tectonic interactions between india and arabia since the jurassic reconstructed from marine geophysics ophiolite geology and seismic tomography gondwana breakup since the jurassic and the northward motion of india toward eurasia were associated with formation of ocean basins and ophiolite obduction between and onto the indian and arabian margins here we reconcile marine geophysical data from preserved oceanic basins with the age and location of ophiolites in nw india and se arabia and seismic tomography of the mantle below the nw indian ocean the north somali and proto owen basins formed due to 160 133 ma n s extension between india and somalia subsequent convergence destroyed part of this crust simultaneous with the uplift of the masirah ophiolites most of the preserved crust in the owen basin may have formed between 84 and 74 ma whereas the mascarene and the amirante basins accommodated motion between india and madagascar east africa between 85 and circa 60 ma and 75 and circa 66 ma respectively between circa 84 and 45 ma oblique arabia india convergence culminated in ophiolite obduction onto se arabia and nw india and formed the carlsberg slab in the lower mantle below the nw indian ocean the nne ssw oriented slab may explain the anomalous bathymetry in the nw indian ocean and may be considered a paleolongitudinal constraint for absolute plate motion nw india asia collision occurred at circa 20 ma deforming the sulaiman ranges or at 30 ma if the hindu kush slab north of the afghan block reflects intra asian subduction our study highlights that the nw india ophiolites have no relationship with india asia motion or collision but result from relative india africa arabia motions instead key points we present a new tectonic model for the evolution of nw indian ocean subducted slab under the carlsberg ridge resulted from arabia india convergence

upper jurassic radiolarians from the naga ophiolite nagaland northeast india abstract radiolarians extracted from cherts collected from an ophiolitic melange near salumi nagaland ne india have well preserved tests and can be assigned to the upper jurassic kimmeridgian lower tithonian these are the first well preserved and clearly imaged radiolarians reported from the naga ophiolite they are significantly older than fossils previously reported from this melange and their ages are similar to those determined radiometrically from associated igneous units

using airborne lidar sensing technology and aerial orthoimages to unravel roman water supply systems and gold works in nw spain eria valley leon lidar technology based on earth s surface scanning allows the compilation of high resolution digital terrain models recently used in archaeological works for the discovery and description of heritage features such as ancient human made structures and building ruins it is particularly effective in areas with dense vegetation or difficult access where surveying becomes complicated among its main advantages over other traditional methods of archaeological research it highlights the possibility of controlling display parameters which in turn facilitates data analysis and interpretation in this study we present an integrated lidar and aerial photography data analysis in order to obtain a detailed map of ancient mining works within a small sector of the roman mining district in northwestern spain the presence of gold deposits led to intensive extractive work during the first century b p t although many of the mining activities were focused on the northwestern area of las medulas and omanas large deposits were also found along the duerna and eria river valleys our results complement previous work carried out in the eria area valderia providing new insights into the hydraulic engineering techniques and the geometry of the main roman exploitations this work highlights the scope of the ancient mining works and their impact on the landscape which are much greater and more important than previously thought

regional mapping of pre metamorphic spilitization and associated chemical mobility in greenschist facies metabasalts of the sw scottish highlands abstract both spilitic and non spilitic metabasaltic sills are hosted by greenschist facies metasediments in the sw scottish highlands spilitization is mainly characterized by enrichment in na 2 o elevated modal plagioclase and epidote segregations mapping of the spatial distribution of spilitic metabasalts reveals an ancient sub sea floor fluid cell centred on the extrusive tayvallich volcanics fluid circulation was most extensive at shallow levels where most sills were spilitized we attribute this to pervasive flow of saline fluid which was thermally driven by the cooling suite of lava flows and sills spilitization below this lithostratigraphic depth was restricted to only a few sills their spilitization is largely unrelated to specific properties of these sills e g width chemistry or host lithology we conclude that fluid channelling was an intrinsic property of sub sea floor fluid flow either at deeper levels or earlier during fluid circulation by profiling of the size distributions of relic phenocrysts in a partly spilitized sill we conclude that spilitization proceeds with the symmetric propagation of a spilitization front from the sill margins towards the sill interior based on chemical profiling across the margin of an epidote segregation we conclude that spilitization is associated with chemical transport on scales ranging from 0 1 to 10 m

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

terrain maps displaying hill shading with curvature article i nfo many types of maps can be created by neighborhood operations on a continuous surface such as provided by a digital elevation model these most commonly include first derivatives slope or aspect and second derivatives planimetric or profile curvature such variables are often used in geomorphic analyses of terrain first derivatives also provide subtle enhancements to hill shaded maps for example some maps combine oblique and vertical illumination with the latter reflecting variations in slope this study illustrates how second derivative maps in conjunction with hill shading can cartographically enhance topographic detail a simple conic model indicates that image tone edges where slope or aspect varies by less than 0 5 are visible on curvature maps hill shaded images combined with curvature enhance the continuity of naturally occurring tonal edges especially in strongly illuminated areas variations in planimetric and profile curvature seem to be especially effective at highlighting convergent and divergent drainages and variations in erosion rate between or within sedimentary units respectively shading curvature with consideration given to illumination models can add detail to hill shaded terrain maps in a manner similar to cognitive models employed by map viewers

mapping of muslim bagh ophiolite complex pakistan using new remote sensing and field data abstract tethys is a relational gis database that combines geophysical remote sensing geochemical and geochronological data developed as a flexible resource for studying magmatic and geodynamic responses to continental collisions in this paper we demonstrate utility of our database by integrating field remote sensing and structural data for detailed mapping and tectonic emplacement of muslim bagh ophiolite of western pakistan this ophiolite forms the uppermost part of a nappe pile which accreted onto the indian continental margin during the closure of the neo tethys during a pre terminal collision that predated the final closure of tethys during the major collision between india and eurasia utilizing the tethys landsat aster imagery and a digital elevation model developed from the aster data are used to characterize the lithology and structure of the area use of image processing techniques improved the geologic map of the area for a better understanding of the tectonic emplacement of the muslim bagh ophiolite for the first time we report that the dikes in the muslim bagh ophiolite are cutting the metamorphic sole our preliminary geochemical data for sheeted dike complex suggest chemical affinities with arc related rocks this observation suggests that dikes were intruded in an island arc environment soon after the ophiolite was formed

formerly emerging crustal blocks in the equatorial atlantic abstract anomalous crustal topographic highs exceeding the level predicted by the thermal contraction model by up to 2 3 km are observed along the romanche transform zone in the equatorial atlantic previous studies of shallow water reef limestones recovered from one of the shallowest sites on these crustal highs indicated that this site was at or above sea level 5 million years ago and subsided since at an average rate one order of magnitude faster than the subsidence estimated by thermal contraction of the crust seismic reflection profiles obtained across the romanche transform zone suggest that the anomalous highs are capped by reef limestones not only where limestones were actually sampled but also at other locations these findings support the idea that long segments of crust reached close to sea level in the past along the romanche transform zone the vertical crustal motions are probably caused by tectonism typical of long offset transforms inasmuch as the romanche has been a ridge ridge transform since the earliest stages of the opening of the equatorial atlantic it is likely that intense vertical tectonic motions occurred along it throughout the evolution of the atlantic support for this hypothesis is provided by the recovery during dsdp leg 4 of shallow water reef limestone of the eocene age from the summit of the north brazilian ridge along the western extension of the romanche fracture zone the presence of shallow or emergent crust across the equatorial zone during the early stages of opening had probably important consequences upon the water circulation between the north and the south atlantic and may even have provided land bridges for faunal migrations between africa and south america in early cenozoic times after the two continents had already separated

propagation of kuroshio extension meanders between 143 and 149 e a two dimensional array of current and pressure recording inverted echo sounders provided synoptic measurements of the upper and deep fluctuations in the kuroshio extension between 1438 and 1498e with mesoscale resolution downstream propagating meanders with periods of 3 60 days were always present between june 2004 and september 2005 propagation speeds were estimated by two methods spectral analysis of path displacements and complex empirical orthogonal functions ceof analysis of along path anomalies the two methods produced similar results phase speeds increased smoothly from 10 km day 21 0 12 m s 21 for meanders with wavelengths and periods l t 5 420 km 40 days to 35 km day 21 0 41 m s 21 for l t 5 220 km 6 days meanders this empirically derived dispersion relationship is indistinguishable from that obtained for gulf stream meanders downstream of cape hatteras the deep ocean was populated with remotely generated upstream propagating eddies composed of a nearly depthindependent current structure upper meandersand deep eddies jointly spun up when they encountered each other with the deep eddy offset about a quarter wavelengthahead of the upper meander subsequently as the upper and deep features moved past each other and the vertical offset changed intensification ceased

regional primitive equation studies of the gulf stream meander and ring formation region abstract primitive equation and quasi geostrophic eddy resolving open ocean models are used for hindcast studies in the gulf stream meander and ring formation region a feature model approach is used to initialize the models based on one month of observations during november to december 1984 flat bottom and topographic calculations are carried out using an initial gulf stream velocity profile based on the pegasus dataset all of the major events observed in the upper thermocline are reproduced by both numerical models the addition of bottom topography is shown to significantly alter the character of the deep velocity fields large basin scale circulations found near the bottom in both flat bottom calculations were replaced by energetic jets and eddies associated with the dominant spatial scales of the bottom topography use of the quasi geostrophic model to dynamically adjust the initial conditions for the primitive equation model is shown to reduce the growth of large scale meanders on time scales o

the nonnormality of coastal ocean flows around obstacles and their response to stochastic forcing abstract the effect of stochastic variability upon the wake downstream of a real headland is investigated from observations taken at bass point australia three sources of stochastic forcing are identified and quantified these being variability in the wind stress in the flow incident on the headland and that generated in the flow by complex reef topography at the headland s tip these sources of stochastic forcing are found to induce a significant degree of unsteadiness in a nonlinear numerical model of flow around bass point that in the absence of stochastic forcing simulates steady recirculating flow the observed stochastic variability of the flow incident on the headland is found to be larger than is necessary to support unsteadiness in the simulated straining zone the dynamics of the perturbation growth observed in the model are understood by applying the techniques of generalized stability theory to the associated tangent linear model tlm the eigenmodes of the tlm confirm that the system

trajectories in gulf stream meanders a simple model based on conservation of stream function and potential vorticity is used to derive theoretical estimates for the horizontal and vertical displacements of fluid particles in gulf stream meanders these displacements are given as functions of the meander s curvature and meridional displacement the theory also provides an estimate of the translation speed of the meander finally comparisons with rafos float trajectories and observational estimates of the components of the potential vorticity budget validate the theory

temporal variation of meandering intensity and domain wide lateral oscillations of the gulf stream the path of the gulf stream exhibits two modes of variability wavelike spatial meanders associated with instability processes and large scale lateral shifts of the path presumably due to atmospheric forcing the objectives of this study are to examine the temporal variation of the intensity of spatial meandering in the stream to characterize large scale lateral oscillations in the stream s path and to study the correlation between these two dynamically distinct modes of variability the data used for this analysis are path displacements of the gulf stream between 75 and 60 w obtained from avhrr derived advanced very high resolution radiometer infrared images for the period april 1982 through december 1989 meandering intensity measured by the spatial root mean square displacement of the stream path displays a 9 month dominant periodicity which is persistent through the study period the 9 month fluctuation in meandering intensity may be related to the interaction of rossby waves with the stream interannual variation of meandering intensity is also found to be significant with meandering being much more intense during 1985 than it was in 1987 annual variation however is weak and not well defined the spatially averaged position of the stream which reflects nonmeandering large scale lateral oscillations of the stream path is dominated by an annual cycle on average the mean position is farthest north in november and farthest south in april the first empirical orthogonal function mode of the space time path displacements represents lateral oscillations that are in phase over the entire study domain interannual oscillations are also observed and are found to be weaker than the annual oscillation the eigenvalue of the first mode indicates that about 21 5 of the total space time variability of the stream path can be attributed to domain wide lateral oscillations the correlation between meandering intensity and domain wide lateral oscillations is very weak

tectonic setting of the bela ophiolites southern pakistan abstract the bela ophiolites consist of a 3 5 km thick sequence of basaltic pillow lava inter flow sedimentary rocks chert argillite limestone and diabase gabbro sills debris of serpentinite up to kilometer sized blocks serpentinite carbonate breccia and less commonly of basalt gabbro peridotite pelagic limestone and their metamorphic equivalents occur throughout the ophiolite sequence and may form extensive horizons the age of the ophiolites as indicated by pelagic microfauna is aptian early maestrichtian the lava flows belong to a spilite keratophyre basaltic andesite suite of tholeiites enriched in fe tio 2 and other trace elements the lava flows although similar to the e type morb differ in details such as la ta ratio ranges 9 62 18 04 for the bela lavas versus 10 15 for the morb the diabase gabbro sills are similar to the associated lava flows however due to their relative enrichment in certain elements e g fe ti hf th and ta etc they may represent more fractionated late melts a comparison of the stratigraphic and structural features of the bela ophiolites with modern oceanic environments reveals that these ophiolites probably originated in a large oceanic fracture zone leaky transform this is based on lithotectonic features such as the common occurrence of debris of foliated serpentinite and serpentinite carbonate breccia bearing rocks in the ophiolite sequence and on geodynamic considerations the fracture zone ancestral to the bela ophiolites probably acted as a boundary between the indian and the neo tethys plates during the cretaceous analogous to the present day owen fracture zone which separates the indian and the arabian plates this ancestral fracture zone was destroyed when transform movement gave way to oblique convergence culminating in the ophiolite obduction in paleocene early eocene time the ophiolite obduction on the west indian continental margin was preceded by alkaline wpb type volcanism which is represented by the porali basalts the bibai lavas and the deccan basalts

petrology of the dykes from the waziristan ophiolite nw pakistan abstract the waziristan ophiolite is located in the suture zone between the indian plate to the east and afghan block to the west it is highly dismembered and divisible into three main sheets or nappes which from east to west are the vezhda sar nappe entirely comprised of pillow basalts the boya nappe made up of ophiolitic melange with an intact section in its basal part and the datta khel nappe consisting mainly of sheeted dykes with smaller proportions of other components faunal evidence suggests that the ophiolite is of tithonian valanginian age it was thrust over the mesozoic shelf slope sediments of the indian plate to the east during the paleocene and is unconformably overlain by sedimentary rocks of early to middle eocene age to the west beside the sheeted dykes best exposed in the hanging wall of the datta khel thrust ene of datta khel the ophiolite also contains isolated dykes these are doleritic and basaltic in composition the dykes contain high na 2 o contents and high feo t mgo and lile hfse ratios and low tio 2 2 o contents non depletion of nb and high lile hfse ratio negate respectively an island arc or mid ocean ridge setting for these dykes enrichment in the lile suggests the involvement of a crustal component driven by fluids along the subduction zone several geochemical parameters suggest that the dykes of waziristan ophiolite have transitional characteristics between mid ocean ridge basalt and island arc tholeiite it is therefore proposed that these dykes may have originated in a back arc basin tectonic setting

a multidisciplinary approach in wetland geoarchaeology survey of the missing southern canal connection of the fossa carolina sw germany abstract in this manuscript we document a multidisciplinary approach in wetland geoarchaeology for detecting artificial structures in a middle european floodplain by means of a large set of different prospection methods cadastral analysis aerial archaeology lidar squid based magnetic prospection electrical resistivity tomography seismic refraction tomography ground penetrating radar and a subsequent geoarchaeological drilling campaign we provide an overview about the potentials and limits of the applied methods our site specific aims focus on the fossa carolina charlemagne s shortcut for linking the rhine main and the altmuhl danube inland navigation systems during the early middle ages our results show that altmuhl meander loops were quasi stable since carolingian times and that an altmuhl floodplain crossing trench of at least 650 700 m was required for linking the altmuhl river with the archaeological known southernmost position of the existing carolingian canal however our large set of remote sensing and geophysical prospection tools and the corresponding drilling campaign do not show any evidence for the missing carolingian trench within the altmuhl floodplain our results support the idea that the carolingian canal was never entirely completed although large parts of the canal were almost finished in the northern sections

machine learning based mapping of micro topographic earthquake induced paleo pulju moraines and liquefaction spreads from a digital elevation model acquired through laser scanning abstract the advent of public open source airborne laser scanning produced digital elevation models als dem has provided new perspectives on glacial geomorphology in the nordic countries seismically induced micro topographic paleo landforms can now be identified and mapped throughout the former fennoscandian ice sheet allowing spatial safety assessment for nuclear waste disposal automated machine learning techniques enable recognition of these fine scale geomorphological features efficiently and in a consistent way nationwide the current study focuses on automated recognition of paleo liquefaction spreads and pulju moraines in northern finland geomorphometric variables in different cell sizes were first derived from the 2 m als dem by gabor and principal curvature filtering to emphasize the elevational multi scale texture of these paleo seismic landforms the gabor textural variables were considered as a baseline method and the principal curvature features including maximum and minimum curvature were used because they have previously been proven critical in recognition of concave and convex elongated features both sets of raster variables were then turned into histogram based features and input into a non linear supervised multilayer perceptron early stop committee which is a neural network classifier the leave one out cross validation performance results indicated principal curvature features to be highly successful with 94 accuracy principal curvatures provided a clear improvement to gabor based features which provided significantly lower accuracies between 83 and 85 the study demonstrates the high success of supervised neural network based classification of als dem data and derived textural features capturing the multi scale nature of the micro topographic liquefaction spreads and pulju moraines the approach could be utilized for time efficient mapping of these paleo seismic geomorphologies to complete paleo seismic databases in formerly glaciated regions

sea level variabilities in the gulf stream between cape hatteras and 50 w a geosat study sea level residuals relative to a 2 year mean sea level in the gulf stream downstream of cape hatteras between 80 w and 50 w longitude are studied using geosat altimetry between november 1986 and december 1988 spectral slopes computed at four nominal locations along the gulf stream 72 w 65 w 60 w and 55 w range between 1 5 and 0 9 significantly less steep than the 2 5 spectral slope found at bermuda because of increased short wavelength energy the spectra tend to become more white going eastward but this trend is not statistically significant energy at the annual cycle decreases eastward from around 40 of the total variance at 72 w to 20 of the total variance at 55 w maximum residual geostrophic sea surface velocities associated with the annual cycle were of the order of 70 cm s comparison between the gulf stream path from sea level residual maps and the north wall edge observed from noaa infrared ir imagery shows an rms difference of 49 km between 75 w and 60 w longitude but not all sea level maps show a clearly defined gulf stream using the ir estimates for gulf stream position sea level residuals were modeled as the meandering of a sea level front shaped as 0 5 m tanh x x0 50 km sin with the angle between the geosat track and the gulf stream edge and x0 is based on the observed ir north wall positions this showed that the annual signal in terms of the location and phase of its maxima is dominated by the meandering of the gulf stream

ensemble based estimates of the predictability of wind driven coastal ocean flow over topography abstract the predictability of coastal ocean circulation over the central oregon shelf a region of strong wind driven currents and variable topography is studied using ensembles of 50 day primitive equation ocean model simulations with realistic topography simplified lateral boundary conditions and forcing from both idealized and observed wind time series representative of the summer upwelling season the main focus is on the balance relevant to practical predictability between deterministic response to known or well predicted forcing uncertainty in initial conditions and sensitivity to instabilities and topographic interactions large ensemble and single simulation variances are found downstream of topographic features associated with transitions between along isobath and cross isobath flow which are in turn related both to the time integrated amplitude of upwelling favorable wind forcing and to the formation of small scale eddies simulated predictability experiments are conducted and model fo

early cretaceous radiolarians from the spongtang massif ladakh nw india implications for neo tethyan evolution abstract the discovery of two early cretaceous mid valanginian mid aptian range radiolarian faunal assemblages from ribbon bedded cherts collected near photoskar in northern ladakh nw india provides the first robust biostratigraphic age constraints associated with the spongtang massif this klippe of relict neotethyan suprasubduction zone ophiolitic rocks and related arc volcanic rocks crops out 30 km south of the indus suture in ladakh the radiolarian assemblages the age assignment of which lies between published radiometric ages provide new constraints on the evolution of this intra oceanic island arc system critically from them it can be inferred that the system was appreciably long lived jurassic cretaceous and more continuous than is commonly considered

magma supply in back arc spreading centre segment e2 east scotia ridge segment e2 is situated in the back arc east scotia ridge the segment is unusual in that it has an axial topographic high underlain by a seismically imaged melt lens the axis of the segment which is 70 km long was sampled at 2 km spacing there is strong correlation between compositions and bathymetry and there is no evidence that lateral flow of magmas along dykes within the segment was more than 25 km magmas are more evolved towards the summit indicating that magma fractionation took place within the imaged melt lens na8 0 is roughly constant at 2 6 implying uniform degree of partial melting except for some samples at the summit that have na8 0 2 2 compositions closest to n morb occur at the segment tips and lree hree ratios increase toward the summit none of the magmas were derived from depleted sub arc mantle nevertheless most compositions in the segment were modified by slab derived components the low na8 0 samples have high ba nb compared with the rest of the segment dredged lavas from the lateral flanks of the summit have the most extreme compositions including ones derived from plume mantle and are end members for magma mixing processes that controlled compositions

lake or floodplain mid holocene settlement patterns and the landscape dynamic of the ižica floodplain ljubljana marshes slovenia the ljubljana marshes ljubljana moor is a large wetland in the southern part of the ljubljana basin in the central part of slovenia with well preserved archaeological evidence of settlements the data have traditionally been interpreted as the remnants of the prehistoric pile dwelling settlements located in a shallow lake in this paper we present new data that challenge these interpretations an aerial lidar survey of the i ica floodplain on the ljubljana marshes has revealed a complex topography of stratified palaeochannels the 14c dates of the channel infills suggest that the first phase of the palaeochannels can be dated to before 3770 cal bc which is contemporary with eneolithic settlements located on its banks we suggest that settlements were located in the floodplain next to active rivers and not in the lake as was traditionally hypothesised

