current variability near the southeast newfoundland ridge abstract a cooperative moored array experiment to measure currents and temperatures in the vicinity of the southeast newfoundland ridge was carried out over a 14 manth period starting september 1979 and ending december 1980 measurements were obtained from an incoherent exploratory army of nine moorings instrumented at 500 800 1500 and 4000 m levels the objectives were to explore the amplitude spatial variability and time scales of the eddy field in the decay region of the gulf stream an additional experiment and mooring to examine the influx of norwegian sea overflow water into the western north atlantic basin was imbedded in the array supplementary ctd and xbt profiles and a single current profile were taken during deployment and recovery cruises to aid in interpretation of the moored measurements and identification of water masses a description of the array experiment and preliminary results are reported mean velocities were weak compared with rms eddy velocities and were not determined with st

short paper detrital mineral ages from the southern uplands using 40ar 39ar laser probe detrital mica ages in the southern uplands range from 458 to 502 ma the evidence favours a source in a basement which was part of an arc complex to the north rather than from the dalradian block which also has mica ages of this range no grenville ages have yet been recorded detrital volcanic clasts dispersed from the south have cooling ages of 560 and 530 ma indicating that they did not come from a contemporary arc but an older arc terrane of uncertain affinities

carbon isotopes and event stratigraphy near the ordovician silurian boundary yichang south china abstract the organic carbon isotope data through the unweathered ordovician silurian boundary strata at the wangjiawan riverside section which is c 180 m southeast of the wangjiawan north section the gssp for the base of the hirnantian stage upper ordovician show that a positive 13 c org excursion begins just below the base of the hirnantian stage and peaks in the lower part of the n extraordinarius biozone this is followed by an interval of slightly reduced 13 c values and a second peak of 2 above pre hirnantian values which occurs in the lower part of the n persculptus biozone upper hirnantian the peaks in 13 c org values can be correlated well with episodes of glacial expansion described from africa and peri gondwanan europe evidence from sedimentological faunal and geochemical data from south china as well as the evidence of glacial sediments in north africa all suggests a short lived glaciation of 1 ma in the ordovician south pole region consisting of at least two major pulses the first phase of gradual glacial expansion began just before the hirnantian epoch and the second phase ended with rapid melting in the late hirnantian early n persculptus biozone

observations of the vertical structure of the eddy field in the kuroshio extension normalized kinetic energy frequency distributions at a site in the kuroshio extension along 152 e are independent of depth as a good first approximation the lowest frequencies are strongly vertically coherent from 350 to 6000 m depths nominal none of the other vertical sets of time series previously examined possess these characteristics to such a degree coherence being typically much lower between the thermocline and abyssal depths with spectral shape changing significantly as well the vertical distributions of eddy kinetic energy at this kuroshio extension site and for the gulf stream along 55 w are very similar if a depth independent contribution of approximately 100 cm2 s 2 be added to the former the latter observation suggests the existence of a more energetic weakly depth dependent component for the eddy field in the north atlantic than for the north pacific at special locations in the vicinity of their mid latitude jets possibly a signature of distinct instability mechanisms

evolution of the northern belt southern uplands implications for the southern uplands controversy conodont and graptolite dating provide a high resolution biostratigraphical framework for correlation across the southern upland fault the establishment of an early caradoc age for the red chert and volcanic sequences within the northern belt of the southern uplands confounds the accretionary prism model and our data support the view that following the obduction of the ballantrae ophiolite fan complexes prograded southeastwards across a narrow fault bounded shelf into the deep basin of the northern belt the fan complexes were initiated by uplift in the hinterland caused by the intrusion of plutons into the midland valley terrane sedimentation was controlled by regional extension subsidence and eustasy through the llanvirn and caradoc basic lavas with attenuated within plate geochemical signatures were erupted during the early caradoc peak of extension and may have just post dated the initiation of southwards subduction beneath the lake district

mapping lightning in the sky with a mini array mini arrays are commonly used for infrasonic and seismic studies here we report for the first time the detection and mapping of distant lightning discharges in the sky with a mini array the array has a baseline to wavelength ratio 4 2 10 2 to record very low frequency electromagnetic waves from 2 to 18 khz it is found that the mini array detects 69 lightning pulses per second from cloud to ground and in cloud discharges even though the parent thunderstorms are 900 1100 km away and a rigorous selection criterion based on the quality of the wavefront across the array is used in particular lightning pulses that exhibit a clockwise phase progression are found at larger elevation angles in the sky as the result of a birefringent subionospheric wave propagation attributed to ordinary and extraordinary waves these results imply that long range lightning detection networks might benefit from an exploration of the wave propagation conditions with mini arrays

the vertical partition of oceanic horizontal kinetic energy to produce an interpretation of the surface kinetic energy as measured by altimeters a survey is made of the vertical structure of kinetic energy profiles in a large number of globally distributed long current meter records although the data are geographically confined primarily to a latitude band in the north pacific to the north atlantic and to a few moorings in the south atlantic the results show generally speaking that most regions are dominated by the barotropic and first baroclinic modes because of the near surface intensification of baroclinic modes altimeters primarily reflect the first baroclinic mode and thus the motion of the main thermocline there is good quantitative agreement with a few exceptions with estimates of the surface kinetic energy obtained from the topex poseidon altimeter and from vertical extrapolations to the surface of the mooring profiles these results are consistent with previous suggestions that barotropic models have little skill in depicting variability as seen in the altimeter data an eof analysis is shown to produce fictitious mode coupling unless the dynamical modes have very different energy levels

array analysis of electromagnetic radiation from radio transmitters for submarine communication the array analyses used for seismic and infrasound research are adapted and applied here to the electromagnetic radiation from radio transmitters for submarine communication it is found that the array analysis enables a determination of the slowness and the arrival azimuth of the wave number vectors associated with the electromagnetic radiation the array analysis is applied to measurements of 20 24 khz radio waves from transmitters for submarine communication with an array of 10 radio receivers distributed over an area of 1 km 1 km the observed slowness of the observed wave number vectors range from 2 7 ns m to 4 1 ns m and the deviations between the expected arrival azimuths and the observed arrival azimuths range from 9 7 to 14 5 the experimental results suggest that it is possible to determine the locations of radio sources from transient luminous events above thunderclouds with an array of radio receivers toward detailed investigations of the electromagnetic radiation from sprites

