occurrence stratigraphy and geochemistry of late quaternary tephra layers in the aegean sea and the marmara sea abstract several discrete tephra layers occur in 2 5 10 3 m long cores from the aegean sea whereas a single tephra is identified in 3 5 9 7 m long cores from the marmara sea major and trace element data on these tephras delineate eight distinct groups the geochemical data and multivariate statistics allow the correlation of the tephra layers with six previously described marine tephras from the eastern mediterranean sea potential terrestrial sources are suggested for the others the chronostratigraphy of the tephra layers was established using several radiocarbon dates and the oxygen isotope stratigraphy from two long piston cores four widespread tephra layers occur within the upper quaternary sediments of the aegean sea the two youngest widespread tephra layers were derived from the santorini volcano of south central aegean sea z2 the minoan eruption ca 3 6 ka and y2 the cape riva eruption ca 21 7 ka the y2 tephra is also identified in three piston cores from the marmara sea the two older widespread tephra layers originated from the eruptions which emplaced the campanian ignimbrite of the italian volcanic provinces i e the y5 tephra ca 39 3 ka and from the nisyros volcano of the southeastern aegean sea the consistent occurrence of the nisyros tephra below the y5 tephra confirms similar findings in a lake core on the island of lesbos linear extrapolations using the oxygen isotope stratigraphy suggest an age of 42 44 ka for the nisyros eruption three additional tephra layers with a limited regional distribution are identified in the aegean sea cores two of these tephras originated from the yali volcano of the southeastern aegean sea and from the aeolian islands i e x1 tephra a series of six mugearite tephra beds in the south skiros basin is interpreted as a set of redeposited turbidites

a proposed methodology for analyses of wide ranged elements in volcanic glass shards in widespread quaternary tephras the abundances of 58 elements from lithium to uranium of volcanic glass shards in 11 quaternary widespread tephras of japan and those of 4 tephras of north america have been analyzed using the laser ablation inductively coupled plasma mass spectrometry la icp ms technique the analytical values of the major components sio2 tio2 al2o3 feo mno mgo cao and k2o were systematically lower 10 than those of analyzed using electron microanalysis techniques in previous researches whereas that na2o tend to be 20 higher than those of previous researches using the electron beam microanalysis technique the higher values of na2o obtained by la icp ms may result from the absence of the na loss phenomenon associated with the electron beam analytical techniques most elements were analyzed with less than 20 of the relative standard deviations rsds whereas some trace elements such as beryllium and some transition metals exhibit higher rsds up to 120 in 5 repeated analyses on the single glass shard the la icp ms technique can be reasonably available for quantitative analyses of the major elements in volcanic glass shards in addition to the trace elements the volcanic glass can be clearly distinguished from each other by the patterns of the element abundances the element abundances and the patterns of the elements of the volcanic glass shards are helpful to more precise identification and correlation of tephra samples

a volcanic marker 92 ka for dating deep east antarctic ice cores tephra layers recorded in east antarctic ice enable reliable linking over long distances and when correlated with well dated eruptions in the source area provide absolute ages for improving the accuracy of model based ice chronology we used chronostratigraphic information and grain specific geochemical data major elements by electron microprobe and trace elements by la icp ms to suggest that a tephra layer from the epica dome c and dome fuji ice cores is the distal counterpart of the mt berlin marie byrd land province west antarctica pyroclastic unit 40ar 39ar dated to 92 5 2 0 and 92 2 0 9 ka such one to one correlation which is proposed here for the first time for the east antarctic deep climatic archives provides independent age constraints for glaciological modelling of core timescales

comment on a synchronized dating of three greenland ice cores throughout the holocene by b m vinther et al no minoan tephra in the 1642 b c layer of the grip ice core denton j s pearce n j g 2008 comment on a synchronized dating of three greenland ice cores throughout the holocene by b m vinther et al no minoan tephra in the 1642 b c layer of the grip ice core journal of geophysical research 113 d04303 7 pp

the application of icp ms methods to tephrochronological problems pearce nicholas westgate j a perkins w t preece s j 2004 the application of icp ms methods to tephrochronological problems applied gechemistry 19 3 pp 289 322 rae2008

ultrahigh temperature metamorphism followed by two stage decompression of garnet orthopyroxene sillimanite granulites from ganguvarpatti madurai block southern india the mg al granulites from ganguvarpatti consist of orthopyroxene sillimanite garnet quartz as peak assemblage with a few porphyroblasts of cordierite and sapphirine these assemblages were strongly overprinted by late symplectites and coronas orthopyroxene inclusions in garnet and porphyroblast cores have the highest xmg 0 80 and al2o3 content 10 7 wt the estimated near peak metamorphic conditions 1 000 50 c and 11 kbar using garnet orthopyroxene geothermobarometry are consistent with those determined using a petrogenetic grid the proposed multi stage evolution process implies an initial decompression deduced from multi phase symplectites followed by cooling during biotite formation further late decompression is explained from the orthopyroxene rims on biotite this proposed p t path thus suggests a unique and complex evolution history for the uht granulites of southern india present results are comparable with similar adjacent terranes in the gondwana supercontinent but the lack of structural and geochronological data makes a link with any major metamorphic event uncertain

some numerical considerations in the geochemical analysis of distal microtephra abstract the use of late quaternary tephra horizons as isochronous markers for high resolution correlation between records is of growing importance in a number of scientific fields particular advancements have been made through the identification of microtephra deposits very distal deposits of volcanic ash invisible to the naked eye the successful correlation of ash layers and volcanic eruptions depends on the acquisition of the major element chemistries of a tephra layer derived from microprobe analyses of individual glass shards this is particularly important for microtephras where aeolian fractionation has removed much of the mineral phase of the ash deposit which often aids tephra discrimination there are however difficulties in distinguishing precisely between different eruptions of the same volcano using major element composition and this may not always be resolved by the use of trace elements given the potential of tephrochronology as a correlative tool in many disciplines it is important to resolve this difficulty one way forward is to perform more robust statistical analyses on the geochemical data as in general analyses are confined to a series of bi plots of major elements here the authors explore some of the problems associated with dealing with microprobe data generated for individual tephras and pay particular attention to the unit sum problem using a subset of data generated as part of a eurodelta project on tephra distribution in the adriatic the authors demonstrate that this problem is detectable in major element data from tephras and have consequently applied the logratio method before further analyses of the data it is demonstrated that the use of logratios combined with discriminant functions analysis provides a more robust assessment of likely chemical correlations between tephras and are superior to the use of bi plots alone and obviate the need for any data normalization a particular point of contention between tephrochronologists

tephrochronology magnetostratigraphy and mammalian faunas of middle and early pleistocene sediments at two sites on the old crow river northern yukon territory canada abstract alluvial and lacustrine sediments exposed beneath late pleistocene glaciolacustrine silt and clay at two sites along the old crow river northern yukon territory are rich in fossils and contain tephra beds surprise creek tephra szt occurs in the lower part of the alluvial sequence at crh47 and little timber tephra ltt is present near the base of the exposure at crh94 surprise creek tephra has a glass fission track age of 0 17 0 07 ma and little timber tephra is 1 37 0 12 ma all sediments at crh47 have a normal remanent magnetic polarity and those near ltt at crh94 have a reversed polarity in agreement with the geomagnetic time scale small mammal remains from sediments near ltt support an early pleistocene age but the chronology is not so clear at crh47 because of the large error associated with the szt age determination tephrochronological and paleomagnetic considerations point to an mis 7 age for the interglacial beds just below szt at crh47 and at chester bluffs in east central alaska but mammalian fossils recovered from sediments close to szt suggest a late irvingtonian age therefore older than mis 7 further studies are needed to resolve this problem

chronostratigraphy of the baringo tugen barsemoi hspdp btb13 1a core 40ar 39ar dating magnetostratigraphy tephrostratigraphy sequence stratigraphy and bayesian age modeling the baringo tugen barsemoi 2013 drillcore btb13 acquired as part of the hominin sites and paleolakes drilling project recovered 228 m of fluviolacustrine sedimentary rocks and tuffs spanning a 3 29 2 56 ma interval of the highly fossiliferous and hominin bearing chemeron formation tugen hills kenya here we present a bayesian stratigraphic age model for the core employing chronostratigraphic control points derived from 40ar 39ar dating of tuffs from core and outcrop 40ar 39ar age calibration of related outcrop diatomaceous units and core magnetostratigraphy the age model reveals three main intervals with distinct sediment accumulation rates an early rapid phase from 3 2 to 2 9 ma a relatively slow phase from 2 9 to 2 7 ma and the highest rate of accumulation from 2 7 to 2 6 ma the intervals of rapid accumulation correspond to periods of high earth orbital eccentricity whereas the slow accumulation interval corresponds to low eccentricity at 2 9 2 7 ma suggesting that astronomically mediated climate processes may be responsible for the observed changes in sediment accumulation rate lacustrine transgression regression events as delineated using sequence stratigraphy dominantly operate on precession scale particularly within the high eccentricity periods a set of erosively based fluvial conglomerates correspond to the 2 9 2 7 ma interval which could be related to either the depositional response to low eccentricity or to the development of unconformities due to local tectonic activity age calibration of core magnetic susceptibility and gamma density logs indicates a close temporal correspondence between a shift from high to low frequency signal variability at 3 ma approximately coincident the end of the mid piacenzian warm period and the beginning of the cooling of world climate leading to the initiation of northern hemispheric glaciation c 2 7 ma btb13 and the baringo basin records may thus provide evidence of a connection between high latitude glaciation and equatorial terrestrial climate toward the end of the pliocene

differentiating the bishop ash bed and related tephra layers by elemental based similarity coefficients of volcanic glass shards using solution inductively coupled plasma mass spectrometry s icp ms volcanic glass samples from the same volcanic center intra source often have a similar major element composition thus it can be difficult to distinguish between individual tephra layers particularly when using similarity coefficients calculated from electron microprobe major element measurements minor trace element concentrations in glass can be determined by solution inductively coupled plasma mass spectrometry s icp ms but have not been shown as suitable for use in large tephrochronologic databases here we present minor trace element concentrations measured by s icp ms and compare these data by similarity coefficients the method commonly used in large databases trial samples from the bishop tuff the upper and lower tuffs of glass mountain and the tuffs of mesquite spring suites from eastern california usa which have an indistinguishable major element composition were analyzed using s icp ms the resulting minor trace element similarity coefficients clearly separated the suites of tephra layers and in most cases individual tephra layers within each suite comparisons with previous instrumental neutron activation analysis inaa elemental measurements were marginally successful this is important step toward quantitative correlation in large tephrochronologic databases to achieve definitive identification of volcanic glass samples and for high resolution age determinations

