86sr the other upper ajata has a high sr content with lower 87sr 86sr in some samples from parinacota the isotopic composition of plagioclase crystal rims or groundmass crystals is significantly higher than that of the high 87sr 86sr mafic magma in others where chemical zoning profiles suggest that recharge was from the low 87sr 86sr magma the 87sr 86sr of the groundmass and crystal rims is higher than expected this indicates either additional parent magmas to the two previously identified or further crustal assimilation either at lower crustal depths before crystallization of plagioclase or just after the last recharge our results illustrate the complexity of magma crust interaction beneath parinacota which is likely to be representative of many other central andean volcanoes formed on thick crust such complex interactions can be revealed by combined study of chemical and isotopic zoning in plagioclase in a textural petrographic context despite a small whole rock isotopic range the distinct contamination patterns of various samples suggest an important role for the geometry location and evolution of the magma plumbing system and in general variations of the thermal and compositional structure of the crust underneath the volcano

the effects of space weathering on apollo 17 mare soils petrographie and chemical characterization the lunar soil characterization consortium a group of lunar sample and remote sensing scientists has undertaken the extensive task of characterization of the finest fractions of lunar soils with respect to their mineralogical and chemical makeup these compositional data form the basis for integration and modeling with the reflectance spectra of these same soil fractions this endeavor is aimed at deciphering the effects of space weathering of soils on airless bodies with quantification of the links between remotely sensed reflectance spectra and composition a beneficial byproduct is an understanding of the complexities involved in the formation of lunar soil several significant findings have been documented in the study of the 2x whereas the abundance of agglutinitic glass increases by only 10 15 this is evidence for a large contribution from surface correlated nanophase fe0 to the is feo values particularly in the 10 m size fraction the surface nanophase fe0 is present largely as vapor deposited patinas on the surfaces of almost every particle of the mature soils and to a lesser degree for the immature soils keller et al 1999a it is reasoned that the vapor deposited patinas may have far greater effects upon reflectance spectra of mare soils than the agglutinitic fe0

viscoelastic perturbations of the earth significance of the incremental gravitational force in models of glacial isostasy summary the incremental gravitational force igf arises from perturbations of the earth s gravitational potential in glacial isostasy its sources are the surjicial and internal mass redistributions associated with the growth and decay of the continental ice sheets we examine the errors caused by the neglect of the igf using closed form solutions of the equations governing surface load induced perturbations of two types of incompressible spherical earth models 1 maxwellian viscoelastic mantle enclosed by elastic lithosphere and 2 maxwellian viscoelustic mantle enclosing inviscid core calculations in the legendre domain of the radial surface displacement for these models show that neglecting the igf causes enhancement of the elastic response and acceleration of the viscous relaxation in the space domain these changes entail corresponding modifications of the calculated land adjustment the magnitude of the error caused by the neglect of the igf strongly depends on the deglaciation history and load radius adopted assuming a typical deglaciation history the error reaches a maximum of less than 20 m at the end of the deglaciation phase for loads comparable in size to the canadian or the fennoscandian ice sheets we also compare sphericul earth models with igf and plane earth models without igf calculations of the radial surface displacement show that the errors due to the neglect of sphericity and the igf partially compensate each other taking the uncertainties of the observational data into account we conclude that the majority of the canadian and fennoscandian glacial isostatic adjustment data can be modelled with sufficient accuracy using a plane earth model without igf

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

effects due to compressional and compositional density stratification on load induced maxwell viscoelastic perturbations summary calculations of viscoelastic perturbations of an incompressible uid earth initially in hydrostatic equilibrium have been conventionally based on models consisting of isocompositional layers a special case is the incompressible isocompositional half space for which the initial density distribution is spatially uniform one of the de ciencies of this model is that it ignores the increase of the initial density with depth in the earth s interior due to compressional and compositional strati cation the presentstudy is concernedwith load induced maxwellviscoelastic perturbations of a half space with a compressional and compositional initial density gradient analytic solutions to this problem are deduced for the limiting cases of purely compressional strati cation earth model p and purely compositional strati cation earth model c the comparison of the solutions for these earth models with that for the special case of no density strati cation earth model r shows that eiects due to the initial density gradient become important for perturbations whose lateral scale length exceeds about 10 3 km using axisymmetric models of the pleistocene fennoscandian and canadian ice sheets and considering the vertical surface displacements near the load axes the maximum diierences are found to be about 10 m fennoscandia or 35 m canada at the beginning of relaxation for earth models p and r and about 50 m fennoscandia or 150 m canada at intermediate times of relaxation for earth models c and r

