constraints on the nature and evolution of the magma plumbing system of mt etna volcano 1991 2008 from a combined thermodynamic and kinetic modelling of the compositional record of minerals maren kahl sumit chakraborty massimo pompilio and fidel costa school of earth and environment university of leeds leeds ls2 9jt uk institut fur geologie mineralogie und geophysik ruhr universit at bochum bochum 44780 germany istituto nazionale di geofisica e vulcanologia sezione di pisa pisa 56126 italy and earth observatory of singapore nanyang technological university singapore 639798 singapore

diffusion of ti and some divalent cations in olivine as a function of temperature oxygen fugacity chemical potentials and crystal orientation the diffusion of titanium along with ni co and mn in pure synthetic forsterite has been studied as a function of temperature oxygen fugacity crystallographic orientation and chemical potentials in the four component system mgo sio2 tio2 tio1 5 in over 100 different experimental conditions no ti diffusion profiles with the classical shape of the error function were observed instead the profiles vary between stepped at high fo 2 probably owing to diffusion on octahedral sites and trapping in tetrahedral sites to hockey stick shapes at low fo 2 owing to concentration dependent diffusion the profile shapes vary systematically between these end members according to oxygen fugacity these profile shapes are also reproduced in experiments using natural san carlos olivine the change in profile shape is interpreted to be a function of valence state change from ti4 to ti3 shown by a sigmoidal log fo 2 diffusivity relationship to distinguish between ti4 to ti3 in forsterite a diffusion profile was also investigated using hydroxylation spectroscopy whereby a crystal from a diffusion experiment was hydroxylated by annealing in an h2o rich fluid at moderate pressure and temperature the point defects associated with the added structural oh were then determined by infrared spectroscopy providing evidence for the presence of ti4 to ti3 at intermediate oxygen fugacity the transition from ti4 to ti3 occurs at considerably higher fo 2 in these diffusion experiments than in equilibrium experiments in similar systems titanium diffusion qualified using a mobility parameter m is fastest along the c axis at high activity of silica low oxygen fugacity and high temperature the rate of ti diffusion is broadly similar to those of mn ni and co and closer to published rates ofmg self diffusion in olivine than si self diffusion the observed ti4 to ti3 diffusion occurs on the m sites from statistical examination of the large mn ni and co diffusivity dataset we determine that there is a 10 2 3 dependence of diffusion on asio 2 the cations diffuse more rapidly at high asio 2 in addition diffusivity has a 10 1 8 dependence on fo 2 suggested to be the result of increased concentration of loosely bound ti3 vacancy pairs which enhance the mobility of other cations this behaviour is likely to be present in natural systems where trivalent e g fe3 al3 cr3 and divalent cations diffuse together consideration should be given to diffusive interference by highly charged fast moving cations when extracting time scales from frozen diffusion profiles

fault patterns within sediment layers overlying rising salt structures a numerical modelling approach abstract faulting of sediments overlying structures caused by salt movement is a widespread phenomenon and important for hydrocarbon production because the faults facilitate hydrocarbon migration to and from the reservoir or may compartmentalize the reservoir a major problem in mapping the intensity of deformation is that many faults and fractures are below the seismic resolution and that the seismic data may appear dimmed and distorted owing to escaping gas another major problem is that the salt displacement causing the deformation is often only reflected in the overlying fracture patterns and hence not directly observable this study uses a numerical spring slider model including vertical as well as horizontal movements of the substrata the salt the model demonstrates how the fracture patterns in the sediments above salt structures are controlled by the salt kinematics the modelling experiments show that concentric faults develop when only vertical salt movements are involved whereas radial faulting dominates when even small levels of horizontal movements are included a case study from the southern danish central graben illustrates that the fault structures in the cover sediments characterizes the salt movement the analysis and prediction of the systematics of these small scale faults which are too small to be recognized on seismic data is important when the fluid migration and hence hydrocarbon production from fields related to salt structures is to be optimized

mixing in mantle magma reservoirs prior to and during the 2011 2012 eruption at el hierro canary islands understanding magmatic systems feeding volcanoes is critical for accurate interpretation of monitoring data and ultimately eruption forecasting following 3 months of precursory unrest the first historical eruption at el hierro canary islands took place 2 km offshore from october 2011 to march 2012 our detailed petrological analysis of lava samples reveals that at least two distinct magmas initially supplied from reservoirs in the mantle underwent hybridization at 15 25 km depth i e also largely within the upper mantle beneath el hierro diffusion chronometry applied to zoned olivine crystals indicates that magma mixing began during the period of preeruptive seismicity and continued for weeks after the eruption onset our data also capture a magma stagnation level at 10 15 km depth in the lower crust consistent with lateral propagation of an intrusion over substantial distances before rapid magma transit to the seafloor the remarkable spatial and temporal correlation of petrological and geophysical data at el hierro suggests that the observed seismicity records magma mixing and forceful intrusion as well as subsequent reservoir dynamics these results demonstrate that eruptions at el hierro are controlled principally by deep seated processes with little influence from shallow crustal levels and have important implications for monitoring of renewed unrest at long dormant volcanoes

crystallization history of enriched shergottites from fe and mg isotope fractionation in olivine megacrysts abstract martian meteorites are the only samples available from the surface of mars among them olivine phyric shergottites are basalts containing large zoned olivine crystals with highly magnesian cores fo 70 85 and rims richer in fe fo 45 60 the northwest africa 1068 meteorite is one of the most primitive enriched shergottites high initial 87 sr 86 sr and low initial e 143 nd it contains olivine crystals as magnesian as fo 77 and is a major source of information to constrain the composition of the parental melt the composition and depth of the mantle source and the cooling and crystallization history of one of the younger magmatic events on mars 180 ma in this study fe mg isotope profiles analyzed in situ by femtosecond laser ablation mc icp ms are combined with compositional profiles of major and trace elements in olivine megacrysts the cores of olivine megacrysts are enriched in light fe isotopes 56 fe irmm 14 0 6 to 0 9 and heavy mg isotopes 26 mg dsm 3 0 0 2 relative to megacryst rims and to the bulk martian isotopic composition 56 fe 0 0 05 26 mg 0 27 0 04 the flat forsterite profiles of megacryst cores associated with anti correlated fractionation of fe mg isotopes indicate that these elements have been rehomogenized by diffusion at high temperature we present a 1 d model of simultaneous diffusion and crystal growth that reproduces the observed element and isotope profiles the simulation results suggest that the cooling rate during megacryst core crystallization was slow 43 21 c year and consistent with pooling in a deep crustal magma chamber the megacryst rims then crystallized 1 2 orders of magnitude faster during magma transport toward the shallower site of final emplacement megacryst cores had a forsterite content 3 2 1 5 mol higher than their current composition and some were in equilibrium with the whole rock composition of nwa 1068 fo 80 1 5 nwa 1068 composition is thus close to a primary melt i e in equilibrium with the mantle from which other enriched shergottites derived

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

detailed stratigraphic subdivision and regional correlation of the southern danish triassic succession this paper provides a regional log based lithostratigraphic correlation of the danish triassic deposits with deposits known from the southern north sea basin including the northwest german and dutch onshore areas a new lithostratigraphic nomenclature mainly adapted from the dutch nomenclature is suggested for the danish area south of the ringkobing fyn high replacing the previously used nomenclature the new nomenclature comprises the lower triassic bunter shale and bunter sandstone formations the lower to middle triassic rot and muschelkalk formations and the uppermost middle triassic and upper triassic keuper and sleen formations in total 22 members are also defined from the southern north sea into the southern danish area this main marine southern facies province is separated from a continental northern facies province by the northern flank of the ringkobing fyn high trend units of the southern province only crossed the central and western part of the ringkobing fyn high during the rot and the muschelkalk transgressions whereas the basin north of the eastern part of the high was influenced by the southern facies province during the early to early late triassic

diagenetic effects on porosity permeability relationships in red beds of the lower triassic bunter sandstone formation in the north german basin abstract carbonate and anhydrite cement clay clasts and inter granular clay are the main components that reduce reservoir quality in the studied bunter sandstone formation the impacts of these parameters on porosity and permeability are determined by combining petrographic mineral quantification with conventional core analysis of samples from the danish part of the north german basin the depositional environments are considered because they largely control the distribution of cements clays and grain sizes the lateral variability of depositional environments is defined by the position in the basin and the proximity to the source areas the stratigraphic distribution of depositional environments is related both to local topography and to climate because high aridity promoted aeolian deposition the bunter sandstone formation has high porosity and permeability in most of the sandstone intervals in the northern north german basin the reservoir quality is good as long as the cements and clays are present as confined bodies that leave the remaining pore spaces available for flow in contrast inter granular clay and pervasive cementation hinder virtually all flow through the sandstone the ephemeral fluvial deposits have an average porosity and permeability of 20 3 and 810 md respectively and the values are 24 6 and 807 md for the aeolian sandstones excluding the unconsolidated aeolian sands which presumably have higher porosity and permeability the aeolian sandstones of the volpriehausen member have very good reservoir quality since they have a thickness of about 25 m are laterally continuous are largely clay free and the cement occurs in small amounts the sandstones of the solling member consist mainly of ephemeral fluvial deposits which generally have good reservoir quality however some intervals have high contents of inter granular clays or pervasive carbonate anhydrite or halite cement and these components reduce the permeability significantly the lateral distribution of the ephemeral fluvial sandstones is variable and therefore difficult to predict when planning a geothermal exploration well thus the volpriehausen member is the preferred target

imaging crustal structure in south central costa rica with receiver functions an array of broadband seismometers transecting the talamanca range in southern costa rica was operated from 2005 until 2007 in combination with data from a short period network near quepos in central costa rica this data is analyzed by the receiver function method to image the crustal structure in south central costa rica two strong positive signals are seen in the migrated images interpreted as the moho at around 35 km depth and an intra crustal discontinuity 15 km depth a relatively flat crustal and moho interface underneath the north east flank of the talamanca range can be followed for a lateral distance of about 50 km parallel to the trench with only slight changes in the overall geometry closer to the coast the topography of the discontinuities shows several features most notably a deeper moho underneath the talamanca mountain range and volcanic arc under the highest part of the mountain ranges the moho reaches a depth of about 50 km which indicates that the mountain ranges are approximately isostatically compensated local deviations from the crustal thickness expected for isostatic equilibrium occur under the active volcanic arc and in south costa rica in the transition region between the active volcanic arc and the talamanca range both the moho and intracrustal discontinuity appear distorted possibly related to the southern edge of the active volcanic zone and deformation within the southern part of the central costa rica deformed belt near the volcanoes irazu and turrialba a shallow converter occurs correlating with a low velocity low density body seen in tomography and gravimetry applying a grid search for the crustal interface depth and vp vs ratio cannot constrain vp vs values well but points to generally low values 1 7 in the upper crust this is consistent with quartz rich rocks forming the mountain range

opaque minerals as keys for distinguishing oxidising and reducing diagenetic conditions in the lower triassic bunter sandstone north german basin abstract the diagenetic evolution in red and white drab parts of the bunter sandstone from outcrops and wells in the north german basin was unraveled by a detailed petrographical mineralogical and chemical study the diagenetic sequences for the red and white drab parts differ in the degree of alteration of iron bearing detrital minerals and in the authigenic opaque minerals in the white drab parts one typically sees reduction of red mica dissolution of hematite and magnetite and alteration of ilmenite and titanomagnetite to leucoxene in contrast the red parts commonly display oxidation of glauconite red zonation in ooids hematisation of magnetite biotite and magnetite host in titanomagnetite and leucoxene replacement of the ilmenite lamellae in titanomagnetite the red colour of the red bed host is due to red coatings of goethite needles and or hematite needles goethite needles precipitated in the prevailing oxidising conditions present shortly after deposition whereas pseudomorphous replacement by hematite occurred during the burial process the white drab colour of the reduced areas is the original colour of the sediment the black core in reduction spots is due to mineralization uranium and vanadium minerals coffinite montroseite and v illite in reduction spots are located close to carbonate fragments which probably contained organic matter isolated reduction spots may have formed immediately after deposition inside these were clasts eroded from algal mats formed in the sabkha environment the copper minerals typically occur in areas with high porosity reflecting the importance of access to chloride rich brines which transported dissolved copper when these brines reached reducing environments chalcocite and chalcopyrite were precipitated possibly by replacement of pyrite in the red areas these saline brines may also have promoted the second stage alteration of ilmenite in which leucoxene the first stage alteration product was impregnated with iron oxide hydroxide needles this study emphasises the importance of opaque minerals especially fe ti oxides and authigenic opaques as diagnostic for the diagenetic environment of the bunter sandstone which can thus be divided into primary reduced primary oxidised secondary reduced and secondary oxidised diagenetic environments furthermore the influence of saline brines can be detected using the opaque mineral assemblage

olivine growth rates in a tholeiitic basalt an experimental study of melt inclusions in plagioclase abstract basaltic glass inclusions trapped in plagioclase phenocrysts an 84 are remnant of their parent magmatic liquid they can be used as natural reactors for the experimental investigation of olivine growth rate as a function of temperature the growth of one olivine nucleus can be observed at constant temperature supercooling from 15 to 150 c have been investigated growth habits vary from equant to feather in qualitative agreement with previous studies growth rates vary from 10 m s 1 to 6 10 7 m s 1 they vary with the direction the growth process planar or dendritic and the degree of supercooling chemical analysis of crystal overgrowth and the remaining liquid composition enables a mass balance calculation which confirms the rates determined optically the small number of results obtained so far does not permit to draw inferences on the growth mechanisms