prediction of the gulf stream path from upstream parameters a linear wiener least squares optimal filter is used to predict the path of the gulf stream in the region between cape hatteras and 70 w using upstream inlet conditions as filter inputs although position angle curvature geostrophic velocity and curvature vorticity measured at 73 w were tested as multiple inlet parameters it was found that inlet position alone was the best predictor with inlet position as the predictor this filter is equivalent to propagating meanders downstream with a typical phase speed and growth rate forecasts of the downstream path position are produced more accurate than persistence 12 days in advance at 140 km from the inlet 24 days in advance at 240 km from the inlet and 28 days in advance at 340 km from the inlet

space time interpolation of oceanic fronts oceanic temperature fronts observed through composite infrared images from the avhrr satellite data are fragmented due mostly to cloud occlusion the sampling frequency of such frontal position observations tends to be insufficiently high to resolve dynamics of the meandering features associated with the frontal contour so that contour reconstruction using a standard space time smoothing often leads to introduction of spurious features augmenting space time smoothing with a simple point feature detection matching scheme however can dramatically improve the reconstruction product this paper presents such a motion compensated interpolation algorithm for reconstruction of open contours evolving in time given fragmented position data the reconstruction task is formulated as an optimization problem and a time sequential solution which adaptively estimates feature motion is provided the resulting algorithm reliably interpolates position measurements of the surface temperature fronts associated with the highly convoluted portions of strong ocean currents such as the gulf stream and kuroshio

early proterozoic oceanic crust in the northern colorado front range implications for crustal growth and initiation of basement faults 1 early proterozoic oceanic crust exposed in a shear zone in the northern colorado front range provides insight into the tectonic evolution of the colorado province tectonically intermingled mylonitic amphibolite locally pillowed metagabbro clinopyroxenite metachert and melange are preserved within the buckhorn creek shear zone west of fort collins whole rock geochemical data support formation of the igneous protoliths in an oceanic environment major and trace element data overlap samples from modern oceanic ridges and are distinct from modern arc trends metagabbros and clinopyroxenites preserve a subhorizontal lineation defined by igneous pyroxenes core and mantle microstructures indicate initial deformation at temperatures 900 c secondary amphiboles define both subhorizontal and subvertical lineations kinematic analysis indicates that the rocks experienced e w strike slip deformation prior to and during amphibolite facies metamorphism followed by n s shortening 40ar 39ar data from secondary hornblende yield age steps as old as 1 9 ga based on the chemical data and kinematic evidence for strike slip deformation we propose that the buckhorn creek rocks originated at an oceanic ridge transform intersection the high t pyroxene fabrics formed during ocean floor deformation prior to 1 7 ga regional deformation of the colorado province the buckhorn creek fragment likely represents original oceanic basement for 1 8 1 7 ga arc magmatism and sedimentation that ultimately formed the colorado province continental crust reactivation of original oceanic fracture zones may be responsible for the network of regularly spaced northeast trending shear zones in colorado once formed subvertical transform faults are likely to survive the transition from oceanic to continental crust and persist as long lived crustal discontinuities

sedimentary fabrics in alpine ophicalcites south pennine arosa zone switzerland many ultramafic complexes in the south pennine nappes of eastern switzerland are covered by serpentinite breccias known as ophicalcites the breccias are overlain by radiolarites or younger oceanic sediments their fabric and their components document a combined tectonic sedimentary origin of the breccias in the davos area the breccias occur along distinct zones in the ultramafic host rock typically nonfragmented peridotite serpentinite grades rapidly through a narrow zone of host rock cut by different generations of dikes into complex breccias dominated by a carbonate matrix the breccias are of polyphase origin as shown by the different phases of fragmentation and generations of cementation and sediment infill these are distinguished by color differences and by a bimodal grain size distribution that also exhibits geopetal structures comparison with breccias from present day oceanic fracture zones suggests that the tethyan serpentinite breccias may have formed in a transform setting a sinistral transform margin along the northern edge of the apulian microplate or promontory is in line with current plate kinematic reconstructions

profiling the gulf stream with a current meter mooring a current meter mooring was deployed for one year at the mean position of the gulf stream at 68 w with instruments from 400 m to 4000 m it provides the first unambiguous evidence that the gulf stream extends from top to bottom of the water column using the strong cross stream temperature structure to derive a horizontal coordinate related to temperature we estimate the width and transport of the gulf stream for four individual events and we determine an average profile of the vertical and cross stream structure of the gulf stream a conservative estimate of transport for this average profile indicates that the gulf stream has a transport of 103 106 m s 1 at 68 w

meanders of the gulf stream downstream from cape hatteras 1975 1978 abstract weekly gulf stream paths within 1000 km downstream of cape hatteras were obtained for 1975 78 from the navy s weekly eofa charts based on satellite ir imagery they displayed two dominant meander modes first a standing meander energetic over periods between 4 months and at least 4 years and second down stream propagating meanders that were most energetic at periods of several weeks the long period standing meander was confined between nodes located at the separation point near cape hatteras i e where the stream s mean path turns seaward and at a point about 600 km farther downstream the rms amplitude was 36 km at the antinode the amplitude of propagating meanders increased rapidly in the first 200 km downstream of the separation point where the capture of warm core eddies was common farther down stream the predominant meanders had a wavelength averaging 330 km a period averaging 1 5 month a phase speed averaging 8 cm s 1 a downstream group speed averaging 17 cm s 1 and downstrea

review of oceanic transform activity and development oceanic transforms generally have a complex morphology and structure and they do not conform to the ideal concept of simple fractures that exactly follow small circles centered on euler poles of relative plate motions it is proposed that the special properties of transforms arise because they are inherently leaky i e new plate area forms along them as transforms have finite widths the adjacent ridge tips are at different distances from the euler poles and the plate boundaries along transforms are slightly oblique to the direction of plate motions such that new plate area forms along them however along transforms the normal process of seafloor spreading is interrupted and new plate area forms by a different process transforms are underlain by crust consisting of variable proportions of a material emplaced in the transform domains and b stretched ridge generated crust the transform structure is further modified by shearing deformation related to irregularities of lateral faults and because of propagation of adjacent ridges transform leakiness is not considered to result merely from changes of plate motions though such changes will influence transform structure but it reflects the segmented structure of mid oceanic ridges the persistence of transforms and their migration in the absolute reference frame with a component perpendicular to their strikes shows that the ridge structure is decoupled from flow in deeper levels thermal anomalies along transforms especially enhanced heat losses stabilize the segmented ridge structure

estimates of the geostrophic stream function in the western north pacific from xbt surveys the upper ocean temperature and dynamic height fields are correlated in the western north pacific ocean this relationship can be used to map a relative geostrophic stream function of the kuroshio extension using temperature data from expendable bathythermograph xbt surveys we have examined the ability of the north pacific ship of opportunity xbt program known as transpac to carry out this procedure estimates of 600 1200 dbar geostrophic shear were generated from the xbt data utilizing objective mapping techniques these estimates were compared with measured currents at 600 m relative to 1200 m along 152 e from 27 n to 42 n the estimated and measured relative currents are positively correlated with an rms error of 6 cm s over a measured dynamic range of 30 cm s however the xbt estimated shears consistently underestimate the measured values by a factor of 2 to 3 the underestimate of the amplitude is the result of both undersampling and mapping produres that eliminate high wavenumber contributions of the dynamic height variability these factors appear to be responsible for previous differences in amplitude between directly measured and transpac xbt estimated values of relative eddy kinetic energy and reynolds stress the transpac xbt survey can only monitor qualitatively the dynamic topography of the kuroshio extension meanders and rings the variability outside of the extension with a temperature range of 3 c cannot be resolved because of inaccuracies in the temperature dynamic height relationship to monitor the kuroshio extension variability in the future it is recommended that transpac xbt resources in the western north pacific concentrate on obtaining a denser sample of the field during the fall and winter seasons because of incomplete ship track coverage in spring and summer

mesozoic cenozoic rift drift sequence of asian fragments from gondwanaland abstract the university of cambridge atlas map plotting computer program has been used to plot a reconstruction of the dispersal of continental blocks from eastern gondwanaland from the late jurassic 160 ma until the late miocene 10 ma the geological basis for the reconstruction rests on the concept of south tibet burma western thailand malaya and sumatra having been part of the eastern gondwana continent during the late palaeozoic and early mesozoic the reconstruction is also based on the view that these asian continental blocks were rifted from eastern gondwanaland in the late jurassic this rifting episode gave rise to the continental margin of central new guinea and northern australia it was associated with the sea floor spreading anomalies preserved in the floor of the northeastern indian ocean the model considers the indication of crustal uplift in the middle jurassic followed by profound subsidence in the cretaceous and palaeogene exposed in the islands of the outer banda arc from seram to timor and the similar jurassic cretaceous facies in eastern sulawesi implies that these areas formed part of this rifted northern margin of australia in the jurassic subsequent tectonic collision and associated major strike slip movements have deformed and disrupted these rock sequences during the cainozoic the date of the rifting that removed south tibet burma western thailand and malaya from gondwanaland is controversial the indications in favour of the rifting episode having occurred in the jurassic rather than in the permo triassic are stratigraphie structural observations on the northwestern australian shelf in the banda arc and in central new guinea the identification of the continental blocks removed by this rifting is based partly on stratigraphie correlation with the banda arc and new guinea and partly on indications that the age of collision of tibet burma western thailand and malaya with asia was a late cretaceous event and not triassic jurassic as is generally held there are very few reliable land based palaeomagnetic measurements to constrain the movements of these dispersed continental fragments from gondwanaland the computer generated map reconstructions put forward here fit the available indian ocean sea floor spreading data although they are not unique solutions much of the critical ocean floor data associated with the rifting and dispersal of these continental fragments has been destroyed in the tectonic collision processes that occurred at the asian continental margin

the nonlinear optimal triggering perturbation of the kuroshio large meander and its evolution in a regional ocean model abstractbased on the regional ocean modeling system roms and the conditional nonlinear optimal perturbation cnop method we explore the nonlinear optimal triggering perturbation of the kuroshio

rapid perturbation growth on spatially and temporally varying oceanic flows determined using an adjoint method application to the gulf stream abstract the stability of the gulf stream flow predicted by a nonlinear quasigeostrophic model is examined by employing an iterative method which uses both the tangent linear equations and the adjoint tangent linear equations of the quasigeostrophic model the basic state flow is the model s representation of the gulf stream as observed during january and february 1988 the growth of perturbation energy is examined as a measure of disturbance growth and linear perturbations are found that are optimal in the sense that they maximize the growth of perturbation energy the structures of optimal perturbations are compared with the structure of the normal modes the optimal perturbations are found to be mere localized and to grow much more rapidly than the normal modes optimal perturbations are of interest because they can be used to plan tight constructive upper bounds on the growth of perturbations to ocean currents such as the gulf stream and they provide valuable information about the predictability of

gulf stream meanders observations on propagation and growth we present a new method for continuously tracking the location of the gulf stream using a moored array of inverted echo sounders time series of lateral displacements of the front shown accurate to 8 km have been collected along three sections spaced 100 150 and 200 km downstream ne of cape hatteras north carolina for a period of 12 months these records are highly coherent at all periodicities longer than 4 days from the observed phase lags a dispersion relationship is presented for the meanders as the period and wavelength t h increase from 4 days 180 km to 30 days 600 km the phase speed decreases smoothly from 40 to 20 km d the meanders exhibited rapid growth at periods longer than 4 days doubling in variance in each 50 km step downstream this downstream growth is most appropriately described by a spatial e folding scale k 400 km for t x 14 days 400 km from an array of seven inverted echo sounders ies and three deep current meters deployed 100 to 200 km northeast of cape hatteras in 2000 4000 m water this array continu ously monitored the path of the gulf stream and the deep currents under it on four deployment and recovery cruises to the area expendable bathythermograph traces xbt and hydrographic data were collected to survey the temperature and density structure along the stream path and on sections normal to it after a brief review of earlier studies on meanders this paper presents a discussion of the measurement techniques using ies in the gulf stream we show by direct compari sons with traditional measurement methods that 1 each ies produces a continuous record of the thermocline depth here taken to be the 15oc isotherm for subsequent comparison with standard methods of determining the position of the north wall of the stream with accuracy of 20 m in a range of variation of 800 m and 2 the array of ies s paired across the stream produces continuous estimates of the stream position with 8 km accuracy the results from the three ies sections located 100 150 and 200 km downstream of cape hatteras show very high coherence throughout the array with rapid 20 to 40 km d l translation of the meanders downstream accompanied by rapid growth of the lateral displacements doubling in variance with each 50 km step downstream in a companion paper w e johns and d r watts manuscript in preparation 1982 we discuss the current meter records and the relationship of the deep currents to gulf stream meanders 1981 they have wavelengths of 150 200 km and propagate downstream at rates of approximately 30 40 km d downstream of cape hatteras the envelope of meandering broadens greatly to 200 300 km figure 1 and the stream can shift through more than its own width in the early shipboard surveys fuglister and worthington 1951 fuglis ter 1963 the path of the stream south of nova scotia was dominated by long wavelength 400 km large amplitude meanders those which were studied in detail were found to be quasi stationary and were characterized by a slowly evolving baroclinic field indicating temporal growth far ther upstream near 72ow however significant eastward propagation was observed one meander crest moved at a rate of approximately 17 km d for 3 days fuglister and worthington 1951 hansen 1970 later conducted monthly path surveys between 75 o and 55ow for 1 year with weekly surveys over a 2 month period using a towed thermistor he found meanders on appreciably shorter scales with wave lengths ranging from 200 to 400 km mean downstream propagation rates of 5 10 cm s and spatial growth rates of 2 x 10 3 km were estimated by constructing lines of constant phase between features on successive path se quences the rapid evolution between monthly paths how ever produced considerable ambiguity in identifying and tracking events weekly paths evolved more continuously and were apparently not aliased by higher frequency wave number phenomena

a tectonic model for ridge transform ridge plate boundaries implications for the structure of oceanic lithosphere abstract the first order geologic and morphologic relationships at along and proximal to ridge transform ridge plate boundaries are used to construct an empirical and speculative tectonic model the distinctive but variable morphotectonic fabric and crustal structure of the transform domain are the product of a tectonic continuum that ranges from very slow rates of strain associated with very thick edges of lithosphere slowly slipping ridge transfrom ridge plate boundaries to extremely high rates of strain associated with very thin edges of lithosphere fast slipping ridge transform ridge plate boundaries the geometry of a ridge transform intersection necessitates the juxtaposition of a relatively cold thick edge of lithosphere against the truncated end of an accreting plate boundary the cold face of lithosphere cools the adjacent wedge of asthenosphere rising beneath the axis of accretion and restricts the amount of partial melting thus attenuating the volume of basaltic melt segregated from the asthenosphere per unit time the shallow level manifestation of this cold edge effect is a thinner oceanic crust at depth the evolving lithosphere thickens rapidly as the cold edge is approached creating changes in the properties of the young lithosphere and forming a weld of upper mantle material against the cold edge of truncating lithosphere the ridge transform weld of upper mantle material creates a shear couple in the lithosphere underlying the intersection resulting in the progressive reorientation of the maximum tensile stress from normal to the ridge axis at some distance from the ridge transform intersection to an oblique angle near the boundary the brittle carapace of oceanic crust that overlies the mantle weld will deform accordingly with the development of oblique dip slip faults the model predicts that the geologic expressions of this cold boundary effect will become more dramatic with increasing thickness of the truncating edge at very slow rates of accretion 100 km juxtapose thick 30 50 km edges of lithosphere against the accreting plate boundary all but nullifying the processes that lead to the emplacement of normal oceanic lithosphere in this environment a relatively strong mantle weld will form at the ridge transform intersection and the thick edges of opposing lithosphere along the length of the transform will tend to confine the strike slip tectonism to a relatively narrow and temporally stable principal transform displacement zone in contrast at very fast rates of accretion large offset transforms 100 km place relatively thin edges of lithosphere

alteration and mineralization of an oceanic forearc and the ophiolite ocean crust analogy mineralogical chemical and isotopic o c s and sr analyses were performed on minerals and bulk rocks from a forearc basement section to understand alteration processes and compare with mid ocean ridges mor and ophiolites ocean drilling program hole 786b in the izu bonin forearc penetrates 103 m of sediment and 725 m into volcanic flows breccias and basal dikes the rocks comprise boninites and andesites to rhyolites most of the section was affected by low temperature 100 c seawater alteration with temperatures increasing downward the rocks are partly 5 25 altered to smectite fe oxyhydroxide calcite and phillipsite and exhibit gains of k rb and p loss of ca variable changes in si na mg fe sr and y and elevated 18o and 87sr 86sr higher temperatures 150 c in the basal dikes below 750 m led to more intense alteration and formation of chlorite smectite corrensite albite k feldspar and quartz chlorite a 5 m thick hydrothermally altered and pyritized zone at 815 m in the basal dikes reacted with mixtures of seawater and hydrothermal fluids to mg chlorite albite and pyrite and gained mg and s and lost si and ca focused flow of hydrothermal fluids produced serialization halos na k sericite quartz pyrophyllite k feldspar and pyrite along quartz veins at temperatures of 200 250 c high 87sr 86sr ratios of chloritized 0 7055 and sericitized 0 7065 rocks indicate involvement of seawater via mixing with hydrothermal fluids low 34s of sulfide 2 to 5 5 and sulfate 12 5 are consistent with input of magmatic so2 into hydrothermal fluids and disproportionation to sulfide and sulfate alteration processes were generally similar to those at mors but the arc section is more intensively altered in part because of the presence of abundant glassy rocks and mafic phases the increase in alteration grade below 750 m and the mineralization in the basal dikes are analogous to changes that occur near the base of the volcanic section in mor and the troodos ophiolite

petrogenesis of late cretaceous lava flows from a ceno tethyan island arc the raskoh arc balochistan pakistan abstract the raskoh arc is about 250 km long 40 km wide and trends in an ene direction the oldest rock unit in the raskoh arc is an accretionary complex early to late jurassic which is followed in age by kuchakki volcanic group the most wide spread unit of the raskoh arc the volcanic group is mainly composed of basaltic to andesitic lava flows and volcaniclastics including agglomerate volcanic conglomerate breccia and tuff with subordinate shale sandstone limestone and chert the flows generally form 3 15 m thick lenticular bodies but rarely reach up to 300 m they are mainly basaltic andesites with minor basalts and andesites the main textures exhibited by these rocks are hypocrystalline porphyritic subcumulophyric and intergranular the phenocrysts comprise mainly plagioclase an 30 54 in nok chah and an 56 64 in bunap they are embedded in a micro cryptocrystalline groundmass having the same minerals apatite magnetite titanomagnetite and hematite occur as accessory minerals major trace and rare earth elements suggest that the volcanics are oceanic island arc tholeiites their low mg 42 56 and higher feo total mgo 1 24 2 67 ratios indicate that the parent magma of these rocks was not directly derived from a mantle source but fractionated in an upper level magma chamber the trace element patterns show enrichment in lile and depletion in hfse relative to n morb their primordial mantle normalized trace element patterns show marked negative nb anomalies with positive spikes on k ba and sr which confirm their island arc signatures slightly depleted lree to flat chondrite normalized ree patterns further support this interpretation the zr versus zr y and cr versus y studies show that their parent magma was generated by 20 30 melting of a depleted mantle source the trace elements ratios including zr y 1 73 3 10 ti zr 81 59 101 83 ti v 12 39 30 34 la yb n 0 74 2 69 ta yb 0 02 0 05 and th yb 0 11 0 75 of the volcanics are more consistent with oceanic island arcs rather than continental margin arcs it is suggested that the raskoh arc is an oceanic island arc which formed due to the intra oceanic convergence in the ceno tethys during the late cretaceous rather than constructed on the southern continental margin of the afghan block as claimed by previous workers it is further suggested that the semail zagros chagai raskoh muslim bagh and waziristan island arcs were developed in a single but segmented cretaceous ceno tethyan convergence zone

vertical crustal movements at the vema fracture zone in the atlantic evidence from dredged limestones abstract a crustal block shallower by over 3 km than the level predicted by the thermal contraction model for the ocean crust is located on the southern side of the vema transform in the atlantic lithology magnetic and gravity data suggest the anomalous block is an uplifted piece of crust and upper mantle and not a constructional volcanic feature the crest and upper slopes of the anomalous block are capped by shallow water reef limestones determination of paleofacies and ages of samples of these limestones suggest that 1 a the crest of the anomalous crustal block reached sea level and was exposed subaerially in middle pliocene time about 3 m y ago and subsequently sank to its present depth at an average rate of about 0 3 mm year that is a rate one order of magnitude faster than that predicted by the thermal contraction model for crust of the same age 2 b the anomalous block reached at or above sea level either continuously or intermittently throughout the late miocene from roughly 10 m y ago 3 c paleocene sediments dated at about 55 58 m y have been recovered from the uplifted block where assuming a spreading rate of 1 1 cm year the crust should not be more than about 35 m y old vertical crustal movements at the vema transform provide an example of vertical tectonism in the large oceanic transform fracture zones

a field chemical and stable isotope study of subseafloor metamorphism of the josephine ophiolite california oregon the josephine ophiolite is a large complete ophiolite generated in a late jurassic back arc basin along western north america the ophiolite underwent subseafloor metamorphism under a steep thermal gradient as indicated by downward changes in mineralogy and 18o values characteristic mineral zonation includes mica orthoclase and hematite in the lower extrusives greenschist facies assemblages in the upper sheeted dikes and amphibolite facies assemblages in the lower sheeted dikes and high level gabbro cumulate gabbros are only incipiently altered but are depleted in 18o indicating high temperature alteration with fluids that evolved at low water w rock r ratios a second off axis circulation system is recorded by metalliferous sediments that occur 8 21 m above the ophiolite alteration in the upper sheeted dike complex and especially the extrusive sequence is heterogeneous at outcrop scale as indicated by large variations in mineralogy chemistry and 18o values within individual pillows and dikes the heterogenity is due to 1 variations in w r ratio and starting material during alteration by downwelling seawater e g pillow cores versus glassy rims and 2 localized discharge mineralization mostly epidosites superimposed on the background recharge alteration epidosites occur largely as dike parallel stringers irregular replacement of pillow and massive lava and replacement of interpillow and pillow breccia matrices the chemistry of most extrusives and sheeted dikes is characterized by loss of ca and gain in na and mg consistent with alteration by downwelling fluids in addition the sheeted dikes are depleted in k2o and the lower sheeted dikes and high level gabbros are depleted in zn and cu the 18o and d values for most samples from the extrusive sequence indicate alteration by seawater at 50 rotation of the entire crustal sequence at the spreading axis suggests that the ophiolite formed at a slow spreading center where magma chambers were episodic