estuarine clay mineral distribution modern analogue for ancient sandstone reservoir quality prediction the spatial distribution of clay minerals in sandstones which may both enhance or degrade reservoir quality is poorly understood to address this clay mineral distribution patterns and host sediment properties grain size sorting clay fraction abundance and bioturbation intensity have for the first time been determined and mapped at an unprecedentedly high resolution in a modern estuarine setting ravenglass estuary uk results show that the estuary sediment is dominated by illite with subordinate chlorite and kaolinite although the rivers supply sediment with less illite and significantly more chlorite than found in the estuary fluvial supplied sediment has been locally diluted by sediment derived from glaciogenic drift deposits on the margins of the estuary detailed clay mineral maps and statistical analyses reveal that the estuary has a heterogeneous distribution of illite chlorite and kaolinite chlorite is relatively most abundant on the northern foreshore and backshore and is concentrated in coarse grained inner estuary dunes and tidal bars illite is relatively most abundant as well as most crystalline and most fe mg rich in fine grained inner estuary and central basin mud and mixed flats kaolinite has the highest abundance in fluvial sediment and is relatively homogenous in tidally influenced environments clay mineral distribution patterns in the ravenglass estuary have been strongly influenced by sediment supply residence time and subsequently modified by hydrodynamic processes there is no relationship between macro faunal bioturbation intensity and the abundance of chlorite illite or kaolinite based on this modern analogue study outer estuarine sediments are likely to be heavily quartz cemented in deeply buried burial temperatures exceeding 80 to 100 c sandstone reservoirs due to a paucity of clay grade material 0 5 to form complete grain coats in contrast chlorite enriched tidal bars and dunes in the inner estuary with their well developed detrital clay coats are likely to have quartz cement inhibiting authigenic clay coats in deeply buried sandstones

caledonian strike slip terrane accretion in w ireland insights from very low grade metamorphism illite chlorite crystallinity and b0 parameter analysis of pelites with detrital white micas in the clew bay galway bay segment of the irish caledonides indicates that b0 data from whole rock and 2 m fractions generally show differences smaller than the errors of the method irrespective of 001 illite crystallinity values probably due to metamorphic recrystallization intermediate pressure metamorphism of the ordovician silurian clew bay group indicates slow subduction allowing partial thermal re equilibration before exhumation in contrast the croagh patrick group laurentian shelf sediments underwent high pressure alteration suggesting rapid subduction exhumation synchronous with strike slip faulting the murrisk group which underwent high intermediate pressure metamorphism in an ordovician back arc forms a separate terrane to the croagh patrick group to the north and also to the ordovician lough nafooey and tourmakeady groups and rosroe formation in the south in which low intermediate pressure alteration occurred these together with the silurian north galway group may have undergone heating due to movement over or deposition on the hot gowlaun detachment as the connemara dalradian was exhumed the south connemara group also underwent a high pressure alteration consistent with its inferred subduction environment evidence of contact alteration due to known or inferred buried late to post caledonian granitoid plutons has been found in the clew bay louisburg clare island croagh patrick murrisk and south connemara groups these show evidence of lower pressure alteration than the surrounding country rocks

metamorphic and post metamorphic fluid flow in the low grade rocks of the harlech dome north wales a combination of fluid inclusion stable isotope and geochemical techniques has been used to study the nature of fluids present and their behaviour during caledonian low grade metamorphism of the harlech dome north wales fluid inclusion studies show that in most of the metasedimentary sequence the peak metamorphic fluid was an aqueous na k cl brine but in the graphitic clogau formation and in parts of the overlying maentwrog formation immiscible h2o rich and ch4 rich fluids coexisted late stage inclusions are of calcium rich brine and a dilute aqueous fluid the chemical composition of chlorite in metamorphic veins and rocks varies between different formations and quartz oxygen isotopic compositions show considerable variation between different units both of these features are taken to indicate that there was little or no pervasive movement of fluid between different units at the peak of metamorphism after the metamorphic peak there was focused flow of fluid upward through the sequence along fractures in response to end caledonian uplift and unloading where the migrating fluid crossed the graphitic shales interaction between the fluid and the shales gave rise to the formation of the auriferous veins of the dolgellau gold belt subsequent to this mineralizing event there was widespread development of 18o enriched calcites and micas in the case of vein minerals it is possible that these crystallized directly from late stage fluids at lower temperature than the quartz in the same veins alternatively the original vein minerals may have re equilibrated with later 18o enriched or cooler fluid in the case of muscovites in the rock matrix it is proposed that the isotopically heavy compositions are the result of re equilibration of initially light grains with an introduced fluid requiring considerable influx of fluid this event may relate to either of two late stage fluids observed as inclusions

tectonothermal history of the western lachlan fold belt australia insights from white mica studies detailed b lattice parameter and illite crystallinity ic studies of k white micas in slates from the stawell and ballarat bendigo zones sz bbz in the western lachlan fold belt of victoria australia reveal a metamorphic pattern characterized by regional metamorphism associated with crustal thickening and younger contact metamorphism accompanied by deformation the ic data indicate that rocks regionally metamorphosed prior to the intrusion of the early and late devonian granitoids vary in grade from epizonal greenschist facies to diagenetic zeolite facies and that most are of epizonal to anchizonal prehnite pumpellyite facies grade in the bbz a decrease in grade from west to east occurs across fault zones ic values show little change indicating that limited vertical displacement has occurred this is in accord with the thin skinned deformation model proposed for the western lachlan fold belt the b lattice parameters x 9 022 a n 137 s n 0 009 indicate baric conditions intermediate between those of new hampshire p al 2 sio 5 triple point and otago intermediate p thus a moderately low geother mal gradient existed 450 430 ma ago when these rocks were deformed k d fe mg actinolite fe mg chlorite values 0 52 0 70 obtained from coexisting actinolite and chlorite in metabasites from fault zones support the moderately high p c 4 kbar metamorphism suggested by the b cell parameter values the metamorphic conditions indicated by these data are contrary to the low p high t conditions pro posed by previous authors who inferred an intimate association between deformation granitoid intrusion and gold mineralization the b lattice parameter of white micas in slates adjacent to early devonian c 400 ma granitoids with schist bearing aureoles in the north eastern part of the bbz x 9 002 a n 27 s n 0 007 indicate pressures in the order of c 2 5 kbar which are in accord with those obtained from andalusite cordierite and zoisite garnet bearing assemblages observed in the higher grade metapelitic and calcareous rocks this contrasts with the higher pressure c 4 kbar existing during regional metamor phism and implies that c 6 5 8 km of metasedimentary rocks in the bbz were removed before the emplacement of the early devonian granitoids metamorphic assemblages in hornfelses associated with late devonian granitoids indicate a further 5 6 km of metasediment were removed in the next 40 ma prior to their emplacement this study shows the value of white mica studies in elucidating the tectono thermal history of a low grade metamorphic terrane dominated by metapelitic rocks

