magmatic fractionation by compositional convection in a sheet like magma body constraints from the nosappumisaki intrusion northern japan the mechanism of fractionation in a sheet like magma body was investigated based on observations from the nosappumisaki intrusion northern japan this is one of a number of late cretaceous shoshonite sills in the nemuro peninsula and has a compound structure comprising a bottom cumulate zone containing 50 vol cumulus crystals and a overlying middle zone free of such cumulus crystals these zones are sandwiched between porphyritic rocks of upper and lower chilled and marginal zones it is inferred that massive crystal settling or flotation from a magma initially laden with 20 vol of crystals primocrysts in a sheet like magma body formed a cumulus pile and an overlying crystal free melt layer after the formation of the compound structure with partial freezing of the upper and lower marginal zones the internal part of the intrusion slowly solidified during this period the melt in the central part of the intrusive sheet underwent fractional crystallization this is shown by patterns of vertical variation in the composition of the interstitial melt the overall patterns are inverted mirrorimage s shaped and s shaped for incompatible and compatible elements respectively the incompatible element abundances show maxima near the bottom of the middle zone which corresponds to the final solidification horizon they show minima in the cumulate zone which suggests discharge of an evolved melt from the crystal pile fractionation is inferred to have taken place via compositional convection without settling of crystals grown after the intrusion event or collapse of the upper boundary layer the melt in the central melt layer descended into the permeable crystal pile counterbalancing discharge of buoyant evolved melt formed by crystallization of the pore melt in the crystal pile this conclusion is based on the following observations 1 there is no accumulation of crystals grown after the intrusion of the magma above the cumulate zone 2 leucocratic pipe like structures which represent relict pathways for the evolved melt are developed in the cumulate zone these structures increase in diameter decrease in number density and increase in abundance of incompatible elements with height 3 cumulus augite in the cumulate zone has ca rich and al poor dissolved rims the extent of dissolution increases with stratigraphic height suggesting downwelling of an h2o rich melt from the overlying melt layer 4 there is no evidence for extensive compaction accompanying pore melt crystallization in the main part of the cumulate zone 5 the initial melt composition estimated from the groundmass of the chilled margin rocks and the average composition of the material interstitial to the primocrysts for the whole sill are statistically identical a mass balance model for compositional convection was constructed to quantify the melt transportation processes model parameters were optimized by fitting the observed vertical variation of the interstitial melt compositions the optimized results suggest that the evolved melts discharged from the crystal pile and rose through the central melt layer as plumes with minor mingling with the surrounding melt the initially formed compound structure is a highly preferential environment for compositional convection

samples from the crystallising boundary layer of a zoned magma chamber the spatial and chemical relationships between the melt occupying the reservoir and the mineral assemblages crystallising at the margins are reconstructed for the magma chamber which produced the 11000 yr b p tephra deposit of laacher see volcano the melt showed vertical chemical zonation immediately prior to eruption and throughout most of the magma volume only a small fraction of crystals were present the eruption also ejected crystal rich nodules ranging from mafic to felsic in composition which are samples of the materials crystallising at the boundaries of the chamber new data on nodule petrography and chemical compositions of whole rocks minerals and interstitial glasses are presented volume fraction of interstitial glass is not systematically related to mineral assemblage and varies typically between 1 and 20 vol i e the crystals interlock one exception is a group of mafic nodules with glass volume fractions between 25 and 40 vol bulk compositions of mafic nodules show strong enrichments or depletions in all major elements relative to the mafic phonolite interstitial melt felsic nodules show much less pronounced differences with their interstitial melt felsic nodules contain interstitial glasses with a range of compositions similar to that in the zoned bulk of the chamber and were probably derived from different heights on the walls mafic nodules have glass compositions similar to those at the base of the zoned liquid column and were probably derived from the floor modal mineralogy glass composition and mineral composition are systematically related in the nodules whereas in individual pumices samples derived from the main body of the chamber a broader range of mineral compositions are often found mineral assemblages were especially diverse in the upper part of the chamber it is deduced that the whole of the essentially liquid part of the chamber was emptied by the eruption that strongly contrasting mineral assemblages were forming simultaneously on the walls and floor that the gradient in crystal content in the crystallisation boundary layer was more gradual at the floor than at the walls and that the pumice mineralogy is not a simple phenocryst assemblage but is a mixture of crystals which grew from melts separated in space and or time

postcumulus processes in layered intrusions during the postcumulus stage of solidification in layered intrusions fluid dynamic phenomena play an important role in developing the textural and chemical characteristics of the cumulate rocks one mechanism of adcumulus growth involves crystallization at the top of the cumulate pile where crystals are in direct contact with the magma reservoir convection in the chamber can enable adcumulus growth to occur to form a completely solid contact between cumulate and magma another important process may involve compositional convection in which light differentiated melt released by intercumulus crystallization is continually replaced by denser melt from the overlying magma reservoir this process favours adcumulus growth and can allow adcumulus growth within the pore space of the cumulate pile calculations indicate that this process could reduce residual porosities to a few percent in large layered intrusions but could not form pure monomineralic rocks intercumulus melt may also be replaced by more primitive melt during episodes of magma chamber replenishment dense magma emplaced over a cumulate pile containing lower density differentiated melt may sink several metres into the underlying pile in the form of fingers reactions between melt and matrix may lead to changes in mineral compositions mineral textures and whole rock isotope compositions another important mechanism for forming adcumulate rocks is compaction in which the imbalance of the hydrostatic and lithostatic pressures in the cumulate pile causes the crystalline matrix to deform and intercumulus melt to be expelled for cumulate layers from 10 to 1000 metres in thickness compaction can reduce porosities to very low values 1 and form monomineralic rocks the characteristic time scale for such compaction is theoretically short compared to the time required to solidify a large layered intrusion during compaction changes of mineral compositions and texture may occur as moving melts interact with the surrounding matrix both compaction and compositional convection can be interrupted by solidification in the pore spaces compositional convection will only occur if the rayleigh number is larger than 40 if the residual melt becomes lower in density and the convective velocity exceeds the solidification velocity measured by the rate of crystal accumulation in the chamber orthocumulates are thus more likely to form in rapidly cooled intrusions where residual melt is frozen into the pore spaces before it can be expelled by compaction or replaced by convection

multistage magma mixing revealed in phenocryst zoning of the yunokuchi pumice akagi volcano japan detailed study of the texture and chemical zoning of phenocrysts in the compositional and thermal histories at the sites a plinian fall deposit yunokuchi pumice from akagi volcano where they grew only recently have such studies been japan permits reconstruction of the subvolcanic magma chamber undertaken focusing on magma chambers as the sites hypersthene phenocrysts are complexly zoned some have spongy of phenocryst formation tait 1988 de silva 1989 cellular textures whereas others exhibit simple reverse zoning augite umino iwano 1992 fodor et al 1993 nakada et phenocrysts have texturally similar cores but al and ti vs mgal 1994 the magma chambers depicted by these number zoning patterns are correlatable with hypersthene cores studies are mainly composed of phenocryst poor magma most plagioclase phenocrysts have a uniform calcic core enclosed surrounded by a comparatively thin crystallizing boundby a normally zoned rim others have variable an contents and ary layer phenocrysts are interpreted to have crysmottled textures these characteristics and melt glass compositions tallized either within the main body of magma or in suggest a complex multistage mixing of low t 940 960 c situ within the boundary layer highly silicic and high t 980 1060 c less silicic magmas combination of geophysical and petrological data stratigraphic variations of the phenocryst types show that the earlier together with fluid dynamical simulations of magmatic erupted magma inherited phenocrysts from more high t magma processes beneath mid oceanic ridges has shown that a components we propose the presence of an inhomogeneous mushy mush of crystals and interstitial melt 25 55 vol chamber filled with a highly silicic magma which was recharged crystals probably makes up the majority of the magma periodically by less silicic magmas the large viscosity contrast and chamber and only a small volume exists as a meltdensity balance of the new magma relative to the mush controlled enriched lens e g sinton detrick 1992 nicolas et al the efficiency of mixing and the position of emplacement of the high1993 barth et al 1994 likewise it is highly probable t magma in the mush tapping the chamber first expelled the that magma chambers beneath island arc volcanoes fluidal mixed magma followed by progressive erosion of the mush largely consist of a mush of crystals and interstitial melt as the eruption continued recent studies on arc volcanic products have presented evidence for the existence of such mushy magma chambers these include an estimation of very high crystallinity

trapped liquid from a nepheline syenite a re evaluation of na zr f rich interstitial glass in a xenolith from tenerife canary islands abstract interstitial glass and pyroxene in a nepheline syenite described by wolff 1987 have been more precisely and accurately re analysed using a cryogenic microprobe technique the glass compositions with na2o 13 4 17 0 wt and na k al 1 81 2 26 at sio2 53 56 5 wt on a 100 normalised basis are more extreme than any known erupted magma zro2 contents of the glasses are 1 4 1 8 by weight while f ranges between 1 and 1 4 the high zr content is due to the failure of a zr silicate phase to precipitate despite predicted zircon saturation of the liquids above their probable quench temperatures partitioning of zr between pyroxene and liquid is highly variable and apparently controlled by sector zoning zr is preferentially incorporated into aegirine 001 growth sectors the glasses demonstrate the extent to which peralkaline phonolitic liquids can be fractionated in closed magma systems

on the interaction between convection and crystallization in cooling magma chambers abstract we investigate the interaction of thermal convection and crystallization in large aspect ratio magma chambers because nucleation requires a finite amount of undercooling crystallization is not instantaneous for typical values of the rates of nucleation and crystal growth the characteristic time scale of crystallization is about 10 3 10 4 s roof convection is characterized by the quasi periodic formation and instability of a cold boundary layer its characteristic time scale depends on viscosity and ranges from about 10 2 s for basaltic magmas to about 10 7 s for granitic magmas hence depending on magma viscosity convective instability occurs at different stages of crystallization a single non dimensional number is defined to characterize the different modes of interaction between convection and crystallization using realistic functions for the rates of nucleation and crystal growth we integrate numerically the heat equation until the onset of convective instability we determine both temperature and crystal content in the thermal boundary layer crystallization leads to a dramatic increase of viscosity which acts to stabilize part of the boundary layer against instability we compute the effective temperature contrast driving thermal convection and show that it varies as a function of magma viscosity and hence composition in magmas with viscosities higher than 10 5 poise the temperature contrast driving convection is very small hence thermal convection is weak in low viscosity magmas convective breakdown occurs before the completion of crystallization and involves partially crystallized magma the convective regime is thus characterized by descending crystal bearing plumes and bottom crystallization proceeds both by in situ nucleation and deposition from the plumes we suggest that this is the origin of intermittent layering a form of rhythmic layering described in the skaergaard and other complexes we show that this regime occurs in basic magmas only at temperatures close to the liquidus and never occurs in viscous magmas this may explain why intermittent layering is observed only in a few specific cases

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

boundary layer fractionation constrained by differential information from the kutsugata lava flow rishiri volcano japan detailed investigation of an erupted magma with limited compositional diversity provides instantaneous information on incremental magma differentiation processes in a magma chamber kutsugata lava a suitable target of such study is a quaternary alkali basalt 51 3 53 2 wt in sio2 from rishiri volcano northern japan despite the narrow range in the whole rock compositional variation chemical and modal compositions of mineral phases crystallized in the magma chamber vary systematically with the whole rock composition in the north lava 51 3 51 9 wt in sio2 the less differentiated portion of the kutsugata lava most crystals which include low ni olivine and plagioclase were derived from the mushy boundary layer the main part of the magma body was principally aphyric 30 vol by such mechanisms as compaction and compositional convection this fractionated melt was mixed with the overlying main magma causing differentiation of the kutsugata magma the average temperature of the extracted melt is 1010 c significantly lower than 1100 c estimated for the main magma a quantitative model of magmatic differentiation which includes thermal and compositional evolution of a mushy boundary layer can successfully reproduce the observed compositional trends of the north lava

phase equilibria of the lower laacher see tephra east eifel germany constraints on pre eruptive storage conditions of a phonolitic magma reservoir laacher see volcano erupted about 12 900 years ago resulting in a tephra blanket widely dispersed in central europe the eruption tapped a chemically and mineralogically strongly zoned phonolitic magma reservoir in order to better constrain the pre eruptive storage of that magma hydrothermal phase equilibria experiments have been performed on a powdered sample from the highly evolved phonolite of the lower laacher see tephra llst experiments were run at water pressures of 75 175 mpa and temperatures of 725 800 c stability fields of sanidine and amphibole the most common crystal phases in llst suggest that the magma last equilibrated at temperatures of 750 760 c and pressures of 115 145 mpa those conditions suggest the magma should have contained between 5 and 6 wt water which agrees well with water contents of 5 7 wt found in glass inclusions that agreement along with the observation that cl and s vary with the composition of the inclusions suggest that the laacher see magma was saturated at depth with a water rich fluid and thus was stored at pressures near those estimated from our experiments such pressures roughly correspond to depths of 5 6 km clinopyroxene and plagioclase did not occur in the experimental runs although present in the natural pumice sample it seems likely that these phases are not inherent to the llst they were formed in other parts of the chemically stratified column and later redistributed a recalculation of the magma density together with a new estimate of the temperature and pressure range suggests a steep density gradient and a thin withdrawal layer which is typical for volatile enriched magma bodies and confirms earlier models of convective fractionation in the laacher see magma reservoir

air and water flows in a vertical sand column 1 the unsteady state drainage of water from a vertical sand column with and without a finer layer on the top was studied theoretically and experimentally to investigate the airflow generated by the finer layer the sand column saturated at its lower portion and initially in the condition of hydrostatic equilibrium is drained at its bottom at constant head the results show that significant vacuum can be generated in the vadose zone of the column with a finer layer on the top the vacuum increases quickly in the earlier stage of the drainage reaches a maximum and gradually becomes zero because of the effect of the vacuum in the vadose zone water is held in and the cumulative outflow from the column with the finer layer is much smaller than without the layer during most of the drainage process ordinary differential equations ode which require only saturated hydraulic properties of the porous media are derived to predict the location of the surface of saturation and vacuum in the vadose zone in air water two phase flow the solutions of ode match very satisfactorily with the experimental data and give better results than tough2

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

in situ crystallization observed in the osumi granodiorite batholith abstract the osumi granodiorite is a 14 ma batholith emplaced in accreted sedimentary rocks in the forearc of southwest japan it has a chemical and mineralogical zonal structure with zones which become progressively more felsic inward feo and mgo decrease while sio2 k2o and rb increase from its margin to the interior in accord with this alkali feldspar and quartz become more abundant in inner zones and biotite and plagioclase vary oppositely the mineral assemblage however remains unvaried major bulk rock compositions form a linear variation trend which is found to be almost identical with the average trend of japanese granitic rocks these petrographic and chemical characteristics are well explained by in situ crystallization model in which the liquid returning from the solidification zone to the chamber has the granitic minimum liquid composition the composition of the liquid in the chamber and that of the cumulate lie on the straight line that connects the granitic minimum and the initial chamber composition

a screening model for nonaqueous phase liquid transport in the vadose zone using green ampt and kinematic wave theory in this paper a screening model for flow of a nonaqueous phase liquid napl and associated chemical transport in the vadose zone is developed the model is based on kinematic approximation of the governing equations for both the napl and a partitionable chemical constituent the resulting governing equation is a first order quasi linear hyperbolic equation to which the generalized method of characteristics can be applied this approach generally neglects the contribution to the napl flux from capillary pressure gradients during infiltration under ponded conditions or when the napl flux exceeds the maximum effective conductivity of the soil the effect of capillary suction is included in the model through the usage of the green ampt model all of the resulting model equations are in the form of ordinary differential equations which are solved numerically by a variable time step runge kutta technique results from a simple column experiment were used to evaluate the vadose zone flow model assumptions independently measured parameters allow simulation without calibration of the model results the match of the model to the data suggests that the model captures the qualitative behavior of the experimental system and is capable of an acceptable degree of quantitative agreement

relationships between chamber margin accumulates and pore liquids evidence from arrested in situ processes in ejecta latera caldera italy biotite and clinopyroxene rich mafic nodules occur together with syenite ejecta in ca 235 to 155 ka tuffs surrounding the latera caldera clinopyroxenites and leucite monzosyenites crystallized along the lower margins of a crustal magma system and record complex crystallization histories of potassic magmas that were parental to a range of lava and tuff compositions the mafic nodules have the mineral assemblage clinopyroxene biotite anorthite orthoclase leucite hauyne titanite apatite amphibole olivine phlogopite and comprise mesocumulate and orthocumulate layers that commonly alternate on the scale of several centimeters despite the apparently ultramafic nature of the early cumulate assemblage the common occurrence of intercumulate orthoclase leucite hauyne salitic clinopyroxene and vesicular glass indicates that interstitial liquids underwent late stage differentiation at relatively shallow depths but under highly variable conditions of volatile saturation many of the mafic nodules exhibit pronounced variations in the type and abundance of mineral reaction textures these range from unreacted assemblages to nodules in which cumulate megacrysts are surrounded by well developed symplectite halos the textural variability indicates strongly localized disequilibrium between cumulate frameworks and vapor saturated pore fluids and is attributed to convective fractionation of liquids through permeable crystal mush lithologic discontinuities exhibited by the xenolith suite and host magmas are best explained by variable communication between a compositionally stratified magma reservoir and its partly crystallized lower chamber margins periodic replenishment of this system by less evolved magmas subsequently promoted mixing and hybridization that are characteristic features of many latera lavas and tephra

tephra fountaining rheomorphism and spatter flow during emplacement of the pitigliano tuffs latera caldera italy abstract toward the end of the main ash flow phase ca 156 ka of the latera caldera central italy explosive eruptions near the nw caldera rim produced coarse grained tephra exposed in 35 m high faces of the toscapomice casa collina quarry the pyroclastic sequence fills a narrow sw ne paleovalley and records the near continuous eruption of a compositionally zoned magma batch white phonolitic pumice clasts abruptly grade upward to and partly intrude black spatter like pumice fragments also of phonolite composition this sequence in turn is overlain by densely welded tuff that grades upward to tephriphonolitic scoriae and ash the upper welded part of this sequence referred to as the vulcanite complessa di pitigliano has long been among the more enigmatic deposits in the latera area this sequence displays evidence for both fall and flow emplacement and is here interpreted as an ash fountain fed deposit that locally welded as spatter yet became sufficiently fluidized in distal parts to behave as a spatter rich pyroclastic flow this mechanism requires that the eruption underwent abrupt transition from a vigorously convecting column to a weakly convecting ash fountain and that this period of explosive activity culminated with unusually high accumulation rates the rapidly emplaced tephra retained sufficient heat to weld by compaction and undergo rheomorphism close to the vent yet contained high enough proportions of fluidized dust to have flowed outward along the northern caldera rim and eventually to have welded by vapor phase sintering

evolution of the laacher see magma chamber evidence from sims and tims measurements of uth disequilibria in minerals and glasses abstract u th disequilibrium was measured by secondary ion mass spectrometry th and thermal ionization mass spectrometry u in mineral separates from pumices and cumulate nodules from the laacher see volcano 12 5 0 5 kyr corrected 14 c age in east eifel germany phonolitic glasses all plot to the left of the equiline with higher u th observed in the most felsic glasses measured partitioning of u and th in the mineral phases is consistent with the observed increase in u th with progressive fractional crystallization apparent ages of crystallization inferred from internal isochrons in the pumices from the main part of the magma chamber are about 13 3 kyr indistinguishable from the eruption age this implies that the residence time of these phenocrysts did not exceed 1 2 kyr older less precise ages for the upper part of the magma chamber 30 kyr suggest mixing of older crystals from cumulates and or longer residence times mineral isochrons for cumulate nodules are not well defined with ages ranging from 10 to 30 kyr suggesting in situ cumulate formation 10 20 kyr prior to the eruption the time required to explain the 230 th 232 th difference between parental basanite and laacher see phonolite is inferred to be about 100 kyr together these observations favor a cooling model where differentiation of parental basanite takes place in a deep magma body over about 100 kyr followed by emplacement of the resulting mafic phonolite into an upper crustal chamber and continued differentiation toward evolved phonolite the time scale for the development of zonation in the laacher see magma chamber is estimated to be 10 20 kyr at most

terminology for layered intrusions the terminology of igneous cumulates was originally formulated on the concept that the rocks were concentrations of minerals accumulated by crystal settling it is now well established for several major intrusions that plagioclase that had been typed as cumulus should in fact have floated in its parental magmatic liquid nevertheless the terminology has been valuable in the classification of the rocks of these and other intrusions and it has been useful in certain aspects of their genetic interpretation the name cumulate is therefore redefined so that crystal settling is a possible but not essential process in the origins of the rocks to which it is applied the overall nomenclature of layered intrusions is then reviewed and definitions of names are refined and systematized to clarify their applications careful distinction is made between descriptive and genetic names a cumulate is defined as an igneous rock characterized by a framework of touching mineral crystals and grains that evidently were concentrated through fractional crystallization of their parental magmatic liquids a layer is a sheetlike unit of cumulate that is a distinctive entity in its compositional and or textural features a lamina is a thin 2 5 cm sharply defined layer igneous lamination is a general name for planar structure that is pervasive through cumulates on the scale of their grain size layering is the overall structure and fabric manifest through combinations of layers laminae and lamination the difference between layers and layering is essentially the difference between individuals and a population and the terms that describe one are not necessarily appropriate to the description of the other but the fundamental variants of all of layering lamination grading in layers and layer contacts can essentially be described by one or more of the four modifiers grain size modal textural and cryptic where the last refers to cumulus miner al compositions a system for subdividing layered intrusions is proposed in which distinction is made between general divisions ranked as series zones and subzones and prominent units that are called groups members rhythmic units and cyclic units applications to the skaergaard bushveld muskox stillwater and other intrusions are briefly described

melt extraction in mush zones the case of crystal rich enclaves at the sabatini volcanic district central italy abstract a peculiar feature of the sabatini volcanic district svd central italy is the occurrence of crystal poor pumices and crystal rich enclaves within the same eruptive host deposit the stratigraphic sequence of pumices and enclaves indicates the tapping of a stratified magma chamber where a crystal poor phonolitic magma lay on top of a more primitive crystal rich magma the crystal rich enclaves are genetically related to the pumices and record the evolution of a solidification front in which a more differentiated melt was produced extracted and eventually erupted we collected and analyzed crystal rich enclaves from one of the largest phonolitic eruptions at the svd and used their petrological and geochemical features to reconstruct magma differentiation and crystal melt separation in the solidification front on this basis three groups of enclaves have been identified porphyritic enclaves holocrystalline enclaves and sanidinites the mineralogical variability faithfully reproduces the spatial and temporal evolution expected of a solidification front from early to intermediate crystallization conditions porphyritic and holocrystalline type to the late stage of solidification sanidinites in which the percolation of a more differentiated melt through the crystal mush triggered the instability of the solidification front results from numerical models indicate that gravitational instability is the most efficient mechanism to explain melt extraction in mush zones of medium sized 10 km 3 short lived 10 4 years magma chambers

chemical evolution of intercumulus liquid as recorded in plagioclase overgrowth rims from the skaergaard intrusion the intercumulus liquid of a crystal mush fills pore spaces and typically solidifies to form overgrowths on cumulus grains and poikilitic post cumulus minerals if the liquid is immobile solidification produces zoned intercumulus minerals as a result of progressive fractionation of the residual liquid convection within the mush results in buffering of the liquid composition and thus limits mineral zonation for fully solidified cumulates fossil changes in liquid composition or porosity are difficult to identify however detailed study of immobile minor components of plagioclase overgrowth rims can provide information about the progressive solidification of intercumulus material ti contents of plagioclase overgrowths in samples from the lowermost parts of the skaergaard intrusion show strong variations with anorthite content with decreasing xan ti concentrations first rise and then fall consistent with changing tio2 contents of the intercumulus liquid during solidification tio2 in plagioclase decreases sharply at an55 reflecting local saturation of fe ti oxides ti in clinopyroxene oikocrysts also falls rimward but zoning in faster diffusing species fe mg is limited other than slight reverse zones that may occur on the plagioclase margins xan falls continuously during crystallization the reverse zoning is interpreted as the result of compaction driven dissolution and reprecipitation of plagioclase the continual decrease in xan is exploited together with back scattered electron images of the cumulates to produce calibrated images showing regions of progressive crystallization this allows the regions crystallizing at each stage of solidification to be visualized these images show that the final remnants of interstitial melt were present in triangular pockets and as thin grain boundary melt films this approach can provide information about the progressive reduction of porosity during cumulate solidification

volatile composition of the phonolitic laacher see magma 12 900 yr bp implications for syn eruptive degassing of s f cl and h 2 o a volatile rich and chemically zoned phonolitic magma reservoir was tapped successively during the eruption of laacher see volcano ca 12 900 years bp and produced a tephra sequence consisting of phenocryst poor highly evolved phonolite at the base and phenocryst rich more mafic phonolite at the top the stratospheric volatile loading was estimated by comparing pre and post eruptive s f cl and h2o contents of undegassed glass inclusions and partially degassed matrix glasses glass inclusions 150 1490 ppm s and host matrix glasses 150 820 ppm s both document a strong s decrease during progressive magmatic differentiation which is interpreted to be partially caused by crystallization of hauyne the s6 stotal ratio of the pre eruptive melt increased with differentiation from 8 to 71 as indicated by s k wavelength shift measurements in glass inclusions sulfate rich highly evolved phonolitic magma was erupted during plinian and sulfide rich more mafic phonolitic magma during late phreatomagmatic phases f and cl became enriched during late stages of differentiation glass inclusions 690 4060 ppm f 1770 4400 ppm cl matrix glasses 680 3660 ppm f 2130 4330 ppm cl the most differentiated melts maximum 13 wt na2o occur only as matrix glass and are extremely f enriched 5080 8780 ppm but cl depleted 460 2820 ppm suggesting that f was retained in the melt whereas some cl was lost during pre and or syn eruptive degassing the h2o contents of glass inclusions increase irregularly with differentiation 2 5 5 7 wt matrix glasses are h2o depleted 0 2 2 8 wt compared to most glass inclusions showing that most h2o was released to the atmosphere by explosive degassing a mass balance calculation yields a syn eruptive volatile release of 1 9 tg stotal 6 6 tg cl and 403 tg h2o from the melt this is a minimum estimate since s and cl could have accumulated in a separate fluid phase as indicated by fluid inclusions in hauyne and pre eruption h2o contents close to saturation level at the likely pressure temperature conditions in the laacher see magma reservoir we estimate that at least ca 20 tg so2 were injected into the stratosphere causing a significant negative climate forcing as reflected by several paleoclimate proxies and as shown by recent modeling

structure and dynamics of the laacher see magma chamber eifel germany from major and trace element zoning in sanidine a cathodoluminescence and electron microprobe study microtextures and zoning patterns in sanidine phenocrysts from the phonolitic laacher see tephra germany were investigated in order to constrain processes occurring in the magma chamber before eruption the laacher see tephra unit is chemically zoned and has been inferred to represent the product of eruption of an inverted layered magma chamber samples from various levels in the deposit were investigated we used a combination of textural studies optical microscopy and back scattered electron bse imaging electron microprobe emp analysis of major minor and trace elements ca na k al si ba sr fe and ti and element mapping the samples studied contain two feldspar phases and the ternary composition of the sanidine thus constrains the temperature of crystallization whereas its trace element content reflects the melt composition the large diversity in textures found in the sanidine crystals can be classified into three types composite c type pseudooscillatory po type and resorbed patchy r type trace elementpoor lamellar composite alkali feldspars c type are found in samples inferred to represent the top and the middle part of the magma chamber they grew as composite crystals from the melt at temperatures as low as 650 c in a highly differentiated and volatilerich boundary layer at the magma chamber roof or wall pseudooscillatory zoning with resorption surfaces po type is found in sanidinesfromsamplesinferredtorepresentthemiddlepartandthebase of the magma chamber repeated large an variations 1 4 mol reflect temperature variations of 100 300 ca ssociated with changes in water content variations of minor and trace elements ba sr and ti in sanidine decoupled from the pseudo oscillations of the major elements reflect chemical changes in the melt and are damped by chemicaldiffusioninthemelt bothmajorandminorelementvariations inpo typecrystalsareinterpretedastheprogressiveinfluenceofamore mafic hotter melt this may be partly explained by the settling of crystals through the thermal and chemical gradient existing in the magma chamber however the additional role of magma recharge may be required to explain the large temperature variations resorbed patchy zoned crystals r type found mainly in samples corresponding to the middle part of the magma chamber reflect early growth in a differentiated boundary layer followed by resorption and overgrowthinthemainmagmabody manyofthelaacherseesanidine crystals did not crystallize for the most part in the melt in which they were erupted in the presence of preserved major and trace element zonation in the magma this observation indicates crystal dispersion within a layered magma chamber without large scale mixing and overturn

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

magma chambers emplaced in carbonate substrate petrogenesis of skarn and cumulate rocks and implications for co2 degassing in volcanic areas crystal rich lithic clasts occurring in volcanic deposits are key tools to understand processes of storage cooling and fractionation of magmas in pre eruptive volcanic systems these clasts represent snapshots of the magma chamber host rock interface before eruption and provide information on crystallization differentiation and degrees of interaction between magma and wall rock in this study we have focused on the petrology of clasts of cumulate and skarn rocks from the colli albani volcanic district with the aim of shedding light on magma carbonate interaction and co2 emission in volcanic areas by means of phase relations bulk rock chemistry mineral compositions and isotope data we have identified different types of cumulates and skarns cumulates containing either clinopyrox

the 12 900 years bp laacher see eruption estimation of volatile yields and simulation of their fate in the plume we estimated the volatile emissions of the 12 900 years bp eruption of laacher see volcano germany using a modified petrological method glass inclusions in phenocrysts and matrix glasses sampled over the laacher see tephra profile were analysed by synchrotron x ray fluorescence microprobe and electron microprobe to obtain the emitted masses of halogens sulphur and water these data were used to initialize the numerical plume model atham in order to investigate the fate of volcanic gases in the plume and to estimate volatile masses injected into the stratosphere the scavenging efficiency of each volatile component depends on its interactions with both liquid water and ice we found a scavenging efficiency of c 5 for the sulphur species and of only c 30 for hydrogen halides despite their high water solubility our simulations showed that the greatest fraction of hydrometeors freeze to ice due to the fast plume rise and great height of the eruption column for the dry atmospheric conditions of the laacher see eruption the amount of liquid water was not sufficient to completely scavenge hcl and hbr so that a large proportion could reach the stratosphere

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

small scale disequilibrium in a magmatic inclusion and its more silicic host basaltic andesite inclusions and their host dacite from the purico chascon complex in northern chile are isotopically distinct textural characteristics of the inclusions are typical of those resulting from magma mingling serial sectioning across the interface of an inclusion and its host dacite complemented by microdrill sampling and detailed microprobe work has enabled us to examine the scale of mixing and chemical isotopic and trace element disequilibrium the results of this work show that 1 the composition of the inclusion is relatively homogeneous 2 the dacite host is generally higher in 87sr 86sr and lower in 143nd 144nd than the enclave but it is heterogeneous on a small scale and probably a hybrid 3 the isotopic composition in the marginal zone apparently on both host and inclusion sides of the weakly chilled interface actually shows the highest 87sr 86sr and lowest 143nd 144nd 4 large plagioclase crystals in the inclusions and host are xenocrystic with higher 87sr 86sr than any of the other samples these observations are reconciled with a model of magma evolution in a crustal magma chamber in such a scenario the mafic magma is overlain by a cap of rhyolite a partial melt of the dacitic ignimbrites which now underlie the purico chascon complex overturn of such a magma system gives rise to a hybrid dacite containing discrete mafic inclusions

insights into continental rift related magma chambers cognate nodules from the kula volcanic province western turkey abstract the quaternary volcanism of kula western turkey occurred in response to miocene lower lithospheric n s extension which resulted in the formation of 80 monogenetic cinder cones each with an associated lava flow basanites tephrites and phono tephrites comprising a total magma volume of 2 3 km 3 many cones form closely spaced genetically related groups of up to 5 cones one such group of cones in the immediate vicinity of kula contains large crystal rich nodules dominated by amphibole and clinopyroxene the nodule suite is varied both compositionally and texturally and is likely to comprise solid fractionates of the kula lavas formed at the floor or roof zones of a suite of synchronously active mid to lower crustal magma lenses or sill like chambers and in narrow tectonically active conduits the local occurrence of nodules is probably because the plumbing system in this region was used by a series of eruptions which occurred over a short time interval during which solidification of the conduit system was incomplete the amphibole nodules generally contain more vesicular glass than clinopyroxene dominated nodules comparison of the textures with those of other studies suggests that the highly porous amphibole dominated nodules were derived from a relatively porous thick mush the highly crystalline clinopyroxene nodules were most likely excavated from the deeper levels in the mush at least part of the crystal mush was layered compositionally with irregular variations in porosity and grain size attesting to the dynamic nature of crystallisation in such a small short lived system the presence of adcumulates together with poikilitic heteradcumulates points to a highly variable degree of liquid exchange with the magma adjacent to the mush zone

cenozoic sediment accumulation on drifts in the northern north atlantic the northern north atlantic sediment drifts have a much greater areal extent than has previously been indicated the northern north atlantic extends from the east greenland to european continental shelves and from the charlie gibbs fracture zone to the greenland scotland ridge within this region are seven major sediment drifts containing some of the best clues for pre quaternary bottom water circulation in the north atlantic feni drift is the oldest in the region originating near the eocene oligocene boundary it was followed by accumulation of bjorn gardar hatton and snorri drifts from the late early to middle miocene eirik drift may have started to accumulate in the late miocene and gloria drift in the early pliocene through analysis of the cenozoic sediment mass age distribution and the change in area of seafloor for the study area through time it can be concluded that there is a deficit of oligocene to miocene sediment in the region this could be explained by sediment cycling the erosion of older sediment to produce young sediment the mass of pliocene to quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of eocene and oligocene sediment by deepwater currents the sediment drift portion of the total regional sediment mass increased significantly three times during the cenozoic each of these drift growth phases lasted between 3 and 4 m y the first two growth phases from the late eocene to early oligocene and from the early to middle miocene were accompanied by northward shifts of depocenters to the newly forming sediment drifts the third and largest growth phase occurred between 7 and 3 ma and may have been preceded by the initiation of accumulation on eirik drift 8 7 ma this most recent growth phase was accompanied by high apparent accumulation rates over southern gardar drift as it expanded to the east erosion rates over reykjanes ridge may have been higher during the mid pliocene than in the quaternary there are two main sites where dense water could have formed and flowed south through the rockall trough to start the accumulation of feni drift if the atmosphere were cool enough dense water could have formed in the norwegian sea or on the faeroe shelf dense water may also have formed on the rockall plateau due to salinity increase through evaporation in an arid climate as an alternative to the hypothesis of arctic ocean water overflowing the iceland faeroe ridge in the early middle miocene it is suggested that dense water formed along shallow segments of the iceland faeroe ridge and then flowed into the south iceland basin to begin accumulation of bjorn gardar and snorri drifts the initiation of sediment drift formation in the south iceland basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a middle miocene uplift event along the iceland faeroe ridge a second uplift event along the greenland scotland ridge and a decreased production of northern component water in the early pliocene may be responsible for increased sediment accumulation in bjorn gardar and eirik drifts

distribution of orthocumulate textures in the jimberlana intrusion the p and u contents and the texture of cumulates have been used to document variations in residual porosity in the jimberlana intrusion the results show that rocks with low residual porosity adcumulate textures occur where heat loss through the floor of the chamber was low or where the viscosity of the melt from which they crystallized was low low residual porosity also correlates with the appearance of plagio clase as a cumulus phase and with zones of well developed rhythmic layering it is suggested that the initial porosity of cumulates is controlled by the balance between nucleation and crystal growth at the crystalliquid interface low initial porosity represents attainment of textural equilibrium and forms when adjacent crystals at the top of the cumulate pile continue to grow expelling the intercumulus magma in the process high initial porosities develop when new crystals nucleate at the top of the crystal pile before a high proportion of the intercumulus magma is expelled low viscosity in

quaternary and upper pliocene glaciations and forest development in the tropical andes evidence from a long high resolution pollen record from the sedimentary basin of bogota colombia pollen analysis of 1230 samples from a 357 m long core of lake sediments from the sedimentary basin of bogota eastern cordillera colombia alt 2550 m above sea level has provided a high resolution record of changes in the andean vegetation belts and long range climatic fluctuations during the last 3 5 ma direct time control is provided by k ar datings and fission track datings of 14 intercalated volcanic ash layers the resulting pollen diagram has been divided into 55 pollen zones representing 27 complete major climatic cycles glacial interglacial cycles a tentative correlation with the marine oxygen isotope chronology and the european stratigraphical climatic subdivision could be established the altitudinal position of the forest line which corresponds with the 9 5 c isotherm shifted between minimal c 1700 1800 m and maximal c 3400 3700 m alt at present situated at c 3100 m alt which rendered the altitudinal position of the high plain of bogota the dry bed of a former lake at 2550 m a sensitive recorder of temperature changes the estimated fluctuations in mean annual temperature at the level of the high plain of bogota are from 15 c a distinct change in the nature of the climatic cycles occurs around 2 5 ma b p the interval of 3 5 2 5 ma b p shows high frequency low amplitude climatic oscillations whereas the last 2 5 ma is characterized by low frequency high amplitude climatic oscillations with a superposed high frequency oscillation it is assumed that these oscillations correspond mainly with the variations in orbital eccentricity and obliquity the major constituents making up the andean forest have been subjected to considerable changes in the course of time in the early pliocene forests vallea and myrica are prominent elements weinmannia was almost absent the role of polylepis in the timberline forests increased markedly around 3 1 ma b p and also migrated by adaptation from the upper andean forest line to higher elevations the closure of the isthmus of panama during the pliocene enabled northern hemisphere elements to migrate into south america alnus reached the area of bogota around 2 7 ma b p and dramatically changed the vegetation especially on the flats around the lake of bogota where alnus swamp forests replaced myrica carr around 2 9 ma b p weinmannia became an important constituent of the upper andean forest but slightly later slope forests of alnus replaced parts of the area which had previously been covered by weinmannia forest the marked role of vallea in the andean forest diminished definitively after 2 5 ma b p quercus migrated more recently to south america and reached the area of bogota 1 ma b p it changed for the last time drastically the aspect of the andean forest all palynologically recognizable elements of the modern andean forest were present from now on and the subsequent adaptation and speciation of quercus and many other elements must have mainly taken place at the species level

the eruptive center of the late quaternary laacher see tephra about 5 km3 of phonolite magma were erupted 11 000 years ago in the laacher see area in plinian and vulcanian eruptions the eruptive vents for all tephra in dispute for over 200 years must have been located entirely within the laacher see basin because 1 all deposits are thickest in the tuffring surrounding the basin with one exception pyroclastic flow deposits are thickest 2 to 6 km away from the rim of the basin having ponded in radial valleys three plinian fallout layers show minor secondary thickness maxima 12 to 16 km east of laacher see 2 axes of all depositional fans and single tephra sheets converge in the laacher see basin 3 diameters of both lithic and pumice clasts reach their maxima in outcrops close to laacher see volcano 4 directions of asymmetric ballistic impact sags indicate the laacher see basin as source area 5 the dimension of laacher see crater roughly corresponds to the erupted volume of phonolitic tephra 5 3 km3 magma dre and lithic clasts 0 7 km3 6 xenolith types are consistent with an eruptive center within the laacher see basin 7 the systematic chemical and mineralogical zonation of the tephra deposits from highly differentiated aphyric phonolite at the base to highly phyric mafic phonolite at the top strongly suggests eruption from a single compositionally zoned magma column 8 several lines of evidence indicate migration of the main eruptive focus from the south to the north during the later part of the eruption both vents however being confined within the laacher see basin

boundary layer crystallization in a basaltic magma chamber evidence from rishiri volcano northern japan the evolution of basaltic magma by mushy boundary layer processes introduction in a magma chamber is documented for an alkali basalt kutsugata the evolution of magma chambers is of major petrologic lava from rishiri volcano northern japan on the basis of zoning interest and has been studied extensively experimental patterns of plagioclase phenocrysts and their spatial distribution in and theoretical studies that have investigated the cooling the lava plagioclase phenocrysts with complex zoning patterns can of magma chambers have demonstrated that a magma be divided into four types type 1 is characterized by an extremely chamber solidifies through formation of a mushy boundan rich core an71 90 which is commonly corroded and filled with ary layer composed of crystals and interstitial melt along sodic plagioclase type 2 has an ab rich core surrounded by a calcic the chamber walls e g brandeis jaupart 1986 turner mantle characteristic of partial dissolution type 3 is characterized by et al 1986 marsh 1988 tait jaupart 1992 layered igneous complexes e g morse 1969 shirley 1987 an ab rich core that is commonly surrounded by a reversely zoned mcbirney 1996 provide useful information on how slightly calcic mantle type 4 has an ab rich core without a calcic mafic magma chambers evolve and consolidate but they mantle the an rich cores of the type 1 plagioclase are too calcic do not offer much insight into the instantaneous state of to have crystallized from a liquid represented by any whole rock a chamber because those intrusions integrate processes composition at the estimated temperatures of the kutsugata magma that occurred over long solidification times mcbirney system the an rich cores are inferred to have been formed in a noyes 1979 tait 1988 volcanic products such as mushy boundary layer along the wall of a magma chamber where lava flows and tephra deposits can sample the inthe magma was relatively cool and rich in water because of significant stantaneous state of a magma chamber there are a few olivine fractionation and possibly because of addition of water studies along this line of approach tait 1988 de silva expelled from the chilled margin and or groundwater from the 1989 nakada et al 1994 these studies focused on surrounding crust the ab rich cores of types 2 4 plagioclase crystal aggregates in volcanic products and concluded phenocrysts are interpreted to have crystallized in the main magma that the crystal formation in a mushy boundary layer body of the reservoir the types 2 and 3 ab rich cores were brought plays a dominant role in magmatic evolution in a magma to the mushy layer by convection the temporal and spatial variations reservoir however these studies were mostly on silicic of zoning patterns of plagioclase phenocrysts in basaltic lava flows magmas and there are significant differences in physical give useful information on the evolution of mafic magma chambers and chemical features between silicic and mafic magma chambers in this paper the magmatic evolution of an alkali basalt kutsugata lava from rishiri volcano northern japan is studied the kutsugata lava is divided into three lava flows on the basis of whole rock chemical

rapid climate transitions in a coupled ocean atmosphere model recent geochemical data1 2 have challenged the view that rapid climate fluctuations in the north atlantic at the end of the last glacial were caused by the thermohaline circulation of the ocean being switched on or off instead these data suggest that the circulation pattern must have switched between a warm deep mode and a cold shallow mode probably associated with different sites of deep convection3 here i present simulations with a three dimensional ocean model coupled to an idealized atmosphere which show this kind of transition the mechanism for the transition is a rearrangement of convection in the north atlantic triggered by a brief freshwater pulse this results in a drop in sea surface temperature in the north atlantic by up to 5 c within less than 10 years the rate of north atlantic deep water nadw forma tion is the same in the cold climate as in the warm climate but nadw sinks to intermediate depths only while antarctic bottom water pushes north to fill the entire abyssal atlantic

sidewall differentiation in an alkalic magma chamber evidence from syenite xenoliths in tuffs of the latera caldera italy feldspathoidal and quartz bearing syenite xenoliths in c 235 to 155 ka tuffs surrounding the latera caldera have textures and mineral assemblages that indicate an origin from the crystalline margins of a shallow magma chamber this lithic suite exhibits a diversity of plutonic fabrics unaltered glass bearing nodules with undeformed sanidine frameworks coexist with completely crystallized clasts many of which show evidence of subsolidus modification the syenites comprise eutectic mineral assemblages with high percentages of titanite apatite and melanite garnet as accessory minerals ubiquitous reaction textures in syenite accompany progressive changes in mineral assemblages and they show the decreasing influence of limestone contamination with distance from the contact of syenite and skarn wallrock diagnostic mineral assemblages include nepheline rich in calcite inclusions coexisting titanite and metamorphic perovskite zircon with baddeleyite inclusions fluorapatite mantled by a possible carbonate bearing apatite francolite melanite garnet intergrown with clinopyroxene and interstitial hauyne rich in pyrrhotite inclusions at latera pumice fragments in the same deposit can exhibit up to ten fold differences in vesicularity and crystal content from 50 vol phenocrysts these clasts in conjunction with glass bearing syenite and skarn xenoliths may represent a range of progressively crystallized magmas that were quenched at the instant of their eruptive entrainment the major element abundances of pumices and syenite reflect the fractionation of plagioclase and sanidine with lesser amounts of fassaitic diopside leucite biotite apatite and alkali amphibole trace element ratios e g rb sr nb ta zr hf lree hree on the other hand are highly variable for crystalline and pumiceous ejecta and some element variations e g li ta nb th cannot be entirely reconciled with simple crystal liquid fractionation the syenite clasts span a range of compositions from strongly fractionated assemblages rich in accessory minerals to compositions that more closely approximate quenched reservoir liquids these features reflect processes that range from pure fractional crystallization to in situ crystallization where fractionated liquid was trapped in the pores of sidewall cumulates along the chamber roof and walls

a trace element geochemical model for imperfect fractional crystallization associated with the development of crystal zoning abstract although many petrological studies of volcanic rocks have suggested that crystallization proceeds within magma bodies highly compatible trace elements do not display the marked variations and extreme depletions predicted to result from perfect fractional crystallization imperfect crystal liquid separation is a key process in explaining this paradox the presence of suspended crystals greatly affects variations in highly compatible elements and has been quantitatively modeled by assuming perfect equilibrium between the suspended crystals and the liquid equilibrium crystallization and imperfect separation ecis however volcanic rocks generally contain zoned phenocrysts that reflect the absence of solid state equilibration the present study develops a mass balance model for zoned crystallization and imperfect separation zcis the zcis process is more efficient than the conventional ecis process in generating depleted compatible elements these two end member models are able to explain the compositional range of igneous rocks that experienced imperfect fractional crystallization under natural conditions the predicted compositional regions in bivariate trace element diagrams successfully account for the sizes and shapes of the regions defined by whole rock and melt inclusion data from the bishop tuff ca usa

high frequency paleovariability in climate and co2 levels from vostok ice core records the high resolution of the vostok records provides a unique look at the causes of paleoclimatic variability during the last complete glacial cycle the records present strong evidence for the interaction between orbital forcing and internal physico chemical mechanisms of variability this interaction appears to account for the great wealth of spectral features found in the records

the 14c record in bristlecone pine wood of the past 8000 years based on the dendrochronology of the late c w ferguson when in 1950 willard libby and his coworkers obtained their first radiocarbon 14 c dates c w ferguson at the university of arizona tree ring laboratory was working on establishing a continuous tree ring series for the newly discovered bristlecone pine pinus aristata before his untimely death in 1986 he had extended the series nearly 8000 years into the past from the ferguson series i obtained for 14 c determinations wood samples grown at various times also two other laboratories obtained such samples for b c times in particular our measured 14 c values that deviated consistently from those calculated from tree rings and the deviations increased with age this general trend was observed by other laboratories but the presence of deviations from these trends of the so called wiggles was questioned by other workers to me these wiggles indicated the existence of a most interesting geophysical parameter valid for the whole terrestrial atmosphere fourier spectra obtained at my request by kruse in 1972 and by neftel demonstrated the consistency of the results and supported my contention that the secular variations of 14 c in atmospheric co 2 are related to variations of solar activity

zoning and exsolution in alkali feldspars from laacher see volcano western germany constraints on temperature history prior to eruption compositional zoning and exsolution patterns of alkali feldspars in carbonatite bearing cognate syenites from the 6 3 km3 d r e phonolitic laacher see tephra lst deposit in western germany 12 9 ka are reported these rocks represent the cooler outer portion and crystal rich products of a cooling magma reservoir at upper crustal levels major and trace element difference between cores and rims in sanidine crystals represent two generations of crystal growth separated by unmixing of a carbonate melt trace element differences measured by la icp ms are in accordance with silicate carbonate unmixing across the core rim boundary we extracted gray scale profiles from multiple accumulations of back scattered electron images gray scales directly represent k na ratios owing to low concentrations of ba and sr 30 ppm diffusion gradients are modeled to solve for temperature using known pre eruptive u th zircon ages 0 20 ky of each sample schmitt et al j petrol 51 1053 1085 2010 estimated temperatures range from 630 c to 670 c for the exsolution boundaries a diffusive homogenization model is constrained by the solvus temperature of 712 725 c and gives short time scales of only 15 50 days based on our results we present a model for the temperature time history of these rocks the model also constrains the thermal variation across the cooling crystal rich carapace of the magma reservoir over 20 ka and suggests a thermal reactivation of cumulates the cooling carapace and probably the entire system only a few years prior to the explosive eruption of the remaining molten core of the phonolitic magma reservoir

evidence for magma mixing within the laacher see magma chamber east eifel germany abstract the final pyroclastic products of the late quaternary phonolitic laacher see volcano east eifel w germany range from feldspar rich gray phonolite to dark olivine bearing rocks with variable amounts of feldspar and al augite megacrysts petrographically and chemically homogeneous clasts occur along with composite lapilli spanning the compositional range from phonolite mgo 0 9 to mafic hybrid rock mgo 7 0 for all major and trace elements both a basanitic and a phonolitic phenocryst paragenesis occur within individual clasts the phonolite derived phenocrysts are characterized by glass inclusions of evolved composition rare inverse zoning and strong resorption indicating disequilibrium with the mafic hybrid matrix basanitic magnesian clinopyroxene and olivine in contrast show skeletal normally zoned overgrowths indicative of post mixing crystallization in accord with petrographical and other chemical evidence mass balance calculations suggest mixing of an evolved laacher see phonolite containing variable amounts of mineral cumulates and a megacryst bearing basanite magma magma mixing occurred just prior to eruption hours of the lowermost magma layer of the laacher see magma chamber but did not trigger the volcanic activity

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

finite element analysis of multiphase immiscible flow through soils a finite element model is developed for multiphase flow through soil involving three immiscible fluids namely air water and a nonaqueous phase liquid napl a variational method is employed for the finite element formulation corresponding to the coupled differential equations governing flow in a three fluid phase porous medium system with constant air phase pressure constitutive relationships for fluid conductivities and saturations as functions of fluid pressures which are derived in a companion paper by j c parker et al this issue and which may be calibrated from two phase laboratory measurements are employed in the finite element program the solution procedure uses backward time integration with iteration by a modified picard method to handle the nonlinear properties laboratory experiments involving water displacement from soil columns by p cymene a benzene derivative hydrocarbon under constant pressure were simulated by the finite element program to validate the numerical model and formulation for constitutive properties transient water outflow predicted using independently measured saturation capillary head data agreed with observed outflow data within the limits of precision of the predictions as estimated by a first order taylor series approximation considering parameter uncertainty due to experimental reproducability and constitutive model accuracy two dimensional simulations are presented for a hypothetical field case involving introduction of napl near the soil surface due to leakage from an underground storage tank subsequent transport of napl in the variably saturated vadose and groundwater zones is analyzed

the role of residual melt migration in producing compositional diversity in a suite of granitic rocks abstract we present a quantitative model for in situ crystallization within a solidification zone or boundary layer based on the trace and major element compositions of plutonic igneous rocks and related geochemical data we developed the model to account for the characteristics of a suite of granitic rocks nearly uniform mineral compositions in rocks that range widely in bulk composition e g 58 76 wt sio 2 linear variation and correlation of all major and trace elements analyzed except ba large and apparently random variations in ba concentration these characteristics cannot be explained by any standard petrogenetic model involving fractionation mixing or restite unmixing but are successfully reproduced by our model of residual melt migration we do not attempt to model the entire crystallization history of a pluton but rather only that interval during which melt migration processes have recognizable geochemical effects for the granitic suite the chemical signature of residual melt migration resulted from the change in ba compatibility with the onset of orthoclase crystallization at a granite minimum our results demonstrate that plutonic rocks can develop large compositional variations comparable to those expected to result from extreme differentiation within a large magma body over short distances by melt migration under conditions of high permeability or slow crystallization rate within the solidification zone melt migration is probably a common process that could be overlooked in large plutons if sampling is sparse and if variations in some components that appear random are not considered our model equations yield estimates for parameters that describe the proportions of residual melt that crystallize within and migrate out of the solidification zone values of these parameters can be used to infer information about permeability and melt mobility within the solidification zone the model parameters derived for the granitic suite have a roughly concentric spatial pattern in the pluton suggesting that residual melt was trapped near the margins accumulated in the interior with a zone of enhanced melt mobility and possibly compositional convection in between our model may be of general usefulness because it requires no assumptions about magma chamber geometry or magma dynamics it is applicable to magmas of any composition and the equations could be formulated to include those variables best constrained by a particular suite of plutonic igneous rocks

assessment of the ore forming process of the gejiu tin district south china abstract the gejiu tin district of southern china is the largest tin polymetallic ore district in the world even though the mining operation has lasted more than 2000 years in this area the metallogenic mechanism of this gigantic tin mineralization is still controversial based on petrographic geochemical and zirconological information from this study we present a particular model of the magma evolution and tin mineralization for the gejiu tin district the ore forming processes involved both a batholithic biotite monzogranite bmg emplaced at 94 ma and a satellitic muscovite alkali feldspar granite mag emplaced at 72 ma the bmg and the mag were produced from a long lived magma chamber by two stages of magmatic activity during intracontinental orogeny in the youjiang block the hiatus between the two magmatic stages indicates that the deep seated magma chamber persisted during the dominant phase of the orogeny progressive fractional crystallization of the magma caused the extreme enrichment of incompatible elements which include ore forming components such as tin aqueous fluids and other volatiles in the residual magma when the regional tectonic environment evolved into the extensional regime at 72 ma the highly fractionated residual magma ascended and once emplaced it formed the highly evolved mag with a mean zircon crystallization age of 71 8 1 2 ma the mag is temporally and spatially associated with cassiterite bearing quartz vein cqv with a mean zircon crystallization age of 72 6 1 6 ma this metallogenic model of the bmg mag cqv association is generally applicable to other granite related metallic deposits in south china southeast asia and elsewhere australia bolivia brazil usa etc the recognition of this bmg mag cqv association in regional geological survey may facilitate the future exploration for this type of deposit

the muscovite granites parental rocks to the nanling range tungsten mineralization in south china abstract muscovite granites mgs in the nanling range south china occur as satellite intrusions within or surrounding batholitic biotite monzogranites bms the mgs are massive and fine grained with a porphyritic texture and contain quartz k feldspar and albite in nearly equal portions the accessory minerals in the mgs include alumina rich minerals e g mn and fe rich garnet andalusite topaz and tourmaline anatase rutile wolframite cassiterite xenotime chalcopyrite molybdenite and volatile rich minerals e g microlite topaz tourmaline fluorite and calcite compared with the bms the mgs are geochemically enriched in major elements of si k and na and incompatible trace elements of rb cs y u nb ta w sn pb bi li and be and depleted in major elements of fe mg ca ti and p and compatible trace elements of ba sr co ni cr cd v as well as zr and hf the chondrite normalized ree patterns of the mgs are flat with large negative eu anomalies the mineralogical and geochemical features of the mgs indicate that they crystallized from highly fractionated granitic magmas zircons separated from the mg samples which were collected from six different tungsten deposits show characters of hydrothermal origin according to their morphologies chemical compositions and inclusions in situ u pb dating of the zircons yields a weighted mean 206pb 238u age of 133 4 1 0 ma this age is similar to the mean age of the zircons from wolframite bearing quartz veins wqvs in the nanling range 133 7 1 3 ma reported from our previous study zircon hf isotopes also reveal that the mgs and the wqvs are homologous these mineralogical geochemical and zirconological features indicate that the mgs are the parental rocks of the tungsten deposits in the nanling range this study provides a new guidance for the exploration of magmatic hydrothermal tungsten deposits

constraints on the pre eruptive magmatic history of the quaternary laacher see volcano germany ba zonation patterns in sanidine phenocrysts from mafic and intermediate phonolite and crystal rich cumulates from the laacher see volcano 12 9 ka in western germany document diffusion times suggestive of periodic recharge events throughout the magma reservoir s entire lifespan of 24 ky phenocrysts analysed from samples that formed late at the base of the compositionally zoned magma reservoir by mixing and mingling between a resident phonolite magma and recharging basanite show resorption and thin 2 10 m late stage ba rich overgrowth short diffusion profiles across these boundaries give diffusion times of 1 5 3 years at most which are interpreted to be the maximum duration between the most recent recharge by the basanite and eruption the lack of such late overgrowth in samples from other parts of the phonolite reservoir suggests that effect of this mixing and mingling was limited to the crystal rich base sanidines in the cumulates by contrast are generally devoid of zoned crystals only rare cumulate crystals with resorbed outer boundaries and very thin overgrowths a few microns with very sharp compositional changes imply the remobilization of cumulates only months before eruption based on the diffusion timescales and storage temperatures obtained in a previous study we present a genetic model for the conditions and timing of storage and re activation of the magma system prior to the eruption of laacher see which is the largest volcanic event in central europe since the last glaciation

role of magma mixing in the petrogenesis of tephra erupted during the 1990 98 explosive activity of nevado sabancaya southern peru the nevado sabancaya in southern peru has exhibited a persistent eruptive activity over eight years following a violent eruption in may june 1990 the explosive activity consisted of alternated vulcanian and phreatomagmatic events followed by declining phreatic activity since late 1997 the mean production rate of magma has remained low 106 107 m3 per year

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

abrupt climate events 500 000 to 340 000 years ago evidence from subpolar north atlantic sediments subpolar north atlantic proxy records document millennial scale climate variations 500 000 to 340 000 years ago the cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle these findings suggest that such climate variations are inherent to the late pleistocene regardless of glacial state sea surface temperature during the warm peak of marine isotope stage 11 mis 11 varied by 0 5 to 1 c less than the 4 to 4 5 c estimated during times of ice growth and the 3 c estimated for glacial maxima coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature

millennial scale climate instability during the early pleistocene epoch climate proxy records of the past 100 000 years show that the earth s climate has varied significantly and continuously on timescales as short as a few thousand years 1 7 similar variability has also recently been observed for the interval 340 500 thousand years ago8 these dramatic climate shifts expressed most strongly in the north atlantic region may be linked to and possibly amplified by alterations in the mode of ocean thermohaline circulation4 5 6 7 8 9 here we use sediment records of past iceberg discharge and deep water chemistry to show that such millennial scale oscillations in climate occurred over one million years ago this was a time of significantly different climate boundary conditions not only was the early pleistocene epoch generally warmer but global climate variations were governed largely by changes in earth s orbital obliguity our results suggest that such millennial scale climate instability may be a pervasive and long term characteristic of earth s climate rather than just a feature of the strong glacial interglacial cycles of the past 800 000 years

stable isotope relations in an open magma system laacher see eifel frg 18o 16o and d h ratios have been measured for matrix glasses and phenocrysts from the zoned phonolitic laacher see tephra sequence 11000 y b p east eifel volcanic field frg to study open system behaviour of the associated magma system mineral and glass 18o values appear to be largely undisturbed by low temperature secondary alteration record isotopic equilibrium and confirm previous conclusions based on radiogenic isotope evidence of early small scale crustal assimilation during differentiation of parental magmas in a crustal magma chamber one sanidine glass pair possibly documents the late stage influx of meteoric fluids into the topmost magma layer prior to eruption a sealing carapace of chilled magma which itself was strongly contaminated prevented large scale fluid exchange up to the point prior to eruption when this carapace was fractured and meteoric water gained access to parts of the magma system d h measurements of various glass types glass inclusions dense and pumiceous glass and amphiboles gave conflicting results suggesting a combination of degassing volatile exchange with country rocks and hydration stable isotope ratios for primitive parental magmas 18o 5 5 to 7 0 and mantle megacrysts 18o 5 5 to 6 0 d 21 to 38 for amphiboles and phlogopite resp suggest a rather variable fluid composition for the sub eifel mantle

laboratory and numerical investigations of immiscible multiphase flow in soil abstract immiscible multiphase flow in porous media is investigated by laboratory experiments and numerical simulations the hydraulic parameters used in mathematical models for multiphase flow are determined experimentally and the interrelations between the individual parameters are analysed the experimental data support the applicability of analytical closed form expressions for the constitutive relations and a scaling procedure is verified in which the interfacial tensions are used to derive scaling factors these simplifications in the parameter requirements are very valuable from an engineering point of view a two dimensional plexiglass flume is used for studying the flow of lighter than water non aqueous phase liquids lnapl in sandy porous media the migration of the lnapl is observed both in the unsaturated zone and in the saturated zone at the bottom of the flume a dual gamma attenuation system is used for measuring the phase saturations of organic fluid water and air simultaneously without disturbing the flow this permits a two dimensional quantitative determination of the lnapl plume in contrast to many earlier qualitative studies a black oil reservoir model is used to simulate immiscible multiphase flow by using the parameter estimation methods presented for establishing the constitutive relations the model is applied to the simulation of the laboratory experiments the experimental and numerical results compare reasonably well thus supporting the adopted model formulation

magmatic inclusions in the holocene rhyolites of newberry volcano central oregon the 1350 years b p big obsidian flow bof at newberry volcano in central oregon contains a wide variety of mafic magmatic inclusions although little grain size variation is observed within single inclusions within the suite textures vary continuously from fine grained quench to coarse grained cumulate the bof inclusion suite therefore defies conventional genetic classifications detailed petrographic and geochemical observations require a new model for inclusion formation only a few of the finer grained inclusions have margins suggestive of liquid liquid interaction interstitial glass content 20 vol and composition high silica rhyolite are approximately constant throughout the suite mineral compositional zoning is greater in the coarse grained than fine grained inclusions whole inclusion compositions vary significantly but do not correlate well with textural diversity we interpret the bof inclusion suite to be a heterogeneous sample set of whole inclusions and parts of disaggregated inclusions the compositional variability of the suite can be explained by a combination of preentrapment hybridization and postentrapment interstitial liquid loss gain processes preentrapment hybridization involved mixing of basaltic andesite magma similar to holocene flank flows and up to 30 rhyolitic liquid the bof inclusions may demonstrate the recent existence of mafic magma in the newberry system inclusion features characteristic of small t are consistent with the crystal free nature of the bof suggesting that the rhyolite may have been superheated if true a crystal fractionation origin for the bof rhyolite is unlikely the disaggregation of grain size and compositionally zoned inclusions which produced the observed textural diversity in the bof suite compounds problems of interpreting mafic inclusions in silicic volcanic rocks and more so in plutonic equivalents