calcic amphibole equilibria and a new amphibole plagioclase geothermometer there is currently a dearth of reliable thermobarometers for many hornblende and plagioclase bearing rocks such as granitoids and amphibolites a semi empirical thermodynamic evaluation of the available experimental data on amphibole plagioclase assemblages leads to a new thermometer based on the aliv content of amphibole coexisting with plagioclase in silica saturated rocks the principal exchange vector in amphiboles as a function of temperature in both the natural and experimental studies is left na square 1 right a left alsi 1 right t1 we have analysed the data using 3 different amphibole activity models to calibrate the thermometer reactions 1 edenite 4 quartz tremolite albite 1 2 pargasite 4 quartz hornblende albite 2 the equilibrium relation for both 1 and 2 leads to the proposed new thermometer t frac 0 677p 48 98 y 0 0429 0 008314 ln k and k left frac si 4 8 si right x ab plag where si is the number of atoms per formula unit in amphiboles with p in kbar and t in k the term y represents plagioclase non ideality rtln ab from darken s quadratic formalism dqf with y 0 for xab 0 5 and y 8 06 25 5 1 xab 2 for xab 0 5 the best fits to the data were obtained by assuming complete coupling between al on the t1 site and na in the a site of amphibole and the standard deviation of residuals in the fit is 38 c the thermometer is robust to ferric iron recalculation procedures from electron probe data and should yield temperatures of equilibration for hornblende plagioclase assemblages with uncertainties of around 75 c for rocks equilibrated at temperatures in the range 500 1100 c the thermometer should only be used in this temperature range and for assemblages with plagioclase less calcic than an92 and with amphiboles containing less than 7 8 si atoms pfu good results have been attained on natural examples from greenschist to granulite facies metamorphic rocks as well as from a variety of mafic to acid intrusive and extrusive igneous rocks our analysis shows that the pressure dependence is poorly constrained and the equilibria are not suitable for barometry

a quantitative approach to trace element and sr isotope evolution in the adamello batholith northern italy a development of de paolo s mathematical procedure 1981 for magmatic afc assimilation fractional crystallization processes is discussed with respect to both trace element and sr isotopic ratio behaviours during the genesis and evolution of adamello batholith northern italy resolution of a two equation system one relative to 87sr 86sr ratio variation in a magma generated by an afc process the other to its trace element content variations gives the f mass of magma at time t mass of initial magma and d bulk partition coefficient values by which one can deduce the r rate of assimilation rate of crystallization value during each step of magmatic evolution this quantitative approach suggests that 1 there was a common precursor magma for all the adamello granitoids with a mg rich tholeiitic composition 2 each intrusive unit appears to have been generated by different extents of afc 3 the trace element distribution in the magma seems essentially influenced by mineral fractionation rather than by the composition of the assimilated crustal material

the tectonic implications of asymmetrically zoned plutons abstract asymmetrically zoned plutons have been mapped in many parts of the world and whereas many of these are asymmetrical for reasons unrelated to regional tectonic environment there are large areas in which the majority of asymmetric plutons are asymmetric in the same direction in these domains of asymmetry either the mechanisms of emplacement or post emplacement deformation have produced a systematic exposure orientation recognition of these domains may lead to discovery of the tectonic mechanisms responsible for systematic orientation ultimately domains of pluton asymmetry may serve to identify the manner of tectonic emplacement or post emplacement deformation

pliocene lower pleistocene chronostratigraphy a re evaluation of mediterranean type sections the pliocene pleistocene stages defined for the mediterranean region are generally used as the standard chronostratigraphic units for the upper neogene and quaternary the recently developed calcareous plankton bio chronology based on results from ocean drilling program leg 107 and numerous outcrop sections provides the necessary time control for evaluating the ages and stratigraphic relationships for the various pliocene pleistocene stages and their associated stratotypes our results indicate that the currently accepted stratotypes do not provide a continuous stratigraphic representation for all of pliocene early pleistocene time on the basis of these findings we propose a revised chronostratigraphic scheme for this time period a tripartite subdivision is proposed for the pliocene series the zanclean stage is retained for the lower pliocene representing the interval from the miocene pliocene boundary ca 4 93 ma to ca 3 5 ma the middle pliocene is represented by the piacenzian stage and it incorporates strata deposited from ca 3 5 to 2 5 ma none of the currently used pliocene stages fully represents the upper pliocene ca 2 5 to 1 6 ma as a result late pliocene time lacks an adequately defined chronostratigraphic unit the selinuntian stage appears to be the most appropriate stage for the lower pleistocene ca 1 6 to 0 8 ma it can be divided into three stratigraphically continuous substages santernian emilian and sicilian the calabrian stage which is commonly used to designate the lowest part of the pleistocene should be abandoned because its stratotype does not include a record of the first 500 000 yr of pleistocene time

factors affecting the nature and rate of dust production from natural dune sands this paper evaluates the influence of natural sand particle characteristics on the amount and particle size distributions of dust produced by aeolian abrasion it contrasts with previous studies of aeolian abrasion by conducting experiments using i whole sand samples as opposed to selected size fractions ii natural mature dune sands rather than artificial or freshly crushed material and iii weathered sands that have acquired a superficial clay coating instead of grains with clean surfaces whilst previous research has found clear positive relationships between particle size sorting roundness and the amount of dust produced by aeolian abrasion the relationships determined in this study show some variation according to the geomorphological context from which the original samples were obtained the most important factor affecting the amount and particle size characteristics of the dust produced was the presence of a clay coating on the grain surface that is removed by the abrasion process the dust produced by this mechanism had a modal size of 2 5 m and material 10 m comprised up to 90 of the particles produced

plio pleistocene palaeogeography of the southern north sea basin 3 75 0 60 ma abstract palaeogeographical maps are presented for the southern north sea basin from approximately 1 w to 7 e and 51 55 n for the period from approximately 3 75 0 60 ma reconstructions centre on 3 75 ma coralline cragbrunssumian 2 55 ma red crag brielle ground reuverian 2 40 ma red crag westkapelle ground praetiglian early tiglian 2 00 ma norwich crag smith s knoll and ijmuiden ground middle tiglian 1 75 1 70 ma cromer forest bed paston winterton shoal late tiglian eburonian 1 40 ma kesgrave yarmouth roads waalian 1 15 ma kesgrave yarmouth roads menapian and 0 60 ma cromer forest bed west runton yarmouth roads cromerian complex from 3 75 2 40 ma the basin is mainly a marine area fringed to the east and south by fluviatile deposition and broadly open via the southwest to the atlantic following marked marine regression and cooling at around 2 40 ma the period from 2 00 1 70 ma is mainly one of renewed marine transgression and warmer conditions during which a great european delta built out fed mainly from the east and south into the southern north sea from 1 40 0 60 ma marine waters were almost entirely excluded from the area and temperate intervals alternated with increasingly glacial episodes whilst the great european delta continued to expand northwards into the northern north sea

trace element evidence for plagioclase recycling in calc alkaline magmas abstract trace element zoning in plutonic plagioclase feldspars from the val fredda complex southern adamello massif italy has been measured using secondary ion mass spectrometry sims the studied samples range from hornblende gabbro through diorite to granitoid with an overall range in plagioclase composition from an96 to an15 individual plagioclases display extensive zonation in anorthite through a considerable variety of zoning textures there is equally extensive zoning in trace elements notably sr and ba broadly similar trace element zoning patterns and concentrations are displayed by all plagioclases irrespective of host rock composition using a relationship betweenxan and the distribution coefficientsdsr anddba trace element concentrations in plagioclase are converted to those of the melt which precipitated each crystal zone the calculated variations in ba and sr are greater than can be attributed to changes in pressure or temperature alone indicating that compositional variation in the coexisting melt was the principal cause of zoning the ba sr melt trend for each crystal describes a two stage crystallisation history the calcic cores of all crystals show melt trends of increasing sr and ba which are attributed to mixing and fractionation in parental hydrous picrobasalt magmas in contrast the melt trends recorded by the rims vary from sample to sample but essentially show decreasing sr and ba consistent with fractionation of sodic plagioclase alkali feldspar and or biotite the plagioclase cores are thought to have crystallised in a common magma chamber at 6 10 kbar pressure while the rims crystallised at the emplacement level 1 5 kbar from interstitial melt whose composition is determined by that of the host magma the data suggest that early formed calcic plagioclase was recycled by the magma during fractionation vigorous convection is invoked to both retain relatively dense calcic plagioclase within the evolving magma and to periodically re entrain cumulus crystals into more evolved magmas the occurrence of calcic plagioclase cores in felsic derivative magmas indicates that fractionation from picrobasalt to tonalite occurred on a relatively short time scale

magnetic mineralogy of sandstones from the lunde formation late triassic northern north sea uk origin of the palaeomagnetic signal the minerals responsible for the magnetic properties of the late triassic lunde formation have been examined using a combination of magnetic mineral extraction microscopy and rock magnetic measurements the magnetic mineralogy is controlled by the depositional environment and the effects of diagenesis by a process of differential preservation and modification of the original detrital minerals the magnetic susceptibility and remanence properties of the sediments are strongly influenced by the proportion of silt and clay sized clastic material which contains most of the magnetic minerals paramagnetic minerals both of depositional origin and produced during diagenesis are largely responsible for the magnetic susceptibility a suite of residual ferrimagnetic oxides chromite and mn substituted magnetite is responsible for the remanence properties in grey sandstones because most of the originally deposited magnetic fe ti oxides have been removed by reducing conditions during diagenesis however a small number of reddened horizons preserve a higher proportion of original detrital fe ti oxides ferrimagnetic ilmenite ferrimagnetic chromite and magnetite although authigenic hematite has replaced most of the original mineralogy in the reddened horizons magnetic oxide inclusions in quartz and feldspars are important contributors to the remanence signal particularly in horizons which have a low content of discrete detrital ferrimagnetic grains either through diagenetic dissolution or paucity of the silt and clay fraction within the grey sandstones the triassic palaeomagnetic signal is carried by magnetite as inclusions in detrital silicates with a contribution from detrital ferrimagnetic chromite a model of the effects of diagenesis on the magnetic mineralogy in deeply buried sequences is proposed

characterization of the aeolian terrain facies in wadi araba desert southwestern jordan abstract the sand dunes in wadi araba desert southwestern jordan conform to the influence of two main wind systems 1 the shamal north wind the main determinant of dune patterns and 2 the southerly winds caused by the red sea trough and khamasin winds wadi araba is a narrow elongated morphotectonic depression bordered by the high eastern and western mountain ranges that would obstruct most of westerlies in winter and the hot dry easterlies in summer wadi araba desert is caused by the rain shadow of the eastern and western topographic highs with an arid hyperarid climate and moisture index between 0 1 and

palaeomagnetic correlation and dating of plio pleistocene sediments at the southern margins of the north sea basin a series of discontinuous sediment sequences of plio pleistocene age occur onshore around the southern north sea margins notably in the east anglian region of britain intensive lithological and palaeontological analyses of these sediments have shown that they record both major and minor oscillations in climate sea level and environmental conditions however significant uncertainties exist regarding the absolute and relative chronostratigraphies of many of these sequences hindering understanding of the relative impacts of climatic eustatic and tectonic changes on the palaeogeographic development of the southern north sea basin here a number of key east anglian plio pleistocene sites are subjected to robust palaeomagnetic and mineralogical examination in order to determine those sediments which display reliable syn depositional magnetic polarities which are thus of use in ascribing a palaeomagnetically determined age from comparison with the geomagnetic polarity timescale gpts based on a range of palaeomagnetic and complementary mineralogical methods reliable palaeomagnetic directions were obtained from eight sites with reversed polarities displayed by sediments from three sites these polarity determinations can be used to infer absolute ages and test published between site correlations

zircon and titanite recording 1 5 million years of magma accretion crystallization and initial cooling in a composite pluton southern adamello batholith northern italy abstract the southern part of the adamello batholith the so called re di castello unit is an example of a composite pluton ranging from gabbro to granodiorite in composition u pb dating of single zircon crystals from four tonalitic to granodioritic lithologies reveals that zircon crystallization is protracted in all studied lithologies showing apparent durations of growth between 90 and 700 ka the youngest zircons crystallized near the solidus and yield identical or slightly older ages than titanite the formation of these autocrystic zircons is considered to approximate the age of emplacement of the melt and its final crystallization in contrast to antecrystic zircons present in the same sample which had formed earlier in the magmatic column or were derived from re mobilized earlier magma the autocryst derived emplacement ages range from 42 43 0 09 ma to 40 90 0 05 ma recording 1 5 ma of intrusion and crystallization history we anticipate that extended periods of zircon crystallization may be common in silicic rocks whereas the zircons from residual melts from initially undersaturated mafic liquids should yield far more precise emplacement ages within our present analytical uncertainties of 0 1 0 2 in 206 pb 238 u age decreasing th u ratios of dated zircons within one melt batch document the depletion of the residual melt portion in th due to the contemporaneous crystallization of titanite preliminary hf isotopic compositions of the dated zircon grains suggest that the early stage melts of the southern re di castello unit represent hybrid melts with an important crustal component e hf between 2 8 and 3 0 subsequently emplaced melts are more juvenile at e hf values at 6 4 to 8 9 and may thus reflect the addition of large volumes of mafic melt to the magmatic system

a combined o sr nd and pb isotopic and trace element study of crustal contamination in central andean lavas i local geochemical variations systematic variations in o sr nd and pb isotopic ratios and in sr nd pb and rb trace element abundances in central andean andesitic lavas are analyzed in terms of combined crustal assimilation and fractional crystallization the results of integrated isotopic model calculations show that observed local isotopic and trace element variations within the arequipa and barroso volcanic groups of southern peru are best fit by a simple model involving shallow or intermediate depth crustal assimilation of charcani gneiss or an equivalent rock accompanied by dominantly plagioclase fractional crystallization a consequence of this result is that the rbsr pseudoisochrons reported for the arequipa and barroso volcanics are wholly artifacts of the combined processes of assimilation and plagioclase fractionation as are all of the pb isotopic variations measured in the same lavas already interpreted by tilton and barreiro 14 to be the result of crustal contamination isotopic and trace element compositions of the primary magmas for the arequipa and barroso volcanic series are obtained by correcting for assimilation and fractional crystallization the starting magmas are characterized over the entire range of permissible primary compositions by high87sr 86sr ratios low143nd 144nd ratios and high sr concentrations relative to normal island arc andesites these results appear to require prior contamination of the magmas but not involving plagioclase fractionation the uncertainty in pb and o isotope ratios computed for possible primary magmatic compositions is sufficiently large however that it is not possible to preclude a subcrustal origin for at least some regional variation in sr and nd isotopic ratios

plio pleistocene foraminiferal stratigraphy and correlation in the central north sea abstract a detailed foraminiferal stratigraphy is presented for the plio pleistocene sequence of the central north sea region these results are based on investigations carried out on seven boreholes and a detailed foraminiferal stratigraphy is presented here for the josephine borehole 30 13 2 x the pliocene pleistocene boundary is placed at the last common occurrence of cibicides grossa in the josephine hole at a depth of 700 m cassidulina teretis is the dominant species in the pliocene and it continues with decreasing frequencies into the early pleistocene the boundary between early and middle pleistocene occurs at a depth of about 210 m in the borehole correlation from west to east in the central north sea reveals an extremely thick pliocene 400 m and early pleistocene 500 m sequence at the josephine site this sequence thins out both to the west and to the east this together with the palaeoenvironmental evidence present at the josephine site indicates that continuous tectonic subsidence occurred during the pliocene and early pleistocene in the central graben variations in the thickness of the middle and late pleistocene units in the region is probably due to pronounced glacial chanelling

characteristics of aeolian grain transport over a fluvio glacial lacustrine braid delta lake tekapo new zealand this paper presents results from one of the few scientific studies to examine the physical characteristics of aeolian sediment transport in an alpine area where topographically reinforced foehn winds initiate dust storm events the major objective of this study is to improve knowledge of aeolian processes in mid latitude alpine regions experiencing extreme wind speeds of particular interest is the role of surface characteristics in contributing to the unusually deep saltation layer which is seen to form over fluvio glacial deposits in the southern alps of new zealand sediment was collected at several heights 0 5 1 2 and 4 m and locations over a large alpine braided river delta and standard laboratory techniques used to examine grain size characteristics an image processing technique was also used to evaluate grain roundness grains filtered from the airstream at 0 5 m and 1 m above such surfaces were found to display a mean grain size of approximately 300 to 435 m resembling grain size characteristics of saltation clouds previously observed in high latitude cold climate locations in contrast to desert and prairie environments samples collected at 2 and 4 m above the surface were found to consist of 60 to 65 per cent sand sized material with some grains exceeding 1 1 5 mm in diameter grain shape analysis conducted on silt and clay sized grains filtered from the airstream above mixed sand and gravel surfaces showed such grains to display an increase in grain roundness with height this characteristic is thought to reflect the airstream s shape sorting ability and has important implications with respect to the often observed increase in grain roundness in aeolian deposits with increasing distance from source areas namely if more rounded grains are preferentially carried higher into the airstream and therefore into regions of higher wind speed they should theoretically be transported further from the entrainment zone before being deposited the high wind speeds observed often exceeding 30 m s 1 are seen to transport significantly larger sediment than reported in the literature for desert and prairie environments in addition the mixture of grain sizes and especially the pebble and cobble sized clasts that dominate the fluvio glacial deposits associated with the braided rivers in this mountain region also appear to increase significantly the trajectory height of saltating sand grains as a result of these two factors the depth of the saltation cloud often exceeds 1 m observations made in this study therefore highlight the need for field and laboratory aeolian process studies to be extended to examine grain transport over coarse grained beds during much higher wind velocities than typically reported in the literature such studies would provide a valuable insight into aeolian processes in high latitude altitude environments such as loess genesis 1997 by john wiley sons ltd

palaeomagnetic evidence for early pleistocene in the central and northern north sea the palaeomagnetic evidence presented here refutes the earlier hypothesis that most of the quaternary succession in the central north sea area is of middle to upper weichselian age a study of the quaternary seismic stratigraphy has been tied to 11 cored boreholes which are being examined for their physical properties and faunal content initial palaeomagnetic studies show a major reversely magnetized zone which can be correlated from borehole to borehole and with the seismic stratigraphy this reversely magnetized zone is thought to represent the matuyama epoch which ended 790 000 yr bp consequently this suggests the presence of early pleistocene strata in the central and northern north sea

roundness parameters of quartz grains of recent aeolian sand deposits in kuwait abstract roundness properties of quartz grains from various types of recent aeolian deposits in kuwait were examined the results confirmed that rounded and well rounded grains are relatively rare the investigated quartz grains were found to be mainly subangular and subrounded although no difference was noted in the roundness properties of the various types of aeolian deposits significant variation was recorded among the size fractions grain size distribution and the maturity of source sediments are considered to be the main factors controlling the roundness properties of recent aeolian sediments

sedimentation geochemistry and palaeomagnetism of the west runton freshwater bed norfolk england the sedimentary succession of the west runton freshwater bed wrfb is described and interpreted the sediments represent a fluvial valley floor accumulation that trends west to east subparallel to the modern cliffline stabilisation of the stream channels was initially followed by deposition of fine grained silt in standing water punctuated by intermittent flood events decreased flood intensity resulted in vertical accretion of fine grained organic fossiliferous sediments in carbonate rich spring water increased organic deposition produced a transition to black detrital sediment periodic flooding continued but flood frequency decreased in response to reduction in accommodation local erosion of channel banks and floors also occurred the sediments were disturbed by water release structures and bioturbation the latter resulting from large mammals locally entering the channel and pools churning the deposits during walking bathing and so on river flow velocity diminished later as forest vegetation stabilised catchment and valley floor ground surfaces stabilisation of the channel led to deposition from low velocity flowing and standing water the uppermost part of the succession indicates vertical accretion sheet like deposition the organic silts were deposited in an anoxic environment and organic sulphur from rotting organic matter allowed formation of early diagenetic sulphides deposition began during the late glacial beestonian stage and continued into the first half of a temperate climate interglacial event the cromerian stage s s the infill comprises an overall finingupward sequence the stream adopted a stable meandering pattern the wrfb stream showed typical chalk stream behaviour the magnetic polarity of the wrfb sediments is normal the palaeomagnetic data indicates that the sediments are of brunhes chron age and imply that they post date mid mis 19

