heat flow study of the emeishan large igneous province region implications for the geodynamics of the emeishan mantle plume abstract the emeishan large igneous province elip is widely considered to be a consequence of a mantle plume the supporting evidence includes rapid emplacement voluminous flood basalt eruptions and high mantle potential temperature estimates several studies have suggested that there was surface uplift prior to the eruption of the emeishan flood basalts additionally the plume s lateral extent is hard to constrain and has been variously estimated to be 800 1400 km in diameter in this study we analyzed present day heat flow data and reconstructed the permian paleo heat flow using vitrinite reflectance and zircon u th he thermochronology data in the elip region and discussed implications for the geodynamics of the emeishan mantle plume the present day heat flow is higher in the inner and intermediate zones than in the outer zone with a decrease of average heat flow from 76 mw m2 to 51 mw m2 thermal history modeling results show that an abnormal high paleo heat flow of 90 110 mw m2 was caused by the emeishan mantle plume activity based on the present day heat flow data we can calculate that there is lithospheric thinning in the central elip region which may be due to the destruction of the lithosphere by mantle plume upwelling and magmatic underplating the permian paleo heat flow anomaly implies that there was a temperature anomaly in the mantle the ascending high temperature mantle plume and the thinned lithosphere may have induced the large scale uplift in the elip region according to the range of the surface heat flow anomaly it can be estimated that the diameter of the flattened head of the emeishan mantle plume could have reached 1600 1800 km our research provides new insights into the geodynamics of the emeishan mantle plume through study of heat flow

thermal evolution and maturation of sinian and cambrian source rocks in the central sichuan basin southwest china abstract the sichuan basin is among the basins with the most abundant oil and gas resources in china the sinian and cambrian strata are the most important source rocks previous studies of the thermal history of the central sichuan basin have focused on the late paleozoic and studies of the early paleozoic thermal history are not available in literature and the thermal evolution of the sinian and cambrian source rocks are yet to be examined a new thermal history was reconstructed using integrated thermal indicators including apatite and zircon u th he zircon fission tracks and equivalent vitrinite reflectance the modeled results indicated that the heat flow was relatively low

lithospheric thermal structure and rheology of the eastern china abstract temperature distributions of the lithosphere beneath the eastern china were estimated by local isostasy equilibrium constrained geothermal calculation in this study maps of the lateral temperature variation at depths of 50 and 100 km as well as moho boundary are presented for the eastern china continent and the 600 c and 1100 c isotherm depth maps are also given meanwhile the thermal thickness of lithosphere is calculated as the depth of 1350 c isotherm the rheological strength of lithosphere is calculated based on a four layer model which consists of the upper lower lowermost crust layers and a wet lithospheric mantle layer the results show that the lithosphere of 160 180 km thick exists under sichuan basin in the western part of yangtze craton but keel is absent beneath the entire north china craton it is notable that the lithospheric thickness is only 130 140 km beneath ordos basin in the western part of north china craton accordingly there is no lithospheric keel beneath ordos basin these geothermal modeling results are in good agreement with those of seismic tomography and other geothermal studies the temperatures in the lower crust of the north china craton estimated are in range of 500 600 c consequently the composition of lower crust of the north china craton should be more mafic than that of previous estimation based on much cooler geotherms the spatial variation of lithospheric rheology in the eastern china is influenced by local geotherms and crustal compositions the creme brulee model which is represent by a strong crust portion but a weak lithospheric mantle portion in vertical strength profile approximates the lithospheric rheological layering for the regions of the western half of north china craton and the northern part of ne china which has thicker crust or moderate to high geotherm on the other hand the jelly sandwich model demonstrates the rheological layering of the western part of the yangtze craton and the eastern half of the north china craton which has low to moderate geotherm and or thinner crust in general thermal age of the tectonic province controls the present day thermal structure and rheology of the lithosphere of the eastern china

preliminary dating of the viluy traps eastern siberia eruption at the time of late devonian extinction events article i nfo ar 39 ar dating in this short note we report new age determinations from four samples of the middle paleozoic viluy traps in siberia east of the more famous permo triassic siberian traps these samples which were collected from three drill cores have been analyzed in parallel and independently in the orsay france and berkeley geochronology center bgc usa geochronology laboratories using respectively the cassignol gillot k ar and the 40 ar 39 ar techniques dating these samples as a concerted effort in two independent laboratories working jointly on their interpretation is a rather rare yet very valuable exercise with the k ar technique ages ranging from 338 to 367 ma with uncertainties on the order of 5 ma were obtained with the 40

tephrochronology of late wisconsin deglaciation and holocene glacier fluctuations near glacier peak north cascade range washington abstract tephra layers near glacier peak in the north cascade range provide limiting dates for four periods of alpine glacier advance field relations suggest that late wisconsin alpine glaciers last advanced prior to the eruption of tephra layers from glacier peak about 11 250 yr b p late wisconsin deglaciation in the central north cascades was complete prior to the glacier peak tephra eruptions glaciers again expanded in the early holocene about 8400 8300 yr b p soil formed in alpine meadows during an episode of mild climate in the middle holocene prior to at least two intervals of glacier expansion an older episode between 5100 and 3400 yr b p and a younger episode within the last 1000 yr

interaction between aggrading geomorphic surfaces and the formation of a late pleistocene paleosol in the palouse loess of eastern washington state abstract variable rates of loess deposition contributed to dramatic regional variation in a soil stratigraphic unit the washtucna soil in the palouse loess deposits in the channeled scabland of eastern washington state throughout most of the channeled scabland the morphology of the washtucna soil is that of a single buried soil but it bifurcates into two well developed and pedologically distinct buried soils in areas immediately downwind of the major source of loessial sediment regional loess stratigraphy confirms that the two well developed soils formed during the same interval of time during which only one soil formed in areas that are distal to loess source areas the variable and perhaps rapid rates of soil formation suggested by the stratigraphy resulted from an interaction between variable rates of loess deposition and the formation of superimposed calcic soils petrocalcic horizons with weak stage iv morphology formed as the zone of carbonate accumulation moved up into former a and cambic horizons that had been profusely burrowed by cicadas the development of cicada burrows in one phase of soil development that were subsequently engulfed by pedogenic carbonate under a rising land surface seems to have greatly accelerated the development of the petrocalcic horizons accelerated rates of formation of the petrocalcic horizons occurred when extrinsic pulses of loess deposition and intrinsic engulfment of burrowed horizons thresholds were exceeded stratigraphic evidence suggests that the soil formation that accompanied the rise in the land surface due to additional loess deposition may have occurred during the late wisconsin glaciation when giant glacial outburst floods in the channeled scabland triggered a new cycle of loess deposition

global shear speed structure of the upper mantle and transition zone s u m m a r y the rapid expansion of broad band seismic networks over the last decade has paved the way for a new generation of global tomographic models significantly improved resolution of global upper mantle and crustal structure can now be achieved provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized here we present a new global vertically polarized shear speed model that yields considerable improvements in resolution compared to previous ones for a variety of features in the upper mantle and crust the model sl2013sv is constrained by an unprecedentedly large set of waveform fits 3 4 of a million broad band seismograms computed in seismogram dependent frequency bands up to a maximum period range of 11 450 s automated multimode inversion of surface and s wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram the equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers going beyond ray theory we calculated the phase of every mode at every frequency and its derivative with respect to sand p velocity perturbations by integration over a sensitivity area in a 3 d reference model the normally small perturbations of the 3 d model required to fit the waveforms were then linearized using these accurate derivatives the equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3 d model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle elaborate outlier analysis was used to control the propagation of errors in the data source parameters timing at the stations etc the selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors increasing the resolution of the imaging our new shear speed model is parametrized on a triangular grid with a 280 km spacing in well sampled continental domains lateral resolution approaches or exceeds that of regionalscale studies the close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark in oceanic regions spreading ridges are very well resolved with narrow anomalies in the shallow mantle closely confined near the ridge axis and those deeper down to 100 120 km showing variability in their width and location with respect to the ridge major subduction zones worldwide are well captured extending from shallow depths down to the transition zone the large size of our waveform fit data set also provides a strong statistical foundation to re examine the validity field of the jwkb approximation and surface wave ray theory our analysis shows that the approximations are likely to be valid within certain time frequency portions of most seismograms with high signal to noise ratios and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting

number and size of last glacial missoula floods in the columbia river valley between the pasco basin washington and portland oregon field evidence and radiocarbon age dating combined with hydraulic flow modeling provide new information on the magnitude frequency and chronology of late pleistocene missoula floods in the columbia river valley between the pasco basin washington and portland oregon more than 25 floods had discharges of 1 0 106 m3 s at least 15 floods had discharges of 3 0 106 m3 s at least six or seven had peak discharges of 6 5 106 m3 s and at least one flood had a peak discharge of 10 106 m3 s a value consistent with earlier results from near wallula gap but better defined because of the strong hydraulic controls imposed by critical flow at constrictions near crown and mitchell points in the columbia river gorge stratigraphy and geomorphic position combined with 25 radiocarbon ages and the widespread occurrence of the ca 13 ka radiocarbon years mount st helens set s tephra show that most if not all the missoula flood deposits exposed in the study area were emplaced after 19 ka radiocarbon years and many were emplaced after 15 ka more than 13 floods perhaps postdate ca 13 ka including at least two with discharges of 6 106 m3 s from discharge and stratigraphic relationships upstream we hypothesize that the largest flood in the study reach resulted from a missoula flood that predated blockage of the columbia river valley by the cordilleran ice sheet multiple later floods probably including the majority of floods recorded by fine and coarse grained deposits in the study area resulted from multiple releases of glacial lake missoula that spilled into a blocked and inundated columbia river valley upstream of the okanogan lobe and were shunted south across the channeled scabland

correlation of upper cenozoic tephra layers between sediments of the western united states and eastern pacific ocean and comparison with biostratigraphic and magnetostratigraphic age data five widespread upper cenozoic tephra layers that are found within continental sediments of the western united states have been correlated with tephra layers in marine sediments in the humboldt and ventura basins of coastal california by similarities in major and trace element abundances four of these layers have also been identified in deep ocean sediments at dsdp sites 34 36 173 and 470 in the northeastern pacific ocean these layers erupted from vents in the yellowstone national park area of wyoming and idaho y the cascade range of the pacific northwest c and the long valley area california l are the huckleberry ridge ash bed 2 0 ma y rio dell ash bed ca 1 5 ma c bishop ash bed 0 74 ma l lava creek b ash bed 0 62 ma y and loleta ash bed ca 0 4 ma c the isochronous nature of these beds allows direct comparison of chronologic and climatic data in a variety of depositional environments for example the widespread bishop ash bed is correlated from proximal localities near bishop in east central california where it is interbedded with volcanic and glacial deposits to lacustrine beds near tecopa southeastern california to deformed on shore marine strata near ventura southwestern california to deep ocean sediments at site 470 in the eastern pacific ocean west of northern mexico the correlations allow us to compare isotopic ages determined for the tephra layers with ages of continental and marine biostratigraphic zones determined by magnetostratigraphy and other numerical age control and also provide iterative checks for available age control relative age variations of as much as 0 5 m y exist between marine biostratigraphic datums for example highest occurrence level of discoaster brouweri and calcidiscus tropicus c macintyrei as determined from sedimentation rate curves derived from other age control available at each of several sites these discrepancies may be due to several factors among which are 1 diachronism of the lowest and highest occurrence levels of marine faunal and floral species with latitude because of ecologic thresholds 2 upward reworking of older forms in hemipelagic sections adjacent to the tectonically active coast of the western united states and other similar analytical problems in identification of biostratigraphic and magnetostratigraphic datums 3 dissolution of microfossils or selective diagenesis of some taxa 4 lack of precision in isotopic age calibration of these datums 5 errors in isotopic ages of tephra beds and 6 large variations in sedimentation rates or hiatuses in stratigraphic sections that result in age errors of interpolated datums correlation of tephra layers between on land marine and deep ocean deposits indicates that some biostratigraphic datums diatom and calcareous nannofossil may be truly time transgressive because at some sites they are found above and at other sites below the same tephra layers

tephrochronologic constraints on the late pleistocene history of the southern margin of the cordilleran ice sheet western washington abstract an ash layer that appears geochemically correlative with mt st helens tephra set s occurs in a sequence of pleistocene lake sediments in the ohop valley of the southern puget lowland below vashon till deposited during the maximum late pleistocene advance fraser glaciation of the puget lobe of the cordilleran ice sheet the puget lobe reached its maximum southern extent ca 14 000 14 500 yr b p and at least part of set s is evidently somewhat older previous radiocarbon and thermoluminescence dates for set s have ranged from 13 000 to 16 000 yr b p geochemically correlative deposits of set s tephra occur in slackwater sediments coeval with the missoula floods in eastern washington produced by jokulhlaups through the purcell trench lobe of the cordilleran ice sheet these relationships suggest that advances of glacier lobes on the southern margin of the cordilleran ice sheet were nonsynchronous as the pucell trench lobe east of the cascade range advanced to its maximum southern extent prior to the time of the eruption of set s before the puget lobe west of the cascades reached its maximum southern extent

rayleigh wave tomography of china and adjacent regions 1 this paper presents a tomographic study on the s wave velocity structure of china and adjacent regions group velocity dispersions of fundamental rayleigh waves along more than 4000 paths were determined with frequency time analysis the study region was divided into a 1 1 grid and velocities in between grid nodes were calculated by bilinear interpolation the occam s inversion scheme was adopted to invert for group velocity distributions this method is robust and allows us to use a fine grid in model parameterization and thus helps to restore a more realistic velocity pattern checkerboard tests were carried out and the lateral resolution was estimated to be 4 6 in china and its eastern continental shelves the resulting group velocity maps from 10 to 184 s showed good correlation with known geological and tectonic features the pure path dispersion curves at each node were inverted for shear wave velocity structures the three dimensional velocity model indicates thick lithospheres in the yangtze and tarim platforms and hot upper mantles in baikal and western mongolia coastal area and continental shelves of eastern china and indochina and south china sea regions the tibetan plateau has a very thick crust with a low velocity zone in its middle beneath the crust a north dipping high velocity zone mimicking a subducting plate reaches to 200 km in depth and reaches to the kunlun mountains northward in northern tibet a low velocity zone immediately below the moho extends eastward then turns southward along the eastern edge of the plateau until it connects to the vast low velocity area in indochina and the south china sea

identification of a kulshan caldera correlative tephra in the palouse loess of washington state northwest usa abstract the kulshan caldera formed at 1 15 ma on the present day site of mt baker washington state northwest usa and erupted a compositionally zoned dacite rhyolite magma and a correlative eruptive the lake tapps tephra this tephra has previously been described but only from the puget lowland of nw washington here an occurrence of a kulshan caldera correlative tephra is described from the quaternary palouse loess at the washtucna site wa 3 site wa 3 is located in east central washington 340 km southeast of the kulshan caldera and 300 km east southeast of the lake tapps occurrence in the puget lowland major and trace element chemistry and location of the deposit at washtucna within reversed polarity sediments indicates that it is not correlative with the mesa falls rockland bishop ash lava creek b or huckleberry ridge tephras instead the washtucna deposit is related to the lake tapps tephra by fractional crystallisation but is chemically distinct a consequence of its eruption from a compositionally zoned magma chamber the correlation of the washtucna occurrence to the kulshan caldera forming eruption indicates that it had an eruptive volume exceeding 100 km3 and that its tephra could provide a valuable early pleistocene chronostratigraphic marker in the pacific northwest

evolution of eureka flat a dust producing engine of the palouse loess usa sedimentologic stratigraphic and pedologic evidence demonstrates that eureka flat ef a narrow 80 km long deflation plain in south central washington usa is the source for the thick and widespread loess of the palouse region located in the southern columbia plateau ef has been a depocenter for abundant clay to sand sized sediment derived from repeated glacial outburst floods that swept through the area during the pleistocene prevailing sw winds that were funneled across ef remobilized flood sediment into sand dunes sand sheets and loess an eolian sand sheet buried beneath 1 8 m of loess at the downwind end of ef attests to bioclimatically driven changes in the style of eolian deposition the depositional transition from sand sheet to loess is characterized by a change from wind rippled strata to structureless bimodal sand and silt with insect burrows and rhizoliths to unimodal sandy loess soil moisture and density of dust trapping vegetation control where sand dunes and loess accumulate up to 4 5 m of post lgm loess mantles the landscape adjacent to and downwind from ef some of the thickest loess deposits owe their origins to the sequestering of eolian sand particles by topographic traps such as the touchet river and its tributary valleys the removal of saltating sand from the eolian system promotes thick accumulation of loess downwind of topographic traps patterns of loess accumulation across the columbia plateau are identified on isopach maps of major pre and post lgm loess units and show that ef has been the major engine for the production of atmospheric dust and loess during both times

heat flow and thermal structure of the lithosphere across the baltic shield and northern tornquist zone abstract terrestrial heat flow data from archean and proterozoic provinces of the baltic shield its southwestern margin and the tectonic transition to the younger tectonic units of central europe northern segment of the european geotraverse are compiled and examined for local and regional variations a 2 d numerical lithospheric temperature and heat flux model is presented covering 1800 km of the deep seismic fennolora profile across the baltic shield and 500 km of eugeno s northern eugemi seismic lines across the northern tornquist zone and the danish and north german basins thermal lithosphere defined as the outer layer with relatively low temperatures t c in which heat transfer is dominantly by conduction is found to vary markedly in thickness from 85 110 km beneath basins and tornquist zone to about 150 km in central shield areas and 200 250 km in areas of low heat flow along the northern shield profile these results are in very good agreement with seismological information from surface wave dispersion analysis and the refraction wide angle seismic interpretation of fennolora data the combined thermal and seismologic evidence indicates that the uppermost mantle region stratified in seismic velocity is restricted to the upper relatively cold thermal layer which is interpreted to constitute shield lithosphere local and to some extent regional variations in surface heat flow are found to be closely related to variations in near surface radiogenic heat production for the southern baltic shield a heat flow heat production relationship of q 0 32 8 7 6 h 0 is derived regional increase in heat flow from northern and central shield provinces to the shield margin and the tornquist zone is interpreted to be related partly to differences in upper crustal heat generation partly and in southernmost areas mainly to an increased heat flux from the upper mantle upper mantle heat flux is estimated at 20 25 mw m 2 along the northern and central shield transect increasing to 30 40 mw m 2 beneath the shield margin basins and tornquist zone lithospheric thickness variations in this region of northern europe are found to be closely associated with variations in heat flux from the uppermost mantle and perhaps to a large extent controlled by geodynamically determined lateral differences in upper mantle heat flux earthquake focal depth data and information on crustal strength show baltic shield seismicity to be limited generally to the upper 20 25 km brittle part of the crust at temperatures less than 300 400 c maximum source depth of magnetic anomalies at temperatures near 600 c is in the deepest part of the crust near the crust mantle boundary in the southern region about 25 km depth along the tornquist zone and about 35 40 km in southern shield areas and in the uppermost mantle 60 70 km depth in the northern shield areas some petrologic implications are discussed the present deep crust is supposed to be at lower temperature pressure conditions than at early stages of formation however also the present deepest parts of the shield crust 35 40 km are within the stability field of eclogites the general absence of significant gravity anomalies in areas of marked crustal thickness variations indicate high density eclogites to be present in significant amounts in the deep shield crust

explosive eruptive record in the katmai region alaska peninsula an overview at least 15 explosive eruptions from the katmai cluster of volcanoes and another nine from other volcanoes on the alaska peninsula are preserved as tephra layers in syn and post glacial last glacial maximum loess and soil sections in katmai national park ak about 400 tephra samples from 150 measured sections have been collected between kaguyak volcano and mount martin and from shelikof strait to bristol bay 8 500 km2 five tephra layers are distinctive and widespread enough to be used as marker horizons in the valley of ten thousand smokes area and 140 radiocarbon dates on enclosing soils have established a time framework for entire soil tephra sections to 10 ka the white rhyolitic ash from the 1912 plinian eruption of novarupta caps almost all sections stratigraphy distribution and tephra characteristics have been combined with microprobe analyses of glass and fe ti oxide minerals to correlate ash layers with their source vents microprobe analyses typically 20 50 analyses per glass or oxide sample commonly show oxide compositions to be more definitive than glass in distinguishing one tephra from another oxides from the kaguyak caldera forming event are so compositionally coherent that they have been used as internal standards throughout this study other than the novarupta and trident eruptions of the last century the youngest locally derived tephra is associated with emplacement of the snowy mountain summit dome 6 ka two tephras 3 700 and 2 700 14c years b p and a summit scoria cone with a crater still steaming today mount katmai has three times produced very large explosive plinian to sub plinian events in 1912 12 16 ka and 23 ka and many smaller pyroclastic deposits show that explosive activity has long been common there mount griggs fumarolically active and moderately productive during postglacial time mostly andesitic lavas has three nested summit craters two of which are on top of a holocene central cone only one ash has been found that is tentatively correlated with the most recent eruptive activity on griggs 3 460 14c years b p eruptions from other volcanoes ne and sw beyond the katmai cluster represented in this area include 1 coignimbrite ash from kaguyak s caldera forming event 5 800 14c years b p 2 the climactic event from fisher caldera 9 100 14c years b p tentatively correlated 3 at least three eruptions most likely from mount peulik 700 7 700 and 8 500 14c years b p and 4 a phreatic fallout most likely from the gas rocks 2 300 14c years b p most of the radiocarbon dating has been done on loess soil and peat enclosing this tephra ash correlations supported by stratigraphy and microprobe data are combined with radiocarbon dating to show that variably organics bearing substrates can provide reliable limiting ages for ash layers especially when data for several sites is available

the timing and extent of the eruption of the siberian traps large igneous province implications for the end permian environmental crisis we present new high precision 40ar 39ar ages on feldspar and biotite separates to establish the age duration and extent of the larger siberian traps volcanic province samples include basalts and gabbros from noril sk the lower tunguska area on the siberian craton the taimyr peninsula the kuznetsk basin vorkuta in the polar urals and from chelyabinsk in the southern urals most of the ages except for those from chelyabinsk are indistinguishable from those found at noril sk cessation of activity at noril sk is constrained by a 40ar 39ar age of 250 3 1 1 ma for the uppermost kumginsky suite the new 40ar 39ar data confirm that the bulk of siberian volcanism occurred at 250 ma during a period of less than 2 ma extending over an area of up to 5 million km2 the resolution of the data allows us to confidently conclude that the main stage of volcanism either immediately predates or is synchronous with the end permian mass extinction further strengthening an association between volcanism and the end permian crisis a sanidine age of 249 25 0 14 ma from bed 28 tuff at the global section and stratotype at meishan china allows us to bracket the p tr boundary to 0 58 0 21 myr and enables a direct comparison between the 40ar 39ar age of the traps and the permo triassic boundary section younger ages 243 ma obtained for basalts from chelyabinsk indicate that volcanism in at least the southern part of the province continued into the triassic

geomorphology of the burnt river eastern oregon usa topographic adjustments to tectonic and dynamic deformation abstract eastern oregon contains the deepest gorge in north america where the snake river cuts vertically down 2300 m this deep gorge is known as hells canyon a landscape containing such a topographic feature is likely undergoing relatively recent deformation study of the burnt river a tributary to the snake river at the upstream end of hells canyon yields data on active river incision in eastern oregon indicating that quaternary faults are a first order control on regional landscape development through 1 24 000 scale geologic mapping a 500 000 year record of fluvial incision along the burnt river was constructed and is chronologically anchored by optically stimulated luminescence dating and tephrochronology analyses a conceptual model of fluvial terrace formation was developed using these ages and likely applies to other non glaciated catchments in eastern oregon mapped terraces inferred to have formed during glacial interglacial cycles provide constraints on rates of incision of the burnt river incision through these terraces indicates that the burnt river is down cutting at 0 15 to 0 57 m kyr 1 this incision appears to reflect a combination of local base level adjustments tied to movement along the newly mapped durkee fault and regional base level control imposed by the downcutting of the snake river deformation of terraces as young as 38 7 5 1 ka indicates quaternary activity along the durkee fault and when combined with topographic metrics slope relief hypsometry and stream steepness reveals a landscape in disequilibrium longer wavelength lithospheric dynamics delamination and crustal foundering that initiated in the miocene may also be responsible for continued regional deformation of the earth s surface

active faulting on the wallula fault zone within the olympic wallowa lineament washington state usa the wallula fault zone is an integral feature of the olympic wallowa lineament an 500 km long topographic lineament oblique to the cascadia plate boundary extending from vancouver island british columbia to walla walla washington the structure and past earthquake activity of the wallula fault zone are important because of nearby infrastructure and also because the fault zone defines part of the olympic wallowa lineament in south central washington and suggests that the olympic wallowa lineament may have a structural origin we used aeromagnetic and ground magnetic data to locate the trace of the wallula fault zone in the subsurface and map a quarry exposure of the wallula fault zone near finley washington to investigate past earthquakes along the fault we mapped three main packages of rocks and unconsolidated sediments in an 10 m high quarry exposure our mapping suggests at least three late pleistocene earthquakes with surface rupture and an episode of liquefaction in the holocene along the wallula fault zone faint striae on the master fault surface are subhorizontal and suggest reverse dextral oblique motion for these earthquakes consistent with dextral offset on the wallula fault zone inferred from offset aeromagnetic anomalies associated with ca 8 5 ma basalt dikes magnetic surveys show that the wallula fault actually lies 350 m to the southwest of the trace shown on published maps passes directly through deformed late pleistocene or younger deposits exposed at finley quarry and extends uninterrupted over 120 km

new stratigraphic markers in the late pleistocene palouse loess novel fossil gastropods absolute age constraints and non aeolian facies four stratigraphic sections in the southern part of the columbia basin preserve a sequence of aeolian and non aeolian sediments ranging in age from 9ae43 to 47ae0 14 c ka based on accelerator mass spectrometry radiocarbon dating of fossil molluscs geochemistry of cascade mountain sourced tephra and association with formally recognized pedostratigraphic units the washtucna and old maid coulee soils study sections are interpreted as representing concurrent deposition of loess and distal missoula flood rhythmites in valleys tributary to main drainages backflooded during the missoula floods and formation of carbonate and iron rich soils sediments belong to the formally recognized l 1 and l 2 loess units established for the palouse loess which were deposited in the columbia basin subsequent to events of glacial outburst flooding sediments associated with the mount saint helens set s and set c tephras in the study sections preserve a fauna of five species of gastropod mollusc which have not been reported previously from sediments of late pleistocene age in the palouse region the fossils comprise two distinct faunules stratigraphically separated by the mount saint helens so tephra accelerator mass spectrometry radiocarbon dating of the fossils collected above the tephra in two of the sections yielded ages of 12ae48 0ae06 and 9ae43 0ae05 14 c kyr these ages suggest that independent determinations of the 13ae35 14 c kyr age of the so tephra in other areas where missoula flood sediments are preserved are probably accurate and help to refine the age of the latest events in the most recent sequence of catastrophic glacial outburst flooding

crustal radiogenic heat production and the selective survival of ancient continental crust if the oldest terrestrial rocks are to be used as a representative sample of the early terrestrial crust it is important to consider the possibility that they may represent a biased sample chemical data indicate that archean crust is on average depleted in potassium uranium and thorium relative to younger crust radiogenic isotopes of these elements produce a significant portion of surface heat flow from continents and low mean heat flow in archean terrains relative to younger terrains also indicates that these elements are relatively depleted in archean crust in stable continental lithosphere the primary variable controlling variations in the geotherm is crustal radiogenic heat production qualitative evidence suggests that terrains with low radiogenic heat production and thus a relatively cool geotherm are less susceptible to magmatic and tectonic reactivation than terrains with higher heat production and a hotter geotherm since crustal radiogenic isotope abundances must have been greater in the past if the isotopes were immobile in stable crust the relative effect of crustal heat production must have been greater and thus the range in geotherms must have been greater for the same mantle heat flow it is suggested that crust with low heat production is less susceptible to orogenic reworking than high heat production crust and thus there may have been selective stabilization of low heat production low potassium uranium and thorium crust early in earth history either archean crustal generation was by a mechanism that perhaps fortuitously produced only low heat production crust or all high heat production crust was reworked by orogenesis during the archean and did not stabilize in significant volumes until the earliest proterozoic perhaps in association with a reduction in mantle temperatures and mean heat flow if selective crustal reworking did operate during the archean surviving archean terrains may represent a biased sample of the early terrestrial continental crust

heat flow and deep lithospheric thermal structure at lac de gras slave province canada 1 temperature measurements in two drill holes near lac de gras in the slave province of the canadian shield yield heat flow values of 43 5 and 48 8 mw m 2 with an average of 46 6 mw m 2 heat production measured on samples from one of these holes is relatively high 1 9 w m 3 confirming measurements made on outcrop samples the surface heat flow and heat generation data imply that below a 10 km thick radioelement enriched layer heat production is comparable to that in other archean provinces of the canadian shield the lithospheric geotherm is very close to the geotherms derived from geothermobarometry on xenoliths variations in crustal heat generation account for 50 k differences in moho temperatures within the slave province

record of pre late wisconsin giant floods in the channeled scabland interpreted from loess deposits loess deposits adjacent to flood coulees on the columbia plateau in eastern washington state record multiple episodes of pre late wisconsin cataclysmic floods evidence in the loess consists of flood cut unconformities upward fining in individual loess strata and flood deposits that consist of basaltic gravel fragments of calcified paleosols and slackwater sediment at least six episodes of floods during the pleistocene are indicated by paleomagnetic measurements tephra correlations and the stratigraphic position of flood indicators one episode of the six occurred prior to 790 ka the most recent episode before the last glacial floods occurred at 36 ka at the latest

long lasting epeirogenic uplift from mantle plumes and the origin of the southern african plateau 1 we investigate under what conditions the present day long wavelength anomalous elevation 500 m of the southern african plateau can be attributed to mesozoic plume events the anomalous long wavelength topography of the southern african plateau cannot be easily explained by recent heating of the upper mantle as opposed to other areas of the african superswell and geomorphological studies provide few hard constraints on the timing of the uplift a mesozoic origin for the plateau uplift is attractive in that southern africa experienced several large magmatic events in the mesozoic we formulate numerical and scaling models to investigate if plume material ponded beneath cratonic lithosphere in the mesozoic could produce 500 m of present day elevation we find that starting plume heads are ineffective at producing much long lasting uplift because the material spreads into a thin layer tens of km thick the ponded plume material also suppresses secondary convection by having a stable boundary at its base over time heat continues to flow out of the top of the lithosphere and a net imbalance of heat flow in the lithosphere develops resulting in subsidence even after the plume material has cooled to the temperature of the mantle adiabat secondary convection supplies less heat to the lithosphere than is lost upward by conduction the cratonic lithosphere returns to its original thermal structure on a timescale of less than 200 m y even two mantle starting plume heads one at the time of karoo volcanism ca 183 ma and the other at the time of kimberlite eruption ca 80 90 ma in our models cannot produce much 200 m of the present day anomalous elevation however significant uplift can be generated by plume tails provided they linger beneath the lithosphere for 25 30 m y and if the uplift effects of mesozoic plume heads and tails are considered together then it is possible to account for 500 m of present day elevation consequently a mesozoic plume model for plateau uplift in southern africa appears to be a viable model if plume tails delivered heat to the southern african lithosphere over a period of 25 m y or more

energy decay of the 2004 sumatra tsunami in the world ocean the catastrophic indian ocean tsunami generated off the coast of sumatra on 26 december 2004 was recorded by a large number of tide gauges throughout the world ocean this study uses gauge records from 173 sites to examine the characteristics and energy decay of the tsunami waves from this event in the indian atlantic and pacific oceans findings reveal that the decay e folding time of the tsunami wave energy within a given oceanic basin is not uniform as previously reported but depends on the absorption characteristics of the shelf adjacent to the coastal observation site and the time for the waves to reach the site from the source region in general the decay times for island and open ocean bottom stations are found to be shorter than for coastal mainland stations decay times for the 2004 sumatra tsunami ranged from about 13 h for islands in the indian ocean to 40 45 h for mainland stations in the north pacific

the role of mobile belts for the longevity of deep cratonic lithosphere the crumple zone model many archean cratons are surrounded by proterozoic mobile belts that have experienced episodes of tectonic re activation over their lifetimes this suggests that mobile belt lithosphere may be associated with long lived inherited weakness it is proposed that the proximity of this weakness can increase the longevity of deep archean lithosphere by buffering archean cratons from mantle derived stresses the physical plausibility of this idea is explored through numerical simulations of mantle convection that include continents and allow for material rheologies that model the combined brittle and ductile behavior of the lithosphere within the simulations the longevity of deep cratonic lithosphere does increase if it is buffered by mobile belts that can fail at relatively low stress levels

high 3he plume origin and temporal spatial evolution of the siberian flood basalts an olivine nephelinite from the lower part of a thick alkalic ultrabasic and mafic sequence of volcanic rocks of the northeastern part of the siberian flood basalt province sfbp yielded a 40ar 39ar plateau age of 253 3 2 6 million years distinctly older than the main tholeiitic pulse of the sfbp at 250 0 million years olivine phenocrysts of this rock showed 3he 4he ratios up to 12 7 times the atmospheric ratio these values suggest a lower mantle plume origin the neodymium and strontium isotopes rare earth element concentration patterns and cerium lead ratios of the associated rocks were also consistent with their derivation from a near chondritic primitive plume geochemical data from the 250 million year old volcanic rocks higher up in the sequence indicate interaction of this high 3he sfbp plume with a suboceanic type upper mantle beneath siberia

lithospheric thickness of the chinese continent abstract we invert for the upper mantle temperatures of the chinese continent in the depth range of 70 240 km from a recent s velocity model the depth where temperatures intersect a mantle adiabat with a potential temperature of 1300 c is in close correspondence with the top of the seismic low velocity zone for most regions this correspondence implies that seismic lithosphere estimated from short time scale seismic information may be equivalent to the long time scale geodynamical lithosphere defining the 1300 c adiabat as coinciding with the lithospheric base we estimate the seismic thermal lithosphere thickness the estimated thickness shows obvious dependence on the tectonic settings beneath eastern china which mainly belongs to the circum pacific tectonic domain it has a thickness of 100 km and beneath the qinghai tibet plateau and south to the tarim craton which belong to the tethyan tectonic domain it has a thickness of 160 220 km the lithospheric thicknesses of the three large para platforms cratons range from 170 km for the western yangtze 140 km for tarim and 100 km for sino korean the three cratons may have been reshaped by phanerozoic tectonic activities and are thinner than most cratons in other continents

emeishan large igneous province sw china in recent years there have been major advances in our understanding of the emeishan large igneous province lip of sw china following publication of a number of lip focused investigations of the terrain and associated rocks this paper reviews the current state of knowledge the volcanic and upper intrusive portion of the province is relatively small 0 3 106 km3 even when offset fragments eroded sections and buried portions are included in the volume calculation the most reliable radiometric age dates zircon u pb shrimp from an associated layered intrusive body several kilometers in area indicate generation at 259 ma consistent with the end guadalupian end middle permian stratigraphic age in addition several ar ar dating studies have been carried out mainly on the volcanic rocks with a number of reported dates 253 251 ma late permian but a consensus is emerging that these ages are problematic because they are in conflict with the stratigraphic data possibly due to a monitor standard miscalibration the ar ar investigations have also yielded a large number of secondary ages which are clustered at 175 142 98 and 42 ma and these are inferred to record sub regional tectonic events that affected the western yangtze block as east asia was assembled and later deformed by india s collision indentation into asia magnetostratigraphic data and field observations suggest that the bulk of the volcanic sequence formed within 1 2 my the geochemistry of the volcanic rocks and bio lithostratigraphic studies of the underlying maokou formation suggests a mantle plume generated the province the basalts can be classified into low and high ti groups with different parental magmas the low ti basalts are confined to the western part of the province and are overlain by the high ti basalts the low ti magmas formed at shallow mantle depths in the spinel garnet field transition zone 60 80 km whereas the high ti magmas formed by low degrees of partial melting within the deeper garnet stability field this observation suggests a deepening of the melting column as the lithosphere thickened due to under plating and a transition from peak basalt generation to the waning stage outstanding issues which might focus future studies are also outlined

isotopic evidence for temporal variation in proportion of seasonal precipitation since the last glacial time in the inland pacific northwest of the usa abstract large scale atmospheric circulation patterns determine the quantity and seasonality of precipitation the major source of water in most terrestrial ecosystems oxygen isotope 18o dynamics of the present day hydrologic system in the palouse region of the northwestern u s a indicate a seasonal correlation between the 18o values of precipitation and temperature but no seasonal trends of 18o records in soil water and shallow groundwater their isotope values are close to those of winter precipitation because the palouse receives 75 of its precipitation during winter palouse loess deposits contain late pleistocene pedogenic carbonate having ca 2 to 3 higher 18o values and up to 5 higher carbon isotope 13c values than holocene and modern carbonates the late pleistocene 18o values are best explained by a decrease in isotopically light winter precipitation relative to the modern winter dominated infiltration the 13c values are attributed to a proportional increase of atmospheric co2 in soil co2 due to a decrease in soil respiration rate and 13c discrimination in plants under much drier paleoclimate conditions than today the regional climate difference was likely related to anticyclonic circulation over the pleistocene laurentide and ice sheet

identification of disseminated trego hot springs tephra in the palouse washington state abstract tephra layers form important chronostratigraphic marker horizons within the wisconsinan loess paleosol stratigraphy of the palouse washington state this paper details the presence of disseminated glass shards of the trego hot springs tephra that has not previously been recognized within the palouse or environs the tephra provides additional chronological control for the regional late wisconsinan stratigraphy and raises the possibility of correlating the paleoclimatic proxy record contained within the palouse to those of lake sequences in oregon california and nevada

distinct upper mantle deformation of cratons in response to subduction constraints from sks wave splitting measurements in eastern china abstract interaction between the subducting slab the overriding continental lithosphere and mantle flow are fundamental geodynamic processes of subduction systems eastern china is an ideal natural laboratory to investigate the behavior and evolution of cratonic blocks within a subduction system in this study we investigate deformation of the upper mantle beneath eastern china we present seismic shear wave splitting measurements from three networks consisting of over 483 broadband stations with 157 stations giving a total of 516 results the splitting parameters exhibit complex regional patterns but are relatively coherent within individual tectonic units tectonic blocks exhibited distinctive fast directions relative to regional features the dominant attitude of fast directions for the north china craton was subparallel to the direction of subduction whereas fast directions for southeastern china were perpendicular to the direction of subduction the shear wave splitting measurements were interpreted according to a high resolution tomographic body wave velocity model combining these two datasets showed that the predominant geodynamic models for the region mantle plume mantle wedge and flat slab subduction models are incompatible with the observations presented here we suggest that the north china craton yangtze craton and the cathaysia block have undergone different deformational events due to differing mantle flow patterns and distinct spatial and temporal subduction histories of the pacific and philippine sea plates

new paleomagnetic investigations of the emeishan basalts in ne yunnan southwestern china constraints on eruption history abstract paleomagnetic and magnetostratigraphic investigations have been conducted on two consecutive sections of the emeishan trap at shuimo sm and dadi dd in northeastern yunnan province southwestern china rock magnetic analysis indicates that the magnetic carrier of the basalts is dominantly low ti magnetite stepwise thermal demagnetization isolates a stable characteristic remanent magnetization chrm at high temperatures 400 585 c the chrms 301 323 at sm section are northeasterly upward of normal polarity with a mean direction of ds is 11 0 5 2 n 12 k 53 7 95 6 0 at dd section the chrms are southwesterly downward of reversed polarity with a mean direction of 205 9 10 0 n 5 k 78 4 95 8 7 the chrms from the basaltic gravels from the overlying conglomerate layer in late permian xuanwei formation at dd section pass the conglomerate test suggesting the primary nature of magnetization together with other magnetostratigraphic studies e g n r pattern of the emeishan basalts and the known radiometric ages ca 260 ma it suggests that the eruption period of the emeishan large igneous province is less than 3 myr

marine continental tephra correlations volcanic glass geochemistry from the marsili basin and the aeolian islands southern tyrrhenian sea italy abstract major minor and trace element analysis of volcanic glass in proximal and distal it is evident that correlation of proximal continental and distal marine tephras at a high level of confidence requires a full complement of major minor and trace element data in conjunction with considerations of the mineralogy and morphology of juvenile deposits these data help define petrological lineages such that precise provenance can be established whilst a precise proximal distal match must be based on identical major minor and trace element concentrations it is clear that resurgent activity from a single volcano can produce magmas with identical compositions in such cases stratigraphic relationships must complement any geochemical study occasionally proximal stratigraphies may be unrepresentative of the complete eruptive history because of a lack of exposure due to burial by more recent effusive and explosive activity or sector collapse which can remove vital stratigraphy particularly on volcanic islands

erosion and sedimentation as processes controlling the bsr derived heat flow on the eastern nankai margin in 2000 a 3d mcs survey was carried out on the eastern nankai trough a strong and widespread bottom simulating reflector bsr was observed and mapped after a preserved amplitude 3d prestack migration of the seismic data we use this bsr to calculate a heat flow map over the 3d survey area this map presents some high and low heat flow areas that cannot be correlated to known active wedge faults and previously observed fluid venting sites since the heat flow anomalies are not correlated to known major faults or fluid venting sites large fluid circulation is not likely to explain the varying bsr derived heat flow distribution in order to explain this heat flow distribution quantitatively we calculate the rates of erosion and sedimentation that are necessary to create these anomalies these rates are in good agreement with observations on seismic profiles and are locally consistent with a sedimentation rate calculated from slope basin depth and reflect the distribution of erosion landsliding and deposition on the margin slope we therefore propose that the observed bsr derived heat flow anomalies are mainly due to active erosion and sedimentation and that heat flow distribution on the margin section of the 3d survey is controlled by surface processes fluid migration could occur where a bsr is absent but is probably episodic or limited where a bsr is present and does not affect the bsr derived heat flow in this part of the margin these surface processes are the consequence of the tectonic and seismic activity of the wedge and are influenced by the subduction of a wide oceanic ridge below the eastern nankai margin

lithospheric mantle deformation beneath the indian cratons abstract the nature of deformation of the deep continental roots beneath the archean early proterozoic terrains opens the question whether these ancient terrains have had stable roots since the precambrian or whether recent plate motions have deformed them in view of this we make an attempt to study the thermal structure beneath the cratonic regions of the indian shield which vary in lithospheric thickness from 65 km in the singhbhum craton to 148 km in the archean dharwars the average depth of 104 km to the top of the underlying asthenosphere is consistent with other termination methods and is in fact less than half the 200 400 km depth found in other stable areas of the earth similarly the average reduced heat flow of about 35 mw m2 and moho temperature of about 550 c range 400 730 c for the indian cratons are also much higher than their counterparts elsewhere our study indicates a large scale deformation of the cratonic mantle lithosphere beneath the indian shield since the mesoproterozoic c

the age of glacier peak tephra in west central montana at sheep mountain bog near missoula montana a late glacial tephra that probably fell in late summer is preserved as an 8 mm thick graded bed overlain by another 8 mm of redeposited ash mixed with lake deposits sediment surrounding the ash was 14c dated to about 11 200 yr b p electron microprobe analyses of the volcanic glass and hornblende phenocrysts from this ash layer indicate that they are similar in major element chemistry to those of glacier peak layer g previously considered to be about 12 000 yr old or older

geologic geochemical and geophysical consequences of plume involvement in the emeishan flood basalt province prevolcanic kilometer scale lithospheric doming in the emeishan large igneous province southwest china allows us to evaluate the spatial and temporal consequences of uplift on the paleogeography geology geochemistry and geophysics of the region systematic spatial variations are observed across the domal structure in the distribution and thickness of clastic and carbonate sediments the extent of erosion thickness and chemistry of volcanic rocks and the crust mantle structure these features which are best explained by a mantle plume may be used to track older plume sites in the geologic record

3 d velocity model beneath the middle lower yangtze river and its implication to the deep geodynamics abstract a mineralization zone exists in the middle and lower yangtze river mlyr region previous studies have shown that this zone might be caused by the rich ejection of magma in the mesozoic we have applied the teleseismic tomography method to determine a 3 d p wave velocity structure of the mantle down to 500 km depth beneath this region by using 14 740 p wave arrival times collected from 519 teleseismic events recorded by 46 portable and 47 static seismic stations located in this region the relative residual times used for the tomography are calculated by the modified multi channel cross correlation method which increases not only the efficiency but also the data precisions up to 0 01 s the grid space is set as 1 1 horizontally and 50 100 km vertically our tomographic results show that the lithosphere with high velocity anomalies is separated into two parts one locates above the depth of 100 km and the other at the depths between 250 km and 400 km and the asthenosphere with low velocity anomalies locates between these two parts of lithosphere which indicates that the lithosphere delaminated together with the asthenosphere upwelling the detachment of lithosphere might relate to the subduction of the western pacific slab therefore our study provides clear evidence to geoscientists for understanding the deep dynamic process beneath this region and a three stage geodynamic process is developed based on the new evidence

high resolution lithospheric structure beneath mainland china from ambient noise and earthquake surface wave tomography abstract we present a new high resolution shear velocity model of the lithosphere down to about 160 km beneath china using rayleigh wave tomography we combined ambient noise and earthquake data recorded at 1316 seismic stations the largest number used for the region to date more than 700 000 dispersion curves were measured to generate group and phase velocity maps at periods of 10 140 s the resolution of our model is significantly improved over previous models with about 1 2 in eastern china and 2 3 in western china we also derived models of the study region for crustal thickness and averaged s velocities for upper and mid lower crust and uppermost mantle these models reveal important lithospheric features beneath china and provide a fundamental data set for understanding continental dynamics and evolution different geological units show distinct features in the moho depth lithospheric thickness and shear velocity in particular the north china craton ncc lithosphere shows strong east west structural variations with thin and low velocity lithosphere in eastern ncc and thick and high velocity lithosphere beneath western ncc and the lithosphere of the ordos block seems to have undergone strong erosion the results support the progressive destruction of the ncc lithosphere from east to west at least partly caused by the thermal chemical erosion of the cratonic lithosphere from the asthenosphere another pronounced feature of our model is the strong lateral variations of the mantle lithosphere beneath the tibetan plateau tp the indian lithosphere beneath the tp shows variable northward advancement with nearly flat subduction in western and eastern tp and steep subduction in central tp with evidence for the tearing of indian lithosphere beneath central tp which may be important for the riftings at the surface in himalayas and southern tp the low velocity zone in northern tp shows strong correlation with the region of the mid miocene to quaternary potassic magmatism suggesting that delamination of lithosphere may have played an important role in the rise of the tp

geothermal modelling of the lithosphere in the central baltic shield and its southern slope lithospheric temperature and heat flow density hfd were studied in the central baltic fennoscandian shield and its subsurface continuation to the south along a transect trending from eastern finland to southern estonia the transect represents an example of a low hfd 30 mw m 2 archaean craton on a thick 150 190 km lithosphere surrounded by early and middle proterozoic mobile belts on a thinner 110 150 km lithosphere with slightly elevated hfd 35 55 mw m 2 numerical 2 d conductive models were constructed in which peridotite solidus temperatures were assigned to those depths which correspond to the seismically determined lithosphere asthenosphere boundary this technique was found to reduce the effect of uncertainties in heat production and thermal conductivity values on the simulation results upper crustal heat production values for the finnish terrain were taken from published geochemical analyses of outcropping rocks for the estonian terrain new heat production values were measured from core samples representing nineteen deep boreholes middle and lower crustal lithologies were estimated with the aid of the deep seismic vpvs data and corresponding heat production values were adapted from global xenolith averages and from data for granulites cropping out in other precambrian areas the results of the modelling suggest that the lithosphere and moho depth variations are only weakly reflected in the measured surface heat flow data which are mainly controlled by heat sources in the upper crust the simulated heat flow densities at 50 km depth approximately at the moho are relatively low and range from 12 mw m 2 at the archaean northeastern end to 19 mw m 2 on the proterozoic southwestern end of the transect simulated temperatures at 50 km depth increase from northeast to southwest ranging from 450 550 c in eastern finland to about 650 c in estonia sensitivity of the simulations to parameter changes was studied by varying the heat production and thermal conductivity values the extreme values for the moho temperature estimates thus obtained may be about 50 k lower or 100 k higher than the values above the corresponding sensitivity of the moho hfd is about 6 mw m 2 and of the surface hfd 5 20 mw m 2 respectively

luminescence dating of loess from the northwest united states thermoluminescence tl and infra red stimulated luminescence irsl ages have been determined for loess from the columbia plateau region of southeast washington and northeast oregon u s a the irsl ed values and ages appear to be tending towards a maximum level lower than that of the tl ed values and ages in general the tl ages are in stratigraphic order and agree well with the age control in the form of 14c and tl dated tephra units derived from various eruptions of mount st helens

a global shear velocity model of the upper mantle from fundamental and higher rayleigh mode measurements we present dr2012 a global sv wave tomographic model of the upper mantle we use an extension of the automated waveform inversion approach of debayle 1999 which improves our mapping of the transition zone with extraction of fundamental and higher mode information the new approach is fully automated and has been successfully used to match approximately 375 000 rayleigh waveforms for each seismogram we obtain a path average shear velocity and quality factor model and a set of fundamental and higher mode dispersion and attenuation curves we incorporate the resulting set of path average shear velocity models into a tomographic inversion in the uppermost 200 km of the mantle sv wave heterogeneities correlate with surface tectonics the high velocity signature of cratons is slightly shallower approximate to 200 km than in other seismic models thicker continental roots are not required by our data but can be produced by imposing a priori a smoother model in the vertical direction regions deeper than 200 km show no velocity contrasts larger than 1 at large scale except for high velocity slabs within the transition zone comparisons with other seismic models show that current surface wave datasets allow to build consistent models up to degrees 40 in the upper 200 km of the mantle the agreement is poorer in the transition zone and confined to low harmonic degrees 10

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

magnetostratigraphic constraints on two stage eruptions of the emeishan continental flood basalts temporal and spatial variations of high and low contents of ti basalts in the permian emeishan large igneous province elip of southwest china and vietnam are crucial for modeling of continental basalt formation and the nature of mantle lithosphere interaction a combined geochemical and magnetostratigraphic study was carried out at yanyuan in the inner zone of the elip geochemical results indicate that the basalts are low ti lt basalts ti y 484 2 511 4 in the luomapu section and high ti ht basalts ti y 558 2 658 9 in the gongmushan section systematic paleomagnetic sampling and stepwise thermal demagnetization demonstrate that the higher temperature component shows two distinct characteristic remanent magnetizations with northeasterly upward and sww downward directions these results indicate a simple magnetostratigraphic normal and reversed polarity pattern from the lower and upper parts of the section respectively by comparing with available magnetostratigraphic and paleomagnetic data carried out in the elip these results imply that the eruption of the emeishan basalts can be divided into early normal polarity subchron and late reversal subchron stages the early stage included lt basalts in the inner zone and most of the ht basalts in the intermediate and outer zones and the late stage contained a part of lt and ht basalts in the upper parts of the sections in the inner zone and a few in the intermediate zone of the elip correlating with available middle late permian magnetostratigraphy and the permian magnetic time scale the new magnetic polarity sequence result suggests that the elip formed over a very short time interval 1 myr

topographic and climatic influences on accelerated loess accumulation since the last glacial maximum in the palouse pacific northwest usa abstract topographic and climatic influences have controlled thick loess accumulation at the southern margin of the palouse loess in northern oregon juniper and cold springs canyons located on the upwind flank of the horse heaven hills are oriented perpendicular to prevailing southwesterly winds these canyons are topographic traps that separate eolian sand on the upwind side from thick accumulations nearly 8 m of latest pleistocene to holocene l1 loess on the downwind side silt and sand rich glacial outburst flood sediment in the umatilla basin is the source of eolian sand and loess for the region sediment from this basin also contributes to loess accumulations across much of the columbia plateau to the northeast downwind of cold springs canyon mt st helens set s and glacier peak tephras bracket 4 m of loess demonstrating that approximately 2500 g m 2 yr 1 of loess accumulated between about 15 400 13 100 cal yr b p mass accumulation rates decreased to approximately 250 g m 2 yr 1 from 13 100 cal yr b p to the present tephrochronology suggests that the bulk of near source palouse loess accumulated in one punctuated interval in the latest pleistocene characterized by a dry and windy climate

lake tapps tephra an early pleistocene stratigraphic marker in the puget lowland washington abstract the rhyolitic lake tapps tephra was deposited about 1 0 myr ago shortly after culmination of the early phase of the salmon springs glaciation in the puget lowland it is contained within sediments that were deposited in ponds or lakes in front of the reteating glacier an herb dominated tundra existed in the southern puget lowland at that time lake tapps tephra is most likely the product of an eruption that in part was phreatomagmatic it forms an early pleistocene stratigraphic marker across the southern sector of the puget lowland and provides a link between puget lobe sediments of the cordilleran ice sheet and sediments deposited by olympic alpine glaciers

last glacial loess in the conterminous usa the conterminous united states contains an extensive and generally well studied record of last glacial loess the loess occurs in diverse physiographic provinces and under a wide range of climatic and ecological conditions both glacial and non glacial loess sources are present and many properties of the loess vary systematically with distance from loess sources united states midcontinent last glacial loess is probably the thickest in the world and our calculated mass accumulation rates mars are as high as 17 500 g m 2 yr at the bignell hill locality in nebraska and many near source localities have mars greater than 1500 g m 2 yr these mars are high relative to rates calculated in other loess provinces around the world recent models of last glacial dust sources fail to predict the extent and magnitude of dust flux from the mid continent of the united states a better understanding of linkages between climate ice sheet behaviour routing of glacial meltwater land surface processes beyond the ice margin and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region r 2003 elsevier ltd all rights reserved

heat flow and heat production in the namaqua mobile belt south africa results of heat flow and heat production surveys at 13 localities in the namaqua mobile belt southern africa are presented twelve stations traverse the 1200 1100 m y old gneissic and metamorphic bushmanland and gordonia subprovinces one station is situated in the richtersveld subprovince a 2000 1730 m y old volcano sedimentary domain mildly affected by the 1200 1100 m y old orogeny surface heat flow in the mobile belt ranges from 39 to 81 mw m 2 and averages at 61 11 mw m 2 surface heat production ranges from 0 8 w m 3 in mafic rocks to extreme values of 6 9 12 3 w m 3 in the springbok district western namaqualand high heat production in the springbok district is associated with a thin tabular granitic intrusive and is not representative of the basement the mean heat production of the remaining stations in the mobile belt is 2 3 1 1 w m 3 linear regression analysis of the heat flow heat production data yields a poor fit correlation coefficient 0 62 and imprecise estimates for the intercept 34 6 mw m 2 and slope 11 3 km the eastern margin of the mobile belt has relatively low heat flow and heat production geothermal geological and gravity data suggest a relative depletion of crustal radiogenic heat production in the region however the average namaqua heat flow is higher than worldwide averages for proterozoic terrains there is no geological or geophysical evidence for recent mantle heating below the namaqua mobile belt suggesting that an elevated crustal radioactive component is largely responsible for the elevated heat flow in this respect the mobile belt is similar to several mid late proterozoic heat flow provinces that are characterized by high average surface heat flow and probably have elevated crustal radiogenic heat input these observations and seismic data suggest that the namaqua crust consists of an upper layer that contributes 40 50 on average to the heat flow and a depleted lower layer the inferred heat flow at midcrustal levels is 50 60 of the average surface heat flow the mobile belt s average surface heat flow is 40 85 higher than that from the basement of the adjacent archaean kaapvaal craton and its inferred midcrustal heat flow is similar to the lowest surface values in the craton heat production data from the kaapvaal craton indicate that its upper crust is not depleted of heat sources while enhanced radiogenic heat input from the namaqua upper crust may account for part of the higher than craton heat flow it cannot account for the full excess consequently a larger equilibrium mantle heat flow related to a reduced lithospheric thickness below namaqualand seems to be required by the new data

thermal evolution of the upper yangtze craton secular cooling and short lived thermal perturbations abstract the upper yangtze craton uyc has stayed in a long term stabilization state its thermal history can be portioned into two parts secular evolutionary trend and short lived thermal perturbations the former is simulated by a two dimensional forward transient thermal model and the latter is discussed by reviewing previous studies the numerical modeling indicates the uyc tended to be cooling as it adjusted to the asynchronous rates of change in the internal radiogenic heat production and in the convecting mantle temperature below the cratonic root the average cooling rate of the uyc has been 58 c ga since the end of archean faster than that of the convecting mantle the surface heat flow presents a decreasing trend from 82 mw m2 at 2 5 ga to 53 mw m2 at present day which constructs the long term evolutionary path the thermal perturbations derived from the occasional tectono thermal events such as mantle plume activity and regional lithosphere extension serves as paroxysmal factors the thermal effects of the emeishan mantle plume were very strong yielding to the maximum heat flow anomaly of 100 mw m2 at the late permian in contrast the influences of regional lithosphere extension during both the early paleozoic period and the early permian middle triassic period were rather weak resulting in a surface heat flow increase of

correlation of late quaternary tephra layers in a long pluvial sequence near summer lake oregon abstract near summer lake in southern oregon 54 tephra beds of late quaternary age are exposed in pluvial lake sediments of lake chewaucan seven of the tephra beds near the top can be correlated with tephra deposits younger than 117 000 yr at mount st helens washington at crater lake oregon and in northwestern nevada in the deposits of pluvial lake lahontan however most of the section at summer lake lies below the correlated units and contains 39 tephra beds older than 117 000 yr major element chemistry of tephra glasses was determined by electron microprobe analysis petrography supports the correlations made from chemical evidence compositions correlated range from 70 to 76 sio 2 the least silicic summer lake glass contained 57 extrapolation of depositional rate suggests that most of the sediments at summer lake are younger than about 335 000 yr but older lake beds containing tephra layers occur at one place the long lacustrine record suggests that lake chewaucan persisted through the last interpluvial stage and that the lake may have dried up at the end of the pleistocene due to diversion of the chewaucan river by relict shore features

lithospheric structure of the chinese mainland determined from joint inversion of regional and teleseismic rayleigh wave group velocities 1 we processed a large number of vertical component seismograms recorded by broadband seismic stations in and around china and ultimately retrieved 33 140 regional and 10 360 teleseismic fundamental mode group velocity measurements at 40 s periods with fewer measurements for shorter and longer periods we directly inverted the processed group velocity measurements for a three dimensional lithospheric s velocity model of the chinese mainland synthetic test results and data fit or misfit analysis demonstrated the reliability of our surface wave tomographic inversion the imaged upper crustal low velocities are consistent with variations in sediment thickness for example the tarim basin which contains a great thickness of sediments is characterized by a strong shallow low velocity anomaly high lithospheric velocities are observed to varying depths in the north china craton yangtze craton and tarim craton indicating varying thicknesses of the lithosphere beneath these cratonic areas low asthenospheric velocities are widely imaged in eastern and southern china around the tarim basin and along a roughly north south belt in central china the low asthenospheric velocities in eastern and southern china are attributed to partial melting of a subducted slab associated with the westward subduction of an oceanic plate while those in central china and around the tarim basin are attributed to indian eurasian collision

synchrony and causal relations between permian triassic boundary crises and siberian flood volcanism the permian triassic boundary records the most severe mass extinctions in earth9s history siberian flood volcanism the most profuse known such subaerial event produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less analysis of 40 ar 39 ar data from two tuffs in southern china yielded a date of 250 0 0 2 million years ago for the permian triassic boundary which is comparable to the inception of main stage siberian flood volcanism at 250 0 0 3 million years ago volcanogenic sulfate aerosols and the dynamic effects of the siberian plume likely contributed to environmental extrema that led to the mass extinctions

thermal evolution of cratons in china abstract craton s thermal state is one of the main gateways to understand the craton dynamics three cratons in china the tarim north china and yangtze cratons are in different thermal states and differ in their stabilities low heat flow usually corresponds to stable craton but not vice versa the tarim craton is cold 44 mw m2 and still keeps its stability now the western north china craton and the upper yangtze craton are not too cold 50 60 mw m2 but also remain stable the eastern north china craton and the middle lower yangtze craton are relatively hot with heat flow of 60 70 mw m2 both have been heated and destroyed in the mesozoic all these cratons have experienced complex tectonothermal events since their formation some tectonothermal events only thin and heat craton but others can destroy craton several sedimentary basins are developed in these cratons which recorded individual thermal histories these thermal records could help to understand the thermal evolution of these cratons and provide constraints on craton dynamics including stability or destruction the thermal results indicate parts of craton in western china tarim and sichuan have secular cooling histories which were locally disturbed by mantle plume activities in the permian the middle lower yangtze craton has undergone similar thermal evolution as the eastern north china craton all parts of cratons in eastern china might all have been destroyed due to subduction and dehydration of the pacific plate during the mesozoic

correlation of distal tephra layers in loess in the channeled scabland and palouse of washington state abstract thirty two distal tephra layers that are interbedded in quaternary loess at 13 sites in the channeled scabland and palouse were sampled as part of a regional study of the stratigraphy and chronology of dominantly windblown sediments on the columbia plateau an electron microprobe was used to determine the elemental composition of volcanic glass in all of the samples and also to determine the composition of ilmenite in 14 of them two of the distal tephra layers correlate with glacier peak eruptions 11 200 yr b p five with mount st helens tephra set s 13 000 yr b p and nine with mount st helens tephra set c ca 36 000 yr b p based on analysis of glass and ilmenite in reference pumices from glacier peak mount st helens mount mazama mount rainier and mount jefferson on the calculation of similarity coefficients for comparisons of both glass and ilmenite reference compositions with those of distal tephras and on considerations of stratigraphic position the composition of glass and ilmenite and the stratigraphic position of one distal tephra layer in the loess suggests that it is from an eruption of mount st helens at least several thousand years older than the set c eruptions glass composition and stratigraphic position of a distal tephra at another site in loess suggested a possible correlation with some layers of the pumice castle eruptive sequence at mount mazama ca 70 000 yr b p but similarity coefficients on ilmenite of only 45 and 48 fail to support the correlation and show why multiple correlation methods should be used similarity coefficients higher than 96 for both glass and ilmenite establish a correlation with mount st helens layer cw for distal layers in two widely separated sites these layers are in sedimentary successions that are closely associated with giant floods in the channeled scabland the 36 000 yr b p radiocarbon age of the mount st helens set c establishes a minimum limiting date for an episode of flooding that predates the widespread late wisconsin floods a correlation of distal tephra layers at two other sites in the scabland and palouse establishes a chronostratigraphic link to a still older episode of flooding within the brunhes normal polarity chron six distal tephra layers in pre late quaternary loess that are not correlated with known or dated eruptions have compositions and distinctive stratigraphic positions relative to magnetic reversal boundaries that make them key markers for future work

radiogenic heat production in the lithosphere of sulu ultrahigh pressure metamorphic belt abstract the chinese continental scientific drilling ccsd project is located at the sulu ultrahigh pressure metamorphic uhpm belt it offers a unique opportunity for studying the radiogenic heat production of both shallower and deeper rocks based on the concentrations of radiogenic elements u th and k on 349 samples from main hole of ccsd ccsd mh pilot holes and exposures we determined radiogenic heat productions of all major rock types in the sulu uhpm belt results show the mean values of orthogneiss and paragneiss are respectively 1 65 0 81 and 1 24 0 61 w m 3 due to different composition and grade of retrogressive metamorphism the eclogites display significant scatter in radiogenic heat production ranging from 0 01 to 2 85 w m 3 with a mean of 0 44 0 55 w m 3 the radiogenic heat production in ultramafic rocks also varies within a large range of 0 02 to 1 76 w m 3 and the average turns out to be 0 18 0 31 w m 3 based on the measurements and crustal petrologic model the vertical distribution model of heat production in sulu crust is established the resulting mean heat production 0 76 w m 3 contributes 24 mw m 2 to the surface heat flow 1 d thermal model indicates that the temperature at the moho reaches above 750 c and the thermal thickness of the lithosphere is 75 km in good agreement with the geophysical results the high teat flow 75 mw m 2 together with thin lithosphere presents strong support for the extension events during the late cretaceous and cenozoic

genesis and relationship of macromorphology and micromorphology to contemporary hydrological conditions of a welded argixeroll from the palouse in idaho abstract soils formed in distal loess of the palouse region have welded profiles that make assessment of their genesis and pedostratigraphic relationships difficult these soils typically have a mollic cambic horizon sequence that is underlain by a well expressed albic e horizon and a strongly developed argillic horizon in this study we utilized hydrological monitoring combined with micromorphological analysis and new stratigraphic data to help establish the genesis of a representative argixeroll of the region and the relationship of its morphology to ancient and contemporary hydrological conditions monitoring results indicate that the argixeroll is seasonally episaturated for approximately 5 6 months per year ferrimanganiferous nodules segregations hypocoatings and depletion mottles are observed in thin section throughout the pedon but dominate within just above and below the present day e horizon measured soil eh is sufficiently low for fe and mn reduction to occur for 1 3 months during the period of episaturation suggesting that at least some of these redoximorphic features are likely to be contemporary other compound redoximorphic features are clearly relict however as they are coated by illuvial clay which is unaffected by fe mn redistribution processes thick illuvial clay coatings on interpedal fissures of the argillic horizon postdate pockets of holocene tephra within deeply bioturbated aggregates while other channel argillans in the same part of the pedon are clearly older this indicates that at least two distinct phases of clay accumulation have occurred the most recent being contemporaneous with loess aggradation during the holocene our results suggest that these welded profiles consist of a mollic cambic horizon sequence that has formed primarily in holocene loess and an albic argillic sequence that has formed in wisconsinan loess the modern day e horizon was initiated as the clay eluvial surface horizon of the regionally recognized washtucna paleosol that continued forming into the late wisconsinan cold phase and upon burial by holocene loess it has been transformed into an albic horizon and even enlarged as a result of redoximorphic processes associated with seasonal saturation

late quaternary stratigraphy of loess in the channeled scabland and palouse regions of washington state abstract loess deposits of late quaternary age in the channeled scabland and western palouse regions of washington state contain distinctive sequences of calcic buried soils loess layers tephra layers and stratigraphic unconformities caused by cataclysmic flooding four new soil stratigraphic units the sand hills coulee soil washtucna soil old maid coulee soil and the devils canyon soil are recognized across a 100 km transect the pedostratigraphic correlations are strengthened by two tephra layers found at several sites that are correlative with the mount st helens set s radiocarbon ages about 13 000 yr b p mount st helens set c radiocarbon ages about 36 000 yr b p and by a third one that may be from an earlier pre set c mount st helens eruption the set s tephra layer separates the sand hills coulee and washtucna soils the set c tephra layer separates the old maid coulee and devils canyon soils and the pre set c tephra layer underlies the devils canyon soil the well known late wisconsin episode of scabland flooding and two older episodes of flooding are marked by regional stratigraphic unconformities that lie between pedostratigraphic units one unconformity that underlies the washtucna and old maid coulee soils was caused by a major episode of scabland flooding that occurred before 35 000 yr b p probably during the early wisconsin 80 000 to 65 000 yr b p a possible second and older episode of flooding recognized by an unconformity that underlies the devils canyon soil may be illinoian ca 130 000 to 200 000 yr b p in age

the structure of the crust and uppermost mantle beneath south china from ambient noise and earthquake tomography summary two years of continuous recordings of ambient seismic noise observed at 354 stations in south china from 2009 to 2010 are used to estimate rayleigh wave group and phase velocity maps from 6 to 40 s period these results are merged with rayleigh wave phase velocity maps from 25 to 70 s period derived from earthquakes in the same time frame eikonal tomography generates the dispersion maps which by monte carlo inversion are used to estimate a 3 d vsv model of the crust and upper mantle down to a depth of 150 km across all of south china with attendant uncertainties a clear image emerges of the west yangtze block a region of the western yangtze craton characterized by relatively thick crust 40 km overlying a seismic mantle lithosphere that extends to at least 150 km that may have been the nucleus for the formation of the yangtze craton in the archean and may present a present day obstacle to the eastward expansion of tibet the west yangtze block contrasts with the thinner crust 30 km and mantle lithosphere 70 80 km beneath the eastern yangtze craton and south china foldbelt these observed differences are consistent with processes associated with flat slab subduction in the mesozoic that may have eroded the lithosphere of the eastern yangtze craton and the south china foldbelt

significance of past and recent heat flow and radioactivity studies in the southern rocky mountains region as reported in the geological society of america bulletin of 1950 francis birch s innovative heat flow research in the colorado front range introduced frequently used terrain correction and thermal conductivity measurement methods that report also presented the first empirical evidence for a positive correlation between above normal flux and radioactive roots in an isostatically compensated mountain area with a thick crust an observation that strongly influenced continental heat flow studies for the next 18 years birch s front range study clearly showed that reliable continental heat flow research requires knowledge of bedrock radioactivity this concept reached an unprecedented level of acceptance in 1968 when linear relations between heat flow and radiogenic heat production were discovered for three contrasting provinces in the united states subsequently such lines have been central to virtually all heat flow and radioactivity research on land heat flow q data for 139 boreholes provide new detail on thermal regimes in the southern rocky mountains and bordering areas as do radiogenic heat production a data for 60 locales interpretations also emphasize reduced and residual heat flow values reduced values correspond to the intercepts of regional q a lines whereas a residual value is the flux at a locale after the probable effect of near surface heat production has been subtracted the observed q a lines demonstrate that the front range and other easterly frontal ranges of the southern rocky mountains in colorado and northern new mexico are characterized by a reduced flux 54 58 mwm 2 that is dramatically higher than that 27 mwm 2 in the wyoming basin southern rocky mountains area in southeastern wyoming because the transitions between these provinces are narrow 50 60 km sources in the upper crust must explain some of the contrasting reduced heat flow values in southeastern wyoming normal heat flow in archean and early proterozoic basement terranes probably reflects deep erosion that produced a thin 7 km near surface granitic layer that overlies a low radioactivity lower crust in the colorado front range proterozoic mesozoic and cenozoic silicic rocks with relatively enriched radiogenic heat could comprise a 20 to 25 km thick granitic layer in the upper crust that produces a large part of the above normal reduced and residual flux here partial melting of deep protolithic rocks in late mesozoic and cenozoic times could have produced a lower crust with low radiogenic heat production by these views birch s high heat flow radioactive mountain root model of the colorado front range is confirmed if a large part of the topography is isostatically compensated by low density pre miocene crystal line masses in the upper crust background reduced heat flow in colorado parts of the southern rocky mountains and the eastern colorado plateau is high 54 68 mwm 2 zones of unusually high residual flux 88 118 mwm 2 occur in the rio grande rift zone in the environs of the colorado mineral belt in the leadville northern sawatch range region eastern parts of the san juan mountains in southern colorado and in the park range mountain parks area near the colorado wyoming border the flux in these areas implies unrealistically high equilibrium temperatures near the crustmantle boundary and the 50 to 60 km wide borders of the leadville northern sawatch range residual heat flow anomaly must be caused by sources in the upper crust there fore young 10 to 1 m y old intrusions in a late cenozoic rhyolitic complex in the upper crust are preferred to explain gravity lows late cenozoic uplift and igneous activity and the high residual flux in the leadville northern sawatch range area similar models may apply elsewhere in the northern rift zone if this interpretation is correct magmatic thickening of the crust not extensional subsidence mechanisms probably explains late cenozoic uplift and extension of the northern rio grande rift southern rocky mountains system because very high regional flux in the northern rift zone and the san juan mountains areas implies above liquidus equilibrium temperatures in the lower crust and upper mantle serious inconsistencies arise when steady state thermal models are examined relative to volumes of late tertiary volcanism uniform crustal thickness and the absence of unusually low p wave velocities in the mantle in the southern rocky mountains

a global analysis of heat flow from precambrian terrains implications for the thermal structure of archean and proterozoic lithosphere previous studies of heat flow from precambrian terrains have yielded two different relationships a global temporal relationship between heat flow and tectonic age and a regional spatial relationship between heat flow and the proximity of archean cratons we analyze heat flow from tectonically stable precambrian terrains worldwide to address questions associated with these two heat flow patterns 1 is the spatial relationship a global pattern 2 do the two heat flow relationships have a common underpinning in answer to the first question our data analysis reveals a widespread spatial pattern between heat flow and the proximity of archean cratons which is characterized by low heat flow in archean cratons and proterozoic terrains adjacent to cratonic margins and higher heat flow in proterozoic terrains that are more than a few hundred kilometers from a craton to address the second question we examine three previous interpretative models of precambrian heat flow 1 simple cooling of a thermal boundary layer 2 thicker lithosphere in archean terrains than in proterozoic and 3 greater heat production in proterozoic crust than in archean model 1 predicts essentially no change in heat flow in terrains older than 1 5 ga and therefore does not likely provide a common underpinning for the precambrian heat flow patterns models 2 and 3 when combined with the special structural configuration of sutures can independently yield both the spatial and temporal heat flow distributions and thus alone or together may be considered candidates to explain the precambrian heat flow patterns however thermal models of the lithosphere in which the heat flow patterns are explained entirely by variations in crustal heat production cannot satisfy constraints on upper mantle temperatures beneath archean cratons derived from xenolith thermobarometry the thermobarometry constraints can be satisfied by models in which differences in lithospheric thickness are the principal factor controlling the surface heat flow distributions if the heat flow patterns result primarily from variations in lithospheric thickness then a different temporal heat flow relationship for precambrian terrains can be proposed one in which heat flow varies inversely with the age of stabilization of the lithosphere

global upper mantle tomography with the automated multimode inversion of surface and s wave forms summary we apply the automated multimode inversion of surface and s wave forms to a large global data set verify the accuracy of the method and assumptions behind it and compute an s vvelocity model of the upper mantle crust 660 km the model is constrained with 51 000 seismograms recorded at 368 permanent and temporary broadband seismic stations structure of the mantle and crust is constrained by waveform information both from the fundamentalmode rayleigh waves periods from 20 to 400 s and from s and multiple s waves higher modes in order to enhance the validity of the path average approximation we implement the automated inversion of surface and s wave forms with a three dimensional 3 d reference model linear equations obtained from the processing of all the seismograms of the data set are inverted for seismic velocity variations also relative to a 3 d reference in this study composed of a 3 d model of the crust and a one dimensional 1 d global average depth profile in the mantle below waveform information is related to shear and compressional velocity structure within approximate waveform sensitivity areas we use two global triangular grids of knots with approximately equal interknot spacing within each a finely spaced grid for integration over sensitivity areas and a rougher spaced one for the model parametrization for the tomographic inversion we use lsqr with horizontal and vertical smoothing and norm damping we invert for isotropic variations in s and p wave velocities but also allow for s wave azimuthal anisotropy in order to minimize errors due to possible mapping of anisotropy into isotropic heterogeneity the lateral resolution of the resulting isotropic upper mantle images is a few hundred kilometres varying with data sampling we validate the imaging technique with a spectral element resolution test inverting a published global synthetic data set computed with the spectral element method using a laterally heterogeneous mantle model we are able to reconstruct the synthetic model accurately this test confirms both the accuracy of the implementation of the method and the validity of the jwkb and path average approximations as applied in it reviewing the tomographic model we observe that low s v velocity anomalies beneath mid ocean ridges and backarc basins extend down to 100 km depth only shallower than according to some previous tomographic models this presents a close match to published estimates of primary melt production depth ranges there in the seismic lithosphere beneath cratons unambiguous high velocity anomalies extend to 200 km pronounced low velocity zones beneath cratonic lithosphere are rare where present south america tanzania they are neighboured by volcanic areas near cratonic boundaries the images of these low velocity zones may indicate hot material possibly of mantle plume origin trapped or spreading beneath the thick cratonic lithosphere

summary of pre 1980 tephra fall deposits erupted from mount st helens washington state usa mount st helens has been a prolific source of tephra fall deposits for about 40 000 years these tephra deposits 1 record numerous explosive eruptions 2 form important regional time stratigraphic marker beds and 3 record repeated changes in composition within and between eruptive periods

strong intracontinental lithospheric deformation in south china implications from seismic observations and geodynamic modeling abstract classical plate tectonics theory predicts concentrated deformation at plate boundaries and weak deformation within plates yet the existence of intracontinental orogens shows that highly deformed regions can occur within continental plates which is geodynamically incompletely understood shear wave splitting measurements in south china show belt parallel i e ne sw fast directions beneath the wulingshan xuefengshan belts while no dominant fast direction is found in the cratonic sichuan basin tomographic studies in the mantle in the same area show that the thickness of lithosphere beneath the intracontinental orogen is larger than that beneath the cratonic sichuan basin in order to better understand these seismic observations we performed numerical experiments of intracontinental lithospheric deformation with the presence of cratonic basin by comparing systematic model results with topography data and constraints on the accumulated amount of shortening in the study region we find that the best fitting result is obtained for models with a strong upper and a wet lower crust and with a weak mantle lithosphere beneath the orogen belt which has an effective viscosity that is 2 orders of magnitude smaller than that of the craton our numerical model successfully explains the belt parallel anisotropy and high velocity anomaly beneath intracontinental orogen and suggests that significant intracontinental lithospheric deformation occurred in south china

precambrian temperature and pressure system of gaoshiti moxi block in the central paleo uplift of sichuan basin southwest china abstract recently trillions of cubic meters gas resources have been found in sinian reservoirs of gaoshiti moxi region in the central uplift of sichuan basin which is the first commercial discovery of primary gas field in precambrian anywhere in the world to obtain a great breakthrough in precambrian hydrocarbon exploration it is necessary to find out the evolution process of temperature and pressure reconstructing the thermal history and pore pressure evolution in carbonate reservoirs are challenging problems especially in deep old layers without available samples and methods to study the temperature and pressure system we conducted a comprehensive analysis combining the paleo thermal indicators and inclusions pressure volume temperature pvt simulation with basin modeling the results showed that the thermal history of the gaoshiti moxi area could be divided into three stages from the late sinian to late paleozoic the thermal regime was stable with low heat flow value

thermoluminescence dating of late pleistocene loess and tephra from eastern washington and southern oregon and implications for the eruptive history of mount st helens the first numeric dating of late pleistocene loess from the palouse region of eastern washington is reported this loess is interbedded with thin distal tephra layers some identified as mount st helens products both the interbedded tephra layers and thick paleosols that have developed in the loess have previously been correlated across the region a thicker correlative of one of these tephra layers mount st helens set c was collected from summer lake oregon for direct dating by thermoluminescence tl polymineral fine grain tl ages for loess from three chosen sections in washington range from 17 to 83 ka these imply ages for some tephra beds that are significantly older than implied by earlier radiocarbon 14c dating for example tl ages of 17 21 ka for loess bracketing a tephra layer correlated to mount st helens set s suggests a somewhat older age for this ash than the previously accepted 14c age of 15 5 0 5 ka cal yr corrected to calendar years tl ages of 46 6 1 ka and 57 7 ka for loess above and of 53 7 ka and 75 6 ka below a tephra bed correlated to a mount st helens set cw layer along with a tl age of 46 5 ka for fine silt sized glass from a mount st helens set cy bed in oregon revise upward from 38 ka cal yr 14c age is 36 ka b p to 50 ka the age of this regionally important marker ash set several tl ages taken together imply a much longer eruptive history for mount st helens than previously thought a tl age of 83 8 ka just below a previously undated tephra layer from mount st helens emsh ash suggests that the eruptive history of the mountain extends back to at least 80 ka furthermore age depth extrapolation through our sections to an ash wa 5c probably correlated to mount st helens suggests an eruptive history of at least 120 ka

contrasting geochemical and sm nd isotopic compositions of archean metasediments from the kongling high grade terrain of the yangtze craton evidence for cratonic evolution and redistribution of ree during crustal anatexis abstract twenty three clastic metasediments from the kongling high grade terrain of the yangtze craton south china were analyzed for major trace and rare earth elements and sm nd isotopic ratios associated dioritic tonalitic trondhjemitic dtt and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance the results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical geochemical and sm nd isotopic compositions group a is characterized by having no to slight negative eu anomalies eu eu 0 82 1 07 being high in cr 191 396 ppm and ni 68 137 ppm and low in th 3 3 7 8 ppm and ree ree 99 156 ppm these characteristics are similar to those of metasediments from archean greenstone belts in addition the group a metasediments have the value of the chemical index of alteration ciw close to felsic gneisses their sm nd isotopic ree and trace element compositions can be interpreted by mixtures of the dtt gneisses and amphibolites dating of detrital zircons from 2 group a samples by shrimp reveals a major concordant age group of 2 87 3 0 ga which is identical to the age of the trondhjemitic gneiss these results strongly suggest that group a was principally the first cycle erosion product of the local kongling dtt gneiss and amphibolite moreover the higher than amphibolite cr content and slight eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3 0 3 3 ga in age also played a role group b is characterized by the presence of graphite and shows a more evolved composition similar to post archean shales with a prominent negative eu anomaly eu eu 0 48 0 77 and high ciw on paired cr th vs la co and co th plots group b samples conform to a two end member mixing line of the kongling granitic gneiss and amphibolite however data on nd model age and ciw suggest that the granite component should be younger than the sampled granitic gneiss and derived from a distal source both groups a and b exhibit a clear positive correlation between ciw and tdm and a negative one between ciw and eu eu these correlations point to the crustal evolution of the yangtze craton towards coupled increasing ciw and eu depletion with decreasing age this in turn reflects the change of granitoid magmatism from local na rich dioritic tonalitic trondhjemitic rocks to widespread k feldspar granite the change led to the intracrustal differentiation stabilization and growth of the craton group c is restite and contains abundant sillimanite and garnet and unusually high ilmenite 7 11vol which can be seen to be dehydration melting products of biotite under the microscope this group shows extremely varied ree distributions from lree enriched to depleted and from negative to strong positive eu eu 1 63 eu anomalies compared to groups a and b group c is severely depleted in na2o k2o lree rb and ba whereas tio2 co v sc and hree and y are considerably enriched this is accompanied by anomalous high sm nd 0 21 0 28 147sm 144nd 0 1361 0 1738 and 143nd 144nd 0 511589 0 511958 ratios tdm correlates clearly with sm nd ratio and 2 out of 3 samples give significantly older to unrealistic tdm 3 9 4 9 ga the results document redistribution of ree and an open behavior of the sm nd isotope system during the biotite dehydration melting of metasediments

long quaternary record in eastern washington u s a interpreted from multiple buried paleosols in loess loess that is from a few meters to 75 m thick covers an area of more than 20 000 km2 on the columbia plateau in washington idaho and oregon the region of deepest loess is in eastern washington and is called the palouse the palouse is downwind of the channeled scabland through which massive outburst floods from glacial lake missoula flowed repeatedly during glacial stages of the pleistocene the deepest stratigraphic section yet studied is in a remnant of the once continuous loess cover that is surrounded by scabland channels a normal over reverse magnetic polarity zonation in this section supports an age of more than 790 000 yr but 15 35 m of loess may be present beneath this section so a total of 1 5 2 million yr is possible upward fining of texture in some layers in the loess at this site and stratigraphic evidence at nearby sites suggest that at least some pulses of loess deposition were triggered by episodes of cataclysmic floods nineteen or more individual paleosols can be recognized in 26 m of section based on field morphology physical and chemical properties and micromorphology the paleosols consist of calcic petrocalcic and duripan horizons many of which are associated with cambic horizons less strongly developed soils in this and other sections have been obscured by partial overlap of soil development in an episodically rising loess landscape paleosols in the loess at other sites reflect a dry to moist climatic gradient from west to east across the region during the pleistocene that was grossly similar to today s accumulation of pedogenic carbonates and silica dominates in a western zone where the present day mean annual precipitation is less than about 450 mm translocation of silicate clays and leaching of carbonates dominate in a central steppe zone where precipitation is between 450 and about 700 mm fragipans are common in an eastern zone along the steppe forest transition at present day precipitation of over 700 mm reconnaissance study suggests that these climatic pedogenic zones have been somewhat stable during many of the episodes of soil development preserved in the loess although some paleosols have different features from the majority of the paleosols in that zone e g paleosols with fragipans in a sequence of paleosols with argillic horizons which suggests that some episodes of soil development took place under different climatic conditions