variable parent magmas and recharge regimes of the parinacota magma system n chile revealed by fe mg and sr zoning in plagioclase abstract zoning patterns of an content and fe mg and sr concentrations in plagioclase phenocrysts in andesites from parinacota volcano n chile reflect alternating recharge events with two chemically distinct mafic magmas these magmas are characterized by low and high sr contents similar to two recent mafic flank eruptions one end member basaltic andesite shows large sr enrichment and heavy rare earth depletions and thus equilibrated with lower crustal rocks at depth where plagioclase high sr is unstable and garnet high hree y is stable a second end member magma is lower in sr ba contents and has ree patterns typical for parent magmas elsewhere in the central andes the number of recorded recharge events increases after a catastrophic sector collapse and during the subsequent rebuilding of the stratocone variations of an fe and mg contents and morphology of zones suggest also changes in water pressure including decompression under water under saturated and water saturated conditions evidence for decompression is more present in post collapse samples suggesting that the change in the volcano dynamics involves changes in magma chamber location this shows the importance of the cone collapse event in the volcano s magmatic evolution we propose that both end members are only seen at the surface of parinacota volcano because of the particular dynamics of this volcanic system and that similar processes might occur in other volcanic centres of the central volcanic zone

crustal attenuation in the southern andean retroarc 38 39 30 s determined from tectonic and gravimetric studies the lonco luan asthenospheric anomaly abstract the western retroarc of the southern andes between 38 and 40 s is formed by a nnw elongated ridge not associated with stacked thrust sheets on the contrary during the last 4 3 ma this ridge was affected by extensional deformation regional uplift and related folding on a very broad scale receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust expected crustal thickness at these latitudes is around 38 km whereas in this part of the retroarc the thickness is less than 32 km the causes for such attenuation have been linked to a moderate steepening of the subducted nazca plate beneath the south american plate which is suggested by a westward shift and narrowing of the magmatic arc during the last 4 to 5 ma gravimetric studies show that the upper plate did not react homogeneously to slab steepening but ancient sutures and lithospheric discontinuities deeply buried under mesozoic to cenozoic sequences in the retroarc were locally reactivated these processes resulted in an asthenospheric anomaly that correlates at the surface with the area of pliocene to quaternary doming widespread extension and three radial troughs two of the troughs have accommodated substantial amounts of extension but the third was probably aborted at an early stage moreover the presence of an anomalous concentration of calderas and large volcanic centers over the proposed asthenospheric anomaly and their age distribution may indicate minor migration of the asthenospheric anomaly between 4 and 2 ma through the western south american plate

observations of east coast upwelling conditions in synthetic aperture radar imagery seasonal coastal upwelling in the u s mid atlantic coastal ocean normally occurs during the summer months because of generally alongshore southerly wind episodes southerly winds force an offshore surface ekman flow over the inner continental shelf colder and nutrient rich waters from below upwell toward the surface replacing offshore flowing surface waters synthetic aperture radar sar observations from the european remote sensing ers satellite ers 2 before and after upwelling favorable wind episodes in early summer 1996 along the new jersey coast are presented lower backscatter conditions appearing in the sar imagery after the onset of upwelling demonstrate the influence of the upwelling regime on the sea surface roughness satellite sea surface temperature sst observations and in situ sea temperature vertical profiles confirm upwelling conditions three key mechanisms are suggested to explain the lower radar returns observed under upwelling conditions an increase in the atmospheric marine boundary layer stability an increase in the viscosity of surface waters and the presence of biogenic surfactants in the upwelling region

climate variability during the last 2000 years in the tagus prodelta western iberian margin benthic foraminifera and stable isotopes abstract a high resolution sedimentary sequence recovered in the tagus prodelta has been studied in order to reconstruct paleoenvironmental conditions on the western iberian margin portugal through the last ca 2000 years including the historical time when anthropogenic influence became significant benthic foraminiferal assemblages as well as stable isotopic composition of the benthic foraminifera uvigerina sp were investigated considerable environmental fluctuations are indicated by all these proxies between ad 400 and 1400 1550 550 cal year bp during a period including the medieval warm period bottom water temperatures as reconstructed from uvigerina sp were high 13 3 c in this time interval species typical for shelf environments cassidulina laevigata nonion asterizans and hyalinea balthica maintained a high abundance along with opportunistic species like bolivina dilatata and bolivina pacifica the most abundant species in the record a faunal change occurred at around ad 1300 1400 650 550 cal year bp at the beginning of the little ice age after this the environment became more variable in the tagus prodelta as reflected by a decrease in faunal diversity and benthic foraminiferal composition and flux values after about ad 1800 150 cal year bp bottom water temperatures rose to maximum values of the record the disappearance of certain benthic taxa and the appearance of the species saidovina karreriana indicate a change in bottom water conditions during the last 100 years possibly induced by anthropogenic pollution

the mesolithic neolithic transition in southern iberia new data and a review of historiographic information from neolithic sites of the malaga and algarve coasts southern iberian peninsula and from the maghreb north africa reveal the existence of a neolithic settlement at least from 7 5 cal ka bp the agricultural and pastoralist food producing economy of that population rapidly replaced the coastal economies of the mesolithic populations the timing of this population and economic turnover coincided with major changes in the continental and marine ecosystems including upwelling intensity sea level changes and increased aridity in the sahara and along the iberian coast these changes likely impacted the subsistence strategies of the mesolithic populations along the iberian seascapes and resulted in abandonments manifested as sedimentary hiatuses in some areas during the mesolithic neolithic transition the rapid expansion and area of dispersal of the early neolithic traits suggest the use of marine technology different evidences for a maghrebian origin for the first colonists have been summarized the recognition of an early north african neolithic influence in southern iberia and the maghreb is vital for understanding the appearance and development of the neolithic in western europe our review suggests links between climate change resource allocation and population turnover

contractional tectonics and magma paths in volcanoes abstract this study aims to contribute a possible explanation for magma migration within volcanoes located in contractional tectonic settings based on field data and physically scaled experiments the data demonstrate the occurrence of large stratovolcanoes in areas of coeval reverse faulting in spite of the widely accepted idea that volcanism can develop only in extensional transcurrent tectonic settings the experiments simulate the propagation of deformation from substrate reverse faults with different attitudes and locations into volcanoes the substrate fault splits into two main shear zones within the volcano a shallow dipping one with reverse motion propagates towards the lower volcano flank and a steeper dipping one with normal motion propagates upwards in plan view the reverse fault zone is arcuate and convex outwards whereas the normal fault zone is rectilinear structural field surveys at volcanoes located in contractional settings show similar features the plio quaternary trohunco and los cardos centinela volcanic complexes argentina lie above plio quaternary reverse faults the late pleistocene holocene el reventador volcano ecuador is also located in a coeval contractional tectonic belt these volcanoes show curvilinear reverse faults along one flank and rectilinear extensional fracture zones across the crater area consistent with the experiments these data consistently suggest that magma migrates along the substrate reverse fault and is channelled along the normal fault zone across the volcano

