the eastern jura relations between thin skinned and basement tectonics local and regional the thesis area of hans cloos in the eastern jura straddles the boundary between the paleogene structures of the tabular jura a part of the southeastern end of the rhine graben and the neogene folds and thrusts of the folded jura a recent reflection seismic survey in the area adjacent to the east provides new information on the subsurface structure and the relation between three superposed tectonic events the main boundary fault zones of a deep and complexly faulted late paleozoic trough trending ene were reactivated in the early tertiary faulted flexures and small folds rooted in the basement and paleozoic with an amplitude of usually 100 to 300 m were produced rather than the normal faults typical for the extensional fields of the rhine bresse graben system in the west and the bavarian molasse basin in the east this suggests their being part of a transform zone between these extensional fields during jura decollement in the neogene these inherited deeply rooted sub decollement structures remained passive their small size is kinematically incompatible with the intense subsequent thrusting and folding of the thin mesozoic tertiary skin however thrust ramps were apparently nucleated at the respective southern foot of these paleogene flexures and folds the best defined and simplest of these composite structures is the mandach structure within the tabular jura a south facing flexure of about 300 m relief developed in the paleogene by reactivation of the northern border fault zone of the paleozoic trough in the neogene a north vergent decollement thrust which is connected with the regional jura decollement in the middle triassic evaporites was initiated at its site

reconstructing the kinematic evolution of curved mountain belts internal strain patterns in the wyoming salient sevier thrust belt u s a analyses of mesoscopic structural and strain patterns in red beds of the triassic ankareh formation and limestones of the jurassic twin creek formation in concert with complementary paleomagnetic studies constrain the three dimensional kinematic evolution of curved fold and thrust systems in the wyoming salient of the sevier thrust belt spaced cleavage fracture and vein networks minor folds and minor faults in limestones and red beds accommodated early layer parallel shortening lps concentrated in front of the growing thrust wedge along with minor strike parallel extension and wrench shear related to the development of orogenic curvature strain estimated using mass balance relations for cleavage seams crinoid ossicles in bioclastic limestone and reduction spots in red beds displays systematic regional patterns principal shortening directions are subperpendicular to structural trend around the salient reflecting a combination of primary curvature and secondary rotation of early lps fabrics lps magnitudes vary from 5 in central parts of the frontal hogsback thrust system where cleavage is absent to 10 30 in the more interior crawford thrust system where cleavage intensity is moderate to strong strain also increases toward the salient ends internal strain is a significant component of total deformation and should be considered when restoring cross sections strain patterns are consistent with a kinematic model involving curved fault slip and differential shortening that produced progressive secondary curvature during thrusting

palaeomagnetic evidence for late miocene rotation of the swiss alps results from the north alpine foreland basin magnetostratigraphic studies in the oligocene to miocene north alpine foreland basin of switzerland suggest a post middle miocene 13 ma clockwise rotation of the swiss alps the angle of rotation is 16 17 with respect to the present day earth s magnetic field this rotation can be observed in 12 sections analysed for palaeomagnetic directions which cover a lateral distance of 250 km sw ne extension the rotation angle shows neither a significant change throughout the examined period of deposition nor is it dependent on the tectonic position of the individual regions in the basin autochthonous or allochthonous molasse

kinematics of orocline and arc formation in thin skinned orogens the regional traces of folds faults and foliations found in many fold thrust belts are bent in plan view it proves valuable to distinguish between two types of bent orogens based on their kinematic evolution oroclines or rotational arcs are bent orogens in which segments of the orogen change strike during the evolution of the bend and nonrotational arcs are bent orogens in which segments of the orogen do not change strike during development of the bend the kinematic evolution of a bend that forms in a thin skinned orogen can be described in terms of three parameters the displacement path trajectories followed by points along the strike of the orogen the magnitude and distribution of tangential extension along the strike of the orogen and the change in position of the endpoints of the orogen with respect to a reference line only slight differences in the displacement path trajectory pattern determine whether an orogen evolves as a nonrotational arc or as an orocline thus the distinction between these two types of bends is not always of major tectonic significance compressional deformation along irregular continental margins or the impact of indentors on continental margins during collisional orogenies more likely leads to formation of nonrotational arcs as can be simulated with a sand wedge model interaction between a fold thrust wedge with obstacles in the foreland or with a wrench fault more likely leads to orocline formation orocline formation is also associated with noncoaxial reactivation of thrust faults tangential extension is a necessary consequence of certain displacement path trajectory patterns and can accompany development of either nonrotational arcs or oroclines two examples one from the umbrian apennines and one from the makran range demonstrate how movement on cross strike fault arrays can accommodate tangential extension in thin skinned bends

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

understanding progressive arc and strike slip related rotations in curve shaped orogenic belts the case of the olevano antrodoco sibillini thrust northern apennines italy 1 we report on a paleomagnetic study of the southern sector of the olevano antrodoco sibillini oas thrust front which corresponds to the southern limb of the northern apennines italy orogenic salient a lively debate has developed regarding the oroclinal progressive arc versus non rotational nature of the oas which has been alternatively interpreted as a dextral strike slip fault dextral transpressive fault or frontal to oblique ramp that reactivated pre existing jurassic normal faults here we document the paleomagnetism integrated with biostratigraphic and structural data of 52 new sites from both the oas hanging wall and footwall on the basis of 39 retained sites we find a peculiar pattern of tectonic rotations along the oas thrust that evidences four rotational domains the thrust footwall is characterized by a southern domain that undergoes an approximately 30 counterclockwise rotation with respect to the stable foreland and an approximately non rotated domain the data from the hanging wall indicate the occurrence of a dextral strike slip component along the southern sector of the oas thrust supported by a strong clockwise rotation close to the ne sw lateral ramp which rapidly fades 1 km from the thrust front a slight but significant cw rotation observed in the remaining sites from the hanging wall confirms the progressive nature of the oas and its structural position as the southern limb of the northern apennines salient our detailed paleomagnetic study is crucial in discriminating between progressive arc and strike slip related components in the main curved orogenic front of the northern apennines

3 d geomechanical restoration and paleomagnetic analysis of fault related folds an example from the yanjinggou anticline southern sichuan basin abstract we examine the development of the yanjinggou anticline a fault propagation fold in the southern longmen shan through an integrated study of structural geometry strain and paleomagnetism the 3 d structural and strain restoration models generated in our analysis reveal that the ne trending yanjinggou fold has a curved map trace that is convex to the southeast the fold has three distinct regions characterized by different strain patterns contraction in the core of the fold extension in the outer arc and a forelimb with distributed shear to further understand the kinematics of the yanjinggou anticline we performed paleomagnetic analysis on 184 oriented samples collected across the structure anisotropy of magnetic susceptibility ams measurements and stepwise thermal demagnetization were conducted a strike test was applied to the high temperature component htc in order to identify rotation around the arc the result indicates that the yanjinggou anticline is a progressive arc with a minor initial curvature and a dominant secondary curvature related to vertical axis rotation synchronous with thrusting the primary curvature and initial development of the structure correlates with the growth of the southern longmen shan in late miocene the secondary curvature correlates with displacement extending since late pleistocene toward the southeast into the central basin along the detachments that underlie the structure lateral gradients in displacement along this underlying detachment provide a mechanism for producing the vertical rotation of the anticline ams results and historical earthquake analysis imply that the fault propagation fold along with other ne trending structures in the southern sichuan basin are tectonically active and accommodate east west crustal shortening in the basin by integrating 3 d structural and strain restoration modeling with systematic ams and paleomagnetic methods using statistical analysis we closely constrain how the yanjinggou anticline developed and provide insights into the formation of fault related folds with curved shapes in map view which are common in other fold and thrust belts around the world

structure and cenozoic kinematics of the eastern cordillera southern bolivia 21 s 1 the eastern cordillera is a main morphotectonic unit of the central andes in southern bolivia it is predominantly composed of ordovician sedimentary rocks as thick as 10 km revision of the ordovician stratigraphy and new structural fieldwork resulted in detailed balanced cross sections improved estimates of crustal shortening and a new kinematic model for the eastern cordillera new estimates of total shortening in the eastern cordillera are up to 95 km 41 44 higher than previous estimates and sufficient to thicken the andean crust to its present state between the eastern foreland and the magmatic arc after initial tertiary uplift at 58 ma first thrusts developed in the middle eocene to early oligocene 40 30 ma exhuming the central part of the eastern cordillera tectonic shortening culminated in late oligocene and early miocene time 25 20 ma when west facing thrust systems developed in the central and western part of the eastern cordillera thrusting terminated in the western part by the end of the early miocene and middle miocene tectonic activity was restricted to minor strike slip faulting in the central part thrusting remained active until the late miocene by 10 ma shortening in the eastern cordillera essentially ceased kinematic fault analyses indicate clockwise rotation of the shortening direction from nne ssw or ne sw in eocene early oligocene time over e w to wnw ese or even nw se in late oligocene to middle miocene time nevertheless wnw ese directed shortening and subvertical extension predominate sinistral oblique motion on many thrusts probably reflects plan view flexural slip in the clockwise rotating southern limb of the bolivian orocline it is proposed that space problems in the oroclinal hinge slowed the rotation there and caused decoupling of the still rotating south limb along ne trending transfer zones

