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

no tectonic rotation of the tuscan tyrrhenian margin italy since late messinian extensive paleomagnetic sampling of 38 late miocene and pliocene sites has been carried out in the western tuscan basins in italy these basins are located along the tyrrhenian margin and the studied formations were deposited at the same time as the opening of the tyrrhenian sea the laboratory analyses show that in most of the sites pseudo single domain magnetites are the main magnetic carrier the paleomagnetic data obtained from 27 suitable sites indicate that the tuscan tyrrhenian margin has not been affected by significant regional rotation since at least the late messinian early pliocene about 5 5 m y these data demonstrate that the rotations previously measured in the meso cenozoic units of the apennines and of the apulia foreland cannot be directly related to the late messinian pliocene phases of rifting in the tyrrhenian sea moreover the data presented here conflict with published results from coeval formations in the apennines and sicily in areas subjected to strong thrusting and shortening in these areas the rotations control the orientation of the main compressional structures and give rise to the typical arcuate shape of the apenninic chain we suggest that the tectonic evolution of the northern tyrrhenian sea apenninic chain system involved thrusting and shortening of the external eastern domains with rotations of the allochthonous units followed by gravitational collapse of the western sector this second phase involved no tectonic rotation of the newly formed extensional basins

tertiary remagnetization of normal polarity in mesozoic marly limestones from se france the results of our new paleomagnetic investigations on 21 sites in the cevennes and lure regions as well as previous studies demonstrate that all mesozoic marly limestones of se france exhibit similar paleomagnetic behavior with remagnetization disputed in age the studied areas have the particularity to have been folded before late eocene the alpine folding oligo miocene samples 201 marly limestones dated from lower jurassic to lower cretaceous have been demagnetized by thermal treatment they all present a well defined component with a normal polarity which was mostly obtained between 200 and 350 c numerous arguments lead from pretectonic to syntectonic widespread remagnetization related to orogenic fluid circulation affecting the whole basin an eocene age between 35 and 40 ma is obtained for this remagnetization thanks both to the comparison of the average inclination of all regional paleomagnetic studies 54 9 1 5 with the expected paleomagnetic inclination and the syntectonic character of remagnetization

measured changes in ocean surface roughness due to atmospheric boundary layer rolls a research aircraft was recently flown over the mid atlantic eight during a mild cold air outbreak to sample the planetary boundary layer at low levels of 15 20 m above the sea surface aircraft sensors measured near surface atmospheric turbulence and at the same time variations in sea surface roughness using laser and radar the aircraft turbulence observations indicate a coherent secondary flow consistent with boundary layer roll vortices of crosswind scale 1 5 2 0 km modulation in measured laser and radar inferred sea surface slope variance occurs at similar scales remarkable correlation is found between the radar backscatter and near surface wind speed data showing that the short wave slope variance is responsive to these large eddies associated small but periodic changes in wind direction do not appear to impact the short wave slope signature differentiation between short and intermediate scale wave roughness using aircraft laser and radar data leads us to conclude that observed fluctuations in intermediate scale wave slope were not directly linked to the local wind a synthetic aperture radar sar image was acquired by the canadian space agency s radarsat coincident with the aircraft measurements widespread streaking in the sar image suggests the surface impacts of atmospheric longitudinal rolls our aircraft results indicate that the dominant term dictating sar backscatter modulations at the eddy scale of 1 2 km is the fluctuation of the along wind velocity nominally associated with regions of near surface convergence or divergence wind speed fluctuations of 7 10 estimated from the sar and aircraft radar are consistent with the aircraft s measured variations in near surface wind speed

paleomagnetism of jurassic to miocene sediments from the apenninic carbonate platform southern apennines italy evidence for a 60 counterclockwise miocene rotation abstract the tectonic evolution of the apennine belt southern tyrrhenian sea system is addressed through a paleomagnetic study of lias to langhian sediments from the apenninic carbonate platform southern apennines italy reliable paleomagnetic data gathered from 21 sites document a regional scale post langhian 80 counterclockwise ccw rotation since previous studies of the plio pleistocene clays spread over the orogen had shown a 20 ccw rotation we conclude that the southern apennines rotated by 60 during middle late miocene our data provide evidence that the southeastward drift of calabrian block and synchronous spreading of the southern tyrrhenian sea induced saloon door like deformation of the southern apennines and sicily which underwent similar magnitude although opposite in sign orogenic rotations a paleomagnetically derived paleogeographic reconstruction shows that at 15 ma late langhian the alpine apennine belt collided with a nne oriented carbonate platform corridor surrounded by oceanic basins we speculate that both the end of the corsica sardinia rotation and the eastward jump of the locus of back arc extension from the liguro provencal to the tyrrhenian sea may have been consequences of this event

evidence for the influence of the agulhas current on regional atmospheric circulation patterns abstract the agulhas current is much the strongest western boundary current in the southern hemisphere transporting about 65 sv of warm water along the southeast coast of africa south of africa it retroflects back into the south indian ocean and flows east as the agulhas return current large amounts of heat are lost to the atmosphere from the warm waters of the southern agulhas current its retroflection and the return current particularly during winter and the transition seasons it is thought that this large exchange of heat may have a significant influence on the regional atmospheric circulation the tracks and intensity of transient weather disturbances such as extratropical cyclones and on rainfall received over large parts of neighboring southern africa in an attempt to investigate the potential influence of the agulhas current on the regional atmosphere two ensembles of year long integrations of an atmospheric general circulation model are analyzed in the first ensemble the sea surface tem

the effect of north pacific sea surface temperature anomalies on the january climate of a general circulation model abstract four perpetual january integrations of an atmospheric general circulation model have been performed in each of which a different sea surface temperature sst anomaly was specified in the north pacific the observed sst anomaly for the 1976 77 winter was chosen as the basic anomaly and 1200 day runs were carded out in which this anomaly was multiplied by 1 and 2 a fifth run was performed which combined the basic midlatitude sst anomaly from 1976 77 with a tropical pacific sst anomaly representative of the mature phase of a warm el nino southern oscillation enso episode an ensemble of eight independent 90 day averaged realizations was extracted from each simulation maps of ensemble mean differences from the model climatology are presented in this paper together with estimates of the statistical significance of some of the features which appear on these maps the model response to the basic sst anomaly and to twice the basic sst anomaly is a midiatitude teleconnection pattern the pacifi

stereo observation of lakes and coastal zones using aster imagery abstract one of the unique features of the visible and near infrared vnir subsystem of the advanced spaceborne thermal emission and reflection radiometer aster is the near infrared back looking view which is obtained 55 s later than the corresponding nadir view although the stereoscopic capability derived from a combination of these two views was originally designed for use in land applications serendipitous observation has shown that it also represents a promising source of data over water bodies in fact when coupled with surface temperature measurements derived from the sensor s thermal infrared tir component stereo viewing forms a powerful observational capability that can be exploited in the monitoring of lake and marine environments one important aspect introduced by the stereo system is the capability to measure the short term displacements associated with surface currents and waves by comparing the nadir and back looking views in initial results presented here surface motion was deduced from the displacement of a ship wake appearing in the sun glitter regime of an aster image of the izu shoto islands which lie to the southwest of tokyo bay japan within the natural limitations imposed by spatial and temporal resolutions this measurement was found to be consistent with simultaneous surface current values derived from a nearby shore based high frequency hf radar system the success of this basic comparison introduces the possibility that stereo imaging from space if well tuned to follow the motion of surface slicks and other surface features within the sun glitter regime could provide a future means of observing surface current on a global scale data from the vnir stereo system also highlights the influence of observational geometry in the case of a surface with sun glitter this often manifests as a brightness reversal between the nadir and back looking views in which relatively bright dark features at nadir appear dark bright in the back looking view such a region of brightness reversal robr can be indicative of a locally rough or smooth surface texture as may be found for example in the vicinity of internal waves rough or ship wakes smooth simple analysis based on a back to nadir ratio of relative radiances shows that the signal strengths measured by aster within a robr can yield a crude estimate of the mean square surface slope which is an important parameter in theories of sea surface roughness imaging by devices such as synthetic aperture radar sar several other potential applications of vnir stereo data in coastal zone and lake monitoring are considered here including the study of internal waves in the strait of gibraltar derivation of wind velocity at cloud height swell wave propagation suspended sediment transport marine traffic monitoring and ship wake patterns as the reflectivity of water in the near infrared reverses from low to high in the presence of sun glitter most of the applications discussed here involve glitter and hence some discussion of the influence of sensor view geometry is presented the general conclusion of the paper is that future missions such as the advanced land observing satellite alos which aim to deploy high spatial resolution stereo viewing systems primarily for land applications should also return data of considerable value in oceanography and limnology particularly if their observational geometry can be adjusted to permit the imaging of sun glitter from water surfaces

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

paleomagnetic data from umbria italy implications for the rotation of adria and mesozoic apparent polar wander paths abstract sixteen new jurassic and cretaceous paleomagnetic sampling sites are located in northern umbria along three river valleys bosso burano sentino the late jurassic and early cretaceous data are consistent in declination but not inclination with previously published data from these valleys early jurassic data from eight sites give site mean declinations which are significantly different from the two site mean declinations of this age which were previously available comparison of the data with cretaceous and jurassic mean directions from the southern alps indicate 20 anticlockwise rotation relative to the southern alps of this part of northern umbria during neogene deformation of the umbrian fold and thrust belt if the umbrian mean directions are rotated to compensate for the tectonic rotation the early jurassic and cretaceous umbrian and southern alpine pole positions coincide closely with a recently derived african apparent polar path apwp implying that adria moved with africa since at least early jurassic times the late jurassic umbrian and southern alpine poles however are not consistent with current apwps and imply rapid apparent polar wander in both african and north american coordinates from high latitude to lower latitude between bathonian and oxfordian times

