strike slip faulting and block rotation in the lake mead fault system strike slip faults in the basin and range province have often been considered passive boundaries between differentially extended domains of tilted normal faults and are thus considered secondary in accommodating regional horizontal deformation paleomagnotic investigation of late miocene age volcanic rocks displaced by the left lateral fault system of lake mead nevada shows 1 that these rocks have not been affected by significant structural tilt the difference between observed and expected inclinations being only 0 6 14 9 and 2 a significant horizontal counterclockwise rotation of 29 4 8 5 about a vertical axis this rotation was accommodated by slip on northwest trending right lateral strike slip faults this implies significant west northwest elongation results of the investigation indicate that strike slip faulting is the primary process accommodating crustal deformation along the lake mead fault system and that tilting in response to normal faulting is secondary

thermal and mechanical structure of the central iberian peninsula lithosphere abstract the central iberian peninsula spain is made up of three main tectonic units a mountain range the spanish central system and two tertiary basins those of the rivers duero and tajo these units are the result of widespread foreland deformation of the iberian plate interior in response to alpine convergence of european and african plates the present study was designed to investigate thermal structure and rheological stratification in this region of central spain surface heat flow has been described to range from 80 to 60 mw m 2 highest surface heat flow values correspond to the central system and northern part of the tajo basin the relationship between elevation and thermal state was used to construct a one dimensional thermal model mantle heat flow drops from 34 mw m 2 duero basin to 27 mw m 2 tajo basin and increases with diminishing surface heat flow strength predictions made by extrapolating experimental data indicate varying rheological stratification throughout the area in general in compression ductile fields predominate in the middle and lower crusts and lithospheric mantle brittle behaviour is restricted to the first 8 km of the upper crust and to a thin layer at the top of the middle crust in tension brittle layers are slightly more extended while the lower crust and lithospheric mantle remain ductile in the case of a wet peridotite composition discontinuities in brittle and ductile layer thickness determine lateral rheological anisotropy tectonic units roughly correspond to rheological domains brittle layers reach their maximum thickness beneath the duero basin and are of least thickness under the tajo basin especially its northern area estimated total lithospheric strength shows a range from 2 5 10 12 to 8 10 12 n m 1 in compression and from 1 3 10 12 to 1 6 10 12 n m 1 in tension highest values were estimated for the duero basin depth versus frequency of earthquakes correlates well with strength predictions earthquake foci concentrate mainly in the upper crust showing a peak close to maximum strength depth most earthquakes occur in the southern margin of the central system and southeast tajo basin seismicity is related to major faults some bounding rheological domains the duero basin is a relative quiescence zone characterised by higher total lithospheric strength than the remaining units

using natural maturation series to evaluate the utility of parallel reaction kinetics models an investigation of toarcian shales and carboniferous coals germany abstract open system pyrolysis is routinely performed on immature samples in order to determine the kinetic parameters of petroleum generation at both bulk and molecular levels this study tested such predictions for type ii and type iii organic matter by making calibrations with both artificial and natural maturity sequences of toarcian shales posidonia shale 0 48 1 44 rr and carboniferous vitrains 0 74 2 81 rr both natural series showed little or no compositional variability attributable to kerogen type artificially matured samples were prepared by non isothermal heating 0 7 k min of the least mature samples up to end temperatures between 375 and 470 c under either closed or open system conditions measured generation rate versus temperature curves were analyzed assuming a distributed system of activation energies and a single frequency factor in each case the resulting kinetic parameters were then used to assess bulk petroleum formation rates for geological heating conditions in the case of all artificially matured samples measured and predicted bulk petroleum formation rate vs temperature curves for each maturation stage remain within the original envelope defined by the least mature sample despite an upward shift of tmax temperatures this confirms that the reactions taking place during both the pyrolysis measurements and simulated maturation processes are the same involving mainly homolytic cracking a similar pattern of measured and predicted rate curves is reproduced by the natural maturation sequence of the toarcian shales in the maturity range of 0 53 to 1 44 rr suggesting that petroleum generation within these natural systems also results from cracking reactions and therefore that petroleum generation over geological time can be reliably extrapolated from open system pyrolysis of the appropriate immature sample by contrast significant deviations are observed for the natural coal series with measured and predicted rate curves extending beyond the immature envelopes in accordance with the pronounced increase of frequency factors and of protonated aromatic carbon concentrations this behavior is attributed to solid state aromatization reactions which compete with product generation during natural coalification but which are not reproducible to the same extent by experimental heating it is concluded that petroleum generation from vitrinitic coals over geological time cannot be reliably extrapolated from open system pyrolysis of low rank samples

intraplate deformation and basin formation during the tertiary within the northern iberian plate origin and evolution of the almazan basin the tertiary almazan basin was a topographic high during the mesozoic rifting at the northern part of the iberian plate it was bordered by two mesozoic basins 1 the castilian basin with a maximum thickness of more than 2000 m to the south and 2 the cameros basin with a maximum thickness of 9000 m to the north to the east the almazan basin is bordered by paleozoic rocks of the nw se trending aragonian range which underwent little subsidence during the mesozoic the two mesozoic basins show an e w direction during the tertiary nne ssw compression mainly late eocene early miocene both mesozoic basins were inverted and uplifted and the almazan basin with an overall synclinal geometry was filled with syn tectonic terrestrial sediments reaching a maximum thickness of 3500 m deformation during the tertiary was strongly controlled by preexisting structures both mesozoic extensional faults and reactivated variscan folds the depocenter of the tertiary basin migrated southward during the paleogene this migration is consistent with a piggyback transport of the whole basin northward due to the movement on the underlying crustal scale north verging cameros thrust the geometry and sedimentary evolution of the almazan thick skinned piggyback basin was controlled by the uplift associated with the main crustal scale thrust which was the main source area and was separated from the foreland basin since the early stages of filling late eocene this makes the main difference with thin skinned piggyback basins controlled by the foreland thrust belt and separated from the foreland basin only at their late stages

block rotation by strike slip faulting structural and paleomagnetic evidence geometric analysis shows that motion of sets of strike slip faults should cause block rotation otherwise the distorted fault domain would not fit with its surrounding the sense of the block rotation depends on the sense of fault slip and the spacing and orientation of the faults all of which can be obtained from structural data the predictions of the geometric model can then be independently tested by paleomagnetic measurements the model was tested in northern israel structural data reveal several domains of contemporaneous right and left lateral strike slip faults paleomagnetic measurements show that in a domain of nnw trending left lateral faults blocks rotated 23 3 8 2 clockwise and in a domain of right lateral faults blocks rotated 22 4 9 0 anticlockwise these results are in agreement with the prediction of the geometric analysis of the structure the combined results of the heterogenous deformation of the area resembles a pure shear which allows n s extension by about 1 3 in other domains rotations of 34 6 9 1 and 53 1 11 0 were found in their original orientation the left and right lateral faults intersected at angles of 60 70 enclosing the principal axis of shortening in accordance with theories of brittle failure as a result of block rotations this angle is now larger and may reach 110 the results demonstrate large block rotations in different senses in domains of strike slip faults the independent structural and paleomagnetic data can be interpreted within the framework of a simple geometric model northern israel is considered to be a good model for this efficient mechanism of intraplate deformation which is expected to occur in similar tectonic settings elsewhere

thermal consequences of thrust faulting simultaneous versus successive fault activation and exhumation abstract when converting temperature time curves obtained from geochronology into the denudation history of an area variations in the isotherm geometry should not be neglected the geothermal gradient changes with depth due to heat production and evolves with time due to heat advection if the deformation rate is high furthermore lateral variations arise due to topographic effects ignoring these aspects can result in significant errors when estimating denudation rates we present a numerical model for the thermal response to thrust faulting which takes these features into account this kinematic two dimensional model is fully time dependent and includes the effects of alternating fault activation in the upper crust furthermore any denudation history can be imposed implying that erosion and rock uplift can be studied independently to each other the model is used to investigate the difference in thermal response between scenarios with simultaneous compressional faulting and erosion and scenarios with a time lag between rock uplift and denudation hereby we aim to contribute to the analysis of the mutual interaction between mountain growth and surface processes we show that rock uplift occurring before the onset of erosion might cause 10 to more than 50 of the total amount of cooling we applied the model to study the cenozoic development of the sierra de guadarrama in the spanish central system aiming to find the source of a cooling event in the pliocene in this region as shown by our modeling this temperature drop cannot be caused by erosion of a previously uplifted mountain chain the only scenarios giving results compatible with the observations are those incorporating active compressional deformation during the pliocene which is consistent with the ongoing nw se oriented convergence between africa and iberia

insights into the tectonic topography of the present day landscape of the central iberian peninsula spain abstract the landscape of today s central iberian peninsula has been shaped by ongoing tectonic activity since the tertiary this landscape comprises a mountain ridge trending e w to nw se the central system separating two regions of smooth topography the basins of the rivers duero and tajo in this study we explore interrelationships between topography and tectonics in the central iberian peninsula regional landscape features were analysed using a digital elevation model dem slope gradients and slope orientations derived from the dem were combined to describe topographic surface roughness topography trend surfaces inferred from harmonic analysis were used to define regional topographic features low roughness emphasizes the smooth nature of the basins topography where surfaces of homogeneous slope gradient and orientation dominate high roughness was associated with abrupt changes in gradient and slope orientation such as those affecting crests valley bottoms and scarp edges present in the mountain chain and in some deep incised valleys in the basins one of the applications of roughness mapping was its capacity to isolate incised valley segments the area distribution of incised rivers shows their prevalence in the east on a regional scale the topographic surface can be described as a train of ne sw undulations or waves of 20 km wavelength these undulations undergo changes in direction and interruptions limited by n s trending breaks e w and ne sw troughs and ridges clearly mark structural uplifts and depressions within the central system these structures are transverse to the compressive nw se stress field that controlled the deformation of the central iberian peninsula from the neogene to the present they represent the upper crustal folding that accommodates alpine shortening n s breaks coincide with late miocene faults that control the basins sedimentation further associated palaeoseismic structures suggest the recent tectonic activity of n s faults in the eastern part of the tajo basin apatite fission track analysis data for this area suggest the occurrence of a significant uplift episode from 7 to 10 ma which induced the river incisions appearing in the roughness map n s and ne sw faults could be seismogenic sources for the current moderate to low seismic activity of the east tajo basin and southeast central system although n s fault activity has already been established we propose its significant contribution to shaping the landscape

displacement transfer from borders to interior of a plate a crustal transect of iberia abstract a n s crustal transect of the whole iberian plate is presented the displacement transfer during the alpine deformation from the border ranges cantabrian and betic chains toward the interior ones was analyzed by means of balanced crustal sections inconsistencies in shortening values between upper and middle lower crust in the cantabrian mountains basque cantabrian zone imply a mid crustal detachment transferring orogenic shortening southward toward the spanish central system depending on the shortening value attributed to the central system this mid crustal detachment could involve the entire iberian plate connecting the cantabrian mountains and the betic chain the very small crustal root in the central system can be explained as a result of the tectonic load caused by the upper crustal shortening that was transferred from the border ranges we conclude that a simple shear model rather than a pure shear with lithospheric folding better explains the whole iberia deformation finally the total alpine shortening of the iberian plate is estimated between 267 and 292 km

paleomagnetic study of the messejana plasencia dyke portugal and spain a lower jurassic paleopole for the iberian plate abstract the only iberian lower jurassic paleomagnetic pole come from the central atlantic magmatic province related messejana plasencia dyke but the age and origin of its remanence have been a matter of discussion with the aim of solving this uncertainty and to go further into a better understanding of its emplacement and other possible tectonic features a systematic paleomagnetic investigation of 40 sites 625 specimens distributed all along the 530 km of the messejana plasencia dyke has been carried out rock magnetic experiments indicate psd low ti titanomagnetite and magnetite as the minerals carrying the nrm the samples were mostly thermally demagnetized most sites exhibit a characteristic remanent component of normal polarity with the exception of two sites where samples with reversed polarities have been observed the paleomagnetic pole derived from a total of 35 valid sites is representative of the whole structure of the dyke and statistically well defined with values of pla 70 4 n plo 237 6 e k 47 9 and a 95 3 5 paleomagnetic data indicates that i there is no evidence of a cretaceous remagnetization in the dyke as it was suggested ii most of the dyke had a brief emplacement time furthermore two dyke intrusion events separated in time from it by at least 10 000 y have been detected iii the high grouping of the vgps directions suggests no important tectonic perturbations of the whole structure of the dyke since its intrusion time iv the pole derived from this study is a good quality lower jurassic paleopole for the iberian plate and v the messejana plasencia dyke paleopole for the iberian plate is also in agreement with quality selected european and north american lower jurassic paleopoles and the magnetic anomalies data sets that are available for rotate them to iberia

three dimensional airflow and sediment transport patterns over barchan dunes abstract airflow dynamics and potential sediment transport were measured and modelled across various barchan dune topographies and incident wind conditions modification of near surface flow was recorded simultaneously in three dimensions 3d using dense arrays of high resolution 3d ultrasonic anemometers in situ measurements provided rigorous validation and calibration for computational fluid dynamics cfd modelling measured and modelled results show good agreement between flow velocity directionality and turbulence intensity modelling of characteristic airflow conditions and surface shear stress beyond the instrument locations elucidated airflow dynamics across the entire landform surface at an unprecedented level of detail emergent turbulent airflow patterns were identified in the form of two counter rotating vortices that converge at the dune centreline downwind of the dune crest integrating a sediment transport function with cfd surface airflow allows for the spatial mapping of flux patterns across the entirety of the dune and interdune surface on the stoss slope and laterally along the outer barchan arms there is strong potential sediment flux in response to increased streamwise stress in lee side locations sediment transport remains at above threshold conditions and is redirected in response to complex turbulent vortices identified in the overlying wake zone the precision of the models allows for the identification of complex flow perturbations and associated surface stresses that prove difficult to measure in the field cfd in combination with a sediment transport function is demonstrated to be a useful tool in investigating morphodynamics of mobile dune systems

the spanish portuguese central system an example of intense intraplate deformation and strain partitioning abstract the intraplate deformation of iberia during the cenozoic produced a series of ranges and deformation belts with a wide variety of structural trends the spanish portuguese central system is the most prominent feature crossing over the whole of central iberia it is a large thick skinned crustal pop up with ne sw to e w thrusts however the 500 km long left lateral strike slip messejana plasencia fault also ne sw oriented bends these thrusts to produce ne sw local paleostresses close to the fault which seems to be consistent with a common deformational arrangement this is also supported by the similar sedimentary infilling characteristics found in the surrounding cenozoic basins the moment of the maximum intraplate deformation is registered at the same time in all these basins during the upper priabonian lower chattian as there are two possible sources for the intraplate compressive stresses the pyrenean n s shortening orogen to the north and the betic nw se shortening orogen to the south neither can simply explain both simultaneous movements ne sw strike slip and ne sw thrusting the deduced age of the main deformation indicates a pyrenean origin in contrast the concept of strain partitioning between the two types of faults gives as a result an overall north trending compression existing data do not support crustal detachment from the betics neither from the pyrenees but are consistent with a crustal uplift related to lithospheric folding the subsequent betic related stress field only slightly reworked previously pyrenean related structures except for the portuguese sector where tectonic activity occurred mainly in the upper miocene

a block model of distributed deformation by faulting it is clear from palaeomagnetic evidence that large and hitherto unexpected rotations about a vertical axis are common in regions of distributed continental deformation we propose a simple two dimensional model to illustrate how fault movement and block rotation within a zone of distributed deformation may be related to the relative motion of the rigid plates that bound the zone one surprizing feature of this model is that the component of strike slip motion on the faults within the deforming zone is in the opposite sense to the strike slip component across the zone as a whole thus slip vectors within the zone are not the same as that between the bounding rigid plates in contrast to deformation at oceanic plate boundaries examples of active fault geometries similar to those of our model can be seen in greece iran and the western usa

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

model of distributed deformation block rotations and crustal thickening for the formation of the spanish central system abstract the spanish central system constitutes an important morphostructural intraplate feature of iberia that resulted from a concentration of crustal strain derived from stresses applied on the boundaries of the betics and pyrenees we propose a tectonic model in which the deformation of this zone was produced by a mid late mesozoic shear zone a type of secondary plate boundary that absorbed part of the iberia eurasia relative motion the deformation within this e w shear zone was compensated by means of block rotations that resulted from the reorganization of multiple and previous faults and fractures the subsequent n s africa eurasia convergence was partly accommodated within this intraplate zone of weakness this caused a concentration of strain that was responsible for the homogeneous thickening of the lower crust and for the blocking of block rotations and forced uplifting of the upper crust

timing and extent of neogene tectonic rotation in the western transverse ranges california paleomagnetic data collected from lower miocene rocks throughout the western transverse ranges province have consistently clockwise deflected magnetic declinations which suggests that the entire province has experienced clockwise tectonic rotation during neogene time paleomagnetic declinations in lower miocene rocks increase westward from 33 5 c 11 in the san gabriel block to 91 7 7 in the western santa ynez range suggesting a westward increase in the net amount of clockwise tectonic rotation paleomagnetic data that constrain the tuning of rotation suggest that the entire western transverse ranges rotated uniformly 50 60 clockwise during the middle miocene this implies a minimum of 200 km of distributed dextral shear along the california coast and offshore during middle miocene time little tectonic rotation appears to have occurred in the western transverse ranges during late miocene time since miocene time continued clockwise rotation in the western santa ynez range 31 3 combined with counterclockwise rotation in the san gabriel block 16 has oroclinally bent the transverse ranges to the west of the san andreas fault the pliocene pleistocene clockwise rotation implies an additional 30 60 km of distributed dextral shear across the southern california coast ranges during post miocene time

integrated gravity and topography analysis in analog models intraplate deformation in iberia in the western part of the iberian microplate the main topographic highs trend e w to ne sw and are periodically spaced with wavelengths of 250 km conversely in the northeastern part the region of the iberian chain topography is more irregular and strike directions vary from nw se to e w and ne sw we relate this phenomenon to shortening of a continental lithosphere which contains two different well defined domains of lithospheric strength our hypothesis is supported by physical analog models a new processing method has been developed to assist the interpretation of the model results it utilizes spectral analysis of gravity and topography data derived from the experiments folding of the crust and mantle lithosphere yields periodic gravity fluctuations while thickening processes lead to localized gravity lows in this way gravity data can be used to distinguish between the two forms of lithosphere deformation and to correlate areas that underwent the same type of deformation gravity modeling has been performed under full in depth control of the experimental lithosphere structure as such gravity signals from the models may be compared to field gravity data for better understanding the underlying deformation mechanism

