phenocryst crystallization during ascent of alkali basalt magma at rishiri volcano northern japan abstract phenocrysts in volcanic rocks are commonly used to deduce crystallization processes in magma chambers a fundamental assumption is that the phenocrysts crystallized in the magma chambers at isobaric and nearly equilibrium conditions on the basis of their large sizes however this assumption is not always true as demonstrated here for a porphyritic alkali basalt kutsugata lava from rishiri volcano northern japan all phenocryst phases in the kutsugata lava plagioclase olivine and augite have macroscopically homogeneous distribution of textures showing features characteristic of rapid growth throughout the crystals rarely a core region with distinct composition is present in all phenocryst phases phenocrysts excluding this core are occasionally in direct contact with each other forming crystal aggregates the equilibrium liquidus temperature of plagioclase the dominant phase 35 vol in the kutsugata lava can never exceed the estimated magmatic temperature unless the liquidus temperature increases significantly due to vesiculation of the magma during ascent this suggests that most phenocrysts in the kutsugata lava were formed by decompression of the magma during ascent in a conduit rather than by cooling during residence in a magma reservoir in the magma chamber before eruption probably located at depth of more than 7 km only cores of the phenocrysts were present and the magma was nearly aphyric 4 wt in the magma chamber and liquidus temperatures of phenocryst phases were significantly suppressed large undercooling caused by decompression and degassing of the magma was the driving force for significant crystallization during ascent because of the increase in liquidus temperature due to vapor exsolution low ascent rate of the kutsugata magma which is suggested by pahoehoe lava morphology and no association of pyroclastics gave sufficient time for crystallization furthermore the large degree of superheating of plagioclase in the magma chamber caused plagioclase crystallization with low population density and large crystal size which characterizes the porphyritic nature of the kutsugata lava alkali basalt is likely to satisfy these conditions and similar phenomena are suggested to occur in other volcanic systems

climatic versus tectonic control on river incision at the margin of ne tibet 10be exposure dating of river terraces at the mountain front of the qilian shan 1 we document late pleistocene holocene aggradation and incision processes at the mountain front of the qilian shan an active intracontinental fold and thrust belt accommodating a significant portion of the india asia convergence the shiyou river cuts through a nne vergent fault propagation fold with miocene red beds in the core and pliocene quaternary growth strata on the northern forelimb south of the anticline miocene strata dip 20 ssw suggesting a similar orientation for the basal decollement after aggradation of an 150 m thick late pleistocene valley fill the shiyou river formed three terraces the highest terrace located 170 m above the river constitutes the top of the fill the other terraces are fill cut terraces their treads are located 130 105 m and 37 m above the river respectively the 10be exposure dating of the terraces suggests that river incision accelerated from 0 8 0 2 mm yr 1 to 10 mm yr 1 at 10 15 kyr we interpret fast holocene river incision as largely unrelated to tectonic forcing the late pleistocene incision rate of 0 8 0 2 mm yr 1 places an upper limit of 2 2 0 5 mm yr 1 on the horizontal shortening rate assuming that incision is solely caused by rock uplift above a decollement dipping 20 however the actual shortening rate may lie between 2 2 mm yr 1 and zero because deformation of the terraces and the valley fill cannot be unequivocally demonstrated our estimate is consistent with the bulk shortening rate of 5 10 mm yr 1 across several faults in ne tibet derived from neotectonic and gps data although in case of the shiyou river holocene deformation is barely discernible owing to intense climate induced river incision

a petrologic re investigation of the adak volcanic center central aleutian arc alaska the adak volcanic center is located in the central part of the aleutian arc and consists of three main volcanic vents andrew bay volcano the oldest center has been mostly removed by erosion the next youngest vent mount adagdak was built in three major volcanic stages whereas mount moffett the largest volcanic edifice consists of a main cone and a parasitic cone each with several magmatic phases adak is unique compared to other modern aleutian volcanic centers in that it contains two xenolith suites conrad and kay 1984 debari et al 1987 one suite consisting predominantly of mafic xenoliths occurs on mount moffett whereas an assemblage of ultramafic and mafic xenoliths is found on mount adagdak lavas erupted at adak span the compositional range from 48 4 to 65 0 wt sio2 and are characterized by significant variations in al2o3 mgo sr ni and cr on harker diagrams this variability produces compositional trends with significant scatter the adak suite has total ree contents that vary from 32 to 154 ppm but do not correlate systematically with silica layb n ratios range from 2 41 to 21 72 with the majority of lavas between 2 41 and 6 06 on process identification diagrams the adak suite plots as steeply sloping trends that contrast with the horizontal patterns of most other aleutian centers measured isotopic ranges are large and nearly equal to those for the entire arc although they span similar silica ranges subtle geochemical and isotopic differences distinguish the different volcanic vents of adak on mount moffett a geochemically and isotopically distinct group of andesites 55 5 57 9 sio2 the mafic andesites occur on its ne flank these lavas have elevated mgo ni and cr but are depleted in al2o3 relative to other mount moffett andesites with similar silica they also have more heterogeneous ree abundances and isotopic ratios than most of the other andesites significant compositional differences exist between adak and the other volcanic centers of the central aleutian arc although these differences are characteristic of all geochemical systems they are greatest for major and rare earth elements and isotopic ratios the lack of coherent relationships on major and trace element harker diagrams the isotopic variability as well as the steeply sloping trends on ree process identification diagrams suggest that the adak volcanic suite was not formed predominantly by closed system crystal fractionation but must be the product of a complex open system process es the significant isotopic variability displayed by the suite suggests that contamination by an isotopically distinct contaminant must also have been an important petrologic component in the evolution of the suite ree data are also suggestive of a role for magma mixing such a complex petrologic evolution is consistent with an immature lithospheric plumbing system based on ree systematics the xenolith suites of adak cannot as previously proposed be related to the host lavas or the rest of the adak suite through crystal fractionation schemes rather they are probably accidental fragments derived from various depths along lithospheric conduits in light of their relation to xenolith bearing units the mafic andesites of adak presumably represent hybrid magmas formed during the interaction of ascending magmas with lithospheric wall rock they are therefore characteristic of immature volcanic centers and unlikely to be related directly to the magmatic processes responsible for the generation of primary arc magmas because of the close proximity of the vents and the subtle compositional differences between their lavas the adak volcanic center was probably supplied by a single deep lithospheric plumbing system that fed separate crustal magma chambers the absence of historic volcanic activity on adak suggests this plumbing system was abandoned before complete conduit development this decline in magmatism may reflect a re adjustment of volcano spacing within this part of the aleutian arc

the life cycle of the northern hemisphere sudden stratospheric warmings motivated by recent evidence of strong stratospheric tropospheric coupling during the northern hemisphere winter this study examines the evolution of the atmospheric flow and wave fluxes at levels throughout the stratosphere and troposphere during the composite life cycle of a sudden stratospheric warming the composite comprises 39 major and minor warming events using 44 years of ncep ncar reanalysis data the incipient stage of the life cycle is characterized by preconditioning of the stratospheric zonal flow and anomalous quasistationary wavenumber 1 forcing in both the stratosphere and troposphere as the life cycle intensifies planetary wave driving gives rise to weakening of the stratospheric polar vortex and downward propagation of the attendant easterly wind and positive temperature anomalies when these anomalies reach the tropopause the life cycle is marked by momentum flux and mean meridional circulation anomalies at tropospheric levels that are consistent with the negative phase of the northern hemisphere annular mode the anomalous momentum fluxes are largest over the atlantic half of the hemisphere and are associated primarily with waves of wavenumber 3 and higher

a new mg in plagioclase geospeedometer for the determination of cooling rates of mafic rocks abstract we present a new mg in plagioclase geospeedometer based on the diffusive exchange of mg between plagioclase and clinopyroxene that allows cooling rates of a wide range of mafic rocks to be determined the major element composition of plagioclase is shown to play an important role in driving the flux of mg as well as the partitioning of mg between plagioclase and clinopyroxene therefore commonly used analytical solutions to the diffusion equation are not applicable in this system and an alternate approach is developed practical aspects of the method such as the role of anorthite zoning patterns and influence of shapes of cooling paths and grain geometries in controlling the mg concentration profile shapes are discussed propagation of uncertainties in the knowledge of diffusion and partition coefficients shows that the method is capable of resolving small differences in cooling rates e g log d t d t c yr 1 3 0 3 in one example the approach is illustrated by application to two samples from the lower oceanic crust

magma emplacement and remobilization timescales beneath montserrat insights from sr and ba zonation in plagioclase phenocrysts received november 22 2001 accepted december 12 2002since 1995 the soufri ere hills volcano on montserrat lesserantilles island arc has erupted crystal rich andesite magmathat is geochemically very similar to the volcanic products of atleast the last 174 3kyr 1s nomarski images of plagio clase phenocrysts from six andesites erupted between 151 4ka 1s and

cumulatic diorites related to post collisional brasiliano pan african mafic magmatism in the vila nova belt southern brazil abstract the capivaras diorite in the vila nova region nw of the sul rio grandense shield is composed of six ne to nne oriented rock bodies of late tectonic emplacement relative to the d3 deformation phase which forms subvertical high strain zones in basement gneiss sequences within these intrusive bodies a shape foliation is present generally parallel to contacts and displaying a local solid state deformational component the internal structure of the capivaras diorite main intrusion is marked by a zone of intense flow and mingling characterized by strong shape foliation and layers of variable texture and composition which result from cumulative processes heterogeneous flow and interaction of coeval compositionally contrasting magmas the central part of this intrusion is texturally homogeneous and slightly foliated even though cumulative processes have remained important during its formation along the contact with basement gneisses fine grained diorites are found which are considered to be compositionally close to the parental magma of the capivaras diorite this magma has a mildly alkaline affinity and shows moderate to high contents of zr ti and p highly fractionated ree patterns low nb contents as well as high contents of k sr ba and rb are suggestive of its provenance from mantle sources which have been previously affected by subduction processes such as those of mature magmatic arcs or post collisional settings magmatic evolution was controlled by cumulative processes and gave origin to pyroxene orthocumulates plagioclase pyroxene orthocumulates pyroxene adcumulates and more rarely plagioclase adcumulates the cumulative origin of these rocks is indicated by field textural and geochemical features which are distinct from those of crystallized liquids the compositional diversity of cumulates has led to the generation of compositionally different melts the early formed pyroxene cumulates have caused ca al na ba and sr enrichment in the magmatic liquid leading to plagioclase crystallization and accumulation coarse grained mafelsic cumulates were formed during the late stages of magmatic crystallization due to volatile enrichment of the intercumulus liquid considering geological relations as well as tectonic and compositional features of the capivaras diorite it is interpreted as part of neoproterozoic magmatism related to the post collisional stage of brasiliano pan african orogenic cycle in southern brazil

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

mid ocean ridge magma chamber processes constraints from olivine zonation in lavas from the east pacific rise at 9 30 n and 10 30 n 1 lavas from the northern east pacific rise with both robust 9 30 n and nonrobust 10 30 n ridge morphologies have compositionally diverse populations of plagioclase and or olivine due to magma mixing we interpret zoning in olivines to be primarily due to diffusion after mixing events which allows us to calculate the residence times of individual crystals in the magma for the four studied samples olivine populations exhibit exponential distributions of calculated diffusion times with short times exponentially more abundant than longer times we model this distribution as resulting from mixing in an open system axial magma chamber magma residence times in axial chambers at east pacific rise 9 30 n and 10 30 n for the four studied samples are of the order of months surprisingly we find that the differences in mineralogy and magma residence times between robust and nonrobust east pacific rise segments are not significant taken together our observations and measurements suggest that the seismically imaged melt lens of the axial magma chamber does not play a significant role in controlling the crystal content and characters of erupted lavas

propagation of planetary waves between the troposphere and stratosphere abstract the propagation of planetary waves between the troposphere and stratosphere is investigated using a linear time dependent primitive equation model it is found that the tropopause acts like a valve for the propagation of planetary waves the key parameters controlling the valve are the vertical gradient of buoyancy frequency and the vertical shear of the zonal winds at the tropopause for a given wind profile smaller gradient of buoyancy frequency enhances the propagation of planetary waves for a given profile of buoyancy frequency the larger the shear the more the wave activity is trapped in the troposphere and therefore there is less left to propagate into the stratosphere the transmission across the tropopause is however not sensitive to zonal winds in the upper stratosphere the propagation of planetary waves is very sensitive to transience more transient waves propagate more vertically within the troposphere and for more transient waves more wave activity is transferred into the

plagioclase zonation styles in hornblende gabbro inclusions from little glass mountain medicine lake volcano california implications for fractionation mechanisms and the formation of composition gaps the rhyolite of little glass mountain 73 74 sio2 is a single eruptive unit that contains inclusions of quenched andesite liquid 54 61 sio2 and partially crystalline cumulate hornblende gabbro 53 55 sio2 based on previous studies the quenched andesite inclusions and host rhyolite lava are related to one another through fractional crystallization and represent an example of a fractionation generated composition gap the hornblende gabbros represent the cumulate residue associated with the rhyolite producing and composition gap forming fractionation event this study combines textural nomarski differential interference contrast ndic imaging major element an content and trace element mg fe sr k ti ba data on the style of zonation of plagioclase crystals from representative andesite and gabbro inclusions to assess the physical environment in which the fractionation event and composition gap formation took place the andesite inclusions 54 61 sio2 are sparsely phyric with phenocrysts of plagioclase augite and fe oxide olivine orthopyroxene hornblende set within a glassy to crystalline matrix the gabbro cumulates 53 55 sio2 consist of an interconnected framework of plagioclase augite olivine orthopyroxene hornblende and fe oxide along with highly vesicular interstitial glass 70 74 sio2 the gabbros record a two stage crystallization history of plagioclase olivine augite stage i followed by plagioclase orthopyroxene hornblende fe oxide stage ii texturally the plagioclase crystals in the andesite inclusions are characterized by complex fine scale oscillatory zonation and abundant dissolution surfaces compositionally an content the crystals are essentially unzoned from core to rim these features indicate growth within a dynamic convecting reservoir of andesite magma in contrast the plagioclase crystals in the gabbros are texturally smooth and featureless with strong normal zonation from an74 at the core to around an30 k and ba abundances increase and mg abundances decrease steadily towards the rim ti fe and sr abundances increase and then decrease towards the rim the trace element variations are fully consistent with the two stage crystallization sequence inferred from the gabbro mineralogy these results indicate progressive closed system in situ crystallization in a quiescent magmatic boundary layer environment located along the margins of the andesite magma body the fractional crystallization that generated the host rhyolite lava is one of inward solidification of a crystallizing boundary layer followed by melt extraction and accumulation of highly evolved interstitial liquid this mechanism explains the formation of the composition gap between parental andesite and rhyolite magma compositions

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

synoptic behavior of baroclinic eddies during the blocking onset abstract synoptic behavior of individual baroclinic eddies in the course of their interactions with amplifying blocking anticyclones is examined based upon a 30 year record of the tropospheric circulation in the northern hemisphere winter high pass filtered as well as unfiltered fields of geopotential height and potential vorticity were composited relative to the onset of the five different types of blocking patterns before the compositing the entire sequence of the fields was slightly shifted in time and space in such a way that the strongest baroclinic eddy during the onset of each blocking event occupies a prescribed position in the upstream storm track when it reaches its maximum intensity since this shifting considerably reduces the cancellation between the individual high frequency migratory eddies this type of compositing can present a more synoptically oriented view of those interactions than conventional compositing in our composite results one or two pairs of cyclonic and anticyclonic

observational evidence of a stratospheric influence on the troposphere by planetary wave reflection abstract recent studies have pointed out the impact of the stratosphere on the troposphere by dynamic coupling in the present paper observational evidence for an effect of downward planetary wave reflection in the stratosphere on northern hemisphere tropospheric waves is given by combining statistical and dynamical diagnostics a time lagged singular value decomposition analysis is applied to daily tropospheric and stratospheric height fields recomposed for a single zonal wavenumber a wave geometry diagnostic for wave propagation characteristics that separates the index of refraction into vertical and meridional components is used to diagnose the occurrence of reflecting surfaces for zonal wavenumber 1 this study suggests that there is one characteristic configuration of the stratospheric jet that reflects waves back into the troposphere when the polar night jet peaks in the high latitude midstratosphere this configuration is related to the formation of a reflecting surface for vertical propagation

diagnostic case studies of the northern annular mode abstract recent observational studies of the northern annular mode nam indicate that significant case to case variability exists in the structural evolution of individual events in particular certain nam events remain confined to stratospheric altitudes whereas others readily penetrate downward into the troposphere we perform observational diagnostic analyses that are targeted at identifying the physical mechanisms behind this distinction our results thereby provide a test of the different existing theories regarding stratospheric influences upon tropospheric climate we contrast robust stratospheric nam events with differing tropospheric signals in order to identify the underlying dynamical reasons for the observed differences piecewise potential vorticity pv inversions and eliassen palm flux analyses are performed to study the roles of different forcing mechanisms during nam onset our results indicate that variations in the tropospheric response are readily explained on the basis of piecewise

magmatic evolution and ascent history of the aries micaceous kimberlite central kimberley basin western australia evidence from zoned phlogopite phenocrysts and uv laser 40ar 39ar analysis of phlogopite biotite the neoproterozoic aries kimberlite was emplaced in the central kimberley basin western australia as a n nne trending series of three diatremes infilled by lithic rich kimberlite breccias the breccias are intruded by hypabyssal macrocrystic phlogopite kimberlite dykes that exhibit differentiation to a minor high na si olivine phlogopite richterite kimberlite and late stage macrocrystic serpentine diopside ultramafic dykes mineralogical and geochemical evidence suggests that the high na si olivine phlogopite richterite kimberlite was derived from the macrocrystic phlogopite kimberlite as a residual liquid following extended phlogopite crystallization and the assimilation of country rock sandstone and that the macrocrystic serpentine diopside ultramafic dykes formed as mafic cumulates from a macrocrystic phlogopite kimberlite chemical zonation of phlogopite biotite phenocrysts indicates a complex magmatic history for the aries kimberlite with the early inheritance of a range of high ti phlogopite biotite xenocrysts from metasomatized mantle lithologies followed by the crystallization of a population of high cr phlogopite phenocrysts within the spinel facies lithospheric mantle a further one to two phlogopite biotite overgrowth rims of distinct composition formed on the phlogopite phenocrysts at higher levels during ascent to the surface ultra violet laser 40ar 39ar dating of mica grain rims yielded a kimberlite eruption age of 815 4 4 3 ma 95 confidence 40ar 39ar laser profiling of one high ti phlogopite biotite macrocryst revealed a radiogenic 40ar diffusive loss profile from which a kimberlite magma ascent duration from the spinel facies lithospheric mantle was estimated assuming an average kimberlite magma temperature of 1000 c yielding a value of 0 23 2 32 days for the north extension lobe of the aries kimberlite

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

synoptic view of the north atlantic oscillation abstract this article investigates the synoptic characteristics of individual north atlantic oscillation nao events by examining the daily evolution of the potential temperature field on the nominal tropopause the 2 pvu surface this quantity is obtained from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis dataset for the winter season for both phases the nao is found to originate from synoptic scale waves as these waves evolve into the low frequency nao pattern they break anticyclonically for the positive phase and cyclonically for the negative phase the results of this analysis suggest that it is the remnants of these breaking waves that form the physical entity of the nao throughout the nao events for both phases the nao is maintained by the successive breaking of upstream synoptic scale waves when synoptic scale disturbances are no longer present mixing processes play an important role in the nao decay as in other recent

crystallization and resorption in plutonic plagioclase implications on the evolution of granodiorite magma gesiniec granodiorite strzelin crystalline massif sw poland abstract granodiorite from the gesiniec intrusion strzelin crystalline massif sw poland contains complexly zoned plagioclases five chemically and structurally distinct zones can be correlated among crystals cores 25 35 an inner mantles 40 45 an outer mantles 40 25 an resorption zones 35 50 an and rims 35 30 an good structural and chemical major and trace elements correlation of zones between crystals indicates that zonation was produced by changes in conditions of crystallization on a magma chamber scale plagioclase being the liquidus phase records a time span from the beginning of crystallization to emplacement and rapid cooling of granodiorite as thin dykes crystallization began with the formation of inner mantles the paucity and different sizes of inner mantles suggests slow crystallization in high temperature magma normally zoned inner mantles were formed under increasing undercooling compositional trends in mantles suggest closed system crystallization the major resorption zones were caused by injection of less evolved magma as indicated by the strontium increase in plagioclase the injection triggered a rapid rise of magma and plagioclase crystals facilitating mixing but also inducing fast kinetically controlled growth of complex multiple oscillatory zonation within resorption zones the ascent of magma caused decompression melting of plagioclase and produced melt inclusions within inner mantles the cores the decompression range is estimated at a minimum of 2 kbar emplacement of granodiorite as thin dykes allow rapid cooling and preservation of magmatic zonation in plagioclases melt inclusions crystallized completely during post magmatic cooling the zonation styles of plutonic plagioclase differ markedly from volcanic ones suggesting different magma evolution zones in plutonic plagioclase are well correlated indicating crystallization in quiescent magma where crystals accumulation and compositional magma stratification may occur crystals probably did not travel between different regimes resorption occurred but as single albeit complex episodes good correlation of zones in plutonic plagioclases allows a distinction between the main processes controlling zonation and superimposed kinetic effects

transient volcano deformation sources imaged with interferometric synthetic aperture radar application to seguam island alaska 1 thirty interferometric synthetic aperture radar insar images spanning various intervals during 1992 2000 document coeruptive and posteruptive deformation of the 1992 1993 eruption on seguam island alaska a procedure that combines standard damped least squares inverse methods and collective surfaces identifies three dominant amorphous clusters of deformation point sources predictions generated from these three point source clusters account for both the spatial and temporal complexity of the deformation patterns of the insar data regularized time series of source strength attribute a distinctive transient behavior to each of the three source clusters a model that combines magma influx thermoelastic relaxation poroelastic effects and petrologic data accounts for the transient interrelated behavior of the source clusters and the observed deformation basaltic magma pulses which flow into a storage chamber residing in the lower crust drive this deformational system a portion of a magma pulse is injected into the upper crust and remains in storage during both coeruption and posteruption intervals this injected magma degasses and the volatile products accumulate in a shallow poroelastic storage chamber during the eruption another portion of the magma pulse is transported directly to the surface via a conduit roughly centered beneath pyre peak on the west side of the island a small amount of this magma remains in storage during the eruption and posteruption thermoelastic contraction ensues this model made possible by the excellent spatial and temporal coverage of the insar data reveals a relatively simple system of interrelated predictable processes driven by magma dynamics

insights into magmatic evolution and recharge history in capraia volcano italy from chemical and isotopic zoning in plagioclase phenocrysts plagioclase phenocrysts in dacites from the high k calc alkaline capraia volcano were investigated for major trace element and sr isotope variations in order to gain better insight into the proposed open system behaviour of the volcano repeated dissolution zones in plagioclases from the early erupted monte castello mc and later monte rucitello mr dacitic units are associated with a sharp increase in an content and variation in isotopic compositions 87sr 86sr 0 70872 0 71004 which argue for repeated magma mixing in particular petrographic and mineralogical evidence suggest that recharge with hot basaltic magma occurred repeatedly during the lifetime of the capraia volcanic system we attempted to correlate shared crystallization and resorption histories using chemical mol an fe and sr isotopic zoning in plagioclase in this correlation framework the observed mismatch between chemical and isotopic data in some phenocrysts is interpreted to reflect either growth of phenocrysts in a separate magma chamber or compositional zoning within a single magma chamber a minor role of crustal contamination is inferred instead the intra crystal variations in isotopic composition in plagioclase reflect the existence of distinct components that may have thoroughly mixed at the end of the mc plagioclase growth history the dominant radiogenic component is similar to lamproites occurring in tuscany recharge with this component occurred throughout the genesis of the mr dacites but was restricted to the early growth history of the mc dacites the mr plagioclases are inferred to have crystallized from separate more differentiated batches of magma that were likely to have evolved at the top of a zoned magma reservoir decrease in the an content after most dissolution zones in all phenocrysts and low temperature estimates from zircon saturation thermometry 800 c also emphasize the importance of crystal fractionation during the evolution of the volcano in agreement with the occurrence of a significant amount of rhyolitic material thus it is inferred that a rather large magma chamber may have existed during the first cycle of eruptive activity

origin of crosscutting dissolution surfaces in magmatic plagioclase crosscutting dissolution surfaces dss are rare features observed in magmatic plagioclase crystals in this study crosscutting dss of dacitic plagioclase crystals from the shirahama group izu peninsula japan were investigated using a nomarski differential interference contrast imaging microscope and chemical compositional data crosscutting ds slopes were examined by tracing digitized images the following features of crosscutting dss are reported for the first time 1 traces of the crosscutting dss showed parabolic like shapes 2 crosscutting dss were found on select adjacent or opposite faces of the crystals suggesting a preferential dissolution of a limited area of the plagioclase 3 projecting points were observed with directional characteristics and 4 square or angular patterns were found in the less dissolved parts of the crystals the formation of crosscutting features is controlled by dissolution and crystal settling into hotter magma process velocities depend on the physical properties of the magma such that a description of crosscutting features can reveal valuable information about the magmatic environment and the dynamic behavior of crystals

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

intraseasonal dynamical evolution of the northern annular mode abstract the northern hemisphere annular mode nam accounts for a significant fraction of the extratropical wintertime atmospheric variability the dynamics of nam events have been studied on monthly time scales but little is known about the physical mechanisms that give rise to nam variability on shorter time scales composite diagnostic analyses based on daily nam indices are performed with a goal of identifying the dominant processes responsible for the growth and decay of large amplitude positive and negative nam events on short intraseasonal time scales transformed eulerian mean piecewise potential vorticity inversions and regional plumb flux diagnoses are employed to deduce the proximate forcings of the zonal mean wind tendency during maturing and declining nam stages a remarkable degree of reverse symmetry is observed between the zonal mean dynamical evolution of positive and negative nam events anomalous equatorward and downward poleward and upward eliassen palm fluxes are observed during

opposing effects of reflective and nonreflective planetary wave breaking on the nao planetary wave breaking pwb over the subtropical north atlantic is observed over 45 winters december 1958 arch 2003 using ncep ncar reanalysis data pwb is manifested in the rapid large scale and irreversible overturning of potential vorticity pv contours on isentropic surfaces in the subtropical upper troposphere as breaking occurs over the subtropical north atlantic an upper tropospheric pv tripole anomaly forms with nodes over the subtropical midlatitude and subpolar north atlantic the northern two nodes of this tripole are quite similar to the spatial structure of the north atlantic oscillation nao with positive polarity nonlinear reflection is identified in approximately a quarter of all pwb events following breaking two distinct circulation regimes arise one in response to reflective events and the other in response to nonreflective events for reflective events anomalies over the north atlantic rapidly propagate away from the breaking region along a poleward arching wave train over the eurasian continent the quasi stationary wave activity flux indicates that wave activity is exported out of the atlantic basin at the same time the regional poleward eddy momentum flux goes through a sign reversal as does the polarity of the nao for nonreflective events the dipole anomaly over the north atlantic amplifies diagnostics for nonreflective events suggest that wave activity over the azores gets absorbed allowing continued enhancement of both the regional poleward eddy momentum flux and the positive nao

oxygen isotope heterogeneity of arc magma recorded in plagioclase from the 2010 merapi eruption central java indonesia chemical and isotopic compositions of magmatic crystals provide important information to distinguish between deep juvenile and crustal contributions in this work high resolution multicollector secondary ion mass spectrometry data reveal strong variations of 18o values in three plagioclase crystals 800 1700 m from two representative basaltic andesite samples of the 2010 merapi eruption central java indonesia the 18o values from 4 6 to 7 9 are interpreted to reflect oxygen isotope heterogeneity in the melt composition during plagioclase growth the lowest 18o values 4 6 6 6 are found in anorthite rich cores an82 97 whereas higher 18o values 5 7 to 7 9 are found in anorthite poorer zones an33 86 typically in crystal rims combining these new plagioclase 18o data with 18o of calc silicate crustal xenoliths erupted between 1994 1998 the composition of glass inclusions hosted by the anorthite rich plagioclase an82 92 available experimental data and the results of thermodynamic modelling using the magma chamber simulator code we conclude that the abundant anorthite rich cores crystallized from a mantle derived hydrous basaltic to basaltic trachyandesite melt that recharged a deeper 200 600 mpa magma storage zone whereas lower anorthite zones crystallized at shallower levels 100 200 mpa the oxygen isotope variations in the plagioclase are explained by a two stage model of interaction of the hydrous mafic mantle derived magma 1 with old crustal rocks depleted in 18o due to high temperature alteration that yielded the low 18o values in the anorthite rich cores at deep levels 13 20 km and later 2 with 18o enriched carbonate material that yielded the high 18o values in anorthite poorer zones at shallow levels 4 5 9 km thermodynamic modelling is consistent with 18 wt assimilation of crustal calc silicate material at 925 950 c and 100 200 mpa by the 2010 merapi basaltic andesite magma prior to eruption timescales for plagioclase phenocryst growth and residence in the magmatic plumbing system are 34 years the combined data thus reveal efficient magma recharge and crustal assimilation processes that characterize the open system magma storage and transport systems associated with the 2010 merapi eruption

deducing anomalous wave source regions during the life cycles of persistent flow anomalies abstract anomalous wave source regions are identified during the life cycles of persistent flow anomalies occurring over the north pacific and north atlantic oceans during boreal winter these cases project strongly upon the pacific north american and eastern atlantic teleconnection patterns respectively and represent two of the primary modes of intraseasonal low frequency variability in the northern hemisphere wintertime circulation in the upper troposphere these cases are manifested by wave trains of large scale and large amplitude flow anomalies extending downstream from key regions near the aleutian islands and south of iceland respectively the occurrence of persistent flow anomalies is closely linked to persistent extremes in surface weather and to variations in the skill of extended range weather forecasts black and dole performed a detailed diagnostic analysis of the onset of persistent cyclonic flow anomalies over the north pacific a key result of their study was that wave activity flux di