structural style and kinematics of an underplated slate belt kodiak and adjacent islands alaska the kodiak formation composed of coherent maastrichtian turbidites is a slate belt whose dominant structures developed during underplating to an accretionary wedge in the latest cretaceous it consists of about 80 coherent landward dipping thrust packets zones of disrupted sandstone associated with a scaly argillite matrix constitute the remainder about half of these disrupted sandstone zones are related to pre accretion deformation and the rest formed along late stage strike slip faults that postdate development of slaty cleavage the formation is divided into three structural belts the landward and seaward belts include steeply dipping structures and the central belt contains shallowly dipping structures and rocks that have experienced the highest strain the central belt probably acted as a low angle southeast verging floor thrust zone beneath the landward belt the structural history of the kodiak formation includes 1 early soft sediment disruption 2 tectonic stratal disruption 3 thrust faulting slaty cleavage s 1 development and folding f 1 4 intrusion of granodioritic plutons dikes and sills and associated normal faulting 5 development of crenulations f 2 and crenulation cleavage s 2 6 thrust faulting and 7 development of right lateral strike slip faults event 3 produced the dominant northwest dipping structural grain and caused the greatest amount of shortening the timing of event 7 relative to events 5 and 6 is not certain the dominant structures of the kodiak formation are interpreted as developing during underthrusting underplating and intra wedge shortening during latest cretaceous time within an accretionary wedge the maximum time from deposition to emplacement was about 12 m y and the timing is constrained by the maximum depositional age 74 m y and the age of plutonic rocks 62 m y that crosscut the dominant fabric pre cleavage zones of stratal disruption reflect deformation on the lower plate during underthrusting slaty cleavage thrusts and f 1 folds developed during underplating that also resulted in the formation of duplexes crenulations are probably related to post underplating subhorizontal shortening of sediments within the accretionary wedge syn deformation dynamic recrystallization of quartz minimum syn accretion metamorphic temperatures between 205 and 250 c and pressures of at least 2 65 kb recorded during the earliest stages of deformation suggest underplating at 10 km

detrital avalonian zircons in the laurentian southern uplands terrane scotland the silurian ordovician southern uplands terrane occupies a key position in the caledonian orogen yet its genesis is controversial marginal basin backarc and forearc tectonic regimes have all been invoked as operative at the laurentian margin of the iapetus ocean fresh andesitic detritus within turbidite sandstones has until now been assumed to provide evidence for an ordovician suprasubduction volcanic arc a central feature of most models however high precision thermal ionization mass spectrometer u pb and laser ablation data for detrital zircons from the sandstone prove neoproterozoic volcanism at 557 6 ma 2 and probably also at 613 12 ma 2 the complex crystallization history recorded by the zircons shows assimilation of 1043 7 ma 2 grenvillian basement into the andesite magma the fact that no zircons have been found having ages that overlap the caradocian depositional age of the host sedimentary rocks undermines all extant terrane models the age profile of the detrital zircons is typical of gondwana and avalonia this finding has important implications for the paleogeography of the iapetus ocean during the ordovician because the zircon data require the introduction of avalonian detritus into a sedimentary basin marginal to laurentia

a statistical description of the mean circulation and eddy variability in the northwestern atlantic using sofar floats abstract velocity data obtained from trajectories of sofar floats launched as part of several experiments carried out in the northwest atlantic during the last two decades are used to give a statistical description of the mean gulf stream and its recirculation the distribution of eddy variability in the region is also presented a mean gulf stream which bifurcates between 55 and 45 w to feed the north atlantic current and a southern recirculation can be clearly identified a weak interior sverdrup flow is also suggested the spatial distribution of eddy variability is consistent with previous descriptions showing a maximum near the gulf stream

ganderia laurentia collision in the caledonides of great britain and ireland during terrane convergence an influx of clastic sediment from an upper plate onto a lower plate is an early indication of terrane juxtaposition in the caledonides of great britain and ireland units accreted to laurentia during the early palaeozoic era include peri gondwanan terrane assemblages that earlier separated from west gondwana however the southern uplands terrane contains detrital zircon populations apparently derived entirely from laurentia characterized by a large asymmetric mesoproterozoic peak and a scarcity of zircon at 600 ma and 2 1 ga in contrast cambrian and ordovician rocks from the lake district and the leinster massif of ireland show abundant grains with these ages together with a range of mesoproterozoic zircon these characteristics are shared with the monian terrane of anglesey and with ganderia in the appalachians indicating probable derivation from amazonia in west gondwana silurian sandstones from the lake district show an influx of laurentia derived zircon and lack the peri gondwanan signal this indicates that in the caledonides ganderia was not accreted to the laurentian margin until c 430 ma in contrast to the ordovician accretion of ganderian fragments recorded in the appalachians suggesting that the configuration of the closing iapetus ocean varied significantly along the strike of the orogen supplementary material details of sample coordinates analytical procedure and u pb detrital zircon analytical data are available at www geolsoc org uk sup18739

television image of a large upward electrical discharge above a thunderstorm system an image of an unusual luminous electrical discharge over a thunderstorm 250 kilometers from the observing site has been obtained with a low light level television camera the discharge began at the cloud tops at 14 kilometers and extended into the clear air 20 kilometers higher the image which had a duration of less than 30 milliseconds resembled two jets or fountains and was probably caused by two localizd electric charge concentrations at the cloud tops large upward discharges may create a hazard for aircraft and rocket launches and by penetrating into the ionosphere may initiate whistler waves and other effects on a magnetospheric scale such upward electrical discharges may account for unexplained photometric observations of distant lightning events that showed a low rise rate of the luminous pulse and no electromagnetic sferic pulse of the type that accompanies cloud to earth lightning strokes an unusually high rate of such photometric events was recorded during the night of 22 to 23 september 1989 during a storm associated with hurricane hugo

the northern belt of the longford down inlier ireland and southern uplands scotland an ordovician back arc basin the northern belt of the southern uplands longford down zone contains two compositionally distinct clastic petrofacies suites each ranging from mid to late ordovician age they extend throughout the length of the belt and are generally separated by a strike fault the northwestern metaclast petrofacies suite is characterized by felsic igneous and metamorphic detritus derived from a continental source to the nw whereas the southeastern basic clast petrofacies suite contains abundant calc alkaline detritus derived from an island arc and plutonic metamorphic root zone complex to the s or se a similar source but located to the north is indicated for younger clastic sequences of similar composition in the northern part of the central belt immediately south of a major sinistral shear zone which defines the boundary between the northern and central belts it is concluded in light of other facets of regional geology and possible palaeogeographic configurations that this pattern reflects a back arc basin in the northern belt margined by a volcanic arc massif which once occupied the space now represented by the shear zone and a fore arc basin to the se central and southern belts the northern belt back arc basin is postulated to have been closed and deformed at the end ordovician and subsequently overthrust northwestward by the allochthonous thrust stack imbricated central and southern belts fore arc sequence at the end silurian this in the northern belt resulted in the development of a major recumbent structure downward facing on regional end silurian cleavage

li and δ7li in mudrocks from the british caledonides metamorphism and source influences mudrocks from three lower paleozoic basins in the british caledonides southern lake district northern lake district and southern uplands were investigated to determine the influence of sub greenschist facies metamorphism on li and the factors that control li in fine grained terrigenous sedimentary rocks metamorphic grade as determined by ki kubler index does not correlate with li content li and 7li indicating that sub greenschist facies metamorphism has negligible effect on li in these rocks collectively the data for all three basins show a negative correlation between li and 7li and a positive correlation between li and the chemical index of alteration cia suggesting that provenance exerts the greatest control on li in mudrocks samples from the northern lake district which were deposited in an extensional basin have homogeneous ree patterns similar to shale composites paas the highest cia th u and li and the lowest 7li and end consistent with their derivation from a highly weathered ancient continental source by contrast mudrocks from the southern uplands range to the lowest cia th u and li and have the highest 7li and end these samples were deposited in a forearc basin on the southern margin of the laurentian craton and contain volcanic detritus their ree patterns are the most variable ranging from average shale like patterns to less lree enriched patterns the compositional heterogeneity within the southern uplands mudrocks is consistent with a mixed provenance that includes juvenile crustal materials lower li end and th u higher 7li likely derived from the arc as well as more highly weathered continental detritus mudrocks from the southern lake district were deposited in a foreland basin and exhibit geochemical characteristics intermediate between the northern lake district and the southern uplands mudrocks indicating their derivation from a mixed source our study shows that li concentrations and 7li can provide additional information on the degree of weathering of the provenance of mudrocks

