eruptive history of earth s largest quaternary caldera toba indonesia clarified single grain laser fusion sup 40 ar sup 39 ar analyses of individual sanidine phenocrysts from the two youngest toba indonesia tuffs yield mean ages of 73 plus minus 4 and 501 plus minus 5 ka in addition glass shards from toba ash deposited in malaysia were dated at 68 plus minus 7 ka by the isothermal plateau fission track technique these new determinations in conjunction with previous ages for the two oldest tuffs at toba establish the chronology of four eruptive events from the toba caldera complex over the past 1 2 m y ash flow tuffs were erupted from the complex every 0 34 to 0 43 m y culminating with the enormous 2500 3000 km sup 3 youngest toba tuff eruption caldera formation and subsequent resurgence of samosir island timing of this last eruption at toba is coincident with the early wisconsin glacial advance the high precision sup 40 ar sup 39 ar age eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exceptionally large explosive eruptions

resolving volatile sources along the western sunda arc indonesia we present the chemical and isotope hecn characterization of active fumaroles and hydrothermal gases and waters from the summits and flanks of 19 volcanic centers along the western sunda arc indonesia samples were collected over two field expeditions 1991 and 2010 and cover 13 volcanic centers in sumatra 5 in java and one in bali in addition we present data from three geothermal sites in sumatra associated with active fault systems in between volcanic centers ibvc the overall aim is to resolve volatiles associated with the sub arc mantle subducting slab and mantle wedge from inputs derived from the over riding arc crust the western sunda arc is a prime locality to assess controls on volatile provenance at subduction zones due to changes in composition and thickness of over riding crust and variations in sediment input rates along the strike of the arc the dry gas chemistry of the majority of volcanic samples is dominated by co2 with inert gas variations hearn2 typical of subduction zone gases however there is a strong crustal control on the heco2 isotope and relative abundance systematics on a number of volcanic centers this effect is most clearly observed at flank localities and in water phase samples filtering the entire database for modifications due to air contamination degassing induced fractionation c isotopes and co2 3he ratios and crustal contamination associated with volatile transport within shallow level hydrothermal systems allows recognition of the magmatic volatile signature of individual volcanoes along the arc helium isotopes at all but two volcanic centers talang and dempo on sumatra range from 5 3 ra to 8 1 ra ra air 3he 4he pointing to the mantle wedge as the principal source of he but with a small input of crustal radiogenic he at some localities samples from java and bali span an even more limited range 6 6 to 7 9 ra implying a relatively smaller input of crustal he carbon isotope and co2 3he ratios vary from 1 4 to 6 4 and 4 38 to 150 109 respectively with higher and more variable values to the north of sumatra this latitudinal effect is not apparent in air corrected n isotope values 15nc 3 91 to 5 92 or various elemental ratios such as n2 ar and n2 he the three ibvc sites all located in sumatra have significantly lower 3he 4he ratios 3 6 ra with co2 3he values both higher and lower than volcanic centers their 13c 15nc and gas ratios overlap with the volcanic centers the elemental and isotopic characteristics of carbon and helium have been modified at ibvc sites due to crustal processes however based upon relationships between ch4 and 3he as well as co variations between hecn isotopes the over riding crust and associated sediments add minimal volatiles to volcanic centers throughout the western sunda arc in turn subducted sediment particularly the nicobar fan which supplies himalayan derived sediment to the slab off sumatra exerts a strong control on the magmatic co2 characteristics although it is less influential for n2 in spite of large sections of incoming sedimentary material being off scraped during subduction our data suggest that a significant fraction must enter the trench enhancing fluid melt production in the mantle wedge we propose that subduction related source contamination plays the dominant role over thick old crustal basement in supplying the major volatile output budget of the western sunda arc

prolonged residence times for the youngest rhyolites associated with long valley caldera 230th 238u ion microprobe dating of young zircons abstract we describe a new ion microprobe method for dating magmatic zircon growth that is based on in situ measurement of the magnitude of238u 230th disequilibrium our results support independent inferences that zircon can remain suspended for long periods 100 ka in the convecting potions of the magma from which it crystallizes because the crystallization ages date when the magma cooled to its zircon saturation temperature even when the zircons have long magmatic residence times 238u 230th zircon dating can be used to constrain the thermochemical evolution of silicic magmas 238u 230th ages have been determined for individual zircons from rhyolites associated with the long valley magmatic system of eastern california the samples are from deer mountain an 115 3 ka low silica moat rhyolite and from the coarsely porphyritic low silica rhyolite of south deadman dome one of the 0 6 ka inyo domes previous investigations have suggested that the two lavas were derived from the same magma reservoir a few of the zircon model ages calculated with respect to the isotopic characteristics of the whole rocks are within error of that for eruption of the deer mountain rhyolite however the majority of zircons from both lavas cluster around an age of 230 ka this common interval of zircon nucleation and growth for petrologically similar lavas suggests that the younger inyo dome lava may have tapped the same magma body from which the deer mountain rhyolite erupted more than 100 ka before on the other hand most of the zircon model ages are younger than previous episodes of silicic volcanism in the long valley caldera suggesting that the rhyolites may have been generated during development of a silicic upper crustal magma chamber in the western portion of long valley caldera zircon saturation temperatures for the rhyolites studied 795 810 c are the same as those obtained from coexisting fe ti oxides 809 4 c showing that the magma cooled to

global gravity wave variances from aura mls characteristics and interpretation abstract the gravity wave gw resolving capabilities of 118 ghz saturated thermal radiances acquired throughout the stratosphere by the microwave limb sounder mls on the aura satellite are investigated and initial results presented because the saturated optically thick radiances resolve gw perturbations from a given altitude at different horizontal locations variances are evaluated at 12 pressure altitudes between 21 and 51 km using the 40 saturated radiances found at the bottom of each limb scan forward modeling simulations show that these variances are controlled mostly by gws with vertical wavelengths z 5 km and horizontal along track wavelengths of y 100 200 km the tilted cigar shaped three dimensional weighting functions yield highly selective responses to gws of high intrinsic frequency that propagate toward the instrument the latter property is used to infer the net meridional component of gw propagation by differencing the variances acquired from ascending a and descending d o

climatology of upper tropospheric lower stratospheric utls jets and tropopauses in merra abstracta global climatology 1979 2012 from the modern era retrospective analysis for research and applications merra shows distributions and seasonal evolution of upper tropospheric jets and their relationships to the stratospheric subvortex and multiple tropopauses the overall climatological patterns of upper tropospheric jets confirm those seen in previous studies indicating accurate representation of jet stream dynamics in merra the analysis shows a northern hemisphere nh upper tropospheric jet stretching nearly zonally from the mid atlantic across africa and asia in winter spring this jet splits over the eastern pacific merges again over eastern north america and then shifts poleward over the north atlantic the jets associated with tropical circulations are also captured with upper tropospheric westerlies demarking cyclonic flow downstream from the australian and asian monsoon anticyclones and associated easterly jets multiple tropopauses associated with the thermal tropopause break

implications of pre eruptive magmatic histories of zircons for u pb geochronology of silicic extrusions zircons in silicic magmas begin to crystallize 10 s to 100 s of thousands of years ka prior to their eruption u pb and u th dating for zircons from 32 young extrusions indicate a range of mean pre eruption ages from 33 to 247 ka with a median of 92 ka explosive large volume widespread eruptions show a narrower range and a younger median of 70 ka these results indicate that the difference between initial zircon growth and eruption age measured by other e g 40ar 39ar techniques is in excess of the achievable analytical uncertainty for eruptions 30 million years ma and likely for eruptions of up to 300 ma protracted pre eruption zircon growth is well established by an increasing number of studies on magma process time scales but this source of eruption age bias has been largely ignored in chronostratigraphic applications of high precision u pb data until intrinsic properties of zircons or their host deposits enable a priori estimates of pre eruption age bias it is prudent to expand the uncertainties attending all u pb zircon ages interpreted as deposition ages in e g chronostratigraphic studies by 0 200 ka

kinematic setting and structural control of arc volcanism abstract the evaluation of the kinematic setting and the structural control of volcanic arcs are important in defining the tectono magmatic processes along convergent plate boundaries however our knowledge is fragmented and the available data highlight different behaviours this study analyzes the kinematic setting the structural control and the volcanic productivity of 16 arcs these arcs are characterized by predominant extensional compressional strike slip or oblique motions there is an overall coupling between the normal vs parallel motions along the arc and those of the underlying slab therefore the higher the trench normal or parallel component of the subduction rate the higher is the amount of arc normal or parallel motion this relation confirms that strain partitioning is in general feasible at many convergent settings involving also the volcanic arc portion the arc normal motion may be characterized by extension or compression as a function of the increase in the trench normal convergence or subduction velocity the lack of an evident relation between the subduction rate or convergence rate and the volcanic productivity of the arc is partly inconsistent with previous studies which highlight a relation between the subduction rate and melt production below arcs this discrepancy mainly suggests that different processes control the generation rise and eruption of magma at different depths varying the intrusive extrusive ratio along arcs the structure of the arc does not control the distribution of the volcanoes however it does control the volcanic output through different processes even though regional or local extension associated with strike slip or compressive structures is the ultimate requisite in any setting in general the higher the amount of extension the higher is the output rate along the arc

trace element evidence for plagioclase recycling in calc alkaline magmas abstract trace element zoning in plutonic plagioclase feldspars from the val fredda complex southern adamello massif italy has been measured using secondary ion mass spectrometry sims the studied samples range from hornblende gabbro through diorite to granitoid with an overall range in plagioclase composition from an96 to an15 individual plagioclases display extensive zonation in anorthite through a considerable variety of zoning textures there is equally extensive zoning in trace elements notably sr and ba broadly similar trace element zoning patterns and concentrations are displayed by all plagioclases irrespective of host rock composition using a relationship betweenxan and the distribution coefficientsdsr anddba trace element concentrations in plagioclase are converted to those of the melt which precipitated each crystal zone the calculated variations in ba and sr are greater than can be attributed to changes in pressure or temperature alone indicating that compositional variation in the coexisting melt was the principal cause of zoning the ba sr melt trend for each crystal describes a two stage crystallisation history the calcic cores of all crystals show melt trends of increasing sr and ba which are attributed to mixing and fractionation in parental hydrous picrobasalt magmas in contrast the melt trends recorded by the rims vary from sample to sample but essentially show decreasing sr and ba consistent with fractionation of sodic plagioclase alkali feldspar and or biotite the plagioclase cores are thought to have crystallised in a common magma chamber at 6 10 kbar pressure while the rims crystallised at the emplacement level 1 5 kbar from interstitial melt whose composition is determined by that of the host magma the data suggest that early formed calcic plagioclase was recycled by the magma during fractionation vigorous convection is invoked to both retain relatively dense calcic plagioclase within the evolving magma and to periodically re entrain cumulus crystals into more evolved magmas the occurrence of calcic plagioclase cores in felsic derivative magmas indicates that fractionation from picrobasalt to tonalite occurred on a relatively short time scale

