testing the sensitivity of geomorphic indices in areas of low rate active folding eastern betic cordillera spain abstract active deformation structures have an incidence in topography that can be quantified by using geomorphic indices most of these indices have been checked in faulted regions with high deformation rates the application of several geomorphic indices hypsometric curve analysis normalized stream length gradient and valley width to valley height ratio to the drainage network of the southern limb of the sierra de las estancias antiform internal zones eastern betic cordillera where low rate active folding has been recognized allows us to investigate the suitability of these indices to identify active structures in such a scenario hypsometric curves clearly identify regions with recent uplift and young topography but they do not provide any constraint on the location of active folds local valley width to valley height index variations have been detected just coinciding whit the position of ene wsw active folds normalized stream length gradient index serves to locate active folds in areas of hard rock substratum but not in those areas with soft sediments neogene quaternary sedimentary basins this is most likely due to the fact that in the basins erosion is much more intense than in the hard rock sectors in view of these results we consider that geomorphic indices constitute a valuable tool for identifying sectors affected by low rate uplift related to active folding with the best results obtained in hard rock areas

a strike slip fault corridor within the alpujarra mountains betic cordilleras spain in a long corridor in the internal zone of the betic cordilleras bounded to the north by the sierra nevada and to the south by the sierras lujar contraviesa and gador two discernible bands of strike slip faults exist these bands lie in an approximately e w direction and are well exposed throughout and beyond the 85 km long belt the characteristic features of strike slip faults such as cataclastic rocks composed of variously textured fault breccia which also include fragments of rocks up to several metres in size incipient foliation and striation demonstrate the right lateral nature of the displacement there are also fractures which run in a nw se and nne ssw direction and apparently originated after formation of the e w faults the magnitude of lateral displacements is difficult to calculate evidence of considerable vertical movement can be found locally these strike slip displacements have essentially occurred since the middle miocene period and might still be taking place

strength and anisotropy of foliated rocks with varied mica contents abstract we have shortened 15 schists and gneisses with varying compositions 15 75 mica by volume at angles of 45 and 90 to foliation s to investigate the influence of micas on the strength and anisotropy of foliated rocks at the conditions tested t 25 c p c 200 mpa and e 10 5 s 1 compressive strengths vary by a factor 4 in the 45 and 90 orientations and individual rock types exhibit directional responses ranging from isotropic to strongly anisotropic trends of decreasing strength decreasing anisotropy and increasing ductility are observed with increasing mica content strains in all samples were localized within inclined shear zones accommodated by dislocation slip and grain scale microkinking in micas and microcracking in all other silicates stress strain response and grain scale deformation microstructures both indicate that mechanical behavior is strongly influenced by the concentration and spatial arrangement of micas shear zone formation is associated either with discrete brittle fracture transitional strain softening or steady strength ductile shear in both brittle and transitional samples extensive microcracking of strong quartzo feldspathic bridges occurs and stress drop magnitudes decrease with decreasing spacing and increasing overlap of adjacent critically oriented micas steady strength ductile shear zones develop in samples containing domains of interconnected micas and isotropic mechanical response is observed in those in which micas are contiguous in nearly all directions

fault generated mountain fronts in southeast spain geomorphologic assessment of tectonic and seismic activity abstract tectonic activity of se spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts the selected fronts are distributed along the two most prominent crustal scale structures of the mediterranean sector of spain the eastern betic shear zone ebsz and the valencia trough geomorphic indexes used in this study are mountain front sinuosity index smf and valley floor width ratio vf this work is largely based on the smf vf regression analysis of the studied fronts together with previous available data from sw usa the development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios tectonic activity classes to be obtained this study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis it is demonstrated that discrete uplift rates of 0 15 0 08 m ka are sufficient to keep relatively low smf values down to 1 4 in active fronts class 1 taking into account the reported uplift rates and preliminary palaeoseismic data for some of the class 1 studied fronts recurrence periods for surface rupture events can be theoretically bracketed for se spain recurrence periods for class 1 fronts could theoretically range between 10 000 and 12 500 years for maximum slip conditions and 1750 and 2600 years for minimum slip conditions inactive fronts class 3 develop under uplift rates down to 0 03 m ka and tested recurrence intervals for rupture events range between 25 000 and 50 000 years class 2 fronts of intermediate characteristics and activity display uplift rates between 0 07 and 0 03 m ka

active faulting and folding along the jumilla fault zone northeastern betics spain abstract the jumilla fault zone jfz is an ene wsw topographic lineament in the external part of the eastern betic cordillera it represents an active fault three small basins are aligned along the jfz the la celia alqueria and jumilla basins the tectonic geomorphology of the la celia and alqueria basins consists of folds a set of normal fault scarps strike slip lineaments fault springs tectonically modified drainage lines and elevated gypsum anhydrite diapirs two of the scarps are normal faults generated by the extensional collapse of one of the folds the other scarps are secondary normal faults generated by transtensional left lateral motions along the jfz normal fault scarps that developed on conglomerates are considerably steeper 30 than those affecting softer marly materials the onset of fault activity is constrained by the late tortonian messinian age of the sedimentary rocks in the basins interbedded lavaflows and lamproitic dykes in the lacustrine sediments have been dated at 7 6 7 2 ma however the morphology of fault scarps and relief of the diapirs suggest a younger age of the deformation results from modelling of fault scarp evolution indicate middle pleistocene and younger ages of faulting and scarp formation furthermore in at least one of the fault scarps quaternary alluvial pediment deposits are involved in the deformation the drainage pattern anomalies and moderate earthquake activity mb 4 2 in the jfz also indicate slow ongoing tectonic activity in addition the ene prolongation of the jfz outside the study area shows geodetic displacement rates of approximately 2 mm year we thus conclude that the jfz is still active despite the general lack of post messinian deposits in the studied basins the discrepancy between the age of the tectonic landforms and the late neogene age of the basin infill can be explained by an endo to exhorheic change in the drainage system due to the capture of the ancient basin lake system by tributaries of the nearby segura river the cessation of sedimentation in the basins resulted in the preservation of tectonic landforms

the summit erosion surfaces of the inner betic cordillera their value as tools for reconstructing the chronology of topographic growth in southern spain erosion surfaces at the top of mountain ranges have suggested to geomorphologists that the earth s crust can undergo rapid pulses of uplift during which rates of denudation fail to balance with rates of crustal uplift thereby preserving much of the initial plateau topography as it rises to greater elevations here we analyze a regionally extensive population of mappable planar surfaces which crown several major tectonically active sierras of the inner south eastern betic cordillera se spain based on a synthesis of long term landscape evolution involving landform reconnaissance dem based morphometric analysis structural geology sediment provenance analysis and field stratigraphy we conclude that the summit surfaces are a mosaic of discrete post orogenic erosion surfaces that each developed in relation to mediterranean marine base levels at a time when the sierras formed a series of low elevation islands they are not therefore fragments of a once regionally continuous paleoplain the summit surfaces were partly the result of shallow angle detachment faulting during the middle miocene in response to lithospheric slab detachment where evidence exists that the resulting low relief topography was reworked by marine abrasion during the tortonian sea level rise the terminal age of the surfaces is latest miocene age bracketing based on stratigraphic correlations among the many depocentres of the region and on published thermochronological data indicates that some erosion surfaces locally formed in less than 3 million years 8 ma 5 7 ma they were subsequently uplifted to their current elevations 1 7 to 2 km by pliocene to quaternary neotectonics in at least two major pulses

problem of folding in ductile shear zones a theoretical and experimental investigation the paper describes micro scale folds within a narrow ductile shear zone of the peninsular gneissic complex south india the characteristics of the folds indicate that they have formed by buckling on the mylonitic foliation parallel to the c fabric this raises the question of how a buckling instability could develop on the mylonitic foliation as there can be no overall shortening along the shear direction on the basis of natural observations we show that mylonitization involves sericitization locally along the c fabrics forming discrete mechanically weak zones which perturb the homogeneous shear stress field in their neighborhood and induce shortening along the bulk shear direction leading to buckling instabilities on the mylonitic foliation the weak zone model is supported with results obtained from physical experiments theoretical analysis shows that the weak bodies with large length to thickness ratios perturb the shear stress field in the shear zone significantly developing compressive stresses along the bulk shear direction required for buckle instabilities to occur on the mylonitic foliation

the late cenozoic landscape development in the westernmost mediterranean southern spain abstract the terrains of the western costa del sol in the westernmost mediterranean represent an outstanding example of the influence of major tectonic and climatic factors in the development of the landscape this region belongs to the alboran domain which is a small continental lithosphere fragment embedded between the large eurasian and african plates the territory between malaga and marbella is composed mainly of the sierra de mijas and three adjacent subsidence areas malaga torremolinos and fuengirola basins from the late miocene dip faults of approximate directions n s ne sw and nw se limited the sierra de mijas with respect to the adjacent subsidence areas and have marked the main features of the coastal morphology since then the sierra underwent mainly erosive processes linked to strong uplifting while the surrounding basins were subjected to alternate stages of sedimentation and erosion thus the paleogeographic and geomorphological evolution has been driven both by the regional tectonics and by significant base level changes ranging from the spectacular messinian low stand to the catastrophic overflow at gibraltar followed by the global late tertiary and quaternary sea level changes in the mountain relief three different erosive leveling surfaces have been recognized which developed in a staggered sequence during the miocene and are currently fragmented by tectonics at different elevations the first two leveling surfaces continental in origin were carved during the middle miocene pro part the late one correlating with upper miocene marine deposits from the malaga basin appears to correspond partially to an abrasion platform developed during the highstand of the late tortonian the strong incision of the fluvial network especially due to the low sea level during the messinian salinity crisis but also to the tectonic rise of the sierra has largely eroded these surfaces which can be recognized only in narrow inter fluvial areas the noteworthy marine transgression in the miocene pliocene transition reached the edge of the sierra de mijas developing both a broad marine abrasion platform around it and the main stage of sedimentary filling in the malaga basin tectonics combined with sea level changes influenced the formation of a lower second abrasion platform in the torremolinos sector and along the s edge of the sierra showing continuity with the late zanclean marine deposits in the torremolinos and fuengirola areas during most of the late pliocene and the gelasian the region remained emerged and subjected to erosion conversely climate eustatic changes throughout the pleistocene and holocene led to the development of three major generations of progradant alluvial fans interrupted by stages of erosion and incision of the fluvial network in parallel up to five episodes of travertine build up occurred usually coinciding with the humid and warm odd numbered isotopic stages

mechanics of kink bands during torsion deformation of muscovite aggregate abstract the growth geometry and bulk mechanical behavior of grain scale kink bands were investigated during layer parallel non coaxial deformation torsion of synthetic polycrystalline aggregates of muscovite at constant displacement rate 3 10 4 s 1 and various confining pressures cp 50 300 mpa temperatures t 300 800 c and finite shear strains 0 2 5 0 the kink instabilities were observed during elastic to plastic transition yield at finite shear strain of ca 0 2 the shear stress required to form the kinks is a function of pressure and temperature and range from ca 20 to 90 mpa within the experimental conditions the kink bands formed in non coaxial torsion tests are asymmetric involve strain partitioning show complex microstructures with increased deformation and have a limited lifetime as the structure is destroyed at ca 5 these results suggest a domain of pressure and temperature conditions where kink band structures should be common results obtained from torsion experiments are compared to those of layer parallel axial compression conducted with the same displacement rate at 600 c and 300 mpa for 5 10 and 17 bulk shortening combining microstructures viewed on surfaces parallel and perpendicular to the torsion plane a 3d geometrical model is constructed to discuss the kink mechanism the microstructural evolution and the mechanical behavior

late quaternary large scale rotational slides induced by river incision the arroyo de gor area guadix basin se spain the arroyo de gor is a highly incised stream up to 200 m that has eroded into the pliocene pleistocene infill of the guadix basin in the betic cordillera se spain this paper concentrates on a particular reach of this stream namely the cenascuras gorafe reach where abundant inactive rotational slides can be recognized on both hillslopes of the canyon shaped valley the rotational slides have surface areas of 5 15 ha and volumes of mobilized material of 5 15 hm3 these rotational slides can be recognized by their main scarps which are still well featured at both margins of the valley as well as by the counter hillslope rotation of the strata in their bodies the surfaces of rupture are concave their width being greater than their length i e the landslides are elongated in a direction perpendicular to the landsliding displacement and parallel to the stream at depth the surfaces of rupture developed on fine grained sediments mostly clays underlying the conglomerates and sands affected by the rotational slides the clays at the surface of rupture are smectite rich and show several features produced by the landsliding such as striations and sigmoidal shaped structures the cenascuras gorafe canyon has been developed by a combination of entrenchment fracturing and landsliding initial deep entrenchment of the stream is attributed to a base level lowering related to the capture of the former endorheic basin by the gualdalquivir river in the late pleistocene this river incision created a canyon with subvertical unstable walls which due to gravitational instability would give way to vertical open tension cracks some distance from the canyon edge the tension cracks would end at depths equal to the base of the canyon which also coincides with the contact between the conglomerates and the underlying clays the rotational slides are thought to have occurred during heavy rains by a combination of piping which would have lengthened the tension cracks and infiltration which would reduce the shear strength along the gently dipping contact between conglomerates and the underlying clays thus the blocks bounded by the tension cracks and the subhorizontal lithological contact would slide under their own weight on the subhorizontal surfaces of reduced shear strength several age constraints lead us to tentatively assign the landslides to the isotope stage 5 around 32 ka an interglacial period agreed to be wetter and slightly warmer than the present day semi arid climate

basal slip and mechanical anisotropy of biotite the basal slip systems of biotite and their mechanical expressions have been investigated by shortening single crystals oriented to maximize and minimize shear stresses on 001 samples loaded at 45 to 001 exhibit gentle external rotations associated with dislocation glide high angle kink bands in these samples unlike those developed in micas loaded parallel to 001 are limited to sample corners samples shortened perpendicular to 001 show no evidence of nonbasal slip and fail by fracture over all conditions tested the mechanical response of biotite shortened at 45 to 001 is nearly perfectly elastic plastic stress strain curves are characterized by a steep elastic slope a sharply defined yield point and continued deformation at low mostly 1 stresses measured beyond the yield point are insensitive to confining pressure over the range 200 to 500 mpa and exhibit weak dependencies upon strain rate and temperature assuming an exponential relationship between differential stress d and strain rate e of the form e cexp d exp q rt the data collected over strain rates and temperatures of 10 7 to 10 4 s 1 and 20 to 400 c respectively are best fit by an exponential constant of 0 41 0 08 mpa 1 and an activation energy q of 82 13 kj mol a power law fits the data equally well with n 18 4 and q 51 9 kj mol samples oriented favorably for slip in directions 100 and 110 are measurably weaker than those shortened at 45 to 010 and 310 consistent with the reported burgers vectors 100 1 2 110 and 1 2 110 the anisotropy of biotite is further revealed by contrasting these plastic strengths with results of samples deformed parallel and perpendicular to 001 previous studies have shown that biotite loaded in the 001 plane is strong prior to the nucleation of kink bands the strength of biotite shortened perpendicular to 001 exceeds that measured parallel to 001 and is pressure dependent application of the results to deformation within the continental crust suggests that biotite oriented favorably for slip is much weaker than most other silicates over a wide range of geologic conditions its presence within foliated rocks and shear zones may limit locally the stresses that can be supported

tectonic significance of the present relief of the betic cordillera abstract tortonian calcarenites of the betic cordillera were deposited in coastal or very shallow marine environments and represent an ideal marker for estimating vertical movements from the late miocene to the present a map showing the heights at which these tortonian marine rocks are situated has a clear correlation with the present relief indicating that today s relief has been formed since the tortonian there is also a good correlation between present relief and the bouguer anomaly distribution in the betic cordillera as well as with crustal thickness likewise the present relief is directly related to the geodynamic setting of a horizontal n s to nnw sse compression and an almost perpendicular extension along with isostatic readjustment existing in the betic cordillera from the tortonian as a result of these regional stresses faults and folds have produced notable vertical movements the highest rates of uplift of the betic cordillera coincide with large antiforms in particular those of the sierra nevada and the sierra filabres several subsiding sectors also exist for example the granada basin or the guadalquivir basin the foreland guadalquivir basin has a complex history because the uplift in its eastern sector and subsidence in the western sector coexisted during the late tortonian today the whole betic cordillera is characterized by differential regional uplift even in the aforementioned subsiding sectors

transposition of foliations and superposition of lineations during polyphase deformation in the nevado filabride complex tectonic implications detailed structural analysis in a ca 80 km2 area of the western nevado filabride complex betic cordillera reveals a heterogeneous internal structure characterized by multiple cross cutting foliations and lineations that locally transpose earlier ones the large scale geometry of these fabrics conflicts with continuous westward to south westward tectonic transport related to thrusting or crustal extension and mismatches a previously inferred extensional detachment in the area multiple crenulation lineations can be distinguished in the field and correlated with five foliation intersection axes fia1 5 preserved in garnet and plagioclase porphyroblasts of the western sierra nevada these indicate crustal shortening in different directions associated with vertical foliation development and intermitted stages of gravitational collapse producing horizontal foliations the large spread of lineation and fold axes trends in the nevado filabride complex results from the mixed presence of multiple generations of these structures whose distinction is critical for tectonic models the five principal fia trends remarkably match successive vectors of relative africa iberia plate motion since the eocene suggesting that deformation of the nevado filabride took place during this period although peak metamorphism in at least some of its parts was reached as late as the middle miocene

progressive development of structures in a ductile shear zone in the singhbhum shear zone of eastern india successive generations of folds grew in response to a progressive ductile shearing during this deformation a mylonitic foliation was initiated and was repeatedly transposed the majority of fold hinges were formed in an arcuate manner at low angles to the y axis in an e w trending subhorizontal position and major segments of the fold hinges were then rotated towards the down dip northerly plunging x axis the striping and intersection lineations were rotated in the same manner the down dip mylonitic lineation is a composite structure represented by rotated early lineations and newly superimposed stretching lineations the consistent asymmetry of the folds the angular relations between c and s surfaces and the evidence of two dimensional boudinage indicate that the deformation was non coaxial but with a flattening type of strain with 1 2 the degree of non coaxiality varied both in space and time from the progressive development of mesoscopic structures it is concluded that the 2 3 km wide belt of ductile shear gave rise to successive anastomosing shear zones of mesoscopic scale when a new set of shear lenses was superimposed on already sheared rocks the preexisting foliation generally lay at a low angle to the lenses no new folds developed where the acute angle was sympathetic to the sense of shear displacements where the acute angle was counter to the sense of shear the pre existing foliation lying in the instantaneous shortening field was deformed into a set of asymmetric folds

time dependent modelling of a mountain front retreat due to a fold to fault controlled lateral spreading abstract the eastern betic cordillera spain exemplifies at the sierra de aitana an impressive case of lateral spreading which involves a mountain anticline ridge dislodged by a post orogenic extensional tectonic the deep trenches testify the ongoing gravitational slope deformation featured by a rock mass lateral spreading the sierra de aitana anticline ridge was dislodged along a normal fault zone which generated a scarp with a kilometric lateral continuity the lateral spreading originated because eocene limestone overlays eocene marls inducing a continuous evolution over time due to visco plastic deformations and isolating huge prismatic blocks to quantify the creep driven stress strain effects at sierra de aitana ridge the mechanical and rheological parameter values of the involved rocks were quantified through field and laboratory tests which allowed to constrain an engineering geological model based on equivalent continuum approach a stress strain numerical modelling aimed at back analysing the sequential morpho structural evolution of the sierra de aitana anticline ridge was performed by reproducing the retreat of the ridge front and the time succession of faults re activations a time dependent solution was approached by assuming a time dependent creep configuration of the modelling and a parametric solution adopted to calibrate rock mass rheology also taking into account tectonic displacement due to the aitana normal fault system by simulating these element as interface in the discretized domain influence of pre existing joint sets by assuming a main anisotropy in the elasto plastic failure solution admissible variations of the regional stress field related to compressive and extensional phases and a generalised visco plastic behaviour representing the ductile marls the numerical modelling outputs that the lateral spreading mainly evolved as a creep driven process while stress release induced by tectonic activity is not sufficient to justify the observed landforms the obtained results highlight a not negligible role of inherited structural elements for regulating the time evolution of the ongoing gravitational process at the sierra the aitana anticline

structure and present day compression in the offshore area between alicante and ibiza island eastern iberian margin abstract this study deals with the structure and recent deformation of the eastern iberian margin extending from basement to seafloor and including the south western margin of the valencia basin the alicante shelf the ibiza channel and its southern margin descending into the algerian basin this area underwent a complex tectonic evolution linked to the back arc opening of the north western mediterranean and the concomitant contraction of the betic belt due to the collision with blocks located between africa and europe this oligo miocene structural heritage gave rise to a complex and continuous deformation through times including late miocene post orogenic extension and pliocene to quaternary compression in the western balearic area and coeval extension in the valencia basin this study presents maps of the depth to basement and base of the pliocene as well as bathymetry data and seismic lines which provide a precise integrated 3d study of the offshore domain it reveals a major reactivation of the area represented by the n80 to n60 trending structures small discontinuous folds and thrusts in the ibiza channel and a large flexure on the alicante shelf the structures are picked out by erosion surfaces or deposits linked to the messinian salinity crisis msc these markers are ubiquitous in the seismic sedimentary sequences and record the lateral and vertical deformation active from the messinian salinity crisis to the present the contraction in the western iberian margin and concomitant extension in the southern valencia basin are consistent with the regional stress field as determined from the focal mechanisms of offshore earthquakes or recent gps measurements the tectonic compression of the studied area casts doubt on the eventual propagation of the present day compressive stress from the algerian margin to the western balearic promontory

serpentine in active subduction zones abstract serpentinization is a key phenomenon for understanding the geodynamics of subduction zones in the 10 200 km depth range serpentines are a major water carrier and their rheological properties have a strong influence on deformation partitioning and seismicity at depths i review experimental investigations that have been conducted on serpentines with emphasis on the large body of data acquired over the past decade determinations of physical properties at the pressure and temperature conditions of subductions allow interpreting geophysical data in active subduction in terms of mineralogy and petrology and to link the presence of serpentinites with deformation and fluid circulation the fluid budget can be partially constrained from geophysical data elasticity data provide a quantitative basis for mapping serpentinization in the mantle wedge and slab from seismic tomography anisotropy suggests the existence of thin serpentinite channels above the plate interface that account for mechanical decoupling inferred from down dip limit of the seismogenic zone and heat flow strain rate dependent rheology of antigorite serpentine is consistent with stable deformation of this thin layer or channel over timescales ranging from those of the seismic cycle to those of thermal equilibration and exhumation of high pressure rocks and with the geological record of subduction related deformation circulation of serpentinizing fluids depends on the permeability structure and is imaged by electrical conductivity tomography it could be controlled by fracturing in the undeformed cold nose of the mantle wedge and by plastic deformation along the plate interface fluid migration mechanisms are similar to those inferred from petrological and geochemical data on exhumed serpentinites estimation of the fluid budget associated with serpentine formation will rely on numerical simulations for which coupling of kinetics of hydration and dehydration at scales ranging from grain size up to faulting pattern needs to be established especially for water cycling to the transition zone in the core of the slab

mountain front development by folding and crustal thickening in the internal zone of the betic cordillera alboran sea boundary the boundary between the alboran sea and betic cordillera is a good example of a fold related mountain front in the internal zone of an alpine mountain range since the late miocene nnw sse convergence between the eurasian and african plates has produced shortening and related orthogonal extension to improve the characterisation of the geometry of the deep structure in the region and to establish the recent tectonic evolution of the mountain front well logs and newly acquired geophysical data multichannel reflection seismic and gravimetric surveys have been interpreted and integrated with available surface data the most marked tectonic structure corresponds to large antiforms and synforms of ene wsw trend which are related to mountain ranges and basins respectively the fold belt continues toward the northern continental shelf of the alboran sea the fold vergence is generally northwards and its amplitude decreases progressively towards sse until disappearring in a sharp boundary where the reflectors are undeformed the deep geometry suggests that fold growth started during upper tortonian times and continued its activity up to pliocene or even quaternary times the nnw sse compression produces crustal thickening and a regional and progressive southwards emersion the location of main present day deformation fronts in the internal zones contrasts with classical models where the deformation progresses towards the frontal part of external zones of cordilleras in addition this fold related deformation mountain front has features different from fault related fronts as it does not show a sharp boundary and folds that determine rectilinear mountain boundaries decrease progressively in amplitude or in wavelength up to undeformed areas

fold and fault interactions during the development of an elongated narrow basin the almanzora neogene quaternary corridor se betic cordillera spain 1 elongated corridors grow in different tectonic settings mainly in areas deformed by fold and fault sets parallel to the borders the almanzora corridor however is a good example of an e w elongated asymmetrical narrow basin developed in a changing stress scenario generated by the interaction of fold and fault sets oriented parallel and oblique to the corridor borders the initial crustal thickening process was mainly related to the development of the e w oriented sierra de los filabres large antiform which constitutes a major heterogeneity during the tortonian a nw se convergent tectonic setting oblique to this already emerged antiform gives rise to a large dextral simple shear band that determines the development of a major fold las estancias antiform the asymmetrical location of minor tectonic structures faults and minor folds and the distribution of sedimentation denudation areas that finally configure the almanzora corridor synform furthermore development of nw se oriented normal faults points to ne sw orthogonal extension in a new stress field oblique to the corridor borders this region illustrates that the elongated character of the corridors may persist inherited from the orientation of previous crustal rheological heterogeneities in addition marine transgression may be produced in compressional settings favored by the synform development during initial stages of crustal thickening finally led to the relief uplift

active shallow extension in central and eastern betic cordillera from cgps data abstract the betic cordillera is an alpine belt formed in the western mediterranean by the westward displacement of the alboran domain in between the eurasian and african convergent plates new cgps data from the central and eastern betic cordillera and its foreland obtained mainly from the topo iberia project allowed us to precisely determine the rate of tectonic deformation most of the displacements of the central and eastern betics are westward with a variable southwestward component in relation to the eurasian stable plate while in the iberian foreland the displacements are extremely low some deformation related to low compressional deformation occurs in the easternmost foreland basin and eastern betic cordillera the displacement increases substantially southwards and westwards in relation to present day extensional deformation major active discontinuities correspond to the nw se normal fault zones which dip westwards they are located in almeria tabernas balanegra and western sierra de gador whereas the padul fault zone located west of sierra nevada extends northwards to the granada basin nw se extensional faults are also observed to the north in the baza basin moreover the activity of dextral faults along the sorbas tabernas alpujarras guajares band generally considered as a transfer fault zone is evidenced by the displacement data these results come to demonstrate the low activity or inactivity of the large northern e w oriented folds of the central and eastern internal zone such as the sierra de los filabres antiform they also point to the possible residual activity of the northern part of the ne sw sierra nevada antiform where the maximum relief of the cordillera is found altogether our data support a heterogeneous present day westward extension that affects the upper crust of the betic cordillera and increases towards the thinned continental crust of the alboran sea and towards the west which is compatible with roll back subduction along the gibraltar arc

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

tethys atlantic interaction along the iberia africa plate boundary the betic rif orogenic system abstract initial se dipping slow subduction of the ligurian tethys lithosphere beneath africa from late cretaceous to middle oligocene twisting to a later faster e dipping subduction of the subcrustal lithosphere is proposed as an efficient geodynamic mechanism to structure the arcuate betic rif orogenic system this new subduction related geodynamic scenario is supported by a kinematic model constrained by well dated plate reconstructions tectonic sedimentary and metamorphic data sets the slow initial se dipping subduction of the ligurian tethys realm beneath the malaguide upper plate unit is sufficient to subduct alpujarride and nevado filabride rocks to few tens of kilometers of depth in middle eocene times the shift from se to e dipping subduction during latest oligocene early miocene was possibly caused by both the inherited geometry of the highly segmented ligurian tethys domain and by the fast roll back of the subducted lithospheric slab the early miocene rather synchronous multiple crustal and subcrustal processes comprising the collision along the betic front the exhumation of the hp lt metamorphic complexes the opening of the alboran basin its flooring by hp alpujarride rocks and subsequent ht imprint can be explained by the fast nw and w directed roll back of the ligurian tethys subcrustal lithospheric slab the w retreat of the ligurian tethys lithosphere in middle late miocene times could partly explain the initiation of its lateral tear and consequent subcrustal processes from latest miocene onward the betic rif system evolved under both the northerly push of africa resulting in tightening at crustal and subcrustal levels and by the distinct current dynamics of the steep lithospheric slab the sw directed scape of the rif fold belt is one of the most striking evidences linked to the recent evolution of the squeezed betic rif system between africa and iberia

eustatic and tectonic controls on quaternary ras leona marine terraces strait of gibraltar northern morocco well preserved quaternary staircased marine terraces appear on ras leona limestone relief this is a peculiar sector of the betic rif cordillera lying in the four way junction between the atlantic and the mediterranean and europe and africa the age and altitude correlation of the ras leona terraces with travertine covered lateral equivalent terraces fashioned in the neighbouring beni younech area and comparison with those along the moroccan atlantic coasts would suggest that the ras leona terraces were mainly formed by eustatic factors the importance of the eustasy is supported by further comparisons with spanish and moroccan mediterranean terraces and with different marine terraces developed on passive margin coasts around the world a tectonic event occurred mainly during the period between the formation of the maarifian and the ouljian terraces i e between 370 and 150 ka the moderate quaternary tectonic uplift deduced from the marine terraces and its comparison with uplifted marine terraces developed in active subduction setting disagrees with the model of an active eastwards subduction below the gibraltar tectonic arc

lithospheric structure beneath the alboran basin results from 3d gravity modeling and tectonic relevance a three dimensional gravity modeling combined with integrated heat flow and elevation modeling is conducted to map out the crustal and lithospheric mantle thickness in the alboran basin in the westernmost mediterranean a sediment corrected bouguer anomaly has been derived using a depth to the basement map and densities determined from well logs and seismic data the gravity effect of the base of the lithosphere has been removed from the sediment corrected bouguer anomaly to obtain a crustal bouguer anomaly which has been inverted for crustal thickness the resulting lithospheric structure is further constrained by elevation data under the assumption of local isostasy the low residual elevation anomalies obtained 100 m in average suggest that the area is in local isostasy particularly the medium and long wavelength topography features variations in crustal thickness range from 36 km underneath the betic and rif chains to 12 km beneath the easternmost part of the alboran sea basin in the transition to the south balearic basin in western alboran the moho lies at a rather constant depth of 18 km deepening sharply toward the gibraltar strait down to 30 32 km the base of the lithosphere shallows from 140 km depth in the gibraltar strait to 45 km depth in the easternmost alboran sea lithospheric thinning penetrates to the southeastern side of the iberian margin crosscutting topographic highs of the central and eastern betic chain our results favor mantle delamination produced by detachment and subsequent peeling away of the lithospheric mantle rather than convective removal of the lithospheric mantle either by orogenic collapse or detachment and sinking of a lithospheric slab

3d geometry of growth strata in a fault propagation fold insights into space time evolution of the crevillente fault abanilla alicante sector betic cordillera spain this work presents a 3d geometric model of growth strata cropping out in a fault propagation fold associated with the crevillente fault abanilla alicante sector from the bajo segura basin eastern betic cordillera southern spain the analysis of this 3d model enables us to unravel the along strike and along section variations of the growth strata providing constraints to assess the fold development and hence the fault kinematic evolution in space and time we postulate that the observed along strike dip variations are related to lateral variation in fault displacement along section variations of the progressive unconformity opening angles indicate greater fault slip in the upper tortonian messinian time span from the messinian on quantitative analysis of the unconformity indicate a constant or lower tectonic activity of the crevillente fault abanilla alicante sector the minor abundance of striated pebbles in the pliocene quaternary units could be interpreted as a decrease in the stress magnitude and consequently in the tectonic activity of the fault at a regional scale comparison of the growth successions cropping out in the northern and southern limits of the bajo segura basin points to a southward migration of deformation in the basin this means that the bajo segura fault became active after the crevillente fault abanilla alicante sector for which activity on the latter was probably decreasing according to our data consequently we propose that the seismic hazard at the northern limit of the bajo segura basin should be lower than at the southern limit

the role of extension in the miocene denudation of the nevado filabride complex betic cordillera se spain the internal zone of the betic cordillera se spain consists of a nappe stack of three complexes the deepest of which is the nevado filabride complex the zone is separated from the overlying alpujarride complex by a crustal scale shear zone that has variously been interpreted as a thrust or an extensional detachment a suite of 74 new apatite and zircon fission track results have been obtained from the nevado filabride complex and these have been used to define regional cooling patterns for the complex rapid cooling 105 c 200 c ma 1 is spatially related to the tectonic contact with the overlying alpujarride complex cooling to near surface temperatures occurred first in the east sierra de los filabres during the mid serravallian 12 1 ma and was completed by the early tortonian 9 8 ma in the west sierra nevada there is no correlation between fission track age and sample elevation these results are consistent with tectonic unroofing of this complex a finding that favors extension as the mechanism by which the two complexes were brought into contact extension spans the middle and earliest upper miocene 12 8 ma in the study area and therefore lasted much longer than previously documented a hypothesis is advanced which links oblique convergence between the iberian plate and the betic internal zones resulting in crustal contraction at depth with orogen parallel extension in the middle and upper crust

salt deposition and brine evolution in the granada basin late tortonian se spain abstract a group of sedimentary basins in the betic chain were formed during the middle late miocene as a result of the closure of the tethys during the alpine orogeny in the late miocene tortonian messinian the connections between the atlantic ocean and mediterranean sea were interrupted and those basins hosted major evaporites the granada basin an inner basin located far from the mediterranean contains a thick rock salt deposited during the latest tortonian in the transition from marine to non marine conditions in the centre of the basin three halite bearing units overlie a basal anhydrite bed the lower halite unit the intermediate sandstone unit and the upper halite unit fluid inclusion compositions and bromine concentrations in halite together with stable isotopes 34 s sulfate 18 o sulfate and 87 sr 86 sr indicate a mixture of different inflow waters in the granada basin beginning with a marine lagoon that evolved into a salt pan strongly isolated from the sea saline waters evolved from sulfate rich marine derived to sulfate depleted non marine brines influenced by the addition of cacl 2 rich inputs these cacl 2 rich waters were probably linked to thermal fluids associated with a major crustal fracture system crevillente or cadiz alicante fault system that cuts through the granada basin

the palomares brittle ductile shear zone of southern spain the palomares shear zone is a major neogene quaternary strike slip zone which transects the crust of the betic cordillera in se spain the shear zone and the mechanisms that led to its formation are discussed and illustrated on the basis of detailed compilations of both the local and regional geology it is emphasized that the formation of the palomares shear zone was not an isolated tectonic event but part of a complex neogene tectonic history the neogene evolution of the betic rif orogen and its central alboran basin is characterised by the following events 1 emplacement of the alboran diapir with resulting nappe shedding from the overlying crust between 25 and 20 ma ago 2 onset of the subsidence of the alboran basin between 20 and 15 ma ago due to cooling of the alboran diapir and the overlying crust 3 formation of the cabo de gata volcanic chain between 15 and 8 ma ago and 4 refolding of the nappe sheets in the betic rif orogen into a basin and range structure about 7 ma ago continuous activity of the crevillente fault of southern spain may have occured over a period from 20 ma ago up to the present the interrelated palomare fault in se spain was probably formed between 15 and 8 ma ago and seem to be active still the palomares shear zone affects a rock volume 44 km wide at least 80 km long and 30 km deep a shear strain distance diagram constructed across the palomares shear zone and its axial palomares fault involves a new method to estimate or constrain the shear strain magnitude along brittle ductile shears the typical tensor shear strain rates in the approximately 20 km thick ductilely deformed walls of the palomares fault are of the order 10 13 10 14 s 1 the tensor shear strain rate along the palomares fault itself is of the order 10 12s 1 and the time averaged relative displacement rate of its walls is about 2 mm a 1 the range of strain rates within the palomares shear zone are interpreted to be due to a combination of various flow softening mechanisms geometric structural thermal and strain rate softening these softening mechanisms might explain the difference in vertically averaged viscosities of 1020 pa s and 1025 pa s or lower suggested for the crustal rocks in the palomares fault proper and that of the relatively rigid boundaries of the palomares shear zone respectively

onshore and offshore compressional tectonics in the eastern betic cordillera se spain abstract this study concerns the northern terminal splay of the eastern betic shear zone betic cordillera se spain where the bajo segura basin lies and its offshore prolongation along the western mediterranean margin we have integrated seismic reflection profiles with gravimetry seismicity wells and outcrop data from the bajo segura basin and the alicante shelf in order to determine the current geodynamic setting of the area the results indicate that the same compressional structures in upper miocene quaternary rocks are observed both on and offshore in the onshore bajo segura basin there are ene wsw growth folds related to reverse faults in the basement in the alicante shelf the main structure is an ene wsw anticlinorium which deforms upper miocene quaternary syntectonic deposits these compressional structures are still active at present as shown by the offshore seismicity from the structural analysis and focal mechanisms of the earthquakes we conclude that the bajo segura basin and its adjacent shelf have been subject to nnw sse compression since late miocene until the present folding and reverse faulting of the upper miocene quaternary sedimentary cover and of its basement have accommodated this compression the main active structures onshore located in the bajo segura basin extend eastwards into the mediterranean sea this fact is interpreted as the eastern betic shear zone continues offshore to the east

on spherical nanoindentations kinking nonlinear elasticity of mica single crystals and their geological implications in this paper we show using cyclic spherical nanoindentation experiments that the deformation mechanisms in mica including basal plane ruptures and delaminations can be explained by invoking the presence of mobile dislocation walls and incipient and regular kink bands our results clearly show that the energy dissipated or that was stored during the deformation of muscovite depends critically on its previous deformation history and or the pre existing defect concentration once nucleated the dislocation based incipient kink bands are believed to be responsible for the nonlinear elastic deformation and hysteretic loops obtained during cyclic loading moreover a model is presented to estimate the number and distribution of dislocations and the energy consumed in their motion under the indenter from the model we also estimate the critical resolved shear stress for the motion of basal plane dislocations under the indenter the implications of this work can be extended beyond mica to understand the nonlinear hysteretic deformation in other geological formations dominated by layered minerals

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

landscape response to strike slip faulting linked to collisional settings quaternary tectonics and basin formation in the eastern betics southeastern spain abstract neotectonic behaviour of the eastern betics southeastern spain has been controlled by the presence of a large left lateral shear zone this is an intraplate transcurrent zone probably decoupled by a mid crustal detachment horizon the morphological expression of this crustal structure is a sigmoidal corridor in which the main quaternary basins are located three types of morphostructural domains can be distinguished in the sigmoidal corridor the central segment and the northern and southern terminal splays the central segment is characterized by wrench tectonics whilst the southern and northern terminal splays are controlled by transtensional and transpressional tectonics respectively the quaternary morphostructural pattern is only the more recent picture of the tectonic processes that have controlled the late orogenic evolution of the eastern betics the indentation of the aguilas arc accompanied by thin skinned thrusting and tectonic escape in its easternmost sector and extensional collapse accompanied by thin skinned stretching in its westernmost sector

pleistocene raised marine terraces of the spanish mediterranean and atlantic coasts records of coastal uplift sea level highstands and climate changes detailed geological mapping morphostratigraphic palaeontological and geochronological uranium series analyses were undertaken on the raised marine terraces and interbedded terrestrial deposits along the spanish peninsular and insular atlantic and mediterranean coasts several sets of pleistocene shallow marine to coastal deposits exposed in a staircase arrangement are interpreted as being emplaced during sea level highstands coeval with interglacials or interstadials correlating with marine oxygen isotopic stages ois 5a 5c 5e 7 9 11 and older up to three highstands have been identified in deposits formed during ois 5e close to the end of ois 5e there is a record of sudden changes in sea surface conditions and climate marked by the disappearance of a major proportion of the warm senegalese fauna switches from oolitic to non oolitic facies and accumulation of boulder beaches dating of the coral cladocora caespitosa found in a layer that also contains strombus bubonius confirms the occurrence of warm fauna in the mediterranean basin during ois 7 as previously suggested by hillaire marcel et al 1986 goy et al 1986a b zazo and goy 1989 also the occurrence of warm faunas in deposits corresponding to an older interglacial probably ois 9 or 11 in the balearic islands suggests similar oceanographic conditions sea surface temperature assuming constant salinity during the last interglacial and at least two interglacials of the middle pleistocene in the western mediterranean a 2002 elsevier science b v all rights reserved

late neogene recent uplift of the cabo de gata volcanic province almeria se spain abstract cabo de gata is a miocene volcanic province in the betic cordillera in southeastern spain the distribution of coastal deposits in the successive marine sedimentary units overlying the last volcanic episode about 7 5 ma old has been used to reconstruct the post volcanic palaeogeographic evolution of the region during the late neogene the current elevation of well dated shoreline marker rocks has been used to estimate uplift amount and rates since the late tortonian a n45 e aligned the strike of the carboneras fault system topographic relief was emergent in the cabo de gata region the extension and height of this island increased throughout the late neogene smaller independent islands were emergent and finally became connected to the main island during the messinian the carboneras and agua amarga pliocene sub basins were the last two marine basins prior to the final emergence of the region since the last volcanic eruption ca 7 5 ma maximum uplift of sedimentary rocks in cabo de gata has taken place on the western margin of the n45 e aligned palaeorelief the altitude of the shoreline marker rocks in the successive sedimentary units decreases eastwards to the present day coast and northwards of the rambla del plomo uplift rates since deposition remain nearly constant for the successive messinian rocks and decrease slightly for the lower pliocene outcrops most of the uplift took place before the pliocene while the main island enlarged uplift amounts and rates since deposition of the upper neogene sedimentary units in the cabo de gata area are similar to the ones estimated for laterally equivalent units in the eastern betic basins approximately 50 m ma despite its volcanic nature and the occurrence of the carboneras fault system the cabo de gata probably became elevated as a consequence of regional uplift in connection with the rest of the betic cordillera

shear wave velocity structure of the south eastern part of the iberian peninsula from rayleigh wave analysis in this study we present the lithospheric structure of the south eastern part of the iberian peninsula by means of a set of 2d images of shear velocity for depths ranging from 0 to 50 km this goal will be attained by means of the inversion of the rayleigh wave dispersion for it the traces of 25 earthquakes occurred on the neighbouring of the study area from 2001 to 2003 will be considered these earthquakes have been registered by 11 broadband stations located on iberia all seismic events have been grouped in source zones to get an average dispersion curve for each source station path the dispersion curves have been measured for periods between 2 and 45 s by combination of two digital filtering techniques multiple filter technique and time variable filtering the resulting set of source station averaged dispersion curves has been inverted according to the generalized inversion theory to get s wave velocity models for each source station path later these models have been interpolated using the method of kriging to obtain a 2d mapping of the s wave velocity structure for the south eastern part of iberia the results presented in this paper show that the techniques used here are a powerful tool to investigate the crust and upper mantle structure through the dispersion analysis and its inversion to obtain shear velocity distributions with depth by means of this analysis principal structural features of the south eastern part of iberia such as the existence of lateral and vertical heterogeneity in the whole study area or the location of the moho discontinuity at 30 km of depth with an average s velocity of uppermost mantle of 4 7 km s have been revealed other important structural features revealed by this analysis have been that the uppermost of iberian massif shows higher velocity values than the uppermost of the alpine domain indicating that the massif is old and tectonically stable the average velocity of the crust in betic cordillera is of 3 5 km s while in the iberian massif is 3 7 km s all these features are in agreement with the geology and other previous geophysical studies

correlation between velocity dependence of friction and strain localization in large displacement experiments on feldspar muscovite and biotite gouge abstract room temperature rotary shear experiments on rock powders of albite feldspar and muscovite and biotite micas show that the degree of localization of shear strain in these materials correlates with the frictional behavior in both feldspar and mica experiments increasing localization correlates with a lower coefficient of friction and a more negative velocity dependence of friction feldspar gouges tend to have localized deformation along one or more boundary parallel shears and a negative velocity dependence more localized deformation correlates with a lower coefficient of friction and a more negative velocity dependence in general micas deform throughout a broader zone than feldspar and have a lower coefficient of friction compared to muscovite biotite is weaker has a negative rather than a positive velocity dependence and shows more localized deformation for materials as diverse as feldspars and micas localization along boundary parallel shears correlates with negative velocity dependence along compliant natural faults a negative velocity dependence would result in a greater tendency for unstable sliding thus localized boundary parallel shears may indicate negative velocity dependence and slip by earthquakes on natural faults

the structure of the alboran sea an interpretation from seismological and geological data abstract almost all the earthquakes included in the catalog for the iberian maghrebian area up to 2000 have been used in order to know the structure of the alboran sea area after the verification of the aleatory nature of the errors in their spatial localization a new focal mechanisms catalog has also been used as well as many of the available geological data during the mesozoic and till the oligocene the betic rif internal zone was situated further e but with the opening of the algero provencal basin in the early miocene the betic rif internal zone moved to the w contemporary the alboran sea was created as the western prolongation of the algero provencal basin the betic rif internal zone overthrused part of the iberian and african plates producing the partial sinking of both plates and being responsible of the intermediate seismicity existing in the western sector of the alboran sea the intermediate earthquakes in the atlas towards the ne and wsw are not related to lithospheric sinking but to significant deep faults limiting a subplate in nw africa in the atlantic the intermediate earthquakes between the gorringe sector and gibraltar are produced in the contact between the iberian and african plates and by the important faults crossing it the existence of four very deep earthquakes is related to the previous sinking of the lithosphere originally associated to the domain in which the betic rif internal zone was situated

patterns and average rates of late neogene recent uplift of the betic cordillera se spain abstract the facies distribution in the sedimentary units infilling a series of neogene basins has been used to reconstruct the relief generation and uplift across the internal zone of the betic cordillera in southern spain uplift amounts and average rates can be estimated using the current elevation of the outcrops of well dated deposits indicative of ancient sea level positions coral reefs and coastal conglomerates record the initial development of emergent betic relief during the langhian continental and marginal marine deposits indicate the existence of a large island centred on the present sierra nevada sierra de los filabres chain by the end of the middle miocene the precursor of the sierra nevada sierra de los filabres chain originally part of this large island remained emerged whilst the surrounding areas were re invaded by the sea during the early tortonian at the end of the tortonian the inland basins granada and guadix basins became continental while the sierras de la contraviesa sierra de gador and sierra alhamilla emerged separating the alboran basin from the alpujarra tabernas and sorbas basins which became narrow passages of the mediterranean sea in contrast the sierra cabrera emerged during the late messinian suggesting a progressive uplift from west to east of the sierras south of the sierra nevada sierra de los filabres chain during the pliocene only the low areas closest to the present day coast remained as marine basins and progressively emerged throughout this stage the highest average uplift rate recorded is 280 m ma for the sierra de gador although the average uplift rates of upper neogene coastal marine rocks since depositon have maximum values of approximately 200 m ma most of the uplift of the betic mountains took place before the early pliocene the recorded uplift of neogene rocks was highest at the margins of western sierra nevada where peaks higher than 3000 m occur the average rates of uplift were lower to the east of this major relief the main sierras and depressions in the present day landscape correspond respectively to the emergent land in which uplift was concentrated and to the marine basins that existed before the final emergence of the region the altitude of the sierras reflects the time at which they became emergent the highest mountains being the first to rise above sea level

experimental deformation of muscovite abstract the strength and mechanical anisotropy of muscovite have been investigated by shortening single crystals at 45 0 and 90 to the basal plane 001 at temperatures t from 20 to 400 c confining pressures pc from 10 to 400 mpa and strain rates e from 2 5 10 7 to 2 3 10 4 s 1 samples deformed as 45 to 001 exhibit smooth undulatory extinction in thin section associated with dislocation glide with few well developed low angle kink boundaries basal shear strengths depend on confining pressure at pc e a exp a exp q rt results from temperature and strain rate stepping experiments performed at pc 200 mpa yield an activation energy q of 47 19 kj mol 1 and an exponential constant a of 0 5 0 2 mpa 1 samples loaded parallel to the basal plane shorten by the development of sharply defined kink bands strengths associated with kink band formation are higher than those associated with glide in samples compressed at 45 to 001 and exhibit significant pressure dependence 0 8 up to confining pressures of 200 mpa kink bands are generated at the ends of samples where contact is made with the pistons samples loaded at 90 to 001 are much stronger than samples of all other orientations and deformation is accomplished by fracture fracture strengths exhibit a strong dependence on confining pressure 0 9 similar in magnitude to other silicates that are brittle at the same conditions by comparison with biotite muscovite is weaker in shear on 001 at the experimental conditions tested with an activation energy for glide q that is significantly smaller than that for glide in biotite

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

downslope migrating sandwaves and platform margin clinoforms in a current dominated distally steepened temperate carbonate ramp guadix basin southern spain during the late tortonian platform margin prograding clinoforms developed at the south western margin of the guadix basin large scale wedge shaped deposits here comprise 26 rhythms of mixed carbonate siliciclastic bedset packages and marl beds these sediments were deposited on a shallow water temperate carbonate distally steepened ramp a downslope migrating sandwave field developed in this ramp with sandwaves moving progressively down the ramp to the ramp slope where they destabilized folded and occasionally collapsed downslope sandwave migration was induced by currents flowing basinwards during the late tortonian the guadix basin was open north to the atlantic ocean via the dehesas de guadix strait and connected east to the mediterranean sea through the almanzora corridor according to the proposed current circulation model for the guadix basin for this time surface marine currents from the atlantic entered the basin from the northern seaway these currents moved counter clockwise and shifted the sediment on the ramp forming sandwaves that migrated downslope the development of platform margin prograding clinoforms by the basinward sediment transport mechanisms inferred here is known relatively poorly in the ancient sedimentary record moreover these wedge shaped geometries are similar to those found in some shelves in the western mediterranean sea and could represent an outcrop analogue to sub recent platform margin clinoforms revealed by high resolution seismic studies

effect of finite deformation and deformation rate on partial melting and crystallization in metapelites 1 strain and strain rate partitioning in partially molten rocks are two of the important mechanisms that govern the process of coupling and or decoupling of the partially molten lithosphere consequently the proportion of partial melt and crystals and their network in partially molten rocks influence the degree of the partitioning along with the bulk rheology of the system this study explores the possible role of finite strain and strain rate on the rate and volume of partial melting and crystallization in a metapelitic system undergoing deformation cylinders of synthetic quartz muscovite aggregate 7 3 volume ratio were deformed in torsion at 750 c 300 mpa and constant shear strain rate 3 1 0 4 s 1 for finite shear strains g 1 15 the deformed samples were studied along the longitudinal tangential lt and axial la sections to obtain the data along a range of strain rates for a given finite strain and vice versa the results showed that deformation plays an important role on the kinetics of partial melting and crystallization with increasing strain rate amount and rate of crystallization comprise the volumetrically dominant process compared to partial melting at a given finite strain in contrast when the strain rate is constant partial melting is the dominant process over crystallization up to moderate strain g 5 the dominant process reverses at higher strain and the system shows more crystallization than partial melting application of the experimental data to geological systems implies that for metapelites a significant amount 20 of partial melt can generate at high strain rate and moderate strain g 7 but at high strain g 15 the system is melt depleted under such conditions decoupling should take place in brittle ductile mode on the other hand rocks undergoing deformation with low strain rates and strain g 3 contain more than 25 partial melt which can act as a major decoupling agent by localizing ductile shear zones

recent fault controlled glacis deformation and its role in the fluvial capture of the guadix baza basin betic cordillera southern spain abstract this work is focussed on the geomorphological changes related to the pleistocene capture of the formerly endorheic guadix baza basin betic cordillera we explore the possible tectonic controls in the basin opening through a combined geomorphological and structural study for this we have selected a study area that includes the connecting zone between the former endorheic basin and the capture channel guadiana menor river this zone also includes the se end of the so called tiscar fault zone tfz that has been active during the upper miocene and onwards we use the glacis surface that marks the end of the endorheic sedimentation middle upper pleistocene as the main reference surface to identify recent deformation structures our results indicate that the main channel crossing the pozo alcon glacis guadalentin river shows evidence of high levels of fluvial incision and that some anomalies in the stream longitudinal profile could be correlated to the presence of pre glacis faults linked to the tfz conversely abrupt changes in the stream orientation seems to be related to post glacis downthrow faults we have identified that the dextral strike slip tiscar fault the northern boundary of the tfz propagates towards the se as far as the guadalentin river giving rise to a deformation band with oblique slip that descends the sw block down to 250 m and affects the glacis surface additionally the pozo alcon glacis has undergone distributed deformation mainly achieved by n s to ne sw downthrow faults and subordinate wnw faults the roughly e w extension within the pozo alcon glacis can be interpreted as developed in the extensional lobe at the tip of a dextral strike slip fault the tiscar fault according to the orientation wnw ese and location of the guadiana menor river following the southern boundary of the tfz and the relief attenuation and tilting produced by the extensional systems in the pozo alcon glacis we interpret that the later stages of tfz activity probably controlled and favoured the localisation of the basin capture

role of pressure and temperature in inclusion induced shear localization an analogue experimental approach abstract using analogue model experiments this study investigates the effects of lithostatic pressure and temperature in controlling the pattern of shear localization around rigid inclusions compression experiments were conducted on polymethylmethaacrylate pmma by varying confining pressure p 30 70 mpa homologous temperature t o 0 67 0 80 corresponding to room temperature 80 c and axial strain yield 15 in a triaxial setup mechanical data showed temperature has a greater influence on the bulk yield strength and steady state flow of the analogue material than confining pressure increasing confining pressures multiply the shear bands in number and their overall pattern becomes progressively more complex leading to composite band structures on the other hand under ambient pressure increasing temperature results in a transition from incipient high strain zones to shear bands with sharp boundaries further increase in temperature switches the mode of shear localization sharp to diffuse type we finally show the inclusion induced shear localization as a two stage process and provide a micro mechanical explanation for the p t dependent shear band patterns attributed to three mechanically distinct domains of the inclusion matrix interface compression extensional and shear localization

deformation of biotite and muscovite tem microstructure and deformation model abstract growth and deformation defects have been observed in 1m and 2m 1 biotites and 2m 1 muscovites using transmission electron microscope tem techniques these have been related to optical observations in deformed biotite the dislocation density increases as the strain increases the density of stacking faults also increases with strain the spatial ordering of stacking faults decreases as the strain increases in muscovites selected from the same areas as the biotites stacking fault and dislocation densities show little or no variation with deformation the different responses of biotite and muscovite to deformation are explained in part by the physical and chemical differences between 1m biotite and 2m 1 muscovite there is strong evidence in both the biotites and muscovites that stacking faults may be result of deformation as well as a crystal growth process the grain size of the deformed mica aggregates is reduced by the nucleation of new micas there is also evidence for a grain size reduction mechanism segmentation in biotites this mechanism appears to achieve the same result as recovery recrystallization mechanisms but not by the same method segmentation may be a mechanism which is favoured in strongly anisotropic minerals with a limited number of slip systems a model is proposed that attempts to correlate response of the biotite to deformation the deformation is synchronous with and post dates the nucleation of the new metamorphic micas

chronology of miocene terrestrial deposits and fossil vertebrates from quebrada honda bolivia abstract at 3500 m above sea level in the eastern andean cordillera quebrada honda basin exposes more than 300 m of middle miocene sedimentary strata developed on distal alluvial fan sediments interstratified with volcanoclastic deposits overlying paleozoic basement these deposits are rich in exotic vertebrate fauna adapted to a wetter and warmer climate at lower paleoelevation as contrasted with the present high elevation cold and dry andean conditions this study provides new magnetostratigraphic and 40ar 39ar age control of the quebrada honda rio rosario and huayllajara fossiliferous areas demonstrating that they are 13 1 12 4 ma part of the succession evidences cyclical deposition of calcretes and reddish mudstones which may be a response to precessional orbital forcing climatic processes paleomagnetic measurements show a significant clockwise tectonic rotation related to postdepositional tectonism associated with evidence of an important uplift after the deposition of quebrada honda sediments this uplift of the andean eastern cordillera was associated with the formation of the subandean fold thrust belt and the development of the amazon and la plata drainage basins proposed uplift rates of 200 m ma are compatible with well established rates of uplift recorded in contemporaneous alpine sections

the baza fault a major active extensional fault in the central betic cordillera south spain in the guadix baza basin betic cordillera lies the baza fault a structure that will be described for the first time in this paper eight gravity profiles and a seismic reflection profile coupled with surface studies indicate the existence of a ne dipping normal fault with a variable strike with n s and nw se segments this 37 km long fault divides the basin into two sectors guadix to the west and baza to the east since the late miocene the activity of this fault has created a half graben in its hanging wall the seismic reflection profile shows that the fill of this 2 000 3 000 m thick asymmetric basin is syntectonic the fault has associated seismicity the most important of which is the 1531 baza earthquake since the late tortonian to the present i e over approximately the last 8 million years extension rates obtained vary between 0 12 and 0 33 mm year for the baza fault being one of the major active normal faults to accommodate the current ene wsw extension produced in the central betic cordillera the existence of this fault and other normal faults in the central betic cordillera enhanced the extension in the upper crust from the late miocene to the present in this regional compressive setting