polyphase low grade metamorphism of the ingleton group northern england uk a case study of metamorphic inversion in a mudrock succession a series of boreholes in horton quarry northwest yorkshire horton in ribblesdale inlier penetrated mudstones and slates belonging to the austwick formation windermere supergroup overlying laminated mudstones of the ingleton group illite ic and chlorite chc crystallinity measurements indicate a metamorphic inversion between the two groups of mudrocks the windermere supergroup mudrocks are mostly in the high anchizone or epizone whereas the ingletonian samples are lower grade in terms of ic and are mostly deep diagenetic zone or low anchizone hence younger strata at higher grades rest on older strata at lower grades creating a metamorphic inversion ingletonian slates exposed at pecca falls on the river twiss show epizonal and anchizonal ic values and greywacke samples from ingleton quarry contain pumpellyite this suggests that grade in the ingletonian may increase to the nw from the horton to ingleton inliers k white mica b cell dimensions show further differences between the ingleton group and the windermere supergroup the ingletonian samples are characterized by low b cell values 8 989 9 035 mean 9 007 a whereas the windermere supergroup has higher values in the range 9 022 9 034 mean 9 027 a the windermere supergroup values are similar to those recorded from the windermere supergroup of the southern lake district and lower palaeozoic rocks from the scottish southern uplands and are consistent with metamorphism in a low heat flow convergent geotectonic setting the ingletonian b cell values suggest metamorphism in a higher heat flow setting most likely an extensional basin the metamorphic inversion at horton and differences in k white mica b cell dimensions suggest that the ingleton group and windermere supergroup strata evolved in different geotectonic settings and record two separate metamorphic events the discovery of the metamorphic inversion at horton provides further evidence in favour of an ordovician rather than neoproterozoic depositional age for the controversial ingleton group

basin thermal history favours an accretionary origin for the southern uplands terrane scottish caledonides there is general agreement that the siluro ordovician southern uplands suspect terrane is an imbricate thrust belt formed adjacent to the laurentian continental margin during closure of the iapetus ocean however there are conflicting models for its tectonosedimentary evolution especially for the initial depositional environment was it a convergent forearc trench with subsequent incorporation of strata into a suprasubduction accretionary prism or was it a back arc or continental margin extensional basin subsequently caught up in a foreland fold and thrust belt to address this issue the different thermal histories of the contrasting convergent and extensional sedimentary basin models have been investigated palaeogeothermal conditions in the southern uplands terrane assessed from regional metamorphic patterns clay mineral assemblages and k white mica composition rule out extension and support deposition in a low heat flow plate convergent setting there is no evidence for a change from extensional to convergent basin regimes from north to south as required in some models instead throughout the terrane there is a close temporal and spatial relationship between deposition burial metamorphism and tectonism that is elsewhere typical of accretion

mapping the radio sky with an interferometric network of low frequency radio receivers 1 the structure of the 100 khz radio sky is determined with two interferometric networks of 10 radio receivers which are distributed over local areas of 1 1 km2 and 10 10 km2 the radio waves arrive at individual receiver pairs with small time differences which are used to determine the arrival direction of the electromagnetic waves including both the bearing and the elevation angle the results show that the major part of the 100 khz radio wave energy comes from the horizon at bearings which are consistent with known locations of long range navigation loran transmitters some part of the radio wave energy arrives from the sky at elevation angles which are consistent with the first and second sky hop waves of loran transmissions a minor part of the 100 khz radio wave energy comes from lightning discharges at distances up to 1000 km with bearings which are consistent with lightning locations reported by the arrival time difference atd lightning detection network of the uk met office the angular resolution for mapping the radio sky depends on the network geometry the instrumental timing accuracy and on the signal to noise ratio of the radio waves the resulting angular resolution of the interferometric networks used in this study is 1 in bearing at zero elevation and several degrees in elevation

the southern uplands as an accretionary prism the importance of analogues in reconstructing palaeogeography fore arc regions whether accretionary erosional or composite vary greatly both along strike and through time in the geometries which they assume in response to subduction there is no well studied modern neogene margin which can be established as the 9type9 accretionary prism all are individual in some respect or other nor is there an example of a well studied modern neogene accretionary margin which can be compared closely to the southern uplands though there are several good analogues for particular stages of its history accretion took place along the southern uplands margin for c 50 million years the range of geometries on modern neogene accretionary active margins and the extent to which the behaviour of those margins can change during periods as long as 50 million years is reviewed emphasizing the accretionary prisms of mexico sw japan and the makran the interpretation of the southern uplands as an accretionary prism as presented in the late 1970s and early 1980s is reassessed in the light of advances made subsequently in understanding modern neogene prisms the recent alternative model of stone et al for the southern uplands envisages that the terrane evolved by the opening and closure by arc subduction of a marginal basin the new model draws heavily on arc type detritus derived from the oceanward side of the ancient southern uplands trough there are areas along the sw japan fore arc where oceanward derived tubidites are accumulating in a trench nankai trough and where active submarine arc type volcanism is occurring outboard of a currently growing accretionary prism such features in an ancient terrane like the southern uplands do not necessarily mean that an alternative model must be sought involving whole new arc systems furthermore analysis of the life spans and sedimentary fills of modern neogene marginal basins begs the conclusion that the southern uplands9 strata were not deposited in a marginal basin it is most unlikely that the c 50 ma history of pelagic sedimentation preserved there can be manifesting anything other than the closure of a sizeable ocean basin of a scale exceeding any known western pacific type marginal basin and with a different sedimentation history from any such marginal basin

the north atlantic current and surrounding waters at the crossroads the north atlantic current is a well defined western boundary current that flows north along the east side of the grand banks from 40 to 51 n where it turns sharply to the east and begins its journey across the ocean the current is unique in transporting warm tropical waters to much higher latitudes than any other western boundary current and thus plays a crucial role in ameliorating the climate of the european subcontinent the north atlantic current originates in the gulf stream when the latter curves north around the southeast newfoundland rise a major submarine ridge that stretches se from the grand banks a well defined front delineates the path of the current as long as it flows north as a western boundary current after the current turns east in the north it broadens into a widening band of eastward drift without a sharp or permanent front in the sense of the eastward flowing gulf stream after it separates from cape hatteras the north atlantic current transports more than 40 sv 1 sv 106 m s 1 in the south and about 20 sv by the time it flows east across the mid atlantic ridge the currents along the northward flowing front are quite swift with typical maximum average speeds in the upper 300 m near 1 m s 1 2 knots the current meanders almost as wildly as a snaking river but unlike steep meanders in the gulf stream these meanders appear to be stable and with one exception have not been observed to break off to form pools of warm and or cold waters as frequently occurs in the gulf stream the meanders appear to be induced by major topographic features along the path of the current namely the southeast newfoundland rise the newfoundland seamounts and flemish cap strong recirculations develop on the concave side of the meanders one of these the mann eddy at the first meander crest of the north atlantic current should be regarded as a permanent feature of the north atlantic circulation other meanders also contain recirculations that can persist for months under certain conditions these can merge together to form an extended sw flow recirculation just east of the north atlantic current