rapid changes in magma storage beneath the klyuchevskoy group of volcanoes inferred from time dependent seismic tomography abstract we present the results of time dependent local earthquake tomography for the kluchevskoy group of volcanoes in kamchatka russia we consider the time period from 1999 to 2009 which covers several stages of activity of kluchevskoy and bezymianny volcanoes the results are supported by synthetic tests that recover a common 3d model based on data corresponding to different time windows throughout the period we observe a robust feature below 25 km depth with anomalously high v p v s values up to 2 2 we interpret this feature as a channel bringing deep mantle materials with high fluid and melt content to the bottom of the crust this mantle channel directly or indirectly determines the activity of all volcanoes of the kluchevskoy group in the crust we model complex structure that varies over time during the pre eruptive period we detected two levels of potential magma storage one in the middle crust at 10 12 km depth and one close to the surface just below kluchevskoy volcano in 2005 a year of powerful eruptions of kluchevskoy and besymiyanny volcanoes we observe a general increase in v p v s throughout the crust in the relaxation period following the eruption the v p v s values are generally low and no strong anomalous zones in the crust are observed we propose that very rapid variations in v p v s are most likely due to abrupt changes in the stress and deformation states which cause fracturing and the active transport of fluids these fluids drive more fracturing in a positive feedback system that ultimately leads to eruption we envision the magma reservoirs beneath the kluchevskoy group as sponge structured volumes that may quickly change the content of the molten phases as fluids pulse rapidly through the system

buoyancy driven fracture ascent experiments in layered gelatine laboratory experiments on air filled fracture propagation in solidified homogeneous and layered gelatine have been carried out providing an analogue model for magma filled dikes ascending in the crust the effects of layering on fracture velocity and shape have been analyzed in detail the free surface is found to accelerate approaching fractures layering accelerates or decelerates fractures approaching discontinuities of the elastic parameters depending on the value of the rigidity contrast the shape of fractures are strongly influenced as they pass from one layer to another the observed cross sectional shape when crossing a layer interface and the acceleration with decreasing rigidity can be explained with theoretical models our experiments also reproduce the arrest of fractures in proximity of joints and the formation of sills in the layer below the interface these findings could help in the interpretation of accelerated seismicity and deformation rates observed in volcanic areas

diatoms as upwelling and river discharge indicators along the portuguese margin instrumental data linked to proxy information high resolution diatom and phytolith quantitative and assemblage analyses have been conducted on two box cores from the tagus pro delta sw portuguese margin in order to compare these common palaeoceanographic proxies to instrumental data describing the upwelling regime and the freshwater input of the tagus river the western portuguese margin is affected by seasonal coastal upwelling controlled by northerly winds and by strong freshwater input through the tagus river which is controlled by precipitation over the whole iberian peninsula for both upwelling and freshwater input instrumental data such as river flow and an upwelling index are available for the last 100 and 50 yr respectively diatoms and phytoliths are used as proxies for salinity and productivity changes resulting from river input and upwelling variability comparison of the proxy and instrumental records confirms that diatom abundance and in particular the genus chaetoceros ehrenberg traces the main periods of intense upwelling

transient shallow reservoirs beneath small eruptive centres constraints from mg fe interdiffusion in olivine abstract small eruptive centres commonly have more primitive lavas than those associated with stratovolcanoes an observation that has been taken to indicate a short magma residence in the crust relative to those reservoirs below stratovolcanoes the caburgua cones of the andean southern volcanic zone from a basaltic small eruptive centre where this can be tested here we use melts simulations and the available thermobarometry data to determine the conditions of olivine crystal rim formation and the mg fe diffusion modelling to determine the magma residence times of those rims in the crust results yield timescales varying from a few days to dozens of days and if freezing is to be avoided can only be explained by some form of storage or slow transport through at least one shallow magma body the longest durations of magma residence seen in the olivine rim zones are up to 471 days these timescales are shorter than those estimated decadal from the nearby more differentiated and well established stratovolcano villarrica which has a dominantly basaltic andesite composition for caburgua cones we propose the existence of a transient reservoir in contrast to a long lived reservoir such as that inferred beneath the adjacent villarrica stratovolcano

physical oceanography of the western iberia ecosystem latest views and challenges the present review is focused on the mesoscale physical processes recognized in the western iberia ecosystem complementing earlier reviews dedicated to larger scales recent studies support the idea that the mesoscale processes superimposed on the larger scale variability are the major factor controlling the ecosystem functioning in the region a complex structure of interleaved alongshore slope shelf and coastal currents that interact with eddies buoyant plumes upwelling filaments and fronts surface layer expressions of the subsurface circulation and internal waves is revealed by the latest research all of these contribute in different ways to have an effect on the ecosystem the supposedly less variable winter circulation also exhibits significant mesoscale activity in the form of eddy shedding from the poleward slope current intermittent upwelling events and transient nearshore poleward flows the present incomplete knowledge of this complex system presents a number of challenges and questions that must be addressed if we are to arrive at a satisfactory understanding and predictive capability for the system as a whole 2007 elsevier ltd all rights reserved

position of the polar front along the western iberian margin during key cold episodes of the last 45 ka 1 this paper documents the migration of the polar front pf over the iberian margin during some of the cold climatic extremes of the last 45 ka it is based on a compilation of robust and coherent paleohydrological proxies obtained from eleven cores distributed between 36 and 42 n planktonic 18o globigerina bulloides ice rafted detritus concentrations and the relative abundance of the polar foraminifera neogloboquadrina pachyderma sinistral were used to track the pf position these three data sets compared from core to core show a consistent evolution of the sea surface paleohydrology along the iberian margin over the last 45 ka we focused on five time slices representative of cold periods under distinct paleoenvironmental forcings the 8 2 ka event and the younger dryas two recent cold events occurring within high values of summer insolation heinrich events 1 and 4 reflecting major episodes of massive iceberg discharges into the north atlantic and the last glacial maximum typifying the highest ice volume accumulated in the northern hemisphere for each event we generated schematic maps mirroring past sea surface hydrological conditions the maps revealed that the polar front presence along the iberian margin was restricted to heinrich events the sea surface conditions during the last glacial maximum were close to those at present day except for the northern sites which briefly experienced subarctic conditions

magma ascent rates from amphibole breakdown an experimental study applied to the 1980 1986 mount st helens eruptions recent 1980 1986 mount st helens dacites contain the phenocryst assemblage plagioclase amphibole low ca pyroxene magnetite ilmenite and rare high ca pyroxene which indicates that they all originated from an 8 km deep reservoir at 900 20 c with xh2o 0 67 in fluid according to experimental data iron titanium oxide phenocryst compositions indicate that all post may 18 dacitic magmas erupted at 900 20 c except for the final lava extrusion in october 1986 the magma reservoir may have cooled to 866 c by october 1986 amphiboles in the post may 18 1980 magma contain one or more amphibole populations characterized by reaction rims of different thicknesses the development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir constant p and t and isothermal decompression experiments show that during a 900 c constant rate decompression from 8 km to the surface no reaction rim develops on amphibole in 4 days a 10 m rim develops in 10 days and a 35 m rim develops in 20 days these experimental data and histograms of rim widths in 1980 1986 mount st helens dacites show that post may 18 eruptions are composed in large part of magma represented by a population of thin rimmed amphiboles magma which ascended from the deep 8 km reservoir in 6 to 10 days the remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 m magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly millimeter scale into the erupting magma the mixing in a viscous slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population the experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post may 18 dacites of about 15 30 m h for magma represented by the thick rimmed amphiboles and from 35 to 50 m hr for magma represented by the thin rimmed crystals an ascent rate of 66 m h is indicated for the may 18 1980 eruption which contains amphiboles with no reaction rims the volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath mount st helens in 1981 1982 was equivalent to a cylinder 8 km long and 8 9 m in radius

productivity and paleoceanographic implications on the tore seamount iberian margin during the last 225 kyr foraminiferal evidence foraminifera counts and climatic assemblages from the tore seamount are used to approach the glacial and interglacial changes in temperature and productivity on the iberian margin over the last 225 kyr chronostratigraphy is based on globigerinoides ruber and globigerina bulloides oxygen isotopes and supported by foraminifera and carbonate stadial fluctuations foraminifera indicate cooling from late interglacial stage 5 to the beginning of termination i ti neogloboquadnna pachyderma s reflects cold conditions during glacial stages 4 2 in contrast glacial stage 6 is dominated by warmer n pachyderma d and dutertrei and a restricted arctic assemblage past sea surface temperatures confirm the general cooling reaching 4 3 c simmax 28 during stage 2 multiple productivity proxies such as organic carbon productivity related foraminifera and 13c constrain the changes observed a productivity increase occurs after interglacial stage 5 enhanced from late glacial stage 3 to ti present day satellite detected phytoplankton plumes off portugal would have accounted in the past glacial stages for the general productivity increase over the tore on top of this welldefined peaks of organic carbon and productivity related foraminifera correspond with heinrich events 1 4

high frequency surface water changes in the tagus prodelta off lisbon eastern north atlantic during the last two millennia abstract a high resolution sedimentary sequence recovered from the tagus prodelta has been studied with the objective to reconstruct multi decadal to centennial scale climate variability on the western iberian margin and to discuss the observations in a wider oceanographic and climatic context between ca 100 bc and ad 400 the foraminiferal fauna and high abundance of globorotalia inflata indicate advection of subtropical waters via the azores current and the winter time warm portugal coastal current between ca ad 400 and 1350 encompassing the medieval climate anomaly mca enhanced upwelling is indicated by the planktonic foraminiferal fauna in particular by the high abundance of upwelling indicator species globigerina bulloides relatively light 18o values and high sea surface temperature sst reconstructed from foraminiferal assemblages point to upwelling of subtropical eastern north atlantic central water between ca ad 1350 and 1750 i e most of the little ice age relatively heavy 18o values and low reconstructed sst as well as high abundances of neogloboquadrina incompta indicate the advection of cold subpolar waters to the area and a southward deflection of the subpolar front in the north atlantic as well as changes in the mode of the north atlantic oscillation in addition the assemblage composition together with the other proxy data reveals less upwelling and stronger river input than during the mca stronger azores current influence on the iberian margin and strong anthropogenic effect on the climate after ad 1750 is indicated by the foraminiferal fauna the foraminiferal assemblage shows a significant change in surface water conditions at ca ad 1900 including enhanced river runoff a rapid increase in temperature and increased influence of the azores current the tagus record displays a high degree of similarity to other north atlantic records indicating that the site is influenced by atmospheric oceanic processes operating throughout the north atlantic as well as by local changes

contrasting nature of deformation along an intra arc shear zone the liquine ofqui fault zone southern chilean andes abstract the liquine ofquifault zone lofz cuts the patagonian batholith and the modern volcanic arc of southern chile for ca 1000 km the rock fabric along three transects of the lofz combined with new and published geochronological data suggest marked differences in the nature and timing of deformation along strike in the liquine transect 39 s a 1 km wide northeast striking subvertical mylonitic zone shows north plunging stretching lineations this mylonitic zone has been juxtaposed by high angle reverse faulting against a nearly undeformed miocene granitoid metamorphic assemblages and microstructures in the mylonites indicate greenschist facies conditions and sinistral reverse displacement deformation pre dates a 100 2 ma undeformed porphyritic dike hornblende 40ar 39ar mean age in the reloncavi transect 41 42 s deformation in cretaceous and miocene plutons is predominantly brittle kinematic analysis of two fault populations yields compressional and dextral strike slip stress regimes interpreted as late miocene in age in the hornopiren transect 42 43 s a 4 km wide mylonitic zone developed in plutons and wallrocks shows subhorizontal stretching lineations and dextral displacement a single fault population overprinting the mylonites supports a dextral strike slip stress regime available u pb k ar and 40ar 39ar dates on deformed cenozoic plutons and wallrock range from 9 to 13 ma on hornblende and from 6 to 3 ma on biotite microstructures and mineral assemblages indicate that the youngest ductile fabrics in the plutons formed at greenschist facies similar to the biotite ar closure temperature subparallel magmatic and solid state fabrics combined with geochronology suggest that dextral displacement was continuous during emplacement and cooling of the plutons dextral oblique subduction of the nazca plate beneath western south america has driven long term intra arc deformation at the southern andes plate boundary zone ridge collision in turn has favored dextral displacement at the leading edge of the continent since the pliocene

tectonic stress controls on ascent and emplacement of magmas abstract the tectonic stresses can significantly affect the propagation of a magma filled crack it has been pointed out that the rheological boundaries control the emplacement of magmas through the effect of stress however it has not been clarified how the role of rheological boundaries depends on the regional tectonic and thermal states we have evaluated the role of rheological boundaries under various tectonic and thermal conditions and found that the level of magma emplacement may jump according to the changes in the tectonic force or the surface heat flow the stress profiles were estimated by a simple model of lithospheric deformation we employed a three layer model of the lithosphere the upper crust the lower crust and the upper mantle have different rheological properties a constant horizontal force is applied to the lithosphere and the horizontal strain is assumed to be independent of depth when realistic tectonic forces 10 11 n m are applied the rheological boundaries mainly control the emplacement of magma the emplacement is expected at the moho the upper lower crust boundary and the brittle ductile boundary for lower tectonic forces 11 n m the tectonic stress no longer plays an important role in the emplacement of magmas when the tectonic stress controls the emplacement the roles of rheological boundaries strongly depend on the surface heat flow when the surface heat flow is relatively high 80 mw m 2 the stress in the mantle is quite low and the moho cannot trap ascending magmas for relatively low heat flow 2 on the other hand the moho acts as a magma trap and the upper lower crust boundary acts as a magma trap only when the magma supply rate is sufficiently high our results suggest that the emplacement depth can change responding to the change in the tectonic force and or that in the surface heat flow this may provide us a key to understand the relation between the evolution of a volcanic region and its tectonic and or thermal history

shallow marine sediment cores record climate variability and earthquake activity off lisbon portugal for the last 2000 years abstract sea surface temperature sst river discharge and biological productivity have been reconstructed from a multi proxy study of a high temporal resolution sedimentary sequence recovered from the tagus deposition center off lisbon portugal for the last 2000 years sst shows 2 c variability on a century scale that allows the identification of the medieval warm period mwp and the little ice age lia high iron fe and fine sediment deposition accompanied by high n alkane concentrations and presence of freshwater diatoms during the lia 1300 1900 ad science 292 2001 662 suggest augmented river discharge whereas higher total alkenone concentrations point to increased river induced productivity during the mwp 550 1300 ad science 292 2001 662 larger mean grain size and low values of magnetic susceptibility and concentrations of fe n alkanes and n alcohols are interpreted to reflect decreased runoff at the same time increased benthic and planktonic foraminifera abundances and presence of upwelling related diatoms point to increased oceanic productivity on the basis of the excellent match found between the negative phases of the north atlantic oscillation nao index and the intensified tagus river discharge observed for the last century it is hypothesized that the increased influx of terrigenous material during the lia reflects a negative nao like state or the occurrence of frequent extreme nao minima during the milder few centuries of the mwp stronger coastal upwelling conditions are attributed to a persistent positive nao like state or the frequent occurrence of extreme nao maxima the peak in magnetic susceptibility centered at 90 cm composite core depth ccd is interpreted as the result of the well known 1755 ad lisbon earthquake the lisbon earthquake and accompanying tsunami are estimated to have caused the loss of 39 cm of sediment 355 years of record most of the lia and the instantaneous deposition of a 19 cm sediment bed

the link between volcanism and tectonics in the southern volcanic zone of the chilean andes a review abstract the nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics the southern andes volcanic zone svz located at the obliquely convergent nazca south america plate margin between 33 s and 46 s offers a unique opportunity to address this question because of along strike changes in crustal thickness tectonic style and well constrained long term and short term kinematic history the complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems main first order factors accounting for the along strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major intra arc fault system the liquine ofqui fault zone lofz second order factors include the local nature of the volcanic arc basement two main categories of volcano tectonic associations have been identified according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second order active inactive basement faults kinematically coupled associations those that are directly related to the current dextral transpressional tectonic regime include ne trending volcanic alignments of stratovolcanoes and or monogenetic cones kinematically uncoupled associations in which coupling with the current regime is not required include stratovolcanoes built on top of ancient reverse and strike slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the lofz whereas mostly primitive magmas are found in the first category more evolved terms can occur genetically associated with the second category we propose a simplified three dimensional model for the magma plumbing system along and across the svz that integrates kinematically coupled and kinematically uncoupled volcano tectonic associations within the framework of first and second order geological and structural constraints

timescales of mixing and mobilisation in the bishop tuff magma body perspectives from diffusion chronometry we present two feldspar thermometry and diffusion chronometry from sanidine orthopyroxene and quartz from multiple samples of the bishop tuff california to constrain the temperature stratification within the pre eruptive magma body and the timescales of magma mixing prior to its evacuation two feldspar thermometry yields estimates that agree well with previous fe ti oxide thermometry and gives a 80 c temperature difference between the earlier and later erupted regions of the magma chamber using the thermometry results we model diffusion of ti in quartz and ba and sr in sanidine as well as fe mg interdiffusion in orthopyroxene to yield timescales for the formation of overgrowth rims on these crystal phases diffusion profiles of ti in quartz and fe mg in orthopyroxene both yield timescales of 150 years for the formation of overgrowth rims in contrast both ba and sr diffusion in sanidine yield nominal timescales 1 2 orders of magnitude longer than these two methods the main cause for this discrepancy is inferred to be an incorrect assumption for the initial profile shape for ba and sr diffusion modelling i e growth zoning exists utilising the divergent diffusion behaviour of ba and sr we place constraints on the initial width of the interface and can refine our initial conditions considerably bringing ba and sr data into alignment and yielding timescales closer to 500 years the majority of which are then within uncertainty of timescales modelled from ti diffusion in quartz care must be thus taken when using ba in sanidine geospeedometry in evolved magmatic systems where no other phases or elements are available for comparative diffusion profiling our diffusion modelling reveals piecemeal rejuvenation of the lower parts of the bishop tuff magma chamber at least 500 years prior to eruption timescales from our mineral profiling imply either that diffusion coefficients currently used are uncertain by 1 2 orders of magnitude or that the minerals concerned did not experience a common history despite being extracted from the same single pumice clasts introduction of the magma initiating crystallisation of the contrasting rims on sanidine quartz orthopyroxene and zircon was prolonged and may be a marker of other processes that initiated the bishop tuff eruption rather than the trigger itself

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

the liquine ofqui fault zone a long lived intra arc fault system in southern chile abstract plate reconstructions for the cenozoic document relatively steady right oblique subduction of the farallon nazca plate beneath the chilean continental margin the kinematic signature recorded along the intra arc liquine ofqui fault zone lofz a major feature of the southern andes may help to understand the way in which the nazca south america slip vector has been partitioned into strain and displacement along and across the continental margin the lofz consists of two nne trending right stepping straight lineaments a strike slip duplex at the right step and curved features which splay off the straight lineaments toward the northwest the lofz runs mostly through heterogeneously deformed cenozoic plutonic rock of the north patagonian batholith and patchy metamorphic wall rock early cenozoic volcano sedimentary rocks and dyke swarms found in close spatial association with the strike slip duplex are believed to have developed in strike slip related basins quaternary volcanoes are aligned parallel to the lofz both ductile and brittle kinematic indicators within centimeter to meter wide high strain zones document late cenozoic dextral shear deformation contrasting left lateral deformation recorded on older and wider mylonitic zones suggests that the lofz may be a long lived shear zone that accommodated continental scale deformation arising from the farallon nazca south america plate convergence a block rotation pattern as indicated by paleomagnetic data is consistent with the geometry and cenozoic kinematics of the lofz

fe mg interdiffusion rates in clinopyroxene experimental data and implications for fe mg exchange geothermometers chemical interdiffusion of fe mg along the c axis 001 in natural diopside crystals x di 0 93 was experimentally studied at ambient pressure at temperatures ranging from 800 to 1 200 c and oxygen fugacities from 10 11 to 10 17 bar diffusion couples were prepared by ablating an olivine x fo 0 3 target to deposit a thin film 20 100 nm onto a polished surface of a natural oriented diopside crystal using the pulsed laser deposition technique after diffusion anneals compositional depth profiles at the near surface region 400 nm were measured using rutherford backscattering spectroscopy in the experimental temperature and compositional range no strong dependence of d fe mg on composition of clinopyroxene fe mg ratio between di93 di65 or oxygen fugacity could be detected within the resolution of the study the lack of fo2 dependence may be related to the relatively high al content of the crystals used in this study diffusion coefficients d fe mg can be described by a single arrhenius relation with d text fe text mg 2 7 7 pm 4 2 7 times 10 7 text exp 3 20 7 pm 1 6 0 text kj text mol text rt m 2 text s d fe mg in clinopyroxene appears to be faster than diffusion involving ca species e g d ca mg while it is slower than d fe mg in other common mafic minerals spinel olivine garnet and orthopyroxene as a consequence diffusion in clinopyroxene may be the rate limiting process for the freezing of many geothermometers and compositional zoning in clinopyroxene may preserve records of a higher compared to that preserved in other coexisting mafic minerals temperature segment of the thermal history of a rock in the absence of pervasive recrystallization clinopyroxene grains will retain compositions from peak temperatures at their cores in most geological and planetary settings where peak temperatures did not exceed 1 100 c e g resetting may be expected in slowly cooled mantle rocks many plutonic mafic rocks or ultra high temperature metamorphic rocks

a middle pleistocene northeast atlantic coccolithophore record paleoclimatology and paleoproductivity aspects abstract changes in paleoclimate and paleoproductivity patterns have been identified by analysing in conjunction with other available proxy data the coccolithophore assemblages from core md03 2699 located in the portuguese margin in the time interval from the marine isotope stage mis 13 14 boundary to mis 9 535 to 300 ka during the mid brunhes event the assemblages associated with the eccentricity minima are characterised by higher nannoplankton accumulation rate nar values and by the blooming of the opportunistic genus gephyrocapsa changes in coccolithophore abundance are also related to glacial interglacial cycles higher nar and numbers of coccoliths g mainly occurred during the interglacial periods while these values decreased during the glacial periods superimposed on the glacial interglacial cycles climatic and paleoceanographic variability has been observed on precessional timescales the structure of the assemblages highlights the prevailing long term influence of the portugal pc and iberian poleward ipc currents following half and full precession harmonics related to the migration of the azores high ah pressure system small gephyrocapsa and coccolithus pelagicus braarudii are regarded as good indicators for periods of prevailing pc influence gephyrocapsa caribbeanica syracosphaera spp rhabdosphaera spp and umbilicosphaera sibogae denote periods of ipc influence our data also highlights the increased percentages of coccolithus pelagicus pelagicus during the occurrence of episodes of very cold and low salinity surface water probably related to abrupt climatic events and millennial scale oscillations of the ah icelandic low il system

volcanism in a compressional andean setting a structural and geochronological study of tromen volcano neuquen province argentina we document evidence for growth of an active volcano in a compressional andean setting our data are surface structures and 39ar 40ar ages of volcanic products on tromen volcano tromen is an active back arc volcano in the andean foothills of neuquen province argentina its volcanic products are unconformable upon mesozoic strata of the neuquen basin the volcano straddles a n s trending pop up which formed during e w shortening the main underlying structures are eastward verging thrusts their traces curve around the eastern foot of the volcano minor folds and faults also occur in the volcanic cover of tromen as a result of e w shortening new 39ar 40ar ages for these volcanic rocks are younger than 2 27 0 10 ma and show that tromen has been active almost continuously from the late pliocene to the holocene we conclude that volcanism and thrusting have been coeval and that magma must have reached the surface in a tectonic setting of horizontal compression our results have wider implications for magmatic processes in such settings

identification of upwelling areas on sea surface temperature images using fuzzy clustering abstract sixteen sea surface temperature sst images obtained over the coastal ocean of portugal during the period september 1992 september 2003 were used aiming to identify automatically the areas covered by upwelling waters suitable high resolution colour scales were applied to the sst images in order to enhance the thermal patterns and easily identify the waters with a coastal upwelling origin the automatic identification of the areas covered by upwelling waters was developed by the authors in a previous work through the application of fuzzy clustering and validation indexes and here is explored as an oceanographic application to the portuguese coastal upwelling the fuzzy c means fcm algorithm showed to be able to find partitions that closely defined the upwelling areas and the visualization of the fuzzy c partitions was achieved through the application of a colour scale the xie beni validation index was used to select the c partition that best represented the stage of the upwelling event and showed an agreement with the oceanographic interpretation in 10 of the 14 sst segmented images used in this work two sst images without upwelling were also used in order to check the response of the algorithm to the absence of the phenomena the computation of the matching rate between a c partition and the two areas split by the hand contoured upwelling boundary also allowed the evaluation of how closely the obtained segmentation reproduced the shape of the areas covered by upwelling waters this method successfully identified the upwelling boundary regions in 10 of the 14 sst images the values obtained for the matching rate were higher than 0 77 thus indicating the good quality of the fuzzy partitions the segmented images with 3 or 4 clusters were the most suitable ones to reproduce the areas covered by upwelling waters but it was also shown that for some cases the upwelling areas could be reasonably well reproduced by the fcm 2 partition images while in the latter the area covered with upwelling waters was coincident with the first cluster in the former the segmented image showed two clusters within the upwelling area the first cluster coincided with the area occupied by the most recently upwelled waters near the coast while the second cluster was coincident with the area occupied by the older upwelling waters with its extensions offshore the so called cold filaments the fcm algorithm revealed to be a promising technique in the automatic identification of upwelling areas on sst images

twentieth century warming and hydrographical changes in the tagus prodelta eastern north atlantic pluri annualproxyrecordsofmarinesedimentcoresfromthetagusprodeltaofflisbon portugal havebeengeneratedtogaininsightintotheclimaticandhydrographicchangesintheareaduringthetwentieth century thestudyincludesbenthicandplanktonicforaminiferalfaunasandthestableisotopiccompositionof one benthic uvigerina celtica and two planktonic globigerina bulloides and globorotalia inflata foraminiferal species sea bottom and surface water temperatures were estimated based on the 18 o values of

hydrographic conditions along the western iberian margin during marine isotope stage 2 the surface water hydrography along the western iberian margin as part of the north atlantic s eastern boundary upwelling system consists of a complex seasonally variable system of equatorward and poleward surface and subsurface currents and seasonal upwelling not much information exists to ascertain if the modern current and productivity patterns subsisted under glacial climate conditions such as during marine isotope stage mis 2 and how north atlantic meltwater events especially heinrich events affected them to help answer these questions we are combining stable isotope records of surface to subsurface dwelling planktonic foraminifer species with sea surface temperature and export productivity data for four cores distributed along the western and southwestern iberian margin md95 2040 md95 2041 md99 2336 and md99 2339 the records reveals that with the exception of the heinrich events and greenland stadial gs 4 hydrographic conditions along the western iberian margin were not much different from the present during the last glacial maximum lgm subtropical surface and subsurface waters penetrated poleward to at least 40 6 n site md95 2040 export productivity was in general high on the western margin during the lgm and low in the central gulf of cadiz in agreement with the modern situation during the heinrich events and gs 4 on the other hand productivity was high in the gulf of cadiz and suppressed in the upwelling regions along the western margin where a strong halocline inhibited upwelling heinrich event 1 had the strongest impact on the hydrography and productivity off iberia and was the only period when subarctic surface waters were recorded in the central gulf of cadiz south of lisbon 39 n the impact of the other heinrich events was diminished and not all of them led to a significant cooling in the surface waters thus climatic impacts of heinrich events highly varied with latitude and the prevailing hydrographic conditions in this region

controls on conduit magma flow dynamics during lava dome building eruptions 1 lava dome eruptions commonly display fairly regular alternations between periods of high and low or no activity with timescales typically of weeks to years and sudden transitions between effusive and explosive activity we develop a transient model of the magma flow in a volcanic conduit from an open system magma chamber with continuous replenishment the model incorporates gas exsolution bubble growth gas escape through the magma and decompression induced crystallization and considers variations in magma temperature water content conduit diameter phenocryst size chamber volume and magma rheology calculations show the presence of periodic variations in discharge rate due to the transition from a stable regime when discharge rate is low and crystals grow efficiently leading to high magma viscosity to another stable state when discharge rate is high and crystallization is negligible the difference in discharge rates between these regimes can be several orders of magnitude periods are similar to the observed timescales and mainly depend on the chamber volume the system shows strongly nonlinear responses to the variation of governing parameters if magma has a bingham rheology pauses in discharge rate occur between peaks of discharge and the peaks are much higher than for the case of newtonian rheology large changes in discharge rate and eruptive behavior can occur as the consequence of small changes in magma temperature water content phenocryst size distribution or conduit diameter the system can fluctuate between low and high discharge rates with transitions to explosive activity

pre eruptive reheating during magma mixing at quizapu volcano and the implications for the explosiveness of silicic arc volcanoes effusive explosive transitions are observed in volcanoes erupting water rich magmas that lack mineralogical evidence of degassing suggesting that gas loss occurred rapidly and ascent was fast despite the high viscosity of rhyodacitic to rhyolitic melts here we show that pre eruptive heating of water rich silicic magma by mixing with hot recharge in subvolcanic chambers controls the effusive explosive transition volcan quizapu chile emitted a 5 km3 mingled dacite andesite lava flow in a d 1846 1847 that was 130 c hotter than the 5 km3 of the same dacite that lead to a plinian eruption in a d 1932 we explain the suppression of explosive fragmentation in the 1846 1847 lavas by enhanced syneruptive magma degassing as a consequence of late reheating following mixing with andesite recharge higher magma temperatures led to the transitioning into effusive eruptive behavior by significantly accelerating volatile diffusion and lowering melt viscosity which facilitated bubble nucleation growth and coalescence while also inhibiting brittle fragmentation thus recharge by mafic magmas in subvolcanic magma chambers may reduce the risk of explosive eruptions in cases where heat can be efficiently transferred to cold volatile rich silicic magmas

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

volcanism in compressional tectonic settings is it possible 1 this study presents the first field evidence of emplacement of a huge stratovolcano within contractional tectonics in spite of the widely accepted idea that volcanism can develop only in extensional or transcurrent tectonic settings el reventador volcano ecuador started to grow 0 32 ma bp and is still active during pre el reventador times its substratum has been affected by n s to nne striking reverse faults during late pleistocene holocene some reverse faults with the same orientations were still active locally with a component of right lateral strike slip motions seismicity shows widespread events with intensity up to 6 9 mw and compression some of these faults cut the volcano creating differential uplift along n s to nne trending tectonic blocks hypocenter swarms and field data indicate east vergent basal thrusting under the volcano and n s trending fault propagation folds to the east a model for magma migration in this setting is proposed suggesting that similar cases of volcanism within a dominantly contractional tectonic regime may be more frequent than previously thought

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

satellite derived phytoplankton pigment structures in the portuguese upwelling area a series of 25 nimbus 7 coastal zone color scanner images obtained from july 1981 to september 1983 in portuguese coastal waters was analyzed in order to study the space time distribution of phytoplankton pigment in the images from winter and spring the phytoplankton distributions showed no significant spatial patterns during the upwelling season from late june to october several recurrent patterns were observed filaments of high pigment concentration extended zonally 200 km off the west coast of portugal north of lisbon pigment rich plumes were observed south of capes along the west coast south of lisbon and parallel to the south coast of portugal the location of the filaments and plumes coincided with topographic features such as submarine ridges south of lisbon the location of plumes was also related to coastal morphology the temporal variability of the pigment patterns was compared with the wind induced offshore ekman transport calculated from measurements made at two meteorological stations located at lisbon and faro on the south coast a significant relationship was found well developed phytoplankton structures were generally related to moderate or intense offshore transport whereas the absence of plumes corresponded to either weak offshore transport or coastal convergence for each of the three coastal areas in this study scatter plots showed linear relationships between digital counts of phytoplankton concentration and sea surface temperature the spatial variation of the temperature range decreased in time after the onset of an upwelling event one cause of this variation could be the north south change in temperature of the upwelled eastern north atlantic central water along the portuguese coast

dynamic plumbing system beneath volcanoes revealed by kinetic modeling and the connection to monitoring data an example from mt etna abstract our ability to monitor volcanoes using seismic signals ground deformation gas fluxes or other ground and satellite based observations as well as our understanding of melt reservoirs that feed eruptions have evolved tremendously in recent years the complex plumbing systems that are thought to feed eruptions are however difficult to relate to the monitoring signals here we show that the record preserved in compositional zoning of erupted minerals may be used to reconstruct sections of the plumbing system kinetic modeling of such zoning can yield information on the residence time of magma in different segments of the plumbing systems this allows a more nuanced evaluation of the link between observed monitoring signals or eruption styles and the magmatic processes and movement of batches of melts at depth the approach is illustrated through a study of the compositional zoning recorded in olivine crystals from the 1991 1993 se flank eruption products of mt etna sicily the zoning patterns in crystals reveal that the plumbing system of the volcano consisted of at least three different magmatic environments between which magma was transported and mixed in the year or two preceding the start of eruption quantification of this history indicates that two main pathways of melt migration and three timescales dominated the dynamics of the system combination of this information with the timing of observation of various monitoring signals allows a reconstruction of the dynamic evolution of this section of the plumbing system during the early stages of the 1991 1993 eruption it is seen for example how the migration of melt through the same sections of the plumbing system can cause pre eruptive triggering enhance strombolian activity and through the ensuing eruption cleanse and flush the plumbing system different kinds of mixing occur simultaneously at different sections of the plumbing system on different timescales a few days up to two years

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

spatiotemporal evolution of upwelling regime along the western coast of the iberian peninsula 1 the spatial and temporal variability of upwelling regime along the western coast of the iberian peninsula ip has been analyzed by means of two different but complementary databases quikscat satellite database which is available from mid 1999 with a high spatial resolution 0 25 0 25 and pacific fisheries environmental laboratory pfel database with a coarser spatial resolution 1 1 but extending back to 1967 the combined use of both databases allows determination of the spatial variability of ekman transport and pumping and identification of temporal trends in upwelling signal upwelling favorable conditions are observed during spring and summer apart from this well known seasonality on upwelling regime along the western coast of the ip some other features have been identified 1 upwelling occurs simultaneously along the entire western coast of the ip but is undoubtedly more complex closer to particular features of the shoreline 2 positive ekman pumping is more intense near capes sao vicente and rocha during spring summer and near cape finisterre all over the year 3 more favorable upwelling conditions have been observed in february and november during the last decade this result is corroborated by sea level pressure composites which show the existence of abnormally high pressures close to the ip during the last decade compared to the historical records 1948 2006 4 the decadal variability of ui is higher in autumn winter than in spring summer 5 monthly upwelling trends indicate a weakening in upwelling intensity during most of the year with the exception of february june and july

proxy calibration to instrumental data set implications for paleoceanographic reconstructions 1 high resolution proxy data analyzed on two high sedimentation shallow water sedimentary sequences po287 26b and po287 28b recovered off lisbon portugal provide the means for comparison to long term instrumental time series of marine and atmospheric parameters sea surface temperature sst precipitation total river flow and upwelling intensity computed from sea level pressure and the possibility to do the necessary calibration for the quantification of past climate conditions xrf fe is used as proxy for river flow and the upwelling related diatom genus chaetoceros is our upwelling proxy sst is estimated from the coccolithophore synthesized alkenones and u37k index comparison of the fe record to the instrumental data reveals its similarity to a mean average run of the instrumentally measured winter jfma river flow on both sites the upwelling diatom record concurs with the upwelling indices at both sites however high opal dissolution below 20 25 cm prevents its use for quantitative reconstructions alkenone derived sst at site 28b does not show interannual variation it has a mean value around 16 c and compares quite well with the instrumental winter spring temperature at site 26b the mean sst is the same but a high degree of interannual variability up to 4 c appears to be determined by summer upwelling conditions stepwise regression analyses of the instrumental and proxy data sets provided regressions that explain from 65 to 94 of the variability contained in the original data and reflect spring and summer river flow as well as summer and winter upwelling indices substantiating the relevance of seasons to the interpretation of the different proxy signals the lack of analogs and the small data set available do not allow quantitative reconstructions at this time but this might be a powerful tool for reconstructing past north atlantic oscillation conditions should we be able to find continuous high resolution records and overcome the analog problem

temperature and productivity changes off the western iberian margin during the last 150 ky abstract present day hydrographic conditions along the western iberian margin are characterized by seasonal upwelling with filaments that can penetrate more than 200 km into the open ocean and constitute areas of cold and highly productive waters in order to investigate spatial and temporal gradients in temperature and productivity conditions during the last 150 ky high resolution proxy records were generated in 3 cores su92 03 md95 2040 md95 2042 located along the iberian coast between 43 12 n and 37 48 n and forming a n s profile in all cores planktonic foraminifera census counts are used to reconstruct summer sea surface temperature sstsu and export productivity pexpsu using the modern analog technique simmax 28 sstsu and pexpsu values similar to the present are observed throughout the holocene and mis 5e periods for each site respectively indicating fairly stable conditions equivalent to the modern ones on glacial interglacial timescales sstsu increases by 2 3 c from the northern to southernmost site pexpsu on the other hand shows a decrease of 30 40 gc m2 yr from north to south at present time and during interglacial periods and no significant variation 90 100 gc m2 yr during glacial periods the northernmost core su92 03 reveals the coldest conditions with records more similar to md95 2040 than to md95 2042 the later of which is as at present more affected by subtropical waters core su92 03 shows higher interglacial productivity similar to open ocean mid to high latitude sites while the other two cores monitor higher glacial productivity conform with other upwelling sites off nw africa a boundary between differences in glacial interglacial productivity appears to be present in our study between 43 12 n and 40 35 n especially north of 40 n coldest sstsu and lowest pexpsu are found during heinrich events h 1 h8 and h10 h11 in contrast lowest pexpsu do not coincide with these events at site md95 2042 but appear to be related to the presence of relatively warm and nutrient poor subtropical eastern north atlantic central water advected with the azores current

interaction between forearc and oceanic plate at the south central chilean margin as seen in local seismic data we installed a dense amphibious temporary seismological network to study the seismicity and structure of the seismogenic zone in southern chile between 37 and 39 s the nucleation area of the great 1960 chile earthquake 213 local earthquakes with 14 754 onset times were used for a simultaneous inversion for the 1 d velocity model and precise earthquake locations relocated artificial shots suggest an accuracy of the earthquake hypocenter of about 1 km horizontally and 500 m vertically crustal events along trench parallel and transverse deep reaching faults reflect the interseismic transpressional deformation of the forearc crust due to the subduction of the nazca plate the transverse faults seems to accomplish differential lateral stresses between subduction zone segments many events situated in an internally structured planar seismicity patch at 20 to 40 km depth near the coast indicate a stress concentration at the plate s interface at 38 s which might in part be induced by the fragmented forearc structure

structural controls of volcanism in transversal chains resheared faults and neotectonics in the cordon caulle puyehue area 40 5 s southern andes abstract the nature of the relationship between tectonics and volcanism in a specific area is the result of the interaction between the crustal structures of the basement and ongoing regional stress field in the southern andes different kinematic environments represented by two nearly orthogonal active fissure systems show apparently incompatible arrays of volcanic chains moreover a local quaternary compressive regime is inferred from basement faults however these mutually orthogonal chains which are also oblique to the volcanic front have contrasting magma evolution and eruptive styles that can be related with their tectonic setting whereas northeast trending monogenetic cones carran los venados can be interpreted as resulting from magma upwelling along regional tension cracks in a quaternary dextral transpressive compressive domain northwest striking fissure system cordon caulle volcanic complex can be the result of extensional fault reactivation and long magma residence in the upper crust different kinematic environments cause contrasting magma evolution and eruptive styles a two way coupling mechanism is suggested for to explain local depart of the regional stress field geometric array of extensional features and final magmatic evolution in these volcanic domains of the southern andes

geochemical variations in andean basaltic and silicic lavas from the villarrica lanin volcanic chain 39 5 s an evaluation of source heterogeneity fractional crystallization and crustal assimilation at 39 5 s in the southern volcanic zone of the andes three pleistocene recent stratovolcanoes villarrica quetrupillan and lanin form a trend perpendicular to the strike of the andes 275 to 325 km from the peru chile trench basalts from villarrica and lanin are geochemically distinct the latter have higher incompatible element abundances and la sm but lower ba la and alkali metal la ratios these differences are consistent with our previously proposed models involving a a west to east decrease in an alkali metal rich high ba la slab derived component which causes an across strike decrease in degree of melting or b a west to east increase in the contamination of subduction related magma by enriched subcontinental lithospheric mantle silicic and mafic lavas from the stratovolcanoes have overlapping sr nd and o isotopic ratios silicic lavas also have geochemical differences that parallel those of their associated basalts e g rhyolite from villarrica has lower la sm and incompatible element contents than high sio2 andesite from lanin at each volcano the most silicic lavas can be modelled by closed system fractional crystallization while andesites are best explained by magma mixing apparently crustal contamination was not an important process in deriving the evolved lavas basaltic flows from small scoria cones 20 35 km from villarrica volcano have high incompatible element contents and low ba la like lanin basalts but trend to higher k rb 356 855 and lower 87sr 86sr 0 70361 0 70400 than basalts from either stratovolcano however all basalts have similar nd pb and o isotope ratios the best explanation for the unique features of the cones is that the sources of svz magmas e g slab derived fluids or melts of the subcontinental lithospheric mantle have varying alkali metal and radiogenic sr contents these heterogeneities are not manifested in stratovolcano basalts because of extensive subcrustal pooling and mixing this model is preferable to one involving crustal contamination because it can account for variable sr isotope ratios and uniform nd and pb isotope ratios among the basalts and the divergence of the cones from across strike geochemical trends defined by the stratovolcanoes

at the land s end marine resources and the importance of fluctuations in the coastline in the prehistoric hunter gatherer economy of portugal abstract this paper focuses on the importance of aquatic resources in economy and subsistence strategies during the middle and upper palaeolithic of portugal modern theoretical biases in archaeology have led to a marginalization of marine resources and a dismissal of their use by palaeolithic hunter gatherers geological and archaeological data show that changes in the position of the coastline had a direct impact on the visibility of marine resources in the archaeological record marine regressions and transgressions have significantly altered the record of pleistocene coastal settlement using recent studies on changes in upwelling intensity during the last glacial we offer a new perspective on palaeolithic hunter gatherer economy that emphasizes the importance of the coast as a focus of subsistence and settlement

seismicity near the slip maximum of the 1960 mw 9 5 valdivia earthquake chile plate interface lock and reactivation of the subducted valdivia fracture zone understanding the processes behind subduction related hazards is an important responsibility and major challenge for the earth sciences few areas demonstrate this as clearly as south central chile where some of the largest earthquakes in human history have occurred we present the first observation of local seismicity in the villarrica region 39 40 s based on a temporary local network of 55 stations installed from the chilean coast into the argentinian back arc for one year while consistent with the chilean national catalog ssn our results allow us to observe smaller magnitudes with a completeness of about 2 0 and image the geometry of the wadati benioff zone from the chile trench down to 200 km offshore a gap in interplate seismicity is observed in the region of the 1960 valdivia earthquake slip above the interface two offshore seismicity clusters possibly indicate ongoing stress relaxation in the subducting nazca plate we find a prominent seismicity cluster along the extrapolated trace of the oceanic valdivia fracture zone vfz the seismicity cluster is observed between 70 and 130 km depth and comprises mainly strike slip events it indicates weakening and reactivation of the major vfz by dehydration of oceanic crust and mantle interpreting the subducted vfz section as a localized reservoir of potential fluid release offers an explanation for the villarrica volcanic complex that is located above the reactivated vfz and shows the highest volcanic activity in south america crustal seismicity is observed near puyehue volcano which recently started to erupt june 2011 key points we observe local seismicity near the 1960 valdivia maximum slip region the subducted valdivia fracture zone is reactivated by fluid release the seismogenic zone is free of seismicity events occur at faults and volcanoes

mesoscale patterns in the cape sao vicente iberian peninsula upwelling region 1 the coastal upwelling region near cape sao vicente the southwestern tip of the iberian peninsula where the southern zonal coast meets the meridional western coast was studied using over 1200 advanced very high resolution radiometer avhrr satellite images of sea surface temperature and time series of sea level height wind velocities and nearshore sea surface temperature recorded at coastal sites within 200 km of the cape summer upwelling is more intense and persistent off the western coast than off the southern coast where a recurrent warm coastal countercurrent flows westward and at times turns northward along the western coast after reaching the cape in this region the equatorward current jet of cold water upwelled off the western coast is no longer bounded by a coast three preferred directions for the spreading of this water are identified the most persistent is eastward along the southern shelf break and slope possibly merging with waters previously upwelled locally which becomes separated from shore by the coastal progression of the warmer counterflow the second preferred direction results in the southward development of a cold filament feature fed by cold waters upwelled farther north and represents the southernmost extent of the intense coastal upwelling jet which overshoots the cape the least frequent feature to develop is a cold filament that grows westward at the latitude of the cape appearing to result from the meandering of the equatorward jet the coastal countercurrent is seen to interact with the equatorward jet at times of relaxation not only by separating the cold upwelled water from the coast but when it is energetic enough breaking westward offshore through the equatorward cold flow and separating the eastward and southward cold features from the upcoast cold waters empirical evidence shows the presence of an alongshore pressure gradient stronger in summer driving the coastal progression of the warm counterflow wind forcing plays an important role in the circulation by augmenting or diminishing the effect of the preexisting alongshore pressure gradients the extent of the progression of the warm coastal countercurrent along the southern and western coast is dictated by the the strength of the upwelling favorable wind stress which is able to balance and reverse the alongshore flow at least in the upper layers

planktonic foraminifera from modern sediments reflect upwelling patterns off iberia insights from a regional transfer function abstract quantitative and qualitative analyses of planktonic foraminiferal assemblages from 134 core top sediment samples collected along the western iberian margin were used to assess the latitudinal and longitudinal changes in surface water conditions and to calibrate a sea surface temperature sst transfer function for this seasonal coastal upwelling region q mode factor analysis performed on relative abundances yielded three factors that explain 96 of the total variance factor 1 50 is exclusively defined by globigerina bulloides the most abundant and widespread species and reflects the modern seasonal may to september coastal upwelling areas factor 2 32 is dominated by neogloboquadrina pachyderma dextral and globorotalia inflata and seems to be associated with the portugal current the descending branch of the north atlantic drift factor 3 14 is defined by the tropical sub tropical species globigerinoides ruber white globigerinoides trilobus trilobus and g inflata and mirrors the influence of the winter time eastern branch of the azores current in conjunction with satellite derived sst for summer and winter seasons integrated over an 18 year period the regional foraminiferal data set is used to calibrate a sst transfer function using imbrie kipp mat and simmaxndw techniques similar predicted errors rmsep correlation coefficients and residuals deviation from sst estimated for both techniques were observed for both seasons all techniques appear to underestimate sst off the southern iberia margin an area mainly occupied by warm waters where upwelling occurs only occasionally and overestimate sst on the northern part of the west coast of the iberia margin where cold waters are present nearly all year round the comparison of these regional calibrations with former atlantic and north atlantic calibrations for two cores one of which is influenced by upwelling reveals that the regional one attests more robust paleo ssts than for the other approaches

magma ascent rates volcanoes can erupt explosively generating high columns of ash and occasional pyroclastic flows or they can erupt slowly forming lava flows and domes this variation reflects significant differences in mass eruption rate e g wilson et al 1980 mass eruption rates in turn are controlled by the rates of magma ascent through the volcanic conduit and the conduit size the magma ascent rate itself is a function of the pressure in the magma storage region the physical properties of the magma such as its density viscosity and crystallinity and the resistance to flow in the conduit that connects the magma storage zone to the surface papale and dobran 1994 mastin and ghiorso 2001 pinkerton et al 2002 sparks et al 2006 a number of important characteristics of volcanic eruptions are affected or controlled by the rate at which magma ascends from depth for example the bubble content i e vesicularity and the degree of crystallization that develop in the melt phase can be significantly different in rapidly vs slowly ascended magma in fact the inability of rapidly ascending magma to effectively lose exsolved gas may be one factor causing an eruption to change from effusive to explosive behavior as recently documented for the soufriere hills eruption on montserrat in the west indies sparks et al 1998 therefore in order to better understand the processes involved and the changes that occur in volcanic eruptions it is important to quantify the rates at which different magmas rise to the surface the fact that the rate of magma ascent controls a number of reactions that occur in volatile rich magmas suggests several ways to study magma ascent rates using reaction data and theoretical flow models one reaction that is a direct result of magma ascent is the exsolution of volatiles from the melt

calbuco volcano and minor eruptive centers distributed along the liquine ofqui fault zone chile 41 42 s contrasting origin of andesitic and basaltic magma in the southern volcanic zone of the andes calbuco volcano is a late pleistocene holocene composite stratovolcano located at 41 20 s in the southern region of the southern volcanic zone of the andes ssvz 37 46 s in contrast to basalt and basaltic andesite which are the dominant lava types on the volcanic front from 37 to 42 s calbuco lavas are porphyritic andesites which contain a wide variety of crustal xenoliths they have sio2 contents in the 55 60 range and have comparatively low k2o rb ba th and lref abundances relative to other ssvz centers incompatible element abundance ratios are similar to those of most ssvz volcanics but 87sr 86sr and 143nd 144nd are respectively higher and lower than those of adjacent volcanic centers basalts from nearby osorno stratovolcano 25 km to the northeast are similar to other basaltic ssvz volcanoes however basalts from several minor eruptive centers mec located east of calbuco and osorno volcano along the liquine ofqui fault zone lofz are enriched in ba nb th and lree and have higher la yb and lower ba la k la and rb la 87sr 86sr and 143nd 144nd in mec basalts are respectively lower and higher than those of osorno and calbuco lavas we suggest that mec basalts were produced by lower extents of mantle melting than basalts from osorno and other ssvz stratovolcanoes probably as a result of lower water content in the source of mec basalts calbuco andesites formed from basaltic parents similar to osorno basalts by moderate pressure crystallization of a hornblende bearing assemblage accompanied by crustal assimilation hornblende stability in the calbuco andesites was promoted by the assimilation of hydrous metasedimentary crustal rocks which are also an appropriate endmember for isotopic trends together with magma storage at mid crustal depths the unique characteristics of calbuco volcano i e the stability of hornblende at andesitic sio2 contents low 143nd 144nd and high 87sr 86sr and abundant crustal xenoliths provide evidence for crustal assimilation that is not apparent at more northerly volcanoes in the ssvz