a climatology of tides in the antarctic mesosphere and lower thermosphere 1 a function that approximates atmospheric tidal behavior in the polar regions is described this function is fitted to multistation radar measurements of wind in the mesosphere and lower thermosphere with the aim of obtaining a latitude longitude height description of the variation of tides over the whole antarctic continent archival wind data sets are combined with present day ones to fill the spatial distribution of the observations and to reduce the potential effects of spatial aliasing multiple years are combined through the compilation of monthly station composite days yielding results for each month of the year despite potential problems associated with year to year variations in the tidal phase a useful climatology of antarctic zonal and meridional tidal wind components is compiled the results of the fits reproduce the major features of the high latitude tidal wind field the dominance of the semidiurnal migrating mode in the winter months and the presence of a semidiurnal zonal wave number one component in the summer months it is also found that the summer semidiurnal tide contains a zonal wave number zero component

wavelet based correlation wbc of zoned crystal populations and magma mixing magma mixing is a common process and yet the rates kinematics and numbers of events are difficult to establish one expression of mixing is the major trace element and isotopic zoning in crystals which provides a sequential but non monotonic record of the creation and dissipation of volumes of distinct chemical potential we demonstrate a wavelet based correlation wbc technique that uses this zoning for the recognition of the minimum number of mixing or open system events and the criteria for identifying populations of crystals that have previously shared a mixing event when combined with field observations of the spatial distribution of crystal populations wbc provides a statistical link between the time varying thermodynamic and fluid dynamic history of the magmatic system wbc can also be used as a data mining utility to reveal open system events where outcrop is sparse an analysis of zoned plagioclase from the tuolumne intrusive suite provides a proof of principle for wbc 1 2002 elsevier science b v all rights reserved

gravity wave generation around the polar vortex in the stratosphere revealed by 3 hourly radiosonde observations at syowa station intensive radiosonde observations were performed at syowa station 69 0 s 39 6 e over about 10 days in each of march june october and december 2002 to examine inertia gravity wave characteristics in the antarctic lower stratosphere based on the 3 hourly observation data two dimensional i e vertical wavenumber versus frequency spectra of wind fluctuations were examined utilizing a double fourier transform method clear signals of gravity waves whose phases propagate upward suggesting downward energy propagation are detected in june and october when the polar night jet pnj was present on the other hand downward phase propagation i e upward energy propagation components are dominant in all months there is a spectral peak around the inertial frequency in a wide range of vertical wavenumbers in december when the background wind was weak whereas large spectral densities are distributed over lower frequency regions in june and october these spectral characteristics are consistent with the results obtained using a gravity wave resolving global circulation model gcm by sato et al dynamical characteristics are examined separately for upward and downward propagating gravity waves in june using a hodograph analysis method as a result it is found that upward and downward propagating wave packets observed simultaneously in the same height regions have similar horizontal wavelengths and phase velocities this fact suggests that these gravity waves are generated from the same source with a similar mechanism when the wave packets were observed both the local rossby number and the residual in the nonlinear balance equation estimated using ncep ncar reanalysis data are large around the pnj situated slightly to the lower latitudes of syowa station therefore it is likely that the observed inertia gravity waves are generated by a spontaneous adjustment around the geostrophically unbalanced pnj and propagate toward syowa station the possibility of spontaneous gravity wave generation around the pnj is confirmed by comparison with the gcm simulation by sato et al

construction of a pluton evidence from an exposed cross section of the searchlight pluton eldorado mountains nevada a top to bottom cross section of the searchlight pluton is exposed in a large tilt block in the colorado river extensional corridor of southern nevada hornblende barometry and geologic relations indicate that the pluton was about 10 km thick extending from approximately 3 to 13 km depth the pluton is stratified with about 2 km of fine grained quartz monzonite below the roof 2 km of granite in the center and 6 km of coarser more mafic quartz monzonite at the bottom the lower unit has a pronounced magmatic foliation that was subhorizontal prior to tilting contacts between the units are gradational over a few centimeters to about 20 m geometry field relations and elemental and isotopic data suggest that the three units mark the terminal stages of evolution of magma that filled a very thick magma chamber the upper unit formed as a solidification front that migrated downward from the roof and the middle unit granite and the lower unit represent complementary segregated melt and crystal rich cumulate thus the dominant part of the pluton appears to have solidified in monotonic fashion from more or less uniform magma that was compositionally similar to the upper unit the basal quartz monzonite and the lower part of the granite enclose widely scattered synplutonic hornblende gabbro and diorite pods that range from centimeter to kilometer scale these rocks are commonly fine grained and formed as quenched mafic melts they are isotopically distinct from the main sequence and represent discrete injections into the magma chamber the mafic magmas were contaminated by but did not strongly affect the main sequence magma the nd and sr isotopic compositions of the main sequence magma are intermediate between those of regional crust and enriched mantle derived basalts like those represented by the mafic pods this suggests that the principal magma was a hybrid with about 60 mantle component and thus the pluton represents both addition to and internal reorganization of the crust

radiosonde observations of gravity waves in the lower stratosphere over davis antarctica radiosonde observations made from davis station antarctica 68 6 s 78 0 e between 2001 and 2012 are used to compile a climatology of lower stratosphere inertial gravity wave characteristics wavelet analysis extracts single wave packets from the wind and temperature perturbations wavelet parameters combined with linear gravity wave theory allow for the derivation of a wide range of wave characteristics observational filtering associated with this analysis preferentially selects inertial gravity waves with vertical wavelengths less than 2 3 km the vertical propagation statistics show strong temporal and height variations the waves propagate close to the horizontal and are strongly advected by the background wind in the wintertime notably around half of the waves observed in the stratosphere above davis between early may and mid october propagate downward this feature is distributed over the observed stratospheric height range based on the similarity between the upward and downward propagating waves and on the vertical structure of the nonlinear balance residual in the polar winter stratosphere it is concluded that a source due to imbalanced flow that is distributed across the winter lower stratosphere best explains the observations calculations of kinetic and potential energies and momentum fluxes highlight the potential for variations in results due to different analysis techniques

inertia gravity waves revealed in radiosonde data at jang bogo station antarctica 74 37 s 164 13 e 2 potential sources and their relation to inertia gravity waves

probing the accumulation history of the voluminous toba magma the age and compositional zonation in crystals from the youngest toba tuff record the prelude to earth9s largest quaternary eruption we used allanite crystals to date and decipher this zoning and found that the crystals retain a record of at least 150 000 years of magma storage and evolution the dominant subvolcanic magma was relatively homogeneous and thermally stagnant for 110 000 years in the 35 000 years before eruption the diversity of melts increased substantially as the system grew in size before erupting 75 000 years ago

remobilization of andesite magma by intrusion of mafic magma at the soufriere hills volcano montserrat west indies the 1995 1999 eruption of the soufriere hills volcano montintroduction serrat has produced a crystal rich andesite containing quenchthe soufriere hills volcano montserrat located in the textured mafic inclusions which show evidence of having been molten lesser antilles island arc in the west indies began to when incorporated into the host magma individual crystals in the erupt on 18 july 1995 after about 350 years of dormancy andesite record diverse histories amphibole phenocrysts vary from young et al 1998b the eruption was preceded by a pristine and unaltered to strongly oxidized and pseudomorphed by period of seismic swarms which began in january 1992 anhydrous reaction products plagioclase phenocrysts are commonly previous earthquake crises have occurred on montserrat reverse zoned often with dusty sieve textures reverse zoned rims are in 1896 1897 1932 1935 and 1966 1967 powell 1938 also common on orthopyroxene phenocrysts pyroxene geothermometry shepherd et al 1971 initial phreatic and phregives an average temperature of 858 20 c for orthopyroxene atomagmatic activity was followed by extrusion of an phenocryst cores whereas reverse zoned rims record temperatures andesitic lava dome in november 1995 pyroclastic flows from about 880 to 1050 c the heterogeneity in mineral rim generated by gravitational collapse of the unstable dome compositions zoning patterns and textures is interpreted as reflecting have been the dominant form of activity throughout the non uniform reheating and remobilization of the resident magma eruption but periods of explosive activity producing body by intrusion of hotter mafic magma convective remobilization pumice flows and falls have also occurred robertson et results in mixing together of phenocrysts that have experienced al 1998 young et al 1998b dome growth ceased different thermal histories depending on proximity to the intruding suddenly in march 1998 and further activity up to may mafic magma the low temperature and high crystallinity are 1999 has mainly involved gravitational collapses of the interpreted as reflecting the presence of a cool highly crystalline dome and periods of ash venting with some small scale magma body beneath the soufriere hills volcano the petrological vulcanian explosive events observations in combination with data on seismicity extrusion rate the soufriere hills volcano is the only active centre and so2 fluxes indicate that the current eruption was triggered by on montserrat the volcano is a composite of at least recent influx of hot mafic magma five andesitic lava domes flanked by pyroclastic deposits rea 1974 identified four other volcanic centres all

mesospheric momentum flux studies at adelaide australia observations and a gravity wave tidal interaction model abstract we present here the results of an analysis of gravity wave momentum fluxes in the mesosphere and lower thermosphere inferred using a dual beam doppler radar near adelaide australia during june 1984 our analysis reveals that over 70 of the momentum flux and of the inferred zonal drag was due to gravity waves with observed periods less than one hour this suggests that it is the gravity waves with high intrinsic frequencies and small horizontal scales that are most effective at transporting momentum into the middle atmosphere the temporal variations in the momentum flux and flux divergence due to high frequency motions were also examined in detail in addition to daily variability a strong diurnal modulation was observed to occur this was found to be correlated with the phase of large amplitude diurnal tidal motions as a result of these observations a gravity wave tidal interaction model was proposed which accounts for all of the major features of the observed data including a reduction i

gravity wave characteristics in the southern hemisphere revealed by a high resolution middle atmosphere general circulation model abstractgravity wave characteristics in the middle to high latitude southern hemisphere are analyzed using simulation data over 3 yr from a high resolution middle atmosphere general circulation model without using any gravity wave parameterizations gravity waves have large amplitudes in winter and are mainly distributed in the region surrounding the polar vortex in the middle and upper stratosphere while the gravity wave energy is generally weak in summer the wave energy distribution in winter is not zonally uniform but it is large leeward of the southern andes and antarctic peninsula linear theory in the three dimensional framework indicates that orographic gravity waves are advected leeward significantly by the mean wind component perpendicular to the wavenumber vector results of ray tracing and cross correlation analyses are consistent with this theoretical expectation the leeward energy propagation extends to several thousand kilometers which explains part of the gravity wave distribution aro