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

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

thermally distinct ejecta blankets from martian craters utilizing the termoskan data set of the phobos 88 mission we have recognized a new feature on mars ejecta blanket distinct in the thermal infrared edith virtually all of the more than 100 features discovered in the termoskan data are located on the plains near valles marineris ediths have a startlingly clear dependence upon terrains of hesperian age implying a spatial or temporal dependence on hesperian terrains almost no thermally distinct ejecta blankets are associated with any of the thousands of craters within the data set that occur on the older noachian units ediths also do not appear on the portions of the younger tharsis amazonian units seen in the data the hesperian terrain dependence cannot be explained by either atmospheric or impactor variations noachian and hesperian terrains must have experienced identical atmospheric and impactor conditions during hesperian times thermally distinct ejecta blankets therefore reflect target material differences and or secondary modification processes not all lobate ejecta blankets are thermally distinct but all ediths correlated with visibly discernible ejecta blankets are associated with lobate ejecta blankets the boundaries of the thermally distinct areas usually follow closely the termini of the fluidized lobate ejecta blankets even when the ejecta blankets show a high degree of sinuosity thus the thermally distinct nature of ediths must be due to the primary ejecta formation process the coupling of these thermal anomalies to morphology is unlike most sharp martian inertia variations which are decoupled from observed surface morphology some thermally distinct ejecta blankets occur near otherwise similar craters that do not have thermally distinct ejecta blankets thus wind patterns or locally available aeolian material cannot provide a single overall explanation for the observed variations we compiled a data base of 110 edith and non edith craters ranging in diameter from 4 2 km to 90 6 km there are almost no correlations within the data base other than occurrence on hesperian terrains we postulate that most of the observed ediths are due to excavation of thermally distinctive noachian age material from beneath a relatively thin layer of younger more consolidated hesperian volcanic material the plausibility of this theory is supported by much geological evidence for relatively thin near surface hesperian deposits overlying massive noachian megabreccias on the edith rich plains units we suggest that absence of thermally distinct ejecta blankets on noachian and amazonian terrains is due to absences of distinctive near surface layering thermally distinct ejecta blankets are excellent locations for future landers and remote sensing because of relatively dust free surface exposures of material excavated from depth

fault geometry and mechanics of marly carbonate multilayers an integrated field and laboratory study from the northern apennines italy abstract sealing layers are often represented by sedimentary sequences characterized by alternating strong and weak lithologies when involved in faulting processes these mechanically heterogeneous multilayers develop complex fault geometries here we investigate fault initiation and evolution within a mechanical multilayer by integrating field observations and rock deformation experiments faults initiate with a staircase trajectory that partially reflects the mechanical properties of the involved lithologies as suggested by our deformation experiments however some faults initiating at low angles in calcite rich layers i 5 20 and at high angles in clay rich layers i 45 86 indicate the important role of structural inheritance at the onset of faulting with increasing displacement faults develop well organized fault cores characterized by a marly foliated matrix embedding fragments of limestone the angles of fault reactivation which concentrate between 30 and 60 are consistent with the low friction coefficient measured during our experiments on marls s 0 39 indicating that clay minerals exert a main control on fault mechanics moreover our integrated analysis suggests that fracturing and faulting are the main mechanisms allowing fluid circulation within the low permeability multilayer and that its sealing integrity can be compromised only by the activity of larger faults cutting across its entire thickness

strain displacement and rotation associated with the formation of curvature in fold belts the example of the jura arc abstract a new simplified genetic classification scheme for arcuate fold thrust belts is proposed based on total strain patterns and displacement vector fields we distinguish three extreme end member models 1 oroclines pure bending of an initially straight belt 2 piedmont glacier with divergent transport directions and 3 primary arcs a simple geometric model set up for the simulation of strain patterns in primary arcs with uniform transport direction demonstrates that divergent strain trajectories and rotations of passive marker lines do not require any divergence in displacement directions these often quoted arguments are insufficient for the identification of oroclinal bending or piedmont glacier type of arc formation only three dimensional restorations of an arc provide the critical information about displacement directions in their absence arc parallel stretches and rotations in comparison with total strains provide the most useful criteria for the distinction of arc formation modes as an example the jura fold thrust belt of the external alps is discussed a large set of strain data includes total shortening estimates based on balanced cross sections local strain axes orientations from the inversion of fault populations homberg c 1996 unpublished phd thesis universite de paris vi france tectonic stylolites and micro strains from twinning in sparry calcite strain trajectories maximum shortening direction computed from these data define a strongly divergent fan with a 90 opening a complete displacement vector field for the entire jura has been determined from balanced cross sections augmented with three dimensional block mosaic restorations philippe y 1995 unpublished phd thesis universite de chambery france displacement vectors diverge by about 40 markedly less than strain trajectories the non parallelism between strain trajectories and transport directions indicates that considerable wrenching deformation did occur in both limbs of the jura arc paleomagnetically determined clockwise rotations of 0 13 from ten sites kempf o et al terra nova 10 6 10 behind the right hand half of the jura arc and two sites with a combined 23 anticlockwise rotation behind the left hand half of the arc are and additional argument in favor of such a wrenching deformation we conclude that the jura arc formed as a primary arc with a minor component of piedmont glacier type divergence in transport directions

geometrical modeling of fault related folds a pseudo three dimensional approach abstract area balanced cross sections of ramp anticlines and tip line folds in thin skinned fold thrust belts can be quantitatively constructed using plane strain fault bend and fault propagation fold models cross sections alone however are somewhat inadequate for interpreting along strike changes in thrust related fold geometry complex interplay between along strike changes in fault slip and fault shape determines a range of geometric configurations which are difficult to visualize without the aid of quantitative three dimensional models we extend conventional two dimensional folding theories into the third dimension by allowing for continuous variations in fault slip and fault shape along strike geometric equations relating map view angles between fold axial surface traces are derived for a case assuming a uniform fault geometry and an along strike displacement gradient the resulting folds possess no unique fold axis but rather are characterized by multiple fold hingelines each corresponding to bends in the fault for typical displacement gradients observed in the field analysis of the models suggests that discernible differences exist between map patterns of fault bend folds and fault propagation folds whereas little difference exists between map patterns of similar and parallel fault bend folds map view angles between axial surface traces for parallel fault bend folds and fault propagation folds are a function of both ramp cutoff angle and fault slip whereas these same angles for similar fault bend folds are solely a manifestation of fault slip examples assuming uniform shortening and continuously varying fault geometry along strike are also presented fault geometry is varied along strike to simulate oblique and lateral ramps depending upon model type and fault shape parameter modified resulting folds exhibit either cylindrical or non cylindrical fold geometries closure is generated by a decrease in fold amplitude where there is a decrease in ramp cutoff angle along strike or where a fault laterally cuts up section in either instance closure develops without varying shortening along strike model map patterns resemble actual thrust related fold geometries and can be compared to maps of real structures to help predict subsurface geology

early rotation and late folding in the pennsylvania salient u s appalachians evidence from calcite twinning analysis of paleozoic carbonates calcite twinning analysis of paleozoic limestones from 42 sites reveals that the change in regional strike along the frontal edge of the pennsylvania salient is accompanied by an equal magnitude rotation of paleostress directions of up to 60 degrees the rotations recorded at 22 reliable sites show no discernible difference between sites with rocks of cambrian ordovician and silurian devonian age evidence for similarly fanned orientations is not present in foreland sites scatter in the data is attributed to grain scale rotations and compaction overprinting as demonstrated in prior studies and it was reduced by data cleaning methods as well as by the use of contouring and data averaging methods comparisons of paleostress directions within the belt reveal only minor rotations in the southwest region of the salient and the bulk of rotation is accommodated by the northern limb we hypothesize that these rotations resulted from convergence in the thrust wedge against a northerly bounding rigid basement block around pennsylvanian times this created a structural anisotropy in the evolving belt that guided the post rotational formation of folds in early permian times and produced the current pattern of the salient this model of decoupled thrusting rotation and folding explains a variety of previously conflicting observations in the area while offering a kinematically consistent scenario that may also apply to other curved orogenic belts

kinematics of a sigmoidal fold and vertical axis rotation in the east of the zagros makran syntaxis southern iran paleomagnetic magnetic fabric and microtectonic approaches abstract the zagros simple fold belt is characterized by elongated curved or sigmoidal folds the trend of these structures together with the structural style change suddenly across the zagros makran syntaxis which separates the continental collision domain of zagros from the oceanic subduction one in makran this work focuses on the minab anticline outcropping in the easternmost part of zagros in order to understand the kinematics of a sigmoidal fold and underscore possible vertical axis rotations in the eastern side of the syntaxis we performed a joint study of magnetic fabric microtectonics and paleomagnetism of the northern termination of this fold the two limbs have been sampled 7 sites 134 samples along three cross sections corresponding to three different orientations of the fold axis the rocks are weakly deformed fine grained mio pliocene reddish siltstones the shortening directions deduced from both magnetic fabric analysis and microtectonic observations are consistent with each other they are horizontal and roughly perpendicular to the local fold axis following the torsion of the fold hinge line and indicating a tectonic origin of the magnetic fabric rockmagnetic analyses thermomagnetic curves hysteresis loops point to the presence of magnetite in the psd and md ranges as the main magnetic carriers together with a minor contribution from hematite apart from a post tilting sub actual vrm and or crm component a paleomagnetic analyses yield mainly two pre tilting magnetization components component b is carried by magnetite spanning the intermediate to high unblocking temperature range 300 c t ubs 580 c component c has unblocking temperatures characteristic of hematite 580 c t ubs 680 c both are ante folding based on positive reversal and fold tests inside each of the cross section but also for the three sections together however because component c is biased by some inclination flattening only component b is taken into account afterwards after full tectonic correction the site mean direction of component b calculated for 6 out of the 7 sites is not statistically different from the individual site mean directions the intersection direction determined by small circle analysis in these six sites is d 18 0 i 33 7 k 482 alpha 95 2 6 compared to the mio pliocene direction expected in this area for africa it corresponds to an overall clockwise rotation of the whole structure of some 18 3 5 1 consistent with the regional geodynamic context the absence of differential paleomagnetic rotation from one cross section to the other and the fact that the magnetic lineation together with the shortening direction deduced from microtectonic analysis follows the fold curvature demonstrate that the torsion of this fold is not secondary but rather coeval with the fold amplification the torsion of the fold would stem from underlying inherited mesozoic structures and the rheological response during the deformation of two incompetent decollement layers undergoing differential velocities and a change of thickness in a constant stress field direction

