isotope geochemistry sr nd pb and petrogenesis of leucite bearing volcanic rocks from colli albani volcano roman magmatic province central italy inferences on volcano evolution and magma genesis the colli albani composite volcano is made up of strongly silica undersaturated leucite bearing rocks magmas were erupted during three main periods but a complex plumbing system dominated by regional tectonics channelled magmas into different reservoirs the most alkali rich magmas restricted to the caldera forming period pre caldera are extremely enriched in incompatible trace elements and display more radiogenic sr 87sr 86sr 0 71057 0 71067 with slightly less radiogenic pb with respect to those of the post caldera period post caldera volcanic activity was concentrated in three different volcanic environments external to the caldera along the caldera edge and within the caldera the post caldera magmas produced melilite to leucitite bearing plagioclase free leucitites in contrast to the pre caldera lavas they are characterised by lower incompatible trace element abundances and less radiogenic sr 87sr 86sr 0 71006 0 71039 magmas evolved through crystal fractionation plus minor crustal assimilation in a large magma chamber during the pre caldera period the multiple caldera collapses dissected and partially obliterated the early magma chamber during the post caldera stage magmas were channelled through several pathways and multiple shallow level magma reservoirs were established a lithospheric mantle wedge previously depleted in the basaltic component and subsequently enriched by metasomatic slab derived component is suggested as the mantle source of colli albani parental magmas two different parental magmas are recognised for the pre and post caldera stages the differences may be related to the interplay between smaller degrees of melting for the pre caldera magmas and more carbonate rich recycled subducted lithologies in the post caldera magmas

advances in global bioavailable strontium isoscapes abstract strontium isotope ratios 87sr 86sr are a popular tool in provenance applications in archeology forensics paleoecology and environmental sciences using bioavailable 87sr 86sr in provenance studies requires comparing the 87sr 86sr of a sample of interest to that of 87sr 86sr baselines historically these baselines required building empirical datasets from plants or local animals to characterize the 87sr 86sr available to local ecosystems bioavailable 87sr 86sr however researchers are increasingly relying on modeled bioavailable 87sr 86sr maps called isoscapes we review the advantages and limitations of existing approaches to mapping bioavailable 87sr 86sr for provenance studies and propose a globally applicable scalable and editable framework for creating bioavailable 87sr 86sr isoscapes this framework relies on 1 compiling global bioavailable 87sr 86sr data 2 mapping 87sr 86sr variability in rocks 3 leveraging global environmental covariates and 4 applying a random forest regression method that integrates these data to predict bioavailable 87sr 86sr when the random forest model is applied at the global scale it performs well explaining 60 of the variance of the global bioavailable 87sr 86sr dataset and accounts for geological geomorphological and atmospheric controls in data rich regions e g europe the global bioavailable 87sr 86sr isoscape can be successfully extrapolated to broad regions without bioavailable 87sr 86sr data however we also show that this extrapolation may not be valid in exceptionally geologically complex and data poor regions e g madagascar we suggest research directions to improve the accuracy of global bioavailable 87sr 86sr isoscapes which include 1 increasing the collection of bioavailable datasets in data poor regions 2 harmonizing data management practices and metadata collection for bioavailable 87sr 86sr data and 3 relying on advances in remote sensing and geological mapping techniques to improve geological covariates while significant potential to refine 87sr 86sr isoscapes remains the data products provided in this review form a basis for using 87sr 86sr data in large scale provenance studies opening new research avenues in a range of fields

the role of hybridization in the genesis of hercynian granitodis in the gredos massif spain inferences from sr nd isotopes the gredos massif is one the better exposed granitoid complexes of the iberian massif it is composed mainly of peraluminous granitoids with subordinate basic and ultrabasic complexes the massif also contains mega enclaves of migmatites with which the granitoids show transitional contacts two major magmatic associations have been distinguished in this study 1 one comprises the granitoids with microgranular enclaves the enclaves and basic rocks 2 the other is formed by leucogranites intrusive into the former series and free of microgranular enclaves field relationships and microstructures indicate that the rocks of the first series are related by a dominant hybridization process the sr nd isotopic study reveals that this process is complex relating different end members of mantle and crustal affinities and occurred around 295 ma ago late with respect to the main deformation phases of the hercynian orogeny the granitoids with microgranular enclaves gme are part of an overall mixing trend involving palaeozoic mantle derived magma and melts of older crustal material amphibole bearing gme in general contain greater proportions of the mantle derived component than the cordierite bearing gme the actual mixing processes took place on a variety of scales sometimes between melts which were themselves hybrids on a local scale this hybridization process can be modelled by simple binary mixing as documented in the case of a composite dyke the isotopic signatures of the basic rocks are probably to a large degree the result of interaction with crustal melts though additionally the presence of an enriched mantle source cannot be elmininated microgranular enclaves and their immediate hosts have differing initial sr and nd isotopic signatures indicating that isotopic equilibrium was not attained this suggests that the enclaves did not reside in their final granitic melt for long before cooling of the whole system the enclaves are considered to have been derived from basaltic melts which had fractionated and hybridised to varying degrees late stage peraluminous leucogranites have similar initial nd isotopic compositions to the evolved gme a crustal source with a radically different nd isotopic composition or age does not need to be invoked in their petrogenesis

isotopic constraints on the structural relationships between the lesser himalayan series and the high himalayan crystalline series garhwal himalaya nd and sr isotope systematics may provide important constraints on the location of major thrust systems that separate lithologically similar sedimentary sequences the potential of the technique is illustrated by this isotopic study of the main central thrust system of the himalaya nd isotope data from the garhwal himalaya indicate that metasedimentary rocks from the vaikrita group nd 14 to 19 correlate closely with those from the high himalayan crystalline series which constitutes the hanging wall lithologies of the main central thrust in contrast metasedimentary rocks from the munsiari group nd 23 to 28 show marked similarities to the lesser himalayan series in the footwall of the main central thrust sr isotopes support the correlations in that the vaikrita group shows partial reequilibration at 500 ma whereas the munsiari group has not undergone sr isotope homogenization since 1800 ma thus the vaikrita thrust that juxtaposes these two formations is recognized as the main central thrust in garhwal himalaya the thrust coincides approximately with the location of the kyanite isograd confirming that inverted metamorphism is characteristic of both hanging wall and footwall of the main central thrust along the tons thrust known locally as the srinagar thrust 50 km south of the main central thrust low grade quartzarenites with nd sr isotope and trace element characteristics typical of lesser himalayan formations have been emplaced on phyllites and siltstones with geochemical characteristics of the high himalayan crystalline series the field relationships most probably result from out of sequence thrusting in which lesser himalayan series rocks to the north were emplaced over low grade equivalents of the high himalayan crystalline series preserved in the external part of the orogen this study establishes the value of isotope data for lithostratigraphic correlations within orogenic belts

geochemical evolution of peraluminous plutons in southern nova scotia canada a pegmatite poor suite three southern nova scotia plutons crystallized rapidly at 375 ma from magma containing both mantle and crustal components isotopic and chemical data suggest that the crustal contribution included both lower crustal material and cambro ordovician turbidites of the host meguma group despite local evidence of mixing and mingling of magmas the bulk of the plutons evolved by assimilation and fractional crystallisation evolved portions of the plutons have compositions appropriate for development of rare metal pegmatite fields but pegmatites are relatively rare and little differentiated like parental plutons pegmatites fall into biotite plagioclase and muscovite potassium feldspar assemblages the latter locally contain mn rich garnet biotite giving calculated p t conditions of pegmatite crystallisation of 620 c 0 44 gpa under water saturated conditions host rocks at the time of emplacement experienced p t conditions varying from 500 to 620 c at 0 44 gpa beryl bearing pegmatites occur only where host rocks were below sillimanite grade and pegmatites of any kind are scarce in sillimanite grade host rocks rarity of pegmatites can be ascribed to a combination of insufficient amounts of f li and b in the magma with rapid cooling which prevented extensive fractionation and undercooling our data suggest rather that peraluminous suites produced by rapid heating due to incursions of lithospheric mantle into supracrustal rocks and typified by biotite rich cordierite bearing plutons are not favorable locales for major rare metal enriched pegmatite fields such fields appear to require relatively prolonged anatexis resulting from crustal thickening or an areally extensive mafic underplate

major explosive activity in the monti sabatini volcanic district central italy over the 800 390 ka interval geochronological geochemical overview and tephrostratigraphic implications abstract a review of the existing chronological stratigraphic and chemo petrologic data of the major eruptive units from the early phase of activity 800 390 ka in the monti sabatini volcanic district msvd belonging to the ultra potassic magmatic region of central italy is presented along with new radioisotopic age determinations and geochemical analyses through the combined use of electron microprobe glass compositions selected trace element compositions and single crystal 40ar 39ar age determinations we provide a new chrono and chemo stratigraphic classification of the products emplaced in the 800 390 ka time interval besides giving insights on the petrologic evolution of the roman comagmatic region the large dataset provides fundamental information that is applicable to tephrostratigraphic studies in the wide region encompassing the tyrrhenian sea margin to the adriatic sea basin distal tephras from this volcanic activity also act as important geochronologic markers for the coastal sedimentary successions deposited in response to glacio eustatic fluctuations as well as for successions in the quaternary tectonic basins of the central and southern apennines an innovative approach based on the use of discrimination diagrams of zr y vs nb y ratios for fingerprinting altered volcanic rocks recently developed and successfully employed in archaeometric studies is here combined to the glass compositions for classifying the msvd deposits and tested on two distal tephra layers showing its potentiality for tephrostratigraphic correlation

geochemistry and petrogenesis of late miocene granitoids cyclades southern aegean nature of source components abstract neogene igneous activity in the aegean region comprised both extrusive volcanism and intrusive granitoid plutonism granitoid plutonism in the cyclades was established in the mid miocene period and lasted until late miocene 18 to 9 ma the timing of granitoid intrusion was associated with the initiation of extensional tectonics in the aegean these intrusions form a broad belt about 200 km long running from the west lavrium and serifos to the eastern aegean both s type and i type granitoids are present the former generally being emplaced earlier than the i types 15 to 8 3 ma major and trace element variations reveal that three end member components are involved in the granitoids but the proportions of these vary in the different plutons initial isotopic compositions of all the granitoids are typical of crust derived magmas from heterogeneous metasedimentary sources i type 87 sr 86 sr 0 7091 0 712 e nd 6 4 to 10 4 s type 0 710 0715 e nd 7 5 to 10 1 three end member sources have been identified 1 one end member appears to be a metasedimentary biotite gneiss greywacke type such as that forming the metamorphic core complexes naxos and paros this is a dominant but not the only component in the s types 2a major trace element and sr nd isotopic composition correlations of the s type granitoids with basement gneiss require an extra source of sr and ca having lower initial 87 sr 86 sr indicating a more depleted metasedimentary source at depth due to possible interaction of metamorphic fluids with marbles and amphibolites and infiltration through the gneissic units at mid crustal levels 2b a possible second end member could be the marble component as indicated by the buffered values of the initial sr isotopic ratios major element variation of the mafic microgranular quartz diorites and tonalites enclaves are compatible with dehydration melting of a mafic source similar to the amphibolites island arc tholeiites at medium pressure 8 kb conditions 3 amphibolite is another end member which may contribute mostly to the source of the younger intrusions along the western flank of the arc

quaternary fluvial volcanic stratigraphy and geochronology of the capitoline hill in rome in and around rome coastal and fluvial sediments influenced by quaternary sea level changes interfinger with accurately datable highly potassic pyroclastic volcanic units we describe the complex internal geology of the capitoline hill for centuries a place of leading importance in ancient rome and more recently a focus of archaeological research outcrops and many new drill cores reveal at least four cycles of valley cutting and filling probably recording the history of the tiber river in response to changes in sea level single crystal 40 ar 39 ar dates on sanidine give ages of 518 6 413 5 and 353 2 ka for three prominent volcanic units filling separate paleovalleys the roman region offers the potential for direct age calibration of the quaternary sea level record

telescoping of three distinct magmatic suites in an orogenic setting generation of hercynian igneous rocks of the albera massif eastern pyrenees abstract the petrogenesis of the hercynian magmatic rocks of the albera massif eastern pyrenees is investigated in this work in order to establish spatial and temporal relationships between deformation episodes high temperature low pressure metamorphism and igneous activity by using fieldwork together with petrological and geochemical methods hercynian magmatic rocks comprise i calc alkaline granitoids of la jonquera composed mainly by biotite and biotite hornblende granodiorites ii the leucogranitic pluton of el castellar iii small mafic complexes composed mainly by amphibole bearing gabbros and diorites and iv stocks of anatectic leucogranites hercynian deformation structures can be classified in two phases d1 and d2 both reflecting progressive deformation first compressional then transpressional closely linked to the development of regional metamorphism spatial relationships between igneous and metamorphic rocks suggest that the emplacement of magmatic bodies was a syn d2 event and was concomitant with the metamorphic climax of the country rocks the compositional and textural variation of the rocks of the mafic complexes is interpreted to reflect fractional crystallization of hydrous mafic magma with a composition similar to that of calc alkaline basalts documenting the involvement of basaltic magmas during the generation of hercynian crustal granitoids the anatectic leucogranites crystallized from peraluminous magmas produced by partial melting of metasediments and orthogneisses similar to those found in the local migmatite zone the similar sr and nd isotope signatures of the el castellar leucogranitic pluton some anatectic leucogranites and the orthogneissess supports the hypothesis that these leucogranites were generated by partial melting of the orthogneisses based on field petrographic geochemical and isotopic lines of evidence la jonquera granodiorite can be clearly distinguished from the gabbros and from the anatectic and el castellar leucogranites the high cao content of the granodiorites precludes an origin by partial melting of local metamorphic rocks and it is suggested that the calc alkaline granitoids la jonquera were produced by fractional crystallization of a granodioritic magma generated by partial melting of metatonalites in the lower crust although the magmatic rocks were emplaced contemporaneously at about 280 my based on rb sr whole rock data they reflect the occurrence of three genetically distinct igneous suites one granodioritic one leucogranitic and one mafic the metamorphic and igneous evolution documented in the albera massif bears strong similarities with those described in the neighbouring hercynian domains from the pyrenees the hercynian regional ht lp metamorphism and magmatism in the pyrenees are two processes linked to the same deep seated thermal anomaly that was generated in a transpressive context

