magnetic remanence and fabric properties of laboratory deposited hematite bearing red sandstone redeposition experiments of disintegrated hematite bearing sandstone have confirmed a tangent relationship between inclinations of the drm and ambient magnetic field pronounced variations of drm intensities with field inclination are attributed to processes acting during the depositional formation of laminated sediments coinciding azimuthal distributions of remanence and maximum susceptibility directions reflect intrinsic properties of flaky hematite grains in which the magnetic moment is parallel to the direction of maximum susceptibility this parallelism probably depends on magnetic domain configurations

confined deep water system development on the accretionary wedge miocene kahramanmaras foreland basin s turkey abstract according to theoretical studies the foreland basin consists of accretionary wedge including wedge top or piggyback basin foredeep forebulge and backbulge depozones all of them are parallel to the orogenic belts of the overlying and underlying plates the closure of the southern branch of the neotethys during the late cretaceous led to an oblique collision of the arabian plate and the anatolide taurides platform leading to the development of the miocene kahramanmaras foreland basin kfb thus the promontory shape of the arabian plate prevented the development of an accretionary wedge parallel to the orogenic belt the accretionary wedge of the kfb includes blocks of various sizes and age mainly mesozoic limestone scattered within an early tertiary matrix mass wasting deposits and shallow to deep marine sediments at the beginning of the miocene transtensional tectonism led to the development of half graben basins on top of the accretionary wedge these basins namely the tekir and cukurhisar also cut the foredeep of the kfb obliquely in contrast with the theoretical study this paper focuses on the evolution and fillings of those basins initially claystone and basin margin reef deposits filled the half graben basins as a consequence of the lower miocene sea invasion then long and narrow conglomeratic channels starting from the northern edge of the basins fan delta progressed southwards passing into sandy lobes then into claystones an activation of the boundary faults of the wedge top basin stopped the progression of the lower middle miocene sediments and led to their deformation then the sedimentation of the kfb shifted towards the basin centre during the middle miocene

paleomagnetism in the precordillera of northern chile 22 30 s implications for the history of tectonic rotations in the central andes abstract widespread clockwise rotations in mesozoic and lower tertiary rocks of northern chile have been interpreted as the sum of two rotational events separated in time an early rotation related to local deformation plus a late rotation related to wholesale rotation of northern chile linked to late cenozoic oroclinal bending in the central andes in this paper we report new paleomagnetic data from cretaceous upper oligocene and miocene sedimentary rocks in the precordillera of northern chile the results suggest that all these rocks acquired their remanence at or close to the time of deposition the lack of rotation in undeformed lower miocene strata clearly indicates that clockwise rotations found in underlying faulted and folded cretaceous rocks were completed before the late cenozoic results from nearby localities in deformed upper oligocene strata would argue for little 5 rotation since the late oligocene data from widely separated miocene localities covering an area of about 5000 km2 in the calama basin strongly suggest that northern chile did not undergo significant wholesale rotation during the late cenozoic this together with previous paleomagnetic evidence against neogene rigid body like rotation of the southern peruvian forearc suggests that the curved shape of the central andean forearc was not significantly enhanced during the late cenozoic by inference all of the rotation in most mesozoic and lower tertiary rocks of northern chile was accomplished in the cretaceous and or early cenozoic when the locus of deformation in the central andes was localized in the present forearc region