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

decollement tectonics in the jura forelandfold and thrust belt abstract interpretation of more than 1500 km of industry seismic reflection lines from theswiss and french jura mountains and the western swiss molasse basin demonstrates that themesozoic and cenozoic cover of the jura fold and thrust belt has been deformed over a veryweak basal decollement and displaced for many kilometers toward the nw and that thebasement is not involved a depth to the basement map derived from depth conversion of theseismic lines shows a rather smooth flat basement dipping 1 3 to the s se the low amplitudebroad folds of the molasse basin and the external plateau jura are controlled by evaporitepillows or anticlines of middle triassic age the high amplitude folds of the haute chaine jura however are related to nw or se vergent thrusts with at least kilometric dipslip displacementthat has doubled the entire jurassic sequence the plateau jura evaporite related folds located in the foreland are interpreted as early stage buckle folds with further deformation afault ramp nucleates and develops into thrust related folds as observed in the haute chaine thus within the fold and thrust belt deformation increases toward the hinterland in the molassebasin however low amplitude folds represent an early deformation stage which could notdevelop further owing to the load of the overlying thick tertiary clastic wedge

geometry and kinematics of fault propagation folds with variable interlimb angle abstract several conceptual approaches have been proposed to account for the development of fault propagation folds whose geometry and kinematics depend on the amount of displacement along a basal decollement level the ramp angle and the slip to propagation ratio among these the variable interlimb angle model of mitra 1990 is able to explain open and close natural folds but its application is limited because the fold geometry and bed thickness evolution rely on imposed parameters that cannot be measured directly here we use the ramp and the interlimb angles as input data to develop a forward fold model that accounts for thickness variations in the forelimb the relationship between the fold amplitude and fold wavelength is subsequently applied to construct balanced geological cross sections from surface parameters only and to propose a kinematic restoration of the folding through time the model can catter for a wide variety of folds reconstruct the deep architecture of anticlines and deduce the kinematic evolution of the folding with time we consider three natural examples to validate the variable interlimb angle model along strike thickness variation in the forelimb of the turner valley anticline in the alberta foothills of canada precisely corresponds to the theoretical values proposed by our model reconstruction at depth of the alima anticline in the southern tunisian atlas implies that the decollement level is localised in the triassic liassic series as highlighted by seismic imaging the kinematic reconstruction of the ucero anticline in the spanish castilian mountains is also in agreement with the fold geometry derived from two cross sections the variable interlimb angle model predicts that the fault propagation fold can be symmetric normal asymmetric with a greater dip value in the forelimb than in the backlimb or reverse asymmetric with greater dip in the backlimb depending on the shortening amount

paleomagnetism and the orocline hypothesis eldredge s bachtadse v and van der voo r 1985 paleomagnetism and the orocline hypothesis in n l carter and s uyeda editors collision tectonics deformation of continental lithosphere tectonophysics 119 153 179 oroclines were originally defined by carey as curved mountain belts which initially were straight or at feast straighter than they are today in the last few years the definition has been broadened to include any curved mountain belt regardless of its original shape since the occurrence of oroclinal bending is best recorded in the change of declination as a function of tectonic setting paleomagnetic and structural data from six potential oroclines have been compiled and analyzed to determine the amount of rotation displayed by the change of paleomagnetic declination relative to the change in strike of the fold belt the arcuate belts investigated are the sicilian calabr n arc and the umbrian arc of italy the swiss portion of the jura mountains the central portion of the appalachian mountains from pennsylvania to virginia u s a the wyoming idaho overthrust belt of western north america and the hercynides of western and central europe the jura mountains and the pennsylvania virginia portion of the appalachians fail to show significant oroclinal bending the wyoming idaho belt shows a combination of rotated possibly oroclinai and unrotated thrust sheets in the sicilian calabrian arc significant oroclinat bending caused by the impingement of the calabria peloritani nappes in the late tertiary can be demonstrated while the umbrian arc of similar age in the northern apennines also shows oroclinal bending on a smaller scale hercynian europe the only belt included in which deformation of basement rocks can be demonstrated shows oroclinal bending at least so as well as a marked original curvature 70 in its western part common to all the orociines studied in this paper is the probable impingement of a rigid block or continental margin during the orogeny causing subsequent deformation and bending of the fold belt

critical taper model of fold and thrust belts and accretionary wedges the fold and thrust belts and submarine accretionary wedges that lie along compressive plate boundaries are one of the best understood deformational features of the earth s upper crust although there is considerable natural variation among the many fold and thrust belts and accretionary wedges that have been recognized and explored several features appear to be universal in cross section fold and thrust belts and accretionary wedges occupy a wedge shaped deformed region overlying a basal detachment or decollement fault the rocks or sediments beneath this fault show very little deformation the decollement fault characteristically dips toward the interior of the mountain belt or in the case of a submarine wedge toward the island arc the topography in contrast slopes toward the toe or deformation front of the wedge deformation within the wedge is generally dominated by imbricate thrust faults verging toward the toe and related fault bend folding two north american fold and thrust belts that exhibit these features are shown in figure 1 neither of these two examples is tectonically active today the southern canadian fold and thrust belt was active during the late jurassic and cretaceous 150 100 ma whereas the southern appa lachians were deformed during the late carboniferous to permian alle ghenian orogeny 300 250 ma figure 2 shows two examples that are currently active the taiwan fold and thrust belt produced by the sub duction of the eurasian plate beneath the philippine sea plate suppe 1981 1987 and the barbados accretionary wedge produced by the sub

structural development and stress evolution of an arcuate fold and thrust system southwestern greater caucasus republic of georgia abstract the southern front of the greater caucasus is quite rectilinear in plan view with the exception of part of the rioni basin where marine and continental deposits of cretaceous neogene age were locally folded and uplifted this resulted in the formation of an arcuate fold and thrust system that extends 45 km into the foreland although previous studies suggested that this system has developed only since miocene times our new detailed and systematic field measurements of brittle and ductile structures show a very complex history consisting in four main phases of brittle deformation and folding dated from eocene to quaternary times we collected microtectonic data at 248 faults and calculated the related paleostress tensors the first two phases which we document here predated folding and were characterised by dominant transcurrent faulting and subordinate reverse motions the greatest principal stress 1 was perpendicular and later parallel to the mountain belt afterwards nw se e w and ne sw trending south vergent asymmetrical folds started to form in the western sector of the study area folds are sinuous in plan view whereas to the east they show a left stepping en echelon geometry another two brittle deformation phases took place after the folding due to the activity of a set of right lateral strike slip faults that strike nw se and ne sw respectively as well as by left lateral strike slip faults mostly striking nw se ne sw and nne ssw these two additional phases were produced by a ne sw to n s trending 1 the arcuate belt is marked by along strike variations in the tectonic regime and deformation geometry plus belt parallel stretching based on our field data integrated with published analogue models we suggest a possible explanation for the rioni structure in terms of the oblique asymmetric indentation of an upper crustal blocks moving to the ssw

recess drawn by the internal zone outer boundary and oblique structures in the paleomargin derived units subbetic domain central betics an analogue modelling approach abstract the subbetic domain comprising the south iberian paleomargin derived units is a fold and thrust belt developed over a ductile substrate showing a complex structural pattern in the central betics a main trend can be defined with respect to which frequent oblique structures are observed these oblique structures often subperpendicular to the main trend are not located along transfer zones but rather are present everywhere in the fold and thrust belt moreover they are coetaneous with those drawing the main trend this complex pattern is situated in front of a recess marked by the outer boundary of the internal zones the alboran domain which acted as backstop analogue models were designed to study the influence of such a recess on a ductile brittle multilayer one of the models in which the backstop recess is symmetric with respect to its direction of movement shows a high variation in the orientation of the resulting structures being not only qualitatively but also quantitatively similar to the studied natural case

frontal belt curvature and oblique ramp development at an obliquely collided irregular margin geometry and kinematics of the nw taiwan fold thrust belt 1 combined structural and tectonic analyses demonstrate that the nw foothills of the taiwan collision belt constitute mainly an asymmetric primary arc type fold thrust belt the arcuate belt developed as a basin controlled salient in the portion of the foreland basin that was initially thicker due to the presence of a precollisional depocenter the taihsi basin additional but limited buttress effects at end points related to interaction with foreland basement highs kuanyin and peikang highs may have also slightly enhanced curvature the complex structural pattern results from the interaction between low angle thrusting related to shallow decollement tectonics and oblique inversion of extensional structures of the margin on the southern edge of the kuanyin basement high the tectonic regimes and mechanisms revealed by the pattern of paleostress indicators such as striated outcrop scale faults are combined with the orientation and geometry of offshore and onshore regional faults in order to accurately define the quaternary kinematics of the propagating units the kinematics of this curved range is mainly controlled by distributed transpressional wrenching along the southern edge of the kuanyin high leading to the development of a regional scale oblique ramp the kuanyin transfer fault zone which is conjugate of the nw trending pakua transfer fault zone north of the peikang basement high the divergence between the n120 regional transport direction and the maximum compressive trend that evolved from n120 to n150 and even to n s in the northern part of the arc effectively supports distributed wrench deformation along its northern limb during the pleistocene the geometry and kinematics of the western taiwan foothills therefore appear to be highly influenced by both the preorogenic structural pattern of the irregularly shaped chinese passive margin and the obliquity of its plio quaternary collision with the philippine sea plate

kinematic flexural and thermal modelling in the central andes unravelling age and signal of deformation exhumation and uplift abstract quantifying age rate and lateral variation of deformation and exhumation in convergent systems relies on integration of geologic map patterns ag and locations of reset thermochronometer systems and synorogenic sediment distribution the central bolivian andes provide an ideal location to examine the influence of variations in shortening and stratigraphic architecture on the structural evolution of the mountain range due to differential age and rates of shortening and distinct sedimentary basin geometries along strike to quantify age and rate of shortening we link thermokinematic modelling of sequentially deformed forward modelled balanced cross sections to synorogenic and thermochronologic histories the preserved basin history in the altiplano and eastern cordillera argues for an early fold and thrust belt located in the now western cordillera with subsequent propagation of shortening eastward around 40 50 ma flexural modelling incorporating isostasy and erosion requires multiple basement thrust sheets with 35 97 km of displacement a temporally evolving effective elastic thickness as well as imposed subsidence in the foreland and uplift in the hinterland is required to reproduce the surface geology increase subandean foreland basin depth limit altiplano sedimentation and facilitate altiplano uplift to modern elevation thermokinematic modelling is compatible with initiation of deformation at 50 40 ma in a marked increase in subandean velocities from 5 5 to 8 10 mm yr from 12 10 ma to present out of sequence thrusting at the westernmost limit of the subandes is required to match measured young and partially reset zircon helium ages out of sequence faulting is supported by high ksn values indicative of active uplift and was likely promoted by the abrupt eastern edge of the paleozoic basin rocks which limited forward propagation of structures and or increased erosion due to focused precipitation our results highlight the importance of incorporating detailed structural modelling in differentiating the geometry kinematics and timing of deformation to reproduce thermochronologic ages and basin histories

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

structural analysis of the lombard thrust sheet and adjacent areas in the helena salient southwest montana usa abstract the helena salient is a prominent craton convex curve in the cordillera thrust belt of montana usa the lombard thrust sheet is the primary sheet in the salient structural analysis of fold trends cleavage attitudes and movement on minor faults is used to better understand both the geometry of the lombard thrust and the kinematic development of the salient early w e to wnw ene shortening directions in the lombard sheet are indicated by fold trends in the center of the thrust sheet the same narrow range of shortening directions is inferred from kinematic analysis of movement on minor faults and the orientations of unrotated cleavage planes along the southern lateral ramp boundary of the salient as the salient developed the amount and direction of shortening were locally modified as listric detachment faults rotated some tight folds to the nw and as right lateral simple shear caused by lock up and folding of the jefferson canyon fault above the lateral ramp rotated other folds northeastward where the lateral ramp and frontal oblique ramp intersect folds were rotated back to the nw our interpretation of dominant w e to wnw ese shortening in the lombard sheet later altered by local rotations supports a model of salient formation by primary parallel transport modified by interactions with a lateral ramp

compatibility constraints on folded and faulted strata and calculation of total displacement using computational restoration unfold program abstract a balanced surface method is proposed that allows one to test the reliability of the interpretation of the structural geometry of folded and faulted strata it also estimates both the finite total displacement field linked to the folding and faulting processes and the finite displacement field linked to the folding the method describes a thin competent folded and faulted sedimentary layer using rigid triangular elements their sizes depending on the curvature of the surface the elements are laid flat and are automatically fit to form a horizontal surface which represents the initial state of the layer the degree of compatibility given by different indicators tests the reliability of the geometric fitting of the layer if folding and faulting occur without bed stretching or if this change is known and introduced as a parameter in the code a plausible interpretation can be perfectly retrodeformed just as a folded and torn sheet of paper may be smoothed with an iron the method has been applied to two natural examples in oil field regions using three or two dimensional depth migrated seismic data the main results reveal in general that the petroleum company s interpretations of the data were nonoptimal a careful reinterpretation of the seismic data was necessary to obtain balanced folded and faulted surfaces the estimation of the finite displacement fields revealed the compatibility between fold and fault deformation and also the strike slip movement or rotation associated with the deformation

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

remagnetization in the tennessee salient southern appalachians usa constraints on the timing of deformation article i nfo the appalachian fold thrust belt is characterized by a sinuous trace in map view creating a series of salients and recesses the kinematic evolution of these arcuate features remains a controversial topic in orogenesis primary magnetizations from clastic red beds in the pennsylvania salient show pennsylvanian rotations that account for about half of the curvature while kiaman aged permian remagnetizations display no relative rotation between the limbs the more southern tennessee salient shows a maximum change in regional strike from 65 in virginia to 10 in northern georgia paleomagnetic results from thirty two sites in the middle to upper ordovician chickamauga group limestones and twenty sites from the middle cambrian rome formation red beds were analyzed to constrain the relative age of magnetization as well as the nature of curvature in the tennessee salient results from three sites of the silurian red mountain formation were added to an existing dataset in order to determine whether the southern limb had rotated after thermal demagnetization all three sample suites display a down and southeasterly direction albeit carried by different magnetic minerals the syn tilting direction of the chickamauga limestones lies on the pennsylvanian segment of the north american apparent polar wander path apwp indicating that deformation was about half completed by the late pennsylvanian the rome and red mountain formations were also remagnetized during the pennsylvanian both the chickamauga limestones and rome red beds fail to show a correlation between strike and declination along the salient suggesting either that the salient was a primary non rotational feature or that secondary curvature occurred prior to remagnetization as it did in pennsylvania moreover remagnetized directions from the red mountain sites show no statistical difference between the southern limb of the salient and the more northeasterly trending portion of the fold thrust belt in alabama thus all of the studied units in the tennessee salient are remagnetized and show no evidence for rotation this confirms that remagnetization was widespread in the southern appalachians and that any

kinematic 3 d retro modeling of an orogenic bend in the south limon fold and thrust belt eastern costa rica prediction of the incremental internal strain distribution the south limon fold and thrust belt in the back arc area of southern costa rica is characterized by a 90 curvature of the strike of the thrust planes and is therefore a natural laboratory for the analysis of curved orogens the analysis of curved fold and thrust belts is a challenge because of the varying structural orientations within the belt based on seismic reflection lines we created a 3 d subsurface model containing three major thrust faults and three stratigraphic horizons 3 d kinematic retro deformation modeling was carried out to analyze the spatial evolution of the fold and thrust belt the maximum amount of displacement on each of the faults is from hinterland to foreland thrust 1 800 m thrust 2 600 m thrust 3 250 m the model was restored sequentially to its pre deformational state the strain history of the stratigraphic horizons in the model was calculated at every step this shows that the internal strain pattern has an abrupt change at the orogenic bend contractional strain occurs in the forelimbs of the hanging wall anticlines while a zone of dilative strain spreads from the anticline crests to the backlimbs the modeling shows that a nne directed transport direction best explains the structural evolution of the bend this would require a left lateral strike slip zone in the north to compensate for the movement and thereby decoupling the south limon fold and thrust belt from northern costa rica therefore our modeling supports the presence of the trans isthmic fault system at least during the plio pleistocene

strain patterns within part of the willard thrust sheet idaho utah wyoming thrust belt abstract the willard thrust sheet located in northern utah usa contains a 10 15 km thick sequence of strata that were internally deformed and translated about 50 km ese upper levels of the sheet are relatively little deformed lower levels have minor folds and cleavage that increase in intensity downward and rotate into parallelism with the thrust and the basal fault zone contains mylonite and ultracataclasite finite strain displays systematic changes with structural position and lithology basal levels have strain ratios r r xz of 3 5 and angles between stretch directions and the thrust of r of 1 5 3 and of 10 35 with overall correlations between increasing r decreasing and greater mica content overlying micaceous quartzite has relatively low strain with r of 1 3 2 and 50 principal stretching x directions trend perpendicular to oblique to minor fold axes which are locally oblique to the overall transport direction reflecting partial decoupling of internal deformation from thrust slip principal axial ratios have r yz r xy but microfabrics indicate only limited extension in the intermediate stretching direction y corresponding to volume losses of about 10 40 strain is factored into components of thrust perpendicular thinning and thrust parallel shear that increase downward and in mica rich layers minor thrust parallel shortening to extension minor longitudinal extension and minor longitudinal wrench shear these patterns reflect litho mechanical layering of the thrust sheet which includes a very weak basal fault zone that formed at elevated fluid pressures a weak mica rich lower level with widespread crystal plastic and mass transfer deformation and a stronger upper part with limited internal deformation

computerized tomographic analysis of displacement trajectories and three dimensional fold geometry above oblique thrust ramps computerized tomographic analysis of physical models of fold thrust structures permits nondestructive systematic analysis of variations in displacement trajectories and variations in three dimensional fold geometry as a function of thrust fault geometry the authors studied models in which sand layers with embedded transport parallel marker lines were shortened incrementally up to a maximum of 24 over rigid footwall fault templates these templates simulated a right stepping oblique ramp connecting two ramps perpendicular to the shortening direction in response to movement over the oblique ramp templates overturned folds formed and marker line deflections indicative of out of plane strains developed marker lines within layers originally truncated by fault templates were deflected leftward away from the right stepping oblique ramp during deformation whereas marker lines within sand layers that originally extended across the upper flat of the fault template were deflected in a more radial pattern differences in marker line deflections imply that displacement trajectories within natural thrust sheets may vary as a function of overburden and structural position furthermore their tomographic studies graphically demonstrate that out of plane strain and differential rotation of layers within thrust sheets occur in the vicinity of oblique ramps

arcuate thrust systems in sandbox experiments a comparison to the external arcs of the western alps in the external western alps two regional structural arcs were generated during tertiary northwest directed collision between the apulian indenter and the european passive margin these arcs distinguished by their geographic position and their age are examined by using a new compilation of structural data and comparing these to the results of sandbox analogue experiments the principal western alpine arc comprises two orthogonal synchronous thrust systems in the late eocene early miocene major shortening 105 km was toward the northwest to west northwest and minor shortening 11 km was toward the southwest shortening in each branch decreased toward the core of the arc during the late miocene and pliocene the jura arc accommodated 35 km of northwest directed shortening while 10 5 km of southwest to south southwest directed shortening was accommodated on the digne thrust system sandbox experiments were used to investigate the role of the motion vector of a rigid rectangular indenter orthogonal diagonal curved or rotational paths and the mechanical stratigraphy of the foreland in the evolution of upper crustal arcuate systems e g presence of a basal easy slip silicone horizon comparison of experimental results with the external alpine arc suggests that the indenter followed a slightly diagonal path with respect to the european margin from the eocene to the early miocene and curved counterclockwise by 10 15 in the middle miocene mechanical stratigraphy experiments support the hypothesis that thick triassic evaporites played a primary role in the evolution of the jura arc the influence of mechanical stratigraphy was most prominent during weak deformation at the external boundaries of the alpine orogen jura fold and thrust belt digne thrust

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

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

paleomagnetism of the gran sasso range salient central apennines italy pattern of orogenic rotations due to translation of a massive carbonate indenter 1 we report on the paleomagnetism 39 new sites of gran sasso an indenter controlled salient of the external central apennines formed by two orthogonal limbs we find that gran sasso is a complex salient paleomagnetically corresponding to neither a nonrotating nor an oroclinal end member data from the core of the arc show that the indenter itself did not undergo any rotation conversely rotations of variable magnitude and sign are observed along the curve shaped thrust fronts rotations are virtually absent at both end points of the arc moving toward the apex progressively greater counterclockwise ccw and clockwise cw rotations occur along the e w and n s fronts respectively the rotations increase continuously and more than linearly reaching their maximum values 80 ccw and 50 cw around the apex here the more strongly ccw and cw rotated fronts are separated by a domain characterized by local block rotations the inequality between the maximum ccw and cw rotation values is likely a consequence of the asymmetry of the indenter displacement direction n70 e with respect to the preorogenic trends of its margins e w and n s from an oroclinal point of view the fronts close to the end points virtually define a nonrotating arc while the pattern around the apex is similar to that of an orocline we conclude that close to end points nonrotational thrusting normal to the indenter margins occurred while in the vicinity of the apex the peritidal carbonates acted as an ice breaker pushing apart and strongly rotating the weaker multilayer located ahead

evolution and dynamics of a fold thrust belt the sulaiman range of pakistan we present observations and models of the sulaiman range of western pakistan that shed new light on the evolution and deformation of fold thrust belts earthquake source inversions show that the seismic deformation in the range is concentrated in the thick pile of sediments overlying the underthrusting lithosphere of the indian subcontinent the slip vectors of the earthquakes vary in strike around the margin of the range in tandem with the shape of the topography suggesting that gravitational driving forces arising from the topography play an important role in governing the deformation of the region numerical models suggest that the active deformation and the extreme plan view curvature of the range are governed by the presence of weak sediments in a pre existing basin on the underthrusting indian plate these sediments affect the stress state in the over riding mountain range and allow for the rapid propagation of the nose of the range and the development of extreme curvature and laterally varying surface gradients

kinematic variation within the fars arc eastern zagros and the development of fold and thrust belt curvature we analyze deformation of the fars arc in the eastern zagros iran including earthquake slip vectors gps velocities paleomagnetism data and fold orientations to understand how this fold and thrust belt works and so better understand the generic issue of fold and thrust belt curvature the fars arc is curved convex southward gps derived rotation rates are 0 5 myr 1 rotation is clockwise west of 53 e and counterclockwise to the east these rotation senses are opposite to previous predictions of passive bookshelf models for strike slip faults during north south convergence west of 53 e average gps vectors thrust earthquake slip vectors strain axes derived from gps data and orthogonal directions to fold trends are all aligned toward 218 east of this meridian the average gps vector is toward 208 but the averages of the other data sets are distinctly different all toward 190 we propose that fault blocks in eastern fars each 20 40 km long rotate predominantly counterclockwise whereas in western fars the regional clockwise rotation takes place mainly on the array of active right lateral faults in this area thus localized block faulting and rotations accumulate to produce the overall strain and regional curvature active folds of different orientations in eastern fars intersect to produce domal interference patterns without involving separate deformation phases indicating that fold interference patterns should not be interpreted in terms of changing stress orientations unless there is clear evidence fars arc curvature is best explained by deformation being restricted at tectonic boundaries at its eastern and western margins with significant gravitational spreading

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

eocene oligocene tectonics and kinematics of the rhine saone continental transform zone eastern france a tectonic analysis of brittle deformaton was performed in the rhine saone transform in order to decipher and understand the deformation processes in a typical continental hansfer zone cenozoic major and minor fault patterns are described and brittle structures are interpreted in terms of paleostress orientations the eocene n s compression related to africa eurasia convergence is marked mainly by strike slip faults it was followed by a major phase of crustal extension mainly oligocene in age related to the west european rifting this extensional phase is expressed by normal faults tension gashes and extensional strike slip faults which are especially abundant in the transform zone these two events are found to be quite different in terms of distribution of horizontal shess trajectories the trend of ol axes is very homogeneous for the n s compression whereas o3 orientations associated with the major extension vary from e w in most of the rift system to i v se within the transform zone finally the mio pliocene tectonic emplacement of the jura fold and thrust belt is marked in the field by strike slip faults associated with a well defined trend of ol oriented w iiw e se to nw se the preexisting basement fracture pattern between the grabens was also considered in order to estimate which faults were likely to have been reactivated during the oligocene transform kinematics and the theoretical shear motion on these inherited fault surfaces when submitted to e w extension was calculated left laterauextensional reactivation of a preexisting 60 n trending fault system in the brittle upper crust is likely to have accommodated the shear strain arising between the rift segments in response to crustal stretching two independent numerical modelings based on distinct element and finite element analyses respectively enabled us to verify and to refine the hypothesis of transform kinematics related to e w extension and inducing regional perturbations of extensional stress trajectories the overall mechanism and the transtensional kinematics of the rhine saone transform zone are thus tightly conshained the inherited crustal anisotropy the large scale perturbations of extensional stress trajectories and the development of distributed brittle deformation within the sedimentary cover are found to play a major role in the tectonic evolution of continental rift transform systems

block rotation induced by the change from the collision to subduction implications for active deformations within the areas surrounding south caspian basin abstract northern of iran is experiencing a complex deformation due to the northward convergence of arabian plate since late cenozoic the majority of this complexity is due to the presence of a rigid old thickened oceanic crust of the south caspian basin scb this rigid block trapping between eurasia and central iran makes an inhomogeneous body in the context of deforming zone composed by alborz talesh apsheron balkhan caucasus and kopeh dagh located in south west northwest north and east of the scb respectively among them the formation and evolution of the alborz orocline are under debates the presence of sinistral strike slip faults with normal separation initially understood by nw motion of northern alborz inferred by gps measurements raised long debates in the latest proposition it is assumed that the scb is rotating clockwise this study however shows that the model of scb s rotation and or nw ward motion of scb is not kinematically consistent therefore it aims at constraining the alborz northern central iran and nw iran as a sliver block are rotating around the scb the block rotation is facilitated by geo sutures inherited since paleozoic therefore this article specifically pays attention to the active extensional tectonic regime as a signal for the area that is under rotational movement the block rotation induced by the change from the collision in kopeh dagh to subduction scb and kura basin beneath alborz talesh apsheron balkhan and great caucasus respectively and consequently the reactivation of ancient geo sutures in northern iran led to a rapid rotation of microcontinents this assumption may account for the ongoing deformational pattern in alborz and nw iran the disharmonic arabian plate convergence and scb s retreating induce forces by the block rotation and cause episodic tectonic activities that are responsible for current tectonic complexity in the north of iran if the climax of the collision was 5 ma then the block rotation and related deformation are younger events with respect to the collision and subduction

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

volumetric strains in neutral surface folding neutral surface folding is a significant contributor to fold development this mechanism produces contrasting strains in the inner and outer arcs of the folded layer that arise from principal stress orientations that are approximately parallel and perpendicular to the layer we demonstrate that such stress patterns imply significant gradients of mean stress across the folding layer being more tensional on the outer arc and more compressive in the inner arc this could pump fluids towards the outer arc during folding and result in heterogeneous volume changes we conclude that the neutral surface folding model should be adapted to accommodate volumetric strains in order to explain dilatational structures e g open fractures veining on the extrados and volume loss structures e g pressure solution seams stylolitic cleavages on the intrados this dilatation has economic implications as it allows prediction of sites of mineralization and zones of secondary permeability in fold related hydrocarbon traps

kinematics of the torcal shear zone transpressional tectonics in a salient recess transition at the northern gibraltar arc abstract complex strain patterns in the gibraltar arc derive from the interaction between the westward drift and concomitant back arc extension of the arc hinterland alboran domain and the europe africa convergence in order to explore strain partitioning modes within the arc and the role played by large scale oblique structures we have studied the kinematics of the torcal shear zone located at the northern branch of the gibraltar arc the torcal shear zone is a 70 km long e w brittle ductile shear zone that underwent overall dextral transpression during the late miocene to quaternary time within the torcal shear zone strain is highly partitioned at multiple scales into shortening oblique extensional and strike slip structures moreover strain partitioning is heterogeneous along strike giving rise to four distinct structural domains in the central sector the strain is pure shear dominated although narrow sectors parallel to the shear walls are simple shear dominated a single n99 e n109 e trending horizontal velocity vector v could explain the kinematics of the entire central sector of the torcal shear zone lateral domains have different strain patterns and are comparable to splay dominated and thrust dominated strike slip fault tips the torcal shear zone provokes the subvertical extrusion of the external betics units against the alboran domain and a dextral deflection of the structural trend moreover the estimated v points to the importance of the westward motion of the hinterland relative to the external wedge and fits well with the radial outward thrusting pattern identified in the arc

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

average regional strain due to slip on numerous faults of different orientations if a region is cut by faults with different orientations and if the faults intersect the boundaries of the region of interest then the average finite rotational strain eij ui xj is given by eij mij v where is the shear modulus v is the volume of the region and mij represents the sum of asymmetric moment tensors mij for each fault mij m0 u n where m0 is the scalar seismic moment and u and n are the unit vectors parallel to the slip vector and perpendicular to the fault plane this result is applicable when the average regional strain occurs primarily by displacements of essentially rigid blocks that together compose the region of interest and hence when both elastic strains and inelastic strains due to folding and bending are small

new constraints for indentation mechanisms in arcuate belts from the jura mountains france the mechanism of indentation in arcuate belts is discussed using the jura mountains as an example using fault inversion analysis from numerous sites the miocene pliocene stress pattern is reconstructed two superimposed compressional stress fields have been recognized considering the theoretical distribution of compression in front of a rigid indenter we interpret the complex stress pattern in the jura mountains as a result of a major change in the mechanism of indentation of the jura by its hinterland initially the indenter was narrower and limited in the southwest by the vuache transfer fault with time it expanded to the southwest and included the entire molasse basin this evolution highlights the importance of decoupling along faults which here controlled the indenter shape

quantifying vertical axis rotation in curved orogens correlating multiple data sets with a refined weighted least squares strike test 1 map scale curvature is a fundamental feature of most contractional orogenic belts and is central to understanding the kinematic and dynamic evolution of mountain systems paleomagnetic analysis combined with detailed structural studies is the most robust means of quantifying vertical axis rotations that produce curvature over a range of temporal and spatial scales this paper explores how vertical axis rotations can best be evaluated for multiple data sets by applying a weighted least squares method to the classic strike test this refined method provides measures of best fit slope confidence interval and goodness of fit between map scale structural trend paleomagnetic rotations and deformation fabric orientations structural trend is estimated by averaging fold axial trace formation contact and bed strike data over kilometer scale areas paleomagnetic and deformation fabric site mean orientations and measurement uncertainties are estimated using vector and bootstrap statistics weighting factors are estimated from combined measurement uncertainty structural noise related to small scale block rotation and stress strain refraction and variations in restoration paths the number of sites needed to obtain a significant confidence interval in strike test slope is a function of combined uncertainty in paleomagnetic or deformation fabric directions and the total range in structural trend around a curved orogen improved estimates of strike test slope and rotation thus require systematic sampling with a wide distribution of sites evaluation of appropriate weighting factors and statistical analysis a case study is presented that highlights application of this refined method to paleomagnetic and deformation fabric data sets from the wyoming salient of the sevier thrust belt paleomagnetic data yield a strike test slope of 0 76 0 11 indicating that the wyoming salient is a progressive arc with 3 4 secondary curvature related to vertical axis rotation synchronous with large scale thrusting and 1 4 initial curvature finite strain anisotropy of magnetic susceptibility and mesoscopic structural orientations which are related to early layer parallel shortening all yield strike test slopes of 0 9 0 1 comparing these slopes with paleomagnetic results indicates that deformation fabrics had initial curvature and thus cannot be used alone to accurately estimate rotations by integrating systematic paleomagnetic and structural data using statistical analysis curvature models for the wyoming salient are closely constrained

formation of dabashan arcuate structures constraints from mesozoic basement deformation in south qinling orogen china abstract the dabashan arcuate structures are composed of the nw striking northern dabashan belt belonging to the southern margin of the south qinling orogen and the curved southern dabashan belt located in the northern margin of the yangtze block with the arcuate chengkou fangxiang fault as their boundary the deep understanding of the orogenesis is indispensable to unravel the mechanism of the dabashan arcuate structures as the basement preserves important clues on the deformational characteristics as well as the timing and orogenic processes here we report integrated field investigation structural analysis and 40 ar 39 ar thermochronological data in the wudang and ankang uplifts in the south qinling orogen to decipher the forming processes and mechanisms of the dabashan arcuate structures the field and microscopic observations reveal a dominantly top to south southwest shear sense at low to medium temperatures the basement deformation expanded southward southwestward in the form of duplex during the continued shortening the basement was uplifted due to thrust stacking within duplex systems according to the deformation temperatures and the new and published 40 ar 39 ar thermochronological data the basement recorded the ca 248 212 ma orogenesis for the wudang uplift and the ca 222 161 ma orogenesis for the ankang uplift based on the tectonic evolution of the study area the formation of composite dabashan arcuate structures included three stages firstly the arcuate master fault accompanied by a series of nw striking faults came into being at ca 450 400 ma based on previous studies secondly the scissor like convergence between the south china block and north china block reactivated the extensional structures and formed the general features of the northern dabashan belt at ca 250 160 ma finally the deformation expanded toward the foreland and formed the curved southern dabashan belt with obstruction by the hannan uplift and shennongjia huangling uplift in the front at ca 160 100 ma

kinematic model for the curvature of the northern subalpine chain france abstract analyses of cross sectional shortening mapped faults and calcite twin strain are used in conjunction with geometric kinematic modeling to interpret the mechanism of curvature formation in the northern subalpine chain of france there is a 45 change in strike around the chain that is convex towards the foreland northwest five models for fold thrust belt curvature are applied to the northern subalpine chain they can reproduce the geometry and the kinematic history of a curved fold thrust belt and can be used to predict the magnitude and orientations of strains and the three dimensional geometry of the curvature the models are pure bending radial thrusting curve parallel simple shear uniform displacement uniform shortening and transport parallel simple shear two principal criteria for distinguishing among the models geometrically are the horizontal tangential strain extension or contraction parallel to strike and cross sectional shortening the transport parallel simple shear model predicts no tangential extension in the central domain and greater radial shortening and significant tangential extension in the northeastern and southern domains this is the pattern observed in the northern subalpine chain therefore the curvature of the northern subalpine chain is attributed to a transport parallel simple shear mechanism

characterization of stress perturbations near major fault zones insights from 2 d distinct element numerical modelling and field studies jura mountains abstract we consider and discuss the presence of discontinuities in the crust as a major source of stress perturbations based on 2 d distinct element modelling we reconstruct the local stress field around a vertical discontinuity in various geological contexts the resulting stress distribution reveals that major directional stress changes occur near the tips of the discontinuity so that stress deviations can reach values as large as 50 we establish simple relationships controlling stress changes around a pre existing fault zone as a function of 1 the remote differential stress magnitude 1 3 2 the friction coefficient on the discontinuity and 3 the strike of the discontinuity relative to the far field stress as a geological example we present the morez fault zone in the internal jura paleostress reconstruction in forty two sites indicates that the trends of the mio pliocene compression are n110 on average near the fault whereas they are n130 in the surrounding areas a comparison between the results of the tectonic study and those of theoretical modelling suggests that the 20 counterclockwise deviation is directly related to the reactivation of this large weak zone we thus evaluate the role of mechanical decoupling along pre existing zones of weakness especially with consideration to the accommodation of the alpine deformation in the jura belt

