numerical modelling of lithosphere shortening application to the laramide erogenic province western usa abstract a two dimensional model of lithosphere shortening is presented which quantifies crustal thickening temperature perturbations and flexural isostatic components the model assumes that the upper brittle layer of the crust deforms by thrusting while the lower ductile lithosphere accommodates compressional deformation by a pure shear or squashing mechanism model results suggest that basement uplift foreland basin development and underlying crustal structure are controlled by the amount and configuration of the compressional deformation in the upper and lower lithosphere the perturbation of the temperature field erosion and the flexural rigidity of the lithosphere the model is applicable to regions of thick skinned thrust tectonics and is applied to the laramide orogenic province in the western usa model simulations of structural cross sections across the laramide province show basement uplifts and adjacent foreland basins that are comparable in magnitude with those suggested by geological data the model has also been used to provide insights into the tectonic evolution of the laramide province and an attempt has been made to determine the flexural rigidity of the lithosphere at the time of laramide deformation as well as quantify both the effects of the post shortening re equilibration of the temperature field and thrust uplift erosion the amount of crustal thickening and post shortening cooling of the geotherm predicted by the two dimensional model of lithosphere shortening are used in strength calculations to determine the relative strength or weakness of the lithosphere the results suggest that the lithosphere is relatively strong immediately following shortening due to the cooling of the geotherm following shortening however gradual weakening occurs as the temperature field returns back to its unperturbed state in the presence of an enhanced crustal thickness the results are compatible with the evolution of the laramide province which has experienced a change in tectonic regime to one of extension over the last 20 30 ma

from orogenic hinterlands to mediterranean style back arc basins a comparative analysis hinterland plateaux and mediterranean style back arc basins both form behind active subduction zones or collisional megathrusts and share many characteristics 1 early crustal thickening to about twice normal continental thickness 2 thin lithospheric mantle 3 mixed magmatism including asthenospheric lithospheric and crustal melts 4 late stage horizontal extension accompanied by vertical shortening horizontal extension and vertical shortening are driven by high gravitational potential energy gpe contrasts between the hinterland and surrounding lithosphere which may reach 7 10 12 n m 1 equivalent to about 2 5 times the ridge push force if extension is rapid relative to the rate of lithospheric cooling gpe may remain positive even as extension continues declining to the mid ocean ridge value as crustal thickness approaches zero this suggests that hinterland plateaux could ultimately evolve into oceanic back arc basins the rate direction and amount of extension and the rate of vertical shortening depend on the plate boundary conditions and the gpe of the surrounding lithosphere vertical shortening in tibet is limited by work required to deform the surrounding asian lithosphere whereas mediterranean back arc basins can extend at the expense of regions of thin continental or oceanic crust

formation and deformation of hyperextended rift systems insights from rift domain mapping in the bay of biscay pyrenees the bay of biscay and the pyrenees correspond to a lower cretaceous rift system including both oceanic and hyperextended rift domains the transition from preserved oceanic and rift domains in the west to their complete inversion in the east enables us to study the progressive reactivation of a hyperextended rift system we use seismic interpretation gravity inversion and field mapping to identify and map former rift domains and their subsequent reactivation we propose a new map and sections across the system illustrating the progressive integration of the rift domains into the orogen this study aims to provide insights on the formation of hyperextended rift systems and discuss their role during reactivation two spatially and temporally distinct rift systems can be distinguished the bay of biscay parentis and the pyrenean basque cantabrian rifts while the offshore bay of biscay represent a former mature oceanic domain the fossil remnants of hyperextended domains preserved onshore in the pyrenean cantabrian orogen record distributed extensional deformation partitioned between strongly segmented rift basins reactivation initiated in the exhumed mantle domain before it affected the hyperthinned domain both domains accommodated most of the shortening the final architecture of the orogen is acquired once the conjugate necking domains became involved in collisional processes the complex 3 d architecture of the initial rift system may partly explain the heterogeneous reactivation of the overall system these results have important implications for the formation and reactivation of hyperextended rift systems and for the restoration of the bay of biscay and pyrenean domains

volcan las navajas a pliocene pleistocene trachyte peralkaline rhyolite volcano in the northwestern mexican volcanic belt volcan las navajas a pliocene pleistocene volcano located in the northwestern portion of the mexican volcanic belt erupted lavas ranging in composition from alkali basalt through peralkaline rhyolite and is the only volcano in mainland mexico known to have erupted pantellerites las navajas is located near the northwestern end of the tepic zacoalco rift and covers a 200 m thick pile of alkaline basaltic lavas one of which has been dated at 4 3 ma the eruptive history of the volcano can be divided into three stages separated by episodes of caldera formation during the first stage a broad shield volcano made up of alkali basalts mugearites benmoreites trachytes and peralkaline rhyolites was constructed eruption of a chemically zoned ash flow then caused collapse of the structure to form the first caldera the second stage consisted of eruptions of glassy pantellerite lavas that partially filled the caldera and overflowed its walls this stage ended about 200 000 years ago with the eruption of pumice falls and ash flows which led to the collapse of the southern portion of the volcano to form the second caldera during the third stage two benmoreite cinder cones and a benmoreite lava flow were emplaced on the northwestern flank of the volcano finally the calc alkaline volcano sanganguey was built on the southern flank of las lavajas alkaline volcanism continued in the area with eruptions of alkali basalt from cinder cones located along nw trending fractures through the area although other mildly peralkaline rhyolites are found in the rift zones of western mexico only las navajas produced pantellerites greater volumes of basic alkaline magma have erupted in the las navajas region than in the other areas of peralkaline volcanism in mexico a factor which may be necessary to provide the initial volume of material and heat to drive the differentiation process to such extreme peralkaline compositions

the fossil accretionary wedge of the bay of biscay critical wedge analysis on depth migrated seismic sections and geodynamical implications abstractthe accretionary wedge of the bay of biscay is an east west compressive belt buried under recent sediments of the abyssal plain at the north iberian margin this structure formed through the partial closure of the previously extended biscay basin during the cenozoic north south collision between europe and iberia the same collision that produced the cantabrian pyrenean range on land three north south seismic sections have been prestack depth migrated showing a narrow tapered wedge 7 8 whose internal structure corresponds to a set of south dipping thrusts converging toward a basal decollement there are differences along strike within the wedge thrust spacing the dip of the basal thrust and the thickness of the sediments at the trough augment toward the east increasing its overall size the two dimensional velocity models obtained through migration analysis reflect values between 2000 km s at the sea floor 4500 m and 5000 km s at 12 km depth the syntectonic package thickness varies fr

the relationship between the hawaiites and basalts of the itcha volcanic complex central british columbia volumetrically subordinate alkaline mafic lava flows form a late capping stage over the earlier felsic lavas that form the shield of the itcha volcanic complex ivc of the anahim volcanic belt avb in central british columbia b c the mafic capping stage of the ivc is dominated by hawaiites which are the earliest of the mafic lavas and are succeeded by alkali olivine basalts aob and then by basanites the alkali olivine basalts can be subdivided into high intermediate and low mgo aob groups all of which share similar hfse ratios e g nb zr with the hawaiites high al contents and sr zr ratios indicate that hawaiites and fe rich evolved aob were derived from primitive aob parental magmas by crystal fractionation of a wehrlitic assemblage at pressures on the order of 8 to 10 kbar high si and low fe contents indicate that the majority of the evolved aob lavas however do not represent an intermediate stage in the liquid line of descent to hawaiites but were most likely produced by gabbroic fractionation from primitive aob magmas at relatively low pressures the parental magmas of the majority of these lavas were distinct from those of the observed high mgo basalts having higher hfse contents and being more si under saturated the high al high sr zr signature of high pressure fractionation of a clinopyroxene dominated assemblage in the ivc is shared by hawaiites of other alkaline volcanic suites of the canadian cordillera such as the edziza volcanic complex in northern b c and appears to be a feature of hawaiites in many localities including hawaii and iceland viscosities calculated for both high and low pressure crystal fractionation models suggest that aphyric hawaiites are residual liquids escaped from a wehrlitic crystalline network at elevated pressures possibly at the base of the crust

cenozoic deformation of iberia a model for intraplate mountain building and basin development based on analogue modeling 1 inferences from analogue models support lithospheric folding as the primary response to large scale shortening manifested in the present day topography of iberia this process was active from the late oligocene early miocene during the alpine orogeny and was probably enhanced by reactivation of inherited variscan faults the modeling results confirm the dependence of fold wavelength on convergence rate and hence the strength of the layers of the lithosphere such that fold wavelength is longest for fast convergence rates favoring whole lithosphere folding folding is associated with the formation of dominantly pop up type mountain ranges in the brittle crust and thickening of the ductile layers in the synforms of the buckle folds by flow the mountain ranges are represented by upper crustal pop ups forming the main topographic relief the wavelengths of the topographic uplifts both in model and nature suggest mechanical decoupling between crust and mantle moreover our modeling results suggest that buckling in iberia took place under rheological conditions where the lithospheric mantle is stronger than the lower crust the presence of an indenter inducing oblique shortening in response to the opening of the king s trough in the north western corner of the atlantic iberian margin controls the spacing and obliquity of structures this leads to the transfer of the deformation from the moving walls towards the inner part of the model creating oblique structures in both brittle and ductile layers the effect of the indenter together with an increase on the convergence rate produced more complex brittle structures these results show close similarities to observations on the general shape and distribution of mountain ranges and basins in iberia including the spanish central system and toledo mountains

