are granitic intrusions scale invariant published length l and thickness t data on 135 laccolith and 21 granite intrusions define power law relationships of the form l kt a typical of systems exhibiting scale invariant fractal behaviour both data sets are characterised by an exponent a 1 0 88 0 1 for laccoliths and 0 80 0 20 for plutons that reflects an inherent preference for scale invariant tabular sheet geometries these power law size relationships can be explained in mechanical terms by the need for an incoming magma sheet to travel laterally some distance before vertical thickening can occur sheet thickness is a function of available magma pressure which for an intrusion fed by a feeder dyke is proportional to the vertical magma transport distance

geochemistry and isotope systematics of small to medium volume neogene quaternary ignimbrites in the southern central andes evidence for derivation from andesitic magma sources the geochemical and isotopic compositions of small to medium volume 10 km3 50 km3 neogene quaternary ignimbrite sheets of the southern central andes 25 00 26 45 s 67 30 69 30 w have been analysed in order to assess the petrogenesis of this type of calc alkaline magma the ignimbrites are derived from the active volcanic zone around salar de la isla sis in chile and from behind the active arc in the area of the salar de antofalla saf argentina the ignimbrites in both areas are characterized by 87sr 86sr t ratios 0 7066 0 7090 that are lower and end t values 2 4 to 5 1 that are higher than in the large volume caldera sourced ignimbrites of cerro galan 100 km further east and those of ignimbrites from other megacalderas of the central andes this difference reflects smaller amounts of crustal material in the sis and saf ignimbrites rather than a change in basement composition as indicated by pb provinciality the isotope signature of the sis and saf ignimbrites is similar to that of late to post miocene composite calc alkalic andesite dacite stratovolcanoes of the frontal arc in this region this finding combined with major and trace element modelling lends support to a petrogenetic model for the sis and saf ignimbrites involving fractional crystallization from a lil depleted andesitic parental magma which was beforehand modified by crustal contamination

relative roles of source composition fractional crystallization and crustal contamination in the petrogenesis of andean volcanic rocks there are well established differences in the chemical and isotopic characteristics of the calc alkaline basalt andesite dacite rhyolite association of the northern n v z central c v z and southern volcanic zones s v z of the south american andes volcanic rocks of the alkaline basalt trachyte association occur within and to the east of these active volcanic zones the chemical and isotopic characteristics of the n v z basaltic andesites and andesites and the s v z basalts basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere conversely the alkaline lavas are derived from basaltic parent magmas formed from mantle of within plate character recent basaltic andesites from the cerro galan volcanic centre to the se of the c v z are derived from mantle containing both subduction zone and within plate components and have experienced assimilation and fractional crystallization a f c during uprise through the continental crust the c v z basaltic andesites are derived from mantle containing subduction zone components probably accompanied by a f c within the continental crust some c v z lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing the petrogenesis of the c v z lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation fractional crystallization and magma mixing during uprise through the continental crust

estimating ocean heat transports and submarine melt rates in sermilik fjord greenland using lowered acoustic doppler current profiler ladcp velocity profiles submarine melting at the ice ocean interface is a significant term in the mass balance of marine terminating outlet glaciers however obtaining direct measurements of the submarine melt rate or the ocean heat transport towards the glacier that drives this melting has been difficult due to the scarcity of observations as well as the complexity of oceanic flows here we present a method that uses synoptic velocity and temperature profiles but accounts for the dominant mode of velocity variability to obtain representative heat transport estimates we apply this method to the sermilik fjord helheim glacier system in southeastern greenland using lowered acoustic doppler current profiler ladcp and hydrographic data collected in summer 2009 we find a mean heat transport towards the glacier of 29 10 9 w implying a submarine melt rate at the glacier face of 650 m a 1 t he resulting adjusted velocity profile is indicative of a multilayer residual circulation where the meltwater mixture flows out of the fjord at the surface and at the stratification maximum

influence of late cretaceous magmatism on the sevier orogenic wedge western montana late cretaceous large volume pluton emplacement and accompanying volcanism within the evolving western montana thrust wedge may have played important roles in determining the geometric and kinematic development of the thrust wedge thereby influencing patterns of sediment dispersal and subsidence in the adjacent foreland basin intrusion of the upper cretaceous boulder batholith and coeval eruption of the elkhorn mountains volcanics were focused mainly at the trailing margin of the lombard eldorado allochthon the resultant thick 16 17 km igneous culmination evolved over a relatively short interval 80 70 ma thickening the orogenic wedge to the point of supercritical taper and facilitating continued motion along the lombard eldorado thrust system thrust imbrication at the wedge toe and forelandward translation of the helena salient delivery of eroded volcaniclastic detritus from the thickened thrust wedge and accelerated basin subsidence due to thrust loading resulted in accumulation of a thick 4 5 km sequence of campanian maastrichtian volcaniclastic strata in the foreland basin livingston group the structural and sedimentological effects of this structural magmatic culmination are similar to those of basement cored culminations elsewhere in the sevier orogen and to the neogene central andean orogenic wedge

on the response of the fjord gullmaren under ice cover an analysis is presented of current salinity and temperature records obtained under ice cover near the mouth of the fjord gullmaren on the sweden skagerrak coast results are compared with an earlier analysis from spring and summer conditions shaffer and djurfeldt 1983 large amplitude vertical fluctuations of the density field of several week periods regularly occurring in the winter season appear to be associated with variations in the baltic sea outflow the local alongshore wind seems to force motions of several day periods in the fjord even under ice cover through interaction with the coastal zone internal seiches prominent features during spring and summer are essentially absent under ice cover which implies that these motions are forced most effectively by the direct action of the local wind on the fjord a method is presented for the determination of significance levels in empirical orthogonal function analysis in the frequency domain

late cenozoic tectonism collapse caldera and plateau formation in the central andes abstract the evolution of andean volcanism including the formation of late miocene to recent collapse calderas on the puna plateau is generally interpreted in terms of the kinematic framework of the nazca and south american plates we present evidence that caldera dynamics and associated ignimbrite volcanism are genetically linked to the activity of first order nw se striking zones of left lateral transtension on the local and regional scales consequently ages of collapse calderas indicate activity of these fault zones which initiated at about 10 ma on the puna plateau the onset of such faulting points to a change in the deformation regime from dominantly vertical thickening to orogen parallel stretching upon reaching maximum crustal thickness and critical surface elevation horizontal magma sheets that formed at mid crustal level possibly due to heat advection by volume increase of asthenospheric mantle below thickened crust were tapped by sub vertical faults this accounts well for the observed tectono magmatic phenomena at surface it follows that formation of collapse calderas and eruption of voluminous ignimbrites appear to be related to the mechanical evolution of the andean plateau rather than to changes in the geometry of the wadati benioff zone or plate boundary kinematics

on the low frequency fluctuations in the eastern skagerrak and in gullmaren abstract an analysis is presented of the fluctuations with periods exceeding approximately one day in the coastal zone of the eastern skagerrak and in the fjord gullmaren based primarily on data from a three month field experiment during the spring of 1979 mean flow in the coastal zone consisted of a strong persistent northward flow in a wedge of brackish water near the coast the baltic current superimposed on a weaker general barotropic northward flow three distinct low frequency bands characterized by high degrees of organized motion and different spatial structure are identified in the coastal zone by coherence and phase analysis for a two day or more band alongshore flow appears to be driven locally by the wind topographic vortex modes in the skagerrak may explain highly organized 56 h fluctuations for the 5 6 day band the fluctuations are related more to the wind stress over the northern north sea than to the local one topographic waves propagating eastward along the norwegian trench may comm

the internal seiches in gullmar fjord part i dynamics abstract internal seiche motions with period 1 3 days in gullmar fjord are investigated based on mooring data with high vertical and time resolution the period and structure of the internal seiches are well described by a simple analytical three layer model taking into account blocking of the basin water at the sill energy budgets for forcing and damping of the seiches are estimated the internal seiches are forced by direct wind stress on the surface and by internal coastal waves of frequency close to the seiches the latter contribution being a little larger the e folding timescale for the internal seiche damping is approximately equal to the seiche periods which means that the seiches are effectively damped but also that the forcing must be in near resonance in order to maintain the observed seiche motions in the basin water the seiches manifest themselves with large vertical motions and clear upward phase propagation the phase propagation is related with a continuous rather than strictly layer

tests of an extension to internal seiches of defant s procedure for determination of surface seiche characteristics in real lakes the success of a defant s method of calculating surface seiche periods and structures in real lakes is well known to test whether it can be adapted and applied with similar success in studies of internal seiches in stratified lakes in which density structure is simulated by two homogeneous layers we compare the predictions of a computerized version of mortimer s modified defant procedure against observations of internal seiche motion in eight lake basins and in three examples against the results of more elaborate models the acceptably close agreement inspires confidence that the modified method is useful for practical predictions which although approximate described the principal characteristics of the often large water mass displacements and oscillations through their influence on mixing and dispersal those motions profoundly affect the chemical and biological economies of many lakes to aid in microcomputer and even pocket calculator applications we set out steps in the calculation in tabular flow chart form a comparable table for surface seiche calculation is added the procedure is not applicable to large lakes in which effects of the earth s rotation are dominant but for the two largest basins tested here leman and ness a modification is introduced to take approximate account of rotation

late cenozoic tectonism and landscape development in the foreland of the andes northern sierras pampeanas 26 28 s argentina the argentine sierras pampeanas are reverse fault bounded mountain blocks of precambrian to paleozoic basement rocks in the foreland of the central andes uplift in the northernmost sierras pampeanas fault blocks of sierra de quilmes sierra cumbres calchaquies and sierra aconquija started about 7 ma and became pronounced between 4 and 3 4 ma the movements culminated after 2 9 ma when the conformable mio pliocene santa maria group was overthrusted faulted and folded in the course of principal basement uplift these movements created climate and base level conditions that resulted in the formation of five pediment levels in the deformed basin strata between 2 5 and 0 3 ma tectonically induced base level changes in the piedmont resulted in three tectonism related pediment surfaces between 2 5 and 0 6 ma which attest to the neotectonic activity in the andean foreland the chronology of young tectonic uplift contradicts models in which early uplift between 20 and 13 ma is due to the interaction between high topography on the subducting nazca plate and the south american craton in conjunction with the principal uplift of the adjacent puna plateau the northernmost sierras pampeanas are better explained by e w compressional stresses superposed on a thinned lithosphere and inherited zones of structural weakness that facilitated uplift

intracrustal derivation of na rich andesitic and dacitic magmas an example from volcan ollague andean central volcanic zone andesitic and dacitic lavas erupted from quaternary stratovolcanoes in the central volcanic zone cvz of the andes have major and trace element compositions similar to proposed melts of subducted mid ocean ridge basalt and na rich trondjhemites tonalites and granodiorites ttg in early archean high grade gneiss terrains suites of lavas from individual volcanoes have average la yb of 25 45 sr y of 30 65 yb contents of 1 5 1 1 ppm and na 2 o contents 3 8 wt with lavas erupted on the volcanic front displaying the most affinity to the early archean suites because slab melting is not involved in the derivation of the cvz magmas these data indicate that rocks with early archean ttg compositions can also be produced through intracrustal differentiation processes isotopic major element and ree data from volcan ollague are consistent with a model incorporating contamination of mantle derived basaltic magmas in garnet bearing deep continental crust to produce basaltic andesite magma followed

geomorphology morphometry spatial distribution and ages of mafic monogenetic volcanoes of the peinado and incahuasi fields southernmost central volcanic zone of the andes abstract the back arc southern puna region south of 24 s in the central volcanic zone of the andes contains hundreds of miocene to quaternary mafic monogenetic volcanoes roughly distributed in several volcanic fields analysis of the geomorphology morphometry spatial distribution and age of 36 mafic monogenetic centers in the peinado and incahuasi fields at the southwestern margin of the puna plateau gives insights on the links that mafic monogenetic volcanism can have with main and secondary structures and the effects of degradation on scoria cone shape degree of preservation morphometry and six new unspiked k ar ages indicate two distinct age groups old centers 2 ma and young centers 1 ma the older mafic centers consist of degraded scoria cones and lava flows with an estimated cumulative bulk volume of 2 2 km3 the younger mafic centers display a variety of well preserved landforms scoria cones lava flows maars tuff rings domes and have an estimated cumulative volume of 6 2 km3 their distribution in a main nne ssw and secondary ene wsw trends suggests a control by the regional nne ssw striking peinado and san francisco fault systems in a dextral strike slip configuration scoria cone and lava flow morphometries are similar in both fields but a marked difference indicating hydrovolcanic activity is the presence of tuff rings maars and tephra fallout deposits only in the peinado field morphometric analysis of dated pristine and degraded scoria cones of the southern puna region shows that parameters related to crater depth and inner crater steepness decrease consistently with age suggesting that crater infilling is the degradation related process that is most sensitive to age at scoria cones in the southern puna high values of crater depth crater width crater depth cone height and mean inner crater slope are indicative of a young 1 ma age as young cones can have initially low values

large 13c enrichment in primary carbonates from andean altiplano lakes northwest argentina abstract we report here extreme 13 c enrichments up to 13 pdb in primary calcite and aragonite precipitates in saline well oxygenated waters from high altitude lakes in the southern andean altiplano northwestern argentina biological effects as well as variations in carbon source inputs and in the exchange rate with atmospheric co 2 are commonly considered the main controls on the carbon isotope values of authigenic lacustrine carbonate we present sedimentological and geochemical evidence that favors physical processes evaporation effects and co 2 degassing as major controls on 13 c enrichment we propose that large enrichments may result from the non equilibrium gas transfer isotope fractionation during co 2 degassing from thermal springs and evaporation effects in arid environments the dilution effect by large quantities of 14 c free co 2 hinders accurate 14 c chronology of these lake records based on lacustrine organic matter and aquatic plants our results indicate that geothermal and volcanic co 2 sources in lake basins located in volcanic settings and physical fractionation may have a greater significance than commonly accepted to explain lacustrine carbon isotope records

characteristics and dynamics of two major greenland glacial fjords the circulation regimes of two major outlet glacial fjords in southeastern greenland sermilik fjord sf and kangerdlugssuaq fjord kf are investigated using data collected in summer 2009 the two fjords show similar flow patterns with a time dependent vertically sheared flow structure dominating over the background estuarine flow driven by buoyancy input we show that this time dependent flow is consistent with circulation induced by density interface fluctuations at the fjord mouth often referred to as intermediary circulation one difference between the fjords is that the hydrographic and velocity structure below a surface modified layer is found to be three layer in kf in summer compared to two layer in sf outside each fjord large scale geostrophic currents dictate the stratification at the mouth although the way in which these large scale flows impinge on each fjord is distinct combining the observations with estimates from existing theories we find the magnitudes of the estuarine qe and intermediary qi circulation and show that qi qe although along fjord winds can also be significant we expect that the critical parameter determining qi qe is the sill depth compared to the fjord depth with shallower sills corresponding to weaker intermediary circulation finally we discuss the implications of strong intermediary circulation on calculating heat transport to the glacier face and its potential feedbacks on the background circulation in these highly stratified estuaries

seismic reflection profiling in the boulder batholith montana seismic reflection profiling combined with gravity data allows more exact determination of the geometry of the controversial boulder batholith of montana reveals laminated structure of the lower crust beneath the batholith and identifies the moho at a depth of 38 km the batholith has inward dipping contacts the dip being about 50 on the west side on the basis of seismic data and the depth to the batholith floor is constrained between 12 and 18 km indicating a great volume for the batholith the boulder batholith was emplaced between 80 and 70 ma during an eastward thrusting in the fold and thrust belt a presumed basal decollement of the thrust system might coincide with the batholith floor and may correspond to the top of the lower crustal layering at a depth of 18 km

two layer tidal circulation in a frictional rotating basin the three dimensional tidal circulation in an elongated basin of arbitrary depth is described with a coupled barotropic and baroclinic two layer model on the f plane as long as friction is not dominant near standing waves are present on the interface as well as on the surface the surface pattern is principally determined by the product of the tidal barotropic wavenumber by the basin length the interface deformation is determined by a baroclinic equivalent usually a much larger number as a result the shape of the interface is characterized by horizontally smaller features than the surface if the product of the tidal baroclinic wavenumber by the basin width is greater than one both lateral and axial modes can be excited at the interface if these modes are near resonant large internal tides can be forced directly by the co oscillating surface tide at the basin entrance the amplitude and phase of the baroclinic component are sensitive functions of the density anomaly and the interface depth as a result the phase and amplitude of the interface vary by large amounts with comparatively small changes in those parameters the model behavior is qualitatively consistent with observations in fjords and straits

tectonic volcanic discontinuity at latitude 27 south andean range associated with nazca plate subduction abstract the area investigated lies between latitude 26 40 and 27 15 south and longitude 69 30 and 68 30 west in the andean range a combination of k ar dating petrology geochemistry and geophysical data has led to the recognition of an important change in the tectonic control of volcanic activity during the early pliocene five volcanic cycles are recognized and grouped into two units according to tectonic control the first unit comprises the following cycles a la coipa maricunga 23 0 15 7 ma b pastillito 13 9 12 9 ma and c wheelwright 8 84 6 14 ma representing a progression of active belts striking n5 e towards the east the second group is represented by penas biancas 4 90 2 64 ma and ojos del salado 1 84 recent active having a n65 e strike extending over a distance of some 250 km in the high andes the volcanic rocks of both groups belong to the calc alkali series ranging from andesitic basalt to andesite dacite and rhyolite though with significant variations in total alkali content changes in the orientation of the volcanic belt may be related to changes in the spreading rate of the nazca plate or to changes in the angle of subduction on either side of latitude 27 s i e along the latitude of the easter hot line

geochemical evolution of st kitts and montserrat lesser antilles the volcanic rocks of st kitts have uniform 87 sr 86 sr ratios c 0 7037 and high 143 nd 144 nd ratios c 0 5130 in a suite which ranges from basalt to rhyolite trace element abundances and the flat chondrite normalized ree patterns resemble those of island arc tholeiitic suites in comparison the montserrat lavas have higher concentrations of alkaline elements and are lree enriched geochemical differences may be related to partial displacement of the axis of the volcanic arc about 9 ma this would have led to the development of the st kitts suite in an essentially new and immature island arc environment being closer to the junction with the former arc axis the composition of the montserrat lavas may reflect previous subduction related mantle enrichment and or the influence of a sedimentary component isotopic ratios and most trace elements in the redonda basalt indicate island arc tholeiite or in some respects morb affinities but it has a high sr content and is lree enriched despite its distinctive composition redonda is situated on the main axis of the volcanic arc and its lavas were evidently contemporaneous with the younger eruptions of st kitts and montserrat

the influence of ice melange on fjord seiches we compute the eigenmodes seiches of the barotropic and baroclinic hydrodynamic equations for an idealized fjord having length and depth scales similar to those of ilulissat icefjord greenland into which jakobshavn isbrae also known as sermeq kujalleq discharges the purpose of the computation is to determine the fjord s seiche behavior when forced by iceberg calving capsize and melange movement poorly constrained bathymetry and stratification details are an acknowledged obstacle we are nevertheless able to make general statements about the spectra of external and internal seiches using numerical simulations of ideal one dimensional channel geometry of particular signifi cance in our computation is the role of weakly coupled ice melange which we idealize as a simple array of 20 icebergs of uniform dimensions equally spaced within the fjord we find that the presence of these icebergs acts to 1 slow down the propagation of both external and internal seiches and 2 introduce band gaps where energy propagation group velocity vanishes if energy is introduced into the fjord within the period range covered by a band gap it will remain trapped as an evanescent oscillatory mode near its source thus contributing to localized energy dissipation and ice melange fragmentation

pb isotopes define basement domains of the altiplano central andes detailed pb isotopic maps of the central andes based on 345 163 previously published 182 new analyses of ores volcanic rocks and their host rocks elucidate the gross structure of the basement and reveal that several isotopically distinct basement domains are juxtaposed in this region the data clearly show that most of the pb in central andean igneous and ore samples is derived from the local basement including pb in ore deposits of the bolivian tin belt some of the isotopic domain boundaries correspond to geologic structures and the residual gravity pattern as well as to metallogenic boundaries such as the western edge of the bolivian tin belt

impact of fjord dynamics and glacial runoff on the circulation near helheim glacier greenland to show that the melting circulation is affected by seasonal runoff from the glacier and by the fjord s externally forced currents and stratification the presence of light arctic and dense atlantic waters in the fjord in particular causes meltwater to be exported at depth and influences the vertical distribution of heat along the ice margin our results indicate that the melting circulation is more complex than hypothesized and influenced by multiple external parameters we conclude that the shape and stability of greenland s glaciers may be strongly influenced by the layering of the arctic and atlantic waters in the fjord as well as their variability

internal waves of the second vertical mode in a stratified lake a time series of measurements of thermal structure and near bottom currents in a stratified lake revealed both first and second vertical mode internal seiching the transition into second mode seiching occurred after first mode waves usually generated by pulses of strong winds died down we describe the major features of the second mode seiche and discuss its effects on mixing in the lake below the thermocline on the basis of calculations of eddy diffusion coefficients there is only weak mixing in the interior of the hypolimnion scaling arguments suggest that mixing at the lake s edges due to motion of the isotherms is not significant despite the larger amplitudes of the second mode seiche the most important mixing region appears to be a turbulent bottom boundary layer driven by seiche currents however resuspension of bottom sediments did not occur probably due to a combination of sediment nature and low current speeds

barometric pressure influence on water table fluctuations in coastal aquifers of partially enclosed seas an example from the adriatic coast italy summary the water table level fluctuations in a coastal phreatic aquifer of the adriatic coast southern po plain italy were recorded to characterize groundwater level response to sea level fluctuations tide induced fluctuations atmospheric pressure loading and recharge from rainfall have all been recognized in the measured water table changes we also identified additional water table fluctuations that are not related to rain atmospheric pressure or tides we propose that these additional fluctuations are related to interaction of groundwater seiche events and inverted barometric effects their amplitude is important because at a distance of 70 m from the coast they have a magnitude of 0 07 m whereas the local tide has a 1 m amplitude seiches are standing waves that create sea water fluxes which affect groundwater below the first row of dunes in the study area we propose that this inverted barometric effect is an important process in creating water fluxes in the coastal zone that may strongly affect the position and width of the mixing zone between salt and fresh water

central andean mantle and crustal seismicity beneath the southern puna plateau and the northern margin of the chilean pampean flat slab earthquake hypocenters recorded in the andean southern puna seismic array 25 28 s 70 65 w provide new constraints on the shape of the subducting nazca plate beneath the puna plateau the transition into the chilean pampean flat slab and the thermal state of the mantle and crust some 270 new mantle hypocenters suggest that the subducting slab under the puna shoals into the flat slab segment more abruptly and farther to the north than previously indicated the revised geometry is consistent with the central volcanic zone incapillo caldera being the southernmost center with pleistocene activity until reaching the southern side of the flat slab region evidence for the revised slab geometry includes three well defined hypocenter clusters in the pipanaco nest 27 5 29 s 68 66 w which are interpreted to reflect slab bending stresses a few low magnitude earthquakes with strongly attenuated s waves in the long recognized antofalla teleseismic gap 25 5 27 5 s support a continuous slab under the southern puna the paucity of gap earthquakes and the presence of mafic magmas are consistent with a hot mantle wedge reflecting recent lithospheric delamination evidence for a hot overlaying puna crust comes from new crustal earthquake hypocenters concentrated at depths shallower than 5 km two notable short duration swarms were recorded under the resurgent dome of the 2 ma back arc cerro galan caldera and the near arc cerro torta dome new crustal earthquake focal mechanisms from 17 events in the array along with two existing mechanisms have strike slip oblique reverse and oblique normal solutions fitting with regional e w compression and n s extension

depositional environments of quaternary lacustrine travertines and stromatolites from high altitude andean lakes northwestern argentina four distinctive depositional subenvironments of fossil travertines and stromatolites are identified in three high altitude 3500 4000 m above sea level lacustrine basins el peinado san francisco las coladas salar subbasin and las peladas southern andean altiplano northwestern argentina these late quaternary occurrences are character ized using geomorphological sedimentological petrographic and stable isotopic data stromatolites of cyanobacterial origin only develop in shallow lacustrine margins of el peinado basin in the same basin macrophytic travertines occur both near thermal spring seepage areas along the lake margin as in situ facies and in littoral lacustrine environments up to water depths of several metres as phytoclastic travertine facies the stromatolites and macrophytic travertines have relatively heavy 18 o compositions suggesting initial 16 o depleted waters and or evaporation effects through time their high 13 c compositions are interpreted as a reflection of intense co2 evasion from the thermal groundwaters feeding the lakes similar laminated travertine facies with no petrographic evidence for biotic origin occur in both las coladas and las peladas basins neither petrographic nor isotopic data alone can differentiate between these two cases besides diagenetic overprint in las peladas facies precludes the use of isotopic values as original isotopic signatures however the depositional environmental conditions defined by the geomorphological and sedimentological features are different laminated aragonitic crusts in las coladas basin formed in a shallow saline lake and are associated with shoreline and terrace deposits cemented by aragonite these travertine crusts represent periods of spring 16 o rich dis charge to the lake as suggested by the lighter oxygen isotopic compositions in contrast travertines from las peladas occur as laminated calcitic and aragonitic units intercalated at the top of fining upward sequences composed of con glomerates sandstones and intraclastic limestones sedimentological data suggest that these travertines originated in fluvial influenced lake margins during low lake level episodes 1283

baroclinic wave drag from two closely spaced sills in a narrow fjord as inferred from basin water mixing 1 the dynamics of the entrance to the ringdalsfjord idefjord at the swedish norwegian border is described for the first time a 1 month long high resolved data set shows that the mixing rate is extremely high in the basin water between the two sills at bjallvarpet and svinesund and that the accompanying horizontal mean buoyancy flux is about 25 mw m 2 during two periods in the observations the density decrease rate d dt below 17 m depth was estimated to be 0 90 and 1 20 kg m 3 d 1 respectively our observations support the idea that the tide is subjected to baroclinic wave drag due to generation of internal tides at sills when a densimetric froude number based on tidal speed and basin stratification is subcritical for supercritical values of the froude number basin stratification becomes unimportant and the tide is subjected to large scale topographic drag with jets developing on the lee side of the sills the total energy loss due to baroclinic wave drag and large scale topographic drag during the two periods are 268 and 198 kw respectively all power supplied to the internal tides and 1 6 of the power supplied to the jets is assumed to sustain the turbulence in the basin water beneath the depths of the sills with a flux richardson number of 0 06 determined from investigations in many fjord basins we find that a process based mixing model explains the observed mixing between the sills to within 90

volcano tectonic segmentation of the northern andes data from landsat images published geologic and geophysical reports and field observations are used to document eight major transverse boundaries that divide the northern andes into segments about 125 km long most of the segment boundaries have no apparent relation to structure on the nazca plate being subducted and may instead represent fundamental and long lasting structures of the continent subduction of the carnegie ridge results in increased uplift of the andes widespread and chemically diverse volcanism and major faulting and seismicity subduction of a highly fractured zone in southern ecuador has led to the formation of a separate platelet with a distinct orientation and to a notable change in volcanic style from andesitic stratovolcanoes to rhyolitic ash flow sheets recognition of the segmented structure of the northern andes provides a framework for interpreting details of the regional geology and illustrates that not all segment boundaries are related to subduction

geology and geochemistry of the ojos del salado volcanic region chile calc alkaline volcanic rocks ranging in age from miocene to recent are encountered in the ojos del salado area 27 09s 68 459w they lie at the southernmost end of the central volcanic zone coinciding with a major morphological seismic and volcanic discontinuity it has previously been suggested that this ojos del salado lineament may represent a continental extension of the chain of islands and seamounts referred to as the 9easter hot line9 the volcanic rocks of the area have been sub divided into five groups based on k ar dates the first three groups all of miocene age show a progressive younging eastwards with a concomitant increase in k 2 o the formation of wheelwright and other caldera structures appears to date from the close of this phase 8 6 ma during the pliocene the group 4 volcanoes were constructed mainly along a line trending n65 e but a number of other cones developed around wheelwright caldera which was partially filled by their products clockwise rotation of the volcanic axis continued in pleistocene recent times with the eruption of the group 5 volcanoes of ojos del salado extensive pumice flows were associated with this new volcanic chain and there is generally a shift to more acidic compositions especially dacite apart from the increase in k and related elements from west to east in groups 1 to 3 there is no evidence for any systematic compositional change in particular the youngest group of volcanoes with an east west trend is geochemically indistinguishable from its predecessors on the dominantly north south axes trace element ratios show similar trends the rare earth element patterns are lree enriched and the 86 sr 87 sr initial ratios are all approximately 0 706 the ojos del salado volcanics are thus devoid of any compositional signature to link them with the easter 9hot line9

vertical mixing in the baltic sea and consequences for eutrophication a review abstract in the transition area between the north sea and the baltic sea entrainment processes dominate the vertical mixing in the inflowing saline bottom water the hot spots of these processes are located at the darss sill and the bornholm channel in the western baltic sea in the central baltic sea the horizontal advection of saline water in deep layers below the permanent halocline dominate the temporal changes and associated transports this is accompanied by the turbulent vertical transport through the halocline into the surface layers the related vertical salt transport into the entire surface mixed layer estimated by various methods is slightly above 30 kg m 2 a during stagnation periods the residence time of the deep water in the eastern gotland basin increases roughly by a factor of five vertical mixing through the halocline is drastically reduced when inflows are lacking the potential processes of diapycnal mixing are discussed to the present knowledge the turbulent motion resulting from breaking internal waves is capable of turbulent transports through the halocline corresponding to the estimates of the salt transport into the surface mixed layer the actual knowledge about boundary mixing due to internal waves in the baltic sea is poor mesoscale eddies may contribute to the vertical mixing but it is not known whether they really do and which of the possible direct and indirect mixing mechanisms is most effective near bottom currents induced by inflow events likely enhance vertical mixing coastal upwelling certainly contributes to the vertical transport but the depth of its origin and the volume transport are hard to determine for large scale quantifications the short spatiotemporal scale of turbulent transports through the halocline resulting in a weakening of the halocline during summer together with the mixing of the entire surface layer down to the halocline in winter form a consistent description of the vertical salt transport it is hypothesised that the longer residence time of the deep water during stagnation periods results from the lack of energy imported by the inflows and directly or indirectly feeding the diapycnal mixing processes the vertical transport of nutrients such as the phosphate is quantitatively not sufficiently understood and needs further interdisciplinary research activities

volcanological and petrological evolution of volcan tata sabaya sw bolivia tata sabaya 19 08 s 68 32 w 5430 m a s l is located on the northern shores of salar de coipasa on the altiplano of bolivia it is a 1700 m high symmetrical composite cone one of two holocene centers in a chain of edifices trending e w from the main n s trending volcanic arc of the andean central volcanic zone cvz four main stages are envisaged for the evolution of the edifice stage 1 formation of a pyroclastic shield possibly around a central dome complex stage 2 formation of an andesitic composite cone on top of the early pyroclastic sequence stage 3 collapse of a 120 sector of the southern flank of the volcano which produced a prominent debris avalanche deposit covering 300 km2 of the salar de coipasa to the south collapse was induced by inflation of the edifice by an input of fresh magma into the sub volcanic magma chamber stage 4 flows and domes which have since healed the edifice tata sabaya shows a restricted range of whole rock compositions most units fall in the range 60 62 5 sio2 with a general evolution to the more silicic stage 4 lavas through time the typical phenocryst assemblage is plagioclase hornblende hypersthene augite oxide biotite is found in the stage 4 lavas and is dominant over pyroxene hornblende and biotite are thought to be a late stage sub liquidus products by far the most mafic compositions at tata sabaya are the hornblende and plagioclase inclusions in two of the stage 4 domes 52 sio2 macroscopic microscopic and chemical evidence for magma mixing mixed phenocryst and matrix populations resorption features mixed glass compositions contraindicative temperature indicators etc are found throughout tata sabaya the whole rock chemistry bears out that magma mixing was a dominant process and that it was responsible for buffering the composition of the magma in an open magmatic system despite being located 35km to the east of the main arc front the rocks of tata sabaya are compositionally similar to those from other centers in the northern 17 19 s segment of the cvz the high k2o calc alkaline suite is characterised by lree and extreme lile enrichments up to 1800 ppm ba and sr 87sr 86sr 0 7056 0 7068 and 143nd 144nd 0 51217 0 51227 are similar to other cvz lavas this is regarded as a baseline signature derived during deep crustal contamination this is corroborated by pb isotope data which indicates influence of the low 206pb 204pb precambrian basement that is thought to underlie the northern portion of the cvz modification of the isotope ratios during open system processes at shallow level is also indicated the most extreme incompatible element enrichments are found in the quenched mafic inclusions these characteristics have been reported from other holocene mafic lavas elsewhere in the northern cvz and may represent a distinct recent magmatic episode

fault controlled pluton emplacement in the sevier fold and thrust belt of southwest montana usa abstract problems associated with syncompressional pluton emplacement center on the need to make room for magma in environments where crustal shortening not extension occurs on a regional scale new structural data from the pioneer and boulder batholiths of southwest montana usa suggest emplacement at the top of frontal thrust ramps as composite tabular bodies at crustal depths between 1 and 10 km frontal thrust facilitated pluton emplacement was accommodated by 1 a magma feeder zone created along the ramp interface 2 providing releasing steps at ramp tops that serve as initial points of emplacement and subsequent pluton growth and 3 localizing antithetic back thrusts that assist in pluton ascent a model of magma emplacement is proposed that involves these elements this model for syntectonic ramp top emplacement of plutons helps explain how space is made for plutons within fold and thrust belts

spatial variability of diapycnal mixing and turbulent dissipation rates in a stagnant fjord basin two microstructure profilers two ships and four moorings with acoustic doppler current profilers and conductivity temperature loggers were used in an intensive effort to map the spatial and temporal variations of vertical mixing in the stagnant deep basin of gullmar fjord sweden during three days in the beginning of august 2001 a continuous time series of turbulent kinetic energy dissipation profiles was obtained with one microstructure profiler at a fixed position near the deepest part of the fjord during the same period the other microstructure profiler was used to obtain six sections of dissipation through the length of the basin two moorings were deployed in the fjord basin for one month from the end of july to the end of august the mapping of dissipation rates reveals that the dissipation in the deep basin is confined to areas just inside the sill more than 77 of the dissipation in the fjord basin happens above the sloping bottoms closest to the sill

oceanographic response to the passage of hurricanes in belle bay newfoundland abstract this study describes the changes in the sea surface elevation temperature and current pattern in belle bay a side basin in a broad fjord on the south coast of newfoundland as a response to the passage of atmospheric instabilities between 11 july and 15 october 2011 belle bay experienced the passage of an oceanic storm july the hurricanes katia and maria september and hurricane ophelia october in spite of the large atmospheric pressure variations wind seems to be the main mechanism driving the sharp fluctuations in temperature and bottom currents the response of belle bay to wind forcing resulted in a combination of barotropic and baroclinic processes the barotropic response was modulated by a topographic effect where the sea level elevation was higher near bathymetric constriction zones the baroclinic response consisted in a deepening of the thermocline in a range of 30 40 m evidenced by a significant increase in the temperature

a geochemical traverse across the north chilean andes evidence for crust generation from the mantle wedge major and trace element and sr and nd isotope analyses are presented on 186 0 ma magmatic rocks along an east west traverse across north chile at 22 s esr ranges from 25 to 100 and end from 6 to 9 but the low end and high esr values are in rocks generated in the last 15 ma it is argued that previous discussions of petrogenesis in north chile have been hampered because the changes in magma chemistry in this area of unusually thick crust reflect not one but two processes one results in a progressive shift of esr from 25 to 20 and end from 6 to 6 in jurassic to recent rocks which is accompanied by increasing ta sm and sr and decreasing th ta the second is largely confined to the younger rocks and it is characterised by esr increasing up to 100 with increasing sio2 and decreasing sr and it results in relatively shallow trends on an end esr diagram the preferred interpretation is that trend 1 is due to the mobilisation of old late proterozoic mantle lithosphere as magmatism migrated eastwards and that trend 2 is due to crustal melting and contamination with differentiation in this area of thickened continental crust it follows that the mantle wedge is the principal site of crust generation and it is argued that 20 of the sr in the recent northern chile rocks is derived from the subducted ocean crust

revised velocity structure of western montana using a one dimensional 1d layered earth approach we determined a new crust and upper mantle velocity model for western montana to improve earthquake hypocenter locations p wave arrival times recorded on 280 stations from 1432 well recorded earthquakes provided input for a sparse damped least squares sensitivity matrix we solved for 1d velocity structure refractor depths station corrections and hypocentral positions by minimizing travel time residuals the new model has three layers with p wave velocities of 5 70 6 12 and 6 53 km sec with corresponding interface depths of 7 0 19 8 and 39 7 km below the surface the upper mantle velocity is 8 00 km sec we determined station corrections and show that the yellowstone caldera is the only regional geologic feature not adequately modeled by our new 1d velocity model use of the new model and station corrections reduced hypocenter location uncertainties and travel time residuals implying improved hypocenter locations for western montana earthquakes online material table of seismographic stations

seismic gravity and petrological evidence for partial melt beneath the thickened central andean crust 21 23 s on the basis of seismic refraction investigations and gravimetric data we have modelled the crustal structure of the southern central andes 21 23 s a pronounced variation in crustal parameters is seen in n s and w e crossing seismic profiles over the entire andean orogene characterized by a crustal thickness of up to 70 km under the magmatic arc and backarc strongly reduced seismic velocities and a bouguer minimum of 450 mgal anomalously low velocities of 5 9 6 0 km s in the deeper crust of the western cordillera and altiplano regions lead to an over compensation of the bouguer minima resulting in values of crustal densities higher than estimates based purely on seismic velocity measurements in an attempt to reconcile these differences the behavior of crystalline rocks based on published laboratory data was studied under varying pressure and temperature conditions up to the range of partial melting if the temperature is increased above the melting point a rapid decrease in seismic velocity is accompanied by a slow decrease in density for the central andes a good fit of the observed and calculated bouguer anomalies is obtained if the densities of the rocks from the low velocity zone lvz beneath the western cordillera and the altiplano are varied model calculations lead to a velocity density relation for partial molten rocks that allows the melt proportions of rocks to be estimated model calculations indicate that 15 20 vol of basaltic to andesitic melt at depth is necessary to explain the lvz and bouguer anomaly beneath the arc and parts of the backarc high heat flow values 100 mw m2 support the idea that large areas of the deeper andean crust are strongly weakened by the presence of partially molten rocks resulting in reduced seismic velocities with the western cordillera the active volcanic arc of the andean mountain range acting as a ductile buffer between the two more rigid crustal blocks of the forearc and backarc regions

quantifying flow regimes in a greenland glacial fjord using iceberg drifters funded by the national science foundation grant numbers oce 1130008 arc 0909274 and the university of oregon

wind forced motions in stratified lakes and their effect on mixed layer shear the solution for the response of a rectangular n layered stratified lake to an arbitrarily varying in time wind stress is presented the case n 3 is considered in detail for a three layered lake the response is made up of the individual responses of one external and two internal modes when the upper layer is shallow relative to the other two layers the mixed layer shear is due almost entirely to the slower second mode response moreover the upper interface can tilt quite severely while the lower interface remains nearly flat calculations based on the three layer model are compared with measurements made in wellington reservoir western australia

magma sources and tectonic setting of central andean andesites 25 5 28 s related to crustal thickening forearc subduction erosion and delamination

structural geologic evolution of the butte district montana the butte district contains two porphyry cu mo deposits and the younger zoned main stage base metal lode deposits that formed in the period from 66 to 62 ma synchronous with laramide compressional thrust faulting and folding in southwest montana new geologic mapping of the butte district reveals three distinct episodes of deformation 1 gentle 20 10 ne tilting produced during laramide compressional deformation uplift and exhumation during and after ore formation in the late cretaceous to paleocene 66 53 ma 2 moderate 10 50 nw tilting of eocene age produced by ne striking normal faults that are limited to the northwest part of the district and synchronous with the eruption of the lowland creek volcanics and 3 miocene to present gentle 15 ese tilting in the hanging walls of the continental east ridge and rocker normal faults stratigraphic relationships isotopic ages hornblende barometry and fluid inclusion data indicate that exposures of the butte granite which hosts mineralization crystallized at 6 to 9 km depth and that early porphyry cu mo deposits formed at similar depths of 5 to 9 km a period of rapid uplift and erosion removed about 7 km of rock from above the ore deposit between 66 to 64 ma and 53 ma but was mostly completed by 59 ma estimated exhumation rates range from 0 5 to 2 mm yr and uplift was likely most rapid between 63 5 and 62 ma during main stage mineralization which occurred at depths of 2 to 6 km the butte granite and boulder batholith were emplaced at 79 to 76 ma into thrust fault ramps which later became inactive near butte as laramide crustal shortening moved eastward in the helena salient the accelerated period of uplift and unroofing is attributed to renewed deformation along the montana disturbed belt south of butte that uplifted the south end of the boulder batholith and produced 20 of gentle ne tilting episode i in the district the exhumation history of the deposit is therefore broadly contemporaneous with ore formation and is consistent with the general transition from lithostatic to hydrostatic conditions that is evident from the telescoping of early porphyry cu mo ores cut by the main stage lode veins within a 5 m y period the laramide compressional regime near butte evolved into an extensional environment characterized by normal faulting the normal faults were synchronous with eruption of the 53 to 48 ma lowland creek volcanics which directly overlie the main stage veins in the northwest part of the district structural reconstruction of the district at the time of mineralization produces orientations of quartz porphyry dikes porphyry cu mo veinlets main stage veins and alteration zonal patterns that are steeply dipping and symmetrical similar to observations from other upright or restored porphyry copper deposits early porphyry cu mo veins and dikes are oriented e w and likely originated as tensile hydrofractures above a ductile magma carapace during laramide shortening additionally during the laramide compressional phase two conjugate fault systems occupied by main stage veins are normal oblique slip faults that record minor e w and vertical shortening and n s extension these normal faults with minor offset likely resulted from brittle failure caused by doming above a volatile rich and buoyant granitic magma chamber and cupola at depth the structural evolution of the butte district therefore reflects the interaction of a far field compressive stress regime with local buoyant magmatic forces

observed damping of barotropic seiches through baroclinic wave drag in the gullmar fjord baroclinic wave drag due to internal wave generation at steep topography is shown to be a mechanism that effectively subdues barotropic seiches in fjords a two layer model for a fjord with a sill at the mouth is applied to the gullmar fjord sweden the damping of the fundamental seiche mode observed from sea level records is well predicted by the model this includes the observed seasonal variation in damping due to the corresponding variation in vertical stratification it is shown that ordinary bottom friction should contribute less than 1 to the damping in this fjord simultaneous current records from different depths obtained on the slope of the sill in the fjord are analyzed spectra of all records show a significant energy peak at the seiche frequency the vertical variation of the phase of the current at this frequency shows that the motion is essentially baroclinic