hydrologic connectivity of oxbow lakes along the lower guadalupe river texas the influence of geomorphic and climatic controls on the flood pulse concept summary hydrologic connectivity between rivers and floodplains is fundamental to the ecological integrity of meandering river corridors this study integrates two important concepts in floodplain hydrology the flood pulse concept and the oxbow lake cycle high temporal resolution 0 5 3 0 h lake level data from vented pressure transducers and river discharge data 0 25 h resolution were utilized to develop standardized indices of hydrologic connectivity for two oxbow lakes along the lower guadalupe river texas over a 3 4 yr period the lakes were influenced by hydrologic conditions representative of the northwestern gulf region notably a severe drought and a wet season associated with la nina and el nino respectively because the data were obtained over the same period it enables a direct comparison of surficial hydrologic connectivity within the evolutionary geomorphic framework of the oxbow lake cycle a recently 13 yr old formed oxbow lake was connected 5 9 times per yr and an older partially infilled oxbow lake was connected 3 8 times per yr during the study period each oxbow lake was connected by discharge pulses below bankfull discharge and the signature of hydrologic connectivity varied significantly the flow duration for connectivity was 18 and 3 for the recently formed and older oxbow lake respectively bivariate relations between discharge and lake stage varied significantly for the two oxbow lakes the recently formed oxbow lake exhibited highly linear relations between discharge and lake levels and lake drainage closely mirrored flood wave recession older oxbow lake connectivity was complex as discharge and lake level relations were nonlinear and exhibited pronounced negative hysteresis which increased with sequential flood pulses while the older oxbow lake was more sensitive to short term low flow conditions both lakes were completely desiccated during an extended la nina influenced drought this indicates a substantial impact to alluvial aquifers which were unable to supply groundwater to oxbow lakes during extended dry periods the flood pulse concept applied with only river discharge data is overly simplistic and does not adequately characterize hydrologic connectivity for distinct types of oxbow lakes along meandering river floodplains with limited lake level data however great potential exists for development of effective integrated floodplain management plans that more appropriately considers variable hydrologic connectivity inherent within the oxbow lake cycle

triassic bedded cherts in central japan are not pelagic although the origin of bedded radiolarian cherts in orogenic belts has been widely debated1 15 their geochemistry is still poorly understood triassic bedded radiolarian cherts occur extensively in the japanese islands and are generally not associated with ophiolitic rocks but rather with clastic rocks we present here chemical data on the triassic bedded cherts of kamiaso in central japan the relationship of sio2 with al2o3 tio2 and zr shows that the bedded cherts have been formed by a simple mixing of biogenic silica derived from radiolarians and sponge spicules with lithogenic materials the ratios of several elements relative to tio2 strongly suggest that the shale partings and lithogenic portions of the cherts are consanguineous sedimentary structures as well as the geochemical evidence suggest that most kamiaso cherts are turbidity current deposits our geochemical and geological data compared with those of recent marine sediments from various environments demonstrate that the triassic cherts and associated shale partings are not deep pelagic in origin but formed in an offshore or marginal sea environment

effect of quartz inclusions on plastic flow in marble to investigate the effect of variations in volume fraction of a second phase on the strength and microstructure of rocks we produced synthetic marbles with a grainsize of 5 25 m containing quartz of similar size with volume fractions of 0 5 1 and 20 4 vol and between 3 to 9 porosity these rocks were deformed in triaxial compression at a strain rate of 3 x 10 5 s 1 confining pressure of 200 mpa and 600 c marbles containing 20 4 vol quartz were almost 5 times stronger than those containing no quartz the work hardening rate at given strain increased with quartz content marbles containing 20 4 vol quartz work hardened up to 10 strain whereas in single phase samples work hardening was negligible beyond 3 strain the dislocation density in the calcite increased with increasing quartz content the data are consistent with models for the strength of ceramic matrix composites or with the hypothesis that strength is increased by decreasing porosity

distribution and transport of hydrocarbons in surface sediments of the alaskan outer continental shelf abstract surface sediments from the outer continental shelf of alaska were analyzed for hydrocarbons as part of an environmental survey sponsored by noaa blm sediments were collected from the proposed oil lease areas of beaufort sea southeastern bering sea norton sound navarin basin gulf of alaska kodiak shelf and lower cook inlet data on normal and branched alkanes and di and triterpenoids from capillary gas chromatography gc and gas chromatography mass spectrometry gc ms indicate that the area displays little evidence of petroleum hydrocarbons i e seeps except at a few isolated stations beaufort sea sediments have the highest hydrocarbon budget whereas kodiak shelf sediments have the lowest the molecular markers of the hydrocarbons are of a mixed marine autochthonous and terrestrial allochthonous origin norton sound and cook inlet sediments contain the highest levels of terrigenous lipids and kodiak shelf the lowest the abundance of alkenes implies that relatively low oxidizing conditions exist in some of the depositional areas studied suggesting that extraneous petroleum hydrocarbons introduced into these sediments would be expected to have a relatively long residence time the distribution of polynuclear aromatic hydrocarbons pah is complex and shows a pyrolytic origin the data on perylene strongly favor the hypothesis that it is performed from terrigenous precursors and transported into the marine environment with no apparent in situ generation polynuclear aromatic hydrocarbons of diagenetic origin are probably dominant in gulf of alaska and kodiak shelf sediments two stations north of kalgin island in lower cook inlet and one in southeastern bering sea show typical weathered petroleum distribution of n alkanes and triterpenoids probable pathways of transport and fate of petroleum hydrocarbons in case of an oil spill are also briefly discussed

stress measurements of deforming olivine at high pressure abstract rheological properties of mantle minerals are critical for understanding the dynamics of the earth s deep interior due to limitations in experimental technique previous quantitative studies of the rheological properties of mantle minerals are limited to either low pressure or low temperature the present understanding of mantle flow is mostly inferred from the extrapolation of relatively low pressure data to mantle high pressure conditions however the effect of pressure represented by activation volume on the rheological properties of olivine is still controversial therefore deformation experiments carried out at mantle pressures are necessary to understand and model mantle flow here we report an experimental study of plastic deformation of san carlos olivine mg fe 2 sio 4 under upper mantle conditions macroscopic differential stress and strain rates have been measured in situ in a large volume high pressure apparatus using newly developed techniques the differential stress at high temperature and high pressure that we measured is significantly lower than that estimated by many currently accepted olivine flow laws we document the first in situ experimental differential stress results in a multi anvil press our results give direct evidence for a relatively small activation volume less than 10 5 m 3 mol 1 this shows that the effect of pressure on dislocation creep is small

depositional environment of sedimentary rocks inferred from normal fatty acid compositions normal saturated fatty acid n fatty acid in marine sediments from coastal and pelagic environments were analyzed the coastal sediments contain both short chained n fatty acids with carbon numbers from 12 to 18 and long chained acids from 22 to 32 whereas the pelagic sediments contain predominantly short chained acids the relative abundance of short chained to long chained n fatty acids expressed by the molar ratio c 16 c26 can be an indicator to assess the depositional environment of sedimentary rocks the ratio of long chained n fatty acids c22 c32 to the total n fatty acids also has the potential to discriminate sedimentary environments the indicators based on the n fatty acids were applied to the franciscan bedded cherts the result shows that the bedded cherts had deposited in continuous environments from the pelagic to the coastal this is in harmony with the same inference based on major trace and rare earth elements and normal paraffins 1999 elsevier science b v all rights reserved

modeling floodplain inundation using an integrated gis with radar and optical remote sensing abstract synthetic aperture radar images from multitemporal l band jers 1 and c band ers 1 satellites a landsat thematic mapper tm time series and gis coverages were used in an integrative approach to model the potential of flood inundation within the lower roanoke river floodplain north carolina a digital elevation model dem with one meter vertical resolution was developed for the region from scan digitized mylar separates of contour lines on usgs 7 5 min quadrangles several models representing potential wetness and potential flood inundation were generated from the dems using both raster grid and vector network analyses the potential inundation surfaces were derived from regression models that related known flood elevations to river position and floodplain location the gis models were assessed by comparison to classifications of flood change detection achieved through the radar data statistical results indicate that the gis derived models successfully identified flooded areas as mapped by the radar change detections further statistical tests assessed the ability of individual radar and optical landsat tm images to discriminate flooding as predicted by the gis models both jers 1 and ers 1 images identified areas of inundation at different flood levels

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

modelling the bulk viscosity of two phase mixtures in terms of clast shape abstract the rheological behaviour of many rock types will depend on how mixtures of different minerals and rock clasts behave together this paper develops two dimensional modelling of the bulk viscosity of two phase viscous mixtures with different shape fabrics in pure shearing based on self consistent mechanics and behaviour of inclusion matrix systems an equation is presented for the bulk viscosity in terms of the phase viscosity contrast phase fractions and clast shape results are given for idealised two dimensional mixtures of circles squares or ellipses with a variety of phase viscosity contrasts in pure shearing parallel perpendicular to the shape fabric the normalised bulk viscosities of all these mixtures fall between the theoretical upper and lower viscous bounds given by homogeneous strain rate and homogeneous stress respectively but nearer to the upper bound with increasing shape fabric mixtures with a particular geometry are shown to have a constant relative horizontal distance between these two bounds as proposed by p d bons using graphs for the normalised bulk viscosities of mixtures with variably elliptical aligned shape fabrics the results for fabrics orthogonal to pure shearing can be extrapolated to a diagonal fabrics in pure shearing and b orthogonal or diagonal fabrics in simple shearing these reveal the bulk viscous anisotropy of mixtures with shape fabric in two dimensions it is speculated that during a progressive finite deformation two phase mixtures might undergo changes in bulk viscosity over time with steady stiffening during pure shear and perhaps cyclic stiffening and softening during simple shear the two dimensional models provide an approximation to the three dimensional properties of mixtures with shape fabrics with potential applications to rocks including conglomerates

geochemical characteristics and depositional environments of cherts and associated rocks in the franciscan and shimanto terranes abstract analyses of 122 jurassic cretaceous rock samples from the franciscan terrane california and 24 cretaceous samples from the shimanto terrane southwest japan show that the cherts and associated rocks accompanied by pillow basalts are enriched in fe and mn which may have been derived from hydrothermal activities the results of the fraction analyses for terrigenous basaltic hydrothermal and biogenic end members in the franciscan rocks show that hydrothermal emanations caused iron and manganese enrichment in the rock samples and played an important role in the formation of siliceous rocks vertical variations of the hydrothermal fraction and tio2 normalized values for hydrothermal elements such as fe mn ni zn y and pb show a possibility that the bedded cherts of the franciscan terrane were deposited in a hydrothermal field on or near some active oceanic ridge for more than 30 ma and were a remnant slice of oceanic crust added to the north american continent on the other hand from the field occurrences and vertical variations of tio2 normalized values of hydrothermal elements the shimanto rocks are inferred to have been deposited in a hemipelagic environment such as marginal and inter arc basins

source rock evaluation and nature of hydrocarbons in the khalda concession shushan basin egypt s western desert abstract organic geochemical studies were undertaken on 241 jurassic cretaceous ditch cuttings samples and 9 gases and 10 crude oils from some productive mesozoic pay zone intervals in the khalda concession shushan basin northern western desert egypt we aim to investigate source rock characteristics origin of gases nature of oils and their inferred source rocks and to establish genetic relationships the middle jurassic khatatba formation and older rocks contain organic rich mature coaly and carbonaceous shales which are the main source for hydrocarbons in egypt s western desert including the shushan basin which generally contains kerogen type iii with some contribution of type iii ii kerogen molecular and isotopic composition indicates that the khalda gases are of thermogenic origin a mature 0 6 2 0 ro source rock with terrigenous organic matter kerogen type iii was identified as a precursor of wet thermogenic gases in the shushan basin geochemical results indicate that the oil samples were derived from a source rock deposited mainly under oxic conditions and containing terrigenous organic matter biomarker data indicate that paraffinic oils and condensates from the shushan basin were derived from mature source rocks within the oil window the light hydrocarbon data suggests that the analyzed oils can be classified into two groups as a result of evaporative fractionation and maturation this signal of a secondary reservoir transformation which is not revealed by biomarker analysis emphasizes the importance of integrating biomarker and light hydrocarbon data to understand variations in the chemical composition and origin of oils

floodplain river ecosystems lateral connections and the implications of human interference abstract floodplains are ecotones that form a transition between aquatic and terrestrial environments these important ecosystems can be described as dynamic spatial mosaics in which water plays an important role in connecting various patches on the floodplain surface hydrological connections facilitate the exchange of carbon and nutrients between the river channel and the floodplain and therefore influence the productivity of the entire river system this paper examines the influence of hydrological connections on the potential exchange of dissolved organic carbon between a large australian floodplain to a river channel and the effects of land and water developments on these exchanges the paper proposes that an understanding of floodplain ecosystems requires an interdisciplinary approach a recognition of the importance of the three disciplines hydrology geomorphology and ecology large scale water resources and floodplain development has significantly altered the spatial and temporal patterns of hydrological characteristics in the lower balonne floodplain australia the magnitude frequency and duration of flooding events have all been reduced the construction of levees and water storages has also reduced the reactive floodplain surface area the presented data show the impacts of these changes on the potential supply of dissolved organic carbon from the floodplain surface during periods of inundation annual reductions of up to 1293 tonnes of dissolved organic carbon supply were noted and reductions were especially significant for floods with an average recurrence interval of 2 years or less some small flood events no longer facilitate the potential supply of dissolved organic carbon from the floodplain to the river channel because of water resources and floodplain developments

latitudinal change of normal paraffin composition in the northwest pacific sediments abstract we analyzed normal saturated paraffins n paraffins in 70 surface sediments in the northwest pacific to examine the spatial distribution of organic materials all sediments show bimodal n paraffin abundance patterns against carbon number with maxima at c 16 and c 31 indicating that n paraffins in marine sediments are a mixture of long chain n paraffins from land based higher plant waxes and short ones from marine organisms we observed in this study a significant change of carbon preference index cpi from 2 5 in low latitudes to 4 5 in mid high latitudes around 19 25 n the following influences are discussed as the cause of cpi offset between low and mid high latitudes 1 meteorological conditions 2 n paraffin composition of higher land plants 3 contribution of petroleum components and 4 mixing ratio of higher land plants and marine organisms however none of them can be the possible cause of the cpi offset because n paraffin content and composition vary significantly according to the species of a bacterium difference of the species of bacterial communities between low and mid high latitudes may be a possible reason for the cpi offset found in sediment from the northwest pacific

a new longitudinal approach to assess hydrologic connectivity embanked floodplain inundation along the lower mississippi river hydrologic connectivity is fundamental to understanding floodplain processes along meandering river corridors this study contributes to understanding hydrologic connectivity by utilizing a high resolution light detection and ranging dem with a new gis based approach for identifying the precise elevation of flood stage the method created a high resolution longitudinal channel bank profile enabling a detailed examination of embanked floodplain hydrologic connectivity a simple channel cross section approach is likely to result in a large underestimation of floodplain inundation and hydrologic connectivity along meandering river floodplains because of differences in the elevation of the natural levee surface relative to floodplain bottoms and the considerable variability in the elevation of the channel bank profile there is a large disparity in discharge duration associated with floodplain inundation in comparison to river channel bank inundation a discharge duration of 10 is associated with inundation of 87 of the floodplain surface whereas only 53 of the channel bank profile is overtopped an apparent threshold in inundation occurs as the discharge duration decreases below about 35 while a duration of 25 results in very little of the channel bank being overtopped it inundates 50 of the floodplain surface floodplain borrow pits which are created in association with dike construction represent a constant anthropogenic influence on the lower mississippi embanked floodplain morphology and are inundated by low discharge magnitudes the results of the investigation shed new light on the topic of hydrologic connectivity for an important embanked fluvial system that has previously received little attention concerning its physical floodplain processes copyright 2013 john wiley sons ltd

flood delineation in a large and complex alluvial valley lower panuco basin mexico determining the extent of flooding is an important role of the hydrological research community and provides a vital service to planners and engineers for large river systems located within distant settings it is practical to utilize a remote sensing approach this study combines a remote sensing and geomorphic approach to delineate the extent of a large hurricane generated flood event in the lower panuco basin 98 227 km2 the seventh largest river system draining into the gulf of mexico the lower panuco basin is located within the coastal plain of eastern mexico and has a complex alluvial valley data sources included a landsat 5tm and landsat 7etm scene and topographic and particle size data from fieldwork and laboratory analysis the landsat 5tm image was acquired after the peak of a large flood event in 1993 whereas the landsat 7etm scene was acquired during the dry season in 2000 the increasing number of days between flood crest and the date of flood image acquisition along the river valley provided the opportunity to examine several methods of flood delineation and to consider differences in floodplain geomorphology backswamp environments were easily delineated in flooded reaches within the panuco and tamuin valleys whereas in the moctezuma valley more sophisticated methods were required because of the greater time between image acquisition and flood peak and the complex floodplain topography this included principal component pc analysis and image classification within the floodplain residual holocene terraces complicated flood mapping classification of both images allowed consideration of the influence of permanent standing water although the flooded areas were greater in the lower reaches of the study area because this portion of the valley contained large floodplain lakes the amount of inundation was actually lower remote sensing offers the ability to examine large alluvial valleys in distant settings but does not imply that geomorphic criteria should be excluded indeed because of heterogeneous floodplain topography this study illustrates the importance of including field based geomorphic analysis so that the complexity of distinct floodplain environments are considered the findings from this study are significant because most remote sensing data obtained for the purpose of flood mapping will not coincide with the flood crest thus this study provides an appropriate method for mapping flood inundation in large and complex floodplain settings after flood crest recession

grain size stabilisation by dispersed graphite in a high grade quartz mylonite an example from naxos greece high grade quartz mylonites from naxos greece consist of alternating thin layers of pure quartz and quartz layers with 0 3 3 vol finely dispersed graphite particles graphite free layers are coarse grained 100 300 mm show undulose extinction subgrains lobate grain boundaries and have a strongly developed crystallographic preferred orientation in these layers dislocation flow is interpreted to be the dominant deformation mechanism in contrast graphite rich layers are fine grained 30 70 mm have equant quartz grain shapes and have a crystallographic preferred orientation that becomes progressively weaker with decreasing quartz grain size given the high temperature of deformation and the need for a c axis fabric destroying mechanism grain boundary sliding is interpreted to be important in these layers analysis shows an inverse relationship between quartz grain size and the graphite dispersion suggesting stabilization of quartz grain size by graphite particles graphite particles larger than 5 mm are concentrated along quartz boundaries suggesting that stabilisation only operates above a certain critical graphite particle size this study shows that a dispersed second phase such as graphite in a naturally deforming rock can inhibit grain boundary migration stabilise the grain size and enhance grain boundary sliding at the expense of dislocation flow q 2002 elsevier science ltd all rights reserved

hydrocarbon geochemistry of the puget sound region ii sedimentary diterpenoid steroid and triterpenoid hydrocarbons cyclic components of the aliphatic hydrocarbon mixtures extracted from puget sound sediment cores include a suite of c19 and c20 diterpenoid hydrocarbons of which fichtelite sandaracopimaradiene and isopimaradiene have been identified although apparently also derived from vascular plants these diterpenoid hydrocarbons have relative abundances distinctly different from the co existing plant wax n alkane suite five c27 c28 and c29 diasteranes and four c29 c30 and c31 17 h 21 h hopanes occur in relatively constant proportion as components of a highly weathered fossil hydrocarbon assemblage these chromatographically resolved cycloalkanes along with the strongly covarying unresolved complex mixture have been introduced to puget sound sediments from adjacent urban centres at increasing levels over the last 100 yr in the absence of any major oil spill naturally occurring triterpenoid hydrocarbons including hop 22 29 ene diploptene are also present a new group of c30 polyenes has been detected which contains compounds apparently structurally related to a co existing bicyclic c25 diene and to c20 and c25 acyclic multibranched hydrocarbons described in a previous paper barrick et al 1980

normal paraffins in shales as an indicator of depositional environment abstract normal paraffin compositions were determined for marine sediments from coastal and pelagic environments and for shales in the jurassic cretaceous bedded chert sequence from the franciscan terrane western north america the pelagic sediments and shales from a lower horizon of the bedded chert sequence are characterized by short chained n paraffins the coastal sediments and shales from the upper horizon show high abundance of n paraffins especially for long chained ones and a strong odd carbon predominence the comparison of n paraffin compositions of shales with those of marine sediments suggests that the bedded chert sequence had deposited in continuous environments from pelagic to coastal this inference is in harmony with that based on the major minor and rare earth element compositions the result suggests that shales in the franciscan bedded chert sequence preserve well the normal paraffin signals acquired at the deposition and demonstrates that the normal paraffin composition can be a useful indicator of sedimentary environment

the hydro geomorphologic complexity of the lower amazon river floodplain and hydrological connectivity assessed by remote sensing and field control abstract hydrological connectivity processes along the lower amazon river floodplain at lago miratuba floodplain lmf were analyzed based on remote sensing and field measurements connectivity processes are related to 12 geomorphic sub units of the floodplain that are interconnected at different stage thresholds through channelized and overbank flow paths while lakes act as reservoirs for flood waters local rainfall and water table saturation seepage hydrological connectivity processes along the floodplain happen through complex internal routings of water flows over space and time mainly along floodplain channels and breached levees the contribution of local recharge mainly rainfall was decoupled from river recharge river hydrological connection to floodplain because precipitations and local runoff also recharge the floodplain the hydrological connectivity of the 12 geomorphic units varied significantly from each other because the inundation and the floodplain connections with the river were initiated at specific river stage thresholds for each sub unit an interesting finding is that connections with the river for all units were initiated through channelized flows below the bankfull stage of the amazon river the connectivity processes over different geomorphic units are also not correlated with their minimum distance shortest lines from the river this implies that a flood pulse model largely concerned with lateral connectivity mostly through overbank diffusion only partially explains the complex hydrological connectivity processes at a regional scale along the complex lower amazon river floodplain thus for hydrological connectivity assessments in the amazon river floodplain reach by reach scale studies have to be carried out relating the hydro geomorphologic processes channelized flow routing paths overbank diffusion and local recharge to the internal geomorphic variability and complexity of the floodplain

relation between chemical composition and sedimentation rate of pacific ocean floor sediments deposited since the middle cretaceous basic evidence for chemical constraints on depositional environments of ancient sediments chemical characteristics of pacific marine sediments were examined for different environments operating since the middle cretaceous as a result of the examinations a procedure for evaluating depositional environments of ancient sediments in orogenic belts is proposed the concentration of hydrogenous authigenic elements such as mn co and ni in sediments has a relationship to the bulk sedimentation rate similarly a new indicator which is a measure of the sedimentation rate of terrigenous lithogenic materials in sediments is proposed this indicator is expressed as the weight ratio of a hydrogenous element to tio 2 because the sedimentation rate of terrigenous materials gradually decreases with distance from land the ratio varies according to depositional environments geochemical examination of pacific dsdp materials has shown that the distribution of element ratios mno tio 2 co tio 2 and others in surface sediments of the pacific has not changed since the middle cretaceous as an

bulk flow strength of forsterite enstatite composites as a function of forsterite content creep experiments have been conducted to investigate the effect of varying forsterite content vfo on the bulk flow strength of dry forsterite enstatite fo en aggregates in order to evaluate the applicability of existing theoretical models to two phase rocks as well as to understand the rheology of polyphase systems in general the experiments were performed at temperatures of 1423 1593 k stresses of 18 100 mpa oxygen fugacities of 10 14 10 2 5 mpa and 0 1 mpa total pressure the fine grained fo 10 17 mm en 14 31 mm composites of various fo volume fractions vfo 0 0 2 0 4 0 5 0 6 0 8 and 1 were synthesized by isostatically hot pressing in a gas medium apparatus at 1523 and 350 mpa our experiments show that flow strength contrasts between fo and en are in the range of 3 8 at the given experimental conditions with fo as the stronger phase the measured stress exponent n and activation energy q values of the fo en composites fall between those of the endmembers the n values show a nearly linear increase from 1 3 to 2 0 while the q values display a non linear increase from 472 to 584 kj mol with en volume fraction from 0 to 1 0 there is no clear dependence of creep rates on oxygen fugacity for the fo en composites the mechanical data and tem microstructural observations suggest no change in deformation mechanism of each phase when in the composites compared to when in a single phase aggregate the en deformed mainly by dislocation creep while the fo deformed by dislocation accommodated diffusion creep for our grain sizes and experimental conditions comparisons between the measured composite strengths and various theoretical models indicate that none of the existing theoretical models can give a precise predication over the entire vfo range from 0 to 1 however the theoretical models based on weak phase supported structures wps yield a good prediction for the flow strengths of the composites with vfo 0 6 no model gives a good prediction for the bulk strength of two phase composites in the transitional regime vfo 0 4 0 6 applications of the wps and sps based models in the transitional regime result in under and over estimations for the composite flow strength respectively thus the effect of rock microstructure should be taken into consideration in modeling the bulk flow strengths of the crust and upper mantle using laboratory determined flow laws of single phase aggregates d 2001 elsevier science b v all rights reserved

re development of fluvial islands along the lower mississippi river over five decades 1965 2015 abstract the development and evolution of islands along the lower mississippi river were examined over a 50 year period between 1965 and 2015 fluvial islands were historically a fundamental component of the riparian corridor serving as important ecological habitat for aquatic and terrestrial species their degradation was associated with channel engineering leading to a pronounced single thread channel continued channel engineering in the latter twentieth century however is associated with a rapid increase in channel islands along the lower mississippi river the study utilizes a gis framework to examine and analyze a range of geospatial data sets including i lidar dems ii historic aerial photos iii historic and recent satellite imagery iv historic topographic maps and vi hydrologic data from gauging stations along the lower mississippi river islands were digitized in google earth pro and arcgis by identification of vegetation lines spatial data polygons were used to extract clip the lidar dem data for subsequent analysis the island data was statistically analyzed using a manova and two way t test to examine the association of dikes with the morphologic characteristics of islands the number of islands 1 ha significantly increased over the five decade study period from 105 in 1965 206 in 1995 to 295 in 2015 the average size of islands decreased from 101 ha hectare to 63 ha because so many new small islands formed within the dike fields the total area of islands within the river channel increased from 103 km2 in 1965 169 km2 in 1995 to 206 km2 in 2015 the total sediment storage within fluvial islands above the average low water surface is 1 81 billion m3 the lower mississippi has sufficient coarse sediment to construct new riparian lands despite the large historic decline in sediment load and overall channel bed degradation that occurred in response to large scale engineering projects over much of the twentieth century the new rapid growth and development of fluvial lands within the riparian corridor of the lower mississippi is a positive outcome of an unintended geomorphic consequence but one that requires additional management considerations

numerical study of creep in two phase aggregates with a large rheology contrast implications for the lower mantle it is generally accepted that the earth s lower mantle is dominated by two minerals magnesiowustite mg fe o mw and mg fe sio3 perovskite mg pv which are thought to exhibit very different rheological properties in order to assess the respective role of those phases in the mechanical properties of the assemblage we have carried out 3d finite element modelling of a model two phase aggregate an isotropic random polycrystal has been built from a voronoi mosaic then each grain has been attributed a hard or weak behavior in such a way that the hard phase represents a volume fraction of 70 the creep law introduced for both phases is a simple power law creep without hardening a contrast of 35 is chosen between the strain rates of both phases under a shear stress of 10 mpa a representative volume element of 470 grains has been shown to provide a satisfactory description of the mechanical response of the aggregate with a relative precision equal to 3 numerical creep experiments conducted under a constant macroscopic shear stress of 10 mpa suggest that the creep rate of lower mantle assemblages would be dominated by the mechanical behavior of the harder phase mg pv the finite element model allows one to extract the individual behavior of the two phases within the aggregate it is shown that during creep the harder mg pv phase carries most of the stress whereas the softer mw phase is responsible for most of the accumulated strain this result should have implications for the development of shape and lattice preferred orientations of mw within the aggregate thus for seismic anisotropy of the lower mantle

human modifications to the sediment regime of the lower mississippi river flood plain the mississippi river is one of the most regulated rivers in the world human modifications constructed mainly after 1920 include dams and reservoirs artificial levees dikes concrete revetments and a series of channel cutoffs this paper examines some of the effects of these modifications on the channel and sediment budget of the river in particular the changes to the thalweg profile and the size of channel bars are examined in detail it is concluded that prior to the 1930s when major modifications were introduced the lower mississippi river was an aggrading meandering river the role of the flood plain has also changed prior to modifications the flood plain was the major sediment source as the result of bank caving today the flood plain provides only a minor amount of sediment it can be shown that major degradation to the channel including the growth of channel bars has occurred as a result of these engineered modifications the data also indicates that the different geomorphic regions respond to modifications in different ways

sedimentary environments of the middle permian phosphorite chert complex from the northeastern yangtze platform china the gufeng formation a continental shelf radiolarian chert abstract radiolarian chert deposited on a continental shelf occurs in the middle permian gufeng formation on the northeastern yangtze platform china the sedimentary environments of radiolarian cherts from accretionary complexes have been well studied however there are few studies about radiolarian chert deposited on continental shelves therefore we have completed a sedimentological and geochemical study of the gufeng formation the gufeng formation is subdivided into the phosphate nodule bearing mudstone member pnmm and the siliceous rock member srm in ascending order the basal pnmm consists of glauconite bearing mudstone which indicates deposition under aerobic shallow marine conditions whereas the upper pnmm is composed of mudstone including abundant phosphate nodules suggesting deposition near the outer shelf in suboxic conditions the srm consists mainly of alternating beds of black chert mudstone and siliceous mudstone with minor tuffaceous mudstone and porous chert beds the black chert contains abundant radiolarians sponge spicules and organic matter framboidal pyrite occurs in the black chert porous chert in the srm includes abundant rhombohedral cavities which are dolomite moulds surrounded by quartz suggesting dolomitization before silicification during early diagenesis the gufeng chert is characterized by high si mo ni cu and zn contents and extremely low mn content the gufeng chert has high normal paraffin concentrations with petroleum like markers these geochemical features suggest that the gufeng chert was deposited under sulfate reducing conditions and is not hydrothermal but rather biogenic in origin the sedimentological and geochemical data suggest that the gufeng formation was deposited mainly on the outer shelf in suboxic anoxic conditions caused by organic matter produced during upwelling the upwelling probably led to high radiolarian productivity abundant silica and organic matter were deposited in the gufeng basin compared with chert from other sites the gufeng chert shows many similarities with chert from platformal basins but not with chert from accretionary complexes especially with respect to age rock type stratigraphy and geochemical features the chert of the gufeng formation is similar to that of the phosphoria formation in the western u s a which is a world class phosphorite giant these similarities suggest that upwelling occurred around the eastern margins of panthalassa and the paleotethys concurrently during the middle permian in general shelf type radiolarian chert represented by the gufeng chert usually shows some of the following features dark color lack of rhythmical bedding association with phosphorite platformal limestone felsic tuff abundant organic matter and sulfides shelf type radiolarian chert is deposited in a poorly aerated restricted basin or in an oxygen minimum zone

high pressure deformation in two phase aggregates abstract we investigate the rheological behavior of multi phase aggregates at high pressure and high temperature using synchrotron x ray radiation as the probing tool we are able to quantify the stress state of individual phases within the aggregates this method provides fundamental information in interpreting the behavior of two phase multi phase mixtures which contribute to our understanding of the deformation process at deep earth conditions we choose mgal2o4 spinel and mgo periclase as our model materials mixtures of various volume proportions were deformed in a multi anvil high pressure deformation apparatus at pressure of 5 gpa and elevated temperatures stress is determined from x ray diffraction providing a measure of stress in each individual phase of the mixture in situ during the deformation macroscopic strain is determined from x ray imaging we compare the steady state strength of various mixtures at 1000 c and 800 c and at the strain rate in the range of 1 8 to 8 8 10 5 s 1 our data indicate that the weak phase mgo is responsible for most of the accumulated strains while the strong phase spinel is supporting most of the stress when the volume proportion is 75 spinel and 25 mgo the intermediate compositions 40 60 are much weaker than either of the end members while the grain sizes for the intermediate compositions submicrons are much smaller than the end members 5 10 m we conclude that a change in flow mechanism resulting from these smaller grains is responsible for the low strength of the intermediate composition mixtures this study demonstrates an approach of using synchrotron x rays to study the deformation behaviors of multi phase aggregates at high pressure and high temperature

texture development in experimentally deformed two phase aggregates of calcite and anhydrite abstract fully quantitative textures have been measured from experimentally deformed two phase aggregates of calcite and anhydrite two sets of deformation experiments were performed firstly to investigate the development of microstructure and texture with composition samples with varying volume proportions of calcite and anhydrite were deformed to 20 strain at identical conditions secondly to study the texture development of the two materials with strain and explore the possible use of texture index as a strain gauge in polyphase materials pure calcite and pure anhydrite were deformed at the same conditions as the two phase rocks to strains of 6 12 and 20 the textures in both calcite and anhydrite were found to be similar but not identical to those reported in previous studies for pure samples our experimental investigations and measured textures show that the textures both of the pure materials and of the two phase rocks depend not only on strain but also on stress and grain size through their influence on the deformation mechanisms the dependence of texture index with change in deformation mechanism is particularly pronounced in the anhydrite component where the texture index decreases with grain size which decreases with anhydrite content the texture in the pure calcite and in the calcite component of the two phase rocks was influenced by a preexisting fabric the intensity of the texture in the deformed samples seems to correlate with the stress in the calcite rather than with strain

the influence of floodplain geomorphology and hydrologic connectivity on alligator gar atractosteus spatula habitat along the embanked floodplain of the lower mississippi river abstract the floodplain geomorphology of large lowland rivers is intricately related to aquatic ecosystems dependent upon flood pulse dynamics the alligator gar atractosteus spatula is native to the lower mississippi river and dependent upon floodplain backwater areas for spawning in this study we utilize a geospatial approach to develop a habitat suitability index for alligator gar that explicitly considers hydrologic connectivity and the floodplain geomorphology along a frequently inundated segment of the lower mississippi river the data sets include landsat imagery a high resolution lidar digital elevation model dem national hydrography dataset nhd and hydrologic and geomorphic data a habitat suitability index is created based on the extent and frequency of inundation water depth temperature and vegetation a comparison between the remote sensing approach and the nhd revealed substantial differences in the area and location of water bodies available for alligator gar spawning the final habitat suitability index indicates that a modest proportion 19 of the overall embanked floodplain is available for alligator gar spawning opportunities exist for management efforts to utilize engineered and natural geomorphic features to facilitate hydrologic connectivity at flow levels below flood stage that would expand the habitat of alligator gar across the floodplain the study results have direct implications regarding environmental restoration of the lower mississippi an iconic example of an embanked meandering river floodplain

two phase deformation of lower mantle mineral analogs abstract the lower mantle is estimated to be composed of mostly bridgmanite and a smaller percentage of ferropericlase yet very little information exists for two phase deformation of these minerals to better understand the rheology and active deformation mechanisms of these lower mantle minerals especially dislocation slip and the development of crystallographic preferred orientation cpo we deformed mineral analogs neighborite namgf3 iso structural with bridgmanite and halite nacl iso structural with ferropericlase together in the deformation dia at the advanced photon source up to 51 axial shortening development of cpo was recorded in situ with x ray diffraction and information on microstructural evolution was collected using x ray microtomography results show that when present in as little as 15 volume the weak phase nacl controls the deformation compared to single phase namgf3 samples samples with just 15 volume nacl show a reduction of cpo in namgf3 and weakening of the aggregate microtomography shows both namgf3 and nacl form highly interconnected networks of grains polycrystal plasticity simulations were carried out to gain insight into slip activity cpo evolution and strain and stress partitioning between phases for different synthetic two phase microstructures the results suggest that ferropericlase may control deformation in the lower mantle and reduce cpo in bridgmanite which implies a less viscous lower mantle and helps to explain why the lower mantle is fairly isotropic

a tale of two viscosities abstract we describe a series of 12 large strain two dimensional simple shear numerical experiments on two phase linear and non linear viscous materials the modal percentage of the two phases their relative viscosities and the stress exponent of the dependence of viscosity on stress were systematically varied allowing us to observe the effects of these parameters on the flow behaviour of the system all experiments exhibited localisation but the extent and type of localisation varied considerably and the range of parameters allows both classical sc as well as sc structures to form the inter granular finite strain geometries also varied systematically although there is a tradeoff between non linearity of viscosity and the viscosity contrast that results in similar geometries for quite different mechanical behaviour the finite rotation of the harder phases was similar within any one experiment originally parallel passive marker lines thus remain sub parallel after deformation and rotation which may be mistaken for non rotation the internal deformability and interaction between grains allows meta stable grain elongation orientations to form without any additional consideration of external slip surfaces the slight variability of initial grain geometry and subsequent grain interactions leads to a wide variability in final grain shapes for the same initial viscosities

assessing the effect of different bathymetric models on hydraulic simulation of rivers in data sparse regions abstract river bathymetry which is vital for accurate hydraulic modeling is not readily available at large scales because of the logistical difficulties in field surveys and uncertainties associated with remote sensing techniques several studies have explored the potential of conceptual models and interpolation algorithms to estimate bathymetry these models have certain underlying assumptions that limit their accuracy and widespread implementation this study aims to provide insights into the choice of bathymetric model for different hydraulic applications by analyzing the effect of different bathymetric models on hydraulic modeling under different geomorphologic and flow settings this study does not aim to reinforce the importance of bathymetry rather its objective is to identify the bathymetric properties that are critical to accurate estimation of different hydraulic outputs the study accomplishes its objectives by implementing three different bathymetric models with varying cost and efficiency at four sites with diverse bathymetric characteristics five hydraulic outputs namely wetted cross sectional area water surface elevation inundation extents velocity and shear are estimated at three characteristic low and high flows and the results from the four sites are grouped together to perform an unbiased and robust evaluation the performance of these models is evaluated using the best available bathymetric representation generated from detailed field surveys as a benchmark the results indicate that 1d flood modeling is somewhat insensitive to channel shape as long as the estimated shape reflects the channel storage accurately velocity and shear related applications should incorporate bathymetry that represent both the cross sectional area and channel thalweg accurately reaches with low sinuosity

the importance of atmospheric input of terrestrial organic material to deep sea sediments the concentrations of lipids were determined in atmospheric particle gas and rain samples collected from the tropical north pacific to assess lipid sources transport mechanisms and fluxes to the ocean surface four lipid compound classes aliphatic hydrocarbons fatty alcohols fatty acid esters and salts all unequivocally show a terrestrial vascular plant source these aerosol lipids originate from wind erosion of asian and american soils and direct emission from vegetation the major fluxes result from rain rather than dry deposition these fluxes are large enough to have a major potential impact on the inventory of terrestrially derived lipid material found in deep sea sediments this has been showm for n alkanes fatty alcohols fatty acids total lipids and for organic carbon by comparing atmospheric and sediment trap fluxes with sediment accumulation rates it is suggested that some biogenic terrestrial material is more protected from degradation than marine derived material

composite flow laws for crystalline materials with log normally distributed grain size theory and application to olivine abstract conventional steady state flow laws describing combined grain size insensitive dislocation creep and grain size sensitive diffusion creep incorporate grain size as a single mean value however rocks exhibit distributed grain size and variations in the shape of the distribution such as its width will accordingly affect rheological behavior to evaluate this effect we have derived composite dislocation diffusion flow laws describing upper and lower bounds on the rate of deformation of materials showing a grain size distribution of the commonly observed log normal type the upper and lower bound flow laws obtained allow systematic investigation of the influence of the grain size distribution parameters i e the median and standard deviation on composite rheology the results demonstrate major effects of distribution width as well as median value application to polycrystalline olivine deforming by coble creep and power law dislocation creep reveals significant implications for interpreting deformation experiments and modeling flow in the earth s mantle the flow laws also provide an improved basis for modeling the deformation of rocks during geological processes in the crust and mantle

spillage sedimentation on large river floodplains active deposition across the floodplains of large rivers arises through a variety of processes collectively these are here termed spillage sedimentation three groups of 11 spillage sedimentation styles are identified and their formative processes described form presences on large river floodplains show different combinations of active spillage styles only some large floodplains have prominent levees some have coarse splays many have accessory channel dispersion and reworking while still water sedimentation in lacustrine environments dominates some lower reaches infills are also commonly funnelled into prior and often linear negative relief forms relating to former migration within the mainstream channel belt 2016 the authors earth surface processes and landforms published by john wiley sons ltd shuttle radar topography mission srtm and landsat 8 data are used to map spillage form types and coverage along a 1700 km reach of the amazon that has an active floodplain width of up to 110 km with a systematic character transformation down valley spillage forms associated directly with mainstream processes rarely account for more than 5 of the floodplain deposits there is a marked decrease in floodplain point bar complexes pbc over 1700 km downstream from 34 to 5 and an increase in the prevalence of large water bodies 2 to 37 and accompanying internal crevasses and deltas 0 to 5 spillage sedimentation is likely within the negative relief associated with these forms depending on mainstream sediment laden floodwater inputs 2016 the authors earth surface processes and landforms published by john wiley sons ltd spillage style dominance depends on the balance between sediment loadings hydrological sequencing and morphological opportunity down river form sequences are likely to follow gradient change prior up river sediment sequestration and the altered nature of spilled loads but also crucially local floodplain relief and incident water levels and velocities at spillage times considering style distribution quantitatively as a spatially distributed set of identifiable forms emphasizes the global variety to spillage phenomena along and between large rivers 2016 the authors earth surface processes and landforms published by john wiley sons ltd

olivine flow mechanisms at 8 gpa abstract the mechanisms responsible for high temperature olivine deformation are investigated at a pressure of 8 gpa and temperatures up to 1780 k san carlos olivine specimens of different average grain sizes 0 5 and 5 m were deformed simultaneously between hard alumina pistons during relaxation experiments these experiments are carried out in a multi anvil high pressure apparatus coupled with synchrotron x ray radiation the different grain size specimens experienced identical p t stress condition at any given time a new method for measuring strains and strain rates 10 6 s 1 of specimens at high pressure is documented this method uses time resolved in situ x ray imaging and an image analysis computation the microstructures of run products recovered after being quenched at different temperatures were characterized by transmission electron microscopy tem we find that high temperature olivine flow is grain size insensitive at 8 gpa which suggests that dislocation creep dominates olivine deformation at high pressure this result is confirmed by the tem investigation of our deformed specimens in which we find evidences of the activation of olivine dislocation slip systems specimen microstructures are consistent with dynamic recrystallization as an assisting process in olivine deformation during the high pressure experiments extrapolation of our results to the low stress level and large grain size expected in the mantle suggests that dislocation creep assisted by dynamic recrystallization may also dominate natural olivine deformation in the upper mantle

rare earth major and trace elements in chert from the franciscan complex and monterey group california assessing ree sources to fine grained marine sediments abstract rare earth element ree major and trace element analyses of 77 samples from the mesozoic franciscan complex and miocene monterey group of california usa indicate that magnitudes of the ce anomaly ce ce and total ree abundances sree in these rocks are controlled dominantly by a the amount of included metalliferous material b the amount of direct terrigenous input and c the overall burial rate the relative importance of these individual processes varies across an ocean basin in such a way that ree relative fractionations and sree correspond with its depositional environment our conclusions are supported by an extensive review of published ree data from various river coastal open ocean and ridge influenced waters as well as terrigenous pelagic and metalliferous sediment the chert sequences record deposition in spreading ridge open ocean basin and continental margin environments the relative importance of metalliferous and terrigenous influences and the role of scavenging from seawater may be estimated from a sample s inferred depositional distance km from the spreading ridge the major element chemistry and the stratigraphie context the ce ce values are low 0 29 in the vicinity of spreading ridges and trend to successively higher 1 values with decreasing metalliferous and increasing terrigenous influences other ree indicators ree lu n la n eu eu also respond to metalliferous and terrigenous influences near the spreading ridge chert ree appears determined by burial rate while shale ree responds to metalliferous abundance in open ocean and continental margin environments ree is controlled by sediment exposure time and therefore is related inversely to burial rate ree data are consistent with the major elements fe2o3 mno and al2o3 in reflecting the respective metalliferous and terrigenous sources p2o5 and cao do not vary with ce ce in any environment but cao shows a weak negative correlation with ree trace element trends e g v cr cu ge si rb sr y th u in general can similarly be accounted for in the context of depositional position relative to metalliferous and terrigenous inputs rees in chert appear less affected by post depositional processes than either major or trace elements indicating that rees are better tools for paleoceanographic or tectonic reconstructions that are based on chert chemistry this work complements recent efforts to elucidate the factors determining large scale ree distributions in marine sediments and has direct bearing on previous attempts to use the ce anomaly in older rocks and sediments as a recorder of secular variations and anoxic events in the overlying water column

overbank sedimentation from the historic a d 2011 flood along the lower mississippi river usa in this study we document sedimentary characteristics of overbank flood deposits associated with the epic a d 2011 flood along the lower mississippi river southern usa and directly compare the findings to sedimentation from a comparable flood event in 1973 with the general purpose of understanding how extreme floods contribute to floodplain depositional patterns and accretion rates of embanked fluvial systems the thicknesses of the 2011 flood deposits averaged 138 mm along natural levee crests 9 mm on meander scrolls and 3 mm in backswamps these thicknesses are considerably less than those documented for the 1973 flood sampled at the same locations we contend that less sedimentation in 2011 occurred because the flood was not supplied with much upstream sediment from the missouri river further the 2011 sediments are coarser than in 1973 indicating that the higher 2011 flood levels were associated with more energetic overbank flows that flushed fine grained sediments downstream within the narrow embanked floodplain corridor the largest recorded flood in north american history is only marginally preserved in the embanked floodplain stratigraphy of the alluvial valley of earth s third largest fluvial system

floodplain response to varied flows in a large coastal plain river abstract the natural flood pulse maintains river floodplain ecosystems through the exchange of freshwater resources between the main stem and floodplain habitats few prior studies have quantified the relationship between flows and floodplain response including estimating inundation area floodwater volumes and slough connectivity floodplain modeling typically uses the flow stage height relationship at river gauge stations in this study we compared a relative elevation model rem and the hydrologic engineering center river analysis system hec ras 1d model using events from 2015 and 2016 covering a range of flows from the 1st to the 99th percentile for the apalachicola river florida because digital elevation models dem from lidar light detection and ranging data lack details of riverbed topography we compared a lidar alone and lidar sonar combined dem to assess their differences estimates from the rem and hec ras models were compared to maps based on landsat imagery derived water and vegetation indices in this river we found a non linear relationship between the inundated area and flow increasing markedly through the 90th flow percentile after which increases are minimal inundated areas from both rem and hec ras models were similar for all selected flow levels except at the 74th percentile 708 m3 s flow at which the rem produced 11 higher inundated area than hec ras near the median flows major sloughs were fully connected with backswamps and low lying patches being inundated at the higher flows only a few anthropogenic features were exposed floodplain inundation estimates from landsat performed poorly detecting 9 with the modified normalized difference water index mndwi and 41 with the open water likelihood index owl these estimates were much lower than the hec ras model 96 flooded largely because the satellite is unable to penetrate dense forests and examine the floodplain surface and the landsat pixel size is twice the width of floodplain sloughs the lidar sonar combined dem produced a higher floodwater volume estimate with the hec ras model than using lidar alone the difference of 1 368 000 m3 at the 1st percentile 142 m3 s and 2 825 000 m3 at the 89th percentile 1133 m3 s demonstrate the limitation of using a lidar alone dem which cannot penetrate the water surface and the importance of surveying floodplains using sonar modeling results under predict historical wetting of the floodplain because corps dredging made the main channel approximately 13 wider from its historical width in 1941 further in the past few decades droughts and low flows have become more common because of varied upstream water uses resulting in less inundation than in the past frequent high flows are required to maintain river floodplain connectivity floodplain forests and other hydroecological functions in the apalachicola river floodplain our findings present a basis to assess the legacy of past and ongoing disturbances inform potential policy decisions for water and floodplain management and provide a baseline for further research

refinements of shear lag model and its applications abstract since it was developed by cox cox h l 1952 the elasticity and strength of paper and other fibrous materials br j appl phys 3 72 79 the shear lag model slm or fiber loading theory has been widely used by material scientists and structural geologists as a powerful analytical method for analyzing mechanical interactions between hard and soft phases layers in composites and two phase rocks we found that several approximations in previous mechanical derivations of the model can be improved in terms of mechanical equilibrium and boundary conditions our refinements make the model more rigorous and elaborate applications of the improved model include 1 prediction of the axial tensile stress in strong inclusions embedded in a continuous weak matrix and consequently interpretation of extension fracture boundinage 2 modeling of the distribution of shear stresses in the weak matrix surrounding the strong inclusions and accordingly interpretation of the variations of dislocation density and of recrystallized grain size in composites and polyphase rocks and 3 prediction of mechanical properties of industrial composites and two phase rocks the analytical results of the improved model agree approximately with those obtained from both experimental investigations and numerical calculations

new developments in deformation experiments at high pressure although the importance of rheological properties in controlling the dynamics and evolution of the whole mantle of earth is well recognized experimental studies of rheological properties and deformation induced microstructures have mostly been limited to low pressure conditions this is mainly a result of technical limitations in conducting quantitative rheological experiments under high pressure conditions a combination of factors is changing this situation increased resolution of composition and configuration of earth s interior has created a greater demand for well resolved laboratory measurement of the effects of pressure on the behavior of materials higher strength materials have become readily available for containing high pressure research devices and new analytical capabilities in particular very bright synchrotron x ray sources are now readily available to high pressure researchers one of the biggest issues in global geodynamics is the style of mantle convection and the nature of chemical differentiation associated with convectional mass transport although evidence for deep mantle circulation has recently been found through seismic tomography e g van der hilst et al 1997 complications in convection style have also been noted they include 1 significant modifications of flow geometry across the mantle transition zone as seen from high resolution tomographic studies fukao et al 1992 masters et al 2000 van der hilst et al 1991 and 2 complicated patterns of flow in the deep lower mantle 1500 2500 km perhaps caused by chemical heterogeneity kellogg et al 1999 van der hilst and karason 1999 these studies indicate that while large scale circulation involving the whole mantle no doubt occurs significant deviations from simple flow geometry are also present two mineral properties have strong influence on convection 1 density and 2 viscosity rheology contrasts in the past the effects of density contrast have been emphasized honda et al 1993 kellogg et al 1999 tackley et al 1993 and the influence of

flow laws of multiphase materials and rocks from end member flow laws abstract rheological properties of polyphase rocks play an important role in the dynamics of the lithosphere and asthenosphere however flow laws for large portions of the polyphase rocks in the earth s crust and mantle have not been well determined an analysis based on the theory of mixtures has been made to calculate the general flow laws of coarse 5 m nearly equant grained aspect ratio 3 and massive polyphase rocks and materials for which only the flow laws and volume fractions of the constituents are taken into consideration in the modeling of the bulk rheology and effects of microstructure could be ignored the theoretical analysis is based on three assumptions 1 the polyphase composite and the monophase aggregates of its constituents obey the same kind of flow laws linear power or exponential 2 there is no change in the operative deformation mechanism of each phase when it is in the composite as compared to when it is in a monophase aggregate and 3 neither chemical metamorphic reactions take place among the constituent phases nor eutectic melting occurs due to the phase mixing the proposed iterative process allows to predict to the first approximation the flow laws for a large number of polyphase rocks in terms of the experimentally determined flow laws of a relatively small number of monomineralic aggregates applications of this approach to typical polyphase rocks such as granite diorite diabase aplite and websterite as well as to synthetic two phase materials such as forsterite enstatite mixtures and water ice ammonia dehydrate aggregates yield quite accurate approximations to the experimental values