cadomian subduction collision and variscan transpression in the badajoz cordoba shear belt southwest spain a discussion on the age of the main tectonometamorphic events

tectonothermal evolution of the badajoz cordoba shear zone sw iberia characteristics and 40ar 39ar mineral age constraints field characteristics indicate that the badajoz cordoba shear zone has had a long polyphase tectonothermal evolution 40ar 39ar cooling ages recorded within central ductile sectors of the badajoz cordoba shear zone range from ca 370 to 360 ma amphibole and 340 to 330 ma muscovite these are interpreted to date post metamorphic cooling through contrasting temperatures required for intracrystalline retention of argon following a regionally significant variscan tectonothermal overprint these results combined with field relationships indicate that the badajoz cordoba shear zone experienced at least 15 km of uplift relative to adjacent areas during late paleozoic sinistral transpression the data also indicate that individual structural units within the shear zone experienced contrasting uplift histories both in total amount and rate the 40ar 39ar cooling ages indicate complete variscan rejuvenation of all older intracrystalline argon systems within central sectors of the badajoz cordoba shear zone

sea level change along the french atlantic and channel coasts since the time of the last glacial maximum abstract holocene sea level change along the french atlantic and english channel coast is not uniform because of the response of the crust to the changing ice and water loads in late pleistocene and holocene time the pattern of the spatial variability is a north south trend of decreasing sea levels levels at any time this results primarily from the isostatic response to the melting of the fennoscandian ice sheet superimposed upon this is a mainly east west trend resulting from the isostatic response of the crust to the addition of the meltwater into the atlantic ocean the combined effect is that at any time sea levels vary spatially along this coastline by amounts that are predicted to reach 20 m from the time of the last glacial maximum to about 10 000 radiocarbon yr ago about 15 m at 8000 yr ago and about 10 m at 6000 yr ago thus observations of past sea levels should not be combined into a single sea level curve unless first corrected for the glacio hydro isostatic factors alternatively the data should only be used to construct regional curves for relatively short sections of the coastline such as pas de calais and picardie normandie cotes du nord finistere or the vendee and charente maritime region even within such constrained regions the spatial variability may still be of the order of a few meters analysis of the observational data by region indicates that major oscillations in sea level are unlikely to have occurred that levels at no location exceeded the present mean sea level and that there may have been a small 3 m increase in eustatic sea level over the past 6000 yr palaeoshorelines and palaeo water depths for the english channel and the atlantic coast shelf have been predicted using the isostatic and eustatic models and the results indicate that in situ marine deposits older than 6000 7000 yr are unlikely to be found along many sections of the present coastline

geochemical evolution of groundwater in sequences of sedimentary rocks abstract a geochemical mass transfer model wategm se is used to illustrate the effect of several major processes on the chemical evolution of groundwater flowing through hypothetical sequences of sedimentary rocks using chemical reactions prevalent in these rock types the simulations demonstrate the influence of the initial soil pco2 temperature pressure and the sequence of encounter of the mineral phases along the flow path of the groundwater the evolution of groundwater in different sequences of limestone and dolostone is simulated with a range of initial pco2 values typical of natural soils temperatures of 10 and 25 c are used the simulations indicate that appreciable differences in the chemical composition of the groundwater and the spring discharge water will occur depending on whether a limestone or dolostone unit is first encountered the cases of more complex stratigraphy are represented by three hypothetical sequences in which each stratum has only one reactive mineral phase the reactions used in these simulations include calcite dissolution and precipitation gypsum dissolution and precipitation cation exchange and the weathering of albite to kaolinite sulfate reduction occurs in the last stratum in each of these sequences the strata in the three sequences are indentical except for the order in which they are encountered by the groundwater considerably different hydrochemistries are calculated for each of these sequences even within the same types of rock units the effect of increasing total pressure is demonstrated with a water initially saturated with both gypsum and calcite under a pressure of 1 bar the system is then closed and the pressure is increased to 1 kbar while the temperature remains constant at 25 c the results indicate that pressure has a significant effect above 50 bar or 500 m hydrostatic head it is commonly expected that groundwater in sedimentary rocks will exhibit trends in chemistry that are the result of the length of the flow path and the groundwater velocity the simulated sequences obtained in this study demonstrate that the order in which the various sedimentary strata are encountered by the groundwater and the partial pressure of the co2 in the soil zone are important factors for groundwater systems that are near equilibrium with the host rock these factors may control the chemical evolution of the water

upper neoproterozoic lower cambrian sedimentary successions in the central iberian zone spain sequence stratigraphy petrology and chemostratigraphy implications for other european zones o3 tio2 zr and nb abundances in shales from all the units strongly suggest a gradual compositional change within this sedimentary succession together with the petrological data the chemical results do not reveal any obvious coeval volcanic contribution to the sediments on the basis of the chemical data a comparison is made with other european zones containing detrital sediments composed of reworked crustal components

geochronological constraints on the evolution of a suture the ossa morena central iberian contact variscan belt south west iberian peninsula one of the main tectonic boundaries of the variscan belt in the iberian peninsula is the ossa morena central iberian contact this contact is marked by a highly deformed unit central unit which recorded an initial high pressure high temperature metamorphic evolution rb sr whole rock isotopic data from three gneissic bodies cropping out in the central unit yield two late proterozoic ages 690 134 and 632 103 ma and an early palaeozoic age 495 13 ma which we interpret as protolith ages the two late proterozoic orthogneisses show initial 87sr 86sr ratios typical of mantle derived materials or those with significant mantle participation 87sr 86sr 0 709 these new radiometric data together with ages previously published and the structural evolution of the central unit lead to the conclusions that 1 there are magmatic protoliths of late proterozoic and early palaeozoic ages 2 the metamorphic evolution of this area including the high pressure event belongs to the variscan orogenic cycle 3 the deformations observed affect the rocks of the entire central unit accordingly they are post ordovician i e variscan and 4 consequently the ossa morena central iberian contact is interpreted here as a variscan suture