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

tracking progressive deformation of an orogenic wedge through two successive internal thrusts insights from structure deformation profile strain and vorticity of the main central thrust mct and the pelling munsiari thrust pt sikkim himalayan fold thrust belt abstract we compare and contrast the structural evolution of two successive internal thrusts the main central thrust mct and the pelling munsiari thrust pt from the crystalline core of the sikkim himalaya in the context of progressive deformation involving a footwall lesser himalayan duplex the pt is its roof thrust the mylonitic foliations in both the shear zones are overprinted by successive cleavages the youngest cleavage from the pt zone continues within the hangingwall mct sheet that records one additional cleavage possibly indicating time transgressive cleavage development the cleavages become steeper while their intensity decreases structurally higher up within individual thrust sheets the rs values and angular shear strain decrease from the mylonite zones to structurally higher up within the sheets both the shear zones are type ii with decelerating strain paths rs relationships and microstructures indicate thrust parallel stretch is greater than thrust perpendicular component both the shear zones record strain partitioning with lesser competent mylonite domains recording higher rxz and a greater proportion of simple shear than the protomylonite domains the shear zones recorded the growth of the duplex during progressive deformation that contributed to pure shear dominated general shear higher flattening strain and greater translation on its roof thrust the pt than the overlying mct

map view retrodeformation of an arcuate fold and thrust belt the jura case 1 the mechanism of arcuate mountain range formation is a matter of debate here we perform a map view restoration of a detailed three dimensional model of the jura arc a typical arcuate mountain range in the foothills of the swiss and french alps this retrodeformation is performed using the unfold surface balanced program based on a block mosaic method it results in a displacement field divergent toward the deformation front this displacement field suggests counterclockwise rigid rotations in the horizontal plane up to 30 in the southern internal jura and a corresponding vertical axis rotation or shear strain of the savoie molasse basin hinterlandward we also predict a 10 clockwise vertical axis rotation of the molasse basin in switzerland all these rotations agree with those documented by paleomagnetic data the former are taken to result from a substantial decrease in shortening at the southern jura end while the divergence of displacements is interpreted to result from variations in the detachment level distribution

reconstructing the kinematic evolution of curved mountain belts a paleomagnetic study of triassic red beds from the wyoming salient sevier thrust belt u s a determining the kinematic history and mechanics of curved fold and thrust belts is fundamental to understanding the tectonic evolution of mountain systems to better understand the development of a classic curved fold and thrust belt we completed an integrated paleomagnetic and strain study of the wyoming salient paleomagnetic data are reported here from 154 sites collected from red beds of the triassic ankareh formation in the salient and nine sites collected from the relatively stable foreland red beds display three components with distinctly different magnetic behaviors 1 a near primary triassic magnetization carried by hematite that is stable up to 680 c tr component 91 sites 2 a cretaceous chemical remagnetization carried partly by magnetite k component 32 sites and 3 a recent viscous magnetization that is mostly removed by 350 c site mean vectors for the tr and k components show a high degree of scatter from expected triassic and cretaceous reference directions suggesting significant tilt and rotation subsequent to magnetization acquisition restoration of tilt and folding for individual site means results in well clustered shallow and moderate inclinations for the tr and k components respectively and in variable declinations related to systematic vertical axis rotations statistical analysis of declinations for both components indicates that 75 of present day salient curvature resulted from secondary rotation and 25 of primary curvature was likely related to sedimentary basin architecture analysis of individual thrust systems indicates a slightly greater component of rotation in more internal sheets 80 compared to the frontal thrust sheets 65 suggesting that rotations were concentrated near the leading edge of the propagating fold and thrust wedge with only minor additional rotation of internal sheets transfer zones oblique ramps and more deformed overturned fold limbs display locally more complex patterns which can be understood through careful structural analysis when combined with internal strain data and regional structural relations paleomagnetic data support a kinematic model of a progressive arc with curved thrust slip paths and differential shortening that rotated early layer parallel shortening fabrics and produced minor strike parallel extension this kinematic history likely reflects a combination of processes including greater initial stratigraphic thickness and subsequent shortening and wedge propagation in the central part of the salient presence of a weak basal detachment and fault zone weakening that favored lower taper and buttressing by laramide foreland uplifts that formed along basement promontories at the north and south ends of the salient

the formation of mountain range curvature by gravitational spreading this paper presents a mechanism by which mountain ranges can form curved range fronts gravitational spreading of mountain ranges that have been thrust onto rigid lowlands will result in the formation of curvature provided that enough gravity driven flow occurs to dominate the shape of the topography whether this mechanism can operate during the lifetime of a given mountain range depends upon the viscosity of the range the square of the along strike length of the range and the cube of the elevation of the range the curvature of the southern edge of the tibetan plateau is consistent with formation by gravitational spreading provided that the viscosity is similar to that previously estimated using other independent methods the low elevation and young age of the zagros mountains mean that large scale curvature has not had time to develop the short along strike extent and possibly low viscosity of the sulaiman ranges in pakistan may have allowed the ranges to form their distinctive arcuate shape the formation of range front curvature plays an important role in controlling the tectonic evolution of the interiors of the ranges with arc parallel extension becoming progressively more important as range front curvature develops

deformation history of the roanoke recess appalachians usa the evolution of the roanoke recess is controversial because agreement is lacking about the timing and continuity of deformation increments because it may or may not have behaved like an adjacent salient and recess because while many salients have been investigated few recesses have and because the role of blind thrusts is unclear to gain insight into these controversies we estimated shortening directions shortening magnitudes and relative timing in the recess from map scale folds outcrop scale stylolites and grain scale solution structures and twins the key results from combining these new data with previous work are as follows 1 the deformation history around the roanoke recess is most simply described as temporally continuous with deformation migrating northeastward while the primary shortening direction rotated counterclockwise from n directed to almost w directed 2 consequently the roanoke recess did not deform in the symmetrical manner of the adjacent pennsylvania salient nor with the two step history of the kingston recess further to the north in the appalachians 3 the timing and magnitude of shortening increments are sufficient to necessitate a blind thrust under the present surface rocks of the inner recess throughout the deformation history

strain models within spreading nappes abstract internal strain within nappes and thrust sheets is especially important in the understanding of emplacement mechanisms in this paper strain patterns within spreading nappes are investigated theoretically and experimentally three types of spreading nappe are distinguished using various boundary conditions spreading gliding spreading and extruding spreading nappes each type is placed in its proper natural environment strain components and strain gradients are summarized from the use of scale models performed with analogue materials mathematical computations from experimental modelling allow the calculation of 1 1 the schistosity trajectories in vertical flow planes 2 2 the relationship between stretch and transport direction and 3 3 the spatial distribution of different types of strain ellipsoid these provide some tests which make it possible to demonstrate in the field whether nappes are or are not gravity induced finally some field examples from the central alps and the pyrenees are briefly discussed they provide good support to the strain models presented in the present paper

paleomagnetism and tectonics of the jura arcuate mountain belt in france and switzerland abstract goethite and hematite in ferriferous oolitic beds of callovian age from the jura mountains switzerland france carry either pre and or post tectonic magnetization the frequent pre tectonic origin of goethite magnetization indicates a temperature range during formation of the arcuate jura mountain belt below the goethite neel temperature of about 100 c the scatter of the pre tectonic paleomagnetic directions d 11 5 e i 55 5 95 4 7 which reside both in goethite and hematite provides strong evidence that the arcuate mountain belt was shaped without significant rotation the paleomagnetic results support tectonic thin skinned models for the formation of the jura mountain belt

control of preexisting faults on geometry and kinematics in the northernmost part of the jura fold and thrust belt 1 this study investigates the formation of the northernmost anticlines of the late miocene to early pliocene thin skinned jura fold and thrust belt and provides evidence that a transition to thick skinned tectonics did occur in this particular area during the late pliocene the northernmost anticlines of the jura fold and thrust belt are characterized by pronounced along strike asymmetries that were predetermined by a fault pattern inherited from paleogene upper rhine graben rifting this fault pattern had disrupted the triassic basal decollement of the jura mountains and controlled the nucleation of thrusts and folds as well as transfer zones during the generally n nw directed transport of the detached sedimentary cover sinistral transpressive oblique ramps nucleated along paleogene nne trending basement normal faults and led to a northward protrusion of the jura front encroaching onto the southernmost upper rhine graben shortening across the frontal anticlines is greatest along the oblique ramps and decreases along strike toward the east necessitating a gentle clockwise rotation of the detached sediments despite the fact that the stress field in the sedimentary cover remained unchanged thin skinned folding and thrusting came to a halt in the early pliocene giving way to thick skinned tectonics very probably governing neotectonic activity in the area this transition might represent a geodynamic reorganization of the northwestern alpine foreland

eastern variscan fold belt paleomagnetic evidence for oroclinal bending the rhenohercynian zone of variscan europe trends from southern portugal around the ibero armorican arc into southern britain belgium northern germany and the moravo silesian zone of the east czech republic although the geodynamic evolution of the central and western segments of this arcuate belt is now fairly well understood the scenario for the more easterly parts remains enigmatic a paleomagnetic study of upper devonian rocks from the moravo silesian zone has been undertaken two ancient directions of magnetization have been identified the first the a magnetization is secondary in origin and relates to a remagnetization of permian carboniferous age the b magnetization passes the fold test is considered late devonian in age and agrees in terms of inclination to previously published paleomagnetic results from coeval rocks of the harz mountains and franconian forest central europe the declination however differs by about 90 restoring the moravo silesian zone to its original devonian orientation as defined by the new paleomagnetic data brings the structural trends of central and eastern europe into agreement because they were previously part of the same tectonostratigraphic unit as suggested by the stratigraphic record this implies that rotational oroclinal bending around the northern and eastern flanks of the bohemian massif occurred sometime between the late devonian and late carboniferous

growth of the central andean plateau by tectonic segmentation is controlled by the gradient in crustal shortening abstract crustal deformation orocline formation and growth of the central andean plateau as well as the mutual relations of these processes with climate are a matter of international debate earthquake focal mechanism fault kinematic paleomagnetic and cross section balancing data are paramount for understanding the morphotectonic evolution of this noncollisional orogen but collectively await an explanation in terms of a comprehensive kinematic model we offer such a model that approximates simple shear in plan view and that predicts the kinematics of first order fault zones in the southern central andes the model indicates that segmentation of the upper crust into rhomb shaped domains confined by transpressive ranges resulted from the decrease in crustal shortening with distance to the central bend of the andes an anastomosing network of kinematically coupled reactivated orogen parallel and newly formed ne trending deformation zones encompassing components of sinistral and dextral strike slip res

interactions between thin and thick skinned tectonics at the northwestern front of the jura fold and thrust belt eastern france 1 this study investigates spatial and temporal interactions of thin and thick skinned tectonics in a classical foreland setting located at the front of the jura fold and thrust belt in eastern france the working area coincides with the intracontinental rhine bresse transfer zone and represents the most external front of the deformed alpine foreland the investigation combines analyses of largely unpublished and newly available subsurface information with our own structural data including an exhaustive paleostress analysis and geomorphologic observations results are provided in the form of a new tectonic map and a series of regional cross sections through the study area the besancon zone forming the most external part of the thin skinned fold and thrust belt encroached onto the eo oligocene rhine bresse transfer fault system until early pliocene times thrust propagation was largely controlled by the late paleozoic to paleogene preexisting fault pattern that characterizes the rhine bresse transfer zone thick skinned deformation dominant throughout the avant monts zone located farther to the west was associated with compressional to transpressional reactivation of such faults overprinting and crosscutting criteria of fault slip data allow distinguishing between systematically fanning maximum horizontal stress axes that define the front of the thin skinned jura fold and thrust belt and consistently nw se directed maximum horizontal stress axes that characterize deformation of the autochthonous cover of the foreland which is affected by thick skinned tectonics tectonic and geomorphic analyses indicate that thick skinned tectonics started at a very late stage of foreland deformation post early pliocene geomorphic observations imply that deformation between mesozoic cover and basement is locally still decoupled however overprinting relationships and recent seismicity suggest that present day tectonic activity is thick skinned which probably reflects ongoing tectonic underplating in the alpine foreland

calabrian arc oroclinal bending the role of subduction 1 paleomagnetic data collected in the last 30 years indicate that a simple orocline model is not sufficient to describe the complex evolution of the calabrian arc present day curvature of the calabrian arc is the result of a different tectonic history between the edges of the arc namely the southern apennines and sicily and its core the calabria peloritani domain these differences mirror the structural architecture and deep lithospheric configuration of the calabrian arc which are related to the geometry and evolution of the ionian subduction system in particular the presence of lateral heterogeneities in the subducting lithosphere and the subsequent progressive decrease in width of the trench during subduction are likely the main causes of calabrian arc formation and of its present day narrow tight shape

experiments on strike slip faulting and block rotation analogue model experiments investigating strike slip faulting in zones of distributed shear deformation show that fault orientations and fault evolution indicate modifications of the stress field with increasing bulk shear strain dextral bulk shear deformation at low strain is accommodated dominantly by synthetic strike slip faults riedel shears at higher strain secondary antithetic and synthetic faults develop mostly between earlier formed major riedel shears closely spaced parallel antithetic faults cross faults delimit domains that rotate about vertical axes with continuing shear deformation rotation of fault bounded domains results in sigmoidal antithetic faults that have a dip slip component and a dip direction that changes along strike there is good agreement between models and natural examples of distributed shear zones where block rotations about vertical axes have been documented

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

structural inheritance and cenozoic stress fields in the jura fold and thrust belt france abstract based on an analysis of 8000 minor fault slip data in the jura mountains france we discuss the influence of pre existing discontinuities on the development of fold and thrust belts we present palinspastic maps showing the stress fields and active faults during the cenozoic pre orogenic events in the jura belt prior to the main late miocene fold and thrust tectonics during the eocene a n s strike slip regime produced a few nne ssw sub vertical strike slip faults in the central external jura and a few e w reverse faults in the eastern jura near the future frontal thrust during the oligocene an average wnw ese extension with irregular stress trajectories resulted in normal faulting along n s to ne sw trends in the external part of the belt wnw ese trends along the future northern and northeastern frontal thrust and nw se trends in the internal jura the late miocene tectonics began with a strike slip regime with a fan shaped compressional trajectory it was followed by a stress field with similar stress direction but local 2 3 stress permutation resulted in strike slip regime domains contrasting with reverse regime domains stress deflections and permutations occurred near inherited cover and basement discontinuities major deformation zones like the jura frontal thrust onto the foreland the thrust of the internal central jura onto the external jura and the narrow deformation bands within the flat lying plateaus formed close to the inherited faults the structural style of the jura belt thus partly mimics the pre orogenic fault pattern stress deflections point to the pre orogenic faults express the indentation process of the jura by its hinterland and highlight successive slip events along major faults during the fold and thrust tectonics this case study illustrates the relevance of minor fault slip studies for characterizing both the pre orogenic tectonics and the kinematics of the deformation

kinematics of the alpine arc and the motion history of adria the alps have been interpreted traditionally in terms of north or northwest directed convergence between africa and europe1 with adria the continental underpinnings of the adriatic sea and northern italy acting as a promontory of the african continent2 this has been supported by recent analyses of africa europe relative plate motions3 5 which indicate dominantly north south directed convergence during the tertiary phase of intracontinental shortening we show here however that kinematic indicators from alpine tectonites are difficult to reconcile with this motion history figs 1 and 2 and are explained best by roughly west northwest directed adria europe motion since about 70 million years ago combined with an arc normal pattern of motion driven by local body forces this implies that adria has moved independently of both africa and europe since at least the late cretaceous

curved fold and thrust accretion during the extrusion of a synorogenic viscous allochthonous sheet the estepa range external zones western betic cordillera spain 1 new structural borehole and time domain electromagnetic data allow us to reconstruct the 3 d geometry of the estepa range external zones of the western betic cordillera which constitutes an isolated curved fold and thrust range made up of jurassic shallow marine carbonates and cretaceous to paleocene marls and marly limestones contraction and rising load linked to the accretion of the subbetic nappe enhanced the expulsion of triassic evaporites and overpressured clays during the early and middle miocene finally forming part of a highly deformed melange unit this plastic extrusion favored the disconnection of external and middle subbetic blocks including the sierra de estepa range there deformation is characterized by northwest vergent curved folds and thrusts associated with ne sw frontal ramps and nw se lateral transfer faults that segmented the folds active between 18 and 12 ma at a local scale curvature was achieved under a nearly uniform nw wnw transport direction suggesting a primary arc type friction variation across the heterogeneous detached plastic basal triassic unit mainly controlled the curvature and segmentation of the fold systems transport direction is consistent with previously published slip data from the internal subbetic and the campo de gibraltar units after the late serravallian accretion slowed down and a shallow marine unit deposited unconformably placed over the main thrust and folds the sequence of deformation and emplacement of these ranges is interpreted as a continuous process linked to the early miocene e continental collision of the iberian margin thin continental crust and subduction of the flysch trough oceanic crust beneath the alboran continental domain

a model of displacement and strain for arc shaped mountain belts applied to the jura arc abstract a plan view geometric model for simple parallel differential displacements is presented as an analogue for models of arcuate mountain belt formation we use the model to predict strain patterns produced by parallel displacement in front of a rigid versus deformable indenter a rigid indenter is simulated by an irregular quadrilateral displaced a constant amount along its hinterland boundary a deformable indenter is simulated by an irregular quadrilateral displaced along a hinterland boundary that is allowed to rotate some simple test cases show that the deformable indenter model leads to a pattern of strain very similar to that encountered in arcuate mountain belts short axes orientations are most deviated from the transport direction along the lateral edges of the model with minimum displacement and shortening and vary across the central domain mirroring strain features with variable orientations from mountain belts such as fold trends and minor deformation features such as horizontal stylolite peaks the rigid indenter model also generates short axes deviated from the transport direction but showing far less variation displacement strain relationships from the jura mountains switzerland and france are quantified based upon a simplified version of the finite displacement field for the jura fold thrust belt of philippe y 1995 rampes laterales et zones de transfer dans le chaines plissees unpublished phd thesis universite de savoie we find that the model short axis orientation pattern is very similar over at least the eastern and central jura to the stylolite patterns from the region whilst the long axes closely match the fold axes trends the model suggests that the jura mountains could have formed as a result of a progressive deformation with uniform transport in a general northwest direction