the age and origin of younger granitic plutons of the shaw batholith in the archaean pilbara block western australia the whole rock pb pb method has been used to date four of the younger mainly adamellite late tectonic plutonic phases within the ca 3 5 ga shaw batholith of the archaean east pilbara block three suites give ages within error of 2966 ma porphyritic granites at 2948 50 ma leuco adamellites at 2943 46 ma and garden creek adamellite at 3007 48 ma the post tectonic cooglegong adamellite gives an age of 2847 34 ma the sm nd model isotopic systematics of all four suites indicate derivation from crust ranging between ca 3200 and 3600 ma in age the sources for these four younger plutonic phases were heterogeneous and although exhibiting some isotopic characteristics of the older 3 5 3 3 ga calc alkali plutonic suites were more depleted in the lil elements rb u and th in addition the garden creek adamellite and the cooglegong adamellite lack the very fractionated and hree depleted ree patterns characteristic of both the older calc alkali plutonic rocks and the porphyritic granites and leuco adamellites the crust underlying the shaw batholith at ca 2950 ma must have been both markedly heterogeneous and variably depleted a conclusion consistent with the complex tectonic and plutonic evolution of this region

rift to collision transition recorded by tectono thermal evolution of the northern pyrenees the impact of rift related processes on tectonic and thermal evolution of collisional orogens is poorly documented here we study the northern pyrenees a region that has preserved a geological record of the transition from rifting to collision using modeling of new low temperature thermochronological data including fission track and u th he on apatite and zircon we propose a temporal reconstruction of the inversion of the european rifted margin our data confirm that rifting and related cooling started in the late paleozoic triassic throughout the jurassic and early cretaceous the european margin recorded slow heating during postrift subdsidence modeling of thermochronological data allows distinguishing subsidence and denudation controlled by south dipping normal faults in granitic massifs that reflect a second episode of crustal thinning at 130 110 ma following onset of convergence at 83 ma shortening accumulated into the weak and hot albian cenomanian rift basins floored by both hyperextended continental crust and exhumed subcontinental mantle the lack of cooling during this initial stage of convergence is explained by the persistence of a high geothermal gradient the onset of exhumation related cooling is recognized in the whole pyrenean region at 50 35 ma this timing reveals that the main phase of mountain building started when hyperextended rift basins closed and collision between proximal domains of the rifted margin occurred

effects of an imposed quasi biennial oscillation in a comprehensive troposphere stratosphere mesosphere general circulation model a 48 yr integration was performed using the geophysical fluid dynamics laboratory skyhi troposphere stratosphere mesosphere gcm with an imposed zonal momentum forcing designed to produce a quasi biennial oscillation qbo in the tropical stratosphere in response to this forcing the model generates a qbo in the tropical circulation that includes some very realistic features notably the asymmetry between the strength of the descending easterly and westerly shear zones and the tendency for the initial westerly accelerations to appear quite narrowly confined to the equator the extratropical circulation in the northern hemisphere nh winter stratosphere is affected by the tropical qbo in a manner similar to that observed in particular the polar vortex is generally weaker in winters in which there are easterlies in the tropical middle stratosphere roughly twothirds of the largest midwinter polar warmings occur when the equatorial 30 mb winds are easterly again in rough agreement with observations despite this effect however the total interannual variance in the zonalmean extratropical circulation in the model apparently is slightly decreased by the inclusion of the tropical qbo the observed qbo dependence of the winter mean stratospheric extratropical stationary wave patterns is also quite well reproduced in the model the qbo was also found to have a profound influence on stratospheric stationary waves at low latitudes near and above 10 mb the nh stationary waves were found to penetrate across the equator during the westerly qbo phase but to be restricted to latitudes poleward of 108n during the easterly phase this means that the equatorial qbo in prevailing wind near and above 10 mb has a significant zonally asymmetric component if this is also true in the real atmosphere there are important implications for the adequacy of the current observational rawindsonde network near the equator analysis of the zonal mean zonal momentum budget in the tropical stratosphere reveals that the resolved waves in the model are strong enough to force the realized accelerations through much of the qbo cycle the exception appears to be the easterly acceleration phase below about 20 mb the implications of this for the generation of a self consistent qbo by gcms will be considered the effects of the imposed qbo on the troposphere were found to be very modest there does appear to be a statistically significant weakening by 1ms 21 of the high latitude winter vortex in the middle and upper troposphere given the very high predictability of the stratospheric qbo itself this effect could possibly be used to enhance the skill of seasonal weather forecasts no significant qbo influence was found in the model precipitation field

post caldera activity in the alban hills volcanic district italy 40ar 39ar geochronology and insights into magma evolution we present 24 40ar 39ar ages for the youngest volcanic products from the alban hills volcanic district rome combined with petrological data on these products we have attempted to define the chronology of the most recent phase of activity and to investigate the magma evolution of this volcanic district the early mainly explosive activity of the alban hills spanned the interval from 561 1 to 351 3 ka after approximately 50 kyr of dormancy a mainly effusive phase of activity took place accompanied by the strombolian activity of a small central edifice monte delle faete this second phase of activity spanned the interval 308 2 to 250 1 ka after another dormancy period of approximately 50 kyr a new hydromagmatic phase of activity started at 200 ka at several centers located to the southwest of the monte delle faete edifice after an initial recurrence period of approximately 50 kyr which also characterized this new phase of activity the longest dormancy period approximately 80 kyr in the history of the volcanic district preceded the start of the activity of the albano and giuturna centers at 70 1 ka results of our study suggest a quasi continuous magmatic activity feeding hydromagmatic centers with a new acme of volcanism since around 70 ka based on data presented in this paper we argue that the alban hills should not be considered an extinct volcanic district and a detailed re assessment of the volcanic hazard for the area of rome is in order

the villa senni eruption alban hills central italy the role of h2o and co2 on the magma chamber evolution and on the eruptive scenario abstract the villa senni eruption unit vseu belongs to the tuscolano artemisio phase of volcanic activity in the alban hills volcanic district the closest to rome of the recent or active volcanoes of central italy the most important products of this eruption are represented by pyroclastic flow deposits named lower and upper flow unit lfu and ufu respectively three main rock types form vseu as follows 1 juvenile k foiditic scoria clasts of the lfu 2 juvenile phonotephritic scoria clasts of the ufu and 3 holocrystalline phonotephritic lithic inclusions italites in the ufu on the basis of the chemistry mineralogy and petrography of the three studied rock types their phase relations have been discussed other petrologic constraints from laboratory melting experiments are presented and used to investigate the role of volatiles on the evolution of the magma chamber system some broad implications on withdrawal pattern are also presented it has been verified the lfu rock type can be obtained from a parental melt of ufu composition by a co2 controlled crystal liquid fractionation of a solid assemblage close in composition to that of italites because it can be proved that the storage of magma occurred at shallow depth within the mesozoic carbonate country rocks it is proposed that co2 diffusion originating from thermal decomposition of wall rock carbonates controlled the evolution trend of the melt at the periphery of the magma chamber whereas the inner part of the magma body retained the volatile component essentially h2o of the original melt the corresponding eruption model is therefore comprehensive of an early eruptive phase lfu rock type involving the more differentiated central magma bulb whereas the late eruptive phase ufu rock type tapped the more mafic peripheral magma the italite xenoliths are believed to represent the chilled margins of the magma chamber

detection of the secondary meridional circulation associated with the quasi biennial oscillation 1 the quasi biennial oscillation qbo signal in stratospheric zonal and meridional wind temperature and geopotential height fields is analyzed based on the use of the national centers for environmental prediction ncep reanalysis 1958 2001 the multitaper method singular value decomposition mtm svd a multivariate frequency domain analysis method is used to detect significant and spatially coherent narrowband oscillations the qbo is found as the most intense signal in the stratospheric zonal wind then the mtm svd method is used to determine the patterns induced by the qbo at every stratospheric level and data field the secondary meridional circulation associated with the qbo is identified in the obtained patterns this circulation can be characterized by negative positive temperature anomalies associated with adiabatic rising sinking motions over zones of easterly westerly wind shear and over the subtropics and midlatitudes while meridional convergence and divergence levels are found separated by a level of maximum zonal wind shear these vertical and meridional motions form quasi symmetric circulation cells over both hemispheres though less intense in the southern hemisphere

strontium and oxygen isotope decoupling in the hercynian trois seigneurs massif pyrenees evidence for fluid circulation in a brittle regime systematic shifts of oxygen isotopic compositions in the higher grade parts of the high temperature low pressure hercynian metamorphic sequence exposed in the trois seigneurs massif have previously been explained as a result of an influx of surface derived water during the prograde part of the metamorphic cycle it has been suggested that this caused a regional lowering of 87sr 86sr in the metamorphic sequence mapping of strontium isotopic compositions across a 15 m meta carbonate horizon in the higher grade pelite psammite sequence shows that strontium isotopic compositions were homogenised over length scales of metres or less during the hercynian metamorphism which brought the carbonate and pelite psammite to oxygen isotopic equilibrium with a common fluid comparison of model pre hercynian 87sr 86sr profiles across the carbonate based on a depositional diagenetic age of 450 ma and initial 87sr 86sr ratio of 0 7086 given by 10 m length scale averaging with the post hercynian 87sr 86sr profile calculated from analysed 87sr 86sr and rb sr compositions implies strontium isotopic diffusion distances of ca 0 4 m in the carbonate and ca 7 m in the pelite psammite the limited sr isotopic diffusion distance of 0 4 0 7 m within the carbonate is compatible with pervasive oxygen isotopic exchange over distances restricted to 4 15 m if fluid strontium concentrations were between 4 and 50 ppm the strontium isotopic transport distances are not compatible with pervasive oxygen isotopic alteration over the observed 5 km regional scale either the flow was perfectly layer parallel or more probably the regional scale alteration of oxygen took place by fluid circulation in the brittle regime early in or prior to the hercynian metamorphic event flow along cracks with incomplete diffusive exchange between fluid and wall rock would allow greater decoupling of oxygen and strontium isotopic transport than pervasive advective transport with local fluid solid equilibrium

nature and evolution of the eastern margin of lapetus geochemical and isotopic constraints from siluro devonian granitoid plutons in the new brunswick appalachians in the gander zone ordovician to devonian metaluminous to slightly peraluminous plutons with within plate affinities intrude a lower paleozoic metasedimentary package during the siluro devonian end t and 18o values of the metasedimentary rocks would have been about 7 to 8 and 10 to 14 respectively granitoid end t values range from 0 3 to 4 2 18o values lie between 6 6 and 10 4 and published pb isotopic compositions are radiogenic 207pb 204pb 15 65 end t values of associated silurian gabbros are somewhat positive 1 2 to 2 3 some plutons exhibit evidence for comingling with this mafic component potential source materials include enriched mantle supracrustal and infracrustal sources although some constraints can be put on the first two sources the nature of infracrustal material is difficult to evaluate heterogeneous data obtained from silurian plutons can be explained by crust mantle mixing if some plutons contain a significant mantle component then mesoproterozoic o

the alban hills and monti sabatini volcanic products used in ancient roman masonry italy an integrated stratigraphic archaeological environmental and geochemical approach abstract the rocks of alban hills and monti sabatini volcanoes central italy and their associated epiclastic deposits have been extensively used as building material in ancient rome from about viiith century bce to ivth century ce however the identification of the source areas of these rocks is difficult due to the lack of an integrated stratigraphic and geochemical analysis of the relationships between the two volcanic districts and to the alteration affecting the primary products as consequence of weathering and pedogenetic processes here a comprehensive upgraded stratigraphic and geochronological review of the two volcanic districts corroborated by new geochronological data for several eruptive units and altered deposits is presented coupled to a complete geochemical background achieved by means of newly determined major and trace element analyses for all the main eruptive units a study of the alteration processes of the primary products is also presented and the age of the main weathering and pedogenetic phases associated to quaternary climatic changes are also investigated the results are integrated with those from literature in order to construct discriminant diagrams based on selected trace elements and allow us to characterize the primary and altered volcanic deposits in the rome area distinguish products of different volcanic districts discuss the effects of different weathering processes on the mobility of some elements and provide a reference frame for the provenance of the volcanic materials employed in ancient roman masonry the interdisciplinary data set and results presented here provide groundwork for volcanological climate pedological and archaeological provenance studies

