time scales of hybridisation of magmatic enclaves in regular and chaotic flow fields petrologic and volcanologic implications this paper describes numerical models of advection diffusion between enclaves and host magmas applied with the aim of estimating time scales during which enclaves can be homogenised in particular advection was simulated using a numerical system consisting of regular and chaotic regions results indicate that the homogenisation time of enclaves in chaotic regions is several orders of magnitude faster than in regular regions for instance an enclave with a diameter of 100 cm may be homogenised in the chaotic region in 380 years assuming an advection velocity of 10 cm year whereas in the regular region it would require 6 5 105 years for complete homogenisation this implies that in the same magmatic system large differences in the degree of homogenisation may co exist generating magmatic masses with large spatial and temporal inhomogeneities

enhanced anticyclonic circulation in the eastern north atlantic during cold intervals of the last deglaciation inferred from deep sea pollen records pollen analyses on two deep sea records recovered in the eastern atlantic between lat 37 and 4 n show two coeval peaks in wind transported terrestrial elements pollen and spores mainly from dry steppe type formations at 15 ka and at 10 3 ka this may reflect the dominance of anticyclonic circulation during the cold phases of the last deglaciation responsible for strong winds leading to the advection of polar air masses equatorward at lat 37 n the predominant influence of the westerlies was established after 9 3 ka

a 300 kyr high resolution aridity record of the north african continent new oxygen isotope data and a high resolution carbonate record of a core from the northwest african margin are presented in combination with geochemical zr rb ratio al ba organic carbon and biogenic opal fluxes and sedimentological median grain size parameters to show variations in african continental aridity wind strength and upwelling productivity the carbonate record is diluted by the supply of aeolian dust from the arid saharan region of north africa and is seen to vary with a characteristic sawtooth pattern indicating rapid increases in dust flux followed by gradual declines spectral analysis of the carbonate profile and comparison with specmap stacked oxygen isotope and etp solar radiation profiles shows that the precessional 23 kyr insolation induced african climate system is decoupled from global ice volume climate changes operating on a 100 kyr frequency detailed studies of glacial terminations i ii and iii confirm the presence of rapid short timescale climatic variations in aridity

rapid magma ascent recorded by water diffusion profiles in mantle olivine mechanisms and rates of magma ascent play a critical role in eruption dynamics but remain poorly constrained phenomena water dissolved in mantle minerals as hydrogen and partitioned into the magma during ascent may provide clues to quantifying magma ascent rates prior to eruption we determined the dehydration profiles in olivine crystals from peridotite mantle xenoliths within the pali aike alkali basalt from patagonia chile the results demonstrate that the amount of water stored in the uppermost mantle has likely been underestimated due to water loss during transport using experimental diffusion data for hydrogen we estimate that the xenoliths reached the surface from 60 70 km depth in several hours a surprisingly rapid rise comparable to ascent rates for kimberlite magmas

magma storage and mixing conditions for the 1953 1974 eruptions of southwest trident volcano katmai national park alaska between 1953 and 1974 approximately 0 5 km3 of andesite and dacite erupted from a new vent on the southwest flank of trident volcano in katmai national park alaska forming an edifice now known as southwest or new trident field analytical and experimental evidence shows that the eruption commenced soon after mixing of dacite and andesite magmas at shallow crustal levels four lava flows 58 3 65 5 wt sio2 are the dominant products of the eruption these contain discrete andesitic enclaves 55 8 58 9 wt sio2 as well as micro and macro scale compositional banding tephra from the eruption spans the same compositional range as lava flows however andesite scoria 56 58 1 wt sio2 is more abundant relative to dacite tephra and is the explosively erupted counterpart to andesite enclaves fe ti oxide pairs from andesite scoria show a limited temperature range clustered around 1000 c temperatures from grains found in dacite lavas possess a wider range however cores from large 100 m magnetite and coexisting ilmenite give temperatures of 890 c taken to represent a pre mixing temperature for the dacite water contents from dacite phenocryst melt inclusions and phase equilibria experiments on the andesite imply that the two magmas last resided at a water pressure of 90 mpa and contained 3 5 wt h2o equivalent to 3 km depth if saturated unzoned pyroxene and sodic plagioclase in the dacite suggest that it likely underwent significant crystallization at this depth highly resorbed anorthitic plagioclase from the andesite suggests that it originated at greater depths and underwent relatively rapid ascent until it reached 3 km mixed with dacite and erupted diffusion profiles in phenocrysts suggest that mixing preceded eruption of earliest lava by approximately one month the lack of a compositional gap in the erupted rock suite indicates that thorough mixing of the andesite and dacite occurred quickly via disaggregation of enclaves phenocryst transfer from one magma to another and direct mixing of compositionally distinct melt phases

kinetics of diffusion controlled evaporation of fe mg olivine experimental study and implication for stability of fe rich olivine in the solar nebula abstract evaporation is a process that caused chemical fractionation in the solar nebula the evaporation rates of meteorite forming minerals and silicate melts are key parameters for constraining the timescale of high temperature processes in the early solar nebula and for understanding the mechanisms of cosmochemical fractionation the kinetics of evaporation of olivine initial fo 92 the most common silicate in meteorites was experimentally investigated at 1414 c for various duration under continuous evacuation the surface of olivine becomes more magnesian and the interior becomes zoned as evaporation proceeds indicating preferential evaporation of the fayalite fa component the weight loss surface composition and interior zoning profile were analyzed using a semi infinite one dimensional diffusion model with boundary migration and the controlling model parameters were optimized by fitting the experimental results the evaporation rate of olivine shows notable composition and orientation dependence as olivine becomes more magnesian the evaporation rates of the 100 010 and 001 surfaces decrease among which the rate at the 001 surface is greatest 1 0 m h at fo 91 8 which is about 2 orders of magnitude faster than that of pure synthetic forsterite the estimated fe mg fractionation factor shows anisotropy ranging from 0 017 to 0 035 which is significantly greater than the equilibrium value of the fe mg distribution coefficient between olivine and gas suggesting kinetic suppression of evaporation of the fa component the fe mg interdiffusion coefficient at 1414 c which also shows notable composition and orientation dependence is estimated to be 8 7 10 15 m2 sec along the c axis the results were applied to constrain the timescale of heating for a spherical fo50 olivine grain to retain the fa component olivine dust 1 m in diameter can retain 80 of the initial fa component for one minute in vacuum and for 30 min at 10 pa ph2 when heated at 1414 c therefore fo50 olivine in chondrite matrices could have survived an incipient heating event depending on the ambient hydrogen pressure if they were originally present in the solar nebula

orbital forcing of dust supply to the north canary basin over the last 250kyr abstract the canary basin lies in a region of strong interaction between the atmospheric and ocean circulation systems trade winds drive seasonal coastal upwelling and dust storm outbreaks from the neighbouring sahara desert are the major source of terrigenous sediment to investigate the forcing mechanisms for dust input and wind strength in the north canary basin the temporal pattern of variability of sedimentological and geochemical proxy records has been analysed in two sediment cores between latitudes 30 30 n and 31 40 n spectral analysis of the dust proxy records indicates that insolation changes related to eccentricity and precession are the main periods of temporal variation in the record si al and grain size of the terrigenous fraction show an increase in glacial interglacial transitions while al concentration and fe al ratio are both in phase with minima in the precessional index hence the results obtained show that the wind strength was intensified at terminations at times of maxima of northern hemisphere seasonal insolation when the african monsoon was enhanced the north canary basin also received higher dust input this result suggests that the moisture brought by the monsoon may have increased the availability of dust in the source region

wavelet based correlation wbc of zoned crystal populations and magma mixing magma mixing is a common process and yet the rates kinematics and numbers of events are difficult to establish one expression of mixing is the major trace element and isotopic zoning in crystals which provides a sequential but non monotonic record of the creation and dissipation of volumes of distinct chemical potential we demonstrate a wavelet based correlation wbc technique that uses this zoning for the recognition of the minimum number of mixing or open system events and the criteria for identifying populations of crystals that have previously shared a mixing event when combined with field observations of the spatial distribution of crystal populations wbc provides a statistical link between the time varying thermodynamic and fluid dynamic history of the magmatic system wbc can also be used as a data mining utility to reveal open system events where outcrop is sparse an analysis of zoned plagioclase from the tuolumne intrusive suite provides a proof of principle for wbc 1 2002 elsevier science b v all rights reserved

a model for garnet and plagioclase growth in pelitic schists implications for thermobarometry and p t path determinations numerical models of the progressive evolution of pelitic schists in the ncmnkfmash system with the assemblage garnet biotite chlorite staurolite plagioclase muscovite quartz h2o are presented with the goal of predicting compositional changes in garnet and plagioclase along different p t paths the numerical models support several conclusions that should prove useful for interpreting the p t paths of natural parageneses i garnet may grow along p t vectors ranging from heating with decompression to cooling with compression p t paths deduced from garnet zoning that are inconsistent with these growth vectors are self contradictory ii there is a systematic relation between garnet and plagioclase composition and growth such that for most p t paths garnet growth requires plagioclase consumption furthermore mass balance in a closed system requires that as plagioclase is consumed the remaining plagioclase becomes increasingly albitic inclusions of plagioclase in the core of garnet should be more anorthitic than those near the rim and zoned matrix plagioclase should have rims that are more albitic than the cores complex plagioclase textures may arise from the local variability of growth and precipitation kinetics iii a decrease of fe fe mg in a garnet zoning profile is a reliable indicator of increasing temperature for the assemblage modelled however there is no single reliable p monitor and inferences about p can only be made by considering plagioclase and garnet together iv consumption of garnet during the production of staurolite removes material from the outer shell of a garnet and may make recovery of peak metamorphic compositions and p t conditions impossible low peak temperatures typically recorded by staurolite bearing assemblages may reflect this phenomenon v diffusional homogenization of garnet affects the computed p t path and results in a clockwise rotation of the computed p t vector relative to the true p t path

