crustal structure and nature of emplacement of the 85 e ridge in the mahanadi offshore based on constrained potential field modeling implications for intraplate plume emplaced volcanism abstract an integrated interpretation of multi channel seismic reflection gravity and magnetic datasets belonging to northern most part of the 85 e ridge in the mahanadi offshore is carried out to study the crustal structure and mode of its emplacement the basement structure map of the ridge reveals that it is 130 150 km wide and is composed of an eastern high which appears as a continuous broad and smooth topographyand the western high characterized by several steep isolated highs the seismic velocities reported for the first time over the ridge indicate several sedimentary sequences ranging in velocities between 1 6 and 4 0 km s above the acoustic basement top the salient aspects of the sedimentary velocities are a low velocity layer 2 6 3 2 km s within the cretaceous sequence in the intervening depressions encompassing the flank region and a regionally widespread higher velocity layer 3 5 3 8 km s belonging to the eocene oligocene section overlying the ridge a layer having a velocity of 4 2 4 7 km s probably made of volcanoclastic rocks is observed immediately below the acoustic basement the sediment isopach maps presented here for three major horizons are used to compute the 3 d sediment gravity effect to obtain a crustal bouguer anomaly map of the region detailed analysis of the gravity and magnetic anomaly maps clearly demonstrates the continuity of ridge up to the mahanadi coast at chilka lake seismically constrained gravity and magnetic models indicate that the ridge is composed of volcanic material that was emplaced on continental crust in the shelf slope areas and over the oceanic crust in the deep offshore areas the modeled crustal structure below the ridge further indicates volcanic emplacement of the ridge on a relatively younger lithosphere we propose two alternative models for the emplacement of the ridge

mean stream coordinates structure of the subantarctic front temperature salinity and absolute velocity 1 the mean synoptic structure of the northern strongest branch of the antarctic circumpolar current southwest of tasmania at the subantarctic front saf is estimated by a stream coordinates analysis of data from overlapping arrays of inverted echo sounders iess and horizontal electric field recorders deployed during the 1995 1997 sub antarctic flux and dynamics experiment the stream coordinates are derived from a daily objective mapping of the temperature field obtained from combining the ies travel time measurements with an empirical look up table constructed from the extensive hydrography acquired during woce full water column stream coordinates sections of temperature salinity and absolute velocity are presented and compared with prior observations the along stream current has a single peak with surface velocities reaching about 50 cm s 1 the vertical structure of the along stream velocity is roughly consistent with a combined external and first internal normal mode description that is adapted to the buoyancy frequency as it varies across the front although there are some significant differences the cross stream structure of along stream velocity is very nearly symmetric about the jet axis but the lateral shear magnitude is slightly larger on the cold side of the saf separating the baroclinic and barotropic currents reveals that the saf currents are diffluent primarily baroclinically in the cross stream direction baroclinic cross stream diffluence of approximately 0 23 sv per km sv 106 m3 s 1 or about 16 sv per degree of longitude at 51 s the 2 year mean total saf transport is 75 sv for a 220 km width the barotropic contribution is small 8 sv but not negligible

thermal stresses differential subsidence and flexure at oceanic fracture zones geosat geoid undulations over four pacific fracture zones have been analyzed after correcting for the isostatic thermal edge effect the amplitudes of the residuals are shown to be proportional to the age offset the shape of the residuals seems to broaden with increasing age both geoid anomalies and available ship bathymetry data suggest that slip must sometimes occur on the main fracture zone or secondary faults existing models for flexure at fracture zones cannot explain the observed anomalies a combination model accounting for slip and including flexure from thermal stresses and differential subsidence is presented our model accounts for lateral variations in flexural rigidity from brittle and ductile yielding due to both thermal and flexural stresses and explains both the amplitudes and the shape of the anomalies along each fracture zone the best fitting models have mechanical plate thicknesses that are described by the depth to the 600 700 c isotherms

a 6 year record of baroclinic transport variability of the antarctic circumpolar current at 140 e derived from expendable bathythermograph and altimeter measurements 1 repeat hydrographic sections across the antarctic circumpolar current are used to derive an empirical relationship between upper ocean temperature and the baroclinic transport stream function cross validation shows this relationship can be used to infer baroclinic transport above and relative to 2500 dbar from temperature measurements with an error of a few per cent the mean transport distribution derived from 31 austral summer expendable bathythermograph xbt sections over a 6 year period consists of westward flow immediately south of tasmania a broad band of strong eastward flow between 50 and 55 s and three cores of eastward flow south of 55 s by defining a second empirical relationship between surface dynamic height and cumulative transport a continuous time series of baroclinic transport is derived from altimeter measurements of sea surface height transports derived from altimetry in this way agree well with simultaneous in situ estimates root mean square error in net transport is 4 106 m3 s 1 suggesting sea level anomalies largely reflect baroclinic changes above 2500 dbar the 10 day sampling of the altimeter transport time series shows the irregular xbt sampling aliases variability at unresolved timescales the standard deviation of net transport above and relative to 2500 m is 4 3 106 m3 s 1 the variability in net transport is largest 2 7 106 m3 s 1 in the quasi annual band periods of 4 months to 1 5 years slightly smaller 2 3 106 m3 s 1 in the mesoscale band 1 5 years 1 5 106 m3 s 1 changes in transport are correlated with local changes in both wind stress and wind stress curl in the quasi annual and interannual bands but the transport time series is too short to draw significant conclusions

geologic and kinematic constraints on late cretaceous to mid eocene plate boundaries in the southwest pacific abstract starkly contrasting tectonic reconstructions have been proposed for the late cretaceous to mid eocene 85 45 ma evolution of the southwest pacific reflecting sparse and ambiguous data furthermore uncertainty in the timing of and motion at plate boundaries in the region has led to controversy around how to implement a robust southwest pacific plate circuit it is agreed that the southwest pacific comprised three spreading ridges during this time in the southeast indian ocean tasman sea and amundsen sea however one and possibly two other plate boundaries also accommodated relative plate motions in the west antarctic rift system wars and between the lord howe rise lhr and pacific relevant geologic and kinematic data from the region are reviewed to better constrain its plate motion history during this period and determine the time dependent evolution of the southwest pacific regional plate circuit a model of 1 west dipping subduction and basin opening to the east of the lhr from 85 55 ma and 2 initiation of northeast dipping subduction and basin closure east of new caledonia at 55 ma is supported west dipping subduction and basin opening were not driven by convergence as has previously been proposed our plate circuit analysis suggests that between at least 74 ma and subduction initiation at 55 ma there was little net relative motion between the pacific plate and lhr

lithospheric flexure at fracture zones bathymetric profiles across six major fracture zones fz s in the north pacific are used to demonstrate the absence of vertical slip on the fossil fault planes the scarp heights on these fz s are constant with age and equal to the initial vertical offsets at the ridge transform fault fz intersections because of the frozen in scarp and the differential subsidence of lithosphere far from the fz the lithosphere bends in the vicinity of the fz this flexure results in a characteristic ridge trough topographic fz signature the flexural amplitude which is the difference between the scarp height and the overall change in depth across the fz increases with age good fits to the bathymetric profiles across the mendocino and pioneer fz s are obtained by modelling the topography as the flexure of a thin elastic plate with an age dependent effective elastic thickness results of the modelling indicate that the base of the elastic lithosphere is approximately defined by the 450 c isotherm maximum bending stresses at fz s are on the order of 100 mpa substantially less than the stresses encountered at subduction zones because the mendocino and pioneer fz s are separated by less than a flexural wavelength they are elastically coupled

strength of fracture zones from their bathymetric and gravitational evolution fracture zone evolution is investigated using dynamic models that allow the fault zones to freely slip this is an improvement over past formulations where bathymetric offsets were imposed kinematically the models use a viscoelastoplastic rheology that incorporates the influence of fault friction on fracture zone slip history using viscoelastic plates we assess the role of small scale convection on removal of the lowermost thermal lithosphere beneath fracture zones through a comparison of synthetic gravity to free air gravity across fracture zones we find that the amplitude of the gravity jump across fracture zones is best fit by models with weak faults that have depth averaged yield strengths 10 mpa fracture zones with such low strengths can convert to subduction zones with 100 km of convergence many fracture zones do not fit plate subsidence models with locked or slipping faults but are better fit by systems that are tectonically deformed by modest amounts of extension

debris flow olistostromes and slumping on a distal passive continental margin the palombini limestone shale sequence of the northern apennines an olistostrome accumulation up to 530 m thick occurs in the casanova area of the northern apennines it lies within or above the calciturbiditic palombini limestone shale sequence and is part of the allochthonous vara complex sediments originally deposited on oceanic crust the olistostromes are poorly sorted monomict matrix supported submarine debris flow deposits with rigid plugs they have a compactional foliation and a compaction modified planar clast fabric created during flow although diachronous in the main part of the area the olistostromes have a vertical gradational contact with the overlying slumped palombini in which recumbent asymmetric fold hinges and trains and slump boudins are present many criteria indicate soft sediment deformation fold asymmetry indicates a uniformly sw dipping palaeoslope the textural gradation from slumps to olistostrome beds plus slump folds and boudins as olistostrome clasts show that the olistostromes are dismembered slumps in vertical sections variations in limestone petrography volume percentage and size of clasts confirm that the olistostromes were derived from the palombini as a series of bed by bed slumps keeping pace with sedimentation of the palombini from olistostrome clast sizes and bed thicknesses a depositional slope of 4 is estimated the olistostromes are not precursor sediments shed from advancing nappes as in the bracco ridge model of some authors rather they were formed at the foot of a distal block faulted passive continental margin long before nappe emplacement

on the strength of oceanic fracture zones and their influence on the intraplate stress field we use the locations and source mechanisms of oceanic intraplate earthquakes to test the hypothesis that the strength of oceanic fracture zones is less than that of normal oceanic lithosphere if fracture zones are weaker than the surrounding lithosphere they should be sites of concentrated intraplate seismicity and the lithospheric stress field should be perturbed in their vicinity the 77 earthquakes selected for the study have well determined focal mechanisms and epicenters in regions where fracture zones are well mapped we have searched for dependence of faulting style fault orientation or principal stress direction on the distance from the nearest fracture zone if fracture zones were generally weaker than the surrounding lithosphere one of the principal horizontal stresses would be oriented nearly perpendicular to the fracture zone we find no evidence that principal stresses near fracture zones are oriented preferentially in this manner there is a slight tendency for earthquakes to occur near fracture zones and patterns of fault orientation and sense of slip support the view that differential cooling and horizontal contraction on fracture zones may contribute seismogenic stress these patterns are not demonstrable at high significance however if oceanic transform fault zones are weak relative to the surrounding lithosphere these results suggest that the strength of the fracture zones increases within a few million years after cessation of transform motion to levels comparable with that of normal oceanic lithosphere

shear strength of the great pacific fracture zones shipboard bathymetry and gravity data from 30 crossings of 6 great pacific fracture zones fzs the mendocino murray molokai clarion clipperton and udintsev are compared with the predictions of a model in which fzs are locked beyond the ridge transform intersection such that no vertical motion occurs on the fault in response to differential thermal subsidence at least some sections of all of these fzs except the molokai are consistent with this model and sustain shear stresses as high as 20 mpa however none of the fzs is locked along its entire length as inferred from observed shear stresses dropping below 75 of the value necessary to maintain a locked fault there is some suggestion that the unlocking may be related to excess volcanism

chronology of warm core ring 82b a chronology constructed from satellite derived thermal imagery is presented to describe the formation and life history of warm core ring 82b this overview provides insight into a classification of features and discrete events associated with gulf stream warm core rings and allows these events as well as our limited shipboard observations to be placed in a broader spatial and temporal context than would otherwise be possible without the satellite data events influencing the evolution of 82b include environmental factors such as meteorological influences and gulf stream interactions as well as those stimulated by encounters with changes in bottom topography the interactions of the ring with surrounding waters are especially noteworthy and the existence of vortex vortex interactions is shown to be a significant cause of local water advection through streamer activity ring events are documented by following changes in ring size shape translation and surface thermal structure our satellite observations are supported by extensive contemporaneous shipboard observations including xbt ctd bops biooptical profiling system temperature profiles and along track sea surface temperature measurements in addition acoustic velocity profiling and drifter trajectories have been used to corroborate hydrographic features of the ring and environs these ship and satellite data form a coherent space time overview of the ring and its environment and show them to be closely related and continually interacting

wavenumber spectrum in the gulf stream from shipboard adcp observations and comparison with altimetry measurements the wavenumber spectra for velocity and temperature in the gulf stream region are calculated from a decade 1994 2004 of shipboard acoustic doppler current profiler adcp measurements taken as part of the oleander project the velocity and temperature spectra have comparable magnitude in terms of the kinetic and potential energy and both indicate a k 23 slope in the mesoscales in contrast the corresponding velocity spectrum determined from satellite altimetry sea surface heights yields a significantly higher energy level and a k 22 slope the discrepancy between altimeter derived and directly measured velocity spectra suggests that altimetric velocity probably is contaminated by noise in sea surface height measurement also the k 23 slope which appears to be in agreement with two dimensional quasigeostrophic turbulence theory does not support the contemporary surface quasigeostrophic theory these results highlight large gaps in the current understanding of the nature of surface geostrophic turbulence

hot spot activity and the break up of pangea abstract the mesozoic and cenozoic positions of the continents that formed pangea in the triassic jurassic were derived from paleomagnetic and intraplate volcanic data paleoclimatic observations such as reef and fossil flora distribution and geological observations major hot spots helped to determine the longitudinal position of pangea and to construct a model of plate motion during the pangean break up the position of the northern part of pangea was constrained using iceland and jan mayen hot spots the iceland hot spot was traced from its present day position to greenland in the paleocene to baffin bay in the late cretaceous to the alpha ridge in the early cretaceous to the chukchi borderland in the middle late jurassic to franz joseph land in the early jurassic the yenisei khatanga trough in the middle triassic and finally to west siberia in the late permian early triassic the hot spot activity is expressed by eastern and western greenland volcanics the siberian trap basalts and perhaps by alpha ridge and chukchi borderland volcanics the chukchi borderland volcanics are related to the early stage of the opening of the canadian basin the position of the southern part of pangea was constrained using the bouvet hot spot this hot spot was tracked from its present day position to western antarctica in the early cretaceous late jurassic and to south africa in the early jurassic late triassic this hot spot activity produced the ferrar and karoo volcanics the model of plate motion obtained agrees with other data on intraplate volcanics which are also related to hot spots at the time of the opening of the central atlantic the cape verde and canary island hot spots were located along the ocean s spreading axis the long lasting location of hot spot and associated mantle upwelling plumes could help to explain forces driving the tethys transit plates opening of the ligurian ocean and eastern mediterranean the european hot spots are related to the several mesozoic phases of rifting for example the rhine graben hot spot may have been located at the rifting axis in the north sea several authors have already discussed the contribution of hot spots to the opening of the south atlantic and indian oceans mantle plumes associated with hot spots play an active role in rifting and initial phases of spreading the lithospheric displacement caused by upwelling combined with sometimes remote collisional forces on the other side of continental plate may result in compression and basin inversion

are segmented fracture zones weak analytical and numerical models constrain anomalous bathymetry at the clarion and murray fracture zones abstract between 150 w and 135 w the clarion fracture zone fz coalesces from six discrete fz traces to a single fz over a period of 30 million years coinciding with a change in plate motion that placed the associated transform fault tf in compression between 160 and 157 the murray fz is also comprised of several closely spaced

are oceanic fracture zones locked and strong or weak new evidence for volcanic activity and weakness traditionally oceanic fracture zones and other lithospheric and crustal faults have been viewed as zones of weakness that are vulnerable to seismic and volcanic activity this notion has recently been questioned on the basis of evidence showing that initial depth offsets scarp height across some pacific fracture zones are preserved even after 100 m y of differential subsidence this evidence suggests that some parts of oceanic fracture zones are locked shortly after they drift away from ridge transform intersections because the fracture zones seem to be strong welds differential cooling stresses cause flexure in the lithosphere on both sides of the fracture in this paper we briefly review the seemingly contradictory evidence for the thermomechanical characteristics of oceanic fracture zones locked and strong vs slipped and weak and present new evidence indicating that parts of some fracture zones are volcanically active volcanism is an indication of relative weakness because strain and failure are required to open volcanic conduits this and other evidence for the inherent weakness of fracture zones can be reconciled with evidence for strength if different segments of fracture zones exhibit contrasting thermomechanical behavior more data are needed to determine whether this is so and whether there are systematic patterns of distribution for weak and strong parts of individual fracture zones

mass heat and salt transport in the southeastern pacific a circumpolar current inverse model a box inverse model for the southeastern pacific is used to combine hydrographic measurements with synoptic information from floats acoustic doppler surface velocity measurements altimeter derived surface geostrophic velocities and wind measurements the southeastern pacific is marked by substantial changes in eddy kinetic energy along the path of the antarctic circumpolar current acc associated with the eltanin and udintsev fracture zones in the east pacific rise the results of the inverse model show that the heat and salt carried by the acc are essentially unchanged as the current passes through regions of high eddy variability thus within the error bars of the available measurements the acc appears not to exchange significant water properties with its surroundings in the southeastern pacific ocean the system is geographically variable and elsewhere in the southern ocean meridional exchanges may be substantial meridional flow through the north side of the inverse model domain is consistent with an overturning circulation that carries surface intermediate water northward and returns deep water southward into the acc diapycnal fluxes identified in the inverse solution indicate that water mass transformation occurs predominantly in the outcropping upper layers of the ocean

mapping gulf stream warm core rings from shipboard adcp transects of the oleander project 1 the flow patterns of the gulf stream warm core rings and surrounding shelf break and slope water are constructed from shipboard acoustic doppler current profiler adcp transects of the oleander project for each warm ring consecutive adcp transects are colocated to a common ring center and are mapped into a stream function methods to locate ring centers from the adcp transect and advanced very high resolution radiometer image are developed and tested two warm rings in 1999 which have relatively complete data coverage are examined to study the ring induced warm and cold streamers for cold streamers the estimated volume flux based on more than 10 independent adcp transects is at least 1 106 m3 s 1 this result agrees well with the previous estimate in the warm core ring experiment for warm streamers the result is new on the basis of a large number of adcp transects the estimated volume flux is about 2 5 106 m3 s 1 by pulling large transports associated with the cold warm streamers the warm rings likely play a fundamental role in the water exchange in the slope sea

depositional systems and paleogeography of upper cretaceous paleogene deep sea flysch deposits of the magura basin western carpathians abstract the outer western carpathians are part of the alpine himalayan orogenic belt and they are formed mostly by the upper cretaceous and paleogene deep sea flysch sequences orava region northern slovakia situated in the central part of the magura nappe has an important position for the solution of the geological structure and development of the magura nappe at the beginning of the research determination of the sedimentary sequences of the magura nappe and the fundamental lithotypes and lithofacies was required a total of 1164 paleocurrent measurements were measured and assigned to lithotypes and lithostratigraphic units obtained during the detailed sedimentological study the main purpose of the research was the interpretation of the filling history and tectonic activity of the magura basin the results of the detailed sedimentological study were integrated with published data from surrounding regions presented palinspastic maps propose a reconstruction of the filling history and tectonic activity in chronological order during the upper cretaceous to oligocene maps focus in detail on the western part of the magura basin but they display its surroundings as well the sedimentary record reflects the activity and gradual shifting of the western carpathian accretionary wedge to the north the uplift of source areas and the changes in the sea level of the magura basin the paleocurrent analyses joined with the sedimentological and petrographic research allowed to reconstruct the paleogeographic properties of the northern sources of detritic material host n fore magura and silesian ridges of the southern source of the material western carpathians accretionary wedge and of intrabasinal sources as well szczawina and southern magura ridges we propose a discussion about the character of filling history defining and position of the source areas and about host n ridge defined here

sedimentary and diapiric melanges in the skrzydlna area outer carpathians of poland as indicators of basinal and structural evolution the dukla nappe in the skrzydlna area exposes two types of melange reflecting two different phases of basinal and tectonic evolution of the outer west carpathian orogen in its polish sector the oligocene age sedimentary melange olistostrome is related to growth of the accretionary wedge whereas the miocene age diapiric melange postdates the orogenic thrusting textural and structural features of the very coarse grained sedimentary melange suggest non cohesive debris flows and high density turbidity currents as predominant emplacement mechanisms growth strata associated with progressive unconformities and facies contrast between the underlying fine grained unit and the overlying olistostrome reflect a considerable uplift of the source area and rotation of the adjacent part of the basin floor the olistostrome and the overlying turbidite succession form a retrogressive sequence interpreted as a submarine canyon infill grading to a small submarine fan the diapiric melange injected into the oligocene age succession of the dukla nappe contains the early and late cretaceous age blocks and matrix derived from the underlying silesian nappe the features reflecting diapiric emplacement include matrix proportion increase and block content decrease towards the melange margins scaly fabric and shear zones both melanges interpreted in the past as chaotic bodies upon detailed examination reveal genesis related subtle internal organization

relative motions between oceanic plates of the pacific basin appendix tables are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b84 012 2 50 payment must accompany order relative motion poles describing the displacement histories between the pacific plate and once adjacent oceanic plates farallon kula izanagi i izanagi ii and phoenix were derived for the late mesozoic and cenozoic eras because fracture zone and magnetic anomaly data are generally available from the pacific plate but not from adjacent plates a new method of analysis for onesided data was required this analysis produced stage poles and rates of relative plate motion and estimates of their confidence regions the following are the main conclusions drawn from our analysis 1 for time intervals of the order of 107 years termed stages relative motion poles for plate pairs remained nearly fixed between stages shifts in poles were commonly both large and abrupt within stages rates of plate motion were commonly observed to change markedly indicating that plates changed speed more frequently than they changed direction 2 the relative motions of all of the plates analyzed changed at about chron m11 135 ma chron 34 85 ma and chron 25 56 ma 3 during the early cretaceous there were five oceanic plates in the pacific basin rather than the four recognized by previous workers 4 to determine the number of farallon plates that existed to the east of the pacific plate during the time interval from chron 34 85 ma to chron 25 56 ma fracture zones and magnetic anomalies that record pacific farallon spreading from the northern central and southern pacific plate were analyzed separately and collectively the analysis shows that a single pacific farallon relative motion pole and a single rate are consistent with all of the data 5 spreading rates along the pacific kula ridge decreased markedly between chrons 32b and 25 72 56 ma probably in response to the arrival of buoyant kula lithosphere at a subduction zone northwest of the bering sea 6 soon after chron 25 56 ma a major reorganization is recorded along the pacific farallon boundary the kula farallon boundary is also thought to have changed during this reorganization 7 kula pacific anomalies north of anomaly 25 are modeled by assuming continued kula pacific spreading after chron 25 56 ma 8 probably by chron 18 43 ma pacific kula spreading had ceased and the kula farallon ridge system had evolved into alignment with the pacific farallon spreading direction however the timing of these events is uncertain because pacific kula data younger than chron 25 56 ma are sparse

direct observations of the current structure east of the bahamas quasisynoptic absolute velocity sections were obtained in the western north atlantic to the east of the bahamas on five cruises from 1992 to 1994 showing complex spatial and temporal variability of the currents throughout the water column lowered acoustic doppler current profilers were used on all cruises for comparison an acoustically tracked free fall profiler was used on the august 1992 and june 1993 cruises where simultaneous profiles from both methods are available depth averaged differences are less than 0 01 m s 1 in the ensemble mean and standard deviation though small the mean difference appears to be statistically non zero for one of the two doppler profilers used no cause has been found the individual velocity sections show a banded structure of currents in the offshore direction with strong baroclinic and depth averaged components extending over the full sampling domain two sections show a picture of the southward flowing deep western boundary current dwbc differing from previous observations during august 1992 and june 1993 the mean dwbc core was located more than 100 km offshore in observations prior to 1990 it was usually near 50 km offshore net southward transport below 800 m integrated from the coast to 400 km offshore varied from 15 to 50 sv with a mean of about 40 sv 1 sv 1 106 m s 1 our mean is consistent with previous estimates our sections add new evidence that the transport is highly variable to at least 400 km offshore

on the southerly extent of the antarctic circumpolar current in the southeast pacific a front at 67 s in the bellingshausen sea at 85 w is shown to be part of the antarctic circumpolar current acc and the southernmost zone of concentrated eastward transport at that longitude the front lies 6 south of the polar front at 88 w and 3 north of the continental water boundary the front is continuous to the east through drake passage where it forms a southern branch of the polar front for which reason we have named it the southern polar front data from a towed profiling ctd were able to distinguish the polar front from the southern polar front even though they were only 0 5 apart thus the width of the acc south of the polar front varied considerably about a third of the transport of the acc also lay south of the polar front with 15 sv carried by the southern polar front alone at 85 w distinguishing features of the southern polar front were a water mass boundary associated with a zone of concentrated baroclinic flow and a surface salinity minimum these features also have been found at the greenwich meridian at 53 s so the southern polar front can be traced round at least a quarter of the globe to the west of the bellingshausen sea both eltanin data and the fine resolution antarctic model show that the aac is at its narrowest at 145 w where its southern boundaries lie as far north as 56 s at this longitude the acc meets the topographic barrier of the pacific antarctic ridge to conserve potential vorticity the current is forced to make a southward loop as it crosses the ridge and the current broadens dramatically the flow remains broad until forced to sharpen by the constriction of drake passage a similar broadening of the acc is seen where it crosses the southwest indian ridge south of africa at 30 e here it remains broad until it encounters the kerguelen plateau thus the eastern boundaries of both the weddell and ross gyres are determined by where the acc crosses midocean ridges

role of the olistostromes and olistoliths in tectonostratigraphic evolution of the silesian basin in the outer west carpathians abstract the silesian series deposited in the proto silesian and silesian basins and preserved within the silesian nappe represents most complete continuous basinal sedimentary succession late jurassic early miocene within the outer carpathians it contains intercalations of numerous olistostromes that occurred during every stage of flysch basin evolution from rift and post rift through orogenic to postorogenic stage the olistostromes represent sediments of sub marine debris flows and avalanches they are of different size and composition and were derived from ridges and their slopes bordering proto silesian and silesian basins 0however the main source was the tectonically active southern slope and adjacent ridges the silesian and bukowiec ridges composition of olistostromes is an important source of knowledge about the geological structure and history of ridges and basin slopes which now are not preserved some large olistoliths and olistoplaques have been incorrectly interpreted as thrust sheets so detail studies of their true origin allowed correct interpretation of local tectonics

evolution and strength of pacific fracture zones previous studies have shown that pacific fracture zones are strong in some locations sustaining the stresses associated with differential subsidence across a locked fault while at other locations they show signs of weakness acting as preferential conduits for volcanism or supporting anomalously low shear stresses we find that half of all geosat crossings of central pacific fracture zones are inconsistent with a flexurally maintained scarp we test two hypotheses for the origin of such anomalous crossings 1 anomalous structures formed at the transform fault during times of changes in plate motions and preserved at strong fracture zones and 2 anomalous structures representing a posttransform response of the fracture zone to subsequent tectonic activity we find that three quarters of the anomalous crossings occur over the parts of fracture zones that formed during or immediately subsequent to times of changes in spreading directions with the exception of several locations overprinted by hot spot volcanism these same crossings show no obvious correlation with regional tectonic processes these observations suggest that most anomalous fracture zone topography is inherited from the transform fault and is not a product of subsequent activity consistent with the hypothesis that fracture zones generally remain strong throughout their lifetimes

an equivalent barotropic mode in the fine resolution antarctic model abstract both the 6 year time mean flow and the eddy kinetic energy in the fine resolution antarctic model are found to be approximately self similar in the vertical with the velocity showing a rapid decay with depth a simple argument is given as to why this would be expected to occur in this and other numerical models and an analysis is given as to the degree of steering of the mean flow by topography

a two dimensional tomographic study of the clipperton transform fault from the marine refraction data recorded on five instruments during the clipperton area seismic survey to investigate compensation classic experiment in 1994 we construct a compressional velocity model for a 108 km long profile across the clipperton transform we apply a new seismic tomography code that alternates between ray tracing and linearized inversions to find a smooth seismic velocity model that fits the observed refraction travel times the solution to the forward ray tracing problem is a hybrid of the graph or shortest path method and a ray bending method the inversion is performed with least squares penalties on the data misfit and first derivatives of the seismic structure starting with a one dimensional compressional velocity model for oceanic crust the misfit in the normalized travel time residuals is reduced by 96 decreasing the median travel time residual from 110 to 25 ms the compressional velocity structure of the clipperton transform is characterized by anomalously low velocities about 1 0 km s lower than average beneath the median ridge and parallel troughs of the transform domain the low compressional velocities can be explained by an increased porosity due to fracturing of the oceanic crust we found crustal thicknesses of 5 6 5 9 km under the transform fault to produce the best fit of the pmp phase arrivals and pg pn crossovers since the crust is not thin beneath the transform parallel troughs and the velocity anomaly is not confined to the median ridge we find uplift by serpentinite diapirs unlikely as an explanation for the relief of the median ridge a median ridge that is the result of brittle deformation due to compression across the transform domain is however compatible with our results the upper crust is thicker to the north of the transform than to the south which is likely a consequence of the contrast in temperature structure of these two spreading segments

geophysical constraints on the shear stress along the marquesas fracture zone we examine bathymetry and gravity observations acquired by surface ships and deflection of the vertical data derived from the geosat radar altimeter for the purpose of determining if the bathymetric relief along the marquesas fracture zone in the central pacific ocean is caused by differential thermal subsidence across a locked fault if the fracture zone can maintain between 20 and 40 mpa of shear stress we would predict that a ridge and a parallel trough would develop to the south and north respectively of the fracture zone on account of flexural modification of the step in bathymetry locked into the plate along the fracture zone at the ridge transform intersection we find that only 2 out of 32 deflection of the vertical profiles from the geosat altimetric mission are consistent with this model while none of the 27 bathymetric profiles or 9 shipboard gravity profiles fits the theoretical predictions in cases where bathymetry and gravity can be modeled simultaneously it appears that the gravity anomaly is simply not large enough in magnitude to be consistent with the moho flexing conformably with the observed bathymetry as required if the relief is produced by deeper thermal variations across the locked fracture zone rather the potential field data allow shear stresses only 25 of those required to lock the fault and are more consistent with a model in which the relief on the moho is opposite in sign to that of the surface topography as would be produced by local or regional compensation of surface loads arising from volcanic activity along the fracture zone thus we conclude that the marquesas fracture zone in contrast to those other pacific fracture zones which fit the predictions of the locked fault high stress model may be unusually weak along almost its entire length

direct velocity measurements in the subantarctic front and over campbell plateau southeast of new zealand 1 flow variability in the subantarctic front saf and over the campbell plateau southeast of new zealand is examined using data from a current meter mooring array along with conductivity temperature depth ctd and satellite altimetry data these data are part of an ongoing study of ocean climate variability in the region contrasting flow regimes were found with very energetic and highly variable flows in the saf flowing along the subantarctic slope and much weaker flows over the campbell plateau currents up to 75 cm s 1 were observed in the core of the saf while flows over the plateau were typically less than 10 cm s 1 estimates of the total bottom referenced transport from three ctd sections across the saf varied between 48 and 68 sv transports were also estimated using topex poseidon altimetry sea truthed with the ctd data the resulting 8 year time series exhibited high variability resulting from current meanders and eddy activity one event in the record appeared to be the result of a cyclonic eddy passing through the mooring array this event was modeled using an idealized geostrophic eddy the simulation reproduces the main features observed in the current meter records and the surface topography from the topex poseidon altimeter inspection of the topex poseidon data suggests that large cyclonic and anticyclonic eddies occur in the frontal region with a frequency of around 9 yr 1

observed and simulated kinematic properties of loop current rings two rings shed by the loop current in 1980 and 1982 were observed for several months by satellite tracked drifters to migrate across the gulf of mexico the drifter path data have been inverted to obtain estimates of the paths of the centers of the two rings ring shape and the swirl velocities three drifters were deployed in the 1980 ring and the analysis of that data set establishes the variability of the above kinematic estimates for one ring a comparison of the analysis of data from both rings provides some idea on inter ring variability both rings impacted the mexican continental slope at about 22 8 n 95 5 w after a brief adjustment period both rings reestablished and maintained a vortex character for several months in the slope region while migrating slowly to the north the paths of the centers of the two rings along the slope are virtually identical the same analysis routine was applied to some simulated drifter data obtained from the hurlburt and thompson 1980 gulf of mexico primitive equation model in the midgulf the agreement between the observed rings and the simulated ring is good although the former showed stronger interaction with the continental slope topography and or circulation than was seen in the latter along the slope the model ring kinematic characteristics were in extraordinary agreement with the observations

influence of a gulf stream warm core ring on water mass and chlorophyll distributions along the southern flank of georges bank during late spring 1997 a gulf stream warm core ring wcr strongly in uenced water mass and chlorophyll distributions along the southern ank of georges bank entrainment of georges bank shelf water by the wcr centered at the central southern ank persisted through may by late may shelf water encircled nearly the entire wcr and horizontal convergence toward the central southern ank was evident scotian shelf water ssw extended across northeast channel onto georges bank near the northeast peak and along the southern ank between the 60 m isobath and the shelfbreak front ssw extended furthest southwest along the southern ank shelfbreak satellite imagery from the ocean color and temperature sensor octs showed that by late may in addition to the high chlorophyll concentrations within the entrained shelf water encircling the wcr pigment rich bands of chlorophyll developed along the 60 and 100 m isobaths where this biological enhancement developed along 100 km of the shelfbreak 100 m isobath shelf waters extended furthest seaward due to entrainment by the wcr the enhanced shelfbreak chlorophyll was sampled in situ along two transects separated by 40 km along shelf along both transects the enhanced chlorophyll coincided with divergent cross shelf ow maximum along shelf ow and minimum surface temperature coincidence of the highest surface chlorophyll and lowest surface temperature with divergent cross shelf ow is consistent with upwelling coincidence with along shelf jets and their associated vertical shear is consistent with turbulent vertical mixing the importance of turbulent vertical mixing was supported maximum velocity at the shelfbreak coincided with the subsurface temperature minimum of ssw near 30 m depth estimated gradient richardson numbers ri above the ssw were below critical 0 25 within the shelfbreak chlorophyll maximum along both transects and surface chlorophyll was signi cantly inversely correlated with ri along the southern ank wcr entrainment of shelf water continued into june as

geodynamic evolution and palaeogeography of the polish carpathians and adjacent areas during neo cimmerian and preceding events latest triassic earliest cretaceous

high accuracy high resolution gravity profiles from 2 years of the geosat exact repeat mission satellite altimeter data from the first 44 repeat cycles 2 years of the geosat exact repeat mission geosat erm were averaged to improve accuracy resolution and coverage of the marine gravity field individual 17 day repeat cycles two points per second were first edited and differentiated resulting in alongtrack vertical deflection i e alongtrack gravity disturbance to increase the signal to noise ratio 44 of these cycles were then averaged to form a single highly accurate vertical deflection profile the largest contributions to the vertical deflection error is short wavelength altimeter noise and longer wavelength oceanographic variability the combined noise level is typically 6 rad both types of noise are reduced by averaging many repeat cycles over most ocean areas the uncertainly of the average profile is less than 1 rad 0 206 arcsec which corresponds to 1 mgal of alongtrack gravity disturbance however in areas of seasonal ice coverage its uncertainty can exceed 5 rad to assess the resolution of individual and average geosat gravity profiles the cross spectral analysis technique was applied to repeat profiles individual geosat repeat cycles are coherent 0 5 for wavelengths greater than about 30 km and become increasingly incoherent at shorter wavelengths this emit of resolution is governed by the signal to noise ratio thus when many geosat repeat profiles are averaged together the resolution limit typically improves to about 20 km except in shallow water areas further improvements in resolution will be increasingly difficult to achieve because the short wavelength components are attenuated by upward continuation from the seafloor to the sea surface these results suggest that the marine gravity field can be completely mapped to an accuracy of 2 mgal and a half wavelength resolution of 12 km by a 4 5 year satellite altimeter mapping mission