glacis geometry as a geomorphic marker of recent tectonics the guadix baza basin south spain abstract the guadix baza basin occupies 4000 km 2 and constitutes the largest intramontane basin of the betic cordillera southern spain it has a well preserved geomorphic surface a glacis which started to be eroded when the basin conditions changed from endorheic to exorheic taking into account its large preserved surface area more than 1200 km 2 and its pre deformational geometry this geomorphic surface is a useful marker of recent deformation combining geological and geomorphological data and high resolution dem topographic profiles of the glacis have been produced to estimate vertical displacements caused by active compression and extension structures these structures have produced relative vertical displacements of up to 100 m from the late middle pleistocene to the present assuming an age for the glacis of between 205 and 600 ka it has been possible to estimate long term minimum and maximum vertical rates of the activity of normal faults and folds using this geomorphic surface as a marker vertical slip rates range from 0 07 to 0 49 mm year for the main active normal faults and vertical folding rates range from 0 05 to 0 17 mm year for several active folds these long term vertical slip and folding rates are in accordance with other values previously estimated in other sectors of the betic cordillera when present detailed geomorphic study of recent glacis is an excellent tool for evaluating active tectonics over large regions

sediment supply from the betic rif orogen to basins through neogene abstract we present a quantification of total and partial divided by time slices sedimentary volumes in the neogene basins of the betic rif orogen these basins include the alboran sea the intramontane basins the guadalquivir and rharb foreland basins and the atlantic margin of the gibraltar arc the total volume of neogene sediments deposited in these basins is 209 000 km3 and is equally distributed between the internal alboran basin and intramontane basins and the external basins foreland basins and atlantic margin the largest volumes are recorded by the alboran basin 89 600 km3 and the atlantic margin 81 600 km3 the guadalquivir and rharb basins amount 14 000 km3 and 14 550 km3 respectively whereas the intramontane basins record 9235 km3 calculated mean sediment accumulation rates for the early middle miocene show an outstanding asymmetry between the alboran basin 0 24 mm yr and the foreland basins 0 06 0 07 mm yr and the atlantic margin 0 03 mm yr during the late miocene sedimentation rates range between 0 17 and 0 18 mm yr recorded in the alboran basin and 0 04 mm yr in the intramontane basins in the pliocene quaternary the highest sedimentation rates are recorded in the atlantic margin reaching 0 22 mm yr sedimentary contribution shows similar values for the inner and outer basins with a generalized increase from late miocene to present from 3500 to 6500 km3 my interestingly the alboran basin records the maximum sedimentary contribution during the late miocene 5500 km3 my whereas the atlantic margin does during the pliocene quaternary 6600 km3 my the spatial and time variability of the sediment supply from the betic rif orogen to basins is closely related to the morphotectonic evolution of the region the high sedimentation rates obtained in the alboran basin during the early middle miocene are related to active extensional tectonics which produced narrow and deep basins in its western domain the highest sedimentary contribution in this basin as well as in the foreland and intramontane basins is recorded during the late miocene due to the uplift of wide areas of the betics and rif chains the analysis of the sedimentary supply also evidences strong relationships with the post tortonian crustal thickening and coeval topographic amplification that occurred in the central betics and rif with the concomitant evolution of the drainage network showing the fluvial capture of some internal basins by rivers draining to the atlantic ocean the ancestral guadalquivir

structure and geological history of the carboneras fault zone se spain part of a stretching transform fault system abstract the carboneras fault zone cfz is a major ne sw trending tectonic lineament in se spain active from upper miocene to recent times it separates the volcanic cabo de gata terrain to the se accumulated over 18 6 ma bp from the tract of uplifted alpine metamorphic basement blocks and post orogenic basins that comprise the betic cordilleras lying to the nw new geological mapping and age determinations have been used to constrain the geometry and geological history of the fault zone the cfz consists of left lateral strike slip faults bearing fault gouge formed in the uppermost 5 km of the crust the faults cut metamorphic basement and folded post orogenic sediments and volcanic rocks and acted as a conduit for calc alkaline volcanic rocks rising to the surface nw of the cfz a series of unconformities and deformation episodes affect successive sedimentary formations of upper miocene age the cfz is interpreted as part of a transform fault system separating ne sw stretched and nw se shortened crust deformed above a south westward retreating subducted slab from a less deformed terrain lying to the south east total offset on the cfz may be up to 40 km but is at least 15 km

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

deformation mechanisms and rheology of serpentines in experiments and in nature microstructures in serpentine samples recovered from deformation experiments performed at high pressure 1 8 gpa high temperature 150 500 degrees c and laboratory strain rates 4 10 4 10 6 s 1 were studied using transmission electron microscopy on thin sections prepared by focused ion beam lizardite crystals deform by easy glide along the basal planes associated with microkink this mechanism is associated with a plastic strength of similar to 100mpa that defines the upper bound of lizardite strength in natural conditions antigorite crystals deform essentially by conjugated slip along 101 and 10 1 over bar planes observed in sections close to 010 this conjugate system results in an apparent global slip system akin to 100 001 in all samples delamination and comminution produce fine grained interconnected regions at grain boundaries because intracrystalline deformation mechanisms are insufficient to satisfy the von mises criterion the deformation laws of lizardite plastic flow and antigorite strain rate dependent differ because of their differing intracrystalline deformation mechanisms subgrain boundary geometry in natural samples and 100 001 crystal preferred orientations indicate the activation of slip systems similar to those observed in experimentally deformed samples suggesting that the strain rate dependent rheology of antigorite derived from experiments applies to subduction zone conditions delamination of antigorite crystals of a few tens to hundreds of nanometers is not observed in natural samples from subduction zones suggesting plastic deformation of serpentinites at natural low strain rates and stresses is likely accompanied by recrystallization through dissolution precipitation processes that act as a low temperature equivalent of dynamic recrystallization through diffusion at high temperature

widespread landslides induced by the mw 5 1 earthquake of 11 may 2011 in lorca se spain abstract on 11 may 2011 a moderate magnitude mw 5 1 earthquake struck the city of lorca se spain and nearby areas causing notable damage injuries and fatalities field inspection of the area affected allowed the location and characterization of more than 250 induced landslides mainly of disrupted type rock soil falls disrupted soil slides and rock avalanches this number was very high when compared with the inventories of previous events of similar magnitude mw 4 7 to 5 0 in the zone and with the results of previous models for predicting slope behavior during earthquakes several factors are proposed here to explain the observed differences i the comparatively high magnitude mw 4 5 of a foreshock of the seismic series that may have weakened the slopes ii the high peak ground motion values recorded for these events and iii the occurrence of topographic site effects the results of this study point out the importance of including such effects as improvements in the models for studying the regional behavior of slopes

rheology of talc sheared at high pressure and temperature a case study for hot subduction zones abstract article history received 24 may 2013received in revised form 8 october 2013accepted 11 october 2013available online 24 october 2013keywords torsion experimentsfrictionslip partitioningearthquakelocalized deformationbrittle ductile transition talcisacommon fault coating mineral occurringina variety oftectonic settingsfromtheimmediatesubsurfacedown to more than 100 km depth along subducting plate interfaces it is considered to stabilize slip atseismogenic depth to gain insight into the rheological behavior of talc and related deformation processesalong the subduction interface of hot oceanic slabs we conducted torsion experiments on intact synthetic talcsamples at 200 600 c under 100 300 mpa con ning pressure at intermediate strain rates 3 10 4 and2 45 10 3 s 1 for bulk shear strains up to 12 6 we also conducted stepping strain rate experiments toinvestigate rate and temperature dependence on sliding velocity and slide hold slide experiments to explorethe re strengthening and frictional healing of the sliding zones the experimental results reveal 1 post yieldstrain hardening followed by brief weakening episodes and then again strain hardening with increasingdeformation and 2 a gradual transition of friction evolution from velocity strengthening to velocity neutral microstructural observations coupled with mechanical data suggest that talc rheology combines localized anddistributed deformation in a state called the brittle ductile transition with a predominance of crystal plasticover cataclastic brittle to semi brittle processes at 600 c and 300mpa con ning pressure these data suggestthat talc cannot accumulate the tectonic stress necessary for earthquake generating rupture along thesubduction interface this result concurs with the concept that in weak heterogeneous talc rich material strongasperities that can resist the tectonic stress to a greater extent are responsible for the consequential earthquakeoccurrence 2014 elsevier b v all rights reserved

geometry microstructures and magnetic fabrics of kink bands in the darrington phyllite northwestern washington usa processes within fixed hinge kinking abstract field thin section and magnetic fabric analyses of monoclinal contractional kink bands in the darrington phyllite of northwestern washington usa provide evidence of kinematic evolution and microstructural processes during kinking relationships among internal external and rotation angles of kink bands suggest that rotation was a primary mechanism of kinking and a significant number of kink bands deviate from the ideal kink band geometry equal internal and external kink angles dilation spaces voids filled with unrecrystallized quartz and or calcite inside kink bands and along the boundaries are commonly observed in kink bands with unequal kink angles evidence for localized interlayer slip inside kink bands includes mica grains protruding into the hinge voids and stair step geometry of the voids interlayer slip allowed for rotation of the internal foliation during kinking pressure solution is not ubiquitous inside kink bands from the study area however significant pressure solution is associated with locked kink bands equal kink angles a new approach using the anisotropy of magnetic susceptibility ams shows that the magnetic fabric and susceptibility inside the kink bands differ more from the outside fabric than can be explained by simple rotation of the outside fabric into the kink attitudes combined our observations suggest that fixed hinge kinking operated at this location and that veining interlayer slip and pressure solution were the dominant deformation mechanisms

is the northwestern betic cordillera mountain front active in the context of the convergent eurasia africa plate boundary the present relief of the betic rif cordillera has been mainly developed since the late miocene in the context of the eurasia africa nw se oblique convergence and other interacting processes like slab roll back or delamination however seismicity distribution and field observations reveal that most of the external mountain front of the betics is not clearly active at present and tectonic activity is generally concentrated towards

recent and present day stresses in the granada basin betic cordilleras example of a late miocene present day extensional basin in a convergent plate boundary the diffuse convergent boundary between the eurasian and african plates in the western mediterranean is associated with a seismicity zone more than 300 km wide although the two plates are converging nw se the betic and rif cordilleras contain extensional structures that have been active since the miocene the extensional tectonics in the region which occurred simultaneously with the uplift of the cordillera have been analyzed in the southeastern sector of the late miocene to recent granada basin using earthquake focal mechanisms the determination of paleostresses from the study of the orientation and kinematics of microfaults and the study of the major structures both the geological surface data and the focal mechanisms indicate present day regional conditions of ne sw extension with triaxial to prolate stress ellipsoids however the stress field is heterogeneous with local variations in stress over time with different stresses sometimes even acting simultaneously in adjacent areas the most frequent changes consist of pluridirectional or ne sw extension favored by the prolate character of the stress ellipsoids and nw se subhorizontal compression favored by the regional tectonic setting strike slip faults are scarce even though they are the most likely structure to be expected in a region with sw ne extension and nw se compression seismicity is concentrated in the upper crust and may correspond to the activity of low to high angle normal faults similar to the surface faults although they can not be correlated with them the lower cutoff of this seismicity probably coincides with the 300 c isotherm and suggests a low thermal gradient for the region present day regional stresses have 1 vertical at the surface but in depth plunge toward the sw

nature and impact of the neotectonic deformation in the western sierra nevada spain abstract the current high relief of the western sector of the sierra nevada was practically nonexistent before the tortonian as attested by the marine late neogene outcrops that reach a height of 1830 m which would easily surpass 2000 m if not for erosion the significant uplift produced over 3500 m has caused considerable thinning detachments and gravitational slides in the alpujarride units the general displacements of these movements are towards the wnw to ssw on the whole the morphology is fan like adapting itself to the border of the sierra nevada this border contains normal conjugate nw se and n s to nne ssw faults the latter also with sinistral strike slip character these faults have accommodated the uplift of the sierra nevada within an almost n s compressive context and linked e w extension this sector coincides with the western boundary of the nevado filabride complex and in its southern continuation with the western limit of the lower alpujarride units seeming to indicate a fault or faults reaching deep into the basement uplift has taken place unevenly over the last few million years with three noteworthy periods during the deposition of the block formation in the late tortonian towards the early middle pleistocene and in the middle late pleistocene this has resulted in considerable deepening of the fluvial net surrounding sierra nevada at the present time

geologic evolution of the betic cordilleras in the western mediterranean miocene to the present abstract the betic cordilleras were formed during the eo meso and neo alpine evolution of the western mediterranean area during the neo alpine stage the northward subduction of the african plate took place and the algerian provencal basin opened with the creation of oceanic floor associated space problems produced the expulsion and extensive stretching of the internal zones to the west which in turn disrupted and deformed the external zones of the betic and rif cordilleras these occurrences essentially took place in the burdigalian and continued with diminished intensity into the middle miocene following the suturing of the transcurrent contact between the internal and external zones important n60 90 e and nw se faults occurred the betic cordilleras are characterized as having been deformed by regional horizontal shortening compression oriented wnw ese or nw se which gradually rotated to the nnw sse in the late miocene when its most important intramontane neogene basins were formed the alboran basin with a thinned continental crust was formed as a western prolongation of the opening of the algerian provencal basin with its basic features already apparent in the burdigalian the volcanism present in the southeast of the betic cordilleras and in northeast morocco crossing the alboran basin is mainly late miocene in age it is linked to fracturing and exhibits chemistry related to the different thickness of the crust

the betic segment of the lithospheric trans alboran shear zone during the late miocene abstract the betic sinistral transcurrent shear zone betic cordilleras crosses the southeastern part of spain the study of the geodynamics of this area is approached from tectonic sedimentary magmatic and geophysical data large strike slip movements tectono sedimentary processes and magmatic events are seen at the boundary between two different lithospheric slabs they are located in a thinned compartment with a high geothermal gradient the large scale movements vertical and horizontal and the intensity of magmatic activity are the expression of the mechanical behaviour of this hot and thin crust all the geological events from the late miocene to recent are integrated in a crustal scale cross section which shows that the betic sinistral transcurrent shear zone widely affects the lithosphere it appears that subduction zones are not the only geodynamic context in which calc alkaline magmatism occurs

ductile to brittle transition in thermally stable antigorite gouge at mantle pressures general shear experiments on antigorite rich serpentinite show a transition from ductile distributed to brittle localized deformation with increasing temperature from 300 c to 500 c at confining pressures from 1 to 2 gpa the coefficient of friction associated with slip along fractures decreases from 0 23 to 0 07 with an increase in temperature from 300 c to 500 c velocity stepping experiments exhibit a positive rate dependence as parameterized by a b values that decrease modestly with increasing temperature from 0 015 at 300 c to 0 01 at 500 c fractures contain fine grained foliated antigorite and there is no evidence of dehydration all samples have a moderate foliation and show microstructural evidence for both plastic and brittle deformation mechanisms under certain conditions the transition to brittle deformation at high pressures and temperatures in antigorite might generate earthquakes which could explain the occurrence of some intermediate depth seismicity within subduction zones in serpentinized regions that are too cold to induce dehydration

foraminiferal isotopic evidence for monsoonal activity in the south china sea a present lgm comparison abstract the relationship between planktonic and benthic foraminiferal stable isotope values and oceanographic conditions and factors controlling isotopic variations are discussed on the basis of oxygen and carbon isotopic analyses of 192 modern surface and last glacial maximum lgm samples from the south china sea scs the harmonic variation of benthic 18o in surface sediments with water depth and temperature implies that the temperature is the main factor influencing benthic 18o variations planktonic 18o fluctuates with sea surface temperature sst and salinity sss the n s temperature gradient results in planktonic 18o decreasing from the northeast to the south cool saline waters driven by the winter monsoon are interpreted to have been responsible for the high 18o values in the northeast scs the east asian monsoons not only bring nutrients into the south china sea and maintain high nutrient concentration levels at the southwestern and northeastern ends which cause depleted 13c both in planktonic surface and benthic bottom samples but also reduce planktonic benthic 18o differences the distribution of 18o and 13c in the surface and lgm samples are strikingly similar indicating that the impact of sst and sss has been maintained and nutrient inputs mainly from the northeastern and southwestern ends have been controlled by monsoons since the lgm comparisons of the modern and lgm 18o indicate a difference of about 3 6 c in bottom water temperature and a large surface to bottom temperature gradient during the lgm as compared to today

a reappraisal of the alpine structure of the alpujarride complex in the betic cordillera interplay of shortening and extension in the westernmost mediterranean abstract the alpujarride complex has concentrated discussion on the extent and role of orogenic extension in the betic rif orogen westernmost mediterranean structural analysis on permo triassic rocks of the alpujarride complex is a firm basis to assess extension and to integrate it in the plate tectonic scenario the main alpine deformation was dominated by top to the ne shearing with rare map scale folds as a whole this deformation attests ductile extension during exhumation of previously subducted rocks some authors have suggested that the alpujarride complex continued evolving extensionally since this early exhumation but in this paper a stage of regional shortening is documented thus km scale overturned nw vergent folds are interpreted as witnessing shortening subsequently post metamorphic low angle faults of burdigalian langhian age cut the train of folds in two ways firstly top to the n thrusts generated stratigraphic and metamorphic superpositions then top to the n low angle normal faults kinematically congruent with the thrusts formed due to accretion at deep levels of the orogenic wedge when the nevado filabride complex underthrust the alpujarride complex the shortening stage occurred at latest oligocene early middle miocene and can be related to fast convergence rates between africa and iberia later a drop in the convergent rates prompted lithospheric rollback and top to the sw crustal extension since serravallian time coexisting with moderate orthogonal shortening that gave way to e w trending upright folds

dislocation interactions in experimentally deformed biotite abstract biotite single crystals shortened experimentally in orientations that maximize critical resolved shear stresses on 001 in directions 110 010 and 310 have been examined by transmission electron microscopy in all samples dislocations are confined to the basal plane with burgers vectors of 1 2 110 and 100 consistent with previous determinations of mica slip systems occasional partial dislocations that bound stacking faults form extended dislocations of these same systems typically dislocations are concentrated in complex arrays in local regions of the samples isolated or widely spaced dislocations are the exception within these arrays a variety of interactions between the dislocations are suggested by the geometrical arrangements of dislocations that cross over one another on parallel 001 planes sufficiently close together for elastic interaction and dislocations on the same 001 plane in networks and parallel arrays crossing dislocations of opposite sign on separate 001 planes form stable dipole segments where they overlap attractive and repulsive interactions between overlapping dislocations of like sign are evident as well dislocation networks occur in all samples and may exhibit a variety of complexly distorted geometries the spacing of dislocations in parallel arrays do not match models for standard dislocation pile ups consistent with observations showing these arrays involve dislocation multipoles the observed dislocation arrays and interactions resemble those reported for stage i easy glide deformation of fcc and hcp metals basal shear strengths are probably largely controlled by the development of multipoles and dislocations that pile up behind them