the statistical analysis and interpretation of imperfectly fitted rb sr isochrons from polymetamorphic terrains abstract rb sr isotopic data for large relatively homogeneous whole rock samples of uivak 1 gneiss from the saglek hebron area of northern labrador exhibit a scatter which exceeds that predicted by experimental error isotopic analyses of adjacent compositionally different layers of uivak gneiss 1 2 cm in width define secondary isochrons with slopes corresponding to an age of ca 1800 ma as field evidence combined with previous isotopic dating demonstrates that the compositional layering did not form at this time the secondary isochrons are interpreted as resulting from localized sr isotopic homogenization along 87sr abundance gradients generated by ageing in the previously layered gneisses the geological scatter in the larger gneiss specimens is therefore attributed to the same phenomenon on a reduced scale viz sr isotopic equilibration at 1800 ma between adjacent volumes of gneiss however regional differences in mean 87 sr 86 sr and mean 87 rb 86 sr are assumed to be unchanged this interpretation has led us to the development of a weighted least squares regression technique that utilizes the geologically induced error structure in the whole rock rb sr data the method encompasses three models in the first the local isotopic equilibrium or free line model it is assumed that the error structure in the whole rock samples is the same as that in the layered gneisses except for an unknown scaling factor common to both 87 rb 86 sr and 87 sr 86 sr in the other two models the initial strontium isotopic composition is constrained to values greater than primordial sr and corresponding to that expected for the contemporary bulk earth by forcing the least squares fit for the data to pass through a fixed point that corresponds to the present day 87 rb 86 sr and 87 sr 86 sr composition of the bulk earth viz approximately 0 085 and 0 7047 respectively in the first of these models bulk earth model 1 no assumptions are made about the error structure of the primary data an estimate of the age can be obtained but no estimate of its uncertainty in the second bulk earth model 2 the first two methods are combined and estimates for both the age and its 95 confidence limits may be found in developing the method nineteen whole rock samples plus the means of the slabbed gneisses yielded the following results for the age and initial 87 sr 86 sr respectively of the uivak 1 gneisses 1 1 free line model 3621 410 686 ma 0 70006 565 354 2 2 bulk earth model 1 3606 ma 0 70020 3 3 bulk earth model 2 3606 175 213ma 0 70020 27 22

the impact of north atlantic storminess on western european coasts a review abstract instrumental and documentary records of storminess along the atlantic coast of western europe show that storm activity exhibits strong spatial and temporal variability at annual and decadal scales there is evidence of periods of increased storminess during the little ice age lia ad 1570 1990 and archival records show that these periods are also associated with sand movement in coastal areas independent evidence of sand movement during the lia is derived from dating the coastal sand deposits using luminescence or radiocarbon methods the holocene record of sand drift in western europe includes episodes corresponding to periods of northern hemisphere cooling particularly at 8 2 ka and provides the additional evidence that these periods like the lia were also stormy

granulometric characterization and evaluation of annually banded mid holocene estuarine silts welsh severn estuary uk coastal change sea level and climate abstract holocene silts salt marshes and highest intertidal supratidal peats are superbly exposed on a 15 km coastal transect which reveals two laterally extensive units of annually banded silts beds 3 7 associated with three transgressive regressive silt peat cycles early sixth early fourth millennium bc bed 3 in places is concordantly and gradationally related to peats above and below but in others transgresses older strata bed 7 also grades up into peat but everywhere overlies a discordance the banding in bed 3 at three main and two minor sites was resolved and characterized texturally at high resolution 2 5 5 mm contiguous slices using laser granulometry ls230 with pids and a comprehensive scheme of data assessment most of bed 3 formed very rapidly at peak values of several tens of millimetres annually in accordance with modelled effects of sea level fluctuations on mature marshes bed concordant and gradational and on marshes growing up after coastal erosion and retreat bed with discordant base using data from the modern severn estuary the textural contrast within bands and its variation between bands points to a variable but overall milder mid holocene climate than today the inter annual variability affected marsh dynamics as shown by the behaviour of the finely divided plant tissues present given local calibration the methodology is applicable to other tidal systems with banded silts in britain and mainland northwest europe

late holocene record from a loire river incised paleovalley french inner continental shelf insights into regional and global forcing factors abstract sediment core kv14bis was retrieved from the fosse du croisic a loire river incised paleovalley located in the inner shelf of the bay of biscay this core 5 4 m length covers the past 2 6 cal kyr bp with high sedimentation rate a multiproxy approach x ray imagery xrf data grain size analyses and benthic foraminiferal assemblages was applied in order to reconstruct the hydrological regime of the loire river during the late holocene this hydrological regime was further linked to climate forcing e g solar activity north atlantic oscillation nao and human activity our data describe a succession of several dry humid periods the humid periods are centered on 2 2 1 3 and 0 5 cal kyr bp and are characterized by high terrigenous flux fine silty sedimentation relatively high organic carbon content and high proportions of the epiphytic foraminiferal species planorbulina mediterranensis this species was probably brought to the study site by the loire river plume attached on floating algae the dry periods are centered on 2 5 1 5 1 2 cal kyr bp and 1900 ce and are characterized by low terrigenous input and high carbonate content due to abundant shell debris during periods of low river runoff deposition of a sand particle population grain size 200 m could indicate increased storminess this latter may have remobilized sediments from shallower depths during these generally dry periods on the continent the overall coherence of our results with several european continental records supports a pluri centennial scale regional climate control of humidity and storminess resembling that of the nao spectral analyses emphasized a possible additional control of solar activity through deforestation and soil erosion early human impact was also probably superimposed on this climatic forcing

accretionary history and crustal evolution of the variscan belt in western europe abstract the variscan belt of western europe is part of a large intra paleozoic belt extending on both sides of the atlantic from the ouachitas in the us and the mauritanides in west africa to the bohemian massif in czechoslovakia and poland the belt was constructed between 500 and 250 ma as a result of convergence and collision between two main continents laurentia baltica and africa after the closure of various oceanic basins iapetus rheic and galicia massif central now recorded as discrete in part cryptic sutures which form the roots of large crystalline nappes in which are found dismembered remnants of oceanic crust and mantle the accretionary history of the variscan belt in western europe is related to the progressive closure of probably two oceanic basins the rheic in the north and another the galicia massif central in the south by respectively southward and northward intraoceanic subduction followed by obduction and intracontinental lithospheric subduction the result is a broad 700 800 km fan like divergent belt which must be considered as a classical obduction collision orogen with a long intracontinental history of about 100 150 ma its arcuate shape is probably due to the northwestward impingement of a promontory of the african continent into laurentia baltica

