seismic tomography of the colorado rocky mountains upper mantle from crest lithosphere asthenosphere interactions and mantle support of topography abstract the crest experiment colorado rocky mountains experiment and seismic transects integrated the earthscope usarray transportable array with portable and permanent stations to provide detailed seismic imaging of crust and mantle properties beneath the highest topography region of the rocky mountains inverting approximately 14 600 p and 3600 s wave arrival times recorded at 160 stations for upper mantle v p and v s structure we find that large v p perturbations relative to ak135 of 7 and v s variations of 8 take place over very short approaching tens of kilometers lateral distances highest heterogeneity is observed in the upper 300 km of the mantle but well resolved low velocity features extend to the top of the transition zone in portions of these images the previously noted low velocity upper mantle aspen anomaly is resolved into multiple features the lowest v p and v s velocities in the region are found beneath the san juan mountains which is clearly distinguished from other low velocity features of the northern rio grande rift taos latir region aspen region and below the never summer mountains we suggest that the san juan anomaly and a similar feature below the taos latir region of northern new mexico are related to delamination and remnant heat and melt beneath these sites of extraordinarily voluminous middle cenozoic volcanism we interpret a northeast southwest grain in velocity structure that parallels the colorado mineral belt to depths near 150 km as being reflective of control by uppermost mantle proterozoic accretionary lithospheric architecture further to the north and west the wyoming province and northern colorado plateau show high velocity features indicative of thick 150 km preserved archean and proterozoic lithosphere respectively overall we interpret the highly heterogeneous uppermost mantle velocity structure beneath the southern rocky mountains as reflecting interfingered chemical proterozoic lithosphere that has been is currently being replaced and modified by upwelling asthenosphere low velocity features resolved here indicate that this process may be sourced as deeply as the top of the mantle transition zone at 410 km one driving mechanism for this is upper mantle interaction between upwelling hydration induced partial melt and destabilized downwelling lithosphere in the deeper upper mantle tomographic imaging of mantle seismic velocity and crustal thickness results and modeling from the crest experiment indicate that the highest elevations of the colorado rocky mountains are substantially supported by the mantle and strong correlations between low velocity mantle and thin crust high topography are noted across the region this along with rich upper mantle seismic heterogeneity suggests that mantle buoyancy and dynamics are central to present day topographic support and recent geomorphic evolution of the region

the influence of unsteady depths and currents of tides on wind wave propagation in shelf seas abstract the influence of unsteady depths and currents on wind wave propagation on the scale of shelf seas such as the north sea is investigated the attention is focused on depth and current variations due to tides which are essentially stationary at the scale of a single wave but unsteady at the scale of wave propagation analytical solutions are derived for changes of monochromatic unidirectional linear waves due to a one dimensional tide in water with a constant bottom level it is shown that the change of absolute frequency due to variations of depth and current in time is of the same order of magnitude as the doppler shift and that it is not negligible as assumed in a quasi stationary approximation the common quasi stationary approximation leads to large errors in the predicted change of wave parameters in all situations considered here

on the impact angle of hurricane sandy s new jersey landfall 1 hurricane sandy s track crossed the new jersey coastline at an angle closer to perpendicular than any previous hurricane in the historic record one of the factors contributing to record setting peak water levels in parts of new jersey and new york to estimate the occurrence rate of sandy like tracks we use a stochastic model built on historical hurricane data from the entire north atlantic to generate a large sample of synthetic hurricanes from this synthetic set we calculate that under long term average climate conditions a hurricane of sandy s intensity or greater category 1 makes nj landfall at an angle at least as close to perpendicular as sandy s at an average annual rate of 0 0014 yr 1 95 confidence range 0 0007 to 0 0023 i e a return period of 714 years 95 confidence range 435 to 1429

evolving geographic patterns of cenozoic magmatism in the north american cordillera the temporal and spatial association of magmatism and metamorphic core complexes four maps are presented here that show the location and extent of magmatic fields between eastern alaska and northern mexico during the successive time intervals of 55 40 40 25 25 10 and 10 0 ma and four others show the distribution of metamorphic core complexes during the same cenozoic time intervals the maps are based on u s geological survey and canadian cordilleran data bases contining about 6000 isotopic dates and extensive literature review for nearly 60 ma the development of metamorphic core complexes has coincided with the locus of a really extensive and voluminous intermediate composition magmatic fields the association is suggestive of a close link between magmatism and core complex formation namely that magma directly and indirectly lowers the strength of the crust magmatism thus controls the location and timing of core complex formation the stresses responsible may be inherited from mesozoic crustal thickening locally created by uplift and magmatic thickening of the crust and imposed by the global pattern of plate motions and driving forces since the miocene rates of magmatism extension and core complex formation have declined the modern basin and range province is not a suitable model for the situation that existed during major magmatic culminations the singular event of early miocene time the merging of two large magmatic fields extinguishing the laramide magmatic gap explains several disconnected observations the hyperextension episode of the colorado river corridor rapid reorientation of stress patterns across much of western north america and subsequent rapid tectonic movements in california magma triggered breakup of western north america lithosphere coincided with development of the san andreas transform system thermal destruction of the laramide magmatic gap created a california microplate about 22 ma ago that moved rapidly away from north america thus two plate tectonic processes thermal destruction of the lithosphere bridge and northward growth of a transform system interacted to produce miocene and later tectonic patterns and events

coupled normal mode sensitivity to inner core shear velocity and attenuation summary we have studied the response of normal modes to perturbations in inner core shear velocity and attenuation using fully coupled mode synthetics our results indicate that i mode pairs n s l n 1 s l are strongly coupled by anelasticity ii this coupling causes shear velocity perturbations to strongly affect the q values of modes through exchange of inner core characteristics iii there is no evidence for a weakly attenuating inner core in shear and iv the discrepancy between attenuation models returned from normal modes and body waves is small these results suggest that inversions for inner core attenuation and shear velocity should be performed simultaneously and should take account of the strong cross coupling due to attenuation

mesozoic plate motion history below the northeast pacific ocean from seismic images of the subducted farallon slab the high resolution seismic imaging of subducted oceanic slabs1 2 has become a powerful tool for reconstructing palaeogeography3 the images can now be interpreted quantitatively by comparison with models of the general circulation of the earth s mantle4 here we use a three dimensional spherical computer model of mantle convection5 6 to show that seismic images of the subducted farallon plate provide strong evidence for a mesozoic period of low angle subduction under north america such a period of low angle subduction has been invoked independently to explain rocky mountain uplift far inland from the plate boundary during the laramide orogeny7 the computer simulations also allow us to locate the largely unknown kula farallon spreading plate boundary the location of which is important for inferring the trajectories of suspect terrain across the pacific basin8

sunglint images of current gradients at high resolution critical angle and directional observing strategy abstract high resolution satellite images of the ocean surface in and around the sunglint often provide unique observations of sub mesoscale upper ocean surface processes local anomalies of wind waves currents or surfactants appear on the images as local anomalies of brightness a quantitative interpretation of those brightness anomalies must relate them to slope properties of the wave field which are to the lowest order described by the mean square slope mss the prevailing paradigm for such interpretation is that of the critical zenith angle it states that for sub critical zenith view angle brightness and mss anomalies have opposite signs and this defines the so called inversion region this prevailing paradigm implicitly builds on the assumption that the mss decomposition between upwind and crosswind components is conserved the mss anomalies are then isotropic and can be reduced to a scalar i e one dimensional quantity in such a case one single sunglint image would be sufficient to retrieve the mss anomaly this isotropic case likely applies for surface wave changes induced by varying wind speed or by surfactants yet satellite and airborne observations at multiple view angles recently revealed anisotropic mss anomalies e g with mss increase in the upwind direction and decrease in the crosswind direction this anisotropic behavior likely characterizes wave modulations by anisotropic surface current gradients this paper details the expected properties of such anisotropic mss modulations it is shown that 1 the classical concept of critical angle does not systematically hold neither for frontal current shear nor for internal wave divergence 2 at least two sunglint images at different zenith and azimuth angles are needed to retrieve the mss anomalies and a single observation is not sufficient 3 a satellite with radiometers looking at multiple zenith angles is capable of providing a geometry favorable to retrieve mss anomalies an illustration is discussed with internal waves observed by the multi angle imaging spectroradiometer misr where the upwind and crosswind components of the retrieved mss anomalies are anisotropic those results provide guidelines to interpret available observations and to help refine strategy for future satellite missions

on the joint distribution of surface elevation and slopes for a nonlinear random sea with an application to radar altimetry the work of longuet higgins 1963 on the effects of wave nonlinearity on the statistics of the sea surface is extended here to obtain the joint distribution of surface elevation and slopes for a nonlinear random sea the results are used to examine the effect of wave nonlinearity on the form of a radar altimeter pulse which is reflected from the sea surface it is shown how wave information may be derived from the return pulse and how this can be used to correct errors in the altimeter mean sea level estimate a problem known as sea state bias

direct measurements of ocean surface velocity from space interpretation and validation the median doppler shift of radar echoes is analyzed in measurements by envisat s advanced synthetic aperture radar asar over the ocean this doppler centroid differs from a predicted signal based on the predicted motion of the satellite and earth this anomaly converted to a surface doppler velocity u d appears to be of geophysical origin two wide swath images over the gulf stream around cape hatteras suggest that u d contains high resolution information on surface currents while on a global scale u d is found to vary with the wind speed in the range direction a simple quantitative forward model is proposed based on a practical two scale decomposition of the surface geometry and kinematics the model represents the effect of the wind through the wave spectrum and gives u d u 10 u c with u 10 and u c as the 10 m wind speed and quasi eulerian current in the line of sight of the radar projected on the sea surface respectively and as a coefficient function of the wind speed wave development and radar geometry it is found that for an incidence angle of 23 0 3 for moderate winds and fully developed seas this model is validated with a global data set of asar wave mode observations with colocated model winds acquired over the global ocean during the years 2003 and 2004 the doppler signal therefore provides the signed parameter u d that can be used to reduce the wind direction ambiguity in the inversion of high resolution wind fields from sar imagery a qualitative validation of current effects is shown for the english channel where tidal currents dominate thus it should be possible to combine this previously ignored geophysical doppler signal with traditional information on sea surface roughness in order to provide very high resolution wind and current fields

synchronous opening of the rio grande rift along its entire length at 25 10 ma supported by apatite u th he and fission track thermochronology and evaluation of possible driving mechanisms one hundred and forty seven new apatite u th he ahe ages are presented from 32 sample locations along the flanks of the rio grande rift in new mexico and colorado these data are combined with apatite fission track aft analyses of the same rocks and modeled together to create well constrained cooling histories for rio grande rift flank shoulders the data indicate rapid cooling due to extension from ca 28 to 5 ma in the sawatch range ca 28 ma to quaternary in the sangre de cristo mountains ca 25 to 5 ma in the albuquerque basin and ca 25 to 10 ma in the southern rio grande rift in southern new mexico rapid cooling of rift flanks followed the oligocene ignimbrite flare up and the northern section of the rio grande rift in colorado exhibits semicontinuous cooling since the oligocene overall however rift flank cooling along the length of the rift was out of phase with high volume magmatism and hence is inferred to have been driven mainly by exhumation due to faulting although each location preserves a unique cooling history when combined with existing ahe data from the gore range in northern colorado and the sandia mountains in new mexico together these data indicate that extension and exhumation of rift shoulders were synchronous along 850 km of the length of the rio grande rift from 25 to 10 ma these time space constraints provide an important new data set with which to develop geodynamic models for initiation and evolution of continental rifting models involving northward propagation of rifting and colorado plateau rotation are not favored as primary mechanisms driving extension instead a geodynamic model is proposed that involves upper mantle dynamics during multistage foundering and rollback of a segment of the farallon plate near the laramide hinge region that extended between the wyoming and se new mexico high velocity mantle domains the first stage of flat slab removal accompanied ca 40 20 ma volcanism in the san juan and mogollon datil ignimbrite centers which initiated asthenospheric upwelling and circulation a second stage involved a ca 30 25 ma detachment of remaining fragments of the farallon slab intensifying asthenospheric upwelling and focusing it along a n s trend beneath colorado and new mexico by 25 ma the north american lithosphere had become weakened critically along this narrow zone so that extension was accelerated resulting in the observed 25 10 ma cooling indicated by the thermochronologic data this developed a central graben with increased fault related high strain rates and resulted in maximum sediment accumulation in the rio grande rift our geodynamic model thus involves oligocene removal of parts of the farallon slab beneath the ignimbrite centers followed by a major oligocene miocene slab break that instigated the discrete n s rio grande rift through focused upper mantle convection beneath the southern rocky mountain rio grande rift region

mantle source volumes and the origin of the mid tertiary ignimbrite flare up in the southern rocky mountains western u s abstract voluminous intermediate to silicic composition volcanic rocks were generated throughout the southern rocky mountains western u s during the mid tertiary ignimbrite flare up principally at the san juan and mogollon datil volcanic fields at both volcanic centers radiogenic isotope data have been interpreted as evidence that 50 or more of the volcanic rocks by mass were derived from mantle derived mafic parental magmas but no consensus exists as to whether melting was largely of lithospheric or sub lithospheric mantle recent xenolith studies however have revealed that thick 100 km fertile and hydrated continental lithosphere was present beneath at least portions of the southern rocky mountains during the mid tertiary the presence of such thick mantle lithosphere combined with an apparent lack of syn magmatic extension leaves conductive heating of lithospheric mantle as a plausible method of generating the mafic magmas that fueled the ignimbrite flare up in this inland region to further assess this possibility we estimated the minimum volume of mantle needed to generate the mafic magmas parental to the preserved mid tertiary igneous rocks conservative estimates of the mantle source volumes that supplied the mogollon datil and san juan volcanic fields are 2 m km3 and 7 m km3 respectively these volumes could have comprised only lithospheric mantle if at least the lower 20 km of the mantle lithosphere beneath the entire southern rocky mountains region underwent partial melting during the mid tertiary and if the resulting mafic magmas were drawn laterally for distances of up to 300 km into each center such widespread melting of lithospheric mantle requires that the lithospheric mantle have been uniformly fertile and primed for melting in the mid tertiary a possibility if the lithospheric mantle had experienced widespread hydration and refrigeration during early tertiary low angle subduction exposure of the mantle lithosphere to hot upwelling sub lithospheric mantle during mid tertiary slab roll back could have then triggered the mantle melting while a plausible source for mid tertiary basaltic magmas in the southern rocky mountains lithospheric mantle could not have been the sole source for mafic magmas generated to the south in that portion of the ignimbrite flare up now preserved in the sierra madre occidental of northern mexico the large mantle source volumes 45 m km3 required to fuel the voluminous silicic ignimbrites deposited in this region 400 k km3 are too large to have been accommodated within the lithospheric mantle alone implying that melting in sub lithospheric mantle must have played a significant role in generating this mid tertiary magmatic event

evolution of surface gravity waves over a submarine canyon 1 the effects of a submarine canyon on the propagation of ocean surface waves are examined with a three dimensional coupled mode model for wave propagation over steep topography whereas the classical geometrical optics approximation predicts an abrupt transition from complete transmission at small incidence angles to no transmission at large angles the full model predicts a more gradual transition with partial reflection transmission that is sensitive to the canyon geometry and controlled by evanescent modes for small incidence angles and relatively short waves model results for large incidence angles are compared with data from directional wave buoys deployed around the rim and over scripps canyon near san diego california during the nearshore canyon experiment ncex wave heights are observed to decay across the canyon by about a factor 5 over a distance shorter than a wavelength however a spectral refraction model predicts an even larger reduction by about a factor 10 because low frequency components cannot cross the canyon in the geometrical optics approximation the coupled mode model yields accurate results over and behind the canyon these results show that although most of the wave energy is refractively trapped on the offshore rim of the canyon a small fraction of the wave energy tunnels across the canyon simplifications of the model that reduce it to the standard and modified mild slope equations also yield good results confirming that evanescent modes and high order bottom slope effects are of minor importance for the energy transformation of waves propagating across depth contours at large oblique angles

evolution of lithospheric strength after thrusting modeling of an eroding thrust belt indicates that immediately after thrusting the lithosphere is about twice as strong as unthickened cratonic lithosphere but after 10 to 20 m y it becomes weaker than cratonic lithosphere reaching a minimum of 40 to 70 of cratonic strength 30 to 100 m y after thrusting this may explain why rifting of thrust belts commonly occurs several tens of million years after thrusting ceases relative weakening results from 1 elevation of the geotherm caused by burial of radioisotope enriched surface rocks and 2 replacement of strong mantle rocks by weak crustal rocks in the lithospheric column low denudation rates enhance weakening by allowing radioisotope enriched rocks to remain buried longer our modeling indicates that 1 magmatism after thrusting is favored by high concentrations of heat producing elements in the lower plate and by slow denudation rates and 2 factors that affect denudation rate such as climate and the development of external drainage can significantly influence evolution of a thrust belt

satellite measurements reveal persistent small scale features in ocean winds four year averages of 25 kilometer resolution measurements of near surface wind speed and direction over the global ocean from the quikscat satellite radar scatterometer reveal the existence of surprisingly persistent small scale features in the dynamically and thermodynamically important curl and divergence of the wind stress air sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields as are the influences of islands and coastal mountains ocean currents such as the gulf stream generate distinctive patterns in the curl field these previously unresolved features have important implications for oceanographic and air sea interaction research

unraveling the geometry of the farallon plate synthesis of three dimensional imaging results from usarray abstract we compare 12 recent three dimensional 3d seismic imaging results that made extensive use of data from the earthscope transportable array ta our goal is to sort out what can be said about the geometry of the farallon plate our main approach is 3d visualization using a kinematic plate motion model as a framework comparison of results from all 12 image volumes indicates that the results are most consistent with a single coherent farallon slab overridden by north american the farallon can be tracked from the trench in the pacific northwest to its remnants in the lower mantle under eastern north america from the trench the lithosphere has a low dip to the volcanic arc immediately east of the arc the slab steepens sharply before undergoing a decrease in dip above the 410 km discontinuity the gently dipping section varies along strike under washington the deflection is minor but to the south the slab flattens to become nearly horizontal beneath southern idaho there is a strong agreement that the high velocity anomaly associated with the slab vanishes under eastern oregon scattered wave imaging results however suggest the top of the anomaly is continuous these can be reconciled if one assumes the wavespeed anomaly has been neutralized by processes linked to the yellowstone system we find that all results are consistent with a 4d kinematic model of the mendocino slab window under nevada and utah in the eastern us the larger scale models all show a lower mantle anomaly related to the older history of farallon subduction the link between the lower mantle and new results in the u s cordillera lies under the high plains where the required usarray coverage is not yet complete image volumes in a unified format are supplied in an electronic supplement

effects of the gulf stream on ocean waves in the present study a third generation numerical wave model is used to study effects of a straight gulf stream and a gulf stream ring on ocean waves in swell and storm conditions the model accounts for all relevant processes of propagation generation and dissipation of the waves including current effects without imposing a priori restraints on the spectral development of the waves the dominating mechanism affecting the waves appears to be current induced refraction even though the short crestedness of the incoming waves tends to mask its effects also in swell conditions depending on wind and wave conditions refraction may trap locally generated waves in the straight gulf stream or it may reflect wave energy back to the open ocean in the gulf stream ring refraction induces a considerable variation in significant wave height and short crestedness but it hardly affects the mean wave direction in storm conditions the processes of generation and dissipation are considerably enhanced in countercurrent situations and reduced following current situations

storm waves focusing and steepening in the agulhas current satellite observations and modeling strong ocean currents can modify the height and shape of ocean waves possibly causing extreme sea states in particular conditions the risk of extreme waves is a known hazard in the shipping routes crossing some of the main current systems modeling surface current interactions in standard wave numerical models is an active area of research that benefits from the increased availability and accuracy of satellite observations we report a typical case of a swell system propagating in the agulhas current using wind and sea state measurements from several satellites jointly with state of the art analytical and numerical modeling of wave current interactions in particular synthetic aperture radar and altimeter measurements are used to show the evolution of the swell train and resulting local extreme waves a ray tracing analysis shows that the significant wave height variability at scales 100 km is well associated with the current vorticity patterns predictions of the wavewatch iii numerical model in a version that accounts for wave current interactions are consistent with observations although their effects are still under predicted in the present configuration from altimeter measurements very large significant wave height gradients are shown to be well captured and also associated with the current vorticity patterns at global scale

postdepositional tilt of the miocene pliocene ogallala group on the western great plains evidence of late cenozoic uplift of the rocky mountains the rocky mountains and adjacent western great plains share a common history of late cenozoic stream incision both epeirogenic uplift and climate change with no associated uplift have been proposed as the cause of thissubcontinental scale erosional episode however the lack of a well defined cenozoic paleoelevation history for the region has hampered our ability to distinguish between the two a tilt analysis of the cheyenne tablelands in the western great plains of wyoming and nebraska provides us with a datum from which postdepositional changes in slope can be determined miocene to earliest pliocene gravels of the ogallala group 17 5 5 ma cap the tablelands which currently tilt down to the east at slopes as great as 10 2 however paleohydraulic analysis of the ogallala gravels indicates depositional slopes of 10 3 to 10 4 implying a postdepositional increase in tilt if a hinge point at the eastern edge of the cheyenne tablelands is assumed this tilt translates into differential uplift of 680 m 815 410 m at the western edge of the great plains flexural isostatic rebound of the tablelands due to known young erosion in surrounding basins only produces a few hundred meters of uplift therefore even if all of the recent erosion in the region can be attributed to climate change the resulting rebound is insufficient to account for the observed uplift of the tablelands thus the tilting of the cheyenne tablelands is most consistent with broad wavelength tectonic uplift centered under the rocky mountains initiated during ogallala deposition and continuing since deposition ceased

apatite fission track analysis apatite fission track aft analysis has been widely used during the past 30 years to constrain the low temperature thermal histories of many igneous metamorphic and sedimentary rocks in a wide range of geological settings applicable geological settings include orogenic belts rifted margins faults sedimentary basins cratons and mineral deposits the types of geologic problems that can be addressed include the timing and rates of tectonic events sedimentary basin evolution the timing of hydrocarbon generation and ore mineralization the absolute age of volcanic deposits the effects of major climatic changes on the near surface geothermal gradient and long term landscape evolution early work by naeser 1967 and wagner 1968 1969 first established the basic procedures that enabled the fission track dating method to be applied routinely to these geologic problems fleischer et al 1975 summarized the early studies of the broader discipline of nuclear track detection in different solid state materials more recent comprehensive overviews of fission track applications have been provided by naeser and mcculloh 1989 wagner and van den haute 1992 gallagher et al 1998 van den haute and de corte 1998 dumitru 2000 and gleadow et al 2002 etched natural fission tracks in several apatite grains are shown in figure 1 successful aft analysis is limited by the following 1 the availability of apatite from which useful aft data can be obtained often due to a lack of apatite of sufficient grain size and quality within available rock types or alternatively the lack of available rock samples due to minimal outcrop exposure or other reasons 2 economic considerations in terms of the time and money required to obtain sufficient aft data 3 the inherent limitations of aft data to resolve geological thermal history information often related to limited numbers of accumulated spontaneous fission tracks due to

cenozoic thermal mechanical and tectonic evolution of the rio grande rift careful documentation of the cenozoic geologic history of the rio grande rift in new mexico reveals a complex sequence of events at least two phases of extension have been identified an early phase of extension began in the mid oligocene about 30 ma and may have continued to the early miocene about 18 ma this phase of extension was characterized by local high strain extension events locally 50 100 regionally 30 50 low angle faulting and the development of broad relatively shallow basins all indicating an approximately ne sw 25 extension direction consistent with the regional stress field at that time extension events were not synchronous during early phase extension and were often temporally and spatially associated with major magmatism a late phase of extension occurred primarily in the late miocene 10 5 ma with minor extension continuing to the present it was characterized by apparently synchronous high angle faulting giving large vertical strains with relatively minor lateral strain 5 20 which produced the modern rio grande rift morphology extension direction was approximately e w consistent with the contemporary regional stress field late phase graben or half graben basins cut and often obscure early phase broad basins early phase extensional style and basin formation indicate a ductile lithosphere and this extension occurred during the climax of paleogene magmatic activity in this zone late phase extensional style indicates a more brittle lithosphere and this extension followed a middle miocene lull in volcanism regional uplift of about 1 km appears to have accompanied late phase extension and relatively minor volcanism has continued to the present we have estimated geotherms and calculated lithospheric strength curves for the two phases of extension using geologic data to constrain earlier events and geophysical data to constrain the modern geotherm and crustal structure a high geotherm was deduced for early phase extension resulting in a shallow crustal brittle ductile transition and negligible mantle strength the lithosphere cooled after early phase extension resulting in a deeper crustal brittle ductile transition and perhaps more significantly a considerable zone of mantle strength immediately beneath the moho these results indicate that early phase extensional style was controlled by a crustal decollement near the brittle ductile transition which was prevented during late phase extension by significant strength in the uppermost mantle late cenozoic uplift of the rift zone cannot be explained by crustal thinning during extension and geotherm evolution predicted from simple cooling however this uplift does not appear to be restricted to the rift zone and pliocene to recent volcanism and heat flow data suggest that uplift may be caused by magmatic thickening of the crust perhaps unrelated to rifting the complex interrelationship among regional and local prerifting synrifting and postrifting events in the rio grande rift suggests that rifting at least in this region should not be considered in isolation of other geologic events

surface roughness imaging of currents shows divergence and strain in the wind direction images of sea surface roughness for example obtained by synthetic aperture radars sar or by radiometers viewing areas in and around the sun glitter at times provide clear observations of meso and submesoscale oceanic features interacting with the surface wind waves particular deformation properties of surface currents are responsible for those manifestations ignoring other sources of surface roughness variations the authors limit their discussion to the mean square slope mss variability this study confirms that vortical currents and currents with shear in the wind direction shall not be expressed in surface roughness images only divergent currents or currents with no divergence but strained in the wind direction can exhibit surfaceroughnesssignatures morespecifically nondivergentcurrentsmightbetracedwitha458sensitivityto the wind direction a simple method is proposed in order to interpret high resolution roughness images where roughness variations are proportional to u x 1 a y y a linear combination of the along wind and crosswind current gradients the polarization parameter a depends upon the sensor look direction and the directional properties of the surface waves selected by the sensor the use of multiple look directions or possible acquisitions with different wind directions shall thus help to retrieve surface currents from surface roughness observations

raising the colorado plateau shallow marine rocks exposed on the 2 km high 45 km thick colorado plateau in the western united states indicate that it was near sea level during much of the phanerozoic isostatic calculations however illuminate the difficulty in maintaining a 45 km thick crust at or near sea level we propose that an isostatically balanced 30 km thick proto colorado plateau crust was thickened during the late cretaceous to early tertiary by intracrustal flow out of an overthickened sevier orogenic hinterland this plateau would have been supported by a thick 70 km crustal root which is proposed to have been the source region for hot and weak mid crustal material that flowed eastward from the plateau toward the low elevation proto colorado plateau

cenozoic tectonics of western north america controlled by evolving width of farallon slab the basin and range province of western north america exemplified by the alternating mountain ridge and valley landscapes across nearly the entire u s state of nevada started to form 50 million years ago through a series of extensions of the continental crust prior to that massive mountain building collisions at the boundary between north america and the pacific ocean formed a subduction zone and compressed the continent by combining observations of global subduction zone velocities with numerical modeling schellart et al p 316 1 demonstrate that the thinning of the subducting portion of the oceanic plate controlled how and when the transition from compression to extension occurred even today where the much smaller remnant oceanic plate continues to slowly subduct below north america in the pacific northwest the width of the slab and not its age controls the velocity of subduction indeed this relation may explain the dynamics of other modern subduction zones from south america to japan 1 lookup doi 10 1126 science 1190366

a physical model of sea wave period from altimeter data a physical model for sea wave period from altimeter data is presented physical roots of the model are in recent advances of the theory of weak turbulence of wind driven waves that predicts the link of instant wave energy to instant energy flux to from waves the model operates with wave height and its spatial derivative and does not refer to normalized radar cross section 0 measured by the altimeter thus the resulting formula for wave period does not contain any empirical parameters and does not require features of particular satellite altimeter or any calibration for specific region of measurements a single case study illustrates consistency of the new approach with previously proposed empirical models in terms of estimates of wave periods and their statistical distributions the paper brings attention to the possible corruption of dynamical parameters such as wave steepness or energy fluxes to from waves when using the empirical approaches applications of the new model to the studies of sea wave dynamics are discussed

tidal modulation of surface gravity waves in the gulf of maine abstractthis study examines the tidal modulation of surface gravity waves in the gulf of maine gom by using in situ observations and numerical model results analysis of observational data demons

mantle provinces under north america from multifrequency p wave tomography this is a survey of mantle provinces large scale seismic anomalies under north america from the surface down to 1500 1800 km depth the underlying p velocity model was obtained by multifrequency tomography a waveform based method that systematically measures and models the frequency dependence of teleseismic body waves a novel kind of three dimensional rendering technique is used to make the considerable structural complexities under north america accessible in the transition zone and below the north american mantle is dominated by seismically fast provinces which represent distinct subduction episodes of the farallon plate i attempt to date and interpret the various slab fragments by reconciling their present positions with paleotrench locations from plate tectonic reconstructions and with major geologic surface episodes differences in vertical sinking velocity have led to large vertical offsets across adjacent coeval slabs some of the mantle provinces have not been discussed much previously including 1 a seismically slow blanket overlying the oldest farallon subduction along the eastern continental margin 2 a transition zone slab coeval with the laramide orogeny ca 80 60 myr which i discuss in analogy to the stagnant slab subduction style commonly found in the western pacific today 3 the lower mantle root of present day cascadia subduction which may have started out as intraoceanic subduction 4 a lower mantle slab under arizona and new mexico the last material to subduct before strike slip motion developed along the san andreas boundary and 5 two narrow plate tears thousands of kilometers long one of which is the subducted conjugate of the mendocino fracture zone

complex subduction and small scale convection revealed by body wave tomography of the western united states upper mantle abstract new high resolution p and s wave tomography of the united states upper mantle from the pacific coast to the great plains reveals strong multi scale heterogeneity closely correlated with tectonic and magmatic activity we invert teleseismic travel time residuals from the earthscope transportable array and more than 1700 additional temporary and permanent stations for 3 d velocity perturbations to a depth of 1000 km the inversion uses recent advances in western u s crust models to better isolate the mantle component of travel time residuals and frequency dependent 3 d sensitivity kernels to map travel time residuals measured in multiple frequency bands into velocity structure in addition to separate v p and v s models we jointly invert the two datasets for v p v s perturbations by imposing a smoothness constraint on the ln v s ln v p field the joint inversion helps us identify regions where partial melt is probable the amplitude of v p v s and v p v s variations is greatest in the upper 200 km of the mantle and the form of velocity anomalies suggests a provincially heterogeneous lithosphere and the occurrence of widespread small scale convection partially molten mantle is inferred beneath yellowstone and the eastern snake river plain srp the salton trough and the clear lake volcanic field the inferred depth extent of partial melt is consistent with a generally hydrated upper mantle and elevated temperatures beneath the eastern srp and yellowstone despite continuous subduction since the cretaceous the distribution of sub lithospheric high velocity anomalies is dissected similar to other recent studies based on our new tomography models western u s geologic history and plate tectonic reconstructions we infer patchy and incomplete removal of the flat subducting laramide slab and slab tearing associated with eocene accretion in the northwestern u s

geomorphic and tectonic forcing of late cenozoic warping of the colorado piedmont late cenozoic warping of the colorado piedmont involved interplay of tectonic forcing river erosion and isostatic response to erosion modeled erosional isostasy closely replicates the observed pattern of deformation but accounts for only about half its magnitude the remainder reflects tectonic rock uplift that increases southward across the piedmont likely reflecting proximity to the northward propagating rio grande rift this differential uplift triggered differential erosion concentrated on southern piedmont river systems particularly the arkansas river which led in turn to differential isostatic rock uplift focused on the arkansas drainage covariation of tectonic uplift erosion and isostatic compensation across the piedmont reflects a positive feedback between uplift induced erosion and erosion induced isostasy which has progressed to the point that isostatic uplift is approximately equal to the initial tectonic forcing

wave current interaction between hurricane matthew wave fields and the gulf stream abstracthurricanes interact with the gulf stream in the south atlantic bight sab through a wide variety of processes which are crucial to understand for prediction of open ocean and coastal haza

ocean wave directional spectra and wave current interaction in the agulhas from the shuttle imaging radar b synthetic aperture radar sir b synthetic aperture radar ocean wave spectra for a 200 km pass crossing the agulhas current off the coast of africa are analyzed a significant enhancement of one spectral peak along the northern edge of the current is attributed both to amplification of the waves by refraction dominated wave current interaction and to transient specular backscatter contributions spatially correlated to the waves

was the laramide orogeny related to subduction of an oceanic plateau numerous models have been presented to explain the late cretaceous early cenozoic laramide orogeny which affected the foreland region of the western cordillera within the us1 the most attractive models invoke low angle subduction2 4 which can develop for various reasons5 6 evidence from south america indicates that one such reason may be the subduction of buoyant ocean floor we here extend the low angle subduction models by attributing the shallowing of the subduction angle during the laramide orogeny to subduction of a large oceanic plateau of anomalously thick and buoyant oceanic crust pacific plate history indicates that a twin to the hess rise may represent the oceanic plateau that triggered laramide events

two stage subduction history under north america inferred from multiple frequency tomography eastward subduction of oceanic tectonic plates has shaped the geologic history of western north america over the past 150 million years the mountain building and volcanism that brought forth the spectacular landscapes of the west are credited to the vast ancient farallon plate which interacted mechanically and chemically with the overlying continent as it plunged back into the mantle here we use finite frequency travel time and amplitude measurements of teleseismic p waves in seven frequency bands to obtain a high resolution tomographic image to approx1 800 km depth we discover several large previously unknown pieces of the plate which show that two distinct stages of whole mantle subduction are present under north america the currently active one descends from the pacific northwest coast to 1 500 km depth beneath the great plains whereas its stalled predecessor occupies the transition zone and lower mantle beneath the eastern half of the continent we argue that the separation between them is linked to the laramide era 70 50 myr ago a time of unusual volcanism and mountain building far inland generally explained by an episode of extremely flat subduction

colorado plateau magmatism and uplift by warming of heterogeneous lithosphere the forces that drove rock uplift of the low relief high elevation tectonically stable colorado plateau are the subject of long standing debate while the adjacent basin and range province and rio grande rift province underwent cenozoic shortening followed by extension the plateau experienced approximately 2 km of rock uplift without significant internal deformation here we propose that warming of the thicker more iron depleted colorado plateau lithosphere over 35 40 myr following mid cenozoic removal of the farallon plate from beneath north america is the primary mechanism driving rock uplift in our model conductive re equilibration not only explains the rock uplift of the plateau but also provides a robust geodynamic interpretation of observed contrasts between the colorado plateau margins and the plateau interior in particular the model matches the encroachment of cenozoic magmatism from the margins towards the plateau interior at rates of 3 6 km myr 1 and is consistent with lower seismic velocities and more negative bouguer gravity at the margins than in the plateau interior we suggest that warming of heterogeneous lithosphere is a powerful mechanism for driving epeirogenic rock uplift of the colorado plateau and may be of general importance in plate interior settings

mantle convection and the recent evolution of the colorado plateau and the rio grande rift valley the colorado plateau contains late cretaceous marine strata that are at a mean elevation of 2 km the timing and amount of uplift since the cretaceous has generated considerable debate with the exception of a few studies topography supported by vertical stresses generated by viscous fl ow in the mantle has not been explicitly considered to contribute to the elevation of this region herein we compute the viscous fl ow beneath north america that is driven by density anomalies inferred from joint seismic geodynamic modeling we fithat the colorado plateau overlies a strong mantle upwelling that is coupled to the sinking farallon slab currently beneath the eastern united states consequently the colorado plateau is currently a focused dynamic topography high within the western u s cordillera moreover this strong upwelling impacts the base of the lithosphere at an oblique angle east of the plateau directly below the rio grande rift we attribute this fl ow as being responsible for some of the recent magmatic activity along the jemez lineament as well as contributing to the recent rifting process in the rio grande rift valley

freak waves under typhoon conditions benjamin feir index bfi and directional spread are measures of nonlinearfour wave interactions and resultant indices of possible conditions for freak waves temporal spatial distributions of bfi and directional spread are examined with numericalsimulations of a spectral wave model using typhoon conditions the spatial distributionsof wave characteristics such as significant wave height wave period bfi and directionalspread are different from each other around the eye of the typhoon bfi is significantlylarge in the fourth quadrant of the typhoon while waves are steep and have narrowfrequencies and directional spectra freak waves resulting from nonlinear four wave waveinteractions have a greater potential of occurring in the fourth quadrant of the typhoonthan in the other quadrants furthermore crossing sea states from two wind wave systemscan be observed behind the eye of the typhoon the crossing two wind systems arealso dangerous sea states although as observed they are closer to linear wave conditions finally the characteristics of possible freak wave conditions during typhoons areverified with field data

paleoearthquakes and eolian dominated fault sedimentation along the hubbell spring fault zone near albuquerque new mexico the hubbell spring fault zone forms the modern eastern margin of the rio grande rift in the albuquerque basin of north central new mexico knowledge of its seismic potential is important because the fault zone transects kirtland air force base sandia national laboratories and underlies the southern albuquerque metropolitan area no earthquakes larger than m l 5 5 have been reported in the last 150 years in this region so we excavated the first trench across this fault zone to determine its late quaternary paleoseismic history our trench excavations revealed a complex 16 m wide fault zone overlain by four tapered blankets of mixed eolian sand and minor colluvium that we infer were deposited after four large magnitude surface rupturing earthquakes although the first oldest rupture event is undated we used luminescence thermoluminescence and infrared stimulated luminescence ages to determine that the subsequent three rupture events occurred about 56 6 29 3 and 12 1 ka these ages yield recurrence intervals of 27 and 17 k y between events and an elapsed time of 12 k y since the latest surface rupturing paleoearthquake slip rates are not well constrained but our preferred average slip rate since rupture event 2 post 56 ka is 0 05 mm yr and interval slip rates between the last three events are 0 06 and 0 09 mm yr respectively vertical displacements of 1 2 m per event and probable rupture lengths of 34 43 km indicate probable paleoearthquake magnitudes m s or m w of 6 8 7 1 future earthquakes of this size likely would cause strong ground motions in the albuquerque metropolitan area

mapping the agulhas current from space an assessment of asar surface current velocities 1 over 2 years of surface current information collected in the agulhas current region and derived from the doppler centroid anomalies of envisat s advanced synthetic aperture radar asar are examined the sources of errors and potential use of asar surface current velocities for oceanographic research are assessed asar surface current velocities are compared to surface drifter data and merged altimetry observations maps of sea surface temperature are used to establish the asar s capacity to capture the synoptic circulation discrepancies between observed and predicted asar velocities result predominantly from inadequate wind corrections combined with radar incidence angles below 30 occasionally observed wind induced outliers cause a bias in the estimated asar velocities but do not affect the ability of the asar to systematically image regions of strong surface current flow and shear time averaged maps of asar derived surface current velocity seem able to accurately capture the position as well as the intensity of the agulhas current the ability of the asar to pick up the smaller features of the circulation along the shelf break also shows that variability along the agulhas bank is of the same order of magnitude as that observed in the agulhas retroflection asar surface current velocities offer a very good complement to altimetry in regions where the mean dynamic topography is poorly resolved the quasi synoptic nature of asar acquisitions combined with the relatively high resolution of asar surface current velocities also make it attractive for studies of submesoscale processes and western boundary current dynamics

tectonomagmatic evolution of cenozoic extension in the north american cordillera the spatial and temporal distributions of cenozoic extension and magmatism in the cordillera suggest that the onset of major crustal extension at a particular latitude was confined to a relatively narrow belt 100 km pre extension and followed the onset of intermediate and silicic magmatism by no more than a few million years extension began in early eocene time in southern british columbia northern washington idaho and montana farther s extension began at about the eocene oligocene boundary in the great basin and slightly later in the mojave sonora desert region the intervening area at the latitude of las vegas remained quiescent until mid miocene time compositional and isotopic characteristics of most pre miocene magmas are consistent with their containing major components of melted continental crust in mid miocene time two major changes occurred widening of the area of extension and the widespread appearance of basaltic magmas the area affected by extension from southwestern montana to the lake mead region widened to several hundred kilometres by this time extension in southern british columbia northern washington and northern montana had ceased probably before the end of the eocene and extension s of lake mead except in the gulf of california had waned regions affected by the broader belt of extension during late miocene pliocene and quaternary time experienced basaltic magmatism which began along a central rift zone in the northern part of the region and which had within a few million years spread to include most of the region later basaltic activity has tended to concentrate in restricted zones especially near the margins of the extended area we recognize a correlation between the amount of earlier crustal thickening and cenozoic extension and between the length of time after shortening but before extension and the degree to which a given region was intruded by late cretaceous plutons the localization of extension in areas of previous crustal thickening and the dependence of the timing of extension on the thermal state of the overthickened crust is consistent with a simple thermal mechanical model developed in a companion paper sonder et al this raises the possibility that stresses inherent in the north american plate dominated over plate interaction forces as controls of the cenozoic tectonomagmatic evolution of the north american cordillera especially in its earlier stages

distributed deformation across the rio grande rift great plains and colorado plateau we use continuous measurements of gps sites from across the rio grande rift great plains and colorado plateau to estimate present day surface velocities and strain rates velocity gradients from five east west profiles suggest an average of 1 2 nanostrains yr east west extensional strain rate across these three physiographic provinces the extensional deformation is not concentrated in a narrow zone centered on the rio grande rift but rather is distributed broadly from the western edge of the colorado plateau well into the western great plains this unexpected pattern of broadly distributed deformation at the surface has important implications for our understanding of how low strain rate deformation within continental interiors is accommodated

swell propagation through submesoscale turbulence abstractthe propagation of ocean swells from generating regions to remote coastlines is affected by submesoscale turbulence in the surface flow field the presence of submesoscale velocity variatio

morphological responses of a long narrow estuary to a restoration scheme and a major storm abstract the fenghe river estuary fre a long narrow estuary located in the west coast new area of qingdao china has suffered severe sediment siltation in the downstream of a tidal barrier over the past decades in order to relieve the sediment siltation and promote local economic development a restoration scheme with new shoreline and bathymetry was proposed for the fre in this study a wave current sediment coupled model was established for the fre based on the numerical model mike21 which was well validated against the observation the model was then applied to estimate hydrodynamic and morphological responses of the long narrow estuary to the restoration scheme and a major storm the numerical results indicate that the restoration scheme has a great influence on the current fields in the estuarine channel resulting in the current speed in the channel to be more spatially uniform under the restoration scheme the spatial pattern of suspended sediment concentration in the estuary is redistributed due to the change of local tidal asymmetry associated with geometry and topography variation the interaction between wave and current during a storm increases bed shear stress on the tidal flat leading to large erosion on the tidal flat and severe sediment siltation in the estuarine channel

circum antarctic shoreward heat transport derived from an eddy and tide resolving simulation almost all heat reaching the bases of antarctica s ice shelves originates from warm circumpolar deep water in the open southern ocean this study quantifies the roles of mean and transient flows in transporting heat across almost the entire antarctic continental slope and shelf using an ocean sea ice model run at eddy and tide resolving 1 48 horizontal resolution heat transfer by transient flows is approximately attributed to eddies and tides via a decomposition into time scales shorter than and longer than 1 day respectively it is shown that eddies transfer heat across the continental slope ocean depths greater than 1 500 m but tides produce a stronger shoreward heat flux across the shelf break ocean depths between 500 m and 1 000 m however the tidal heat fluxes are approximately compensated by mean flows leaving the eddy heat flux to balance the net shoreward heat transport the eddy driven cross slope overturning circulation is too weak to account for the eddy heat flux this suggests that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around antarctica though likely modulated by tides and surface forcing

wave attenuation through an arctic marginal ice zone on 12 october 2015 2 numerical modeling of waves and associated ice breakup many processes that affect ocean surface gravity waves in sea ice give rise to attenuation rates that vary with both wave frequency and amplitude here we particularly test the possible effects of basal friction scattering by ice floes and dissipation in the ice layer due to dislocations and ice breakup by the waves the possible influence of these processes is evaluated in the marginal ice zone of the beaufort sea where extensive wave measurements were performed the wave data includes in situ measurements and the first kilometer scale map of wave heights provided by sentinel 1 sar imagery on 12 october 2015 up to 400 km into the ice we find that viscous friction at the base of an ice layer gives a dissipation rate that may be too large near the ice edge where ice is mostly in the form of pancakes further into the ice where larger floes are present basal friction is not sufficient to account for the observed attenuation in both regions the observed narrow directional wave spectra are consistent with a parameterization that gives a weak effect of wave scattering by ice floes for this particular event with a dominant wave period around 10 s we propose that wave attenuation is caused by ice flexure combined with basal friction that is reduced when the ice layer is not continuous this combination gives realistic wave heights associated with a 100 200 km wide region over which the ice is broken by waves as observed in sar imagery

propagation of swell across a wide continental shelf the transformation of ocean swell across a wide shallow nominal depths 25 50 m continental shelf is examined with data from a 100 km long transect of bottom pressure recorders extending from the shelf break to the beach at duck north carolina the analysis is restricted to periods with light winds when surface boundary layer processes e g wave generation by wind and wave breaking in the form of whitecaps are expected to be relatively unimportant the majority of the observations with low energy incident swell conditions significant wave heights 1 m shows weak variations in swell energy across the shelf in qualitative agreement with predictions of a spectral refraction model although the predicted ray trajectories of waves propagating over the irregular shelf bathymetry are quite sensitive to the deep water incident wave directions the predicted spatial energy variations for broadbanded wave fields are small and relatively insensitive to incident wave conditions consistent with the observations whereas swell dissipation on the shelf appears to be insignificant in low energy conditions strong attenuation of swell energy levels a factor 4 between the shelf break and nearshore sites was observed in high energy conditions significant wave height 2 5 m this decay not predicted by the energy conserving refraction model indicates that dissipative bottom boundary layer processes can play an important role in the transformation of swell across wide continental shelves

beyond goce for the ocean circulation estimate synergetic use of altimetry gravimetry and in situ data provides new insight into geostrophic and ekman currents accurate estimate of ocean surface currents is both a challenging issue and a growing end users requirement in this paper ocean currents are calculated at two levels surface and 15 m depth as the sum of the geostrophic and ekman components first a new global 14 mean dynamic topography called the cnes cls13 mdt has been calculated and is now available for use by the oceanographic community by exploiting information from surface drifters and argo floats the new mdt resolves spatial scales beyond the resolution permitted by the recent gravity and ocean circulation experiment goce geoid models 125 km associated mean geostrophic speeds in strong currents are increased by 200 on average compared to goce based mean currents in addition for the first time a two level monthly empirical ekman model that samples a spiral like behavior is estimated we show that combining both pieces of information leads to improved ocean currents compared to other existing observed products

mesoscale to submesoscale transition in the california current system part i flow structure eddy flux and observational tests in computational simulations of an idealized subtropical eastern boundary upwelling current system similar to the california current a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to o 1 km this first paper in a series of three describes the transition in terms of the emergent flow structure and the associated time averaged eddy fluxes in addition to the mesoscale eddies that arise from a primary instability of the alongshore wind driven currents significant energy is transferred into submesoscale fronts and vortices in the upper ocean the submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers in turn some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll up vortices associated with this phenomenon are a large vertical vorticity and rossby number a large vertical velocity relatively flat horizontal spectra contrary to the prevailing view of mesoscale dynamics a large vertical buoyancy flux acting to restratify the upper ocean a submesoscale energy conversion from potential to kinetic a significant spatial and temporal intermittency in the upper ocean and material exchanges between the surface boundary layer and pycnocline comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean with characteristics similar to the simulations

deep probe imaging the roots of western north america analysis of the lithoprobe deep probe and southern alberta refraction experiment data sets focusing on the region between deep probe shots 43 and 55 has resulted in a continental scale velocity structural model of the lithosphere of platformal western laurentia reaching depths of 150 km three major lithospheric blocks were investigated i the hearne province a typical continental archean cratonic province lying beneath the western canada sedimentary basin ii the wyoming province an even older block of phanerozoic modified archean crust with an enigmatic lower lithosphere and iii the yavapai mazatzal province proterozoic terranes underlying the colorado plateau and southern rocky mountains in this study the northern two of these regions are investigated with a modified ray theoretical traveltime inversion routine that respects the spherical geometry of the earth the resulting crustal velocity structure combined with supporting geological and geophysical data reveals that the medicine hat block mhb lying between the hearne and wyoming provinces is a third independent archean crustal block the subcrustal lithosphere along the profile is homogeneous in velocity structure but two significant northward dipping reflectors are apparent and interpreted as relic subduction zones associated with sutures between the three archean blocks the hearne crust is typical of an archean shield or platform both in its thickness of 34 50 km and its seismic velocity structure the crust of the archean mhb and wyoming province which ranges in thickness from 49 to 60 km includes a 10 30 km thick high velocity layer interpreted to be proterozoic in age such a feature is unexpected beneath archean crustal provinces but if the region is considered to be the remanent marginal portion of a larger archean continent then the interpreted proterozoic underplating and lack of an archean lithospheric root can be explained the variable topography along the reflective upper and lower boundaries of this layer especially within the mhb suggests considerable variability in its emplacement and subsequent tectonic history

drift and mixing under the ocean surface revisited stratified conditions and model data comparisons 1 a one dimensional model of the ocean near surface currents is presented it includes the enhanced near surface mixing due to the waves the wave induced stokes drift the stokes coriolis sc effect and the stratification near surface current shears from this model are compared with the shears of the quasi eulerian currents measured using a wave following platform during the shelf mixed layer experiment smile it is shown that the downwind current shears observed during smile are well modeled however the observed crosswind shears are in poor agreement with the model the stokes coriolis sc term could qualitatively explain this misfit but it is one order of magnitude too weak the ekman stokes spiral of the model is compared with the spiral observed during the long time series of measurements long term upper ocean study 3 the effects of stratification are taken into account the mean velocity profiles of the model closely agree with observations however there is no evidence of the sc effect on the shape of the observed current profile the observed profile is found to be a consequence of the current rectification due to the time varying stratification the sc effect calculated from a numerical wave hindcast is weak but should have been observed in fact it is estimated that the wave induced bias in the current measurements is larger than the sc effect finally it is shown that the variation of surface drift with wave age which was estimated to be small in unstratified conditions is important in the presence of shallow mixed layers

observations of surface wave current interaction abstractwave current interaction can result in significant inhomogeneities of the ocean surface wave field including modulation of the spectrum wave breaking rates and wave statistics this study presents novel airborne observations from two experiments 1 the high resolution air sea interaction hires experiment with measurements across an upwelling jet off the coast of northern california and 2 an experiment in the gulf of mexico with measurements of waves interacting with the loop current and associated eddies the significant wave height and slope varies by up to 30 because of these interactions at both sites whereas whitecap coverage varies by more than an order of magnitude whitecap coverage is well correlated with spectral moments negatively correlated with the directional spreading and positively correlated with the saturation surface wave statistics measured in the gulf of mexico including wave crest heights and lengths of crests per unit surface area show good agreement with seco

cooling rates and the depth of detachment faulting at oceanic core complexes evidence from zircon pb u and u th he ages oceanic detachment faulting represents a distinct mode of seafloor spreading at slow spreading mid ocean ridges but many questions persist about the thermal evolution and depth of faulting we present new pb u and u th he zircon ages and combine them with magnetic anomaly ages to define the cooling histories of gabbroic crust exposed by oceanic detachment faults at three sites along the mid atlantic ridge ocean drilling program odp holes 1270d and 1275d near the 15 20 n transform and atlantis massif at 30 n closure temperatures for the pb u 800 c 850 c and u th he 210 c isotopic systems in zircon bracket acquisition of magnetic remanence collectively providing a temperature time history during faulting results indicate cooling to 200 c in 0 3 0 5 myr after zircon crystallization recording time averaged cooling rates of 1000 c 2000 c myr assuming the footwalls were denuded along single continuous faults differences in pb u and u th he zircon ages together with independently determined slip rates allow the distance between the 850 c and 200 c isotherms along the fault plane to be estimated calculated distances are 8 4 4 2 km and 5 0 2 1 km from holes 1275d and 1270d and 8 4 1 4 km at atlantis massif estimating an initial subsurface fault dip of 50 and a depth of 1 5 km to the 200 c isotherm leads to the prediction that the 850 c isotherm lies 5 7 km below seafloor at the time of faulting these depth estimates for active fault systems are consistent with depths of microseismicity observed beneath the hypothesized detachment fault at the tag hydrothermal field and high temperature fault rocks recovered from many oceanic detachment faults

ocean surface current retrieval from space the sentinel 2 multispectral capabilities abstract the sentinel 2 multispectral instrument msi collects multiple spectral band images corresponding to specific sensing wavelengths and spatial resolutions i e 10 m 20 m and 60 m respectively images are collected one at the time with a given time lag between observations under favorable conditions spatio temporal characteristics of propagating ocean surface waves can thus uniquely be retrieved a method for surface current vector field reconstruction is then developed demonstrated over different deep ocean regions the retrieved surface current fields well compare with medium resolution ocean circulation model or derived velocities from altimeter measurements at finer scales the surface wave conservation law is recovered with the associated relationship between current vorticity and wave ray curvature over shallow water regions the wave propagation properties well follow sea depth variations consistent with etopo1 data finally time lag between detector bands can also be exploited to estimate speed and direction properties of detected surface wave breaking whitecaps an analysis of velocity reconstruction errors further reveals that sentinel 2 msi inter channel co registration is realized with an accuracy better than 0 1 pixel overall these results confirm very promising capabilities of optical imagery to provide direct surface current velocity measurements from space over relatively large areas o 100 km with a spatial resolution down to o 1 km

enhanced freak wave occurrence with narrow directional spectrum in the north sea 1 wind and wave records obtained from the kvitebjorn platform 2 3 e 61 0 n 190 m deep in the northern north sea from 2003 to 2005 were analyzed among the 2723 20 min records taken during storm conditions 57 cases included freak waves exceeding twice the significant wave height comparisons between various wave parameters and the freak wave occurrence index did not show any significant correlation thus the in situ wave record was used to select the days when relatively more or less freak waves were observed the days were classified into freakish and non freakish days respectively on freakish days the icelandic low was enhanced hindcasts performed by a third generation wave model suggest that this synoptic atmospheric pressure difference produces approximately 7 6 degrees narrower directional spreading of the wave spectra during freakish days at the kvitebjorn platform this result is consistent with the physical mechanism of freak wave generation through nonlinear self focusing in random wave fields

space time patterns and tectonic controls of tertiary extension and magmatism in the great basin of the western united states structural and stratigraphic relations in the great basin indicate widespread pre middle miocene crustal extension that appears to define two north trending belts most extension in these belts was oligocene age but locally it began earlier or lasted into early miocene time the eastern belt straddles the nevada utah border and includes the snake range nevada area with its southern end near 37 5 n and its western edge at the seaman butte mountains breakaway the southern boundary of the eastern belt is occupied by the 26 15 ma caliente caldera complex and approximately coincides with the present east west trending margin of the great basin north of saint george utah crust north of this boundary extended approximately east west before volcanism began at 30 32 ma but to the south extension began after about 15 ma this boundary may have been a rooted zone of left slip faults that allowed the footwall of the stampede detachment to move west relative to unextended terrain to the south the eastern margin of the eastern belt is probably located near the present eastern edge of the great basin but its northern end is poorly defined the western belt runs from the funeral and grapevine mountains california to the ruby mountains nevada and north northeast to the albion range idaho tens of kilometers of crustal extension occurred at least locally in both belts but magnitude of extension is poorly known for large areas of each tertiary volcanism in the great basin began in the north in eocene time with predominantly effusive volcanism and swept southward ending with voluminous oligocene miocene ignimbrite eruptions from calderas in an irregular discontinuous belt between marysvale utah and reno nevada a result of the south ward migration of volcanism is that the onset of extension in both belts was syn or post volcanic in the north but was pre volcanic in the south late paleogene extension and crustal magmatism coincided in both time and space only locally where south migrating magmatism overlapped active north south trending extensional belts most calderas in the southern great basin formed in previously extended belts or on their margins southward migration of ignimbrite sources was apparently blocked by unextended crust to the south in contrast volcanism north of the ignimbrite province was dominated by nonexplosive effusion of lava prior to or during crustal extension this is consistent with observations in the southern basin and range where volcanism and crustal extension were generally synchronous and volcanism was dominantly effusive thus caldera formation may be controlled by the distribution of upper crustal extension although the physical mechanism for this control remains speculative the space time patterns of late paleogene extension in the great basin are consistent with extension being triggered by thermal weakening of subducted oceanic lithosphere rather than by effects transmitted from the plate margin but being driven by gravitational collapse of thick crust space time patterns of tertiary volcanism in the basin and range also appear to conform to patterns of thermal weakening or destruction of the subducted slab both active and passive rifting mechanisms are inapplicable on the scale of the extensional belts because both predict close spatial and temporal association of extension and magmatism which is not generally observed

p and s wave tomography of the mantle beneath the united states mantle seismic structure beneath the united states spanning from the active western plate margin to the passive eastern margin was imaged with teleseismic p and s wave traveltime tomography including usarray data up to may 2014 to mitigate artifacts from crustal structure 5 40 s rayleigh wave phase velocities were used to create a 3 d starting model major features of the final p and s models include two distinct low velocity anomalies at depths of 60 300 km beneath the central and northern appalachians and passive margin the central appalachian low velocity anomaly coincides with eocene basaltic magmatism and the northern anomaly is located along the cretaceous track of the great meteor hot spot at depths of 300 700 km beneath the central and eastern u s large high velocity anomalies are inferred to be remnants of the farallon slab that subducted prior to 40 ma during the laramide orogeny

anatomy and global context of the andes main geologic features and the andean orogenic cycle the andes make up the largest orogenic system developed by subduction of oceanic crust along a continental margin subduction began soon after the breakup of rodinia in late proterozoic times and since that time it has been intermittently active up to the present the evolution of the pacifi c margin of south america during the paleozoic occurred in the following stages 1 initial proterozoic rifting followed by subduction and fi nal re amalgamation of the margin in early cambrian times as depicted by the puncoviscana and tucavaca basins and related granitoids in southern bolivia and northern argentina 2 a later phase of rifting in the middle cambrian and subsequent collisions in middle ordovician times of parautochthonous terranes derived from gondwana such as paracas arequipa and antofalla and exotic terranes originating in laurentia such as cuyania chilenia and chibcha 3 fi nal permian collision between south america and north america to form pangea during the alleghanides orogeny leaving behind rifted pieces of laurentia as the tahami and tahuin terranes in the northern andes and other poorly known orthogneisses in the cordillera real of ecuador in the late permian early triassic and 4 amalgamation of the mejillonia and patagonia terranes in early permian times representing the last convergence episodes recorded in the margin during the gondwanides orogeny these rifting episodes and subsequent collisions along the continental margin were the result of changes of the absolute motion of gondwana related to global plate reorganizations during proterozoic to paleozoic times generalized rifting during pangea breakup in the triassic concentrated extension in the hanging wall of the sutures that amalgamated the paleozoic terranes the opening of the indian ocean in early jurassic times was associated with a new phase of subduction along the continental margin the northeastward absolute motion of western gondwana produced a negative trench roll back velocity that controlled subduction under an extensional regime until late early cretaceous times the northern andes of venezuela colombia and ecuador record a series of collisions of island arcs and oceanic plateaus from the early cretaceous to the middle miocene as a result of interaction with the caribbean plate the remaining central and southern andes record periods of orogenesis and mountain building alternating with periods of quiescence and absence of deformation as recorded in parts of the oligocene based on the generalized occurrence of fl at slab subduction episodes through time as recorded in most ramos v a 2009 anatomy and global context of the andes main geologic features and the andean orogenic cycle in kay s m ramos v a and dickinson w r eds backbone of the americas shallow subduction plateau uplift and ridge and terrane collision geological society of america memoir 204 p 31 65 doi 10 1130 2009 1204 02 for permission to copy contact editing geosociety org 2009 the geological society of america all rights reserved

rocky mountain foreland uplifts products of a rotating stress field or strain partitioning stress tensor analysis of minor faults near the structural range fronts of diversely oriented laramide foreland uplifts in the central rocky mountains wyoming indicates that paleo 1 was horizontal and oriented nearly perpendicular to uplift trends trend directions for 1 vary from east northeast in the north trending laramie range to northeast in the northwest trending bighorn mountains to north at east trending casper mountain and in the east trending central owl creek mountains although these compression directions are compatible with models invoking temporally changing stress directions during the laramide orogeny the apparent similarity in timing of uplift in these ranges suggests that the computed stress tensors may not reflect regional stress conditions recent stress determinations in transpressional regimes suggest that strain partitioning may be an important factor in considering local stress patterns in the vicinity of mountain belt structures oblique to regional trends in light of these studies caution should be used in interpreting regional paleostress from structures measured close to the tectonic fronts of laramide uplifts

estimating southern ocean storm positions with seismic observations author s hell momme c gille sarah t cornuelle bruce d miller arthur j bromirski peter d crawford alex d

sun glitter imagery of surface waves part 2 waves transformation on ocean currents under favorable imaging conditions the sentinel 2 multi spectral instrument msi can provide spectacular and novel quantitative ocean surface wave directional measurements in satellite sun glitter imagery ssgi owing to a relatively large swath with high spatial resolution 10 m ocean surface roughness mapping capabilities changes in ocean wave energy and propagation direction can be precisely quantified at very high resolution across spatial distances of 10 km and more this provides unique opportunities to study ocean wave refraction induced by spatial varying surface currents as expected and demonstrated over the grand agulhas current area the mesoscale variability of near surface currents documented and reconstructed from satellite altimetry can significantly deflect in coming south western swell systems based on ray tracing calculations and unambiguously revealed from the analysis of sentinel 2 msi ssgi measurements the variability of the near surface current explains significant wave current refraction leading to wavetrapping phenomenon and strong local enhancement of the total wave energy in addition to its importance for wave modeling and hazard prediction these results open new possibilities to combine different satellite measurements and greatly improve the determination of the upper ocean mesoscale vorticity motions

present day motion and deformation of the colorado plateau 1 we analyze data from continuous gps stations in the southwestern united states and present the first observations of a systematic motion of the colorado plateau region relative to a north america fixed reference frame westward velocities increase rapidly across the wasatch fault system which comprises the plateau s northwestern margin but increase more gradually between the great plains and the mojave desert province we detect no significant extension across most of the rio grande rift but extension could be as high as 0 5 mm yr 1 along its southernmost portion we suggest that the motion between the plateau and stable continent may partly be accommodated instead across the jemez lineament only when we consider gps velocities within the plateau s center do the data support a rigid body rotation of 0 103 ma 1 around a pole in the northern rocky mountains we conclude that active extension has encroached into the plateau from both the east and west

small scale open ocean currents have large effects on wind wave heights tidal currents and large scale oceanic currents are known to modify ocean wave properties causing extreme sea states that are a hazard to navigation recent advances in the understanding and modeling capability of open ocean currents have revealed the ubiquitous presence of eddies fronts and filaments at scales 10 100 km based on realistic numerical models we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km including important variations down to 10 km model results are consistent with wave height variations along satellite altimeter tracks resolved at scales larger than 50 km the spectrum of significant wave heights is found to be of the order of 70 hs 2 g2 tm0 1 2 times the current spectrum where hs is the spatially averaged significant wave height tm0 1 is the energy averaged period and g is the gravity acceleration this variability induced by currents has been largely overlooked in spite of its relevance for extreme wave heights and remote sensing

franciscan complex calera limestones accreted remnants of farallon plate oceanic plateaus the calera limestone part of the franciscan complex of northern california may have formed in a palaeoenvironment similar to hess and shatsky rises of the present north west pacific1 we report here new palaeomagnetic results palaeontological data and recent plate motion models that reinforce this assertion the calera limestone may have formed on farallon plate plateaus north of the pacific farallon spreading centre as a counterpart to hess or shatsky rises in one model2 the plateaus were formed by hotspots close to the farallon pacific ridge axis on accretion to north america plateau dissection in the late cretaceous to eocene 50 70 myr could explain the occurrence of large volumes of pillow basalt and exotic blocks of limestone in the franciscan complex partial subduction of the plateaus could have contributed to laramide 70 40 myr compressional events3

location of the antarctic polar front from amsr e satellite sea surface temperature measurements abstract the location of the southern ocean polar front pf is mapped from the first 3 yr of remotely sensed advanced microwave scanning radiometer for the earth observing system amsr e sea surface temperature sst measurements in agreement with previous studies the mean path of the antarctic pf and its standard deviation are strongly influenced by bottom topography however the mean pf path diverges slightly from previous studies in several regions where there is high mesoscale variability although the sst and sst gradient at the pf show spatially coherent seasonal variations with the highest temperature and the lowest temperature gradient during summer the seasonal variations in the location of the pf are not spatially coherent the temporal mean sst at the pf corresponds well to the mean pf path the temperature is high in the atlantic and indian ocean sections and is low in the pacific ocean section where the pf has a more southerly position the relationship of the wind field with the antar

retracking ers 1 altimeter waveforms for optimal gravity field recovery summary we have reprocessed ers 1 radar altimeter waveforms using an algorithm designed to minimize sea surface slope error and decouple it from significant wave height swh error standard waveform retracking estimates three parameters arrival time swh and amplitude we show that errors in retracked estimates of arrival time and swh are inherently correlated because of the noise characteristics of the returned waveform this suggests that some of what is called sea state bias in the literature may be caused by correlated errors rather than true electromagnetic or skewness bias we have developed a retracking algorithm that reduces this error correlation and makes the resolution of sea surface slope signals independent of sea state the main assumption is that the swh varies smoothly along the satellite track over wavelengths of 90 km this approach reduces the rms error in sea surface slope to only 62 per cent of that of standard retracking methods while our method is optimized for gravity field recovery it may also improve the resolution of sea surface height signals of interest to physical oceanographers

improved measurement of fission track annealing in apatite using c axis projection apatite fission track length data are used extensively for thermal history inversion however several studies have documented instances of poor reproducibility of length data we address this problem by using c axis projection to normalize track lengths for crystallographic angle in the extensive laboratory annealing data set acquired by barbarand et al 2003a 2003b a new simplification reduces the c axis projection model from six to four fitted parameters normalizing for track angle using c axis projection improves every aspect of length measurement reproducibility examined it accelerates convergence of mean length in single analyses increases consistency among replicate measurements by a single analyst enhances consistency of measurements of the same mounts by different analysts and improves the match between analyses conducted with and without cf irradiation c axis projection is also shown to enhance the thermal sensitivity of length data based on these results we assert that c axis projection is a good means of compensating for observer bias although it does not overcome differences caused by experimental error

cyclogeostrophic balance in the mozambique channel three methods are proposed for the inclusion of inertia when deriving currents from sea surface height ssh in the mozambique channel gradient wind perturbation expansion and an iterative method they are tested in a model and applied to satellite altimetry for an eddy of 25 cm amplitude and 100 km radius typical of mozambique channel rings at 18 s the error made with geostrophy is 40 for the anticyclones and 20 for the cyclones inertia could reach one third of the pressure gradient geostrophy underestimates subsurface currents by up to 50 cm s 1 resulting in errors of 30 40 the iterative method results in errors of 50 in mozambique channel rings geostrophic eke reaches 1400 cm2 s 2 while it attains 1800 cm2 s 2 when inertia is added applied to the gulf stream these methods confirm the hypothesis of maximenko and niiler 2006 that centrifugal accelerations should be the main cause for the difference observed between geostrophic and drifter eke this methodology should result in a net improvement for operational surface ocean currents

laramide crustal thickening event in the rocky mountain foreland and great plains the rocky mountain foreland and great plains of the western united states were formerly part of a continental platform adjusted by erosion and deposition in cambrian through jurassic time to near mean sea level and therefore to a near uniform crustal thickness of approximately 33 km today the region stands at regional elevations up to 2 km isostatically supported by a crust exceeding 50 km in thickness reasonable estimates of tertiary sedimentation and laramide strain do not account for more than 15 of the implied thickening however from approximately 70 40 m y b p this region was underlain by a horizontally subducting slab of farallon plate lithosphere moving northeast this slab could have been the cause of the thickening finite difference thermal models with specified kinematics show only a temporary cooling of the base of the north american lithosphere by this slab the excess weight of the slab would have depressed the region plate bending calculations show a quantitative agreement of predicted depression with upper cretaceous isopachs since depression by this slab lasted until the eocene at least the latest cretaceous regression was probably caused by a laramide crustal thickening event the farallon slab might have caused crustal thickening in two ways its excess weight would have drawn in ductile lower crust from surrounding regions however calculations show that this effect is too slow too local and too reversible to explain most of the crustal thickening therefore it seems likely that ductile lower crust was transported from sw to ne by shear stresses which the farallon plate exerted on the base of the north american lithosphere a preliminary finite element calculation based on this hypothesis shows the correct general pattern of crustal thickening an unexpected but encouraging result is that predicted principal compression directions are orthogonal to many laramide basement uplifts

relation of flat subduction to magmatism and deformation in the western united states flat subduction of the farallon plate beneath the western united states during the laramide orogeny was caused by the combined effects of oceanic plateau subduction and unusually great suction in the mantle wedge the latter of which was caused by the shallowing slab approaching the north american craton root once in contact with basal north america the slab cooled and hydrated the lithosphere upon removal asthenospheric contact with lithosphere resulted in magma production that was especially intense where the basal lithosphere was fertile in what now is the basin and range province and this heating weakened the lithosphere and made it convectively unstable small scale convection has since affected many areas with slab sinking and unloading the western united states elevated into a broad plateau and the weak portion gravitationally collapsed with development of a transform plate boundary the western part of the weak zone became entrained with the pacifi c plate and deformation there is dominated by shear 2 humphreys mwr204 04 1st pages e surface heat flow p wave velocity d seismic velocity at 100 km background s wave velocity 2 100 175 km c s wave velocity

gulf stream dynamics along the southeastern u s seaboard abstractthe gulf stream strongly interacts with the topography along the southeastern u s seaboard between the straits of florida and cape hatteras the dynamics of the gulf stream in this region is investigated with a set of realistic very high resolution simulations using the regional ocean modeling system roms the mean path is strongly influenced by the topography and in particular the charleston bump there are significant local pressure anomalies and topographic form stresses exerted by the bump that retard the mean flow and steer the mean current pathway seaward the topography provides through bottom pressure torque the positive input of barotropic vorticity necessary to balance the meridional transport of fluid and close the gyre scale vorticity balance the effect of the topography on the development of meanders and eddies is studied by computing energy budgets of the eddies and the mean flow the baroclinic instability is stabilized by the slope everywhere except past the bump the flow

formation of the rocky mountains western united states a continuum computer model one hypothesis for the information of the rocky mountain structures in late cretaceous through eocene time is that plate of oceanic lithosphere was underthrust horizontally along the base of the north american lithosphere the horizontal components of the motion of this plate are known from paleomagnetism and the edge of the region of flat slab can estimated from reconstructed patterns of volcanism new techniques of finite element modeling allow prediction of the thermal and mechanical effects of horizontal subduction on the north american plate a model that has a realistic temperature dependent rheology and a simple plane layered initial condition is used to compute the consequences of horizontal underthrusting in the time interval 75 million to 30 million years before present successful prediction of this model include i the location amount and direction of horizontal shortening that has been inferred from laramide structures ii massive transport of lower crust from southwest to northeast iii the location and timing of the subsequent extension in metamorphic core complexes and the rio grande rift and iv the total area eventually involved in basin and range style extension in a broad sense this model has predicted the belt of laramide structures the transport of crust from the coastal region to the continental interior the subsequent extension in metamorphic core complexes and the rio grande rift and the geographic region of late tertiary basin and range extension its principal defects are that i many events are predicted about 5 million to 10 million years too late and ii the wave of crustal thickening does not travel far enough to the east reasonable modifications to the oceanic plate kinematics and rheologies that were assumed may correct these defects the correspondence of model predictions to actual geology is already sufficiently close to show that the hypothesis that horizontal subduction caused the laramide orogeny is probably correct the rocky mountain thrust and reverse faults formed in an environment of east west to northeast southwest compressive stress that was caused by the viscous coupling between the oceanic plate and the base of the north american crust nonuniform crustal thickening by simple shear transport also caused relative uplifts therefore this model is consistent with both of the range forming mechanisms that have been inferred 1 a new proposal that arises from this simulation is that horizontal subduction also caused the subsequent extensional basin and range taphrogeny by stripping away the mantle lithosphere so that the crust was exposed to hot asthenosphere after the oceanic slab dropped away

the role of oceanic plateau subduction in the laramide orogeny the cause of the laramide phase of mountain building remains uncertain conceptual models implicate the subduction of either ocean ridges or conjugates of the buoyant hess or shatsky oceanic plateaux independent verification of these models has remained elusive because the putative ridges or plateaux are no longer at the earth s surface inverse convection models have identified two prominent seismic anomalies on the recovered farallon plate here we combine inverse convection models with reconstructions of plate motions to show that these seismic anomalies coincide palaeogeographically with the restored positions of the shatsky and hess conjugate plateaux as they subducted beneath north america specifically the distribution of laramide crustal shortening events tracked the passage of the shatsky conjugate beneath north america whereas the effects of the hess conjugate subduction were restricted to the northern mexico foreland belt we propose that continued subduction caused the oceanic crust to undergo the basalt eclogite phase transformation during which the shatsky conjugate lost its extra buoyancy and was effectively removed increases in slab density and coupling between the overriding and subducting plates initially dragged the surface downward followed by regional scale surface rebound we conclude that laramide uplift resulted from the removal rather than emplacement of the shatsky conjugate

interpreting data dispersion and inverted dates in apatite u th he and fission track datasets an example from the us midcontinent abstract new apatite u th he ahe and apatite fission track aft data were acquired for cratonic basement samples from an 80 m span of drillcore in northeastern kansas the short depth interval over which the samples were collected indicates that they should have undergone thermal histories that would be indistinguishable using low temperature thermochronometry techniques individual ahe dates from four samples range from 99 to 464 ma three samples yield dates 300 ma higher eu 39 113 ppm and substantial data dispersion uncorrelated with eu and grain size these apatites have strong and variable eu zonation aft dates for five samples range from 242 to 291 ma the sample with the highest eu apatites and oldest ahe dates yields the youngest aft results these results are inverted with ahe dates distinctly older than the corresponding aft date we explore both the causes of data dispersion and the overall compatibility of this cratonic dataset we find that geologically reasonable thermal histories can 1 explain the distribution of the moderate eu ahe data when accounting for the influence of radiation damage grain size and eu zonation on apatite he diffusivity 2 reproduce the observed dispersion in the high eu ahe data when using a viable range of eu zonation and grain size and 3 explain the aft data for the same samples the ahe and aft data are mutually consistent and viable thermal histories successfully predict the observed pattern of older ahe than aft dates for the high eu apatites together these results suggest that appropriately accounting for the known controls on apatite he diffusivity can explain the observed dispersion and inverted ahe and aft results in some thermochronometry datasets a range of ahe dates should be especially common in cratonic data because small differences in apatite he diffusivity are amplified by the thermal histories that typify cratonic settings we use these results to develop some guidelines for interpreting dispersed ahe datasets first date eu and date grain size correlations should be evaluated and if these patterns occur they can be used to better resolve the thermal history second for samples that yield inexplicably large dispersion of ahe dates uncorrelated with eu and crystal size the appropriate strategy is either to reject these samples from the suite used for thermal history interpretation or to acquire additional data to help decipher the significance of the age distribution

refining the footwall cooling history of a rift flank uplift rio grande rift new mexico 1 apatite fission track aft and u th he data from the sandia mountains and hagan embayment provide new insights into the thermal and tectonic evolution of the eastern flank of the rio grande rift in northern new mexico aft and u th he data reveal rapid cooling in the sandia mountains between 22 and 17 ma followed by a decrease in cooling rate at 16 to 14 ma that temporally corresponds to a hiatus in deposition in the albuquerque basin a second increase in cooling rate at approximately 14 ma was followed by continued slow cooling until present cooling ages from jurassic to permian sandstones in the hagan embayment northeast of the sandia mountains are used to constrain the thermal conditions in oligocene time that are necessary to map cooling histories into exhumation histories thereby providing a limit on the amount of section removed during rift flank development thermal modeling geologic constraints and low temperature thermochronology are used to demonstrate that the heat flow in the sandia mountain region was at least 25 mw m2 higher during oligocene time compared to today furthermore at least 3 1 km of material has been exhumed from the sandia mountains and 2 4 km of rock uplift occurred during flexural tilting of the block since middle miocene time

imaging mesoscale upper ocean dynamics using synthetic aperture radar and optical data a synergetic approach for quantitative analysis of high resolution ocean synthetic aperture radar sar and imaging spectrometer data including the infrared ir channels is suggested this approach first clearly demonstrates that sea surface roughness anomalies derived from sun glitter imagery compare very well to sar roughness anomalies as further revealed using these fine resolution similar to 1 km observations the derived roughness anomaly fields are spatially correlated with sharp gradients of the sea surface temperature sst field to quantitatively interpret sar and optical in visible and ir ranges images equations are derived to relate the surface roughness signatures to the upper ocean flow characteristics as developed a direct link between surface observations and divergence of the sea surface current field is anticipated from these satellite observations intense cross frontal dynamics and vertical motions are then found to occur near sharp horizontal gradients of the sst field as a plausible mechanism it is suggested that interactions of the wind driven upper layer with the quasi geostrophic current field via ekman advective and mixing mechanisms result in the generation of secondary ageostrophic circulation producing convergence and divergence of the surface currents the proposed synergetic approach combining sst sun glitter brightness and radar backscatter anomalies possibly augmented by other satellite data e g altimetry scatterometry ocean color can thus provide consistent and quantitative determination of the location and intensity of the surface current convergence divergence upwelling downwelling this in turn establishes an important step toward advances in the quantitative interpretation of the upper ocean dynamics from their two dimensional satellite surface expressions

an algorithm for u pb isotope dilution data reduction and uncertainty propagation this is the publisher s version also available electronically from http onlinelibrary wiley com