three dimensional inversion of large scale earthscope magnetotelluric data based on the integral equation method geoelectrical imaging of the yellowstone conductive mantle plume 1 interpretation of the earthscope mt magnetotelluric data requires the development of a large scale inversion method which can address two common problems of 3d mt inversion computational time and memory requirements we have developed an efficient method of 3d mt inversion based on an ie integral equation formulation of the mt forward modeling problem and a receiver footprint approach implemented as a massively parallel algorithm this method is applied to the mt data collected in the western united states as a part of the earthscope project as a result we present one of the first 3d geoelectrical images of the upper mantle beneath yellowstone revealed by this large scale 3d inversion of the earthscope mt data these images show a highly conductive body associated with the tomographically imaged mantle plume like layer of hot material rising from the upper mantle toward the yellowstone volcano the conductive body identified in these images is west dipping in a similar way to a p wave low velocity body

lithospheric thickness beneath the dabie shan central eastern china from s receiver functions summary p and s receiver functions obtained from a portable array of 34 broad band stations in east central china provide a detailed image of the crust mantle and lithosphere asthenosphere boundaries lab in the dabie shan and its adjacent areas clear s to p converted waves produced at the lab show a thin lithosphere beneath the whole study area based on our results the thickest lithosphere of 72 km is observed beneath the southern part of the area within the yangtze craton whereas beneath the north china platform the lithosphere is only 60 km thick s receiver functions also reveal in good agreement with p receiver functions a maximum depth of the moho beneath the dabie shan orogen at approximately 40 km furthermore we interpret the structural difference at 32 latitude as the probable location of

toroidal mantle flow through the western u s slab window the circular pattern of anisotropic fast axis orientations of split sks arrivals observed in the western u s cannot be attributed reasonably to either preexisting lithospheric fabric or to asthenospheric strain related to global scale plate motion a plume origin for this pattern accounts more successfully for the anisotropy field but little evidence exists for an active plume beneath central nevada we suggest that mantle flow around the edge of the sinking gorda juan de fuca slab is responsible for creating the observed anisotropy seismic images and kinematic reconstructions of gorda juan de fuca plate subduction have the southern edge of this plate extending from the mendocino triple junction to beneath central nevada and flow models of narrow subducted slabs produce a strong toroidal flow field around the edge of the slab consistent with the observed pattern of anisotropy this flow may enhance uplift extension and magmatism of the northern basin and range while inhibiting extension of the southern basin and range

crust and upper mantle structure beneath the pacific northwest from joint inversions of ambient noise and earthquake data 1 we perform a joint inversion of phase velocities from both earthquake and ambient noise induced rayleigh waves to determine shear wave velocity structure in the crust and upper mantle beneath the pacific northwest we focus particularly on the areas affected by mid miocene to present volcanic activity the joint inversion combined with the high density seismic network of the high lava plains seismic experiment and data from the earthscope transportable array provides outstanding resolution for this area in oregon we find that the pattern of low velocities in the crust and uppermost mantle varies between the high lava plains physiographic province and the adjacent northwestern basin and range these patterns may be due to the presence of the brothers fault zone which separates the clockwise rotating northwest basin and range from the relatively undeformed areas further north further to the east the owyhee plateau snake river plain srp and northeastern basin and range are characterized by high crustal velocities though the depth extent of these fast wave speeds varies by province of particular interest is the mid crustal high velocity sill previously only identified within the srp we show this anomaly extends significantly further south into utah and nevada we suggest that one possible explanation is lateral crustal extrusion due to the emplacement of the high density mafic mid crustal sill structures within the srp

variations in melt layer frequency in the gisp2 ice core implications for holocene summer temperatures in central greenland the rare melt features in the gisp2 central greenland deep ice core have decreased in frequency over the most recent 7000 years calibration of this change in melt frequency against modern spatial variation of melt frequency and temperature in central greenland and against modern temporal variability of temperatures in central greenland indicates that mean mid summer temperatures have cooled over the most recent 7000 years probably by slightly more than l c if variability of summer temperatures has not changed comparison to grip isotopic records from central greenland and to the melt record from the agassiz ice cap arctic canada suggests some seasonal and regional coherence for this cooling signal as well as for a cold event about 8000 8500 bp

multi proxy records showing significant holocene environmental variability the inner n iceland shelf hunafloi abstract over the last 50 yr the n iceland margin has seen dramatic changes in temperature and salinity associated with the relative dominance of warm atlantic water versus cold arctic or polar waters we report a study of holocene environmental changes to assess the sensitivity of this area on a longer timescale we present sedimentologic isotopic and biotic coccolith proxies from a 5 5 m piston core b997 330pc that was retrieved from a small basin on the inner n iceland shelf seven ams dates indicate a relatively constant rate of sediment accumulation which averaged 55 cm kyr sampling resolution of our proxies varied between 16 and 90 yr sample our data indicate substantial variability in environmental conditions over the last 10 000 cal yr total carbonate content and coccolith concentrations track each other and indicate that the early holocene was a time of low net carbonate accumulation net accumulation of carbonate reached maximum values in the mid to late holocene 4 2 cal ka but there has since been a substantial decrease with a minima during the little ice age north atlantic drift coccolith species show peaks in accumulation rates at 2 and 8 cal ka and low influx between 3 5 and 6 cal ka reworked neogene coccoliths occur also 8 ka and coincide with light 18 o values in the epifaunal foraminifera cibicides lobatulus principal component analysis indicates considerable covariance between biotic isotopic and sedimentological parameters three axes explain 84 of the variance in the data set and define three groups of interrelated variables a major change occurs ca 5 cal ka after which conditions become more variable with a 1 5 kyr cyclicity

crust and upper mantle electrical conductivity beneath the yellowstone hotspot track combining long period magnetotelluric data from the spatially uniform earthscope usarray and higher resolution profiles we obtain a regional three dimensional electrical resistivity model in the snake river plain and yellowstone areas idaho and wyoming united states and provide new constraints on the large scale distribution of melt and fluids beneath the yellowstone hotspot track contrary to what would be expected from standard mantle plume models the electromagnetic data suggest that there is little or no melt in the lower crust and upper mantle directly beneath yellowstone caldera instead low mantle resistivities 10 m and below which we infer to result from 1 3 partial melt are found 40 80 km beneath the eastern snake river plain extending at least 200 km southwest of the caldera beneath the area of modern basaltic magmatism the reduced resistivities extend upward into the mid crust primarily around the edges of the snake river plain suggesting upward migration of melt and or fluid is concentrated in these areas the anomaly also shallows toward yellowstone where higher temperatures enhance permeability and allow melts to ascend into the crust the top of the conductive layer is at its shallowest in the upper crust directly beneath the modern yellowstone supervolcano

mantle structure beneath the western united states and its implications for convection processes 1 we present tomographic images of the mantle structure beneath the western united states our dynamic north america models of p and s velocity structure dna07 p and dna07 s use teleseismic body waves recorded at 600 seismic stations provided by the earthscope transportable array and regional networks dna07 p and s benefit from the unprecedented aperture of the network while maintaining a dense station distribution providing high resolution body wave imaging of features through the transition zone and into the lower mantle the main features imaged include 1 the juan de fuca subduction system that bottoms at 400 km beneath oregon implying interaction with the yellowstone anomaly 2 a low velocity conduit beneath yellowstone national park that bottoms at 500 km and dips toward the northwest 3 shallow low velocity anomalies upper 200 km beneath the eastern snake river plain esrp and the high lava plains and a deep low velocity anomaly 600 km beneath the esrp but not newberry 4 a low velocity slab gap to 400 km depth immediately south of the mendocino triple junction and south of the gorda slab and 5 high velocity drips beneath the transverse ranges the southern central valley sierra nevada and central nevada these observations reveal extremely heterogeneous mantle structure for the western united states and suggest that we are only just beginning to image the complex interactions between geologic objects the transportable array allows for analysis of the relationships between these anomalies in an internally consistent single tomographic model the dna velocity models are available for download and slicing at http dna berkeley edu

spatial and temporal patterns of iceberg rafting ird along the east greenland margin ca 68 n over the last 14 cal ka twelve 1 2 m 10 cm diameter gravity cores collected in 1988 and 1991 from the continental shelf and fjords of east greenland near kangerlussuaq fjord trough ca 68 n 32 w have distinct changes in lithofacies and in the quantity of iceberg rafted ird sediments these changes are readily observed in x radiographs of the split cores we quantify the ird contribution through grain size analyses and counting the number of clasts 2 mm from the x radiographs chronological control is provided by acclerated mass spectroscopy 14c dates on foraminifera during deglaciation after 14 cal ka there was one interval of ird accumulation ca 12 13 cal ka followed by a brief return to ird conditions centred at 9 cal ka thereafter a prominent feature of most cores on the shelf is an increase in ird accumulation that started ca 5 6 cal ka and which has increased toward the present indicators of iceberg rafting such as the net sand flux and numbers of clasts 2 mm ka 1 follow a power law distribution when graphed against distance from the present east greenland coast a measure of the position of the glacier margins the form of the relationship indicates that there is a dramatic decrease in the supply of sediment from the fjords to the shelf these relationships are used to estimate changes in the location of the ice margin during the late quaternary based on a site on the east greenland slope denmark strait and to discuss factors that can negate such a simple transfer function 1997 by john wiley sons ltd

plumes in a convecting mantle models and observations for individual hotspots the motion of hotspots and the deformation of their underlying plume conduits as calculated within models of global mantle flow are presented a new list of 44 possible hotspots with associated tracks has been compiled for all of them calculations have been performed under consideration of individual age and anomalous mass flux for three different models of plume buoyancy and mantle flow plume source depth has usually been assumed to be the top of d but an alternative source depth at the 670 km discontinuity has also been considered using models of relative plate motions and boundaries hotspot tracks on plates have been calculated and compared with age data ocean floor topography and distribution of volcanics on continents absolute plate motions have been redetermined under consideration of hotspot motion using a new least squares method for the hawaiian and yellowstone hotspots source locations and hotspot motion have been computed for a total of up to 23 different models the results show plume conduits being tilted with source regions at the d moving in the lowermost mantle flow generally toward large scale upwellings under southern africa and the south central pacific hotspot surface motion often represents the horizontal component of midmantle flow which is frequently opposite to plate motion toward ridges and away from subduction zones in particular almost all models tested predict southward motion of the hawaii and kerguelen hotspots and westward motion of the iceland hotspot for models including hotspot motion the agreement between calculated and observed hotspot tracks is frequently about as good as or better than for the fixed hotspot model but sometimes fixed hotspots give the best fit in some cases where the track ends at a subduction zone e g for the bowie hotspot results can give indications about the otherwise unknown age of the hotspot in other cases especially for the tahiti hotspot results suggest an origin shallower than d and in yet other cases particularly east africa the failure of the hotspot models used supports other evidence indicating the presence of comparatively broad upwellings rather than localized plumes

stratigraphic record of the yellowstone hotspot track neogene sixmile creek formation grabens southwest montana abstract the sixmile creek formation fills deep grabens in southwest montana and preserves a stratigraphic record of the evolution of the yellowstone hotspot track from 17 ma to 2 ma the ruby beaverhead big hole deer lodge medicine lodge grasshopper three forks canyon ferry jefferson melrose wise river and paradise grabens were active during outbreak of the hotspot they appear to be parts of a radial system of extensional structures that may have formed on a broad dome that was centered on the hotspot outbreak area in southwest idaho and southeast oregon early in the evolution of the grabens massive debris flows surged down paleogene paleovalleys from uplifted and tilted horst blocks and accumulated in the grabens the grabens captured runoff from the hotspot dome with thick deposits of river gravel that appear to have been derived in part from east central idaho as the hotspot track propagated along the eastern snake river plain silicic ash fell into the graben drainage basins and was reworked into thick fluvial beds along graben axes the grabens were cross cut by northwest trending late neogene grabens that propagated on the flanks of silicic volcanic centers along the hotspot track the late neogene grabens diverted the middle miocene drainage patterns in southwest montana

temperature of the plume layer beneath the yellowstone hotspot recent studies show that the yellowstone hotspot is associated with a plume like lowvelocity pipe that ascends from the transition zone to the lithosphere asthenosphere boundary where the plume is sheared to the southwest by north american plate motion rayleigh wave tomography shows this plate sheared plume layer has an extremely low s wave velocity of 3 8 0 1 km s at 80 km depth 0 15 0 3 km s lower than the velocity observed beneath normal mid ocean ridges to constrain the temperature of the plume layer a grid search with respect to grain size and temperature is performed to fi observed rayleigh wave phase velocities this search fi nds that the excess temperature of the plume layer is 55 80 c at 95 confi dence for two different temperature velocity and two different melt velocity models confi rming that a thermal mantle plume exists

the yellowstone magmatic system from the mantle plume to the upper crust the yellowstone supervolcano is one of the largest active continental silicic volcanic fields in the world an understanding of its properties is key to enhancing our knowledge of volcanic mechanisms and corresponding risk using a joint local and teleseismic earthquake p wave seismic inversion we revealed a basaltic lower crustal magma body that provides a magmatic link between the yellowstone mantle plume and the previously imaged upper crustal magma reservoir this lower crustal magma body has a volume of 46 000 cubic kilometers 4 5 times that of the upper crustal magma reservoir and contains a melt fraction of 2 these estimates are critical to understanding the evolution of bimodal basaltic rhyolitic volcanism explaining the magnitude of co2 discharge and constraining dynamic models of the magmatic system for volcanic hazard assessment

foraminiferal reconstruction of mid to late holocene ocean circulation and climate variability in disko bugt west greenland benthic foraminifera from two cores collected from disko bugt a large marine embayment in west greenland are used to investigate hydrographic changes during the mid to late holocene the records document fluctuations in the west greenland current wgc linked to large scale changes in north atlantic circulation and for one core impacts of local climate changes in particular changes in the cold east greenland current egc and the warm more saline irminger current ic influence the wgc and propagate into disko bugt the cores record subsurface warming associated with the holocene thermal maximum htm from c 6 to 5 ka cal bp gradual cooling of wgc from 5 ka cal bp was interrupted by an abrupt warm interval from 3 9 to 3 5 ka cal bp before cooling became more prominent from 3 5 to 2 ka cal bp this cold period corresponds to the well documented northern hemisphere cooling of the neoglacial and we interpret it as reflecting enhanced flux from the egc and reduced ic flux to the wgc in disko b

p wave tomography of the western united states insight into the yellowstone hotspot and the juan de fuca slab abstract we used 190 947 high quality p wave arrival times from 8421 local earthquakes and 1 098 022 precise travel time residuals from 6470 teleseismic events recorded by the earthscope usarray transportable array to determine a detailed three dimensional p wave velocity model of the crust and mantle down to 1000 km depth under the western united states us our tomography revealed strong heterogeneities in the crust and upper mantle under the western us prominent high velocity anomalies are imaged beneath idaho batholith central colorado plateau cascadian subduction zone stable north american craton transverse ranges and southern sierra nevada prominent low velocity anomalies are imaged at depths of 0 200 km beneath snake river plain which may represent a small scale convection beneath the western us the low velocity structure deviates variably from a narrow vertical plume conduit extending down to 1000 km depth suggesting that the yellowstone hotspot may have a lower mantle origin the juan de fuca slab is imaged as a dipping high velocity anomaly under the western us the slab geometry and its subducted depth vary in the north south direction in the southern parts the slab may have subducted down to 600 km depth a slab hole is revealed beneath oregon which shows up as a low velocity anomaly at depths of 100 to 300 km the formation of the slab hole may be related to the newberry magmatism the removal of flat subducted farallon slab may have triggered the vigorous magmatism in the basin and range and southern part of rocky mountains and also resulted in the uplift of the colorado plateau and rocky mountains

crustal structure and thickness along the yellowstone hot spot track evidence for lower crustal outflow from beneath the eastern snake river plain 1 receiver functions from seismic stations about the yellowstone hot spot track are migrated to depth using a vp vs map constructed from stacking of the direct and free surface moho reverberations i e h k analysis and a shear velocity tomogram constructed from surface wave measurements the thickest crust 48 54 km resides in the wyoming province beneath the sampled laramide age blocks and the thinnest crust 32 37 km resides in the montana basin and range province the eastern snake river plain esrp crust is thickest 47 km at its ne end beneath the young calderas and thinnest 40 km at its sw end beneath the older twin falls caldera two esrp crustal thickness domains are found 1 at the older twin falls and picabo calderas the mean esrp crust is 4 km thicker with respect to its margins and 2 adjacent to the heise caldera field the mean esrp crust is 4 km thicker with respect to its se margin crust but no thicker with respect to its nw margin crust this lobe of anomalously thick crust is explained as resulting from lower crustal outflow from beneath the heise caldera field confirmation of these crustal thickness variations is provided by inspection of common conversion point ccp stacks that delineate several secondary features the top of a thick high velocity 3 9 km s lower crust layer within the wyoming province up to 17 km thick and a paired negative and positive amplitude arrival at 12 km depth and 18 km depth beneath the yellowstone caldera this paired arrival would be consistent with a low velocity zone perhaps associated with magma staging beneath the caldera our most important finding is that the magmatic loads injected into the esrp crust over the last 4 12 myr in tandem with the esrp crustal viscosity structure have been sufficient to drive significant outflow of the esrp lower crust

mass transfer along the yellowstone hotspot track ii kinematic constraints on the volume of mantle derived magma abstract this paper evaluates the neogene kinematic evolution of the eastern snake river plain esrp to estimate the volume of mafic magma transferred from mantle to crust during passage over the yellowstone hotspot four major kinematic processes affected the esrp including densification due to emplacement of gabbro into the middle crust subsidence and consequent filling of a 6 km deep basin with volcanic and plutonic rocks 20 extension via dike injection or faulting ductile attenuation and lower crustal flow from esrp to the adjacent basin and range two kinematic models involving these processes are proposed overall the two models are viable only if the initial crustal thickness were 43 47 km thick otherwise the lost mass of the esrp is not balanced by the excess mass in the basin and range in the first model densification eruption and extension by dike injection the esrp crust receives mantle derived gabbro equivalent to a 16 km thick layer but would need to lose 10 km of crust via lower crustal flow in the second model densification eruption and extension by faulting and ductile attenuation the esrp crust receives a 9 4 km equivalent thickness of mantle derived gabbro and would need to lose 6 km of crust via lower crustal flow the cumulative amount of mantle derived gabbro in the esrp crust derived by this kinematic analysis equivalent to a 9 4 16 km thick layer is nearly identical to the amount estimated independently using a mass balance petrologic model suggesting it is a robust result

origin of the newberry hotspot track evidence from shear wave splitting abstract located in the northwestern united states the newberry hotspot track consists of a sequence of age progressive silicic volcanic domes and lava flows showing a monotonic age progression from east to west ending at the newberry caldera while mantle plumes are often called upon to explain hotspot tracks the newberry track cannot be the direct product of plate motion over a stationary mantle source as its orientation is 120 to plate motion making it a good case study for alternative causal mechanisms of hotspot tracks four end member tectonic models have been proposed 1 subduction counterflow 2 gravitational flow along the base of the lithosphere 3 lithospheric faulting and 4 extension of the basin and range to get fabric information about the asthenosphere and constrain the possible flow fields beneath the newberry track sks splitting measurements were made for 27 events at 12 stations of the oregon array for teleseismic study oats along the track a gradual rotation of the fast direction is observed from ene wsw at the northwest end of the array to e w to the southeast and the delay times average 1 65 s we infer that the sks splits are the product of anisotropy in the asthenosphere and the anisotropy orientation does not vary with depth beneath the track the average fast directions ene wsw to the northwest are consistent with generation by mantle shear parallel to the subduction of the juan de fuca plate and the more e w fast directions to the east are perhaps due to shear caused by the basin and range extension since the observed fast directions are not parallel to the newberry track as the subduction counterflow model or the gravitational flow model suggests the age progressive volcanism is unlikely a direct product of asthenospheric flow instead we propose that the newberry track is the product of lithosphere controlled processes

holocene sea ice variations in greenland onshore evidence the oldest dated driftwood log from northern greenland is c 9300 cal years old which is about 2000 years younger than the beginning of the last deglaciation and 2000 years younger than the oldes

the fate of the juan de fuca plate implications for a yellowstone plume head beneath the pacific northwest the juan de fuca plate a remnant of the farallon plate continues subducting beneath the north american continent to the east of the cascadia subduction zone lies the yellowstone hotspot track the origins of this track can be traced back to the voluminous basaltic outpourings in the columbia plateau around 17 ma if these basalts are the result of a large melting anomaly rising through the mantle to the base of the north american continent such as a mantle plume head the anomaly would need to punch through the subducting juan de fuca slab here we use teleseismic body wave travel time tomography to investigate the fate of the subducted slab and its possible interaction with a plume head our dataset is derived from the oregon array for teleseismic study oats deployment in oregon and all other available seismic data in this region during the same period in our jdf07 models we image the subducted juan de fuca plate in the mantle east of the cascades beneath oregon where the slab has not been imaged before to a depth of 400 km but no deeper the slab dips similar to 50 degrees e and has a thickness of similar to 75 km immediately beneath the slab we image a low velocity layer with a similar geometry to the slab and extending down to at least similar to 575 km depth in the v model the total length of the high velocity slab is similar to 660 km about 180 km longer than the estimated length of slab subducted since 17 ma assuming similar slab geometry to today this 180 km length of slab would reach similar to 60 km depth comparable to the thickness of continental lithosphere we propose that the absence of the slab below 400 km today is due to the arrival of the yellowstone plume head similar to 17 ma which destroyed the juan de fuca slab at depths greater than the thickness of the continental lithosphere given this scenario the low velocity anomaly beneath the slab is likely the remnant plume head material which has been pulled down by traction with the subducting plate the amplitude of the observed low velocity anomaly is comparable with that expected for plume head material 100 300 degrees c hotter than the surrounding asthenosphere c 2007 elsevier b v all rights reserved

multiple frequency sh wave tomography of the western us upper mantle summary we estimate the sh wave velocity and attenuation structures of the western us upper mantle using the dense network of the usarray and new techniques we observe a multiple frequency data set of both traveltime and amplitude anomalies and interpret these with full 3 d finitefrequency sensitivity kernels amplitudes show stronger frequency dependence than traveltimes we perform a joint inversion on the measured traveltime and amplitude anomalies interpreting them in terms of velocity and attenuation heterogeneities aside from the expected clear division between the slow tectonically active region in the west and the fast craton in the east several interesting smaller velocity anomalies are observed the subduction along the cascades at 100 300 km depths shows lateral discontinuity with a slab hole absence of fast anomalies observed around 45 n the delaminated sierra nevada mountains root is observed to have sunk to 200 km depth the yellowstone plume seems to have an origin weak slow velocity anomalies near 1000 km depth but the plume conduit seems to be interrupted by a fast anomaly which is identified as a fragment of the farallon slab the s velocity model shows a trench perpendicular slab gap absence of fast anomalies at almost the same location as in the p model recently published by sigloch et al 2008 the methodological improvements described in the first paragraph have several benefits amplitude data help to sharpen the edges of narrow velocity heterogeneities in the shallow upper mantle the focusing effect from velocity heterogeneity dominates over that of attenuation and must be considered when interpreting amplitude anomalies in general velocity and attenuation heterogeneities correlate positively suggesting that temperature plays a major role in forming the anomalies

a deep low velocity body under the yellowstone caldera wyoming delineation using teleseismic p wave residuals and tectonic interpretation in previously published papers iyer 1975 iyer and stewart 1977 iyer 1979 evidence was presented for the presence of a large body of anomalous material with compressional velocities considerably lower than normal from the surrounding rock in the crust and upper mantle under yellowstone national park wyoming in this paper we give a detailed analysis of p residual data from the 26 element telemetered seismic array and three groups of portable stations operated by the u s geological survey in the yellowstone region using a variety of analytical techniques we delineate the shape of the low velocity body determine the velocity structure inside the body and interpret the nature of the material that constitutes the body we will also outline some tectonic implications of our model the spectacular surface geothermal phenomena for which yellowstone is famous result from deep seated volcanism the volcanic evolution of yellowstone is discussed by christiansen and blank 1972 and summarized by eaton and others 1975 briefly the geothermal manifestations in yellowstone are results of three cycles of quaternary volcanism each culminating in a devastating pyroclastic eruption and resulting in large collapse calderas and predominantly rhyolitic flows the oldest cycle ended about 1 9 m y ago forming a caldera from island park to perhaps the central part of the present yellowstone caldera the second cycle climaxed about 1 2 m y ago and was confined to the island park caldera the third cycle began soon after the second and is responsible for the 75 by 45 km yellowstone caldera as it is outlined today this caldera is the result of a catastrophic eruption approximately 600 000 yr ago the most recent episode of volcanism probably began about 150 000 yr ago in the western half of the caldera near old faithful geyser and the youngest flows in yellowstone about 70 000 yr old are probably associated with this episode

the global middle and late miocene and the deep earth model for earlier orogenies abstract the 11 ma middle and late miocene interval forms only 2 of phanerozoic time but includes two broadly contemporaneous global orogenies one reaching across southern eurasia and the other spanning the circumpacific these two global orogenies caused many global events and because they are close to us in time causality links between these orogenies and these far scattered events are much more apparent than in older orogenies these teleconnections include establishment of the present world oceanic current system the beginnings of oceanic cooling at 14 ma an increase in hemipelagic mud bordering the continents changes in continental tilts and river systems great biological changes increased desertification replacement of c 3 by c 4 grasses a major shift in siliceous microfossils from the atlantic to the pacific at 15 ma and first development of the earliest hominids in east africa starting at 10 ma in addition spreading rates of oceanic ridges increased volcanism increased there was movement along many transform faults and continental elevations increased short bulleted statements set forth these near and far field events immediate causes were increased rates of plate motions and or changes of directions only a strong short 11 ma pulse of heat from the earth s core provides the logical ultimate source of this energy only such a pulse of heat from the core has sufficient magnitude and acts globally thus the deep earth cycle is a plausible easy to understand overarching explanation that should be increasingly considered by geologists and geophysicists studying the outer crust a flow diagram links major earth surface features on the continents to the deep earth alternative explanations for these events are considered and seem totally inadequate

lithospheric topography tilted plumes and the track of the snake river yellowstone hot spot 1 the trace of the snake river yellowstone hot spot is the world s best example of a mantle plume that has been overridden by continental lithosphere the standard model calls for the plume head to rise under northern nevada and be forced northward to form basalts of the columbia plateau subsequent movement of north america to the southwest over the plume tail created a hot spot trace on the surface we present a new conceptual model for the origin of this feature that resolves inconsistencies in the current standard model and explains the recent documentation of a thermal anomaly in the mantle below yellowstone today that plunges 65 wnw our model implies that the plume tail was forced beneath thinned cratonic lithosphere to the se along with part of the plume head and has remained in this orientation for the last 12 ma we infer that almost all of the volcanism in se oregon and sw idaho prior to 12 ma results from overriding the southern extension of the plume head not the plume tail and that a distinct plume tail hot spot track was not established until formation of the bruneau jarbidge eruptive center around 12 ma the plume tail track may also be controlled by a preexisting structural boundary in lithosphere that is thinner than adjacent lithosphere this model demonstrates the potential importance of lithospheric topography on controlling the surface manifestation of plume volcanism and the complexity that may arise when lithospheric thickness is nonuniform

testing five of the simplest upper mantle anisotropic velocity parameterizations using teleseismic s and sks data from the billings montana passcal array 1 five of the simplest parameterizations of upper mantle anisotropy are tested and ranked for a data set collected on a dense temporary passcal seismic array located 100 km ne of yellowstone these hexagonal symmetry anisotropy models possess either one or two layers with either flat or dipping fast velocity axis fva recordings from fifteen high quality direct s and sks arrivals are stacked to provide accurate waveform and error estimates source normalization is accomplished using the cross convolution technique a direct monte carlo neighborhood algorithm is used to map the posteriori model probability density ppd volume using the f test we find that models with purely flat fva can be rejected at 97 probability our best model p5 is a two layer dipping fva parameterization albeit the two layer model with one flat and one dipping fva can only be rejected at 80 probability the best model has a lower layer with a n65 e fva strike and a 12 dip down to the southwest and an upper layer with a n20 w fva strike and a 47 fva dip down to the southeast the bottom asthenospheric layer fva strikes parallel to north america s absolute plate motion direction and dips opposite to what passive plate shear of the asthenosphere would predict the upper lithospheric layer is consistent with lpo accretion associated with north directed drift of the north american plate during the mesozoic comparison between the sks and direct s wave data sets shows that the direct s waves improve resolution of the double layer anisotropic model parameters

regional uplift associated with continental large igneous provinces the roles of mantle plumes and the lithosphere the timing and duration of surface uplift associated with large igneous provinces provide important constraints on mantle convection processes here we review geological indicators of surface uplift associated with five continent based magmatic provinces emeishan traps 260 million years ago ma siberian traps 251 ma deccan traps 65 ma north atlantic phase 1 61 ma and phase 2 55 ma and yellowstone 16 ma to recent all five magmatic provinces were associated with surface uplift surface uplift can be measured directly from sedimentary indicators of sea level in the north atlantic and from geomorpholocial indicators of relative uplift and tilting in yellowstone in the other provinces surface uplift is inferred from the record of erosion in the deccan north atlantic and emeishan provinces transient uplift that results from variations in thermal structure of the lithosphere and underlying mantle can be distinguished from permanent uplift that results from the extraction and emplacement of magma transient surface uplift is more useful in constraining mantle convection since models of melt generation and emplacement are not required for its interpretation observations of the spatial and temporal relationships between surface uplift rifting and magmatism are also important in constraining models of lip formation onset of surface uplift preceded magmatism in all five of the provinces biostratigraphic constraints on timing of uplift and erosion are best for the north atlantic and emeishan provinces where the time interval between significant uplift and first magmatism is less than 1 million years and 2 5 million years respectively rifting post dates the earliest magmatism in the case of the north atlantic phase 1 and possibly in the case of siberia the relative age of onset of offshore rifting is not well constrained for the deccan and the importance of rifting in controlling magmatism is disputed in the emeishan and yellowstone provinces in these examples rifting is not a requirement for onset of lip magmatism but melting rates are significantly increased when rifting occurs models that attempt to explain emplacement of these five lips without hot mantle supplied by mantle plumes often have difficulties in explaining the observations of surface uplift rifting and magmatism for example small scale convection related to craton or rift boundaries edge driven convection cannot easily explain widespread 1000 km scale transient surface uplift emeishan deccan north atlantic and upper mantle convection initiated by differential incubation beneath cratons the hotcell

teleseismic p wave tomogram of the yellowstone plume 1 inversion of a new data set of teleseismic p wave travel times from three passcal seismic deployments around the yellowstone hotspot reveals a 100 km diameter upper mantle plume that extends from the yellowstone volcanic caldera to 500 km depth and dips 20 to the northwest a monotonic decrease in the velocity perturbation of the plume from 3 2 at 100 km to 0 9 at 450 km is consistent with a uniform thermal anomaly of 180 c where the plume crosses the 410 km discontinuity previous research shows a depression in the 410 km discontinuity consistent with a warm plume fee and dueker 2004 additionally a region of high velocities extends to 250 km beneath the wind river basin in nw wyoming that may represent a convective downwelling of the lithosphere

holocene boreal molluscs in greenland palaeoceanographic implications abstract boreal molluscs now extinct in greenland waters occur as subfossils in west greenland between lat 65 30 and 68 30 n a number of new localities for these warmth demanding molluscs are described and the list of species now comprises the gastropod emarqinula fissura and the bivalvalves heteranomia squamula modiolus arctica islandica panopea norvegica and zirphaea crispata during their time the molluscs formed an isolated northern outpost located in the area which as a result of the complex oceanic circulation today has greenland s highest ocean surface temperatures the occurrences are 14c dated to the interval 8400 4900 yr b p and summer surface temperatures were 1 3 c higher than now for its beginning this period coincides with similar marine optimal periods in east greenland and on the baffin island shelf whereas it took 1000 years before the beginning of warmer than present temperatures on land on the basis of this evidence it is concluded that the rise of sea surface temperatures was afforded by a decrease in inflow of cold polar water and or increase in inflow of warm atlantic water into davis strait rather than climatic change

crustal structure of the newer volcanics province se australia from ambient noise tomography abstract intraplate volcanism is a widespread phenomenon and is generally regarded to be independent of plate tectonics the newer volcanics province nvp of se australia represents the most recent and arguably still active intraplate volcanism on the australian continent and has been postulated to originate from the combined effect of localized shear flow and edge driven convection in this study we adopt ambient noise tomography and monte carlo inversion methods to construct the first local scale 3d crustal vs model of the nvp region with a resolution of 35 km the model displays distinct crustal velocity features near the eastern and western margins of the nvp which may point to the existence of a lithosphere scale plumbing system for the migration of melt associated with the boundary between the delamerian orogen and the lachlan orogen which underlies the nvp in particular exceptionally high velocities are observed in the middle crust of the delamerian orogen and are best explained by buried magmatic arcs this interpretation is consistent with a subduction accretion origin for the delamerian orogen trans lithospheric faults might have developed during the accretion processes providing possible pathways for the migration of nvp magmas to the crust and surface our 3d model also images small localized velocity reductions in the lower crust at the region where the two distinct lithospheric units meet the low velocity zone is spatially correlated with the top of a prominent lithosphere scale low resistivity zone 10 30 m which we interpret to represent intruded magmatic sills with small proportions of melt remaining

the diversity of tectonics from fluid dynamical modeling of the lithosphere mantle system abstract numerical modeling of the lithosphere has been carried out from many points of view most popular and prevalent is the use of the kinematic boundary conditions to move the lithosphere about in the dynamics we have approached the numerical modeling of the lithosphere mantle system by treating this as a fluid dynamical system in which crustal and mantle rheologies and thermal and compositional buoyant forces play dominant roles in delivering the dynamics in a self consistent manner we have investigated the development of extensional and compressional tectonic regimes from variations of the crustal density and compare their temporal evolutions in comparing with kinematically driven thickening of the lithosphere we find that the timescales are more self consistently determined in a full fluid dynamical treatment than in kinematic models we emphasize the delicate nature of balancing the chemical buoyancy of the crust with the thermal negative buoyancy of the mantle lithosphere as the modes and associated timescales of the delamination process are controlled critically by their relative importance the role of an actively participating buoyant crust cannot by ignored in the overall lithosphere mantle dynamics

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

ubiquitous low velocity layer atop the 410 km discontinuity in the northern rocky mountains receiver functions from three 30 station iris passcal small aperture arrays 2 15 km station spacing operated for 10 months each in the northern rocky mountains show a ubiquitous negative polarity p to s conversion just preceding the 410 km discontinuity arrival data from the three arrays were sorted into nw se and sw back azimuth quadrants and stacked to form nine quadrant stacks remarkably the negative polarity arrival npa is apparent in 8 of the 9 quadrant stacks with 7 of the 8 having well correlated waveforms each quadrant stack also contains clear p to s conversions from the 410 and 660 km discontinuities moveout analysis shows that all the major phases display the correct moveout for forward scattered p s phases the waveshapes for the seven similar npa 410 km discontinuity arrivals are modeled with a five parameter double gradient slab model that is parameterized as follows a top gradient thickness and shear velocity decrease a constant velocity layer bottom gradient thickness and shear velocity increase model misfit is assessed via a grid search over the model space using a reflectivity code to calculate synthetic seismograms model likelihood is determined by calculating 1 and 2 d marginal probability density functions pdf for the five parameters the 1 d marginals display a range of peak values although significant overlap is observed for the top gradient thickness and its associated velocity decrement from the peak value of the summary pdf we find the top velocity gradient to be sharp 6 4 km and the shear velocity decrement to be large 8 9 vs defining an effective thickness of the low velocity layer as the mean layer thickness plus half the mean gradient thicknesses the 410 low velocity layer thickness is found to be 22 km a review of changes in the physical state required to match our new 410 lvl constraints suggests that the water filter model remains an operative hypothesis to test

earthquake depth distributions in central asia and their relations with lithosphere thickness shortening and extension this paper examines the relationship between seismogenic thickness lithosphere structure and rheology in central and northeastern asia we accurately determine earthquake depth distributions which reveal important rheological variations in the lower crust these variations exert a fundamental control on the active tectonics and the morphological evolution of the continents we consider 323 earthquakes across the tibetan plateau the tien shan and their forelands as well as the baikal rift ne siberia and the laptev sea and present the source parameters of 94 of these here for the first time these parameters have been determined through body wave inversion the identification of depth phases or the modelling of regional waveforms lower crustal earthquakes are found to be restricted to the forelands in areas undergoing shortening and to locations where rifting coincides with abrupt changes in lithosphere thickness such as the ne baikal rift and w laptev sea the lower crust in these areas is seismogenic at temperatures that may be as high as 600 c suggesting that it is anhydrous and is likely to have great long term strength lower crustal earthquakes are therefore a useful proxy indicating strong lithosphere in places that are too small in areal extent for this to be confirmed independently by estimating effective elastic thickness from gravity topography relations the variation in crustal rheology indicated by the distribution of lower crustal earthquakes has many implications ranging from the support of mountain belts and the formation of steep mountain fronts to the localization and orientation of rifting in combination these processes can also be responsible for the separation of the front of the thin skinned mountain belts from their hinterlands when continents separate

reconstruction of the late holocene changes in the sub arctic front position at the reykjanes ridge north atlantic changes in the dynamics of the north atlantic subpolar gyre are involved in the modulation of the northward salinity and heat transport in the northern north atlantic via the north atlantic current nac variations in the strength of the east greenland current egc can influence the gyre dynamics by impacting deep convection in the labrador sea oxygen isotope data of three planktonic foraminiferal species surface water neogloboquadrina pachyderma dextral coiling and globigerina bulloides thermocline recorder globorotalia inflata from a site located close to the present sub arctic front at the reykjanes ridge suggest significant strengthening or shifting of the sub arctic front throughout the late holocene the oxygen isotope based inferences are supported by mg ca derived temperature reconstructions from neogloboquadrina pachyderma dextral coiling alkenone derived sea surface temperature and other paleoclimatic proxy data the late holocene strengthening shift of the sub arctic front appears caused

lithosphere asthenosphere interaction beneath the western united states from the joint inversion of body wave traveltimes and surface wave phase velocities summary the relation between the complex geological history of the western margin of the north american plate and the processes in the mantle is still not fully documented and understood several pre usarray local seismic studies showed how the characteristics of key geological features such as the colorado plateau and the yellowstone snake river plains are linked to their deep mantle structure recent body wave models based on the deployment of the high density large aperture usarray have provided far more details on the mantle structure while surface wave tomography ballistic waves and noise correlations informs us on the shallow structure here we combine constraints from these two data sets to image and study the link between the geology of the western united states the shallow structure of the earth and the convective processes in mantle our multiphase dna10 s model provides new constraints on the extent of the archean lithosphere imaged as a large deeply rooted fast body that encompasses the stable great plains and a large portion of the northern and central rocky mountains widespread slow anomalies are found in the lower crust and upper mantle suggesting that low density rocks isostatically sustain part of the high topography of the western united states the yellowstone anomaly is imaged as a large slow body rising from the lower mantle intruding the overlying lithosphere and controlling locally the seismicity and the topography the large e w extent of the usarray used in this study allows imaging the slab graveyard a sequence of farallon fragments aligned with the currently subducting juan de fuca slab north of the mendocino triple junction the lithospheric root of the colorado plateau has apparently been weakened and partly removed through dripping the distribution of the slower regions around the colorado plateau and other rigid blocks follows closely the trend of cenozoic volcanic fields and ancient lithospheric sutures suggesting that the later exert a control on the locus of magmato tectonic activity today the dna velocity models are available for download and slicing at http dna berkeley edu

a mid holocene shift in arctic sea ice variability on the east greenland shelf records of iceberg rafting and palaeohydrography from two east greenland shelf cores jm96 1206 1 gc and jm96 1207 1 gc are reported benthic foraminifera stable isotopes and ird e uxes indicate a shift toward colder lower salinity polar conditions c 5 cal ka a new proxy of iceberg rafting on the east greenland shelf is the e ux of calcium carbonate tic thought to be derived from glacial erosion of cretaceous calcareous mudstones a change in the regularity and spacing of carbonate e ux peaks at c 4 7 cal ka in jm96 1207 coincides with the onset of neoglacial cooling in the renland ice core d 18 o record we propose that the carbonate e ux peaks between 4 7 and 0 4 cal ka are related to sea surface coolings associated with increased e ux of polar water and sea ice in the east greenland current these peaks are synchronous with sea surface coolings interpreted from north atlantic deep sea cores but additional peaks centred around 2 4 and 3 8 cal ka in jm96 1207 suggest that the shelf site captures higher frequency events the data indicate that severe arctic sea ice events began in the neoglacial interval and that earlier holocene cool events in deep sea records are associated with other processes such as release of meltwater from residual glacier ice and glacial lakes

characteristics of oxygen 18 and deuterium composition in waters from the pecos river in american southwest abstract the pecos river situated in eastern new mexico and western texas receives snowmelt from winter storms in the headwater region of the southern rocky mountains and runoff from warm season monsoonal rainfall in the lower valley the isotopic composition of the two water sources differs from each other due to their different geographical origins in the pacific north and the gulf of mexico to better assess the physical features of the pecos river oxygen and hydrogen isotopic compositions 18 o and d major ion concentrations and other physical variables e g water temperature and electrical conductivity were measured on water samples collected from the main stem and its selected tributaries during a growing season march may and july in 2005 the results of this work indicate that stream water from the pecos river contains a relatively large magnitude of variations in 18 o and d with 18 o ranging from 8 9 to 3 6 and d from 64 5 to 1 6 the average value of 18 o is around 3 which is significantly larger than that of the snowmelt but almost identical to that of the mexican monsoonal rainfall on the other hand the average value of d is around 30 which is significantly larger than that of the snowmelt but lower than that of the mexican monsoonal rainfall application of a dual isotope index deuterium excess d excess allows us to assess the relative contribution of various hydrologic components and processes that shape the stream hydrology of the pecos river the river water from the upper valley is characterized by relatively low values of 18 o and d and relatively high values of d excess d 10 documenting the isotopic fingerprint of the snowmelt the middle basin is topographically gentle and its water quality has been severely affected by anthropogenic disturbances e g water impoundments and diversions as a result chemical and isotopic composition of the water from the middle basin is highly variable depending on its time location and degree of disturbances both 18 o and d increase significantly from upstream to downstream and from cold to warm seasons because of evaporation induced isotopic enrichments the average 18 o value of the heavy isotope enriched waters from the middle basin is identical to that of the waters from the lower valley in contrast d excess of the waters from the middle basin usually is negative and substantially lower than that of the waters from the lower valley using a simple d excess based hydrologic model we estimated that there was up to 85 of stream flow which was derived from local freshwater sources mainly from the mexican monsoonal rainfall in the lower valley and that there was up to 33 of stream water which was lost through evaporation occurring in stream channels and fields of the middle basin additionally the correlation of d excess and electrical conductivity further highlights the role of evaporative enrichments in regulating stream chemistry and isotope hydrology this study demonstrates the usefulness of combined isotopic and geochemical data especially the applicability of d excess for watershed baseline assessments

yellowstone hotspot continental lithosphere interaction the snake river plain represents 17 m y of volcanic activity that took place as the north american continent migrated over a relatively fixed magma source or hotspot we present new pb sr and nd data for a suite of 25 basalts collected from western and central snake river plain srp the new isotope data combined with previously published data from the srp provide a traverse of the wyoming craton margin from the 87sr 86sr 0 706 line boundary of western srp with phanerozoic accreted terranes east through the central and eastern srp to the yellowstone plateau low k basalts from the western srp overlain by high k basalts provide a temporal record of regional source variation from 16 8 to 0 2 ma principal component analysis pca of the new and previously published srp basalt pb isotopes reveals that 97 of the total variability is accounted for by mixing between three end members and is consistent with a sublithospheric yellowstone hotspot mantle source with a radiogenic isotope composition similar to the mantle source of the early columbia river basalt group crbg and two continental lithosphere end members heterogeneous in age and composition we use the srp pb sr and nd isotope data to model the yellowstone hotspot continental lithosphere interaction by three component mixing between two continental lithospheric components archean lithosphere cl1 that represents older lithosphere underlying the yellowstone plateau in the east and paleoproterozoic lithosphere cl2 representing the younger lithosphere underlying the srp in the west near the craton margin and a sublithospheric end member representing the yellowstone hotspot pl the results suggest a continuous flow of pl material westward as the na continental lithosphere migrated over the upwelling hotspot along a shoaling gradient in the sub continental mantle lithosphere the model shows a decrease in total lithosphere end members cl1 cl2 and the lithosphere ratio cl1 cl2 from the craton interior at yellowstone toward its western margin consistent with geologic and geophysical evidence that the continental lithosphere beneath the srp decreases in age and thickness from east to west the lithosphere ratio shows step like decreases from yellowstone in the east to the 87sr 86sr 0 706 line in the west indicating that the srp cuts across geochemically distinct parcels of lithospheric mantle consistent with terrane accretion models for the craton margin in the western srp young high k basalts have a lower mass fraction of total lithospheric compared to the underlying low k tholeiites but the same lithosphere ratio consistent with a recent 700 900 ka decrease in lithosphere contribution between eruption of early low and younger high k basalts

regional variation of coda q in kopili fault zone of northeast india and its implications abstract kopili fault has been experiencing higher seismic and tectonic activity during the recent years these kind of active tectonics can be inspected by examining coda wave attenuation and its dependence with frequency exploiting single back scattering model we have endeavored to measure coda q and its associated parameters such as frequency dependent factor n and attenuation coefficient covering seven lapse time windows spanning from 30 to 90 s and central frequencies 1 5 3 5 6 9 and 12 hz the average estimated values of qc increase s with frequency and lapse time window from 114 at frequency 1 5 hz to 1563 at frequency 12 hz for 30 s window length and from 305 at frequency 1 5 hz to 2135 at frequency 12 hz for 90 s window length the values of q0 and n are also estimated for the entire kopili fault zone for this study region the q0 values vary from 62 to 348 and n varies from 0 57 to 1 51 within the frequency range 1 5 to 12 hz furthermore depth variation of attenuation of this region reveals that there is velocity anomaly at depth 210 220 km as there arises sharp changes in and n which are supported by available data reported by other researcher for this region finally we have tried to separate the intrinsic and scattering attenuation for this area it is observed that the entire region is dominated by mainly scattering attenuation but we can see an increase in intrinsic attenuation with depths in two stations namely tzr and bkd furthermore the obtained results are comparable with the available global data

holocene palaeoceanographic evolution off west greenland benthic foraminiferal assemblages from a core southwest of disko bugt provide a holocene perspective last 7 ka bp on ice sheet ocean interactions between the west greenland current wgc and the west greenland ice sheet changes in the fauna reveal significant variations in the water mass properties temperature and salinity of the wgc through time from 7 3 to 6 2 ka bp a relatively warm strong wgc influences ice sheet melt in disko bugt and causes enhanced meltwater production resulting in low surface water productivity the most favourable oceanographic conditions occur from 5 5 to 3 5 ka bp associated with thermal optimum like conditions encompassing minimum ice sheet extent in the disko bugt area these conditions are attributed to 1 reduced meltwater influence as the ice sheet is land based and 2 enhanced contribution of warm saline water masses from the irminger current to the wgc the transition into the late holocene last 3 5 ka bp is characterized by a cooling of oceanographic conditions caused by increased advection of cold low salinity water masses from the east greenland current a longer term late holocene cooling trend within the wgc is attributed to the onset of neoglacial cooling within the north atlantic region superimposed on this cooling trend multicentennial scale variability within the wgc matches reconstructions from a nearby coring site in disko bugt as follows 1 cooling at 2 5 ka bp linked to the 2 7 ka bp cooling event 2 a warm phase centred at 1 8 ka bp associated with the roman warm period 3 slight warming between 1 4 and 0 9 ka bp linked to the medieval climate anomaly 4 severe cooling of the wgc after 0 9 ka bp culminating at 0 3 ka bp during the little ice age we show that multicentennial scale palaeoceanography variability along the west greenland margin is driven by ocean forcing i e variations in the relative contribution of atlantic irminger current and polar east greenland current water masses to the wgc during the last 7 ka bp influencing ice sheet dynamics

mantle plume influence on the neogene uplift and extension of the u s western cordillera espite its highly extended and thinned crust much of the western cordillera in the united states is elevated more than 1 km above sea level therefore this region cannot be thought of as thick crust floating isostatically in a uniform mantle rather the lithospheric mantle and or the upper asthenosphere must vary in thickness or density across the region utilizing crustal thickness and density constraints we modeled the residual mass deficit that must occur in the mantle lithosphere and asthenosphere beneath the western cordillera a major hot spot broke out during a complex series of cenozoic tectonic events that included lithospheric thickening backarc extension and transition from a subduction to a transform plate boundary we suggest that many of the characteristics that make the western cordillera unique among extensional provinces can be ttributed to the mantle plume that created the yellowstone hot spot

a fixed sublithospheric source for the late neogene track of the yellowstone hotspot implications of the heise and picabo volcanic fields the heise and picabo volcanic fields of eastern idaho are part of the more extensive time transgressive yellowstone snake river plain hotspot track calderas associated with these two silicic volcanic fields are buried under 1 to 3 km of younger basalt so their locations and eruption record histories have been based on analysis of silicic units along the margins of the eastern snake river plain along with some limited geophysical data a 1 5 km borehole penetrating through basalt into underlying silicic rocks provides new data we used to reassess caldera locations and the timing of eruptions of these volcanic fields using these new caldera locations we calculate an extension adjusted rate of 2 35 cm yr for the north american plate over the last 6 66 m y and a velocity of 2 30 cm yr over the 10 27 m y recalculation of a previously determined plate velocity based migration of the deformation field surrounding the eastern snake river plain yields an extension adjusted rate of 2 38 0 21 cm yr these migration rates all fall within the previously published range of north american plate velocities of 2 2 0 8 cm yr 2 4 cm yr and 2 68 0 78 cm yr based on a global hot spot reference frame the consistency of these rates suggest that over the last 10 m y the yellowstone hot spot is fixed with respect to the motion of the north american plate and therefore consistent with a classical deep sourced hotspot model

hitting the ice sheets where it hurts in both hemispheres glacier discharge to the sea has increased markedly in recent years as warm water from intermediate depths is melting the floating ends of glaciers from below accelerating them

geodynamics of the yellowstone hotspot and mantle plume seismic and gps imaging kinematics and mantle flow abstract integration of geophysical and geological data show that the yellowstone hotspot resulted from a mantle plume interacting with the overriding north america plate a process that has highly modified continental lithosphere by magmatic and tectonic processes and produced the 16 17 ma 700 km long yellowstone snake river plain ysrp silicic volcanic system accessibility of the ysrp allowed large scale geophysical projects to seismically image the hotspot and evaluate its kinematic properties using geodetic measurements seismic tomography reveals a crustal magma reservoir of 8 to 15 melt 6 km to 16 km deep beneath the yellowstone caldera an upper mantle low p wave velocity body extends vertically from 80 km to 250 km beneath yellowstone but the anomalous body tilts 60 wnw and extends to 660 km depth into the mantle transition zone we interpret this conduit shaped low velocity body as a plume of up to 3 5 vp and 5 5 vs perturbation that corresponds to a 1 2 partial melt models of whole mantle convection reveal eastward upper mantle flow beneath yellowstone at relatively high rates of 5 cm yr that deflects the ascending plume into its west tilted geometry a geodynamic model of the yellowstone plume constrained by vp and vs velocities and attenuation parameters suggests low excess temperatures of up to 120 k corresponding to a maximum 2 5 melt and a small buoyancy flux of 0 25 mg s i e properties of a cool weak plume the buoyancy flux is many times smaller than for oceanic plumes nonetheless plume buoyancy has produced a 400 km wide 500 m high topographic swell centered on the yellowstone plateau contemporary deformation derived from gps measurements reveals sw extension of 2 3 mm yr across the yellowstone plateau one fourth of the total basin range opening rate which we consider to be part of basin range intraplate extension locally decadal episodes of subsidence and uplift averaging 2 cm yr characterize the 80 year yellowstone caldera monitored history and are modeled as hydrothermal magmatic sources moreover a recent episode 2004 2009 of accelerated uplift of the yellowstone caldera at rates up to 7 cm yr has been modeled as resulting from magmatic recharge of a 10 km deep sill at the top of the crustal magma reservoir regionally gravitational potential energy of the yellowstone swell drives the lithosphere southwest and downhill from the yellowstone plateau 400 km where it coalesces with basin range province wide westward extension based on the geometry and its assumed 660 km depth we extrapolate the plume source southwest to its original location at 17 ma and 600 km southwest and 200 km north of the ysrp importantly this location is beneath the southern part of the columbia plateau flood basalt field of the same age and implies that the yellowstone mantle plume may be the common source for both of these large volcanic fields our time progression model suggests that the original plume head rose vertically behind the juan de fuca plate but at 12 ma it lost the protection of the subducting plate from eastward mantle flow and encountered cooler thicker continental lithosphere becoming entrained in eastward upper mantle flow these results reveal that yellowstone plume plate processes have had a profound effect on late cenozoic geologic evolution and topography of a large part of the western u s

early holocene palaeoceanography and deglacial chronology of disko bugt west greenland two new cores from disko bugt a large marine embayment in west greenland are used to assess the deglacial chronology and palaeoceanography of the area during the early holocene deglaciation of the main part of disko bugt is directly dated for the first time to a minimum of ca 10 2 ka cal bp by this time the jakobshavn isbrae ice stream had retreated to the eastern margins of disko bugt initial deglaciation took place before the relatively warm west greenland current wgc was initiated a strengthening in the wgc is identified from ca 9 2 ka cal bp accompanied by retreat of the ice stream to a shallow bank immediately west of the present day jakobshavn isfjord while in this position the calving and melting ice stream produced large volumes of sediment and meltwater the large volumes of meltwater prevented the relatively warm waters of the wgc reaching the eastern margins of disko bugt the ice stream remained grounded on this bank for over a thousand years until ca 7 9 ka cal bp when reduced sedimentation rates and an increase in boreal fauna point to its retreat inside the present day fjord system

detailed three dimensional shear wave velocity structure of the northwestern united states from rayleigh wave tomography abstract since the mid miocene the northwestern united states has experienced extensive flood basalt volcanism followed by the formation of two time progressive tracks of silicic volcanism the yellowstone snake river plains ysrp and the high lava plains hlp the ysrp track progresses towards the northeast parallel to north american plate motion and has therefore often been attributed to a deep mantle plume source however the hlp track progresses to the northwest over the same time frame in a direction not consistent with any regional plate motion the causes of the mid miocene flood basalts and the tracks of the ysrp and hlp are a matter of ongoing debate we present results of rayleigh wave phase velocity inversions and inversions for 3 d shear wave velocity structure of the northwestern united states using data collected from the high lava plains seismic experiment and the earthscope usarray transportable array ta the large number of stations used in these inversions allows us to show an unprecedented level of detail in the seismic velocity structures of this tectonically complex area our velocity images indicate that low s wave velocities in the uppermost mantle do not well match the track of hlp volcanism while at the surface the newberry caldera appears to anchor the nw end of the hlp hotspot track the seismic results show that it lies in a separate north south trending low velocity band just east of the cascades that is distinct from the main hlp trace the ultra low s wave velocities beneath the ysrp track extend locally to at least 175 km depth and are by far the most prominent seismic anomalies in the region along axis the ysrp hotspot track is characterized by a discrete low velocity channel in the upper mantle that shallows narrows and intensifies to the northeast but then deepens rapidly to the north beneath yellowstone the shallowing of the low velocity anomaly to the northeast is consistent with a stationary heat source beneath a moving plate coupled with basin and range extension and heating

spatial and temporal variability of holocene temperature in the north atlantic region the early holocene climate of the north atlantic region was influenced by two boundary conditions that were fundamentally different from the present the presence of the decaying laurentide ice sheet lis and higher than present summer solar insolation in order to assess spatial and temporal patterns of holocene climate evolution across this region we collated quantitative paleotemperature records at sub millennial resolution and synthesized their temporal variability using principal components analysis pca the analysis reveals considerable spatial variability most notably in the time transgressive expression of the holocene thermal maximum htm most of the region but especially areas peripheral to the labrador sea and hence closest to the locus of lis disintegration experienced maximum holocene temperatures that lagged peak summer insolation by 1000 3000 years many sites from the northeastern north atlantic sector including the nordic seas and scandinavia either warmed in phase with maximum summer insolation 11 000 9000 years ago or were less strongly lagged than the baffin bay labrador sea region these spatially complex patterns of holocene climate development which are defined by the pca resulted from the interplay between final decay of the lis and solar insolation forcing

high resolution paleoproductivity fluctuations during the past 24 kyr as indicated by benthic foraminifera in the marginal arctic ocean abstract analyses of benthic foraminifera in sediment cores taken at about 1000 m water depth at the yermak plateau and the barents sea slope adjacent to the position of the ice sheet edge during the last glacial maximum show that paleoproductivity was reduced to about a third of its present level during peak glacial stadials these reduced values are still higher than values for modern permanently ice covered regions suggesting that the core locations were at least partially ice free even during stadials paleoproductivity at the core locations was higher than or equal to that of today during initial deglaciations and warm substages peak paleoproductivity occurred in samples with low salinity surface waters as indicated by oxygen isotope values of planktonic foraminifera and slightly after increased abundance of atlantic species suggesting that enhanced advection of warmer waters from the atlantic supported the initial ice sheet retreat during the holocene climatic optimum productivity was much less than at present on the yermak plateau high at the barents sea site perhaps because of increased advection of atlantic water to the latter site and heavier ice coverage at the former after this optimum paleoproductivity at both sites was similar with slightly lower values during cold periods such as the little ice age

subduction triggered magmatic pulses a new class of plumes article i nfo a variety of atypical plume like structures and focused upwellings that are not rooted in the lower mantle have recently been discussed and seismological imaging has shown ubiquitous small scale convection in the uppermost mantle in regions such as the mediterranean region the western us and around the western pacific we argue that the three dimensional return flow and slab fragmentation associated with complex oceanic subduction trajectories within the upper mantle can generate focused upwellings and that these may play a significant role in regional tectonics the testable surface expressions of this process are the outside arc alkaline volcanism topographic swell and low velocity seismic anomalies associated with partial melt using three dimensional simplified numerical subduction models we show that focused upwellings can be generated both ahead of the slab in the back arc region though five times further inward from the trench than arc volcanism and around the lateral edges of the slab in the order of 100 km away from slab edges vertical mass transport and by inference the associated decompression melting in these regions appears strongly correlated with the interplay between relative trench motion and subduction velocities the upward flux of material from the depths is expected to be most pronounced during the first phase of slab descent into the upper mantle or during slab fragmentation we discuss representative case histories from the pacific and the mediterranean where we find possible evidence for such slab related volcanism

multivariate analysis and quantitative paleoecology of benthic foraminifera in surface and late quaternary shelf sediments northern canada abstract benthic foraminifera in surface sediments from northeastern canada and the beaufort shelf were studied to determine the quantitative relationship between recent assemblage distributions and modern water depth temperature and salinity factor analysis shows that 7 factor assemblages account for 92 of the variance between samples multiple linear regression shows that different factors are significantly related to water depth august bottom water temperature or salinity multiple correlation coefficients for depth temperature and salinity are 0 94 0 72 and 0 92 respectively labrador fjords contain arenaceous faunas dominated by eithersaccammina atlantica andreophax fusiformis or byeggerella advena regression analysis shows that thesaccammina reophax factor is most strongly related to salinity theeggerella factor is related to depth and temperature a fauna dominated bytrochammina nana andbuliminella elegantissima is correlated with warm deep water in davis strait calcareous assemblages dominated byelphidium excavatum orcassidulina reniforme are found in arctic bays and shelf areas these factor assemblages are strongly related to temperature and depth cassidulina is also related to salinity anislandiella helenae fauna on the inner labrador shelf is strongly correlated with depth and salinity anonionellina labradorica fauna in deep shelf basins is closely related to salinity the multiple regression model for the sea bed data estimates water depth august bottom water temperature and salinity within confidence limits of 67 m 1 3 c and 1 0 paleoecological transfer functions were used to quantify environmental changes recorded by the foraminifera in two piston cores on a transect across the labrador shelf paleo depth estimates obtained from the core data produce relative sea level curves which are similar in shape to theoretical curves for this region paleo salinity and temperature estimates for offshore core 12 show that the change from a postglacialnonionellina fauna to a late glaciale excavatum fauna is accompanied by a decrease of about 2 in salinity and 4 c in temperature paleoecological estimates for fjord core 111 show that the change from a modernsaccammina reophax fauna to a mid holocenei helenae fauna corresponds to a salinity increase of 3 5 and temperature increase of 1 2 c

geochronology of age progressive volcanism of the oregon high lava plains implications for the plume interpretation of yellowstone 1 the high lava plains province hlp is a late cenozoic bimodal volcanic field at the northern margin of the basin and range province in southeastern oregon that hosts a westward younging trend of silicic volcanism that crudely mirrors northeastward migration of silicic volcanism along the yellowstone snake river plain ysrp trend we present 40ar 39ar ages for 19 rhyolite domes 5 rhyolite ash flow tuffs and 34 basaltic lavas from the hlp the previously identified trend of westward migration of hlp rhyolites is confirmed the rate of propagation is 33 km m y from 10 to 5 ma slowing to 13 km m y after 5 ma the duration of silicic volcanism at any locus is 2 m y three older hlp dacite domes yielded ages of 15 5 ma basalts are not age progressive we identify several episodes of increased basaltic activity at 7 5 7 8 5 3 5 9 and 2 3 ma with the younger episode likely continuing into the recent the hlp and ysrp trends emerged from the axis of middle miocene basaltic volcanism of the columbia river and steens basalts we propose a model in which 1 miocene flood basalts and widespread silicic rocks are the result of emplacement of a plume head near the craton margin enhanced by flow up a topographic gradient along the base of the lithosphere at the craton margin 2 the hlp trend is the result of westward flow originating at the craton margin and 3 the ysrp trend is the trace of the motion of the north american plate over the tail of the plume

reactivation of an archean craton constraints from p and s wave tomography in north china 1 the unusual reactivation of the north china craton ncc challenges the classical views concerning the strength and stability of cratonic lithosphere by using teleseismic body waves recorded at 250 seismic stations this paper presents high resolution north china models of p and s wave velocity based on finite frequency kernel tomography both p and s wave velocity models reveal that 1 an obvious n s trending narrow low velocity region is located at the base of the lithosphere beneath the central block cb of the ncc which extends to more than 500 km depth 2 a region of high velocity extends to more than 250 300 km depth beneath the western block in contrast to the much shallower high velocity zones beneath the cb and shallower high velocities beneath the eastern block these features suggest that warm mantle material with a source at least as deep as the transition zone possibly a mantle plume may be responsible for the reactivation of the ncc the central block may have behaved as a sublithospheric corridor for the warm mantle material due to its pre existing weakness

late holocene environment and climatic changes in ameralik fjord southwest greenland evidence from the sedimentary record sedimentological and geochemical xrf data together with information from diatom and benthic foraminiferal records of a 3 5 m long gravity core from ameralik fjord southern west greenland is used for reconstructing late holocene environmental changes in this area the changes are linked to large scale north atlantic ocean and climate variability ams 14c dating of benthic foraminifera indicates that the sediment core records the last 4400 years and covers the termination of the holocene thermal maximum htm the late htm 4 4 3 2 ka bp is characterized by high accumulation rates of fine silty sediments related to strong meltwater discharge from the inland ice the htm benthic foraminiferal fauna demonstrates the presence of well ventilated saline bottom water originating from inflow of subsurface west greenland current water of atlantic irminger sea origin the hydrographic conditions were further characterized by limited sea ice probably related to a mild and relatively windy winter climate af

mantle transition zone topography and structure beneath the yellowstone hotspot 1 the depths of the 410 and 660 km discontinuities beneath the yellowstone hotspot are constrained using common conversion point imaging of p wave receiver functions the mean depth of the 410 and 660 is 411 1 5 km and 656 1 6 km with 36 40 km of peak to peak topography this topography is spatially uncorrelated providing no evidence for a lower mantle plume currently beneath the hotspot the topography suggests that 200 c thermal anomalies exist with respect to an average mantle adiabat two warmer than normal regions are found at the 410 to the nnw of the hotspot and at the 660 to the ne colder temperatures exist at the 410 under central wyoming upper mantle convection and or intermittent heat and mass transfer across the 660 may be responsible for the uncorrelated topography three negative arrivals about the 410 and 660 are observed that display correct pds moveout

evaluation of the evolving stress field of the yellowstone volcanic plateau 1988 to 2010 from earthquake first motion inversions abstract although the last rhyolite eruption occurred around 70 ka ago the silicic yellowstone volcanic field is still considered active due to high hydrothermal and seismic activity and possible recent magma intrusions geodetic measurements document complex deformation patterns in crustal strain and seismic activity likewise reveal spatial and temporal variations in the stress field we use earthquake data recorded between 1988 and 2010 to investigate these variations and their possible causes in more detail earthquake relocations and a set of 369 well constrained double couple focal mechanism solutions were computed events were grouped according to location and time to investigate trends in faulting the majority of the events have normal faulting solutions subordinate strike slip kinematics and very rarely reverse motions the dominant direction of extension throughout the 0 64 ma yellowstone caldera is nearly ene consistent with the perpendicular direction of alignments of volcanic vents within the caldera but our study also reveals spatial and temporal variations stress field solutions for different areas and time periods were calculated from earthquake focal mechanism inversion a well resolved rotation of 3 was found from nne ssw near the hebgen lake fault zone to ene wsw near norris junction in particular the 3 direction changed throughout the years around norris geyser basin from being ene wsw as calculated in the study by waite and smith 2004 to nne ssw while the other 3 directions are mostly unchanged over time the presence of chocolate tablet structures with two sets of nearly perpendicular normal faults was identified in many stages of the deformation history both in the norris geyser basin area and inside the caldera

new constraints on the properties of the yellowstone mantle plume from p and s wave attenuation tomography 1 we estimate attenuation t for teleseismic p and s arrivals to seismometers in the yellowstone intermountain seismic array tomographically invert these data for upper mantle qp 1 and qs 1 structure and with the aid of the upper mantle velocity model of waite et al 2006 interpret the results for mantle temperature partial melt and water content because attenuation analysis is susceptible to contamination by noise we employ time and frequency domain analyses and a careful assessment of the uncertainty associated with each estimate by using the misfit between actual and predicted traces or spectra the greatest noise source is signal generated noise which affects s wave results more than p wave results s waves also appear more susceptible to the effects of plume focusing we find the upper mantle to be highly attenuative but that above 200 250 km the low velocity plume is progressively less attenuative than the adjacent mantle with decreasing depth we conclude that water dissolved in mantle minerals causes the upper mantle to be highly attenuative that the yellowstone plume is only 50 c warmer than the surrounding mantle below the north america lithosphere and that melting within this plume begins at depths of 200 250 km we attribute the lower attenuation in the partially molten plume to the dehydration of the solid matrix as water partitions into the melt the source of the upper mantle hydration is attributed to subduction including water flux from a hydrated transition zone and laramide age shallow subduction and direct hydration of north america lithosphere

modeling elastic properties of siliciclastic rocks we have modeled the effective elastic moduli and hence the compression and shear wave velocities of dry sandstones the modeling is distinctly different in two ranges of porosity from zero to the consolidation limit con consolidated regime where the rock is treated as continuous material containing pores and cracks and from con to the critical porosity c where the rock is transitioning to a granular material unconsolidated regime in the consolidated regime the modeling is micromechanics based and yields the moduli in terms of porosity pore shape factor and crack density based on the noninteraction approximation with the mori tanaka correction for interactions by necessity it contains empirical parameters reflecting highly irregular shapes of pores and microcracks in the unconsolidated regime we propose empirical relations of the mori tanaka type where pore shape factors assume large values consistent with very soft concave pore shapes typical in this regime combined the two

variable north atlantic climate seesaw patterns documented by a late holocene marine record from disko bugt west greenland abstract the reconstruction of past sea surface conditions in the labrador sea is essential for understanding climate fluctuations in the north atlantic region we here study late holocene sea surface conditions off west greenland in order to elucidate the possible relationship between a north atlantic seesaw and centennial to millennial scale climate fluctuations in the labrador sea region for that purpose we have studied the particulate organic matter especially dinoflagellate cysts and acritarchs from two marine sediment cores from disko bugt central west greenland our data show significant variations in sea surface temperature and sea ice cover during the last ca 3200 years after a cooling at ca 2 9 ka cal bp presumably related to the neoglacial cooling seen in large parts of the northern hemisphere the area was subjected to significant variability both in the entrainment of atlantic water west greenland current water and in atmospheric temperatures from 2 0 1 5 ka cal bp corresponding to the later part of the roman warm period the area experienced a return to a stronger influx of atlantic water and an increased fresh water influx from land probably related to increased precipitation or to melt water outflow from the nearby inland ice the dark ages 1 5 1 3 ka cal bp were characterised by an only minor cooling of the surface waters however as seen in other records from the labrador sea region the beginning of the medieval warm period 1 3 0 9 ka cal bp signified a severe cooling presumably due to a significant reduction in atlantic water entrainment the cold conditions continued through the little ice age after 0 9 ka cal bp although the area seems to have experienced a minor decrease in sea ice cover until 0 5 ka cal b p after which sea ice cover may again have increased the period of modern warming is not represented in our data our study shows that a north atlantic oscillation type pattern played a significant role in the late holocene centennial to millennial scale climate fluctuations in the labrador sea region however this cannot explain the full complexity of the climate signal the fact that a simple pattern of cold versus warm climate scenario does not exist demonstrates that it will hardly be feasible to select the correct baseline data set when modelling future climate development

a high resolution study of holocene paleoclimatic and paleoceanographic changes in the nordic seas 1 high resolution records from images core md95 2011 in the eastern norwegian sea provide evidence for relatively large and small scale high latitude climate variability throughout the holocene during the early and mid holocene a situation possibly driven by consistent stronger westerlies increased the eastward influence of arctic intermediate and near surface waters for the late holocene a relaxation of the atmospheric forcing resulted in increased influence of atlantic water the main changes in holocene climate show no obvious connection to changing solar irradiance and spectral analysis reveals no consistent signature for any periodic behavior of holocene climate at millennial or centennial timescales there are however indications of consistent multidecadal variability

intraplate deformation and microplate tectonics of the yellowstone hot spot and surrounding western u s interior 1 contemporary deformation of the yellowstone hot spot and surrounding western united states is analyzed using tectonic microplate modeling employing constraints from gps observations corrected for postseismic deformation of m7 earthquakes fault slip rates and earthquake focal mechanisms we focus primarily on the kinematics of the yellowstone hot spot and the eastern snake river plain volcanic field esrp and secondarily on basin range and columbia plateau provinces our results reveal southwest motion of the yellowstone plateau excluding localized volcanic deformation at 0 9 0 1 mm a that decreases to 0 8 0 1 mm a in the esrp block the southwest to west motion of the yellowstone esrp introduces shear in the northern rocky mountain block which is translating east at 0 78 0 08 mm a there is 0 5 mm a differential motion between the esrp and the block at its northern boundary and none at the southern boundary the eastern basin range block moves west at 3 0 0 1 to 4 6 0 1 mm a while velocities of the western basin range microplates rotate to a northwest direction accompanied by a transition from normal to oblique shear deformation columbia plateau block velocities are notably eastward an effect enhanced by postseismic relaxation following the m9 1700 cascadia subduction zone paleoearthquake this study reveals that the overall motion of the western united states is characterized by clockwise rotation with westward extension and northwest shear in the basin range province northeast to east contraction in the columbia plateau and southwest extension of the yellowstone snake river plain block that is driven by the high gravitational potential of the yellowstone swell

petrogenesis and volcanology of anorogenic rhyolites a special issue dedicated to bill bonnichsen the occurrence of large volume high temperature silicic volcanic rocks is apparently confined to continental regions and is a manifestation of significant energy input into the continental crust over extended time periods in the western united states such magmatism occurs predominantly in extensional settings in the cenozoic great basin and transpecos west texas volcanic provinces it is particularly prolific in the late cenozoic snake river plain yellowstone province that forms a time transgressive hot spot track across southern idaho where rhyolites were extruded as large lava flows and even larger ignimbrites volumes of individual eruptions range up to at least 100 km 3 for the lava flows and to as much as 3 000 km 3 for the ignimbrites cumulative volumes of silicic magma produced likely exceed 10 5 km 3 making this province one of the most prolific rhyolite outpourings on earth these rhyolites are characterized by high magmatic temperatures sometimes exceeding 1 000 c anhydrous phenocryst assemblages low oxygen fugacities and a type trace element chemistry in all these respects the anorogenic rhyolites contrast sharply with silicic magmas from orogenenic settings i e convergent margins and mid cenozoic calcalkaline silicic magmas of the great basin and colorado plateau including

warming and freshening of baffin bay 1916 2003 1 regression analysis of historical hydrographic data is used to determine changes in temperature and salinity in baffin bay for the time period from 1916 to 2003 we find two distinct sets of changes in the baffin first areas affected by the atlantic inflow to baffin bay show substantial and statistically significant warming trends in the more than 2000 m deep basin the warming peaks at 0 11 0 06 c decade at 700 m depth below the 640 m sill depth of davis strait connecting baffin bay to the north atlantic ocean a vertical heat flux divergence of 0 25 w m2 is required to warm baffin bay below 900 m by the amount observed the required heat appears to be advected from the shelf and slope regions of the eastern labrador sea via davis strait along the west greenland shelf break and diffuses vertically and horizontally into the deep central basin the north atlantic oscillation index accounts for about 30 of the interannual variance of temperature fluctuations below the davis strait sill depth second areas affected by arctic inflow to baffin bay show a marginally significant freshening of up to about 0 086 0 039 psu decade this freshening trend extends along the western margin of baffin island to davis strait and into the labrador sea the freshening in the northern reaches of baffin bay is similar in size to that at its southern reaches temporal variability of annual composites between these locations appears to be in phase suggesting a swift transition of arctic waters at 76 n to labrador sea waters at 62 n

sea surface temperatures and ice rafting in the holocene north atlantic climate influences on northern europe and greenland abstract the oceanographic conditions in the high latitude north atlantic ocean during the holocene were reconstructed through analyses of sea surface temperature sst alkenone unsaturation ratios and ice rafting mineralogy and grain size from two sediment sequences one recovered from the reykjanes ridge at 59 n and the other from the norwegian sea at 68 n comparison of our records to published ice core and terrestrial proxy climate data sets suggests that atmospheric temperature changes over northern europe and greenland were coupled to sst variability and ice rafting the records outline four major climatic phases i an early holocene thermal maximum that lasted until approximately 6 7 kyr bp ii a distinctly cooler phase associated with increased ice rafting between 6 5 and 3 7 kyr bp iii a transition to generally warmer but relatively unstable climate conditions between 3 7 and 2 kyr bp and iv a second distinct sst decline that took place between 2 and 0 5 kyr bp in contrast to the dominant control of northern hemisphere summer insolation on early holocene climate development via strong seasonality the trigger for the onset of relatively unstable climatic conditions in the north atlantic at 3 7 kyr bp is not straightforward however it is possible that this change was triggered by late holocene winter insolation increase at high northern latitude and or by inter hemispheric changes in orbital forcing the late holocene neoglaciation trend which is characteristic of numerous terrestrial archives in northern europe may not only be attributed to a gradual decrease in orbitally forced summer temperature but also to increase snow precipitation at high northern latitudes during generally milder winters

upper mantle origin of the yellowstone hotspot fundamental features of the geology and tectonic setting of the northeast propagating yellowstone hotspot are not explained by a simple deep mantle plume hypothesis and within that framework must be attributed to coincidence or be explained by auxiliary hypotheses these features include the persistence of basaltic magmatism along the hotspot track the origin of the hotspot during a regional middle miocene tectonic reorganization a similar and coeval zone of northwestward magmatic propagation the occurrence of both zones of magmatic propagation along a first order tectonic boundary and control of the hotspot track by preexisting structures seismic imaging provides no evidence for and several contraindications of a vertically extensive plume like structure beneath yellowstone or a broad trailing plume head beneath the eastern snake river plain the high helium isotope ratios observed at yellowstone and other hotspots are commonly assumed to arise from the lower mantle but upper mantle processes can explain the observations the available evidence thus renders an upper mantle origin for the yellowstone system the preferred model there is no evidence that the system extends deeper than 200 km and some evidence that it does not a model whereby the yellowstone system reflects feedback between upper mantle convection and regional lithospheric tectonics is able to explain the observations better than a deep mantle plume hypothesis

upper mantle seismic structure beneath the pacific northwest a plume triggered delamination origin for the columbia river flood basalt eruptions abstract we invert teleseismic p and s body waves constrained by an ambient noise surface wave model and moho depth inferred from receiver function analysis gao et al 2011 to image mantle structures continuously from the surface to the base of the upper mantle the major structures coincide with prominent geological features we focus on a ne oregon structure termed here the wallowa anomaly which coincides with the source area for the 16 ma columbia river flood basalt eruptions and a circular area of topographic relief created during and after these eruptions resolution tests indicate that the curtain like structure previously interpreted as farallon lithosphere connects with the wallowa anomaly above 150 km along the northeast margin of the wallowa anomaly this connection along with the pre flood basalt magmatic and tectonic history of the pacific northwest lead us to conclude that arrival of the yellowstone plume to south central oregon initiated delamination of remnant farallon lithosphere from the base of ne oregon exposing ocean crust to yellowstone asthenosphere this hypothesis accounts for the propagation of flood basalt volcanism far north of the yellowstone hotspot track and for the high silica composition of most of the flood basalt magmas

thermal structure beneath the snake river plain implications for the yellowstone hotspot basaltic magmatism associated with the yellowstone hotspot has been widely attributed to upwelling of a mantle plume yet the temporal and spatial distribution of these magmas and their compositional characteristics are distinctive from oceanic hotspot magmatism fundamental questions concern the influence of continental cratonic lithosphere in producing the differences and the extent to which upper plate processes contribute to magma production to better understand scenarios of melt generation p t conditions are estimated for segregation of primitive snake river plain srp basalts from the mantle combined with analysis of trace element and seismic constraints we conclude from this that 1 melt production was concentrated at depths between roughly 70 100 km 2 mantle temperature was only slightly higher than ambient conditions with a maximum potential temperature of 1450 c and 3 the mantle source was relatively fertile mg 90 these results suggest that the seismically imaged plume below yellowstone is significantly cooler than upwellings beneath hawaii iceland and many other oceanic hotspots our findings in combination with other geochemical and geodynamic considerations are permissive of magma generation within the ancient lithospheric mantle keel associated with the wyoming craton plume contributions while not excluded involve physical and geochemical implications that suggest they are subordinate

receiver function imaging of upper mantle complexity beneath the pacific northwest united states abstract small scale topographic variations on the upper mantle seismic discontinuities provide important constraints on the thermal influences of upwellings and downwellings in geodynamically complex regions subduction of the juan de fuca plate and other tectonic processes dominating the pacific northwest united states in the cenozoic involve massive thermal flux that likely result in an upper mantle that has strong 3 d temperature variations we address the interaction of such processes in the region using receiver functions to image the upper mantle seismic discontinuities at 410 and 660 km we utilized over 15 000 high quality receiver functions gathered from 294 teleseismic earthquakes recorded at 277 regional broadband seismic stations primarily those of the earthscope usarray transportable array we find the average depths of the discontinuities to be 412 km and 658 km respectively with no obvious 520 km discontinuity detected the peak to peak range is greater on the 410 than the 660 suggesting the possibility of more significant regional dynamic processes at upper mantle depths our results are not consistent with a mantle plume below central oregon in the high lava plains region our observation of a thinner transition zone beneath the western snake river plain region however is consistent with a regional increase in mantle temperatures perhaps due to either asthenospheric flow from beneath and around the southern edge of the juan de fuca plate or to vertical flow in the form of regional mantle upwelling related to the snake river plain yellowstone hotspot track further our results are not consistent with a simple subducting juan de fuca slab morphology but rather suggest similar levels of significant complexity in slab structure found by recent regional tomographic studies we find evidence for a thickened and therefore cooler mantle transition zone beneath the wallowa idaho batholith region consistent with tomographic models which suggest broad scale increased seismic velocities to transition zone depths we speculate that this region may be the location of mantle downwelling at larger scales than previously proposed

changes in major element hydrochemistry of the pecos river in the american southwest since 1935 abstract the pecos river situated in eastern new mexico and western texas receives water from a drainage area of 91 000 km 2 there are primarily two major water inputs namely snowmelt from winter storms in the headwater region of the southern rocky mountains and runoff from warm season monsoonal rainfall in the lower valley the pecos river suffers from high levels of total dissolved solids tds 5000 mg l 1 under normal flow conditions this not only poses serious problems for agricultural irrigation and safe drinking water supply but also results in a permanent loss of biodiversity this study examines changes in stream flow and water chemistry of the pecos river over the last 70 a to better understand the long term variability in stream salinity and the role of agricultural practices in salt transfer a tds record from the lower pecos river near langtry texas back to 1935 was extracted to show a distinct pattern of decadal variability similar to the pacific decadal oscillation pdo in which stream salinity is overall above average when the pdo is in positive warm phase and below average when the pdo is in negative cold phase this is due to 1 the dissolved salts contributed to the river are largely from dissolution of nacl and caso 4 bearing minerals e g halite and gypsum in the upper basin 2 the amount of the dissolved salts that reach the lower basin is mainly determined by the stream flow yield in the upper basin and 3 the stream flow yield from the upper basin is positively correlated with the pdo index this further attests that large scale climatic oscillation is the major source of long term changes in stream flow and salinity of the pecos river on the other hand there is also a strong indication that the rate of salt export has been affected by reservoir operations and water diversions for agricultural practices