glacial stage ice core records from the subtropical dunde ice cap china the first ice core record of both the holocene and wisconsin wiirm late glacial stage lgs from the subtropics has been extracted from three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau ice thicknesses at the ice cap summit average 138 m the bedrock surface is relatively flat surface and basal temperatures are 7 3 and 4 7 c respectively and the ice cap exhibits radial flow away from the summit dome these records reveal a major change in the climate of the plateau 10 000 years ago and suggest that lgs conditions were colder wetter and dustier than holocene conditions this is inferred from the more negative 6180 ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes which characterize the lgs part of the cores total b radioactivity from shallow ice cores indicates that over the last 24 years the average accumulation rate has been 400 mm a 1 at the summit the ice cores have been dated using a combination of annual layers in the insoluble dust and 6180 in the upper sections of core visible dust layers which are annual and ice flow modeling the oxygen isotope record which serves as a temperature proxy indicates that the last 60 years have been the warmest in the entire record

lithosphere density model in italy no hint for slab pull the lithosphere asthenosphere system of the italic region in terms of shear velocity and density distribution with depth is suitable to investigate the geodynamic context of the region the velocity structure is obtained through nonlinear inversion of dispersion curves compiled from surface wave tomography on cells 1 1 and a smoothing optimization method to choose the representative cellular model whose layering is used as fixed a priori information to obtain a density model by means of linear inversion of gravimetric data seismicity and heat flow are used as independent constraints in outlining both the crustal and the seismic lid thickness the nonlinear moment tensor inversion of recent damaging earthquakes allows some insight in the ongoing kinematic processes asymmetry between west directed apennines and east directed alps dinarides subductions is a robust feature of the velocity model while density model reveals that slabs are not denser than the ambient mantle thus supplies no evidence for slab pull

dynamic modelling of stress accumulation in central italy we develop a viscoelastic dynamic model to calculate the stress distribution in central italy induced by different geodynamic processes likely active in the region africa eurasia convergence adriatic underthrusting subduction and asthenospheric upwelling underneath tuscany model results are compared with the hypocentral distribution of earthquakes and with the orientation of p and t axes available for the region the first order characteristics of the seismotectonic observations in central italy are subcrustal seismicity the pair extension compression in tuscany and in the outer apennines and the flexural behaviour evident in long wavelength orientation of t axes these features are reproduced by the combination of two processes underthrusting of the adriatic plate under the apennines and asthenospheric upwelling underneath tuscany the comparison with available data does not give insights about slab pull as an ongoing process

subduction kinematics and dynamic constraints the kinematics of subduction zones shows a variety of settings that can provide clues for dynamic understandings two reference frames are used here to describe the simple 2d kinematics of subduction zones in the first the upper plate is assumed fixed whereas in the second frame upper and lower plates move relative to the mantle relative to a fixed point in the upper plate u the transient subduction hinge h can converge diverge or be stationary similarly the lower plate l can converge diverge or be stationary the subduction rate vs is given by the velocity of the hinge h minus the velocity of the lower plate l vs vh vl the subduction rate 1 increases when h diverges and 2 decreases when h converges combining the different movements at least 14 kinematic settings can be distinguished along the subduction zones variable settings can coexist even along a single subduction zone as shown for the 5 different cases occurring along the apennines subduction zone apart from few exceptions the subduction hinge converges toward the upper plate more frequently along e or ne directed subduction zone whereas it mainly diverges from the upper plate along w directed subduction zones accompanying backarc extension before collision orogen growth occurs mostly at the expenses of the upper plate shortening along e ne directed subduction zones whereas the accretionary prism of w directed subduction zones increases at the expenses of the shallow layers of the lower plate the convergence shortening ratio is 1 along e or ne directed subduction zones whereas it is 1 along accretionary prisms of w directed subduction zones backarc spreading forms in two settings along the w directed subduction zones it is determined by the hinge divergence relative to the upper plate minus the volume of the accretionary prism or in case of scarce or no accretion minus the volume of the asthenospheric intrusion at the subduction hinge since the volume of the accretionary prism is proportional to the depth of the decollement plane the backarc rifting is inversely proportional to the depth of the decollement on the other hand along e or ne directed subduction zones few backarc basins form e g aegean andaman and can be explained by the velocity gradient within the hangingwall lithosphere separated into two plates when referring to the mantle the kinematics of subduction zones can be computed either in the deep or in the shallow hotspot reference frames the subduction hinge is mostly stationary being the slab anchored to the mantle along w directed subduction zones whereas it moves w or sw ward along e or ne directed subduction zones surprisingly along e or ne directed subduction zones the slab moves out of the mantle i e the slab slips relative to the mantle opposite to the subduction direction kinematically this subduction occurs because the upper plate overrides the lower plate pushing it down into the mantle as an example the hellenic slab moves out relative to the mantle i e sw ward opposite to its subduction direction both in the deep and shallow hotspot reference frames in the shallow hotspot reference frame upper and lower plates move westward relative to the mantle along all subduction zones this kinematic observation casts serious doubts on the slab negative buoyancy as the primary driving mechanism of subduction and plate motions w directed subduction zones rather provide about 2 3 times larger volumes of lithosphere re entering into the mantle and the slab is pushed down this opposite behavior is consistent with the down dip extension seismicity along e ne directed subduction zones and the frequent down dip compression along the w directed subduction zones subduction kinematics shows that plate velocity is not dictated by the rate of subduction along the w directed subduction zones the rate of subduction is rather controlled i by the hinge migration due to the slab interaction with the easterly trending horizontal mantle wind along the global tectonic mainstream ii by the far field plate velocities and iii by the value of negative buoyancy of the slab relative to the country mantle alternatively e ne nne directed subduction zones have rates of sinking chiefly determined i by the far field velocity of plates and ii by the value of negative buoyancy of the slab relative to the country mantle along this type of subduction the subduction hinge generally advances e ne ward toward the upper plate decreasing the subduction rate but it moves w sw ward relative to the mantle all this indicates that subduction zones have different origin as a function of their geographic polarity and the subduction process is more a passive feature rather than being the driving mechanism of plate motions a rotational component combined with mantle density and viscosity anisotropies seems more plausible for generating the global tuning in the asymmetry of subduction zones

occurrence and distribution of the foraminifer ammonia beccarii tepida cushman in water bodies recent and quaternary of the dead sea rift israel the euryhaline foraminifer ammonia beccarii tepida has lived in water bodies of the dead sea rift from at least 2 0 ma to the present day it was found in the mazar formation the samra formation the ubeidiya formation and the 30 year old navit pool near mount sedom the lakes in which these formations were deposited are athalassic i e not marine relicts and are mutually unconnected in time and space their ammonia faunas were not inherited but a result of repeated colonization most probably by avian transport ammonia beccarii tepida though hardy and opportunistic flourishes mainly in shallow saline to brackish environments its fossil distribution in the dead sea rift shows that in mature lakes it tends to disappear either due to competition from non foraminiferids or due to excessive freshening of the aqueous environment

tropical glaciers potential for ice core paleoclimatic reconstructions the objective of this work is to evaluate the potential of tropical glaciers and ice caps for the reconstruction of past climatic conditions by the analysis of firn and ice cores samples were collected in pits and from cores retrieved on three snow fields in the south american andes quelccaya ice cap and huascaran in peru and chimborazo in ecuador these are compared with results from west africa and indonesia measurements include the microparticle concentration oxygen isotopic abundance ratios and total beta radioactivity which in polar regions often exhibit seasonal depositional cycles annual variations in these three parameters are fairly well defined on quelccaya and huascaran and are apparently absent on chimborazo the quelccaya ice cap contains the best preserved annual signal for all three parameters and although in some instances the annual cycle is difficult to distinguish the measurement of more than one stratigraphic parameter aids in the interpretation of the firn core records the relatively flat bottom topography under quelccaya suggests a simple ice flow regime and depth age calculations indicate that an ice core to bedrock should contain a record of 600 to 1300 years this inference was confirmed by drilling to bedrock in 1983 this investigation of tropical glaciers indicates that the quelccaya ice cap on the eastern edge of the peruvian andes has excellent potential to contain a lengthy and interpretable record of climatic conditions within the tropics of south america

slab mantle flow interaction influence on subduction dynamics and duration we investigate the influence of mantle flow relative to the lithosphere on subduction dynamics we use 2d thermo mechanical models assuming incompressible non newtonian fluid rheology different mantle flow velocities consistent with absolute plate motion models are tested as well as both directions of flow either sustaining or opposing slab dip the effects of different inflow outflow velocity profiles slab strengths and upper lower mantle viscosity contrasts are also evaluated slab dip deviations between models with opposite mantle flow directions range from 37 for relatively strong slabs max 1025 pa s to 50 for weaker slabs max 1024 pa s accounting for a significant amount of natural slab dip variability for imposed mantle flow supporting the slab the initial stage of slab steepening is followed by a stage of continuous slab dip decrease this slab shallowing eventually leads to mantle wedge closure subduction cessation and slab break off possibly driving subduction flips

climatological significance of δ18 o in precipitation and ice cores a case study at the head of the urumqi river tien shan china stable oxygen isotope ratios 18 o of precipitation and ice core samples collected from the headwaters of the urumqi river tien shan china were used to test the relationship between 18 o and contemporaneous surface air temperature t a a strong temporal relationship is found between 18 o in precipitation and t a particularly for the monthly averages which remove synoptic scale influences such as changes in condensation level condensation temperature and moisture sources yao and others 1996 linear fits as high as 0 95 c for precipitation events and 1 23 c for monthly averages are found although the 18 o amplitude in ice cores drilled at the nearby urumqi glacier no 1 2 km from the precipitation sampling site decreased dramatically compared to the precipitation samples the ice core records of annually averaged 18 o are still positively correlated with contemporaneous air temperature especially summer air temperature at the nearby daxigou meteorological station nevertheless the relationship between the ice core 18 o records and contemporaneous air temperature is less significant than that for the precipitation samples due to depositional and post depositional modification processes which are highlighted by the successive snow pit 18 o profiles from the urumqi glacier no 1 our results might extend the application of high altitude and subtropical ice core 18 o t a records for palcoclimate reconstruction

comment on a study on holocene foraminifera from the aral sea and west siberian lakes and its implication for migration pathways by riedel f kossler a tarasov p and wunnemann b quaternary international 229 105 111 riedel et al 2011 discuss the processes of foraminifera transportation and colonization and their implication to the holocene history ofwestern siberia and aral sea using work by gusskov et al 2008 and other papers see below as case studies upon acquaintance with the arguments presented and their evaluation it is necessary to give comments and replies to riedel et al 2011 due to their views and misrepresentation of our work see gusskov et al 2008 there are two main topics which deserve discussion 1 transport of living foraminifera by birds and colonization of lacustrine environments and 2 geological history of the caspian and aral seas in relation to the spread of benthic organisms primarily foraminifera and mollusks the major issue raised by riedel et al 2011 is the possibility of foraminifera transport by birds as concluded riedel et al 2011 109 this is based on studies by different authors resig 1974 cann and de deckker 1981 patterson 1987 almogi labin et al 1992 1995 perthuisot 1995 boudreau et al 2001 abu zied et al 2007 wennrich et al 2007 see riedel et al 2011 105 in our opinion the migration of foraminifera by water birds is unproven first nobody has ever observed the transport of living foraminifera by waterfowl to the best of our knowledge and this is in accord with riedel et al 2011 109 second the examples of foraminifera existence in inland lakes and other reservoirs used by riedel et al 2011 are not convincing and they can be sub divided into two groups as for the first group in the references cited the transportation by birds of foraminifera is not discussed these are resig 1974 and cann and de deckker 1981 in the second group the authors are convinced that birds transported foraminifera however they do not consider other ways of their appearance in lakes and other basins and this should be briefly commented on information presented by patterson 1987 shows that the foraminifera complex in lake tecopa california usa does not represent a natural assemblage this is supported by the distribution of foraminifera in the lake section the majority of species are represented by single shells the degree of shell preservation is quite poor and is most

a review of central asian glaciochemical data the glaciers of central asia provide suitable locations from which to recover continuous high resolution glaciochemical records on a continental scale although the glaciochemical investigations undertaken to date in central asia are few in number and limited in terms of spatial coverage and length of record some preliminary observations can be made concerning regional and seasonal trends in snow chemistry in this region the sodium chloride ratio for most snow samples collected in central asia approaches the ratio found in sea water 0 86 in leq kg i reflecting a marine source for these constituents sodium and chloride concentrations are on average 3 10 times higher in the himalayas than in the karakoram demonstrating the greater influence of monsoonal sources of moisture in the himalayas very high sodium concentrations from khel khod glacier probably reflect a local crustal source from surrounding ice free areas low nitrate concentrations were found in snow collected from the southern margin of the himalayas and high concentrations in snow deposited on the north margin of the himalayas this strong regional trend in the spatial distribution of nitrate suggests the influx of continental aerosols rich in nitrate originating from the arid regions of central asia high calcium concentrations measured in snow from mount everest and the north west corner of china are also indicative of dust derived from the arid regions of central asia very high sulfate concentrations found in snow from the tien shan and the bogda shan most likely reflect local anthropogenic sources the altitude effect on isotopic composition is not apparent from snow samples collected in central asia understanding the processes which control the chemical content of snow the local to regiona l scale complexities

3 d simulation of tectonic evolution of the mariana arc back arc system with a coupled model of plate subduction and back arc spreading abstract we developed a mechanical model for the nonlinear coupled system of plate subduction and back arc spreading on the basis of mathematical formulation for internal deformation due to a moment tensor in an elastic viscoelastic layered half space under gravity in our modeling the plate subduction and the back arc spreading are rationally represented by the increase of tangential displacement discontinuity at the plate interface and normal displacement discontinuity at the spreading center respectively through 3 d numerical simulation with this model we obtained a possible scenario for the tectonic evolution of back arc basins as follows at the first stage steady plate subduction gradually forms tensile stress fields in the back arc region when the accumulated tensile stress reaches a critical level back arc spreading starts at a structurally weak portion of the overriding plate the back arc spreading pushes out the frontal part of the overriding plate toward the plate boundary and leads to the increase of slip rates at the plate interface the local increase of slip rates at the plate interface produces additional tensile stress in the back arc region the incremental tensile stress is canceled out by further back arc spreading such a feedback mechanism is necessary to maintain steady back arc spreading the long duration of slip rate excess due to back arc spreading leads to the gradual protrusion of the plate boundary toward the descending plate trench retreat as the plate boundary moves away from the back arc spreading center the accumulation rate of tensile stress at the spreading center gradually decreases and the slip rate excess at the plate interface due to back arc spreading also decreases then the original back arc spreading center becomes less effective in releasing the tectonic tensile stress and new active back arc spreading will start somewhere closer to the plate boundary such a qualitative scenario accords with the evolution history of back arc basins in the mariana region we obtained the slip rate excess of 7 mm year at the plate interface and the 20 km trench retreat for the last 4 5 myr these simulation results are significantly smaller than observations in the mariana region the discrepancy between simulation results and observations can be ascribed to the effect of the negative buoyancy acting on cold descending slab which advances spontaneous plate subduction and directly increases the slip rate excess and the trench retreat in our model

isotope studies of inner snow layers in a temperate region post depositional change of isotope concentration was investigated in a temperate snow pack daily snow pit studies were carried out at moshiri hokkaido for about a week in april 1998 during this time the snow layers were at the melting point isotope analysis was conducted on snow particles and the liquid water in between the particles every 5 cm in depth and on the precipitation and the runoff water from the bottom of the snow pack collected during the observation period it was found that the oxygen isotope concentration in the liquid part was smaller by about 2 than the solid part of the wet snow the difference between the isotope concentrations of the liquid and the solid was low in the surface snow layer but increased at the bottom the results suggested that isotope fractionation took place between the liquid and the solid when liquid water formed by melting at the snow surface layer flowed groundwards copyright 2002 john wiley sons ltd

a study on holocene foraminifera from the aral sea and west siberian lakes and its implication for migration pathways abstract late holocene cored sediments from the aral sea were examined in respect of foraminiferal diversity and the tests of 4 species of foraminifera were differentiated the species are listed and documented by sem photographs all of the identified species from the aral sea belong to the ponto caspian faunal complex another ponto caspian foraminiferal species is found in the mid holocene sediments of kushmurun lake located in the turgai valley in the southern part of the west siberian lowland during the holocene neither the water level of the caspian sea nor that of the aral sea was high enough to create a northern connection with west siberia via the turgai valley during the late glacial such a waterway may have existed due to overflowing of huge proglacial lakes in northern west siberia the water flow however would have been directed to the south preventing foraminiferal migration to the north moreover the freshwater conditions would not have allowed foraminifers to survive thus foraminifera were transported to the west siberian lakes from the caspian sea or from the aral sea by water birds avian mediated colonization of lacustrine ecosystems by foraminifera is not an exception but a regular process the aral sea was re colonized during the holocene several times with the aid of water birds from the caspian sea

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

seismology speed and size of the sumatra earthquake we now have a clearer picture of the seismic features of last year s gigantic event our seismological results reveal that indonesia s devastating sumatra andaman earthquake on 26 december 2004 was 2 5 times larger than initial reports suggested second only to the 1960 chilean earthquake in recorded magnitude they indicate that it slowly released its energy by slip along a 1 200 km fault generating a long rupture that contributed to the subsequent tsunami now that the entire rupture zone has slipped the strain accumulated from the subduction of the indian plate beneath the burma microplate has been released and there is no immediate danger of a similar tsunami being generated on this part of the plate boundary although large earthquakes on segments to the south still present a threat

present day vertical isostatic readjustment of the western alps revealed by numerical modelling and geodetic and seismotectonic data the active tectonics of the western alps reveals contrasting regimes ongoing extension at the heart of the chain and transpression compression at its external sectors the active processes currently affecting this region are still a matter of debate the classical models proposed in the literature invoke eurasia adria plate collision counterclockwise motion of the adria micro plate slab retreat of the subducted continental lithosphere and slab detachment more recently several authors prefer the hypothesis of tectonics driven by isostasy buoyancy forces to better understand the influence of these processes on the velocity strain and stress fields at the surface and in the crust we developed 2d viscoelastic numerical models along a vertical cross section perpendicular to the western alps we run our models with different driving forces in order to investigate one by one the geodynamic processes proposed in the literature results are compared with available geodetic geological and seismotectonic data in order to bring into coincidence model predictions and observations an important vertical isostatic readjustment must be included in the modelling together with a slight horizontal compression 0 5 mm year 1 probably due to africa eurasia convergence we show that the subduction process in this alpine region is likely to be dead and that buoyancy forces may be dominating the present day tectonics the geological society of london 2010

interpretation of the chemical and physical time series retrieved from sentik glacier ladakh himalaya india analyse a partir de mesures de la radioactivite d analyses chimiques chlorures sodium fer silicates phosphates ammonium d 18 o et ph et de donnees physiques des variations cycliques temporelles des glaciers application aux paleoclimats

el nino southern oscillation events recorded in the stratigraphy of the tropical quelccaya ice cap peru snow accumulation measured during 1982 1983 on the quelccaya ice cap peru was 70 percent of the average from 1975 through 1983 inspection of 19 years 1964 through 1983 of accumulation measured near the summit of quelccaya reveals a substantial decrease 30 percent in association with the last five el nino southern oscillation enso occurrences in the equatorial pacific the enso phenomenon is now recognized as a global event arising from large scale interactions between the ocean and the atmosphere understanding this extreme event with the goal of prediction requires a record of past occurrences the quelccaya ice cap which contains 1500 years of annually accumulated ice layers may provide a long and detailed record of the most extreme enso events

use of ice cores from glaciers with melting for reconstructing mean summer temperature variations this study examines a new method for reconstructing mean summer temperature variations by using an ice core from a wet snow zone on a summer accumulation type glacier in july 2001 a 25 1 m deep ice core was recovered from the accumulation area of sofiyskiy glacier 49847 0 n 87843 0 e 3435 m a s l located in the southern chuyskiy range of the russian altai mountains and a 4 5 m deep pit was excavated about 50 m northwest of the drill site the observation site has a positive balance even during summer when melting occurs the summer balance for each year from 1990 to 2000 was estimated from pinaceae and artemisia pollen peaks in these samples pinaceae pollen marks spring whereas artemisia pollen marks autumn moreover meltwater intrusion did not reach the previous year s accumulation thus the ice between these pollen peaks in the same year was used to estimate a summer balance the reconstructed summer balance variations were negatively correlated with mean summer temperature variations r 0 72 p 0 05 this study shows that for summer accumulation type glaciers such as sofiyskiy glacier the most important climate factor controlling the glacier s surface mass balance is mean summer temperature therefore the summer layer thickness in an ice core can be used as a proxy for reconstructing mean summer temperature variations

accumulation and flow rates of ice on chhota shigri glacier central himalaya using radio active and stable isotopes systematic isotopic studies based on natural and artificial radio isotopes 32 si 137 cs stable isotopes 18 o and total activity measurements have been carried out on chhota shigri glacier himachal pradesh central himalaya to study the dynamics of the ice meltwater composition and to identify the deposition of the chernobyl fall out in the himalayan region using 32 si concentrations the snout ice has been dated at 250 years based on which the past average surface ice flow rate has been estimated as 28 m year 1 based on 18 o variations in a shallow ice core the accumulation rate of the ice has been estimated at 520kgm 2 year 1 32 si measurements of snout ice and englacial meltwaters indicate that at least 55 of the snow meltwater mixed with 45 of the old ice melt water that emerged from englacial streams in the month of august 1987 deposition of the artificial radionuclide 137 cs and the very high total activity observed in snow samples on chhota shigri glacier give the first evidence of chernobyl fall out deposition in the indian himalaya

huge ice age lakes in russia during an early phase of the last ice age weichselian valdaian about 90 000 yr ago an ice sheet formed over the shallow barents and kara seas the ice front advanced on to mainland russia and blocked the north flowing rivers yenissei ob pechora dvina and others that supply most of the freshwater to the arctic ocean the result was that large ice dammed lakes were formed between the ice sheet in the north and the continental water divides to the south here we present reconstructions and calculations of the areas and volumes of these lakes the lake on the west siberian plain was nearly twice as large as the largest lake on earth today the well mapped lake komi in northeast europe and a postulated lake in the white sea basin would also rank before the present day third largest lake the lakes overflowed towards the south and thus the drainage of much of the eurasian continent was reversed the result was a major change in the water balance on the continent decreased freshwater supply to the arctic ocean and increased freshwater flow to the aral caspian black and baltic seas a sudden outburst of the lakes water to the arctic ocean when the ice sheet thinned is postulated copyright 2001 john wiley sons ltd

narrow subducting slabs and the origin of backarc basins abstract both tectonic and seismic data suggest that horizontally wide in the direction parallel to the axis of the trench dipping subducting slabs typically move stably at fixed angles to the horizontal and that their associated trenches migrate very slowly or not at all in contrast where backarc basins babs exist the associated trenches typically migrate at rates of several cm year this behavior may be related to the finite width of the slabs under babs analysis shows that hydrodynamic suction created by the downdip motion of a wide slab is sufficient to balance the pull of gravity on the heavy slab however for a narrow slab sideways asthenospheric flow into the slab overriding plate corner effectively eliminates the suction which results in the rapid sinking of the slab hydrodynamic modeling is used to quantify this hypothesis modeling is used also to show that wide slabs are stable in their inclined position not because of the gravitational wing like sliding but due to the lifting force produced by the negative pressure suction in the slab overriding plate corner finally the model results confirm that for relatively narrow slabs this lifting force is small and cannot counterbalance gravity therefore when bending moments in a narrow slab exceed the plastic yield limit the slab becomes unstable this instability can cause the rapid migration of the slab s hinge and the associated arc at rates of 10 20 cm year and thus form the bab

teleconnections with tropical precipitation surges abstract precipitation surges in the equatorial pacific dry zone as delineated in a study by doberitz reveal statistically significant teleconnections with midlatitude tropospheric flow patterns during all seasons these connections are strongest however during winter and agree with linear numerical model results there is evidence that deep troughs in the central north pacific antecede precipitation surges in the equatorial dry zone during that season suggesting the possibility of triggering of such surges by middle latitude planetary wave perturbations nonlinear numerical model results also indicate that the midlatitude planetary wave response is strongest when north pacific cold sea surface temperature anomalies and equatorial east pacific warm anomalies are present simultaneously the planetary wave pattern associated with equatorial pacific precipitation surges appears to be in phase with orographically generated wave patterns whereas an anomalous low latitude heat source over the extreme eq

role of faults nonlinear rheology and viscosity structure in generating plates from instantaneous mantle flow models concentrated strain within plate margins and a significant toroidal component in global plate motion are among the most fundamental features of plate tectonics a significant proportion of strain in plate margins is accommodated through motion on major tectonic faults the decoupling influence of faulted plate margins primarily results from history dependent lithospheric deformation rather than from instantaneous stress weakening rheologies for instantaneous mantle flow models we argue that faults should be treated as preexisting mechanical structures with models incorporating preexisting faults a power law rheology with an exponent of 3 and slab pull and ridge push forces we demonstrate that nonlinear interaction between weak faults and this power law rheology produces plate like motion our models show that in order to produce plate like motion the frictional stress on faults needs to be small and the asthenosphere viscosity should be much weaker than that of lithosphere while both plateness and the ratio of toroidal to poloidal velocities are reduced with increasing fault coupling the viscosity contrast between the lithosphere and asthenosphere only influences plateness this shows that both diagnostics plateness and the ratio of toroidal to poloidal velocities are necessary to characterize plate motion the models demonstrate that weak transform faults can guide plate motion this guiding property of transform faults and the decoupling of thrust faults result in oblique subduction where the strike of subducted slabs is oblique to transform faults subducted slabs beneath a dipping fault produce oceanic trench and fore bulge topography and principal stresses consistent with subduction zone observations

the little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap the analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent annual variations in visible dust layers oxygen isotopes microparticle concentrations conductivity and identification of the historical a d 1600 huaynaputina ash permit accurate dating and time scale verification the fact that the little ice age about a d 1500 to 1900 stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event

state of stress in slabs as a function of large scale plate kinematics the state of stress of slabs subducting worldwide as revealed by seismicity is extremely variable both with depth and between different subduction zones although in principle slab pull should enhance downdip extension in the slab the reconstructed stress fields for intermediate depths between 100 and 300 km range from downdip compression to downdip extension using 2 d viscoelastic plane strain models we investigate the dependency of the stress field of slabs on geometry dip of the slab and kinematics velocity of convergence between upper and lower plates and their absolute velocity with respect to the underlying mantle of subduction zones we conclude that although the state of stress in slabs is also controlled by other processes downdip compression in the subducting slab is enhanced by mantle flow opposing the direction of the dip of the slab whereas downdip extension is favored by mantle flow in the same direction of the slab dip i e sustaining it these predictions are in agreement with available geophysical observations although exceptions to this simple pattern are observed worldwide in addition if the slab is decoupled from the upper plate convergence between upper and lower plates induces a downdip compressional component of stress within the slab decreasing the magnitude of extension in models characterized by mantle flow sustaining the slab and increasing compression in models with mantle flow opposing subduction however these are second order variations when compared to the control exerted by absolute plate kinematics and by the magnitude of slab pull sensitivity analysis of rheological parameters allows us to conclude that these results are generally consistent although low values of viscosity of the lithospheric mantle render this prediction less stable

subduction zones and back arc basins a review in the framework of plate tectonics the basic mechanism operating in the trencharc back arc systems is believed to be the subduction of oceanic lithosphere this model however was developed more or less as a logical consequence of sea floor spreading the question then is whether or not the subduction model can explain all the major features of the trench arc back arc systems many features such as thrust type inter plate earthquakes and deep earthquakes along wadati benioff zones are readily explained but the occurrences of extentional spreading and high heat flow in the back arc region and arc volcanism are difficult to explain an approach to solve these problems may be found in what may be called comparative subductology there seem to exist two basically different modes of subduction one chilean type causing compressional stress regime in the arc and back arc regions the other mariana type causing tensional world s subduction zones are classified in terms of the postulated two modes and some tectonic implications and causes of the two modes are discussed

the large scale circulation and heat sources over the tibetan plateau and surrounding areas during the early summer of 1979 part i precipitation and kinematic analyses abstract the time evolution of the large scale precipitation low level 850 mb wind moisture and vertical motion fields over the tibetan plateau and surrounding areas during a 40 day period from late may to early july 1979 is studied based on the objectively analyzed fgge level ii b data set during this period the general circulation over east asia undergoes a distinct change characterizing the onset of the summer monsoon circulation the tibetan plateau exerts profound orographic and thermal influences upon the low level wind field the inflow towards the eastern part of the plateau with a marked diurnal change in its intensity is the most prominent feature of the low level wind field the areas of organized precipitation are well related to synoptic systems seen in the 850 mb flow the quasi stationary burma india trough the disturbances forming on the trough the mei yu baiu front and the transverse trough extending eastward from the plateau there is a sharp contrast between the western an

double seismic zones kinematics the kinematics of a double seismic zone of subducting lithosphere at an intermediate depth is studied a simple geometrical argument shows that the strain rate due to unbending of subducting lithosphere can be as large as 10 15 s 1 and large enough to account for the seismic strain rate in this depth range the geometrical unbending of subducting lithosphere in the mantle and the presence of a double seismic zone there can be therefore considered essentially equivalent phenomenon we model a double seismic zone required from this unbending in order to investigate what constraint the presence of a double seismic zone can place on the properties of the descending lithosphere the thickness of a double seismic zone is controlled by the thermal structure and the rheological properties of the subducting slab a preliminary result for the double seismic zone beneath tohoku japan indicates a possibility that the currently available flow law of dry olivine does not properly describe the double seismic zone or at least presents some inconsistency in our knowledge of the mechanical properties e g thermal structure rheology of oceanic lithospheres

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

crustal types and tertiary tectonic evolution of the alboran sea western mediterranean multichannel seismic reflection images across the transition between the east alboran and the algero balearic basins show how crustal thickness decreases from about 5 s two way traveltime twtt 15 km thick in the west east alboran basin to 2 s twtt typical of oceanic crust 6 km thick in the east algero balearic basin we have differentiated three different crustal domains in this transition mainly on the basis of crustal thickness and seismic signature boundaries between the three crustal domains are transitional and lack evidence for major faults tilted blocks related to extension are very scarce and all sampled basement outcrops are volcanic suggesting a strong relationship between magmatism and crustal structure stratigraphic correlation of lithoseismic units with sedimentary units of southeastern betic basins indicates that sediments onlap igneous basement approximately at 12 ma in the eastern area and at 8 ma in the western area linking seismic crustal structure with magmatic geochemical evidence suggests that the three differentiated crustal domains may represent from west to east thin continental crust modified by arc magmatism magmatic arc crust and oceanic crust middle to late miocene arc and oceanic crust formation in the east alboran and algero balearic basins respectively occurred during westward migration of the gibraltar accretionary wedge and shortening in the betic rif foreland basins arc magmatism and associated backarc oceanic crust formation were related to early to middle miocene subduction and rollback of the flysch trough oceanic basement subduction of this narrow slab beneath the alboran basin was coeval with collision of the alboran domain with the iberian and african passive margins and subsequent subcontinental lithosphere edge delamination along the betic rif margins

patterns of deep seismicity reflect buoyancy stresses due to phase transitions thermal perturbation of mantle phase relations in subduction zones gives rise to significant buoyancy anomalies finite element modeling of stresses arising from these anomalies reveals transition from principal tension to compression near 400 km depth down dip compression over 400 690 km peaking at 550 km and transition to rapidly fading tension below 690 km such features even when complicated by olivine metastability are consistent with observed patterns of deep seismicity that such a simple model neglecting all effects other than buoyancy anomalies due to temperature and to thermal perturbation of olivine phase relations successfully generates so many observed features of deep seismicity suggests that these buoyancy anomalies are significant contributors to the stress field in subducting slabs it also suggests that the depth distribution of deep seismicity may largely reflect the state of stress in the slab rather than simply a particular mechanism of stress release

two and three dimensional numerical simulations of the stress field at the thrust front of the northern apennines italy 1 two and three dimensional mechanical models simulating the seismic cycle along thrust faults are devoted to the active front of the northern apennines buried under the plio pleistocene sediments of the eastern po plain the models aim at understanding two peculiar characters of the stress field in the region 1 analyses of borehole breakouts and other well data integrated with seismological information and field evidence show along depth variations from extensional to strike slip to compressional for increasing depth of the stress style along the active mirandola anticline and 2 seismic and borehole breakout data suggest strong lateral rotations of the stress axes along the frontal and lateral ramp portions of the mirandola thrust fault modeling results allowed us to understand that the mechanical decoupling along faults strongly affects the stress distribution in their vicinity under the form of strong rotations of the principal stress axes as a consequence the slip either fast or slow along active blind thrust faults could drive to local stress fields very different from that associated with regional tectonics this could explain together with other processes such as differential compaction the along depth variation of the stress field observed in the mirandola region and the strong lateral rotations of the principal stress axes observed along the lateral ramp of the mirandola thrust fault finally the seismic activity along one of the thrust fault ramps along the apennines front should not interfere with the state of stress along adjacent ramps

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

the role of subduction on the horizontal motions in the tyrrhenian basin a numerical model the horizontal motions in the tyrrhenian basin and surrounding chains induced by subduction along the calabrian arc and northern apennines are analyzed by means of numerical models based on finite element techniques the driving mechanism in 2 dimensional vertical cross sections perpendicular to the trench is the slab pull due to the negative buoyancy of a stratified viscoelastic plate that models the ionic oceanic lithosphere or adriatic plate sinking in the upper mantle for the modern tectonic setting of the area we test the sensitivity of extension in the back arc and of roll back of the overriding plate to variations in the viscosity structure and in the geometry of subduction our results are compared with extensional velocities inferred from geology and slr vlbi data

on the relationships between slab dip back arc stress upper plate absolute motion and crustal nature in subduction zones 1 statistical analysis of modern oceanic subduction zone parameters such as the age of a downgoing plate or the absolute plate motions is performed in order to investigate which parameter controls the dip of a slab and conversely what the influence of slab geometry is on upper plate behavior for that purpose parameters have been determined from global databases along 159 transects from all subduction zones that are not perturbed by nearby collision or ridge plateau seamount subduction on the basis of tomographic images slabs that penetrate through or lie on the 670 km discontinuity are also identified the results of the statistical analysis are as follows 1 back arc stress correlates with slab dip i e back arc spreading is observed for deep dips deeper than 125 km larger than 50 whereas back arc shortening occurs only for deep dips less than 30 2 slab dip correlates with absolute motion of the overriding plate the correlation is even better when the slab lies on or even more penetrates through the 670 km discontinuity 3 slabs dip more steeply by about 20 on average beneath oceanic overriding plates than beneath continental ones 4 slabs dip more steeply on average by about 10 near edges 5 slab dip does not correlate with the magnitude of slab pull the age of subducting lithosphere at the trench the thermal regime of the subducting lithosphere the convergence rate or the subduction polarity east versus west the present study provides evidence that the upper plate absolute motion plays an important role on slab dip as well as on upper plate strain retreating overriding plates are often oceanic ones and thus may partially explain the steeper slab dips beneath oceanic upper plates one can infer that low slab dips correlate well with compression in continental advancing upper plates whereas steep dips are often associated with extension in oceanic retreating upper plates excess weight of old slabs is often counterbalanced by other forces probably asthenospheric in origin such as lateral mantle flow near slab edges or anchor forces to determine slab dip

interplay between subduction and continental convergence a three dimensional dynamic model for the central mediterranean summary the mediterranean region is attracting considerable attention due to the complexities of its tectonic setting which is considered worldwide a unique natural laboratory for studying the occurrence of extensional tectonics in a general context of continental convergence the tyrrhenian apennine system is controlled by the west dipping subduction of the adria ionian lithosphere and by the near north south convergence between the african and eurasian plates we provide the first 3 d dynamic model of the central mediterranean that quantifies the effects of subduction and convergence on surface deformation in simplified geometry the axis of the model extends from sicily to the alps along the subduction hinge line a convergence rate of 1 cm yr 1parallel to the subduction hinge has been applied to the tyrrhenian block in agreement with global plate motion models density contrasts within the slab cause the gravitational sinking and roll back of the slab in the southern tyrrhenian domain modelling results show a gradual decrease of hinge retreat from south to north with values ranging between 8 and 2 mm yr 1 indicating that the arculate geometry of the hinge line along the italian peninsula is ultimately controlled by the interplay between subduction and convergence the pattern of vertical velocity along directions perpendicular to the hinge with subsidence in the foredeeps and uplift at the eastern border of the tyrrhenian domain is maintained along the whole italian peninsula with higher values in the southern areas

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

present day stress field in subduction zones insights from 3d viscoelastic models and data abstract 3d viscoelastic fe models were performed to investigate the impact of geometry and kinematics on the lithospheric stress in convergent margins generic geometries were designed in order to resemble natural subduction our model predictions mirror the results of previous 2d models concerning the effects of lithosphere mantle relative flow on stress regimes and allow a better understanding of the lateral variability of the stress field in particular in both upper and lower plates stress axes orientations depend on the adopted geometry and axes rotations occur following the trench shape generally stress axes are oriented perpendicular or parallel to the trench with the exception of the slab lateral tips where rotations occur overall compression results in the upper plate when convergence rate is faster than mantle flow rate suggesting a major role for convergence in the slab along strike tension occurs at intermediate and deeper depths 100 km in case of mantle flow sustaining the sinking lithosphere and slab convex geometry facing mantle flow or in case of opposing mantle flow and slab concave geometry facing mantle flow along strike compression is predicted in case of sustaining mantle flow and concave slabs or in case of opposing mantle flow and convex slabs the slab stress field is thus controlled by the direction of impact of mantle flow onto the slab and by slab longitudinal curvature slab pull produces not only tension in the bending region of subducted plate but also compression where upper and lower plates are coupled a qualitative comparison between results and data in selected subductions indicates good match for south america mariana and tonga kermadec subductions discrepancies as for sumatra java emerge due to missing geometric e g occurrence of fault systems and local changes in the orientation of plate boundaries and rheological e g plasticity associated with slab bending anisotropy complexities in the models

geomorphological evidence for the late holocene evolution and the holocene lake level maximum of the aral sea abstract during the holocene the aral sea underwent various transgressive and regressive phases of different magnitudes however previous work has not yet fully clarified the evolution and chronology of the individual phases research presented here throws light on the evolution of the aral sea during the past 2000 years it includes field surveys tachymetric and dgps derived altitude measurements analysis of sediments from two areas of the northern and southern aral basin tastubek bay and karaumbet bay and their correlation with gis based lake area models geomorphological and sedimentological evidence from the study areas shows a transgression of the aral sea around 200 ad ending at a lake level maximum of 54 to 55 m after a medieval regression the lake reached this level again between the late 16th and early 19th century ad the digital elevation model srtm 3 was used to estimate a lake size of 72 400 km2 for the lake level maximum elevated palaeoshorelines specifically at 72 73 m are completely absent in the study areas local remains of escarpments at elevations of 66 m and 73 m are due to resistant miocene caprock and are therefore not interpretable as shoreline features