kinematic constraints on thrust belt curvature from syndeformational magnetizations in the lagos del valle syncline in the cantabrian arc spain a detailed paleomagnetic study in a single first order refolded syncline in the western hinge zone of the variscan foreland fold and thrust belt of northern spain was carried out to constrain the tectonic deformation of the cantabrian arc results show a complex pattern of structural deformation and acquisition of at least two secondary syntectonic magnetizations on the basis of local and regional fold tests we document an early permian b component that postdates earlier f1 westphalian and stephanian thrusting and folding and a late carboniferous to earliest permian c component that is synfolding acquired during fl the b component only resides in the carbonates and is carried by magnetite the c component is carried by magnetite in the gray carbonates and by hematite in the red beds both b and c components reveal significant vertical axis rotations that indicate that an originally cylindrical lagos del valle syncline was refolded f2 about a vertical axis after acquisition of the b component magnetization the pattern of rotations suggests that the entire cantabrian arc may have originated as a much more linear fold and thrust belt which was later modified by significant oroclinal bending with relative rotations totaling at least 120 the temporal distribution of remagnetization and deformation also suggests a protracted variscan orogeny in the area lasting from at least the late carboniferous into the permian

tectonic evolution of nw iberia during the paleozoic inferred from the geochemical record of detrital rocks in the cantabrian zone the cantabrian zone of nw iberia preserves a voluminous almost continuous sedimentary sequence that ranges in age from ediacaran to early permian its tectonic setting is controversial and recent hypotheses include i passive margin deposition along the northern margin of gondwana ii an active continental margin or iii the margin of a drifting ribbon continent and iv a combination of the three aforementioned possibilities in this paper we present geochemical data from 21 samples taken in detrital rocks in the cantabrian zone from ediacaran to early permian age the results together with previously published detrital zircon ages from these strata allow a comprehensive analysis of changing tectonic scenarios and provenance through time collectively these data indicate that this portion of iberia was an active margin during the ediacaran that evolved to become part of the passive margin of gondwana at least from ordovician to late devonian times changes in geochemistry zircon age distribution and sm nd isotopes during the carboniferous are attributed to the far field effects of the onset of the collision between gondwana and laurussia and related processes such as recycling of older sedimentary sequences as well as the involvement of the rocks formed during the variscan orogeny and oroclinal buckling latest carboniferous and permian show a more juvenile sm nd and higher values of illite cristallinity that may support the hypothesis of lithospheric foundering after oroclinal buckling

distributed subglacial discharge drives significant submarine melt at a greenland tidewater glacier this is the publisher s final pdf the article is copyrighted by american geophysical union and published by john wiley sons inc it can be found at http agupubs onlinelibrary wiley com agu journal 10 1002 28issn 291944 8007

late paleozoic iberian orocline s and the missing shortening in the core of pangea paleomagnetism from the iberian range supercontinents are usually interpreted to be single and rigid continental plates how and when pangea became a rigid supercontinent is disputed and age estimations vary from 330 to 240 ma the gondwana laurussia collision formed the variscan alleghanian belt the most prominent witness of pangea s amalgamation in iberia this orogen draws an s shape featured by the cantabrian orocline and the central iberian curve the curvature of central iberia is particularly evident in galicia tras os montes and in a change of trend that it draws in the aragonese branch of the iberian range recent research showed that both curvatures are not coeval and that the central iberian curve had to form prior to ca 318 ma i e not a secondary orocline we report paleomagnetic and structural results from paleozoic rocks in the santa cruz syncline aragonese branch of the iberian range that indicate two main vertical axis rotations events 1 a cenozoic alpine clockwise rotation of 20 and 2 a late carboniferous counterclockwise rotation of 70 once the cenozoic rotation is restored the change in structural trend that allegedly evidences the outer arc of the central iberian curve disappears whereas the cenozoic rotation is incompatible with a central iberian curve the late carboniferous rotation is fully compatible with the cantabrian orocline enlarging the area affected by its counterclockwise rotations and the existence of a nonrigid pangea until at least 295 ma

saddle reef auriferous veins in a conical fold termination oldham anticline meguma terrane nova scotia canada reconciliation of structural and age data many auriferous veins dated at 370 ma in the meguma terrane of nova scotia are concentrated in tight domes and conical fold hinges that are transected by 378 ma low pressure and high temperature metamorphic isograds and 380 370 ma granitoid plutons published experiments suggest that such folds are diachronous initiating at inhomogeneities and propagating both in amplitude and along their length thus fold terminations are typically conical in geometry and record only the youngest increment of folding the northeastern termination of the oldham anticline is characterized by 1 a conical fold 2 saddle reef auriferous veins 3 divergent and convergent cleavage fans 4 a downdip lineation on the slaty cleavage defined by biotitic mineral aggregates inferred to have developed during fold growth the age of the biotitic mineral aggregates is bracketed between peak metamorphism at 600 c defined by a nearly concordant 378 ma u pb monazite age from a xenolith in lamprophyre dyke and 366 ma 40 ar 39 ar muscovite biotite ages recording cooling through 400 300 c this suggests that the conical termination of the oldham anticline grew between 378 and 366 ma an observation that reconciles the empirical structural control of the saddle reef auriferous veins with the 370 ma age dating of vein minerals application of this conclusion to saddle reef auriferous veins in domes suggests that mineralization was related to the youngest increment of fold amplification

analysis of variscan dynamics early bending of the cantabria asturias arc northern spain calcite twinning analysis in the cantabria asturias arc caa of northern spain provides a basis for evaluating conditions of variscan stress and constrains the arc s structural evolution twinning typically occurs during earliest layer parallel shortening offering the ability to define early conditions of regional stress results from the somiedo correcilla region are of two kinds early maximum compressive stress oriented layer parallel and at high angles to bedding strike d1c1 and later twin producing compression oriented sub parallel to strike d2c1 when all d1 compressions are rotated into a uniform east west reference orientation a quite linear north south trending fold thrust belt results showing a slight deflection of the southern zone to the south southeast north south directed d2c1 compression was recorded prior to bending of the belt calcite twinning data elucidate earliest structural conditions that could not be obtained by other means whereas the kinematics of arc tightening during d2 is constrained by paleomagnetism a large and perhaps protracted d2c1 is suggested by our results as manifested by approximately 50 arc tightening prior to acquisition of paleomagnetic remagnetizations throughout the caa early east west compression d1c1 likely resulted from the ebro aquitaine massif docking to laurussia whereas the north directed collision of africa d2c1 produced clockwise bending in the northern zone radial folding in the hinge and rotation of thrusts in the southern zone fl 2000 elsevier science b v all rights reserved

mega fold interference patterns in the beishan orogen nw china created by change in plate configuration during permo triassic termination of the altaids abstract kilometer size fold interference patterns in the beishan orogenic collage boc in the southernmost altaids formed by fold superimposition in fossiliferous permian sedimentary rocks first phase f 1 upright and almost north trending folds were refolded by e to ene trending f 2 folds whose axial planes and axes are vertical or subvertical from east to west there is a regional change in style of interference patterns from lobate cuspate to crescent to mushroom shape this variation is accompanied by a westward decrease in the f 2 interlimb angle and related to a higher percentage of coarse grained clastic rocks suggesting a dependence of the f 2 deformation on lithology axial planar slaty cleavages are well developed in f 1 and poorly developed in f 2 folds the superposed folds mainly underwent flexural slip and flexural flow folding to give rise to the lobate cuspate pattern and to the crescent pattern caused by flattening and flexural flow folding where the sediments were unconsolidated and enriched in fluids the two folding events are interpreted to result from a major change in plate configuration that caused the inversion of an inter arc basin during the final amalgamation of the boc in the latest permian to early to mid triassic the two folding events bracketed between a maximum detrital zircon age of

the formation of an orocline by multiphase deformation a paleomagnetic investigation of the cantabria asturias arc northern spain the variscan orogeny in the cantabria asturias arc caa of northern spain represents a multiphase deformation history associated with pangea s amalgamation to determine the timing and kinematic history of deformation a paleomagnetic investigation was carried out on devonian limestones in three structural domains of the caa s hinge zone two characteristic remagnetizations in the caa are distinguished an early permian b component that postdates initial westphalian stephanian aged folding f1 and f2 and a late carboniferous c component that postdates f1 deformation both the b and c magnetizations experienced a later f3 folding phase the kinematics and geometry of post magnetization deformation are determined by bringing measured magnetic directions into agreement with reference directions these structural corrections also allow separation of deformation events in time we conclude that generally east west trending but variably plunging fold axes characterize f3 folding in the hinge zone of the caa this post magnetization deformation involved significant amounts of tilting and sub vertical axis rotation which together produced clockwise rotation in the north of the arc and counterclockwise rotation in the south of the arc to form the horseshoe shaped orocline that is observed today f3 fold axes change from near vertical to moderately inclined between and within structural domains due to the structural fabric imposed by f1 and f2 based on calculated f3 fold properties we can reconstruct pre existing f1 and f2 structural geometries of the hinge zones this analysis shows that f1 and f2 structures are the result of late carboniferous deformation as part of the same east west but temporally discrete compression regimes on the other hand f3 is controlled by permian north south

superimposed folding and thrusting by two phases of mutually orthogonal or oblique shortening in analogue models abstract orogens may suffer more than one phase shortening resulting in superposition of structures of different generations superimposition of orthogonal or oblique shortening is studied using sandbox and centrifuge modelling results of sand models show that in orthogonal superimposition the two resulting structural trends are approximately orthogonal to each other in oblique superimposition structures trend obliquely to each other in the relatively thin areas of the model foreland and mutually orthogonal in areas where the model is thickened during the first phase of shortening i e the hinterland thrusts formed during the first shortening phase may be reactivated during the later shortening phase spacing of the later phase structures is not as wide as expected considering they across the pre existing thickened wedge superposition of structures results in formation of type 1 fold interference pattern bedding is curved outwards both in the dome and basin structures folded layers are dipping and plunging outwards in a dome while they are dipping and plunging inwards in a basin in the areas between two adjacent domes or basins i e where an anticline is superimposed by a syncline or a syncline is superimposed by an anticline bedding is curved inwards and the anticlines plunge inwards and the synclines outwards the latter feature could be helpful to determine the age relationship for type 2 fold interference pattern in tectonic regions where multiple phases of shortening have occurred the orogenic scale dome and basin and arrowhead shaped interference patterns are commonly formed as in the models however in some areas the fold interference pattern might be modified by a later phase of thrusting similar to models results superimposition of two and or even more deformation phases may not be recorded by structures all over the tectonic area

conical fold terminations in the bannisdale slates of the english lake district abstract the structure of an area of silurian rocks in the non metamorphic caledonides near kendal cumbria u k is briefly described the main folds are periclinal and die away in the southeast of the area the uniform thickness of sandstone beds around folds shows that they deformed dominantly by buckling and only locally is flattening important a model is developed to explain the conical attitude of bedding within the periclinal terminations the model is erected on the basis of buckling alone and is developed to examine the effects of flattening inhomogeneity in buckling and flattening over the area is demonstrated using the model and discussed the pattern of folding is compared to that predicted by earlier published experimental work

correlating deformation in variscan nw iberia using porphyroblasts implications for the ibero armorican arc abstract 3 d microstructural analysis of 30 porphyroblastic samples from the variscan orogen in nw iberia has revealed four sets of inclusion trails with distinctive geographic trends and relative timing the chronological and orientational consistency of these microstructures provides a reference frame for the correlation of macroscopic structural successions the two younger inclusion trail sets correlate with the main map scale structures of middle to upper carboniferous age whereas the two older sets correspond to mesoscopic structures preserved locally in low strain pods and dating back as far as 365 ma upper devonian inclusion trail orientations appear uninfluenced by a major orocline in the study area ibero armorican arc outlined by late stage folds and thrusts with variable trends it is proposed that the orocline developed by wnw ese trending transpression superposed on originally n s to ne sw trending structures during a late stage of the orogeny upper carboniferous domains of low or zero strain e g porphyroblasts are inferred to have maintained relatively constant orientations in the zone of transpression presumably due to deformation partitioning effects consequently they preserve a succession of pre orocline structural trends the collected microstructural data also indicate moderate preferred vertical and horizontal orientations of inclusion trails in the analysed samples as reported earlier in other variscan regions this probably witnesses a dynamic equilibrium between tectonic forces and gravity during four periods of differently oriented crustal shortening that generated the four recognised sets of inclusion trails

paleomagnetism of the central iberian curve s putative hinge too many oroclines in the iberian variscides abstract the variscan mountain belt in iberia defines a large s shape with the cantabrian orocline in the north and the central iberian curve an alleged orocline belt of opposite curvature to the south the cantabrian orocline is kinematically well constrained but the geometry and kinematics of the central iberian curve are still controversial here we investigate the kinematics of the central iberian curve which plays an important role in the amalgamation of pangea since it may have accommodated much of the post collisional deformation we have performed a paleomagnetic study on carboniferous granitoids and cambrian limestones within the hinge of the curve our paleomagnetic and rock magnetic results show a primary magnetization in the granitoids and a widespread carboniferous remagnetization of the limestones syn kinematic granitoids show ca 70 counter clockwise rotations consistent with the southern limb of the cantabrian orocline post kinematic granitoids and cambrian limestones show consistent inclinations but very scattered declinations suggesting that they were magnetized coevally to and after the 70 rotation our results show no differential rotations between northern southern limb and the hinge zone therefore we discard a late carboniferous oroclinal origin for the central iberian curve

genesis and rank distribution of upper carboniferous coal basins in the cantabrian mountains northern spain abstract the cantabrian mountains located in the nw of the iberian peninsula constitute the most important coal mining district of spain anthracitic and bituminous coals high and medium rank coals have been mined in the area since the end of the nineteenth century and they currently account for about 70 of the total coal resources of the country the region forms part of the cantabrian and west asturian leonese zones of the iberian variscan fold belt and is strongly deformed by a set of imbricate thrusts coeval folds and high angle faults coal bearing successions are westphalian and stephanian pennsylvanian in age and are exposed in numerous coalfields of variable size arranged roughly parallel to the tectonic structures coal rank varies from medium rank bituminous d coals rr 0 5 to high rank anthracites a coals rr

role of erosion in creating thrust recesses in a critical taper wedge an example from eastern tibet abstract mechanical models and analog experiments show that erosion plays an important role in controlling along strike variations in thrust belt deformation despite this fundamental insight natural examples of focused erosion causing local variations of thrust belt geometry such as the formation of salients and recesses remain underappreciated in this study we address this issue by integrating theoretical model predictions with structural morphological and erosion pattern analyses along the thrust system defining the eastern margin of the tibetan plateau our work shows a nearly constant surface slope across and an overall cylindrical fault related fold geometry along the thrust belt these phenomena can be explained by the development of a critically tapered thrust wedge along the plateau margin a prominent recess exists at the intersection between the transverse minjiang river and the range bounding thrust there the surface trace displays a much higher curvature than the rest of the thrust belt and the local fold geometry is conical rather than cylindrical we infer a warped passive roof duplex under the recess we build a classification diagram for recesses developing in critical taper wedges in which six independent variables lead to three morphotectonic scenarios regarding the effects of mass influx mass efflux and intrinsic properties of a thrust wedge formation of the dujiangyan recess and its spatial correlation to the minjiang river can be best attributed to localized fluvial erosion during forward propagation of the thrust wedge in eastern tibet this study sets a type example for map view curves in thrust belts undergoing deformation erosion interactions

ice flow in greenland for the international polar year 2008 2009 a digital representation of ice surface velocity is essential for a variety of glaciological geologic and geophysical analyses and modeling here we present a new reference comprehensive high resolution digital mosaic of ice motion in greenland assembled from satellite radar interferometry data acquired during the international polar year 2008 to 2009 by the envisat advanced synthetic aperture radar asar the advanced land observation system alos s phase array l band sar palsar and the radarsat 1 sar that covers 99 of the ice sheet in area the best mapping performance is obtained using alos palsar data due to higher levels of temporal coherence at the l band frequency but c band frequency sar data are less affected by the ionosphere the ice motion map reveals various flow regimes ranging from patterned enhanced flow into a few large glaciers in the cold low precipitation areas of north greenland to diffuse enhanced flow into numerous narrow fast moving glaciers in the warmer high precipitation sectors of northwest and southeast greenland we find that the 100 fastest glaciers v 800m yr drain 66 of the ice sheet in area marine terminating glaciers drain 88 of greenland and basal sliding motion dominates internal deformation over more than 50 of the ice sheet this view of ice sheet motion provides significant new constraints on ice flow modeling copyright 2012 by the american geophysical union

rotational kinematics of a curved fold the balzes anticline southern pyrenees abstract this study deals with how vertical axis rotations are accommodated in thrust fronts studies on the rotational kinematics of fold and thrust belts are limited owing to the scarcity of the record of syntectonic rocks and other data required for 4d reconstruction approaches we studied the balzes anticline a 17 km long thrust related arc shaped anticline with dense paleomagnetic sampling 75 sites to unravel the origin of its curvature about 50 of arc in map view the availability of both synfolding and synrotational indicators enables us to decipher the complete kinematic history of the fold reliable paleomagnetic data more than 500 specimens and about 1000 measurements were obtained from ypresian to priabonian rocks typically with six demagnetization steps the chrm is unblocked between 420 and 575 c in most samples 85 and at 675 c in the others the primary direction displays two polarities and passes the fold test vertical axis rotation values for the structure range from non significant up to 80 clockwise a strike vs rotation diagram clearly relates this variability to the fold curvature var 46 0 5 trend r 0 97 and reveals the addition of primary and secondary curvatures the original primary curvature is related to the emplacement of the thrust sheet underlying the balzes anticline it shows an obliquity of approximately 15 with respect to the expected pyrenean trend progressive unconformity in the field santa marina site provides a record of a middle late lutetian major folding event the detailed analysis of the synrotational sedimentary record together with accurate temporal calibration based on previous magnetostratigraphic data allows us to date the rotation stage as lutetian bartonian and to estimate the rotation velocity of the balzes anticline to have been about 5 2 ma both in agreement with previously published observations for the south pyrenean front

conical folding in the core of an orocline a geometric analysis from the cantabrian arc variscan belt of nw iberia abstract the cantabrian arc of the variscan belt has been recently defined as a true orocline constraining kinematics and deformation timing this curved sector of the orogenic belt is characterized by two different fold sets 1 one runs parallel to the outcrops of the main thrusts and describes a horseshoe shape concave towards the east and 2 another is radial to the arc a detailed geometric study of the fold interference patterns in the cantabrian arc revealed the conical nature of the folds belonging to the radial set these conical folds developed with different geometrical characteristics semi apical angles and axis attitudes depending on the initial orientation and geometry of the folded surfaces they are interpreted to result from a vertical axis rotation during oroclinal buckling of the variscan belt in nw iberia this study of conical folds in the cantabrian arc highlights that conical folds in curved orogenic arcs are a powerful tool for establishing the sequence of tectonic events because interference patterns due to vertical axis secondary differential rotations provide unique geometrical characteristics observed in the cantabrian arc that can be extrapolated to other oroclines

investigating the kinematics of local thrust sheet rotation in the limb of an orocline a paleomagnetic and structural analysis of the esla tectonic unit cantabrian asturian arc nw iberia the esla tectonic unit lies along the southern boundary of the cantabrian asturian arc a highly curved foreland fold thrust belt that was deformed during the final amalgamation of the pangea supercontinent previous structural and paleomagnetic analyses of the cantabrian asturian arc suggest a two stage tectonic history in which an originally linear belt was bent into its present configuration creating an orocline the esla tectonic unit is a particularly complex region due to the interaction of rotating thrust sheets from the southern limb of the arc and the southward directed thrusts of the picos de europa tectonic domain during late stage north south shortening and oroclinal bending these structural interactions resulted in intense modification of early phase thin skinned tectonic structures that were previously affected by a deeper out of sequence antiformal stack that passively deformed the early thrust stack a total of 75 paleomagnetic sites were collected from the portilla and santa lucia formations two carbonate passive margin reef platform units from the middle devonian similar to other regions of the cantabrian asturian arc esla unit samples carry a secondary remanent magnetization that was acquired after initial thrusting and folding of variscan deformation in the late carboniferous protracted deformation during late stage oroclinal bending caused reactivation of existing thrust sheets that include the esla and younger corniero and valbuena thrusts when combined with existing structural data and interpretations these data indicate that the present day sinuosity of the esla unit is the consequence of both secondary rotation of originally linear features in the western esla exposures e g frontal thrusts and secondary modification and tightening of originally curvilinear features in the eastern esla exposures e g hanging wall lateral oblique ramps differences in structural style between the esla and other tectonic units of the arc highlight the complex kinematics of oroclinal bending which at the orogen scale buckled an originally linear north south in present day coordinates trending cantabrian asturian thrust belt during the final stages of pangea amalgamation

high resolution bed topography mapping of russell glacier greenland inferred from operation icebridge data detailed maps of bed elevation and ice thickness are essential for understanding and projecting the evolution of the ice sheets such maps are traditionally obtained using airborne radarsounding profiler data interpolated onto regular grids using geostatistical tools such as kriging here we compare three mapping techniques applied to a dense radar survey of russell glacier west greenland by nasa operation icebridge 1 radar tomography rt processing of the radar data to map the bed elevation 2 interpolation of radar derived thickness by ordinary kriging kr and 3 reconstruction of ice thickness based on the principles of mass conservation mc combining radar sounding profiler and ice motion data rt eliminates ambiguities caused by off nadir reflections but is spatially limited kr yields a standard error in bed elevation of 35 m but large errors 300m a 1 in flux divergence when combined with ice motion data mc yields a comparable performance in bed elevation mapping and errors smaller than 1m a 1 in flux divergence when the number of radar sounding tracks is reduced the performance of kr decreases more rapidly than for mc our study site shows that mc is capable of maintaining precision levels of 60m at 400m posting with flight tracks separated by 5 km 2014 publishing technology

paleomagnetic evaluation of the orocline hypothesis in the central and southern appalachians the axial traces of the major appalachian folds change azimuthal direction from a ne sw orientation to a n s orientation in the area of the pennsylvania salient and swing back to a ne sw orientation in the vicinity of the virginia reentrant all available paleomagnetic data from the folded appalachians have been examined to test the appalachian orocline hypothesis pre deformational site mean directions from suitable studies were rotated by the amount required to bring the strike of the sampled beds into coincidence with an average trend of the central and southern appalachians n35e a comparison of clustering of site means before and after this correction reveals that in all cases unbending of the arc causes site mean directions to disperse this dispersal demonstrates that the curvature of the appalachian orogen is to a very large degree a primary feature rather than a feature which resulted from the bending of initially straight fold axes

new time constraints on lithospheric scale oroclinal bending of the ibero armorican arc a palaeomagnetic study of earliest permian rocks from iberia abstract the palaeozoic variscan orogeny was a large scale collisional event that involved amalgamation of multiple continents and microcontinents previous palaeomagnetic and structural analyses of the western variscan orogen notably the ibero armorican arc suggest that this region underwent oroclinal bending of an originally near linear orogen during the latest stages of variscan deformation in the late palaeozoic these analyses necessitate a two stage tectonic history with east west compression forming a linear belt in the carboniferous followed by a change in regional compression directions resulting in crustal block rotation and formation of the present day arc this study presents new palaeomagnetic analyses of early permian samples from the sotres and cabranes formations 41 3 n 222 5 w 95 13 1 in the northern inner limb and the viar basin 51 8 n 199 2 w 95 6 7 in the southern outer limb of the arc both locations yield expected early permian palaeomagnetic pole positions for stable iberia implying that measured magnetizations have undergone no significant vertical axis rotation since acquisition and thus were acquired subsequent to oroclinal bending this new result places a time constraint of about 10 ma for oroclinal bending of the ibero armorican arc which agrees well with recent geodynamical models that relate oroclinal bending to lithospheric delamination in this region

remagnetizations and postfolding oroclinal rotations in the cantabrian asturian arc northern spain devonian carbonates in the cantabrian arc reveal characteristic magnetizations with coherent shallow upward inclinations the magnetizations appear to be carried by magnetite within site directions are very well grouped but site mean declinations range from easterly to south southwesterly in in situ as well as tilt corrected coordinates as has also been observed in previous studies of other formations in the arc the widely varying declinations of all studies roughly correlate with the overall structural trends of the arc and suggest that the sites underwent rotations in a process that involved folding about vertical axes and tightening of arc upon tilt correction the inclinations of our study on the other hand become scattered and it is concluded that the magnetizations were acquired after late carboniferous folding about horizontal axes the oroclinal rotations therefore also must have occurred after the late carboniferous folding phase the previous paleomagnetic results had been interpreted mostly as primary magnetizations residing in hematite however inclination only fold tilt tests applied to these results suggest that many if not all of the directions were acquired during the earlier stages of the late carboniferous folding thus all paleomagnetic results from the cantabrian arc appear to be remagnetizations but the ages of the remagnetizations vary from pre to synfolding for the mostly hematitic formations to postfolding for the devonian carbonates the reversed polarity inclinations of the hematite bearing formations have mean values ranging from 25 to 5 whereas the carbonates have a mean inclination of 8 on the basis of inclinations predicted for the area from results from stable europe the pyrenees and the iberian meseta the ages of these remagnetizations can be inferred to range from about 320 ma to 260 ma because all the remagnetizations reveal rotated declination patterns the oroclinal rotations occurred well after the main phase of hercynian deformation 320 280 ma while the timing of the rotations is unconstrained at the younger end they must have occurred during or after the permian best estimate is less than 260 ma which is much later than anticipated from other geological considerations

tectonothermal evolution of a foreland fold and thrust belt the cantabrian zone iberian variscan belt nw spain analysis of the conodont colour alteration index and the kubler index of illite allowed us the characterization of four types of very low or low grade metamorphism in the cantabrian zone cz and determination of their regional and temporal distri bution these types are 1 an orogenic variscan metamorphism present only in restricted areas of the western and north western parts of the cz where epizonal conditions are reached 2 a burial metamorphism that appears in the basal part of some nappes where anchizonal conditions are sometimes achieved the thermal peak preceded emplacement of the nappes 3 a late variscan metamorphism in the southern and south eastern parts of the cz a cleavage cutting most of the variscan folds is associated with this metamorphism which has been related to an extensional episode 4 a contact metamor phism and hydrothermal activity associated with minor intru sive bodies the extension continued after the variscan deformation giving rise to hydrothermal activity during permian times

strain partitioning in the footwall of the somiedo nappe structural evolution of the narcea tectonic window nw spain abstract the somiedo nappe is a major thrust unit in the cantabrian zone the external foreland fold and thrust belt of the north iberian variscan orogen exposed at the narcea tectonic window are precambrian rocks below the basal decollement of the somiedo nappe which exhibit a different deformation style than the overlying paleozoic rocks above the basal decollement during variscan deformation folding and widespread subhorizontal bedding parallel decollements were produced in the hanging wall within the paleozoic rocks vertical folding with related axial planar cleavage at a high angle to the decollement planes developed simultaneously in the upper proterozoic narcea slates of the footwall below the detachment the relative magnitude of finite strain measured in the footwall rocks diminishes towards the foreland these observations indicate that 1 significant deformation may occur in the footwall of foreland fold and thrust belts 2 the shortening mechanism in the footwall may be different from that of the hanging wall and 3 in this particular case the partitioning of the deformation implies the existence of a deeper blind decollement surface contemporaneous with the first stages of the foreland development that does not crop out in the region this implies a significant shortening in the footwall which must be taken into account when restoration and balancing of cross sections is attempted a sequential diagram of the evolution of the narcea tectonic window with a minimum shortening of 85 km is proposed explaining the complete variscan evolution of the foreland to hinterland transition in the north iberian variscan orogen

combined thrusting and wrenching in the ibero armorican arc a corner effect during continental collision this paper is an attempt to reconcile strain pattern and deformation history in an overall arcuate structure with continental collision processes geological data are first presented for the early history 400 ma of the variscan orogenic belt in france principal stretch trajectories are on a large scale more or less parallel with the trend of the belt they became strongly oblique to this trend near the basal surfaces of the nappes a kinematic model combining two orthogonal shear components is proposed to explain such a strain pattern it is concluded that the observed strain trajectories result from a combination of a southward thrusting and a sinistral wrenching this conclusion is in good agreement with previous conclusions gained by several local microtectonic studies the geodynamic significance of combined thrusting and wrenching at the scale of the ibero armorican arc is discussed and a progressive deformation model is proposed

rapid circulation of warm subtropical waters in a major glacial fjord in east greenland the recent rapid increase in mass loss from the greenland ice sheet is primarily attributed to an acceleration of outlet glaciers oceanographic data obtained in summer 2008 show that subtropical waters that reside year round in the shelf ocean off greenland continuously enter a large glacial fjord in east greenland and contribute to melting at the glacier terminus the recent rapid increase in mass loss from the greenland ice sheet1 2 is primarily attributed to an acceleration of outlet glaciers3 4 5 one possible cause of this acceleration is increased melting at the ice ocean interface6 7 driven by the synchronous warming8 9 10 of subtropical waters offshore of greenland however because of the lack of observations from greenland s glacial fjords and our limited understanding of their dynamics this hypothesis is largely untested here we present oceanographic data collected in sermilik fjord east greenland by ship in summer 2008 and from moorings our data reveal the presence of subtropical waters throughout the fjord these waters are continuously replenished through a wind driven exchange with the shelf where they are present all year the temperature and renewal of these waters indicate that they currently cause enhanced submarine melting at the glacier terminus key controls on the melting rate are the volume and properties of the subtropical waters on the shelf and the patterns of along shore winds suggesting that the glaciers acceleration has been triggered by a combination of atmospheric and oceanic changes our measurements provide evidence for a rapid advective pathway for the transmission of oceanic variability to the ice sheet margins

superposed deformation in the peninsula mitre recess fuegian thrust fold belt southern argentina and implications for orogenic curve kinematics abstract a detailed study of the structure of the peninsula mitre recess in the fuegian thrust fold belt of southern argentina reveals superposed deformation related to contrasting shortening directions one group of structures trend parallel to the recess and verge either towards the foreland or towards the hinterland a second group of structures accommodate contraction superposed on the previous group analysis of fault slip data reveals that the first group is related to 1 perpendicular to the surface traces of thrusts and or fold axes and are therefore compressive structures in contrast the paleostress tensors of the second group of structures show 1 orientations parallel or at a low angle with respect to local structural trends the style of the superposed structures of the second group which mostly indicate contraction subparallel to the trend of the recess is consistent with structures resulting from tangential longitudinal shortening associated with oroclinal bending this scenario implies that the peninsula mitre recess formed as a progressive curve involving rotation due to slip trajectories convergent toward the recess causing the observed tangential contraction this kinematic model supports previous interpretations of buttressing of the thrust fold belt against a basement promontory

oroclines thick and thin an orocline is a thrust belt or orogen that is curved in map view due to it having been bent or buckled about a vertical axis of rotation two distinct types of oroclines are recognized progressive and secondary progressive oroclines are restricted to the scale of a thrust sheet to thrust belt are thin skinned and develop during thrust sheet emplacement secondary oroclines are larger occurring at the scale of an orogen and are plate scale features that affect crust and lithospheric mantle unlike progressive oroclines which develop during initial orogenesis and in response to the same orogen perpendicular stress responsible for thrust sheet emplacement secondary oroclines are extra orogenic developing after initial orogenesis and in response to an orogen parallel principal compressive stress that is oriented at a high angle to the stress responsible for orogen development we present case studies of the wyoming salient a progressive orocline that characterizes the sevier thrust belt of the western united states and the coupled cantabrian and central iberian oroclines which are linked secondary oroclines affecting the variscan orogen of iberia the vertical axis rotations involved in progressive and secondary orocline formation are most readily quantified through paleomagnetic analysis detailed three dimensional palinspastic restoration that incorporates translation rotation and strain can distinguish the role if any of primary curvature in progressive oroclines the use of tectonic vectors such as paleocurrent directions provides a means of recognizing and characterizing the initial geometry of secondary oroclines because secondary oroclines involve the entire lithosphere detailed studies of coeval metamorphism and magmatism provide a means of constraining the fate of the mantle lithosphere during oroclinal buckling

deeply incised submarine glacial valleys beneath the greenland ice sheet the bed topography beneath the greenland ice sheet controls the flow of ice and its discharge into the ocean a combination of sparse radar soundings of ice thickness and high resolution ice motion data suggest that many submarine ice covered valleys extend significantly deeper below sea level and farther inland than thought

geochronology and geochemistry of the pola de allande granitoids northern spain their bearing on the cadomian avalonian evolution of northwest iberia the pola de allande pre variscan tonalite granodiorite plutons are located in the narcea antiform at the boundary zone between the cantabrian and west asturian leonese zones of the iberian variscan belt these granitoids were intruded into a neoproterozoic siliciclastic sedimentary sequence with subordinate volcanic intercalations and were subsequently overprinted by variscan thrust related shear deformation u pb laser ablation inductively coupled plasma mass spectrometry icp ms dating of zircons from two plutons yielded concordant ages of intrusion of 605 10 and 580 15 ma to the authors knowledge this is the first reported u pb cadomian avalonian age for igneous rocks in this section of the iberian variscan belt these intrusions are coeval with the main episode of dominantly calc alkaline magmatic activity related to cadomian avalonian subduction major and trace element composition of the granitoids is characteristic of i type high k calc alkaline granitoids generated in continental arc se

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

analysis of kilometric scale superposed folding in the central coal basin cantabrian zone nw spain abstract the carboniferous paralic sequence of the central coal basin cantabrian zone hercynian nw spain contains an outstanding example of kilometric scale superposed folding that allows comparison with previous experimental models first generation folds have a n s trend and mainly constitute a fold train of fault propagation folds in which an increase of interlimb angle and an increase in the dip of the axial plane is observed from west to east a second folding phase gave rise to two types of upright roughly e w oriented superposed folds the superposed folds generated in general by buckling but their trend and situation are controlled by lateral ramps of the previous thrusts in many cases superposed folds of the first type are the most common and have developed on the limbs of previous folds without folding their axial surfaces they occur in zones and usually have kilometre scale hinge lines with syngenetic curved traces these folds present wavelengths distinctly smaller than those of the previous folds the second type of superposed folds affect both the limbs and axial planes of the previous folds these second type folds are in some cases smaller than previous folds and have developed on closed early folds but in other cases they are large wavelength folds related to the tightening of lateral ramps of the thrusts

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

are the oroclines of the variscan belt related to late variscan strike slip tectonics terra nova 23 241 247 2011 abstract early variscan structures and magnetic anomalies delineate four oroclines along the variscan belt the arcs bend the lithostratigraphic zones of the autochthon and the allochthonous terranes which include ophiolites of the rheic suture and units of gondwanan derivation subducted on both sides of the rheic ocean a transcurrent model dominated by right lateral motion explains the genesis and evolution of the oroclines and a simple plate tectonics scenario links late variscan dextral strike slip movements in the variscides to a broad intracontinental shear zone kinematically equivalent to a transform fault terra nova 00 1 7 2011

kinematic constraints on buckling a lithospheric scale orocline along the northern margin of gondwana a geologic synthesis abstract the paleozoic variscan orogeny was a large scale collisional event involving amalgamation of multiple continents and micro continents existing data suggests oroclinal buckling of an originally near linear convergent margin during the last stages of variscan deformation in the late paleozoic closure of the rheic ocean resulted in e w shortening present day coordinates in the carboniferous producing a near linear n s trending east verging belt subsequent n s shortening near the carb permian boundary resulted in oroclinal buckling this late stage orogenic event remains an enigmatic part of final pangea amalgamation the present day arc curvature of the variscan has inspired many tectonic models with little agreement between them while there is general consensus that two separate phases of deformation occurred various models consider that curvature was caused by dextral transpression around a gondwana indentor strike slip wrench tectonics or a change in tectonic transport direction due to changing stress fields more recent models explain the curvature as an orocline with potentially two opposite facing bends caused by secondary rotations deciphering the kinematic history of curved orogens is difficult and requires establishment of two deformation phases an initial compressive phase that forms a relatively linear belt and a second phase that causes vertical axis rotation of the orogenic limbs historically the most robust technique to accurately quantify vertical axis rotation in curved orogens is paleomagnetic analysis but recently other types of data including fracture geochemical petrologic paleo current and calcite twin data have been used to corroborate secondary buckling a review of existing and new variscan data from iberia is presented that argues for secondary buckling of an originally linear orogenic system together these data constrain oroclinal buckling of the cantabrian orocline to have occurred in about 10 ma during the latest carboniferous which agrees well with recent geodynamical models and structural data that relate oroclinal buckling with lithospheric delamination in the variscan

geometry kinematics and tectonic models of the kazakhstan orocline central asian orogenic belt abstract the central asian orogenic belt caob is one of the largest accretionary orogens on earth and is characterized by the occurrence of tight oroclines kazakhstan and tuva mongolian oroclines the origin of these large scale orogenic curvatures is not quite understood but is fundamentally important for understanding crustal growth and tectonic evolution of the caob here we provide an outline of available geological and paleomagnetic data around the kazakhstan orocline with an aim of clarifying the geometry kinematics and geodynamic origin of the orocline the kazakhstan orocline is evident in a total magmatic image and can be traced by the continuation of high magnetic anomalies associated with the devonian volcanic belt and the late devonian to carboniferous balkhash yili arc paleomagnetic data show 112 126 clockwise rotation of the northern limb relative to the southern limb in the late devonian to early carboniferous as well as 15 28 clockwise rotation of the northern limb and 39 40 anticlockwise rotation of the southern limb relative to the hinge of the orocline during the late carboniferous to permian we argue that the kazakhstan orocline experienced two stage bending with the early stage of bending late devonian to early carboniferous 112 126 driven by slab rollback and the later stage late carboniferous to permian 54 68 possibly associated with the amalgamation of the siberian tarim and baltic cratons this new tectonic model is compatible with the occurrence of rift basins the spatial migration of magmatic arc and the development of large scale strike slip fault systems during oroclinal bending

increase in radon emission due to rock failure an experimental study 1 radon anomalies are commonly observed prior to dynamic failure in the crust and are interpreted as cracking of the medium thus attracting considerable attention in understanding the precursory phenomena of earthquakes and volcanic activity in this study we have compared the starting radon emissions from low porosity crystalline lava phonolite samples with those from damaged and failed samples the damaged sample was loaded up to just beyond the end of the linear elastic phase as evidenced by the output of ae energy the increase in total porosity and a decrease in p wave and s wave velocity relative to the intact sample whereas the failed sample showed deformation behaviour characteristically brittle with increasing values of ae output and porosity as the sample approached macroscopic failure radon measurements have evidenced that dilatational microcracking of deformed sample produced no significant variation in radon emanation with respect to the intact sample in contrast after macroscopic failure radon emanation drastically increased therefore major finding from this study is that in the case of low porosity and relatively high strength crystalline lavas the development of a macroscopic fracture provides new large exhaling surface resulting in a substantial increase in radon emission rate

diachronous post orogenic magmatism within a developing orocline in iberia european variscides 1 u pb zircon crystallization ages of 52 late variscan granitoid intrusions from nw iberia 19 from new data 33 from previous studies constrain the lithospheric evolution of this realm of the variscan belt of western europe and allow assessment of the relationship between oroclinal development and magmatism in late carboniferous early permian times the u pb ages in conjunction with a range of geological observations are consistent with the following sequence of events i oroclinal bending starts at 310 305 ma producing lithospheric thinning and asthenospheric upwelling in the outer arc of the orocline accompanied by production of mantle and lower crustal melts ii between 305 and 300 ma melting continues under the outer arc of the orocline central iberian zone of the iberian variscan belt and mid crustal melting is initiated coevally the lithospheric root beneath the inner arc of the orocline thickened due to progressive arc closure iii between 300 and 292 ma foundering of the lithospheric root followed by melting in the lithospheric mantle and the lower crust beneath the inner arc due to upwelling of asthenospheric mantle iv cooling of the lithosphere between 292 and 286 ma resulting in a drastic attenuation of lower crustal high temperature melting by 285 ma the thermal engine generated by orocline driven lithospheric thinning delamination had cooled down beyond its capability to produce significant amounts of mantle or crustal melts the model proposed explains the genesis of voluminous amounts of granitoid magmas in post orogenic conditions and suggests that oroclines and similar post orogenic granitoids common constituents of numerous orogenic belts may be similarly related elsewhere

radar mapping of isunnguata sermia greenland ice thickness estimates using advanced nadir sounding and tomographic radar processing techniques are compared and combined in a study of isunnguata sermia glacier greenland using an ensemble of operation icebridge flight lines spaced at 500m intervals and running approximately along the flow direction we find there is a statistically excellent comparison between subglacial terrains derived from two dimensional tomography and gridded nadir sounding analysis shows that tomographic data better capture short wavelength 1 2 km patterns in basal terrain but interpolated nadir sounding data yield more spatially extensive and continuous coverage across the glacier especially in deep subglacial troughs using derived surface and basal topography maps we find that driving stress and measured and modeled surface velocity comparisons indicate that basal sliding is an important component of the glacier motion but is also only weakly coupled to the detailed bed topography save for the deepest troughs as might be expected for this land terminating relatively slow moving glacier the subglacial and proglacial topography is similar suggesting the erosional processes acting on the modern glacier bed once helped sculpt the now exposed land

a revised geodynamic model for the lapland kola orogen abstract the paleoproterozoic lapland kola orogen in fennoscandia has been studied for decades and several plate tectonic models have been proposed including one sided subduction zone either towards sw or nw or two opposite verging subduction zones before the collision based on new structural and isotope data from finland and recently published data from russia we propose a revised tectonic model for the paleoproterozoic lapland kola orogen the main components are foreland in the ne followed by cryptic suture inari arc retro arc basin and retro arc foreland in the sw the latter three constitute the inari orocline subduction towards present sw and subsequent arc magmatism inari arc started at ca 1 98 ga followed by voluminous sedimentation in the deepening retro arc basin underplating of a mid ocean ridge caused flat subduction and magmatic flare at 1 92 ga over a broad distance in the retro arc basin rapid heating led to melting of the retro arc basin sediments and voluminous amounts of granulite facies diatexites formed during collision d1 at 1915 1910 ma large thrust nappes formed on the foreland deformation in the retro arc basin is seen as recumbent folding and shearing of diatexites in the lower parts of the basin and thrusting of metatextite diatexite packages in the upper parts a post collisional stage is seen as 1904 ma appinites and decompression derived granites at 1 90 1 89 ga renewed shortening d2 due to far field effects in sw at 1 88 1 87 ga led to thick skin shortening of the archean middle crust large scale crustal duplexing of already cooled granulites towards the retro arc foreland and inclined upright folding of granulites in the opposite direction towards the inari arc a switch in the stress field from ne sw to nw se led to orogen parallel contraction and buckling started along a dextral strike slip fault zone to form the inari orocline buckling is seen in the bending of pre orocline fabrics and formation of syn orocline fabrics radial conical folds d3 radial fractures a strike slip fault zone and thrusting at the hinge zone the end result is a mega scale parallel multi layer fold composed of the inari arc retro arc basin and possibly also the heated retro arc foreland

undercutting of marine terminating glaciers in west greenland marine terminating glaciers control most of greenland s ice discharge into the ocean but little is known about the geometry of their frontal regions here we use side looking multibeam echo sounding observations to reveal that their frontal ice cliffs are grounded deeper below sea level than previously measured and their ice faces are neither vertical nor smooth but often undercut by the ocean and rough deep glacier grounding enables contact with subsurface warm salty atlantic waters aw which melts ice at rates of meters per day we detect cavities undercutting the base of the calving faces at the sites of subglacial water sgw discharge predicted by a hydrological model the observed pattern of undercutting is consistent with numerical simulations of ice melt in which buoyant plumes of sgw transport warm aw to the ice faces glacier undercutting likely enhances iceberg calving impacting ice front stability and in turn the glacier mass balance

factors affecting finite strain estimation in low grade low strain clastic rocks the computer strain analysis methods sape mrl and dtnnm have permitted the characterization of finite strain in two different regions with contrasting geodynamic scenarios 1 the talas ala tau tien shan kyrgyzs republic and 2 the somiedo nappe and narcea antiform cantabrian to west asturian leonese zone boundary variscan belt nw of iberia the performed analyses have revealed low strain values and the regional strain trend in both studied areas this study also investigates the relationship between lithology grain size and percentage of matrix and strain estimates the two methodologies used the results show that these methods are comparable and the absence of significant finite strain lithological control in rocks deformed under low metamorphic and low strain conditions

oroclinal bending and evidence against the pangea megashear the cantabria asturias arc northern spain the cantabria asturias arc of southwestern europe is a highly curved variscan belt that formed along the ancient plate boundary between gondwana and laurussia during the assembly of pangea new paleomagnetic data from 59 sites in the southern limb of the arc were combined with previously published data from 109 sites to determine the evolution of the arc a previously unrecognized postrotation magnetization is found in the southern limb refuting earlier models of arc formation that concluded secondary rotation of only 50 of present day arc curvature the new data show that the arc underwent true 100 oroclinal bending of an originally linear belt in a two stage tectonic history this history represents two regional compression phases 1 east west in the late carboniferous pennsylvanian and 2 north south in the permian both in present day coordinates the north south compression phase coincides with the northward movement of gondwana and its final collision with laurussia this tectonic scenario argues against an indentor scenario and does not support a 3500 km dextral megashear proposed in earlier reconstructions

provenance analysis of the paleozoic sequences of the northern gondwana margin in nw iberia passive margin to variscan collision and orocline development abstract the cantabrian zone of nw iberia preserves a voluminous almost continuous sedimentary sequence that ranges from neoproterozoic to early permian in age its tectonic setting is controversial and recent hypotheses include i passive margin deposition along the northern margin of gondwana or ii an active continental margin or iii a drifting ribbon continent in this paper we present detrital zircon u pb laser ablation age data from 13 samples taken in detrital rocks from the cantabrian zone sequence ranging from early silurian to early permian in depositional age the obtained results together with previously published detrital zircon ages from ediacaran ordovician strata allow a comprehensive analysis of changing provenance through time collectively these data indicate that this portion of iberia was part of the passive margin of gondwana at least from ordovician to late devonian times zircon populations in all samples show strong similarities with the sahara craton and with zircons found in libya suggesting that nw iberia occupied a paleoposition close to those regions of present day northern africa during this time interval changes in provenance in the late devonian are attributed to the onset of the collision between gondwana and laurussia additionally the middle carboniferous to permian samples record populations consistent with the recycling of older sedimentary sequences and exhumation of the igneous rocks formed before and during the variscan orogeny late devonian to permian samples yield zircon populations that reflect topographic changes produced during the variscan orogeny and development of the lithospheric scale oroclinal buckling

conical folds produced by dome and basin fold interference and their application to determining strain examples from north canterbury new zealand abstract conical folds associated with dome and basin interference are analysed using equal area plots which provide data on the geometry of the fold surface and estimates of the finite shortening to describe individual folds they are subdivided into subareas defining the domains of each interfering fold set the resulting plots demonstrate that numerous partial cones of distinct geometry are required to adequately describe the folded surface to help identify the presence and accurately determine the geometries of such folds the expected variations in conical fold geometry for interfering folds with varying hinge curvature tightness and limb dips are analysed and illustrated with examples from north canterbury the resulting cone geometries are complex and often difficult to detect which may in part explain the apparent absence of conical folds in some areas of dome and basin interference where parallel folds interfere the divergence of poles to the conical fold surface and cone apical angle provide estimates of the finite shortening associated with folding these shortening estimates are consistently larger than those determined by constructing profiles parallel to shortening along the hinge line of the second fold set

oroclines of the variscan orogen of iberia paleocurrent analysis and paleogeographic implications abstract coupled structural and paleomagnetic analyses have shown that the northern iberian bend of the variscan orogen referred to as the cantabrian orocline developed by vertical axis rotation of an originally linear orogen however palinspastic restoration of the orocline has proven difficult owing to 1 an unusually great orogenic width of over 700 km and 2 exposure of shallow water strata of the gondwanan margin in the northern and southern portions of the orogen we present paleocurrent data from lower ordovician shallow marine clastic sedimentary rocks across the variscan of northern and central iberia collected to constrain palinspastic restoration of the orogen paleocurrent data were collected from over 50 sites and include cross bed foresets ripple crests and casts as well as rare ball and pillow structures syn sedimentary slump folds and incised channels paleocurrent directions fan around the cantabrian orocline are consistently oriented at a high angle to structural strike and yield a consistent offshore direction outward from the oroclinal core similarly changes in structural strike and paleocurrent direction across central iberia imply the presence of a second more southerly orocline the central iberian orocline that is continuous with but convex in the opposite direction of the cantabrian orocline together the cantabrian and central iberian oroclines define an s shaped pair of continental scale buckle folds palinspastic restoration of the oroclines yields a linear continental margin 1500 km long characterized by consistent offshore paleoflow to the west defining a westerly oceanic domain presumably the rheic ocean and an easterly landward direction presumably gondwana recognition of the southern orocline explains the unusual width of the orogen the geometry of aeromagnetic anomalies attributable to variscan rocks and is consistent with available structural data paleomagnetic declination data and the distribution of correlative paleozoic and older rock sequences including shallow water strata of the gondwanan margin the s geometry of the oroclines is similar to the z geometry of the alaskan oroclines of the north america cordillera suggesting that as in the cordillera the iberian oroclines may record a significant margin parallel translation event

geodynamic evolution of the sw europe variscides 1 the early evolution of sw europe variscides started by opening of the rheic ocean at 500 ma splitting avalonia from armorica iberia subduction on the se side of rheic generated the paleotethys back arc basin 430 390 ma splitting armorica from iberia with development of porto tomar ferreira do alentejo ptfa dextral transform defining the boundary between continental armorica and finisterra microplate to the w obduction of paleotethys was followed by armorica iberia collision and emplacement of nw iberian allochthonous units at 390 370 ma whereas toward the west of ptfa there was antithetic ophiolite obduction beja acebuches and rheic ophiolites plus finisterra continental slices on top of ossa morena zone with simultaneous development of eclogites and orogenic magmatism under a flake double wedge tectonic regime continued convergence 370 ma proceeded by intracontinental deformation with progressive tightening of the ibero armorican arc through dextral transpression on the cantabrian indentor from iberia to armorica the proposed model is discussed at the light of the driving mechanism of soft plate tectonics

emplacement of the cuera and picos de europa imbricate system at the core of the iberian armorican arc cantabrian zone north spain new precisions concerning the timing of arc closure the final stages of the variscan orogeny mostly carboniferous in the western european variscan belt involved the development of the iberian armorican arc which is cored by the cantabrian zone nw iberia the cantabrian zone is the foreland of the western european variscan belt and it is interpreted to record the waning stages of the closure of the rheic ocean the distalmost tectonic units within the cantabrian zone the cuera unit and the picos de europa province were the last tectonic units emplaced at the core of the western european variscan belt orocline together they form an imbricate system and associated wedge top basins that are key to understanding the development of the orocline the emplacement of the cuera unit and the picos de europa province occurred in the latest pennsylvanian between moscovian and gzhelian times new detailed mapping together with stratigraphic sedimentologic and biostratigraphic data analysis of syntectonic successions and structural information constrain the timing and evolution of this imbricate system our analysis indicates that the thrust sheets were emplaced roughly perpendicular to previous tectonic units of the cantabrian variscan foreland fold and thrust belt most probably during the oroclinal bending of the sw european variscan belt that formed the iberian armorican arc the n s directed imbricate system was characterized by a shallow dip of the topographic surface 150 15 km and complex structure of the orogenic wedge are thought to result from the progressive increase in the dip of the basal decollement during bending of the underlying gondwana lithosphere and may reflect the closure of the iberian armorican arc

kinematics of orocline tightening in the core of an arc paleomagnetic analysis of the ponga unit cantabrian arc northern spain 1 paleomagnetic and structural analyses of the western european variscan belt wevb suggest that the most viable kinematic model for variscan deformation in northern iberia is oroclinal bending of an originally linear belt in a two stage tectonic history this history represents two regional compression phases e w in the late carboniferous and n s in the permian both in present day coordinates which resulted in the refolding about steeply plunging axes of initially north south trending thrusts and folds in the hinge zone and oroclinal tightening due to vertical axis rotation of the belt s limbs however the orocline model has yet to be critically tested in the wevb s core this study reports new paleomagnetic rock magnetic and structural data from the inner core of the wevb in order to test opposing kinematic models for the well documented fault and fold interference structures formed by late stage variscan deformation and to better understand the overall development of the wevb arc map scale structural features within the wevb core have a highly sinuous geometry characterized by transverse and thrust parallel fold systems formed by fault bend folding over footwall ramps the intersections of these two fold systems produce steeply plunging interference folds which are best exposed in the ponga thrust unit a total of 67 paleomagnetic sites were collected in the barcaliente formation of the ponga unit with emphasis placed on detailed spatial coverage of individual structural domains a multicomponent paleomagnetic remanence was measured which is interpreted to be composed of two components a low unblocking temperature recent viscous magnetization and a high unblocking temperature ancient magnetization that was acquired in the latest stephanian to early permian after initial d1 thrusting and folding bur prior to major secondary rotation rock magnetic experiments show that the characteristic remanence magnetization is carried by secondary authigenic pseudosingle domain magnetite these paleomagnetic results are used to determine the kinematics and geometry of postmagnetization deformation by restoring in situ magnetic vectors back to a defined reference direction on the basis of the restored ponga unit geometry the steeply plunging interference folds found in the wevb core are best described by a combination of secondary buckling of frontal ramp parallel hanging wall anticlines and modification of d1 lateral oblique ramps as frontal ramps during late stage north south shortening this combination of structural modification of the inner core of the wevb was necessary to accommodate oroclinal bending during the final amalgamation of pangea in the late paleozoic

behaviour of minor arcuate shapes hosted in curved fold and thrust belts an example from the northern apennines italy s satolli et al minor arcs in curved fold and thrust belts arcuate fold and thrust belts have been extensively studied in the literature less attention however has been paid to the characteristics of local scale arcuate structures meaning 5 10 km long fold or thrust traces that display map view curvature nevertheless detailed investigation of small arcuate structures hosted in major arcs can contribute to understanding the pervasiveness of deformation mechanisms we performed a combined geological and palaeomagnetic study on 21 sites from a c 60 km 2 area in the northern apennines in order to analyse minor arcs at a kilometric scale as evidenced by the geological and structural analysis performed on the 21 sites the fold axial trend changes from n s to nw se in the study area the comparison with palaeomagnetic results shows the lack of correlation between vertical axis rotations and fold axial trends as a consequence the minor arcuate shapes of thrusts and related folds are interpreted as mostly primary features inherited from the geometry of the palaeomargin represented by pre orogenic faults according to a context of inversion tectonics

superimposed folding and w sn vein type mineralisation in the central iberian zone associated with late variscan oroclinal buckling a structural analysis from the regoufe area portugal abstract the cantabrian orocline is a major orocline that bends the variscan belt of western europe despite a wealth of studies its timing and relationship with the late variscan folding stages in the iberian massif are still debated this study provides an integrated structural analysis of the variscan fold generations and associated w sn bearing vein systems within the southern central iberian zone regoufe portugal giving insight into their kinematic relationship with oroclinal buckling two superimposed fold generations with mutually parallel steep to vertical fold axes have been identified isoclinal f 1 folds with e w striking axial planes formed during coaxial shortening and are spatially localised f 3 folds with nw se axial planes are associated with late variscan transpressional deformation and constrain the structural outline of the major folds temporal and kinematic considerations indicate that vertical axis asymmetric f 3 folding corresponds with the expected deformation style within the southern limb of the cantabrian orocline the regoufe area is characterised by two types of w sn vein type mineralisation granite hosted hydrothermal quartz veins show a concentric distribution and are associated with the stress regime during granite emplacement the vein system within the metasedimentary host rock however is emplaced along a regional subhorizontal cross fold joint system this cross fold joint system developed orthogonal to the subvertical f 3 fold axes and is interpreted to be coeval with oroclinal buckling these results impact the understanding of i the relative significance and geometry of the main deformation stages in the iberian massif reconciling the timing and kinematics of f 3 regional folding with oroclinal buckling and ii the kinematic relationship between late to postorogenic deformation and w sn vein type mineralisation

thin skinned tectonics in the ponga region cantabrian zone nw spain the variscan thrust and associated fold structures of the ponga region cantabrian zone nw spain are interpreted in terms of thin skinned tectonics with a dominant eastward transport direction

bending the bolivian orocline in real time global positioning system gps data from the central andes record vertical axis rotations that are consistently counterclockwise in peru and bolivia north of the bend in the mountain belt and clockwise to the south in southern bolivia argentina and chile these geologically instantaneous rotations have the same sense as rotations that have accrued over millions of years and are recorded by paleomagnetic and geologic indicators the change in sign of the rotation at both decadal and million year time scales occurs across the axis of topographic symmetry that defines the bolivian orocline when extrapolated to a common time interval the magnitudes of rotation from geologic features and from gps are surprisingly similar given that a significant part of the instantaneous deformation field is probably elastic and due to interseismic locking of the plate boundary some of the interseismic deformation field must reflect permanent deformation and or some of the current elastic deformation will be converted to upper plate permanent deformation over time rather than be recovered by elastic rebound during interplate earthquakes we suggest that the spatial patterns of the elastic and the permanent modes of bending are similar because they are driven by the same stress field

crustal structure of the external variscides in northwest spain from deep seismic reflection profiling abstract recent deep crustal seismic reflection profiling escicantabrica 1 provides a detailed image of the external parts of the variscan belt in northwest spain these seismic data together with surface geological information provide constraints on the crustal structure of the foreland thrust and fold belt cantabrian zone and the transition to the hinterland areas narcea antiform area the image in the cantabrian zone includes strong inclined reflections in the upper 5 s that correspond to mappable paleozoic rocks at the surface which have been deformed by thrusting and folding during the carboniferous some of the major thrust faults imaged show a ramp flat geometry at depth and merge into a highly reflective band between 5 and 6 s that corresponds to the cantabrian zone detachment the precambrian basement is almost transparent underneath the cantabrian zone detachment there are a few subhorizontal discontinuous reflections at 11 s that may correspond to the reflection moho at the transition to the hinterland the seismic profile includes short inclined reflections grouped in several reflective bands in the upper 6 s these correspond to the narcea antiform which comprises at the surface a stack of thrust sheets containing precambrian rocks the narcea antiform is placed above a crustal scale ramp imaged by strong w dipping reflections between 6 and 9 s these reflections merge upwards into the cantabrian zone detachment at 6 s and downwards into a reflective lower crustal zone located between 9 and 12 s these midcrustal reflectors are interpreted as a major variscan shear zone that marks the transition between the thin skinned tectonics of the external areas and the thick skinned tectonics of the hinterland areas the lower crust is highly reflective below the narcea antiform area and reflectivity fades out to the east beneath the foreland thrust and fold belt the different seismic responses at middle and lower crustal levels in the foreland and hinterland areas suggest that variscan tectonics strongly affected deep crustal levels in the hinterland areas whereas they remained undeformed beneath the foreland

conical folds an artefact of using simple geometric shapes to describe a complex geologic structure abstract reliance on diagrams and tangent plots to describe fold geometry has created an unwarranted status for conical folds at the expense of periclines analysis of virtual periclines using synthetic stereograms tangent diagrams and geologic curvature analysis demonstrates small portions of periclines are cylindrical the more significant non cylindrical portion of periclines allows for a mathematically permissible but unrealistic geometrical representation as portions of cones we demonstrate cones are an extremely poor geometric representation of both the virtual periclines and examples of natural non cylindrical folds conical folds if they exist terminate at a point the amplitude to width ratio and the plunge of the crestal line must remain constant towards the fold terminus with a gaussian curvature of zero in contrast the amplitude to width ratio plunge along the crestal line and gaussian curvature of periclines vary towards the fold terminus these differences have important implications for the rheological modeling of folds and while realistic dynamic models for periclines exist models for conical fold formation remain conceptual we suggest that in order to advance our understanding of how folds form it may be pointless to continue the misconception of conical folds as an accurate geometric representation of how folds end

a mass conservation approach for mapping glacier ice thickness the traditional method for interpolating ice thickness data from airborne radar sounding surveys onto regular grids is to employ geostatistical techniques such as kriging while this approach provides continuous maps of ice thickness it generates products that are not consistent with ice flow dynamics and are impractical for high resolution ice flow simulations here we present a novel approach that combines sparse ice thickness data collected by airborne radar sounding profilers with high resolution swath mapping of ice velocity derived from satellite synthetic aperture interferometry to obtain a high resolution map of ice thickness that conserves mass and minimizes the departure from observations we apply this approach to the case of nioghalvfjerdsfjorden 79north glacier a major outlet glacier in northeast greenland that has been relatively stable in recent decades the results show that our mass conserving method removes the anomalies in mass flux divergence yields interpolated data that are within about 5 of the original data and produces thickness maps that are directly usable in high spatial resolution high order ice flow models we discuss the application of this method to the broad and detailed radar surveys of ice sheet and glacier thickness copyright 2011 by the american geophysical union

new kinematic constraints on the cantabrian orocline a paleomagnetic study from the penalba and truchas synclines nw spain abstract the cantabrian orocline is a large structure that bends the variscan orogen of western europe in nw iberia the extensively studied kinematics of its core the foreland of the orogen indicates that the structure is secondary i e acquired after the formation of the orogenic edifice however the extent of the cantabrian orocline away from its core is under debate in this paper we study the kinematics of the cantabrian orocline beyond the foreland we collected and analyzed samples from the northern and central parts of the truchas syncline which provides new data within the hinterland of the orogen in nw iberia the analysis of 320 samples shows a late carboniferous remagnetization with an e to ne declination and shallow downward inclinations these results suggest a counter clockwise rotation of 60 and peri equatorial but still southern hemisphere latitude for iberia during the uppermost carboniferous early permian this rotation fits with the expected kinematic evolution of the truchas syncline if it indeed was part of the cantabrian orocline

high resolution mapping of offshore and onshore glaciogenic features in metamorphic bedrock terrain melville bay northwestern greenland abstract geomorphological studies of previously glaciated landscapes are important to understand how ice sheets and glaciers respond to rapidly changing climate melville bay in northwestern greenland contains some of the most sensitive but least studied ice sheet sectors in the northern hemisphere where the bathymetric knowledge previously was restricted to a few sparsely distributed single beam echo soundings we present here the results of high resolution geomorphological mapping of the offshore and onshore landscapes in melville bay using multibeam sonar and satellite data at 5 and 10 m resolutions respectively the results show a similar areally scoured bedrock dominated landscape with a glacially modified cnoc and lochan morphology on the inner shelf 150 500 m depth and on the nearby exposed coast this is manifested by the presence of u shaped troughs moutonee type elongated landforms stoss and lee forms and streamlined features the submarine landscape shows features that are characteristic of bedrock in folded faulted and weathered metamorphic terrain and to a lesser extent glacially molded bedforms while coastal landforms exhibit higher relief irregular shaped basins and more subdued fracture valleys although generally similar the onshore and offshore landscapes contain examples of distinctly different landform patterns which are interpreted to reflect a longer exposure to long term deep weathering as well as to more recent periglacial weathering processes on land the spatial variability in the distribution of landforms across the landscape in both study areas is mostly attributed to differences in lithological properties of the bedrock the lack of sediment cover on the inner shelf is likely a result of a capacity for sediment erosion and removal by the west greenland current flowing northward over the area in combination with limited sediment supply from long sea ice cover seasons the distribution and orientation of the landforms in the offshore part indicate ice movement toward the nw and suggests that this area acted as a tributary or onset region for the major paleo ice stream that formed the present day melville bay trough

the neutral lines in buckle folds abstract the neutral line in a buckle fold dividing areas of outer arc extension from areas of inner arc shortening is a fundamental concept in structural geology in the past folds have been constructed kinematically from a given neutral line geometry using the tangential longitudinal strain pattern in this study a mechanical finite element model is used to numerically buckle single layer folds with newtonian and power law viscous rheology two neutral lines can be distinguished the incremental neutral line zero layer parallel strain rate and the finite neutral line zero finite layer parallel strain the former develops first and migrates through the layer from the outer towards the inner arc ahead of the latter both neutral lines are discontinuous along the fold and terminate either at the bottom or top interface of the layer for decreasing viscosity ratio between layer and matrix and for decreasing initial amplitude the neutral lines develop later during folding and for some cases no neutral line develops the dynamical behaviour of the neutral lines is similar for newtonian and power law viscous rheology if the viscosity ratio is large but substantially different for small viscosity ratios the results are discussed in light of fold related structures such as outer arc extension structures and inner arc shortening structures

dating of lithospheric buckling 40ar 39ar ages of syn orocline strike slip shear zones in northwestern iberia abstract orogenic curvature is a ubiquitous feature of mountain belts and the plate tectonic and geodynamic setting responsible for the development of curved orogens is a subject of debate in order to distinguish between different models of orocline formation it is necessary to tightly constrain the absolute timing of oroclinal development however determining the absolute isotopic timing of oroclinal bending is challenging the most direct method available to constrain the time interval during which an orocline formed is to obtain absolute age constraints on fabrics generated within syn orocline strike slip shear zones that accommodated rotations around a vertical axis during the development of crustal or lithospheric scale orogenic curvature here we present a data set of 40ar 39ar ages obtained from five shear zones some of which display curved traces parallel to the cantabrian orocline structural grain in nw iberia and are interpreted to have been generated coevally to it the 40ar 39ar ages were obtained by laser rastering induced step heating on single muscovite crystals that grew synkinematically during shearing all five samples yielded ages that cluster tightly at 308 3 ma providing direct evidence for the age of oroclinal bending this age is consistent with the age constraints obtained from paleomagnetic and structural data that place the onset of oroclinal bending in moscovian times our 40ar 39ar age determinations therefore provide a reliable absolute constraint on the age of buckling of the variscan orogen around a vertical axis and provide further evidence that oroclinal bending is unrelated to variscan convergence collision or the subsequent extensional collapse of the mountain belt

the eastern iranian orocline abstract the eastern iranian range is seen as a large scale india eurasia collisional event and the subsequent amalgamation of the afghan and lut micro continents including the neo tethyan accretionary complexes and associated island arcs revised examination of the nature of tectono stratigraphic units distributed in both sides of the n s elongated eastern iranian orogen reveals two remarkable facts first from a general perspective it is structurally a giant parallel antiform in profile view second lithologically the most time equivalent comparable tectonic units from both northern and southern domains comprising the eastern iranian orogen are connectable follow the strike of hinge and limbs zones of the antiform and a m shaped disharmonic pattern in its core these characters are thought to be formed in response to two principal deformational phases resulting from two perpendicular stress directions the first was n s associated with the north dipping subduction of the tethyan oceanic lithosphere beneath the roughly ribbon shaped cimmerian supercontinent including the afghan and lut blocks before late eocene afterward the second was e w shortening originated by the westward escape of the afghan block as a consequence of the indian plate indentation into eurasia this orogen parallel stress was correspondingly accommodated by tens of degrees counter clockwise rotation of the lut block around a vertical axis the result of such shortening was oroclinal buckling and concomitant retreating of the subduction zone and closure of the sistan ocean a remaining wedge shaped part of the neotethys ocean formed by the ribbon curvature the development of the eastern iranian orogen already included the sistan suture zone an enormous mass of folded eocene flysch deposits with a general n s axial surface and some cretaceous ophiolitic remnants the plate scale buckling which was formed by this late stage orogenic event is hereby considered as an orocline call eastern iranian orocline lithosphere buckling around a vertical axis caused a large scale crustal folding coeval with the bending of its mantle part increasing the lithospheric thickness of the orocline compared to adjacent regions the syn orocline deformation associated delamination and resulting magmatic events took place in eastern iran during a short period of about 10 to 20 ma in the late paleogene the orocline hinge zone is occupied by the khorasan outer arc and the birjand core while its limbs are composed of the baluch inner arc and the southwestern and southeastern terminations of the lut and afghan blocks the eastern iranian orocline seems to be the middle segment of a triple bending belt with n s two opposite facing bend including afghan lut and sanandaj sirjan blocks this large curvature is possibly an example of secondary oroclines which was formed by collision related escape tectonics although the limited available kinematic data show a kind of progressive orocline

timing and structural evolution in the limb of an orocline the pisuerga carrion unit southern limb of the cantabrian orocline nw spain abstract oroclines are the largest scale folds on earth and the process of oroclinal formation is a key topic in tectonics however most studies of oroclines have focused on the hinge areas where the changes in strike and therefore the orocline shape are most obvious in this paper we investigate the deformation mechanisms the timing and the structural and tectonic evolution of the pisuerga carrion unit situated on the southern limb of the cantabrian orocline at the nw of the iberian peninsula the cantabrian orocline located in the variscan belt of western europe has been recently defined as a secondary orocline constraining kinematics and deformation timing our study in the pisuerga carrion unit reveals that an out of sequence thrust system developed and reactivated existing structures by a flexural slip mechanism that was diachronous with respect to oroclinal formation joint analysis of unconformity bounded rock sequences provide a late moscovian age for oroclinal initiation ca 308 ma at least locally additionally comparing those joint sets found in different series we quantify a minimum of 40 counterclockwise vertical axis rotation for the pisuerga carrion unit during the late pennsylvanian

fold reactivation involving angular unconformable sequences theoretical analysis and natural examples from the cantabrian zone northwest spain abstract during the reactivation of folds truncated by unconformable layers the unconformity surface adopts various geometrical shapes depending on the fold reactivation mechanisms the paleorelief slope is also a determining factor for location and development of cover structures it can be theoretically shown that the reactivation of flexural flow and flexural slip folds below an unconformity produces folds of the same sense of curvature in layers above and below the unconformity viewed in profile that is to say these mechanisms give rise to a cover synform over a basement synform or antiform over antiform when the axes of both folds are subhorizontal folds reactivated by tangential longitudinal strain also behave in the same way in this case the cover folds may become tight even for initially high angles of unconformity which does not happen with flexural mechanisms the reactivation of chevron folds may give rise to opposite curvatures of basement and cover beds hence paradoxical structures such as a cover synform over a basement antiform or viceversa may be produced even if their axes are horizontal when two adjacent parts of the basement sequence are deformed by different folding mechanisms cover beds and unconformity are folded over the homoclinal sequence of each limb in the basement fold during fold reactivation the unconformity surface usually becomes a surface of decollement owing to the structures that have to be developed in the cover in order to accommodate the changes in length of the unconformity the development of extensional or compressional structures in the cover can be predicted from a geometrical study of the unconformity surface natural examples of reactivated folds under unconformable sequences of carboniferous age in the cantabrian zone show a good agreement with the above mentioned theoretical conclusions conclusions obtained on the distribution of folding mechanisms in the limbs and hinge zones and in layers or multilayers of different nature from the geometrical study of folded unconformable sequences in the cantabrian zone also agree with results from published experimental data

analysis techniques for coherent airborne radar sounding application to west antarctic ice streams 1 analysis of coherent radar sounding echoes from polar ice sheets can provide information suitable for classifying the subglacial environment echoes from a general interface consist of both specularly reflected and diffusely scattered contributions specular reflection results from smooth uniform interfaces whereas diffuse scattering results from rough nonuniform interfaces and inhomogeneous media this article discusses how these phenomena are important to the acquisition and analysis of coherent radar sounding data reflection results are presented from airborne surveys conducted in 1987 over the downstream portions of whillans ice stream and ice stream c west antarctica additionally reflection and scattering analyses along with new results are presented for repeat profiles flown in 2001 over ice stream c analysis methods include using echo amplitudes to compute reflection coefficients which are used for inferring the dielectric properties of the subglacial material echo phase analysis provides the locations of dominant scattering centers which relate to reflection or scattering from the interface as well as provide interface roughness estimates comparison of low and high resolution imaging obtained from synthetic aperture radar techniques indicates a reflecting and or scattering interface combining the results from these independent analyses provides classification of the subglacial environment classified regions include smooth seawater smooth saturated sediments accreted marine ice rough bottom crevasses mixed conditions with partial subglacial water and dry frozen conditions

determining the timing of formation of the rawil depression in the helvetic alps by palaeomagnetic and structural methods determining the timing of formation of the rawil depression in the helvetic alps with the use of paleomagnetic and structural methods

bedmachine v3 complete bed topography and ocean bathymetry mapping of greenland from multibeam echo sounding combined with mass conservation greenland s bed topography is a primary control on ice flow grounding line migration calving dynamics and subglacial drainage moreover fjord bathymetry regulates the penetration of warm atlantic water aw that rapidly melts and undercuts greenland s marine terminating glaciers here we present a new compilation of greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach a new 150 m horizontal resolution bed topography bathymetric map of greenland is constructed with seamless transitions at the ice ocean interface yielding major improvements over previous data sets particularly in the marine terminating sectors of northwest and southeast greenland our map reveals that the total sea level potential of the greenland ice sheet is 7 42 0 05 m which is 7 cm greater than previous estimates furthermore it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which aw can access glaciers with marine based basins thereby highlighting sectors of greenland that are most vulnerable to future oceanic forcing

conical folds and apparent rotations in paleomagnetism a case study in the southern pyrenees abstract the so called apparent rotation was defined as the angular deviation between a local paleomagnetic direction after the standard bedding correction and their corresponding paleomagnetic reference j geophys res 85 1980 3659 in this paper we make a theoretical exploration on this concept and we conclude that depending on the number sequence orientation and magnitude of the deformation axes that have affected to the rock volume the apparent rotation may be the addition of a vertical axis rotation plus a spurious rotation the later is an error whose origin is the inappropriate application of the bedding correction during the restoration which does not fit the reverse sequence of deformations then apparent rot s l spurious rot vertical axis rot conical folds are complex geometries that cannot be restored by using the bedding correction however appearance of apparent and spurious rotations has not been studied even though the presence of this kind of folds is very common in fold and thrust belts in this paper we show a way to restore these structures and its associated paleomagnetic data by means of forward modelling on a stereographic projection the modelling has to be based on a good characterization of the geometry fold axis orientation and understanding of the kinematics of the fold general modelling has also allowed us to predict the apparent rotation in conical synclines its magnitude depends on the semiapical angle and on the degree of development of the fold the sense of the rotation clockwise or counter clockwise will depend on the sense of rotation the fold axis the western external sierras provide an excellent case study of apparent rotations due to the presence of a conical fold in the footwall ebro foreland basin of the south pyrenean sole thrust in addition a vertical axis clockwise rotation up to 47 32 in average has been detected in the hagingwall an apparent rotation up to 28 20 in average is observed in the footwall of the structure when a simple bedding correction is used this deviation does not fit with the expected ebro basin direction reference and is caused by the effect of the riglos conical syncline developed by the flexure of the foot wall ramp of the south pyrenean sole thrust the forward modelling carried out considering the geometry and kinematics non significant rotations in the autochthonous foot wall of this structure predicts very well the paleomagnetic observations in the field geographic coordinates with angular departures of only 5 in average the only application of the bedding correction would introduce errors spurious rotations up to 21 12 in average related to the conical geometry that would not allow the differentiation of these distinct structural units

the interpretation of fold axial data from regions of polyphase folding a region with two interfering fold phases is considered if it is assumed that the early fn and later fn 1 fold phase are cylindrical and that fn 1 formed by shear folding then it is shown how the a b directions of fn 1 can be determined a technique for determining the original orientation of fn and sn is presented provided that similar amounts of simple shear occurred on opposing limbs of fn 1 folds the cause of variability in fold axial orientations is investigated and information to be extracted from fold axial distributions is presented

self subduction of the pangaean global plate one of the most striking and rare occurrences in the earth s history is the amalgamation of most of the continental lithosphere into one supercontinent the most recent supercontinent pangaea lasted from 320 to 200 million years ago here we show that after the continental collisions that led to the formation of pangaea plate convergence continued in a large wedge shaped oceanic tract we suggest that plate strain at the periphery of the supercontinent eventually resulted in self subduction of the pangaean global plate when the ocean margin of the continent subducted beneath the continental edge at the other end of the same plate our scenario results in a stress regime within pangaea that explains the development of a large fold structure near the apex of the palaeotethys ocean extensive lower crustal heating and continental magmatism at the core of the continent as well as the development of radially arranged continental rifts in more peripheral regions of the plate

evolution of rhonegletscher switzerland over the past 125 years and in the future application of an improved flowline model to study the past and future evolution of rhonegletscher switzerland a flowline model was developed to include valley shape effects more accurately than conventional flowband models in the model the ice flux at a gridpoint was computed by a two dimensional ice flow model applied to the valley cross section the results suggested the underestimation of the accumulation area which seems to be a general problem of flowline modelling arising from the model s one dimensional nature the corrected mass balance was coupled with the equilibrium line altitude ela change which was reconstructed for the period 1878 2003 from temperature and precipitation records to run the model for the past 125 years the model satisfactorily reproduced both changes in the terminus position and the total ice volume derived from digital elevation models of the surface obtained by analyses of old maps and aerial photographs this showed the model s potential to simulate glacier evolution when an accurate mass balance could be determined the future evolution of rhonegletscher was evaluated with three mass balance conditions the mean for the period 1994 2003 and the most negative 2003 and positive 1978 mass balance values for the past 50 years the model predicted volume changes of 18 58 and 38 after 50 years for the three conditions respectively

a non cylindrical model for the northwest iberian allochthonous terranes and their equivalents in the hercynian belt of western europe abstract a case is made for a non cylindrical development of the european hercynian belt far travelled allochthonous terranes in the belt consist of a mixture of units including catazonal units ophiolites and units derived from the continental margin of gondwana they often depict a metamorphic history of intermediate to high pressure type and caledonian to eo hercynian age and are thought to have been put together in the early stages of the orogeny through a process partly obductive directed onto the continental margin of gondwana considerations upon the disposition of the terranes their relationships with the paleogeography of the gondwana realm and the structures in them suggest that their emplacement took place in an oblique fashion at a small angle to the margin of the continent the proposed allochthon could be related to the development of an island arc or a wedge like subplate in the southern part of the baltica plate later convergence between gondwana and laurussia involving transcurrent mostly dextral movements combined with tectonic escape phenomena would account for the present complexity of the belt and for the narrow strip the allochthonous terranes delineate in westernmost europe

modes of superposed buckling in single layers controlled by initial tightness of early folds in a series of experiments with soft test models superposed buckling folds were produced in a competent layer resting on a slab of incompetent painter s putty the angle between the hinge lines of the first set of cylindrical folds f1 and the direction of the second compression p2 was varied in the different experiments the experiments showed that with an increase in the initial tightness of f1 there was a transition from one mode of superposed buckling to another when the interlimb angle of f1 was very large the superposed deformation gave rise to a dome and basin pattern the first mode of superposed buckling the second mode with small f2 folds riding over larger f1 folds developed when the initial interlimb angle ranged roughly between 135 and 90 the third mode was observed when the f1 interlimb angle was less than about 90 but the fold was not very tight in the third mode a set of non plane non cylindrical folds developed however the sinuous hinge line of the non cylindrical structure was newly created by replacing the old f1 hinge when f1 was very tight or isoclinal the fourth mode of superposed buckling led to the development of non plane non cylindrical folds without concomitant hinge replacement

late quaternary ice flow in a west greenland fjord and cross shelf trough system submarine landforms from rink isbrae to uummannaq shelf and slope sea floor landforms and acoustic stratigraphic records allow interpretation of the past form and flow of a westward draining ice stream of the greenland ice sheet rink isbrae the late pliocene pleistocene glacial package is several hundred metres thick and down laps onto an upper miocene horizon several acoustic facies are mapped from sub bottom profiler records of the 400 km long uummannaq fjord shelf slope system an acoustically stratified facies covers much of the fjord and trough floor interpreted as glacimarine sediment from rain out of fine grained debris in turbid meltwater beneath this facies is a semi transparent deformation till unit which includes buried streamlined landforms landform distribution in the uummannaq system is used to reconstruct past ice extent and flow directions the presence of streamlined landforms mega scale glacial lineations drumlins crag and tails shows that an ice stream advanced through the fjord system to fill uummannaq trough reaching the shelf edge at the last glacial maximum beyond the trough there is a major fan built mainly of glacigenic debris flows turbidity current channels were not observed on uummannaq fan contrasting with well developed channels on disko fan 300 km to the south ice retreat had begun by 14 8 cal ka ago grounding zone wedges gzw in uummannaq trough imply that retreat was episodic punctuated by several still stands ice retreat between gzws may have been relatively rapid there is little sedimentary evidence for still stands in the inner fjords except for a major moraine ridge marking a little ice age maximum position on the shallow banks either side of uummannaq trough iceberg ploughing has reworked any morphological evidence of earlier ice sheet activity

structural metamorphic and magmatic history of the mondonedo nappe hercynian belt nw spain abstract the mondonedo nappe is one of the main units in the internal zone of the hercynian belt in the iberian peninsula it consists of low to medium grade metasediments late precambrian and palaeozoic in age folded by large d 1 e verging recumbent structures and thrusted several tens of km towards the east during a d 2 deformation episode at the base of the thrust sheet a shear zone of up to 3 km thick was developed granitoid bodies which were intruded after d 1 and before or during d 2 were deformed in this basal zone the geometry of d 1 and d 2 structures and that of the isograds are described as well as the relationships between metamorphism and deformation a structural evolution is inferred which shows an episode of generalized ductile deformation d 1 followed by another in which the deformation tended to concentrate in a subhorizontal ductile shear zone d 2 and culminated with the thrusting along an important fracture the shear zone originated in a thermally softened level which according to metamorphic data was at temperatures in the range 550 600 c the structural metamorphic and magmatic features of the mondonedo nappe suggest a relationship with a crustal scale overthrusting of the continental mass to which the nappe belongs this could be a consequence of the collision against another continental mass to the west

restoring paleomagnetic data in complex superposed folding settings the boltana anticline southern pyrenees abstract complex kinematic scenarios in fold and thrust belts often produce superposed and non coaxial folding interpretation of primary linear indicators must be based on a careful restoration to the undeformed stage following the reverse order of the deformation events therefore sequential restoration to the ancient coordinate system is of key importance to obtain reliable kinematic interpretations using paleomagnetic data in this paper a new paleomagnetic study in the western flank of the boltana anticline southern pyrenees illustrates a case study of a complex tectonic setting having superposed non coaxial folds the first stage of nw se folding linked to the oblique boltana anticline took place during lutetian times the second stage was linked to the vertical axis rotation and placed the boltana anticline in its present day n s configuration our data support a long lasting lutetian to priabonian period with main rotational activity during the bartonian priabonian other authors support a var coeval with anticlinal growth the third stage resulted in southwards tilting related to the emplacement of the n120e striking guarga basement thrust oligocene early miocene based on this deformational history a sequential restoration was applied and compared with the classic bedding correction at the site scale single bedding correction gives errors ranging between 31 and 31 in the estimation of vertical axis rotations at the locality scale in sites grouped in three folds from w to e arbella planillo and san felizes the bedding corrected data display rotation values in accordance with those found in the ainsa basin by other authors sequential restoration based on the afore mentioned evolution in three steps improves both some locality means and the internal consistency of the data therefore reasonably constrained sequential restoration becomes essential to reconstruct the actual history of superposed folding areas

orocline timing through joint analysis insights from the ibero armorican arc abstract the timing and kinematics of oroclinal bending in the core of the ibero armorican arc iaa has recently been constrained using paleomagnetic data from the cantabrian zone in northern iberia this study analyzes the joint patterns present in rock units deposited pre syn and post oroclinal bending systematic changes in the orientations of tensional joint sets in superimposed stratigraphic units are interpreted to record the progressive stages of oroclinal bending in the core of the iaa time constrains for joint set development are constrained by the known ages of the bounding unconformities that limit the studied stratigraphic units joint azimuth variability in the pre orocline rocks neoproterozoic to pre upper carboniferous is comparable to the present arc curvature of the orocline about 180 the joints in the syn orocline rocks upper pennsylvanian or stephanian 304 to 299 ma show a lower azimuthal variability that is comparable to about 50 70 of the total curvature seen in pre orocline rocks finally post orocline rocks permian contain joints that have uniform azimuths for each set across the entirety of the present day arc together these spatially and temporally distinct joint sets suggest that rotations in the cantabrian zone took place in the upper pennsylvanian during a ca 10 ma time period which agrees well with previous paleomagnetic arguments the data also provides supporting evidence for oroclinal bending by rotation around vertical axes of an initially linear or nearly linear orogenic belt and finally these data highlight the potential power in using tectonic joint sets for constraining thrust belt kinematics in curved orogenic systems when unconformity bounded stratigraphic sequences are present that are coeval with orocline development

superposed buckle folding in the eastern iberian chain spain abstract the aliaga area eastern iberian chain shows large scale examples of buckle superposition developed during tertiary folding in most cases ene trending folds overprint earlier nnw sse trending ones the resulting structures are mapped analysed and genetically classified by comparison with analogue models described by several authors the following types are found standard type 1 1a dome and basin structure 1b unequal wavelength overprinted folds modified type 1 1c t shaped joined folds 1d t shaped abutting folds 1e l shaped folds 1f snake like folds standard type 2 2a non cylindrical buckling of earlier axial surfaces involving hinge replacement different superposed sets of flexural slip striations record successive folding episodes in snake like folds and hinge replacement in the case of type 2a superpositions types 1 and 2 apparently develop where the earlier folds have interlimb angles over and below 90 respectively which fits the results of analogue modelling and theoretical analysis by previous authors types 1b and 1d are associated with higher w1 w2 wavelength ratios than types 1a and 1c other controlling factors are viscosity contrast and erosion processes specifically erosion of competent limestone beds in the hinge zone of a nnw sse trending anticline allowed the near vertical eastern limb to be refolded into snake like folds