pre eruptive storage evolution and ascent timescales of a high mg basaltic andesite in the southern cascade arc crustal storage and transit play a critical role in the compositional evolution of arc magmas however the enigmatic nature of lower crustal magma storage and early differentiation limit our understanding of the connections between the physical processes of subduction zones and the architecture of the arc crust we present new geochemical data and applications of existing barometric and chronometric tools to interrogate the mantle source compositions crustal storage depths and ascent timescales of a primitive high mg clinopyroxene bearing cinder cone the basaltic andesite of box canyon located in the vicinity of lassen volcanic national park ca in the southern cascades petrographic examination in addition to bulk and in situ geochemical analyses xrf la icp ms and epma of tephra and lava derived samples reveals co crystallization of clinopyroxene and olivine as phenocrysts and glomerocrysts with mg 80 and fo85 respectively phase equilibria experiments of analogous cascade arc magma compositions estimate crustal storage of the observed phase assemblage at pressures in the lower crust 700 mpa reverse zonation in olivine and clinopyroxene phenocryst interiors from core rim analytical profiles record a lower crustal mafic mixing event results from one dimensional multi elemental olivine and clinopyroxene diffusion models fit to these interior mixing zones provide an assessment of available trace element ti la yb ce and nd diffusion chronometers in clinopyroxene by considering multiple element profiles within two phases that experienced the same pre eruptive conditions while multi elemental and multi phase diffusion timescales span two to three orders of magnitude ni in olivine profiles provide the most robust estimate of 19 1 8 6 years from mixing to eruption our results provide new constraints on arc crustal differentiation processes indicate rapid crustal transit timescales in agreement with a growing database of diffusion based ascent timescales of basaltic magmas and demonstrate significant systematic deviation of diffusion timescales calculated from natural zonation of rare earth elements in clinopyroxene and ti in clinopyroxene and olivine

frozen melt rock reaction in a peridotite xenolith from sub arc mantle recorded by diffusion of trace elements and water in olivine this research was supported by natural environment research council algorithm doctoral studentship nerc 10 000497448 to pete tollan

permian and triassic rifting in northwest europe the permo triassic roughly coincided with the life span of pangaea so far as europe is concerned pangaea s creation began in the early carboniferous visean when the northward drifting megacontinent gondwana began to collide with the iberian portion of the slower moving laurussia while proto tethys was subducted beneath the southern margin of central europe creation was complete by the end of the carboniferous or early in the permian with the final development of the variscan orogenic belt which trends from brittany eastward through central europe and with the addition of western siberia along the line of the ural orogen ziegler 1989 despite or perhaps because of its bulk pangaea was not a stable megacontinent no sooner had it formed than it tried to break apart again the disintegration of pangaea had already started before the end of the triassic with the westerly extension of tethys between iberia and africa though not yet underlain by oceanic crust and by early in the jurassic rifting was taking place between africa and the americas in the newly forming central atlantic ocean ziegler 1988 indeed e w extensional movements within a proto atlantic ocean possibly began as early as the late carboniferous haszeldine russell 1987 whilst mid permian extension is well documented in east greenland surlyk et al 1984 these extensional movements may have propagated southward to initiate fracturing in the viking and central grabens of the north sea along which the late permian zechstein sea was to break into the subsiding rotliegend basins and towards the central atlantic where a shallow seaway eventually developed early in the jurassic thus in the northern half of pangaea the continued existence of the former laurussia was already at risk in the permian although crustal separation in the north atlantic which possibly started in the rockall trough in the early cretaceous was finally achieved along the line of the reykjanes ridge only in the paleocene these major events on the periphery of what is now europe separately and jointly were factors that probably controlled a whole sequence of tectonic events within the continent which in turn controlled its patterns of mostly terrestrial sedimentation climatically the northward drift of laurussia had carried nw europe from a region of equatorial rain forest during the later carboniferous to the latitudes of a trade wind desert like the modern sahara in the permian the late permian basins of upper rotliegend and zechstein deposition were arid rotliegend sediments are characterized by dune sand and the saline mudstones of a semipermanent desert lake and the zechstein by shallow water carbonates and anhydrite and deeper water halite during the triassic however brackish water fluvial and lacustrine sediments occupied the basinal areas although even here halite horizons e g rrt muschelkalk and keuper in the north sea area associated with local transgressions from tethys testify that arid conditions were never far away

thermal and crystallization histories of magmatic bodies by monte carlo inversion of mg fe isotopic profiles in olivine a random search modeling approach is introduced to retrieve the thermal histories of magmatic bodies from chemical and isotopic analyses of olivine crystals the sample used for demonstration is an olivine phenocryst from kilauea iki lava lake hawaii random time temperature t t paths were used to model diffusion accompanying crystal growth although a large number of t t paths yielded acceptable fits to the mg fe chemical profiles measured in olivine only a small fraction resulted in acceptable fits to the mg fe isotopic profiles the best fit cooling path was close to the independently inferred cooling history of this sample use of isotopic profiles in minerals coupled with a random search method can be a powerful tool for recovering thermal histories of rocks with little geologic context

time scales of magma transport and mixing at kīlauea volcano hawai i modeling of volcanic processes is limited by a lack of knowledge of the time scales of storage mixing and final ascent of magmas into the shallowest portions of volcanic plumbing systems immediately prior to eruption it is impossible to measure these time scales directly however micro analytical techniques provide indirect estimates based on the extent of diffusion of species through melts and crystals we use diffusion in olivine phenocrysts from the a d 1959 k lauea iki hawai i usa eruption to constrain the timing of mixing events in the crustal plumbing system on time scales of months to years before eruption the time scales derived from zonation of fe mg in olivines combined with contemporaneous geophysical data suggest that mixing occurred on three time scales 1 as much as 2 yr prior to eruption in the deep storage system 2 in a shallow reservoir between incoming hot melts and resident melt for several weeks to months prior to eruption and 3 in the conduit and summit reservoir between the resident magma and cooled surface lava draining back into the vent on time scales of hours to several days during pauses between episodes synchronous inflation of the shallow reservoir with deep earthquake swarms and mixing suggests an intermittently open transcrustal magmatic system

discerning crystal growth from diffusion profiles in zoned olivine by in situ mg fe isotopic analyses mineral zoning is used in diffusion based geospeedometry to determine magmatic timescales progress in this field has been hampered by the challenge to discern mineral zoning produced by diffusion from concentration gradients inherited from crystal growth a zoned olivine phenocryst from kilauea iki lava lake hawaii was selected for this study to evaluate the potential of mg and fe isotopes for distinguishing these two processes microdrilling of the phenocryst 300 m drill holes followed by mc icpms analysis of the powders revealed negatively coupled mg and fe isotopic fractionations 26mg from 0 1 to 0 2 and 56fe from 1 2 to 0 2 from core to rim which can only be explained by mg fe exchange between melt and olivine the data can be explained with ratios of diffusivities of mg and fe isotopes in olivine scaling as d2 d1 m1 m2 with mg 0 16 and fe 0 27 la mc icpms and mc sims fe isotopic measurements are developed and are demonstrated to yield accurate 56fe measurements within precisions of 0 2 1 sd at spatial resolutions of 50 m 56fe and 26mg stay constant with fo in the rim late stage overgrowth whereas in the core original phenocryst 56fe steeply trends toward lighter compositions and 26mg trends toward heavier compositions with higher fo a plot of 56fe vs fo immediately distinguishes growth controlled from diffusion controlled zoning in these two regions the results are consistent with the idea that large isotopic fractionation accompanies chemical diffusion in crystals whereas fractional crystallization induces little or no isotopic fractionation the cooling timescale inferred from the chemical isotope zoning profiles is consistent with the documented cooling history of the lava lake in the absence of geologic context in situ stable isotopic measurements may now be used to interpret the nature of mineral zoning stable isotope measurements by la mc icpms and mc sims can be used as standard petrologic tools to identify samples for diffusion based geospeedometry

beryllium diffusion in olivine a new tool to investigate timescales of magmatic processes abstract the diffusion of beryllium be in pure synthetic forsterite fo 100 and san carlos olivine fo 90 was studied between 950 1475 c at atmospheric pressure as a function of silica activity a sio 2 crystallographic orientation oxygen fugacity f o 2 for diffusion in san carlos olivine and water fugacity f h 2 o at 1 15 gpa pressure p the diffusivity of be in olivine is faster than that of mg 2 or fe 2 but slower than that of h and appears to be insensitive to a sio 2 f h 2 o and p but is highly anisotropic with diffusivities described by 001 log d 0 5 82 0 15 e a 227 6 4 1 kj mol 1 010 log d 0 4 64 0 38 e a 285 8 11 6 kj mol 1 100 log d 0 4 20 0 27 e a 326 1 7 9 kj mol 1 diffusion of be 2 in natural san carlos olivine was determined at 1160 to 1350 c and was found to be similar to that in forsterite the exception was one experiment in natural olivine in relatively oxidising conditions where diffusion was slightly faster than its lower f o 2 or pure forsterite counterparts the equilibrium solubility of be in forsterite in equilibrium with beo bromellite and mgo periclase is lower than when in equilibrium with beo and mg 2 si 2 o 6 proto enstatite this shows that be 2 substitutes into olivine forming a defect with the stoichiometry be 2 sio 4 the sensitivity of be diffusion in olivine to only temperature and crystal orientation means that only these two factors need to be known to extract timescales from natural diffusion profiles our preliminary experiments show that the dependence of diffusion on f o 2 is minor or negligible in geologically relevant conditions this represents a considerable advantage over using diffusion profiles of other cations e g fe 2 mg 2 ni 2 or ca 2 where all of the above mentioned variables must be constrained before accurate timescale determinations can be made two examples of the potential for using be diffusion profiles to determine timescales in natural olivine xenocrysts are presented

carbonate dissolution in mesozoic sand and claystones as a response to co2 exposure at 70 c and 20mpa abstract the response to co2 exposure of a variety of carbonate cemented rocks has been investigated using pressurised batch experiments conducted under simulated reservoir conditions 70 c and 20 mpa and with a durations of up to14 months calcite dolomite ankerite and siderite cement were present in the unreacted reservoir rocks and caprocks core plugs of the reservoir rocks were used in order to investigate the alterations in situ crushing of the caprock samples was necessary to maximise reactions within the relatively short duration of the laboratory experiments synthetic brines were constructed for each batch experiment to match the specific formation water composition known from the reservoir and caprock formations in each well chemical matched synthetic brines proved crucial in order to avoid reactions due to non equilibra of the fluids with the rock samples for example observations of the dissolution of anhydrite which were not associated with the co2 injection but rather caused by mismatched brines carbonate dissolution as a response to co2 injection was confirmed in all batch experiments by both petrographical observations and geochemical changes in the brines increased ca and mg concentrations after 1 month reaction with co2 and crushed caprocks are ascribed to calcite and dolomite dissolution respectively though not verified petrographically ankerite and possible siderite dissolution in the sandstone plugs are observed petrographically after 7 months reaction with co2 and are accompanied by increased fe and mn contents in the reacted fluids clear evidence for calcite dissolution in sandstone plugs is observed petrographically after 14 months of reaction with co2 and is associated with increased amounts of ca and mg in the reacted fluid dolomite in sandstones shows only minor dissolution features which are not clearly supported by increased mg content in the reacted fluid silicate dissolution cannot be demonstrated either by chemical changes in the fluids as si and al concentrations remain below the analytical detection limits nor by petrographical changes as partly dissolved feldspar grains and authigenic analcime are present in the sediments prior to the experiments it is noteworthy that authigenic k feldspar and authigenic albite in sandstones show no signs of dissolution and consequently seem to be stable under the experimental conditions

triassic and jurassic structural development along the tornquist zone denmark abstract in the danish area the old crustal weakness zone the tornquist zone was repeatedly reactivated during the triassic and jurassic early cretaceous causing minor dextral movements along the major boundary faults these tectonic events were minor as compared to the tectonic events of the late carboniferous early permian and the late cretaceous early tertiary although a dynamic structural and stratigraphical analysis indicate that the zone was highly active compared to the surrounding areas during the middle to late permian the area was exposed to erosion and became a peneplane a regional triassic subsidence produces seismic onlap towards the northeast where the youngest triassic sediment is found supercropping the precambrian basement during mainly the early triassic several of the major early permian faults became reactivated probably with dextral strike slip along the borglum fault the jurassic early cretaceous subsidence became restricted primarily to the area between the two main faults in the tornquist zone the grena helsingborg fault and the borglum fault this restricted basin development indicates a change in the regional stress field that seems to have come into existence during the transition between the triassic and the jurassic the subsidence in the middle jurassic and the late jurassic early cretaceous follows the early jurassic pattern with local subsidence in the tornquist zone but even more restricted to the zone the subsidence seems to have decreased in the middle jurassic hereafter subsidence increased again during late jurassic early cretaceous times a set of small faults were generated during the mesozoic internally in the tornquist zone this fault pattern indicates a broad transfer of strike slip oblique slip motion from the grena helsingborg fault to the borglum fault

four thousand years of seismicity along the dead sea rift a study of major earthquake occurrence along the dead sea transform 35 5 36 5 e 27 2 37 5 n during the past four millenia has been attempted geological archaeological biblical historical and seismological evidence were integrated in an effort to quantify the space time distribution of seismicity in the said province the overall earthquake activity in the conterminous near east indicates a stable pattern and appeared to have been stationary over the examined time window about 110 earthquakes in the magnitude range 6 7 ml 8 3 affected the area during the past 2500 years of these 42 originated along the dead sea fault system itself while 68 were imported from the helenic cyprian arcs and the anatolian elburz zagros fault systems these events were responsible for the repeated destruction of many cultural centers in the dead sea region proper the major seismic activity since 2100 b c e before christian era has been confined to the vicinity of its eastern shore with extremal seismicity at its southern tip near the prehistorical site of bab a dara a 31 15 n 35 32 e this may constitute the first solid evidence that the biblical cities of the plain sodom gommorah etc were located there recent studies of earthquake deformations in the lisan deposits near bab a dara a agree with our findings at the present time a magnitude 6 earthquake is pending at the northern edge of the levant rift with its average recurrence interval 83 years exceeded by one standard deviation 32 years

diffusion kinetics of cr in olivine and 53mn 53cr thermochronology of early solar system objects we have determined the diffusion coefficient of cr in olivine as function of temperature oxygen fugacity fo2 and crystallographic orientation and used these data to develop a quantitative understanding of the resetting of the short lived 53 mn 53 cr decay system in olivine during cooling within meteorite parent body the diffusion of cr in olivine was found to be anisotropic and effectively indepen dent of fo2 between wustite iron buffer and two orders of magnitude above this buffer the diffusion data were used to calculate the spatially averaged mean closure temperature of the 53 mn 53 cr decay system in olivine as function of the initial temperature cooling rate and grain size and also the closure age profile of this system in olivine single crystal as function of radial distance and a dimensionless parameter that incorporates the effects of various parameters that affect the closure age we also present a thermochronolgic formulation that permits retrieval of cooling rates from the extent of resetting of the bulk 53 mn 53 cr closure age of olivine during cooling this method was applied to determine the cooling rate of the pallasite omolon which showed 53 mn 53 cr bulk age of olivine that is 10 myr younger than the age of the solar system the calculated cooling rate which is 20 40 c myr at 985 1000 c is in good agreement with the metallographic cooling rate at 500 c when the two results are considered in terms of a cooling model in which the reciprocal temperature increases linearly with time the inferred cooling rate of omolon which seems to be a sample from the core mantle boun dary yields a burial depth of 30 km in a parent body of at least 100 km radius

comment on the permian triassic transition and the onset of mesozoic sedimentation at the northwestern peri tethyan domain scale palaeogeographic maps and geodynamic implications by s bourquin a bercovici j lopez gomez j b diez j broutin a ronchi m durand a arche b linol and f amour palaeogeography palaeoclimatology palaeoecology 299 2011 265 280 abstract the recent paper by bourquin et al 2011 describes the regional palaeogeographic evolution of the late permian to middle triassic on a pan european scale whilst useful data and interpretations are provided for their southern and intra variscan belt domains additional well and seismic data from the central and northern north sea and the atlantic margin region together with results from recent publications allow us to refine and improve their interpretation of their northern domain the presence of a regional unconformity at the permian triassic boundary with only localised induan sedimentation is less clear in the northern region where multiple extensional events through late permian and triassic time led to the development of localised footwall and rift flank unconformities as arctic rifting propagated southwards and entered the north sea and the atlantic margin regions the hardegsen unconformity may be locally identifiable in the southern portion of the northern domain but again forms one of a number of unconformities marking the onset of rifting data from the northern domain suggest that early triassic aeolian activity was ubiquitous on the distal fringes of terminal fluvial systems but with no evidence of the discrete episode of increased aridity in the smithian identified in the south the onset of vegetation cover in the northern domain was also more diachronous in this region appearing in the central north sea at approximately the same time as muschelkalk flooding of the adjacent southern permian basin and later in basins further to the north in most cases the middle triassic fluvial systems in the north were terminal in nature failed to discharge into marine basins and were not exorheic in character their advance and retreat was independent of sea level fluctuations or the presence of a marine water body and fluvial expansion and retreat aeolian reworking and vegetation cover appear to have been linked to catchment runoff the disconnect with the observations to the south may be in part a product of the more northern latitudinal position of these systems or at least that of the headwaters of the fluvial drainage

zoning of phosphorus in igneous olivine we describe p zoning in olivines from terrestrial basalts andesites dacites and komatiites and from a martian meteorite p2o5 contents of olivines vary from below the detection limit 0 01 wt to 0 2 0 4 wt over a few microns with no correlated variations in fo content zoning patterns include p rich crystal cores with skeletal hopper or euhedral shapes oscillatory zoning structures suggesting replacement of p rich zones by p poor olivine and sector zoning melt inclusions in olivines are usually located near p rich regions but in direct contact with low p olivine crystallization experiments on basaltic compositions at constant cooling rates 15 30 c h reproduce many of these features we infer that p rich zones in experimental and natural olivines reflect incorporation of p in excess of equilibrium partitioning during rapid growth and zoning patterns primarily record crystal growth rate variations occurrences of high p phenocryst cores may reflect pulses of rapid crystal growth following delayed nucleation due to undercooling most cases of oscillatory zoning in p likely reflect internal factors whereby oscillating growth rates occur without external forcings but some p zoning in natural olivines may reflect external forcings e g magma mixing events eruption that result in variable crystal growth rates and or p contents in the magma in experimental and some natural olivines al cr and p concentrations are roughly linearly and positively correlated suggesting coupled substitutions but in natural phenocrysts cr zoning is usually less intense than p zoning and al zoning weak to absent we propose that olivines grow from basic and ultrabasic magmas with correlated zoning in p cr and al superimposed on normal zoning in fe mg rapidly diffusing divalent cations homogenize during residence in hot magma al and cr only partially homogenize and delicate p zoning is preserved because p diffuses very slowly this interpretation is consistent with the fact that zoning is largely preserved not only in p but also in al cr and divalent cations in olivines with short residence times at high temperature e g experimentally grown olivines komatiitic olivines groundmass olivines and the rims of olivine phenocrysts grown during eruption p zoning is widespread in magmatic olivine revealing details of crystal growth and intra crystal stratigraphy in what otherwise appear to be relatively featureless crystals since it is preserved in early formed olivines with prolonged residence times in magmas at high temperatures p zoning has promise as an archive of information about an otherwise largely inaccessible stage of a magma s history study of such features should be a valuable supplement to routine petrographic investigations of basic and ultrabasic rocks especially because these features can be observed with standard electron microprobe techniques