new late permian paleomagnetic data from argentina refinement of the apparent polar wander path of gondwana the late paleozoic early mesozoic apparent polar wander path of gondwana is largely constructed from relatively old paleomagnetic results many of which are considered unreliable by modern standards paleomagnetic results derived from sedimentary sequences which are generally poorly dated and prone to inclination shallowing are especially common here we report the results of a joint paleomagnetic geochronologic study of a volcanic complex in central argentina u pb dating of zircons has yielded a robust age estimate of 263 0 1 6 2 0 ma for the complex paleomagnetic analysis has revealed a pretilting primary permian magnetization with dual polarities rock magnetic experiments have identified pseudo single domain titano magnetite and hematite as the mineralogic carriers of the magnetization lightning induced isothermal remagnetizations are widespread in the low coercivity magnetic carriers the resulting paleomagnetic pole is 80 1 s 349 0 e a95 3 3 n 35 and it improves a late permian mean pole calculated from a filtered south american paleomagnetic data set more broadly this new high quality igneous based paleomagnetic pole falls between the previously distinct late permian segments of the laurussian and gondwanan apparent polar wander paths suggesting that the long recognized disparity between these large paleomagnetic data sets may be primarily due to the inclusion of low quality or systemically biased data

magnetostratigraphy and mid palaeolatitude vgp dispersion during the permo carboniferous superchron results from parana basin southern brazil rhythmites summary a detailed magnetostratigraphic and rock magnetism study of two late palaeozoic rhythmite exposures itu and rio do sul from the itarare group parana basin brazil is presented in this paper after stepwise alterning field procedures and thermal cleaning were performed samples from both collections show reversed characteristic magnetization components which is expected for late palaeozoic rocks however the itu rocks presented an odd flat inclination pattern that could not be corrected with mathematical methods based on the virtual geomagnetic pole vgp distributions correlation tests between the maximum anisotropy of the magnetic susceptibility axis k1 and the magnetic declination indicated a possible mechanical influence on the remanence acquisition the rio do sul sequence displayed medium to high inclinations and provided a high quality palaeomagnetic pole after shallowing corrections of f 0 8 of 347 5 e 63 2 s n 119 a95 3 3 k 31 which is in accordance with the palaeozoic apparent wander pole path of south america the angular dispersion sb for the distribution of the vgps calculated on the basis of both the 45 cut off angle and vandamme method was compared to the best fit model g for mid latitudes both of the sb results are in reasonable agreement with the predicted palaeo latitudinal s relationship during the cretaceous normal superchron cns although the sb value after the vandamme cut off has been applied is a little lower than expected this result in addition to those for low palaeolatitudes during the permo carboniferous reversed superchron pcrs previously reported indicates that the low secular variation regime for the geodynamo that has already been discovered in the cns might have also been predominant during the pcrs

massif central france new constraints on the geodynamical evolution from teleseismic tomography the massif central the most significant geomorphological unit of the hercynian belt in france is characterized by graben structures which are part of the european cenozoic rift system ecris and also by distinct volcanic episodes the most recent dated at 20 ma to 4000 years bp in order to study the lithosphere asthenosphere system beneath this volcanic area we performed a teleseismic field experiment during a six month period a joint french german team operated a network of 79 mobile short period seismic stations in addition to the 14 permanent stations inversion of p wave traveltime residuals of teleseismic events recorded by this dense array yielded a detailed image of the 3 d velocity structure beneath the massif central down to 180 km depth the upper 60 km of the lithosphere displays strong lateral heterogeneities and shows a remarkable correlation between the volcanic provinces and the negative velocity perturbations the 3 d model reveals two channels of low velocities interpreted as the remaining thermal signature of magma ascent following large lithospheric fractures inherited from hercynian time and reactivated during oligocene times the teleseismic inversion model yields no indication of a low velocity zone in the mantle associated with the graben structures proper the observation of smaller velocity perturbations and a change in the shape of the velocity pattern in the 60 100 km depth range indicates a smooth transition from the lithosphere to the asthenosphere thus giving an idea of the lithosphere thickness a broad volume of low velocities having a diameter of about 200 km from 100 km depth to the bottom of the model is present beneath the massif central this body is likely to be the source responsible for the volcanism it could be interpreted as the top of a plume type structure which is now in its cooling phase

role of spherical particles on magnetic field recording in sediments experimental and numerical results abstract we report deposition experiments using spherical glass beads that possess remanent magnetizations stemming from iron impurities 15 g of glass beads with a well characterized size distribution were loaded in two different sets of tubes with diameters of 2 0 and 3 6 cm each tube contains identical column heights of de ionized water thereby allowing us to assess the effect of sediment concentration on the results 352 versus 90 kg m3 g l respectively the tubes were placed in magnetic fields of variable inclination and intensity in a temperature controlled environment the full vector magnetization and sediment accumulation rates were measured upon deposition times ranging from 10 min to 10 days experiments were run in triplicate to evaluate data reproducibility together with the lack of magnetic interaction and the absence of clumping the experiments elucidate an end member scenario of how sediments acquire remanent magnetizations in the absence of flocculation our results show that inclination shallowing in the range of 7 20 for field inclinations of 30 and 60 is indeed possible with solely spherical particles more importantly we observe a field dependence on the inclination error field dependence on the moment acquisition and inclination error both exhibit non linearity which may complicate interpretations of relative paleointensity data in paleomagnetic records a newly developed numerical model whereby particle collision during settling combined with both rolling and slipping translation on the substrate is consistent with the experimental results

compaction induced inclination shallowing in synthetic and natural clay rich sediments experiments using single clay slurries consisting of acicular or equidimensional magnetite mixed with either kaolinite illite montmorillonite or chlorite were conducted to determine the effect of compaction on inclination a natural marine sediment and a reconstructed marine sediment made up of the clays used in our single clay experiments were also studied a laboratory postdepositional remanence imparted to the slurries by stirring had its inclination shallowed by compaction for both the single clay samples as seen previously anson and kodama 1987 and the natural and reconstructed marine sediments suggesting that our single clay sediments are valid analogues of natural sediments magnetic intensity also decreased by 30 50 during compaction the greatest decrease occurring for samples with the steepest initial inclination altering the ph of a slurry so that the magnetite would have a negative surface charge and be repelled by clay particles did not affect a slurry s inclination shallowing behavior suggesting that electrostatic attraction between magnetite and clay is probably not a major contributor to inclination shallowing however most of the inclination shallowing observed in our experiments occurs at low pressures when void ratios are high comparison with a clay microfabric compaction study mcconnachie 1974 suggests that volume loss at these pressures is accommodated by reorientation of clay particles or clay particle aggregates clay domains since pore spaces are large at these low pressures inclination shallowing is probably caused by magnetite particles either being attached to clay particles perhaps by van der waals forces or having been incorporated into clay domains alternating field demagnetization of compacted samples which contain magnetite with a range in grain sizes supports this model indicating that the smallest magnetic grains are slightly more shallowed by compaction than larger grains our results suggest that a sediment s clay content may be an important contributor to inclination shallowing

a pure dipole analysis of the gondwana apparent polar wander path paleogeographic implications in the evolution of pangea the paleogeography of prebreakup pangea at the beginning of the atlantic spreading has been a subject of debate for the past 50 years reconciling this debate involves theoretical corrections that cast doubt on available data and paleomagnetism as an effective tool for performing paleoreconstructions this 50 year old debate focuses specifically on magnetic remanence and its ability to correctly record the inclination of the paleomagnetic field in this paper a selection of paleopoles was made to find the great circles containing the paleomagnetic pole and the respective sampling site the true dipole pole tdp was then calculated by intersecting these great circles effectively avoiding nondipolar contributions and inclination shallowing in an innovative method the great circle distance between each of these tdps and the paleomagnetic means show the accuracy of paleomagnetic determinations in the context of a dominantly geocentric axial and dipolar geomagnetic field the tdps calculated allowed a bootstrap analysis to be performed to further consider the flattening factor that should be applied to the sedimentary derived paleopoles it is argued that the application of a single theoretical correction factor for clastic sedimentary derived records could lead to a bias in the paleolatitude calculation and therefore to incorrect paleogeographic reconstructions the unbiased apwp makes it necessary to slide laurentia to the west in relation to gondwana in a b type pangea during the upper carboniferous later evolving during the early permian to reach the final a type pangea configuration of the upper permian 2017 american geophysical union all rights reserved

post middle oligocene origin of paleomagnetic rotations in upper permian to lower jurassic rocks from northern and southern peru abstract we report paleomagnetic data from 28 sites of upper permian to lower jurassic strata from northern and southern peru in northern peru 6 s a stable magnetic component from six permo triassic sites passes fold and reversal tests the overall mean pole agrees well with late permian to triassic poles from cratonal south america suggesting this part of peru has experienced neither significant rotation nor latitudinal transport since the permo triassic in southern peru 13 to 16 s thermal demagnetization isolates stable magnetic components in 16 of 22 upper permian to lower jurassic sites collected along the transition between the altiplano and the eastern cordillera these 16 sites are rotated 14 to 147 counterclockwise and pass an inclinations only fold test within the same structural zone three other permo triassic sites as well as 10 paleocene sites also show important counterclockwise rotations roperch and carlier j geophys res 97 1992 17233 17249 butler et al geology 23 1995 799 802 the large magnitude and exclusively counterclockwise sense of rotation suggest that the tectonic regime included an important sinistral shear component no correlation exists between rotation amount and rock age suggesting the rotations are post paleocene in age because the rotations occur along the fringe of the eastern cordillera they were likely produced during its structural formation hence from the late oligocene to present sinistral shear acting in the northern part of the bolivian orocline appears much more pronounced than that north of the abancay deflection which likely arises from differences in convergence obliquity

evidence for late paleozoic and mesozoic non dipole fields provides an explanation for the pangea reconstruction problems abstract paleomagnetic pole positions have long been calculated with the assumption that the ancient geomagnetic field was purely that of a geocentric dipole but in recent years it has become a concern that this assumption is not always valid because of long term contributions from non dipole fields in particular octupole fields we tested for the presence of a zonal octupole field in the late carboniferous permian mesozoic and early tertiary by comparing the observed paleomagnetic paleolatitude distributions for the laurentian north america and greenland and european landmasses with those predicted from the mean paleopoles such a test is possible for a good sized continent not subsequently deformed when numerous and reliable paleomagnetic results exist from sites that cover a wide range of paleolatitudes if the field were purely dipolar coeval results should form a coherent dataset such that a regression line through the individual points in an observed versus predicted paleolatitude plot has a slope of 1 if the slopes of regression lines are systematically different from 1 0 for successive time intervals and granted that the earth s radius stayed the same then it is likely that non dipole fields can be held responsible regression line slopes standard errors for three intervals analyzed are 0 78 0 04 200 300 ma 0 93 0 11 120 200 ma and 0 82 0 06 40 120 ma as might be expected with a non dipole contribution to the total geomagnetic field paleomagnetic results from the most northerly areas of laurentia and europe i e ellesmere greenland and svalbard show clearly anomalous paleolatitudes because of the agreement between the equatorial locations determined independently by paleomagnetism and equatorial rain forest occurrences d v kent p e olsen earth planet sci lett 179 2000 311 324 we argue that long term quadrupole fields are less likely than octupole fields to be the cause of the paleolatitude discrepancies estimates of the magnitude of the octupole dipole field ratio are not very precise but center around 0 1 which could cause errors in conventional paleopole determinations using the dipole formula of 7 5 because of the antisymmetry of octupole fields a comparison of paleomagnetic poles from mid northern and mid southern hemisphere locations could thus be off by as much as 15 the well known misfit between the paleomagnetic results from the laurentia european and gondwana continents in a classical pangea a configuration could be explained by such errors due to octupole fields this explanation would negate the need to seek tectonic pangea b type solutions for the misfit these solutions have generally remained unacceptable in terms of the geology of the gondwana laurussia borderzone

paleomagnetic constraints on the permian triassic boundary in terrestrial strata of the karoo supergroup south africa implications for causes of the end permian extinction event the closure of the palaeozoic witnessed the greatest biotic crisis in earth history surprisingly little is known about the effects and timing of the terrestrial counterpart of the well described end permian mass extinction from known marine successions worldwide in the present study reliable paleomagnetic results were obtained from a pt boundary section in the terrestrial karoo basin of south africa permo triassic aged mudstones from a locality in the eastern cape province yielded two magnetic chrons reverse followed by normal with the boundary possibly close to the reversal this extends to results from a previous study thereby jointly identifying a r n r polarity pattern for this boundary interval the ptb interval is constrained below the red mudstones of the beaufort group at the present locality and within reverse magnetised green mudstone implying a diachronic relation between the marine and terrestrial end permian mass extinction events

correction to apparent and true polar wander and the geometry of the geomagnetic field over the last 200 myr 1 in the paper apparent and true polar wander and the geometry of the geomagnetic field over the last 200 myr by jean besse and vincent courtillot journal of geophysical research 107 b11 2300 doi 10 1029 2000jb000050 2002 the data in the top part of table 4 were incorrect the correct table 4 is given here journal of geophysical research vol 108 no b10 2469 doi 10 1029 2003jb002684 2003

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

two stage collision exploring the birth of pangea in the variscan terranes abstract the variscan suture exposed in nw iberia contains a stack of terranes including two allochthonous units with continental affinity and gondwanan provenance upper and basal units separated by an ophiolite belt where the most common units show protolith ages at c 395 ma recent lu hf zircon data obtained from these ophiolites indicate interaction between the gabbroic magmas and old continental crust hence the ophiolites could not have originated in a deep ocean basin associated with a mature mid ocean ridge or intraoceanic subduction the tectonothermal evolution of the continental terranes bounding the suture zone records two consecutive events of deep subduction the upper units record an initial high p ultra high p metamorphic event that occurred before 400 390 ma while the basal units were affected by a second high p low to intermediate t metamorphic event dated at c 370 ma continental subduction affected the most external margin of gondwana and developed in a setting of dextral convergence with laurussia development of the two high p events alternated with the opening of an ephemeral oceanic basin probably of pull apart type in early devonian times this ephemeral oceanic domain is suggested as the setting for the protoliths of the most common ophiolites involved in the variscan suture current ideas for the assembly of pangea advocate a single collisional event between gondwana and laurussia in the carboniferous however the new evidence from the allochthonous terranes of the variscan belt suggests a more complex scenario for the assembly of the supercontinent with an interaction between the colliding continental margins that started earlier and lasted longer than previously considered based on modern analogs of continental interaction the development of complex collisions as here suggested for gondwana and laurussia during the assembly of pangea could have been the norm rather than the exception throughout earth history

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

new african lower carboniferous paleomagnetic pole from intrusive rocks of the tin serririne basin southern border of the hoggar algeria a paleomagnetic study has been conducted on intrusive doleritic rocks cropping out within devonian horizontal tabular formations of the saharan craton tin serririne basin south of hoggar shield the 40k 40ar dating of the dolerites gave an age of 347 6 8 1 ma i e tournaisian the paleomagnetic data present three different directions the first has a paleomagnetic pole close to the previous african poles of permian age this direction is therefore interpreted as a permian remagnetization the second direction which is defined by both linear regression and remagnetization circles analysis is considered as the primary magnetization it yields a new african tournaisian paleomagnetic pole 18 8 s phi 31 2 e k 29 a95 7 5 very close to the ben zireg tounaisian pole aifa t feinberg h pozzi j p 1990 devonian carboniferous paleopoles for africa consequences for hercynian geodynamics tectonophysics 179 288 304 the third direction has intermediate orientation between those of the first or second directions and that of the upper cenozoic field it is interpreted as related to a composite magnetization this new tin serririne pole improves the apwp of gondwana for this key period of the evolution of the pangea this apwp confirms the previous paleogeographic reconstruction which shows that the pre hercynian ocean between gondwana and laurussia is still not close during the beginning of the carboniferous