identification of aniakchak alaska tephra in greenland ice core challenges the 1645 bc date for minoan eruption of santorini pearce nicholas westgate j a eastwood w j preece s j 2006 identification of aniakchak alaska tephra in greenland ice core challenges the 1645 bc date for minoan eruption of santorini geochemistry geophysics and geosystems 5 pp q03005 rae2008

u pb single zircon pb evaporation and sm nd isotopic study of a granulite domain in se madagascar madagascar is a poorly known precambrian domain at the eastern border of the mozambique belt strongly affected by the pan african orogeny this large island represents a key part of gondwanaland and the accurate dating of the major metamorphic event is critical for the reconstruction of that supercontinent in the southeastern zone of the island metamorphism has reached high temperature and low pressure conditions 850 c and 5 kbar with moderate retrogression a u pb conventional multigrain single zircon stepwise pb evaporation and sm nd geochronological study on meta felsic rocks has shown that basement of at least lower proterozoic age was strongly metamorphosed around 570 580 ma this tectometamorphic event nearly obliterated any pre pan african zircon isotopic memory the granulite facies metamorphism is associated with the syn metamorphic emplacement of the anosyan charnock ites and granites a strong channelized fluid contribution at 545 ma has produced the re crystallization of biotite apatite

mid pleistocene silicic tephra beds in the auckland region new zealand their correlation and origins based on the trace element analyses of single glass shards abstract the trace element composition of individual glass shards from twelve distinct mid pleistocene silicic tephra beds from the auckland region new zealand has been determined by laser ablation la icp ms analysis this is the first application of such data to tephra correlation studies in new zealand these analyses support earlier major element based correlations between three surface sections oruarangi and okariha at port waikato and st kentigern s at east auckland and a long core patiki road west auckland the correlations provide a higher resolution record of taupo volcanic zone tvz activity than is preserved in more proximal deposits where burial and erosion obscure much of the volcanic record a combination of major and trace element analysis enables the correlation of three units exposed in the auckland region with their proximal equivalents ignimbrites from the tvz namely deposits associated with 1 the ongatiti ignimbrite 1 21 0 04 ma 2 an un named post ahuroa pre unit e ignimbrite sample ut1274 from the rocky hill section king country and 3 the unit e ignimbrite 1 ma combined major and trace element data show a marked evolution in magma chemistry with the large ongatiti and unit e ignimbrite eruptions occurring after a change in composition caused by replenishment reactivation of the magma chamber changes in magma chemistry between these deposits resulted from a combination of assimilation of metasedimentary country rocks and periods of fractional crystallisation of a plagioclase dominated assemblage trace element data and the wider dispersal of the silicic tephras in the auckland region suggests that they are all sourced from the mangakino volcanic centre mvc in the tvz this study illustrates for the first time in a new zealand context the potential for correlating tephra deposits using single glass shard trace element chemistry

sm nd dating and cooling history of scourian granulites sutherland the scourian gneisses of the lewisian complex of north west scotland have been the subject of many geochronological investigations sm nd whole rock measurements suggest that the protoliths of the lewisian complex differentiated 2 92 0 05 gyr ago from an approximately chrondritic mantle1 rb sr and pb pb whole rock ages between 2 8 and 2 6 gyr reflect subsequent depletion in rb and u refs 2 3 which has generally been associated with granulite facies metamorphism zircons which are thought to have crystallized during this metamorphism have also given u pb ages of 2 66 gyr ref 4 this granulite facies metamorphism involving pressures in excess of 10 kbar and peak temperatures estimated between 820 50 c ref 5 and 1 250 c refs 6 7 affects a terrain including supracrustal rocks7 and thus implies a major tectonic event we report here the first geochronological data measured on mineral assemblages that have also provided estimates of the conditions of metamorphism such measurements are possible because the major minerals of granulite facies assemblages show an unusually favourable spread in sm nd ratios garnet especially is strongly enriched in sm ref 8 data for three garnetiferous basic gneiss assemblages suggest that closure of the sm nd system occurred significantly later than the peak of the metamorphism

the intav intercomparison of electron beam microanalysis of glass by tephrochronology laboratories results and recommendations abstract the international focus group on tephrochronology and volcanism intav of the international union for quaternary research inqua has conducted an intercomparison of tephrochronology laboratories with electron beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries this assessment includes most active tephrochronology laboratories and represents the largest intercomparison exercise yet conducted by the tephrochronology community the intercomparison was motivated by the desire to assess the quality of data currently being produced and to stimulate improvements in analytical protocols and data reporting that will increase the efficacy of tephra fingerprinting and correlation participating laboratories were each supplied with a mount containing three samples for analysis 1 rhyolitic lipari obsidian id3506 2 phonolitic sheep track tephra from mt edziza british columbia canada and 3 basaltic laki 1783 a d tephra a fourth sample rhyolitic old crow tephra was also distributed most laboratories submitted extensive details of their analytical procedures in addition to their analytical results most used some combination of defocused or rastered beam and modest beam current to reduce alkali element migration approximately two thirds reported that they routinely analyze one or more secondary standards to evaluate data quality and instrument performance despite substantial variety in procedures and calibration standards most mean concentrations compare favorably between laboratories and with other data typically four or fewer data contributions had means for a given element on a given sample that differed by more than 2 standard deviations from the overall means obtaining accurate na 2 o concentrations for the phonolitic tephra proved to be a challenge for many laboratories only one half of the data sets had means within 1 standard deviation of the 8 2 wt na 2 o value obtained by other methods one mean is higher and 14 are lower three of the data set means fall below 7 wt na 2 o most submissions had relative precision better than 1 5 for the major elements for low abundance elements the precision varied substantially with relative standard deviations as small as 10 and as large as 110 because of the strong response to this project the tephrochronology community now has a large comparative data set derived from common reference materials that will facilitate improvements in accuracy and precision and which can enable improved use of published data produced by the participating laboratories finally recommendations are provided for improving accuracy precision and reporting of electron beam microanalytical data from glasses

late quaternary tephrostratigraphy ahklun mountains sw alaska radiocarbon dated sediment cores from six lakes in the ahklun mountains south western alaska were used to interpolate the ages of late quaternary tephra beds ranging in age from 25 4 to 0 4 ka the lakes are located downwind of the aleutian arc and alaska peninsula volcanoes in the northern bristol bay area between 159 and 161 w at around 60 n sedimentation rate age models for each lake were based on a published spline fit procedure that uses monte carlo simulation to determine age model uncertainty in all 62 14c ages were used to construct the six age models including 23 ages presented here for the first time the age model from lone spruce pond is based on 18 ages and is currently the best resolved holocene age model available from the region with an average 2 age uncertainty of about 109 years over the past 14 5 ka the sedimentary sequence from lone spruce pond contains seven tephra beds more than previously found in any other lake in the area of the 26 radiocarbon dated tephra beds at the six lakes and from a soil pit seven are correlated between two or more sites based on their ages the major element geochemistry of glass shards from most of these tephra beds supports the age based correlations the remaining tephra beds appear to be present at only one site based on their unique geochemistry or age the 5 8 ka tephra is similar to the widespread aniakchak tephra 3 7 0 2 1 ka but can be distinguished conclusively based on its trace element geochemistry the 3 1 and 0 4 ka tephras have glass major and trace element geochemical compositions indistinguishable from prominent aniakchak tephra and might represent redeposited beds only two tephra beds are found in all lakes the aniakchak tephra 3 7 0 2 ka and tephra b 6 1 0 3 ka the tephra beds can be used as chronostratigraphic markers for other sedimentary sequences in the region including cores from cascade and sunday lakes which were previously undated and were analyzed in this study to correlate with the new regional tephrostratigraphy copyright 2012 john wiley sons ltd

identification of a kulshan caldera correlative tephra in the palouse loess of washington state northwest usa abstract the kulshan caldera formed at 1 15 ma on the present day site of mt baker washington state northwest usa and erupted a compositionally zoned dacite rhyolite magma and a correlative eruptive the lake tapps tephra this tephra has previously been described but only from the puget lowland of nw washington here an occurrence of a kulshan caldera correlative tephra is described from the quaternary palouse loess at the washtucna site wa 3 site wa 3 is located in east central washington 340 km southeast of the kulshan caldera and 300 km east southeast of the lake tapps occurrence in the puget lowland major and trace element chemistry and location of the deposit at washtucna within reversed polarity sediments indicates that it is not correlative with the mesa falls rockland bishop ash lava creek b or huckleberry ridge tephras instead the washtucna deposit is related to the lake tapps tephra by fractional crystallisation but is chemically distinct a consequence of its eruption from a compositionally zoned magma chamber the correlation of the washtucna occurrence to the kulshan caldera forming eruption indicates that it had an eruptive volume exceeding 100 km3 and that its tephra could provide a valuable early pleistocene chronostratigraphic marker in the pacific northwest

lead isotope ratios of volcanic glass by laser ablation inductively coupled plasma mass spectrometry application to miocene tephra beds in montana usa and adjacent areas abstract recent improvements in spatial resolution and sensitivity of laser ablation inductively coupled plasma mass spectrometry allow exploration of the tephrochronologic potential of pb isotope ratios of volcanic glass in particular their use in characterization and provenance detection of distal tephra beds measurements have good accuracy and precision as determined by comparison with reference materials a test suite of samples was taken from miocene tephra beds in montana and sw saskatchewan all of which come from the yellowstone hotspot track yhst but only those tephra beds of known age were used because of the need to track any temporal changes in the pb isotope ratios samples of a few quaternary tephra beds from the yellowstone plateau volcanic field were also included the pb isotope ratio analyses form three distinct clusters on a 207 pb 208 pb 206 pb 208 pb plot with ages of 0 6 2 0 ma 5 5 7 8 ma and 7 4 11 1 ma the same pb isotope age clusters were reproduced when published pb isotope information on dated rocks from the yhst is used rocks from the heise volcanic field and from a core recovered between the heise and picabo volcanic fields all fall within the younger miocene group whereas rocks from the bruneau jarbidge volcanic field plot in the older miocene group therefore pb isotope ratios of glass shards do help in provenance detection of distal tephra beds at least in the tectono volcanic setting of the yhst and will be a useful addition to the criteria necessary to establish a reliable miocene tephrostratigraphic framework for montana and adjacent areas

