comment on identification of an underfilled foreland basin system in the upper devonian of the central pyrenees implications for the hercynian orogeny by souquet et al international journal of earth sciences 92 316 337 2003

middle jurassic shear zones at cap de creus eastern pyrenees spain a record of pre drift extension of the piemonte ligurian ocean the cap de creus peninsula in ne spain consists of greenschist to amphibolite facies metasediments and granitoid bodies of the variscan axial zone of the pyrenees overprinted in the north by anastomosed greenschist facies shear zones current tectonic interpretations ascribe these shear zones to the waning stages of the variscan orogeny we present muscovite 40ar 39ar data from the shear zones yielding middle jurassic ages between 159 33 0 43 and 175 18 1 10 ma and one tertiary age of 58 57 0 55 ma we suggest that the present day structure at cap de creus resulted from variscan deformation and ht lp metamorphism followed during the jurassic by crustal stretching and development of ductile normal faults reflecting pre drift continental extension related to opening of the piemonte ligurian basin east of iberia tilting during alpine convergence caused steepening in the northern part of the penisula with the ductile normal faults rotated to their present orientations appearing as dextral reverse shear zones the shear zone yielding a tertiary age could reflect either an alpine structure or reactivation of an earlier presumably jurassic shear zone the cap de creus structure may thus represent a continental margin that has undergone ductile stretching equivalent to the now buried west iberian or newfoundland margin

from granulites to eclogites in the sesia zone italian western alps a record of the opening and closure of the piedmont ocean the sesia zone italian western alps offers one of the best preserved examples of pre alpine basement reactivated under eclogite facies conditions during the alpine orogenesis a detailed mineralogical study of eclogitized acid and basic granulites and related amphibolites is presented in these rare weak to undeformed rocks microstructural investigations allow three main metamorphic stages to be distinguished a a medium to low p granulite stage giving rise to the development of orthopyroxene garnet plagioclase brown amphibole ilmenite biotite in basic granulites and garnet k feldspar plagioclase cordierite sillimanite biotite ilmenite in acid granulites b a post granulite re equilibration associated with the development of shear zones producing discrete amphibolitization of the basic granulites and widespread development of biotite sillimanite cordierite spinel in the acid rocks c an eo alpine eclogite stage giving rise to the crystallization of high p and low t assemblages in an effort to quantify this evolution independent well calibrated thermobarometers were applied to basic and acid rocks for the granulite event p t estimates are 7 9 kbar and 700 800 c and for subsequent retrograde evolution p t was 4 5 kbar and 600 c for the eo alpine eclogite metamorphism pressure and temperature conditions were 14 16 kbar and 550 c the inferred p t path is consistent with an uplift of continental crust produced by crustal thinning prior to the subduction of the continental rocks in the light of the available geochronological constraints we propose to relate the pre alpine granulite and post granulite retrograde evolution to the permo jurassic extensional regime the complex granulite eclogite transition is thus regarded as a record of the opening and of the closure of the piedmont ocean

permian magmatism and basin dynamics in the southern pyrenees a record of the transition from late variscan transtension to early alpine extension

hercynian structure of the axial zone of the pyrenees the aran valley cross section spain france abstract in the axial zone of the pyrenees palaeozoic rocks crop out with superimposed hercynian and alpine deformation the hercynian structures present two domains infrastructure and suprastructure a complete crosssection of the central part of the axial zone of the pyrenees is presented in which hercynian structures of both domains can be observed in the aran valley cross section the infrastucture corresponds to the garona dome domain where the main hercynian structures are north vergent recumbent folds with an associated mainly flatlying foliation s 2 in the garona dome domain the peak of the medium to high grade metamorphism is simultaneous with the main hercynian structures the aran valley and noguera ribagorca areas correspond to the suprastructure in these domains the main hercynian structures are upright folds with an associated mainly steep lying foliation s 3 in these suprastructural domains low grade syn s 3 metamorphism is present this crosssection relates the structures of the infra and the suprastructure suggesting a deformational sequence for the axial zone of the pyrenees this sequence is deduced from the fact that the north vergent folds observed in the garona dome are earlier than the main structures of the suprastructure the boundary of the garona dome and the suprastructure is a decollement level observed at the base of the silurian the deformational sequence proposed here provides some constraints for models of hercynian evolution and the emplacement of the alpine structures of the pyrenees

late to post collisional brittle ductile deformation in the himalayan orogen evidences from structural studies in the lesser himalayan crystallines kumaon himalaya india abstract the chiplakot crystalline belt ccb is a broad shear zone located within the meta sedimentary zone of the lesser himalaya evidence from mesostructures and microstructures reveals development of this shear zone in a compressional ductile tectonic regime during continental collision in the himalaya by top to sw shearing along ne dipping shear surfaces the shear surfaces are parallel to both the upper and basal thrust planes of the ccb a hitherto unrecognized late to post collisional brittle ductile tectonic regime comprised of two discrete phases is established from dynamic analysis of the kink bands extensional shear fractures foliation boudinage competent layer boudinage quartz veins and associated flanking folds and brittle normal and reverse faults in the ccb kink bands foliation parallel slip and general shear were major consequences of this late to post collisional brittle ductile tectonic episode and were associated with the intrusion of a swarm of quartz veins quartz veins associated with flanking folds are developed at high angles with respect to the mylonitic foliation and parallel to the axial plane of the kink bands throughout the ccb the geometry of the flanking folds along the quartz veins is a consequence of the fracturing and not vice versa the precise shape of the folds depends on the nature of general shearing along the wall of quartz veins and various orientations to the shear direction

identification of an underfilled foreland basin system in the upper devonian of the central pyrenees implications for the hercynian orogeny a foreland basin succession has been identified in the frasnian of the central pyrenees this succession comprises a carbonate dominated transgressive system which recorded the cratonward migration of the foreland basin subsidence and siliciclastic depocenters which recorded the progression of the thrust fold deformation the foreland basin system has always been maintained in deep marine environments i e at an underfilled depositional state it was associated with a thrust wedge which descended toward a deep marine hinterland i e with a type of orogenic wedge usually related to subduction zones the frasnian foreland basin system differs from the one known in the carboniferous which evolved to overfilled depositional state and was associated with a thrust wedge rising toward a mountainous hinterland consequently the hercynian orogeny in the pyrenees seems to result first from a frasnian thrusting controlled by a subduction zone located north of the pyrenees and second from a carboniferous thrusting controlled by the surrection of a frontal thrust belt in the pyrenees the association of underfilled foreland basin systems and hinterland dipping thrust wedges as exemplified in the frasnian of the pyrenees can be interpreted as illustrative of the initial stages of thrust wedge growth in deep marine settings

hercynian tectonics in the pyrenees a new view based on structural observations around the bassie s granite pluton abstract the structural study of the metasedimentary rocks surrounding the bassie s granite pluton allows definition of the succession and kinematics of the hercynian tectonic events in this part of the pyrenees and supports a model of syntectonic emplacement of the pluton the following sequence of events has been identified i an early phase of n s compression essentially resulting in southwards thrusting ii emplacement of the granite body along a ne sw sinistral strike slip shear zone which could be a late effect of the first phase iii a major dextral and transpressive phase responsible for themain fold structures trending on average n100 and following a sigmoidal pattern around the granite body this succession of events and their kinematics could be extended to the whole hercynian basement of the pyrenees

tectonic levels in the palaeozoic basement of the pyrenees a review and a new interpretation reply abstract two different structural domains developed during the main hercynian deformation events were recognized by de sitter zwart in the hercynian basement of the central pyrenees a deep seated level infrastructure made of medium to high grade metasediments and orthogneisses with dome shaped gently dipping foliations contrasts with a shallow level suprastructure of low to very low grade metasediments with rather steep foliations since the recognition of this structural zonation different interpretations have been proposed disagreements concern timing of deformation and tectonic regime considered to be prevalent of the structural development of each tectonic level the proposed interpretation regards the progressive development and differentiation of both structural domains and considers the following factors to be significant for the structural arrangement of the pyrenean segment of the hercynian belt an increase with depth of the horizontal shear component of deformation related to tangential and transcurrent tectonics a marked inhomogeneity of deformation and penetrability of related foliations and the gradual evolution from an earlier compressive crustal shortening event to a late transpressive event responsible for crustal shortening and trend parallel stretching

permian granites in the pyrenees the aya pluton basque country we show that the permian volcanism in the pyrenees was accompanied with emplacement of granite plutons with transitional chemistry reassessment of age structure and petrological characteristics of the aya pluton intrusive in the cinco villas massif basque country indicates that it was emplaced at 267 1 1 1 ma in a dextral transtensive context and that it marks a transition between the high k calcalkaline and the alkaline emissions of the first and second permian volcanic cycles respectively this age is close to that of c 267 ma reported for lamprophyres dykes of the pyrenean axial zone these data characterize a period of transition between the variscan orogeny and the subsequent alpine cycle in the pyrenees with an earlier extensive regime that became widespread in the pyrenees during the mesozoic times

probabilistic description of topographic slope and aspect 1 local topographic features such as slope and aspect play a crucial role in a number of morphological ecological and hydrological processes we propose a simple yet realistic probabilistic description of local slope and aspect as a function of properties of the field of elevation changes we consider different classes of models of elevation changes and obtain the theoretical distribution of slope and aspect we relate the features of the obtained distributions to large scale landscape structures such as regional trends and anisotropy we find that the theoretical distribution of slope is strongly impacted by the parameters used to represent the distribution of elevation changes while large scale features play a secondary role conversely the distribution of aspect is also controlled by regional trends and anisotopy even when they are weak the proposed statistical description of slope and aspect is applied to assess the effects of topographic features on direct solar radiation mean and standard deviation the main control on direct solar radiation is exerted by the partial derivative variance we consider four different landscapes across the continental united states and compare the proposed theoretical description of slope and aspect distributions to the observed histograms

the biotite isograd central pyrenees a deformation controlled reaction the biotite isograd reaction in cambro ordovician pelites from the garonne dome in the central pyrenees involves the production of biotite at the expense of chlorite and the gradual reduction in the celadonite si content of individual white micas the mineral assemblages in the biotite bearing rocks in the melles area retain abundant evidence of chemical disequilibrium due to the sluggish nature of major element diffusion within the white micas the progress of the isograd reaction is strongly controlled by the progressive development of regional variscan fabrics and chemical exchange in the white micas in these metamorphic conditions is only possible during active deformation chemical resetting of the white micas takes place via the development of compositional zoning in the deforming micas this probably occurs as a consequence of the introduction of defects and dislocations causing more efficient diffusion within parts of individual grains in the absence of deformation this biotite isograd reaction would take place at significantly higher temperature and be controlled by the relatively high closure temperature of major element diffusion in white micas thus assigning thermal significance to such continuous isograd reactions is impossible without independent constraints kinetic factors such as deformation may be the dominant influence in many cases not the thermodynamic controls

petrological arguments for high temperature extensional deformation in the pyrenean variscan crust saint barthelemy massif ariege france abstract the saint barthelemy massif is one of the variscan massifs of the north pyrenean zone thermobarometric analysis has been completed across a sequence comprising from bottom to top basal granulitic gneisses the main mylonite band and migmatites pt estimates are correlated with textures which represent progressive stages of gneissification and mylonitization the main foliation and the mylonitic textures were developed during the retrogressive evolution of the lp ht granulitic metamorphism retrogressive conditions are characterized by high heat flow associated with a pressure reduction the main penetrative deformation of the saint barthelemy massif is interpreted as resulting from a continuous extensional event

kinematics of orogenic collapse in the variscan pyrenees deduced from microstructures in porphyroblastic rocks from the lys caillaouas massif in the pyrenees a phase of bulk vertical shortening d3 is indicated by a horizontal crenulation cleavage s3 which is developed in a pre existing schistosity s2 porphyroblasts of the lys caillaouas massif regionally preserve 1 1 the initial pre d3 orientation of s2 in the form of a vertical and e w trending preferred orientation of their inclusion trails 2 2 a vertical l2 stretching lineation defined by the elongation of the inclusions these data are consistent with n s compression and crustal thickening during d2 the angle between the inclusion trails s2 i and the external schistosity s2 e records the subsequent rotation of s2 from vertical to gently dipping orientations at higher crustal levels s2 remained steep suprastructure and little d3 deformation is evidenced with depth d3 deformation progressively intensifies and zones can be distinguished with opposite dip directions of s2 opposite apparent porphyroblast rotation senses and opposite f3 crenulation asymmetries these micro structures on a n s section through the lys caillaouas and the garonne dome massifs record a regional partitioning of bulk coaxial vertical shortening this deformation partitioning was probably controlled by a not exposed gneiss dome which behaved relatively rigid as compared to its metasedimentary cover in zones of non coaxial d3 deformation s2 was extended reactivated and forms the dominant schistosity where d3 was locally more coaxial s2 was shortened isoclinally crenulated and s3 forms the macroscopic cleavage the fact that d3 extension in the lys caillaouas massif immediately followed d2 compression and that similar extension is recorded in large parts of the variscan foldbelt suggests gravitational collapse of a thickened orogen this is consistent with the flattening type of d3 strain recognized in a number of pyrenean variscan massifs peak high t low p metamorphic conditions coincide with the onset of orogenic extension when very little crustal thinning could have been accomplished yet this suggests that heat induced strain softening within the orogen may have triggered its collapse

porphyroblast non rotation during crustal extension in the variscan lys caillaouas massif pyrenees abstract the dominant foliation s 2 in the variscan lys caillaouas massif central pyrenees france spain formed in a subvertical orientation during crustal thickening d 2 subsequent non coaxial crustal extension produced a subhorizontal crenulation cleavage s 3 whereby s 2 was folded and rotated andalusite staurolite cordierite and biotite porphyroblasts grew very early during this extension d 3 and included s 2 as straight curved and weakly crenulated inclusion trails these inclusion trails exhibit a strong subvertical preferred orientation which is independent of the local magnitude of d 3 strain the dip angle of the external main foliation s 2 or the aspect ratio and shape orientation of porphyroblasts this indicates that porphyroblasts did not rotate in the d 3 deformation field and hence preserve the orientation of s 2 at the time it was trapped in the porphyroblast relative to the bulk d 3 flow plane porphyroblasts could maintain a stable orientation in the d 3 flow due to complete accommodation of the bulk flow vorticity by heterogeneous shear strain the lack of vorticity of local volumes of zero shear strain such as porphyroblasts was balanced by concentration of shear strain in planar zones anastomosing around them it is likely that s 2 maintained a subhorizontal orientation throughout the d 3 crustal extension which would imply that porphyroblasts also remained stationary relative to the earth s surface during d 3 whereas s 2 in the deforming matrix experienced shear induced rotation a late brittle ductile folding event d 4 involving differential rigid block rotations dispersed the orientation of inclusion trails to some degree these late rotations could be corrected for by artificial unfolding of the f 4 folds

multi scale strainfield analysis using geostatistics investigating the rheological behavior of the hot variscan crust of the pyrenees axial zone the present study provides a quantitative way to analyze and interpolate strainfields from ductile fabric field measurements using geostatistics based on variogram analysis and kriging interpolations the developed methodology allows computing automatic cleavage and lineation trajectory maps at different scales from a same field structural dataset for the example provided by the hot variscan crust of the pyrenees the analysis of cleavage stretching lineations orientation and kinematic data document pure shear conditions recorded during convergence strain was vertically partitioned between an upper crust submitted to homogeneous thickening responding to n s orogen normal shortening and a hot and partially molten mid lower crust affected by horizontal longitudinal orogen parallel flow the emplacement of plutons and gneiss domes generated heterogeneities in the upper crust and induced strain localization into steep anastomosed transpressional shear zones flanking those structures the results show that geostatistics applied to structural geology are powerful tools for retrieving tectonic regimes of large orogenic segments by identifying and quantifying perturbations in the strainfields induced by protracted and potentially complex tectonic histories the variogram analysis also gives first order clues to evaluate whether the considered structural domains underwent single continuous ductile or polyphased brittle ductile deformation

tectonic evolution of the rehamna metamorphic dome morocco in the context of the alleghanian variscan orogeny structural and 40ar 39ar geochronological investigations of the rehamna massif meseta moroccan variscan belt provide new constraints on the tectonic evolution of the alleghanian variscan orogen during the upper paleozoic three main tectonic events have been recognized 1 southward thrusting of an ordovician sequence over the proterozoic basement its cambrian sedimentary cover and the overlying devono carboniferous basin this event caused subhorizontal shearing and prograde barrovian metamorphism of the buried rocks 2 continuous shortening resulting in the development of a synconvergent extrusion of metamorphosed units to form a dome elongated e w this was responsible for synconvergent detachment of the ordovician upper crustal sequence the timing of these two episodes is constrained to 310 295 ma by cooling and metamorphic amphibole and mica ages 3 a nw wnw convergence in a direction orthogonal to the previous one and characterized by the accretion of the rehamna dome to the continental basement in the east based on 40ar 39ar cooling ages from a syntectonic granitoid and its host rocks and metamorphic 40ar 39ar ages from greenschist facies mylonite the timing of this event falls between 295 and 280 ma the end of the variscan orogeny in the moroccan meseta is constrained by the 40ar 39ar cooling age of a posttectonic pluton dated at 275 ma the tectonic events highlighted in morocco coincide with the late variscan alleghanian tectonic evolution of southern europe and north america and can be correlated with the global reorganization of plates that accompanied suturing of pangaea at around 295 ma

polyphase magmatic pulses along the northern gondwana margin u pb zircon geochronology from gneiss domes of the pyrenees abstract alkaline granitic dikes intruding the metasedimentary mantle and orthogneiss cores of the aston and hospitalet domes of the axial zone of the pyrenees are subjects of a laser ablation icp ms u pb zircon geochronology study the age spectra recorded by detrital magmatic xenocrystic and inherited zircons reveal a more complex nearly continuous paleozoic magmatic history of the variscan basement of the pyrenees than previously known inherited and detrital zircons of mesoarchean paleoproterozoic to ediacaran ages attest to the peri gondwana location of the cambrian sediments that later form the metamorphic core of the variscan pyrenees the youngest magmatic zircon ages fall into the late carboniferous and earliest permian ranging from ca 306 297 ma and represent the emplacement ages of the dikes and small granite intrusions the age spectra of magmatic xenocrystic zircons contain several maxima middle 475 465 ma and late ordovician 455 445 ma early 415 402 ma and late devonian 385 383 ma early 356 351 ma and middle carboniferous ca 328 ma middle ordovician and middle carboniferous ages are obtained from xenocrystic zircons that were assimilated from the rocks the dikes intruded the aston and hospitalet orthogneisses and the soulcem granite the presence of early mid carboniferous magmatic zircons in several samples lends further support to a wide spread early variscan magmatic activity in the central pyrenees the other age peaks do not have equivalent igneous or metaigneous rocks in the central axial zone but are thought to be present in the pyrenean crust not exposed and yet to be identified the diversity of ordovician devonian and carboniferous up to permian magmatic ages indicates polyphase emplacement of intrusive bodies during pre variscan and variscan orogenies the source of the heat for the devonian to early mid carboniferous magmatic activity remains elusive and may involve intracontinental subduction zone lithospheric scale shearing or a mantle plume tuzo

variscan extension in the pyrenees evidence for variscan extension in the pyrenees is summarized and used with other geological and geochronological data to reconstruct the variscan extensional geometry and kinematics at a crustal scale a regionally consistent pattern of ese wnw trending synmetamorphic stretching directions indicates variscan extension roughly parallel to the present alpine trend of the belt the spatial distribution of variscan low pressure high temperature metamorphic domes is interpreted as being possibly due to the activity of few moderately dipping crustal scale shear zones allowing heterogeneous ductile extension of the variscan middle and lower crust extension occurred synchronous with uplift and emergence of large parts of the crust and deposition during the upper carboniferous and permian of up to 2500 m of continental sediments and intercalated basaltic andesitic volcanics in fault bounded extensional halfgrabens the extensional structures and related metamorphism postdate a namurian to early westphalian stage of crustal thickening characterized by thrusting and steep folding it is suggested that variscan extension in the pyrenees was driven by the gravitational potential energy of an initially thickened lithosphere enhanced by detachment of a cold and gravitationally unstable lithospheric root which caused progressive uplift tectonic denudation and a highly anomalous thermal structure of the variscan crust leading to extensive lower crustal melting and granodioritic intrusion during the early permian

power law scaling of topographic depressions and their hydrologic connectivity topographic depressions areas of no lateral surface flow are ubiquitous characteristics of the land surface that control many ecosystem and biogeochemical processes high density of depressions increases the surface storage capacity whereas lower depression density increases runoff thus influencing soil moisture states hydrologic connectivity and the climate soil vegetation interactions with the widespread availability of high resolution lidar based digital elevation model ldem data it is now possible to identify and characterize the structure of the spatial distribution of topographic depressions for incorporation in ecohydrologic and biogeochemical studies here we use ldem data to document the prevalence and patterns of topographic depressions across five different landscapes in the united states and quantitatively characterize the probability distribution of attributes such as surface area storage volume and the distance to the nearest neighbor through the use of a depression identification algorithm we show that these probability distributions of attributes follow scaling laws indicative of a structure in which a large fraction of land surface areas can consist of high number of topographic depressions of all sizes and can account for 4 to 21 mm of depression storage this implies that the impacts of small scale topographic depressions in the landscapes on the redistribution of material fluxes evaporation and hydrologic connectivity are quite significant

anatomy of an extensional shear zone leading to the exhumation of the middle crust within the canigou dome eastern pyrenees axial zone abstract to investigate the mechanism of exhumation of deep crustal rocks in hot orogens we focus on the southwestern part of the variscan canigou gneiss dome pyrenees where the transition between the middle and upper crust can be observed on the basis of new structural data geological mapping cross sections microstructural analyses and petrologic observations we propose that flat lying foliation within the gneiss dome and steep cleavage developed above it formed coevally we note the presence of regional scale shear zones at the boundary between the middle crust nuria canigou unit and upper crust puigmal unit at this boundary the e w south canigou shear zone is an extensional shear zone showing top to the southwest kinematics deformation which is localized within the andalusite biotite transition zone occurred under retrogressive conditions from high grade ductile to brittle conditions during the main deformation stage d2 the tectonic contact was folded during a later stage d3 we propose that the shape of the canigou dome resulted from the activation of extensional shear zones at the top of the orthogneiss leading to partial exhumation of high grade rocks the canigou gneiss dome can be considered an extensional dome that formed during late variscan ca 310 290ma transpression

polymetamorphism and ductile deformation of staurolite cordierite schist of the bossost dome indication for variscan extension in the axial zone of the central pyrenees the bossost dome is an e w trending elongated structural and metamorphic dome developed in cambro ordovician metasedimentary rocks in the variscan axial zone of the central pyrenees a steep fault separates a northern half dome cored by massif granite from an e w trending doubly plunging antiform with granitic sills and dykes in the core to the south the main foliation is a flat lying s 1 2 schistosity that grades into a steeper dipping slaty cleavage at the dome margins three major deformational and two metamorphic phases can be differentiated s 1 2 schistosity is an axial planar cleavage to w vergent recumbent folding that probably occurred in mid westphalian time peak regional metamorphism m 1 is characterized by static growth of staurolite and garnet following thermal relaxation of the previously thickened crust strong non coaxial deformation recording uniform top to the se extension during d 2 a is preserved in staurolite garnet schists in a 1 5 km thick shallowly se dipping zone in the southeastern dome a 500 m thick contact aureole m 2 was imprinted on the regionally metamorphosed rocks following the intrusion the bossost granite during d 2 b more coaxial deformation prevailed during synkinematic growth of m 2 phases in the inner part of the contact aureole around the northern part of the dome where it obliterated d 2 a fabrics progressive non coaxial deformation continued in the southeastern antiform and is recorded by late synkinematic growth of cordierite successive overprinting of the m 1 staurolite garnet assemblage by andalusite and cordierite of m 2 is preserved in the southern part the assemblage muscovite cordierite staurolite biotite is considered metastable given the low mn and zn contents of staurolite and cordierite and interpreted as the result of prograde metamorphism during decompression p t conditions during m 2 were approximately 3 kbar and 600 c pervasive crenulations and mesoscopic to regional southerly verging folds are the result of d 3 nne ssw compression post dating ductile deformation and contact metamorphism polymetamorphic assemblages of the bossost dome preserve a regionally confined zone of ese directed extensional shearing within an overall n s compressional setting exact timing of extensional shearing is not known but can be constrained by recumbent folding during the mid westphalian and granitic intrusions which confine it to late carboniferous time c 305 ma crustal scale flat lying extensional shear zones with similar orientation and time frame are observed in the hospitalet massif of the eastern axial zone this suggests that crustal extension though probably restricted by regional strain partitioning over orthogneiss or intruding granitic bodies within an overall compressive setting was not uncommon in late carboniferous time in the axial zone of the pyrenees

syntectonic emplacement of the maladeta granite pyrenees deduced from relationships between hercynian deformation and contact metamorphism the relationships between hercynian deformation and contact metamorphism in the aureole of the aneto unit a constituent pluton of the maladeta granite complex spanish pyrenees provide new data relevant to the controversy between the syn and post tectonic models of emplacement for the pyrenean granites the deformation in the aneto aureole is related to two superimposed hercynian episodes the first was a top to the sw thrusting which induced sw verging recumbent folds the second which was essentially compressive in the aneto area is represented by e w trending subvertical cleavage and folds with subhorizontal axes this second episode can be assigned to the d2 main hercynian tectonic event of the pyrenees the contact metamorphic assemblages grew during the d2 event and were deformed by it close to the contact the conclusion that the pluton was emplaced during d2 is strengthened by the structural and kinematic similarities between the magmatic deformation in the southern rim of the pluton and the d2 deformation in the country rocks this syntectonic timing is supported by new geochronological data that conflict with an existing rb sr post tectonic permian whole rock age for the maladeta granite more generally in accordance with some very recent structural and u pb zircon studies our results contradict the geodynamical models of the pyrenees which relate the granite intrusions to a late extensional event

zooming on northern cap de creus shear zones abstract the northern cap de creus shear belt provides fine examples of shear zones developed at different scales in rocks bearing pre existing penetrative foliations the shear zones developed under retrograde metamorphic conditions and they are preferentially located in crystalline schists lower grade metasedimentary rocks accommodated deformation by folding the shear zones are linked in an anastomosing framework with self similar properties they are interpreted to have formed as the result of a progressive wrench dominated deformation affecting anisotropic rocks a progressive non coaxial deformation regime is considered responsible for the development of the complex kinematic pattern wherein shear zones with opposite senses of shear may come to lie in close parallelism in such a framework individual shear zones are characterised by marked strain gradients not only across the shear zone but also along it these features together with the geometrical analysis of shear zone marginal domains indicate that these structures developed with a component of shortening across the shear zones the shear zones are interpreted to have nucleated as buckling instabilities that gradually evolved to become shear zones approaching the simple shear model microstructural and quartz c axis fabric analyses indicate that shear zone formation is associated with strong strain partitioning on all scales

late brittle tectonics in a precambrian ductile belt evidence from brittle structures in the singhbhum shear zone eastern india abstract the singhbhum shear zone a 200 km long tectonic lineament passes close to the boundary between the archaean singhbhum craton and the proterozoic singhbhum mobile belt evidence from meso structures reveals development of this shear zone in a ductile tectonic regime 1 6 2 2 ga by thrusting of the northern block over the southern block along the n dipping shear surface a hitherto unrecognized late brittle tectonic regime 1 6 ga comprising two discrete phases is established from dynamic analysis of the fractures and veins in the shear zone episodic extension parallel and normal to the shear zone was a major consequence of this middle proterozoic 1 6 ga brittle tectonic episode and was associated with the intrusion of a swarm of basic dykes

dynamic puddle delineation and modeling of puddle to puddle filling spilling merging splitting overland flow processes 1 surface microtopography affects overland flow infiltration soil erosion pollutant transport and other fundamental hydrologic and environmental processes across scales under the influence of surface depressions overland flow essentially features a series of progressive puddle to puddle p2p filling spilling merging and splitting processes the objectives of this study are to characterize puddles and their hierarchical relationships and model the microtopography controlled p2p processes we proposed a new modeling framework for simulating the p2p overland flow dynamics through cell to cell c2c and p2p routing for a set of puddle based units pbus in a well delineated cascaded p2p drainage system testing of the p2p model demonstrated its potential to improve overland flow modeling and hydrologic connectivity analysis by explicitly incorporating the hydrologic roles of depressions and quantifying the real microtopography controlled p2p dynamics

hercynian crustal scale extensional shear zone in the pyrenees detailed structural analysis of metasedimentary rocks and gneisses in the hospitalet massif pyrenees has revealed that upright structures in low grade rocks are in a structurally higher position and older than gently inclined to flat lying structures in higher grade rocks the steep structures were sub vertically flattened during formation of the flat lying structures indicating that the higher grade rocks formed as part of a shear zone system a similar conclusion can be drawn from the relation between deformation and metamorphism in the higher grade rocks we suggest that the shear zone may have accommodated crustal extension

hercynian tectonometamorphic evolution of the bosost dome french spanish central pyrenees metamorphic and structural studies show that the bosost dome central pyrenees is a metamorphic as well as a structural dome developed in cambro ordovician to devonian metasediments around a migmatitic core during the hercynian orogeny the structural metamorphic dome occurs in epizonal terranes and is twice as large as originally described the structural dome shows a concentric zoning of d2 and d3 local deformations developed around the migmatites and superimposed on the d1 regional hercynian deformation the structural data suggest that migmatites were emplaced diapirically into palaeozoic metasediments during d1 and are responsible for the local d2 and d3 deformations an early medium pressure high temperature metamorphism occurred during d1 leading to anatexis under water rich conditions then evolved progressively to a high temperature low pressure metamorphism during the d2 and d3 deformations the corresponding p t time path is a clockwise loop representing the evolution of the metamorphism from migmatiza tion to the diapiric emplacement of migmatites in a compressional setting pressure values obtained from geobarometry are three times as high as expected from sedimentological data this suggests that the hercynian metamorphism developed in a thickened crust during the n s shortening responsible for the large scale e w folding observed throughout the pyrenean axial zone

development and steady states of transverse dunes a numerical analysis of dune pattern coarsening and giant dunes we investigate the development and steady states of transverse dunes for ranges of flow depths and velocities using a cellular automaton dune model subsequent to the initial bed instability dune pattern coarsening is driven by bed form interactions collisions lead to two types of coalescence associated with upstream or downstream dominant dunes in addition a single collision ejection mechanism enhances the exchange of mass between two adjacent bed forms throughpassing dunes the power law increases in wavelength and amplitude exhibit the same exponents which are independent of flow properties contrary to the wavelength dune height is limited not only by flow depth but also by the strength of the flow superimposed bed forms may propagate and continuously destabilize the largest dunes we identify three classes of steady state transverse dune fields according to the periodicity in crest to crest spacing and the mechanism of size limitation in all cases the steady state is reached and maintained through the dynamic equilibrium between flow strength and dune aspect ratio in the limit of low flow strength where it becomes the primary factor of size limitation the bed shear stress in the dune trough regions is close to its critical value for motion inception comparisons with natural dune fields suggest that many of them may have reached a steady state finally we infer that the sedimentary patterns in the model may be used to bring new constraints on the development of modern and ancient dune fields