mean winds and tides in the arctic mesosphere and lower thermosphere 1 a new meteor radar has been deployed at esrange 68 n 21 e near kiruna in sweden the radar has been used to measure winds and tides in the arctic mesosphere lower thermosphere region over the interval august 1999 to july 2000 conspicuous features of the measured mean winds include a strong shear of up to 5 m s 1 km 1 in the summer zonal flow resulting in eastward flows of in excess of 30 m s 1 at the upper heights observed 97 km an equatorward meridional flow is observed in summer and winter which reaches maximum values of 13 m s 1 in a summer jet poleward flow in comparison is weak and only occurs at the equinoxes the monthly mean and seasonal mean behaviors of the amplitudes and phases of the 12 and 24 hour tides are examined and compared to the global scale wave model 98 the observations are generally very close to the model predictions for the 24 hour tide and for the 12 hour tide in winter in other seasons particularly summer the observed 12 hour tidal amplitudes are significantly larger than those predicted in spring and summer the wavelength of the 12 hour tide is significantly larger than that predicted

seasonal variations in lower stratospheric gravity wave energy above the falkland islands 1 the gravity wavefield in the lower stratosphere between 15 km and 22 km altitude above mount pleasant airport 51 49 s 58 26 w on the falkland islands is studied using over 2100 high resolution radiosonde soundings from 2002 to 2010 the seasonal variation in vertical direction of propagation shows a small decrease in numbers of upward propagating waves that is related to critical level filtering however there is a very large increase in numbers of downward propagating waves between july and september this is attributed to the proximity of the edge of the polar vortex there is a seasonal variation in gravity wave energy density with a large peak during the austral autumn equinox this is markedly different to results in the literature both from rothera on the antarctic peninsula and stations on the main antarctic continent this seasonal pattern has been shown to be linked to variations in the sources of upward propagating gravity waves the seasonal variation in gravity wave characteristics above mount pleasant airport seen in our results suggests that the gravity wavefield in this region is determined by a combination of different gravity wave sources located above and below the lower stratosphere

three dimensional properties of andes mountain waves observed by satellite a case study the southern andes region has been clearly identified in previous satellite and balloon observations and in global models as a hot spot of small scale gravity wave activity with monthly mean momentum fluxes exceeding 10 times background values in fall winter and spring seasons this makes this region a focus of interest for global circulation and climate studies we analyze a case study on 8 may 2006 combining observations from the atmospheric infrared sounder instrument on the aqua satellite and the high resolution dynamics limb sounder instrument of the aura satellite to form a three dimensional picture of the wave field the observations show a widespread wave pattern over the southern andes extending eastward over the south atlantic simulations with the weather research forecasting model clearly identify the waves as orographic in origin but the observed wave pattern is far from the simple two dimensional wave field forced by steady flow over a mountain ridge the morphology of the pattern is consistent with three dimensional linear theoretical calculations of downstream propagation and latitudinal focusing of mountain waves into the stratospheric jet the observations confirm the importance of this process in the stratosphere and we find the process also occurring in the global analysis and forecasts from the european centre for medium range weather forecasting our analysis evaluates some strengths and weaknesses of current orographic wave drag parameterizations in global models and the relevance of parameterization assumptions in global models with high resolution copyright 2011 by the american geophysical union

melts mush and more evidence for the state of intermediate to silicic arc magmatic systems understanding the physical state of intermediate to silicic arc magmatic systems is necessary for our petrologic models of these systems researchers have generated a plethora of data geophysical geochronological petrological theoretical over the past few decades these data have changed how we view arc magmatic systems leading to a model of crystal mush that is rejuvenated repeatedly over the lifespan of the magmatic system however much data are either circumstantial or incomplete paterson et al 2016 october issue use a combined set of textural geochemical and temporal data to demonstrate the changing physical state of the tuolumne intrusive complex in california over its 10 million year history they offer evidence for magmatic erosion and recycling along with the potential for a surge growth of the batholith that allows for significant volumes of magma to exist ephemerally under arc volcanoes most intermediate to silicic arc magmas henceforth arc magma are stored 3 km depth so direct observation is impossible instead this question has been approached in four main ways 1 geophysical inspections of active arcs 2 mineral geochronology 3 field observations of plutons and 4 thermal and physical modeling of magmatic systems each of these four avenues has their own strengths and shortcomings many times the interpretation of these data appears to be at odds some overarching observations can be made about what we know of the state of active intermediate to silicic arc magmatic systems geophysical observations such as seismic tomography have yielded little evidence for large bodies of fully molten magma persistently underneath arc volcanoes if anything only small lenses of partial melt are observed at

formation of low δ18o rhyolites after caldera collapse at yellowstone wyoming usa we present a new model for the genesis of low 18o rhyolites of the yellowstone caldera based on analyses of zircons and individual quartz phenocrysts low 18o rhyolites were erupted soon after the massive caldera forming lava creek tuff eruption 602 ka 1000 km3 and contain xenocrysts of quartz and zircon inherited from precaldera rhyolites these zircons are isotopically zoned and out of equilibrium with their host low 18o melts and quartz diffusion modeling predicts that magmatic disequilibria of oxygen isotopes persists for as much as tens of thousands of years following nearly total remelting of the hydrothermally altered igneous roots of the depressed cauldron in which the alteration resistant quartz and zircon initially retained their 18o values these results link melting to caldera collapse rule out rapid or catastrophic magma meteoric water interaction and indicate wholesale melting rather than assimilation or partial melting

regional granulite facies metamorphism in the ivrea zone is the mafic complex the smoking gun or a red herring one widely accepted paradigm for the development of continental lower crust is that regional granulite facies metamorphism is caused by intrusion of mafic magma beneath or into the crust magmatic accretion the amphibolite to granulite facies supracrustal section exposed in the ivrea zone southern alps northern italy is commonly cited as a classic example establishing this postulated genetic relationship our interpretation of the pattern of metamorphic isograds compositional trends in high grade metasedimentary rocks and textural evidence in metapelite however indicates that final emplacement of the mafic plutonic rocks the mafic complex occurred subsequent to the regional thermal maximum field and petrographic relations suggest that a spatially restricted contact melting event in crustal rocks accompanied the emplacement of the mafic complex this inference is consistent with leucosome compositions in migmatites and a low pressure high temperature metamorphic overprint recorded by mineral assemblages in wall rocks proximal to the intrusion therefore evidence of anatexis and metamorphism of crustal rocks associated unequivocally with emplacement of the mafic complex is found only within an 2 km wide contact aureole overlying the intrusion the narrow aureole associated with emplacement of the mafic complex demonstrates that in some cases emplacement of large volumes of mafic magma within the crust does not inexorably lead to regional scale granulite facies metamorphism and large ion lithophile element depletion by melt loss

inertia gravity waves in antarctica a case study using simultaneous lidar and radar measurements at mcmurdo scott base 77 8 s 166 7 e 1 this study presents the first coincident observation of inertia gravity waves igws by lidar and radar in the antarctic mesopause region this is also the first known observation of two simultaneous igws at the same location an fe boltzmann lidar at arrival heights 77 8 s 166 7 e provides high resolution temperature data and a co located mf radar provides wind data on 29 june 2011 coherent wave structures are observed in both the fe lidar temperature and mf radar winds two dominant waves are determined from the temperature data with apparent periods of 7 7 0 2 and 5 0 0 1 h and vertical wavelengths of 22 2 and 23 2 km respectively the simultaneous measurements of temperature and wind allow the intrinsic wave properties to be derived from hodograph analyses unambiguously the analysis shows that the longer period wave propagates northward with an azimuth of 11 5 clockwise from north this wave has a horizontal wavelength of h 2 2 0 2 103 km and an intrinsic period of i 7 9 0 3 h the intrinsic horizontal phase speed cih for this wave is 80 4 m s while the horizontal and vertical group velocities cgh and cgz are 48 3 m s and 0 5 0 1 m s respectively the shorter period wave has i 4 5 0 3 h and 100 4 with h 1 1 0 1 103 km and cih 68 5 m s its group velocities are cgh 58 5 m s and cgz 1 1 0 1 m s therefore both waves propagate with very shallow elevation angles from the horizon 0 6 0 1 and 1 1 0 1 for the longer and shorter period waves respectively but originate from different sources our analysis suggests that the longer period igw most likely originates from the stratosphere in a region of unbalanced flow

rupture termination and jump on parallel offset faults proper evaluation of seismic hazard depends on accurate estimates of potential earthquake size in areas with complex multisegment fault systems such an estimate in turn depends on an ability to predict the circumstances under which rupture may jump between fault segments many observational and numerical studies have analyzed the phenomenon of jumping rupture but none has focused on how the process of rupture termination on the primary nucleating fault segment affects the ability of rupture to jump to a secondary fault segment in the current study i model the dynamics of a simple 2d strike slip fault system with two parallel segments arranged with either a compressional or extensional stepover i vary the suddenness with which the initial shear stress tapers to zero on the primary section if the initial shear stress goes to zero over a very small 100 m distance rupture readily jumps both compressional and extensional stepovers of 1 km if the initial shear stress tapers to zero over 1 km rupture can jump the compressional stepover but not the extensional stepover if the initial shear stress tapers to zero over 2 5 km rupture cannot jump either the compressional or the extensional stepover the results illustrate the importance of the slip gradient and the resultant static stress field and the acceleration of the rupture front and the resultant generation of stopping phases in determining the probability of jumping rupture

a climatology of gravity wave motions in the mesopause region at adelaide australia abstract a statistical study of gravity wave motions in the mesosphere and lower thermosphere measured with a mf partial reflection radar located at buckland park new adelaide 35 s 138 e in the period november 1933 to december 1984 is presented the analyses am confined to waves with ground based periods between 1 and 24 h time height cross sections show that the mean square amplitudes u 2 and v 2 of the zonal and meridional perturbation velocities respectively vary in a predominantly semiannual manner such that the minima in wave activity coincide with the reversals in the zonal circulation in the middle atmosphere in most instances v 2 is greater than u 2 which together with the small but nonzero u v fluxes shows that the gravity wave field is partially polarized a technique similar to that used to analyse partially polarized electromagnetic waves suggests that on a seasonal basis the wave field is polarized by about 10 to 20 but for shorter periods the degree of polarization may be signi

