integrating the uranium series and elemental diffusion geochronometers in mixed magmas from volcan quizapu central chile magma mixing is a ubiquitous process in silicic magmatic systems we present pre and post mixing time scales for a single magma mixing event associated with the 1846 1847 eruption of volcan quizapu we compare and contrast 226 ra 230 th crystal residence ages between the mixed lavas of the 1846 1847 effusive eruption and the largely homogeneous plinian dacite eruption of 1932 both eruptions are dominated by the same dacite magma whereas the ear lier eruption contains evidence for a single episode of mafic recharge and mixing the use of uranium series mineral separate dating on a mixed magma requires deconvolution of different crystal populations we present a four component mixing model for the crystal separates to obtain dacite derived plagioclase model ages as well as andesite derived recharge plagioclase ages plagioclase model ages average 3 6 ka for dacite derived plagioclase from the mixed 1846 1847 eruption 1 4 kyr older than average plagioclase model ages of the 1932 eruption suggesting that magma mixing and reheating led to some resorption of young crystal rims in the 1846 1847 magmatic episode and or that some growth of plagioclase rims occurred during the repose time of 86 years the andesite derived plagioclase residence ages are younger than the corresponding dacite derived plagioclase residence ages but they are still of the order of thousands of years in addition we use mg diffu sion in plagioclase to constrain time scales of magma mixing we show that the 1846 1847 eruption was triggered by large volume mafic recharge magma that mixed and mingled with the resident dacite within probably days to weeks of the ensuing eruption

u series constraints on intraplate basaltic magmatism intraplate magmatism represents approximately one tenth of the flux of magma to the earth s surface sleep 1990 this type of magmatism has received considerable attention from petrologists and geochemists as it generally exhibits a wider range of chemical compositions than the more uniform mid ocean ridge basalts hence it is rather paradoxical that our understanding of intraplate magmatism is rather poor in this chapter we review the insights that have been gained from using u series measurements combined with other chemical and isotopic constraints to better understand the sources and processes related to intraplate volcanism several unique constraints can be obtained from measurement of u series disequilibria in basalts first u series fractionation can tell us about the residual phases present during melting as small differences in partitioning behavior between the nuclides will induce distinct signatures second as has been shown by the earlier work of allegre and condomines 1982 th isotope ratios can be used to infer the th u ratio of the mantle source providing another useful probe for mapping mantle heterogeneities lastly as detailed below the time dependence of u series fractionation during melting and melt migration can place constraints on several rate dependent parameters such as the melt production rate and melt velocities an important feature of hotspot magmatism is that in many cases the timing of hotspot activity seems to be decoupled from the motion of the lithospheric plate this observation which has been the basis for proposing the existence of mantle plumes suggests that magmas erupted at hotspots should reveal something about the nature of the deeper mantle understanding the processes of hotspot magmatism should also tell us about the nature of convective motion responsible for hotspots in the following section we first review some of the outstanding issues that need to be resolved to better understand intraplate magmatism we then

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

226ra 230th 238u disequilibria of historical kilauea lavas 1790 1982 and the dynamics of mantle melting within the hawaiian plume abstract the geochemical variations of kilauea s historical summit lavas 1790 1982 document a rapid fluctuation in the mantle source and melting history of this volcano these lavas span nearly the entire known range of source composition for kilauea in only 200 yr and record a factor of 2 change in the degree of partial melting in this study we use high precision measurements of the u series isotope abundances of kilauea s historical summit lavas and two ingrowth models dynamic and equilibrium percolation melting to focus on the process of melt generation at this volcano our results show that the 226 ra 230 th 238 u disequilibria of these lavas have remained relatively small and constant with 12 4 excess 226 ra and 2 5 1 6 excess 230 th both are 2 model calculations based mostly on subtle variations in the 230 th 238 u disequilibria suggest that lavas from the 19th to early 20th centuries formed at significantly higher rates of mantle melting and upwelling up to a factor of 10 compared to lavas from 1790 and the late 20th century the shift to higher values for these parameters correlates with a short term decrease in the size of the melting region sampled by the volcano which is consistent with fluid dynamical models that predict an exponential increase in the upwelling rate and thus the melting rate towards the core of the hawaiian plume the pb sr and nd isotope ratios of lavas derived from the smallest source volumes correspond to the kilauea end member of hawaiian volcanoes whereas lavas derived from the largest source volumes overlap isotopically with recent loihi tholeiitic basalts this behavior probably arises from the more effective blending of small scale source heterogeneities as the melting region sampled by kilauea increases in size the source that was preferentially tapped during the early 20th century when the melt fractions were lowest is more chemically and isotopically depleted than the source of the early 19th and late 20th century lavas which formed by the highest melt fractions this inverse relationship between the magnitude of source depletion and melt fraction suggests that source fertility i e lithology controls the degree of partial melting at kilauea thus rapid changes in the size of the melting region sampled by the volcano in the presence of these small scale heterogeneities may regulate most of the source and melting related geochemical variations observed at kilauea over time scales of decades to centuries

petrology of lavas from the puu oo eruption of kilauea volcano iii the kupaianaha episode 1986 1992 the puu oo eruption has been remarkable in the historical record of kilauea volcano for its duration over 13 years volume 1 km3 and compositional variation 5 7 10 wt mgo during the summer of 1986 the main vent for lava production moved 3 km down the east rift zone and the eruption style changed from episodic geyser like fountaining at puu oo to virtually continuous relatively quiescent effusion at the kupaianaha vent this paper examines this next chapter in the puu oo eruption episodes 48 and 49 and presents new icp ms trace element and pb sr and nd isotope data for the entire eruption 1983 1994 nearly aphyric to weakly olivine phyric lavas were erupted during episodes 48 and 49 the variation in mgo content of kupaianaha lavas erupted before 1990 correlates with changes in tilt at the summit of kilauea both of which probably were controlled by variations in kilauea s magma supply rate these lavas contain euhedral olivines which generally are in equilibrium with whole rock compositions although some of the more mafic lavas which erupted during 1990 a period of frequent pauses in the eruption accumulated 2 4 vol olivine the highest forsterite content of olivines 85 in kupaianaha lavas indicates that the parental magmas for these lavas had mgo contents of 10 wt which equals the highest observed value for lavas during this eruption the composition of the puu oo lavas has progressively changed during the eruption since early 1985 episode 30 when mixing between an evolved rift zone magma and a more mafic summit reservoir derived magma ended the normalized to 10 wt mgo abundances of highly incompatible elements and cao have systematically decreased with time whereas ratios of these trace elements and pb sr and nd isotopes and the abundances of y and yb have remained relatively unchanged these results indicate that the hawaiian plume source for puu oo magmas must be relatively homogeneous on a scale of 10 20 km3 assuming 5 10 partial melting and that localized melting within the plume has apparently progressively depleted its incompatible elements and clinopyroxene component as the eruption continued the rate of variation of highly incompatible elements in puu oo lavas is much greater than that observed for kilauea historical summit lavas e g ba y 0 09 a 1 vs 0 03 a 1 this rapid change indicates that puu oo magmas did not mix thoroughly with magma in the summit reservoir thus except for variable amounts of olivine fractionation the geochemical variation in these lavas is predominantly controlled by mantle processes

high enrichment of carbon and volatile elements in the surface layers of luna 16 soil sample 1635 result of comet or meteorite impact abstract surface analysis by x ray photoelectron spectroscopy xps in combination with ar etching was performed on a lunar regolith sample from the luna 16 drill core the sample contains only 10 of glass spherules these are of highly variable composition which distinguishes them from the pristine volcanic lunar glasses with their restricted compositional range the xps analyses revealed that practically all grains in this sample are coated by layers of different chemical composition the outer 1200 a have a normal fe mg silicate composition the middle zone between 1200 and 4400 a is strongly enriched in carbon up to 60 at and in zn 4 at from the electron binding energy of the carbon atoms it can be concluded that most of the carbon is present in the form of nanodiamonds and graphite other volatile elements cd pb ga p and cl were detected at the 0 1 0 2 at level in this zone the inner zone below 4400 a has again a silicate composition but is more refractory than the outer zone i e higher in ca and al we propose that this layering was formed by condensation from a carbon rich cloud originating from the impact of a comet or a carbonaceous chondrite like body xps analysis of the surface layers showed variations in the chemical state of the main elements mg si al ca fe in these layers corresponding to different molecular structures similar variations were found in condensate films produced in laser pulse impact simulation experiments

dating of thaw depths in permafrost terrain by the palaeomagnetic method experimental acquisition of a freezing remanent magnetization summary the acquisition of a freezing remanent magnetization frm has been studied in controlled magnetic and thermal environments by successive freezing and thawing 18 to 20 c of samples of natural sediments from a frost polygon near ny alesund spitsbergen successive freeze thaw cycles cause a significant decrease in the intensity of the initially induced shock remanent magnetization srm associated with directional trends towards the ambient magnetic field direction during the freezing phase a slow increase in intensity commences after seven to 10 freeze thaw cycles the acquisition of a frm in samples carrying an isothermal remanent magnetization shows a significantly smaller reduction in intensity and only minor directional variations this result indicates that only a fraction of the magnetic grains in a natural sediment contributes to the natural remanent magnetization insignificant changes in lengths and directions of the principal susceptibility ellipsoid axes also indicate that magnetic fabric and remanent magnetization are carried by partly different populations of magnetic grains the acquisition of a frm in nature has yet to be explored if such a process is confirmed however it has the potential for obtaining age estimates of ancient thaw depths and for providing insights into material transport processes in frost polygons

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

case studies of plagioclase growth and residence times in island arc lavas from tonga and the lesser antilles and a model to reconcile discordant age information abstract the time scales of crystal growth and residence in magmas have received much attention because such information can constrain the physical processes involved however crystals and liquids can have different ages leading to apparently contradictory information from different dating methods two case studies are presented from island arc lavas that highlight such dichotomies plagioclase crystal size distributions and u th ra isotope data are presented for lavas from late and metis shoal in tonga and from soufriere st vincent in the lesser antilles in all three lavas mineral data yield apparent u th ages of 30 50 kyr yet 226 ra excesses are preserved in both the minerals and the whole rocks the crystal size distributions suggest crystal growth over 100s of years but also frequently indicate the presence of mixed crystal populations furthermore a cumulate from soufriere yields the same u th age as its host lava on 226 ra ba versus time evolution diagrams curves for melts in equilibrium with plagioclase provide apparent ages of 1700 3300 yr for tonga but for soufriere they are displaced below that of the whole rock our interpretation is that the phenocrysts from all three lavas are zoned in both composition and age the apparent u th ages reflect mixtures of old cores and young rims and indicate a volume integrated age of 10s of kyr for the time for initial crystal growth crystal liquid segregation the time of storage as a cumulate plus the time spent during entrainment and growth in the new magma prior to eruption the 226 ra excesses were imparted to overgrowths on the old cumulate cores during entrainment by subsequent injections of new magma because crystal growth segregation and entrainment can all appear to occur in 100s to a few thousand years at most the bulk of the u th time scale is inferred to record storage in cumulates which are then incorporated into new magma batches plagioclase growth rates of 3 9 10 13 cm s 1 would reconcile the combined ra th and crystal size distribution data magma differentiation time scales and eruptive periodicity are one to three orders of magnitude shorter than the inferred cumulate storage times indicating complex phenocryst liquid behaviour beneath island arc volcanoes

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

geochemical evolution of a shallow magma plumbing system during the last 500 years miyakejima volcano japan constraints from 238u 230th 226ra systematics abstract in order to unravel magma processes and the geochemical evolution of shallow plumbing systems beneath active volcanoes we investigated u series disequilibria of rocks erupted over the past 500 years 1469 2000 ad from miyakejima volcano izu arc japan miyakejima volcanic rocks show 238u 230th 226ra disequilibria with excess 238u and 226ra due to the addition of slab derived fluids to the mantle wedge basaltic bombs of the 2000 ad eruption have the lowest 230th 232th ratio compared to older miyakejima eruptives yielding the youngest 238u 230th model age of 2 kyr this reinforces our previous model that fluid release from the slab and subsequent magma generation in the mantle wedge beneath miyakejima occur episodically on a several kyr timescale in the last 500 years miyakejima eruptives show 1 a vertical trend in a 230th 232th 238u 232th diagram and 2 a positive linear correlation in a 226ra 230th 0 1 230th diagram which is also observed in lavas from some of the single eruptions e g 1940 1962 and 1983 ad the variations cannot be produced by simple fractional crystallization in a magma chamber with radioactive decay of 230th and 226ra but it is possibly produced by synchronous generation of melts in the mantle wedge with different upwelling rate or addition of multiple slab derived fluids a much more favorable scenario is that some basaltic magmas were intermittently supplied from deep in the mantle and injected into the crust subsequently modifying the original magma composition and producing variations in 230th 232th and 226ra 230th 0 ratios via assimilation and fractional crystallization afc the assimilant of the afc process would be a volcanic edifice of previous miyakejima magmatism due to the relatively short timescales involved the interaction between the assimilant and recent miyakejima magmatism has not been recorded by the sr nd pb isotopic systems in such cases th isotopes and 226ra 230th ratio are excellent geochemical tracers of magmatic evolution

a dynamic balance between magma supply and eruption rate at kilauea volcano hawaii the dynamic balance between magma supply and vent output at kilauea volcano is used to estimate both the volume of magma stored within kilauea volcano and its magma supply rate throughout most of 1991 a linear decline in volume flux from the kupaianaha vent on kilauea s east rift zone was associated with a parabolic variation in the elevation of kilauea s summit as vent output initially exceeded then lagged behind the magma supply to the volcano the correspondence between summit elevation and tilt established with over 30 years of data provided daily estimates of summit elevation in terms of summit tilt the minimum in the parabolic variation in summit tilt and elevation or zero elevation change occurs when the magma supply to the reservoir from below the volcano equals the magma output from the reservoir to the surface so that the magma supply rate is given by vent flux on that day the measurements of vent flux and tilt establish that the magma supply rate to kilauea volcano on june 19 1991 was 217 000 10 000 m3 d or 0 079 0 004 km3 yr this is close to the average eruptive rate of 0 08 km3 yr between 1958 and 1984 in addition the predictable response of summit elevation and tilt to each east rift zone eruption near puu oo since 1983 shows that summit deformation is also a measure of magma reservoir pressure given this the correlation between the elevation of the puu oo lava lake 4 km uprift of kupaianaha and 18 km from the summit and summit tilt provides an estimate for magma pressure changes corresponding to summit tilt changes the ratio of the change in volume to the change in reservoir pressure dv dp during vent activity may be determined by dividing the ratio of volume erupted to change in summit tilt dv dtilt by the ratio of pressure change to change in summit tilt dp dtilt this measure of dv dp when combined with laboratory measurements of the bulk modulus of tholeitic melt provides an estimate of 240 50 km3 for the volume of kilauea s magma reservoir this estimate is much larger than traditional estimates but consistent with seismic tomographic imaging and geophysical modeling of kilauea s magma system

constraints on the nature of the subvolcanic reservoir at south sister volcano oregon from u series dating combined with sub crystal trace element analysis of plagioclase and zircon abstract we present sub crystal scale 238u 230th zircon ages and 238u 230th 226ra plagioclase ages of bulk mineral separates from the holocene 2 0 2 3 ka eruptions of the rock mesa rm and devil s hills dh rhyolites at south sister volcano oregon we link these age data with sub crystal trace element analyses of zircon and plagioclase to provide insight into the subvolcanic system at south sister as an example of a small volume continental arc volcano our results document the presence of coeval yet physically distinct regions within the magma reservoir and constrain the timescales over which these heterogeneities existed zircons from the rm and dh dominantly record ages from 20 to 80 ka with some grains recording ages 350 ka whereas plagioclase records 230th 226ra ages of 2 3 6 8 ka rm and 4 0 9 6 ka dh 3 and a 238u 230th age of 10 34 ka dh 3 we interpret zircons with ages 50 ka within a heterogeneous magmatic system and coexisted as physically distinct dominantly liquid bodies prior to eruption thus we favor a model where rhyolites are generated in independent batches by accumulation of evolved liquids in a heterogeneous largely crystalline reservoir similarities in crystal age and chemical data to that at other young silicic systems e g mount st helens okataina caldera complex suggest that this model may be more generally applicable to silicic magmas

chronology chemistry and origin of trachytes from hualalai volcano hawaii 1 hualalai volcano is unique among hawaiian volcanoes in that it possesses a relatively high proportion of evolved trachytic lavas that were erupted at the beginning of the alkalic postshield phase of volcanism these evolved lavas yield insights into magma sources magma supply rates and the evolution of the subvolcanic magmatic plumbing system at this time trachyte lavas are exposed at the puu waawaa pumice dome and puu anahulu flow as blocks in maars on the south flank of the volcano and as flows in water wells drilled on the west flank of hualalai new 40ar 39ar dates show that the puu waawaa and puu anahulu complex is 114 ka a block from the waha pele maar is 103 ka and water well trachytes range from 107 to 92 ka in age indicating a range for trachyte volcanism of 20 ka nd and pb isotopic compositions overlap with younger alkalic basalts from hualalai but are distinct from hualalai tholeiitic basalts and pacific mid ocean ridge basalts linking the trachytes to alkalic parental magmas that underwent extensive crystallization to yield trachytic residual magmas both sr and o isotopic ratios are higher in the trachytes than in hualalai alkalic lavas which is best explained by reaction with or assimilation of altered hualalai shield basalts at shallow depth major trace element and isotopic variations between trachytes are consistent with their evolution by fractional crystallization from a puu anahulu parent the short time gap between the end of tholeiitic volcanism 133 ka and the onset of trachytic alkalic volcanism and the lack of deep origin xenoliths place the magma reservoir within which the trachytes evolved rapidly at shallow 7 km depth whereas mauna kea and kohala volcanoes produced small volumes of highly evolved lavas as magma supply rates dwindled through the postshield stage postshield magma intrusion rates at hualalai were lowest during trachyte formation and increased through a more recent period of alkalic basalt eruptions subtle rare earth element and radiogenic isotopic distinctions between trachytes from the three localities indicate that the roof of the shallow magma reservoir may have been irregular allowing some trachytes to evolve independently from others

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

magmatic residence times of zoned phenocrysts introduction and application of the binary element diffusion modelling bedm technique this paper describes a general technique binary element diffusion modelling bedm for determining single crystal residence times in magmas that relies on modelling the diffusion of two or more elements in the crystal bedm has the advantage over other diffusion based models in that it does not need a precisely defined initial compositional profile for the crystal at zero time and instead requires that the concentrations of the two elements are correlated during crystallisation any differences subsequently observed between the two elements are caused by intracrystalline diffusion during residence in hot magma these differences are removed by artificially ageing the slower diffusing of the two elements and the amount of time taken to undo the difference between the elements is simply related to the crystal residence time decoupling time at high temperatures the bedm principle is demonstrated using artificial data and is then applied to literature data for sr and ba in a zoned sanidine crystal from the bishop tuff anderson et al in j petrol 41 3 449 473 2000 for this crystal the method gives a residence time estimate of 114 ka at 800 c which is then compared with estimates from other methods in theory the method can be further expanded for use as a geothermometer as well as geochronometer however this is not easily possible with the diffusivity data currently available

crystal size distribution systematics and the determination of magma storage times the 1959 eruption of kilauea volcano hawaii abstract the theory of crystal size distribution csd theory is based on a steady state population balance that monitors the flux of crystals growing into and out of specificed size categories in precipitating solutions the conservation equation describing this balance permits crystal growth and nucleation rates to be determined directly from crystal size distribution data in this investigation it is shown that csd analysis can alternatively be used to calculate the residence time of crystals in the system or in volcanologic terms the magma storage time prior to eruption if the characteristic crystal growth rate can be independently determined or estimated the crystal size data needed for storage time determinations are easily obtained from thin sections of glassy eruption samples and the mathematical calculations are relatively simple analysis of the errors inherent in this new technique predicts storage estimates accurate to within an order of magnitude

on the time scales of magmatism at island arc volcanoes precise information on timescales and rates of change is fundamental to an understanding of natural processes and the development of quantitative physical models in the earth sciences useries isot

uranium decay series the discovery of the 238u decay chain of course started with the seminal work of marie curie in identifying and separating 226ra through the work of the curies and others all the members of the 238u decay chain were identified an important milestone for geochronometrists was the discovery of 230th called ionium by bertram boltwood the yale scientist who also made the first age determinations on minerals using the u pb dating method boltwood in 1906 established the antiquity of rocks and even identified a mineral from sri lanka then ceylon as having an age of 2 1 billion years the application of the 238u decay chain to the dating of deep sea sediments was by piggott and urry in 1942 using the ionium method of dating actually they measured 226ra itself through 222rn assuming secular equilibrium had been established between 230

origin of differentiated lavas at kilauea volcano hawaii implications from the 1955 eruption kilauea s 1955 eruption was the first major eruption longer than 2 days on its east rift zone in 115 years it lasted 88 days during which 108 106 m3 of lava was erupted along a discontinuous 15 km long system of fissures a wide compositional range of lavas was erupted including the most differentiated lavas 5 0 wt mgo from a historic kilauea eruption lavas from the first half of the eruption are strongly differentiated 5 0 5 7 wt mgo later lavas are weakly to moderately differentiated 6 2 6 7 wt mgo previous studies using only major element compositions invoked either crystal fractionation macdonald and eaton 1964 or magma mixing wright and fiske 1971 as models to explain the wide compositional variation in the lavas to further evaluate these models detailed petrographic mineralogical and whole rock major and trace element xrf analyses were made of the 1955 lavas plagioclase and clinopyroxene in the early and late lavas show no petrographic evidence for magma mixing olivines from both the early and late lavas show minor resorption which is typical of tholeiitic lavas with low mgo contents core to rim microprobe analyses across olivine augite and plagioclase mineral grains give no evidence of disequilibrium features related to mixing instead plots of an ab vs distance from the core d and fo vs d 4 5 generated essentially linear trends indicative of simple crystal fractionation least squares mass balance calculations for major and trace element data using observed mineral compositions yield excellent results for crystal fractionation sum of residuals squared 0 01 for major elements and 5 for trace elements magma mixing produced less satisfactory results especially for cr furthermore trace element plots of zr vs sr cr and a12o3 generate curved trends indicative of crystal fractionation processes there is no evidence that mixing occurred in the 1955 lavas instead the data are best explained by crystal fractionation involving a reservoir that extends at least 15 km along kilauea s east rift zone a dike was intruded into the rift zone from the summit reservoir eight days after the eruption started instead of causing magma mixing the dike probably acted as a hydraulic plunger forcing more of the stored magma to be erupted

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

the effect of assimilation fractional crystallization and ageing on u series disequilibria in subduction zone lavas abstract although most arc lavas have experienced significant magma differentiation the effect of the differentiation process on u series disequilibria is still poorly understood here we present a numerical model for simulating the effect of time dependent magma differentiation processes on u series disequilibria in lavas from convergent margins our model shows that in a closed system with fractional crystallization the ageing effect can decrease u series disequilibria via radioactive decay while in an open system both ageing and bulk assimilation of old crustal material serve to reduce the primary u series disequilibria in contrast with recharge of refresh magma significant 226ra excess in erupted lavas can be maintained even if the average residence time is longer than 8000 years the positive correlations of 226ra 230th between sr th or ba th in young lavas from convergent margins have been widely used as evidence of fluid addition generating the observed 226ra excess in subduction zones we assess to what extent the positive correlations of 226ra 230th with sr th and ba th observed in the tonga arc could reflect afc process results of our model show that these positive correlations can be produced during time dependent magma differentiation at shallow crustal levels specifically fractional crystallization of plagioclase and amphibole coupled with contemporaneous decay of 226ra can produce positive correlations between 226ra 230th and sr th or ba th to a lesser extent therefore the correlations of 226ra 230th with sr th and ba th cannot be used to unambiguously support the fluid addition model and the strength of previous conclusions regarding recent fluid addition and ultra fast ascent rates of arc magmas is significantly lessened

differentiation and magma mixing on kilauea s east rift zone a further look at the eruptions of 1955 and 1960 part ii the 1960 lavas new and detailed petrographic observations mineral compositional data and whole rock vs glass compositional trends document magma mixing in lavas erupted from kilauea s lower east rift zone in 1960 evidence includes the occurrence of heterogeneous phenocryst assemblages including resorbed and reversely zoned minerals in the lavas inferred to be hybrids calculations suggest that this mixing which is shown to have taken place within magma reservoirs recharged at the end of the 1955 eruption involved introduction of four different magmas these magmas originated beneath kilauea s summit and moved into the rift reservoirs beginning 10 days after the eruption began we used microprobe analyses of glass to calculate temperatures of liquids erupted in 1955 and 1960 we then used the calculated proportions of stored and recharge components to estimate the temperature of the recharge components and found those temperatures to be consistent with the temperature of the same magmas as they appeared at kilauea s summit our studies reinforce conclusions reached in previous studies of kilauea s magmatic plumbing we infer that magma enters shallow storage beneath kilauea s summit and also moves laterally into the fluid core of the east rift zone during this process if magmas of distinctive chemistry are present they retain their chemical identity and the amount of cooling is comparable for magma transported either upward or laterally to eruption sites intrusions within a few kilometers of the surface cool and crystallize to produce fractionated magma magma mixing occurs both within bodies of previously fractionated magma and when new magma intersects a preexisting reservoir magma is otherwise prevented from mixing either by wall rock septa or by differing thermal and density characteristics of the successive magma batches

magma solidification processes beneath kilauea volcano hawaii a quantitative textural and geochemical study of the 1969 1974 mauna ulu lavas sents a late magma component formed in the summit magma storage region our results are consistent with the hypothesis that the components of the mu magmas followed two different routes the deformed olivine bearing magma moved along the deep basal

reappraisal of uranium series isotope data in kamchatka lavas implications for continental arc magma genesis uranium series isotopes can be used to determine constraints on the timescale of slab dehydration and melt production at subduction zones however interpretations of u th ra data suggest very different timescales of slab dehydration here we present new u th ra data from kamchatka along with a number of alternative models for production of radioactive disequilibrium variations in 226ra 230th and 231pa 235u activity ratios are best explained by crystal fractionation with host rock assimilation for a duration of less than c 6000 years the association of the largest 226ra excesses with high sr th in the most primitive lavas suggests that ra th fractionation is controlled by slab dehydration less than 10 ka ago we show that u th data can be explained by dynamic melting of a recently ka metasomatized mantle wedge dynamic melting of an oxidized source metasomatized several hundreds of thousands of years ago cannot produce significant 231pa excess because 238u 230th disequilibrium is inferred to be controlled by partial melting there is no requirement for multi stage slab dehydration commencing 150 ka we suggest that ra th disequilibria constrain the timing of slab dehydration whilst u th fractionation is dominated by partial melting at least at the kamchatka arc

extreme u th disequilibrium in rift related basalts rhyolites and granophyric granite and the timescale of rhyolite generation intrusion and crystallization at alid volcanic center eritrea received september 20 2005 accepted june 14 2006 advance access publication july 14 2006rhyolite pumices and co erupted granophyric granite xenolithsyield evidence for rapid magma generation and crystallization priorto their eruption at 15 2 2 9 ka at the alid volcanic center inthe danikil depression eritrea whole rock u and th isotopicanalyses show

experimental determination of ra mineral melt partitioning for feldspars and 226ra disequilibrium crystallization ages of plagioclase and alkali feldspar radium and other trace element partition coefficients have been experimentally determined for plagioclase and alkali feldspar in equilibrium with silicate melts in anorthitic plagioclase alkalis e g na k rb cs and the heavy earth alkalis e g ba ra are incompatibles in albitic plagioclase na is compatible whereas ca and sr are always compatible in plagioclase draplagioclase melt was determined to be 0 017 0 006 an91 0 025 0 009 an81 and 0 47 0 08 an34 for three different an contents the ratio dra dba increasing with decreasing an component in alkali feldspar k rb ba ra and sr are compatible whereas na cs and ca are incompatible draalkali feldspar melt was determined to 2 54 0 04 for a or75ab21an4 composition the ratio dra dba is 0 55 0 01 for plagioclase dra and xan are related as rt lndra kj mol 52 54 5 75 xan 4 25 1 51 and dra dba exp 9 47 6 21 xan 13 66 1 52 rt kj mol allowing calculation of dra from the an content of magmatic plagioclase for alkali feldspar we propose the equation dra dba exp 16 06 0 58 15 52 0 67 xor rt kj mol the experimentally determined partition coefficients are then used to recalculate th ra ba model ages leading to generally shorter feldspar residence times the variations encompass 20 to 90 shorter crystallization ages with respect to the originally calculated ones in two cases feldspar crystallization ages increase slightly for several cases the measured plagioclase and melt have either never been in equilibrium or the th ra ba system has been disturbed after crystallization

magma differentiation rates from 226ra 230th and the size and power output of magma chambers we present a mathematical model for the evolution of the 226ra 230th activity ratio during simultaneous fractional crystallization and ageing of magma the model is applied to published data for four volcanic suites that are independently known to have evolved by fractional crystallization these are tholeiitic basalt from ardoukoba djibouti morb from the east pacific rise alkali basalt to mugearite from vestmannaeyjar iceland and basaltic andesites from miyakejima izu bonin arc in all cases 226ra 230th correlates with indices of fractional crystallization such as th and the data fall close to model curves of constant fractional crystallization rate the best fit rates vary from 2 to 6 10 4 yr 1 consequently the time required to generate moderately evolved magmas f 0 7 is of the order of 500 to 1500 yrs and closed magma chambers will have lifetimes of 1700 to 5000 yrs these rates and timescales are argued to depend principally on the specific power output i e power output per unit volume of the magma chambers that are the sites of fractional crystallization equating the heat flux at the epr to the heat flux from the sub axial magma chamber that evolves at a rate of ca 3 10 4 yr 1 implies that the magma body is a sill of ca 100 m thickness a value which coincides with independent estimates from seismology the similarity of the four inferred differentiation rates suggests that the specific power output of shallow magma chambers in a range of tectonic settings covers a similarly narrow range of ca 10 to 50 mw km 3 their differentiation rates are some two orders of magnitude slower than that of the basaltic makaopuhi lava lake hawaii that cooled to the atmosphere this is consistent with the two orders of magnitude difference in heat flux between makaopuhi and the east pacific rise 226ra 230th data for magma suites related by fractional crystallization allow the magma differentiation rate to be estimated and from this the thermal budget of the magma chamber addressed and where an independent measurement of heat flux exists to place constraints on the size of the magma chamber such results have the potential to constrain the likely timescale and size of future eruptions of evolved magmas

differentiation and magma mixing on kilauea s east rift zone the lavas of the 1955 east rift eruption of kilauea volcano have been the object of considerable petrologic interest for two reasons first the early 1955 lavas are among the most differentiated ever erupted at kilauea and second the petrographic character and chemical composition of the lava being erupted changed significantly during the eruption this shift from more differentiated mgo 5 0 5 7 to more magnesian mgo 6 2 6 8 lava has been variously interpreted as either due to systematic excavation of a zoned differentiated magma body or to invasion of the differentiated magma by more primitive magma followed by rapid mixing and eruption of the resulting hybrid magmas petrologic examination of several nearvent spatter samples of the late 1955 lavas shows abundant evidence for magma mixing including resorbed and or reversely zoned crystals of olivine augite and plagioclase in addition the compositional ranges of olivine plagioclase and groundmass sulfide are very large implying that the assemblages are hybrid core compositions of olivine phenocrysts range from fo85 to fo77 the most magnesian olivines in these samples must have originally crystallized from a melt containing 8 0 8 5 mgo which is distinctly more magnesian than the bulk composition of the late 1955 lavas the majorelement and trace element data are either permissive or supportive of a hybrid origin for the late 1955 lavas in particular the compositional trends of the 1955 lavas on plots of cao vs mgo and the virtual invariance of al2o3 and sr in these plagioclase phyric lavas are more easily explained by magma mixing than by fractionation the pattern of internal disequilibrium re equilibration in the late 1955 spatter samples is consistent with reintrusion and mixing having occurred at least twice during the latter part of the 1955 eruption plagioclase zonation preserves possible evidence for additional earlier reintrusion events least squares modelling the mixing of early 1955 bulk compositions with various summit lavas olivine pick the 1952 summit lava as most like the primitive component the results also indicate the primitive component had mgo 7 5 8 0 corresponding to liquidus temperatures of 1165 1175 c the absence of fe ti oxide phenocrysts in the late 1955 lavas implies that the cooler component of the hybrid had t 1110 c thus the thermal contrast between the two components may have been as much as 55 65 c sufficient to produce the conspicuous disequilibrium effects visible in the spatter samples

a petrologic perspective of kīlauea volcano s summit magma reservoir two hundred years of magmatic history are documented by the lavas and tephra sampled from k olauea s historical summit eruptions this paper presents detailed petrographic and geochemical data for a comprehensive suite of samples erupted within or near k olauea s summit caldera since the 17th century our results elucidate the range of magmatic processes that operate within the volcano s summit magma reservoir and document two compositional trends that span nearly the entire known range for the volcano prior to the 1924 summit crater collapse a trend of increasing incompatible element and cao and decreasing sio2 abundances at a constant mgo prevailed thereafter the trend reversed direction and has persisted for the rest of the 20th century including during the current puau a oa o eruption the rapid and systematic nature of these temporal geochemical variations indicates that the summit reservoir is a single relatively small body rather than a plexus of dikes and sills olivine fractionation is the dominant petrologic process within this reservoir petrographic observations and olivine and whole rock geochemical data suggest that the summit reservoir has a crown of aphyric more evolved low density magma differentiation within this crown involving clinopyroxene and plagioclase is more extensive than previously recognized in k olauea summit lavas the effects of crystal fractionation are superimposed upon an evolving hybrid magma composition produced by mixing new mantle derived magmas with more fractionated reservoir magma frequent eruptions of these hybrid reservoir magmas document the rapid variation in parental magma composition these compositional variations correlate with magma supply rate both are thought to be influenced by the degree of melting of small scale source heterogeneities within the hawaiian plume however k olauea s source compositions and partial melting processes have varied only within a narrow range over the past 350 kyr

experimental study of radium partitioning between anorthite and melt at 1 atm we present the first experimental radium mineral melt partitioning data specifically between anorthite and a cmas melt at atmospheric pressure 226 ra disequilibria are an important chronometer of recent magmatic activity ion microprobe measurement of coexisting anorthite and glass phases produces a molar d ra 0 040 0 006 and d ra d ba 0 24 0 05 at 1400 c our results indicate that lattice strain partitioning models fit the divalent ca sr ba ra partition coefficient data of this study well supporting previous work on crustal melting and magma chamber dynamics that has relied on such models to approximate radium partitioning behavior in the absence of experimentally determined values

crystal and magma residence at kilauea volcano hawaii 230th 226ra dating of the 1955 east rift eruption abstract previous estimates of crustal storage time of magmas at kilauea volcano hawaii range from a few years to a few thousand years leading to considerable uncertainty in the time scales of processes of magmatic storage and differentiation we present a new approach for determining minimum magma residence times which involves dating phenocrysts in a magma using 226ra 230th disequilibria and apply this approach to the early phase of the 1955 east rift eruption at kilauea when fractionation of ra from ba a proxy for initial ra in the crystals during crystal growth is considered along with the effects of inclusions in the minerals the data are consistent with co precipitation of plagioclase and clinopyroxene from a melt represented by the groundmass at a mean age of 1000 300 400 a unless a significant fraction 30 of the crystals are remnants from an earlier batch of evolved magma in the system these data constrain the minimum magmatic residence time to be 550 yr considerably longer than most previous estimates of storage time at kilauea as well as those for some other basaltic systems for the temperature interval of augite plagioclase growth in the early 1955 magma a maximum constant cooling rate of 0 1 c yr 1 10 5 c h is derived from the minimum magmatic residence time of 550 yr the total magma storage time would be 2500 yr if this cooling rate applied to the entire thermal history of the magma although a more complex cooling history where cooling rates were more rapid early in the storage history is permissive of a total residence time which is not much longer than 550 yr the disparate estimates of magma residence at kilauea may reflect the uncertainties in the methods of estimation in addition to true variations in storage time for different batches of magma more work is necessary in order to determine whether a long residence time is characteristic of rift zone lavas and or of kilauean lavas in general

diffusion coupling between trace and major elements and a model for calculation of magma residence times using plagioclase residence times of plagioclase crystals in magma reservoirs can be determined by modeling the compositional zoning of trace elements in these crystals we present a formulation to model diffusion of trace elements in plagioclase paying special attention to certain thermodynamic and kinetic aspects in particular we account for the compositional dependence on anorthite content of the chemical potential and diffusion coefficients of trace elements e g mg the choice of suitable boundary conditions and potential effects of diffusion in more than one dimension we show that contrary to intuition diffusive fluxes of trace elements may be coupled to major element concentration gradients and ignoring such coupling can lead to incorrect estimates of timescales we illustrate application of the model using plagioclase crystals from a suite of gabbroic xenoliths from a holocene dacitic lava flow of volcan san pedro chilean andes 36 s the inferred timescale for metasomatism of the xenoliths by evolved liquids is on the order of 100 30 to 148 yr and serves to illustrate how trace element zoning in plagioclase provides a window into timescales of magmatic processes inaccessible by isotopic or other methods

ra partitioning between phlogopite and silicate melt and 226ra ba 230th ba isochrons in this study we experimentally determine phlogopite melt partition coefficients of ra and other trace elements in a lamproitic system this work was achieved using an analytical technique la icp ms with low detection limits 0 01 fg permitting the measurement of the very low ra concentrations feasible in experiments 1 ppb d ra phlogopite melt was determined to 2 28 0 44 and 2 84 0 47 in two experiments the ratio d ra d ba is around 1 6 the compatibility of ra in phlogopite results from an ionic radius being close to the apex of the lattice strain parabola for earth alkalis in the large xii coordinated interlayer site of phlogopite a re evaluation of d ra and d ra d ba for magmatic minerals containing appreciable ra yields d ra mineral melt ranging from 2 6 for phlogopite down to 2 3 10 5 for pyroxenes and d ra d ba mineral melt from 4 for leucite to 2 10 2 for orthopyroxene the influence of melt composition on d ra d ba is less than 10 all investigated minerals have different d ra d ba strongly fractionating ra from ba thus for magmatic systems 226 ra ba in the various minerals is not constant these minerals do not form a straight line in the 226 ra ba 230 th ba system at the time of crystallization and thus there is no 226 ra ba 230 th ba isochron at t 0 226ra 230th ba mineral dating is thus applicable only to model ages calculated from mineral glass pairs with known d ra