relationship between the fractal dimension anisotropy of the spatial faults distribution and the paleostress fields on a variscan granitic massif central spain the f parameter the spatial distribution of faults is usually described as a fractal set characterised by the fractal dimension in this work we have filtered fault patterns interpreted from digital elevation models aerial photographs and field maps by using structural geological parameters of the stress ellipsoid stress tensor direction and stress ratio r0 and age of deformation from these filtered structural maps we have obtained the fractal dimension associated with the fracture patterns developed during permo triassic and alpine tectonic events on a variscan granitic massif located in the spanish central system oriented fractal dimensions were calculated on several transects crossing the fault filtered maps the fractal dimension d calculated by 1 d box counting describes an ellipse on a polar plot with the short axis as the minimum value dhmin and the long axis as the maximum value dhmax of the fractal dimensions measured from these analyses we have defined the f parameter as a function of the maximum value minimum value and vertical value of fractal dimension dz fz dzkdhmin dhmaxk dhmin finally we have established from a local scale analysis a perpendicular relationship between the principal axes of the ellipse of the fractal spatial anisotropy of fractures and the principal axes of the stress tensor shmax shmin and sz that generates this dynamic pattern of fractures furthermore the f parameter and the stress ratio r0 are equivalents and applied in this area both show a triaxial extension

lateral inhomogeneities of the hercynian crust in central spain abstract an azimuthal layout of deep seismic profiles has been partially completed in the central iberian massif data from two new profiles and a reinterpretation of previous profiles make possible two dimensional models for the hercynian crust in central spain from which some lateral crustal inhomogeneities can be established these inhomogeneities due to alpine intraplate tectonics coincide with the spanish central system and consist of a 5 km crustal thickening with respect to the surrounding areas

fault mechanics and the kinematics of block rotations in many strike slip tectonic settings large rotations up to 100 of crustal blocks have been inferred from paleomagnetic data these blocks are bounded by sets of parallel faults which accommodate the relative motion between the blocks as regional deformation progresses simple geometrical considerations require that the faults must also rotate in this paper we show that on the basis of mechanical considerations the amount of fault rotation permissible under a stationary stress field is limited to 20 to 45 consequently block rotations that are larger than 40 or 45 require more than one set of accompanying faults to accommodate the block rotation examples of such multiple sets with 40 to 45 between them as predicted by the model were recognized in sistan iran in yerington the lake mead area nevada and in southern california

the role of pre existing faults in basin evolution constraints from 2d finite element and 3d flexure models the lithospheric driving forces which cause intraplate basin deformation are relatively constant over large areas consequently lateral variations in deformation and stress and strain concentrations seem to be primarily caused by pre existing heterogenities in the rheological signature of the continental lithosphere underlying the sedimentary basins in this paper we explore the weak character of upper crustal faults and their control on basin shape for a number of case studies on intraplate phanerozoic basin settings using a 2d finite element and a 3d flexure model of key importance is the integration of seismic data and field observations with the tectonic modelling allowing the investigation of deformation processes and their expressions on different scales operating on different levels of the lithosphere finite element models for sub basin scales incorporating weak upper crustal faults predict strong control of these weak zones on local stress distributions and subsequent deformation in agreement with observed deformation patterns slip along upper crustal faults control stress distribution and subsequent faulting in overlying sedimentary rocks the effect of weak upper crustal fault movements on basin wide regional upper crustal flexure is looked at in two case studies on 1 extensional tectonics in the lake tanganyika rift zone east africa and 2 compressional tectonics in the central system and tajo basin central spain both settings indicate that basement warpings are controlled by large amounts of slip along so called weak crustal scale border faults which are mostly planar adopting border fault displacements in the 3d flexure model the results indicate low effective elastic thickness eet values in a range of 3 7 km for induced basement deflection patterns in accordance with observations the low eet values most likely reflect a partly decoupling of upper crustal and subcrustal deformation facilitated by the weak lower crust and in agreement with standard rheological assumptions for phanerozoic lithosphere in contrast the inferred weakness of upper crustal faults relative to surrounding rock is not evident from uniform rheological assumptions however observations of reactivations of faults which are not preferably aligned with the stress field and reactivations of basin deformation on long time scales are in support of this feature