chemical studies of l chondrites vi variations with petrographic type and shock loading among equilibrated falls to study compositional trends associated with open and closed system metamorphism and or shock induced heating of the l4 6 chondrite parent s we used icpms and rnaa to quantify 51 trace elements in 48 chemically representative fall samples with these data we used graphic and two multivariate statistical methods for examining evidence for compositional differences with respect to petrographic type and degree of shock loading comparisons of mildly shocked s1 s3 l5 and l6 suites 9 and 8 chondrites respectively yield no convincing statistical evidence for a difference in trace element content our multivariate comparisons show a difference on a model dependent basis but yield indeterminate results on a model independent basis compositionally suites of strongly shocked s4 s6 and mildly shocked l4 6 chondrites 26 and 19 samples respectively can be distinguished at statistically significant levels on both model dependent and independent bases in the strongly shocked suite contents of refractory lithophiles are higher and siderophiles and volatiles are lower than those of the mildly shocked suite at moderately p 0 05 to highly significant p 0 01 levels our studies suggest that chemical differences from vaporization and loss of volatiles along with metal silicate partitioning are present from extended cooling of shock heated bodies produced by intermittent impacts especially the massive impact s that disrupted the l chondrite parent s 500 ma ago

is there a relationship between magmatic fabrics and brittle fractures in plutons a view based on structural analysis anisotropy of magnetic susceptibility and thermo mechanical modelling of the tanvald pluton bohemian massif abstract the present study focuses on the thermal and mechanical aspects of cooling of plutonic systems with respect to their internal structure analysis of the tanvald pluton and the nearby liberec granite the krkonose jizera plutonic complex bohemian massif using the anisotropy of magnetic susceptibility ams method indicates the decoupled magnetic fabrics formed by different processes in these two plutons two regional sets of vertical fractures cut across the plutons and their host rocks they are interpreted as having been formed as opening mode fractures joints after emplacement and cooling our thermo mechanical finite element modelling indicates that the thermal stresses within the tanvald pluton were compressive and that fracture criteria were not met during pluton cooling these results imply that the emplacement depth and confining pressure significantly affect the state of stress within a pluton during cooling and may play a crucial role in the formation of early fractures in plutons consequently the formation of early fractures during pluton cooling is driven by external conditions overriding the role of internal magmatic fabrics we argue that no genetic geometric or temporal correlation can exist between magmatic fabrics and fractures in granitoid plutons and thus that the original concept of hans cloos based on fabric joints relationships should be reconsidered instead an alternative classification of fractures in plutons should include cooling fractures syntectonic fractures uplift fractures and post uplift fractures

alluvial architecture of the holocene lower mississippi valley u s a and a comparison with the rhine meuse delta the netherlands abstract the proportion and arrangement of channel belt deposits in alluvial successions alluvial architecture is not known in detail for most modern settings therefore the alluvial architecture of the holocene lower mississippi valley lmv between greenville mississippi and baton rouge louisiana was studied to improve estimation of parameters relevant to alluvial architecture modeling alluvial architecture parameters sand body width thickness ratio sbw sbt channel belt deposit proportion cdp overbank deposit proportion odp and connectedness ratio cr are estimated from three cross valley sections based on lithologic borings sbw sbt and cdp decrease in a downstream direction for example cdp is 0 6 upstream and 0 3 downstream odp shows an opposite trend and is at a maximum 0 7 in the downstream part of the study area cr is low throughout the study area because most channel belts in our cross sections are unconnected the alluvial architecture in the lmv also seems to change over time because late holocene channel belts tend to be wider than the early holocene channel belts the observed trends in the alluvial architecture parameters are related to the ratio between channel belt width and floodplain width variations in aggradation rate location of the cross sections relative to avulsion sites and differential subsidence the alluvial architecture of the lmv is compared to that of the holocene rhine meuse delta to identify common controls on alluvial architecture despite differences in geographic setting the alluvial architecture of the lmv is similar to that of the rhine meuse delta we conclude that alluvial architecture of both fluvial systems is strongly controlled by channel belt geometry floodplain geometry and aggradation rate these in turn are influenced by extrinsic factors i e base level discharge sediment supply tectonics and pre existing topography as well as intrinsic factors i e lateral channel migration rate subsoil erodibility differential floodplain aggradation and avulsion mechanisms therefore the interaction between extrinsic and intrinsic factors should be considered in all alluvial architecture studies

evolution of the holocene mississippi river floodplain ferriday louisiana insights on the origin of fine grained floodplains abstract the alluvial architecture and soil characteristics of holo cene mississippi river floodplain deposits in the southern lower mississippi valley provide evidence for significant changes in floodplain development in response to sea level rise floodplain cores acquired near ferriday louisiana show that holocene deposits consist of 15 30 m ave 20 m of sands silts and clays which overlie late wisconsin sands and gravels on the basis of differences in sediment grain size sediment body geometry and the abundance of soil features the holocene deposits are subdivided into lower and upper holocene units lower holocene deposits 5000 yr b p consist of lacustrine and poorly drained backswamp muds that contain authigenic siderite pyrite and vivianite and show little evidence of soil formation muds encase crevasse splay and floodplain channel sand bodies 1 km wide and collectively these deposits represent a mosaic of shallow lakes poorly drained backswamps and multichannel streams similar to modern examples in the atchafalaya basin 100 km south of ferriday upper holocene deposits 5000 yr b p are represented by large mississippi river meander belt sand bodies that are up to 15 km wide and 30 m thick natural levee silts and sands and well drained backswamp muds are present between meander belt sands upper holocene deposits contain abundant soil features and sandy and silty soils are entisols inceptisols and alfisols whereas clayey soils are vertisols the presence of isolated sand bodies surrounded by mud and the scarcity of soil features suggest that lower holocene sediments reflect a period of rapid floodplain aggradation during which crevassing lacustrine sedimentation and avulsion dominated floodplain construction no evidence of large meandering mississippi river channels represented by buried thick tabular sands exists near ferriday and discharge in lower mississippi valley flow was probably conveyed by a network of small multichannel floodplain streams upper holocene sediments record a dramatic change ca 5000 yr b p from rapid to slower floodplain aggradation which was accompanied by extensive lateral channel migration overbank deposition and soil formation on the basis of differences in meander belt dimensions and numbers of abandoned channels upper holocene meander belts are subdivided into simple and complex forms relative age relationships suggest that the smaller and older simple meander belts represent periods of divided mississippi river flow and early attempts to establish a large single channel meandering regime this type of meandering regime is represented by the larger and younger complex meander belts and includes the modern meander belt similarities in the timing of changes in floodplain processes and fluvial style and decreasing rates of holocene sediment accumulation in the southern lower mississippi valley strongly suggest that decelerating holocene sea level rise in the gulf of mexico affected floodplain development at least 300 km inland from the present day coast the alluvial architecture of the lower holocene deposits and the absence of large meandering mississippi river channel deposits older than 5000 yr b p near ferriday indicates that most of the floodplain muds were deposited by avulsion related crevassing and lacustrine sedimentation rather than by overbank flooding of large mississippi river channels similarities between the floodplain history of the mississippi river and those of modern and ancient rivers elsewhere further suggest that avulsion rather than simple overbank deposition contributes to the construction of fine grained floodplains to a greater degree than generally recognized

timing of glaciation during the last glacial cycle evaluating the concept of a global last glacial maximum lgm abstract it has long been known that mountain glaciers and continental ice sheets around the globe reached their respective maximum extent at different times during the last glacial cycle often well before the global last glacial maximum lgm c 23 19 ka which is formally defined by peaks in global sea level and marine oxygen isotope records however there is increasing evidence from around the world that it was not only mountain glaciers which were asynchronous with the global lgm but also some regions of the large continental glaciers the barents kara ice sheet in northern eurasia together with a majority of ice masses throughout asia and australasia reached their maximum early in the last glacial cycle a few thousand years before the global lgm period the east antarctic ice sheet also reached its maximum extent several millennia before the global lgm in numerous mountainous regions at high mid and low latitudes across the world glaciers reached their maximum extent before marine isotope stage mis 2 in mis 5 4 and 3 this is in contrast to most sectors of the laurentide ice sheet the cordilleran ice sheet the se sector of the fennoscandinavian ice sheet and the alpine ice sheet in central europe which appear to have reached their maximum close to the global lgm in mis 2 the diachronous maximum extents of both mountain glaciers and continental ice sheets during the last glacial cycle means that the term and acronym last glacial maximum lgm has limited chronostratigraphical meaning when correlating glacial deposits and landforms

sedimentology and hydrogeology of two braided stream deposits abstract two approaches were used to quantify the spatial distribution of hydrofacies in braided stream deposits one approach involved mapping a 50 by 60 by 3 3 m section of a proximal braided stream deposit in a second study we generated a 400 by 400 by 2 6 m section of a medial braided stream deposit using a computer model in both cases we produced three dimensional images showing connected hydrofacies with high permeabilities that form preferential flow paths this information was input to a groundwater flow model and flow paths were analyzed by following the transport of imaginary particles in both systems particles that were uniformly distributed at the up gradient end of the model clustered along preferential flow paths during transport showing that connection among high permeability facies is a critical factor in hydrogeological investigations involving assessment of contaminant movement and remediation

process of magnetite fabric development during granite deformation this study evaluates the fabric defined by magnetite grains in a syntectonically deformed granite and deciphers the processes that led to magnetite fabric development anisotropy of anhysteretic re

chemical studies of h chondrites 8 on contemporary meteoroid streams using date and time of fall and petrographic classification as criteria many equilibrated h chondrites that fell during september and october from 1812 to the present form four significant clusters denoted as cluster 2 through cluster 5 on day year plots using radiochemical neutron activation analysis we determined 15 trace elements u au co sb ga rb ag se cs te zn cd bi tl and in ordered by increasing putative volatility during nebular condensation in 27 members of these four clusters we used model dependent and model independent multivariate statistical techniques to compare contents of the 10 most volatile elements separately in the four clusters with those of a 33 member suite of random h chondrite falls from 1773 to 1970 the clusters 2 and 5 suites that fell in september 1880 1991 and october 1919 1984 respectively each of which is represented by 10 h chondrite falls are not compositionally distinguishable from the suite of random falls however the 17 member combined suite of clusters 3 and 4 chondrites that fell during september october 1812 1992 proves compositionally distinguishable from random falls at moderate to strong significance levels of 0 01 0 001 this 17 member suite is less readily distinguished from random falls than are the previously reported suite of cluster 1 falls may 1855 1895 or antarctic h chondrites with nominal terrestrial ages 50 kyr each of which is highly significant at 0 001 levels all suites are genomict and exhibit a range of cosmic ray exposure ages with a plurality having 6 8 ma ages inconclusive results are obtained in the cases of clusters 2 and 5 however three h chondrite suites clusters 1 3 and 4 distinguishable from the random background by one property time of fall are also distinguishable by another contents of volatile trace elements or thermal history temporal change of h chondrite sources sampled by earth are indicated by these data

silver isotope variations in chondrites volatile depletion and the initial 107pd abundance of the solar system abstract the extinct radionuclide 107pd decays to 107ag half life of 6 5 ma and is an early solar system chronometer with outstanding potential to study volatile depletion in the early solar system here a comprehensive ag isotope study of carbonaceous and ordinary chondrites is presented carbonaceous chondrites show limited variations e107ag 2 1 to 0 8 in ag isotopic composition that correlate with the pd ag ratios assuming a strictly radiogenic origin of these variations a new initial 107pd 108pd of 5 9 2 2 10 5 for the solar system can be deduced comparing the pd ag and mn cr data for carbonaceous chondrites suggests that mn cr and pd ag fractionation took place close to the time of calcium aluminium rich inclusion cai and chondrule formation 4568 ma ago using the new value for the initial 107pd abundance the revised ages for the iron rich meteorites gibeon iva 8 5 3 2 4 6 ma grant iiiab 13 0 3 5 4 9 ma and canyon diablo ia 19 5 24 1 10 4 ma are consistent with cooling rates and the closure temperature of the pd ag system in contrast to carbonaceous chondrites ordinary chondrites show large stable isotope fractionation of order of 1 permil for 107ag 109ag this indicates that different mechanisms of volatile depletion were active in carbonaceous and ordinary chondrites nebular processes and accretion as experienced by carbonaceous chondrites did not led to significant ag isotope fractionation while the significant ag isotope variations in ordinary chondrites are most likely inflicted by open system parent body metamorphism

silver contents and cu ag ratios in martian meteorites and the implications for planetary differentiation abstract silver and cu show very similar partitioning behavior in sulfide melt silicate melt and metal silicate systems at low and high pressure temperature p t experimental conditions implying that mantle melting fractional crystallization and core mantle differentiation have at most modest within a factor of 3 effects on cu ag ratios for this reason it is likely that cu ag ratios in mantle derived magmatic products of planetary bodies reflect that of the mantle and in some circumstances also the bulk planet composition to test this hypothesis new ag mass fractions and cu ag ratios in different groups of martian meteorites are presented and compared with data from chondrites and samples from the earth s mantle silver contents in lherzolitic olivine phyric and basaltic shergottites and nakhlites range between 1 9 and 12 3 ng g the data display a negative trend with mgo content and correlate positively with cu contents in spite of displaying variable initial 143 nd values and representing a diverse spectrum of magmatic evolution and physiochemical conditions shergottites and nakhlites display limited variations of cu ag ratios 1080 320 1 s n 14 the relatively constant cu ag suggests limited fractionation of ag from cu during the formation and evolution of the parent magmas irrespectively of whether sulfide saturation was attained or not the mean cu ag ratio of martian meteorites thus reflects that of the martian mantle and constrains its ag content to 1 9 0 7 ng g 1 s carbonaceous and enstatite chondrites display a limited range of cu ag ratios of mostly 500 2400 ordinary chondrites show a larger scatter of cu ag up to 4500 which may have been caused by ag redistribution during parent body metamorphism the majority of chondrites have cu ag ratios indistinguishable from the martian mantle value indicating that martian core formation strongly depleted cu and ag contents but probably did not significantly change the cu ag ratio of the mantle compared to bulk mars bulk mars is richer in moderately volatile elements than earth however the martian mantle displays a much stronger depletion of the moderately volatile elements cu and ag e g by a factor of 15 for cu this observation is consistent with experimental studies suggesting that core formation at low p t conditions on mars led to more siderophile behavior of cu and ag than at high p t conditions as proposed for earth in contrast cu ag ratios of the mantles of mars and earth cu ag earth 3500 1000 display only a difference by a factor of 3 which implies restricted fractionation of cu and ag even at high p t conditions the concentration data support the notion that siderophile element partitioning during planetary core formation scales with the size of the planetary body which is particularly important for the differentiation of large terrestrial planets such as earth collectively the ag and cu data on magmatic products from the mantles of mars and earth and the data on chondrites confirm experimental predictions and support the limited fractionation of cu and ag during planetary core formation and high temperature magmatic evolution and probably also in early solar nebular processes

late pleistocene glacial equilibrium line altitudes in the colorado front range a comparison of methods abstract six methods for approximating late pleistocene pinedale equilibrium line altitudes elas are compared for rapidity of data collection and error rmse from first order trend surfaces using the colorado front range trend surfaces computed from rapidly applied techniques such as glaciation threshold median altitude of small reconstructed glaciers and altitude of lowest cirque floors have relatively high rmses 97 186 m because they are subjectively derived and are based on small glaciers sensitive to microclimatic variability surfaces computed for accumulation area ratios aars and toe to headwall altitude ratios thars of large reconstructed glaciers show that an aar of 0 65 and a thar of 0 40 have the lowest rmses about 80 m and provide the same mean ela estimate about 3160 m as that of the more subjectively derived maximum altitudes of pinedale lateral moraines rmse 149 m second order trend surfaces demonstrate low elas in the latitudinal center of the front range perhaps due to higher winter accumulation there the mountains do not presently reach the ela for large glaciers and small front range cirque glaciers are not comparable to small glaciers existing during pinedale time therefore pleistocene ela depression and consequent temperature depression cannot reliably be ascertained from the calculated ela surfaces

spatial and temporal distribution of sand containing basin fills in the holocene rhine meuse delta the netherlands the quantitative significance of coarse grained deposits in the overbank realm such as crevasse splay deposits has not been studied at the delta scale or at the holocene timescale such knowledge would be beneficial for understanding and explaining sediment distribution in delta plains this study addresses delta scale distribution of sand containing basin fills and their sand body proportion variability based on eight valleywide cross sections in the holocene rhine meuse delta in the netherlands we found that sand containing basin fills form 7 1 of the fluviodeltaic wedge of which splay deposits are most frequently observed midway between the delta apex and the coast organic clastic lake fills and bay head delta deposits in contrast are limited to the distal delta plain over four successive periods between 9000 and 800 cal yr bp the largest proportions of splay deposits remain at 50 150 km downstream of the upstream shifting delta apex we show that intermediate floodbasin widths between 3 1 and 3 6 km in the holocene rhine meuse delta yield the highest proportions of splay deposits high rates of base level rise and wide floodplains both facilitate the creation of accommodation which in turn provides conditions for peat forming wetlands in which organic clastic lake fills can develop the results show that sand bodies form 26 30 of sand containing basin fills this proportion is shown to be controlled by among other variables channel planform and superelevation of the trunk channel and substrate composition we conclude that potentially large volumes of nonchannel sand bodies exist in distal delta plains they constitute up to 39 of the reservoir volume in the distal rhine meuse delta and yield relatively high connectedness ratios 2011 by the university of chicago all rights reserved

the central iberian arc an orocline centered in the iberian massif and some implications for the variscan belt an arcuate structure comparable in size with the ibero armorican arc is delineated by variscan folds and magnetic anomalies in the central iberian zone of the iberian massif called the central iberian arc its sense of curvature is opposite to that of the ibero armorican arc and its core is occupied by the galicia tras os montes zone of nw iberia which includes the rheic suture other zones of the iberian massif are bent by the arc but the ossa morena and south portuguese zones are not involved the arc formed during the late carboniferous at final stages of thermal relaxation and collapse and an origin related with right lateral ductile transpression at the scale of the variscan belt is proposed the central iberian arc explains the width of the central iberian zone clarifies the position of the allochthonous terranes of nw iberia and opens new perspectives for correlations with the rest of the variscan belt in particular with the armorican massif whose central zone represents the continuation of the southwest branch of the arc detached by strike slip tectonics

chemical studies of h chondrites 11 cosmogenic radionuclides in falls 1 we measured the long lived cosmogenic radionuclides 10be 26al and 36cl in 47 h chondrite falls 13 cluster 1 members 9 cluster 5 members and 25 random falls from the date and time of fall clusters 1 and 5 were previously identified as possible coorbital meteoroid streams with distinctive thermal histories being confirmed by contents of volatile trace elements here we use model data including a three radionuclide plot 10bebulk 26albulk versus 36clmetal 26albulk and the multivariate statistical techniques of logistic regression and linear discriminant analysis to compare radionuclide levels and their utility to differentiate specific suites from other h chondrites from our radionuclide results and from noble gas data from other workers we identified 35 falls with simple irradiation histories and cosmic ray exposure ages 4 ma eight others exhibit evidence for shorter 4 ma exposure three of which had complex exposure histories two having been reported by others previously three others may have had such a history in any event the small proportion of h chondrite falls with complex exposure histories supports recent suggestions that they are not commonly encountered as earlier workers suggested although cosmogenic radionuclides do not differentiate between cluster 1 and a random set of h chondrites h chondrites that lost 3he from solar heating are distinguishable from those with normal 3he levels

multistage magma emplacement and progressive strain accumulation in the shallow level krkonose jizera plutonic complex bohemian massif 1 field relationships combined with new u pb zircon geochronology suggest that the shallow level krkonose jizera plutonic complex northern bohemian massif was assembled successively from bottom to top starting with emplacement of the separately evolved s type tanvald granite 317 3 2 1 ma followed by at least two voluminous batches of the i type porphyritic liberec 319 5 2 3 ma and jizera 320 1 3 0 ma and 319 3 3 7 ma granites the intrusive sequence was completed by uppermost minor intrusions of the equigranular harrachov 315 0 2 7 ma and krkonose granites the i type granites exhibit an unusually complex pattern of superposed feldspar phenocryst and magnetic fabrics as revealed from the anisotropy of magnetic susceptibility ams the outer liberec granite preserves margin parallel foliations and lineations interpreted to record emplacement related strain captured by cooling from the pluton floor and walls in contrast the inner jizera harrachov and krkonose granites were overprinted by synmagmatic strain resulting from dextral movements along regional strike slip faults cutting the opposite ends of the plutonic complex late stage felsic dikes in the liberec and jizera granites reorient from horizontal to vertical lineation perpendicular attitude in response to changing the least principal stress direction whereas mafic schlieren do not do so representing only randomly oriented small scale thermal mechanical instabilities in the phenocryst framework in general this case example challenges the common approach of inferring pluton wide magma flow from interpolated foliation lineation and schlieren patterns more likely magmatic fabrics in large plutons record complex temporal succession of superposed strains resulting from diverse processes at multiple scales

surprisingly small increase of the sedimentation rate in the floodplain of morava river in the stražnice area czech republic in the last 1300 years abstract sediment profiles from the floodplain of morava river in the czech republic have been collected from exposed river banks 4 6 m long sections and cores 2 4 m deep and investigated using a set of geochemical proxies validated by granulometry and conventional geochemical analysis outlined in our previous paper the work was conducted to evaluate the increase in sedimentation rate during medieval and modern time periods correlation of sediments along the current channel belt allows identification of two most important synchronous changes in the channel structure over the past 1300 years in the 13th century and at the end of the 16th century these changes could be related to central european climatic extremes rather than to land cover land use practises analysis of the pollen record in peaty deposits at the floodplain edge allows excluded dramatic deforestation in medieval times maps of the area from the last five centuries revealed direct and indirect signs of past avulsions and clearly show how the original multichannel system was transformed into a single meandering channel in the early 20th century the extrapolated aggradation rate net vertical accretion of floodplain fines except for levee sediments increased from 0 2 0 3 cm year in 700 ad to 0 3 0 4 cm year in 2000 ad depending on the grain size of the sediment this is the smallest yet reported enhancement of siliclastic deposition although morava river watershed has been intensively used for agriculture and its land cover has changed in a manner similar to west and central european rivers

collisional history of h chondrites the cosmic ray exposure histories of ordinary chondrites were recently reviewed marti and graf 1992 here we discuss in detail currently available cosmic ray exposure records and the adopted exposure ages of individual h chondrites we further present analyses of the distinct histograms of petrographic subgroups and the implications for orbital evolution and collisional records in addition to the stochastic events 7 to 8 m y ago a peak at 33 ma represents a statistically significant deviation from an exponential age distribution and signals a major collisional event at this time the h6 subgroup also recorded a similar event 24 m y ago these records present significant arguments against a continuous supply of h chondrites from the asteroid belt we show that the records of fall times for h5s are distinct from other subgroups and that a different orbit for the h5 parent is indicated in collisional events 7 to 8 m y ago the systematics of noble gas losses in the h5 subgroup are consistent with this interpretation the evidence for stochastic fragmentation and subsequent delivery to earth of h chondrites suggests that their present predominance among falls may represent a deviation from a representative population distribution

chemical studies of h chondrites i mobile trace elements and gas retention ages abstract trends for 16 trace elements ag as au bi cd co cs ga in k rb sb se te tl and zn chosen to span a broad geochemical and thermal response range in 44 h4 6 chondrites differ widely from those in l4 6 chondrites in particular h chondrites classified as heavily shocked petrologically do not necessarily exhibit 40 ar loss and vice versa the clear cut causal relationship between siderophile and mobile element loss with increasing late shock seen in l chondrites is not generally evident in the h group h chondrite parent material experienced an early high temperature genetic episode that mobilized a substantial proportion of these trace elements so that later thermal episodes resulted in more subtle collateral fraction ations mildly shocked l chondrites escaped this early high temperature event indicating that the two most numerous meteorite groups differ fundamentally in genetic history

a 100 kyr periodicity in the flux of extraterrestrial 3he to the sea floor most of the helium 3 in oceanic sediments comes from interplanetary dust particles idps and can therefore be used to infer the accretion rate of dust to the earth through time 3he records from slowly accumulating pelagic clays indicate that the accretion rate varies considerably over millions of years probably owing to cometary and asteroidal break up events muller and macdonald have proposed that periodic changes in this accretion rate due to a previously unrecognized 100 kyr periodicity in the earth s orbital inclination might account for the prominence of this frequency in climate records of the past million years here we report variations in the 3 he flux to the sea floor that support this idea we find that the flux recorded in rapidly accumulating quaternary sediments from the mid atlantic ridge oscillates with a period of about 100 kyr we cannot yet say however whether the 100 kyr climate cycle is a consequence of a cause of or an effect independent of these periodic changes

palaeozoic amalgamation of central europe new results from recent geological and geophysical investigations abstract multidisciplinary studies of geotransects across the north european plain and southern north sea and geological reexamination of the variscides of the north bohemian massif permit a new 3 d reassessment of the relationships between the principal crustal blocks abutting baltica along the trans european suture zone tesz accretion was in three stages cambrian accretion of the bruno silesian lysogory and malopolska terranes end ordovician early silurian accretion of avalonia and early carboniferous accretion of the armorican terrane assemblage ata palaeozoic plume influenced metabasite geochemistry in the bohemian massif explains the progressive rifting away of peri gondwanan crustal blocks before their accretion to baltica geophysical data faunal and provenance information from boreholes and dated small inliers and cores confirm that avalonian crust extends beyond the anglo brabant deformation belt eastwards to northwest poland the location and dip of reflectors along the tesz and beneath the north european plain suggest that avalonian crust overrode the baltica passive margin marked by a high velocity lower crustal layer on shallowly southwest dipping thrust planes forming the heligoland pomerania deformation belt the variscan orocline of southwest poland masks two junctions between the armorican terrane assemblage ata and previously accreted crustal blocks to the east is a dextrally transpressive contact with the bruno silesian and malopolska blocks accreted in the cambrian while to the north is a thrust contact with easternmost avalonia deeply buried beneath younger sedimentary cover in the northeast bohemian and rhenohercynian massifs devonian early variscide deformation dominated by wnw and nw directed thrusting records closure of ordovician devonian seaways between detached islands of the ata and avalonia

emplacement setting of the granite sheeted pluton of esperanca brasiliano orogen northeastern brazil abstract anisotropy of magnetic susceptibility ams and isotopic u pb sm nd data were combined to study the emplacement setting of the granite sheets that constitute the esperanca pluton in the borborema province northeastern brazil the sheets dip moderately to the se along the contact zone between the paleoproterozoic basement rocks and early neoproterozoic orthogneisses and metasediments granite fabrics were determined mainly using ams in 136 sites distributed within the central and western part of the pluton the sheets normally have susceptibility lower than 0 35 msi but locally where a ti poor magnetite appears with titanite the susceptibility increases up to 5 msi comparison between the silicate fabric and ams showed inconsistencies between the shape of mineral and magnetic ellipsoids despite of their orientations that fit fairly well to each other ams indicated the deformation was partitioned between the lower tonalite syenogranite and upper leucogranite and coarse porphyritic granite sheets in the lower sheets the curvilinear lineation trajectory is attributed to a dominant heterogeneous pure shear event that flattened laterally the still molten tonalite and syenogranite into the regional foliation the associated microstructures are typically magmatic zircon u pb data of the syenogranite yielded a crystallization age of 592 5 ma in the upper sheets the fabric recorded a component of simple shear deformation that displaced the coarse porphyritic granite and the top gneissic host rocks to the southwest microstructures are mostly of post full crystallization type tdm model ages and nd t 0 values indicate that the magma contaminated by partial melting of the regional host rocks sheet propagation at the emplacement level would have exploited the contact zone between crustal blocks of different rheologies when the melt pressures would be able to tensionally fail the anisotropy of the host rocks

magmatic fabric acquisition mechanisms in a syenite results of a combined anisotropy of magnetic susceptibility and image analysis study the structural significance of the anisotropy of magnetic susceptibility ams and acquisition mechanisms of silicate and ferrimagnetic mineral fabrics are investigated in the archean lebel syenite intrusion ontario canada bulk mineral subfabrics are determined by intercept counting of mineral phases in classified digital images of thin sections cut parallel to the principal planes of the magnetic fabric ellipsoids of the samples intensities shapes and principal direction orientations of the resulting intercept ellipsoids are generally similar to the corresponding ams ellipsoids differences are due mainly to bimodal distribution of mineral fabrics observed on foliation planes of some samples showing pre full crystallization textures and structural overprinting in samples deformed after crystallization subfabrics of clinopyroxene and magnetite in samples showing pre full crystallization microstructure are investigated by measuring inertia tensors of individual grain shapes the resulting inertia tensor ellipsoids indicate that magnetic fabrics in these rocks are strongly correlated to the shape preferred orientation of magnetite which is similar to the overall petrofabric of the samples crystal size distributions of clinopyroxene and magnetite indicate that they formed during in situ crystallization and that magnetite probably appeared late in the crystallization and flow history of the magma analysis of preferred orientations of these grains suggests that the petrofabrics of the samples were acquired during flow with strongly interacting grains analogous to a logjam in a river the final characteristics of the ams and silicate petrofabric are the end points of a continuous crystallization and flow history in the magma rather than transient late features

glacial cirques as palaeoenvironmental indicators their potential and limitations abstract glacial cirques are armchair shaped erosional hollows typified by steep headwalls and often overdeepened floors they reflect former regions of glacier initiation and their distribution is therefore linked to palaeoclimate because of this association cirques can be analysed for the information they provide about past environments an approach that has a strong heritage and has seen resurgence over recent years this paper provides a critical assessment of what cirques can tell us about past environments and considers their reliability as palaeoenvironmental proxies specific focus is placed on information that can be obtained from consideration of cirque distribution aspect altitude and morphometry the paper highlights the fact that cirques potentially provide information about the style duration and intensity of former glaciation as well as information about past temperatures precipitation gradients cloud cover and wind directions in all cirques are considered a valuable source of palaeoenvironmental information if used judiciously particularly as they are ubiquitous within formerly glaciated mountain ranges globally thus making regional or even global scale studies possible furthermore cirques often occupy remote and inaccessible regions where other palaeoenvironmental proxies may be limited or lacking

cirque overdeepening and their relationship to morphometry abstract shape and size characteristics of cirques and their changes and mutual relationships include not only spatial and descriptive aspects but also genetic attributes the goals of this article were to define an application of k curve sensu haynes 1968 that describes the extent of cirque overdeepening and to identify k curve equation input variables the k values depend on the profile location and hence a clear definition of the cirque profile position is necessary therefore ideal profiles were delineated through the steepest part of the cirque headwall k steepest k s or through a point on the cirque crest that had a maximal elevation k highest k h knowledge of the cirque headwall height allows for the mathematical theoretical calculation of cirque overdeepening i e the maximum depth of the cirque floor sedimentary filling of the cirque floor further the goal of this study was to analyse and compare cirque classification methods according to the extent of overdeepening and standard morphometric characteristics as a training data set 27 example cirques of the bohemian massif giant mts sumava mts and hrub jesenik mts and a total of 12 morphometric characteristics were used in the analyses cirques were classified into two groups using cluster analysis based on the extent of overdeepening k values k h and k s a mutual relationship between cluster analysis classifications and classifications based on morphometric characteristics l w h and 3d 2d was determined using general discriminant analysis the classification of cirques based on other characteristics corresponded closely in total 81 for the first group and the cross validation group with cirque classifications based on the degree of overdeepening k value

geomorphological and sedimentary evidence of probable glaciation in the jizerske hory mountains central europe abstract the jizerske hory mountains in the czech republic have traditionally been considered to be a highland that lay beyond the limits of quaternary glaciations recent work on cirque like valley heads in the central part of the range has shown that niche glaciers could form during the quaternary here we report geomorphological and sedimentary evidence for a small glacier in the pytlacka jama hollow that represents one of the most enclosed valley heads within the range shape and size characteristics of this landform indicate that the hollow is a glacial cirque at a degraded stage of development boulder accumulations at the downslope side of the hollow probably represent a relic of terminal moraines and the grain size distribution of clasts together with micromorphology of quartz grains from the hollow indicate the glacial environment of a small glacier this glacier represents the lowermost located such system in central europe and provides evidence for the presence of niche or small cirque glaciers probably during pre weichselian glacial periods the glaciation limit 1000 m asl and paleo ela 900 m asl proposed for the jizerske hory mountains implies that central european ranges lower than 1100 m asl were probably glaciated during the quaternary

geochronology and nd sr systematics of lusatian granitoids significance for the evolution of the variscan orogen in east central europe a variety of pre variscan granitoids and two variscan monzogranites occurring in the central and western parts of the lusatian granodiorite complex lgc saxonia were dated by the single zircon evaporation method complemented by whole rock nd isotopic data and rb sr whole rock and mineral ages the virtually undeformed pre variscan granitoids constitute a genetically related mostly peraluminous magmatic suite ranging in composition from two mica granodiorite muscovitebearing biotite quartz diorite tonalite and granodiorite to biotite granodiorite and monozogranite

geomorphological facies reconstruction of late quaternary alluvia by the application of fluvial architecture concepts abstract this paper investigates the methodical implications the benefits and the constraints of applying the fluvial architecture concept to late quaternary shallow subsurface alluvial deposits the focus is upon a typical small to mesoscale valley floor of the temperate zone the studied reach is part of the river wetter catchment 517 km 2 in central germany a large number of studies on late quaternary terrestrial paleoenvironmental change of the temperate zone refer to such small to mesoscale catchments which are mostly occupied by mixed to suspended load rivers as in many cases mostly coring based evidence is available the observation and measurement is limited to lithology and lithofacies boundaries facies geometry must be inferred moreover in those environments differences in lithofacies are obscured by a significantly reduced range of grain size distributions an example of an ancient channel belt of late glacial to holocene age serves to delineate the methodical practice and utility of the fluvial architecture approach field evidence is obtained from detailed cross sectional surveys and comprises descriptions of lithofacies structural pedogenetical biotic features munsell color and total organic carbon magnetic volume susceptibility cross sectional lithofacies information is represented by spatially attributed scaled borehole logs the example also accentuates the need for applying additional stratigraphical methods such as physical age determination macrofossil analysis and tephrological stratigraphy these methods form the basis to discern stacked channel facies and derive a diachrony of channel forms thus the adapted architecture approach provides a significant surplus of information on channel dimensions ages and channel floodplain interconnectedness distinct fluvial landforms such as channels levees abandoned channels swamps and floodplain flats can be highlighted a number of methodical constraints are discussed in detail e g the sharpness of channel element geometry and the underlying ordering of bounding surfaces moreover it is shown that the analytical process resembles an iterative looping process that is led by deduction many geomorphologists and multi disciplinary floodplain researchers collect sedimentary data but still neglect utilizing the potential of architectural analysis the study makes clear that sedimentological approaches used in big river floodplains also apply to small valleys in fact the procedures for facies reconstruction need to be adjusted to each individual case study alluvial architecture analysis provides the tools to reveal interconnectedness or disconnectedness of channel near channel and overbank fluvial landforms which is essential for a geomorphological understanding of floodplain evolution

10be exposure age chronology of the last glaciation in the krkonose mountains central europe abstract a new chronology of the last glaciation is established for the krkonose giant mountains central europe based on in situ produced 10be in moraine boulders exposure ages and schmidt hammer rebound values obtained for terminal moraines on the northern and southern flank of the mountains suggest that the oldest preserved moraines represent early phases of the last glacial maximum lgm large moraines at the outlet of the snowy cirques niezne kotly and in the middle part of the upa ob i d l trough were deposited around 21 ka while a series of smaller moraines above the lgm deposits represent readvances that occurred no later than 18 1 0 6 ka 15 7 0 5 ka 13 5 0 5 ka and 12 9 0 7 ka an exposure age of 13 8 0 4 ka obtained for protalus ramparts at the foot of the upska jama cirque headwall indicates that glaciers advanced only in north to east facing cirques during the lateglacial the last glacier fluctuation was synchronous with the younger dryas cold event the timing of local glacier advances during the last glacial episode correlates with the late weichselian glacier phases in the alps and in the bavarian bohemian forest

classification of poorly sorted sedimentary rocks abstract the classification and nomenclature of sandstones has evolved over the years into a system which is now generally accepted as standard however no equivalent system exists for the poorly sorted sedimentary rocks which include grain sizes from clay to gravel a descriptive classification is proposed based on an earlier system but using updated nomenclature and lithological fields such a scheme is needed to clearly define lithological terms currently used in the description of sedimentary sequences

are the oroclines of the variscan belt related to late variscan strike slip tectonics terra nova 23 241 247 2011 abstract early variscan structures and magnetic anomalies delineate four oroclines along the variscan belt the arcs bend the lithostratigraphic zones of the autochthon and the allochthonous terranes which include ophiolites of the rheic suture and units of gondwanan derivation subducted on both sides of the rheic ocean a transcurrent model dominated by right lateral motion explains the genesis and evolution of the oroclines and a simple plate tectonics scenario links late variscan dextral strike slip movements in the variscides to a broad intracontinental shear zone kinematically equivalent to a transform fault terra nova 00 1 7 2011

application of indicator simulation to modelling the lithological properties of a complex confining layer abstract this paper describes a three dimensional simulation of the texture distribution of a complex confining layer indicators are used to characterize statistically the spatial variability of the different texture classes sequential indicator simulation is then used to generate equiprobable realisations of texture classes conditional on the textures found at the drilling sites by successively assigning values for conductivities and porosities to the simulated texture classes fields of conductivities and porosities can be obtained these can in turn be used as input for a groundwater model in a monte carlo analysis a case study is presented to demonstrate the application of sequential indicator simulation to the stochastic modelling of the texture distribution of a complex confining layer in the netherlands the results are validated using the data from a lithological cross section with a very small borehole spacing

10 be exposure age chronology of the last glaciation of the rohacska valley in the western tatra mountains central europe abstract 10 be exposure ages from moraines and bedrock sites in the rohacska valley provide chronology of the last glaciation in the largest valley of the western tatra mts the western carpathians the minimum apparent exposure age of 19 4 2 1 ka obtained for the oldest sampled boulder and the mean age of 18 0 0 8 ka calculated for the terminal moraine indicate that the oldest preserved moraine was probably deposited at the time of the global last glacial maximum lgm the age of this moraine coincides with the termination of the maximum glacier expansion in other central european ranges including the adjacent high tatra mts and the alps the equilibrium line altitude ela of the lgm glacier in the rohacska valley estimated at 1400 1410 m a s l was 50 80 m lower than in the eastern part of the range indicating a positive ela gradient from west to east among the north facing glaciers in the tatra mts lateglacial glacier expansion occurred no later than 13 4 0 5 ka and 11 9 0 5 ka as indicated by the mean exposure ages calculated for re advance moraines this timing is consistent with the exposure age chronology of the last lateglacial re advance in the high tatra mts alps and lower mountain ranges in central europe the ela in the rohacska valley estimated at 1690 1770 m a s l in this period was located 130 300 m lower than in the north facing valleys in the high tatra mts 10 be exposure ages obtained for a rock glacier constrains the timing of this landform stabilization in the salatinska valley and provides the first chronological evidence for the lateglacial activity of rock glaciers in the carpathians

nivation forms and processes in unconsolidated sediments ne greenland in the periglacial unconsolidated sediment landscape of zackenberg in high arctic ne greenland perennial and seasonal snowpatches dominate the geomorphological development in large areas and control the distribution of the vegetation the existence and distribution of snowpatches and their associated landforms are mainly controlled by the dominating winter wind direction and the amount of snow precipitation with aspect exerting much less influence this makes them an important source of information on past environmental change and knowledge of the combination of geomorphological processes and forms that result from their existence is thus essential the main nivation processes are backwall failure sliding and flow niveo aeolian sediment transport supra and ennival sediment flows niveo fluvial erosion development of pronival stone pavements accumulation of alluvial fans and basins and pronival solifluction the importance of failure sliding and flow in the continuous retrogressive extension of nivation hollows and niches is emphasized under the term backwall failure a morphological assemblage of landforms clearly demonstrates the direct nival sediment transfer link between the eroded nivation hollows their associated meltwater eroded channels and the pronival alluvial fans or basins all landform elements and their formative processes are integrated into a comprehensive model 1998 john wiley sons ltd

modeling hydraulic conductivity of a complex confining layer at various spatial scales the spatial variation of the hydraulic conductivity of a complex confining layer in the netherlands is modeled at four different scales the scale of sediment cores 10 1 100 m the scale of the numerical model blocks 101 102 m the local scale 102 103 m and the regional scale 103 105 m two stochastic methods are combined 1 conditional multiple indicator simulation of texture classes to obtain three dimensional images of the lithology of the confining layer from borehole descriptions and 2 the statistical upscaling procedure of indelman and dagan 1993a b to derive the first and second order statistics of hydraulic conductivities at the scale of the numerical model blocks when the upscaling of the core scale conductivities is ignored the local and regional scale groundwater flow through the confining layer is predicted wrongly

quantifying the impact of former glaciation on catchment wide denudation rates derived from cosmogenic10be glacial denudation can significantly perturb terrestrial cosmogenic nuclide depth profiles and if this is not corrected for derived apparent denudation rates will overestimate the actual denudation rates here we determine how much 10be derived denudation rates calculated under the assumption of steady state deviate from actual denudation rates as a function of three parameters 1 the total amount of glacial denudation 2 the post glacial denudation rate and 3 the time elapsed since deglaciation we provide correction lines for the full parameter space explored glacial denudation 0 01 100 m post glacial denudation rate 1 1000 mm ka deglaciation 1 100 ka before present to evaluate and if necessary correct denudation rates for the impact of glacial denudation applied to 10be derived catchment averaged denudation rates for formerly glaciated catchments in the black forest germany we find that uncorrected denudation rates overestimate actual rates by up to a factor of three

recognition of the sedimentary architecture of dryland anabranching anastomosing rivers abstract the application of rigorous criteria for identifying fluvial style from sedimentary deposits is crucial if environmental reconstructions from stratigraphy are to be reliable from modern observations it appears that anabranching anastomosing rivers can be divided into separate humid and dryland classes each class has dissimilar characteristics to the other necessitating different criteria for their recognition in the rock record the criteria being used by sedimentologists to recognize deposits of anabranching rivers are derived solely from modern examples in humid regions heavily biased to a few specific cases in canada these criteria are dominated by the concept of ribbon sandstone bodies encased in fine grained floodplain sediment with an overall low sand to mud ratio in the succession there has been a general failure to appreciate that dryland anabranching rivers have characteristics significantly different from these and almost certainly leave a sedimentary record quite dissimilar to that previously expected avulsion or obtrusion the gradual formation of an alternative channel are the characteristic dynamic of anabranching rivers forming and maintaining coexisting multiple anabranch channels avulsion or obtrusion require stream banks to have a high resistance to erosion usually achieved by cohesive bank sediments or the reinforcement of banks by vegetative root mats in some drylands riparian vegetation can be sparse and bank resistance may depend in large part on a high clay content here channel fills are mud dominated and floodplains have a uniform fine grained character which is usually structureless because of intense pedoturbation and some bioturbation the evidence from such present day dryland anabranching rivers suggests that their sedimentary record is likely to be one of laterally extensive mud rich beds with weak or enigmatic fluvial indicators elsewhere dryland anabranching systems are sand dominated their banks reinforced with riparian gallery forests sustained by infrequent flow and a shallow water table though the stratigraphy of these has barely been investigated they are clearly different from humid region anabranching systems for their channels and islands are predominantly sandy anabranching rivers with prominent channel sandbodies separated by muddy islands have never been described from contemporary drylands the interpretation of a dryland origin for ancient stratigraphic successions with this form is made therefore without evidence that they can actually exist in the light of this such interpretations should be reevaluated

noble gases and h chondrite meteoroid streams no confirmation eleven meteorites suggested to belong to a meteoroid stream of 17 h chondrites cluster 1 have been analyzed for their noble gases together with literature data the noble gas record of all these stones is discussed cluster 1 chondrites belong to different chemical petrologic types and three are regolith breccias as proven by solar type gases the thermal history of the parent body of cluster 1 stones is not the same for all as seen in the radiogenic 40ar and diffusive loss of helium in four of them suggests small perihelion distances for these specimens and thus different orbits from the rest of this group exposure ages vary between about 4 and 70 ma thus the orbital elements of the stream must have been undisturbed for about 70 ma the exposure age distribution of cluster 1 chondrites is not distinct from that of normal h chondrites these data appear inconsistent with the suggestion that cluster 1 chondrites belong to a specific meteoroid stream with very similar orbits

last glacial maximum and lateglacial in the polish high tatra mountains revised deglaciation chronology based on the 10 be exposure age dating abstract deglaciation chronology of the polish high tatra mountains has been reconstructed based on 10 be exposure age dating fifty seven rock samples were collected from boulders located on the terminal and lateral moraines that limit the horizontal extent of the lgm and the lateglacial glaciers in the biala woda and sucha woda catchments the uncertainty weighted mean age of 21 5 2 5 ka obtained for the maximum terminal moraine in the sucha woda valley indicates that the oldest preserved moraines were formed during the global lgm the age population ranges between 15 1 1 0 and 28 3 2 0 ka and suggests that glaciers reached their maximum position lgm i as early as 28 25 ka and the final stabilization of the form occurred much later possibly after melting of buried dead ice the younger glacial oscillation lgm ii occurred no later than 20 5 ka and is represented by well preserved termino lateral moraine systems in the panszczyca valley the first lateglacial stage lg1 in the study area is documented in the rybi potok valley at the rp1 moraine 1300 m a s l which was stable at around 16 6 0 3 ka the younger lg2 stage has no defined absolute age however it is constrained between 16 5 and 15 5 ka by the timing of the lg3 stage this cold event is represented by well formed moraines in the roztoka piec stawow polskich rybi potok and panszczyca valleys of which exposure age indicates their deposition between 15 0 0 5 and 15 6 0 1 ka the lg1 lg2 and lg3 stages likely occurred during the oldest dryas cold stage greenland stadial 2 1a related to the north atlantic cooling heinrich event 1 the youngest glacial oscillation is evidenced by moraines in the pusta and panszczyca valleys these moraines are composed of very large granitic blocks of which exposure ages often exhibit isotope inheritance this is reflected by the youngest p3 moraine in the panszczyca valley with a mean age of deposition close to the lgm the r4 moraine system in the pusta valley however indicates two oscillations phases that occurred at around 13 ka and correlates well with the timing of rp5 moraine formation in the za mnichem valley the lg4 stage is related to the climate cooling during the younger dryas greenland stadial 1 lgm elas reconstructed for the biala woda and sucha woda panszczyca glaciers were located at 1460 1480 m a s l during the oldest dryas stages the ela in the high tatras rose from 1600 to 1650 m a s l in the rybi potok valley and from 1700 to 1800 m a s l in the roztoka piec stawow polskich valley the younger dryas ela depending on glacier s exposition was located between 1950 and 2000 m a s l climate modelling results show that the lgm glaciers maximum advance could have advanced in the high tatras when the mean annual temperature was lower than today by 11 12 c and precipitation was reduced by 40 60 during the lateglacial stages the temperature decrease in the study area changed from 10 c during the oldest dryas to 6 c during the younger dryas and precipitation lowering decreased from 50 to 30 or even 10 respectively compare to modern conditions

rates of processes in magmatic arcs implications for the timing and nature of pluton emplacement and wall rock deformation abstract the construction of arcs and in many cases the emplacement of plutons occur in tectonically active regions it is critical therefore to evaluate the rates of structural and magmatic processes when trying to understand the evolution of arcs and the associated pluton wall rock systems our best estimates of average rates or durations of processes in shallow to moderate level arc environments are the following 1 crystal growth rates in magma of 10 4 cm year 1 2 growth rates of metamorphic porphyroblasts between 10 5 and 10 2 cm year 1 3 long term magma supply rates of 10 1 km 3 year 1 and short term rates of up to 350 km 3 year 1 4 diapiric ascent rates for mafic plutons of 1 3 m year 1 5 cooling of plutons to ambient wall rock temperatures in 10 5 10 6 years 6 final crystallization of plutons in a small fraction of the time needed for complete cooling 7 fault displacements of 3 cm year 1 8 development of cleavages in fault zones in less than 10 6 years at strain rates of 10 13 s 1 or higher and 9 the development of regional cleavages in 10 6 years at strain rates of 10 14 s 1 these rates indicate that processes operating in magmatic arcs are relatively rapid pluton emplacement cleavage development etc occur over time spans of tens of thousands to no more than a few million years however the rate of ascent and crystallization of plutons at shallow levels is generally shorter than that needed to get large displacements on faults or widespread cleavages developed at deeper levels or in zones undergoing faster strain rates the time spans of the various processes approach one another thus plutons with otherwise similar characteristics emplaced in regions undergoing fast strain rates or at deeper crustal levels may appear quite different structurally from those emplaced at shallow levels or in regions undergoing slower strain rates comparison of these data also suggests that the rate at which wall rock deforms is the limiting factor controlling the rates of other structural processes during emplacement of plutons unless fast strain rates or multiple deformation mechanisms are considered thus emplacement mechanisms that rely on the transport of magma over 10 5 to 10 6 years are favored and need further consideration finally we argue that the structural and other characteristics of pluton wall rock systems will depend on rates of various processes involved and that these rates at the very least influence and sometimes invalidate the timing criteria previously published by us and others

noncoaxial k feldspar and ams subfabrics in the land s end granite cornwall evidence of magmatic fabric decoupling during late deformation and matrix crystallization 1 a comparative study of the anisotropy of magnetic susceptibility ams and k feldspar phenocryst fabrics in the land s end granite demonstrates that the ams fabric predominantly reflects late magmatic deformation tensor analysis of the k feldspar fabric shows a complex pattern characterized by meter scale variations in orientation symmetry and intensity mainly related to heterogeneous flow of the phenocryst rich magma during emplacement in contrast the ams fabric is predominantly homogenous subhorizontal and oblate and is stable at the pluton scale quantitative microstructural analysis suggests that the ams fabric is controlled by deformation of the partially crystallized matrix resulting from the combined effects of late internal adjustment within the pluton and regional deformation a general model of fabric development associated with a vertical pure shear overprint on a variable vertical fabric is evaluated by numerical modeling the study demonstrates how the memory of different fabric elements may be dependent upon their grain size crystallization sequence and recorded previous strain

reducing concentration uncertainty using the coupled markov chain approach abstract this paper presents a framework for coupling the stochastic technique that is called coupled markov chain elfeki and dekking 2001 which is used for stochastic site characterization with numerical groundwater flow and transport models the purpose is to study the reduction of uncertainty on concentration distribution by conditioning on a number of boreholes using the monte carlo approach this study addresses some issues that have not been given much attention in the literature namely 1 using the so called cmc coupled markov chain model for modeling heterogeneity as a non gaussian field characterized by multi dimensional transition probabilities rather than variograms or autocorrelation functions 2 considering a hydrodynamic flow field that is non uniform in the mean flow due to boundary conditions where flow is driven from the left top corner moving to the right domain boundary and 3 utilizing the concept of forward modeling in the framework of conditioning on geological borehole information geometrical configuration rather than conditioning on direct measurements of the hydrogeological parameters e g hydraulic conductivity porosity etc the model is applied on an unconsolidated deposit located in the central rhine meuse delta in the netherlands the data at the site is merely used to calculate the transition probabilities used in the cmc model to generate a reference geological model for the rest of the analysis the results show the potential applicability of the cmc model in reducing the uncertainty in concentration fields when a sufficient number of boreholes are available reproduction of peak concentrations breakthrough curves and plume spatial moments require many conditioning boreholes in this case study 25 31 boreholes with 10 8 m spacing over a distance of 240 m however reproduction of plume shapes requires a lot less boreholes in this case study five boreholes with 60 m spacing over a distance of 240 m

implications of quartz grain microtextures for onset eocene oligocene glaciation in prydz bay odp site 1166 antarctica abstract this paper presents the results of the scanning electron microscopic sem analysis of quartz grains from a selection of samples at site 1166 ocean drilling program leg 188 drilled site 1166 on the prydz bay continental shelf antarctica to document onset and fluctuations of east antarctic glaciation this site recovered upper pliocene holocene glacial sediments directly above cretaceous through lower oligocene sediments recording the transition from preglacial to early glacial conditions sem analysis of quartz grains at site 1166 was used to characterize the glacial and preglacial sediments by their diagnostic textures angular edges edge abrasion as well as arcuate to straight steps are the most frequent features in glacial deposits the highest frequency of grains with round edges is present in middle late eocene fluvio deltaic sands however angular outlines fractured plates with subparallel linear fractures and edge abrasion indicating glacier influence are also present preglacial carbonaceous mudstone and laminated gray claystone show distinctive high relief quartz grains and some chemical weathering on grain surfaces the results of the microtextural analysis of quartz grains are used to verify some critical periods of ice sheet evolution such as the transition from the east antarctic preglacial to glacial conditions on the continental shelf from middle late eocene to late eocene early oligocene time

evaluating controls on crevasse splay size implications for floodplain basin filling abstract although crevasse splays are often considered important contributors to floodplain basin filling evidence from modern and ancient fluvial deposits indicates that they may not play a significant role in all river systems in order to better understand controls on the abundance and scale of crevasse splays produced in fluvial systems we used aerial photography to observe crevasse splay deposits along three rivers and conducted a targeted numerical modeling study to explore factors which promote widespread crevasse splay deposition on fluvial floodplains results demonstrate that splay size does not always scale directly with channel size or discharge and that hydrodynamic factors primarily sediment size and floodplain drainage conditions play a significant role in determining whether a fluvial system is likely to produce large floodplain filling splays this work suggests that widespread crevasse splays demand both a large supply of relatively coarse suspended sediment and a steep water surface slope away from the channel across the floodplain without both these conditions the role of crevasse splays in flood basin filling is limited

noble gases in h chondrites and potential differences between antarctic and non antarctic meteorites abstract thirty one antarctic h chondrites from the allan hills have been analyzed for their noble gases seven of the specimens contain solar gases thirteen have a cosmic ray exposure age around 8 ma both fractions are as observed for h chondrites from the rest of the world scrutiny of the data for paired samples yields a minimum number of 17 independent falls with 6 falls required for the 8 ma peak of exposure age the distribution of exposure ages as well as that of radiogenic 4 he and 40 ar yield no evidence that h chondrites from the allan hills region represent a mixture of populations that is different from that brought to moderate latitudes of the earth in more recent times

surface and sub surface schmidt hammer rebound value variation for a granite outcrop this study presents rock strength variations at granite outcrops and in subsurface vertical profiles in the jizerske hory mountains czech republic schmidt hammer rebound values in subsurface profiles change gradually from the bedrock surface downward an exponential relation has been observed between the r values and depth in rock outcrops to a depth of around 4 5 m the exponential nature of the curve indicates that rock hardness increases more rapidly with depth in the uppermost 1 m section of the rock profile a detailed study of rebound values obtained from both intact and polished rock exposures reveal effects of surface grinding on results of the schmidt hammer method the range of data collected increases after grinding allowing more precise discrimination of rock surfaces in respect of age and weathering the schmidt hammer method may be used effectively as a relative age dating tool for rock surfaces that originated during the late pleistocene it is concluded that this time limitation can be significantly mitigated by surface grinding before measurement copyright 2010 john wiley sons ltd

the breakup of a meteorite parent body and the delivery of meteorites to earth whether many of the 10 000 meteorites collected in the antarctic are unlike those failing elsewhere is contentious the antarctic h chondrites one of the major classes of stony meteorites include a number of individuals with higher induced thermoluminescence peak temperatures than observed among non antarctic h chondrites the proportion of such individuals decreases with the mean terrestrial age of the meteorites at the various ice fields these h chondrites have cosmic ray exposure ages of about 8 million years experienced little cosmic ray shielding and suffered rapid postmetamorphic cooling breakup of the h chondrite parent body 8 million years ago may have produced two types of material with different size distributions and thermal histories the smaller objects reached earth more rapidly through more rapid orbital evolution

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

thermochronological constraints on the long term erosional history of the karkonosze mts central europe abstract a combination of zircon u th he zhe apatite fission track aft and apatite u th sm he ahe thermochronology is used to constrain the long term exhumation and erosional history of the karkonosze mts in north eastern bohemian massif by analyzing samples from the highly elevated summit planation surface zhe ages from the south eastern part of the planation surface are 285 19 295 20 and 308 21 ma indicating that the area remained at temperatures below 190 c since the permian in contrast zhe ages in the western part of the planation surface are mid cretaceous proving that this part was residing at temperatures above 190 c prior to exhumation the exhumation occurred in the late cretaceous as evidenced by aft and ahe ages ranging from 82 5 to 90 8 ma and from 77 5 to 91 6 ma respectively modelled cooling trajectories are characterized by a two stage cooling history fast cooling through the apatite partial annealing zone and helium partial retention zone to surface conditions between 90 and 75 ma and slow cooling or even thermal stagnation from 75 ma to present although our data do not allow us to resolve the age of the planation surface completely we narrowed down the number of explanatory options and propose two alternative solutions for the formation of the planation surface i the planation surface represents the remnant of a permian peneplain which was buried by mesozoic sediments of the central european basin system and was re exposed in the late cretaceous or ii the planation surface formed after 75 ma after termination of a period of massive erosion documented by thermochronological data and by the sedimentary record in adjacent basins cenozoic relief production and uplift of the planation surface evident from regional landforms and the sedimentary record is not recorded by thermochronological data this shows that erosion on the uplifted planation surface since 75 ma was less than 1 2 km

an h chondrite stream identification and confirmation fall data indicate that a significant elongate cluster of co orbital h chondrite falls in may between 1855 and 1895 h cluster 1 records encounters with two or three closely spaced and probably related meteoroid stream components each of which was met near its perihelion although meteorites included in the cluster vary widely in petrographic type 3 6 shock facies a d and 21ne exposure age 5 to 50 ma they have a distinct labile trace element signature that confirms a common thermal history and thus a common source region within an h chondrite parent body hence meteorites selected by one criterion fall parameters as distinguishable from all other h chondrites are distinguished from them by another completely different criterion contents of labile trace elements

a relationship between alluvial backswamps and avulsion cycles an example from the willwood formation of the bighorn basin wyoming abstract stratigraphically limited intervals from the lower eocene willwood formation contain laterally extensive carbonaceous shales and ribbon sandstone networks associated with channel avulsion we present data from one such interval that documents the avulsion sequence vertical sections measured along the outcrop of this interval are similar and comprise a basal carbonaceous shale overlain by fine grained deposits on which weakly developed hydromorphic paleosols formed the paleosols enclose and are locally incised by ribbon sandstones some of which cut down to and partly through the carbonaceous shale the ribbons have width thickness ratios between 3 and 13 some ribbons cluster at a particular stratigraphic level which together with paleocurrent trends suggests that they formed channel networks sections are capped by yellow brown paleosols showing moderate pedogenic development we suggest that the carbonaceous shales developed in low lying topogeneous swamps in distal portions of the floodplain far from the trunk channel such a location set limits on the sediment that they received the mudrocks with weakly developed paleosols and associated ribbon sandstones are interpreted as crevasse splay complexes resulting from avulsion of the trunk river the ribbon sandstones represent ancient feeder channels of the avulsion complex the rapid influx of avulsion deposits appears to have been crucial to preserving the organic material and this study reveals an important and as yet uncharacterized link between trunk channel processes and the accumulation of organic rich deposits in distal alluvial swamps similar deposits are found in other stratigraphic units in the rocky mountain region and the development of these and other organic rich deposits should be reassessed in terms of channel avulsion

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

geostatistical analysis of overbank deposits of anastomosing and meandering fluvial systems rhine meuse delta the netherlands the architecture of overbank deposits of anastomosing and meandering rivers in the central rhine meuse delta the netherlands is analysed by geostatistical investigation of three detailed cross sections in two study areas the thickness of the overbank deposits in the cross sections were examined by semivariogram analysis the cross sections show that two different types of overbank deposits are found at different depths at the same location at greater depths lithologically complex overbank deposits with many crevasse splays and a varying thickness are found at shallow depths lithologically uniform overbank deposits with a more or less constant thickness are found the semivariogram analysis serves as a tool to distinguish between these two types of overbank deposits semivariograms of the lithologically complex overbank thicknesses strongly differ from the semivariograms of the more uniform overbank deposits the former show large nugget values combined with large sill values and a small range the latter show small nugget values and a clear trend and no sill is reached the complex overbank deposits are thought to be deposited by anastomosing rivers the uniform overbank deposits by meandering rivers maximum boring intervals for mapping of the overbank deposits can be derived from the semivariograms if a complete understanding of the fluvial architecture in the study areas is needed e g for reservoir characterization a sampling grid of 25 m perpendicular and 100 m parallel to main flow direction is necessary

paleo climate of the central european uplands during the last glacial maximum based on glacier mass balance modeling during the last glacial maximum lgm glaciers existed in scattered mountainous locations in central europe between the major ice masses of fennoscandia and the alps a positive degree day glacier mass balance model is used to constrain paleo climate conditions associated with reconstructed lgm glacier extents of four central european upland regions the vosges mountains the black forest the bavarian forest and the giant mountains with reduced precipitation 25 75 reflecting a drier lgm climate the modeling yields temperature depressions of 8 15 c to reproduce past glaciers more severe cooling is required in the west than in the east indicating a strong west east temperature anomaly gradient

weathering mantles and their significance for geomorphological evolution of central and northern europe since the mesozoic abstract weathering mantles saprolites are very widespread in central western and northern europe where they form thick near surface residual deposits often in excess of 50 m they vary in the type of weathering the bedrock lithology involved the topographic setting and the age and stratigraphic context this review paper provides information about the distribution and major characteristics of weathering mantles from a number of key areas including the british isles the central european belt of mid mountains and uplands the scandinavian mountains and the fennoscandian shield it also examines the evidence for weathering etched origin of various landforms including boulders tors inselbergs basins and some regional landforms assemblages major types of regionally important weathering mantles include ferrallitic lateritic saprolites kaolinite rich saprolites sandy to grus mantles and various residuals left after partial dissolution of carbonate rocks although dating of weathering mantles is often circumstantial it appears sufficiently precise to argue for various ages of deep weathering mesozoic pre late cretaceous mantles are particularly widespread but there are also early tertiary and miocene saprolites widely present whilst most grus weathering is likely to be of miocene to pleistocene age individual upland areas have been subjected to multiple episodes of weathering whose legacy is the present day co existence of different weathering products continental and shallow marine deposits around the uplands particularly in the north sea and intra continental graben structures are often dominated by quartz and kaolinite pointing to deeply weathered land surfaces as the source areas and extending the record of weathering on the geological time scale they demonstrate that weathering mantles repeatedly formed and were subjected to erosion and new cycles of weathering were initiated we suggest that deep unroofing of basement structures in many parts of europe has been mainly accomplished by deep weathering and stripping of pre weathered rock the phenomenon of deep weathering has been very important for geomorphology etched landforms vary in size from small residual boulders up to regional characteristic landscapes etchsurfaces such as joint valley landscapes of southern sweden or undulating multi convex and multi concave landscapes of many uplands in central europe deep weathering has played a major part in the geomorphological evolution of europe since at least the late triassic and the concept involving long term etching and stripping provides an appropriate framework to describe and explain both erosional landscapes and sediment features

chemical studies of h chondrites 9 volatile trace element composition and petrographic classification of equilibrated h chondrites to examine the thermal history of the parent body bodies of equilibrated h chondrites we treated data for 11 volatile trace elements co rb ag se cs te zn cd bi tl and in in order of putative volatility in 90 falls 15 h4 46 h5 and 29 h6 using univariate statistical tests contents of few of these elements differ significantly between any two of these suites one element cs differs systematically between all three pairs of suites co and tl differ between two pairs of suites for co and cs contents varied as h4 h5 h6 while for tl contents varied as h4 600 k with the suites deriving from a stratified parent body bodies

spatial variation of overbank aggradation rate and its influence on avulsion frequency river avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges and the associated increase in cross valley slope relative to either the down channel slope or the down valley slope the latter is termed the slope ratio in the present paper therefore spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion dominated models of alluvial architecture detailed evidence on centennial to millennial scale floodplain deposition has to date been largely unavailable new data on such long term overbank aggradation rates from the rhine meuse and mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto and can be similar to observations for single overbank floods this leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios potentially resulting in increased avulsion frequencies a revised input parameter for overbank aggradation rate was used in a three dimensional model of alluvial architecture to study its effect on avulsion frequency realistic patterns of avulsion and interavulsion periods 1000 years were simulated with input data from the holocene rhine river with avulsions occurring when the slope ratio is in the range 3 5 however caution should be practised with respect to uncritical use of these numbers in different settings evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value irrespective of whether critical slope ratios are used as in the present study or superelevation as has been proposed by other investigators

impact of the german harz mountain weichselian ice shield and valley glacier development onto palaeolithic and megafauna disappearances abstract three pleistocene stages are recorded by 3d google earth geomorphology cave sediments river terraces megafauna archaeological sites of the harz mountain range and its forelands of northern germany central europe peak 1141 a s l late pleistocene glaciation stages are modeled preliminary in valley elevations between 407 and 760 a s l starting all southeast below the brocken ice field above 750 a s l the 14 11 km long oder and bode valley glaciers left typical moraines kames or dead ice depressions such as fluvial cave relic sediments the bode river glacier passed during the lgm the rubeland caves where it deposited reworked kames lateral moraines in the baumann s cave which floods mixed a neanderthal camp leopard lair and cave bear den area 60 km downstream fluvial to aeolian deposits were trapped in the gypsum karst doline westeregeln neanderthal camp hyena den late aurignacians replaced in the region neanderthals but a gap of late palaeolithic gravettian magdalenian 26 000 16 000 bp settlement and latest starting speleothem genesis around 24 260 568 bp correlate to the lgm when an arctic reindeer fauna with alpine elements ibex chamois accumulated in bone assemblages of a wolverine polar fox mustelid such as european eagle owl dens which allow landscape reconstructions

longitudinal facies architectural changes of a middle holocene anastomosing distributary system rhine meuse delta central netherlands abstract longitudinal changes in channel planform and facies architecture occur over a 22 km long reach of an anastomosing middle holocene distributary system in the rhine meuse delta central netherlands a geological map and a sequence of cross sections show that the channel belt is characterized by sand body width thickness ratios which decrease within the study area from approximately 25 upstream to well below 10 downstream accompanied by a change in channel planform as indicated by a downstream increase of the number of crevasse splays the lithological composition of the sand body is relatively homogeneous but there is always a well developed fining upward sequence from sandy channel deposits to clayey natural levee deposits within channel vertical aggradation appears to have been restricted during most of the period of activity of the distributary system and since lateral accretion was also limited especially in the downstream part rapid accumulation of channel deposits seems to have occurred predominantly during the avulsion stage leaving a narrow and shallow residual channel as the last remnant the longitudinal change in channel pattern is mainly attributed to a downstream increase in the rate of ground water level rise that resulted from holocene sea level rise in the rhine meuse delta a rate of ground water level rise of 1 5 mm yr 1 is required for the creation of fully developed anastomosing fluvial systems ribbons with a width thickness ratio of

chronology of the late weichselian glaciation in the bohemian forest in central europe abstract a glacial chronology based on in situ produced 10 be surface exposure dating of moraines in the bohemian forest central europe was established eleven exposure ages obtained for moraine boulders in the prasilske lake and laka lake valleys czech republic were complemented by 10 be ages from kleiner arbersee germany recalculated according to recently calibrated production rates in the northern hemisphere the glacial phases in the bohemian forest occurred during the last glacial maximum around 24 1 2 5 23 6 2 4 21 8 2 0 and 19 5 2 1 ka following phases of local glaciation occurred during the northern hemisphere deglaciation period around 16 ka and 14 ka the last indicated phase may correlate with older dryas the glacial chronology of the bohemian forest is in agreement with local glaciation chronologies in the giant mts krkonose mts and the eastern alps

microstructure and magnetic susceptibility applied to emplacement kinematics of granites the example of the foix pluton french pyrenees abstract the variscan foix granite 40 km 2 central pyrenees was subjected to detailed microstructural magnetic susceptibility and anisotropy studies magnetic susceptibility is shown to be of dominant paramagnetic origin its magnitudes clearly define a zoning which compares with the petrographic zoning and reveals that the pluton is the southern remnant of a normally zoned pluton truncated during alpine tectonics magnetic susceptibility anisotropy characterizes the planar and linear preferred orientations of the main iron bearing silicates namely biotite and accessory amphibole it is argued that these fabrics also reflect the flow pattern of the granite microstructural observations aid in distinguishing the magmatic and late magmatic fabric signatures main body from the post magmatic solid state signature leucogranite in order to account for the consistently subhorizontal and ne sw directed magmatic lineations in the northern sector of the foix granite an oblique intrusion is proposed it may be coeval with the early variscan regional sw trending shearing event steepening of the structures in at least part of the southern sector may be coeval with the late development of upright folds and vertical cleavage in the country rocks the utility of combined microstructural and magnetic susceptibility studies is demonstrated as an aid in the structural interpretation of granite intrusions which act as kinematic markers of their host terranes

chemical studies of h chondrites 5 temporal variations of sources we report 36cl 301 kyr half life data obtained by accelerator mass spectrometry allowing nominal terrestrial ages to be determined for 39 antarctic h4 6 chondrites for which contents of volatile trace elements are known the compositional difference between these antarctic meteorites and 58 non antarctic falls increases with terrestrial age and using multivariate statistical techniques becomes highly significant for antarctic samples with ages 50 kyr the compositional difference is inconsistent with trivial causes such as weathering and seems to reflect differences in thermal histories of parent sources temporal source variations for the h chondrite flux on earth thus exist not only on a short term 40 years basis dodd et al 1993 but also on a long term 50 kyr basis

the role of landslides in downslope transport of caprock derived boulders in sedimentary tablelands stolowe mts sw poland abstract escarpment slopes in sedimentary tablelands are often mantled by extensive boulder blankets while lithology shows beyond doubt that caprock is the source of boulders the processes involved in boulder movement and their distribution patterns are rarely examined in this paper we investigate the role of landslides initiated within middle and lower escarpment slopes in redistributing boulder covers on the example of the stolowe mountains in sw poland quartz sandstones form caprock and give rise to precipitous albeit rather low 30 m high at most typically 10 15 m uppermost slope sections and are the source of boulders which occur at distances even 1 km away from the caprock on the nearly flat footslope sedimentary series beneath caprock include fine grained rocks such as mudstones claystone and calcareous sandstones geomorphological mapping and geomorphometric analysis of a high resolution dem allowed us to identify landform patterns interpreted as resulting from landslides both rotational and translational the latter produced distinctive tread and riser topography with risers up to 10 m high results of geophysical prospecting using electrical resistivity tomography ert confirm the presence of allochthonous sandstone derived upper layer that wedges out downslope and indicate resistivity contrasts at depth of 5 15 m interpreted as basal boundaries of landslide material sandstone boulders rafted on top of slid masses and reached very distant footslope settings the primary role of landsliding consists of transporting allochthonous boulders further than would be possible otherwise and accumulating boulders in clusters and linear belts across the slope notably on risers

rapid changes in the nature of the h chondrites falling to earth we have previously identified a subgroup of antarctic h chondrites that are significantly different from h chondrites among the modern falls in terms of induced thermoluminescence tl metallographic cooling rate and cosmogenic inert gas contents here we examine their terrestrial and thermal history as apparent in their natural tl and radioactive cosmogenic isotope abundances these meteorites have a tendency towards high 26al activities and fairly short 14c and 36cl terrestrial ages generally 1 2 au to 1 au within the last 105 years we suggest that the nature of the meteorites falling to earth is not independent of time but depends on stochastic events such as the breakup of parent bodies and recent variations in orbit

formation conditions of igneous regions in ordinary chondrites chico rose city and other heavily shocked h and l chondrites we report microprobe and radiochemical neutron activation analysis rnaa data for hosts and igneous inclusions in the heavily shocked ordinary chondrites rose city h5 yanzhuang h6 farmington l5 malakal l5 chantonnay l6 chico l6 and tuan tuc l6 based on these analytical results equilibrium crystallization calculations ghiorso and sack 1995 phase equilibrium analysis e g sack and ghiorso 1994a b sack et al 1994 and experimental cooling rate studies e g walker et al 1976 we have assessed the metamorphic and magmatic histories of these seven heavily shocked chondrites we infer that 1 unfractionated chondritic liquids were intruded to depths 0 1 km in the parent asteroid of rose city 2 early chondritic liquids experiencing 5 10 olivine fractionation were erupted onto the surface of the parent asteroid s of yanzhuang and chantonnay and 3 near surface crystallization is also indicated for the liquids in tuan tue and farmington with chico and malakal crystallizing at slightly greater depths in all but chantonnay liquids appear to have derived from melting of chondrite types corresponding to their hosts in the l chondrite chantonnay the intrusive liquids derive from melting an h chondrite source region in which chondritic melts were stored for a sufficient time to produce pigeonite in zoned pyroxene xenocrysts heating effects are also reflected in the trace element contents of the chondrites our rnaa data for rose city seem to reflect only the siderophile lithophile fractionation evident in the metal distribution the yanzhuang rnaa data are generally similar to those of other h chondrites severe shock not involving phase transport seems to leave h chondrites unaffected compositionally contents of the four most mobile elements cd bi t1 in and cs in chico indicate loss so that this assemblage experienced extended low temperature cooling after injection of dike material into the chico host rnaa data for the other four l chondrites examined indicate more rapid cooling

a structural model for the western central sudetes a deformed stack of variscan thrust sheets a model based on new structural and geochemical data is presented it unifies the structural history of the izera rudawy janowickie and kaczawa complexes with the fore sudetic block despite their current separation by the intra sudetic and marginal sudetic faults above the granitoid izera kowary and w droze gneisses at the base of the structural sequence the ductile kowary shear zone marks the basal decollement of the wierzawa thrust sheet comprising often highly strained metasediments associated with enriched tholeiitic and alkaline metabasites above it the ductile kaczorow shear zone corresponding to the main mylonitic zone within the leszczyniec shear zone in the rudawy janowickie complex marks the base of the dobromierz thrust sheet characterized by voluminous morb like meta tholeiites and minor metasediments in the higher parts of the rudawy janowickie and kaczawa complexes and the pyszczynska hill area of the fore sudetic block in the east the sleza ophiolite and the gory sowie block override the entire nappe stack kinematic fabrics in the major and related shear zones indicate d 1 compressional transport towards the northwest followed by minor d 2 extensional movements the thrust stack was deformed during d 3 by southwest verging folds was subsequently intruded by post orogenic granites and later disrupted by the intra sudetic marginal sudetic and associated faults

middle holocene avulsion belt deposits in the central rhine meuse delta the netherlands abstract the schoonrewoerd fluvial system in the central rhine meuse delta was active as a rhine distributary between 3900 and 3800 14c years bp based on planform patterns cross sectional facies architecture reconstructed paleodischarge and its short period of activity the schoonrewoerd fluvial system is interpreted to represent a failed avulsion the schoonrewoerd system consists of a complex of ribbon channel sand bodies encased in a lens of clayey deposits and it can be traced for more than 35 km in a downstream direction prominent features of the system are longitudinal facies architecture change with channel sand body width thickness ratio decreasing downstream from 40 to 5 and high lateral facies variability multiple anastomosing sand bodies occur in its upper and middle reaches paleodischarge reconstruction indicates that the schoonrewoerd system was only a minor distributary within the rhine meuse deltaic system specific stream power in the lower reach is estimated to have been low 0 5 to 1 8 w m2 the short period of activity of the schoonrewoerd system suggests that very high floodplain sedimentation rates were associated with the avulsion process with the formation of meters thick fine grained sedimentary successions in 100 years the facies architecture of the short lived schoonrewoerd system is interpreted to reflect the first stages of avulsion broadly analogous to the modern saskatchewan river avulsion in canada smith et al 1989 sedimentology v 36 p 1 23 having escaped from later erosion by a more mature channel belt many other systems often partly eroded with similar facies architecture exist in the west central rhine meuse delta suggesting that avulsion belt deposits are a major component of the holocene delta deposits the facies architecture model of the schoonrewoerd avulsion belt deposits presented in this paper may provide clues for the interpretation of fine grained sedimentary successions in ancient fluviodeltaic deposits

magnetic fabric vs magnetite and biotite shape fabrics of the magnetite bearing granite pluton of gameleiras northeast brazil abstract a well defined orientation pattern has been evidenced by the magnetic fabric lineation and foliation of the granite pluton of gameleiras northeast brazil this magnetic fabric is roughly parallel to the magmatic fabric defined by the elongate mafic enclaves and by the planar arrangement of tabular k feldspar phenocrysts low field anisotropy of magnetic susceptibility properties as well as magnetic mineralogy studies and optical microscopy observations indicate that multidomian iron rich magnetite is the main carrier of the magnetic susceptibility and its anisotropy to examine in more detail the relationships between the magnetic and magmatic fabrics measurements of two dimensional shape fabrics of grain populations of biotite and magnetite have been carried out on a total of 500 grains using an automatic shape fabric analysis procedure on carefully selected and oriented thin sections angular departure has been calculated between the maximum elongation of the mineral shape fabric of the given grain population and the maximum susceptibility axis of the corresponding macroscopic specimen we found that the fabric of biotite correlates strongly with the magnetic fabric 7 8 the fabric of magnetite although not as well defined mainly because of its weak shape anisotropy still correlates with the magnetic fabric 12 18 origin of low field magnetic fabric in the pluton of gameleiras is concluded to be controlled principally by the statistical alignment of the long axes of inequant magnetite grains magnetic interactions between the grains of magnetite where they form clusters may account for the observed scattering or abnormal magnitudes of the magnetic anisotropy concerning the orientation of the magnetic fabric as the long dimensions of the magnetites preferentially align with the boundaries of the other minerals particularly biotite and titanite the magnetic fabric as defined by the grains of magnetite is concluded to approximate closely the magmatic fabric defined by the shape fabric of biotite however as no correlation exists between shapes or clustering of magnetites and strain undergone by the deforming magma the strength of the magnetic fabric in ferromagnetic granites cannot be used in a simple way as a measure of strain intensity

sequential granite emplacement a structural study of the late variscan strzelin intrusion sw poland the strzelin massif in sw poland central european variscides records a protracted igneous evolution with three main magmatic stages 1 tonalitic i 2 granodioritic and 3 tonalitic ii granitic in the northern part of this massif the strzelin intrusion proper comprises three successively emplaced rock types a medium grained biotite granite 303 2 ma a fine grained biotite granite 283 8 ma and a fine grained biotite muscovite granite based on field evidence the third variety postdates both types of the biotite granites the structural data from the three granites including their parallel approximately e w striking and steeply dipping lithological contacts and ene wsw trending subhorizontal magmatic lineations suggest that the emplacement of all three successive granite varieties was controlled by an active long lived strike slip fault striking ese wnw with a dextral sense of movement after the emplacement of the youngest biotite muscovite granite the intrusion underwent brittle extension which produced q joints striking nnw sse to n s and dipping at 55 70 wsw to w and showing evidence of broadly n s directed sinistral displacements the structural observations supported by new geochronological data indicate that the internal structure of the composite granitoid intrusion including the faint magmatic foliation and lineation formed in a long lived strike slip setting different from the subsequent post emplacement extensional tectonics that controlled the development of brittle structures

ordinary chondrites multivariate statistical analysis of trace element contents abstract we used standard multivariate discriminant functions borrowed from linear discriminant analysis and logistic regression to compare contents of mobile trace elements co au sb ga se rb cs te bi ag in tl zn cd in various populations of l4 6 or h4 6 chondrites to aid in our analysis we developed a non standard randomization simulation method that permits probability assignments on a distribution free basis because the sample database for antarctic l4 6 chondrites is very limited we could not establish that mildly and strongly shocked

chemical studies of h chondrites 4 new data and comparison of antarctic suites we report data for the trace elements au co sb ga rb ag se cs te zn cd bi tl and in ordered by putative volatility during nebular condensation and accretion determined by neutron activation analysis in 13 h5 chondriles from victoria land and 20 h4 6 chondrites from queen maud land antarctica these and earlier results provide antarctic sample suites of 34 chondrites from victoria land and 25 from queen maud land treatment of data for the most volatile 10 elements rb in in these suites by multivariate statistical techniques more robust as well as more conservative than conventional linear discriminant analysis and logistic regression demonstrates that compositions differ at marginally significant levels this difference cannot be explained by trivial terrestrial causes and becomes more significant despite the smaller size of the database when comparisons are limited to data from a single analyst and when all upper limits arc eliminated from consideration the victoria land and queen maud land suites have different mean terrestrial ages 300 kyr and 100 kyr respectively and age distributions suggesting that a time dependent variation of chondritic sources with different thermal histories is responsible as a result these two antarctic suites are on average chemically distinguishable from each other since h chondrites serve as a paradigm for other meteorite classes these results indicate that the near earth populations of planetary materials varied with time on the 105 year timescale

chemical studies of h chondrites 6 antarctic non antarctic compositional differences revisited we report data for the trace elements au co sb ga rb ag se cs te zn cd bi t1 and in ordered by putative volatility during nebular condensation and accretion determined by radiochemical neutron activation analysis of 14 additional h5 and h6 chondrite falls data for the 10 most volatile elements rb to in treated by the multivariate techniques of linear discriminant analysis and logistic regression in these and 44 other falls are compared with those of 59 h4 6 chondrites from antarctica various populations are tested by the multivariate techniques using the previously developed method of randomization simulation to assess significance levels an earlier conclusion based on fewer examples that h4 6 chondrite falls are compositionally distinguishable from the antarctic suite is verified by the additional data this distinctiveness is highly significant because of the presence of samples from victoria land in the antarctic population which differ compositionally from falls beyond any reasonable doubt however it cannot be proven unequivocally that falls and antarctic samples from queen maud land are compositionally distinguishable trivial causes e g analyst bias weathering cannot explain the victoria land antarctic non antarctic compositional difference for paradigmatic h4 6 chondrites this seems to reflect a time dependent variation of near earth meteoroid source regions differing in average thermal history

the orbit and atmospheric trajectory of the peekskill meteorite from video records on 9 october 1992 a bright fireball appeared over west virginia travelled some 700 km in a northeasterly direction and culminated in at least one impact a 12 4 kg ordinary chondrite was recovered in peekskill new york1 fortuitously the event was captured on several video recordings which provide a detailed record of both the fragmentation of the object and related atmospheric effects these are the first motion pictures of a fireball from which a meteorite has been recovered we report here the preliminary analysis of 14 video recordings of the event from which we determine the ground path and the original orbit of the object

fabric development in syn tectonic intrusive sheets as a consequence of melt dominated flow and thermal softening of the crust the temperature dependence of ductile deformational processes suggests that the thermal anomaly associated with a cooling syn tectonic intrusion will produce a crustal low viscosity horizon that will concentrate deformation in the vicinity of the pluton during cooling this effect should be most prominent when magma is present but should also occur after solidification of the magma when flow is by solid state processes this paper evaluates this hypothesis for sheet like intrusions using one dimensional time dependent thermal models and accompanying predictions of viscosity vs time history based on experimental flow laws these models predict that for systems with an initial normal geothermal gradient e g extensional systems strike slip systems or thrust systems with low displacement rates the base of a large plutonic sheet cools more slowly than the top and fabric development should be most pronounced on the floor of the pluton in contrast in megathrust systems where displacements are sufficiently rapid to produce temperature inversions cooling is also upside down and fabric development should preferentially occur along the top of plutonic sheets moreover when a pluton is emplaced within a zone of inverted isotherms the heat may be trapped within the inversion a natural system characterized by this history should show a sharp thermal front coincident with the top of a paleo temperature inversion if a pluton is weaker than its country rock it will form a weak horizon in the crust throughout its cooling history and the plutonic sheet should take up the bulk of the deformation throughout its cooling history if a pluton is stronger than its country rock under conditions of solid state flow however models predict a two phase deformational history prior to solidification the deformation should be concentrated in the pluton with the magma representing a weak horizon in the crust but upon crystallization the pluton should become relatively rigid with respect to its country rock and deformation should be concentrated in the wall rocks these two cases predict markedly different structural histories and the history could easily be misinterpreted in the first case static mineral growth might be prominent in the wall rocks and these textures could be misinterpreted as evidence for post tectonic emplacement in the second case the extensive high t deformation of the wall rocks could be readily ascribed to non tectonic emplacement related deformation rather than a consequence of syn tectonic emplacement the model predictions are tested with three examples of well exposed plutonic sheets a neogene extensional system in death valley california and two megathrust systems in southern alaska border ranges fault system and mclaren metamorphic belt structural observations from these systems are broadly consistent with the model predictions and lend support to first order characteristics of the models nonetheless more sophisticated 2 d models of the coupled thermal mechanical system are needed to thoroughly test the hypothesis

refinement of a technique for determining rock mass strength for geomorphological purposes use of a field technique recently devised by selby for the measurement of rock mass strength has resulted in the understanding of the relationship between rock mass strength and slope form it is suggested that the accuracy of rock mass strength assessments may be enhanced by further subdividing the rating scales for intact rock strength and the spacing of partings the relationship between rock mass strength and gradient is reformulated using southern african data and statistically based confidence limits for identifying strength equilibrium slopes are proposed

the effects of interannual climate variability on the moraine record valley glacier moraines are commonly used to infer past mean annual precipitation and mean melt season temperature however recent research has demonstrated that even in steady climates multi decadal kilometer scale fluctuations in glacier length occur in response to stochastic year to year variability in mass balance when interpreting moraine sequences it is important to include the effect of interannual weather variability on glacier length moraines record advances that are forced either by interannual variability or by a combination of climate change and interannual variability we address this issue for the last glacial maximum lgm glaciers of the colorado front range united states using a linear glacier model that allows thorough exploration of parameter uncertainties supplemented by a shallow ice flowline model our analyses suggest that 1 glacial standstills longer than 50 years were unlikely 2 mean glacier lengths are 10 15 up valley from maximum glacier lengths and 3 individual lgm terminal moraines were formed by a combination of a climate change and interannual variability forced advances

grain scale processes in actively deforming magma mushes new insights from electron backscatter diffraction ebsd analysis of biotite schlieren in the jizera granite bohemian massif abstract in the porphyritic jizera granite bohemian massif three distinct types of lattice preferred orientations of biotite grains were revealed in schlieren delineated magmatic structures using the electron backscatter diffraction ebsd method 1 biotite basal planes 001 reorient from schlieren subparallel near the schlieren base to schlieren perpendicular in the upper part of the schlieren both orientations share subhorizontal n s to nne ssw trending a axes 2 in some domains the a axes are steep and at a high angle to the schlieren plane while the c axes plunge shallowly and rotate around an ill defined a axis 3 in other domains the ebsd coincides with background magnetic fabric of the host granite revealed using the anisotropy of magnetic susceptibility ams method that is the a axes plunge shallowly to the se or nw while the c axes are subhorizontal and cluster around the ne sw trend these multiple biotite orientations in the schlieren are interpreted to reflect 1 velocity gradient in laminar magma flow along channel like conduits localized within the high strength host phenocryst framework 2 grain scale gravity driven constrictional deformation of the magma mush and 3 overprinting background tectonic deformation transmitted across large parts of the magma chamber prior to its final crystallization the grain scale mechanisms of biotite fabric acquisition in the schlieren presumably involved rotation of biotite crystals during flow with the biotite alignment reflecting the flow geometry and kinematics replaced after flow cessation by melt aided grain boundary sliding of those biotite crystals still enclosed in melt pockets within otherwise static highly crystallized magma mush the latter process was sufficient to reorient biotite grains but not to cause destruction of the schlieren using the jizera granite as a case example we argue that the lattice preferred orientation of mineral grains in mafic schlieren is highly sensitive to reorient in response to processes both associated with the schlieren formation e g localized magma flow and those that occur later and are superimposed onto the effectively solid high strength magma mush

granite fabrics and regional scale strain partitioning in the serido belt borborema province ne brazil 1 fabrics of the brasiliano age granitoid plutons of the serido belt northeastern brazil were organized following the partitioned regional strain field which shaped larger areas of the basement and its metapelitic cover nine plutons located at the central and western portions of the belt have been investigated by means of anisotropy of magnetic susceptibility these plutons emplaced between 580 and 575 ma are mainly potassic calk alcalic magnetite bearing monzogranites the presence of primary coarse grained magnetite as the main magnetic mineral is indicated by optical and electronic microscopy magnetic susceptibilities hysteresis ratios and thermomagnetic curves the plutons show a strong internal coherence of magnetic fabric with foliation poles distributed around a zone axis parallel to the gently plunging mean lineation the magnetic fabric was used to trace the strain partitioning along the belt in the central transpressive shear belt the magnetic lineations are parallel to north trending regional stretching on the other hand in the western basement block a voluminous granitic magmatism was emplaced as a consequence of a transtensional extensional deformation lineations in these granites trend in a ne direction which is parallel to the transport inferred from kinematic indicators along the shear zones a crustal scale east trending dextral shear zone connects both the transtensional and transpressional domains

sem analysis of quartz sand grain surface textures indicates alluvial colluvial origin of the quaternary glacial boulder clays at huangshan yellow mountain east central china abstract geomorphic features and pleistocene deposits on huangshan have been attributed to glaciation recent reassessment questions this interpretation as part of the reassessment quartz sand grains from deposits identified as glacial boulder clays till composed of boulders in a clay or silt matrix were analyzed by scanning electron microscope for evidence of their sedimentary history surface textures found on the boulder clay grains were compared with those on grains with known sedimentary histories including glacial grus colluvial and alluvial grains the analysis shows that the grains lack typical glacial textures the surface textures present indicate a complex history nonuniformly weathered grain surfaces point to chemical weathering of the source rock this is supported by the deep weathering of the nonquartz clasts in the sand sized fraction as well as in boulders at the outcrops the close correspondence in surface texture frequencies with those of the alluvial grains indicates an alluvial component to the grains history the similarity with the colluvial grains and the outcrops structures suggest an alluvial colluvial origin for the deposits the history indicated by the surface textures agrees with the recent reassessment of the geomorphic features and points to warm climatic conditions in east central china for at least part of the pleistocene