automatic conversion of magnetic data to depth dip and susceptibility contrast using the spi tm method the source parameter imaging spi method computes source parameters from gridded magnetic data the method assumes either a 2 d sloping contact or a 2 d dipping thin sheet model and is based on the complex analytic signal solution grids show the edge locations depths dips and susceptibility contrasts the estimate of the depth is independent of the magnetic inclination declination dip strike and any remanent magnetization however the dip and the susceptibility estimates do assume that there is no remanent magnetization image processing of the source parameter grids enhances detail and provides maps that facilitate interpretation by nonspecialists the spi method tests successfully on synthetic profile and gridded data spi maps derived from aeromagnetic data acquired over the peace river arch area of northwestern canada correlate well with known basement structure and furthermore show that the ksituan magmatic arc can be divided into several susceptibility subdomains

foreland shortening and crustal balancing in the andes at 30 s latitude excellent surface exposures known benioff zone geometry a dynamic morphology and the availability of industry seismic reflection data all make the andes at 30 s an excellent transect for investigating crustal scale balanced sections 150 170 km of horizontal shortening has occurred in three major belts located between the trench and the foreland the thin skinned east verging precordillera of western argentina accounts for 60 75 of the total shortening and formed mostly since major volcanism ceased at 10 ma industry seismic reflection data show that the decollement of the precordillera belt is located anomalously deep at 15 km the belt is dominated by fault propagation folds and contains several prominent out of sequence thrust faults seismic stratigraphie analysis shows that miocene strata in the iglesia valley located between the precordillera and the crest of the andes accumulated in a piggy back basin onlap relations on the western side indicate that the high cordillera was uplifted as a major fault bend fold over a buried ramp thrusting in the two western belts both in the high cordillera of chile formed during the waning stages of arc volcanism 11 16 ma and account for 25 40 of the shortening the observed shortening is probably greater than can be accounted for with reasonable crustal thicknesses indicating the possibility of continental truncation or erosion along the plate margin or an anomalously thick root held down by the nearly flat subducted nazca plate our preferred crustal geometry puts the ramp between upper and lower crustal deformation west of the high topography requiring crustal scale tectonic wedging to thicken the crust beneath the crest of the andes this non unique model provides a simple explanation of the first order morphology of the andes at this latitude

thick skinned deformation observed on deep seismic reflection profiles in western argentina one of the first deep seismic reflection profiles in south america has resulted from reprocessing nearly 90 km of 96 channel vibroseis data that were originally collected by ypf the argentine national oil company across the sierra de la huerta in the sierras pampeanas of western argentina reprocessed sections show the following features in the upper 20 km of crust 1 prominent layering within carboniferous to quaternary strata and 2 a complex suite of faint reflections which are interpreted to define both extensional and compressional faults the mesozoic strata are bounded by one or more west dipping normal faults one or two east dipping thrust faults shallow with depth a geometry similar to the rocky mountain foreland of the western u s a one thrust has a clear surface trace although lacking evidence of surface scarps or clear fault plane reflections panels of constant dip domain seen in the seismic data justify the application of fault bend folding techniques to suggest that a second deeper fault becomes nearly flat at 15 20 km cumulative cenozoic offset on the thrusts beneath the sierra de la huerta is about 13 km a well located earthquake hypocenter lies within the footwall block of a major thrust and is presumed to represent susidiary thrust motion along a secondary high angle fault gravity models suggest that the thrust ramps may nucleate at an anomalous dense mass in the middle or lower crust interpretation of lower crustal structure is hampered by the lack of clear reflections presumably due to small scale and low amplitude impedance contrast variations of lithologic units at those depths consideration of recorrelation limitations and signal penetration constraints provide likely rationale for the scarcity of clear reflections in the basement rocks of the region but low reflectance of mafic metamorphic rocks remains a possible explanation

new standards for reducing gravity data the north american gravity database the north american gravity database as well as data bases from canada mexico and the united states are being revised to improve their coverage versatility and accuracy an important part of this effort is revising pro cedures for calculating gravity anomalies taking into ac count our enhanced computational power improved ter rain databases and datums and increased interest in more accurately defining long wavelength anomaly components users of the databases may note minor differences be tween previous and revised database values as a result of these procedures generally the differences do not impact the interpretation of local anomalies but do improve re gional anomaly studies the most striking revision is the use of the internationally accepted terrestrial ellipsoid for the height datum of gravity stations rather than the conven tionally used geoid or sea level principal facts of gravity observations and anomalies based on both revised and pre vious procedures together with germane metadata will be available on an interactive web based data system as well as from national agencies and data centers the use of the revised procedures is encouraged for gravity data reduc tion because of the widespread use of the global position ing system in gravity fieldwork and the need for increased accuracy and precision of anomalies and consistency with north american and national databases anomalies based on the revised standards should be preceded by the adjec tive ellipsoidal to differentiate anomalies calculated us ing heights with respect to the ellipsoid from those based on conventional elevations referenced to the geoid

ground truth from the opportunity rover for mars thermal inertia data 1 the temperature of the martian surface has been measured by a number of spacecraft and numerical models of the surface thermal response constrain the near surface physical properties the results allow inferences regarding the surface layer and help determine potential hazards for landed spacecraft however thermal models generally do not incorporate the degree of surface complexity that is seen from landers here we examine potential contributions to the thermal response along the opportunity rover s traverse by using ground truth in conjunction with orbiter data from the themis instrument on mars odyssey we show that the size distribution of the ubiquitous hematite spherules varies in a way that is consistent with expectations from orbiter data secondly exposures of bedrock along opportunity s traverse have no observable effect on the bulk thermal response seen from orbit these field observations are an important step toward improving understanding of the physical composition of the martian surface

zircon and whole rock nd pb isotopic evidence for a grenville age and a laurentian origin for the basement of the precordillera in argentina suggestions that the precordillera of argentina has an early paleozoic connection to the appalachian ouachita rifted margin of the southern u s have been based on cambro ordovician stratigraphy and faunal assemblages further support comes from comparing precambrian grenville appalachian basement with xenoliths brought up in precordil leran miocene volcanic rocks u pb zircon ages and whole rock pb and nd isotopic data from the xenoliths show that precordilleran basement along with some part of the westernmost sierras pampeanas pie de palo range to the east is essentially unique in south america and is best interpreted as being derived from laurentia a grenville age is substantiated by u pb zircon upper intersect ages of 1102 pm 6 ma for a mafic xenolith and near 1100 ma for acidic xenoliths both xenolith types contain pink doubly terminated prismatic igneous zircons with relatively high u and pb concentrations rounded colorless low u and pb zircons with overgrowths produced in a later pre

lithospheric flexure and bending of the central andes gravity anomaly and topography data are used to define the effective elastic thickness of the lithosphere t in the bend region of the central andes values of z increase from nearly zero north and south of the bend to values greater than 50 km at the bend in bolivia there is a close correlation between t and the style and magnitude of the shortening in the central andes since the late miocene in the bend region where the lithosphere is flexurally strong with large t foreland deformation is concentrated into a thin skinned fold and thrust belt above a basal decollement which has absorbed more than 100 km of shortening further north and south where the lithosphere is flexurally weak with low t foreland deformation is more complex involves basement and has absorbed less shortening the along strike gradients in foreland shortening have accommodated both clockwise and anticlockwise rotations about a vertical axis of almost the entire width of the bolivian andes we speculate that the observed variation in t is related to the proximity of the brazilian shield and has been an important factor in controlling the nature and amount of foreland deformation and hence bending of the central andes the flexural properties of the lithosphere may play an important role in determining the large scale evolution of mountain belts

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

a structural study of an interior layered deposit in southwestern candor chasma valles marineris mars using high resolution stereo camera data from mars express 1 an interior layered deposit ild within western candor chasma of valles marineris mars is examined using data from the high resolution stereo camera of the mars express mission most ild layers dip in the same direction as the topographic slope exposed rotated fault blocks of basement lithology appear to penetrate the cover of this ild deposit in at least two locations these features suggest a simple drape morphology over basement topography consisting of rotated fault blocks this interpretation constrains possible hypotheses of ild formation and suggests a limit on total volume of ild material draping implies low energy deposition either subaerially or in deep water and that the total volume of ild is considerably less than indicated by the size of the mound a dark competent unit unconformably caps part of the ild indicating a multistage depositional history

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

spectral and geological study of the sulfate rich region of west candor chasma mars sulfates have been discovered by the omega spectrometer in different locations of the planet mars they are strongly correlated to light toned layered deposits in the equatorial regions west candor chasma is the canyon with the thickest stack of layers and one with the largest area covered by sulfates a detailed study coupling mineralogy derived from omega spectral data and geology derived from hrsc imager and other datasets leads to some straightforward issues the monohydrated sulfate kieserite is found mainly over heavily eroded scarps of light toned material it likely corresponds to a mineral present in the initial rock formed either during formation and diagenesis of sediments or during hydrothermal alteration at depth because it is typically found on outcrops that are eroded and steep polyhydrated sulfates that match any ca na fe or mg sulfates with more than one water molecule are preferentially present on less eroded and darker outcrops than outcrops of kieserite these variations can be the result of a diversity in the composition and or of the rehydration of kieserite on surfaces with longer exposure the latter possibility of rehydration in the current or recent atmosphere suggests the low surface temperatures preserve sulfates from desiccation and also can rehydrate part of them strong signatures of iron oxides are present on sulfate rich scarps and at the base of layered deposits scarps they are correlated with tes gray hematite signature and might correspond to iron oxides present in the rock as sand size grains or possibly larger concretions that are eroded and transported down by gravity at the base of the scarp pyroxenes are present mainly on sand dunes in the low lying terrains pyroxene is strongly depleted or absent in the layered deposits when mixed with kieserite local observations favor a spatial mixing with dunes over layered deposits sulfates such as those detected in the studied area require the presence of liquid water to form by precipitation either in an intermittent lacustrine environment or by hydrothermal fluid circulation both possibilities require the presence of sulfur rich groundwater to explain fluid circulation the elevation of the uppermost sulfate signatures suggests the presence of aquifers up to 2 5 km above datum only 1 km below the plateau surface

thrust front zone of the precordillera argentina a thick skinned triangle zone the frontal thrust zone of the precordillera thrust belt of western argentina only superficially resembles a classical alberta style triangle zone in this thick skinned triangle zone the thrust front is the result of interaction between the eastward verging thin skinned central precordillera and the westward verging thick skinned eastern precordillera system the western boundary formed by the niquivil thrust plate has been refolded and faulted by thrust faults from the eastern precordillera at several localities the deformation is still active we divide the thick skinned triangle zone into three segments based on the system s activity independent late interfering and collision zones balanced cross sections across a thick skinned triangle zone show a uniform s ortening for the eastern precordillera 17 km the structural geometry suggests multiple reactivation of the main faults the thick skinned triangle zone began to grow after 2 6 ma and is still active episodic and alternating opposing movement is controlled by buttressing of the thin skinned thrust system against the basement structures of the eastern precordillera

gravity isostasy and andean crustal shortening between latitudes 30 and 35 s we started the work by analyzing an e w crustal section at 33 s latitude which extends from the western chilean trench crosses the andean belt and goes inland into argentina a two layer gravity seismic model was prepared here it provided a maximum moho depth of 62 km beneath the andean axis this model is consistent with a one layer standard crustal model with normal thickness t 33 km and densities of 2 9 g cm3 and 3 3 g cm3 for the crust and the upper mantle respectively then we analyzed the andean isostatic behaviour on four andean gravimetric sections at latitudes of 30 32 33 and 35 s based on one layer simple models these results show antiroots near the chilean trench and crustal thickenings beneath the andean belt which locate the moho discontinuity at depths of 70 km at 30 s 65 km at 32 and 33 s and 57 km at 35 s from the crustal gravimetric models the following provisional charts for the sector were prepared and compared 1 topography 2 bouguer gravity 3 isostatic corrections 4 moho contours these charts are consistent with each other and they point out that the compensation of the andean belt trends approximately to isostasy in the airy concept other results also confirm this 1 the remarkable decrease of the isostatic anomalies in each of the analyzed sections as regards the bouguer anomalies and 2 the relationships between the exceeding areas and the corresponding crustal root areas which are consistent with the airy numerical relations as to the perfect isostatic equilibrium thus the bouguer anomalies are mainly controlled by the m discontinuity finally shortenings in the andean sector were fixed based on the crustal thicknesses found from gravity inversion these are 150 km at 30 s decreasing southwards and reaching only 90 km at 35 s these shortenings explain the cenozoic andean uplift without requiring other mechanisms such as magmatic intrusions

coherent fluctuations of extratropical geopotential height and tropical convection in intraseasonal time scales abstract coherent fluctuations between extratropical circulation and tropical conviction in the intraseasonal time scale are studied possible relationships between 500 mb height field and outgoing longwave radiation olr are examined using correlation complex eof and composite techniques results show that in the 20 70 day bands data there is a systematic evolution of extratropical wavetrains from eurasia across the pacific to north america and the north atlantic in the time scale of 5 to 10 days over the tropics the dominant mode of intraseasonal variation in convection is an east west dipole like feature which propagates from the western indian ocean eastward to the dateline with a quasi period of 40 50 days the space time evolution of these extratropical wavetrains is found to he coherent with the tropical dipolar convection and with the strongest convection over indonesia central pacific in approximate quadrature with the peak phase of the eurasia and pacific north america wavetrains while the

an unusual spectral unit in west candor chasma evidence for aqueous or hydrothermal alteration in the martian canyons abstract high spatial resolution observations made by orbiting spacecraft from the viking and phobos missions suggest the local development of crystalline ferric oxides in a small area in mars valles marineris canyon system quantitative color analysis of viking orbiter multispectral images identifies two spatially coherent regions of unique hue among the interior layered deposits in western candor chasma the anomalous color indicates a local compositional difference between these regions and the surrounding high albedo materials the unusual appearance of the unit in the viking color observations could be explained by a small increase in the degree of crystallinity or abundance of hematite near infrared spectra obtained by the ism imaging spectrometer aboard phobos 2 confirm a local enrichment in ferric oxides or oxyhydroxides in the region and suggest the presence of another phase in addition to hematite in high resolution the spectral unit can be seen to occur within two 20 km long depressions on the margins of an hesperian aged layered deposit which forms a plateau on the chasma floor water is implicated in the formation of the iron oxides since the same sedimentary layers seen in the depressions are exposed on steep surfaces elsewhere on the plateau but show no evidence of unusual coloration this suggests that the mineralization occurred through secondary alteration of preexisting rocks and developed locally in association with the depressions which could have ponded surface runoff or groundwater seepage

elastic thickness structure of south america estimated using wavelets and satellite derived gravity data abstract we used a wavelet formulation of the classical spectral isostatic analysis to invert satellite derived gravity and topography bathymetry for elastic thickness te over south america and its surrounding plates to provide a homogeneous representation of the gravity field for this vast region we corrected free air anomalies derived from a combination of terrestrial marine gravity data with data from the grace and champ satellite missions model eigen cg03c by a simple bouguer slab using a smoothed representation of surface relief wavelengths 125 km the resulting bouguer anomaly compares well with terrestrial data acquired in the central andes and allows te to be confidently estimated for values greater than 10 km the te map resolves regional scale features that are well correlated with known surface structures and shows maximum values of 100 15 km over the archean neoproterozoic core of the continent decreasing to less than 30 km around continental margins several regions of the oceanic plates and continental margins have an elastic thickness less than 10 km we performed a quantitative analysis by comparing the elastic thickness with the thermal structure predicted from the age of oceanic crust and igneous metamorphic rocks this demonstrates that oceanic plates have been weakened by thermal interaction with hotspots and locally by fracturing and hydration near the trench we observe that only the nucleus of the continent has resisted the thermomechanical weakening induced by the rifting of africa and south america along the passive margin and the andean orogeny along the active margin this latter region shows along strike variations in te that correlate with the geotectonic segmentation of the margin and with the pattern of crustal seismicity our results reveal that the rigidity structure follows the segmentation of the seismogenic zone along the subduction fault suggesting a causal relationship that should be investigated in order to improve the understanding and predictability of great earthquakes and tsunamis

summer arctic atmospheric circulation response to spring eurasian snow cover and its possible linkage to accelerated sea ice decrease abstractanticyclonic circulation has intensified over the arctic ocean in summer during recent decades however the underlying mechanism is as yet not well understood here it is shown that earlier spring eurasian snowmelt leads to anomalously negative sea level pressure slp over eurasia and positive slp over the arctic which has strong projection on the negative phase of the northern annular mode nam in summer through the wave mean flow interaction specifically earlier spring snowmelt over eurasia leads to a warmer land surface because of reduced surface albedo the warmed surface amplifies stationary rossby waves leading to a deceleration of the subpolar jet as a consequence rising motion is enhanced over the land and compensating subsidence and adiabatic heating occur in the arctic troposphere forming the negative nam the intensified anticyclonic circulation has played a contributing role in accelerating the sea ice decline observed during the last two decades the results here provid

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

crustal structure of the south central andes cordillera and backarc region from regional waveform modelling summary we investigate the crustal structure in the andes cordillera and its backarc region using regional broadband waveforms from crustal earthquakes we consider seismic waveforms recorded at regional distances by the chile argentina geophysical experiment charge during 2000 2002 and utilize previous seismic moment tensor inversion results for each single station earthquake pair we fixed the source parameters and performed forward waveform modelling using ray paths that sample the crust of the highest elevation cordillera and the accreted terranes in the backarc region our investigation indicates that synthetic seismograms for our earthquake station geometry are most sensitive to crustal parameters and less sensitive to mantle parameters we performed a grid search around crustal thickness p wave seismic velocity vp and p t os wave seismic velocity ratio vp vs fixing mantle parameters we evaluated this waveform analysis by estimating an average correlation coefficient between observed and synthetic data over the three broadband components we identified all acceptable crustal models that correspond to high correlation coefficients that provide best overall seismogram fits for the data and synthetic waveforms filtered mainly between 10 and 80 s our results indicate along strike variations in the crustal structure for the north south high cordillera with higher p wave velocity and thickness in the northern segment north of 33 s and persistently high vp vs ratio 1 85 in both segments this is consistent with a colder mafic composition for the northern segment and a region of crustal thickening above the flat slab region in contrast the results for the current volcanic arc south of 33 s agree with a warmer crust consistent with partial melt related to quaternary volcanism presumably of an intermediate to mafic composition a distinctive feature in the backarc region is the marked contrast between the seismic properties of the cuyania and pampia terranes that correlates with their heterogeneous crustal composition the cuyania terrane composed of mafic ultramafic rocks exhibits high vp high vp vs and a thicker layered crust versus the thinner more quartzrich crust of the eastern sierras pampeanas associated with low vp and low vp vs these differences may have some effect on the mechanism that unevenly generates crustal seismicity in the upper 30 km in this active compressional region in particular the seismic properties of the cuyania terrane which shows evidence for a high vp and high vp vs crust may be reflecting the complex tectonic evolution history of this terrane including accretion rifting and re accretion processes since the palaeozoic that promote a high level of crustal seismicity in the upper 30 km enhanced by the flat slab subduction in the segment between 31 s and 32 s another possible mechanism could be directly related to the presence of a strong lower crust above the flat slab that efficiently transfer stresses from the slab to the upper crust generating higher seismicity in the cuyania terrane between 30 s and 34 s

the impact of the initial flow on the extratropical response to madden julian oscillation convective heating abstractthe response to the madden julian oscillation mjo over the pacific north american pna region is investigated in addition the sensitivity of this response to the interaction between madden julian oscillation forcing and the extratropical initial flow is explored first a simple dynamical model is run with an ensemble of 100 randomly selected initial conditions from era interim data with no heating mjo phase 1 like heating and mjo phase 5 like heating the 300 hpa geopotential height field is separated into a part that would evolve without an active mjo present and a part that is a consequence of the mjo heating a negative 300 hpa geopotential height anomaly centered over northeastern china bounded by positive anomalies on its equatorward and poleward flanks is found to be followed by a large amplitude negative pna like response for mjo phase 1 and a positive pna like response for phase 5 a similar study is carried out using observational data an analog approach using projections to det

early gondwanan connection for the argentine precordillera terrane abstract the precordillera of argentina is widely accepted as an exotic terrane of laurentian north american affinity newly acquired u pb ages on individual detrital zircons from lower cambrian and upper ordovician quartz sandstone beds in the argentine precordillera indicate a gondwanan provenance not associated with any known part of laurentia accordingly the precordillera terrane is likely underlain by basement rock of gondwanan affinity in addition detrital zircons from the upper ordovician sandstone bed provide no evidence for a mid ordovician position against the inboard famatina arc these results demand critical re evaluation of widely held assumptions regarding the paleogeography of the argentine precordillera

the mesoproterozoic maz terrane in the western sierras pampeanas argentina equivalent to the arequipa antofalla block of southern peru implications for west gondwana margin evolution the rocks of sierra de maz and sierra del espinal western sierras pampeanas represent pre famatinian ordovician basement isotope compositions nd and pb of metasedimentary rocks and shrimp u pb dating of detrital zircons combined with other geological evidence show that three parallel n s domains can be recognized the central maz domain contains pre grenvillian metasedimentary rocks deposited between 1 2 and 1 6 ga that underwent grenvillian granulite facies metamorphism and were intruded by mafic igneous rocks and massif type anorthosites metasedimentary rocks have high nd tdm ages 1 7 2 7 ga and very radiogenic pb 9 8 10 2 suggesting provenance from reworked early proterozoic or archean continental crust the domains to the east and west of the maz domain consist of three metasedimentary sequences with nd tdm ages between 1 2 and 1 6 ga and variably radiogenic pb 9 6 10 0 u pb shrimp dating of detrital zircons nd tdm model ages and comparison with other data suggest that these sequences are post grenvillian i e neoproterozoic and or early paleozoic the maz domain is interpreted as a suspect terrane similar to the northern arequipa antofalla craton that forms the basement of the central andes both underwent grenville age orogeny and were probably once continuous along the western margin of amazonia west gondwana

the influence of the mjo on the intraseasonal variability of northern hemisphere spring snow depth abstractintraseasonal variability in springtime northern hemisphere daily snow depth change sd by phase of the mjo was explored in this study principal findings of the relationship between sd and the mjo included the following 1 statistically significant regions of lagged sd anomalies for multiple phases of the mjo were found in march april and may in both north america and eurasia 2 in each month lagged sd anomalies were physically supported by corresponding lagged anomalies of 500 hpa height z500 and surface air temperature sat spearman rank correlation coefficients indicated a moderate to strong relationship between both z500 and sd and sat and sd in both eurasia and north america for phases 5 and 7 in march in april a moderately strong relationship between z500 and sd was found over eurasia for phase 5 but the relationship between sat and sd was weak in may correlations between sd and both z500 and sat over a hemisphere wide latitude band from 60 to 75 n were close to 0

thermophysical properties of the mer and beagle ii landing site regions on mars 1 we analyzed remote sensing observations of the isidis basin gusev crater and meridiani planum landing sites for beagle ii mer a spirit and mer b opportunity spacecraft respectively we emphasized the thermophysical properties using daytime and nighttime radiance measurements from the mars global surveyor mgs thermal emission spectrometer and mars odyssey thermal emission imaging system themis and thermal inertias derived from nighttime data sets themis visible images mgs mars orbiter camera moc narrow angle images and mgs mars orbiter laser altimeter mola data are incorporated as well additionally the remote sensing data were compared with ground truth at the mer sites the isidis basin surface layer has been shaped by aeolian processes and erosion by slope winds coming off of the southern highlands and funneling through notches between massifs in the gusev region surface materials of contrasting thermophysical properties have been interpreted as rocks or bedrock duricrust and dust deposits these are consistent with a complex geological history dominated by volcanic and aeolian processes at meridiani planum the many layers having different thermophysical and erosional properties suggest periodic deposition of differing sedimentological facies possibly related to clast size grain orientation and packing or mineralogy

wind driven response of the upper ocean along the u s west coast to tropical mjo convection in this study time lagged composites of oscar upper ocean currents from february to may of 1993 2016 were binned by active phase of the leading atmospheric mode of intraseasonal variability the madden julian oscillation mjo seven days after the convectively active phase of the mjo is present in the tropical indian ocean anomalously strong south southeastward upper ocean currents are seen along nearly the entire u s west coast seven days after the convectively active phase is present in the tropical western pacific ocean upper ocean current anomalies reverse along the u s west coast with weaker southward flow a physical pathway to the ocean was found for both of these phases a tropical mjo convection modulates upper tropospheric heights and circulation over the pacific ocean b those anomalous atmospheric heights adjust the strength and position of the aleutian low and hawaiian high c surface winds change in response to the adjusted atmospheric pressure patterns and d those surface winds project onto upper ocean currents

the decompensative gravity anomaly and deep structure of the region of the rio grande rift an isostatic correction is commonly made to bouguer anomaly gravity data to remove the gravity effect of isostatic compensation of topographic loads in the ussr a decompensative correction has then been made to the isostatic gravity anomaly to remove the gravity effect of isostatic compensation of geologic loads as well under an hypothesis of local as opposed to regional compensation the gravity effect of a shallow geological body can be separated from that of its inferred deep compensating root by deconvolution by contrast with the procedure originally defined by zorin we employ here calculations in the wave number domain leading to an efficient and exact solution the decompensative transfer function acts to increase amplitude of the isostatic anomaly at all wavelengths but especially at the low end of the isostatic anomaly spectrum in the 200 600 km wavelength region where anomaly amplitudes may increase by as much as a factor of 2 in a 1200 1200 km region centered on the rio grande rift the decompensative correction ranges from about 35 to 25 mgal the rift is not particularly apparent in the decompensative correction nor is the rift any more apparent in the decompensative anomaly than in the isostatic anomaly the decompensative anomaly however highlights an arcuate gravity low and a system of gravity highs inferred to reflect prerift welts of mass concentration which have indirectly influenced the position of the rift and its segmentation and zones of accommodation under the assumptions made if the decompensative anomaly is subtracted from the bouguer anomaly then the residual is the gravity anomaly field of deep structure without gravity effects of shallow sources in the upper crust we suppose this gravity field to be dominated by the gravity effects of the density contrast across the crust mantle boundary moho and the density contrast at the lithosphere asthenosphere boundary using available seismic data to weakly constrain the moho surface we invert the residual gravity field for topography of the base of the lithosphere lithosphere is found to be 200 km thick in the high plains 40 50 km in the eastern great basin 75 100 km in the colorado plateau and as thin as 40 km in the southern rio grande rift in the area studied the thickness of the lithosphere is everywhere greater than that of the crust an asthenosphere bulge closely tracks the axis of the rift and is symmetrical to it by contrast with asymmetry that might be inferred from broad features of the bouguer anomaly the separation of gravity effects made possible by the decompensative correction shows how the rift is fundamentally controlled by thinning of the lithosphere yet in detail is deflected by long lived tectonic welts in the shallow brittle crust

boreal winter links between the madden julian oscillation and the arctic oscillation abstract there is increasing evidence that the madden julian oscillation mjo modifies the mid to high latitude circulation and in particular appears to have a relationship to the leading mode of extratropical variability the arctic oscillation ao in this study new insights into the observed similarities between the mjo and the ao are explored it is shown that the eastward progression of the convectively active phase of the mjo is associated with a corresponding shift in the tendency and sign of the ao index moreover the ao and the mjo share several analogous features not only in the global circulation but also in surface temperature fields also the ao is linked to a pattern of eastward propagating mjo like variability in the tropics that is partially reproduced in free runs of the ncep climate forecast system cfs model finally it is shown that the structure of the ao as defined by the leading mode in the 1000 hpa geopotential height field is significantly altered based on the phase o

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

proterozoic early paleozoic evolution in western south america a discussion abstract the hypothesis of exotic terranes in peru bolivia argentina and chile generated discussions on the mode of transfer and extent of accretional events that may have occurred in the southern andes during the late proterozoic early paleozoic initially a tectogenesis based on autochthonous mobile fold belts was discussed following ideas emphasised the fragmentation of the supercontinent rodinia laurentia moving along the west gondwana border and colliding with the gondwana western margin the most important effect of this laurentia gondwana relationship was attributed to the argentine precordillera or cuyania terrane splitting off from laurentia and docking to gondwana in the early paleozoic in this study the most cited arguments for this laurentia precordillera relationship are discussed emphasising paleontological considerations it is shown that these arguments do not exclude a close original vicinity of the precordillera terrane to gondwana the precordillera terrane is suggested to be part of a hypothetical platform which developed between south america africa and antarctica safran platform and which was displaced to its actual position by transcurrent faults the collisional events in the sierras pampeanas ensued from strike slip movements and were responsible for the s and i type transpressional magmatism along the pampean and famatinian terranes the final result of this continent parallel movement of terrane slices is similar to that of a terrane split off from laurentia but the first named way of formation easier explains the general continuity of plate convergence at the western border of gondwana than the laurentia precordillera connection does

the linear and nonlinear extratropical response of the atmosphere to tropical intraseasonal heating abstract this study examines the dynamical nature of the linear and nonlinear extratropical response of the atmosphere to tropical intraseasonal heating with various temporal and spatial structures a global two level model is used it is found that the midlatitude response is very sensitive to the phase speed of the forcing and to a lesser extent to its spatial scale for a narrow monopolar heating source traveling eastward uniformly with an around the world period of 40 days as in gcm simulations of the madden julian oscillation mjo the response is weak and explains very little of the extratropical variance for dipolar beating with zonal scale around 15 000 km k 2 3 and wave period of 40 days propagating slowly eastward within a confined longitudinal domain a good approximation of the outgoing longwave radiation fields associated with the real mjo the extratropical response is wavelike and well defined and stands significantly above the background variability the nonlinear wavetrains evolv

high resolution thermal inertia mapping of mars sites of exobiological interest we have mapped thermal inertia at high resolution for selected regions of mars that are of potential biological relevance using observations made by the mars global surveyor thermal emission spectrometer thermal inertia is a direct indicator of physical properties of the surface at the decimeter to meter scale our goal is to understand the geological processes by which the sites formed and their subsequent evolution their current state and their safety and science potential as landing sites for future lander rover and sample return spacecraft missions the thermal inertia values at 3 km scale for the sites considered span the entire range of values measured at mars thermal inertias range from low values indicative of substantial aeolian mantling up to high values suggesting surfaces covered predominantly with bedrock exposed rocks or blocks or well indurated crusts the highest thermal inertias correlate strongly with local morphology while areas with intermediate and low thermal inertias generally show no such correlation this suggests that selection of future landing sites will be plagued by a choice of a well mantled site that is safe but less interesting scientifically versus an unmantled site that is more interesting scientifically but less safe

the global atmospheric circulation response to tropical diabatic heating associated with the madden julian oscillation during northern winter abstractthe detailed dynamical mechanisms of the upper tropospheric circulation response to the madden julian oscillation mjo convection are examined by integrating a primitive equation model a series of initial value calculations with the climatological boreal winter background flow forced by the mjo like thermal forcing successfully capture the key aspects of the observed circulation response to the mjo convection this suggests that a large fraction of mjo related circulation anomalies are direct responses to tropical heating in both the tropics and extratropics and can be largely explained by linear dynamics it is found that mjo like dipole heatings not only intensify tropical upper tropospheric anomalies but also weaken them at certain regions because of the interaction between equatorial kelvin and rossby waves the rossby wave train primarily excited by horizontal divergence of upper level perturbation flow propagates northeastward and then heads back to the equator in this way rossby wave act

the influence of the madden julian oscillation on canadian wintertime surface air temperature abstract using the homogenized canadian historical daily surface air temperature sat for 210 relatively evenly distributed stations across canada the lagged composites and probability of the above and below normal sat in canada for different phases of the madden julian oscillation mjo in the winter season are analyzed significant positive sat anomalies and high probability of above normal events in the central and eastern canada are found 5 15 days following mjo phase 3 which corresponds to an enhanced precipitation over the indian ocean and maritime continent and a reduced convective activity near the tropical central pacific on the other hand a positive sat anomaly appears over a large part of northern and northeastern canada about 5 15 days after the mjo is detected in phase 7 an analysis of the evolution of the 500 hpa geopotential height and sea level pressure anomalies indicates that the canadian sat anomaly is a result of a rossby wave train associated with the tropical convection anomal

persistent north pacific circulation anomalies and the tropical intraseasonal oscillation abstract a composite analysis of multiyear 1985 93 global reanalyses produced by the ncep ncar and the nasa dao is used to show that the development of persistent north pacific pnp circulation anomalies during nh winter is linked to tropical intraseasonal oscillations the development is initiated over the tropical west pacific by anomalous convection characterized by an east west dipole structure one to two weeks prior to the extratropical onset time in both reanalyses as tropical heating moves eastward toward the central pacific anomalous divergent outflow associated with the local hadley circulation generates an anomalous rossby wave sink source in the subtropics consistent with the retraction extension of the pacific jet prior to onset the signature of the forced anomalies is a pair of cyclonic anticyclonic circulation anomalies centered near the node of the tropical heating dipole wave trains extending from the region of anomalous convection into the extratropics set the stage for th

lithospheric and upper mantle structure of central chile and argentina summary the tectonics of central chile and argentina have been greatly affected by the shallow dips of the subducting nazca plate which controlled patterns of magmatism and deformation nearly 1000 km away from the plate boundary we calculate receiver functions from data recorded by the charge array which transected the andes and sierras pampeanas in central chile and argentina to better constrain the crustal structure of this region beneath the northern transect of the charge array where the nazca slab flattens near 100 km we find the crust is over 60 km thick beneath the andes and thin to the east the thick crust however extends 200 km to the east of the high elevations estimates of vp vs obtained from receiver functions vary along ancient terrane boundaries exhibiting higher values to the west interestingly we observe that the amplitude of the phase corresponding to the moho on receiver functions diminishes to the west complicating our images of crustal structure we proposed that the observations presented here of thickened crust within a region of low elevations diminished receiver function arrivals and reports of high shear wave speeds atop of the mantle wedge overlying the shallowly subducted nazca slab can be explained by partial eclogitization of the lower crust the moho appears simpler across the southern transect where it can be identified near 50 km depth at its deepest point beneath the andes and shallows eastwards volcanism remains active near the latitudes of our southern transect and we observe multiple crustal lowvelocity zones indicative of regions of partial melt near the centres of volcanism signals related to the nazca slab remain more elusive suggestive of a small impedance contrast between the slab and overlying mantle

a deterministic approach toward isostatic gravity residuals a case study from south america a new deterministic method for correcting isostatic effects in gravity data sets overcomes the deficiencies of empirically based methods this technique produces a superior gravity image for south america and has application to other continental scale gravity data sets the basis for the correction is the airy heiskanen isostatic model which assumes that surface topography is supported by crustal thickening the three key parameters 1 the crustal thickness at sea level 2 the surface reduction density and 3 the density contrast between the crust and the mantle are determined directly from the elevation free air gravity and bouguer gravity data sets the surface density parameter of 2 60 g cc is determined using a new fractal technique this technique assumes that the topography is fractal the best value for density is that which minimizes the fractal component caused by topographic effects the new value is substantially different than the 2 67 g cc density assumed by many previous workers for most continental scale data sets the crust mantle density contrast parameter of 0 45 g cc is determined by comparison between the densities determined from crossplots of the bouguer values versus elevation the crustal thickness parameter of 30 km is determined using a spectral method applied to the free air gravity the results of this work are not only an isostatic residual map but a methodology that cross checks the data for quality control the final isostatic residual map can be used with confidence for basin evaluation throughout the continent of south america basins at high elevations like the eastern foreland basins of the andes and the altiplano basin are imaged better by using this method

the mars regional atmospheric modeling system model description and selected simulations the mars regional atmospheric modeling system mrams is introduced and selected model results are presented and compared with landed meteorological data when possible mrams is descended from a nonhydrostatic earth mesoscale and cloud scale model that is widely used for forecasting weather and simulating atmospheric systems over complex terrain mesoscale models such as mrams are ideal tools for making use of the high resolution data sets arriving from mars global surveyor experiments simulation of the mars pathfinder mpf landing site at lsd 142 using 1 2 degree mars orbiter laser altimeter mola derived topography and thermal emission spectrometer thermal inertia is shown to be in good agreement with observed near surface temperature pressure and wind direction simulations of topographically induced thermal circulations and mountain induced gravity waves are shown to be consistent with theory and earlier studies that tie large amplitude mountain waves to strong winds capable of producing dust streaks and local dust lifting events a large eddy simulation of the convective boundary layer provides estimates of vertical profiles of heat flux momentum flux turbulent kinetic energy and vertical velocity variance the model results suggest that the martian atmosphere is roughly two to three times more turbulent than the terrestrial atmosphere during the afternoon but fluxes are roughly an order of magnitude smaller due to the lower density dust devillike circulations are also predicted in the large eddy simulation finally a simulation that examines atmosphere surface interactions near big crater is discussed predicted surface wind stress patterns are consistent with aeolian processes inferred through mars orbiter camera imagery of big crater located near the mpf landing site c 2001 academic press

the interaction of the madden julian oscillation and the arctic oscillation abstract tropical and extratropical interactions on the intraseasonal time scale are studied in the context of the arctic oscillation ao and the madden julian oscillation mjo to simplify the discussion a high low mjo phase is defined as strong suppressed convective activity over the indian ocean in the northern hemisphere nh winter season a high low ao phase is found more likely coupled with a high low mjo phase based on the regressed patterns and composites of various dynamical fields and quantities possible mechanisms linking the ao and the mjo are examined the analysis indicates that the mjo influence on extratropical circulations seems more evident than the ao influence on tropical circulations the mjo interacts with the ao through meridional dispersion of rossby waves in the pacific sector the geopotential height anomaly center over the north pacific associated with the mjo can either reinforce or offset the ao pacific action center as a result the ao pattern can be greatly a

structural evolution of the argentine precordillera the rio san juan section abstract the argentine precordillera ap represents a high level fold and thrust belt which was formed during the andean tertiary crustal shortening in a w e transect studied mostly e directed imbrications are combined with folding and involve a pile of cambrian to tertiary sediments the thrust belt is detached above a main decollement within the ordovician to lower devonian strata to the east it is bounded by a back thrust zone directed westwards restored sections allow an estimate of crustal shortening and also provide insight into the structural development during pre tertiary times carbonate platform sequences of cambrian to ordovician age grade into a volcani clastic succession with transitional melanges representing deposits along a western continental slope in the western and easternmost parts of the ap cambrian to silurian deposits are affected by a first folding which to the west is combined with a slight metamorphic overprint during carboniferous to permian times intensified mobility along the eastern rim and in the western parts of the ap leads to crustal extension which partly was triggered by the formation of synsedimentary normal faults in the central ap no angular unconformities at the base of carboniferous permian deposits were found there was no field evidence found to postulate a terrane boundary within the ap area and an onset of thrust tectonics during cretaceous to early tertiary times

the response to mjo like forcing in a nonlinear shallow water model this study examines the response to madden julian oscillation mjo like heat forcing in a nonlinear shallow water model including monopolar heating source traveling eastward with an around the world period of 48 days and dipolar heating with zonal wave period of 48 days with zonal wave number 2 confined in longitude to the mjo active regions a jet localized in the pacific is compared to a zonally uniform boreal basic flow the results show that the rossby wave response downstream exhibits intensified quasi stationary anomalies in the pacific jet exit region when the mjo like heat forcing passes the maritime continent in accord with the observational analysis by adames and wallace 2014 the dynamical mechanism suggested in this study can be used to interpret the intraseasonal mjo pacific north american pattern coherence and other extratropical intraseasonal events

new insights into magnetic derivatives for structural mapping magnetic and gravity derivatives can be likened to seismic attributes in that they can help define estimate the physical properties of the source structure causing the anomaly this contribution looks at the tilt derivative first reported in 1994 and more recently used to derive the local wavenumber 1997 we will show that the combination of the tilt derivative and its total horizontal derivative are highly suitable for mapping shallow basement structure and mineral exploration targets and that they have distinct advantages over many conventional derivatives we provide the simple theory behind the derivatives use a range of simple 2d models to illustrate their response and apply them to mapping a mineral target in namibia

evolution of sulfide mineralization on mars the presence of komatiitic igneous rocks on marks based on geochemical evidence from snc meteorites and viking x ray fluorescence analyses of the regolith suggests that massive and disseminated iron sulfide mineralization occurs near the martian surface analogies are drawn between possible ultramafic fe ni sulfides on mars and terrestrial pyrrhotite pentlandite ore deposits associated with archean komatiites formed during early crustal development on earth partial melting of the mantle as a result of high radiogenic heat production then extrusion of turbulent high temperature ultramafic lavas segregation of immiscible fes melts during cooling gravitational settling and fractional crystallization of sulfide minerals in magma chambers or lava flows produced massive and disseminated sulfide mineralization associated with terrestrial komatiites comparable processes probably occurred on mars where on account of the inferred higher fe fe mg ratio of the x ray mantle estimated to contain approximately 4 5 wt s iron rich basaltic magmas were produced by partial melting at depths and temperatures exceeding 165 km and 1 400 degree c respectively adiabatic diapiric emplacement of these iron rich very low viscosity basaltic melts transported significant concentrations of dissolved sulfur as s sup 2 minus and hs sup minus from the mantle ensuing sulfide mineralization may have been either thinly disseminated within ultramafic lavas eruptingmore over large areas of mars or concentrated locally at the base of structural depressions cumulate ore deposits several meters thick may occur at the base of intrusions or in near surface magma chambers the evidence for insignificant plate tectonic activity on mars and minimal interactions of martian mantle with crust hydrosphere and atmosphere has restricted the evolution of sulfide ore deposits there less

variability of central united states april may tornado day likelihood by phase of the madden julian oscillation 1 april may tornado day likelihood from 1990 to 2011 was calculated for the central united states for phases of the madden julian oscillation mjo an april tornado day was found more likely during mjo phases 6 and 8 and less likely during phases 3 4 and 7 a may tornado day was found more likely during phases 5 and 8 and less likely in phases 2 and 3 during phases with above normal tornado day likelihoods positive anomalies of convective available potential energy bulk vertical wind shear and storm relative helicity were found in the central united states negative anomalies were found during phases with below normal tornado day likelihoods anomalies of such environmental parameters were connected to the mjo via variability in tropospheric circulation these results provide an important starting point for extended range prediction of u s tornado activity

the global response to tropical heating in the madden julian oscillation during the northern winter a life cycle of the madden julian oscillation mjo was constructed based on 21 years of outgoing long wave radiation data regression maps of ncep ncar reanalysis data for the northern winter show statistically significant upper tropospheric equatorial wave patterns linked to the tropical convection anomalies and extratropical wave patterns over the north pacific north america the atlantic the southern ocean and south america to assess the cause of the circulation anomalies a global primitive equation model was initialized with the observed three dimensional 3d winter climatological mean flow and forced with a time dependent heat source derived from the observed mjo anomalies a model mjo cycle was constructed from the global response to the heating and both the tropical and extratropical circulation anomalies generally matched the observations well the equatorial wave patterns are established in a few days while it takes approximately two weeks for the extratropical patterns to appear the model response is robust and insensitive to realistic changes in damping and basic state the model tropical anomalies are consistent with a forced equatorial rossby kelvin wave response to the tropical mjo heating although it is shifted westward by approximately 20 longitude relative to observations this may be due to a lack of damping processes cumulus friction in the regions of convective heating once this shift is accounted for the extratropical response is consistent with theories of rossby wave forcing and dispersion on the climatological flow and the pattern correlation between the observed and modelled extratropical flow is up to 0 85 the observed tropical and extratropical wave patterns account for a significant fraction of the intraseasonal circulation variance and this reproducibility as a response to tropical mjo convection has implications for global medium range weather prediction copyright 2004 royal meteorological society

goce satellite derived gravity and gravity gradient corrected for topographic effect in the south central andes region summary global gravity field models derived from satellite measurements integrated with terrestrial observations provide a model of the earth s gravity field with high spatial resolution and accuracy the earth gravity model egm08 a spherical harmonic expansion of the geopotential up to degree and order 2159 has been used to calculate two functionals of the geopotential the gravity anomaly and the vertical gravity gradient applied to the south central andes area the satellite only field of the highest resolution has been developed with the observations of satellite goce up to degree and order 250 the topographic effect a fundamental quantity for the downward continuation and validation of satellite gravity gradiometry data was calculated from a digital elevation model which was converted into a set of tesseroids this data is used to calculate the anomalous potential and vertical gravity gradient in the southern central andes region the geological structures are very complex but not well resolved the processing and interpreting of the gravity anomaly and vertical gradients allow the comparison with geological maps and known tectonic structures using this as a basis a few features can be clearly depicted as the contact between pacific oceanic crust and the andean fold and thrust belt the seamount chains over the oceanic nazca plate and the famatinian and pampean ranges moreover the contact between the rio de la plata craton and the pampia terrain is of great interest since it represents a boundary that has not been clearly defined until now another great lineament the valle fertil desaguadero mega lineament an expression of the contact between cuyania and pampia terranes can also be clearly depicted the authors attempt to demonstrate that the new gravity fields can be used for identifying geological features and therefore serve as useful innovative tools in geophysical exploration

anatomy of the andean subduction zone three dimensional density model upgraded and compared against global scale models summary we present an upgraded version of a previously published 3 d density model of the andean subduction zone between 18 s and 45 s this model consists of 3 d bodies of constant density which geometry is constrained by independent seismic data and is triangulated from vertical cross sections these bodies define the first order morphology and internal structure of the subducted nazca slab and south american plate the new version of the density model results after forward modelling the bouguer anomaly as computed from the most recent version of the earth gravitational model egm2008 the 3 d density model incorporates new seismic information to better constrain the geometry of the subducted slab and continental moho cmh and has a trench parallel resolution doubling the resolution of the previous model as an example of the potential utility of our model we compare the geometry of the subducted slab and cmh against the corresponding global models slab1 0 and crust2 0 respectively this exercise demonstrates that although global models provide a good first order representation of the slab and upper plate crustal geometries they show large discrepancies up to 40 km with our upgraded model for some well constrained areas the geometries of the slab lithosphere asthenosphere boundary below the continent cmh and intracrustal density discontinuity that we present here as supporting information can be used to study andean geodynamic processes from a wide range of quantitative approaches

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

a new isostatic residual gravity map of the conterminous united states with a discussion on the significance of isostatic residual anomalies to display more clearly the gravity anomalies caused by geologic bodies in the upper parts of the crust a new colored isostatic residual gravity map of the conterminous united states has been prepared using the gravity data set compiled for the gravity anomaly map of the united states society of exploration geophysicists 1982 the new isostatic residual gravity map is based on an airy heiskanen model of local compensation in which the surface load requiring compensation is defined by 5 min topographic and bathymetric data sets a colored first vertical derivative map of isostatic residual gravity further enhances the short wavelength anomalies produced by bodies at or near the surface and emphasizes the regional fabrics and trends in the gravity field for the purpose of displaying gravity anomalies caused by shallow bodies of geologic significance the nature of the isostatic model and the values of its parameters are of lesser importance than the application of an isostatic correction of some sort most isostatic models result in residual gravity maps that appear nearly identical in their main patterns and features anomalies on isostatic residual gravity maps should not be casually interpreted in terms of undercompensation or overcompensation because large amplitude anomalies can be produced by crustal bodies in complete local isostatic equilibrium many isostatic residual gravity anomalies less than several hundred kilometers wide can be related to known geologic bodies we present here a classification scheme that attempts to categorize such anomalies on the basis of tectonic environment in general highs correlate with intruded or accreted mafic material or with upthrusted crustal sections whereas lows occur over low density sedimentary or volcanic sections felsic intrusive bodies or down warped crustal sections although some longer wavelength anomalies such as the broad gravity high centered over montana could be manifestations of density contrasts deep in the mantle many such anomalies can also be modeled by geologically reasonable density contrasts that are isostatically compensated and confined to depths of less than several hundred kilometers so that their source bodies need not be deep the fact that certain of these broader anomalies have well defined boundaries which correlate with near surface geologic features increases the likelihood that their sources lie entirely within the lithosphere if so then the density contrasts required to explain the gravity data imply fundamental anomalies in chemical composition or thermal state for the crustal and upper mantle columns under these regions we have investigated spectral analysis as a method to quantitatively characterize regional anomaly patterns contoured plots of normalized amplitude spectra were prepared for various areas of the isostatic residual gravity field of the united states these fourier domain representations show characteristic patterns that can be interpreted in terms of the trends and wavelengths of anomalies and may help to more objectively distinguish geologic basements with different origins or tectonic histories

three dimensional structure and evolution of the mjo and its relation to the mean flow abstractthe two leading principal components of the daily 850 minus 150 hpa global velocity potential in the interim european centre for medium range weather forecasts ecmwf re analysis era interim 1979 2011 data are used as time varying madden julian oscillation mjo indices regression maps and meridional cross sections based on these indices are used to document the structure and evolution of the zonal wind u and geopotential height z anomalies in the mjo cycle the data are daily and they are not separated by season at upper tropospheric levels the mjo signature is dominated by eastward propagating planetary wave packets consisting of equatorial kelvin waves flanked by rossby waves centered along 28 n s for which the westerly jet streams serve as waveguides at lower tropospheric levels the pattern more closely resembles the response to a pulsating heat source over the maritime continent where the andes block the eastward propagating kelvin wave pulse the contrasting upper and lower

geological context of water altered minerals in valles marineris mars 1 greater than 15 000 km2 of the layered deposits within valles marineris are associated with water altered minerals yet their origin and history of alteration remain a mystery there are numerous competing hypotheses for the formation of the interior layered deposits including aeolian lacustrine and volcanic recent orbiter spectroscopic data have indicated that water has played a role in their geological history thermal emission spectrometer tes measurements have revealed significant crystalline hematite bearing deposits within valles marineris typically related to interior layered deposits these hematite deposits found with a wide range of albedo values are associated with relatively steep bedrock exposures but can also be seen downslope on flat surfaces where they may be a lag deposit more recently observatoire la mineralogie l eau les glaces et l activite omega data have shown hydrated sulfates covering more than 13 000 km2 area of valles marineris sulfates are found in numerous topographic settings and geological units but are typically located along the flanks of interior layered deposits and nearby low lying floor units here we study the detailed morphologies of hematite and sulfate bearing units such as mantled wall units mass wasting blocky deposits massive floor deposits and tectonically altered floor units all of these terrains have diverse erosional styles and varied crater populations in both hematite and sulfate bearing units occasionally found in conjunction with one another formation processes require contributions from water the results indicate a wide range of diversity within an individual mineral class between mineral classes and also among morphological types the diversity of geological settings and properties suggest that any single unified formation mechanism is improbable

the relationship between the madden julian oscillation mjo and southeastern new england snowfall abstractthe winter of 2014 15 brought record snow totals to portions of southeastern new england additionally over 90 of boston logan airport snowfall during the winter fell during phases 7 and 8 of the madden julian oscillation mjo index this motivated the authors to investigate potential connections between intense southeastern new england snowstorms and the mjo in the historical record it was found that southeastern new england snowfall measured since the 1930s at several stations in the region recorded higher than average winter snowfalls when enhanced mjo convection was located over the western pacific and the western hemisphere phases 7 8 similarly snowfall was suppressed when enhanced mjo convection was located over the maritime continent phases 4 5 the mjo also modulates the frequency of nor easters which contribute the majority of new england s snowfall as measured by reanalysis derived cyclone tracks these tracks were more numerous during the same mjo phases that lead to enhan

bouguer reduction density why 2 67 one of the most widely recognized parameters in solid earth geophysics is the assumed density of the surface rocks of the continental crust 2 67 g cm 3 or 2670 kg m 3 in today9s preferred si units in the calculation of bouguer and isostatic gravity anomalies which are widely used for geological studies the gravitational effect of the earth mass between an observation site and a datum is calculated assuming an infinite flat slab of a specified density that approximates the mass the datum for most surveys is sea level or in the case of surveys of limited areas it may be the elevation of the lowest station in the survey although the choice of datum is arbitrary commonly sea level is used in an attempt to standardize anomalies from different surveys similarly a density of 2 67 g cm 3 is generally assumed for the density of the included mass in regional gravity surveys

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

another look at influences of the madden julian oscillation on the wintertime east asian weather 1 as one of the major predictability sources on an intraseasonal time scale the madden julian oscillation mjo exerts a profound influence on the subseasonal forecast of the east asian ea surface air temperature sat and precipitation in this study we examine the direct link of the mjo with the ea sat and precipitation and its dynamical mechanism to represent the mjo we perform an empirical orthogonal function eof analysis on pentad outgoing longwave radiation olr over 20 s 20 n 60 e 150 w the eof1 mode is mostly characterized by a single convection center near the maritime continent 90 150 e whereas the eof2 mode has an east west dipole structure with enhanced convection over the eastern indian ocean and suppressed convective activities over the tropical western pacific at the same pentad of a positive eof1 phase large areas of cold anomalies with reduced precipitation emerge in the ea region north of 20 n and persist through two pentads later at the same pentad of a positive eof2 phase sat and precipitation exhibit a zonal dipole pattern with cold and dry anomalies covering the ea region west of 120 e and warm and wet anomalies to the east these dipole anomalies in sat and precipitation systematically move eastward in the next two pentads a linearized global primitive equation model is utilized to assess the cause of the intraseasonal variability in sat and precipitation over east asia associated with the tropical heating of the mjo the model responses to heating sources that mimic the eof1 and eof2 olr patterns match well the general features of the observed circulation anomalies under forcing of a positive phase of the eof1 pattern strengthened local hadley cell or monsoon circulations within 90 e 150 e are reproduced with anomalous northerly winds and dry anomalies prevailing in the lower troposphere over east asia the processes that influence east asia are mainly associated with intraseasonal changes in local hadley circulation and the northern hemisphere branch of the equatorially trapped rossby wave gyres forced by the mjo heating

geophysical characterization of the upper crust in the transitional zone between the pampean flat slab and the normal subduction segment to the south 32 34 s andes of the frontal cordillera to the sierras pampeanas fil sanchez marcos ariel universidad nacional de san juan facultad de ciencias exactas fisicas y naturales instituto geofisico sismologico volponi argentina consejo nacional de investigaciones cientificas y tecnicas argentina

summer evolution of the north polar cap of mars as observed by omega mars express the observatoire pour la mineralogie l eau les glaces et l activite omega visible infrared imaging spectrometer extensively observed regions of mars with latitudes above 70 n in late 2004 heliocentric longitude from ls 93 to ls 127 the extent of water ice at the surface and the size of ice grains were monitored as a function of time bright small grained frost which initially covered a large fraction of the polar cap waned in favor of large grained ice in outlying regions dominated by large grained ice the albedo increased over the period evaluating the dust content was model dependent however contamination of ice by dust was low

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

effective elastic thickness variations along the andean margin and their relationship to subduction geometry 1 we present a new map of the spatial variations in effective elastic thickness te along the andes estimated using bouguer coherence the te variations reflect interactions between subducting slab and preexisting terrane structure in the forearc conductive cooling of the continent by the subducting slab exerts primary control on rigidity resulting in te that is highest 40 km where the oceanic lithosphere is oldest and coldest 20 s in the central andes te is relatively low 20 km along the volcanic chain and the altiplano and puna plateaus we interpret this weakening to reflect a high geothermal gradient maintained by advective magmatic processes a shallow and hot asthenosphere and a very weak lower crust throughout this region east of the plateaus high te delineates underthrusting of the brazilian shield finally north and south of the plateaus flat subduction areas are characterized by high te high shear wave velocity thick thermal lithosphere and low heat flow indicating that continental lithosphere there is thicker colder and stronger on the basis of these relationships we suggest that variations in slab dip along the margin relate to variations in structure of the continental lithosphere in particular we propose that upper plate structure influences the width and viscosity of the asthenospheric wedge which control the suction moment responsible for the subduction angle at depths 70 100 km for example when oceanic lithosphere subducts beneath thin continental lithosphere the low viscosity asthenosphere allows the slab to detach from the continent and sink into the mantle at normal angles however when oceanic lithosphere subducts close or beneath thick and strong continental lithosphere the asthenospheric wedge narrows and corner flow drags high viscosity mantle from the base of the thick 150 km cold continent into the wedge suction forces increase with both narrowing of the wedge and its increasing viscosity we estimate the asthenospheric viscosity underneath thick cold continents to be 1020 pa s sufficient to induce flat subduction later after prolonged hydration and weakening of the continent s base asthenospheric flow into the wedge may resume allowing the slab to sink again into the mantle at normal angles

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

recent mafic volcanism on mars the evidence for volcanism on mars is commonly accepted but none has been documented in the valles marineris equatorial rift system a recent survey of the troughs in this valley revealed dark patches that are interpreted to be volcanic vents the configuration and association of these patches with tectonic structures suggest that they are of internal origin their albedo and color ratios indicate a mafic composition and their stratigraphic position crispness of morphologic detail and low albedo imply that they are young perhaps even recent

continental and oceanic crustal structure of the pampean flat slab region western argentina using receiver function analysis new high resolution results summary the pampean flat slab of central chile and argentina 30 32 s has strongly influenced cenozoic tectonics in western argentina which contains both the thick skinned basement cored uplifts of the sierras pampeanas and the thin skinned andean precordillera fold and thrust belt in this region of south america the nazca plate is subducting nearly horizontally beneath the south american plate at 100 km depth to gain a better understanding of the deeper structure of this region including the transition from flat to normal subduction to the south three iris passcal arrays of broad band seismic stations have been deployed in central argentina using the dense siembra array combined with the broader charge and esp arrays the flat slab is imaged for the first time in 3 d detail using receiver function rf analysis a distinct pair of rf arrivals consisting of a negative pulse that marks the top of the oceanic crust followed by a positive pulse which indicates the base of the oceanic crust can be used to map the slab s structure depths to moho and oceanic crustal thicknesses estimated from rf results provide new more detailed regional maps an improved depth to continental moho map shows depths of more than 70 km in the main cordillera and 50 km in the western sierras pampeanas that shallow to 35 km in the eastern sierras pampeanas depth to moho contours roughly follow terrane boundaries offshore the hotspot seamount chain of the juan fernandez ridge jfr is thought to create overthickened oceanic crust providing a mechanism for flat slab subduction by comparing synthetic rfs based on various structures to the observed rf signal we determine that the thickness of the oceanic crust at the top of the slab averages at least 13 19 km supporting the idea of a moderately overthickened crust to provide the additional buoyancy for the slab to remain flat the overthickened region is broader than the area directly aligned with the path of the jfr however and indicates along with the slab earthquake locations that the flat slab area is wider than the jfr volcanic chain observed in the offshore bathymetry further rfs indicate that the subducted oceanic crust in the region directly along the path of the subducted ridge is broken by trench parallel faults one explanation for these faults is that they are older structures within the oceanic crust that were created when the slab subducted alternatively it is possible that faults formed recently from tectonic underplating caused by increased interplate coupling in the flat slab region

crustal wedging triggering recent deformation in the andean thrust front between 31 s and 33 s sierras pampeanas precordillera interaction 1 we document a new model of crustal structure of the andean front in argentina where numerous historic earthquakes destroyed the cities of mendoza in 1861 ms 7 and san juan in 1944 mw 7 0 the cerro salinas anticline is formed above the west directed cerro salinas thrust an east facing monocline with an amplitude of about 2 km folds the cerro salinas thrust and overlying neogene succession this monocline is formed above a blind crustal thrust in the basement its dip of 14 west is inferred from fold geometry this thick skinned east directed blind thrust and the thin skinned west directed cerro salinas thrust define a tectonic wedge the wedge tip occurs at a depth of 5 4 km growth of the monocline after 8 5 ma is revealed on multichannel seismic msc profile 31017 repsol ypf rates of cerro salinas thrust displacement are of the order of 1 mm yr whereas vertical uplift of 0 45 mm yr results from the combined displacement on the cerro salinas thrust and growth of east facing monocline the lateral extent of the east directed crustal blind ramp corresponds with the along strike extent of the eastern precordillera when combined with the low displacement rate a long earthquake recurrence interval is implied smaller magnitude earthquakes however indicate that segments of the blind thrust ramps ruptured in historic events if all the segments of the blind thrust ruptured together the fault area is 7000 km 2 and could produce a mw 7 7 earthquake the crustal wedge model provides new constraints on the origin and potential size of earthquakes that threaten the densely populated region

the continuum of north pacific sea level pressure patterns intraseasonal interannual and interdecadal variability this study combines k means cluster analysis with linear unidimensional scaling to illustrate the spatial and temporal variability of the wintertime north pacific sea level pressure slp field daily wintertime slp data derived from the ncep ncar reanalysis are used to produce 16 slp anomaly patterns that represent a discretized approximation of the continuum of north pacific slp patterns this study adopts the continuum perspective for teleconnection patterns which provides a much simpler framework for understanding north pacific variability than the more commonly used discrete modal approach the primary focus of this research is to show that variability in the north pacific on intraseasonal interannual and interdecadal time scales can be understood in terms of changes in the frequency distribution of the cluster patterns that compose the continuum each of which has a time scale of about 10 days this analysis reveals 5 6 pacific north american like pna like patterns for each phase as well as dipoles and wave trains a self organizing map som analysis of coupled slp and outgoing longwave radiation data shows that many of these patterns are associated with convection in the tropical indo pacific region on intraseasonal time scales the frequency distribution of these patterns in particular the pna like patterns is

the tropical madden julian oscillation and the global wind oscillation abstract the global wind oscillation gwo is a subseasonal phenomenon encompassing the tropical madden julian oscillation mjo and midlatitude processes like meridional momentum transports and mountain torques a phase space is defined for the gwo following the approach of wheeler and hendon for the mjo in contrast to the oscillatory behavior of the mjo two red noise processes define the gwo the red noise spectra have variance at periods that bracket 30 60 or 30 80 days which are bands used to define the mjo the correlation between the mjo and gwo is 0 5 and cross spectra show well defined coherent phase relations in similar frequency bands however considerable independent variance exists in the gwo a basic dynamical distinction occurs in the direction of midlatitude wave energy dispersion being predominantly meridional during a mjo and zonal during the gwo this is primarily a winter season feature centered over the pacific ocean a case study during april may 2007 focuses on the gwo and two

a new analytical solution estimating the flexural rigidity in the central andes summary we present a new 2 d analytical solution of the fourth order differential equation which describes the flexure of a thin elastic plate the new analytical solution allows the differential equation for an elastic plate to be solved for any irregular shaped topography with a high spatial resolution we apply the new method to the central andes the flexural rigidity distribution calculated by this technique correlates well with tectonic units and the location of fault zones for example the central andean gravity high correlates with the presence of a rigid high density body