circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

on the average absolute transport of the deep western boundary currents east of abaco island the bahamas abstract data obtained from a line of absolute current profiler pegasus and ctd stations at 26 5 n east of abaco island in the northern bahamas are used to estimate the average transport and overall level of variability of the deep below 800 m southward flow associated with the so called deep western boundary current dwbc at this latitude from april 1985 to september 1987 a total of 11 sections were made along a line extending from near the island boundary to 85 km offshore as part of the subtropical atlantic climate studies stacs program in all but two cases when pegasus data were obtained over the total depth absolute velocities were determined from 0 to about 3000 db while ctd derived relative velocities were determined over the total depth using the combined datasets it is possible to reference the relative geostrophic velocity with pegasus data thereby obtaining an estimate of the absolute southward transport of the deep flow the average value of transport determined in this man

determining the strength of the deep western boundary current using the chlorofluoromethane ratio abstract the dilution of a passive tracer during deep water formation and the subsequent advection mixing in a deep boundary current is modeled with application to chlorofluoromethanes cfms in the north atlantic two different types of boundary currents are considered a uniform flow and a simple shear flow in each case the core of the flow mixes with surrounding water which continually accumulates cfms in an extreme case the coupled systems predicts that the cfm ratio in the current is unaltered from the ratio of its source water save for a time lag more realistic cases however suggests that the ratio is not a conserved quantity but is substantially altered in both the overflow basin and boundary current matching the model results to cfm data collected near the grand banks gives a predicted average core speed of 5 10 cm s 1 for the deep western boundary current and provides a constraint on the transport and diffusivity of the flow as well

the flux and mixing rates of antarctic bottom water within the north atlantic calculation was made of the northward flow of antarctic bottom water into the western north atlantic basin through a passageway approximately 300 km wide between the ceara rise and the mid atlantic ridge at about 4 n two moorings carrying four current meters each were placed in the region where currents were expected to be the greatest and were left for 360 days the current was not steady but exhibited large surges with approximately a 60 day time scale whose cause is unknown current meters in the fastest flowing region all exhibited a net northward flow it is estimated that approximately 0 8 106 m3 s 1 of water colder than 1 9 c potential temperature flowed on the average into the north atlantic with this number possibly being too small by 0 3 106 m3 s 1 or too big by 0 1 106 m3 s 1 depending upon estimates of the width of the region which the current meters sample however these numbers differ from geostrophic estimates of 1 98 106 m3 s 1 the disagreement coming almost entirely from the fact that the geostrophic estimates give a sizeable flux of water colder than 1 2 c while the current meters do not based upon the two different flux rates residence times and mixing coefficients are calculated for antarctic bottom water for each 0 1 c potential temperature interval from 1 0 c to 1 9 c finally some comments on the dynamics of the northward flow are made

path of the north atlantic deep water in the brazil basin recent hydrographic sections and high quality historical data sets are used to determine geostrophic currents at subtropical latitudes in the western basin of the south atlantic levels of no motion are determined from water mass information and a mass balance constraint to obtain the transport field of north atlantic deep water nadw in this region the incoming nadw transport of about 20 sv from the north at 19 degrees s appears to be balanced by only one third of this transport leaving in the south and two thirds leaving to the east or northeast at the mid atlantic ridge a simple model is proposed to determine the cause of the nadw branching it is shown that potential vorticity preservation in the presence of topographic changes leads to a similar flow pattern as observed with branching near the vitoria trindade ridge and also an eastward turning of the southward western boundary current at about 28 degrees s the latitude where a balance of planetary vorticity change and stretching can be expected

structural control and tectonic setting of mesozoic volcanism in hong kong middle jurassic to lower cretaceous silicic volcanic rocks and granitoid plutons in hong kong form part of the broad ne trending yanshanian tectonomagmatic belt that extends through se china pyroclastic deposits in hong kong are typically proximal and infill linear flared vents and ellipsoidal calderas these pass down through elongate rift like conduits into extensive multiple fault and shear zone hosted 9sheeted9 dyke complexes and granitoid plutons dykes also emphasize the limits of calderas the spatial distribution and geometry of the vents calderas dykes and plutons are structurally controlled during each of four temporally well constrained periods of petrogenetically related volcanism and plutonism e and ene trending axes of extension and transtension were dominant nw trending faults increased in importance with time and their intersections with ene trending faults influenced the loci of volcanic centres nesting of the calderas confirms persistent reactivation of some faults the loci of magmatism migrated over 25 ma from nw to se zones of silicic crust created during these magmatic episodes have a broadly tripartite crustal 9stratigraphy9 pluton dyke volcanic reminiscent in very general terms of ophiolites the zones were created during periods of unusually rapid extension as the continental margin of se china changed from an active margin dominated by subduction to a back arc regime and dextral strike slip along ene trending faults gave way to sinistral strike slip

petrology and geochemistry of syn to post collisional metaluminous a type granites a major and trace element and nd sr pb o isotope study from the proterozoic damara belt namibia abstract leucocratic a type granites of the proterozoic damara orogen namibia are a distinctive groups of rocks based on their mineralogical chemical and isotopic characteristics a type granites can be distinguished from the leucocratic s type granites on the basis of fe rich amphibole and biotite and higher abundances of zr nb y and lree but lower values of 87 sr 86 sr 500 ma and 18 o in the a type granites in comparison with a type granites described in the literature the damaran a type granites are enriched in cao al2o3 mgo feo ba sr and eu but depleted in ga and zn low k rb rb sr rb ba and sr ba ratios indicate that these melts are not fractionation products of calc alkaline source rocks and therefore these chemical criteria are interpreted as a feature of the source rocks i e undepleted metatonalites the a type granites have high calculated zircon and monazite saturation temperatures mostly in excess of 800 c and it is concluded that these granites represent high temperature partial melts the relationship between major and trace element data and isotopic composition demonstrates that the a type granites originate from several sources and have undergone different processes the lack of evidence for shallow crustal contamination e g lack of country rock xenoliths the low viscosities of the melts as inferred from their high calculated temperature and their high nd concentrations relative to the country rocks suggest that the isotopic characteristics were acquired from an enriched mantle initial sr isotopic compositions vary over a narrow range 0 70486 0 70928 but the initial nd isotopic compositions vary considerably with initial end values between 0 03 and 6 35 this wide range in the nd isotope values is probably the result of interaction of mantle derived magmas with crustal rocks a type granites at baukwab have negatively correlated initial end values and 207 pb 204 pb and 206 pb 204 pb ratios indicating interaction of mantle derived magmas low initial end low 207 pb 204 pb and 206 pb 204 pb with continental crust high initial end high 207 pb 204 pb and 206 pb 204 pb a type granites from albrechtstal and oetmoed have positively correlated pb isotope ratios and show also positive correlations between nd isotopes and pb isotopes suggesting interaction of at least two different source materials the relationship between nd isotopes and nd concentrations precludes simple assimilation instead mixing of different sources seems to be more realistic for the a type granites from oetmoed oxygen isotopes are negatively correlated with sr isotopes indicating that the crustal end member has high 18 o values and rather low initial 87 sr 86 sr ratios whereas a hypothetical mantle component has lower 18 o values but higher initial 87 sr 86 sr ratios the chemical and isotope data suggest that the damaran a type granites were generated by a variety of processes including partial melting of mantle derived tonalitic sources limited crystal fractionation and interaction of these magmas with crustal material these data indicate that the damaran a type suites mark episodes of continental growth during which mantle material although limited in extent is added to the crust

hemispheric asymmetry of deep water transport modes in the western atlantic subtropical studies of the atlantic meridional cold water flow show a hemispheric contrast in the dominant southward transport mode below 2000 m in the north atlantic lower deep water ldw 1 8 2 4 c dominates with small transport of middle deep water mdw 2 4 3 2 c while in the south atlantic the opposite is observed we use numerous observations in the western basins of the tropics to show that the transition occurs rapidly near the equator in the western atlantic a meridional section in the central brazil basin suggests zonal flows are responsible for the transition ldw transport from the guiana basin north of the equator flows eastward in the northern brazil basin and is inferred to continue on through the romanche fracture zone into the eastern atlantic an opposing flow of mdw from the eastern tropical atlantic flows toward the western boundary where it bifurcates to supply mdw to the deep western boundary current dwbc of the brazil basin as well as to feed the northward flow of mdw in the guiana basin offshore of the dwbc the magnitude of each of these oppositely directed flows is roughly 7 sv we furthermore speculate that they are connected predominantly by upwelling from ldw to mdw within the low latitude eastern basin the overall deep water transport system below 2000 m in the western basins of the mid and low latitude atlantic is thus found to comprise the following three distinct components 1 a strong dwbc transport of ldw with associated recirculation dominates the guiana basin north of the equator 2 in the northern brazil basin just south of the equator a narrow eastward flow absorbs the ldw and carries it eastward while a somewhat broader westward flow imports mdw into the western basin 3 this mdw flow then bifurcates with the southward branch causing the mdw dominance in the brazil basin where the mdw dominated dwbc and associated recirculations are the third component of the deepwater transport system

eastward flow through the mid atlantic ridge at 11 n and its influence on the abyss of the eastern basin abstract the dilute antarctic bottom water of the north atlantic eastern trough is supplied from the western trough through fractures in the mid atlantic ridge in particular the influence on eastern trough property distributions of flow through the romanche and vema fracture zones near the equator and 11 n respectively has been noted previously here new observations are reported that document the abyssal circulation of the northeastern atlantic basins gambia abyssal plain south canary basin and north canary basin in particular the dominance of vema influence the absence of romanche influence and the existence of a system of deep western boundary currents and estimated transport deep isopycnals slope steeply across the vema s eastern end near 39 w corresponding to a geostrophic transport through the vema of 2 1 to 2 3 106 m3s 1 colder than 2 0 c this is half or more of the estimated bottom water that flows north across the equator into the subtropical western north atlantic this transp

deep flow along the western boundary south of the blake bahama outer ridge abstract in june july 1990 hydrographic chlorofluorocarbon cfc and velocity observations were taken along the western boundary of the north atlantic south of the blake bahama outer ridge from 30 to 24 n between the northern bahamas and 71 w the deep flow in the region associated with the deep western boundary current forms a pattern of strong narrow currents and cyclonic gyres close to the continental slope with broad slower southward flow offshore the cfcs reveal that the most recently ventilated water i e having the highest cfc concentrations due to more recent contact with the atmosphere in the northern north atlantic is found along the western boundary in two distinct cores between potential temperatures 4 6 c and 1 9 2 4 c geostrophic transport streamlines were constructed for the deep flow referenced using direct velocity observations at 26 5 n and assuming mass conservation between closed areas bounded by the hydrographic sections the tracers and transports are used together

on the baroclinic instability of cold core coupled density fronts on a sloping continental shelf a theory is presented to describe the linear baroclinic instability of coupled density fronts on a sloping continental shelf the new baroclinic model equations used to study the instability process correspond to an intermediate lengthscale dynamical balance specifically the frontal dynamics while geostrophic is not quasigeostrophic because frontal height deflections are not small in comparison with the frontal scale height the evolution of the frontal height is strongly coupled to the geostrophic pressure in the surrounding slope water through the hydrostatic balance which expresses the continuity of the dynamic pressures across the frontal interface the deeper surrounding slope water evolves quasi geostrophically and is coupled to the front by baroclinic vortex tube stretching compression associated with the perturbed density front allowing the release of mean frontal potential energy and the topographic vorticity gradient associated with the sloping bottom it is shown that the baroclinic stability characteristics are principally determined by a so called non dimensional interaction parameter denoted p which physically measures the ratio of the destabilizing baroclinic vortex tube stretching compression to the stabilizing topographic vorticity gradient for a given along front mode wavenumber it is shown that a minimum p is required for instability several other general stability results are presented necessary conditions for instability growth rate and phase speed bounds the existence of a high wavenumber cutoff and a semicircle theorem for the unstable modes the linear stability equations are solved exactly for a parabolic coupled density front and a detailed description of the spatial and temporal characteristics of the instabilities is given for physically realistic parameter values the instabilities are manifested as amplifying topographic rossby waves in the slope water and on the density front the unstable perturbations take the form of amplifying anticyclones which have maximum amplitude on the offshore side

observations of internal wave reflection off sloping bottoms current and temperature spectra exhibit intensification and polarization near sloping bottoms over a band of frequencies centered at the local internal wave critical frequency examples are drawn from a variety of island seamount and continental slope observations waves propagating down from mid depth change energy density wave number and azimuth when they reflect off the bottom providing a natural perturbation to the deep ocean interior internal wave spectrum deviations from linear theory are interpreted as evidence for dissipation through subsequent shear instability and or nonlinear interaction topographic features appear likely to be energy sinks for internal wave energy

characterization and origin of aluminous a type granites from the lachlan fold belt southeastern australia the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are a distinctive group of igneous rocks on the basis of chemical and mineralogical criteria those granites that contain 65 72 sio2 can be distinguished from other types on the basis of higher abundances of fetotal fetotal mg high field strength elements trivalent rare earth elements ga and zn mineralogically they contain fe rich hydrous mafic minerals and primary ilmenite and hence are reduced relative to the ni nio buffer however the extremely felsic a type granites sio2 72 have the same chemical and mineralogical characteristics as felsic fractionated i type granites recent analyses indicate that the lachlan fold belt a type granites have sc f alkali element trace transition element and h2o contents similar to those of other unfractionated i type granites rb sr and nd sm isotopic compositions are highly variable probably reflecting source region heterogeneity the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are distinct from peralkaline rocks in terms of chemical composition petrography and field associations although these rocks have been grouped together as a single type in current classification schemes we propose that the metaluminous to weakly peraluminous a type granites such as those of the lachlan fold belt should be defined as aluminous a type granites and should not be grouped with peralkaline granites the lachlan fold belt aluminous a type granites have relatively high calculated zircon saturation temperatures we suggest that these granites were produced by high temperature partial melting of a felsic infracrustal source

geochronology and geochemistry of the late triassic longtan pluton in south china termination of the crustal melting and indosinian orogenesis the indosinian orogeny is recorded by triassic angular unconformities in vietnam and south china and by widely occurring granitoids in the yunkai nanling and the xuefengshan belts of south china the longtan pluton in the northwestern part of the xuefengshan belt is a typical high k calc alkaline i type granitoid which can shed light on the relationship between the indosinian tectonic and magmatic activity in the region three precise zircon u pb ages yielded a mean of 218 0 8 ma which is taken as the age of crystallization the pluton consists of both granodiorite 64 59 68 01 sio2 and 3 25 4 22 k2o and granite 70 49 71 80 sio2 and 4 07 4 70 k2o the granodiorites are characterized by relatively high mg 54 57 low contents of na2o 3 2 4 3 wt low abundances of incompatible elements lile nb and p high initial 87sr 86sr 0 7175 0 7184 and negative end t 9 98 to 9 72 ree patterns show moderate fractionation la yb cn 8 07 18 80 with negative eu anomalies eu eu 0 62 0 86 compared with the granodiorite the granite has a wider range of mg 49 59 lower contents of na2o 2 8 4 2 wt higher initial 87sr 86sr 0 7232 0 7243 and more negative end t 12 07 to 11 24 values ree patterns are relatively flat la yb cn 14 73 29 37 with smaller negative eu anomalies eu eu 0 48 0 63 the granodiorite has lower k2o na2o and al2o3 mgo feotot values than the granite based on major and trace element geochemistry and sr nd isotopes we interpret the longtan granodioritic magma to have been derived by partial melting of interlayered proterozoic metabasaltic to metatonalitic source rocks whereas the granite was probably derived from a mixture of proterozoic metagraywackes and metaigneous rocks field petrographic and geochemical evidence indicate that partial melting and fractional crystallization were the dominant mechanism in the evolution of the pluton the longtan granodiorites and granites are petrologically and geochemically similar to typical indosinian varieties and are considered to have been produced in a similar manner the indosinian granitoids in the region show a magmatic peak age of 238 ma from the yunkai nanling belt in the southeast and a magmatic peak age of 218 ma of the xuefengshan belt to the northwest these early and late magmatic episodes of the indosinian granitoids also display slight variations of regular compositions end t values and t dm ages thus we propose a syncollisional extension model that indosinian granitoids were generated by decompressional partial melting of crustal materials triggered by two extensions during collision of the indochina and south china blocks the longtan pluton in the northwesternmost part of the orogenic belt marks the termination of the indosinian magmatism and orogenesis

magma sources for mesozoic anorogenic granites of the white mountain magma series new england usa the magma sources for granitic intrusions related to the mesozoic white mountain magma series in northern new england usa are addressed relying principally upon nd isotopes many of these anorogenic complexes lack significant volumes of exposed mafic lithologies and have been suspected of representing crustal melts sm nd and rb sr isotope systematics are used to evaluate magma sources for 18 felsic plutons with ages ranging from about 120 to 230 ma the possibility of crustal sources is further examined with analyses of representative older crust including paleozoic granitoids which serve as probes of the lower crust in the region multiple samples from two representative intrusions are used to address intrapluton initial isotopic heterogeneities and document significant yet restricted variations 1 in end overall mesozoic granite plutons range in end t from 4 2 to 2 3 with most 2 to 0 and in initial 87sr 86sr from 0 7031 to 0 709 the isotopic variations are roughly inversely correlated but are not obviously related to geologic geographic or age differences older igneous and metamorphic crust of the region has much lower nd isotope ratios with the most radiogenic paleozoic granitoid at end 180 ma of 2 8 these data suggest mid proterozoic separation of the crust in central northern new england moreover the bulk of the mesozoic granites cannot be explained as crustal melts but must have large mantle components the ranges of nd and sr isotopes are attributed to incorporation of crust by magmas derived from midly depleted mantle sources crustal input may reflect either magma mixing of crustal and mantle melts or crustal assimilation which is the favored interpretation the results indicate production of anorogenic granites from mantle derived mafic magmas

petrogenesis of the red mountain pluton laramie anorthosite complex wyoming implications for the origin of a type granite abstract the red mountain pluton the youngest intrusion in the laramie anorthosite complex is one of five monzonitic to granitic a type plutons intruded at 1 43 ga in the laramie mountains of southeastern wyoming the red mountain pluton ranges in composition from fayalite monzonite clinopyroxene quartz monzonite and biotite hornblende quartz syenite to granite the red mountain pluton is petrologically and geochemically distinct from the northern and southern sherman batholith the sybille intrusion and the maloin ranch pluton it has higher feo t feo t mgo and higher k 2 o is more strongly enriched in rees and at any given silica content it has lower abundances of tio 2 feo mgo cao and p 2 o 5 the fayalite monzonite in the red mountain pluton crystallized at temperatures around 1000 c and oxygen fugacities 1 2 log units below that of the fmq buffer similar to the crystallization conditions of the sybille and maloin ranch plutons the biotite hornblende quartz syenite crystallized at oxygen fugacities near or slightly below those of fmq most of the units in the pluton carry mantle like nd sr and pb isotopic compositions similar to the least contaminated anorthositic and ferrodioritic rocks of the lac indicating that the pluton evolved mainly via differentiation substantial crustal assimilation occurred only in the late dikes and the granite we suggest that all of the 1 43 ga a type intrusions in southeastern wyoming are ultimately derived from tholeiites extreme differentiation or partial melting produced monzonitic magmas that have assimilated varying amounts of siliceous crust the differences between the red mountain pluton and other a type granitoids in southeastern wyoming are related to the extent of differentiation prior to crustal assimilation the compositional ranges of a type granitoids in southeastern wyoming suggest that the geochemical spectrum of a type granites worldwide similarly are produced from evolved mantle derived melt that has assimilated varying proportions of crustal material

hydrography of the romanche and chain fracture zones the romanche and chain fracture zones rfz and cfz are known as pathways for the lower north atlantic deep water lnadw and the antarctic bottom water aabw from the western trough to the eastern trough of the equatorial atlantic ocean across the mid atlantic ridge we report hydrographic observations describing the evolution of the lnadw and aabw properties during their transit through the equatorial fracture zones to the west of the rfz and cfz sills the lnadw and aabw cores are separated by a deep thermocline pycnocline which marks the transition between the two water masses the deep thermocline is eroded eastward and vanishes in the eastern basin this zonal asymmetry is the signature of a zonal baroclinic pressure gradient associated in each fracture zone with eastward flows of lnadw and aabw below 3800 m depth during the eastward transit through the rfz the near bottom aabw becomes less dense saltier 0 07 and warmer 0 7 c richer in oxygen 0 3 ml l 1 but less rich in silicate 30 mol l 1 simultaneously the lnadw core becomes fresher and colder at a given density and the oxygen maximum characterizing the lnadw core weakens by 0 2 ml l 1 we argue that the property changes within the aabw and lnadw are due to intense vertical mixing in addition to vertical mixing with the aabw it seems likely that isopycnal mixing of the lnadw with the eastern basin deep water contributes to the property evolution of the lnadw exiting the rfz in the cfz evidence is also given of mixing occuring within the aabw and the lnadw a sudden change in the aabw properties observed across the cfz main sill suggests the blocking of the eastward progression of the densest aabw by the cfz main sill however this dense water can reach the eastern basin by flowing northeastward through valleys the sills of which are deeper than thoses of the cfz finally a simple hydraulic control model applied to the rfz and cfz flows predicts a transport of 1 4 0 1 106 m3 s 1 of water colder than 1 9 c across the rfz cfz main sill

a type granitoids from the eastern pontides ne turkey records for generation of hybrid a type rocks in a subduction related environment the eastern pontides is characterized by the many of intrusive bodies formed throughout the late mesozoic early cenozoic most of these are i type granitoids but here we present for the first time an a type pluton from the region to assess source characteristics and geodynamic implications the a type pirnalli pluton has a shrimp zircon u pb age of 81 2 1 ma it is composed of granite syenite and quartz monzonite and its enclaves are monzonitic in composition with elevated ga al ratios and low mg 42 the pluton is dominantly metaluminous a cnk 0 88 to 1 00 and belong to shoshonitic and ultra potassic series the samples are highly enriched in lree and show significant negative eu eu eu 0 33 to 0 92 ba nb sr and ti anomalies in the spidergrams the host rocks and their enclaves posses quite similar sr nd isotopic compositions isr 0 70693 to 0 70736 end 81 ma 2 6 to 2 0 tdm 0 94 to 1 12 ga pointing to a lower crustal parental magma with a minor contribution of lithospheric mantle we hypothesize that upwelling of asthenosphere triggered melting of chemically enriched upper mantle and basic magma formed melting of lower crust was provided by the underplating of this basic magma mixing between lower crust and mantle derived melts at depths of lower crust appears to be most reasonable petrogenetic process responsible for generation of the pluton sr nd isotope modeling suggests mixing of 82 90 of the lower crustal derived melt with 10 18 of the mantle derived melt then the hybrid melt ascended to shallower crustal level and underwent a limited fractionation process to generate a variety of rock types our data also suggest that the a type pirnalli pluton likely formed at an extensional environment of active continental margin throughout the late cretaceous ongoing extension then led to opening of black sea as a back arc basin further north of the eastern pontides

generation of metaluminous a type granites by low pressure melting of calc alkaline granitoids melting experiments on two calc alkaline rocks a tonalite and a granodiorite demonstrate that shallow dehydration melting of hornblende and biotite bearing granitoids generates metaluminous a type granitic melts profuse crystallization of calcic plagioclase orthopyroxene during low pressure p 4 kbar incongruent melting explains all of the major and trace element characteristics of a type granites e g their low al ca mg sr and eu contents and high ga al and k na ratios as well as their common association with anorthositic and mangeritic rocks the residual assemblage produced during melting of the same rocks in the deep crust p 8 kbar is dominated by clinopyroxene and as a consequence most of the chemical features diagnostic of a type granites are lost the high temperatures 900 c and low h 2 o contents 4 wt that are characteristic of a type magmas are adequately explained by the h 2 o poor nature of the granitoid source materials and require neither a granulitic nor a f rich source previous attempts to explain the origin of a type granites have focused on the nature of the source material these experiments show that pressure of melting is at least as important as source composition in engendering a type melts

transport of bottom water in the romanche fracture zone and the chain fracture zone abstract two moored arrays deployed in the romanche fracture zone and chain fracture zone in the equatorial atlantic ocean provide two year long time series of current and temperature in the lower north atlantic deep water and the antarctic bottom water total time averaged transport of antarctic bottom water potential temperature 1 9 c across the mid atlantic ridge amounts to 1 22 106 m3 s 1 eastward with a standard deviation of 0 25 106 m3 s 1 a time averaged transport of 0 36 0 23 106 m3 s 1 eastward is found for the lower north atlantic deep water in the 1 9 2 1 c temperature range but this may represent only a fraction of the total flow of this water mass across the ridge contributions of the romanche fracture zone and chain fracture zone to the antarctic bottom water transport are similar while the chain fracture zone has the greater share of lower north atlantic deep water transport semiannual and annual periods are detected in the transport time series and together expl

measured and modeled cfc distribution of lower north atlantic deep water in the guiana basin the circulation of the overflow lower north atlantic deep water olnadw in the guiana basin is studied by the measured and modeled distribution of the chlorofluorocarbon component cfc 11 the olnadw is formed in the northern atlantic and transported south to the equatorial region as the densest part of the deep western boundary current dwbc characterized by cfc and oxygen maxima some former studies proposed a northwestward recirculation of the boundary current in the guiana basin because the measured southeastward dwbc transport was larger than the calculated net transport across the entire width of the basin despite the variability of the dwbc reported recently this discrepancy seems to hold an advective diffusive model is presented which includes recirculation in the northern guiana basin as well as horizontal diffusion and the results are compared with a cfc survey in march 1994 because of high cfc concentration in the boundary current one would expect to find a high cfc signal in the recirculated water mass near the mid atlantic ridge as well however this was not observed modeled cfc distributions and observations only agree if the presumed recirculation is located in the center of the northern guiana basin or if no westward recirculation exists at all it was found that the strength of the recirculation is about 3 1 5 sv which is smaller than previously supposed

petrogenesis and tectonic implications of neoproterozoic highly fractionated a type granites from mianning south china abstract the origin of neoproterozoic intrusions ca 860 750 ma along the western part of the yangtze craton has been the subject of debate in recent years with two competing models proposed the plume model argues for an extensional setting and emphasizes the role of a superplume in the rodinia breakup whereas the arc model argues for the presence of a subduction zone in the yangtze craton as a contribution to this animated dispute geochronologic and geochemical analyses have been carried out on the mianning granite which is the largest pluton 700 km2 in the northern kangdian rift of the western yangtze craton it is shown that the mianning granites were emplaced at ca 780 ma and display highly fractionated feature i e sio2 75 wt eu eu 0 03 0 50 enrichment of k rb th u zr hf y and rees depletion of nb ta ba sr p eu and ti they are metaluminous to strongly peraluminous a cnk 0 93 1 55 and contain abundant perthite and minor alkali riebeckite and sphene sharing the petrological and geochemical characters of a2 type granites positive nd t 2 97 5 24 and zircon hf t 9 2 12 1 values are consistent with a derivation by partial melting of a relatively young crust formed about 1000 900 ma given the general absence of a type granites in arc settings the mianning a type granites are suggestive of an anorogenic crustal extensional environment for the western yangtze craton during the neoproterozoic the data presented in this study are therefore consistent with an intracontinental rift model but are not sufficient to identify plume involvement in the neoproterozoic magmatism

saline outflow from the arctic ocean its contribution to the deep waters of the greenland norwegian and iceland seas abstractsince 1985 various investigators have proposed that norwegian sea deep water nsdw is formed by mixing of warm and saline deep water from the arctic ocean with the much colder and fresher deep water formed by convection in the greenland sea gsdw we here report on new observations which suggest significant modification and expansion of this conceptual model we find that saline outflows from the arctic ocean result in several distinct intermediate and deep salinity maxima within the greenland sea the southward transport of the two most saline modes is probably near 2 sv mixing of gsdw and the main outflow core found over the greenland slope derived from about 1700 m in the arctic ocean cannot by itself account for the properties of nsdw instead the formation of nsdw must at least in part involve a source which in the arctic ocean is found below 2000 m the mixing of various saline outflows is diapycnal while significant nsdw production appears to occur in northern fram strait large amounts of saline arctic ocean outflow also traverse the western greenland sea without mixing and enter the iceland sea during the past decade deep convection in the greenland sea has been greatly reduced while deep outflow from the arctic ocean appears to have continued resulting in a markedly warmer slightly more saline and less dense deep regime in the greenland sea american geophysical union 1991

transequatorial flow of antarctic bottom water in the western atlantic ocean abyssal geostrophy at the equator abstract in its general northward flow along the western trough of the atlantic antarctic bottom water aabw must pass over several sills separating the various abyssal basins at the equator the western trough is deformed by major east west offsets of the mid atlantic ridge and the continental margin of brazil forming a newly zonal abyssal channel about 250 km wide centered at the equator and extending approximately 1000 km along its axis in which the aabw is confined thus the general northward flow of aabw is topographically constrained to be westward as it crosses the equator a hydrographic section across this channel at 37 w shows the aabw isopycnals to be bowl shaped within and beneath the level of the channel walls the equatorial geostrophic relation permits us to compute a zonal velocity from the well defined parabolic distribution of dynamic height relative to a reference level at the transition between aarw and the overlying deep water here 4 3 106 m3 s 1 is estimated for the wes

application of proton microprobe data to trace element partitioning in volcanic rocks abstract in situ proton microprobe analyses are used to calculate partition coefficients d for mn fe cu zr ga rb sr y zr ba and pb and more restricted data for ni ge nb and as in pyroxenes olivines biotites hornblendes feldspars and fe ti oxides from 32 volcanic rocks all with glassy matrices these range from leucitite and picritic basalt to high silica and peralkaline rhyolites data for pigeonite aenigmatite allanite and leucite are included where these occur as additional phases coefficients have also been rayleigh fractionation corrected this correction being significant for those elements with high coefficients in specific mineral phases and where pronounced crystallisation has occurred partition coefficients are presented as plots vs nbo t ratios of coexisting glasses melts negative correlations are observed based on log transformed data for mn zn fe and y pyroxenes mn zn and fe olivines mn and zn fe ti oxides nb y sr and zr hornblendes sr plagioclase and ba cu zn and fe feldspars these element partition coefficients are not correlated with bulk mineral compositions zr and ga are not correlated with either glass or mineral compositions except zr in hornblende the correlations support the role of melt polymerisation in controlling element partitioning at least for those elements listed although possible effects of temperature cannot be uniquely isolated in the present data set the coefficients presented here are generally consistent with published values for equivalent rock compositions one difference being that some of the higher published coefficients e g sr in plagioclase are not matched in the present data set from a practical viewpoint the relative regularity of the coefficient data presented does facilitate choice of relevant coefficient values that are required for petrogenetic modelling procedures

structure of the deep spillway in the western part of the romanche fracture zone structure of the deep spillway was studied on the basis of conductivity temperature depth lowered acoustic doppler current profiler and mooring measurements in 2011 2014 in the romanche fracture zone 22 27 22 32 w the spillway exists quasi permanently in the regime of hydraulic control overflow and consists of two flows in the layer 1 20 c deeper than 4 150 m the first flow enters the fracture from the south through a gap in the southern wall the second flow is directed to the east along the narrow valley of the fracture the sill depths of these passages are 4 570 and 4 430 m respectively the depths over the surrounding ridges are shallower than 4 100 m both flows descend to the local depression of the fracture with 5 000 m depth bottom potential temperatures over both sills were 0 51 c and the measured velocities were 20 40 cm s when the flows descend down the slope they accelerate in supercritical regime maximal measured velocities were up to 65 cm s analysis of the 189 day time series of velocities on the mooring deployed in the flow descending from the gap showed a very high level of fluctuation energy 10 times greater than the energy of the barotropic tide at this point the only energy source of these fluctuations is the available potential energy of the deep thermocline in the west atlantic transforming to the kinetic energy of the deep spillway the total transport of the bottom water below 1 2 c based on the lowered acoustic doppler current profiler measurements is estimated at 0 29 0 35 sv which agrees with the predicted values

nd isotope evidence for crust mantle interaction in the generation of a type granitoid suites in labrador canada early proterozoic a type granite suites in labrador northeastern canada have initial nd isotopic compositions that lie between those of a depleted mantle reservoir and the local basement rocks one of these a type granite suites consists of a linear array of discrete plutons that crosses the boundary between an archean craton and an adjoining early proterozoic crustal block the nd of these granites at formation t 1720 ma changes from 8 to 4 across this boundary reflecting changes in the nature and antiquity of the continental crust however in both domains the granites cannot be derived entirely by anatexis of the local basement rocks and apparently require significant amounts of juvenile mantle derived material a type granites have been widely interpreted as anatectic derivatives of lower crustal rocks that were depleted by previous melt extraction the nd isotopic data suggest that these labrador examples were instead mixtures of mantle derived magmas and overlying lower crustal rocks and that new material may have been the volumetrically dominant component 50 90 in most cases as an alternative to the prevalent residual source model it is proposed that the distinctive geochemical characteristics of these a type granites are a function of the high liquidus temperatures and primitive mg rich character of subcrustal magma fluxes in post orogenic and anorogenic environments where such magmas are emplaced into stabilized continental crust further nd isotope studies of other a type granite suites are required to ascertain if models invoking crust mantle interaction are more widely applicable

a type granite of the hasan robat area nw of isfahan iran and its tectonic significance abstract the late precambrian hasan robat granite occurs in the northwestern part of the sanandaj sirjan zone nw of iran the granitoid rocks are composed of biotite bearing syenogranite alkali feldspar granite and minor amount of monzogranite the main minerals are quartz microcline plagioclase albite oligoclase green biotite and amphibole ferrohornblende with subsolvus to subordinate hypersolvus affinities chemically the rock suite is characterized by high sio2 fe mg total alkali k2o na2o zr nb y hf ta ga al and ree except for eu and low contents of mgo cao p2o5 and sr they display a type characteristics being ferroan alkali calcic to calc alkalic and metaluminous to peraluminous with minor of peralkaline nature crystallization of such magmas has produced the iron enrichment and alkali composition of the hasan robat granite which likely occurred in an extensional environment low abundances of ba sr p ti eu the positive correlation between ba and eu anomalies and the negative correlation between rb and k rb reveal fractional crystallization of alkali feldspar produced at the final compositions of these granites the low ratios of y nb

numerical simulations of the baroclinic dynamics of density driven coupled fronts and eddies on a sloping bottom numerical simulations of the baroclinic dynamics of density driven coupled fronts and eddies are described the simulations are based on a two layer intermediate length scale model which filters out barotropic instability and focuses on the subinertial baroclinic evolution of density driven flows within the context of allowing finite amplitude height variations in the lower layer the baroclinic destabilization of a bottom trapped coupled front on a sloping bottom is described in the overlying fluid the instability takes the form of amplifying topographic rossby waves in the coupled front the perturbations to the downslope incropping are preferentially amplified compared to those on the upslope incropping the perturbations to the downslope incropping develop into downslope propagating plumes which eventually evolve into relatively coherent along slope propagating domes we discuss the propagation characteristics of these domes we also simulate the evolution of density driven eddies or domes the first eddy simulation we describe is for an initial eddy configuration which satisfies a zero topographic rossby wave condition in the upper layer we show that these traveling solutions remain remarkably coherent over a period of about 40 eddy circulation times or about 250 days for typical continental slope values for a sufficiently large initial eddy height upper layer fluid parcels can be transported in the along slope direction by the baroclinic eddy we also simulate the evolution of an initial eddy configuration which does not satisfy a zero topographic rossby wave condition in the upper layer a relatively intense cyclonic circulation develops in the overlying fluid over the traveling dome as does a topographic rossby wave tail however even these solutions remain surprisingly coherent over many eddy circulation times

detection and processing of bistatically reflected gps signals from low earth orbit for the purpose of ocean remote sensing we will show that ocean reflected signals from the global positioning system gps navigation satellite constellation can be detected from a low earth orbiting satellite and that these signals show rough correlation with independent measurements of the sea winds we will present waveforms of ocean reflected gps signals that have been detected using the experiment onboard the united kingdom s disaster monitoring constellation satellite and describe the processing methods used to obtain their delay and doppler power distributions the gps bistatic radar experiment has made several raw data collections and reflected gps signals have been found on all attempts the down linked data from an experiment has undergone extensive processing and ocean scattered signals have been mapped across a wide range of delay and doppler space revealing characteristics which are known to be related to geophysical parameters such as surface roughness and wind speed here we will discuss the effects of integration time reflection incidence angle and examine several delay doppler signal maps the signals detected have been found to be in general agreement with an existing model based on geometric optics and with limited independent measurements of sea winds a brief comparison is presented here these results demonstrate that the concept of using bistatically reflected global navigation satellite systems signals from low earth orbit is a viable means of ocean remote sensing

the atlantic deep western boundary current water masses and transports near the equator the distributions and transports of deepwater masses at the western boundary in the tropical atlantic off brazil have been studied on three surveys along 35 degrees w and 5 degrees s and one at 10 degrees s transports are obtained from direct measurements of the velocity fields pegasus profiling system and lowered acoustic doppler current profiler and from geostrophic computations using chlorofluoromethane cfm and hydrographic distributions four water masses could be identified forming the north atlantic deep water nadw system two of these have a high cfm content the shallow upper nadw sunadw and the overflow lower nadw olnadw these exhibit the highest velocity signals at 35 degrees w where distinct flow cores seem to exist most of the southeastward flow of the sunadw centered around 1600 m occurs 320 km offshore between 3 degrees 09 s and 1 degrees 50 s 9 7 3 3 sv farther north in that section a highly variable reversing flow is found in a second velocity maximum the transport of olnadw centered around 3800 m of 4 6 2 6 sv is guided by the parnaiba ridge at 1 degrees 45 s 35 degrees w the water masses located between the two cfm maxima the labrador sea water lsw and the lnadw old water mass lnadw old did not show any persistent flow features however a rather constant transport of 11 1 2 6 sv was observed for these two layers the total southeastward flow of the nadw at 35 degrees w showed a transport of 26 8 7 0 sv if one neglects the reversing sunadw north of 1 degrees 50 s at 5 degrees s the flow of all deepwater masses shows vertically aligned cores the main southward transport occurred near the coast 19 5 5 3 sv the boundary current is limited offshore by a flow reversal present in all three surveys but located at different longitudes at 10 degrees s a southward transport of 4 7 sv was observed in november 1992 however the section extended only to 32 degrees 30 w so that probably a significant part of the flow has been missed an important result is the large transport variability between single cruises as well as variability of the spatial distribution of the flow at 35 degrees w which could lead to large uncertainties in the interpretation of single cruise observations despite these uncertainties we suggest a circulation pattern of the various deepwater masses near the equator by combining our mean transport estimates with other observations

crossing of the equator by the deep western boundary current in the western atlantic ocean abstract property distributions and geostrophic shear from a hydrographic section near 37 w in the atlantic ocean show the deep western boundary current dwbc in the north atlantic deep water nadw established against the western boundary of the brazil basin immediately south of the equator between 2 and 5 s the dwbc thus has directly crossed the equator to the south atlantic following the east southeast trend of the continental slope isobaths the estimated dwbc transport of nadw is 35 106 m3 s 1 similar to other estimates from the tropics discussed here these large dwbc transports are opposed by flow of deep water to the north atlantic immediately offshore of the dwbc with as much as two thirds of the dwbc transport being returned as these recirculations one recirculation center is the guiana basin north of the equator but extends at least a few hundred kilometers south of the equator another is visible at 11 s in the brazil basin the degree of connection of these two observed recirculatio

abyssal ocean overturning shaped by seafloor distribution the abyssal ocean is broadly characterized by northward flow of the densest waters and southward flow of less dense waters above them understanding what controls the strength and structure of these interhemispheric flows referred to as the abyssal overturning circulation is key to quantifying the ocean s ability to store carbon and heat on timescales exceeding a century here we show that north of 32 s the depth distribution of the seafloor compels dense southern origin waters to flow northward below a depth of about 4 kilometres and to return southward predominantly at depths greater than 2 5 kilometres unless ventilated from the north the overlying mid depths 1 to 2 5 kilometres deep host comparatively weak mean meridional flow backed by analysis of historical radiocarbon measurements the findings imply that the geometry of the pacific indian and atlantic basins places a major external constraint on the overturning structure

chronology geochemistry and sr nd isotope studies of jurassic intrusions in the diyanqinamu porphyry mo mine central inner mongolia china abstract available cores of porphyritic granite and aplitic granite from the diyanqinamu porphyry mo deposit in the north central great xing an range presented an opportunity to examine and analyze mesozoic igneous rocks far from the paleo pacific subduction zone the diyanqinamu granites are highly fractionated i type distinguished from the m a or s type granite by high sio 2 and rb low zr nb y and ce low fe 2 o 3 total mgo and k 2 o na 2 o cao ratios low alumina saturation index sr ratios 0 70137 0 70451 positive e nd t values 2 37 3 77 and negative correlation between p 2 o 5 and sio 2 the aplitic granites were generated by fractional crystallization of the porphyritic granite as evidenced by spatial proximity consistent zircon u pb ages 156 ma within error correlations between other oxides and sio 2 in haker diagrams low ba sr nb p ti eu linear relationship in both la yb n vs la and sr vs ba diagrams and decreasing lree and ree with increasing sio 2 the diyanqinamu granites have young depleted mantle two stage model ages avg t dm2 660 ma similar to those of most mesozoic voluminous felsic magmas in northeastern china and were likely sourced from pre existent crustal components both old and juvenile that had been juxtaposed during the tectonic evolution of the paleo asian ocean these granites project in the transitional field from syn collision to post collision tectonic settings on tectonic discrimination diagrams implying emplacement in an extensional environment extensional volcanism and basin formation in the great xing an range region in late jurassic is coeval with the diyanqinamu granites demonstrating that post orogenic lithospheric extension related to the closure of the mongol okhotsk ocean was the main driving force for late jurassic magmatism in this region

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

genesis of the graphite orbicules in the huangyangshan graphite deposit xinjiang china evidence from geochemical isotopic and fluid inclusion data abstract the huangyangshan graphite deposit in the east junggar orogen china contains intriguing graphite orbicules this contribution is designed to present reasonably comprehensive assessment of their origin in this deposit the intrusive orebodies are mechanically juxtaposed against contacts with granitic wall rocks the orbicules are typically concentrically zoned in texture with a notable binary configuration involving a central core and an outer shell the orbicule cores possess mineralogical and compositional variations that are more or less similar to those of the granitic wall rocks the orbicule shells are composed of various ferromagnesian minerals clinopyroxene hornblende in stark contrast to the matrix where hornblende sanidine and albite have higher mg ab and an values respectively the replacement of silicates by graphite and sulfides pyrrhotite chalcopyrite pyrite is common the graphite throughout the matrix and orbicules features a patchy distribution of major elements c and dispersed elements cr ni co s cu zn as pb etc the carbon isotopic compositions of the orbicular ore are 20 9 to 20 5 analogous to those of the surrounding strata i e 25 6 to 19 3 the sulfur isotopic compositions of sulfides in the orbicular ore are 4 8 to 2 6 which differ from those of the surrounding strata i e 16 0 23 0 fluid inclusions principally comprise the volatile component ch4 and solid daughter minerals graphite chalcopyrite with tm 450 c vapor liquid two phase fluid inclusions formed under conditions of th 143 6 367 5 c p 3 194 bar and fo2 52 76 to 31 15 the hydrogen and oxygen isotopic values of the orbicular ore are d 110 3 to 107 0 and 18owater 10 1 11 7 zircons from the orbicular ore have 206pb 238u ages of 304 359 ma with a weighted average of 319 0 6 4 ma overlapping the geochronological age of the granitic host rocks 305 1 321 4 ma the orbicular ore has sio2 concentrations ranging from 53 30 to 72 61 wt falling within the compositional fields of granite quartz monzonite granodiorite diorite and monzodiorite in the tas classification diagram the sr nd and hf isotopic data from the orbicular ore indicate mixing between materials derived from the depleted mantle and materials derived from the crust with a dominant mantle contribution the petrographic geochemical isotopic and fluid inclusion characteristics indicate that the processes of incorporation of h2o and wall rock fragments liquid immiscibility and exsolution of a late magmatic fluid were responsible for orbicule formation in the huangyangshan deposit the following genetic model is proposed 1 in the late carboniferous a new orbicular magma containing organic matter derived ch4 and deep mantle so2 emplaced within the huangyangshan pluton contemporaneously crystal fragments and h2o were incorporated into the orbicular magma from the granitic host rocks 2 h2o saturation was reached in the orbicular magma and fostered segregation of a hydrous ferromagnesian melt orbicules with a silicic residual melt matrix 3 at approximately 630 c 2000 bar and 18 lgfo2 graphite and sulfides formed en masse through deuteric alteration 3ch4 2so2 2 fe2 7 si4o11 2 oh 2 hornblende 3c graphite 2fes pyrrhotite 8sio2 quartz 2 fe3si4o10 oh 2 fe3 oh 6 chlorite following the expulsion of a late magmatic fluid from the ferromagnesian melt

zonal circulation across 52 w in the north atlantic 1 in july august 1997 a hydrographic acoustic doppler current profiler adcp tracer section was occupied along 52 w in the north atlantic as part of the world ocean circulation experiment hydrographic program underway and lowered adcp ladcp data have been used to reference geostrophic velocities calculated from the hydrographic data additional small velocity adjustments provided by an inverse model constraining mass and silicate transports in 17 neutral density layers yield the absolute zonal velocity field for 52 w we find a vigorous circulation throughout the entire section with an unusually strong gulf stream 169 sv and southern deep western boundary current dwbc 64 sv at the time of the cruise at the northern boundary on the west side of the grand banks of newfoundland we find the westward flowing labrador current 8 6 sv whose continuity from the labrador sea east of our section has been disputed directly to the south we identify the slopewater current 12 5 sv eastward and northern dwbc 12 5 sv westward strong departures from strictly zonal flow in the interior which are found in the ladcp data make it difficult to diagnose the circulation there isolated deep property extrema in the southern portion associated with alternating bands of eastward and westward flow are consistent with the idea that the rough topography of the mid atlantic ridge directly east of our section causes enhanced mixing of antarctic bottom water properties into overlying waters with distinctly different properties we calculate heat and freshwater fluxes crossing 52 w that exceed estimates based on air sea exchanges by a factor of 1 7

the intrusion of a density current along the coast of a rotating fluid when light rotating fluid spreads over heavier fluid in the vicinity of a vertical wall coast a boundary jet of width forms the leading edge or nose of which propagates with speed along the coast a certain fraction 8 of the boundary transport is not carried by the nose but is deflected backwards detrained and left behind the propagating nose theoretical and experimental results for and are given for a quasi equilibrium constant regime over longer time intervals the laboratory observations suggest that the nose slows down and stagnates whereupon the trailing flow separates from the coast and an intermittent boundary current forms these processes may be relevant to the mixing of oceanic coastal currents and the maintenance of the mean current

vapor absent melting at 10 kbar of a biotite and amphibole bearing tonalitic gneiss implications for the generation of a type granites vapor absent melting experiments on a biotite and amphibole bearing archean tonalitic gneiss agc150 at 10 kbar and 875 to 1050 c show that amphibole breaks down from 900 to 950 c producing garnet orthopyroxene and granitic melt biotite dehydration melting produces 10 wt melt up to 950 c via incongruent melting reactions that produce garnet orthopyroxene and titanomagnetite widespread biotite dehydration melting occurs between 950 and 975 c and produces orthopyroxene magnetite titanomagnetite and 20 wt fluorine rich melt up to 0 31 wt f minor f rich 2 7 wt biotite is present even at 1000 c our experiments show that under vapor absent conditions intrusion of hot mantle derived magmas into the lower crust is necessary to initiate widespread biotite dehydration melting in rocks with compositions like agc150 we propose that the high thermal stability of biotite in agc150 suggests that this rock is residual after a previous episode of partial dehydroxylation that left behind somewhat f enriched biotite we show that dehydration melting of such f enriched biotite produces f rich granitic liquids with compositions within the range of a type granite and leaves behind a granulitic residue consisting of orthopyroxene plagioclase quartz titanomagnetite and magnetite

antarctic bottom water flux in the equatorial western atlantic a moored array at the equator in the western basin of the atlantic provides a 604 day time series of abyssal currents and temperatures spanning the full breadth of the antarctic bottom water aabw flowing from the brazil basin to the guiana basin mean aabw transport is estimated to be 2 0 sv sv 106 m3 s21 comprising organized westward flow of 2 24 sv and return flow of 0 24 sv the low frequency variability is dominated by a quasi annual transport cycle of amplitude 0 9 sv and a 120 day period of amplitude 0 6 sv maximum transports occur in september october while minimum transports occur in february march allowing for this quasiannual cycle and extrapolating the 604 day record to a full two years adds about 7 to the estimated mean aabw transport the array also provides limited sampling in the overlying lower north atlantic deep water lnadw where a southern boundary intensified flow of lnadw gives the strongest recorded mean speed through the array 9 9 cm s21 into the brazil basin the lnadw records also have a quasi annual cycle with strong lnadw flow episodes occurring in april may time series of temperature indicate that the lnadw aabw transition layer rises and falls in synchrony with the quasi annual aabw transport cycle uplifted transition layer during strong aabw transport periods an observed overall warming trend appears to be accompanied by a decline in aabw transport

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

savers a simulator of gnss reflections from bare and vegetated soils the mean power of the reflected global navigation satellite system gnss signals acquired by a gnss reflectometry gnss r receiver can be modeled through the integral bistatic radar equation by weighting the contributions of all scatterers on the surface by the system impulse response the geophysical properties of the scattering surface affect the magnitude of the reflected navigation signals through the bistatic scattering coefficient which in case the observed surface is land is a function of the soil dielectric properties surface roughness and vegetation cover in this paper the gnss r signal simulator developed in the framework of the land monitoring with navigation signal leimon project supported by european space agency is presented the simulator is able to predict the power reflected by land taking as input the system and observation parameters as well as the land surface parameters the latter are used to simulate both the coherent and the incoherent scattering taking advantage of widely used theoretical models of bistatic scattering from bare soils and vegetated surfaces first the geometrical formulation is discussed and then the problem of polarization mismatch due to real antennas at circular polarization is faced following the polarization synthesis approach finally a comparison with some experimental data collected during the leimon campaign is presented the simulations display the same trend of the experimental data thus showing that the simulator can be used as an efficient tool for the interpretation of gnss r measurements

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

mineralization of biogenic materials in the water masses of the south atlantic ocean i assessment and results of an optimum multiparameter analysis abstract this is the first of two manuscripts dealing with the circulation mixing ventilation and organic matter mineralization of the south atlantic ocean sao the present work quantifies the complex mixing of water masses in the sao using a constrained least squares regression optimum multiparameter omp analysis the omp based on temperature salinity silicate and the conservative parameter no was applied on two world ocean circulation woce lines a17 and a14 in the western and eastern sao respectively the constrained omp sensitivity to sources of error in the end member characteristics measured parameters equation weights and oxygen to nitrogen mineralization ratio rn was carefully assessed using perturbation tests perturbation of rn was the only test that changed significantly the mixing proportions although by less than 5 the constrained omp method allowed defining the realm and identifying the core of flow of each water mass to study its circulation the evolution of its chemical composition and eventually to separate the contribution of physical and biogeochemical processes relevant specific outputs of this first manuscript are 1 north of the south equatorial current the silicate maximum is primarily composed of antarctic intermediate water aaiw rather than circumpolar deep water cdw 2 the two degree discontinuity tdd experiences a dramatic meridional change of water masses composition being dominated by north atlantic deep water nadw north of the vema channel and by cdw southwards 3 the 50 proportion horizon of weddell sea deep water wdsw with a of 0 3 c at the entry of the sao defines the upper limit of the wsdw realm more properly than the classical isopycnals of 46 04 or 46 06 4 where the proportion of wsdw is around 75

geochemistry of cretaceous granites from mianning in the panxi region sichuan province southwestern china implications for their generation abstract the cretaceous granites of mianning located in the northern panxi region were emplaced after collision of the tibetan plateau and yangtze block these granites have very high k 2 o na 2 o ga zr nb y ree except eu and very low mgo cao p 2 o 5 and sr contents relative to m i or s type granites based on the chemical discrimination criteria of whalen et al whalen j b currie k l chappell b w 1987 a type granites geochemical characteristics distribution and petrogenesis contributions to mineralogy and petrology 95 407 419 most of them are a type granites moreover the granites plot in the range of post collision granites and belong to the a2 type elevated initial sr isotopic ratios 0 72 suggest their derivation dominantly from a crustal source these features are consistent with granite formation in a post orogenic setting such as after subduction or collision between of the tibetan plateau and yangtze block in addition the granites are characterized by low abundances of ba sr p ti and eu positive correlation between ba and eu anomalies and negative correlation between rb and k rb plots of rb vs sr suggest that fractional crystallization affected the final compositions of these granites after melting from a dominantly crustal source from the late proterozoic to late mesozoic the crustal composition compared to that of the mantle appears to have increased in the panxi region while the mantle component played an important part in the generation of cretaceous granites in southeastern china its influence was relatively minor in the panxi region thus there was a significant difference in mantle evolution between southeastern china and the panxi region which led to different metallogenic processes

scobi veg a generalized bistatic scattering model of reflectometry from vegetation for signals of opportunity applications scobi veg stands for signals of opportunity coherent bistatic scattering model for vegetated terrains it simulates polarimetric reflectometry of vegetation canopy over a flat ground using a monte carlo scheme the model is aimed at assessing the value of navigation and communication satellite signals of opportunity in a range of frequencies from p to s bands for remote sensing of a number of geophysical land parameters such as soil moisture and biomass a fully polarimetric expression for bistatic scattering from a vegetation canopy is first formulated for a general case and is then specialized to the practical case of ground based low altitude platforms with passive receivers overlooking vegetation using the signals transmitted from large distances using analytical wave theory in conjunction with distorted born approximation the transmit and receive antenna effects i e polarization crosstalk mismatch orientation and altitude are explicitly accounted for the forward model developed here enables the understanding of the effect of different geophysical parameters and system configurations on the coherent and incoherent components of the reflected signatures it can thus help developing robust inverse algorithm for extraction of soil moisture and biomass the model is applied to p band signals of geostationary communication satellites to describe polarimetric reflections from tree canopies as observed from down looking platforms at various altitudes the relative contributions of diffuse and specular scattering on total reflected power and reflectivity are quantified for various observing scenarios

western boundary current structure and variability east of abaco bahamas at 26 5 n abstract during april 1987 to june 1988 a four mooring transport resolving current meter array was deployed in a section extending 70 km eastward from abaco bahamas at 26 5 n mean currents in the upper layer 800 m showed a clockwise rotation that appears to be associated with a small scale quasi permanent anticyclonic gyre centered just northeast or the bahamas deep mean currents were persistenly southward and indicated a strong deep jet the deep western boundary current dwbc reaching core speeds of 20 cm s 1at 2500 m depth about 25 km seaward of the western boundary vertically integrated meridional volume transport over the section showed a surprisingly large variability ranging from approximately 20 sv northward to 70 sv southward 1 sv 106m3s 1 the mean meridional volume transport was 30 sv to the south with about 3 sv flowing northward above 800 m which could be produced by a weak antilles current and 33 sv flowing southward below 800 m the deep southward transport of 33 sv i

an estimate of the upwelling rate in the equatorial atlantic based on the distribution of bomb radiocarbon and quasi geostrophic dynamics estimates of the near surface upwelling in the tropical atlantic ocean 15 s to 15 n made by broecker et al 1978 from a radiocarbon box model and by wunsch 1984 from a quasi geostrophic inversion differ considerably in the former case the range was estimated as about 17 20 sv while the latter obtained an absolute maximum of about 10 sv to understand these two apparently contradictory results 14c constraints were added to the inverse model with realistic estimates of the observational errors in all fields including the radiocarbon it is found that the radiocarbon constraints are consistent with the quasi geostrophic model and with an upwelling estimated as 7 10 sv the near surface circulation in the tropical atlantic is dominated by a northward flux of warm water across the equator necessary to feed the heat losses at high northern latitudes the 14c balance is maintained by the advection of southern hemisphere waters of comparatively low radiocarbon concentration into the tropical zone by upwelling from below of very low radiocarbon water and by its removal to the north also by advection the major uncertainty in the radiocarbon calculations derives from the sparcity of sampling so that very great extrapolations are required to estimate the zonal mean 14c concentrations and the time histories between the prebomb period and 1972

land geophysical parameters retrieval using the interference pattern gnss r technique in the past years the scientific community has placed a special interest in remotely sensing soil moisture and vegetation parameters radiometry and radar techniques have been widely used for years global navigation satellite systems opportunity signals reflected gnss r over the earth s surface are younger but they have already shown their potential to perform these observations this paper presents a gnss r technique based on global positioning system gps measurements that allows the retrieval of several geophysical parameters from land surfaces this technique measures the power of the interference signal between the direct gps signal and the reflected one after scattering over the land so it is called interference pattern technique ipt this paper presents the results obtained after applying the ipt for topography soil moisture and vegetation height retrievals over vegetation covered soils

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

tracer distributions and deep circulation in the western tropical atlantic during cither 1 and etambot cruises 1993 1996 this paper presents cfc and nontransient tracer observations in the western equatorial atlantic ocean on repeated sections along 7 30 n the 35 w meridian and a transect crossing the ceara rise three world ocean circulation experiment cruises have been carried out in this area in february march 1993 cither 1 and september october 1995 and april may 1996 etambot 1 and 2 together with the tracer data the direct current measurements are used to deduce the circulation pathways the data confirm the principal circulation features of the upper north atlantic deep water within the area the deep western boundary current flows southward along the continental slope while adjacent to the dwbc there is a northward flow corresponding to the dwbc recirculation whose origin appears variable the largest variability is observed along the 35 w meridional section where the dwbc bifurcates eastward north of 3 s but the eastward equatorial flow does not appear to be permanent at the middle north atlantic deep water level cfc distributions exhibit the most important contrast between waters of northern and southern origin the circulation at the lower north atlantic deep water level mainly controlled by the topography looks more permanent because the dwbc is regularly observed during the three cruises and there is no evidence for a northwestward recirculation along the mid atlantic ridge the transient behavior of cfc distributions which is superimposed on local circulation effects can be seen clearly through their temporal evolution within the dwbc the variability of the deep circulation observed during the 1993 1996 interval rules out a dominant variability in response to semi annual forcing

deep cross equatorial flow in the atlantic measured with sofar floats neutrally buoyant sofar floats at nominal depths of 800 1800 and 3300 m were tracked for 21 months in the vicinity of tropical boundary currents in the atlantic near 6 n and at several sites near 11 n as well as along the equator trajectories at 1800 m show a swift 50 cm s narrow 100 km wide southward flowing deep western boundary current dwbc extending from 7 n to the equator the average transport per unit depth in the dwbc was estimated to be 13 8 103 m2 s coupling this value with mean velocities measured in the dwbc by current meters gave a volume transport of 15 106 m3 s between depths of 900 m and 2800 m approximately 6 106 m3 s recirculated northward between the dwbc and the mid atlantic ridge leaving 9 106 m3 s as cross equatorial transport no obvious dwbc nor swift equatorial current was observed by the 3300 m floats a low mean velocity at this depth lay between f 11 and higher velocity cores above and below the 1800 m trajectories also suggest that at times february march 1989 the north atlantic deep water in the dwbc turned eastward and flowed along the equator and at other times august september 1990 the dwbc crossed the equator and continued southward the velocity near the equator calculated by grouping floats in a box along the equator was eastward at 4 1 cm s from february 1989 to february 1990 and westward at 4 6 cm s from march 1990 to november 1990 thus the amount of cross equatorial flow in the dwbc appeared to be linked to low frequency variability of the structure of the equatorial current system floats in antarctic intermediate water at 800 m revealed a northwestward western boundary current although flow patterns were complicated three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cm s six 800 m floats drifted eastward along the equator between 5 s and 6 n at a mean velocity of 11 cm s one reached 5 w in the gulf of guinea suggesting that the equatorial currents at this depth extended at least 35 40 along the equator three of these floats reversed direction near the end of the tracking period

tracing lower north atlantic deep water across the equator water whose ultimate source is the overflow at the denmark strait can be traced using maps of salinity dissolved oxygen and silica concentration on deep density surfaces south along the american continent to at least 5 s several property extrema whose resolution is at the limit of accuracy of the measurements occur on these density surfaces which nevertheless may indicate areas of stronger mixing along the crest of the mid atlantic ridge transport estimates for that part of the southward flow within 600 km of the western boundary near 10 n suggest that 10 3 106 m3 s 1 of lower north atlantic deep water moves south there the total southward deep water transport near 10 n is estimated to be closed to 25 106 m3 s 1