the north atlantic current based on trajectories of satellite tracked buoys and hydrographic sections both dietrich s and worthington s schemes of the north atlantic current are reconsidered ninety satellite tracked buoys have been analyzed in order to distinguish between these schemes neither could be confirmed the north atlantic current appears as a superposition of a broad west wind drift and a frontal jet in the western part of the north atlantic north of 40 n which becomes independent from the subtropical gyre neither a permanent branching suggested by dietrich nor a confinement of the subpolar gyre to the east of newfoundland per worthington can be found the north atlantic current extends over the entire north atlantic carrying more than 20 sverdrups sv toward the north this northward transport is mainly due to the northward flow around flemish cap and a sudden turn of the north atlantic current east of the mid atlantic ridge the buoy tracks have been used to determine speed and direction in the upper layers 100 m we combine these results with hydrographic data in order to obtain an estimate of the mass transport transport across the mid atlantic ridge is based on recent sections fahrbach et al 1985 while transport in the northeastern north atlantic has been derived from the erika dan sections at 53 5 n and 59 5 n according to these two sections the return flow occurs mainly below 1000 m after water mass conversion in the northern areas the results imply that about 7 sv of atlantic water are transformed into deep water in the area between 53 5 n and 60 n

an automatic seismic event processing for detection and location the p m c c method we present a new method for automatic detection and location of seismic events recorded on a network it is based on a progressive study of the interstation correlation functions which leads to a consistent set of time delays when a seismic phase is present three different examples are processed on networks of different sizes

map of low frequency electromagnetic noise in the sky the earth s natural electromagnetic environment is disturbed by anthropogenic electromagnetic noise here we report the first results from an electromagnetic noise survey of the sky the locations of electromagnetic noise sources are mapped on the hemisphere above a distributed array of wideband receivers that operate in a small aperture configuration it is found that the noise sources can be localized at elevation angles up to 60 in the sky well above the horizon the sky also exhibits zones with little or no noise that are found toward the local zenith and the southwest of the array these results are obtained by a rigorous analysis of the residuals from the classic dispersion relation for electromagnetic waves using an array analysis of electric field measurements in the frequency range from 20 to 250 khz the observed locations of the noise sources enable detailed observations of ionospheric modification for example caused by particle precipitation and lightning discharges while the observed exclusion zones enable the detection of weak natural electromagnetic emissions for example from streamers in transient luminous events above thunderclouds

compositional controls on coexisting prehnite actinolite and prehnite pumpellyite facies assemblages in the tal y fan metabasite intrusion north wales implications for caledonian metamorphic field gradients the tal y fan intrusion is a 110 m thick sub concordant metabasite sheet intruded into volcaniclastic and pyroclastic rocks of ordovician age in north wales despite low grade metamorphism primary textural zones resulting from initial cooling of the sheet are preserved and retain primary mineralogical and chemical variations which influenced the nature and extent of metamorphic recrystallization this has resulted in a vertical sequence of secondary mineral assemblages through the intrusion during early hydrothermal alteration k feldspar replaced plagioclase micropheno crysts in the marginal and contact zones and olivine in the central zone was replaced by saponite subsequent regional metamorphism resulted in the development of metastable prehnite pumpellyite epidote assemblages in two sub zones characterized by high fe2o3 elsewhere the assemblage prehnite actinolite epidote developed except in the contact and marginal zones where activity of co2 suppressed both prehnite and pumpellyite both assemblages contain excess albite quartz and chlorite and on the basis of uniform mineral compositions over the area of an individual thin section are considered to represent buffered equilibrium assemblages indicative of prehnite pumpellyite and prehnite actinolite facies conditions a metamorphic temperature of 310 c at 1 85 kbar is obtained using the p t x grid of liou maruyama cho 1985 which implies a field gradient of 44 c km 1 assuming that metamorphism relates to burial an overburden thickness of 7 km is indicated total maximum thicknesses however of ordovician silurian and lower devonian strata in the area do not exceed 6 km indicating a field gradient of 52 c km 1 these relatively high gradients may possibly be related to concealed late caledonian intrusions or alternatively may result from high heat flow as a consequence of crustal thinning rapid sedimentation and intense magmatic activity in a marginal basin setting

diagenesis to metamorphism transition in an episutural basin the late paleozoic st mary s basin nova scotia canada the late devonian early carboniferous st mary s basin in the canadian appalachians consists of horton group fluviatile and lacustrine clastic rocks the basin occurs along the boundary between the avalon and meguma ter ranes and developed during coeval dextral shear along that boundary x ray diffraction reveals that the rocks contain ubiq uitous quartz k white mica and albite illite smectite mixed layers and chlorite are very common and na k mica kaolinite chlorite smectite mixed layers k feldspar berthierine and rutile occur in some samples crystal chemical pa rameters of white mica indicate the pressure and temperature of mineral growth and discriminate between diagenetic an chizone and low grade metamorphic processes kubler index values measured in the 5 a u peak and the presence of chlorite mica stacks are indicative of high anchizone epizone grades with a crystallinity crystal size and number of de fects that increases towards the chedabucto fault which defines the northern margin of the basin kubler index values measured in the 10 a u peak indicate that a late fluid rich event could have produced the observed illite smectite mixed layers the overall clay mineral content and the b cell dimension of the k white micas are typical of postdepositional evo lution in extensional sedimentary basins with high heat flow 35 8c km taken together our data record two superposed events related to deformation along the basin margins and coeval regional fluid flow in which retrograde reactions at tem perature t 300 8c regional syntheses indicate that this fluid flow may have occurred during epi sodes of late carboniferous dextral shear along the avalon meguma terrane boundary

observation of the circulation in the newfoundland basin in winter 1997 a hydrographic survey was performed in january february 1997 to document the winter circulation of the north atlantic current system in the newfoundland basin as part of the fronts and atlantic storm tracks experiment fastex eighty seven conductivity temperature depth ctd stations were occupied along a foursection trapezoid which spanned the northwest corner and the branching of the north atlantic current along 358w realistic sea surface temperature analyses were produced every 15 days using all available data collected in this area during the two months of the fastex experiment these maps were combined with sea level anomaly fields from the topex poseidon anders 2 satellites at the same time intervals to analyze the features of the main currents in the area and their evolution these combined analyses providing a coherent overview of the fronts and jets identified along the ship track and the ctd stations are further used to estimate their transports the general pattern is a 15 sv sv 106 m3 s21 transport by the north atlantic current at 478n 438w the existence of a recirculating gyre inside the northwest corner and a complex branching of the circulation associated with significant surface fronts the recirculating gyre forms a closed circulation in which a very deep warm eddy 100 km wide was sampled at the end of february its mixed layer was 800 m deep and its transport was 27 sv along 358w three fronts were identified between 458 and 528n the northern subarctic front the southern subarctic front and the mid atlantic front whose origins are precisely located the currents associated with these fronts transport 26 sv toward the east before crossing the mid atlantic ridge and supplying the eastern part of the north atlantic basin an important transport 14 sv was calculated near 46 8n 378w which mostly fed the current associated with the mid atlantic front

the structure of the temsamane fold and thrust stack eastern rif morocco evolution of a transpressional orogenic wedge abstract the structure of the temsamane fold and thrust stack corresponds to four units limited by anastomosing ductile shear zones cutting a trend of south verging recumbent folds this ductile stack was formed in an inclined left handed transpressional zone at the north african paleomargin during chattian to langhian times producing two main deformational events the first event d p produced a s p l p planar linear fabric generated in a non coaxial deformation with a top to the wsw sense of movement and was associated to metamorphic p t conditions varying from late diagenesis in the southernmost temsamane outcrops to epizone in the north according to the 40 ar 39 ar ages this deformation occurred at chattian aquitanian times the second deformational event d c event generated ene wsw trending folds with sse vergence and a set of anastomosing shear zones with s m l m planar linear fabric the latter units were generated at around 15 ma langhian and indicate a strong localization of the simple shear component of the transpression moreover this orientation is compatible with the kinematics of the temsamane detachment which can explain most of the uplift of the temsamane rocks from the middle to the uppermost crust the described evolution indicates that collision between the western mediterranean terranes and the north african paleomargin and the formation of the rifean orogenic wedge occurred at chattian to langhian times

style scale and significance of sand bodies in the northern and central belts southwest southern uplands sedimentological and biostratigraphical data from the rhinns of galloway and adjacent areas in sw scotland confirm that deep water depositional systems consistently operated along and were sourced from the northwestern margin of an asymmetrical basin during the late ordovician and early silurian while pelagic facies accumulated simultaneously to the se providing a scenario analogous to many modern trench systems most of the observed sedimentological anomalies with regard to this general model can be explained within the context of the varied styles of trench filling depositional systems briefly reviewed here and the major stratigraphic and sedimentologic features can be best explained in terms of a geotectonically evolving fore arc region two main phases of development are recognized a llandeilo late ashgill during this time interval the fore arc trench region was tectonically juxtaposed against an active continental margin arc small to medium scale se prograding sand rich fans were formed within a relatively narrow trench leading to axial diversion of the fans initially to ne but later mainly to sw simultaneously a coarse volcanilithic sediment apron flanking the arc migrated gradually northeastwards probably in response to relative fault displacement of the arc and trench b llandovery during this time interval the fore arc trench region was dominated by a variety of mainly fan type depositional systems which were exclusively sourced at least until the uppermost llandovery from the northwestern margin the juxtaposition of coeval depositional systems differing significantly in sedimentological style and composition strongly suggests that the llandovery sedimentation in this region occurred in several structurally separated sub basins within the main trench system

strain related differences in the crystal growth of white mica and chlorite a tem and xrd study of the development of metapelitic microfabrics in the southern uplands thrust terrane scotland tem and xrd techniques were used to study crystal growth characteristics of the fabric forming phyllosilicates which developed in response to low grade metamorphism and tectonic imbrication in part of the southern uplands thrust terrane prograde regional metamorphism ranging from late diagenesis through the anchizone to the epizone was accompanied by the development of a slaty cleavage which is commonly bedding parallel tem measured mean thicknesses of white mica and chlorite crystallite populations increase with advancing grade and correlate with xrd measured crystallinity indices analytical tem data show that prograde changes in composition lead to a net loss of si ca and minor fe from the fabric forming phyllosilicates white micas are paragonite poor phengites with a mean b lattice parameter of 9 037 a and indicate an intermediate pressure series of metamorphism with a field gradient of 25 c km chlorite compositions evolved from diabantite with intergrown corrensite to ripidolite over an estimated temperature range of 150 320 c field gradient and temperature estimates suggest that crystal growth and fabric development occurred at burial depths ranging from 6 km to at least 13 km in the thrust terrane during late diagenesis crystal growth of white mica and chlorite was predominantly a consequence of polytypic and phase transitions and resulted in similar size distributions which resemble typical ostwald ripening curves under anchizonal and epizonal conditions white mica grew more rapidly than chlorite because of its greater ability to store strain energy and recover from subgrain development as a result crystal thickness distributions are not typical of ostwald ripening in contrast chlorite crystals which grew under these conditions developed subgrain boundaries at high strain rates which were only partially recovered at low strain rates these retained dislocations reduce the crystallite thicknesses detected by tem and xrd compared with those of white mica these differences in strain induced crystal growth indicate that white mica illite and chlorite crystallinity indices are likely to show significant differences where low grade metamorphism is closely associated with tectonic fabric development

eddy kinetic energy of the north atlantic subpolar gyre from satellite altimetry the surface eddy kinetic energy field of the north atlantic subpolar gyre 40 65 n 5 60 w is studied using the altimetric satellites geosat 1987 1988 and ers 1 1992 1993 this is on the whole an area of low eddy activity previous studies of the north atlantic have usually concentrated on the highly variable gulf stream system we review what is known of the surface circulation of the region we confirm that there is a close relationship between the eddy kinetic energy and the mean currents and that it is strongly constrained by the topography the eddy field occurs in deep water and follows the contours particularly around the flemish cap high eddy kinetic energy is seen on the flanks of topography and is higher where the slope is steeper this is particularly clear on both east and west flanks of the rockall plateau interannual changes in the currents are revealed by the differences between the geosat and ers 1 eddy kinetic energy maps in some years 1988 and 1992 1993 the northern core of the north atlantic current nac usually assumed to be tied to the charlie gibbs fracture zone 52 n is considerably weaker and may not exist at all while in 1987 there is a distinct core here in 1988 and 1992 1993 the main eddy region shifts farther to the south to about 49 n in 1988 and 50 n in 1992 1993 in 1987 there is also a current core even farther south centered at about 47 n implying that in that year the nac is arranged into two distinct branches

interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data clay mineral crystallinity and crystallite domain size data determined by x ray diffraction xrd are methods extensively used in the characterization of very low grade metamorphic conditions however the lack of sufficient interlaboratory standardization has made comparisons between different research groups unreliable due to significant variations in numerical results obtained a consequence of the different machine conditions measurement methods and sample preparations used during analysis a calibration approach to the standardization of data using rock chip standards is presented which allows data sets produced by different research groups to be directly and quantitatively compared a standardized scale the crystallinity index standard cis is proposed with illite crystallinity anchizonal boundary limits of 0 25d 2 and 0 42d 2 and equivalent illite crystallite sizes of 52 and 23 nm respectively determined by the warren averbach method calibrating both old and new data will enable more reliable comparisons between similar and contrasting geological environments and should improve the accuracy and reliability of correlations made between xrd data and other indicators of very low grade metamorphism hence increasing the value of such clay mineral studies

a sequential back arc and foreland basin thrust duplex model for the southern uplands of scotland thrust imbrication of ordovician and silurian submarine fan sequences overlapping pelagic deposits in the southern uplands has been interpreted in terms of an accretionary prism formed above a nw directed subduction zone structural features invoked to support accretion are not definitive and could be explained in terms of a thin skinned thrusting model new palaeocurrent and compositional evidence from llandeilo to mid llandovery age turbidites in the northern part of the southern uplands proves interdigitation of sediments with strongly contrasting petrography turbidites derived from the south contain significant quantities of fresh andesitic detritus whereas those from the north form more mature quartz rich formations this implies a back arc situation the turbidites being deposited in a basin with a relatively mature continental landmass to the north and a rifted continental fragment containing an active volcanic arc to the south oblique collision of the opposing continental margins of the iapetus ocean during the llandovery caused the cessation of subduction underthrusting of the southern margin initiated a se propagating thrust stack which deformed the back arc basin sequence and may eventually have ramped over the eroded and faulted remains of the volcanic arc a southward migrating foreland basin formed ahead of the rising thrust stack and is now represented by the late llandovery hawick group and wenlock sequences mid to end silurian sinistral strike slip resulted from oblique collision and produced a transpressional regime during which reactivation of deep seated structures allowed the intrusion of lamprophyre dykes and granites

eastward jets over diverging isobaths with applications to the gulf stream past the grand banks a three dimensional primitive equation model is employed to investigate how an initially eastward jet responds to isobaths that diverge eastward this problem is investigated using first a barotropic model and then a baroclinic model in the barotropic regime the diverging isobaths force an initially supercritical jet to widen and become subcritical after a hydraulic jump increasing eastward advection of vorticity moves the diverging point eastward and narrows the jet locally but widens the jet farther downstream the incoming jet axis is fixed at a preferred latitude due to the steep meridional bottom slope upstream in the baroclinic regime the eastward divergence of the jet becomes much more pronounced this strong divergence leads to the bifurcation of the jet downstream the northern branch flows northeastward and the main branch continues eastward the former is a western boundary current along the northeastward continental slope the bifurcation of baroclinic jets is caused by hydraulic jumps reinforced by instabilities of the baroclinic current system among possible applications the model is particularly relevant to the bifurcation of the gulf stream to the south of the grand banks where the essentially zonal isobaths begin to bifurcate eastward

very low and low grade metamorphism in the trinity peninsula group permo triassic of northern graham land antarctic peninsula the permo triassic trinity peninsula group is a widespread regionally metamorphosed metasedimentary sequence in northern graham land antarctica which forms the local basement to the mainly jurassic cretaceous antarctic peninsula magmatic arc the metamorphic grade thermal evolution and pressure series of this major tectono stratigraphical unit are largely unknown determining the nature of the metamorphism has relied hitherto on conventional optical identifications of the major phases mainly in rare volcanic beds however diagnostic mineral parageneses are generally absent and the precise metamorphic grade is unknown or has to be inferred over large areas using white mica illite crystallinity of interbedded mudrocks the trinity peninsula group is now shown to have been pervasively altered mainly at anchizonal and epizonal grades conditions ranged from upper anchizonal in the northeast to thoroughly epizonal in the southwest outwith thermal aureoles near plutonic intrusions the alteration temperatures ranged mainly from 250 to 325 c exceeding 300 c in the highest grade epizone greenschist facies parts of the sequence the facies series k white mica b cell dimension measurements and mineral phases present are characteristic of an intermediate pressure series altered under moderate geothermal gradients 35 c km corresponding to burial depths of c 7 10 km unroofing and substantial erosion of the trinity peninsula group took place during polyphasal vertical tectonic movements linked to the development of the magmatic arc in northern graham land the geological setting of the trinity peninsula group is ambiguous and could have been a foreland or back arc basin or the mid to upper levels of an accretionary prism

synchronous very low grade metamorphism contraction and inversion in the central part of the welsh lower palaeozoic basin a metamorphic map white mica crystallinity based on 663 data points has been generated for the recently published british geological survey 1 50 000 geological sheets 178 llanilar and 179 rhayader epizone upper anchizone lower anchizone and sub anchizone are delineated metamorphic cross sections are drawn and superimposed on structural cross sections assumptions made in order to draw metamorphic cross sections are 1 the anchizone spans 100 c 2 the metamorphic field gradient was 36 ckm 1 3 metamorphic surfaces were initially generated parallel to the contemporary ground surface restoration of the sections indicates that at the time of metamorphism a contractional phase had begun because reverse movement on earlier extensional faults development of back thrusts footwall short cuts and limited growth of precursor folds had taken place metamorphism continued locally during later stages of the contractional phase as a strain related phenomenon finally tensional faulting followed the cessation of folding and metamorphism

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

the branching of the gulf stream southeast of the grand banks during march april 1987 101 hydrographic stations were occupied on three sections spanning a triangle between the azores faial the southern tip of the grand banks of newfoundland and bermuda information on the near surface processes in the interior of the triangle were obtained from 32 satellite tracked buoys deployed during the cruise and a composite infrared image based on cloud free noaa 9 data during april 1987 the data were combined to analyze the eddy field and the branching of the gulf stream into the north atlantic current and the azores current calculations of mass transports through the legs of the triangle gave a total of 46 sv supplied by the gulf stream 31 sv of which left the area as the north atlantic current and westwind drift north of the azores the remaining 14 sv continued towards east southeast as the azores current and southern recirculation additional conductivity temperature depth stations from a cruise in april 1986 into the same area allowed also study of the large scale circulation within that triangle in deeper layers the azores current appears as a baroclinic stream which reaches down to approximately 1000 m intensive mixing was observed at the continental slope of newfoundland between water of the labrador current and the gulf stream mixed water owing to cabbeling and consecutive convective mixing this water penetrates down to 2000 m depth and creates horizontal density gradients to the surrounding gulf stream water which intensifies the north atlantic current this process is considered to be an important energy source for this current

on the origin of the azores current the azores current south of the azores archipelago is part of the subtropical north atlantic gyre using an international hydrographic data set we analyze mean and seasonal geostrophic transport fields in the upper 800 m of the ocean in order to determine the origin of the azores current in the western basin and seasonal changes in the related flow geostrophic currents are obtained by using the method applied by stramma 1984 in the eastern basin the azores current is found to originate in the area of the southwest newfoundland rise figure 10 in winter an almost uniform current connects this region of origin with the azores current while a branching into two current bands is observed in summer with the southern band forming a marked cyclonic loop within the upper 800 m all of the transport in the northern band and about 70 of the transport in the southern band recirculates in the eastern basin additionally expendable bathythermograph data from the azores current region indicate an increase of eddy potential energy from winter to summer

the contribution of anisotropic conductivity in the ionosphere to lightning flash bearing deviations in the elf ulf range lightning flash bearing deviations in the elf ulf range are monitored at two independently operating measurement instruments in hollister california and silberborn germany the lightning flash bearing deviation at hollister exhibits a rotational dependence 12 associated with the conductivity contrast between the earth s crust and the nearby pacific ocean the bearing deviations at both stations exhibit a pronounced diurnal local time variation 11 this diurnal variation is attributed to the anisotropic conductivity in the ionosphere during day and nighttime conditions no bearing deviation dependency from the source receiver distance can be distinguished correction for the mean rotational dependence at hollister and the mean diurnal variation at both locations results in residual bearing deviations 10 which are related to the variability of anisotropic conductivity in the ionosphere on a subdiurnal time scale

high frequency variability of western boundary currents using ers 1 three day repeat altimeter data ers 1 three day repeat altimeter ocean products have been analyzed from september 3 to december 9 1991 in the high mesoscale energy areas of the world ocean the obtained height variability is comparable to that derived from 2 years of geosat altimeter data 17 day repeat while it is slightly lower elsewhere the data reveal some high frequency variability of western boundary currents but not the seasonal signals nor the low frequency mesoscale signal which dominates elsewhere isocorrelation maps show that the e folding time is around 10 to 15 days in strong currents the sea height variance integrated over all wavelengths in the frequency wavenumber spectrum corresponds to less than 5 of the total 3 month variance for periods shorter than 20 days up to 15 of this variance for periods shorter than 34 days which are respectively the nyquist frequencies of the topex poseidon and geosat data this signal covers a whole range of wavelengths that cannot be obtained from current meter data in the gulf stream area the total dynamic height signal is estimated by adding a climatological dynamic topography to the mesoscale variability near 60 w the height variations apparently correspond to meanders with periods of 30 to 40 days and latitudinal extension about 200 km they are consistent with westward propagation at about 10 cm s and their surface transport varies by about 50 on this timescale which is in agreement with in situ observations

pyroxenous greywackes in the southern uplands of scotland and their petrotectonic implications detrital clinopyroxenes occur abundantly in several greywacke formations in the southern uplands both as single grains and within andesite lithoclasts compositionally these pyroxenes fall into two main groups those from the oldest unit the early caradoc galdenoch formation were derived from a simple tholeiitic volcanic arc in contrast the pyroxenes in the younger portpatrick late caradoc and glenlee ashgill formations and the gala group early llandovery show initial strongly calc alkaline affinities followed by a more complex calc alkaline to transitional calc alkaline to tholeiitic volcanic arc signature the latter may be due to a mixture of calc alkaline and tholeiitic components a presently exposed source for the andesites has not yet been established although the ballantrae complex is a potential candidate for a tholeiitic component

transition from diagenesis to metamorphism in extensional and collision settings areas in which there is a transition from diagenesis to metamorphism occur in a variety of tectonic settings some of which are of an extensional character rather than the collision setting normally associated with regional metamorphism in collision settings the diagenetic to metamorphic transition is typically followed by a continuum into the highest grades of metamorphism the baric type is usually of an intermediate pressure variety and metamorphism occurs at a late stage in the tectonic cycle in extensional settings such as marginal basins a restricted facies series is developed that ranges from diagenetic levels up to a low greenschist facies maximum the metamorphism is normally of a low pressure type and develops early in the tectonic cycle these characteristics suggest that it is possible to subdivide broadly the field of low grade regional metamorphism into compressional orogenic and extensional settings

low frequency current variability at the straits of crete eastern mediterranean current meter data from six moorings are analyzed to study current variability at the straits of the cretan arc which connect the south aegean sea with the eastern mediterranean the three layers in which the current meters were deployed show different current characteristics the upper layer shows evidence of the asia minor current in the rhodes strait and a clockwise eddy in the karpathos strait water in the middle layer moves slowly into the south aegean the bottom current meters in kassos and antikithira straits recorded currents steady in amplitude and direction with speeds equal to or higher than those observed in the upper layer the observations suggest a significant outflow 0 5 sv of cretan dense water cdw to the levantine and ionian seas rotary empirical orthogonal functions are used to extract and describe the coherent part of the variability forty four percent of the total variability is described by the first three empirical orthogonal functions less than 20 of the current variability of the western strait is coherent with variability of the eastern straits the coherent part of the variability refers mainly to periods longer than 20 days the current meter data are compared with atmospheric pressure showing good correlation during the first period of the measurements when a major atmospheric pressure low passed over the aegean

use of the lattice parameter b 0 of dioctahedral illite muscovite for the characterization of p t gradients of incipient metamorphism the p t gradient or baric type of low grade metamorphic terranes can be characterized on the basis of cumulative frequency curves of the lattice parameter b0 of dioctahedral micas sassi and scolari 1974 which essentially reflects celadonite content and increases with pressure the method is here applied to illite muscovite of sub greenschist incipient metamorphism and low greenschist facies terranes from the marginal zones of the swedish caledonides swiss alps and venezuelan andes where the grade of metamorphism was determined on the basis of illite crystallinity

late quaternary sea surface conditions in the laurentian fan evidence from coccolith and dinocyst assemblages abstract the analyses of coccoliths and dinocysts from the images core md95 2033 collected on the laurentian fan 44 39 87n 55 37 21w water depth 1412 m in the northwest north atlantic provide a new dataset to assess the magnitude of climatic changes during the holocene with a millennial time resolution coccolith and dinocyst data were combined to reconstruct changes in past sea surface conditions in addition the dinocyst assemblages were used to reconstruct the sea surface temperature sst and salinity sss based on the modern analog technique the distribution of the coccolith and dinocyst assemblages suggests a succession of climatic events during the late quaternary and early holocene linked to change in the influence of the labrador current and or the st lawrence river discharge the dinocyst assemblages recorded a thermal optimum during the mid holocene in the late holocene coccolith concentrations show two peaks at 2 3 and 1 1 ky which coincide with the presence of species with different ecological properties likely due to the localized influence of the slope water jet swj current the presence of this current has played a role in the development of the coccolith and dinocyst assemblages and sst fluctuations especially in the last 2 ky overall the interaction between the st lawrence river the swj the lc and the nac has all controlled the sss ssts and the development of the coccolith and dinocyst assemblages confirming a significant regionalism of the entire area

incipient metamorphism in the lower palaeozoic marginal basin of wales a diagenctic through anchizone to epizone transition is demonstrated in pelitic rocks of the lower palaeozoic marginal basin of wales by examination of variations in phyllo silicate mineralogy illite crystallinity and bo parameter of white micas this transition represents a temperature range from 150 c to 400 c and the metamorphism is of a low pressure facies series type with a geothermal gradient of 40 ckm 1 variations in grade can be correlated largely with the original basin and shelf form suggesting a depth related metamorphism however in areas closer to the site of caledonian plate collision an increasingly syn tectonic metamorphic event is apparent correlation of pelite data with metabasite assemblages is variable the most consistent relationship being between epizone crystallinity values andepidote actinolite greenschist facies assemblages diagenetic clay mineral assemblages are found associated with prehnite pumpellyite assemblages in metabasites and it is suggested that the latter represent non buffered and therefore non diagnostic assemblages