soil moisture fluctuations recorded in saharan dust deposits on lanzarote canary islands over the last 180 ka abstract aeolian sediments trapped in volcanically dammed valleys on lanzarote canary islands were investigated in order to reveal environmental changes over the last 180 ka clay content and frequency dependent magnetic susceptibility were used as proxies for pedogenesis and palaeo soil moisture during the last 180 ka these proxies showed a general pattern of enhanced soil moisture during glacials and stadials and more arid conditions during interglacials and interstadials comparisons of these results with proxies from regional palaeoclimate studies identified a positive correlation with proxies of trade wind strength off northwest africa and inverse correlations with both sea surface temperatures in the northeast atlantic and the extent of mediterranean vegetation possible causes for the observed pattern include a glacial enhancement of precipitation from westerly cyclones a change in relative humidity due to fluctuating air temperatures and an occasional influence of the african summer monsoon although it is not yet possible to clearly differentiate among these factors it is clear that the first two factors must have been primarily dominant these results represent the first quasi continuous terrestrial data testifying to environmental changes in the northwest african coastal area for the last 180 ka and complement the abundant data derived from marine cores of the region high latitude dynamics had a major influence in this area and were intermediated by north atlantic sea surface temperatures a possible negative correlation can also be observed with the orbital obliquity cycle with a 10 ka time lag which is similar to the lag recorded from north atlantic sea surface temperatures

observations of plagioclase zoning using interference imaging abstract interference imaging techniques laser interference microscopy in transmitted light and nomarski differential interference contrast in reflected light have been used to study different types of zoning in magmatic plagioclase crystals samples studied come from a wide range of rock types and geological environments analysis of zoning profiles for individual unit zones shows that a saw tooth pattern in which an initially high an decreases as growth proceeds is the most common type of zoning configuration we recognize 2 major types of zoning type 1 small zones usually less than 10 microns thick with compositional amplitudes up to 10 an and type 2 zones up to50 microns thick with large compositional amplitudes of up to 35 an detailed analysis of zoning patterns shows that oscillatory zoning is not actually oscillatory in the sense of a sine wave it is discontinuous unit zones are characteristically bounded by discontinuities this common pattern is consistent with alternating periods of growth and periods of dissolution reaction and lack of growth or possibly very slow growth our observations firmly establish that dissolution and magmatic reaction involving both growth and dissolution are common during growth of the magmatic plagioclase which we have studied type 1 zonation appears consistent with perturbations of local conditions in a diffusion controlled boundary layer around the growing crystal type 2 zoning is probably due to large scale conditions faceted planar growth surfaces appear to be the rule in magmatic crystallization although in some instances rounded or irregular convolute zonation can occur the repetitive nature of many of the features we have observed is consistent with and suggestive of some form of self organization

loess in europe mass accumulation rates during the last glacial period abstract upper pleistocene loess palaeosol sequences provide excellent high resolution terrestrial archives of climate forcing due to improvements in numerical age determinations especially in luminescence dating methods a more reliable time based reconstruction of the past climate and environmental change has become available for the loess record in europe chronological information was collected from 43 sites along a northwest to southeast transect in europe thirty three of these sites had sufficient age information to allow estimation of mass accumulation rates and it was possible to isolate the mass accumulation rates of primary loess during the last glacial period 28 13 ka bp at 21 of these locations these sites fall along a coarse climatic gradient from the relatively coastal climate of belgium and france to the drier more continental climate of central europe interpreting mass accumulation rates of loess in terms of this climatic gradient is not straightforward as these deposits are dominated by sources in floodplains and large river systems thus accumulation rates are influenced strongly by regional wind and precipitation patterns but mostly by the availability of glacially derived material from the alps and the periglacial terrains that characterized european fluvial systems during and immediately following glaciation

last glacial maximum to early holocene wind strength in the mid latitudes of the southern hemisphere from aeolian dust in the tasman sea dust transported by southern hemisphere mid latitude westerly winds from australia and deposited in the tasman sea shows no evidence for stronger winds during the last glacial maximum lgm compared to the holocene features of the particle size distributions of the dust do however indicate enhanced dry deposition of dust in the lgm changing to rainfall scavenging during deglaciation and the early holocene as climate ameliorated from these results it appears that activation of desert dunefields over 40 of australia during the lgm was the result of a reduction in stabilizing vegetation and more frequent episodes of sand movement rather than of increased wind strength the lgm climate of inland australia must have been considerably more stressful for plants as a result of lower precipitation and or carbon dioxide stress to achieve the implied levels of surface destabilization enhanced atmospheric dust loads in the southern hemisphere and deposition over antarctica were most likely the result of greatly expanded source areas in the mid latitude southern continents and a weaker hydrological cycle rather than greater entrainment or more efficient transport by stronger winds during the lgm wind strength appears to have varied regionally and predominantly in high latitudes rather than uniformly for all zonal winds

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

storminess control over african dust input to the moroccan atlantic margin nw africa at the time of maxima boreal summer insolation a record of the last 220 kyr abstract precessional forcing of dust flux from northwest africa to the atlantic during the last 220 kyr is recognised through changes in physical and chemical sediment properties sediment colour reflectance magnetic susceptibility x ray fluorescence element intensity in a core from the moroccan margin sediment colour reflectance magnetic susceptibility and ca and fe element intensity changes are thought to be driven by dust input from north africa spectral analysis of the sediment properties records displays a dominant periodicity in the 1 23 kyr 1 frequency band that is associated with the earth s orbital precession peaks in terrigenous supply match precessional minima this suggests a close link between maxima of boreal summer solar radiation monsoon activity and dust generation enhanced precession driven solar radiation would have caused increased seasonal temperature contrasts which amplified atmospheric turbulence and stimulated storminess such a scenario is similar to today s summer conditions when frequent storms cause distinct dust plumes to form in the area and transport fine terrigenous material to the adjacent north atlantic ocean

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

loess like and palaeosol sediments from lanzarote canary islands spain indicators of palaeoenvironmental change during the late quaternary abstract on lanzarote canary islands quaternary saharan dust and weathered local volcanic material were trapped in miocence to pliocene valleys dammed by younger volcanic edifices these sediments show sequences of alternating reddish clayey and loess like yellowish silty material in order to investigate if reddish clayey layers contain material derived from local pedogenesis and if so which pedogenetic processes were active we performed sedimentological micromorphological and environmental magnetic analyses the analyses demonstrate that these layers contain material derived from local soils these soils were characterised by clay formation rubefication and the formation of superparamagnetic particles during periods of enhanced soil moisture thus they can serve as natural archives in order to reconstruct the terrestrial palaeoclimatic history of lanzarote the distribution of soil material in the profiles shows that cold periods of the late quaternary were characterised by more humid conditions than today using palaeontological remains and a comparison with recent soils on tenerife we can roughly estimate maximal palaeoprecipitation values during more humid periods

rates of hydrothermal cooling of new oceanic upper crust derived from lithium geospeedometry episodic emplacement and cooling of lavas and dikes at mid ocean ridges leads to large fluctuations in hydrothermal fluxes and biological activity however the processes operating beneath the seafloor during these transient events such as permeability creation and dike cooling are poorly understood we have developed a new approach to determine the cooling rate of the sheeted dike complex based on the extent of diffusion of lithium from plagioclase into clinopyroxene during cooling we have calibrated this li geospeedometer using new high temperature experiments to determine both the temperature dependence of the partitioning of li between plagioclase and clinopyroxene and the diffusion coefficient for li in clinopyroxene application of this method to lavas and dikes from odp hole 504b shows that cooling rates vary dramatically with depth in the upper oceanic crust extremely rapid cooling rates 450 c hr 1 in the upper part of the sheeted dike complex are sufficient to power hydrothermal megaplume formation within the overlying water column

inter and intracrystalline isotopic disequilibria techniques and applications in the last 20 years we have seen a significant expansion of techniques related to geochemical and isotopic microsampling of materials in the earth sciences from constraining pre eruptive histories of flood basalt magmas to identifying the natal rivers of origin of anadromous fishes these techniques have had significant impacts in a wide variety of scientific fields nowhere has the impact been greater than in identifying the sources processes and timing of processes involved in igneous magmatic systems both technique refinements and the development of new technologies have aided in advancing microsampling applications thus allowing for a better understanding of the sources and mechanisms responsible for changing geochemical and isotopic signatures in natural systems in this chapter we focus on the techniques and technologies associated with radiogenic isotope microsampling and review applications of these techniques as utilized in scientific investigations isotope microsamping is a logical extension of earlier studies that evaluated individual components of magmas and magma systems including melts and minerals from the use of petrographic microscopes and the later introduction of the electron microprobe the focus on internal chemical variations in melts and minerals is critical to assessing the petrogenetic histories of igneous rocks even today these technologies are used to ensure that further trace element and isotopic analyses are undertaken in a textural and major element context for trace elements and isotopes early studies e g cortini and van calsteren 1985 confirmed variations in the melt and mineral components of many igneous rocks but focused on mineral or glass separates potential information associated with isotopic variations retained by individual crystals or internal variations within individual crystals was lost later studies such as geist et al 1988 focused on isotope variations within single megacrysts to constrain mixing scenarios between basaltic andesitic and rhyolitic magmas and davidson et al 1990 used

geomorphological investigations of sediment traps on lanzarote canary islands as a key for the interpretation of a palaeoclimate archive off nw africa abstract on lanzarote canary islands late quaternary saharan dust and volcanic material were trapped in miocence to pliocene valleys dammed by volcanic lava flows these trapped sediments are potentially interesting as they can be natural archives useful to reconstruct the terrestrial palaeoclimate history of the nw african margin nevertheless slope wash processes altered the primarily eolian deposits making climatic interpretation not straightforward geomorphological mapping gis calculations and sedimentological investigations were used to unravel these processes influencing the temporal resolution of the palaeoclimatic archive demonstrating that they average the palaeoclimatic signal by some ka thus despite the colluvial geomorphic environment the valley fillings can be used for palaeoclimatic interpretation of events with a length of at least some ka the youngest sediments deposited since at least 2 5 ka are anthropogenically triggered and thus cannot be used for palaeoclimatic interpretation the results show that the input of saharan dust at lanzarote increased during the last 1 0 ka and especially during the early middle holocene