diffusion of phosphorus in olivine and molten basalt the diffusivity of phosphorus in san carlos olivine sco was measured at near atmospheric pressure and 650 850 c by in diffusion of p from a surface powder source consisting of pre reacted sco and alpo 4 the experiments were conducted in evacuated silica glass ampoules at oxygen fugacities fixed by solid state buffers generally ni nio but also including two experiments buffered at wustite magnetite phosphorus uptake profiles were characterized by rutherford backscattering spectroscopy rbs and nuclear reaction analysis nra the temperature dependence of p diffusion in sco conforms to the expected arrhenius relation d d 0 exp e a r t where the constants are as follows log d 0 m 2 s 10 06 0 80 and e a 229 16 kj mol these values characterize p as a relatively slow diffuser in olivine slower by about an order of magnitude than cr and ca at basalt near liquidus temperatures but substantially faster than si with a view toward modeling p uptake during rapid growth of natural olivines p diffusion was also characterized in dry morb basalt melt over the temperature range 1250 1500 c at 1 gpa using traditional diffusion couples contained in graphite phosphorus diffusion profiles in the quenched and depressurized samples were quantified by laser ablation icp ms phosphorus diffusion in basaltic melt is similar to that of si with log d 0 m 2 s 6 30 0 7 and e a 147 22 kj mol the new data for p diffusion in olivine and basalt melt can be used to explore the acquisition of fine scale zoning in natural olivine phenocrysts through kinetic models as well as the survival of p zoning in olivine with time spent at elevated temperature models of growth entrapment of a p enriched near surface layer in the olivine lattice indicate that crystal growth at plausible sustained rates is indeed likely to result in regions of anomalously high p content in the resulting crystal phosphorus concentrations above the equilibrium partitioning value can also result from development of a diffusive boundary layer in the melt against a rapidly growing crystal but this mechanism is ineffective at typical sustained olivine growth rates requiring dendrite forming growth speeds preservation of p zoning on the scale of a few micrometers apparently requires cooling within a few months of formation of the zoning

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

numerical simulations of an ocean continent convergent system influence of subduction geometry and mantle wedge hydration on crustal recycling the effects of the hydration mechanism on continental crust recycling are analyzed through a 2 d finite element thermomechanical model oceanic slab dehydration and consequent mantle wedge hydration are implemented using a dynamic method hydration is accomplished by lawsonite and serpentine breakdown topography is treated as a free surface subduction rates of 1 3 5 7 5 and 10 cm yr slab angles of 30 45 and 60 and a mantle rheology represented by dry dunite and dry olivine flow laws have been taken into account during successive numerical experiments model predictions pointed out that a direct relationship exists between mantle rheology and the amount of recycled crustal material the larger the viscosity contrast between hydrated and dry mantle the larger the percentage of recycled material into the mantle wedge slab dip variation has a moderate impact on the recycling metamorphic evolution of recycled material is influenced by subduction style tpmax generally representative of eclogite facies conditions is sensitive to changes in slab dip a direct relationship between subduction rate and exhumation rate results for different slab dips this relationship does not depend on the used mantle flow law thermal regimes predicted by different numerical models are compared to pt paths followed by continental crustal slices involved in ancient and recent subduction zones making ablative subduction a suitable precollisional mechanism for burial and exhumation of continental crust

decadal time gaps between mafic intrusion and silicic eruption obtained from chemical zoning patterns in olivine abstract intrusion of mafic magma in a silicic crustal reservoir has been reported in numerous studies of subduction related volcanoes and is considered a main process for triggering explosive eruptions and for transferring geochemical signatures from the mantle to the crust here we determine the timescales between mafic silicic encounters and eruption by exploiting the fact that during such interactions magmas exchange crystals and their mineral compositions will strive to equilibrate to the new environmental conditions specifically we model the fe mg zoning patterns of olivine found in the dacites andesite and quenched mafic inclusions of the holocene zoned eruption of volcan san pedro 36 s chilean andes the san pedro eruption is an example where mixing between silicic and mafic magmas produced intermediate compositions e g andesite at depth in the magma reservoir for modeling the compositional profiles we took into account the anisotropy of fe mg diffusion in olivine and also the effects of diffusion in multiple dimensions aspects that have been largely neglected in previous works the retrieved timescales for olivine melt equilibration by diffusion display an array ranging from 1 year for the most silica rich dacite to 50 years for the andesite this array of timescales rather than a single value provides new insight into the details of mafic silicic mixing at depth they reveal processes that occur on a longer timescale than the days to weeks time gap for cases where the mafic intrusion triggered the eruption and they might be associated with the instances where seismic activity or significant inflation of the volcanic edifice was not immediately followed by eruption on the other hand the year to decade timescales that we report for producing magmas of intermediate composition e g andesites are much shorter than the 10 3 10 5 years inferred from u series disequilibria data for igneous differentiation by closed system fractionation to produce similar magma compositions at subduction zones

combined fe mg chemical and isotopic zoning in olivine constraining magma mixing to eruption timescales for the continental arc volcano irazu costa rica and cr diffusion in olivine

an unusual muddy epeiric carbonate reservoir the lower muschelkalk middle triassic of the netherlands the mud dominated lower muschelkalk carbonates middle triassic are a unique reservoir currently producing gas in the dutch de wijk field numerous gas shows scattered over the netherlands onshore and offshore suggest further currently unrecognized potential this study complements an extensive subsurface data set with selected outcrop information to localize missed opportunities and evaluates the factors controlling the development of this unusual reservoir type the muddy carbonates are deposits of a storm dominated epeiric carbonate ramp with negligible depositional gradient different marlstone dolomudstone and lime mudstone facies types reflect the low energy coastal plain to inner ramp and higher energy midramp to proximal outer ramp depositional environments the best reservoir facies is recognized in distal inner ramp algal dolomudstones porosity up to 24 and permeability up to 32 md because of the variable intensity of early facies related diagenesis the reservoir quality of dolomudstones decreases markedly in landward and seaward direction from the distal inner ramp the stacking of decimeter to meter thick reservoirs is reflected by a fourfold hierarchy of depositional cycles that can largely be recognized with conventional wire line logs high resolution outcrop and subsurface correlations reveal that stacks of thin bedded reservoir units most probably pinch out within a few kilometers and that their lateral continuity should not be overestimated despite the epeiric layer cake setting local reservoir occurrences are commonly situated above paleohighs of tectonic or halokinetic origin not only the reduced thickness of the lower muschelkalk above these paleohighs but also the presence and lateral extent of local reservoirs might be detected with seismic data the general facies and reservoir patterns exemplified by the lower muschelkalk may also be of use for reservoir prediction in similar epeiric settings elsewhere for instance in the middle east

hanging wall deformation and gas migration associated to a major salt detaching fault in the norwegian danish basin abstract the central and southern regions of the north sea basin are characterized by mobile zechstein salt and represent an excellent area to study listric normal fault development related to halokinesis the north sea basin in spite of being a mature explored hydrocarbon producing basin contains a generally not fully understood hydrocarbon plumbing system faults and associated fluid migration routes represent critical elements of the plumbing system here we present a combined 3d seismic mapping of a listric fault and detailed seismic attribute analysis of shallow gas anomalies near the fault implying a close and complex relationship between a major detaching fault hangingwall deformation and fluid migration and entrapment the fault and associated antithetic and secondary synthetic faults is controlled by the growth of the underlying salt structure three separate segments of the fault are recognized showing distinct and varying characteristics of structural maturity and fluid migration the studied fault and shallow gas anomalies thus represent an example of a complex faulted shallow fluid migration system developing in relation to an underlying salt structure which could be relevant for understanding similar salt fault and fluid migration systems around the world

effects of asthenospheric heat flow in basin modelling exemplified with the danish basin a mathematical model is developed to simulate the process of basin formation by rifting subsidence is driven by crustal thinning and influenced by the transient temperature variation within the lithosphere the model offers possibilities for multiple phases of rifting superimposing non steady state conditions important features in the model are two layered heat production and a definition of the lower boundary in terms of heat flow instead of one of constant temperature as opposed to other models furthermore phase transformations caused by rift induced pressure and temperature changes are suggested as an additional syn rift subsidence mechanism the relevant phase transformations are assumed to be those occurring during an amphibolite to granulite facies transition perturbation of the steady state temperature profile is performed by one or several phases of rifting with finite stretching rates by sill intrusion or by changes in asthenospheric heat flow the greatest deviation from the steady state geotherm occurs at the lower boundary because of the flow definition of the lower boundary the consequence of this is a much longer duration of anomalous heat flow the model is applied to the danish basin north jylland denmark this basin was formed in permian times and since then it has been thermally subsiding apart from a minor event of stretching in the late cretaceous the higher present day heat flow in the basin compared to the adjacent fennoscandian shield area is successfully explained by the model presented in this paper it is concluded that transient temperature conditions still today contribute significantly to present surface heat flow although main rifting took place for more than 240 m y ago this cannot be explained by models using a fixed temperature definition of the lower boundary the modelled contribution by phase transformations to subsidence explains why the syn rift early and middle triassic subsidence was accompanied by insignificant faulting activity as evidenced by the seismic data available

the horn graben and its relationship to the oslo graben and the danish basin abstract the tectonic development of the horn graben the danish basin and the oslo graben are compared with special emphasis on the timing of their initiation the comparison is based on seismic interpretation and is supported by analysis of tectonic subsidence devonian and carboniferous sedimentary strata and rotliegende volcanics constitutes the pre rift succession in the horn graben in the central part of the graben it rests unconformably on precambrian possibly dalslandian basement to the south on caledonian metamorphic basement whereas lower palaeozoics occur to the north the distribution of these pre devonian assemblages suggests initial early devonian uplift of the ringkobing fyn high as the lower palaeozoic sediments are believed to have covered the high originally further uplift appears to have taken place in the early permian a subdivision of the horn graben into a northern and a southern segment are recognized the rifting was apparently heralded only in the southern segment in the rotliegende and the main rifting phase did not start before the triassic subsidence modelling shows that the thermal anomaly created by rifting of the horn graben was less significant than in the danish basin and resulted in much less post rift thermal subsidence the reduced thermal anomaly may account for an earlier consolidation of the crust thereby rendering the area resistant to late cretaceous early tertiary inversion tectonism the oslo graben was tectonically active during late carboniferous to early permian times and essentially became inactive during triassic times when the main tectonism of the horn graben occurred subsidence modelling shows that the danish basin south of the fjerritslev trough was tectonically active mainly during the zechstein whereas the rapid triassic subsidence is modelled to be caused by phase transformations as indicated by the minor amount of basement attached faulting based on the differing subsidence patterns it is concluded that the three basins did not develop simultaneously and that they are not genetically related

isotope fractionation by chemical diffusion between molten basalt and rhyolite abstract experimental diffusion couples were used to study chemical diffusion between molten rhyolite and basalt with special emphasis on the associated fractionation of calcium and lithium isotopes diffusion couples were made by juxtaposing firmly packed powders of a natural basalt suny morb and a natural rhyolite lake county obsidian and then annealing them in a piston cylinder apparatus for times ranging from 0 1 to 15 7 h temperatures of 1350 1450 c and pressures of 1 2 1 3 gpa profiles of the major elements and many trace elements were measured on the recovered quenched glasses the diffusivities of all elements except lithium were found to be remarkably similar while the diffusivity of lithium was two to three orders of magnitude larger than that of any of the other elements measured chemical diffusion of calcium from molten basalt into rhyolite was driven by a concentration ratio of 18 and produced a fractionation of 44ca from 40ca of about 6 because of the relatively low concentration of lithium in the natural starting materials a small amount of spodumene lialsi2o6 was added to the basalt in order to increase the concentration difference between basalt and rhyolite which was expected to increase the magnitude of diffusive isotopic fractionation of lithium the concentration ratio between li doped basalt and natural rhyolite was 15 and the resulting diffusion of lithium into the rhyolite fractionated 7li from 6li by about 40 we anticipate that several other major rock forming elements such as magnesium iron and potassium will also exhibit similarly larger isotopic fractionation whenever they diffuse between natural melts with sufficiently large differences in the abundance of these elements

modeling of gas driven magmatic overturn tracking of phenocryst dispersal and gathering during magma mixing 1 we present a combined multiphase numerical and crystal tracking approach that provides a framework to investigate the transport and zoning of crystals associated with a gas driven mixing event mixing in compositionally intermediate to silicic magmatic systems is often initiated by gas exsolution in the recharging magma causing a density inversion and subsequent overturn the overturn is simulated for a range of bubble volume fractions bubbles and therefore indirectly for a range of reynolds numbers re all simulations show chaotic flow dynamics with fast overturn timescales of minutes to hours the large scale mixing is inefficient during a single overturn resulting in a continuously stratified system with respect to bubble volume fraction the crystal tracking algorithm provides us with information on the small scales i e 10 cm on this length scale we observe gathering of different crystals during the overturn that typically ranges on the order of tens of meters thus a complex crystal population may arise within a single overturn this gathering and dispersal of crystals is strongest and most uniform for high re for low re crystal populations are characterized by less gathering of crystals that originated from distal portions of the magma body during the overturn the crystals pass through environments of changing chemical potential we apply the damkohler number da which compares the crystallization or dissolution to the advection timescale results show an asymmetry between crystallization and dissolution crystallization times are too slow during gas driven overturn to record transient changes in chemical potential crystals most likely only record their initial as well as their final chemical environment in contrast dissolution and advection rates are of similar order suggesting potential dissolution during the overturn on the basis of the results for gas driven overturn we expect that slower physical mixing processes may be continuously recorded in the zonation pattern of the crystal phases as long as the changes in chemical potential produce crystal growth

