present day kinematics of the mediterranean a comprehensive overview of gps results i combine recently published gps results to derive a geodetic horizontal velocity field consistent at the scale of the mediterranean and the surrounding alpine belts the velocity field is then used to discuss the boundary conditions around each major deforming area in the mediterranean to describe the main patterns of motion and deformation to critically review the existing kinematics models and to finally point out the main unresolved kinematics questions strain rate in europe north of the alpines belt is dominated by the signature of the glacial isostatic adjustment and tectonic strain remains below the current accuracy of gps results in the western mediterranean deformation is restricted to the betics the alboran and the morrocan rif with west to southwestward motion with respect to iberia which is part of stable europe shortening consistent with the relative nubia eurasia plate motion is found throughout the maghrebides but the distribution of deformation in northern africa remains largely unknown the central mediterranean is dominated by the counter clockwise rotation of the adriatic the junction between the southern adriatic domain and nubia has yet to be firmly established the deformation over a wide area east of the maghrebides in tunisia and the gulf of sirte in libya still remains to be quantified in the eastern mediterranean the velocity field is dominated by a general anti clockwise rotation and a general trend towards the hellenic trench with velocity magnitude increasing with decreasing distances from the trench this trend is observed not only in the aegean and anatolia but also in the southern balkans geodetic results emphasize that the convergence of the nubia and arabia plates towards eurasia directly controls the deformation across only very few segments along the plate boundary zone additional processes are therefore required to explain the observed velocity field and deformation pattern

do extrusion ages reflect magma generation processes at depth an example from the neogene volcanic province of se spain the high k calc alkaline volcanic rocks along the neogene volcanic province of se spain represent crustal anatectic melts mixed with mantle components during the opening of the alboran sea partially melted metapelitic enclaves along with the geochemical signature provide evidence of their crustal source u pb shrimp geochronology on monazite and zircon from enclaves and their hosting lavas in the localities of el hoyazo mazarron and mar menor reveals variable delays between the melting at depth and the eruption of the volcanics these data indicate that 1 the most important event of anatexis in the neogene spanned at least the 3 m y interval between 12 and 9 ma 2 there is no trend in age of crustal melting and 3 the delay between magma generation and extrusion varies from more than 3 m y at el hoyazo to 0 5 m y and possibly 2 5 m y at mar menor with no significant delay measurable at mazarron the variable time delay between anatexis and lava extrusion indicates that radiometric ages of volcanics may provide misleading information on the timing of magma genesis occurring at depth this highlights the pitfall of basing detailed geodynamic models on volcanic extrusion ages alone

the ultrapotassic rocks from southeastern spain the ultrapotassic rocks of orenditic affinity from southeastern spain have variable sio2 and mgo contents high k2o p2o5 ni cr ba ce th zr values and high k2ona2o nimgo ratios on the contrary tio2 nb y are moderate and feot cao v sc are low the parent magmas possibly generated from a phlogopite bearing mantle source enriched in many incompatible elements by metasomatic processes and probably they were characterized by very co2 co2 h2o ratio the low tip ratio and the moderate tio2 and nb contents in spite of the high alkaline element contents of the magmas suggest that titanium and niobium were retained in the source of the metasomatic fluids the low na contents may depend in part on the loss of this element via naf separation during the latest stage of crystallization crustal contamination cannot be excluded

mantle dynamics beneath the gibraltar arc western mediterranean from shear wave splitting measurements on a dense seismic array 1 controversial evolutionary models have been proposed for the gibraltar arc system a complex interaction zone between the eurasia and african plates here we derive new mantle anisotropic constraints from sks splitting measurements on a dense network of about 90 broad band stations deployed over south iberia and north morocco the inferred fast polarization directions fpd clearly show a spectacular rotation along the arc following the curvature of the rif betic chain while stations located at the south and south east edges show distinct patterns these results support geodynamical processes invoking a fast retreating slab rather than convective removal and delamination models the fpd variations along the gibraltar arc can be explained by fossil anisotropy acquired during the western mediterranean eocene subduction while changes to the south and south east of the rif betic chain could be the imprint of a flow episode around an alboran high velocity slab during its miocene fragmentation from the algerian slab

origin and petrogenetic implications of tourmaline rich rocks in the sierra nevada betic cordillera southeastern spain tourmaline rich rocks up to 60 tourmaline associated with low medium grade metamorphic assemblages occur in the sierra nevada area betic cordillera southeastern spain tourmaline appears in a variety of forms 1 stratiform tourmalinites 2 quartz tourmaline nodules 3 porphyroclasts in felsic orthogneisses and 4 disseminations in psammopelitic metasediments and gneisses tourmaline within these lithologic groups exhibits textural and chemical variations that reflect complex premetamorphic growth under open system conditions and subsequent changes due to alpine regional metamorphism microprobe analyses of the tourmalines reveal a wide compositional variation between schorl and dravite end members with variable contents of x site vacancies av 0 084 0 225 apfu ca av 0 095 0 269 apfu and excess of al up to 6 588 apfu compared with the theoretical value of 6 in ideal schorl and dravite the amount of ca may be significant in porphyroclasts from the gneisses fe fe mg ratios for tourmalines in tourmalinites metasediments and gneisses range from 0 34 to 0 95 0 16 to 0 92 and 0 28 to 0 97 respectively na na ca ratios are also variable mostly ranging from 0 5 to 0 9 many of the tourmalines have complex chemical and colour zoning patterns including significant fluctuations in al fe mg na ca ti and f based on petrographic and chemical data three generations of tourmaline have been established the first generation corresponds to magmatic postmagmatic tourmaline that is represented by tourmaline porphyroclasts within the orthogneisses the second generation of tourmaline formed during tourmalinization of psammopelitic rocks giving rise to tourmalinites the third generation of tourmaline is represented by cellular textures pale reaction rims and overgrowths developed during the alpine regional metamorphic overprint d 2002 elsevier science b v all rights reserved

evolution of 3 d subduction induced mantle flow around lateral slab edges in analogue models of free subduction analysed by stereoscopic particle image velocimetry technique abstract we present analogue models of free subduction in which we investigate the three dimensional 3 d subduction induced mantle flow focusing around the slab edges we use a stereoscopic particle image velocimetry spiv technique to map the 3 d mantle flow on 4 vertical cross sections for one experiment and on 3 horizontal depth sections for another experiment on each section the in plane components are mapped as well as the out of plane component for several experimental times the results indicate that four types of maximum upwelling are produced by the subduction induced mantle flow the first two are associated with the poloidal circulation occurring in the mantle wedge and in the sub slab domain a third type is produced by horizontal motion and deformation of the frontal part of the slab lying on the 660 km discontinuity the fourth type results from quasi toroidal return flow around the lateral slab edges which produces a maximum upwelling located slightly laterally away from the sub slab domain and can have another maximum upwelling located laterally away from the mantle wedge these upwellings occur during the whole subduction process in contrast the poloidal circulation in the mantle wedge produces a zone of upwelling that is vigorous during the free falling phase of the slab sinking but that decreases in intensity when reaching the steady state phase the position of the maximum upward component and horizontal components of the mantle flow velocity field has been tracked through time their time evolving magnitude is well correlated to the trench retreat rate the maximum upwelling velocity located laterally away from the subducting plate is 18 24 of the trench retreat rate during the steady state subduction phase it is observed in the mid upper mantle but upwellings are produced throughout the whole upper mantle thickness potentially promoting decompression melting it could thereby provide a source for intraplate volcanism such as mount etna in the mediterranean the chiveluch group of volcanoes in kamchatka and the samoan hotspot near tonga

evidence for a 4700 2100 bc palaeoearthquake recorded in a fluvial archaeological sequence of the segura river se spain abstract the archaeological excavation of a rock shelter abrigo del pozo in one of the slopes of the segura river se spain has revealed a exceptionally preserved sedimentary record spanning from the paleolithic to the present day which includes an anomalous layer of stones rfb fallen from the roof the sedimentary analysis of the stratigraphic sequence exhumed by the excavation indicates that human occupation of the rock shelter was controlled by fluvial environmental evolution however the rfb level resulted in a disturbance of human occupation and normal fluvial sedimentation from the sedimentary and archaeological pieces of evidence the rfb level has been interpreted as related to a palaeoearthquake responsible for the collapse of the roof and walls of the rock shelter the palaeoearthquake has been dated between 5820 50 bp the 14 c age of the neolithic occupation level directly below the rfb and 3710 40 bp the 14 c age of the chalcolithic level above the rfb a nearby earthquake of m 5 5 6 5 appears as the most plausible cause for the shelter collapse these data suggest that the seismic activity of this sector in the eastern betics has been continuous during the holocene but with larger magnitudes than the ones instrumentally recorded nowadays more palaeoseismic data are required to determine whether or not regional faults such as the nearby socovos fault are silent faults with a discontinuous seismic behaviour that could modify the current hazard assessment

precipitation of secondary minerals in acid sulphate chloride waters traced by major minor and rare earth elements in waters the case of purace volcano colombia abstract major minor and rare earth elements were analyzed in the acid sulphate chloride thermal springs associated to purace volcano hydrothermal system the waters of purace were classified in 2 different groups as a function of the physico chemical parameters and element distributions group 1 is characterized by the highest ph 3 5 an outlet temperature of 81 c and a strong depletion of fe al si and ba with respect to the isochemical dissolution of the average volcanic local rock group 2 waters have lower ph values 1 9 and temperature 48 c compared with group 1 moreover group 2 is not characterized by a typical pathway representing the congruent dissolution of the rock and shows a distribution of major and minor elements that is more close to the near congruent dissolution of the average volcanic local rock with respect to group 1 these geochemical features of major and minor elements allow to propose that the chemical composition of the waters of group 1 is strongly affected by the precipitation of secondary minerals such as alunite jarosite kaolinite barite and polymorphs of sio2 the grouping of waters is also supported by the distribution of dissolved ree normalized to the average volcanic local rock group 1 shows ree patterns strongly depleted in light rare earth elements lree typical of water that formed alunitic and or kaolinitic rocks on the contrary group 2 is characterized by flat patterns in according to the near congruent dissolution of the rocks ree dissolved in waters of purace were compared with ree in the acidic waters of nevado del ruiz and azufral colombian volcanoes and with ree in minerals recognized in advanced argillic alteration alunite gypsum and kaolinite precipitation of secondary minerals is proposed as a common process depleting lree in acidic sulphate chlorine waters in volcano hydrothermal systems furthermore the chemical fractionation of the major and minor elements was interpreted together with the corresponding distributions of ree in order to trace the water rock interaction processes saturation indexes of most common secondary minerals identified in advanced argillic alterations were calculated using phreeqc software in a range of temperature from 25 to 250 c this geochemical approach allows to identify the possible mineral precipitation or dissolution of secondary minerals as well as the temperature at which the water reached equilibrium with a given set of minerals in group 1 the precipitation of secondary minerals lree enriched alunite minerals and kaolinite was traced at temperature of precipitation higher than 101 c

constraints on the frontal crustal structure of a continental collision from an integrated geophysical research the central western betic cordillera sw spain 1 melange rocks outcrop widely in the central and western frontal sectors of the betic cordillera as in many other collisional orogens where they form part of the accretionary wedges extrusion of triassic plastic clays and evaporites was favored by the progressive accretion of the betic external zones mixing rocks of different provenance and forming a synorogenic frontal melange unit mt data coupled with gravity data are a valid combined methodology to characterize the geometry of these melange units since the characterization of plastic rocks geometry is usually uncertain using seismic techniques the results correlate well with known geological features sedimentary basins calcareous ranges evaporitic rocks and reveal the deep geometry a resistive body slightly dipping toward the se points to the continuity of the iberian massif below the guadalquivir basin 2 and the external zones 6 8 to the south gravity models show the iberian continental crust subducting below the internal zones with a roughly 20 35 slope the main conductive bodies are related to the location of evaporitic rocks involved in the frontal melange they overlie the iberian massif and southwards the frontal jurassic and cretaceous limestone sequences of the external and median subbetics in this setting thick plastic rock units placed above the foreland could act as a lubricant facilitating continental subduction and being progressively accreted toward a frontal melange

a cross section of the eastern betic cordillera se spain according field data and a seismic reflection profile abstract the bt3 multichannel seismic profile was acquired by the c g g compagnie general de geophysique in 1977 for hydrocarbon exploration in the eastern betic cordillera reximseis ltd scanned and vectorized a paper copy and then performed post stack processing including coherence filtering and deconvolution the receiver functions of a broad band seismic station located near the village of velez rubio at the se end of the profile were analysed by julia et al julia j mancilla f morales j 2005 seismic signature of intracrustal magmatic intrusions in the eastern betics internal zone se iberia geophysical research letters 32 l16304 doi 10 1029 2005gl023274 to determine the structure of the underlying crust we have used these vp data to convert the profile to depth the profile has a mean se nw trend with a se section 44 km in length followed by a nw section 20 km in length the record includes the first 4 s twtt which corresponds to 11 km two main areas can be seen in the profile at the se end a band of high amplitude discontinuous reflectors dips towards the north the band is 100 to 200 ms thick increasing even more northwards this band reaches the surface at the top of the malaguide complex the upper complex of the internal zones above these reflectors an area with chaotic seismic facies and no reflectors corresponds to the outcrops of the olistostromes and turbidites of the solana formation and it is in turn overlain by discontinuous reflectors of the subbetic rocks at the nw end of the profile a set of high amplitude continuous reflectors with se dips point to the location of the prebetic below this section oblique reflectors of intermediate amplitude indicate the variscan basement over the prebetic we have marked the basal thrusts of the intermediate units and the subbetic using this seismic data as well as field observations we propose a geological cross section of the upper crust of the eastern betic cordillera and a model of the most recent evolution of the orogen in this model the internal zones and the subbetic have been welded together from the middle burdigalian to the present day and acted as an orogenic wedge that deformed the intermediate units and the prebetic

crustal thinning and mafic underplating beneath the neogene volcanic province betic cordillera se spain evidence from crustal xenoliths three metapelitic xenolith suites in the neogene volcanic province nvp of se spain from sw to ne el hoyazo mazarron and mar menor originated by partial melting at different crustal depths decreasing from 20 25 km in the sw to 9 12 km in the ne peak temperatures reached c 900 c the xenolith source level is equated with the base of a felsic upper crust of high melting potential fertility at el hoyazo this matches a thin intracrustal low velocity zone recently inferred from seismic studies isostatic calculations indicate that this zone increases in thickness from sw to ne a model of increasing upper crustal thinning from sw to ne in the nvp accompanied by mafic underplating is consistent with the 9 ma petrological data with current heat flow seismic data and gravimetry it is concluded that significant crustal extension occurred in the nvp in the late miocene i e after the main phase of widespread extension exhumation of high pressure rocks and formation of the alboran sea

neogene tectonic evolution of the gibraltar arc new paleomagnetic constrains from the betic chain new paleomagnetic results from neogene sedimentary sequences from the betic chain spain are here presented sedimentary basins located in different areas were selected in order to obtain paleomagnetic data from structural domains that experienced different tectonic evolution during the neogene whereas no rotations have been evidenced in the late tortonian sediments in the guadalquivir foreland basin clockwise vertical axis rotations have been measured in sedimentary basins located in the central part of the betics the aquitanian to messinian sediments in the alcala la real basin and the tortonian and messinian sediments in the granada basin moreover counterclockwise vertical axis rotations associated to left lateral strike slip faults have been locally measured from sedimetary basins in the eastern betics the middle miocene to lower pliocene sites from the lorca and vera basins and locally the tortonian units of the huercal overa basin our results show that conversely from what was believed up to now paleomagnetic rotations continued in the betics after late miocene enhancing the role of vertical axis rotations in the recent tectonic evolution of the gibraltar arc

geodynamic control on orogenic and anorogenic magmatic phases in sardinia and southern spain inferences for the cenozoic evolution of the western mediterranean abstract the genetic relationships between orogenic i e subduction related and anorogenic i e intra plate cenozoic igneous phases have been investigated in two regions of the western mediterranean area sardinia and southern spain in sardinia the orogenic magmatism 38 12 ma is followed by the anorogenic volcanism mostly since about 6 ma whereas in southern spain the anorogenic volcanism follows the orogenic phase 34 6 ma after a gap of 0 4 ma in the betic calatrava districts the older orogenic magmatism tholeiitic calcalkaline and more potassic products of both areas is related to the subduction of the ionian oceanic lithosphere which developed beneath the paleo european iberian continental margin probably since middle late eocene this subduction system migrated southeastwards with time up to its present position in the eolian calabrian arc and the betic alboran regions along the apennine maghrebide belt relics of subducted lithosphere are geophysically recorded as nearly vertical bodies down to 500 600 km flattening for several hundreds of kilometres under the tyrrhenian sardinia and betic calatrava areas respectively these relics of subducted slabs which pond over large areas of the mantle transition zone appear to play a significant role also in the genesis of the younger anorogenic magmas whose major volcanic fields lie above the frontal part of the subducted slab where convective instabilities and upward mantle flow components are geophysically supported by laboratory and 3d numerical models this dynamic response to subduction involving localised mantle upwellings and remobilization of pre existing mantle components may have been a fundamental factor in the generation of anorogenic magmas due to slab roll back and inter arc extension in both eolian tyrrhenian and betic alboran regions the magma sources of the previous orogenic phases can be completely replaced by fresh mantle diapirs from whic h anorogenic magmas will be generated these magmas are invariably characterised by oib isotopic signatures himu and emi which are classically interpreted as long term recycling of oceanic crust plus variable sedimentary components via ancient pre paleozoic subduction events we propose that the recent cenozoic subduction from which the orogenic series was generated also had a dynamic influence on the younger anorogenic magmatism by remobilization of long term isolated mantle components which resulted in the secular evolution of oib type magmas in this view the on going subduction processes of the mediterranean orogenic belts did not provide chemical ingredients to the mantle sources of the anorogenic magmas but induced reactivation of older metasomatised mantle domains ultimately triggering magma genesis

the gibraltar subduction a decade of new geophysical data the gibraltar arc spans a complex portion of the africa eurasia plate boundary marked by slow oblique convergence and intermediate and deep focus seismicity the seemingly contradictory observations of a young extensional marine basin surrounded by an arcuate fold and thrust belt have led to competing geodynamic models delamination and subduction geophysical data acquired in the past decade provide a test for these models and support a narrow east dipping subduction zone seismic refraction studies indicate oceanic crust below the western gulf of cadiz tomography of the upper mantle reveals a steep east dipping high p wave velocity body beneath gibraltar the anisotropic mantle fabric from sks splitting shows arc parallel fast directions consistent with toroidal flow around a narrow westward retreating subducting slab the accompanying wsw advance of the rif betic mountain belt has constructed a thick pile of deformed sediments an accretionary wedge characterized by west vergent thrust anticlines bathymetric swath mapping images an asymmetric embayment at the deformation front where a 2 km high basement ridge has collided subduction has slowed significantly since 5 ma but deformation of recent sediments and abundant mud volcanoes suggest ongoing activity in the accretionary wedge three possible origins for this deformation are discussed gravitational spreading overall nw se convergence between africa and iberia and finally a wsw tectonic push from slow but ongoing roll back subduction in the absence of arc volcanism and shallow dipping thrust type earthquakes evidence in favor of present day subduction can only be indirect and remains the object of debate continued activity of the subduction offers a possible explanation for great m 8 5 earthquakes known to affect the area like the famous 1755 great lisbon earthquake recent gps studies show sw motion of stations in n morocco at velocities of 3 6 mm yr indicating the presence of an independent block a rif betic alboran microplate situated between iberia and africa

tectonic adaptation of the external zones around the curved core of an orogen the gibraltar arc abstract there is no real curvature in the external zones of the arc of gibraltar these external zones are made up by the juxtaposition of segments with nnw sse or e w trending structures juxtaposition does not result from late tectonics nor from a paleogeographic layout but only from miocene tectonics during and after the late burdigalian relative motion between europe and africa was essentially a n s convergence which accounts for the e w structural trends the nnw sse trends are the result of offset of the two main plates along sinistral strike slip fault zones that cross cut the previously mobile block of the internal zones and that shifted southward through time to explain the sharp juxtaposition of different trending structures two tectonic stages must be considered in each area of the external rif during the first one the rocks behaved plastically while during the second they could only move as a block the internal zones alboran block slid independently between europe and africa only until early burdigalian after this time they were locked in the main plates and broken together with them to allow further displacements

geodynamic evolution of the lithosphere and upper mantle beneath the alboran region of the western mediterranean constraints from travel time tomography an edited version of this paper was published by the american geophysical union copyright 2000 agu see also http www agu org pubs crossref 2000 2000jb900024 shtml http atlas geo cornell edu morocco publications calvert2000 htm

an evaporite bearing accretionary complex in the northern front of the betic rif orogen the guadalquivir accretionary complex forms a largely oblique prism at the northern edge of the betic rif orogen where miocene sediments plus allochthonous evaporite bearing units were accreted during the displacement of the alboran domain towards the west traditional interpretations end the tectonic structuring of the betic cordillera at the present topographic front beyond which gravitational and or diapiric processes would predominate however this study shows pervasive tectonic deformation in the outer prism with coherent oblique shortening kinematics which is achieved through an alternation of roughly n s arcuate thrust systems connected by e w transfer fault zones these structures accord well with the geophysical models that propose westward rollback subduction the main stage of tectonic activity occurred in the early middle miocene but deformation lasted until the quaternary with the same kinematics evaporite rocks played a leading role in the deformation as evidenced by the suite of ductile structures in gypsum distributed throughout the area s and l gypsum tectonites scaly clay fabrics and brittle fabrics coexist and consistently indicate westward motion top to 290 with subordinate n s contraction almost perpendicular to the transfer zones this work reveals ductile tectonic fabrics in gypsum as a valuable tool to elucidate the structure and deformational history of complex tectonic melanges involving evaporites above the decollement level of accretionary wedges

lateral variation of the crust in the iberian peninsula new evidence from the betic cordillera abstract new results from a seismic refraction wide angle reflection survey carried out in the betic cordillera in autumn 1989 contribute to a better picture of its deep structure one nw se profile cuts across the iberian massif the external and internal betics the structure of the crust in the iberian massif shows characteristics similar to those found in previous experiments the lower crust is found as a distinct layer 12 km thick with an average velocity of 6 8 km s 1 the moho is found at about 35 km depth this structure extends southeastward until a 3 4 km upwelling of the moho about 30 km north of the present day surface boundary between the external and internal betic units further southeast the moho deepens to 38 km and the lower crust is no longer seismically detected the absence of differentiated lower crust beneath part of the external betics may be related with the mesozoic rifting of the south iberian passive margin instead this absence under the internal betics may be caused by rifting in conjunction with the collisional evolution of the orogen a wnw ese profile lying in the internal betics shows the presence of a prominent reflector at 10 12 km depth this seems to be a widespread feature in the internal betics and may be interpreted as a detachment surface the moho is found at 38 km depth rising strongly in the easternmost betics seismic data suggest a thin crust in the offshore area southwest of malaga probably containing a massive zone of high velocity rocks which is also supported by available geophysical and geological data

seismic anisotropy beneath southern iberia from sks splitting abstract seismic anisotropy of the south iberian upper mantle is investigated using shear wave splitting of sks phases we analyzed teleseismic events recorded by sixteen permanent broadband stations installed on the southern iberian peninsula and in northern africa and we determined fast polarization directions and delay times t between fast and slow components the area of investigation extends across two important geological structures in the variscan iberian peninsula the variscan iberian massif in its center and the gibraltar arc in the southeast that represents the most westerly alpine belt in the western mediterranean shear wave splitting measurements from stations in the betic domain show homogeneous ene wsw fast directions nearly parallel to the trend of the mountain belt and smooth spatial variations stations in the north toward the southern part of the variscan iberian massif show homogeneous fast directions however trending ns to ne sw different from those recorded in the betic these observations may reflect a post hercynian variscan deformation of the ossa morena zone related to the main stages in the tectonic evolution of this part namely transpressional stage transtensional stage and shortening episode or a deformation related to the posterior alpine orogeny along the gibraltar arc we observe a smoothly varying trend changing from ene wsw in the eastern betics to ns in the area of gibraltar and ceuta following more or less the general trend of the mountain belt around the alboran sea and the coastline since a similar rotation is also visible in results from pn anisotropy this suggests that the anisotropy is vertically coherent starting from just below the moho comparing the anisotropy pattern expected from various geodynamic models with the observed sks splitting suggests that the anisotropy is best explained by a model of slab rollback rather than by delamination models

emplacement of the cabezo maria lamproite volcano miocene se spain lamproite volcanoes are uncommon in the geological record but are exceptionally well preserved in the betic cordilleras of se spain where they erupted during the late miocene tortonian to messinian stages the parent melts are thought to have been channelled through major lithospheric faults to erupt at or near the faulted margins of neogene sedimentary basins lamproite magmas are thought to be relatively co2 poor 1 wt and are typically characterised by an effusive eruption style and the development of lava lakes and scoria cones cabezo maria is a relatively small 550 m diameter lamproite volcano that was emplaced within the shallow water marine influenced vera basin the lamproites are compositionally similar to those of the roman province and generally less potassic k2o 5 wt than other ultra potassic rocks in se spain e g cancarix fortuna the initial eruption stages were dominated by explosive magma water interactions and the formation of peperites these are characterised by angular fragments of glassy lamproite lavas and isolated lobes incorporated in sediments locally showing the effects of thermal metamorphism further elutriation pipes and jigsaw fit textures are observed in the peperites the lavas and peperites are overlain by outward dipping well stratified scoria deposits defining part of a cinder cone which is inferred to have emerged above sea level steep internal contacts with inward dipping structureless breccias likely represent the inner wall deposits of a central conduit the deposits are cross cut by late stage dykes which supplied fissure eruptions of geochemically similar lavas capping the scoria cone the transition from explosive to effusive behaviour may reflect the decreased availability of water possibly due to downward migration of the feeder conduit below the level of water saturated sediments

k rich mantle metasomatism control of localization and initiation of lithospheric strike slip faulting a conceptual model is proposed in which bulk transtension or local transtension during bulk simple shear resulting from mantle anisotropy contrasts or lithosphere rheology contrasts of heterogeneously enriched lithospheric mantle triggers localized k rich magmatism which focuses strain and causes nucleation of lithosphere scale transtensional or strike slip shear zones transtension triggered magmatism is most likely to be located at sites of maximum metasomatism of the lithospheric mantle magma generated fractures propagate upwards nucleating zones of lithospheric weakness which focus shear in narrow transcurrent faults or at basin margins in this way magmatism controls fault timing and location although volcanism will be coeval with fault development and volcanoes will appear fault controlled counterintuitively our model suggests that faults are in a sense volcanocontrolled we suggest that this new transtension k rich magmatism transcurrent faulting association represents a hitherto unrecognized genetic relationship as significant as for example the ocean island magma series

crustal structure of the central sector of the betic cordillera se spain deep seismic reflection gravimetric and magnetometric data allow the main features of the deep structure of the central sector of the betic cordillera to be established the moho is horizontal or dips slightly toward the s below the mountain chain and its morphology has no direct relationship with the region s topography the deep reflectors are not deformed by the neogene kilometric scale folds that produced the main topographic features probably due to the existence of detachment levels in the crust the crust is slightly thickened in the betic cordillera almost 35 km and has an abrupt transition to the thin crust of the alboran sea 15 km in the central alboran sea along an e w oriented narrow band subparallel to the coast line where the moho dips more than 60 n the neogene evolution of the mountain chain caused compressive deformation in the external zones in the internal zones pre tortonian low angle normal faults developed after the alpine metamorphism and later high and low angle normal faults and strike slip faults occurred up to the quaternary geophysical and field geology data can be used to establish a geological model for the recent evolution of the crustal deformation in this model the recent evolution of the region is probably determined by thrusting of the thin continental crust of the alboran sea toward the nw over the southern margin of the iberian massif this deformation could be a consequence of the oblique convergent movement between the african and eurasian plates which may have uplifted the entire region causing regressions in the sedimentary basins and the formation of folds and extensional structures in the upper part of the thickened crust

inversion of moment tensor focal mechanisms for active stresses around the microcontinent iberia tectonic implications the iberian microcontinent and its connected oceanic crust are affected by deformations related to the eurasian african plate boundary active stress inversions from populations of moment tensor focal mechanisms have been performed around and inside the iberian peninsula using a total of 213 moment tensor estimates main results are 1 the tensorial solutions show better consistency and lower misfits compared to those obtained previously from first p arrival focal mechanisms 2 along the eurasia africa western boundary the type of active stresses progressively changes easternwards from triaxial extension to uniaxial compression along the terceira ridge the gloria fault zone and the gulf of cadiz 3 in the betics alboran rif zone uniaxial extension predominates with shmax n155oe trending 4 in n algeria uniaxial compression reappears 5 the iberian foreland is currently under strike slip to uniaxial extension tensorial conditions

stress and palaeostress in the betic rif cordilleras miocene to the present palaeostress orientation in the betic rif cordilleras can be determined for the miocene to the quaternary by analysis of brittle microstructures faults joints striated pebbles and stylolites in the central and northern south iberian domain 1 was subhorizontal and trended nw se from the early miocene to the present in the northern alboran domain from the burdigalian to the serravallian palaeostress ellipsoids were oblate with 3 subhorizontal and trending ene wsw in the southern part of the south iberian domain and in the northern part of the alboran domain betic cordillera from the tortonian to the quaternary palaeostress ellipsoids were variable in the granada region they were prolate with 1 subvertical but in the almeria region they were triaxial with 2 subvertical and 3 subhorizontal and trending ne sw to e w in the rif the alboran and african maghrebian domains were affected by palaeostresses with 1 subhorizontal varying from ne sw in tortonian times to n s in the plio quaternary a study of earthquake focal mechanisms by the right dihedra method indicates that the present day general stress field around the betic rif cordilleras is compressional with 1 subhorizontal and trending nw se in the betic rif cordilleras this general stress field is modified and the present day orientations of 1 2 and 3 are nearly the same as those of the palaeostresses in the pliocene and quaternary the distribution and evolution of stresses in the betic rif cordilleras from the miocene to the present can be correlated with the main neogene deformations extensional structures in the central and northern alboran domain and the southern part of the south iberian domain and compressional structures in the south iberian and african maghrebian domains and in the southern part of the alboran domain

geochemical and temporal evolution of cenozoic magmatism in western turkey mantle response to collision slab break off and lithospheric tearing in an orogenic belt post collisional magmatism in western anatolia began in the eocene and has occurred in discrete pulses throughout the cenozoic as it propagated from north to south producing volcano plutonic associations with varying chemical compositions this apparent sw migration of magma tism and accompanying extension through time was a result of the thermally induced collapse of the western anatolian orogenic belt which formed during the collision of the sakarya and tauride anatolide continental blocks in the late paleocene the thermal input and melt sources for this prolonged magmatism were provided first by slab break off generated aesthenospheric flow then by lithospheric delamination related aesthenospheric flow followed by tectonic extension driven upward aesthenospheric flow the first magmatic episode is represented by eocene granitoid plutons and their extrusive carapace that are linearly distributed along the izmir ankara suture zone south of the marmara sea these suites show moderately evolved com positions enriched in incompatible elements similar to subduction zone influenced subalkaline magmas widespread oligo miocene volcanic and plutonic rocks with medium to high k calc alkaline compositions represent the next magmatic episode partial melting and assimilation fractional crystallization of enriched subcontinental lithospheric mantle derived magmas were important processes in the genesis and evolution of the parental magmas which experienced decreasing subduction influence and increasing crustal contamination during the evolution of the eocene and oligo miocene volcano plutonic rocks collision induced lithospheric slab break off provided an influx of aesthenospheric heat and melts that resulted in partial melting of the previously subduction metasomatized mantle lithosphere beneath the suture zone producing the eocene and oligo miocene igneous suites the following magmatic phase during the middle miocene 16 14 ma developed mildly alkaline bimodal volcanic rocks that show a decreasing amount of crustal contamination and subduction influence in time both melting of a subduc tion modified lithospheric mantle and aesthenospheric mantle derived melt contribution played a significant role in the generation of the magmas of these rocks this magmatic episode was attended by region wide extension that led to the formation of metamorphic core complexes and graben systems aesthenospheric upwelling caused by partial delamination of the lithospheric root beneath the western anatolian orogenic belt was likely responsible for the melt evolution of these mildly alkaline volcanics lithospheric delamination may have been caused by peeling off during slab rollback the last major phase of magmatism in the region starting c 12 ma is represented by late miocene to quaternary alkaline to super alkaline volcanic rocks that show oib like geochemical features with progressively more potassic compositions increasing toward south in time these rocks are spatially associated with major extensional fault systems that acted as natural conduits for the transport of uncontaminated alkaline magmas to the surface the melt source for this magmatic phase carried little or no subduction component and was pro duced by the decompressional melting of aesthenospheric mantle which flowed in beneath the atte nuated continental lithosphere in the aegean extensional province this time progressive evolution of cenozoic magmatism and extension in western anatolia has been strongly controlled by the interplay between regional plate tectonic events and the mantle dynamics and provides a realistic template for post collisional magmatism and crustal extension in many orogenic belts

strain and stress fields along the gibraltar orogenic arc constraints on active geodynamics abstract the gibraltar orogenic arc in the western mediterranean represents a complex region of active deformation related to the oblique nubia eurasia convergence process to increase the knowledge on the ongoing active processes in this region we have used the most up to date and comprehensive geodetic crustal motion and stress fields to this end we analyzed both continuous and campaign mode gps data collected between 1999 00 and 2011 00 across the area and compiled a multidisciplinary dataset of well constrained stress indicators to be compared with the geodetic results the main results highlight the oblique nature of the nubia eurasia convergence which provides the largest component of the observed stress pattern and is responsible for a significant strain rate field along the gibraltar orogenic arc we discuss our findings with respect to available geological seismological and geophysical data in order to verify their coherency compared to more relevant geodynamical models proposed in literature according to previous studies we confirmed how much of the secondary stress pattern can be related to the gravitational potential energy field which may also be responsible for some 2d stress strain rate angular discrepancies observed in large areas of the betics in addition taking into account the sub orthogonal azimuthal relationship between the shmax and ehmin directions and the fast polarization directions we conjectured a deep dynamic process controlling both the crustal stress field and the surface deformation on large areas of the orogenic arc finally although the models proposed to explain the geodynamic pattern of the gibraltar orogenic arc are supported by a discrete number of geological and geophysical observations it is only the back arc extension and westward rollback model that is able to adequately account for the vast majority of the observations based on our findings and other evidences we retain that this process could still be active beneath the gibraltar orogenic arc

stress distribution at the transition from subduction to continental collision northwestern and central betic cordillera 1 we analyze focal mechanisms of shallow intermediate earthquakes in a nw se transect along the western betic cordillera and alboran sea and deep earthquakes located in the central betics to constrain the state of stress at the gibraltar arc slow convergence area shallow earthquakes 620 km show very similar focal mechanisms fitting the general slab behavior of resistance to further descent at the 660 km discontinuity seismicity features evidence the present day stress distribution in a context of transition from subduction to continental collision

sr and o isotope constraints on source and crustal contamination in the high k calc alkaline and shoshonitic neogene volcanic rocks of se spain the neogene volcanic province of se spain nvps is characterized by calc alkaline ca high k calc alkaline kca shoshonitic sh ultrapotassic up and alkaline basaltic ab volcanic series all these series except the ab have high lilerlree lilerhfse and brbe ratios and high but variable sr pb and o isotope compositions the kca and sh lavas contain metapelitic xenoliths whose mineralogical and chemical composition are typical of anatectic restites the geochemical characteristics of ca kca sh and up series suggest that they originated from the lithospheric mantle previously contaminated by fluids derived from pelagic sediments additionally the presence of restite xenoliths in the kca and sh lavas indicates some sort of interaction between the mantle derived magmas and the continental crust trace element and isotope modeling for the kca and sh lavas and the restites point towards the existence of two mixing stages during the first stage the lithospheric mantle was contaminated by 1 5 of fluids derived from pelagic sediments which produced

age distribution of lamproites along the socovos fault southern spain and lithospheric scale tearing lithospheric scale tearing is commonly linked to the lateral termination of subduction rollback and slab segmentation the upper crustal expression of this process can be associated with the development of arcuate orogenic belts oroclines generated by a combination of vertical axis block rotations and strike slip faulting however the link between such strike slip faults and slab tearing is relatively poorly constrained we show here an example from the gibraltar arc in the westernmost mediterranean where lithospheric scale tear faulting during the late miocene accommodated westward subduction rollback the dextral strike slip socovos fault in the eastern betics may represent one of the surface expressions of this process we document a high concentration of mantle derived volcanic rocks lamproites along the socovos fault which were intruded as dikes during the late miocene phlogopite and whole rock 40ar 39ar ages of lamproites along the socovos fault show a spatial age zonation with older ages 9 3 8 2ma in the east and younger ages 7 3 7 1ma in the west this age distribution of the lamproites along the socovos fault is compatible with the westward retreat of the lithospheric slab that was active beneath the eastern betics in the late miocene we therefore hypothesize that tearing allowed pathways for lamproite melts in the subcontinental lithospheric mantle and lower crust with the socovos fault channelizing these magmas in the upper crust

partial crustal melting beneath the betic cordillera se spain the case study of mar menor volcanic suite abstract the neogene volcanic province nvp within the betic cordillera se spain consists of three main metapelitic enclave suites from sw to ne el hoyazo mazarron and mar menor since the nvp represents a singular place in the world where crustal enclaves were immediately quenched after melting their microstructures provide a photograph of the conditions at depth just after the moment of the melting the thermobarometric information provided by the different microstructural assemblages has been integrated with the geophysical and geodynamical published data into a model of the petrologic evolution of the mar menor enclaves they were equilibrated at 2 3 kbar 850 900 c and followed a sequence of heating melt producing reactions a local cooling event evidenced by minor melt crystallization preceded the eruption the lower crustal studies presented in this work contribute to the knowledge of i the partial melting event beneath the mar menor volcanic suite through a petrologic detailed study of the enclaves ii how the microstructures of fast cooled anatectic rocks play an important role in tracing the magma evolution in a chamber up to the eruption and how they can be used as pseudothermobarometers iii the past and current evolution of the alboran domain betic cordillera and mediterranean sea and how the base of a metapelitic crust has melted within an active geodynamic setting

modeling the evolution of the guadalquivir foreland basin southern spain 1 previous quantitative studies dealing with the origin of foreland basins have focused primarily either on the rheological basis of the lithosphere mechanical response or on the relationship between orogenic loading and sediment geometry to link the evolution of the guadalquivir foreland basin south iberia with the thermomechanical stratification of the iberian lithosphere we combine quantitative approaches to deep and shallow processes thrust loading lithospheric flexure thickness changes of the crust and the lithospheric mantle and surface mass transport a planform flexural analysis of the present day load distribution shows that basement subsidence is related not only to upper crustal thrusting but also to a deep seated additional load on the basis of the observed gravity and geoid fields we propose this additional load to be related to a lithospheric mantle thickening larger than the coeval crustal thickening further modeling of the evolution of a basin cross section reveals that the architecture of the sedimentary basin is additionally related to the lithosphere rheological response the quantitative study of the evolution of basement faulting and the forebulge uplift of sierra morena leads us to conclude that viscous stress relaxation and or plastic yielding within the lithosphere are key processes to explain the flexural evolution of the basin

messinian salinity crisis regulated by competing tectonics and erosion at the gibraltar arc the persistent shallow connection between the atlantic ocean and the mediterranean sea that caused the messinian salinity crisis may have been sustained by a balance between tectonic uplift and erosion due to inflow about six million years ago a series of geological factors drastically reduced the exchange of water between the atlantic ocean to the mediterranean sea through what is now the strait of gibraltar the resulting widespread salt precipitation in the mediterranean linked to a decrease in sea level of about 1 5 kilometres due to evaporation is known as the messinian salinity crisis the exact mechanism that caused the crisis remains uncertain here daniel garcia castellanos and antonio villasenor propose a competition between the obstruction of the gibraltar arc seaway by tectonic uplift and its erosional deepening by water inflow controlled by the resulting changes in sea level difference across the gibraltar arc as a possible mechanism for the crisis the messinian salinity crisis1 2 5 96 to 5 33 million years ago was caused by reduced water inflow from the atlantic ocean to the mediterranean sea resulting in widespread salt precipitation and a decrease in mediterranean sea level of about 1 5 kilometres due to evaporation3 the reduced connectivity between the atlantic and the mediterranean at the time of the salinity crisis is thought to have resulted from tectonic uplift of the gibraltar arc seaway and global sea level changes both of which control the inflow of water required to compensate for the hydrological deficit of the mediterranean1 4 however the different timescales on which tectonic uplift and changes in sea level occur are difficult to reconcile with the long duration of the shallow connection between the mediterranean and the atlantic5 needed to explain the large amount of salt precipitated here we use numerical modelling to show that seaway erosion caused by the atlantic inflow could sustain such a shallow connection between the atlantic and the mediterranean by counteracting tectonic uplift the erosion and uplift rates required are consistent with previous mountain erosion studies with the present altitude of marine sediments in the gibraltar arc6 7 and with geodynamic models suggesting a lithospheric slab tear underneath the region8 9 10 the moderate mediterranean sea level drawdown during the early stages of the messinian salinity crisis3 5 can be explained by an uplift of a few millimetres per year counteracted by similar rates of erosion due to atlantic inflow our findings suggest that the competition between uplift and erosion can result in harmonic coupling between erosion and the mediterranean sea level providing an alternative mechanism for the cyclicity observed in early salt precipitation deposits and calling into question previous ideas regarding the timing of the events that occurred during the messinian salinity crisis1

the nature origin and thermal influence of the granite source layer of central iberia abstract the central iberian zone comprises low grade metamorphic zones alternating with variscan thermal domes apparently equilibrated at the same pressure the variscan thermal domes are composed of authochtonous to allochtonous granites and anatectic complexes that represent remnants of the granite source layer the anatectic complexes consist of 90 high grade metasediments and 10 cadomian documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 543 pm 6 end document ma felsic metaigneous rocks the latter being extremely ra

on the ability of pyroclastic flows to scale topographic obstacles we present a simple analysis of momentum dissipation in a pyroclastic flow with high initial velocity and show that the deceleration is inversely proportional to the volumetric flow rate consequently for a given mass flow rate dense flows slow down more rapidly than dilute flows the analysis ignores density stratification and flow unsteadiness and assumes that deceleration is due to turbulent dissipation alone but the results have implications for a wide range of flow regimes we apply our analysis to the distribution of the 1800 year old deposits of the taupo pyroclastic flow the velocity of which is constrained by the height of topographic obstacles that it scaled the volumetric flow rate required to maintain velocities high enough to overtop the rugged topography is consistent with a dilute flow but strongly argues against the dense flow hypothesis the same conclusion applies to other pyroclastic flow deposits distributed over rugged terrain

active transfer fault zone linking a segmented extensional system betics southern spain insight into heterogeneous extension driven by edge delamination pliocene and quaternary tectonic structures mainly consisting of segmented northwest southeast normal faults and associated seismicity in the central betics do not agree with the transpressive tectonic nature of the africa eurasia plate boundary in the ibero maghrebian region active extensional deformation here is heterogeneous individual segmented normal faults being linked by relay ramps and transfer faults including oblique slip and both dextral and sinistral strike slip faults normal faults extend the hanging wall of an extensional detachment that is the active segment of a complex system of successive wsw directed extensional detachments which have thinned the betic upper crust since middle miocene two areas which are connected by an active 40 km long dextral strike slip transfer fault zone concentrate present day extension both the seismicity distribution and focal mechanisms agree with the position and regime of the observed faults the activity of the transfer zone during middle miocene to present implies a mode of extension which must have remained substantially the same over the entire period thus the mechanisms driving extension should still be operating both the westward migration of the extensional loci and the high asymmetry of the extensional systems can be related to edge delamination below the south iberian margin coupled with roll back under the alboran sea involving the asymmetric westward inflow of asthenospheric material under the margins

deep electrical resistivity structure of the northern gibraltar arc western mediterranean evidence of lithospheric slab break off terra nova 23 179 186 2011 abstract uncertainties about the lithospheric structure of the gibraltar arc have led to the proposal of several contradictory models to explain its geodynamic setting herein we present a novel 3 d model of the lithospheric electrical resistivity distribution beneath the whole betic cordillera obtained by inverting both broad band and long period magnetotelluric data the lithosphere asthenosphere boundary under sw iberia is shown to be deeper than under the alboran basin in addition the sensitivity tests confirm the presence of a n s oriented low resistivity anomaly at lithospheric mantle depths east of the 4 w meridian it coincides with an area of low velocities without earthquake hypocenters and is interpreted as asthenospheric material intruded by the lateral lithospheric tearing and breaking off of the e directed subducting ligurian slab under the alboran domain this scenario suggests that the opening of the alboran basin is related to the westward rollback of this e directed subducting slab

role of strike slip faults in the betic rifian orogeny abstract a new model for the betic rifian orogeny of the western mediterranean spain and north africa is proposed in which four strike slip faults play an important role the faults are not of the same age two faults the left lateral jebha fault to the south in morocco and principally in the mediterranean sea and the right lateral north betic fault southern spain to the north define the boundaries of the alboran block betic and rifian internal zones final movement along these faults was during the burdigalian time two other faults the left lateral nekor fault north africa to the south of the jebha fault and the right lateral crevillente fault somewhat to the north of the north betic fault define a larger alboran block including part of the betic and rifian external zones that was present during the tortonian the following sequence of events is proposed 1 a during the eocene and oligocene the african and european plates converged in a n s sense causing the breakup and overthrusting of the betic rifian and kabyle internal zones and then the movement towards the wsw of the alboran block by slip along the jebha and north betic faults 2 b by the end of burdigalian time movement along the jebha and north betic faults ceased 3 c with continued n s convergence the nekor and crevillente faults which bound a larger alboran block were formed during the mid and late miocene the arc of gibraltar the zone lying between the four major faults seems to be a result of wsw motion of a crustal block being thrust over external zones the model proposed adds to the earlier idea that tectogenesis proceeds from the interior to the exterior of an erogenic belt in the betic rifian orogeny major strike slip fracture zones shifted to the exterior of the orogenic belt as the orogeny progressed in order to relieve the stress caused by locking of the more internal faults

lithosphere tearing at step faults response to edges of subduction zones abstract slab edges are a relatively common feature in plate tectonics two prominent examples are the northern end of the tonga subduction zone and the southern end of the new hebrides subduction zone near such horizontal terminations of subduction trenches ongoing tearing of oceanic lithosphere is a geometric consequence we refer to such kinks in the plate boundary as a subduction transform edge propagator or step other steps are the north and south ends of the lesser antilles trench the north end of the south sandwich trench the south end of the vrancea trench and both ends of the calabria trench volcanism near steps is distinct from typical arc volcanism in some cases slab edges appear to coincide with mantle plumes using 3d mechanical models we establish that step faults are stable plate tectonic features in most circumstances in the probably rare cases that the resistance to fault propagation is high slab break off will occur relative motion along the transform segment of the plate boundary often is non uniform and the step is not a transform plate boundary in the rigid plate tectonics sense of the phrase step propagation may result in substantial deformation rotation topography and sedimentary basins with a very specific time space evolution surface velocities are substantially affected by nearby steps

testing oceanic subduction and convective removal models for the gibraltar arc seismological constraints from dispersion and anisotropy we discuss mantle structure and dynamics under the gibraltar arc for that region a large variety of geodynamic models has been proposed and there was up to recently no consensus on which of these models is the best one to describe the geodynamic situation of the region the key to distinguishing the different models probably lies in the upper mantle and we propose two specially adapted seismological techniques that help to distinguish each of the two models that are more frequently invoked these are on one hand the subduction rollback sr model and on the other continental delamination or convective removal cdcr the first technique that we use is based on observations of dispersed p wavetrains that are expected for certain ray directions observations made on the gibraltar arc suggest the presence of subducted oceanic lithosphere under the alboran sea the second technique is based on shear wave splitting of sks phases and it allows us to look for the radially oriented flow that must be present in the mantle beneath the alboran sea for a cdcr mechanism there are however no indications of any radial flow up to this point both approaches therefore suggest that subduction rollback is the best model to explain the complex geodynamic situation under the region

metasedimentary and igneous xenoliths from tallante betic cordillera spain inferences on crust mantle interactions and clues for post collisional volcanism magma sources abstract the deep seated xenolith association exhumed in the pliocenic volcano of tallante betic cordillera spain includes protogranular mantle peridotites felsic metasedimentary crustal rocks as well as cumulus igneous rocks such as norites and amphibole phlogopite clinopyroxenites the whole xenolith suite equilibrated at the same pressure 0 7 0 9 gpa representing the local crust mantle boundary moho characterized by extreme lithological heterogeneity this heterogeneity resulted from orogenic processes that induced the juxtaposition of crustal rocks variably depleted in fusible components within mantle domains including metasomes as it is commonly observed in orogenic mantle massifs of the mediterranean area in this contribution we report new mineral compositions of igneous parageneses recorded in these xenoliths and we present sr nd isotope data on both igneous and metasedimentary xenoliths that integrate those from the literature sr nd isotopes coherently indicate a restitic character of the metasedimentary xenoliths which according to model ages were affected by partial melting in paleozoic times sr nd isotopic errorchrons on the igneous xenoliths on the other hand qualitatively indicate tertiary ages which are corroborated by u pb zircon datings of one norite xenolith and two composite xenoliths having zircon bearing norite veinlets the new data are discussed proposing that moho lithologies of tallante could provide significant source compositions for the genesis of the neogene volcanics of the betic area which included calcalkaline lavas as well as more potassic products such as lamproites

crustal types and tertiary tectonic evolution of the alboran sea western mediterranean multichannel seismic reflection images across the transition between the east alboran and the algero balearic basins show how crustal thickness decreases from about 5 s two way traveltime twtt 15 km thick in the west east alboran basin to 2 s twtt typical of oceanic crust 6 km thick in the east algero balearic basin we have differentiated three different crustal domains in this transition mainly on the basis of crustal thickness and seismic signature boundaries between the three crustal domains are transitional and lack evidence for major faults tilted blocks related to extension are very scarce and all sampled basement outcrops are volcanic suggesting a strong relationship between magmatism and crustal structure stratigraphic correlation of lithoseismic units with sedimentary units of southeastern betic basins indicates that sediments onlap igneous basement approximately at 12 ma in the eastern area and at 8 ma in the western area linking seismic crustal structure with magmatic geochemical evidence suggests that the three differentiated crustal domains may represent from west to east thin continental crust modified by arc magmatism magmatic arc crust and oceanic crust middle to late miocene arc and oceanic crust formation in the east alboran and algero balearic basins respectively occurred during westward migration of the gibraltar accretionary wedge and shortening in the betic rif foreland basins arc magmatism and associated backarc oceanic crust formation were related to early to middle miocene subduction and rollback of the flysch trough oceanic basement subduction of this narrow slab beneath the alboran basin was coeval with collision of the alboran domain with the iberian and african passive margins and subsequent subcontinental lithosphere edge delamination along the betic rif margins

dynamics of slab tear faults insights from numerical modelling tear resistance at the edge of a slab is an important parameter controlling the evolution of subduction zones however compared with other subduction parameters such as plate strength plate viscosity plate thickness and trench width the dynamics of tearing are poorly understood here we obtain a first order understanding of the dynamics and morphology of subduction zones to resistance during tear propagation by developing and using a novel computational modelling technique for subducting slabs with side boundaries described by visco plastic weak zones developing into tear faults our 3d model is based upon a visco plastic slab that sinks into the less dense mantle generating poloidal and toroidal flows the asthenospheric mantle field is static and only develops flow due to the subducting slab we use the finite element code escript finley and the level set method to describe the lithosphere to solve this fluid dynamics problem our results show the importance of tear resistance for the speed of trench migration and for shaping the final geometry of subduction systems we show that slab tearing along a weak layer can result in a relatively straight slab hinge shape while increasing the strength in the weak layer results in the curvature of the hinge increasing substantially high tear resistance at the slab edges may hinder rollback to the extent that the slab becomes stretched and recumbently folded at the base of the domain tear resistance also controls whether the subducting lithosphere can experience accelerating rollback velocities or a constant rollback velocity 2009 elsevier b v all rights reserved

magmatic evolution of the alboran region the role of subduction in forming the western mediterranean and causing the messinian salinity crisis the magmatic evolution of the alboran region westernmost mediterranean contains important clues for improving our understanding of the origin of mediterranean style back arc basins and the desiccation of the mediterranean sea in the messinian we use new laser 40ar 39ar age and geochemical major and trace element and o sr nd pb isotope data from igneous rocks from southern spain the alboran sea and northern morocco to reconstruct the magmatic evolution of the westernmost mediterranean since the eocene lower oligocene dikes near malaga 33 6 0 6 ma and middle to upper miocene volcanic rocks from the alboran sea area 6 57 0 04 to 11 8 0 4 ma can be subdivided into two groups 1 lree depleted relative to n morb primarily tholeiitic series and 2 lree enriched primarily calc alkaline series volcanic rocks both groups are generally enriched in fluid mobile elements e g rb th u k and pb relative to fluid immobile elements e g nb ta lree the lree depleted group has 143nd 144nd 0 5128 0 5130 isotope ratios similar to atlantic morb but higher 87sr 86sr 0 7046 0 7100 in contrast the lree enriched group has less radiogenic nd 0 5121 0 5126 and tend to more radiogenic sr 0 7066 0 7205 isotopic composition pb isotope ratios are surprisingly uniform and have compositions similar to marine sediments analyses of mineral separates show that mafic melts with relatively low 18o 5 6 7 2 had high 87sr 86sr 0 7048 0 7088 7 4 10 6 14 1 and 8 4 40 0 49 3 modeling of the trace elements and sr nd pb o isotopic compositions provides compelling evidence for the contamination of the mantle source with hydrous fluids melts which can be explained through subduction of oceanic lithosphere beneath the alboran basin but not through detachment delamination of lithospheric mantle we present a geodynamic model that reconstructs the late eocene to quaternary evolution of the western mediterranean through westward roll back of subducted tethys oceanic lithosphere slab roll back resulted in a large scale reorganization of the western mediterranean paleogeography causing the closure of marine gateways linking the atlantic ocean to the mediterranean sea isolation of the mediterranean sea led to its desiccation causing the messinian salinity crisis

miocene lamproite volcanoes in south eastern spain an association of phreatomagmatic and magmatic products abstract a series of small miocene 8 3 6 7 ma lamproite rock occurrences as monogenetic volcanoes and or dykes cover a large area in southeastern spain these rocks are associated with extensional basins filled by neogene deposits in the betic and subbetic structural units at cancarix sierra de las cabras calasparra barqueros cerro de monagrillo jumilla and vera eruptions occurred whereas at fortuna mula and zeneta there were only small scale intrusions mainly dykes this paper describes volcanic centers at cancarix calasparra and barqueros which show initial phreatomagmatic eruptions driven by interaction of rising lamproite magma with groundwater tuff ring formed during this volcanic activity subsequent activity consisted of dome extrusion in the vent areas of cancarix and calasparra and by explosive to effusive magmatic activity accompanied by extensive lava flows at barqueros calasparra and cancarix are relatively symmetric monogenetic tuff rings filled by late stage massive vertical plug extruded as degassed crystalline high viscosity magma along the volcanic conduit barqueros was initially a tuff ring whose late stage hawaiian style fountaining generated spatter and clastogenic lavas that built the intra tuff ring cone of cabezo del morron finally extensive lava flows spread from the base of the cone toward the northern part of the edifice variations in the tectonic extensional regime and local hydrogeologic conditions shallow aquifers influenced the occurrence of these lamproite volcanoes late stage magma rise was dependent on the magmatic volatile regime being already degassed at calasparra and cancarix by showing higher viscosity high crystallization rate of intra tuff ring dome extrusions or still rich in volatiles at barqueros displaying lower viscosity lava fountaining and then lava flows

seismic signature of intracrustal magmatic intrusions in the eastern betics internal zone se iberia 1 receiver functions at three broad band stations located in the most easterly inner betics have been analyzed to investigate the structure of its underlying crust and uppermost mantle these stations are located within a geologically distinctive block bounded by the palomares alhama de murcia faults which is characterized by high heat flow values widespread strike slip faulting and neogene volcanism our analysis shows that a low velocity zone pervades the uppermost mantle beneath the stations and that the overlying crust has a high vp vs ratio and a prominent intracrustal low velocity zone i between the palomares and alhama de murcia faults and ii east of murcia perhaps thermally perturbing the upper crust north and east of cartagena independent studies show that the seismic velocities of the intervening mantle lid are normal beneath the stations and we suggest that our observations result from rapidly ascending magma diapirs ponding at intracrustal levels within the distinctive block

kinematics of subduction and subduction induced flow in the upper mantle 1 results of fluid dynamical experiments are presented to model the kinematics of lithospheric subduction in the upper mantle the experiments model a dense high viscosity plate subducting lithosphere overlying a less dense low viscosity layer upper mantle the overriding lithosphere is not incorporated several important features of slab behavior were investigated including the temporal variability of hinge line migration the kinematic behavior of the slab and the subduction induced upper mantle flow both fixed and free trailing edge boundary conditions of the subducting plate were investigated results show that hinge line retreat is a natural consequence of subduction of a negatively buoyant slab the migration rate increases until the slab approaches the upper lower mantle discontinuity resulting in a decrease in migration rate followed by a renewed increase and finally approaching a steady state slab retreat results in mantle flow with material initially located underneath the slab flowing around the lateral slab edges toward the mantle wedge experimental results indicate that all rollback induced flow occurs around the lateral slab edges forcing the hinge line to attain a convex shape toward the direction of retreat no signs for poloidal flow underneath the slab tip have been detected only a small component of toroidal type flow was observed underneath slanting slab tips for a fixed trailing edge the slab does not sink vertically downward but sinks at an angle in a regressive manner for a free trailing edge slab sinking is oriented more vertically while the surface part of the subducting plate is pulled into the subduction zone

neogene and quaternary rollback evolution of the tyrrhenian sea the apennines and the sicilian maghrebides reconstruction of the evolution of the tyrrhenian sea shows that the major stage of rifting associated with the opening of this basin began at similar to10 ma it involved two episodes of back arc extension which were induced by the rollback of a west dipping subducting slab the first period of extension 10 6 ma was prominent in the northern tyrrhenian sea and in the western part of the southern tyrrhenian sea the second period of extension mainly affected the southern tyrrhenian sea began in the latest messinian 6 5 ma and has been accompanied by subduction rollback at rates of 60 100 km myr 1 slab reconstruction combined with paleomagnetic and paleogeographic constraints indicates that in the central apennines the latest messinian 6 5 ma arrival of a carbonate platform at the subduction zone impeded subduction and initiated a slab tear and major strike slip faults these processes resulted in the formation of a narrow subducting slab beneath the ionian sea that has undergone faster subduction rollback and induced extreme rates of back arc extension

changes in dip and frictional properties of the basal detachment controlling orogenic wedge propagation and frontal collapse the external central betics case thin skinned fold and thrust belts ftbs have been extensively studied through both field examples and modelling the overall dynamics of ftbs are therefore well understood one less understood aspect is the combined influence of across strike changes in the detachment properties and the basement topography on the behaviour of an orogenic wedge in this paper we use field data together with reflection seismic interpretation from the external zones of the central betics ftb s spain to identify a significant increase in the wedge basal dip a basement threshold coinciding with the pinch out of a weak substrate this induced both changes to the wedge geometry and to the basal friction which in turn influenced the wedge dynamics the changing dynamics led to a transient stagnation of the ftb propagation topographic build up and subsequent collapse of the ftb front this in turn fed an important langhian depocenter made up of mass transport deposits coevally with the ftb propagation extension took place both parallel and perpendicular to the orogenic trend this case study illustrates how across strike changes in wedge basal properties can control the detailed behaviour of a developing ftb front but questions remain regarding the time space interaction and relative importance of the basal parameters

evidence for active subduction beneath gibraltar we report on a marine seismic survey that images an active accretionary wedge west of gibraltar ramp thrusts offset the seafloor and sole out to an east dipping decollement indicating ongoing westward vergent tectonic shortening new traveltime tomographic re sults image a slab of oceanic lithosphere descending from the atlantic domain of the gulf of cadiz passing through intermediate depth 60 120 km seismicity beneath the west ernmost alboran sea and merging with a region of deep focus earthquakes 600 660 km below granada spain together these new data provide compelling evidence for an active east dipping subduction zone

delamination in the betic range deep structure seismicity and gps motion subduction comes to an end when all oceanic lithosphere is consumed and continental or transitional crust with positive buoyancy becomes involved during continental collision the final stage of subduction may be characterized by slab breakoff limited continental subduction and delamination below the fold and thrust belt we report receiver function images constructed from a dense array of seismic broadband stations that reveal the underthrusting of iberia beneath the alboran plate the underthrusted crust is delaminating beneath part of the betic mountain range still connected to the foreland lithosphere on one side and interrupted discontinuously along the other side intermediate deep earthquakes associated with the delamination process do not respond to downdip stresses like subduction earthquakes the gps velocity field and source mechanisms for shallow earthquakes demonstrate ongoing active shortening on top of the hinge of delamination and localized perpendicular extension on top of the edge of delamination introducing independent motion of the overriding crustal block delamination beneath the betic range drives seismicity by inducing fundamental changes in deformation patterns within the collision orogen