discrimination between maturity and composition of lunar soils from integrated clementine uv visible near infrared data application to the aristarchus plateau the reflectance spectrum of a lunar soil is mainly dominated by the composition and the degree of exposure to space weathering processes such as micrometeorite bombardment and solar wind implantation the spectral alteration effects of space weathering should be removed for accurately investigating the composition of the lunar surface using remote sensing data in this paper we show that the integration of the clementine uv visible uvvis and near infrared nir channels provides an improved evaluation of the spectral alteration the depth of the mafic absorption feature at 0 95 m is also better defined by combining the uvvis and nir data laboratory spectra of lunar soil samples indicate that the continuum slope derived from the 1500 750 nm ratio is closely related to the concentration of fine grained submicroscopic iron is the continuum slope therefore provides an evaluation of the spectral alteration of the surface which can be subtracted from the 1 or 2 m absorption band depths to retrieve compositional information this method has been applied to the aristarchus plateau which exhibits a broad range of mineralogical composition and maturity a nine channel multispectral mosaic of 680 clementine images of the aristarchus plateau has been processed eight telescopic spectra have been used to check the validity of the reduction process for the near infrared bands the 1 m absorption band once corrected for spectral alteration provides an evaluation of the initial feo content in mafic silicates mafic iron lunar soil samples show that it is possible to quantitatively map mafic iron with this technique our results are in good agreement with those obtained using the algorithm of lucey et al 1995 1998a which is based on uvvis bands alone the mafic iron content and total iron content which can be derived from the combined uvvis and nir data sets are less sensitive to local slopes than that derived from lucey et al s method this new method could therefore be useful for investigating areas at middle to high latitudes removing spectral alteration from the 2000 1500 nm ratio also makes possible a better discrimination between olivine and pyroxene within identified mare basalts on the aristarchus plateau

tomography the geoid and plate motions the dynamics of the earth s mantle and its relationship to mantle structure as revealed by seismic tomography the geoid and plate motions are discussed in a critical review of u s research from the period 1987 1990 sections are devoted to plates and mantle convection seismic anomalies flow and the geoid subducted slabs and the 670 km discontinuity the physical properties of the mantle plumes and computational and experimental modeling efforts also included is a comprehensive bibliography for the period 248 refs

reappraisal of uranium series isotope data in kamchatka lavas implications for continental arc magma genesis uranium series isotopes can be used to determine constraints on the timescale of slab dehydration and melt production at subduction zones however interpretations of u th ra data suggest very different timescales of slab dehydration here we present new u th ra data from kamchatka along with a number of alternative models for production of radioactive disequilibrium variations in 226ra 230th and 231pa 235u activity ratios are best explained by crystal fractionation with host rock assimilation for a duration of less than c 6000 years the association of the largest 226ra excesses with high sr th in the most primitive lavas suggests that ra th fractionation is controlled by slab dehydration less than 10 ka ago we show that u th data can be explained by dynamic melting of a recently ka metasomatized mantle wedge dynamic melting of an oxidized source metasomatized several hundreds of thousands of years ago cannot produce significant 231pa excess because 238u 230th disequilibrium is inferred to be controlled by partial melting there is no requirement for multi stage slab dehydration commencing 150 ka we suggest that ra th disequilibria constrain the timing of slab dehydration whilst u th fractionation is dominated by partial melting at least at the kamchatka arc

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

quantitative mineralogical characterization of lunar high ti mare basalts and soils for oxygen production efficient lunar resource utilization requires accurate and quantitative evaluation of mineral and glass abundances distribution and extraction feasibility especially for ilmenite with this in mind true modal analyses were performed on high ti mare basalts and soils with x ray backscattered electron signal digital imaging techniques and these data indicate that 1 ilmenite concentrations are similar for basalts and immature submature soils with similar tio2 content 2 ilmenite liberation of crushed mare basalts and immature submature mare soils are comparable i e both contain similar amounts of free ilmenite and 3 because of impact melting and agglutination of primary minerals mature mare soils contain less ilmenite both free and attached modal analyses of magnetic separates of high ti mare basalts and soils show that 1 ilmenite was concentrated by a factor of 3 3 and 2 soil ilmenite was concentrated to factors of 1 7 2 3 the lower soil ilmenite separation efficiency is attributed to fe bearing agglutinitic glass and amorphous rinds adhered to soil particles mass yields of magnetically generated feedstocks were generally less than 5 wt in most cases calculation of oxygen yield as released by hydrogen gas reduction of ilmenite show that 1 beneficiated basalt will provide the most oxygen 8 10 because of higher ilmenite concentration 2 reduction of raw immature submature mare soils and basalts will produce similar amounts of lunar liquid oxygen llox 2 1 3 1 and 3 raw fe rich pyroclastic soil 74220 will provide more oxygen 5 4 than beneficiated high ti mare soils and half that of beneficiated high ti mare basalts high ti mare soils are attractive resources for lunar liquid oxygen llox production because of their unconsolidated nature high ilmenite abundance and widespread occurrence energy intensive excavation and comminution likely prohibits the basalt mining during early lunar occupation orange soils are important resources for llox and various volatile elements but slower reaction kinetics and glass sintering pose potential difficulties for large scale operations

u series disequilibria of trachyandesites from minor volcanic centers in the central andes abstract young trachyandesite lavas from minor volcanic centers in the central andes record the magma differentiation processes at the base of the lower continental crust here we report u series disequilibrium data for the historical lavas from the andagua valley in southern peru to define the time scale and processes of magmatism from melting in the mantle wedge to differentiation in the crust the andagua lavas show 230 th 238 u 231 pa 235 u and 226 ra 230 th above unity except for one more evolved lava with 230 th depletion likely owing to fractional crystallization of accessory minerals the 226 ra excess indicates that the time elapsed since magma emplacement and differentiation in the deep crust is within 8000 years based on the correlations of u series disequilibria with sio 2 content and ratios of incompatible elements we argue that the andagua lavas were produced by mixing of fresh mantle derived magma with felsic melt of earlier emplaced basalts in the deep crust because of the lack of sediment in the chile peru trench there is no direct link of recycled slabs with 230 th and 231 pa excesses in the andagua lavas instead 230 th and 231 pa excesses are better explained by in growth melting in the upper mantle followed by magma differentiation in the crust such processes also produced the 226 ra excess and the positive correlations among 226 ra 230 th sr th and ba th in the andagua lavas the time scale of mantle wedge melting should be close to the half life of 231 pa ca 33 ka while it takes less than a few thousand years for magma differentiation to form intermediate volcanic rocks at a convergent margin

geochemistry of gas and water discharge from the magmatic hydrothermal system of guallatiri volcano northern chile this work presents the first chemical and isotopic 13c co2 13c ch4 3he 4he 20ne 40ar 36ar 18o and d data for fluid discharges from guallatiri volcano a remote and massive stratovolcano which is considered as the second most active volcano of the central volcanic zone cvz in northern chile fumarolic gases had outlet temperatures of between 80 2 and 265 c and showed a significant magmatic fluid contribution marked by the occurrence of so2 hcl and hf that are partially scrubbed by a hydrothermal aquifer the helium isotope ratios 3 2 were relatively low compared to those of other active volcanoes in cvz possibly due to contamination of the magmatic source by 4he rich crust and or crustal fluid addition to the hydrothermal reservoir geothermometry in the h2o co2 co h2 ch4 system suggests equilibrium temperatures of up to 320 c attained in a vapor phase at redox conditions intermediate between those typical of hydrothermal and magmatic environments thermal springs located 12 km northwest of the volcano s summit had outlet temperatures of up to 50 1 c neutral to slightly basic ph and a sodium bicarbonate composition typical of distal fluid discharges in volcanic systems cold springs at the base of the volcanic edifice showing a calcium sulfate composition were likely produced by interaction of shallow meteoric water with co2 and h2s rich gases a geochemical conceptual model was constructed to graphically represent these results which can be used as an indication for future geochemical monitoring and volcanic hazard assessment

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle