geobarometry geothermometry and late archean geotherms from the granulite facies terrain of south india geobarometry and geothermometry of garnet bearing chamockitic and metapelitic assemblages from the high grade terrain from south india indicate three fields of equilibration high pressure granulites p 8 3 pm 1 0 kb t 760 pm 40 circ c are restricted to the charnockites and mafic granulites of the north slopes of the nilgiris these place a minimum constraint of 30 km on the maximum thickness of late archean crust medium pressure granulites p 6 4 pm 1 0 kb t 735 pm 40 circ c characterize the charnockites of the central nilgiris and the madras granulites to the east low pressure granulites p 5 0 pm 1 0 kb t 700 pm 20 circ c characterize the charnockites and metapelites south of the bhavani shear zone although migmatites from the kodaikanal massif may reflect somewhat higher temperatures all three granulite fields lie on a metamorphic geotherm piezothermic array which is strongly convex to the temperature axis and characteristic of convective heat transfer

vertical crustal motions from the doris space geodesy system five years 1993 1997 of doris data on the spot and topex poseidon satellites have been analyzed to estimate vertical motions at 33 sites of the permanent doris network rates have been determined assuming constant velocity over the 5 year time span except for a few stations vertical rates are lower than 5 mm yr comparison with solutions provided by gps slr or vlbi at colocated sites shows good agreement for most stations some space geodesy vertical rates however disagree significantly this may result from interannual to decadal fluctuations affecting the vertical motions giving rise to different apparent linear trends if estimated over different time spans except for six high latitude stations post glacial rebound produces negligible signal and cannot explain the observed motions other local or regional phenomena from geophysical or anthropogenic origin may be responsible for the estimated vertical motions

contrasting carbon and oxygen isotopic evolution in metacarbonates from the kerala khondalite belt southern india abstract the kerala khondalite belt is a proterozoic metasupracrustal granulite facies terrain in southern india comprising garnet biotite gneiss garnet sillimanite gneiss and orthopyroxene granulites as major rock types calc silicate rocks and marbles occurring as minor lithologies in the kerala khondalite belt show different mineral assemblages and reaction histories of which indicate a metamorphic p t fluid history dominated by internal fluid buffering during the peak metamorphism followed by external fluid influx during decompression the carbon and oxygen isotopic compositions of calcite from three representative metacarbonate localities show contrasting evolutionary trends the ambasamudram marbles exhibit carbon and oxygen isotope ratios 13c 0 and 18o 20 typical of middle to late proterozoic marine carbonate sediments with minor variation ascribed to the isotopic exchange due to the devolatilization reactions the 13c and 18o values of 9 and 11 respectively for calcite from calc silicate rocks at nuliyam are considerably low and heterogeneous the wollastonite formation here possibly corresponds to an earlier event of fluid infiltration during prograde to peak metamorphism which resulted in decarbonation and isotope resetting further petrologic evidence supports a model of late carbonic fluid infiltration that has partially affected the calc silicate rocks with subsequent isotope resetting more towards the contact between calc silicate rock and charnockite at korani only oxygen isotopes have been significantly lowered 18o 13 and the process involved might be a combination of metamorphic devolatilization accompanied by an aqueous fluid influx supported by petrologic evidence the stable isotope signatures obtained from the individual localities thus indicate heterogeneous patterns of fluid evolution history within the same crustal segment

estimates of vertical crustal motion derived from differences of topex poseidon and tide gauge sea level measurements 1 we have computed estimates of the rate of vertical crustal motion from differences of sea level measurements made by the topex poseidon radar altimeter and a globally distributed network of 114 tide gauges a rigorous error analysis was performed which suggests the accuracy of the estimated vertical rates is approximately 1 2 mm year for roughly half of the tide gauges which is sufficiently accurate to detect a variety of geophysical phenomena while only a cursory analysis of the estimated crustal motion rates was performed we observed many interesting phenomena including significant uplift at volcanic islands in the pacific and uplift of 7 9 mm year along the southwest coast of alaska the results reported here will be useful in a variety of geophysical studies as well as for validation of similar estimates of vertical crustal motion provided by precise geodetic techniques such as slr doris gps and vlbi

ultrahigh temperature metamorphism followed by two stage decompression of garnet orthopyroxene sillimanite granulites from ganguvarpatti madurai block southern india the mg al granulites from ganguvarpatti consist of orthopyroxene sillimanite garnet quartz as peak assemblage with a few porphyroblasts of cordierite and sapphirine these assemblages were strongly overprinted by late symplectites and coronas orthopyroxene inclusions in garnet and porphyroblast cores have the highest xmg 0 80 and al2o3 content 10 7 wt the estimated near peak metamorphic conditions 1 000 50 c and 11 kbar using garnet orthopyroxene geothermobarometry are consistent with those determined using a petrogenetic grid the proposed multi stage evolution process implies an initial decompression deduced from multi phase symplectites followed by cooling during biotite formation further late decompression is explained from the orthopyroxene rims on biotite this proposed p t path thus suggests a unique and complex evolution history for the uht granulites of southern india present results are comparable with similar adjacent terranes in the gondwana supercontinent but the lack of structural and geochronological data makes a link with any major metamorphic event uncertain

skin friction behind isolated hemispheres and the formation of obstacle marks we have measured the mean magnitude and direction and the rms fluctuation intensity of the skin friction behind plain hemispherical obstacles and behind hemispheres with tapered artificial tails one and four obstacle heights long downstream of reattachment the mean skin friction magnitude is about 20 greater than its free stream value along the centre line and comparably reduced to either side of it the horizontal divergence of the skin friction vector field is positive divergent along the centre line and negative convergent to either side of it neither of these conditions favours development of a ridge longer than the separation length along the centre line the development of ridges or tails many obstacle heights long commonly observed in nature requires considerable modification of the simple sediment free wakes we have studied

glacial isostatic adjustment observed using very long baseline interferometry and satellite laser ranging geodesy in global space geodetic solutions radial site motions are usually estimated relative to the geocenter the center of figure of the solid earth most geodesists estimate the motion of the geocenter assuming both that sites do not move radially and that sites move laterally as predicted by plate motion model nuvel 1a demets et al 1990 1994 here we estimate the motion of the geocenter assuming that the plate interiors deform radially and laterally as predicted by the postglacial rebound model of peltier 1994 or that of peltier 1996 without assuming a priori knowledge about relative plate motion radial site motions estimated relative to this rebound adjusted geocenter are in the same reference frame as the rebound model predictions whereas site motions estimated without adjusting for rebound are not we further constrain the motion of the rebound adjusted geocenter using satellite laser ranging s sensitivity to the center of mass of the solid earth the oceans and the atmosphere by assuming that the mean velocity between the rebound adjusted geocenter and the center of mass is negligible over the time period of geodetic measurement twenty years of observation with satellite laser ranging and very long baseline interferometry record the isostatic response of the solid earth to the unloading of the late pleistocene ice sheets the misfits of the postglacial rebound model of peltier 1994 and that of peltier 1996 are 34 and 16 less respectively than the misfit of the rigid plate model sites at onsala sweden and algonquin park ontario are observed to be rising at 3 mm yr and 2 mm yr respectively reflecting unloading of the fennoscandian and laurentide ice sheets sites along the east coast of the united states are subsiding at 2 mm yr indicating that the forebulge produced by the laurentide ice sheet is currently collapsing very slowly sites beneath the margins of the ice sheets during the last glacial maximum are currently moving laterally away from the ice sheet centers at 1 5 mm yr in disagreement with the moderately fast outward motion predicted by the model of peltier 1996

crustal evolution in south india constraints from nd isotopes nd isotope analyses from a range of lithologies including charnockites metasediments and granitoids that comprise the high grade terrain of south india define contrasting age provinces north of the palghat cauvery shear zone the karnataka craton and the granulite blocks of nilgiri and madras are characterized by model nd ages from 3 4 to 2 4 ga with significant crustal growth during the late archean south of the palghat cauvery shear zone a pan african granulite facies event resulted in sm nd fractionation as observed in several incipient charnockite localities model nd age calculations that allow for sm nd fractionation at 550 ma yield ages in the range of 2 9 to 1 3 ga this range compares closely with published model nd ages from the high grade terrain of sri lanka mid proterozoic crustal growth 1 1 ga observed in the vijayan complex of sri lanka may have provided source material for metasediments characterized by young model nd ages in southern peninsular india the palghat cauvery shear z

granulite facies spinel cordierite assemblages from the kerala khondalite belt southern india abstract granulite facies metapelites at koliacode in the kerala khondalite belt show compositional bands of cordierite spinel sillimanite and biotite alternating with quartz feldspar rich bands reaction textures involving cordierite and garnet show evidence for decompression mineral phase equilibria computations provide temperatures of ca 700 750c and pressures of 4 5 5 0 kbar spinel in these rocks is remarkably enriched in zn zno up to 9 4 wt the metamorphic p t conditions and mineral reactions indicate that the terrain underwent rapid and near isothermal decompression

an investigation of the flow and scour mechanisms around isolated spur dikes in a shallow open channel 1 conditions corresponding to the initiation of the erosion and deposition process 1 the present study investigates the flow physics and the role played by the main coherent structures in the scouring processes around a vertical spur dike in a straight channel at conditions corresponding to the start flat bed of the scouring process large eddy simulation les is performed at a relatively low channel reynolds number re 18 000 in the range where most flume studies with clear water scour conditions are conducted similar to these studies the incoming flow is fully turbulent and contains realistic turbulence fluctuations visualization experiments are conducted to better understand the nature of the interactions between the dominant coherent structures playing a role in the erosion process it is found that the structure of the horseshoe vortex hv system at the base of the spur dike changes considerably in time and in vertical sections perpendicular to the trajectory defined by the axis of the main necklace vortex however its intensity is the largest at vertical sections situated around the tip of the spur dike it is in this region that the core of the main necklace vortex oscillates aperiodically between two preferred modes in one of them zero flow mode the necklace vortex is closer to the spur dike and more compact and the near bed jet flow beneath it is weak in the other one back flow mode a strong near bed jet flow convects the primary necklace vortex away from the spur dike and its core is more elongated and less compact this explains the large amplification by about 1 order of magnitude compared to the surrounding turbulent flow of the turbulent kinetic energy and pressure fluctuations inside the hv system in the region situated around the tip of the spur dike and the double peak distribution of the turbulent kinetic energy past the spur dike in the legs of the necklace vortex the intensity of the bimodal oscillations decreases such that they are not observed in spanwise sections situated at more than one channel depth behind the spur dike it is found that the legs of the horseshoe vortices can interact at times with the vortex tubes shed in the detached shear layer dsl and with the tip of the spur dike these events typically result in a significant change in the coherence of the hv system the largest bed shear stress values in the mean flow are present in the strong acceleration region near the tip of the spur dike but high bed shear stress values are also observed beneath the upstream part of the dsl the bed shear stress fluctuations around the local mean values can be very high especially in the region situated beneath the upstream part of the dsl at random times some of the vortices shed in the dsl merge or interact with eddies from the recirculation region this leads to an increase in their strength and to a large increase of the bed shear stress along their path

nature of flow and turbulence structure around an in stream vertical plate in a shallow channel and the implications for sediment erosion 1 detailed knowledge of the dynamics of large scale turbulence structures is needed to understand the geomorphodynamic processes around in stream obstacles present in rivers detached eddy simulation is used to study the flow past a high aspect ratio rectangular cylinder plate mounted on a flat bed relatively shallow channel at a channel reynolds number of 2 4 105 similar to other flows past surface mounted bluff bodies the large amplification of the turbulence inside the horseshoe vortex system is because the core of the main necklace vortex is subject to large scale bimodal oscillations the presence of a sharp edge at the flanks of the obstruction fixes the position of the flow separation at all depths and induces the formation and shedding of very strong wake rollers over the whole channel depth compared with the case of a circular cylinder where the intensity of the rollers decays significantly in the near bed region because the incoming flow velocity is not sufficient to force the wake to transition from subcritical to supercritical regime in the case of a high aspect ratio rectangular cylinder the passage of the rollers was found to induce high bed shear stresses at large distances 6 8 d behind the obstruction also the nondimensional values of the pressure root mean square fluctuations at the bed were found to be about 1 order of magnitude higher than the ones predicted for circular cylinders overall this shows that the shape of the in stream obstruction can greatly modify the dynamics of the large scale coherent structures the nature of their interactions and ultimately their capability to entrain and transport sediment particles and the speed at which the scour process evolves during its initial stages

fluid evolution and exhumation path of the trivandrum granulite block southern india in charnockites and host garnet biotite gneis ses of the trivandrum granulite block tgb southern india fluid inclusions are mainly represented by co2 rich categories aqueous inclusions with low salt concentration 0 33 13 5 wt nacl equiv occur sub ordinately we recognize three generations of co2 rich inclusions which have contrasting fluid densities that correlate with the different stages of metamorphic evo lution established from mineral phase equilibria studies although some of these inclusions show variable depression in melting temperatures laser raman spec troscopic studies revealed no volatiles other than co2 we report here the occurrence of high density co2 rich inclusions for the first time from this region with homogenization temperatures in the range of 21 9 to 15 6 c q 1 041 1 012 g cm 3 the marked secondary character of these high density inclusions and their tex tural association with late brittle deformational features indicate their entrapment at low temperature conditions 250 300 c post dating charnockite formation regional metamorphism in tgb stage m1 took place at ca 700 c and 5 36 kbar although higher tempera tures prevailed in the northern part of the terrain a subsequent period of decompression of the order of 6 7 km was accompanied by partial recrystallization of host rocks and intensive processes of charnockite for mation m2 that extended to subisobaric cooling from 785 805 to 680 700 c the relatively small population of aqueous inclusions in charnockites and their low salinity preclude any major role for metasomatic pro cesses involving increase of potassium activity and confirm the important role of co2 rich fluids in stabi lizing low water activities during the final phase of exhumation of the region ca 9 km in depth additional heat input resulted in mineralogical alterations corre lated to stage m3 while the source of heat and fluids involved in charnockite formation is postulated to be magmas derived from sublithospheric sources the late heat and fluid transfer are correlated to late pan african ultrabasic and alkaline intrusives emplaced at shallow depths

cordierite gneisses of southern kerala india petrology fluid inclusions and implications for crustal uplift history the cordierite bearing gneisses occurring as elongate patches in an 8 to 10 km wide zone along the achankovil fault lineament at the northern margin of the southern kerala crustal segment represent an important lithological unit in the archaean granulite terrane of south india the textural relationships in these rocks are consistent with the following main reactions 1 garnet quartz cordierite hypersthene 2 garnet sillimanite quartz cordierite 3 hypersthene sillimanite quartz cordierite 4 sillimanite spinel cordierite corundum and 5 biotite quartz sillimanite cordierite k feldspar many of the mineral associations and reaction textures including the remarkable preservation of symplectites are indicative of partial replacement of high pressure assemblages by cordierite bearing lower pressure ones during an event of rapid decompression temperature estimates from coexisting mineral phases show 710 garnet biotite 791 garnet cordierite and 788 c garnet orthopyroxene pressure estimates from mineral assemblages range from 5 4 to 7 kb detailed fluid inclusion studies in quartz associated with cordierite show high density co2 0 80 0 95 g cm3 as the dominant fluid phase with traces of probable ch4 in the sillimanite bearing rocks the isochore for the higher density fluid inclusions defines a pressure of 5 5 kb the fracture bound co2 and co2 h2o ch4 inclusions indicate simultaneous entrapment at 400 c and 1 7 kb in the cordierite hypersthene assemblage and 340 c and 1 2 kb in the cordierite sillimanite assemblage the p t path delineated from combined solid and fluid data corresponds to the piezothermic array of the gneisses and is characterized by t convex nature indicative of rapid and virtually isothermal crustal uplift probably aided by extensional tectonics

gold occurrences in madagascar south india and sri lanka significance of a possible pan african event abstract gold occurs in various quantities mainly in the central and southern parts of sri lanka although gold is recovered mainly from river sediments at present it has been mined in the past also from a concordant quartz reef in central sri lanka and from other types of sediments such as marshy beds surrounding dykes of ultramafic composition in southern sri lanka the sedimentary gold has been interpreted as being derived from the mineralizations of the latest deformational features such as ductile and brittle shears and fractures consisting of quartz veins minor pegmatites and sulphide mineralizations mainly of pyrite pyrrhotite and chalcopyrite the mineralization of gold is exclusively in the highland complex rocks of sri lanka which represent archaean late proterozoic metamorphic complexes in madagascar gold is present in the precambrian basement rocks consisting of some greenstone belts and metasediments as a diffused mineral in the rocks concordant quartz reefs and more recent discordant quartz veins the concordant quartz veins and diffused gold are related to both archaean and proterozoic rock associations and the discordant veins which have been identified as permo triassic are found mainly in the north within the contact zone of proterozoic rocks and the phanerozoic cover gold is also recovered form ancient and recent alluvial accumulations and lateritic earth the mineralization of vein deposits is mainly gold quartz and gold sulphide associations the sulphides being galena chalcopyrite and pyrite in south india gold occurs in archaean metamorphic units comprising of granite greenstone complexes in the kolar classic gold field and in granulite terranes in more southerly occurrences such as the historic wynad fields in both cases gold occurs in gold quartz veins which occupy fissures and shears within the archaean metavolcanics gold also occurs in the attapadi area of kerala both in sediments and in primary epigenetic gold deposits which are hosted by precambrian amphibolites and granitic gneisses the attapadi lode veins are predominantly structurally controlled and are closely associated with the proterozoic bhavani shear zone gold is recovered both from the primary and placer deposits and the primary deposits contain gold quartz veins gold quartz carbonate veins and gold quartz sulphide veins the sulphide minerals are mainly galena pyrite chalcopyrite and arsenopyrite the rocks in the southern madagascar southern india and sri lanka belong to granulite terranes that have peak metamorphic imprints and tectonic development during the pan african the emplacement of gold mineralization mainly in madagascar and south india can be correlated in the archaean the gold deposition in the later deformational structures with concordant and discordant gold bearing veins can be correlated also with those in sri lanka as a pan african mineralizing event it is also evident that co2 rich fluids from a deep seated source has continued from archaean and were still active during the proterozoic being responsible for the pan african event of gold deposition particularly in the younger structures in these countries

jtrf2014 the jpl kalman filter and smoother realization of the international terrestrial reference system we present and discuss jtrf2014 the terrestrial reference frame trf the jet propulsion laboratory constructed by combining space geodetic inputs from very long baseline interferometry vlbi satellite laser ranging slr global navigation satellite systems gnss and doppler orbitography and radiopositioning integrated by satellite submitted for the realization of itrf2014 determined through a kalman filter and rauch tung striebel smoother assimilating position observations earth orientation parameters and local ties jtrf2014 is a subsecular time series based trf whose origin is at the quasi instantaneous center of mass cm as sensed by slr and whose scale is determined by the quasi instantaneous vlbi and slr scales the dynamical evolution of the positions accounts for a secular motion term annual and semiannual periodic modes site dependent variances based on the analysis of loading displacements induced by mass redistributions of terrestrial fluids have been used to control the extent of random walk adopted in the combination with differences in the amplitude of the annual signal within the range 0 5 0 8 mm jtrf2014 derived center of network to center of mass cm cn is in remarkable agreement with the geocenter motion obtained via spectral inversion of gnss gravity recovery and climate experiment grace observations and modeled ocean bottom pressure from estimating the circulation and climate of the ocean ecco comparisons of jtrf2014 to itrf2014 suggest high level consistency with time derivatives of the helmert transformation parameters connecting the two frames below 0 18 mm yr and weighted root mean square differences of the polar motion polar motion rate in the order of 30 as 17 as d

sediment pick up functions experimental research has been performed to determine the sediment pick up by a uniform flow without initial sediment load a sediment lift was designed by which the sediment particles were moved upwards at a constant rate through a circular opening in the flume bottom five types of bed material sand have been used with d d5 d0 values in the range 130 1500 m the mean flow velocities were in the range 9 5 1 0 m s the experimental results have been used to derive an empirical pick up function the results have also been used to evaluate several existing pick up functions finally the proposed empirical pick up function has been applied to predict the bed load and suspended load transport in the latter application the proposed function has been used as a bed boundary condition in a mathematical model for suspended sediment transport

multistage metamorphic evolution of the trivandrum granulite block southern india abstract the trivandrum granulite block tgb southern india records evidence for three distinct stages of evolution m1 m3 during the pan african high grade metamorphism with possible temperature gradient from north to south of the terrain as detected from mineral phase equilibria thermobarometry in three classic localities namely nuliyam kunnanpara and nellikkala the charnockites both incipient and massive were formed during the first stage m1 at temperatures higher than their host rocks and at appreciably lower pressures charnockite formation was dominantly controlled by an increase in partial pressure of co 2 along structural locales during subisothermal decompression although an increase of potash activity could have also been an important factor in this process the charnockites at nellikkala in the northern margin of tgb were formed under appreciably more h 2 o rich conditions x h 2 o 0 53 0 03 than those at nuliyam x h 2 o 0 25 0 02 in the southern margin it is inferred that during the period between the metamorphic stages m1 and m2 the terrain experienced subisobaric cooling comparison of results from thermobarometry with data on absolute age determinations from geochronology of the metamorphic rocks in tgb allows the interpretation that the m1 metamorphic event took place during 540 600 ma m2 at about 530 ma and m3 in the interval of 440 470 ma mineralogic and thermobarometric evidence for earlier high grade metamorphic processes if any have been erased from these rocks the processes of charnockite formation and post peak retrograde metamorphism in the tgb took place under high geothermal gradients 40 150 km this probably testifies to the existence of a local heat source either magmas at depth or mantle plume beneath the region the general metamorphic cycle in the tgb is estimated to be ca 100 160 ma which is much shorter in time span than that in the other regions of southern peninsular india such as the karnataka craton and the eastern ghats mobile belt during this period the terrain experienced rapid exhumation of approximately 6 7 cm year with the total amplitude of vertical movements estimated to be about 16 17 km

interpreting granulite facies events through rare earth element partitioning arrays the use of rare earth element ree partition coefficients is an increasingly common tool in metamorphic studies linking the growth or modification of accessory mineral geochronometers to the bulk silicate mineral assemblage the most commonly used mineral pair for the study of high grade metamorphic rocks is zircon and garnet the link from u pb ages provided by zircon to the p t information recorded by garnet can be interpreted in relation to experimental data the simplistic approach of taking the average ree abundances for zircon and garnet and comparing them directly to experimentally derived partition coefficients is imperfect in that it cannot represent the complexity of a natural rock system this study describes a method that uses all the zircon analyses from a sample and compares them to different garnet compositions in the same rock using the most important ree values it is possible to define zircon garnet equilibrium using an array rather than an average the array plot describes partitioning between zircon and garnet using dyb and dyb dgd as the defining features of the relationship this approach provides far more sensitivity to mineral reactions and diffusional processes enabling a more detailed interpretation of metamorphic history of the sample this article is protected by copyright all rights reserved

predictions of antarctic crustal motions driven by present day ice sheet evolution and by isostatic memory of the last glacial maximum detectable crustal motion and secular rate of change of solid surface gravity may be produced by the earth s response to present day and past ice mass changes in antarctica scenarios of present day ice mass balance previously utilized to explore the global geodetic signatures of the antarctic ice sheet produce elastic crustal responses that are typically bounded by uplift rates 5 mm yr horizontal motion 1 mm yr and solid surface gravity change rates 1 gal yr in a restricted locality one scenario produces uplift rates slightly in excess of 10 mm yr and correspondingly enhanced horizontal and gravity rates in contrast the viscoelastic response to ice mass changes occurring since last glacial maximum lgm exceeds 5 mm yr uplift over substantial portions of west antarctica for a wide range of plausible choices of timing and magnitude of deglaciation and mantle viscosity similarly viscoelastic gravity rate predictions exceed 1 gal yr decrease over large regions confirming suggestions that a global positioning system gps and absolute gravity based program of crustal monitoring in antarctica could potentially detect postglacial rebound a published revision to the climap model of the antarctic ice sheet at lgm herein called the d91 model features a substantially altered west antarctic ice sheet reconstruction this revision predicts a spatial pattern of present day crustal motion and surface gravity change that diverges strikingly from climap based models peak d91 crustal rates assuming deglaciation begins at 12 kyr and ends at 5 kyr are around 16 mm yr uplift 2 mm yr horizontal and 2 5 gal yr gravity tabulated crustal response predictions for selected antarctic bedrock sites indicate critical localities in the interior of west antarctica where expected responses are large and d91 predictions differ from climap based models by a factor of 2 or more observations of the postglacial rebound signal in antarctica might help constrain antarctic mass balance and contribution to sea level rise over the past 20 000 years

dehydration melting phenomena in leptynitic gneisses and the generation of leucogranites a case study from the kerala khondalite belt southern india

on the stability of a geodetic no net rotation frame and its implication for the international terrestrial reference frame 1 one of the important implications of a no net rotation nnr model of the earth s horizontal surface velocity is that it is used as a constraint in the definition of the international terrestrial reference frame itrf we present here our most recent estimates of an nnr model gsrm nnr 2 that uses over 5700 geodetic station velocities we test the sensitivity of our model by varying data input and model assumptions the difference between our various models is maximally 0 6 mm yr 1 but can be larger if we use only a geographically limited core velocity data set or if a significant bias in frame origin translation rate exists although plate boundary zones should not be considered as being part of rigid plates kreemer and holt 2001 the details of the velocity field within the plate boundaries have an insignificant effect on the nnr frame the difference between the various nnr models that we test is small compared to the difference between our nnr models and itrf2000 which can be up to 3 1 mm yr 1 we conclude that the itrf2000 does not satisfy the nnr condition when considering an nnr model that is based on the actual present day velocity of the entire earth s surface instead of nnr nuvel 1a

constraints on the timing of pan african granulite facies metamorphism in the kerala khondalite belt of southern india shrimp mineral ages and nd isotopic systematics abstract the supracrustal kerala khondalite belt kkb southern india constitutes an important but little understood terrain in the evolution of east gondwana here we report shrimp u pb zircon and titanite ages for a suite of metasedimentary rocks from the kkb metamorphic ages at documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 530 2 pm 4 4 end document and documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd us

tests of the rigid plate hypothesis and bounds on intraplate deformation using geodetic data from very long baseline interferometry the geodetic results of ma et al 1994 from very long baseline interferometry are used to assess rates of intraplate deformation we analyze the resulting set of velocities of 18 plate interior sites nine on the north american plate four western european sites on the eurasian plate three on the pacific plate and two on the australian plate we formulate three alternative error budgets based partly on the work of ryan et al 1993a an optimistic error budget a conservative error budget and an upper bound error budget all three budgets assume the existence of a previously unmodeled error that is inversely proportional to the time span of observations at a site use of the conservative error budget indicates no significant motion between sites on any one of the four plates use of the upper bound error budget designed to be precisely large enough to be consistent with rigid plates places a usefully small upper bound on how fast any site might be moving relative to the rest of its plate speeds faster than 2 mm yr are excluded at the 95 confidence level for seven of the 18 plate interior sites adjustments of the site velocities for motion due to postglacial rebound as predicted from the model of tushingham and peltier 1991 give an insignificant improvement to the fit of the horizontal velocities to the rigid plate model the velocities of six sites near the western margin of the interior of the north american plate were also analyzed use of the conservative error budget indicates that a site near fairbanks alaska has an upper bound of 3 mm yr on its speed a site in nome alaska has an upper bound on its speed of 8 mm yr and a site in penticton british columbia has an upper bound on its speed of 4 mm yr of three sites on the colorado plateau two move marginally significantly and one moves insignificantly relative to stable north america upper limits on their speeds relative to stable north america range from 4 to 5 mm yr we conclude that the data do not yet demonstrate significant velocities between sites in the stable interior of any one plate but do provide useful and small upper bounds of 2 mm yr or less on the speeds of the best observed intraplate sites six sites near the western margin of the north american interior have upper bound speeds of 3 to 8 mm yr

electron microprobe dating of monazites from high grade gneisses and pegmatites of the kerala khondalite belt southern india monazites of five samples one leptynitic garnet biotite gneiss one khondalite one augen gneiss and two pegmatites from the central and northern part ponmudi unit of the kerala khondalite belt kkb in southern india were analyzed with the electron microprobe dating technique monazites in the augen gneiss and the pegmatites yield grain sizes between 200 800 m th abundances are rather low 10 wt and the distribution of th u and pb within single grains is fairly homogeneous contrasting to this monazites in the leptynitic gneiss and the khondalite are small 150 m they often display very complex th u pb patterns and contain high th concentrations up to 20 wt the statistical treatment of individual ages from the investigated samples revealed three populations of lower proterozoic 1 9 ga upper proterozoic 580 ma and ordovician age 470 ma as well as mid proterozoic ages between 0 8 1 7 ga which are not regarded to be of geological significance lower proterozoic ages are preserved in the cores of monazites from leptynitic gneisses and khondalites they fairly agree with sm nd model ages for similar rocks of the kkb and give a minimum age for first monazite growth or complete homogenization the prominent pan african population with mean values between 540 and 580 ma is present in the leptynitic gneiss the khondalite and the augen gneiss and in line with published isotope ages for the kkb the ordovician population finally marks the emplacement of granitic pegmatites subsequent to the pan african high grade metamorphic event there is an obvious discrepancy between khondalites and leptynitic gneisses on the one hand and augen gneisses on the other concerning the presence of lower proterozoic ages while these are abundant in the former often rimmed by upper proterozoic ages they are completely absent in the latter it appears unlikely that lower proterozoic ages were completely reset during a pan african event exclusively in the augen gneisses while they were preserved in leptynitic gneisses and khondalites it is further concluded that the augen gneisses are of magmatic origin and were derived from porphyritic granites thus the upper proterozoic age of 605 37 ma calculated for the investigated sample approximates the time of magma emplacement which slightly precedes the peak stage of pan african high grade metamorphism in the kkb and of monazite crystallization from the granitic melt a characteristic feature of the investigated monazites is the resetting of lower proterozoic and pan african ages to significantly younger values due to partial pb loss monazites not shielded by other minerals e g garnet suffered selective mobilization of pb along fractures or at their rims while th and u concentrations remained almost unchanged the results presented in this study indicate that this was mainly due to fluid rock interaction it is concluded that thermal diffusion of pb even at the suggested temperatures of 900 c only had minor influence on the th u pb composition in monazite and that the closure temperature for this system must be significantly higher than previously assumed 750 c

evolution of the continental crust in the kerala khondalite belt southernmost india evidence from nd isotope mapping u pb and rb sr geochronology in order to decipher crustal genesis and evolution as well as to refine the metamorphic history of the kerala khondalite belt kkb southernmost india we have applied u pb monazite rb sr biotite feldspar dating and nd isotope geochemistry the kkb belonged to an eastern gondwana mobile belt that underwent ultra high temperature metamorphism at pan african times it is dominated by nd model ages ranging between 2 0 and 3 0 ga except at its northernmost boundary the achankovil unit au where middle proterozoic nd model ages were recognised 1 3 1 6 ga the new data show that these ages are not restricted to cordierite bearing metasediments alone but can be found in other lithologies of the achankovil unit as well peak metamorphism occurred between 590 and 550 ma as recorded by u pb dating of monazite from charnockites and garnet biotite gneisses rb sr ages of minerals in pegmatite intrusions record cooling to ca 400 500 c by 490 470 ma based on a systematic regional sampling this contribution confirms and refines former models based on smaller datasets the major issue is that the kerala khondalite belt must have undergone an extremely slow cooling history 3 6 c ma comparable to the one described for sri lanka and madagascar still such ultra high temperatures associated to slow cooling processes cannot be satisfactorily fit into a common tectonic context 2004 published by elsevier b v

vlbi baseline variations from the ice 4g model of postglacial rebound an analysis is presented of selected vlbi baseline variations expected as a consequence of the continuing process of glacial isostatic adjustment although these baseline variations are for the most part dominated by the radial component of the motion the tangential component can also be an important contributor to the net effect and is in fact dominant for short baselines the new calculations have been performed with the recently derived ice 4g model of the last deglaciation event of the current ice age peltier 1994 and the results demonstrate that those obtained with the previous ice 3g model are not reliable

controlling mechanism of local scouring experimental study of clear water scouring around a circular cylinder shows that the scour mechanism is coupled to the three dimensional separation of the upstream boundary layer and the periodic vortex shedding in the wake of the cylinder the first scour appears in the wake of the cylinder the main scouring agent in the upstream region is a system of horseshoe vortices the vortices have a periodical character that causes a triple scour profile to develop in the upstream region during scouring the number and periods of horseshoe vortex shedding undergo no appreciable change despite the clear water stage the transport phenomenon is periodical transport of sediment takes place through turbulent scales of comparable size to macro length scales the size of horseshoe vortices are representative for the macroscale wake scouring is caused by the primary wake vortices and the accelerated side flow the process is characterized by a strong periodical transport and the formation of ripples the periodicity is controlled by the shedding frequency of the wake vortices collars attached to the cylinder cannot prevent the formation of the vortices

a new gps velocity field for the pacific plate part 1 constraints on plate motion intraplate deformation and the viscosity of pacific basin asthenosphere

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

constraining models of postglacial rebound using space geodesy a detailed assessment of model ice 5g vm2 and its relatives summary using global positioning system very long baseline interferometry satellite laser ranging and doppler orbitography and radiopositioning integrated by satellite observations including the canadian base network and fennoscandian bifrost array we constrain in models of postglacial rebound the thickness of the ice sheets as a function of position and time and the viscosity of the mantle as a function of depth we test model ice 5g vm2 t90 rot which well fits many hundred holocene relative sea level histories in north america europe and worldwide ice 5g is the deglaciation history having more ice in western canada than ice 4g vm2 is the mantle viscosity profile having a mean upper mantle viscosity of 0 5 1021 pa s and a mean uppermost lower mantle viscosity of 1 6 1021 pa s t90 is an elastic lithosphere thickness of 90 km and rot designates that the model includes rotational feedback earth s response to the wander of the north pole of earth s spin axis towards canada at a speed of 1 myr 1 the vertical observations in north america show that relative to ice 5g the laurentide ice sheet at last glacial maximum lgm at 26 ka was 1 much thinner in southern manitoba 2 thinner near yellowknife northwest territories 3 thicker in eastern and southern quebec and 4 thicker along the northern british columbia alberta border or that ice was unloaded from these areas later thicker or earlier thinner than in ice 5g the data indicate that the western laurentide ice sheet was intermediate in mass between ice 5g and ice 4g the vertical observations and grace gravity data together suggest that the western laurentide ice sheet was nearly as massive as that in ice 5g but distributed more broadly across northwestern canada vm2 poorly fits the horizontal observations in north america predicting places along the margins of the laurentide ice sheet to be moving laterally away from the ice centre at 2 mm yr 1 in ice 4g and 3 mm yr 1 in ice 5g in disagreement with the observation that the interior of the north american plate is deforming more slowly than 1 mm yr 1 substituting vm5a t60 for vm2 t90 that is introducing into the lithosphere at its base a layer with a high viscosity of 10 1021 pa s greatly improves the fit of the horizontal observations in north america ice 4g vm5a t60 rot predicts most of the north american plate to be moving horizontally more slowly than 1 mm yr 1 in agreement with the data ice 5g vm5a t60 rot well fits both the vertical and horizontal observations in europe the space geodetic data cannot distinguish between models with and without rotational feedback in the vertical because the velocity of earth centre is uncertain and in the horizontal because the areas of the plate interiors having geodetic sites is not large enough to detect the small differences in the predictions of rotational feedback going across the plate interiors

defining the translational velocity of the reference frame of earth summary earth s centre is fundamental to geodesy and geoscience because motions of sites on the surface are estimated relative to it international terrestrial reference frames itrf2000 and itrf2005 are defined by the centre of mass of earth s system cm consisting of solid earth the ice sheets the oceans and the atmosphere satellite lageos rotates about cm satellite laser ranging slr is used to estimate the velocity of cm relative to sites on the surface however itrf2000 and itrf2005 differ by 1 8 mm yr 1 suggesting that the velocity of cm is constrained poorly by slr in this study we define earth s reference frame with the centre of mass of solid earth ce site velocities estimated using slr vlbi gps and doris are corrected for a postglacial rebound model and inverted for the rotational velocities of the plates and the rotational and translational velocities of the four space techniques because the postglacial rebound predictions are relative to ce the velocity of ce relative to sites on the surface is estimated because the input slr site velocities are relative to cm the output slr translational velocity is the velocity of cm relative to ce the estimated velocity of ce does not depend strongly on the postglacial rebound model corrected for equal within uncertainties and having a root mean square of 0 5 mm yr 1 are estimates of the velocity of ce determined assuming that plate interiors are deforming radially as predicted by three postglacial rebound models and an estimate of the velocity of ce determined assuming that parts of plate interiors neither beneath nor along the margins of the late pleistocene ice sheets are not deforming laterally the velocity of ce equals within uncertainties probability greater than 5 per cent the velocity of cm in itrf2000 the velocity of ce differs significantly 0 05 per cent probability from the velocity of cm in itrf2005 earth s reference frame and we believe itrf s should be defined with the tightly constrained velocity of ce not with the poorly constrained velocity of cm because ce is believed to be moving relative to cm no faster than 0 5 mm yr 1 the velocity of ce estimated in this study is likely to be nearer the true velocity of cm than is the velocity of cm estimated using slr

the theoretical foundations and potential for large eddy simulation les in fluvial geomorphic and sedimentological research abstract large eddy simulation les is a method for resolving the time dependent structure of high reynolds number turbulent flows with les it is possible to model and track the behaviour of coherent turbulent structures and study their effect on the flow field hence les is potentially an important research tool in the fluvial sciences where flow mixing sediment entrainment and sediment transport are all affected by the presence of coherent vortices and their interactions with channel boundaries and other flow structures this paper introduces the les methodology discusses a variety of ways for representing small scale processes within les the subgrid scale modelling problem and provides some examples of early work into the use of les in a fluvial context a number of advances in computational power and numerical methods are required before les can be effectively applied at the river reach scale this paper considers some recent developments and their potential for providing validated large eddy simulations of river flow at the channel scale

metamorphic p t conditions of the kerala south india khondalite belt a granulite facies supracrustal terrain the khondalite belt of southernmost india is an immense section of granulite facies metasediments of probable early proterozoic age dominant rock types are migmatized khondalites garnet sillimanite pm cordierite metapelites acid biotite garnet graphitic gneisses and charnockites quartzofeldspathic gneisses with orthopyroxene throughout much of southern kerala the biotite gneisses are in a state of arrested conversion to charnockite partially decrepitated co 2 inclusions in quartz at the ponmudi mixed biotite gneiss charnockite quarry have significant ch 4 and or n 2 and are texturally late the probable sequence of events in metasediments was 1 migmatization 2 charnockite formation 3 symplectitic cordierite formation and 4 late co 2 entrapment phase equilibrium diagrams of anatexis in aluminous systems and fe mg exchange between garnet and biotite indicate metamorphic temperatures of 650 850 c for the khondalites temperatures based on garnet orthopyroxene

carbonic fluid inclusions in south indian granulites evidence for entrapment during charnockite formation field evidence and fluid inclusion studies on south indian incipient charnockites suggest that charnockite formation occurred during a decompressional brittle regime following the peak of metamorphism and regional deformation the most abundant type of inclusions in quartz and garnet grains in these charnockites contain high density carbonic fluids although lower density fluids occur in younger arrays of inclusions discrete fluid inclusion generations optically are observed to decrepitate over well defined temperature intervals and quantitative measurements of co2 abundance released from these inclusions by stepped thermal decrepitation show up to a four fold increase by volume in the incipient charnockites relative to the adjacent gneisses from which they are derived studies based on optical thermometry visual decrepitation and stepped heating inclusion release together indicate that entrapment of carbonic fluids coincided with charnockite formation we confirm that an influx of carbon dioxide rich fluids is associated with the amphibolite granulite transition as recorded by the incipient charnockites the remnants of which are commonly preserved as the earliest generation of high density fluid inclusions

constraining proposed combinations of ice history and earth rheology using vlbi determined baseline length rates in north america we predict the present day rates of change of the lengths of 19 north american baselines due to the glacial isostatic adjustment process contrary to previously published research we find that the three dimensional motion of each of the sites defining a baseline rather than only the radial motions of these sites needs to be considered to obtain an accurate estimate of the rate of change of the baseline length predictions are generated using a suite of earth models and late pleistocene ice histories these include specific combinations of the two which have been proposed in the literature as satisfying a variety of rebound related geophysical observations from the north american region a number of these published models are shown to predict rates which differ significantly from the vlbi observations

a comparison of vlbi data with the ice 3g glacial rebound model crustal motion predicted by the ice 3g glacial rebound model exhibits a pattern of tangential horizontal divergence away from the centres of uplift which in north america and europe are located around hudson bay and the gulf of bothnia tangential velocities reach peak magnitudes of 1 2 mm yr and must be included when predicting very long baseline interferometry vlbi baseline length change rates due to post glacial rebound out of 18 observed vlbi baselines examined 3 are situated such that their predicted length rates are around their 2 uncertainties or greater it is encouraging that 2 of these baselines exhibit predicted length rates within 2 of the observed rates

pan african charnockite formation in kerala south india sm nd mineral ages of gneisses and associated granulites from the ponmudi incipient charnockite locality south india indicate that granulite metamorphism occurred at or shortly after 558 ma proterozoic ages recorded by garnet separates reflect a detrital age or an earlier metamorphic event preserved by inclusions within garnet the age of post metamorphic uplift 440 460 ma is constrained by sr isotope equilibration between biotite and plagioclase since charnockite formation and subsequent uplift north of the palghat cauvery shear zone had terminated by earliest proterozoic time these results confirm two distinct periods of granulite formation in south india and suggest that the palghat cauvery shear zone represents the boundary between two blocks of strongly contrasting geological histories both incipient charnockite formation and subsequent uplift at ponmudi may be correlated with the tectonothermal evolution of the highlands group in sri lanka the similarity between nd and sr model ages for charnockites and gneisses from ponmudi indicates that no significant rb sr fractionation has occurred during the crustal history of these incipient charnockites pb isotopic ratios suggest that th u ratios were fractionated during charnockite formation at about 500 ma in contrast to charnockites found north of the palghat cauvery shear zone fractionation of u pb during the archaean did not occur in the ponmudi granulites

site displacement due to variation in earth rotation we study site displacement caused by changes in the rate of rotation of the earth and in the orientation of the earth s pole we include small effects which have been previously neglected most notably those caused by polar motion induced ocean loading using very long baseline interferometry vlbi data we estimate the real and imaginary love numbers associated with vertical and horizontal deformations caused by polar motion the estimates of the real part of the love numbers are consistent with theoretical predictions although the imaginary parts are too large including the loading effect improves the agreement of the real part

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

deformation of mexico from continuous gps from 1993 to 2008 1 we combine the velocities of 13 continuous global positioning system stations from mexico and 448 north american plate stations to better understand deformation and earthquake cycle effects in mexico velocities estimated at the mexican sites from high quality gps data collected since 2003 show no evidence for a previously reported eastward bias at sites in and near the yucatan peninsula the new velocities are compared to the predictions of two models one in which all motion in mexico is attributed to north american plate motion and the second of which attributes site motions to a combination of plate motion and the elastic effects of frictional coupling along the mexican subduction zone and faults in the gulf of california the second model fits the velocities within their estimated uncertainties mainland mexico thus moves with the north american plate to within 1 mm per year and undergoes elastic interseismic deformation far into its interior two stations inland from the guerrero and oaxaca segments of the mexican subduction zone have alternated between several year long periods of landward motion and several month long periods of trenchward motion frequently since 1993 consistent with previously described repeating transient slip events along the subduction interface the motions of two stations inland from the rivera plate subduction zone are dominated by the coseismic and postseismic effects of the m 8 0 9 october 1995 colima jalisco earthquake and m 7 5 22 january 2003 tecoman earthquake offshore from western mexico

3d calculations of equilibrium conditions in loose bed open channels with significant suspended sediment load the flow sediment transport and bathymetry at equilibrium conditions in loose bed open channels are predicted using a fully three dimensional 3d reynolds averaged navier stokes model that was validated for cases in which the bed load transport is dominant the paper focuses on two test cases corresponding to laboratory experiments performed in an s shaped channel in which the suspended sediment load is comparable to the bed load a modified version of the original model that accounts for gravitational force effects due to the total sediment load is proposed it is shown that the way bed slope effects are accounted for plays a major role in improving the predictive capabilities of the model for a case in which the equilibrium bathymetry is characterized by relatively large values and sharp variations of the transverse slope the model is then used to qualitatively and quantitatively analyze the distributions of several flow variables that are difficult to measure in the laboratory they include the dis

numerical and experimental investigation of flow and scour around a circular pile the flow around a vertical circular pile exposed to a steady current is studied numerically and experimentally the numerical model is a three dimensional model the model validation was achieved against new experimental data which include two component laser doppler anemometry lda flow measurements and the hot film bed shear stress measurements and reported in the present paper and the data of others and a k w turbulence model was used for closure the model does not have a free surface facility and therefore is applicable only to cases where the froude number is small fr 0 0 2 the flow model was used to study the horseshoe vortex and lee wake vortex flow processes around the pile the influence on the horseshoe vortex of three parameters namely the boundary layer thickness the reynolds number and the bed roughness was investigated in the latter investigation the steady solution of the model was chosen a study of the influence of the unsteady solution on the previously mentioned flow processes was also carried out the ranges of the parameters covered in the numerical simulations are the boundary layer thickness to pile diameter ratio is varied from 2 x 10 2 to 10 2 the pile reynolds number from 10 2 to 2 10 6 and the pile diameter to roughness ratio from 2 to about 10 3 the amplification of the bed shear stress around the pile including the areas under the horseshoe vortex and the lee wake region was obtained for various values of the previously mentioned parameters the steady state flow model was coupled with a morphologic model to calculate scour around a vertical circular pile exposed to a steady current in the case of non cohesive sediment the morphologic model includes i a two dimensional bed load sediment transport description and ii a description of surface layer sand slides for bed slopes exceeding the angle of repose the results show that the present numerical simulation captures all the main features of the scour process the equilibrium scour depth obtained from the simulation agrees well with the experiments for the upstream scour hole some discrepancy up to 30 was observed however for the downstream scour hole the calculations show that the amplification of the bed shear stress around the pile in the equilibrium state of the scour process is reduced considerably with respect to that experienced at the initial stage where the bed is plane

influence of turbulence on bed load sediment transport this paper summarizes the results of an experimental study on the influence of an external turbulence field on the bed load sediment transport in an open channel the external turbulence was generated by 1 a horizontal pipe placed halfway through the depth ih 2 a series of grids with a clearance of about one third of the depth from the bed and extending over a finite length of the flume and 3 a series of grids with a clearance in the range 0 1 1 0 ih from the bed but extending over the entire length of the flume two kinds of experiments were conducted plane bed experiments and ripple covered bed experiments in the former case the flow in the presence of the turbulence generator was adjusted so that the mean bed shear stress was the same as in the case without the turbulence generator in order to single out the effect of the external turbulence on the sediment transport in the ripple covered bed case the mean and turbulence quantities of the streamwise component of the velocity were measured and the shields parameter due to skin friction was determined the shields parameter together with the rms value of the streamwise velocity fluctuations was correlated with the sediment transport rate the sediment transport increases markedly with increasing turbulence level

paleomagnetism of ca 2 3 ga mafic dyke swarms in the northeastern southern granulite terrain india constraints on the position and extent of dharwar craton in the paleoproterozoic abstract the pole positions reported for the mafic dykes occurring in the northeastern southern granulite terrain and easterly trending dykes of dharwar craton are alike while their ages differ by ca 700 ma confounding tectonic reconstruction to resolve the discordance and to constrain the position of the indian continent in the proterozoic paleomagnetic and geochronological studies have been carried out on the mafic dyke swam in the northeastern southern granulite terrain two distinct pole positions are obtained one from the group of tiruvannamalai dykes as 27 7 s 231 5 e dp dm 12 14 with corresponding mean declination dm and inclination im as 125 and 73 8 95 22 7 6 respectively and second from the east coast dykes as 2 32 s 188 2 e dp dm 5 8 with corresponding mean dm and im as 88 9 and 33 8 95 48 7 1 respectively the remanent efficiency of magnetization values between 0 01 and 0 08 suggest that the dykes have been cooled through curie temperature of magnetite which is the carrier of magnetization the baked contact test confirms that the characteristic remanent magnetization is the primary magnetization the sm nd mineral whole rock isochron from one of the tiruvannamalai dykes yielded an age of 2318 60 ma mswd 1 9 this age is the time of intrusion of the tiruvannamalai dykes and is similar within errors to the age of dykes in the dharwar craton thus the contiguity of dharwar craton with the northern block of southern granulite terrain as early as 2 3 ga ago is established the pole position thus obtained corresponds to a high latitudinal position of dharwar craton during early paleoproterozoic

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

coherent structure dynamics and sediment erosion mechanisms around an in stream rectangular cylinder at low and moderate angles of attack 1 local scour around elongated in stream structures e g high aspect ratio rectangular bridge piers is mainly driven by the interactions between the erodible bed and the large scale coherent structures generated by the presence of the flow obstruction the present investigation uses eddy resolving numerical simulations to study the mean flow and turbulence structure around a high aspect ratio rectangular cylinder placed in a flat bed channel simulations are conducted for three angles of attack 0 15 and 30 at a channel reynolds number of 2 4 105 this paper focuses on the dynamics of the large scale coherent structures forming around the rectangular cylinder and their role in controlling sediment entrainment at conditions corresponding to the start of the scour process simulation results show that most of the sediment is entrained from the bed by the eddies shed inside the separated shear layers ssls by the legs of the necklace vortices and by the strongly accelerated flow on the outer side of the ssls for 0 and 15 the horseshoe vortex hv system plays a relatively minor role in the entrainment of sediment in front of the cylinder and the passage of the wake vortices rollers results in a small amplification of the bed friction velocity in contrast for 30 the unsteady dynamics of the main necklace vortices part of the hv system and of the roller vortices results in a significant amplification of the instantaneous bed friction velocity the mean flux of sediment entrained from the bed calculated on the basis of the mean flow field is found to underestimate by 2 3 times the same quantity when estimated more correctly on the basis of the instantaneous flow fields the primary reason for this underestimation is sediment entrainment in regions where the mean flow bed friction velocity is smaller than the critical value for entrainment quantitative information on the extent of the regions of high values of the bed friction velocity and its standard deviation and on the sediment entrainment flux as a function of the angle of attack is essential to guide scour protection measures around the in stream noncircular obstructions

constraints on vertical crustal motion for long baselines in the central mediterranean region using continuous gps abstract gps determination of vertical crustal velocity relative to a globally defined reference frame is limited by the accuracy of the reference frame origin and scale however the precision of relative vertical rates at regional distance scales remains largely unexplored we investigated the precision of regional scale vertical velocity estimates using data from seven continuously operating gps stations located in the central mediterranean the stations form a network of aperture 500 km and each has been in operation for at least 5 yr we used published constraints on recent crustal uplift inferred from late quaternary shoreline data to aid in the definition of a local vertical reference frame for gps rates to facilitate an assessment of gps vertical precision we explored different methods of defining the local reference frame the simplest method involves the estimation of a single scalar translation parameter adjusting the reference frame by this simple method yields agreement between cgps and holocene shoreline data sets at the level of 0 2 to 0 4 mm yr relative rates determined using cgps are also consistent with tide gauge records and sea level determined by satellite altimetry at the level of about 0 2 mm yr these results suggest that regional scale relative velocity precision well below the mm yr level is now possible using continuous gps

the angular velocities of the plates and the velocity of earth s centre from space geodesy summary using space geodetic observations from four techniques gps vlbi slr and doris we simultaneously estimate the angular velocities of 11 major plates and the velocity of earth s centre we call this set of relative plate angular velocities geodvel for geodesy velocity plate angular velocities depend on the estimate of the velocity of earth s centre and on the assignment of sites to plates most geodetic estimates of the angular velocities of the plates are determined assuming that earth s centre is fixed in an international terrestrial reference frame itrf and are therefore subject to errors in the estimate of the velocity of earth s centre in itrf2005 and itrf2000 earth s centre is the centre of mass of earth oceans and atmosphere cm the velocity of cm is estimated by slr observation of lageos s orbit herein we define earth s centre to be the centre of mass of solid earth ce we determine the velocity of ce by assuming that the portions of plate interiors not near the late pleistocene ice sheets move laterally as if they were part of a rigid spherical cap the geodvel estimate of the velocity of ce is likely nearer the true velocity of cm than are the itrf2005 and itrf2000 estimates because 1 no phenomena can sustain a significant velocity between cm and ce 2 the plates are indeed nearly rigid aside from vertical motion and 3 the velocity of cm differs between itrf2005 and itrf2000 by an unacceptably large speed of 1 8 mm yr 1 the velocity of earth s centre in geodvel lies between that of itrf2000 and that of itrf2005 with the distance from itrf2005 being about twice that from itrf2000 because the geodvel estimates of uncertainties in plate angular velocities account for uncertainty in the velocity of earth s centre they are more realistic than prior estimates of uncertainties geodvel differs significantly from all prior global sets of relative plate angular velocities determined from space geodesy for example the 95 per cent confidence limits for the angular velocities of geodvel exclude those of revel sella et al for 34 of the 36 plate pairs that can be formed between any two of the nine plates with the best constrained motion the median angular velocity vector difference between geodvel and revel is 0 028 myr 1 which is up to 3 1 mm yr 1 on earth s surface geodvel differs the least from the geodetic angular velocities that altamimi et al determine from itrf2005 geodvel s 95 per cent confidence limits exclude 11 of 36 angular velocities of altamimi et al and the median difference is 0 015 myr 1 geodvel differs significantly from nearly all relative plate angular velocities averaged over the past few million years including those of nuvel 1a the difference of geodvel from updated 3 2 myr angular velocities is statistically significant for all but two of 36 angular velocities with a median difference of 0 063 myr 1 across spreading centres eight have slowed down while only two have sped up we conclude that plate angular velocities over the past few decades differ significantly from the corresponding angular velocity averaged over the past 3 2 myr

dehydration reaction and isotope front transport induced by co2infiltration at nuliyam south india the field relations from a quarry at nuliyam south india illustrate dehydration of an amphibolite facies gneiss to granulite facies charnockite by co2 influx over a scale of 30 m both the calc silicate source of the fluids and the full extent of their penetration into the gneiss are preserved in a continuous section fluid flow is by a hydraulic fracture mechanism but is thought to be pervasive the sharp reaction front predicted by the continuum mechanical theory for advective fluid transport is not observed the front spreading is on too large a scale for either diffusive or dispersive control and is due to local kinetic disequilibrium between the fluid and rock although the divariant nature of the reaction may also have a limited effect the time integrated fluid flux varies from the instantaneous porosity at the fluid front to 20 vol adjacent to the calc silicate carbon isotope budgets suggest that decarbonation of the calc silicate by a rayleigh fractionation process provides a sufficient source for the co2 influxing into the gneiss graphite abundances vary from 0 01 to 0 1 by weight it is principally derived by precipitation from the fluid and may be modelled from phase equilibria carbon isotope fronts coincide with the reaction front on the scale of sampling although isotopic disequilibrium between graphite and inclusion co2 also implies local fluid rock disequilibrium

a model for the simulation of coupled flow bed form evolution in turbulent flows 1 we develop a three dimensional numerical model to simulate bed form dynamics in a turbulent boundary layer in the numerical model hydrodynamics is solved in a moving generalized boundary fitted curvilinear coordinate system such that the domain boundary exactly follows complex time dependent bed form geometry the resolved turbulent features are computed via large eddy simulation while the subgrid scale turbulent motions are modeled with a dynamic mixed model a second order accurate arbitrary lagrangian eulerian method is used to guarantee conservation of sediment mass while the grid moves arbitrarily due to the motion of the bed transport of suspended load is modeled using the eulerian approach with a pickup function as the bottom boundary condition for sediment entrainment at the bed transport of bed load and suspended load are combined in a mass balance equation for the bed which evolves due to the spatiotemporally varying bed stress induced by the turbulent flow field above the bed and gravity gravity induced avalanche flow motion of the bed in turn affects the flow field in a coupled hydrodynamic moving bed simulation in which bed features evolve due to resolved details of the turbulent flow we compare different bed elevation models and demonstrate the capability of the present model through simulation of sand ripple formation and evolution induced by turbulence in an oscillatory flow a resolution study demonstrates the need for fine grid resolution to resolve a bulk of the near wall turbulence which is essential for bed form initiation

the application of single zircon evaporation and model nd ages to the interpretation of polymetamorphic terrains an example from the proterozoic mobile belt of south india the technique of single zircon dating from the thermal evaporation of 207pb 206pb kober 1986 1987 provides a means of dating successive periods of growth and nucleation of zircons in polymetamorphic assemblages in contrast nd model ages may provide a measure of the period of crustal residency for the sample or its protolith these two techniques have been combined to elucidate the tectonic history of the proterozoic mobile belt of southern india exposed south of the palghat cauvery shear zone that marks the southern boundary of the archaean craton of karnataka the two main tectonic units of this mobile belt comprise the madurai and trivandrum blocks both of which are characterised by massive charnockite uplands and low lying polymetamorphic metasedimentary belts that have undergone a complex tectonic history throughout the proterozoic evidence for early palaeoproterozoic magmatism is restricted to the madurai block where single zircon evaporation ages from a metagranite 2436 4 ma are similar to model nd ages from a range of lithologies suggesting crustal growth at that time the trivandrum block to the south of the achankovil shear zone is comprised of the kerala khondalite belt the nagercoil charnockites and the achankovil metasediments single zircon evaporation ages together with conventional zircon and garnet chronometry suggest that all three units underwent upper amphibolite facies metamorphism at 1800 ma an event unrecorded in the metagranite from the madurai block this implies that the madurai and trivandrum blocks represent distinct terrains throughout the palaeoproterozoic model nd ages from the achankovil metasediments are much younger 1500 1200 ma than those from the adjacent kerala khondalite belt and madurai blocks 3000 2100 ma but there is no evidence for zircon growth in these metasediments during the mesoproterozoic hence the comparatively young model nd ages of the metasediments are indicative of a mixed provenance rather than a discrete period of crustal growth zircon overgrowths from the madurai block 547 17 ma and achankovil metasediments 530 21 ma suggest that all tectonic units of the proterozoic mobile belt of south india shared the same metamorphic history from the early palaeozoic this event has been recognised in the basement lithologies of sri lanka and east antarctica confirming that the constituent terrains of east gondwana had assembled by this time

cooling history of the puttetti alkali syenite pluton southern india abstract the puttetti alkali syenite pluton in southern india belongs to the suite of felsic magmatic intrusives emplaced during the late neoprotrozoic cambrian time during the final phase of amalgamation of the gondwana supercontinent in this study we evaluate the cooling history of this pluton based on various isotopic systems we present whole rock pb pb data on the syenite which yields an isochron age of 508 25ma three phlogopite separates from the syenite pluton give k ar ages of 454 0 9 0 448 5 8 9 and 445 6 8 8 ma indicating cooling age at temperatures of 415 c u pb analyses of zircons from this syenite yielded an age of 572 2 ma in a previous study with u pb closure temperatures 800 o c this age probably indicates the timing of emplacement of the puttetti pluton collectively we estimate from the isotopic age data and respective closure temperatures that the syenite body cooled at about 3 2 o c ma from about 800 o c to about 415 o c the markedly low cooling rate of the syenite pluton absence of chilled margin effects and common occurrence of pyroxene feldspar phlogopite and zircons megacrysts in the rock indicate that the host granulites were at high temperatures during the emplacement of the syenite magma the cooling history of puttetti syenite estimated in this study is closely comparable with the 3 4 o c ma cooling rate estimated for a granite pluton in a previous study from madagascar our study suggests protracted cooling rates for the late pan african intrusives emplaced within the gondwana crust with a long residence history in a hot crust bore they were exhumed to shallower levels

postglacial rebound from vlbi geodesy on establishing vertical reference difficulty in establishing a reference frame fixed to the earth s interior complicates the measurement of the vertical radial motions of the surface i propose that a useful reference frame for vertical motions is that found by minimizing differences between vertical motions observed with vlbi ma and ryan 1995 and predictions from postglacial rebound predictions peltier 1995 the optimal translation of the geocenter is 1 7 mm yr toward 36 n 11l e when determined from the motions of 10 vlbi sites this translation gives a better fit of observations to predictions than does the vlbi reference frame used by ma and ryan 1995 but the improvement is statistically insignificant the root mean square of differences decreases 20 to 0 73 mm yr and the correlation coefficient increases from 0 76 to 0 87 postglacial rebound is evident in the uplift of points in sweden and ontario that were beneath the ancient ice sheets of fennoscandia and canada and in the subsidence of points in the northeastern u s germany and alaska that were around the periphery of the ancient ice sheets

local scour at vertical wall abutments under clear water flow conditions 1 new clear water tests on abutment scour are presented thirty one tests with sand bed and nine tests with lightweight pumice bed were carried out in a 28 m long 4 m wide flume tests typically lasted for 1 week or more vertical wall abutments with length to depth l d ratios from 9 up to 36 were used other test campaigns in the literature are added to the data focusing on abutments with 2 l d 100 the critical flow for scour inception at the abutment nose is found to decrease as l d increases the whole data are analyzed for searching the equilibrium scour depths with different methods the slope change in the plot of scour depth against the logarithm of time is the method selected for the group of tests run close to the threshold condition some trends regarding the dimensionless equilibrium scour depth are 1 dependence on the bed material specific gravity in the sense that pumice tests produce less scour and 2 increase of the scour depth as l d increases finally the morphology of the scour area in terms of volume and plan dimensions is given by new regression equations