timescales of mingling in shallow magmatic reservoirs arrival of magma from depth into shallow reservoirs has been documented as one of the possible processes leading to eruption magma intruding and rising to the surface interacts with the already emplaced degassed magmas residing at shallower depths leaving chemical signatures in the erupted products we performed two dimensional numerical simulations of the arrival of gas rich magmas into shallow reservoirs we solve the fluid dynamics for the two interacting magmas evaluating the space time evolution of the physical properties of the mixture convection and mingling develop quickly into the chamber and feeding conduit dyke leading on longer timescales to a density stratification with the lighter gas richer magma mixed with different proportions of the resident magma rising to the top of the chamber due to buoyancy over timescales of hours the magmas in the reservoir appear to have mingled throughout and convective patterns become harder to identify our simulations have been performed changing the geometry of the shallow reservoir and the gas content of the initial end member magmas horizontally elongated magma chambers as well as higher density contrasts between the two magmas cause faster ascent velocities and also increase the mixing efficiency

a new method to quantify the real supply of mafic components to a hybrid andesite the eruption of soufriere hills volcano montserrat has been ongoing since 1995 the volcano is erupting a crystal rich hornblende plagioclase andesite with ubiquitous mafic inclusions indicating mixing with mafic magma this mafic magma is thought to be the driving force of the eruption supplying heat and volatiles to the andesite resident in the magma chamber as well as producing macroscopic mafic inclusions the magma mixing process involves incorporation of phenocrysts from the andesite into the mafic magma these inherited phenocrysts show clear disequilibrium textures e g sieved plagioclase rims and thermal breakdown rims on hornblende approximately 25 of all phenocrysts in the andesite show these textures indicating very extensive mass transfer between the two magma types fragments of mafic inclusions down to sub mm scale are found in the andesite together with mafic crystal clusters which are commonly found adhered to the rims of phenocrysts with disequilibrium features mineral chemistry also points to the transfer of microlites or microphenocrysts initially formed in the mafic inclusions into the andesite this combined evidence suggests that some of the mafic inclusions disaggregate during mingling and or ascent possibly due to shearing and raises the question what proportion of the andesite groundmass actually originated in the mafic inclusions and thus what is the true amount of mafic magma in the magmatic system we present a new method for quantifying the relative proportions of groundmass plagioclase derived from mafic and andesitic magma based on analysis of back scattered electron images of the groundmass preliminary results indicate that approximately 16 of all groundmass plagioclase belongs genetically to the mafic inclusions together with the crystal clusters disequilibrium phenocryst textures and mm scale inclusions there is a cryptic mafic component in the andesite of approximately 6 by volume this is significant compared with the proportion of macroscopic mafic inclusions typically 1 5 the new method has the potential to allow tracking of the mafic fraction through time and thus to yield further insights into magma hybridisation processes

zircons reveal magma fluxes in the earth s crust magma fluxes regulate the planetary thermal budget the growth of continents and the frequency and magnitude of volcanic eruptions and play a part in the genesis and size of magmatic ore deposits however because a large fraction of the magma produced on the earth does not erupt at the surface determinations of magma fluxes are rare and this compromises our ability to establish a link between global heat transfer and large scale geological processes here we show that age distributions of zircons a mineral often present in crustal magmatic rocks in combination with thermal modelling provide an accurate means of retrieving magma fluxes the characteristics of zircon age populations vary significantly and systematically as a function of the flux and total volume of magma accumulated in the earth s crust our approach produces results that are consistent with independent determinations of magma fluxes and volumes of magmatic systems analysis of existing age population data sets using our method suggests that porphyry type deposits plutons and large eruptions each require magma input over different timescales at different characteristic average fluxes we anticipate that more extensive and complete magma flux data sets will serve to clarify the control that the global heat flux exerts on the frequency of geological events such as volcanic eruptions and to determine the main factors controlling the distribution of resources on our planet

zircon trace element chemistry at sub micrometer resolution for tarawera volcano new zealand and implications for rhyolite magma evolution zoned crystals can be important recorders of magmatic processes in space and time however in most situations the temporal dimension is difficult to quantify here we have employed secondary ion mass spectrometry depth profiling to excavate parallel pits into non polished crystal faces of zircon to obtain 5 m resolution u th disequilibrium ages one pit that can be correlated with trace element zoning at sub m resolution derived from a second pit data from 17 crystals representing each of the four rhyolite eruptions of tarawera volcano an intra caldera edifice within the okataina volcanic centre reveal diverse zircon growth conditions over time most crystals display rimward depletions in zr hf and ti broadly consistent with cooling and crystallization however a significant fraction of crystals lacks these patterns and displays rimward trace element variations consistent with isothermal or prograde crystallization oscillatory zonation patterns in y th and u are superimposed on the zr hf and ti trends despite the limited number of crystals analyzed in this way the striking lack of ubiquitous trace element zoning patterns in crystals from the same hand sample implies that fractional crystallization upon cooling was punctuated by magma recharge and crystal mixing affecting different parts of the magma reservoir by combining data from all crystals a systematic change to more heterogeneous trace element abundances is revealed by zircon crystal domains 100 ka prior to caldera formation and is best explained by the post caldera system consisting of small isolated melt pockets that evolved independently an important conclusion is that the zircon cargo in volcanic rocks reflects thermally and compositionally divergent processes that act near simultaneously in a magma storage region and not exclusively the conditions in the eruptible magma

lake ohrid albania provides an exceptional multi proxy record of environmental changes during the last glacial interglacial cycle multi proxy analyses on core jo2004 1 recovered from lake ohrid 40 55 000 n 20 40 297e 705 m a s l provide the first environmental and climate reconstruction in a mountainous area in southern europe over the last 140 000 years the response of both lacustrine and terrestrial environments to climate change has been amplified by the peculiar geomorphological and hydrological setting with a steep altitudinal gradient in the catchment and a karstic system feeding the lake the karstic system was active during interglacials leading to high carbonate production in the lake and blocked during glacials as a result of extremely cold climate conditions with permafrost in the mountains at the riss eemian transition termination 2 the increase in lacustrine productivity predated forest expansion by about 10 000 years in contrast the late glacial holocene transition termination 1 was characterized by the dramatic impact of the younger dryas which initially prevented interglacial carbonate production and delayed its maximum until the mid holocene in contrast forest expansion was progressive starting as early as ca 38 000 ago the proximity of high mountains and the probable moderating lake effect on local climate conditions promoted forest expansion and contributed to make the surroundings of lake ohrid favourable to forest refugia during the last glacial usually steppic period our study of sedimentology mineralogy geochemistry magnetics palynology and isotopes illustrates the non linear response of terrestrial and lacustrine ecosystems to similar climate events and demonstrates the potential of lake ohrid as an excellent paleoclimatic archive during the quaternary

internal structure and emplacement of the papoose flat pluton an integrated structural petrographic and magnetic susceptibility study the papoose flat pluton of eastern california is commonly cited in the geologic literature as a classic example of a forcibly emplaced pluton although the relative importance attributed to magmatic versus tectonic processes in controlling the structural evolution of the pluton has been controversial reexamination of this late cretaceous 83 ma pluton using a combination of new structural petrographic microstructural and anisotropy of magnetic susceptibility ams data on the pluton wall rock system has shown that the pluton is an inclined and internally zoned tabular structure assembled by forcible intrusion of successive pulses of magma at a crustal depth of 12 15 km initial pluton formation involved magma ascent in a vertical west northwest striking feeder dike which was arrested at a stratigraphically controlled mechanical discontinuity in the overlying cambrian metasedimentary rocks leading to formation of a southwest dipping sill subsequent sill inflation accompanied by horizontal infilling from the feeder dike at the base of the sill resulted in deformation and vertical translation of previously emplaced magma pulses and local raising of the sill roof facilitated by thermal weakening as the wall rock temperatures progressively rose during emplacement of successive magma pulses cooling from the roof of the pluton downward resulted in cessation of vertical inflation on the west side of the pluton and promoted lateral expansion toward the northeast and floor depression below the eastern part of the pluton we have been unable to document any regional scale structures e g of equivalence to similar age synplutonic strike slip shear zones in the sierra nevada batholith to the west that may have controlled emplacement of the papoose flat pluton however this fact does not preclude the likelihood that the country rocks were subjected to a regional deviatoric stress field at this time indeed tectonic overpressuring was probably essential for producing sufficiently high magma pressures for laccolith formation at this midcrustal level simple thermal modeling using microstructural and thermobarometric data indicates that the total duration of emplacement of the pluton did not exceed 30 000 yr this rapid emplacement rate may explain why the pluton appears to be anorogenic even though it was emplaced during a period of regional scale deformation

early miocene kirka phrigian caldera western turkey eskisehir province preliminary volcanology age and geochemistry data abstract large rhyolitic ignimbrite occurrences are closely connected to the early miocene initiation of extension in the central western anatolia crossing the tavsanli afyon zones field and laboratory data performed at the apex of the eskisehir afyon isparta volcanic area allowed recognition of newly identified caldera structure named here kirka phrigian caldera transtensive distensive tectonic stresses since 25 ma ago resulted in the nnw sse elongation of the magma chamber and influenced the roughly elliptical shape of the subsided block caldera floor the caldera which is roughly oval 24 km 15 km in shape formed during a series of collapse events starting at 19 ma by the generation of a huge volume of extra and intracaldera ignimbrites intracaldera post collapse sedimentation and further volcanism at the northern edge at 18 6 ma were controlled through subsidence related faults with generation of a series of volcanic structures domes and lavas showing a large compositional range enriched mantle components within the subcontinental lithospheric mantle began to melt via decompression melting during the initiation of extension the heat resulting from the fractionation of ascending mantle melts produced the silicic compositions in large mushy crustal reservoirs interaction of these melts with fertile crustal rocks further caused crustal anataxis and consequently two different compositions rhyolite 1 and rhyolite 2 the eruptions of kirka phrigian caldera related ignimbrites were probably triggered by basaltic intrusion rock volumes and geochemical evidence suggest that silicic volcanic rocks come from a long lived complex magma chamber system after caldera generation there was a northern shift to small volume extra and intra caldera episodic rhyolitic basaltic trachy andesitic trachytic and lamproitic volcanism the latter being the youngest 16 2 ma indicating a more primitive magma input which originated in an enriched mantle lithosphere the rock succession provides a direct picture of the state of the magmatic system at the time of eruptions that generated caldera and post caldera structures and offers an excellent example of silicic magma generation and associated potassic and ultrapotassic intermediate mafic rocks in a post collisional extensional setting

the role of magma mixing in triggering the current eruption at the soufriere hills volcano montserrat west indies the andesite lava currently erupting at the soufriere hills volcano montserrat contains ubiquitous mafic inclusions which show evidence of having been molten when incorporated into the andesite the andesite phenocrysts have a range of textures and zonation patterns which suggest that non uniform reheating of the magma occurred shortly before the current eruption reheating resulted in remobilisation of the resident magma and may have induced eruption

quantum magmatism magmatic compositional gaps generated by melt crystal dynamics compositional gaps are common in volcanic series worldwide the pervasive generation of compositional gaps influences the mechanical and thermal properties of the crust and holds clues on how our planet differentiates we have explored potential mechanisms to generate these gaps using numerical simulations coupling crystallization kinetics and multiphase fluid dynamics of magma reservoirs we show that gaps are inherent to crystal fractionation for all compositions as crystal liquid separation takes place most efficiently within a crystallinity window of 50 70 vol crystals the probability of melt extraction from a crystal residue in a cooling magma chamber is highest in this crystallinity window due to 1 enhanced melt segregation in the absence of chamber wide convection 2 buffering by latent heat of crystallization and 3 diminished chamber wall thermal gradients this mechanical control of igneous distillation is likely to have played a dominant role in the formation of the compositionally layered earth9s crust by allowing multiple and overlapping intrusive episodes of relatively discrete or quantized composition that become more silicic upward

late holocene high frequency east asia winter monsoon variability inferred from the environmentally sensitive grain size component in the distal shelf mud area east china sea the b2 b2g and i4 sediment cores recovered from the centre of the distal mud area of the east china sea ecs were analysed for grain size distribution proxies for environmentally sensitive grai

effects of chaotic advection on the timescales of cooling and crystallization of magma bodies at mid crustal levels we numerically define the thermochemical evolution of a subduction related crystal bearing magmatic mass at mid crustal levels 0 7 gpa 20 25 km two main dynamic mechanisms are considered 1 a pure buoyancy driven system where the convective flow is induced by density changes during magma cooling 2 a buoyancy driven convective system governed by chaotic advection the non newtonian rheology of natural magmas is taken into account linking the herschel bulkley formulation with the results of fractional crystallization experiments of magmas with the same composition and at the same conditions of temperature and pressure of the studied system the latent heat of crystallization is also considered in order to address the thermal release in the system induced by the crystallization results indicate that the development of chaotic advection generates a complex thermochemical evolution of the system speeding up the crystallization process and the timing required to reach the jamming condition relative to the pure buoyancy driven convective system nearly 2 times faster our results have important implications for both the rheological history of the magmatic body and the refilling of shallower magmatic systems in particular 1 a time dependent composition ranging from basalt to andesite can be extracted from an initial basaltic magmatic batch 2 at the attainment of the maximum packing fraction i e just before the jamming condition homogeneous andesitic melts can be potentially extracted from the system and 3 the development of chaotic advection within the system allows for the extraction of andesitic melt in shorter times compared to a buoyancy dominated system

a continuum model of multi phase reactive transport in igneous systems multiphase reactive transport processes are ubiquitous in igneous systems a challenging aspect of modelling igneous phenomena is that they range from solid dominated porous to liquid dominated suspension flows and therefore entail a wide spectrum of rheological conditions flow speeds and length scales most previous models have been restricted to the two phase limits of porous melt transport in deforming partially molten rock and crystal settling in convecting magma bodies the goal of this paper is to develop a framework that can capture igneous system from source to surface at all phase proportions including not only rock and melt but also an exsolved volatile phase here we derive an n phase reactive transport model building on the concepts of mixture theory along with principles of rational thermodynamics and procedures of non equilibrium thermodynamics our model operates at the macroscopic system scale and requires constitutive relations for fluxes within and transfers between phases which are the processes that together give rise to reactive transport phenomena we introduce a phase and process wise symmetrical formulation for fluxes and transfers of entropy mass momentum and volume and propose phenomenological coefficient closures that determine how fluxes and transfers respond to mechanical and thermodynamic forces finally we demonstrate that the known limits of two phase porous and suspension flow emerge as special cases of our general model and discuss some ramifications for modelling pertinent two and three phase flow problems in igneous systems

continuous mixing of crystal mush and replenished magma in the ongoing unzen eruption zoning profiles of magnetite phenocrysts in the successively effused dacite of the ongoing unzen eruption from 1991 wereanalyzed to estimate the time scale of magma mixing the dacite was formed by mixing of relatively high and low temperature t end member magmas the magnetite phenocrysts derived from the low t magma are reversely zoned by the mixing with high t magma a diffusion calculation for reequilibration of the reverse zonings gives the time interval from magma mixing to quenching for the mixed dacite erupted from may 1991 to may 1993 the typical diffusion time was estimated to be a few months regardless of the effused sequence for 2 yr this indicates that the mixing was continuous during the effusion the invariability of the other mixing signatures such as the thickness of reaction rims around biotite phenocrysts also supports the continuous mixing model low t end member magma is estimated by mass balance calculation to be a crystal rich mush of dacitic composition these observations lead to a model wherein the highly crystallized remnant magma of the preceding activity has been mixed with the newly injected hot magma of similar bulk composition just prior to the effusion the proposed mechanism implies that this type of magma mixing is an inevitable process in periodically erupting polygenetic volcanoes

magma sponge hypothesis and stratovolcanoes case for a compressible reservoir and quasi steady deep influx at soufriere hills volcano montserrat 1 we use well documented time histories of episodic gps surface deformation and efflux of compressible magma to resolve apparent magma budget anomalies at soufriere hills volcano shv on montserrat wi we focus on data from 2003 to 2007 for an inflation succeeded by an episode of eruption plus deflation we examine mogi type and vertical prolate ellipsoidal chamber geometries to accommodate both mineralogical constraints indicating a relatively shallow pre eruption storage and geodetic constraints inferring a deeper mean pressure source an exsolved phase involving several gas species greatly increases andesite magma compressibility to depths 10 km i e for water content 4 wt crystallinity 40 and this property supports the concept that much of the magma transferred into or out of the crustal reservoir could be accommodated by compression or decompression of stored reservoir magma i e the magma sponge our results suggest quasi steady deep mainly mafic magma influx of the order of 2 m3s 1 and we conclude that magma released in eruptive episodes is approximately balanced by cumulative deep influx during the eruptive episode and the preceding inflation our magma sponge model predicts that between 2003 and 2007 there was no evident depletion of magma reservoir volume at shv which comprises tens of km3 with radial dimensions of order 1 2 km in turn implying a long lived eruption

diatom response to the last glacial interglacial transition in the ioannina basin northwest greece implications for mediterranean palaeoclimate reconstruction uncertainty as to the pattern of lateglacial and early holocene climate change in the western balkans and greece has persisted despite extensive investigation of the ioannina i 284 lake sediment sequence northwest greece here we present a new diatom record from i 284 for this time period after dominance by eurytopic small fragilariales the lateglacial interstadial ca 14 9 12 7 cal kyr bp is marked clearly by a relative increase in planktonic cyclotella ocellata a return to small fragilariales from ca 12 7 to 11 6 cal kyr bp approximately coincides with the younger dryas chronozone it is followed by a major transition to dominance by cyclotella spp at the pleistocene holocene boundary we interpret these shifts as a response to both lake level and productivity change induced by shifts in effective moisture and temperature demonstrating that the diatom record provides the first strong evidence for a younger dryas event in northwest greece and for both warming and wetting during the lateglacial interstadial and early holocene we also present clear evidence for an abrupt phase of catchment instability during the early holocene in this case we must await the results of further research to test whether it was driven by climatic or tectonic forcing

multi approach back analysis of a roof bed collapse in a mining room excavated in stratified rock roof bed deformation mechanics is a complex topic in mining practice there are a number of empirical analytical and numerical techniques that can be used to analyze and design underground excavations in stratified rock masses each has particular drawbacks however so the use of just one approach in order to obtain consistent and economic designs is not practical to deepen understanding of this topic it is useful to study real failure in mines in this paper we describe how a roof bed failure in an underground mine excavated in a stratified rock mass was back analyzed using different approaches namely the empirical stability graph method the analytical voussoir techniques and the numerical discrete element method the study enabled us to better understand the conditions of failure and to define the most significant parameters affecting the failure it has also been shown how relaxation or loss of confinement stress can play an important role in roof bed deformation

phase equilibrium geobarometers for silicic rocks based on rhyolite melts part 1 principles procedures and evaluation of the method constraining the pressure of crystallization of magmas is an important but elusive task in this work we present a method to derive crystallization pressures for rocks that preserve glass compositions either glass inclusions or matrix glass representative of equilibration between melt quartz and 1 or 2 feldspars the method relies on the well known shift of the quartz feldspar saturation surface toward higher normative quartz melt compositions with decreasing pressure the critical realization for development of the method is the fact that melt quartz and feldspars need to be in equilibrium at the liquidus for the melt composition the method thus consists of calculating the saturation surfaces for quartz and feldspars using rhyolite melts over a range of pressures and searching for the pressure at which the expected assemblage quartz 1 feldspar or quartz 2 feldspars is found at the liquidus we evaluate errors resulting from uncertainties in glass composition using a series of monte carlo simulations for a quartz hosted glass inclusion composition from the bishop tuff which reveal errors on the order of 20 45 mpa for the quartz 2 feldspars constraint and on the order of 25 100 mpa for the quartz 1 feldspar constraint we suggest actual errors are closer to the lower bounds of these ranges we investigate the effect of fluid saturation in two ways 1 by applying our procedure over a range of water contents for three glass compositions we show that the effect of fluid saturation is more important at higher pressures 300 mpa than at lower pressures 100 mpa but reasonable pressure estimates can be derived irrespective of fluid saturation for geologically relevant h2o concentrations 3 wt and 2 by performing the same type of pressure determinations with a preliminary version of rhyolite melts that includes a h2o co2 mixed fluid phase we use a range of h2o and co2 concentrations for two compositions characteristic of early erupted and late erupted bishop tuff glass inclusions and demonstrate that calculated pressures are largely independent of co2 concentration for co2 1 000 ppm at least for relatively high h2o contents as expected in most natural magmas such that co2 concentration can be effectively neglected for application of our method finally we demonstrate that pressures calculated using the rhyolite melts geobarometer compare well with those resulting from h2o co2 glass inclusion barometry and al in hornblende barometry for an array of natural systems for which data have been compiled from the literature the agreement is best for quartz hosted glass inclusions while matrix glass yields systematically lower rhyolite melts pressures suggestive of melt evolution during eruptive decompression

rates of magma differentiation and emplacement in a ballooning pluton recorded by u pb tims tea adamello batholith italy abstract geochemical structural field and geochronological data have been used to arrive at very different models for the construction of upper crustal batholiths models for pulsed intrusion of small magma batches over long timescales 1 ma versus transfer of larger magma bodies on shorter timescales predict a different thermal metamorphic and rheological state of the crust highlighting the importance of robust time constraints this study focuses on a well characterized upper crustal intrusion the 15 km2 lago della vacca complex lvc adamello batholith n italy previous studies used structural and petrologic data to argue that the lvc was emplaced through pulsed magma injection and in situ expansion or ballooning of a short lived 105 yr magma chamber we test this model using a dense sampling strategy and high precision id tims u pb geochronology of zircon and titanite combined with hafnium isotope and trace element analyses of the same volume of dated mineral u pb tims tea these data show that the marginal mafic pulses of magma crystallized zircon with primitive hf isotopes and negligible eu anomalies during fractional crystallization and ascent through the crust on 10 30 ka timescales subsequent more felsic pulses yield individual zircon dates spanning as much as 200 ka within single handsamples and restrict the total construction time of the lvc to

rapid priming accumulation and recharge of magma driving recent eruptions at a hyperactive caldera volcano a major challenge in volcanology is determining the factors that control the frequency and magnitude of eruptions at hazardous caldera volcanoes understanding the critical sequence of events that may lead to future eruptions is vital for volcanic monitoring and risk assessment here we use magma chemistry and mineral diffusion modeling to interpret the magmatic processes and time scales involved in the youngest three eruptions 2 15 1 7 ka from taupo volcano new zealand which peaked with the voluminous a d 232 eruption of the rhyolites erupted since ca 12 ka the 2 75 ka rhyolites that were tapped from the same magma reservoir orthopyroxene fe mg diffusion time scales indicate that the onset of rapid heating and priming of the host silicic mush occurred 120 yr prior to the 2 15 ka eruptions with subsequent melt accumulation occurring in only decades elevated mafic magma supply to the silicic mush pile rapid melt accumulation and high differential tectonic stress built up and culminated in the 105 km3 a d 232 eruption one of the largest and most violent holocene eruptions globally these youngest eruptions demonstrate how taupo s magmatic system can rapidly change behavior to generate large eruptible melt bodies on time scales of direct relevance to humans and monitoring initiatives

insights into the mechanisms and timescales of pluton assembly from deformation patterns of mafic enclaves 1 we propose a novel method to constrain both timescales and assembly styles of intrusive bodies using the strain recorded by mafic enclaves a common component of granitic rocks petrology thermal modeling and magma rheology are combined to investigate the evolution of strain recorded by enclaves during the piecemeal assembly of a pluton growing at various rates of magma input the different compositions and hence phase relations of host magma and enclaves limits homogeneous deformation of these two materials to restricted temperature ranges which we term windows of mutual deformability outside these windows only the less viscous host granite records any appreciable deformation and enclaves are mainly transported as rigid objects the temporal and spatial development of the windows of mutual deformability reflects the emplacement rate of magmas into the pluton consequently the radial distribution of strain recorded by enclaves can provide a picture of the thermal and rheological evolution of a magmatic body during its construction our approach is applied to deformation patterns of mafic enclaves in the lago della vacca complex lvc of the adamello massif italy to estimate the timescales of pluton emplacement our calculations suggest total emplacement timescales of the order 50 to 150 ky in excellent agreement with recent high precision radiometric dating of zircons from the lvc

the diatom stratigraphy and palaeoecology of lake ohrid yugoslavia abstract an 8 85 m core no 9 was taken from lake ohrid yugoslavia in august 1973 at a depth of 210 m approximately 6 km offshore of gorcia yugoslavia the core was sampled at 10 cm intervals and analyzed for moisture organic and caco3 content and diatoms there is a slight but steady decrease of moisture with depth probably due to sediment compaction the organic content showed little variation throughout the core x 2 73 0 39 of total weight the caco3 content from 885 110 cm depth also showed little change x 2 32 0 55 of total weight but increased in the top meter of the core 100 0 cm x 11 03 8 86 of total weight throughout the core there is an inverse relationship between organic and caco3 content particularly in the top meter extrapolation to the bottom of the core using linear regression based on 14c dating yields a date of ca 30 000 years b p results indicate that lake ohrid has remained an oligotrophic lake throughout the period represented by core 9 diatom analysis shows one persistent group of diatoms throughout the core this group consists of cyclotella fottii c hustedtii and c hustedtii var 1 and is referred to as the cyclotella complex between 885 650 cm ca 30 000 20 000 yr b p there is a sharp increase in numbers and a slight increase in diversity of species this may correspond with the beginning of the warmer more humid middle pleniglacial between 650 100 cm ca 20 000 10 000 yr b p the cyclotella complex appears usually alone in small number there are a few other scattered species in this section mainly opephora martyi and fragilaria pinnata this section of the core probably corresponds with the cold upper pleniglacial of the wurm weichselian between 100 0 cm ca 10 000 0 yr b p there is the largest increase in number and diversity of species particularly above 60 cm the cyclotella complex c ocellata cyclotella sp 1 stephanodiscus astraea var intermedia fo 11 and stephanodiscus sp 1 are dominant this is the only section of the core in which stephanodiscus species occur and probably corresponds with the holocene

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

on the mechanical effects of poroelastic crystal mush in classical magma chamber models author posting american geophysical union 2018 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research solid earth 123 11 2018 9376 9406 doi 10 1029 2018jb015985

short eruption window revealed by absolute crystal growth rates in a granitic magma giant volcanic eruptions occur when large volumes of magma accumulate in crustal reservoirs and do not cool and crystallize to form a solid pluton of rock within the crust geochronological dating of a pluton from elba italy shows that the magma solidified in the crust within just 10 40 thousand years of being injected into the crust implying that the time window for an eruption was short

zircon petrochronology and 40ar 39ar thermochronology of the adamello intrusive suite n italy monitoring the growth and decay of an incrementally assembled magmatic system the adamello intrusive suite is a composite batholith in northern italy with an estimated 2000 km3 volume assembled incrementally over a time span of 10 to 12 million years the history of crysta

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

p and s velocity structure of the yellowstone volcanic field from local earthquake and controlled source tomography the three dimensional p and s velocity from vp vs ratios distribution and improved hypocenters for the yellowstone volcanic field have been determined from inversion of first arrival times from 7942 local earthquakes and 16 controlled source explosions the p velocity model has an rms residual of 0 09 s whereas the vp vs ratio model calculated from 511 earthquakes has an rms residual of 0 29 s high p and s velocities outside the yellowstone caldera represent thermally undisturbed basement and sedimentary rocks a caldera wide 15 decrease from regional p velocities at depths of 6 to 12 km is coincident with a 60 mgal gravity anomaly and is interpreted as a hot subsolidus granitic batholith with a quasi plastic rheology localized 30 reductions from regional seismic velocities and higher vp vs ratios 8 km beneath yellowstone s resurgent domes are interpreted as partial melts and vestigial magma systems associated with youthful less than 2 ma silicic volcanism additional low seismic velocities and vp vs ratios and a 20 mgal gravity low less than 4 km beneath the northeast caldera rim are interpreted as a hydrothermal fracture zone thermally driven by underlying partial melt hypocenters relocated with the three dimensional p velocity model show subparallel alignment with nw se trending postcaldera volcanic vents and normal faults northwest of the caldera focal depths of relocated earthquakes decrease from more than 11 km outside the caldera to less than 6 km within the caldera reflecting thinning and heating of the seismogenic crust

correlation of rock mass classification parameters obtained from borecore and in situ observations abstract the paper describes an investigation carried out to establish correlation trends between rock mass classification parameters derived from borecore and in situ observations the purpose of this study was to determine the reliability of classifying rock masses for engineering purposes from borecore data alone rock mass classification parameters were obtained from three tunnels excavated in widely differing geological environments two in johannesburg and one in the cape province of south africa these parameters from the borecore and in situ measurements were used separately to classify the rock masses encountered both the geomechanics and q classification systems were employed in determining the quality of rock masses the paper describes the geological environments encountered the methods of observation used and the results obtained from the comparison of the in situ and borecore classification results conclusions are reached and discussed some comments are also offered regarding the applicability of the two classification systems under the conditions specified

fractional crystallization of primitive hydrous arc magmas an experimental study at 0 7 gpa differentiation of mantle derived hydrous basaltic magmas is a fundamental process to produce evolved intermediate to sio2 rich magmas that form the bulk of the middle to shallow continental and island arc crust this study reports the results of fractional crystallization experiments conducted in a piston cylinder apparatus at 0 7 gpa for hydrous calc alkaline to arc tholeiitic magmas fractional crystallization was approached by synthesis of starting materials representing the liquid composition of the previous higher temperature experiment temperatures ranged from near liquidus at 1 170 c to near solidus conditions at 700 c h2o contents varied from 3 0 to more than 10 wt the liquid line of descent covers the entire compositional range from olivine tholeiite 1 170 c to high silica rhyolite 700 c and evolves from metaluminous to peraluminous compositions the following crystallization sequence has been established olivine clinopyroxene plagioclase spinel orthopyroxene amphibole titanomagnetite apatite quartz biotite anorthite rich plagioclase and spinel are responsible for a marked increase in sio2 content from 51 to 53 wt at 1 040 c at lower temperatures fractionation of amphibole plagioclase and fe ti oxide over a temperature interval of 280 c drives the sio2 content continuously from 53 to 78 wt largest crystallization steps were recorded around 1 040 c and at 700 c about 40 of ultramafic plutonic rocks have to crystallize to generate basaltic andesitic liquids and an additional 40 of amphibole gabbroic cumulate to produce granitic melts andesitic liquids with a liquidus temperature of 1 010 c only crystallize 50 over an 280 c wide range to 730 c implying that such liquids form mobile crystal mushes 50 crystals in long lived magmatic systems in the middle crust allowing for extensive fractionation assimilation and hybridization with periodic replenishment of more mafic magmas from deeper magma reservoirs

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

biot number and thermos bottle effect implications for magma chamber convection thermal boundary conditions model the coupling between a convecting magmatic body and its host such conditions need to be considered in models of igneous systems that involve thermal histories crystallization and fractionation of melt formation of aureoles by contact metamorphism and any other processes in which transport of heat plays a role usually investigations of magmatic systems have tended to emphasize modeling the interior convective regime relative to treatment of the thermal coupling yet it is found that the thermal nature of an intrusion is likely to be influenced more by coupling to its host than by the details of internal convective flows evaluation of a parameter having the form of a biot number bi provides a basis for estimating which boundary conditions are most appropriate it is found that bi 0 1 constant heat flux limit for models of several caldera systems for such values of the biot number the host regime behaves somewhat like a thermos bottle by limiting the flow of heat through the magma host system so that convective stirring of magma has little effect on the cooling rate of the intrusion because of this insulating effect boundary temperatures assumed in convection models should approach magmatic values even if an active hydrothermal system is present however high boundary temperatures do not imply that melting and assimilation of host rock by magma must occur despite the thermos bottle effect magmatic convection can still be quite vigorous

petrochronology of zircon and baddeleyite in igneous rocks reconstructing magmatic processes at high temporal resolution zircon zrsio4 and baddeleyite zro2 are common accessory minerals in igneous rocks of felsic to mafic composition both minerals host trace elements substituting for zr among them hf th u y rees and many more the excellent chemical and physical resistivity of zircon makes this mineral a perfect archive of chemical and temporal information to trace geological processes in the past utilizing the outstanding power and temporal resolution of the u pb decay schemes baddeleyite is a chemically and physically much more fragile mineral it preserves similar information only where it is shielded from dissolution and physical fragmentation as an inclusion in other minerals or in a fine grained or non reactive rock matrix it offers the potential for dating the solidification of mafic rocks with high precision through its crystallization in small pockets of zr enriched melt after extensive olivine and pyroxene fractionation zircon and baddelelyite u pb dates are for an overwhelming majority of cases and where we can assume a closed system considered to reflect the time of crystallization the development of the u pb dating tool ca id tims chemical abrasion isotope dilution thermal ionization mass spectrometry since 2005 has led to unprecedented precision of better than 0 1 in 206pb 238u dates bowring et al 2005 increased sensitivity of mass spectrometers and low laboratory blanks due to reduction of acid volumes allow routine u pb age determinations of micrograms of material at sufficiently high radiogenic common lead ratios see schoene and baxter 2017 this volume in situ u pb age analysis using laser ablation or primary ion beam sputtering allows analysis of sub microgram quantities of zircon material from polished internal sections or zircon surfaces with spot diameters ranging from 30 m for laser ablation inductively coupled plasma mass spectrometry la icp ms to 10 m for secondary ion mass spectrometry sims lateral resolutions of 2 5 m for nanosims

carbonate deposition in an ephemeral siliciclastic alluvial system jurassic shuttle meadow formation newark supergroup hartford basin usa abstract nonmarine carbonate accumulation from a sedimentologic perspective has multiple possible origins clastic load springs groundwater discharge soil development biochemical seasonal changes cave speleothems and eolian influx many of these carbonates contain diagnostic textures from which origin is easy to ascertain however differentiating between clastic and spring groundwater carbonates especially in depositional systems dominated by siliciclastics is not always simple here criteria for recognition are developed subsurface hydrology and tectonic origin of the depositional basin source rocks surrounding the basin sedimentologic packaging and extent of the carbonates in question as well as their sedimentary structures and fossil content and stable isotopic analyses of the carbonates can all aid in determining carbonate origin and correctly assessing sedimentary and basin evolution the present study focuses on a nonmarine carbonate deposit found within the jurassic shuttle meadow formation of the hartford basin one of many rift basins which formed as a result of the opening of the north atlantic ocean during the late triassic to early jurassic the upper 50 m of the formation at plainville connecticut is interpreted as continental in origin and is composed of five facies red ripple cross laminated muddy siltstones to sandstones fr sr massive red siliciclastic mudstones fm buff fine to medium grained horizontally laminated sandstones sh red to white disrupted calcareous shales fl3 and rare micritic carbonates pm facies fr sr sh and fm are interpreted as an alluvial plain system in an ephemeral setting with bedload sheetflooding as the dominant depositional mechanism similar to the channel country drainage system of central australia in addition preservation of lateral accretion sandstone sheets accretionary benches indicate that the shuttle meadow alluvial system was rapidly accreting the anomalous existence of carbonate beds in facies fl3 and pm in the smf bedload dominated siliciclastic sequence is attributed mainly to the unique nature of the clastic sediment load in the basin no direct evidence for a spring groundwater input is apparent the shallow carbonate lake margin or a pond with vegetation and periodic exposure is envisioned as the depositional environment the intraclastic texture of the micrites with rare primary relict lamination indicates early diagenetic alteration from root penetration desiccation cracks and burrowing

chronology and evolution of caldera forming and post caldera magma systems at okataina volcano new zealand from zircon u th model age spectra u th disequilibrium model age data are presented for zircons from four young eruptive units from okataina volcano new zealand these data highlight contrasts in the time scales over which eruptible silicic magma bodies are generated and accumulated below a highly active rhyolite volcano prior to and following the 61 ka caldera forming rotoiti eruption 80 120 km 3 magma the rotoiti event was followed by 12 explosive eruptions of the mangaone subgroup between 45 and 30 ka a change in eruptive styles between 30 and 25 ka brackets the major oruanui eruption of taupo volcano 80 km away subsequently eight rhyolitic lava dominated and two basaltic explosive eruptions occurred between 25 ka and 1886 ce we present 238 u 230 th zircon model age data determined by secondary ion mass spectrometry sims and thermal ionization mass spectrometry tims from the rotoiti ngamotu unit b 45 ka mangaone unit i 33 ka and rotorua 15 4 ka eruptive units we couple these data with published and new compositional information to trace magma crystallization and storage patterns population density curves of sims model ages from zircons in the two pumice types biotite free and biotite bearing from the rotoiti eruption differ zircons from the former yield a model age peak coincident with eruption age whereas zircons from the latter show a peak at 70 90 ka and little variation in tims model age values from different crystal size fractions concentration weighted means of model ages from the two pumices however are the same within 1 sd error and their sr isotopic values overlap at 2 sd precision suggesting that they are genetically linked model age spectra for the ngamotu mangaone and rotorua pumices are complex indicating recycling of crystals from multiple older populations that largely pre date the 61 ka caldera forming eruption superimposed on the older age spectra are variably developed younger pre eruptive suites of ages reflecting varying amounts of crystallization prior to each eruption a lack of commonality in these younger peaks in the post caldera eruptive rocks along with compositional and isotopic differences between and sometimes within the eruptive units collectively precludes their origin from a single melt bearing mush system okataina contrasts with taupo where comparable age eruption deposits have simpler age spectra consistent with larger scale crystallization cycles and thermal events in the magma chambers there when compared with other caldera related silicic systems for which suitable data are available okataina differs in lacking a simple pre eruptive history prior to its caldera forming event and having a complex non coherent magmatic history of post caldera eruptions

rethinking the emplacement and evolution of zoned plutons geochronologic evidence for incremental assembly of the tuolumne intrusive suite california new u pb geochronologic data indicate that the tuolumne intrusive suite california was assembled over a period of at least 10 m y between 95 and 85 ma and that the half dome granodiorite intruded over a period approaching 4 m y simple thermal considerations preclude the possibility that a magma chamber the size of the half dome pluton could have existed as a liquid at shallow crustal depths for that long rather field evidence for sheeting along the margins of the suite the range of ages and the regular decrease of ages toward the center of the suite and within individual plutons suggest incremental assembly geochronologic evidence for incremental assembly is consistent with the failure of geophysical methods to detect large magma chambers with more than 20 melt even in active volcanic areas because it is unlikely that the individual plutons composing the tuolumne ever coexisted as liquid rich magmas the chemical evolution of the suite cannot be the result of simple fractionation and or mixing between exposed units but instead must reflect processes occurring during magma generation

the temporal record of magmatism at cerro uturuncu bolivian altiplano twenty six new 40ar 39ar plateau ages for 23 lavas and domes from the uturuncu volcano in the altiplano of sw bolivia reveal a protracted eruptive history from 1050 5 to 250 5 ka eruptions have been exclusively effusive producing some 50 km3 of high k dacites and silicic andesites bimodal mineral compositions complex mineral textures the presence of andesitic magmatic enclaves within dacites and linear chemical trends on binary element plots all indicate that magma mixing is an important petrogenetic process at uturuncu post 458 ka distinct high and low mgo cr magmas are resolved these magmas erupt during similar times suggesting that eruptions are tapping different parts of the magma system albeit from the same vent system volcanic and petrological features are consistent with the existence of a vertically extensive magma mush column beneath uturuncu and calculated buoyancy forces are sufficient to drive effusive eruptions eruptive activity is episodic with six eruptive periods separated by hiatuses of 50 kyr cumulative volume curves demonstrate that the majority of the edifice formed between 595 and 505 ka the episodicity of eruptions is most likely to be related to fluctuations in the magma supply to the underlying altiplano puno magma body

melt segregation and the architecture of magmatic reservoirs insights from the muroto sill japan the separation of melt from crystals is a fundamental process driving the chemical differentiation of magmas and can lead to the formation of pockets of potentially eruptible magmas in highly crystallised magma reservoirs while geochemical and geophysical evidence exists for the presence of such isolated pockets of eruptible melt the processes that control their volume and spatial arrangement remain unclear the muroto sill in japan provides an excellent opportunity to study these processes as it is perfectly exposed and shows clear evidence for melt segregation we collected geochemical and structural data across the sill and performed thermal modelling to quantify extraction timescales and to constrain the range of crystallinity at which melt extraction occurred our data and calculations show that the middle lower portion of the sill experienced melt extraction at crystal fractions between 0 65 and 0 8 over 100 150 years until magma was too crystalline for further segregation to occur we propose a new approach that can be used to invert measured geochemical profiles and identify the range of crystallinity at which melt extraction takes place with this approach the results we obtain for the muroto sill can be generalised to magma reservoirs of different sizes and chemistries our calculations and the comparison with natural magmatic systems show that the volume of melt rich pockets in a magma reservoir is proportional to the reservoir volume while their spatial arrangement depends on the physiochemical properties of magmas the results of this study increase our understanding of the factors controlling the distribution and volume of pockets of eruptible magmas in large magma reservoirs our calculations show that eruptible magma in dacitic and rhyolitic magma reservoirs which are responsible for some of the largest eruptions on earth tend to be distributed in lenses of small volume within highly crystallised magma such architecture diminishes our capacity of identifying eruptible magma in large magma reservoirs such as yellowstone using geophysical methods and jeopardises our capacity of assessing the potential of a reservoir to feed a large eruption

incremental growth of the patagonian torres del paine laccolith over 90 k y the miocene paine granite in the torres del paine intrusive complex southern chile is an extraordinary example of an upper crustal mafic and granitic intrusion the granite intruded as a series of three sheets each one underplating the previous sheet along the top of the basal paine mafic complex high precision u pb geochronology on single zircons using isotope dilution thermal ionization mass spectrometry yields distinct ages of 12 59 0 02 ma and 12 50 0 02 ma respectively for the first and last sheet of the laccolith this age relationship is consistent with field observations the zircon ages define a time frame of 90 40 k y for the emplacement of a 2000 m thick granite laccolith these precise u pb zircon ages permit identification of the pulses in a 20 k y range the data obtained for the paine granite fill the gap between 100 k y and 100 1000 yr pulses described in the literature for crustal magma chambers

the potential of lake ohrid for long term palaeoenvironmental reconstructions abstract lake ohrid at the macedonian albanian border was likely tectonically formed during the tertiary and therefore is one of the oldest lakes in europe however only a few studies exist concerning the potential of lake ohrid sediments for long term palaeoenvironmental reconstructions within the scope of future potential deep drilling campaigns therefore as a first step a transect of short surface sediment cores was investigated for chronology physical properties grain size and biogeochemistry the results were compared with information derived from a shallow hydro acoustic seismic survey the investigations indicate a rather uniform and bioturbated sedimentation in the central part of the lake basin with mean sedimentation rates of ca 0 5 1 mm year the sediment composition is dominated by authigenetic carbonates diatom frustules or fragments form the major part of biogenic matter deposits as indicated by the relatively high contents of biogenic opal and low contents of total organic carbon and total nitrogen the shallow hydro acoustic seismic survey indicates that horizons of sediment redeposition occur sporadically towards the shore of the lake the sedimentation rate increases and sedimentation is increasingly influenced by local inflows or mass movement processes triggered by tectonic activities thus lake ohrid has a high potential for palaeoenvironmental reconstructions on a multi decadal scale and provides additional information concerning tectonic activity in the region

magma convection and mixing dynamics as a source of ultra long period oscillations many volcanic eruptions are shortly preceded by injection of new magma into a pre existing shallow 10 km magma chamber causing convection and mixing between the incoming and resident magmas these processes may trigger dyke propagation and further magma rise inducing long term days to months volcano deformation seismic swarms gravity anomalies and changes in the composition of volcanic plumes and fumaroles eventually culminating in an eruption although new magma injection into shallow magma chambers can lead to hazardous event such injection is still not systematically detected and recognized here we present the results of numerical simulations of magma convection and mixing in geometrically complex magmatic systems and describe the multiparametric dynamics associated with buoyant magma injection our results reveal unexpected pressure trends and pressure oscillations in the ultra long period ulp range of minutes related to the generation of discrete plumes of rising magma very long pressure oscillation wavelengths translate into comparably ulp ground displacements with amplitudes of order 10 4 10 2 m thus new magma injection into magma chambers beneath volcanoes can be revealed by ulp ground displacement measured at the surface

the temporal evolution of chemical and physical properties of magmatic systems exactly 100 years ago the great canadian born petrologist n l bowen published two seminal works on the chemical differentiation of magmas in which he posed the basis for a physico chemical understanding of the fractionation of crystals from melts in molten rock a subsequent century of research and technological advances has enhanced our understanding of the physics and chemistry of magmatic systems and their temporal evolution the image of sub volcanic magmatic systems has evolved greatly in that time from a simple boiling vat concept of molten rock in which bubbles crystals and melt separate gravitationally to a recognition that magma vats are relatively rare and that most magmatic systems spend much of their lifetime in a partially molten or mushy state real magmatic systems appear to be organized into a series of storage regions periodically connected by feeding structures transferring magma and heat at different fluxes magma fluxes between the different portions of this plumbing system and the variation of the chemical and physical properties of magma as it rises through the crust exert essential controls on the eruptive modalities of volcanoes and the geochemistry of their products this book presents a collection of contributions that use petrology geochemistry geochronology and numerical modelling to identify the processes operating at different depths within magmatic systems and to characterize the fluxes of magma between them

the effect of particle shape on suspension viscosity and implications for magmatic flows 1 the rheology of crystal bearing magma and lava depends on both the shape and volume fraction of the suspended crystals we present the results of analogue rheometric experiments on monodisperse suspensions of solid particles in a newtonian liquid in which particle volume fraction and aspect ratio rp are varied systematically we find that the effect of on viscosity is well captured by the maron pierce model and that this model is valid across the range of particle aspect ratios investigated 0 04 rp 22 i e strongly oblate to strongly prolate when the maximum packing fraction m is treated as a fitting parameter the value of m derived from fitting to our experimental data depends strongly and systematically on particle aspect ratio hence m represents an effective proxy for the influence of particle shape on suspension rheology we present a simple relationship for m rp which allows the viscosity of a suspension to be calculated as a function of and rp only we investigate the impact of accounting for crystal shape when modelling volcanic flows by simulating the eruption of magma carrying crystals of different aspect ratio and conclude that the effect of crystal shape should not be neglected

vertically extensive and unstable magmatic systems a unified view of igneous processes volcanoes are an expression of their underlying magmatic systems over the past three decades the classical focus on upper crustal magma chambers has expanded to consider magmatic processes throughout the crust a transcrustal perspective must balance slow plate tectonic rates of melt generation and segregation in the lower crust with new evidence for rapid melt accumulation in the upper crust before many volcanic eruptions reconciling these observations is engendering active debate about the physical state spatial distribution and longevity of melt in the crust here we review evidence for transcrustal magmatic systems and highlight physical processes that might affect the growth and stability of melt rich layers focusing particularly on conditions that cause them to destabilize ascend and accumulate in voluminous but ephemeral shallow magma chambers

linking rapid magma reservoir assembly and eruption trigger mechanisms at evolved yellowstone type supervolcanoes the geological record contains evidence of volcanic eruptions that were as much as two orders of magnitude larger than the most voluminous eruption experienced by modern civilizations the a d 1815 tambora indonesia eruption perhaps nowhere on earth are deposits of such supereruptions more prominent than in the snake river plain yellowstone plateau srp yp volcanic province northwest united states while magmatic activity at yellowstone is still ongoing the heise volcanic field in eastern idaho represents the youngest complete caldera cycle in the srp yp and thus is particularly instructive for current and future volcanic activity at yellowstone the heise caldera cycle culminated 4 5 ma ago in the eruption of the 1800 km3 kilgore tuff accessory zircons in the kilgore tuff display significant intercrystalline and intracrystalline oxygen isotopic heterogeneity and the vast majority are 18o depleted this suggests that zircons crystallized from isotopically distinct magma batches that were generated by remelting of subcaldera silicic rocks previously altered by low 18o meteoric hydrothermal fluids prior to eruption these magma batches were assembled and homogenized into a single voluminous reservoir u pb geochronology of isotopically diverse zircons using chemical abrasion isotope dilution thermal ionization mass spectrometry yielded indistinguishable crystallization ages with a weighted mean 206pb 238u date of 4 4876 0 0023 ma mswd 1 5 n 24 these zircon crystallization ages are also indistinguishable from the sanidine 40ar 39ar dates and thus zircons crystallized close to eruption this requires that shallow crustal melting assembly of isolated batches into a supervolcanic magma reservoir homogenization and eruption occurred extremely rapidly within the resolution of our geochronology 103 104 yr the crystal scale image of the reservoir configuration with several isolated magma batches is very similar to the reservoir configurations inferred from seismic data at active supervolcanoes the connection of magma batches vertically distributed over several kilometers in the upper crust would cause a substantial increase of buoyancy overpressure providing an eruption trigger mechanism that is the direct consequence of the reservoir assembly process

magnetotelluric images of magma distribution beneath volcan uturuncu bolivia implications for magma dynamics the altiplano puna volcanic complex in the central andes records a history of major caldera forming eruptions over the past 10 m y geophysical and geodetic data indicate that magma is still present and perhaps mobile in the crust broadband magnetotelluric data were used to generate two dimensional and three dimensional electrical resistivity models of the altiplano puna magma body apmb with a focus on the zone of inflation around volcan uturuncu in southern bolivia low electrical resistivities 20 the upper surface of the apmb is shallowest beneath uturuncu and the geometry is consistent with geodynamic models that require the upward movement of a melt layer at this location the shallower resistivity structure is characterized by discrete electrically conductive bodies oriented east west near sea level depth of 5 km which are interpreted as a combination of partial melt and fluids

conditions for the growth of a long lived shallow crustal magma chamber below mount pelee volcano martinique lesser antilles arc 1 the compositional homogeneity of silicic andesites emitted during the 13 500 year long last eruptive cycle of mount pelee suggests that the physical state of the magma chamber was largely unmodified during this period experimental phase equilibria on mount pelee recent products indicate that pre eruptive magma temperatures and pressures were in the range of 875 900 c and 2 0 5 kbar respectively the estimated average eruption rate was 7 5 10 4 km3 a with an average volume of about 0 3 km3 per eruption an analytical model for a spherical magma chamber indicates that a magma flux of 4 5 10 4 km3 a can maintain a magma chamber of 0 3 km3 above 875 c below mount pelee however observations of plutons suggest that magma chambers may grow by addition of sheet like intrusions with numerical simulation we show that a minimum sheet accretion rate of a few centimeters per year is required to grow a persistently active magma chamber independently of the intruded volumetric flux this minimum injection rate is higher if the heat transfer is enhanced by convection processes the limited ability of an arc crust to extend and accommodate dikes suggests that magma injections are sills or if they are dikes that most of the volume injected in the magma chamber is eventually erupted in a conductively cooling igneous body formed by sills injected at a rate of a few centimeters per year most of the injected magma completely solidifies and only a small part of the body about 10 20 is above 875 c and able to feed eruptions

determining the size and shape of blocks from linear sampling for geotechnical rock mass classification and assessment classifying and assessing geotechnical aspects of rock masses involves combining parameters in various ways guided by empirical considerations to derive quantitative geotechnical parameters geological structures and the deformation history of rocks underpin the nature of rock masses the kinematics of a deforming rock mass may occur as sliding along throughgoing discontinuities or as distributed sliding on block faces distributed sliding will tend to disrupt the continuity of planar structures such that data on the size and shape of blocks is needed rather than relying on discontinuity orientation data alone orientation and spacing data can be combined to provide a geometric analysis of block systems from linear samples such as drill core dihedral angles and spacing of sequential pairs of discontinuities provides a sample of the size and shape of blocks that can be interpreted stereologically further detail can be derived by combining neighbouring intersections that enclose or partially enclose individual blocks the shape and size of a block can be represented on a stereograph with the enclosing faces shown as poles and their perpendicular distance from an arbitrary point inside the block shown as a number identifying the size and shape of specific blocks rather than relying on statistical methods is beneficial to critical aspects of design such as analysing keyblocks that would be exposed during excavations the detailed characterization of block size and shape is also a step toward interpreting the kinematics of rock mass deformation and the analysis of rock masses as ultra close packed dilatant granular systems

decoupled crystallization and eruption histories of the rhyolite magmatic system at tarawera volcano revealed by zircon ages and growth rates we obtained u th disequilibrium age data on zircons from each of the four rhyolite eruptions that built tarawera volcano in the last 22 ka within the okataina volcanic center ovc caldera new zealand secondary ion mass spectrometry analyses on unpolished euhedral crystal faces that lack resorption features show that crystal growth variously terminated from near eruption age to 100 ka prior to eruption age depth profiling of crystals reveals long periods of continuous 34 ka and discontinuous growth 90 ka growth hiatuses of up to 40 ka duration occur but do not all relate to obvious resorption surfaces age differences up to similar magnitude are found on opposing faces of some crystals suggesting episodes of partial exposure to melts these features are best explained by periodic complete or partial sub solidus storage and or inclusion in larger crystal phases followed by rapid liberation prior to eruption this is supported by high abundances of u and th 500 2 000 ppm in some zircons consistent with periods of high crystallinity 70 in the magmatic system based on crystal melt partitioning contemporaneous but contrasting rim ward trends of these elements within crystals even in the same lava hand sample require synchronous growth in separate melt bodies and little connectivity within the system but also significant crystal transport and mixing prior to eruption many crystals record continuity of growth through the preceding 60 ka ovc caldera collapse and subsequent eruptions from tarawera this demonstrates a decoupling between eruption triggers such as shallow crustal extension and mafic intrusion and the crystallization state of the ovc silicic magmatic system the data highlights the need to distinguish between the time for accumulation of eruptible magma and the long term magma residence time based on the age of crystals with high closure temperatures when assessing the potential for catastrophic eruptions

magma chamber properties from integrated seismic tomography and thermal modeling at montserrat it is widely believed that andesitic magmas erupted at arc volcanoes are stored in shallow reservoirs prior to eruption but high resolution images of focused regions of magma in the shallow crust are rare we integrate seismic tomography with numerical models of magma chamber growth to constrain the magma chamber beneath soufriere hills volcano montserrat our approach reveals the characteristics and dynamics of the magmatic system with a level of detail that no single method has yet achieved the integrated analysis suggests that a magma chamber of 13 km3 with over 30 melt fraction formed between 5 5 and at least 7 5 km depth a significantly higher melt fraction than inferred from the seismic data alone the magma chamber may have formed by incremental sill intrusion over a few thousand years and is likely to be a transient geologically short lived feature these volume and geometry estimates are critical parameters to model eruption dynamics which in turn are key to hazard assessment and eruption forecasting

ascent driven crystallisation of dacite magmas at mount st helens 1980 1986 we introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system qz ab or h2o in order to relate variations in volcanic glass chemistry to changing pressure p and temperature t conditions in the sub volcanic magma system by this means an important distinction can be made between ascent driven and cooling driven crystallisation under water saturated or undersaturated conditions in samples containing feldspar and a silica phase quartz or tridymite quantitative p t estimates of the conditions of last equilibrium between crystals and melt can be made formation of highly silicic melts i e 77 wt sio2 is a simple consequence of the contraction of the silica phase volume with decreasing pressure such that high silica glasses can only form by crystallisation at low pressure resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation groundmass and inclusion glasses in dacites from the 1980 1986 eruption of mount st helens volcano wa span a wide range in sio2 68 80 wt anhydrous the compositions of the least evolved sio2 poor inclusions in amphibole phenocrysts record entrapment of silicic liquids with 5 4 wt water corresponding to a water saturation pressure of 200 mpa at 900 c the compositions of more evolved higher sio2 plagioclase hosted inclusions and groundmass glasses are consistent with extensive ascent driven fractional crystallisation of plagioclase oxide and orthopyroxene phenocrysts and microlites to low pressures during this polybaric crystallisation plagioclase phenocrysts trapped melts with a wide range of dissolved water contents 3 5 5 7 wt magmas erupted during the plinian phase of the 18 may 1980 eruption were derived from a large reservoir at depths of 6 km subsequent magmas ascended to varying depths within the sub volcanic system prior to extraction from glass chemistry and groundmass texture two arrest levels have been identified at depths of 0 5 1 and 2 4 km a single dome sample from february 1983 contains groundmass plagioclase tridymite and quartz testifying to temperatures of at least 885 c at 11 mpa these shallow storage conditions are comparable to those in the cryptodome formed during spring 1980 the corresponding thermal gradient 0 2 c mpa 1 is consistent with near adiabatic magma ascent from 8 km we argue that the crystallisation history of mount st helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation this challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980 1986 eruption because the crystallisation process is both polybaric and fractional it cannot be simulated directly using isobaric equilibrium crystallisation experiments however calculation of the phase proportions in water saturated 910 15 c experiments by rutherford et al 1985 over the pressure range 220 125 mpa reproduces the crystallisation sequence and phenocryst modes of mount st helens dacites from 18 may 1980 by allowing for the effects of fractional versus equilibrium crystallisation entrained residual source material and small temperature differences between nature and experiment phase compositions can also be matched to the natural samples we conclude that decompression of water saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres

a high resolution late glacial to holocene record of environmental change in the mediterranean from lake ohrid macedonia albania lake ohrid macedonia albania is the oldest extant lake in europe and exhibits an outstanding degree of endemic biodiversity here we provide new high resolution stable isotope and geochemical data from a 10 m core co1262 through the late glacial to holocene and discuss past climate and lake hydrology tic 13ccalcite 18ocalcite as well as the terrestrial and aquatic vegetation response to climate toc toc n 13corganic rock eval pyrolysis the data identifies 3 main zones 1 the late glacial holocene transition represented by low tic and toc contents 2 the early to mid holocene characterised by high toc and increasing toc n and 3 the late holocene present which shows a marked decrease in tic and toc in general an overall trend of increasing 18ocalcite from 9 ka to present suggests progressive aridification through the holocene consistent with previous records from lake ohrid and the wider mediterranean region several proxies show commensurate excursions that imply the impact of short term climate oscillations such as the 8 2 ka event and the little ice age this is the best dated and highest resolution archive of past late glacial and holocene climate from lake ohrid and confirms the overriding influence of the north atlantic in the north eastern mediterranean the data presented set the context for the international continental scientific drilling program scientific collaboration on past speciation conditions in lake ohrid project cores recovered in spring summer 2013 potentially dating back into the lower pleistocene and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history

evolution of major and trace element composition during melt migration through crystalline mush implications for chemical differentiation in the crust we present the first quantitative model of heat mass and both major and trace element transport in a mush undergoing compaction that accounts for component transport and chemical reaction during melt migration and which is applicable to crustal systems the model describes the phase behavior of binary systems both eutectic and solid solution with melt and solid compositions deter mined from phase diagrams using the local temperature and bulk composition trace element concentration is also determined the results demonstrate that component transport and chemical reaction generate compositional variation in both major and trace elements that is not captured by existing geochemical models in particular we find that even for the simplest case of a homogenous insulated column that is instantaneously melted then allowed to compact component transport and reaction leads to spatial variations in major element composition that in this case produces melt that is more enriched in incompatible elements than predicted by batch melting in deep crustal hot zones dchz created by the repeated intrusion of hot mantle derived magmas buoyant melt migrating upwards accumulates in high porosity layers but has a composition corresponding to only a small fraction of batch melting because it has locally equilibrated with mush at low temperature moreover melt migration and chemical reaction in a layered protolith may lead to the rapid formation of high porosity melt layers at the interface between different rock compositions in both of these cases the melt in the high porosity layer s is less enriched in incompatible trace elements than predicted if it is assumed that melt with the same major element composition was produced by batch melting this distinctive decoupling of major and trace element fractionation may be characteristic of magmas that originate in dchz application of the model to a number of crustal systems including the ivrea verbano zone the rum layered intrusion and the holyoke flood basalt suggests that composi tional heterogeneity can be explained by buoyancy driven melt migration and compo nent transport through a reactive crystalline mush