the role of continental margins in the final stages of arc formation constraints from teleseismic tomography of the gibraltar and calabrian arc western mediterranean abstract the deep seismicity and lateral distribution of seismic velocity in the central western mediterranean point to the existence under the alboran and tyrrhenian seas of two lithospheric slabs reaching the mantle transition zone gibraltar and calabrian narrow arcs correspond to the slabs similarities in the tectonic and mantle structure of the two areas have been explained by a common subduction and roll back mechanism in which the two arcs are symmetrical end members we present a new 3 d tomographic model at mantle scale for the calabrian arc and compare it with a recently published model for the gibraltar arc by monna et al 2013a the two models calculated with inversion of teleseismic phase arrivals have a scale and parametrization that allow for a direct comparison the inclusion in both inversions of ocean bottom seismometer broadband data improves the resolution of the areas underlying the seafloor networks this additional information is used to resolve the deep structure and constrain the reconstruction of the central western mediterranean geodynamic evolution the gibraltar tomography model suggests that the slab is separated from the atlantic oceanic domain by a portion of african continental margin whereas the calabrian model displays a continuous oceanic slab that is connected via a narrow passage 350 km to the ionian basin oceanic domain starting from the comparison of the two models we propose the following interpretation within the mediterranean geodynamic regime dominated by slab rollback the geometry of the african continental margin located on the lower plate represents a critical control on the evolution of subduction as buoyant continental lithosphere entered the subduction zones slab pull caused tears in the subducted lithosphere this tectonic response which occurred in the final stages of arc evolution and was strongly controlled by the paleogeography of the subducted plates explains the observed differences between the gibraltar and calabrian arcs

dynamics of the polish and eastern slovakian parts of the carpathian accretionary wedge insights from palaeostress analyses the arcuate outer carpathian accretionary wedge formed in front of the east alpine carpathian pannonian alcapa megablock during the eocene sarmatian the wedge accreted sediments of the subducting remnants of the carpathian flysch basin a large oceanic tract left in front of the alpine orogen the palaeostress data for the orogenic hinterland particularly the data related to the early miocene extension that was expanding towards the ne combined with coeval subduction related volcanism that was expanding towards the ne indicate that the uneven roll back of the subduction zone was the main mechanism controlling the development of the northern west carpathian arc the palaeostress data for the tertiary accretionary wedge from the same time period are characterized by outward fanning 1 trajectories that changed gradually during the wedge development in contrast the palaeostress data for the hinterland are characterized by preferred directional stress events that changed abruptly during the wedge development these palaeostress results are in accordance with the behaviour of the wedge and the hinterland as the wedge behaved as a weak continuum and the hinterland behaved as a block mosaic with weak boundaries the fault traces of the northern west carpathian arc converge to both ends of the arc and suggest that the pre existing basin was the factor that controlled the arc location these fault trace patterns are asymmetric indicating a slightly oblique overall convergence in a ne sw direction in accordance with this convergence the palaeostress data for the accretionary wedge indicate that the western part of the wedge which is characterized by nw se oriented maximum principal compressional stress 1 was undergoing sinistral transpression meanwhile the eastern part which is characterized by ne sw oriented 1 was undergoing compression apparently the dynamics of the accretionary wedge was further influenced by the shape of an elongated ne sw trending alcapa megablock which was located behind the wedge and advanced in the direction of the general early miocene convergence during the most pronounced stages of the wedge development this megablock served as the local indenter as its strength surpassed that of the accretionary wedge located to its front further dynamic complexities were added because of the complex shape of the magura unit which was located in the most proximal portion of the wedge and was stronger than the units in front of it wedge outcrops indicate that the large scale shortening which is characterized by the development of detachments and ramps was preceded by an initial layer parallel shortening this is indicated by scaly fabrics and minor reverse faults that rotated into locked positions during the later accretion several outcrops with a wedge detachment fault indicate that there was a relatively low amount of friction during its development the decollement zone is several hundred metres thick and shows evidence of transient fluid flow that was driven by pressure gradients this is documented by frequent hydrofracturing sandstone dykes and fibrous veins that opened against the weight of the whole wedge all of which indicate cycles of higher pore fluid pressures that lowered the basal friction

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

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

fluvial landsculpting and the fractal dimension of topography abstract quantitative models of landform development can help us to understand the evolution of mountains and regional topography and the effects of tectonic motions and climate on landscape including its fractal geometry this paper presents a general and powerful three dimensional model of fluvial erosion and deposition at hill to mountain range scale the model works by accumulating the effects of randomly seeded storms or floods precipitons that cause diffusional smoothing then move downslope on digital topography grids that erode portions of elevation differences that transport a slope limited amount of eroded material and that deposit alluvium when their sediment carrying capacity is exceeded the iteration of these simple and almost linear rules produce very complicated simulated landscapes demonstrating that complex landscapes do not require complex laws each process implemented in the model is affected differently by changes in horizontal scale erosion a scale free process roughens topography at all wavelengths this roughening is balanced by diffusive processes scaling as 1 l 2 at short wavelengths and deposition scaling scaling as 1 l 2 at long wavelenghts such a mixture of scale free and scale dependent processes can produce multifractal behavior in the models the fractal dimension of the model topography is much more sensitive to climatic variables than to tectonic uplift landscape evolution may be fractal but it does not seem to be chaotic analysis of topography of areas in southern arizona using variograms shows approximately fractal behavior with mean fractal dimension around 2 2 2 3 departures from an exact fractal relatioship imply that the topography is in detail multifractal the fractal dimension at short wavelengths is less than that at long wavelengths this variation could either be caused by the relative strengths of diffusive and erosional processes shaping the topography or a result of changes in climatic or tectonic conditions still preserved in the landscape

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

geometry and kinematics of vertical axis rotations in fold and thrust belts abstract vertical axis rotations indicated by palaeomagnetic study are a common and important component of deformation in fold and thrust belts the kinematics of rotating thrust sheets may be best described as a combination of a far field rotation or translation in a planar geometry and a near field or local rotation so that the instantaneous rotation axis lies outside the body of the sheet this simplifies the thrust sheet kinematics significantly as it means that all the points on the sheet have a component of forward motion and the bounding fault is a thrust over all its area the consequences of a simple thrust sheet rotation for the interpretation of fault lineation data are investigated the lineations recorded in the footwall and the hangingwall are likely to be different the hangingwall lineations being skewed towards the direction of rotation the principal mechanism for local thrust sheet rotation is differential shortening either on folds or thrusts or by a combination of these structures the forward propagation of thrusting towards the foreland can accumulate large 120 rotations on the uppermost sheets these rotational thrust sheets cannot extend indefinitely along strike instead they terminate against lateral ramps or transfer faults sidewall duplexes may form as a consequence of rotation over a lateral ramp examples of rotational geometries from the subbetic zone of southern spain are described on a larger scale obliquely convergent orogenic wedges can evolve by rotation of faults with an initial thrust geometry into progressively greater components of strike slip motion reliable palaeomagnetic data are not always available for fold and thrust belts so independent evidence for rotational deformation is of great importance fold and thrust geometries particularly along strike variability in fold geometries highly variable axial traces of folds evidence for near synchronous refolding and the deviation of regional trends may all be a consequence of thrust sheet rotation detailed mapping and particularly the identification of the position of footwall and hangingwall cut offs can also provide strong evidence for rotation

compressional tectonic inversion of the algero balearic basin latemost miocene to present oblique convergence at the palomares margin western mediterranean interpretation of new multichannel seismic reflection profiles indicates that the palomares margin was formed by crustal scale extension and coeval magmatic accretion during middle to late miocene opening of the algero balearic basin the margin formed at the transition between thinned continental crust intruded by arc volcanism and back arc oceanic crust deformation produced during the later positive inversion of the margin offshore and onshore is partitioned between n50 e striking reverse faults and associated folds like the sierra cabrera and abubacer anticlines and n10 20 e sinistral strike slip faults like palomares and terreros faults parametric subbottom profiles and multibeam bathymetry offshore structural analysis available gps geodetic displacement data and earthquake focal mechanisms jointly indicate that tectonic inversion of the palomares margin is currently active the palomares margin shows a structural pattern comparable to the north maghrebian margins where africa eurasia plate convergence is accommodated by ne sw reverse faults nnw sse sinistral faults and wnw ese dextral ones contractive structures at this margin contribute to the general inversion of the western mediterranean since 7 ma coeval to inversion at the algerian margin shortening at the alboran ridge and al idrisi faults occurred later since 5 ma indicating a westward propagation of the compressional inversion of the western mediterranean