tracking the evolution of large volume silicic magma reservoirs from assembly to supereruption the most voluminous silicic volcanic eruptions in the geological past were associated with caldera collapses above giant silicic magma reservoirs the thermal evolution of these subcaldera magma reservoirs controls the volume of eruptible magma and eruptive style here we combine high precision zircon u pb geochronology trace element analyses of the same mineral grains and mass balance modeling of zircon trace element compositions allowing us to track the thermal and chemical evolution of the oligocene fish canyon tuff magma reservoir colorado united states as a function of absolute time systematic compositional variations in u pb dated zircons record 440 k y of magma evolution an early phase of volumetric growth was followed by a period of cooling and crystallization during which the fish canyon magma approached complete solidifi cation subsequent remelting due to underplated andesitic recharge magmas began 219 45 k y prior to eruption and led to the generation of 5000 km3 of eruptible crystal rich 45 vol dacite age equivalent but compositionally different zircons in an andesite enclave from late erupted fish canyon tuff tie the growth and thermal evolution of the upper crustal reservoir to a lower crustal magma processing zone our results demonstrate that the combination of high precision dating and trace element analyses of accessory zircons can reveal invaluable information about the chemical and thermal histories of silicic magmatic systems and provides critical input parameters for fl uid dynamic modeling

volcanic winter and accelerated glaciation following the toba super eruption the eruption of toba in sumatra 73 500 years ago was the largest known explosive volcanic event in the late quaternary1 it could have lofted about 1015 g each of fine ash and sulphur gases to heights of 27 37 km creating dense stratospheric dust and aerosol clouds here we present model calculations that investigate the possible climatic effects of the volcanic cloud the increase in atmospheric opacity might have produced a volcanic winter 2 a brief pronounced regional and perhaps hemispheric cooling caused by the volcanic dust followed by a few years with maximum estimated annual hemispheric surface temperature decreases of 3 5 c the eruption occurred during the stage 5a 4 transition of the oxygen isotope record a time of rapid ice growth and falling sea level3 we suggest that the toba eruption may have greatly accelerated the shift to glacial conditions that was already underway by inducing perennial snow cover and increased sea ice extent at sensitive northern latitudes as the onset of climate change may have helped to trigger the eruption itself4 we propose that the toba event may exemplify a more general climate volcano feedback mechanism

laacher see revisited high spatial resolution zircon dating indicates rapid formation of a zoned magma chamber high spatial resolution 230 th 238 u disequilibrium dating reveals rapid zircon crystallization prior to the 12 900 yr b p laacher see germany phonolite eruption zircons from lower laacher see tephra llst and syenitic subvolcanic nodules share ree and low u th characteristics and define an isochron age of 17 1 1 3 ka 1 zircons also show higher initial 230 th 232 th 0 and oxygen isotopic disequilibrium compared to their host phonolite thus llst zircons shortly predate the eruption and yet are not strictly part of the phonolite crystallization sequence based on their similarity to zircons in subvolcanic nodules they are instead interpreted to be scavenged from a precursor syenite intrusion which implies short a few k y filling and differentiation timescales for the laacher see magma chamber thorium and oxygen isotopes in zircon as well as evidence for abundant crustal xenocrysts further indicate extensive crustal contamination which allows for considerably faster basanite phonolite differentiation than the 100 k y time span previously estimated from bulk u series data

observations of a nonmigrating component of the semidiurnal tide over antarctica 1 data obtained from the mf radars situated at davis syowa and rothera in antarctica are used to detect a nonmigrating component of the semidiurnal tide in the mesosphere and lower thermosphere these radars are at similar latitudes and so share a common migrating tidal component by fitting semidiurnal tide vectors to each stations data and performing subtractions of these vectors for pairs of stations the migrating component can be removed and the difference between the nonmigrating components revealed non zero differences in the summer months december to march indicate the presence of a significant nonmigrating component modeling studies and observations at other sites suggest that it is most likely the westward propagating wavenumber 1 nonmigrating component that is contributing to the semidiurnal tide the data presented here are found to be consistent with this hypothesis a climatology of this nonmigrating component is presented and discussed comparisons with the global scale wave model suggest that latent heat release is not a significant forcing mechanism at these heights and latitudes

application of proton microprobe data to trace element partitioning in volcanic rocks abstract in situ proton microprobe analyses are used to calculate partition coefficients d for mn fe cu zr ga rb sr y zr ba and pb and more restricted data for ni ge nb and as in pyroxenes olivines biotites hornblendes feldspars and fe ti oxides from 32 volcanic rocks all with glassy matrices these range from leucitite and picritic basalt to high silica and peralkaline rhyolites data for pigeonite aenigmatite allanite and leucite are included where these occur as additional phases coefficients have also been rayleigh fractionation corrected this correction being significant for those elements with high coefficients in specific mineral phases and where pronounced crystallisation has occurred partition coefficients are presented as plots vs nbo t ratios of coexisting glasses melts negative correlations are observed based on log transformed data for mn zn fe and y pyroxenes mn zn and fe olivines mn and zn fe ti oxides nb y sr and zr hornblendes sr plagioclase and ba cu zn and fe feldspars these element partition coefficients are not correlated with bulk mineral compositions zr and ga are not correlated with either glass or mineral compositions except zr in hornblende the correlations support the role of melt polymerisation in controlling element partitioning at least for those elements listed although possible effects of temperature cannot be uniquely isolated in the present data set the coefficients presented here are generally consistent with published values for equivalent rock compositions one difference being that some of the higher published coefficients e g sr in plagioclase are not matched in the present data set from a practical viewpoint the relative regularity of the coefficient data presented does facilitate choice of relevant coefficient values that are required for petrogenetic modelling procedures

tropopausal mountain waves over arecibo a case study abstract vertically variable horizontal winds observd over arecibo by to and woodman which were previously interpreted as a manifestation of inertia gravity waves having intrinsic periods comparable to the local inertial period are reinterpreted as quasi stationary gravity waves of much shqrter intrinsic period induced orographically by airflow over the island and mountains of puerto rico the ellipticity of the viated halograph is attributed to an effect of background wind shears in the presence of such waves this new interpretation carries implicationsboth for the study of similar wind patterns elsewhere and for the reproducibility ofwind fields at arecibo where a natural laboratory for the study of mountain waves of critical layer interactions and of associated turbulence appears to be available

case studies of plagioclase growth and residence times in island arc lavas from tonga and the lesser antilles and a model to reconcile discordant age information abstract the time scales of crystal growth and residence in magmas have received much attention because such information can constrain the physical processes involved however crystals and liquids can have different ages leading to apparently contradictory information from different dating methods two case studies are presented from island arc lavas that highlight such dichotomies plagioclase crystal size distributions and u th ra isotope data are presented for lavas from late and metis shoal in tonga and from soufriere st vincent in the lesser antilles in all three lavas mineral data yield apparent u th ages of 30 50 kyr yet 226 ra excesses are preserved in both the minerals and the whole rocks the crystal size distributions suggest crystal growth over 100s of years but also frequently indicate the presence of mixed crystal populations furthermore a cumulate from soufriere yields the same u th age as its host lava on 226 ra ba versus time evolution diagrams curves for melts in equilibrium with plagioclase provide apparent ages of 1700 3300 yr for tonga but for soufriere they are displaced below that of the whole rock our interpretation is that the phenocrysts from all three lavas are zoned in both composition and age the apparent u th ages reflect mixtures of old cores and young rims and indicate a volume integrated age of 10s of kyr for the time for initial crystal growth crystal liquid segregation the time of storage as a cumulate plus the time spent during entrainment and growth in the new magma prior to eruption the 226 ra excesses were imparted to overgrowths on the old cumulate cores during entrainment by subsequent injections of new magma because crystal growth segregation and entrainment can all appear to occur in 100s to a few thousand years at most the bulk of the u th time scale is inferred to record storage in cumulates which are then incorporated into new magma batches plagioclase growth rates of 3 9 10 13 cm s 1 would reconcile the combined ra th and crystal size distribution data magma differentiation time scales and eruptive periodicity are one to three orders of magnitude shorter than the inferred cumulate storage times indicating complex phenocryst liquid behaviour beneath island arc volcanoes

record of magma chamber processes preserved in accessory mineral assemblages aztec wash pluton nevada field relations and geochemistry indicate that aztec wash pluton had a complex open system history the tilted pluton represents a 2 5 km thick chamber that was recharged with both felsic and mafic magma the lower portion is highly heterogeneous with mafic sheets cumulates hybrid rocks mafic felsic and composite dikes and sheets and pods of granite heterogeneous h zone the upper part is granite that is generally homogeneous in texture and geochemistry granite g zone at the base of the g zone a discontinuous zone buffer b zone records interaction between the g and h zones complexity of the h zone makes detailed reconstruction of magma chamber history difficult and the relatively homogeneous g zone appears to offer few clues about the evolution of the pluton or the interaction between the felsic and underlying more mafic magmas accessory mineral textures zoning and assemblages in the g zone however are far from homogeneous and provide clear evidence for fluctuating conditions that elucidates magma chamber history mafic rocks of the h zone contain the accessory mineral assemblage ilmenite magnetite quench apatite or late sphene and zircon g zone rocks have magnetite apatite sphene zircon or allanite ilmenite and chevkinite the magnetite allanite early sphene apatite and zircon association that characterizes much of the g zone indicates a lower temperature and possibly higher f o2 than the h zone assemblage mineral textures and zoning however document fluctuations in the stable g zone assemblage 1 as many as five rounded surfaces truncate internal zones in zircon each indicating a dissolution event 2 in addition to euhedral concentric zoning sphene contains regions of highly irregular zoning that are rich in inclusions especially anhedral ilmenite 3 ilmenite and allanite are mutually exclusive but allanite is present in the matrix of rocks that contain sphene with ilmenite inclusions and sphene grains in some samples have alternating regions with allanite and ilmenite inclusions we attribute fluctuations in the stable g zone accessory assemblage to fluctuations in temperature and possibly f o2 with appearance of the high t reduced assemblage indicating interaction with hot mafic h zone magma these interactions certainly involve heat transfer and may involve limited chemical contamination we infer that they must have taken place near the h zone g zone boundary the most frequent and intense fluctuations marked by zircon with the highest number of truncation surfaces and by sphene with irregular zoning and abundant ilmenite inclusions affected rocks that are near the boundary but ilmenite inclusions in sphene and truncation surfaces in zircon are present to the top of the pluton we conclude that granitic magma was subjected to multiple cycles of thermally induced vertical transfer convection that at least initially affected the entire upper part of the chamber

southern argentina agile meteor radar system design and initial measurements of large scale winds and tides 1 the southern argentina agile meteor radar saamer was installed at rio grande on tierra del fuego 53 8 s 67 8 w in may 2008 and has been operational for 24 months this paper describes the motivations for the radar design and its placement at the southern tip of south america its operating modes and capabilities and observations of the mean winds planetary waves and tides during its first 20 months of operation saamer was specifically designed to provide very high resolution of large scale motions and hopefully enable direct measurements of the vertical momentum flux by gravity waves which have only been possible previously with dual or multiple beam radars and lidars or in situ measurements saamer was placed on tierra del fuego because it was a region devoid of similar measurements the latitude was anticipated to provide high sensitivity to an expected large semidiurnal tide and the region is now recognized to be a hot spot of small scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere perhaps the most dynamically active location on earth saamer was also intended to permit simultaneous enhanced meteor studies including head echo and nonspecular measurements which were previously possible only with high power large aperture radars initial measurements have defined the mean circulation and structure exhibited planetary waves at various periods and revealed large semidiurnal tide amplitudes and variability with maximum amplitudes at higher altitudes often exceeding 60 m s 1 and amplitude modulations at periods from a few to 30 days

rejuvenation of crustal magma mush a tale of multiply nested processes and timescales some relatively crystal rich silicic volcanic deposits including large volume ignimbrites preserve evidence of a history where a rheologically locked high crystallinity magma was rejuvenated unlocked through enthalpy mass exchange with newly injected recharge magma of higher specific enthalpy this is one event in a possible complex history that is the volcanic product of an eruption reflects an array of sequential and nested processes including melt formation and segregation ascent cooling crystallization crustal assimilation magma recharge unlocking shallow ascent fluid exsolution and eruption deconvolution of these these nested processes and concomitant timescales is complicated and relies on a multidisciplinary approach studies that do not clearly associate process and correlated timescale have the potential to provide misleading timescale information we report the results of thermodynamic and heat transfer calculations that document mass energy and phase equilibria constraints for the unlocking of near solidus rhyolite mush via magma mingling heat exchange only with basaltic recharge magma of higher specific enthalpy to achieve unlocking defined as the transition from near solidus to 50 percent melt of the host silicic magma phase equilibria computations provide 1 the enthalpy required to unlock mush 2 the mass ratio of recharge magma to mush mr mm when the two magmas achieve thermal equilibrium and 3 the changes in melt mineral and fluid phase masses compositions and temperatures during the approach to unlocking the behavior of trace elements is computed with knowledge of mineral fluid and melt proportions and solid fluid and solid melt partition coefficients evaluation of unlocking for relatively dry 0 5 wt h2o and wet 3 9 wt h2o rhyolitic mushy locked magma by basaltic recharge at upper crustal pressures indicates minimum values of mr mm can be significantly less than 1 assuming the mingling process is isenthalpic with no waste heat for active volcanic systems estimates of mr may be tested using geodetic data wet mush has lower energy requirements for unlocking and thus requires lower mr mm than dry mush wet rejuvenated magmas therefore may be more abundant in the volcanic rock record and unlocked dry mushes may be restricted to extensional tectonic settings with high recharge flux temperature changes in dry mush as it unlocks are pronounced greater than 150 c compared to those in wet mush which are smaller than the resolution of classical geothermometry 15 c phase equilibria calculations show that as required the net volume of crystals decreases during unlocking interestingly calculations also indicate reactive crystal growth by chemical re equilibration at the crystal size scale during unlocking may also take place in either dissolution by unidirectional resorption or reactive dissolution new growth the chemical signatures of unlocking potentially preserved in crystals or parts of crystals for example rims are predictable and hence testable independent of unlocking thermodynamics the phase equilibria and elemental consequences of isentropic magma ascent a transport event that follows unlocking can also be predicted detailed examination of several canonical cases reveals a marked contrast with isenthalpic unlocking thereby providing a means of process deconvolution unlocking timescales are estimated by two methods one that calculates the time to reach thermal equilibrium for recharge magma dispersed in mush as clumps of fixed size and the second where the required volume of recharge magma is initially a single clump and evolves to smaller size through clump stretching and folding for a range of magma volumes from 0 1 to 5000 km3 unlocking times range from 10 2 to 106 years the shorter timescales for any magma volume requires a large number of relatively small clumps n 106 which implies that large volumes of mush purported to unlock over short timescales 102 103 years and less should preserve and exhibit evidence of intimate magma mingling the key result of our analysis is that multiple timescales are operative during the potentially long and complex history of silicic mush formation rejuvenation and ascent to correctly ascribe timescales to unlocking requires a holistic understanding of the myriad processes that affect the magma before during and after enthalpy exchange in the absence of this context unlocking timescales may be incorrectly constrained which in turn may hinder eruption forecasting and associated hazard mitigation

sources of mesoscale variability of gravity waves part i topographic excitation abstract aircraft measurements of winds and temperatures collected during the gasp program are used to study the effects of topography as a source of mesoscale variability variances of fluctuations at the mesoscale over rough terrain are enhanced up to nearly two orders of magnitude compared to nonsource regions in some cases and are frequently enhanced by an order of magnitude the implications of these episodic enhancements of variances for the vertical transports of energy and momentum are considered in the framework of gravity wave theory the observed flight data are used to estimate the momentum flux u w on several flight segments results show that the flux is generally negative with mean value 0 26 m2 s 2 and with magnitudes ranging up to 1 5 m2 s 2 spectral analysis shows that the largest contributions to the net flux come from horizontal scales of 25 x 60 km finally the observed momentum fluxes are used to infer the anisotropy factor of gravity waves over rough terrain which is foun

diverse late stage crystallization and storage conditions in melt domains from the youngest toba tuff revealed by age and compositional heterogeneity in the last increment of accessory phase growth the chemical record contained within the final increment of growth on crystals is utilized to reveal the dynamics and timescales of magma assembly and storage before eruption of the cataclysmic 2800 km3 youngest toba tuff ytt indonesia in situ u th disequilibrium dates and trace element concentrations were obtained via secondary ionization mass spectrometry sims on unsectioned and unpolished faces of individual zircon and allanite crystals the six high silica 73 wt sio2 pumices from which crystals were derived are among the more evolved and lower crystallinity 25 wt pumices from the ytt eruption and likely represent the melt dominated portion of the magma system discrete sims measurement cycles were coupled with statistical treatments to detect zircon and allanite surface zoning domains at the 1 m scale coupled r melts and accessory phase saturation modeling indicates that at the granite ternary minimum or eutectoid conditions that define this portion of the ytt zircon and allanite crystallization is dependent on and proportionate to major phase crystallization and is more limited than at pre eutectoid conditions a lower proportion of near eruption zircon surface ages in the comparatively cool and wet ytt relative to other hotter and drier voluminous silicic eruptions could reflect the influence of eutectoid storage conditions on magmatic responses to remobilization related magmatic recharge

on the distribution and separation of crystals in convecting magma abstract fractionation of crystals from magma stands squarely as the central principle of igneous petrology and the critical balance is the competition between crystal settling or rising velocity and magmatic convective velocity a ratio we call s the convective velocity is intimately related to the rate of heat transfer from the system although the theory of sediment distribution in rivers establishes the critical parametric balance and it has been often applied to igneous systems this method turns out to be valid only for small concentrations of crystals and it is not clear if it is accurate for other than turbulent flows where the prandtl number is near unity a generalized theory of particle crystal or bubble behavior is presented scaling of the generalized result shows for the magmatic conditions of small crystallinities small particle reynolds number and newtonian viscosity that the exact distribution of crystals in a convecting magma can be found analytically regardless of the flow field critical retention occurs only for 0 s s 0 for sinking crystals retention is centered in the region of maximum updraft for floating particles retention occurs in regions of downflow which for a simple cellular convective pattern produces a torus shaped retention region against the walls about the midsection of the body for a stack of flattened convective cells which in the crudest sense is analogous to double diffusive convection the zones of retention form depending on the exact flow field either a stack or staggered stack of pillows through the central region crystals settling from top to bottom around this stack take a tortuous path and may exhibit a complex but regular compositional zoning additional effects of fluids possessing a yield strength turbulence particle shape and wall and particle dispersive effects are more qualitatively evaluated for each flow field the amount of retention and the effective settling velocity of all crystals is found as a function of s the critical parameter s controlling retention can be estimated from a parametric representation involving stokes s law and the rayleigh number this shows that some retention probably occurs in all magmas and it increases with approach of the magma to the earth s surface although both crystal settling rate and convection decrease with increasing magmatic viscosity the overall effect is to increase retention decrease s magmas having a viscosity near and beyond about 10 4 poise and chambered in the nearsurface environment should show large degrees of crystal retention retention is however never complete for magmas and the flux of settling crystals leading to differentiation varies as a function of crystallinity this flux or flux probability p f is zero both at the liquidus and the point of maximum packing of crystals which for basalts is about 60 the importance of differentiation is regulated by the amount of time spent in the high crystal flux state and a relative measure of this time is given by the thermal probability p t introduced previously thus the probability of differentiation p d is given by the product p f p t which shows that differentiation must occur over a restricted range of crystallinities from about 20 to 45 for basalts and from about 10 to 30 for rhyolitic magmas the most basic lessons learned here are that the full range of crystallinities is not equally accessible to crystal fractionation and the most fundamental information describing the dynamic state and behavior of magma may well be the distribution of crystal sizes found in lavas

modeling the thermal evolution of fault controlled magma emplacement models implications for the solidification of granitoid plutons a two dimensional finite diaerence model is used to simulate the conductive thermal regime attend ing construction and maintenance of a continental magma chamber by intrusion of granite dikes into grano diorite host rocks displaced at various spreading rates final intrusion shapes include tabular square and vertical rectangular bodies emplaced in the shallow crust 5 15 km and tabular bodies emplaced in the middle crust 15 20 km fed by dikes with widths of between 20 and 100 m the formation of a steady state chamber is defined as the point at which the ambient temperatures surpass the intrusion solidus forestalling the solidifi cation of subsequently intruded material for spreading rates 10 mm year 1 construction of a steady state magma chamber in the shallow crust took 260 ka rectangular 360 ka square and 1 ma tabular whereas in the mid crust a steady state was reached in less than 30 ka tabular at faster spreading rates 25 and 50 mm year 1 ambient temperatures pass the solidus isotherm forming a steady state reservoir within 55 ka depending on intrusion depth and size for 10 25 mm year 1 spreading rates sheeted dikes make up from 10 to 100 of the intrusion the thermal modeling supports the following conclusions a episodic magma emplacement into a fault con trolled setting is a thermally viable means of constructing a steady state chamber at moderate to fast spreading rates only if the duration of faulting and intrusion are long enough to elevate ambient temperatures above the intrusion solidus b isotherms will migrate outward during successive intrusion before converging back on the center of the intrusion after chamber construction c the margins of most intrusions formed by this scen ario should contain sheeted dikes d the solidus isotherm and thus the solidification front that it tracks will become progressively curviplanar during the construction of the magma chamber and will not represent the in itial shape of the intrusions i e sheets e the steady state chamber will be smaller than the total intrusion dimensions and f magmatic fabrics will form diachronously and not always parallel to sheet margins as they track the migrating solidification front because it is unlikely that most large intrusions formed instan taneously the eaects of continued addition of heat on the migration of solidification fronts may have signifi cant implications for magmatic processes in many emplacement scenarios 1998 elsevier science ltd all rights reserved

