accuracy of timescales retrieved from diffusion modeling in olivine a 3d perspective diffusion modeling in olivine is a useful tool to resolve the timescales of various magmatic processes practical olivine geospeedometry applications employ 1d chemical transects across sections that are randomly sampled from a given 3d crystal population but the accuracy and precision with which timescales can be retrieved from this procedure are not well constrained here we use numerical 3d diffusion models of fe mg to evaluate and quantify the uncertainties associated with their 1d counterparts the 3d diffusion models were built using both simple and realistic olivine morphologies and incorporate diffusion anisotropy as well as different zoning styles the 3d model crystals were sectioned along ideal or random planes which were used to perform 1d models and timescale comparisons results show that the timescales retrieved from 1d profiles are highly inaccurate and can vary by factors of 0 1 25 if diffusion anisotropy is not taken into account even when anisotropy is corrected for timescales can still vary between 0 2 10 times the true 3d diffusion time due to crystal shape and sectioning effects simple grain selection procedures are described to reduce the misfit between calculated and actual diffusion times and achieve an accuracy and precision of 5 and 15 25 relative respectively provided that the grains are carefully selected about 20 concentration profiles and associated 1d models suffice to achieve this accuracy

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

magma reservoir response to transient recharge events the case of santorini volcano greece igneous bodies are built incrementally by episodic magma injection events that vary in rate and duration such recharge events can either grow an upper crustal magma reservoir or trigger an eruption this bifurcation in behavior remains poorly constrained but is essential to volcanic hazard assessment here we use a numerical model that couples the thermal and mechanical processes in a magma reservoir to study the evolution of the santorini magmatic system greece over the past 20 k y our results constrain the recharge rate and duration that are necessary to trigger an eruption for the known long term average inflow rate of 10 3 km3 yr the size of the chamber and its exsolved volatile content are dominant controls on the critical recharge rate and duration that will trigger an eruption our model successfully reproduces the main features of the minoan eruption and nea kameni activity providing volume estimates for the active part of the current subvolcanic reservoir as well as information regarding the presence of exsolved volatiles thermomechanical models offer a new framework to integrate the historic eruption record with geodetic measurements and provide a context to understand the past present and future of active volcanic centers

a branched magma feeder system during the 1669 eruption of mt etna evidence from a time integrated study of zoned olivine phenocryst populations the 1669 eruption of mt etna was one of the most voluminous and devastating of its flank eruptions in historical times despite a large body of relevant research knowledge of the timing and duration of magma transfer and magma recharge through the internal plumbing system preceding and during the eruption is still limited to address that lack of knowledge we apply a three way integrated method linking systems analysis of crystals a time integrated study of zoned olivine populations and a forward modelling approach using thermodynamic calculations analysis of 202 olivine crystals erupted during the initial pre march 20 i e set1 and the final post march 20 i e set2 and mtrs stages of the eruption reveals the existence of three magmatic environments mes in which the majority of the olivine cores m 1 fo 75 78 and rims i e m 5 fo 51 59 and m 3 fo 65 69 formed application of the rhyolite melts software allowed us to constrain the key intensive variables associated with these mes we find that temperature water content and oxidation state vary between these mes application of diffusion modelling to the zoned olivine crystals allowed us to reconstruct the timing and chronology of melt and crystal transfer prior to and during the 1669 flank eruption we find that following the formation of the olivine cores m 1 fo 75 78 the reservoir m 1 was intruded by batches of more evolved degassed and possibly aphyric m 5 type magma commencing 1 center dot 5 years prior to eruptive activity this is the origin of the set1 olivine rims i e fo 51 59 in the months prior to eruption timescale data show that recharge activity along the newly established pathway m 1 m 5 increased notably starting in november 1668 only a few weeks after the first intrusive episode into the m 1 reservoir a second pulse of magma injections m 3 type magma occurred and a new pathway m 1 m 3 opened this is how the set2 olivine rims i e fo 65 69 formed for several weeks a bifurcated transport system with two dominant magma pathways developed along m 1 m 5 and m 1 m 3 dyke injections accompanied by vigorous seismicity in the days immediately before eruption the local magma transfer dynamics changed and the m 1 m 5 recharge activity slowed down as shown by a relative lack of crystals recording shorter timescales m 1 m 3 recharge however remained high and persisted following the eruption onset on march 11 during which the set1 lavas were drained we propose that the change of the local magma transfer dynamics might be linked to changes in the local stress field brought on during eruption this may potentially have been due to repeated dyke injections into etna s shallow plumbing system disrupting the early m 1 m 5 pathway and at the same time stabilizing the m 1 m 3 route as a dominant feeder this transfer of system feeding would reproduce the observed syn eruptive recharge and mixing in the weeks following eruption onset culminating in the eruption of the later set2 lavas

on the use of cycle thickness diagrams as records of long term sealevel change during accumulation of carbonate sequences analysis of variation in changing rates of accommodation space creation as represented by stratigraphic thickness has become an integral part of ongoing investigations into the origin of ancient meter scale upward shoaling cyclic marine carbonates groupings of thicker than average and thinner than average cycles within long stratigraphic sections have been thought to represent the influence of long term eustatic sealevel variation on rates of accommodation space creation under conditions of constant basin subsidence statistical analysis demonstrates that a large percentage of early paleozoic cyclic carbonate sequences contain thickness distributions indistinguishable from those anticipated for random associations of cycles and that only a few have characteristics commensurate with long term changes in rate of accommodation space creation moreover in those cases where some extraneous control is suggested computational considerations readily demonstrate that change in subsidence rate and or diffe

a rapid mechanism to remobilize and homogenize highly crystalline magma bodies the largest products of magmatic activity on earth the great bodies of granite and their corresponding large eruptions have a dual nature homogeneity at the large scale and spatial and temporal heterogeneity at the small scale this duality calls for a mechanism that selectively removes the large scale heterogeneities associated with the incremental assembly of these magmatic systems and yet occurs rapidly despite crystal rich viscous conditions seemingly resistant to mixing here we show that a simple dynamic template can unify a wide range of apparently contradictory observations from both large plutonic bodies and volcanic systems by a mechanism of rapid remobilization unzipping of highly viscous crystal rich mushes we demonstrate that this remobilization can lead to rapid overturn and produce the observed juxtaposition of magmatic materials with very disparate ages and complex chemical zoning what distinguishes our model is the recognition that the process has two stages initially a stiff mushy magma is reheated from below producing a reduction in crystallinity that leads to the growth of a subjacent buoyant mobile layer when the thickening mobile layer becomes sufficiently buoyant it penetrates the overlying viscous mushy magma this second stage rapidly exports homogenized material from the lower mobile layer to the top of the system and leads to partial overturn within the viscous mush itself as an additional mechanism of mixing model outputs illustrate that unzipping can rapidly produce large amounts of mobile magma available for eruption the agreement between calculated and observed unzipping rates for historical eruptions at pinatubo and at montserrat demonstrates the general applicability of the model this mechanism furthers our understanding of both the formation of periodically homogenized plutons crust building and of ignimbrites by large eruptions

magma reservoirs from the upper crust to the moho inferred from high resolution vp and vs models beneath mount st helens washington state usa the size frequency and intensity of volcanic eruptions are strongly controlled by the volume and connectivity of magma within the crust several geophysical and geochemical studies have produced a comprehensive model of the magmatic system to depths near 7 km beneath mount st helens washington state usa currently the most active volcano in the cascade range data limitations have precluded imaging below this depth to observe the entire primary shallow magma reservoir as well as its connection to deeper zones of magma accumulation in the crust the inversion of p and s wave traveltime data collected during the active source component of the imush imaging magma under st helens project reveals a high p wave vp s wave vs velocity anomaly beneath mount st helens between depths of 4 and 13 km which we interpret as the primary upper middle crustal magma reservoir beneath and southeast of this shallow reservoir a low vp velocity column extends from 15 km depth to the moho deep long period events near the boundary of this column indicate that this anomaly is associated with the injection of magmatic fluids southeast of mount st helens an upper middle crustal high vp vs body beneath the indian heaven volcanic field may also have a magmatic origin both of these high vp vs bodies are at the boundaries of the low vp middle lower crustal column and both are directly above high vp middle lower crustal regions that may represent cumulates associated with recent quaternary or paleogene neogene cascade magmatism seismicity immediately following the 18 may 1980 eruption terminates near the top of the inferred middle lower crustal cumulates and directly adjacent to the inferred middle lower crustal magma reservoir these spatial relationships suggest that the boundaries of these high density cumulates play an important role in both vertical and lateral transport of magma through the crust

compositionally zoned crystals and real time degassing data reveal changes in magma transfer dynamics during the 2006 summit eruptive episodes of mt etna one of the major objectives of volcanology remains relating variations in surface monitoring signals to the magmatic processes at depth that cause these variations we present a method that enables compositional and temporal information stored in zoning of minerals olivine in this case to be linked to observations of real time degassing data the integrated record may reveal details of the dynamics of gradual evolution of a plumbing system during eruption we illustrate our approach using the 2006 summit eruptive episodes of mt etna we find that the history tracked by olivine crystals and hence most likely the magma pathways within the shallow plumbing system of mt etna differed considerably between the july and october eruptions the compositional and temporal record preserved in the olivine zoning patterns reveal two mafic recharge events within months of each other june and september 2006 and each of these magma supplies may have triggered the initiation of different eruptive cycles july 14 24 and august 31 december 14 correlation of these observations with gas monitoring data shows that the systematic rise of the co2 so2 gas values is associated with the gradual pre and syn eruptive supply of batches of gas rich mafic magma into segments of etna s shallow plumbing system where mixing with pre existing and more evolved magma occurred

years to weeks of seismic unrest and magmatic intrusions precede monogenetic eruptions seismic deformation and gas activity unrest typically precedes volcanic eruptions tracking the changes of this activity with monitoring data makes it increasingly possible to successfully forecast eruptions from stratovolcanoes however this is not the case for monogenetic volcanoes eruptions from these volcanoes tend to be small but are particularly difficult to anticipate since they occur at unexpected locations and there is very limited instrumental monitoring data many monogenetic volcanic fields occur in high density populated areas and or tourist destinations and thus even a small eruption can have a major economic and societal impact we have gathered the available instrumental data for unrest and combined it with new historical accounts of seismicity our occurrences are mainly from high magmatic flux oceanic islands canary islands iceland papua new guinea mexico and japan we find that seismic activity may start one or two years before eruption but it intensifies at approximately two or three months and one or two weeks the petrological and geochemical characteristics of the deposits show that multiple magma batches interacted in a subvolcanic reservoir and multiple intrusions occurred on a similar time scales to the seismicity we propose a general model for these eruptions where early dike intrusions in the crust do not erupt e g stalled intrusions and make small plumbing systems but they probably are key in creating a thermal and rheological pathway for later dikes to be able to reach the surface these observations provide a conceptual framework for better anticipating monogenetic eruptions in similar settings and magmatic fluxes and should lead to improved strategies for mitigation of their associated hazards and risks

linking petrology and seismology at an active volcano many active volcanoes exhibit changes in seismicity ground deformation and gas emissions which in some instances arise from magma movement in the crust before eruption an enduring challenge in volcano monitoring is interpreting signs of unrest in terms of the causal subterranean magmatic processes we examined over 300 zoned orthopyroxene crystals from the 1980 1986 eruption of mount st helens that record pulsatory intrusions of new magma and volatiles into an existing larger reservoir before the eruption occurred diffusion chronometry applied to orthopyroxene crystal rims shows that episodes of magma intrusion correlate temporally with recorded seismicity providing evidence that some seismic events are related to magma intrusion these time scales are commensurate with monitoring signals at restless volcanoes thus improving our ability to forecast volcanic eruptions by using petrology

the yellowstone magmatic system from the mantle plume to the upper crust the yellowstone supervolcano is one of the largest active continental silicic volcanic fields in the world an understanding of its properties is key to enhancing our knowledge of volcanic mechanisms and corresponding risk using a joint local and teleseismic earthquake p wave seismic inversion we revealed a basaltic lower crustal magma body that provides a magmatic link between the yellowstone mantle plume and the previously imaged upper crustal magma reservoir this lower crustal magma body has a volume of 46 000 cubic kilometers 4 5 times that of the upper crustal magma reservoir and contains a melt fraction of 2 these estimates are critical to understanding the evolution of bimodal basaltic rhyolitic volcanism explaining the magnitude of co2 discharge and constraining dynamic models of the magmatic system for volcanic hazard assessment

time scales of crystal mixing in magma mushes magma mixing is widely recognized as a means of producing compositional diversity and preconditioning magmas for eruption however the processes and associated time scales that produce the commonly observed expressions of magma mixing are poorly understood especially under crystal rich conditions here we introduce and exemplify a parameterized method to predict the characteristic mixing time of crystals in a crystal rich magma mush that is subject to open system reintrusion events our approach includes novel numerical simulations that resolve multiphase particle fluid interactions it also quantifies the crystal mixing by calculating both the local and system wide progressive loss of the spatial correlation of individual crystals throughout the mixing region both inertial and viscous time scales for bulk mixing are introduced estimated mixing times are compared to natural examples and the time for basaltic mush systems to become well mixed can be on the order of 10 days

timescales of mixing and mobilisation in the bishop tuff magma body perspectives from diffusion chronometry we present two feldspar thermometry and diffusion chronometry from sanidine orthopyroxene and quartz from multiple samples of the bishop tuff california to constrain the temperature stratification within the pre eruptive magma body and the timescales of magma mixing prior to its evacuation two feldspar thermometry yields estimates that agree well with previous fe ti oxide thermometry and gives a 80 c temperature difference between the earlier and later erupted regions of the magma chamber using the thermometry results we model diffusion of ti in quartz and ba and sr in sanidine as well as fe mg interdiffusion in orthopyroxene to yield timescales for the formation of overgrowth rims on these crystal phases diffusion profiles of ti in quartz and fe mg in orthopyroxene both yield timescales of 150 years for the formation of overgrowth rims in contrast both ba and sr diffusion in sanidine yield nominal timescales 1 2 orders of magnitude longer than these two methods the main cause for this discrepancy is inferred to be an incorrect assumption for the initial profile shape for ba and sr diffusion modelling i e growth zoning exists utilising the divergent diffusion behaviour of ba and sr we place constraints on the initial width of the interface and can refine our initial conditions considerably bringing ba and sr data into alignment and yielding timescales closer to 500 years the majority of which are then within uncertainty of timescales modelled from ti diffusion in quartz care must be thus taken when using ba in sanidine geospeedometry in evolved magmatic systems where no other phases or elements are available for comparative diffusion profiling our diffusion modelling reveals piecemeal rejuvenation of the lower parts of the bishop tuff magma chamber at least 500 years prior to eruption timescales from our mineral profiling imply either that diffusion coefficients currently used are uncertain by 1 2 orders of magnitude or that the minerals concerned did not experience a common history despite being extracted from the same single pumice clasts introduction of the magma initiating crystallisation of the contrasting rims on sanidine quartz orthopyroxene and zircon was prolonged and may be a marker of other processes that initiated the bishop tuff eruption rather than the trigger itself

mechanisms of decadal sea level variability in the eastern north atlantic and the mediterranean sea decadal sea level variations from tide gauge records along the western european coast and in the mediterranean sea commencing in the late 19th and early 20th centuries are examined relative to large scale atmospheric forcing recent studies have provided evidence for a link between sea level in the eastern north atlantic and atmospheric forcing however the nature of this relationship is still unclear here the outputs of a regional barotropic model and a nearly global baroclinic model are used in conjunction with wind stress and heat flux data to explore the physical mechanisms responsible for the observed sea level variability all tide gauge records show significant decadal variability up to 15 cm and are highly correlated with the nao and among themselves at decadal periods there is a coherent sea level signal that affects the eastern boundary of the north atlantic northward of 25 n and is limited to a narrow band of the order of a few hundred kilometers along the coast this band tends to become narrower towards higher latitudes we find that longshore wind and wave propagation along the boundary are the major contributors to coastal sea level variability but no significant contribution from mass redistribution linked to changes in the strength of the subtropical gyre is observed the mass component dominates sea level in the mediterranean and is mainly driven by mass exchanges with the atlantic which explains the correlation between both regions southward of 25 n sea level changes are mainly driven by heat advection through ekman fluxes

time scales and temperatures of crystal storage in magma reservoirs implications for magma reservoir dynamics the thermal and therefore physical state of magma bodies within the crust controls the processes and time scales required to mobilize magmas before eruptions which in turn are critical to hazard a

multi mode li diffusion in natural zircons evidence for diffusion in the presence of step function concentration boundaries abstract micron to submicron scale observations of li distribution and li isotope composition profiles can be used to infer the mechanisms of li diffusion in natural zircon extreme fractionation 20 30 within each single crystal studied here confirms that li diffusion commonly occurs in zircon sharp li concentration gradients frequently seen in zircons suggest that the effective diffusivity of li is significantly slower than experimentally determined cherniak and watson 2010 trail et al 2016 otherwise the crystallization metamorphic heating of these zircons would have to be unrealistically fast years to tens of years charge coupling with ree and y has been suggested as a mechanism that may considerably reduce li diffusivity in zircon ushikubo et al 2008 bouvier et al 2012 we show that li diffused in the direction of decreasing li y ratio and increasing li concentration uphill diffusion in one of the zircons demonstrating charge coupling with ree and y quantitative modeling reveals that li may diffuse in at least two modes in natural zircons one being slow and possibly coupled with ree y and the other one being fast and not coupled with ree y the partitioning of li between these two modes during its diffusion may depend on the pre diffusion substitution mechanism of ree and y in the zircon lattice based on our results sharp li concentration gradients are not indicative of limited diffusion and can be preserved at temperatures 700 c on geologic timescales finally large 7 li variations observed in the hadean jack hills zircons may record kinetic fractionation rather than a record of ancient intense weathering in the granite source materials

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

constraints on crystal storage timescales in mixed magmas uranium series disequilibria in plagioclase from holocene magmas at mount hood oregon abstract uranium series crystal ages interpreted within a textural and geochemical framework can provide insight into crystal storage timescales especially in cases where crystals may derive from multiple sources we report here 230 th 226 ra model ages of two distinct populations of plagioclase from low silica dacites from mount hood oregon a volcano where previous studies show that the compositions of erupted magmas are controlled by magma recharge mixing and incorporation of plagioclase derived from mafic and silicic end member magmas we have measured trace element concentrations and 238 u 230 th 226 ra disequilibria in four plagioclase size fractions from the timberline 1500 a and old maid 215 a eruptive sequences after correction for groundmass and apatite contamination average 230 th 226 ra model ages of large 500 m plagioclase are 4 5 ka timberline and 5 5 ka old maid with ages of cores that are 10 ka in each case indicating that plagioclase derived from silicic magmas crystallized thousands of years before eruptions these model ages are longer than timescales of repose between eruptions indicating that these crystals resided in the sub surface over multiple eruptions likely stored in a silicic crystal mush zone that periodically interacts with mafic recharge magmas remobilizing a fraction of the large plagioclase crystals during each eruptive event after correction for large plagioclase contamination small 226 ra ba relative to equilibrium with liquid proxies groundmass and mafic inclusion leading to 230 th 226 ra model ages that are 230 th 226 ra disequilibria require that the majority of crystals in the separate are young 226 ra ba could potentially be explained by rapid crystallization immediately prior to and or during mixing events consistent with evidence of rapid crystallization of rims rapid crystallization of mafic intrusions may trigger eruption at mount hood by producing a partially crystalline mafic magma capable of mixing with a reheated silicic crystal mush

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

rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals silicic volcanic eruptions pose considerable hazards yet the processes leading to these eruptions remain poorly known a missing link is knowledge of the thermal history of magma feeding such eruptions which largely controls crystallinity and therefore eruptability we have determined the thermal history of individual zircon crystals from an eruption of the taupo volcanic zone new zealand results show that although zircons resided in the magmatic system for 103 to 105 years they experienced temperatures 650 to 750 c for only years to centuries this implies near solidus long term crystal storage punctuated by rapid heating and cooling reconciling these data with existing models of magma storage requires considering multiple small intrusions and multiple spatial scales and our approach can help to quantify heat input to and output from magma reservoirs

space geodesy constrains ice age terminal deglaciation the global ice 6g_c vm5a model a new model of the last deglaciation event of the late quaternary ice age is here described and denoted as ice 6g c vm5a it differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available global positioning system gps measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal additional space geodetic constraints have also been applied to specify the reference frame within which the gps data are described the focus of the paper is upon the three main regions of last glacial maximum ice cover namely north america northwestern europe eurasia and antarctica although greenland and the british isles will also be included if peripherally in the discussion in each of the three major regions the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the gravity recovery and climate experiment satellites as an independent means of verifying the improvement of the model achieved by applying the gps constraints several aspects of the global characteristics of this new model are also discussed including the nature of relative sea level history predictions at far field locations in particular the caribbean island of barbados from which especially high quality records of postglacial sea level change are available but which records were not employed in the development of the model although ice 6g c vm5a is a significant improvement insofar as the most recently available gps observations are concerned comparison of model predictions with such far field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration

decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano caldera forming volcanic eruptions are low frequency highimpact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days with devastating effects on local and global scales1 because no such eruption has been monitored during its long build up phase the precursor phenomena are not well understood geophysical signals obtained during recent episodes of unrest at calderas such as yellowstone usa and campi flegrei italy are difficult to interpret and the conditions necessary for large eruptions are poorly constrained2 3 here we present a study of pre eruptive magmatic processes and their timescales using chemically zoned crystals from the minoan caldera formingeruption of santorini volcano greece4 which occurred in the late 1600s bc the results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption5 6 despite the large volume of erupted magma4 40 60 cubic kilometres and the 18 000 year gestation period between the minoan eruption and the previous major eruption most crystals in the minoan magma record processes that occurred less than about 100 years before the eruption recharge of the magma reservoir by large volumes of silicic magma and some mafic magma occurred during the century before eruption and mixing between different silicicmagmabatches was still taking place during the final months final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period with major growth phases immediately before eruption these observations have implications for the monitoring of long dormant but potentially active caldera systems

uranium series accessory crystal dating of magmatic processes complex and protracted crystallization histories over geologic timescales are recorded in accessory minerals e g zircon allanite although magmatic crystallization was traditionally assumed to occur essentially instantaneously for the purposes of interpreting mineral geochronometers with low absolute time resolution for ancient samples it emerged relatively recently that magmatic crystallization can occur over extended durations this discovery arose from applying high spatial resolution accessory mineral dating techniques for uranium series isotopes to young volcanic and cognate plutonic rocks the emerging pattern from these studies is that individual crystals and crystal populations record crystallization episodes lasting from 1 000 to many hundreds of thousands of years accessory mineral dating of volcanic rocks and cognate plutonic xenoliths opens new research avenues for crystal age fingerprinting that correlates pyroclastic deposits lavas and plutonic rocks by using characteristic age dis

sequence sequence stratigraphy sea level changes and depositional systems in the cambro ordovician of the north china carbonate platform abstract the cambro ordovician strata in north china were deposited over a very extensive craton extending some 1500 km east west and 1000 km north south the dominantly shallow water carbonate succession reaches up to 2000 m in thickness and two megasequences transgressive regressive cycles can be distinguished lower cambrian through lower ordovician strata and middle through upper ordovician strata separated by a major palaeokarst the first megasequence consists of nine sequences which are generally 50 150 m in thickness the lower cambrian sediments consist of phosphorites and phosphatic sandstones deposited during the flooding of the craton carbonates mudrocks and evaporites were deposited in the early cambrian under an arid climate laying the foundation for the subsequent long period of shallow water carbonate deposition which lasted some 70 m y the middle and lower upper cambrian sequences consist predominantly of mudrocks and storm deposits tempestites in the lower part and oolitic grainstones and tidal flat lime mudstones in the upper part these represent outer mid and mid inner ramp depositional systems respectively of the transgressive and highstand systems tracts these sequences have strong similarities with the grand cycles in the cambro ordovician successions of north america in the upper cambrian there is a distinctive unit of glauconitic purple red mudstone several metres thick which is interpreted as the deposits of the maximum flooding of the first megasequence in the upper cambrian there was a phase of tilting of the north china carbonate platform to the north and storm deposits especially intraclastic conglomerates and hummocky cross stratified grainstones packstones were very common at this time also common in upper middle and lower upper cambrian strata are stromatolitic thrombolitic bioherms several metres in diameter the upper upper cambrian through lower ordovician strata are dominantly fine grained limestones and dolomites deposited in shallow subtidal and inter to supra tidal environments on a low energy epeiric sea platform this part of the succession is the regressive part of the first megasequence so that overall the platform shows an evolution from platform initiation to platform foundation to a ramp depositional system and then an extensive epeiric platform on a small scale the succession is composed of metre scale shallowing upward cycles parasequences arranged into cycle sets of 10 30 m thick the middle upper ordovician megasequence consists mostly of shallow water carbonates with several thick evaporite units minor palaeokarsts and palaeosoils separate the sequences which are composed of metre scale cycles regional uplift affected the north china platform in the ordovician and sedimentation did not resume until the carboniferous there is a good correlation of the two transgressive regressive megasequences described here with the global 2nd order relative sea level curve for the cambro ordovician

months between rejuvenation and volcanic eruption at yellowstone caldera wyoming rejuvenation of previously intruded silicic magma is an important process leading to effusive rhyolite which is the most common product of volcanism at calderas with protracted histories of eruption and unrest such as yellowstone caldera wyoming long valley caldera california and valles caldera new mexico in the united states although orders of magnitude smaller in volume than rare caldera forming supereruptions these relatively frequent effusions of rhyolite are comparable to the largest eruptions of the 20th century and pose a considerable volcanic hazard however the physical pathway from rejuvenation to eruption of silicic magma is unclear particularly because the time between reheating of a subvolcanic intrusion and eruption is poorly quantified this study uses nanometer scale trace element diffusion in sanidine crystals to reveal that rejuvenation of a near solidus or subsolidus silicic intrusion occurred in 10 mo or less following a protracted period 220 k y of volcanic repose and resulted in effusion of 3 km3 of high silica rhyolite lava at the onset of yellowstone s last volcanic interval the future renewal of effusive silicic volcanism at yellowstone will likely require a comparable energetic intrusion of magma that remelts the shallow subvolcanic reservoir and generates eruptible rhyolite on month to annual time scales

protracted near solidus storage and pre eruptive rejuvenation of large magma reservoirs building super eruptive magma reservoirs in the cold upper parts of earth s crust requires a significant influx of magma over an extended period sufficient to allow the magma to accumulate differentiate and periodically erupt some models favour magma storage in a cold non eruptible state requiring extensive reactivation of the reservoirs before eruption whereas others suggest storage at higher temperature and lower crystallinity implying that magma in such reservoirs is readily eruptible consequently constraining volcanic hazards requires observations directly linking magma residence timescales to the thermal state and crystallinity of storage here we simultaneously determine crystallization temperatures and ages of magmatic crystals of zircon and titanite in the 900 km3 kneeling nun tuff new mexico usa which allows us to place tight constraints on the long term thermal evolution of the magma reservoir we show that zircon and titanite crystals record more than 600 000 years of magma assembly and constrain the dominant storage conditions to low temperatures set between the granitic solidus 680 to 700 c and the temperature of the onset of titanite crystallization about 720 to 730 c we apply the zircon titanite systematics to a suite of other super eruptions and suggest that protracted low temperature storage culminating in late stage reheating is a widespread feature of large crystal rich eruptions super eruptions are fed by large magma reservoirs geochemical analyses of volcanic rocks erupted in new mexico suggest the magma was stored under cool conditions in the crust for 600 000 years before late stage heating triggered an eruption

open system dynamics and mixing in magma mushes magma in earth s crust is in a crystal rich mushy state yet must be fluidized before eruptions numerical simulations show that rapid injection of new magma into a reservoir creates a mixing bowl of fluid and crystals that are able to erupt

incremental heating of bishop tuff sanidine reveals preeruptive radiogenic ar and rapid remobilization from cold storage abstract accurate and precise ages of large silicic eruptions are critical to calibrating the geologic timescale and gauging the tempo of changes in climate biologic evolution and magmatic processes throughout earth history the conventional approach to dating these eruptive products using the 40ar 39ar method is to fuse dozens of individual feldspar crystals however dispersion of fusion dates is common and interpretation is complicated by increasingly precise data obtained via multicollector mass spectrometry incremental heating of 49 individual bishop tuff bt sanidine crystals produces 40ar 39ar dates with reduced dispersion yet we find a 16 ky range of plateau dates that is not attributable to excess ar we interpret this dispersion to reflect cooling of the magma reservoir margins below 475 c accumulation of radiogenic ar and rapid preeruption remobilization accordingly these data elucidate the recycling of subsolidus material into voluminous rhyolite magma reservoirs and the effect of preeruptive magmatic processes on the 40ar 39ar system the youngest sanidine dates likely the most representative of the bt eruption age yield a weighted mean of 764 8 0 3 0 6 ka 2 analytical full uncertainty indicating eruption only 7 ky following the matuyama brunhes magnetic polarity reversal single crystal incremental heating provides leverage with which to interpret complex populations of 40ar 39ar sanidine and u pb zircon dates and a substantially improved capability to resolve the timing and causal relationship of events in the geologic record

dynamic plumbing system beneath volcanoes revealed by kinetic modeling and the connection to monitoring data an example from mt etna abstract our ability to monitor volcanoes using seismic signals ground deformation gas fluxes or other ground and satellite based observations as well as our understanding of melt reservoirs that feed eruptions have evolved tremendously in recent years the complex plumbing systems that are thought to feed eruptions are however difficult to relate to the monitoring signals here we show that the record preserved in compositional zoning of erupted minerals may be used to reconstruct sections of the plumbing system kinetic modeling of such zoning can yield information on the residence time of magma in different segments of the plumbing systems this allows a more nuanced evaluation of the link between observed monitoring signals or eruption styles and the magmatic processes and movement of batches of melts at depth the approach is illustrated through a study of the compositional zoning recorded in olivine crystals from the 1991 1993 se flank eruption products of mt etna sicily the zoning patterns in crystals reveal that the plumbing system of the volcano consisted of at least three different magmatic environments between which magma was transported and mixed in the year or two preceding the start of eruption quantification of this history indicates that two main pathways of melt migration and three timescales dominated the dynamics of the system combination of this information with the timing of observation of various monitoring signals allows a reconstruction of the dynamic evolution of this section of the plumbing system during the early stages of the 1991 1993 eruption it is seen for example how the migration of melt through the same sections of the plumbing system can cause pre eruptive triggering enhance strombolian activity and through the ensuing eruption cleanse and flush the plumbing system different kinds of mixing occur simultaneously at different sections of the plumbing system on different timescales a few days up to two years

magmatic perturbations in the okataina volcanic complex new zealand at thousand year timescales recorded in single zircon crystals abstract using single crystals to trace the chemical evolution of a magmatic system has long been a goal of igneous petrology crystals utilized for in situ dating hold great potential to link compositional and temporal information to better understand the evolution of a magmatic system if micron scale zoning of trace elements within a single zircon can be directly associated with volcanic events in magmatic systems then new insights into long term maintenance and storage of eruptible magma can be unlocked this study presents new data that directly links the geochemical history recorded in individual zircon crystals with over 50 000 yrs of changing physical and chemical conditions within a magma reservoir trace elements hf and y in zircon have not diffusively equilibrated with their host melt so that they store information about the melt when that zone crystallized thus different stages of growth can be associated with discrete time periods in the magmatic system zircon from the two most recent rhyolite eruptions kaharoa and whakatane within the okataina volcanic complex ovc new zealand have both isotopic age and trace element signatures that correspond with distinct changes in the temperature and phase assemblage of pulses of erupted magma within the caldera system this discrete change is associated with caldera collapse and reflects a change from cold wet source rhyolite to a relatively hotter and drier source rhyolite and back the kaharoa and whakatane eruptions are separated by 4000 yrs and 15 km distance yet the zircon populations record the same distinct thermal and chemical pulse that occurred following caldera collapse suggesting an interconnected magmatic system that houses at least small volumes of rhyolite melt for timescales of 10 3 to 10 5 yrs that is periodically extracted during eruption

the upper mississippian bluefield formation in the central appalachian basin a hierarchical sequence stratigraphic record of a greenhouse to icehouse transition abstract the upper mississippian chesterian bluefield formation is the basal unit of the predominantly siliciclastic mauch chunk group in the appalachian basin this formation developed in a northeast southwest oriented foreland trough fronting the alleghanian highlands to the southeast regional cross sections and isopach maps of the bluefield formation in southeastern west virginia southwestern virginia and southeastern kentucky define a depocenter in the southeastern part of the study area and a paleovalley system along the basin margin to the northwest at most localities facies that make up the bluefield formation are stacked into 1 15 m thick upward shallowing parasequences each of which is capped by a flooding surface these parasequences are stacked into four regionally correlatable depositional sequences on the margins of the depocenter incised valleys and fewer meter scale parasequences characterize the depositional sequences stacking of parasequences into sequences reflects a hierarchy of greenhouse type fifth order and icehouse type fourth order sea level cycles superimposed on a differential subsidence history related to early alleghanian thrust loading the bluefield depocenter experienced greater total accommodation which prevented incision during lowstands instead lowstands are typified by preservation of fifth order coal bearing parasequences in the depocenter basin margin areas experienced less total accommodation which resulted in development of fourth order lowstand valleys and erosion of parasequences this study demonstrates that both tectonic and eustatic forcing mechanisms controlled stratigraphic evolution of the bluefield formation

relationship between plagioclase crystallization and cooling rate in basaltic melts rock textures commonly preserve a record of the near surface crystallization history of volcanic rocks under conditions of simple cooling without convection or mixing textures will reflect sample cooling rate the temperature at which crystallization was initiated and the distribution of mineral phase precipitation across the crystallization interval compilation of plagioclase size and number density data on natural dike sill and lava lake and experimental samples suggests that 1 growth and nucleation rates of plagioclase in natural basaltic samples are a predictable function of cooling rate and 2 the observed crystallization rate dependence on cooling rate is similar to that observed in experiments initiated at subliquidus temperatures comparison of natural and experimental samples thus suggests that most basalts crystallize under conditions of heterogeneous nucleation with the number density of preexisting nucleii partially controlling textural responses to cooling rate changes time scales of crystallization and cooling in magmatic systems are intimately linked through a balance between heat removal from the system and heat evolved through crystallization evaluation of textural data in the context of recent numerical models of crystallization in simple one and two component systems provides new insight into regularities in the crystallization behavior of basaltic magmas for example the rate of change in crystal size and number density as dictated by mass balance has been used as a measure of the relative importance of time scales of crystallization and cooling in numerical models of crystallizing systems in natural samples plagioclase size scales with the length scale of cooling such that a logarithmic plot of grain size as a function of normalized distance across the dike has a slope that appears approximately independent of dike width solidification time comparison with available textural data for other phenocryst phases suggests that the same may be true for pyroxene and magnetite crystallization with each phase having a characteristic slope probably controlled by the thermodynamic properties of the crystallizing phase measured crystal size distributions are unimodal and show maximum frequencies in the smaller size classes distributions broaden and the grain size at peak frequency increases with increasing crystallization times decreasing cooling rates in contrast partially crystallized makaopuhi lava lake samples have crystal size distributions that decrease exponentially with increasing crystal size measured size distributions in dikes can be explained by late stage modification of makaopuhi type distributions through loss of small crystals possibly the consequence of growth without nucleation finally this compilation of the textural response of basaltic magmas to changes in cooling rate suggests that empirical calibrations of crystallization rate dependence on cooling rate from natural samples provide a reasonable model for plagioclase crystallization in near surface basaltic systems predicted growth rates will be slow and relatively constant 10 10 10 11 cm s for crystallization times expected in most shallow volcanic systems 1000 years

changes in magma storage conditions following caldera collapse at okataina volcanic center new zealand large silicic volcanic centers produce both small rhyolitic eruptions and catastrophic caldera forming eruptions although changes in trace element and isotopic compositions within eruptions following caldera collapse have been observed at rhyolitic volcanic centers such as yellowstone and long valley much still remains unknown about the ways in which magma reservoirs are affected by caldera collapse we present 238u 230th age trace element and hf isotopic data from individual zircon crystals from four eruptions from the okataina volcanic center taupo volcanic zone new zealand in order to assess changes in trace element and isotopic composition of the reservoir following the 45 ka caldera forming rotoiti eruption our data indicate that 1 mixing of magmas derived from crustal melts and mantle melts takes place within the shallow reservoir 2 while the basic processes of melt generation likely did not change significantly between pre and post caldera rhyolites post caldera zircons show increased trace element and isotopic heterogeneity that suggests a decrease in the degree of interconnectedness of the liquid within the reservoir following collapse and 3 post caldera eruptions from different vents indicate different storage times of the amalgamated melt prior to eruption these data further suggest that the timescales needed to generate large volumes of eruptible melt may depend on the timescales needed to increase interconnectedness and achieve widespread homogenization throughout the reservoir

neoproterozoic chuar group 800 742 ma grand canyon a record of cyclic marine deposition during global cooling and supercontinent rifting abstract chuar group sediments were deposited in a marine cratonic basin synchronously with marine deposition in other basins of western north america and australia the top of the chuar group is 742 ma thus this succession offers a potentially important record of global climatic and tectonic changes during the mid neoproterozoic a critical time leading to possible global glaciation during supercontinent rifting chuar group cycles and sequences may record glacioeustatic fluctuations during the climatic transition into the sturtian ice age 750 700 ma as well as extension related to the dispersal of rodinia the mid neoproterozoic chuar group 1600 m thick is predominantly composed of mudrock with subordinate meter scale beds of dolomite and sandstone facies analysis leads to the interpretation of a wave and tidal influenced marine depositional system diagnostic marine features include 1 marine fossils and high local pyrite content in the mudrock facies 2 mudcracked mud draped symmetric ripples and reverse flow indicators in the sandstone facies 3 facies associations between all facies and 4 no unequivocal terrestrial deposits chuar facies stack into 320 dolomite and sandstone capped meter scale cycles 1 20 m thick and non cyclic intervals of uniform mudrock facies 20 150 m thick nearly all cycles have mudrock bases indicating subtidal water depths dolomite capped cycles shallow to peritidal environments peritidal cycles some indicating subaerial exposure of varying degrees exposure cycles sandstone capped cycles shallow to peritidal environments with no evidence of prolonged exposure peritidal cycles non cyclic intervals represent the deepest water depths 10s of meters peritidal cycles and non cyclic intervals dominate the lower and middle chuar group in the upper chuar group the percentage of exposure cycles increases as does the thickness of individual cycles and non cyclic intervals and the degree of subaerial exposure in the cycle caps correlation of cycles across 10 km shows that many cycles are laterally continuous and some vary in thickness some thickness changes are coincident with local and regional extensional structures these cycle trends reflect a resolvable mixture of tectonic and climatic controls cycles are interpreted to be high frequency and glacioeustatically controlled based on comparison of cycle character and thickness to phanerozoic examples and lateral continuity of many cycles respectively cycles in the lower and middle chuar group show characteristics suggestive of low amplitude sea level changes similar to meter scale cycles from global greenhouse climates in the phanerozoic upper chuar group cycles show characteristics suggestive of moderate amplitude sea level changes similar to phanerozoic greenhouse icehouse transition climates indicating an increase in continental ice volume variability in cycle thickness and lateral pinching of some cycle caps is controlled by variable tectonic subsidence evidenced by thickening trends coincident with active rift related structures and also by variability in sediment supply the presence of dolomite caps in this otherwise siliciclastic succession is interpreted to be due largely to rapid changes in climate related to short term glacioeustatically controlled sea level changes four crude lithostratigraphic sequences 150 775 m thick are defined based on dolomite poor to dolomite rich stratigraphic intervals long term changes in cycle cap lithology may be driven by long term changes in climate similar to short term glacioeustatic controls on meter scale cycle cap lithology large scale thickness variability in these sequences is due to local differential tectonic subsidence

crustal forensics in arc magmas abstract the geochemical characteristics of continental crust are present in nearly all arc magmas these characteristics may reflect a specific source process such as fluid fluxing common to both arc magmas and the continental crust and or may reflect the incorporation of continental crust into arc magmas either at source via subducted sediment or via contamination during differentiation resolving the relative mass contributions of juvenile mantle derived material versus that derived from pre existing crust of the upper plate and providing these estimates on an element by element basis is important because 1 we want to constrain crustal growth rates 2 we want to quantitatively track element cycling at convergent margins and 3 we want to determine the origin of economically important elements and compounds traditional geochemical approaches for determining the contributions of various components to arc magmas are particularly successful when applied on a comparative basis studies of suites from multiple magmatic systems along arcs for which differentiation effects can be individually constrained can be used to extrapolate to potential source compositions in the lesser antilles arc for example differentiation trends from individual volcanoes are consistent with open system evolution however such trends do not project back to a common primitive magma composition suggesting that differentiation modifies magmas that were derived from distinct mantle sources we propose that such approaches should now be complemented by petrographically constrained mineral scale isotope and trace element analysis to unravel the contributing components to arc magmas this innovative approach can 1 better constrain true end member compositions by returning wider ranges in geochemical compositions among constituent minerals than is found in whole rocks 2 better determine magmatic evolution processes from core rim isotopic or trace element profiles from the phases contained in magmas and 3 constrain rates of differentiation by applying diffusion controlled timescales to element profiles an example from nguaruhoe volcano new zealand underscores the importance of such a microsampling approach showing that mineral isotopic compositions encompass wide ranges that whole rock isotopic compositions are consequently simply element weighted averages of the heterogeneous crystal cargo and that open system evolution is proved by core rim variations in sr isotope ratios nguaruhoe is just one of many systems examined through microanalytical approaches the overwhelming conclusion of these studies is that crystal cargoes are not truly phenocrystic but are inherited from various sources the implication of this realization is that the interpretation of whole rock isotopic data including the currently popular u series needs careful evaluation in the context of petrographic observations

carbonate deposition and sequence stratigraphy of the terminal cambrian grand cycle in the southern appalachians u s a abstract the cessation of shale and carbonate deposition of the conasauga group grand cycles middle to upper cambrian and the establishment of the widespread peritidal carbonate deposition of the knox group upper cambrian to lower ordovician represent a prominent change in sedimentation along the early paleozoic passive continental margin in the southern appalachians to evaluate the causes for this change this study focuses on the maynardville formation which is the uppermost carbonate unit of the conasauga group the maynardville consists of 1 a lower subtidal facies succession which is underlain by the nolichucky shale and resembles the rest of the conasauga group carbonate deposits and 2 an upper peritidal facies succession which is conformably overlain by similar peritidal deposits of the copper ridge dolomite knox group deposition of shale and subtidal carbonate took place in deep ramp nolichucky to shallow ramp subtidal shoal and lagoonal settings lower maynardville the carbonate ramp was westward sloping toward the conasauga intrashelf shale basin to the east the ramp was linked to a broad semiarid carbonate tidal flat encompassing a variety of peritidal environments upper maynardville and copper ridge the maynardville is a shallowing upward succession that formed by carbonate platform aggradation and basinward progradation the transition between the maynardville and the copper ridge dolomite is within a conformable peritidal carbonate succession that contains common siliciclastic sand size detritus this interval is interpreted as a sequence boundary correlative with the craton wide late steptoean dresbachian franconian or sauk ii sauk iii unconformity the change from a conasauga to a knox depositional style may be related to distinct stages in passive margin evolution the end of grand cycle deposition in the early late cambrian is coincident with the cessation of tectonic activity along extensional features an intracratonic graben and other fault systems and marks the transition into a mature passive margin setting the mature margin was characterized by decreased rates of thermal subsidence which coupled with the infilling of the conasauga intrashelf basin favored shallow water carbonate deposition the final stabilization of the margin is reflected in the deposition of the thick peritidal carbonate strata of the knox group

preferential eruption of andesitic magmas through recharge filtering at subduction zones andesite lavas erupt in greater abundance than the individual magmas that mix to produce them textural and geochemical analyses of andesites from mount hood oregon reveal that injection and mixing of iron and magnesium rich magma in the magma chamber can initiate the volcanic eruption andesitic volcanic rocks are common in subduction zones and are argued to play an important role in the formation and evolution of the continental crust at convergent margins1 2 3 4 andesite formation is dominated by mixing between iron and magnesium rich mafic magmas and silica rich felsic magmas1 2 4 the abundance of andesites in many subduction zones suggests they erupt in preference to the magmas that mix to produce them4 however the reasons for this remain unclear here we use textural and geochemical analyses of andesites from mount hood oregon to show that eruptions are closely linked with episodes of mafic recharge the intrusion of mafic magma into a shallow felsic magma reservoir the felsic and mafic magmas involved rarely erupt by themselves probably because the former are too viscous and the latter too dense mafic recharge overcomes these barriers to eruption and as it also promotes efficient mixing results in preferential eruption of mixed andesitic magmas the abundance of andesites therefore relates to local crustal conditions and the ability of magmas to erupt we suggest that volcanoes such as mount hood that erupt homogeneous andesitic compositions through time are those that are the most reliant on mafic recharge to initiate eruptions

high resolution sequence stratigraphy of the upper ordovician montoya group southern new mexico and western texas outcrop analog of an unconventional chert and carbonate reservoir the upper ordovician montoya group crops out in southern new mexico and westernmost texas and records predominantly subtidal deposition on a gently dipping carbonate ramp that was subsequently almost entirely dolomitized the montoya group is a third order composite sequence composed of six regionally correlative shallowing upward third order depositional sequences m0 m5 sequence m0 has sandstone at its base that is overlain by skeletal packstone grainstone sequence m0 occurs only locally and was likely deposited in a topographic low formed during regional development of the unconformity following el paso group deposition sequence m1 marking the initial widespread transgression over the ellenburger unconformity consists of sandstone updip that passes downramp into skeletal packstone the highstand systems tract hst of m1 consists of a prograding skeletal grainstone that was subaerially exposed upramp sequence m2 which contains the second order maximum flooding surface has abundant subtidal cherty carbonate at its base which shallows upward into a widespread prograding coral packstone grainstone in the hst sequence m3 also contains abundant downramp chert that passes upramp into an aggrading crinoidal shoal and farther upramp into peritidal mudstone sequence m4 records an extensive basinward shift in facies as peritidal burrowed and cryptalgalaminated mudstone prograded over subtidal carbonate sequence m5 is only locally developed downramp and consists of crinoidal grainstone with abundant evidence of subaerial exposure a regional unconformity separates the montoya group from the silurian fusselman dolostone or younger units parasequences meter scale cycles recording low to moderate amplitude relative sea level fluctuations are ubiquituous features at individual outcrops but are difficult to correlate regionally the abundance of syn or early depositional chert in the subtidal facies indicates that the montoya group was deposited within a region of strong regional upwelling along southern laurentia this early formed chert was the reservoir facies in a successful upper ordovician gas play in ward and reeves counties texas

diffusion in solid silicates a tool to track timescales of processes comes of age understanding how processes occurring on a wide range of temporal and spatial scales combine to produce a stable dynamic earth is a major goal of the earth scientist determining durations of processes is a key step toward attaining that goal records of incomplete diffusive equilibration preserved in minerals are uniquely suited for the purpose of unraveling timescales of a variety of processes compositional zoning in minerals is like the tracks of a cd that can be decoded with suitable technology this review discusses the causes for the limited use of this tool until recently and how these hindrances are being overcome examples are presented to illustrate that diffusion modeling can clock processes that last from only a few days to those that last over tens of millions of years recorded in rocks that range in age from current volcanic eruptions to condensates from the early solar nebula

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

on the longevity of large upper crustal silicic magma reservoirs understanding the processes involved in the formation and maturation of upper crustal magma reservoirs ultimately sourcing the largest volcanic eruptions on earth is one of the most fundamental aspects of volcanology while such reservoirs are known to assemble incrementally over extended periods of time debate persists regarding the time scales of melt preservation in the cold upper crust if rapid cooling individually freezes incoming replenishing intrusions accumulations of eruptible magma are impossible precluding the construction of voluminous volcanic reservoirs for all but the highest magma emplacement rates recent numerical thermal models have been used to assess the viability of upper crustal silicic magma survival and have suggested that supervolcanic reservoirs must form on geologically short time scales with anomalously high injection rates and subsist only ephemerally making their long term evolution less predictable motivated by geological observations suggesting the contrary we have improved upon these models by incorporating two fundamental features of natural systems not previously considered 1 a nonlinear crystallization temperature relationship adapted for upper crustal silicic magmas and 2 a temperature dependent thermal conductivity we demonstrate that the incorporation of both of these properties can allow an upper crustal reservoir to remain above its solidus for hundreds of thousands of years when fed by magma fluxes typical of large magmatic provinces while the crystallization temperature path plays the most significant role in maintaining a large pool of eruptible magma the incorporation of temperature dependent thermal properties significantly extends the lifetime of such reservoirs furthermore while deeper emplacement levels e g 10 km depth can both extend magma survival and increase melt availability we show that a 5 km depth can also provide an adequate magma storage environment these results provide strong support for long lived upper crustal mushes as a staging ground for accumulation of highly eruptible crystal poor silicic magmas and further assert the evolutionary link between volcanic and plutonic systems

evidence for a persistent magma reservoir with large melt content beneath an apparently extinct volcano abstract most active volcanoes display eruption frequencies of 10 1000s years but a class of volcanic systems has extremely long repose time 10 s kyr and are deemed as extinct yet some reawaken posing a particular threat because little is known about the way they endure and stir back to life reawakening primarily depends on the nature of the subvolcanic magma reservoir especially the presence and distribution of melt here we integrate petrology thermobarometry thermomechanical models geophysics and in situ electrical conductivity measurements to show that the magma storage beneath ciomadul a seemingly inactive volcano in eastern central europe that last erupted 30 ka may still hold 20 to 58 km3 of water rich silicic melt constituting up to 20 58 in parts of the upper crustal crystal mush body such a melt volume exceeds the volume of erupted lava over the entire history of the volcano this illustrates the important longevity of a magmatic reservoir at temperature above the solidus which implies that there is still a potential for rapid mush rejuvenation that a seemingly dead volcano like ciomadul is actually capable of erupting in the future calls for renewed attention to inactive volcanoes worldwide and perhaps for a redefinition of their activity inactivity status

evaluation of the effects of 3d diffusion crystal geometry and initial conditions on retrieved time scales from fe mg zoning in natural oriented orthopyroxene crystals abstract volcano petrologists and geochemists increasingly use time scale determinations of magmatic processes from modeling the chemical zoning patterns in crystals most determinations are done using one dimensional traverses across a two dimensional crystal section however crystals are three dimensional objects with complex shapes and diffusion and re equilibration occurs in multiple dimensions given that we can mainly study the crystals in two dimensional petrographic thin sections the determined time scales could be in error if multiple dimensional and geometrical effects are not identified and accounted for here we report the results of a numerical study where we investigate the role of multiple dimensions geometry and initial conditions of fe mg diffusion in an orthopyroxene crystal with the view towards proper determinations of time scales from modeling natural crystals we found that merging diffusion fronts i e diffusion from multiple directions causes additional diffusion that has the greatest influence close to the crystal s corners i e where two crystal faces meet and with longer times the affected area widens we also found that the one dimensional traverses that can lead to the most accurate calculated time scales from natural crystals are along the b crystallographic axis on the ab plane when model inputs concentration and zoning geometry are taken as measured rather than inferred from other observations more specifically accurate time scales are obtained if the compositional traverses are highly symmetrical and contain a concentration plateau measured through the crystal center on the other hand for two dimensional models the ab and ac planes are better suited if the initial pre diffusion concentration and zoning geometry inputs are known or can be estimated although these are a priory unknown and thus may be difficult to use in practical terms we also found that under certain conditions a combined one dimensional and two dimensional model performed on the ab section can reveal the initial pre diffusional concentration and thus offer a unique opportunity to recover lost petrologic information the influence of three dimensional diffusion on the one dimensional two dimensional model estimates is the combined result of the crystal shape in particular the presence of facets and somewhat of the aspect ratio our study focuses on fe mg in orthopyroxene but many of the effects we report are also applicable to other minerals and elements

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

chronometry and speedometry of magmatic processes using chemical diffusion in olivine plagioclase and pyroxenes the magmatic processes that fuel volcanism crustal growth ore formation and discharge of volcanic gases and aerosols to the atmosphere occur across a range of timescales from millions of years to just a few seconds for example the production of new oceanic crust at mid ocean ridges is a near continuous process that can operate in any one ocean basin on timescales of more than 100 m y however the driving force for such processes is the spreading of the ocean plates that happens on a cm yr timescale at the other end of the spectrum explosive volcanic eruptions involve the ascent and fragmentation of magma at velocities of the order of 100 m s such that the journey from a magma chamber to an ash cloud may take place in a matter of minutes in this case the driving force is the rapid expansion of magmatic gas in response to changes in pressure at intermediate timescales magmatic processes may give rise to hydrothermal ore deposits on timescales of less than a million years for an individual deposit while growth of giant granite batholiths may require piecemeal assembly of magma batches on timescales of a few million years although each of these processes has a characteristic time averaged timescale on which it operates this is typically the end result of one or more natural processes that operate on much shorter timescales for example mid ocean ridges do not extrude magma continuously onto the ocean floor mineralising fluids do not discharge continuously through the shallow crust and granitic magmas do not dribble continuously into evolving batholithic chambers in some cases it is the long term timescales that are important for example the spreading rate of ocean basins in others it is the short term timescales that are important for example the episodic growth of lava domes at active volcanoes although

time scales of magmatic processes from modeling the zoning patterns of crystals the advent of polarized light microscopy in the middle of the 19th century allowed mineralogists and petrologists interested in igneous rocks to recognize the widespread occurrence of fine scale heterogeneities in the optical properties of minerals e g see young 2003 for details the interpretation of mineral zoning patterns as archives of magmatic processes has been with us for some time e g larsen et al 1938 tomkeieff 1939 the development of the electron microprobe in the 1960 s allowed mineral zoning profiles to be quantitatively analyzed and modeled e g bottinga et al 1966 moore and evans 1967 enhanced textural observations permitted recognition of many kinds of detailed structures during the growth and dissolution of magmatic minerals fig 1 e g anderson 1983 pearce and kolisnik 1990 and these processes were also explored using experimental and numerical models e g albarede and bottinga 1972 lofgren 1972 kirkpatrick et al 1976 loomis 1982 major element zoning patterns are routinely measured and with the arrival of the ion microprobe the identification of heterogeneous distribution of trace elements opened the window for more realistic and sophisticated scenarios and models fig 1 e g kohn et al 1989 blundy and shimizu 1991 singer et al 1995 we now measure abundances of naturally occurring isotopes at the scale of tens of micrometers e g davidson et al 2007a ramos and tepley 2008 and this allows in situ dating of crystals e g cooper and reid 2008 figure 1 a nomarski dic image of a plagioclase crystal from a gabbroic xenolith of volcan san pedro costa et al 2002 the crystal shows a well defined core and a rim separated by an oscillatory zoned interval ion microprobe analysis pits and the trace of the electron microprobe traverse between the pits are evident b major

ca isotopes record rapid crystal growth in volcanic and subvolcanic systems kinetic calcium isotope effects can be used as growth rate proxies for volcanic and subvolcanic minerals here we analyze ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects 2 can occur during magmatic plagioclase crystallization experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase ca diffusivity r d plagioclase phenocrysts from the 1915 mount lassen rhyodacite eruption the 650 y old deadman creek dome eruption and several mafic subvolcanic orbicules and plagioclase comb layers from northern california have disequilibrium ca isotopic compositions that suggest rapid crystal growth rates 1 cm y to 15 cm y the ca isotope results combined with complementary crystal size distribution analyses suggest that magmatic rejuvenation and eruption events as reflected in crystal growth times can be as short as 10 3 y although mafic systems are predicted to have shorter magmatic rejuvenation periods we find similarly short timescales in both mafic and silicic systems these results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption by focusing on a common mineral such as plagioclase this approach can be applied across all major magmatic compositions suggesting that ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions

improved and extended tide gauge records for the british isles leading to more consistent estimates of sea level rise and acceleration since 1958 abstract this paper describes methods of obtaining improved estimates of long term sea level trends for the british isles this is achieved by lengthening the sea level records where possible then removing known sources of variability and then further adjusting for datum errors that are revealed by the previous processes after verification using metadata from archived sources local sea level variability is accounted for using a tide and surge model far field variability is accounted for using a common mode this combination reduces the residual variability seen at tide gauges around the coast of the british isles to the point that a number of previously unrecognised steps in individual records become apparent permitting a higher level of quality control to be applied a comprehensive data archaeology exercise was carried out which showed that these step like errors are mostly coincident with recorded site specific changes in instrumentation and that in many cases the periodic tide gauge calibration records can be used to quantify these steps a smaller number of steps are confirmed by buddy checking against neighbouring tide gauges after accounting for the observed steps using levelling information where possible and an empirical fit otherwise the records become significantly more consistent the steps are not found to make a large difference to the trend and acceleration observed in uk sea level overall but their correction results in much more consistent estimates of first order sea level rise and second order sea level acceleration trends over this 60 year period we find a mean rate of sea level rise of 2 39 0 27 mm yr 1 and an acceleration of 0 058 0 030 mm yr 2 between jan 1958 and dec 2018 the cleaner dataset also permits us to show more clearly that the variability other than that derived from local meteorology is indeed consistent around the uk and relates to sea level changes along the eastern boundary of the north atlantic

some remarks on u th mineral ages from igneous rocks with prolonged crystallisation histories abstract mineral isochron dating is a frequently used geochronological tool one of its assumptions is that the minerals grow over a time period that is small compared to the half life of the radiogenic isotope system used in recent years increasing analytical precision has promoted the use of the short lived u series isotope system in order to date young crystallisation events three whole rock zircon u th isochrons from the 26 5 ka oruanui eruption in the taupo volcanic zone new zealand yield pre eruptive model ages of 5 5 0 8 ka 9 7 1 7 ka and 12 3 0 8 ka for the sub 63 m 63 125 m and 125 250 m zircon size fractions respectively this suggests that in this case the assumption of instantaneous crystal growth breaks down instead the u th data may be explained by continuous zircon growth over a period of 90 ka however cathodoluminescence shows that crystals are typically composed of an euhedral core surrounded by a sector zoned euhedral rim and the u th data can also be modelled by mixing an older 27 ka model age population of zircon crystals with a young zircon rim that formed shortly prior to eruption of the oruanui rhyolite this indicates that detailed petrographic studies are critical for deciphering the histories of prolonged crystallisation in the magmatic environment it is concluded that conventional u series mineral isochrons may underestimate the age of the onset of crystallisation by more than an order of magnitude in future microanalytical techniques will lead to significant advances in the understanding of crystallisation processes and timescales