contrasting responses of rb sr systematics to regional and contact metamorphism laramie mountains wyoming usa archean supracrustal sequences of pelitic quartzitic calcareous and mafic compositions in the central laramie mountains wyoming have been affected by two metamorphic events a 1 78 ga amphibolite grade regional metamorphism and a 1 43 ga contact metamorphism resulting from the intrusion of the laramie anorthosite complex lac rb sr whole rock isotopic data from both outside and within the lac contact aureole define a linear array that lies along a 1 78 ga isochron this date has been independently established as the time of amphibolite facies regional metamorphism associated with collision of the archean wyoming province and the proterozoic colorado province along the cheyenne belt the rb sr isotopic data require that sr was redistributed during regional metamorphism on a scale of at least tens of metres although within the 2 km wide aureole of lac the pelitic rocks were thermally metamorphosed at temperatures greater than 800 c none of the whole rock rb sr data from samples within the lac aureole show evidence of resetting at 1 43 ga it is interpreted that the regional metamorphism involved fluid transport which facilitated sr isotopic resetting whereas the contact metamorphism occurred in a relatively dry environment in which isotopic mobility was restricted to centimetre scale or less rb sr data for biotite feldspar and whole rock from a regional metamorphosed pelitic schist give an isochron age of 1450 40 ma which is interpreted as a cooling age resulting from crustal uplift rb sr data for biotite quartz feldspar and whole rock from a pelitic schist affected by contact metamorphism give an isochron age of 1420 43 ma the time of isotopic re equilibration in response either to crustal uplift or to both contact metamorphism and crustal uplift this study demonstrates that although the response of isotopic systems to metamorphism is complex isotopic data provide insight into metamorphic processes that is difficult to obtain by other means

a strontium neodymium and oxygen isotope study of hydrothermal metamorphism and crustal anatexis in the trois seigneurs massif pyrenees france nd sr and o isotope analyses have been made on metamorphic and igneous rocks and minerals from a 310 340 ma hercynian age metamorphic terrane in the pyrenees france lower paleozoic shales and phyllites have 87sr 86sr values of 0 707 0 717 at 310 ma but model values at 310 ma of 0 709 0 736 based on assumed depositional age of 450 ma and an initial 87sr 86sr 0 707 on a regional scale 87sr 86sr was homogenized to about 0 713 to 0 717 in the higher grade pelitic schists during metamorphism much of this 87sr 86sr exchange occurred at very low grades below the biotite isograd but significant changes also accompanied the 18o lowering of the phyllites 13 to 16 during their transformation to andalusite and sillimanite grade schists 18o 11 to 12 all of these effects are attributed to pervasive interactions with hydrothermal fluids wickham and taylor 1985 the data also show that a syn metamorphic plutonic complex dominated by a biotite granite body was derived by mixing of a relatively mafic magmatic end member 87sr 86sr 0 7025 0 7050 and 18o 7 5 to 8 0 with two metasedimentary sources both having 87sr 86sr 0 715 and 18o 10 0 to 12 0 but with one being more homogeneous than the other the more homogeneous component and the mantle derived magmatic end member dominate at low structural levels within the complex the less homogeneous end member that dominates at high levels is clearly derived from the local paleozoic pelitic schists a rb sr age of 330 20 ma was obtained on hornblende from a deep level within the complex which fixes this age for the regional metamorphism as well although a post metamorphic granodiorite magma body at trois seigneurs also displays heterogeneities in 18o and 87sr 86sr and thus does not give a clear cut rb sr isochron the data are consistent with an emplacement age between 260 and 310 ma similar to ages of other late granodiorites in the pyrenees 143nd 144nd is very uniform within the hercynian crust both at trois seigneurs nd 3 to 7 and elsewhere in the pyrenees almost all igneous lithologies have depleted mantle mid proterozoic model ages consistent with efficient recycling of crustal material following original crustal accretion in this area at about 1600 ma or earlier rb sr mineral ages exhibit a complex cooling history reflecting late hercynian and mesozoic thermal events our results show that profound homogenization of the 87sr 86sr and 18o 16o ratios of large volumes of the crust can occur during regional metamorphism and crustal anatexis particularly in regions undergoing extensional tectonics such processes can significantly modify the isotopic compositions of the protoliths of granitic magmas this may explain why many peraluminous hercynian granitoids of western europe have anomalously low 87sr 86sr initial values compared to their probable sedimentary parent rocks

genesis of a variscan batholith field petrological and mineralogical evidence from the corsica sardinia batholith abstract the genesis of the corsica sardinia batholith csb can be explained in a continental collision setting during the time of construction of the batholith which is dated at about 70 ma three magmatic associations were emplaced mg k calc alkaline u1 composite mafic silicic calc alkaline u2 and post collisional alkaline u3 in addition the level of intrusion became progressively shallower from 5 6 kbar for u1 to less than ikbar for u3 in a large scale uplift associations u1 and u2 exhibit non cogenetic mafic and felsic components the processes and products of interaction between mantle and crustal derived melts are however different and may be related to the thickness of the crust which controls both the parameters t pco2 ph2o andptot and the time of mingling of the products of anatexis and basaltic melts both u1 and u2 granitoids were formed by crystallization of a magma derived by fusion of a source of greywacke composition the melting occurred successively under granulitic u1 and amphibolite facies conditions u2 in association u1 basaltic melts displaying potassic lamprophyre like composition up to 8 k2o are of uncertain affinity furthermore crustal interaction with the basic magma precludes precise definition of the source in the u2 composite association the primary tholeiitic character of the mantle derived basic rocks is constrained by both mineralogical and geochemical data dry and hydrated subunits are distinguished among the basic rocks associated with the granitoids no hybridization processes have been identified in the core of the mafic complexes of the dry subunits but they are recognized at the level of emplacement at the margins at the contact with the granitoids contamination in the mafic hydrated subunit is due to the increase in water content of crustal origin in the magma during the ascent and emplacement of the basic complexes leading to the development of abundant green amphibole extensive hybridization is restricted to the base of the crust where it led to incomplete mixing yielding granodiorites and enclaves the genesis and emplacement of the composite calc alkaline u2 association took place in an extensional setting in an uplifting basement postdating a collisional event during the devonian an eastern austro alpine block was thrust onto the western ebro balearic continent the u1 mg k granitoids resulted from anatexis under conditions of pco2 ph2o this took place at the base of the austro alpine crust which was undergoing fusion due to its adiabatic ascent the u2 calc alkaline granitoid rocks were derived in a hydrated environment by fusion of the same austro alpine crust in corsica and of the ebro balearic crust on sardinia and in the pyrenees the conditions of interaction between mafic and felsic magmas may serve as a geodynamic marker providing information on the thickness of the crust in time and space and on the genesis of continental crust the persistence during the palaeozoic of dominantly tholeiitic mafic magmatism suggests that hot spot activity occurred in this area of southwestern europe during pre variscan and variscan times up to the time of opening of the liguro piedmontese ocean birthplace of the alpine orogen

isotopic evidence for closed system anatexis at midcrustal levels an example from the acadian appalachians of new england we have investigated the sr and o isotope systematics of granitoid and metasedimentary samples from the central maine terrane cmt of new england granitoid samples were taken from interior and contact zones within the acadian aged 410 m y synmetamorphic and syntectonic kinsman quartz monzonite kqm which is a member of the new hampshire plutonic series metasedimentary samples were taken from silurian and devonian formations hosting the kqm initial sr isotope ratios sri and 18o values for the kqm range from 0 70799 to 0 71246 and 1 6 to 12 9 respectively and sri and 18o values of the metasedimentary rocks range from 0 70770 to 0 75008 and 6 2 to 14 1 respectively we observe a linear and slightly positive correlation between sri and 18o for interior kqm samples that can be duplicated by a mixing curve calculated for metasedimentary endmembers whereas the sri and 18o values of contact kqm samples cluster near the sri and 18o values of the metasedimentary rocks with which they are in contact mixing calculations provide no evidence for a measurable primitive mantle component in either interior or contact kqm samples and we conclude that the sr o isotopic composition of the kqm is most likely a reflection of isotopic heterogeneities inherited from a complex package of midcrustal metasedimentary source rocks we propose that the kqm is the product of midcrustal partial melting that was initiated due to excess thermal energy from the decay of anomalously high concentrations of heat producing elements in silurian source rocks within the cmt because we see no isotopic evidence for a lower crustal or mantle component in the kqm we suggest that midcrustal anatexis may have occurred as a closed system process requiring no accompanying mantle derived magma or above normal mantle heat flow

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

sr nd isotopic constraints on the petrogenesis of the central bohemian pluton czech republic the sr nd isotopic data for selected granitoids of the central bohemian pluton show a broad negative correlation with the total range of 87sr 86sr 330 0 7051 0 7129 and nd330 0 2 to 8 9 the older intrusions have more depleted sr nd compositions and calc alkaline geochemistry sazava suite whereas the younger intrusions shift towards k rich calc alkaline blatna suite and shoshonitic rocks icany and certovo b emeno suites with more evolved isotopic signatures the distribution of the data is interpreted as reflecting a diversity of sources and processes rather than a single progressive crustal contamination trend the sazava suite could have originated by partial melting of metabasites or of a mantle source with an isotopic composition close to bulk earth or by hybridization of crustally derived tonalitic and mantle derived magmas variation within the blatna suite is modelled by mixing between a moderately enriched 87sr 86sr 330 0 708 nd330 3 mantle component with either an isotopically evolved metasedimentary component or with more evolved magmas of the suite the icany suite was most probably produced by partial melting of peraluminous lithologies possibly of the adjacent moldanubian unit the certovo b emeno suite evolved from strongly enriched mantle derived magmas 87sr 86sr 330 0 7128 end330 7 either through closed system fractional crystallization or interaction with magma corresponding to leucogranites of the central bohemian pluton

the volcanic aggregate of ancient roman mortars from the capitoline hill petrographic criteria for identification of rome s pozzolans and historical implications abstract we present a petrographic study of the pyroclastic flow deposits used to produce mortar aggregates pozzolane rosse pozzolane nere and pozzolanelle as well as dimension stones tufo del palatino and tufo lionato in ancient roman times in which we describe the characteristic textures and mineralogic assemblages of their juvenile fraction this petrographic dataset is employed to compare and classify through observation in thin section at the optical microscope and complementary trace element analyses as well as emp analyses on matrix glass on archaeological and bulk natural samples the composition of the volcanic aggregate of 11 samples of ancient roman mortars collected from several archaeological structures excavated on the capitoline hill by means of the combined petrographic and geochemical identification criteria illustrated in this work we recognize two main types of mortar aggregates characteristic of the republican and imperial ages respectively and a third type pertaining to the mediaeval epoch

sr z sbnd nd isotopic record of multi stage interactions between mantle derived magmas and crustal components in a collision context the ultramafic granitoid association from vivero hercynian belt nw spain late stage epizonal calc alkaline granitoids of the hercynian belt are often associated with coeval more basic rocks such granitoids have been the focus of special attention when studying the role of mantle derived magmas in granitoid genesis these studies conclude that basic magmas are involved in granitoid production but their contribution to the chemical composition of granitoids is often controversial the vivero massif nw spain includes calc alkaline granitoids and coeval ultramafic and mafic rocks but these granitoids are syntectonic and intruded into middle crustal levels during an early stage scattered major and trace element chemistry together with heterogeneous sr nd isotopic results preclude an origin of this ultramafic to granitoid association by any closed system fractionation process ultramafic rocks include peridotites pyroxenites and homblendites with endi from 3 5 to 1 3 and 87sr86sr i ratio from 0 7059 to 0 7080 they are interpreted as cumulates formed by in situ fractional crystallization from contaminated basaltic magmas particularly by interaction with 87sr enriched fluids mafic rocks comprise biotite amphibole diorites quartz diorites and tonalites with ndi from 3 8 to 0 0 and 87sr86sr i ratio from 0 7058 to 0 7073 they represent either cumulates or more evolved magmas of calc alkaline affinity these rocks display an inverse correlation between the degree of differentiation and the degree of contamination inferred from isotope data this points to wall rock assimilation by thermal erosion during ascent of basic magmas up to the middle crust and supports the participation of mantle sources with positive end and 87sr86sr i 0 7058 granitoids range from amphibole biotite tonalites through biotite granodiorites to monzonitic granites they show an isotopic trend which diverges from that of ultramafic and mafic rocks endi 6 0 to 1 9 decreases while 87sr86sr i ratio 0 7061 to 0 7082 increases from tonalites to monzonitic granites reflecting an increasing contribution of crustal components in more differentiated rocks assimilation and fractional crystallization mixing included account for such an evolution contamination of basic magmas by this process occurring at deeper crustal level produced hybrid tonalites and related mafic magmatic enclaves only monzonitic granites are interpreted as pure crustal melts their hree fractionated patterns gd yb 4 5 suggest equilibrium with a garnet rich residuum partial melting of moderate time integrated rb sr protolith such as greywackes and or meta igneous rocks of intermediate acid composition could account for the isotopic composition of these monozogranites this example shows that at least some calc alkaline granitoids of collisional setting are not produced by pure intra crustal melting they are formed through a complex multi stage hybridization process involving mantle derived magmas crustal components and several concomitant magmatic processes

variscan dextral transpression in the french pyrenees new data from the pic des trois seigneurs granodiorite and its country rocks abstract new structural data from both the trois seigneurs granodiorite and its country rock lead to new conclusions about the variscan tectonic history of this part of the pyrenees sedimentary rocks of the massif that increase in metamorphic grade from north to south are imprinted by a single major deformation responsible for both the tight upright e w trending folds with vertical to steeply n dipping foliations and the gently w plunging stretching lineations syntectonic emplacement of the pic des trois seigneurs granodiorite is demonstrated by the parallelism between structures of the pluton as determined by magnetic fabric measurements and the foliations and lineations imprinted in the country rocks large deformation of the granodiorite magma during emplacement is indicated by strong anisotropy and ubiquitous magmatic microstructures the high thermal gradients of regional metamorphism which is also syntectonic are attributed to a large thermal aureole provided by deep seated magma reservoirs shear sense criteria in xz thin sections of the metasedimentary country rocks indicate a dextral sense of the non coaxial component of strain throughout the massif and regardless of metamorphic grade the overall structure of the massif is concluded to have derived from a major shearing event that is equated with the d 2 main phase observed in the entire variscan pyrenees as the e w oriented stretch and dextral shear cannot be separated from compressive structures generally considered to be characteristic of d 2 this phase is concluded as representing regional transpression

