strain gradients in zones of ductile thrusting insights from the external hellenides abstract new finite strain data from a thrust sense shear zone which extends for 600 km along strike in the high pressure belt of the external hellenides greece were used to describe the variation of ductile strain with structural distance d from the basal thrust sampling was carried out along four traverses across the central and southeastern parts of the zone the strain ratio in xz sections r xz of 120 samples was obtained using the theta curve the mean object ellipse and the mean radial length methods all methods give very consistent results based on these results four strain profiles were constructed depicting a non linear increase of r xz values with proximity to the basal thrust these profiles in combination with published strain data from the northwestern parts of the zone enabled us to obtain an empirical logarithmic function describing the relationship between r xz and d this function includes only one varying parameter which represents the strain gradient in linear r xz ln d space the value of strain gradient is directly correlated with the strain level in the thrust zone and provides information for strain localization at its base the proposed function may also be used for quantifying the strain profiles of ductile to semi ductile thrust zones in other orogenic belts such as the alps the appalachians and himalaya

low latitude zonal and vertical ion drifts seen by de 2 horizontal and vertical ion drift data from the de 2 spacecraft have been used to determine average zonal and vertical plasma flow electric field characteristics in the plus minus 26 degree dip latitude region during a time of high solar activity the data base consists of over 800 equatorial passes horizontal ion drift data were projected along magnetic field lines to the magnetic equator using a dipole model to yield their apex height dependence the average data local time profile for an apex height bin centered at 400 km indicates westward plasma flow from 0600 to 1900 solar local time slt with a maximum westward velocity of 80 m s in the early afternoon there is a sharp change to eastward flow at approximately 1900 hours with an early evening peak of 170 m s a secondary nighttime maximum exists a 0430 slt preceeding the reversal to westward flow this profile is in good agreement with jicamarca radar measurements made under similar solar maximum conditions harmonic analysis indicates a net superrotation which is strongest at lower apex altitudes the diurnal term is dominant but higher order terms through th quatradiurnal are significant vertical ion data taken at low plus minus 5 degree dip latitudes while possessing greatermore scatter generally agree wtih jicamarca values copyright american geophysical union 1989 less

equatorial zonal plasma drifts measured by the c nofs satellite during the 2008 2011 solar minimum 1 we use the measurements by the vector electric field investigation vefi on board the communication navigation outage forecasting system c nofs satellite to study the local time and seasonal and longitudinal dependent climatology of equatorial f region zonal plasma drifts during 2008 2011 these drifts are essentially westward during the day and eastward at night over jicamarca radio observatory the satellite measurements are in good agreement with incoherent scatter radar drifts our data show strong longitudinal variations particularly in the south american sector during the solstices the equinoctial data exhibit short lived and largely enhanced westward drifts near sunrise and wave 4 structures from the early afternoon to late night equinoctial periods the nighttime eastward drifts are largest near the western american sector at all seasons the june solstice postmidnight eastward drifts decrease sharply at longitudes of about 310 and have much smaller values in the entire eastern hemisphere we also briefly discuss the relationship between the longitude dependent vertical and zonal plasma drifts

models of passive margin inversion implications for the rhenohercynian fold and thrust belt belgium and germany abstract positive tectonic inversion is related to the transmission of compressional stresses along a decollement into the foreland of an orogenic zone this stress and strain concentration in regions remote from the main orogenic front is commonly related to the presence of pre existing rheological heterogeneities such as normal syn depositional faults during inversion these pre existing normal faults are reactivated as reverse faults tectonic inversion in the rhenohercynian fold and thrust belt during the variscan orogeny shows that inversion is likely synchronous with the onset of collision in the hinterland here we present the results of a simplified thermo mechanical model stm which allows one to study strain partitioning between two orogenic zones we show that if the two orogenic zones have the same mechanical properties the viscosity of the decollement which links them controls the initial strain partitioning during subsequent finite shortening erosional processes determine the partitioning of strain rate the presence of a weak structure in the inverted zone and of a low viscosity decollement leads to initial strain concentration in the inverted track rather than in the collision zone and a progressive decrease in strain partitioning between the two orogenic zones the stm results are in good agreement with results of a 2d finite element model we conclude that in the western part of the rhenohercynian massif simultaneous uplift and deformation within the mid german crystalline rise the main collision zone and the ardenne anticlinorium the inverted zone lead to interpreting this orogenic event as a case of vice tectonic rather than the propagation of a wave of folding towards the variscan front as suggested by previous authors

fold axis parallel extension in an arcuate fold and thrust belt the case of the helvetic nappes abstract the helvetic nappes of western switzerland are discussed as an example of an arcuate foreland fold and thrust belt in which active fold axis parallel stretching occurred fold axis parallel extension is recorded by 1 1 incremental strain data from pressure shadow fibres the significance of pressure shadow fibres for the determination of the deformation history of a region is discussed pressure shadows are used to quantify the amount of and to describe the distribution of fold axis parallel extension occurring in the helvetic nappes 2 2 the extension directions of conjugate systems of en echelon veins it is shown that an analysis of the geometry of conjugate vein systems can reveal a regional deformation pattern the relative age of the conjugate en echelon vein systems in the helvetic deformation history can be assessed the geometry of the conjugate sets relative to the local anisotropy plane is described and the significance of the preferred orientation of their extension directions is discussed 3 3 fold axis parallel sections a comparison of the regional distribution of the fold axis parallel strain with the shape of the helvetic nappes in fold axis parallel sections shows that the fold axis parallel strain cannot be related to the footwall topography of the nappes it is concluded that the fold axis parallel extension in the helvetic nappes was induced by a change of direction of overthrust shear this change occurred late in the deformation history and was superposed on the already formed nappes the changing direction of overthrust shear is the expression of an overall anticlockwise rotation going on in the overthrusting alpine nappe pile relative to the european plate a rotation which lead to the arcuate shape of the western alps

high resolution oi 630 nm image measurements of f region depletion drifts during the guara campaign a high performance all sky imaging system has provided data on the evolution and drift motions of f region depletions above the magnetic dip equator at alc ntara brazil 2 3 s 44 5 w monochromatic images of depletions in the oi 630 nm nightglow were recorded on eight nights during 1 16 october 1994 as part of the guara campaign the drift motions of the depletions were typically 80 100 m s eastward prior to local midnight and reduced to a minimum of 30 50 m s in the morning hours in accord with previous observations however on october 2 3 and 12 13 the depletions were observed to reverse direction for 60 90 min achieving westward speeds of 30 m s before the motion reverted to eastward around 0100 lt and accelerated to 35 45 m s near dawn magnetic activity and other evidence suggests that these reversals in the motion of the airglow depletions probably result from reversals in the f region dynamo rather than from shifts in the altitude of the shear in the nighttime f region plasma drift

plate and intraplate processes of hercynian europe during the late paleozoic abstract it is speculated that until late carboniferous time the region of hercynian europe was occupied by an elongated island arc system underlain by a segment of continental crust in the upper carboniferous two subduction zones are assumed to have extended from the north and south beneath hercynian europe an extensive zone of hot partially molten upper mantle lay above and between these and diapiric uprise of portions of this material led to separation of mafic magmas widespread partial melting in the lower and middle crust high temperature low pressure metamorphism in crustal rocks and regional uplift and extension of the crust as indicated by intermontane troughs and their associated volcanic rocks in visean to westphalian time hercynian europe collided with both the large neighbouring plates north america europe and africa during these diachronous collisions and owing to reduced rigidity of the relatively hot island arc crust the irregular continental margins of the larger and thicker continental plates induced oroclinal bending of hercynian europe after the collision processes had been terminated processes of upper mantle activity continued causing further crustal uplift and even enhanced crustal extension for several tens of million years into the lower permian decline of the upper mantle activity beneath hercynian europe is indicated by crustal subsidence and formation of a peneplain in permian time followed by the upper permian transgression of both the zechstein sea and the tethys sea which mark the end of the hercynian geodynamic cycle

fluid rock interaction processes related to hydrothermal vein type mineralization in the siegerland district germany implications from inorganic and organic alteration patterns altered wallrocks of vein type pb zn sb mineralization siegerland district rheinisches schiefergebirge have been investigated by a combination of inorganic and organic geochemical methods including major and trace element analysis vitrinite reflectance measurements c isotope and elemental analysis of kerogen alteration features of the siliciclastic pelitic psammitic lower devonian wallrocks are increased k na ratios significant desilicification and relative immobility of a number of elements notably al ti zr cr v wallrock kerogens display elevated vitrinite reflectance values decrease in h c atomic ratios coupled with increase in s c atomic ratios and heavier c isotope compositions compared to the unaltered precursor sedimentary rocks interaction processes between the hydrothermal fluids and the respective wallrocks related to injection of high temperature silica undersaturated solutions are dominated by quartz dissolution coupled with sericitization reactions heat transfer due to fluid infiltration convection and wallrock reactions caused fluid cooling which promoted the sequential deposition of quartz and stibnite sulphosalts within the vein systems hydrocarbons detected in ore assemblages of pb zn and sb mineralization were most probably derived from the lower devonian very low grade meta sedimentary rocks high maturity levels and pronounced typical organic alteration patterns indicate that thermochemical so2 4 reduction tsr played an important role in precipitation of metal sulphides the present study demonstrates that a combination of inorganic and organic investigations on fluid rock interaction processes is particularly useful for deciphering precipitation mechanisms of base metal sulphides

strains developed in the hangingwalls of thrusts due to their slip propagation rate a dislocation model reply abstract fault planes propagate radially from a point source and this failure propagation process is very similar to the movement of a dislocation through a crystal lattice an elastic strain represented by an extra half plane is necessarily imparted to the lattice at an edge dislocation and this is equivalent to the ductile bead which accompanies the propagating tip of a thrust fault this ductile bead migrates with the fault tip and imparts a characteristic internal strain to the thrust sheet a two dimensional model is presented to illustrate the inter relationship between fault plane slip fault tip propagation and internal strain in multilayered sequences internal strain is usually represented by asymmetric folds verging in the thrust transport direction a simple technique the displacement distance plot utilizes the fact that displacement dies out towards the fault tip this plot can be used to quantify the relative stretch measured parallel to the fault movement which is dependent on the slip propagation rate and it may be used to define exactly the position of the fault tip on a cross section examples of fold thrust structures from devon england and pembrokeshire wales are used to illustrate the technique

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

ionospheric conditions affecting the evolution of equatorial plasma depletions model studies have been carried out to specify the ionospheric conditions and electrodynamical processes required to describe the geometry of westward tilting and bifurcating equatorial plasma depletions inferred from airglow imaging measurements taken on ascension island in early 1981 the results indicate that if the westward tilts are to be associated with eastward plasma drifts that decrease with altitude above the f peak this shear must be set up by a zonal wind pattern of decreasing speed at increasing distances from the equator below the peak calculations of flux tube integrated pedersen conductivity including both e and f region contributions are in agreement with the simulations of zalesak et al 1982 that show bifurcated depletions to be associated with a mild gradient in the bottomside conductivity profile

simulation study of the longitudinal variation of evening vertical ionospheric drifts at the magnetic equator during equinox 1 quiet time low latitude ionospheric electric fields and vertical drifts in the evening sector at equinox are examined as a function of longitude and solar activity using simulations from the magnetosphere thermosphere ionosphere electrodynamics general circulation model mtiegcm the model inputs are held fixed with respect to universal time in order to evaluate the contributions to longitudinal variations of the equatorial electric fields and drifts associated with zonal variations in the geomagnetic field the simulated upward evening drift is somewhat larger than observations it increases with solar activity at a similar rate in all longitude sectors this rate about 0 32 0 37 m s per unit of 10 7 cm solar flux is quantitatively consistent with observations in the peruvian sector but is considerably greater than observations in the indian sector the simulations agree with observations in finding larger vertical drifts in the american atlantic sector than in the east asian pacific sector generally associated with longitudinal variations in the strength of the geomagnetic field relations among the longitude variations of the vertical drift the conductivity the eastward wind velocity the geomagnetic declination and gradients of the wind and declination are examined revealing few clear correlations however extrema of many of these quantities are noted in the american atlantic sector

open system constant volume development of slaty cleavage and strain induced replacement reactions in the martinsburg formation lehigh gap pennsylvania no important changes in the volume of mudrocks occur across the mudstone to slate transition in the martinsburg formation at lehigh gap pennsylvania mass balance calculations based on chemical analyses and specific gravity measurements of 48 mudstones and 26 graywackes from the martinsburg formation across this 130 m strain gradient show constant ratios of al2o3 tio2 feot mgo mno y v and zr this reflects the relatively low differential mobility of these components during diagenesis and slaty cleavage development as well as the uniformity of compositions of the mudstones and graywackes at deposition using minimum strain samples and al2o3 as references the calculations show no loss in sio2 but large losses of cao na2o ba and sr from the outcrop that are directly proportional to strain and reflect an open system on the scale of kilometers analyses of graywacke mudstone metagraywacke slate pairs show that losses in sio2 na2o and volume and gains in k2o and ba in the graywacke metagraywacke are balanced by opposite changes in the adjacent mudstone slate this documents a local mobility of sio2 on the scale of centimeters the inertness of most major components over the 100 m outcrop especially sio2 however requires 1 that the composition of the fluid passing through the rocks was closely buffered by the quartz albite muscovite chlorite assemblage 2 that the volume of the fluid was small and 3 that the p t gradient down which it traveled was gentle the changes in chemical composition identified can be explained by the inferred replacement reaction plag 1m musc k 2m musc qz ca 2 na sr 2 ba 2 the strong correlation of minor element chemistry and strain indicates that this reaction was strain induced and that changes in bulk chemical composition are defined by the progress of this reaction

late metamorphic veins record deep ingression of meteoric water a la icpms fluid inclusion study from the fold and thrust belt of the rhenish massif germany abstract the fluid evolution of late metamorphic quartz vein systems in the fold and thrust belt of the rhenish massif has been studied by microthermometry and la icpms microanalysis the quartz veins are hosted by very low grade organic matter rich metasiltstones and metapelites of the hunsruck nappe complex the veins record two major stages of textural evolution a massive vein filling assemblage with elongate blocky quartz chlorite albite and apatite and a later open space filling assemblage with euhedral crystals of quartz ankerite dolomite and minor calcite and sulfides the euhedral quartz crystals host well preserved fluid inclusion assemblages which made it possible to reconstruct the chemical evolution of the fluid system with time the fluid inclusions are all aqueous two phase with low salinity and three successive fluid generations record a systematic decrease in salinity from 4 7 5 3 to 3 1 3 9 and then to 1 4 1 7 wt eqv nacl the salinity decrease is paralleled by a decrease in homogenization temperatures from 210 225 c to 148 164 c and 124 139 c using la icpms microanalysis of individual fluid inclusions reproducible elemental concentrations of li na k rb cs mg ca ba sr b al as sb s cl and br could be determined the concentrations of the alkali metals and of boron arsenic and antimony are correlated with the fluid salinity element concentrations are highest in the early fluid generation and decrease systematically in the latter two generations the systematic changes in fluid composition salinity homogenization temperature and elemental concentrations are best explained by fluid mixing between a hot metamorphic fluid of moderate salinity that carried elevated concentrations of b as and sb and a cooler dilute fluid that was of meteoric origin the fluid evolution therefore signals deep ingression of meteoric water during late metamorphic exhumation and uplift the molar cl br ratios of the fluid inclusions lie on a linear array that extends from close to seawater to values that are substantially below seawater because evaporitic sources are conspicuously absent in the shallow water marine sequence of the rhenish massif the elevated br concentrations and cl br ratios below seawater are best explained by fluid rock interaction and liberation of br from the organic matter in the metasediments

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

strain patterns and shortening in a folded thrust sheet an example from the southern appalachians abstract total strain patterns estimated across the pulaski thrust sheet of the southwest virginia appalachians show an approximately homogeneous plane strain deformation associated with folding and distortion above a subsurface decollement estimated strains are low 1 2 x z

large volume loss during cleavage formation hamburg sequence pennsylvania green reduction spots in red slate of the hamburg sequence exposed near shartlesville pennsylvania have axial ratios of 1 42 1 0 0 28 on the limbs of near isoclinal folds and 1 0 0 79 0 41 in fold hinge zones conodont cusps and denticles within the reduction spots have been brittlely pulled apart and give independent measures of extension in various directions comparison of conodont extensions with reduction spot shapes on limbs and hinges indicates that sedimentary compaction of 44 preceded the tectonic strain associated with cleavage formation this strain having identical maximum extensions but greater shortening in fold hinges as compared to limbs was characterized by 41 extension in x no change in y 50 to 59 shortening in z and 29 to 42 tectonic volume loss the general lack of directed overgrowths on grains reflects the large volume loss and contrasts with other slates where deformation was an almost constant volume process and extension in x compensated for shortening in z

geological interpretation of dekorp deep seismic reflection profiles 1c and 9n across the variscan saar nahe basin southwest germany abstract deep seismic reflection results across the variscan saar nahe basin in southwest germany recorded as parts of dekorp lines 1c and 9n provide excellent images of the geometry of the basin and also of the structures in the underlying basement this basement consists of several discrete units some of which are highly reflective whereas others are essentially non reflective two of these units consist of well layered dipping reflectors that are interpreted as having been telescoped by thrusting adjacent to the south hunsruck fault the sedimentary pile within the saar nahe basin is over 8 km thick but it thins dramatically towards the southeast and east the position of continuous reflectors both in the basin and the basement indicate that the south hunsruck fault is subvertical and not a listric normal fault as proposed in several earlier interpretations this implies that the basin did not form by normal extension but that it is transtensional in character its geometry predominantly being controlled by strike slip movements on the south hunsruck fault

concepts of the evolution of the austroalpine basement complex eastern alps during the caledonian variscan cycle the austroalpine basement complex has a complicated pre alpidic history which begins with the caledonian era in the late precambrian and early paleozoic a magmatic sedimentary rock sequence is formed presumably in an island arc or active continental margin environment subduction with eclogite formation is followed by collision high grade metamorphism and anatexis in the ordovician this caledonian basement is preserved in parts of the austroalpine crystalline mass the post caledonian deposits are mainly shelf type sediments with intercalated volcanics although there is evidence for an oceanic basin to the south the variscan facies zones are arranged in sw ne direction oblique to the alpidic trend in a first stage of variscan orogeny in the carboniferous south east vergent decollement nappes syntectonic flysch deposits and granitoids are formed along with regional metamorphism this is followed by a second stage in the permian with north west vergent thrusting renewed granite formation and metamorphism the variscan nappe pile is today exposed in a deeper level in the west or northwest than in the east or southeast