trace element composition of single glass shards in distal minoan tephra from sw turkey volcanic glass from the seventeenth century bc c 3600 bp minoan eruption of santorini thera has been recovered from a 4 cm thick tephra deposit at golhisar golu a small lake in sw turkey analysis of single grains of this glass by laser ablation inductively coupled plasma mass spectrometry la icp ms provides for the first time an accurate determination of the trace element composition of the juvenile glass component of this eruption free from contaminants such as phenocrysts or detrital material individual glass shards 150 m show a large degree of variation in their trace element composition indicative of substantial small scale compositional heterogeneity in the magma this is a result of the proximity of crystallizing phases and provides insights into the chemical evolution of the minoan magma the range of elemental compositions displayed by individual glass shards combined with the consistency of many trace element ratios are characteristics of the minoan glass these features provide a trace element signature for the minoan tephra which will be of value in stratigraphic correlation across the eastern mediterranean

recognition of santorini minoan tephra in lake sediments from golhisar golu southwest turkey by laser ablation icp ms laser ablation inductively coupled plasma mass spectrometry la icp ms has been applied to the analysis of fine grained volcanic ash shards separated from a tephra layer deposited by the mid second millenniumbc minoan eruption of santorini or thera in holocene lake sediments from golhisar golu a small intramontane lake in southwest turkey in this study we have used minor isotopes of two major elements routinely determined by epma in tephrochronological studies as the internal standard in la icp ms analyses these are30si and57fe for fully quantitative and single internal standard multi element calibration so called semi quantitative analysis respectively the results show that the determination of trace elements by la icp ms is a quick and accurate method typical accuracies are better than 20 and precision measured as the mean rsd relative standard deviation is better than 15 for most petrogenetically significant trace elements these levels of precision actually reflect within sample heterogeneity as repeat analyses on the homogenous nist 612 glass standard show that instrument precision is typically 5 for most elements the level of accuracy and precision obtained during this study is quite acceptable in tephrochronological studies and provides us with the confidence to proceed to the analysis of single glass shards by using a modified small spot laser ablation system

discovery of mount mazama cryptotephra in lake superior north america implications and potential applications this research was supported by a regents professor grant by the university of minnesota to johnson

nd and sr systematics in an eclogite xenolith from tanzania evidence for frozen mineral equilibria in the continental lithosphere combined isotopic nd sr and petrographic analyses are reported for an eclogitic xenolith from the vissury mine tanzania an exceedingly large difference in measured nd values in garnet and clinopyroxene 200 units suggest a major mineral equilibration at 1 75 0 014 ga nd isotopic heterogeneities are demonstrated in different generations of garnet and zonation in sr and nd isotope compositions is present within the clinopyroxene the variation in measured nd isotope compositions in different generations of garnet corresponds to 16 units exsolution of garnet from clinopyroxene occurred in an essentially closed system with respect to sr and nd petrographically different generations of garnet are present one garnet with rutile inclusions as well as the rims of clinopyroxene are clearly off the isochron features like this can originate either if a system is not closed e g affected by a migrating fluid or if a remanent isotopic heterogeneity survived the homogenisation at 1 75 ga the subsolidus partitioning of sm and nd between garnet and clinopyroxene results in higher fractionation of the smnd ratio in garnet than in the liquid crystal partitioning since the closure temperature for the sm nd exchange between garnet and clinopyroxene may be around 850 c in a dry system many of the lithospheric ultramafic rocks may exhibit frozen mineral equilibria the isotopic data suggest that this eclogite was emplaced at 1 75 ga into the lithosphere mantle at temperatures of about 1040 c and then cooled as a closed system at a rate of 6 50 c my down to 840 c where all the exchange reactions were efficiently frozen in at 1 75 ga ago the coincidence of the emplacement of granites 1 7 1 8 ga into the central part of the tanzanian craton with the age of the eclogite suggests that lower crustal melting was triggered by a thermal event in the upper lithosphere

new findings of late glacial etna pumice fall deposits in ne sicily and implications for distal tephra correlations in the mediterranean area pumice fall deposits found in the nebrodi mountains and along the alcantara river close to the town of randazzo ne sicily have been studied to derive information about their volcanic source and age the geochemical na alkaline affinity of juvenile products benmoreite to trachyte clearly indicates they originated from etna volcano sicily major empa and trace la icp ms element compositional data on matrix glasses indicate that the investigated deposits have a compositional affinity consistent with the tephra deposits of unit d produced by the ellittico caldera forming eruptions between ca 17 and 19 cal ka bp furthermore their compositions correspond to the distal tephra equivalent found in some lacustrine and marine cores in central italy y 1 tm 11 tyrrhenian sea et 1 md10 and adriatic sea pal94 66 358 pal94 8 353 we applied the principal components analysis pca a statistical tool able to reduce the variability of a complex system to compare the compositions of the proximal samples with the possible distal counterparts found in drill cores of the mediterranean area on the basis of northward dispersal of the studied deposits and their geochemical features we suggest they represent a previously unreported sub plinian plinian eruption of ellittico volcano producing medial distal pumice fall deposits in the nebrodi mountains and close to randazzo named here the d1c layer the discovery of these deposits helps solve the problem of distal correlations of the northerly dispersed tephra from etna related to unit d for which no definitive attribution with proximal units was given in previous studies the results presented here add to the knowledge of the eruptive history of the volcano and contribute to expanding the proximal geochemical glass dataset for distal tephra correlation in the mediterranean region during the late glacial period

rhyolitic and dacitic component of the askja 1875 tephra in southern and central finland first step towards a finnish tephrochronology tephra from icelandic volcanic eruptions is frequently dispersed to northern europe but so far tephra has not been detected in finnish sedimentary records we report the first finding of a cryptot

laser ablation inductively coupled plasma mass spectrometry and tephras a new approach to understanding arc magma genesis the development of laser ablation inductively coupled plasma mass spectrometry has revolutionized the analysis of tephras by providing 1 an efficient and precise method for determining abundances of a wide variety of trace elements at low concentrations in individual glass shards and 2 assessment of geochemical heterogeneities within individual ash horizons this development is important for petrogenetic studies of intraoceanic arc systems where tephras provide the most complete temporal record of magmatism results from the izu bonin and mariana arc systems indicate that despite close geographical proximity and similar tectonic evolution they contrast strongly in terms of geochemical evolution since 35 ma whereas the mariana tephras have exceptional compositional diversity ranging from low k oligocene to high k miocene and subsequently medium k compositions pliocene quaternary the izu bonin arc has been dominated by low k compositions throughout the mariana increases in k are paralleled by increases in abundances of incompatible trace elements and by increased values of diagnostic ratios e g nb yb and th yb regarded as monitors of potential mantle source fertility the relative uniformity of nb yb and nb zr ratios in izu bonin tephras indicates that cyclic processes of backarc basin development and mantle depletion do not necessarily induce large scale temporal geochemical variations in the associated arc temporal variability within the mariana arc and its divergence from the izu bonin arc ca 13 ma can be traced to a major injection of subducted sediment in the mariana system at this time

ultra high temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the palni hill ranges southern india sapphirine granulites from a new locality in the palni hill ranges southern india occur in a small enclave of migmatitic highly magnesian metapelites mg 85 72 within massive enderbitic orthogneiss they show a variety of multiphase reaction textures that partially overprint a coarse grained high pressure assemblage of bt opx ky grt pl qtz the sequence of reactions as deduced from the corona and symplectite assemblages together with petrogenetic grid considerations records a clockwise p t evolution with four distinct stages 1 equilibration of the initial high p assemblage in deep overthickened crust 12 kbar 800 900 c was followed by a stage of near isobaric heating presumably as a consequence of input of extra heat provided by the voluminous enderbitic intrusives during heating kyanite was converted to sillimanite and biotite was involved in a series of vapour phase absent melting reactions which resulted in the ultra high temperature assemblage opx crd kfs spr sil grt qtz bt coexisting with melt equilibration at c 950 1000 c 11 10 kbar 2 subsequently as a result of decompression of the order of 4 kbar at ultra high temperature a sequence of symplectite assemblages opx sil spr spr crdopx spr crdopx crdopx crd spl crd spl developed at the expense of garnet orthopyroxene and sillimanite this stage of near isothermal decompression implies rapid ascent of the granulites into mid crustal levels possibly due to extensional collapse and erosion of the overthickened crust 3 development of late biotite through back reaction of melt with residual garnet indicates a stage of near isobaric cooling to c 875 c at 7 8 kbar i e relaxation of the rapidly ascended crust to the stable geotherm 4 a second period of near isothermal exhumation up to c 6 5 kbar 850 c is indicated by the partial breakdown of late biotite through volatile phase absent melting reactions available isotope data suggest that the early part of the evolutionary history stages 1 3 is presumably coeval with the early proterozoic metamorphism in the extended granulite terrane of the nilgiri biligirirangan and shevaroy hills to the north while the exhumation of the granulites from mid crustal levels stage 4 occurred only during the pan african thermotectonic event which led to the accretion of the kerala khondalite belt to the south

age of some pleistocene interglacial beds and associated fossils in eastern beringia defined by fission tracks in glass shards of chester bluff tephra

a north atlantic tephrostratigraphical framework for 130 60 ka b2k new tephra discoveries marine based correlations and future challenges abstract building chronological frameworks for proxy sequences spanning 130 60 ka b2k is plagued by difficulties and uncertainties recent developments in the north atlantic region however affirm the potential offered by tephrochronology and specifically the search for cryptotephra here we review the potential offered by tephrostratigraphy for sequences spanning 130 60 ka b2k we combine newly identified cryptotephra deposits from the ngrip ice core and a marine core from the iceland basin with previously published data from the ice and marine realms to construct the first tephrostratigraphical framework for this time interval forty three tephra or cryptotephra deposits are incorporated into this framework twenty three tephra deposits are found in the greenland ice cores including nine new ngrip tephras and twenty separate deposits are preserved in various north atlantic marine sequences major minor and trace element results are presented for the new ngrip horizons together with age estimates based on their position within the ice core record basaltic tephras of icelandic origin dominate the framework with only eight tephras of rhyolitic composition found new results from marine core md99 2253 also illustrate some of the complexities and challenges of assessing the depositional integrity of marine cryptotephra deposits tephra based correlations in the marine environment provide independent tie points for this time interval and highlight the potential of widening the application of tephrochronology further investigations however are required that combine robust geochemical fingerprinting and a rigorous assessment of tephra depositional processes in order to trace coeval events between the two depositional realms

volcanism and the greenland ice cores the tephra record abstract in recent years increased awareness of the considerable potential offered by tephrochronology in palaeoclimatic studies has fuelled a renewed interest in the tephra record preserved within the greenland ice cores this renewal has occurred in tandem with the development of continuous flow analysis techniques which provide high resolution volcanic aerosol records these chemical records are of considerable value for identifying tephra horizons composed of glass shards and also provide the basis for a new high precision ice core timescale thus allowing ages to be assigned to volcanic events tephra horizons of glass shards in the ice cores play a critical role for 1 testing and building chronological frameworks for the ice cores and other sequences 2 synchronising disparate palaeoclimatic sequences and testing phase relationships 3 atmospheric pathway reconstruction and 4 verifying the source of volcanic aerosol peaks here we review the results of over 25 years of research into tephra horizons in the grip gisp2 and ngrip cores we provide high precision ages for horizons based on recently developed timescales and draw together geochemical characterisations of the products of 45 volcanic events deposited on the greenland ice sheet and identified in the cores there is a clear disparity between the number of volcanic aerosol peaks and the number of tephra horizons of glass shards identified thus far however this synthesis highlights the critical role of the greenland ice cores firstly in the reconstruction of the history of icelandic volcanic eruptions and secondly the considerable value of some tephra horizons in facilitating the correlation of these key climatic archives to north atlantic marine sequences other noteworthy issues include the potential of these cores to preserve tephra horizons from more distal volcanic sources such as north america to resolve the debate surrounding the thera eruption and the observation that some tephra horizons are preserved within the ice without coeval volcanic aerosol signals

norwegian sea tephrostratigraphy of marine isotope stages 4 and 5 prospects and problems for tephrochronology in the north atlantic region abstract this paper presents an account of the tephrostratigraphy of south eastern norwegian sea core md99 2289 for the interval spanning marine isotope stage mis 5 and part of mis 4 from 70 000 to 130 000 years ago tephra deposits from in the order of 100 mainly basaltic volcanic eruptions in iceland and on jan mayen are described in terms of their stratigraphic context and geochemical composition representing the most comprehensive record of iceland and jan mayen volcanism over this time span the most important transport mechanism of tephra to the core site is considered to have been iceberg rafting which is thought to be responsible for a centennial to millennial scale time lag between the volcanic eruption events and the subsequent deposition of tephra in deep sea sediments while this clearly limits the use of some of the tephras as isochronous markers twelve discrete tephra deposits show stratigraphical and geochemical characteristics that suggest them to have been deposited near contemporaneously with their source volcanic events and hence suitable candidates as regional isochrones four of these accords with the geochemical signatures of tephra deposits previously described from the nordic seas region potential problems for the application of tephrochronology highlighted by this work are discussed and recommendations for strategies to overcome them are proposed

developments in the analysis of volcanic glass shards by laser ablation icp ms quantitative and single internal standard multielement methods abstract laser ablation inductively coupled plasma mass spectrometry la icp ms has been applied to the analysis of fine grained 125 250 m volcanic glass shards separated from tephra deposits our earlier calibration strategies used ce as an internal standard which required the use of another trace element analytical technique to determine ce followed by off line data correction by comparison with well characterised glass separates we have progressed from these earlier studies to use a minor isotope of a major element routinely determined by epma in tephrochronological studies as an internal standard for la icp ms analysis internal standards used during this study include 29si 30si or 44ca for fully quantitative determinations or 57fe for a single internal standard multi element calibration so called semiquantitative analysis no subsequent off line data correction is required the differences between each technique are minimal and choice of technique depends largely upon instrument sensitivity as little as 80 g of material is consumed during a single determination which takes approximately two minutes and detection limits are below 1 part per million accuracy is generally 15 when compared with other analytical techniques and precision may vary between 5 and 20 the worse precisions reflecting within sample variability rare earth and other trace element data can be used to correlate or distinguish individual tephra deposits with confidence and specific examples are illustrated with quaternary tephra deposits from alaska and india and cretaceous tephra deposits from banks island in arctic canada

cryptotephra detection using high resolution trace element analysis of holocene marine sediments southwest japan abstract detection techniques for invisible tephra known as cryptotephra have been exploited to construct precise and high resolution correlations for a broad range of sedimentary sequences we demonstrate that continuous trace element profiles are an effective means for detecting probable positions of distal cryptotephra in holocene hemipelagic sediments instrumental neutron activation analyses were performed on specimens of bulk sediments from five piston and gravity cores water depths 300 1500 m taken from the southern japan east sea the down core variations in the ta sc ratio identify the positions of one to three alkaline cryptotephra in four of these cores the cr sc profiles show the position of one rhyolitic cryptotephra in three of the cores the existence of tephra derived components glass crystals was confirmed by microscopic observation sem epma analysis and refractive index measurement on grains extracted from these layers based on microscopic observation and the stratigraphic correlations between cores we identified eruption ages of the cryptotephras at 6 3 7 5 and 9 3 14 c kyr bp and two source volcanoes around 800 and 400 km from the study area the tephra layers visible to the naked eye contained volcanic grains coarser than 200 m and the alkaline and rhyolitic tephra component comprised 20 and 33 of the sediment on weight basis respectively in contrast the range of particle sizes of the cryptotephras detected in this study is finer than 125 m and almost all of the glass shards were finer than 40 m the alkaline and rhyolitic cryptotephras made up only 2 17 and 22 24 respectively of the sediment on weigh basis the high sensitivity of this method stems from the significant difference in trace element contents between the tephras and enclosing hemipelagic sediments in the core alkaline u oki tephra was enriched in ta by one order of magnitude over that of the sediment and depleted in sc by one order the rhyolitic tephra k ah was depleted by about one order in cr relative to that of enclosing the sediment the differences in chemical composition between within plate alkaline tephras and hemipelagic sediments are usually so large that trace element geochemical method is likely to be useful for alkaline cryptotephra detection in other areas with similar tectonic characteristics

ultra distal tephra deposits from super eruptions examples from toba indonesia and taupo volcanic zone new zealand abstract voluminous rhyolitic eruptions from toba indonesia and taupo volcanic zone tvz new zealand have dispersed volcanic ash over vast areas in the late quaternary the 74 ka youngest toba tuff ytt eruption deposited ash over the bay of bengal and the indian subcontinent to the west the 340 ka whakamaru eruption tvz deposited the widespread rangitawa tephra dominantly to the southeast in addition to occurrences northwest of vent extending across the landmass of new zealand and the south pacific ocean and tasman sea with distal terrestrial exposures on the chatham islands these super eruptions involved 2500 km 3 and 1500 km 3 of magma dense rock equivalent dre respectively ultra distal terrestrial exposures of ytt at two localities in india middle son valley madhya pradesh and jurreru river valley andhra pradesh at distances of 2000 km from the source caldera show a basal primary ashfall unit 4 cm thick although deposits containing reworked ash are up to 3 m in total thickness exposures of rangitawa tephra on the chatham islands 900 km from the source caldera are 15 30 cm thick at more proximal localities 200 km from source rangitawa tephra is 55 70 cm thick and characterized by a crystal rich basal layer and normal grading both distal tephra deposits are characterized by very fine ash with high pm 10 fractions and are crystal poor glass chemistry stratigraphy and grain size data for these distal tephra deposits are presented with comparisons of their correlation dispersal and preservation using field observations ash transport and deposition were modeled for both eruptions using a semi analytical model hazmap with assumptions concerning average wind direction and strength during eruption column shape and vent size model outputs provide new insights into eruption dynamics and better estimates of eruption volumes associated with tephra fallout modeling based on observed ytt distal tephra thicknesses indicate a relatively low

u pb and sm nd dating of high pressure granulite and upper amphibolite facies rocks from sw sweden abstract geochronological data from different radiometric systems on high grade metamorphic rocks in the southwest swedish granulite region southwestern sweden are generally analytically precise but sometimes in conflict with each other age data from seven samples on which a variety of radiometric methods have been applied are presented the age of peak metamorphism is determined by metamorphic zircons from two garnet amphibolites at c 975 ma using the conventional u pb isotope and pb pb evaporation methods titanites from the same type of rocks give ages of c 923 3 ma and 945 2 ma the sm nd data on mafic granulites and garnet amphibolites yield surprisingly young ages between 945 and 900 ma similar to previous sm nd ages these ages are comparable to or even younger than the 40 ar 39 ar hornblende ages that range between 1030 and 930 ma assuming that the sm nd systematics are entirely controlled by volume diffusion the closure temperature of the sm nd system in minerals from these rocks would be comparable to or lower than that of ar diffusion in hornblende i e around 500 c

towards a late quaternary tephrochronological framework for the southernmost part of south america the laguna potrok aike tephra record abstract a total of 18 tephra samples have been analysed from the composite sediment sequence from site 2 of the laguna potrok aike icdp expedition 5022 from southern patagonia argentina which extends back to ca 51 ka cal bp analyses of the volcanic glass show that all layers but one are rhyolitic in composition with sio2 contents ranging between ca 74 5 and 78 wt and suggest an origin in the austral andean volcanic zone avz 49 55 s nonetheless two main data clusters occur one group with k2o contents between ca 1 5 and 2 0 wt indicating an origin in the mt burney volcanic area and one group with k2o contents between ca 2 7 and 3 9 wt tentatively correlated with viedma lautaro and the aguilera volcanoes in the northern part of the avz the early holocene tephra mb1 and the late pleistocene reclus r1 tephra occur in the upper part of the sequence periods with significant tephra deposition occurred between ca 51 44 ka cal bp and ca 31 25 ka cal bp with a decrease in tephra layer frequency between these two periods

tephrochronology and the extended intimate integration of ice core marine and terrestrial records event stratigraphy 8 128 ka b2k the comparison of palaeoclimate records on their own independent timescales is central to the work of the intimate integrating ice core marine and terrestrial records network for the north atlantic region an event stratigraphy has been established from the high precision greenland ice core records and the integrated gicc05 chronology this stratotype provides a palaeoclimate signal to which the timing and nature of palaeoenvironmental change recorded in marine and terrestrial archives can be compared to facilitate this wider comparison without assuming synchroneity of climatic change proxy response intimate has also focussed on the development of tools to achieve this in particular the use of time parallel marker horizons e g tephra layers volcanic ash coupled with the recent temporal extension of the greenland stratotype as part of this special issue we present an updated intimate event stratigraphy highlighting key tephra horizons used for correlation across europe and the north atlantic we discuss the advantages of such an approach and the key challenges for the further integration of terrestrial palaeoenvironmental records with those from ice cores and the marine realm

a detailed framework of marine isotope stages 4 and 5 volcanic events recorded in two greenland ice cores sulphate records from greenland ice cores indicate that marine isotope stages 4 and 5 were charactensed by a higher incidence of large volcanic eruptions than other periods during the last glacial