sr nd isotope and trace element geochemistry of late variscan volcanism in the pyrenees magmatism in post orogenic extension abstract we obtained sr nd isotope and trace element data on late variscan volcanic rocks in the pyrenees felsic lavas and andesites from the ossau and the serra de cadi massifs and calc alkaline andesites and alkali basalts from the la rhune and the anayet volcanic massifs the calc alkaline volcanic rocks have crustal trace element and sr nd isotopic characteristics the andesites probably originated from melting of pan african paragneisses with a limited contribution of mantle derived sources having lithospheric characteristics the andesitic lavas were more or less contaminated in magma chambers by palaeozoic sedimentary rocks which can be interpreted as a recycled proterozoic crust the felsic lavas are principally derived from anatexis of the palaeozoic products the rhyolites providing even peraluminous characteristics the anayet andesites show mantle derived characteristics and are interpreted as a mixture between a strongly undersaturated continental alkali basalt and a peraluminous end member however sr and nd contents rale out any simple process the late anayet alkali basalts show typical asthenospheric sr and nd isotopic characteristics the la rhune basalts exhibit sr and nd sub continental lithospheric isotopic characteristics very similar to those of the triassic pyrenean continental basalts it is thought that the granulite facies metamorphism dated at 310 ma was caused by the ascent of the asthenosphere inducing a thermal anomaly the mafic magmas ascending from the mantle are responsible for the crustal anatexis this results in the emplacement of both the pyrenean composite plutons such as the querigut massif and the ossau volcanic rocks the pyrenean late variscan volcanic rocks were emplaced in either pull apart basins opened by the reactivation of the major variscan pyrenean fault in a distensive setting or better in basins resulting from a post orogenic collapse both these models involve a thinning of the subcontinental lithosphere until its disappearance consequently the inferred mantle derived end member of the anayet lavas which occurs in a post variscan distensive setting clearly derives from the asthenosphere

trace element and isotopic sr nd pb o arguments for a mid crustal origin of pan african garnet bearing s type granites from the damara orogen namibia geochronological data major and trace element abundances nd and sr isotope ratios 18o whole rock values and pb isotope ratios from leached feldspars are presented for garnet bearing granites locality at oetmoed and outcrop 10 km north of omaruru from the damara belt namibia for the granites from outcrop 10 km n omaruru reversely discordant u pb monazite data give 207pb 235u ages of 511 2 ma and 517 2 ma similar to previously published estimates for the time of regional high grade metamorphism in the central zone based on textural and compositional variations garnets from these granites are inferred to be refractory residues from partial melting in the deep crust because p t estimates from these xenocrystic garnets are significantly higher 800 c 9 10 kbar than regional estimates 700 c 5 kbar the monazite ages are interpreted to date the peak of regional metamorphism in the source of the granites sm nd garnet whole rock ages are between 500 and 490 ma indicating the age of extraction of the granites from their deep crustal sources for the granites from oetmoed both sm nd and pb pb ages obtained on igneous garnets range from 500 to 490 ma these ages are interpreted as emplacement ages and are significantly younger than the previously proposed age of 520 ma for these granites based on rb sr whole rock age determinations major and trace element compositions indicate that the granites are moderately to strongly peraluminous s type granites high initial 87sr 86sr ratios 0 716 high 18o values of 13 8 negative initial end values between 4 and 7 and evolved pb isotope ratios indicate formation of the granites by anatexis of mid crustal rocks similar to the exposed metapelites into which they intruded the large range of pb isotope ratios and the lack of correlation between pb isotope ratios and nd and sr isotope ratios indicate heterogeneity of the involved crustal rocks evidence for the involvement of isotopically highly evolved lower crust is scarce and the influence of a depleted mantle component is unlikely the crustal heating events that produced these granites might have been caused by crustal thickening and thrusting of crustal sheets enriched in heat producing elements very limited fluxing of volatiles from underthrust low to medium grade metasedimentary rocks may have also been a factor in promoting partial melting furthermore delamination of the lithospheric mantle and uprise of hot mantle could have caused localized high t regions the presence of coeval a type granites at oetmoed that have been derived at least in part from a mantle source supports this model

strontium and oxygen isotopic variations in mesozoic and tertiary plutons of central idaho regional variations in initial 87sr 86sr ratios r i of mesozoic plutons in central idaho locate the edge of precambrian continental crust at the boundary between the late paleozoic mesozoic accreted terranes and precambrian sialic crust in western idaho the r i values increase abruptly but continuously from less than 0 704 in the accreted terranes to greater than 0 708 across a narrow 5 to 15 km zone characterized by elongate lens shaped highly deformed plutons and schistose metasedimentary and metavolcanic units the chemical and petrologic character of the plutons changes concomitantly from ocean arc type diorite tonalite trondhjemite units to a weakly peraluminous calcic to calcalkalic tonalite granodiorite granite suite the idaho batholith plutons in both suites yield late cretaceous ages but permian through early cretaceous bodies are confined to the accreted terranes and early tertiary intrusions are restricted to areas underlain by precambrian crust the two major terranes were juxtaposed between 75 and 130 m y ago probably between 80 and 95 m y oxygen and strontium isotopic ratios and rb and sr concentrations of the plutonic rocks document a significant upper crustal contribution to the magmas that intrude precambrian crust magmas intruding the arc terranes were derived from the upper mantle subducted oceanic lithosphere and may have been modified by anatexis of earlier island arc volcanic and sedimentary units plutons near the edge of precambrian sialic crust represent simple mixtures of the precambrian wall rocks with melts derived from the upper mantle or subducted oceanic lithosphere with r i of 0 7035 rb sr varies linearly with r i producing pseudoisochrons with apparent ages close to the age of the wall rocks measured 18o values of the wall rocks are less than those required for the assimilated end member by sr o covariation in the plutons however indicating that wall rock 18o was reduced significantly by exchange with circulating fluids metasedimentary rocks of the belt supergroup are similarly affected near the batholith documenting a systematic depletion in 18o as much as 50 km from the margin of the batholith plutons of the bitterroot lobe of the idaho batholith are remote from the accreted terranes and represent mixtures of precambrian wall rocks with melts dominated by continental lower crust r i 0 708 rather than mantle pseudoisochrons resulting from these data are actually mixing lines that yield apparent ages less than the true age of the wall rocks and meaningless ri assimilation fractional crystallization models permit only insignificant amounts of crystal fractionation during anatexis and mixing for the majority of plutons of the region

isotopic sr nd and major element fingerprinting of distal tephras an application to the middle late pleistocene markers from the colli albani volcano central italy abstract we describe the diagnostic lithological and chemical features of distal tephras from major middle late pleistocene 560 36 ka explosive eruptions of the colli albani volcanic district central italy in particular we explore the time dependent variability of the sr and nd isotope compositions as a tool for recognising and pinpointing individual colli albani tephra in distal settings the distal tephras investigated are in lacustrine and fluvial sediments of central apennine intermountain basins located 70 km 100 km east of colli albani the recognition of the colli albani tephras is essentially based on the k foiditic composition of their glass which within the italian volcanological framework is a distinctive character of the colli albani pyroclasts in detail these tephras are attributed to the following eruptive units tufo pisolitico di trigoria 561 2 ka tufo del palatino tufo di bagni albule 530 2 527 2 ka tufo di bagni albule pozzolane rosse air fall sequence 517 1 to 500 3 ka pozzolane rosse 457 4 ka villa senni 365 4 ka and albano 5 7 41 7 to 36 1 ka these correlations are supported by 40 ar 39 ar dating of the distal tephras correlated to the pozzolane rosse 457 4 1 7 ka villa senni 365 2 ka and albano 5 7 41 9 ka and by 87 sr 86 sr measured on clinopyroxene crystals and fresh glassy scoria from distal colli albani tephras that range from 0 711 to 0 709 these ratios are similar to those that characterise the individual proximal correlative units and show the same decreasing trend over time in contrast the 143 nd 144 nd ratios for proximal and distal bulk samples and clinopyroxene increase from 0 51212 to 0 51215 from the oldest to the youngest tephra deposit in summary the study of sr and nd isotope compositions that is here applied on products from the colli albani volcanic district is a powerful complementary tool to the more traditional tephrostratigraphic methods e g componentry and electron microprobe analysis for fingerprinting of distal tephras over a large region of the central mediterranean and over a large time interval such as from 560 ka to 36 ka

regional scale cretaceous albitization in the pyrenees evidence from in situ u th pb dating of monazite titanite and zircon abstract albitization is a common metasomatic process active in various geodynamic contexts in the northern pyrenees there are several occurrences of albitites but until now only one occurrence has been dated 117 ma ar ar dating this paper presents new u th pb ages for several albitite occurrences throughout the pyrenees to test whether they are contemporaneous and if so to specify the regional extent of the albitization event ages obtained from large euhedral titanite and monazite grains from distinct albitites are 110 8 and 98 2 ma respectively the zircon u th pb isotopic system did not record this cretaceous metasomatic event even when grains were selected in metasomatically zr enriched rocks or in hydrothermal structures millimetre sized veins cross cutting granitoids we argue that the total time span of 20 ma recorded by albitites corresponds to a long lived hydrothermal system that was active during the rotation of iberia around europe along the north pyrenean fault because albitization and talc mineralization have the same spatial and temporal distribution in the pyrenees we argue that these two metasomatic phenomena are two independent records of this single regional scale long lived hydrothermal system

generation and emplacement of shear related highly mobile crustal melts the synkinematic leucogranites from the variscan tormes dome western spain the tormes dome consists of s type granites that intruded into ordovician augen gneisses and neoproterozoic lower cambrian metapelites metagreywackes at different extents of migmatization s type granites are mainly equigranular two mica granites occurring as 1 enclave laden subvertical feeder dykes 2 small external sill like bodies with size and shape relations indicative for self similar pluton growth and 3 as large pluton bodies emplaced at higher levels than the external ones these magmas were highly mobile as it is inferred from the high contents of fluxing components the disintegration and alignment of pelitic xenoliths in feeder dykes and at the bottom of some sill like bodies field relations relate this 311 ma magmatism u pb monazite to the regional shearing of the d3 variscan event partial melting modeling and the relatively high estimated liquidus temperatures indicate biotite dehydration partial melting 800 840 c and 400 650 mpa rather than water fluxed melting implying that there was no partial melting triggered by externally derived fluids in the shear zones instead the subvertical shear zones favored extraction of melts that formed during the regional migmatization event around 320 ma nd isotope variation among the granites might reflect disequilibrium partial melting or different protoliths mass balance and trace element partial melting modeling strongly suggest two kinds of fertile crustal protoliths augen gneisses and metapelites slight compositional variation among the leucogranites does not reflect different extent of protolith melting but is related to a small amount of fractional crystallization 13 for the equigranular granites which is generally more pronounced in shallower batholitic leucogranites than in the small and homogeneous sill like bodies the lower extent of fractional crystallization and the higher pressure emplacement conditions of the sill like bodies support a more restricted movement through the crust than for batholitic leucogranites

permian granites in the pyrenees the aya pluton basque country we show that the permian volcanism in the pyrenees was accompanied with emplacement of granite plutons with transitional chemistry reassessment of age structure and petrological characteristics of the aya pluton intrusive in the cinco villas massif basque country indicates that it was emplaced at 267 1 1 1 ma in a dextral transtensive context and that it marks a transition between the high k calcalkaline and the alkaline emissions of the first and second permian volcanic cycles respectively this age is close to that of c 267 ma reported for lamprophyres dykes of the pyrenean axial zone these data characterize a period of transition between the variscan orogeny and the subsequent alpine cycle in the pyrenees with an earlier extensive regime that became widespread in the pyrenees during the mesozoic times

characteristics and mode of emplacement of gneiss domes and plutonic domes in central eastern pyrenees abstract gneiss domes and plutonic granitoid domes make up almost 50 of the pre hercynian terrains in the central and eastern pyrenees from a structural study of the shape and internal structure of the domes and of their relationships with the enclosing rocks it can be shown that both types of domes were emplaced diapirically during the major regional deformation phase and the peak of regional metamorphism the study also shows that the internal structure the overall shape and general behaviour relative to the host rocks are similar for plutonic domes and for gneiss domes this appears to be in good agreement with h ramberg s 1967 gravity deformation and the earth s crust academic press london 1970 model studies in relation to intrusion of plutonic bodies in mechanisms of igneous intrusion edited by newall g rast n geol j spec issue 2 261 286 model studies showing that dome or mushroom like structures similar to those observed develop when there is a small viscosity ratio between the rising body and its enclosing medium this implies a high crystal content for the granitoid magma this crystal content has been estimated by i calculating the viscosity and density in natural conditions from petrological data for the magma considered as a suspension using the model and program of j p carron et al 1978 bull soc geol fr 20 739 744 ii using the recent results of experimental deformation of partially melted granites of i van der molen m s paterson 1979 contr miner petrol 70 299 318 and ii comparing the preceding results with the data obtained by deformation experiments on rocks similar to those enclosing the domes the minimum crystal content for the development of a dome like structure has been thus estimated to about 70 i e a value very close to that estimated by van der molen paterson 1979 to be the critical value separating the granular framework flow from suspension like behaviour the effect of small variations in the viscosity of the rising body are then simulated by centrifuge experiments these small variations appear to exert a strong control on the shape and rate of rise of the domes they are thought to be sufficient to account for the variations in shape and structure and the level of emplacement of the different types of gneissic and plutonic domes finally more complex experiments with models built in order to simulate as closely as possible the natural structural evolution of the region as deduced from petrological and structural data are reported their implications for the regional interpretation of the relationships between gneissic and plutonic domes is then discussed