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

jurassic sedimentary record and tectonic evolution of the northwestern corner of africa abstract the history of the opening seaway from the westernmost tethys to the central atlantic is traced by the analysis of the sedimentary facies development in the external rif basin of northern morocco and the geological and seismic data from the moroccan atlantic continental margin in the rif basin after the early sinemurian sedimentary facies dated by ammonites foraminifers and brachiopods indicate a progression of rapid subsidence resulting from extensional tectonic tilted blocks escarpment fault breccias neptunian dykes etc from the n and ne to the s and sw from the toarcian to the bajocian deltas progress from the w and sw into the rides sud rifaines realm from the late bathonian to the oxfordian deep sea fans develop in the external rif during the same period deltaic sediments fill in the middle atlas basin of eastern morocco and progress into the external rif the top of the jurassic is characterised by carbonate deposits at the northwestern corner of africa the subsidence of the sedimentary basins by rifting is initiated in the late triassic however at the mazagan transect of the atlantic continental margin the tectonic pattern characteristic of a passive continental margin appears clearly only in the early jurassic at the foot of the mazagan escarpment the sedimentary record shows a foundering of the first bloc during early to middle lias a thermal uplift phase is indicated by emersion of the african margin shoulder in late liassic and thermal relaxation starts in the middle jurassic the morphology of this transect compared with the conjugate side of the american continent is most easily explained by the uniform sense simple shear model

fractals in geology and geophysics the definition of a fractal distribution is that the number of objectsn with a characteristic size greater thanr scales with the relationn r d the frequency size distributions for islands earthquakes fragments ore deposits and oil fields often satisfy this relation fractals were originally introduced by mandelbrot to relate the length of a coastline to the length of the measuring stick this application illustrates a fundamental aspect of fractal distributions scale invariance the requirement of an object to define a scale in photographs of many geological features is one indication of the wide applicability of scale invariance to geological problems scale invariance can lead to fractal clustering geophysical spectra can also be related to fractals these are self affine fractals rather than self similar fractals examples include the earth s topography and geoid

palaeomagnetic study of the ronda peridotites betic cordillera southern spain abstract a palaeomagnetic study of the ronda peridotites southern spain has been carried out on 301 samples from 20 sites spread along the three main outcrops of the ultrabasic complex ronda ojen and carratraca massifs different lithologies and outcrops with different degrees of serpentinization have been sampled and analysed rock magnetic experiments have been carried out on a representative set of samples these measurements include curie curves hysteresis cycles isothermal remanent magnetization irm acquisition curves thermal demagnetization of irm imparted along three orthogonal axes and magnetic bulk susceptibility results indicate that magnetite is the main magnetic mineral present in the samples stepwise thermal and alternating field af demagnetization of the natural remanent magnetization nrm reveals the presence of a characteristic remanent magnetization chrm carried by magnetite and in some sepentinized samples a northward component with variable unblocking temperatures up to 250 575 c the appearance and the relative intensity of this northward component are strongly related to serpentinization degree taking into account the geological history of the peridotites the chrm has been considered as a thermo chemical remanent magnetization acquired during the first serpentinization phase associated to the post metamorphic cooling of this unit on the basis of radiometric and fission track analysis the chrm is proposed to have been acquired between 20 and 17 18 ma the inclination of the mean direction of the chrm statistically coincides with the expected inclination for stable iberia during the oligocene miocene the declination of the chrm differs from the expected declination indicating clockwise block rotations of 41 12 about vertical axes since the cooling of the peridotites when applying a compositional layering correction the chrm directions fail to pass this kind of fold test thus the compositional layering was not a palaeohorizontal during chrm acquisition time normal and reversed polarities of the chrm are reported showing that at least one reversal of the earth s magnetic field took place during chrm acquisition process a tentative polarity zonation within the peridotitic outcrops is also suggested no evidence is found from these data for the previously proposed simultaneity between post metamorphic cooling and rotation of the peridotites

structure and palaeogeography of the external betic cordillera southern spain abstract a structural interpretation of the external betic cordillera in the granada jaen area of southern spain is proposed based on the interpretation of seismic reflection profiles subsurface well control and a balanced cross section restoration of this balanced cross section results in a new palaeogeographical interpretation for the area and a total estimated shortening of approximately 200 km traditionally the betic fold thrust belt has been described as a series of north vergent imbricate thrust sheets each having relatively little displacement 10 15 km restoration of this structural model to an undeformed state results in a mesozoic palaeogeographical scenario of three carbonate platforms separated by two deep basins an alternative interpretation is presented in this paper that the structural style of the granada jaen area is characterized by large displacement thrust faults restoration of the proposed cross section leads to the palaeogeographical interpretation of a single mesozoic basin along the transect of the cross section this palaeo basin is bounded to the north and south by platformal margins the major implication of this study is that the palaeogeographical interpretation of a fold thrust belt can be highly dependent on the structural interpretation

comment on deep structure recent deformation and analog modeling of the gulf of cadiz accretionary wedge implications for the 1755 lisbon earthquake by gutscher et al 2009 abstract gutscher et al 2009b address a very interesting and unsolved problem which is the continuation of the azores gibraltar plate boundary to the e of the gorringe bank this comment comprises three parts 1 short introduction to the geologic setting 2 comment on the analogue modelling the relationship of the setup with the prototype and the relationship of the experimental results with the prototype 3 short discussion of proposed subduction to the e

unidirectional slip vectors in the western betic cordillera implications for the formation of the gibraltar arc we have investigated the kinematics of deformation in a sector of the gibraltar arc in sw spain by synthesizing lineation data from major faults the variation in structural trends and palaeomagnetically determined vertical axis rotations the kinematic data show that transport directions throughout formation of the arc were consistently wnw regardless of structural trend which varies between 050 and 350 in the study area the data suggest that this part of the gibraltar arc can be explained simply by oblique convergence with a curved indenter taken together with other published data it appears likely that the variation in thrust transport direction within the betic cordillera as a whole may be considerably less than that in the moroccan part of the arc unidirectional convergence combined with the presence of palaeomagnetic rotations implies either eycient overprinting of old rotated lineations and or a convergence rate that is much greater than the rotation rate also required is a low degree of partitioning in the thrust wedge the latter probably increases east of the study area where the structural trend becomes more oblique to the transport direction and major strike slip faults occur