fitful and protracted magma assembly leading to a giant eruption youngest toba tuff indonesia the paroxysmal eruption of the 74 ka youngest toba tuff ytt of northern sumatra produced an extraordinary 2800 km3 of nonwelded to densely welded ignimbrite and coignimbrite ashfall we report insights into the duration of ytt magma assembly obtained from ion microprobe u th and u pb dates including continuous age spectra over 50 of final zircon growth for pumices and a welded tuff spanning the compositional range of the ytt a relatively large subpopulation of zircon crystals nucleated before the penultimate caldera related eruption at 501 ka but most zircons yielded interior dates 100 300 ka thereafter zircon nucleation and growth was likely episodic and from diverse conditions over protracted time intervals of 100 to 500 ka final zircon growth is evident as thin rim plateaus that are in th u chemical equilibrium with hosts and that give crystallization ages within tens of ka of eruption the longevity and chemical characteristics of the ytt zircons as well as evidence for intermittent zircon isolation and remobilization associated with magma recharge is especially favored at the cool and wet eutectoid conditions that characterize at least half of the ytt wherein heat fluxes could dissolve major phases but have only a minor effect on larger zircon crystals repeated magma recharge may have contributed to the development of compositional zoning in the ytt but considered together with limited allanite quartz and other mineral dating and geospeedometry regular perturbations to the magma reservoir over 400 ka did not lead to eruption until 74 ka ago

estimation of gravity wave momentum flux and phase speeds from quasi lagrangian stratospheric balloon flights part i theory and simulations a methodology for estimating gravity wave characteristics from quasi lagrangian observations provided by long duration superpressure balloon flights in the stratosphere is reviewed wavelet analysis techniques are used to detect gravity wave packets in observations of pressure temperature and horizontal velocity an emphasis is put on the estimation of gravity wave momentum fluxes and intrinsic phase speeds which are generally poorly known on global scales in the atmosphere the methodology is validated using monte carlo simulations of time series that mimic the balloon measurements including the uncertainties associated with each of the meteorological parameters while the azimuths of the wave propagation direction are accurately retrieved the momentum fluxes are generally slightly underestimated especially when wave packets overlap in the time frequency domain or for short period waves a proxy is derived to estimate by how much momentum fluxes are reduced by the analysis retrievals of intrinsic phase speeds are less accurate especially for low phase speed waves a companion paper part ii implements the methodology to observations gathered during the vorcore campaign that took place in antarctica between september 2005 and february 2006

gravity wave tidal interactions in the mesosphere and lower thermosphere over rothera antarctica 68 s 68 w 1 a simple technique for measuring gravity wave activity has been used to investigate gravity wave tidal interactions in the polar mesosphere and lower thermosphere mlt the technique uses the radial velocities of individual meteors recorded by meteor radar to derive a statistical measure variance of the activity of the high frequency gravity wave field this technique can measure gravity waves with horizontal wavelengths of up to about 400 km and periods up to approximately 3 hours interactions between the observed gravity wave field and the background wind are investigated using data collected between february 2005 and december 2008 by a meteor radar based at rothera antarctica 68 s 68 w the results reveal the presence of significant modulations of the observed gravity wave field at tidal periods of 12 and 24 hours correlations between the hourly zonal winds and the gravity wave field measured by the meteor radar reveal an in phase relationship between the hourly zonal winds and gravity wave variance in winter and an anti phase relationship in summer this is consistent with the theory of filtering by tidal winds acting on a zonally asymmetric gravity wave field in which westward waves dominate in winter and eastward waves dominate in summer the limitations of the technique and the effect this has on the interpretation of these results are also considered the effects of the diurnal cycles in meteor count rates the uncertainty in recorded radial velocities and the uncertainty in the measured heights of meteors are considered

southern argentina agile meteor radar initial assessment of gravity wave momentum fluxes 1 the southern argentina agile meteor radar saamer was installed on tierra del fuego 53 8 s in may 2008 and has been operational since that time this paper describes tests of the saamer ability to measure gravity wave momentum fluxes and applications of this capability during different seasons test results for specified mean tidal and gravity wavefields including tidal amplitudes and gravity wave momentum fluxes varying strongly with altitude and or time suggest that the distribution of meteors throughout the diurnal cycle and averaged over a month allows characterization of both monthly mean profiles and diurnal variations of the gravity wave momentum fluxes applications of the same methods for real data suggest confidence in the monthly mean profiles and the composite day diurnal variations of gravity wave momentum fluxes at altitudes where meteor counts are sufficient to yield good statistical fits to the data monthly mean zonal winds and gravity wave momentum fluxes exhibit anticorrelations consistent with those seen at other midlatitude and high latitude radars during austral spring and summer when no strong local gravity wave sources are apparent when stratospheric variances are significantly enhanced over the drake passage hot spot during austral winter however mlt winds and momentum fluxes over saamer exhibit very different correlations that suggest that mlt dynamics are strongly influenced by strong local gravity wave sources within this hot spot saamer measurements of mean zonal and meridional winds at these times and their differences from measurements at a conjugate site provide further support for the unusual momentum flux measurements

recharge in volcanic systems evidence from isotope profiles of phenocrysts strontium isotope ratios measured from core to rim across plagioclase feldspar crystals can be used to monitor changes in the isotope composition of the magma from which they grew in samples from three magma systems from convergent margin volcanoes sudden changes in major element composition petrographic features and strontium isotope composition were found to correspond to discrete magmatic events most likely repeated recharge of more mafic magma with lower ratios of strontium 87 to strontium 86 into a crustally contaminated magma

introduction to u series geochemistry during the last century the earth sciences underwent two major revolutions in understanding the first was the recognition of the great antiquity of the earth and the second was the development of plate tectonic theory these leaps in knowledge moved geology from its largely descriptive origins and established the modern quantitative earth sciences for any science and particularly for the earth sciences time scales are of central importance until recently however the study of time scales in the earth sciences was largely restricted to the unraveling of the ancient history of our planet for several decades earth scientists have used a variety of isotope chronometers to unravel the long term evolution of the planet a fuller understanding of the physical and chemical processes driving this evolution often remained elusive because such processes occur on time scales 1 105 years which are simply not resolvable by most conventional chronometers the u series isotopes however do provide tools with sufficient time resolution to study these earth processes during the last decade the earth sciences have become increasingly focused on fundamental processes and u series geochemistry has witnessed a renaissance with widespread application in disciplines as diverse as modern oceanography and igneous petrology the uranium and thorium decay series contain radioactive isotopes of many elements in particular u th pa ra and rn the varied geochemical properties of these elements cause nuclides within the chain to be fractionated in different geological environments while the varied half lives of the nuclides allows investigation of processes occurring on time scales from days to 105 years u series measurements have therefore revolutionized the earth sciences by offering some of the only quantitative constraints on time scales applicable to the physical processes that take place on the earth the application of u series geochemistry to the earth sciences was thoroughly summarized in 1982

volcanism and the dynamics of open magma chambers the repeated eruption of many volcanoes is now accounted for by events taking place in a subterranean magma chamber which is open in the sense that the inflow of material to the chamber from below leads to a magma pressure p which exceeds the lithostatic pressure pl by an amount greater than the tensile strength of the chamber walls before the contents of the magma chamber have reached thermodynamic and geochemical equilibrium this is the condition which must be satisfied when an eruption occurs we have now derived a relationship giving the critical volume of added material v required to cause an eruption as a function of magma compressibility and the volume by which the chamber expands

estimation of gravity wave momentum flux and phase speeds from quasi lagrangian stratospheric balloon flights part ii results from the vorcore campaign in antarctica the stratospheric gravity wave field in the southern hemisphere is investigated by analyzing observations collected by 27 long duration balloons that flew between september 2005 and february 2006 over antarctica and the southern ocean the analysis is based on the methods introduced by boccara et al in a companion paper special attention is given to deriving information useful to gravity wave drag parameterizations employed in atmospheric general circulation models the balloon dataset is used to map the geographic variability of gravity wave momentum fluxes in the lower stratosphere this flux distribution is found to be very heterogeneous with the largest time averaged value 28 mpa observed above the antarctic peninsula this value exceeds by a factor of 10 the overall mean momentum flux measured during the balloon campaign zonal momentum fluxes were predominantly westward whereas meridional momentum fluxes were equally northward and southward a local enhancement of southward flux is nevertheless observed above adelie land and is attributed to waves generated by katabatic winds for which the signature is otherwise rather small in the balloon observations when zonal averages are performed oceanic momentum fluxes are found to be of similar magnitude to continental values 2 5 3 mpa stressing the importance of nonorographic gravity waves over oceans last gravity wave intermittency is investigated mountain waves appear to be significantly more sporadic than waves observed above the ocean

tides in the mesopause region over antarctica comparison of whole atmosphere model simulations with ground based observations almost a quarter century ago first optical and radar observations from the south pole revealed rich dynamics unexpected from classical tidal theory a strong semidiurnal wind oscillation was detected near the mesopause implying substantial deviations from the classical view that the semidiurnal variation is dominated by the migrating tide subsequent systematic observations exhibited large seasonal variations of both the diurnal and semidiurnal tide with dramatic reduction in amplitude from summer to winter first numerical simulations with a realistic general circulation model extending into the lower thermosphere indicated the presence of nonmigrating tides with substantial amplitudes in the polar regions however direct model data comparisons have been limited to idealized linear models here whole atmosphere model wam simulations for january and july are compared with available wind climatologies based on multiyear radar observations at different locations in antarctica as well as with first summertime lidar measurements of temperature the diurnal tide simulation agrees well with most of the independent radar and satellite wind observations in both seasons the strong semidiurnal tide comprised of migrating and nonmigrating components is well reproduced in summer while in winter the model tends to overestimate the amplitudes over the continental edge besides model validation a self consistent numerical solution also enables cross validation of observations made with different instruments at different locales

observations and modeling of the 6 hour tide in the upper mesosphere 1 this paper presents observations and modeling of the 6 hour tide radar observations of horizontal winds at esrange 68 n 21 e indicate that this tidal periodicity is a consistent part of the diurnal variation and is largest during midwinter vertical structure and phase coherence provide strong support that the observed oscillations are tidal model simulations generate a tide that has many similarities to the observed tide at esrange diagnostic model tests indicate that the tide is forced primarily by the 6 hour component of solar heating globally the monthly mean simulated tide is dominated by the migrating component except near the poles although the contribution from nonmigrating modes is not negligible according to the model both migrating and nonmigrating 6 hour tides have small amplitude in low latitudes

small scale wind disturbances observed by the mu radar during the passage of typhoon kelly abstract this paper describes small scale wind disturbances associated with typhoon kelly october 1987 that were observed by the mu radar one of the mst mesosphere stratosphere and troposphere radars continuously for about 60 hours with fine time and height resolution first in order to elucidate the background of small scale disturbances synoptic scale variation in atmospheric stability related to the typhoon structure during the observation is examined when the typhoon passed near the mu radar site the structure was no longer axisymmetric there is deep convection only in the front north northeast side of the typhoon while convection behind it is suppressed by a synoptic scale cold air mass moving eastward to the west of the typhoon a drastic change in atmospheric stability over the radar site as indicated by echo power profiles is likely due to the passage of the sharp transition zone of convection strong small scale wind disturbances were observed around the typhoon passage it is show

seasonal variations of gravity wave activity in the lower stratosphere over an antarctic peninsula station an 8 year series of 965 high resolution radiosonde soundings over rothera 67 degrees s 68 degrees w on the antarctic peninsula are used to study gravity wave characteristics in the lower stratosphere the gravity wave energy is shown to have a seasonal variation with peaks at the equinoxes the largest peak is around the spring equinox during the winter months and extending into the spring there is both an enhancement in the downward propagating wave activity and a reduction in the amount of critical level filtering of upward propagating mountain waves the horizontal propagation directions of the gravity waves were determined using hodographs it was found that there is a predisposition toward northward and westward propagating waves above rothera this is in agreement with previous observations of gravity wave momentum flux in the wintertime mesosphere over rothera these results are consistent with a scenario whereby the stratospheric gravity wavefield above rothera is determined by a combination of wind flow over topography generating waves from below and sources such as the edge of the polar stratospheric vortex generating waves from above especially during winter and spring

generation of mesoscale gravity waves in upper tropospheric jet front systems abstract multiply nested mesoscale numerical simulations with horizontal resolution up to 3 3 km are performed to study the generation of mesoscale gravity waves during the life cycle of idealized baroclinic jet front systems long lived vertically propagating mesoscale gravity waves with horizontal wavelengths 100 200 km are simulated originating from the exit region of the upper tropospheric jet streak in a manner consistent with past observational studies the residual of the nonlinear balance equation is found to be a useful index in diagnosing flow imbalance and predicting wave generation the imbalance diagnosis and model simulations suggest that balance adjustment as a generalization of geostrophic adjustment is likely responsible for generating these mesoscale gravity waves it is hypothesized that through balance adjustment the continuous generation of flow imbalance from the developing baroclinic wave will lead to the continuous radiation of gravity waves

lidar observations of persistent gravity waves with periods of 3 10 h in the antarctic middle and upper atmosphere at mcmurdo 77 83 s 166 67 e persistent dominant and large amplitude gravity waves with 3 10 h periods and vertical wavelengths 20 30 km are observed in temperatures from the stratosphere to lower thermosphere with an fe boltzmann lidar at mcmurdo antarctica these waves exhibit characteristics of inertia gravity waves in case studies yet they are extremely persistent and have been present during every lidar observation we characterize these 3 10 h waves in the mesosphere and lower thermosphere using lidar temperature data in june from 2011 to 2015 a new method is applied to identify the major wave events from every lidar run longer than 12 h a continuous 65 h lidar run on 28 30 june 2014 exhibits a 7 5 h wave spanning 60 h and 6 5 h and 3 4 h waves spanning 40 and 45 h respectively over the course of 5 years 323 h of data in june reveal that the major wave periods occur in several groups centered from 3 5 to 7 5 h with vertical phase speeds of 0 8 2 m s these 3 10 h waves possess more than half of the spectral energy for 93 of the time a rigorous prewhitening postcoloring technique is introduced for frequency power spectra investigation the resulting spectral slopes are unusually steep 2 7 below 100 km but gradually become shallower with increasing altitude reaching about 1 6 at 110 km two dimensional fast fourier transform spectra confirm that these waves have a uniform dominant vertical wavelength of 20 30 km across periods of 3 5 10 h these statistical features shed light on the wave source and pave the way for future research

micro analytical perspectives on the bishop tuff and its magma chamber new in situ major and trace element analytical data are presented for crystals sanidine plagioclase biotite orthopyroxene clinopyroxene and matrix glasses from juvenile materials representing the full bishop tuff sequence from the earliest fall unit f1 to the latest ignimbrite package ig2nc these data are combined with published information to investigate the nature and zonation of the pre eruptive bishop magma chamber our data confirm that this magma chamber was a single unitary body that was thermally and compositionally zoned the zonation was largely established prior to the growth of crystals and also prior to mixing in the lower parts of the chamber induced by late stage intrusion of a magma of contrasting composition and slightly higher temperature the bright rim magma sparse mixed swirly and dacitic pumices show enrichments in ba sr and ti that identify these pumices as possible representatives of the bright rim magma a model revised from previously published work for the pre eruptive magma chamber comprises three main parts 1 an upper volumetrically dominant 2 3 relatively unzoned region that was the source of the earlier eastern erupted ignimbrite units and their coeval fall units 2 a volumetrically minor transition zone that shows evidence for minor degrees of mixing and was the dominant source for the latest eastern erupted part of ig1eb sherwin subunit and the earlier part of the northern erupted ignimbrite ig 2na 3 a lower volumetrically subordinate 1 3 region that was affected by mixing with the bright rim invasive magma in the lead up to the eruption and fed later northern erupted units ingress of the bright rim magma introduced orthopyroxene and bright rimmed zircon crystals and induced partial resorption then overgrowth of rims enriched in ti sr and ba on sanidine and quartz and development of zoning in clinopyroxene based on pumice proportions and associated crystal and glass chemistries through the eruptive sequence we infer that the roof and floor of the magma chamber were stepped down to the north such that the transition zone magma formed the floor of the southern part of the melt dominant chamber and the roof of the northern part our data reinforce the previous concept of a single compositionally and thermally zoned bishop magma chamber and additionally support a temporally constrained role for pre eruptive magma mixing and the introduction of melts and minerals with contrasting compositions to the resident bishop magma

wavelet analysis and the governing dynamics of a large amplitude mesoscale gravity wave event along the east coast of the united states detailed diagnostic analyses are performed upon a mesoscale numerical simulation of a well observed gravity wave event that occurred on 4 january 1994 along the east coast of the united states the value of using wavelet analysis to investigate the evolving gravity wave structure and of using potential vorticity pv inversion to study the nature of the flow imbalance in the wave generation region is demonstrated the cross stream lagrangian rossby number the residual in the nonlinear balance equation and the unbalanced geopotential height field obtained from pv inversion are each evaluated for their usefulness in diagnosing the flow imbalance all of these fields showed clear evidence of strong imbalance associated with a middle to upper tropospheric jet streak and tropopause fold upstream of the large amplitude gravity wave several hours before the wave became apparent at the surface analysis indicates that a train of gravity waves was continuously generated by geostrophic adjustment in the exit region of the unbalanced upper level jet streak as it approached the inflection axis in the height field immediately downstream of the maximum imbalance associated with the tropopause fold a split front in the middle troposphere characterized by the advance of the dry conveyor belt above the warm front was overtaken by one of these propagating waves during this merger process a resonant interaction resulted which promoted the rapid amplification and scale contraction of both the incipient wave nonlinear wave development and the split front frontogenesis the gravity wave and front aloft became inseparable following this merger the situation became even more complex within a few hours as the vertical motion enhanced by this front wave interaction acted upon a saturated potentially unstable layer to produce elevated moist convection an analysis of the temporal changes in the vertical profile of wave energy flux suggests that moist convective downdraughts efficiently transported the wave energy from the midlevels downward beneath the warm front surface where the wave became ducted however pure ducting was not sufficient for maintaining and amplifying the waves rather wave cisk conditional instability of the second kind was crucial this complex sequence of nonlinear interactions produced a long lived large amplitude gravity wave that created hazardous winter weather and disrupted society over a broad and highly populated area although gravity waves with similar appearance to this large amplitude wave of depression occasionally have been seen in other strong cyclogenesis cases involving a jet streak ahead of the upper level trough axis it is unknown whether other such events share this same sequence of interactions

terdiurnal tide in the extended canadian middle atmospheric model cmam 1 we use the extended canadian middle atmosphere model cmam a general circulation model gcm to investigate the nature of the terdiurnal tide temperature and horizontal winds from a model run are analyzed to delineate the character of this tide for zonal wave numbers s 5 to 5 descriptions of the annual mean amplitudes seasonal variations and total tide superposed from the migrating and 10 nonmigrating components are provided the amplitudes and vertical wavelengths of the various components and the total terdiurnal tide are found to depend strongly on season latitude and altitude the migrating terdiurnal component maximizes at mid and high latitudes with significant amplitudes annual mean amplitude in wind temperature 10 m s k in the upper mesosphere and lower thermosphere mlt region between 80 and 100 km maximum amplitudes occur in winter in both hemispheres whereas above 100 km maximum amplitudes occur during solstices for the zonal wind field the nonmigrating terdiurnal components te5 te3 te4 tw4 and tw5 tend to peak at 50 n s with amplitudes between 2 and 8 m s the other nonmigrating components maximize in the polar regions with amplitudes of 2 10 m s possible generation mechanisms solar heating and nonlinear interactions for the migrating terdiurnal tide in the mlt region are also examined correlation analysis indicates that nonlinear interactions between the migrating diurnal and semidiurnal tides are unlikely to be the source of the migrating terdiurnal tide

