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

satellite remote sensing of surface oceanic fronts in coastal waters off west central florida abstract two algorithms designed to detect deepwater oceanic features and arbitrary edge profiles were tuned to automatically delineate fronts in coastal waters off west central florida using satellite derived sea surface temperature sst chlorophyll a concentration chl normalized water leaving radiance nlw and fluorescence line height flh images during select periods in the spring and fall of 2004 and 2005 the dates correspond to recreational king mackerel scomberomorus cavalla tournaments a histogram based algorithm was useful to detect coastal surface sst nlw and flh fronts specifically a gradient based algorithm with a smaller kernel box of 3 3 pixels best identified nearshore

evidence for the inherent unsteadiness of a river plume satellite observations of the niagara river discharge we present satellite data from the niagara river plume showing that a large eddy or bulge forms and grows in the plume near the mouth of the river the plume consists of a semicircular bulge region immediately offshore of the mouth and a narrow current that propagates east along the shoreline during the low wind period from 27 to 29 may 1999 the width of the bulge more than doubled and the current width increased only slightly approximately one third of the niagara river water accumulated in the bulge near the mouth during this period implying that the transport rate in the shore parallel current was reduced to two thirds of the river discharge rate the effective radius and the growth rate of the bulge computed from the satellite images was in good agreement with previous laboratory results and a numerical model of the niagara river plume this is the first field evidence of the unsteadiness of the bulge

a numerical study on convergence of alongshore flows over the texas louisiana shelf 1 a hydrodynamic model is used to investigate convergent alongshore flows over the texas louisiana shelf characterized by down coast flows over the northern shelf encountering up coast flows over the southern shelf the model s ability to reproduce realistic current salinity and surface elevation fields is demonstrated through positive model skill scores when comparing model simulations to observational data the convergent flows are explored on both weather band and seasonal time scales for weather band scales this study focuses on wintertime convergent events the model predicted locations of convergent flows are supported by current measurements we find that the formation of convergent flows is primarily caused by along coast variation in the alongshore component of wind forcing which in turn is due to the curvature of the texas louisiana coastline in general the alongshore currents are well correlated with alongshore winds however the convergence points of currents and winds are not colocated but rather convergence points in ocean currents typically occur down coast of convergence points in the wind this offset is demonstrated to be mainly caused by buoyancy forcing that can drive the convergence location in the currents farther down coast no specific temporal pattern is found for the weather band convergence locations whereas at seasonal time scales the monthly mean convergence exhibits a prominent seasonal pattern with up coast migration of convergence locations in spring and summer and down coast migration in fall and winter

petrogenesis of post collisional a type granitoids from the urumieh dokhtar magmatic assemblage southwestern kerman iran constraints on the arabian eurasian continental collision abstract three plutons deh siahan bande bagh and baghe khoshk sharghi collectively referred to as the dbb hereafter in southwestern kerman in the southeastern part of the urumieh dokhtar magmatic assemblage udma of the zagros orogenic belt differ from the typical calc alkaline metaluminous i type intrusions of the region the dbb intrusions have a distinct lithological assemblage varying from diorite through monzogranite and monzonite to alkali feldspar syenite and alkali granite the dbb granitoids are metaluminous to slightly peraluminous alkaline to shoshonitic in composition and have high total alkali contents with k2o na2o high feot mgo values and low cao and mgo contents they are enriched in some liles such as rb and th and hfses such as zr y and rees except eu and depleted in sr and ba relative to primordial mantle and have low concentrations of transitional metals these features along with various geochemical discriminant diagrams suggest that the dbb granitoids are post collisional a type granitoids which had not been recognized previously in the udma the chondrite normalized ree patterns of the dbb granitoids show slightly enriched light rees la sm n 2 26 4 13 negative eu anomalies eu eu n 0 19 0 74 and flat heavy ree patterns gd yb n 0 80 1 87 the negative eu anomaly indicates an important role for plagioclase and or k feldspar during fractional crystallization whole rock rb sr isotope analysis yields an isochron age of 33 1 ma with an initial 87sr 86sr value of 0 7049 0 0001 whole rock sm nd isotope analysis gives endt values from 2 56 to 3 62 at 33 ma the positive endt and low isr values of the dbb granitoids together with their tdm of 0 6 0 7 ga suggest their formation from partial melting of a lithospheric mantle source modified by fluids or melts from earlier subduction processes melting of lithospheric mantle occurred via a dehydration melting process at pressures below the garnet stability field as a consequence of lithospheric mantle delamination or break off of a subducted slab and melting of the lithospheric mantle by upwelling of hot asthenosphere on the basis of rb sr age dating and the post collisional geochemical signatures of the dbb granitoids along with extensive pre collisional volcanic eruptions in middle eocene we suggest late eocene for the time of collision between the arabian and central iranian plates this also implies that the calc alkaline i type intrusions in the southwestern kerman and in other parts of the udma may have formed in a post collisional context

regional setting and geochronology of the late cretaceous banatitic magmatic and metallogenetic belt the 1 500 km long banatitic magmatic and metallogenetic belt bmmb of romania serbia and bulgaria is a complex calc alkaline magmatic arc of late cretaceous age it hosts a variety of magmatic hydro thermal cu au mo zn pb and fe deposits including europe s only world class porphyry copper deposits regional metallogeny can be linked to subduction of the vardar ocean during the late cretaceous as part of the closure of the neotethys ocean that had separated europe and africa in the mesozoic porphyry cu au mo and intimately associated epithermal massive sul phides dominate in the central segments of the belt in southernmost banat romania serbia and north west bulgaria these districts are the economically most im portant today including major active cu au mines at moldova noua in romania majdanpek veliki krivelj and bor in serbia and elatsite assarel and chelopech in bulgaria more numerous and mostly mined in the past are fe cu and zn pb skarns which occur mainly at the two ends of the belt in eastern bulgaria and in romania this paper summarises some of the deposit characteristics within the geodynamic framework of terminal vardar subduction heterogeneous terranes of the belt including the apuseni mountains at the western end are aligned parallel to the vardar front following continental collision of the dacia and tisza blocks all available geochronological data numerous k ar and some u pb and re os ages are compiled and are complemented by a new high precision re os date for the dognecea skarn deposit south west romania 76 6 0 3 ma these data indicate that magmatism extended over at least 25 million years from about 90 to 65 ma in each segment of the belt within apuseni mountains and banat where magma emplacement was related to syn collisional extension in the orogenic belt of carpathians ore formation seems to be restricted in time and maybe constrained by a shared tectonic event

a numerical study of the long and short term temperature variability and thermal circulation in the north sea a three dimensional numerical study is presented of the seasonal semimonthly and tidal inertial cycles of temperature and density driven circulation within the north sea the simulations are conducted using realistic forcing data and are compared with the 1989 data of the north sea project sensitivity experiments are performed to test the physical and numerical impact of the heat flux parameterizations turbulence scheme and advective transport parameterizations of the surface fluxes with the monin obukhov similarity theory provide a relaxation mechanism and can partially explain the previously obtained overestimate of the depth mean temperatures in summer temperature stratification and thermocline depth are reasonably predicted using a variant of the mellor yamada turbulence closure with limiting conditions for turbulence variables the results question the common view to adopt a tuned background scheme for internal wave mixing two mechanisms are discussed that describe the feedback of the turbulence scheme on the surface forcing and the baroclinic circulation generated at the tidal mixing fronts first an increased vertical mixing increases the depth mean temperature in summer through the surface heat flux with a restoring mechanism acting during autumn second the magnitude and horizontal shear of the density flow are reduced in response to a higher mixing rate thermal and salinity fronts generate a seasonal circulation pattern in the north sea their impact on the horizontal temperature distributions is found to be in good agreement with the observations it is shown that in the absence of strong wind forcing both the vertical temperature distribution and the thermal circulation experience semimonthly variations in response to the spring neap cycle in tidal mixing at spring tides the surface mixed layers are shallower in agreement with observations at two mooring stations and the baroclinic circulation intensifies whereas the opposite occurs at neaps

enhancement of alongshore freshwater transport in surface advected river plumes by tides abstracta recent numerical study by isobe showed that imposing alongshore tidal forcing on buoyant coastal discharge enhances the net freshwater transport in the coastal currents the mechanisms for this transport enhancement are studied using a three dimensional primitive equation ocean model regional ocean modeling system roms lagrangian drifters are used to trace the freshwater transport paths it is found that the river plume bulge circulation largely follows the rigid body motion i e constant vorticity the buoyant fluid near the bulge s outer edge is thinner and faster behaving as a baroclinic jet the bulge currents then split after impinging on the coast the outer fluid feeds the downshelf flowing coastal currents while the inner fluid recirculates to form the bulge the coastal current transport estimated from the present and prior studies corresponds well to a baroclinic jet theory with the incident angle of bulge currents at the coast being a key parameter without tides the bulg