long range transport of giant aeolian quartz grains linkage with discrete sedimentary sources and implications for protective particle transfer abstract several articles have documented the presence of large particles 62 5 m that have been transported great distances 1000 km through the atmosphere at present we do not understand the mechanisms that lead to mineral grains being carried aloft far beyond the limits imposed by conventional gravitational settling models typically marine geologists refer to ice rafting and or advective transport by ocean currents as the dominant transport processes that deliver large mineral grains to deep sea sediments textural analyses of giant quartz grains from six sedimentary deposition events collected from various sources including a single site in the north pacific ocean and sites in the british isles and france strongly support the idea that in each case all of the grains were initially eroded from a discrete sediment type and often a discrete point source and subsequently transported via the atmosphere to our sampling sites up to 10 000 km away these findings suggest that at least at times erosional events fuelling long distance atmospheric transport are exceedingly specific and operate upon geologically distinctive assemblages and are able to effect long distance transfer of large grains with no grain to grain collisions this work also suggests that atmospheric transport should be included as a possible means of delivery for significant quantities of giant sedimentary particles to remote marine sites such as the lord howe rise

complexity of quaternary aeolian dynamics canary islands abstract carbonate aeolianites are important quaternary archives at the point of intersection between marine and terrestrial systems since they are composed of alternating aeolian sediments and several paleosol units these sequences are highly suitable to reconstruct palaeoenvironmental conditions in northern fuerteventura at least five different areas are characterised by successions of different dune generations and paleosols few studies have addressed the stratigraphic order of individual dune areas therefore a comprehensive consideration spanning several dune fields is needed here we aim to present a detailed stratigraphy of two different dune areas and to identify the contribution of different materials shelf origin dust origin volcanic origin along with processes accumulation soil formation erosion preservation that build up these archives four key sections were selected and sampled for laboratory analyses texture elemental composition caco3 content palaeoenvironmental magnetics luminescence dating and gastropod assemblages based on main stratigraphic features five major sedimentary sequences were identified indicating differences in prevailing sediment supply humidity and volcanic activity first luminescence dating irsl of the sequences revealed sedimentation ages between 360 ka and 15 ka finally we are able to demonstrate that different dune areas show comparable stratigraphic patterns but each studied site is defined by certain characteristics depending on the respective features of the closer surrounding the knowledge of these peculiarities and the underlying background is essential in order to correlate different sites and to attempt an appropriate environmental interpretation of the sedimentary sequences

low δ18o rhyolites from yellowstone magmatic evolution based on analyses of zircons and individual phenocrysts the yellowstone plateau volcanic field is one of the largest centers exchange time to form zoned zircons is between a few hundred and a few thousand years which reflects the residence time of lowo of rhyolitic magmatism on earth major caldera forming eruptions are followed by unusual lowo rhyolites new oxygen isotope magmas after formation and before eruption petrologic and geochemical data from rhyolites belonging to the 2 0 my eruptive history of yellowstone are presented with emphasis on the genesis of lowo magmas erupted after the huckleberry ridge tuff 2 0 ma 2500 km and lava creek tuff 0 6 ma

holocene climatic change in morocco a quantitative reconstruction from pollen data annual precipitation july and january temperatures were reconstructed from a continuous holocene pollen sequence from the middle atlas morocco using the best modern analogues method the reconstructions show a clear difference between the early and late holocene from 10 ka to 6 5 ka the climate was drier and warmer than during the period since 6 5 ka the average value of annual precipitation was 870 mm until 6 5 ka then rose to 940 mm between 10 ka and 6 5 ka january and july temperatures were about 4 c higher than the present both temperatures show a marked decrease between 7 ka and 6 ka after 6 5 ka july and january temperatures fluctuated between 21 and 23 c and 2 5 and 5 c respectively january temperatures show a period of intermediate values 3 5 c between 4 ka and 5 5 ka the reconstructed climate values generally match palaeolimnological data from the same core which show five intervals of low lake level during the holocene they are also consistent with regional scale cohmap simulated palaeoclimate that shows contrasting patterns of rainfall variation between the northwesternmost part of africa and the intertropical band

the temporal evolution of three magmatic systems in the west eifel volcanic field germany abstract the quaternary west eifel volcanic field is the surface expression of a mantle plume that is thought to contain 1 melt the volcanoes range in age from 0 7 ma to 10 000 yr bp and the average recurrence rate of volcanism is around 3 5 10 4 eruptions per year giving a mean time between eruptions of 2875 years assuming that the field is monogenetic the presence of mafic and ultramafic xenoliths is taken as evidence for rapid single stage emplacement of magmas at velocities around 0 5 km h however the presence of clinopyroxene that preserves evidence of polybaric crystallisation belies this simple model this study uses variations in the fo content of olivine in mantle derived xenoliths and in olivine xenocrysts enclosed in cumulate xenoliths to calculate the time scale of evolution of three volcanic centres in the eifel field core rim variations in olivine are interpreted to result from fe mg interdiffusion between it and a surrounding melt using experimental determinations of the interdiffusion coefficient and approximations of magma temperature contact times have been calculated using planar and radial diffusion models the three volcanic centres studied were meerfelder maar gemundener maar and baarley the cumulate xenoliths at meerfelder maar formed at a depth of 13 km and record a magma emplacement event at between 1 and 3 years prior to eruption two suites of mantle derived olivine clinopyroxenites record a further two events at 1 8 days and 3 h prior to eruption the final event is interpreted to record the eruption of this volcano and the 3 h contact time records the time required for transport of peridotite xenoliths from the mantle to surface giving an average emplacement velocity of around 15 km h the cumulate xenoliths at gemundener maar crystallised at depths of between 4 and 22 km there are four distinct events recorded by the zoned olivine grains in the clinopyroxene rich cumulates from this locality the maximum residence time is similar to that at meerfelder maar however in this case the final magma resided in the chamber for between 23 days and 2 7 months prior to eruption allowing enough time for any entrained peridotite xenoliths to be filtered out the cumulate xenoliths from the baarley locality record a much longer history than those at the other localities in this case initially peridotitic olivine has been completely re equilibrated over 175 years prior to eruption in common with the other two localities there is evidence of multiple intrusive events at depths up to 7 km prior to final eruption the duration of the final eruption event and the interpreted depth to source of the xenoliths indicate an emplacement velocity of around 3 km h the data derived from modelling of diffusion profiles in olivine from cumulate xenoliths indicate that the magmatic systems feeding these three volcanoes were dynamic and very short lived in addition these data can be used to place constraints on the rate of cumulate formation in subvolcanic magma chambers on the basis of the data presented here it would seem that an appreciable thickness of cumulates can form over relatively short time spans days to a few years

effect of pressure on fe mg ni and mn diffusion in fexmg1 x 2sio4 olivine abstract the pressure dependence of fe mg interdiffusion coefficients as well as of diffusion coefficients of the trace elements ni and mn in olivine have been determined from diffusion anneals carried out using oriented single crystals in multianvil presses this is the first determination of activation volumes of diffusion of trace elements ni mn in olivine results from an isothermal polybaric 1673 k 6 12 gpa and an isobaric polythermal 1623 1823 k 12 gpa set of experiments were combined to constrain an internally consistent set of arrhenius parameters for the diffusion processes it is found that within the uncertainty of the data a diffusion rates of fe mg mn and ni are very similar to each other at all conditions consistent with more detailed observations from 1 atmosphere experiments petry et al 2004 b apparent activation volumes using different fitting protocols lie between 4 and 7 cm 3 mol 1 but a value of 5 3 1 0 cm 3 mol 1 cf misener 1974 farber et al 2000 describes the pressure dependence of diffusivity of these elements in olivine over its entire stability range in pressure adequately along the ni nio f o 2 buffer c the activation volume at constant f o 2 is higher 7 cm 3 mol 1 and d at depths corresponding to the lowermost stability of olivine 12 gpa activation energies of diffusion are 100 kj mol 1 higher than at near surface conditions which means that closure temperatures are higher by several hundred degrees along geothermal gradients within the earth diffusion rates increase with depth in the lithosphere but decrease with depth in spite of the increase in temperature in the convective asthenospheric part of the mantle consequently there is a maxima in diffusion rates at the lithosphere asthenosphere boundary and for the olivine part of the mantle this is likely to be the region where most geochemical mixing and eradication of heterogeneities occur

east asian monsoon variation during the last 130 000 years evidence from the loess plateau of central china and lake biwa of japan abstract the loess paleosol sequence on the loess plateau of central china constitutes an excellent proxy record of variations in asian monsoon climate over the past 2 5 ma magnetic susceptibility of loess and paleosols has been used as a proxy indicator for summer monsoon intensity while the median diameter of quartz isolated from the loess and paleosols has been regarded as a proxy index of the strength of winter monsoon winds that were responsible for most of the dust transport the eolian quartz flux to lake biwa of central japan during the last 130 000 yr provides direct information on variations of the east asian winter monsoon whereas the fluvial quartz flux reflects significant changes in paleoprecipitation over the lake area the intervals of high eolian quartz flux values during marine oxygen isotope substages 5d and 5b and stages 4 and 2 correspond to the periods of large quartz median diameter values of the chinese loess and paleosols indicating strengthened winter monsoon winds whereas the intervals of high fluvial quartz flux values during isotope substages 5e 5c and 5a and stages 3 and 1 correlate to the periods of high magnetic susceptibility values of the chinese loess and paleosols suggesting increased summer monsoon intensity variations in winter monsoon strength indicated by the eolian quartz flux and quartz median diameter proxies bear a general inverse relation to those in summer monsoon intensity inferred from the fluvial quartz flux and magnetic susceptibility proxies

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

the analysis of zoning in magmatic crystals with emphasis on olivine many of the observed features of zoning in magmatic phenocrysts may be due to the orientation of the section rather than inherent properties of the crystals an ideal section for the studying of zoning in magmatic crystals has two characteristics it goes through the center of the crystal and is perpendicular to one or more crystal faces using a model zoned olivine crystal it is possible to construct accurate zoning profiles for different types of section centered symmetrical and skewed the probability of obtaining a random section which passes within x of the center of a crystal is shown to be p 0 0x while the probability that a random section will be within a degrees of perpendicular to a given plane is p sin a a systematic approach to the study of zoned crystals is outlined in particular it is suggested that composition be plotted against distance cubed in order to correct for the volume versus size problem a method of determining if a given section goes through or near the center of a zoned crystal is also presented the reasoning in this work applies to other types of magmatic crystals such as pyroxenes and plagioclase

the evolution of saharan dust input on lanzarote canary islands influenced by human activity in the northwest sahara during the early holocene an overall holocene increase of saharan dust input to the canary islands and to the north canary basin is accompanied by a strong coarsening of saharan dust in loess like sediments deposited on lanzarote from 7 8 ka no similar coarsening events are indicated in investigations of the sedimentological record for the last 180 ka a period showing several dramatic climate changes therefore a mobilisation of holocene dust by anthropogenic activity in the northwest sahara east of the canary islands is assumed although scarce archaeological data from the coastal area of that region does not point to strong anthropogenic activity during the early holocene a high density of unexplored archaeological remains is reported from the coastal hinterlands in the western sahara thus the hypothesis of early anthropogenic activity cannot be excluded

element zoning trends in olivine phenocrysts from a supposed primary high magnesian andesite an electron and ion microprobe study electron and ion probe microanalysis have been used to obtain zoning profiles for major and trace elements in olivine phenocrysts from a high magnesian andesite from shodo shima island southwest japan this rock was previously thought to represent undifferentiated primary magma some crystals have unzoned cores while others show cores which are reversely zoned with respect to mg mg fe ni mn and cr in addition some ni profiles show a normally zoned hump at the most central portions of the reversely zoned crystals all crystals show normally zoned rims the li concentrations are constant throughout the cores of all crystals studied but rise sharply by a factor of up to at least six in the rims the ca and co concentrations are essentially constant throughout all the crystals mechanisms for producing the observed zoning profiles are discussed and it is concluded that the reverse zoning was produced by the introduction of crystals into a less differentiated magma than that in which they grew the reversely zoned crystals could therefore represent xenocrysts which were introduced into an undifferentiated magma or phenocrysts introduced into a more primitive magma by a magma mixing process the ni profiles are used to estimate the residence time of these crystals in the more primitive magma the following trace element partition co efficients have been estimated for the olivine groundmass system in this rock dni 16 dmn 1 1 dco 4 2 dca 0 02 dti 0 005 dv 0 05 dsc 0 2 dna 0 0002 studies of trace element zoning will become increasingly important as the new generation of trace element microprobes become available but a larger database of experimentally determined values for trace element partition coefficients and diffusion coefficients in crystals and magmas and a better understanding of other disequilibrium processes are required to fully exploit the new data

strontium diffusion kinetics in plagioclase feldspars abstract a pronounced systematic variation by a factor of 104 in strontium tracer diffusion kinetics has been measured in four feldspar specimens that span the range of plagioclase compositions the experiments were carried out in air using isotopically enriched 86sr and analyzed with an ion microprobe the arrhenius relations for strontium diffusion are plagioclase ab d 0 m 2 s q kj g atom sr temperature range c albite 98 1 05e 279 550 1080 oligoclase 73 7 4e 7 261 750 1100 labradorite 36 1 1e 6 295 800 1300 anorthite 4 5 7e 9 267 900 1300 no difference was found within the measurement uncertainty between these results and those for albite under hydrothermal conditions at one kbar 100 mpa strontium diffusion rates parallel to and normal to the albite twin lamellae are the same there is no effect on the strontium diffusion rate in albite between an oxygen partial pressure of 0 2 bar air and 10 19 bar graphite buffer a relation is developed that permits calculation of the strontium diffusion arrhenius parameters for any normal plagioclase composition the large variation in diffusion rate with composition has a major effect on the ease of strontium isotope exchange at high temperatures between plagioclases and coexisting phases in rocks which may prove useful in determining thermal histories

on eustatic sea level history last glacial maximum to holocene abstract this paper addresses the question of the magnitude and time dependence of the globally averaged eustatic rise of sea level that occurred subsequent to the time of last glacial maximum lgm at approximately 21 000 calendar years before present through the analysis of relative sea level rsl histories predicted by a realistic mass conserving and gravitationally self consistent theory of postglacial sea level change it is demonstrated that there are preferred oceanic locations at which this eustatic function is well approximated by local sea level history one such location is the island of barbados in the caribbean sea a site from which a coral based record exists that extends from mid holocene to lgm because of the sea level ambiguity that is inherent to coral based records however it is important that the global ice equivalent eustatic sea level curve inferred on the basis of the barbados data be tested against observations at other locations from which similarly extensive records are also available but which are derived on the basis of sea level indicators which are not subject to the ambiguities inherent to corals it is shown that when the eustatic function employed in the global theoretical model is tuned so as to enable the model to fit the barbados observations where the maximum relative sea level rsl depression is assumed to be near 120 m then the theory misfits the record from the sunda shelf in the indonesian archipelago as well as the record from j bonaparte gulf in northern australia both of these recently published records appear to constrain the lgm low stand of rsl to a value above 120 m the implications of these results for interpretation of the long coral derived records from the huon peninsula of papua new guinea and the island of tahiti are also discussed

an assessment of human versus climatic impacts on holocene soil erosion in ne peloponnese greece soil erosion is a natural geomorphological process which can be triggered by both natural climate tectonics or both and anthropogenic e g agriculture perturbation of the ecosystem evidence has accrued that the holocene climate experienced large fluctuations in amplitude and suggestions of human impact on the ecosystem provided by the neolithic revolution dating back to the early holocene have been made the question of whether man or climate was the dominant factor responsible for holocene soil erosion remains unresolved to resolve the reasons for holocene sediment redistribution high resolution chronometric data on sediments derived from colluvial and alluvial archives from southern greece were obtained and combined with available archaeological and paleoclimatic data from the eastern mediterranean these data show a significant correlation between sedimentation rates and settlement history climatic fluctuations are only weakly correlated with sedimentation history the results show high sedimentation rates during the early neolithic 7th millennium bc in southern greece suggesting that holocene soil erosion was triggered by human activity and then amplified by enhanced precipitation this would explain the high sedimentation rates during the early neolithic in connection with enhanced precipitation in the eastern mediterranean which continued until the mid holocene

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

coupled caal nasi diffusion in plagioclase feldspar experiments and applications to cooling rate speedometry abstract the rate of caal nasi interdiffusion in plagioclase feldspar was determined under 1 atm anhydrous conditions over the temperature range 1400 to 1000 c in calcic plagioclase an80 81 by homogenizing coherent exsolution lamellae the dependence of the average interdiffusion coefficient on temperature is given by the expression d 10 99 cm 2 sec exp 123 4 kcal mol rt t in k this value is for diffusion perpendicular to the 03 1 interface of the lamellae caal nasi interdiffusion is 4 to 5 orders of magnitude slower than oxygen diffusion in the temperature range 1400 to 1200 c and possibly 10 orders of magnitude slower at subsolidus temperatures the large differences in diffusion rates explain the apparent contradiction posed by the plagioclases of large layered intrusions e g the skaergaard which retain delicate ca na compositional zoning profiles on the micron scale but have undergone complete oxygen isotopic exchange with heated meteoric groundwater from the surrounding wall rocks caal nasi diffusion is slow the closure temperature is high within the solidus liquidus interval and ca na zoning is preserved oxygen diffusion is faster the closure temperature is lower 350 400 c and the feldspars exchange oxygen with the low temperature hydrothermal fluids the complex micron scale oscillatory zones in plagioclase can also be used as cooling rate speedometers for volcanic and plutonic plagioclase cooling histories typical of large mafic intrusions e g the stillwater are slow begin at high initial temperatures 1200 c and result in homogenization of oscillatory zones on the scale of 10 microns the oscillatory zones found in the plagioclase of granodioritic plutons are preserved because cooling is initiated at a lower temperature 1000 c limiting diffusion to submicron length scales despite the slow cooling rate of the intrusion

in situ u pb ages of zircons from the bishop tuff no evidence for long crystal residence times ion microprobe u pb isotope analyses of zircons from fallout and intercalated ash flow deposits of the early most chemically evolved bishop tuff east central california yield a weighted mean age of 823 11 ka mean square of weighted deviates mswd 0 8 n 22 a similar mean age of 839 36 ka mswd 0 6 n 15 obtained on unpolished zircon rims suggests that the difference between these ages and that of 760 ka for the bishop tuff obtained by recent ar isotope determinations may be largely analytical in origin considerations based only on the effect of 230 th 234 u disequilibria on the u pb ages yield an apparent maximum mean crystal residence time for zircon of 100 k y the zircon residence times are significantly shorter than those inferred from previous estimates for the timing of phenocryst growth and suggest that once evolved the early bishop tuff rhyolite was not stored for long before erupting

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

numerical simulations of crystallization processes of plagioclase in complex melts the origin of major and oscillatory zoning in plagioclase numerical simulations of the growth of a large crystal face of plagioclase in response to an instantaneous undercooling below the equilibrium temperature are presented for model granodiorite and basalt melts with varying water contents the simulations suggest that the anorthite content of plagioclase decreases uniformly from the composition in equilibrium with the bulk melt as undercooling is increased and that the water content in the melt has little influence on this result comparison of the simulations with sharp compositional changes in natural profiles suggests that undercoolings of tens of degrees c can be rapidly imposed on plutonic phenocrysts large changes of undercooling most likely result from chilling of the magma and local convection around growing crystals the observation in experiments that growth rate does not increase rapidly with increasing water content in the starting melting composition can be attributed to the concentration of water at the crystal face during growth the action of water to reduce liquidus temperature and undercooling has a greater effect on growth rate than its action to increase transport rates even at large undercooling there is no significant increase in temperature at the interface caused by the release of heat of crystallization

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

plagioclase residence times at two island arc volcanoes kameni islands santorini and soufriere st vincent determined by sr diffusion systematics the diffusive relaxation of trace element profiles in plagioclase phenocrysts may provide important constraints on magma residence times in crustal magma chambers initial trace element profiles in plagioclase phenocrysts are governed by variations in the concentration of a trace element in the melt and by the plagioclase melt partition coefficient trace element diffusion will subsequently act to modify this initial profile and given enough time produce a profile that is in equilibrium with the anorthite variations within the crystal we argue that the trace element partition coefficient da b between two parts a and b of a plagioclase crystal of variable anorthite content is equal to the ratio of their crystal liquid partition coefficients and that the equilibrium profile of the crystal can be calculated the time required to establish diffusive equilibrium is dependent on the wavelength and amplitude of the initial trace element concentration range and on the diffusivity of the trace element in plagioclase strontium plagioclase melt partition coefficients and diffusivities are calculated for a range of magmatic temperatures and plagioclase compositions a one dimensional diffusion model is developed that describes the diffusive destruction of oscillatory trace element zoning with time and allows the calculation of upper limits for plagioclase crystal residence times in a magma reservoir the model is tested using major and trace element concentrations measured along crystal traverses of plagioclase phenocrysts from the kameni island dacites santorini and from the 1979 soufriere andesite st vincent three out of eight plagioclase phenocrysts have sr concentration profiles that are not in diffusive equilibrium for these the diffusion model is employed to calculate maximum crystal residence times from incomplete diffusive equilibration of trace element zoning in plagioclase maximum crystal residence times range from 100 to 450 years this is in good agreement with estimates from crystal size distribution and from ra th disequilibrium studies for the kameni islands for soufriere however such short residence times are incompatible with u th mineral errorchron data that suggest residence times of 40 ka in a thermally buffered magma reservoir to reconcile these apparently different ages we invoke a more complicated magmatic history for soufriere where an initially buffered magma reservoir is disturbed by magma mixing and suffers limited additional crystal fractionation prior to eruption

isotopic evidence for the eolian origin of quartz and mica in soils developed on volcanic materials in the canary archipelago quartz and mica contents of soils developed on volcanic materials in the canary archipelago lanzarote tenerife gomera and la palma islands off western africa are often higher in surficial horizons with higher rainfall and older landscape age the soil quartz particles are fine grained less than 53 m in diameter and well sorted the oxygen isotopic abundance 18osmow of fine aerosol sized quartz 1 10 m in diameter showed a range of 16 0 to 18 2 the values are compatible with those of the same sized quartz from two holocene deep sea sediments in cape verde rise 16 0 and 16 1 and saharan dusts 15 8 la laguna tenerife 16 2 barbados west indies a distinct 87sr 86sr ratio of 0 717 for a micaceous horizon from lanzarote is comparable with those of saharan dusts 0 715 to 0 721 but not with reported values 0 7032 from local volcanics these geochemical parameters show that the fine grained quartz together with mica in soils of the canary archipelago are transported from north african sahara deserts by trade winds and negate both possibilities of authigenesis and inheritance from weathering of local volcanics

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

continental record of the southwest monsoon during the last 130 ka evidence from the southern margin of the thar desert india abstract field stratigraphy sedimentology and luminescence dating of the exposed fluvial and aeolian sequences from the southern desert margin were used to discern the pattern of southwest monsoon variability during the last 130 ka the sedimentary architecture and textural attributes of the sediments belonging to the period 130 120 ka suggests the existence of a meandering river system consequent to enhanced southwest monsoon conditions a shift from a meandering to a braided pattern during 120 100 ka indicates a phase of reduced precipitation presence of flood plain fines and bedded calcretes during 100 70 ka suggest a period of enhanced monsoon with seasonality following this a phase of weak monsoon activity was observed during 70 60 ka regional flood plain aggradation and pedogenesis during the period termination of a regional fluvial phase around 30 ka and incision of dunes dated to 20 11 ka suggest that the present rivers occupied their course between 11 ka drowned valleys in the estuarine zones suggest that the incision began during the low sea stand around 20 ka when the rivers were graded to the exposed shelf the incision intensified with the re establishment of monsoon during the early holocene

residence time and crystallization history of nickeliferous olivine phenocrysts from the northern yatsugatake volcanoes central japan application of a growth and diffusion model in the system mg fe ni abstract the chemical zoning of nickeliferous olivine phenocrysts in calc alkaline andesites from the northern yatsugatake volcanoes central japan is examined by a growth and diffusion model in the system mg fe ni nickeliferous olivine phenocrysts are included in the high alumina basaltic end member magma which forms the mixed calc alkaline andesites in the northern yatsugatake volcanoes the olivine phenocrysts can be divided into three types on the basis of chemical composition zoning profile and occurrence type 1 olivine is rich in ca and mg and the zoning profile of type 1 forms a slightly more fe rich trend than the maximum fractionation trend in the nio versus forsterite content fo diagram the most mg and ni rich and mn poor core of type 1 fo 91 5 mol nio 0 40 wt mno 0 13 wt can be in equilibrium with peridotite in the upper mantle by contrast type 2 olivine is ca poor and rich in fe and ni compared to type 1 the zoning patterns of type 2 are more variable the nio content in fe rich type 2 phenocrysts decreases rapidly from core to rim within a narrow range of fo the maximum nio content of type 2 is 0 53 wt the transitional type olivine has an intermediate composition between type 1 and type 2 and a similar zoning profile as that of type 1 type 1 olivine mainly occurs as isolated phenocrysts while fe rich type 2 occurs as crystal clots the growth and diffusion calculation in the system mg fe ni revealed that the composition of normally zoned olivine is enriched in fe by diffusion without a marked depression in the ni content due to a larger fe mg interdiffusion coefficient than the ni tracer diffusion coefficient in olivine the zoning patterns of both type 1 and type 2 can be reproduced by calculation the residence time of type 1 olivine in the magma is estimated to be less than 10 0 5 1 y at 1150 1050 c whereas the residence time of fe enriched type 2 olivine is from ten to one hundred times longer than that of type 1 the long residence time and occurrence as crystal clots suggest that the fe enriched type 2 olivine phenocrysts were captured and crystallized in the crystal mush at the roof and bottom of a magma chamber

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

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

mineral textures and zoning as evidence for open system processes investigations of mineral textures and zoning as evidence for open system processes during magmatic evolution have always been a centerpiece of petrological studies and have provided some of the best evidence for magma mixing and crustal contamination for many decades e g milch 1905 kuno 1936 eichelberger 1975 sato 1975 anderson 1976 in fact evidence from mineral studies was instrumental in the acceptance of magma mixing as important petrological process ever since it was initially proposed by bunsen 1851 in recent years mineral studies are invigorated by the development of high precision high resolution analytical instruments and techniques through which textural information and compositional data are combined e g jerram and davidson 2007 as minerals respond texturally and compositionally to changing magmatic environments they preserve in their crystal growth stratigraphy a wealth of information regarding their past history of magmatic processes and compositions cf ginibre et al 2007 on the other hand magmatic liquids melts are snapshots of current magmatic states and provide less direct evidence of the processes responsible for their evolution in addition liquids may crystallize thereby destroying the direct evidence they provide with an appropriate set of observations and measurements we can correlate textures with mineral compositions and thus produce a richer composite picture of magmatic evolution than compositional data of minerals alone this contribution reviews the zoning and textures of minerals frequently encountered in volcanic rocks many of which apply equally to plutonic rocks and the interpretations ascribed to these features in terms of open system magmatic processes first i will address the analytical tools that are used to acquire textural and compositional data followed by a brief review of open system processes and a summary of the relevant textures from that point on i will address some mineral specific aspects followed by a discussion

mg diffusion in anorthite implications for the formation of early solar system planetesimals we have measured the self diffusion coefficients of mg ca and sr in anorthitic plagioclase in order to assess the potential of mg isotopic heterogeneities in early solar system planetesimals to survive thermal metamorphism diffusion couples were constructed from polished single crystals of natural anorthite and synthetic isotopically enriched anorthite glass couples were annealed at atmospheric pressure and 1200 1400 c and isotopic concentration profiles were measured with an ion microprobe the results show that mg diffusion in anorthite is surprisingly fast with d mg being over 2 orders of magnitude greater than d sr this indicates that the diffusion coefficient of mg in anorthite cannot be approximated with that for sr mg diffusion in the c direction is also slightly faster than in the b direction while ca and sr diffusion appear to be isotropic the results provide important constraints on the thermochronological history of anorthite bearing mineral assemblages that preserve radiogenic 26 mg excesses in a planetesimal heated by the decay of 26 al the temperature at any point depends on the planetesimal size time of formation thermal conductivity and depth within the planetesimal given sufficient heating 26 mg heterogeneities produced by the in situ decay of 26 al in ca al rich inclusions cais and chondrules will be erased by diffusive equilibration using the self diffusion coefficient for mg in anorthite measured in this study we show that the common occurrence of 26 mg excesses in these inclusions requires that they must be stored in small 15 km bodies or the outermost rims of larger bodies for the first 1 2 million years of the solar system s history for early formed bodies larger than 15 km most of the mass will have been heated sufficiently for any radiogenic 26 mg to have been diffusively homogenized in the mg rich planetary environment

variability in terrigenous sedimentation processes off northwest africa and its relation to climate changes inferences from grain size distributions of a holocene marine sediment record variations in deposition of terrigenous fine sediments and their grain size distributions from a high resolution marine sediment record offshore northwest africa 30 51 0 n 10 16 1 w document climate changes on the african continent during the holocene end member grain size distributions of the terrigenous silt fraction which are related to fluvial and aeolian dust transport indicate millennial scale variability in the dominant transport processes at the investigation site off northwest africa as well as recurring periods of dry conditions in northwest africa during the holocene the terrigenous record from the subtropical north atlantic reflects generally humid conditions before the younger dryas during the early to mid holocene as well as after 1 3 kyr bp by contrast continental runoff was reduced and arid conditions were prevalent at the beginning of the younger dryas and during the mid and late holocene a comparison with high and low latitude holocene climate records reveals a strong link between northwest african climate and northern hemisphere atmospheric circulation throughout the holocene due to its proximal position close to an ephemeral river system draining the atlas mountains as well as the adjacent saharan desert this detailed marine sediment record which has a temporal resolution between 15 and 120 years is ideally suited to enhance our understanding of ocean continent atmosphere interactions in african climates and the hydrological cycle of northern africa after the last deglaciation

kinematic significance of morphological structures generated by mixing of magmas a case study from salina island southern italy morphological features of mixing mingling structures of heterogeneous juveniles from the 13 ka old upper pollara eruption salina island southern italy are studied these heterogeneous rocks result from the mixing between an andesitic and a rhyolitic magma concentration patterns generated by magma mixing are analyzed on digital images and results have been compared with those obtained from numerical simulations of mixing processes coupling chaotic advection and chemical diffusion results show that the upper pollara rocks were produced by mixing 24 49 of andesite and 76 51 of rhyolite multifractal analysis of the mixing structures is performed and the mixing intensity i e the degree of interaction between the two end member magmas has been deduced from the analysis of the singularity spectrum results show that narrower is the multifractal spectrum the higher is the degree of homogenization of magmas reynolds number re during mixing has been estimated from the geometrical analysis of mixing structures by using experimentally defined relationships between shape parameters and re results show that re is between ca 500 and 7000 there is a positive correlation between the estimated initial percentage of mafic magma in the different analyzed samples and re in agreement with the observation that the higher is the percentage of the mafic lower viscosity magma the higher is the turbulence of the mixing system in addition our analysis reveals an unexpected inverse relationship between the calculated re and the degree of magma homogeneity suggesting that energy dissipation may have had a major role in the controlling mixing process because dissipation is inversely proportional to the mixing efficiency results suggest that mixing processes between the andesitic and rhyolitic magmas mainly developed in the conduit it is also suggested that mixing occurred in a shear layer type or pipe type flow

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

saharan dust on fuerteventura island canaries chemical and mineralogical characteristics air mass trajectories and probable sources from april 12 to 19 1984 dust was collected by cascade impactor on fuerteventura island 100 km from the saharan coast the samples were analyzed by x ray fluorescence spectrometry elemental composition by x ray diffraction mineral constituents and by scanning electron microscope sem and energy dispersive x ray analyzer edxa examination shape surface features and mineralogy of particles with the aim of determining the possible source areas of the dust on the scale of dust clouds another method allowed us to define the displacements of the dust using remote sensing meteosat ii national oceanic and atmospheric administration noaa and computing trajectories for any starting or ending point at any time these various methods gave complementary results and pointed out two successive episodes of dust with two different continental origins the first originated from a nearby source in the souss plain southern morocco and was characterized by very fine quartz particles the second drifted above more remote calcareous regions this study allows us to show how different methods can be used to characterize dust and to find the source areas the results suggest some general questions about the occurrence of coarse particles in the atmosphere and their role in the atmospheric deposition flux budget

metamorphism of metapelites calculations of equilibrium assemblages and numerical simulations of the crystallization of garnet this work uses a simplified model of equilibrium to predict the assemblage sequence and compositional zoning in garnet that should result from prograde metamorphism of common bulk compositions of pelitic rocks an internally consistent set of model thermodynamic data are derived for natural mineral compositions from natural assemblages equilibrium assemblages can be calculated for pelitic compositions with excess quartz and either muscovite or k feldspar at any pressure and water pressure the compositions and abundances of phases in equilibrium assemblages can be calculated where the elements mg fe and mn are exchanged among phases the prograde metamorphic assemblage sequences and the effects of pressure on assemblages predicted by the simulation method presented here are similar enough to natural observations to suggest that the simulations can be used to analyse natural equilibrium and growth processes the calculated phase diagrams at moderate and high crustal pressures explain the mineral assemblage sequence produced by prograde metamorphism in common pelitic compositions garnet appears by continuous reaction of biotite and chlorite as the garnet biotite chlorite divariant field migrates toward higher mg fe ratios over the bulk composition staurolite appears in common bulk compositions when garnet and chlorite become incompatible an aluminum silicate phase can appear when staurolite and chlorite react staurolite breaks down at an extremum point to produce garnet continuous reaction of biotite and sillimanite causes growth of abundant garnet the reaction sequence involving garnet staurolite and aluminum silicates is probably different at low pressure but the main reason that staurolite and garnet are rare is the restricted compositional range over which their assemblages exist andalusite appears by the divariant reaction of chlorite and cordierite appears at low temperature in low pressure assemblages for common bulk compositions by the extremumpoint breakdown reaction of chlorite compositional zoning of garnet and the systematic variation of biotite composition in metamorphic sequences indicate that garnet is probably fractionated during growth fractionation of garnet causes garnet consuming univariant reactions to become multivariant the metastable persistence of garnet should reduce the abundance and stability range of staurolite fractionation of even small quantities of garnet should deplete the equilibrating bulk composition of mn but have little effect otherwise the simulations show that the prograde assemblage sequence in pelitic rocks can be complex in detail with some assemblages lasting over temperature intervals of only a few degrees the major prograde reactions that release water are the breakdown of chlorite to form garnet at low grade and the breakdown of muscovite at high grade the volume of water released by formation of garnet at high grade is also important these reactions have the capacity to buffer water pressure the density of anhydrous pelitic rock increases markedly when chlorite breaks down and by the continuous reaction forming garnet at high grade the heat content is controlled principally by heat capacity and continuous reactions discontinuous reactions have little thermal buffering capacity simulations of garnet fractionation show that commonly observed garnet zoning profiles can be formed by garnet growth in the assemblage garnet biotite chlorite in common bulk compositions a reversal of fe zoning in garnet can occur when garnet resumes growth above staurolite grade in the assemblage garnetbiotite sillimanite discontinuities in zoning profiles can be caused only by disequilibrium the disequilibrium can be due to either metastable persistence during a hiatus in growth or to growth by irreversible reaction because the appearance of garnet is controlled by a continuous rather than a discontinuous reaction the appearance of garnet is very sensitive to bulk composition the early development of garnet is also sensitive to the pressure and water pressure of metamorphism as a consequence the first garnet isograd is of limited thermometric value metastable persistence of kyanite and manite at high grades could reduce the abundance of garnet and allow biotite to persist metastable persistence would also limit the of cordierite formation

centennial scale late pleistocene to mid holocene synthetic profile of the medjerda valley northern tunisia during the late pleistocene to mid holocene the medjerda river system in mediterranean tunisia shows events of increased flooding and aggradation of relatively coarse overbank deposits geomorphic activity in river systems within this region correlate with aridification of the climate but not with temperature the late pleistocene to mid holocene synthetic profile of the ghardimaou floodplain mid medjerda river indicates fluvial activity from 12 4 to 11 8 6 6 to 6 0 and after 4 8 ka cal bp external correlations imply global and regional causes of the late pleistocene to mid holocene climatic development such as north atlantic deep water formation fluctuations in saharan humidity and impacts of local mediterranean weather phenomena palaeomagnetic records offer additional opportunities to interpret fluvial activity in river systems especially for detecting chronological hiatuses in apparently homogeneous sediment sequences

modern and last glacial maximum eolian sedimentation patterns in the atlantic ocean interpreted from sediment iron oxide content eolian dust derived from the desert regions of north africa is blown far into the tropical atlantic ocean by persistent easterly and northeasterly winds in this paper we demonstrate that the iron oxides hematite and goethite are a worthwhile addition to proxy monitors of eolian sedimentation in the tropical atlantic iron oxides are identified by diffuse reflectance spectrophotometry a technique capable of identifying these minerals in concentrations as low as 0 01 by weight we analyze samples from both the modern and last glacial maximum lgm synoptic levels from 178 sample locations yielding a total of 356 samples distributed throughout the atlantic ocean to determine the relative contribution of the iron oxides we factor analyzed the modern and lgm levels as a single data set the iron oxide factor explains about 25 of the variance in the combined core top and lgm data set mapped factor scores for the lgm and modern ocean indicate high iron oxide values are present in just two regions one off eastern north america and the other off northwest africa in the region off eastern north america iron oxide occurs primarily during the lgm as the previously noted brick red lutite a unique sediment type derived from the erosion of permo carboniferous red beds in atlantic canada a larger lobe shaped area of iron oxide rich sediment is present off northwest africa in both the modern and lgm levels the modern iron oxide lobe is coincident with the distribution of eolian dust as determined by observations from ships satellites and analysis of air samples during the lgm iron oxides exhibit a similar distribution except the southern margin of the region shifts equatorward and iron oxide concentration increases

exhumation history of a section of the sikkim himalayas india records in the metamorphic mineral equilibria and compositional zoning of garnet the exhumation history of pelitic migmatite samples from the high himalayan crystalline complex hhc near the south tibetian detachment system in the sikkim darjeeling section has been determined on the basis of thermo barometric analyses retrograde breakdown reactions and compositional zoning of garnet the peak metamorphic condition is estimated to be 10 4 kbar 800 c from thermo barometric and phase equilibrium constraints the observed retrograde breakdown of garnet to spinel and cordierite requires near isothermal and hence extremely rapid 15 mm yr exhumation up to the depth of 15 km numerical modeling suggests that the initial rapid exhumation must have been followed by a much slower process 2 mm yr up to at least 5 km depth to lead to the development of the observed compositional zoning of garnet the dramatic change of the exhumation velocity vz might reflect a process of tectonic thinning followed by erosion and or horizontal flow at shallow depth assuming that the vz did not change significantly below 5 km depth these results suggest that the hhc samples studied in this work exhumed from a depth of 34 km within 8 ma

sm nd dating of spatially controlled domains of garnet single crystals a new method of high temperature thermochronology ganguly and tirone meteorit planet sci 36 2001 167 175 recently presented a method of determining the cooling rates of rocks from the difference between the core and bulk ages of a crystal as determined by a single decay system here we present the first application of the method using the core and bulk ages of garnet single crystals according to the sm nd decay system in two rock samples with contrasting cooling rates which can be constrained independently the samples belong to the metamorphic core complex valhalla british columbia and the mid crustal magmatic arc exposure of the salinian terrane california we have micro sampled the garnet crystals over specific radial dimensions and measured the nd isotopes of these small sample masses as ndo via solid source mass spectrometry to determine the sm nd age difference between the core and bulk crystals using a peak metamorphic p t condition of 8 1 kbar 820 30 c spear and parrish j petrol 37 1996 733 765 the core 67 3 2 3 ma and bulk 60 9 2 1 ma ages of the british columbian garnet sample yield a cooling rate of 2 13 c myr which is in very good agreement with the cooling rates that we have derived by modeling the retrograde fe mg zoning in the same garnet and assuming the same peak metamorphic p t condition considering earlier cooling rate data derived from closure temperature vs age relation of multiple geochronological systems spear and parrish j petrol 37 1996 733 765 a cooling rate of v15 20 c myr seems most reasonable for the valhalla complex diffusion kinetic analysis shows that the sm nd core age of the selected garnet crystal could not have been disturbed during cooling consequently the core age of the garnet crystal 67 3 2 3 ma corresponds to the peak metamorphic age of the valhalla complex the salinian sample on the other hand yields indistinguishable core 78 2 2 7 ma and bulk 77 9 2 9 ma ages as expected from its fast cooling history which can be constrained by the results of earlier studies the sm nd decay system in garnet has relatively high closure temperature usually s 650 c therefore the technique developed in this paper fills an important gap in thermochronology since the commonly used thermochronometers are applicable only at lower temperatures simultaneous modeling of the retrograde fe mg zoning in garnet spatially resolved sm nd ages of garnet single crystals and resetting of the bulk garnet sm nd age

stratigraphy chronology and paleoenvironmental reconstruction of the quaternary sedimentary infilling of a volcanic tube in fuerteventura canary islands abstract la cueva del llano is a volcanic tube of pleistocene age on fuerteventura island in the canary islands part of it is infilled with sediments of external origin these deposits are exceptional in stratigraphic complexity and thickness compared with other known tube infillings and they comprise nine stratigraphic units deposited in five phases in phase i which has not been dated sedimentation of cinder from a nearby cone occurred phase ii began ca 16 830 900 14 c yr b p whereas phase iv dates to 9280 370 14 c yr b p the interpretation of sedimentary features shows that phases iii and v correspond to a dry climate similar to the present one whereas the climate was much wetter during phases ii and iv this paleoclimatic sequence agrees with those suggested by the study of deposits formed in other sedimentary environments not only in fuerteventura but on other islands of the canary group and the sud maroc region

petrology and fe ti oxide reequilibration of the 1991 mount unzen mixed magma a dacitic magma 64 5 wt sio2 a mixture of phenocryst rich rhyodacite and an aphyric mafic magma was erupted during the recent 1991 1995 mount unzen eruptive cycle the experimental and analytical results of this study reveal additional details about conditions in the premixing and postmixing magmas and the nature of the mixing process the preeruption rhyodacitic magma was at a temperature of 790 20 c according to fe ti oxide phenocryst cores and at a depth of 6 to 7 km 160 mpa according to al in hornblende geobarometry the mafic magma that mixed with the rhyodacite is found as andesitic 54 to 62 wt sio2 enclaves in the erupted magma and was essentially aphyric when intruded phase equilibria indicate that an aphyric andesite at 160 mpa is 1030 c h2o saturated and possibly as high as 1130 c 2 wt h2o the composition of the rhyodacite which was mixed with the andesite is estimated to lie between 67 and 69 wt sio2 using these compositions and temperatures the temperature of the unzen magma after mixing is estimated to be at least 850 to 870 c the groundmass fe ti oxide microphenocrysts and those in pargasite bearing reaction zones around biotite phenocrysts both give 890 20 c temperatures the oxide oxide contacts give temperatures of 910 20 c the 900 30 c postmixing temperatures are consistent with phase equilibria experiments which show that the magma was not above 930 c at 160 mpa our fe ti oxide reequilibration experiments suggest that the mixing of the two magmas began within a few weeks of the eruption which is a shorter time than is calculated using available diffusion data there is also evidence that some mixing took place much closer to the time of extrusion based on the presence of unrimmed biotite phenocrysts in the magma

three dimensional quantitative textural analysis of metamorphic rocks using high resolution computed x ray tomography part ii application to natural samples three dimensional quantitative textural analysis coupled with numerical modelling has been used to assess the dominant mechanisms governing crystallization of garnet porphyroblasts in rocks from diverse regional metamorphic environments in every case spatial dispositions crystal size distributions and compositional zoning patterns of porphyroblasts indicate the dominance of diffusion controlled nucleation and growth mechanisms nine samples from three geological areas were studied a suite of semi pelitic rocks from the picuris mountains new mexico usa a suite of mafic samples from the llano uplift texas usa and a kyanite schist from mica dam british columbia canada the semi pelitic suite exhibits post deformational garnet growth whereas garnet in the mafic suite and in the kyanite schist grew synkinematically in rocks displaying weak and strong penetrative fabrics respectively for each sample the centres and radii of thousands of garnet crystals were located and measured in three dimensions using images produced by high resolution computed x ray tomography statistical measures of the degree of ordering and clustering of nucleation sites and estimates of crystal isolation for each porphyroblast were then computed from the measured spatial dispositions these measures can be reproduced in simple numerical models only by diffusion controlled nucleation and growth mechanisms normalized radius rate relations computed from compositional zoning patterns in the garnets require thermally accelerated diffusion controlled growth providing independent confirmation of the conclusions based on textural analysis the unexpected similarity of results from all samples indicates that diffusion controlled nucleation and growth mechanisms may govern porphyroblast crystallization in many metamorphic regimes

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

the last 140 ka in the afro asian arid semi arid transitional zone abstract during the last ten years a great number of geological or other proxy records provided radiocarbon u th or tl dated information on the past climatic oscillations in the arid semi arid zones extending between the atlantic and the pacific comparisons and a synthetic view of these results can now be attempted for the last 140 ka and compared with global changes as registered in oceanic or ice cores and with palaeomonsson models for this purpose wide spatial and time scales have to be used on the whole arid humid alternations roughly fit global changes cold phases corresponding to an extension of the arid areas to the south warm phases corresponding to the shrinking of the same to the north the last interglacial is associated with an increase of precipitation throughout the area considered isotopic stage 4 brings no evidence whatsoever of humid conditions two wetter episodes are registrated during stage 3 a major rainfall decrease is everywhere associated with the last glacial maximum 21 15 ka in most regions the arid or semi arid zones extending several hundred kilometers southwards relative to the present day pattern the two abrupt deglaciation steps and the younger dryas are recorded in all of the most sensitive regions at the margins of the present day monsoonal range during the holocene the precipitation increases everywhere by 100 400 mn relative to the present day values the optimum being at 8 5 6 5 ka a climatic deterioration follows with an irregular pattern of dry wet episodes according to the different geographic conditions the humid phase terminates at 3 5 3 ka in the whole transitional zone the major southward shift of the monsoonal precipitation range since its optimum some 8000 years ago fits the astronomical neoglacial trend and may possibly be correlated with past stage 5d although its rapidity and spatial importance may just reflect one of the sharp successive cold warm variations registered by grip during the whole stage 5

relationship between cooling rate and cooling age of a mineral theory and applications to meteorites we reviewed here the recent development on the mathematical formulation of closure temperature of a cooling geochronological system which permits direct retrieval of cooling rate from cooling age when the diffusion parameters grain size and initial temperature are known this formulation is used to show how the cooling rate can be retrieved by comparing the core and bulk age of a mineral determined by a single decay system the cooling rates of seven h chondrites of the metamorphic types h4 h5 and h6 were retrieved from the available data on the pb pb model ages of the phosphates and the diffusion kinetic data of pb in apatite the results are in excellent agreement with the metallographic cooling rates and show an inverse relation with the metamorphic grade of these chondrites we also addressed the problem of 90 ma younger sm nd mineral isochron age defined by orthopyroxene phosphate and plagioclase of the morristown mesosiderite compared to the pb pb age of the estherville mesosiderite it is shown that this younger age could have been a consequence of resetting during cooling instead of an impulsive heating event as suggested earlier

a 300 kyr record of aridity and wind strength in southwestern africa inferences from grain size distributions of sediments on walvis ridge se atlantic abstract the terrigenous fraction of sediments recovered from walvis ridge se atlantic ocean reveals a history of southwestern african climate of the last 300 kyr end member modelling of a data set of grain size distributions n 428 results in three end members the two coarsest end members are interpreted as eolian dust the third end member as hemipelagic mud the ratio of the two eolian end members reflects the eolian grain size and is attributed to the intensity of the se trade winds trade winds were intensified during glacials compared to interglacials changes in the ratio of the two eolian end members over the hemipelagic one are interpreted as variations in southwestern african aridity late quaternary southwestern african climate was relatively arid during the interglacial stages and relatively humid during the glacial stages owing to meridional shifts in the atmospheric circulation system during glacials the polar front shifted equatorward resulting in a northward displacement of the zone of westerlies causing increased rainfall in southwestern africa the equatorward shift of the polar front is coupled with an increase of the meridional pressure gradient leading to enhanced atmospheric circulation and increased trade wind intensity

oxygen isotope disequilibrium between quartz and sanidine from the bandelier tuff new mexico consistent with a short residence time of phenocrysts in rhyolitic magma abstract oxygen isotope analyses are reported from co existing quartz and feldspar from the bandelier tuff and cerro toledo high silica rhyolitic pyroclastic deposits erupted from the valles caldera new mexico quartz shows little variation outside analytical error but 18 o in feldspar varies over 1 in most samples 18 o 16 o fractionation between quartz and feldspar is significantly less than is predicted for equilibrium at temperatures appropriate for rhyolitic magma in the tshirege upper member of the bandelier tuff isotopic fractionation between mineral pairs is close to equilibrium in the later erupted ignimbrite but non equilibrium in the initial plinian deposit these relationships are interpreted in terms of a model where most phenocrysts are derived from a highly porphyritic carapace around the magma chamber that was disrupted by eruption thus scattering crystals throughout the magma carapace quartz and feldspar are initially isotopically lighter than the bulk aphyric magma due to chemical communication with low 18 o country rock in the meteoric hydrothermal system surrounding the chamber we assume that quartz and feldspar were initially in isotopic equilibrium diffusive re equilibration of crystals begins when the carapace disintegrates and the minerals are immersed in the bulk magma just prior to and during eruption feldspar is isotopically lighter than quartz at equilibrium but responds more rapidly than quartz to an external change due to a higher diffusion coefficient for oxygen hence immersion in the isotopically heavier bulk magma causes feldspar and quartz 18 o values to initially converge over 10 2 years and then diverge over 10 3 10 4 years as first feldspar and then quartz re equilibrate with the new magma higher 18 o variability of feldspar than quartz indicates that the shorter timescale applies to the bandelier and cerro toledo rhyolites two important implications of this interpretation are 1 that the bandelier magmas developed in an aphyric condition and their porphyritic character is an artifact of eruption and 2 that a protective mechanically rigid cognate carapace around a silicic magma chamber may limit interaction with low 18 o hydrothermally altered crust thus hindering the development of significant volumes of low 18 o silicic magma

provenance of present day eolian dust collected off nw africa 1 atmospheric dust samples collected along a transect off the west african coast have been investigated for their physical grain size distribution mineralogical and chemical major elements composition on the basis of these data the samples were grouped into sets of samples that most likely originated from the same source area in addition shipboard collected atmospheric meteorological data modeled 4 day back trajectories for each sampling day and location and total ozone mapping spectrometer aerosol index data for the time period of dust collection february march 1998 were combined and used to reconstruct the sources of the groups of dust samples on the basis of these data we were able to determine the provenance of the various dust samples it appears that the bulk of the wind blown sediments that are deposited in the proximal equatorial atlantic ocean are transported in the lower level 900 hpa ne trade wind layer which is a very dominant feature north of the intertropical convergence zone itcz however south of the surface expression of the itcz down to 5 s where surface winds are southwesterly we still collected sediments that originated from the north and east carried there by the ne trade wind layer as well as by easterly winds from higher altitudes the fact that the size of the wind blown dust depends not only on the wind strength of the transporting agent but also on the distance to the source hampers a direct comparison of the dust s size distributions and measured wind strengths however a comparison between eolian dust and terrigenous sediments collected in three submarine sediment traps off the west coast of nw africa shows that knowledge of the composition of eolian dust is a prerequisite for the interpretation of paleorecords obtained from sediment cores in the equatorial atlantic

geoarchaeological and chronometrical evidence of early human occupation on lanzarote canary islands abstract two desert loess paleosol sequences in sediment traps were investigated using pedo stratigraphy sedimentology soil mineralogy and irsl dating so far we cannot recognise significant irsl age underestimates from the polymineral fine grain fraction of our samples we establish a first palaeoclimatic sequence spanning the past ca 200 ka which can be compared to data from other canary islands and surrounding areas including terrestrial and deep sea records more humid phases on lanzarote are apparently triggered by milankovich forcing but the climate remained semi arid to arid all over the past 200 ka the onset of human occupation of the island during a slightly moister period is bracketed between 5 and 10 ka based on the occurrence of archaeosediments containing bones of ovicaprid this is the first proof of much earlier occupation than witnessed so far from archaeological records the early subsidiary economy had a strong impact on soil stability and landscape shaping of the island

saharan dust transport and high latitude glacial climatic variability the alboran sea record millennial to submillennial marine oscillations that are linked with the north atlantic s heinrich events and dansgaard oeschger cycles have been reported recently from the alboran sea revealing a close ocean atmosphere coupling in the mediterranean region we present a high resolution record of lithogenic fraction variability along images core md 95 2043 from the alboran sea that we use to infer fluctuations of fluvial and eolian inputs to the core site during periods of rapid climate change between 28 000 and 48 000 cal yr b p comparison with geochemical and pollen records from the same core enables end member compositions to be determined and to document fluctuations of fluvial and eolian inputs on millennial and faster timescales our data document increases in northward saharan dust transports during periods of strengthened atmospheric circulation in high northern latitudes from this we derive two atmospheric scenarios which are linked with the intensity of meridional atmospheric pressure gradients in the north atlantic region

dating saharan dust deposits on lanzarote canary islands by luminescence dating techniques and their implication for palaeoclimate reconstruction of nw africa 1 lava flow dammed valleys vegas on lanzarote canary islands represent unique sediment traps filled with autochthonous volcanic material and allochthonous saharan dust these sediments and the intercalated palaeosoil sediments document past environmental change of the last glacial interglacial cycles both on lanzarote and in nw africa a reliable chronology must be established to use these sediment archives for palaeoclimate reconstructions owing to the lack of organic material and the limiting time range of the 14c dating method luminescence dating is the most promising method for these sediments however the fluvio eolian character of these sediments is a major problem for luminescence dating because these sediments are prone to insufficient resetting of the parent luminescence signal bleaching prior to sedimentation to check for the best age estimates we compare the bleaching behavior of 1 different grain sizes coarse versus fine grain quartz osl and 2 different minerals fine grain feldspar irsl versus fine grain quartz osl the results show that owing to its bleaching characteristics quartz is the preferable mineral for luminescence dating on the basis of the fine and coarse grain quartz osl age estimates a chronostratigraphy up to 100 ka could be established beyond this age limit for osl quartz the chronostratigraphy could be extended up to 180 ka by correlating the vega sediments with dated marine sediment archives

nature and timing of magma interactions before during and after the caldera forming eruption of volcan ceboruco mexico volcan ceboruco mexico erupted 1 000 years ago producing the jala pumice and forming a 4 km wide caldera during that eruption 2 8 to 3 5 km3 of rhyodacite 70 wt sio2 magma and 0 2 to 0 5 km3 of mixed dacite 67 wt sio2 magma were tapped and deposited as the jala pumice subsequently the caldera was partially filled by extrusion of the dos equis dome a low silica 64 wt sio2 dacite dome with a volume of 1 3 km3 petrographic evidence indicates that the jala dacite and dos equis dacite originated largely through the mixing of three end member magmas 1 rhyodacite magma 2 dacite magma and 3 mafic magma linear least squares modeling and detailed modal analysis indicate that the jala dacite is predominantly a bimodal mixture of rhyodacite and dacite with a small additional mafic component whereas the dos equis dacite is composed of mostly dacite mixed with subordinate amounts of rhyodacite and mafic magma according to fe ti oxide geothermometry before the caldera forming eruption the rhyodacite last equilibrated at 865 c whereas the dacite was originally at 890 c but was heated to 960 c by intrusion of mafic magma as hot as 1 030 c zoning profiles in plagioclase and or magnetite phenocrysts indicate that mixing between mafic and dacite magma occurred 34 47 days prior to eruption whereas subsequent mixing between rhyodacite and dacite magmas occurred only 1 4 days prior to eruption following the caldera forming eruption continued inputs of mafic magma led to effusion of the dos equis dome dacite in this case timing between mixing and eruption is estimated at 93 185 days based on the thickness of plagioclase overgrowth rims

north atlantic control on precipitation pattern in the eastern mediterranean black sea region during the last glacial based on proxy records from western black sea cores we provide a comprehensive study of climate change during the last glacial maximum and late glacial period in the black sea region for the first time we present a record of relative changes in precipitation for nw anatolia based on variations in the terrigenous supply expressed as detrital carbonate concentration the good correspondence between reconstructed rainfall intensity in nw anatolia and past western mediterranean sea surface temperatures ssts implies that during the glacial period the precipitation variability was controlled like today by mediterranean cyclonic disturbances periods of reduced precipitation correlate well with low ssts in the mediterranean related to heinrich events h1 and h2 stable oxygen isotopes and lithological and mineralogical data point to a significant modification in the dominant freshwater sediment source concomitant to the meltwater inflow after 16 4 cal ka bp this change implies intensification of the northern sediment source and with other records from the mediterranean region consistently suggests a reorganization of the atmospheric circulation pattern affecting the hydrology of the european continent the early deglacial northward retreat of both atmospheric and oceanic polar fronts was responsible for the warming in the mediterranean region leading simultaneously to more humid conditions in central and northern europe

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