continental crust formation seen through the sr and nd isotope systematics of s type granites in the hercynian belt of western france the isotopic compositions of sr nd and pb in leucogranites which are intercorrelated bernard griffiths et al 1985 1 may be explained by the mixing of ancient basement 1800 ma with juvenile crust late precambrian or early palaeozoic this hypothesis does not involve the existence of mid proterozoic crust as apparently indicated by thetdm model ages of the leucogranites ranging between 1600 and 1100 ma the nd isotopes reveal the crustal reworking while sr isotopes mainly record juvenile crust formation this paradox is explained by the geochemical heterogeneity of the sources involved

rb sr and u pb isotope studies on migmatites from the schwarzwald germany constraints on isotopic resetting during variscan high temperature metamorphism mineral and isotope studies were undertaken on migmatites from the schwarzwald moldanubian zone of the variscan belt the aims of the study were to date the migmatite formation and to determine the processes involved in migmatization in order to evaluate their influence on isotopic resetting textural evidence and the comparison of mineral compositions from leucosomes and mesosomes of two centimetre scale migmatite profiles respectively suggest that migmatitic textures and mineral assemblages were formed by metamorphic segregation deformation enhanced mass transport rather than by partial melting anatexis the results of rb sr thin slab dating on these profiles indicate that sr isotopes were not completely reset during migmatization no true isochron ages but ages of approximate isotopic homogenization were obtained on the thin slabs by calculating 87sr 86sr ratios back to various stages in their evolution the coincidence of these rb sr data with u pb ages of monazites from migmatites and non migmatitic gneisses shows that gneisses and migmatites were formed during the same high temperature event in the carboniferous 330 335 ma the observation that high temperature metamorphism failed to equilibrate sr isotopes on the centimetre scale imposes limitations on the use of conventional whole rock isochron techniques in dating migmatites

petrogenesis of the gross spitzkoppe topaz granite central western namibia a geochemical and nd sr pb isotope study abstract the early cretaceous gross spitzkoppe granite is one of several igneous complexes that formed in the damaraland of namibia during an episode of continental rifting and magmatism associated with opening of the south atlantic this is a classic setting of rift related anorogenic magmatism showing the typical association of mantle derived mafic and alkaline rocks along with silicic units the gross spitzkoppe granite is an important example of the latter because its peraluminous composition and crustal isotopic signature makes it well suited to characterize the crustal contribution to magmatism the gross spitzkoppe stock gss is composed of three texturally distinct topaz bearing biotite monzogranites average 76 wt sio 2 30 wt rb sr and 0 5 wt f iron rich biotite is the only mafic silicate in proximity to the stock are numerous felsic dikes rhyodacites to rhyolites the elevated high field strength elements hfse contents and high ga al ratios of the granites and felsic dikes are typical of a type granites the granites and dikes show similar geochemical differentiation trends and the compositions of the more evolved dikes overlaps with the granites this and similar initial isotope ratios suggest that the dikes and granites have a common origin major and trace element modeling confirms that the composition of the gross spitzkoppe granite can be produced by fractional crystallization from magma with the average felsic dike composition rb sr isotope data for nine whole rock samples of the gss yield an age for emplacement of the complex at 125 1 ma initial 87 sr 86 sr ratios vary from 0 710 to 0 716 neodymium isotope compositions of the granites and dikes yield initial e nd 125 values from 5 6 to 6 4 the pb isotopic ratios k feldspar or age corrected whole rock fall in the range 206 pb 204 pb 18 70 18 82 207 pb 204 pb 15 66 15 71 and 208 pb 204 pb 38 57 39 07 these geochemical and isotopic characteristics are consistent with derivation of the gross spitzkoppe granitic magma from a granulite facies metasedimentary source batch melting calculations suggest that low 10 20 degree partial melting of a felsic granulitic source is capable of producing melt compositions similar to those of the felsic dikes with further fractional crystallization being required to produce the granites the source rocks are thought to be damara belt metasediments that were melt depleted in the early paleozoic by extraction of the s type damara granites the most likely scenario for crustal melting is by basaltic underplating of the source region in the lower crust the range in initial nd and sr values is attributed to minor mixing of basaltic magma with the crustal melts although sr was also affected by minor contamination from the radiogenic damara granites near the level of emplacement

interaction of the quasi biennial oscillation and stratopause semiannual oscillation analysis of rawinsonde and rocketsonde data at ascension island 7 6 s 14 4 w and kwajalein 8 7 n 167 e in 1962 1991 suggests that the quasi biennial oscillation qbo in the middle stratosphere is synchronized with the seasonal cycle and that descending westerly phases of the stratopause semiannual oscillation sao are strongly influenced by the underlying qbo the effect of the seasonal cycle on the qbo in the middle stratosphere is revealed in two perhaps unrelated observations first a tendency for deseasonalized qbo westerly maxima to occur in local winter or to avoid local summer second a smooth uninterrupted connection between descending sao westerly shear zones and the formation of a new qbo westerly shear zone aloft the timing of deseasonalized qbo westerly maxima in the middle stratosphere allows a simple composite of 2 and 3 year cycles to be constructed from the data illustrating the effect of the qbo on descending westerly phases of the stratopause sao

fluid flow and diffusion in the waterville limestone south central maine constraints from strontium oxygen and carbon isotope profiles oxygen carbon and strontium isotopic profiles across the margin of the waterville limestone member are used to investigate advective and diffusive transport during metamorphism of the waterville formation in south central maine usa rb sr isotopic systematics were homogenized on the 10 cm hand specimen scale at ages that are within error of the 366 6 ma rb sr whole rock age of the syn metamorphic hallowell pluton this is consistent with a plutonic heat source for this low pressure andalusite and sillimanite grade acadian metamorphic terrane advective displacements of all three isotope profiles at the garnet grade blue rock quarry indicate fluid flow to the east into the limestone and the oxygen isotope profile implies a time integrated fluid flux of 3 2 1 5 m 3 m 2 2 error this cross layer flux is insufficient to cause the observed reaction progress of the muscovite ankerite quartz to biotite anorthite in plagioclase calcite reaction in the 100 m thick waterville limestone member and much of the fluid flow responsible may have been layer parallel the isotope profiles indicate advective diffusive homogenization over distances of 1 5 m 13 c to 6 m 18 o and such homogenization distances are difficult to reconcile with observations of order of magnitude variations in reaction progression the centimetre scale or less it is possible that infiltration occurred during events short lived compared with diffusion that the reactions started at different temperatures dependent on bulk composition or that diffusion of water from layers with less reactants to layers with more reactants was important in driving the biotite producing reaction however variations of fluid composition inferred from the mineral assemblages are apparently inconsistent with diffusion driving reactions progress and models of precursor assemblages do not indicate significant compositional control of the temperature of the first appearance of biotite in the rocks irrespective of the details of flow and diffusive exchange on the centimetre scale the average reaction progress in the waterville limestone member requires significant layer parallel fluid fluxes

magmagenesis associated with extension in orogenic belts examples from the himalaya and tibet abstract structures in mountain belts which accommodate layer extension may be synchronous with either ongoing thickening or reduction in crustal thickness either case may be associated with magmagenesis because they contribute to the thermal regime in the lithosphere and the chemistry of magmas produced can reveal source compositions and thereby conditions of melting in the high himalaya exhumation of upper amphibolite facies metamorphic rocks in the footwall of a major normal shear zone occurred during crustal thickening this rapid decompression enhanced fluid absent melting reactions in micaceous pelites and produced the high himalayan leucogranite suites which were subsequently intruded into the zone of normal shear similar leucogranites are seen in the cretaceous north lhasa terrane nlt in association with a calc alkaline series these suites are also crustally derived but their chemistry indicates higher melting temperatures than in the himalaya suggesting that heat flow into the base of the crust was enhanced this thermal anomaly was most probably associated with lithosphere attenuation following an episode of thickening the tibetan plateau is currently a topographically elevated region of thick crust that appears to be undergoing orogenic collapse active structures are stretching and thinning the crust the plateau is underlain by a thin hot mantle lithosphere supporting theoretical models that suggest that a lithospheric root of a thick orogen would become unstable and be removed by convection consequent thermal perturbations in the mantle lithosphere cause melting in suitably fertile horizons leading to widespread volcanism comparisons have been drawn between the tibetan model and the late stages of the variscan belt in europe magmatic rocks of diverse composition occur throughout the late variscan many of them indicating derivation from a previously enriched lithospheric source suggesting thermal anomalies in the subcontinental mantle akin to those inferred for tibet taken with structural and sedimentary evidence these indications strongly support the hypothesis that the variscan orogen underwent orogenic collapse in the tibetan style

the kinematic interpretation of obliquely transected porphyroblasts an example from the trois seigneurs massif france abstract obliquely transected porphyroblasts otps contain a straight inclusion pattern that is continuous with the external foliation but oblique in orientation otps are interpreted to form by porphyroblast growth between two phases of deformation the obliqueness of the inclusion pattern and external foliation is due to the second deformation phase and has been variously explained by porphyroblast rotation in the kinematic reference frame of bulk flow or by foliation rotation around a stationary porphyroblast the two models imply opposite sense of vorticity also loosely referred to as sense of shear to produce the same geometry and their relevance should be known if otps are to be used as sense of vorticity indicators andalusite otps in the trois seigneurs massif french pyrenees have a spool shape in three dimensions that is interpreted to result from passive overgrowth of andalusite on a spaced s 2 cleavage subsequent non coaxial d 3 flow led to development of an s 3 crenulation cleavage and the otp geometry although the porphyroblasts rotated rotation of the foliation in the kinematic reference frame of bulk flow was mainly responsible for the otp geometry this example shows that otps can indeed develop by foliation rotation in non coaxial flow similar looking otps can apparently develop in flows with opposite sense of vorticity depending on whether foliation or porphyroblast rotation is dominant the dominance of either development mechanism depends on the importance of flow partitioning and solution transfer during progressive deformation

the variscan geology of the pyrenees abstract the main outlines of the geology of the variscan part of the pyrenees are discussed rocks involved in this cycle are high grade basement gneisses palaeozoic sediments and their metamorphic equivalents late intrusive granodiorites and early pre variscan granites the main features of the stratigraphy of the palaeozoic are given structures fall into two domains a low grade suprastructure essentially with steep folds and cleavages and a high grade infrastructure with dominantly low dipping foliations an important phase of early pre cleavage folding occurs in low grade rocks mainly along the southern border of the axial zone in high grade rocks most structures and the metamorphism postdate the main cleavage phase in low grade rocks the influence of the alpine orogeny on the variscan structures consists mainly of faults steep reverse faults in the northern and south directed thrusts in the southern part of the pyrenees metamorphism took place under high geothermal gradients and low pressures as indicated by the abundant occurrence of andalusite and cordierite

co2 driven large mafic explosive eruptions the pozzolane rosse case study from the colli albani volcanic district italy generally the intensity and magnitude of explo sive volcanic activity increase in parallel with sio2 content pyroclastic flow forming eruptions in the colli albani ultrapotassic volcanic district italy represent the most striking exception on a global scale with volumes on the order of tens of cubic kilometres and k foiditic composi tions sio2 even 42 wt here we reconstruct the pre eruptive scenario and event dynamics of the 456 ka pozzolane rosse pr eruption the largest mafic explosive event of the colli albani district in particular we focus on the driving mechanisms for the unusually explosive eruption of a low viscosity mafic magma geologic petrographic and geochemical data with mass balance calculations supported by experimental data for colli albani magma compositions provide evidence for signif icant ingestion of carbonate wall rocks by the pozzolane rosse k foiditic magma moreover the scattered occurrence of cored bombs in pozzolane rosse pyroclastic flow deposits records carbonate entrainment even at the eruptive time scale as also tested quantitatively by thermal modelling of magma carbonate interaction and carbonate assimilation experiments we suggest that the addition of free co2 from decarbonation of country rocks was the major factor controlling magma explosivity high co2 activity in the volatile component coupled with magma depressurisation produced extensive leucite crystallisation at short time scales resulting in a dramatic increase in magma viscosity and volatile pressurisation which was manifested a change of eruptive dynamics from early effusion to the pozzolane rosse s highly explosive eruption climax