particle sorting due to off road vehicle traffic in a high andean paramo summary in the paramo de piedras blancas venezuelan andes unrestricted access by off road vehicles orv s within the past 10 years has caused widespread soil damage by generating numerous tire tracks pebbles and vagant lichens thamnolia vermicularis have been sharply segregated in the vicinity of the tracks both are concentrated in the elongated depressions creating an unusual type of sorted stripes materials migrate to tire tracks due to frequent ground frost and formation of needle ice a ubiquitous geomorphic agent of this high paramo lichens also have been concentrated in the tracks by wind activity the role of needle ice in transporting pebbles to hollow depressions is discussed and illustrated with other examples of recent patterned ground from this paramo

petrogenesis of the late cretaceous demirkoy igneous complex in the nw turkey implications for magma genesis in the strandja zone abstract the srednogorie zone in bulgaria and its eastern continuation in nw turkey the strandja zone consist of a late cretaceous magmatic belt comprised of plutonic volcanic and associated volcano sedimentary rocks the demirkoy igneous complex is the biggest cretaceous pluton within the strandja zone and its age is between 71 and 84 ma the demirkoy pluton and additional smaller plutons are intruded into triassic and older metamorphic basement rocks a contact metamorphic aureole with hornblende hornfels facies conditions was developed around the demirkoy pluton the wnw trending demirkoy pluton has an elliptical shape and a concentrically zoned internal structure in this structure gabbro diorites and quartz diorites are only seen in the sw corner of the pluton while granodiorites form the main body of the pluton surrounded by a zone of granite the granodiorites contain dioritic mafic microgranular enclaves small quartz monzonite lenses and or bodies and mafic dykes are also observed in the demirkoy igneous complex geochemically the demirkoy igneous complex has calc alkaline metaluminous and medium k characteristics there is a significant correlation between the lree hree ratios and sio 2 values chondrite normalized ree patterns are relatively flat la n lu n 2 in gabbros this ratio ranges from 3 to 11 for the diorite granodiorites and from 14 to 35 for the granites dioritic enclaves have ree patterns similar to those of the main body and have la n lu n values between 3 and 6 relatively enriched lile sr k rb ba and th and relatively depleted hfse ta nb and ti values indicate the classic subduction related origin of the complex the initial isotopic signatures range from e nd i 0 45 to 2 57 and 87 sr 86 sr i 0 7042 0 7064 for gabbros and e nd i 0 43 to 2 67 and 87 sr 86 sr i 0 7048 0 7059 for granodiorites and granites 18 o values range from 6 18 to 7 80 vsmow for gabbros and from 6 86 to 8 89 vsmow for granodiorites and granites based on geochemical and isotopic characteristics this magmatic complex can be subdivided into 4 groups a gabbro b diorite to alkali granite main body c syenite monzonite and d mafic dykes geochemical data and modelling results favour a typical subduction related enriched lithospheric mantle and lower crustal source for the demirkoy igneous complex slab derived fluids and crustal contamination also played a key role in the petrogenesis of this magmatic suite

estuary shelf interactions off the changjiang delta during a dry wet seasonal transition abstract estuary shelf interaction is very complex and vital for maintaining healthy ecosystem in the estuaries and adjacent seas the topic has been intensively studied through cruise observations and numerical models but less by long term observations at a fixed station we present here for the first time roughly 2 months adcp and ctd continuous data from the xiaoqushan pilot station of seafloor observatory aiming to deliberate river plume frontal processes off the changjiang estuary in response to river discharge transition from the dry to wet season in 2009 multiple lines of evidence attest that inner river plume is always in a bottom trapped form but isohalines and isothermals are very sensitive to seasonal variations in freshwater input wind climate and surface heating semidiurnal oscillations of salinity and temperature are good tracers for seasonal variations in plume frontal processes in the dry season both salinity and temperature have weak semidiurnal oscillations due to minimal cross shore straining under strong mixing conditions near the inner plume front where isohaline and isothermal are nearly vertical with small horizontal salinity and temperature gradient they are suddenly interrupted by a sharp increase of semidiurnal salinity oscillations owing to the arrival of newly established plume front with a less steep isocline slope but a maximum horizontal salinity gradient of 0 8 psu km the response time of inner plume front to the first discharge increasing pulse is roughly two weeks but should change a lot when examined at different plume locations and under varied river discharge increasing magnitudes and rates the frontal processes mirror well the river discharge fluctuations in the transitional period which lasts for a few weeks before entering a typical wet season the latter features strongest semidiurnal temperature oscillations linked with summer surface heating and highly depressed semidiurnal salinity oscillations because the main plume path shifts from southward to northeastward due to alternating southerly to northerly prevailing winds the three stages of inner plume frontal processes can be more clearly demarcated by the wavelet power spectral and the amplitudes of semidiurnal diurnal oscillations of salinity and temperature through wavelet transform and the associated band pass filtering methods the seasonal plume frontal transition has been vividly portrayed for the first time through secular observation at the fixed station in the river plume region significantly improving our understanding their controlling factors and mechanisms

millimeter scale microrelief affecting runoff yield over microbiotic crust in the negev desert abstract the negative effect of microrelief upon runoff yield explained by the increase in water storage and the slowdown in flow velocity is a known phenomenon however research concerning surface roughness hitherto focused on decimeter or centimeter scale microrelief owing to the heterogeneous character of many natural plots the effect of centimeter scale microrelief was mainly shown under controlled sprinkling experiments whereas no data was yet made available concerning the possible effect of a millimeter scale microrelief upon runoff yield under natural field conditions when runoff yield was measured over crusted i e surfaces covered by 1 3 mm of cyanobacterial crust and scalped 2 6 m 2 plots at the hallamish dune field negev desert israel during 5 winter seasons 1990 1995 no runoff was generated from the scalped plots during the first year following scalping while meagre quantities were received during the second year nevertheless during the third season and onward runoff yield at the scalped plots was consistently and significantly higher than that of the crusted control plots and this was so albeit the fact that the crust chlorophyll content of the scalped plots during the third season was as low as half the amount of the crusted plots these findings appeared to contradict previous findings that showed the existence of a positive linear relationship between the crust chlorophyll content and runoff yield the apparent contradiction was explained by the differences in the plot microrelief indicating that minute differences even of a millimeter scale may greatly affect runoff yield and thus may compensate for lower crust chlorophyll content surface smoothness which characterizes many of the arid zones may thus explain at least partially the high runoff yield obtained in deserts

a three dimensional model of density driven circulation in the irish sea abstract a semi implicit version of the princeton ocean model ecomsi was used to simulate the cyclonic gyre that is found in the western irish sea during the spring and the summer mesoscale seasonal density driven circulations such as this are an important component of the long term flow in shelf seas and they pose a challenge to coastal ocean models extensive comparisons are made here with observational data to assess model performance the model successfully reproduced the development of the temperature field and the associated density driven currents throughout seasonal simulations the results demonstrate conclusively that the gyre is density driven and reinforce the dynamical importance of strong nearbed horizontal density gradients maximum baroclinic currents of 0 14 m s 1 were obtained and results showed that the regional kinetic energy due to the residual flow was 20 25 of that due to tidal flow during periods in which density gradients were strongest the model revealed important int

cenozoic k rich adakitic volcanic rocks in the hohxil area northern tibet lower crustal melting in an intracontinental setting it is generally accepted that the cenozoic potassic volcanic rocks of northern tibet were derived from a lithospheric mantle source here we report new chronological geochemical and isotopic data for the miocene ca 18 15 ma k rich adakitic volcanic rocks from the hohxil area of the songpan ganzi block in northern tibet we contend that these rocks were generated by partial melting of the mafic lower crust in an intracontinental setting unrelated to subduction of oceanic crust the hohxil rocks exhibit high sr y and la yb ratios high sr and la contents but low yb and y concentrations similar to adakites formed by slab melting associated with subduction however their relatively low e n d values 2 09 to 4 58 high 8 7 sr 8 6 sr 0 7072 0 7075 th u th ba and rb ba ratios and distinctive potassium enrichments k 2 o na 2 o are very different from the composition of typical adakites in addition those k rich adakitic rocks with the highest sio 2 contents 61 wt exhibit the lowest 8 7 sr 8 6 sr ratios and highest e n d values and are the oldest cenozoic volcanic rocks exposed in the songpan ganzi block suggesting that they were derived neither directly from a mantle source nor by differentiation of a shoshonitic magma taking into account the composition of lower crustal mafic xenoliths in tibet as well as the tectonic and geophysical evidence we conclude that the hohxil adakitic magmas were produced by partial melting of amphibole bearing eclogites with a k rich mafic bulk composition in the lower part 55 km of the thickened northern tibetan crust partial melting of the lower crust may have been triggered by dehydration release of fluids from sedimentary materials in the southward subducted continental lithosphere