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

neutron activation analysis of mediterranean volcanic rocks an analytical database for archaeological stratigraphy abstract pumice has been used as a serviceable abrasive or religious artifact since antiquity and has therefore been an object of trade by analyzing pumice samples from archaeological excavations and comparing the results to an analytical database it is possible to establish the origin of the sample and thereby get information on the maximum age and the transport route of the pumice sample in addition the deposition of primary tephra deposits can be used as time markers and place constraints on the ages of archaeological materials neutron activation analysis naa was applied to determine the concentrations of 25 elements as ba ce co cr cs eu fe hf k la lu na nd rb sb sc sm ta tb th u yb zn and zr in pumice samples from the mediterranean region milos santorini kos giali and nisyros greece lipari italy and cappadokia turkey it was found that eruption products like pumice or volcanic ash can be correlated in many cases to their volcanic sources by comparison of the typical main and trace elemental concentration patterns chemical fingerprint such a distinction is possible if the volcanic rocks are homogenous enough with respect to the concentrations of geochemically relevant elements using only the pure glass fraction of tephra a sample size of 5 mg is sufficient for identification by naa

cryptotephrochronology of the eemian and the last interglacial glacial transition in the north east atlantic the eemian interglacial and the onset of the subsequent glacial period serve as the most recent analogue for the natural operation of the climate system during the current interglacial pronounced climatic oscillations occurred during this period but their nature and pattern are poorly understood due to dating limitations and unknown phase relationships between different regions and archives tephrochronology offers considerable potential for precise correlation of disparate palaeoclimatic archives preserving evidence of these rapid climatic transitions through the tracing of common isochronous tephra horizons we outline the identification of three previously unknown cryptotephra horizons within a marine core from the rockall trough north east atlantic this sequence preserves a high resolution record of this interval and shard size geochemical heterogeneity and the co variance of shard concentrations with ice rafted debris data are utilized to demonstrate that primary airfall was the most likely transport and depositional pathway the main geochemical populations of these horizons have similar transitional alkali major and trace element compositions suggesting that they were derived from a common icelandic source potentially the oraefajokull volcanic system these tephra horizons represent additions to the north atlantic event stratigraphy for this period and tentative correlations to icelandic terrestrial deposits are proposed for two horizons

identification of cryptotephra horizons in a north east atlantic marine record spanning marine isotope stages 4 and 5a 60 000 82 000 a b2k abstract tephrochronology is one of the few techniques that offer considerable but as yet largely unrealised potential for the correlation of north atlantic palaeoclimatic archives spanning the mis 4 and 5a substage period a phase of pronounced global cooling during the initiation of the last glacial period in this investigation two previously unidentified rhyolitic tephra horizons believed to be sourced from iceland were isolated within the giant piston core md04 2822 retrieved from the rockall trough north east atlantic one horizon was deposited at the beginning of greenland stadial 19 70 150 a b2k and the other around the cooling transition at the end of greenland interstadial 20 75 320 a b2k density separation epma and la icp ms techniques were utilised for the identification of these cryptotephra within the fine fraction sediment

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

upb geochronology of the sri lankan basement abstract u pb ages of zircons and monazites from ortho and paragneisses representing the major crystalline basement units of sri lanka establish a new geochronological framework which is consistent with previously published work on sm nd model ages rb sr whole rock ages and u pb mineral ages in the highland complex three newly dated orthogneisses one previously dated by baur et al 1991 and one dated by kroner and williams 1992 all intruded 1 85 to 1 9 ga ago this widespread intrusion event occurred soon after the end of sediment deposition which is estimated at 1 9 to 2 0 ga using upper intercept ages of zircons from metapelites in the highland complex within the boundaries of this complex established by sm nd model age mapping milisenda et al 1994 only one orthogneiss has been found which is substantially younger than 1 8 ga this is the metatonalite from polonnaruwa which intruded 670 ma ago baur et al 1991 three orthogneisses from the vijayan complex which lies to the east of the highland complex yield similarly consistent crystallization ages of 1023 8 1016 28 and 1033 121 ma in the wanni complex which lies to the west of the highland complex a sillimanite bearing gneiss which is apparently of metasedimentary origin but contains zircons of igneous appearance yields a primary crystallization age of 793 4 ma consistent with a previously dated orthogneiss from kurunegala of 770 ma baur et al 1991 in addition single zircon data by kroner et al 1994 indicate primary crystallization ages of 1 0 to 1 1 ga for orthogneisses from the vavuniya charnockite province which is considered to be part of the wanni complex these results confirm the age contrast between the highland complex on the one hand and the vijayan complex and wanni complex on the other as previously inferred from sm nd model ages milisenda et al 1988 1994 post tectonic granitoids and pegmatites intruded throughout all three complexes 550 ma ago the age of regional high grade metamorphism mostly granulite facies in the highland complex mostly amphibolite facies in the vijayan complex and both granulite and amphibolite facies in the wanni complex is constrained to be less than 670 ma the primary crystallization age of the polonnaruwa metatonalite it is more closely defined by lower intercept zircon ages which include one concordant age of 608 4 ma and one discordant but well defined age of 611 23 ma and by a nearly concordant monazite age of 592 2 ma this indicates that peak metamorphic conditions occurred 610 ma ago numerous other lower intercept ages between 590 and 550 ma and post tectonic intrusion ages of 550 ma set a lower age limit for high grade conditions and deformation the temperature history between 610 and 550 ma is not yet well resolved and it is not clear whether there was a separate thermal event 550 ma ago previously published whole rock rb sr and sm nd isochrons for gneisses from the highland complex yielding ages of 2 ga and greater and previously interpreted to date the time of granulite grade metamorphism must be reinterpreted in the light of the new data presented here as well as other recently published results e g burton and o nions 1990b baur et al 1991 and in view of the accumulated evidence for very limited element mobility during high grade metamorphism these whole rock ages are in fact identical or close to the ages of primary granitoid emplacement rather than the age of granulite facies metamorphism

three years 2011 2013 of eruptive activity at mt etna working modes and timescales of the modern volcano plumbing system from micro analytical studies of crystals abstract tracking magma dynamics at active volcanoes by using the compositional and textural records of minerals is becoming an important aspect of modern volcanology to solve key issues such as temporal relationships between magma recharge and eruption duration of magma storage and final ascent upward to the surface these issues are relevant at mt etna where the style of volcanic activity during the last years showed drastic variations in duration and intensity the paroxysmal activity between 2011 and 2013 at the volcano summit has given the opportunity to investigate the chemical physical processes driving the activity and to fix their spatial temporal relationships into the plumbing system an extensive compositional dataset of plagioclase and olivine crystals from lavas emitted between the 2011 and 2013 at mt etna has been used to constrain modes and timescales of magma storage and transfer to the surface plagioclase crystals display either near equilibrium or disequilibrium textures at the core and rim that indicate complex histories of magma crystallization under variable chemical and physical conditions crystals with different textures have been characterized for major an minor fe and mg and trace elements sr ba textural relationships at the plagioclase cores support the idea that crystals undergo variable decompression rates in the deep parts of the plumbing system fe and mg zoning vs anorthite in correspondence of plagioclase sieve textures at the rim suggest that processes of gas flushing have a dominant role in triggering paroxysmal eruptions determining a sudden intensification of the eruptive activity up to the fountaining phase the sr ba ratio in oscillatory zoned plagioclase revealed the dominant presence into the plumbing system of high sr magma volumes coexisting with low sr magma batches that preserve a geochemical signature similar to that of magmas feeding the pre 1971 activity through sr diffusion modeling in plagioclase the maximum time of magma storage during the considered eruptive period has been evaluated timescales of crystal residence in the plumbing system are short five years to three decades suggesting limited magma storage and faster transfer dynamics to the surface chemical zoning of olivine crystals highlights processes of multi step magma transfer and residence at different levels of the plumbing system the upward migration of magmas occurred primarily through multiple episodes of injection and mixing between five compositionally distinct magmatic environments m i whose p t o 2 characteristics and concentrations in dissolved volatiles were constrained by thermodynamic modeling on the basis of the forsterite contents found at the olivine cores from a deepest reservoir located at depth of 600 mpa the most primitive magma m00 fo 84 moved along dominant pathways intercepting the m0 fo 80 82 at 390 mpa and or m1a fo 78 250 mpa m1b fo 75 140 mpa and finally the shallow m2 fo 70 73 40 mpa storage zones for some eruptive episodes olivine zoning highlights a preferential route of transfer connecting the m00 and m2 storage zones that facilitated the fast migration of primitive magma at shallow depth fe mg diffusion modeling on olivine normal and reverse zoning defines the timescales of magma transfer and storage across these magmatic environments which vary from 1 to 18 months whereas intrusion and mixing by more basic magma into the shallowest reservoir occurred always within 5 months before the eruption relevance of this study mainly relies on the quantification of volcanic processes at depth that may have considerable consequences in development of unusual high energy eruptions at basaltic volcanoes generally acknowledged for their weak to mild explosive activity

geochemical fingerprinting of the widespread toba tephra using biotite compositions toba caldera sumatra is one of the largest and most explosive volcanoes on earth erupting some of the most voluminous volcanic deposits chronologically these eruptions are 790 ka older toba tuff 500 ka middle toba tuff and 74 ka younger toba tuff ash from these eruptions is dispersed over the entire region from india through malaysia to indonesia where it forms isochronous markers that have been documented in a variety of sedimentary sequences including palaeoclimate archives and archaeological sites the chemistry of the volcanic glass shards usually enables distal volcanic ash units to be correlated to a known eruption however the magmas involved in the three largest toba eruptions are compositionally similar and consequently the glass chemistry that is used to differentiate eruption units cannot be used to identify distal deposits here we show that the composition of biotite crystals which occur with glass in the distal deposits can be used to fingerprint the deposits of the younger toba tuff biotite in younger toba tuff has a lower feo mgo 2 1 2 6 than in the products of older eruptions 2 8 3 7 correlations using these distinct biotite compositions indicate that the ash found in malaysia and in archaeological sites in india was from the 74 ka younger toba tuff eruption

correlation and characterisation of individual glass shards from tephra deposits using trace element laser ablation icp ms analyses current status and future potential pearce nicholas denton j s perkins w t westgate j a 2007 correlation and characterisation of individual glass shards from tephra deposits using trace element laser ablation icp ms analyses current status and future potential journal of quaternary science 22 7 pp 721 736 rae2008

timing and rate of isothermal decompression in pan african granulites from rundvagshetta east antarctica geochronological data combined with field and petrological evidence constrain the timing and rate of near isothermal decompression at granulite facies temperatures in rocks from the lutzow holm complex of east antarctica granulite facies gneisses from rundvagshetta in lutzow holm bay experienced a peak metamorphic temperature of over 900 c at c 11 kbar as evidenced by primary orthopyroxene sillimanite bearing assemblages and secondary cordierite sapphirine bearing assemblages in metapelites peak metamorphic assemblages show strong preferred mineral orientation interpreted to have developed synchronously with pervasive ductile deformation zircon from a syndeformational leucosome has a u pb age of 517 9 ma which is interpreted as a melt crystallization age this age provides the best estimate of the time of peak metamorphic conditions the post peak metamorphic history is characterized by near isothermal decompression recorded by mineral textures in a variety of rock compositions field and textural relations indicate that decompression post dated pervasive ductile deformation k ar and 40ar 39ar ages from hornblende and biotite represent closure ages during cooling subsequent to decompression and indicate cooling to temperatures between c 350 and 300 c by c 500 ma thus placing a lower time limit on the duration of the high temperature isothermal decompression episode the combination of the zircon age from a syndeformational melt with k ar and 40ar 39ar closure ages indicates that near isothermal decompression from c 11 to c 4 kbar at granulite facies temperatures followed by cooling to c 300 c took place within a time interval of 20 10 myr simple one dimensional models for exhumation controlled cooling indicate that these data require exhumation rates of the order of c 3 km myr 1 for several million years then cessation of exhumation followed by relatively isobaric cooling during thermal re equilibration

cryptotephras the revolution in correlation and precision dating from its icelandic origins in the study of visible tephra horizons tephrochronology took a remarkable step in the late 1980 s with the discovery of a ca 4300 year old microscopic ash layer in a scottish peat bog since then the search for these cryptotephra deposits in distal areas has gone from strength to strength indeed a recent discovery demonstrates how a few fine grained glass shards from an alaskan eruption have been dispersed more than 7000 km to northern europe instantaneous deposition of geochemically distinct volcanic ash over such large geographical areas gives rise to a powerful correlation tool with considerable potential for addressing a range of scientific questions a prerequisite of this work is the establishment of regional tephrochronological frameworks that include well constrained age estimates and robust geochemical signatures for each deposit with distal sites revealing a complex record of previously unknown volcanic events frameworks are regularly revised and it has become apparent that some closely timed eruptions have similar geochemical signatures the search for unique and robust geochemical fingerprints thus hinges on rigorous analysis by electron microprobe and laser ablation inductively coupled plasma mass spectrometry historical developments and significant breakthroughs are presented to chart the revolution in correlation and precision dating over the last 50 years using tephrochronology and cryptotephrochronology

petrology of granulite facies metapelites of the highland complex sri lanka implications for the metamorphic zonation and the p t path in the pan african granulite facies highland complex of sri lanka the metamorphic grade increases from the central northwestern part towards boththe east and the southeast in metapelites the following prograde changes in metamorphic assemblage are recognized biotite ilmenite garnet or co cordierite sillimanite alkali feldspar quartz in the central northwestern part give way to garnet rutile sillimanite ilmenite or biotite alkali feldspar quartz in the e and se and are replaced by gar garnet cordierite biotite magnetite ilmenite alkali feldspar quartz bearing assemblages in the southwest cordierite coexisting with garnet is restricted to the western highland complex where metamorphic pressures of 5 7 kbar havebeen determined in the eastern highland complex where garnet clinopyroxene quartz is stable in metabasic rocks metamorphic pressures of 8 10 kbar have been obtained from barometers on metapelites phase relations of metapelites as well as geobarometry point to a continuous metamorphic transition between the eastern and the western part of the highland complex a clockwise p t path for the whole highland complex is indicated by the succession kyanite sillimanite andalusite an even earlier stage of the prograde metamorphism documented by sillimanite needles older than kyanite inclusions in garnet hhave been found in two samples of the eastern highland complex this points to a strong pressure increase at amphibolite facies conditions probably due to tectonic thickening of the crust during prograde metamorphism other inclusion assemblages in garnet and reaction textures indicate the breakdown of staurolite to kyanite spinel garnet and subsequent continued garnet growth in the sillimanite field at the expense of biotite sillimanite and quartz during further heating ternary feldspars in metapelites bear evidence of extreme metamorphic temperatures of about 900 c previously only indicated by coexisting pyroxenes in metabasic and charnockitic rocks within a few garnets inclusions of staurolite which are ti rich 1 34 wt tio2 and richer in fe xfe 0 745 than the enclosing garnet have survived the very high grade metamorphism the high grade stage of the prograde metamorphism was accompanied by strong flattening and a general n s stretching which is many metapelites ceased after peak temperatures but proceeded in others tectonic uplift of the whole highland complex occurred only after a phase of near isobaric cooling in the lower crust zircon 610 ma and biotite cooling ages 460 ma holzl et al 1991 as well as retrograde p t paths which passed the andalusite stability field are similar in the eastern and western part of the highland complex this suggests that the lower crustal cross section exposed in the highland complex was already tilted during cooling

old crow tephra across eastern beringia a single cataclysmic eruption at the close of marine isotope stage 6 abstract old crow tephra is the largest and most widespread quaternary eruption presently known in eastern beringia its major and trace element geochemistry fe ti oxides and stratigraphic and paleoecological context indicate that it is the result of a single cataclysmic eruption the proximal region may well have experienced tephra fallout from small eruptions just prior to or after the old crow event but there is no evidence to indicate that the distal area was affected we recalculate the glass fission track age at 124 10 ka which coupled with stratigraphic and paleoenvironmental reconstructions indicates that deposition occurred prior to development of the last interglacial boreal forest which suggests a latest marine isotope stage mis 6 age the bulk tephra volume erupted is estimated by three different approaches that are in broad agreement at 200 km 3 but this result must be considered as tentative given the poor controls on definition of isopachs over such a large area the source caldera although presently unrecognized is located in the eastern aleutian arc possibly at or near the emmons lake volcanic center

deformation of a high grade gondwana fragment sri lanka abstract the sri lankan gondwana fragment is a high grade gneiss terrain consisting of at least three crustal units namely the wanni complex wc the highland complex hc and the vijayan complex vc which were juxtaposed during the pan african collision at least six phases of ductile deformation were recognized in the smallest gondwana fragment sri lanka there is microscopic and mesoscopic evidence for a first deformation d 1 which occurred during prograde metamorphism but before the main granulite facies metamorphism this first deformation is represented by straight to curved and crenulated inclusion trails in garnet porphyroblasts microfolds in some metapelites and quartzo feldspathic gneisses and by a s 1 foliation preserved in crenulation folds and some rootless intrafolial folds d 2 has two main stages of which the second phase is the most intense and dominant deformation which produced most part of the major composite and transposed compositional layering as well as the prominent stretching lineation l 2 the first stage of d 2 may have been responsible for the formation of a crenulation cleavage of s 1 as seen in garnet porphyroblasts in some metapelites the compositional layering s 2 in metapelites and metasemipelites appears to have formed through the development of a crenulation cleavage f 2 folds are mesoscopic isoclinal rootless and occur as intrafolial folds and their limbs are highly attenuated major part of the deformation during the latter stage of d 2 was non coaxial many minor and large scale recumbent isoclinal folds f 3 were produced during d 3 both d 2 and d 3 were coeval with the peak conditions of granulite facies metamorphism d 4 produced very large gentle nearly e w upright folds probably during the beginning of uplift of the entire high grade assemblage from deeper crustal levels still under granulite facies conditions d 5 is the second strongest deformation and was responsible for the large scale upright folds f 5 which control the present map pattern of sri lanka the superimposition of d 5 folds on d 4 folds gave rise to a large scale type i fold interference pattern of ramsay 1967 d 6 deformation caused local refolding of the f 5 folds and was accompanied by amphibolite facies conditions during uplift the deformation represented by the majority of vein type structures such as patchy charnockite veins cordierite bearing veins and graphite veins clearly post date d 5 it is argued that the wc the hc and the vc in sri lanka may be three distinctly different proterozoic crustal units brought into contact by tectonism in late proterozoic at two different stages

steric sea level variations over 2004 2010 as a function of region and depth inference on the mass component variability in the north atlantic ocean 1 we investigate the regional ocean depth layer down to 2000 m contributions to global mean steric sea level from january 2004 to march 2010 using argo based ocean temperature and salinity data from the scripps oceanographic institution database we find that indian ocean warming is almost compensated by atlantic ocean cooling so that the total global mean steric sea level increases only slightly over the considered period 0 35 0 30 mm yr salinity variations also contribute at lower rate to the observed steric compensation meanwhile the pacific steric sea level increases only slightly 0 35 0 25 mm yr in the north atlantic region the mass component estimated by the difference between satellite altimetry based minus steric sea level over the same area is negatively correlated over 2004 2010 with the steric component during that period north atlantic sea level variability seems mostly driven by the north atlantic oscillation nao this is unlike during the previous years 1997 to 2004 a period during which we observe significant correlation between north atlantic sea level and el nino southern oscillation enso with positive sea level corresponding to enso cold phases la nina

microanalysis of tephra by la icp ms strategies advantages and limitations assessed using the thorsmork ignimbrite southern iceland abstract micron scale analysis of vesicular volcanic glass can be problematic because thin vesicle walls and junctions limit the area available for analysis subsurface vesicles limit the vertical thickness available microcrysts at or below the surface may contaminate glass analyses and some glasses show compositional banding in addition distal tephra are very small 10 100 m and material may be sparse we have analysed the mpi ding reference glasses and natural tephra samples pumice scoria and fiamme from the thorsmork ignimbrite southern iceland using laser ablation inductively coupled plasma mass spectrometry la icp ms three different reduction strategies are used averaging uncertainty weighting and log linear regression we then assess the data quality achieved using the various strategies using our technique we show that the main limiting factor on data quality is precision particularly for natural tephra analyses at 20 000 cps relative standard deviations rsds in the thorsmork tephra are 5 10 approximately twice those achieved in the mpi ding glasses 3 5 at the same conditions rhyolitic pumice and fiamme from the thorsmork ignimbrite are compositionally homogenous the proximal deposit also contains subordinate basalt scoria therefore the deposit is bimodal the thorsmork rhyolite correlates with the north atlantic ash zone 2 naaz2 tephra described in a marine sediment core lacasse and garbe schonberg 2001 jvgr 170 113 147

towards a protocol for the trace element analysis of glass from rhyolitic shards in tephra deposits by laser ablation icp ms laser ablation inductively coupled plasma mass spectrometry la icp ms is used widely to analyse single volcanic glass shards from quaternary tephra deposits for stratigraphic correlation as yet no generally accepted protocol for these analyses exists and published methods report significant differences in crater size and calibration strategies using ca as the internal standard cai s and not sii s for the analysis of rhyolitic glass can cause significant problems because of ablation of i ca rich phenocrysts notably ubiquitous plagioclase but also calcic amphibole apatite and allanite or ii mounting epoxy resin which can contribute to the ca internal standard signal using cai s can cause underreporting of many elements which concentrate in ca rich phenocrysts making their ablation difficult to recognize but when using sii s no such underreporting occurs additionally larger ablation craters 50 m diameter potentially incorporate even small volumes of phenocryst material whereas smaller craters 20 m diameter more frequently miss phenocrysts thus for the la icp ms analysis of rhyolitic glass shards smaller ablation craters should be employed and calibrated using sii s allowing recognition and removal of analyses incorporating ca rich phenocrysts and avoiding issues related to the ablation of the mounting resin

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

trace element microanalysis by la icp ms the quest for comprehensive chemical characterisation of single sub 10 μm volcanic glass shards funder nerc rono ne f021445 1 enhancing tephrochronology and its application intrepid project hiroshi machida commemorative volume

reconstructing the quaternary evolution of the world s most active silicic volcanic system insights from an 1 65 ma deep ocean tephra record sourced from taupo volcanic zone new zealand abstract the taupo volcanic zone tvz central north island new zealand is the most frequently active quaternary rhyolitic system in the world silicic tephras recovered from ocean drilling programme site 1123 41 47 16 s 171 29 94 w 3290 m water depth in the southwest pacific ocean provide a well dated record of explosive tvz volcanism since 1 65 ma we present major minor and trace element data for 70 quaternary tephra layers from site 1123 determined by electron probe microanalysis 1314 analyses and laser ablation inductively coupled plasma mass spectrometry 654 analyses trace element data allow for the discrimination of different tephras with similar major element chemistries and the establishment of isochronous tie lines between three sediment cores 1123a 1123b and 1123c recovered from site 1123 these tephra tie lines are used to evaluate the stratigraphy and orbitally tuned stable isotope age model of the site 1123 composite record trace element fingerprinting of tephras identifies 4 5 m and 7 9 m thick sections of repeated sediments in 1123a 49 0 53 5 mbsf metres below seafloor and 1123c 48 1 56 0 mbsf respectively these previously unrecognised repeated sections have resulted in significant errors in the site 1123 composite stratigraphy and age model for the interval 1 15 1 38 ma and can explain the poor correspondence between 18o profiles for site 1123 and site 849 equatorial pacific during this interval the revised composite stratigraphy for site 1123 shows that the 70 tephra layers when correlated between cores correspond to 37 38 individual eruptive events tephras 7 of which can be correlated to onshore tvz deposits the frequency of large volume tvz derived silicic eruptions as recorded by the deposition of tephras at site 1123 has not been uniform through time rather it has been typified by short periods 25 50 ka of intense activity bracketed by longer periods 100 130 ka of quiescence the most active period at least 1 event per 7 ka occurred between 1 53 and 1 66 ma corresponding to the first 130 ka of tvz rhyolitic magmatism since 1 2 ma 80 of tephras preserved at site 1123 and the more proximal site 1124 were erupted and deposited during glacial periods this feature may reflect either enhanced atmospheric transport of volcanic ash to these sites up to 1000 km from source during glacial conditions or more speculatively that these events are triggered by changes in crustal stress accumulation associated with large amplitude sea level changes only 8 of the 37 38 site 1123 tephra units 20 can be found in all three cores and 22 tephra units 60 are only present in one of the three cores whether a tephra is preserved in all three cores does not have any direct relationship to eruptive volume instead it is postulated that tephra preservation at site 1123 is patchy and influenced by the vigorous nature of their deposition to the deep ocean floor as vertical density currents at this site at least 5 cores would need to have been drilled within a proximity of 10 s to 100 s of metres of each other to yield a 99 chance of recovering all the silicic tephras deposited on the ocean surface above it in the past 1 65 ma

structural environment around th4 in silicate glasses implications for the geochemistry of incompatible me4 elements the structural environment around th4 in several silicate glasses containing 1 3 wt th4 was investigated as a function of melt composition and polymerization using extended x ray absorption fine structure exafs spectroscopy one set of glasses had the bulk chemical composition of monticellite mo diopside di anorthite an albite al olivine basalt o bas tholeiitic basalt t bas calc alkaline dacite dac and calc alkaline rhyolite rhy a second set of th bearing glasses had the bulk al composition but also contained either 5 5 wt f or 2000 ppm cl in glasses containing 3 wt th th coordination varies from 8 d viiith o 2 41 0 02 a in mo and di to a mixture of 8 and 6 coordinations d vi viiith o 2 35 2 36 0 02 a in all other compositions the presence of viiith is related to the thorianite tho2 saturation in the glass in al glasses containing 1 wt th 6 fold coordinated th dominates d vith o 2 32 0 02 a no clear evidence for f or cl complexes around th is observed in any of the halogen containing glasses weak but significant interactions of th with tetrahedral si al network and or alkali elements are observed especially in highly polymerized compositions rhy in which th si ai na k contributions are detected between 3 25 and 3 50 0 05 a these results suggest that in this set of glasses th does not form complexes but rather acts as a weak network modifier the presence of vith in silicate glasses an unusual low coordination for th suggests that the ionic radius of th in magmatic systems is lower than previously reported rth 0 94 a the resulting high th o bond strength 0 7 vu unknown in minerals may explain the observed low crystal melt partition coefficients of th4 i e its incompatible character during magmatic differentiation increasing polymerization is predicted to favor higher coordination around th viii ix as a result of a shortage of nbo to which th preferentially bonds hence dramatic changes in the crystal chemistry of th are predicted i e the incorporation of th in minerals comparison with u4 suggests that vith is less abundant in similar glass melt systems compared with viu this may explain the u th fractionation often observed in zircon as well as the preferential incorporation of th in accessory minerals containing large sites in which th4 can be substituted e g the ca2 site in titanite apatite or zirkelite

re evaluation and extension of the marine isotope stage 5 tephrostratigraphy of the faroe islands region the cryptotephra record previous studies of marine sequences from the faroe islands region have identified a series of coarse grained tephra horizons deposited during marine isotope stage mis 5 here we reassess the mis

trace element geochemistry of individual glass shards of the old crow tephra and the age of the delta glaciation central alaska abstract two widespread tephra deposits constrain the age of the delta glaciation in central alaska the old crow tephra ca 140 000 10 000 yr identified by electron microprobe and ion microprobe analyses of individual glass shards overlies an outwash terrace coeval with the delta glaciation the sheep creek tephra ca 190 000 yr is reworked in alluvium of delta age the upper and lower limiting tephra dates indicate that the delta glaciation occurred during marine oxygen isotope stage 6 we hypothesize that glaciers in the delta river valley reached their maximum pleistocene extent during this cold interval because of significant mid pleistocene tectonic uplift of the east central alaska range

developing a robust tephrochronological framework for late quaternary marine records in the southern adriatic sea new data from core station sa03 11 tephra layers are assuming an increasingly important role in the dating and correlation of late quaternary marine sequences here we demonstrate their potential by reporting a new study of the sediment sequence of marine core sa03 11 recovered from the southern adriatic sea which spans the last c 39 ka a total of 28 discrete tephra layers are reported from this sequence 10 of which are visible in the core and a further 18 are non visible cryptotephra layers these have been analysed using more than 1400 wds epma measurements of glass chemistry and results have been compared with published chemical measurements obtained from relevant proximal and distal sites which preserve eruptive material dating to within the same time interval the data show that a high proportion of the layers originate from the campi flegrei volcanic field but more distinctive layers are sourced from vesuvius the aeolian islands and vulcano and these provide key marker horizons the results show that the sequence extends in time to the campanian ignimbrite at the base that a number of the layers have robust age estimates that permit a better constrained age depth model to be constructed for the sequence and that the potential exists for importing terrestrially based age estimates into marine contexts thereby circumventing problems of incorporating reservoir uncertainties associated with marine radiocarbon dates the wds epma dataset generated here also provides important new data that constrain key late quaternary tephra layers in the central mediterranean region

chemical composition of volcanic glasses in visible tephra layers found in a 2503 m deep ice core from dome fuji antarctica twenty six ash layers were found in a 2503 m deep ice core from dome fuji station east antarctica in order to gain information about the sources of ash particles found in the layers major and trace element abundances have been measured the particles found in 21 of the 26 layers were commonly a few tens of m in size suggesting that they originated from volcanoes located in and around the antarctic on the basis of comparison of the major element compositions of these tephras with reference to volcanic rocks and ash the tephras were divided into three types 1 tholeiitic basalt to dacite 2 calc alkaline andesite and 3 trachyandesite to trachyte the source regions appear to be 1 south sandwich islands southern ocean 2 south shetland islands antarctica and or a southern part of the volcanic zone of the andes and 3 marie byrd land and or victoria land antarctica respectively the tephras found in the other five ash layers were significantly smaller 5 m suggesting that they traveled over longer distances abundances of trace elements for the alkaline tephra collected from one layer revealed a possible genetic link to volcanic rocks from marie byrd land in order to correlate between ice cores from dome fuji and vostok antarctica which are widely separated we found coeval ash layers serving as stratigraphic markers of antarctic ice cores a comparison of profiles of 18o 16o 18o and 2h 1h d for the dome fuji and vostok cores indicates that eight ash layers are equivalent in the two cores a clear correlation was found for the chemical compositions of six of these ash layers indicating a high potential for key correlation beds between the deep ice cores from dome fuji and vostok

cryptotephra as a dating and correlation tool in archaeology a new development in archaeological chronology involves the use of far travelled volcanic ash which may form discrete but invisible layers within a site s stratigraphy known as cryptotephra these horizons can provide isochrons for the precise correlation of archaeological records at single moments in time removing or at least significantly reducing temporal uncertainty within inter site comparisons when a tephra can be dated elsewhere its age can be imported between records providing an independent check on other dating methods in use and valuable age estimates for difficult to date sequences the use of cryptotephra layers to date and correlate palaeoenvironmental archives is well established and there exists a wealth of tephra compositional data and regional tephrostratigraphic frameworks from which archaeological cryptotephra studies can benefit greatly existing approaches to finding and analysing cryptotephra are easily adapted to archaeological sequences so long as the often complex nature of archaeological stratigraphies and sediment taphonomy are borne in mind

integrating the intimate records using tephrochronology rising to the challenge little has challenged our understanding of climate change more so than the abruptness with which large scale shifts in temperature occurred during the late quaternary the causal mechanisms driving

evidence for prograde metamorphic evolution of sri lankan pelitic granulites and implications for the development of continental crust petrological evidence for prograde metamorphic evolution is obtained for pelitic granulites of the newly defined highland complex in sri lanka it includes the occurrences of relict kyanite quartz staurolite corundum kyanite hercynite kyanite and sapphirine kyanite spinel within garnet in the sillimanite quartz rich rocks of special interest is the mineralogy of khondalites graphitic garnet sillimanite k feldspar quartz gneisses the matrix of which is free of hydrous minerals indicating that dehydration reactions have been completed in this kind of rocks however relict hydrous minerals such as al ti rich more than 58 wt al2o3 and more than 1 wt tio2 staurolite and extremely ti rich up to 9 8 wt tio2 biotine occur as inclusions within garnet the local relict mineral assemblages within garnet in khondalites indicate the following continuous staurolite breakdown reactions which may have progressed as temperature increased and pressure decreased staurolite quartz kyanite garnet h2o staurolite corundum kyanite garnet h2o staurolite kyanite hercynite garnet h2o staurolite sillimanite hercynite garnet h2o some of these dehydration reactions are inferred to have also taken place in other widespread pelitic granulites of the highland complex moreover garnet in the highland complex pelitic granulites occasionally preserves growth zoning though modified slightly to extensively by post growth volume diffusion based on the evidence a clockwise prograde p t path of evolution is inferredfor meta sedimentary granulites belonging to the highland complex on the other hand no evidence for prograde metamorphism has so far been obtained in lower grade rocks of the wanni complex to the northwest of the highland complex such a difference between these complexes may be the first petrological feature which supports the new geotectonic division of the sri lankan basement rocks based virtually on the distinctly different neodymium model ages it suggests that these two complexes were amalgamated during the very last part of prograde metamorphism of the highland complex rocks that is during decompression and heating probably by the lower crustal lateral flow after tectonic overthickening and delamination the clockwise prograde p t t path followed by the meta sedimentary granulites of the highland complex is in marked contrast with the near isobaric cooling path for meta igneous granulites suggested by some authors it is proposed that both types of p t t paths albeit for different rock types are possible and resulted from diverse deep crustal processes such as underplating of continental crust by sediments and magmas or near convergent plate boundaries

correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods review and evaluation abstract we define tephras and cryptotephras and their components mainly ash sized particles of glass crystals in distal deposits and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental geological and archaeological research we then document and appraise recent advances in analytical methods used to determine the major minor and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures a narrow electron beam diameter 3 5 m can now be used to analyze smaller glass shards than previously attainable reliable analyses of microshards defined here as glass shards in part 2 of the review we describe critically assess and recommend ways in which tephras or cryptotephras can be correlated in conjunction with other information using numerical or statistical analyses of compositional data statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components usually glass or crystals phenocrysts than heuristic alternatives they enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations in common with other scientific hypothesis testing it is easier to infer using such analysis that two or more tephras are different rather than the same adding stratigraphic chronological spatial or palaeoenvironmental data i e multiple criteria is usually necessary and allows for more robust correlations to be made a two stage approach is useful the first focussed on differences in the mean composition of samples or their range which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures similarity coefficients hierarchical cluster analysis informed by distance measures or similarity or cophenetic coefficients and principal components analysis pca some statistical methods cluster analysis discriminant analysis are referred to as machine learning in the computing literature the second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis this stage may involve discriminant function analysis dfa support vector machines svms canonical variates analysis cva and anova or manova or its two sample special case the hotelling two sample t2 test randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices hierarchical cluster analysis and pca such transformations may make the assumption of multivariate normality more appropriate a sequential procedure using mahalanobis distance and the hotelling two sample t2 test is illustrated using glass major element data from trachytic to phonolitic kenyan tephras all these methods require a broad range of high quality compositional data which can be used to compare unknowns with reference training sets that are sufficiently complete to account for all possible correlatives including tephras with heterogeneous glasses that contain multiple compositional groups currently incomplete databases are tending to limit correlation efficacy the development of an open online global database to facilitate progress towards integrated high quality tephrostratigraphic frameworks for different regions is encouraged

crystal residence times from trace element zoning in plagioclase reveal changes in magma transfer dynamics at mt etna during the last 400 years abstract trace element zoning in plagioclase of selected alkaline lavas from the historic 1607 1892 ad and recent 1983 2013 ad activity of mt etna volcano has been used to explore the possible role that volcano tectonics exert on magma transfer dynamics the observed textural characteristics of crystals include near equilibrium textures i e oscillatory zoning and textures with variable extent of disequilibrium patchy zoning coarse sieve textures and dissolved cores historic crystals exhibit lower k concentrations at lower anorthite contents a feature in agreement with the general more potassic character of the recent lavas if compared to the historic products historic plagioclases have statistically higher ba and lower sr concentrations than the recent crystals which result in different sr ba ratios for the two suites of plagioclase variations in the anorthite content along core to rim profiles obtained on crystals with different types of textures for both the historic and recent eruptive periods were evaluated particularly versus sr ba at comparable average an contents crystals characterized by oscillatory zoning which are representative of near equilibrium crystallization from the magma display distinct sr ba ratios we suggest that these features are primarily related to recharge of a new geochemically distinct magma into the storage and transport system of the volcano in addition to distinct trace element and textural characteristics of plagioclase sr diffusion modeling for plagioclase suggests that residence times are generally shorter for crystals found in recently erupted lavas 25 77 years average 43 years compared to those of the historic products 43 163 years average 99 years shorter residences times correlate with gradual increases in eruption volume and eruption frequency rates through time we attribute these features to an increasing influence since the 17th century of extensional tectonic structures within the upper 10 km of the etnean crust which have promoted shorter residence times and higher eruption frequency

extreme crustal metamorphism during a neoproterozoic event in sri lanka a study of dry mafic granulites abstract garnet clinopyroxene quartz granulites of the central highland complex of sri lanka preserve textural and compositional features indicative of high pressure ultrahigh temperature hp uht crustal metamorphism and multistage retrogression grains of the peak metamorphic assemblage garnet clinopyroxene quartz are commonly separated and embayed by late orthopyroxene plagioclase symplectites however in some domains rare grain to grain associations of the peak assemblages are still preserved thermodynamic modeling in the cao na2o k2o feo mgo al2o3 sio2 system indicates peak metamorphic conditions of 12 5 kbar at 925 c the temperature estimates using garnet and clinopyroxene core compositions are in the range 844 982 c in agreement with the thermodynamic modeling in conclusion the textural geochemical and thermodynamic modeling and thermobarometric data indicate a multistage decompression after hp uht metamorphism u pb zircon laser ablation inductively coupled plasma mass spectrometry

individual glass shard trace element analyses confirm that all known toba tephra reported from india is from the c 75 ka youngest toba eruption uncertainty over the identity and age of toba tephras across peninsular india persists with radiometric age dates contradicting earlier compositional data which have been used to identify this important stratigraphic marker as the youngest toba tuff ytt to address this issue new single glass shard analyses have been performed for samples from morgaon and bori north western india which have recently been dated at c 800 ka these and indeed all toba tephra samples thus far analysed from india show the presence of four populations of glass shards defined by their ba y ratio which uniquely identifies them as products of the c 75 ka youngest toba eruption confirmation that the ytt fingerprint is characteristic comes from new analyses of oldest toba tuff ott glass shards from five sites in the indian ocean these are compositionally identical to layer d from the odp site 758 sediment core c 800 ka and belong to a single low ba population clearly different from ytt these analyses show that there is essentially no reworked ott material in the ytt eruption and indicate unequivocally that all known toba tephra occurrences in india belong to the c 75 ka youngest toba eruption