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

miocene extension and extensional folding in an anticlinal segment of the black mountains accommodation zone colorado river extensional corridor southwestern united states 1 recent studies demonstrate that rifts are characterized by linked tilt domains each containing a consistent polarity of normal faults and stratal tilt directions and that the transition between domains is typically through formation of accommodation zones and generally not through production of throughgoing transfer faults the mid miocene black mountains accommodation zone of southern nevada and western arizona is a well exposed example of an accommodation zone linking two regionally extensive and opposing tilt domains in the southeastern part of this zone near kingman arizona east dipping normal faults of the whipple tilt domain and west dipping normal faults of the lake mead domain coalesce across a relatively narrow region characterized by a series of linked extensional folds the geometry of these folds in this strike parallel portion of the accommodation zone is dictated by the geometry of the interdigitating normal faults of opposed polarity synclines formed where normal faults of opposite polarity face away from each other whereas anticlines formed where the opposed normal faults face each other opposed normal faults with small overlaps produced short folds with axial trends at significant angles to regional strike directions whereas large fault overlaps produce elongate folds parallel to faults analysis of faults shows that the folds are purely extensional and result from east northeast stretching and fault related tilting the structural geometry of this portion of the accommodation zone mirrors that of the black mountains accommodation zone more regionally with both transverse and strike parallel antithetic segments normal faults of both tilt domains lose displacement and terminate within the accommodation zone northwest of kingman arizona however isotopic dating of growth sequences and crosscutting relationships show that the initiation of the two fault systems in this area was not entirely synchronous and that west dipping faults of the lake mead domain began to form between 1 m y to 0 2 m y prior to east dipping faults of the whipple domain the accommodation zone formed above an active and evolving magmatic center that prior to rifting produced intermediate composition volcanic rocks and that during rifting produced voluminous rhyolite and basalt magmas

low pressure granulite facies metamorphism in the larsemann hills area east antarctica petrology and tectonic implications for the evolution of the prydz bay area thermobarometric studies on various granulite facies areas along the prydz bay coast east antarctica 73 79 e 68 70 s show that at around 1100 ma during a late proterozoic orogeny the rocks of the larsemann hills suffered a lower pressure metamorphic peak than the surrounding areas along the prydz bay coast the rocks affected by this event include parts of the vestfold hills block plus all of the rauer group the larsemann hills and the munro kerr mountains the dykes in the south west corner of the vestfold hills were recrystallized during this event with little deformation at temperatures not quite as high as in the areas further south west 650 c 6 5 kbar collerson et al 1983 the rauer group was metamorphosed at 800 c and 7 5 kbar harley 1987a the larsemann hills at 750 c and 4 5 kbar and the munro kerr mountains probably at around 850 c and 5 kbar retrograde equilibration in the different areas occurred during decompression to about 10 km depth in all areas followed by isobaric cooling at this depth this paper shows that the peak metamorphism in the larsemann hills occurred at a pressure which is too low to have been the consequence of thermal relaxation of overthickened crust with normal mantle heat flow although other areas in prydz bay were metamorphosed at sufficiently high pressures so that their decompression paths are not inconsistent with a continental collision model the inferred pre metamorphic peak histories and the requirement of consistency with the larsemann hills make it unlikely that collision followed by erosion driven decompression is an appropriate model we suggest that the thermal regime of the crust in the larsemann hills region was controlled by a perturbation in the asthenosphere with magma invasion of the crust we suggest that the 500 ma event represented in prydz bay by granitic outcrops at landing bluff and by several k ar ages from the larsemann hills area was responsible for the final excavation of the terrane

palaeostress analysis of the northern nijar and southern vera basins constraints for the neogene displacement history of major strike slip faults in the betic cordilleras se spain this paper presents the results of a detailed structural analysis of the northern nijar and southern vera basins with special emphasis on the evolution of the regional stress field and the associated timing of movement of the serrata gafarillos and palomares strike slip fault zones these major fault zones control the neogene deformation of the se internal betic cordilleras in spain detailed stress analysis on neogene sediments of the vera and nijar basins shows a strike slip regime with nw se oriented subhorizontal maximum principal stress 1 during tortonian and earliest messinian times under the influence of this stress field dextral displacement along the n090e trending gafarillos fault zone resulted in deformation of the sediments of the southern sorbas and northeastern nijar basins during the early messinian a clock wise rotation of the stress field occurred stress analysis in rocks with late early messinian up to quaternary ages in the nijar and vera basins indicates a strike slip regime with n s oriented subhorizontal maximum principal stress 1 under the influence of this stress field the main activity along the n010e striking palomares strike slip fault zone took place resulting in deformation of the neogene sediments of the southeastern vera basin and culminating in a maximum sinistral displacement of more than 20 km at the same time the stress field was not suitably oriented to exert a large shear component on the gafarillos fault zone which activity ended after the earliest messinian fault and outcrop patterns of syntectonic neogene sediments in the vera basin show that displacement along the palomares fault zone decreased at the end of the middle miocene although minor displacement phases may still have occurred during the late miocene and possibly even pliocene from the middle miocene onward deformation in the nijar basin was controlled by sinistral displacement along the n040e trending serrata strike slip fault zone

successive overprinting granulite facies metamorphic events in the anmatjira range central australia the anmatjira range and adjacent reynolds range central australia comprise early proterozoic metasediments and othogneisses that were affected by three and possibly four temporally distinct metamorphic events m1 4 and deformation events d1 4 in the period 1820 1590 ma the north western portion of the range around mt stafford preserves the effects of 1820 ma m1 d1 and shows a spectacular lateral transition from muscovite quartz bearing schists to interlayered andalusite bearing migmatites and two pyroxene granofelses that reflect extremely low pressure granulite facies conditions over a distance of less than 10 km orthopyroxene cordierite garnet k feldspar quartz bearing gneisses occur at the highest grade implying peak conditions of 750 c and 2 5 0 6 kbar an anticlockwise p t path for m1 is inferred from syn to late d1 sillimanite overprinting andalusite petrogenetic grid considerations and quantitative estimates of metamorphic conditions for inferred overprinting assemblages the effects of m1 have been variably overprinted to the south east by a c 1760 ma m2 d2 event much of the central anmatjira range around ingellina gap comprises orthogneiss deformed during d2 and metapelites that have m1 andalusite and k feldspar overprinted by m2 sillimanite and muscovite the south eastern portion of the range around mt weldon comprises metasediments and orthogneisses that were completely recrystallized during m2 d2 with metapelitic gneisses characterized by spinel sillimanite k feldspar quartz bearing assemblages that suggest peak m2 conditions of 750 c and 5 5 1 kbar overprinting parageneses in metapelitic gneisses imply that d2 occurred during essentially isobaric cooling a third granulite facies event m3 affected rocks in the reynolds range immediately to the south of the anmatjira range at c 1730 ma a possible fourth event m4 with a minimum age of c 1590 my affected both ranges but resulted in only minor overprinting of m1 3 assemblages the superimposed effects of m1 4 mapped for the entire anmatjira reynolds range area indicate that only minor or no dislocation of the regional geology occurred during any of the metamorphic and accompanying folding events although the immediate cause of each of the metamorphic events involved advection the ultimate causes were external to the metasediments and most probably external to the crust

moment tensor solutions for small and moderate earthquakes in the ibero maghreb region 1 we applied time domain moment tensor inversion of local and regional waveforms to small and moderate mw 3 5 5 7 shallow earthquakes from the iberian peninsula northern morocco and northern algeria for the 6 years period from november 1995 to march 2002 and the previous network of autonomously recording seismograms nars experiment moment tensor solutions were obtained for 58 events considerably increasing the total number of available solutions in the study area for each event we performed a moment tensor inversion and a double couple grid search for simple faulting events the grid search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation the computed mechanisms show regional consistency a large part of the iberian peninsula is characterized by normal faulting mechanisms with sw ne oriented t axes thrusting and se nw compression is dominant in algeria in the alboran sea the westernmost part of the mediterranean and the transition between both regimes strike slip mechanisms dominate with approximately n s oriented p axes this pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations

nd and sr isotopic systematics of central australian granulites chronology of crustal development and constraints on the evolution of lower continental crust nd and sr isotopic data are reported for a granulite terrain in the proterozoic arunta block of central australia sm nd data from a wide range of rock types define a crust formation age of 2 070 125 ma and provide further evidence for voluminous crustal growth in the proterozoic an nd value of 1 5 0 8 indicates a depleted mantle source for this crustal segment and there is no evidence for a large component of significantly older sialic crust field relationships geochemistry and rb sr data for mafic and felsic granulites indicate that intracrustal differentiation and polyphase deformation were followed by granulite facies metamorphism rb depletion at 1 800 ma rb sr data for strongly retrogressed granulites define an age of 1 700 ma which is interpreted as the time of retrograde biotite growth partial melting at the presently exposed crustal level and anatexis at deeper crustal levels were broadly coeval with the retrograde metamorphism sm nd and rb sr isotopic systematics of minerals indicate that the terrain cooled slowly did not experience significant uplift until 1 000 ma and remained at temperatures above 320 c until the late palaeozoic the mineral data are consistent with geological relationships and petrological evidence for a prolonged period of isobaric cooling followed by uplift late in the metamorphic evolution of the terrain the granulite protoliths appear to have formed in a rift which closed within 280 ma of initial separation deformation and granulite facies metamorphism at 1 800 ma are interpreted to be a consequence of collision between the continental blocks which defined the rift regional retrogression and granitoid magmatism at 1 700 ma are attributed to underthrusting of the granulites by lower grade rocks in the final stages of collision subsequent events in the cooling and uplift history appear to have been controlled by the presence of long lived major faults in the crust and a prolonged history of episodic compression in the continental lithosphere the results of this study suggest that granulite terrains in general cannot be equated with lower continental crust but instead represent assemblages of mainly supracrustal rocks which in some instances have been involved in major collision events

role of decollement material with different rheological properties in the structure of the aljibe thrust imbricate flysch trough gibraltar arc an analogue modelling approach abstract the miocene aljibe thrust imbricate flysch trough in the external zone of the gibraltar arc shows large changes in structural style towards the foreland rheological variation of the decollement rocks triassic evaporitic rocks and mesozoic limestones appears to be the main factor controlling the contrasts in structural style that characterise adjacent wedge domains in order to test this hypothesis we carried out analogue experiments involving three dimensional variations of decollement material a plate of viscous material was placed in the central part of the models at the base of the sand multilayers different geometries of the viscous plate were used experimental results show a strong link between the rheological properties of the decollement material and the structure of the overlying thrust wedge these results compare well with the internal geometry and vergence distribution in the aljibe thrust imbricate indeed the tectonic style of the wedge can be explained as a consequence of variations of rock type along the basal decollement

the p t deformation path for a mid proterozoic low pressure terrane the reynolds range central australia the proterozoic low pressure high temperature lpht terrane of the reynolds range occurs in a 130 km long nw trending belt in the central part of the arunta block central australia the reynolds range has been affected by two mid proterozoic tectonic cycles di and dii associated with two metamorphic events mi and mii di mi effects are restricted to the older of two sedimentary successions the lander rock beds which are separated from the younger reynolds range group by an angular unconformity the dominant structural metamorphic features formed during dii mii affected both sedimentary successions and the various granites that intruded them and reworked most di mi effects the dii deformation history can be subdivided into one prograde two peak and one retrograde stage average p t calculations in the southeastern half of the range indicate a peak metamorphic pressure of 4 1 0 3 kbar because the calculated values are derived from the same stratigraphic level corresponding to the base of the reynolds range group which is exposed throughout the area it is likely that pressures were similar in the entire range in fact however the peak metamorphic temperature shows a dramatic increase from greenschist facies c 400 c in the northwest to granulite facies 740 60 c in the southeast indicating that mii was associated with anomalously high heat flows the p t path is anticlockwise with isobaric cooling from the metamorphic peak indicated by corona textures however the evidence of a prograde increase in pressure is indirect and based on the compressional nature of the structures peak metamorphic mineral assemblages and retrograde mineral assemblages in amphibolite facies shear zones show the same metamorphic zonation suggesting they formed in response to the same thermal event if this is true the implication is that a thermal perturbation external to the crust was maintained for a considerable period of time 110 ma based on zircon dating as it is not clear whether proterozoic asthenosphere active thermal perturbations operated for this long the alternative interpretation must be considered namely that the peak metamorphic events are separate from the shear zone event associated with reheating of the area

deformation in neogene sediments of the sorbas and vera basins se spain constraints on simple shear deformation and rigid body rotation along major strike slip faults abstract detailed structural analyses are presented of the neogene sorbas basin adjacent to the e w striking gafarillos fault zone and the vera basin adjacent to the 020 striking palomares fault zone in southeastern spain a stress regime with an e w oriented subhorizontal maximum principal stress 1 existed in pre tortonian 11 3 ma time a strike slip regime with nw se oriented compression during tortonian and earliest messinian time caused dextral displacement along the e w trending gafarillos fault of approximately 10 km structural analysis indicates that most displacement took place in the early tortonian deformational patterns within the adjacent pull apart basin reflect a dextral simple shear zone of at least 500 m width kinematical analysis of folds in the sorbas basin suggests however that rotational effects are largely caused by rigid body rotation without much internal deformation sinistral strike slip displacements occurred along the palomares fault zone under the influence of the same stress regime an abrupt change in the orientation of the stress field to n s directed compression in earliest messinian time 6 5 ma caused the termination of displacements along the gafarillos fault zone whereas the 020 trending palomares fault zone continued to accumulate sinistral strike slip displacements of about 25 km volcanism occurred along splays of the fault zone a wider shear zone of a few kilometers width evolved in which considerable anti clockwise rotation of folds occurred kinematic analysis of these folds shows that these rotational effects are again dominantly rigid body rotations assuming rotations are merely caused by simple shear deformation overestimates the amounts of strain a better way to deal with simple shear deformation is to compare observed shortening caused by folding with the magnitude of rotation of fold hinges

a sequence of partial melting reactions at mt stafford central australia metasedimentary gneisses show a rapid change in grade in a 10 km wide low p high t regional aureole at mt stafford in the arunta block central australia migmatite occurs in all but the lowermost of five metamorphic zones which grade from greenschist zone 1 through amphibolite zones 2 3 to granulite facies zones 4 5 the sequence of partial melting reactions inferred for metapelitic rocks is dependant upon protolith temperature and fluid conditions the metapelite solidus in zone 2 reflects vapour present melting at p 3 kbar and t 640 c melting having initially been controlled by the congruent breakdown of the assemblage crd kfs bt qtz at slightly higher temperature andalusite in leucosome formed via the reaction kfs qtz bt h2oand melt and melt having been stabilized by the presence of boron sillimanite coaxially replaces andalusite in the high grade portion of zone 2 in zone 3 large aluminosilicate aggregates in leucosome are armoured by spl crd grt symplectites garnet partially pseudomorphs biotite cordierite or spinel in high grade portions of zone 3 zone 4 grt crd opx bearing metapsammite assemblages and garnet bearing leucosome reflect t 800 c and p 2 2 0 9 kbar in the model kfmash system the principal vapour absent melting step reflected significant modal changes related to the breakdown of the as bt tie line and the establishment of the spl crd tie line the bulk rock geochemistry of migmatite samples straddle the spl crd tie line the aluminous bulk rock composition of the common bedded migmatite restricted its potential to witness garnet forming and orthopyroxene forming reactions minor textural and modal changes in and above zone 3 reflecting biotite destablization in biotite poor assemblages

late holocene tectonics and paleoseismicity southern cascadia subduction zone holocene deformation indicative of large subduction zone earthquakes has occurred on two large thrust fault systems in the humboldt bay region of northern california displaced stratigraphic markers record three offsets of 5 to 7 meters each on the little salmon fault during the past 1700 years smaller and less frequent holocene displacements have occurred in the mad river fault zone elsewhere as many as five episodes of sudden subsidence of marsh peats and fossil forests and uplift of marine terraces are recorded carbon 14 dates suggest that the faulting subsidence and uplift events were synchronous relations between magnitude and various fault offset parameters indicate that earthquakes accompanying displacements on the little salmon fault had magnitudes of at least 7 6 to 7 8 more likely this faulting accompanied rupture of the boundary between the gorda and north american plates and magnitudes were about 8 4 or greater

recent large fold nucleation in the upper crust insight from gravity magnetic magnetotelluric and seismicity data sierra de los filabres sierra de las estancias internal zones betic cordillera abstract rheological heterogeneities in the upper crust have a close relationship with the fold position where rigid bodies could constitute initial perturbations that allow the nucleation of folds consequently establish the position and geometry of anomalous rocks located in the upper crust by geophysical studies help to understand the folded structure observed on surface new geological observations in the field along with gravity magnetic magnetotelluric and seismicity data reveal the subsurface structure in the sierra de los filabres sierra de las estancias folded region part of the alpine belt in southern spain the geometry of the upper crust is determined by geological field data 2d gravity models 2d magnetic models and 2d mt resistivity model while seismicity evidences the location of the deep active structures these results allow us to propose that a basic rock body at 4 to 9 km depth has determined the nucleation and development of the sierra de los filabres kilometric antiform n vergent large late folds are subjected to a variable present day stress field earthquake focal mechanisms suggest the presence in depth of a regional nw se compressive stress field however most of the seismogenetic structures do not extend up to the surface where nw se and wnw ese outcropping active normal faults are observed thus indicating a ne sw extension in the upper crust simultaneous to orthogonal nw se compression related to reverse faults and minor folds developed in the eastern almanzora corridor and in the nearby huercal overa basin the recent and active tectonic studies of cordilleras hinterland subjected to late folding greatly benefits from the integration of surface observations together with geophysical data

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

crustal scale ductile fault systems in the arunta inlier central australia detailed geologic observations along three 100 km long traverses across the early proterozoic arunta inlier central australia indicate that paleozoic ductile shear zones are organized into crustal scale structural systems which control the map pattern and distribution of metamorphic zones two provinces can be distinguished 1 1 a southern one where shear zones form a series of hinterland dipping and south verging imbricate reverse faults in the west redbank area grading eastward into a foreland dipping duplex in the arltunga nappe complex directly north of this complex flat lying paleozoic south directed ductile shear affects a large portion of the crust a point which has been underestimated so far 2 2 the northern province is characterized by both south and north dipping shear zones showing reverse motion to produce a crustal scale pop up structure presumably resulting from a more coaxial deformation history strike slip shear zones become predominant in the eastern part of this province stratigraphic and cross cutting relationships indicate that the southern systems developed first the northern systems probably developed in response to the lock up stages of overthrusting in the southern province one important result of this work is that the distribution of granulite facies rocks and major geophysical anomalies throughout the arunta inlier is best explained by their position relative to the paleozoic ductile fault systems described above there is no need to invoke extensive proterozoic uplift of these lower crustal materials

lateral interaction between metamorphic core complexes and less extended tilt block domains the alpujarras strike slip transfer fault zone betics se spain abstract the alpujarras area in southeastern spain exhibits one of the scant documented examples of extension related strike slip faults bordering core complexes in the world faults of the alpujarras fault zone define a regional scale complex ene striking transfer zone that marks the boundary among the sierra nevada elongated dome a highly extended constricted core complex and a less extended domain formed by large scale tilt blocks detailed mapping and structural analysis show that the alpujarras fault zone is an integral part of the wsw directed normal fault systems that thinned the betic hinterland during the middle miocene to recent time fault patterns and palaeostress analysis both indicate that dextral movement along the strike slip faults was induced by a local stress field with a sub horizontal e w to ese wnw trending maximum principal stress axis which is synchronous with the regional stress field driving the normal fault systems palaeostress analysis also indicates subsequent variations in the stress field with a sub horizontal nw se to n s trending maximum principal stress axis thus producing both the tectonic inversion of the northern fault of the alpujarras system and shortening of the unloaded extensional detachment footwall a simplified kinematic model for the tectonic evolution of the alpujarras area from the middle miocene to recent emphasizes the kinematic coupling of normal faults and strike slip transfer zones in the extensional process

neogene coralline algal growth forms and their palaeoenvironments in the almanzora river valley almeria s e spain abstract the almanzora river valley is an elongate e w depression containing mainly neogene sediments during the late tortonian several horizons of crustose coralline algae developed in three distinct sedimentary contexts a on coastal platforms and talus slopes b on fan deltas and c associated with corals in patch reefs growing at the furthermost extremes of coastal fan deltas in the former two cases the predominant growths are as rhodoliths associated with mobile substrates in the coastal systems an increase in depth results in a change in both the morphology and the composition of the rhodoliths with depth there is a significant increase in the diversity of algal species and a concomitant increase in the size of the algal covering compared to the nucleus and thus the morphology of the rhodolith depends less and less on the shape of the nucleus itself the massive crusts and columns which mark the limit of development of the shallow water rhodoliths in the deeper examples are covered by branching and thin leafy laminar growths in the fan deltas the development of the rhodoliths is similar to that of the deeper coastal zones in the patch reefs the specific composition of the algal associations changes somewhat and the growths developed on a stable substrate under low energy conditions are mainly vertical branches arising from thin crusts

stratigraphic and structural constraints on the proterozoic tectonic history of the olary block south australia abstract the lower proterozoic of the olary block is divided into five rock suites defining a conformable stratigraphic sequence correlated with the willyama supergroup of the broken hill block which has a probable depositional age no greater than 1800 ma the sequence was deformed and metamorphosed during the olarian orogeny at 1580 ma definition of the stratigraphy permits regional structural analysis and the resolution of two folding events an initial recumbent fold terrain redeformed by upright folds with a near vertical axial surface the olarian orogeny comprises a single regional compression axis with both folding events indicating a se direction of transport the described tectonic fabrics are consistent with simple shear deformation generating the early recumbent terrain

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

timing of tectonic events in the alpujarride complex betic cordillera southern spain ar ar and fission track dating from four low grade sections in the alpujarride complex sheds light on the timing of the early contractional history of these high pressure metamorphic units and their subsequent exhumation during the early miocene extensional collapse of the betic orogen white mica grains from the lowest grade rocks yield partly reset detrital ar ar ages where deformation and recrystallization are more intense however they yield reproducible ages as old as c 48 ma which we interpret as the approximate timing of the main contractional event and associated high pressure metamorphism in these units rocks from slightly higher grade sections give reproducible ar ar ages between 30 and 40 ma but these younger ages probably reflect the interplay of growth and cooling in fine grained micas heated to between 300 c and 400 c during prograde metamorphism in each of the four areas studied the low grade rocks are separated by an extensional detachment or shear zone from medium grade rocks below in two areas these detachments have been folded around major overturned north vergent folds ar ar data from structurally below the detachments and fission track ages from all structural levels indicate the onset of significant cooling in the early miocene which corresponds to the age of the extensional event the folds must therefore be early miocene or younger

decompressional coronas and symplectites in granulites of the musgrave complex central australia abstract in granulite facies metapelitic rocks in the musgrave complex central australia reaction between s1 garnet and sillimanite involves the development in s2 of both garnet cordierite hercynitic spinel biotite and hercynitic spinel cordierite sillimanite biotite the s2 assemblages occur either in coronas and symplectites mainly around garnet or in rocks in which s2 is more strongly developed as recrystallized assemblages ignoring the presence of biotite and ilmenite the mineral textures can be accounted for qualitatively by a consideration of the model system feo mgo al2o3 sio2 fmas the textural relationships accord with decompression accompanying the change from s1 to s2 however since biotite and ilmenite are involved in the assemblages the parageneses are better accounted for in terms of equilibria in the expanded model system k2o feo mgo al2o3 sio2 h2 tio2 fe2o3 kfmashto i e afm tio2 fe2o3 the coronas reflect the tectonic unroofing of at least part of the musgrave complex from peak s1 conditions of about 8 kbar to s2 conditions of about 4 kbar

seismic transpressive basement faults and monocline development in a foreland basin eastern guadalquivir se spain 1 we examine the late tortonian to present day deformation of an active seismic sector of the eastern iberian foreland basement of the betic cordillera in southern spain transpressive faults affecting paleozoic basement offset up to triassic rocks late triassic clays and evaporites constitute a decollement level decoupling the basement rocks and a 100 m thick cover of jurassic carbonates monoclines trending ne sw to ene wsw deform the jurassic cover driven by the propagation of high angle transpressive right lateral basement faults they favor the migration of clays and evaporites toward the propagated fault tip i e the core of the anticline resulting in fluid overpressure fluid flow and precipitation of fibrous gypsum parallel to a vertical 3 the overall geometry of the studied monoclines as well as the intense deformation within the clays and evaporites reproduces three layer discrete element models entailing a weak middle unit sandwiched between strong layers late tortonian syn folding sediments recorded the initial stages of the fault propagation folding equivalent unexposed transpressive structures and associated monoclines reactivated under the present day nw se convergence are recognized and analyzed in the sabiote torreperogil region using seismic reflection gravity and borehole data a seismic series of more than 2100 low magnitude earthquakes was recorded within a very limited area of the basement of this sector from october 2012 to may 2013 seismic activity within a major ne sw trending transpressive basement fault plane stimulated rupture along a subsidiary e w n95 e strike slip relay fault the biggest event mblg 3 9 mw 3 7 occurred at the junction between them in a transpressive relay sector

the alpujarride nevado fibabride extensional shear zone betic cordillera se spain in the betic cordillera the initial thickening of the alboran domain produced an alpine high pressure low temperature hp lt metamorphism in the alpujarride and nevado filabride complexes after 19 ma this thickening process evolved to an extensional stage with uplift rates of between 1 and 2 mm year 1 the extensional stage generated structures in a heterogeneous shear regime with a top to the west sense of movement the present day alpujarride nevado filabride contact is a detachment fault generated in this shearing regime in the footwall the first structure developed in this extensional stage is a planar linear fabric characterized by constrictive strain that is axial planar to kilometric recumbent tight to isoclinal folds the planar linear fabric is folded by inclined close to open folds with axes parallel to the stretching lineation the planar linear fabric and folds are deformed by a late extensional crenulation cleavage near the detachment surface finally brittle deformation was generated within the same kinematic framework as that of the ductile structures in the hanging wall meanwhile deformation had a brittle character producing faults and joints

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

evidence for pre regional metamorphic fluid infiltration of the lower calcsilicate unit reynolds range group central australia grandite garnet rich calcsilicate rocks from the lower calcsilicate unit of the regionally metamorphosed reynolds range group central australia crop out along a strike parallel section in which a transition zone from m22 amphibolite to granulite facies rocks is exposed across this transition the grandite rich layers do not show systematic changes in mineral assemblages compositions and modes or stable isotope compositions these layers are deformed by f22 folds that are associated with the peak of regional low pressure high temperature metamorphism therefore the grandite rich layers appear to pre date regional metamorphism and to have acted as closed chemical systems during prograde m22 metamorphism mineral assemblages in the grandite rich layers are consistent with their formation through the infiltration of oxidized water rich fluids xco2 0 1 0 3 log fo2 16 to 14 the stable isotope values of calcite 13c 4 2 to 0 8 0 pdb 18o 10 5 14 0 0 v smow and bulk silicate fractions 18o 6 1 to 10 8 of the grandite rich layers are most consistent with the infiltrating fluid being from a magmatic source it is most likely that fluid infiltration occurred during the pre m22 contact metamorphism m21 that affected much of the reynolds range group the preservation of these assemblages is probably due to their high variance and little pervasive fluid rock interaction having occurred during m22 the clinopyroxene and feldspar rich calcsilicate rocks that host the grandite rich layers contain poikiloblastic grandite garnet that formed during prograde m22 metamorphism thin marbles that locally occur with the grandite rich layers contain a third garnet generation that is post or late m22 this grossular rich garnet occurs in coronas around calcite plagioclase clinopyroxene wollastonite and scapolite these coronas are consistent with cooling and or compression however because the marble assemblages are themselves overprinted by m21 grandite rich layers the development of coronal garnet does not reflect a continuous p t t path rather it more probably reflects the partial re equilibration of m21 contact metamorphic assemblages to post m22 conditions

resolving denudational histories in orogenic belts with apatite fission track thermochronology and structural data an example from southern spain interpreting apatite fission track thermochronology aftt data obtained from orogenic belts presents a considerable challenge because of the complexity of denudational processes operating in this tectonic setting an approach which integrates kinematic foliation and thermochronologic data is advocated and an example from southern spain is used as an illustration aftt ages from the sierra nevada are negatively correlated with their elevation precluding interpretation in terms of simple erosive denudation however when additional structural data is included in the analysis a complex denudation history is obtained an initial phase of tectonic denudation was responsible for the cooling that produced the oldest apparent ages thereafter folding accompanied by differential erosive denudation caused cooling of samples inferred to have been as much as 4 5 km below the detachment the second phase of cooling began in the late miocene early pliocene

the current tectonic motion of the northern andes along the algeciras fault system in sw colombia abstract riedel synthetic and antithetic type faults principal displacement zones pdz pull apart basins such as lazy s shaped releasing bend extensive and rhomboidal shaped and releasing sidestep basins and minor folds located oblique to the main trace of the algeciras fault system afs are interpreted from landsat tm 5 images and geological mapping these tectonic features are affecting quaternary deposits and are related to major historical earthquakes and recent registered seismic events indicating neotectonic activity of the structure the afs is classified as a right lateral wrench complex structure with an important vertical component in which sedimentary cover and basement rocks are involved in addition the system represents a simple shear caused by the oblique convergence between the nazca plate and the northern andes the transpressive boundary in sw colombia was previously located along the eastern frontal fault system however this paper shows that the afs constitutes the actual boundary of the current transpressive regime along the northern andes which begins at the gulf of guayaquil in ecuador and continues into colombia and venezuela

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

late orogenic doming in the eastern betic cordilleras final exhumation of the nevado filabride complex and its relation to basin genesis the geometry timing and kinematics of late orogenic extension in the betic cordilleras pose the problem of a decoupling of upper crustal and lower crustal deformation regimes perpendicular directions of extension in metamorphic domes and nearby sedimentary basins remain unexplained this paper puts kinematic constraints on the final exhumation of the nevado filabride complex focusing on the formation of metamorphic domes and their relations with the adjacent basins structural fabrics and kinematic indicators below the main shear zones as well as their relations with both published changing metamorphic p t conditions and geochronological data were studied our approach describes 1 a consistent top to the west shear parallel to dome axes of during d2 i e during decompression with distributed ductile flow and the onset of strain localization along major shear zones 2 further strain localization along the major shear zones under greenschist facies conditions during d3 leading to s c mylonites formation accompanied with a rock strong thickness reduction 3 the divergence of shear direction on either limbs of domes during d3 showing the appearance of the dome geometry and 4 a local evolution toward n s brittle extension d4 in the upper plate and formation of sedimentary basins continuous ductile to brittle top to the west shear is compatible with the slab retreat hypothesis from the miocene the formation of domes which adds gravitational forces responsible for the final stages of exhumation is thus characterized by important kinematics changes necessary to explain coeval n s opened basins later from the upper tortonian a contractional event d5 amplified the earlier domal structures forming the present north vergent folds

stepping stones and pitfalls in the determination of an anticlockwise p t t deformation path the low p high t cooma complex australia low pressure high temperature low p high t metamorphic rocks of the cooma complex southeastern australia show evidence of an anticlockwise pressure temperature time deformation p t t d path similar to those of some other low p high t metamorphic areas of australia prograde paths are reasonably well constrained in cordierite andalusite schists cordierite k feldspar gneisses and andalusite k feldspar gneisses these paths are inferred to be convex to the temperature axis involving increase in pressure with increase in temperature evidence of the retrograde path is inconclusive but is consistent with approximately isobaric cooling as are available isotopic data on the cooma granodiorite which indicate initially rapid cooling following attainment of peak temperatures the retrograde path is inconsistent with either a clockwise p t t d path involving rapid or even moderate decompression immediately post dating the peak of metamorphism or a path in which the retrograde component simply reverses the prograde component because both these paths should cross reactions forming cordierite from aluminosilicate for which no evidence has been observed determination of the deformational metamorphic history of the complex is not straightfoward and depends on careful examination of critical samples evidence necessary for successful elucidation of the prograde and part of the retrograde deformational metamorphic history in the cooma complex includes 1 sequentially grown porphyroblasts that can be timed relative to surrounding foliations 2 partial replacement microstructures providing relative timing of metamorphic reactions that cannot be timed relative to foliation development 3 a tectonic marker foliation s4 at cooma that allows correlation of foliations from one location to another and 4 single samples containing all of the foliations and all generations of porphyroblast growth within a single metamorphic zone the latest two or three foliations involve low strain accumulation allowing relative timing relationships between foliations and porphyroblasts to be more clearly determined sequential porphyroblast growth and foliation development in the cordierite andalusite schists is examined for situations involving rotation and non rotation of porphyroblasts relative to geographically fixed coordinates although the number of foliations developed varies in the rotational situation depending on the deformation history proposed the sequential order of porphyroblast growths does not differ from the non rotational situation thus whether or not porphyroblasts rotated in the cooma rocks the sequence of reactions and therefore p t t paths inferred from the relative timing of porphyroblast growths remain the same for the deformational histories evaluated

extension versus compression during the miocene tectonic evolution of the betic chain late folding of normal fault systems the westernmost part of the mediterranean alpine belt is represented by the betic rif orogenic belt around the gibraltar arc which in turn surrounds the alboran basin in the betic chain early and middle miocene crustal thinning of the alboran basement is well established as extensional low angle normal faults and detachment faults developed in both ductile and brittle conditions thinned a previously thickened crust in the alboran domain of the central betics two main extensional episodes are evidenced a langhian one with a north northwestward transport direction followed by a west southwestward extension serravallian in age therefore all the units heretofore considered to be thrust nappes are in reality extensional units bounded by low angle normal faults the cortical segment studied formed the basement of the miocene alboran basin in which progressively deeper basement units were covered by younger marine sediments as a result of extensional denudation processes the age of these sediments clearly dates the faulting the extensional evolution during the miocene is much more complex than the past models suggest during the upper miocene these extensional systems were folded as the result of a compressive regime which allowed them to be well exposed compression in the gibraltar arc is nearly contemporaneous with extension and the westward migration of the compression through its footwall is related with the extensional spreading

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

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

exhumation of the danubian nappes system south carpathians during the early tertiary inferences from kinematic and paleostress analysis at the getic danubian nappes contact abstract a detailed kinematic study based on the analysis of brittle structures combined with a description of structures in the adjacent foredeep allows for the definition of three major tectonic episodes during the late cretaceous tertiary evolution of the central part of the south carpathians following middle cretaceous and older orogenic phases the first tectonic event that affected the studied area was a late cretaceous nnw sse oriented contraction which led to the final major emplacement of the danubian and getic nappes during the paleogene early miocene an extension event induced rapid exhumation of the danubian units leading to the formation of large normal faults dipping towards both the foreland and the hinterland this extension together with dextral rotation of the south carpathians around the western corner of the moesian platform allows for the ne ward movement of the internal continental blocks with respect to the foreland platforms in the late miocene e ward translation of the internal south carpathians units with respect to the moesian platform was accommodated through a large scale e w oriented strike slip corridor within the south carpathians the general paleogene early miocene ne to e ward rotation and the late miocene e ward translation of the rhodopian fragment allowed for the accommodation of roll back and contraction taking place in the east carpathians

neotectonics and plio quaternary landscape development within the eastern huercal overa basin betic cordilleras southeast spain abstract the huercal overa basin is one of a series of neogene sedimentary basins located within the betic cordillera of southeast spain its geological and geomorphological history has been controlled by tectonic activity culminating in basin inversion during the plio quaternary deformation of the huercal overa basin is associated with left lateral strike slip faulting in relation to its position within the trans alboran shear zone in this paper we focus upon the eastern portion of the huercal overa basin and make the first attempt to reconstruct the long term landscape development during the plio quaternary this is done through integration of geological and geomorphological data obtained through field observations and gis and remote sensing techniques in particular this paper provides a case study that contributes to the understanding of landscape development within tectonically active shear zones within the eastern part of the huercal overa basin the main tectonic activity is associated with the left lateral strike slip lorca alhama fault oriented ne sw during the late pliocene and early pleistocene the interaction of this fault with older miocene ene wsw to e w orientated structures formed a subsiding area with pull apart basin characteristics termed the cubeta del saltador subsidence within the cubeta del saltador enabled sedimentary infilling by braided rivers with sediment being derived from the sierra de las estancias to the north and the sierra de almagro to the south sedimentary deformation has resulted in the development of a series of progressive unconformities angular unconformities and faulting within the alluvial sediments towards the end of this stage of landscape development an increase in tectonic activity resulted in the creation of elevated tectonic highs in the north alto de la garita del diablo and east loma de garcia of the cubeta del saltador from the middle pleistocene onwards a progressive decrease in tectonic activity is recorded alluvial sediments infilled the cubeta del saltador these were dominated by braided river sediments that formed part of a fan shaped alluvial distributary system derived from the sierra de las estancias to the north in contrast smaller debris flow dominated alluvial fans were derived from the sierra de almagro along the southern margin currently the study area presents an asymmetric configuration reflecting the different topographic characteristics of the northern and southern limiting mountain fronts

geodynamic evolution of the central dinarides abstract the central part of the dinarides unlike the northwestern and southeastern dinarides shows a consistent pattern in the distribution of the large tectonostratigraphic units from southwest apulia to northeast the following five main units originating in different parts of the mesozoic tethys can be distinguished 1 adriatic dinaridic carbonate platform formations 2 carbonate clastic units flysch bosniaque of the passive continental margin 3 ophiolite bearing formations of the dinaridic ophiolite zone also containing radiolarites greywackes and shales including melange formations and overstepped late jurassic to cretaceous cover sequences 4 active continental margin units represented by upper cretaceous palaeogene trench sediments with blueschists tectonized ophiolite melange alpine medium pressure metamorphic rocks originated from upper cretaceous palaeogene sediments and alpine synkinematic granitoids 5 a nappe consisting of allochthonous palaeozoic triassic formations which is thrust onto the ophiolites and genetically related sedimentary formations the frontal parts of this nappe directly overlie the northeastern margin of the adriatic dinaridic carbonate platform i e the external dinarides the evolution of the central dinarides was controlled by a sequence of tectonic events which took place within the alpine cycle 1 rifting processes lasting some 40 50 ma which started in the late permian and ended in the norian 2 opening of the oceanic dinaridic tethys commenced in the late triassic and persisted for some 70 80 ma until the end of the jurassic 3 subduction processes and emplacement of ophiolites started in late jurassic early cretaceous times during the closing phase of the dinaridic ocean or dinaridic tethys the palaeozoic triassic nappe was emplaced on the ophiolites the thrusting was accompanied by alpine metamorphism 120 100 ma 4 the main alpine deformational event and medium pressure metamorphism with synkinematic granite plutonism took place in late eocene early oligocene times when the ophiolite and palaeozoic triassic nappes were emplaced on the adriatic dinaridic carbonate platform which at the same time was deformed resulting in the development of the external dinarides fold and thrust belt

seismic sources on the iberia african plate boundary and their tectonic implications the plate boundary between iberia and africa has been studied using data on seismicity and focal mechanisms the region has been divided into three areas a the gulf of cadiz b the betics alboran sea and northern morocco and c algeria seismicity shows a complex behavior large shallow earthquakes h 30 km occur in areas a and c and moderate shocks in area b intermediate depth activity 30 h 150 km is located in area b the depth earthquakes h 650 km are located to the south of granada moment rate slip velocity andhvalues have been estimated for shallow shocks and show similar characteristics for the gulf of cadiz and algeria and quite different ones for the central region focal mechanisms of 80 selected shallow earthquakes 8 mb 4 show thrust faulting in the gulf of cadiz and algeria with horizontal nnw sse compression and normal faulting in the alboran sea with e w extension focal mechanisms of 26 intermediate depth earthquakes in the alboran sea display vertical motions with a predominant plane trending e w solutions for very deep shocks correspond to vertical dip slip along n s trends frohlich diagrams and seismic moment tensors show different behavior in the gulf of cadiz betic alboran sea and northern morocco and northern algeria for shallow events the stress pattern of intermediate depth and very deep earthquakes has different directions vertical extension in the nw se direction for intermediate depth earthquakes and tension and pressure axes dipping about 45 o for very deep earthquakes regional stress pattern may result from the collision between the african plate and iberia with extension and subduction of lithospheric material in the alboran sea at intermediate depth the very deep seismicity may be correlated with older subduction processes

the role of small scale fold and fault development in seismogenic zones example of the western huercal overa basin eastern betic cordillera spain the nw se shortening between the african and the eurasian plates is accommodated in the eastern betic cordillera along a broad area that includes large n vergent folds and kilometric ne sw sinistral faults with related seismicity we have selected the best exposed small scale tectonic structures located in the western huercal overa basin betic cordillera to discuss the seismotectonic implications of such structures usually developed in seismogenic zones subvertical ese wnw pure dextral faults and e w to ene esw dextral reverse faults and folds deform the quaternary sediments the la molata structure is the most impressive example including dextral ese wnw neogene faults active southward dipping reverse faults and associated ene wsw folds a molar m1 assigned to mimomys savini allows for precise dating of the folded sediments 0 95 0 83 ma strain rates calculated across this structure give 0 006 mm a 1 horizontal shortening from the middle pleistocene up until now the widespread active deformations on small scale structures contribute to elastic energy dissipation around the large seismogenic zones of the eastern betics decreasing the seismic hazard of major fault zones copyright 2009 john wiley sons ltd

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

the structure and tectonic evolution of the aguilon fold nappe sierra alhamilla betic cordilleras se spain abstract detailed structural work in the sierra alhamilla se spain shows that the aguilon nappe comprising triassic and older metasedimentary rocks is a fold nappe the most prominent set of small scale folds changes from dominantly n vergent in the upper right way up limb to s vergent in the greatly thinned lower limb the nappe closes to the north and must have been emplaced in this direction nappe formation was accompanied by small scale folding and extensive solution transfer producing a pronounced differentiated crenulation cleavage these structures overprint an earlier set of folds and cleavage and are overprinted in turn by late n vergent structures the lower limb of the nappe was thinned and disrupted during continued nappe transport pre triassic schist in the core of the nappe was affected by medium grade metamorphism of probable post triassic age the contact with low grade permo triassic sediments above and below the schist coincides with a distinct change in metamorphic grade this contact may be a post metamorphic extensional fault that is now folded around the nappe which suggests that nappe formation was preceded by extensional faulting this is consistent with gravity spreading as the driving process for nappe emplacement

sequential porphyroblast growth during progressive deformation and low p high t lpht metamorphism cooma complex australia the use of microstructural analysis to better understand deformation and metamorphic histories abstract detailed microstructural analysis has been conducted in the cooma complex which is one of the most thoroughly studied areas structurally and metamorphically in australia this was done to demonstrate the usefulness of microstructural analysis for better understanding deformation and metamorphic histories and the results add significant new information about deformation and metamorphism of this area microstructural relationships in the schists and gneisses indicate that four coaxially superposed foliations formed with alternating subhorizontal s 1 and s 3 and subvertical s 2 and s 4 orientations and the meso and macrostructural relationships are easily understood within this deformational framework three stages of sequential porphyroblast growth involve cordierite and andalusite in the schists and cordierite andalusite and k feldspar in the gneisses the porphyroblasts overgrew and preserved progressive stages in the structural development of these rocks with each period of growth occurring during a different deformation event d 2 d 3 and d 4 the sequential timing of these porphyroblasts is consistent with kfmash reaction curve topology and indicates a prograde p t t path convex to the temperature axis combining this with isobaric cooling inferred from previous studies gives an anti clockwise p t t path subvertical and subhorizontal foliations in porphyroblasts contrast with the variable orientations of the same foliations measured in the field however careful field work and microstructural analysis demonstrate that matrix foliation rotation rather than porphyroblast rotation relative to geographic coordinates is largely responsible for the contrasting observations even where bedding has been overturned after porphyroblast growth

metamorphism in the olary block south australia compression with cooling in a proterozoic fold belt the sedimentary and igneous rocks comprising the lower proterozoic olary block south australia were deformed and meta morphosed during the mid proterozoic olar ian orogeny the area is divided into three zones on the basis of assemblages in metapelitic rocks higher grade conditions occurring in the south east mineral assemblages developed during peak metamorphism which accom panied recumbent folding include andalusite in zones i and i1 and sillimanite in zone 111 upright folding and overprinting of mineral assemblages occurred during further com pression the new mineral assemblages includ ing kyanite in zone i1 and kyanite and sillimanite in zone 111 the timing relationships of the aluminosilicate polymorphs together with the peak metamorphic and overprinting parageneses imply an anticlockwise p t path for the olarian orogeny pressure increasing with cooling from the metamorphic peak