superimposed folding and oblique structures in the palaeomargin derived units of the central betics sw spain the subbetic units consist of a deformed wedge of sedimentary rocks deriving from the south iberian palaeomargin in the westernmost segment of the alpine mediterranean orogenic belt in the central betics shortening produced folding thrusting and nappe stacking the structural trend is ne sw to ene wsw and the internal structure of the thrust sheets which shows no preferred vergence is strongly controlled by the rheology of the decollement level a viscous layer of triassic evaporites and of the overlying carbonate rock sequence the relationships of piggyback basin miocene sediments with the main structures show that the latter developed during the aquitanian burdigalian transition superimposed folding is described for the first time in the study area the origin of the interference cannot be determined at present but may be related to initially oblique structures refolded during progressive deformation a revision of previously published palaeomagnetic data in the light of the data presented in this paper in conjunction with a model of the structural evolution of the subbetic units of the western betics permits us to establish milestones of the tectonic evolution of the external zones in the northern branch of the gibraltar arc

quantitative morphology of bedrock fault surfaces and identification of paleo earthquakes the quantitative analysis of morphologic characteristics of bedrock fault surfaces may be a useful approach to study faulting history and identify paleo earthquakes it is an effective complement to trenching techniques especially to identify paleo earthquakes in a bedrock area where trenching technique cannot be applied in this paper we calculate the 2d fractal dimension of three bedrock fault surfaces on the huoshan piedmont fault in the shanxi graben china using the isotropic empirical variogram we show that the fractal dimension varies systematically with height above the base of the fault surface exposures indicating a segmentation of the fault surface morphology we interpret this segmentation as being due to different exposure duration of parallel fault surface bands caused by periodical earthquakes and discontinuous weathering we take the average of fractal dimensions of each band as a characteristic value to describe its surface morphology which can be used to estimate the exposure duration of the fault surface band and then the occurrence time of the earthquake that exposed the band combined with previous trenching results we fit an empirical relationship between the exposure duration and the morphological characteristic value on the fault d 0 049 t 2 246 the average width of those fault surface bands can also be regarded as an approximate vertical coseismic displacement of characteristic earthquake similar to the hongdong m8 earthquake of 1303 based on the segmentation of quantitative morphology of the three fault surfaces on the huoshan piedmont fault we identify three earthquake events the coseismic vertical displacement of the characteristic earthquake on the huoshan piedmont fault is estimated to be 3 4 m the average width of these fault surface bands gaps with a width of 0 1 0 3 m between two adjacent bands in which the fractal value increases gradually with fault surface height are inferred to be caused by weathering between two earthquakes or interseismic slip on the fault

kinematics of a twisted core complex oblique axis rotation in an extended terrane betic cordillera southern spain 1 the sierra de las estancias is a metamorphic core complex that developed during the late oligocene to early miocene extensional collapse of the betic cordillera structural and paleomagnetic analysis shows that the northern half of the complex has been strongly modified by rotation about an inclined axis requiring reassessment of the kinematics of the extensional phase of deformation the extensional tectonic event produced two major detachment faults associated mylonitic foliation and lineation and pervasive sets of shear bands and brittle normal faults with a top to ne shear sense an older foliation was largely transposed and reoriented during this event the regional foliation now defines a broad antiform with a steep north dipping limb and the trend of shear related lineations swings from nne to ene from the southern gently dipping limb into the north dipping limb the remanent magnetization in a suite of near vertical early miocene mafic dikes intruded into the north dipping limb has a declination of 243 and an inclination of 27 assuming that the dikes were originally vertical a rotation of approximately 50 about an inclined ssw plunging axis preserves the near vertical orientation of the dikes and brings the remanence into agreement with the expected orientation for an early miocene age correction for this rotation brings the foliation and lineation in the surrounding schists into orientations subparallel to those on the present southern limb of the antiform and the dikes into a vertical e w orientation the corrected orientation of the shear related lineation nne normal faults and dikes suggests that the original direction of extension during the late orogenic extensional event in the internal betic cordillera may therefore have been around nne ssw rather than e w as currently accepted the observed net tectonic rotation can be decomposed into a series of geologically plausible rotations involving domino style rotation due to slip on the late brittle normal faults tilting about the regional fold axis related to thrust ramping onto the iberian margin during miocene collision and a 30 clockwise rotation about a vertical axis related to oblique convergence with the iberian margin

along strike variations of morphotectonic features in the western foothills of taiwan tectonic implications based on stream gradient and hypsometric analysis abstract the taiwan mountain belt provides a key example for analyzing the relation between morphology and tectonics in an active compressional environment there is a striking geometrical relationship between the location of salients and reentrants of the mountain belt and the presence of major crustal inhomogeneities such as structural highs in the foreland basin major along strike variations of structural styles occur in range front rock units of the fold thrust belt stream gradient and hypsometric analysis has been carried out to highlight the along strike variations of morphotectonic features and to illustrate the relative activities in different tectonic regimes of the western foothills the normalized stream length gradient index sl index and the hack profile are two of the stream gradient indices that effectively reflect the tectonic uplift in a region de trending and residual analysis of the hypsometric integral hi eliminates the spatial dependency of small drainage basins and the residual hypsometric integral corresponds to differential uplift activity integration of stream gradient indices and hypsometry provides more robust tectonic interpretation five morphotectonic provinces have been identified in the western foothills based on stream gradient indices and hypsometry each province is bounded by a series of n140 e trending transfer fault zones either inherited from the eurasian passive margin and or newly formed in the sedimentary cover in response to the presence of basement highs within the foreland basin the peikang and kuanyin highs the morphotectonic features as well as deformation styles vary within each province a high uplift but low shortening rate typifies the crustal deformation style in the transpressional regime north of the peikang basement high on the contrary a low uplift but high shortening rate characterizes the crustal deformation style in the transtensional regime south of the peikang basement high the higher geomorphic indices suggest that greater tectonic activity occurs in central than in southwestern taiwan this inference is also supported by the coseismic deformation of the 1999 chi chi earthquake

are topographic data sets fractal the scale invariant properties of fractal sets make them attractive models for topographic profiles because those profiles are the end product of a complex system of physical processes operating over many spatial scales if topographic data sets are fractal their power spectra will be well represented by lines in log log space with slopess such that 3 s 1 the power spectra from a digital elevation model 30 meter sample spacing of the sierra nevada batholith and from seabeam center beam depths 425 meter sample spacing along a flowline in the south atlantic are curved straight sections in the spectra can be identified but the slopes of those sections are strongly dependent upon the particulars of the data analysis fractal geometry must be used with caution in the discussion of topographic data sets

distinguishing lateral folds in thrust systems examples from corbieres sw france and betic cordilleras se spain abstract folds with axes almost parallel to the mean tectonic transport direction are frequent in fold thrust belts particularly along the borders of arcuate belts such structures have been frequently explained in terms of superimposed tectonic events but in some cases they are most realistically understood in terms of lateral folds inherited from lateral footwall ramps and initiated subparallel to the tectonic transport direction in order to distinguish frontal and lateral folds we have established criteria based on field examples from two regions where folds occur parallel to the regional transport direction the betic cordilleras southern spain and the corbieres thrust front northeast pyrenees france the main differences between frontal and lateral folds concern the geometry the evolution of the structures and the modes of strain accommodation in the roof strata enveloping imbricate stacks recalling that above a duplex or even on individual horse the roof layers are thinned along sections normal to transport we examine the precise location where the extension is expressed illustrated by examples from the two regions this leads us to address some tectonic problems of these erogenic zones such as the thrust sequence and development of thrust related cleavage

predicting the geometry of channelized deep sea turbidites analytical relationships between the dynamic properties of a deposit forming turbidity current propagating across a sea floor with small slope and the geometry of the resulting deposit have been confirmed experimentally for a wide range of particle sizes initial concentrations and volumes of the driving suspension these simple expressions provide a basis for inferring the dynamics of natural flows from their deposits we surmise that the turbidity current responsible for depositing the black shell turbidite in the northwestern atlantic ocean had an initial sediment concentration on the order of 100 g of silt per litre and a volume on the order of 1000 km 3

paleomagnetic evidence for rotation of the iberian peninsula and the external betic cordillera southern spain abstract paleomagnetic investigations of jurassic cretaceous and tertiary sites in the external betic cordillera indicate that while the observed remanence vectors have inclinations which are conformable with the expected inclinations for stable iberia declinations deviate significantly these results indicate that 1 the mesozoic limestones of the penibetic have been rotated clockwise with respect to stable iberia and 2 there is a differential rotation between the cretaceous sites dec 61 11 and the jurassic sites dec 38 8 the differential rotation of 23 between the late jurassic and late cretaceous is consistent with the cretaceous anticlockwise rotation of the iberian peninsula with respect to eurasia it follows that during this time period this part of the betic mobile belt waspart of the continental margin of the iberian peninsula a study which was confined to a single unbroken stratigraphic section west of ronda indicates that most of the anticlockwise rotation 20 probably occurred between the cenomanian and the campanian the anticlockwise rotation of these rocks must have been followed by a clockwise rotation of at least 60 to account for the observed clockwise declination anomalies

vertical axis rotations in fold and thrust belts comparison of ams and paleomagnetic data in the western external sierras southern pyrenees abstract geometry and kinematics of fold and thrust belts can be complex settings when oblique structures and vertical axis rotations var take place during thrust emplacement many techniques can be used to unravel such complex tectonic histories from classic ones like strain analysis and changes of paleocurrents to more modern approaches such as paleomagnetism and calcite twin analysis in this paper anisotropy of magnetic susceptibility is compared to vertical axis rotations deduced from paleomagnetic data along three cross sections in the external sierras and the jaca basin southwestern pyrenees these data enable us to state that 1 ams represents pre tilting deformation fabrics and magnetic lineation behaves like a passive marker during later deformation and 2 a primary record of the paleomagnetic field can be found in the area therefore the difference with the paleomagnetic reference is the local var the comparison of the two datasets allows us to draw the following conclusions a the changes in both paleomagnetic var and magnetic lineation orientation between neighbouring sites are similar and b there is a significant linear regression between var and trend changes in magnetic lineation deviations in magnetic lineation with respect to the expected local magnetic lineation permit vertical axis rotations to be quantified using the ams dataset the combined analysis of paleomagnetic and ams data enables 1 a quicker comparison of the kinematic evolution in areas with similar ams patterns 2 the identification of anomalous orientations of magnetic lineation linked to vars and 3 the use of ams analysis as a homogeneity test for vars determined from other techniques ams is proposed as a suitable preliminary technique to select further sites for paleomagnetic analysis since paleomagnetic laboratory procedures are much more time consuming than ams measurements ams does not usually modify sample remanence and hence samples can be used for both types of analysis

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

the central italy seismic sequence 2016 spatial patterns and dynamic fingerprints the paper investigates spatio temporal aspects of the seismic sequence that started in central italy amatrice lazio region in august 2016 causing hundreds of fatalities and producing major damage to settlements on one hand scaling properties of the landscape topography are identified and related to geomorphological processes supporting the identification of preferential spatial directions in tectonic activity and confirming the role of the past tectonic periods and ongoing processes with respect to the driving of the geomorphological evolution of the area on the other hand relations between the spatio temporal evolution of the sequence and the seismogenic fault systems are studied the dynamic fingerprints of seismicity are established with the help of events thread analysis eta which characterizes anisotropy in spatio temporal earthquake patterns eta confirms the fact that the direction of the seismogenic normal fault oriented n nw s se is characterized by persistent seismic activity more importantly it also highlights the role of the pre existing compressive structures neogenic thrust and transpressive regional fronts with a trend oriented n ne s sw in the stress transfer both the fractal features of the topographic surface and the dynamic fingerprint of the recent seismic sequence point to the hypothesis of an active interaction between the quaternary fault systems and the pre existing compressional structures

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

palaeomagnetic constraints on the geodynamic evolution of the gibraltar arc subduction zone roll back was recently put forward as a convincing model to explain the geometry and evolution of the gibraltar arc for other subduction related arc systems of the mediterranean such as the calabrian arc and the hellenic arc palaeomagnetic rotation data from neogene extensional basins provided important constraints on geodynamic evolution models here we present the results of a palaeomagnetic study of 13 continuous sections that are located in e w transects across the neogene sedimentary basins of morocco and spain they provide evidence that no significant rotation about vertical axes has occurred in the gibraltar arc since the late tortonian comparison with other mediterranean arc systems shows strong similarities as regards geodynamic evolution the timing of rotation in the gibraltar arc is markedly older than in the calabrian and hellenic arcs and suggests that it is related to the first neogene extensional phase of the western mediterra

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

the malaguide alpujarride boundary a major extensional contact in the internal zone of the eastern betic cordillera se spain abstract the internal zone of the betic cordillera in southern spain was formed by thrusting and horizontal ductile shortening in the late cretaceous palaeogene but was subjected to a major phase of vertical thinning during the neogene the contact between the malaguide the structurally highest thrust complex and the underlying alpujarride complex is an example of several major tectonic contacts across which the stratigraphy has been repeated by thrusting but the metamorphic grade increases abruptly downwards detailed work in the eastern betic cordillera documents the relationships across this contact in the sierra espuna petrographic and illite crystallinity studies show that the highest imbricate thrusts of malaguide rocks have only been diagenetically altered whereas the deeper parts of the thrust stack exhibit anchizone facies metamorphism in the northern sierra de las estancias apatite fission track studies confirm that there too malaguide rocks have never been above 200 c in both areas the underlying alpujarride rocks exhibit epizone or greenschist facies metamorphism and a major fault zone with both brittle and ductile structures separates the two complexes the observed rapid increase in metamorphic grade over very small structural thicknesses suggests that part of the original metamorphic zonation has been excised across the contact thus in its present form we interpret the malaguide alpujarride boundary as an extensional contact the extensional motion took place in early middle miocene times as constrained by fission track cooling ages the fault zone at the contact is sub horizontal in the sierra espuna but in the sierra de las estancias it is mainly sub vertical kinematic data from a 5 20 m thick calcmylonite layer within the fault zone in the sierra de las estancias corrected for later tilting indicates that the extensional movement was originally directed with the top to the east northeast the interpretation of the malaguide alpujarride boundary as an extensional contact is similar to recent interpretations of the nevado filabride alpujarride contact at deeper structural levels in the central and eastern betics the identification of another major extension fault system confirms that miocene extension was widespread at all structural levels during the early middle miocene the sierra espuna and the northern margin of the sierra de las estancias lay on the boundary between the region undergoing horizontal extension in the internal zones and the alboran sea to the south and the region undergoing horizontal shortening in the external zones to the north as a result the detailed history of the alpujarride malaguide contact is complicated extensional structures cross cut structures related to earlier alpine shortening and were then affected by further shortening as convergence with the external zones continued

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

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

fractal strain distribution and its implications for cross section balancing abstract rock units having different physical properties show contrasts in structural styles massive competent rocks have relatively simple geometry and control the structural framework whereas thin bedded less competent units are characterized by complex deformation at smaller scales these contrasting structural styles can be quantified by a fractal dimension d a fold profile with a d close to 1 has a simple geometry a value of 2 d 1 indicates a fractal profile a fractal profile has a fractal strain distribution such that the measured shortening increases with resolution for rock units having different values of d the shortening strains measured with the same resolution cannot be compared because a significant amount of deformation takes place at smaller scales for these units with a larger d proper balancing requires high resolution analysis for these units to resolve strain at smaller scales in the central appalachians west virginia the cacapon mountain anticlinorium has a large ramp anticline in cambrian ordovician rocks which has a net shortening of 10 510 km as measured by section restoration in contrast restoration of the overlying complexly folded and faulted upper ordovician through devonian units indicated a 3 660 km shortening thin section analysis revealed a 15 20 strain equivalent to another 3 km shortening and the remaining difference in shortening between the cover and the underlying blind thrust sheet has been previously attributed to forethrusting fractal analysis indicates that the cambrian ordovician thrust sheet has a d 1 001 and the cover fold profile has a d 1 072 which indicates a fractal geometry if thin section scale through outcrop scale to map scale strains are included in the cross section balancing the cover sequence has a comparable shortening to that in the underlying thrust sheet

structure and origin of the fleurieu and nackara arcs in the adelaide fold thrust belt south australia salient and recess development in the delamerian orogen abstract the regional map pattern of structural trends in the early paleozoic adelaide fold thrust belt of south australia resembles an upright letter s in general structures in the fold thrust belt verge toward the gawler craton to the west so the northern curve nackara arc of the s is a salient whereas the southern curve fleurieu arc is a recess the map view axial trace of the nackara arc coincides with the thickest portion of the adelaidean late proterozoic basin and the map view axial trace of the fleurieu arc coincides with the intersection between the adelaidean and kanmantoo cambrian basins our structural analysis of the adelaide fold thrust belt demonstrates that the cross sectional structural geometry of the nackara arc contrasts markedly with that of the fleurieu arc in the nackara arc the belt consists of open detachment folds that probably formed above an evaporite hosted decollement whereas in the fleurieu arc the belt consists of an imbricate fan of basement involved thrusts further the foreland edge of the nackara arc coincides with a blind ramp whose strike parallels fold axes of the arc whereas the foreland edge of the fleurieu arc coincides with emergent thrusts that cut obliquely across earlier formed folds of the arc in the transition region between the two arcs the fold thrust belt consists of an intensely sheared basal duplex overlain by open folds structural contrasts between the nackara and fleurieu arcs indicate that the two curves did not form in the same way we present a model for development of these curves based on a comparison of their structural features to those of curves in other fold thrust belts and based on previous studies of curve formation using sandbox analogs we suggest that curvature of the nackara arc reflects the control of basin stratigraphy on the width of a fold thrust belt while curvature of the fleurieu arc reflects oroclinal bending of the fold thrust belt when it impinged on the southeastern corner of the gawler craton our model explains the structural contrast between the two arcs and illustrates correlations between fold thrust belt curve formation and pre deformational basin geometry

preliminary palaeomagnetic results from the subbetic zone betic cordillera southern spain kinematic and structural implications abstract we present palaeomagnetic evidence from jurassic limestones and basic submarine volcanic rocks sills pillow lavas and intrusive material from the central part of the subbetic zone of the betic cordillera isothermal remanent magnetization acquisition experiments performed on limestones and thermomagnetic curves and measurements of the magnetic susceptibility determined for the volcanic rocks demonstrate strong dependence of rock magnetic properties on lithology in most cases a stable magnetization could be isolated after thermal and or alternating field demagnetization locally declinations of the characteristic remanent magnetization from interbedded limestones and volcanics are similar but inclinations tend to vary regionally declinations for both limestones and volcanics show significant clockwise rotation these results cannot be explained by the anticlockwise rotation of iberia during the cretaceous opening of the bay of biscay considering the long and complex history of large scale shear between africa and europe accommodated in southern spain the anomalous declinations can be explained by a model with rotation of crustal blocks within a zone of wrench tectonics

the flysch trough thrust imbricate betic cordillera a key element of the gibraltar arc orogenic wedge 1 within the betic rif orogenic system the flysch trough units are formed mainly by siliciclastic rocks upper jurassic to lower miocene in age in the gibraltar arc area they are presently deformed as an accretionary prism sandwiched between the fold and thrust belt derived from the south iberian paleomargin sedimentary series and the metamorphic rocks of the alboran domain on top in the northern branch of the gibraltar arc the main tectonic unit of the flysch complex is the aljibe unit which shows a well organized structure of thrust imbricates post lower burdigalian in age in this unit various domains separated by major accommodation zones are characterized by their structural style and vergence this change in structural style can be explained as a consequence of the variations of rock type along the basal decollement finally these thrust systems were affected by extensional low to medium angle faults and large scale very open folds successively the organization of the aljibe unit fits a push from behind mechanism for its emplacement in which the relatively rigid back stop would be represented by the alboran domain with the data presented in this paper it is definitely shown that the aljibe unit is not chaotic as claimed in previous papers and that the tectonic transport direction around the gibraltar arc swings from a northwestward to a westward direction along its northern branch in the vicinity of the straits

lower miocene deformation in the hanging wall of the internal external zone boundary of the betic cordillera deformation at the edges of vertical axis rotation domains in oblique convergent margins

effect of drainage area on hypsometry from an analysis of small scale drainage basins in the siwalik hills central nepal hypsometry of drainage basins area elevation analysis has generally been used to infer the stage of geomorphic development and to study the influence of varying forcing factors i e tectonics climate lithology on topography however the scale dependence of hypsometry has generally been neglected in order to assess the scale dependence of hypsometry this study focuses on the sensitivity of hypsometry to different digital elevation model dem resolutions and on the influence of drainage area hypsometry inferred from different dems is shown to be robust against variations of their resolution however hypsometry appears to be dependent on drainage area we propose that this scale dependence may reflect the varying importance of river and hillslope processes with basin area copyright 1999 john wiley sons ltd

contractional transcurrent rotational and extensional tectonics examples from northern taiwan abstract contraction transcurrent faulting block rotation and even extension are four essential tectonic mechanisms involved in the progressive deformation of arcuate collision belts the neotectonic evolution of the taiwan mountain belt is mainly controlled by the oblique convergence between the eurasian plate and the philippine sea plate as well as the corner shape of the plate boundary based on field observations and tectonic analysis and taking geophysical data and experimental modelling into account we interpret the curved belt of northern taiwan in terms of contractional deformation with compression thrust sheet stacking folding and transcurrent faulting combined with increasing block rotation bookshelf type strike slip faulting and extension as a consequence the formation of the extensional taipei basin the division of conjugate strike slip faulted domains and the variable nature and distribution of paleostresses should not be interpreted in terms of distinct plio quaternary episodes but should reflect a single albeit complicated regional pattern of deformation our study demonstrates that in taiwan contractional extensional and transcurrent tectonics as well as rotations combine together and interact within a single complex framework the crescent shaped mountain belt develops in response to oblique indentation by an asymmetric wedge indenter the distribution nature and relative importance of these deformation modes are a function of the shape of the indenter and the average direction of convergence

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

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

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

the internal external zone boundary in the eastern betic cordillera se spain reply abstract the internal external zone boundary iezb in the betic cordillera of southern spain separates the internal zone which was deformed and in part metamorphosed before the early miocene from the external zone which consists of the cover rocks of the iberian margin shortened to form a thin skinned fold and thrust belt in early to middle miocene times over much of its length the iezb is roughly linear trending approximately 070 it has been referred to as a major dextral strike slip zone and has even been considered as the northern boundary of a westward moving alboran microplate field and kinematic data from the eastern betic cordillera show that the iezb crops out over a 60 km distance as a gently dipping thrust with displacement to the southeast or south southeast oblique to its regional trend there is no evidence of dextral strike slip movement along the boundary new micropalaeontological studies of calcareous nannoplankton indicate that the oligo miocene basin along the boundary was the site of continuous deposition until the beginning of the middle miocene the thrust at the iezb cuts early miocene rocks and is overlapped by the middle miocene thrusting therefore occurred in this time interval the iezb is therefore unlikely to have been the dextral boundary of a westward moving alboran microplate at this time but was more likely to have been the locus of nw directed dextrally oblique convergence

tertiary extension development and extension compression interplay in the west carpathian mountain belt abstract this paper describes palaeostresses calculated from fault striae data the inferred palaeostrain patterns and determines the inter relation of the compression and extension during the tertiary development of the west carpathians the calculated stress and inferred strain patterns for the palaeogene burdigalian indicate that the ancestral west carpathians formed a more or less straight orogenic belt this belt underwent contraction and uplift in its narrow frontal zone stretching along its strike during the paleocene chattian and regional contraction and uplift during the chattian burdigalian the strain stress pattern is similar to the collision related pattern known from the eastern alps for the paleocene burdigalian during the burdigalian tortonian the calculated and inferred west carpathian stress and strain patterns indicate narrow frontal contractional and lateral sinistral transpressional zones in the orogenic front and broad extensional and dextral transtensional zones in the orogenic interior the stress strain pattern is similar to the subduction related pattern known from areas such as the hellenic or sunda banda arcs

machine learning predicts reach scale channel types from coarse scale geospatial data in a large river basin author s guillon herva byrne colin f lane belize a sandoval solis samuel pasternack gregory b

self affinity dimensions of topography and its implications in morphotectonics an example from taiwan abstract this paper discusses the self affinity dimensions of landscape surfaces at a short range scale and the link to morphotectonic features of the young orogenic belts of taiwan the variogram method is adopted to estimate such parameters as the fractal dimension d the ordinate intercept and the range r from data subsets of the digital elevation model dem in a moving window operation the fractal morphology expressed by d and is found to be useful in defining geomorphic provinces that are related to tectonic features the mountainous terrain is characterized by high gamma values and low fractal dimensions in contrast to the coastal plains where low gamma values and high fractal dimensions are found a zone defined by the fractal parameters 2 4 d

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

quaternary landscape evolution driven by slab pull mechanisms in the granada basin central betics abstract the granada basin is one of the largest neogene quaternary intramontane basins of the betic cordillera in se spain the landscape evolution in this basin is complex and does not respond to a simple model of headward erosion following river capture of a former endorheic catchment in the ne border of the basin the drainage network is highly incised and reveals two different stages of river development since the pleistocene the older drainage network presents low incision being locally controlled by ene wsw open folds the present day drainage network features deep incised valleys with a well defined local base level controlled by nw se normal faults the ene wsw open folds were generated by compressional stresses and affect a geomorphic surface that caps the local sedimentary sequence these folds are thought to reactivate a pliocene roll over formed in the hanging wall of ene wsw normal faults that bound the granada basin to the north and the deepest pliocene depocenter on the contrary quaternary depocenters are located in the hanging wall of the nw se oriented normal faults that control the present day drainage network nw se oriented the activity of these faults also contributes to the erosion of the pliocene depocenter located to the north thus suggesting a southwestward migration of the loci of extension to the center of the basin the broad scale scenario envisaged to explain the pliocene quaternary evolution of the ne border of the granada basin is one dominated by mantle slab pull coeval with the africa iberia continuous convergence

palaeomagnetic rotations and fault kinematics in the rif arc of morocco palaeomagnetic and structural investigations in the rif arc of morocco indicate that there have been large rotations associated with a pattern of outwardly directed thrusting rock magnetic experiments in conjunction with thermal and alternating field demagnetization demonstrate that eight sites in jurassic and cretaceous limestones along the internal external boundary have a stable remanent magnetization this is in most cases rotated anticlockwise by as much as 100 from the expected mesozoic declination but in the tetuan area there are large clockwise rotations kinematic indicators from fault surfaces indicate the following 1 in the eastern rif there has been predominantly south directed thrusting partly overprinted by extensional and sinistral strike slip faults 2 at the eastern end of the n 70 e striking jebha fault zone there is a pattern of dominant sinistral ne trending and subsidiary dextral se trending strike slip faults overprinted by normal faults while at the western end deformation consists largely of south directed thrusting 3 in the northern section of the chain where the structural trends are dominantly n s thrusting is directed w to nw it is suggested that the data are best explained by differential motion and rotation of thrust sheets during outwardly directed thrusting around the arc

glacial geomorphology and geographic information systems recent developments in the field of glacial geomorphology have dramatically increased the need to acquire maintain manipulate and analyze large amounts of landform landscape and sediment data the use of geographic information systems gis has provided new platforms and tools for analysis and visualization of geomorphic data glacial geomorphologists have used gis to integrate multi source data manage multi scale studies identify previously unrecognized spatial and temporal relationships and patterns in geomorphic data and to link landform data with numerical models as part of model calibration and verification gis based analyses associated with numerical modeling are improving our understanding of glacial landscape evolution and are allowing new quantitative and systematic examinations of spatial and temporal patterns of glacial landforms and processes this has allowed for the development of insights and concepts that would be unlikely to arise using traditional methods alone key recommendations for future research and applications in glacial geomorphology include enhanced gis education and dissemination the development of standards and conventions for glacial geomorphic data community projects to collect data into readily accessible databases and enhanced use of linked gis model frameworks to address major issues in glacial geomorphology

fractal interrelationships between topography and structure fractal interrelationships between topography and structure are investigated in two areas of the north american central appalachian mountains one in the intensely deformed valley and ridge province and the other in the relatively undeformed foreland area of the appalachian plateau province in the valley and ridge province the fractal dimensions of topographic and structural relief vary systematically along the strike of major folds following a second order polynominal trend cross correlation of the fractal dimensions of topography to structure indicates that there is a significant positive correlation between the two fractal analysis of topography in the relatively undeformed foreland area of the appalachian plateau revealed no significant variation in the fractal characteristics of topography across the study area consistent with the lack of near surface structure however fractal analysis of deeper structures beneath the plateau area undertaken using reflection seismic data revealed step wise increases in fractal dimension from the deeply buried precambrian basement to the near surface these vertical changes in fractal dimension can be related to the tectonic history of the area taken together these studies indicate that fractal analysis provides a means to quantify and compare the influence of near surface structure on topographic development and lateral and vertical structural variability fractal analysis provides a means to characterize the systematic changes in the complex patterns formed by topography and structure and the interrelationships between them similarity in their fractal characteristics implies similarity in the relative amplitude and abundance of different wavelength features in the topographic or structural profile 1998 john wiley sons ltd

tectonic climatic and lithologic influences on landscape fractal dimension and hypsometry implications for landscape evolution in the san gabriel mountains california east west variation in tectonic activity and strong north south climatic gradients provide a unique opportunity to study tectonic climatic and lithologic influences on landscape evolution in the san gabriel mountains california the competing tendencies of constructive tectonic and degradational climatic effects act against lithologic resistance to influence fluvial systems and thus the nature of adjacent and nested drainage basins landscape fractal dimension d a measure of surface roughness over a variety of scales and the hypsometric integral i a measure of the distribution of landmass volume above a reference plane are useful measures of altitudinal variation with scale as such they may provide clues as to the relative influences of tectonism climate and rock type topographic analyses of the san gabriel mountains clearly indicate that tectonism strongly influences d at range wavelength scales while rock type variation apparently influences d and i at smaller scales tectonism is also shown to influence i across the mountain piedmont junction at all scales investigated tectonic activity shows strong negative correlation with both i and d because tectonically active portions of the mountain front do not allow time for much landscape dissection by lower order streams three dimensional topographic modeling suggests climatic parameters exert a stronger influence on d than does tectonism this modeling also suggests an inverse correlation between range scale d and i with varying climate and uplift rate a positive correlation is observed in the san gabriel mountains we suggest this difference results from 1 differences in uplift style between the san gabriel mountains and the models and or 2 variation in rock type erodibility present in the san gabriel mountains but which was not modeled we postulate that the interaction of tectonic climatic and lithologic parameters influences the stable i and d to which a landscape evolves key questions remaining include 1 the time required to reach a stable i or d after a climatic or tectonic change 2 what does the fractal nature of topography tell us about the scaling characteristics of major landforming processes 3 how does climate influence range scale i and both range and small scale d and 4 what are the effects on i and d of range scale lithologic variation both in the models and in real landscapes

clues for a tortonian reconstruction of the gibraltar arc structural pattern deformation diachronism and block rotations abstract we proposed a reconstruction of one of the tightest orogenic arcs on earth the gibraltar arc system this reconstruction which includes onshore and offshore data is completed for approximately 9 ma the clues that lead us to draw it are based on a review in terms of structures and age of the superposed deformational events that took place during miocene with special attention to the external zones this review and new structural data presented in this paper permit us to constrain the timing of vertical axis rotations evidenced by previously published paleomagnetic data and to identify homogeneous domains in terms of relationships between timing of deformation events re magnetization and rotations in particular remagnetization in the betics took place after the main shortening which produced the external fold and thrust belts pre upper miocene but was mostly previous to a contractive reorganization that affected the whole area it should have occurred during lower tortonian between 9 9 and 11 ma from tortonian to present block rotations as high as 53 took place together with plate convergence they accommodated a tightening and lengthening of the gibraltar arc system and drastically altered its geometry as the orientation and position of any pre 9 ma kinematic indicator or structural element is also modified our reconstruction should be used as starting point for any pre tortonian model of the westernmost orogenic segment of the alpine mediterranean system

palaeomagnetic rotations in the eastern betic cordillera southern spain palaeomagnetic declinations from the external zones of the eastern betic cordillera southern spain and an adjacent area of the internal zone indicate variable and locally very large clockwise rotations the rotations occurred after latest oligocene times and probably before the late miocene this overlaps a period of dextrally oblique convergence during the early to middle miocene along the internal external zone boundary and within the external zone rotations in the external zone are recorded by palaeomagnetic results from 27 sites in upper jurassic ammonitico rosso facies limestones from the subbetic zone and one site of a similar age from the prebetic the sites show either two or three component behaviour the low temperature component is coincident with the present field direction the intermediate temperature component was probably acquired during miocene folding the high temperature component passes fold tests miocene age and a conglomerate test eocene early oligocene age palaeomagnetic declinations from individual tectonic blocks in the subbetic are consistent but indicate large differential rotations between blocks these blocks are underlain by low angle thrust faults which probably accommodated much of the rotation the largest rotations occur on relatively small isolated blocks of jurassic carbonates in a highly deformed triassic evaporite sequence the single site in the prebetic has not rotated significantly relative to stable iberia in malaguide rocks of the sierra espun a in the adjacent internal zone stable palaeomagnetic components were measured at one site in upper miocene sedimentary rocks at three sites in upper oligocene lower miocene red marls at one site in oligocene marls at one site in jurassic limestones and at two sites in permo triassic red beds the palaeomagnetic results suggest that about 60 of clockwise rotation occurred in the latest oligocene earliest miocene and a further 140 of clockwise rotation subsequently one site in late miocene sedimentary rocks yields unrotated declinations which if not representing an overprinted direction indicate that the rotation was complete by the end of the miocene

mode of extensional tectonics in the southeastern betics se spain implications for the tectonic evolution of the peri alboran orogenic system the gibraltar arc which closes the westernmost part of the mediterranean basin is a miocene a type subduction arc formed by the continental collision of various pre miocene terranes in the major zone of collision between the iberian and african cratons the hanging wall block known as the alboran domain has undergone more than 300 km migration from a more easterly position where it was the continuation of the alpine cretaceous paleogene orogen contemporaneous with thin skinned thrusting in the footwall the alboran domain underwent two episodes of nearly orthogonal extension in which extensional systems developed with directions of extension varying from a nnw sse system orthogonal to the belt axis in the late burdigalian langhian to a wsw directed orogen parallel one in the serravallian the superposition of these two systems resulted in a chocolate tablet megastructure this extensional pattern is not satisfactorily explained in previously proposed models for the evolution of the arc orthogonal extension is plausible in a process of the gravitational collapse of an overthickened crust nevertheless orogen parallel extension is more difficult to explain in this context we advocate that the wsw directed low angle normal faults formed during large scale extension in connection with important westward arc migration the driving force of extension in a general context of convergence is controversial and varies between a convective removal model and a delamination model constraints on both the timing and the kinematics of extension as presented in this paper seem to support the contribution of both mechanisms convective removal may have started the process but continued n s convergence could have resulted in westward tectonic escape and asymmetric lateral inflow of asthenospheric material accompanying lithospheric delamination

the fractal properties of topography as controlled by the interactions of tectonic lithological and geomorphological processes landscape topography widely exhibits fractal structure because of the complexity of relief geometry this structure is not homogeneous in space and the study of its spatial characteristics represents a powerful method for investigating the interrelationships between landforms and underlying processes we explore these interrelationships using the digital elevation model dem of an area located in central italy where landscape topography is strongly linked to its geological evolution being characterized by alternating intermountain basins and mountain ranges trending nw se a modified version of the method based on the standard deviation of relief elevations is used to evaluate the fractal parameters of relief after tiling the dem in spatial units characterized by homogeneous fractal geometry and statistical methods in conjunction with spatial analysis techniques are applied to the resulting terrain datasets both the lowest and to a lesser extent the highest values of fractal dimension are found to follow the ridge and valley trend low fractal dimension is observed in the mountain ranges characterized by massive strata of limestone and along the fault scarps defining the contact between the intermountain basins and the surrounding slopes where sediment deposition prevails high fractal dimension is observed in regions characterized by highly erodible terrigenous lithology and in areas where tectonic activity favors erosional processes mainly by rivers the analysis of the fractal power law parameters also suggests that each major lithological complex has its own characteristic fractal signature these results provide new insights into the link between the fractal properties of topography and the tectonic lithological and geomorphological features of the area and show that the analysis approach proposed is useful to depict key aspects about the geomorphological and geological setting of an area using only a dem

active deformation of taiwan from gps measurements and numerical simulations using a two dimensional distinct element model we evaluate the relationships between plate kinematics and present day deformation in taiwan where active collision occurs in particular the distribution of velocity fields calculated in our models is compared with the actual velocity field revealed by the most recent geodetic data gps obtained in taiwan and the surrounding islands of the philippine sea plate and the eurasian shelf the main aim of this paper is to produce a mechanically consistent 2 d model that accounts for the observed velocity field taken as whole within the limits of acceptable rheological parameters and reasonable boundary displacement conditions we evaluate how the active deformation of taiwan is influenced by the presence of strong and weak zones such as the structural highs in the foreland and subduction zones with accretionary prisms respectively major mechanical discontinuities such as the main fault zones in the mountain belt and the opening of the okinawa trough particular attention is paid to the role of preexisting discontinuities since the presence of mechanical decoupling along major faults strongly affects the distribution of the velocity and stress patterns we show that despite parameter uncertainties several tectonic factors the presence of the strong kuanyin and peikang highs in contrast to the weak subduction zone to the south the weak active regional shear zones and the opening of the back arc okinawa trough concur to provide an acceptable mechanical model for this regional deformation these sources are related not only to the geometry of the plate boundary the direction of plate convergence and the shape of the chinese margin but also to the presence of major zones of relative weakness and mechanical decoupling such as the longitudinal valley fault zone and the western thrust belt of taiwan

new palaeomagnetic data from the betic cordillera constraints on the timing and the geographical distribution of tectonic rotations in southern spain a palaeomagnetic investigation has been carried out at 14 sites on jurassic red nodular limestones from the central and eastern part of the external zones of the betic cordillera subbetic and prebetic zones progressive thermal demagnetisation of samples from the subbetic zone reveals the presence of two stable magnetic components of the natural remanent magnetisation 1 a secondary neogene syn folding component and 2 the original jurassic magnetisation as similar characteristics have been reported in jurassic limestones from the western subbetic zone a widespread remagnetisation event took place within 106 years in the entire subbetic region during neogene times in contrast in the prebetic region no evidence for a secondary overprint has been detected palaeomagnetic jurassic declinations indicate variable and locally very large clockwise rotations 35 140 but the two sites in the north westernmost part of the investigated region are not rotated the use of both components of magnetisation and the incremental fold test results allowed the timing of block rotations in the subbetic zone to be constrained rotations in the western subbetic occurred after the acquisition of the secondary overprint whereas in the central part of the subbetic zone they were completed by the time of the remagnetisation event

geometry and quaternary kinematics of fold and thrust units of southwestern taiwan structural and paleostress analyses provide new insights into the quaternary kinematics of the outermost fold and thrust units of southwestern taiwan foothills the frontal folds are interpreted as fault related folds and their tectonic evolution through space and time is tightly constrained fold development is correlated with reef building on top of the anticlines moreover we provide field evidence that nw se fault zones oblique to the structural grain of the belt probably acted as transfer fault zones during the the quaternary fold thrust emplacement two successive quaternary stress regimes are evidenced in southwestern taiwan a nw se compression followed by a recent nearly e w compression the latter shows an along strike change from pure e w contraction to the north to perpendicular n s extension in the south this southward decrease in n s confinement probably represents the on land signature of the incipient quaternary tectonic escape predicted by analogue and numerical modelling and evidenced at present day by global positioning system data

structure and kinematics of the south iberian paleomargin and its relationship with the flysch trough units extensional tectonics within the gibraltar arc fold and thrust belt western betics abstract the superposition of structures observed in a selected area of the external zones of the betic orogen situated in the westernmost segment of the peri mediterranean mountain belt reveals an alternation of compressional and extensional events during the overall convergence of the african and eurasian plates that bound the system an early miocene compressional event produced the formation of the so called gibraltar arc fold and thrust belt formed by the units derived from the south iberian paleomargin and the flysch trough this wedge constitutes the footwall of the gibraltar thrust whose hanging wall corresponds to the alboran domain the outward migration of the compressional front w to nwward in the south iberian segment was followed by the outward migration of the extensional locus related to the middle miocene rifting that led to the alboran basin subsidence the tectonic inversion of the gibraltar thrust was accompanied by normal faulting of the innermost part of the paleomargin and the flysch trough units finally the alboran region underwent n s to nw se compression from late miocene onwards which caused the uplift of the gibraltar arc area

genesis of soils and landscapes in the ridge and valley province of central pennsylvania abstract the characteristics and properties of the soils on the ridge tops footslopes and adjacent limestone valley areas in the ridge and valley of central pennsylvania have been strongly influenced by their parent material and geomorphic history the ridge top soils have developed in sandstone colluvium which mantles sandstone residuum the upper part of the original residual ridge top soil was truncated during late wisconsinan time and then covered with local colluvium or it was cyroturbated these sandstone parent materials have been stable since the late wisconsinan and have sandy skeletal dystrochrepts and haplorthods developed in them the haplorthods are minor soils and are associated with local concentrations of coniferous vegetation during the late wisconsinan the sandstone colluvium also moved downslope and was mixed with bedrock and residual material from shale and limestone and deposited on the footslope over a pre wisconsinan soil developed in older colluvium or limestone residuum the footslope surface colluvial soils vary in texture and drainage because of their parent material their location in discharge areas and fragipan development the age of the brown surface colluvium is considered late wisconsinan and the age of the pre wisconsinan buried soils is not known the buried soil s bright red rubified color and argillic horizon indicate a much greater degree of soil development than noted in the brown surface colluvium and its age may be correlated with isotope stage 6 the soils developed at the surface in the colluvium are mainly ultisols although some poorly drained soils particularly in limestone material are alfisols the ultisols are parent material ultisols and the poorly drained alfisols have a high base status in their parent material or were recharged with bases from the groundwater the soils of the limestone valleys are developed in residuum the residuum accumulated from the insoluble residues after the caco 3 was leached from the bedrock if the residuum is thick 2 to 3 m the soils date back many hundreds of thousands of years but are still classified as hapludalfs in addition to being old the surface of the hapludalfs has been modified by periglacial truncation and the addition of eolian materials these processes have given the upper 50 cm of the hapludalfs a late wisconsinan age but the bulk of the b horizon is many thousands of years older eolian material has also been added to the ridge top soils as well as the colluvial soils the mineralogy of all the soils in this landscape including the buried paleosols does not show significant clay mineral weathering this appears anomalous considering the degree of oxidation of the buried paleosols and the limestone soils and their estimated age

curved fold and thrust accretion during the extrusion of a synorogenic viscous allochthonous sheet the estepa range external zones western betic cordillera spain 1 new structural borehole and time domain electromagnetic data allow us to reconstruct the 3 d geometry of the estepa range external zones of the western betic cordillera which constitutes an isolated curved fold and thrust range made up of jurassic shallow marine carbonates and cretaceous to paleocene marls and marly limestones contraction and rising load linked to the accretion of the subbetic nappe enhanced the expulsion of triassic evaporites and overpressured clays during the early and middle miocene finally forming part of a highly deformed melange unit this plastic extrusion favored the disconnection of external and middle subbetic blocks including the sierra de estepa range there deformation is characterized by northwest vergent curved folds and thrusts associated with ne sw frontal ramps and nw se lateral transfer faults that segmented the folds active between 18 and 12 ma at a local scale curvature was achieved under a nearly uniform nw wnw transport direction suggesting a primary arc type friction variation across the heterogeneous detached plastic basal triassic unit mainly controlled the curvature and segmentation of the fold systems transport direction is consistent with previously published slip data from the internal subbetic and the campo de gibraltar units after the late serravallian accretion slowed down and a shallow marine unit deposited unconformably placed over the main thrust and folds the sequence of deformation and emplacement of these ranges is interpreted as a continuous process linked to the early miocene e continental collision of the iberian margin thin continental crust and subduction of the flysch trough oceanic crust beneath the alboran continental domain

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities