dryline on 19 june 2002 during ihop part i airborne doppler and leandre ii analyses of the thin line structure and convection initiation the evolution and finescale structure of a dryline that initiated a line of thunderstorms is presented both the along line variability and mean vertical structure were examined using data collected by an airborne doppler radar and a water vapor differential absorption lidar dial the initiation of convection appeared to result from the diurnally induced easterly flow in the maritime air east of the dryline that typically develops late in the day this flow increased the low level convergence and allowed rising parcels of air to reach the level of free convection the along line variability was largely attributed to numerous misocyclones distorting the thin line of radar reflectivity by advecting dry moist air across the dryline south north of the misocyclone the misocyclones also influenced the location of the updrafts with most of the peak values positioned north of the circulations as a result these updrafts were fortuitously positioned in regions of high mixing ratio where the first convective cells initiated

major pathways of atlantic water in the northern north atlantic and nordic seas toward arctic 1 the major pathways of near surface atlantic water in the northern north atlantic and nordic seas are identified as current speeds above 30 cm s using 1014 lagrangian drifters combined with previously published hydrography the inflow over the scotland greenland ridge and establishment of the two branch norwegian atlantic current nwac are described in light of the circulation in the northern north atlantic the western branch of the nwac appears as a jet in the polar front topographically guided from the iceland faroe front through the nordic seas toward fram strait the eastern branch starts as a shelf edge current above the irish scottish continental shelf and after passing through the faroe shetland channel it continues northward along the norwegian shelf edge toward the arctic with a branch bifurcating into the barents sea the nwac appears to maintain its two branch structure throughout the nordic seas with the atlantic water confined to a 200 600 km wide wedge

seasonal cycle of mesoscale instability of the west spitsbergen current abstractthe west spitsbergen current wsc is a topographically steered boundary current that transports warm atlantic water northward in fram strait the 16 yr 1997 2012 current and temperature salinity measurements from moorings in the wsc at 78 50 n reveal the dynamics of mesoscale variability in the wsc and the central fram strait a strong seasonality of the fluctuations and the proposed driving mechanisms is described in winter water is advected in the wsc that has been subjected to strong atmospheric cooling in the nordic seas and as a result the stratification in the top 250 m is weak the current is also stronger than in summer and has a greater vertical shear this results in an e folding growth period for baroclinic instabilities of about half a day in winter indicating that the current has the ability to rapidly grow unstable and form eddies in summer the wsc is significantly less unstable with an e folding growth period of 2 days observations of the eddy kinetic energy eke show a p

crustal shortening at the sierra pie de palo sierras pampeanas argentina near surface basement folding and thrusting the sierras pampeanas consist of basement uplifts that are mainly controlled by w verging crustal thrusts one of these the sierra pie de palo is controlled by a blind thrust whose kinematics is debated we analysed the reverse faults located along the eastern side of the range and show that these are characterized by small displacements few hundreds of metres of the neogene and quaternary deposits controlled by the inherited basement metamorphic foliation and shear zones at the sierra scale the inherited foliation pattern appears already folded before the cenozoic shortening forming a series of antiforms and synforms with various wavelengths we propose that this structure is amplified during the plio quaternary shortening resulting in a large asymmetrical basement cored anticline where foliation parallel slip can act as folding mechanism the overall kinematics is consistent with an e verging fault propagation fold this proposed kinematics is an alternative to the frequently suggested w verging fault bend fold model finally we propose a new alternative and speculative crustal and lithospheric structure for this region consisting of two e verging basement thrusts coeval to w verging pampean thrusts both rooting below the precordillera above an eclogitized lower crust

multiple migmatite events and cooling from granulite facies metamorphism within the famatina arc margin of northwest argentina the famatina margin records an orogenic cycle of convergence metamorphism magmatism and extension related to the accretion of the allochthonous precordillera terrane new structural petrologic and geochronologic data from the loma de las chacras region demonstrate two distinct episodes of lower crustal migmatization the first event preserves a counterclockwise pressure temperature path in kyanite k feldspar pelitic migmatites that resulted in lower crustal migmatization via muscovite dehydration melting at 12 kbar and 868 c at 461 1 7 ma the shape of the pressure temperature path and timing of metamorphism are similar to those of regional midcrustal granulites and suggest pervasive ordovician migmatization throughout the famatina margin one dimensional thermal modeling coupled with regional isotopic data suggests ordovician melts remained at temperatures above their solidus for 20 30 ma following peak granulite facies metamorphism throughout a time period marked by regional oblique convergence the onset of synconvergent extension occurred only after regional migmatites cooled beneath their solidus and was synchronous with the cessation of precordillera terrane accretion at 436 ma the second migmatite event was regionally localized and occurred at 700 c and 12 kbar between 411 and 407 ma via vapor saturated melting of muscovite migmatization was synchronous with extension exhumation and strike slip deformation that likely resulted from a change in the plate boundary configuration related to the convergence and collision of the chilenia terrane

seismic evidence for shallow gas escape features associated with a retreating gas hydrate zone offshore west svalbard active gas venting occurs on the uppermost continental slope off west svalbard close to and upslope from the present day intersection of the base of methane hydrate stability bmhs with the seabed in about 400 m water depth in the inter fan region between the kongsfjorden and isfjorden cross shelf troughs from an integrated analysis of high resolution two dimensional pre stack migrated seismic reflection profiles and multibeam bathymetric data we map out a bottom simulating reflector bsr in the inter fan region and analyze the subsurface gas migration and accumulation gas seeps mostly occur in the zone from which the bmhs at the seabed has retreated over the recent past 1975 2008 as a consequence of a bottom water temperature rise of 1 c the overall margin parallel alignment of the gas seeps is not related to fault controlled gas migration as seismic evidence of faults is absent there is no evidence for a bsr close to the gas flare region in the upper slope but numerous gas pockets exist directly below the predicted bmhs while the contour following trend of the gas seeps could be a consequence of retreat of the landward limit of the bmhs and gas hydrate dissociation the scattered distribution of seeps within the probable hydrate dissociation corridor and the occurrence of a cluster of seeps outside the predicted bmhs limit and near the shelf break indicate the role of lithological heterogeneity in focusing gas migration

mid crustal deformation in a continental margin orogen structural evolution and timing of the famatinian orogeny nw argentina new structural data from a mid crustal segment in the eastern sierras pampeanas coupled with geochronological methods and p t estimates reveal polyphase contractional deformation and metamorphism during the famatinian orogeny over a long period of time peaks of metamorphic monazite and zircon ages are recorded at c 500 ma between 484 and 465 ma and at c 440 ma between 484 and 465 ma the region attained high temperature ht low pressure lp conditions that resulted in widespread partial melting peak at c 470 ma a contractional phase occurred during this event as suggested by syn anatectic structures as well as folding at subsolidus conditions renewed contraction under subsolidus conditions is evidenced by reverse ductile shearing and folding at c 440 ma thrusting along the la chilca shear zone caused metamorphic inversion the consistent orientation of folds in the quebrada del molle metamorphic complex el portezuelo metamorphic igneous complex and the la chilca shear zone as well as wsw directed thrusting at the later shear zone indicate uniform wsw ene directed shortening this late deformation records the ocloyic tectonic phase and brought the famatinian orogeny to an end in the late ordovician to early silurian supplementary material analytical methods methods and description of the calculated p t pseudosection diagrams bulk compositions and electron microprobe u pb and 40ar 39ar data are available at https doi org 10 6084 m9 figshare c 4697189

finescale vertical structure and dynamics of some dryline boundaries observed in ihop abstract several radar fine lines all with a humidity contrast were sampled in the central great plains during the 2002 international h2o project ihop this study primarily uses aircraft and airborne millimeter wave radar observations to dynamically interpret the presence and vertical structure of these fine lines as they formed within the well developed convective boundary layer in all cases the fine line represents a boundary layer convergence zone this convergence sustains a sharp contrast in humidity and usually in potential temperature across the fine line the key question addressed herein is whether at the scale examined here 10 km the airmass contrast itself in particular the horizontal density virtual potential temperature difference and resulting solenoidal circulation is responsible for the sustained convergence and the radar fine line for the 10 cases examined herein the answer is affirmative

cuyania an exotic block to gondwana review of a historical success and the present problems abstract a review of the early history of the cuyania terrane and the numerous pioneering works of the past century provides the present robust framework of evidence supporting a derivation from laurentia travel towards gondwana as an isolated microcontinent and final amalgamation to the protomargin of western gondwana in middle to late ordovician times the major remaining uncertainties and inconsistencies such as the time of deformation and collision with gondwana the lack of evidence of famatinian derived zircons the effects of strike slip displacements proposed along the suture as well as the potential sutures defined by ophiolite assemblages are discussed the precise boundary along the northern and southern limits is not yet well defined the most suitable hypothesis based on present data is that cuyania originated as a conjugate margin of the ouachita embayment south of the appalachian platform during early cambrian times the subsequent travel toward the gondwana protomargin is clearly depicted by the changing faunal assemblages in the carbonate platform new geochemical and age data on k bentonites presented by several authors reinforce the strong connection between cuyania ash fall tuffs and famatina volcanics by 468 470 ma indicating cuyania and gondwana were in close proximity at that time extension related to flexural subsidence preceded by the drowning of the carbonate platform in early llanvirnian times is recorded by abrupt facies changes in the sedimentary cover during late llanvirnian and early caradocian times this episode marked the beginning of contact between cuyania and gondwana the subsequent evolution of the foreland basin indicates that deformation lasted until latest silurian early devonian times the time of collision is tracked by the cessation of arc related magmatic activity in the upper plate gondwana protomargin at about 465 ma in western sierras pampeanas and ages around 454 ma corresponding to syncollisional and postcollisional magmatism the age of the collision is also preserved in the lower plate cuyania where both angular unconformities in the sedimentary cover and the ages of peak of regional metamorphism in the basement rocks point to 460 ma as the most probable age for the beginning of the collision evidence from the upper plate is essentially identical with an age of 463 ma thermal gradients along this suture vary from 13 c km in the lower plate to 18 c km in the fore arc upper plate reaching more than 30 c km along the famatinian arc based on these data a llandelian caradocian age for the collision can be postulated on firm grounds deformation continued through most of the early paleozoic until amalgamation of the chilenia terrane by the late devonian

k bentonites in the argentine precordillera contemporaneous with rhyolite volcanism in the famatinian arc new u pb radiometric dates for k bentonite horizons within the lower cambrian to middle ordovician platform carbonates from the precordillera terrane of nw argentina provide further constraints on models for the allochthonous or parautochthonous accretion of this terrane two k bentonite layers from the talacasto section yield indistinguishable sensitive high resolution ion microprobe shrimp u pb zircon dates of 469 5 3 2 ma and 470 1 3 3 ma respectively these are within uncertainty of the u pb shrimp zircon date of 468 3 3 4 ma for a porphyritic rhyolite from the famatinian magmatic arc sierra de las planchadas near rio chaschuil geochemical and isotope data also demonstrate the similarity of the k bentonite and chaschuil rhyolite parent magmas thus it is highly probable that the famatinian arc volcanoes provided the ash for the k bentonite horizons suggesting proximity to the precordillera terrane during the deposition of the lower cambrian to middle ordovician platform carbonates this implication supports a mid ordovician collision model but could also be compatible with a parautochthonous model for docking of the precordillera terrane by movement along the pacific margin of gondwana rather than across the iapetus ocean

convective initiation on 19 june 2002 during ihop high resolution simulations and analysis of the mesoscale structures and convection initiation 1 the 19 june 2002 convective initiation ci case from the international h2o project ihop is simulated using the arps at 1 km grid spacing it involves three distinct ci groups ci a ci b and ci c associated with a cold front dryline system initial condition at 1800 utc 19 june 2002 was created using the arps 3dvar including standard as well as special observations the simulation captured the three groups of cis rather well with small timing and spatial errors ci a is most typical of dryline initiation vertical cross sections through the initiation locations show typical dryline structures with an upward moisture bulge forced by lifting along the dryline convergence for ci b the model predicted mesoscale structures agree with special ihop aircraft dropsonde observations closely strong low level convergence from opposing cold front and dryline circulations produces deep symmetric upwelling of moist air and the convection is initiated at the crest of the moisture bulge ci c is more typical of frontal convection where deep convection is first initiated at the front edge of the cold air for ci b and ci c north south moisture bands that have dryline characteristics and can be considered multiple drylines and contain enhanced vertical motion and upward moisture bulges intercept the dryline and cold front respectively providing the most favored locations on the dryline or cold front for initiation furthermore the air parcels feeding the initial cells at ci b and ci c have trajectories along the moisture bands and have already experienced uplifting when they reach the dryline and cold front locations

early paleozoic accretionary orogenies in nw argentina growth of west gondwana abstract two early paleozoic orogenic cycles in the gondwana margin of nw argentina were driven by subduction and interrupted by collision of continental ribbons of laurentian affinity subduction started at the passive margin of gondwana possibly in response to the end of amalgamation of the supercontinent the passive margin was underlain by a hyper extended continent ocean transition and low angle subduction gave rise to a wide and hot fore arc region during the pampean orogenic cycle the arrival of the first continent ribbon ended the pampean cycle steepened the subduction further heating the fore arc and restarting arc magmatism after a magmatic lull 250 300 km trenchwards initiating the famatinian orogenic cycle this cycle started with a 30 ma long period of extension and marine sedimentation followed by the arrival of the second continent ribbon and inversion the back arc initiating a 20 ma long shortening event culminating with the shutting down of the arc this event gave rise to a 300 km wide low topography hot orogeny thus the many peculiarities of the two paleozoic orogens of nw argentina result from a subduction history that efficiently transferred heat to a 300 400 km wide belt of turbidite dominated sediments that was first part of the pampean fore arc and then part of the famatinian retroarc developed at the extended continental margin of gondwana the two orogenies with continued high heat flux lasted 110 ma giving rise to two calc alkaline arcs separated by a 300 km belt of high t low p migmatites and peraluminous granites formed by anatexis of sediments deposited on the passive margin as well as those deposited in the wide pampean fore arc these turbidite dominated sequences were metamorphosed and melted to form a continental crystalline basement and accreted to the cratonic margin adding 500 km of crystalline rocks to the margin of gondwana at the same time that a similar process was happening in eastern australia along the same continental margin interestingly this wide accretionary orogen has now become the region where the andean system developed a wide orogeny above flat slab subduction

tectono metamorphic evolution of a convergent back arc the famatinian orogen sierra de quilmes sierras pampeanas nw argentina

decline of subpolar north atlantic circulation during the 1990s observations of sea surface height reveal that substantial changes have occurred over the past decade in the mid to high latitude north atlantic ocean topex poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation combining the data from earlier satellites we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s direct current meter observations in the boundary current of the labrador sea support the weakening circulation trend of the 1990s and together with hydrographic data show that the mid to late 1990s decline extends deep in the water column analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation

thermodynamic variability within the convective boundary layer due to horizontal convective rolls abstract data from the convection and precipitation electrification cape experiment conducted during the summer of 1991 are used to examine and quantify the horizontal variability of temperature and moisture within the convective boundary layer cbl potential temperature variations were only about 0 5 k while variations in water vapor mixing ratio values of 1 5 2 5 g kg 1 were observed throughout the cbl using radar aircraft and sounding data it is shown that horizontal convective rolls are the likely cause of these variabilities the enhanced moisture occurred within the roll updraft regions thus rolls were transporting moist air from the surface upward the observed cloud base heights obtained from cloud photogrammetry were produced from the highest moisture values within the roll updraft regions since the roll ascending branches contained moisture values that were most representative of the observed cloud base heights it is likely that measurements from within the roll updrafts would prov

a high resolution modeling study of the 24 may 2002 dryline case during ihop part i numerical simulation and general evolution of the dryline and convection abstract results from a high resolution numerical simulation of the 24 may 2002 dryline convective initiation ci case are presented the simulation uses a 400 km 700 km domain with a 1 km horizontal resolution grid nested inside a 3 km domain and starts from an assimilated initial condition at 1800 utc routine as well as special upper air and surface observations collected during the international h2o project ihop 2002 are assimilated into the initial condition the initiation of convective storms at around 2015 utc along a section of the dryline south of the texas panhandle is correctly predicted as is the noninitiation of convection at a cold front dryline intersection triple point located farther north the timing and location of predicted ci are accurate to within 20 min and 25 km respectively the general evolution of the predicted convective line up to 6 h of model time also verifies well mesoscale convergence associated with the confluent flow around the dryline is shown to produce an u

ordovician back arc foreland and ocloyic thrust belt development on the western gondwana margin as a response to precordillera terrane accretion 1 the famatina belt southern central andes records a circa 470 m y shortening episode ocloyic orogeny affecting the peri gondwanan back arc basin in response to the accretion of the precordillera terrane collision created distinct features across and along the margin some of which persisted into the present andean structure from east to west the ocloyic deformation is recorded across the telescoped region of famatina represented by 1 an east vergent fold thrust belt evftb involving a major angular unconformity between early and middle ordovician rocks 2 a highly deformed volcano sedimentary belt and 3 an east vergent ductile shear zone affecting famatinian granites axis attitudes of ordovician refolded anticlines in the evftb show west east tectonic transport in agreement with kinematics of ocloyic high strain belts indicating shortening orthogonal to the present pacific margin eastward displacement of the ordovician volcanic arc at 27 s latitude together with a documented sinistral slip zone across the proto andean margin suggests tectonic indentation

a laurentian grenville age oceanic arc back arc terrane in the sierra de pie de palo western sierras pampeanas argentina

near surface circulation in the northern north atlantic as inferred from lagrangian drifters variability from the mesoscale to interannual 1 the near surface circulation of the nordic seas is basically cyclonic and consists of jets and recirculation cells which are tightly linked to the bottom topography variable forcing by the large scale rotation of the wind leads to a modulation in the strength of the gyres and their interconnecting jets this is seen in drifter and altimeter data currents are stronger during winter and during phases of high north atlantic oscillation index the exchanges between the north atlantic and the nordic seas do not seem to be directly affected by this variable forcing the narrow boundary currents and the intergyre jets are subject to instability causing mesoscale current fluctuations which contribute to the stirring and mixing of polar and atlantic water masses

pathways of the greenland sea warming 1 progressive warming of the west spitsbergen current wsc has been observed since 2004 during summer 2006 temperature and salinity of the core of atlantic water aw reached the highest ever observed by the institute of oceanology polish academy of sciences iopas values the structure of the wsc the heat content and the extent of aw in the fram strait fs region has also changed temperature changes resulted from the upstream warming of the norwegian atlantic current nwac the structure of the wsc and its heat content were modified by the northward advection of large mesoscale eddies observed within the western branch of the wsc in summer 2005 these changes may have large impacts on the arctic ocean ao climate and ecosystem

0 3 byr of drainage stability along the palaeozoic palaeo pacific gondwana margin a detrital zircon study the palaeo pacific margin of gondwana in the present day south central andes is marked by tectonic activity related to subduction and terrane accretion we present detrital zircon u pb data encompassing the palaeozoic era in northern chile and northwestern argentina cathodoluminescence images reveal dominantly magmatic zircon barely affected by abrasion and displaying only one growth phase the main age clusters for these zircon grains are ediacaran to palaeozoic with an additional peak at 1 3 0 9 ga and they can be correlated with grenvillian age and the brasiliano pampean and famatinian orogenies the zircon data reveal main transport from the nearby ordovician famatinian arc and related rocks the silurian sandstone units are more comparable with cambrian units with brasiliano and transamazonian ages 2 2 1 9 ga being more common because the silurian deposits were situated within or east of the extinct famatinian arc hence the arc acted as a transport barrier throughout palaeozoic time the complete suite of zircon ages does not record the accretions of exotic terranes or the palaeozoic glacial periods we conclude that the transport system along the palaeo pacific margin of gondwana remained stable for c 0 3 byr and that provenance data do not necessarily reflect the interior of a continent hence inherited geomorphological features must be taken into account when detrital mineral ages are interpreted supplementary material u pb data cl images and detailed geological maps are available at www geolsoc org uk sup18796

empirical relationships between summertime oceanic heat anomalies in the nordic seas and large scale atmospheric circulation in the following winter a lagged regression analysis between an index of observed summertime atlantic water temperature awt variability at the entrance to the barents sea in the period 1982 2005 and year round atmospheric ncep ncar reanalysis data is used to show that subsurface oceanic heat anomalies in high latitudes are significant precursors of wintertime atmospheric variability in middle latitudes in particular positive awt anomalies precede predominantly westerly wind anomalies in high latitudes and easterly wind anomalies in middle latitudes the mid latitude wind anomalies while being generally equivalent barotropic in the upper troposphere have a strong low level baroclinic contribution over eurasia the near surface easterly wind anomalies in this area are locally deflected southward maintaining cold spots near orography the summertime oceanic anomalies explain about 40 of the variance in the surface air temperature averaged over eurasia from 35 to 45 n and about 50 of the variance in surface winds over the far east asia in the following winter we suggest that the remote connections arise from reorganization of the mid latitude storm tracks the awt anomalies explain about 60 of the variance in the upper tropospheric storm track activity averaged over the pacific and eurasia from 35 to 55 n and in the lower tropospheric poleward synoptic eddy heat flux over western eurasia finally we show that the awt associated wintertime atmospheric anomalies appear in quadrature with the concurrent anomalies associated with the north atlantic oscillation these findings suggest that oceanic heat anomalies in high latitudes may be a useful predictor of atmospheric variability

the role of convectively generated gravity waves on convective initiation a case study abstracta case study of a convection initiation ci event involving a mesoscale gravity wave is presented this severe convection event occurred in east china on 5 june 2009 high frequency automatic weather station aws data visible satellite data and doppler radar data were combined to depict the features of the gravity wave and the development of several convection centers the gravity wave was manifested by a surface pressure dip and surface wind shift propagating westward away from the early convection the pressure dip propagated at a speed of 30 m s 1 which is comparable with that in previous observational studies of convectively generated gravity waves a special focus is on the initiation of a deep convection cell in anhui province which resulted in 25 deaths surface observations showed two precursors before ci including a convergence line and wind shift at the eastern end of the convergence line high resolution numerical simulations with the weather research and forecasting wrf model

analysis of convergence boundaries observed during ihop_2002 abstract an analysis of six convergence boundaries observed during the international h2o project ihop 2002 is presented the detailed kinematic and thermodynamic structure of these boundaries was examined using data collected by an airborne doppler radar and a series of dropsondes released by a jet flying at 500 mb the former and latter platforms were able to resolve the meso and meso scale circulations respectively convection initiated on three of the days while no storms developed in the regions targeted by the mobile platforms on the other days referred to as null cases the airborne radar resolved the finescale structure of four drylines a cold front and an outflow boundary on the six days horizontal profiles through radar detected thin lines revealed bell shaped distributions and there appeared to be a seasonal dependence of the peak values of radar reflectivity the echo profiles through the fine line in may were in general greater than those plotted for the june cases there was