strontium alteration in the troodos ophiolite implications for fluid fluxes and geochemical transport in mid ocean ridge hydrothermal systems new and published strontium isotope analyses from the troodos ophiolite constrain fluid solid exchange processes and the magnitude and circulation paths of the hydrothermal fluids the87sr 86sr profile reflects alteration in the recharge zone of an evolving hydrothermal system fluid rock strontium isotope exchange in the upper 1 5 km of extrusive lavas was kinetically limited and seawater derived fluids emitted from the base of this zone were buffered to87sr 86sr ratios between 0 7047 and 0 7059 in contrast over the next 1 km depth interval of sheeted dykes and the uppermost plutonics 87sr 86sr values cluster about0 7054 7 2 and fluid flow is inferred to have been pervasive with near equilibrium fluid rock exchange quartz chlorite and epidosite zones the probable pathways of the concentrated high temperature upwelling fluids have identical87sr 86sr ratios to adjacent diabase dykes on troodos a time integrated fluid flux in excess of2 9 107 kg m 2 is required to transport the strontium isotope composition of 0 7054 set in the kinetically controlled exchange zone through the 1 km of sheeted dykes and into the zones of concentrated upwelling the uniformity of the87sr 86sr ratios in the diabase sheeted dykes and high temperature epidosite and quartz chlorite rocks indicate that the strontium isotopic alteration took place during the high temperature phase of hydrothermal circulation the inferred minimum time integrated fluid flux of2 9 107 kg m 2 substantially exceeds that of 5 106 kg m 2 inferred from thermal models of high temperature circulation but is comparable with estimates of the hydrothermal flux from oceanic budgets of3he mg and87sr the high flux estimate for troodos is consistent with the ophiolite venting fluids with87sr 86sr elevated significantly above rock values which contrasts with the near morb87sr 86sr ratios of fluids from active high temperature vents at mid ocean ridges and the87sr 86sr profile in dsdp hole 504b this requires that either the modern systems are immature and there is a protracted phase of lower temperature circulation or that circulation in the troodos ophiolite differed from that in normal mid ocean ridges and oceanic strontium budgets are balanced by another source the lack of very elevated87sr 86sr values in the vent fluids precludes significant channelling in the recharge zones of the active systems

geology and geochronology of the arnea sithonia and ouranopolis intrusions chalkidiki peninsula northern greece abstract the chalkidiki peninsula comprises the greek geotectonic units of the vardar axios zone and the serbo macedonian massif several granitic bodies of various ages intrude this area and many of them are of unknown or disputed age the ages of the arnea sithonia and ouranopolis granitoids are investigated using 40 ar 39 ar stepheated mineral and rb sr whole rock analyses the arnea granite has experienced intense but variable deformation recrystallization and retrogression in general it lacks easily datable minerals because of it s highly evolved silica rich composition however coarse grained phlogopitic mica separated from a minor less evolved porphyritic part of the intrusion yields an excellent 40 ar 39 ar plateau age of 136 1 ma rb sr whole rock samples give a regression line of age 155 11ma and an initial 87 sr 86 sr ratio of 0 7174 0 0017 mswd 280 the scatter may reflect the widespread recrystallization and deformation of the arnea granite the arnea granite is at least late jurassic in age and has undergone regional greenschist metamorphism during the early cretaceous biotite from the sithonia granitoid yields a plateau age of 43 0 6 ma muscovites from crosscutting pegmatites within the granitoid give slightly saddle shaped age spectra with minimum ages of 49 ma and 50 ma suggesting argon 40 excess biotite and muscovite from the ouranopolis granitoid yield plateau ages of 44 1 1 ma and 47 0 7 ma respectively it is suggested that this granitoid is coeval and cogenetic with the sithonia granitoid both intrusions are eocene in age rb sr whole rock samples from the sithonia and ouranopolis granitoids failed to provide any isochrons this is interpreted to be due to inhomogeneities in these young intrusions the age data strongly suggest that the sithonia and ouranopolis granitoids are unrelated to the arnea granite coupled with geochemical and petrographic data these results clarify the relationships between some of the granitic intrusions and have important regional implications

equatorial quasi biennial oscillation influence on northern winter extratropical circulation 1 this study investigated the holton tan relationship between the equatorial quasi biennial oscillation qbo and the polar vortex as seen in the era 40 reanalysis and era interim analysis 1980 2004 25 years data sets and in ensemble simulated data sets five members covering the period 1980 2004 125 years by using the meteorological research institute chemistry climate model mri ccm and focusing on the northern hemisphere winter the primary tools employed were composite differences in zonal wind temperature and eliassen palm ep fluxes although not many global circulation models can simulate the qbo realistically the mri ccm which includes the interaction between qbo dynamics and the ozone hence heating distribution reproduces a self generated qbo that is fairly realistic in agreement with the finding of previous studies our results revealed that the conventional holton tan explanation that the equatorial winds in the lower stratosphere act as a waveguide for midlatitude planetary wave propagation cannot explain the winter circulation in either the era 40 data or the simulation although the composite differences in zonal wind and temperature show a slight yet statistically significant holton tan effect i e the stratospheric polar vortex is weaker and more disturbed under easterly qbo conditions the ep flux diagnostics do not show more poleward propagation in the midlatitude stratosphere rather planetary waves propagate more equatorward as well as more upward during the easterly phase of the qbo

the role of trace minerals in chemical weathering in a high elevation granitic watershed estibere france chemical and mineralogical evidence we investigated chemical weathering in a high elevation granitic environment in three selected watersheds located in the pyrenees france the sites were located on glacial deposits derived from similar hercynian 300 ma granites characterized by the occurrence of zoned plagioclases and trace calcic phases epidote prehnite sphene apatite the surface waters at those sites show high ca na molar ratios 1 which could not be explained by the dissolution of the major plagioclase oligoclase present in the rocks the coupled approach of investigating stream water chemistry and the mineralogy and chemistry of rocks and soils allowed us to explore the role of the weathering of trace calcic minerals in calcium export at the watershed scale the weathering of the trace calcic minerals which represent 1 of the total rock volume are responsible for more than 90 of the calcium export at the sites annual cationic fluxes 23 104 eq km2 yr calculated for the estibere watershed are among the highest reported for high elevation systems draining granitic rocks and 80 of this annual cationic flux can be attributed to the weathering of trace calcic phases calculations based on isotopic values 87sr 86sr go in the same direction except apatite the trace calcic phases appear to be mainly silicates thus the type of chemical weathering observed in the estibere watershed may have an influence on atmospheric co2 consumption by granite weathering however comparison with other watersheds draining granitic environments worldwide and with the two other sites in the pyrenees indicate that the role of trace calcic phases is important in most young environments exposed to chemical weathering e g high elevation catchments on glacial deposits other factors such as the date of glacial retreat the physical denudation rate the hydrological functioning of the watershed and the nature and structure of the soil cover are also important

seasonal asymmetry of the low and middle latitude qbo circulation anomaly abstract it is usually assumed that the circulation anomaly induced directly by the quasi biennial oscillation qbo in the equatorial zonal wind is approximately a seasonally independent two cell structure symmetric about the equator and confined to the tropics it is shown here using a simple two dimensional model that although the two cell structure exists at equinox at solstice the summer cell disappears and the winter cell is greatly strengthened about three times stronger than at equinox and expanded strong cross equatorial flow is induced near the shear zone where the qbo winds are easterly this result may explain why the observed anomalies in trace gases are small in the summer hemisphere and it also reduces the need for a modulation of the planetary wave fluxes at low and middle latitudes in order to explain the modulation of the circulation there at low latitudes the shape of the isopleths of a modeled tracer closely resemble those observed in both easterly and westerly phases of the q

a unique sequential melting mechanism for the generation of anatectic granitic rocks from the penafiel area northern portugal abstract granitic rocks derived by sequential partial melting are very uncommon occurrences worldwide with only three known cases in portugal tourem guarda sabugal and penafiel and one in argentina achiras complex the suite documented in this paper comprises two of the three main phases of a batholith in the penafiel area these variscan peraluminous two mica granite and granodiorites formed at 310 and 305 ma during and near the end of the variscan d3 deformation and have the characteristics of s type granites none of the metamorphic country rocks have an adequate sr isotopic composition to be a protolith it is argued that progressive isotopic re equilibration of crustal material probably a metagreywacke for g1 and g3 with also some metapelitic contribution for g2 during granulization of the lower variscan crust explains the difference in isotopic composition between outcropping granitic rocks and metamorphic country rocks biotite muscovite granite g1 and biotite muscovite granodiorite g3 have similar 87 sr 86 sr i and end t values and were derived by sequential partial melting of the same source material this is indicated by coherent trends of the whole rock major and trace element compositions the compositions of feldspar biotite muscovite and tourmaline the presence and type of xenocrystic mineral phases and xenoliths and whole rock oxygen isotope compositions this mechanism was the result of post thickening variscan extension and mantle upwelling another member of the same batholith is a biotite muscovite granodiorite g2 with an intermediate age of 307 ma but with geochemical characteristics suggesting that it corresponds to a chemically distinct pulse of magma although likely stemming from a comparable though more metapelitic lower crustal source

recycling processes in granite granodiorite complex genesis the querigut case studied by ndsr isotope systematics abstract using the isotopic rb sr and sm nd petrogenetic tracers we have studied the calc alkaline plutonic complex of querigut pyrenees france which is famous for its acid to mafic rock association and is a typical post tectonic hercynian granitoid its age of 280 m y is already known 2 23 24 and our purpose is to examine the relationship between its different petrographic units and the problem of their source composition the sm nd isotopic results rule out any genetic process involving a unique homogeneous source and imply the presence of old recycled continental materials in contrast the rb sr isotope system seems to have been homogenized by hot fluids maybe post magmatic this is also true for pb isotopes as shown previously by michard vitrac et al 18 on the basis of the isotopic results and the major element data a model of combined fractional crystallization assimilation of country rocks is proposed for the basic part of the complex in contrast acid parts are mainly the result of the continental anatexis this study also constrains the basement s age 1200 1900 m y of the area and suggests a scheme for the gological history of the eastern pyrenees

climatology of the equatorial lower stratosphere abstract twenty years of radiosonde data have been analyzed in an attempt to develop a latitudinal structure climatology of winds temperature and geopotential at 30 and 50 mb in the equatorial stratosphere the fine latitudinal resolution provided by the wmo station network reveals several interesting features in the latitudinal structure of the annual and quasi biennial cycles which dominate this region for example the westerly and easterly acceleration phases of the quasi biennial oscillation are markedly different westerly accelerations appear first at the equator spreading outward with time to higher latitude and an more intense on average than the easterly accelerations the easterly accelerations are more uniform in latitude but leer uniform in time sometimes occurring in two stages the quasi biennial wind and temperature oscillations are symmetric about the equator while the annual harmonic in zonal wind is antisymmetric about the equator but is not proportional to the coriolis paramete

geochemical and isotopic disequilibrium in crustal melting an insight from the anatectic granitoids from toledo spain in the hercynian anatectic complex of toledo act the anatectic granitoids include leucogranitic leucosomes leucogranitic massifs and restite rich granites they show a broad range of initial sr and nd isotope ratios from 0 711 to 0 720 and 0 51164 to 0 51203 respectively which clearly indicate the absence of isotopic homogenization in the melts broadly the ranges reflect the isotopic variation of the metapelitic protoliths if crustal melting occurs under water undersaturated conditions as is the case of the act the generated melts do not isotopically and chemically equilibrate with the granulitic residuum the preservation of heterogeneities could arise through a number of processes 1 duration of the process in which the presence of melts with disequilibrium features and the high solid content of several of the granites in the act point to a very short lived magmatic system 2 limited diffusion in which poorly segregated and volatile undersaturated granitoids have a very restricted opportunity for isotopic and chemical homogenization and 3 magma dynamics in which the low melting rates the high restite and low water contents and the silica rich composition of these granites together with the small volume and high viscosity values of the melts seriously restrict the physical processes leading to homogenization

an extended episode of early mesoproterozoic metamorphic fluid flow in the reynolds range central australia the products of metamorphic fluid flow are preserved in zones within the marbles and metamorphosed semipelites of the upper calcsilicate unit in the granulite portion of the late palaeoproterozoic reynolds range group northern arunta block central australia the zones of retrogression characterized by minerals such as wollastonite grossular and clinohumite local resetting of oxygen isotopic compositions and local major element metasomatism were channelways for water rich fluids derived from granulite facies metapelites u th pb isotopic ages measured by the shrimp ion microprobe on zircon and monazite from a granulite facies semipelite an early semiconcordant aluminous quartz rich fluid flow segregation and a late discordant quartz rich segregation record some of the extended thermal history of the area zircon cores from the semipelite show its likely protolith to be an igneous rock 1812 11 ma old itself derived from a source containing zircon as old as 2 2 ga low th u overgrowths on the zircon grew during granulite facies metamorphism at 1594 6 ma monazite cooled to its blocking temperature at 1576 8 ma zircon cores from the semiconcordant segregation are dominantly 2 3 ga old indicating that the source of the fluids was not the particular metamorphosed semipelite studied two generations of low th u overgrowths on the zircon give indistinguishable ages for the older and younger of 1589 8 and 1582 8 ma respectively the monazite age is the same 1576 12 ma zircon from the late discordant segregation gave 1568 4 ma fluid flow occurred for at least 18 3 ma and ended 26 3 ma after the peak of metamorphism suggesting a very slow cooling rate of 3 c ma 1 the last regional high grade metamorphism in the reynolds range occurred at 1 6 ga not 1 78 ga as previously thought the high grade event at 1 78 ga is a separate event that affected only the basement to the reynolds range group

crustal origin of hercynian peraluminous granitic batholiths of central spain petrological geochemical and isotopic sr nd constraints abstract in central spain it is possible to distinguish two main types of peraluminous late hercynian granites the pi types and the ps types the distinction between both types is made on the basis of differences in peraluminosity ps types are more peraluminous than pi types and also on the appearance of some characteristic mafic minerals ps types have biotite cordierite and monazite as the most typical accessory phase whereas pi types have biotite amphibole in the less evolved facies and allanite as the accessory mineral both granite types have similar trace element ratios and initial sr nd and pb isotopic signatures initial 87sr 86sr ratios of both types exhibit a large range from 0 7073 to 0 7193 whereas initial end varies in a restricted range from 5 4 to 6 6 the scarce associated basic rocks do not play a significant role in the chemical variability of these peraluminous granites which follow low pressure crystal fractionation trends from granodiorite monzogranite parental magmas mixing and afc modelling of sr and nd isotopic data reveal an unrealistically high mantle contribution based on major and trace element and isotopic data an orthogneissic protolith for both granitic series is proposed nevertheless none of the metamorphic country rocks of central spain has the appropriate sr isotopic composition to satisfy the origin of these granitic rocks and so it is argued that progressive isotopic re equilibration of crustal material during the granulization of the lower hercynian crust together with the possibility of isotopic disequilibrium during melting as has been demonstrated in migmatitic terranes in nearby areas may explain the isotopic differences between the granites and the high level metamorphic country rocks

global qbo in circulation and ozone part 2 a simple mechanistic model abstract although the phenomenon of equatorial quasi biennial oscillation is relatively well understood the problem of how the equatorially confined qbo wave forcing can induce a signal in the extratroics of comparable or larger magnitude remains unsolved a simple mechanistic model is constructed to provide a quantitative test of the hypothesis that the phenomenon of extratropical qbo is mainly caused by an anomalous seasonal circulation induced by an anomalous eliassen palm flux divergence the anomaly in e p flux divergence may be caused in turn by the relative poleward and downward shift of the region of irreversible mixing breaking of the extratropical planetary waves during the easterly phase of the equatorial qbo as compared to its westerly phase the hemispheric nature of the anomaly wave forcing in solstice seasons viz no wave breaking in the summer hemisphere induces a global circulation anomaly that projects predominantly into the first few zonal hough modes of plumb such a global qbo c

rb sr whole rock investigations in the aston massif central pyrenees rb sr whole rock data are presented from four magmatic units in the aston massif central pyrenees the data are interpreted to reflect the following variscan events 1 an almost complete homogenization of the sr isotopic composition through the aston orthogneiss about 315 ma ago obscuring the original age of gneiss 2 intrusion of the ax granite 301 15 ma ago and of the soulcem pegmatite muscovite granite 292 13 ma ago both from crustal sources the variscan bassies granodiorite partly suffered later rb sr whole rock resetting presumably related to the development of alpine shear zones

variscan extension in the pyrenees evidence for variscan extension in the pyrenees is summarized and used with other geological and geochronological data to reconstruct the variscan extensional geometry and kinematics at a crustal scale a regionally consistent pattern of ese wnw trending synmetamorphic stretching directions indicates variscan extension roughly parallel to the present alpine trend of the belt the spatial distribution of variscan low pressure high temperature metamorphic domes is interpreted as being possibly due to the activity of few moderately dipping crustal scale shear zones allowing heterogeneous ductile extension of the variscan middle and lower crust extension occurred synchronous with uplift and emergence of large parts of the crust and deposition during the upper carboniferous and permian of up to 2500 m of continental sediments and intercalated basaltic andesitic volcanics in fault bounded extensional halfgrabens the extensional structures and related metamorphism postdate a namurian to early westphalian stage of crustal thickening characterized by thrusting and steep folding it is suggested that variscan extension in the pyrenees was driven by the gravitational potential energy of an initially thickened lithosphere enhanced by detachment of a cold and gravitationally unstable lithospheric root which caused progressive uplift tectonic denudation and a highly anomalous thermal structure of the variscan crust leading to extensive lower crustal melting and granodioritic intrusion during the early permian

feasibility of afc models for the petrogenesis of calc alkaline magma series one of the most popular petrogenetic concepts is that of simultaneous assimilation and fractional crystallisation afc the equations governing these processes are well known and widely applied the power and attraction of the model are that with the minimum of constraints petrogenetic schemes can be erected for essentially any group of rocks these models are usually based on the observed variations in a small number of trace elements and or isotopic systems in this paper we have generated well constrained afc models for the variscan calc alkaline querigut complex in the french pyrenees our models are based on geological constraints on the identities of the parent magma and candidate assimilants and the sm nd and rb sr isotope systematics of the rocks the modelling is successful in mimicking the isotope array for the actual rocks however the results are massively inconsistent with those produced using the major and trace element concentrations our major conclusion is that afc modelling should be undertaken only with robust initial constraints on the compositions of the parent magma and the proposed assimilant with due respect for crystal liquid partition coefficients in so far as they are known the results should then be accepted only if the isotope based model parameters are consistent with those derived from major and trace element variations

homogenization and lowering of 18o 16o in mid crustal rocks during extension related magmatism in eastern nevada the oxygen isotope systematics of tertiary volcanic rocks of east central nevada and of plutonic and metamorphic rocks of the ruby mountains east humboldt range core complex provide complementary evidence for major18o depletion and 18o 16o homogenization of mid crustal rocks during metamorphism and magmatism the 18o value of crustal source material for silicic volcanic rocks decreased from between 9 and 11 to between 7 and 8 over 5 ma mid crustal metasedimentary and granitic rocks in the east humboldt range have 18o values very similar to the volcanic rocks and values are lower and more homogeneous at deeper structural levels exchange with deep seated mantle derived igneous rocks or fluids derived therefrom is the most plausible18o depletion mechanism intrusion of these mafic magmas promoted crustal melting and fluid migration homogenization of 18o 16o resulted from migration of high temperature fluids and melts at mid crustal levels and was less effective at higher structural levels where the crust was dominated by less permeable carbonate rocks

the quasi biennial oscillation analysis using era 40 data 1 the era 40 data set is used to examine the equatorial quasi biennial oscillation qbo the data set extends from the ground to 0 1 hpa 65 km and covers a 44 year period january 1958 to december 2001 including 18 5 qbo cycles analysis of this data set of unprecedented spatial and temporal coverage has revealed a threefold structure in height in the qbo zonal wind anomalies at the equator in addition to the well known twofold structure in the lower and middle stratosphere that is easterlies overlying westerlies or vice versa there is a third anomaly in the upper stratosphere the sign of this upper stratospheric anomaly is the same as the lower stratospheric anomaly thus forming anomalies of alternating sign throughout the depth of the equatorial stratosphere the amplitude of this upper stratospheric anomaly is 10 m s 1 approximately one third of the amplitude of the lower stratospheric signal the frequency and descent rates of the east and west qbo phases are analyzed in detail with particular attention to any 11 year solar cycle influence in addition to the observed solar modulation of the duration of the qbo west phase the analysis shows a solar modulation of the mean descent rate of the easterly shear zone the mean time required for the easterly shear zone to descend from 20 to 44 hpa is 2 months less under solar maximum conditions than under solar minimum conditions 7 4 months versus 9 7 months this rapid descent of the easterly shear zone cuts short the west phase of the qbo in the lower stratosphere during solar maximum periods

eruptive history and petrologic evolution of the albano multiple maar alban hills central italy a comprehensive volcanological study of the albano multiple maar alban hills italy using i 40ar 39ar geochronology of the most complete stratigraphic section and other proximal and distal outcrops and ii petrographic observations phase analyses of major and trace elements and sr and o isotopic analyses of the pyroclastic deposits shows that volcanic activity at albano was strongly discontinuous with a first eruptive cycle at 69 1 ka producing at least two eruptions and a second cycle with two peaks at 39 1 and 36 1 ka producing at least four eruptions contrary to previous studies we did not find evidence of magmatic or hydromagmatic eruptions younger than 36 1 ka the activity of albano was fed by a new batch of primary magma compositionally different from that of the older activity of the alban hills moreover the ree and 87sr 86sr data indicate that the albano magma originated from an enriched metasomatized mantle according to the modeled liquid line of descent this magma differentiated under the influence of magma limestone wall rock interaction our detailed eruptive and petrologic reconstruction of the albano maar evolution substantiates the dormant state of the alban hills volcanic district

a rifted tectonic setting for hercynian high thermal gradient metamorphism in the pyrenees abstract hercynian regional metamorphic terrains in the pyrenees contain evidence of very high temperature gradients within the crust during metamorphism with temperatures as high as 700 c attained at 10 12 km below the surface stable isotope studies demonstrate that the crust was simultaneously flushed by marine fluids to at least this depth the absence of any evidence for crustal collision and the upper palaeozoic stratigraphic record for the area suggest that the tectonic setting for the metamorphism was a zone of continental rifting associated with strike slip movement in this zone anatexis occurred at two distinct levels cambro ordovician pelites at the base of the palaeozoic sedimentary pile melted to produce per aluminous magmas while in the lower hercynian crust very large scale melting generated voluminous granodioritic magmas which then invaded high structural levels the thermal structure of the hercynian crust was profoundly influenced by both convective and advective heat transfer due to movement of surface derived aqueous fluids and intrusion of magmas

origin of the 3500 3300 ma calc alkaline rocks in the pilbara archaean isotopic and geochemical constraints from the shaw batholith abstract calc alkaline plutonic rocks intruded at 3450ma comprise a major component of the shaw batholith in the archaean east pilbara block western australia new whole rock pb isotopic geochronology confirms the extent of these rocks but a minor plutonic phase is dated at 3338 52 ma and represents a second plutonic event of the same age as much of the nearby mt edgar batholith the sm nd isotopic systematics of the 3450ma rocks imply their derivation from a heterogeneous source which probably included a slightly older crustal component as well as a depleted mantle component the 3338 52 ma pluton includes components derived from crustal sources older than 3600 ma the geochemistry and sm nd isotopic systematics of these rocks are consistent with crustal growth in the early archaean from upper mantle sources as depleted as the modern upper mantle the shaw batholith calc alkaline suites exhibit very similar chemical trends on variation diagrams to modern calc alkaline plutonic rocks which can be modelled by a combination of mixing and fractionation a suite collected from outcrops displaying prominent igneous layering shows distinct geochemical trends which can be modelled by differentiation into a component enriched in ferromagnesian minerals principally hornblende and possibly sphene magnetite and epidote and into a leucocratic component containing quartz plagioclase and k feld par these archaean calc alkaline plutonic rocks in common with rocks from many other archaean calc alkaline provinces exhibit very fractionated ree patterns with depleted hree contents a feature considered to result from equilibrium with garnet at depth in lower crustal regions the geochemistry of the pilbara archaean calc alkaline rocks is identical to the subset of modern continental margin calc alkaline plutonic rocks with fractionated ree patterns such as those from the central and eastern peninsular ranges batholith western usa the tectonic setting in which the archaean calc alkaline rocks formed is still not known this reflects both uncertainty associated with the petrogenesis and environments of modern calc alkaline rocks as well as the limited knowledge of the precise timing and relationships of plutonic depositional and tectonic events in the pilbara archaean

metallogenesis in the french part of the variscan orogen part i u preconcentrations in pre variscan and variscan formations a comparison with sn w and au abstract in the french part of the variscan orogen the pre variscan metamorphic rocks and the variscan granites resulting from pure crustal recycling are enriched in uranium and tin data on tungsten and gold are too scarce for a reasonable estimation of the average concentrations of these elements to be obtained the spatial distribution of uranium preconcentrations is transverse to the main variscan structural domains and the distribution of the sn w mineralizations prompts the same conclusions u sn w and au metal enrichment in crustal domains in europe seems to result from late proterozoic to early palaeozoic basic and acid magmatism for uranium at least two main stages of partial melting early palaeozoic and late carboniferous lead to enrichment of the metal in peraluminous leucogranites these leucogranites represent the main source of late variscan uranium and tin within the peraluminous granitic complexes the main metal source is related to the late intrusion of small granitic cupolas strongly enriched in metals in the case of uranium the efficiency of the hydrothermal remobilization depends on the proportion of metal located in uraninite which is easily leachable by hydrothermal solutions the emplacement of these cupolas is structurally controlled in well defined areas by large shear zones these shear zones are continuously active during the successive emplacement of the granitic magmas most of the hydrothermal uranium mineralization is related to the permian reactivation of the shear zones in a brittle stage these zones then channel the hydrothermal fluids involved in the last metal concentration step leading to the formation of the orebodies the efficiency of metal remobilization is dependent on a close spatial relationship between magmatic structures enriched in uranium and brittle structures channeling the hydrothermal fluids

is there a time lag between the metamorphism and emplacement of plutons in the axial zone of the pyrenees detailed petrographic and geochemical studies conducted on zircons from the lys caillaouas pluton reveal their igneous and metamorphic affinities the igneous zircons constrain the emplacement of the pluton to 300 2 ma by contrast the metamorphic zircons yield an older age of 307 3 ma which probably dates the thermal peak of the ht lp variscan metamorphism therefore a short time lag of c 7 ma emerges between the metamorphic climax and emplacement of the pluton in the axial zone pyrenees