new structural and stratigraphic insights for northwestern pakistan from field and landsat thematic mapper data the remote waziristan region of northwestern pakistan includes outcrops of the india asia suture zone the excellent exposure of the waziristan ophiolite and associated sedimentary lithosomes and their inaccessibility made the use of landsat thematic mapper tm data desirable in this study landsat tm data were used to create a spectral ratio image of bands 3 4 5 4 and 7 5 displayed as red green and blue respectively and a principal component analysis image of bands 4 5 and 7 rgb these images were interpreted in the context of available geologic maps limited field work and biostratigraphic lithostratigraphic and radiometric data they were used to create a coherent geologic map of waziristan and cross section of the area that document five tectonic units in the region and provide a new and more detailed tectonic history for the region the lowest unit is comprised of indian shelf sediments that were thrust under the waziristan ophiolite the ophiolite has been tectonically shuffled and consists of two separate tectonic units the top thrust sheet is a nappe comprised of distal triassic to lower cretaceous neotethyan sediments that were underthrust during the late cretaceous by the ophiolite riding on indian shelf strata the uppermost unit contains unconformable tertiary and younger strata the thrust sheets show that the waziristan ophiolite was obducted during late cretaceous time and imply that the paleocene and eocene deformation represents collision of india with the kabul block and or asia

visualization of lidar derived relief models for detection of archaeological features abstract this paper presents visualisation techniques of high resolution digital elevation models dems for visual detection of archaeological features the methods commonly used in archaeology are reviewed and improvements are suggested one straightforward technique that has so far not been used in archaeology the shift method is presented the main purpose of this article is to compare and evaluate different visualisation methods two conclusions have been reached where a single method must be chosen for printing or producing digital images for non professionals the use of sky view factor or slope gradient is endorsed both presented in greyscale otherwise interpreters should choose different techniques on different terrain types shift on flat terrain sky view factor on mixed terrain slope gradient on sloped terrain and sky view factor preferably as a composite image with slope gradient on rugged terrain

petrotectonic significance of the chemistry of chromite in the ultramafic mafic complexes of pakistan abstract the suture zones which border the indian craton in pakistan are characterized by several large mafic ultramafic complexes from south to north these include 1 bela 2 muslimbagh zhob valley 3 waziristan 4 dargai skhakot qila 5 shangla mingora 6 jijal and 7 sapat besides these there is the huge 300x 40 km chilas mafic ultramafic complex in the cretaceous kohistan magmatic arc the sapat jijal shangla and dargai skhakot qila complexes are distributed along the indus suture the waziristan zhob valley and bela complexes lie along the suture on the western margin of the indian plate all these complexes were emplaced during late cretaceous paleocene time at ca 65 ma these complexes largely consist of ultramafic and mafic plutonic rocks ranging from dunite and peridotite to gabbro the mafic ultramafic rocks of the sapat chilas and jijal complexes are generally well layered and appear to be mainly cumulates in addition to cumulate plutonic rocks the remaining five complexes also contain abundant residual peridotites sheeted dykes a variety of lava flows locally pillowed and associated pelagic sediments disseminated and segregated chromite occurs in all the complexes on the basis of the chromium number cr 100 cr cr al of their chromite the complexes can be divided into three groups 1 the sapat and jijal complexes contain chromites with cr 60 2 the shangla mingora dargai skhakot qila waziristan muslimbagh zhob and bela rocks contain chromites that display a wide range of composition with cr varying from 15 to 90 and 3 rocks of the chilas complex are characterized by low cr chromites cr mostly the chromite compositions appear to indicate different tectonic settings for the origin of the complexes under consideration those with high cr chromite belong to an island arc type tectonic setting opinion differs on the origin of the group 2 chromite bearing complexes they may well be of complex origin with components which originated in different tectonic settings the chilas complex of group 3 contains low cr chromite similar to oceanic rocks supporting the idea that it is related to rifting within an island arc setting

successive shifts of the india africa transform plate boundary during the late cretaceous paleogene interval implications for ophiolite emplacement along transforms abstract the arabian sea in the nw indian ocean is a place where two major transform boundaries are currently active the owen fracture zone between india and arabia and the owen transform between india and somalia these transform systems result from the fragmentation of the india africa transform boundary which initiated about 90 myrs ago when the india seychelles block separated from madagascar to move towards eurasia therefore the geological record of the arabian sea makes it possible to investigate the sensitivity of a transform system to several major geodynamic changes here we focus on the evolution of the india africa transform system during the 47 90 ma interval we identify the late cretaceous 90 65 ma transform plate boundary along chain ridge in the north somali basin from 65 to 42 47 ma the india africa transform is identified at the chain fracture zone which crossed both the owen basin and the north east oman margin finally the transform system jumped to its present day location in the vicinity of the owen ridge these shifts of the india africa boundary with time provide a consistent paleogeographic framework for the emplacement of the masirah ophiolitic belt which constitutes a case of ophiolite emplaced along a transform boundary the successive locations of the india africa boundary further highlight the origin of the owen basin lithosphere incoming into the makran subduction zone

high resolution interpretative geomorphological mapping of river valley environments using airborne lidar data the availability of airborne lidar data provides a new opportunity to overcome some of the problems associated with traditional field based geomorphological mapping such as restrictions on access and constraints of time or cost the combination of airborne lidar data and gis technology facilitates the rapid production of geomorphological maps of floodplain environments however unfiltered lidar data which include vegetation and buildings are currently more suitable for geomorphological mapping than data that have been filtered to remove these features classification of lidar data according to elevation in a gis enables the user to identify and delineate geomorphological features in a manner similar to field mapping but it is necessary to use a range of classification intervals in order to map the various types of feature that occur within a single reach comparison of a lidar derived geomorphological map with an independently produced field geomorphological map showed a high degree of similarity between the results of the two methods although ground truthing is essential in cases where a high degree of accuracy is required ground truthing of a lidar derived geomorphological map showed that around 80 of features mapped using both methods were identified from the lidar data suggesting that the method is suitable for applications such as production of base maps for use in field mapping and selection of sites for detailed investigation copyright 2007 john wiley sons ltd

on the meridional surface profile of the gulf stream at 55 w nine month records from nine inverted echo sounders iess are analyzed to describe the mean baroclinic gulf stream at 55 w ies acoustic travel times are converted to thermocline depth which is optimally interpolated kinematic and dynamic parameters gulf stream meridional position velocity and vorticity are calculated primary gulf stream variability is attributed to meandering and changes in direction a mean stream coordinate relative to gulf stream instantaneous position and direction meridional profile is derived and compared with results presented by other investigators the mean velocity is estimated at 0 84 m s 1 directed 14 to the right of eastward and the thermocline 12 c drops 657 m north to south corresponding to a baroclinic rise of the surface of 0 87 m the effect of gulf stream curvature on temporal mean profiles is found to be unimportant and of minimal importance overall the derived downstream current profile is well represented by a gaussian function and is about 190 km wide where it crosses zero surface baroclinic transport is estimated to be 8 5 104 m2 s 1 and maximum shear flanking the maximum is 1 2 10 5 s 1 results compare well with other in situ observational results from the same time period on the other hand analyses by others of concurrent satellite altimetry geosat suggest a considerably narrower more intense mean gulf stream

diagnoses of an eddy resolving atlantic ocean model simulation in the vicinity of the gulf stream part ii eddy potential enstrophy and eddy potential vorticity fluxes abstract output of an eddy resolving model of the north atlantic is diagnosed in the vicinity of the gulf stream gs using quasigeostrophic potential vorticity qgpv quasigeostrophic potential enstrophy qgpe and modified divergent eddy potential vorticity flux v hq d a tongue or an elongated island of large mean qgpv along the model gs in the top 1000 m is associated with predominantly downgradient v hq d suggesting that the horizontal eddy fluxes are balancing a sink of eddy qgpe in most of the tongue or island by converting the mean qgpe into eddy qgpe some large upgradient v hq d is observed to the north of the center of the tongue or island however suggesting that some of the eddy fluxes in the northern half of the tongue or island of high qgpv are balancing a source of eddy qgpe there by converting eddy qgpe into the mean qgpe at the intermediate levels of the model under the gs eddy qgpe is small and the role of eddies appears to be mixed they are forcing the mean to some

the late nordic iron age and viking age royal burial site of borre in norway als and gpr based landscape reconstruction and harbour location at an uplifting coastal area abstract the nordic iron age and viking age royal burial site of borre on the western coast of the oslofjord in norway is an exceptional archaeological site in northern europe the burial mounds associated archaeological structures as well as geomorphological features have been analysed by a 1 1 m digital terrain model derived from airborne laser scanning the interpretation of this data used different derivates of the digital elevation model including hillshade slope map local relief model and their combination additionally ground penetrating radar profiles have been measured to investigate the internal structure of selected micro topographic features based on the high resolution topographic data four smaller burial mounds were added to those previously known scandinavia is strongly affected by ongoing post glacial isostatic recovery and consequently a sequence of elevated beach ridges were documented within the burial site down to the present shoreline local sea level reconstructions in the oslofjord indicate that the burial site of borre was located close to the shoreline in the period of its use when the local sea level was 3 5 5 m higher than today two prominent ridges between 4 5 and 0 m above present day sea level are interpreted as viking age jetties facilitating safe landing on an otherwise unprotected coast

automated feature extraction for prospection and analysis of monumental earthworks from aerial lidar in the kingdom of tonga abstract recent lidar light detection and ranging survey in tonga has documented a dense and complex archaeological landscape particularly on the principal island of tongatapu among the features revealed by the lidar are a profusion of earthen mounds most of which are associated with residence sporting or burial in the period 1000 1850 ce for identification and mapping of the mounds we use and evaluate two automated feature extraction afe techniques object based image analysis and an inverted pit filling algorithm imound accuracy of these methods was measured using an f1 score harmonic mean of precision and recall variable afe results indicate that continual and iterative fine tuning is required successful mapping of some 10 000 mounds on tongatapu reveals a distinct spatial structure that relates to traditional land division and tenure

evidence of growth fault and forebulge in the late paleocene 57 9 54 7 ma western himalayan foreland basin india abstract the evolution of the himalayan foreland is the result of continent continent collision and related large scale tectonics in the region the initial foredeep basin sequences are exposed in limited areas of the western himalaya which makes these areas very significant in unraveling the earliest evolution of the foreland system the basal interval of the himalayan foredeep is exposed in the jammu area india which preserves silicified breccia formed by the erosion of hanging walls of shallow faults two paleocene sections are analyzed that suggest the existence of growth faults which developed in response to the india asia collision in the late paleocene 57 9 54 7 ma the pebble size clasts and their derivation entirely from the basement demonstrate rapid sedimentation in response to rapid subsidence at the onset of basin evolution the angular unconformity showing effects of erosion associated with a thin soil horizon may be due to a forebulge at the site of the unconformity the reworked bauxite above this soil horizon demonstrates erosion of another forebulge from the cratonward side

observations on the long period variability of the gulf stream downstream of cape hatteras to examine the long period variability of the gulf stream sea level residuals relative to a 2 year mean sea level in the gulf stream downstream of cape hatteras between 75 w and 60 w longitude are used residuals as derived from geosat altimetry between november 1986 and december 1988 were gridded in space and time at a temporal resolution of 10 days and spatial resolution of 1 4 complex empirical orthogonal function ceof analysis was applied to the data set to extract the spatially correlated signal with the original data sub sampled to 1 2 in addition to determining the space time scales and propagation characteristics of the different modes wavenumber frequency spectral techniques were used to separate the variability into propagating and stationary components the ceof technique applied to the data set indicated that the first four ceof modes accounted for 60 of the variability and were found to be above the noise level 99 of the time ceof 1 was associated with westward propagation at 5 km d at a wavelength of 2000 km and eastward propagation at 1 2 km d centered at a 500 km wavelength this first ceof is in good agreement with thin jet equivalent barotropic models which predict westward propagation for wavelengths greater than 1130 km a deflection of the wavelike pattern at 65 w also indicates a possible topographic effect a simple scaling of the effect of topography indicates that for length scales longer than the internal rossby radius of deformation the topographic term is at least of the same order of magnitude as the beta effect the second ceof was more broadbanded in wavenumber space with eastward propagation occurring in a wavenumber frequency band between 300 and 1400 km and 0 5 and 2 0 cycles yr the third ceof is similar in structure to the first but with less energy ceof 4 was clearly identifiable with higher frequencies than the first three with westward propagation at 4 km d the spatial location of this mode along with the westward propagation indicates possible influences from eddy stream interactions thus topography rossby wave dynamics and eddy stream interactions all appear to have a significant role in determining the space time scales and propagation properties of the long period response of sea level in the gulf stream

mesoscale stratocumulus bands caused by gulf stream meanders abstract examination of visible and infrared imagery from geosynchronous and polar orbiter satellites reveals the occasional existence of mesoscale cloud bands of unusual width and area originating over the open northwest atlantic ocean during cold air outbreaks this phenomenon is of both dynamic and synoptic interest as a dynamic phenomenon it represents a mesoscale flow that is driven by transient surface features which are meanders in the gulf stream the forcing geometry and the resulting cloud pattern are similar in many respects to the anomalous cloud lines observed downwind of chesapeake and delaware bays in similar conditions these open ocean cloud bands are often of a larger scale however because the gulf stream meanders represent the largest scale high amplitude coastal features in the western north atlantic these cloud bands are of synoptic interest because when present they play a major role in determining the cloud pattern over much of this oceanic region examination of surface

late cretaceous early tertiary convergence between the indian and arabian plates recorded in ophiolites and related sediments abstract remnants of ocean floor forming the eastern ophiolite belt in oman and the western ophiolite belt in pakistan have a common plate tectonic history culminating in emplacement at the cretaceous tertiary boundary fragments of ocean floor in these two belts have ages between 150 and 65 ma and recorded tectonic events in the early indian ocean at 150 ma 130 120 ma 110 100 ma and 70 65 ma new radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving indian ocean which was characterised by the stepwise breakup of gondwana at 158 ma east and west gondwana 130 ma southern atlantic breakup of east gondwana 95 84 ma madagascar and india seychelles 65 ma india and seychelles and finally at 40 ma rifting between africa and arabia the 150 ma old oceanic rocks of masirah island in oman originally formed the extension of the basins now preserved along the eastern edge of the afro arabian plate masirah drifted together with india seychelles when a new ridge formed at approximately 130 ma separating microplates e g kabul block from the northern edge of greater india parts of this new ocean were later emplaced to form the western ophiolite belt in pakistan consumption of oceanic crust and emplacement of ophiolites during the closure of the neotethys occurred not only north of india seychelles but also along two or three subduction zones between the afro arabian plate and india seychelles documented by the formation of metamorphic soles beneath ophiolites relics of ocean floor formed approximately 65 70 ma ago now form the upper units in the western ophiolite belt of pakistan where they overlie an accretionary prism of pillow lavas of dominantly aptian albian age and sedimentary rocks the breakup of india and the seychelles at 65 ma was associated with the eruption of flood basalts deccan and seychelles and enhanced counter clockwise movement of india this breakup possibly caused the late jurassic early cretaceous fragments of ocean floor e g masirah to be thrust onto the eastern edge of oman the ophiolites which were emplaced onto the western edge of india drifted as part of this plate farther north where collision with eurasia and the accreted microplates occurred in the eocene 55 ma

sea surface temperature variability of the iceland faeroe front several advanced very high resolution radiometer avhrr images with spatial resolution of 1 1 3 3 km together with several concurrent aircraft deployed expendable bathythermograph axbt surveys and conductivity temperature depth ctd stations from spring 1989 are used to describe the iceland faeroe sea surface temperature sst front in the avhrr images sst fronts are located by maximizing sst single large gradient segments of the sst front do exist with some exceeding 100 km in length indicating a multiple frontal structure these single frontal lines are also segments where 2sst is small and they can be followed uniquely by a single isotherm eastward from iceland for a distance of 300 km with a 35 km sampled axbt survey two small subsurface cold eddies were located south of the surface front in an area 170 km 270 km east of iceland from a may 1987 avhrr image on 1 1 km resolution a population of seven such cold eddies are found between iceland and the faroes they appear to be generated along the surface expression of the iceland faroes front and populate the northern slope of the iceland faroes ridge historical data from towed high resolution instruments suggest that the cold eddies are 30 50 km in size and uplift the main thermocline by 150 m

the smectite chlorite transition in drillhole nj 15 nesjavellir geothermal field iceland xrd bse and electron microprobe investigations abstract in well nj 15 of the nesjavellir geothermal field iceland the transition of discrete smectite into discrete chlorite has been studied from drill cuttings recovered at depths of less than 1714 m and over a continuous range of temperatures between 60 and 300 c at temperatures below 180 c the clay fractions contain mixtures of di and trioctahedral smectites whose layer charge increases with depth between 200 and 240 c discrete smectites have transformed into smectite rich randomly interstratified chlorite and smecite r0 c s because the abundance of chlorite interlayers in this c s is generally 20 its presence can be detected only by electron microprobe techniques and not by x ray diffraction between 245 and 265 c both regularly r1 and randomly interstratified c s are the predominant layer silicates discrete chlorite first appears at approximately 270 c and coexists with minor amounts of r0 c s at higher temperatures r0 and r1 c s form a nearly complete compositional series between trioctahedral saponite and discrete chlorite end members the interlayer cation and si content of smectites and c s decrease with increasing temperature the mg mg fe content of smectite c s and chlorite is unrelated to temperature the percentage of chlorite in c s as determined by electron microprobe analyses increases continuously with increasing temperature except for occurrences of smectite rich c s in fresh basaltic dykes which have not thermally equilibrated with the higher grade country rocks

40ar 39ar dating of the emplacement of the muslim bagh ophiolite pakistan abstract the obduction related basal part of the muslim bagh ophiolite baluchistan pakistan and the underlying metamorphic sequence were studied structurally which demonstrated a wsw ene trending thrusting sequence for the initial obduction 40ar 39ar measurements on amphiboles and plagioclase from the subophiolitic metamorphic rocks and on plastically deformed and recrystallized dolerite samples from the base of the sheeted dyke complex give apparent ages between 70 7 5 0 and 65 1 4 1 ma interpreted as cooling ages dating approximately the formation of the plastic deformation and obduction the results indicate that the muslim bagh ophiolite represents a segment of ocean floor from the small and slow spreading ocean branch of the neo tethys located between the indo pakistani and the afro arabian plates the wsw ene oriented obduction of the muslim bagh ophiolite onto the indo pakistani continental margin occurred with the convergence of the neo tethys branch during the late cretaceous and before the tertiary collision of the indo pakistani plate with the eurasian plate

mesozoic ophiolites sutures and arge scale tectonic movements in afghanistan abstract the tectonic history of afghanistan appears to be the result of successive accretion of fragments of gondwana to the active margin of laurasia since the end of the paleozoic the margin in afghanistan lies along the present herat and panjshir faults south of hindu kush swings around the central pamirs and can presumably be traced along the present western altyn tagh and kunlun faults in tibet north of this boundary paleozoic rocks have been deformed in the upper paleozoic whereas south of it there is no trace of the hercynian orogeny the first collision of gondwanian fragments with laurasia probably occurred in the early mesozoic along the hindu kush and kunlun to the south ophiolites along the panjao and pangong nu chiang sutures respectively in central afghanistan and central tibet testify for another suturing event in the upper jurassic or lower cretaceous the indus tsangpo suture between india and tibet corresponds in eastern afghanistan to two ophiolite subbelts near kabul and khost both ophiolite complexes have been emplaced between maestrichtian and lower eocene by choking of two northward dipping subduction zones after complete contact between the indian and asian continents was achieved presumably in the end of eocene the penetration of india into asia caused large scale intra continental shortening a large part of the shortening was accommodated by strike slip faulting along mesozoic and more ancient sutures central afghanistan in particular was extruded to the west along the herat suture by the protrusion of the pamir wedge it subsequently collided with the lut block

sea surface topographic variability near the new england seamounts an intercomparison among in situ observations numerical simulations and geosat altimetry from the regional energetics experiment intercomparisons are made among three sets of results for two regions of the gulf stream upstream and downstream of the new england seamount chain nesc observational records from 12 inverted echo sounders with pressure gauges ies pgs concurrent geosat altimeter crossover point differences and results from a primitive equation model of the region standard deviations of sea surface topography show generally good agreement for the three data sources no significant difference between the upstream and downstream regions is observed in the actual data ies pg records and geosat topographic variability have values of about 30 cm on both sides of the nesc although model results show a discrepancy in the eastern region barotropic fluctuations account for about 30 of the total surface topographic variability and are only partially correlated with baroclinic fluctuations

archaeological prospection of forested areas using full waveform airborne laser scanning abstract airborne laser scanning als is a potential tool for recognising and measuring topographic earthwork features in wooded areas to explore its potential for archaeological reconnaissance in a densely forested area a test scan covering an iron age hillfort in the eastern part of austria was carried out during the first phase of a research project als sensors can penetrate vegetation canopies allowing the underlying terrain elevation to be accurately modelled the latest generation of airborne laser scanners was used in the project this sensor digitally records the entire waveform of the received laser echoes we argue that the digital terrain model dtm generated from entire waveform als data could be classified with greater confidence providing a more accurate dtm than with previous als devices the processing algorithms used to create the interpretative dtm are discussed in detail using the described procedures it was possible to remove most of the forest canopy and understorey brushwood and low level vegetation covering the archaeological features the als dtm was compared with a detailed topographic mapping of the visible archaeological traces collected by a terrestrial survey significantly very low earthwork features which were not recognized by the trained surveyors in the field were identified in the als derived dtm therefore in this study area als has been demonstrated as an important tool for systematic archaeological prospection in vegetated areas there are however some restrictions which are discussed in the paper