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

palsar radiometric and geometric calibration this paper summarizes the results obtained from geometric and radiometric calibrations of the phased array l band synthetic aperture radar palsar on the advanced land observing satellite which has been in space for three years all of the imaging modes of the palsar i e single dual and full polarimetric strip modes and scanning synthetic aperture radar scansar were calibrated and validated using a total of 572 calibration points collected worldwide and distributed targets selected primarily from the amazon forest through raw data characterization antenna pattern estimation using the distributed target data and polarimetric calibration using the faraday rotation free area in the amazon we performed the palsar radiometric and geometric calibrations and confirmed that the geometric accuracy of the strip mode is 9 7 m root mean square rms the geometric accuracy of scansar is 70 m and the radiometric accuracy is 0 76 db from a corner reflector analysis and 0 22 db from the amazon data analysis standard deviation polarimetric calibration was successful resulting in a vv hh amplitude balance of 1 013 0 0561 db with a standard deviation of 0 062 and a phase balance of 0 612deg with a standard deviation of 2 66deg

detection and estimation of equatorial spread f scintillations using synthetic aperture radar a significant amount of the data acquired by sun synchronous space borne low frequency synthetic aperture radars sars through the postsunset equatorial sector are distorted by the ionospheric scintillations due to the presence of plasma irregularities and their zonal and vertical drift in the focused sar images the distortions due to the postsunset equatorial ionospheric scintillations appear in the form of amplitude and or phase stripe patterns of high spatial frequency aligned to the projection of the geomagnetic field onto the sar image plane in this paper a methodology to estimate the height and the drift velocity of the scintillations from the stripe patterns detected in the sar images is proposed the analysis is based on the fact that the zonal and vertical drift of the plasma irregularities are at the equatorial zone perpendicular to the geomagnetic field which is almost parallel aligned to the orbit the methodology takes advantage of the time lapse and change of imaging geometry across azimuth subapertures the obtained height estimates agree well with the reference measurements and independent estimates reported in the literature while the drift velocities appear slightly overestimated this can be attributed to a suboptimum geometry configuration but also to a decoupling of the ambient ionosphere and the plasma irregularities

tectonosedimentary evolution related to extreme crustal thinning ahead of a propagating ocean example of the western pyrenees 1 in this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme crustal thinning in a transtensional setting ahead of a propagating ocean in the western pyrenees the labourd mauleon area situated in the western pyrenees at the termination of the v shaped bay of biscay is an ideal natural laboratory to study how such complex basins evolve in time and space because of a mild inversion of the basin during pyrenean compression the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field the basin shows a complex polyphase evolution that starts with left lateral dominated transtension in latest jurassic early aptian time this event is overprinted by a late aptian early albian extension that is related to the counterclockwise rotation of iberia away from europe leading to the opening of the bay of biscay during this stage the late triassic to jurassic carbonate platform was stretched salt migrated and detachment faults exhumed upper and lower crustal and mantle rocks to the seafloor the final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by n40 to n60 transfer faults the sedimentary architecture is characterized by late aptian synrift sediments e g urgonian limestones that were deposited in fault bounded basins and are overlain by thick latest aptian to albo cenomanian sediments e g flysch noir that define a sag sequence the complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic thermal event that postdates mantle exhumation

the deep seismic reflection marconi 3 profile role of extensional mesozoic structure during the pyrenean contractional deformation at the eastern part of the bay of biscay abstract the new marconi 3 deep seismic profile allows recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution it denotes that the easternmost part of the bay of biscay consists of a thick wedge of uppermost cretaceous to cenozoic synorogenic sediments lying unconformably on the top of a thinned continental crust with the mesozoic parentis basin to the north and the coeval landes high to the south the parentis basin appears as a major half graben bounded southwards by a north dipping planar fault it is filled by a thick sequence of jurassic upper cretaceous carbonates affected by salt domes and squeezed diapirs made up of triassic evaporites and mudstones these salt tectonic structures also affect the overlying uppermost cretaceous to lower miocene synorogenic deposits which are folded upon these structures the landes high includes a thin pre upper cretaceous cover tilted to the south in the basque shelf it is deformed by a basement involving thrust wedge emplaced during the late eocene miocene that constitutes the north pyrenean contractional front geometric relationships and thickness variations depict that this overall structure results from the following mesozoic extensional stage which includes a late jurassic late aptian syn rift stage in which the parentis basin formed and an albian early late cretaceous post rift stage in which diapirs of triassic evaporites grew close to this major fault compressive deformational stage coeval to the pyrenean orogeny which led to 1 the development of a latest cretaceous up to middle miocene foreland basin and 2 from late eocene the formation of a basement involving thrust wedge in the innermost foreland basin the squeezing of the diapiric structures formed previously in the parentis basin and later middle miocene the partial inversion of some pre existent faults located in the southern parentis basin margin this geodynamic evolution together with the structure of the area evidences that the extensional structure resulting from the opening of the bay of biscay played an important role both in the location of the north pyrenean front and in the north pyrenean foreland contractional deformation features specially the lack of significant inversion structures in the parentis basin despite that it belongs to a severely thinned crustal area before the alpine compression denotes that the mesozoic landes high acted as an important buffer for the propagation of the pyrenean contractional deformation to the north this deformational buffer was active until early miocene and probably vanished afterwards during the last stages of pyrenean orogen development when some basement faults reactivated in the parentis basin

three dimensional gravity and magnetic modeling of crustal indentation and wedging in the western pyrenees cantabrian mountains 1 the complex crustal structure of the boundary zone between the iberian and european plates from the western pyrenees to the cantabrian mountains is probed by three dimensional 3 d gravity and magnetic modeling constrained by deep seismic profiles the 3 d modeling results support the presence of a continuous iberian crustal root and suggest that the geometry of the orogenic belt that formed in latest cretaceous tertiary times along the northern margin of iberia was conditioned by oblique structures separating areas characterized by different tectonic styles in the western pyrenees and the basque cantabrian basin a thick mesozoic basin presently incorporated to the pyrenean cantabrian belt the relatively narrow thinning of the crust inherited from the mesozoic rifting stage conditioned a structural style in which portions of the southward indenting european lower crust are interpreted to be back thrusted toward the north and uplifted to shallow depths promoting the appearance of significant potential field anomalies in the basque cantabrian basin the strongest aeromagnetic anomaly of the whole iberian mainland is superimposed on the eastern part of a well defined positive gravity anomaly similar in amplitude and wavelength to those located along the north pyrenean zone these observations suggest that the eastern part of the dense lower crustal causative body is strongly magnetized and may correspond to a gabbroic cumulate originated in the axis of the ancient mesozoic rift to the west tertiary compression affected the north iberian cantabrian passive continental margin whose geometry and inherited structures conditioned the formation of a double crustal delamination and the uplift of the cantabrian mountains

the midcontinent rift in the lake superior region with emphasis on its geodynamic evolution abstract the midcontinent rift is a middle proterozoic continental rift which records about 15 m y of extension subsidence and voluminous volcanism in the period 1109 1094 ma in the central part of north america during that time the crust was nearly totally separated and as much as 25 km of subaerial basalts accumulated in a deep central depression following extension and volcanism a longer period of subsidence resulted in development of a post rift sedimentary basin in which as much a 8 km of fluvial and lacustrine clastic rocks were deposited partial inversion of the central depression occurred about 30 50 m y after extension to produce the current configuration of a central horst composed mostly of thick volcanic accumulations between shallower flanking basins

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

iberian plate kinematics a jumping plate boundary between eurasia and africa the rotation of iberia and its relation to the formation of the pyrenees has been difficult to decipher because of the lack of detailed sea floor spreading data although several models have been proposed1 7 here we use detailed aeromagnetic measurements from the sea floor offshore of the grand banks of newfoundland to show that iberia moved as part of the african plate from late cretaceous to mid eocene time with a plate boundary extending westward from the bay of biscay when motion along this boundary ceased a boundary linking extension in the king s trough to compression along the pyrenees came into existence finally since the late oligocene iberia has been part of the eurasian plate with the boundary between eurasia and africa situated along the azores gibraltar fracture zone

mantle flow through the northern cordilleran slab window revealed by volcanic geochemistry the northern cordilleran slab window formed beneath western canada concurrently with the opening of the californian slab window beneath the southwestern united states beginning in late oligocene miocene time a database of 3530 analyses from miocene holocene volcanoes along a 3500 km long transect from the northern cascade arc to the aleutian arc was used to investigate mantle conditions in the northern cordilleran slab window using geochemical ratios sensitive to tectonic affi nity such as nb zr we show that typical volcanic arc compositions in the cascade and aleutian systems derived from subduction hydrated mantle are separated by an extensive volcanic fi eld with intraplate compositions derived from relatively anhydrous mantle this chemically defi ned region of intraplate volcanism is spatially coincident with a geophysical model of the northern cordilleran slab window we suggest that opening of the slab window triggered upwelling of anhydrous mantle and displacement of the hydrous mantle wedge which had developed during extensive early cenozoic arc and backarc volcanism in western canada high heat fl ow throughout the western canadian cordillera is broadly coincident with the fi eld of intraplate volcanism and is linked to slab window induced mantle upwelling

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

performance analysis of l band geosynchronous sar imaging in the presence of ionospheric scintillation an l band geosynchronous synthetic aperture radar geo sar will be inevitably affected by ionosphere scintillation because of its low carrier frequency meanwhile compared with the low earth orbit leo sar a higher orbit of geo sar makes it have a longer integration time and a longer operation time within the susceptible regions of ionospheric scintillation thus its imaging is more sensitive to ionospheric scintillation and the corresponding degradation will have a different pattern however few works are focused on the quantitative analysis of the ionospheric scintillation impacts on l band sar moreover the parameters of ionospheric irregularities utilized in the analyses are hard to be determined in this paper we first deduced the azimuth point spread function with the consideration of both the amplitude and phase scintillation then based on the measurable statistical parameters of ionospheric scintillation performance specifications including azimuth resolution azimuth peak to sidelobe ratio pslr and azimuth integrated sidelobe ratio islr are obtained to fully evaluate the impacts the analysis suggests that in geo sar imaging the azimuth islr severely deteriorates whereas degradations of the azimuth resolution and pslr are negligible finally the simulations and a real ionospheric scintillation monitoring experiment by employing global positioning system satellites receivers were conducted verifying the conclusions that the serious degraded contrast and focus quality of the images are brought by the raised azimuth islr

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

on the tectonic origin of iberian topography the present day topography of the iberian peninsula can be considered as the result of the mesozoiccenozo ic tectonic evolution of the iberian plate including rifting and basin formation during the mesozoic and compression and mountain building processes at the borders and inner part of the plate during the tertiary followed by neogene rifting on the mediterranean side and surface processes acting during the quaternary the northern central part of iberia corresponding to the geological units of the duero basin the iberian chain and the central system shows a mean elevation close to one thousand meters above sea level in average some hundreds of meters higher than the southern half of the iberian plate this elevated area corresponds to i the top of sedimentation in tertiary terrestrial endorheic sedimentary basins paleogene and neogene and ii planation surfaces developed on paleozoic and mesozoic rocks of the mountain chains surrounding the tertiary sedimentary basins both types of surfaces can be found in continuity along the margins of some of the tertiary basins the bouguer anomaly map of the iberian peninsula indicates negative anomalies related to thickening of the continental crust correlations of elevation to crustal thickness and elevation to bouguer anomalies indicate that the dierent landscape units within the iberian plate can be ascribed to dierent patterns 1 the negative bouguer anomaly in the iberian plate shows a rough correlation with elevation the most important gravity anomalies being linked to the iberian chain 2 most part of the so called iberian meseta is linked to intermediate elevation areas with crustal thickening this pattern can be applied to the two main intraplate mountain chains iberian chain and central system 3 the main mountain chains pyrenees and betics show a direct correlation between crustal thickness and elevation with higher elevation crustal thickness ratio for the central systemvs the betics and the pyrenees other features of the iberian topography namely the longitudinal pro le of the main rivers in the iberian peninsula and the distribution of present day endorheic areas are consistent with the tertiary tectonic evolution and the change from an endorheic to an exorheic regime during the late neogene and the quaternary some of the problems involving the timing and development of the iberian meseta can be analysed considering the youngest reference level constituted by the shallow marine upper cretaceous limestones that indicates strong dierences induced by i the overall tertiary and recent compression in the iberian plate responsible for dierences in elevation of the reference level of more than 6 km between the mountain chains and the endorheic basins and ii the eect of neogene extension in the mediterranean margin responsible for lowering several thousands of meters toward the east and uplift of rift shoulders a part of the recent uplift within the iberian plate can be attributed o sostatic uplift in zones of crustal thickening

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

insar time series estimation of the ionospheric phase delay an extension of the split range spectrum technique repeat pass interferometric synthetic aperture radar insar observations may be significantly impacted by the propagation delay of the microwave signal through the ionosphere which is commonly referred to as ionospheric delay the dispersive character of the ionosphere at microwave frequencies allows one to estimate the ionospheric delay from insar data through a split range spectrum technique here we extend the existing split range spectrum technique to insar time series we present an algorithm for estimating a time series of ionospheric phase delay that is useful for correcting insar time series of ground surface displacement or for evaluating the spatial and temporal variations of the ionosphere s total electron content tec experimental results from stacks of l band sar data acquired by the alos 1 japanese satellite show significant ionospheric phase delay equivalent to 2 m of the temporal variation of insar time series along 445 km in chile a region at low latitudes where large tec variations are common the observed delay is significantly smaller with a maximum of 10 cm over 160 km in california the estimation and correction of ionospheric delay reduces the temporal variation of the insar time series to centimeter levels in chile the ionospheric delay correction of the insar time series reveals earthquake induced ground displacement which otherwise could not be detected a comparison with independent gps time series demonstrates an order of magnitude reduction in the root mean square difference between gps and insar after correcting for ionospheric delay the results show that the presented algorithm significantly improves the accuracy of insar time series and should become a routine component of insar time series analysis

the role of the bay of biscay mesozoic extensional structure in the configuration of the pyrenean orogen constraints from the marconi deep seismic reflection survey 1 seismic interpretation of the marconi deep seismic survey enables recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution the new data denotes that two domains with different pyrenean and north foreland structures exist in the bay of biscay in the eastern or basque parentis domain the north pyrenean front is located close to the spanish coast and the northern foreland of the pyrenees is constituted by a continental crust thinned by a north dipping fault that induced the formation of the early cretaceous parentis basin in the western or cantabrian domain the north pyrenean front is shifted to the north and deforms a narrower and deeper foreland basin which lies on the top of a transitional crust formed from the exhumation of lithospheric mantle along a south dipping extensional low angle fault during the early cretaceous the transition between these two domains corresponds to a soft transfer zone linking the shifted north pyrenean fronts and a north to wnw directed thrust that places the continental crust of the landes plateau over the transitional crust of the bay of biscay abyssal plain comparison between this structure and regional data enables characterization of the extensional rift system developed between iberia and eurasia during the late jurassic and cretaceous and recognizes that this rift system controlled not only the location and features of the pyrenean thrust sheets but also the overall structure of this orogen

archaean orogenic ultrapotassic magmatism an example from the southern abitibi greenstone belt the clericy pluton in the southern abitibi greenstone belt of quebec is a syenitic intrusion cross cut by nordmarkitic dykes it is probably one of the oldest known ultrapotassic intrusions about 2 7 ga it crystallized in a crustal environment under low ph20 2 5 kbar and low fo2 conditions most trace elements behaved as compatible elements suggesting that sphene and apatite were involved together with clinopyroxene during low pressure crystal fractionation the large range of initial isotopic ratios calculated for 2 68 ga nd 1 9 to 2 3 as well as the trace element distribution suggest that the syenitic pluton is the product of differentiation from a parental magma with a composition similar to that of timiskaming type archaean shoshonites contaminated by a crustal component on the other hand the nordmarkitic dykes are probably the result of crustal anatexis of metasedimentary rocks and some addition of the syenitic magma the clericy peralkaline syenite differs chemically from typical intraplate syenites in being saturated with respect to quartz and displaying lower ti and hfse contents it is related to an ultrapotassic volcano plutonic event which characterized the last 20 ma of igneous activity in the abitibi greenstone belt it may represent an increased rate of convergence of small heterogeneous plates during a subduction driven accretion tectonic event which possibly marked the culmination of the kenoran orogeny in the superior province of the canadian shield

a seismic geotraverse across the iberian variscides orogenic shortening collisional magmatism and orocline development 1 a crustal geotraverse through the iberian variscides is presented by integrating the available geological and seismic profiling data different modes of orogenic shortening are identified with varying degrees of coupling between upper and lower crust in northern and southern regions of the geotraverse a decoupling in the middle crust permits the lower crust to subduct underthrust thus compensating for strong upper crustal shortening this behavior does not result in great crustal thickening except in sectors of crustal underthrusting in southern central iberia moderate upper crustal shortening is due to a mechanically strong lower crust impeded to subduct underthrust in this region shortening is partitioned between upper and lower crust deformation being distributed in the upper crust while localized at major fault zones in the lower crust finally the central region of the geotraverse northern central iberia shows a coupled crustal deformation having given way to the largest orogenic thickening in the iberian variscides the thermal maturity of this much thickened crust originated voluminous crustal melting and concomitant normal fault detachments developed while shortening dominated in other regions theoretical models suggest that compressive stresses may prevail in the lower crust beneath the extending upper crust thus explaining the efficient syncollisional exhumation in this part of the orogen a particular feature of the iberian variscan geotraverse is the great importance of out of section mass movements mainly left lateral shear zones concentrated in two suture boundaries which displaced to the nw present coordinates central and northern iberia with respect to southern iberia

rift related inheritance in orogens a case study from the austroalpine nappes in central alps se switzerland and n italy the austroalpine nappe systems in se switzerland and n italy preserve remnants of the adriatic rifted margin based on new maps and cross sections we suggest that the complex structure of the campo grosina languard and bernina nappes is inherited largely from jurassic rifting we propose a classification of the austroalpine domain into upper middle and lower austroalpine nappes that is new because it is based primarily on the rift related jurassic structure and paleogeography of these nappes based on the alpine structures and pre alpine rift related geometry of the lower bernina and middle campo grosina languard austroalpine nappes we restore these nappes to their original positions along the former margin as a means of understanding the formation and emplacement of the nappes during initial reactivation of the alpine tethyan margin the campo and grosina languard nappes can be interpreted as remnants of a former necking zone that comprised pre rift upper and middle crust these nappes were juxtaposed with the mesozoic cover of the bernina nappe during jurassic rifting we find evidence for low angle detachment faults and extensional allochthons in the bernina nappe similar to those previously described in the err nappe and explain their role during subsequent reactivation our observations reveal a strong control of rift related structures during the subsequent alpine reactivation on all scales of the former distal margin two zones of intense deformation referred to as the albula zebru and lunghin mortirolo movement zones have been reactivated during alpine deformation and cannot be described as simple monophase faults or shear zones we propose a tectonic model for the austroalpine nappe systems that link inherited rift related structures with present day alpine structures in conclusion we believe that apart from the direct regional implications the results of this paper are of general interest in understanding the control of rift structures during reactivation of distal rifted margins

