trace element transport rates in subduction zones evidence from th sr and pb isotope data for tonga kermadec arc lavas abstract trace element and th sr and pb isotope data for young lavas from the tonga kermadec arc in the southwest pacific suggest that geochemical variations in the lavas along the arc are linked to differences in the material being subducted beneath the arc lavas from the southern kermadec segment of the arc have relatively radiogenic pb isotope compositions which reflects a contribution from subducted sediment in contrast much of the pb in tonga lavas is derived from the altered oceanic crust in the subducting pacific plate and lavas from the northernmost tonga islands of tafahi and niuatoputapu contain pb and sr derived from the subducted part of the louisville seamount chain the origin of the pb in the lavas from these two islands can thus be traced to a point on the subducting slab and this observation is used to estimate the rate at which trace elements are transported beneath the arc our calculations suggest that fluid soluble elements such as u sr and pb are transported from the subducted slab across the mantle wedge and back to the surface in lavas over a period of approximately 2 3 ma and that magmas are erupted at the surface less than 350 ka after the melts are generated in the mantle wedge

triggering and runaway processes of catastrophic tsaoling landslide induced by the 1999 taiwan chi chi earthquake as revealed by high velocity friction experiments pliocene sedimentary rocks of about 130 mm3 in volume slid along bedding planes dipping by 14 with an average speed of about 35 m s during the tsaoling landslide we conducted friction experiments to reproduce the initiation processes of this landslide by idealizing landslide movements during the earthquake as accelerating decelerating motion experiments were done on shale from the field at 3 mpa normal stress corresponding to the overburden pressure results indicate that the accelerating decelerating motion causes weakening and strengthening at each oscillation cycle and results in overall slip weakening which can be approximated as an exponential slip weakening behaviors during oscillatory slip are fairly similar to those during sliding at constant slip rates newmark analysis with measured frictional properties reveals that the landslide can be triggered with wet gouge properties but the landslide motion stops with parameters for dry shale gouge delayed initiation of the landslide is consistent with a survivor s witness

the key role of the western boundary in linking the amoc strength to the north south pressure gradient abstracta key idea in the study of the atlantic meridional overturning circulation amoc is that its strength is proportional to the meridional density gradient or more precisely to the strength of the meridional pressure gradient a physical basis that would indicate how to estimate the relevant meridional pressure gradient locally from the density distribution in numerical ocean models to test such an idea has been lacking however recently studies of ocean energetics have suggested that the amoc is driven by the release of available potential energy ape into kinetic energy ke and that such a conversion takes place primarily in the deep western boundary currents in this paper the authors develop an analytical description linking the western boundary current circulation below the interface separating the north atlantic deep water nadw and antarctic intermediate water aaiw to the shape of this interface the simple analytical model also shows how available potential energy is converted into

break up of the atlantic deep western boundary current into eddies at 8 s the existence in the ocean of deep western boundary currents which connect the high latitude regions where deep water is formed with upwelling regions as part of the global ocean circulation was postulated more than 40 years ago1 these ocean currents have been found adjacent to the continental slopes of all ocean basins and have core depths between 1 500 and 4 000 m in the atlantic ocean the deep western boundary current is estimated to carry 10 40 times 106 m3 s 1 of water2 3 4 5 transporting north atlantic deep water from the overflow regions between greenland and scotland and from the labrador sea into the south atlantic and the antarctic circumpolar current here we present direct velocity and water mass observations obtained in the period 2000 to 2003 as well as results from a numerical ocean circulation model showing that the atlantic deep western boundary current breaks up at 8 s southward of this latitude the transport of north atlantic deep water into the south atlantic ocean is accomplished by migrating eddies rather than by a continuous flow our model simulation indicates that the deep western boundary current breaks up into eddies at the present intensity of meridional overturning circulation for weaker overturning continuation as a stable laminar boundary flow seems possible

frictional sliding of dolomite a variation in constitutive behavior fault slip occurs via earthquakes or stable creep depending on the manner in which frictional resistance varies with sliding velocity and displacement if the form of this dependence is a function of rock type observed spatial variations in slip behavior along faults could be explained by lithologic variation we have used a rotary shear apparatus to investigate the frictional response of dolomite marble to changes in sliding velocity we have modeled the results using a state variable constitutive law for rock friction and a numerical method to solve for the interaction between the friction law and the compliance of our machine dolomite marble displays steady state velocity strengthening as contrasted with granite and quartzite which show velocity weakening at the same conditions to model the dolomite results it is necessary to use two state variables and surprisingly the parameters specifying the decay magnitudes associated with these state variables differ in sign from each other the magnitude of the parameter associated with the longer decay is negative leading to a downward decay of frictional strength associated with a decrease in velocity if the shorter decay is of sufficient magnitude as we observe at low velocity it is possible for the machine rock system to exhibit instability and oscillatory behavior even though the steady state response is velocity strengthening another way in which dolomite contrasts with granite and quartzite is that the friction parameters vary strongly with velocity a transition from unstable to stable sliding with increasing velocity has been observed previously and our observed variation of the constitutive parameters with velocity can explain this behavior there is some indication that the evolution of the state variables for dolomite occurs as a function of time rather than displacement in contrast with granite and quartzite the frictional behavior of dolomite shows that the constitutive laws that have been developed based on results from granite and quartzite are inadequate to describe all rock types and that more general laws are required

on the boundary flow off brazil at 5 10 s and its connection to the interior tropical atlantic 1 within the context of the german clivar program an observational program in the western tropical atlantic with shipboard sections profiling floats and a moored array aims at studying the role of the shallow thermohaline subtropical cell stc in tropical subtropical interactions and the cold water transports underneath from 6 repeated shipboard profiling sections off brazil near 5 s a northward warm water transport above 1100 m of 25 0 4 4 sv is determined of which 13 4 2 7 sv occur in the thermocline layer supplying the equatorial undercurrent trajectories of 15 profiling floats released near the western boundary are presented that drift at shallow levels 200 m and 400 m and delineate the different stc branches for the southward flow of north atlantic deep water nadw a section mean transport of 31 7 9 2 sv was determined at 5 s however different from the steady nadw flow observed earlier along the topography north of the equator the nadw currents at 5 10 s are much more variable with long periods of northward counterflow along the topography

moored observations of western boundary current variability and thermohaline circulation at 26 5 n in the subtropical north atlantic abstract a 5 8 year time series of moored current meter observations is used with hydrographic section data cme model results and gridded wind fields over the north atlantic to describe the mean structure and variability of circulation and volume transports east of abaco bahamas at 26 5 n a mean antilles current with 5 sv of northward transport is confined against the bahamas boundary in the upper 800 m and combines with approximately 19 sv of florida current transport to balance the sverdrup interior circulation and does not contribute to interhemispheric exchange the mean transport of the deep western boundary current dwbc off the bahamas is approximately 40 sv of which 13 sv compensates the upper branch of the thermohaline circulation requiring a 27 sv deep recirculation robust annual and semiannual cycles of meridional are found in both moored observations and model results with remarkable agreement in amplitude 13 sv and phase maximum northward transports occur in winter and summer

fault roughness at seismogenic depths from lidar and photogrammetric analysis fault surface roughness is a principal factor influencing earthquake mechanics and particularly rupture initiation propagation and arrest however little data currently exist on fault surfaces at seismogenic depths here we investigate the roughness of slip surfaces from the seismogenic strike slip gole larghe fault zone exhumed from ca 10 km depth the fault zone exploited pre existing joints and is hosted in granitoid rocks of the adamello batholith italian alps individual seismogenic slip surfaces generally show a first phase of cataclasite production and a second phase with beautifully preserved pseudotachylytes of variable thickness we determined the geometry of fault traces over almost five orders of magnitude using terrestrial laser scanning lidar ca 500 to 1 10 m is not anisotropic and less evolved than at smaller scales these observations are consistent with an evolution of roughness due to fault surface processes that takes place only at scales smaller or comparable to the observed net slip differences in roughness evolution between shallow and deeper faults the latter showing evidences of seismic activity are interpreted as the result of different weakening versus induration processes which also result in localization versus delocalization of deformation in the fault zone from a methodological point of view the technique used here is advantageous over direct measurements of exposed fault surfaces in that it preserves in cross section all of the structures which contribute to fault roughness and removes any subjectivity introduced by the need to distinguish roughness of original slip surfaces from roughness induced by secondary weathering processes moreover offsets can be measured by means of suitable markers and fault rocks are preserved hence their thickness composition and structural features can be characterised providing an integrated dataset which sheds new light on mechanisms of roughness evolution with slip and concomitant fault rock production

fracture surface energy of the punchbowl fault san andreas system the energetics of earthquake rupture slip weakening and rupture surface formation are poorly understood by measuring the energy associated with fracture damage along the punchbowl fault in the devil s punchbowl los angeles county park part of the san andreas system chester et al show that the fracture surface energy for rupture along a mature fault of this type accounts for only a small fraction of the energy released during large earthquakes as determined by seismologists this suggests that mechanisms such as melt lubrication and thermal pressurization are responsible for slip weakening fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening1 2 3 fracture energy has been estimated from seismological and experimental rock deformation data4 5 6 7 8 yet its magnitude mechanisms of rupture surface formation and processes leading to slip weakening are not well defined8 9 10 here we quantify structural observations of the punchbowl fault a large displacement exhumed fault11 12 in the san andreas fault system and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake if fracture energy is attributed entirely to the production of fracture surfaces then all of the fracture surface area in the punchbowl fault could have been produced by earthquake displacements totalling 1 km but this would only account for a small fraction of the total energy budget and therefore additional processes probably contributed to slip weakening during earthquake rupture

nonmarine sedimentation in an early cretaceous extensional continental margin arc byers peninsula livingston island south shetland islands upper jurassic lower cretaceous rocks of the byers group exposed on byers peninsula livingston island record the expansion of gondwana margin continental arc facies into a marine intra arc basin at least 1 3 km of marine clastic rocks are overlain by about 1 4 km of lower cretaceous nonmarine volcaniclastic strata assigned to the cerro negro formation the base of the nonmarine succession is marked by a low angle unconformity the lower 200 240 m is largely pale green and gray weathering and consists mainly of welded and nonwelded silicic ignimbrites with subordinate reworked silicic tuffs and ignimbritic conglomerates a change in color to dark red purple at the top of this interval broadly coincides with a change to a largely basaltic intermediate provenance the rest of the succession consists mainly of poorly sorted lithic lapilli tuffs and tuffaceous breccias largely interpreted as debris flow and flood flow deposits it also includes two welded silicic ignimbrite units rich in basaltic clasts and is considered to represent a volcaniclastic apron flanking one or more basaltic andesite stratovolcanoes though it is dominated by syneruption deposits this upper division also includes laterally impersistent subsidence driven inter eruption facies including basaltic conglomerates deposited in incised fluvial channels minor lacustrine intervals and rare paleosols a thicker 100 m peninsula wide mudstone sandstone dominated horizon represents a more extended period of inter eruption deposition during which the area was the site of a substantial lake throughout the cerro negro formation thickness and facies changes provide evidence of synsedimentary displacement across a series of ene trending normal faults most with downthrow to the south in the upper part of the formation resulting differential subsidence led to southward thickening accompanied by increased preservation of inter eruption facies and on a smaller scale trapping of a fluvial channel against the footwall of a synsedimentary fault this tectonism appears to form part of an early cretaceous episode of arc perpendicular extension well documented elsewhere in the antarctic peninsula region

low frictional strength of quartz rocks at subseismic slip rates 1 laboratory experiments on rocks at low sliding velocity typically yield values of the friction coefficient of 0 6 0 85 here we demonstrate that an extraordinary decrease in friction coefficient accompanies sliding of room dry quartz rocks at rates faster than in most laboratory experiments but slower than seismic slip rates in some cases the friction coefficient decreases from low speed values by more than a factor of 3 this extraordinary weakening likely results from the formation of finely comminuted amorphous wet material on the sliding surface

experimental rock on rock frictional wear application to subglacial abrasion 1 rock on rock wear under known normal loads was measured experimentally using 62 mm diameter rotating discs machined from a range of silicic rock types one granite two metamorphic rocks and three sandstones of porosities varying between 7 and 28 wear debris was removed continuously from the contacting surfaces by water we obtained a wear law of the form dt dx a n m where is contact normal stress mpa dt dx is a dimensionless wear rate meter wear t per meter shear displacement x is porosity and a n and m are empirical constants 10 8 11 8 33 and 4 50 respectively low porosity rocks displayed surface polishing and abraded particle size was substantially smaller than the starting grain size whole grains were plucked from high porosity rocks without any surface polishing so that the wear product particle size remained the same as that of the starting material the empirical wear law describes abrasion beneath a hard bedded temperate glacier provided we can estimate both the in situ normal stress between entrained clasts and the bed and the horizontal velocity of the clasts in the flowing ice normal stress concentration is expected to develop at clast bed contacts from drag against ice flowing toward the bed where pressure melting occurs these experimental data are consistent with wear rates inferred from silt outflow in subglacial streams provided a tenfold stress concentration can occur relative to the ice overburden pressure the rate of production of fine grained wear products under subglacial conditions is substantially less than by tectonic faulting

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

variability of shallow and deep western boundary currents off the bahamas during 2004 05 results from the 26 n rapid moc array data from an array of six moorings deployed east of abaco bahamas along 26 5 n during march 2004 may 2005 are analyzed these moorings formed the western boundary array of a transbasin observing system designed to continuously monitor the meridional overturning circulation and meridional heat flux in the subtropical north atlantic under the framework of the joint u k u s rapid climate change rapid meridional overturning circulation moc program important features of the western boundary circulation include the southward flowing deep western boundary current dwbc below 1000 m and the northward flowing antilles current in the upper 1000 m transports in the western boundary layer are estimated from direct current meter observations and from dynamic height moorings that measure the spatially integrated geostrophic flow between moorings the results of these methods are combined to estimate the time varying transports in the upper and deep ocean over the width of the western boundary layer to a distance of 500 km offshore of the bahamas escarpment the net southward transport of the dwbc across this region inclusive of northward deep recirculation is 26 5 sv sv 10 6 m 3 s 1 which is divided nearly equally between upper 13 9 sv and lower 12 6 sv north atlantic deep water nadw in the top 1000 m 6 0 sv flows northward in a thermocline intensified jet near the western boundary these transports are found to agree well with historical current meter data in the region collected between 1986 and 1997 variability in both shallow and deep components of the circulation is large with transports above 1000 m varying between 15 and 25 sv and deep transports varying between 60 and 3 sv much of this transport variability associated with barotropic fluctuations occurs on relatively short time scales of several days to a few weeks upon removal of the barotropic fluctuations slower baroclinic transport variations are revealed including a temporary stoppage of the lower nadw transport in the dwbc during november 2004

variability of the deep western boundary current at 26 5 n during 2004 2009 five years of data from a line of dynamic height moorings dhm bottom pressure recorders bpr and pressure equipped inverted echo sounders pies near the atlantic ocean western boundary at 26 51n are used to evaluate the structure and variability of the deep western boundary current dwbc during 2004 2009 comparisons made between transports estimated from the dhm bpr and those made by the pies demonstrate that the two systems are collecting equivalent volume transport information correlation coefficient r 0 96 root mean square difference 6 sv 1 sv 10 6 m 3 s 1 integrated to 450 km off from the continental shelf and between 800 and 4800 dbar the dwbc has a mean transport of approximately 32 sv and a standard deviation during these five years of 16 sv both the barotropic full depth vertical mean and baroclinic flows have significant variability changes exceeding 10 sv on time scales ranging from a few days to months with the barotropic variations being larger and more energetic at all time scales the annual cycle of the deep transport is highly dependent on the horizontal integration distance integrating 100 km offshore yields an annual cycle of roughly similar magnitude but shifted in phase relative to that found from current meter arrays in the 1980 1990s while the annual cycle becomes quite weak when integrating 450 km offshore variations in the dwbc transport far exceed those of the total basin wide meridional overturning circulation standard deviations of 16 sv vs 5 sv transport integrated in the deep layer out to the west side of the mid atlantic ridge still demonstrates a surprisingly high variance indicating that some compensation of the western basin deep variability must occur in the eastern basin published by elsevier ltd

late cretaceous to early tertiary subduction history of the antarctic peninsula quantitative estimates of the rates and azimuths of phoenix plate convergence with the antarctic peninsula have been derived from plate rotation calculations for two periods in the late cretaceous and early tertiary 83 0 67 7 and 61 1 53 4 ma published marine magnetic anomaly identifications and flow lines interpreted from gravity anomaly maps were used in simple spherical geometry calculations to derive phoenix pacific stage rotations these were combined with published pacific antarctic rotation data to determine contemporaneous phoenix antarctic stage rotations the results indicate a significant change in azimuths of relative motion between the late cretaceous and early tertiary late cretaceous and perhaps earlier oblique subduction probably caused migration of fore arc slivers along the margin resulting in variations in width of the accretionary prism comparison between synthetic magnetic profiles and a 900 km long magnetic profile across ocean floor produced at the antarctic phoenix ridge during the early tertiary establishes the time of a major decrease in spreading rate and hence also in convergence rate as chron c23r 52 3 ma the associated change in subduction dynamics may have caused the dextral transtensional deformation observed in the george vi sound region and initiated uplift of blueschist facies rocks now exposed on smith island the calculated convergence history does not provide a simple explanation for the occurrence of high mg andesite lavas on alexander island which were erupted more than 20 ma before the antarctic phoenix ridge arrived at the margin the existence of these lavas implies either earlier subduction of another ridge or slab break up beneath alexander island

energy partitioning during seismic slip in pseudotachylyte bearing faults gole larghe fault adamello italy thedeterminationoftheearthquakeenergybudgetremainsachallengingissueforearthscientists asunderstandingthepartitioningofenergyisa keytowardsthe understandingthe physicsofearthquakes here weestimatethe partitionofthe mechanical workdensity intoheatandsurfaceenergy energyrequiredtocreatenewfracturesurface duringseismicsliponalocationalongafault earthquakeenergypartitioningisdeterminedfromfield and microstructural analyses of a fault segment decorated by pseudotachylyte solidified friction induced melt produced during seismic slip exhumed from a depth of 10 km typical for earthquake hypocenters in the continental crust frictional heat per unit fault area estimated from the thickness of pseudotachylytes is 27 mj m 2 surface energy estimated from microcrack density inside clast i e cracked grains entrapped in the pseudotachylyte and in the fault wall rock ranges between 0 10 and 0 85 mj m 2 our estimates for the studied fault segment suggest that 97 99 of the energy was dissipated as heat during seismic slip we conclude that at 10 km depth less than 3 of the total mechanical work density is adsorbed as surface energy on the fault plane during earthquake rupture 2008 elsevier b v all rights reserved

combined sr nd pb and li isotope geochemistry of alkaline lavas from northern james ross island antarctic peninsula and implications for back arc magma formation abstract we present a comprehensive geochemical data set for a suite of back arc alkaline volcanic rocks from james ross island volcanic group jrivg antarctic peninsula the elemental and isotopic sr nd pb and li composition of these cenozoic basalts emplaced east of the antarctic peninsula is different from the compositions of the fore arc alkaline volcanic rocks in southern shetlands and nearby bransfield strait the variability in elemental and isotopic composition is not consistent with the jrivg derivation from a single mantle source but rather it suggests that the magma was mainly derived from a depleted mantle with subordinate oib like enriched mantle component em ii the isotopic data are consistent with mantle melting during extension and possible roll back of the subducted lithosphere of the antarctic plate magma contamination by triassic early tertiary clastic sediments deposited in the back arc basin was only localized and affected li isotopic composition in two of the samples while most of the basalts show very little variation in 7 li values as anticipated for mantle driven li isotopic composition these variations are difficult to resolve with radiogenic isotope systematics but li isotopes may prove sensitive in tracking complex geochemical processes acting through the oceanic crust pile including hydrothermal leaching and seawater equilibration

advection of north atlantic deep water from the labrador sea to the southern hemisphere recently formed labrador seawater lsw and overflow water from denmark strait dsow are main components of the atlantic meridional overturning circulation both exhibit a distinct chlorofluorocarbon cfc maximum here we use 25 years of cfc observations in the atlantic to study the main features of the circulation of lsw and dsow from the cfc data the age and fraction of young deep water are inferred due to the superior spatial data resolution compared to former attempts regional differences in the spreading velocity and pathways of young deep water become evident dependent on the regional circulation the observed distributions of young lsw and dsow showed that the dwbc is the fastest pathway to reach the southern hemisphere the downstream decrease of the fractions of young lsw in the dwbc is slower compared to model studies from 47 n to 42 n dwbc transports of young lsw and dsow decrease by 44 and 49 respectively at 26 n the dwbc transport of young water is still 39 of the lsw formation rate and 44 of the dsow overflow transport interior pathways also exist especially in the subpolar north atlantic and in the transition zone between the subpolar and subtropical gyre compared to dsow the distributions indicate a higher tendency for lsw to follow additional interior pathways north of 45 n the major part of lsw is younger than 20 years the general weakening of new lsw formation since the 1990s worked toward a homogenization between the lsw in the western and the eastern subpolar north atlantic

constitutive behavior and stability of frictional sliding of granite an understanding of the frictional sliding on faults that can lead to earthquakes requires a knowledge of both constitutive behavior of the sliding surfaces and its mechanical interaction with the loading system we have determined the constitutive parameters for frictional sliding of initially bare surfaces of westerly granite using a recently developed high pressure rotary shear apparatus that allows long distances of sliding and therefore a greater assurance of attaining steady state behavior from experiments conducted at room temperature and normal stresses of 27 84 mpa several important results have been found 1 a gouge layer 100 to 200 m thick was developed from the initially bare rock surfaces after 18 to 70 mm of sliding 2 the steady state frictional resistance attained after about 10 mm of sliding is proportional to the negative of the logarithm of the sliding velocity 3 abrup changes in the velocity of sliding result in initial changes in the frictional resistance which have the same sign as the velocity change and are followed by a gradual decay to a new steady state value over a characteristic distance of sliding this velocity weakening behavior is essentially identical with that found by several previous workers on the same material at lower normal stress 4 our results are well described by a two state variable constitutive law the values of the constitutive parameters are quite similar to those found previously at low normal stress but the characteristic distance is about an order of magnitude smaller than that found at 10 mpa normal stress with thicker layers of coarser gouge 5 we have approximated our results with a one state variable constitutive law and compared the results with the predictions of existing nonlinear stability analysis in addition we have extended the stability analysis to systems possessing two state variables with such formulations good agreement is found between the experimentally observed and theoretically predicted transitions between stable and unstable sliding these results allow a better understanding of the instabilities that lead to earthquakes

growth of molten zone as a mechanism of slip weakening of simulated faults in gabbro during frictional melting 1 to understand how frictional melting affects fault instability we performed a series of high velocity friction experiments on gabbro at slip rates of 0 85 1 49 m s 1 at normal stresses of 1 2 2 4 mpa and with displacements up to 124 m experiments have revealed two stages of slip weakening one following the initial slip and the other immediately after the second peak friction the first weakening is associated with flash heating and the second weakening is due to the formation and growth of a molten layer along a simulated fault the two stages of weakening are separated by a marked strengthening regime in which melt patches grow into a thin continuous molten layer at the second peak friction the frictional coefficient decays exponentially from 0 8 1 1 to 0 6 during the second weakening the host rocks are separated completely by a molten layer during this weakening so that the shear resistance is determined by the gross viscosity and shear strain rate of the molten layer melt viscosity increases notably soon after a molten layer forms however a fault weakens despite the increase in melt viscosity and the second weakening is caused by the growth of molten layer resulting in the reduction in shear strain rate of the molten layer very thin melt cannot be squeezed out easily from a fault zone so that the rate of melting would be the most critical factor in controlling the slip weakening distance effect of frictional melting on fault motion can be predicted by solving a stefan problem dealing with moving host rock molten zone boundaries

deformation of mafic schists from subducted oceanic crust at high pressure and temperature conditions abstract we conducted triaxial deformation experiments using a griggs type solid pressure medium apparatus on two mafic schists that experienced different peak metamorphic conditions from the sambagawa metamorphic belt a greenschist and an epidote amphibole schist at a confining pressure of 1 gpa 400 c and strain rate of 10 5 1 s differential stresses for all mafic schists were higher than 1 gpa the greenschist samples were weaker than epidote amphibolite samples under all experimental conditions microstructures of recovered samples of greenschist indicate that deformation of mafic schist is accommodated by semi brittle deformation samples of the epidote amphibole schist deformed at 500 c show shear localization along a single fault oriented parallel to the foliation while mechanical data shows no rapid stress drop on the surface of the fault we observe the formation of slickensides with little gouge all sample types exhibit a high stress exponent n 15 and strain rate strengthening i e positive a b values frictional behavior that inhibits earthquake nucleation differential stress increased with increasing confining pressure while the friction coefficient decreased with increasing confining pressure and temperature greenschist and epidote amphibolite facies metamorphism typically occurs at hot subduction zones such as cascadia and southwest japan the lack of seismicity within the subducting oceanic crust at hot subduction zones could be explained by semi brittle deformation or frictional sliding with a positive a b during deformation of these types of metamorphic rocks weak and aseismic fault zones in subducting slabs might promote slab mantle decoupling at the corner of the mantle wedge and detachment and underplating of oceanic crust from the subducting slab to forearc crust

diagnosing the influence of mesoscale eddy fluxes on the deep western boundary current in the 1 10 storm ncep simulation abstractusing a 0 1 ocean model this paper establishes a consistent picture of the interaction of mesoscale eddy density fluxes with the geostrophic deep western boundary current dwbc in the at

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

late quaternary glacial interglacial variations in sediment supply in the southern drake passage abstract geochemical characteristics of marine sediment from the southern drake passage were analyzed to reconstruct variations in sediment provenance and transport paths during the late quaternary the 5 95 m gravity core used in this study records paleoenvironmental changes during the last approximately 600 ka down core variations in trace element rare earth element and nd and sr isotopic compositions reveal that sediment provenance varied according to glacial cycles during glacial periods detrital sediments in the southern drake passage were mostly derived from the nearby south shetland islands and shelf sediments in contrast interglacial sediments are composed of mixed sediments derived from both west antarctica and east antarctica the east antarctic provenance of the interglacial sediments was inferred to be the weddell sea region sediment input from the weddell sea was reduced during glacial periods by extensive ice sheets and weakened current from the weddell sea sediment supply from the weddell sea increased during interglacial periods especially those with higher warmth such as mis 5 9 and 11 this suggests that the influence of deep water from the weddell sea increases during interglacial periods and decreases during glacial periods with the degree of influence increasing as interglacial intensity increases

amorphous material formed by the mechanochemical effect in natural pseudotachylyte of crushing origin a case study of the iida matsukawa fault nagano prefecture central japan abstract pseudotachylytes from the iida matsukawa fault central japan iida pseudotachylytes are described down to the nanometer scale using high resolution electron microscopy scanning electron microscopy analyses of chemical compositions and mercury intrusion porosimetry the pseudotachylyte matrix chiefly consists of nanoscale particles and elongated submicron fragments with biotite composition amorphous material of several tens of nanometers in size is also observed despite the absence of melt textures lattice fringe images reveal that the amorphous phase coexists with lattice distortion in deformed biotite fragments that are several hundreds of nanometers in size the presence of these submicrostructures indicates that the amorphous material formed by mechanical stress during the comminution process that is via the mechanochemical effect we conclude that amorphous material does not always provide evidence of the rapid cooling of melt in pseudotachylyte the amorphous materials present in the iida pseudotachylyte resulted from the mechanochemical effect due to both shear stress and normal stress during the comminution process that accompanied fault motion

the north atlantic ocean is in a state of reduced overturning the atlantic meridional overturning circulation amoc is responsible for a variable and climatically important northward transport of heat using data from an array of instruments that span the atlantic at 26 n we show that the amoc has been in a state of reduced overturning since 2008 as compared to 2004 2008 this change of amoc state is concurrent with other changes in the north atlantic such as a northward shift and broadening of the gulf stream and altered patterns of heat content and sea surface temperature these changes resemble the response to a declining amoc predicted by coupled climate models concurrent changes in air sea fluxes close to the western boundary reveal that the changes in ocean heat transport and sst have altered the pattern of ocean atmosphere heat exchange over the north atlantic these results provide strong observational evidence that the amoc is a major factor in decadal scale variability of north atlantic climate

wear processes in rocks at slow to high slip rates abstract frictional wear experiments are performed on diorite granite and sandstone at sliding velocities of 0 004 0 27 m s under normal stresses of 0 21 6 3 mpa using a rotary shear apparatus to establish velocity dependent wear laws of rocks and to determine the partition of frictional work used for gouge generation power laws between normal shear stresses and steady state wear rate defined as thickness of gouge formed fault displacement account for our data for diorite and granite at low velocities and most experimental data on wear of rocks reported in the literature but an exponential law holds for wear of diorite at velocities greater than 0 11 m s and its wear rate increases dramatically at seismic slip rates a change from the power law to the exponential law seems to be caused by frictional heating and thermal fracturing both power and exponential laws can describe data for granite sandstones exhibit complex wear behavior possibly due to development of shiny slickenside surface that suppresses wear our data for diorite indicate that at the investigated normal stresses only 0 004 of frictional work is consumed for gouge formation at velocities less than 0 11 m s but this fraction increases markedly with increasing velocity energy partition for gouge formation is not constant and changes with velocity during earthquakes

frictional behavior of granite at low and high sliding velocities to study how the velocity dependence of steady state friction of granite varies as a function of sliding rate we slid initially bare surfaces of westerly granite at rates of from 0 001 m s 32 mm yr to over 3 mm s accumulating 376 mm of total displacement the normal stress was 50 mpa we find that the velocity dependence measured by a b changes from negative velocity weakening at 32 m s modeling of experimental data using a simple constitutive law shows that the magnitude of a the direct dependence of friction on velocity remains nearly constant at all rates up to at least 100 m s the increase in a b with velocity is due to a reduction in the magnitude of b our results are consistent with the view that a measures the deformation rate sensitivity of the fault zone material and that b measures the amount of change of some fault zone property

multiple oxygen 16o 17o and 18o and sulfur 32s 33s 34s and 36s isotope signatures of the dissolved sulfate from deception island antarctic peninsula implications on sulfate formation transportation and deposition in the antarctic region abstract oxygen 16 o 17 o and 18 o and sulfur 32 s 33 s 34 s and 36 s isotope ratios of and major ion na ca 2 cl no 3 and so 4 2 concentrations in lakes ponds and creeks from deception island antarctic peninsula were analyzed to study the sources of sulfate its oxidation and the surficial processes of the dissolved sulfate the positive relationship between the 34 s sulfate 8 1 to 17 3 and the cl so 4 2 molar ratio suggests mixing of sulfate from atmospheric deposition and from oxidation of sulfide minerals the average sea salt fraction 28 and 34 s nss values from 5 6 to 15 9 indicate that a combination of sea salt and marine biogenic sulfide provide the high 34 s end member of the dissolved sulfates the relatively low 18 o sulfate from 4 6 to 0 7 of deception island water suggests a role of local water in the formation of sulfate slightly negative but mass dependent 17 o sulfate values imply that atmospheric oxidation by o 3 and h 2 o 2 are negligible while these values might suggest a significant role of oxidation by molecular oxygen and oh the distinctly low 34 s sulfate value of two samples dcw 2 and dcw 3 suggests the input of sulfate from sulfide oxidation slight elevation of 34 s sulfate values up to 17 3 compared to a typical atmospheric value indicates a minimal role for dissimilatory microbial sulfate reduction of deception island water and sediments both 33 s sulfate and 36 s sulfate values are homogeneous and near zero implying that the dominant atmospheric oxidation process is tropospheric and that there are minimal to no contributions of stratospheric sulfate to deception island water

transient water adsorption on newly formed fault gouge and its relation to frictional heating determination of the amount of frictional heating on faults during slips provides insight into the mechanics of faulting fault slips cause frictional heating as well as production of gouge materials newly formed gouge is mechanochemically stimulated to gain a transient water adsorption ability we showed that the synthetic gouge from friction tests on rocks at a 1 mm s slip rate without frictional heating adsorbed a large amount of water comparable to that adsorbed by clay minerals the amount of adsorbed water decreased significantly with increasing slip rate to 100 mm s where the fault temperature increased above 400 c we confirmed there was no additional adsorption on the heated gouges after termination of the slip we conclude that the adsorption state can be considered a new indicator of a temperature rise of 400 c by frictional heating associated with recent near surface faulting

eulerian and lagrangian isopycnal eddy diffusivities in the southern ocean of an eddying model abstractlagrangian isopycnal diffusivities quantify the along isopycnal mixing of any tracer with mean gradients along isopycnal surfaces they are studied in the southern ocean of the 1 10 parallel ocean program pop model using more than 50 000 float trajectories concurrent eulerian isopycnal diffusivities are estimated directly from the eddy fluxes and mean tracer gradients consistency spatial variation and relation to mean jets are evaluated the diffusivities are calculated in bins large enough to reduce contributions from the rotational components that do not lead to net tracer mixing because the mean jets are nonzonal and nonparallel meridional dispersion includes standing eddies and is significantly different from cross stream dispersion with the subtraction of the local eulerian mean the full lagrangian diffusivity tensor can be estimated along stream diffusivities are about 6 times larger than cross stream diffusivities along streamline averages of eulerian and lagrangian isopycnal d

isotopic and trace element constraints on mixing and melting models of marginal basin volcanism bransfield strait antarctica bransfield strait is a narrow marginal basin separating the south shetland islands from the northern end of the antarctic peninsula quaternary volcanism occurs in the strait as subaerial and submarine volcanoes aligned on the inferred axis of rifting and as two subaerial off axis volcanoes on the northern margin of the strait the bransfield strait lavas are similar to published analyses from other marginal basins ranging from basalts and basaltic andesites to trachytes they exhibit moderate enrichments in alkali and alkaline earth elements relative to high field strength elements that are typical of many back arc basin basalts the seamount basalts have trace element chemistry similar to enriched mid ocean ridge basalts e morb but with variously higher alkali and alkaline earth element concentrations and frequently lower nb low pressure fractional crystallization accounts for most of the compositional variation within individual volcanoes but it does not explain intervolcano differences even though the volcanoes are closely spaced and presently or recently active melting of depleted mantle mixed with 0 5 2 crust or sediment explains the isotopic and trace element variations not accounted for by magma chamber processes the off axis volcanoes are the products of less partial melting than the on axis volcanoes one of the off axis volcanoes also contains more of an enriched component in its source some of the lavas have rb sr too low to account for their 87sr 86sr perhaps due the loss of rb during mantle metasomatism or interaction between slab derived fluids and the mantle source of the basalts strontium neodymium and 207pb 204pb isotopic signatures remained constant during the transition from tertiary island arc volcanism to quaternary marginal basin volcanism but 206pb 204pb increased high cen smn of basalts from some volcanoes requires residual garnet in the source thus the young 15 25 ma at the trench subducted slab is either deeper than 60 km beneath the volcanoes or it has fractured and is no longer a coherent barrier to melts generated below it

the shallow and deep western boundary circulation of the south atlantic at 5 11 s repeated shipboard observation sections across the boundary flow off northeastern brazil as well as acoustic doppler current profiler adcp and current meter records from a moored boundary array deployed during 2000 04 near 11 s are analyzed here for both the northward warm water flow by the north brazil undercurrent nbuc above approximately 1100 m and the southward flow of north atlantic deep water nadw underneath at 5 s the mean from nine sections yields an nbuc transport of 26 5 3 7 sv sv 106 m3 s 1 along the boundary at 11 s the mean nbuc transport from five sections is 25 4 7 4 sv confirming that the nbuc is already well developed at 11 s at both latitudes a persistent offshore southward recirculation between 200 and 1100 m depth reduces the net northward warm water flow through the 5 s section west of 31 5 w to 22 1 5 3 sv and through the 11 s section to 21 7 4 1 sv west of 32 0 w the 4 yr long nbuc transport time series from 11 s yields a seasonal cycle of 2 5 sv amplitude with its northward maximum in july interannual nbuc transport variations are small varying only by 1 2 sv during the four years with no detectable trend the southward flow of nadw within the deep western boundary current at 5 s is 25 5 8 3 sv with an offshore northward recirculation yielding a nine section mean of 20 3 10 1 sv west of 31 5 w for antarctic bottom water a net northward flow of 4 4 3 0 sv is determined at 5 s for the 11 s section the moored array data show a pronounced energy maximum at 60 70 day period in the nadw depth range which was identified in related work as deep eddies translating southward along the boundary based on a kinematic eddy model fit to the first half of the moored time series the mean nadw transfer by the deep eddies at 11 s was estimated to be about 17 sv given the large interannual variability of the deep near boundary transport time series which ranged from 14 to 24 sv the 11 s mean was considered to be not distinguishable from the mean at 5 s

slowing of the atlantic meridional overturning circulation at 25 n the atlantic meridional overturning circulation carries warm upper waters into far northern latitudes and returns cold deep waters southward across the equator its heat transport makes a substantial contribution to the moderate climate of maritime and continental europe and any slowdown in the overturning circulation would have profound implications for climate change a transatlantic section along latitude 25 n has been used as a baseline for estimating the overturning circulation and associated heat transport here we analyse a new 25 n transatlantic section and compare it with four previous sections taken over the past five decades the comparison suggests that the atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004 whereas the northward transport in the gulf stream across 25 n has remained nearly constant the slowing is evident both in a 50 per cent larger southward moving mid ocean recirculation of thermocline waters and also in a 50 per cent decrease in the southward transport of lower north atlantic deep water between 3 000 and 5 000 m in depth in 2004 more of the northward gulf stream flow was recirculating back southward in the thermocline within the subtropical gyre and less was returning southward at depth

characterization of fault roughness at various scales implications of three dimensional high resolution topography measurements accurate description of the topography of active fault surfaces represents an important geophysical issue because this topography is strongly related to the stress distribution along fault planes and therefore to processes implicated in earthquake nucleation propagation and arrest to date due to technical limitations studies of natural fault roughness either performed using laboratory of field profilometers were obtained mainly from 1 d profiles with the recent development of light detection and ranging lidar apparatus it is now possible to measure accurately the 3 d topography of rough surfaces with a comparable resolution in all directions both at field and laboratory scales in the present study we have investigated the scaling properties including possible anisotropy properties of several outcrops of two natural fault surfaces vuache strike slip fault france and magnola normal fault italy in limestones at the field scale digital elevation models of the fault roughness were obtained over surfaces of 0 25 m2 to 600 m2 with a height resolution ranging from 0 5 mm to 20 mm at the laboratory scale the 3 d geometry was measured on two slip planes using a laser profilometer with a spatial resolution of 20 m and a height resolution less than 1 m

deformational evolution of a cretaceous subduction complex elephant island south shetland islands antarctica abstract new structural data from elephant island and adjacent islands are presented with the objective to improve the understanding of subduction kinematics in the area northeast of the antarctic peninsula on the island a first deformation phase d 1 produced a strong sl fabric with steep stretching and mineral lineations partly defined by relatively high pressure minerals such as crossite and glaucophane d 1 is interpreted to record southward subduction along an e w trench with respect to the present position of the island a second phase d 2 led to intense folding with steep e w trending axial surfaces the local presence of sinistral c type shear bands related to this phase and the oblique inclination of the l 2 stretching lineations are the main arguments to interpret this phase as representing oblique sinistral transpressive shear along steep approximately e w trending shear zones with the northern pacific block going down with respect to the southern antarctic peninsula block the sinistral strike slip component may represent a trench linked strike slip movement as a consequence of oblique subduction lithostatic pressure decreased and temperature increased to peak values during d 2 interpreted to represent the collision of thickened oceanic crust with the active continental margin the last deformation phase d 3 is characterised by post metamorphic kink bands partially forming conjugate sets consistent with e w shortening and n s extension the rock units that underlie the island probably rotated during d 3 in cenozoic times together with the trench from an ne sw to the present ene wsw position during the progressive opening of the scotia sea the similarity between the strain orientation of d 3 and that of the sinistral ne sw shackleton fracture zone is consistent with this interpretation

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

labrador sea water tracked by profiling floats from the boundary current into the open north atlantic fifteen profiling floats were injected into the deep boundary current off labrador they were ballasted to drift in the core depth of labrador sea water lsw at 1500 m depth and were deployed in two groups during march and july august 1997 initially for about three months the floats were drifting within the boundary current and the flow vectors were used to determine the mean horizontal structure of the deep labrador current which was found to be about 100 km wide with an average core speed of 18 cm s 1 north of flemish cap the boundary current encounters complicated topography around orphan knoll and there the lsw outflow splits up into different routes one obvious lsw path is eastward through the charlie gibbs fracture zone and another route is a narrow recirculation toward the central labrador sea a surprising result was that none of the floats were able to follow the boundary current southward to the grand banks area and exit into the subtropics trajectories and temperature profiles of the eastward drifting floats indicate the importance of the north atlantic current for dispersing the floats even at the level of lsw

gouge formation by dynamic pulverization during earthquake rupture it is proposed here that fault gouge forms by rock pulverization within the tip region of a fast propagating earthquake due to the intensity of stress and rates of strain in this zone to examine this mechanism we calculate the deformation conditions of a dynamic shear fracture propagating close to the limiting rayleigh wave velocity the mechanical conditions close to the fracture tip are extreme tensile stresses approach 5 gpa volumetric strain rates exceed 105 s 1 and volumetric expansion alternates with volumetric contraction it is expected that a localized zone a few millimeters wide will be pulverized under these conditions this mechanism of dynamic gouge formation provides new insight to recent observations of the texture of gouge from the san andreas fault zone and from rupture zones in south african mines further as such extreme conditions develop only during fast propagating earthquakes presence or absence of pulverized gouge may serve as an indicator of earthquake propagation velocity

cross arc geochemical variations in the kurile arc as a function of slab depth lavas from transects across the kurile islands arc showed geochemical variations related to changes in the compositions of fluids derived from the subducting slab enrichment factors for boron cesium arsenic and antimony all elements with strong affinities for water decreased across the arc this decrease is presumably related to losses of water rich fluids during the dehydration of the subducting plate enrichments of potassium barium beryllium 10 and the light rare earth elements remained constant these species may move in silica rich fluids liberated from the slab at greater depths

measurements of frictional heating in granite a large 150 150 40 cm granite sample sawn diagonally in half to simulate a fault was deformed in a biaxial rock press at normal stress up to 6 41 mpa displacements and local shear stress were monitored along the fault 200 40 cm temperature transients as large as 10 m c were recorded following stick slip events at distances of 0 2 to 1 0 cm from the fault and were related to stress displacement and total work the temperature measurements were used to calculate the heat generated on the fault during slip frictional heating was found to be 94 2 of the total work expended in each event implying a seismic efficiency of 4 8 when water was injected onto the fault both fractional stress drop and static frictional stress increased the efficiency of frictional heating was not lowered by the presence of water heat generated during deformation of a 0 15 cm thick layer of simulated gouge was also measured for sliding rates from 0 09 to 9 1 m s in these gouge experiments temperature rises were less than 0 1 c and were proportional to sliding rate

variability in deep western boundary current transports preliminary results from 26 5 n in the atlantic 1 transport fluctuations of the deep limb of the meridional overturning circulation moc near the western boundary are presented from a line of inverted echo sounders bottom pressure sensors and a deep current meter east of abaco island bahamas at 26 5 n from september 2004 through september 2005 the mean southward flow between 800 dbar and 4800 dbar was 39 106 m3 s 1 with a northward recirculation of 28 106 m3 s 1 leaving a net southward flow of 11 106 m3 s 1 as the through flow of the deep western boundary current dwbc the mean southward dwbc flow essentially equals previous values that were measured at the same location by arrays of current meters deployed from 1986 to 1992 dwbc transport spectra indicate that barotropic and baroclinic changes have very similar energy levels at most periods less than 10 days and that barotropic changes dominate at periods of 10 80 days

a joint inversion of receiver function and rayleigh wave phase velocity dispersion data to estimate crustal structure in west antarctica we determine crustal shear wave velocity structure and crustal thickness at recently deployed seismic stations across west antarctica using a joint inversion of receiver functions and fundamental mode rayleigh wave phase velocity dispersion the stations are from both the uk antarctic network ukanet and polar earth observing network antarctic network polenet anet the former include for the first time 4 stations along the spine of the antarctic peninsula 3 in the ellsworth land and 5 stations in the vicinity of the pine island rift within the west antarctic rift system wars we model a crustal thickness range of 18 28 km and show that the thinnest crust 18 km is in the vicinity of the byrd subglacial basin and bentley subglacial trench in these regions we also find the highest ratio of fast vs 4 0 4 3 km s likely mafic lower crust to felsic intermediate upper crust the thickest mafic lower crust we model is in ellsworth land a critical area for constraining the eastern limits of the wars although we find thinner crust in this region 30 km than in the neighbouring antarctic peninsula and haag ellsworth whitmore block hew the ellsworth land crust has not undergone as much extension as the central wars this suggests that the wars does not link with the weddell sea rift system through ellsworth land and instead has progressed during its formation towards the bellingshausen and amundsen sea embayments we also find that the thin wars crust extends towards the pine island rift suggesting that the boundary between the wars and the thurston island block lies in this region 200 km north of its previously accepted position the thickest crust 38 40 km we model in this study is in the ellsworth mountain section of the hew block we find thinner crust 30 33 km in the whitmore mountains and haag nunatak sectors of the hew consistent with the composite nature of the block in the antarctic peninsula we find a crustal thickness range of 30 38 km and a likely dominantly felsic intermediate crustal composition by forward modelling high frequency receiver functions we also assess if any thick low velocity subglacial sediment accumulations are present and find a 0 1 0 8 km thick layer at 10 stations within the wars thurston island and ellsworth land we suggest that these units of subglacial sediment could provide a source region for the soft basal till layers found beneath numerous outlet glaciers and may act to accelerate ice flow

amorphous material in safod core samples san andreas fault evidence for crush origin pseudotachylytes 1 several types of amorphous material in ultracataclastic core samples recovered from 3194 m and 3294 m depth of the main bore hole of the san andreas fault observatory at depth are identified and described with transmission electron microscopy and scanning electron microscopy we observed 1 amorphous material on a slickenside surface 2 glassy bands contained in an ultracataclastic matrix and 3 amorphous rims surrounding quartz or feldspar clasts chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix we suggest that all amorphous material was formed by comminution of clasts crush origin pseudotachylytes rather than by melting melt origin pseudotachylytes the observed amorphous phases may act as lubricating layers that reduce friction in the san andreas fault

modeling of subduction components in the genesis of the meso cenozoic igneous rocks from the south shetland arc antarctica abstract isotope data and trace elements concentrations are presented for volcanic and plutonic rocks from the livingston greenwich robert king george and ardley islands south shetland arc antarctica these islands were formed during subduction of the phoenix plate under the antarctica plate from cretaceous to tertiary isotopically 87sr 86sr o ratios vary from 0 7033 to 0 7046 and 143nd 144nd o ratios from 0 5127 to 0 5129 end values vary from 2 71 to 7 30 that indicate asthenospheric mantle source for the analysed samples 208pb 204pb ratios vary from 38 12 to 38 70 207pb 204pb ratios are between 15 49 and 15 68 and 206pb 204pb from 18 28 to 18 81 the south shetland rocks are thought to be derived from a depleted morb mantle source dmm modified by mixtures of two enriched mantle components such as slab derived melts and or fluids and small fractions of oceanic sediment em i and em ii the isotopic compositions of the subduction component can be explained by mixing between at least 4 wt of sediment and 96 wt of melts and or fluids derived from altered morb

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv