near equatorial eddies in the north atlantic surveys of the large scale near equatorial eddies 400km across off the northeast coast of south america with expendable bathythermographs from ships of opportunity and aircraft indicate that a large eddy 6n 11n to the north and a southern eddy like feature 2n 6n probably are a permanent part of the circulation both features were observed during the periods of seasonal extremes march and september although during the latter period the structure of the eddies had enlarged and deepened indicating a pronounced seasonal variability

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

precambrian u pb zircon ages in eclogites and garnet pyroxenites from south brittany france an old oceanic crust in the west european hercynian belt abstract u pb zircon ages have been determined for two eclogites from the vendee and for two garnet pyroxenites from the baie d audierne in an episodic pb loss model the two discordia would give upper intercept ages around 1300 1250 ma and lower intercepts ages of 436 384 ma two interpretations are proposed 1 the 1250 1300 ma ages may reflect an unspecified upper mantle event or process the paleozoic ages correspond to the tectonic emplacement of an eclogitic mantle fragment into the continental crust 2 the protolith may have been extracted from the upper mantle 1250 1300 ma ago and stored in a crustal environment until it was metamorphosed under high pressure conditions around 400 ma ago this latter model is favoured by available geologic and isotopic data consequently we propose that a 1300 ma old oceanic crust was tectonicly incorporated into a sialic basement during the proterozoic this mixture was subsequently subducted during the paleozoic

teleconnections of the southern oscillation in the tropical atlantic sector in the osu coupled upper ocean atmosphere gcm abstract the oregon state university coupled upper ocean atmosphere gcm has been shown to qualitatively simulate the southern oscillation a composite analysis of the warm and cold events simulated in this 23 year integration has been performed during the low phase of the southern oscillation when warm anomalies occur in the eastern pacific the model simulates for the atlantic region during march may 1 a deficit of precipitation over the tropical south american continent 2 caribbean and gulf of mexico sea level pressure and sea surface temperature are in phase with the eastern pacific anomalies while those east of the nordeste region are out of phase and 3 northeast trade winds are anomalously weak and southwest trade winds are anomalously strong as inferred from surface current anomalies the anomalies in the oceanic processes are induced by perturbations in the atmospheric circulation over the atlantic and are coupled to changes in the walker circulation during the high phase of the simulate

rare earth element mobility in the roffna gneiss switzerland the roffna gneiss a deformed hercynian granite porphyry within the penninic nappes of eastern switzerland underwent extreme cataclasis with the progressive development of phengite towards the margins of the nappe under conditions of the glaucophane schist to greenschist facies this resulted in the selective mobilization of major and trace elements over distances of 10 s to 100 s of meters and the resetting of the rb sr whole rock isotopic systems some 100 my ago the component ratios and compositionvolume relationships of progressively deformed gneiss samples studied here suggest that this process was essentially isovolumetric the mineralogy of the deformation sequence appears to have been controlled by a reaction involving the breakdown of microcline albite and biotite and the formation of phengite and quartz the fluids introduced mg and h2o promoting the development of phengite and removed the na being released by the breakdown of albite the fluids were most probably derived from the surrounding triassic carbonates and quartzites these relatively high fo2 and carbonate rich fluids also introduced rare earth elements ree into the gneiss the gneiss was progressively enriched in eu up to 60 y up to 40 and yb up to 100 these enrichments are associated with the development of epitaxial xenotime around zircon in the most phengite rich sample while the ree were mobile uranium and thorium were essentially immobile the formation of xenotime was suggested to explain the observed heavy ree enrichment when large differences in the ree contents were found for replicate analyses using hf and then lithium metaborate for dissolution these differences arose because xenotime like monazite can be difficult if not impossible to dissolve in hydrofluoric acid due to the possibility of incomplete sample dissolution we now recommend fusion with lithium metaborate for all ree lu hf or sm nd studies

a mid twentieth century reduction in tropical upwelling inferred from coralline trace element proxies abstract the cariaco basin is an important archive of past climate variability given its response to inter and extratropical climate forcing and the accumulation of annually laminated sediments within an anoxic water column this study presents high resolution surface coral trace element records montastrea annularis and siderastrea siderea from isla tortuga venezuela located within the upwelling center of this region a two fold reduction in cd ca ratios 3 5 1 7 nmol mol is observed from 1946 to 1952 with no concurrent shift in ba ca ratios this reduction agrees with the hydrographic distribution of dissolved cadmium and barium and their expected response to upwelling significant anthropogenic variability is also observed from pb ca analysis observing three lead maxima since 1920 kinetic control of trace element ratios is inferred from an interspecies comparison of cd ca and ba ca ratios consistent with the sr ca kinetic artifact but these artifacts are smaller than the environmental signal and do not explain the cd ca transition the trace element records agree with historical climate data and differ from sedimentary faunal abundance records suggesting a linear response to north atlantic extratropical forcing cannot account for the observed historical variability in this region

the variscan calc alkalic plutonism of western corsica mineralogy and major and trace element geochemistry abstract petrographic and structural observations on the calc alkalic plutonism of western corsica revealed the existence of several successively emplaced units associated with large basic bodies the present mineralogical and geochemical study deals with the genesis evolution and relationships of these different units basic plutonism is represented by three genetically linked types of rock norites and troctolites with cumulate textures characterized by low ree contents and either no eu anomaly or a positive eu anomaly gabbros with enriched lree relatively to hree patterns probably close to an initial basaltic liquid and diorites ranging up to charnockites which represent liquids evolved to varying degrees mainly by fractional crystallization trace element data and studies on the evolution of pyroxene pairs demonstrate the consanguinity of these calc alkaline basic rocks which are derived from a high alumina basaltic melt the various granitoids granodiorites monzogranites and leucocratic monzogranites i e adamellites have distinct evolution trends as shown by the composition of their mafic minerals and by trace element distributions they cannot be considered as being derivatives of the basic suite and they cannot be related by a common fractionation sequence rather they represent distinctive batches of crustal anatexis in addition hybridization phenomena with the basic melt are noticed in granodiorites the particular problem of the low la yb eu eu and the high u th cs leucocratic monzogranites is discussed in detail in addition to more conventional trace element diagrams the simultaneous statistical treatment of all the geochemical data by correspondence factor analysis is shown to be a very use tool in distinguishing between the different units and to classify the elements according to their geochemical properties

u pb zircon rb sr and sm nd geochronology of high to very high pressure meta acidic rocks from the western alps three meta acidic rocks from the western italian alps a magnesiochloritoid bearing metapelite from the monte rosa massif a coesite pyrope quartzite from the dora maira massif and the monte mucrone granite in the sesia zone have been studied by u pb zircon rb sr on whole rock apatite and phengite and sm nd wholerock methods the mineral parageneses of the investigated rocks indicate high to very high pressure and medium to high temperature metamorphism this combined isotopic study has enabled us to constrain the ages of magmatic and metamorphic events and also to compare the behaviour of u pb zircon systems in three intensely metamorphosed areas of the pennine domain the u pb zircon data have yielded a magmatic age for the monte mucrone granite at 286 2 ma this result confirms the occurence of late hercynian magmatism in the sesia zone as in other austro alpine units and in other areas of the european crystalline basement in the monte rosa massif a geologically meaningless lower intercept age of 192 2 ma has been interpreted as an artefact due to a complex evolution of the u pb zircon system the magmatic shape of the zircons implies a magmatic or volcano sedimentary protolith for this rock originally considered as a metasediment the very high pressure metamorphism in the dora maira quartzite has produced an opening of the u pb zircon system at 121 12 29 ma the rb sr data support the occurence of high grade metamorphism during cretaceous times phengites model ages are slightly younger than the u pb zircon lower intercept ages due to cooling phenomena or possible response of the phengites to a later deformation the nd model ages from the whole rock samples as well as the u pb upper intercept ages from zircons of all three investigated rocks indicate the presence of proterozoic crustal components inherited from the precursors of these meta acidic rocks the studied zircon populations and their u pb systems apparently showed open system behaviour only when affected by extreme metamorphic conditions 700 750 c 28 kbar whereas eclogite facies conditions of 500 550 c and 14 16 kbar were not enough to disturb significantly the u pb zircon evolution it is also probable that the sedimentary or magmatic origin of the protoliths of these meta acidic rocks which involved different characteristics such as grain size and fluid phase concentration and composition could be another important factor controlling the u pb zircon system behaviour during metamorphic events

the impact of sea surface temperature anomalies on the rainfall over northeast brazil abstract the response of the tropical atmosphere to the sea surface temperature sst anomalies in the northern hemisphere spring of 1984 is investigated the methodology for investigation consists of comparing simulations with and without the global distribution of sst anomalies in the boundary conditions of the ucla general circulation model gcm at low levels the response includes weaker southeast trade winds over the atlantic increased precipitation off the northeast coast of brazil and reduced precipitation west of this region the increased precipitation is due to enhanced convergence of moisture advected by the southeast trade winds although the trades themselves are weaker the results for the western equatorial atlantic am in apparent agreement with the observed anomalous southern migration of the itcz in years with warm sst anomalies in the southern tropical atlantic there are strong anomalous trade winds over the pacific extending east of the date line and weak wind anomalies over the ma

continental crust formation seen through the sr and nd isotope systematics of s type granites in the hercynian belt of western france the isotopic compositions of sr nd and pb in leucogranites which are intercorrelated bernard griffiths et al 1985 1 may be explained by the mixing of ancient basement 1800 ma with juvenile crust late precambrian or early palaeozoic this hypothesis does not involve the existence of mid proterozoic crust as apparently indicated by thetdm model ages of the leucogranites ranging between 1600 and 1100 ma the nd isotopes reveal the crustal reworking while sr isotopes mainly record juvenile crust formation this paradox is explained by the geochemical heterogeneity of the sources involved

on the changing nature of the regional connection between the north atlantic oscillation and sea surface temperature 1 evidence is presented that the correlation between the north atlantic oscillation nao in terms of the nao index and the north atlantic sea surface temperature sst is not stationary this is inferred from both reanalysis data from the u s national centers for environmental prediction national center for atmospheric research ncep ncar and the kaplan sea surface temperature data set two phases of winterly north atlantic atmosphere ocean covariability are identified by means of linear regression and correlation analysis during the recent decades since the late 1960s early 1970s and during the first 3 decades of the twentieth century the north atlantic sst is strongly correlated to the regional atmospheric circulation in the north atlantic sector i e the north atlantic oscillation during these periods the nao index defined as the difference of normalized sea level pressures on the azores and iceland is characterized by pronounced decadal variability and by mainly positive values in contrast the nao index is only weakly correlated to the north atlantic sst from the 1930s to the early 1960s when the nao index is characterized by weak decadal variability remote influences in particular from the tropical pacific region become important especially for the sst in the western tropical north atlantic

atlantic pacific links in observed multidecadal sst variability is the atlantic multidecadal oscillation s phase reversal orchestrated by the pacific decadal oscillation abstractthe atlantic and pacific basin are found linked in the context of multidecadal sst variability from analyses of 118 years of observational data recurrent spatiotemporal variability includ

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

prediction of northeast brazil rainfall anomalies abstract expanding on earlier research empirically based methods are developed for predicting march september rainfall in northern northeast brazil from a network of 27 raingage stations in brazil s nordeste new rainfall index series are constructed for march september ms and october january oj data input to stepwise multiple regression models further include january values of the tahiti minus darwin pressure index an index of sea surface temperature sst in the equatorial pacific pwt and indices of the fields of meridional v and zonal u wind components and of sst in the tropical atlantic between 30 n and 30 s afv arj and aft respectively empirical orthogonal function eof analysis of the v u and sst fields was used in constructing the latter three indices throughout the study a sharp distinction is kept between a dependent dataset 1921 42 and 1948 57 used as a training period and an independent portion of the record 1958 87 reserved for prediction experiments preseaso

evolution of the enso signal over the tropical pacific atlantic domain 1 space time evolution of the dominant el nino southern oscillation enso signal in the tropical eastern pacific atlantic domain is investigated 1979 2004 multi taper method singular value decomposition mtm svd and complex empirical orthogonal functions ceof are applied to four variables sea surface temperature sst upper ocean heat storage hst zonal surface wind zsw and sea level pressure slp anomalous evolution for all variables find a dominant enso signal 3 4 5 7 years band period composed of mixed standing modes and propagating modes the latter evolve eastward from the eastern pacific ocean into the tropical atlantic basin at 20 cm s 1 as such peak signals in the equatorial atlantic lag that in the eastern equatorial pacific by 12 18 months the slow sst slp coupled wave propagating through the caribbean sea resembles the global enso wave identified by white and cayan 2000

kyanite eclogite to amphibolite fades evolution of hydrous mafic and pelitic rocks adula nappe central alps in the southern adula nappe central alps two stages of regional metamorphism have affected mafic and pelitic rocks earlier eclogite facies with a regional zonation from glaucophane eclogites to kyanite hornblende eclogites was followed by a tertiary overprint which varied from greenschist to high grade amphibolite facies despite a common metamorphic history contrasting equilibration conditions are often recorded by high pressure mafic eclogite and adjacent predominantly lower pressure pelite assemblages this pressure contrast may be explained by different overprinting rates of the two bulk compositions during unloading the rates are controlled by a mechanism in which dehydrating metapelites provide the h2o required for simultaneous overprinting of enclosed mafic eclogites by hydration

interannual variability in the tropical atlantic the anomalous meteorological and oceanic conditions in the tropical atlantic basin during 1983 84 can be seen as an extreme example of a common historical pattern here we present time series of rainfall in subsaharan west africa swa and north east brazil neb which show that departures in 1983 84 were severe but not unprecedented the associated sea surface temperature sst anomaly patterns included one that had previously been shown to accompany earlier years of extreme rainfall in swa and neb and others that contained key elements of that pattern the pattern concerned was recently shown to be a major mode of tropical atlantic sst variation

u pb dating of an early paleozoic bimodal magmatism in the french massif central and of its further metamorphic evolution in the marvejols area southern french massif central the gneissic marvejols supergroup is overthrust on the metasedimentary serie du lot deposited in part prior to 540 ma the allochtonous terranes are characterized by the occurrence of a leptyno amphibolitic group a complex association of mafic and felsic rocks of igneous and sedimentary derivation a 480 10 ma age has been obtained by u pb dating of zircons for the crystallization of both mafic and felsic meta igneous rocks these rocks were emplaced during an important extensional tectonics relics of eclogites pyrigarnites coronite gabbros and hp trondhjemites are clear evidence for a further hp ht event dated at 415 6 ma on zircons from a hp trondhjemite subsequently the marvejols supergroup underwent an amphibolite facies metamorphism with incipient mobilization dated at 345 10 ma

on the north brazilian eddy field abstract the region of large eddies occurring off the coast of brazil between approximately 3 n 10 n is revealed in some detail by repeated temperature observations on the along shore sea lane by ships of opportunity augmented by one airborne xbt expendable bathythermograph survey the general pattern of the circulation implied by the temperature structure is similar to that indicated by past hydrographic measurements and drifter tracks in general a large anticyclonic eddy to the north 7 n 10 n as well as a southern eddy like feature 3 n 6 n appear to be permanent patterns of the western north equatorial circulation this pattern somewhat resembles that found in the somali basin during the southwest monsoon

tube wave to shear wave conversion at borehole plugs abstract in hydraulic fracturing experiments perforation shots excite body and tube waves that sample and thus can be used to characterize the surrounding medium while these waves are routinely employed in borehole operations their resolving power is limited by the experiment geometry the signal to noise ratio and their frequency content it is therefore useful to look for additional complementary signals that could increase this resolving power tube to body wave conversions scattering of tube to compressional or shear waves at borehole discontinuities are one such signal these waves are not frequently considered in hydraulic fracture settings yet they possess geometrical and spectral attributes that greatly complement the resolution afforded by body and tube waves alone here we analyze data from the jonah gas field wyoming usa to demonstrate that tube to shear wave conversions can be clearly observed in the context of hydraulic fracturing experiments these waves are identified primarily on the vertical and radial components of geophones installed in monitoring wells surrounding a treatment well they exhibit a significantly lower frequency content 10 100 hz than the primary compressional waves 100 1000 hz tapping into such lower frequencies could help to better constrain velocity in the formation thus allowing better estimates of fracture density porosity and permeability moreover the signals of tube to shear wave conversion observed in this particular study provide independent estimates of the shear wave velocity in the formation and of the tube wave velocity in the treatment well

ellenbergerite a new high pressure mg al ti zr silicate with a novel structure based on face sharing octahedra ellenbergerite occurs as purple millimetre size grains associated with talc kyanite clinochlore rutile and zircon in composite inclusions within decimetre large pyrope crystals 90 98 mole percent end member in the quartzite layer of the dora maira massif western alps from which coesite has been recently reported chopin 1984 it is hexagonal a 12 255 8 c 4 932 4 a z 1 space group p63 mohs hardness 6 5 dmes 3 15 dcal 3 10 no cleavage uniaxial negative and vividly pleochroic colourless e colourless to deep lilac with colour zoning the intensely coloured variety has 1 6789 5 e 1 670 1 microprobe analysis yields sio2 39 1 p2o5 0 45 al2o3 25 1 tio2 4 0 mgo 22 2 feo 0 20 sum 99 05 wt including h2o 8 0 coulometrically the formula calculated on a o28 oh 10 basis implying 7 5 wt h2o is mg6 71 fe0 03 ti0 61 al6 00 si7 92 p0 08 o28 oh 10 the colour zoning is due to nearly complete ti zr substitution in addition ellenbergerite may contain more than 8 wt p2o5 with strictly correlated changes of si mg al and ti zr contents over 80 of which represent the sial pmg substitution

petrogenesis of hercynian leucogranites from the southern armorican massif contribution of ree and isotopic sr nd pb and o geochemical data to the study of source rock characteristics and ages abstract ree geochemistry and isotopic pb sr nd o compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in south brittany ages decrease from 340 ma in the north to 300 ma in the south whereas initial 87 sr 86 sr ratios increase from 0 706 to 0 710 0 717 ree abundances are relatively low la n 20 80 chondrites with a strong enrichment of lree relative to hree la n lu n 13 4 26 6 pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 ma ago 18 o 16 o ratios are high and relatively uniform at 10 7 to 12 8 mean 11 9 u pb studies on zircon indicate the presence of an inherited radiogenic pb component and that the sediment dominated source region had been metamorphosed during the siluro devonian ligerian negativee nd t values imply that the source region had been enriched in lree prior to the melting episode based on the combined data large scale partial melting of crustal material dominantly of sedimentary origin is proposed the model age of the source rocks is not very old 600 700 to 1200 ma the pb and sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites

on the functioning of the southern oscillation in the south american sector part i surface climate abstract the functioning of the southern oscillation so over south america and the surrounding tropical atlantic and eastern pacific oceans is studied through analyses of bimonthly patterns of correlation between an so index and the fields of pressure wind temperature and rainfall hydrometeorological anomalies being further ascertained from river discharge and lake level records and measurements of outgoing longwave radiation most pronounced is the anomalously low pressure over the eastern pacific during the negative so phase defined by anomalously low high pressure at tahiti darwin consistently positive so pressure correlations over the eastern tropical pacific extend eastward into the north atlantic region and southern south america during the respective winter semester during the austral winter the tendency for anomalously abundant rainfall in central chile during the negative so phase appears related to an anomalously weak and northward displaced south pacific subtropical high while relativ