a new inclination shallowing correction of the mauch chunk formation of pennsylvania based on high field air results implications for the carboniferous north american apw path and pangea reconstructions abstract a new magnetic anisotropy study was performed on samples of the lower carboniferous mauch chunk formation of pennsylvania these red beds had been sampled for an inclination shallowing study by tan and kodama 2002 however application of a high field anisotropy of isothermal remanence magnetization hf air technique specifically designed to measure the anisotropy of hematite provides considerably different results from those previously reported the newly measured fabric has smaller anisotropy 9 17 as opposed to 25 40 and shows a pronounced ene wsw magnetic lineation that is sub parallel to the trend of the appalachians and interpretable as a hematite intersection lineation that occurred during local nnw directed shortening the measured magnetic fabric yields a new inclination correction with a corrected paleopole that is in better agreement with recently corrected carboniferous paleopoles than the previously corrected mauch chunk paleopole defining a more consistent apw path the corrected paleopoles allow calculation of new mean early 325 ma and late 312 ma carboniferous inclination corrected paleopoles for north america which can be compared to coeval but uncorrected paleopoles from gondwana results suggest a pangea b assemblage unless inclination shallowing is considered for gondwana estimating an inclination correction for gondwana sedimentary rock derived paleopoles permits a pangea a type assemblage at higher southern latitudes than previous reconstructions which we term pangea a3

late permian to early triassic magnetostratigraphy a late permian to early triassic magnetostratigraphic reference section is presented the lower triassic part is based on results from marine limestone sections in south china published earlier 1 2 reliable new permian data are added here which have been collected in the nammal gorge salt range northwest pakistan where marine sediments have been deposited quasi continuously with occasional minor hiatuses during the late palaeozoic to early mesozoic about 50 of the permian samples from the nammal section contain hidden beneath a strong recent or tertiary overprint a characteristic remanent magnetization chrm which is very likely of permian age this component which was imprinted on the southern hemisphere has normal as well as reversed polarity with a normal mean direction decl 289 3 incl 50 3 95 4 3 n 113 which is in close agreement with the palaeofield direction expected for a site belonging to the indian plate as part of gondwanaland during the permian in the lower upper permian several normal polarity zones are recognized this contradicts the current assumption that rocks of this age belong to the long reversely polarized kiaman hyperzone the kiaman interval must end and the illawarra hyperzone of mixed polarity must begin in or prior to the lowermost upper permian the permian triassic boundary at nammal as well as in the chinese sections is situated very close to a transition from a reversed to a normal polarity zone the upper permian at nammal together with the lower triassic south china sections is estimated to cover about 20 ma nearly 30 polarity changes are observed which result in an average reversal frequency very similar to that observed during the early tertiary the reversal rate after the end of the long lasting reversed kiaman hyperchron apparently increases in a manner similar to that after the end of the cretaceous long normal superchron only a few polarity zones are found in the lower upper permian while progressively more frequent reversals follow in the lower triassic

roots reinforcement by riparian trees in restored rivers abstract riparian vegetation directly and indirectly affects many fluvial processes in particular the root system of riparian trees and shrubs may greatly influence river morphodynamics by imparting higher shear strength to riverbanks compared to unvegetated channel margins therefore the bank stabilizing role of riparian vegetation should be quantitatively considered in river restoration projects this work aims to quantify the additional strength due to the root systems of naturally established riparian vegetation after two river restoration projects carried out in the italian alps ahr and mareit rivers south tyrol these projects represent the largest restoration interventions carried out so far in italian rivers and the two sites feature contrasting channel patterns along with varying river floodplain dynamics the mechanical properties of roots and their distribution in the floodplain soils in the two sites have been measured to estimate root cohesion distribution associated to gray alder alnus incana and pioneering willows salix spp results show that roots of plants colonizing the gravelly substrate of building islands in the mareit river have less tensile strength than those belonging to trees growing in the floodplain of the ahr river rich in fine sediments however the higher root contribution to the overall soil strength occurs in the island site due its lack of fine sediments

support for an a type pangea reconstruction from high fidelity late permian and early to middle triassic paleomagnetic data from argentina 1 a major disparity is observed between the late paleozoic early mesozoic apparent polar wander paths apwps of laurussia and gondwana when the landmasses are re assembled in a conventional a type pangea this discrepancy has endured from the earliest paleomagnetic reconstructions of the supercontinent and has prompted discussions of non dipole paleomagnetic fields and alternative paleogeographic models here we report on a joint paleomagnetic geochronologic study of late permian and early to middle triassic volcanic and volcaniclastic rocks from argentina which demonstrates support for an a type model without requiring modification to the geocentric axial dipole hypothesis new shrimp u pb and 40ar 39ar isotopic dating has reinforced the inferred age of the sequences which we estimate at 264 ma upper choiyoi group and 245 ma puesto viejo group field stability tests demonstrate that the volcanic rocks are carrying early primary magnetizations which yield paleopoles 73 7 s 315 6 e a95 4 1 n 40 upper choiyoi and 76 7 s 312 4 e a95 7 3 n 14 puesto viejo a comprehensive magnetic fabric analysis is used to evaluate structural restorations and to correct for magnetization anisotropy the paleomagnetic results derived from volcaniclastic rocks are interpreted to be affected by inclination shallowing and corrections are discussed a comparison of these new results with the existing permian triassic paleomagnetic data from gondwana suggests the presence of widespread bias in the latter we contend that such bias can explain the observed apwp disparity at least for late permian middle triassic time and that alternative paleogeographic reconstructions or non dipole paleomagnetic fields do not need to be invoked to resolve the discrepancy

granitoid emplacement by multiple sheeting during variscan dextral transpression the saint laurent la jonquera pluton eastern pyrenees abstract the structural study of the saint laurent la jonquera pluton eastern pyrenees a variscan composite laccolithic intrusion emplaced in metasedimentary and gneissic rocks of the roc de frausa dome by means of the anisotropy of magnetic susceptibility ams technique has allowed the determination of the nature and orientation of its magmatic fabrics the magmatic foliation has a predominant ne sw strike and the mean lineation is also ne sw trending with a shallow plunge a strain gradient is measured so that the tonalites to granodiorites that form the basal parts of the pluton and are intruded into amphibolite facies metamorphic rocks recorded the highest anisotropies whereas the monzogranites and leucogranites emplaced into upper crustal low grade metamorphic rocks are weakly deformed these results point to the synkinematic sequential emplacement of multiple granitoid sheets from less to more differentiated magmatic stages during the late carboniferous d 2 event characterized by an e w trending dextral transpression the magmatic foliation appears locally disturbed by the effects of two tectonic events the first of them d 3 produced mylonitization of granitoids along nw se retrograding shear zones and open folds in the host ediacaran metasediments of the roc de frausa massif likely during late variscan times interference between d 2 and d 3 structures was responsible for the dome geometry of the whole roc de frausa massif the second and last perturbation consisted of local southward tilting of the granitoids coupled to the mesozoic cenozoic cover during the alpine

concordant late paleozoic paleomagnetizations from the atacama desert implications for tectonic models of the chilean andes abstract paleomagnetic results are reported from three formations of late paleozoic age from the northern chilean andes of the atacama desert for the first time primary nrm components are resolved for paleozoic units along the western flank of the central andes pole positions are calculated for the formations and compared with apw data for cratonic south america these comparisons reveal that the collecting sites in the northern domeyko and almeida ranges of the central andes have undergone no paleomagnetically defined rotations or translation with respect to cratonic south america since the time of nrm acquisition which is likely to have been in the lower parts of the kiaman reverse interval if growth of the south american lithosphere has involved accretion of exotic microplates they are either likely to be substantially older than units sampled here or be restricted to more coastal terranes the results taken together with other paleomagnetic data from northern chile and southern peru which have showed a wide range of discordance in their declinations when compared to each other or apw data lead to the conclusion that this region of the andes during the mesozoic or cenozoic has not been affected by simple processes of clockwise oroclinal bending from peru to chile nor regionally consistent patterns of block rotations