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

seismic image of the cantabrian mountains in the western extension of the pyrenees from integrated escin reflection and refraction data abstract integrated analysis of normal incidence and large aperture seismic reflection data collected in 1992 and 1993 within the spanish escin and complementary projects provide a first complete n s crustal transect across the northern iberian peninsula and continental margin images of the crustal structure of the cantabrian mountains and their transition to the duero basin and to the cantabrian margin are obtained from a a 65 km long vertical reflection profile escin 2 on land b a 200 km long reversed refraction profile and c wide angle recordings of the marine escin 4 profile consistent results between reflectivity pattern and velocity depth distribution reveal important lateral variations in the deep structure the reflective crust imaged in the escin 2 profile changes its attitude from sub horizontal beneath the duero basin to north dipping beyond the mountain front basement thrusts are observed in the upper crust merging into a detachment at 6 s twt and may have triggered the alpine uplift of the range the moho is identified at the bottom of the reflective lower crust and deepens from 12 to 15 s at the northern end of the profile about 35 km inland modelling of the refraction data laterally extends the seismic image and provides evidence for variscan crustal features beneath the duero basin northwards the velocity in the lower crust decreases and the moho constrained by the wide angle data from profile escin 2 deepens to about 60 km ending abruptly at the shoreline the velocity depth model is constrained along the asturian platform up to the continental slope where the crust mantle boundary is located at 24 km depth this margin moho shows a progressive deepening southwards and extends to the coast where it is found at 30 km depth the present seismic data support an important alpine reworking and thickening of the crust under the cantabrian mountains the onshore offshore transition is marked by an imbrication of two crusts of very different thicknesses this signature offers a strong parallelism with the one previously observed further east across the pyrenees in the ecors seismic profile

imaging the crustal structure of the central iberian zone variscan belt the alcudia deep seismic reflection transect alcudia is a 230 km long vertical incidence deep seismic reflection transect acquired in spring 2007 across the southern central iberian zone part of the pre mesozoic gondwana paleocontinent of the variscan orogen of spain the carefully designed acquisition parameters resulted in a 20 s twtt deep 60 90 fold high resolution seismic reflection transect the processed image shows a weakly reflective upper crust the scarce reflectivity matching structures identified at surface a thick highly reflective and laminated lower crust and a flat moho located at 10 s twtt 30 km depth the transect can be divided into three segments with different structural styles in the lower crust in the central segment the lower crust is imaged by regular horizontal and parallel reflectors whereas in the northern and southern segments it displays oblique reflectors interpreted as an important thrust north and tectonic wedging involving the mantle south the alcudia seismic image shows that in an intracontinental orogenic crust far from the suture zones the upper and lower crust may react differently to shortening in different sectors which is taken as evidence for decoupling the interpreted structures as deduced from surface geology and the seismic image show that deformation was distributed homogeneously in the upper crust whereas it was concentrated in wedge thrust structures at specific sectors in the lower crust the seismic image also shows the location of late variscan faults in spatial association with the lower crustal thickened areas

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

chronology of the peralkaline late cenozoic mount edziza volcanic complex northern british columbia canada the late cenozoic mount edziza volcanic complex covers an area of about 1 000 km 2 in north central british columbia 300 km east of the transcurrent boundary between the north american and pacific plates it is made up of a group of overlapping basaltic shields and intermediate to salic peralkaline composite domes flows and central volcanoes that are associated with extensional structures in the underlying basement new k ar and fission track dates 45 and rb sr and sr isotope analyses 12 from the mount edziza volcanic complex are reported the age dates are for the most part consistent with the stratigraphy and indicate that frequent eruptive activity occurred during the past 8 m y five major magmatic cycles each began with the eruption of basalt and culminated with the eruption of oversaturated peralkaline magma low 87 sr 86 sr initial ratios 0 7028 0 0001 indicate a mantle source for the basalts low sr contents and high 87 sr 86 sr ratios in the salic end members suggest that the oversaturated rocks were derived from the basaltic magma by crystal fractionation in crustal reservoirs rb sr isochrons suggest that residence times for the fractionating magma were about 0 7 to 1 m y early removal of large amounts of plagioclase followed by fractionation of potash feldspar can account for most of the observed petrological and isotopic relationships a few individual compositions and one suite of mainly intermediate samples contain anomalously large amounts of both 87 sr and radiogenic argon this indicates that contamination with crustal material and possibly mixing of parental basalt with partly fractionated magma from previous events may have produced the relatively small volume of intermediate rocks

ionospheric correction of insar time series analysis of c band sentinel 1 tops data the copernicus sentinel 1a b satellites operating at c band in terrain observation by progressive scans tops mode bring unprecedented opportunities for measuring large scale tectonic motions using interferometric synthetic aperture radar insar although the ionospheric effects are only about one sixteenth of those at l band the measurement accuracy might still be degraded by long wavelength signals due to the ionosphere we implement the range split spectrum method for correcting ionospheric effects in insar with c band sentinel 1 tops data we perform insar time series analysis and evaluate these ionospheric effects using data acquired on both ascending dusk side of the sentinel 1 dawn dusk orbit and descending dawn side tracks over representative midlatitude and low latitude geomagnetic latitude areas we find that the ionospheric effects are very strong for data acquired at low latitudes on ascending tracks for other cases ionospheric effects are not strong or even negligible the application of the range split spectrum method despite some implementation challenges largely removes ionospheric effects and thus improves the insar time series analysis results

differentiation of calc alkaline magmas evidence from the coquihalla volcanic complex british columbia abstract the coquihalla volcanic complex is part of the miocene calc alkaline pemberton volcanic belt whose formation in southwestern british columbia is associated with subduction of the juan de fuca plate the complex consists of voluminous rhyolitic ash flow tuffs cross cut by hypabyssal andesitic to dacitic intrusive bodies and a diorite stock whole rock compositions of members of the coquihalla volcanic complex show a range in silica from 54 to 76 wt volatile free uniform initial strontium isotopic ratios 0 7037 0 00008 argue against derivation of magmas by crustal melting or mixing of basaltic magmas with crustal material trace element concentrations of whole rocks cannot be modelled by varying degrees of partial melting of mantle material compositional variations among whole rocks and constituent phenocrysts form the basis for major element mass balance calculations which indicate that 1 hornblende dacites can be derived from basaltic andesites by 50 crystallization of a mixture of plagioclase hornblende clinopyroxene titanomagnetite and apatite and 2 rhyolites can be derived from dacites by roughly 45 crystallization of a mixture of plagioclase hornblende biotite titanomagnetite and apatite mineral liquid distribution coefficients for eight trace elements and the observed mineral assemblages plagioclase clinopyroxene hornblende titanomagnetite biotite apatite and zircon have been compiled in an appendix large uncertainties in these values have led to a reformulation of the rayleigh fractionation model so that an internally consistent set of distribution coefficients has been calculated for the proposed differentiation sequence

the madrid basin and the central system a tectonostratigraphic analysis from 2d seismic lines abstract data from deep boreholes seismic surveys and surface geology are used to reconstruct the sedimentary infilling of the cenozoic madrid basin eight main depositional sequences and seismic units are recognised from the paleogene the latter four of these sedimentary sequences were deposited in a continental environment under the influence of tectonic activity in the central system the toledo mountains the iberian chain and the sierra de altomira the sedimentary infill shows an overall coarsening upward trend from upper cretaceous formations to syn tectonic conglomerate deposits followed by a fining upward sequence and moderate reactivation of some faults during the late miocene pliocene the syn tectonic sediments are oligocene early miocene in age the foredeep is oriented northeast southwest and shows a sediment thickness of up to 3800 m in areas close to the central system several types of tectonic structures are recognised including imbricate thrust systems thrust triangle zones fault propagation folds back thrust systems and pop up structures the frontal thrusts were subjected to significant erosion and late miocene sediments onlap the anticlines of the onshore foreland nw se trending positive flower structures have been recognised in the eastern part of the basin the total northwest southeast shortening across the contact between the madrid basin and the central system is approximately 5 km of which 2 3 km occurred across the southern border thrust the simultaneous basement uplift of the central system and the tectonic escape of the sierra de altomira have been interpreted as a consequence of constrictive deformation within the pyrenean foreland of the iberian microplate

dnieper donets palaeorift abstract the devono carboniferous intra cratonic dnieper donets palaeorift transects the southwestern part of the east european platform in a nw se direction it is characterized by linear bounding faults penetrating much of the crust substantial crustal thinning and syn rift volcanic activity the dnieper donets rift developed on cold precambrian shield type continental crust its rifting stage spans early frasnian to late visean times during its post rift evolution an elongate saucer shaped basin subsided the axis of which coincides with the trace of the underlying rift the palaeozoic donets rift is superimposed on a late proterozoic rift a thermal perturbance of the asthenosphere is thought to have provided the driving mechanism for the development of the palaeozoic dnieper donets rift rapid thinning of the subcrustal lithosphere in response to advecting asthenospheric melt was coupled with tensional fracturing of the crust and melting of its lower part this caused an upward displacement of the moho discontinuity post rift subsidence of the dnieper donets graben was governed by lithospheric cooling the southeastern parts of this rift system were inverted during the uralian orogeny

impacts of ionospheric irregularities on l band geosynchronous synthetic aperture radar an l band geosynchronous synthetic aperture radar geo sar system has to be confronted by an intractable issue of the decorrelations imposed by ionospheric irregularities on the one hand the phase and amplitude scintillations will bring about the decorrelation within the synthetic aperture and result in azimuth imaging degradation on the other hand the imposed scintillation history is spatially decorrelated across the ultra large geo sar scene in this article a signal model of the geo sar acquisitionis established with the two way ionospheric transfer function itf modulation to incorporate these two types of decorrelations this model meanwhile takes the anisotropic and flowing irregularities into account by using this model the l band geo sar azimuth imaging is evaluated in terms of five indexes whose performances are dependent on nine ionospheric parameters furthermore the spatial correlation of the phase and intensity scintillation histories is investigated for the l band geo sar scene both in simulation and statistics the statistical result implies a sized scene in which the phase scintillation history tends to be consistent finally the interferometric performance is investigated between the pure and contaminated geo sar images the simulation result shows that the degradation of the interferometric coherence results from the in aperture decorrelation

initiation of an active margin at the north iberian continent ocean transition 1 the north iberian or cantabrian margin located at the southern flank of the bay of biscay underwent successive tectonic regimes of rifting passive margin and compression from mesozoic to tertiary times a complete crustal cross section of the north iberian margin from the abyssal plain to the shoreline and a reconstruction of its undeformed upper cretaceous structure are presented here it is constrained after the compilation and interpretation of different geophysical data sets recently available in the area the reflective pattern is provided by deep seismic reflection profile escin 4 complemented by commercial profiles and well information from the north iberian platform and the velocity depth control comes from an onshore offshore wide angle seismic profile tested also with gravity modeling the detailed cross section of the meso tertiary basins that fill the platform and abyssal plain shows structures from the three main tectonic events 1 normal faults and asymmetric basins from the permian to lower cretaceous extensional stage 2 upper cretaceous sediments deposited under stable conditions during the passive margin period and 3 inverted faults thrusts and folds related to the tertiary compression the deep structure of the crust beneath the margin is poorly constrained from escin 4 profile that shows reflectivity in the lower crust only at a small area under the platform however the corresponding wide angle experiment provides a conspicuous image of the moho that shows a continued deepening toward the continent on the basis of the geophysical results we propose a new model for this margin where the lower crust is detached and underthrusted to the south as a result of the partial closure of the bay of biscay an interpreted mesozoic crustal scale extensional detachment could be the weakness zone that allowed the lower crust to slide southward under the upper crust resulting in the indentation of the cantabrian margin lower crust into the iberian crust plate convergence stopped at an early stage making this a unique area to study the initial stages of deformation of a passive margin

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

crystal fractionation of the basalt comendite series of the mount edziza volcanic complex british columbia major and trace elements abstract the mount edziza volcanic complex in north central british columbia includes a group of overlapping basaltic shields salic composite volcanoes domes and small calderas that range in age from 7 5 ma to less than 2000 years b p the volcanic assemblage is chemically bimodal comprising voluminous alkali olivine basalt and hawaiite a salic suite of mainly peralkaline trachyte and comendite plus a relatively small volume of intermediate rocks trachybasalt tristanite mugearite benmoreite the complex is the product of five cycles of magmatic activity each of which began with alkali olivine basalt and culminated with the eruption of salic magma the regular chemical variation shown by almost 100 major and trace element analyses suggests a genetic lineage between the basic and salic members of each cycle least squares mathematical modelling indicates that the salic rocks trachyte and comendite have formed by fractionation of observed phenocryst and cumulate nodule mineral phases from a common alkali olivine basalt parent magma hawaiite is thought to be a cumulate rock formed by partial fractionation and feldspar accumulation within rising columns of primary alkali olivine basalt fractionation leading from alkali olivine basalt through trachybasalt and trachyte to comendite is believed to have taken place where primary basalt became trapped in large crustal reservoirs the early removal of olivine clinopyroxene and plagioclase leading to a trachytic residuum and subsequent fractionation of mainly alkali feldspar leading to the peralkaline end members is consistent with major and trace element variation and with isotopic and ree data the chemical diversity of the complex is attributed to its location over a zone of crustal extension where mantle derived basalt trapped in large high level reservoirs underwent prolonged fractionation

accuracy and resolution of alos interferometry vector deformation maps of the father s day intrusion at kilauea we assess the spatial resolution and phase noise of interferograms made from l band advanced land observing satellite alos synthetic aperture radar sar data and compare these results with corresponding c band measurements from european space agency remote sensing satellite ers based on cross spectral analysis of phase gradients we find that the spatial resolution of alos interferograms is 1 3times better than ers interferograms the phase noise of alos i e line of sight precision in the 100 5000 m wavelength band is 1 6times worse than ers 3 3 mm versus 2 1 mm in both cases the largest source of error is tropospheric phase delay vector deformation maps associated with the june 17 2007 father s day intrusion along the east rift zone of the kilauea volcano were recovered using just four alos sar images from two look directions comparisons with deformation vectors from 19 continuous gps sites show rms line of site precision of 14 mm and rms azimuth precision flight direction of 71 mm this azimuth precision is at least 4times better than the corresponding measurements made at c band phase coherence is high even in heavily vegetated areas in agreement with previous results this improved coherence combined with similar or better accuracy and resolution suggests that l band alos will outperform c band ers in the recovery of slow crustal deformation

evolution of an englacial volcanic ridge pillow ridge tindar mount edziza volcanic complex ncvp british columbia canada abstract glaciovolcanic deposits are critical for documenting the presence and thickness of terrestrial ice sheets and for testing hypotheses about inferred terrestrial ice volumes based on the marine record deposits formed by the coincidence of volcanism and ice at the mount edziza volcanic complex mevc in northern british columbia canada preserve an important record for documenting local and possibly regional ice dynamics pillow ridge located at the northwestern end of the mevc formed by ice confined fissure fed eruptions it comprises predominantly pillow lavas and volcanic breccias of alkaline basalt composition with subordinate finer grained volcaniclastic deposits and dykes the ridge is presently 4 km long 1000 m in maximum width and 600 m high fifteen syn and post eruptive lithofacies are recognized in excellent exposures along the glacially dissected western side of the ridge we recognize five lithofacies associations 1 poorly sorted tuff breccia and dykes 2 proximal pillow lava dykes and tuff breccia 3 distal pillow lava poorly sorted conglomerate and well sorted volcanic sandstone 4 interbedded tuff lapilli tuff and tuff breccia units and 5 heterolithic volcanogenic conglomerate and sandstone given the abundance of pillow lavas and the lack of surrounding topographic barriers capable of impounding water we agree with souther souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp that the bulk of the edifice formed while confined by ice but have found evidence for a more complex and variable eruption history than that which he proposed preliminary estimates of water ice depths derived from ftir analyses of h2o give ranges of 300 to 680 m assuming 0 ppm co2 and 857 to 1297 m assuming 25 ppm co2 variations in depth estimates among samples may indicate that water ice depths changed during the evolution of the ridge which is consistent with our interpretations for the origins of different lithofacies associations given that the age of the units are likely to be ca 0 9 ma souther j g 1992 the late cenozoic mount edziza volcanic complex geol soc can mem vol 420 320 pp pillow ridge may be the best documentation of a regional high stand of the cordilleran ice sheet cis in the middle pleistocene and an excellent example of the lithofacies and stratigraphic complexities produced by variations in water levels during a prolonged glaciovolcanic eruption

high resolution moho topography map beneath iberia and northern morocco from receiver function analysis abstract crustal thickness maps at regional scales are typically compiled using estimations inferred from different geophysical datasets providing a variable coverage of the investigated area consequently spurious effects related to changes in data resolution or artifacts in grid interpolation may affect significant zones of those maps the topoiberia iberarray broad band seismic network covering the iberian peninsula and northern morocco with stations distributed on a regular 60 60 km grid provides a unique opportunity to avoid such technical problems and to obtain a crustal thickness map derived from a same method sampling evenly all the region data from more than 340 stations has been gathered and analyzed using the p to s conversion phases at the moho discontinuity receiver functions the crustal thickness has been inferred applying the classical h stacking technique though in regions of complex crustal structure we have preferred to estimate the thickness directly from the arrival time of the converted phase at some sites the topography of the moho discontinuity is strongly correlated with tectonic processes the investigated area extending from the sahara platform to the bay of biscay has a great geodynamic diversity including north to south crustal imbrication in the pyrenean and cantabrian range a large and relatively undisturbed variscan massif in the center of iberia and areas of complex and still not completely understood geodynamics in the alboran crust domain and the atlas range the crustal thickness map reflects this diversity showing variations reaching 30 km between the thickest and thinnest zones of continental crust the final map has an overall similarity with previous estimations of the crustal thickness using independent data as those coming from more sparse deep seismic sounding profiles but provides further constraints at regional scale

intraplate deformation in the nw iberian chain mesozoic extension and tertiary contractional inversion the iberian chain developed within the iberian plate during the palaeogene and early miocene as a result of convergence between the african and eurasian plates it is a fold and thrust belt which involves the hercynian basement and the mesozoic and cenozoic cover a generalized cross section of the nw part of the chain of 195 km length is presented mesozoic basins developed on the hercynian basement display thickness variations across normal faults that bounded them and that can be recognized in the field the tertiary contraction deformed and inverted the mesozoic basins and it is inferred to have produced a thrust sheet about 5 km thick in its frontal northeastern part which thickens to the sw the total tertiary shortening in the section is 66 6 km 26 the structure and the crustal shortening and thickening of the iberian chain are explained by a major upper crustal thrust system with simple flat and ramp geometry which may branch to the pyrenees or the betics this is combined with internal deformation of the thrust sheet the contribution of the iberian chain shortening to the convergence of the african and eurasian plates during the tertiary is about one half of that of the pyrenees and should be taken into account in any reconstruction of the kinematics of these plates

centrifuge modelling of folding in high grade rocks during rifting centrifuge modelling is used to simulate the progressive development of structures in a simplified crustal profile during rifting this paper focuses on folding of ductile layers representing the middle to lower crust displacement along a pre existing cut in the layer representing mantle lithosphere creates a broad shear zone in overlying ductile layers and an asymmetric rift in upper layers the footwall of the mantle lithosphere layer and overlying shear zone are rotated to sub horizontal during rise of the basal ductile layer representing asthenosphere as an isostatic response to thinning in the extended model synthetic and antithetic faults develop in models with thicker ductile crustal layers although upper semi brittle layers representing upper crust constitute a simple fault bounded or sag basin the underlying ductile layers are complexly folded open upright folds developed over the crest of the footwall mantle lithosphere layer are tightened and increased in amplitude as they progressively rotate to a recumbent attitude refolding occurs during rise of the basal ductile material representing asthenosphere and from boudinage of overlying competent layers this study suggests that regional scale folds in some high grade terrains previously interpreted as evolving in a convergent margin tectonic setting may instead be produced as a result of flow of the ductile crust during rifting

quantitative assessment to the impact of insar ionospheric and tropospheric corrections on source parameter modelling application to the 4th nuclear test north korea

chronology chemistry and origin of trachytes from hualalai volcano hawaii 1 hualalai volcano is unique among hawaiian volcanoes in that it possesses a relatively high proportion of evolved trachytic lavas that were erupted at the beginning of the alkalic postshield phase of volcanism these evolved lavas yield insights into magma sources magma supply rates and the evolution of the subvolcanic magmatic plumbing system at this time trachyte lavas are exposed at the puu waawaa pumice dome and puu anahulu flow as blocks in maars on the south flank of the volcano and as flows in water wells drilled on the west flank of hualalai new 40ar 39ar dates show that the puu waawaa and puu anahulu complex is 114 ka a block from the waha pele maar is 103 ka and water well trachytes range from 107 to 92 ka in age indicating a range for trachyte volcanism of 20 ka nd and pb isotopic compositions overlap with younger alkalic basalts from hualalai but are distinct from hualalai tholeiitic basalts and pacific mid ocean ridge basalts linking the trachytes to alkalic parental magmas that underwent extensive crystallization to yield trachytic residual magmas both sr and o isotopic ratios are higher in the trachytes than in hualalai alkalic lavas which is best explained by reaction with or assimilation of altered hualalai shield basalts at shallow depth major trace element and isotopic variations between trachytes are consistent with their evolution by fractional crystallization from a puu anahulu parent the short time gap between the end of tholeiitic volcanism 133 ka and the onset of trachytic alkalic volcanism and the lack of deep origin xenoliths place the magma reservoir within which the trachytes evolved rapidly at shallow 7 km depth whereas mauna kea and kohala volcanoes produced small volumes of highly evolved lavas as magma supply rates dwindled through the postshield stage postshield magma intrusion rates at hualalai were lowest during trachyte formation and increased through a more recent period of alkalic basalt eruptions subtle rare earth element and radiogenic isotopic distinctions between trachytes from the three localities indicate that the roof of the shallow magma reservoir may have been irregular allowing some trachytes to evolve independently from others

post depositional fracturing and subsidence of pumice flow deposits lascar volcano chile unconsolidated pyroclastic flow deposits of the 1993 eruption of lascar volcano chile have with time become increasingly dissected by a network of deeply penetrating fractures the fracture network comprises orthogonal sets of decimeter wide linear voids that form a pseudo polygonal grid visible on the deposit surface in this work we combine shallow surface geophysical imaging tools with remote sensing observations and direct field measurements of the deposit to investigate these fractures and their underlying causal mechanisms based on ground penetrating radar images the fractures are observed to have propagated to depths of up to 10 m in addition orbiting radar interferometry shows that deposit subsidence of up to 1 cm year 1 occurred between 1993 and 1996 with continued subsidence occurring at a slower rate thereafter in situ measurements show that 1 m below the surface the 1993 deposits remain 5 c to 15 c hotter 18 years after emplacement than adjacent deposits based on the observed subsidence as well as estimated cooling rates the fractures are inferred to be the combined result of deaeration thermal contraction and sedimentary compaction in the months to years following deposition significant environmental factors including regional earthquakes in 1995 and 2007 accelerated settling at punctuated moments in time the spatially variable fracture pattern relates to surface slope and lithofacies variations as well as substrate lithology similar fractures have been reported in other ignimbrites but are generally exposed only in cross section and are often attributed to formation by external forces here we suggest that such interpretations should be invoked with caution and deformation including post emplacement subsidence and fracturing of loosely packed ash rich deposits in the months to years post emplacement is a process inherent in the settling of pyroclastic material

sequential faulting explains the asymmetry and extension discrepancy of conjugate margins rifted continental margins are the sites that record the thinning and break up of continents to form new oceans cesar ranero and marta perez gussinye use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this to crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy in which crustal thinning appears to be greater than the extension caused by brittle faulting by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins these authors use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this with crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy where crustal thinning seems to be greater than the extension caused by brittle faulting during early extension cold continental lithosphere thins and subsides creating rift basins if extension continues to final break up the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins although basins and margins are ubiquitous structures the deformation processes leading from moderately extended basins to highly stretched margins are unclear as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1 2 3 4 this extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2 but that does not readily explain the typical asymmetric structure of conjugate margins5 6 in cross section one margin displays gradual thinning accompanied by large faults and the conjugate margin displays abrupt thinning but smaller scale faulting5 whole crust detachments active from early in the rifting could in theory create both thinning and asymmetry1 but are mechanically problematical furthermore the extension discrepancy occurs at both conjugate margins leading to the apparent contradiction that both seem to be upper plates to a detachment fault7 8 alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic resolution faulting9 invisible deformation along top basement 100 km scale detachments8 or the structural complexity of cross cutting arrays of faults3 here we use depth migrated seismic images to accurately measure fault extension and compare it with crustal thinning the observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins contrary to current wisdom the observations support the idea that thinning is to a first degree explained by simple andersonian faulting that is unambiguously visible in seismic data

continental rift development in precambrian and phanerozoic europe europrobe and the dnieper donets rift and polish trough basins abstract upper crustal structure and lower crustal and mantle character of the european continental lithosphere differ significantly from west to east the processes of rifting of phanerozoic western europe s hotter thinner crust compared with the more stable thicker 45 vs 30 km proterozoic crust of the east european craton is being investigated by europrobe case studies of western and eastern european sedimentary basins the dnieper donets basin transects the southwestern part of the east european platform in a nw se direction lying between the ukrainian shield and the voronezh massif rifting took place from early frasnian until perhaps the late visean and was accompanied by major volcanic activity the distribution of both was affected by pre existing basement fault systems the syn and post rift sedimentary succession may be as thick as 20 km in the donets trough basin evolution and the present crustal geometry have been much affected by inversion during the permian in association with uralian orogenesis tectonic events of bathonian oxfordian 168 154 ma and turonian santonian 91 84 ma age are also recorded in the basin stratigraphy the polish trough lies along the boundary between the phanerozoic and proterozoic european crustal domains coincident with the trans european suture zone the presence of this rheological boundary may be paramount in structurally controlling the position of the trough tectonic subsidence analysis indicates an initial late rotliegendes early triassic syn rift phase of development subsequently episodes of increased tectonic subsidence rate occurred during the oxfordian tithonian 157 146 ma and beginning in the cenomanian 95 90 ma the oxfordian tithonian episode is likely the signature of a second extensional event correlated with intensification of rifting within the arctic north atlantic rift system while the cenomanian and later is a precursor to mild compressional intraplate orogenic movements present day crustal structure reflects the docking of phanerozoic crust against the proterozoic during palaeozoic orogenies permo carboniferous wrenching and transtensional modifications leading to formation of the polish trough as well as modifications during the late cretaceous early tertiary inversion process

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

the influence of equatorial scintillation on l band sar image quality and phase it is well known that many of the nighttime acquisitions of the l band advanced land observing satellite alos phased array type l band synthetic aperture radar palsar instrument over equatorial regions show significant distortions of the image amplitude information these distortions have the form of amplitude stripes that are roughly aligned with the local geomagnetic field while ionospheric scintillation has been identified as the source of these distortions the exact nature of the induced artifacts on synthetic aperture radar sar image quality and sar signal phase has not yet been studied in sufficient detail hence this paper provides a quantitative analysis of equatorial scintillation effects on sar image quality and sar phase we have performed a statistical analysis of alos palsar images over equatorial regions to describe the observed distortions and relate them to ionospheric parameters an ionospheric simulator was developed and validated that is capable of simulating ionospheric distortions based on ionospheric scintillation parameters using this simulator we found that ionospheric scintillation in the equatorial zone can cause significant distortions of sar image amplitudes image focus and sar signal phase we determined threshold ionospheric environmental conditions that lead to the formation of these image distortions based on these thresholds we quantified the likelihood of occurrence of ionospheric distortions for the global equatorial belt and for l band sensors alos palsar alos 2 palsar 2 and nasa isro sar nisar

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

distribution nature and origin of neogene quaternary magmatism in the northern cordilleran volcanic province canada the northern cordilleran volcanic province encompasses a broad area of neogene to quaternary volcanism in northwestern british columbia the yukon territory and adjacent eastern alaska volcanic rocks of the northern cordilleran volcanic province range in age from 20 ma to ca 200 yr b p and are dominantly alkali olivine basalt and hawaiite a variety of more strongly alkaline rock types not commonly found in the north american cordillera are locally abundant in the northern cordilleran volcanic province these include nephelinite basanite and peralkaline phonolite trachyte and comendite the most mgo rich nephelinites basanites and alkaline basalts from throughout the northern cordilleran volcanic province show trace element abundances and isotopic compositions that are consistent with an asthenospheric source region similar to that for average oceanic island basalt and for post 5 ma alkaline basalts from the basin and range our petrologic observations help constrain the origin of northern cordilleran volcanic province magmatism as well as lithosphere changes between the four major basement terranes that underlie the province results from phase equilibria calculations and the spatial distributions of volcanic rock types and magmatic inclusions are more consistent with the existence of thicker lithosphere beneath stikinia which underlies the southern part of the northern cordilleran volcanic province than beneath the cache creek and yukon tanana terranes which underlie the northern part of the northern cordilleran volcanic province our results support a model for initiation of northern cordilleran volcanic province magmatism due to incipient rifting of the northern cordillera driven by changes in relative plate motion between the pacific and north american plates ca 15 10 ma

3d architecture of a complex transcurrent rift system the example of the bay of biscay western pyrenees abstract the parentis and arzacq mauleon basins located in front of the v shaped oceanic propagator in the bay of biscay present evidence for extreme crustal thinning in this paper we investigate the 3d structure of these rift basins based on field observations and the interpretation of seismic data we compare these results with those obtained from two different and independent inversion methods first a 3d gravity inversion and second the standard euler deconvolution for the mauleon basin our results show that the positive gravimetric anomaly identified above its southern margin is the consequence of two shallower high density bodies that are separated by the pamplona fault and a deeper high density body the high density bodies can be explained by the presence of mid crustal and mantle rocks that were exhumed or uplifted at shallower depth during early cretaceous rifting before they were reworked and integrated to the pyrenean chain during compression phase also during this reactivation phase some slices of the exhumed mid crustal and mantle rocks were sheared off and were integrated in the present day thrust belt in the mauleon basin for the parentis basin we can demonstrate based on seismic data and gravimetric inversion methods a decrease in extension from west to east which is compatible with the v shape geometry of the overall basin along strike a change in the fault geometry from downward concave top basement detachment faults to upward concave high angle faults can be observed eastwards i e towards the termination of the basin a key structure controlling the evolution of the parentis basin is the east west trending ibis fault we interpret this fault to have initially formed as a strike slip fault before it was reactivated during later crustal thinning at present it forms the limit between an upper plate sag basin to the north and a lower plate sag basin floored at least locally by a top basement detachment faults to the south the strong asymmetry of the basin is supported by the shape of the basin and the results of standard euler deconvolution

mid crustal detachment in the betic system of southeast spain abstract the tertiary orogenic belts of eastern spain can be interpreted using the principles of thin skinned thrusting with a fundamental detachment at mid crustal level in the eastern betics the compression involves an oblique restacking of a stretched continental margin much of the shortening is transmitted on permian and triassic detachments which emerge as forward and back thrust duplexes an interpretation of the guadarrama range of central spain is presented in which significant shortening is shown on a mid crustal detachment propagating from the southeast it is suggested that this represents the external limit of a compressive system linked to the betics the pyrenees and eastern cantabrians are a separate tertiary compressive system again resulting from restacking of an extensional basin during the collision of iberia and france previous authors have proposed mid crustal detachment in the pyrenees observation of the geological map of the iberian ranges suggests a broadly similar structural origin may apply in which case the iberian ranges may represent the most external zone of a major pyrenean system again linked by a mid crustal detachment thus it is suggested that the whole of eastern spain is made up of two major compressive systems linked at mid crustal level

decorrelation of l band and c band interferometry over vegetated areas in california temporal decorrelation is one of the main limitations for recovering interseismic deformation along the san andreas fault system using interferometric synthetic aperture radar to assess the improved correlation properties of l band with respect to c band we analyzed l band advanced land observation satellite alos interferograms with a range of temporal and spatial baselines over three vegetated areas in california and compared them with corresponding c band european remote sensing satellite ers interferograms over the highly vegetated northern california forests in the coast range area alos remains remarkably well correlated over a 2 year period whereas an ers interferogram with a similar temporal and spatial baseline lost correlation in central california near parkfield we found a similar pattern in decorrelation behavior which enabled the recovery of a fault creep and a local uplifting signal at l band that was not apparent at c band in the imperial valley in southern california both alos and ers have low correlation over farmlands alos has lower correlation over some sandy surfaces than ers probably due to low signal to noise ratio in general l band interferograms with similar seasonal acquisitions have higher correlation than those with dissimilar season for both l and c band correlation over vegetated areas decreases with time for intervals less than 1 year and then remains relatively constant at longer time intervals the decorrelation time for l band is more than 2 years in the forest in california whereas that for c band is less than 6 months overall these results suggest that l band interferograms will reveal near fault interseismic deformation once sufficient data become available

the satah mountain and baldface mountain volcanic fields pleistocene hot spot volcanism in the anahim volcanic belt west central british columbia canada the satah mountain and baldface mountain volcanic fields smvf bmvf comprise more than three dozen small volcanic centers and erosional remnants thereof these fields are located in the chilcotin highland of west central british columbia canada and are spatially associated with the anahim volcanic belt avb a linear feature of alkaline to peralkaline plutonic and volcanic centers of miocene to holocene ages the avb has been postulated to be the track of a hot spot passing beneath the westward moving cordilleran lithosphere we test the avb hot spot model by applying whole rock 40ar 39ar geochronology n 24 and geochemistry whole rock chemical compositions of volcanic rock samples n 59 from these two fields suggest a strong geochemical affinity with the nearby itcha range shield volcano however smvf and bmvf centers are mostly small in volume 1 km3 and differ in composition from one another even where they are in close spatial proximity trace element and ree patterns of mafic avb lavas are similar to ocean island basalts oib suggesting a mantle source for these lavas the age ranges for the smvf n 11 2 21 to 1 43 ma and bmvf n 7 3 91 to 0 91 ma are largely coeval with the itcha range the distribution of volcanoes in these two volcanic fields is potentially consistent with the postulated avb hot spot track eruption rates in the smvf were high enough to build an elongated ridge that deviates from the e w trend of the avb by almost 90 this deviation might reflect the mechanisms and processes facilitating magma generation and ascent through the lithosphere in this tectonically complex region and may also indicate interaction of the potential hot spot with pre existing fracture systems in vicinity of the itcha range

lithospheric folding in iberia integration of stress indicator data gravity data crustal kinematics data and analysis of topography and recent vertical motions demonstrates the occurrence of consistently oriented spatial patterns of large scale alpine to recent intraplate deformation in iberia the inferred upper crustal and lithospheric deformation patterns and the timing of the associated expressions at or near the surface support the existence of a close coupling with plate boundary processes operating at the margins of iberia patterns of lithosphere and upper crustal folds are oriented perpendicular to the main axis of present day intraplate compression in iberia inferred from structural analysis of stress indicator data and focal mechanism solutions these findings suggest the presence of lithospheric folds with wavelengths compatible with theoretical predictions of folding wavelengths of variscan lithosphere stress induced intraplate deformation set up by plate interactions is compatible with indications for the absence of present day deep mantle lithosphere interactions inferred from seismic tomography

post eruptive alteration of silicic ignimbrites and lavas gran canaria canary islands strontium neodymium lead and oxygen isotopic evidence abstract isotopic analyses of miocene comenditic pantelleritic and trachyphonolitic ignimbrites and lavas from gran canaria canary islands provide evidence for posteruptive mobility of rb sr and o calculated initial 87 sr 86 sr ratios in whole rock samples from basaltic lavas and feldspar mineral separates from ignimbrites define a magmatic trend in the stratigraphic section from ratios of 0 70340 at the base of the mogan formation to 0 70305 in the lower fataga formation however calculated apparent initial 87 sr 86 sr ratios in hydrated vitrophyre and devitrified matrix separates range from 0 7035 to 0 7090 18o ratios in basalts and feldspars vary little from 5 7 to 6 1 yet range from 6 5 to 15 0 in the ignimbrite matrices in contrast to the sr and o isotope ratios pb and nd isotope ratios are identical within analytical error in feldspars and their silicic ignimbrite matrices sequential leaching experiments and the oxygen data suggest that low temperature posteruptive interaction with meteoric water perhaps containing a small seawater component has modified rb and sr concentrations in the matrices such that calculated apparent initial 87 sr 86 sr ratios are not those of the magmas when they were erupted mobilization of rb and sr must occur significantly after eruption nd and pb isotope systems appear to be unaffected by this process therefore 87 sr 86 sr ratios determined by whole rock analysis of silicic rocks from hotspottype oceanic islands are suspect and should not be incorporated into mantle tracer studies although analysis of phenocrysts may produce useful data

crustal structure beneath the iberian peninsula and surrounding waters a new compilation of deep seismic sounding results abstract we present here an updated compilation of crustal parameters beneath the iberian peninsula and surrounding waters inferred from extensive deep seismic exploration performed in the last three decades firstly the more relevant experiments developed in both terrestrial and marine domains are revisited together with the corresponding seismic velocity depth models published that reveal the characteristics of the different tectonic domains sampled including oceanic zones continental margins orogenic and rift belts the results are summarized in three crustal transects sketched along representative directions secondly we compiled the moho depths along all the available seismic profiles to produce a geo referred database this database has then been interpolated using kriging algorithms to obtain a continuous moho depth model in the form of a regular grid file this integrative moho map for a key area in the western mediterranean documenting the interaction between european and african plates can contribute to constrain further regional studies either at crustal lithospheric or mantle scales

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

some examples and mechanical aspects of continental lithospheric folding abstract recent theoretical and observational advances in understanding the dynamics of lithosphere processes have yielded strong evidence in favour of the existence of large scale lithosphere folds intraplate compressional stresses generated by plate tectonic forces can reach magnitudes that approach the plastic buckling strength of mechanical models of lithosphere with brittle ductile rheological stratification the models predict lower plastic buckling stresses for continental lithosphere than for oceanic lithosphere intraplate folding of relatively strong oceanic lithosphere documented extensively in the northeastern indian ocean occurs where stresses are concentrated by restricted geometric and dynamic conditions resulting in unusually high stress levels several hundreds mpa on continents where geophysical data suggest that lithosphere folding may have occurred during the development of sedimentary basins in northern canada and central australia buckling stresses can have magnitudes that are of a similar order to those thought typically to occur in the lithosphere several tens mpa folding of continental lithosphere although more difficult to document is likely to be an important mechanism of large scale continental deformation in particular thinned continental lithosphere with a history of superposition of thick sedimentary successions might be the preferential locus of such folding lithosphere folding could also be a controlling factor in the near surface deformation of rifted basins as reflected by tectonic basin inversion

crustal structure of an intraplate thrust belt the iberian chain revealed by wide angle seismic magnetotelluric soundings and gravity data abstract the iberian chain is a cenozoic intraplate thrust belt located within the iberian plate unlike other belts in the iberia peninsula the scarcity of geophysical studies in this area results in a number of unknowns about its crustal structure the iberian chain crust was investigated by means of a ne sw refraction wide angle reflection seismic transect and two magnetotelluric profiles across the chain oriented along the same direction the seismic profile was designed to sample the crust by means of three shots designed to obtain a reversed profile the resulting velocity depth model shows a moderate thickening of the crust toward the central part of the profile where crustal thickness reaches values above 40 km thinning toward de sw tajo and ne ebro foreland basins the crustal thickening is concentrated in the upper crust the seismic results are in overall agreement with regional trends of bouguer gravity anomaly and the main features of the seismic model were reproduced by gravity modeling the magnetotelluric data consist of 39 sites grouped into two profiles with periods ranging from 0 01 s to 1000 s dimensionality analyses show significant 3d effects in the resistivity structure and therefore we carried out a joint 3d inversion of the full impedance tensor and magnetic transfer functions the mesozoic and cenozoic basins along the chain are well characterized by shallow high conductive zones and low velocities elongated conductors reaching mid crustal depths evidence the presence of major faults dominating the crustal structure the results from the interpretation of these complementary geophysical data sets provided the first images of the crustal structure of the iberian chain they are consistent with a cenozoic shortening responsible of the upper crust thickening as well as of the uplift of the iberian chain and the generation of its present day topography

transpressional inversion in an extensional transfer zone the saltacaballos fault northern spain abstract this paper deals with an extensional transfer zone and its main structure the saltacaballos fault developed during early cretaceous times and obliquely inverted during the alpine shortening geological mapping and structural analysis were carried out to determine the kinematic history of the deformation the saltacaballos ridge is the relay zone between two major and conjugate normal fault systems the bilbao and the la granja samano fault systems three distinct phases in the structural evolution of this transfer zone can be identified 1 during the initial stages of extensional deformation shallow water marine limestones were deposited on the relay ridge and deep water marls on the flanking depocenters at the same time submarine landslides developed on paleoslope generated either by normal drag or by a fault propagation fold related to the saltacaballos normal fault 2 with increasing displacement normal faults antithetic to the saltacaballos fault were developed probably in response to the collapse of its hanging wall 3 during the subsequent alpine compressional stage these normal faults were reactivated as dextral strike slip faults as a result of transpressional inversion whereas previous extensional fault related folds were tightened at the same time some normal faults were overturned as a consequence of passive rotation in fold limbs

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

some remarks on the origin of foredeeps abstract geological observations show that there are two main types of foredeep basins on the base of their subsidence rate and their relationship with the associated orogen or accretionary wedge high rates of subsidence up to 1600 m myr and a ratio lower than 1 between the area of the elevated belt and the area of the basin characterize the foredeeps associated with w dipping subduction low rates of subsidence up to 300 m myr and a ratio higher than 1 between the area of the orogen and the area of the basin characterize the foredeeps associated with e or ne dipping subductions this observation enables us to interpret the slow filling of foredeeps of the first type and the much faster filling of foredeeps of the second type moreover w dipping subductions have a steeper and faster monocline bounding the base of the deep foredeep in contrast to e or ne dipping subductions which have a shallower monocline this differentiation supports the notion of the eastward mantle flow with respect to the lithosphere detected in the hot spot reference frame in this view the foredeep depth in w dipping subductions is mainly controlled by the roll back of the subduction hinge pushed by the relative eastward mantle flow while foredeep depth in e or ne dipping subductions is instead mainly generated by the load of the thrust sheets and by the roll back of the subduction hinge due to the advancing upper plate contrasting the upward push of the mantle the shape of the foredeeps is regularly arcuate in case of w dipping subduction while is linear or following the shape of the inherited continental margin in case of e or ne dipping subduction fold development in the two opposite foredeeps is significantly different in w dipping subduction the folds are transported down in subduction while they are forming and consequently they are poorly eroded syntectonic sediments drape a preserved fold in the e ne dipping subduction folds and thrust sheets are instead uplifted and deeply eroded this is also predicted by the envelope of the crests in the two distinct accretionary wedges in the w dipping case the envelope may dip toward the subduction while it is rising toward the hinterland in the other cases this approach may explain the differences in terms of geometries amount and rates of subsidence between the foredeeps around the adriatic plate for instance the foredeep of the southern alps back thrust belt foredeep is deformed in the western part by the later apenninic foredeep development associated with the sinistral oblique ramp of the w dipping adriatic plate subduction the relationship in the frontal parts of a thrust belt between accretion and eustacy has to be analyzed in terms of when where and how fast thrusts propagation took place with respect to the randomly distributed sea level third order fluctuations and by the type of subduction which is connected to the foredeep and thrust belt or accretionary wedge therefore the stratigraphic patterns in foredeep basins are peculiar and casual successions that record the combination of regional tectonic evolution with independent wider scale sea level changes

cenozoic right lateral wrench tectonics in the western pyrenees spain the ubierna fault system abstract a study of macro and mesostructural deformation patterns of the southern margin of the cantabrian area western pyrenees spain has revealed a complex cenozoic tectonic framework right lateral tectonics reactivated inherited wnw ese striking faults which developed during late paleozoic and early triassic events and late jurassic to early cretaceous main rifting stage the ubierna fault represents the southern boundary of the mesozoic basin during the oligocene even eocene to present day deformation this fault and the ventaniella fault located to the south in the study area acted as right lateral slightly transpressive elements forming a 120 km long and 15 km wide overstep area here named ubierna fault system where the cumulative right lateral displacement exceeds 15 km the cenozoic tectonic framework of the ubierna fault system includes reactivation along the wnw ese faults development of negative and mostly positive flower structures branch faults strike slip duplexes and releasing and restraining bends ne sw to ene wsw striking reverse faults and contractional horsetail terminations and nnw sse striking normal faults and joints are produced by the wnw ese right lateral strike slip motion the extensional elements are well developed and deformation progression implied their incorporation in the strike slip system as right lateral faults forming part of strike slip duplexes the abundance of flower structures striking wnw ese and paralleling the main strike slip faults together with the overall uplift of the overstep area testifies for a slight compressional component at a regional scale the ubierna fault system represents the most prominent element of a cenozoic transpressional belt which incorporates the western portion of the basque cantabrian basin and the asturian massif area lateral transition between this transpressive belt and the dip slip belt located to the east occurs across an area experiencing along strike shortening which developed to accommodate the eastward extrusion of the transpressional belt

extensional subsidence contractional folding and thrust inversion of the eastern cameros basin northern spain tectonic analysis of the cameros massif northern spain demonstrates the need to integrate detailed structural analysis with stratigraphic studies in order to understand the development of inverted basins the cameros massif underwent three major tectonic events each characterized by different mechanisms of deformation the first event tithonian early albian manifested as continental rifting and formation of the cameros basin and was attended by normal faulting and related folding of pre and syn rift sedimentary sequences up to 9 km thick it corresponded to the beginning of rifting and opening of the bay of biscay to the north of the massif the second event occurred at the end of the early cretaceous the basin underwent contraction manifested as gentle folds containing axial plane cleavage this contraction was due to the migration of the center of rifting away from the basin and toward the northeast and correlates with the onset of oceanic spreading in the bay of biscay deformation happened during a low grade metamorphism period that reached its thermal peak after folding and cleavage formation 90 100 ma the final stage of deformation eocene miocene following a structurally quiescent period of approximately 40 ma occurred during the convergence collision between iberia and europe it formed contractional folds related to large e w striking overthrusts the mesozoic basin was inverted and transported 25 km toward the north during this stage both unfolding and tightening of the former folds occurred as determined from analysis of cleavage orientation associated with the previous shortening

seismic evidence of alpine crustal thickening and wedging from the western pyrenees to the cantabrian mountains north iberia 1 the alpine collision between the iberian and european plates resulted in a complex crustal structure beneath the northern iberian peninsula as revealed from a new set of seismic refraction wide angle reflection profiles the study area is characterized by two major e w ranges the cantabrian mountains and the pyrenees which are relayed to the south by the iberian chain important variations in crustal thickness and velocity distribution are found in a 560 km long e w transect in contrast to the typical 30 to 32 km thick european variscan crust of the western end of the profile a continuous alpine crustal root is evidenced from the cantabrian mountains to the central pyrenees with a moho depth of 46 48 km locally rising to 40 km depth in between beneath the basque cantabrian basin another outstanding feature is the inferred presence of high velocities of 6 40 6 75 km s at midcrustal depths which can be associated with portions of a lower crustal wedge from the northern european domain indenting the southern iberian crust during the alpine stage of compression this indentation produces the delamination of the iberian crust with northward underthrusting of its lower half and the consequent crustal thickening the indenting wedge has a discontinuous presence along the longitudinal section as it was controlled and or affected by n s to ne sw structures further evidence of the northward subduction of the iberian plate is provided by another profile toward the aquitaine basin while a n s profile across the iberian chain reveals an alpine midcrustal thickening beneath this belt with moho depths of 42 km

a 2 5 d interpretation of the basque country magnetic anomaly northern spain geodynamical implications the basque country magnetic anomaly follows a nw se trend over the basque country northern spain with intensities up to 250 nt measured at 3000 m above sea level the paired negative part of the anomaly is located to the north and presents intensities down to 60 nt a model of the magnetic properties of the crust in the area taking into account previous geological and geophysical data indicates a wedge of material with a magnetic susceptibility of 0 07 si emplaced along a ne directed basal thrust the anomalous wedge is composed of basic and or ultrabasic cretaceous intrusives and lower crustal rocks and reaches a minimum depth which increases towards the northwest from 5 7 to 12 km according to previous works geological features of the rocks on top of the anomalous wedge indicate that during the cretaceous this zone constituted a deep marine environment which underwent important crustal thinning related to rifting the transition towards the southwest was to a normal continental platform alpine deformation gave rise to displacement on a basal thrust which can be correlated with the lower contact of the magnetic wedge and emplacement of this wedge towards the northeast the southeastern termination of the anomaly can be related to the lateral termination of the basic rocks which constitute the anomalous wedge in a transform fault related to the rifting event

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined