chlorofluorocarbons in the central north pacific and southward spreading time of north pacific intermediate water from august to october 1992 cross sections of chlorofluorocarbons cfcs trichlorofluoromethane cfc 11 and dichlorofluoromethane cfc 12 were obtained between 48 n and 15 s along 175 e in the central north pacific on the basis of the distribution of cfcs apparent ages of the north pacific intermediate water npiw along 175 e were determined for the isopycnal horizons of 26 40 to 27 40 the apparent age of npiw was usually older toward the south and with increase of along the section the oldest npiw on all isopycnal horizons in the north pacific was located near 10 n north of 20 n npiw on isopycnal horizons less than 26 80 outcrops in winter in subpolar regions and appears to have formed after 1970 it is suggested that npiw on isopycnal horizons less than 26 80 is laterally well mixed between subpolar and subtropical regions on timescales of a few decades npiw on isopycnal horizons greater than 26 80 near 37 n was older than its surroundings it is suggested that new npiw formed in the subpolar region is not transported directly southward and that the major current of npiw is zonal in the central north pacific flowing eastward in the subpolar region and then turning more to the south flowing toward 10 n near the eastern boundary thus we also estimated the zonal mean apparent ages of npiw the mean ages of npiw suggested that the apparent southward spreading rates and the apparent southward spreading times of npiw from the subpolar region to 10 n were approximately 80 170 km yr 1 and 20 45 years respectively it is concluded that the southward spreading time of npiw is a few decades at most

the tritium krypton 85 age of denmark strait overflow water and gibbs fracture zone water just south of denmark strait the opposite time trends of the input of tritium and 85kr to the surface ocean produce a tritium 85kr ratio for surface water that is a strong function of time and this ratio was used to determine the age of denmark strait overflow water dsow and gibbs fracture zone water gfzw just south of denmark strait dsow and gfzw were identified by their temperature salinity oxygen and silica characteristics in a section of stations 460 km south of denmark strait taken during the transient tracers in the ocean north atlantic study expedition in 1981 dsow was the densest water observed in the section and there were two types a low salinity type and a slightly higher salinity more dense type both types originated from arctic intermediate water aiw behind the greenland iceland ridge the tritium and 85kr data reveal that the low salinity type resided behind the greenland iceland ridge for about 1 year before flowing into the irminger sea compared to about 15 years for the higher salinity type the volume transport of the low salinity type of dsow was estimated to have a lower limit of 0 8 sv gfzw forms in the northeastern atlantic from a mixture of water flowing out of the norwegian sea at about 900 m depth and the northeastern atlantic water into which it flows about 70 of the tritium and 85kr burden of gfzw comes from northeastern atlantic water and 30 from norwegian sea water the age of gfzw just south of denmark strait relative to its formation in the northeastern atlantic is 7 5 4 6 5 years which corresponds to a mean current speed of 1 6 10 1 0 6 cm s

the sarcheshmeh porphyry copper deposit kerman iran a mineralogical analysis of the igneous rocks and alteration zones including halogen element systematics related to cu mineralization processes abstract the giant sarcheshmeh porphyry copper deposit is located 65 km southwest of kerman city southeastern iran numerous miocene porphyry stocks and dykes intruded thick sequences of upper cretaceous sedimentary and eocene volcanic rocks hypogene and supergene porphyry cu mineralization occurs within the granodioritic porphyry and host rock sequence which was extensively altered to a dominantly potassic phyllic and argillic assemblage with interstitial to distal propylitic types biotite bearing assemblages occur as both primary phenocrysts and secondary replacements showing variable size colour and shape fluorine contents 0 22 to 1 33 wt and x mg 0 54 to 0 71 in biotites from the potassic and phyllic zones are higher than those of non mineralized granitoids f 0 09 to 0 56 wt x mg 0 43 to 0 54 whereas their cl contents cl 0 05 to 0 24 wt are lower than those of the non mineralized granitoids cl 0 11 to 0 45 the biotites from the phyllic zone have higher log f h 2 o f hf and log f h 2 o f hcl values than those of the potassic zone as well as the granitoid and andesitic dykes the log f hf f hcl values determined for the granitoid potassic and phyllic zones are similar though more negative than those of the andesitic dykes the log f hf f hcl values have a similar range for biotite from the granitoid and potassic and phyllic zones the halogen fugacity ratios established for fluids associated with the sarcheshmeh deposit from their f and cl contents in biotite show that the granitoid potassic zone and phyllic zone are increasingly affected by meteoric waters the fluids that circulated in the phyllic zone are predominantly of meteoric origin possibly overprinting original phyllic zone halogen contents the cl intercept values of biotite in the granitoid and phyllic and potassic are similar to other ore forming systems and tend to be more cl rich than cl intercept values of biotites in common igneous rocks calculated f cl intercept values for biotite in the granitoid and potassic zone are also consistent with many other porphyry copper forming systems

in situ la mc icp ms trace element and nd isotopic compositions and genesis of polygenetic titanite from the baogutu reduced porphyry cu deposit western junggar nw china abstract titanite sphene catisio 5 is sensitive to changes in temperature oxygen and water fugacity and fluid composition in order to understand formation processes and the nature of hydrothermal fluids various types of titanite from cu ores at the baogutu reduced porphyry cu deposit were chosen for detailed study magmatic titanite is associated with biotite plagioclase and k feldspar whereas hydrothermal titanite occurs with k feldspar chlorite actinolite and calcite the formation of hydrothermal titanite was related to hydration of igneous minerals under high f h 2 o whereas the widespread replacement of ilmenite by titanite without magnetite indicates a relatively low oxygen fugacity magmatic titanite has low al high fe y sn zr nb and ree contents relative to hydrothermal titanite on the basis of the zr in titanite and al in chlorite geothermometers formation temperatures for magmatic and hydrothermal titanite are estimated to be 687 739 c and 250 670 c respectively the gradual decrease in ree y and sn contents from magmatic to late hydrothermal titanite was probably caused by precipitation of ree bearing minerals magmatic and hydrothermal titanites have similar chondrite normalized ree patterns with negative eu anomalies and relatively flat hree randomly selected titanites have nd isotopic compositions similar to the host rocks thus both magmatic and hydrothermal titanite are believed to have been predominantly derived from a mantle source

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

intra tooth isotope variations in late miocene bovid enamel from afghanistan paleobiological taphonomic and climatic implications abstract the rich mid turolian site of molayan afghanistan has yielded more than 100 mandibles from the bovid tragoportax afghanicus in this study we document different aspects of the paleobiology and paleoecology of this fossil bovid by examining patterns of inter and intra tooth carbon and oxygen isotopic analyses in m1 to m3 molars from five specimens accurate paleoecological and paleoclimatic inferences based on carbon and oxygen isotope analyses in fossil enamel are directly dependent upon the way in which teeth are sampled as well as taphonomic processes which are responsible for fossil accumulation because this sampling methodology provides a unique opportunity to detect seasonal changes in diet and environment during tooth formation it also offers the possibility of testing between catastrophic and progressive deposition at this site preservation of 13c and 18o values is shown to be good and permits inter individual comparisons of isotopic trends to be made timing of molar crown formation and enamel growth rate were deduced from the pattern of intra tooth carbon and oxygen isotope variation the pattern of 18o variation found in the first and second molars is similar in all the individuals which suggests that a single birth season occurred probably before the hot dry season large differences in average 18o values 2 5 are found within a single cohort and indicate that fossil accumulation was progressive rather than catastrophic the hypothesis that t afghanicus evolved in an open environment is supported by high 13c values in a c3 context increasing temperature and or aridity eastward along the greco irano afghan biogeographic province is strongly suggested by increasing 18o values between greece and afghanistan

using a cfc effective age to estimate propagation and storage of climate anomalies in the deep western north atlantic ocean 1 1990s chlorofluorocarbon cfc observations are used to estimate an effective age of 20 years for north atlantic deep water nadw at the equator the effective age is found by subtracting a relic age from pcfc 11 age the effective age is several to 10 years younger at the equator than other methods from the effective age equatorward effective spreading rates of 1 2 cm s are found which are similar for the nadw components effective spreading rates take into account recirculation gyres along equator flow and mixing which slow spreading of climate anomalies from the north atlantic to the southern hemisphere the difference between direct velocities and tracer effective spreading rates suggests that the buffering effect due to storage in the western north atlantic and equatorial region is about 20 years even so warming and freshening due to greenhouse gases will be first felt in the deep waters of the western north atlantic

chlorofluorocarbon derived formation rates of the deep and bottom waters of the weddell sea the spreading and mixing of deep and bottom waters from the weddell sea originating with potential temperature 0 c are investigated through analysis of new and historical cfc measurements we investigate the component that enters the southern indian ocean with a simple one dimensional advection diffusion model of the deep boundary current this model does not require a condition of mixing solely with tracer free water to be imposed as boundary conditions we derive time histories for the cfc concentrations of newly formed weddell sea deep and bottom waters a range of best fit velocities is obtained by determining which model velocities produce model tracer concentrations closest to measured concentrations from this we derive a formation rate of 3 2 1 5 sv for the waters originating with temperatures lower than 0 c that subsequently enter the southern indian ocean this compares to an upper limit for these waters of 5 7 sv derived from the cfc 11 cfc 12 ratio whilst the former value is dependent on the highly idealized concepts of the model used the latter is a more robust upper limit using the cfc 11 cfc 12 ratio measured at vema channel during the world ocean circulation experiment cruise a23 an upper limit of 0 9 sv is derived for the formation rate of waters colder than 0 c that enter the south atlantic overall an upper limit of 6 6 sv is derived for the rate of formation of the deep and bottom waters of the weddell sea a better representation is obtained by combining the upper limit to the south atlantic component with the model derived southern indian ocean estimate we thus estimate the formation rate of the deep and bottom waters in the weddell sea to be 3 7 1 6 sv whilst the range obtained is large and the assumptions implicit in the calculations are potentially significant we believe this more realistically represents the true formation rate than estimates derived using an imposed condition of tracer free mixing the range can be narrowed in future as more data become available

geochronology and isotope geochemistry of the baogutu porphyry copper deposit in the west junggar region xinjiang china abstract the baogutu copper deposit a newly discovered middle sized porphyry copper deposit is located in the west junggar region of xinjiang nw china baogutu is associated with a late carboniferous intrusive complex that was emplaced into lower carboniferous volcano sedimentary strata the intrusive complex comprises main stage diorites and minor late stage diorite porphyries their intrusive activity occurred in 313 0 2 2 ma to 312 3 2 2 ma based on u pb zircon sims analyses molybdenite separated from ore bearing quartz veins yields re os model ages from 309 4 4 4 ma to 314 1 4 5 ma with a weighted mean age of 312 4 1 8 ma biotites separated from fresh diorite and hydrothermal breccias in main stage diorites yield 40ar 39ar plateau ages of 308 26 1 88 and 305 69 1 76 ma respectively these dates obtained from three independent dating techniques constrain the ore forming age of the baogutu deposit stable isotopes h o s and radiogenic isotope pb have been used to discriminate the sources of the ore forming fluid at baogutu the 18o 1 14 1 74 and d 74 to 98 data indicate that the water of the ore forming fluids was derived from magmatic water the 34s values 0 24 to 0 4 show that the sulfur isotope composition of the ore fluids is characterized by magma sulfur lead isotope compositions 206pb 204pb 17 92 18 89 207pb 204pb 15 45 15 62 208pb 204pb 37 68 38 36 indicate that the lead of the ore fluids is derived from the mantle these data confirm the occurrence of a cu au mo mineralizing event at late carboniferous in the baogutu region and the ore forming fluids are mainly derived from the mantle the event is inferred to be associated with late carboniferous junggar oceanic crust subduction

tracing the thermohaline circulation in the western north atlantic using chlorofluorocarbons abstract measurement of chlorofluorocarbons cfcs f 11 and f 12 were obtained from vertical sections extending across the deep western boundary current dwbc along the western margin of the north atlantic ocean between 32 45 n in 1983 and 1986 these sections revealed an upper and a deep cfc maximun with highest concentrations along the continental slope the upper maximum had a potential temperature ranging from 4 2 4 6 c a core density of 1 5 34 56 and occurred at a depth of about 800m adjacent to the continental slope water with classical labrador sea water s characteristics occurs just above the cfc minimum between the upper and lower maxima and indicates that a significant volume of classical labrador sea water has not entered the region south of the grand banks for the last 3 decades the deep cfc maximum is from dense water overflowing the greenland iceland scotland ridge it occurred at about 3500m depth and had a potential temperature range of 2 02 2 18 c and a core density of 4 45 87 a source function of f 11 and f 12 for the deep maximum was estimated using temperature salinity and tracer data from previous studies the core of the dwbc defined by the deep cfc maximum was estimated to consist of roughly 2 3 gibbs fracture water and 1 3 denmark strait overflow water however 80 or more of the f 11 and f 12 signal was derived from denmark strait overflow water ages for the upper and lower cfc maxima in the dwbc were estimated from the cfc data these ages ranged from 11 12 years at the northernmost section to 18 years at the southernmost section for both features this corresponds to apparent mean current speeds of about 0 8cm s 1 for the upper maximum and 1 4cm s 1 for the deep maximum an age of 8 9 years with a corresponding apparent mean current speed of 2 2 2 5cm s 1 was also estimated for the deep cfc maximum from the observed increase in the f 11 concentration at 41 n between 1983 and 1986 the apparent mean current speeds are significantly less than current speeds measured with long term current meter moorings two reasons for this are 1 mixing between the dwbc core and adjacent water causes ages estimated from cfc data to be overestimated and hence the associated current speed to be underestimated pickart hogg and smethie 1989 and 2 water propagating along the western boundary spends some time in recirculation gyres the northern recirculation gyre south of the eastern north american continental margin is clearly apparent in the lateral distributions of f 11 and f 12 the apparent mean current speed in the northern recirculation gyre was estimated to be 1 3cm s 1 from the cfc data seaward of the dwbc north of the new england seamount chain high cfc low silica parcels of water were observed interspersed with low cfc high silica parcels of water along the bottom the high cfc low silica water is overflow water with a slightly greater component of denmark strait overflow water than contained in the dwbc deep cfc maximum the low cfc high silica water is of southern origin and has a component of antarctic bottom water

the origin of brown hornblende in the artfjallet gabbro and dolerites brown hornblende occurs in minor amounts in the artfjallet gabbro and dolerites except in quartz dolerites where a pale green hornblende occurs in the gabbro brown hornblende is mostly ti bearing pargasite or kaersutite it occurs along veins of orthopyroxene as rims around and blebs in pyroxenes with orthopyroxene in coronas between olivine and plagioclase and in coronas between ilmenite and plagioclase in the olivine dolerites and orthopyroxene dolerites brown hornblende is ferroan titanian pargasite or ferroan kaersutite the pale green hornblende in the quartz dolerites is a magnesio hornblende the hornblendes in the dolerites are interstitial or granular in some dolerites occurring as coarse oikocrysts it is proposed that under certain conditions the ti content of hornblende can be used as a thermometer derived from experimental data of helz 1973 microstructures compositions and formation temperatures 1 040 c show that the brown hornblende in the gabbro is not magmatic but of subsolidus origin probably it formed as a result of the introduction of water into the gabbro during a deformation event that occurred early in the cooling history of the gabbro least squares modelling of hornblende formation indicates that all magmatic minerals must have participated in the reaction and that the reaction probably was not isochemical microstructures compositions and formation temperatures 1 030 965 c of brown hornblende in the dolerites are consistent with late stage crystallization from the magma for the pale green hornblende in the quartz dolerites a magmatic origin is likely but cannot be proven

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

country rock contamination of magmas associated with the baogutu porphyry cu deposit xinjiang china abstract the baogutu porphyry cu deposit located in the west junggar region xinjiang china has the reduced mineralization features baogutu is associated with a late carboniferous intrusive complex that was emplaced into lower carboniferous volcano sedimentary sequences the complex consists of a main stage diorite stock and late stage diorite porphyry dikes the former hosts the most of the cu mineralization the main stage stock has a wide range of composition from minor gabbro through dominant diorite to tonalite porphyry these are all inhomogeneous over a few meters with no distinct boundary between the gabbro diorite and tonalite porphyry some felsic microgranular enclaves and heterogeneous phenocrysts occur in these rocks the latter is a single mineral with a range of compositions the elemental and sr nd compositions of the tonalite porphyry have a transitional character from the gabbro and diorite to the country rocks these findings suggest possible country rock contamination mineral composition data suggest that the primary magma at baogutu is oxidized i type magma the gabbro and diorite have high positive e nd t 3 3 to 6 0 and low initial 87 sr 87 sr ratios 0 7035 0 7038 and are characterized by moderately fractionated rare earth element ree patterns pronounced nb depletion and weak negative eu anomalies these observations suggest that the baogutu magmas were derived from partial melting of a metasomatized mantle wedge and underwent significant country rock contamination after emplacement the contamination process involved the felsic components and reduced materials e g carbonaceous sediment which caused the chemical variation of the baogutu rocks and the reduced mineralization features in the baogutu deposit thus contamination played an important role in the formation of the host rocks and associated mineralization at baogutu

testing the application of in situ sm nd isotopic analysis on detrital apatites a provenance tool for constraining the timing of india eurasia collision provenance tools are applicable to many problems in sedimentary geology as they help unravel the tectonic and metamorphic history of the hinterland and provide insights into the erosional pathways and origins of sediments in many cases it is more appropriate to use single grain approaches as opposed to bulk sediment methods in order to discover the precise input of the contributing geological terranes since the input of subordinate sources may not be detectable in bulk rock studies using a selection of modern river sediments we characterise the sm nd isotopic composition of individual detrital apatites from the main himalayan geological terranes our analyses allow us to effectively distinguish between apatites derived from the eurasian plate relatively high end values and low 147sm 144nd ratios from those derived from the indian plate low to high end values and moderate to high 147sm 144nd ratios we then apply this approach to tertiary indus basin sedimentary rocks to attempt to better determine the timing of india eurasia collision we find that detrital apatites in the tertiary indus basin have been sourced solely from eurasia lacking a mixed india eurasia provenance input which would document the india eurasia collision this study illustrates the use of this relatively novel provenance tool and provides a sound framework for similar studies in the future concerning the tectono metamorphic erosional evolution of the himalaya

feeding ecology of tragelaphini bovidae from the shungura formation omo valley ethiopia contribution of dental wear analyses abstract to better understand the environmental conditions that prevailed in the plio pleistocene shungura formation lower omo valley ethiopia we analyze the feeding preferences of tragelaphini the third most common tribe of shungura bovids molar mesowear and dental microwear texture analyses were applied to three species tragelaphus rastafari t nakuae and t gaudryi and body mass estimates were calculated for the t rastafari nakuae lineage to test whether dietary shifts were linked to body mass changes we compare our results with previous work on stable carbon isotopes 13c of enamel which indicated that tragelaphins from the shungura formation possessed dietary flexibility we found that the both the t rastafari nakuae lineage and t gaudryi maintained a mixed feeding dietary niche with varying proportions of c3 versus c4 inputs from 3 6 to 2 ma our results show that t rastafari consumed more browse than its descendant t nakuae which was a mixed feeder consuming a greater proportion of c4 dicots 2 8 ma the t rastafari t nakuae dietary shift may reflect environmental changes in the shungura formation during this time but appears to be offset from body mass increases in this lineage which occurred gradually through the plio pleistocene this study highlights the importance of a multi proxy approach to precisely determine the dietary ecologies of extinct bovids and points to how each proxy offers a slightly different perspective on the ecology of fossil organisms

time series measurements of transient tracers and tracer derived transport in the deep western boundary current between the labrador sea and the subtropical atlantic ocean at line w time series measurements of the nuclear fuel reprocessing tracer 129i and the gas ventilation tracer cfc 11 were undertaken on the ar7w section in the labrador sea 1997 2014 and on line w 2004 2014 located over the us continental slope off cape cod to determine advection and mixing time scales for the transport of denmark strait overflow water dsow within the deep western boundary current dwbc tracer measurements were also conducted in 2010 over the continental rise southeast of bermuda to intercept the equator ward flow of dsow by interior pathways the labrador sea tracer and hydrographic time series data were used as input functions in a boundary current model that employs transit time distributions to simulate the effects of mixing and advection on downstream tracer distributions model simulations of tracer levels in the boundary current core and adjacent interior shoulder region with which mixing occurs were compared with the line w time series measurements to determine boundary current model parameters these results indicate that dsow is transported from the labrador sea to line w via the dwbc on a time scale of 5 6 y corresponding to a mean flow velocity of 2 7 cm s while mixing between the core and interior regions occurs with a time constant of 2 6 y a tracer section over the southern flank of the bermuda rise indicates that the flow of dsow that separated from the dwbc had undergone transport through interior pathways on a time scale of 9 y with a mixing time constant of 4 y this article is protected by copyright all rights reserved

thermal tectonic history of the baogutu porphyry cu deposit west junggar as constrained from zircon u pb biotite ar ar and zircon apatite u th he dating abstract understanding postmineralization tectonic movements in porphyry deposits is critical to interpreting the complete thermal tectonic history this study reports new zircon u pb ages hydrothermal biotite 39ar 40ar age and zircon and apatite u th he ages from the baogutu porphyry copper deposit which in conjunction with pre existing geochronology and thermochronology and inverse modeling simulations constrain the thermal tectonic history of the deposit zircon la icp ms u pb concordia ages indicate a late carboniferous age of 320 1 2 2 ma for the diorite complex and 309 8 2 2 ma for the mineralized granodiorite porphyry hydrothermal biotite selected from a quartz biotite chalcopyrite vein yields a plateau age of 311 0 1 8 ma which agrees with the age of the granodiorite porphyry and a previously reported molybdenite re os age and suggests that hydrothermal fluid circulated about 310 m y ago diorite and granodiorite porphyry yield weighted mean zircon u th he ages of 200 6 5 7 ma and 241 1 8 1 ma respectively with ages ranging from 221 0 ma to 174 3 ma and 225 9 to 261 6 ma weighted mean diorite and granodiorite porphyry apatite u th he ages of 87 4 2 3 ma and 120 0 4 2 ma were obtained with ages ranging from 68 9 ma to 100 8 ma and from 91 0 ma to 152 0 ma respectively the wide range of zircon u th he ages may be due to the combined effects of u and th zonation and radiation damage and radiation damage effect may also account for the wide range of apatite u th he ages the combined effects of depth and cooling due to meteoric water circulation contribute to an older u th he age for the granodiorite porphyry relative to the diorite a five episode cooling rate history for the diorite can be deduced by inverse model simulation fast cooling moderate fast cooling relatively slow cooling fast cooling again very slow cooling the thermal and tectonic history of the wall rock indicates that it suffered significant far field effects from the qiangtang eurasia and lhasa qiangtang collision however no visible thermal effect from the india asia collision is observed

temperature and salinity variability in the deep western boundary current abstract a ten year time series 1984 1993 of repeat hydrographic sections from offshore abaco island the bahamas 26 5 n is used to define the mean and time dependent characteristics of the deep western boundary current dwbc the dwbc flow is divided into four vertical layers based on chlorofluorocarbon cfc concentration and formation regions upper layer cfc core 3 9 5 0 c second layer classical labrador sea water 3 2 3 9 c third layer cfc minimum 2 4 3 2 c deepest layer cfc core 1 85 2 4 c time series analysis of mean layer properties and their anomalies showed that the temperature and salinity of each layer did not increase or decrease monotonically with time variations in temperature and salinity were characterized by 2 3 yr period oscillations variability between years is illustrated by subtracting repeat sections of temperature and salinity along levels of both constant pressure and constant potential density to determine an original water mass modificati

a finfoot from the late miocene of toros menalla chad africa palaeobiogeographical and palaeoecological implications a fossil humerus from the hominid fossiliferous area of toros menalla ca 7 ma chad africa belongs to the heliornithidae aves gruiformes it is the second documented fossil record for the family and the first in the old world it is compared with all the living species the sungrebe heliornis fulica the masked finfoot heliopais personata and the african finfoot podica senegalensis it belongs to the genus heliopais and is very similar to the only species h personata the masked finfoot appears to have evolved little morphologically since the miocene this poorly known and threatened genus and species is today confined to tropical south east asia its presence in the late miocene of chad is a further asian element in the late neogene african avifaunas today the distribution of heliopais is highly relictual and some heliornithidae will certainly be encountered in the paleogene and the miocene deposits of the palearctic region the african finfoot is today the heliornithidae geographically the closest to the site area and occurs in forested regions south of the sahelian area apparently this genus was already absent further north where the asian genus was present in the late neogene palaeoecologically the presence of this heliornithidae is indicative for toros menalla of a freshwater body with thick overhanging vegetation and partly forested edges this kind of precise indication about a component of the palaeoenvironment is critical for the study of hominid sites and early hominid evolution a growing number of fossil birds from african hominid localities is yielding important clues regarding biogeography and environment

the interaction of recirculation gyres and a deep boundary current abstractmotivated by the proximity of the northern recirculation gyre and the deep western boundary current in the north atlantic an idealized model is used to investigate how recirculation gyres

relative oxidation states of magmas inferred from ce iv ce iii in zircon application to porphyry copper deposits of northern chile major and trace element compositions of zircons and whole rocks from 14 barren and seven ore bearing calc alkaline intrusions from the chuquicamata el abra porphyry copper belt of northern chile have been measured in situ by excimer laser ablation ela icp ms these data permit the ce iv ce iii ratio within zircon to be calculated using a lattice strain model for mineral melt partitioning of ce iv and ce iii zircon ce iv ce iii and eun eun ratios and by inference magmatic oxidation states generally increase from older mafic to younger felsic units within this sequence porphyry copper mineralization is directly associated only with intrusions with zircon ce iv ce iii 300 and eun eun 0 4 such trends can be understood in terms of interdependent relations between oxygen fugacity sulfur speciation and solubility and chalcophile element partitioning in silicate magmas because zircon occurs in most calc alkaline intrusions and is resistant to subsolidus alteration zircon ce iv ce iii ratios provide a useful tool for evaluating the economic potential of such rocks for magmatic hydrothermal cu au mineralization the approach is general and may provide a means to infer relative oxidation state in a wide range of intermediate to felsic igneous rocks

tracer dating and ocean ventilation the interpretation of transient tracer observations depends on difcult to obtain information on the evolution in time of the tracer boundary conditions and interior distributions recent studies have attempted to circumvent this problem by making use of a derived quantity age based on the simultaneous distribution of two complementary tracers such as tritium and its daughter helium 3 the age is defined with reference to the surface such that the boundary condition takes on a constant value of zero we use a two dimensional model to explore the circumstances under which such a combination of conservation equations for two complementary tracers can lead to a cancellation of the time derivative terms an interesting aspect of this approach is that mixing can serve as a source or sink of tracer based age we define an idealized ventilation age tracer that is conservative with respect to mixing and we explore how its behavior compares with that of the tracer based ages over a range of advective and diffusive parameters transient tracers such as tritium and tritiugenic helium 3 chlorofiuorocarbons especially cfc 11 and cfc 12 and radiocarbon produced by nuclear bomb tests have entered the oceans primarily during the past 30 years the inherent time scale of these tracers matches very well typical time scales for thermocline ventilation as well as other important oceanic processes such as deep water formation they have been used with some success to study the time scales of thermocline ventilation e g sarrniento 1983 jenkins 1987 and oxygen utilization rates our e g jenkins 1977 1980 1982 1987 as well as other processes such as equatorial upwelling rates broecker et al 1978 quay et al 1983 wunsch 1984 and transport of upper north atlantic deep water weiss et al 1985 the problem of coping with the nonsteady state aspect of these tracers has been dealt with in many ways few of them truly satisfactory for example rooth and ostlund 1972 chose to estimate the diapycnic diffusivity in a region where there was some evidence that the tracer distributions were approximately in steady state at the time of their measurements wunsch 1984 used a similar steady state assumption in his study of equatorial upwelling using bomb radiocarbon such an argu ment cannot be applied in most regions of the ocean however indeed one can question whether it applies even in the above situations therefore one generally would expect that it would be necessary to know something about the evolution of the tracer concentration in time as well as the time history of the boundary conditions for that tracer over the same span of time for example sarrniento s 1983 tritium box model of the thermocline solved the conserva tion equation for the period of time between 1952 before nuclear bomb tests had injected a significant amount of tritium into the oceans and 1972 when a single realization of the tracer field was obtained by a series of field studies the surface concentration time history of dreisigacker and roether 1978 was used as a boundary condition such an l now at deutsche forschungs und versuchasanstalt ftir luft

geology and palaeontology of the late miocene middle awash valley afar rift ethiopia the middle awash study area of ethiopia s afar rift has yielded abundant vertebrate fossils 10 000 including several hominid taxa1 2 3 4 the study area contains a long sedimentary record spanning late miocene 5 3 11 2 myr ago to holocene times exposed in a unique tectonic and volcanic transition zone between the main ethiopian rift mer and the afar rift sediments along the western afar rift margin in the middle awash provide a unique window on the late miocene of ethiopia these deposits have now yielded the earliest hominids described in an accompanying paper5 and dated here to between 5 54 and 5 77 myr these geological and palaeobiological data from the middle awash provide fresh perspectives on hominid origins and early evolution here we show that these earliest hominids derive from relatively wet and wooded environments that were modulated by tectonic volcanic climatic and geomorphic processes a similar wooded habitat also has been suggested for the 6 0 myr hominoid fossils recently recovered from lukeino kenya6 these findings require fundamental reassessment of models that invoke a significant role for global climatic change and or savannah habitat in the origin of hominids

experimental measurements of zircon melt trace element partition coefficients abstract zircon was grown from trace element doped hydrous peralkaline rhyolite melts with buffered oxygen fugacities in cold seal experiments at 0 1 and 0 2 gpa and 800 c and piston cylinder experiments at 1 5 gpa and 900 1300 c zircon and glass were present in all run products and small monazite crystals were present in eight of the 12 experiments average diameters of zircon crystals ranged from 5 to 20 m at 800 c to 30 50 m at 1300 c zircon crystals have thin rims and adjacent glass has a narrow 1 m thick compositional boundary layer concentrations obtained through in situ analysis of cores of run product zircon crystals and melt pools were used to calculate trace element partition coefficients dzircon melt for p sc ti v y la ce pr nd eu gd ho yb lu hf th and u in most cases lu was the most d 12 105 and la the least 0 06 0 95 compatible elements d values from this study fall within the range of previously measured values for rare earth elements ree however d values measured experimentally show less fractionation than those recently measured using natural phenocryst matrix pairs for example dlu dla measured experimentally in this study range between 27 and 206 compared to a value of 706 522 for a natural zircon dacite pair sano y terada k and fukuoka t 2002 high mass resolution ion microprobe analysis of rare earth elements in silicate glass apatite and zircon lack of matrix dependency chem geol 184 217 230 although d values from this study show good agreement with the lattice strain model d values from natural phenocryst matrix pairs combined with measured zircon compositions better reproduce host rock magma compositions of igneous rocks they also yield more reasonable estimates of magma compositions when combined with compositions of out of context zircons for example compositions of the hadean detrital zircons from jack hills australia yield lree enriched magmas when combined with d values from phenocryst matrix pairs yields but yield lree depleted magmas when experimentally determined d values are used we infer that experimentally measured dzircon melt values represent disequilibrium partitioning resulting from rapid zircon growth during short laboratory timescales rapid growth causes development of observed diffusive boundary layers in the melt adjacent to zircon crystals d values from phenocryst matrix pairs are therefore recommended for petrogenetic modeling

methane rich fluid evolution of the baogutu porphyry cu mo au deposit xinjiang nw china abstract baogutu is the first porphyry cu mo au deposit discovered in western junggar xinjiang nw china the ore bearing intrusion is a dioritic intrusive complex that includes stage 1 diorites and minor stage 2 diorite porphyries the stage 1 diorites have produced concentric potassic and propylitic alteration zone and overprinted phyllic alteration and host much of the cu mo au mineralization at baogutu the baogutu porphyry cu mo au deposit consists of unusually disseminated and minor vein style mineralization the fluid evolution occurred in stage 1 diorite from late magmatic stage to hydrothermal stage stages 1b and 1c is constructed based on alteration and fluid inclusion analysis by microthermometry raman spectroscopy and quadrupole mass spectrometer five fluid types are distinguished and they are l1 liquid rich 2 phase l2 liquid vapor 2 phase v1 vapor rich 2 phase v2 mono phase vapor and h multi phase solid the dominant inclusions rich in reductive ch4 plus h2o while minor inclusions rich in ch4 and co2 the inclusions in quartz from the late magmatic stage contain the most brine inclusions and less other inclusions with ch4 rich and h2o rich compositions the inclusions in quartz from stage 1b contain all fluid types and have ch4 rich and ch4 h2o compositions with rare co2 the inclusions in quartz from stage 1c are characterized by more vapor inclusions without brine inclusions and a clear co2 concentration in a few assemblages with ch4 co2 composition using microthermometry we estimate fluid trapping conditions at t 400 c and p 1500 to 3100 bar in late magmatic stage t 200 to 400 c and p 50 to 320 bar in disseminated quartz in stage 1b t 180 to 400 c and p 20 to 260 bar in vein quartz in stage 1b and t 170 to 400 c and p 20 to 230 bar in stage 1c such late magmatic conditions are compatible with the fluid evolution as a result of ch4 rich inclusions derived from mantle magma such hydrothermal conditions in stages 1b and 1c with small p t fluctuations are compatible with the dominant disseminated mineralization at baogutu that indicates a weak fracturing the overall fluid path at baogutu is toward lower pressure and small changed temperature with composition transit of fluid from a high halite ch4 rich system to low halite ch4 co2 system it may lead to the formation of this cu mo au deposit

sulfur partition coefficient between apatite and rhyolite the role of bulk s content experimental studies have been performed to constrain sulfur behavior during apatite crystallization and to determine sulfur partition coefficient between apatite and melt kd s apatite melt at oxidizing conditions crystallization experiments have been conducted with a hydrous rhyolitic melt and different bulk sulfur contents 0 15 to 2 wt s at 900 and 1 000 c 200 mpa and log f rm o 2 nno 3 6 the sulfur content in the glass increases with increasing amount of added s anhydrite crystallizes for s added 0 75 wt 0 10 and 0 13 wt so3 in glass at 900 and 1 000 c respectively the amount of anhydrite increases and the amount of apatite decreases with increasing amount of added sulfur the sulfur exchange reaction in apatite is influenced by the bulk composition of the melt e g p content however changing melt composition has only little effect on kd s apatite melt for the investigated rhyolitic composition the kd s apatite melt does not depend directly on temperature decreases from 14 2 to 2 7 with increasing s content in glass from so3 0 03 to 0 19 wt respectively and can be predicted from the following equation ln kd 0 0025 s in melt in ppm 2 9178 the combination of experimental data obtained for rhyolitic and andesitic melts reveals that the sulfur partition coefficient tends toward a value of 2 for high sulfur content in the glass 0 2 wt so3 using s in apatite as proxy for determining s content in melt is promising but additional experimental data are needed to clarify the individual effects of t f rm s 2 and p and ca content in the melt on s partitioning

variable regimes in magma systems documented in plagioclase zoning patterns el misti stratovolcano and andahua monogenetic cones abstract magmas may experience closed or open system evolution during their ascent and evolution in the upper crust chemically closed system processes can involve heat transfer from underplating mafic magmas or decompression due to magma ascent on the other hand newly injected magmas can mix with the residing magma and hybridize plagioclase zonation patterns and electron microprobe major and trace element analysis constrain these contrasting scenarios for andesites from the 80 km3 el misti stratovolcano 5822 m and a field of relatively small monogenetic andahua scoria cones both in southern peru in particular fe concentration in plagioclase reveals valuable information within a magmatic system to explore the dominance of closed vs open system processes large and correlated anorthite fe contrasts at resorption zones identify compositional mixing related to recharge subhorizontal an fe variations record thermal or water induced effects el misti volcano a large but still relatively youthful stratovolcano is dominated during most of its approx 120 ka history by closed system effects during its evolution recharge and mixing mostly occurred cryptically as it is not recorded in drastic compositional changes in magmas or their phenocrysts a small volume erupted at el misti however is affected by strong open system behaviour as reflected in strongly correlated variations in an and fe contents of plagioclase compositions its crystal population is texturally and chemically very similar to lavas of the monogenetic cinder cones of the andahua volcanic field for the el misti magma reservoir resorption events caused by thermal effects or magma ascent are more frequent in comparison to the actual eruption frequencies many cycles of closed system evolution heat transfer and decompression therefore occurred without resulting in an eruption plagioclase zonations from lavas of the monogenetic andahua field indicate that any mafic batch that intruded the much smaller reservoirs immediately triggered an eruption by contrast a large magma system that feeds el misti volcano can easily accommodate a new batch without causing eruption

rare earth elements in synthetic zircon part 1 synthesis and rare earth element and phosphorus doping zircon crystals were grown from a li mo flux 7 5 mol li2moo4 86 5 mol moo3 to which equal molar proportions zro2 and li2sio3 were added 3 mol each the crystals were initially grown undoped but later dy was added to the flux without any other charge compensating species with dy and p added in equal molar proportions the zircon crystals incorporated 1 37 mol 6 99 wt dy and 1 36 mol 1 33 wt p a factor of 5 3 increase in dy over the crystals grown without p intentionally added to the flux the other p ree doped zircon crystals displayed an approximately 1000 fold increase in ree and p from la through lu a result of decreasing ionic radii the incorporation of p5 allowed in a general sense the xenotime type coupled substitution of ree3 y3 p5 zr4 si4 from la to nd however p exceeds ree from sm to gd the ree are generally equal to p and from tb to lu the ree exceed p the y and p doped zircon behaved more like middle ree mree doped zircon than heavy ree hree doped zircon crystals in their ability to incorporate y and p and to maintain charge neutrality to investigate the incorporation of dy with no p added to the flux the p to lree excess and the hree to p excess in the doped zircon secondary ion mass spectrometry sims analyses were completed on selected crystals in the dy doped crystals the sims analyses revealed minor amounts of p li and mo in the crystals these elements contributed to charge balance required by the excess dy in ree and p doped zircon the sims analyses detected li and mo and the li and mo may also provide charge balance for excess ree in the hree p doped crystals

mineralogical evidence for crystallization conditions and petrogenesis of ilmenite series i type granitoids at the baogutu reduced porphyry cu deposit western junggar nw china mossbauer spectroscopy epm and la mc icpms analyses abstract primary ore forming minerals retain geochemical signatures of magmatic crystallization information and can reveal the petrochemical conditions prevalent at the time of their formation the baogutu deposit is a typical reduced porphyry cu deposit amphibole and biotite fe 3 fe ratios minerals feldspar biotite amphibole zircon and apatite in situ elemental and apatite nd isotopic compositions were determined by mossbauer spectroscopy electron probe microanalysis and laser ablation multiple collection inductively coupled plasma mass spectrometry respectively to investigate the magma oxidation state petrogenesis source features and to constrain the carbon species at magmatic stages for the intrusive phases the results show that the primary plagioclase and amphibole in the mineralized diorite to granodiorite porphyry and post ore hornblende diorite porphyry are distinct an 26 55 versus an 60 69 mg hornblende versus tschermakite in particular the amphibole shows distinct major and trace element compositions with light rare earth element enrichments and negative eu anomalies in mg hornblende and light rare earth element depletions and no eu anomalies in tschermakite all the analyzed biotites are primary igneous phases with a biotite phenocryst profile showing significant variations of zn cr sc and sr from core to rim these results may indicate the occurrence of mixing between two distinct magmas during mineral formation titanium in zircon and si in amphibole thermometries indicate that magma crystallized at 900 c and continued to 650 c in situ apatite nd isotope end t 5 6 7 6 t dm2 620 460 ma indicate absence of significant reduced sedimentary contamination and the source of juvenile lower crust slightly decreasing fe 3 fe ratios from biotite and amphibole to whole rock indicate decreasing oxygen fugacity during magma crystallization recalculated biotite compositions according to fe 3 fe ratios indicate f o 2 values of less than ni nio buffer nno which show slightly lower values than that estimated according to zircon melt distribution coefficients ce anomalies nno 0 6 these values are consistent with the features of reduced porphyry cu deposits crystallization of other mineral phases significantly affects the reliability of oxybarometer of zircon melt distribution coefficients eu anomalies and mn contents in apatite this oxidation state suggests that only co 2 was present at the magmatic stage and implies that ch 4 formed during co 2 reduction occurring later hydrothermal alteration the alteration of primary amphibole to actinolite released ti al fe mn na and k to the fluid with later precipitation of titanite albite and minor ilmenite and magnetite during actinolite alteration

sedimentary and rock magnetic signatures and event scenarios of deglacial outburst floods from the laurentian channel ice stream abstract eastern canadian margin sediments bear testimony to several catastrophic deglacial meltwater discharges from the retreating laurentide ice sheet the reddish brown plumite layers deposited on the levees of the laurentian fan valleys have been recognized as indications of multiple outburst floods between heinrich events 2 and 1 five event layers have been consistently recorded in three new gravity cores retrieved on the sw grand banks slope and comply with the previously published laurentian fan core md95 2029 the apparently huge extent of these outburst plumes around the laurentian fan as well as their causes and consequences are investigated in this study using physical properties rock magnetic and grain size analyses together with seismoacoustic profiling we provide the first detailed 14c ages of the outburst event sequence and discuss their recurrence intervals in the context of regional ice retreat compared to the hemipelagic interlayers event layers have overall uniform and systematic changes of rock magnetic properties hematite contents increase over time and proximally while magnetite grain sizes fine upwards and spatially away from the fan based on the sediment composition and load we argue that these plumites were formed by recurrent erosion of glacial mud deposits in the laurentian channel by meltwater outbursts three alternative glaciological scenarios are evaluated in each case the provenance of the transported sediment is not an indicator of the precise source of the meltwater

evolution of grasses and grassland ecosystems the evolution and subsequent ecological expansion of grasses poaceae since the late cretaceous have resulted in the establishment of one of earth s dominant biomes the temperate and tropical grasslands at the expense of forests in the past decades several new approaches have been applied to the fossil record of grasses to elucidate the patterns and processes of this ecosystem transformation the data indicate that the development of grassland ecosystems on most continents was a multistage process involving the paleogene appearance of c3 and c4 open habitat grasses the mid late cenozoic spread of c3 grass dominated habitats and finally the late neogene expansion of c4 grasses at tropical subtropical latitudes the evolution of herbivores adapted to grasslands did not necessarily coincide with the spread of open habitat grasses in addition the timing of these evolutionary and ecological events varied between regions consequently region by region investigations using both direct plant fossil

diatom phytolith and pollen records from a 10be 9be dated lacustrine succession in the chad basin insight on the miocene pliocene paleoenvironmental changes in central africa abstract a discontinuous 200 m long borehole drilled in the bol archipelago 13 n lake chad provided 25 samples which were dated using the 10 be 9 be method and analyzed for their micro biological content the dating provided ages ranging from 6 3 0 1 to 2 6 0 1 ma a period contemporaneous with the pliocene fossil localities located in the current djurab desert of chad 16 17 n well preserved diatom assemblages first occurred at 4 7 0 1 ma and were dominated by the freshwater planktonic genera aulacoseira and stephanodiscus until the end of the pliocene this supports the recurrence of lacustrine conditions at bol during all the pliocene the presence of pelite and argillaceous deposits in the core before 4 7 0 1 ma however suggests that the lake settled earlier at least since 6 3 0 1 ma the abundance of afromontane pollen taxa at 4 2 0 1 ma and the occurrence of trapeziform polylobate phytoliths throughout the sequence suggest significant vegetation inputs from the southern highlands while the importance of kaolinite in the clay sediments indicates a water supply predominantly from the south during the pliocene phytolith assemblages are all dominated by lobate grass silica short cells and by blocky and elongate types which attest to the presence of herbaceous dominated vegetation around bol and or in the southern drainage basin during the pliocene this result is also supported by the pollen assemblage described at 4 2 0 1 ma which shows highest affinity for the savanna biome moreover low values for the xerophytic grass phytolith index indicate the presence of humid loving mesophytic and aquatic grass communities in this vegetation at last significant variations in the abundance of blocky and elongate phytoliths are indicative of local alternations of fully lacustrine and marshy conditions at bol particularly between 3 6 and 2 7 ma the abundance of silicified bulliform cells combined with the absence of diatoms support a significant lacustrine reduction at bol favoring the increasing of local marshy vegetation

lagrangian observations of the deep western boundary current in the north atlantic ocean part i large scale pathways and spreading rates twenty six rafos floats were deployed in the deep western boundary current dwbc of the north atlantic ocean between the grand banks and cape hatteras in 1994 95 and tracked acoustically for up to two years half of the floats were launched in the upper chlorofluorocarbon cfc maximum associated with upper labrador sea water 800 m and the other half near the deep cfc maximum that identifies the overflow water from the nordic seas 3000 m the float observations reveal the large scale pathways of these recently ventilated water masses in the subtropics the shallow float tracks show directly that upper labrador sea water is diverted away from the western boundary and into the interior at the location where the dwbc encounters the gulf stream near 368n the crossover region consistent with previous hydrographic studies east of the crossover region only one upper labrador sea water float out of seven 15 permanently crossed to the south side of the stream in two years caught in a cold core ring formation event the other shallow floats recirculated north of the gulf stream apparently confined by the mean potential vorticity gradient aligned with the stream the deep floats closely followed the topography to the crossover region then revealed a bifurcation in fluid parcel pathways one branch continues equatorward along the western boundary and the other turns first eastward along the gulf stream path then southward the deep float pathways including the bifurcation in the crossover region can be explained in terms of the deep potential vorticity distribution comparison of the float results with results from recent modeling studies suggests that the deep flow is strongly influenced by both the depth of the main pycnocline and bottom depth the effective spreading rates of upper labrador sea water and overflow water estimated directly from the float data southward at 0 6 6 0 2 cm s21 and 1 4 6 0 4 cm s21 respectively agree well with tracer derived spreading rates mean velocities in the dwbc equatorward at 2 4 cm s21 upper labrador sea water and 4 5 cm s21 overflow water are consistent with other in situ measurements one deep float drifted almost 4000 km along the western boundary in two years revealing a fast track for the spreading of overflow water in the dwbc these observations emphasize the importance of the crossover region in the spreading and mixing of recently ventilated water masses addressed in part ii of this study

plagioclase zoning as an indicator of magma processes at bezymianny volcano kamchatka back scattered electron bse derived zoning patterns of plagioclase phenocrysts are used to identify magma processes at bezymianny volcano kamchatka based on the 2000 2007 sequence of eruptive products the erupted magmas are two pyroxene andesites which last equilibrated at 915 c temperature 77 87 mpa pressure and a water content of 1 4 wt textural and compositional zoning of individual plagioclase phenocrysts typically includes a repeated core to rim sequence of oscillatory zoning an50 60 truncated by a dissolution surface followed by an abrupt increase in an content up to an85 which then gradually decreases rimward this zoning pattern is interpreted to be the result of frequent replenishments of the magma chamber which cause both thermal and chemical interaction between resident and recharge magmas the outermost 70 to 150 m wide zoning patterns of plagioclase phenocrysts are composed of dissolution surface with a subsequent increase in an and fe contents zoning patterns of the rims exhibit correlation among plagioclase phenocrysts within one eruption rims are interpreted as a result of crystallization of a batch of magma in the conduit after recharge event

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

geochemical signature of porphyries in the baogutu porphyry copper belt western junggar nw china article i nfo the baogutu porphyry copper belt lies in the darbut transitional island arc of the western junggar in the western section of the central asian orogenic belt in nw china our new petrographic results for the ore bearing porphyry stocks in the baogutu porphyry copper belt recognize them as diorite porphyry stocks rather than the granodiorite porphyry stocks as previously identified the copper mineralization is hosted in the diorite diorite porphyries and related breccias of the diorite porphyry stocks geochemical data indicate that the ore bearing porphyries have a predominantly intermediate composition with a transitional character from tholeiite to calc alkaline and are enriched in large ion lithophile elements lile and depleted in highfield strength elements hfse with a clear negative nb anomaly ree patterns show distinctenrichmentsin lree relative to hree the rocks also exhibit high initial end t 2 7to 6 3 ratios and low initial 87 sr 86 sr values 0 70359 0 70397 many samples are chemically similar to adakites

genesis of oxidized and reduced type granites the genesis of oxidized type magnetite series and reduced type ilmenite series granites is discussed on the basis of thermodynamic considerations we show that so 2 in the magma can oxidize augite to form magnetite with decreasing temperature because the so 2 h 2 s buffer line intersects with the augite magnetite quartz buffer line on a 1 t f sub o 2 diagram when the magma contains so 2 above 250 ppm and the f sub o 2 is constrained by the so 2 h 2 s buffer the magma forms oxidized type granites 0 2 modal magnetite on the other hand when the so 2 content is less than 250 ppm the magma solidifies as a reduced type granite 0 2 modal magnetite if the f sub o 2 of the magmas is buffered by h 2 o h 2 co 2 co or ch 4 co 2 no magnetite will crystallize and reduced type granites will be formed as a result the genesis of oxidized type and reduced type granites can be attributed to the difference in volatile components in magmas

temporal evolution of the tracer signal in the deep western boundary current tropical atlantic four world ocean circulation experiment woce repeat cruises october 1990 to march 1994 in the tropical atlantic off brazil are used to study the spatial and temporal evolution of the chlorofluorocarbon cfc components cfc 11 and cfc 12 and tritium signal in the upper north atlantic deep water nadw its shallowest part located in the tropical atlantic around 1600 m depth is the shallow upper north atlantic deep water sunadw it is characterized by a distinct tracer maximum which is presumably received through winter time convection in the subpolar north atlantic here we discuss the tracer fields and the temporal evolution of the tracer signal of the sunadw in the tropical atlantic along two meridional sections at 44 degrees and 35 degrees w and two zonal sections at 5 degrees and 10 degrees s off brazil the spatial and temporal development of the tracer field in the tropical atlantic as well as the correlation with hydrographic parameters show that the temporal tracer change being due to the arrival of younger water is disturbed by other processes in particular the impact of variable mixing and spreading pathways on the observed tracer variability in the sunadw is evident in the observations

insights into the patterns and locations of erosion in the himalaya a combined fission track and in situ sm nd isotopic study of detrital apatite understanding the role that climate erosion and tectonics play in determining the mean relief elevation and general form of a mountain range over time has become the focus of much recent research in the field of tectonic geomorphology a crucial constraint in these studies is the long term exhumation rate which is increasingly being examined using detrital minerals from the sedimentary rock record that represent the eroded remnants of the orogen a classic field area of such studies is the himalayan orogen the earth s largest mountain range we describe here a novel approach that uses the in situ analysis of nd isotopes by laser ablation multicollector inductively coupled plasma mass spectrometry of fission track dated apatite grains to unambiguously tie them to their source regions we demonstrate the capability of this new approach on several modern and holocene river sand samples from the himalayan orogen and determine because of the large isotopic differences in the constituent tectonostratigraphic units both the location and magnitude of long term erosion in agreement with previous studies we are able to show that in the central and eastern himalaya long term denudation is focussed within the high himalayan crystalline series hhcs at average rates of not vert similar 2 mm yr average long term rates are similar in the western himalaya sampled by the indus river and largely reflect erosional denudation of the western indian himalaya and the western syntaxis the nanga parbat haramosh massif and south karakoram metamorphic complex notably the asian continent supplies significantly more apatites to the mouth of the indus than they do to the bengal delta the ability to reconstruct the patterns of long term erosion in the himalaya using detrital apatites from a few samples collected from major transverse drainages provides confidence in the utility of this approach to examine the locations and magnitude of long term erosion in the past

magma mixing controlling the origin of the early cretaceous fangshan granitic pluton north china craton in situ u pb age and sr nd hf and o isotope evidence abstract in situ u pb age and sr nd hf and o isotope analysis of accessory minerals zircon apatite and titanite have been obtained for mafic microgranular enclaves and their host granites from the early cretaceous fangshan pluton in the north china craton in order to constrain their sources and petrogenesis the fangshan pluton is composed of quartz monzodiorite at the margins and granodiorite with abundant mafic microgranular enclaves in the core zircons from the marginal quartz monzodiorite record u pb ages of 130 to 133 ma identical to those of granodiorite in the core the enclaves have zircon u pb ages of 133 to 134 ma identical within error to those of the host granodiorite establishing that the mafic and felsic magmas were coeval furthermore apatite and titanite from the enclaves and host granodiorite have the same u pb ages as the zircons indicating rapid cooling of the fangshan pluton the granodiorites have relatively high sio 2 and low mgo concentrations they have variable negative e hf t values of 25 1 to 18 2 and 18 o values for zircon of 6 2 to 8 3 the negative e nd t values of 19 7 to 14 0 for titanite and apatite with initial 87 sr 86 sr ratios of 0 7052 0 7058 for apatite indicate that they were derived from an ancient lower crustal source with addition of materials with higher e hf t and e nd t values and low 18 o values the enclaves have relatively high mgo contents up to 15 5 wt at intermediate silica concentrations indicating that their parental magmas were derived from a mantle source their zircons have strongly negative hf isotopic compositions e hf t 22 9 to 14 9 the nd isotopic composition of titanite and apatite is also strongly negative e nd t 17 6 to 12 1 all these features combined with the 18 o zircon values of 4 8 8 2 for zircons and relatively low initial sr isotopic compositions of apatite initial 87 sr 86 sr 0 7051 0 7058 indicate that they were derived from an enriched and or depleted mantle source but with involvement of crustal materials the marginal quartz monzodiorites have transitional geochemical features between those of the enclaves and host granodiorites in situ sr nd hf and o isotopic data of accessory minerals coupled with field observations and whole rock geochemical data rule out simple crystal liquid fractionation or wall rock contamination as the major genetic link between the enclaves and host rocks instead mixing of mantle derived mafic magmas with crustal derived felsic magmas coupled with assimilation of wall rocks is compatible with the data our study shows that in situ hf o nd and sr isotopic analyses of accessory minerals are powerful geochemical tracers that provide unique petrogenetic information regarding the origin of granitoids

cosmogenic nuclide dating of sahelanthropus tchadensis and australopithecus bahrelghazali mio pliocene hominids from chad ages were determined at two hominid localities from the chad basin in the djurab desert northern chad in the koro toro fossiliferous area kt 12 locality 16 00 n 18 53 e was the site of discovery of australopithecus bahrelghazali abel and in the toros menalla fossiliferous area tm 266 locality 16 15 n 17 29 e was the site of discovery of sahelanthropus tchadensis toumai at both localities the evolutive degree of the associated fossil mammal assemblages allowed a biochronological estimation of the hominid remains early pliocene 3 3 5 ma at kt 12 and late miocene 7 ma at tm 266 atmospheric 10be a cosmogenic nuclide was used to quasicontinuously date these sedimentary units the authigenic 10be 9be dating of a pelite relic within the sedimentary level containing abel yields an age of 3 58 0 27 ma that points to the contemporaneity of australopithecus bahrelghazali abel with australopithecus afarensis lucy the 28 10be 9be ages obtained within the anthracotheriid unit containing toumai bracket by absolute dating the age of sahelanthropus tchadensis to lie between 6 8 and 7 2 ma this chronological constraint is an important cornerstone both for establishing the earliest stages of hominid evolution and for new calibrations of the molecular clock

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

recharge in volcanic systems evidence from isotope profiles of phenocrysts strontium isotope ratios measured from core to rim across plagioclase feldspar crystals can be used to monitor changes in the isotope composition of the magma from which they grew in samples from three magma systems from convergent margin volcanoes sudden changes in major element composition petrographic features and strontium isotope composition were found to correspond to discrete magmatic events most likely repeated recharge of more mafic magma with lower ratios of strontium 87 to strontium 86 into a crustally contaminated magma

baogutu an example of reduced porphyry cu deposit in western junggar abstract classic oxidized porphyry copper deposits opcd are characterized by high tonnage and elevated f o 2 and contain highly oxidized minerals including primary anhydrite and hematite in contrast the baogutu deposit contains abundant hypogene pyrrhotite and methane rich fluid inclusions characteristic of lower tonnage reduced porphyry copper deposits rpcd mineral paragenesis and mineral chemistry studies reveal two mineralization periods magmatic and hydrothermal with the hydrothermal period further subdivided into three paragenetic stages including ca na alteration potassic alteration and propylitization locally overlapped by phyllic alteration several independent geothermometers indicate that the temperatures of the magma potassic and propylitization alteration are estimated to be 600 900 c 200 400 c and 200 300 c respectively multiple indicators including mineral assemblages apatite so 3 content whole rock fe 2 o 3 feo ratios and fluid compositions indicate the f o 2 of the magma and hydrothermal fluid to be nno and nno nno 2 respectively hydrothermal fluids associated with primary biotite yield log f h 2 o f hcl fluids values of 4 8 6 2 for diorite and 4 1 4 5 for granodiorite porphyry the log f s2 of the magmatic and potassic alteration are estimated to be 0 7 to 3 0 and 5 5 to 11 0 respectively based on pyrrhotite and sulfide assemblages mineral assemblage and hessite composition suggest the log f te2 of the potassic alteration is 8 5 to 14 5 the low tonnage baogutu deposit displays significantly lower f o 2 than opcds nno 2 and on this basis could be classified as a rpcd other physicochemical conditions including t f s2 log f h2o f hcl fluid do not show obvious differences to those of opcds we deduce that the low f o 2 of baogutu metallogenic granitoids and aqueous fluids likely produced the unusual pyrrhotite arsenopyrite mineral assemblage and the nacl h 2 o ch 4 co 2 ore forming fluids and small tonnage typical of rpcds previous obtained fluid inclusion h o isotope data and sulfide s pb isotope data suggest the methane rich ore forming fluids were derived from deep mantle source with little contamination from sedimentary components however detailed studies are needed to clarify the origin of the ch 4

tracking labrador sea water property signals along the deep western boundary current observations of the deep western boundary current dwbc at line w on the western north atlantic continental slope southeast of cape cod from 1995 to 2014 reveal water mass changes that are consistent with changes in source water properties upstream in the labrador sea this is most evident in the cold dense and deep class of labrador sea water dlsw that was created and progressively replenished and deepened by recurring winter convection during the severe winters of 1987 1994 the arrival of this record cold fresh and low potential vorticity anomaly at line w lags its formation in the labrador sea by 3 7 years complementary observations along the path of the dwbc provide further evidence that this anomaly is advected along the boundary and indicate that stirring between the boundary and the interior intensifies south of the flemish cap finally the consistency of the data with realistic advective and mixing time scales is assessed using the waugh and hall 2005 model framework the data are found to be best represented by a mean transit time of 5 years from the labrador sea to line w with a leading order role for both advection by the dwbc and mixing between the boundary flow and interior waters

origin and ages of mode waters in the brazil malvinas confluence region during austral winter 1994 the ventilation of the main thermocline associated with the formation of subtropical mode water stmw and subantarctic mode water samw within the brazil malvinas confluence region is investigated using satellite data hydrographic data and dissolved cfcs as transient tracers during the winter of 1994 two types of stmw were observed both types 26 24 and 26 46 were formed within the warm pool of the south atlantic central water sacw the samw is found on the 27 10 density surface this surface lies in the minimum salinity layer of the antarctic intermediate water aaiw the mode waters are dated using cfc ratios to our knowledge this is the first estimate of the age of the mode waters in the region using the cfc 113 cfc 11 ratio method the lighter stmw was being formed during the cruise the heavier stmw was found to be 6 3 years old and is thought to have circulated in the subtropical gyre without losing its primary properties the samw or the lightest aaiw has an age of 3 2 years this water is very young compared with the oldest 10 5 years and heaviest component of the aaiw which circulates within the subtropical gyre the formation of the stmw in the confluence region is dependent on the southward extension of the brazil current

basin wide circulation and ventilation study in the east sea sea of japan using chlorofluorocarbon tracers abstract near synoptic basin wide distributions of the chlorofluorocarbon cfc tracers were observed during the summer of 1999 in the east sea sea of japan to study its circulation and ventilation the cfcs penetrate throughout the water column and the bottom water bw cfc concentrations have increased over measurements made in 1995 and 1996 indicating a continuous weak renewal of deep waters in the east sea during this recent period the cfc 11 water column inventory estimated in 1999 2000 5500 nmol m 2 is substantially higher than that of the adjacent north pacific ocean a striking anticorrelation between the bw dissolved oxygen and cfc concentrations in the japan basin is attributed to more active vertical mixing along the basin boundary a dynamically isolated deep eastern japan basin and recent changes in deep water ventilation the bw of the eastern japan basin with the lowest cfc content is the oldest water parcel in the east sea although it is colder and contains higher oxygen concentration than the surrounding bw active entrainment of overlying deep water is inferred from the unexpectedly higher bw cfc concentrations in the yamato basin this may explain why the yamato basin bw is warmer and less oxygenated than the other basins in the east sea although it is believed to be a terminus of the ventilated dws mesoscale anticyclonic eddies which have been fused with other deeply convected waters in the northwestern east sea seem to play an important role in transferring surface water properties to depths greater than 2500 m the subsurface cfc maximum centered within the typical east sea intermediate water esiw layer is more widely distributed south of the subpolar front than previously reported the esiw consists primarily of the colder and fresher winter surface water in the northern region that has subducted below the subpolar front

eddies of newly formed upper labrador sea water a new type of submesoscale eddy has been observed south of the labrador sea during late winter embedded in equatorward flow along the western boundary the eddy radius is 20 km with a weak dynamic signature swirl speed of 0 5 cm s the center of the eddy is characterized by weak stratification elevated concentrations of oxygen and anthropogenic tracers and low tracer ages all indicative of newly ventilated water strong lateral intrusions distort the shape of the feature the water mass contained in the eddy is not classical labrador sea water from the central labrador sea but is significantly fresher and hence lighter it is of the correct density to be the source of the high chlorofluorocarbon layer of the shallow deep western boundary current observed further south and hence is termed upper labrador sea water using a combination of hydrographic data sets along the western boundary to implement a simple lateral diffusion model it is shown that such eddies decay of the order of several months and are difficult to observe equatorward of the grand banks of newfoundland this is in contrast to deeper lenses of classical labrador sea water which persist further equatorward tracer derived ages of the upper labrador sea water eddy range from 3 to 5 years much older than the lifetime deduced from their lateral diffusion a simple convection model of tracer age shows that this age discrepancy is caused by gas exchange being unable to maintain equilibrium between the deep convecting mixed layer and the atmosphere during formation

the role of bottom pressure torques on the interior pathways of north atlantic deep water abstractfour versions of the same global climate model one with horizontal resolution of 1 8 3 6 and three with 0 2 0 4 are employed to evaluate the role of ocean bottom topography and viscosity on the spatial structure of the deep circulation this study is motivated by several recent observational studies that find that subsurface floats injected near the western boundary of the labrador sea most often do not continuously follow the deep western boundary current dwbc in contrast to the traditional view that the deep water formed in the north atlantic predominantly follows the dwbc it is found that with imposed large viscosity values the model reproduces the traditional view however as viscosity is reduced and the model bathymetry resolution increased much of the north atlantic deep water nadw separates from the western boundary and enters the low latitude atlantic via interior pathways distinct from the dwbc it is shown that bottom pressure torques play an important role in maintai

the influence of eddies on tracer transport in the abyssal ocean abstract tracer transport mechanisms in a deep western boundary current dwbc are explored using a three layer eddy resolving quasigeostrophic model the model is forced with a steady sinusoidal wind stress the effects of the wind stress coupled with instabilities create an unsteady zonal surface jet at the boundary between the model subtropical and subpolar gyres the bottom layer includes a dwbc created by specifying a mass inflow at the northern boundary and a mass outflow at the southern boundary a numerical tracer is introduced into the dwbc with the mass source at the northern boundary the surface jet creates an effective boundary to tracer transport in the dwbc this barrier to meridional tracer transport causes approximately 70 of the tracer moved out of the northern part of the dwbc to be transported zonally into the interior with only 30 continuing southward in the dwbc in model runs with a flat bottom approximately 20 of the total meridional tracer flux is due to the eddy field w

lagrangian observations of the deep western boundary current in the north atlantic ocean abstract in this study the authors analyze the trajectories of 18 rafos floats launched in the deep western boundary current dwbc between the grand banks and cape hatteras to investigate the kinematics and dynamics in the region where the dwbc crosses under the gulf stream near 36 n the crossover region floats deployed in the chlorofluorocarbon cfc maximum associated with upper labrador sea water depth 800 m illustrate the entrainment process of this water mass into the gulf stream the behavior of the floats and fluid parcels in the crossover region is strongly dependent on the meandering of the gulf stream when the stream is close to its mean position fluid parcels entrained from the upper dwbc travel along the northern edge of the stream when a meander trough is present downstream of the entrainment location dwbc fluid parcels cross the gulf stream and sometimes are expelled on the south side this represents a previously unrecognized mechanism for transporting upper labrador sea w

correlated signals and causal transport in ocean circulation this article presents a framework for interpreting the time lagged correlation of oceanographic data in terms of physical transport mechanisms previous studies have inferred aspects of ocean circulation by correlating fluctuations in temperature and salinity measurements at distant stations typically the time lag of greatest correlation is interpreted as an advective transit time and hence the advective speed of the current in this article we relate correlation functions directly to the underlying equations of fluid transport this is accomplished by expressing the correlation functions in terms of the green s function of the transport equation two types of correlation function are distinguished field forcing correlation and field field correlation their unique relationships to the green s function are illustrated in two idealized models of geophysical transport a leaky pipe model and an advective diffusive model both models show that the field forcing correlation function converges to the green s function as the characteristic time or length scale of forcing autocorrelation decreases the leaky pipe model provides an explanation for why advective speeds inferred from time lagged correlations are often less than the speed of the main current the advective diffusive model reveals a structural bias in the field field correlation function when used to estimate transit times

float trajectories in the deep western boundary current and deep equatorial jets of the tropical atlantic abstract fourteen neutrally buoyant sofar floats at a nominal depth of 1800 m were tracked acoustically for 3 7 yr in the vicinity of the western boundary and the equator of the atlantic ocean the trajectories revealed a swift narrow southward flowing deep western boundary current dwbc extending from 7n across the equator two floats crossed the equator in the dwbc and went to 10s two other floats left the dwbc and drifted eastward in the equatorial band 3s 3n three floats entered the dwbc from the equatorial current system and drifted southward these results suggest that at times the dwbc flows directly southward across the equator with a mean velocity of 8 9 cm s averaged over long distances 2800 km at other times dwbc water is diverted eastward near the equator for long periods 2 3 yr which can reduce the mean along boundary velocity to 1 2 cm s this is much less than the instantaneous along boundary velocities in the dwbc which are often above 25 cm s and occasionally exceed 50 cm s mean eastward flowing jets were observed near 2n and 2s bounding a mean westward jet centered on the equator 1s 1n the southern jet at 2s coincides with a cfc rich plume centered south of the equator the cfc plume is inferred to have been advected by the southern jet across the atlantic and into the gulf of guinea

radiocarbon decay and oxygen utilization in the deep atlantic ocean a parameter based on the sum of the concentrations of po4 and o2 divided by the redfield coefficient o2 po4 is used to separate the contributions of the northern and southern components to deep waters in the atlantic this separation allows the amount of radiocarbon lost by radiodecay and the amount of oxygen lost to respiration during residence in the deep atlantic to be calculated maps of these quantities reveal strong west to east gradients and weak north to south gradients consistent with ventilation along the western boundary from both ends of the ocean coupled with mixing outward from the boundary the o2 and 14c deficiences are highly correlated suggesting an o2 utilization rate of 12 m kg per century the apparent mean isolation time of water in the deep atlantic is about 200 years

a generalized transport theory water mass composition and age abstract a general theory to describe and understand advective and diffusive ocean transport is reported it allows any passive tracer field with an atmospheric source to be constructed by superposing sea surface contributions with a generalized green s function called the boundary propagator of the passive tracer equation the boundary propagator has the interpretation of the joint water mass and transit time distribution from the sea surface the theory thus includes the classical oceanographic idea of water mass analysis and extends it to allow for a distribution of transit times from the sea surface the joint water mass and transit time distribution contains complete information about the transport processes in the flow it captures this information in a more accessible way than using velocity and diffusivity fields however at least for the case of sequestration and transport of dissolved material by the ocean circulation the boundary propagator is thus the natural quantity to consider when discus

the late miocene paleoenvironment of afghanistan as inferred from dental microwear in artiodactyls abstract dental microwear of late miocene artiodactyls from afghanistan can yield information on paleodiet and thus inferences can be drawn about their paleoenvironment the molayan locality lies at the border between the greek iranian and siwalik bioprovinces knowledge of the paleoenvironment will further our understanding of the faunal exchanges between these two provinces during the late miocene ninety nine specimens of seven bovid and one giraffid species are considered the number and diversity of the samples provide objective data which enable the reconstruction of the paleoenvironment prostrepsiceros aff vinayaki and sporadotragus tadzhikistanicus have similar dental microwear pattern which suggests a meal by meal mixed feeding diet phronetragus aff secondus gazella sp and the giraffid palaeotragus cf rouenii can only be characterized as mixed feeders in a general sense dorcadoxa porrecticornis was an obligate grazer and the two species of tragoportax were variable grazers the analysis also brings out clear similarities between extinct grazers and equus przewalskii which is a c3 grazer isotopic evidence from previous studies supports the microwear data comparisons with data from the late miocene of the potwar plateau suggest strong environmental differences with the afghan locality when brought together this disparate evidence about diet suggests an open and dry environment composed mainly of c3 grasses and evergreen bushes during the late miocene in afghanistan

diversity and paleoecology of greek late miocene mammalian faunas abstract the late miocene of macedonia has yielded several rich faunal assemblages ranging from late vallesian to late turolian they may be compared to the classical localities of pikermi samos and maragheh taxonomic comparisons based upon updated faunal lists allowed us to compute faunal similarity indices which were submitted to principal component and cluster analysis on the graphs ravin de la pluie is always remote from the other macedonian fossil mammal localities it can only be explained by its vallesian age the other macedonian sites cluster next demonstrating some provinciality of this area during the turolian comparisons of the frequencies of the various taxonomic groups support the installation of a more forested environment in the latest faunal set dytiko the indices of diversity and the rank abundance curves seem also to reflect a change of the ecological conditions during the turolian the fauna of ravin de la pluie and of the vathylakkos prochoma ravin des zouaves group is marked by the predominance of 1 or 2 species while the species frequency of the dytiko set is more balanced suggesting warmer climate and less contrasted climatic conditions another way of evaluating the ecological significance of the fossil assemblages is the analysis of the distribution of the body weight of each category of mammals in each fauna when possible we used the cenogram method or a multivariate analysis of the number of species in each weight class excluding small mammals which are very rare in macedonia we have analysed in this way 25 fossil and 23 recent localities we show that although all the fossil localities are separated from the recent ones it is possible to deduce an open environment in ravin de la pluie and a more forested one in dytiko

reduced porphyry copper gold deposits a new variation on an old theme it is a widely accepted fact that porphyry cu au deposits form from highly oxidized ore fluids despite this assertion several otherwise typical porphyry cu au deposits exhibit clear evidence of having formed from relatively reduced ore fluids these reduced porphyry cu au deposits lack primary hematite magnetite and sulfate minerals i e anhydrite but contain abundant hypogene pyrrhotite commonly have carbonic rich ore fluids with substantial ch 4 and are associated with ilmenite bearing reduced i type granitoids based on a synthesis of theoretical experimental and field data a variation on the classic porphyry cu model is proposed to explain the formation of reduced porphyry cu au deposits and their relatively cu poor but au rich nature the proposed reduced porphyry cu au model does not contradict the current understanding of porphyry cu au formation rather it adds yet another variation on the theme of porphyry cu au genesis

intensified turbulent mixing in the boundary current system of southern greenland 10 4 m 2 s 1 commonly occur in the dwbc these diffusivities estimated with an internal wave strain based parameterisation are independently confirmed by budgets of density and dissolved o2 moderate mixing rates 10 4 m 2 s 1 over the dwbc path between denmark strait and cape farewell 1000 km drive a similar net increase in volume transport by diapycnal entrainment to the more intense 10 3 m 2 s 1 localised mixing rates found near the denmark strait overflow sill therefore turbulent mixing associated with the dwbc south of denmark strait is instrumental in establishing the magnitude of the north atlantic meridional overturning circulation elevated mixing rates are also seen in the east and west greenland currents this may be significant in preconditioning seasonal restratification of the intermediate layers of the irminger and labrador basins citation lauderdale j m s bacon a c naveira garabato and n p holliday 2008 intensified turbulent mixing in the boundary current system of southern greenland geophys res lett 35 l04611

magmatic process recorded in plagioclase at the baogutu reduced porphyry cu deposit western junggar nw china abstract despite the fact that porphyry cu deposits contain large amounts of cu in one or more small stocks few studies have discussed evidence for significant magma recharge in porphyry cu deposits a systematic elemental and sr isotopic study of plagioclase crystals from mineralized diorite and granodiorite porphyry constrains the processes of crystallization and magma recharge at the baogutu reduced porphyry copper deposit western junggar nw china large compositional changes in an 12 24 mol are observed along with strong positive correlations between an and feo significant resorption textures are also preserved in plagioclase crystals as well as repeated oscillatory zoning in an and feo and complex sr isotope variations three types of crystals with different core to rim sr isotope variations are recognized type i crystals have core to rim increases in 87sr 86sr i that could be explained by diffusion for example sr isotope variations recorded in bck2 1 2 crystal could be generated by diffusion with simulated maximum crystal residence times of 100 500 years with the proximate value of 300 years type ii crystals with different variation trends in 87sr 86sr i on opposite sides of the core could be produced either by multi stage crystallization or by analytical uncertainty whereas type iii crystals with complex core to rim variations in 87sr 86sr i may record repeated magma recharge events all these results suggest repeated recharging of the magma chamber by hotter more mafic and less radiogenic sr isotope melts therefore more mafic melt injection recorded in plagioclase profiles may provide significant metal contributions to the magma chamber which ultimately results in cu mineralization at the baogutu reduced porphyry copper deposit

propagation of tracer signals in boundary currents abstract the propagation of a range of tracer signals in a simple model of the deep western boundary current is examined analytical expressions are derived in certain limits for the transit time distributions and the propagation times tracer ages of tracers with exponentially growing or periodic concentration histories at the boundary current s origin if mixing between the boundary current and the surrounding ocean is either very slow or very rapid then all tracer signals propagate at the same rate in contrast for intermediate mixing rates tracer ages generally depend on the history of the tracer variations at the origin and range from the advective time along the current to the much larger mean age close agreement of the model with chlorofluorocarbon cfc and tritium observations in the north atlantic deep western boundary current dwbc is obtained when the model is in the intermediate mixing regime with current speed around 5 cm s 1 and mixing time scale around 1 yr in this regime anomalies

geology and palaeontology of the upper miocene toros menalla hominid locality chad all six known specimens of the early hominid sahelanthropus tchadensis come from toros menalla site 266 tm 266 a single locality in the djurab desert northern chad central africa here we present a preliminary analysis of the palaeontological and palaeoecological context of these finds the rich fauna from tm 266 includes a significant aquatic component such as fish crocodiles and amphibious mammals alongside animals associated with gallery forest and savannah such as primates rodents elephants equids and bovids the fauna suggests a biochronological age between 6 and 7 million years taken together with the sedimentological evidence the fauna suggests that s tchadensis lived close to a lake but not far from a sandy desert perhaps the oldest record of desert conditions in the neogene of northern central africa

a chlorofluoromethane and hydrographic section across drake passage deep water ventilation and meridional property transport new hydrographic and nutrient data obtained on a section across drake passage f s meteor january 1990 world ocean circulation experiment hydrographic program section s1 are in close agreement with property sections reported previously the chlorofluoromethanes cfm 11 and cfm 12 were measured in drake passage for the first time cfm concentrations are found to decrease from the surface down into the upper circumpolar deep water for which they confirm water renewal from the south for the lower circumpolar deep water in which cfm concentrations were above detection limit only south of the polar front very little water renewal on the cfm time scale is implied nonvanishing cfm is again found in the weddell sea deep water and the southeast pacific deep water toward the bottom in the south but recent ventilation for the latter water mass is rejected cfm 11 and cfm 12 concentrations vary essentially in constant proportion down to very low concentrations questioning the possibility of using cfm ratios as age markers the observed ratios are shown to be a natural feature of the upwelling regime of the southern ocean property concentrations on isopycnal surfaces display large undulations reaching down into the upper circumpolar deep water their extrema due to varying contribution of young water of southern origin are situated at the boundaries of the current bands of the antarctic circumpolar current the feature is ascribed to property advection by rings and is taken to support previous claims that rings are an important transport mechanism across the antarctic circumpolar current and that they might assist in maintaining its fronts

dental mesowear analysis of the late miocene bovidae from toros menalla chad and early hominid habitats in central africa this study aimed to reconstruct the environmental conditions that prevailed in the chadian palaeo lake basin ca 7 ma ago based on the feeding preferences of late miocene bovidae from toros menalla chad this is a key issue for understanding the circumstances regional landscapes under which the earliest known hominid sahelanthropus tchadensis evolved a dental mesowear analysis was applied to 117 specimens of bovids representing the four tribes present in the anthracotheriid unit localities hippotragini reduncini antilopini and bovini all these bovids fed on grasses at least partially previous analyses and the present results indicate the presence of a mosaic like environment containing various habitats from grasslands to woodlands in the surroundings of the chadian lake basin indeed our data support the availability of grass or grass like plants and therefore open patches in the vicinity of the chadian palaeo lake shores

a laboratory model of exchange and mixing between western boundary layers and subbasin recirculation gyres chaotic advection is suggested as a possible mechanism for fluid exchange and mixing among a western boundary current and subbasin recirculation gyres applications include the north atlantic deep western boundary current and its adjacent mesoscale recirculation gyres visualization and quantification of certain aspects of chaotic advection in a laboratory analog are described depending on the strength of the forcing recirculating fluid offshore of the western boundary layer may be contained in a single gyre not favorable for chaotic advection or twin gyre with a figure eight geometry favorable for chaotic advection when time dependence is imposed on these steady flows by varying the forcing periodically the resulting fluid exchange stirring and mixing is most dramatic in the case of the twin gyre a template for these processes can be formed by highlighting certain material contours invariant manifolds using dye and other techniques these objects can be used to identify blobs of fluid turnstile lobes that are carried into and out of the gyres the associated transports and flushing times can be estimated the preferential stirring and mixing in the twin gyre case is quantified by calculating the effective diffusivity of the flow field based on snapshots of the dye fields at longer times the experiment suggests how tracers in a western boundary current might be transported into and out of neighboring recirculations and where regions of strong zonal or meridional transport might occur