some thermal constraints on crustal assimilation during fractionation of hydrous mantle derived magmas with examples from central alpine batholiths following assimilation at different levels in the crust we test by heat and mass balance the extent of assimilation of crustal country rocks in different local plutonic

modelling magnetization data using simplex two new approaches to modelling magnetization data are described the first approach models the magnetic properties of natural materials in terms of mixtures of possible source materials the second approach models the magnetic properties of natural materials in terms of mixtures of magnetite and haematite crystals of varying concentrations and grain sizes in the second approach the magnetic characteristics of magnetite and haematite and their variation with grain size are described by bicubic spline functions the methods are applied to remanence and susceptibility measurements on a suite of lake sediment particle size fractions and on a set of samples from a soil profile

the initiation of particle movement by wind when air blows across the surface of dry loose sand a critical shear velocity fluid threshold ut must be achieved to initiate motion however since most natural sediments consist of a range of grain sizes fluid threshold for any sediment cannot be defined by a finite value but should be viewed as a threshold range which is a function of the size shape sorting and packing of the surface sediment in order to investigate the initiation of particle movement by wind a series of wind tunnel tests was carried out on a range of pre screened fluvial sands and commercially available glass beads with differing mean sizes and sorting characteristics a sensitive laser monitoring system was used in conjunction with a high speed counter to detect initial grain motion and to count individual grain movements test results indicate that when velocity is slowly increased over the sediment surface the smaller or more exposed grains are first entrained by the fluid drag and lift forces either in surface creep rolling or in saltation bouncing or hopping downwind as velocity continues to rise larger or less exposed grains may also be moved by fluid drag on striking the surface saltating grains impart momentum to stationary grains this impact may result in the rebound of the original grain as well as the ejection of one or more stationary grains into the air stream at shear velocities lower than that required to entrain a stationary particle by direct fluid pressure as a result there is a cascade effect with a few grains of varying size initially moving over a range of shear velocities the fluid threshold range and setting in motion a rapidly increasing number of grains results of the tests showed that the progression from fluid to dynamic threshold based on grain movement can be characterized by a power function the coefficients of which are directly related to the mean size and sorting characteristics of the sediment

the magnetic properties of quaternary and tertiary sediments in the southern north sea cores from boreholes penetrating late quaternary glacial interglacial and postglacial sediments and the underlying late cenozoic delta complex of the southern north sea have been examined for their magnetic properties a magnetic polarity stratigraphy has been established as an aid to biostratigraphic dating of the sediments the kaena gauss and gauss matuyama transitions and the base and top of the olduvai subchron have been identified the strength and stability of laboratory induced isothermal remanent magnetisation display clear magneto petrological variations which match lithostratigraphic changes in the cores principal component analysis has picked out a basin wide and palaeoenvironmental consistency in the magnetic data large multi domain magnetite grains predominate in the post deltaic and fluvio deltaic sediments whereas smaller greigite or titanomagnetite grains are concentrated in the intertidal and marine deltaic facies since heavy mineral analysis indicates that most of the deltaic detritus derived from common source areas the differences in magnetic mineralogy have probably been caused by the sediment transport processes operating within the delta complex

palaeomagnetic study of cenozoic sediments in north sea boreholes an example of a magnetostratigraphic conundrum in a hydrocarbonproducing area

high resolution seismic profile through a late cenozoic delta complex in the southern north sea abstract a digitally recorded and processed multichannel seismic profile between cromer england and sylt germany has provided the first continuous section through the miocene to middle pleistocene delta complex of the southern north sea basin the profile depicts the progressive westward expansion of deltaic sedimentation that eventually filled in this gently subsiding epicontinental basin significant basinward shifts in seismic facies occur above all but one of 14 seismic sequence boundaries that punctuate the deposition of up to 830 m of deltaic sediments on the profile these sequence boundaries and the morphology of prodelta delta front delta top and fluvio deltaic seismic facies record the interaction between subsidence cyclic fluctuation in sediment supply to and cyclic change of relative sea level within the basin two submarine slides were developed within delta front facies in the pliocene section and the profile has intersected a swarm of elsterian middle pleistocene glacial palaeovalleys that have been incised into the upper part of the delta complex

the vedrette di ries rieserferner plutonic complex petrological and geochemical data bearing on its genesis data on co sc rb sr th zr ta hf and ree contents are reported for tonalites granodiorites granites and one diorite from the alpine plutonic complex of vedrette di ries in the eastern alps co and sc range respectively between 19 6 1 2 ppm and 32 3 3 ppm showing a good negative correlation with the differentiation index d i rb values range between 61 197 ppm displaying a positive correlation with d i all the samples have variably fractionated light and heavy ree with lan smn 1 7 5 55 and tbn ybn 0 58 1 65 and no important europium anomalies on the basis of the hree fractionation two groups of rocks can be distinguished one showing higher tbn ybn values which range between 1 27 1 65 and are positively correlated with the d i and a second group with tbn ybn values less than unity which decrease with the differentiation the rocks with high tbn ybn ratio also display a positive sr versus d i variation whereas the samples with flat or upward concave hree patterns i e with tbn ybn 1 define negative sr versus d i trends th ta hf zr and lree show an overall tendecy to increase and then to decrease with the differentiation with a large scattering of values

entrainment threshold of natural grains in liquids determined empirically from dimensionless settling velocities and other measures of grain size abstract grain size plays a crucial role in sediment transport but different methods of size analysis do not yield comparable results particle diameters obtained by settling tube for example cannot be employed in equations based on sieve sizes although the majority of experiments on the initiation of sediment motion has been based on sieve data settling tube analysis is probably superior as both the settling rate and the entrainment threshold of grains are determined by the same factors of size shape and density in this paper empirical equations are provided which allow the determination of a non dimensional critical shear stress directly from the equivalent sedimentation diameter the equations apply to the entrainment of well sorted grains with a high sphericity on flat sediment beds and are valid for particles and liquids of different densities

zircon petrochronology and 40ar 39ar thermochronology of the adamello intrusive suite n italy monitoring the growth and decay of an incrementally assembled magmatic system the adamello intrusive suite is a composite batholith in northern italy with an estimated 2000 km3 volume assembled incrementally over a time span of 10 to 12 million years the history of crysta

age and tectonic setting of bocsa and ocna de fier dognecea granodiorites southwest romania and of associated skarn mineralisation the granodiorite intrusion at ocna de fier dognecea in the western south carpathians romania triggered the formation of a classic fe pb zn skarn deposit the intrusive is related to the larger composite bocsa laccolith five kilometres north that is part of the regional banatite suite previous work indicated a k ar age of 65 57 ma and postulated an andean type subduction related tectonic setting for the intrusions we report ion probe u pb zircon ages of 79 6 2 5 ma for the bocsa laccolith and 75 5 1 6 ma for the ocna de fier pluton which date their emplacement fission track dating on titanite gives slightly younger ages 78 4 ma for bocsa and 73 4 ma for ocna de fier together with zircon and apatite data from the same samples average cooling rates of 52 c ma and 83 c ma are calculated for the bocsa and ocna de fier intrusives respectively a post collision tectonic setting is proposed on the basis of field evidence the timing of intrusions in the context of regional tectonic evolution and trace element geochemistry

magnetic carriers and remanence mechanisms in magnetite poor sediments of pleistocene age southern north sea margin pleistocene sedimentary sequences in the east anglian region of britain record both major and minor climatic oscillations and the impact of isostatic and eustatic variations intensively studied in terms of their lithology and biostratigraphy the sequences have been difficult to place in an absolute timeframe dating and correlation by magnetostratigraphy has been attempted over a num ber of years however these sediments are difficult to date by palaeomagnetic means because they are poor in detrital magnetite are subject to post depositional deformation and diagenesis and have unknown rates of sedimentation determining whether their natural remanence magnetisation nrm directions are reliable thus requires information on the mode and timing of remanence acquisition here we apply palaeomagnetic rock magnetic and mineralogical analyses to identify the nrm carriers in these sediments and hence their palaeomagnetic reliability within oxidised fluvial sediments the kesgrave formation the magnetic carriers appear to be relict magnetic minerals fer rian ilmenites chromites haematite and goethite which sometimes carry a reliable primary deposi tional remanence drm but often an overprinting viscous time varying remanence vrm within some reduced marine and intertidal sediments within the crag basin the iron sulphide greigite has been found to carry a reliable syn depositional chemical remanence crm in all the sediments magnetic inclusions within silicates are abundant are significant for the mineral magnetic signal but contribute little to any recoverable palaeomagnetic information copyright 2005 john wiley sons ltd

lower pleistocene dinoflagellate cyst foraminiferal and pollen assemblages in four boreholes in the southern north sea neogene and lower pleistocene stratigraphy in the southern north sea has been investigated in four i g s boreholes between east anglia and the netherlands the foraminifera of the red crag formation in borehole 81 51 are closely similar to upper pliocene assemblages in holland the overlying succession is clearly punctuated by unconformities in seismic profiles separating four early pleistocene formations in the boreholes and indicating intervals of significant stratigraphic hiatus offshore the westkapelle ground and smith s knoll formations correlate with thurnian and antian stage deposits in east anglia pollen spectra in the winterton shoal and yarmouth roads formations are similar to baventian and bramertonian assemblages in britain the autochthonous marine and allochthonous terrestrial microfauna and flora provide conflicting evidence of early pleistocene palaeoclimate the dinoflagellate cysts and foraminifera indicate that each formation was deposited in a warm temperate neritic environment the pollen record containing evidence of fluctuation between boreal and mixed coniferous deciduous regional forest cover suggests alternation between cool and warm temperate palaeoclimate

magnetic properties of lake sediments from lake chalco central mexico and their palaeoenvironmental implications lake chalco 99 0 w 19 5 n in the basin of mexico was formed during the pleistocene after the emplacement of the chichinautzin volcanic field that closed the former drainage system the lake sediment record has been influenced by a number of factors including glacial interglacial cycles local volcanism erosion of soils and anthropogenic disturbances the magnetic properties of the lake sediments and the associated tephra layers of the last 16500 yr have been studied it is found that the magnetic properties of the lake chalco sediments are very distinctive magnetic concentration varies by a factor of 1000 and magnetic stability also varies over an extremely wide range the predominant magnetic mineral is titanomagnetite in addition to an imperfect antiferromagnetic phase possibly goethite an unusually large range of coercivities is found in certain of the tephras down core variations in magnetic properties closely follow climatic environmental changes previously established by other proxy methods the late pleistocene and late holocene lake sediments display a higher concentration of magnetic minerals than the early middle holocene sediments in the non volcanic sediments fluctuations in the magnetic concentration reflect changes in both the intensity of erosion as represented by ferrimagnetic and paramagnetic minerals and by the maturing of soils as represented by geothite copyright 2000 john wiley sons ltd

the gabbro shoshonitic monzonite granodiorite association of khankandi pluton alborz mountains nw iran abstract the khankandi pluton forms part of a group of gabbro granodiorite intrusions in the alborz mountains of nw iran a petrographical and geochemical study of this plutonic association reveals the existence of several magmatic cycles with different origins and slight differences in age the oldest cycle c1 is represented by granodiorites a second cycle c2 is formed by a gabbro monzonite association with a clear shoshonitic affinity that dominates most of the intrusive volume gabbros and monzonites form a co magmatic association zircons from the monzonites were analyzed by la icp ms for u pb dating an average age of 28 9 ma ranging from 23 7 to 33 6 ma was obtained gabbros monzonites and granodiorites share a nearly common isotopic ratio for sr and nd both initial sr and nd ratios are clustered within a narrow range from 0 7045 to 0 7047 for the 87sr 86sr ratio and end from 1 46 to 1 89 comparison with experimental studies together with mantle like isotopic ratios and comparisons of ree patterns points to an origin by variable melting rates from a common metasomatised mantle source for gabbros and monzonites melting of a subducted melange is suggested for the granodiorite magmas predating the gabbro monzonite intrusion the two sources a metasomatised mantle and ascending silicic plumes are direct consequence of subduction

post collision magmatism and tectonics in northwest anatolia a suite of biotite hornblende granodiorite intrusions has been emplaced into blueschist facies metasediments in northwest anatolia following collision between two continental margins now represented by the tavsanli and sakarya zones the 40ar 39ar ages of phengites and glaucophanes from the blueschists metamorphosed under unusually high p low t conditions p 20 2 kbar t 430 30 c suggest that metamorphism apparently occurred over a period spanning at least 20 ma from 108 to 88 ma post tectonic granodiorites were emplaced during the eocene 53 to 48 ma resulting in a cordierite and andalusite bearing thermal aureole indicative of pressures of 3 kbar trace element systematics of the granodiorites are consistent with a derivation either from mantle derived magmas by fractional crystallisation in shallow magma chambers or from anatexis of crustal lithologies of internediate composition at pressures 10 kbar the preservation of high p low t assemblages in the blueschists together with the range of ages determined for blueschist facies metamorphism are indicative of rapid exhumation of delaminated fragments from a subducted continental margin however decompression melting of the crust is unlikely to have been a significant cause of magmatism both because exhumation of the blueschists from deep crustal levels predated magmatism by at least 25 ma and because of the small melt fraction 0 1 that may be generated in crustal lithologies by this process melting in the mantle wedge is required either to generate a primary melt for the derivation of magmas of intermediate composition or to provide an advective heat source for crustal melting the cause of melt formation in the upper mantle may be related to the termination of subduction following collision during the mid eocene

the magnetic susceptibility of continental shelf sediments west coast vancouver island canada abstract measurements of magnetic susceptibility of continental shelf sands off central vancouver island revealed two areas of anomalously high values 1 at the mouths of coastal inlets suggesting a reworking of glacial and glacio fluvial sediments and 2 the outer shelf downslope from outcropping deformed tertiary pleistocene strata resulting from the winnowing of these older sediments during periods of lowered sea level magnetic susceptibility was highest within the silt and fine sand fractions and lowest in the clay and coarse sand fractions though because of the grain size distributions the fine sand invariably contributed more to the overall sample susceptibility than the other size fractions although no apparent relationships were found between magnetic susceptibility and commonly measured grain size statistics the highest values were concentrated within a narrow range of size sorting skewness and kurtosis magnetic susceptibility is a readily determined parameter of marine sediments which can contribute to the interpretation of the depositional history of a region and which may have direct economic applications because of the association between magnetite and heavy mineral placers

cohesions friction angles and other physical properties of martian regolith from mars exploration rover wheel trenches and wheel scuffs 1 the mars exploration rovers spirit and opportunity investigated the physical properties of martian regolith in 7 wheel trenches and 20 wheel scuffs distributed along traverses at gusev crater and meridiani planum specialized wheel trenching sequences allowed analysis of wheel motor and suspension telemetry to determine regolith friction angle and cohesion c at trench sites friction angles were 30 37 and cohesions were 0 2 kpa simpler wheel scuff maneuvers were analyzed for cohesion by assuming the range of determined from trenches cohesions in wheel scuffed regoliths were from 0 to 11 kpa regolith and c can be related to regolith origins grain sorting compaction shape size and angularity influence impact cratering and aeolian processes have affected grain angularity and sorting of martian regolith at both mars exploration rover mer landing sites and contend in opposing ways to determine grain characteristics in the regolith friction angles are consistent with dry rigid nonplaty grains with particle size frequencies dominated by very fine sand as seen by the microscopic imager or mi with at least some grain rounding unresolved by mi reflecting physical weathering from aeolian saltation friction angle results from mer trenches therefore indicate that regolith states are between fully mature aeolian materials and impact debris mi and color pancam views show trench tailings and trench floors are redder brighter and have more intermixed extremely fine unresolved grains than regolith closer to the surface disturbed and exposed only by rolling tracks

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

the history of quaternary sedimentation in the uk sector of the north sea basin reconnaissance seismic and sampling surveys have shown that up to 500 m of lower and early middle pleistocene deltaic sediments are preserved in the uk sector of the north sea the distributions of delta related facies record the progressive expansion of peripheral delta systems northwards across the southern north sea during the early pleistocene a late middle pleistocene unconformity is present throughout the uk sector and sedimentation above the unconformity was dominated by glacial erosional and depositional processes a complex system of deeply incised valleys was eroded during each of three regional middle and upper pleistocene glaciations and the valleys have been filled or partially filled by glaciolacustrine or glaciomarine and interglacial marine sediments the valleys of the earliest elsterian glaciation are up to 400 m deep in the southern north sea the saalian and weichselian valleys are commonly more than 100 m deep they are eroded through their contemporary tills nearshore but occur well beyond the limits of these tills offshore the origins of these valleys are attributed to a combination of fluvial subglacial and periglacial processes

evolution of the bayramic magmatic complex northwestern anatolia abstract during the oligocene middle miocene period widespread magmatic activity developed in western anatolia following the continental collision between the sakarya continent and the tauride anatolide platform this produced both intrusive and extrusive rocks which appear to be associated in space and time as exemplified from the bayramic area in the bayramic area the magmatic activity started with the intrusion of the evciler granite and the coeval lower volcanic association this was followed by the development of the upper volcanic association these rock groups form collectively the bayramic magmatic complex which was generated under an on going north south compressional regime the bayramic magmatic complex has a subalkaline composition displaying a calcalkaline trend trace elements and ree contents resemble to island arc and collision related magmas according to the isotope values the bayramic magmatic complex was derived from the magmas of lithospheric mantle origin which were later contaminated while passing through the thick continental crust in a post collisional tectonic setting during the oligocene early miocene period the latest product of the magmatism is the late miocene pliocene basalt lavas their geochemical properties are clearly different from the oligocene early miocene magmatic rocks the basalts were generated when the north south compression gave way to the north south extensional regime

young alpine dykes south of the tauern window austria a k ar and sr isotope study fortyfive new k ar ages and sr isotope data on amphiboles biotites clinopyroxenes and whole rock samples from subvolcanic dykes south of the tauern window establish that alkalibasaltic dykes were intruded 30 m y ago and shoshonitic volcanism occured between 30 and 24 m y ago two calc alkaline rocks of high potassium composition yielded ages of 40 and 26 m y resp a spread which may or may not be real calc alkaline dykes with medium and low potassium contain excess argon and are hence undatable alkalibasaltic dykes have 87sr 86sr ratios of 0 7056 0 7070 shoshonitic rocks 0 7075 0 7133 potassium rich calc alkaline dykes 0 7077 0 7100 87sr 86sr of all other calc alkaline rocks scatter between 0 7074 and 0 7150 sr data indicate that dykes studied do not represent closed sr systems but that sr characteristics result from selective strontium assimilation en route to surface primary sr isotopic ratios of alkalibasaltic dykes point to an origin of these rocks in enriched sub continental upper mantle the source region of shoshonitic and high potassium calcalkaline rocks could have 87sr 86sr around 0 707 which is assigned to the input of a component rich in alkalies lree and lil elements genetic relationships with other tertiary magmatites of similar geotectonic position are explained in terms of plate tectonic models of the eastern alps

zircon inheritance in an igneous rock suite from the southern adamello batholith italian alps zircons from a suite of basic to acidic calcalkaline igneous rocks from the southern adamello batholith s ab southern alps n italy display complex u pb isotopic patterns which are mainly due to the presence of variable amounts of isotopically heterogeneous inherited radiogenic pb and to minor postmagmatic loss of pb inherited pb is mainly composed of 1 a 1100 ma pb component located in zircons devoid of visible cores and 2 a 450 ma component associated with conspicuous bubble rich turbid cores in concordia representation the data points conform to lower intercept ages of 40 ma a linear fit of three samples devoid of visible cores from the granodiorite defines an intrusion age of 39 3 ma u pb systematics of zircon in particular u content and crystal morphology are clearly related zircons of type g1 which form relatively late in the zircon crystallization sequence consistently show the highest u contents in each zircon population these late zircons however are not devoid of inherited radiogenic lead in a population from a granodiorite cores are randomly distributed throughout the morphological spectrum the presence of old inherited zircon components in all investigated samples furnishes proof for involvement of crustal material in the genesis of the s ab rocks samples characterized by crustal nd and sr values usually show enhanced zircon inheritance inheritance varies with differentiation and reaches a maximum for intermediate to acidic members these compositions show the highest zr saturation temperatures calculated for the rock spectrum studied textural relations between zircon and major phases indicate that the magmas of the leucocratic rocks were saturated with zr at an early stage of crystallization on the other hand zr solubilities and textural relations consistently show that melts of basic to intermediate rocks were not saturated with zr extension of the zr solubility model to mineral melt mixtures of tonalitic bulk composition demonstrates that zr solubility in the residual melt is drastically reduced by crystallization of plagioclase and amphibole survival of xenocrystic zircons in the mafic to intermediate rocks of the s ab can best be explained in terms of dissolution kinetics since temperature and h2o content of these zr undersaturated melts were favourable for relatively rapid zircon dissolution inherited zircons in particular trace element rich unstable cores cannot have been exposed to such conditions over extended time periods therefore the tonalitic or more basic magmas of the s ab cannot have been derived from crustal sources by slow processes such as burial metamorphism

estimation of some aeolian saltation transport parameters a re analysis of williams data a new method for analysing observed aeolian sand transport rate profiles of the kind obtained by williams is presented the method involves a mathematical model of aeolian saltation detailed information about the saltation process can be calculated from the transport rate profile by means of this model the method is used to perform a re analysis of williams trap data among the main findings of this analysis is that the grain borne shear stress appears to be a smaller fraction of the total shear stress than assumed by bagnold owen in their theories of aeolian saltation other findings are that the probability distribution of the jump height of the grains does not depend much on the wind speed once the saltation is established and that the vertical component of the mean launch velocity decreases with the grain size it is approximately inversely proportional to the grain diameter our estimates of the landing angles indicate that estimates of the impact angles obtained from photographically recorded trajectories are too small due to biased sampling the influence of grain shape on the transport characteristics is mainly due to changes in the grains ability to jump when hitting the bed it is found that angular grains have a lower mean jump height than spherical grains

roundness parameters in barrier lagoon systems in northeastern shandong peninsula china limitations to environmental discrimination twenty five samples from six subenvironments in the barrier lagoon systems in northeastern shandong province china are examined a statistical method is used to study the roundness variation of grains of different sizes roundness of very fine pebble and very coarse sand varies significantly in different subenvironments it is possible to discriminate among aqueous depositional environments using the roundness of grains of these sizes roundness of grains finer than 0 84 is not distinguishable in different subenvironments

dissolution and pyritization of magnetite in anoxie marine sediments concentrations of magnetite were determined with depth in sediments of varying h2s content taken from long island sound foam nwc and sachem sites and from a site in the rapidly depositing subaqueous portion of the mississippi delta for the three long island sound sites dissolution of magnetite during burial is clearly demonstrated and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide by combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide we find that magnetite dissolution is well described by the following rate law dcmagdt 1 1 10 5c0 5bcmagamag where cmag is the concentration of magnetite grams per gram of sediment cs is the concentration of dissolved sulfide mm and amag is the specific surface area of magnetite in the sediment cm2 per gram of magnetite this equation means that for a typical range of magnetite surface areas and dissolved sulfide concentrations the half life of magnetite in anoxic marine sediments ranges from about 50 to 1000 years sem observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite this only occurs if magnetite is in contact with high concentrations of h2s 1 mm for relatively long periods of time several hundred years with low concentrations of h2s 1 mm magnetite dissolution occurs without identifiable pyrite replacement we suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator

subseabed disposal a geosciences perspective billions of dollars are spent every year in the search for natural resources utilizing the most sophisticated technology available to assess the geological geochemical and geophysical characteristics of a particular region this technology can also be used however to search for the most desolate isolated useless terrain available to be used as a repository for high level nuclear waste this terrain is not limited to the 30 of the planet s surface upon which we live it includes the 70 lying beneath the ocean waters as well

diagenesis of magnetic minerals in recent haemipelagic sediments rapidly deposited sediments from marine and lake environments are being used increasingly to study decadal to millennial fluctuations in the earth s magnetic field the objectives are to gain more fundamental understanding of the geodynamo and to establish a new dating technique for sediments while lacustrine sections are generally restricted to temperate latitude glacial lakes 20 000 yr old rapidly deposited marine sediments along continental margins potentially offer continuous high resolution yet long term records of geomagnetic secular variation however to interpret the sedimentary magnetic record accurately geochemical processes that affect the reliability of the magnetic signal must be understood we now report downcore magnetic profiles from undisturbed kasten cores taken in rapidly deposited laminated sediments from the gulf of california and in bioturbated haemipelagic muds on the oregon continental slope which give apparently reliable directions but show dramatic decreases in the intensities of natural nrm and artificial arm irm remanences with depth downcore porewater and solid sulphur analyses show concave down decreases in porewater sulphate and systematic increases in pyrite and metastable monosulphides the maximum curvature of the sulphide profile occurs directly below the high magnetization zone combined with other compositional and mineralogical analyses these data suggest that due to oxidative decomposition of organic matter magnetites and other iron oxides become progressively reduced and subsequently sulphidized and pyritized with depth iron reduction seems to occur before sulphide formation changes in magnetic stability parameters are consistent with selective dissolution of the finer sized grains causing downcore coarsening of the magnetic fraction

late weichselian to early holocene litho and biostratigraphy in the devil s hole area central north sea and its relation to glacial isostasy the 6 m long british geological survey vibrocore 56 01 170 from the devil s hole area central north sea comprises glaciomarine and marine sediments of late weichselian and holocene age besides the foraminiferal pollen and ams 14c data presented in this study amino acid and ostracod data exist for the core the accumulation of the sediment in the core began ca 15 7 14c ka bp on an erosional surface on overconsolidated saalian sediment when the lower part of the core facies 1 accumulated the core area is interpreted to have been around 40 m lower than present this interpretation is based on two assumptions first that the sediment is now ca 20 m above the global sea level at the time of deposition and second that the marine microfaunal content reflects a water depth of about 20 m at that time crustal downflexure caused by late weichselian glacial loading of the core area is considered as the most plausible explanation of this difference glacial overriding would also explain the overconsolidation of the underlying saalian sediment the erosional surface on the saalian sediment and the absence of weichselian sediment older than ca 15 7 ka bp at the core site indications of a regressional trend with a minimum age of 12 1 ka bp support the suggestion that the devil s hole area was glaciated during the weichselian as the fall in sea level at that time probably reflects local isostatic rebound

geochemistry of the adamello massif northern italy the tertiary adamello massif outcropping over an area of more than 550 km2 in the southern alps northern italy is composed mainly of granitoid rocks granodiorite tonalite quartz diorite with minor amounts of diorite and gabbro the major and trace element composition of these rocks is comparable to calc alkaline volcanic rocks of continental margins the granitoid rocks display spatial and temporal variations in their composition particularly in na p sr la nb and y contents and 87sr 86sr ratios the variations were probably produced by concurrent contamination wall rock assimilation and fractional crystallization of high alumina basaltic magma

shape effects in aeolian grain transport wind tunnel experiments are reported the results of which show that grain transport rate is responsive to characteristic grain shape it is relatively less sensitive to changes of sorting unless these involve the fraction smaller than 50 m a cubic relationship between transport rate and velocity gradient appears to be valid only for well worked natural grains having high sphericity

shear zones and magma ascent a model based on a review of the tertiary magmatism in the alps 1 the alpine oligocene plutons are spatially and temporally associated with the activity of the periadriatic fault system pfs an orogen parallel crustal scale transpressive mylonitic belt excellent three dimensional exposure combined with a wealth of structural seismic petrological geochronological geochemical and paleomagnetic data collected over the last decades help to constrain the relationships between deformation ascent and emplacement of the plutons magmas were channeled from the base of the thickened continental crust into the narrow mylonitic belt of the periadriatic fault system which was used as ascent pathway to cover vertical lengths of 20 to 40 km therefore the linear alignment of the plutons at the surface is not the expression of a linear source region at depth ascent of the melts is controlled by the mylonitic foliation of the pfs which forms the only steep anisotropy continuously traversing the entire alpine crust in contrast the flow direction is not influenced by the specific kinematics of the faults final emplacement of the plutons occurred by extrusion from the periadriatic fault system into the adjacent country rocks the transition from ascent to final emplacement is favored by partitioning of transpressive deformation

transport by wind of granular materials of different grain shapes and densities aeolian transport rates were measured for three sands a quartz sand relative density 2 68 sphericity 0 73 a shelly sand relative density 2 64 sphericity 0 59 carbonate content 67 and granular aluminium oxide relative density 3 95 sphericity 0 67 low sphericity depresses the transport rate particularly at high wind speeds high density also does so but the effect is more marked at low transporting wind speeds the sand of low sphericity undergoes longer saltations than the other materials but is dislodged less frequently than they are and is transported less freely in a given wind of the more spherical materials the denser was the least effective at extracting energy from the wind for grain transport in the range of our experiments both of the more spherical materials showed evidence of a fairly sudden transition of transport behaviour at modest wind speed it is inferred that this marks the transfer of the function of grain dislodgement from direct wind action to inter granular collision the transition did not occur in experiments on the material of lower sphericity for a given transport rate wind speed near the bed is highest for the grains of low sphericity by a considerable margin and lowest for the more compact quartz grains propensity for transport by wind is greatest for the quartz sand less so for the heavy material and least for the material of low sphericity

post collisional transition from calc alkaline to alkaline magmatism during transcurrent deformation in the southernmost dom feliciano belt braziliano pan african uruguay abstract in the southernmost dom feliciano belt of uruguay highly fractionated calc alkaline granites mildly alkaline granites shoshonitic volcanics and peralkaline intrusions and volcanics are spatially and temporal associated with the evolution of shear zones four representative magmatic unites of this diverse association were petrographic and geochemically investigated the solis de mataojo complex a medium to high k2o calc alkaline granite with signature typical of mature continental arcs and post collisional settings the maldonado granite highly fractionated calc alkaline to alkaline with characteristics that are transitional between both types of series the pan de azucar pluton with characteristics typical of post collisional alkaline granites and the las flores shoshonitic basalts geochemistry and geotectonic setting point out that slab breakoff was most likely the mechanism associated with the generation of high k calc alkaline magmas solis de mataojo and maldonado shortly after collision extension associated to the formation of molassic basins and emplacement of dolerites and basalt flows with shoshonitic affinity las flores 15and finally a shift to magmas with alkaline signatures pan de azucar simultaneous with a second transpressional phase were probably linked with lithospheric thinning through delamination this evolution took place between 615 and 575 ma according to available data contrary to previous proposals which considered this magmatism to represent the root of a continental magmatic arc a post collisional environment transitional from orogenic to anorogenic during transcurrent deformation is proposed

nd sr isotopic and geochemical characteristics of the southern adamello northern italy intrusives implications for crustal versus mantle origin among the periadriatic tertiary calc alkaline intrusions in northern italy the adamello batholith displays the most convincing evidence for a mafic parentage this is particularly the case for the southern adamello where minor ultramafic to gabbroic bodies form the margins of several distinct and dominantly tonalitic plutons isotopic analyses are presented for the val fredda and blumone ultramafic gabbroic to tonalitic leucoquartzdioritic suites for the more felsic rock types of the spatially predominant re di castello group as well as for a lamprophyre this dike of picrobasaltic composition is thought to represent the parental magma field relations and a large body of petrographic geochemical and mineral chemical data point to a cogenetic origin for all of these rocks and to magmatic differentiation with fractional crystallization and accumulation as the main evolutionary mechanism this is compatible with the isotopic results for the blumone series and the mafic rocks of val fredda with end 3 8 to 1 5 and esr 9 1 to 4 6 a common parental magma similar to the lamprophyre end 3 1 esr 4 4 also seems plausible the isotopically homogeneous felsic lithologies of val fredda end 0 1 to 0 3 esr 2 9 to 0 7 structurally intimately associated with their mafic counterpart indicate crustal contamination incurred prior to their differentiation for the re di castello group progressing crustal affinity of isotopic compositions end of 1 9 to 4 9 and esr of 16 5 to 40 9 with chemical differentiation implies large scale interaction with a granitoid crustal component attempts at quantifying this process reveal individual characteristics and evolution for each pluton the data indicate extraction of this component from a source in the lower crust with time integrated low rb sr esr approximating 50 and en close to 6 corresponding to a 1000 ma crustal residence age if a two stage evolution is assumed formation of a gabbroic reservoir from the above parental melt would require uptake of some 4 12 wt of granitoid component by combined assimilation fractional crystallization whereas subsequent evolution to tonalitic compositions would necessitate admixing of 40 70 wt of granitoid partial melt assimilation thus mainly occurs during evolution from gabbroic to tonalitic compositions when the mafic magma is ponded near the mantle crust boundary and where homogenization prior to resuming buoyant ascent is assured precise locations and more detailed petrography of the samples is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document 91b 002 2 50 payment must accompany order