synthetic aperture radar observations of currents colocated with slicks during low wind conditions our synthetic aperture radar sar imagery of the ocean contains examples of strong perturbations in the geometry of persistent turbulent ship wakes at the intersection of wakes with dark slicklike features the perturbations in the wakes are presumably caused by currents and are invariably colocated with slicklike submesoscale features the current dynamics influencing the geometry of turbulent wakes are hypothesized to contribute to the efficient accretion of a biotic and abiotic microlayer in a localized surface zone which is observed as a dark slick in our sar imagery time displaced sar imagery allows us to track the time evolution of the turbulent wake perturbations to determine the differential surface current responsible for the perturbations and to estimate the associated shear in addition the time displaced imagery also allows us to observe the temporal stability of the slicklike features

thermoviscous remagnetization in some appalachian limestones experimental evidence shows that blocking temperature relaxation time theory for single domain magnetite can grossly underestimate laboratory thermal demagnetization temperatures of a present day viscous remanence in devonian limestones of new york state thermoviscous remagnetization at moderately elevated burial temperatures during the late paleozoic cannot therefore be readily excluded for the origin of the stable secondary component in these rocks more generally these results emphasize that single domain thermal activation theory cannot be assumed a priori to correctly predict temperature of thermoviscous remanence acquisition in all magnetite bearing rocks the prob leto

satellite measurements reveal persistent small scale features in ocean winds four year averages of 25 kilometer resolution measurements of near surface wind speed and direction over the global ocean from the quikscat satellite radar scatterometer reveal the existence of surprisingly persistent small scale features in the dynamically and thermodynamically important curl and divergence of the wind stress air sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields as are the influences of islands and coastal mountains ocean currents such as the gulf stream generate distinctive patterns in the curl field these previously unresolved features have important implications for oceanographic and air sea interaction research

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

late miocene remagnetization within the internal sector of the northern apennines italy abstract paleomagnetic and geologic evidence indicates that upper jurassic radiolarian cherts of both the tuscan cherts formation continental margin tuscan units and the monte alpe cherts formation oceanic crust ligurian units were remagnetized during miocene orogenesis of the northern apennines of italy characteristic overprint magnetizations with reversed polarities have been found over a large area within the internal sector of the northern apennines including eastern liguria elba island and the thyrrenian margin and west of the middle tuscan ridge the reversed polarity overprint average direction d 177 i 52 95 15 was most likely acquired during late miocene uplift and denudation of the orogenic chain and thermochemical remagnetization was a probable consequence of increased circulation of orogenic fluids similarly mostly reversed polarity directions of magnetization have been found by other workers in overlying post orogenic messinian sediments d 177 i 57 95 3 which show little counterclockwise ccw vertical axis rotation with respect to stable europe 8 5 the monte alpe cherts sampled at sites in the external sector of the northern apennines close to major tectonic features have normal polarity overprint directions with in situ w sw declinations since the overlying post orogenic messinian sediments have not been substantially rotated about vertical axes the evidence points to an earlier pre late miocene remagnetization in the external parts of the orogenic chain

hidden terranes in the northern apennines italy a record of late cretaceous oligocene transpressional tectonics we propose that a very oblique or transpressional tectonic regime was dominant during the early pre collisional orogenic evolution of the northern apennines late cretaceous to early oligocene this hypothesis resolves many inconsistencies in the previous reconstructions of this orogenic belt which were based on a classic model of orthogonal convergence between the european and adriatic plates the crucial lines of evidence that point to a major role of oblique tectonics in the structuring of the northern apennines are 1 the plate tectonics framework that indicates left lateral oblique convergence along the europe adria plate margin 2 the lack of a magmatic arc during the entire pre collisional convergent history of the chain a time span 45 m y from late cretaceous to early oligocene 3 the long 20 m y residence time of turbidite sequences in the trench the dormant trench 4 the multiple source areas of turbidites from both sides of the basin and the associated coarse gravity d

paleomagnetism and paleogeography of jurassic radiolarian cherts from the northern apennines of italy oriented samples of jurassic radiolarian chert were collected from the tuscan domain continental margin and the ligurid domain oceanic of the northern apennines for paleomagnetic study to determine the paleogeographic origins of these rocks the oceanic rocks are all thermochemically overprinted by a mostly reversed polarity component of magnetization b that was likely acquired during late miocene regional uplift of the northern apennines this component also dominates the lower brittle chert of the tuscan cherts but disappears upsection in the more clay rich and ductile siliceous marlstones in addition the tuscan cherts retain an inferred primary magnetization c isolated at temperatures between 560 and 660 c which passes a fold test and shows a polarity stratigraphy this component indicates a paleolatitude of 11 4 n and a counterclockwise vertical axis rotation of 29 9 with respect to the southern alps of italy of 49 8 with respect to africa and of 91 8 with respect to eurasia our results suggest that the tuscan domain was farther south than other deep water continental margin sections of adria and that transcurrent faulting might have played a significant role in the orogenic evolution of the northern apennines

remagnetization during cretaceous normal superchron in eastern san juan islands wa implications for tectonic history abstract the eastern san juan islands expose an island arc ophiolite sequence and one or more ocean floor terranes cover rocks of the former including red radiolarian tuff and arc derived sandstone have no penetrative fabric and lack high pressure minerals in contrast pillow basalts and ribbon cherts of the latter are strongly deformed and the overlying metagraywacke is folded with a penetrative axial plane cleavage all ocean floor rocks have aragonite in veins indicative of higher pressure conditions than experienced by the island arc rocks a downward magnetization is common to the ocean floor rocks consistent with widespread remagnetization during the cretaceous normal superchron this magnetization is carried by magnetite and in red rocks by hematite fluid flow during or after deformation and high p metamorphism likely facilitated remagnetization at low temperature the magnetic directions are somewhat scattered but most are moderately to steeply down to the southeast they are far from directions expected with or without northward transport of baja bc rotation of observed directions into agreement with those expected for either present or more southerly locations also rotate structural elements in the host rocks three alternative rotation histories explored here all produce structural reconstructions that differ considerably from the present structure a tectonic history of the eastern san juan islands based on any of these reconstructions would be superior to one based on present attitudes of structures this is because at least a constraint that the restored paleomagnetic directions match a paleomagnetic field direction is satisfied choices among alternative reconstructions would become clearer with better understanding of relative ages of specific structures and their magnetizations improved geologic understanding of the regional setting where the rocks could have been deformed and remagnetized would also help

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

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

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

paleomagnetic evidence for displacement from the south of the coast plutonic complex british columbia the mid cretaceous spuzzum and porteau plutons of the coast plutonic complex of british columbia have two magnetizations a and b the a magnetization eight sites 83 specimens d 30 3 i 56 7 95 4 9 paleolatitude 37 5 n paleopole 65 0 n 14 9 w a95 6 2 is considered to have been acquired in the age range 105 90 ma this result differs from the field established for cratonic north america in this time range the difference could be caused either by previously undetected tilting about a horizontal axis of the plutons or by their rotation about a vertical axis and lateral displacement relative to the craton previously observed mid cretaceous magnetizations from other rock units from the western canadian cordillera and the cascades of washington united states are similarly discordant with respect to the craton this similarity over such a large area indicates that although local undetected tilting could be partly responsible it is unlikely to be the prime cause and we argue ther

observations of near surface current shear help describe oceanic oil and plastic transport plastics and spilled oil pose a critical threat to marine life and human health as a result of wind forcing and wave motions theoretical and laboratory studies predict very strong velocity variation with depth over the upper few centimeters of the water column an observational blind spot in the real ocean here we present the first ever ocean measurements of the current vector profile defined to within 1 cm of the free surface in our illustrative example the current magnitude averaged over the upper 1 cm of the ocean is shown to be nearly four times the average over the upper 10 m even for mild forcing our findings indicate that this shear will rapidly separate pieces of marine debris which vary in size or buoyancy making consideration of these dynamics essential to an improved understanding of the pathways along which marine plastics and oil are transported

the differences between early and midwinter atmospheric responses to sea surface temperature anomalies in the northwest atlantic abstract using an atmospheric global spectral model it is shown that the winter atmosphere in the midlatitudes is capable of reacting to prescribed sea surface temperature sst anomalies in the northwest atlantic with two very different responses the nature of the response is determined by the climatological conditions of the winter regime experiments are performed using either the perpetual november or january conditions with or without the prescribed sst anomalies warm sst anomalies in november result in a highly significant anomalous ridge downstream over the atlantic with a nearly equivalent barotropic structure in january the response is a statistically less significant trough the presence of the sst anomalies also causes a northward southward shift of the atlantic storm track in the november january cases a diagnostic analysis of the anomalous heat advection in the simulations reveals that in the january cases the surface heating is offset primarily by the strong horizontal cold advect

a climatology of southern hemisphere extratropical cyclones a climatology of extratropical cyclones determined by an objective automatic scheme applied to 15 years 1975 89 of once daily australian bureau of meteorology hemispheric analyses is presented contour maps of the positions of formation cyclogenesis dissipation cyclolysis together with other cyclone statistics are presented the distribution of cyclones through the hemisphere was found to be dominated by a permanent high latitude core coincident with the circumpolar trough during the winter and intermediate seasons two mid latitude branches are evident in the cyclone density originating in the tasman sea and south american sectors both spiraling poleward and merging with the circumpolar core in the southern oceans systems were observed to move in an castsouth east direction away from their location of formation exhibiting peak speeds of migration in the mid latitudes little seasonality was evident in the densitiy distribution of cyclones through the southern oceans but a considerable amount was found in their central pressure