the depth of the earthquake activity in the central betics southern spain in this study we used relatively velocity independent methods wadati diagrams to estimate and check the focal depth of the seismic activity in a sector of the betic cordilleras alboran sea in southern spain to understand the behaviour of the seismic activity a total of 335 earthquakes have been analyzed the most interesting feature found in the analyzed sector is the strong variation of the focal depth on average the focal depth distribution in the granada basin is restricted to h 20 km the lower cut off in the seismic activity which is interpreted to mark the brittle ductile transition this cut off is coincident with a midcrustal reflector detected in the zone by previous seismic refraction and deep reflection experiments that was interpreted as an extensional detachment the seismic activity in the malaga zone reaches depths up to 100 km in this case the seismic activity affect to the crust and upper mantle the deepest activity coincides with low values of heat flow possibly thus indicating a thicking of the lithosphere towards the w in the centre of the alboran sea the activity is shallower and corresponds with a higher heat flow we think that our results support models that have proposed active delamination towards the west such a model may explain the increase in the lithosphere thickness in this direction which would be congruent with the depth of the earthquakes

low pressure granulite facies metapelitic assemblages and corona textures from macrobertson land east antarctica the importance of fe2o3and tio2in accounting for spinel bearing assemblages low pressure granulite facies metasedimentary gneisses exposed in macrobertson land east antarctica include hercynitic spinel bearing metapelitic gneisses peak metamorphic mineral assemblages include spinel rutile ilmenite sillimanite garnet spinel ilmenite sillimanite garnet cordierite ortho pyroxene magnetite ilmenite garnet spinel cordierite biotite ilmenite and orthopyroxene cordierite biotite each with quartz k feldspar and melt the presence of garnet biotite and cordierite orthopyroxene bearing assemblages implies crossing tie lines in afm projection for the k2o feo mgo al2o3 sio2 h2o kfmash system this apparent contradiction and the presence of spinel rutile and ilmenite in the assemblages is acounted for by using the kfmash tio2 o2 system i e afm tio2 fe2o3 we derive a petrogenetic grid for this system applicable to low pressure granulite facies metamorphic conditions retrograde assemblages are interpreted from corona textures on hercynitic spinel and fe ti oxides the relative positions of the peak and retrograde metamorphic assemblages on the petrogenetic grid suggest that corona development occurred during essentially isobaric cooling

orthogonal folding of extensional detachments structure and origin of the sierra nevada elongated dome betics se spain 1 a close relationship of the kinematics and timing between low angle extensional faulting and upright folding is established for the miocene detachment systems in the hinterland of the betics in southeastern spain folding accompanied tectonic denudation developing elongated domes with fold axes both parallel and perpendicular to the direction of extension the geometry kinematics and tectonic evolution of two major sequentially developed extensional fault systems have been characterized in several e w elongated mountain ranges of the central betics on the basis of new cartographic and structural data and a comprehensive revision of other available geological and geophysical observations the extensional systems have an average wsw direction of extension and led to exhumation of the two lower metamorphic complexes of the betics the nevado filabride and the alpujarride during the middle and upper miocene serravallian to tortonian the extended domain contains a core complex with distal and proximal antiformal hinges separated by around 60 km and with a fold amplitude of 6 km measured parallel to the direction of extension the total amount of extension across the core complex is about 109 116 km corresponding to a stretching factor of 3 5 3 9 estimated using the distance between fold axial surfaces and a geometrical model accomplishing footwall deformation during tectonic denudation via subvertical simple shear the elongated domal and basinal geometry of the detachments and their respective footwalls is due to the interference between two sets of orthogonal large scale open folds trending n s and e w longitudinal n s trending folds are interpreted as isostatic folds i e folds that developed in response to differential unloading of the extensional detachment footwalls inducing ductile flow in the middle crust these folds formed in a rolling hinge anticline in which rotation migrates westward through the footwall as it is progressively unroofed in contrast e w trending folds being subparallel to the direction of extension have a contractional origin and progressively affect to the west the isostatically readjusted segments of the detachments once they are inactive orthogonal folding occurred since the serravallian to lower pliocene extension is still active from the rolling hinge anticline in sierra nevada to the west the middle miocene to pliocene tectonic evolution of the sierra nevada elongated dome at the core of the betic hinterland is another example of the coexistence of extension and contraction during continued overall convergence and mountain building

late holocene evolution of the east eliki fault gulf of corinth central greece abstract trench stratigraphy and morphotectonic analysis was used to examine the recent evolution of the helike eliki plain and eliki fault the entire alluvial plain of the kerynites and vouraikos rivers which cross the eliki fault has subsided at rate of 1 4 mm yr resulting in the burial of the late hellenistic roman occupation horizons under 3 m of fluvial and colluvial sediments along the eastern segment of the eliki fault five trenches have been excavated and their 5000 yr old fluvial and colluvial deposits have been studied in association with the fault strand imprinted on them the kerynites river crosses at high angle the eliki fault and appears to be sensitive in tectonic movements related with the eliki fault sedimentation in the alluvial plain and the fluvial geomorphology of the kerynites river is important for understanding the fault evolution and the burial of the ancient 4th century bc helike city the kerynites river course highlights breaching deformation is the more likely to connect east and west eliki fault segments and that postseismic deformation is a significant mechanism for stress accommodation for part of the west end of the gulf of corinth

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

metamorphic events in the eastern arunta inlier part 1 metamorphic petrology abstract in the entia dome of the eastern arunta inlier kyanite facies metamorphism is recorded over a substantial area at least 160 km 2 and thus contrasts with the regionally extensive belts of high temperature low pressure andalusite sillimanite facies metamorphism documented elsewhere in the arunta inlier this amphibolite facies event appears to postdate regional granulite facies metamorphism evidence for which is almost totally obliterated in the entia dome prograde kyanite occurs in meta basites in comparatively rare associations involving hornblende staurolite and anorthite and in other rocks in association with gedrite and hornblende or garnet and biotite these kyanite bearing assemblages equilibrated at intermediate temperatures 570 710 c at peak pressures of 7 kbar and are overprinted by lower pressure assemblages including hornblende gedrite cordierite and sillimanite while this sequence of reactions may be simply interpreted in terms of a single clockwise orogenic cycle textural evidence and the available mineral isotopic data suggest a more complex history involving multiple heating and cooling episodes during the mesoproterozoic and possibly the palaeozoic the occurrence of regional retrogressive kyanite facies assemblages in the eastern arunta inlier provides evidence that the widely held perception that proterozoic crustal evolution in australia involved a distinct ensialic orogenic style characterised by high geothermal gradients etheridge et al 1987 loosveld and etheridge 1990 sandiford and powell 1991 is not universally true rather petrological evidence presented here with isotopic constraints described by foden et al 1995 suggests that the harts range region has experienced substantial crustal reworking at elevated temperatures during both the proterozoic and palaeozoic under thermal regimes more familiar to modern continental collision zones

origin of the western subbetic arc south spain palaeomagnetic and structural evidence abstract an integrated structural and palaeomagnetic study in late cretaceous eocene rocks of the western subbetic arc in the betic cordillera of southern spain shows that the change in fold trend around the arc is significantly greater than the variation in primary magnetic declination this suggests that the arcuate geometry is not primarily a consequence of differential rotation the area has experienced a regional clockwise rotation of at least 40 which was most probably imposed during oblique wnw directed convergence along the southern iberian margin in early miocene time before the arcuate structure was formed kinematic indicators associated with the arcuate folds and thrust traces arc for the most part consistently wnw directed suggesting that the arc is not primarily a result of variations in the direction of tectonic transport the arcuate structure was probably initiated without significant rotation by the wnw directed indentation of the curved western end of the alboran domain into the iberian margin and was then tightened involving up to about 35 of further rotation in different segments of the arc finally one sector in the arc was rotated anticlockwise by about 40 with respect to the rest of the region reorientating the magnetic declinations the fold trends and the kinematic indicators this rotation was associated with local sinistral shear

neogene evolution of the sorbas basin se spain determined by paleostress analysis abstract the neogene subsidence history of the sorbas basin situated in the internal zone of the betic cordilleras of southeastern spain is strongly controlled by strike slip deformation the sedimentary sequence of the basin offers a good control on the timing of separate phases of fault activation the southern border of the sorbas basin is formed by a major east west trending fault zone the gafarillos fault zone which consists of intermixed slivers of pre neogene basement blocks and neogene basin sediments fault patterns and paleostress analysis both indicate that major displacement along this fault zone was dextral with a n310e oriented maximum principal stress axis strike slip movement along the east west oriented faults ended during the earliest messinian after a minimum of 6 ma of activation paleostress analysis indicates a subsequent phase of strike slip fault movement present in sites of up to early pliocene age the maximum principal stress axis orientation is n350e for this phase this deformation is synchronous with sinistral displacement along the palomares fault zone situated directly to the east of the study area subsequently our paleostress analysis indicates an extensional regime during the late pliocene to quaternary however extensional tensors were calculated at a number of sites possibly representing local stress regimes coexisting with the main strike slip deformation and sorbas basin subsidence folding of tortonian sediments points out that local compressional deformation took place as well during the neogene basin history observed wide ranges for the ellipsoid shapes of the calculated tensors support the existence of lateral stress variations

low p high t metamorphism in the okiep copper district western namaqualand south africa the okiep copper district part of the 1 2 1 0 ga high grade terrane in western namaqualand is composed of a mid proterozoic supracrustal sequence and several pre to post orogenic intrusive suites affected by two high grade events m2a m2b m3 of kibaran and one low grade event m4 of pan african age peak assemblages in quartz bearing pelites are characterized either by garnet cordierite coexisting with sillimanite biotite or by biotite sillimanite garnet a difference controlled by bulk composition and variation in water activities 0 1 0 7 during dehydration melting maximum p t conditions were reached during m2a coevally with the major deformational event d2a and are estimated at 750 820 c and 5 6 kbar a counterclockwise p t path is indicated by regionally occurring pseudomorphs of sillimanite after andalusite and by prograde reaction textures preserved as relics in m2a porphyroblasts two stages of retrograde metamorphism are distinguished m2a garnet cordierite bearing assemblages were retrogressed to biotite sillimanite quartz m2b along discontinuous foliation planes and shear zones d2b retrograde m3 corona assemblages formed at similar p t conditions 580 660 c and 5 8 0 5 kbar to the m2b assemblages but m3 crystallization postdates penetrative d2 deformation intrusion of 1 06 ga granitoids and formation of associated w mo deposits it is concluded that a kibaran high grade metamorphism in the okiep copper district is thermally punctuated and b reaction textures documenting apparent isobaric cooling of this low p high t terrane must be interpreted with caution

microseismicity and tectonics in the granada basin spain a microseismic experiment carried out in 1994 in the granada basin spain permitted the precise recording of more than 80 local earthquakes the dense distribution of the local network with 40 to 50 instrumental records for each event enabled us to have well controlled hypocenters and also 10 reliable focal mechanisms the above observations are interpreted together with topographic data neotectonics and sub surface information microtectonic observations in sierra elvira padul and zafarraya gave a set of fault planes and striae which were interpreted in terms of the recent regional stress tensor the actual stress tensor obtained from the microseismic campaign data gives a regime in radial extension with r1 vertical and r3 oriented ns to nne microtectonic information is coherent with these orientations but closer to 3 axial extension a set of 64 mechanisms obtained from the permanent andalusian network favors a ns orientation for r3 this results are interpreted in terms of the general model implying the lateral ejection of the betic ranges towards the atlantic d 2002 elsevier science b v all rights reserved

an assessment based on u_pb zircon data of rb_sr dating in the arunta inlier central australia abstract the chronology of the arunta inlier was originally based mostly on rb sr dating although some of the ages derived from that technique are now shown to be erroneous those which were constrained by structural observations and which relied only on whole rock and not mineral analyses have proven to be remarkably realistic ion microprobe data show that even conventional multigrain u pb zircon analysis is not a particularly appropriate dating technique in a region of this complexity three new u pb zircon ages and others previously derived from the same isotopic system date three of the main tectonic events that were imposed on the arunta inlier the widespread strangways orogeny of the northern and central provinces occurred at 1760 1750 ma the argilke event is not older than 1680 ma demonstrating that the southern province is the youngest in the inlier the dominantly thermal ormiston event is dated at 1140 ma

metamorphic evolution of the bunger hills east antarctica evidence for substantial post metamorphic peak compression with minimal cooling in a proterozoic orogenic event the bunger hills east antarctica experienced a low pressure granulite facies orogenic event during the proterozoic the stable coexistence of the s1 foliation parallel m1 assemblages garnet cordierite spinel ilmenite and garnet sillimanite spinel ilmenite rutile in quartz bearing pelitic gneisses is evidence for metamorphic peak pressures of around 4 kbar during m1 at temperatures of about 800 c the growth of massive reaction coronas of garnet and cordierite around hercynitic spinel and iron titanium oxides during m2 is evidence for the destabilization of the m1 assemblages during compression thermodynamic calculations on the m2 assemblages indicate formation pressures of 6 7 kbar at temperatures of about 750 c thus the gneisses from the bunger hills indicate about 2 kbar or more of compression during minimal cooling such a p t path is different from that of many other proterozoic terranes which are characterized by isobaric cooling or decompression a large charnockite body which is undeformed was intruded at 950 c towards the end of compression the low pressures during m1 can be best explained by metamorphism at mid crustal levels in thin continental crust in thin lithosphere above a thermal perturbation in the underlying asthenosphere we suggest that the compression during cooling was a result of gravitational backflow in which the action of body forces between adjacent normal thickness crust and the thin crust of the bunger hills is switched on by the thermal perturbation within such a model the timing of intrusion of the charnockite exposed in the bunger hills is consistent with its generation by partial melting during the metamorphic maximum of the lowermost crust

influence of strike slip fault segmentation on drainage evolution and topography a case study the palomares fault zone southeastern betics spain abstract the palomares fault zone pfz is one of the main sinistral strike slip faults in the betics se spain with approximately 16 km of north south displacement the pfz initiated during the tortonian messinian as a transfer structure linking areas subject to nw se shortening during the plio quaternary the fault zone lengthened cutting previous fold structures and widened towards the east displacing the active mountain front to the western border of sierra almagrera sierra almenara these sierras which show moderate uplift rates of 0 05 0 15 m ka formed in response to the oblique slip regime of the pfz the drainage system in the vicinity of the pfz is asymmetric with respect to a main axial valley that runs parallel to the pfz on the downthrown fault block in this block the drainage density is lower and the streams are longer than in the uplifted block furthermore west of the main axial valley the streams describe eastward directed deflections indicating the progressive eastward migration of the main axial valley during the pleistocene the drainage system on the uplifted ranges shows a consequent pattern indicating recent uplift and folding under nnw sse convergence recent activity along segments of the pfz has increased topographical gradients favouring dissection of previous streams by headward erosion of streams transverse to the active fault segments

recent tectonic structures in a transect of the central betic cordillera the betic cordillera has undergone recent alpine deformations related to the eurasian african plate interaction boundary most of the present day relief has been built up since tortonian times and is related to the development of folds and faults that are overprinted on older deformations and some of the faults may be considered as out of sequence the combination of geophysical and geological data makes it possible to determine the main features of the recent tectonic structures or those recently active in its central transect the main fault is a crustal detachment that separates a footwall constituted by the iberian massif and a hanging wall formed by the rocks of the betic cordillera while the footwall is practically undeformed the hanging wall has been folded and faulted the folds are mainly e w to ne sw and have larger sizes and higher related relieves towards the south the reverse faults are mainly concentrated in the northern mountain front however normal faults affect the southern part of the cordillera and are associated with the development of large asymmetrical basins such as the granada depression in this setting the slip along the crustal detachment is variable and should increase southwards the model of the recent tectonics in the central transect of the cordillera is compatible with the presence of an active subduction in the alboran sea and contrasts notably with the setting of the eastern betic cordillera mainly deformed by transcurrent faults

evolution of near surface ramp flat ramp normal faults and implication during intramontane basin formation in the eastern betic cordillera the huercal overa basin se spain 1 the nucleation propagation and associated folding of ramp flat ramp normal faults were analyzed from field examples developed in a brittle ductile multilayer sequence of the huercal overa basin se spain gently dipping sandy silt layers which display a low cohesive strength c0 7 kpa 34 favor the development of extensional detachments a tectonic origin instead of a possible gravitational origin is supported by the perpendicularity between the paleoslope direction of the fluvial deltaic environment inferred from imbricated pebbles and the senses of movement deduced from fault slicken lines the link between high angle normal faults hanfs formed at different levels in the layered sequence with horizontal fault segments comes to develop ramp flat ramp normal faults with associated roll over in the hanging wall observed extensional duplexes are formed by parallel detachments connected through synthetic riedel faults these riedel faults would produce the back rotation of the individual blocks horses i e extensional folding of the originally subhorizontal layers there is no correlation between the analyzed ramp flat ramp normal faults accommodating south southeastward extension during serravallian lower tortonian and either the regional alpujarride nevado filabride west directed extensional shear zone or the top to the north detachments within alpujarride units which are clearly sealed by serravallian lower tortonian sediments therefore the studied normal faults are restricted to the brittle ductile multilayer fluvio deltaic sequence and accommodate moderate late extension instead of belonging to a large crustal extensional system connected with a regional detachment at depth therefore the basin formed in a moderate crustal thickness context where small and medium scale extensional systems were subordinate structures these natural examples support the development of low angle normal faults at very shallow crustal levels in multilayer sequences with suitable rheological conditions

emplacement of giant mud volcanoes in the south caspian basin 3d seismic reflection imaging of their root zones exceptional quality 3d data for the largest mud volcano yet described provide the first detailed imaging of the plumbing architecture that connects a major volcanic edifice to its source layer at depth the volcano is in the south caspian basin and consists of an extruded submarine mud bicone 10 km wide and 1 4 km thick overlying an oval caldera 1 2 1 6 km in width and 0 5 km in depth the caldera narrows downwards into a zone of collapsed country rock forming a downward tapering cone 1 km in height the vertex of which is located close to the top of the mud source layer the imaged structural elements lead to an evolutionary model a narrow steep fluidization pipe fed the oldest pioneer cone we propose that numerous additional fluidization pipes injected the country rock forming a densely intruded cylindrical zone similar to gryphon swarms observed at outcrop onshore wall rock erosion and compaction of the intruded zone led to collapse of the downward tapering cone that linked upwards into ring faults that define the caldera margins later mud flowage focused on the conical sheared margins volumetric contraction of the extruded volcanic cone led to an unusual concentric system of minor outward facing normal faults this model has many similarities to syntheses of igneous maar diatreme caldera systems for which it may be analogous

geochronological constraints on orogenic events in the arunta inlier a review early workers subdivided the arunta inlier central australia into three major tectonic provinces classified the principal tectonostratigraphic units into three divisions and separated the tectonomagmatic history into five discrete events ranging in age from 1800 ma to 300 ma a review of the evidence for tectonic boundaries within the arunta inlier suggests that no major structural discontinuity exists between the northern and central tectonic provinces but that the redbank thrust zone is at least in part a province boundary the tectonostratigraphic division concept also requires revision as division 3 rocks of the northern and southern arunta cannot be time equivalents division 1 rocks grade into division 2 in the northern region and division 3 of the northern region may be equivalent to division 1 in the central region rocks originally assigned to divisions are better grouped into a larger number of lithological assemblages until better stratigraphic and isotopic correlations can be made compilation of rb sr and 40ar39ar age determinations obtained before 1984 indicate an almost complete age spectrum from 1800 ma to 1000 ma but age clusters exist at 1400 ma 1100 ma and 400 300 ma which have geological significance subdivision of older ages into discrete tectonic events was not justified from this data alone but more recent u pb isotopic analysis of zircons in rocks designated to particular structural metamorphic events has revealed a complex tectonic history in the 1880 1600 ma interval the northern and central provinces underwent major tectonism between 1780 1730 ma but much of the southern province was not deformed until 1600 ma the revised tectonic history nomenclature is proposed for the arunta inlier following deposition of a widespread turbiditic unit at or before 1880 ma possibly on thinned archaean crust the northern and central provinces underwent localized tectonism magmatism at 1880 ma yuendumu tectonic event and 1820 ma stafford tectonic event prior to the widespread strangways orogeny which is subdivided into an early phase at 1780 1770 ma and late phase at 1745 1730 ma it is not clear whether the strangways orogeny is a single arunta wide event or a series of separate short lived smaller scale events although the major deformation in all areas appears to have involved w to sw directed thrusting in the southern province the major events occurred at 1680 ma argilke tectonic event and 1600 ma chewings orogeny the latter involving n directed thrusting that was penecontemporaneous with post tectonic pegmatite intrusion in the northern province suggesting linkage of both regions at this stage the younger history of the inlier is characterised by several stages of uplift and isolated thermal magmatic events major mesoproterozoic crustal exhumation anmatjira uplift phase has been interpreted from widespread 1500 1400 ma ages including regional scale closure of 40ar 39ar systems in hornblende from mafic granulite outcrop scale rb sr total rock isotopic systems in mylonitized granitoids and sm nd garnet hornblende pairs in mylonitized amphibolites a 1150 ma thermal event in the southern part of the inlier teapot magmatic event is recorded by intrusion of granite pegmatites and the alkaline mordor igneous complex and by isotopic resetting of rb sr mineral systems dolerite dyke injection at 1050 ma reflects limited extensional tectonism that may have related to formation of the amadeus basin the second major uplift event was the alice springs orogeny at 400 300 ma an unusual intracratonic thick and thin skinned thrust event that involved limited retrograde amphibolite facies but extensive greenschist facies metamorphism and restricted pegmatite intrusion

the recent upper miocene to quaternary and present tectonic stress distributions in the iberian peninsula a general synthesis of the recent and present stress situation and evolution in the iberian peninsula was obtained from microstructural and seismological analysis the stress evolution was deduced from 1 fault population analysis fpa from 409 sites distributed throughout the iberian peninsula 2 paleostress indicators given by 324 stations taken from the bibliography and 3 seismic data corresponding to 161 focal mechanisms evenly spread in the studied region the application of fpa together with the determination of stress tensors and focal mechanisms for the whole iberian microplate has provided two main results 1 the iberian peninsula is undergoing a nw se oriented compression except for the northeastern part pyrenees ebro basin and iberian chain where it is n s to ne sw and the gulf of cadiz where it seems to be e w and 2 the main trends of the stress field have remained almost constant since the upper miocene the analysis performed by zones suggests the presence of local heterogeneities in the stress field

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

metamorphic and tectonic evolution of granulites arunta block central australia petrographical and chemical evidence presented here indicate a prolonged metamorphic evolution of the granulite terrain in the northern strangways range arunta block central australia nsr in fig 1 beginning with migmatization followed by dry granulite metamorphism at high temperatures t and moderate pressures p estimated at 850 920 c 8 1 kbar1 this occurred at 1 800 myr refs 2 3 very shortly after deposition of the protolith4 a bimodal volcanic suite5 and associated sediments granulite metamorphism was followed by isobaric cooling during which there was an episode of pervasive but partial hydration later retrogression and hydration localized along shear zones occurred at the normal geothermal gradient in the kyanite stability field a tensional rift like regime best describes the geological environment in which the protolith formed was deeply buried metamorphosed with high heat flow and then remained in isostatic equilibrium metamorphic parageneses recording uplift may be matched with mid palaeozoic tectonic events in central australia if this correlation is correct the rocks of the northern strangways range may have remained deeply buried for 1 400 myr during which the shear zones were reactivated several times fig 2

isobaric cooling of proterozoic high temperature metamorphites in the northern arunta block central australia implications for tectonic evolution abstract protoliths of metamorphites in the proterozoic reynolds range region northern arunta block central australia included mafic and felsic igneous rocks pelites calcareous rocks and quartzites metamorphism began with an early high t low p facies stage followed by early rehydration in higher grade areas isobaric cooling and late high t low p facies hydration in and near shear zones metamorphic grade increases southeastwards shown by the change from andalusite in metapelites in the northwest to sillimanite in the southeast and by the incoming of cordierite cordierite biotite cordierite k feldspar sillimanite and cordierite garnet migmatites kornerupine quartz spinel and orthopyroxene k feldspar assemblages occur in the highest grade rocks downwarping at near peak temperatures is shown by garnet sillimanite replacing cordierite and by sillimanite pseudomorphing andalusite early in the near isobaric cooling that followed peak temperatures freezing of partial melts released water and biotite formed the hydrated retrograde assemblages formed after temperatures had fallen considerably are also zoned from northwest to southeast with andalusite sillimanite or kyanite bearing assemblages developed in appropriate bulk compositions the early high t metamorphism is best explained by tectonic models based on extension crustal delamination and underplating the hydration and deformation were caused by processes unrelated to the early history occurring at least 200 ma later possibly as late as the mid palaeozoic

the relative locations of multiplets in the vicinity of the western almeria southern spain earthquake series of 1993 1994 summary we have analysed 721 earthquakes 1 5jmbj5 0 of the 1993 1994 western almero a southern spain series and the following seismicity in the area until 1998 among the data there are several multiplets events characterized by very similar seismograms at the short period stations of the local network we detected similar seismograms using crosscorrelation analysis of the p and s arrivals and classified similar events into families or clusters we found 39 multiplet clusters of 3 33 events within each cluster relocations relative to a master event have been calculated by using the interpolated cross correlation maxima for the precise relative timing of p and s phases at each station relative arrival times have been compared for all the possible selections of the master event and adjusted by forming the mean value after removing the outliers the distribution of the stations does not permit a satisfactory resolution of focal depths but relative epicentres have been determined with an accuracy of a few tens of metres typically they draw well defined lineaments and show two dominant strike directions n120u 130ue and n60u 70ue these directions are coincident with known fault systems in the area and with the source parameters of three of the largest events mw 4 8 3 6 and 4 9 which were estimated from waveform modelling of near field acceleration records at a single station consistent with previous studies distances within multiplets typically several tens of metres are for the most part clearly smaller than the fracture radii of these events this indicates repeated slip on the same fault segment it was possible to obtain precise relative locations between several nearby clusters thereby imaging a very heterogeneous seismotectonic fine structure of the source area i e the positions of adjacent active fault segments and the fragmentation of the crust into small approximately 1 km tectonic blocks

deformation style and controlling geodynamic processes at the eastern guadalquivir foreland basin southern spain the tectonic structure of the guadalquivir foreland basin becomes complex eastwards evolving from a single depocenter to a compartmented basin the deformation pattern within the eastern guadalquivir foreland basin has been characterized by combining seismic reflection profiles boreholes and structural field data to output a 3d model high dipping nne ssw to ne sw trending normal and reverse fault arrays deform the variscan basement of the basin these faults generally affect tortonian sediments which show syntectonic features sealed by the latest miocene units curved and s shaped fault traces are abundant and caused by the linkage of nearby fault segments during lateral fault propagation preexisting faults were reactivated either as normal or reverse faults depending on their position within the foreland at tortonian time reverse faults deformed the basin forebulge while normal faults predominated within the backbulge along strike variation of the betic foreland basin geometry is supported by an increasing mechanical coupling of the two plates alboran domain and variscan basement towards the eastern part of the cordillera thus subduction would have progressed in the western betics while it would have failed in the eastern one there the initially subducted iberian paleomargin nevado filabride complex was incorporated into the upper plate promoting the transmission of collision related compressional stresses into the foreland since the middle miocene nowadays compression is still active and produces low magnitude earthquakes likely linked to nne ssw to ne sw pre exiting faults reactivated with reverse oblique slip kinematics seismicity is mostly concentrated around fault tips that are frequently curved in overstepping zones