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

deep fluid circulation in alpine shear zones pyrenees france field and oxygen isotope studies a combined field stable isotope and whole rock chemical study was made on late cretaceous to tertiary metasomatic shear zones cutting hercynian gneisses in the aston massif pyrenees france mylonitisation occurred during the early stages of alpine compression under retrograde conditions at 400 450 c and about 10 km depth whole rock 18o values of 11 to 12 in the gneisses was lowered to 5 to 9 in the shear zones with the quartz muscovite 18o 16o fractionations of about 2 to 4 essentially unchanged these 18o 16o systematics together with d muscovite 40 to 50 indicate that large volumes of formation waters or d rich meteoric waters passed through the shear zones during deformation the same fluids also redistributed major elements as shown by the correlation of 18o shift with muscovitisation and albitisation reactions in granitic wall rocks however even though 18o was universally lowered within the shear zones the 18o 16o ratios were not homogenised nor do they correlate in detail with the presence or absence of muscovitisation suggesting that fluid flow was probably fracture controlled and episodic field mapping shows that along the length of a particular shear zone muscovitisation of granite gneiss dies out 150m above the contact with underlying sillimanite gneiss thus muscovitisation and albitisation of granite gneiss in shear zones and their wall rocks probably occurred during re equilibration of acidic chloride rich aqueous fluids that had previously moved upward within the shear zones through underlying sillimanite gneiss extremely high material balance fluid rock ratios 103 are required to explain the extent of muscovitisation along this shear zone implying integrated fluid mass fluxes of about 108 kg m2 this is probably close to the maximum value for other shear zones in the network similar volumes of a more chemically evolved fluid must have passed through the unmuscovitised mylonites showing that the absence of alteration cannot necessarily be used to infer low values of fluid flux for reasonable pressure gradients and time scales of fluid movement effective permeabilities of 10 15 to 10 17 m2 are required such values can be accounted for by short lived widely spaced cracks produced during seismic activity a model is presented in which formation waters were seismically pumped down an underlying shallow southward dipping decollement and then upward through the steeply dipping shear zone network

the significance of himalayan rivers for silicate weathering rates evidence from the bhote kosi tributary the significance of weathering by himalayan runoff for both the sr isotope marine record and the removal of atmospheric co2 through silicate dissolution has been examined by systematic sampling of dissolved loads and bedloads from the bhote kosi a tributary of the ganges that rises in tibet from tethyan sediment bedrock and traverses the major himalayan lithologies of eastern nepal before debouching onto the gangetic plains throughout the section the cation geochemistry of water samples is dominated by ca and mg ions suggesting that carbonates are the predominant lithology undergoing dissolution particularly within the lesser himalayas as the river transects the metasedimentary and granitic lithologies of the high himalayas the sr isotope ratio of the bedload rises rapidly closely reflecting the isotope geochemistry of the bedrock in contrast the 87sr 86sr ratio of the dissolved load remains roughly constant 0 719 0 723 downstream of the main central thrust where the river transects the carbonate bearing lithologies of the lesser himalayas the 87sr 86sr ratio of the dissolved load rises sharply 0 768 the relative contributions of silicate and carbonate weathering from each of the main himalayan units has been estimated from major cation sr concentration and sr isotope mass balance equations these calculations suggest that the high sr and high 87sr 86sr characteristics of riverine analyses arise initially from a component dissolved from the tibetan sedimentary series which is substantially enhanced by input weathering fluxes particularly as the river traverses the lesser himalayas whilst mechanical erosion is maximised within the high himalayan crystalline series as confirmed by 143nd 144nd ratios from the bedload at least 63 of the dissolved load is acquired by chemical weathering of bedrock lithologies and or of transported particulates within the lesser himalayas enhanced by higher ambient temperatures and slower discharge rates this may involve continued dissolution of the high himalayan crystalline series particulates in addition to lesser himalayan lithologies although himalayan rivers collectively have a major influence on the sr isotope marine record the high 87sr 86sr ratios of their dissolved load results from the mixing of a small component 90 of carbonate derived material some of which is characterised by a high 87sr 86sr ratio up to 0 8 elevated 87sr 86sr ratios in rivers are therefore not necessarily indicative of anomalously high dissolution rates of silicates

the arburese igneous complex sw sardinia italy an example of dominant igneous fractionation leading to peraluminous cordierite bearing leucogranites as residual melts abstract the arburese massif sw sardinia italy is a zoned shallow pluton emplaced in the frontal part of a nappe pile at the end of the hercynian orogeny its main lithologies are a pyroxene bearing biotite granodiorites and b cordierite bearing peraluminous leucogranites they form a sequence of sharply bounded multiple intrusions the leucogranites lg form the core of the intrusive complex and are younger than the granodiorites three types of granodiorites gd 1 gd 2 gd 3 have been distinguished on the basis of their field relations and their pyroxene content dark coloured enclaves are common in the granodiorites their compositions range from biotite bearing norite to pyroxene biotite quartzdiorite quartz monzodiorite a small body of olivine bearing quartz monzogabbro norite mg forms an independent intrusion in the border zone of the igneous massif it is crosscut by the granodiorite the whole rock sequence from mg to gd 3 is characterized by the same mafic assemblage opx cpx bt ilm it formed by dominant crystal liquid fractionation processes from a mantle derived olivine bearing magma from gd 3 to three types of leucogranites lg 1 lg 2 and lg 3 the rocks are progressively enriched in al reaching a peraluminous composition in the leucogranites cordierite makes its appearance among the primary mineral phases though confined to the later products of crystallization remarkably cordierite was also observed among the latest crystallization products in some granodiorites and even in some dark monzodioritic enclaves independent whole rock age determinations were made on the mg to gd 3 series and on the leucogranites these gave very similar values of 309 19 and 304 21 ma respectively some textural and mineralogical features common to both gd 3 granodiorite and the leucogranites e g both contain ti biotites characterized by a common trend of al and fe enrichment suggest a genetic linkage between these two rock types the extreme iron rich compositions displayed by the mafic minerals biotite cordierite of the leucogranites suggest that they crystallized from highly evolved melts petrochemical trace element and ree distribution patterns strongly support a common origin for the whole igneous sequence including the leucogranites strontium isotope compositions do not conflict with the above conclusion the oxygen isotopic composition changes progressively with time of emplacement 18 o increases from 7 6 in the granodiorites up to 11 9 in the leucogranites this probably reflects some degree of magma contamination due to assimilation of crustal material the sr and o isotope systematics reveal that the mg gd series is characterized by very small variations of the sr ratio and by pronounced changes in 18 o on account of the rather high sr initial ratios the observed trend is interpreted as due to afc assimilation fractional crystallization processes of a source contaminated parental magma modelling the evolution path from mg to lg in terms of afc processes shows the following a the assumed fractionation steps give realistic mineral assemblages compatible with the observed lithologies b they are able to produce high proportions of both leucogranitic and granodioritic rocks as observed in the field and c they can produce a progressive increase of alumina up to the peraluminous compositions observed in the more evolved members good results were also obtained by modelling the behaviour of trace elements such as rb sr and ba whose distribution is mainly governed by the major mineral phases the geochemical fingerprint of the whole igneous sequence is typical of a k rich calc alkaline series only some rare grey enclaves in the gd 3 granodiorite and in the leucogranites display a typical shoshonitic character their presence probably reflects the open system condition of the deep seated magma reservoir

the origin of pyrenean hercynian volcanic rocks france spain ree and smnd isotope constraints reply abstract the hercynian orogeny of the pyrenees generated a suite of basalt to rhyolite calc alkaline volcanic rocks that were erupted subaerially these melts may either have been generated above a subduction zone or by lower crustal melting after input of mantle derived magmas in an extensional environment sm nd garnet whole rock mineral isochrons date a rhyolitic ignimbrite from the coll de oli ignimbrite member at 313 14 ma 2 mswd 0 7 and a rhyolitic lava of the coll de pi region at 320 2 ma 2 mswd 0 2 these ages suggest that some of the volcanism was synchronous with high temperature low pressure metamorphism and partial melting deep in the hercynian crust as seen in rocks now exposed in the axial and northern pyrenean zones and dated by u pb on zircon at between 309 5 and 315 5 ma the silicic volcanic rocks are peraluminous and have highly fractionated ree patterns with low abundances of the hree and la yb n 70 mineral and whole rock ree abundances suggest derivation of the silicic rocks by partial melting of a metasedimentary source in equilibrium with garnet and or garnet fractionation in melts derived from peraluminous sources nd isotope compositions of the entire volcanic rock suite mafic silicic compositions are within the same range as those of sediments metamorphosed during the hercynian orogeny and hercynian basement rocks they have mid proterozoic depleted mantle model sm nd ages and do not exhibit mixing trends with mantle sources even the most mafic of the volcanic rocks appear to have interacted extensively with the crust analysis of the chemistry of the volcanic rocks does not unequivocally constrain the hercynian tectonic setting of the pyrenees

sensitivity of the boreal winter circulation in the middle atmosphere to the quasi biennial oscillation in maecham5 simulations the polar vortex in the northern hemisphere exhibits high intraseasonal and interannual variability which to some degree may be controlled by the quasi biennial oscillation qbo in the tropical stratosphere here we analyze the qbo signal in the northern hemisphere polar vortex in a model simulation using the general circulation model maecham5 middle atmosphere european center hamburg model which simulates the qbo as an internal mode of variability composites have been computed for the westerly and easterly qbo phases from early winter to late winter november december december january and january february of a 50 year experiment containing 20 complete qbo cycles this method identifies tropical and midlatitude patterns in wind and temperature that are related to the secondary meridional circulation of the qbo extending towards the winter pole in the tropics significant qbo signature is observed in the mesosphere up to 0 05 hpa only in early winter and mainly in the easterly qbo phase forced by the parameterized gravity waves mean flow interaction at high latitudes maecham5 shows a significantly warmer colder polar stratosphere in the easterly westerly qbo phase at 30 hpa accompanied by a weaker stronger polar vortex in the late winter months from december to february december to january in the easterly westerly phase of the qbo in early winter there is no significant change in temperature and zonal mean zonal wind in the polar stratosphere the analysis of ep fluxes shows a different behavior between qbo phases with changes in the waveguide wave propagation occurs upwards and polewards in the easterly qbo phase at 30 hpa while waves are refracted equatorward in the westerly phase no relationship has been found between the tropical qbo and the final warming at the end of the boreal winter

forcing mechanism of the seasonally asymmetric quasi biennial oscillation secondary circulation in era 40 and maecham5 1 the seasonality of the quasi biennial oscillation qbo and its secondary circulation is analyzed in the european reanalysis era 40 and middle atmosphere european centre hamburg model maecham5 general circulation model data sets through the multitaper method singular value decomposition mtm svd in agreement with previous studies the results reveal a strong seasonal dependence of the qbo secondary circulation this is characterized by a two cell structure symmetric about the equator during autumn and spring however anomalies strongly weaken in the summer hemisphere and strengthen in the winter hemisphere leading to an asymmetric qbo secondary circulation characterized by a single cell structure displaced into the winter hemisphere during the solstices in era 40 this asymmetry is more pronounced during the northern than during the southern winter these results provide the first observation of the qbo secondary circulation asymmetries in the era 40 reanalysis data set across the full stratosphere and the lower mesosphere up to 0 1 hpa the mtm svd reconstruction of the seasonal qbo signals in the residual circulation and the qbo signals in eliassen palm ep flux divergences suggest a particular mechanism for the seasonal asymmetries of the qbo secondary circulation and its extension across the midlatitudes the analysis shows that the qbo modulates the ep flux in the winter hemispheric surf zone poleward of the qbo jets the zonal wind forcing by ep flux divergence is transformed by the coriolis effect into a meridional wind signal the seasonality in the stratospheric ep flux and the hemispheric differences in planetary wave forcing cause the observed seasonality in the qbo secondary circulation and its hemispheric differences

nature and composition of the lower continental crust in central spain and the granulite granite linkage inferences from granulitic xenoliths xenolith bearing alkaline ultrabasic dykes were intruded into the of the hercynian basement of the spanish central system in early mesozoic times the suite of lower crustal xenoliths in the dykes divided into three groups felsic peraluminous granulites metapelitic granulites and charnockitic granulites the felsic granulites form 95 of the total volume of the xenoliths whereas the charnockitic and metapelitic granulites are much less abundant 0 01 5 respectively thermobarometric calculations based on mineral paragenesis indicate equilibration conditions around 850 950 c 7 11 kbar thus the xenoliths represent lower continental crustal material superimposed on this high t high p assemblage is a high t low p paragenesis represented mainly by kelyphitic coronas reflecting re equilibration during transport in the clearly restitic mineral assemblages with up to 50 garnet and 37 sillimanite major and trace element modelling supports the idea that the late hercynian peraluminous granites of central spain represent liquids in equilibrium with restitic material of similar composition to the studied lower crustal xenoliths 87sr 86sr and end of the felsic xenoliths calculated at an average hercynian age of 300 ma are in the range 0 706 0 712 and 1 4 to 8 2 respectively these values match the isotopic composition of the outcropping late hercynian granites the sr isotopic composition of the xenoliths is lower than that of the outcropping mid crustal lithologies orthogneisses pelites a major contribution from the lower crust to the source of hercynian granites greatly reduces the necessity of invoking a large mantle contribution in models of granite petrogenesis the felsic nature of the lower continental crust in central spain contrasts with the more mafic lower crustal composition estimated in other european hercynian areas suggesting a non underplated crust in this region of the hercynian orogenic belt

stable isotopic evidence for large scale seawater infiltration in a regional metamorphic terrane the trois seigneurs massif pyrenees france oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a hercynian metamorphic sequence in the trois seigneurs massif pyrenees france indicate that all lithologies at higher metamorphic grades than the andalusite in isograd have relatively homogeneous 18o values the extent of homogenization is shown by the similarity of 18o values in metacarbonates metapelites and granitic rocks 11 to 13 and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies these values contrast with the 18o values of metapelites of lower metamorphic grade 18o about 15 homogenization was caused by a pervasive influx of hydrous fluid mass balance calculations imply that the fluid influx was so large that its source was probably high level groundwaters or connate formation water hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at d 25 to 30 suggesting a seawater origin many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water rich fluid the composition of which was externally buffered deep penetration of surface waters in such environments has been hitherto unrecognized and may be a key factor in promoting major anatexis of the continental crust at shallow depth three types of granitoid are exposed in the area the leucogranites and the biotite granite quartz diorite are both mainly derived from fusion of local paleozoic pelitic metasediment because all these rocks have similar whole rock 18o values 11 to 13 the post metamorphic biotite granodiorite has a distinctly different 18o 9 5 to 10 0 and was probably derived from a deeper level in the crust rare mafic xenoliths within the deeper parts of the biotite granite quartz diorite also have different 18o 8 0 to 8 5 and possibly represent input of mantle derived magma which may have provided a heat source for the metamorphism