juxtaposed and superimposed paleomagnetic primary and secondary components from the folded middle carboniferous sediments in the reggane basin saharan craton algeria abstract a paleomagnetic study was carried out on the middle carboniferous sediments of the eastern margin of the reggane basin of algeria seven sites 108 samples in the lower serpukhovian and 11 sites 129 samples in the upper serpukhovian bashkirian and lower moscovian levels were investigated besides a common but generally limited viscous remanent magnetization component a and a recent chemical remanent magnetization of reversed polarity a two main components were identified one of these component b is characterized by a negative fold test and has been identified as a lower jurassic remagnetization the associated paleomagnetic pole obtained in the seven zones by combining characteristic remanent magnetization directions chrm and great circles 71 1 n 251 4 e a95 3 8 k 254 lies in the vicinity of the nw african poles of similar ages the second component c displays both normal and reversed polarities also determined by the combination of chrm or stable end points and remagnetization circles it yields a positive fold test which constrains the magnetization acquisition time and a positive reversal test which argues in favor of a non composite nature of the component c the normal polarities observed in the lower serpukhovian levels represent the latest normal event observed in africa before the kiaman superchron the paleomagnetic south pole calculated from 10 sites n 64 data gathered in four large areas 26 5 s 44 7 e a95 4 7 k 383 is the first african carboniferous pole founded on both positive reversal and fold tests it lies only slightly apart from other middle carboniferous poles previously published for the northern part of africa where no intraformational test were available to constrain the magnetization age

a paleomagnetic study of permian and triassic rocks from the toulon cuers basin se france evidence for intra pangea block rotations in the permian 1 the identification of a massive shear zone separating gondwana from laurasia during late palaeozoic times is one of the prerequisites for the controversial pangea b to a transition here we present new paleomagnetic data from permian and triassic sediments and volcanic rocks from the toulon cuers basin se france likely to be situated within this intra pangea shear zone a total of 150 samples from 14 sites were collected in the field 108 samples yielded reliable paleomagnetic component directions based on stepwise thermal demagnetization up to maximum temperatures of 690 c after removal of an initial viscous magnetic component from room temperature up to 200 c a second component of reverse polarity oriented to the south and up was identified in almost all samples of permian age the triassic samples behave similarly with the notable difference that here two polarities of magnetization are present positive field tests suggest the primary character of this characteristic magnetization the latitudes of the resulting early to mid permian paleopoles agree well with the corresponding segment of the apparent polar wander path apwp for europe whereas the longitudes are strung out along a small circle segment indicating relative rotations between the sampled regions and stable europe the triassic poles instead plot close to the triassic segment of the european apwp and provide an upper time limit for the observed rotations these results suggest a wrench faulting event associated with intra pangea crustal instability and transformation during the permian

paleogene building of the bolivian orocline tectonic restoration of the central andes in 2 d map view using available information on the magnitude and age of tectonic shortening as well as paleomagnetically determined tectonic rotations we have run a series of 2 d map view restorations of the central andes neogene shortening in the foreland belt induced only slight orogenic curvature of the central andes the constraints on the ages of the large observed fore arc rotations average of 37 counterclockwise in southern peru and 29 clockwise in northern chile indicate that the bolivian orocline formed during the eocene oligocene as a consequence of differential shortening focused in the eastern cordillera to minimize local block rotations along the fore arc the restoration that best fits the central andean rotation pattern requires about 400 km of total paleogene plus neogene shortening near the arica bend this value corresponds to the upper bound of estimates of maximum horizontal shortening for the central andes along strike variations in horizontal shortening in the back arc induced bending of the continental margin block rotations with fore arc along strike extension and or orogen parallel transport of upper crustal material toward the symmetry axis of the orocline