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

crustal age between the clipperton and clarion fracture zones magnetic anomalies of 52 80 ma age have been mapped in the equatorial pacific in a region where they were previously unrecognized these anomalies now at 7 n are best modeled with crustal rocks of negative inclination apparently because the crust was formed at a spreading ridge that was south of the magnetic equator in late cretaceous early tertiary time magnetic anomalies recorded along a 5900 km trackline that follows a flowline of crustal generation show one long period from 12 to 31 ma of apparent constant half spreading rate over the 0 to 80 ma represented

sedimentary basins evolution and olistoliths formation the case of carpathian and sicilian regions abstract comparative research carried out within two different basins one in the carpathians of poland late jurassic to early miocene and another in the apenninic maghrebian mountain chain of sicily triassic miocene indicate significant similarity not only in their evolution but also in the sedimentary features of horizons with olistoliths the olistolith bearing units are genetically related to stages of tectonic evolution and are independent of the size of the basins and of duration of these stages however the observed differences in composition and size of olistoliths suggested among the others relationship with the size of source areas and thickness of their sedimentary cover

discussion of olistostromes of the pieniny klippen belt northern carpathians j golonka m krobicki a wa kowska m cieszkowski a l czka reply we welcome the comments by our slovakian colleagues and their critique of our results particularly as we have discussed and published papers together several times about our ideas sometimes more or less disputable aubrecht et al 2003 2006 krobicki et al 2003 krobicki aubrecht golonka 2003 golonka et al 2006 pienkowski et al 2008 we are pleased to see such warm reaction to our work paper which is focused on one of the rudimentary questions in the pieniny klippen belt pkb area how many what kind of olistoliths olistostromes occur within the inner structure of the pkb and when and why did they originate mostly during the palaeogene part of the mesozoic cenozoic history of this region we expected this discussion earlier the content of our paper was presented at the 6 th meeting of the central european tectonic studies group ceteg in upohlav pieniny klippen belt slovakia cieszkowski et al 2008 and later at the xix congress of the carpathian balkan geological association in thessaloniki greece cieszkowski et al 2010 golonka et al 2010 some ideas were also briefly mentioned in the paper by cieszkowski et al 2009 in a journal issue edited by d plasienka we assume that the comments are based on recent investigation because the authors list the grants received to conduct the research therefore the submitted comments sometimes present a point of view different from that published previously by some of the authors of the comments ra jm see aubrecht et al 2003 krobicki aubrecht golonka 2003 wierzbowski et al 2006 pienkowski et al 2008 the statement certainly there are many still unresolved problems in the geology of the pkb and it ought to be said that the co authors of this discussion also do not fully agree with all interpretations formulated and illustrated by the first author perhaps explains this controversy of course we agree that there are many still unresolved problems in the geology of the pkb we also agree with the statement olistostromes and olistoliths are quite frequent but not omnipresent we depicted the distribution of the olistoliths and their relationship to the non olistolith tectonic units of the pkb in golonka et al 2015 figs 3 8

bottom currents derived from a shipborne adcp on woce cruise a11 in the south atlantic abstract this paper is divided into two parts the first describing an enhancement of the shipborne adcp system and the second describing information about bottom currents that have been obtained therefrom on woce cruise a11 in the south atlantic punta arenas to cape town rrs discovery has been fitted with a gps3df receiver and an array of antennas about its bridge which determine the instantaneous attitude of the ship the heading record from this instrument has been compared with the ship s gyrocompass throughout the 40 day cruise differences have been calculated and examined according to heading speed and movements underway differences are found insensitive to heading except in a southerly sector but on station differences exhibit a sinusoidal dependence on heading with range 3 steaming from a station led to transient behavior with recognizable effects for 1 hour the results are generally consistent with earlier reports and are attributed to gyro error an improved heading measurement has a

a mean synoptic view of the subantarctic front south of australia abstract a mean synoptic view of the subantarctic front saf is obtained from current meter and hydrographic data by averaging absolute and baroclinic velocity measurements in bins defined by a cross stream coordinate that moves with the current the cross stream coordinate is derived from current meter measurements of vertical shear of the horizontal velocity and is expressed in terms of specific volume anomaly at 780 dbar 780 by averaging absolute and baroclinic velocity measurements in stream coordinates the spatial smoothing that results from eulerian averaging of measurements of a meandering current is avoided the mean saf velocity profile is composed of one central peak and several smaller peaks in the central peak the 2 yr mean absolute velocity from current meters reaches 52 cm s 1 at 420 dbar the mean baroclinic velocity from six ctd sections reaches 34 cm s 1 the saf flow is coherent at all levels reaches the seafloor and is at least 220 km wide the cross stream structure of barocl

fracture zones in the north atlantic morphology and a model a morphology is presented for the typical cross section of an inactive fracture zone in the atlantic inactive fracture zones typically consist of an asymmetric valley to the young side of the fracture zone plane and a high wall or scarp to the old side large offset fracture zones may be accompanied by a marginal valley on the other side of the high wall this topography is superimposed on the depth age step due to lithospheric cooling a model is developed which accounts for this morphology the model relates the inactive fracture zone morphology to the topography found at present day intersections of the spreading axis with transform faults the asymmetry of the median valley near fracture zones plays an important role in explaining the typical fracture zone morphology the existence of a median valley is related to the viscous delay of the upwelling mantle material at the spreading axis its asymmetry near fracture zones can be accounted for by modelling the viscous drag exerted by the lithosphere on the asthenosphere if the viscosity is low as under reykjanes ridge and the east pacific rise no median valley develops and a different morphology may be expected the occurrence of marginal valleys is interpreted as the result of lithospheric warping when the graben walls in the transform domain which are caused by tension due to horizontal thermal contraction are excessively high

evidence for diffuse extension of the pacific plate from pukapuka ridges and cross grain gravity lineations satellite altimeter measurements of marine gravity reveal 100 to 200 km wavelength lineations over a wide area of the pacific plate oriented roughly in the direction of absolute plate motion at least three mechanisms have been proposed for their origin small scale convective rolls aligned in the direction of absolute plate motion by shear in the asthenosphere diffuse n s extension of the lithosphere resulting in lineated zones of extension boudins and minihotspots that move slowly with respect to major hotspots and produce intermittent volcanism recently several chains of linear volcanic ridges have been found to be associated with the gravity lineations following ridgelike gravity signatures apparent in high resolution geosat gravity measurements we surveyed a series of volcanic ridges that extend northwest from the east pacific rise flank for 2600 km onto 40 ma seafloor our survey data as well as radiometric dates on samples we collected from the ridges provide tight constraints on their origin 1 individual ridge segments and sets of ridges are highly elongate in the direction of present absolute plate motion 2 the ridges formed along a band 50 to 70 km wide in the trough of one of the more prominent gravity lineations 3 radiometric dates of the largest ridges show no hotspot age progression moreover the directions predicted for minihotspot traces older than 24 ma do not match observed directions of either the gravity lineations or the ridges based on this last observation we reject the minihotspot model the occurrence of the ridges in the trough of the gravity lineation is incompatible with the small scale convection model which would predict increased volcanism above the convective upwelling we favor the diffuse extension model because it is consistent with the occurrence of ridges in the trough above the more highly extended lithosphere however the multibeam data show no evidence for widespread normal faulting of the crust as predicted by the model perhaps the fault scarps are buried under more than 30 m of sediments and or covered by the elongated ridges finally we note that if ridge push force is much smaller than trench pull force then near the ridge axis the direction of maximum tensile stress must be perpendicular to the direction of absolute plate motion

absolute geostrophic velocity within the subantarctic front in the pacific ocean velocity measurements from a shipboard acoustic doppler current profiler adcp are used as a reference for geostrophic current calculations on six sections across the subantarctic front saf in the pacific ocean the resulting cross track velocity estimates near the bottom range from 4 to 10 cm s 1 to the east in the eastward jet at the saf in adjacent regions of westward surface flow the near bottom velocity is usually to the west on one section where simultaneous lowered adcp velocity profiles are available they confirm the results from the shipboard adcp annual mean velocity sections from the parallel ocean program numerical model also show near bottom velocities exceeding 5 cm s 1 with the same tendency for the zonal velocity component near the bottom to match the direction of the surface jets transport across the entire antarctic circumpolar current acc cannot be estimated accurately from adcp referenced geostrophic sections because even a very small cross track bias integrates to a large error a preliminary look at the 1992 model transport stream function shows that the effect of bottom referencing varies from section to section it can cause 40 sv recirculations to be missed and can cause net transport to be underestimated or overestimated by o 30 sv

evolution of neoproterozoic lower palaeozoic lufilian arc central africa a new model based on syntectonic conglomerates the lufilian arc a segment of the neoproterozoic lower palaeozoic pan african orogenic network within southern and central africa deforms the sedimentary succession of the katanga supergroup and contains large bodies of fragmental rocks previously considered as tectonic friction breccias these are re interpreted as syntectonic conglomerate complexes which reveal the existence of two previously unrecognized basins and shed new light on the katangan stratigraphy and tectonics a prominent uplift in the southern part of the roan rift at c 760 ma resulted in conglomerates olistostromes underlying the succeeding guba rift sequence during post 735 ma orogenesis north advancing nappes supplied coarse detritus into the fungurume foreland

the effects of changes in plate motions on the shape of the marquesas fracture zone the marquesas fracture zone mfz one of the great fracture zones that formed on the pacific farallon ridge system shows dramatic variations in morphology along its strike that cannot be explained by models for lithospheric flexure in response to thermal stresses and differential subsidence marine geophysical data collected by the r v maurice ewing in fall 1991 show that major structures in the mfz can be correlated with changes in plate motions as the fracture zone formed the western mfz shows two significant changes in trend at 209 e and at 224 e the change in strike at 209 e records a reorientation that put the transform fault under compression and created a 100 km long sinuous ridge within the fracture zone the change in plate motions at 224 e induced extension in the transform fault creating three subparallel fracture zones these results are in accord with observations of morphological changes observed at active transform faults and other fracture zones and suggest that even relatively small changes 6 in spreading direction can produce significant structures that are preserved in the fracture zone

how do long offset oceanic transforms adapt to plate motion changes the example of the western pacific antarctic plate boundary 1 oceanic transform faults respond to changes in the direction of relative plate motion studies have shown that short offset transforms generally adjust with slight bends near the ridge axis while long offset ones have a remarkably different behavior the western pacific antarctic plate boundary highlights these differences a set of previously unpublished seismic profiles in combination with magnetic anomaly identifications shows how across a former 1250 km long transform the emerald fracture zone plate motion changes have produced a complex geometric readjustment three distinct sections are recognized along this plate boundary an eastern section characterized by parallel multiple fault strand lineaments a central section shallower than the rest of the ridge system overprinted by a mantle plume track and a western section organized in a cascade of short spreading axes transform lineaments this configuration was produced by changes that occurred since 30 ma in the australia pacific relative plate motion combined with a gradual clockwise change in pacific antarctic plate motion these events caused extension along the former emerald fracture zone originally linking the pacific antarctic spreading ridge system with the southeast indian ridge then an intra transform propagating ridge started to develop in response to a 6 ma change in the pacific antarctic spreading direction the close proximity of the euler poles of rotation amplified the effects of the geometric readjustments that occurred along the transform system this analysis shows that when a long offset transform older than 20 ma is pulled apart by changes in spreading velocity vectors it responds with the development of multiple discrete parallel fault strands whereas in younger lithosphere locally modified by thermal anisotropies tensional stresses generate an array of spreading axes offset by closely spaced transforms

the elastic thickness of the lithosphere in the pacific ocean abstract in this study we present determinations of the effective elastic thickness t e of the oceanic lithosphere along pacific chains or archipelagoes t e is determined by computing the deflection of a continuous elastic plate under the load of volcanoes and constrained by geoid heights provided by seasat in the south central pacific estimates of 14 km for the marquesas and 6 km or less for the pitcairn mururoa gloucester chain are in good agreement with a previous work in this region cook austral and society chains around the line islands chain seasat data reveal that the bathymetry is poorly known preventing fine analysis meanwhile t e looks globally very low 6 km except for three volcanoes but these results may be unreliable the easter chain features low t e values 6 km with no noticeable variation along the chain higher values are found for a samoan island manuae 24 km and along the hawaiian emperor seamounts chain from 32 km at the eastern end of the chain to 21 5 km for the hawaiian volcanoes and from 25 5 to 15 km for the emperor seamounts the large number of t e estimates obtained in this study points out a noticeable difference between north and south pacific results those from the north pacific agree with the general trend increase with the square root of age plate at loading time while those from the south central pacific are much lower according to their plate age these low t e results from the south pacific are only partly explained by taking account of thermal perturbations using the rejuvenation model therefore these results then point out a regional difference in oceanic lithosphere

occurrence of upper jurassic lower cretaceous black organic rich pelitic sediments as targets for unconventional hydrocarbon exploration in the outer carpathians and adjacent part of the alps our work on the dark pelitic sediments of the polish carpathians and eastern alps shows that these jurassic through lower cretaceous sediments owe their organic content to a combination of global processes such as climatic changes and changes to the carbonate compensation depth ccd and local controls such as basin morphology input of terrestrial organic material and local volcanic activity these sediments developed in basins both floored by oceanic crust as well as within the continental crust north european platform our data show that these anoxic or poorly oxygenated deposits average total organic carbon toc value is around 2 5 wt were laid down in the individual basins at different times from the late jurassic to the barremian and almost continuously up to the early cenomanian a period of 30 to 50 m y and their thickness reached hundreds of meters this long time span made it impossible to distinguish precisely the known aptian and albian oceanic anoxic events oae our data show that sedimentation of dark organic rich deposits was not only controlled by global events such as climatic and ccd changes but also by local ones as a result of differences in their basin morphology and development input of land plant detritus and local volcanic activity as an example of the anoxic succession a detailed description of the black sediments of the proto silesian basin is presented some of these anoxic shales were buried to a depth of a few thousand meters during the folding and overthrusting movements we propose that these shales could represent a unique shale oil and shale gas resource in an intensely structured basin

a model for the analysis of drifter data with an application to a warm core ring in the gulf of mexico a model developed primarily for the analysis of drifter data is discussed the model is based on a parametric representation of the drifter velocity in terms of monge potentials two of which are constants following the motion of the fluid in the application presented here one of the potentials is taken as the frequency of rotation about a ring by a parcel a more restricted interpretation of the velocity gradient in variant for horizontal flow is also discussed the other potential is taken as the streamline of a parcel that is locally approximated as a conic section for the restricted interpretation solutions to the model equations are critically dependent on the relative sizes of the squares of the vertical vorticity and the total deformation rate this model differs from drifter cluster models in that each drifter provides independent estimates of the vorticity and deformation rates application is made to path data from three drifters that were seeded in a warm core ring in the gulf of mexico in november 1980 the model provided estimates of the ring translation and swirl velocities along with the ring geometry the analysis showed that the ring was persistently elliptical with the major axis aligned in the east west direction a satellite infrared photo on january 21 1981 confirmed this orientation

the tectonic fabric of the ocean basins 1 we present a global community data set of fracture zones fzs discordant zones propagating ridges v shaped structures and extinct ridges digitized from vertical gravity gradient vgg maps we use a new semi automatic fz tracking program to test the precision of our hand digitized traces and find a mean absolute deviation of less than 3 4 km from the raw vgg minima that most clearly delineate each feature and less than 5 4 km from the fz location predicted by fitting model profiles to the vgg data that represent the morphology of the individual fzs these offsets are small considering gravity data only provide an approximation for the underlying basement morphology we further investigate the origin of non fz seafloor fabric by combining published abyssal hill heights computed from gravity anomalies with global half spreading rates a residual abyssal hill height grid with spreading rate effects removed combined with our interpreted tectonic fabric reveals several types of seafloor fabric distinct from typical abyssal hills where discordant zones do not overprint abyssal hill signals residual abyssal hill height anomalies correspond to seafloor that accreted near mantle thermal anomalies or zones of melt depletion our analysis reveals several areas where residual abyssal hill height anomalies reflect pseudo faults and extinct ridges associated with ridge propagation and or microplate formation in the southern pacific ocean

a compendium of causes and effects of processes at transform faults and fracture zones a flowchart has been constructed which consolidates into a single conceptual framework a large number of the phenomena and processes which have been observed or postulated at transform faults tfs and fracture zones fzs oceanic ridge ridge transform faults and their aseismic extensions are emphasized the upstream end of the flowchart contains large scale boundary conditions imposed by the position of a particular transform fault in space and time for example slip rate the downstream end of the flowchart contains small scale features characteristic of individual tfs or fzs for example the existence of a fz parallel ridge features of both the upstream and the downstream ends of the flowchart can be mapped measured or otherwise derived by direct observation the middle of the flow chart includes processes and phenomena which are inferred to result from the upstream boundary conditions and to cause the downstream small scale features for example thermal conduction across the plate boundary phenomena in this black box in the center of the flowchart cannot be directly observed with present technology but must be inferred the advantages of ordering knowledge into such a flowchart are that inconsistancies gaps in understanding self limiting phenomena feedback loops and previously unrecognized relationships stand out and that the boundary between inference and observation is clearly drawn

thermomechanical evolution of oceanic fracture zones a fracture zone fz model is constructed from existing models of the thermal and mechanical evolution of the oceanic lithosphere as the lithosphere cools by conduction thermal and mechanical boundary layers develop and increase in thickness as age 1 2 surface expressions of this development such as topography and deflection of the vertical i e gravity field are most apparent along major fz s because of the sharp age contrast a simple model including the effects of lateral heat transport but with no elastic layer predicts that variations in seafloor depth and deflection of the vertical will become increasingly smooth and ultimately disappear as the fz ages observations however show that both the fz topography and the deflection of the vertical remain sharp as the fz evolves these two observations as well as the observed asymmetry in deflection of the vertical profiles across the udintsev romanche and mendocino fz s are explained by including a continuous elastic layer in the model the asymmetry in deflection of the vertical is a consequence of elastic thickness variations across the fz modeling also shows that the evolution of the fz topography is extremely sensitive to the initial thermal structure near the ridge transform intersection model geoid steps and their development with age are used to access techniques for measuring geoid offsets across fz s reasonable step estimation techniques will underestimate the overall step amplitude by up to 50 this implies that abnormally thin thermal boundary layers derived from studies of geoid height versus age are not required by the data

changes in plate motions and the shape of pacific fracture zones geosat passes the new 2 min global gravity grid smith and sandwell 1995 and shipboard bathymetry across central pacific fracture zones were used to identify features common to fracture zone segments that formed during times of changes in plate motions these features are not predicted by current locked fault fracture zone models during a change in spreading direction that induces tension across the transform fault large offset greater than 500 km transforms develop multiple parallel faults spaced 50 to 100 km apart the gravity signature of small offset transform faults under tension includes a broader and more symmetric trough than observed on segments that formed during periods of steady spreading parts of fracture zones that form subsequent to a spreading reorientation that causes compression across the transform fault generally exhibit a single fault scarp that fits the locked fault model seafloor formed during a period of change usually marks a transition between structural styles for example between multiple fracture zone strands and a narrower single fault fracture zone widening of the transform fault zone under tension and narrowing under compression are consistent with the assumption that during a change in spreading direction the new spreading ridges propagate to but not across the old transform fault

thermal stresses in the oceanic lithosphere evidence from geoid anomalies at fracture zones models for the thermal and mechanical evolution of the oceanic lithosphere predict the progressive development of large thermal stresses in the thickening plate however there has so far been little direct evidence for the magnitude and distribution of thermal stresses we present theoretical models which examine the effect of thermal stresses at fracture zones and show that an anomaly of the predicted form can be observed in geoid profiles which cross fracture zones specifically our models predict the development of thermal bending moments which depend on lithosphere thickness or age and therefore change across fracture zones including the effect of varying thermal bending moments thin plate theory predicts vertical nonisostatic displacements of the lithosphere by plate flexure the predicted amplitude of the resulting geoid anomaly is large enough to be observed in seasat altimeter profiles furthermore the general form of this anomaly differs sufficiently from other predicted components of the geoid anomaly at fracture zones to be discernable the anomaly due to thermal stresses has been clearly identified in geoid profiles across the clarion and the udintsev fracture zones the amplitude of this observed anomaly is well predicted if cooling lithosphere begins to accumulate elastic stresses at a temperature of 700 c consistent with the maximum depth of seismicity in the oceanic lithosphere the distribution of thermal stresses with depth is also consistent with focal mechanisms of intraplate earthquakes

evidence for small scale mantle convection from seasat altimeter data evidence for the early development of convective instability in the thermal boundary layer associated with cooling plates has been found from gravity anomalies and residual sea surface heights derived from seasat altimeter data subtle lineated patterns trending in the direction of plate motion in the hot spot reference frame are observed over the younger portions of the fast moving pacific and indo australian plates in particular for the east central pacific ocean the seasat derived data sets reveal lineations with 1 wavelengths in the range 150 500 km perhaps increasing with plate age and 2 peak to trough amplitudes of 5 20 mgal for gravity anomalies the lineated pattern over the pacific plate which first becomes discernable over seafloor 5 to 10 m y old west of the east pacific rise is clearly oblique to the trends of the prominent pacific farallon fracture zones onset of convective instability at such early ages can be understood if young oceanic lithosphere is underlain by a layer having a viscosity of about 1018 pa s 1019 p which is about 3 orders of magnitude less than mantle viscosity inferred from postglacial rebound studies recent numerical studies of convection in fluids with a temperature and pressuredependent viscosity support an early onset time for convective instability and low viscosity zones in the upper mantle beneath young lithosphere such low viscosity zones may correspond to similarly located regions of low shear wave velocities resolved through studies of surface waves

thermal stress and the spacings of transform faults bathymetric charts are used with satellite altimeter profiles to locate major ridge transform intersections along five spreading ridges the ridges are the mid atlantic ridge the east pacific rise the chile rise the pacific antarctic rise and the southeast indian ridge analysis of these data show spacings between transform faults w increase linearly with spreading rate w 6 28 m y this linear correlation is explained by a thermoelastic model of a cooling strip of lithosphere spreading at a rate the traction free boundaries of the thin elastic strip simulate cracks in the lithosphere at transform faults a two dimensional thermoelastic solution for the in plane stress shows the largest stress component is tensional and parallel to the ridge stresses are zero at the ridge and increase as age to a maximum value at an age of w 4 all stress components are small for ages greater than w when the transform spacing is large compared with the spreading rate w 100 m y thermal stresses exceed the strength of the lithosphere for ages between 0 and 30 ma the observed maximum ratio of transform spacing to spreading rate w 10 m y results in low thermal stresses that only exceed the strength of the lithosphere for ages less than 1 ma thus transform faults relieve most of the thermal stress model predictions also agree with earthquake studies showing that normal faults in young lithosphere have tensional axes aligned with the ridge moreover oceanic intraplate earthquakes rarely occur in lithosphere older than 30 ma as predicted by the model these and other geophysical observations confirm turcotte s hypothesis that transform faults are thermal contraction cracks

the trace fossil gyrophyllites in deep sea siliciclastic deposits of the istebna formation upper cretaceous palaeocene of the carpathians an example of biologically controlled distribution abstract gyrophyllites kwassizensis glocker occurs abundantly in deep sea density current siliciclastics of the istebna formation silesian nappe outer western carpathians poland slovakia and czech republic close to the cretaceous palaeogene boundary it is composed of petal shaped lobes radiating from a thin shaft forming rosettes on a few levels in the sediment the trace fossil is interpreted as a feeding structure produced by a soft body worm which actively filled the lobes with mud transported from the underlying layer probably in response to migration of redox boundary in a generally poorly oxygenated environment probably due to microbial decomposition of cellulose and other organic particles the mud from below was more nutritional than the more fresh mud from the sea floor the number of lobes in a rosette from 7 to 15 is referred to ontogenetic development of the tracemaker and indirectly to time of burrow occupation the number varies between localities and may indicate a more hospitable habitat in the areas where the number is higher g kwassizensis occurs only in a narrow stratigraphic interval after a significant drop of sedimentation rate caused by non eustatic reasons in facies conditions which are not unique during the long history late jurassic miocene of the external carpathian subbasins this suggests that facies control was less important for distribution of this trace fossil than some undetermined biological factors which enabled successful but incidental invasion of the tracemaker to deep sea floor of one of the subbasins the silesian basin

vertical structure and transport of the antarctic circumpolar current in drake passage from direct velocity observations 1 the structure of the antarctic circumpolar current acc in drake passage is examined using 4 5 years of shipboard acoustic doppler current profiler adcp velocity data the extended 1000 m depth range available from the 38 khz adcp allows us to investigate the vertical structure of the current the mean observed current varies slowly with depth while eddy kinetic energy and shear variance exhibit strong depth dependence objectively mapped streamlines are self similar with depth consistent with an equivalent barotropic structure vertical wavenumber spectra of observed currents and current shear reveal intermediate wavenumber anisotropy and rotation indicative of downward energy propagation above 500 m and upward propagation below 500 m the mean observed transport of the acc in the upper 1000 m is estimated at 95 2 sv or 71 of the canonical total transport of 134 sv mean current speeds in the acc jets remain quite strong at 1000 m 10 20 cm s 1 vertical structure functions to describe the current and extrapolate below 1000 m are explored with the aid of full depth profiles from lowered adcp and a 3 year mean from the southern ocean state estimate sose a number of functions including an exponential are nearly equally good fits to the observations explaining 75 of the variance fits to an exponentially decaying function can be extrapolated to give an estimate of 154 38 sv for the full depth transport

adcp referenced geostrophic circulation in the bering sea basin abstract a month long circumnavigation of the bering sea basin in august 1991 was designed to study the basin scale circulation for the first time in this region vessel mounted acoustic doppler current profiler adcp measurements provided an absolute reference for geostrophic currents transport in the alaskan stream 01 1500 db was 24 sv sv 106 m3 s 1 westward considerably higher than the 10 15 sv usually inferred from geostrophic calculations referred to 1500 db but in good agreement with previous work relative to moored current meters as previously reported the stream separated from the aleutian ridge forming an anticyclonic eddy that restricted inflow to the bering sea flow through the aleutians varied substantially across the passes the kamchatka current was traceable for 800 km until it left the bering sea carrying 14 sv 0 3000 db eddies were detected from the clustering of centers of curvature of sequential adcp vectors incompletely spanned eddies can bias transports counterrotat

evolution models of two flysch basins the northern carpathians and the southern apennines abstract the geological evolution of the external domains of the northern carpathians and southern apennines is compared and two models of flysch basins are proposed the first related to a tensile stage of the orogeny is applied only to the northern carpathian area during the cretaceous the latter related to a compressive stage is present in both areas during the cenozoic the different evolutions of the basins have counterparts in the present day continental margin and the thinning of the crust during the tensile stage controls the flysch sedimentation in the first model and during the compressive stage of subduction along mobile plate junctions enables the accumulation of deposits in trench like basins to take place

why there are no earthquakes on the marquesas fracture zone although the plate tectonic paradigm does not predict relative horizontal motion between lithosphere on opposing sides of a fracture zone the fact that younger more rapidly subsiding seafloor lies adjacent to older seafloor implies relative vertical motion the observation that fracture zones are notably aseismic has led to the proposition of high strength along fracture zones such that the differential subsidence is accommodated by flexure across a locked fault this model predicts that a ridge develops on the young side of the fracture zone flanked by a foredeep trough on the old side with parallel warping of the moho and large associated gravity anomalies previous analyses of satellite altimetric passes over pacific fracture zones have shown that the amplitude and shape of the gravity anomalies frequently do not conform to the predictions of this simple model one of the most notable departures has been the marquesas fracture zone mfz where only one limited section was determined to be high strength curiously the only earthquake to rupture the mfz in the last 35 years is located in this locked region elsewhere where we would predict vertical slip must be occurring the fault is aseismic to better understand the history of vertical motion on this fault we have analyzed geophysical data obtained during the recent survey ew9106 aboard the r v maurice ewing our detailed hydrosweep gravity and seismic data resolve this paradox by showing no evidence for vertical slip along the fault shear stresses caused by differential thermal subsidence do not exceed the strength of this fault rather the failure of the altimetry signal to conform to the predictions of the high strength model along much of the mfz is caused by changes in the pacific farallon pole of rotation reorientation of the plate boundary was accommodated by propagating rifts intratransform tension or compression and changes in transform offset that complicated the signal from differential subsidence across a locked fault for example a counterclockwise rotation of the transform in the cretaceous caused overthrusting in the transform and thus compensation of the depth differential by flexural loading of a very young plate a clockwise rotation of this right stepping transform fault at about 35 ma led temporarily to a crenulated plate boundary and later to the development of intra transform spreading centers after accounting for these complications the fracture zone appears capable of sustaining at least 20 mpa of shear stress and remains locked along the entire length of the fault except perhaps locally where it passed over the tuamotu and society hot spots

comparisons of gravity anomalies at pseudofaults fracture zones and nontransform discontinuities from fast to slow spreading areas published mechanisms for rift tip propagation at spreading centers include extensional deformation and an initial period of slow spreading we investigate whether the gravity signal and inferred crustal structure at pseudofaults formed in medium to superfast spreading environments resemble the gravity signal at fracture zones or nontransform discontinuities formed in slow spreading environments we find that altimetry based gravity anomalies on the mathematician bauer easter juan fernandez and northern chile ridge pseudofaults located in 75 150 mm yr full rate seafloor spreading environments are similar in amplitude and form to atlantic fracture zones with 20 30 mm yr spreading rates a 5 15 mgal positive mantle bouguer anomaly is observed on the pseudofault bounding the eastern juan fernandez microplate comparable to those at some similar age offset nontransform discontinuities in slow spreading environments our results suggest that the deeps associated with active propagating rift tips result from both a dynamic mantle component and anomalous crust the latter of which remains frozen at pseudofaults we predict that any pseudofaults with age offsets more than 1 m y and not coincident with hotspot volcanism will be associated with thin and possibly unusually dense crust even in superfast seafloor spreading environments

tectonic history and new isochron chart of the south pacific we have developed an internally consistent isochron chart and a tectonic history of the south pacific using a combination of new satellite altimeter data and shipboard magnetic and bathymetric data highly accurate vertical deflection profiles 1 2 rad derived from 22 repeat cycles of geosat altimetry reveal subtle lineations in the gravity field associated with the south pacific fracture zones these fracture zone lineations are correlated with sparse shipboard bathymetric identifications of fracture zones and thus can be used to determine paleospreading directions in uncharted areas the high density of geosat altimeter profiles reveals previously unknown details in paleospreading directions on all of the major plates magnetic anomaly identifications and magnetic lineation interpretations from published sources were combined with these fracture zone lineations to produce a tectonic fabric map the tectonic fabric was then used to derive new poles of rotation for 12 selected times in the late cretaceous and cenozoic from our reconstructions we estimated the former location of the spreading centers in order to derive a new set of isochrons interpreted unes of equal age on the ocean floor we believe that the use of new geosat altimeter data in combination with a multi plate reconstruction has led to an improvement in our understanding of south pacific tectonics

local lithospheric relief associated with fracture zones and ponded plume material 1 buoyant plume material ponds at the base of oceanic lithosphere it is a natural probe for the relief on the base of the lithosphere owing to plate age because it flows laterally along an upside down drainage pattern geomorphic and geochemical studies of near ridge and on ridge hot spots indicate as expected that the oceanic lithosphere thickens as it ages corridors of thin lithosphere channel plume material along the axis while the thick lithosphere at the end of ridge segments dams this along axis flow channel hot spots extend from plumes toward ridge axes however a good correlation between local lithospheric thickness and local age is not evident at fracture zones within the old ocean basins such a correlation would be expected if the lithosphere cooled only by conduction then pressure release melting and volcanoes would occur preferentially near fracture zones where plume material cascades from thick old to thin young lithosphere this concentration of volcanic edifices does not occur this lack of correlation between lithosphere thickness and plate age is an expected consequence of small scale convection at the base of the lithosphere scaling relationships and numerical models indicate that modestly vigorous convection of several milliwatt per meter squared is sufficient to perturb local lithospheric relief beneath fracture zones without changing the gross correlation of lithospheric thickness with plate age typically the step in lithospheric thickness moves toward the old side of the fracture zone

the net transport of the antarctic circumpolar current through drake passage abstract estimates of the net transport through drake passage are made for three periods during which the year long drake 79 current meter array spanning the passage was in operation relative geostrophic shears from hydrographic surveys in january 1979 april 1979 and january 1980 were referenced to directed speed measurements to give profiles of net speed direct measurements were averaged in time to make them more compatible with the spatially averaged baroclinic shears the agreement between directly measured and baroclinic shears is generally good except in regions of large bathymetric relief and during periods when current cores were shifting past or between moorings the presence of cold core rings during two of the drake 79 hydrogaphic surveys resulted in intensified flow and increased transport within fronts but did not affect the net transport through the passage the three latest estimates of net transport 117 144 and 134 106 m3 s 1 are in close agreement with a previous estimate of 124

mass transport deposits overprinted by contractional tectonics a case study from the southern apennines of italy mass transport deposits mtds created by gravity driven deformation of unlithified sediments and tectonic melanges produced by contractional deformation are characterized by a similar chaotic appearance it follows that distinguishing structures formed by soft sediment deformation during mass transport from those produced by contractional tectonics can be problematic in fact deformation occurring along detachment levels may completely obliterate the original sedimentary fabric although a number of advances have been made during recent decades field criteria for discriminating structures within mtds that are overprinted by later regional contraction are not readily applicable to all the exposed examples we address some of these general issues through a detailed case study of the monte facito formation in italy this triassic unit was formed during the africa europe continental separation and since the miocene has been involved in contractional deformation during the construction of the apennines the monte facito formation consists of a series of stratigraphically coherent units separated by chaotic and often deformed intervals whose origin has been previously attributed to either tectonic or sedimentary processes an example is provided by a characteristic pebbly mudstone or paraconglomerate which has been interpreted as either a triassic gravity flow deposit or alternatively as a product of shearing along regional contractional detachments during the miocene this detailed field based study allows us to recognize structures related to the depositional processes that created these chaotic intervals and which can therefore be interpreted as mtds we also discriminate structures connected to later contractional tectonics that locally produced intense reworking of the mtds