magma mixing and crustal recycling recorded in ternary feldspar from compositionally zoned peralkaline ignimbrite a gran canaria canary islands miocene ignimbrite a on gran canaria contains three compositional endmember fiamme types two rhyolites and one trachyte each of which crystallized distinct feldspar various textural and compositional criteria are interpreted as reflecting a complex scenario within the magma chamber in which the crystals formed about 25 30 of the feldspar phenocrysts contain evidence for magma mixing in the form of 1 partial to severe dissolution resorption rims 2 distinct zones of drastically different compositions and 3 overgrowth textures on formerly resorbed crystals four major types of zoning in the oligoclase to anorthoclase feldspars of ignimbrite a include a normal and a reversely zoned type and two complexly zoned types the feldspars with normal and reverse zonation show only minor compositional amplitudes between individual zones ab or 4 whereas the complexly zoned types show compositional differences between zones of up to 18 mol ab and 20 mol or and are commonly associated with an internal dissolution surface complex zoning with large compositional amplitudes and dissolution textures is taken as evidence of crystal movements within the magma and across compositional boundaries between magma batches a multiple step cycle model involving growth and transport of a crystal into another magma batch and its return to the original host magma is suggested by the data moreover feldspars from one rhyolite compositional group are found to be substantially elevated in 18o suggesting an input of a high 18o component to this rhyolite the other endmember rhyolite appears to be related to the endmember trachyte by mainly crystal fractionation of anorthoclase feldspar this observation is consistent with trace element and rare earth element concentrations for the magma endmembers and their feldspars where contamination led to a depletion in incompatible trace elements and light rare earth elements in the contaminated rhyolite and its feldspar phenocrysts we suggest that the combination of textural and compositional variation in ternary feldspar of peralkaline rhyolitic systems is well suited to reconstruct dynamic processes such as magma mixing and contamination in evolving rhyolitic magma chambers

dwm07 global empirical model of upper thermospheric storm induced disturbance winds 1 we present a global empirical disturbance wind model dwm07 that represents average geospace storm induced perturbations of upper thermospheric 200 600 km altitude neutral winds dwm07 depends on the following three parameters magnetic latitude magnetic local time and the 3 h kp geomagnetic activity index the latitude and local time dependences are represented by vector spherical harmonic functions up to degree 10 in latitude and order 3 in local time and the kp dependence is represented by quadratic b splines dwm07 is the storm time thermospheric component of the new horizontal wind model hwm07 which is described in a companion paper dwm07 is based on data from the wind imaging interferometer on board the upper atmosphere research satellite the wind and temperature spectrometer on board dynamics explorer 2 and seven ground based fabry perot interferometers the perturbation winds derived from the three data sets are in good mutual agreement under most conditions and the model captures most of the climatological variations evident in the data

on the dynamics of magma mixing by reintrusion implications for pluton assembly processes many plutons have formed by repeated intrusion with complex internal contacts characterized by sharp and diause kinematic and compositional domains we performed numerical experiments of mixing following magma chamber recharge that explicitly considers the fluid dynamics of multiphase mixtures in the limit of zero diausivity of intensive scalar quantities and low stokes number mingling by fluid instability is equivalent to deformation and persistent fluid structures are kinematic attractors three distinct regimes are exemplified and can be described by their multiphase reynolds or grashof number for a reynolds number greater than about 100 an internal intrusive contact will collapse by internal wave breaking and chaotic magma mingling and mixing yield a nearly chamber wide stratification this flow may scour mushy regions at the walls and widely distribute previously crystallized material for reynolds numbers from 10 to 100 the internal wave does not break and the stratification occupies less of the chamber leaving islands of unmixed material for reynolds numbers around 1 internal slumping and folding can occur and is the most likely to be preserved by a mineral fabric internal sub vertical contacts require a high absolute viscosity in the resident magma representing a time break between episodes of reintrusion the shape of perched mafic domains captures the progress of sinking from higher levels into regions of increasing strength and crystallinity 7 2000 elsevier science ltd all rights reserved

thermal requirements for extensional emplacement of granitoids numerical models of magma emplacement during crustal extension show that shallow 10 km rhyolitic to andesitic magma chambers can form and be maintained at typical rates of extension of continental crust chambers at depths of 8 km form within 90 ka after emplacement of a total width of 4 km of magma at half extension rates of 2 cm yr once even a small 1 km wide shallow chamber has formed by any process it can be maintained by extension at a half rate of 1 cm yr high temperatures are maintained at a half rate of 0 5 cm yr continental rifts and dilational jogs along strike slip faults in arcs provide areas where extension rates are most appropriate large granitoids and batholiths can form by this process over millions of years actual chambers at any one time may be considerably smaller than preserved granitoids

crystal scale anatomy of a dying supervolcano an isotope and geochronology study of individual phenocrysts from voluminous rhyolites of the yellowstone caldera a voluminous 600 km3 and long lived 520 75 ka phase of rhyolitic eruptions followed collapse of the yellowstone caldera 640 ka whether these eruptions represent a dying cycle or the growth of a new magma chamber remains an important question we use new u th zircon ages and 18o values determined by ion microprobe and sanidine pb isotope ratios determined by laser ablation to investigate the genesis of voluminous post caldera rhyolites the oldest post caldera rhyolites erupted between 520 and 470 ka exhibit extreme age and oxygen isotopic heterogeneity requiring derivation from individual parcels of low 18o melts we find a progressive increase in zircon homogeneity for rhyolite eruptions from 260 to 75 ka with homogeneous low 18o zircon values of 2 7 2 8 that are in equilibrium with low 18o host melts for the majority of the youngest eruptions new sanidine pb isotope data define separate arrays for post caldera rhyolites and the caldera forming tuffs that preceded them indicating that they were not sourced from a mushy lava creek tuff batholith that remained after caldera collapse rather our new age and isotopic data indicate that the post caldera rhyolites were generated by remelting of a variety of intracaldera source rocks consisting of pre lava creek tuff volcanic and plutonic rocks and earlier erupted post lava creek tuff rhyolites batch assembly of low 18o melts starting at 260 ka resulted in progressive homogenization followed by differentiation and cooling up until the last rhyolite eruption 75 ka a trend that we interpret to be characteristic of a dying magma reservoir beneath the yellowstone caldera

inertia gravity wave generation by the tropospheric midlatitude jet as given by the fronts and atlantic storm track experiment radio soundings 1 generation of inertia gravity waves by the midlatitude tropospheric jet is studied on the basis of the data obtained from the radio soundings over the north atlantic during the fronts and atlantic storm track experiment campaign a sample of 224 radio soundings is used to analyze the wave activity as a function of the distance to the jet it is shown that radio soundings displaying the most intense gravity wave activity both in the stratosphere and in the troposphere are the ones closest to the jet axis thus the jet region is the dominant source of gravity waves in this region far from orography further examination allows for identification of two specific regions of the flow that are associated with intense gravity wave activity the vicinity of the maximum of the jet velocity and the regions of strong curvature of the jet the detailed case studies we provide suggest that geostrophic adjustment is the dynamical mechanism responsible for the generation of large amplitude inertia gravity waves in the regions of the strong curvature of the wind the generation of waves in the vicinity of the regions where the wind veers in the deep troughs of the geopotential appears to be systematic

time scales of pluton construction at differing crustal levels examples from the mount stuart and tenpeak intrusions north cascades washington deciphering the magmatic history of continental magmatic arcs in general and the growth history of individual intrusions in particular is key to understanding the complex history of magma generation segregation and transport that define the dynamics of crustal growth we utilize high precision u pb geochronology to resolve a detailed magmatic history from two composite intrusions the 2 4 kbar mount stuart batholith and the 7 10 kbar tenpeak pluton emplaced in the cretaceous north cascades arc this temporal framework provides a way to evaluate models of pluton growth that explain common features of intrusions such as concentric compositional zoning and internal magmatic contacts u pb zircon crystallization ages were obtained from 12 samples of the mount stuart batholith and 8 samples of the tenpeak intrusion representing the range of compositional diversity and geographical extent these dates indicate that the mount stuart batholith was constructed over a 5 5 m y time period that was punctuated by four intervals of high magma flux the durations of the high flux periods are short a few hundred thousand years relative to the duration of the batholith the consistent pattern of magmatic fabrics and the lack of distinct contacts in the batholith may be explained by the juxtaposition of melt rich and mush zones with subtle contacts between mineralogically and texturally similar tonalite and time transgressive magma fabrics in contrast the tenpeak intrusion was constructed over a 2 6 m y time period with magma influx distributed throughout the intrusive history and texturally distinct magma bodies the tenpeak intrusion lacks distinct age domains which suggests that any magma reservoir was smaller in size and potentially more ephemeral although the distinct age domains and discrete compositional and textural phases indicate that pluton growth occurred incrementally neither pluton bears resemblance to a purely end member incremental growth model whereby a pluton is constructed from hundreds to thousands of discrete magma pulses that have little if any interaction in particular ages from the youngest domain of the mount stuart batholith indicate that a melt rich magma reservoir of 520 km 3 existed over a 170 90 k y time span

mineral disequilibrium in lavas explained by convective self mixing in open magma chambers characteristic features of many porphyritic andesite and dacite lavas are that they are rich in crystals and display a range of disequilibrium features including reversely zoned crystals resorption surfaces wide ranges of mineral compositions and minerals which are not in equilibrium with the surrounding rock matrix these features are often interpreted as evidence of the mixing of magmas of contrasting composition temperature and origin1 2 here however we propose that such features can also be caused by convection within a magma body with a single composition that is heated from below and cooled from above we describe petrological observations of andesite lava erupted at the soufriere hills volcano montserrat which indicate a heating event and the intermingling of crystals that have very different thermal histories we present experimental data on a representative groundmass composition of this lava which indicate that it is difficult to explain the calcic compositions of plagioclase overgrowth rims and microphenocrysts unless parts of the magma were at temperatures much higher than the inferred average temperature the concept of convective self mixing allows us to explain the occurrence of compositions of minerals that apparently cannot coexist under equilibrium conditions

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du

phenocrysts versus xenocrysts in the youngest toba tuff implications for the petrogenesis of 2800 km3 of magma the petrogenesis of the 2800 km 3 of magma erupted as the youngest toba tuff has been investigated using experimental petrology and 40 ar 39 ar dating of biotite sanidine hornblende and plagioclase from the tuff we find that hornblende does not crystallize experimentally from the magma at temperatures and pressures indicated by the natural mineral assemblage hornblende is also not in isotopic equilibrium with biotite and sanidine both of which grew experimentally hornblende thus appears xenocrystic despite being a major phase in the tuff some plagioclase is also xenocrystic on the basis of ar isotopes but others are probably phenocrystic because plagioclase grew experimentally crystal clots of hornblende plagioclase observed in the tuff suggest that the xenocrysts came from a common source which was at least 1 5 ma the oldest hornblende 40 ar 39 ar age our results suggest that the toba tuff magma resided at nearly water saturated pressures of 100 150 mpa and that xenocrysts were entrained as recently as 10 yr before the eruption the ubiquitous presence of hornblende in the tuff indicates that entrainment occurred throughout the 2800 km 3 of magma