using non conservative tracers to characterise karstification processes in the merinos colorado carrasco carbonate aquifer system southern spain the systematic sampling of the chemical composition of the groundwater from five karst springs including an overflow spring and one outflowing borehole have permitted to determine distinctive chemical changes in the waters that reflect the geochemical processes occurring in a carbonate aquifer system from southern spain the analysis of the dissolution parameters revealed that geochemical evolution of the karst waters basically depends on the availability of the minerals forming aquifer rocks and the residence time within the aquifers in the three proposed scenarios in the aquifers which include the preferential flow routines the more important geochemical processes taking place during the groundwater flow from the recharge to the discharge zones are co2 dissolution and exsolution outgassing calcite net dissolution calcite and dolomite sequential dissolution gypsum anhydrite and halite dissolution de dolomitization and calcite precipitation a detailed analysis of the hydrochemical data set saturation indices of the minerals and partial pressure of co2 in the waters joined to the application of geochemical modelling methods allowed the elaboration of a hydrogeochemical model of the studied aquifers the developed approach contributes to a better understanding of the karstification processes and the hydrogeological functioning of carbonate aquifers the latter being a crucial aspect for the suitable management of the water resources

morphological responses of an estuarine intertidal mudflat to constructions since 1978 to 2005 the seine estuary france abstract since 1834 the seine estuary france has been the site of numerous construction projects with the aim to accommodate and secure boat traffic since 1978 the increasing of the activities of le havre port located at the mouth of the estuary has accelerated the construction work rate several dykes a bridge and new port facilities have been constructed in rapid succession modifying considerably the hydrodynamic conditions which sustain a partially vegetated sandy muddy tidal flat located in the north bank of the estuary between the new port of le havre and the normandy bridge achieved in 1995 the present study deals with the morphological evolution of this zone from 1978 to 2005 the use of a low altitude remote sensing technique combined with traditional methods of ground survey and probes allow to demonstrate the impact of human activities on sedimentary and vegetation dynamics the northern mudflat of the estuary is the most affected by these human activities which surface have reduced of 62 during the last 27 years with an intensified local erosion during the last 27 months corresponding to a loss 1 250 000 m 3 of fine grained sediment at the same time the general sanding up in the channel of the zone has caused a loss of more than 31 of the tidal prism more than three quarters of which occurred during the last three years results also establish that the response times of the sedimentary or topographic readjustment to an installation depend on the extent and the nature of the construction in fact the sedimentary readjustments to an installation can be delayed by up to 10 years in the case of the seine estuary this delay is explained by a rapid succession of construction works which may occult the effect of a single installation except in the case of a dyke built perpendicular to ebb and flood currents the impacts of these installations reach a hydro sedimentary equilibrium on the level between 1 and 7 years after their completion

superposed hercynian and cadomian orogenic cycles in the ossa morena zone and related areas of the iberian massif polyphase ductile deformation and metamorphism in the ossa morena zone of the iberian massif are related to a complex evolution including two major tectonothermal episodes of cadomian late proterozoic to early cambrian and hercynian age middle to late paleozoic petrological structural and geochronological data attest to a number of tectonic episodes in the 620 480 ma interval the model presented for this orogeny comprises stages of volcanic arc generation backarc extension tectonic inversion crustal thickening and cratonization in an andean type continental margin the hercynian cycle began in the early paleozoic with episodes of continental rifting orogenic events occurred in the 390 300 ma interval and affected both the cadomian basement which was heterogeneously reworked and overprinted and the paleozoic cover hercynian regional metamorphism was generally of low grade high pressure assemblages and thermal domes developed locally and were related to subduction and late extensional events the geodynamic model proposed for the cadomian and hercynian orogenies and the correlation with comparable areas from pre mesozoic massifs elsewhere in western europe account for the geodynamic scenarios that drove the fate of cadomian terranes

relative importance of the saturated and the unsaturated zones in the hydrogeological functioning of karst aquifers the case of alta cadena southern spain summary from analysis of the hydrodynamic and hydrochemical responses of karst springs it is possible to know the behaviour of the aquifers they drain this manuscript aims to contribute to the characterization of infiltration process and to determine the relative importance of the saturated zone and of the unsaturated zone in the hydrogeological functioning of carbonate aquifers using natural hydrochemical tracers thus chemical components together with temperature and electrical conductivity both punctual and continuous records have been monitored in three springs which drain alta cadena carbonate aquifer southern spain an evaluation of the percentage of the electrical conductivity frequency peaks determined for each of the three springs is linked to the chemical parameters that comprise the conductivity signal one of these springs responds rapidly to precipitation conduit flow system due to the existence of a high degree of karstification in the unsaturated zone and in the saturated zone both of which play a similar role in the functioning of the spring another spring responds to precipitation with small increases in water flow somewhat lagged because the aquifer has a low degree of karstification even in the unsaturated zone which seems to influence its functioning more strongly than does the saturated zone the third spring drains a sector of the aquifer with a moderately developed degree of karstification one that is intermediate between the other two in which both the unsaturated zone and the saturated zone participate in the functioning of the spring but with the latter zone having a stronger influence these three springs show different hydrogeological functioning although they are in similar geological and climatic contexts which show the heterogeneity of karst media and the importance of an adequate investigation for groundwater management and protection in karst areas

tectonic evolution of the boundary between the central iberian and ossa morena zones variscan belt southwest spain three tectonometamorphic units can be differentiated in the boundary between the central iberian and ossa morena zones of the iberian massif variscan belt the three units have been named the northern unit central unit and southern unit the northern unit corresponds to the border of the central iberian zone it evolved at low temperature and intermediate or low pressure metamorphic conditions and was affected by top to the se ductile shearing the central unit placed under the northern unit preserves high pressure silurian eclogitic assemblages retrograded by high to medium temperature and finally low temperature ductile shearing with top to the nw sense of movement oblique left lateral the central unit is superposed on the southern unit the latter corresponds to the border of the ossa morena zone and underwent low pressure intermediate temperature metamorphism synchronous with right lateral top to the se ductile shearing the envisaged tectonic evolution is as follows after a stage of lower paleozoic rifting subduction of the central unit under the northern unit took place in silurian times as a result of the crustal thickening a gravitational instability developed giving way to left lateral extensional shearing that affected the entire central unit the combined action of oblique thrusting at the front of the wedge and oblique extensional shearing at the rear caused the exhumation of the high pressure rocks of the central unit this tectonic evolution reveals that the boundary between the central iberian and ossa morena zones is a suture of the variscan belt

sea level changes in the holocene over the last 30 years the emphasis in studies of the recovery from low last glaciation sea levels has changed significantly the search for a eustatic sea level curve having global relevance has ended studies into the rheology of the earth s crust and recognition that the geoid has not remained stable over time have resulted in the recognition that there must have been regional differences in eustatic response to deglaciation as a part of this re appraisal there has been a growing appreciation that crustal isostatic response to the removal of the weight of ice sheets has been accompanied by a consequential hydro isostatic response particularly in the areas of the shelf seas in the later part of the post war period attention has additionally been focussed on the much greater potential for error over the whole field of palaeoenvironmental reconstruction in the holocene including not only errors in dating but also a large number of possible sources of errors in heighting as a result of this an increasing number of scientists are withholding judgement on the nature of sea level rise and more particularly on the problem of higher than present late holocene eustatic sea levels the problems outstanding in the early 1960s have not yet been resolved but the bases of uncertainty have changed

rb sr evidence for the presence of ordovician gsranites in the deformed basement of the badajoz cordoba belt sw spain a rb sr whole rock investigation of suites of samples from two orthogneiss bodies in the almendralejo area of the oporto portalegre badajoz cordoba belt points to an ordovician age for the granitic magmatism about 470 ma for the almendralejo gneiss peralkaline metagranite and about 425 ma for the ribera del fresno gneiss leucocratic subaluminous metagranite both with high initial87sr 86sr ratios this points to a post ordovician hercynian age for the metamorphism and tectonic deformation that affected the area including the gneisses and rules out the alleged cadomian or even older age

isotopic dating of the mylonitization of the azuaga group in the badajoz cordoba belt sw spain on the basis of rb sr muscovite dating an age of about 355 ma late tournaisian early visean is assigned to the m1 metamorphism and associated mylonitization of the ultramylonites of the las grullas formation in the azuaga group badajoz cordoba belt this age may possibly be related to the accretion process suturing of the ossa morena zone to the central iberian zone thought to be responsible for the metamorphism and mylonitization muscovite from the valencia de las torres formation displays a somewhat lower rb sr age of about 337 ma the corresponding k ar ages indicate that after the termination of the metamorphism it took some 20 ma before the rocks had cooled below the closure temperature of muscovite to k ar whole rock rb sr data indicate that the las grullas ultramylonites were probably derived from ordovician granitoids

radiometric discrimination of pre variscan amphibolites in the ediacaran serie negra ossa morena zone sw iberia new results on the geochronology of metabasites hosted by the neoproterozoic late ediacaran serie negra of the ossa morena zone iberian massif are presented these rocks record a protracted subduction at least since the latest cryogenian followed in a continuum by early cambrian rifting the serie negra country rocks are continental crust forearc segments of the thinned continental margin of gondwana the metabasite suite exhibits e and n morb as well as volcanic arc signatures and discloses the existence of a diverse late ediacaran early cambrian magmatism across the ossa morena zone protoliths of the e morb metabasites are clearly ediacaran they exhibit geochemical characteristics typical of younger island arcs notably of their forearc zones affected by extension soon after the initiation of subduction radiometric dating of n morb metabasites shows that these rocks are significatively younger than their country rocks whose age has been stratigraphically and paleontologically constrained as ediacaran they record early cambrian rifting developed in a continuum after a protracted subduction metabasite petrological zonation permits to reconstruct a single ediacaran subduction zone located to the s of the current omz and dipping towards the n in present day geographical coordinates

combined zircon upb and luhf isotopes study of magmatism and high p metamorphism of the basal allochthonous units in the sw iberian massif ossa morena complex upb and luhf isotope ratios measured in zircon crystals from magmatic and metamorphic rocks provide crucial information to understand the origin and tectonothermal evolution of allochthonous terranes and can contribute to paleogeographic reconstructions and to the understanding of orogenic processes we investigate the age of magmatic and tectonothermal events and the provenance of a high pressure unit from the ossa morena complex sw iberian massif zircons for la icp ms analyses were separated form garnet bearing amphibolites retroeclogites and quartzo feldspathic gneisses from the central unit coimbra cordoba shear zone recent geological correlations propose that the high pressure units cropping out in the ossa morena complex of the sw iberian massif are equivalent to the basal allochthonous units of nw iberian massif and one of the objectives of the study is to check the validity of the proposed correlation the new obtained ages presented in this study indicate that the high pressure metamorphism of the central unit developed in the variscan cycle the metamorphic zircons reveal two distinct events a younger one well constrained by an age of 339 4 ma and an older one of 377 19 ma the former coincide with the age of the high grade and post high p metamorphism described in other areas of the ossa morena complex whereas the second one is interpreted as the age of the high p metamorphism the igneous ages of metabasites and metagranitoids c 585 615 ma and c 480 577 ma respectively reveal a diachronism between magmatic events in allochthonous units from the sw and the nw iberian massif suggesting that both domains were located in different parts of the north gondwanan margin the magmatic ages of the metagranitoids resemble the evolution described for the lower paleozoic rifting in the ossa morena complex the relatively juvenile character of the basic and acid cadomian magmatism in the central unit revealed by the new luhf data indicate limited mixing of mantle melts with crustal components which is compatible with a generation in a continental magmatic arc these similarities in the metamorphic and magmatic evolution support the correlation of the basal allochthonous units from the sw and nw domains of the iberian massif

factors which determine the hydrogeochemical behaviour of karstic springs a case study from the betic cordilleras spain the cabra alcaide karstic massif situated in the south of spain constitutes an important part of the so called natural park of the subbetic sierras this aquifer system is drained by various springs which supply a population of some 100 000 inhabitants the feed areas of these springs show very different characteristics with respect to their geological structure size of the drainage area thickness of the vadose zone elevation and degree of karstification in addition the carbonate rocks lie over a clayey substratum which contains large masses of intercalated evaporites due to these conditions the hydrochemical composition of the springs is relatively variable in this study a hydrogeochemical characterization of the aquifer in both space and time is undertaken and the factors that determine it are discussed to achieve this 19 monthly samples were taken from the 6 most significant springs of the hydrogeological system the commencement of sampling coincided with the transition from a period of several years of severe drought and a very wet two year period which amplified considerably the hydrochemical and hydrodynamic response of the springs to the recharge identification of hydrogeochemical processes was performed by studying hydrographs the temporal evolution of physico chemical parameters ionic ratios mainly mg ca and by means of simple and multivariate statistical analyses the saturation status was established using the wateqf program and the mass transfer was quantified using phreeqc with the exception of the epikarstic subsystem i e the zarza spring the majority of the results indicate that the aquifer exhibits a diffuse flow model in which piston flow phenomena are seen closely linked to the most intense precipitation along the direction of flow hydrochemical trends are seen as the water type changes from ca hco3 to ca mg hco3 at the same time enrichment in some ions derived from the dissolution of evaporitic minerals of the impermeable substratum and dedolomitization processes occur in this way almost 90 of the water samples were oversaturated in calcite the majority of cases being a consequence of the dissolution of the gypsum of the substratum only in the epikarstic springs can it be considered that the oversaturation in calcite is due to loss of co2 from the emerging groundwater it is concluded that hydrodynamic aspects together with hydrogeochemical characteristics need to be taken into account to correctly explain the hydrochemical evolution of the karstic springs moreover the use of both approaches permits a more accurate establishment of the degree of aquifer karstification which in turn needs to be known in order to assess its vulnerability to contamination and to protect recharge zones

variscan intracontinental deformation the coimbra cordoba shear zone sw iberian peninsula the coimbra cordoba shear zone is a major lineament roughly parallel to the nw se variscan structures of the southern iberian peninsula inside the shear zone evidence for a non coaxial strain path exists from structural microstructural and lattice preferred orientation data on quartz plane strain is suggested by the study of microstructures in the xy and yz sections in all formations occurring in the shear zone with increasing strain a mylonitic series develops the deformation contemporaneous with epizonal to mesozonal metamorphism is responsible for 1 1 the regional subvertical foliation oblique to the shear zone 2 2 the well defined subhorizontal lineation striking nw se 3 3 the discrete planes of shear roughly parallel to the shear zone the data are interpreted as resulting from a left lateral slip motion with a displacement of at least 72 km in the light of plate tectonics it is inferred that the coimbra cordoba lineament could have been a suture zone which evolved into an intracontinental left lateral shear zone during the variscan orogeny of the ibero armorican arc

fluvio lagoonal sedimentary sequences in leyre delta and arcachon bay and holocene sea level variations along the aquitaine coast france abstract along the aquitaine coast bay of biscay france scarcity of recent coastal deposits corresponding to post holocene sea level variations is a direct consequence of the strong erosional processes observed in this coastal zone the general transgressive trend may be due to various geodynamic events such as contemporary sea level rise or regional subsidence related to tectonic or isostatic post glacial adjustments of this southern part of the european plate this paper is a discussion of new data about sedimentary sequences described in recent deposits infilling the mesotidal arcachon bay and its inner fluvial delta of the leyre river enlighted by geophysical and geomorphological information on the geodynamic evolution of the central part of the aquitaine basin the conclusion is that the transgressive trend of this coast is related to both subsidence and sea level elevation

the amphibolites from the ossa morena central iberian variscan suture southwestern iberian massif geochemistry and tectonic interpretation abstract basic rocks included in the ossa morena central iberian variscan suture of sw iberia have been studied in order to decipher the pre orogenic evolution along this major boundary these rocks appear as garnet free amphibolites and garnet bearing amphibolites previous geochronological data on these basic rocks suggest the existence of two different protolith ages upper precambrian and lower palaeozoic ordovician upper precambrian amphibolites form small size up to several metres thick lense dike or elongated shaped bodies while lower palaeozoic ones form elongated bodies with thicknesses up to several hectometres the chemical compositions of the amphibolites enable us to separate cumulate rocks from those representing more basaltic magmas as for the originally basaltic rocks their geochemical characteristics indicate a shallow melting with different proportions of at least three end members namely i a morb like asthenospheric source ii a more enriched plume derived or subcontinental lithosphere mantle source and iii a continental crust component moreover upper precambrian and lower palaeozoic amphibolites have different geochemical affinities in the former group we envisage an advanced intra continental rifting situation or an intra continental back arc setting related to the cadomian orogeny while for the latter we propose an environment of oceanic crust formation predating variscan subduction and collision the recognition of these remains of oceanic affinity basic rocks along the omz ciz boundary allows us to propose that some sort of ocean may well have existed between the two zones during early palaeozoic times and that this ocean was presumably closed at a later stage probably during the devonian by oceanic subduction under the ciz crust

ediacaran palaeozoic tectonic evolution of the ossa morena and central iberian zones sw iberia as revealed by sm nd isotope systematics abstract sm nd isotopic analyses of palaeozoic sedimentary and igneous rocks in the southwest iberian massif western end of the european variscan belt are presented in order to unravel its complex poly orogenic evolution during the closure of the rheic ocean and the amalgamation of pangea the gondwanan margin in southwest iberia sw iberia is subdivided into the ossa morena and central iberian zones separated by the badajoz cordoba shear zone which represents a cryptic suture zone between these terranes the relationships between these terranes and between units preserved within the suture zone e g the sierra albarrana group during the palaeozoic and neoproterozoic are controversial sm nd isotopic studies of representative sedimentary sequences covering the entire pre variscan record of the ossa morena and central iberian zones show very similar characteristics from the uppermost ediacaran onwards these data indicate that their accretion to one another must have been completed by the late neoproterozoic ediacarin that time an event assigned to cadomian orogeny and that they never separated substantially from each other since that time the sm nd isotopic composition of the sierra albarrana group metasedimentary rocks is similar to that of the pre cadomian sequences of the ossa morena zone serie negra suggesting derivation from a common source the common provenance of the palaeozoic sequences in the two zones is identical to that of the pre cadomian serie negra of the ossa morena zone which in accordance with the data presented herein and published u pb zircon data indicates a west african affinity

geological constraints on the paleozoic tectonic evolution of tectonostratigraphic terranes in the iberian massif abstract the presence of oceanic paleozoic sequences in the iberian variscan fold belt is used to identify and separate suspected exotic terranes from a reference iberian autochthon terrane which constitutes the greater part of it in this paper the relevant data characterizing the pre accretionary evolution of the paleozoic iberian terranes are presented as well as the available evidence concerning the accretionary process itself emphasis is placed on the analysis of the sedimentary igneous and structural expression of the major events which affected the iberian terranes before during and after their amalgamation the main conclusions of such an analysis may be summarized as follows 1 a recognition of rift and passive margin stages in all the iberian massif terranes during the early paleozoic 2 b late paleozoic accretion of the exotic terranes to the iberian autochthon via a long and complex process variscan orogeny which involved initial subduction underneath the latter and eventual obduction followed by oblique collision of a promontory the iberian autochthon northwestern margin with a northwestern continental block this latter process could account for the large scale crustal imbrication shown by the northern branch of the orogen coeval with predominant strike slip faulting in the southern branch as well as with the formation of the typical arcuate shape of this orogenic belt major present uncertainties relate to the palinspastic provenance of continental suspect terranes and their correlation with similar units in other circum atlantic paleozoic orogens a discussion and speculations on this subject are dealt with in the final section of this paper

cadomian subduction collision and variscan transpression in the badajoz cordoba shear belt southwest spain abstract the tectonothermal evolution of the badajoz cordoba shear belt southwest iberian massif spain involved the build up of a cadomian upper proterozoic lower paleozoic subduction collision orogenic wedge complex made up of five stacked tectonic slices and its deformation under transpression during hercynian late paleozoic intracontinental shearing episodes cadomian metamorphism in the high grade gneissic units of the wedge complex is characterized by peak metamorphic conditions of 720 c 8 kbar for the lowermost tectonic slice higuera de llerena mylonite gneiss and 670 c 10 kbar in the overlying gneissic slice blastomylonitic migmatic gneisses the p t conditions recorded by eclogites structurally overlying the previous gneisses enhance a scheme of inverted metamorphism since these eclogites equilibrated at 685 700 c 15 kbar during peak metamorphic conditions after the high pressure event the highest temperatures attained by the eclogites correspond to a period of nearly isothermal decompression with a drastic decrease in pressure later on the retrogressed eclogites experienced a pressure increase before they began to reequilibrate under progressively lower pandt conditions similar to those recorded by the retrogression of gneisses such a p increase in eclogites might be related to a period of underthrusting below continental crust responsible for the amalgamation of the different tectonic units of the badajoz cordoba shear belt the present results unravel that the models concerned with the geotectonic evolution of the ibero armorican arc and the respective correlations among hercynian and pre hercynian cadomian for our aims terranes across the north atlantic must be reconsidered

contribution of saharan dust to mediterranean soils assessed by sequential extraction and pb and sr isotopes abstract measurements of the concentrations and isotopic composition of pb and sr in al silicates and fe oxides of two soil profiles developed in the guadalquivir river basin andalusia southwestern spain are used in order to estimate the significance of local versus foreign sources lead concentrations are 10 6 mg kg in deep more than 100 cm soil samples and reach 30 60 mg kg near the surface 206 pb 207 pb values range from 1 200 to 1 206 in deep samples and from 1 186 to 1 191 in the upper most samples sr concentrations range from 30 to 69 mg kg showing no systematic trend with depth 87 sr 86 sr ratios range from 0 71753 to 0 72526 also with no systematic changes with depth in the fe oxide fraction but with a systematic increase in values with depth in the al silicate fraction of one of the soil profiles in all the samples the isotopic composition of pb in the al si fraction is slightly more radiogenic than its value in the fe oxide fraction the isotopic composition of sr exhibits the opposite behavior and 87 sr 86 sr values in the fe oxide fraction are always higher than in the al silicate fraction based on our data we calculate that al silicates in the fine soil fraction less than 5 m in both sites contain 33 86 of saharan dust and that the fe oxides contain less saharan dust and more material released by the weathering of basement granitoid type rocks in the case of pb a third source is present in the upper part of the soil i e anthropogenic pb probably added to the soil over millennia the results of the present study suggest that saharan dust makes up a significant fraction in al silicates and fe oxides of mediterranean soils but that local sources both natural rock derived and anthropogenic are not trivial

geodynamic evolution of a cadomian arc region the northern ossa morena zone iberian massif abstract ductile deformation and polyphase metamorphism in the ossa morena zone of the iberian massif are related to two major tectonothermal episodes of cadomian late neoproterozoic to early cambrian and variscan age middle to late paleozoic the available petrological structural and geochronological data suggest that a number of tectono metamorphic and magmatic episodes occurred during the 620 480 ma interval that would comprise a complete cadomian wilson cycle the geodynamic scenario was that of an andean type continental margin an evolutionary model is presented for this orogeny comprising stages of volcanic arc generation crustal thickening back arc extension tectonic inversion and cratonization a correlation with comparable areas from pre mesozoic massifs elsewhere in europe is proposed in particular with the armorican massif of northern france

chemical evolution of groundwater in triassic gypsum bearing carbonate aquifers las alpujarras southern spain a hydrochemical study employing modelling techniques was carried out using samples taken at 65 points springs and wells in triassic carbonate aquifers lujar gador unit alpujarride complex betic cordillera these aquifers are made up of limestones and dolomites with some gypsum scattered or interbedded though the area is semi arid recharge is relatively high because of their mountainous nature the carbonate rocks contain dense microfissuration the groundwater flow regime is predominantly diffuse the karstic forms are in general poorly developed two main hydrochemical processes have been identified in these aquifers one is incongruent dissolution of dolomite that determines the chemical composition of the less mineralised water the other is dedolomitisation dolomite dissolution together with calcite precipitation caused by dissolution of gypsum which becomes predominant when the flow encounters interbedded gypsum this reaction is also frequently associated with low temperature thermalism and can play a part in more intense local karstification cavities sinkholes high transmisivity in wells observed in the sectors of these aquifers where gypsum is more abundant a reaction path model has been used to simulate the geochemical processes through a hypothetical aquifer with similar lithology to the alpujarride carbonate aquifers successive stages of evolution through the carbonate sequence represented by different saturation states with respect to calcite dolomite gypsum and co2 have been modelled and then compared with the field data

the structure of a major suture zone in the sw iberian massif the ossa morena central iberian contact abstract we have investigated the stratigraphy structure and metamorphism of the boundary between the ossa morena zone omz and the central iberian zone ciz two significant continental portions of the variscan iberian massif the omz ciz contact is marked by a strongly deformed and metamorphosed nw se trending narrow band namely the central unit in which partially retrogressed eclogites are included during the middle late devonian the ciz overthrust the omz and in the footwall km scale recumbent folds and thrusts developed with decoupling and underplating of the lower crust at the same time in the hanging wall there took place intense though localized back folding and back shearing in the early carboniferous a transtensional tectonic regime sank the overthrust block resulting in the exhumation of eclogites these eclogites probably came from the underthrust omz lower crust and they are at present included in the suture zone central unit of this continental collision the extension is responsible for the origin of a basin and bimodal magmatism on the southern border of the ciz a late episode of folding and fracturing significantly contributed to the final complex picture of this suture boundary

a new model for the hercynian orogen of gondwanan france and iberia discussion the study by shelley and bossieare 2000 is an important contribution to the discussion concerning the ibero armorican arc iaa generation model this model comes as one of a sequence of previous ideas already published in several papers bard 1971 matte and ribeiro 1975 lefort and ribeiro 1980 ribeiro et al 1980 burg et al 1981 brun and burg 1982 julivert 1987 ribeiro et al 1990 dias and ribeiro 1995 ribeiro et al 1995 silva 1997 a common feature of the interpretations in these papers is the great importance attributed to two major transcurrent faults the dextral porto tomar shear zone ptsz and the sinistral tomar badajoz cordoba shear zone bcsz to explain the extension of the iberian structures into the armorican massif in the form of trace the arcuate shape of the iaa the large scale migration rotation and accretion of microplates controlled by oblique interactions have been a matter of controversy since researchers applied different kinematic models to reconstruct such global tectonic movements for example badham 1982 interpreted the hercynides as the result of dextral interaction between europe and africa and considered the arcuate geometry of the iaa as a secondary structure in contrast matte 1986 compared the present example of the himalayas with the structures of the iaa in terms of an indentation of crustal fragments and proposed the progressive development of the symmetrical outward lateral escape of blocks in france and iberia in this model the indentor migration caused opposing strike slip movements on either side represented by the major transcurrent faults of the armorican massif and the iberian massif this geometry and kinematics were considered to be syngenetic with the formation of the arcuate structure of the iaa however the main geologic lines linking these western european hercynian massifs through major shear zones are still questionable e g lefort 1989 in this comment we believe that the regional approach regarding the transcurrent faults of hercynian iberia bcsz and ptsz cannot be considered to be well established in the following text we will comment on signi cant omissions concerning available work of the last decade and also focus our discussion on eld data and the structural interpretation of hercynian iberia portugal and spain

high resolution holocene record in the southeastern bay of biscay global versus regional climate signals abstract core ks10b north east atlantic 43 50 n 2 03 w water depth 550 m was recovered at a location of high sediment deposition and hence includes a high resolution palaeoclimatic record for the southeastern bay of biscay over the last 9000 cal yr bp the effect of global and regional climatic forcing factors e g orbital forcing north atlantic oscillation nao and their subsequent control on water temperature sea level hydrology and continental influence were investigated by studying planktic and benthic foraminiferal faunas 150 m sedimentology and stable isotopes results indicate probable episodic long term incursions of the warm and salty iberian poleward current ipc into the bay of biscay during the holocene by the intermittent presence of subtropical globigerinoides ruber in the otherwise temperate fauna these incursions seem to be triggered by negative nao like conditions our data show five main climatic periods which are in general agreement with the literature data on the climatic variability in the north atlantic and the iberian peninsula the early holocene 9000 7400 cal yr bp is characterized by low sea level significant downslope transport eutrophic benthic settings and high surface water productivity these environmental characteristics are probably due to the general wet and warm climate under a prevailing negative nao increasing precipitation and river runoff and favouring the incursion of the ipc into the bay of biscay the climatic optimum appears between 7400 and 6000 cal yr bp under a generally positive nao index in the following 6000 3500 cal yr bp surface water cooling is matching a steep decline of the northern hemisphere summer insolation meanwhile benthic settings are changing progressively towards present day trophic conditions the time interval from 3500 to 1800 cal yr bp encompasses the iberian roman humid period characterized by warm and humid conditions and increasing primary production under a prevailing negative nao index the last 1800 years were characterized by stable cool conditions reflecting a change towards a positive nao state

u pb dating of an early paleozoic bimodal magmatism in the french massif central and of its further metamorphic evolution in the marvejols area southern french massif central the gneissic marvejols supergroup is overthrust on the metasedimentary serie du lot deposited in part prior to 540 ma the allochtonous terranes are characterized by the occurrence of a leptyno amphibolitic group a complex association of mafic and felsic rocks of igneous and sedimentary derivation a 480 10 ma age has been obtained by u pb dating of zircons for the crystallization of both mafic and felsic meta igneous rocks these rocks were emplaced during an important extensional tectonics relics of eclogites pyrigarnites coronite gabbros and hp trondhjemites are clear evidence for a further hp ht event dated at 415 6 ma on zircons from a hp trondhjemite subsequently the marvejols supergroup underwent an amphibolite facies metamorphism with incipient mobilization dated at 345 10 ma

the boundary between the ossa morena and southportuguese zones southern iberian massif major suture in the european hercynian chain the ossa morena zone omz and the southportuguese zone spz represent the southernmost domains of the iberian massif european hercynian belt lithostratigraphic petrographic and structural differences exist between both zones the boundary between the omz and the spz is marked by a narrow belt of amphibolites of tholeiitic oceanic affinity bard mmunha et al 1986 and associated serpentinites flaser gabbros pillowed metabasalts castro et al 1987 which are highly sheared along their southern border these beja acebuches ophiolites op cit are exposed for over 200 km in the southernmost part of the omz and the northernmost area of the spz several zones have been distinguished on the basis of structural and lithological criteria the southernmost area of the omz which bounds the acebuches amphibolites is composed of high grade metamorphic rocks and an another important shear zone mark the omz northern boundary the boundary between the omz and the spz is considered to be a suture zone between two continental areas represented by the northern omz and the southern spz sinistral transpression associated with large scale recumbent folds are characteristic of the suture which can be tentatively correlated through the ibero armorican arc with the lizard complex sw england

dolomite dissolution rates and possible holocene dedolomitization of water bearing units in the edwards aquifer south central texas abstract rates of dolomite dissolution can be used to test the concept based on geomorphologic evidence that a major part of the edwards aquifer could have formed within the holocene a timeframe of approximately 10 000 years during formation of the aquifer in the edwards limestone cretaceous albian of the balcones fault zone dolomite dissolution and porosity development were synchronous and the result of mixing zone dedolomitization initiation of the mixing zone in the early holocene 11 000 years before present is suggested by the maximum age of formation of major discharge sites that allowed the influx of meteoric water into brine filled dolomitic preaquifer units dedolomitization the dissolution of dolomite and net precipitation of calcite has left aquifer units that are calcitic and 40 vol interconnected pore space the mass of dolomite missing is obtained by comparison of stratigraphically equivalent altered and unaltered units one dissolution rate 1 76 10 4 mmol dolomite kg h 2 o 1 yr 1 is determined from this mass 10 4 yr reaction time and a log linear function describing the increase in mass discharge three orders of magnitude during aquifer formation the second estimated dissolution rate is obtained from the mass transfer of dolomite to solution calculated from the increase in magnesium in pore fluids selected from the modern aquifer to represent a typical flowpath during aquifer formation a reaction time of 10 4 yr for this mass transfer yields a rate of 0 56 10 4 mmol dolomite kg h 2 o 1 yr 1 both of these rates are comparable to modern rates of dolomite dissolution 0 3 to 4 5 10 4 mmol dolomite kg h 2 o 1 yr 1 calculated from measured reaction times in the tertiary floridan aquifer system in florida and the madison aquifer in the mississippian madison limestone of the northern great plains similarity of these rates to the estimated paleo rates of dolomite dissolution supports a 10 4 yr reaction timeframe the holocene reaction time also can be compared to a series of reaction times calculated by assuming that the mass of dolomite missing from the edwards was removed at rates observed in the floridan and madison aquifers these reaction times for complete removal of dolomite range from 2700 to 58 500 yr and span the pleistocene holocene boundary finally an estimated dolomite reaction rate during dedolomitization of the edwards aquifer based on surface area of exposed dolomite mmol cm 2 s 1 millimoles per square centimeter per second may be approximated from reaction times this rate is directly a function of the mass of dolomite removed and the surface area exposed per pore volume passing through the rock the surface area is available from the observed dolomite rhomb size in unaltered rock the rate of pore fluid movement is obtained from the averaged annual discharge rates during formation of the edwards aquifer calculated from all reaction times range from 10 13 to 10 14 mmol dolomite cm 2 s 1 these rates are faster than rates 10 18 mmol cm 2 s 1 measured in the pure laboratory system camg co 3 2 co 2 h 2 o but slower than rates determined in an alpine stream study 10 10 to 10 11 mmol cm 2 s 1 where cold glacial melt water flows over dolostone dolomite dissolution rates from both the edwards and other aquifers support the concept that a major part of the edwards aquifer could have formed within the holocene

geochemical evolution of groundwater in carbonate aquifers in taiyuan northern china abstract thirty nine samples of both cold and thermal karst groundwater from taiyuan northern china were collected and analyzed with the aim of developing a better understanding of the geochemical processes that control the groundwater quality evolution in the region s carbonate aquifers the region s karst groundwater system was divided into three geologically distinct sub systems namely the xishan mountain karst groundwater subsystem xmk the dongshan mountain karst groundwater subsystem dmk and the beishan mountain karst groundwater subsystem bmk hydrochemical properties of the karst groundwaters evolve from the recharge zones towards the cold water discharge zones and further towards the thermal water discharge zones in the xmk and the dmk the hydrochemical type of the groundwater evolves from hco 3 ca mg in the recharge flow through zone to hco 3 so 4 ca mg so 4 hco 3 ca mg in the cold water discharge zone and further to so 4 ca mg in the thermal water discharge zone by contrast the water type changes from hco 3 ca mg to hco 3 so 4 ca mg in the bmk with almost invariable tds and temperatures all along from the recharge to the discharge zone the concentrations of sr si fe f and of some trace elements al b li mn mo co ni increase as groundwater temperature increases different hydrogeochemical processes occur in the three karst groundwater sub systems in the xmk and the dmk the geochemical evolution of the groundwater is jointly controlled by carbonate dissolution precipitation gypsum dissolution and dedolomitization while only calcite and dolomite dissolution precipitation occurs in the bmk without dedolomitization the hydrogeochemical data of the karst groundwaters were used to construct individual geochemical reaction models for each of the three different karst groundwater sub systems the modeling results confirm that dedolomization is the major process controlling hydrochemical changes in the xmk and the dmk in the thermal groundwaters the dissolution rates of fluorite siderite and strontianite were found to exceed those of the cold karst groundwater systems which can explain the higher concentrations of f fe and sr 2 that are found in these waters

flandrian sea level changes in the fenland ii tendencies of sea level movement altitudinal changes and local and regional factors stratigraphic micropalaeontologic and radiocarbon data show that since c 6500 bp the fenland has been influenced by 7 periods of positive sea level tendencies and by 6 periods of negative sea level tendencies despite the numerous problems associated with the reconstruction of past altitudes of sea level the periods of positive sea level tendencies were clearly characterised by a rise in sea level the development of transgressive overlaps and a landward movement of the coastline the periods of negative sea level tendencies were characterised by the development of regressive overlaps a seaward movement of the coastline and a reduced or negative rate of sea level rise the various altitudinal errors do not permit the incontrovertible distinction of periods of falling sea levels all changes within the fenland were not synchronous and local factors influenced the exact nature of each sea level indicator dominant regional and local factors have been identified for different areas and different time periods the chronological and spatial characteristics of the sequences within the fenland are best explained by a palaeocoastline without supratidal barriers controlling sedimentation the data indicate an average crustal subsidence in the fenland of 0 9m 1000 years since c 6500 bp and the pattern of positive and negative tendencies of sea level movement is also seen in the chronologies for north west england and north east scotland