quantitative morphologic analysis of boulder shape and surface texture to infer environmental history a case study of rock breakdown at the ephrata fan channeled scabland washington boulder morphology reflects both lithology and climate and is dictated by the combined effects of erosion transport and weathering at present morphologic information at the boulder scale is underutilized as a recorder of environmental processes partly because of the lack of a systematic quantitative parameter set for reporting and comparing data sets we develop such a parameter set incorporating a range of measures of boulder form and surface texture we use standard shape metrics measured in the field and fractal and morphometric classification methods borrowed from landscape analysis and applied to laser scanned molds the parameter set was pilot tested on three populations of basalt boulders with distinct breakdown histories in the channeled scabland washington 1 basalt outcrop talus 2 flood transported boulders recently excavated from a quarry and 3 flood transported boulders extensively weathered in situ on the ephrata fan surface size and shape data were found to distinguish between flood transported and untransported boulders size and edge angles 120 of flood transported boulders suggest removal by preferential fracturing along preexisting columnar joints and curvature data indicate rounding relative to outcrop boulders surface textural data show that boulders which have been exposed at the surface are significantly rougher than those buried by fan sediments past signatures diagnostic of flood transport still persist on surface boulders despite ongoing overprinting by processes in the present breakdown environment through roughening and fracturing in situ further use of this quantitative boulder parameter set at other terrestrial and planetary sites will aid in cataloging and understanding morphologic signatures of environmental processes

stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

pedogenic carbonate carbon isotopic constraints on paleoprecipitation evolution of desert in the pacific northwest usa in response to topographic development of the cascade range abstract the cascade range in the northwestern u s acts as an orographic barrier to the easterly movement of humid air masses from the pacific ocean producing a massive rain shadow with arid to semi arid climate conditions on the leeward side of the range pedogenic carbonates formed in the c3 dominated landscapes east of the range have 13ccarbonate that is enriched by approximately 4 relative to carbonates formed in sub tropical c3 dominated ecosystems we measured stable isotopic compositions of pedogenic carbonates preserved in the quaternary and neogene sedimentary rock units in the inland pacific northwest and examined the impact of long term aridification and paleohydrology on their isotopic compositions the determined 13ccarbonate record shows a gradual increase of 5 from approximately 10 in older pedogenic carbonates to 5 in younger ones whereas 18ocarbonate record indicates a decrease of approximately 4 in the late neogene in addition the quaternary 13ccarbonate and 18ocarbonate records indicate the highest 13c and 18o among the samples during the pleistocene and significant fluctuation over the time period the gradual increase in the 13ccarbonate and the decrease in the 18ocarbonate in the late neogene are interpreted by the development of the rain shadow as a result of topographic development of the cascade range changes in the quaternary isotope records suggest a decrease in regional precipitation and isotopically depleted winter precipitation resulting from changes in large scale atmospheric circulation patterns due to advance and retreat of northern hemisphere continental ice sheet the isotope record from pedogenic carbonates provides a direct record of climatic change suggesting that long term carbon isotope data can provide useful constraints on timing and intensity of regional desertification and its associated climate and topographic interaction

glacial outburst floods and loess sedimentation documented during oxygen isotope stage 4 on the columbia plateau washington state abstract stratigraphy and age control of late pleistocene loess associated glacial outburst flood deposits and flood cut unconformities in the channeled scabland washington state united states indicate a significant cordilleran ice sheet advance during marine oxygen isotope stage 4 glacial outburst flood deposits from stage 2 classic bretz flood deposits ca 21 to 13 ka and related features in the channeled scabland overlie a widespread layer of loess that contains buried soils and the mount st helens set c tephra ca 46 ka this loess in turn overlies deposits of the penultimate episode of giant outburst floods and an unconformity cut by those floods regional trends in the thickness texture and overall composition of the older loess are strikingly similar to those from the youngest loess known to be derived from stage 2 flood deposits we conclude that the older loess also is derived from fine grained flood deposits luminescence ages tephrochronology and soil development rates indicate that the bulk of deposition of the older loess occurred during stage 3 following glacial outburst flooding marked by a regional flood cut unconformity the apparent cyclical pattern of cold climate buried soils flood deposits and thick loess accumulations demonstrate that sediment supply renewed by flood episodes is a major control on accumulation of loess on glacial timescales

sequential crystal overproduction triggering mg cr ti v p mree enrichment in a single pulse tholeiitic mafic sill in the central iberian zone spain abstract we study the causes of mg cr ti v p mree enrichment in a 134 m thick mafic sill emplaced in a single magma pulse whole rock chemistry indicates that tio2 up to 5 51 wt and p2o5 up to 1 60 wt enrichment occurred in a closed system immiscibility processes during magmatic crystallization and interaction with late fluids seem to have played little or no role for the ti p distribution liquid lines of descent for anhydrous and hydrous conditions reveal that the melt did not follow a fenner trend anhydrous which may lead to strong ti or p enrichment but a bowen trend hydrous during crystallization at low fo2 fmq 2 and low water contents 0 5 h2o the mg cr ti v p mree rich samples are cumulates and their composition is offset from the liquid line of descent due to postcumulus compaction and compositional convection theoretical formulation of compaction and compositional convection demonstrates that classical postcumulus scenarios of strong undercooling sill cr ti v or p mree rich cumulates the efficiency of postcumulus processes declines once the latent heat does not compensate heat loss to the country rock leading to cumulates with high intergranular liquid fractions and without cr ti and p enrichment high water contents in the upper level of the sill facilitate postcumulus processes and migration of residual liquids and fluids upwards leading to the formation of abundant pegmatoid pockets and the development of a sandwich horizon that does not follow the liquid line of descent

the eckler mountain basalts and associated flows columbia river basalt group recent mapping of flows of the columbia river basalt group between lewiston and pomeroy southeast washington places the chemically distinctive shumaker creek flow as a new member between the fren

post 12 m y rotation of southwest washington paleomagnetic field directions from the basalt of pack sack lookout are compared to those from the pomona member of the saddle mountains basalt of the columbia river basalt group the pomona crops out over a wide region on the columbia plateau east of the cascade range and the basalt of pack sack lookout crops out well to the west of the cascades about 30 to 60 km east of the washington coast our paleomagnetic results support existing geologic and geochemical evidence that both these units are part of a single 12 m y old flow that erupted in western idaho and flowed to the washington coast the magnetic data further indicate that southwest washington has undergone clockwise rotation with respect to the columbia plateau and stable north america the data suggest that both a large scale regional rotation of 16 and locally complex small scale rotations exist the two being present to different degrees in the eastern and western regions of southwest washington the cascade range appears to coincide with the tectonic boundary separating rotated and unrotated regions of washington state rotation of southwest washington appears to have been associated with the rotation of large pieces of western oregon and southern washington possibly as a result of either a ridge push force from the basin and range province or shear along the pacific north america plate boundary

miocene global change recorded in columbia river basalt hosted paleosols paleosols preserved between flows of the columbia river basalt province record hiatuses in basalt emplacement and provide detailed information about paleoclimatic and pedogenic conditions during pedogenesis the relatively long duration of pedogenesis 104 to 106 yr for these paleosols makes them unlikely to have been influenced by short duration climate fluctuations and allows them to accurately reflect long term climate trends related to global climate change ten paleosols hosted by the grande ronde and wanapum formations of the columbia river basalts were identified on the basis of pedogenic features such as horizon development root traces and saprolitization and they were studied as paleoclimatic indicators relationships between the ages of the paleosols and their clay mineral compositions suggest that pedogenic processes changed in the eastern columbia river basalt province at ca 15 8 ma analyses of mass balance trends and chemical alteration in a ca 16 0 ma paleosol indicate that it formed under warm humid climate conditions we suggest that the absence of similar warm humid paleosols and the presence of 2 1 clay rich paleosols that formed after ca 15 8 ma represent a cooling and drying climate change related to the termination of the middle miocene climate optimum a development not previously captured in paleosol studies in addition the well constrained dates of the basalts provide better resolution on the timing of this termination when combined with other middle miocene paleoclimate estimates from the columbia river basalt province our results suggest a geographic control on mean annual precipitation in the middle miocene columbia river basalt province leading to an increasing to the east precipitation gradient

sulfur release from the columbia river basalts and other flood lava eruptions constrained by a model of sulfide saturation abstract a very likely cause of widespread environmental impacts of flood basalt eruptions is the emission of sulfur chlorine and possibly fluorine from the erupting magma we present new data on the s contents of rare glass inclusions and matrix glasses preserved in quenched lava selvages from lava fields of the columbia river basalt group crbg ginkgo sand hollow and sentinel gap flows wanapum basalt formation we compare these results with published data from neral and jawar formation lavas deccan traps india and the roza flow crbg crbg glass inclusions have up to 2000 ppm s and 15 16 wt feototal by contrast the deccan examples have about 1400 ppm s and 10 wt feototal several of the glass inclusions are partly degassed indicating entrapment during magma rise and matrix glasses are typically more evolved than glass inclusions due to small amounts of in situ crystallization using only the highest s inclusions and taking account of the effect of in situ crystallization and degassing on the s content of the residual matrix glasses indicates s yields of about 0 07 to 0 1 wt from deccan eruptions and about 0 15 wt from wanapum crbg eruptions the pre eruptive s contents of these magmas correlate with weight feototal in the same way as undegassed sulfide saturated mid ocean ridge basalts using oceanic basalts to define a sulfide saturation line and data on s contents of degassed basalts we propose an equation to estimate the weight s yield s from initially sulfide saturated basalt liquid without the need to find well preserved rare undegassed glass inclusions and matrix glasses s 0 0 1418 feo total 0 0 6381 0 0 2635 this compares well with independent estimates derived from the petrologic method by taking the difference in s concentration of glass inclusions and matrix glass applying our method to the aphyric grande ronde basalts of the crbg implies a total yield of about 1000 gt so2 delivered into the miocene atmosphere in intermittent bursts of

deformation of the southeast part of the columbia plateau four structural elements north of the olympic wallowa lineament in the southeast part of the columbia plateau washington idaho and oregon are 1 the offlap of progressively younger basalt units from pre basalt topographic highs 2 east west open folds associated with reverse faulting 3 northwest southeast northeast southwest and north south faults with predominantly vertical displacement and 4 vertical north northwest south southeast feeder dikes these may be explained by 1 a regional east to west tilting of the plateau caused by the isostatic rise of older rocks on the eastern margin 2 a stress regime with a horizontal maximum principal stress in a north northwest south southeast direction and a horizontal minimum principal stress in a west southwest east northeast direction and 3 reactivation of an older northwest southeast northeast southwest and north south structural grain in the pre miocene basement the stress regime is similar to that envisaged for the area southwest of the olympic wallowa lineament and the difference in the type of deformation on either side of that feature may be attributed to differences in the thickness of the crust across the ancient boundary

ages of the steens and columbia river flood basalts and their relationship to extension related calc alkalic volcanism in eastern oregon stratigraphic and chemical correlations of tertiary volcanic units in eastern oregon confirm that the steens basalt represents the earliest eruptions of the columbia river flood basalt province field correlations are supported by major and trace element analyses and confirmed by 4 0 ar 3 9 ar dates within the basalt of malheur gorge situated between steens mountain and the southernmost extent of the previously mapped columbia river basalt group the lowest unit correlates with the steens basalt and the conformably overlying middle and upper units correlate with the imnaha and grande ronde basalt formations of the columbia river basalt group new dates indicate that imnaha and grande ronde basalt formations on the columbia plateau 90 of the columbia river basalt group erupted between 16 1 and 15 0 ma these were immediately preceded by the steens basalt a plagioclase phyric tholeiite that erupted above the calculated position of the yellowstone hotspot at 16 6 ma in eastern oregon the flood basalt tholeiites of steens mountain and malheur gorge form a voluminous but brief interlude 16 6 15 3 ma superimposed on the low volume calc alkalic to mildly alkalic volcanism associated with continuing eocene to present east west extension

a lava flow without a source the cohassett flow and its compositional components sentinel bluffs member columbia river basalt group abstract the eruption of sentinel bluffs member lava flows at approximately 15 5 ma marked the end of grande ronde basalt volcanism the most voluminous period of the columbia river basalt group more than 10 000 km3 of lava erupted from northerly trending feeder dikes in eastern washington and northern oregon and flowed westward down an ancestral paleoslope covering more than 169 700 km2 of the flood basalt province the sentinel bluffs member consists of six phases or types defined by their compositions lava flows having the first compositional type were the most voluminous and reached the pacific ocean the volume of later lava flows having the other compositional types declined with time until the final eruption produced the second largest volume of basalt at the source area compositional variation in sentinel bluffs lava flows is relatively small this homogeneity allows the individual compositional types and thus phases of the eruption to be easily recognized farther west however composition

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

lithostratigraphy and volcanology of the serra geral group parana etendeka igneous province in southern brazil towards a formal stratigraphical framework abstract the volcanic rocks of the lower cretaceous parana etendeka igneous province in brazil are grouped in the serra geral group the province can be chemically divided into low tio 2 and high tio 2 in southern brazil the low tio 2 lava pile reaches a thickness of 1 km and is formed of heterogeneous lava packages here divided into four lava formations torres formation tf is characterized by chemically more primitive basaltic 5 wt mgo compound pahoehoe flow fields these lavas stratigraphically overly aeolian sandstones of botucatu formation and represent the onset of the volcanic activity vale do sol formation vsf groups vertically stacked sheet like rubbly pahoehoe basaltic andesites sio 2 51 wt mgo 2 lava sequence sedimentary interbeds are preserved throughout the whole lava pile and were deposited during quiescence periods of volcanic activity and represent important stratigraphic markers e g tf vsf contact the newly proposed stratigraphy provides promptly recognized stratigraphic units in a regional framework of fundamental importance for future correlations and provide vital information in the understanding of how the parana etendeka igneous province evolved through time

distribution and geochronology of oregon plateau u s a flood basalt volcanism the steens basalt revisited the timing and petrogenesis of mid miocene flood basalt volcanism in the northwest united states has been extensively addressed yet the chemical characteristics and temporal details of the steens basalt exposed on the oregon plateau are poorly defined steens basalt volcanism has generally been accepted to have occurred at 16 6 ma coeval and or just prior to the onset of columbia river basalt group volcanism to the north new major and trace element analyses and nine 40 ar 39 ar ages ranging from 15 51 0 28 to 16 58 0 18 ma were obtained on oregon plateau flood basalt lava flows from stratigraphic sections in close proximity to steens mountain additionally new 40 ar 39 ar ages were obtained on the uppermost and thirty first lava flow down from the top of the 1 km section of steens basalt exposed at steens mountain and yield eruption ages of 16 59 0 10 and 16 55 0 10 ma respectively field relations between these basalt sections suggest that multiple eruptive centers were present in the vicinity of steens mountain the chemical and chronologic data presented in this study illustrate that flood basalts with the steens basalt chemical signature erupted across the southern oregon plateau over a much greater timespan than what is typically quoted for the steens mountain type section these data suggest that the main volume of steens basalt volcanism erupted over at least an 1 m y duration from eruptive loci in the vicinity of steens mountain while likely much less voluminous volcanism and lithospheric input of mafic magma appears to have occurred for n2 ma across the oregon plateau these new geochemical and geochronological constraints verify a common temporal link between steens malheur gorge region and columbia river basalt group crbg volcanism this direct temporal link requires that petrogenetic and tectonic models of mid miocene northwestern u s flood basalt volcanism recognize that the northern columbia plateau and southern oregon plateau portions of this mid miocene basalt province were erupting simultaneously during portions of the regional event 2007 elsevier b v all rights reserved

intracanyon flows in the deccan province india case history of the rajahmundry traps the rajahmundry traps form small exposures of basaltic flows on either side of the godavari river near the east coast of india and they are thought to be late cretaceous early paleocene in age because they lie 400 km from the nearest surface exposures of the deccan traps their mode of formation remains unknown furthermore the rajahmundry traps show normal magnetic polarity indicating that they cannot be exact time equivalents of the large volumes of the deccan traps which show reversed magnetic polarity geochemical analyses reveal that the rajahmundry traps are of very uniform composition geochronological studies suggest an age of 64 ma marginally younger than the main sections western ghats of the deccan traps the only section of the main deccan province that may be stratigraphically equivalent on the basis of age geochemical signatures and magnetic polarity is the kolhapur formation at the southern end of the deccan province near the west coast 800 km from the rajahmundry traps we suggest that the rajahmundry traps and other basaltic material found near the mouth of the godavari river represent remnants of intracanyon flows that flowed eastward down the ancestral river systems of peninsular india away from the domed structure caused by the plume that led to the formation of the deccan traps similar intracanyon flows that have traveled 600 km from their source to the pacific coastline are well documented in association with the columbia river basalt province united states in the case of the rajahmundry traps the distance traveled would appear to be 1000 km

compositional and kinetic controls on liquid immiscibility in ferrobasalt rhyolite volcanic and plutonic series we present major element compositions of basalts and their differentiation products for some major tholeiitic series the dry low pressure liquid lines of descent are shown to approach or intersect the experimentally defined compositional space of silicate liquid immiscibility ferrobasalt rhyolite unmixing along tholeiitic trends in both volcanic and plutonic environments is supported by worldwide occurrence of immiscible globules in the mesostasis of erupted basalts unmixed melt inclusions in cumulus phases of major layered intrusions such as skaergaard and sept iles and oxide rich ferrogabbros closely associated with plagiogranites in the lower oceanic crust liquid immiscibility is promoted by low pressure anhydrous fractional crystallization that drives the low al2o3 high feo liquids into the two liquid field kinetic controls can be important in the development of two liquid separation the undercooling that occurs at the slow cooling rates of plutonic environments promotes early development of liquid immiscibility at higher temperature in contrast rapid cooling in erupted lavas leads to large undercoolings and liquid immiscibility develops at significantly lower temperatures unmixing leads to the development of a compositional gap characterized by the absence of intermediate compositions a feature of many tholeiitic provinces the compositions of experimental unmixed silica rich melts coincide with those of natural rhyolites and plagiogranites with high feotot and low al2o3 suggesting the potential role of large scale separation of immiscible si rich liquid in the petrogenesis of late stage residual melts no trace of the paired ferrobasaltic melt is found in volcanic environments because of its uneruptable characteristics instead fe ti p rich gabbros are the cumulate products of immiscible fe rich melts in plutonic settings the immiscibility process may be difficult to identify because both melts crystallize the same phases with the same compositions the two liquids might form incompletely segregated emulsions so that both liquids continue to exchange as they crystallize and remain in equilibrium even if segregated both melts evolve on the binodal surface and exsolve continuously with decreasing temperature the two liquids do not differentiate independently and keep crystallizing the same phases with differentiation further evolution by fractional crystallization potentially drives the bulk liquid out of the twoliquid field so that very late stage liquids could evolve into the single melt phase stability field

genesis of flood basalts from eclogite bearing mantle plumes on the basis of the geochemistry of flood basalts we investigate the hypothesis that the source material for these magmas includes a significant eclogite component derived from ancient subducted oceanic crust entrained into mantle plumes at the core mantle boundary we present finite element models of the melting in starting plumes plume heads in both continental and oceanic regions starting plume models in which the plume heads are composed solely of pyrolite mantle are incapable of generating sufficient volumes of melt or any melt at all for reasonable plume head temperatures 1400 1600 c or lithosphere ages 6 25 100 m y this result is in contrast to the results of farnetani and richards 1994 whose models require higher plume head temperatures 1600 1700 c and a weak mobile lithosphere in order to generate volumes of melt similar to flood basalts plumes composed of 15 wt eclogite yield volumes of melt comparable to flood basalts in both oceanic and continental settings the maximum extent of melting in these models is about 10 30 this agrees with the model of hofmann and white 1982 who argued that ocean island basalts are derived from subducted oceanic crust if the embedded eclogite thermally reequilibrates with the surrounding plume material then melt volumes and total extents of melting increase by a additional factor of 2 3 a simple two dimensional rifting model for a slow spreading ocean basin underlain by a lens of hot plume material shows that plume related melting occurs over 50 60 m y a much longer period than for flood basalts

secular variation of the middle and late miocene geomagnetic field recorded by the columbia river basalt group in oregon idaho and washington usa

influence of paleorelief on the mid miocene climate variation in southeastern washington northeastern oregon and western idaho usa abstract terrestrial climate proxy records repeatedly show spatial heterogeneity because regional climate condition is largely influenced by the relationship between large scale atmospheric circulation patterns and regional topographic features the paleosols developed on the top of columbia river basalt flows emplaced between 15 3 and 15 8 ma in the northwestern united states show significant spatial variations in the mid miocene soil forming processes the paleosol in the northwestern part of the study area has the least degree of chemical weathering fine scale and very shallow penetrating depth of root traces with the estimated paleoprecipitation and paleotemperature of about 550 mm and 16 c respectively the paleosols in the southeastern part of the study area indicate more intense chemical weathering with the estimated paleoprecipitation and paleotemperature of approximately 1400 to 1500 mm and 17 c respectively the spatial variations in paleo pedogenesis were predominantly affected by spatial heterogeneity in the mid miocene regional climate and regional paleotopographic features taking the other ancient soil forming factors including time parent rock materials and biological activities into account we suggest that intrusions of hot columbia river basalt magma into the crust were responsible for the regional surface uplift and the paleoclimate heterogeneity because the major vent systems of the columbia river basalt eruptions were located in the area where development of the mid miocene high topography existed within the blue mountains paleotopography of the earth s surface can be reconstructed by the paleoprecipitation and paleotemperature estimations from several spatially distributed chrono stratigraphic paleosols although it is difficult to estimate the magnitude of the paleorelief precisely

cosmogenic 3he production rate in ilmenite and the redistribution of spallation 3he in fine grained minerals cosmogenic nuclide surface exposure dating and erosion rate measurements in basaltic landscapes rely primarily on measurement of 3he in olivine or pyroxene however geochemical investigations using 3he have been impossible in the substantial fraction of basalts that lack separable olivine or pyroxene crystals or where such crystals were present but have been chemically weathered fine textured basalts often contain small grains of ilmenite a weathering resistant mineral that is a target for cosmogenic 3he production with good he retention and straightforward mineral separation but with a poorly constrained production rate here we empirically calibrate the cosmogenic 3he production rate in ilmenite by measuring 3he concentrations in basalts with fine grained 20 m cross section ilmenite and co existing pyroxene or olivine from the columbia river and snake river plain basalt provinces in the western united states the concentration ratio of ilmenite to pyroxene and olivine is 0 78 0 02 yielding an apparent cosmogenic 3he production rate of 93 6 7 7 atom g 1 yr 1 that is 20 30 greater than expected from prior theoretical and empirical estimates for compositionally similar minerals the production rate discrepancy arises from the high energy with which cosmic ray spallation reactions emit tritium and 3he and the associated long stopping distances that cause them to redistribute within a rock fine grained phases with low cosmogenic 3he production rates like ilmenite will have anomalously high production rates owing to net implantation of 3he from the surrounding higher 3he production rate matrix semi quantitative modeling indicates implantation of spallation 3he increases with decreasing ilmenite grain size leading to production rates that exceed those in a large grain by 10 when grain radii are 150 m the modeling predicts that for the ilmenite grain size in our samples implantation causes production rates to be 20 greater than expected for a large grain and within uncertainty resolves the discrepancy between our calibrated production rate theory and rates from previous work the redistribution effect is maximized when the host rock and crystals differ substantially in mean atomic number as they do between whole rock basalt and ilmenite

geochemistry of flood basalts of the toranmal section northern deccan traps india implications for regional deccan stratigraphy unpublished data 1998 andthe southeastern deccan particularly the poladpur andambenali formations mitchell widdowson 1991 bilgrami 1999 for as much as 350 km from their south western type sections in addition lavas isotopically andchemicallyequivalenttothoseoftheambenaliformation fm arepresentinthenortheastern sectoroftheprovinceas far as 900 km from their southwesternmost counter parts mahoney 1988 deshmukh

modeling magma flow and cooling in dikes implications for emplacement of columbia river flood basalts 1 the columbia river flood basalts include some of the world s largest individual lava flows most of which were fed by the chief joseph dike swarm the majority of dikes are chilled against their wall rock however rare dikes caused their wall rock to undergo partial melting these partial melt zones record the thermal history of magma flow and cooling in the dike and consequently the emplacement history of the flow it fed here we examine two dimensional thermal models of basalt injection flow and cooling in a 10 m thick dike constrained by the field example of the maxwell lake dike a likely feeder to the large volume wapshilla ridge unit of the grande ronde basalt two types of models were developed static conduction simulations and advective transport simulations static conduction simulation results confirm that instantaneous injection and stagnation of a single dike did not produce wall rock melt repeated injection generated wall rock melt zones comparable to those observed yet the regular texture across the dike and its wall rock is inconsistent with repeated brittle injection instead advective flow in the dike for 3 4 years best reproduced the field example using this result we estimate that maximum eruption rates for wapshilla ridge flows ranged from 3 to 5 km3 d 1 local eruption rates were likely lower minimum 0 1 0 8 km3 d 1 as advective modeling results suggest that other fissure segments as yet unidentified fed the same flow consequently the maxwell lake dike probably represents an upper crustal 2 km exposure of a long lived point source within the columbia river flood basalts

lava sediment interaction and drainage system development in a large igneous province columbia river flood basalt province washington state u s a abstract large igneous provinces lips have been implicated in some of the largest environmental perturbations to have affected the earth through geological time yet the impact of lip development on drainage and ecosystem development in the immediate vicinity of these provinces are still poorly constrained to date based on a detailed integrative facies scheme we characterize the interaction between volcanism and fluvial lacustrine and wetland environments in the miocene columbia river flood basalt province crbp lip exposed in central washington state usa the facies scheme proposed here comprises a detailed description and interpretation of siliciclastic bioclastic diatomite volcaniclastic and paleosol facies and subfacies intercalated with lavas of the columbia river basalt group crbg facies and facies associations of individual interbeds are further correlated to reconstruct changes in sedimentary settings and topography of lava fields during deposition field observations and facies analysis help to explain the effects of flood basalt volcanism on drainage system development we propose a generic model of lava drainage interplay and distribution of sedimentary settings in flood basalt provinces which will contribute to our understanding of sedimentological environmental and volcanic processes in the crbp hydrocarbon exploration in volcanic terrains requires detailed information on the distribution and development of sedimentary settings this model will help to better predict the character and distribution of sedimentary bodies and potential hydrocarbon reservoirs in volcanic terrains

stratigraphy and petrogenesis of the grande ronde basalt from the deep canyon country of washington oregon and idaho deep canyons cut by the snake salmon grande ronde and imnaha rivers near the point where washington oregon and idaho join expose 800 m of grande ronde basalt flows the grande ronde basalt erupted 16 5 to 14 5 m y b p makes up 85 vol of the columbia river basalt group an area enclosing 1 000 km 2 of the deep canyon country dominated by this basalt was mapped and samples from 16 measured sections in the grande ronde basalt were analyzed for major minor and trace elements three magnetostratigraphic units r 1 n 1 and r 2 were helpful in mapping the area using physically distinct flows the magnetostratigraphic units and certain chemical variations a detailed flow by flow stratigraphy was developed and the lateral extent of many individual flows was traced the number of flows and thickness of each stratigraphic unit decrease from west to east these tholeiitic flows are fine grained and aphyric clinopyroxene and plagioclase are the predominant minerals but olivine orthopyroxene pigeonite and accessory minerals are minor but important phases the flows are primarily of the low mg chemical type with lesser amounts of the high mg chemical type a cyclical trend in the over all major and trace element chemistry through the stratigraphic section is dominated by a ca rich clinopyroxene chemistry rare earth elements show significant light over heavy enrichment but overall patterns remain similar from flow to flow a small negative eu anomaly is present in many flows three models employing fractional crystallization schemes and one combining fractional crystallization and partial melting were tested using least squares modeling a petrogenetic model is proposed wherein partial melting of a heterogeneous clinopyroxene dominated mantle supplied magma that ascended to the crust was temporarily stored and recurrently erupted during storage new basaltic melt with slightly different isotopic and trace element abundances was added and mixed into the liquid that remained after previous eruptions orthopyroxene plagioclase and to a lesser extent olivine fractionated from these temporarily stored liquids upon eruption clinopyroxene and plagioclase with accessory minerals crystallized at the surface

phase relations and liquid lines of descent in hydrous ferrobasalt implications for the skaergaard intrusion and columbia river flood basalts crystallization experiments using a hydrous ferrobasalt as starting material conducted at 200mpa 940 12008c at a wide range of water activities 0 1 1 and redox conditions qfm 3 to qfm 4 where qfm is the quartz fayalite magnetite oxygen buffer show that h2o influences significantly the differentiation history of ferrobasaltic magmas a combination of our data with published experiments on dry ferrobasalt at 1atm provides an extensive experimental database for modeling and quantifying crystallization and differentiation processes within a typical fe rich tholeiitic system under both dry and hydrous conditions the addition of h2o decreases liquidus temperatures and changes significantly the proportions temperature range and sequence of crystallizing mineral phases the dry liquidus is at about 11708c whereas the liquidus for h2o saturated melts is at 10608c the main phases crystallizing from h2o bearing ferrobasalt at the investigated conditions are olivine ol clinopyroxene cpx plagioclase pl magnetite mt hematite hm ilmenite ilm and amphibole am the phase assemblage is similar to that of the dry system except for the presence of hm at extremely oxidizing conditions and am at low temperatures 59508c and h2o saturated conditions the important observation made in this study is that the stability of fe ti oxides and in particular mt as well as the simultaneous coprecipitation of mtand ilm are almost independent of the activity of h2o ah2o in the system whereas the liquidus temperatures of the silicate minerals are dramatically depressed by increasing ah2o the stabilities of oxides are controlled mainly by the redox conditions prevailing in the system the most pronounced effect of ah2o on the liquidus temperatures of silicates is observed for pl which shows a considerable delay in crystallization with progressive magma differentiation early crystallization of fe ti oxides in h2o bearing ferrobasaltic compositions precludes any significant fe enrichment during differentiation as fe enrichment is a characteristic feature of the skaergaard intrusion it implies that the skaergaard parental magma did not contain considerable amounts of water on the other hand our experiments indicate that the differentiation of some ferrobasaltic series from the columbia river flood basalt province might have occurred in magmatic systems containing significant amounts of volatiles 0 5 3 wt h2o

physical and chemical constraints on the evolution of the columbia river basalt physical and chemical constraints require that columbia river basalt flows were fed from a large 700 km 3 magma reservoir near the crust mantle boundary and prohibit significant crystal fractionation or crustal assimilation between reservoir and surface demonstrable fractionation of plagioclase olivine pyroxene in the reservoir largely obviates the need for an unusual iron rich pyroxenite source variation of sr and nd isotope ratios with age in the main series of columbia river basalt and variation in such incompatible trace element ratios as ba p suggest lower crustal assimilation at the top of the reservoir combined with crystal fractionation however decoupling between isotope ratios and incompatible element ratios implies two separate processes in addition to crystal fractionation of which lower crustal assimilation may be one the other process may involve the participation of a vertically heterogeneous mantle resulting from metasomatism in the continental lithosphere

lava fingerprinting using paleomagnetism and innovative x ray fluorescence spectroscopy a case study from the coso volcanic field california 1 we demonstrate an efficient method of rigorously separating difficult to distinguish lavas into eruptive units based on paleomagnetic remanence direction and rapid x ray fluorescence spectroscopy xrf for rb sr y zr and nb of polished paleomagnetic core samples called pc xrf combined use of paleomagnetic remanence and pc xrf for lava fingerprinting allows correlation of individual eruptive units from one locality to another permitting compilation of composite stratigraphy and paleomagentic measurement of relative vertical axis rotation of fault bounded blocks we test this lava fingerprinting method on rocks from the coso volcanic field california against similar fingerprinting using xrf analysis by established methods resulting unit definitions and correlations are the same by both xrf techniques when coupled with paleomagnetic data but at great time and cost savings with pc xrf pc xrf analysis is possible because 1 matrix and grain size effects are minimal for the element set analyzed 2 moderately phyric to aphyric polished paleomagnetic cores are already homogenous on spatial scales of 2 cm and 3 use of element ratios cancels out some analytical uncertainties as well as minimizes effects of concentration variations due to fractional crystallization paleomagnetic remanence direction is an indispensable part of fingerprinting because it distinguishes flows of similar chemistry and can also place constraints on the duration of emplacement of each eruptive unit

uplift rupture and rollback of the farallon slab reflected in volcanic perturbations along the yellowstone adakite hot spot track field geochemical and geochronological data show that the southern segment of the ancestral cascades arc advanced into the oregon back arc region from 30 to 20 ma we attribute this event to thermal uplift of the farallon slab by the yellowstone mantle plume with heat diffusion decompression and the release of volatiles promoting high k calc alkaline volcanism throughout the back arc region the greatest degree of heating is expressed at the surface by a broad ene trending zone of adakites and related rocks generated by melting of oceanic crust from the farallon slab a hiatus in eruptive activity began at ca 22 20 ma but ended abruptly at 16 7 ma with renewed volcanism from slab rupture occurring in two separate regions the eastern rupture resulted in the extrusion of steens basalt during the ascent and melting of a dry mantle plume source contaminated with depleted mantle the contemporaneous western rupture resulted in renewed subduction melting of a wet mantle source and the rejuvenation of high k calc alkaline volcanism near the nevada california border at 16 7 ma here the initiation of slab rollback is evident in the westward migration of arc volcanism at 7 8 km ma today the uplifted slab is largely missing beneath the oregon back arc region replaced instead by a seismic hole which is bound on the south by the adakite hotspot track we attribute slab destruction to thermal uplift and mechanical dislocation that culminated in rapid tearing of the slab from 17 15 ma and possible foundering and sinking of slab segments from 16 10 ma

seven ambiguities in the mediterranean palaeoenvironmental narrative abstract a review of seven outstanding issues on mediterranean palaeoenvironments is presented these are related to the dominant orbital pacing of climate variability the length of the interglacial vegetation succession the influence of the african summer monsoon the seasonality of precipitation during boreal insolation maxima the moisture balance during glacial maxima and the appearance of the mediterranean type climate rhythm and evolution of mediterranean sclerophyllous plants what emerges is that 1 marine 18oplanktonic and sst records show that precession has been a fundamental tempo of mediterranean climate change representing both a low latitude signal runoff from north africa and the direct influence of insolation at mediterranean latitudes but high latitude glacial effects 41 kyr and 100 kyr cycles became superimposed after 2 8 ma sapropel and dust deposition patterns in marine cores reveal that obliquity also has an effect on mediterranean climate through dry wet oscillations which are independent of glacial interglacial variability 2 the temperate part of interglacial vegetation succession has a duration of approximately half a precession cycle this persisted during the interval of obliquity dominated glacial cycles 2 8 1 ma with distinct forest successions following the precessional cycles however these are not always separated by an open vegetation phase because of minimal ice growth producing an impression of a prolonged interglacial forest interval 3 the effect of an enhanced african monsoon during summer insolation maxima has been mainly indirect in terms of nile discharge and runoff along the north african coast leading to increased freshwater input into the mediterranean sea reduced deep water ventilation and sapropel deposition 4 the notion of an accentuated summer rain regime in the northern mediterranean borderlands also contributing to a freshening of the mediterranean sea during boreal insolation maxima is not supported by the available evidence which suggests increased summer aridity 5 recent improvements in chronological precision and data resolution point to an increase in aridity and decreased temperatures during the last glacial maximum 21 2 ka but suggest an increase in effective moisture during the immediately preceding interval of 24 27 ka 6 the mediterranean type climate is not exclusively a post 3 6 ma phenomenon but may have appeared intermittently during the course of the tertiary or before 7 if that is the case then the paradigm that the sclerophyllous evergreen habit represents a pre adaptation to summer drought may need re evaluation

regional correlation of grande ronde basalt flows columbia river basalt group washington oregon and idaho the tholeiitic flood basalts of the columbia river basalt group of middle and late miocene age cover more than 200 000 km2 in washington oregon and idaho the most voluminous formation of the group the grande ronde basalt erupted for 2 m y from north northwest trending fissure systems concentrated in southeast washington and adjacent oregon and idaho four magnetostratigraphic units designated r1 n1 r2 and n2 from oldest to youngest are recognized on the basis of polarity in the grande ronde and provide the broad stratigraphic framework for the formation in this study major element chemistry and relative stratigraphic position within the polarity intervals are used to identify and correlate individual flows and sequences of flows within the grande ronde basalt on a regional scale systematic examination of more than 350 analyses from 47 stratigraphic sections show that most flows fall into one of five major chemical groupings which are distinguished primarily by small but significant variations in mgo tio2 and p2o5 content in addition four minor chemical types local to the eastern part of the province have been identified feeder dikes of each chemical type have also been located flows or packets of flows of each chemical type can be correlated between field sections to define specific chemical stratigraphic subunits these subunits consist of several flows collectively 30 150 m thick subunits of most chemical types are repeated at irregular intervals throughout the formation no progressive chemical trend occurs within the grande ronde many of the chemical stratigraphic subunits extend to the margins of the province although most are confined to the source region in eastern washington although the total number of subunits is less in the west away from the fissure systems the total thicknesses of the n2 and r2 magnetostratigraphic units are each as thick or thicker than the corresponding units in eastern washington the greatest thicknesses occur in the central part of the province within the pasco basin the distribution of basalt relative to the location of vents as well as the relative east west thicknesses suggests that basalt flowed hundreds of kilometres westward during the most voluminous grande ronde eruptions ponding against the irregular margin of the cascade range and being diverted through the ancestral columbia gorge toward the washington oregon coast between these huge sheetflood events smaller eruptions blanketed areas within the source region and ongoing regional subsidence created a shallow westward draining basin in the center of the province

chemical discrimination of columbia river basalt flows 1 the homogeneity and distinctive chemical composition of individual columbia river basalt flows are illustrated in a series of chemical plots and the procedure for flow identification is outlined the unique characterization of many individual eruptions permits units to be mapped from feeder dike to flow margins across the columbia plateau for hundreds of kilometers and so provides critical constraints on the physical and chemical evolution of this continental flood basalt province

the saddle mountains the evolution of an anticline in the yakima fold belt the saddle mountains uplift is an asymmetrical north vergent anticline with a length of about 110 km it varies from an open to tight fold and is divided into six segments based upon differences in geometry flows of the columbia river basalt group intercalated sedimentary deposits of the ellensburg formation and suprabasalt sediments thin over the uplift and thicken into the synclines variations in thickness are used to determine the timing of deformation and age of major and minor structures the close correlation of growth rate of the folds with rate of magma supply of the columbia river basalt group suggests that the yakima fold belt resulted from the same tectonic processes that produced eruption of the columbia river basalt modified journal abstract

basalts of the northeastern deccan traps india isotopic and elemental geochemistry and relation to southwestern deccan stratigraphy the northeastern deccan traps include flows with strong isotopic and elemental affinities to lavas in the southwest as far as 900 km away however many of the northeastern flows show a negative correlation of 206pb 204pb with end t and positive correlation of 206pb 204pb with 87sr 86sr t distinct from any of the isotopic fields for the southwestern formations this array from end t 5 87sr 86sr t 0 7041 206pb 204pb 17 9 to end t 0 87sr 86sr 0 7068 206pb 204pb 20 5 overlaps the ambenali formation fm field and runs toward that of the common signature peng et al 1994 that appears to have been an important magma type in several of the lower formations of the southwest this array appears to represent mixing between an ambenali type and 1 a common signature end member or 2 an end member with even higher 206pb 204pb and 87sr 86sr and lower end than the common signature such mixing has been postulated but not documented previously for the deccan lavas isotopically and chemically indistinguishable from the ambenali fm form the tops of sections near jabalpur and chikaldara beneath them are flows that chemically resemble the poladpur fm which sits immediately below the ambenali in the southwest and several lavas similar to the khandala fm beneath the poladpur and intervening bushe fm in the southwest given the general stratigraphic correspondence with the southwestern sequence many of these northeastern flows may be petrogenetically related to the respective southwestern formations lavas with broadly poladpurand khandala like elemental compositions are also abundant in a thick section south of mhow several other mhow area flows resemble the distinctive bushe fm however nearly all of the poladpur and khandala like northeastern deccan lavas analyzed have higher 206pb 204pb man any southwestern poladpur or khandala fm basalts if they indeed are related petrogenetically to these formations many of the northeastern magmas interacted less with low 206pb 204pb continental material and thus must have erupted from different feeder systems