vestiges of an ordovician west vergent thin skinned ocloyic thrust belt in the argentine precordillera southern central andes collision of the down going laurentia derived argentine precordillera terrane with the gondwanan margin drove the ordovician ocloyic orogeny including subduction volcanism metamorphism and top to west shearing east of the precordillera in the precordillera above passive margin carbonates lower ordovician san juan limestone and older carbonates a middle to upper ordovician westward prograding synorogenic clastic wedge of black shale gualcamayo shale and coarser clastic sediment las vacas conglomerate and trapiche formation fills a peripheral foreland basin new research has identified vestiges of a west directed thin skinned ocloyic foreland thrust belt that has been fragmented by east directed andean thrusting the el corral thrust sheet with hanging wall detachment in the san juan limestone extends over a west directed footwall frontal ramp and extensive flat to low angle footwall cutoff in the gualcamayo and las vacas formations las vacas conglomerates in the footwall include olistoliths 10 m scale exclusively of san juan limestone and gualcamayo shale the beds in some olistoliths are folded the advancing el corral thrust sheet successively supplied and overrode the stratigraphically restricted olistoliths in the el corral footwall tight west vergent folds and faults within an anticlinorium in the san juan limestone and gualcamayo shale suggest a deeper unexposed thrust fault the los celestitos fault west of the anticlinorium easterly dip restored to remove andean deformation beneath an angular unconformity between las vacas and trapiche beds is consistent geometrically with the trailing limb of a west vergent fault propagation anticline in the hanging wall of the subsurface los celestitos fault the same angular unconformity truncates the el corral fault and hanging wall strata in the trapiche formation contrasting sedimentary facies from sandy turbidites westward to limestone clast megabeds and olistoliths suggest another frontal ramp from a stratigraphically deeper detachment in a break forward sequence none of these observations separately defines an ocloyic thrust belt taken together however these vestiges of thrust belt style indicate the consistent geometry of an ordovician west vergent thin skinned ocloyic thrust belt

branching of atlantic water within the greenland spitsbergen passage an estimate of recirculation atlantic water aw supplies the largest source of heat mass and salt to the arctic ocean via fram strait greenland spitsbergen passage yet it represents only a fraction of the atlantic water that resides in the greenland iceland norwegian and barents seas this is a result of both the branching of the central core of aw along its northward flow and the modification of its t s signature through air sea ice interactions and internal mixing this paper addresses the quantitative analysis of the three dominant atlantic water cores within fram strait and north of 76 n using an 11 year 1977 to 1987 hydrographic database spatial variations of heat volume and salt along its flow path of some 600 km showed that the major core of atlantic water that directly enters the arctic ocean svalbard branch did not extend past 20 e of the 9719 km3 of atlantic water existing within the region one third resided within the svalbard branch the remainder 22 and 45 were held within the return atlantic current and the yermak branches respectively restricting the analysis to a southern limit of 79 n effectively removed the return atlantic current and showed a nearly equal split between the two remaining branches work completed by bourke et al 1988 indicated that the yermak branch is largely recirculated to the south if true this analysis supports rudels 1987 model estimate of a 50 recirculation of aw within this region

a review of the famatinian ordovician magmatism in southern south america evidence of lithosphere reworking and continental subduction in the early proto andean margin of gondwana abstract along the proto pacific margin of gondwana from venezuela to northeastern patagonia the early middle ordovician famatinian orogeny was the first orogenic event following assembly of the supercontinent previous isotope studies of the igneous and meta sedimentary rocks of southwestern gondwana yield ambiguous implications for the role of juvenile mantle addition during the early crustal growth at the supercontinental margin to interpret the geological and tectonic evolution of the orogen and the magma sources in different episodes we look at evidence from a large area of southern south america including the 700 600 km type sector of the orogen in the sierras pampeanas 27 33 s the precordillera and northeastern patagonia previous geological geochemical and geochronological results are reviewed together with new u pb shrimp crystallization ages 177hf 176hf and 18o 16o data for dated zircon and whole rock sr and nd isotope compositions four geological domains are recognized in the sierras pampeanas western central eastern and foreland famatinian domains magmatism is mostly restricted to the interval 463 4 to 486 7 ma with the most intense period of emplacement between 468 and 472 ma constituting a magmatic flare up granitoid emplacement in both northeastern patagonia and the cordon de lila puna altiplano chile was effectively synchronous with that in the sierras pampeanas defining a continuous belt combined geochemical and isotopic data whole rock sr nd hf o in zircon indicate that the source of calcic metaluminous suites is the subcontinental lithosphere both mantle and mafic lower crust with variable contamination by the early paleozoic metasedimentary country rocks the lithospheric mantle involved is assumed to underlie the outcropping 1330 1030 ma age basement of the western domain which exhibits tectonic characteristics of active continental margin in the north and oceanic arc back arc in the south the latter sector is the potential source of some minor famatinian igneous rocks with less evolved isotopic compositions although a restricted asthenospheric addition cannot be discarded in this case minor peraluminous granites are spatially associated with the metaluminous sequence but major highly peraluminous batholiths occur on the eastern flank of the central domain field relations and geochemical isotopic evidence indicate that the most obvious source of these crustal melts was the very thick post early cambrian metasedimentary sequence comprising the host country rocks episodic tectono magmatic evolution of the famatinian magmatic belt in two overlapping stages is invoked to explain different characteristics in the four recognized domains in the type sector ca 474 486 ma roll back stage this is a mainly extensional interval involving asthenospheric upwelling and thinning of the subcontinental mantle full development of the marine ensialic basins and early emplacement of both metaluminous granites and highly peraluminous batholiths in the central and eastern famatinian domains trondhjemite plutons with an adakitic signature were emplaced in the foreland domain ca 468 472 ma slab break off stage steepening of the oceanic slab and arc migration to the southwest ended with slab break off due to subduction of continental crust during continental collision with the precordillera terrane this stage produced voluminous metaluminous magmatism at the western edge of the central domain the flare up episode k bentonites in the precordillera leucogranites in the western domain and scattered metaluminous and peraluminous plutons in all famatinian domains both slab roll back and break off stages developed during a high t regime typical of hot orogens although asthenospheric mantle was a necessary heat source for lithospheric melting its material contribution to the growth of early paleozoic crust was apparently very minor recycling of mesoproterozoic lithosphere including the subcontinental mantle coupled with crustal melting of early paleozoic metasedimentary sequences accounts for most famatinian magmatism comparable results from the central andes and east antarctica confirm that the early stages of the terra australis orogen in sw gondwana were dominated by lithospheric reworking processes

a cambrian mixed carbonate siliciclastic platform in sw gondwana evidence from the western sierras pampeanas argentina and implications for the early paleozoic paleogeography of the proto andean margin the western sierras pampeanas wsp of argentina record a protracted geological history from the mesoproterozoic assembly of the rodinia supercontinent to the early paleozoic tectonic evolution of sw gondwana two well known orogenies took place at the proto andean margin of gondwana in the cambrian and the ordovician i e the pampean 545 520 ma and famatinian 490 440 ma orogenies respectively between them an extensive continental platform was developed where mixed carbonate siliciclastic sedimentation occurred this platform was later involved in the famatinian orogeny when it underwent penetrative deformation and metamorphism the platform apparently extended from patagonia to northwestern argentina and the eastern sierras pampeanas and has probable equivalents in sw africa peru and bolivia the wsp record the outer deepest part of the platform where carbonates were deposited in addition to siliciclastic sediments detrital zircon u pb shrimp ages from clastic metasedimentary successions and sr isotope compositions of marbles from the wsp suggest depositional ages between ca 525 and 490 ma the detrital zircon age patterns further suggest that clastic sedimentation took place in two stages the first was sourced mainly from re working of the underlying neoproterozoic metasedimentary rocks and the uplifted core of the early cambrian pampean orogen without input from the paleoproterozoic rio de la plata craton sediments of the second stage resulted from the erosion of the still emerged pampean belt and the neoproterozoic brasiliano orogen in the ne with some contribution from the rio de la plata craton an important conclusion is that the wsp basement was already part of sw gondwana in the early cambrian and not part of the exotic precordillera cuyania terrane as was previously thought

summary of convective storm initiation and evolution during ihop observational and modeling perspective abstract the data rich international h2o project ihop 2002 experiment is used to study convective storm initiation and subsequent evolution for all days of the experiment initiation episodes were almost evenly divided between those triggered along surface based convergence lines and elevated initiation episodes that showed no associated surface convergence the elevated episodes occurred mostly at night and the surface based episodes occurred during the afternoon and evening surface based initiations were mostly associated with synoptic fronts and gust fronts and less so with drylines and bores elevated initiations were frequently associated with observable convergent or confluent features in the rapid update cycle ruc wind analysis fields between 900 and 600 hpa the ruc10 3 h forecast of the precipitation initiation episodes were correct 44 of the time allowing a tolerance of 250 km in space and for the forecast being early by one period however the accuracy was closely tied to the scale of

the early paleozoic evolution of the argentine precordillera as a laurentian rifted drifted and collided terrane a geodynamic model paleontologic and stratigraphic evidence points to the early paleozoic precordilleran terrane of western argentina as being the conjugate rift pair of the appalachians stratigraphic similarities of the cambrian and early arenig carbonate series and very strong affinities among trilobite conodont and brachiopod faunas show their close relationship the most probable provenance areas are the appalachian ouachita rifted margin and the newfoundland appalachians although the former fits better with geometric and drifting paths suggested by faunal affinities increasing celtic and baltic brachiopod genera and divergent stratigraphy since the arenig indicate the drifting of the precordilleran terrane collisional foredeeps developed on collapsed former platform carbonates as flexural subsidence progressed the collision of the precordillera with western gondwana occurred during the mid llanvirn to llandeilo a magmatic arc related to eastward subduction present coordinates was active in the famatina range east of the precordillera this region of celtic affinity shows faunal exchange with the precordilleran terrane since the late arenig and may represent accreted intra iapetus volcanic island arc complexes the rifting and drifting stages are consistent with paleoclimatic and paleomagnetic data that show the migration of the precordilleran terrane from periequatorial to peripolar latitudes between the cambrian and latest ordovician the deep ocean to the west of the precordillera started to close by the late ordovician with the eastward drift of the chilenian terrane absence of volcanic or pyroclastic arc derived rocks in the precordillera indicate west dipping subduction as chilenia approached the continental margin a new forebulge was established on the former collided precordilleran terrane developing an erosional unconformity in central precordillera talacasto tambolar arch a gondwanic signature was fully developed by the middle silurian when the malvinokaffric clarkeia fauna flourished before then the late ordovician glacial record and associated hirnantia fauna were the first clear tie to gondwana during the silurian the marginal basin behaved as a foreland with lithosphere rheology and eustasy governing the sequence stratigraphy wrench faulting along its eastern boundary displaced the precordillera toward the south continued shortening during closure with the chilenian terrane in the mid devonian produced thrust loading of the basin and generated a thick graywacke succession final accretion of chilenia late devonian generated a regional angular unconformity between the lower and upper paleozoic new eastward subduction was initiated west of the accreted chilenian terrane during the late permian triassic as indicated by the choiyoi volcanic complex which presently outcrops in the frontal cordillera

the proto andean margin of gondwana an introduction a basic background is presented for the discussion of the early palaeozoic geology of western argentina covered by this book this includes the definition and terminology of orogenic cycles on this part of the gondwana margin represented by the eastern sierras pampeanas the pampean orogeny early cambrian relates to an intense but short lived period of terrane collision predating the rifting of the precordillera terrane from laurentia the famatinian cycle is predominantly represented by intense subductionrelated magmatism of early middle ordovician age developed on the continental margin of gondwana during the rifting and drifting of the precordillera terrane the grenvillian basement of the latter is further exemplified by a new rb sr whole rock isochron age of 1021 12 ma for orthogneisses from the western sierras pampeanas a mid ordovician granite in this area dated at 481 6 ma by u pb ion microprobe data may be related to rifting while the precordillera terrane was still attached to laurentia a divergence of opinion is pointed out between some authors in this book who favour mid ordovician collision of the precordillera with gondwana and others who place it much latter in silurian or devonian times

formation and diurnal variation of the dryline abstract the formation and diurnal evolution of the dryline during fair weather have been investigated through the use of a two dimensional mesoscale model that includes condensation evaporation budget equations of surface energy and moisture field as well as turbulence and radiation parameterizations a moderately strong vertical wind shear was introduced on a sloping terrain where the soil is very dry on the west side but moist on the east initially a weak easterly geostrophic wind exists to the east but a weak westerly geostrophic wind to the west of the dryline during daytime deepening of the mixed layer due to vertical mixing especially on the west side forces the dryline to advance eastward the westerly wind on the west side is maintained by downward transport of westerly momentum due to strong vertical mixing the easterly wind on the east side is strengthened due to the inland sea breeze circulation therefore the resulting low level convergence sustains a strong moisture gradient along

observations of convection initiation failure from the 12 june 2002 ihop deployment abstract observations of the development of cumulus convection which reached depths of several kilometers but failed to develop into sustained precipitating cumulonimbus clouds an event the authors term convection initiation failure are presented from the 12 june 2002 international h2o project ihop case the investigation relies heavily on remote and in situ data obtained by mobile truck borne doppler radars mobile mesonets mobile soundings and stereo cloud photogrammetry data collection was focused in northwestern oklahoma near the intersection of an outflow boundary and dryline thunderstorms developed along the dryline during the late afternoon approximately 40 km east of the domain intensively observed by the ground based observing systems farther west within the region of dense observations analyzed herein cumulus congestus clouds formed along an outflow boundary multiple doppler wind syntheses revealed that the boundary layer vertical velocity field was dominated by thermals rather t

characteristics of dryline passage during cops 91 abstract the characteristics of dryline passage are documented through an analysis of data from an instrumented surface mesonetwork in the texas panhandle and western and central oklahoma during the cooperative oklahoma profiler studies field program some eastward moving drylines at the surface during the day were characterized by monotonic drops in dewpoint after dryline passage others were marked by a series of rapid drops punctuated by periods of no change after dryline passage which suggests that the dryline often progresses in discrete steps rather than continuously the dryline during the daytime was not always collocated with a pressure trough although the strongest dryline observed was analyses of surface pressure traces indicated that westward moving drylines during the evening did not display behavior characteristic of strong intense density currents as had been found in other studies evidence is presented in one case of 90 min oscillations in water vapor and wind behind the dryline

on anomalous sea surface temperatures in the nordic seas abstract gridded sea surface temperature sst sea level pressure 10 m wind field and ice concentration data from the winters 1982 98 are used in a study of the large scale variability of the ssts in the nordic seas mean fields are extracted and areas of maximum variability identified a complex principal component analysis is applied to identify coherent structure of variability in the sst field the leading mode accounting for 39 of the variance reveals a band of high correlations at increasing phase lags along the west coast of norway across the greenland sea and south through the denmark strait the sst data contain two cycles of low frequency variability during the 17 winters studied having approximately 5 yr and 12 yr periods for the eastern parts of the nordic seas propagation speeds agree with other transport estimates this indicates that sst anomalies are representing upper ocean heat anomalies advected by the mean flow from north of scotland toward the barents sea this is not true

the triple point on 24 may 2002 during ihop part ii ground radar and in situ boundary layer analysis of cumulus development and convection initiation abstract cumulus formation and convection initiation are examined near a cold front dryline triple point intersection on 24 may 2002 during the international h2o project ihop a new lagrangian objective analysis technique assimilates in situ measurements using time dependent doppler derived 3d wind fields providing output 3d fields of water vapor mixing ratio virtual potential temperature and lifted condensation level lcl and water saturated i e cloud volumes on a subdomain of the radar analysis grid the radar and lagrangian analyses reveal the presence of along wind i e longitudinal and cross wind i e transverse roll circulations in the boundary layer bl a remarkable finding of the evolving radar analyses is the apparent persistence of both transverse rolls and individual updraft vertical vorticity and reflectivity cores for periods of up to 30 min or more while moving approximately with the local bl wind satellite cloud images and single camera ground photogrammetry imply tha

the iglesia basin in the southern central andes a record of backarc extension before wedge top deposition in a foreland basin abstract the iglesia basin hosts a key sedimentary archive of the evolution of the southern central andes this basin is classically interpreted as recording the transition from an outer to an inner wedge top piggyback basin depozone in the early bermejo foreland basin system in this study we reevaluate the tectonic evolution of the iglesia basin based on the interpretation of 2d seismic reflection data structural geology zircon u pb geochronology and provenance analysis we report an extensional event that initiated the basin opening our results indicate normal faulting development and synextensional deposition from the latest oligocene earliest miocene to middle miocene since the middle miocene extensional activity experienced a progressive decrease in changing to shortening and basin inversion between the middle late miocene the latter stage coincided with the full development of pampean flat slab subduction indicating maximum plate coupling at that time our findings challenge the idea of uninterrupted paleogene to neogene flexural subsidence related to the andean orogenic load in the backarc area therefore the results of this study have important consequences for the early evolution of the bermejo foreland basin and ultimately for the growth of the southern central andes

on the spatial coherence of the atlantic water inflow across the nordic seas the co variability of the atlantic water aw branches in the nordic seas is investigated over the period 1979 2012 using an eddy permitting model a noticeable circulation change is found in the mid 1990s prior to the mid 1990s the leading mode of variability defines a large scale pattern with concomitant variations in the atlantic water aw inflow in the faroe shetland channel fsc the norwegian atlantic slope current nwasc the aw inflow to the barents sea and the west spitsbergen current wsc after the mid 1990s the co variability between the nwasc and the aw inflow in both the fsc and the wsc is lost consequently the northern barents sea circulation anomaly pattern which is present throughout the full period becomes the leading mode of circulation in the northern nordic seas after the mid 1990s the circulation change of the mid 1990s appears to be linked to a weakening of the southwesterly wind anomalies in norwegian sea as the northern center of action of the first mode of sea level pressure nao weakens passive tracer experiments suggest that this circulation change may be accompanied by increased heat transfer from the aw current to the interior nordic seas this in turn may have limited the influence of the recently observed aw warming in the iceland scotland passage on the nwasc downstream

the crustal evolution of south america from a zircon hf isotope perspective hf isotope data of 1100 detrital zircon grains from the palaeozoic south central andean gondwana margin record the complete crustal evolution of south america which was the predominant source the oldest grains with crustal residence ages of 3 8 4 0ga are consistent with complete recycling of existing continental crust around 4ga we confirm three major archaean palaeoproterozoic transamazonian and late mesoproterozoic to early neoproterozoic crust addition phases as well as six igneous phases during proterozoic to palaeozoic time involving mixing of juvenile and crustally reworked material a late mesoproterozoic to early neoproterozoic grenville age igneous belt can be postulated along the palaeo margin of south america this belt was the basement for later magmatic arcs and accreted allochthonous microcontinents as recorded by similar crustal residence ages crustal reworking likely dominated over juvenile addition during the palaeozoic era and proterozoic and archaean zircon was mainly crustally reworked from the eroding thickened ordovician famatinian arc

structural evolution of a composite middle to lower crustal section the sierra de pie de palo northwest argentina 1 the sierra de pie de palo of northwest argentina preserves middle to lower crustal metamorphic rocks that were penetratively deformed during ordovician accretion of the precordillera terrane to the gondwana margin new structural petrologic and geochronologic data from a 40 km structural transect reveals that the sierra de pie de palo preserves a middle to lower crustal ductile thrust complex consisting of individual structural units and not an intact ophiolite and cover sequence top to the west thrusting occurred intermittently on discrete ductile shear zones from 515 to 417 ma and generally propagated toward the foreland with progressive deformation ordovician crustal shortening and peak metamorphic temperatures in the central portion of the sierra de pie de palo were synchronous with retro arc shortening and magmatic flare up within the famatina arc accretion of the precordillera terrane resulted in the end of arc flare up and the onset of synconvergent extension by 439 ma continued synextensional to postextensional convergence was accommodated along progressively lower grade shear zones following terrane accretion and the establishment of a new plate margin west of the precordillera terrane the results support models of cordilleran orogens that link voluminous arc magmatism to periods of regional shortening the deformation metamorphic and magmatic history within the sierra de pie de palo is consistent with models placing the region adjacent to the famatina margin in the middle cambrian and not as basement to the precordillera terrane

mesoscale thermodynamic influences on convection initiation near a surface dryline in a convection permitting ensemble abstractin this study the authors examine initiation of severe convection along a daytime surface dryline in a 10 member ensemble of convection permitting simulations results indicate that the minimum buoyancy bmin of pbl air parcels must be small bmin 0 5 c for successful deep convection initiation ci to occur along the dryline comparing different ensemble members reveals that cape magnitudes allowing for entrainment and the width of the zone of negligible bmin extending eastward from the dryline act together to influence ci since pbl updrafts that initiate along the dryline move rapidly northeast in the vertically sheared flow as they grow into the free troposphere a wider zone of negligible bmin helps ensure adequate time for incipient storms to mature which itself is hastened by larger cape local bmin budget calculations and trajectory analysis are used to quantify physical processes responsible for the reduction of negative buoyancy prior to ci here the grid resolved forcing and fo

fast sediment underplating and essentially coeval juvenile magmatism in the ordovician margin of gondwana western sierras pampeanas argentina metasedimentary high pressure upper amphibolite facies gneisses 1 2 0 1 gpa and 780 45 c at las chacras sierra de valle fertil are tectonically juxtaposed to the westernmost parts outboard of the famatinian early ordovician magmatic arc which underwent syn plutonic middle crust high grade metamorphism at lower pressure u pb shrimp zircon data suggest that the gneisses contain famatinian igneous detritus so that their sedimentary protoliths were probably deposited in a forearc basin and then rapidly underthrust and accreted to the lower crust of the arc essentially coevally with arc magmatism at 468 4 ma chemically and isotopically juvenile garnetiferous amphibolites within the gneisses are recognised as representing the most primitive magmas so far observed in this belt which has often been considered to be a continental arc derived from isotopically mature sources this is consistent with the idea that at least part of the dominant famatinian magmatism originated in depleted mantle but was heavily contaminated by crustal components

coherent variability of the norwegian atlantic slope current derived from topex ers altimeter data 1 this study deals with large scale variability of the norwegian atlantic current nwac transporting warm and saline atlantic water toward the arctic ocean we concentrate on the eastern branch of the nwac the norwegian atlantic slope current nwasc an about 3500 km long nearly barotropic shelf edge current comparison of variations of cross slope sea level gradient based on the cls topex ers altimeter data and the nwasc from direct current measurements 1995 2002 in the svinoy section at about 63 n shows significant coherence for periods of 1 to 12 months motivated by this the analysis is extended to the entire nwasc using the local cross slope sea level gradient from the altimeter data as a proxy the leading nwasc mode represents along slope current variations of similar sign from the irish scottish shelf to the fram strait that can be interpreted as a quasi steady direct response to the large scale wind field

finescale radar observations of the 22 may 2002 dryline during the international h2o project ihop abstract the dryline has long been associated with the development of severe thunderstorms in the southern plains during the spring and early summer months the propagation and structure of the dryline are closely tied to surface processes that are neither well understood nor well resolved with current observational capabilities as a result there are often large errors in forecasts of dryline position and structure improvements in radar technology have allowed for better observations of the dryline in recent years here very finescale radar observations taken with the university of massachusetts amherst umass mobile w band radar during an international h2o project ihop double dryline event on 22 may 2002 in the oklahoma panhandle are presented the observations are placed in the context of the dryline secondary circulation which describes flow in a plane normal to the dryline the narrow half power beamwidth of the antenna on the w band 0 18 permitted the measurements of channels of upward 8

prediction of convective initiation and storm evolution on 12 june 2002 during ihop_2002 part i control simulation and sensitivity experiments abstract the 12 13 june 2002 convective initiation case from the international h2o project ihop 2002 field experiment over the central great plains of the united states is simulated numerically with the advanced regional prediction system arps at 3 km horizontal resolution the case involves a developing mesoscale cyclone a dryline extending from a low center southwestward with a cold front closely behind which intercepts the midsection of the dryline and an outflow boundary stretching eastward from the low center resulting from earlier mesoscale convection convective initiation occurred in the afternoon at several locations along and near the dryline or near the outflow boundary but was not captured by the most intensive deployment of observation instruments during the field experiment which focused instead on the dryline outflow boundary intersection point standard and special surface and upper air observations collected during the field experiment are assimilated into the arps at hourly inte

convective initiation at the dryline a modeling study abstract a nonhydrostatic three dimensional version of the colorado state university regional atmospheric modeling system csu rams is used to deduce the processes responsible for the formation of drylines and the subsequent initiation of deep moist dryline convection a range of cumuliform cloud types are explicitly simulated along drylines on 15 16 and 26 may 1991 in accordance with observations in the simulations narrow convergence bands along the dryline provide the lift to initiate deep moist convection the thermally direct secondary convective boundary layer cbl circulations along the dryline are frontogenetic and solenoidally forced maximum updrafts reach 5 m s 1 and the bands are 3 9 km wide and 10 100 km or more in length the updrafts penetrate and are decelerated by the overlying stable air above the cbl reaching depths of about 2000 m in the cases studied moisture convergence along the mesoscale updraft bands destabilizes the local sounding to deep convection while simultaneously

mantle echoes associated with deep convection observations and numerical simulations abstract finescale radar observations of intense thermals starting plumes during the early stages of precipitation formation were collected by an airborne doppler radar on two separate days the radar data were recorded as the aircraft flew underneath the developing echoes mantle echoes echoes that often appear as an inverted u shape were observed on both days striking in one of the scans was the resemblance of the echo to a mushroom cloud resulting from a nuclear explosion numerical simulations using a two dimensional cloud resolving model were run to augment the interpretation of the observations one of the important conclusions was the proposed modification to the default bulk microphysical scheme used in the model the default scheme yields a rush to precipitation leading to the early establishment of large precipitation contents which is not supported by the observations suggested modifications to the scheme are presented

sr c and o isotope geochemistry and stratigraphy of precambrian and lower paleozoic carbonate sequences from the western sierras pampeanas of argentina tectonic implications abstract sr c and o isotope data are presented for carbonate rocks from the sierra de pie de palo and other crystalline outcrops of the western sierras pampeanas these are used to distinguish three groups of rocks of quite different ages within the nappe pile that constitutes the sierra de pie de palo carbonates from the grenville age ophiolitic unit at the bottom of the pile probably resulted from the interaction between hot seawater and contemporaneous oceanic crust these carbonates are tentatively classified as ophicalcites carbonates from the difunta correa sedimentary sequence are part of a cover sequence to a grenvillian basement together forming the upper nappes isotope stratigraphy suggests a middle to late neoproterozoic age 580 720 ma for these carbonates this cover might be correlated with cover sequences to the archean and early to middle proterozoic cratons that are well preserved over large areas of brazil this fact together with the apparently absence of an equivalent neoproterozoic carbonate bearing cover in the appalachian margin of laurentia suggests that the western sierras pampeanas which are considered part of the exotic argentine precordillera terrane of allegedly laurentian derivation could be autochthonous or para autochthonous to gondwana other geochemical and geological arguments reinforce this hypothesis the caucete group carbonates underlie the nappe pile and are separated from it by a first order thrust the pirquitas thrust these latter carbonates are cambrian in age and isotopically similar to the carbonate platform of the precordillera we thus conclude that the pirquitas thrust is the boundary between the exotic precordillera terrane and the autochthonous or para autochthonous western sierras pampeanas

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

kinematic observations of misocyclones along boundaries during ihop during the international h2o project mobile radars collected high resolution data of several 0 5 2 kmwide vertically oriented vortices or misocyclones along at least five mesoscale airmass boundaries this study analyzes the properties of the misocyclones in three of these datasets 3 10 and 19 june 2002 to verify findings from finescale numerical models and other past observations of misocyclones and to further the understanding of the role that they play in the initiation of deep moist convection and nonsupercell tornadoes misocyclones inflect or disjoint the swath of low level convergence along each boundary to varying degrees depending on the size of their circulations when several relatively large misocyclones are next to each other the shape of low level convergence along each boundary is arranged into a staircase pattern mergers of misocyclones are an important process in the evolution of the vorticity field as a population of small vortices consolidates into a smaller number of larger ones additionally merging misocyclones may affect the mixing of thermodynamic fields in their vicinity when the merger axis is perpendicular to the boundary misocyclones interact with linear and cellular structures in the planetary boundary layers pbls of the air masses adjacent to each boundary cyclonic low level vertical vorticity generated by both types of structures makes contact with each boundary and sometimes is incorporated into preexisting misocyclones intersections of either type of pbl structure with the boundary result in strengthened pockets of low level convergence and typically strengthened misocyclones

late paleozoic deformation and exhumation in the sierras pampeanas argentina 40 ar 39 ar feldspar dating constraints systematic 40ar 39ar feldspar data obtained from the sierras pampeanas are presented filling the gap between available high 300 c and low temperature 150 c thermochronological data results show silurian devonian exhumation related to the late stages of the famatinian ocloyic orogeny for the sierra de pocho and the sierra de pie de palo regions whereas the sierras de san luis and the sierra de comechingones regions record exhumation during the carboniferous comparison between new and available data points to a carboniferous tectonic event in the sierras pampeanas which represents a key period to constrain the early evolution of the proto andean margin of gondwana this event was probably transtensional and played a major role during the evolution of the paganzo basin as well as during the emplacement of alkaline magmatism in the retroarc

timing constraints on building an intermediate plutonic arc crustal section u pb zircon geochronology of the sierra valle fertil la huerta famatinian arc argentina 1 the sierra valle fertil range in northwestern argentina exposes a tilted crustal section through the ordovician famatinian arc from 25 km to shallow crustal paleodepths fourteen new u pb zircon crystallization ages of magmatic rocks from sierra valle fertil area show that this section of the arc was built over a short time interval during the ordovician between 485 and 465 ma zircon rim ages demonstrate that high grade metamorphism and migmatization were synchronous with magmatic emplacement inherited ages in some of the plutonic rocks as well as detrital zircons in the metasedimentary framework suggest that the famatinian arc was emplaced into a thick miogeoclinal cover to the thinned margin of the proto south american continent in the ordovician which represents a part of gondwana docking of the precordilleran terrane outboard of proto south america led to the cessation of arc magmatism in the valle fertil area and preservation of the arc in its early stages after 60 myr of subduction during the pampean and famatinian magmatic stages our age data from the sierra valle fertil indicate that wet mafic magmas were emplaced into the section at a rate typical for modern island arcs 30 km3 km 1 myr 1 the production of intermediate to felsic magmas in the upper plate was a result of partial melting of the metasedimentary framework and hybridization with mantle derived melts and resulted in the generation of tonalites granodiorites and granites in the upper crust at a rate of 100 km3 km 1 myr 1 similar to major magmatic flare ups in the mature arcs of north american cordillera the sierra valle fertil arc section is a type example of an immature cordilleran arc before major crustal thickening and crustal overturn takes place in the upper plate the famatinian arc section may also be an equivalent to the crustal architecture of more mature modern island arcs such as parts of the aleutians caribbean and japan

models of garnet differential geochronology abstract rayleigh distillation models are developed to describe theoretical growth zoning of lu hf rb sr sm and nd in typical garnet crystals from metapelites and metabasites effects of diffusion limited transport within the matrix and intracrystalline diffusion are also considered qualitatively theoretical zoning profiles show strong depletions of lu in garnet rims compared to cores but virtually invariant hf rb sr sm and nd profiles generally consistent with natural profiles for lu and hf and previously published models theoretical isochron diagrams for lu hf exhibit distinctive arcuate distributions and high mswds consistent both with himalayan data and with expectations that garnet growth durations exceed chronologic resolution by as much as an order of magnitude predicted isochron diagrams for sm nd and rb sr exhibit vertical arrays for garnet and high mswds that are generally lower than for lu hf in metapelites inherent chronologic resolution for bulk separates is best for lu hf in metapelites and rb sr but analytical considerations favor rb sr or sm nd for chronologic zoning studies diffusion limited transport in the rock matrix strongly influences zoning profiles but does not change the main trends on isochron diagrams intracrystalline diffusion will initially rotate lu hf isochrons to steeper slopes giving older apparent ages the natural himalayan data indicate growth of garnet in one rock from the greater himalayan sequence at 34 ma consistent with previously measured monazite ages from the same rock data from another himalayan rock suggest polymetamorphism that includes a paleozoic component

age constraints on the tectonic evolution and provenance of the pie de palo complex cuyania composite terrane and the famatinian orogeny in the sierra de pie de palo san juan argentina abstract new u pb age determinations confirm earlier interpretations that the strongly deformed and metamorphosed mafic and intermediate igneous rocks of the pie de palo complex represent a mesoproterozoic fragment of suprasubduction zone oceanic crust a gabbroic pegmatite interpreted to have formed during arc rifting or subsequent back arc spreading yielded a u pb age of 1204 5 3 4 7 ma highly tectonized ultramafic mafic cumulates occurring at the structural base of the pie de palo complex and previously interpreted to represent remnants of a primitive arc phase prior to rifting and back arc spreading could not be dated but should be older than 1204 ma if these inferences are correct tabular sill like bodies of leucogabbro diorite and calc alkaline tonalite granodiorite sills yielded ages of 1174 43 and 1169 8 7 ma respectively they may represent a younger more evolved arc phase established after arc rifting or a younger tectonically unrelated mesoproterozoic arc shrimp analysis of metamorphic zircon rims with low th u ratios in vvl 110 gave a 206pb 238u age of 455 10 ma similar to lower intercept dates determined by discordia lines combined these data indicate that the bulk of the amphibolite facies metamorphism present in the pie de palo complex was generated during the famatinian orogeny analysis of six single detrital zircon grains in a metasedimentary quartzofeldspathic garnet mica schist tectonically interleaved with the igneous rocks of the pie de palo complex and tentatively correlated with the difunta correa metasedimentary sequence of other workers yielded three age populations 1150 1160 ma 1050 1080 ma and 665 ma indicating that these sedimentary rocks were deposited during the late neoproterozoic or early paleozoic in addition they confirm structural evidence that intercalation of rocks of the pie de palo complex with isolated slivers of these sedimentary rocks is due to tectonic imbrications these ages are also consistent with a laurentian provenance and earlier interpretations that these rocks once represented a sedimentary cover to the pie de palo complex the zircon population of 1050 1080 ma could be derived from grenville age felsic plutons identified elsewhere in the pie de palo complex by other workers however no evidence has been found in our samples for a grenville age orogenic event invoked previously to explain accretion of the oceanic pie de palo complex to laurentia prior to the late neoproterozoic early cambrian rifting and drift of cuyania

water mass modification in an arctic fjord through cross shelf exchange the seasonal hydrography of kongsfjorden svalbard 1 kongsfjorden and the west spitsbergen shelf is a region whose seasonal hydrography is dominated by the balance of atlantic water arctic waters and glacial melt regional seasonality and the cross shelf exchange processes have been investigated using conductivity temperature depth ctd observations from 2000 2003 and a 5 month mooring deployment through the spring and summer of 2002 modeling of shelf fjord dynamics was performed with the bergen ocean model observations show a rapid and overwhelming intrusion of atlantic water across the shelf and into the fjord during midsummer giving rise to intense seasonality pockets of atlantic water from the west spitsbergen current form through barotropic instabilities at the shelf front these leak onto the shelf and propagate as topographically steered features toward the fjord model results indicate that such cross front exchange is enhanced by north winds normally atlantic water penetration into the fjord is inhibited by a density front at the fjord mouth this geostrophic control mechanism is found to be more important than the hydraulic control common to many fjords slow modification of the fjord water during spring reduces the effectiveness of geostrophic control and by midsummer atlantic water intrudes into the fjord switching from being arctic dominant to atlantic dominant atlantic water continues to intrude throughout the summer and by september reaches some quasi steady state condition the fjord adopts a cold or warm mode according to the degree of atlantic water occupation horizontal exchange across the shelf may be an important process causing seasonal variability in the northward heat transport to the arctic

finescale vertical structure and evolution of a preconvective dryline on 19 june 2002 abstract high resolution airborne cloud radar data and other international h2o project datasets are used to describe the vertical structure of an unusual prefrontal dryline this dryline observed in northwestern kansas on 19 june 2002 first progressed eastward and tilted toward the west and later became more stationary and reversed its tilt toward the moist side the convective boundary layer cbl depth difference also reversed only in the later phase did the dry side cbl become deeper than on the moist side echo and single dual doppler velocity data in a vertical transect across the dryline suggest a solenoidal circulation dynamically consistent with the observed horizontal buoyancy gradient both this gradient and the solenoidal circulation reversed in the later phase simultaneously confluence toward the dryline increased resulting in an increasing moisture gradient as well as a deepening cbl in the dryline convergence zone it is speculated that the baroclinically generated horizontal vortici

barotropic instability in the west spitsbergen current 1 barotropic instability in the shoreward branch of the west spitsbergen current is investigated on the basis of data from an array of current meter moorings along 78 83 n across the upper continental slope and shelf break west of svalbard the slowly varying background current profile is modeled as an along slope asymmetric jet anchored to the shelf break numerical linear stability analyses are performed on the idealized current profile and topography revealing the characteristic period wavelength and growth rate of unstable vorticity waves detailed analysis of the ambient current profile in 2007 2008 shows that unstable conditions are present during 40 of the 10 month measurement record depending on the localization width and amplitude of the current jet the resulting vorticity waves are localized at the shelf break and are able to exchange water masses across the oceanic arctic front typical wavelengths and periods are 20 40 km and 40 70 h respectively wavelet coherence and complex demodulation analyses of the current meter data confirm that transient signals of similar periodicity as predicted by the stability analysis exist in the data record prominently during the winter and spring months estimates of the heat loss contribution from isopycnal diffusion reach 1 4 tw during the time intervals when unstable vorticity waves are active at the shelf break implying that the dynamics of the west spitsbergen current play a significant role in the cooling process of the atlantic water on the way to the arctic ocean this cooling corresponds to an along shelf cooling rate of 0 08 c per 100 km

one more step toward a warmer arctic this study was motivated by a strong warming signal seen in mooring based and oceanographic survey data collected in 2004 in the eurasian basin of the arctic ocean the source of this and earlier arctic ocean changes lies in interactions between polar and sub polar basins evidence suggests such changes are abrupt or pulse like taking the form of propagating anomalies that can be traced to higher latitudes for example an anomaly found in 2004 in the eastern eurasian basin took 1 5 years to propagate from the norwegian sea to the fram strait region and additional 4 5 5 years to reach the laptev sea slope while the causes of the observed changes will require further investigation our conclusions are consistent with prevailing ideas suggesting the arctic ocean is in transition towards a new warmer state

an observational study of the dryline abstract this study presents analyses of data collected in the vicinity of a cloud free dryline that occurred in western oklahoma on 24 may 1989 observations reveal sharp contrasts across the quasi stationary north south dryline during midafternoon of greatest significance is a pronounced gradient of virtual potential temperature although horizontal convergence and vorticity also maximize at the dryline the environment of the 24 may dryline is dominated by vertical mixing that maintains a convective boundary layer cbl on both sides of the dryline the dryline resembles a mixing zone containing varying proportions of hot dry air to the west side and warm moist air from the lowest 200 m within 10 km to the east of the dryline the mixing zone slopes eastward from the surface dryline location then becomes a quasi horizontal elevated moist layer above the cbl east of the dryline saturation point analysis indicates that the mixing zone is characterized by a single mixing line structure defined by

new evidence of warming propagating toward the arctic ocean 1 the dramatic changes in the arctic climate observed in recent years have generated an urgent need to investigate the arctic ocean s heat budget mooring data and synoptic observations in the fram strait fs region have shown that increasing amounts of heat have been transported into the arctic ocean ao in recent times here we present results from observations conducted in the west spitsbergen current wsc in summers 2000 2005 the study was motivated by the strong warm anomalies seen in the atlantic water aw layer over a large area of the wsc and changes in the wsc structure we conclude that the warm signal was only approaching the fs and we expect that high heat transport through the strait will continue and be even higher than during the last 6 years mostly due to increasing activity and temperature of the western branch of wsc