large scale current and thermohaline structures along 156 e during the coare intensive observation period from december 1992 to february 1993 18 me ridional sections of temperature salinity and current were col lected along 156 e from 5 s to 5 n during the intensive obser vation period of the coupled ocean atmosphere response ex periment the average conditions were characteristic of the ongo ing ei nino event with a relatively shallow thermocline and fresh surface waters altemating westerly and easterly wind forcing was observed and the warm surface layer the warm pool responded in a time scale of a few days by corresponding altemating flows the equatorial current system was less affected at depth the upper layer oceanic temperature variability in volved several mechanisms including surface cooling by evapo ration during westerly winds and entrainment from the thermo cline

use of topex poseidon sea level data for ocean analyses and enso prediction some early results abstract in this study two sets of pacific ocean analyses for 1993 96 were analyzed both analyses were produced with the assimilation of subsurface temperature data from expendable bathythermographs and tropical atmosphere ocean moorings in addition one analysis also assimilated sea level data from topex poseidon sea level variability in the two analyses agreed well with each other and both agree with tide gauge and altimetry data for 1993 95 however beginning in late 1995 through 1996 large sea level differences of 5 8 cm were found in the tropical western pacific between the two analyses furthermore large sea level discrepancies were also found between dynamic height estimated from tao temperatures and tide gauge altimetry observations in the same region during 1996 these discrepancies are consistent with the sea level differences between the two model based analyses historical conductivity temperature depth data along 165 e near the equator were also analyzed and it was found that salinity

mesozoic volcanism in the middle east geochemical isotopic and petrogenetic evolution of extension related alkali basalts from central lebanon mesozoic picritic and alkali basalts from central lebanon represent a significant part of an extension related upper jurassic to upper cretaceous discontinuous volcanic belt which occurs throughout the middle east volcanism was associated with an episode of intraplate extension that followed a period of continental break up where mesozoic micro continental blocks separated from gondwana as the neotethys ocean opened in jurassic times this volcanic episode produced mafic lava flows ranging in thickness from 5 to 20 m along with some minor pyroclastic flows these flows are stratigraphically intercalated with thick carbonate platform deposits the basalts are made up of about 15 20 olivine fo 78 91 30 35 clinopyroxene salite 40 50 plagioclase an 56 71 and opaque fe ti oxides 5 geochemically the rocks exhibit a relatively wide range of sio 2 40 4 to 50 5 wt and mgo 5 1 to 15 5 wt contents are relatively enriched in tio 2 1 7 to 3 7 wt and vary in composition from alkali picrite and basanite to alkali basalt the mg numbers range from 0 56 to 0 70 with an average of 0 63 the rocks are enriched in incompatible trace elements such as zr 86 247 ppm nb 16 66 ppm and y 19 30 ppm such compositions are typical of those of himu oib and plume related magmas the ree patterns are fractionated la yb n 11 lree enriched and are generally parallel to subparallel elemental ratios such as k p 1 1 4 7 la ta 11 13 la nb 0 57 0 70 nb y 0 68 1 55 and th nb 0 20 0 36 suggest that crustal contamination was minor or absent this may be related to a rapid ascent of the magma in agreement with the nature mafic oceanic like and the small thickness about 12 km of the mesozoic crust of the eastern mediterranean region the 143 nd 144 nd isotopic compositions of the lavas range from 0 512826 to 0 512886 and 87 sr 86 sr from 0 702971 to 0 703669 suggesting a himu like mantle source trace element compositions indicate a melt segregation depth of 100 110 km well within the garnet lherzolite stability field the geochemical characteristics of the rocks are typical of within plate alkali basalts and suggest that the magmas were derived from a fertile possibly plume related enriched mantle source petrogenetic modelling indicates that the magmas were produced by very small degrees of batch partial melting f 1 5 of a primitive garnet bearing mantle source garnet lherzolite

oceanic equatorial waves and the 1991 93 el nino abstract equatorial kelvin and rossby waves associated with the 1991 93 el nino warm event were detected in temperature observations made by the tropical atmosphere ocean tao buoy array intraseasonal kelvin waves were a prominent part of equatorial thermocline depth variability and were well represented by a simple model consisting only of first and second mode baroclinic kelvin waves the second mode was essential to properly represent the observed amplitude thermocline depth variability at 5 n and 5 s was dominated by annual and interannual rossby waves which were found to have been largely wind forced in midbasin with little if any signal associated with eastern boundary reflection an evaluation of the wyrtki buildup hypothesis and the delayed oscillator hypothesis in connection with the 1991 93 events showed that a long lag about two years occurred between the arrival of the downwelling signal in the west and the subsequent initiation of el nino this was considerably longer than suggested

mechanisms of the 1997 1998 el nino la nina as inferred from space based observations 1 the intensity of the 1997 el nino and the 8 c sudden drop in sea surface temperature sst around 0 130 w during the turn into la nina in 1998 were a surprise to the scientific community this succession of warm and cold events was observed from start to finish with a comprehensive set of remotely sensed and in situ observations in this study we employ space based observations to demonstrate for the first time their maturity in capturing the preconditioning onset evolution and decay of the 1997 el nino and its transition into the 1998 la nina an accumulation of warm water in the west and equatorial wave reflection on the western ocean boundary appeared favorable for the development of el nino however the action of a series of westerly wind bursts from december 1996 to june 1997 notably in march 1997 was instrumental in setting up this huge el nino the westerly wind bursts excited equatorial downwelling kelvin waves and advected the eastern edge of the warm pool eastward which triggered a distinct warming over the central and eastern parts of the equatorial basin once these warmed regions joined the coupling between the sst and surface winds was fully effective and el nino reached its mature phase by that time much of the warm waters of the western equatorial pacific was transferred toward the east by surface eastward currents the demise of el nino and its turn into la nina in spring 1998 were due to the arrival in the east of various interrelated phenomena upwelling was brought from the west by favorable off equatorial wind stress curl and equatorial kelvin waves generated by easterly winds and wave reflection on the western ocean boundary additional upwelling was brought from the east by equatorial rossby waves generated by westerly winds these various upwelling signals were added to the general uplifting of the thermocline because of the slow discharge of the upper layer of the equatorial basin by diverging surface currents a series of equatorial kelvin and rossby waves characterized by upwelling and opposite surface currents led to the breakup of the warm waters the surfacing of the thermocline and the drastic drop in sst in may 1998 around 0 130 w with the arrival of cold water in the east the easterly winds expanded from the west and la nina turned into a growing mode this view of the 1997 1998 el nino la nina afforded from space enables the testing of various el nino theories

modelling of groundwater mound formation resulting from transient recharge an analytical solution of a linearized boussinesq equation is obtained to predict water table fluctuations as a result of time varying recharge from a strip basin for any number of recharge cycles the analytical solution is obtained by using finite fourier sine transform applications of the solution for the prediction of water table fluctuations and sensitivity analysis are demonstrated with the help of example problems copyright 2001 john wiley sons ltd

iron titanium oxide geothermometry and petrogenesis of lava flows and dykes from mandla lobe of the eastern deccan volcanic province india abstract compositional studies on different forms of magnetite ulvospinel ilmenite and hematite mineral phases occurring in 37 lava flows and 6 dykes of the mandla lobe are presented in this paper ilmenite 0001 in equilibrium with titanomanetite show high values of temperature of equilibration ranging from 1172 974 c for high alumina quartz normative tholeiitic lava flows of chemical type a 1129 1229 c for low alumina quartz normative tholeiitic lava flows of chemical type b 1283 1124 c for tholeiitic lava flows of chemical type f and 1243 c and 99o c for two diopside olivine normative tholeiite flows of chemical type d high olivine normative flows of chemical type g and h show 1095 c and 1092 c respectively whereas high hypersthene normative tholeiite flow of chemical me c shows temperature of 1187 c data plots disposition over iron titanium oxide equilibration temperature vs logfo 2 diagram for mandla lava flows and other parts of the deccan igatpuri mahabaleshwer nagpur and sagar areas revealed that tholeiitic evolved basalt of the eastern deccan volcanic province formed at high temperatures whereas picritic primitive lavas of igatpuri and tholeiitic basalt of mahabaleshwar areas were formed at low temperatures mahabaleshwer basalts follow fmq fayalite magnetite quartz buffer curve but plots of the mandla basalts lie above this curve indicating higher temperatures of crystallisation of ilmenite titanomagnetite than that of the lava flows from other parts of deccan raps the eastern deccan traps are most evolved types of lava as characterised by its low mg number and ni content whereas igatpuri lava flows are picritic primitive having high mg number and ni contents temperature vs feo fe 2 o 3 feo fe 2 o 3 mgo ratio data plots for mandla and other deccan lava flows and liquidus data for hawaiian tholeiites indicated that igatpuri basalts lie parallel to the liquidus line of hawaiian tholeiite but at lower temperatures large data plots of mandla lava flows lie along the liquidus line of the hawaiian lava the highly vesicular nature of compound lava flows having large amount of volatile is responsible for low temperature values whereas lava flows represented by high temperatures show high modal values of glass and opaque minerals

geochemistry of the palitana flood basalt sequence and the eastern saurashtra dykes deccan traps clues to petrogenesis dyke flow relationships and regional lava stratigraphy recent studies of large mafic dyke swarms in the deccan traps flood basalt province india indicate that some of the correlative lava flows reached several hundred kilometers in length here we present field petrographic mineral chemical and whole rock geochemical including sr nd isotopic data on the palitana lava sequence and nearby dykes in the saurashtra region of the northwestern deccan traps these rocks are moderately evolved many with low ti nb characteristics we infer that most dykes are notably and systematically less contaminated by ancient continental crust than the palitana flows but four dykes are equally or significantly more contaminated with some of the most extreme sr nd isotopic compositions seen in the entire deccan traps initial end is as low as 18 0 a bhimashankar type and a poladpur type dyke are present several hundred kilometers from the type section of these magma types in the western ghats escarpment we find no geochemical correlations between the palitana sequence and three subsurface sequences in ne saurashtra containing abundant picritic rocks surface lavas previously studied from saurashtra or the western ghats sequence intriguingly the eastern saurashtra dykes cannot have been feeders to any of these lava sequences feeder dykes of these sequences may be located in southwestern or central saurashtra or in the dhule nandurbar dediapada areas across the gulf of cambay 200 300 km east of palitana our results indicate polycentric flood basalt eruptions not only on the scale of the deccan traps province but also within the saurashtra region itself

tidal correction of topex poseidon altimetry for seasonal sea surface elevation and current determination off the pacific coast of canada altimetry from the topex poseidon satellite is analyzed for the waters off british columbia canada tides are removed using harmonic constants from two coastal and two global models and the accuracy of this detiding is assessed by using these same models and one digital filter to remove the tide from the time series of three representative coastal tide gauges it is demonstrated that inaccurate m2 s2 and k1 tide removal from topex poseidon altimetry can introduce systematic biases to the calculation of seasonally averaged fields average summer and winter sea surface heights are calculated from the detided altimetry and estimates of their accuracy nearshore are computed using concurrent time series from 11 tide gauges finally these seasonal elevations are blended with those from the 11 tide gauges and the associated surface currents are calculated using a diagnostic finite element model these currents are compared with those calculated from historical conductivity and temperature versus depth measurements and those measured by historical near surface current meters

ocean tides in the continental margin off the pacific northwest shelf a comparison of bottom pressure observations and global tide models shows that the regional distributions of the diurnal and semidiurnal tides off the oregon and washington shelves are determined mainly by the large scale amphidromic systems in the north pacific ocean these cause the tidal amplitudes to increase toward the northeast and the phase lags to increase toward the northwest within 200 500 km of the shelfbreak the curving continental boundary causes the cophase lines to be closely packed near cape mendocino and more widely spread in the bight to the north farther seaward the m2 tide is consistent with a kelvin wave propagating along the british columbia boundary 315 t while the k1 tide decays offshore more slowly than expected from kelvin wave theory a long term 4 2 year bottom pressure series at axial seamount 45 58 n 130 00 w depth 1540 m yields a nongravitational s 2 tide that is consistent with a large scale barotropic tide extending seaward from the coast at lower frequencies the observed mf amplitude matches recent global models while the mf phase lag is marginally earlier than model phases nearby mf currents are bottom trapped and consistent in phase with quasi geostrophic dynamics their magnitudes near the bottom are much larger than barotropic mf currents observed farther west in the north pacific the models reproduce the distributions of the diurnal and semidiurnal harmonic constants but with broad scale offsets in the amplitudes and phase lags these offsets cause errors standard deviation 3 0 cm in predicted time series of the diurnal and semidiurnal tides that fluctuate on fortnightly to interannual timescales the 29 seasonal variations of the errors are largest in winter and are modulated by 4 5 year fluctuations associated with the nodal cycle in situ measurements can be used to remove these regional offsets this would improve the temporal and spatial resolution of nontidal sea level estimates that are based on satellite altimeter data

open ocean validation of topex poseidon sea level in the western equatorial pacific during the verification phase of the topex poseidon radar altimeter mission a rigorous open ocean validation experiment was conducted in the western equatorial pacific ocean from august september 1992 to february march 1993 two tropical ocean and global atmosphere toga tropical atmosphere ocean moorings at 2os 156 e 1739 m depth and 2os 164 4 e 4400 m depth were outfitted with additional temperature salinity and pressure sensors to measure precisely the dynamic height from the surface to the bottom at 5 min intervals directly beneath two topex poseidon crossovers bottom pressure gauges and inverted echo sounders were deployed as well a predeployment design study using full depth conductivity temperature depth casts subsequently confirmed by postdeployment analyses indicated this suite of instruments was capable of measuring sea surface height fluctuations to within 1 2 cm the validation experiment also benefited from the comprehensive set of ocean atmosphere measurements that were made in the region during the toga coupled ocean atmosphere response experiment intensive observation period of november 1992 to february 1993 the surface relative to bottom dynamic height fluctuations observed in situ during the 6 7 month experiment had a standard deviation of 5 cm with excursions of order t 15 cm energetic steric sea level variability was found to exist on short timescales of order hours to a few days most notably the quasi permanence of strong semidiurnal internal tides such internal tides were noted to induce changes in surface dynamic height with a standard deviation of 2 dynamic centimeters at the shallower of the two sites 2 s 156 e a possible nonlinear rectification of the internal tide was observed occasionally to change the dynamic height by as much as 30 cm over less than an hour on timescales longer than the 10 day repeat of the topewposeidon satellite the low frequency fluctuations of dynamic height were related to interannual variations corresponding to the 1991 1993 ei nino southern oscillation to the seasonal cycle and to intraseasonal variations associated with the 40 to 60 day oscillations of the equatorial zonal wind field instantaneous comparisons between the 1 s topex poseidon altimeter retrievals and the 5 min dynamic height were performed with regard to several tide models the barotropic tide measured in situ european centre for medium range weather forecasts surface air pressure and the surface air pressure measured in situ depending on the choice of altimeter and of the environmental corrections applied to the altimeter data the rms differences between the satellite and the in situ measurements of sea level were as low as 3 3 cm at 2os 156 e and 3 7 cm at 2os 164 4 e when additional satellite data in the general vicinity of the mooring are included and after the use of a 30 day low pass filter the satellite and in situ data were found to be highly correlated with correlation coefficients of about 0 95 and rms differences around 1 8 cm

the fortnightly and monthly tides resonant rossby waves or nearly equilibrium gravity waves abstract the fortnightly and monthly tides are discussed in the light of recent sea level observations and numerical modeling results within the tide gauge network of the low latitude pacific the fortnightly tide is shown to possess a large scale phase lag of roughly 10 40 degrees although the nonequilibrium part of the fortnightly tide is traditionally thought to be dominated by rossby wave dynamics it is shown via global shallow water modeling studies that this large scale phase lag is explicable in terms of remotely forced gravity waves whose origin is mainly in the arctic ocean although future observations outside the low latitude region of the pacific may eventually reveal rossby wave excitation the fortnightly tidal signal in the tide gauge network at hand appears to reveal at most only weak excitation of rossby waves compared to the phase lag due to remotely forced gravity waves the observed monthly tide appears to be only slightly closer to equilibrium than the fortnightly tide the reaso

the basement of the deccan traps and its madagascar connection constraints from xenoliths paleogeographic reconstructions of india and madagascar before their late cretaceous rifting juxtapose the antongil block of madagascar against the deccan traps of india indicating that the western dharwar craton extends below the deccan lavas some recent studies have suggested that the south maharashtra shear zone along the northern konkan coast of india limits the northern extent of the western dharwar craton implying that the craton does not extend below the deccan traps raising a question mark on paleogeographic reconstructions of india and madagascar the continuity of the western dharwar craton north of the south maharashtra shear zone below the deccan traps or its lack thereof is critical for validating tectonic models correlating madagascar with india in this study zircons in tonalitic basement xenoliths hosted in deccan trap dykes were dated in situ using the u pb isotope system the data furnish u pb ages that define three populations at 2527 6 2456 6 and 2379 9 ma the 2527 6 ma ages correspond to the igneous crystallization of the tonalites whereas the 2456 6 and 2379 9 ma ages date metamorphic overprints the results help to establish for the first time that the basement is a part of the neoarchean granitoid suite of the western dharwar craton which extends northward up to at least talvade in central and kihim beach in the western deccan by implication the south maharashtra shear zone cannot be the northern limit of the western dharwar craton the granitoids are correlated with the neoarchean felsic intrusions 2 57 2 49 of the masaola suite in the antongil block of madagascar supporting the existence of a neoarchean greater dharwar craton comprising the western dharwar craton and the antongil masora block

stratigraphy structure and volcanology of the se deccan continental flood basalt province implications for eruptive extent and volumes the deccan volcanic province is one of the world9s largest continental flood basalt provinces and derives additional importance because its eruptions 64 67 ma straddle the cretaceous tertiary boundary to better assess the environmental impact of deccan volcanism and its possible effect upon cretaceous tertiary boundary biota it is necessary to document the stratigraphy chronology and volume of the eruptions new chemostratigraphical data permit mapping of the se deccan these data strengthen the likelihood that the rajahmundry traps of eastern india were originally fed by long distance flows and are an extension of the main deccan volcanic province an east west cross section reveals a depression or moat around the se periphery of the deccan volcanic province this provided a site in which shallow lakes initially formed and along which later lava eruptions became channelled and confined published palaeomagnetic data indicate that the lavas of the se deccan were erupted during chron 29r coeval with the cretaceous tertiary boundary and the chemostratigraphic data place the associated lake sediments i e lameta group beneath and within lavas of the wai subgroup finally these new map data are combined with previous work to provide a quantitative estimate for the original deccan volcanic province eruptive volume of c 1 3 10 6 km 3

clinopyroxene compositions in the deccan and rajmahal traps and their bearing on magma types and evolution abstract electron probe analyses of clinopyroxenes from several areas of the deccan and rajmahal traps consisting mostly of subalkalic and alkalic basalts picritic basalts and a few dolerite dykes have been obtained evaluation of the data indicate the absence of pigeonite from subalkalic basalts that occur in close spatial association with mild or strongly alkalic basalts in areas such as rajpipla navagam and central kachchh co existence of augite and pigeonite however has been noticed in subalkalic basalts dykes and picritic basalts from a number of deccan localities such as sagar igatpuri kalsubai triambak pavagarh and girnar besides the one sample from rajmahal diopside salite and wollastonite rich compositions dominate the basanites and foidites of kachchh whereas chrome diopside and salite are the main types in the picrite basalt samples from anila botad and paliyad in saurashtra akin to those found in contiguous areas in the east from borehole flows at dhandhuka and wadhwan studied in detail previously compositional variations in zoned clinopyroxenes indicate differentiation of the parental magma and also mixing of different magma types subalkalic and alkalic from areas such as igatpuri rajpipla and kachchh based on host rock chemistry total alkalis silica plot cipw norms estimated temperatures of eruption and augite pigeonite thermometry it has been inferred that clinopyroxene compositions especially the incidence of pigeonite appear to be very sensitive to bulk chemistry of host rocks especially their na 2 o k 2 o sio 2 total iron and tio 2 contents non quadrilateral cationic components in the clinopyroxenes such as al in tetrahedral and octahedral positions together with si na ti and cr abundances have been found to be useful to discriminate clinopyroxenes from alkalic and subalkalic basalt types besides inferences on the ferric iron component in them evaluation of host rock compositions in the ternary olivine clinopyroxene quartz plot indicate polybaric conditions of crystallization and evolution especially in samples that are picritic e g pavagarh anila and kachchh and which could also breach the olivine clinopyroxene plagioclase thermal divide that exists in part between alkalic and subalkalic basalts under atmospheric conditions

petrogenetic significance of ferro enstatite orthopyroxene in basaltic dikes from the tapi rift deccan flood basalt province india abstract some basaltic dikes from the tapi rift in the deccan flood basalt province india contain abundant clusters of prismatic quench crystals of ferro enstatite orthopyroxene fe 39 42 mg 53 57 ca 2 4 such profuse orthopyroxene clusters are not yet known from any other flood basalt province in the world based on petrography mineral chemistry and whole rock chemistry we conclude that these crystals are formed due to assimilation of shale by deccan basalt magma this interpretation is consistent with the known bedrock geology of the area these quench crystals constitute the first direct petrographic evidence for crustal contamination in the deccan province the liquidus temperature for the dikes is estimated at 1220 10 c with the crystallization temperature of the orthopyroxene at 1080 c or less

the cretaceous igneous province of madagascar geochemistry and petrogenesis of lavas and dykes from the central western sector 1999 similarly the buchan 1997 crops out in the area between thecontributions of hotspot usually taken to be plume mailaka limestones and the contact between the permo mantle and non hotspot asthenosphere to ood basalt triassic sedimentary rocks of the morondava basin andmagmas appear to vary greatly from province to province the precambrian basement fig 1b the dykes reach e g kent

essexite occurrence in the deccan volcanic province of saurashtra western india abstract the occurrence of essexite in the deccan volcanic province of saurashtra india is reported here for the first time the essexite body occurs as a large stock like intrusion in horizontal flow basalts petrographically it is characterized by the presence of titanaugite labradorite olivine iron oxides and accessory amounts of alkali feldspar analcite biotite and apatite chemically it is characterized by enrichment in lile hfse and ree as compared to the other tholeiitic and alkaline basalts of the area it is therefore concluded that the essexite magma has not formed by differentiation out of the tholeiitic magma predominantly encountered in the deccan volcanic province but possibly represents a separate melt derived as a 5 to 10 partial melt at shallower depth 15 kb pressure within the upper mantle

spherulites and thundereggs from pitchstones of the deccan traps geology petrochemistry and emplacement environments spherulites and thundereggs are rounded typically spherical polycrystalline objects found in glassy silicic rocks spherulites are dominantly made up of radiating microscopic fibers of alkali feldspar and a silica mineral commonly quartz they form due to heterogeneous nucleation in highly supercooled rhyolitic melts or by devitrification of glass associated features are lithophysae stone bubbles which have an exterior sometimes concentric shells of fine quartz and feldspar and internal cavities left by escaping gas when filled by secondary silica these are termed thundereggs here we describe four distinct occurrences of spherulites and thundereggs in pitchstones mostly rhyolitic some trachytic of the deccan traps india the thundereggs at one locality were previously misidentified as rhyolitic lava bombs and products of pyroclastic extrusive activity we have character ized the thundereggs petrographically and geochemically and have determined low contents of magmatic water 0 21 0 38 wt in them using fourier transform infrared spectros copy we consider that the spherulite bearing outcrops at one of the localities are of lava flows but the other three represent subvolcanic intrusions based on the structural disposition of the deccan sheet intrusions studied here and considerations of regional geology we suggest that they are cone sheets emplaced from a plutonic center now submerged beneath the

a tectono geomorphological perspective of micro earthquake swarm activity prone areas around bhavnagar and jamnagar in saurashtra western india abstract areas around bhavnagar and jamnagar in eastern and northern parts of saurashtra respectively are identified previously as prone to recurrent earthquake swarm activity sparse seismotectonic studies so far have not revealed any linkage with known faults in bhavnagar area while no structures are known to occur in the area around jamnagar we carried out detailed tectono geomorphic studies with contrasting geomorphic settings with a view to provide an insight into the swarm activity from a geomorphological perspective the study is based on extensive field studies and quantitative geomorphic analysis of landscape and drainage the area around bhavnagar is divisible into two tectono geomorphic domains the e w trending sihor fault zone located to the west of bhavnagar domain i and the terrain to its south which shows undulating landscape controlled by n s trending structural trends domain ii the quadrant in the sw between these two domains consists of southward titled trappean hills which form source area for drainages flowing northward through sihor fault zone and those flowing eastward through domain ii late quaternary possibly holocene tectonic activity along the sihor fault is indicated by the northward tilt of alluvial plain surface knickpoint in rivers and small scale minor faults along the fault zone prominent decrease in depth of fluvial incision away from the fault zone and youthful landscape indicated by drainage basin analysis domain ii comprises the largely erosional pediplain developed over trappean and tertiary rocks to the south of bhavnagar the drainages show an early stage of landscape development due to ongoing tectonic activity the area around jamnagar is dominantly a peneplain formed over subhorizontal trappean lava flows the peneplain is a manifestation of the prolonged period of non erosion and deposition during the cenozoic the rivers show youthful landscape in the central part of the peneplain which includes large knickpoints rapids anomalous river bends steepening of channel gradient and large potholes this ene wsw trending zone of anomalous fluvial geomorphic anomalies points to the existence of a fault or fold in the subsurface the structure appears to be active as indicated by the denser cluster of earthquake swarm along this zone we infer that the generation of earthquake swarm activity comprising low to moderate magnitude shocks is caused by the sheared rocks along the sihor fault near bhavnagar and the ene wsw trending subsurface structure near lalpur which provide avenues for downward percolation of rainwater to deeper levels causing loss the frictional resistance along the weak planes

major element records of variable plume involvement in the north atlantic province tertiary flood basalts major element variations in north atlantic tertiary province primitive early erupted alkaline transitional tholeiite basalts recalculated to a restricted value of mgo give insights into the process of plume related magmatism basalts primitive enough to be crystallizing only olivine were recalculated to a proposed primary magma composition of 15 wt mgo the recalculated dataset shows clear inter element correlations including a strong significant negative correlation between fe and si indicating polybaric melt segregation overlap between basalt compositions and experimental melts from a fertile fe rich low mg number 85 5 peridotite suggests that relative to normal peridotite with mg number 89 the north atlantic basalt source was fe rich linear regression of the experimental data gives apparent pressures of magma segregation of 17 5 37 kbar with intra region variability in the depth derivation from the melt column for each sample thus suggesting that lithospheric thickness lid effect control on magma generation may have been overemphasized in recent studies comparable source composition magma segregation depth and calculated mantle potential temperature 1440 1460 c throughout the province supports the previously suggested plume impact model arriving below east greenland derived from a variably enriched and depleted lower mantle source given the good agreement between conclusions drawn from major element data and previously published results we suggest that restricted mgo recalculated datasets may be usefully applied to study other large igneous provinces

recharge to aquifers with mixed boundaries abstract the problem of localized groundwater recharge from a strip basin to an aquifer bounded by stream and impermeable boundaries was solved by the use of extended finite fourier transforms the solution was evaluated by comparison with the method of images and with numerical and experimental results the existing expression for the inverse of the extended finite fourier cosine transform was corrected

internal solitary waves in the warm pool of the western equatorial pacific abstract during the spring tides of late november 1992 early january and early february 1993 solitary internal wave packets were observed at 2 s 156 15 e in the western equatorial pacific apparently generated in the nuguria island group 3 s 153 e the waves propagate northeastward at 2 4 2 8 m s 1 appearing in fixed phase with the underlying semidiurnal baroclinic tide the initial solitary wave crests have downward displacements in excess of 60 m and peak velocities greater than 80 cm s 1 groups of 1 3 crests are observed with vertical structure resembling a first mode internal wave and horizontal variability consistent with third order comb kdv solitons many of the packets exhibit an overall organization reminiscent of undular bores this borelike behavior is confined primarily to the upper 70 m not sharing the mode one dependency of the crests the solitons displace the ambient equatorial currents including the equatorial undercurrent both vertically 80 m and laterally 1 2 km with l

were the deccan flood basalts derived in part from ancient oceanic crust within the indian continental lithosphere abstract deep mantle plumes supposedly incorporate deeply subducted eclogitized oceanic crust and continental flood basalts cfbs are now thought by some to be derived from such eclogite bearing peridotite plumes eclogite peridotite mixtures have much lower solidi and produce much greater melt fractions for a given temperature than peridotite fe rich eclogite or pyroxenite bearing sources have been inferred for many cfbs however plumes with considerable amounts of eclogite should have difficulty in upwelling owing to the high density of eclogite besides cfbs are always located along pre existing lithospheric structures suture zones edges of thick cratons and commonly associated with lithospheric rifting and continental breakup india s major late mesozoic cfb the deccan traps erupted through rift zones and a new continental margin that had developed along ancient suture zones traversing the subcontinent many deccan basalts are too fe rich to have been in equilibrium with a peridotite mantle source and have commonly been considered to be significantly fractionated derivatives of picritic liquids however it is possible to view them as relatively less evolved liquids derived from a source with extra fertility i e an fe rich source a new non plume plate tectonic model for icelandic hotspot volcanism involves melting of a shallowly recycled slab of eclogitized iapetus oceanic crust formerly trapped along the caledonian suture the model explains the geochemical petrological characteristics of icelandic basalts and is consistent with passive upper mantle upwelling under iceland inferred from recent seismic tomography based on the petrological and geochemical features of the deccan flood basalts of the type section in the western ghats i propose that old eclogitized oceanic crust trapped in the ancient indian suture zones could have produced voluminous basaltic melts during the deccan event

estimating sea level slope on the equator abstract a new method for diagnosing the zonal gradient of sea level on the equator from in situ data is proposed and validated using satellite altimetry a no turbulent stress level boundary condition in the pacific equatorial undercurrent core constrains the average flux of zonal momentum above uniquely determining the zonal sea level gradient the method is applied to simultaneous data from tropical atmosphere ocean array moorings spanning 154 165 e and adcp moorings in the vicinity of 157 5 e from 6 october 1992 to 21 december 1993 an independent estimate of sea level slope is obtained from contemporaneous daily equatorial crossings of the first european remote sensing satellite ers 1 and ocean topography experiment topex poseidon altimeters the slope is also estimated by assuming no pressure gradient at 500 m depth when accelerations and the pressure gradient can be estimated at the same location 5 day averages of the no stress level estimate explain 59 of the variance in the altimetry dat

site specific accentuation of heavy metals in groundwaters from ankaleshwar industrial estate india the seasonal behavior of environmentally sensitive polymetallic contaminants in groundwaters from ankaleshwar industrial estate aie india was studied the potentially toxic elements co cr cu mn fe mo and ni demonstrated accentuated enrichment signatures during post monsoon besides colossal spatial variability on temporal scale gis based accrual factor raster mapping facilitated the spot specific quantitative and comparative appraisal of metallic distensions during post monsoon with a decreasing hierarchy of seasonal augmentation ni cu mn fe co mo cr high inconsistencies and spot pixel strict exceedingly high accrual factors over these maps concur with diverse land use and surface polluting sources inter annual adiabatic extension of heavy metals in groundwaters implies their widespread availability in soil and atmospheric backgrounds in the region dissimilar performance with contrasting accretion patterns of redox sensitive metals fe and mo is revealed by three component color composites heavy metal hyper accrual realms warrant an immediate demand for upgrading the existing waste management methodologies and aquifer remediation as the region is highly cultivated and groundwater is the sole source of water supply for drinking agricultural and other purposes

seismic evidence of crustal heterogeneity beneath the northwestern deccan volcanic province of india from joint inversion of rayleigh wave dispersion measurements and p receiver functions abstract the northwestern deccan volcanic province nwdvp of india encompassing the saurashtra peninsula and the adjoining gulf of cambay is investigated through joint inversion of surface wave dispersion measurements and teleseismic p receiver functions to estimate the crustal and shallow upper mantle shear wave velocity vs structure the mw 7 7 bhuj earthquake and the post bhuj regional events recorded during the period 2001 2010 at 7 stations along 37 source receiver paths were used along with 35 teleseismic events a joint curve fitting inversion technique is applied to obtain a best fit for the fundamental mode rayleigh wave group velocity dispersion curves for time periods 5 50 s and high quality crustal p wave receiver functions obtained at each station significant crustal heterogeneity is observed within the study region with the average crustal vs ranging from 3 5 km s to 3 8 km s with the paths cutting across the gulf of cambay exhibiting large reduction in shear wave velocities utilizing the average crustal vs 3 66 km s estimated for saurashtra together with the average crustal p wave velocity vp 6 54 km s derived independently through deep seismic sounding studies yields a bulk vp vs ratio of 1 786 or an equivalent crustal poisson s ratio of 0 271 a major contribution to the high poisson s ratio comes from the 12 to 16 km thick lower crustal layers with shear velocities ranging from 3 8 km s to 4 19 km s suggesting widespread magmatic underplating due to emplacement of mafic cumulates in the lower crust the shallow uppermost mantle shear velocities are in the range 4 2 4 5 km s averaging 4 36 km s which is less than that observed for the indian shield indicating the effects of residual thermal anomaly the variation in the crustal vs high poisson s ratios and low upper mantle shear velocities reflect the thermal and compositional effects of the deccan volcanism which are manifested in terms of pervasive presence of mafic dykes volcano plutonic complexes lower crustal mafic cumulates and possible partial melt due to elevated geotherms the significant crustal alterations are possibly a result of weakening of the lithosphere by a mantle thermal source leading to a thin and weak lithosphere which facilitated the deccan volcanism through the rift zones of northwestern india

an extended kalman filter to assimilate satellite altimeter data into a nonlinear numerical model of the tropical pacific ocean method and validation a new implementation of the extended kalman filter scheme is developed for the purpose of assimilating observations into a high resolution nonlinear numerical model of the tropical pacific ocean it is characterized by two successive stages 1 approximation of the error covariance matrix by a singular low rank matrix which leads to making corrections only in those directions for which the error is not naturally attenuated by the system in this respect it is quite similar to the approach adopted by cane et al 1996 and 2 modification of these directions over time according to the model dynamics thus reflecting the evolutive nature of the filter the filter is initialized by a method based on the empirical orthogonal functions obtained from free runs of the model the reduction of the error covariance matrix avoids the overwhelming burden of computing the temporal evolution of the prediction error with all the degrees of freedom of the full state vector this assimilation scheme is implemented in the gent and cane 1989 primitive equation reduced gravity model this model has the advantage of using a coordinate in the vertical which allows a geographical refinement of the vertical resolution for thermocline gradients it is forced by the florida state university database winds and the chen et al 1994 hybrid scheme parameterization is assumed for the mixed layer the domain of application is the tropical pacific ocean basin between 120 e and 80 w longitude and 30 s and 30 n latitude the resolution is finest at the equator and steadily increases away from the equator in a first application validation twin experiments are conducted in which observations are assumed to be synthetic altimeter data sampled according to the topex poseidon mission features the method is shown to be efficient under various conditions and in particular to be capable of transferring information in the vertical from the surface only altimeter data to the deepest ocean layers and therefore of adequately constraining the thermal and the velocity profiles within the 300 or 400 m upper ocean in a second application real topex poseidon data are used and the results evaluated against independent in situ data namely tropical ocean global atmosphere toga tao mooring observations improvements in the model behavior are clear in terms of the time variability of the tropical ocean it therefore seems that the reduced state kalman filter with empirical orthogonal function eof initialization can be applied with success to such a primitive equation model of the pacific for the assimilation of altimeter data however at this stage the evolutivity of the filter seems to have a limited impact on the performances which was not the case for tests in the strongly nonlinear midlatitudes pham et al 1998a

internal tides observed at 2 s 156 e by in situ and topex poseidon data during the coupled ocean atmosphere response experiment coare during the enhanced monitoring phase of the coupled ocean atmosphere experiment coare semidiurnal baroclinic tides were observed at 2 s 156 e 1739 m depth the tropical atmosphere ocean tao mooring outfitted with additional sensors from surface to bottom provides an interesting tool for describing the internal tides m2 s2 and n2 baroclinic components were detected explaining 59 of the semidiurnal variance on surface dynamic height at the semidiurnal frequency vertical displacements of isopycnals highly variable in time can reach 30 m and are mostly a combination of the m2 s2 and n2 internal waves the two first baroclinic modes explain 70 of the variance in vertical displacement m2 and s2 internal waves have different vertical structure m2 resembles the first baroclinic mode and s2 resembles the second baroclinic mode the m2 and s2 internal waves projected on their respective baroclinic mode are highly related to the modeled barotropic tide two topex poseidon tracks cross over the mooring every 10 days and the internal wave signature can be expected in sea level along the tracks despite the weakness of the signal sea level spectra along both ascending and descending tracks show the existence of energy around the 250 km and the 120 km wavelength respectively which is in accordance with a first baroclinic wave propagating northeastward as suggested in previous studies from wavelet transform the baroclinic tide signatures on the ascending descending track are centered around 2 5 s 3 5 s with a 1 2 latitudinal extension respectively limited to the ontong java plateau we confirm the northeastward propagation of the baroclinic tides and their source could be a series of islands parallel to the kilinailau trench or the large sloping topography between the kilinailau trench and the ontong java plateau

infiltration mechanism simulation of artificial groundwater recharge a case study at pingtung plain taiwan this paper discusses the artificial groundwater recharge effect of high infiltration basins for this purpose the hydrogeological parameters of the study area are collected to construct a conceptualized physical model the tough2 numerical simulation software is then used to simulate the infiltration behavior of an artificial recharge into an underground aquifer four wells mw 1 mw 2 mw 3 and mw 4 are observed at the field site after which the groundwater levels are compared with the simulation results it is found that good agreement exists between the observed and numerical data for mw 1 and mw 2 however the observed groundwater level in mw 3 is higher than the simulated level we also find that mw 3 is at the edge of the artificial recharge lake and that the high groundwater level may well be the result of a portion of the infiltration load following the well border into the well screen conversely the groundwater level in mw 4 is found to be lower than in the simulated well due to local permeability in the well location finally the numerical results predict that the groundwater level will attain a steady state at approximately 47 h after the onset of infiltration

equatorial wave sequence associated with warm pool displacements during the 1986 1989 el nino la nina in the pacific equatorial band the zonal displacement of the eastern edge of the warm pool subject to insignificant seasonal variations is dominated by strong interannual variations almost in phase with the southern oscillation index over the 1971 1973 el nino la nina period gill 1983 suggested that such displacement was caused solely by horizontal advection by zonal current anomaly basin wide geosat derived zonal surface current anomalies are available during the 1986 1989 period and they agree quite well with observed equatorial currents in the western and central pacific within the 4on 4 s equatorial band the cumulative contribution of first baroclinic kelvin and first symmetric m 1 rossby modes to surface zonal equatorial current anomalies account for most of the geosat derived current variability from these geosat derived currents it is demonstrated that the eastward westward displacement of the eastern edge of the warm pool was primarily due to horizontal advection by zonal current anomalies during the 1986 1987 el nino 1988 1989 la nina as a corollary the el nino la nina warm cold sea surface temperature sst anomaly in the central western pacific was the result of anomalous zonal advection the 1986 1989 displacement of the warm pool appeared as a low frequency movement resulting from high frequency forcing i e a succession of local wind forcing and its remote kelvin and m 1 rossby wave responses in the equatorial waveguide in the central western pacific a in 1 downwelling rossby wave issued from the eastern pacific shifted the displacement from eastward to westward and therefore seems to have been the cause for el nino to turn to la nina in boreal fall 1987 in the eastern pacific the simultaneous occurrence of free propagating downwelling upwelling kelvin waves with the seasonal sst warming cooling appeared necessary for the development of local el nino la nina sst anomaly over most of the equatorial pacific slow migration of sst anomalies clearly showed up distinct during el nino and la nina these zonal migrations appeared to result from the delayed association of two phenomena the zonal advection in the central western pacific and the arrival of downwelling upwelling kelvin waves into the eastern pacific synchronous with the seasonal sst warming cooling albeit different in terms of equatorial wave action as compared to the delayed action oscillator theory our results suggest that zonal advection and wave dynamics were both important for the generation and migration of el nino southern oscillation sst anomalies in 1986 1989 finally our observational results about warm pool displacements equatorial wave sequence the shift from el nino to la nina and the slow sst migrations are presented in a schematic form involving sequential ocean atmosphere coupling which appears continuously over the november 1986 to a

relationship of topex poseidon altimetric height to steric height and circulation in the north pacific topex poseidon altimetric height is compared with 20 transpacific eddy resolving realizations of steric height the latter are calculated from temperature expendable bathythermograph xbt and salinity expendable conductivity and temperature profiler xctd profiles along a precisely repeating ship track over a period of 5 years the overall difference between steric height and altimetric height is 5 2 cm rms on long wavelengths 500 km containing 17 of the steric height variance the 3 0 cm rms difference and lowered coherence are due to the sparse distribution of altimeter ground tracks along the xbt section the 2 4 cm rms difference in the basin wide spatial mean appears to be due to fluctuations in bottom pressure differences between steric height and altimetric height increase near the western boundary but data variance increases even more and so the signal to noise ratio is highest in the western quarter of the transect basin wide integrals of surface geostrophic transport from steric height and altimetric height are in reasonable agreement the 1 9 104 m2 s 1 rms difference is mainly because the interpolated altimetric height lacks spatial resolution across the narrow western boundary current a linear regression is used to demonstrate the estimation of subsurface temperature from altimetric data errors diminish from 0 8 c at 200 m to 0 3 c at 400 m geostrophic volume transport 0 800 m shows agreement that is similar to surface transport with 4 8 sverdrup sv 106 m3 s 1 rms difference the combination of altimetric height with subsurface temperature and salinity profiling is a powerful tool for observing variability in circulation and transport of the upper ocean the continuing need for appropriate subsurface data for verification and for statistical estimation is emphasized this includes salinity measurements which significantly reduce errors in specific volume and steric height

variability in equatorial pacific sea surface topography during the verification phase of the topex poseidon mission l abstract as part of the verification phase of the topewposeidon mission 10 day gridded fields of altimeter data derived from topex geophysical data records are compared with 10 day gridded fields of dynamic height derived from more than 60 moorings of the tropical ocean and global atmosphere tropical atmosphere ocean toga tao array in the equatorial pacific ocean access to tao data in real time permits the first 500 days of the topewposeidon mission to be placed in the context of complementary in situ measurements of surface winds sea surface temperatures and upper ocean thermal structure as well as the time history of these variables prior to launch analysis of the space time structure in the topex and tao surface topography data indicates sea level variability primarily due to equatorial kelvin wave activity generated by intense wind bursts west of the date line in association with the 1991 1993 el nino cross correlations between the two data sets are generally 0 7 witha rms differences 5 cm north of the equator in the central and eastern pacific

semidiurnal tides observed in the western equatorial pacific during the tropical ocean global atmosphere coupled ocean atmosphere response experiment the semidiurnal tide within a 100 km square region of the western equatorial pacific centered at 1 8 s 156 1 e is examined using shipboard survey and mooring data collected during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare baroclinic and barotropic tidal amplitudes and phases are estimated from the survey and mooring observations in the upper 300 m of the 1800 m deep ocean by specifying their horizontal and vertical structures the barotropic tide is assumed to have zero horizontal wavenumber over the domain while a component of the baroclinic tide that is phase locked to the barotropic tide is determined by a searching method using plane wave fits to the data the estimated barotropic tidal current is in good agreement with tide models derived from topex poseidon observations the plane wave analysis indicates a dominant mode one baroclinic wave propagating toward the northeast the second vertical mode can also be detected given the phase differences between the m2 and s2 constituents in the barotropic and baroclinic tides the source of the baroclinic tidal signal is determined to be about 320 km southwest of the observing region at a series of islands and shallow ridges the combined estimates of the barotropic and baroclinic tides typically account for only 40 60 of the observed semidiurnal band current variance in the mooring data indicating the high degree of temporal and spatial variability of the baroclinic tide in this region the results of this study suggest however that coherent barotropic and baroclinic tidal signals can be successfully distinguished in the deep ocean using shipboard survey data even when the data are limited to the upper 300 m

constraints on the mantle sources of the deccan traps from the petrology and geochemistry of the basalts of gujarat state western india the late cretaceous early tertiary flood basalts in the gujarat area of the northwestern deccan traps kathiawar peninsula pavagadh hills and rajpipla exhibit a wide range of compositions from picrite basalts to rhyolites moreover the basaltic rocks have clearly distinct tio2 contents at any given degree of differentiation and strongly resemble the low titanium and hightitanium basalts found in most of the gondwana continental flood basalt cfb suites four magma groups are petrologically and geochemically distinguished 1 a low ti group characterized by rocks with varying sio2 saturation and with tio2 1 8 wt in picrites nb 19 p p m zr av 6 5 and tt v av 47 3 an intermediate ti group with tio2 contents slightly lower than the high ti rocks at the same degree of evolution and with correspondingly lower incompatible trace element contents and ratios in particular k2o nb ba and zr y av 5 2 4 a potassium rich group kt broadly similar in geochemical character to the high ti group but showing more extreme k rb and ba enrichment av k20 na20 l ba y 20 the most primitive low ti and high ti picrites when corrected for low pressure olivine fractionation show distinct major and trace element geochemistry in particular for cao ai2o3 cao tio2 and al2o3 tio2 and moderate but significant variations in their sio2 and fe2ost contents these characteristics strongly suggest the involvement of different mantle sources more depleted for the low ti picrites and richer in cpxfor the high ti picrites but with broadly the same pressures of equilibration 27 14 kbar this in turn suggests a strong lateral heterogeneity in the gujarat trap mantle low ti picrites and related differentiates in kathiawar are reported systematically for the first time here and suggest the existence of hfse depleted mantle in the northwestern deccan traps with extension at least to the seychelles islands and to the area of the bushe formation near bombay in the pre drift position before the development of the carlsberg ridge the absence of correlations between lile hfse ratios and sio2 argues against crustal contamination processes acting on the low ti picrites possibly owing to their probably rapid uprise to the surface consequently the mantle region of this rock group was probably re enriched by small amounts of ule rich materials the substantially higher trace element enrichment of the least differentiated high ti picrites relative to the basalts of the ambe noli and mahableshwar formations of the western ghats testifies also to the presence of more incompatible element rich oib4ike mantle sources in northern and northwestern gujarat these sources were geochemicaily similar to the present day reunion mantle sources

geochemistry of flood basalts of the toranmal section northern deccan traps india implications for regional deccan stratigraphy unpublished data 1998 andthe southeastern deccan particularly the poladpur andambenali formations mitchell widdowson 1991 bilgrami 1999 for as much as 350 km from their south western type sections in addition lavas isotopically andchemicallyequivalenttothoseoftheambenaliformation fm arepresentinthenortheastern sectoroftheprovinceas far as 900 km from their southwesternmost counter parts mahoney 1988 deshmukh

use of the geostrophic approximation to estimate time varying zonal currents at the equator moored thermistor chains at 2 n and 2 s and current temperature moorings at 0 are used to examine the accuracy of geostrophically estimated zonal velocity on the equator in the eastern 110 w and western 165 e pacific the meridionally differentiated form of the geostrophic balance is used to eliminate large errors due to wind balanced cross equatorial pressure gradients statistical analyses indicate that for time scales longer than 30 50 days the observed and geostrophically estimated zonal velocities are similar correlation coefficients of 0 6 0 9 and comparable amplitudes thus low frequency equatorial current oscillations are reasonably well represented by the geostrophic approximation however the mean currents are poorly resolved with the available array in the eastern pacific the mean zonal speed difference over the 10 month comparison period is 25 cm s 1 at 25 m and increases to 60 cm s 1 at 125 m at 165 e mean differences in the upper 250 m are typically 50 cm s 1 over a 4 month record the principal reason for these large mean differences is that the meridional scale of the mean currents is smaller than the spacing of the moorings comparison of observed and geostrophic velocity profiles obtained from shipboard sampling indicates that meridional spacing of about 1 latitude would be optimum for estimating the zonal velocity

recharge from rectangular areas to finite aquifers abstract a generalized analytical solution is derived for the growth of groundwater mound in finite aquifers bounded by open water bodies in response to recharge from rectangular areas finite fourier transforms are used to solve the linearized differential equation of groundwater flow unlike earlier solutions the method presented here does not require the use of tables for evaluation of complicated functions the solution is evaluated by comparison with existing numerical and analytical results in stream aquifer systems similar to those described above application of the proposed solution is more realistic than using solutions available for infinite aquifers

a comparison of coincidental time series of the ocean surface height by satellite altimeter mooring and inverted echo sounder altimetric measurements of sea surface height at two locations in the western tropical pacific ocean are compared to estimates of the dynamic sea surface height computed from cotemporal surface to bottom temperature salinity measurements on moorings and acoustic travel time measured by bottom moored inverted echo sounders the results show statistically high correlation between the in situ measurements at periods greater than 5 days and between the altimeter and in situ measurements at periods greater than 20 days the rms difference between any two modes of observation is consistently between 2 and 3 cm

upper ocean water masses and transports in the western tropical pacific 165 e abstract as part of the international toga program the orstom center in noumea new caledonia initiated in january 1984 a series of semi annual cruises along the 165 e meridian from 20 s to 10 n across the equatorial current system of the western pacific this paper presents an analysis of the first six hydrographic 0 1000 m and current 0 600 m sections a detailed description of typical january 1986 vertical structures of temperature salinity and zonal measured velocity is offered differences are noted with structures previously obtained in the tropical pacific compared to the central and eastern pacific the 165 e dataset evidences a much weaker equatorial upwelling and deeper surface isothermal layer and subsurface currents compared to the few western pacific measurements the two speed cores of the equatorial undercurrent euc previously reported at 100 and 200 m are not observed here special attention is given to the eastward equatorial jet 2 s 2 n 0 75 m measured in january 1985 wh

the effect of diffusive re equilibration time on trace element partitioning between alkali feldspar and trachytic melts abstract we present new experimental data on major and trace element partition coefficients between alkali feldspar and trachytic melt experiments were conducted at 500 mpa 870 890 c to investigate through short disequilibrium and long near equilibrium experiments the influence of diffusive re equilibration on trace element partitioning during crystallization our data show that ba and sr behave compatibly and their partition coefficients are influenced by re equilibration time orthoclase or content growth rate and cation order disorder high field strength elements hfse and rare earth elements except eu are strongly incompatible but alkali feldspar efficiently fractionates light lree from heavy rare earth elements hree our crystallization experiments reveal a strong influence of disequilibrium crystal growth on the partitioning of ba and sr in particular short duration experiments show that rapid alkali feldspar crystal growth after nucleation promotes disordered growth and less selectivity in the partitioning of compatible trace elements that easily enter the crystal lattice e g ba and sr this produces partition coefficients of compatible elements higher than those obtained through long duration experiments in which growth is slower and more selective on approach to equilibrium decreasing growth rate and timescales of diffusive re equilibration facilitates the incorporation of compatible elements within the crystal lattice through ordered growth on the basis of the charge and size of the octahedral site resulting in lower partition coefficients of ba and sr therefore our results indicate that besides crystal chemical effects i e lattice strain the substitution mechanisms during growth with different degrees of ordering of ba and sr in alkali feldspar are strongly influenced by diffusive re equilibration and crystal growth kinetics this implies that partition coefficients of ba and sr can be used to establish timescales of crystallization processes under pre and syn eruptive conditions the application of our results to alkali feldspar in rocks from campi flegrei constrain the magma residence time at subliquidus conditions in a reservoir to a maximum of 6 days under disequilibrium conditions and to a minimum of 9 days upon approaching near equilibrium conditions

solitary waves in the western equatorial pacific ocean during the spring tides of early january and february 1993 groups of solitary intemal waves were observed propagating through the intensive flux array of the toga coare experiment the waves appear to originate near the islands of nugarba 3 s 30 s 154 30 e they travel north eastward at 2 5 3 ds closely coupled with the semi diumal baroclinic tide peak amplitudes exceed 60 m velocities are in excess of 8 ds sea surface vertical displacements of order 3 m can be inferred directly from the lateral acceleration of surface waters the equatorial undercurrent is displaced by soliton passage but apparently is unaffected otherwise the intrinsic shear of the solitary crests is small compared to ambient equatorial shears the crests while not themselves unstable are effective at triggering instabilities on the background flow the motions potentially contribute 10 15 wattdm2 to the flux of heat into the mixed layer

regional identification in the tropical atlantic ocean of residual tide errors from an empirical orthogonal function analysis of topex poseidon altimetric data two years october 1992 to september 1994 of topex poseidon data have been processed over the tropical atlantic ocean to produce monthly sea level anomalies four different oceanic tide corrections have been applied in order to quantify the effect of this correction on the large scale altimetrically determined sea level variability and to identify potential residual tide errors two tide corrections are drawn from the u s university of texas tide model and two others are drawn from the french grenoble tide model comparison of the altimetric sea level anomalies with tide gauge data gives rms differences of between 2 and 5 cm equivalent to those already observed by several authors during recent topex poseidon studies however this paper demonstrates that the 2 monthly oscillations which were previously identified in investigations using old versions of tide corrections still remain to some extent independently of the new tide models being used these 2 monthly oscillations are not only located along the western boundary and therefore cannot be attributed to 40 to 60 day oscillations observed in several mooring records in that area an empirical orthogonal function analysis of the altimetric data clearly shows that these oscillations are due to tide aliasing this approach also emphasizes the improvement finalized by the more recent versions of the university of texas and the grenoble tide models however the most convincing result of this analysis is that it allows regional quantification of the impact of tidal residual error aliasing which persists even when the more sophisticated tide models are used

the chogat chamardi subvolcanic complex saurashtra northwestern deccan traps geology petrochemistry and petrogenetic evolution abstract the saurashtra region in the northwestern part of the deccan continental flood basalt province india is notable for its many volcano plutonic complexes compositional diversity and the abundance of rhyolite and granophyre in this first detailed study of the chogat chamardi subvolcanic complex in eastern saurashtra we report microgranite and granophyre plutons gabbro plutons cut by basaltic andesite dykes as well as rhyolite plugs bulk rock geochemical including nd sr isotopic data suggest a strong contribution from ancient rb rich basement crust to the silicic magmas the mafic rocks are also crustally contaminated but less than the silicic rocks in conformity with observations elsewhere e g the skye and skaergaard granophyres the chogat chamardi silicic rocks have initial 87sr 86sr for t 65 ma as high as 0 72914 and initial end values as low as 13 9 trends defined by the chogat chamardi and other deccan rhyolitic suites on plots of sr concentration vs sr isotopic ratio are modeled with concurrent assimilation and fractional crystallization afc processes involving a basaltic magma and granitic basement rocks considering both nd and sr isotopic variations the chogat chamardi silicic rocks notably require crustal end members very different from those inferred in most previous isotopic studies of deccan rocks

gravity and magnetic signatures of volcanic plugs related to deccan volcanism in saurashtra india and their physical and geochemical properties abstract the bouguer anomaly and the total intensity magnetic maps of saurashtra have delineated six circular gravity highs and magnetic anomalies of 40 60 mgal 10 5 m s 2 and 800 1000 nt respectively three of them in western saurashtra coincide with known volcanic plugs associated with deccan volcanic province dvp while the other three in se saurashtra coincide with rather concealed plugs exposed partially the dvp represents different phases of eruption during 65 5 2 5 ma from the reunion plume the geochemical data of the exposed rock samples from these plugs exhibit a wide variation in source composition which varies from ultramafic mafic to felsic composition of volcanic plugs in western saurashtra and an alkaline composition for those in se saurashtra detailed studies of granophyres and alkaline rocks from these volcanic plugs reveal a calc alkaline differentiation trend and a continental tectonic setting of emplacement the alkaline plugs of se saurashtra are associated with ne sw oriented structural trends related to the gulf of cambay and the cambay rift basin along the track of the reunion plume this indicates a deeper source for these plugs compared to those in the western part and may represent the primary source magma the junagadh plug with well differentiated ring complexes in western saurashtra shows well defined centers of magnetic anomaly while the magnetic anomalies due to other plugs are diffused though of the same amplitude this implies that other plugs are also associated with mafic ultramafic components which may not be differentiated and may be present at subsurface levels paleomagnetic measurements on surface rock samples from dvp in saurashtra suggest a susceptibility of 5 5 10 2 si units with an average koenigsberger ratio q n of almost one and average direction of remanent magnetization of d 147 4 and i 56 1 the virtual geomagnetic pole vgp position computed from the mean direction of magnetization for the volcanic plugs and deccan basalt of saurashtra is 30 n and 74 w which is close to the vgp position corresponding to the early phases of deccan eruption modeling of gravity and magnetic anomalies along two representative profiles across junagadh and barda volcanic plugs suggest a bulk density of 2900 and 2880 kg m 3 respectively and susceptibility of 3 14 10 2 si units with a q n ratio of 0 56 which are within the range of their values obtained from laboratory measurements on exposed rock samples the same order of gravity and magnetic anomalies observed over the volcanic plugs of saurashtra indicates almost similar bulk physical properties for them the inferred directions of magnetization from magnetic anomalies however are d 337 and 340 and i 38 and 50 which represent the bulk direction of magnetization and also indicate a reversal of the magnetic field during the eruption of these plugs some of these plugs are associated with seismic activities of magnitude 4 at their contacts based on this analysis other circular semi circular gravity highs of nw india can be qualitatively attributed to similar subsurface volcanic plugs

groundwater dynamics due to general stream fluctuations in an unconfined single or dual porosity aquifer subjected to general areal recharge abstract analytical solutions of groundwater dynamics in an elongated aquifer subjected to general time dependent recharge are presented the lateral boundaries are specified heads with the head variations governed by general time dependent functions general recharge function was not considered in previous works of this kind both single and double porosity aquifers are considered the solution is obtained using fourier sine and laplace transformations followed by an inverse fourier laplace transform involving residue theorem and convolutional integral for the unconfined single porosity aquifer case the exact time domain solution is obtained using the residue theorem for the unconfined double porosity aquifer case the time domain head is calculated using the de hoog inverse laplace algorithm the presented solution can be used to estimate the hydraulic parameters of 1 groundwater head variation of a river basin aquifer subjected to general lateral head variation and recharge 2 groundwater head variation in a double porosity elongated fractured anticline 3 groundwater depletion of an elongated fractured anticline subjected to recharge due to rainfall or snowmelt to its adjacent alluvial aquifer in addition the presented solution can be utilized to optimize the irrigation pattern in a cropland between two trench drains to control the groundwater mound

tidal corrections for topex altimetry in the coral sea and great barrier reef lagoon comparisons with long term tide gauge records 1 the well known capability of topex poseidon altimetry to map sea levels precisely in the deep oceans motivates its application to the topographically complex coral sea and ne australian continental margin we assess several global tidal models for correcting topex altimetry in the coral sea and find csr3 0 offers good overall performance based on comparisons of model predicted and tide gauge harmonic constituents using csr3 0 tidal corrections we evaluate residual sea surface height ssh root mean square rms variability and residual m2 tidal alias errors away from large reefs and islands csr3 0 amplitude and phase errors for m2 are typically less than 5 cm and 8 deg respectively with rms tidal errors of 5 cm or less and rms ssh residuals approximating 10 cm since model deficiencies appear in the macro tidal region of the southern great barrier reef lagoon near broad sound we employ a high resolution hydrodynamic model in this area to compute the tidal corrections predicted m2 amplitude and phase in this region are within 3 cm and 5 deg of observations rms errors are mostly under 4 cm and coastal rms ssh residuals are as low as 15 cm in spite of coastal trapped waves and submesocale eddies in the lagoon daily and monthly smoothed ssh residual time series respectively yield optimal lagged correlations with in situ sea level data in the range 0 3 0 9 and 0 6 0 9 for locations spanning the coral sea and in the lagoon lag correlations of monthly smoothed geostrophic current anomalies derived from topex ssh gradients with long term currents from the continental slope yield optimal correlations of 0 5 and 0 8 respectively near jewell lat 14 deg s and myrmidon reef 19 deg s our results demonstrate that low frequency sea level and geostrophic current variations can be reliably observed using altimetry over the coral sea and ne australian continental slope and for selected locations on the continental shelf if appropriate tide correction models are employed

the response of groundwater to artificial recharge schemes analytic solutions are presented for the groundwater flow in an unconfined aquifer under seasonal artificial recharge schemes of variable duration the results can be used for a preliminary assessment of the response of groundwater to artificial recharge variations in storage and outflow from the aquifer apart from the siting of recharge are also highly dependent on both the aquifer characteristics and the duration of recharge

sea level response to pressure forcing in a barotropic numerical model abstract a barotropic shallow water model is used to study the large scale sea level response to realistic barometric forcing at periods ranging from 1 day to 1 year results are presented from coarse resolution open ocean experiments i e no shallow continental shelf regions or marginal seas with coastal geometries and bottom topography representative of the north atlantic and pacific basins the validity of the inverted barometer ib approximation is examined in detail including nonlocal effects which result from taking into account the constant volume of the ocean these effects are found to be important at low latitudes where a considerable part of the sea level variability is related to pressure forcing over higher latitudes root mean square deviations from an ib response in the range of 1 3 cm are typical with most of the variance occurring at high frequencies basin averaged estimates yield ib deviations of only a few percent at time scales longer than 1 week increasing to 5 20 over the

validation of the geostrophic method for estimating zonal currents at the equator from geosat altimeter data the applicability of satellite altimeter data for estimating zonal current variability at the equator is assessed using the meridionally differenced form of the geostrophic balance estimates of geostrophic zonal flow anomalies in the equatorial pacific have been deduced from 17 day collinear altimeter data during the first year of the geosat exact repeat mission november 1986 to november 1987 altimeter derived geostrophic estimates agree well with in situ zonal current variability comparison of low frequency near surface zonal current observed from equatorial moorings at 165 e 140 w and 110 w yield correlations of 0 83 0 85 and 0 51 respectively with a mean rms difference of 23 cm s 1 the geostrophic currents were calculated from all available ascending and descending geosat tracks within 4 5 of longitude from each mooring site the inclusion of up to 11 ascending and descending geosat tracks within the 9 band for every 17 day repeat effectively reduced the temporal sampling interval to 1 5 days at 165 e and 140 w however only ascending tracks were available at 110 w alongtrack sea surface heights were first smoothed using a combination of linear and nonlinear filters the 6 8 km alongtrack spacing of the altimeter measurements provides sufficient resolution for the effective filtering of small scale meridional noise both instrumental and oceanic high frequency temporal variability such as noise and ageostrophic motions was suppressed with a 31 day hanning filter sea level and zonal velocity solutions from a tropical pacific numerical model were used as proxy data sets in order to estimate errors induced into the geostrophic calculation by the geosat space time sampling

analytical solutions for strip basin recharge to aquifers with cauchy boundary conditions abstract analytical solutions for groundwater recharge from strip basins to finite aquifers are presented the problem concerns the impact of either continuous or periodic seasonal recharge schemes on aquifers with a boundary condition of the third kind cauchy the solutions can be useful for assessing aquifer response as well as for calibrating numerical computer models

the mount pavagadh volcanic suite deccan traps geochemical stratigraphy and magmatic evolution abstract the patterns of eruption and dispersal of flood basalt lavas on the surface or as magmas in dykes and sills within the crust determine the volcanological and stratigraphic development of flood basalt provinces this is a geochemical and sr isotopic study of lavas of varied compositions that outcrop around mount pavagadh 829 m deccan traps an important outlier north of the main basalt outcrop most of the 550 m thick exposed section at pavagadh is made up of subalkalic basalts rich in the incompatible elements particularly nb ba and sr picrite and rhyolite dacite flows also occur the latter capping the sequence the relatively high initial 87sr 86sr ratios up to 0 7083 and chemical characteristics of the rhyolitic rocks of pavagadh are consistent with a small but significant involvement of the granitic basement crust in their genesis an assimilation fractional crystallization afc model involving the picrite lava and either a southern indian or a western indian granite as the contaminant explains the geochemical and sr isotopic variation in the basalts and the rhyolites quite well a systematic comparison of the basaltic lavas with binary plots normalized multielement patterns and discriminant function analysis to the well established lava stratigraphy of the western ghats 400 500 km to the south precludes any chemical genetic relationships between the two basalts exposed in sections closer to pavagadh 150 200 km in the toranmal navagam and barwani mhow areas have several flows with some similar chemical characteristics however the pavagadh sequence is significantly different from all of these sequences geochemically petrogenetically and in magnetic polarity to be considered independently built this result is significant in terms of eruptive models for the deccan traps as it is increasingly apparent that there were separate but possibly coeval eruptive centers with their own distinctive chemistries developed in various areas of this vast province

basalts of the eastern deccan volcanic province india abstract the mandla lobe in the eastern part of the deccan volcanic province represents an isolated lava pile having a thickness of 900 m the large thickness of this lava pile and its spatial detachment from the western deccan outcrop points to a plausible second source the stratigraphic configuration of the central and eastern deccan lava sequences and their possible stratigraphic correlation are primarily based on geology and chemical signatures of the lava flows based on variations in the incompatible element ratios the lava sequences of chindwara jabalpur seoni and jabalpur piparia sections were classified into four informal formations showing similarity with the southwestern formations major and trace element abundances in fifteen lava flows of jabalpur area are similar to that of the southwestern deccan lava flows it has been found that the ambenali fm and a few khandala and bushe fm flows are present in the northeastern deccan the regional mapping and detailed petrographic studies coupled with the lateral tracing have enabled the recognition of thirty seven physically distinct lava flows and is justified by their major elemental chemistry the intraflow variations studied in some of the flows is very low for most of the major oxides these thirty seven lava flows are grouped into eight chemical types the order of superposition in this sequence reflects that the older flows occur in the west of the outlier at the seoni jabalpur sahapura sector whereas the younger flows are confined to the dindori amarkantak sector in the east the spatial disposition of the lava flows suggests that the structural complexity in the lava flow sequence in the mandla lobe lies between jabalpur and dindori the juxtaposition of distinct groups of lava flows are observed near deori flows 1 to 4 abeted aginst flows 5 to 14 and dindori areas at dindori and towards its south the distinct lava packages flows 15 to 27 and flows 28 to 37 are juxtaposed along the course of narmada river the possible explanation for this could be the presence of four post deccan faults at nagapahar kundam deori and dindori areas the vertical shift of chemically distinct lava packages at different sectors in the outlier contravenes the idea of small regional dip and favours the presence of four ne sw trending post deccan faults major geochemical breaks when traced out from section to section exhibit shifting in heights by approximately 150 m near nagapahar and 300 m near deori and dindori areas the field petrographic and major oxide data sets considered in conjuction with the magnetic chron reversal heights support the inference that four faults trending ne sw are present in the mandla lobe a commonality in the mineralo chemical attributes of the infra lametas inter trappean as well as weathered deccan basalt further favours their derivation from deccan basalt implying the availability of deccan basalt during the maastrichtian lameta sedimentation this observation does not match with the models suggesting an extremely short duration of deccan volcanism

using an altimeter derived internal tide model to remove tides from in situ data internal waves at tidal frequencies i e the internal tides are a prominent source of variability in the ocean associated with significant vertical isopycnal displacements and currents because the isopycnal displacements are caused by ageostrophic dynamics they contribute uncertainty to geostrophic transport inferred from vertical profiles in the ocean here it is demonstrated that a newly developed model of the main semidiurnal m2 internal tide derived from satellite altimetry may be used to partially remove the tide from vertical profile data as measured by the reduction of steric height variance inferred from the profiles it is further demonstrated that the internal tide model can account for a component of the near surface velocity as measured by drogued drifters these comparisons represent a validation of the internal tide model using independent data and highlight its potential use in removing internal tide signals from in situ observations

nonstationary internal tides observed using dual satellite altimetry abstractdual satellite crossover data from the jason 2 and cryosat 2 altimeter missions are used in a novel approach to quantify stationary and nonstationary tides from time lagged mean square sea surface height ssh differences computed for lags from 1 to 1440 h 60 days the approach is made feasible by removing independent estimates of the stationary tide and mesoscale ssh variance which greatly reduces the sampling error of the ssh statistics for the semidiurnal tidal band the stationary tidal variance is approximately 0 73 cm2 and the nonstationary variance is about 0 33 cm2 or 30 of the total the temporal correlation of the nonstationary tide is examined by complex demodulation and found to be oscillatory with first 0 crossing at 400 h 17 days because a significant fraction of the time variable mesoscale signal is resolved at time scales of roughly 150 h by the present constellation of satellite altimeters the results suggest that it may be feasible to predict the nonstationary tide fr

recharge to finite aquifers from strip basins abstract the problem of groundwater recharge from strip basins to finite aquifers is solved analytically by the method of finite fourier transforms both impermeable and recharge boundaries are considered the analytical solutions are evaluated by comparison with experimental results in sand tank models reported in the literature

analytical solutions for periodic well recharge in rectangular aquifers with third kind boundary conditions abstract analytical solutions for groundwater flow in rectangular aquifers are presented in the case of single well recharge the problem concerns the impact of a seasonal periodic recharge scheme of variable duration on aquifers with various boundary conditions of which at least one is of the third kind results can be obtained for any combination of boundary conditions and can be used in a preliminary assessment of the groundwater response to artificial recharge schemes

ocean currents and sea surface heights estimated across the west florida shelf abstract the across shelf structures of the ocean circulation and the associated sea surface height ssh variability are examined on the west florida shelf wfs for the 3 yr interval from september 1998 to december 2001 five sets of characteristic circulation patterns are extracted from 2 day low pass filtered data using the self organizing map extreme upwelling and downwelling structures with strong currents asymmetric upwelling and downwelling structures with moderate currents and a set of transitional structures with weak currents the temporal variations of these structures are coherent with the local winds on synoptic weather time scales on seasonal time scales they are related to both the local winds and the water density variations the circulation is predominantly upwelling during autumn to spring months october april and downwelling during summer months june september coastal sea level fluctuations are related to both the dynamical responses of the inner shelf circulation to meteorol

assimilation of topex poseidon altimetric data in a primitive equation model of the tropical pacific ocean during the 1992 1996 el nino southern oscillation period four years of topex poseidon data october 1992 to october 1996 are assimilated into a high resolution primitive equation model gent and cane 1989 of the tropical pacific ocean the assimilation method used is a degraded version of the singular evolutive extended kaiman filter approach pham et al 1998 in which the reduced order basis is fixed the along track topex poseidon sea surface height residuals are introduced in the model every 3 days initialization of the model runs appears to be crucial this is particularly true for the 1992 1996 period which is characterized by several el nino and la nina events and exhibits quite anomalous climatological behavior an in situ database dedicated to this period was built and used to initialize the model properly the simulation results with and without assimilation were compared with expendable bathythermograph and tropical atmosphere ocean in situ observations the impact of sea surface height assimilation is observed both on the surface and subsurface temperature and velocity fields the deficiencies of the free model in terms of means and variability structures are significantly reduced more importantly the evolution of the model fields over time is considerably improved by the assimilation these supposedly more realistic assimilated four dimensional fields are used to investigate the mechanism responsible for the 1992 1996 warm pool replenishment and depletion this approach provides insights into the combined role of zonal and meridional transports in balancing volume changes in the warm pool

cenozoic volcanism in the middle east petrogenesis of alkali basalts from northern lebanon large discontinuous exposures of basaltic lava flows ranging in age mostly from miocene to recent are present in several localities extending from sinai jordan palestine israel to lebanon and syria dubertret 1955 baldridge et al 1991 mouty et al 1992 heimann et al 1996 shaw et al 2003 these form the cenozoic volcanic province of the middle east occurring mostly along or near the transform faulted boundary the dead sea ghab transform fault system between the arabian and african plates and the levantine subplate fig 1 further to the south several other extensive cenozoic volcanic provinces occur in arabia and east africa mostly ethiopia figure 1 regional geological map showing the distribution of the various cenozoic volcanic provinces in east africa arabia and the middle east the cenozoic continental flood basalts in ethiopia yemen western arabia and jordan have been extensively studied camp roobol 1989 1992 altherr henjes kunst baumann 1990 stein hofmann 1992 baker thirlwall menzies 1996 baker et al 1997 shaw et al 2003 the cenozoic volcanic province of ethiopia is clearly related to the east african rift system barberi et al 1975 mohr 1983 the quaternary intraplate basaltic volcanic field in yemen appears to be the result of melting shallow mantle perhaps in response to small amounts of lithospheric extension that were metasomatized and hydrated by the afar plume during or shortly after oligocene flood volcanism baker et al 1997 the lavas of this basaltic field of western yemen were subjected to variable degrees of contamination 0 20 of an early proterozoic to late archaean silicic lower crustal component baker thirlwall menzies 1996 baker et al 1997 the cenozoic continental flood basalt provinces of

evaluation of topex and basin wide tropical ocean and global atmosphere tropical atmosphere ocean sea surface topographies and derived geostrophic currents fields of topex derived sea level anomalies are validated against and compared with fields of tropical ocean and global atmosphere tropical atmosphere ocean toga tao dynamic height anomalies for the first 470 days of the topex poseidon mission at periods longer than 35 days topex sea level anomalies compare extremely well with toga tao dynamic height anomalies throughout the whole basin with a mean correlation of 0 79 and mean rms differences of 2 6 cm zonal geostrophic current anomalies are then derived from both data sets and validated against in situ current meter measurements at the equator topex derived geostrophic current anomalies at the equator are in good agreement with in situ currents at 0 165 e 0 170 w 0 140 w and 0 110 w toga tao derived current anomalies compare well with in situ currents at 0 110 w 0 140 w and 0 170 w but poor comparisons at 0 165 e are thought to be linked to the absence of instantaneous salinity measurements in the dynamic height calculation despite localized discrepancies basin wide toga tao geostrophic currents compare reasonably well with topex derived geostrophic currents the discrepancies in the comparison between topex and tao are shown to be mostly associated with gaps in toga tao space time sampling and subsequent gridding procedures

geology petrochemistry and genesis of the bimodal lavas of osham hill saurashtra northwestern deccan traps abstract the saurashtra region in the northwestern deccan continental flood basalt province india is notable for compositionally diverse volcano plutonic complexes and abundant rhyolites and granophyres a lava flow sequence of rhyolite pitchstone basaltic andesite is exposed in osham hill in western saurashtra the osham silicic lavas are ba poor and with intermediate zr contents compared to other deccan rhyolites the osham silicic lavas are enriched in the light rare earth elements and have end t 65 ma values between 3 1 and 6 5 and initial 87sr 86sr ratios of 0 70709 0 70927 the osham basaltic andesites have initial end values between 2 2 and 1 3 and initial 87sr 86sr ratios of 0 70729 0 70887 large ion lithophile element concentrations and sr isotopic ratios may have been affected somewhat by weathering notably the sr isotopic ratios of the silicic and mafic rocks overlap however the nd isotopic data indicate that the silicic lavas are significantly more contaminated by continental lithosphere than the mafic lavas we suggest that the osham basaltic andesites were derived by olivine gabbro fractionation from low ti picritic rocks of the type found throughout saurashtra the isotopic compositions and the similar al2o3 contents of the osham silicic and mafic lavas rule out an origin of the silicic lavas by fractional crystallization of mafic liquids with or without crustal assimilation as previously proposed for some icelandic rhyolites and supported here by melts modelling the osham silicic lavas may have been derived by partial melting of hot mafic intrusions emplaced at various crustal depths due to heating by repetitively injected basalts the absence of mixing or mingling between the rhyolitic and basaltic andesite lavas of osham hill suggests that they reached the surface via separate pathways

altimeter derived variability of surface velocities in the california current system 1 evaluation of topex altimeter velocity resolution in this paper we evaluate the temporal and horizontal resolution of geostrophic surface velocities calculated from topex satellite altimeter heights moored velocities from vector averaging current meters and an acoustic doppler current profiler at depths below the ekman layer are used to estimate the temporal evolution and accuracy of altimeter geostrophic surface velocities at a point surface temperature gradients from satellite fields are used to determine the altimeter s horizontal resolution of features in the velocity field the results indicate that the altimeter resolves horizontal scales of 50 80 km in the along track direction the rms differences between the altimeter and current meters are 7 8 cm s 1 much of which comes from small scale variability in the oceanic currents we estimate the error in the altimeter velocities to have an rms magnitude of 3 5 cm s 1 or less uncertainties in the eddy momentum fluxes at crossovers are more difficult to evaluate and may be affected by aliasing of fluctuations with frequencies higher than the altimeter s nyquist frequency of 0 05 cycles d 1 as indicated by spectra from subsampled current meter data the eddy statistics that are in best agreement are the velocity variances eddy kinetic energy and the major axis of the variance ellipses spatial averaging of the current meter velocities produces greater agreement with all altimeter statistics and increases our confidence that the altimeter s momentum fluxes and the orientation of its variance ellipses the statistics differing the most with single moorings represent well the statistics of spatially averaged currents scales of 50 100 km in the ocean besides evaluating altimeter performance the study reveals several properties of the circulation in the california current system 1 velocity components are not isotropic but are polarized strongly so at some locations 2 there are instances of strong and persistent small scale variability in the velocity and 3 the energetic region of the california current is isolated and surrounded by a region of lower energy starting 500 700 km offshore this suggests that the source of the high eddy energy within 500 km of the coast is the seasonal jet that develops each spring and moves offshore to the central region of the california current rather than a deep ocean eddy field approaching the coast from farther offshore

oceanic tides from geosat altimetry direct tidal analysis of the altimetry from the geosat exact repeat mission s first year is used to derive estimates of the diurnal and semidiurnal oceanic tides the geoid is removed by collinear differences at 34 1 day separation and the orbit error is reduced by subtracting a slowly modulated 1 cycle revolution term a sequence of independent analyses at grid areas of 1 latitude 1 5 longitude using orthotide functions ensures complete definition of the diurnal and semidiurnal species global admittance maps for m2 and s2 within the latitudes 58 n and 59 s compare well with ground truth at 66 open ocean sites maps of differences between geosat and the naval surface weapons center model show important areas of the order of 10 15 cm the integral for the global power input from the moon gives 2 51 tw m2 0 44 tw s2 lower than many previous estimates but in agreement with figures deduced from a recent analysis of satellite orbits

validating satellite altimeter measurements of internal tides with long term tao triton buoy observations at 2 s 156 e satellite altimetry is regularly used to map the global distribution of mode 1 internal tides validating altimeter measurements of internal tides with in situ data is difficult as the mooring observations typically are too short compared with the altimetry here taking advantage of the long term since 1999 tropical atmosphere ocean triangle trans ocean buoy network tao triton buoy observations at 2 s 156 e located at a topex poseidon crossover in a region of strong internal tides direct comparisons are made between altimeter and in situ measurements over a common 15 year period the hourly buoy data are decimated every 9 9 day to emulate altimeter measurements the altimeter and decimated buoy data are highly coherent at the aliased semidiurnal period 60 day and they agree well for the stationary semidiurnal internal tide for the nonstationary internal tide which consists of a significant annual cycle the demodulated amplitude from the altimeter appears to be contaminated by nontidal signals the demodulated amplitude from the decimated buoy data on the other hand is capable of resolving the temporal variability this suggests the potential of mapping nonstationary internal tides from satellites

basalts of the northeastern deccan traps india isotopic and elemental geochemistry and relation to southwestern deccan stratigraphy the northeastern deccan traps include flows with strong isotopic and elemental affinities to lavas in the southwest as far as 900 km away however many of the northeastern flows show a negative correlation of 206pb 204pb with end t and positive correlation of 206pb 204pb with 87sr 86sr t distinct from any of the isotopic fields for the southwestern formations this array from end t 5 87sr 86sr t 0 7041 206pb 204pb 17 9 to end t 0 87sr 86sr 0 7068 206pb 204pb 20 5 overlaps the ambenali formation fm field and runs toward that of the common signature peng et al 1994 that appears to have been an important magma type in several of the lower formations of the southwest this array appears to represent mixing between an ambenali type and 1 a common signature end member or 2 an end member with even higher 206pb 204pb and 87sr 86sr and lower end than the common signature such mixing has been postulated but not documented previously for the deccan lavas isotopically and chemically indistinguishable from the ambenali fm form the tops of sections near jabalpur and chikaldara beneath them are flows that chemically resemble the poladpur fm which sits immediately below the ambenali in the southwest and several lavas similar to the khandala fm beneath the poladpur and intervening bushe fm in the southwest given the general stratigraphic correspondence with the southwestern sequence many of these northeastern flows may be petrogenetically related to the respective southwestern formations lavas with broadly poladpurand khandala like elemental compositions are also abundant in a thick section south of mhow several other mhow area flows resemble the distinctive bushe fm however nearly all of the poladpur and khandala like northeastern deccan lavas analyzed have higher 206pb 204pb man any southwestern poladpur or khandala fm basalts if they indeed are related petrogenetically to these formations many of the northeastern magmas interacted less with low 206pb 204pb continental material and thus must have erupted from different feeder systems

bimodal tholeiitic and mildly alkalic basalts from bhir area central deccan volcanic province india geochemistry and petrogenesis abstract bimodal tholeiitic and mildly alkalic basalts occur near bhir in the central part of deccan volcanic province dvp major and trace element concentrations show that of the ten flows nine are tholeiitic and one is an alkalic basalt the bhir basalts have a wide range of chemical composition geochemical variations in the stratigraphic section define three distinct phases of evolution zones 1 to 3 crystal fractionation of plagioclase clinopyroxene olivine and fe ti oxide expanded the compositional range low mg s 39 55 low concentrations of ni and cr and high zr suggest the evolved nature of the bhir basalts fractionation modeling suggests about 42 fractional crystallization in spite of the dominant role of fractional crystallization in the evolution of bhir basalts some other processes must be sought to explain the chemical variations crustal contamination magma mixing and degree of partial melting are suggested to explain the observed chemical variations resorption reverse zoning and compositional bimodality in plagioclase phenocrysts indicate magma mixing samples of flows one and four suspected of being contaminated all have enriched sio2 and lile k rb and ba contents and depletion in ti and p believed to be due to granitic crustal contamination as compared to tholeiitic basalts the alkalic basalts are characterized by low sio2 and high tio2 na2o k2o and p2o5 alkalic basalts are richer in lile rb and ba hfse nb zr and y and ree than the tholeiitic basalts the alkalic basalt occurrence is important from a petrogenetic point of view and also suggests that the sources of alkalic basalt magmas may be of variable ages under different parts of the dvp based on major trace and rare earth element distributions it is suggested that asthenospheric mantle having affinities with the source of oib was the source material of the magmas and the range in the composition of tholeiitic and alkalic basalts was probably controlled by different degrees of melting and or inhomogeneities in the mantle source