ebb tide dynamics and spreading of a large river plume abstract momentum balances in the near field region of a large tidally pulsed river plume are examined the authors concentrate on a single ebb tide of the columbia river plume using the regional ocean modeling system roms configured to hindcast flow conditions on the washington and oregon shelves and in the columbia river estuary during ebb plume interior streamwise balances are largely between advection pressure gradient and frictional forces stream normal balances in this region reduce to centrifugal cross stream pressure gradient and coriolis terms i e the gradient wind balance commonly assumed in river plume bulge investigations temporal derivatives are most important at the plume front and as the ebb progresses winds were light and contributed little to the force balance midebb stress and vertical salt flux were largest at a midplume depth where stratification and vertical shear were also high consistent with shear induced mixing internal stress slows the spreading plume consi

ballooning of river plume bulge and its stabilization by tidal currents when freshwater debouches into an adjacent ocean an anticyclonic eddy bulge is formed in front of the river mouth it is well known that a bulge growing offshore ballooning hardly reaches a steady state in the absence of either ambient currents or wind forcing this study provides a physical interpretation for the ballooning of river plume bulges by conducting numerical experiments in which a river plume is induced by a coastal freshwater source part of the freshwater released to the model ocean undergoes inertial instability near inertial oscillations are predominant when disturbances are not forced in ambient waters of the river plume these isotropic disturbances are amplified by inertial instability so that unstabilized freshwater can move in arbitrary directions thus unstabilized freshwater does not need to move toward the coastal boundary current on the right hand side of the river mouth freshwater unstabilized for a long time can stay in the bulge for a long time unstabilized freshwater accumulates gradually in the bulge and so ballooning occurs when the direction of disturbances is prescribed in ambient waters unstabilized freshwater is forced to move in the same direction thereby the motion of unstabilized freshwater is restricted in the alongshore direction when background disturbances are induced by alongshore tidal currents it is therefore concluded that tidal currents play a role in stabilizing the offshore growth of river plume bulges in coastal and shelf waters

annually re forming miniature sorted patterned ground in the high drakensberg southern africa an analysis of miniature sorted circles and polygons provides the first detailed assessment of sorted patterned ground from a southern african alpine region pattern dimensions and particle sorting were determined from two sites in the high drakensberg although the sorted patterns in the high drakensberg are somewhat polygenetic in developmental origin they are primarily frost induced miniature sorted patterned ground below 3200 m a s l on the drakensberg plateau develops annually during the winter months and disintegrates towards summer the development of miniature sorted patterns within five to six weeks demonstrates the effect of regular freeze thaw cycles at higher altitudes in the drakensberg 1997 by john wiley sons ltd

rainwash experiments on the erodibility of loose sediments laboratory experiments using simulated rainfall splash boards and trays were conducted in order to obtain information on the erodibility of loose sediments as a time dependent phenomenon in all ten different sediments ranging from silt d50 24 m to coarse sand d50 593 m were studied the effect of three different initial states of the sediments namely the air dry state t1 the field capacity state t2 and the desiccated state t3 on the erodibility was also assessed variations in detachability during a rain erosion experiment can be explained by change in water content including liquefaction and the development of a water layer on the surface cohesion and granulometric composition of the top layer the coarsest sandy sediments almost always yielded the highest detachability when starting from an initial field capacity state t2 for the finer sediments the highest detachability was found for the homogeneous and not yet compacted initial air dry state t1 the effect of the initial desiccated state t3 on the detachability of the finer sediments was also a function of the rainfall duration the relationship between detachability and median grain size of the sediments was very similar to the relation between grain size and the susceptibility to runoff and wind erosion established by other investigators the highest detachability was found for a fine very well sorted sand with a median grain size of 96 m

generation of sodium rich magmas from newly underplated basaltic crust sodium rich rocks of trondhjemite tonalite dacite ttd or granodiorite ttg suites form much of precambrian continental crust1 they are thought to have formed by partial melting of subducted oceanic crust2 3 a process that would have been much more widespread early in earth history than at present owing to the higher thermal gradients prevailing at that time4 phanerozoic ttd suites do exist however and seem also to relate to subduction zones5 defant and drummond6 proposed that these suites form where young 25 myr hot oceanic lithosphere is subducted and melts thus locally simulating the conditions that led to widespread crustal growth in the archaean here we describe plutonic and volcanic rocks from the cordillera blanca complex in peru which have characteristics of the high al ttd suite but which were produced above a subduction zone containing a 60 myr old slab we present evidence that the complex formed by partial melting of newly underplated basaltic crust and argue that this mechanism should be considered more generally as an additional way of generating sodium rich arc magmas

sea surface temperature fronts in the yellow and east china seas from trmm microwave imager data abstract swath data from the tropical rainfall measuring mission microwave imager of sea surface temperatures sst from 1998 to 2005 have been used to analyze the climatology and seasonal variability of the sst fronts in the yellow and east china seas yes seven fronts have been identified and placed into three categories namely 1 the shelf break front kuroshio front 2 the coastal fronts zhe min jiangsu shangdong peninsula western korean and western chejudo fronts and 3 the shelf front western yellow sea shelf front the kuroshio front exists from december through may with the maximum sst gradient and highest frontal probability in april the five coastal fronts exist year round all with their maximum sst gradient and highest frontal probability in february the shelf front in the western yellow sea exists only from january to march frontogenesis in winter is due to effects of both air sea heat exchange and advection by currents the coastal fronts in the stratified months are expressed as tidal fronts the coastal frontal zones coincide with the major spawning grounds of fish in the yes the overwintering fishery ground in the yellow sea overlaps with the narrow band of favorable water temperature in the frontal zone the overwintering grounds in the east china sea are broad and bounded by fronts

western versus eastern black sea tectonic evolution pre rift lithospheric controls on basin formation abstract we demonstrate the key role of pre rift rheology on the kinematics of basin formation in the western and eastern black sea basins constraints on modelling results are provided by a large data set based on more than 50 000 km of multichannel seismics offshore and onshore wells regional gravity and magnetic surveys refraction seismics and field studies the model supports the presence of important differences in the thickness and in the thermal state of the lithosphere which rifted to form the western middle barremian and the eastern middle paleocene black sea subbasins a 200 km and a 80 km thick pre rift lithosphere appear to have driven the deformation in the western and in the eastern black sea respectively differences in the geometry and in the mechanical properties of the pre rift lithosphere have a strong control on the depth of necking and thus on the basin morphology the model sheds light on palaeotectonic and palaeogeographic reconstructions duration of rifting events location of subsiding areas and erosional surfaces the western and the eastern parts of the black sea appear to be two distinct basins characterised by different evolutionary paths determined by different pre rift conditions

combined chronological and mineral magnetic approaches to reveal age variations and stratigraphic heterogeneity in the yangtze river subaqueous delta abstract delta deposits show large spatial heterogeneity in terms of depositional rate and age which is critical to the study of delta erosion in response to the declining fluvial sediment load observed at many river mouths in the world in this study we show that the magnetic susceptibility can be an indicator to reveal age variations and stratigraphic heterogeneity in the yangtze river subaqueous delta ages of three short sediment cores 1700 years the cores at shallow water depths are younger than those from deeper sites modern deposits i e 800 a show lower and uniform values due to the reductive dissolution of ferrimagnetic minerals while younger sediments

1 700 myr greenstone volcanic successions in southwestern north america and isotopic evolution of proterozoic mantle 1 700 myr greenstone volcanic successions in southwestern north america and isotopic evolution of proterozoic mantle

laboratory experiments simulating a coastal river inflow the dynamics of buoyant water entering a rotating basin are studied using a series of laboratory experiments designed to elucidate the alongshore transport mechanisms in river plumes inflowing water which is discharged perpendicular to the tank wall is observed to form a growing anticyclonic bulge and a coastal current downstream of the bulge detailed simultaneous measurements of the velocity and buoyancy fields in the plume confirm that the bulge momentum is in a gradient wind balance and the coastal current is geostrophic the growth of the bulge and accumulation of fluid within it coincides with a reduction in coastal current transport to approximately 50 of the inflow discharge the bulge is characterized by a depth scale h w hich is proportional to the geostrophic depth hg and two time dependent horizontal length scales yc the displacement of the bulge centre from the wall and rb the effective radius of the bulge these two length scales are proportional to the inertial radius

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

semidiurnal switching of stratification in the region of freshwater influence of the rhine observations in the rhine region of freshwater influence rofi system in the north sea show evidence of large semidiurnal oscillations in stability superimposed on a mean stratification occurring throughout the stratified region at times of reduced mixing the amplitude of this semidiurnal variation is of the same order as the mean stability and frequently results in conditions being mixed or nearly mixed once per tide it is deduced that this semidiurnal variation results primarily from cross shore tidal straining which interacts with the density gradient to induce stratification this conceptual picture of the contributing processes has been tested in a one dimensional point model forced by the observed slopes and the local density gradients the model exhibits the same qualitative behavior as the observations produces oscillations in stratification of the amplitude observed and confirms the critical role of cross shore tidal straining the large cross shore shear nder stratified conditions is identified with the changes in ellipse configuration which are observed between mixed and stratified conditions the occurrence of semidiurnal variations in stability in the rhine rofi is thus inferred to be a consequence of the development of mean stability whenever the horizontal density gradients relax in conditions of low stirring

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

tidal modulation of estuarine plumes abstract off an estuary mouth the nonlinear transfer of vorticity from the oscillating onshore offshore tidal currents to the mean field generates a pair of counter rotating eddies that flows seaward near the center axis of the inlet and landward on both sides the coriolis deflection strengthens the anticyclonic eddy but weakens the cyclonic one a seaward sloping shelf enhances these eddies but a seaward sloping estuary weakens them these tidal residual eddies strengthen and hasten the expansion of a river forced plume off an estuary mouth but weaken and retard the development of the coastal jet farther downcoast to lowest order this is the primary effect of tides on an estuarine plume in a coupled estuary shelf system tidal effects on the subtidal river forced circulation inside the estuary are secondary

tidal modulation on the changjiang river plume in summer 1 tide effects on the structure of the near field changjiang river plume and on the extension of the far field plume have often been neglected in analysis and numerical simulations which is the focus of this study numerical experiments highlighted the crucial role of the tidal forcing in modulating the changjiang river plume without the tidal forcing the plume results in an unrealistic upstream extension along the jiangsu coast with the tidal forcing the vertical mixing increases resulting in a strong horizontal salinity gradient at the northern side of the changjiang river mouth along the jiangsu coast which acts as a dynamic barrier and restricts the northward migration of the plume furthermore the tidal forcing produces a bidirectional plume structure in the near field and the plume separation is located at the head of the submarine canyon a significant bulge occurs around the head of the submarine canyon and rotates anticyclonically which carries a large portion of the diluted water toward the northeast and merges into the far field plume a portion of the diluted water moves toward the southeast which is mainly caused by tidal rectification this bidirectional plume structure is more evident under certain wind conditions during the neap tide with the reduced tidal energy the near field plume extends farther offshore and the bulge becomes less evident these dynamic behaviors are maintained and are fundamentally important in the region around the river mouth even under the summer monsoon and the shelf currents although in the far field the wind forcing and shelf currents eventually dominate the plume extension

the influence of amphibole fractionation on the evolution of calc alkaline andesite and dacite tephra from the central aleutians alaska petrologic studies of tephra from kanaga adak and great sitkin islands indicate that amphibole fractionation and magma mixing are important processes controlling the composition of calc alkaline andesite and dacite magmas in the central aleutians amphibole is ubiquitous in tephra from kanaga and adak islands whereas it is present only in a basaltic andesite pumice from great sitkin dacitic tephra from great sitkin do not contain amphibole hornblende dacite tephra contain hb plag ox opx cpx phenocrysts with simple zoning patterns suggesting that the dacites evolved in isolated magma chambers andesitic tephra from adak contain two pyroxene and hornbelende populations and reversely zoned plagioclase indicating a more complex history involving mixing and fractional crystallization mass balance calculations suggest that the andesitic tephra may represent the complements of amphibole bearing cumulate xenoliths both formed during the evolution of high al basalts the presence of amphibole in andesitic and dacitic tephra implies that aleutian cale alkaline magmas evolve in the mid to lower crust under hydrous 4 wt h2o and oxidizing ni nio conditions amphibole bearing andesites and pyroxene bearing dacites from great sitkin indicates fractionation at several levels within the arc crust despite its absence in many calc alkaline andesite and dacite lavas open system behavior involving amphibole fractionation can explain the trace element characteristies of lavas found on adak island neither open nor closed system fractionation involving a pyroxene bearing assemblage is capable of explaining the trace element concentrations or ratios found in the adak suite we envision a scenario where amphibole was initially a liquidus phase in many calc alkaline magmas but was later replaced by pyroxenes as the magmas rose to shallow levels within the crust the mineral assemblage in these evolved lavas reflects shallow level equilibration of the magma whereas the trace element chemistry provides evidence for a earlier amphibole bearing mineral assemblage

the tectonics of the strandja massif late variscan and mid mesozoic deformation and metamorphism in the northern aegean the strandja massif is a mid mesozoic orogenic belt in the balkans build on a late variscan basement of gneisses migmatites and granites new single zircon evaporation ages from the gneisses and granites indicate that the high grade metamorphism and plutonism is early permian in age 271 ma the late variscan basement was unconformably overlain by a continental to shallow marine sequence of early triassic mid jurassic age during the late jurassic early cretaceous oxfordian barremian the lower mesozoic cover and the basement were penetratively deformed and regionally metamorphosed in greenschist facies possibly due to a continental collision an rb sr biotite whole rock age from a metagranite dates the regional metamorphism as late jurassic 155 ma deformation involved north vergent thrust imbrication of the basement and the emplacement of allochthonous deep marine triassic series over the jurassic metasediments the metamorphic rocks of the strandja massif are unconformably overlain by the cenomanian shallow marine sandstones during the senonian the northern half of the strandja massif formed a basement to an intra arc basin and to a magmatic arc generated above the northward subducting tethyan oceanic lithosphere the srednogorie arc closed during the early tertiary through renewed northward thrusting of the strandja massif

structure and eastward extension of the changjiang river plume in the east china sea 1 the hydrographic structure and offshore extension of freshwater plume discharged from the changjiang also known as the yangtze river in the northern east china sea were investigated by analyzing conductivity temperature depth ctd data and drifter trajectories collected during the summers of 1997 and 1998 from june to early september when southerly winds prevail the plume tends to move northeast in the chinese coastal area and then separates from the coastal zone to travel eastward over 400 km offshore across the western shelf of the northern east china sea during other seasons when northerly winds prevail the plume is confined to the chinese coast in the summer the plume in the midshelf confined to a thin surface layer 10 to 15 m thick extends eastward in the form of patches of low salinity water rather than spreading as a tongue shaped pattern from the changjiang mouth the eastward movement of patches in the western shelf is primarily due to upwelling favorable southerly winds upon reaching the vicinity of cheju do an island in the middle of northern east china sea the patches are advected to the korea tsushima strait by either the cheju warm current or a northward flowing mean current of the kuroshio branch current and then finally flow into the east japan sea

patterned ground by rainstorm erosion on the colorado plateau utah this short notice deals with the effect of highly intensive rainstorms more than 25 mm h or 8 mm 10 min on bare surfaces producing cones and needles of earth up to 12 cm in cryptogamic surface layers of canyonlands national park by splash erosion and widespread stone stripes resembling periglacial features on the steeper slopes up to more than 40 by rainwash in the areas of red canyon and bryce canyon national park a large amount of coarse material can be moved within a very short time and the surface patterns survive at least for several months

the kapanbogazi formation a key unit for understanding late cretaceous evolution of the pontides n turkey abstract the pontides forming the south western continental margin of the black sea consist of two tectonic units the istanbul zone in the west and the sakarya zone in the central and eastern parts the sinop basin in the sakarya zone is filled from base to top by hauterivian to albian turbidites cenomanian turonian red pelagic sediments turonian campanian magmatic arc and related deposits and by the uppermost campanian to middle eocene post magmatic units developed on the southern passive margin of the black sea based on nannofossil dinoflagellate foraminifera and radiolaria data we describe the kapanbogazi formation a cenomanian turonian unit in the sinop basin represented by red calcareous siliceous pelagic shales limestones and cherts passing gradually from the albian black shales these sediments possibly represent deepest depositional conditions of the basin during the cenomanian turonian interval and also reflect the transition from an anoxic to an oxic palaeoenvironmental setting the istanbul zone to the west was emerged during the deposition of the kapanbogazi formation in the sakarya zone in the pontides red pelagic sediments were deposited at different times during the cenomanian maastrichtian interval because the kapanbogazi formation was deposited only in the sakarya zone and because it is present in limited outcrops due to structural reorganization and thick overlying volcanoclastic pile most previous authors assumed cenomanian turonian hiatus herein we describe detailed palaeontological data from this unit and discuss their importance to the interpretation of depositional history and tectonics of the black sea region as well as climatic and eustatic implications

low frequency circulation on the texas louisiana continental shelf for the texas louisiana coast west of 92 5 w long series of data from near freeport texas together with shorter series from other locations show strong response of coastal current to wind stress in agreement with coastal jet concepts we infer from coastal winds scattered current measurements and distributions of sea surface salinity and geopotential that a cyclonic gyre elongated along the shelf is the dominant feature of the prevailing shelf circulation the inshore limb of the gyre is the coastal jet driven by wind with a west or southward downcoast component which prevails along much of the coast except in july august because the coast is concave the shoreward prevailing wind results in a convergence of coastal currents which marks the downcoast extent of the gyre corresponding to the convergence is a seaward flow which forms the southwest limb of the gyre a prevailing countercurrent north or eastward flow along the shelf break includes the outer limb of the gyre the eastern shoreward flowing limb of the gyre corresponds to divergence along the coast centered near 92 5 w the convergence at the western or southern end of the gyre migrates seasonally with the direction of the prevailing wind reaching south of the rio grande mouth in fall and the cameron offing in july the gyre is normally absent in july but reappears in august september when a downcoast wind component develops

characteristics and palaeoenvironmental significance of relict sorted patterned ground drakensberg plateau southern africa abstract relict large sorted periglacial circles are described from the drakensberg plateau of southern africa morphological and sedimentological data for three populations of patterns occurring on high summit 3400 m a s l interfluves are presented the patterns range between 85 and 904 cm in diameter with centres encircled by primary and in some cases secondary borders patterns are sorted to maximum depths of 85 cm or more with borders occupying trough like depressions to a depth of 26 cm although it is found that contemporary freeze to 40 cm depth still permits some cryogenic activity within smaller patterns it is argued that the larger patterns are degrading owing to limited moisture and freeze duration and intensity the paper provides a literature summary of contemporary environmental parameters from 10 northern hemisphere localities where active relict large periglacial patterns occur findings suggest that patterns over 80 cm in diameter develop where the maat is 1 6 c or less it is demonstrated that the drakensberg palaeo maat reached such low temperatures during the lgm it is thus argued that the patterns developed during the lgm and that smaller varieties became reactivated during holocene cold phases the relict sorted circles provide confirmation for late quaternary permafrost above 3400 m a s l in southern africa the results further suggest pronounced palaeo climatic environmental variation over short spacial scales over southern africa s high plateau

tectonics of the banat srednogorie rift abstract the banat srednogorie rift is located on the balkan peninsula in the northeastern part of the alpine system it is superimposed on a continental type basement which cuts across older structures the rift is filled with a 3 8 km thick layer of upper cretaceous sedimentary and volcanogenic rocks the volcanic and plutonic formations belong to four series calc alkaline tholeiitic potassic alkaline and peralkaline the rift was formed in three stages 1 1 the formation of the sedimentary trough 2 2 subsidence accompanied by intense volcanic activity and tephroidal flysch sedimentation 3 3 inversion expressed in the laramide deformation the epicontinental rifting occurred in the preorogenic stage of the geotectonic development of the balkanide dinarides after the closure of the vardar paleo ocean and the formation of an embryonal orogenic arc

spatiotemporal variations in suspended sediments over the inner shelf of the east china sea with the effect of oceanic fronts abstract suspended sediments are important contributors to the material exchanges between the sea surface and bottom and between the coastal waters and shelf seas the east china sea ecs connecting the chinese continent and the western pacific receives a large amount of yangtze river delivered sediments however due to the climate change and intense human activities in recent years the amount of yangtze river delivered sediment decreased by two thirds fewer work has been conducted on the accompanying changes of suspended sediment concentration ssc over the inner shelf of the ecs thus in this study based on the long term water temperature salinity and ssc data derived from modis during 2003 2018 the spatiotemporal variations of ssc and the effects from oceanic fronts were studied the results indicated a typical seasonal change of the ssc with the effect of a thermocline in summer and thermal saline front in winter respectively regarding the long term variation of the ssc from 2003 to 2018 it displayed significant differences in spatial distribution the ssc anomaly exhibited the opposite phases between the north and south parts of 28 29 n and between the landside and seaside of the front at the isobaths of 20 m 40 m along the zhe min coast in general wind is the controlling factor that affects the ssc in most area of the zhe min coast especially in spring and winter seasons

the upstream spreading of bottom trapped plumes it is well known that numerical simulations of freshwater discharges produce plumes that spread in the direction opposite to that of the propagation of coastally trapped waves the upstream direction the lack of a theory explaining these motions in unforced environments deemed the numerical results suspect thus it became a common practice in numerical studies to add a downstream mean flow to arrest the development of the upstream perturbation this approach is generally unjustified and it remains a matter of interest to determine if the upstream displacement produced by models is a geophysical phenomenon or a consequence of erroneous assumptions in the model setup in this article the results of highly idealized numerical experiments are used to investigate these matters it is shown that this phenomenon is associated with the geostrophic adjustment of the discharge and that upstream motion is endemic to the baroclinic structure of bottom trapped plumes it is also shown that downstream displacements are generated by the cross shelf barotropic pressure gradient generated by the propagation of coastally trapped waves sensitivity experiments indicate that the speed of upstream propagation and the density structure of the plume are affected by bottom friction the slope of the bottom and the magnitude of the density anomaly bottom friction in particular slows down the progression of the plume and changes its density structure producing a more homogeneous downstream region and a more stratified upstream region

the influence of tide and wind on the propagation of fronts in a shallow river plume in this study we used field data and radar images to investigate the influence of winds and tides on the propagation of tidal plume fronts the measurements were collected in a shallow shelf region off the dutch coast 10 km north of the rhine river mouth and they clearly show the passage of distinct freshwater lenses and associated fronts at the surface that propagate all the way to the coastline these fronts are observed as a sudden drop in near surface salinity accompanied by high cross shore shear with onshore velocities at the surface we determined the arrival time to our measurement site frontal propagation speed and structure of the fronts by combining the in situ data and radar images frontal froude numbers show a wide range of values with an average of 0 44 our results show that fronts during spring tides are thinner more mixed and move faster relative to the ground during calm spring tides when compared to calm neap tides downwelling winds during spring tides result in thicker and faster fronts however the intrinsic frontal propagation speed indicates that the wind and tide control the frontal propagation mainly due to advection rather than by changing the frontal structure strong return currents in the near bed layer resulting from fast and thick fronts increase near bed turbulence and bed stresses these high stresses suggest that the passage of fronts in shallow coastal areas can initiate sediment resuspension and contribute to transport processes

fortnightly variation in the bottom thermal front and associated circulation in a semienclosed sea abstractsummer hydrographic data from 1971 to 2000 demonstrate the presence of bottom cold water bcw and a bottom thermal front around the bcw in a semienclosed sea in the seto inland sea of japan the horizontal gradient of water temperature across the bottom front was larger in neap tide than in spring tide which is the opposite the pattern observed in the fortnightly variations in other areas e g the irish sea a numerical model for the inland sea reproduced the presence of bcw and a bottom front as well as the same fortnightly variation in the horizontal gradient of water temperature across the bottom front as in observational data being the same bcw as those in other areas the presence of bcw in the inland sea is also caused by spatial variation in tidal mixing the intensification of the bottom front in neap tide in the inland sea results from a combination of tidal mixing and horizontal advection of warm water to the bcw the presence of a bottom residual current in the direction across th

soil hydrophobicity effects on rainsplash simulated rainfall and photographic evidence laboratory rainfall simulation experiments indicate greater splash losses for hydrophobic water repellent than for wettable sandy loam soils at different rainfall intensities durations and soil surface inclinations using synchronized video cameras with different shutter speeds and stroboscopically illuminated 35 mm still photography differences in splash droplets and ejection trajectory characteristics are examined for hydrophobic soil raindrop impact gives rise to fewer larger slower moving daughter ejection droplets which carry more sediment and hence follow shorter range trajectories compared with wettable soil implications for erosion of hydrophobic soils are discussed

quaternary volcanism near the valley of mexico implications for subduction zone magmatism and the effects of crustal thickness variations on primitive magma compositions the valley of mexico and surrounding regions of mexico and morelos states in central mexico contain more than 250 quaternary eruptive vents in addition to the large composite volcanoes of popocatepetl iztaccihuatl and nevado de toluca the eruptive vents include cinder and lava cones shield volcanoes and isolated andesitic and dacitic lava flows and are most numerous in the sierra chichinautzin that forms the southern terminus of the valley of mexico the chichinautzin volcanic field cvf is part of the e w trending mexican volcanic belt mvb a subduction related volcanic arc that extends across mexico the crustal thickness beneath the cvf 50 km is the greatest of any region in the mvb and one of the greatest found in any arc worldwide lavas and scoriae erupted from vents in the cvf include alkaline basalts and calc alkaline basaltic andesites andesites and dacites both alkaline and calc alkaline groups contain primitive varieties that have whole rock mg mgo and ni contents and liquidus olivine compositions fo90 that are close to those expected of partial melts from mantle peridotite primitive varieties also show a wide range of incompatible trace element abundances e g ba 210 1080 ppm ce 25 100 ppm zr 130 280 ppm data for primitive calc alkaline rocks from both the cvf and other regions of the mvb to the west are consistent with magma generation in an underlying mantle wedge that is depleted in ti zr and nb and enriched in large ion lithophile k ba rb and light rare earth la ce elements extents of partial melting estimated from ti and zr data are lower for primitive calc alkaline magmas in the cvf than for those from the regions of the mvb to the west where the crust is thinner the distinctive major element compositions low cao and al2o3 high sio2 of the primitive calc alkaline magmas in the cvf indicate a more refractory mantle source beneath this region of thick crust in contrast primitive alkaline magmas from the cvf and other regions of the mvb show compositional similarities to intraplate type alkali basalts erupted behind the arc in the mexican basin and range province these similarities are consistent with the hypothesis that slab induced convection in the mantle wedge beneath the mvb causes advection of asthenospheric mantle from behind the arc to the region of magma generation trace element systematics of primitive magmas in the mvb reveal substantial variability in both the extent of mantle wedge enrichment by subduction processes and in the composition of mantle heterogeneities that are related to previous extraction of alkaline to sub alkaline basaltic melts

trace element and isotopic evidence for two types of crustal melting beneath a high cascade volcanic center mt jefferson oregon mt jefferson is an andesite dacite composite volcano in the cascade range the locus of andesite and dacite dominated volcanism for at least 1 million years a large trace element data set for mt jefferson and its surrounding mafic volcanic platform effectively rules out any fractionation based model fc or afc for the generation of mt jefferson andesites several incompatible element zr nb y concentrations decrease in the range from basalt to andesite and then increase in the range from andesite to rhyodacite others ba rb la th remain constant or show a slight increase in the basalt to andesite range with modest increases from andesite to rhyodacite systematic variations in highly incompatible element ratios such as ba la and rb th suggest magma mixing dominates the trace element signatures rhyodacites are isotopically uniform 87sr 86sr 0 70325 0 70343 206pb 204pb 18 75 18 85 18o 6 3 0 3 whereas andesite and dacite are more variable 87sr 86sr 0 70291 0 70353 206pb 204pb 18 59 18 86 18o 6 0 0 6 typical basaltic andesite has 87sr 86sr 0 70326 0 70358 206pb 204pb 18 78 18 85 and 18o 5 9 0 4 sr rich 1 000 ppm basaltic andesite is more variable 87sr 86sr 0 70300 0 70360 206pb 204pb 18 70 18 89 18o 5 9 0 4 the data define mixing arrays with one end member at 87sr 86sr 0 7029 206pb 204pb 18 59 another at rhyodacite and a third at 87sr 86sr 0 7036 206pb 204pb 18 89 the first end member is defined by sr rich 800 1 200 ppm andesite with high al2o3 and low k2o ba and rb th the third one by k2o and very sr rich 2 000 ppm shoshonite isotopic data for basalts in northern oregon preclude any fractionation relationship between basalt and either rhyodacite or sr rich andesite e g the minimum 206pb 204pb ratio in basalt is 18 83 considered in light of geophysical models for the cascades these data suggest two types of crustal melting beneath the arc rhyodacite may be generated at 25 30 km depth by partial melting of arc basalt like amphibolite at 850 900 c sr rich andesite may be formed by partial melting of depleted morb like mafic granulite at 35 45 km depth at 1 000 1 100 c experimental and ree evidence supports these interpretations as does the restriction of sr rich andesite in the cascades to the area south of the 100 mw m2 heat flow contour between mt jefferson and mt hood thick crust and high heat flow are necessary to produce such andesite

mineral chemistry crystallization conditions and geodynamic implications of the oligo miocene granitoids in the biga peninsula northwest turkey abstract widespread plutonic rocks in nw turkey occur within the southward younging and overlapping magmatic belts across the aegean region post collisional magmatism is represented by a series of granitoidic intrusions and volcanic successions k ar and u pb la icp ms zircon dating of the kazdag and yenice plutons yielded ages between 20 5 0 5 ma and 27 89 0 17 ma late oligocene early miocene the granitoid samples are high k calc alkaline and metaluminous to slightly peraluminous the 87sr 86sr values for the granitoids enclaves and leucocratic rocks range between 0 705168 and 0 708357 the initial 143nd 144nd ratios calculated for the crystallization ages of ca 23 27 ma are between 0 512425 and 0 512614 and the end values vary from 3 5 to 0 2 the nd tdm model ages range between 0 73 and 1 13 ga these samples are enriched in liles and lree and depleted in hfses with negative eu anomalies indicating that the melts were derived from an enriched lithospheric mantle modified by subducted slab derived melts energy constrained assimilation and fractional crystallization ec afc modelling indicates that fractional crystallization and crustal assimilation modified the parent magma s composition during its residence in the upper crust the mineral chemistry of amphiboles pyroxenes biotites and feldspars is used to constrain the pressure p temperature t oxygen fugacity log o2 and water contents h2omelt during the crystallization of the magmas in the studied granitoids the clinopyroxene temperatures are in the range of 823 910 45 c the amphibole temperatures for the studied plutonic rocks are in the range of 707 926 c mean 798 45 c and the crystallization depths are estimated to be in the interval of 1 02 10 2 km the nw anatolian plutonic rocks can be considered to have been equilibrated at the oxygen fugacities of calcic amphiboles log o2 between 8 99 and 13 96 bars mean 12 11 bar and h2omelt contents between 1 63 and 6 79 mean 4 15 meanwhile the biotites which display consistent oxygen fugacity values 10 65 to 13 22 suggest their reliability with the typical values of calc alkaline magma crystallization these values suggest a relatively higher oxidation state during crystallization and are related to arc magmatism all of the calculated values indicate that all of the plutons were emplaced at shallow crustal levels it can be inferred that the oligo miocene magmatism in nw turkey may be linked to crustal thinning that resulted from slab roll back and a back arc extensional regime after the collision between the sakarya zone and anatolide tauride platform

a simple theory for the fate of buoyant coastal discharges abstract a simple theory that predicts the vertical structure and offshore spreading of a localized buoyant inflow onto a continental shelf is formulated the theory is based on two competing mechanisms that move the buoyant fluid offshore 1 the radial spread of the lighter water over the ambient water being deflected by the coriolis force and producing an anticyclonic cyclostrophic plume and 2 offshore transport of buoyant water in the frictional bottom boundary layer that moves the entire plume offshore while maintaining contact with the bottom the surface expression of the cyclostrophic plume moves offshore a distance ys 2 3g h0 2i 2g h0 2i 1 2f where g is reduced gravity based on the inflow density anomaly h0 is the inflow depth i is the inflow velocity and f is the coriolis parameter the plume remains attached to the bottom to a depth given by hb 2l ih0f g 1 2 where l is the inflow width both scales are based solely on parameters of the buoyant inflow at its source there

alkalic ocean island basalt type and calc alkalic volcanism in the mexican volcanic belt a case for plume related magmatism and propagating rifting at an active margin the mexican volcanic belt has been traditionally regarded as a classic case of subduction related calc alkalic volcanism however a series of geologic geophysical and petrological arguments makes this simple relationship doubtful a seismic gap beneath the belt a large scale mantle anomaly a graben triple junction domain and the presence of volumetrically important oceanic island basalt oib volcanism throughout the belt suggest a more complex tectonic scenario involving plume and subduction related processes we here propose a model involving the development of a propagating rift opening from west to east in response to plume activity the process started in miocene time within the western sector of the belt guadalajara and gave rise to a graben triple junction and oib type and calc alkalic volcanism extension and volcanism proceeded to the east giving rise to progressively younger ages for the initiation of oib type volcanism 1 miocene in the west e g guadalajara 2 pliocene in the central zone e g michoacan guanajuato and 3 quaternary farther east e g chichinautzin geochemical evidence suggests that part of the modern calc alkalic volcanism e g chichinautzin may be derived from magma mixing between the oib mafic magmas and silicic crust derived magmas however we do not preclude some influence of the subducting slab in the generation of other e g jorullo calc alkalic volcanic rocks our model suggests a currently unrooted upper plume attached to the subcontinental lithosphere which defines a hot zone beneath the mexican volcanic belt

does the taiwan warm current exist in winter 1 it has been argued for many years whether the taiwan warm current twc exists in winter though there is no question about its existence in summer a regional ctd survey and anchored adcp measurements were conducted off the mouth of the changjiang on the western shelf of the east china sea from 24 february to 10 march 2001 both hydrographic and current data showed an evidence of the twc which flowed northeastward along the 50 m isobath and intruded into the submerged river valley off the changjiang this current is sub surface intensified with a maximum velocity of 30 cm s occurring at a depth of 30 m below the surface this finding was consistent with the satellite derived sst image received on 26 30 january 1986 and modis sst image received on 18 february 2001 it suggests that the twc is at least an episodic feature in the east china sea and its occurrence and duration might vary due to meandering of the kuroshio around the taiwan strait

absence of cocos plate subduction related basic volcanism in southern mexico a unique case on earth the relationship between volcanism and subduction of the cocos plate is examined on the basis of new as well as published sr nd and pb isotopic and geochemical data on late miocene to holocene ca 9 0 ma basic volcanic rocks from southern mexico and central america basic rocks with sio 2 52 were chosen in order to minimize the effects of crustal assimilation processes and therefore to test the contribution from deeper sources the subducted cocos plate and the mantle wedge by using fluid mobile to relatively fluid immobile elements and radiogenic isotope ratios for such rocks i show that the subduction of the cocos plate does not contribute to the basic volcanism in all of southern mexico as opposed to that in central america from guatemala to northwestern costa rica south mexican volcanism is related to ongoing rifting processes inferred from field geology seismology gravity tectonics and volcano alignments this lack of subduction relationship probably represents the first case on earth where the ongoing subduction of an oceanic plate does not give rise to basic volcanism such as is present throughout southern mexico

generalizations of the wedderburn number parameterizing upwelling in stratified lakes the effect of lake geometry on wind induced upwelling in a two layer stratified lake with a variable bottom slope and generic planar shape is investigated 1 the traditional linearized classification parameter for upwelling the wedderburn number is extended to include finite amplitude effects in a rectangular basin this extension is important when the wedderburn number is 3 2 the wedderburn number is generalized to incorporate the influence of a bottom slope and a variable width basin for both the linear large wedderburn number and nonlinear small wedderburn number assumptions laboratory and numerical experiments of a two layer stratification were performed and used to validate these extensions 3 both extensions are combined to derive a methodology to estimate the interface displacement in real lakes where both geometry effects may act together and this methodology is used to discuss the response of the thermocline to the onset of wind in lake como and mundaring weir reservoir in most cases symmetry of the basin geometry along the fetch is the key characteristic that defines tilting of the interface for real lakes asymmetries in terms of bottom slopes induce shortening or stretching of the effective internal fetch while a larger excursion of the interface results in narrower upwind areas of the lake due to horizontal redistribution of displaced water volumes this paper gives the correct definition of the length scales to define the wedderburn number for any stratified basin

adakites the key to understanding lile depletion in granulites abstract for more than 20 years it has been argued that granulites of the lower continental crust are depleted in fluid mobile elements such as cs rb u and th either because they were removed by melting of the lower crust or through dehydration we argue that there is little evidence for a simple relationship between granulite facies metamorphism and element depletion and propose that for felsic orthogneisses the depletion may be a primary feature of crust generation processes modern adakites show a range of fluid mobile element ratios and adakites from the austral volcanic zone avz chile show fluid mobile element ratios very similar to those found in lower crustal felsic granulites this suite of adakites has a strong slab derived component we propose that modern adakites of the type found in the austral volcanic zone are analogous in their genesis to lower crustal felsic granulites and that their mafic precursors were already depleted in fluid mobile trace elements prior to melting an incremental melting model in which fluid mobile elements are released from an eclogitic slab prior to partial melting can explain the fluid mobile element behaviour of both modern adakites and lower crustal felsic granulites

magmatism and metallogeny of the ridanj krepoljin belt eastern serbia and their correlation with northern and eastern analogues in the southwestern carpathians of sw romania and e serbia calc alkaline upper cretaceous paleogene subduction related magmatic rocks occur in two main zones the ridanj krepoljin belt e serbia represents the southern part of the western zone in this belt early maastrichtian dacites and subordinate andesites occur but there are indications of an unexposed granodioritic magmatism about 60 ma old pb zn ag and only subordinate cu mineralization is associated with this igneous activity the timok magmatic complex e serbia composed of upper cretaceous paleocene andesites and analogue intrusives represents the eastern zone south of the danube associated with this magmatism are cu au and very subordinate zn pb mineralization to the north sw romania in both zones mainly intrusive bodies diorites quartz diorites granodiorites monzonites of campanian paleocene age are exposed porphyry copper mo and in north pb zn cu mineralization are related to those intrusives the petrological and geochemical features of all these calc alkaline rocks are very similar it appears however that the associated polymetallic and the copper mineralization are both spatially and vertically separated

fracture zones in the north atlantic from combined geosat and seasat data we present a new tectonic fabric map of the northern and central north atlantic ocean floor from 10 s to 66 n based on combined geosat and seasat altimetry data short wavelength vertical gravity along track was derived by hilbert transforming and high pass filtering geosat and seasat deflection of the vertical profiles the along track gravity data were used in conjunction with magnetic anomaly data to locate a large number of fracture zones as well as extinct spreading ridges and v shaped structures we traced many fracture zones more continuously and closer to adjacent continental margins than was previously possible we also mapped a number of unnamed fracture zones and fracture zone segments many of which were previously uncharted we have evaluated the agreement between the mapped fracture zones and synthetic flow lines as predicted from recent plate models for the opening of the north central north and south atlantic most fracture zones in this area correlate quite well with synthetic flow lines supporting the proposition that geosat seasat altimetry data serve as a useful tool to map fracture zones where insufficient bathymetric data are available many fracture zones including some small offset fracture zones in the central north atlantic have been stable and follow tectonic flow lines for tens of millions of years however many other fracture zones do not reflect a railroad track pattern of plate motions the geometry of many small and medium offset fracture zones indicates that the ridge axis discontinuities that produce them can migrate along the ridge causing off axis traces that deviate from tectonic flow lines velocity space diagrams constructed using a recent relative and absolute present day plate motion model indicate that some low angle v shaped troughs and ridges are likely formed by migration of the plate boundary relative to a mesospheric reference frame other low angle v shaped structures reflect slow migrations oscillations of small offset ridge axis discontinuities that are distinct from both tectonic flow lines and v shapes reflecting absolute plate motions high angle v shaped structures are the result of fast migrating ridge axis discontinuities propagating rifts

trace element and isotope sr nd geochemistry of porphyry and skarn mineralising late cretaceous intrusions from banat western south carpathians romania geochemical and isotopic strontium neodymium data have been obtained from 24 samples of seven late cretaceous intrusions associated with skarn tincova bocsa ocna de fier dognecea and porphyry copper molybdenum skarn deposits oravi a ciclova sasca and moldova nou in the south carpathians of romania the intrusions cut the supragetic getic nappes and form a 100 km long nne ssw trending lineament in the banat metallogenic province the samples range in composition from gabbro to granodiorite and define in major and trace element variation diagrams a calc alkaline to high potassium calc alkaline trend ranging from 50 to 67 sio2 they are magnetite bearing i type granitoids enriched in lile lree and depleted in nb ta and zr common features for magmas associated with subduction zones the lack of cumulate textures and of positive europium anomalies seems to indicate that the samples represent liquid compositions the observed trend thus approximates a liquid line of descent resulting from fractional crystallisation of parental magmas with similar major and trace element compositions initial strontium isotopic ratios sri vary from 0 7042 to 0 7058 and end t values range from 3 9 to 0 2 variations of sri and end t values with sio2 show minor crustal assimilation the generally positive end t values together with moderate sri indicate that the parental magmas result from partial melting of a rubidium enriched and lree depleted source such as a heterogeneous lithospheric mantle or a young mafic lower crust derived from it selective rubidium enrichment probably occurred during a previous subduction event by metasomatism of the overlying mantle wedge either in the early cretaceous or earlier as suggested by tdm model ages ca 600 ma the cu mo pb zn fe deposits are intimately associated with the intrusions and the banat romania region can be subdivided in two metallogenic zones in northern banat fe cu pb zn skarns occur whereas in southern banat porphyry style copper and molybdenum deposits predominate these differences result from a combination of several parameters 1 magma composition whereby copper and molybdenum rich deposits tend to be associated with calc alkaline compositions 2 an increase of the present day erosion level from south to north as indicated by the presence of large equigranular plutons in northern banat and of porphyritic cupolas and apophyses associated with porphyry style mineralisation in southern banat 3 the nature of the host rocks with skarns preferentially developed in calcareous host rocks and 4 local variations of conditions controlling the infiltration of fluids and the precipitation of ore minerals

middle permian early triassic magmatism in the western pontides nw turkey geodynamic significance for the evolution of the paleo tethys abstract permian triassic magmatic rocks are widely exposed in different tectonic terranes and continental blocks in the aegean region this study is focussed on the istanbul zone and the istranca strandja massif which are located in the western pontides of nw turkey the kirklareli and the tepecik plutons intruded into the metamorphic basement rocks of the istranca massif and the sancaktepe pluton is emplaced into the istanbul paleozoic sedimentary sequences we present new geochemical data for these plutons in order to interpret their petrogenesis and time of emplacement and use this information for geodynamic interpretation the zircon u pb crystallization ages are 268 3 2 1 ma for the kirklareli pluton 249 4 1 5 ma for the tepecik pluton and 257 3 1 5 ma and 253 7 1 75 ma for the the sancaktepe pluton they are high k calc alkaline to shoshonitic granitoids with aluminum saturation index asi values between 0 9 and 1 3 which define them as peraluminous and slightly metaluminous 87sr 86sr i values for the studied plutons range between 0 701123 and 0 707704 143nd 144nd i ratios calculated for crystallization ages are between 0 512052 and 0 512431 and end i values vary from 4 71 to 2 22 tdm model ages range between 0 83 and 1 41 ga these plutons are enriched in liles and lree and depleted in hfses with negative eu anomalies indicating that the melts were derived from mafic crustal sources our new data suggest that the kirklareli pluton was generated in a subduction related magmatic arc and the highly fractionated sancaktepe and tepecik plutons were formed in a back arc setting in response to the northward subduction of the paleo tethys ocean during the mid permian early triassic

3 geochronology and geodynamics of late cretaceous magmatism and cu au mineralization in the panagyurishte region of the apuseni banat timok srednogorie belt bulgaria abstract the apuseni banat timok srednogorie abts belt europe s most extensive belt of calc alkaline magmatism and cu au mineralization is related to the subduction of the tethys ocean beneath the european continental margin during the late cretaceous phase of the alpine himalayan orogeny economic deposits are restricted to certain segments along the belt and all major porphyry style and high sulphidation ore deposits in bulgaria are aligned on the panagyurishte corridor a narrow zone obliquely crossing the abts belt this paper reviews the geology geochemistry and geochronology of igneous and hydrothermal events along this corridor in a profile extending from the european continental basement in the north to the accretionary complex of the rhodopes in the south extensive u pb dating of zircons from subvolcanic intrusions and major plutons supplemented by published age data for magmatic rocks and hydrothermal ore deposits obtained by other methods reveals a general younging of magmatism from ca 92 ma in the north elatsite to ca 78 ma in the south capitan dimitrievo cu au deposits are restricted to the northern and central parts of the profile ranging in age from 92 to 86 ma while the southernmost part exposes more deeply eroded mid crustal plutons devoid of economic mineralization the age progression correlates with a north to south geochemical trend of decreasing crustal input into mantle derived magmas magmatism and ore formation in individual magmatic hydrothermal complexes along the profile is much shorter lived for example subvolcanic intrusions and porphyry cu au mineralization at the elatsite deposit and andesitic volcanism and high sulphidation au as cu mineralization at chelopech all occurred within a time span of about 1 million years the age progression of calc alkaline magmatism within the panagyurishte region bulgaria from north to south is explained as a consequence of slab retreat during oblique subduction this led to transtensional block faulting and subsidence and thus to the preservation of near surface magmatic hydrothermal products including economic cu au deposits accretion of continental fragments in the rhodopes south of the abts belt led to greater uplift of the youngest late cretaceous intrusions this removed any ore deposits that might have been formed in this area

slab detachment control on mafic volcanic pulse and mantle heterogeneity in central mexico seismic tomography studies and plate reconstructions suggest that the farallon slab broke off shortly before subduction ended off southern baja california however the progress of detachment in time and space and its consequences on the volcanism of central mexico have not so far been considered here i use the neogene geologic record of central mexico to propose a lateral propagation of slab detachment beneath the trans mexican volcanic belt during the late miocene i suggest that the trace of the detachment is expressed by a short 2 3 m y eastward migrating pulse of mafic volcanism that took place from ca 11 5 to ca 6 ma to the north of the pliocene quaternary volcanic arc as hot subslab material flowing into the slab gap produced a transitory thermal anomaly in the mantle wedge slab detachment of the deeper and denser part of the plate was initiated in the southern gulf of california area by the incoming of progressively younger oceanic lithosphere at the paleotrench that produced an increasing coupling between the magdalena microplate and the overriding north american plate the tear in the slab propagated eastward from the gulf of california to the gulf of mexico paralleling the southern mexico trench system the decrease in the rivera north america convergence rate between ca 9 and 7 ma appears to be related to the loss of slab pull after the detachment sparse oceanic island type basalts emplaced since the end of the miocene in the trans mexican volcanic belt are located above a trench parallel slab window between the inferred detachment trace and the leading edge of the present slab which has been detected seismically in this context the occurrence of these unusual intraplate magmas is easily explained by the infiltration of enriched asthenosphere into the subarc mantle

characterizing the depositional settings for sedimentary organic matter distributions in the lower yangtze river east china sea shelf system grain size distributions total organic carbon toc and total nitrogen tn concentrations and toc tn ratios c n were analysed for surface sediments from the lower yangtze river east china sea ecs shelf system hierarchical cluster analysis of grain size parameters mode mean sorting skewness and kurtosis has been employed to characterize grain size compositions the results suggest there are five grain size compositional types type i v that fingerprint distinct depositional conditions in areas with high sedimentation rates hydrological sorting preferentially enriches the fraction coarser than 6 4o 12 m in shallow seafloor sediments water depth 30 m and thus forms grain size compositional type i shallow and type ii deep in the open shelf where modern sediment supply is very limited grain size types iii v are identified according to different winnowing intensity overall toc contents significantly correlate with mud proportions suggesting muddy sediments are the primary control on om accumulation however de association of terrestrial om from fine sediments in the estuary and the occurrence of presumably relict om in the open shelf exert additional controls on om dispersal and carbon cycling in the ecs by considering geography oceanography sediment source and the relation between sedimentation conditions and sedimentary om distributions we define six depositional settings the lower river the estuary the coast the offshore upwelling area the erosional area and the open shelf these settings describe the sediment dispersal and associated organic matter cycling in the lower yangtze river ecs shelf system

a numerical study on the changjiang diluted water in the yellow and east china seas 1 a numerical simulation is performed using the princeton ocean model pom to investigate the behavior of the changjiang diluted water cdw and to evaluate the freshwater budget in the yellow and east china seas in addition the major process controlling the behavior of the cdw is discussed the simulated cdw distributions are fairly consistent with the observed distributions showing a remarkable seasonal variation the cdw extends to the northeast toward the tsushima korea straits during summer while it hugs the chinese coast to the southwest within a narrow band in winter tracer experiment is carried out to track the freshwater originating only from the changjiang and to evaluate the freshwater budget in the yellow and east china seas the result shows that about 68 percent of the changjiang discharge is transported through the tsushima korea straits and that about 27 percent is transported through the taiwan strait in autumn and winter to investigate the main process controlling the behavior of the cdw mentioned above another experiment is carried out without wind forcing it is found that the eastward extension of the cdw is strongly constrained by the taiwan tsushima warm current system over the shelf regime the wind is however responsible for the northeastward extension of the cdw in summer in addition the southwestward extension at the taiwan strait during winter is done by strong northeasterly monsoon the experiment without wind forcing shows that freshwater transport through the tsushima korea straits increases to 90 percent of the total changjiang discharge