the liuyuan volcanic belt in nw china revisited evidence for permian rifting associated with the assembly of continental blocks in the central asian orogenic belt the basaltic pillow lavas in the liuyuan region of nw china considered to be part of an ophiolitic suite have been central to the models on tectonic setting evolution and timing of the final closure of the palaeo asian ocean new field evidence on the sedimentary units associated with the basalts reveals comparable sequences in the northern and southern flanks of the liuyuan volcanic belt with coarse to fine sediments from periphery to the centre the dacites and rhyolites formed coevally with the pillow basalts the pillow basalts are interlayered with lacustrine sandstone claystone and clayey lake deposits detrital zircons from these sediments yield zircon u pb ages of 291 285 ma andesites dacites and rhyolites from the basaltic sequence yield u pb ages of 280 277 ma similar to the 282 280 ma ages of gabbros that intrude the pillow lavas all these rocks cover the 460 440 ma granite and greenschist basement and have been intruded by gabbros of c 272 ma age with subsequent 230 227 ma north south contractional thrusting and folding the data from our study are incompatible with the existing models that consider the basalts as part of an ophiolitic suite along the northern continental margin of china from west to east the tarim dunhuang alxa and north china cratonic areas all show evidence for regional extension through rifting during early middle permian time these rift features and basaltic eruptions occurred coevally with the assembly of various microcontinental blocks against the siberian craton at c 300 250 ma synchronous with amalgamation of the central asian orogenic belt caob on the northern side of the liuyuan rift these events were also broadly synchronous with formation of the global supercontinent pangea

on the average absolute transport of the deep western boundary currents east of abaco island the bahamas abstract data obtained from a line of absolute current profiler pegasus and ctd stations at 26 5 n east of abaco island in the northern bahamas are used to estimate the average transport and overall level of variability of the deep below 800 m southward flow associated with the so called deep western boundary current dwbc at this latitude from april 1985 to september 1987 a total of 11 sections were made along a line extending from near the island boundary to 85 km offshore as part of the subtropical atlantic climate studies stacs program in all but two cases when pegasus data were obtained over the total depth absolute velocities were determined from 0 to about 3000 db while ctd derived relative velocities were determined over the total depth using the combined datasets it is possible to reference the relative geostrophic velocity with pegasus data thereby obtaining an estimate of the absolute southward transport of the deep flow the average value of transport determined in this man

determining the strength of the deep western boundary current using the chlorofluoromethane ratio abstract the dilution of a passive tracer during deep water formation and the subsequent advection mixing in a deep boundary current is modeled with application to chlorofluoromethanes cfms in the north atlantic two different types of boundary currents are considered a uniform flow and a simple shear flow in each case the core of the flow mixes with surrounding water which continually accumulates cfms in an extreme case the coupled systems predicts that the cfm ratio in the current is unaltered from the ratio of its source water save for a time lag more realistic cases however suggests that the ratio is not a conserved quantity but is substantially altered in both the overflow basin and boundary current matching the model results to cfm data collected near the grand banks gives a predicted average core speed of 5 10 cm s 1 for the deep western boundary current and provides a constraint on the transport and diffusivity of the flow as well

the arcs of the western alps and the northern apennines an updated view abstract the arcs of the western alps and the northern apennines and the link between them are in the process of being investigated using the european geotraverse and they have historically been interpreted in many different ways new information particularly geophysical further constrains possible models both arcs have evolved in several stages sometimes complexly interrelated and sometimes independent of each other compressional belts produced in these stages have either been of the push arc type indentation into a deformable mass or the pull arc type backward migration of hinge of a subduction zone leading to small extensional basins known as back arc basins and pores with an arcuate mountain range on the subduction side extensional periods with the possible formation of pull arcs in the alps comprise the gosau period between the eo and meso alpine push arc phases and the oligocene lull period between the meso and the neo alpine push arc phases in the northern apennines remainders of the meso alpine nappes were involved in oligocene early miocene pull arc formation associated with spreading in the balearic sea followed by push arc formation particularly in the middle miocene and by renewed pull arc formation from the latest late miocene to the present during all of these developments the moho was modified by such processes as lithospheric stretching asthenospheric intrusions subhorizontal shearing and isostatic uplift the present moho configuration is consequently a collage of moho patches formed at different intervals both push and pull arcs are laterally bounded by complementary strike slip or transform zones these too were modified in the course of history and their final geometry is consequently of a very complex nature in the alps for instance the insubric fault zone appears to have been the main dextral transform fault of the neogene push arc until it was sinistrally kinked by the giudicarie fault zone and probably deactivated dextral transpression being briefly transferred to the en echelon brachyanticlines of the late alpine windows in the case of the oligocene apennines the sinistral rotations of corsica and sardinia otherwise hard to understand may be attributed in part to sinistral transform motions along the eastern border zone of the oligocene early miocene balearic extension

subaqueous rhyolite block lavas in the miocene ushikiri formation shimane peninsula sw japan abstract a rhyolite mass of the miocene ushikiri formation in the western part of the shimane peninsula sw japan is a small subaqueous edifice about 600 m high and 4 km wide formed at water depths between 200 and 1000 m it consists mainly of three relatively flat lava flow units 50 300 m in maximum thickness each of which includes lobes and their polyhedral fragments the lava lobes are poorly to well vesiculated glassy to microcrystalline and flow banded and folded compared with mafic pillows they are large having thick quenched and brecciated glassy crusts because of their high viscosity surface tension and thermal conductivity their surfaces disintegrate into polyhedral fragments and grade into massive volcanic breccia the massive volcanic breccia composed of the lobe fragments is poorly sorted and covered with stratified volcanic breccia of the same rock type the rhyolite lavas commonly bifurcate in a manner similar to mafic pillow lavas however they are highly silicic with 1 5 vol phenocrysts and have elongated vesicles and flow folds implying that they were visco plastic during flowage their surface features are similar to those of subaerial block lava with respect to rheological and morphological features they are subaqueous equivalents of block lava

morphology and formation of spreading cracks on pillow lavas at cape grim northwestern tasmania australia tertiary basaltic pillow lobes at cape grim northwestern tasmania australia display well preserved spreading cracks in the glassy crust the spreading cracks are lens shaped or rectangular in plan view in cross section they consist of a graben like depression with a broad floor bounded by steep scarps the floor of spreading crack contains an axial crack and a number of ridges that are arranged symmetrically with respect to the axial crack the ridges within spreading cracks are inferred to have formed by the regular repeated production and splitting of new crust at the centre of the spreading crack this new interpretation of ridges in spreading cracks differs from the previous interpretation in which they are regarded as elongate normal fault blocks our interpretation provides new insight into the propagation mechanisms of pillow lavas

the flux and mixing rates of antarctic bottom water within the north atlantic calculation was made of the northward flow of antarctic bottom water into the western north atlantic basin through a passageway approximately 300 km wide between the ceara rise and the mid atlantic ridge at about 4 n two moorings carrying four current meters each were placed in the region where currents were expected to be the greatest and were left for 360 days the current was not steady but exhibited large surges with approximately a 60 day time scale whose cause is unknown current meters in the fastest flowing region all exhibited a net northward flow it is estimated that approximately 0 8 106 m3 s 1 of water colder than 1 9 c potential temperature flowed on the average into the north atlantic with this number possibly being too small by 0 3 106 m3 s 1 or too big by 0 1 106 m3 s 1 depending upon estimates of the width of the region which the current meters sample however these numbers differ from geostrophic estimates of 1 98 106 m3 s 1 the disagreement coming almost entirely from the fact that the geostrophic estimates give a sizeable flux of water colder than 1 2 c while the current meters do not based upon the two different flux rates residence times and mixing coefficients are calculated for antarctic bottom water for each 0 1 c potential temperature interval from 1 0 c to 1 9 c finally some comments on the dynamics of the northward flow are made

miocene pillowed sills in the shimane peninsula sw japan abstract two miocene basaltic andesite pillowed sills in the shimane peninsula sw japan were intruded into wet marine sediments plastically deforming them the pillows are elongated constricted interconnected and relatively closely packed individual pillows have a poorly to moderately vesiculated somewhat crystalline rind thinner than a few centimeters and a moderately to well vesiculated more crystalline core contraction cracks and spreading cracks are poorly developed the pillows in the sills morphologically resemble pillow lava flows and during sill intrusion the magma bifurcated into pillow lobes in a manner similar to pillow lavas formation of pillows in sill probably occurs when the magma is intruded into wet sediments and protrudes fingers by the instability of the magma sediment interface with little turbulence of magma flow

path of the north atlantic deep water in the brazil basin recent hydrographic sections and high quality historical data sets are used to determine geostrophic currents at subtropical latitudes in the western basin of the south atlantic levels of no motion are determined from water mass information and a mass balance constraint to obtain the transport field of north atlantic deep water nadw in this region the incoming nadw transport of about 20 sv from the north at 19 degrees s appears to be balanced by only one third of this transport leaving in the south and two thirds leaving to the east or northeast at the mid atlantic ridge a simple model is proposed to determine the cause of the nadw branching it is shown that potential vorticity preservation in the presence of topographic changes leads to a similar flow pattern as observed with branching near the vitoria trindade ridge and also an eastward turning of the southward western boundary current at about 28 degrees s the latitude where a balance of planetary vorticity change and stretching can be expected

newly discovered submarine flank eruption at stromboli volcano aeolian islands italy 1 the nw submarine portion of stromboli volcano has been investigated by deep towed sidescan sonar bathymetric surveys video camera runs and dredging during two research cruises in 2002 and 2004 the surveys resulted in the identification of an extensive pillow lava field 106 107m3 at about 2300 m of water depth and 9 km from the shoreline of stromboli island the pillow lavas have a unique composition that does not match any known subaerial product although a limited affinity exists with those erupted during the neostromboli eruptive cycle of the island 13 6 ka this is the first finding of a submarine eruption on the northern side of stromboli and improves the knowledge of its flank activity and volcanic hazards this eruption is interpreted as marking the onset of a new volcanic cycle from the edifice periphery fed by a new distinct magma mixed with traces of the previous magma that survived the emptying of the neostromboli magma chamber

delineation of the north central italian upper mantle anomaly the italian peninsula is the focus of intense deformational tectonic activity it is underlain by mantle material whose inferred relatively anomalous properties1 2 are not inconsistent with the seismic volcanic and thermal activity that is manifested in this region the most effective geophysical tool for mapping the structure of the uppermost 200 300 km of the earth is the observation and analysis of seismic surface wave dispersion on a regional scale here we synthesize the interpretations of rayleigh wave dispersion measurements made by several authors each for different parts of north central italy3 8 to delineate the lateral extent of the upper mantle anomaly in this region

hemispheric asymmetry of deep water transport modes in the western atlantic subtropical studies of the atlantic meridional cold water flow show a hemispheric contrast in the dominant southward transport mode below 2000 m in the north atlantic lower deep water ldw 1 8 2 4 c dominates with small transport of middle deep water mdw 2 4 3 2 c while in the south atlantic the opposite is observed we use numerous observations in the western basins of the tropics to show that the transition occurs rapidly near the equator in the western atlantic a meridional section in the central brazil basin suggests zonal flows are responsible for the transition ldw transport from the guiana basin north of the equator flows eastward in the northern brazil basin and is inferred to continue on through the romanche fracture zone into the eastern atlantic an opposing flow of mdw from the eastern tropical atlantic flows toward the western boundary where it bifurcates to supply mdw to the deep western boundary current dwbc of the brazil basin as well as to feed the northward flow of mdw in the guiana basin offshore of the dwbc the magnitude of each of these oppositely directed flows is roughly 7 sv we furthermore speculate that they are connected predominantly by upwelling from ldw to mdw within the low latitude eastern basin the overall deep water transport system below 2000 m in the western basins of the mid and low latitude atlantic is thus found to comprise the following three distinct components 1 a strong dwbc transport of ldw with associated recirculation dominates the guiana basin north of the equator 2 in the northern brazil basin just south of the equator a narrow eastward flow absorbs the ldw and carries it eastward while a somewhat broader westward flow imports mdw into the western basin 3 this mdw flow then bifurcates with the southward branch causing the mdw dominance in the brazil basin where the mdw dominated dwbc and associated recirculations are the third component of the deepwater transport system

eastward flow through the mid atlantic ridge at 11 n and its influence on the abyss of the eastern basin abstract the dilute antarctic bottom water of the north atlantic eastern trough is supplied from the western trough through fractures in the mid atlantic ridge in particular the influence on eastern trough property distributions of flow through the romanche and vema fracture zones near the equator and 11 n respectively has been noted previously here new observations are reported that document the abyssal circulation of the northeastern atlantic basins gambia abyssal plain south canary basin and north canary basin in particular the dominance of vema influence the absence of romanche influence and the existence of a system of deep western boundary currents and estimated transport deep isopycnals slope steeply across the vema s eastern end near 39 w corresponding to a geostrophic transport through the vema of 2 1 to 2 3 106 m3s 1 colder than 2 0 c this is half or more of the estimated bottom water that flows north across the equator into the subtropical western north atlantic this transp

the submarine volcanic system of the errigoiti formation albian santonian of the basque cantabrian basin northern spain stratigraphic framework facies and sequences abstract the errigoiti formation located in the central domain of the basque cantabrian basin is an albian to santonian bathyal submarine volcanic system of alkali basaltic character these volcanics occurred in an extensional geodynamic context generated by the drifting of the iberian plate with respect to the european plate stratigraphic analyses reveal the facies distribution and depositional architecture of a longitudinal cross section of the errigoiti volcanic system four facies groups were distinguished sheet lavas sl derived from low viscosity lava flows at high magma discharge rate pillow lavas pl derived from intermediate viscosity lava flows at moderate discharge rate pillow breccias pb derived either from in situ fragmentation of lavas pb1 or rock falling from pillow lava slopes pb2 and stratified volcaniclastites vc derived from volcaniclast resedimentation through gravity flows either by early remobilization vc1 or post volcanic reworking vc2 the facies groups occur in a predictable repetitive succession essentially from base to top an sl pl pb vc stacking pattern this is interpreted to reflect an upward waning in the magma discharge rate five major volcanic sequences make up the errigoiti formation each comprises packages tens to hundreds of meters thick deposited during short time spans of volcanic activity separated by long time intervals of volcanic inactivity consequently boundaries between sequences are associated with marked hiatuses reworked volcaniclasts and or turbidite pelagic sedimentation analysis of lateral and vertical facies evolution enabled us to propose a depositional model consisting of three depositional environments from proximal to distal settings these are amalgamated pillow volcanoes scattered pillow volcanoes and volcanic fringe basically responding to a proximal to distal pl pb pl vc and sl vc evolution of facies associations contemporaneous fossiliferous turbidite pelagic sequences that surround the volcanic succession allow paleobathymetry to be estimated on the basis of biofacies sites with the highest rate of volcanic emission correspond to an average depth of 900 m sites with thinner volcanic pile accumulated at a minimum depth of 1100 m the facies sequence established in this work and the processes involved in its formation are comparable with the sequences and processes described in other submarine basic volcanic systems consequently the depositional model for the errigoiti formation can perhaps serve as a reference model for this type of volcanic system

deep flow along the western boundary south of the blake bahama outer ridge abstract in june july 1990 hydrographic chlorofluorocarbon cfc and velocity observations were taken along the western boundary of the north atlantic south of the blake bahama outer ridge from 30 to 24 n between the northern bahamas and 71 w the deep flow in the region associated with the deep western boundary current forms a pattern of strong narrow currents and cyclonic gyres close to the continental slope with broad slower southward flow offshore the cfcs reveal that the most recently ventilated water i e having the highest cfc concentrations due to more recent contact with the atmosphere in the northern north atlantic is found along the western boundary in two distinct cores between potential temperatures 4 6 c and 1 9 2 4 c geostrophic transport streamlines were constructed for the deep flow referenced using direct velocity observations at 26 5 n and assuming mass conservation between closed areas bounded by the hydrographic sections the tracers and transports are used together

crustal structure of northern latium central italy from receiver functions analysis new evidences of a post collisional back arc margin evolution abstract the crustal velocity structure in a region of central apennines of italy at the hinge between the highly stretched portion of the monte argentario promontory and the magmatic province of the tolfa domes complex northern latium is discussed in this study s wave velocities at depth have been constrained by the modeling of p wave receiver functions rf from both temporary and permanent broadband seismic stations the computer 3d vs models show a thin crust 19 25 km made of a shallow and thin sedimentary cover a very high velocity and anisotropic layer related to a metamorphic basement and a low vs anisotropic layer in the middle lower crust above a shallow moho discontinuity modeled at about 20 km depth the volcano tectonic evolution of this portion of tyrrhenian back arc margin has been strongly influenced by its peculiar crustal architecture the low vs layer acted as a shear zone in the middle lower crust during the tyrrhenian extension also helping the development of plio quaternary magmatism our findings potentially give new constraints on the evolution of the area and to the general comprehension of back arc development in collisional regions

the textures formation and dynamics of rare high mgo komatiite pillow lavas abstract pillow lavas are an abundant morphological lava type both on earth and on some extraterrestrial bodies we examine pillows from kambalda western australia komatiites that uniquely preserve pillow necks inter pillow cavities and internal crusts our study is the first description of true pillows from an archaean high mgo 31 komatiite their size ranges from 0 5 to 5 cm and most have equal vertical and horizontal axes due to very low melt viscosities 0 01 0 1 pa s these komatiite pillows are one to two orders of magnitude smaller than modern basaltic counterparts true high mgo komatiites such as those at kambalda require a low flow rate potentially found on distal flow edges such low flow rates are in conflict with the high flow velocities generally assumed for komatiites and hence explains the rarity of komatiite pillow lavas

pipe vesicles in basalt trails left by dense immiscible melt droplets sinking through a viscous basal thermal boundary layer abstract pipe vesicles tubular cavities found in the basal parts of p hoehoe lava flows worldwide constitute one of their fundamental primary structures like other vesicles pipe vesicles have been ascribed to gas bubbles whether rising buoyantly through viscous lava or trapped in an inward moving solidification front these models involve special and unrealistic conditions and still poorly explain characteristic features of pipe vesicles in a new model proposed here pipe vesicles are postulated to be hollow trails left by droplets of dense immiscible iron rich silicate or sulphide melt sinking through a viscous thermal boundary layer just above the lower chilled margin of a p hoehoe flow unit driven by gravity the droplets sink vertically in static lava but obliquely in mobile lava such as lava undergoing gravitational spreading viscous and fluid dynamic forces tend to deform the sinking droplets and resist their motion the characteristic inverted y inverted v and lambda shapes of individual pipe vesicles reflect downward branching with a large droplet breaking up in partially crystallized highly polymerized basalt in the basal thermal boundary layer pipe vesicles do not yield lava flow directions even on a local centimeters to meters scale but are indirect indicators of widespread liquid immiscibility processes in basalts and potential commercial fe cu ni mineralization as pipe vesicles are not vesicles cavities left by gas escape a new term is necessary and the term vermiform p hoehoe having good descriptive power but no genetic connonations is suggested for p hoehoe with pipe vesicles

shape of empirical and synthetic isoseismals comparison for italian m 6 earthquakes we present results from a comparative analysis of empirical and synthetic shapes for isoseismals of low intensity i iv vi on the mcs scale for six italian earthquakes of ml 4 5 6 our modeling of isoseismals is based on a plane stratified earth model and on the double couple point source approximation to calculate seismograms in the frequency range f 1 hz with a minimum of parameter variation we demonstrate that the low intensity isoseismals provide information on source geometry we strive to avoid subjectivity in isoseismal constructions by using the new diffuse boundary method which visualizes isoseismals with their uncertainty similar results in this direction are known for large earthquakes m l 6 or greater with extended sources and for the higher isoseismals i vi on the mm scale the latter studies disregard the earth structure use a greater number of parameters and therefore have greater possibilities for fitting the data than our approach

multiple rind structure in pillow lava as an indicator of shallow water multiple rind structure is common among shallow water pillows with diameters larger than about 1 m in oamaru new zealand on the columbia plateau usa and elsewhere a rind consists of sideromelane tachylyte and tachylytic basalt a multiple rind is a concentric set of repeated rinds in various forms e g a portion of a broken rind thrust under another part a series of short and detached subparallel rinds or a pouch shaped depression transitions and combinations of these three forms are common multiple rind structure develops at any part of the pillow perimeter but does not cover the pillow completely it is always accompanied by a rupture in the outermost rind up to 13 rinds have been observed but two to four rinds are most common the multiple rind structure is formed by implosion resulting from condensation of exsolved h2o when h2o condenses a pressure difference between the interior and exterior of a pillow is created above a certain threshold pressure difference the outer skin of a pillow is torn at weak points such as radial joints and thrusts under the neighboring skin buckles to form a pouch shaped depression or produces some variation of these one set of multiple rinds is thus formed further exsolution and condensation of h2o in solidifying pillows may cause development of additional rinds h2o exsolution and condensation and subsequent implosion are limited to low pressure environments so that multiple rind structure is characteristic of shallow water pillow lava

a miocene island arc volcanic seamount the takashibiyama formation shimane peninsula sw japan abstract the miocene volcanic complex of the takashibiyama formation consists largely of subalkali subaqueous basalt to andesite lavas and andesite to dacite subaqueous volcaniclastic flow deposits most of subaqueous lavas are moderately to intensely brecciated with rugged rough surfaces and ramp structures similar to subaerial block lava volcaniclastic flow deposits commonly include basalt to andesite lava fragments and or pyroclastic materials and are similar in internal features to debris flow and turbidite deposits subaqueous block lavas and minor pillow lavas form volcanic piles above the vents being flanked or covered with volcaniclastic flow deposits each volcanic pile is several kilometers wide and several hundred meters thick and overlaps one after another as the major eruptive center migrates from time to time thus the volcanic complex comprises three or more superimposed volcanic piles which are intruded by basalt to andesite dikes and sills and are underlain by mafic to intermediate large hypabyssal to plutonic bodies hydrothermal alteration occurs in places but especially concentrates in the lower part of the volcanic complex after the cessation of opening of the japan sea the volcanic complex started to erupt in a middle bathyal environment on the japan sea side and became emergent as it grew to a thickness over 1500 m during 4 m y under a n s trending horizontal compressional stress it is a volcanic seamount probably in a typical island arc setting

hydrography of the romanche and chain fracture zones the romanche and chain fracture zones rfz and cfz are known as pathways for the lower north atlantic deep water lnadw and the antarctic bottom water aabw from the western trough to the eastern trough of the equatorial atlantic ocean across the mid atlantic ridge we report hydrographic observations describing the evolution of the lnadw and aabw properties during their transit through the equatorial fracture zones to the west of the rfz and cfz sills the lnadw and aabw cores are separated by a deep thermocline pycnocline which marks the transition between the two water masses the deep thermocline is eroded eastward and vanishes in the eastern basin this zonal asymmetry is the signature of a zonal baroclinic pressure gradient associated in each fracture zone with eastward flows of lnadw and aabw below 3800 m depth during the eastward transit through the rfz the near bottom aabw becomes less dense saltier 0 07 and warmer 0 7 c richer in oxygen 0 3 ml l 1 but less rich in silicate 30 mol l 1 simultaneously the lnadw core becomes fresher and colder at a given density and the oxygen maximum characterizing the lnadw core weakens by 0 2 ml l 1 we argue that the property changes within the aabw and lnadw are due to intense vertical mixing in addition to vertical mixing with the aabw it seems likely that isopycnal mixing of the lnadw with the eastern basin deep water contributes to the property evolution of the lnadw exiting the rfz in the cfz evidence is also given of mixing occuring within the aabw and the lnadw a sudden change in the aabw properties observed across the cfz main sill suggests the blocking of the eastward progression of the densest aabw by the cfz main sill however this dense water can reach the eastern basin by flowing northeastward through valleys the sills of which are deeper than thoses of the cfz finally a simple hydraulic control model applied to the rfz and cfz flows predicts a transport of 1 4 0 1 106 m3 s 1 of water colder than 1 9 c across the rfz cfz main sill

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

transport of bottom water in the romanche fracture zone and the chain fracture zone abstract two moored arrays deployed in the romanche fracture zone and chain fracture zone in the equatorial atlantic ocean provide two year long time series of current and temperature in the lower north atlantic deep water and the antarctic bottom water total time averaged transport of antarctic bottom water potential temperature 1 9 c across the mid atlantic ridge amounts to 1 22 106 m3 s 1 eastward with a standard deviation of 0 25 106 m3 s 1 a time averaged transport of 0 36 0 23 106 m3 s 1 eastward is found for the lower north atlantic deep water in the 1 9 2 1 c temperature range but this may represent only a fraction of the total flow of this water mass across the ridge contributions of the romanche fracture zone and chain fracture zone to the antarctic bottom water transport are similar while the chain fracture zone has the greater share of lower north atlantic deep water transport semiannual and annual periods are detected in the transport time series and together expl

morphology and propagation styles of miocene submarine basanite lavas at stanley northwestern tasmania australia miocene submarine basanite pillows lava lobes megapillows and sheet lavas in the stanley peninsula northwestern tasmania australia are well preserved in three dimensions the pillows have ropy wrinkles transverse wrinkles symmetrical wrinkles contraction cracks and three types of spreading cracks on their surfaces and concentric and radial joints in the interior the lava lobes have ropy wrinkles and contraction cracks on their surfaces the megapillows are cylindrical with a smoothly curved upper surface and steep sides and are characterized by distinct radial columnar joints in the interior they are connected to pillows that propagate radially from its basal margin the sheet lavas are tabular and have vertical columnar joints in the interior the largest sheet lava shows a remarkable gradation from a lower 5 m thick pillow facies to an upper massive facies the pillows lava lobes megapillows and sheet lavas are inferred to have been emplaced completely below sea level but in a shallow marine environment their morphological features suggest that the pillows grew by episodic rupture of a near solid crust and emergence of hot lava whereas the lava lobes propagated by continuous stretching of the outer skin at the flow front the megapillows and sheet lavas were master feeder channels by which molten lava was conveyed to the advancing pillows the sheet lavas propagated by repeated processes of pillow formation and overriding by an upper massive part alternating pillow and massive facies commonly found in ocean floor drill cores and exposed in cross section in many subaqueous volcanic successions may have formed by propagation of pillows from the basal margins of advancing sheet lavas

measured and modeled cfc distribution of lower north atlantic deep water in the guiana basin the circulation of the overflow lower north atlantic deep water olnadw in the guiana basin is studied by the measured and modeled distribution of the chlorofluorocarbon component cfc 11 the olnadw is formed in the northern atlantic and transported south to the equatorial region as the densest part of the deep western boundary current dwbc characterized by cfc and oxygen maxima some former studies proposed a northwestward recirculation of the boundary current in the guiana basin because the measured southeastward dwbc transport was larger than the calculated net transport across the entire width of the basin despite the variability of the dwbc reported recently this discrepancy seems to hold an advective diffusive model is presented which includes recirculation in the northern guiana basin as well as horizontal diffusion and the results are compared with a cfc survey in march 1994 because of high cfc concentration in the boundary current one would expect to find a high cfc signal in the recirculated water mass near the mid atlantic ridge as well however this was not observed modeled cfc distributions and observations only agree if the presumed recirculation is located in the center of the northern guiana basin or if no westward recirculation exists at all it was found that the strength of the recirculation is about 3 1 5 sv which is smaller than previously supposed

saline outflow from the arctic ocean its contribution to the deep waters of the greenland norwegian and iceland seas abstractsince 1985 various investigators have proposed that norwegian sea deep water nsdw is formed by mixing of warm and saline deep water from the arctic ocean with the much colder and fresher deep water formed by convection in the greenland sea gsdw we here report on new observations which suggest significant modification and expansion of this conceptual model we find that saline outflows from the arctic ocean result in several distinct intermediate and deep salinity maxima within the greenland sea the southward transport of the two most saline modes is probably near 2 sv mixing of gsdw and the main outflow core found over the greenland slope derived from about 1700 m in the arctic ocean cannot by itself account for the properties of nsdw instead the formation of nsdw must at least in part involve a source which in the arctic ocean is found below 2000 m the mixing of various saline outflows is diapycnal while significant nsdw production appears to occur in northern fram strait large amounts of saline arctic ocean outflow also traverse the western greenland sea without mixing and enter the iceland sea during the past decade deep convection in the greenland sea has been greatly reduced while deep outflow from the arctic ocean appears to have continued resulting in a markedly warmer slightly more saline and less dense deep regime in the greenland sea american geophysical union 1991

transequatorial flow of antarctic bottom water in the western atlantic ocean abyssal geostrophy at the equator abstract in its general northward flow along the western trough of the atlantic antarctic bottom water aabw must pass over several sills separating the various abyssal basins at the equator the western trough is deformed by major east west offsets of the mid atlantic ridge and the continental margin of brazil forming a newly zonal abyssal channel about 250 km wide centered at the equator and extending approximately 1000 km along its axis in which the aabw is confined thus the general northward flow of aabw is topographically constrained to be westward as it crosses the equator a hydrographic section across this channel at 37 w shows the aabw isopycnals to be bowl shaped within and beneath the level of the channel walls the equatorial geostrophic relation permits us to compute a zonal velocity from the well defined parabolic distribution of dynamic height relative to a reference level at the transition between aarw and the overlying deep water here 4 3 106 m3 s 1 is estimated for the wes

magnetic interpretation related to geo magnetic provinces the italian case history abstract a comparison of the results obtained from the geophysical interpretation with the available information regarding the italian geological situation permitted us to establish our so called geo magnetic provinces the relationship between the magnetic characteristics and the tectonic evolution permitted the identification of each of the four following provinces that exist inside the global tectonic confines 1 1 the sardo corso block which represents the eastern boundary of stable europe this province is characterized by medium wavelength low amplitude anomalies that originate in an outcropping basement hercynian granites s l 2 2 the orogenic belt which constitutes the double alps apennines system from a magnetic standpoint this system is characterized by short wavelength low amplitude anomalies that are due to a paleozoic outcropping and or buried acid crystalline basement these anomalies are found to overlie long wavelength medium amplitude regional anomalies that are related to a deep apenninic basement central northern apennines 3 3 the foreland area which occurs from sicily hyblean plateau and apulia northwards to ancona and the po plain this area is characterized by a crystalline basement which is typically differentiated from the standpoint of basicity 4 4 the rifting zone which is represented by the part of the tyrrhenian sea lying south of the 41st parallel discontinuity the ionian abyssal plain and the pantelleria and linosa troughs in the sicily channel the main characteristic of this province is its extreme basicity differentiation in the crystalline basement which is induced by the geochemical processes connected with the deep geodynamic events these phenomena do not permit the correlation of the semioceanic basement of the rifting zone with the continental basement by means of interactive modeling a structural tectonic picture of the basement of the various italian geo magnetic provinces has been obtained the main result was found to be that the orogenic belt basement is undergoing intense tectonic compression and overlies the structural highs of the foreland area which mainly show tensive events

morphology and growth style of a miocene submarine dacite lava dome at atsumi northeast japan abstract a miocene submarine lava dome at tate iwa atsumi yamagata japan displays well preserved primary morphological features the dome currently rises above a wave cut coastal platform and is 55 m high and 90 180 m across it comprises a massive core and a lava lobe hyaloclastite rim both of which are composed of compositionally uniform feldspar phyric dacite sio2 64 wt the boundary between these two zones is distinct but gradational the massive core consists of homogeneous coherent dacite and is characterized by flow banding along the margin and by columnar joints radiating from the centre to the margin the lava lobe hyaloclastite rim encircles the massive core and consists of a complex of 80 90 dacitic lava lobes and 10 20 hyaloclastite the lava lobes are 1 6 m thick 3 12 m wide and more than 5 m long each lobe consists of a radially columnar jointed core and a glassy rim 10 30 cm thick the hyaloclastite comprises polyhedral dacite clasts 5 100 cm across in a matrix of dacite fragments up to 5 mm across the lava lobes and hyaloclastite have gradational contacts in places paleobathymetric studies based on foraminifera in sediment beneath the dome and the k ar age of the dome suggest that it was extruded in a middle bathyal environment 1500 2000 m below sea level at 12 9 0 6 ma the internal structures of the dome suggest that it formed by a combination of exogenous growth involving extrusions of small dacite lobes and endogenous growth involving a continuous magma supply and simple expansion from the interior the presence of small lava lobes along the rim suggests that the magma had relatively low viscosity at the time of extrusion in spite of its high silica content magma temperatures calculated by two pyroxene and fe ti oxide geothermometers were 999 1042 and 957 1005 c respectively the inferred low viscosity may be attributed to the high temperature of the magma and or a high confining pressure resulting from the deep sea environment

morphological and sedimentological characteristics of the neogene submarine coherent lavas and hyaloclastites in southwest hokkaido japan abstract the neogene formations in southwest hokkaido japan are mostly composed of submarine volcanic products such as submarine coherent lavas and hyaloclastites associated with feeder dikes this paper presents criteria for recognition of submarine effusion products through description of the morphological and sedimentological characteristics of coherent lavas such as pillow lobes sheet flow lava lobes and pseudo pillow lavas and hyaloclastites and feeder dikes and a small amount of associate pyroclastic rocks

morphology and distribution of lava flows on mid ocean ridges a review abstract both pillow lavas and sheet flows are important features of oceanic volcanism at mid ocean ridges submersible surveys of the neovolcanic zone and off axis areas of these complex seafloor volcanic terrains conducted during the past two decades have uncovered a wide array of basaltic surface forms with pillow basalts displaying bulbous spherical and elongate tubular patterns and sheet flows exhibiting smooth lobate rippled wrinkled ropy whorly hackly and jumbled configurations the genesis of pillow lavas and sheet flows appears to be coupled to variations of spreading rates within the plate boundary zone while pillow lavas predominate at slow spreading centers i e mid atlantic ridge sheet flows prevail along the active volcanic zones at intermediate i e galapagos rift and juan de fuca ridge fast and superfast i e east pacific rise spreading centers yet both types of flows are present at each setting the distribution of pillow lavas and sheet flows along a ridge segment is related to the topographic gradient of the ridge axis hence the formation of sheet flows tends to be favored by the development of topographic highs between ridge segment boundaries where the crustal lid is thinnest and rifting directly taps the underlying magma chamber fissure eruptions here release copious amounts of surface fed fluid lavas which decrease in volume down the topographic gradient away from the bathymetric high of the ridge segment lava flows become more distal and channelized thereby fostering greater concentrations of tube fed pillow flows toward the segment boundaries the type of lava flow morphologies encountered at any specific site on the seafloor is contingent upon the effusion rate cooling rate and slope as demonstrated by laboratory simulations

the atlantic deep western boundary current water masses and transports near the equator the distributions and transports of deepwater masses at the western boundary in the tropical atlantic off brazil have been studied on three surveys along 35 degrees w and 5 degrees s and one at 10 degrees s transports are obtained from direct measurements of the velocity fields pegasus profiling system and lowered acoustic doppler current profiler and from geostrophic computations using chlorofluoromethane cfm and hydrographic distributions four water masses could be identified forming the north atlantic deep water nadw system two of these have a high cfm content the shallow upper nadw sunadw and the overflow lower nadw olnadw these exhibit the highest velocity signals at 35 degrees w where distinct flow cores seem to exist most of the southeastward flow of the sunadw centered around 1600 m occurs 320 km offshore between 3 degrees 09 s and 1 degrees 50 s 9 7 3 3 sv farther north in that section a highly variable reversing flow is found in a second velocity maximum the transport of olnadw centered around 3800 m of 4 6 2 6 sv is guided by the parnaiba ridge at 1 degrees 45 s 35 degrees w the water masses located between the two cfm maxima the labrador sea water lsw and the lnadw old water mass lnadw old did not show any persistent flow features however a rather constant transport of 11 1 2 6 sv was observed for these two layers the total southeastward flow of the nadw at 35 degrees w showed a transport of 26 8 7 0 sv if one neglects the reversing sunadw north of 1 degrees 50 s at 5 degrees s the flow of all deepwater masses shows vertically aligned cores the main southward transport occurred near the coast 19 5 5 3 sv the boundary current is limited offshore by a flow reversal present in all three surveys but located at different longitudes at 10 degrees s a southward transport of 4 7 sv was observed in november 1992 however the section extended only to 32 degrees 30 w so that probably a significant part of the flow has been missed an important result is the large transport variability between single cruises as well as variability of the spatial distribution of the flow at 35 degrees w which could lead to large uncertainties in the interpretation of single cruise observations despite these uncertainties we suggest a circulation pattern of the various deepwater masses near the equator by combining our mean transport estimates with other observations

flow direction and magnetic mineralogy of lava flows from the central parts of the peninsula of baja california mexico magnetic properties of two apparently unrelated lava suites one tholeiitic and the other alkalic coexisting in the central parts of the peninsula of baja california mexico were measured in this study macroscopic indicators and measurements of anisotropy of magnetic susceptibility ams were combined to infer the flow direction on those lavas these measurements were used to investigate the likelihood of the existence of an abnormally long tholeiitic lava flow in this part of the peninsula the obtained results indicate that the tholeiitic flows in the region constitute regular length flows and are likely to have been issued through vents located within the area of study additionally comparison of the magnetic signature of tholeiitic and alkalic lavas reveals a systematic difference in some of the magnetic parameters bulk susceptibility and curie temperatures in particular it is proposed that the narrow range of curie temperatures characteristic of each lava type can be used as a reliable proxy for the identification of each lava type in the region all of these findings show that the alkalic and tholeiitic lavas of the region are more closely related to each other than previously suspected

crossing of the equator by the deep western boundary current in the western atlantic ocean abstract property distributions and geostrophic shear from a hydrographic section near 37 w in the atlantic ocean show the deep western boundary current dwbc in the north atlantic deep water nadw established against the western boundary of the brazil basin immediately south of the equator between 2 and 5 s the dwbc thus has directly crossed the equator to the south atlantic following the east southeast trend of the continental slope isobaths the estimated dwbc transport of nadw is 35 106 m3 s 1 similar to other estimates from the tropics discussed here these large dwbc transports are opposed by flow of deep water to the north atlantic immediately offshore of the dwbc with as much as two thirds of the dwbc transport being returned as these recirculations one recirculation center is the guiana basin north of the equator but extends at least a few hundred kilometers south of the equator another is visible at 11 s in the brazil basin the degree of connection of these two observed recirculatio

abyssal ocean overturning shaped by seafloor distribution the abyssal ocean is broadly characterized by northward flow of the densest waters and southward flow of less dense waters above them understanding what controls the strength and structure of these interhemispheric flows referred to as the abyssal overturning circulation is key to quantifying the ocean s ability to store carbon and heat on timescales exceeding a century here we show that north of 32 s the depth distribution of the seafloor compels dense southern origin waters to flow northward below a depth of about 4 kilometres and to return southward predominantly at depths greater than 2 5 kilometres unless ventilated from the north the overlying mid depths 1 to 2 5 kilometres deep host comparatively weak mean meridional flow backed by analysis of historical radiocarbon measurements the findings imply that the geometry of the pacific indian and atlantic basins places a major external constraint on the overturning structure

lateral variations in the european lithosphere and seismic activity abstract in the mediterranean region an interesting correlation between the model of the lithospheric structure and the distribution of epicentres of shallow earthquakes with magnitudes larger or equal to 6 5 can be established in some areas these areas namely northern and southern italy the calabrian and hellenic arcs correspond to belts where high rigidity values in the lid are associated with very rapid changes in the lithospheric thickness

thermo mechanical modeling of the tyrrhenian sea lithospheric necking and kinematics of rifting we present the results of quantitative forward modeling of the sardinian rifted margin of the tyrrhenian sea the purpose of this study is to investigate the thermo mechanical structure that affects the thinning of the lithosphere across the margin the role of lithospheric necking during basin formation constrained by basement topography moho depth and gravity anomalies is modeled for different compensation models independent constraints are obtained from the analysis of the predicted thermal structure a deep level of necking 25 km is required to explain the observed crustal geometries and gravity anomaly signature the model predicts spatial and temporal variations in rheology during extension with important implications for kinematics of lithospheric thinning prerift lithospheric conditions strain rate and temperature during extension appear to be the key controls on the style of lithospheric rifting and necking in the tyrrhenian sea a forward model for basin stratigraphy is presented for the polyphase history of the tyrrhenian rifting this model provides quantitative estimates of time space dependent crustal thinning and rates of extension

vp vs estimation in southwestern europe from p wave and surface wave tomography analysis abstract for 10 regions in southwestern europe a comparison has been made between the surface wave and p wave tomography results available in the literature starting from the p wave models inferred by p wave tomography theoretical phase velocities have been computed adjusting the ratio between p wave and s wave velocities in order to simultaneously fit the observed rayleigh wave phase velocities the v p v s ratio is an important variable that can be used to investigate the nature of variations in the propagation velocity of seismic waves in the earth s interior more specifically it can be used to discriminate between thermal and compositional influences on the velocities of seismic waves in this sense the largest value in the distribution of the v p v s ratio that we have obtained in the modelling is associated with a specific region in north central italy where the presence of fluids at crustal level is well known

structure and organization of submarine basaltic flows sheet flow transformation into pillow lavas in shallow submarine environments distal pillows occur associated with a sheet flow and megapillows in the menakoz outcrops of the basque cantabrian basin n spain basaltic volcanic rocks are interbedded with turonian sediments and depict typical features of shallow submarine emissions an exceptional basaltic flow displays four types of morphology 1 sheet lava with columnar jointing 2 welded columnar breccia 3 megapillows and 4 pillow lavas with sparse megapillows the field data from menakoz combined with experimental and field data from the literature for similar volcanic facies can be integrated into a new propagation model for the transition from sheet flows to pillow lavas in underwater environments at near vent high emission rates lava flows develop a thin crust immediately after its emplacement and break at the front under the magma pressure allowing for the massive propagation of lava as a sheet flow increased cooling promotes thickening of the lava outer crust far from the vent while continuous supply of fresh magma increases the pressure onto the thick crust until its rupture the lava emitted in small volumes from the flow front promotes the formation of megapillows and pillow lavas that are later on covered by the advancing sheet flow the lava flow freezes progressively toward more distal parts gradually increasing its viscosity until it stops the crust temporarily holds the residual melt pressure increasing the volume of the flow distal section by inflation finally the internal magma pressure breaks the crust and liberates lava at moderate to low flow rates producing pillows while lava drainage inside the inflated sheet flow produces lava tunnels and gravitational collapse of the roofs by hydrostatic pressure to form breccias nurtured by columnar lava fragments

the early archaean nondweni greenstone belt southern kaapvaal craton south africa part ii characteristics of the volcanic rocks and constraints on magma genesis the early archaean nondweni greenstone belt is dominated by mafic volcanic rocks which have a wide range in compositions primary volcanic structures and compositional characteristics point to this succession being unique in archaean geology and an important indicator of controls of magma formation and environment of deposition compositionally the nondweni lavas are broadly similar to those of the barberton sequence high values for cao al2o3 ti y and low al2o3 tio2 they are also distinctly different in that sio2 content is markedly higher and incompatible trace element ratios are also different the high silica content has promoted the subdivision of komatiitic and basaltic rocks into the following categories komatiite komatiitic andesite komatiitic basalt basalt and basaltic andesite the recognition of the distinct suite of komatiitic andesites is aided by the lower zr ti ratios than those lithologies of equivalent mgo content reported from other greenstone belts and sio2 contents as high as 58 these characteristics suggest similarity to recent high mg andesites none of the lava compositions exceed 23 mgo anhydrous and pyroxene rather than olivine dominates the crystallization assemblage olivine spinifex textures are entirely absent in the nondweni greenstone belt and instead pyroxene or amphibole after pyroxene spinifex is abundantly developed and is characterised by spectacular radial conical structures which have their apices towards the tops of the flow units some of the spinifex cone structures attain heights of up to 6 m branching pyroxene crystals and feathery textured plagioclase typify the spinifex textures of the komatiitic andesites the common occurrence of coned and branching spinifex textures in a wide range of magma compositions indicates that these were controlled by thermal characteristics and depositional environment for the flow units rather than solely by composition this may have been facilitated by emplacement in shallow water rather than in deep water as envisaged for the onverwacht group of the barberton sequence shallow water depositional environments in the nondweni group are supported by sedimentary lithofacies well preserved pillow structures also show a wide range in textural forms sizes of pillows degree of welding of pillow margins development of hyaloclastite and formation of shelf structures formed by repeated filling of lava tubes are related to both compositional type as well as physical controls such as extrusion rate and nature of the substrate komatiites seldom form pillows and very large pillow formation is restricted to the komatiitic andesite lava type komatiite flow successions are typified by spinifex textured units as well as by massive and highly brecciated aphyric flow units unaltered pyroxene and plagioclase characterise some of the massive flow units and pillowed basalts of the witkop formation the present paper is the second part of a series on the nondweni greenstone belt part i wilson and versfeld 1994 describes the stratigraphy sedimentology mineralization and depositional environment there are strong of kaapvaal craton may have been different to that of the barberton greenstone belt a present day analogue to the nondweni tectonic setting may be an ensialic back arc basin adjacent to a continental margin

zonal circulation across 52 w in the north atlantic 1 in july august 1997 a hydrographic acoustic doppler current profiler adcp tracer section was occupied along 52 w in the north atlantic as part of the world ocean circulation experiment hydrographic program underway and lowered adcp ladcp data have been used to reference geostrophic velocities calculated from the hydrographic data additional small velocity adjustments provided by an inverse model constraining mass and silicate transports in 17 neutral density layers yield the absolute zonal velocity field for 52 w we find a vigorous circulation throughout the entire section with an unusually strong gulf stream 169 sv and southern deep western boundary current dwbc 64 sv at the time of the cruise at the northern boundary on the west side of the grand banks of newfoundland we find the westward flowing labrador current 8 6 sv whose continuity from the labrador sea east of our section has been disputed directly to the south we identify the slopewater current 12 5 sv eastward and northern dwbc 12 5 sv westward strong departures from strictly zonal flow in the interior which are found in the ladcp data make it difficult to diagnose the circulation there isolated deep property extrema in the southern portion associated with alternating bands of eastward and westward flow are consistent with the idea that the rough topography of the mid atlantic ridge directly east of our section causes enhanced mixing of antarctic bottom water properties into overlying waters with distinctly different properties we calculate heat and freshwater fluxes crossing 52 w that exceed estimates based on air sea exchanges by a factor of 1 7

orogens and slabs vs their direction of subduction abstract subduction zones appear primarily controlled by the polarity of their direction i e w directed or e to nne directed probably due to the westward drift of the lithosphere relative to the asthenosphere the decollement planes behave differently in the two end members in the w directed subduction zone the decollement of the plate to the east is warped and subducted whereas in the e to nne directed it is ramping upward at the surface there are w directed subduction zones that work also in absence of active convergence like the carpathians or the apennines w directed subduction zones have shorter life 30 40 ma than e or ne directed subduction zones even longer than 100 ma the different decollements in the two end members of subduction should control different ptt paths and therefore generate variable metamorphic assemblages in the associated accretionary wedges and orogens these asymmetries also determine different topographic and structural evolutions that are marked by low topography and a fast eastward migrating structural wave along w directed subduction zones whereas the topography and the structure are rapidly growing upward and expanding laterally along the opposite subduction zones the magmatic pair calc alkaline and alkaline tholeiitic volcanic products of the island arc and the back arc basin characterise the w directed subduction zones magmatic rocks associated with e or ne directed subduction zones have higher abundances of incompatible elements and mainly consist of calc alkaline shoshonitic suites with large volumes of batholithic intrusions and porphyry copper ore deposits the subduction zones surrounding the adriatic plate in the central mediterranean confirm the differences among subduction zones as primarily controlled by the geographic polarity of the main direction of the slab the western margin of the adriatic plate contemporaneously overridden and underthrust europe toward the west to generate respectively the alps and the apennines while the eastern margin subducted under the dinarides hellenides these belts confirm the characters of the end members of subduction zones as a function of their geographic polarity similarly to the pacific subduction zones

large scale waveform inversions of surface waves for lateral heterogeneity 2 application to surface waves in europe and the mediterranean linear surface wave scattering theory is used to reconstruct the lateral heterogeneity under europe and the mediterranean using surface wave data recorded with the network of autonomously recording seismographs nars the waveform inversion of the phase and the amplitude of the direct surface wave leads to a variance reduction of approximately 40 and results in phase velocity maps in the period ranges 30 40 s 40 60 s and 60 100 s a resolution analysis is performed in order to establish the lateral resolution of these inversions using the phase velocity perturbations of the three period bands a two layer model for the s velocity under europe and the mediterranean is constructed the s velocity perturbations in the deepest layer 100 200 km are much more pronounced than in the top layer 0 100 km which confirms that the low velocity zone exhibits pronounced lateral variations in both layers the s velocity is low under the western mediterranean while the s velocity is high under the scandinavian shield in the deepest layer a high s velocity region extends from greece under the adriatic to northern italy several interesting smaller features such as the massif central are reconstructed one of the spectacular features of the reconstructed models is a sharp transition in the layer between 100 and 200 km near the tornquist tesseyre zone this would indicate that there is a sharp transition at depth between central europe and the east european platform the waveform inversion of the surface wave coda leads to good waveform fits but the reconstructed models are chaotic this is due both to a lack of sufficient data for a good imaging of the surface wave energy on the heterogeneities and to an appreciable noise component in the surface wave coda