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

cracking the olivine zoning code distinguishing between crystal growth and diffusion olivine composition and zoning patterns are widely used to reconstruct the evolution of mafic magmas from source to surface and to extract time scales of magmatic processes deciphering the olivine zoning code is challenging because the contributions of growth and diffusion may overlap a detailed multielement fe mg p al and ni examination of zoning in an exceptional olivine with skeletal morphology allows unequivocal discrimination between these two processes using simple but powerful geometrical arguments olivine crystals initially grow rapidly and diagonally from corner locations whereas diffusion effectively tracks mutually perpendicular crystal lattice orientations generating the zoning patterns for our case study olivine required at least 4 5 months of diffusive reequilibration of fe mg further demonstrating that crystal morphologies produced by rapid growth can survive at magmatic temperatures for extended periods no significant major element zoning is preserved after rapid growth lending further credibility to time scales retrieved via diffusion modeling extending multielement approaches to decoding olivine zoning patterns can help determine whether the kinetic relationship between growth and diffusion induced zoning recognized herein is widely applicable such studies will improve our understanding of time scales of magma storage solidification mixing and or transit toward the surface

site specific hydrogen diffusion rates during clinopyroxene dehydration the rate of hydrogen diffusion in clinopyroxene is relevant to interpreting hydrogen water concentrations in xenoliths phenocrysts and clinopyroxene hosted melt inclusions to provide insight into the deep earth water cycle and volcanic explosivity here we determine bulk and site specific hydrogen diffusivities in two diopsides and an augite by heating initially homogeneous water bearing samples in a 1 atm co co2 gas mixing furnace at 800 1000 c and oxygen fugacity at the quartz fayalite magnetite buffer and observing h loss profiles the o h stretching range between wavenumbers 3000 and 4000 cm 1 in ftir spectra is resolved into 4 6 peaks each of which is assumed to represent a distinct defect site for the hydrogen to determine peak specific diffusivities using our previously published whole block method for the diopside from the kunlun mts in china arrhenius relations are reported for peaks at 3645 3617 3540 3443 and 3355 cm 1 based on measurements at 816 904 and 1000 c bulk and site specific diffusivities are determined for the same set of peaks at 904 c for the second diopside jaipur the augite pmr 53 was a triangular thin slab and hydrogen diffusivities were determined for bulk hydrogen and peaks at 3620 3550 3460 and 3355 cm 1 in the thickness direction at 800 c bulk hydrogen diffusivity in the jaipur diopside is consistent with previous work and hydrogen diffusivity in augite pmr 53 is slightly lower than the fast direction diffusivities measured 100 and 001 in jaipur diopside both diopsides show 1 2 orders of magnitude differences in the peaks specific diffusivities with the fastest diffusivities at 3450 cm 1 and the slowest at 3645 cm 1 however the hydrogen diffusivities in jaipur diopside are 2 4 orders of magnitude higher than those in kunlun diopside for bulk hydrogen and all peaks thus peak specific differences cannot by themselves adequately explain the 5 orders of magnitude range in hydrogen diffusivities observed experimentally in different diopsides the results are broadly consistent with a previously proposed increase in hydrogen diffusivity in diopside with fe up to 0 6 0 8 a p f u although there may be an opposing relationship with al iv the results of this study and others predict high water diffusivities in fe bearing mantle xenolith clinopyroxene on the order of 10 9 to 10 11 m2 s at 1000 c the common observation of hydrogen zonation in mantle xenolith olivine but not in clinopyroxene implies that hydrogen diffusion is much faster in olivine than in pyroxene which then requires the operation of the fastest diffusion mechanism quantified in olivine and diffusivities in clinopyroxene at the lower end of this 2 orders of magnitude range such high diffusivities strongly suggest that water in mantle xenoliths has at least partially equilibrated with the host magma and that the diffusion profiles observed in mantle xenolith olivine reflect only the final stage of ascent after water begins to exsolve

symmetrical and segmented variation of physical and geochemical characteristics of the central american volcanic front abstract the regional variation of physical and geochemical characteristics of central american volcanoes occurs in two fundamentally different patterns the first pattern is symmetrical about nicaragua crustal thickness silica contents of mafic lavas and volcanic edifice heights are lowest in nicaragua and increase smoothly toward costa rica to the south and guatemala to the north magma density is maximum in nicaragua and decreases smoothly outward the regional variation in crustal thickness is just enough so that magma densities calculated at appropriate moho pressures are the same at the base of the crust throughout the region this is consistent with magma ponding at the base of the crust the bulk compositions of central american basalts show the same symmetrical variation suites of nicaraguan basalts plotted in pseudo ternary cmas projections indicate large olivine and plagioclase primary phase volumes toward costa rica and guatemala the olivine and plagioclase fields inferred from suites of basaltic lavas are smaller which is consistent with fractionation at increasing depth the second pattern is the segmentation of the volcanic front and the plate margin in general the segmentation strongly affects the spacing and size of volcanic centers at segment boundaries volcanic centers are generally small and unusually widely spaced toward segment interiors volcano spacing and size increase systematically the lil element contents of lavas strongly reflect this pattern for lavas with similar silica contents the larger the volcano the higher the lil element contents the relationships between segmentation volcano spacing and volcano size are compatible with diapiric rise of magma accumulated in narrow ribbons near the upper surface of the underthrust slab the relationship between volcano volume and lil element content is qualitatively in agreement with an open system fractionation model

reassessing the cooling rate and geologic setting of martian meteorites mil 03346 and nwa 817 abstract lithium concentration and isotopic fractionation profiles across augite grains from two martian meteorites mil 03346 and nwa 817 were used to determine their thermal history and implications for their geologic setting the iron magnesium zoning and associated magnesium isotopic fractionation of olivine grains from nwa 817 were also measured and provide a separate estimate of the cooling rate the observed correlation of concentration with isotopic fractionation provides the essential evidence that the zoning of these grains was in fact due to diffusion and thus can be used as a measure of their cooling rate the diffusion rate of lithium in augite depends on the oxygen fugacity which has to be taken into account when determining a cooling rate based on the lithium zoning the fe mg exchange in olivine is much less sensitive to oxygen fugacity but it is significantly anisotropic and for this reason we determined the direction relative to crystallographic axes of the line along which the fe mg zoning was measured we found that the cooling rate of nwa 817 determined from the lithium zoning in augite grains and that based on the fe mg zoning of olivines are in good agreement at an oxygen fugacity close to that of quartz fayalite magnetite oxygen buffer the cooling rate of mil 03346 was found to be resolvably faster than that of nwa 817 of the order of 1 c h for the former and of the order of 0 2 c h for the latter an important observation regarding the history of mil 03346 and nwa 817 is that the lithium and fe mg zoning are only observed where the augite or olivine is in contact with the mesostasis which implies that they were already about 80 crystallized at the time diffusion began the augite and olivine core compositions while very homogeneous are not in equilibrium with each other which we interpret to imply that prior to the rapid cooling there must have been a protracted period of the order of years above the solidus during which the much faster fe mg exchange in olivine compared to that in augite allowed the olivine to maintain equilibrium with a changing melt composition while the augite was not significantly affected we suggest two possible geological settings for the origin and evolution of mil 03346 and nwa 817 1 a slow cooling stage in a crystallization front in a crustal magma chamber followed by eruption of melt plus portions of the crystallization front onto the surface where the final fast cooling took place at the bottom of a lava flow or melt pond and 2 eruption of a crystal laden melt as a thick long lived lava flow where the crystals continued to grow as a cumulate and were rapidly cooled when the overlying lava layer was suddenly drained