temperature and velocity structure of the gulf stream northeast of cape hatteras modes of variability thirty five expendable bathythermograph sections and 10 pegasus velocity sections taken approximately normal to the gulf stream northeast of cape hatteras were used to examine the variability of the current s structure the regridded profiles were superimposed in a stream coordinate system such that the temperature variance associated with the superposition was minimized the resulting variance field was examined using empirical orthogonal functions the temperature variability is heavily weighted by seasonal warming hence the following results exclude temperatures from the upper 200 m the first mode 48 of the variance is due to a deepening of the thermocline relative to the mean on the offshore side of the gulf stream and a shoaling on the inshore edge associated with a change of geostrophic velocity and baroclinic transport the amplitudes of this transport mode indicate a slight downstream increase in baroclinic transport 2 per 100 km and a seasonal modulation 5 sverdrups rms that peaks in may june the second temperature mode below 200 m 13 21 of the variance is associated with a change in horizontal shear a vorticity mode and is positively correlated with measured path curvature and layer thickness the directly observed pegasus velocity sections were combined with corresponding temperature sections to compute their joint empirical modes the dominant combined mode has a thermocline structure change as in the transport mode that is coupled with an increase in alongstream velocity and for levels above the main thermocline an inflow from both sides toward the center both temperature and velocity data indicate that high transport in the gulf stream is associated with lateral displacement offshore of its mean position

observations on the propagation growth and predictability of gulf stream meanders during a 3 year period gulf stream positions determined by satellite infrared imagery on a grid northeast of cape hatteras have been correlated against inlet path parameters displacement from the mean position angle and curvature monitored by an array of inverted echo sounders ies by cross spectral calculations between these measurements we determined the downstream coherences phase speeds and spatial growth rates the downstream path predictability from these inlet parameters was tested in a multiple input linear response model the most energetic meanders with periods of 33 50 days remained highly coherent for 300 km downstream roughly the dominant wavelength with marginal coherence again at 500 575 km phase speeds are frequency dependent and decrease with distance downstream for the 50 33 day meanders phase speeds decreased from 10 17 km d at the inlet to 6 8 km d at a distance downstream of about 550 km the average growth rate spatial e folding wave number over the entire region is 1 3 10 3 km 1 within 300 km of the inlet the multiple coherence accounts for 55 65 of the total path displacement variance with displacement and angle being the best individual predictors in the first and last halves of this region respectively

application of singular vector analysis to the kuroshio large meander 1 singular vector analysis is applied to the formation of the kuroshio large meander south of japan we use a simulation run of an ocean general circulation model ogcm in which a large meander occurs as the background state singular vectors are calculated by the lanczos method in which the tangent linear and adjoint models of the ogcm are used we apply an incremental correction approach for setting up the initial perturbation and averaging for the final norm in order to get modes reflecting nonlinear physics by filtering out high frequency variations the perturbation extracted as the leading right singular vector affects the formation of the large meander most if it is set to the background state two months before when the perturbation is added it enhances an anticyclonic eddy southeast of kyushu in the upper layer which induces downwelling north of it and develops an anticyclonic eddy in the deep layer the anticyclonic eddy produces a cold anomaly at the downstream edge and produces baroclinic instability there resulting in further development of the large meander in contrast the anticyclonic eddy in the deep layer is weakened when the perturbation is subtracted the development of the cold anomaly in the deep layer is delayed and consequently the meander is not so well developed thus singular vector analysis reveals the role of the anticyclonic eddy approaching southeast of kyushu in the upper layer and indicates the importance of the anticyclonic eddy in the deep layer

gulf stream path analysis near the new england seamounts as part of the naval ocean research and development activity s regional energetics experiment 12 inverted echo sounders iess were deployed from june 1985 to july 1986 in two arrays across the historical mean path of the gulf stream near 67 w and 58 w slightly upstream and downstream of the new england seamount chain gulf stream positions and directions were computed at half day intervals for adjacent ies pairs levels of variability at the two array locations were similar but the characteristics of the meanders in terms of propagation and current direction were quite different evidence was found for a quasi stationary meander near 58 w features deduced from ies measurements are compared with concurrent infrared air dropped expendable bathythermograph and geosat altimetry observations

automated classification of landform elements using object based image analysis this paper presents an automated classification system of landform elements based on object oriented image analysis first several data layers are produced from digital terrain models dtm elevation profile curvature plan curvature and slope gradient second relatively homogenous objects are delineated at several levels through image segmentation these object primatives are classified as landform elements using a relative classification model built both on the surface shape and on the altitudinal position of objects so far slope aspect was not used in classification the classification has nine classes peaks and toe slopes defined by the altitudinal position or the degree of dominance steep slopes and flat gentle slopes defined by slope gradients shoulders and negative contacts defined by profile curvatures head slopes side slopes and nose slopes defined by plan curvatures classes are defined using flexible fuzzy membership functions results are visually analyzed by draping them over dtms specific fuzzy classification options were used to obtain an assessment of output accuracy two implementations of the methodology are compared using 1 romanian datasets and 2 berchtesgaden national park germany the methodology has proven to be reproducible readily adaptable for diverse landscapes and datasets and useful in respect to providing additional information for geomorphological and landscape studies a major advantage of this new methodology is its transferability given that it uses only relative values and relative positions to neighboring objects the methodology introduced in this paper can be used for almost any application where relationships between topographic features and other components of landscapes are to be assessed

gulf stream path and thermocline structure near 74 w and 68 w the synoptic ocean prediction synop experiment had the goal of providing a physical understanding of energetic mesoscale eddy processes in the gulf stream in the synop inlet array off cape hatteras and in the central array near 68 w modred observations were collected from october 1987 through august 1990 the inlet array measured the surface path and bottom currents where the gulf stream leaves the continental margin to enter the deep water regime small amplitude propagating and growing meanders characterized the variability there the central array measured velocity and temperature as a proxy for density at four levels in the water column as well as the upper and deep level streamfunctions all with mesoscale resolution near 70 w the path envelope exhibited a relative node confined within a 40 km band 55 of the time near 68 w the path envelope was over 3 times as wide due to several elongated steep meander troughs and relatively steep meander crests the crests typically propagated downstream without much growth the troughs often stalled near 68 w steepened and persisted for one to several months two cases evolved into s shaped paths and subsequently formed rings even the time averaged fields showed a small trough in the mean path and thermocline structure whereas meanders of 20 to 60 day periods had similar spectral levels throughout 70 67 w meanders with long periods 85 day accounted for the local minimum in variance at 70 w bottom pressure and velocity observations revealed repeated periods of intense swirl speeds 0 30 m s 1 abyssal eddies the time averaged deep currents exhibited a mean cyclone centered 30 km offshore and downstream of the upper layer mean trough the cross stream slope of the thermocline steepened linearly with path curvature consistent with gradient wind balance structures are illustrated in the mapped fields consistent with baroclinic instability wherein troughs steepen and rings form

the dynamics of error growth and predictability in a model of the gulf stream part i singular vector analysis abstract the recently developed ideas of generalized linear stability theory for dynamical systems are applied to time evolving flows of the gulf stream using a quasigeostrophic numerical model the potential for the growth of perturbations arising from errors and uncertainties in forecasts of the gulf stream is investigated by computing the singular vectors or so called optimal perturbations of time evolving flows using a linearized model and its adjoint the authors calculations reveal that the potential for rapid perturbation growth is greatest in regions of developing straining and shearing flows such regions include developing meanders and regions where eddies form and where existing eddies interact with the main gulf stream it is found that the optimal perturbations of the gulf stream share many features in common with those of the jet streams in the atmosphere the ideas and techniques developed in this paper have been applied to the problem of ensemble prediction of the gulf stream in part ii

geology and hydrocarbon potential of offshore indus basin pakistan geologic notes the indus offshore basin located in the south of the karachi trough and thar slope between murray ridge and the indian border 23 to 25 n lat 66 to 68 e long has been investigated geologically from the point of view of hydrocarbon potential nine wells were drilled in the area two onshore wells karachi 1 2 three wells near the karachi shore dabbo creek patiani creek and korangi creek one well on the offshore platform karachi south a 1 and three wells in offshore depressions indus marine a 1 b 1 and c 1 no oil or gas deposit was discovered but gas shows and traces were recorded however considering the large area 7 700 mi2 20 000 km2 the number of wells drilled represents an insufficient effort of exploration and drilling tectonically the indus offshore basin can be divided into three units 1 an offshore depression on the west between murray ridge and the hinge line 2 the offshore karachi trough platform in the middle between the hinge line and the karachi shoreline and 3 offshore thar slope platform or indus river deltaic area on the east the hinge line zone and the outer margin of the carbonate platform where there is a possibility of reef buildups seem to be potential areas for hydrocarbons and further investigation and drilling for suitable structural traps should be pursued

the spongtang massif in ladakh nw himalaya an early cretaceous record of spontaneous intra oceanic subduction initiation in the neotethys abstract the spongtang massif is a remnant of neotethyan ocean crust emplaced onto the indian passive margin along the indus yarlung tsangpo suture in the nw himalayan region of ladakh the age tectonic evolution and timing of ophiolite obduction are critical to our understanding of the mechanisms via which entire oceans are formed consumed and partly preserved before the onset of terminal continent continent collisions geochemistry of the gabbro and basaltic units suggest the presence of both morb type and primitive arc related mafic rocks zircons extracted from the spongtang massif gabbros yield u pb shrimp ages of 136 133 ma with initial ehf values of 14 to 16 indicating early cretaceous juvenile depleted mantle sources devoid of contamination by older continental crust previously middle jurassic 177 ma zircon ages were obtained from gabbro and we suggest these represent morb type neotethyan oceanic crust through which a younger intra oceanic island arc spong arc developed in response to subduction initiation during the early cretaceous 136 ma our zircon ages are consistent with early cretaceous ages obtained for radiolarian cherts within the spong arc complex subduction beneath the spong arc continued until its collision with the northern indian continental margin during the early eocene we suggest that the spongtang massif is equivalent to the nearby dras island arc terrane intra oceanic subduction beneath this system was possibly initiated along nne ssw trending transform faults in the neotethyan ocean along which different ages of ocean crust was juxtaposed thereby development of the early cretaceous spong arc is superimposed on the older jurassic spongtang n morb crust the juvenile hf signature indicates the subduction system that spawned the spong island arc was not related to the coeval trans himalayan ladakh gangdese arc that developed along the southern margin of eurasia the age composition and nature of geological relationships with the underlying indian rocks indicate the spong arc was a juvenile intra oceanic terrane that first collided with india before the onset of final continent continent collision therefore final late eocene neotethys closure was between the kohistan ladakh eurasian continental arc and the already inactive indian spongtang margin

origin of deccan trap lavas evidence from combined trace element and sr nd and pb isotope studies abstract geochemical and isotope results are presented from a new study of the most southern basalts in the deccan trap india three chemical formations are recognised two of which can be correlated with the established stratigraphy in mahabaleshwar and imply a regional southerly dip of 0 06 over a distance of 250 km in detail sr isotope variations within the ambenali and mahabaleshwar formations can be shown to reflect three distinct end members which provide new constraints for petrogenetic models pb isotope data for selected basalts exhibit a wide range with 206 pb 204 pb 16 87 22 45 and a linear correlation on a pb pb diagram the least contaminated ambenali basalts plot within the pb array and interaction with mantle lithosphere involves a shift to less radiogenic pb whereas contamination with crust is characterised by more radiogenic pb unlike the karoo and parana continental flood basalt provinces only four flow units within the southern deccan appear to contain a significant contribution from mantle lithosphere the mahabaleshwar and ambenali formation basalts exhibit a striking negative pb sr isotope trend which is presently regarded as one of the features of interaction with shallow level lithospheric mantle it further suggests that basalts from the walvis ridge kerguelen and ninetyeast ridge all remobilised such shallow level material and that the deccan basalts which were not affected by crustal contamination reflect interaction between asthenospheric material similar to t type morb but related to the reunion hotspot and continental mantle lithosphere of the indian plate

origin and holocene geomorphological evolution of the landslide dammed basin of la narse de la sauvetat massif central france this work is the first geomorphological analysis of la narse de la sauvetat a hydromorphic basin located in the southern limagne plain french massif central which had never been studied despite its great palaeoenvironmental interest we explore the potential of its sedimentary archives to provide valuable data on holocene geomorphic dynamics and their sensitivity to local and regional hydro climatic changes in order to characterize the nature and the morphostratigraphic and pedosedimentary evolution of the basin we used an integrative approach involving geomorphological mapping hand auger stratigraphic cross sections topographic analysis based on lidar data and stereophotogrammetric reconstruction geophysical prospection and radiocarbon dating results revealed a palaeotopography fossilized under 6 m of sedimentary infilling with a clear shift from fluvial to hydromorphic conditions circa 2800 cal bce separated by a level with colluvial and lacustrine features a detailed analysis of the eastern border of the basin also suggests the existence of a former open valley in place of the current closed depression now locked in by a topographic threshold forming a dam the sedimentary aggradation of the basin started with an alluvial phase during the upper pleistocene and probably continued into the middle and late holocene consistently with regional alluvial dynamics in the early subboreal a massive landslide occurred on the western slopes of the puy de corent volcanic plateau thereby damming the valley and forming a closed depression this episode coincided with the mid holocene climatic shift and an associated phase of slope instability and increased landslides in western europe due to changing climatic conditions this depression evolved into a hydromorphic basin with several high energy hydro sedimentary episodes after 2800 cal bce however hydro sedimentary conditions gradually became more stable towards the late holocene around 500 cal ce the drainage deteriorated towards palustrine conditions and caused the formation of a marsh and its consequent evolution into a shallow lake throughout the middle ages this lake was drained in the late xviiith century the long term sedimentary record of la narse de la sauvetat sensitive to climatic instability periods of the middle holocene makes this landslide dammed basin a valuable site with an important potential to further development of palaeoenvironmental and geoarchaeological studies

when and where did india and asia collide timing of the collision between india and asia is the key boundary condition in all models for the evolution of the himalaya tibetan orogenic system thus it profoundly affects the interpretation of the rates of a multitude of associated geological processes ranging from tibetan plateau uplift through continental extrusion across eastern asia as well as our understanding of global climate change during the cenozoic although an abrupt slowdown in the rate of convergence between india and asia around 55 ma is widely regarded as indicating the beginning of the collision most of the effects attributed to this major tectonic episode do not occur until more than 20 ma later refined estimates of the relative positions of india and asia indicate that they were not close enough to one another to have collided at 55 ma on the basis of new field evidence from tibet and a reassessment of published data we suggest that continent continent collision began around the eocene oligocene boundary 34 ma and propose an alternative explanation for events at 55 ma

do major oxide tectonic discrimination diagrams work evaluating new log ratio and discriminant analysis based diagrams with indian ocean mafic volcanics and asian ophiolites many geochemical diagrams exist that classify old volcanic terranes of ambiguous provenance into various modern plate tectonic settings with variable success recently proposed diagrams based on log ratios and linear discriminant analysis with large datasets of major oxides were tested here with data for ocean island arc and mid ocean ridge lavas from the indian ocean success rates are 45 100 with misclassifications potentially caused by alteration although alteration demonstrably need not cause misclassification the diagrams were further applied to some asian ophiolites representing tethyan and indian ocean crusts to see if the diagrams confirm their tectonic setting inferred from trace and isotopic data lower success rates 30 60 but 75 100 for specific suites are not surprising in view of the ubiquitous and complex alteration in ophiolites log ratio transformation and linear discriminant analysis appear to be powerful methods when discrimination diagrams are based on major oxide data alone

middle cretaceous back arc formation and arc evolution along the asian margin the shyok suture zone in northern ladakh nw himalaya abstract the shyok suture zone of the ladakh palaeovolcanic arc is made of cretaceous volcanosedimentary formations intruded by granodioritic plutons field observations show a tectonic stacking of litho units from different volcanic arc and back arc environments in the western part skardu area the shyok suture zone can be subdivided into two groups 1 the northern group which consists of olistolith basaltic blocks and tuffs the basalts are lree depleted with a lile enrichment and a slight nb depletion suggesting a back arc basin origin 2 the southern group which consists predominantly of andesites that show lree enrichment a flat hree pattern strong nb ta depletion and lile enrichment the volcanic rocks of the southern group appear to have island arc tholeiite iat to calc alkaline affinities in the eastern part of the suture zone nubra shyok area albian to cenomanian age silicoclastic sediments predominate these sediments correspond to a large detrital platform built on the northern part of the ladakh arc at the top these sediments interlayer with basaltic to andesitic lavas these lavas appear to be more differentiated and calc alkaline in nature than the skardu southern group lavas but show similar volcanic arc affinities no evidence of a back arc basin was found in this area our data from these two areas shows a northwest southeast evolution from back arc to arc formations in northern ladakh opening of this back arc basin occurred on the northwestern side of the ladakh arc this back arc was progressively closing eastward the arc itself was more mature in the east resembling the southern tibetan continental arc and was characterised by more continental sedimentation subsequent himalayan tectonometamorphic evolution closure of the back arc basin and deformation along the shyok suture reflects an early asymmetrical geometry along the asian margin and kohistan ladakh arc

the estimation of geoid profiles in the northwest atlantic from simultaneous satellite altimetry and airborne expendable bathythermograph sections in the nw atlantic the temporal mean circulation results in large amplitude surface topography precluding the reasonable use of mean altimetric surfaces or profiles for precise estimation of the geoid we examine a procedure which 1 uses airborne expendable bathythermograph axbt sections collected along altimeter ground tracks to estimate the single pass or instantaneous surface dynamic topography 2 employs concurrent or simultaneous satellite altimeter overflights to provide a measure of instantaneous sea level and 3 arrives at a precise estimate of the alongtrack geoid profile by differencing the instantaneous altimetric sea level and the axbt derived dynamic topography this technique is applied to several geosat exact repeat mission erm ground tracks in the area of the nw atlantic regional energetics experiment rex using axbt survey data collected in april and july 1987 geoid profile estimates are repeatable between these two independent data sets to within 10 20 cm rms this is near the estimated noise level due to barotropic variability in the gulf stream region these axbt geosat derived profiles provide a more consistent estimate of the alongtrack geoid gradient than do available gravimetric geoids analysis of the statistics of the ensemble of collinear passes provides an estimate of the geographically uncorrelated orbit error of approximately 1 2 m the total surface topography derived as the difference between adjusted instantaneous sea level profiles and the axbt geosat derived geoid profiles does not suffer significant contamination by either geographically uncorrelated or correlated orbit error

five year climatological survey of the gulf stream system and its associated rings a 5 year climatological survey of the gulf stream system s landward surface edge defines the mean standard deviation extreme limits annual and interannual variabilities and frequency distributions along 0 5 longitudinal transects from 91 to 44 w the climatology covers the loop current in the gulf of mexico and the gulf stream in the northwest atlantic ocean autocorrelations and power spectra are derived for longitudinal transects between 79 5 and 57 5 w the study also investigates the observed warm core ring and cold core ring movements and their areal extent the observed data are compiled from the oceanographic analysis charts produced by the national oceanic and atmospheric administration which utilize infrared satellite imagery and in situ observations east of cape hatteras the gulf stream system landward surface edge exhibits both interannual and annual signals the interannual variability is equal to the annual variability the mean monthly gulf stream position for the longitudinal band 70 44 w shifts from farthest north in september to farthest south in february the magnitude of the annual shift is largest near the grand banks frequency distributions of the gulf stream system position are quasi normal nearly everywhere autocorrelation plots from the 5 year time series of gulf stream positions at longitudinal transects 79 5 57 5 w exhibit three well defined e folding time regimes with a maximum time of 10 weeks at 72 w power spectrums from 79 5 to 57 5 w are red spectrums having dominant peaks of 1 year period or greater the largest total spectra energies are found at 61 w the loop current sheds rings at two apparent spatial scales which are labeled major 307 km mean and minor 185 km mean warm core rings annually the loop current sheds about one major warm core ring which translates into the western basin of the gulf of mexico and one minor warm core ring which is usually reabsorbed by the loop current the major loop current warm core ring sheddings have no seasonal preference loop current warm core rings have a mean velocity of 2 4 km d west southwest an average of 22 gulf stream warm core rings are formed and absorbed annually between 75 and 44 w the largest frequency of warm core ring formations is seen near the new england seamounts while the largest frequency of warm core ring absorptions is found near cape hatteras gulf stream warm core rings can absorb each other as occurred in 14 of the absorption cases with the highest frequency just upstream of the new england seamounts the gulf stream warm core rings have a surface diameter decay rate of 0 026 per week loop current warm core rings are similar the gulf stream warm core rings have a mean velocity of 2 4 km d west southwest cold core rings have a mean cool core surface diameter of 105 km and a mean velocity of 1 km d southwest more definitive conclusions on cold core rings are not possible as ring identification and tracking by satellite infrared imagery is tentative

gulf stream meanders over steep topography observations of the gulf stream thermocline as it meanders over the continental slope off cape hatteras are presented daily vertical sections of temperature and geostrophic velocity to 1500 m are calculated from an array of inverted echo sounders aligned across the gulf stream these accompany time series of deep currents from a simultaneous array of bottom current meters the vertical sections are computed using a previously derived technique which assumes the gulf stream variability is primarily first baroclinic mode the sections reveal that the gulf stream front systematically shoals when it meanders offshore an effect not observed farther downstream this is accompanied by a compression of the main thermocline that in turn increases the core velocity of the jet but has little effect on overall transport to explain this shoaling the gulf stream is treated as a two layer flow the lower layer vorticity balance suggests that the shoaling is caused by deep water columns preserving their layer thickness in the presence of the steep topography