giant rafted pumice blocks from the most recent eruption of taupo volcano new zealand insights from palaeomagnetic and textural data abstract giant blocks of pumice lie strewn along a former shoreline of intracaldera lake taupo new zealand and are the sole subaerial evidence of the most recent volcanism at the taupo supervolcano geochemically they are identical to material erupted during the complex and multiphase 1 8 ka taupo eruption which they post date by one to two decades the blocks some of which are 10 m long show complex jointing patterns indicative of both surface chilling and continued interior expansion as well as heterogeneous vesicularity with dense rims mean density 917 kg m3 grading via an intervening transition zone mean density 844 kg m3 into a more highly vesicular interior mean density 815 kg m3 analysis of thermal demagnetisation data indicates significant reorientation of the blocks as they cooled through a series of blocking temperatures some parts of block rims cooled to below 580 c well before emplacement on the shore whereas other parts in the interior and transition zones which cooled more slowly acquired different orientations before stranding some block interiors cooled after blocks were finally deposited and record the direction of the 1 8 ka field the blocks are believed to be derived from one or both of a pair of rhyolitic lava domes that developed on the bed of lake taupo several decades after the climactic taupo eruption over the inferred vent area these and similar giant rafted pumice blocks in other marine and lacustrine settings raise a number of questions about how volatile rich felsic magma can be erupted underwater with only limited thermal fragmentation furthermore the prolonged flotation of out sized fragments of vesiculated magma formed during subaqueous dome growth contrasts with the rapid sinking of smaller pieces of hot plinian pumice under laboratory conditions the genesis of pumice forming the blocks is not entirely clear most simply the blocks may represent part of a vesiculated carapace of a growing lava dome broken loose as the dome grew and deformed then rising buoyantly to the surface parts of the carapace could also be released by local magma water explosions some textures of the pumice however suggest fresher magma released from beneath the carapace this may suggest that silicic dikes and pillows pods intruded into a growing mound of silicic hyaloclastite itself formed by quench fragmentation and thermal granulation of the dike margins this fragmental cover would have inhibited cooling of a still hot and actively vesiculating interior which was then released to float to the surface by gravitational destabilisation and collapse of the growing pile following their formation the large fragments of pumice floated to the lake s surface where they were blown ashore to become embedded in accumulating transgressive shoreface sediments and continue cooling

the main characteristics of the lithosphere asthenosphere system in italy and surrounding regions we present a summary of the available information on rayleigh wave dispersion data for the italian area the dispersion curves can be grouped into two main families according to their shape one with an almost linear trend in the period range from 40 to 150 sec the other with a relatively flat portion in the period range from 40 to 80 sec the inversion of these data shows that there are strong lateral variation in the lithosphere system a very rapid transition in the lithospheric thickness from about 130 km to about 30 km as well as in the s wave velocity of the lithosphere and asthenosphere

polygonal feeder tubes filled with hydroclasts a new volcanic lithofacies marking shoreline subaerial submarine transition this paper describes for the first time a new lithofacies that formed in the passage zone during the construction of pahoehoe lava fed deltas in the north and ne coastal areas of gran canaria canary islands atlantic ocean these lava fed deltas which are pliocene in age present similar lithofacies associations to those previously described in the literature except for two distinct features low abundance of hyaloclastites and a new lithofacies in the passage zone this new lithofacies which we propose to name polygonal feeder tubes filled with hydroclasts comprises metre scale lava feeder tubes with decimetre scale coherent poorly vesicular and aphanitic rinds of polygonal morphology filled with closely packed hydroclasts generated in situ it represents the first stage in the interaction between seawater and thick lava flows entering the sea under the influence of a tidal regime thus marking sea level this lithofacies should be easily recognizable in ancient successions and thus represents a useful marker of palaeoshorelines supplementary material sample preparation and sample geochemistry are available at http www geolsoc org uk sup18785

the complex facies architecture and emplacement sequence of a miocene submarine mega pillow lava flow system muriwai north island new zealand the early miocene waiatarua formation at maori bay muriwai north island new zealand consists of a complex association of basaltic andesite volcanic facies including entablature jointed thick massive facies colonnade jointed thin massive sheet facies mega pillow facies normal pillow facies and minor associated fragmental facies including vitric sandstone and breccia interpreted as hyaloclastite and peperite field observations suggest that the facies which form the waiatarua formation lava were emplaced as multiple flow lobes in a single lava flow from one sustained eruption magma discharge rate at the vent was high however magma supply rate to the more distal and lateral portions of the flow as its surface area increased varied considerably higher magma supply rates produced thick massive and thin sheet facies whereas mega pillow facies and normal pillow facies were produced contemporaneously with the thick and thin massive sheet facies but were restricted to portions of the distal flow subjected to lower magma supply rates the evolution of the waiatarua formation lava flow at maori bay has been reconstructed from the complex facies architecture this suggests that the propagation of the lava involved 7 discrete lobes that were emplaced successively

antarctic bottom water flux in the equatorial western atlantic a moored array at the equator in the western basin of the atlantic provides a 604 day time series of abyssal currents and temperatures spanning the full breadth of the antarctic bottom water aabw flowing from the brazil basin to the guiana basin mean aabw transport is estimated to be 2 0 sv sv 106 m3 s21 comprising organized westward flow of 2 24 sv and return flow of 0 24 sv the low frequency variability is dominated by a quasi annual transport cycle of amplitude 0 9 sv and a 120 day period of amplitude 0 6 sv maximum transports occur in september october while minimum transports occur in february march allowing for this quasiannual cycle and extrapolating the 604 day record to a full two years adds about 7 to the estimated mean aabw transport the array also provides limited sampling in the overlying lower north atlantic deep water lnadw where a southern boundary intensified flow of lnadw gives the strongest recorded mean speed through the array 9 9 cm s21 into the brazil basin the lnadw records also have a quasi annual cycle with strong lnadw flow episodes occurring in april may time series of temperature indicate that the lnadw aabw transition layer rises and falls in synchrony with the quasi annual aabw transport cycle uplifted transition layer during strong aabw transport periods an observed overall warming trend appears to be accompanied by a decline in aabw transport

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

geothermal structure of the tyrrhenian sea over 200 heat flow measurements have been carried out in the tyrrhenian sea mostly since 1977 as part of the heat flow map for italy and surrounding seas italian program as well as part of the french italian tyrrhenia program all data have been corrected for the influence of the plio quaternary sedimentation measured heat flow values were evaluated according to the sedimentary environment following criteria outlined by sclater et al 1980 in this way areas affected mainly by shallow thermal effects in the zones with maximum density of data have been displayed filtering out these shallow contributions the major regional geothermal trends were obtained the tyrrhenian basin can be divided in two distinct regions with different geothermal characteristics the northern part of the basin appears to be connected with the continental structures involved in the interaction between the corsica and tuscan margins the maximum heat flow area located offshore civitavecchia is related to the tensile structures of the tuscan geothermal province the most important thermal features of the central and southern part are located along the central belt trending nw se the lowest heat flow values are located in the peri tyrrhenian areas and are related to the continental margins of the basin while the maxima are connected with the stretched and thinned area localized in the bathyal plain taking into account the heat flow data as well as other geological and geophysical information an evolutionary model for the tyrrhenian sea is presented suggesting a generalized stretching of an initially continental crust accompanied by intensive rifting phases which may have favoured the onset of oceanic type crust

upper mantle properties of the tuscan tyrrhenian area a framework for its recent tectonic evolution abstract within the alpine mediterranean deformational system several interesting features in the physical properties of the upper mantle have been recognized through the regional analysis of surface wave dispersion a large upper mantle anomaly uma here called the tuscan uma has been identified in the area northeast of corsica which includes part of the northern tyrrhenian sea and part of the north central apennines this anomalous upper mantle area together with the upper mantle characteristics of the tyrrhenian sea located further to the south provides a natural framework for comprehensive interpretation of the large data set of geological and geophysical observations such as land and marine geology volcanism gravity magnetic data seismic data and seismology deep temperatures and surface heat flow

growth of pillow lobes evidence from pillow lavas of hokkaido japan and north island new zealand pillow lavas of cretaceous and neogene age well exposed in hokkaido japan and those of neogene age in north island new zealand provide evidence of their mode of growth some pillow lobes diverge by formation of longitudinal surface spreading cracks the others grow by formation of transverse spreading cracks leaving one or more crusts ending toward the front of the lobes and constrictions therefore it is possible to determine the direction of growth of pillow lobes by tracing the crusts and or constrictions

western boundary current structure and variability east of abaco bahamas at 26 5 n abstract during april 1987 to june 1988 a four mooring transport resolving current meter array was deployed in a section extending 70 km eastward from abaco bahamas at 26 5 n mean currents in the upper layer 800 m showed a clockwise rotation that appears to be associated with a small scale quasi permanent anticyclonic gyre centered just northeast or the bahamas deep mean currents were persistenly southward and indicated a strong deep jet the deep western boundary current dwbc reaching core speeds of 20 cm s 1at 2500 m depth about 25 km seaward of the western boundary vertically integrated meridional volume transport over the section showed a surprisingly large variability ranging from approximately 20 sv northward to 70 sv southward 1 sv 106m3s 1 the mean meridional volume transport was 30 sv to the south with about 3 sv flowing northward above 800 m which could be produced by a weak antilles current and 33 sv flowing southward below 800 m the deep southward transport of 33 sv i

evolution of a subglacial basaltic lava flow field tennena volcanic center mount edziza volcanic complex british columbia canada abstract studies of terrestrial glaciovolcanic deposits have elucidated the utility of these deposits as tools to constrain ice conditions at the time of their emplacement very few studies however have documented the emplacement of effusion dominated basaltic glaciovolcanic eruptions the tennena volcanic center tvc located at 57 40 57 705 n 130 39 43 138 w on the western flank of mount edziza volcanic complex mevc in northwestern british columbia canada preserves a detailed record of interactions between coherent basaltic lavas and a local regional ice sheet inferred to be associated with the last glacial maximum lgm here we describe the field characteristics of five primary volcanic lithofacies and five associated glaciogenic lithofacies and discuss their spatial distribution within the volcanic center we find that 1 the distribution of primary hydrovolcanic clastic deposits tuff breccias and lapilli tuffs is confined to tennena cone 2 pillow lavas are present throughout the extent of the surrounding lava field with morphologies that include distinctive structures comprising vertically oriented distended pillows 3 multiple lobes of massive non pillowed lavas that represent high initial magma discharge rates are confined to medial distances from the cone and 4 associated glaciogenic facies that underlie or onlap the tvc lavas indicate a variable sediment water ratio during subglacial meltwater drainage at the time of the eruption or shortly afterwards analyses of h 2 o co 2 in pillow rim samples give broad constraints for emplacement pressures equivalent to 500 1400 m of overlying ice no subaerial lava morphologies are found on the cone or in the proximal medial and distal lithofacies and the sequence is interpreted as documenting an eruption of basaltic lava flows beneath either the lgm cordilleran ice sheet or a younger dryas expansion of the still extant edziza ice cap the tvc lavas especially medial and distal ones display excellent examples of textures and morphologies that can be used to 1 help identify other terrestrial and martian basaltic lava flows emplaced beneath ice and 2 further our understanding on how sub ice lava flows are emplaced

constraints on the dynamics of subglacial basalt eruptions from geological and geochemical observations at kverkfjoll ne iceland the kverkfjoll area ne iceland is characterised by subglacial basalt pillow lavas erupted under thick ice during the last major glaciation in iceland the water contents of slightly vesiculated glassy rims of pillows in six localities range from 0 85 0 03 to 1 04 0 03 wt the water content measurements allow the ice thickness to be estimated at between 1 2 and 1 6 km with the range reflecting the uncertainty in the co2 and water contents of the melt the upper estimates agree with other observations and models that the ice thickness in the centre of iceland was 1 5 2 0 km at the time of the last glacial maximum many of the pillows in the kverkfjoll area are characterised by vesiculated cores 40 60 vesicles surrounded by a thick outer zone of moderately vesicular basalt 15 20 vesicles the core contains 1 mm diameter spherical vesicles distributed uniformly this observation suggests a sudden decompression and vesiculation of the still molten core followed by rapid cooling the cores are attributed to a jokulhlaup in which melt water created by the eruption is suddenly released reducing the environmental pressure mass balance and solubility relationships for water allow a pressure decrease to be calculated from the observed change of vesicularity of between 4 4 and 4 7 mpa depressurization equivalent to a drop in the water level in the range 440 470 m consideration of the thickness of solid crust around the molten cores at the time of the jokulhlaup indicates an interval of 1 3 days between pillow emplacement and the jokulhlaup upper limits for ice melting rates of order 10 3 m s are indicated this interpretation suggests that jokulhlaups can reactivate eruptions

mineralization of biogenic materials in the water masses of the south atlantic ocean i assessment and results of an optimum multiparameter analysis abstract this is the first of two manuscripts dealing with the circulation mixing ventilation and organic matter mineralization of the south atlantic ocean sao the present work quantifies the complex mixing of water masses in the sao using a constrained least squares regression optimum multiparameter omp analysis the omp based on temperature salinity silicate and the conservative parameter no was applied on two world ocean circulation woce lines a17 and a14 in the western and eastern sao respectively the constrained omp sensitivity to sources of error in the end member characteristics measured parameters equation weights and oxygen to nitrogen mineralization ratio rn was carefully assessed using perturbation tests perturbation of rn was the only test that changed significantly the mixing proportions although by less than 5 the constrained omp method allowed defining the realm and identifying the core of flow of each water mass to study its circulation the evolution of its chemical composition and eventually to separate the contribution of physical and biogeochemical processes relevant specific outputs of this first manuscript are 1 north of the south equatorial current the silicate maximum is primarily composed of antarctic intermediate water aaiw rather than circumpolar deep water cdw 2 the two degree discontinuity tdd experiences a dramatic meridional change of water masses composition being dominated by north atlantic deep water nadw north of the vema channel and by cdw southwards 3 the 50 proportion horizon of weddell sea deep water wdsw with a of 0 3 c at the entry of the sao defines the upper limit of the wsdw realm more properly than the classical isopycnals of 46 04 or 46 06 4 where the proportion of wsdw is around 75

crust and upper mantle models along the active tyrrhenian rim the volcanic complexes from the eolian islands to the campania roman regions and tuscany further north rest on lithospheric sectors which overlie the adriatic continental lithosphere sinking along the apennine maghrebian orogenic belt evidence for this stems from the melting at mantle depth of upper crustal materials as indicated by the widespread interaction of s type and k alkaline melts the genesis of atypical magmas of the roman province central southern italy appears to be the result of an important block faulting and deep lithospheric rifting of the apennine continental margin lying parallel to and above relic sinking slabs intermediate and deep focus earthquakes indicate that the lithospheric slab is still seismically active under the eolian calabrian area and sporadically at the southern end of campania on the other hand in the roman tuscan region it seems to be almost inactive few earthquakes having been located with hypocentral depths not exceeding 150 km the analysis of the spectral content of seismic sources supports the existence of two distinct zones of lithospheric shortening in correspondence of tuscany and south tyrrhenian sea which are separated by a tensional region which extends from latium to calabria the existence of distinct lithospheric slabs along the tyrrhenian rim is supported by surface wave dispersion and scattering measurements as well as p wave residuals and is confirmed by the trend of long wavelength gravity anomalies bidimensional gravity models along transects in the tyrrhenian sea and italian peninsula interpreted within the geometrical constraints imposed by the results of the interpretation of aeromagnetic seismic and seismological data have been used to delimit the spatial distribution of the density contrasts in the upper mantle which might be due to the existence of the above mentioned lithospheric slabs

a facies model for a submarine volcaniclastic apron the miocene manukau subgroup new zealand submarine volcaniclastic aprons of emergent volcanoes provide a long term record of their history and are preserved long after the source has been eroded following the cessation of volcanism a facies model for submarine volcaniclastic aprons is necessary to guide interpretation of ancient uplifted successions and to understand the sedimentary and volcanic processes associated with apron formation the manukau subgroup new zealand includes a well exposed miocene submarine apron consisting of the products eroded and erupted from a basaltic andesite volcanic island complex the depositional environment setting and stratigraphy of the volcaniclastic apron are well constrained allowing us to conduct a detailed facies analysis and to assess the apron architecture lateral downslope and vertical progradational sequences reflect erosion of the subaerial edifice and the direct and subsequent products of contemporaneous volcanism the volcaniclastic facies vary largely as a function of proximity to source and the types of rock resedimented the dominant transport method was high density turbidity currents with lesser contributions from debris avalanches debris flows and dilute turbidity currents in addition eruptions from volcanic vents located within the apron are recorded as interbedded water settled and resedimented pumice and scoria deposits explosive eruptions lavas hyaloclastite and crosscutting dikes effusive eruptions the proximal apron is largely composed of coarse breccia conglomerate that is locally chaotically disrupted due to the instability promoted by steep depositional slopes and rapid sedimentation rates the subangular cobbles and boulders originated from nearby probably coastal variably vesicular and variably oxidized lavas and were deposited as lithic lags in this highly energetic environment very little sandstone was deposited or preserved and freshly erupted pumice deposits were quickly resedimented in the medial apron poorly sorted conglomerate and thickly bedded sandstone which includes pumice lapilli built up over the distal apron sequence of thinly bedded fine grained volcaniclastic mudstone sandstone the presence of pumice lapilli suggests that progradation was a response to voluminous explosive eruptions due to their low densities and easy entrainment pumice lapilli largely bypassed deposition on the steep proximal apron and were sedimented onto the more gently sloping medial apron hence coarse pumice clasts were transported much farther from their source than their dense lithic counterparts the apron records a shallowing upward sequence and the final submarine volcaniclastic facies was deposited within channels that incised the medial and distal apron the channels record an initial eruption hiatus and erosion of the edifice well rounded clasts recycled from the uplifted breccia conglomerate were initially deposited followed by pumiceous and scoriaceous pebbly sandstone from renewed explosive eruptions submarine volcaniclastic aprons involve rapid and prolific sedimentation from multiple source locations clasts of different densities and origins and can include the direct products of contemporaneous volcanism the facies architecture however can be clearly divided into proximal medial and distal volcaniclastic apron environments the proximal apron is dominated by the coarsest clasts steep slopes rapid sedimentation rates and seismic activity in the steep proximal apron promote slumping the medial and distal aprons are more likely to record explosive activity debrisflow events and eruption hiatuses due to the gentler slopes and depositional rather than erosional setting

flexural behavior of the continental lithosphere in italy constraints imposed by gravity and deflection data a procedure is developed that systematically matches observations of plate flexure and gravity anomalies at simple convergent boundaries to the bestfitting two dimensional flexural geometry obtained by a thin elastic sheet of specified elastic strength the procedure allows analytical solution for three independent variables one of which is the initial preflexure elevation of the reference surface and two of which are related to the vertical forces and bending moments that act on the plate application to four profiles constructed across the apennine convergent system in italy shows that the observed depth of the basal pliocene surface which marks the base of the foredeep basin and the observed bouguer gravity anomalies can be fit by a two dimensional elastic plate model with an effective elastic thickness of about 20 km on three profiles and about 10 km on the fourth profile the initial elevation prior to flexure is determined to have been about 1000 m below sealevel on all profiles large bending moments and or vertical shear forces are required to act at the effective plate ends in order to maintain the observed deflection moments between 0 5 1017 and 3 1017 n and shear forces between 3 1012 and 3 1012 n m gravity modelling indicates that on the two northernmost profiles these terminal forces can not be supplied by a static mass at crustal depths and suggests that on all four profiles the terminal forces are supplied by anomalously dense material present at depths of 75 150 km beneath and west of the west coast of italy this dense material probably corresponds to westward subducted lithosphere of the adriatic plate extending from the northern apennines to the southern apennines and calabria this study suggests that in subduction systems like the apennines that are characterized by backarc extension forces acting on subducted lithosphere at depth can be expressed at the surface in the geometry of the foredeep basin that forms adjacent to the subduction zone

the north tyrrhenian northern apennines post collisional system constraints for a geodynamic model the north tyrrhenian northern apennines post collisional system ntas has been analysed on the basis of marine reflection profiles and bibliographic sources with the aim of providing an up to date geotectonic and evolutive framework consistent with structural data the continental rifting began to affect the most internal western side of the system in the middle upper miocene while the most external eastern zones were touched by rifting only in pleistocene times the birth and development of extensive asymmetric basins took place with a progressive speeding up of rifting towards the external sectors a diachronous regionally extended and eastward rejuvenating unconformity recognizable within the neogene quaternary basins marks the passage from the syn rift to the post rift tectonic regime while the first is everywhere dominated by extension the second one produces vertical movements reflection terminations related to this unconformity are interpreted in terms of vertical tectonic component three zones that experienced different post rift vertical movements are thus recognized in the ntas subsidence in the north tyrrhenian deep water region tectonic stability or alternation of moderate subsidence and uplift in the continental shelf and western tuscany strong uplift in eastern tuscany the updated structural data demonstrate that the ntas upper crust is crosscut by both tyrrhenian dipping and apennine dipping low angle detachment planes above which the upper crustal blocks rotated and experienced extensional transport along two opposite directions to the west and to the east respectively the coexistence of opposite dipping crustal surfaces bears two fundamental implications for the ntas geodynamics first it stresses the importance of the anti apennine transfer faults since they separate crustal blocks of opposite extension polarity secondly it testifies that the extension tectonics not only re utilized former crustal thrust planes but also gave origin to new significant e and ne dipping detachment planes plan and crossview geometries of faults together with considerations on the role of the metamorphic core complexes point to an interpretation of the ntas structure that is more consistent with the anastomosing shear model rather than the simple shear or the delamination ones

an estimate of the upwelling rate in the equatorial atlantic based on the distribution of bomb radiocarbon and quasi geostrophic dynamics estimates of the near surface upwelling in the tropical atlantic ocean 15 s to 15 n made by broecker et al 1978 from a radiocarbon box model and by wunsch 1984 from a quasi geostrophic inversion differ considerably in the former case the range was estimated as about 17 20 sv while the latter obtained an absolute maximum of about 10 sv to understand these two apparently contradictory results 14c constraints were added to the inverse model with realistic estimates of the observational errors in all fields including the radiocarbon it is found that the radiocarbon constraints are consistent with the quasi geostrophic model and with an upwelling estimated as 7 10 sv the near surface circulation in the tropical atlantic is dominated by a northward flux of warm water across the equator necessary to feed the heat losses at high northern latitudes the 14c balance is maintained by the advection of southern hemisphere waters of comparatively low radiocarbon concentration into the tropical zone by upwelling from below of very low radiocarbon water and by its removal to the north also by advection the major uncertainty in the radiocarbon calculations derives from the sparcity of sampling so that very great extrapolations are required to estimate the zonal mean 14c concentrations and the time histories between the prebomb period and 1972

morphological features of miocene submarine coherent lavas from the green tuff basins examples from basaltic and andesitic rocks from the shimokita peninsula northern japan basaltic and andesitic volcanic rocks of miocene age exposed in the shimokita peninsula northern japan illustrate morphological features of typical submarine coherent lavas of the green tuff basins in japan they are pillow lobes with surface structures such as ropey wrinkles corrugations spreading cracks and tensional cracks and lava lobes composed of a lithic core and glassy border zone or rim with an in situ breccia zone grading outward into surrounding hyaloclastite in addition they include massive lavas with columnar joints and jointed dykes the submarine coherent lavas and dykes are commonly associated with hyaloclastic breccias such as pillow fragment breccia and angular fragment breccia the descriptions of the miocene volcanic rocks in the shimokita peninsula provide good criteria for recognition of submarine coherent lavas of basalt and andesite

tracer distributions and deep circulation in the western tropical atlantic during cither 1 and etambot cruises 1993 1996 this paper presents cfc and nontransient tracer observations in the western equatorial atlantic ocean on repeated sections along 7 30 n the 35 w meridian and a transect crossing the ceara rise three world ocean circulation experiment cruises have been carried out in this area in february march 1993 cither 1 and september october 1995 and april may 1996 etambot 1 and 2 together with the tracer data the direct current measurements are used to deduce the circulation pathways the data confirm the principal circulation features of the upper north atlantic deep water within the area the deep western boundary current flows southward along the continental slope while adjacent to the dwbc there is a northward flow corresponding to the dwbc recirculation whose origin appears variable the largest variability is observed along the 35 w meridional section where the dwbc bifurcates eastward north of 3 s but the eastward equatorial flow does not appear to be permanent at the middle north atlantic deep water level cfc distributions exhibit the most important contrast between waters of northern and southern origin the circulation at the lower north atlantic deep water level mainly controlled by the topography looks more permanent because the dwbc is regularly observed during the three cruises and there is no evidence for a northwestward recirculation along the mid atlantic ridge the transient behavior of cfc distributions which is superimposed on local circulation effects can be seen clearly through their temporal evolution within the dwbc the variability of the deep circulation observed during the 1993 1996 interval rules out a dominant variability in response to semi annual forcing

deep cross equatorial flow in the atlantic measured with sofar floats neutrally buoyant sofar floats at nominal depths of 800 1800 and 3300 m were tracked for 21 months in the vicinity of tropical boundary currents in the atlantic near 6 n and at several sites near 11 n as well as along the equator trajectories at 1800 m show a swift 50 cm s narrow 100 km wide southward flowing deep western boundary current dwbc extending from 7 n to the equator the average transport per unit depth in the dwbc was estimated to be 13 8 103 m2 s coupling this value with mean velocities measured in the dwbc by current meters gave a volume transport of 15 106 m3 s between depths of 900 m and 2800 m approximately 6 106 m3 s recirculated northward between the dwbc and the mid atlantic ridge leaving 9 106 m3 s as cross equatorial transport no obvious dwbc nor swift equatorial current was observed by the 3300 m floats a low mean velocity at this depth lay between f 11 and higher velocity cores above and below the 1800 m trajectories also suggest that at times february march 1989 the north atlantic deep water in the dwbc turned eastward and flowed along the equator and at other times august september 1990 the dwbc crossed the equator and continued southward the velocity near the equator calculated by grouping floats in a box along the equator was eastward at 4 1 cm s from february 1989 to february 1990 and westward at 4 6 cm s from march 1990 to november 1990 thus the amount of cross equatorial flow in the dwbc appeared to be linked to low frequency variability of the structure of the equatorial current system floats in antarctic intermediate water at 800 m revealed a northwestward western boundary current although flow patterns were complicated three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cm s six 800 m floats drifted eastward along the equator between 5 s and 6 n at a mean velocity of 11 cm s one reached 5 w in the gulf of guinea suggesting that the equatorial currents at this depth extended at least 35 40 along the equator three of these floats reversed direction near the end of the tracking period

morphometric study of pillow size spectrum among pillow lavas measurements of h and v dimensions in the horizontal and vertical directions of pillows exposed in vertical cross section were made on 19 pillow lavas from the azores cyprus iceland new zealand tasmania the western usa and wales the median values of h and v plot on a straight line that defines a spectrum of pillow sizes having linear dimensions five times greater at one end than at the other basaltic toward the small size end and andesitic toward the large size end the pillow median size is interpreted to reflect a control exercised by lava viscosity pillows erupted on a steep flow foot slope in lava deltas can however have a significantly smaller size than pillows in tabular pillowed flows inferred to have been erupted on a small depositonal slope indicating that the slope angle also exercised a control pipe vesicles generally abundant in the tabular pillowed flows and absent from the flow foot pillows have potential as a paleoslope indicator pillows toward the small size end of the spectrum are smooth surfaced and grew mainly by stretching of their skin whereas disruption of the skin and spreading were important toward the large size end disruption involved increasing skin thicknesses with increasing pillow size and pillows toward the large size end are more analogous with toothpaste lava than with pahoehoe and are inferred from their thick multiple selvages to have taken hours to grow pseudo pillow structure is also locally developed an example of endogenous pillow lava growth that formed intrusive pillows between normal pillows is described from sicily isolated pillow like bodies in certain andesitic breccias described from iceland were previously interpreted to be pillows but have anomalously small sizes for their compositions it is now proposed that they may lack an essential attribute of pillows namely the development of bulbous forms by the inflation of a chilled skin and are hence not true pillows para pillow lava is a common lava type in the flow foot breccias it forms irregular flow sheets that are locally less than 5 cm thick and failed to be inflated to pillows perhaps because of an inadequate lava supply rate or too high a flow velocity

tracing lower north atlantic deep water across the equator water whose ultimate source is the overflow at the denmark strait can be traced using maps of salinity dissolved oxygen and silica concentration on deep density surfaces south along the american continent to at least 5 s several property extrema whose resolution is at the limit of accuracy of the measurements occur on these density surfaces which nevertheless may indicate areas of stronger mixing along the crest of the mid atlantic ridge transport estimates for that part of the southward flow within 600 km of the western boundary near 10 n suggest that 10 3 106 m3 s 1 of lower north atlantic deep water moves south there the total southward deep water transport near 10 n is estimated to be closed to 25 106 m3 s 1

genesis of crystal rich epiclastic rocks from subaqueous silicic lava domes role of thermal shock on quartz phenocrysts abstract deposits in the palaeozoic marine basin of the sarrabus region se sardinia western mediterranean italy show the presence of rhyolitic micropillow lithofacies in the uppermost sector of extrusive subaqueous acid domes these particular volcanic rocks contain quartz phenocrysts affected by curved fractures attributed to thermal shock produced in the magma water interface the flanks of subaqueous domes contain proximal epiclastic sandstones and greywackes characterized by the presence of non mature angular quartz clasts very similar to the occurrences detected in the rhyolitic micropillows therefore a syngenetic referred to acid domes and proximal unreworked character is inferred for these epiclastic deposits a genetic model is proposed to explain the association of lithofacies volcanic and epiclastic in direct relationship with the subaqueous growth and erosion of the domes this process of genesis of texturally unmature epiclastic rocks not related to explosive acid volcanism seems rather new and the conclusions of the paper may be in sharp contrast with some of the criteria previously described for distinguishing between pyroclastic and epiclastic crystal rich rocks

magma emplacement in a thrust ramp anticline the gavorrano granite northern apennines italy 1 magma emplacement in the upper crust is often associated with crustal extension whereby space for intrusions is made by dilation along transtensive and strike slip faults the lenticular shape of several intrusions indicates that a further mechanism for magma intrusion is laccolith emplacement with roof uplift of the overburden additionally melts exploit rheological discontinuities e g sedimentary layering during their ascent we present an emplacement model for intrusion of the shallow level gavorrano granite northern apennine italy which is located at the core of an open anticline the shape of the intrusion and structural features of the host rocks are indicative of a synkinematic emplacement in a growing thrust anticline space was provided by the opening of dilatation zones at the core of anticline as a consequence of different amounts of translation between hanging wall and footwall units which were separated by evaporitic rocks these evaporitic units acted as major decollement layers analog models provide results in good agreement with the structural setting of the anticline and emphasize the possibility that melts filled the dilatation zone with the decollement layers further facilitating intrusion