the composition and role of the fluid in migmatites a fluid inclusion study of the front range rocks monophase negative crystal shaped co2 inclusions occurring isolated in small clusters or in well healed intragranular fractures are common in the leucosome quartz of the 1700m y old migmatites from the east central colorado front range they are however quite rare in the mafic selvage and paleosome host rock quartz the mode of occurrence suggests that these are the earliest inclusions to form in addition to the difference in abundance of the inclusions there is a difference in co2 density distribution between migmatitic zones the temperatures of homogenization for the leucosome inclusions range and l c from 67 c to 20 c with two maxima at 21 c while those for the paleosome and selvage inclusions are 37 c to 20 c with a single maximum at 5 c these differences between the migmatitic zones which occur on the scale of a few centimeters suggest that the formation of these inclusions was related to the migmatization process the densities corresponding to the th maxima are appropriate for the p t conditions for migmatization estimated from the mineral geobarometer geothermometer these inclusions must contain nearly pure co2 as their final melting temperatures 56 5 to 57 2 c are very close to that of the triple point of co2 their composition also was confirmed by raman spectroscopic analyses

high integrated fluid rock ratios during metamorphism at naxos evidence from carbon isotopes of calcite in schists and fluid inclusions a dicussion of the paper by kreulen 1988 contributions to mineralogy and petrology 98 28 32

intraseasonal modulation of south american summer precipitation intraseasonal variation of convection over south america is examined using singular spectrum analysis ssa the dipole convection pattern with centers of action over the sacz and the subtropical plains is modulated by modes of different timescales both oscillatory modes with periods of 36 40 days mode 40 and 22 28 days mode 22 influence convection over the sacz with the faster mode mode 22 leading the variability over the subtropical plains mode 40 is related to the madden julian oscillation outgoing longwave radiation anomalies olra propagate eastward from the western pacific to the central pacific with a period of 40 48 days the 200 hpa streamfunction composites show a wavenumber 1 structure in the tropics and a wave train propagating downstream from the convective area in the tropical pacific the development of the dipole pattern is also contributed by mode 22 which features the meridional propagation of olra over south america from midlatitudes to the tropics the streamfunction composites for mode 22 show a wave train extending from the central pacific eastward to about 608s and curving toward the northeast over south america when the sacz is enhanced these two modes become meridionally aligned locally such episodes are characterized by a wave train propagating northeastward from southern south america toward the tropics composites based on the ssa decomposition indicate that the dominant periods of variability 22 and 40 days cancel out over the pacific region and reinforce each other over the sacz for times close to onset of the enhanced sacz episodes

extensive deformations of rock slopes in southern coast mountains southwest british columbia canada extensive deformations of mountain slopes occur in crystalline intrusive rocks in the southern coast mountains of british columbia typical morphological evidence of slope movement includes extensive systems of tension cracks grabens and antislope scarps collectively referred to here as linears these landforms involve displacements along penetrative joints observed in surface exposures kinematic tests on rock structural data indicate that the observed patterns of linears are generally consistent with the feasible gravitational movements along the dominant discontinuities most sites indicate sliding as the most likely initial mode of movement followed by or accompanied by toppling and toppling induced sliding movements and do not support the view that linears are the traces of active faults

isotopic dating of pre alpidic rocks from the island of ios cyclades greece the lower tectonic unit of ios provides evidence of an at least four stage metamorphic and intrusive history which well might be generalized for large parts of the internal pelagonian

onset and timing of deep seated gravitational slope deformations in the eastern alps italy abstract a previously unrecognised complex of deep seated gravitational slope deformations dsgsd extends 20 km along upper venosta valley in the eastern alps italy mt watles exhibits spectacular features indicative of dsgsds including double ridges trenches and counterscarps the slope deformation occurs along a nappe boundary now corresponding to the schlinig normal fault is also conditioned by recent faults marked by shallow earthquakes and shows glacial paraglacial controls on slope evolution the mt watles dsgsd is a complex deep seated compound slide along a basal shear zone involving the schlinig fault gravitational reactivation of ne trending fractures formed gravitational scarps counterscarps and half grabens in the upper slope whereas the lower part of the slope partially collapsed although our work indicates the importance of the schlinig fault and recent fracturing on slope failure the trigger seems to be postglacial debuttressing of the valley walls radiocarbon dating of peat deposits within one of the major counterscarps indicates that slope deformation started during the lateglacial period and continued during the holocene in several slope sectors

active and break phases in the south american monsoon system the south american monsoon system sams refers to the austral summer season features of deep convective activity and large scale circulation this study examines intraseasonal variations in the low level wind circulation in the amazon and their modulating effects on active and break phases in sams daily averages of outgoing longwave radiation olr ncep ncar reanalysis and gridded rainfall station data in brazil are used from 1 november to 28 february 1980 99 the direction of wind anomalies 10 70 days in the rondonia state brazil is used to classify periods of westerly w and easterly e low level wind regimes composites of w regime show low level wind anomalies crossing the equator southward and closing in a cyclonic anomalous circulation off the coast of argentina and uruguay broad areas of enhanced convection and rainfall are observed in central and southeast brazil suppressed convection is observed over the bolivian altiplano and in northern south america in contrast in the e regime opposite patterns are observed in the low level circulation con vection and rainfall anomalies the duration of active w regimes and break e regimes periods are quite similar with median values of 4 and 5 days respectively further investigation showed that the region of convection and rainfall anomalies over venezuela and northwest brazil is observed only in the 10 30 day band comparison of the results shown here with previous studies indicates the importance of intraseasonal variations in the activity of sams

the south american rainfall dipole a complex network analysis of extreme events intraseasonal rainfall variability of the south american monsoon system is characterized by a pronounced dipole between southeastern south america and southeastern brazil here we analyze the dynamical properties of extreme rainfall events associated with this dipole by combining a nonlinear synchronization measure with complex networks we make the following main observations i our approach reveals the dominant synchronization pathways of extreme events for the two dipole phases ii while extreme rainfall synchronization in the tropics is directly driven by the trade winds and their deflection by the andes mountains extreme rainfall propagation in the subtropics is mainly dictated by frontal systems and iii the well known rainfall dipole is in fact only the most prominent mode of an oscillatory pattern that extends over the entir ec ontinent this provides further evidence that the influence of rossby waves which cause frontal systems over south america and impact large scale circulation patterns extends beyond the equator

recent changes in the precipitation driving processes over the southern tropical andes western amazon analyzing december february djf precipitation in the southern tropical andes sta 12 circ hbox s 20 circ hbox s 3000 m a s l allows revisiting regional atmospheric circulation features accounting for its interannual variability over the past 35 years 1982 2018 in a region where in situ rainfall stations are sparse the chirps precipitation product is used to identify the first mode of interannual djf precipitation variability pc1 andes a network of 98 rain gauge stations further allows verifying that pc1 andes properly represents the spatio temporal rainfall distribution over the region in particular a significant increase in djf precipitation over the period of study is evident in both in situ data and pc1 andes using the era interim data set we found that aside from the well known relationship between precipitation and upper level easterlies over the sta pc1 andes is also associated with upward motion over the western amazon wa a link that has not been reported before the ascent over the wa is a component of the meridional circulation between the tropical north atlantic and western tropical south america wtsa 80 circ hbox w 60 circ hbox w 35 circ hbox s 10 circ hbox n indeed the precipitation increase over the last 2 decades is concomitant with the strengthening of this meridional circulation an intensified upward motion over the wa has moistened the mid troposphere over wtsa and as a consequence a decreased atmospheric stability between the mid and the upper troposphere is observed over this region including the sta we further show that over the last 15 years or so the year to year variability of sta precipitation periodicity 8 years has been significantly associated with upward motion over the wa while upper level easterlies are no longer significantly correlated with precipitation these observations suggests that the sta have experienced a transition from a dry to a wet state in association with a change in the dominant mode of atmospheric circulation in the former dominant state zonal advection of momentum and moisture from the central amazon associated with upper level easterlies is necessary to develop convection over the sta since the beginning of the 21st century djf precipitation over the sta seems to respond directly and primarily to upward motion over the wa beyond improving our understanding of the factors influencing sta precipitation nowadays these results point to the need of exploring their possible implications for the long term evolution of precipitation in a context of global warming

synthetic fluid inclusions vii re equilibration of fluid inclusions in quartz during laboratory simulated metamorphic burial and uplift p t conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations these observations suggest that inclusions formed during early stages of regional metamorphism continue to re equilibrate during burial and subsequent uplift in response to differential pressure p t conditions accompanying burial and uplift were experimentally simulated by initially forming pure h2o inclusions in quartz at elevated temperatures and pressures and then re equilibrating the inclusions in the presence of a 20 wt nacl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re equilibration in all samples re equilibrated at confining pressures below the internal pressure some inclusions were formed that had compositions of 20 wt nacl and densities in accord with the final p t conditions additionally some inclusions were observed to contain fluids of intermediate salinities between 0 and 20 wt nacl densities of these inclusions were also consistent with formation at the re equilibration p t conditions the remainder of the fluid inclusions observed in these samples contained pure h2o and their homogenization temperatures corresponded to densities intermediate between the initial and final p t conditions in short term experiments 7 days where the initial internal overpressure exceeded 1 kbar no inclusions were found that contained the original density and none were found to have totally re equilibrated instead most h2o inclusions re equilibrated until their internal pressures were between 750 and 1500 bars above the confining pressure regardless of the initial pressure differential in a long term experiment 52 days inclusions re equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar i e total re equilibration and 1 2 kbar above the confining pressure in experiments where the confining pressure during re equilibration exceeded the initial internal pressure densities of pure h2o inclusions increased to values intermediate between the initial and final p t conditions additionally these inclusions were generally surrounded by a three dimensional halo of smaller inclusions also of intermediate density resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure in extreme cases where confining pressures were 4 5 kbar above the initial pressure the parent inclusion almost completely closed leaving only the three dimensional array of small 5 m inclusions the outline of which may be several times the volume of the original inclusion groups of such inclusions closely resemble textures commonly observed in medium to high grade metamorphic rocks inclusions containing 10 and 42 wt nacl solutions trapped at 600 c and 3 kbar were re equilibrated at 600 c and 1 kbar for 5 days in dry argon to evaluate the importance of h2o diffusion as a mechanism of lowering the inclusion bulk density salinities of re equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved density changes similar to those previously described were noted in these experiments in inclusions showing no visible microfractures therefore density variations observed in inclusions in this study re equilibrated under rapid deformation conditions are considered to result from a change in the inclusion volume without significant loss of contents by diffusion or leakage

fluid record of rock exhumation across the brittle ductile transition during formation of a metamorphic core complex naxos island cyclades greece fluid inclusions trapped in quartz veins hosted by a leucogneiss from the southern part of the naxos metamorphic core complex attic cycladic massif greece were studied to determine the evolution of the fluid record of metamorphic rocks during their exhumation across the ductile brittle transition three sets of quartz veins v m2 v bd v b are distinguished the v m2 and v bd are totally or respectively partially transposed into the foliation of the leucogneiss they formed by hydrofracturing alternating with ductile deformation accommodated by crystal plastic deformation the v b is discordant to the foliation and formed by fracturing during exhumation without subsequent ductile transposition fluids trapped during crystalplastic deformation comprise two very distinct fluid types namely a co2 rich fluid and a high salinity brine that are interpreted to represent immiscible fluids generated from metamorphic reactions and the crystallization of magmas respectively they were initially trapped at approximate to 625 degrees c and 400mpa and then remobilized during subsequent ductile deformation resulting in various degrees of mixing of the two end members with later trapping conditions of approximate to 350 degrees c and 140mpa in contrast brittle microcracks contain aqueous fluids trapped at 250 degrees c and 80mpa all veins display a similar 13c pointing to carbon that was trapped at depth and then preserved in the fluid inclusions throughout the exhumation history in contrast the d signature is marked by a drastic difference between i v m2 and v bd veins that are dominated by carbonic aqueous carbonic and high salinity fluids of metamorphic and magmatic origin characterized by d between 56 parts per thousand and 66 parts per thousand and ii v b veins that are dominated by aqueous fluids of meteoric origin characterized by d between 40 parts per thousand and 46 parts per thousand the retrograde pt pathway implies that the brittle ductile transition separates two structurally chemically and thermally distinct fluid reservoirs namely i the ductile crust into which fluids originating from crystallizing magmas and fluids in equilibrium with metamorphic rocks circulate through a geothermal gradient of 30 degrees c km1 at lithostatic pressure and ii the brittle upper crust through which meteoric fluids percolate through a high geothermal gradient of 55 degrees c km1 at hydrostatic pressure

influence of the frontal systems on the day to day convection variability over south america abstract cold cloud top fractions derived from international satellite cloud climatology project images and latitude time diagrams are used to study the interaction of frontal systems with tropical convection over south america sa an 11 yr climatology for three frequent types of frontal system tropical convection interaction is built and the associated day to day convection variability is described using satellite images complex principal components and wavelet transforms type 1 is frequent throughout the year especially in austral summer and is characterized by the penetration of a cold front in subtropical sa that interacts with tropical convection and moves with it into lower tropical latitudes type 2 is also more frequent in austral summer and is characterized by amazon convection and enhancement of a quasi stationary northwest southeast oriented band of convection extending from the amazon basin to subtropical sa along the passage of a cold front in the subtropics when the type 2 pattern

detachment zones of cordilleran metamorphic core complexes thermal fluid and metasomatic regimes metamorphic core complexes in arizona are characterized by extensional tectonics in which listrically faulted and unmetamorphosed volcanic rocks of an upper plate are tectonically superimposed on high grade rocks of a lower plate along low angle detachment faults the detachment faults are marked by microbreccias and chloritic breccias which developed by hydraulic fracturing and metasomatism that overprinted subjacent amphibolite facies mylonites oxygen and hydrogen isotope data indicate that the mylonites formed at 500 c under conditions of low water rock ratio chloritic breccias developed at 300 350 c during incursion of hydrothermal fluids along the detachment fault hydrothermal alteration involved massive additions of fe mn and mg with concomitant depletions of k and na reflecting the hydrolysis of k feldspar and plagioclase to chlorite

processes controlling the mean tropical pacific precipitation pattern part ii the spcz and the southeast pacific dry zone the nature of the south pacific convergence zone spcz is addressed by focusing on the dry and cool zone bounded by it and the coast of south america through numerical experiments as shown in a companion paper this dry zone is due to a large extent to orographically forced subsidence here it is shown that the northwestward expansion of this dry zone can be explained by advection of low moist static energy by the trade winds these results provide an explanation of the geometry of the western edge of the dry zone and therefore of the eastern edge of the adjacent spcz sea surface temperature underneath the spcz is enhanced by relatively high near surface humidity through evaporative processes which feeds back into its organization however in this model this feedback is not critical for the existence of the spcz the subsidence associated with the itcz in the north hemisphere negatively affects the precipitation rate in the spcz it was also found that the sensitivity of the forced response is largest for peak orographic heights below 3000 m which indicates that the exact representation of the andes in numerical models might not be as critical as that of lower orography such as that in southern africa

on frontal zone analysis in the tropical region of the northeast brazil a frontal structure in the tropical region is different than in the extratropical region and traditional methods of frontal identification are not accurate the use of a horizontal distribution of the equivalent potential temperature and its advection is the new aspect in frontal identification and will support forecasters in their daily operational practice six fronts over 3 years were identified by the method used in operational practice twenty fronts were registered by cloud bands together with the equivalent potential temperature and its advection maps a cold front separated from the cyclone s center and affected weather on the northeast brazil

variability of the south atlantic convergence zone simulated by an atmospheric general circulation model interannual and decadal variability of the south atlantic convergence zone sacz during austral summer season january february march jfm is investigated an attempt is made to separate the forced variability from the internal variability this is accomplished by applying a signal to noise optimization procedure to an ensemble of multidecadal integrations of the latest version of the ncar community climate model ccm3 forced with observed sst the result yields two dominant forced atmospheric responses a local response to atlantic sst anomalies with interannual decadal timescales and a remote response to pacific sst anomalies at interannual timescales the former is localized within the south atlantic ocean with almost no signal over land consisting of a dipolelike structure in precipitation close to the coast of south america accompanied by a clockwise anomalous circulation of surface winds the latter manifests itself mainly in the upper level circulation consisting of a northeastward shift of the sacz with associated rainfall anomalies during warm enso events

isotopic and petrological evidence for the infiltration of water rich fluids during the miocene m2 metamorphism on naxos greece abstract a detailed carbon and oxygen isotopic study in conjunction with petrological work has been carried out across calcite dolomite marble layers in the high grade metamorphic sequence on the island of naxos greece the purpose of this study is to examine fluid flow during the miocene barrovian metamorphic event individual marble bands show two dominant styles of isotopic alteration from core values of 22 to 29 in 18o and 1 to 3 in 13c firstly contacts between the marble bands and surrounding pelitic rocks have altered isotopic ratios across a metre wide boundary layer the isotopic values of the marble along the contacts drop to 15 to 17 in 18o and 1 to 5 in 13c secondly there is a drop in the isotopic composition of the marbles along vein networks associated with the development of calc silicates the isotopic compositions in these veins drop to 14 to 16 in 18o and 3 to 4 in 13c cross cutting relationships observed between these two alterations allow the relative timing of infiltration to be determined the development of boundary layers is shown to result from the infiltration of fluids with isotopic signatures of 12 to 16 in 18o and 3 to 12 in 13c and an xco2 less than 0 3 these fluids are derived from dehydration of graphite bearing pelites during the prograde metamorphism these conclusions are at odds with those of previous workers who suggested that the prograde metamorphism was a result of the pervasive influx of mantle derived fluids with xco2 greater than 0 5 the alteration associated with vein networks results from peak to post peak infiltration of fluids which drive decarbonation reactions at least some of these fluids have an xco2 less than 0 05 but this is obscured by the production of co2 during the decarbonation reactions these fluids were most probably produced from the crystallising partial melts formed during the prograde metamorphism these infiltrating fluids are thought to have 18 o 10 and 13c of 5 to 7

textural and isotopic development of marble assemblages during the barrovian style m2 metamorphic event naxos greece a detailed petrological analysis of the marble assemblages observed within the m2 metamorphic complex on naxos is presented two distinct periods of mineral growth are documented the first is associated with prograde m2 metamorphism and the second with retrograde m2 metamorphism occurring during ductile extensional thinning of the complex the textural and miner alogical characteristics and the carbon and oxygen isotope compositions of each generation are described and the p t xco2 conditions at which these two mineral generations were stable and the compositions of the fluids present during metamorphism are characterised whereas the low variance and stable isotope compositions of prograde siliceous dolomite assemblages are consistent with internally buffered fluid evolution the retrograde mineral generation is shown to have grown as a result of the infiltration of a water rich fluid phase that transported silica al2o3 na2o and feo into the host rocks this observation together with the stable isotope compositions of the retrograde calcite and the fact that occurrences of veins of this type are limited to marbles in the highest grade areas t 600 c of the metamorphic complex suggests that the fluids responsible for vein formation were generated during the crystallisation of melts as the metamorphic complex cooled from peak temperatures the existence of this second generation of minerals has significant implications for previous studies of heat transport by fluid flow on naxos because many of the unusually low 18o compositions of pelites at high grades may be ascribable to the effects of interaction with retrograde m2 fluids rather than with prograde fluids

high integrated fluid rock ratios during metamorphism at naxos evidence from carbon isotopes of calcite in schists and fluid inclusions calcite in schists of the metamorphic complex at naxos is depleted both in 13c and in 18o with respect to massive marbles this effect is attributed to isotope exchange with circulating co2 rich fluids which had an x text co text 2 0 5 according to fluid inclusions the carbon isotopic composition of the calcites is close to equilibrium with fluid inclusion co2 at metamorphic temperatures mass balance calculations assuming initial 13c values of 0 for calcite and 5 for the fluid give integrated fluid rock volume ratios between 0 1 and 2 0 such high fluid rock ratios are supported by observations on the distribution of co2 h2o ratios of fluid inclusions carbon isotopic compositions of fluid inclusion co2 and oxygen isotope systematics of silicates

influence of south america orography on summertime precipitation in southeastern south america impacts of the main south american orographic structures the andes the brazilian plateau and the guiana shield on the regional climate and associated global teleconnection are investigated through numerical experiments in which some of these features are suppressed simulations are performed with a two way nesting system coupling interactively the regional and global versions of the lmdz4 atmospheric general circulation model at regional scale the simulations confirm previous studies showing that both the andes and the brazilian plateau exert a control on the position and strength of the south atlantic convergence zone sacz mainly through their impact on the low level jet and the coastal branch of the subtropical anticyclones the northern topography of south america appears to be crucial to determine the leading mode of rainfall variability in eastern south america which manifests itself as a dipole like pattern between southeastern south america and the sacz region the suppression of south america orography also shows global scale effects corresponding to an adjustment of the global circulation system changes in atmospheric circulation and precipitation are found in remote areas on the globe being the consequences of various teleconnection mechanisms when the brazilian plateau and the andes are suppressed there is a decrease of precipitation in the sacz region associated with a weakening of the large scale ascendance changes are described in terms of anomalies in the walker circulation meridional displacements of the mid latitude jet stream southern annular mode anomalies and modifications of rossby wave train teleconnection processes

discovery controls and hazards of widespread deep seated gravitational slope deformation in the etsumi mountains central japan deep seated gravitational slope deformation dsgsd is a largely unnoticed but important long term mass wasting process that may result in catastrophic failure of mountain slopes manifested by small topographic irregularities such as ridge parallel scarps and linear depressions it has been predominantly reported in alpine landscapes above timber lines on the basis of area wide high resolution topographic data acquired by light detection and ranging lidar surveys we here show that 96 of existing gravitational scarps have been hidden under forest canopies in the etsumi mountains central japan the scarps are surprisingly widespread over the mountains with a mean line density of as large as 0 87 km km2 our analyses of the scarp distribution suggest that uphill facing scarps are primary geomorphic signals of dsgsd with a destabilized rock mass larger than 105 m2 whereas downhill facing scarps principally occur in response to more localized slope deformation in terms of controls topography is by far the most influential factor in triggering and promoting dsgsd despite the m 7 5 earthquake in 1891 impact of large local earthquakes proves to be not very strong comparison with preexisting landslide maps further suggests that dsgsd and large scale landslide are not different slope processes but represent different stages of the same process our results highlight limitation of aerial photograph interpretation in forest covered mountains and the need for lidar assisted mapping for deeper understanding of this long term process and interactions between surface and tectonic processes

influence of cross andes flow on the south american low level jet abstract by analyzing the 15 yr 1979 93 reanalysis data of the european centre for medium range weather forecasts ecmwf it has been found that the seasonal and synoptic time scale variations of the south american low level jets lljs are largely controlled by an upper level trough and associated low level zonal flow rather than by horizontal temperature gradients along the slope of the andes the northerly lljs are maintained by strong zonal pressure gradients caused by the upstream trough and westerly flow crossing the andes through lee cyclogenesis the process involves both baroclinic development of the upper level trough and mechanical deflection of the westerly flow by the andes when an anticyclonic circulation replaces the trough and westerly flow over the eastern south pacific the northerly lljs tend to diminish or reverse into southerly lljs the dependence of the lljs upon the upstream wind pattern helps to explain how the seasonal variation of the south american lljs is related to the s

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

the role of sst on the south american atmospheric circulation during january february and march 2001 precipitation deficits were observed over southeastern northeastern and central brazil during the 2001 austral summer they contributed to the worsening of the energy crisis that was occurring in the country a low level anomalous anticyclonic circulation observed over eastern brazil enhanced the deviation of moisture transport that usually occurs from the amazon basin to southeastern brazil and inhibited the occurrence of south atlantic convergence zone events in that period however an anomalous low level northerly moisture flux was observed over the la plata basin and positive precipitation anomalies occurred over bolivia paraguay northeastern argentina and southern brazil using the ensemble technique a numerical study was carried out to investigate the role of different sea surface temperature sst forcings observed over this anomalous south american atmospheric circulation reynolds sst monthly means were used as boundary conditions to study the influence of south atlantic south indian south pacific and equatorial pacific oceans the simulations were run from september 2000 to april 2001 using the community climate model version 3 6 general circulation model ten integrations using different initial conditions were done to each experiment numerical experiments suggested that the combined influence of south pacific and equatorial pacific oceans could be responsible for the drought observed over central brazil these experiments simulated the low level anticyclonic anomaly observed over eastern brazil however both experiments have poorly reproduced the intensity of the anomalous low level northerly moisture flux observed over the la plata basin therefore the intensity of the simulated precipitation anomalies over the subtropical regions was much weaker than observed

the recent fault scarps of the western alps france tectonic surface ruptures or gravitational sackung scarps a combined mapping geomorphic levelling and 10be dating approach abstract in the western alps some recent scarps were previously interpreted as surface ruptures of tectonic reverse and normal faults that agree with microseismicity and gps measurements our analysis shows that in fact there are hundreds of recent scarps up to 30 m high and 2 1 km long with only pure normal motions they share the same characteristics as typical sackung scarps the scarps are mainly uphill facing parallel to the ridge crests and the contour lines they are relatively short less than 2 1 km with respect to tectonic fault ruptures and organized in swarms they cut screes and relict rock glaciers with a slow commonly 1 mm year average slip rate in the aiguilles grives massif these sackung scarps clearly express the gravitational toppling of sub vertical bedding planes in hard rocks in contrast the belledonne outer crystalline massif exhibits scarps that stem from the gravitational reactivation of conjugate tectonic faults the recent faults extend to about 1600 m beneath the rognier ridge crest but are always above the valley floor the main scarp swarm is 9 2 km long and constitutes the largest sackung ever described in the western alps 10 be dating of a scarp and offset surfaces shows that 4 m slip may have occurred rapidly in less than 3800 years sometimes between the end of the glaciation and 8800 1900 years ago this dating together with the location of some faults far from the deep glacial valleys suggests that sagging might have been triggered by strong earthquakes during a post glacial period of probably enhanced seismicity the belledonne and synclinal median faults just beneath the rognier sackung could have been the sources of this seismicity

variability in warm season atmospheric circulation and precipitation patterns over subtropical south america relationships between the south atlantic convergence zone and large scale organized convection over the la plata basin warm season precipitation variability over subtropical south america is characterized by an inverse relationship between the south atlantic convergence zone sacz and precipitation over the central and western la plata basin of southeastern south america this study extends the analysis of this south american seesaw precipitation dipole to relationships between the sacz and large long lived mesoscale convective systems llcss over the la plata basin by classifying sacz events into distinct continental and oceanic categories and building a logistic regression model that relates llcs activity across the region to continental and oceanic sacz precipitation a detailed account of spatial variability in the out of phase coupling between the sacz and large scale organized convection over the la plata basin is provided enhanced precipitation in the continental sacz is found to result in increased llcs activity over northern northeastern and western sections of the la plata basin in association with poleward atmospheric moisture flux from the amazon basin toward these regions and a decrease in the probability of llcs occurrence over the southeastern la plata basin increased oceanic sacz precipitation however was strongly related to reduced atmospheric moisture and decreased probability of llcs occurrence over nearly the entire la plata basin these results suggest that continental sacz activity and large scale organized convection over the northern and eastern sections of the la plata basin are closely tied to atmospheric moisture transport from the amazon basin while the warm coastal brazil current may also play an important role as an evaporative moisture source for llcss over the central and western la plata basin

chaco low level jet events characterization during the austral summer season 1 previous studies showed a relationship between convection maxima and the convergence of vapor flux over southeastern south america nicolini and saulo 2000 explored the hypothesis of an intensification of this mutual dependency during the chaco jet events they defined these events as extreme cases of low level jets east of the andes that penetrate southernmost to 25 s using eta operative products during the 1997 1998 austral warm season the interest of the present paper centers on the climatic characterization of the chaco jet events cjes and the possibility of researching this hypothesis using the european centre for medium range weather forecasts reanalyses era which cover a 15 year period 1979 1993 the cjes represent a subensemble of low level jet events east of the andes that are infrequent in the era data set their duration varies from 1 to 10 days more frequently extending from 1 to 5 days the outstanding features of the circulation and the thermodynamic field that represent this ensemble are a maximum contrast of air masses in a latitude close to 39 s the presence of a trough centered on 70 w within a baroclinic wave train penetrating from the pacific ocean and a maximum of heat and moisture over northen argentina and paraguay during the cjes there is an important flux of moisture and convergence at low and mid levels that is about 10 times more intense than the summer mean the intensity found in the water vapor flux anomaly reinforces the importance of studying these episodes for the purpose of determining the water balance over southeastern south america the statement that the cjes represent an important characteristic of the southeastern south american climate is founded on the fact that although the cjes only represent 17 of the austral summer days they account for a significant fraction of the precipitation a maximun of 55 over northeastern argentina however it is indispensable to contrast these results with future field experiments to test the hypothesis addressed in this paper

climatological lower tropospheric frontogenesis in the midlatitudes due to horizontal deformation and divergence abstract the frontogenetic function given by petterssen is calculated for the four months january april july and october and the year as a whole using the climatological wind and temperature data for 85 and 70 kpa levels over the global band between 45 n and 45 s the well known frontogenetic regions of the northern hemisphere nh off the rockies and japan sea are reproduced satisfactorily four nw se inclined bands of frontogenesis are observed in the southern hemisphere sh the mid south pacific and the western south atlantic bands correspond respectively to the south pacific convergence zone spcz and the south atlantic convergence zone sacz which are observed in the outgoing longwave radiation olr charts the other two are located in the western indian ocean and west australia the frontogenetic function in the sacz region is strongest in southern summer in contrast to the nh case which is dominant in winter

mylonite fabric development on naxos greece abstract the miocene structural evolution of the metamorphic complex on naxos occurred within a mid to lower crustal sub horizontal shear zone the deformation style and the regional stress field in the aegean during the miocene are consistent with exhumation of the metamorphic complex during ductile crustal thinning deformation in this shear zone initiated possibly before and continued after the peak of localized high temperature barrovian style metamorphism kinematic indicators in non coaxial fabrics indicate that upper structural levels were displaced to the nne throughout the miocene structural history of the metamorphic complex this displacement was accompanied during its latter stages by compression in an e w direction

subpolar high anomaly preconditioning precipitation over south america abstract the mechanisms associated with the intraseasonal variability of precipitation over south america during the spring season are investigated with emphasis on the influence of a quasi stationary anomalous circulation over the southeastern south pacific ocean sep a spectral analysis performed to the bandpass filtered time series of daily precipitation anomalies for the la plata basin lpb and the south atlantic convergence zone sacz regions revealed several statistically relevant peaks corresponding to periods of roughly 23 days and 14 16 days with the lower higher frequency peaks more prevalent for the sacz lpb the large scale circulation patterns preconditioning precipitation variability over both regions were explored by means of a regression analysis performed on the daily 500 hpa geopotential anomaly field provided by the ncep ncar reanalysis dataset the most prominent feature of the regression fields is the presence of a quasi stationary anomalous anticyclonic cyclonic circulation

a late holocene deep seated landslide in the northern french pyrenees abstract a very large deep seated landslide dsl in the northern pyrenees with over 1 4 10 9 m 3 was mapped and dated based on sedimentation rates and 10 be terrestrial cosmogenic radionuclide surface exposure cre dating our analysis on the landslide reveals the role of inherited structures in the landslide process and highlighted typical gravitational morpho structures and a small lake trapped at the toe of the landslide head scarp the rate of lake sedimentation 0 86 0 57 mm yr 1 also provided us with the approximate age of the landslide 1106 540 yr the cre dating result highlights two main slope destabilization phases then we discussed the history of dsl activity and its controlling factors information related to historic markers and the absence of particular climate markers and changes during the medieval dark ages point to a single event in ad 1380 due to a major seismic event lavedan earthquake

geomorphology and geochronology of sackung features uphill facing scarps in the central spanish pyrenees abstract the paper analyses uphill facing scarps and associated troughs developed in the oversteepened slopes of two neighbouring glacial valleys in the central spanish pyrenees previous studies of sackung landforms in the pyrenees have argued for deglacial unloading as the genetic mechanism but this causal and temporal relationship has not been proved due to the lack of chronological data the antislope scarps in the two studied locations vallibierna and estos are developed in palaeozoic metasedimentary rocks parallel to the contour lines and the structural grain occur in the intermediate sector of the hillslope and are up to 0 5 km long and several meters high a trench was excavated in a sackung trough fill in each of the valleys in order to gain information about their chronology and genesis charcoal from the lowermost unit in vallibierna provided an age of 5 9 cal ka for the sackung and extrapolation of the three dates obtained in estos indicates that the trough formed ca 7 6 7 8 cal ka deglaciation of the studied sectors of the valleys occurred between 16 and 13 ka the time lag of 5 ka suggests that glacial erosion and the subsequent debutressing of the oversteepened valley walls created slopes predisposed to sackung development but did not initiate the movement seismic shaking is proposed as a probable triggering factor this hypothesis although supported by the sudden deformation event recorded by a failure plane exposed in vallibierna trench and by the seismic and neotectonic activity of the area cannot be proved due to the lack of chronological information about paleoearthquakes

negative ocean atmosphere feedback in the south atlantic convergence zone 1 the temporal evolution of the coupled variability between the south atlantic convergence zone sacz and the underlying sea surface temperature sst during austral summer is investigated using monthly data from the ncep ncar reanalysis a maximum covariance analysis shows that the sacz is intensified weakened by warm cold sst anomalies in the beginning of summer drifting northward this migration is accompanied by the cooling warming of the original oceanic anomalies the results confirm earlier analyses using numerical models that suggest the existence of a negative feedback between the sacz and the underlying south atlantic sst field a linear regression of daily anomalies of sst and omega at 500 hpa to the equations of a stochastic oscillator reveals a negative ocean atmosphere feedback in the western south atlantic stronger during january and february directly underneath the oceanic band of the sacz

structural characteristics of convective systems over south america related to cold frontal incursions abstract international satellite cloud climatology project isccp dx and microwave sensor data collected by the tropical rainfall measuring mission trmm are used to identify and describe structural characteristics of convective systems css over continental south america sa related to cold frontal incursions in a 3 yr period an austral wet season climatology for cs events of the three most important types of front tropical convection interaction is built by applying latitude time diagrams and a cloud tracking method to dx data type 1 is characterized by the penetration of a cold front over subtropical sa that interacts with convection and moves with it into lower tropical latitudes type 2 refers to amazon convection and its enhancement in a quasi stationary northwest southeast oriented band extending from the amazon to subtropical sa along with the passage of a cold front in the subtropics and characterizes the synoptic formation of the south atlantic convergence zone a quasi stationary cold fro

late holocene intensification of colds fronts in southern brazil as indicated by dune development and provenance changes in the sao francisco do sul coastal barrier abstract holocene coastal barriers from southern brazil present great geomorphological changes during their late stages of development in this study we investigate the holocene evolution of the sao francisco do sul sfs barrier through geomorphological heavy minerals and grain size analyses constrained by optically stimulated luminescence osl dating the sfs barrier stands out among the southern brazilian barriers due to its well preserved morphology with a parabolic dune belt in the seaward portion the progradation of the sfs barrier started at least 4914 478 years ago and had a pronounced morphodynamic shift around 1891 155 years ago this shift is characterized by episodic development of parabolic dunes migrating to nnw associated with sand coarsening and a marked variation in sediment provenance represented by the input of sands derived from local coastal watersheds southward from the sfs barrier this morphodynamic provenance shift resulted from the strengthening of sse winds and associated wave systems responsible for the northward alongshore drift implying intensification of cold fronts coupled with higher precipitation since 1891 155 years ago osl dating combined with grain size heavy minerals and geomorphological analyses allowed assessing the response of coastal barriers to the impacts of centennial to millenial climate events occurred during the late holocene reconstruction of the late holocene climate variability and associated impacts on coastal sedimentation is a key issue to evaluate the sensitivity of coastal barriers to future climate changes

post metamorphic co2 rich fluid inclusions in granulites in granulite facies samples from the adirondack mountains ny estimates of peak metamorphic co2 fugacities based on mineral equilibria are not consistent with estimates based on data for high density co2 rich fluid inclusions of the 21 adirondack samples investigated for this study all contain co2 rich inclusions inclusions occur in quartz apatite and garnet they range in size from 3 to 50 m and are without visible h2o in a few of the inclusions freezing point determinations and preliminary laser raman spectroscopy show the presence of small amounts 3 of other fluids n2 and h2s co2 liquid vapor homogenization temperatures are between 46 and 31 c corresponding to densities between 1 14 and 0 5 gm cc some of these densities are consistent with peak metamorphic entrapment 1 06 to 1 1 gm cc

the nature and distribution of fluids during amphibolite facies metamorphism naxos greece on the basis of fluid inclusion evidence pervasive influx of deep seated co2 rich fluids has been invoked to account for mid to upper amphibolite facies m2b metamorphism on the island of naxos cyclades greece in this paper mineral devolatilization and melt equilibria are used to constrain the composition of both syn and post peak m2b fluids in the deepest exposed levels of the metamorphic complex the results indicate that peak m2b fluids were spatially and compositionally heterogeneous throughout the high grade core of the complex whereas post peak m2b fluids were generally water rich the observed heterogeneities in syn m2b fluid composition are inconsistent with pervasive co2 flushing models invoked by previous workers on the basis of fluid inclusion evidence it is likely that few co2 rich fluid inclusions on naxos preserve fluids trapped under peak metamorphic conditions it is suggested that many of these inclusions have behaved as chemically open systems during the intense deformation that accompanied the uplift of the metamorphic complex a similar process may explain the occurrence of some co2 rich fluid inclusions in granulite facies rocks

on the origin of co2 rich fluid inclusions in migmatites nearly pure co2 fluid inclusions are abundant in migmatites although h2o rich fluids are predicted from the phase equilibria processes which may play a role in this observation include 1 the effects of decompression on melt 2 generation of a co2 bearing volatile phase by the reaction graphite quartz biotite plagioclase melt orthopyroxene co2 rich vapour 3 selective leakage of h2o from co2 h2o inclusions when the pressure in the inclusion exceeds the confining pressure during decompression and 4 enrichment of grain boundary vapour in co2 by subsolidus retrograde hydration reactions

crystal chemistry of a mg vesuvianite and implications of phase equilibria in the system cao mgo al2o3 sio2 h2o co2 chemical analysis including h f feo fe o of a mg vesuvianite from george town calif usa yields a formula r 9 mgl bbfe 0 a 10 7si1 81 06 oh 8 4 0 4 in good agreement on a cation basis with the analysis reported by pabst 1936 x ray and electron diffraction reveal sharp reflections violat ing the space group p4 nnc as consistent with domains having space groups p4 n and p4nc refinement of the average crystal structure in space group p4 nnc is consistent with occupancy of the a site with ai of the half occupied b site by 0 8 mg and 0 2 fe of the half occupied c site by ca of the ca i 2 3 sites by ca and the oh and o 10 sites by oh and 0 we infer an idealized formula for mg vesuvianite to be cai9mg mga1 ai4si 8069 oh 9 which is related to fe3 vesuvianite by the substi tutions mg oh fe3 0 in the b and o 10 sites and fe a1 in the alfe site thermodynamic calculations using this formula for mg vesuvianite are consistent with the phase equilibria of hochella liou keskinen kim 1982 but inconsistent with those of olesch 1978 further work is needed in determining the composition and entropy of synthetic us natural vesuvianite before quantitative phase equilibria can be dependably generated a qualitative analysis of reactions in the system cao mgo

high density co2 inclusions in the colorado front range a fluid density in an inclusion is commonly observed to be too low for the p t estimates for the postulated time of trapping and is generally attributed to a fluid loss during the uplift process it is more difficult to explain a fluid density which is too high in the 1700 m y front range migmatites such high densities occur in some of co2 inclusions which were deduced to have formed during the migmatization episode the peak p t estimates for migmatization in the front range are 4 6 kb and 650 700 c in sillimanite field but pressures required to form the most dense inclusions are 7 6 kb in kyanite field the high density is not likely to be a relic of a higher pressure condition earlier than the main migmatization episode for the following reasons a no kyanite or any other relic high pressure phase has been found in the precambrian front range b the high density inclusions are rare in zones with least signs of deformation and melting paleosomes and quartz inclusions within feldspar grains which instead contain relatively undisturbed early inclusions c high density inclusions with th 30 c are associated with heavily altered plagioclase caused by hydrothermal activity which was a late event in leucosome formation further there is evidence for post entrapment change s in density an intragranular trail in quartz contains co2 inclusions that exhibit almost the whole range in th 40 to 24 c as displayed by the entire population of the early co2 inclusions 66 to 30 c the density of an inclusion in the trail is not related to inclusion size but to the position of the inclusion relative to apparent micro shear zones crossing the co2 trail a change to a higher density a smaller volume could have resulted from an initially isobaric cooling path which intersects co2 isochores with increasingly higher densities additional excess pressure may have resulted from overthrusting however because high density inclusions occur selectively in the zones in which plagioclase shows alteration indicating a high a h 2 o and because there is a correlation between shear zones and high density inclusions it is postulated that local hydrolytic weakening of quartz was necessary for the decrease of inclusion volume which occurred during deformation the localized deformation may also result in an excess pressure however the introduction of a small amount of h2o into these inclusions as a possible cause of high density inclusions cannot be ruled out

columbia mountain landslide late glacial emplacement and indications of future failure northwestern montana usa abstract the well preserved and undissected columbia mountain landslide which is undergoing suburban development was studied to estimate the timing and processes of emplacement the landslide moved westward from a bedrock interfluve of the northern swan range in montana usa onto the deglaciated floor of the flathead valley the landslide covers an area of about 2 km2 has a toe to crown height of 1100 m a total length of 3430 m a thickness of between 3 and 75 m and an approximate volume of 40 million m3 deposits and landforms define three portions of the landslide from the toe to the head they are i clast rich diamictons made up of gravel sized angular rock fragments with arcuate transverse ridges at the surface ii silty and sandy deposits resting on diamictons in an internally drained depression behind the ridges and iii diamictons containing angular and subangular pebble to block sized clasts some of which are glacially striated in an area of lumpy topography between the depression and the head of the landslide drilling data suggest the diamictons cover block to slab sized bedrock clasts that resulted from an initial stage of the failure the landslide moved along a surface that developed at a high angle to the ne dipping thinly bedded metasediments of the proterozoic belt supergroup the exposed slope of the main scarp dips 30 37 w a hypothetical initial rotational failure of the lower part of a bedrock interfluve may have transported bedrock clasts into the valley the morphology and deposits at the surface of the landslide indicate deposition by a rock avalanche sturzstrom derived from a second stage of failure along the upper part of the scarp the toe of the columbia mountain landslide is convex west in planview except where it was deflected around areas now occupied by glacial kettles on the north and south margins landsliding therefore occurred during deglaciation of the valley while ice still filled the present day kettles available chronostratigraphy suggests that the 1 km thick glacier in the region melted before 12 000 14c years bp within 3000 years of the last glacial maximum deglaciation and hillslope failure are likely causally linked failure of the faceted interfluve was likely due tensile fracturing of bedrock along a bedding normal joint set shortly after glacial retreat from the hillslope open surficial tension fractures and grabens in the swan range are limited to an area above the crown of the landslide movement across these features suggests that extensional flow of bedrock sackung is occurring in what remains of the ridge that failed in the columbia mountain landslide the fractures and grabens likely were initiated during failure but their morphologies suggest active extension across some grabens continued movement of bedrock above the crown may result in future mass movements from above the previous landslide scarp landslides sourced from bedrock above the scarp of the late glacial columbia mountain landslide which could potentially be triggered by earthquakes are geologic hazards in the region

a primitive equations model study of the effect of topography on the summer circulation over tropical south america abstract a nonlinear primitive equations model with five levels in a coordinate is applied to study the effects of idealized topography on the summer circulation pattern over tropical south america the model circulation is forced by prescribed latent heating centered over the amazon basin both the steady and the transient components of the response are considered and compared with the corresponding components in the absence of topography it is found that topography blocks low level inflow from the equatorial pacific and leads to the development of a steady northerly jet that is fed from the tropical atlantic other important effects of topography on the response to steady heating are found in the low level field of vertical motion the effects of topography on the response to transient heating are described in terms of a component reflected to the east and a component transmitted to the west by the topography

the el nino impact on the summer monsoon in brazil regional processes versus remote influences the el nino impact on brazil s summer monsoon has not been adequately assessed through seasonal analysis because it shows significant subseasonal variations in this study the el nino influence on the summer monsoon circulation rainfall and temperature is analyzed with monthly resolution using data from a dense network of stations the expected precipitation percentiles during the monsoon season of el nino en events are calculated as well as anomalies of surface temperature and thermodynamic parameters this information is analyzed jointly with anomaly composites of several circulation parameters the analysis shows that some precipitation and circulation anomalies which are consistent and important during part of the season are smoothed out in a seasonal analysis there are abrupt changes of anomalies within the summer monsoon season suggesting the prevalence of regional processes over remote influences during part of the season the probable role of remote influences and regional processes is assessed the anomalous heat sources associated with el nino perturb the walker and hadley circulations over south america and generate rossby wave trains that produce important effects in the subtropics and extratropics in the early summer monsoon season remotely produced atmospheric perturbations prevail over brazil anticyclonic low level anomalies predominate over central east brazil in the tropics and subtropics due to the subsidence over the amazon and to rossby waves in the subtropics easterly moisture inflow from the atlantic is favored but diverted toward northern south america sa and south brazil there are negative precipitation anomalies in north and central east brazil and positive ones in south brazil these precipitation anomalies are favored by the perturbation in the walker and hadley circulation over the east pacific and south america and by a rossby wave train over southern sa that originates in the eastern pacific in january with the enhancement of the continental subtropical heat low by anomalous surface heating during the spring there is anomalous low level convergence and cyclonic circulation over southeast brazil while at the upper levels anomalies of divergence and anticyclonic circulation prevail this anomalous circulation directs moisture flux toward central east brazil causing moisture convergence in this region a favorable thermodynamic structure enhances precipitation over central east brazil the dry anomalies in north brazil are displaced northward and the anomalies in south brazil almost disappear in february after the above normal precipitation of january the surface temperature anomalies turn negative and the precipitation diminishes in central east brazil there are negative rainfall anomalies in north brazil and in the south atlantic convergence zone sacz and positive ones in south brazil influence function analysis shows that while the anomalies of circulation over southeast brazil in the spring of el nino years are mostly due to remote influences from the tropical east pacific those in january are probably due to local influence during this month the monsoonlike circulation is enhanced simultaneous and lagged correlation analysis of sst and rainfall in central east brazil shows that sst anomalies in the atlantic ocean off the southeastern coast of brazil fluctuate on the same timescale as the circulation and precipitation anomalies

serial upstream propagating mesoscale convective system events over southeastern south america abstract serial mesoscale convective system mcs events with lifetimes over 18 h and up to nearly 70 h are routinely observed over southeastern south america from infrared satellite imagery during the spring and summer these events begin over the southern la plata river basin with individual convective systems generally moving eastward with the cloud layer mean wind however an important and common subset of these serial mcs events shows individual mcss moving to the east or southeast yet the region of convective development as a whole shifts upstream to the north or northwest analyses of the composite mean environments from 10 of these upstream propagating serial mcs events using ncep ncar reanalysis data events indicates that the synoptic conditions resemble those found in mesoscale convective complex environments over the united states the serial mcs events form within an environment of strong low level warm advection and strong moisture advection between the surface and 700 hpa from the amazon

differentiating between gravitational and tectonic faults by means of geomorphological mapping trenching and geophysical surveys the case of the zenzano fault iberian chain n spain abstract the zenzano fault scarp has been developed on the top of a 475 m high erosional escarpment underlain by an upper brittle sequence and a lower halite bearing evaporitic formation the 1850 m long fault with a maximum displacement of 45 m and parallel to the escarpment has offset the back of a dip slope generating an antislope scarp with prominent triangular facets up to 38 m high and obstructing consequent transverse drainages defeated streams both gravitational and tectonic interpretations were previously proposed for this active surface rupture the fault scarp has been investigated by detailed geological and geomorphological mapping geophysical surveys gpr and ert and two trenches excavated across the fault in disrupted drainages the geophysical profiles clearly imaged the fault helping to site the trenches and roughly estimate the thickness of the deposits accumulated in the downthrown block although the maximum displacement to length ratio dmax l of the fault fall within the range of tectonic faults of similar length according to the world database the geological and geomorphological context together with several parameters reveal that this structure corresponds to a gravitational failure 1 anomalously high vertical displacement per event 1 4 m 2 high apparent vertical slip rate 0 6 mm year and 3 short recurrence interval of faulting events the negligible horizontal displacement component on the dip slip fault as well as the presence of very large caprock collapse sinkholes and saline springs strongly suggest that interstratal karstification of the halite bearing evaporites has played a primary role in the development of the gravitational failure the formation of this morphostructure has been favoured by pre existing tectonic faults erosional unloading related to the removal of an overburden ca 800 m thick and enhanced groundwater recharge due to the blockage of the drainage this work illustrates that the proposed multidisciplinary approach allows the identification of features and calculation of parameters that may help to elucidate whether an active failure has a gravitational or a tectonic origin

the influence of the andes mountains on the south american low level flow 1 a dry hydrostatic three dimensional primitive equation model is used to evaluate the mechanical effect of the andes mountains on the south american low level flow llf the model simulations reproduce the evolution of a baroclinic wave over the continent under winter and summer conditions in both seasons as a consequence of the interaction between the basic flow and the andes northerly llf was reproduced east of the andes which resembles the main characteristics of the observed flow moreover seasonal changes of cyclone activity have a significant impact on the location of maximum llf and its alignment which exhibits a nw se orientation during winter and more meridional orientation in the warm season

simulations of the summer circulation over the south american region with an eta coordinate model abstract a multilevel limited area primitive equations model in eta coordinate is used to simulate the effects of the amazonian latent heat source and the andean topography on the summer december january february circulation over the south american region the observed circulation features such as the bolivian high and the trough near the coast of northeast brazil in the upper troposphere the elongated south atlantic convergence zone sacz oriented northwest to southeast from the southern amazon region into the atlantic ocean and the subtropical anticyclones in the south pacific and south atlantic oceans in the lower levels are well simulated although heating alone produces the sacz the mountain and the basic flow put it in the observed position it is found that regular daily pulses of heating are necessary for the maintenance of the sacz the position and intensity of the sacz change rather substantially from the no mountain case to the mountain case thus showing the importance of the effect

fluid inclusions in rocks from the amphibolite facies gneiss to charnockite progression in southern karnataka india direct evidence concerning the fluids of granulite metamorphism fluid inclusion studies of rocks from the late archaean amphibolite facies to granulite facies transition zone of southern india provide support for the hypothesis that co2 rich h2o poor fluids were a major factor in the origin of the high grade terrain charnockites closely associated leucogranites and quartzo feldspathic veins contain vast numbers of large co2 rich inclusions in planar arrays in quartz and feldspar whereas amphibole bearing gray gneisses of essentially the same compositions as adjacent charnockites in mixed facies quarries contain no large fluid inclusions inclusions in the northernmost incipient charnockites as at kabbal karnataka occasionally contain about 25 mol of immiscible h2o lining cavity walls whereas inclusions from the charnockite massif terrane farther south do not have visibile h2o microthermometry of co2 inclusions shows that miscible ch4 and n2 must be small probably less than 10mol combined densities of co2 increase steadily from north to south across the transitional terrane entrapment pressures calculated from the co2 equation of state range from 5 kbar in the north to 7 5 kbar in the south at the mineralogically inferred average metamorphic temperature of 750 c in quantitative agreement with mineralogic geobarometry this agreement leads to the inference that the fluid inclusions were trapped at or near peak metamorphic conditions calculations on the stability of the charnockite assemblage biotite orthopyroxene k feldspar quartz show that an associated fluid phase must have less than 0 35 h2o activity at the inferred p and t conditions which agrees with the petrographic observations high tio2 content of biotite stabilizes it to lower h2o activities and the steady increase of biotite tio2 southward in the area suggests progressive decrease of ah2o with increasing grade oxygen fugacities calculated from orthopyroxene magnetite quartz are considerably higher than the graphite co2 o2 buffer which explains the absence of graphite in the charnockites the present study quantifies the nature of the vapours in the southern india granulite metamorphism it remains to be determined whether co2 flushing of the crust can by itself create large terranes of largeion lithophile depleted granulites or whether removal of h2o bearing anatectic melts is essential

bimodal behavior of extended continental lithosphere modeling insight and application to thermal history of migmatitic core complexes abstract extensional migmatitic core complexes micc expose partially molten crustal rocks exhumed during post thickening extension low heat flow in active collisional mountains suggests that there is i either input from extra crustal heat sources or ii under assessment of the pre extensional collisional heat content to form high grade metamorphic core complexes we evaluate these two hypotheses by varying thermal gradients and crustal thicknesses of two dimensional thermo mechanical numerical models simulating the extension of a stratified lithosphere for moho temperatures 35 and 50 km extension leads to a rifting mode dictated by the upwelling of the asthenosphere in that case no micc is formed for moho temperatures 700 c and or crustal thicknesses 60 km extension develops micc while maintaining a flat moho similar to wide extensional systems such as the aegean and the basin and range however when crustal strain softening is switched on it produces for both mentioned conditions miccs with similar crustal geometries testifying that partial melting in miccs can result from both extra crustal syn extensive heat asthenospheric advection and collisional heat typically miccs induced by asthenospheric heat show the sequence lower crustal migmatization doming and crustal ultra high temperature uht conditions and mantle melting in a short temporal range from 5 to 10 model ma after asthenospheric upwelling the convective migmatitic dome is shifted horizontally with respect to the asthenospheric culmination and dome migmatites experience isobaric heating to peak conditions in contrast collisional heat induced miccs exhibit pre extensional migmatization and subsequent doming at 3 4 model ma in this case the asthenosphere generating lower crustal uht conditions and mantle melts upwells lately and is not symptomatic for micc formed in short extensional pulses

roles of the brazilian plateau in the formation of the sacz abstractthe role of the brazilian plateau bp in maintaining the south atlantic convergence zone sacz has been examined by statistical analysis and numerical experiments statistical analysis using 27 years of data showed that the sacz is most intense when it is over the bp in this case low level cyclonic circulation appears over the southwestern part of the bp and forms westerly flow which intensifies low level convergence along the sacz with northeasterly flow from the amazon and northerly flow along the western edge of the south atlantic subtropical high a vorticity budget analysis indicates that precipitation over the bp that accompanies stretching maintains the cyclonic circulation sensitivity experiments using a regional atmospheric model for two different cases indicate that precipitation over the bp plays a dominant role as an atmospheric heat source in maintaining the cyclonic circulation and the sacz in model experiments in which rain was stopped around the bp but the topography was kept

rock slope movements along the mount currie fault scarp southern coast mountains british columbia rock slope movements are reported from mount currie ridge near pemberton in the southern coast mountains of british columbia the site displays linear trenches antislope scarps and tension cracks typical of mountain ridges undergoing slow deformation however the most prominent linear scarp on the ridge has been previously interpreted as a fault scarp kinematic tests on rock discontinuities demonstrate the feasibility of both toppling and plane sliding at this site ground motion vectors based on a 4 year laser electronic distance measurement edm record of slope movements are generally compatible with the results of the kinematic tests these results cast doubt on a strictly seismic interpretation of the mount currie scarp

new insights into the rainfall variability in the tropical andes on seasonal and interannual time scales in this study we analyze the atmospheric mechanisms associated with the main rainfall patterns in the tropical andes 20 circ hbox s 1 circ hbox n on seasonal and interannual time scales using a homogeneous and high spatial resolution precipitation data set 0 05 circ times 0 05 circ at monthly time step chirps 1981 2016 in situ precipitation from 206 rain gauge stations power spectrum and eof analysis we identify three andean regions characterized by specific seasonal and interannual rainfall modes the equatorial andes ea 5 circ hbox s 1 circ hbox n the transition zone tz 8 circ hbox s 5 circ hbox s and the southern tropical andes sta 20 circ hbox s 8 circ hbox s on seasonal time scales the main mode of precipitation in the ea and sta are characterized by a unimodal regime while the tz is represented by a bimodal regime the ea and the tz share the same wet season in the february april period which is associated with a weakened walker cell the southerly position of the intertropical convergence zone itcz and a strong westward humidity transport from the equatorial amazon this latter mechanism and a reduced elevation of the andes are associated with the october november wet season in the tz the presence of the bolivian high and the northward extension of the low level jet are associated with the precipitation over andean regions between 20 circ s and 8 circ s in the december march period on interannual time scales extreme monthly wet events emwe in the sta tz are related to convection over the western equatorial amazon during the december march february april period showing an atmospheric relationship between the amazon and the andes extreme monthly dry events emde in the tz and in the ea during the february april period are related to a strengthened walker cell especially in the eastern pacific in addition emwe emde in the ea are associated with an anomalous southward northward displaced eastern pacific itcz moreover we find a relationship between precipitation at higher elevations in the andes north of 10 circ hbox s and easterly winds at 200 hpa during february april emwe finally extreme monthly events in the ea sta are related to sea surface temperature anomalies in the western central equatorial pacific

the link between oxygen isotope resetting partial melting and fluid flow in metamorphic terrains a correlation between the style of partial melting and synmeta morphic fluid flow exists in metapelites from the mount lofty ranges reynolds range and omeo zone australia mount lofty ranges migmatites comprise granitic leucosomes in rocks that are still biotite rich with no indications of other mafic minerals being formed along with the melts by contrast in the reynolds and omeo migmatites garnet cordierite and or spinel formed along with the melts oxygen isotope data are most consistent with the mount lofty ranges undergoing significant fluid rock interaction during regional metamorphism which may have fluxed fluid present partial melting by contrast regional metamorphic fluid flow in the reynolds range and omeo zone was limited leading to partial melting via fluid absent reactions the style of melting reactions may help to constrain the timing of isotopic resetting and fluid flow in metamorphic terrains which is currently a contentious issue

mesoscale convective systems over southeastern south america and their relationship with the south american low level jet abstract prior studies have shown that the low level jet is a recurrent characteristic of the environment during the initiation and mature stages of mesoscale convective systems mcss over the great plains of the united states the south american low level jet sallj over southeastern south america sesa has an analogous role advecting heat and moisture from the amazon basin southward into the central plains of southeastern south america generating ideal environmental conditions for convection initiation and growth into mcss this research has two purposes one is to describe the characteristics of a 3 yr mcs sample in south america south of the equator and its related geographical distribution of convection frequency the other is to advance the knowledge of the evolution of favorable environmental conditions for the development of large mcss specifically those that mature under sallj conditions high horizontal and temporal resolution satellite images are used to detect mcss in the area for the

evolution stages of large deep seated landslides at the front of a subalpine meridional chain maritime alps france abstract studying long term evolution of gravitational slope evolution is a key to understanding deep seated landslide processes this paper deals with three large deep seated landslides dsls at a front of a subalpine meridional chain on the la marbriere slope near the town of grasse alpes maritimes france the geological framework controlling the stability and morphology of the dsls is associated with thick and tamped triassic layers of mudstone with gypsum overlain by highly faulted jurassic limestone gravitational deformation affects the entire slope involving a movement of about 1 1 10 8 m 3 of rock material it creates large disturbances in landscape morphology such as scarps counter slope scarps trenches and other typical gravitational morpho structures geomorphological mapping coupled with deep electrical resistivity tomography ert reveals a strong correlation between these morpho structures and inherited brittle tectonic features this observation relies on spatial and geometrical relations on the surface and at the depth of more than 150 m checked by ert between the most persistent fault and the gravitational morpho structures the specific distribution of the morpho structures on the basis of their morphological typologies and variations in the stage of evolution of three dsls provides an interpretation of their kinematics during the last 400 ka it appears that soft substratums combined with inherited persistent anisotropies are key factors in the development of the dsls indeed outflow of mudstone due to the lithostatic pressure imposed by individual limestone compartments has led to general slope subsidence then a progressive toppling of a rock mass may have led to the catastrophic rock collapse along bedding planes the evolution of the dsls can be divided into three distinct stages represented by three zones a young collapse stage zone 1 a pre collapse stage zone 2 and an old mature stage 400 ka zone 3 as the dsls occur on the same slope and in the same geological context this area offers interesting perspectives for understanding factors controlling the long term gravitational evolution of slopes

the geodynamic evolution of the alpine orogen in the cyclades aegean sea greece insights from diverse origins and modes of emplacement of ultramafic rocks

a mechanism for preferential h 2 o leakage from fluid inclusions in quartz based on tem observations preferential leakage of h2o from fluid inclusions containing multiple gas components has been suspected in natural metamorphic rocks and has been demonstrated experimentally for synthetic h2o co2 rich inclusions in natural quartz knowledge of the physical and chemical characteristics of the leakage mechanism which may be very complex increases the value of natural fluid inclusions to metamorphic geology it is proposed that crystal defects play a major role in nondecrepitative preferential h2o leakage through quartz and remain effective during metamorphism inclusions with either an internal overpressure or underpressure produce strain in the adjacent quartz crystal via the nucleation of many dislocations and planar defects like dauphine twin boundaries these defects allow preferential loss of h2o from h2o co2 rich inclusions at supercritical conditions the transport capacity of this leakage mechanism is enhanced by nucleation of small bubbles on defect structures the nucleation of these bubbles seems to be a recovery process in strained crystals solubility gradients of quartz in water in a crystal with internally underpressurized inclusions may result in optical visible implosion halos in a three dimensional spatial arrangement caused by the growth of small bubbles at the expense of the larger original fluid inclusion natural fluid inclusions from naxos greece are always associated with numerous interlinked dislocations these dislocations may have been produced by plastic derormation or by crystal growth related processes e g crack healing the presence of small bubbles on these dislocations indicates that a similar leakage mechanism for h2o must have occurred in these rocks

synergism between the low level jet and organized convection at its exit region abstract previous studies suggest that the enhanced meridional extent of some south american low level jet events known as chaco jets is a consequence of a positive feedback between the low level wind and strong convection that is usually observed at their exit region to assess how this interaction takes place a chaco low level jet event observed between 18 and 19 december 2002 i e during the south america low level jet experiment and the associated mesoscale convective system that evolved at its exit region have been selected to perform numerical experiments where diabatic heating effects associated with phase changes can be quantified this case study has also been used to analyze the diurnal oscillations related to planetary boundary layer pbl mechanisms in order to describe whether the observed evolution of the low level wind can be explained either by pbl related forcing or by the interaction with convection the sensitivity experiments confirm that there is a positive feedback at low level

magnitude and frequency of rock falls and rock slides along the main transportation corridors of southwestern british columbia the two main transportation corridors of southwestern british columbia are subject to a range of rock slope movements rock falls rock slides and rock avalanches that pose significant risks to r

tectonic vs gravitational morphostructures in the central eastern alps italy constraints on the recent evolution of the mountain range abstract deep seated gravitational slope deformations dsgsds influence landscape development in tectonically active mountain ranges nevertheless the relationships among tectonics dsgsds and topography are poorly known in this paper the distribution of dsgsds and their relationships with tectonic structures and active processes surface processes and topography were investigated at different scales over 100 dsgsds were mapped in a 5000 km2 sector of the central eastern alps between the valtellina engadine and venosta valleys detailed lineament mapping was carried out by photo interpretation in a smaller area about 750 km2 including the upper valtellina and val venosta fault populations were also analysed in the field and their mechanisms unravelled allowing to identify different structural stages the youngest being consistent with the regional pattern of the ongoing crustal deformation finally four dsgsd examples have been investigated in detail by geological and 2d geomechanical modelling dsgsds affect more than 10 of the study area and mainly cluster in areas where anisotropic fractured rock mass and high local relief occur their onset and development is subjected to a strong passive control by mesoscopic and major tectonic features including regional nappe boundaries as well as nw se n s and ne sw trending recent brittle structures the kinematic consistency between these structures and the pattern of seismicity suggests that active tectonics may force dsgsds although field evidence and numerical models indicate slope debuttressing related to deglaciation as a primary triggering mechanism

multiscale analysis of the summertime precipitation over the central andes precipitation over the central andes in south america exhibits a marked annual march with most of the rainfall concentrated during the austral summer season december february when the atmospheric circulation favors the uplifting of moist air from the lowlands to the east of the mountain range within its rainy season the central andes experiences week long rainy and dry episodes the large scale and local conditions during these episodes are investigated using satellite imagery reanalyzed atmospheric fields and in situ data despite the deep layer of conditional instability prevalent during most summertime afternoons deep convection can occur only on those days in which the mixing ratio within the local boundary layer exceeds some threshold 7gk g 21 yielding saturation of near surface air parcels rising more than 600 m above ground convective cloudiness anomalies over the central andes extend southeastward and tend to be concurrent with anomalies of opposite sign over the eastern part of the continent rainy dry episodes are also associated with anticyclonic cyclonic anomalies centered over subtropical south america that extend through the depth of the troposphere accompanied by easterly westerly wind anomalies over the central andes these anomalies are presumably forced by planetary waves originating in the southern hemisphere extratropics to gain insight into the regional processes linking the large scale and local conditions the pennsylvania state university national center for atmospheric research mesoscale model version 5 2 was used to simulate contrasting rainy and dry episodes the most marked and relevant differences are the strength and extent of diurnally varying flow over the eastern slope of the andes during the rainy simulation strong easterly winds reach the upper part of the slope by midmorning initiating an intrusion of warm and moist air high ue air originating in the eastern lowlands into the central andes in the dry case the moisture transport from the east is restricted to the eastern slope of the andes and the central andes is flooded by low ue air from the western foothills that cannot support deep convection even in the presence of localized updrafts the momentum balance based on the model output indicates that turbulent momentum mixing from aloft determined by the large scale anomalies of the upper level flow into the convective boundary layer is the leading term causing the differences in the daytime upslope flow and hence moisture transport over the upper part of the eastern side of the andes between rainy and dry simulations

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

the geology of the polymetamorphic complex of ios cyclades greece and its significance for the cycladic massif the geological structure of the island of ios cyclades greece is a dome consisting of an augengneiss core and a mantle of garnet mica schists that together form the basement which is overthrust by a marble schist series this series is mainly made up of meta volcanics and metamorphosed sediments presumably mesozoic in age it is a tectonically composed pile of marbles alternating with glaucophane schists actinolite schists and chlorite schists petrological relations and isotope dating indicate the polymetamorphic character of ios two alpine metamorphic phases m1 and m2 and relicts of a high grade metamorphic or magmatic phase mo that only affected the basement are demonstrated radiometric ages obtained for the basement confirm the interpretation that the mo phase is pre alpine the m1 and m2 were dated at 43 ma and 25 ma respectively the p t conditions of metamorphism are estimated as 9 11 kb and 350 to 400 c for the m1 phase and 5 7 kb and 380 420 c for the m2 phase the metamorphic history of the cyclades is discussed and it is suggested that pre alpine basement occurs also on sikinos and naxos