tectonic versus mineralogical contribution to the magnetic fabrics of epimetamorphic slaty rocks an example from the ardennes massif france belgium abstract the discrimination of the respective contribution of strain and mineralogy of the bulk anisotropy of low field magnetic susceptibility ams of rocks is addressed by a study of the ardennes variscan thrust belt unmetamorphosed to low medium grade rocks in the study area define a succession of magnetic parageneses hematite maghemite hematite maghemite magnetite magnetite pyrrhotite a direct control of the magnetic mineralogy on the magnitude of ams axes is shown in addition in all cases the interpretation of the directions of ams axes as kinematic indicators also applies to these rocks we show a progressive change in shearing direction from the south of the rocroi massif where the nappe transport is n directed in the north the vergence changes to northwestward

comparison of nighttime zonal neutral winds and equatorial plasma bubble drift velocities over brazil 1 we present results from the first extended period of coincident observations of thermospheric zonal neutral winds and equatorial plasma bubble epb zonal drift velocities over northeastern brazil during the october to december months of 2009 and 2010 the epb zonal drift velocities are estimated utilizing images of the o i 630 0 nm emissions recorded by a wide angle imaging system at cajazeiras thermospheric neutral wind estimates are based upon common volume observations made by a bistatic fabry perot interferometer fpi experiment using fpis located at cajazeiras and cariri in brazil observing the doppler shift of the o i 630 0 nm emission the results illustrate a similar pattern of nighttime and night to night variations in the zonal neutral winds and epb zonal drift velocities in general the geomagnetic zonal neutral winds and the epb velocities show an excellent agreement illustrating that the f region dynamo is fully developed however in the early evening hours the epb zonal speed is slower than that of the background winds on several occasions we conclude that this indicates that during the bubble evolution period in the early evening the f region dynamo is not fully activated

east west ion drifts at mid latitudes observed by dynamics explorer 2 zonal ion drifts measured from the polar orbiting de 2 spacecraft are examined to determine the effects of dynamo electric fields and penetration of high latitude electric fields at middle latitudes construction of a local time distribution from satellite data results in a mixture of local time and season as well as a range of magnetic activity encompassing kp le 2 and kp ge 3 thus some combination of magnetospheric effects expected to dominate during disturbed times are seen during both quiet and disturbed times and solar tidal influences are most easily observed during quiet times during quiet times at invariant latitudes near 25 degrees the solar diurnal tide dominates the local time distribution of the ion drift at latitudes above 50 degrees a diurnal component of comparable magnitude is also present but its magnetospheric origin produces a shift in phase of almost 180 degrees from the lower latitude diurnal tide in the intervening region between 20 degrees and 50 degrees invariant latitude semidurnal and terdiurnal components in the local time distribution of the drift velocity are also seen these components are generally larger than those seen by ground based radars during quiet times and may be attributable in part to a difference in solarmore activity and in part to a combination of the solar tides and magnetospheric penetration fields less

dependence of the evening prereversal enhancement of the vertical plasma drift on geophysical parameters 1 the variability of the evening prereversal enhancement pre of the vertical plasma drift has been investigated by using the average velocity at a fixed local time range but this method does not provide a clear distinction between the pre occurrence frequency and magnitude in this study we examine the dependence of the occurrence frequency occurrence local time and magnitude of the pre on geophysical parameters by using the retrievals of the individual pre from the first republic of china satellite data our result shows that the seasonal longitudinal variation of the average vertical velocity in the evening that has been identified in previous studies is associated with both the pre occurrence frequency and pre magnitude the magnitude of the pre shows an increasing trend with an increase of the solar flux and with a decrease of the conjugate e region sunset time lag the seasonal longitudinal variation of the occurrence local time of the peak pre shows a dependence on the e region sunset time at the magnetic equator rather than on the magnetic declination or the sunset time lag in the conjugate e regions this observation indicates that the optimum time for the creation of the peak pre is when the sunset terminator at the e region height and the magnetic meridian intersect near the magnetic equator

accretion of a rifted passive margin the late paleozoic rhenohercynian fold and thrust belt middle european variscides in the western rhenish massif the rhenohercynian fold and thrust belt of the middle european varsicides exposes a telescoped complete devonian to early carboniferous passive margin this permits the analysis of geometry and kinematic processes of passive margin accretion to an erogenic wedge during variscan collision 330 300 ma the sedimentary cover of the passive margin was shortened by some 50 or 180 km crustal scale balancing and restoration reveals a wide symmetric rift with a central graben a marginal plateau separated this failed lower devonian rift from an emsian middle devonian oceanic basin in the south remnants of which are preserved in the southernmost imbricates and the giessen harz nappes the seismically well imaged aachen midi detachment faille du midi acted as the basal decollement of this thin to thick skinned orogenic wedge it shows a ramp and flat geometry from the blind tip down to middle crustal levels owing to its position below the base of the basin fill the thick synrift sequence and structure controlled structural evolution during contraction by localizing thrust branch lines and by inversion of rift structures synthetic to the subduction direction with formation of basement footwall shortcuts moreover the three dimensional detachment geometry shows large scale oblique ramp flat features which control the architecture of the belt and the distribution of metamorphic grade rocks and fabrics from the detachment show that the latter was located at the transition into the ductile field at the fossil 300 400 c isotherm in the restored section the detachment trajectory displays a saucershaped geometry rising to the surface at the rear and at the front this suggests that the basal detachment propagated into the passive margin by ductile failure during lithospheric flexure under the load of an advancing upper plate the regional pattern of synkinematic metamorphic grade shows varying modes of margin accretion basal underplating into the orogenic wedge by the shelf slope and marginal plateau with formation of duplex stacks and elongate thrust sheets and frontal accretion of the remaining thicker failed rift in the north into the propagating wedge with formation of several imbricate fans cyclical changes in accretion history and or critical taper are suggested by spaced domains of out of sequence thickening these are also related to internal domainal kinematic partitioning of the wedge controlled by oblique collision

deformation within foreland thrust sheets by populations of minor faults the dominant deformation mechanism within foreland thrust sheets is the displacement of blocks of weakly deformed rock on discrete mineral coated minor faults in highly deformed layers at the bases of three southern appalachian foreland sheets such minor faults are members of families or populations of consistently oriented structures the deformation style is similar in all three sheets rock nearest each thrust was shortened in the direction of sheet transport and thickened by a family of faults oriented at low angles to the thrusts rock further above each thrust experienced only the first of these two deformation stages statistical analyses of fault populations from these three sheets demonstrate that their deformation is quantitatively as well as qualitatively similar deformation due to movement on minor faults is statistically homogeneous at the scale of an outcrop in one of these sheets strain due to minor faults can be measured in that sheet a strain profile across this sheet is similar to strain profiles across continuously deformed sheets from internal portions of mountain belts suggesting that their responses to emplacement are similar

equatorial f region vertical plasma drifts seasonal and longitudinal asymmetries in the american sector longitudinal and seasonal asymmetries in the evening ionospheric f region plasma vertical drift v sub z enhancements between two longitudinally separated stations situated along the magnetic equator in the american sector are investigated under solar maximum conditions based on results obtained from the analysis of ionosonde data for these stations the two stations are huancayo peru and fortaleza brazil which have markedly different magnetic declination angles the observed asymmetries are interpreted using a detailed numerical simulation of the e and f region electrodynamic coupling process that takes into account also its asymmetry about the magnetic equator arising from the finite magnetic declination angle the results of the simulation show in agreement with observations that the occurrence time of the evening f region vertical drift prereversal peak and its seasonal variation at a station are controlled by the magnetic declination angle at that station which determines the seasonal variation of the sunset times and hence the integrated pedersen conductivity longitudinal gradient at its magnetic conjugate e layers the amplitude of the prereversal peak on the other hand undergoes the influence of the magnetic declination angle as well as of the thermospheric zonal wind component

the problem of strain marker centers and the fry method abstract the fry method and its variants will underestimate finite strain when applied to strain markers deformed heterogeneously at marker scale despite homogeneous behavior at a population scale this difference results from the post deformation centers not coinciding with the original pre deformation centers the amount of error may rapidly approach 50 for small strains in ideal cases but is likely to be in the range of 20 30

strain partitioning between structural domains in the forearc of the hikurangi subduction zone new zealand the pacific plate obliquely converges with the australian plate at latitude 39 50 s along the hikurangi margin off the east coast of the north island of new zealand an extensive and youthful subaerially exposed forearc on the east coast of the north island in the hawke s bay area provides the opportunity to document contemporaneous forearc deformation in this obliquely convergent margin setting geologic mapping and analysis of strain at both mesoscale and megascale indicates that strain is partitioning into domains of extension contraction and strike slip the domains are elongate and trend parallel to the margin measurements of net shortening and transcurrent slip in the forearc show that the obliquely convergent motion is transferred across the plate interface deformation rates calculated for the past 1 2 m y for structures in all six forearc domains account for 50 70 of the margin parallel motion required by pacific australian plate convergence and about 6 of the plate motion perpendicular to the plate boundary at the surface in the forearc this obliquely convergent motion is manifest not by transpressional faults but rather by paired structural domains that consist of a strike slip fault zone and an accompanying contractional fault and fold zone on the trenchward side there are two such transcurrent faulting and contraction couplets one where the backstop daylights at the arcward edge of the forearc and another couplet trenchward of a relatively undisturbed forearc basin the small amount of shortening relative to strike slip in the onshore part of the forearc suggests that shortening perpendicular to the plate boundary may be concentrated offshore and that most of the component of plate motion perpendicular to the plate boundary may be accommodated by slip along the subduction zone megathrust

aspects of the reconstruction of the stress history of a fold and thrust belt rhenish massif federal republic of germany abstract by use of faults and striations parts of the deviatoric stress tensors and thereby essential aspects of the paleostress history of the rhenish massif can be reconstructed the stress history is unexpectedly complex even on the local scale the region under investigation is subdivided into various areas each of which exhibits somewhat different sequences of stress states several mutual aspects are evident in lower devonian rocks in the north which show only very slight deformation a pre folding stress state is preserved with a preferentially n s trending extension attributed to the stage of basin development the stage of folding itself during the carboniferous shows strong regional and temporal heterogeneity under frequently altering stress states after an initial stage of a semi homogeneous stress field this development occurs simultaneously with partial stress uncoupling at larger thrust zones with diverging deformation histories of hangingwalls and footwalls movement patterns in the north evidence subsequent clockwise rotation of the stress field which is only weakly represented in the south on the other hand there is clear evidence of a still younger counterclockwise rotation of the stress field which only affects the southern massif this is probably due to the superpositioning of orthogonal relative movements on the southern rim of the fold belt by a dextral strike slip component during final deformation thus indicating late dextral transpression succeeded by dextral transtension the final extensional stage is related to late paleozoic uplift and crustal stretching perpendicular to the strike of the fold belt followed by a change of direction of extension this state of stress obviously extends into the present although complex the various stress conditions are clearly correlated with other fabric elements in particular with cleavage fold geometry and mineralization

results of the dekorp 1 belcorp dekorp deep seismic reflection studies in the western part of the rhenish massif summary within the dekorp project dekorp deutsches kontinentales reflexionsseismisches programm a joint deep seismic reflection venture with the belcorp belgian continental reflection seismic programme group of the belgian geological survey was carried out in 1987 across the rhenish massif a part of the mid european variscides this orogenic belt developed in the upper devonian carboniferous mostly devonian rocks crop out at the surface the rhenish massif is bordered by two sedimentary troughs the sub variscan foredeep in the north and the permo carboniferous saar nahe basin in the south in the east west direction it is subdivided by the axial depression of the eifel nord sud zone the aim of the survey which totals almost 220 km of seismic profiling was to investigate the crustal structure of the western part of the rhenish massif and to compare it with the line dekorp 2 n which crosses the eastern portion of the massif the results indicate the presence of nw vergent tectonics of various styles that can often be traced down to deep parts of the crust horizontal variscan compression plays a dominant role in the northern part while post variscan extension seems to dominate in the saar nahe basin although even there traces of variscan compression seem to be preserved in the middle crust common characteristics of the pre palaeozoic basement differences between the western and eastern parts of the rhenish massif and the deep extension of the aachen thrust faille du midi have been clearly observed this prominent thrust in the north with its characteristic ramp and flat structure has been followed over 100 km length down

a comparison of methods used in measuring finite strains from ellipsoidal objects abstract the available methods for measuring strains in two and three dimensions from passive ellipsoidal objects are compared in an attempt to determine the most useful and precise procedure for the structural geologist a comparison of data collection techniques showed that the use of thin orthogonally cut slabs or mylar overlays used with a monocomparater provides the most reproducible data lisle s theta curve and shimamoto and ikeda s algebraic methods provided the most precise and probably most accurate two dimensional data while miller and oertel s procedure and possibly dunnet s phase 5 program gave the best three dimensional results an examination of errors encountered in strain analyses suggests that all of the available methods give accurate orientations of the finite strain ellipsoid however the magnitudes of strain ratios show large variations that are dependent on the sample size and procedure used shimamoto and ikeda s method again proved to be the most precise giving reproducible results with as few as ten elliptical objects the samples used in the above comparison are part of a larger analysis of strains occurring in southeastern maine structural elements observed in four selected areas of avalonian belt rocks and the strain data collected suggest that the region has undergone at least three non coaxial deformations with d1 d2 d3

volume loss during cleavage formation in the meguma group nova scotia canada abstract diffusive mass transfer pressure solution is a widely recognized cleavage forming mechanism under low grade conditions the amount of accompanying volume change during cleavage development however is difficult to quantify and remains controversial the distance between sites of mineral dissolution and reprecipitation and transport mechanisms also are controversial the structural history of the cambrian ordovician meguma group nova scotia canada is well known and abundant strain markers provide an opportunity to assess geometrically volume changes accompanying cleavage development during diagenesis about 70 compaction in muds and 15 in silts and sands occurred the pelitic to psammitic meguma group was cleaved prior to being folded pressure solution was the dominant cleavage forming deformation mechanism under chlorite grade metamorphic conditions during the early devonian acadian orogeny measurement of tectonic strain in principal directions x y z shows that bedding parallel coaxial shortening z is 60 and there is no evidence of fold hinge parallel extension y estimation of tectonic vertical extension x in the cleavage plane is complicated by diagenetic compaction corrections to primary strain markers but is insufficient to compensate for the observed 60 shortening in z indicating 40 60 volume loss during cleavage formation because cleavage formed at least 50 ma after deposition and under approximately 6 km of silurian to early devonian strata porosity of the sediments upon onset of cleavage was likely less than 15 pore space reduction therefore cannot account for the apparent volume loss during cleavage formation cleavage related volume loss applies regionally and to a stratigraphic thickness of several thousand meters implying that a large amount of material was removed and transported large distances when combined with 50 shortening by folding a bulk tectonic shortening of 80 is estimated for the meguma group during the acadian orogeny

superrotation of the ionosphere and quiet time zonal ion drifts at low and middle latitudes observed by republic of china satellite 1 rocsat 1 1 local time variations of zonal drifts at different latitudes longitudes and seasons are investigated using ion drift measurements from the republic of china satellite 1 rocsat 1 we select a quiet time period defined when dst 100 nt and kp 3 the ion drifts in the magnetic zonal direction are latitude apex height dependent and differ for different longitude sectors and seasons superrotation of the ionosphere is observed in the zonal drift measurements particularly at the lower latitudes the ionospheric superrotation generally decreases with increasing latitude and is attributed mainly to the f region dynamo where the features of the neutral wind and conductance affect the characteristics of the superrotation at different latitudes longitudes and seasons we suggest that the latitudinal variation of the superrotation is mainly produced by the decrease in latitude of the neutral winds in the f region a decrease of conductance with increasing latitude is also present but evidence shows that neutral winds decrease faster with latitude than the conductance for high solar flux conditions the longitudinal and seasonal variations of the superrotation are more influenced by changes in the f region conductance that is modified by vertical e b ion drift motions and neutral wind induced ion drift motions along magnetic field lines

equatorial ionospheric zonal drift by monitoring local gps reference networks 1 the propagation of electromagnetic waves through the turbulent ionosphere produces scintillations through diffraction and understanding the physical nature of scintillations is important for engineers and technologists as well as for scientists in recent years the establishment of the global positioning system gps provided a new technique that can be used to study ionospheric scintillations the usual way of doing that is the deployment of gps receivers closely spaced in east west magnetic direction and then estimating the zonal drift velocities based on the signal power observations one of the weaknesses of this method is that high rate sampling such as 20 hz is required for close spaced stations and generally no such data are available for studying ionospheric scintillation in the past years in this research work a scintillation monitoring method based on slant tec stec observations of local gps continuously operating reference station cors network is proposed first the past research works on the equatorial ionospheric drift velocities are summarized then by comparing the scintillation pattern of the signal power and stec observations of california local gps reference network we find that the stec is a good choice for estimating the ionospheric zonal drift velocity then it is illustrated how to calculate the ionospheric scintillation velocity based on stec finally the proposed method is applied to hong kong gps reference network and several cases of the calculated ionospheric zonal velocities are given

an application of two dimensional finite element modelling for studying the deformation of the variscan fold and thrust belt belgium abstract this paper presents 2d finite element simulations of fold and thrust belts with a focus on the variscan foreland thrust belt in belgium the numerical models are limited to the deformation of a 5 km thick sedimentary layer separated from a backstop by a deformable zone the sedimentary layer obeys an elastic plastic law and can include one detachment horizon with some ramps our study deals with the effects of rheological and geometrical parameters on the structural characteristics of the belt for regular basin geometries rectangular and wedge shapes results of numerical simulations show that deformation continuously propagates and decreases towards the foreland in agreement with sandbox experiments the basal friction appears to be a major parameter controlling the tectonic style of a fold and thrust belt our analysis has also shown that the strain propagation in time and space is strongly controlled by the presence of a weak intra detachment and of ramps which initiate shear bands for the rhenohercynian fold and thrust belt a major decollement is usually considered within the palaeozoic sediments and the existence of steps in the basin geometry is proven by numerous geological data showing the activity of pre orogenic normal faulting during the variscan orogeny this irregular detachment horizon influenced the regional tectonics simulation results show that ramps create strongly deformed anticlinioria separated by weakly deformed synclinoria which is the basic structure observed in the western and northern rhenohercynian belt

fault zone reactivation kinematics and mechanisms the kinematics and mechanisms of fault zone reactivation are reviewed reactivation is dependent upon fault zone orientation and the existence of weak mylonites along these zones the recognition of reactivation within mylonite zones and the softening processes that first concentrate deformation into these and secondly provide a weak medium for reactivation are discussed attention is given to the darling mobile zone western australia and the redbank zone see obee white this symposium as examples of reactivated zones

post variscan hydrothermal vein mineralization taunus rhenish massif germany constraints from stable and radiogenic isotope data abstract post variscan hydrothermal base metal mineralization of the taunus ore district se rhenish massif germany has been studied through combination of stable s c o and radiogenic pb isotope geochemistry based on field and textural observations five hydrothermal mineralization types can be distinguished these are 1 tetrahedrite tennantite bearing quartz ankerite veins 2 quartz veins with pb zn cu ores 3 giant quartz veins 4 metasomatic dolomite in devonian reef complexes and 5 calcite quartz mineralization in devonian reefs the 18ov smow quartz values of base metal veins are in the range of 18 0 21 5 whereas those of giant quartz veins have lower values of 15 9 18 6 this difference reflects the higher fluid fluxes and smaller extent of rock buffering for the giant quartz veins hydrothermal carbonates from the tetrahedrite and pb zn cu veins have variable but distinctly negative 13cv pdb values they can be explained by contributions from fluids that had picked up low 13cv pdb carbon via oxidation of organic matter and from fluids that interacted with devonian reef carbonate having positive 13cv pdb metasomatic dolomite has positive 13cv pdb values that closely reflect those of the precursor limestone by contrast carbonates of calcite quartz mineralization have negative 13cv pdb values which are negatively correlated with the 18o values this pattern is explained by fluid mixing processes where contributions from descending cooler fluids with rather low salinity were dominant the isotope data suggest that tetrahedrite veins pb zn cu veins and giant quartz veins formed from fluid mixing involving two end members with contrasting chemical features this is supported by fluid inclusion data adeyemi 1982 that show repeated alternation between two different types of fluid inclusions which are hotter intermediate to high salinity nacl cacl2 fluids and cooler low salinity nacl dominated fluids the metal rich saline fluids were likely generated at the boundary between the pre devonian basement and the overlying devonian carboniferous nappe pile fault activation resulted in strong fluid focusing and upward migration of large volumes of hot na ca brines which mixed with cooler and more dilute fluids at shallower crustal levels variable contributions from both fluid types local fluid fluxes temperature variations and variations in ph and oxidation state have then controlled the vein mineralogy and metal inventory

influences of geomagnetic fields on longitudinal variations of vertical plasma drifts in the presunset equatorial topside ionosphere on the basis of the measurements from the ion drift meter on the defense meteorological satellite program f13 satellite from 2000 to 2002 the relative longitudinal variations of e x b vertical plasma drifts in the presunset equatorial topside ionosphere at 1745 lt are examined obvious influences of geomagnetic fields on longitudinal variations of e x b vertical plasma drifts which also show a seasonal dependence have been found during the june solstice the relative vertical plasma drifts is most significantly influenced by the geomagnetic field declination however the relative vertical plasma drifts during the december solstice more strongly correlates with the geomagnetic field strength although the relative vertical plasma drifts during equinox are also influenced by the geomagnetic field declination an underlying dependence on magnetic field magnitude as seen in december is also present

constraints on geological strain rates arguments from finite strain states of naturally deformed rocks a summary of known finite strain states is presented longitudinal strains 1 e as measured in many rocks often range from 1 to 40 and 1 to 0 025 the time span available to produce such measureable strains in young orogenic zones seems to be less than 10 m y possibly less than 1 m y which constrains conventional strain rates into the range of 10 sup 13 s sup 1 to 10 sup 15 s sup 1 for both pure and simple shear the most efficient way and much less efficient way to accumulate incremental strains respectively the ellipticity of the finite strain ellipse increases in a nonlinear manner finite strain variations in adjacent layers which give rise to features such as cleavage refraction arise with only slight differences in the strain rates within these layers

the earth s thermospheric superrotation from dynamics explorer 2 neutral thermospheric zonal winds measured from the wind and temperature experiment on dynamics explorer 2 have been analyzed to provide a measure of the superrotation of the neutral thermosphere the data were averaged in local time in 10 degree bands from the equator to 40 degrees latitude the results show an average wind velocity on the order of 18 m s to the east at the equator and a westward wind of the same magnitude at mid latitudes within the range of altitudes of the data base 200 to 700 km no evidence of any significant altitude dependence was found averaging our data over the latitude bands studied indicates a net corotation of the thermosphere this result is not in agreement with the superrotation value reported by king hele and walker on the basis of satellite drag analysis

altitudinal dependence of evening equatorial f region vertical plasma drifts we use jicamarca incoherent scatter radar measurements to study for the first time the altitudinal variations of late afternoon and early night equatorial f region vertical plasma drifts we also present the initial vertical drift measurements over the altitudinal range from about 200 to 2000 km these data show that the afternoon drifts decrease weakly with altitude near their evening prereversal enhancements the vertical drifts generally increase with altitude below about the f layer peak decrease with height near the f layer peak and above and are nearly height independent in the solar flux dependent topside ionosphere the transition altitudes from height decreasing to height independent evening upward drifts decrease with altitude from solar maximum to solar minimum after their reversal to downward the vertical drifts do not change much with height the altitudinal dependence of the evening vertical drifts has large day to day variability and is closely related to the time dependence of the zonal drifts as expected from the curl free electric field condition

global positioning system measurements of the ionospheric zonal apparent velocity at cachoeira paulista in brazil ionospheric irregularities and their zonal apparent drift were studied using global positioning system gps measurements at cachoeira paulista 22 41 s 45 00 w 26 dip angle in brazil during november 6 19 1998 radio scintillations at the gps l1 frequency 1 575 ghz were monitored using four gps receivers spaced geomagnetically east west and north south total electron content tec was measured through the ionospheric advance of the gps l1 and l2 1 227 ghz phases strong amplitude scintillations coincided with tec fluctuations associated with spread f bubbles elongated along the magnetic field movement of the presnel scale 400 m ionospheric irregularity layers caused the scintillation to drift and their zonal apparent drift velocities were measured using a cross correlation technique our measurements show that the apparent eastward velocity varies from 200 m s to 150 m s at 2000 lt and then it decreases to 100 50 m s at midnight on a magnetically disturbed day reversal of the zonal apparent drift was observed just after midnight and the apparent westward velocities observed at early in the morning showed large variations with location in the sky from the receivers spaced in the geomagnetic north south direction we measured near zero time shifts from which we conclude that the correlation length of several hundred meter scale irregularities is much larger than 70 m separation between the north and south receivers

equatorial ionospheric vertical plasma drift model over the brazilian region comparison between equatorial inospheric f region vertical plasma drift from satellite measurements fejer et al 1995 for the brazilian longitude sector and the drifts derived from ionosonde measurements around sunset shows significant differences on the prereversal peak behavior during solstices of high solar activity periods using ionosonde measurements around sunset and satellite measurements at other local times we constructed an ionospheric vertical plasma drift model that is representative of the equatorial region over the brazilian longitudes where the magnetic declination is around 20 the so derived drift model here called idm ionosonde drift model is used as an input to the sheffield university plasmasphere ionosphere model supim it is shown that the f layer heights given by supim with idm are in good agreement with ionosonde measurements over the brazilian longitudes and that idm better simulates the f layer heights than the averaged drifts given by the satellite drift model fejer et al 1995

strain partitioning across a fold and thrust belt the rhenish massif mid european variscides abstract strain data across the entire western rhenish massif illustrate the pattern of deformation partitioning within a fold and thrust belt from the foreland on the northern front of the european variscides to the suture with the internal zones of higher metamorphic grade shortening perpendicular to cleavage increases from 16 to 27 constant volume assumed in the northern rhenish massif to 51 at the southern border these values correspond to a weak general layer parallel shortening of the basin filling in cross section on the order of about 5 15 and more in the case of volume loss the geometry of apparent finite strain is nearly plane strain except in the venn anticlinorium where strain is apparent prolate and near the southern margin of the massif where it is apparent oblate net orogenic shortening in the upper crust of the fold and thrust belt is approximately 42 it is mainly achieved by folding and tectonic stacking of the deformed basin filling which was apparently detached from the lower crust distribution of strain in the orogenic wedge is controlled by different factors at different scales heterogeneity is caused by changes in lithology and average grain size by the structural position of samples in folds and their distance from thrusts in the hangingwall at deeper crustal levels and by the regional distribution of the metamorphic grade i e by the dominant deformation mechanism this last factor causes an exponential increase of strain with approach to the ductile lower crust the superposition of strain partitioning mechanisms on different scales creates a complex regional strain pattern the southern part of the thrust belt apparently suffered late westward motion in gently dipping imbricates or strike parallel motion in steeply dipping imbricates which is probably due to oblique convergence between the rhenohercynian and saxothuringian microplates

including strain data in balanced cross sections abstract almost all published balanced cross sections include cleaved and or strained rocks and may therefore violate the requirement that bed lengths and formation areas are preserved between undeformed and deformed states knowledge of distortions presence and type of cleavage and overprinting relations in poly deformed segments are necessary to define area changes related to volume loss strike elongation and poly deformation work in the southern and central appalachians has shown variation in structural complexity and changing deformation styles both along and across the thrust belt this necessitates separate treatment of individual sheets during balancing regions of little or no interstratal slip pinning points should be chosen for each thrust sheet and each fold strain in the sheet in external sheets where deformation intensity increases towards thrusts pin points should be back limb inflection points in intermediate and internal sheets where cleavage is approximately coeval with folding pin points should be at fold hinges where cleavage and strain are heterogeneously developed throughout a stratigraphic sequence a line length balance using massive relatively uncleaved beds e g knox group southern appalachians can be used as a basis for restoring the section unstraining of deformed layers given strain data and cleavage trajectories for individual thrust sheets provides line lengths and formation areas which can be fitted to the key bed of the undeformed section cleavages which partially or fully postdate folding indicate continued shortening in the thrust wedge and modify earlier pinning points in upper sheets these cleavages and poly deformed segments are difficult to restore as strain data are generally scarce in the metamorphosed internal thrust sheets

orogenic wedge growth during collision constraints on mechanics of a fossil wedge from its kinematic record rhenohercynian ftb central europe abstract the kinematic evolution of the rhenohercynian fold and thrust belt of the central european variscides can be reconstructed from incremental strain and palaeostress data synkinematic metamorphism geochronology synorogenic sediments and the geometry of shortening this data set allows to infer the mechanical development with respect to the mohr coloumb theory of critically tapered orogenic wedges growth of the rhenohercynian orogenic wedge was kinematically partitioned into a broad orogen normal moving and a narrow obliquely moving domain the ratio of the final widths of these domains varies from 1 6 to 2 3 this low ratio indicates strong basal coupling growth averages are 14 km ma of shortening and a strain rate of 6 10 16 s 1 the mode of mass transfer from lower to upper plate which controlled the accretion geometry and the particle paths evolved in the long term from dominantly basal to frontal accretion this evolution was accompanied by a decrease in taper from precollisional 18 28 to final 5 8 4 6 accretionary subsystems assemble the wedge each is characterised by a sequence of basal to frontal accretion both rooting in a common detachment the development of the subsystems is supported by the observation of stepwise migration of a foreland bulge ponding flysch subbasins these features imply shorter termed ca 2 ma cyclic mass transfer above a high friction detachment with episodes of basal accretion followed by episodes of a quickly forward propagating thrust front transfer of the basal detachment from ductile mid crustal to brittle conditions via a crustal ramp and particle flow across the ramp provoked large scale adjustment of wedge geometry internal wedge thickening is spatially and chronologically related to the formation of the ramp and was supported by surficial erosion of ca 3 kbar for keeping a critical taper three growth stages of the wedge can be reconstructed the high taper of the precollisional stage plots in the tectonically erosive field in a taper stability diagram then taper decreases to 10 after emplacement of a flysch nappe stack during the final stage of contraction an eastern and a western branch develop with geometries fluctuating around a critically stable state the two branches link with differences in large scale wedge architecture bulk contraction and detachment geometry the latter being controlled by the former basin geometry

on the height variation of the equatorial f region vertical plasma drifts we have used improved incoherent scatter radar measurements at the jicamarca radio observatory to study the height variation of the f region vertical plasma drift velocity driven by the zonal electric field during moderately quiet conditions preliminary results indicate a nearly linear change of the vertical drift velocity with altitude between 200 and 700 km but with considerable day to day variations in the value of the slope on the average the velocity gradients are positive in the late night and morning periods and negative during the afternoon and evening hours simultaneous vertical and zonal drift measurements confirm that the measured height variation of the vertical drift is consistent with the existence of a curl free electric field in the low latitude ionosphere the time dependence of the jicamarca vertical drifts extrapolated to higher altitudes closely resembles the diurnal variation of the drift component due to the zonal electric field observed at f region heights over arecibo

crustal scale balanced cross sections through the variscan fold belt germany the central egt segment abstract this paper presents crustal scale geometrically and isostatically balanced cross sections through the rhenohercynian and saxothuringian zones of the variscan fold belt of germany the cross sections are based on surface geological data and on results of the dekorp deep reflection profiles they were constructed by means of computer assisted iterative forward modelling the rhenohercynian zone corresponding to the externides of the variscan belt developed out of a some 300 km wide rifted continental margin sedimentary prism limited to the south by the narrow giessen oceanic basin during carboniferous imbrication this shelf sequence is stripped of its basement above one or more decollements and shortened by some 150 km closure of the giessen ocean and emplacement of the ophiolite bearing giessen nappe entailed a minimum additional 200 km of crustal shortening the structure of the model correlates well with the present outcrop pattern of rock units their metamorphic history the seismic and magnetotelluric architecture of the crust and its present regional distribution of thickness the deeper crust beneath the rhenish massif is probably devoid of extremely weak decollement horizons and pronounced rheological stratification in the southward adjacent saxothuringian zone nappe development involving the stacking of crustal slices during middle devonian to visean times accounts for a further 170 km of crustal shortening above an infracrustal partly blind thrust system with flat ramp geometry total crustal shortening in the analyzed profiles is estimated to be of the order of 520 km this figure is a conservative value prominent uncertainties include the unknown importance of crustal wrenching the state of strain within thrust units the distribution of strain within the lower crust and major changes in thrusting directions during the course of orogenic history

the role of pore water circulation during the deformation of foreland fold and thrust belts volume loss strain accompanying pressure solution of calcite occurred within both the umbria marches apennines of italy and the appalachian mountains of western new york data from strain markers show that volume loss strain was greater within the shallow portions of the apennines than within the appalachians within the deeper portions of both fold and thrust belts strain was nearly volume constant calcite solubility data suggest that downward circulation of meteoric water is necessary for the 35 volume loss strain of the limestones within the apennines strain at a depth of about 1 km was volume constant and is interpretated as indicative of restricted pore fluid circulation in the appalachians calcite comprises less than 1 of the clastic rocks and a 10 volume loss of this calcite may occur during circulation of connate or dehydration water derived from dewatering of the shales but in an environment that restricts the circulation of meteoric water here the volume of calcite removed 0 1 of the total rock is so small that circulation of meteoric water is not necessary for strain by pressure solution

polykinematic foreland basins initiated during orthogonal convergence and terminated by orogen oblique strike slip faulting an example from the northeastern variscan belt abstract an extensive early carboniferous foreland basin the moravosilesian culm basin mscb delineates the northeastern margin of the bohemian massif variscan orogenic belt the basin overlays a complex suture between the outer brunovistulia microplate forming a promontory previously accreted to laurussia and inner gondwana derived units that form the remainder of the bohemian massif our structural paleomagnetic and magnetic anisotropy data from the eastern portion of the mscb indicate that its depositional architecture internal fabric and deformation by folding and faulting record a major switch from orthogonal convergence to orogen oblique strike slip shearing first the brunovistulia microcontinent was subducted frontally towards w during 346 335 ma followed by a shift of the subduction vector towards ssw at around 335 330 ma from 330 ma onwards the underthrusting had ceased and the wnw ese dextral elbe shear zone related to the westward movement of gondwana with respect to laurussia controlled deformation of this region displacement of the northerly eastern sudetes block towards ese produced regional wnw ese pure shear shortening against the brunovistulia indentor and resulted in an overall doubly vergent structure of the mscb simultaneously the southerly moldanubian unit was translated towards wnw away from the brunovistulian microplate and likely contributed to an extensional regime related to orogenic collapse progressing outward from the internal domains of the bohemian massif on a larger scale we suggest that the mscb is an illustrative example of a polykinematic foreland basin where deposition syn to post sedimentary deformation and thus geodynamic processes changed significantly during basin evolution starting off with microplate impingement into a continental margin reentrant and terminated by strike slip shearing our data also do not support previous models for the tectonic development of the northeastern termination of the variscan belt which suggested either a large magnitude vertical axis oroclinal rotation of the foreland or its translation along an orogen perpendicular strike slip fault

ductile structures and instabilities their implication for variscan tectonics in the ardennes abstract increasing consideration of instabilities may explain the development of structures at all scales in naturally deformed rocks this address is a review of geometric scale free concepts applied to the tectonic study of ductile structures the notion of instabilities is first given to introduce non equilibrium dynamics such as strain localisation and single deformation events producing superimposed structures these concepts lead to the idea that orogens are regions of accumulated strain in zones dominated by non coaxial deformation consequently stretching lineations depend on finite strain and do not represent the plate motions repeated phases of deformation represent local perturbations during a kinematic and dynamic event rather than being correlatable as regional phases the fold and thrust belt of the northern variscan belt in the ardennes is taken as a natural example where superposed structures represent the instable response to forces among which plate tectonic forces play a subsidiary role

the prereversal enhancement of the zonal electric field in the equatorial ionosphere the electric fields in the ionospheric e and f regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward normally daytime field reverses to westward several theoretical models of the low latitude fields suggest that this enhancement is caused mainly or entirely by f region winds the f region dynamo but some authors have suggested that it could be produced solely by e region tidal winds we give here additional calculations and arguments in support of the f region source the enhancement of the eastward field for an eastward f region wind turns out to be a simple direct consequence of the fact that after sunset the ionospheric conductivity decreases far more rapidly in the e region than in the f region

sulphur isotope geochemistry of black shale hosted antimony mineralization arnsberg northern rhenish massif germany implications for late stage fluid flow during the variscan orogeny vein type and bedding concordant mesothermal 180 410 c stibnite sulphosalt mineralization at arnsberg ne rhenish massif germany is hosted by carboniferous pyrite rich black shales and siliceous limestones a detailed sulphur isotope study of the stibnite sulphosalt mineralization and pyrite from a variety of regional host rock lithologies has been carried out using an in situ laser combustion technique the 34 s values of stibnite of various textural types are distinctly negative and lie in a narrow range between 23 9 and 17 1 mean 20 1 in contrast regional sedimentary diagenetic pyrites display a large variation of their 34 s values between 45 4 and 9 3 there is little evidence for significant modification of the hydrothermal fluid during deposition and the s isotope signatures suggest that the sulphur of the stibnite mineralization was not locally derived the 34 s values of pyrite in givetian shales display a significantly narrower range of 28 2 to 7 5 and their mean composition 17 1 is close to the 34 s values of the arnsberg stibnite deposits considering the temperature dependent isotopic fractionation between stibnite and reduced sulfur species the 34 s values of the mineralizing fluid 16 8 200 c and the givetian rock source are essentially identical therefore we propose a model of leaching and isotopic homogenization of sulphur from the middle devonian shales and a subsequent northward migration of these fluids the fluids were trapped in permeability controlled positions within anticlinal zones where fluid cooling induced deposition of stibnite and sulphosalts

strain refraction in layered systems abstract strain refraction across competence contrasts is presented as a simple model consisting of two components a homogeneous strain and a heterogeneous simple shear for newtonian materials the ratio of the layer parallel simple shear component in adjacent layers is the inverse of their viscosity ratio strong changes in ellipsoid size shape and orientation are predicted across viscosity contrasts the geological implications of strain refraction theory are considered within the context of the cleavage strain debate the particular relationships of relative competence and strain revealed by the refraction model may contribute to the problem of why cleavages of different morphologies in rocks of different lithologies and kinematic histories should appear to be subparallel to the xy planes of measured strain ellipsoids competent rocks should develop dominantly layer orthogonal strain and incompetent layers shear dominated deformation a variety of structural features ranging from cleavage refraction changing lineation orientations folds transected by cleavage changes from coaxial to non coaxial deformation and ramp flat fault geometry may be the result of stress and strain refraction in rocks

influence of basin architecture on the style of inversion and fold thrust belt tectonics the southern adelaide fold thrust belt south australia abstract the southern adelaide fold thrust belt involves neoproterozoic adelaidean strata deposited during protracted rift and sag phases and an overlying cambrian kanmantoo sequence represented by a thick wedge of turbidites rapidly deposited in an eastwards deepening basin deeply incised into the underlying rocks the belt was deformed during the delamerian orogeny developed at the southeastern margin of the australian craton during early palaeozoic nw directed displacement during this shortening event the margin of the kanmantoo basin was reactivated and formed a significant strain guide that controlled key features of the fold thrust belt strain integrated and restored sections reveal contrasting geometric and kinematic styles along the strike of the belt a transpressional zone is developed at the steep basin margin in the south oriented oblique to the structural grain the central parts of the belt are dominated by strong buttressing growth fault reactivation and basement involved footwall shortcut thrusting in the northern part of the belt shortening is accommodated by homogeneous folding above a master de collement these variations in regional structural style and internal strain partitioning reflect significant variations in the original kanmantoo basin margin geometry rheological parameters control the partitioning of strain associated with pervasive fabrics for example cleavage and transposed bedding folding is accompanied by negative line length changes shortening in the northern part of the belt in its thrusted central part pelites commonly show positive line length changes psammites were least affected by line length changes and thus provide key beds for section balancing pervasive strain makes a full restoration of cross sections impossible however incorporating regional strain data assists establishment of balanced and restorable sections which provide a powerful tool in understanding both pre deformational basin geometry and its shortening

crustal scale thrusting and extension in the hercynian schwarzwald and vosges central europe the hercynian outcrop areas in the schwarzwald of sw germany and vosges of easternmost france consist from north to south of three major lithotectonic complexes very low to medium grade metamorphics of the saxothuringian belt the polymetamorphic central gneiss complex and the tectonic melange of the southern complex juxtaposition of these three complexes occurred by oblique convergent motions in early carboniferous time the saxothuringian belt is part of a major se dipping accretionary wedge that consists of lower paleozoic meta sedimentary and metaigneous rocks and superimposed upper devonian to lower carboniferous synorogenic volcanics and elastics the central gneiss complex consists of polymetamorphic paragneisses orthogneisses metabasites and meta ultramafics dipping to the nw the southern complex consists of an imbricated melange of north to nw dipping synorogenic elastics volcanics and blocks of ultramafics and gneissic basement the central gneiss complex cgc experienced pervasive hercynian low pressure high temperature metamorphisrn before it was emplaced against and thrust over the sedimentary and volcanic fill of the adjacent synorogenic basins this convergence 340 330 ma produced mylonitic cataclastic shear zones in the cgc the most significant shear zones are the se verging todtnau fault zone between the cgc and the southern complex and the nw verging lubine fault zone between the central gneiss complex and the rocks of the saxothuringian belt these two fault zones enclose a bivergent pop up of the polymetamorphic basement the todtnau fault zone probably extends for more than 100 km along strike and can be traced to a depth of 10 km by deep seismic reflection studies detachment probably occurred along a mid crustal zone of anatexis expressed by a domain of low seismic reflectivity between about 10 and 15 km crustal thickening during early carboniferous convergence led to an extensional phase of crustal reordering between about 330 and 280 ma that was accompanied by the massive rise of posttectonic granitic plutons from middle to high crustal levels simultaneous creation of a structural lamination in the refractory lower crust neglected the main convergent tectonic boundaries it produced a basin and range type lower crust and mantle crust transition in early permian time and involved a major advective input of heat

on the latitudinal variations of the ionospheric electric field during magnetospheric disturbances a joint alert campaign was organized during the month of october 1980 by the incoherent scatter radars in the american sector namely jicamarca arecibo millstone hill and chatanika the campaign which met with success was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions the arecibo data in this campaign support present and previous observations at jicamarca that suggest that when the convection e field suddenly decreases the alfven layer shielding field becomes unbalanced and penetrates the plasmasphere while this type of observation is reasonably convincing others are more difficult to categorize we suggest that beside the high latitude electric fields time varying auroral conductivity models will have to be considered in order to understand the morphology of the low latitude e field disturbances we present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30 geometric latitude arecibo to the field at 0 jicamarca other highlights of the paper are a discussion of dp2 which may help clarify the controversy surrounding it and a discussion of the sensitivity of low and mid latitude radars to disturbances of magnetospheric origin we show that this sensitivity maximizes at the magnetic equator

f region east west drifts at jicamarca f region east west drifts have been measured at jicamarca for almost 10 years using incoherent scatter the drifts are westward during the day and eastward at night the daytime drift velocities are about 50 m s and change very little with season or solar cycle the evening reversal occurs at about 1600 local time throughout the solar cycle the maximum nighttime eastward drifts are about 105 and 130 m s during solar minimum and maximum respectively the daytime and nighttime drifts show very litle variation with magnetic activity these jicamarca incoherent scatter results especially the reversal times differ appreciably from results obtained using other techniques but there appear to be fairly simple explanations for the apparent disagreements

on the lag time between internal strain and basement involved thrust induced exhumation the case of the colombian eastern cordillera abstract thrust sheets accumulate internal strain before they start moving along discrete fault planes however there are no previous studies evaluating the time difference between initiation of strain and fault displacement in this paper we use observations from the eastern cordillera of colombia to evaluate this interval we utilize multiple thermochronometers and paleothermometers to refine the timing of deformation based on these new data we build time temperature path estimates that together with geometric outcrop based structural analysis and fluid inclusions allow us to assign relative timing to features associated with strain such as cleavage veins and certain types of fractures and compare that with the timing of thrusting we find that cleavage was only formed close to maximum paleotemperatures almost coeval with the onset of thrust induced denudation by the late oligocene the corresponding structural level of fold related veins suggest that they were formed later but still when the country rocks were at temperatures higher than 160 c mostly during the early miocene and still coexisted with the latest stages of cleavage formation our data show that the main period of strain hardening was short probably a few million years and occurred before first order basement thrusting was dominant but was associated with second order folding

fluid rock interaction during formation of metamorphic quartz veins a ree and stable isotope study from the rhenish massif germany we have investigated fluid rock interaction processes during formation of metamorphic quartz veins that are abundant in the fold and thrust belt of the rhenish massif southwest germany these veins record two successive assemblages that were formed in a different fluid rock environment which are 1 massive vein filling elongate blocky quartz chlorite apatite albite and 2 open space filling euhedral quartz crystals ankerite dolomite calcite sulfides building on previous work that studied the field relationships mineralogy vein textures fluid inclusion and wall rock alteration features we have performed a detailed ree and stable isotope investigation of vein minerals altered wall rocks selvages and least altered host rock metapelites the ree and oxygen isotope data of vein quartz and altered wall rocks in conjunction with mass balance analysis support the conclusion that local mobilization of material was dominant during formation of the early massive vein filling assemblage but that contributions from advecting fluids were also important the pronounced shift in k na ratios in altered wall rocks and model fluid temperatures that are substantially higher 350 400 c than estimates for the surrounding host rocks clearly point to substantial fluid advection formation of the veins can be essentially explained by a crack flow seal model which involves multiple repetition of vein opening fluid advection and vein sealing events consistent with the elongate blocky textures of massive vein quartz each cycle was initiated with vein opening resulting in enhanced permeability and considerable fluid advection leading to hydrothermal alteration of wall rocks conditions during each cycle then evolved towards a decrease in fluid advection coupled with substantial diffusional leaching of silica from the wall rocks and precipitation in the veins the formation of the later open space filling assemblage records a transition from an overall advection to a diffusion dominated regime this is supported by vein mineral and fluid inclusion textures recording conditions of slow and undisturbed mineral growth fluid inclusion data that point to a thermally equilibrated state 150 200 c and stable isotope data that demonstrate a local source for the vein minerals

crustal structure of the rhenish massif results of deep seismic reflection lines dekorp 2 north and 2 north q the reflection seismic line dekorp 2 n reveals an almost complete cross section through the rhenohercynian zone the most external part of the variscan orogen in europe

folds and the strain ellipsoid a general model abstract a new general model is proposed to account for non orthogonal relationships of fold axes and axial surfaces to the axes of the finite strain ellipsoid descriptions in the literature of such relationships e g plunge variations and transecting cleavage are reviewed and the development of the model is outlined the model is described in which plane strain k 1 or slight flattening strain k 0 71 or slight constrictional strain k 1 85 are imposed on a suite of layers with oblique orientations to the bulk strain axes x y z folds will initiate perpendicular to the direction of shortening in the layer and develop as non material lines moving through the layer by angular migration at geologically realistic finite strains the folds will be transected by xy cleavage in slight flattening strain folds are likely to be cylindroidal with axes not measurably oblique to xy in slight constrictional strain en echelon periclines are predicted with marked transection by cleavage in some examples the interference of two directions of folding will give rise to severe plunge variations and even downward facing although strain markers frequently indicate finite strains in the flattening field this may result from the superimposition of slightly constrictional tectonic strain on compactional flattening

incoherent scatter radar ionosonde and satellite measurements of equatorial f region vertical plasma drifts in the evening sector studies of equatorial f region evening vertical plasma drifts using different measurement techniques have produced conflicting results we examine the relationship of incoherent scatter radar and ionosonde drift observations over the peruvian equatorial region and ae e satellite drifts for different geophysical conditions our data show that there is large day to day variability on the ratios of radar and ionosonde drifts but on the average the measurements from these two techniques are in fair agreement during low and moderate solar flux conditions for high solar activity however the jicamarca evening drifts during equinox and december solstice are significantly larger than the ionosonde drifts these results can be explained by the different height ranges of the radar and ionosonde measurements and the increase of the upward drift velocity with height below the f region peak this altitudinal variation is related to the longitudinal gradient of the zonal plasma drifts as a result of the curl free electric field condition our results also indicate that during equinox the increase of the vertical prereversal velocity enhancement with solar activity is largely longitude independent

comparison of zonal neutral winds with equatorial plasma bubble and plasma drift velocities 1 a one year dataset spanning march 2011 to march 2012 of coincident observations of nighttime thermospheric zonal neutral winds equatorial plasma bubble epb velocities and zonal plasma drifts is used to examine the relationship between the thermosphere and the ionosphere near the geomagnetic equator over peru thermospheric neutral winds are determined by using a bistatic fabry perot interferometer fpi experiment located at merihill and nazca in peru the ambient plasma drift velocities were obtained using the incoherent scatter radar at the jicamarca radio observatory in peru the epb zonal velocities were estimated utilizing images of the oi 630 0 nm emission recorded by a narrow field optical imaging system at the cerro tololo inter american observatory in chile the joint analysis of these datasets illustrates that the nighttime and night to night variations in the zonal neutral winds epb velocities and plasma drifts are well correlated this consistent result of the local time variations of the neutral winds with that of epb and plasma drifts illustrates that the f region dynamo is in general fully activated however at times the magnitude of the epb velocities and the plasma drifts are different from the neutral winds it is plausible that such a difference is due either to the effect of polarization electric fields developed inside the epb or due to the latitudinal gradient of the neutral winds and epb velocity measurements since the epb velocities are estimated at a higher latitude corresponding to an apex altitude of 400 km than the wind estimates which derive from an apex altitude of 250 km

lead isotope systematics of vein type antimony mineralization rheinisches schiefergebirge germany a case history of complex reaction and remobilization processes mesothermal vein type sb mineralization in the rheinisches schiefergebirge germany is characterized by two different mineralization styles which are 1 extensional quartz stibnite vein systems and 2 cu pb sb sulphosalt assemblages in overprinted pre existing pb zn veins a detailed pb isotope study of 52 representative samples from both mineralization types indicates distinct compositional patterns cu pb sb sulphosalts meneghinite boulangerite bournonite formed by reaction remobilization are characterized by pb isotope compositions 206pb 204pb 18 179 18 223 which are identical to the precursor galena 206pb 204pb 18 168 18 223 the pb isotope composition of sulphosalt minerals in these vein systems was controlled by lead inherited from pre existing galena stibnite and pb sulphosalts zinkenite semseyite plagionite formed in quartz stibnite vein systems display pb isotope ratios 206pb 204pb 18 250 18 354 which are more radiogenic than galenas from variscan pb zn ore veins 206pb 204pb 18 162 18 303 detailed small scale investigation of thrust zones hosting pb zn ores and crosscutting quartz ankerite fissure veins ramsbeck deposit indicates that the pb isotope compositions of recrystallized galena and remobilized phases boulangerite semseyite bournonite are arranged along a linear trend this is interpreted as mixing between primary galena with 206pb 204pb 18 206 and overprinting hydrothermal fluids with a more radiogenic composition 206pb 204pb 18 354 expressed by intermediate compositions 206pb 204pb 18 256 18 334 of newly formed sulphosalts the pb isotope systematics of the vein type sb mineralization is in accordance with a model of pb extraction from similar crustal sources palaeozoic sedimentary sequences at different times

orogenic mass transfer and reflection seismic patterns evidence from dekorp sections across the european variscides central germany abstract orogenic wedges evolve by different mass transfer modes which control different styles of deformation metamorphic pattern and bulk reflectivity structural patterns and reflectivity strongly vary depending mainly on the length thickness ratio of thrust sheets and on their displacement length ratio reevaluation of dekorp seismic sections across the central european variscides lines dekorp 1a c 9n 2n 2s 3b underlines the usefulness of the integrated interpretation strategy in establishing orogenic growth mode and evolution the results are in contrast with reflectivity patterns predicted from critical taper theory the northern flank of the mid european variscides is formed by a doubly vergent orogenic wedge system which evolved from collision of a passive margin rhenohercynian zone with a continental arc mid german crystalline rise mgcr of the saxothuringian zone the two fold and thrust wedges show inward dipping shear zone related reflections above subhorizontal mid crustal reflection bands evidence of dominantly frontal accretion of upper crustal material in both wedges in contrast the sections crossing the axial zone mgcr either show arched reflection stacks related to underplated amphibolite facies rocks in exposed antiformal nappe stacks or a transparent wedge shaped unit related to low grade calcalkaline magmatics and steeply dipping devono carboniferous sediments of the former upper plate magmatic arc analysis suggests that part of this arc was tectonically eroded prior to collision in combination with isograd and structural patterns the observed features indicate that heterogeneous basal accretion was the dominant accretion mode in the axial zone during collision the discussed patterns are suggested to reflect the material transfer site into the orogenic wedge and therefore also growth mode and material provenance in collisional belts

quiet time equatorial f region vertical plasma drift model derived from rocsat 1 observations 1 we have used five years of measurements on board the rocsat 1 satellite to develop a detailed quiet time global empirical model for equatorial f region vertical plasma drifts this model describes the local time seasonal and longitudinal dependence of the vertical drifts for an altitude of 600 km under moderate and high solar flux conditions the model results are in excellent agreement with measurements from the jicamarca radar and also from other ground based and in situ probes we show that the longitudinal dependence of the daytime and nighttime vertical drifts is much stronger than reported earlier especially during december and june solstice the late night downward drift velocities are larger in the eastern than in the western hemisphere at all seasons the morning and afternoon december solstice drifts have significantly different longitudinal dependence and the daytime upward drifts have strong wave number four signatures during equinox and june solstice the largest evening upward drifts occur during equinox and december solstice near the american sector the longitudinal variations of the evening prereversal velocity peaks during december and june solstice are anti correlated which further indicates the importance of conductivity effects on the electrodynamics of the equatorial ionosphere

equatorial f region zonal plasma drifts we have examined in detail the f region plasma drifts measured at jicamarca peru during 1978 1981 a period of high solar activity and compared these drifts with jicamarca data taken during periods of lower activity as well as with other equatorial zonal neutral wind and plasma drift measurements the increase in solar activity causes larger nighttime eastward plasma drifts at jicamarca and delays the morning reversal time from eastward nighttime to westward daytime drifts the radar data seem to be in good agreement with nighttime neutral wind measurements made by the de 2 satellite but are systematically smaller than spaced receiver drifts measured with both the scintillation and the vhf polarimeter techniques for integration times of 20 30 min but perhaps not for shorter integrations the jicamarca zonal plasma drifts measured with both the incoherent scatter and the radar interferometer technique change little with altitude near the f region electron density peak and above however at nighttime below the f peak there is a clear shear in the zonal plasma drifts with decreasing eastward drifts below the f peak reversing to westward drifts at lower altitudes the nighttime profiles of the equatorial plasma drifts are in good agreement with the results from recent numerical models of the equatorial ionosphere

a seismic refraction study of the western tuz golu basin central turkey summary in 1970 the turkish petroleum company carried out a seismic refraction experiment in the tuz golu salt lake basin of central turkey we present our interpretation using time term analysis and ray tracing of data from one of the two lines shot this confirms the presence of a thick sequence of sedimentary layers varying from about 3 km below the southwestern end of the profile to about 10 km at two points along the line a p wave velocity of 4 0 4 2 km s 1 found beneath the low velocity surface layer indicates that the principal sedimentary layer consists of evaporites the lowermost layer of the model has a p wave velocity of 6 15 km s 1 which is consistent with the sedimentary layers being underlain either by cretaceous metamorphic basement or by lavas of andesitic type the extensive coverage provided by this data set has enabled the construction of a detailed 2 d model which shows the complex topography of the subsurface layers we identify two major faults and one minor fault affecting both the basement and overlying layers the character of these features and the associated layer displacements leads us to speculate that these may be growth faults associated with the aksaray ereflikochisar and karapinar cihanbeyli haymana hinge structures which have controlled the development of the tuz golu basin