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

diagenetic magnetite carries ancient yet secondary remanence in some paleozoic sedimentary carbonates many sedimentary carbonate rocks carry stable magnetizations that can be shown to reside in magnetite when such magnetizations are observed it is often argued or demonstrated that the magnetite was incorporated into the sediment during deposition however paleomagnetic and rock magnetic studies in conjunction with analyses of magnetic extracts from the helderberg and bonneterre carbonates united states indicate that the magnetite present in these rocks is most likely of diagenetic i e postdepositional origin

paleomagnetism and paleogeography of the northern calcareous alps austria prefolding magnetization components have been resolved at 38 sites of liassic adnet limestones in the central northern calcareous alps nca and at one site in the drauzug the site mean directions are northeasterly and down and are closer to coeval european directions than to southern alpine african directions the western end of both the nca and of the drauzug yield different site mean directions and negative fold tests indicating remagnetization the sampling localities have been rotated relative to one another during thrusting however comparison of paleomagnetic poles with the european apparent polar wander path implies an average clockwise rotation of about 30 for the nca relative to europe larger scale clockwise rotations in excess of 80 relative to the southern alps are implied by comparison with the southern alpine african polar wander path facies analysis of jurassic and lower cretaceous basinal sediments in the central part of the nca suggests that liassic subsidence was related to presently e w sinistral strike slip faults whereas malm berriasian subsidence was controlled by presently e w south dipping normal faults both paleomagnetic and facies data tend to indicate that the nca did not undergo the african rotation seen in southern alpine paleomagnetic data this implies the existence of a short lived tract of triassic jurassic ocean floor between the nca and the southern alps which linked the pindos ocean to the ligurian trough and allowed adria to rotate independently from the nca during the late jurassic eo alpine deformation and metamorphism are associated with the early cretaceous closure of this hallstatt trough

deposition of franciscan complex cherts along the paleoequator and accretion to the american margin at tropical paleolatitudes red radiolarian cherts from three localities within the franciscan subduction complex of northern california contain three components of remanent magnetization which are best isolated by progressive thermal demagnetization the first component usually removed by 300 c has an in situ direction similar to the present axial dipole field and is probably a recently acquired thermoviscous overprint a second component generally removed between 300 and 630 c has constant normal polarity and direction within each section and is interpreted to have been acquired by low temperature chemical alteration during subduction and accretion at the continental margin the third component isolated between 560 and 680 c has both normal and reversed polarities passes a fold test and is inferred to have been acquired during or soon after deposition the available paleomagnetic biostratigraphic and geochemical data indicate deposition of these cherts along the paleoequator 0 2 n or s paleolatitude between pliensbachian and oxfordian time as the oceanic plate moved eastward relative to north america beneath the equatorial zone of high biologic productivity between bathonian and cenomanian time the chert sequences apparently moved progressively away from the paleoequator 2 15 n or s and were soon after accreted to the american continental margin plate reconstruction models for the farallon plate corroborate low paleolatitude trajectories from ridge crest to subduction zone for example from 3 s to 11 n and they imply subsequent northward translation of the franciscan complex 4 000 km by strike slip faulting related to relative motions between the farallon kula pacific and north american plates

isotope and chemical microsampling constraints on the history of an s type rhyolite san vincenzo tuscany italy fine scale heterogeneities in strontium isotope ratios 40ar 39ar ages and chemical com sition have been determined for individual mineral grains and enclaves in the rhyolites of san vincenzo italy the rhyolites are peraluminous with phenocrysts of alkali feldspar piagioclase biotite and cordierite and have previously been divided into two groups on the basis of whole rock major element chemistry group b lavas are distinguished from group a in having higher mgo and cao contents as well as containing two pyroxenes and chilled latite enclaves the group b lavas show textural evidence for d sequilib um such as resorption and sieve zones in feldspars laser fusion 40ar 39ar dating of individual alkali feldspar crystals suggests that the eruption of these rhyolites took place 4 38 0 04 ma though small amounts of excess argon are present in subhedral and cloudy crystals the groundmass in the group a sample has a higher initial r7sr 86sr 0 725 than that of the group b 0 7 13 the sr isotope compositions of chemically and texturally characterized individual grains reveal marked disequilibrium between minerals and the host glass as well as within grain zonation the feldspars and coarse grained biotites have initial 87sr 8 sr that are intermediate between those of the group a and b glasses with alkali feldspar generally having higher initial 87sr 86sr ratios than plagioclase chilled latite enclaves which are present in only the group b lavas have relatively low initial 8 sr 86sr ratios in the range 0 7082 0 7088 the mineral chemistry and isotope data indicate that restite does not form a significant portion of the crystalline assemblage and therefore cannot be the source of the strontium isotope dis equilibrium xenocrysts mixed into the rhyolite from a mafic magma were identified as clinopyroxene megacrysts clinopyroxene orthopyroxene clots orthopyroxene plagioclase clots and plagioclase with extensive sieve textures these grains all have relatively low initial 87sr 86sr ratios other grains that may be xenocrysts are cordierites with cores containing inclusions of biotite spinel and sillimanite and alkali feldspars with excess 4 ar the strontium isotope di quilib um in phenocrysts of plagioclase alkali feldspar and biotite is attributed to a changing melt chemistry that was too rapid for strontium diffusive equilibration a mode1 for the san vincenzo magma chamber is proposed in which the sr isotope evolution of the group b rhyolites is due to magma mixing of a crustal melt with latite magma containing unra diogenic strontium the variable initial strontium isotope compositions of group a phenocrysts may be due to assimilation or crystallization along the interface between mingled group a and b magmas

crustal extension in the northern apennines the transition from compression to extension in the alpi apuane core complex an interpretation of northern apennine geology is presented which relates the temporal and spatial occurrence of both compressional and extensional deformation features in terms of the changing dynamic evolution within an accretionary wedge after a model proposed by platt 1986 followed by the initiation and development of continental rifting during cretaceous to eocene time an accretionary wedge formed as remnant tethyan oceanic crust subducted beneath the rotating corsica sardinia microplate microplate collision during the oligocene was characterized by the rapid imbrication of buoyant continental crust of the italian continental margin the record of which is preserved within the duplex structure geometry of the alpi apuane region the overthickened wedge geometry returned to a more stable configuration by developing extensional features during the miocene both listric normal faults at upper crustal levels and shear zones indicating evidence of distributed ductile extensional strain at mid crustal levels are recorded it is proposed that large scale regional extension with associated volcanism beginning in the messinian was represented by the intrusion of asthenospheric material from the subducted plate into the already attenuated accretionary complex further rifting perhaps aided by subduction and back arc processes in the southern apennines led to the formation of the tyrrhenian sea as an oceanic basin both the apennines and north american core complexes record evidence of crustal thickening followed by crustal thinning and finally of continental rifting this suggests that the similar histories of these regions with vastly different plate tectonic settings may both be explained by processes linked to the changing internal dynamics of accretionary wedges

first paleomagnetic data from the sedimentary cover of the french penninic alps evidence for tertiary counterclockwise rotations in the western alps abstract we present a paleomagnetic study performed in the brianconnais sedimentary cover of the western alpine arc france sampling was focused on upper jurassic rocks of the brianconnais cover in the briancon guillestre area more than 100 samples from 11 sites were collected essentially from ammonitico rosso limestones and sedimentary dykes of the upper jurassic thermal and alternating field demagnetizations revealed three components of magnetization carried dominantly by magnetite 1 a low temperature component with present day magnetic field direction of viscous origin 2 a well defined reverse polarity component with a maximum unblocking temperature of 440 c a component and 3 a weak high temperature component b component that experienced a viscous overprint during heating and was difficult to isolate the a component exhibits a negative fold test and shows a better clustering when corrected for tilting associated with late alpine extension this component is interpreted as a secondary remagnetization acquired during the cooling path related to late eocene early oligocene metamorphism the mean a component direction corrected for late alpine extensional tilting is d 142 i 57 k 44 95 8 this direction significantly differs by 47 13 from the expected direction for eurasia we interpret this difference to be related to a post eocene counterclockwise rotation about a vertical axis of the penninic zone relative to stable europe

palaeomagnetism of middle triassic red bedded cherts from southwest japan equatorial palaeolatitude of primary magnetization and widespread secondary magnetization summary middle triassic anisian red bedded cherts were collected from the ajiro area in kyushu island southwest japan for a palaeomagnetic study thermal demagnetization showed five distinct remanent magnetization components from the cherts the lowest temperature component below 200 c component a is a present day viscous overprint the second up to 420 c component b and third demagnetized up to 580 c component c components are secondary magnetizations of thermoviscous and chemical origin respectively both of which reside in magnetite the fourth removed component component d was demagnetized at 630 c and is a secondary magnetization carried by haematite components b and c are considered to be a result of widespread remagnetization in southwest japan during the cretaceous the basis of this consideration is that red chert remagnetizations from an area about 600 km away from the present study area are of the same origins with unblocking spectra similar to those observed in this study the last removed component during thermal demagnetization up to 695 c component e is a primary magnetization carried by haematite the directions of this component after correction for the inclination flattening yielded a mean palaeolatitude of 2 s at the time of deposition in the middle triassic the ajiro cherts accreted as part of an accretionary complex to the eastern margin of the south china block during the middle jurassic and were then translated northwards from the continental margin to their present position through a margin parallel translation process owing to the oblique convergence of the oceanic plate

equilibrium atmospheric response to north atlantic sst anomalies abstract the equilibrium general circulation model gcm response to sea surface temperature sst anomalies in the western north atlantic region is studied a coarse resolution gcm with realistic lower boundary conditions including topography and climatological sst distribution is integrated in perpetual january and perpetual october modes distinguished from one another by the strength of the midlatitude westerlies an sst anomaly with a maximum of 4 c is added to the climatological sst distribution of the model with both positive and negative polarity these anomaly runs are compared to one another and to a control integration to determine the atmospheric response in all cases warming cooling of the midlatitude ocean surface yields a warming cooling of the atmosphere over and to the east of the sst anomaly center the atmospheric temperature change is largest near the surface and decreases upward consistent with this simple thermal response the geopotential height field displays a baroclinic

dynamics and early post tsunami evolution of floating marine debris near fukushima daiichi the devastating tsunami triggered by the t hoku oki earthquake of 11 march 2011 caused a crisis at the fukushima daiichi nuclear power station where it overtopped the seawall defences on retreating the tsunami carried loose debris and wreckage seaward and marshalled buoyant material into extensive plumes widespread concern over the fate of these and numerous other t hoku tsunami depositions prompted attempts to simulate debris dispersion throughout the wider pacific however the effects of locally perturbed wind and wave fields active langmuir circulation and current induced attrition determine a complex and poorly understood morphology for large floating agglomerations here we show that the early post tsunami evolution of marine debris plumes near fukushima daiichi was also shaped by near surface wind modifications that took place above relatively calm lower surface roughness waters covered by surface films derived from oil and other contaminants high spatial resolution satellite tracking reveals faster than expected floating debris motions and invigorated plume evolution within these regions while numerical modelling of turbulent air flow over the low drag film covered surface predicts typically metre per second wind strengthening at centimetric heights sufficient to explain the observed debris speed increases wind restructuring probably stimulates the dispersion of flotsam from both biological and anthropogenic sources throughout a global ocean of highly variable surface roughness the tsunami triggered by the 2011 t hoku oki earthquake carried debris seaward satellite data and numerical simulations suggest that small scale wind modifications over a smooth film covered sea surface affected debris motions

early establishment of seafloor hydrothermal systems during structural extension paleomagnetic evidence from the troodos ophiolite cyprus abstract paleomagnetic data from the troodos ophiolite are used to help constrain models for the relationship between extensional normal faulting and hydrothermal alteration related to production of large tonnage sulfide deposits at oceanic ridges we have sampled dikes from the troodos sheeted complex that have been subjected to variable hydrothermal alteration from greenschist alteration typical of the low water rock mass ratio interactions outside of hydrothermal upflow zones as well as from severely recrystallized rocks epidosites altered within high water rock mass ratio hydrothermal upflow zones in the root zones beneath large sulfide ore deposits these dikes are moderately to highly tilted from their initial near vertical orientations due to rotations in the hangingwalls of approximately dike parallel oceanic normal faults comparison of characteristic remanence directions from these dikes with the late cretaceous troodos reference direction therefore allows a tilt test to determine whether remanent magnetizations were acquired prior to or subsequent to tilting remanence directions for both greenschist and epidosite dikes show similar magnitudes of tilting due to rotational normal faulting and restore to the late cretaceous troodos reference direction upon restoration of dikes to near vertical positions about a nnw trending horizontal axis these data along with field observations of focused alteration along normal faults suggest that epidosite alteration occurred during the early stages of extensional tilting and prior to significant rotation this sequence of events is similar to that observed for creation of large tonnage sulfide bodies at intermediate to slow spreading centers which form soon after cessation of magmatism and during the early stages of structural extension we suggest that the dike parallel normal faults were initiated as extensional fractures during this early stage of crustal extension thus providing the necessary permeability for focused fluid flow and that later slip along these structures during rotational planar normal faulting caused reduction in permeability due to gouge formation

neogene remagnetization of normal polarity in the late jurassic black shales from the southern subalpine chains french alps evidence for late anticlockwise rotations abstract this study presents paleomagnetic investigations of 23 sites from the late jurassic black shales the so called terres noires that outcrop in the southern subalpine chains ssc six sites are located in the diois six sites in the trieves and devoluy and eleven sites in the digne nappe the magnetizations are weak and are carried by titanomagnetites we found generally one component per site within the medium range of temperature 200 to 500 c all magnetizations are characterized by the lack of reverse polarity the directions of magnetization are generally better grouped in geographic coordinates in the trieves the devoluy and the digne nappe fold testing at one site from the trieves demonstrated a late synfolding acquisition of magnetization in contrast pre tilting magnetizations are suggested in the diois and locally in the digne nappe given an average inclination close to late tertiary expected inclinations in geographic coordinates we propose that these magnetizations are neogene overprints our results point to two major results 1 the lack of reverse polarity which is puzzling during the neogene where 50 of the magnetic field is reverse 2 the discovery of quite systematic anticlockwise rotations these anticlockwise rotations do not occur in the diois and are larger in the southern part of the digne nappe we presume that these rotations were active during the late stage of alpine folds emplacement and are still active today

where did rotational shortening occur in the himalayas inferences from palaeomagnetic remagnetisations in metacarbonates of the lesser lh and tethyan th himalayas of kumaon garhwal n india characteristic remanent magnetisations carried by pyrrhotite unblocking temperatures 250 330 c and magnetite demagnetising spectra 15 50 mt have been identified negative fold tests indicate remanence acquisition after the main folding phase which is of short wavelength character and occurs during the early orogenese of the himalayas a thermal or thermochemical origin of magnetisation is likely and the age of remanence acquisition is indicated to be about 40 ma by 40 k 39 ar cooling and 40 ar 39 ar crystallisation ages in the kumaon lh a long wavelength tilting is indicated by a distribution of the remanence directions along a small circle in n s direction steepening of the remanence directions in the th related to ramping on the main central thrust mct was not observed in contrast to other related studies in the alaknanda valley of lh a 38 8 ma age of remanence acquisition is supported by comparison of observed inclinations to the apparent polar wander path of india clockwise rotation of 20 3 11 7 lh alaknanda valley and 11 3 8 5 th with respect to the indian plate is observed indicating that there is no significant evidence for rotational shortening along the mct since about 40 ma our results suggest that most of rotational underthrusting and oroclinal bending has not been accommodated by the mct but by the main thrusts south of it the latest miocene pliocene age of the main boundary thrust indicates that oroclinal bending is a late orogenic process

belt bending driven by lateral bending of subducting lithospheric slab geophysical evidences from the northern apennines italy abstract many of the mountain belts displaying a curved shape are oroclines i e are produced after progressive bending of an originally straight fold and thrust belt the bending process was previously explained as a consequence of several possible events taking place in the crustal orogenic wedge such as occurrence of obstacles non coaxial deformation and movements on wrench faults recent paleomagnetic results from the northern apenninic arc document that this belt is properly an orocline and results from late messinian early pliocene bending of a messinian straight belt foredeep system tomographic images in turn show the presence of a high velocity body interpreted as subducted slab in the upper mantle beneath the northern apennines between 35 and 670 km depth down to 100 km this body displays an arcuate shape which closely mirrors the geological outlines while it appears to be straight and parallel to the messinian pre rotated belt at depth we explore here the possibility that the arcuate shape of the northern apennines is a consequence closely following in time of much deeper processes than previously suggested i e the lateral bending of the subducting adriatic plate

genesis and evolution of a curved mountain front paleomagnetic and geological evidence from the gran sasso range central apennines italy abstract the gran sasso range is a striking salient formed by two roughly rectilinear e w and n s limbs in the past 90 counterclockwise ccw rotations from the eastern gran sasso were reported tectonophysics 215 1992 335 suggesting west east increase of rotation related northward shortening along the e w limb in this paper we report on paleomagnetic data from meso cenozoic sedimentary dykes and strata cropping out at corno grande central part of the e w gran sasso limb the highest summit of the apennine belt predominant northwestward paleomagnetic declinations in the normal polarity state from both sedimentary dykes and strata are observed when compared to the expected declination values for the adriatic foreland our data document no thrusting related rotation at corno grande the overall paleomagnetic data set coupled with the available geological information shows that the gran sasso arc is in fact a composite structure formed by an unrotated low shortening western e w trending limb and a strongly ccw rotated eastern salient late messinian and post early pliocene shortening episodes documented along the gran sasso front indicate that belt building and arc formation occurred during two distinct episodes we suggest that the southern part of a late messinian n s front was reactivated during early middle pliocene time forming a tight range salient due to ccw rotations and differential along front shortening rates the formation of a northward displacing bulge in an overall nw se chain is likely a consequence of the collision between the latium abruzzi and apulian carbonate platforms during northeastward propagation of the apennine wedge inducing lateral northward extrusion of latium abruzzi carbonates towards ductile basinal sediment areas

paleomagnetic evidence for neogene tectonic rotations in the northern apennines italy abstract paleomagnetic analysis was carried out in the northern apennines on eocene to pliocene epiligurian units five early miocene and two middle miocene sites yielded dual polarity site mean directions which show signs of clustering after correction for bedding tilt these likely primary magnetizations in conjunction with data from the literature give an overall mean late oligocene middle miocene paleomagnetic pole which shows a large and significant counterclockwise rotation of 52 8 with respect to the africa reference paleopoles or a similar amount of rotation with respect to the coeval europe reference paleopole however this paleopole falls close to the roughly coeval paleopole for corsica sardinia which is here calculated by averaging data from the literature three additional early miocene sites from an area west of parma affected by pliocene tectonics yielded site mean directions which pass the fold test and are rotated counterclockwise by a lesser amount than the rest of the miocene sites most of the remaining sites bear paleomagnetic directions acquired after tilting during a recent phase of remagnetization we suggest that the large scale rotation observed in the northern apennines was associated with the motion of the corsica sardinia block within the general context of the africa europe relative motions a compilation of published data from the central apennines also shows a differential rotation of the northern relative to the southern umbria belt which occurred after the motion of corsica sardinia and may have been due to pivoting of the northern umbria belt against a deep seated lineament during the non rotational opening of the tyrrhenian sea