comparison of magnetic and gamma ray logging for correlations in chronology and lithology example from the aquitanian basin france summary precise time and facies correlations between drilled holes are fundamental for a better understanding of the geological evolution of sedimentary basins a downhole magnetic measurement device called the geological high sensitivity magnetic tool ghmt has been run within two wells drilled by gaz de france in the landes oil field southwest france as part of a gas storage exploration program the method of interpretation of downhole magnetic measurements yielded a magnetostratigraphy within each well allowing absolute dating and time correlations between the wells magnetic susceptibility and natural gamma ray intensity are useful parameters for establishing high resolution lithological correlations at a basin scale we present a correlation parameter established from a simultaneous analysis of the susceptibility and the gamma ray logs within each well the correlation parameter appears to provide a new tool for delineating lithological elements when local lithological changes are too subtle to show clear well to well correlations either from susceptibility logs or from gamma ray logs this new approach is interpreted as a sensitive way to detect relative variations between the detrital and clay content of the penetrated sediment

impact of backstop thickness lateral variations on the tectonic architecture of orogens insights from sandbox analogue modeling and application to the pyrenees 1 we performed sandbox analogue models to investigate the influence of along strike tapering of the backstop on the three dimensional architecture of natural doubly vergent thrust fold belts applying the results to a natural example as the pyrenees available geological and geophysical data indicate that the european crust which provided the backstop in the pyrenean orogen has a westward tapering on both the upper westward thickening of the mesozoic cover rocks and the lower westward rising of the moho envelope surfaces accordingly we performed laboratory models characterized by backstops with an along strike tapering of either the upper or the lower surface our results indicate a significant impact of backstop lateral tapering in thrust wedge architecture in terms of the outward propagation of the deformation fronts the width and elevation of the axial zone and the timing of thrust polarity reversal along strike when compared to the pyrenees our results support the inferred westward tapering of the european basement and its commonly accepted backstop role in the pyrenean orogen moreover comparison between the map pattern of the pyrenees and of laboratory experiments suggests that the along strike tapering of the bottom envelope surface of the backstop played a most important role on the three dimensional thrust wedge architecture than the tapering of the upper envelope surface

paleomagnetic evidence for dextral strike slip motion in the pyrenees during alpine convergence mauleon basin france abstract the paleomagnetic study of the aptian albian black marls from the inverted early cretaceous mauleon basin in the northern pyrenees reveals two components of magnetization that both yield negative fold tests the carriers of each component show different unblocking temperatures indicating that ferrimagnetic iron sulphides are the main carriers of the intermediate temperature component itc unblocks around 360 400 c and magnetite is the main carrier of the high temperature component htc unblocks around 460 500 c both components show a clockwise deviation in declination with respect to the reference field directions itc di and htc di both in in situ coordinates the reference direction for stable europe for the cenozoic is d i 001 50 d 5 i 3 however the reversal test for both of the magnetization components in situ is positive the structural evolution of the basin involves transtensional deformation during the main stage of basin formation and inversion during compression with migration of hydrocarbons and development of thrusts and folds with axial planar cleavage secondary magnetizations were acquired at the latest stages of the evolution of the inverted basin post folding as the result of a chemical mechanism and they were blocked during two different and likely close spaced in time polarity chrons the blocking of the two different magnetizations with different carriers implies chemical changes in the environment from anoxic sulphate reduction to oxic inferred clockwise rotation of the paleomagnetic vectors can be interpreted in terms of dextral shear across the north pyrenean zone during the tertiary probably eocene according to the plate tectonic scenario this distributed dextral shear was probably favored by discrete shear along cleavage planes as shown by geologic markers of consistent dextral strike slip motion in non competent units with strong cleavage development there is no evidence of such dextral movement in the south pyrenean zone thus indicating a strong partitioning of deformation during the pyrenean orogeny

the supra ophiolitic sedimentary cover of the asbestos ophiolite quebec canada first geochemical evidence of transition from oceanic to continental sediment flux abstract the 473 5 3 myr asbestos ophiolite complex of the quebec appalachians was formed in a forearc basin and obducted on a margin of laurentia 460 myr ago the complex together with its sedimentary cover is well exposed at burbank hill 130 km sw of quebec city where eight distinct lithologies have been identified 1 pyroxenites and wehrlites with minor dunitic layers 2 fractured gabbros 3 breccia containing gabbro and diabase fragments 4 polygenic conglomerates 5 red mudstone chert sandstone succession 6 tuffs with intercalated grey chert 7 greenish grey mudstones and 8 slates and sandstones of the saint daniel melange the gabbroic and mafic volcanic rocks show the characteristics of arc tholeiites tio2 0 8 0 85 wt and boninites tio2 45 la sm n 1 9 3 3 these rock types also occur as mafic fragments in the polygenic conglomerate the mafic fragments crystals and rocks within the conglomerate and the ophiolitic sandstones also show the same greenschist facies metamorphism as the mafic igneous rocks of the complex the conglomerate was probably formed after the forearc crust was fragmented by pre obduction normal faults these fault scarps would have promoted the erosion of the oceanic crust leading to the accumulation of diverse detritus in grabens the sedimentary lithologies which overlie the conglomerate exhibit a gradual increase in continent derived material la sm n 5 and la yb 20 and a decrease in ophiolitic material moving upward in the stratigraphic sequence the sedimentary rocks at the bottom of the sequence group 3 are mostly composed of ophiolite material with only 20 of crustal material they also have a high content of cr and mgo with values of 350 480 ppm and 5 7 8 respectively the rocks of the uppermost part of the pile group 1 which contain up to 80 crustal material have low abundances of cr and mgo 30 100 ppm and 2 7 4 5 wt continental detritus on the top of the asbestos ophiolite suggests the complex formed near the laurentian continental margin and that the eroded continental material had access to the basin where the ophiolite was formed this is consistent with the obduction of the asbestos and thetford mines ophiolites on the laurentian margin shortly after their formation the proximity of thick laurentian continental crust near the trench could explain why the subduction zone blocked up soon after the ophiolites formation

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

triple junctions of bay of biscay and north atlantic new constraints on the kinematic evolution recently surveyed triple junction trajectories in the bay of biscay and newly available magnetic maps constrain the early oceanic evolution of the north atlantic and bay of biscay from chrons m0 to a33o 118 to 80 ma the opening of the bay of biscay is of the scissors opening type with a pole of rotation located near bordeaux lat 44 6 n long 0 3 w and predicted simultaneous compression in the central and eastern pyrenees structural directions west of iberia do not fit the north america iberia motion therefore a second triple junction of the ridge ridge fault type is postulated just south of the first one which propagated north ward from a more southerly position

paleomagnetism of the zambales ophiolite luzon northern philippines abstract paleomagnetic results are reported from 52 sites in the zambales ophiolite the sites provide vertical sampling from the overlying sediments in the north and south to layered gabbros and dunites in the acoje and coto mines in the west they extend over an area of approximately 100 by 50 km a late miocene pliocene intrusion in the tarlac region gives a direction marginally distinguishable from the present field indicating a small clockwise rotation this is consistent with other indications of clockwise rotation since late miocene in luzon early and mid miocene sediments from barlo in the north and tarlac in the south indicate a period of rapid counterclockwise rotation during the miocene again consistent with other results from luzon eocene oligocene sediments overlying the ophiolite in the north and south indicate further counterclockwise rotation with northerly translation the interpretation of the directions in the ophiolite itself is more problematical directions similar to those in the eocene oligocene and in mid miocene sediments probably reflect secondary magnetizations and magnetization associated with the unroofing of the ophiolite we interpret the most strongly counterclockwise rotated magnetizations represented by a 44 ma sill in the barlo area and of the 46 ma dykes at coto as the primary direction of the ophiolite the counterclockwise rotation and northward translation interpreted from our results is consistent with the holloway model of the origin of the philippines however this model neglects the role of the philippine sea plate in the tectonic history of the philippines the counterclockwise rotation is also consistent with rotation of luzon in the left lateral shear between the philippine sea plate and asia as suggested by sarewitz and karig our data do not distinguish between counterclockwise rotation of a single block or of a number of smaller blocks the data suggest post late miocene clockwise rotation for luzon when it was coupled to the philippine sea plate our data are not consistent with a philippine sea plate origin for zambales

stratigraphical and palaeogeographical significance of the continental sedimentary transition across the permian triassic boundary in spain abstract the permian triassic transition a time of phenomenal palaeoenvironmental and palaeogeographical change represents the largest episode of mass extinctions known to palaeontologists this episode is however very poorly understood and a lack of sediments and palaeontological data particularly in the continental record is a feature common to every basin despite compelling information on the continental permian triassic boundary ptb emerging from recent efforts evaluating vertebrate evolution fungal events and isotope curves results are still insufficient to make any valuable correlations among continental basins and are even less appropriate for relating sediments of continental to those of marine origin the present report discusses and attempts to locate the ptb in the basins of iberia and balearic islands through an analysis of the palaeontological and sedimentary record across the permian triassic transition the aim of the paper is to contribute to our present knowledge of the palaeogeographical and stratigraphical significance of the permian and triassic continental units of western europe the present day iberian ranges catalonian ranges and balearic islands hold the most complete late permian early triassic sedimentary record in iberia this record consists of alluvial sediments mainly of braided fluvial systems corresponding to the saxonian and buntsandstein facies all the units examined so far have been dated through palynological associations the two saxonian facies formations are of thuringian age although the lower one shows some palynological elements of autunian affinities the buntsandstein units range from thuringian to anisian in age there being no evidence up to now of the scythian in iberia the exact position of the ptb in iberia is up to now impossible to pinpoint with the precision of the marine series sedimentary characteristics and palynological data in the iberian ranges point that it lies at the sedimentary interval 10 to 30 m thick formed by the upper member of the la hoz del gallo formation and the lowermost beds of the canizar formation or its time equivalent the prades and eramprunya units in the catalonian ranges and the asa and b 1 in the balearic islands we compare a normalized standard late permian middle triassic column of the iberian ranges with standards from western and central europe and the southern urals using recent permian time scales a palaeogeographic essay map of the permian triassic transition is provided for the iberian plate the plate was located in a northern subtropical position 200 400 km from the westernmost tethys coast as part of the central pangean mountain range comprised of the appalachian mauretanide variscan orogenic belts of estimated altitudes 2000 4000 m based on this palaeogeographic location sedimentary characteristics and the main wind flows established for the tethys we can infer conditions of high precipitation dominated by monsoon and seasonal regimes with isolated semiarid areas for the iberian plate during the transition

acoustic scattering by internal solitary waves in the strait of gibraltar high frequency underwater acoustic transmissions across the strait of gibraltar were used to examine acoustic scattering caused by the unique internal wave field in the strait internal solitary waves of 100 m in amplitude propagate along the interface between an upper layer of atlantic water and a lower layer of mediterranean water the interface is also strongly modulated by internal tides of comparable amplitude as internal solitary waves cross the acoustic path they cause sharp soundspeed gradients which intermittently refract acoustic rays away from normal sound channels internal tides vertically shift soundspeed profiles for additional travel time variability although the acoustic scattering is quite complicated it is also surprisingly robust making it a good candidate for modeling key features of the acoustic arrival pattern can be accounted for in some detail by a model description of the complex hydraulics in the strait

the ainsa fold and thrust oblique zone of the central pyrenees kinematics of a curved contractional system from paleomagnetic and structural data this work was funded by the project intectosal cgl2010 21968 c02 01 and by the grup de recerca de geodinamica i analisi de conques 2009sgr1198 secretaria d universitat i recerca del departament d economia i coneixement de la generalitat de catalunya josep poblet acknowledges financial support by research projects geociencias en iberia estudios integrados de topografia y evolucion 4d topo iberia csd2006 041 and desarrollo de fracturas y venas asociadas al plegamiento fraveple cgl2011 23628 funded by spanish ministries

regional trends in the timing of alleghanian remagnetization in the appalachians pole positions related to remagnetized components isolated in appalachian limestone and redbed rock units range over about 60 m y of the permian carboniferous apparent polar wander path for north america apparent ages of remagnetization are older in the southern appalachians and younger to the north if the remagnetizations are associated with fluids expelled during the alleghany orogeny then the apparent remagnetization age trend could describe the timing of thrust sheet emplacement

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

paleomagnetic direction obtained by strain removal in the pyrenean permian redbeds at the col du somport france abstract in order to investigate the possibility and limitations of paleomagnetic works within strained regions a paleomagnetic study related with strain analysis has been conducted in the deformed pyrenean permian redbeds in the col du somport area paleomagnetic sampling together with strain estimates have been conducted in 6 sites through a fold the results obtained by measuring the orientation and axial ratios of elliptical reduction spots show that 1 the shale beds have undergone a penetrative strain 2 the sandy beds can be regarded as tectonically unstrained with reduction spots flattened in the bedding showing that they recorded the compaction it is shown that the total strain recorded in the slaty beds probably results from the superimposition of tectonic strain upon the compaction fabric the paleomagnetic study shows that the primary pretectonic magnetization is widely overprinted by a secondary syn or post tectonic magnetic component as both components appear to be carried by hematite pigment their separation using classical demagnetization procedures has been difficult a characteristic remanent magnetization chrm has however been determined when possible as the hardest component in demagnetization curves then the chrm direction distributions are represented in stereographic density plots although these chrm directions exhibit a clear tendency towards se declinations and shallow inclinations characteristic of permian paleomagnetic field direction for the iberian plate the tilt correction does not induce a clustering of these directions strain is inferred to be responsible for this situation assuming that both pretectonic magnetization directions and bedding planes closely follow the material plane and line strain response model of march 1 an attempt has been made to remove the effect of strain upon the remanent magnetization it is shown that when using a reconstructed tectonic strain tensor i e the total strain tensor as measured in the field corrected for an estimated compaction we obtain a significant clustering of chrm directions the computation of the relevant vgp gives a pole position 210 5 e 42 0 n compatible with the reference apwp for the iberian plate it is therefore inferred that the strain removal technique is a usable tool in order to obtain paleomagnetic results within such strained rocks

palaeomagnetic evidence for rotations and deformation in the nogueras zone central southern pyrenees spain a multicomponent palaeomagnetic remanence from the lower triassic buntsandstein redbeds of the central southern pyrenees has been interpreted as being composed of three components a low blocking temperature recent viscous magnetization l an intermediate blocking temperature eocene remagnetization i and a high blocking temperature lower triassic remanence h these palaeomagnetic results can be used in conjunction with structural evidence to identify poles of rotation during the development of the nogueras zone antiformal stack poles from individual sites reflect local deformation and folding including vertical rotation due to shearing between adjacent thrust sheets the i component was sometimes acquired syn tectonically during thrust motion and can be used to define intermediate stages of structural development results from sites located on a single thrust sheet no 7 indicate that it rotated by 45 clockwise during emplacement this is reflected in an easterly increase in displacement estimated from the construction of balanced cross sections thrust sheets appear to have been pinned close to the present day location of pont de suert during the later stages of structural development the arcuate path of thrust sheet motions and the potential movements in and out of cross section can lead to over and under estimates of minimum displacement when using line length cross section balancing techniques

petrology and geochemistry of siliciclastic rocks of mixed feldspathic and ophiolitic provenance in the northern apennines italy provenance in clastic sedimentary rocks in the northern apennines is determined by integrated petrographic and geochemical criteria thus mafic poor arkoses in the gottero formation senonian paleocene deposited prior to the alpine orogeny were derived from granitic provenance in the sardinian corsican massif in the gottero formation chemical criteria distinguish between very low input of detrital mafic material and co c and ni added entirely by adsorption on clay minerals post alpine orogeny feldspathic sandstones in the macigno formation mid oligocene lower miocene and cervarola formation lower miocene reflect a more diverse provenance of granitic metamorphic ophiolitic and sedimentary rocks in the apennines and alps the macigno and cervarola rocks are distinguished by serpentine gabbro and diabase fragments and higher chlorite contents than in the gottero rocks chemically the macigno and cervarola rocks contain distinctive signatures expressed in higher mgo co cr and ni contents of the mafic ultramafic detritus a wider range and more scattered cr and ni variation and higher niggli ti for a given niggli al alk content the mgo co cr and ni abundances indicate up to 10 ultramafic ophiolitic detritus in the macigno and cervarola sandstones and up to 17 ophiolitic detritus in associated shales estimated by comparison of mixtures of feldspathic sands with ligurian peridotites up to 10 basaltic ophiolitic detritus in these sediments is suggested by cao and fe2o3 total abundances petrographic data indicate that a major part of the detritus in the macigno and cervarola formations is from alpine granitic basement of calc alkaline granite to tonalite plutons and gneisses but apart from higher ba in macigno and cervarola sandstones than in the gottero sandstones this is difficult to identify chemically the trace elements cr ni ba rb ce la y co cu ga pb and zn generally have positive correlations with niggli al alk a chemical surrogate measure of sheet mineral clays micas and chlorites content whereas sr which is associated with carbonate and feldspar shows negative correlation with al alk an olistostrome unit contains the most weathered detritus but otherwise shows similar chemical variation to the other formations methods to 1 identify separately mafic and ultramafic inputs 2 recognize in shales co cr and ni derived from ophiolitic sources and non ophiolitic sources 3 estimate the minimum mafic ultramafic proportion in a sediment may have general application elsewhere in sedimentary and metasedimentary rocks

evidence of widespread cretaceous remagnetisation in the iberian range and its relation with the rotation of iberia a palaeomagnetic investigation has been carried out at 13 sites of jurassic age in the iberian range northern spain two components of remanent magnetisation have been found at each site a primary high temperature component shows an average counterclockwise rotation with respect to the north of 33 2o clockwise about a vertical axis corresponding to the absolute rotation of the iberian plate since the jurassic a secondary low temperature component shows a systematic declination difference of 16 4o with respect to the primary component this indicates that a rotation of iberia must have occurred between the two acquisition times comparison of the magnetisation directions with previous palaeomagnetic data and with sea floor spreading data constrains the age of the remagnetisation between 95 and 125 ma the remagnetisation may be associated with the extensional phases in the iberian basin in the early cretaceous barremian early albian or late cretaceous cenomanian a principal characteristic of the remagnetisation is its widespread character in the iberian range 1998 elsevier science b v all rights reserved

did the european dinosaurs disappear before the k t event magnetostratigraphic evidence abstract debate on the non catastrophic or catastrophic extinction of the dinosaurs by an asteroid impact k t event remains a controversy and is mainly based on the interpretation of the sedimentary continental sequences in the north american western interior the global aspect of this event needs to be tested in sedimentary record from all continents where continuous terrestrial deposits through the cretaceous paleogene are well preserved in the western mediterranean realm recognition of the cretaceous paleogene boundary is limited by the lack of biostratigraphic data in the upper cretaceous lower tertiary continental sedimentary sequences new magnetostratigraphic results were obtained from the analysis of two sections in southern france and compared to previous results in northern spain the last occurrence of in situ dinosaurs eggshells the only dinosaur remains found is located in chron 30n southeast france or 31n southwest france and northern spain this last occurrence could demonstrate that the extinction of the european dinosaurs occurred prior to the cretaceous paleogene boundary and would therefore support the idea of a gradual or stepwise extinction unlinked to the k t event

apparent western termination of the north pyrenean fault and tectonostratigraphic units of the western north pyrenees france and spain the surface geology of the north pyrenees southern france is markedly different east and west of longitude 0 25 w a line just west of lourdes east of this longitude the north pyrenean fault npf the major structure in the north pyrenees is clearly identifiable and this fault and other faults in the north pyrenean zone are subvertical west of longitude 0 25 w the npf is not identifiable at the earth s surface suggesting to some that the npf is not continuous and is not a regionally significant feature and that low angle as well as high angle faults are present in the fault zone while east of lourdes there is both a relatively continuous belt of mesozoic metamorphic rock and a geophysically detected 15 km step in depth to the moho neither is clearly recognized west of lourdes again bringing into question the continuity of the npf however in order to accommodate opening of the bay of biscay as much as 400 km of translation along a continuous npf or north pyrenean fault zone npfz is required we have compiled a map covering a 100 km long area in the western pyrenees the compilaation is based on our mapping and published maps by others the compilation and our field work provide the data to delineate four new tectonostratigraphic units these units are coherent stratigraphic sequences characterized by marked differences in stratigraphic thickness and depositional history each unit is bounded by regional faults that delineate four tectonic sheets the principal stratigraphic differences between the four tectonostratigraphic units were produced during deposition in cretaceous basins along the northern pyrenees the regional bounding faults are reverse and were formed during the main phase of the pyrenean orogeny that is during late cretaceous and tertiary times some are reactivated basin boundary faults and some of these are reactivated faults of cretaceous or older age in the western pyrenees the npf which was an active left slip fault during the late jurassic and early cretaceous is cut by these faults and is covered by tectonic sheets these sheets formed during the paleogene account for the apparent termination of the npf near longitude 0 25 w and obscure the step in the moho

paleomagnetic investigations in the thuringer forest g d r abstract in the thuringer forest the whole rotliegende is well exposed and was chosen as beginning of a permian traverse via czechoslovakia austria into italy rockmagnetic experiments established haematite as main carrier of the nrm except a few localities where magnetite was found to be present sediments and volcanites show consistent chrm directions the comparison with krs s 1978 compilation proves a good permian pole position

onland signatures of the palawan microcontinental block and philippine mobile belt collision and crustal growth process a review abstract the collision of the palawan microcontinental block with the philippine mobile belt had significantly influenced the geological evolution of the philippines multiple collisions involving several fragments through space and time resulted into the collage of terranes of varying origin exposed in this part of central philippines cusping of the overriding plate volcanic arc gap ophiolite emplacement incipient back arc rifting island rotation and tilting raised coastal terraces metamorphism intrusion of igneous rocks and steepened subducted slab as seen in focal mechanism solutions are some of the manifestations of this collision a late early miocene to early middle miocene age 20 16 ma is proposed for the major collision between the palawan indenter and the philippine mobile belt the collision boundary is located from the northern part of mindoro through the central mountain range swinging east of sibuyan island in the romblon island group and finally threading along the buruanga peninsula and eastern side of the antique ophiolite complex before exiting and connecting with the negros trench the collision through accretion and crustal thickening has contributed to the crustal growth of the philippine archipelago

accretionary history and crustal evolution of the variscan belt in western europe abstract the variscan belt of western europe is part of a large intra paleozoic belt extending on both sides of the atlantic from the ouachitas in the us and the mauritanides in west africa to the bohemian massif in czechoslovakia and poland the belt was constructed between 500 and 250 ma as a result of convergence and collision between two main continents laurentia baltica and africa after the closure of various oceanic basins iapetus rheic and galicia massif central now recorded as discrete in part cryptic sutures which form the roots of large crystalline nappes in which are found dismembered remnants of oceanic crust and mantle the accretionary history of the variscan belt in western europe is related to the progressive closure of probably two oceanic basins the rheic in the north and another the galicia massif central in the south by respectively southward and northward intraoceanic subduction followed by obduction and intracontinental lithospheric subduction the result is a broad 700 800 km fan like divergent belt which must be considered as a classical obduction collision orogen with a long intracontinental history of about 100 150 ma its arcuate shape is probably due to the northwestward impingement of a promontory of the african continent into laurentia baltica

paleomagnetism of the lower cretaceous redbeds from northern spain evidence for a multistage acquisition of magnetization abstract an extensive study of the wealden series from the cantabric chain and the sierra de los cameros northern spain reveals that the n r m contains four types of components tentatively classified in decreasing ages the older components group 1 are considered as the primary magnetization they yield a paleomagnetic pole located at lat 41 n long 237 e n 6 k 186 95 5 this pole position implies the existence of a large upper jurassic lower cretaceous swing in the iberian polar wander path the comparison with other polar paths north america africa supports the hypothesis of an initial lower cretaceous rotation of iberia prior to the main mid cretaceous shift the remainder of the components represent remagnetizations the major phase groups 2 and 3 extended from the upper cretaceous to the eocene at least a period closely correlated with the period of convergence between the european and iberian plates the directions of group 3 are characterized by low inclination this is a common behaviour for eocene directions in the mediterranean area previous data obtained from the wealden redbeds largely agrees with the directions of one or other of the groups 2 and 3 as there is strong evidence of an acquisition subsequent to the main mid cretaceous movement of iberia the geodynamical inferences of the paleomagnetic data have to be re examined the last type of components group 4 was built up during recent remagnetization and is of little interest

role of strike slip faulting in the evolution of allochthonous terranes in the philippines concepts of allochthonous terrane transport and emplacement are dominated by the assumption that most terranes originate on the subducting plate collide with the upper plate and are emplaced there movement of terranes along the convergent margin is recognized but is generally attributed to postcollision slip in the northern philippines allochthonous terranes originate primarily within the arc system have been translated along it by strike slip faults and were emplaced by cessation of that slip the authors suggest that in the philippines some originally vertical strike slip boundaries may have evolved into shallow dipping sutures marked by fold and thrust systems this mode of terrane evolution may be more common than generally appreciated particularly in orogenic belts developed in response to oblique convergence

new chronostratigraphy of the cretaceous paleogene boundary interval at bidart france abstract the cretaceous paleogene boundary section at bidart french basque coast was prevented for a long time to be considered as a reference section for the k t boundary due to a suspected hiatus comprising most of chron c29r in our new magneto and biostratigraphic study of this section we discovered that the underlying primary magnetic polarity is not revealed in the vector directions but in a small but consistent intensity excursion during laboratory demagnetization trends magnetite and maghemite are the main carriers of remanence with contribution of hematite to the magnetic mineralogy of the red brown lowermost danian and maastrichtian marly limestones magnetite is the main magnetic mineral in the white to pink danian limestones the nrm of marls and marly limestones is characterized by 1 a present day field overprint 2 a medium temperature 300 400 c reversed component interpreted as a relic of the characteristic remanent magnetization chrm carried by magnetite grains which are not completely oxidized into maghemite and 3 a high temperature up to 590 c normal component due to late diagenesis hematite growth the nrm of danian limestones is characterized by 1 a present day field overprint and 2 a chrm component of normal or reversed polarity the chrm directions allow a new correlation of the magnetic polarity sequence with the geomagnetic polarity time scale gpts chron c29r corresponds to the maastrichtian unit and extends up to 3 5 m above the k t boundary and chron c29n occurs at the top of the section there is no evidence for a hiatus at or below the k t boundary and the section does not extend up to chron c28r as previously suggested these new chronostratigraphic assignments are in good agreement with the previous biostratigraphic data and from the new biostratigraphic analyses based on calcareous nannofossils presented in this paper our study demonstrates that the section of bidart can be considered as a key section to study the k t boundary event s

new and revisited paleomagnetic data from permian triassic red beds two kinematic domains in the west central pyrenees abstract new paleomagnetic results of permian triassic red beds from bielsa aure and somport anayet sectors in the pyrenean axial zone are presented and combined with revisited and reviewed paleomagnetic data from the west central pyrenees the paleomagnetic data from the red beds vary between different sectors that share similar structural position i e whilst all sectors share the existence of a characteristic prefolding component a cenozoic postfolding component is found only in one area but not in other areas with similar structural position and kinematics previous paleomagnetic data to the west of the studied zone reveal a pre turonian remagnetization component but this secondary component is not found in an area that shares a similar structural position aure this variability suggests that the paleomagnetic behavior is the result of a series of factors related to the particular tectonic history of the region sedimentation burial and deformation during basin inversion and therefore paleomagnetic data demands careful assessment in order to unravel the kinematics of areas with equivalent structural positions in orogens however important kinematic implications that hold in the pyrenees can be inferred from the restoration of the permian triassic characteristic magnetizations to positions previous to the paleomagnetic rotations recorded by cretaceous or cenozoic paleomagnetic data the restoration reveals on one hand the lack of large rotations in the south pyrenenan zone except in the nogueras area according to bates 1989 and on the other hand the contrasting rotations recorded to the west of the studied zone in the paleozoic basque massifs pbm and the south pyrenean zone indicating the existence of two different tectonic domains in the west central sector of the pyrenees the strong clockwise rotations postdating the early cretaceous remagnetization that are recorded in the pbm and in the north pyreneean zone suggest a late dextral shear deformation affecting areas near the north pyrenean fault zone

evolution of a turbiditic foreland basin and analogy with an accretionary prism example of the eocene south pyrenean basin the south pyrenean tertiary basin was an east west trending foreland trough which developed from early eocene to miocene times in a north south trending compressive regime a turbiditic series of lower and middle eocene age hecho group enables us to define the typical features of the tectono sedimentary evolution of the basin 1 slope and shelf derived carbonate turbidites and megaturbidites bear witness to the seismic activity of the basin borders 2 the southern basin border evidenced by the onlap of the turbidites onto slope and shelf deposits migrated progressively southwards in time and 3 the deformation pattern is characterized in the meso cenozoic sediments by a complex thrust fold system of thin skinned tectonics style its specific geometry and kinematics were influenced by the pre deformation geometry onlap this thrust fold system is related to south directed basement nappes and its front advanced progressively southwards in time from this data we infer an evolutionary model for this highly mobile basin it was a flexural basin linked to the northward bending of the lithosphere in the foreland of a south directed crustal accretionary prism as the nappes advanced the basin migrated progressively southwards in the foreland direction as for the actual basin evolution many analogies with accretionary prism trench systems of active margins exist

cretaceous tertiary tectonic inversion of the cotiella basin southern pyrenees spain the cotiella nappe includes one of the most important mesozoic basins of the southern pyrenees which was subsequently inverted during the tertiary compression the late cretaceous cotiella basin is here interpreted as the western sector of the cretaceous cotiella boixols basin 100 20 km wide located in the central part of the southern pyrenees the present day complex structure of the cotiella nappe is the result of the inversion process linked to the emplacement of basement thrust sheets of the axial zone in its western sector the cotiella nappe consists of several superimposed thrust sheets with complex geometry becoming simpler towards the east with a single thrust surface and smaller displacements the cotiella boixols basin underwent strong subsidence during the early cretaceous at its eastern sector and its depocentre migrated westward during the late cretaceous the reconstruction of the sedimentary basin to the pre compressional stage shows that during the mesozoic the cotiella boixols basin was located to the south of a basement high which later became the pyrenean axial zone from a balanced cross section it can be inferred that the cotiella north verging extensional system was connected with the north pyrenean rift by means of a 10 km deep horizontal detachment the compressional tertiary detachment within the upper crust was shallower than the extensional detachment and individualised four basement thrust sheets which form the axial zone antiform

post emplacement history of the zambales ophiolite complex insights from petrography geochronology and geochemistry of neogene clastic rocks abstract the zambales ophiolite complex in luzon philippines is made up of two blocks with differing geochemical signatures and ages the middle jurassic to early cretaceous acoje block san antonio massif that is of island arc tholeiite composition and the eocene coto block cabangan massif which is of transitional mid ocean ridge basalt island arc tholeiite affinity these ophiolitic bodies are overlain by miocene to pliocene sedimentary units whose petrochemistry are reported here for the first time varying degrees of influences from ophiolitic detritus and from arc volcanic materials as shown by petrography and indicator elements including cr co and ni are observed in these sedimentary formations from north to south and from the oldest to the youngest the early to middle miocene cabaluan formation whose outcrops are found to overlie only the acoje block registers a more dominant ophiolitic signature as compared to the late miocene to pliocene santa cruz formation the santa cruz formation is generally characterized by fewer ophiolitic clasts and higher amounts of felsic components additionally within this formation itself a pronounced compositional change is observed relative to its spatial distribution from the south to the north an increase in ophiolitic components and a relative decrease in felsic signature is noted in units of the santa cruz formation it is therefore inferred that changes in the petrochemistry of rocks from the older cabaluan to the younger santa cruz sedimentary formations record a decline in the influx of ophiolitic detritus or conversely the introduction of more diverse sediment sources as the deposition progressed detrital zircon u pb ages from the santa cruz formation with peaks at 46 73 0 94 and 5 78 0 13 ma reflects this change in provenance from the unroofing of an early eocene oceanic crust to fresh contributions from an active volcanic arc during the late miocene the contrast in compositions of the southern and northern santa cruz formation also indicates a closer proximity of the southern units to the source of these non ophiolitic sources which most likely corresponds to the pliocene volcanoes of the west luzon arc

do reduction spots predate finite strain a magnetic diagnosis of cambrian slates in north wales abstract the purple cambrian slates of north wales contain green colored irregular patches drawn out along cleavage and the more familiar ellipsoidal reduction spots that are parallel to cleavage because parallelism of pre strain ellipsoids could only be produced by extremely high strain we reject the hypothesis that these are strain markers here we use magnetic methods to resolve this argument the magnetic analysis reveals that the magnetic fabric of purple slate differs from the green variety of the slate only in the oxidation state and indicates that the reduction process postdates cleavage this suggests that the shape of reduction spots reflects the anisotropy of diffusion during reduction not finite strain and alignment of an initially ellipsoidal object in the slates

geology of the southern zambales ophiolite complex philippines juxtaposed terranes of diverse origin abstract the zambales ophiolite complex which is made up of three massifs masinloc cabangan and san antonio was generated in a subduction related marginal basin combined field geological and geochemical evidences show that the cabangan and san antonio massifs are genetically related to the coto transitional mid ocean ridge island arc and acoje island arc blocks of the masinloc massif respectively a tectonic contact the subic bay fault zone is believed to separate the san antonio and cabangan massifs the san antonio massif is a displaced terrane rifted from the acoje block and translated southward to its present position through the west luzon shear subic bay fault zone the zambales ophiolite complex could have not formed through the rifting or folding of the arc related acoje block san antonio massif to generate the transitional mid ocean ridge island arc like coto block cabangan massif

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

permian clockwise rotations of the ebro and corso sardinian blocks during iberian armorican oroclinal bending preliminary paleomagnetic data from the catalan coastal range ne spain abstract paleomagnetic investigations of early permian and triassic magmatic rocks from catalan coastal ranges provide three magnetic directions which are interpreted as primary magnetizations and partly as overprints the succession of magnetic directions is interpreted in terms of a succession of large scale clockwise rotations which bring the whole assembly of pyrenees catalonia corsica sardinia and maures esterel massifs from the southeast of the massif central to the west during permian this major movement is associated with clockwise rotation of northern limb of the iberian orocline during latest carboniferous and early permian 305 290 ma subsequently permian large scale dextral transtensional extensional shearing operated along aquitanian shear belt between the massif central in the northeast and the iberian variscan massifs in the southwest the latest phase of the rotation in the late permian early triassic is associated with alkaline magmatism probably linked to neo tethys opening activity in western europe

zircon u pb geochronology of the zambales and angat ophiolites luzon philippines evidence for an eocene arc back arc pair two basement terranes the zambales ophiolite in the west and the angat ophiolite in the east are exposed on the island of luzon separated by a circa 10 km thick and circa 100 km wide sedimentary basin the structural and age relationships between the two ophiolitic blocks are central to understanding the geologic and tectonic development of the northern philippines and evaluating models of terrane evolution proposed for this area of the western pacific we analyzed zircons from the zambales and angat terranes to better constrain their origin two zircon fractions from tonalite in the acoje block of the zambales ophiolite give concordant u pb ages at 44 2 0 9 ma two zircon fractions from plagiogranite and one fraction from diorite in the coto block of the zambales ophiolite give concordant u pb ages of 45 1 0 6 ma these results provide a middle eocene age for the zambales ophiolite in agreement with the minimum late eocene age of the overlying aksitero formation no age difference is discerned between the arc like acoje block and morb like coto block of the zambales ophiolite four zircon fractions from two sample sites in the angat ophiolite give concordant ages of 48 1 0 5 ma this age is considerably younger than the late cretaceous age based on radiolarian fauna derived from a sheeted dike pillow lava sediment sequence south southeast of the main ophiolite the small age difference between the zambales and angat ophiolites suggests a common origin and obviates the need for a major structural discontinuity west of the southern sierra madre beneath the central valley of luzon the cretaceous biostratigraphic ages of the ophiolitic rocks southeast of the eocene angat ophiolite implies that there are two ophiolitic basements exposed in the southern sierra madre the relationship between the two ophiolites is constrained by the overlying stratigraphic relations which indicate that an eocene volcanic arc and associated volcaniclastic apron was built on both the eocene and cretaceous ophiolitic basement this suggests that the zambales angat ophiolite represents a preserved eocene back arc basin that opened behind an eocene arc that developed within cretaceous oceanic basement in this model the zambales angat ophiolites are therefore not allochthonous terranes but part of a single plate generated in situ forming part of the autochthonous basement of luzon

ophiolitic source rocks for taconic age flysch trace element evidence flysch generated along the appalachian orogen during the ordovician taconic orogeny ranges in age from late arenig to early caradoc allochthonous flysch and from late llanvirn to ashgill autochthonous flysch sandstones in these units are dominantly lithic arenites with a heavy mineral suite containing common to abundant mg rich chromite north of the canada united states border the only reasonable sources for the chromite were the lower ultramafic units of obducted ophiolites trace element analyses cr ni v cu ti zr y of flysch sandstones indicate a striking increase in cr and ni concentrations from the united states appalachians to the canadian appalachians in the united states units cr is in the range of 10 to 50 ppm canadian flysch units average an order of magnitude more cr these results suggest that ophiolite obduction either did not occur or was of minor importance during the taconic orogeny in the united states appalachians the difference in ophiolite abundance between the canadian and united states appalachians suggests a fundamental difference in tectonic style along the orogen a feature that must be accommodated by plate tectonic models new models will probably need to consider both obliquity of subduction and geological complexity of the ordovician collision zone in order to explain the spatial distribution of obducted ophiolite sheets

triassic paleomagnetism from the western pyrenees revisited implications for the iberian eurasian mesozoic plate boundary since the pioneering studies of van der voo tectonophysics 7 1969 5 and van der voo and boessenkool j geophys res 78 1973 5118 paleomagnetism of permo triassic redbeds and volcanics from the western pyrenees has furnished important contributions for delineating the mesozoic boundary between the iberian and eurasian plates in this paper we present a new paleomagnetic study focussed on triassic red beds 23 sites of the paleozoic basque massifs pbm the aim of this study is to complement previous studies done in those massifs to better constrain the complex kinematics of the western pyrenees two stable magnetic components have been isolated 1 a dual polarity pre folding magnetisation carried by specular hematite and 2 a secondary normal polarity component also carried by hematite our data confirm both the origin and the rotation pattern of the primary remanence described in previous works nevertheless field tests performed on the secondary component do not confirm the earlier interpretations by schott and peres tectonophysics 156 1988 75 as they indicate a synfolding nature of the remagnetisation instead of a post folding origin we consider that the secondary component is better explained if a cretaceous age is considered the presence of such remagnetisation in the western pyrenees strengthens the widespread occurrence of similar remagnetisation events reported in northern iberia in connection with the extensional tectonic events that occurred during cretaceous times a comparison of the rotations recorded by the triassic component and by the remagnetisation indicate that the paleozoic units underwent variable tectonic rotations before the remagnetisation was acquired most likely in connection with the counterclockwise rotation of iberia with respect to eurasia these results favour that the mesozoic plate boundary between the iberian and eurasian plates was a wide domain of distributed deformation and therefore contradict previous interpretations claiming for a discrete plate boundary

paleomagnetism of permo triassic red beds in the western pyrenees evidence for strong clockwise rotations of the paleozoic units abstract the paleomagnetic study of permo triassic red bed outcrops located in several basement units and slices of the western pyrenees is presented despite strong overprintings attributed to remagnetization processes connected with the early tertiary compressional phase we were able to identify the original magnetization in all sites the directions yielded reveal the occurrence in the whole area of clockwise rotations varying with respect to the european reference direction from nearly 0 to 102 the secondary directions are interpreted as more or less contemporary with the inferred rotations the paleomagnetic data are discussed in the light of two kinematic models for the iberian plate the examination of the models involving a left lateral displacement of iberia during the mid cretaceous is most conclusive and leads us to suggest that at that time the boundary between europe and iberia was located south of the cinco villas and aldudes massifs the clockwise rotations were induced by the early tertiary convergence of the plates which markedly disturbed the rather simple pattern inferred for the mid cretaceous period

the anso transect of the southern pyrenees basement and cover thrust geometries a balanced geological section through the western central pyrenees allows the alpine geometry of hercynian basement to be determined this shows marked differences with other transects of the southern part of the chain basement involved thrust sheets do not form an antiformal stack but are imbricated and define steps separated by frontal culmination limbs basement thrusts propagate upwards and have formed distinct thrust systems in the cover in this transect the north pyrenean zone is bounded to the south by gently dipping thrusts of large displacement and the axial zone massif at its western termination area is a flat topped culmination caused by a single thrust fault the gavarnie thrust this thrust emerges to the south in the interior of the syntectonic jaca basin the geometry of which is also controlled by underlying basement thrusts various generations of structures can be correlated with distinct episodes of syntectonic sedimentation a sequential restoration of the section illustrates how successive foreland sedimentary wedges were generated and progressively involved in deformation tectonic shortening is 48 km almost half of that estimated further to the east for the southern pyrenees the structure deduced at the ecors pyrenees seismic section cannot be translated to this transect

widespread inclination shallowing in permian and triassic paleomagnetic data from laurentia support from new paleomagnetic data from middle permian shallow intrusions in southern illinois usa and virtual geomagnetic pole distributions abstract recent paleomagnetic work has highlighted a common and shallow inclination bias in continental redbeds the permian and triassic paleomagnetic records from laurentia are almost entirely derived from such sedimentary rocks so a pervasive inclination error will expectedly bias the apparent polar wander path of laurentia in a significant way the long standing discrepancy between the apparent polar wander paths of laurentia and gondwana in permian and triassic time may be a consequence of such a widespread data pathology here we present new middle permian paleomagnetic data from igneous rocks and a contact metamorphosed limestone from cratonic laurentia the exclusively reversed middle permian magnetization is hosted by low ti titanomagnetite and pyrrhotite and yields a paleomagnetic pole at 56 3 s 302 9 e a95 3 8 n 6 this pole which is unaffected by inclination shallowing suggests that a shallow inclination bias may indeed be present in the laurentian records to further consider this hypothesis we conduct a virtual geomagnetic pole distribution analysis comparing theoretical expectations of a statistical field model tk03 gad against published data sets this exercise provides independent evidence that the laurentian paleomagnetic data is widely biased likely because of sedimentary inclination shallowing we estimate the magnitude of this error from our model results and present and discuss several alternative corrections

passive rotation of hematite during deformation a comparison of simulated and natural redbeds fabrics abstract a simulation model is used to generate pole figures assuming strain induced passive rotation of hematite crystals comparison of simulated and natural hematite fabrics allows us to distinguish between dominant passive rotation and other grain scale deformation mechanisms two natural examples are discussed redbeds from the french maritime alps and pyrenean redbeds fabrics indicate that passive rotation is the dominant reorientation mechanism of primary hematite grains during progressive deformation of redbeds

unraveling the mesozoic and cenozoic tectonothermal evolution of the eastern basque cantabrian zone western pyrenees by low temperature thermochronology this is a contribution of the geotec group idi 2018 000216 and projects misterios cgl2013 48601 c2 2 r consolider ingenio 2010 topo iberia csd2006 00041 and esf topoeurope project pyrtec sv pa 10 03 ip2 pyrtec we thank additional financial support by the university of oviedo banco santander the government of the principality of asturias through the science technology and innovation plan pcti the european union through feder funds and the spanish ministry of education culture and sport through the training programme for academic staff fpu grant for idf

geochemistry and mineralogy of sediments from the ventersdorp and transvaal supergroups south africa cratonic evolution during the early proterozoic approximately 100 pelite and 12 quartzite samples from the ventersdorp 2 7 ga and transvaal supergroups 2 6 2 1 ga have been analyzed to monitor the early proterozoic evolution of the kaapvaal craton southern africa from oldest to youngest pelites were sampled from the ventersdorp bothaville bot transvaal selati sel black reef br timeball hill th strubenkop str and silverton sil formations paleocurrent measurements in transvaal quartzites indicate sources lying predominantly to the north and east relative to the bot sel br pelites from the th str sil are enriched in heavy ree lile zr hf nb and ta depleted in k2o mgo ni and cr and have lower cr zr sc th k2o na2o and k rb ratios compared to sel br bot th str sil pelites have higher light ree contents and la yb ratios and lower eu eu ratios 0 61 0 66 relative to nasc north american shale composite thstr sil pelites are enriched in light ree th u ta nb sc cs have higher la yb ratios and are depleted in k2o and mgo bot sel br pelites are enriched in k2o mgo cr and ni have higher k2o na2o sc th and eu eu ratios and are depleted in th u heavy ree and high field strength elements hfse relative to nasc compositions of th str sil pelites suggest a provenance similar to average phanerozoic uppercontinental crust this source is more evolved than that of bot sel br pelites indicating a transformation from primitive mafic rich to evolved felsic rich upper crust at 2 2 ga this transition follows earlier primitive to evolved trends in moodies pongola 3 3 3 0 ga and witwatersrand 2 8 ga successions these data suggest that several cycles of changing upper continental crust occurred in the kaapvaal craton between 3 3 2 1 ga

palaeomagnetism and isotopic age data from upper cretaceous igneous rocks of w portugal geological correlation and plate tectonic aspects summary palaeomagnetic results and k ar age data for the sintra and sines intrusive complexes w portugal and further details on the palaeomagnetic structure of the lisbon volcanics are reported the sintra complex consists of two main intrusive phases having been emplaced in the upper cretaceous at around 90 ma and 75 ma respectively the radiometric results show that the sines complex formed concurrently with the second sintra magmatism the early main sintra pluton has a characteristic magnetization of d 358 i 27 95 3 3 this remanence direction is defined by gabbros and diorites as the granitic rocks constituting the bulk of the complex are shown to possess stable secondary magnetization imposed during quaternary weathering the characteristic magnetization of the younger intrusive event as defined by the sines rocks has a mean direction of d 041 i 41 95 3 3 these two upper cretaceous palaeomagnetic directions are significantly different at the 95 per cent probability level the lisbon volcanics show the presence of the 75 ma magnetization suggesting that also this volcanic complex dates from the upper cretaceous in addition the palaeomagnetic results from the lisbon complex have given further substance to a previously reported magnetization component with shallow inclination and north northwest declination now defined by d 333 i 14 95 7 4 it is inferred that this magnetization which has a dual polarity structure formed through low temperature oxidation in late cretaceous to lower tertiary time the declination difference between the 90 ma and 75 ma magnetizations may be interpreted in terms of a two phase rotation of iberia in the upper cretaceous prior to the assumed late cretaceous early tertiary secondary magnetic imprint implying a counterclockwise rotation of minimum 40 followed by a clockwise rotation of similar magnitude however if the relevant palaeomagnetic reference frame for iberia before and after its independent tectonic movements in the late cretaceous is the african plate then the clockwise rotation is about 20 larger than the counterclockwise one apparently accounting for the compressive tectonism in the bay of biscay

the rotation of iberia during the aptian and the opening of the bay of biscay abstract the cretaceous rotation of the iberian plate in a geodynamical active setting between africa and europe is contemporaneous with the opening of the northern atlantic ocean and provides fundamental temporal and kinematical constraints on the evolution of the bay of biscay and the pyrenees here we report new paleomagnetic data from 50 sites 1109 drilled cores from marine sediments of the cretaceous organya basin in the southern pyrenees to constrain the timing and magnitude of the rotation of iberia berriasian to barremian directions in exclusively limestone lithology are remagnetised in agreement with previous organya basin studies the aptian to cenomanian marls and limestones in the organya basin however provide primary magnetisations asserted by rock magnetic experiments and positive fold tests our results constrain the rotation of iberia to be finished just before the albian paleomagnetic data cannot well constrain the onset of the rotation but sea floor anomaly studies restrict the onset of the rotation to anomaly m0 or the barremian aptian boundary this implies that the entire rotation of iberia happened in one single phase and is confined to the aptian this is in contrast to earlier studies that suggested a two phase rotation of iberia but we argue that the large errors in published ages are not in disagreement with our results in summary we constrain the 35 rotation of iberia to the aptian period which implies a rotation rate of 2 7 5 1 myr depending on the controversial duration of the aptian

a new kinematic model for iberia further palaeomagnetic and isotopic age evidence abstract palaeomagnetic results and k ar age data from the algarve igneous province have uncovered three ancient relative field components it is inferred that the principal magnetization of the monchique complex with a mean direction of d 42 i 181 95 4 5 was acquired at around the time of the pluton s emplacement some 72 2 ma ago a second magmatic pulse affected the region at 68 2 ma leaving behind a relative field component of d 42 i 341 95 1 7 furthermore an overprinted magnetization characterized by shallow inclination and somewhat smeared northwesterly southeasterly declination most likely originates from the lower tertiary the new palaeomagnetic data are seen in conjunction with previously published upper cretaceous results from the sintra and sines intrusive complexes the resulting database gives entirely new perspectives for evaluating the plate tectonic history of the peninsula in upper cretaceous lower tertiary time a two phase rotation of the iberian micro plate an anticlockwise one of 40 followed by a clockwise one of 70 is clearly in evidence the net clockwise rotation provided a major impetus for the compressive deformation in the pyrenees and the bay of biscay and led to extensive remagnetization of older rock formations in the northern regions of iberia previous palaeomagnetic conclusions in favour of a single anticlockwise rotation of 35 supposed to be directly connected with the formation of the bay of biscay appear to be artefacts which stem from an incorrectly adopted palaeomagnetic reference frame

the late palaeozoic early mesozoic from the catalan pyrenees spain 60 myr of environmental evolution in the frame of the western peri tethyan palaeogeography the eastern catalan pyrenees form the southernmost segment of the pyrenean axial zone they experienced complex multistage process as the result of both the variscan and the pyrenean orogenic cycles after the late palaeozoic several small extensional sub basins were filled by continental successions as a response to the changing tectonic setting within the frame of the southwestern europe this stratigraphic record perfectly exposed in the studied eastern pyrenean areas preserves the signatures of the late palaeozoic pangea break up during the progressive dismantling of the variscan chain up to the triassic diffused extension despite structural network being severely affected by cenozoic reworking the stratigraphic framework can be unravelled by the detailed sedimentological and stratigraphical analysis of the well exposed sequences in short this paper addresses facies patterns and architectural elements of late carboniferous permian triassic continental sections studied in the catalan pyrenees and aims to use these signatures for correlation not only at a regional scale but also within the broader picture of the southwestern europe our stratigraphical reconstruction clearly demonstrates that the thick studied succession consists of fluvial lacustrine basal units affected by intense volcanic activity and overlaying predominantly fluvial fining upwards units for each unit several lithofacies architectural elements and bounding surfaces of different order have been identified and their lateral and vertical staking characterized deposition and erosion processes are controlled by alternating periods of tectonic activity producing different stages of high and low subsidence the uplift of the sub basin margins and subsequent extended erosive events marked by angular unconformities on the strength of the major rank bounding surfaces analysis the studied sedimentary packages have been grouped into different tectono stratigraphic units and then correlated they have been contextualized within the latest palaeogeographic reconstructions of the studied sector contributing to detail the role of the study area within the frame of the s european palaeogeography

magnetic reorientation induced by pressure solution a potential mechanism for orogenic scale remagnetizations abstract new paleomagnetic analyses of triassic cretaceous and eocene strata in the south central pyrenees show evidence for a widespread remagnetization located along the southern border of the axial zone the internal sierras and the northern part of the jaca pamplona basin this remagnetization always reversed in polarity was acquired after an extensive period of late eocene early oligocene folding and tilting in the area and affects limestones sandstones marls and red beds in addition a characteristic prefolding component was identified in 30 of upper cretaceous and triassic red beds these results together with a revaluation of previously published paleomagnetic data from the central pyrenees indicate that the spatial distribution of the postfolding remagnetization coincides with that of a domain of pressure solution cleavage a relationship between the intensity of the remagnetization and the characteristic prefolding component with respect to the density of cleavage surfaces leads us to propose a mechanism for the remagnetization related to the development of pressure solution cleavage that is framed within the tectonic evolution of the central pyrenees partial dissolution of rock under tectonic compression leads to the liberation and subsequent accumulation of insoluble minerals in cleavage planes magnetic grains are part of the relatively insoluble residue and they reorient in the presence of the ambient field after they are freed during dissolution of the rock matrix chemical reequilibrium dissolution and or neoformation of magnetic carriers during this process cannot be excluded the remagnetization mechanism we propose can help to explain widespread remagnetizations in low to moderately deformed rocks without the need of large scale migration of orogenic fluids

new paleomagnetic results from cretaceous sediments near lisboa portugal and implications for the rotation of iberia abstract paleomagnetic study of outer platform sediments of late jurassic early cretaceous age from portugal lisboa area leads to characteristic remanent magnetization directions for the hauterivian barremian d 317 i 58 and the aptian d 344 i 47 the absolute rotation of iberia between 125 and 110 ma is consequently of about 27 in an anticlockwise sense a later rotation of about 14 follows the first one in the same sense from 110 ma the total absolute rotation of iberia from the hauterivian age determined by paleomagnetism is thus about 41 the comparison of declinations measured with paleodeclinations calculated in lisboa from the eurasian and african poles of similar age indicates that the main phase of relative rotation of iberia with respect to eurasia occurs during the first stage of relative motion i e hauterivian to aptian the tectonic history of the bay of biscay is in good agreement with these two stages of rotation the total relative rotation with respect to europe is 34 this value is consistent with results previously established by van der voo 2 3 25 but we have established that the main phase of rotation 30 occurs in the hauterivian aptian interval the movement of iberia is clearly linked to the movement of africa in direction and age but the amount of rotation of iberia during the early cretaceous is much larger and implies that iberia was not a real part of the african plate

the age and timing of folding in the central appalachians from paleomagnetic results comparison of the paleomagnetic pole positions of late paleozoic secondary magnetizations with a time averaged reference apparent polar wander path for north america shows that sedimentary rocks within the central appalachians were remagnetized in the later half of the permian between ca 255 and 275 ma ages of remagnetization do not vary for sites distributed along or across strike of the central appalachian fold and thrust belt or across the appalachian plateau in new york nor do they vary with stratigraphic position of the host rocks however the pattern of folding relative to remagnetization across the valley and ridge and great valley in pennsylvania maryland and west virginia shows a distinct temporal variation individual fold tests yield postfolding magnetizations near the hinterland margin of the fold and thrust belt synfolding magnetizations in the central part of the belt and prefolding magnetizations near the foreland because of the similar age of the late paleozoic magnetization we conclude that rocks across the central appalachians were remagnetized in a relatively short period of time as folding and thrusting propagated more slowly toward the foreland we interpret this pattern to indicate that older folds near the hinterland grew prior to remagnetization folds in the central region grew during remagnetization and folds near the foreland grew after remagnetization rapid remagnetization relative to folding is also evident from the physical characteristics and magnetic properties of secondary hematite in remagnetized synfolding folds in such folds rocks were apparently remagnetized during an increment of fold growth in which there was partial and possibly negligible fold limb rotation collectively these results may constrain the mechanism for basinal fluid mobilization during deformation current models for remagnetization involve the migration of chemically active brines into the foreland during tectonism if realistic our results bear on this model by suggesting that brine migration was not directly related to the successive emplacement of individual thrust sheets as has been suggested for other fold and thrust belts

paleomagnetic structural and stratigraphic constraints on transverse fault kinematics during basin inversion the pamplona fault pyrenees north spain 1 the pamplona fault in the pyrenees is a major transverse structure that has been classically interpreted as a strike slip fault however lack of consensus concerning the sense of movement casts doubt on its actual kinematics and as a consequence its role in the cenozoic evolution of the pyrenees remains controversial in order to assess its kinematics we have conducted a paleomagnetic structural and stratigraphic study focused on the mesozoic and tertiary sedimentary rocks that outcrop around the southern segment of the fault restoration of balanced cross sections allows us to examine the present day spatial relationship of the sedimentary sequences on both sides of the fault and to reconstruct the geometry of the extensional basins formed during mesozoic rifting episodes in the bay of biscay and pyrenean domains paleomagnetic results indicate that no significant tectonic rotations occurred around the fault during tertiary inversion of the pyrenees the lack of tectonic rotations and revaluation of previous hypotheses argues against a strike slip movement of the fault we propose a new model in which the pamplona fault is treated as a large scale hanging wall drop fault whose kinematics was determined by variations in the geometry and thickness of mesozoic sequences on both sides of the fault these variations influenced the geometry of the thrust sheet developed during tertiary compression we are unaware of any other transverse fault that has been interpreted in this fashion thus the pamplona fault serves as a case study for the evolution of transverse faults involved in basin inversion processes

rotational basement kinematics deduced from remagnetized cover rocks internal sierras southwestern pyrenees 1 paleomagnetic data from the internal sierras unravel the kinematic relationship between basement guarga gavarnie bielsa and cover thrusts larra monte perdido the new data come from an area of 100 km along strike and 5 15 km across strike of the southwestern pyrenees the area covers a variety of structural positions that range from cover to basement thrusts from 84 sites located in upper cretaceous two meaningful magnetic components are found 1 the higher temperature c component unblocks at 575 c presents two polarities is prefolding has a mean declination and inclination d i of 010 44 95 8 k 15 and is considered primary and 2 the intermediate b component unblocks between 250 c and 450 c has a mean d i of 198 43 95 4 k 18 and has always reverse polarity and postfolding the nine sites located in the eocene flysch south of the upper cretaceous show the same postfolding component b the acquisition of this intermediate component alludes to a widespread tectonic related remagnetization event affecting the internal sierras this event must be younger than the folding of the flysch deposits middle upper eocene the tilting induced by the basement thrust gavarnie bielsa in the axial zone does not alter the inclination of the b so that the sediments acquire the b component later than priabonian emplacement age of the gavarnie thrust the b component is rotated clockwise with respect to the tertiary reference this means that the rotation takes place after the remagnetization event the position of the c component before the rotation of the b component is negligibly rotated d i of 002 44 95 7 k 94 with respect to the cretaceous reference therefore the b component records the last and only rotational event in the region the rotation is related to the latest basement deformation guarga thrust during upper oligocene times and it reflects the regional shortening gradient in the southwestern pyrenees the emplacement of the larra monte perdido cover thrust system that took place prior to basement thrusts mentioned above did not undergo any significant rotation

iberian plate motions during the mesozoic abstract as more data are collected on the deep parts of the conjugate margins of canada and eurasia models of the early kinematics of iberia become better constrained in order to specify the motions during phases of continental rifting to the west and to the north of iberia we used recent data on the early oceanic spreading in the tagus abyssal plain and added simple assumptions on the geometry the tagus abyssal plain was formed after the end of continental rifting on the southwest portuguese margin in latest jurassic time before chron m 0 118 ma as a first step we close the space adjacent to the m 0 anomaly to keep open only the oldest oceanic part of the tagus plain which is assumed to be latest jurassic to earliest cretaceous in age in a second step we close this space the main results are as follows 1 1 the galicia bank slid along the southern flank of flemish cap this motion is interpreted as a strike slip motion or as a very oblique rifting 2 2 a late jurassic reconstruction of iberia and north america is obtained without considerable overlap and without large motion of microplates such as galicia bank this is possible because a large amount of continental extension occurred over a long time to the north of the grand banks and permitted early motion between north america and eurasia 3 3 a tight initial reconstruction can only be reached if strike slip motion is located between southern eurasia and northern eurasia along a shear zone following the english channel and the transform area between galicia bank and flemish cap

the red bed controversy revisited shape analysis of colorado plateau units suggests long magnetization times several triassic and earliest jurassic sedimentary units from the colorado plateau region have distributions of virtual geomagnetic poles vgps that are highly elongate along the path of apparent polar wander apw this suggests that the remanent magnetizations measured in these units were acquired over an extended period of time possibly approaching 35 m y and are not precisely coeval with the stratigraphic age of the rock comparison with other paleomagnetic studies shows that the observed elongation is not a general attribute of the age of the rock nor is it related to paleolatitude the rocks that yield elongate vgp distributions are dominantly red to brown mudstones and it is possible that their remanence is dominated by a slowly acquired chemical remanent magnetization as suggested by larson et al j geophys res 87 1982 1081 and other authors however several superficially similar units from the colorado plateau have nearly circular vgp distributions the process by which remanence is acquired in clastic sedimentary rocks merits further study d 2002 elsevier science b v all rights reserved

geology of the zambales ophiolite luzon philippines abstract the zambales ophiolite of western luzon philippines exposes a typical succession of basalt flows diabasic dikes gabbro and tectonized harzburgite the age established by limiting strata is late eocene lack of evidence of thrust faulting and the general domal disposition of the lithologie units indicate that the ophiolitic rocks are exposed by uplift highly complex internal layered structures within the complex are related to processes developed during formation of the ophiolite and the zambales ophiolite may be one of the least disturbed by emplacement ophiolitic masses known the exposed mass trends north and the upper surface plunges at low angles a few degrees to the north and south the chemistry and composition of the rocks in the northwest part of the zambales area acoje block is distinct from that in the southeastern segment coto block the acoje block according to evans 1983 and hawkins and evans 1983 resembles on a chemical basis arc tholeiite series rocks from intra island arcs and the rocks in the coto block are typical back arc basin rock series the present writer believes that the ophiolite composes a single genetic unit and that the changes in composition are the result of changes that took place during the initial formation the gabbro probably formed below a spreading center in an elongate in cross section v shaped magma chamber the gabbro is estimated by the writer to be less than 2 km thick and may be less than 1 km in places numerous erosional windows through the gabbro in the northern and eastern side of the zambales area show that the gabbro remaining in those areas is likely to be only a few hundred meters thick harzburgite is exposed to a depth of about 800 m in the bagsit river area and this may be the deepest part of the ophiolite accessible for study on which there is any control on depth a transitional zone about 200 m thick lying between the gabbro and harzburgite is composed of serpentinized dunite commonly the dunite contains disseminated sulfide minerals and at the acoje mines platinum group elements a compositional layering within the gabbro is in places cumulate in the lower part of the unit but may have formed by nucleation higher up on the relatively steep sides of the magma chamber a widespread gneissic banding in the gabbro forms large mappable structures which are many times more complex than is the disposition of the major rock units these structures are believed to be the result of extensive slumping in the magma chamber the structure produced by the cumulate layering merges with the gneissic banding commonly without discernible change in attitude this tectonic layered structure crosses the gabbro peridotite boundary at any angle without seeming to disturb the original rock distribution at greater depths below the boundary ca 800 m the harzburgite contains low dipping banding which probably reflects the result of differential movement within the mantle chromite occurs almost exclusively in a zone that generally lies no more than 200 300 m below the gabbro peridotite boundary refractory grade chromite is found in this zone below the olivine gabbro in the goto block and as low grade metallurgical grade chromite below norite in the acoje block at acoje mines the chromite is present in layers in dunite which the writer interprets as being distributed in a zone along the gently dipping ca 25 gabbro peridotite boundary the steeply dipping ca 60 80 individual layers lie en echelon along the boundary at an angle ca 50 to the contact at coto the chromite forms large discontinuous masses in the lowest dunite and in the uppermost harzburgite except for the chromite present as layers at acoje the regional tectonic layering crosses the chromite deposits without structural deviation the chromite deposits and associated peridotite may be cumulate in origin but have been modified to such an extent that cumulate textures are generally obliterated the angle of repose of cumulate layers in the acoje area and in the coto block dip towards each other raising the possibility that the zambales area may contain the relics of a spreading center initial emplacement of the zambales ophiolite took place by uplift and the ultramafic portion was exposed to erosion in the earliest miocene or late oligocene submergence of some of the ophiolite followed the previous uplift and on the west side of the zambales range submergence of several kilometers is indicated final emergence appears to have taken place in pliocene or pleistocene time by block uplift and areas of greatest uplift closely conform to the present topographic surface

zircon u pb and hf isotopic constraints from eastern transhimalayan batholiths on the precollisional magmatic and tectonic evolution in southern tibet abstract before the indian collision with asia northward subduction of the neo tethyan oceanic lithosphere produced an andean type convergent margin in south asia characterized by arc magmatism starting from the early jurassic and lasting until the eocene the magmatic arc is now represented by widespread intrusive bodies or the so called transhimalayan batholiths in the lhasa terrane of southern tibet that have been divided into two main magmatic suites i e the northern plutonic belt and the southern gangdese batholith their temporal distribution concerning how exactly the magmatic suites correlate eastwards and then southeastwards around the eastern himalayan syntaxis however remains poorly constrained here we report the first combined zircon u pb and hf isotopic study of the transhimalayan batholiths from the eastern part of the lhasa terrane 95 97 5 e and 28 5 30 n se tibet zircon u pb dating results of 24 granitoids indicate that the rocks were emplaced principally in the early cretaceous 133 110 ma and subordinately in the paleocene 66 57 ma long after an older granite intrusion in the earliest jurassic 198 ma the zircon ehf t values range from 5 to 20 yielding hf crustal model ages tdmc between 0 8 and 2 4 ga that peak at 1 7 ga suggesting a major episode of crustal growth in the proterozoic and a predominantly or even exclusively crustal source for the granitoid petrogenesis these zircon u pb and hf isotopic constraints together with whole rock geochemical characteristics allow us to correlate them to s type granitoids in the northern plutonic belt rather than to the i type gangdese batholith from the central part of the southern lhasa terrane in contrast to the gangdese magmatism that formed with a significant juvenile mantle input related to the neo tethyan subduction these s type granitoids show geochemical similarities to the north american cordilleran interior batholiths that did not form directly from a subduction setting thus we attribute the petrogenesis of the widespread early cretaceous granitoids in the northern belt and eastern himalayan batholiths to a postcollisional regime due to the late jurassic early cretaceous continental collision between the lhasa and qiangtang terranes under this framework the s type magmatism was generated in response to collision induced crustal thickening which may have capabilities of causing crustal anatexis by itself in the region however continued interplay with the neo tethyan subduction zone processes such as back arc extension could also have played a crucial and long lasting role in the magma generation

alpine remagnetization and tectonic rotations in the french pyrenees a palaeomagnetic study of the 100 to 90 m y old alkaline igneous rocks of the french pyrenees has in part revealed large between site scatter caused by highly variable declination magnetomineralogical evidence suggests that the original titano magnetite has undergone variable low temperature oxidation through martitization and maghemitization processes suggesting that the rocks have been remagnetized when viewed in the context of the upper cretaceous lower tertiary inclination pattern based on portuguese palaeomagnetic data it is concluded that the rocks most likely acquired their present magnetization during early campanian maastrichtian time i e 20 30 m y after their original cooling on the other hand this magnetization postdates a major phase of late cretaceous compressive deformation subsequent strike slip movement along the pyrenean zone in the lower tertiary led to variable rotation of cover units along the orogenic belt producing the inconsistent palaeomagnetic declination picture presently observed it is concluded that the geological history of the alkaline rocks of the french pyrenees from the magmatic stage to the subsequent events of remagnetization and tectonic deformation is strongly associated with the alpine age rotational instability of iberia the principal kinematic history of the peninsula comprised ca 40 counterclockwise rotation relative to europe during cenomanian turonian time 100 90 m y ago followed by ca 70 clockwise rotation in the early campanian ca 75 m y ago

kinematics and strain distribution in an orogen scale shear zone insights from structural analyses and magnetic fabrics in the gavarnie thrust pyrenees abstract this work aims to characterize the gavarnie thrust one of the large scale thrusts that define the alpine structure of the west central sector of the pyrenees a detailed comparison of structural analysis and magnetic fabrics is carried out for the paleozoic phyllonites of the gavarnie thrust in order to decipher strain distribution and transport direction the ams at room rt ams and low lt ams temperature and the airm can be correlated with the structural patterns kmin axes are mainly parallel to the pole of the s c or c planes and kmax axes are parallel to the transport direction and related to ductile s c structures furthermore the pj t changes across the shear zone characterize strain variations larger pj and t are found in the basal most deformed part of the shear zone and lower values are found where the interaction between alpine and variscan related petrofabrics is stronger we also interpret the reactivation of variscan inherited fabrics within the alpine shear zone in spite of the heterogeneous strain markers indicate a common top to the south n190e alpine transport direction which contrasts with the strong obliquity of the genetically related structures developed in the southern mesozoic sedimentary cover in this sense our data suggest a complete decoupling between basement and cover units during the alpine compression

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

accreted terranes in the northern part of the philippine archipelago the philippine archipelago consists of a complex array of ophiolites continental fragments and island arc elements that can be identified as accreted terranes similar to those increasingly recognized as components of orogenic zones the northern philippines including luzon mindoro and nearby smaller islands can be divided into at least six of these tectonic elements from west to east across central luzon there are the neogene accretionary prism of the west luzon arc the eocene zambales ophiolite the cretaceous angat ophiolite and a late cretaceous early paleogene volcanic arc built on an older metamorphic basement this arc terrane is repeated by offset along the philippine fault to the south the western luzon terranes are juxtaposed against the metamorphic basement block of mindoro which itself is colliding with the north palawan microcontinental fragment the ophiolites appear to have originated in back arc basins rather than in oceanic plateaus and the metamorphic belts have protoliths indicating deformation along active margins perhaps deep within accretionary prisms the philippine terranes are interpreted as fragments that originated within the complex pacific eurasian plate boundary rather than as intra pacific basin units these terranes have been assembling at least since the oligocene by strike slip and convergent displacements strike slip displacement either along transcurrent faults or as a component of convergence played a very important if not dominant role in this assembly most terranes identified in the northern philippine appear to be plate fragments with attached crust and upper mantle their characteristics contrast with those usually interpreted for terranes in the north american cordillera where near orthogonal convergence and shallow dipping terrane sutures are favored

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

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