dynamical analysis of the upwelling circulation off central chile 1 in this article we analyze the momentum and vorticity balances of a numerical simulation of the upwelling circulation off central chile 34 40 s and its response to interannual local wind changes our analysis indicates that the path of the upwelling jet is strongly controlled by the bottom topography this topographic steering causes the jet to separate from the coast at the punta lavapie cape 37 s although the zeroth order momentum balance is dominated by the geostrophic terms the circulation is also affected by nonlinear processes which lead to the formation of large meanders and the shedding of cyclonic eddies north of punta lavapie during periods of wind relaxation the relative contributions of the zeroth order vorticity balance and the advective terms are also strongly controlled by changes in the coastline geometry and the bottom topography vorticity is created along the current axes and transported toward the coast and the peru chile trench where it dissipates south of punta lavapie the across shelf transports are weaker with equatorward flows that are more stable than in the north additional numerical simulations

geochronology geochemistry and fluid characterization of the late miocene buritica gold deposit antioquia department colombia buritica is an intermediate sulfidation epithermal gold deposit located 75 km north of medellin colombia it is hosted by the late miocene buritica andesite porphyry a shallow level pluton dated at 7 41 0 40 ma 2 mswd 2 30 40 ar 39 ar on hornblende which intrudes volcanic and sedimentary rocks of the cretaceous barroso formation and the buritica stock gold mineralization is associated with proximal sericite adularia and distal epidote dominant propylitic alteration and is hosted in two different sets of veins striking and dipping 072 87 s and 105 87 s hydrothermal muscovite from altered host rock yielded a weighted average 40 ar 39 ar age of 7 74 0 08 ma for two samples which is within error of the age of the buritica andesite porphyry sulfur isotope oxygen isotope and fluid inclusion data indicate that a relatively hot and saline fluid 310 c up to 8 wt nacl equiv of probable magmatic origin was dominant during stage 1 of the vein paragenesis and mixed with cooler and less saline groundwater during stages 2 and 3 fluid inclusion assemblages indicate that boiling was likely the main control on gold precipitation with cooling and dilution during fluid mixing as a possible secondary control

strontium isotope variations in lower tertiary quaternary volcanic rocks from the kurile island arc average 87sr 86sr ratios for lavas from quaternary and pleistocene volcanoes of the kurile island arc nw pacific decrease from 0 7035 in the south to 0 7032 in the north the northern kuriles are characterised by k2oricher volcanics and by an older crust varying ratios show no simple relation to crustal thickness or geochemical indicators of crustal contamination this is thought to reflect the immature character of the crust its simatic composition low rb sr ratios and youthfulness older lavas from the kuriles lower tertiary miocene have similar or slightly higher 87sr 86sr ratios some have suffered slight alteration and possibly crustal contamination quaternary volcanics from the kurile and aleutian arcs have the lowest 87sr 86sr ratios of all circum pacific arcs and this may be ascribed to a the isotopic individuality of the landward north american plate and or b the high degree of mechanical coupling between the pacific and north american plates reducing the amount of subducted 87sr rich sediments and seawater an isotopic boundary between island arcs is located in central hokkaido the primary basaltic magmas of the kuriles were derived from mantle recently contaminated by radiogenic sr subsequent fractionation to andesites and dacites occurred by closed system fractional crystallization

pb sr and nd isotopic and chemical evidence for a primitive island arc emplacement of the el arco porphyry copper deposit baja california mexico the el arco porphyry copper deposit is located in central baja california and is a resource containing 600 mt of ore with 0 6 copper it was emplaced within a relatively primitive jurassic island arc and it was subsequently metamorphosed and intruded by the cretaceous peninsular ranges batholith the porphyritic stock intrusion and ore formation at el arco has recently been dated at 165 ma valencia et al geos 24 189 2004 this age is much older than aptian albian k ar ages previously reported from el arco barthelmy geology of el arco calmalli area baja california mexico msc thesis san diego state university ca 1975 baja california geology san diego state university ca pp 127 138 1979 the copper mineralization at el arco is concentrated in a core of potassic alteration in a dioritic porphyritic stock surrounded by propylitic alteration in andesitic lavas mafic dikes that intruded the deposit are not mineralized but they are affected by post ore low grade metamorphism the dikes are compositionally the most primitive rocks while host rock andesites and the porphyry stock display typical volcanic arc characteristics the pb isotope data from sulfides feldspars quartz and whole rock samples indicate that 1 the copper bearing porphyry stock and the surrounding andesites evolved from a similar source with an average value of 9 43 2 no external pb was added during mineralization 3 some pb isotope compositions were slightly disturbed by a later metamorphic event strontium and nd isotopes show that the magmas evolved from a depleted mantle reservoir with no involvement of older continental crust our data favor a model for the formation of the el arco deposit linked to a triassic to jurassic intra oceanic arc system cropping out at the western margin of central baja california in the cedros vizcaino region the intra oceanic arc together with the el arco deposit was accreted to the active continental margin of north america and metamorphosed during the early cretaceous this model is in disagreement to earlier models that favor the el arco deposit formation being linked to the cretaceous continental margin

geochemical evidence for the volcanic arc tectonic setting of the dhanjori volcanics singhbhum craton eastern india geochemical data on the dhanjori volcanics of the singhbhum craton indicate that they range from basalt to andesite and show an iron enrichment trend various chemical characteristics suggest that they are differentiated along the trend similar to that of orogenic suites and have a strong affinity with island arc tholeiites the field relationships as well as other geological information also support this conclusion and indicate their eruption on a thin continental margin it is inferred that the dhanjori volcanics were probably erupted as a result of plate convergence in northern singhbhum with subduction of oceanic crust below the singhbhum craton

ages and petrogenesis of the late triassic andesitic rocks at the luerma porphyry cu deposit western gangdese and implications for regional metallogeny abstract the tibetan plateau is one of the most significant cu poly metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry cu mineralization this study investigates a new occurrence of cu mineralization related andesitic porphyries in the western domain of the gangdese magmatic belt and assesses its petrologic zircon u pb geochronology whole rock chemistry and sr nd hf pb isotope data zircon u pb dating of three ore related porphyries yields crystallization ages of 212 211 ma these ages are consistent with previous molybdenite re os dating indicating a late triassic magmatic and cu mineralization event in the western gangdese magmatic belt nb ta and ti depletion th and lree enrichment and high la yb and th yb ratios in addition to high u yb ratios from zircons suggest that the magma was generated in an active continental arc setting the porphyries have radiogenic isotopic compositions with 87sr 86sr i 0 70431 0 70473 end t 1 1 to 3 8 207pb 204pb i 15 601 15 622 and 208pb 204pb i 38 450 38 693 as well as high positive zircon ehf t values from 6 2 to 10 6 mean value 8 3 corresponding to model ages tdm ranging from 509 ma to 819 ma mean 646 ma this suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment derived melts during the subduction of the neo tethys ocean the mineralization related porphyries contain amphibole and epidote as well as high whole rock fe2o3 feo and zircon ce4 ce3 ratios suggesting hydrous and highly oxidized parent magmas considering the existing cu mineralization and highly oxidized magma of the well preserved triassic andesitic igneous rocks in the western gangdese belt the subduction related continental arc magma system is favorable for subduction related porphyry cu deposits the existence of luerma porphyry mineralization demonstrates that there are at least five generations of porphyry cu mo au mineralization in the gangdese magmatic belt which advances the timeframe of porphyry mineralization to the late triassic

petrogenesis of calc alkaline shoshonitic and associated ultrapotassic oligocene volcanic rocks from the northwestern alps italy along the western alps there is geological evidence of late alpine oligocene magmatic activity which clearly postdates the lepontine eocene early oligocene metamorphism and related deformation of the alpine nappe pile this magmatic activity was notably delayed in relation to the most important convergent processes and may be related to buoyancy of lithosphere tensional tectonics and thermal updoming subsequent to the collision between the eurasian and african plates the geochemical features of the rocks and the geophysical characteristics of the alpine chain suggest that a shoshonitic and calcalkaline melts may have been generated by partial melting of metasomatized peridotitic material and subsequent fractional crystallization and crustal contamination silicic andesites and latites however could have been also derived from metasomatized eclogite or deep continental crust material b the ultrapotassic lamprophyres with high k p lree th zr u and high 87sr 86sr ratios were generated by partial melting of strongly metasomatized mantle the varied sr isotopic ratios may partially also reflect additional radiogenic component from the continental crust following magma segregation from the source

relationships between mineral composition and relative ages of iron nodules in jurassian soil sequences abstract iron nodules with several kinds of morphology occur in upland and lowland soil toposequences of the jura the upland soils contain spherical concretions m and tubular coatings both types being newly formed in the present pedoenvironments impregnative micritic concentrations in soil matrix and surrounding roots nodule fragments show concentric rings wherein goethite cements quartz grains and encloses feldspars and chamosite these minerals are characteristic of the eolian post wurmian dust and enable the upland nodules to be dated to post wurmian age the lowland soils contain polished and dense spherical concretions 500 m and twin nodules they are considered as inherited from a pre wurmian period of pedogenesis because they do not include eolian post wurmian minerals the spherical nodules are goethitic they are thought to be inherited from periglacial periods that induced hydromorphic environments such as those occurring currently in the uplands the twin nodules are hematitic they are thought to be relics of older weathering

friction frontogenesis and the stratification of the surface mixed layer the generation and destruction of stratification in the surface mixed layer of the ocean is understood to result from vertical turbulent transport of buoyancy and momentum driven by air sea fluxes and stresses in this paper it is shown that the magnitude and penetration of vertical fluxes are strongly modified by horizontal gradients in buoyancy and momentum a classic example is the strong restratification resulting from frontogenesis in regions of confluent flow frictional forces acting on a baroclinic current either imposed externally by a wind stress or caused by the spindown of the current itself also modify the stratification by driving ekman flows that differentially advect density ekman flow induced during spindown always tends to restratify the fluid while wind driven ekman currents will restratify or destratify the mixed layer if the wind stress has a component up or down front i e directed against or with the geostrophic shear respectively scalings are constructed for the relative importance of friction versus frontogenesis in the restratification of the mixed layer and are tested using numerical experiments of mixed layer fronts forced by both winds and a strain field the scalings suggest and the numerical experiments confirm that for wind stress magnitudes mixed layer depths and cross front density gradients typical of the ocean wind induced friction often dominates frontogenesis in the modification of the stratification of the upper ocean the experiments reveal that wind induced destratification is weaker in magnitude than restratification because the stratification generated by up front winds confines the turbulent stress to a depth shallower than the ekman layer which enhances the frictional force ekman flow and differential advection of density frictional destratification is further reduced over restratification because the stress associated with the geostrophic shear at the surface tends to compensate a down front wind stress

geochemistry and u pb zircon ages of metamorphic volcanic rocks of the paleoproterozoic luliang complex and constraints on the evolution of the trans north china orogen north china craton abstract the paleoproterozoic luliang complex is situated in the central part of the western margin of the trans north china orogen and consists of volcanic rocks sedimentary rocks and paleoproterozoic granitoid intrusions the volcanic rocks and earlier granitoid rocks were strongly deformed and metamorphosed into the greenschist to amphibolite facies these metamorphosed volcanic rocks are dominated by basalts to basaltic andesites the parental mafic magmas of these metamorphosed volcanic rocks were mainly derived from the 5 to 30 partial melting of spinel lherzolites to spinel garnet lherzolites which had been enriched by the subduction melts mafic magma experienced fractional crystallization and crustal assimilation u pb zircon dating on two metamorphosed volcanic rocks from the yejishan and luliang groups reveals that they formed at 2210 13 ma and 2213 47 ma respectively and were metamorphosed at 1832 ma this suggests that the metamorphosed volcanic rocks in the yejishan and luliang groups formed synchronously in the paleoproterozoic these new ages integrated with recently reported u pb zircon ages for the jiehekou group and paleoproterozoic granitoids suggest that all of the lithological assemblages of the luliang complex formed and were metamorphosed in the paleoproterozoic not in the neoarchean petrological geochronological and geochemical data suggest that the geodynamic evolution of the paleoproterozoic luliang complex was involved in the development of a magmatic arc system at an active continental margin generating widespread arc related magmatism at 2 2 ga the luliang complex then underwent intense deformation and metamorphism and was incorporated into the trans north china orogen during the 1 88 1 83 ga collisional event which was followed by post collision extension at 1 80 ga

reconstructing multiple arc basin systems in the altai junggar area nw china implications for the architecture and evolution of the western central asian orogenic belt abstract the altai junggar area in northwestern china is a critical region to gain insights on the tectonic framework and geological evolution of the western central asian orogenic belt caob in this study we report results from integrated geological geochemical and geophysical investigations on the wulungu depression of the junggar basin to determine the basement nature of the basin and understand its amalgamation history with the chinese altai within the broad tectonic evolution of the altai junggar area based on borehole and seismic data the wulungu depression is subdivided into two nw trending tectonic units suosuoquan sag and hongyan high by southward vergent thrust faults the suosuoquan sag consists of the middle late devonian basaltic andesite andesite dacite tuff tuffaceous sandstone and tuffite and the overlying early carboniferous volcano sedimentary sequence with lava flows and shallow marine sediments from a proximal juvenile provenance zircon e hf t 6 0 14 9 compared to the late carboniferous andesite and rhyolite in the hongyan high zircon sims u pb ages for dacites and andesites indicate that these volcanics in the suosuoquan sag and hongyan high erupted at 376 3 ma and 313 4 ma respectively the middle late devonian basaltic andesites from well lc1 are calc alkaline and exhibit primitive magma like mgo contents 7 9 8 6 and mg values 66 68 with low initial 87 sr 86 sr 0 703269 0 704808 and positive e nd t values 6 6 7 6 and relatively high zr abundance 98 2 116 0 ppm and zr y ratios 5 1 5 4 enrichment in lrees and liles e g th and u and depletion in nb ta and ti suggesting that they were probably derived from a metasomatized depleted mantle in a retro arc extensional setting the well lc1 andesitic tuffs well l8 dacites well wl1 dacitic tuffs and well l5 andesites belong to calc alkaline and metaluminous to peraluminous a cnk 0 8 1 7 series and display low mg values 35 46 and variably positive e nd t 4 5 8 5 and e hf t 10 2 16 8 values as well as young isotopic model ages these devonian carboniferous intermediate felsic volcanics are interpreted as the products of partial melting of a juvenile lower crust with some contributions from mantle components in an evolved island arc setting from immature to mature island arc the basin filling pattern and the distribution of arc volcanics and their zircon hf model ages with the eruptive time suggest that the wulungu depression represents an island arc basin system with the development of a carboniferous retro arc basin in combination with previous work we propose that the northern junggar area comprises three arc basin belts from south to north the darbut luliang karamaili wulungu yemaquan and saur fuhai dulate such tectonic subdivisions are consistent with the regional gravity and magnetic anomaly data the recognition of the wulungu arc basin system demonstrates that the junggar basin is likely underlain by juvenile continental crust rather than ancient precambrian basement and also implies that the caob was built by amalgamation of multiple linear arcs and accretionary complexes

stratigraphy and tectonic setting of the cretaceous and paleogene volcanic sedimentary successions in northwest sulawesi indonesia implications for the cenozoic evolution of western and northern sulawesi abstract new field and laboratory data from nw sulawesi indonesia integrated with existing information provide a tectonostratigraphic framework for the cretaceous and paleogene of this region the study area straddles two distinct provinces referred to as western and northern sulawesi western sulawesi forms the rifted continental margin of eastern sundaland it consists of a metamorphic basement partly of australian origin overlain by late cretaceous turbidites that were deposited in a fore arc setting latimojong formation these are in turn covered by volcanic sedimentary successions that were deposited during the early middle eocene to earliest miocene they represent a transgressive cycle from syn rift siliciclastics through nummulitic limestone and associated shelf sediments to deeper marine mudstones and turbidites budungbudung and tinombo formations during the same period northern sulawesi developed as an oceanic island arc characterized by bimodal volcanism papayato volcanics founded on back arc oceanic crust the cretaceous and paleogene volcanic and sedimentary suites show lithological and geochemical characteristics that reflect the contrasting tectonic setting of the two provinces the tectonic relationship between the two domains is not clear they probably formed a more or less continuous belt throughout the cenozoic but were definitely connected not later than the early miocene strong deformation in the paleogene formations in the northern part of nw sulawesi and their unconformable relationship with the overlying formations may be the result of the collision of the north arm of sulawesi with a continental fragment of australian derivation during the early miocene or it may be related to the formation of a metamorphic core complex in a mid miocene extensional tectonic setting a second major tectonic event which commenced in the pliocene and is still ongoing affected the entire region

silver base metal epithermal vein and listwanite hosted deposit crnac rogozna mts kosovo part ii a link between magmatic rocks and epithermal mineralization abstract crnac is an intermediate sulfidation pb zn ag epithermal deposit located within the vardar suture zone of the central balkan peninsula the epithermal pb zn ag mineralization consists of i a series of steeply dipping veins hosted within the jurassic amphibolites and ii overlying hydrothermal explosive breccia with angular level iv or rounded fragments of listwanite surface cemented by epithermal mineralization the mineralization is related to the oligocene quartz latite dykes that crosscut the crnac antiform quartz latite rocks predominantly display a shoshonitic character the obtained 40ar 39ar age of fresh quartz latite is 28 9 0 3 ma fine grained sericite from altered quartz latite is dated at 28 6 0 5 ma early alteration related fluid inclusions within quartz latite show coexistence of high density brine and a low density vapor saturated phase that homogenized at 280 405 c phase separation occurs at a paleodepth of 0 6 to 0 9 km epithermal mineralization developed in three stages i early pyrite arsenopyrite pyrrhotite quartz kaolinite ii main sphalerite galena tetrahedrite chalcopyrite and iii late carbonate pyrite arsenopyrite assemblage the onset of mineral deposition within epithermal veins was initiated by boiling of na cl k ca mg fluid at a paleodepth of 0 6 to 0 9 km coexisting vapor and liquid rich inclusions display salinities and trapping temperatures of 4 wt nacl equiv 280 370 c and 2 27 wt nacl equiv 230 375 c respectively boiling continued throughout the deposition of the sphalerite galena tetrahedrite chalcopyrite assemblage late stage carbonate was deposited from diluted non boiling low temperature na ca mg cl co2 fluid 0 2 to 4 8 wt nacl equiv 115 280 c about 100 150 m higher in the system precipitation of listwanite breccia cement began as a result of boiling na cl ca mg k fluid of medium salinities 2 6 to 12 1 wt nacl equiv at temperatures of 245 370 c boiling and dilution of fluids continue throughout the precipitation of the main sphalerite galena tetrahedrite and late mainly carbonate assemblage surface listwanite breccia contain quartz phenocrysts deposited from a homogeneous fluid with a medium salinity 8 10 wt nacl equiv and high temperatures th 295 315 c whereas the early and main stage of a surface listwanite breccia cement precipitated from a boiling fluid of decreasing salinity and temperature aqueous co2 high salinity 16 to 18 wt nacl equiv low temperature 120 c homogeneously trapped fluid that precipitated late stage carbonates is most likely a remnant of boiled off fluid the epithermal assemblage of the surface listwanites precipitated at a paleodepth of 0 4 to 0 6 km the 13c values of the late stage ankerite range from 4 2 to 4 1 whereas 18o range from 9 6 to 17 5 the calculated 18o of fluid that precipitated carbonates within epithermal veins and listwanite breccia cement range from 6 3 to 11 3 indicating a contribution of magmatic water deposition of all mineralization types was initiated by neutralization of primary acidic magmatic fluid by water rock reactions that caused widespread propylitization and sericitization extensive and long lasting boiling combined with dilution by meteoric water increased the ph towards the final stage of hydrothermal activity

carboniferous granites on the northern margin of gondwana anatolide tauride block turkey evidence for southward subduction of paleotethys abstract carboniferous metagranites with u pb zircon crystallization ages of 331 315 ma crop out in the afyon zone in the northern margin of the anatolide tauride block which is commonly regarded as part of gondwana during the late palaeozoic they are peraluminous calc alkaline and are characterized by increase in rb and ba decrease in nb ta and enrichment in sr and high lile hfse ratios compatible with a continental arc setting the metagranites intrude a metasedimentary sequence of phyllite metaquartzite and marble both the carboniferous metagranites and metasedimentary rocks are overlain unconformably by lower triassic metaconglomerates metavolcanics and upper triassic to cretaceous recrystallized limestones the low grade metamorphism and deformation occurred at the cretaceous tertiary boundary there is no evidence for carboniferous deformation and metamorphism in the region carboniferous arc type granites and previously described carboniferous subduction accretion complexes on the northern margin of the anatolide tauride block suggest southward subduction of paleotethys under gondwana during the carboniferous considering the variscan related arc granites in pelagonian and sakarya zones on the active southern margin of laurasia a dual subduction of paleotethys can be envisaged between early carboniferous and late permian however the southward subduction was short lived and by the late permian the gondwana margin became passive

the northeast kingdom batholith vermont magmatic evolution and geochemical constraints on the origin of acadian granitic rocks five devonian plutons west charleston echo pond nulhegan derby and willoughby that constitute the northeast kingdom batholith in vermont show wide ranges in elemental abundances and ratios consistent with major crustal contributions during their evolution the batholith consists of metaluminous quartz gabbro diorite and quartz monzodiorite peraluminous granodiorite and granite and strongly peraluminous leucogranite contents of major elements vary systematically with increasingsio 40 and have small negative eu anomalies the strongly peraluminous willoughby leucogranite has unique trace element abundances and ratios relative to the rest of the batholith including low contents of hf zr sr and ba low values of k rb 80 164 th ta 9 rb cs 7 40 k cs 0 1 0 5 ce pb 0 5 4 high values of rb sr 1 18 low to moderate ree contents and light ree enriched patterns with small negative eu anomalies flat ree patterns with large negative eu anomalies are found in a small hydrothermally altered area characterized by high abundances of sn up to 26 ppm rb up to 670 ppm li up to 310 ppm ta up to 13 1 ppm and u up to 10 ppm there is no single mixing trend fractional crystallization assemblage or assimilationscheme that accounts for all trace elementvariations from quartz gabbro to granite in the northeast kingdom batholith the plutons originated by mixing mantle derived components and crustal melts generated at different levels in the heterogeneous lithosphere in a continental collisional environment hybrid rocks in the batholith evolved by fractional crystallization and assimilation of country rocks 50 by mass and some of the leucogranitic rocks were subsequently disturbed by a mild hydrothermal event that resulted in the deposition of small amounts of sulfide minerals

demographics of mesoscale eddies in the california current 1 demographics and variability of persistent mesoscale eddies in the california current have been investigated in a systematic manner using a decade 1995 2004 of merged satellite altimeter data the number of persistent eddies formed each year varied almost 3 fold 4 fold for cyclones anticyclones and was strongly modulated by the 1997 1998 el nino event over the 10 year period cyclone formation was maximum in both winter and summer while maximum anticyclone formation occurred only in winter the majority of long lived eddies 70 day lifespan originated seaward of the 1000 m isobath and with the exception of 2 anticyclones did not form between 45 and 50 n maximum westward propagation of long lived eddies was almost 800 km with similar mean propagation speeds for cyclones and anticyclones

the significance of source versus process in the tectonic controls of magma genesis arculus r j 1987 the significance of source versus process in the tectonic controls of magma genesis in s d weaver and r w johnson editors tectonic controls on magma chemistry j volcanol geotherm res 32 1 12 despite the association of certain characteristic trace element signatures with particular tectonic environments of eruption there are accumulating data which would result in significant tectonic misassignments ambiguity of signals appears in active arc back arc systems of the southwestern pacific and particularly in some intracontinental plate suites given the selective preservation of continental as opposed to oceanic lithosphere inappropriate paleotectonic inferences are probable using trace element criteria alone strong relative fractionation of the alkalis and alkaline earth elements aee with respect to the rare earth elements ree in the majority of arc related magmas and a number of intraplate continental basalts is strongly suggestive of the involvement of hydrous fluids at some stages in the respective petrogenetic processes occurring in these two tectonic regimes in contrast fractionation of high field strength elements hfse such as nb and ta with respect to the ree in the same suites is most readily explained by the involvement at some stage in the magma formation process of high sio2 melts a number of widely applied tectonic discriminants makes use of aee hfse fractionation but the processes and sources involved in subduction zone petrogenesis may be duplicated during interaction of mantle derived basalt with the heterogeneous components of continental lithosphere both mantle and crust a significant role for both volatile dominated fluids and silicate melts is implicated in collision and some intracontinental plate magmatism

geochemical investigation of the igneous rocks from the nurali ophiolite melange zone southern urals abstract the nurali massif is a small ophiolite located along the main uralian fault in the southern urals it includes a mantle sequence a transition zone and a melange zone with an intrusive gabbro to oxide diorite unit interposed between the transition zone and the melange various igneous rocks occur as exotic blocks within the nurali melange including tholeiitic gabbro to diorite and calc alkaline diorite tonalite granodiorite and granite intrusives tholeiitic basalt and calc alkaline basaltic andesite to dacite the poljakovka complex basalts of silurian age are similar to the tholeiitic effusives and are also intruded by gabbros similar to those in the melange zone calc alkaline intrusives the rocks of tholeiitic affinity in the tectonic melange are the remnants of an oceanic stage both intrusive and effusive calc alkaline products can likely represent a subduction related magmatism developed in an arc environment intra oceanic arc or continental margin they are analogous to those from the kraka massif which occur west of the main uralian fault

seasonal dynamics of the near surface alongshore flow off central chile 1 the seasonal cycle of the near surface circulation off central chile was analyzed using satellite altimetry and an oceanic model to evaluate the role of the wind stress curl on the circulation we performed two identical simulations except for the wind forcing the control run used long term monthly mean wind stress and the no curl run used a similar wind stress field but without curl the observed and modeled control run surface currents showed a strong seasonal cycle and a well defined equatorward flow with a jet like structure this jet develops during spring and summer consistent with the presence of a low level wind jet south of punta lavapie cape 37 s the equatorward surface current remains close to the coast after the flow passes this cape however it separates to become an offshore jet in contrast in the no curl simulation the separation at punta lavapie is not observed and the offshore jet farther north is not present demonstrating the importance of the wind stress curl on the dynamics of this flow although the offshore integrated sverdrup transport was similar to the model transport the offshore jet was not located where the wind stress curl was maximum instead the position of the jet followed approximately the zero wind stress curl which corresponds to the climatological location of the low level wind jet axis these results illustrate the importance of the offshore upwelling downwelling associated with curl driven ekman pumping which tilts isopycnals upward downward toward the east west of the wind jet forcing a northward flow through thermal wind balance

the holonda porphyrites norwegian caledonides geochemistry and tectonic setting of early mid ordovician shoshonitic volcanism petrological and geochemical data denote that the late arenig early llanvirn holonda porphyrites belong to the subduction related shoshonite association original compositions ranged from absarokite through shoshonite to latite and their very evolved nature signifies a mature arc aynity in an active continental margin setting much of the geochemical variation can be interpreted in terms of fractional crystallization followed by a varying admixture of cumulus phases to the ascending melt and accumulation of phenocrysts within the magmatic feeder system their eruptive products covered an area which was at least 20 25 km across forming local islands with carbonate rich shelves in a shallow to deeper marine environment the immediate substrate to the volcanosedimentary holonda basin is the lokken ophiolite which formed in a primitive oceanic arc marginal basin setting some 10 20 ma prior to the shoshonitic magmatic event arc continent collision led to emplacement of the oceanic arc and marginal basin crust onto the continental margin in pre late arenig times strong uplift of the obducted oceanic plate occurred in response to the buoyancy effect of the underthrusting less dense continental margin this is interpreted to have been followed by a reversal of subduction polarity and formation of a steeply dipping subduction zone against the continental margin lithosphere and was succeeded by the very evolved holonda porphyrite shoshonitic magmatism in volcanic islands along this submerged continental margin

interannual variability of the subsurface eddy field in the southeast pacific the southeast pacific which encompasses the coasts of peru and chile is one of the world s most productive regions resulting principally from the upwelling of subsurface nutrient rich waters over the satellite altimetry era there have been numerous evidence that surface mesoscale eddies play an important role in the offshore transport of rich coastal waters but it has been only recently that few observational numerical studies have highlighted the importance of the subsurface eddies the eddy field variability is explored using the results of a high resolution model experiment from 1979 to 2012 the model results indicate an asymmetry of the surface and subsurface eddy fields while surface intensified cyclones are slightly more frequent than anticyclones the subsurface field is dominated by anticyclones intrathermoclineeddies ites triggered by the instability of the subsurface peru chile undercurrent pcuc composite maps are consistent with in situ observations ites are associated with maximum vorticity around 150 200 m depth warmer and more saline core characteristic of the equatorial subsurface water from the pcuc we find that the variability of the ites is significantly correlated with the enso equatorial signal during strong el nino events e g 1982 1998 we find that while the pcuc transport increases the volume of coastal waters transported by ites however decreases during those periods we find that the relaxation of the isopycnals along the coast during el nino events leads to weakened baroclinic instability and to a decrease of the ites transport

tectonic evolution of the paleozoic barluk continental arc west junggar nw china abstract the barluk arc situated in west junggar is an important component of the kazakhstan domain in the central asian orogenic belt caob however the nature of the barluk arc active continental margin or oceanic island arc is in debate the igneous rocks in the shiwu area barluk arc have diagnostic petrologic geochronologic and geochemical signatures that uncover the attributes of the barluk arc in this paper we report detailed petrology whole rock geochemistry and sr nd isotopic zircon u pb dating and hf isotopic data of igneous rocks in the shiwu area our results reveal that 1 except for 302 2 ma gabbro igneous rocks from barluk arc in the shiwu area are dioritic and granitic have ages ranging from 323 8 to 310 5 ma and they have geochemical signatures originated from typical continental arcs including calc alkaline series rocks enrichment of lile depletion of hfse and higher th yb and ta yb values 2 the granitic porphyry and rhyolite in barluk arc have old tdm2 hf ages up to 1091 ma suggesting the existence of precambrian crust or similar materials as their sources and 3 the 302 2 ma gabbro dike has high values of end t 7 54 and ehf t 12 8 to 15 5 and a young t2dm nd age 455 ma and therefore it was possibly related to upwelling of asthenosphere mantle in a post subduction extensional tectonic setting based on these parameters we suggest that the barluk arc is defined as a late paleozoic continental margin arc along the margin of the kazakhstan continent westward subduction of the junggar oceanic plate in the barluk area started in early devonian and continued to the late carboniferous 310 ma subsequent post collisional tectonic processes between the junggar oceanic plate and kazakhstan continent continued to the late carboniferous 302 ma

metavolcanic rocks of the la ronge domain in the churchill province saskatchewan geochemical evidence for a volcanic arc origin the la ronge domain in the churchill province of the canadian shield is a volcanic sedimentary plutonic belt of early proterozoic age geochemical data supported by geological evidence strongly suggest that the la ronge metavolcanics were emplaced in an island arc setting the metavolcanic rocks range from basalt through andesite to dacite and rhyolite calcalkaline and tholeiitic types are dominant with minor alkaline varieties classification based on the major elements produces ambiguous results because of mobility of these elements during metamorphism however relatively immobile minor and trace elements provide reliable characterization of the basalts in particular the latter display distinctive trace element properties and morb normalized geochemical patterns similar to those of recent volcanic arc basalts being enriched in incompatible elements of low ionic potential and depleted in those of high ionic potential the calcalkaline basalts are in addition enriched in th p ce and sm a minor within plate component is also displayed by some metabasalts suggesting that magma genesis in parts of the la ronge arc involved sub continental lithosphere rare earth element patterns show enrichment in the lree with little or no eu anomaly interpretation by means of trace element discrimination diagrams incorporating elements such as ti y nb zr cr th yb and ce provides clear evidence for emplacement in a volcanic arc tectonic setting

origin and dynamics of mesoscale eddies in the catalan sea nw mediterranean insight from a numerical model study past observations and satellite sea surface temperature imagery indicate the presence of mesoscale anticyclonic eddies drifting along the catalan coast in september 2001 one of these anticyclonic eddies was surveyed over the shelf break during an oceanographic cruise which permitted the 3 d description of its structure in this work we investigate the origin and dynamics of such catalan eddies using a numerical circulation model of the northwest mediterranean at 3 km resolution driven by high resolution atmospheric analyses and compare model eddies with the observations in the catalan sea we identify two zones of eddy formation in the gulf of lions in front of the city of marseille and at the southeast of coast of roussillon from which anticyclonic eddies are observed to drift toward the catalan sea the hydrology and dynamics of the structures observed in the simulations are characterized sensitivity experiments and energy analysis are performed which allow us to identify the mechanisms associated with their generation properties of the eddy observed during the 2001 cruise at the catalan shelf break are found to compare well with model eddies generated at the southeast of the roussillon coast the model relates the origin of these eddies to the separation of the coastal current downstream from creus cape flow separation is linked to intense downwelling taking place in front of the roussillon coast when strong northwesterly winds events occur

tertiary subduction and slab break off model of the carpathian pannonian region abstract this paper illustrates the application of multidisciplinary data analysis to the carpathian pannonian region and presents a new tertiary development model that incorporates all multidisciplinary parameters during the late cretaceous eocene the future carpathian orogen was part of the larger alpine carpathian orogen formed by the southeastward subduction 135 55 ma of the penninic ocean and the ultimate collision 55 40 ma of the european and adriatic continents the subduction in the alpine region ended by the slab break off of the subducting oceanic lithosphere from the continental one and by the related magmatism 43 24 ma while the eocene alps were under continental collision the eocene remnant carpathian flysch basin rcfb was still subducting the carpathians and eastern parts of the alps started to occupy the region of the present carpathians during the early miocene the oceanic plate underlying the rcfb subducted southwestwards later westwards while the northeastward and eastward migration velocity of the accreting plate boundary decreased through time the slower subduction rate caused a steeper dip of the subducting slab the beginning of the eggenburgian 22 19 ma and following duration of extension in the orogenic hinterland accompanied by the asthenosphere upwelling the onset of the crustally derived volcanism above the risen asthenosphere and the younger mantle derived volcanism progressively less contaminated by the crustal material all contemporaneous with a shortening in the carpathian accretionary wedge the subduction of the rcfb finally led at the end of the early miocene to a collision with the continental margin along the westernmost part of the present carpathian arc the subduction roll back of the subducting slab of the rcfb under the advancing inner carpathians the oblique closure of the basin the progressive change of the subduction to collision from the west to the east along the carpathian arc drove a scissors like break off of the subducting oceanic slab along the west carpathians the break off in the east carpathians was driven by the weight of a subducting oceanic slab and buoyancy of the attached continental slab the break off started in the west of the carpathian arc in the early miocene ran along the arc to its present position in the bend area between the east and south carpathians and separated the oceanic slab that subducted passively under its own weight from the european continental margin the lateral propagation rate of the slab tear decreased with time the break off related volcanism was synchronous with the final stages of the collision

how biophysical interactions associated with sub and mesoscale structures and migration behavior affect planktonic larvae of the spiny lobster in the juan fernandez ridge a modeling approach abstract the juan fernandez ridge jfr is a chain of topographical elevations in the eastern south pacific 33 35 s 76 81 5 w rich in endemic marine species this ridge is frequently affected by the arrival of mesoscale eddies originating in the coastal upwelling zone off central southern chile the impacts of these interactions on the structure and dynamics of the jfr pelagic system have however not been addressed yet the present model based study is focused on the coupled influence of mesoscale submesoscale processes and biological behavior i e diel vertical migration on the horizontal distribution of planktonic larvae of the spiny lobster jasus frontalis around the jfr waters two case studies were selected from a hydrodynamic regional ocean modeling system to characterize mesoscale and submesoscale structures and an individual based model ibm to simulate diel vertical migration dvm and its impact on the horizontal distribution and the patchiness level dvm behavior of these larvae has not been clearly characterized therefore three types of vertical mechanisms were assessed on the ibm 1 no migration lg 2 a short migration 0 50 m depth dvm1 and 3 a long migration 10 200 m depth dvm2 the influence of physical properties eddy kinetic energy stretching deformation and divergence on larval aggregation within meso and submesoscale features was quantified the patchiness index assessed for mesoscale and submesoscale structures showed higher values in the mesoscale than in the submesoscale however submesoscale structures revealed a higher accumulation of particles by unit of area both vertical migration mechanisms produced larger patchiness indices compared to the no migration experiment dvm2 was the one that showed by far the largest aggregation of almost all the aggregation zones larval concentrations were highest in the submesoscale structures these zones were characterized by low eddy kinetic energy negative stretching deformation and slight convergence stretching deformation flow appeared to be triggered by the eddy eddy interactions and the robinson island barrier effect and it likely promotes the aggregation of the spiny lobster larvae in the juan fernandez system these results highlighted the importance of the coupled effect of physical mesoscale and submesoscale oceanographic features and biological processes dvm in the generation of larval patchiness and concentration of spiny lobster larvae around the jfr which could be key for their survival and retention in those waters

a census of meddies tracked by floats recent subsurface float measurements in 27 mediterranean water eddies meddies in the atlantic are grouped together to reveal new information about the pathways of these energetic eddies and how they are often modified and possibly destroyed by collisions with seamounts twenty meddies were tracked in the iberian basin west of portugal seven in the canary basin during february 1994 14 meddies were simultaneously observed 11 of them in the iberian basin most 69 of the newly formed meddies in the iberian basin translated southwestward into the vicinity of the horseshoe seamounts and probably collided with them some meddies 31 passed around the northern side of the seamounts and translated southwestward at a typical velocity of 2 0 cm s into the canary basin some meddies observed there were estimated to be up to 5 yr old four meddies in the canary basin collided with the great meteor seamounts and three meddies were inferred to have been destroyed by the collision overall an estimated 90 of meddies collided with major seamounts the mean time from meddy formation to a collision with a major seamount was estimated to be around 1 7 yr combined with the estimated meddy formation rate of 17 meddies yr from previous work this suggests that around 29 meddies co exist in the north atlantic therefore during february 1994 we observed about half of the population of meddies

geochemical criteria for a refined tectonic discrimination of orogenic andesites abstract minor trace element and sr isotope data are compiled for tertiary recent orogenic andesites of three tectonic settings 1 oceanic island arcs divided into low k and other andesites 2 continental island arcs and thin continental margins and 3 thick continental margins andean from 1 to 3 there is a steady overlapping increase in la ce ree la yb la y th th u zr y hf yb and ni co and a decrease in k la p la sc cr and sc ni optimum discriminationis achieved with a plots of la yb vs th and la yb vs sc ni and b cluster analysis using the critical parameters listed above shoshonitic andesites and high mg andesites boninites are considered separately orogenic andesites are distinguished from non orogenic andesites by high contents of al low contents of ti zr ree y nb ta and ga and the absence of pronounced negative eu anomalies

magmatic record of prototethyan evolution in sw yunnan china geochemical zircon u pb geochronological and lu hf isotopic evidence from the huimin metavolcanic rocks in the southern lancangjiang zone abstract the huimin metavolcanic rocks consisting mainly of basalt andesite and dacite are exposed predominantly in the huimin area of the southern lancangjiang zone sw yunnan three metavolcanic rock samples yielded zircon u pb ages of 456 3 ma 456 7 ma and 459 14 ma suggesting that the eruption occurred in the late ordovician these metavolcanics are characterized by sub alkaline rocks with high al2o3 12 45 17 68 wt and low tio2 0 60 0 96 wt the rocks are enriched in lrees and liles with weakly negative eu anomalies eu eu 0 37 0 99 and depleted in hfses which is geochemically similar to typical subduction related arc volcanic rocks zircons with late ordovician magmatic ages 456 ma have homogeneous lu hf isotopic compositions with in situ ehf t values of 4 36 3 30 and hf model ages of 1 51 1 55 ga indicating that the huimin metavolcanic rocks might have originated from a metasomatic mantle source our data provide reliable evidence for the presence of ordovician magmatism in the sanjiang area represent the magmatic record of prototethyan evolution in sw yunnan and identify a hitherto unknown early subduction event at the northeastern gondwana margin

geochemistry and tectonic setting of pre collision cretaceous and paleogene volcanic rocks of ecuador pre collision cretaceous lower tertiary volcanic rocks of western ecuador from the coastal area pinon and san lorenzo formations and western cordillera macuchi and celica formations consist of three rock suites the first suite includes tholeiites of ocean floor affinities that have distinct light ree depleted patterns and low la nb la hf and th hf ratios the island arc tholeiites of the second suite have lower contents of ti zr hf and nb the third suite comprises calc alkalic rocks mainly continental margin andesites and dacites the continental volcanic arc rocks crop out in an area east of the tholeiitic rocks the boundary between the two areas is the major suture separating continental south america from accreted terrenes to the west a model is suggested for the geodynamic evolution of what is now western ecuador during the late cretaceous it includes two east dipping subduction zones of turonian to santonian ages and the accretion of the oceanic island arc to the continent

crustal assimilation in the burnt lake metavolcanics grenville province southeastern ontario and its tectonic significance three intimately interbedded suites of volcanic rocks are identified geochemically in the burnt lake area of the belmont domain in the central metasedimentary belt and their petrogenesis is evaluated the burnt lake back arc tholeiitic suite comprises basalts similar in trace element signature to tholeiitic basalts emplaced in back arc basins formed in continental crust the burnt lake continental tholeiitic suite comprises basalts and andesites similar in trace element composition to continental tholeiitic sequences the burnt lake felsic pyroclastic suite comprises rhyolitic pyroclastics having major and trace element compositions that suggest that they were derived from crustal melts rare earth element models suggest that the burnt lake back arc tholeiitic rocks were formed by fractional crystallization of mafic magmas derived by approximately 5 partial melting of an amphibole bearing depleted mantle enriched in light rare earth elements by a subduction component the modelling also suggests that t

difference of ti zr y and p content in calc alkaline andesites from island arcs and continental margin central andes ti zr y and p known to be chemically immobile elements during alteration and metamorphism have been ploted in a set of diagrams in order to discriminative between calc alkaline andesites from island arcs and continental margin this method may be an appropiate procedure to help in the discrimination between ancient volcanics of both groups

carboniferous arc magmatism in the qiangtang area northern tibet zircon u pb ages geochemical and lu hf isotopic characteristics and tectonic implications abstract the longmu co shuanghu suture zone lssz which lies between the southern qiangtang baoshan block and northern qiangtang qamdo block on the tibetan plateau represents remnants of the paleo tethys ocean previous investigations have focused on the ophiolite high pressure zone and metamorphic belt in this zone whereas few studies have considered the arc magmatism the present study examines a suite of carboniferous arc magmatic rocks in the western region of the lssz that consist of acidic to basic volcanic rocks including rhyolite dacite andesite basaltic andesite basalt and pyroclastics zircon u pb dating of three samples two andesites and one dacite by laser ablation inductively coupled plasma mass spectrometry demonstrates that these rocks were emplaced at ca 351 346 ma the basalts have low cr and ni abundances indicating that they were generated by varying degrees of partial melting of an enriched lithospheric mantle that was metasomatized by subduction derived components zircons in the felsic rocks have positive e hf t values of 0 8 14 8 indicating an origin by varying degrees of partial melting of juvenile basaltic lower crust consisting mainly of underplated magmas with similar compositions to the basalts geochemical data show that the volcanic rocks are enriched in light rare earth elements and large ion lithophile elements e g th u and pb but are strongly depleted in high field strength elements e g nb ta and ti have high al 2 o 3 and low zr concentrations and are calc alkaline these magmas are therefore subduction related volcanic arc rocks indicating that paleo tethys subduction began in the early carboniferous

spatial temporal framework for the closure of the junggar ocean in central asia new sims zircon u pb ages of the ophiolitic melange and collisional igneous rocks in the zhifang area east junggar abstract the closure time of the junggar ocean is one of the hottest topics surrounding the tectonic evolution of the central asian orogenic belt caob this paper reports sims zircon u pb ages of the ophiolitic melange and collisional igneous rocks in the zhifang area east junggar our new results reveal the following evidence 1 the west hill ophiolitic melange in the zhifang area contains segments of the 371 ma morb type layered rocks and 363 ma oceanic islands which were intruded by the 348 ma syn collisional quartz diorites 2 the ophiolitic melange and 348 ma syn collisional quartz diorites are overlain by the 342 ma andesitic tuffs and 3 the 342 ma andesitic tuffs and successive 332 ma granodiorites gabbro were formed at late collisional setting whereas the 314 ma granitic porphyry at post collisional setting we suggest that the junggar ocean in the zhifang area was opened before 371 ma and 363 ma and possibly closed before 348 ma by combining the published u pb ages of the mayile tangbale darbute kalamaili zhifang daheishan mtdkzd ophiolite belt early carboniferous volcanic rocks unconformably overlying the mtdkzd ophiolite belt bimodal volcanic rocks and granitoids within and adjacent to the mtdkzd ophiolite belt it is suggested that the junggar ocean was possibly opened scissors like from the neoproterozoic ordovician mayile tangbale ocean eastwards through the silurian devonian darbute karamay ocean finally to the devonian early carboniferous kalamaili zhifang ocean and closed scissors like from the zhifang kalamaili area in the eastern segment westwards to the darbute karamay area in the western segment tectonic collage between the yemaquan xiemisitai arc and junggar block occurred at approximately 343 348 ma the junggar orogenic belt went through late collisional stage at 343 330 ma post collisional period after 330 ma and post collisional extensional regime after 320 ma with an intensive stage at around 303 ma

geological characteristics and genesis of the jurassic no i porphyry cu au deposit in the xiongcun district gangdese porphyry copper belt tibet abstract the xiongcun district located in the western segment of the gangdese porphyry copper belt gpcb hosts the only known jurassic mineralization in the gpcb tibet prc the no i deposit in the xiongcun district is related to the middle jurassic quartz diorite porphyry 167 161 ma and the mineralization was formed at ca 161 5 2 7 ma ore bearing middle jurassic quartz diorite porphyry emplaced into the early jurassic volcano sedimentary rock sequences of the xiongcun formation veinlets and disseminated mineralization developed within the middle jurassic quartz diorite porphyry and the surrounding metamorphosed tuff hosting a measured and indicated resource of 1 04 mt copper 143 31 t gold and 900 43 t silver with an average grade of 0 48 copper 0 66 g t gold and 4 19 g t silver the mineralization can be assigned to four stages including three main stages of hypogene mineralization and one epigenetic stage the main alteration associated with mineralization is potassic seven mineralization related hydrothermal veins have been recognized including quartz sulfide biotite sulfide magnetite sulfide quartz molybdenite sulfide chalcopyrite pyrite pyrrhotite pyrite and polymetallic veins the s and pb isotopic compositions of the ore sulfides and the re contents of the molybdenite suggest a mantle source for the ore forming materials with minor contamination from the subducted sediments hydrogen and oxygen isotope compositions of quartz in the ores suggest that both magmatic and meteoric waters were involved in the ore forming process the ore bearing porphyry 167 161 ma and ore forming 161 5 2 7 ma ages of the no i deposit correspond to the time of northward subduction of neo tethys oceanic slab the geochemical data of the ore bearing porphyry indicate that the no i deposit formed in an intra oceanic island arc setting and the ore bearing porphyry originated from the partial melting of mantle with limited contribution of subducted sediments the genesis of the ore bearing porphyry and no i deposit is interpreted as being related to northward intra oceanic subduction of neo tethys oceanic slab in the middle jurassic time 167 161 ma

petrology geochemistry and la icp ms u pb geochronology of paleoproterozoic basement rocks in bangladesh an evaluation of calc alkaline magmatism and implication for columbia supercontinent amalgamation abstract the paleoproterozoic 1 7 ga basement rocks from maddhapara bangladesh show a large range of chemical variations e g sio2 50 7 74 7 and include diorite quartz diorite monzodiorite quartz monzonite and granite the pluton overall displays metaluminous calc alkaline orogenic suite mostly i type suites formed within subduction related magmatism the observed major elements show general trends for fractional crystallization trace element contents also indicate the possibility of a fractionation or assimilation explain the entire variation from diorite to monzonite even granite the pluton may have evolved the unique chemical features by a process that included partial melting of calc alkaline lithologies and mixing of mantle derived magmas followed by fractional crystallization and by assimilation of country rocks the pluton shows evidence of crystal fractionation involving largely plagioclase amphibole and possibly biotite some of the fractionated magmas may have mixed with more potassic melts from distinct parts of the continental lithosphere to produce granites and or pegmatites new geochronological results of granitic pegmatite 1722 10 ma are indisputably consistent with diorite and tonalite and those data showing credible geochronological sequence i e diorite tonalite granitic pegmatite identical paleoproterozoic age 1 7 ga with distinctive magmatism of the maddhapara basement rocks have agreeable relationship with the citz india the consistent magmatism is also common in the transamazonian of south america trans hudson orogeny in north america bohemian massif and the svecofennian poland have identified the sequential growth of the continent through the amalgamation of juvenile terrains succeeded by a major collisional orogeny such paleoproterozoic subduction related orogens in australia have similar counterparts in antarctica and other part of the world these types of paleoproterozoic magmatism dominantly contributed to assemble amalgamation and breakup of the enormous columbia supercontinent

late jurassic early cretaceous episodic development of the bangong meso tethyan subduction evidence from elemental and sr nd isotopic geochemistry of arc magmatic rocks gaize region central tibet china abstract the bangong meso tethys plays a critical role in the development of the tethyan realm and the initial elevation of the tibetan plateau however its precise subduction polarity and history still remain unclear in this study we synthesize a report for the late jurassic early cretaceous two phase magmatic rocks in the gaize region at the southern margin of the qiangtang block located in central tibet these rocks formed during the late jurassic earliest cretaceous 161 142 ma and early cretaceous 128 106 ma peaking at 146 ma and 118 ma respectively the presence of inherited zircons indicates that an archean component exists in sediments in the shallow qiangtang crust and has a complex tectonomagmatic history geochemical and sr nd isotopic data show that the two phase magmatic rocks exhibit characteristics of arc magmatism which are rich in large ion incompatible elements liies but are strongly depleted in high field strength elements hfses the late jurassic earliest cretaceous magmatic rocks mixed and mingled among mantle derived mafic magmas subduction related sediments or crustally derived felsic melts and fluids formed by a northward and steep subduction of the bangong meso tethys ocean crust the magmatic gap at 142 128 ma marks a flat subduction of the meso tethys the early cretaceous magmatism experienced a magma mash melting assimilation storage and homogenization process among mantle derived mafic magmas or crustally derived felsic melts and fluids as a result of the meso tethys oceanic slab roll back which triggered simultaneous back arc rifting along the southern qiangtang block margin

mean surface circulation and mesoscale turbulent flow characteristics in the eastern south pacific from satellite tracked drifters 1 circulation of the eastern south pacific region 10 34 s 70 100 w was studied using drifting buoy trajectories from 1979 to 2003 three different current regimes were highlighted the south equatorial current flowing westward north of 26 s with surface velocities of 7 8 cm s 1 the south pacific current an eastward current of 2 cm s 1 south of 25 30 s and the chile peru current a northwestward flow of 6 cm s 1 found to the east of 82 w and south of 22 s the velocity variance distribution showed the regional flow to be anisotropic in nature maps of eddy kinetic energy obtained from drifter measurements and satellite altimetry data showed similar patterns with higher energy levels near the south american coast the lagrangian time and length scales of the turbulent flow revealed typical values of 5 9 0 6 days and 40 7 5 4 km in the zonal direction and of 3 5 0 4 days and 29 3 4 km in the meridional direction the estimated diffusivities were 4 9 0 5 107 cm2 s 1 and 2 6 0 3 107 cm2 s 1 in the eastward and northward directions respectively finally we estimated the respective role of horizontal advection and lateral diffusion on the mixed layer heat and salt budgets near the coast the lateral turbulent fluxes in the surface layer were two times larger than the horizontal transports associated with the large scale circulation mean horizontal heat and salt diffusive fluxes were around 25 w m 2 and 50 g m 2 d 1

volcanic dykes in the north chilean coast range dense swarms of predominantly mafic dykes outcrop in the north chilean coast range these rocks are not lamprophyres they mark channelways used by jurassic to lower cretaceous extrusives

eddy activity in the four major upwelling systems from satellite altimetry 1992 2007 eddy activity in the four major eastern boundary upwelling systems ebus is investigated using 15 years of satellite altimetry data based on the analysis of more than 4000 long lived eddy trajectories in every ebus we show that mesoscale structures are mainly generated along the continental coasts and south of the main archipelagos and propagate westward with velocities increasing toward the equator these mesoscale eddies having radii of 70 160 km are then frequently observed along the coastal transition zones and frontal regions and some large oceanic areas are preferentially populated by cyclonic or anticyclonic eddies temporal variations of the number of newly formed eddies and the associated eddy activity index defined as the mean eddy energy density are finally examined at seasonal and interannual scales the strongest seasonal interannual respectively variations are observed in the california benguela upwelling systems the proposed indices also exhibit contrasted long term trends in each ebus which suggests that eddy activity might be sensitive to a warming climate

main eddy vertical structures observed in the four major eastern boundary upwelling systems in the four major eastern boundary upwelling systems ebus mesoscale eddies are known to modulate the biological productivity and transport near coastal seawater properties toward the offshore ocean however little is known about their main characteristics and vertical structure this study combines 10 years of satellite altimetry data and argo float profiles of temperature and salinity and our main goals are i to describe the main surface characteristics of long lived eddies formed in each ebus and their evolution and ii to depict the main vertical structure of the eddy types that coexist in these regions a clustering analysis of the argo profiles surfacing within the long lived eddies of each ebus allows us to determine the proportion of surface and subsurface intensified eddies in each region and to describe their vertical structure in terms of temperature salinity and dynamic height anomalies in the peru chile upwelling system 55 of the sampled anticyclonic eddies aes have subsurface intensified maximum temperature and salinity anomalies below the seasonal pycnocline whereas 88 of the cyclonic eddies ces are surface intensified in the california upwelling system only 30 of the aes are subsurface intensified and all of the ces show maximum anomalies above the pycnocline in the canary upwelling system 40 of the aes and 60 of the ces are subsurface intensified with maximum anomalies extending down to 800 m depth finally the benguela upwelling system tends to generate 40 50 of weak surface intensified eddies and 50 60 of much stronger subsurface intensified eddies with a clear geographical distribution the mechanisms involved in the observed eddy vertical shapes are discussed

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

cretaceous volcanic rocks in south qiangtang terrane products of northward subduction of the bangong nujiang ocean the subduction of the bangong nujiang ocean is a long standing problem in the study of the geological evolution of the tibetan plateau based on recent data acquired from the abushan volcanic rocks in the qiangtang terrane we will discuss the relationship between the cretaceous volcanism and the evolution of the bangong nujiang ocean the abushan volcanic rocks are mainly composed of trachy andesites dacites and rhyolites zircon u pb dating constrains the time of emplacement as the middle cretaceous 102 6 1 6 96 1 2 4 ma major element geochemistry shows that the volcanic rocks belong to the high k calc alkaline and calc alkaline series all of the volcanic rocks are enriched in light rare earth elements lree and some large ion lithophile elements lile rb th and u and are depleted in heavy rare earth elements hree and some high field strength elements hfse nb ta and ti the geochemical characteristics of the abushan volcanic rocks are correlated with those of the volcanic arc rocks in the subduction zone the petrogenesis of the abushan volcanic rocks suggests that they were derived from the partial melting of the relict subducted oceanic crust combined with the input of oceanic sediments oceanic crust will melt upon reaching its hydrous solidus in the amphibolite facies after plate collision this induces the formation of the abushan volcanic rocks our data compared with the previous studies on volcanism in the lhasa terrane leads us to propose that the bangong nujiang ocean crust was subducted beneath the qiangtang terrane and underwent bidirectional subduction during the cretaceous

the variscan post collisional volcanism in late carboniferous permian sequences of ligurian alps southern alps and sardinia italy a synthesis abstract in the considered wide sector of the west mediterranean southern europe the collisional phase of the variscan orogeny during late carboniferous and permian times was followed by magmatic intrusive and effusive activity and sedimentation into intracontinental alluvial to lacustrine basins originated by wrench to normal fault systems the first volcanic cycle generally late carboniferous early permian in age is represented by early calc alkaline andesites and rhyolites in variable amounts and by following large volume of rhyolites and by dacites both andesites and rhyolites show k normal and high k calc alkaline character the origin of the liquids of the first cycle is ascribed to partial melting processes at the mantle crust interface telescoped within a thickened crust the melting is considered as the consequence of thermal re equilibration following isostatic disequilibrium and the subsequent collapse of the orogenic belt the ascent of liquids occurred in a trans tensional regime the second magmatic cycle is represented by alkaline magmatism and exhibits typical anorogenic features consistent with a rifting regime this event was no more related with the collapse of the variscan belt but rather to the post variscan global re organization of plates that evolved during late triassic times to the neo tethyan rifting in both cycles important differences in timing areal distribution and outpoured volumes arise

genesis and tectonic setting of the giant diyanqin amu porphyry mo deposit in great hingan range ne china constraints from u pb and re os geochronology and hf isotopic geochemistry abstract the great hingan range is located in the eastern sector of the central asia orogenic belt and is the second important mo province in china next to the qinling dabie orogenic belt previous studies concluded that all the mo deposits mo only or mo dominated polymetallic in the area were formed in the mesozoic and related either to the syn to post collisional setting following the closure of the paleo asia ocean or to the westward subduction of the pacific plate however the fluids forming the giant diyanqin amu porphyry mo deposit in the area disagree with the features of collision type mo deposits but accord with those of the subduction or continental arc type the mo mineralization is hosted in the late jurassic volcanic rocks and genetically related to the buried porphyritic granite and aplitic granite two porphyritic granite samples yield la icp ms zircon weighted mean 206 pb 238 u ages of 158 7 0 8 ma mswd 0 64 2 and 158 0 0 9 ma mswd 0 38 2 respectively the aplitic granite yields a zircon u pb weighted mean 206 pb 238 u age of 156 9 1 1 ma mswd 0 48 2 slightly younger than the porphyritic granite seven molybdenite samples from the ores yield re os isotope ages of 156 1 2 2 to 158 1 4 3 ma these ages constrain that the diyanqin amu mo system was formed in the period of 159 156 ma the granites at the deposit have high contents of sio 2 k 2 o and al 2 o 3 and low contents of tio 2 mgo and cao showing a peraluminous high k calc alkaline affinity these granites and the host volcanic rocks are characterized by enrichment of k rb u pb th and lree and depletion of nb ta ti and hree with negative eu anomaly which are similar to magmatic rocks in the andean arc zircon grains from the granites show positive e hf t values of 4 2 9 0 with t dm2 hf ages of 0 63 0 94 ga these geochemical data imply that the granites at diyanqin amu are highly fractionated i type formed in a continental arc generated by the southeastward subduction of the mongol okhotsk oceanic plate

geochemistry of meta sedimentary rocks associated with the neoarchean dagushan bif in the anshan benxi area north china craton implications for their provenance and tectonic setting abstract the anshan benxi area is situated in the northeastern part of the north china craton ncc and consists predominantly of neoarchean supracrustal rocks and plutons with minor eoarchean to mesoarchean rocks these supracrustal rocks were originally considered to be formed synchronously 2 5 ga at different localities on an active continental margin recently more detailed petrographic geochemical and geochronological analyses showed that the supracrustal strata in the benxi area 2 56 2 53 ga were slightly older than those in the anshan area 2 53 2 51 ga which further indicates that they were formed during opening and closure of the back arc basin respectively however the dagushan banded iron formation bif and associated supracrustal rocks in the anshan area were interpreted to be deposited in mesoarchean 3 10 ga which constructs a clear contrast with other supracrustal rocks in the anshan benxi area and renders previous tectonic models controversial on the basis of detailed field investigations in the dagushan area we present in situ zircon u pb hf isotopic whole rock geochemical and sm nd isotopic data of a suite of meta sedimentary rocks i e meta arenites meta shales and high fe meta shales in order to provide constraints on their depositional age provenance and tectonic setting the weighted mean u pb ages of the youngest group of detrital zircons for the meta arenite in the dagushan area coupled with the maximum metamorphic age of 2 51 ga in the anshan benxi area suggest that the dagushan bif was deposited between 2 53 and 2 51 ga geochemical features such as the al2o3 tio2 and th zr values and ree patterns suggest that the meta arenites and meta shales were mainly derived from felsic igneous sources whereas the high fe meta shales were predominantly sourced from mafic rocks the u pb age spectrum diagram of detrital zircons within meta arenites further indicates that the dominant source rocks may be the coeval volcanic rocks in the benxi area our zircon hf isotopes coupled with other previously published zircon hf isotopic data from neoarchean supracrustal rocks in the anshan benxi area suggest that major juvenile crustal growth and reworking events occurred at 2 9 2 7 ga and 2 5 ga respectively in all the dagushan meta sedimentary rocks were probably deposited in a back arc basin on the ancient continental margin

mesoscale variability and nutrient phytoplankton distributions off central southern chile during the upwelling season the influence of mesoscale eddies abstract mesoscale features are recurrently found in the coastal transition zone ctz off central southern chile 35 40 s a region characterized by seasonal wind driven coastal upwelling in this study oceanographic data from two consecutive cruises carried out during the upwelling season january 2009 were combined with satellite time series data in order to characterize the structure and evolution of mesoscale eddies and to explore their influence on phytoplankton structure and nutrient distribution in the context of organic carbon exchanges between the coastal upwelling zone and the ctz two coastally generated contiguous mesoscale eddies 2 months old were characterized a surface cyclonic eddy cc1 and a subsurface anticyclonic eddy aa1 the distributions of salinity and dissolved oxygen together with nutrients suggested that both eddies were sites of vertical injection of high nutrient concentrations from the equatorial subsurface water mass essw into the upper layer in the ctz in addition eddy aa1 in combination with an upwelling plume was involved in the offshore advection of nutrients from the core of the essw located in the coastal zone at shallow depths

intrathermocline eddies in the coastal transition zone off central chile 31 41 s 1 the three dimensional structure and the origin of mesoscale anticyclonic intrathermocline eddies ites in the coastal transition zone ctz off central chile 31 41 s were analyzed through the combination of data from oceanographic cruises and satellite altimetry and the application of an eddy resolving primitive equation ocean model coupled with a numerical experiment using a passive tracer in this region ites are represented by subsurface lenses 100 km diameter 500 m thickness or vertical extension of nearly homogeneous salinity 34 5 and oxygen deficient 1 0 ml l 1 waters properties which are linked to the equatorial subsurface water mass essw transported poleward by the peru chile undercurrent pcuc in the coastal band at least five to seven ites were observed simultaneously in the area between 31 and 38 s during winter cruises in 1997 and 2009 satellite data indicated that the ites identified from in situ data moved westward each at a mean speed of 2 km d 1 and transported a total volume of 1 106 m3 s 1 1 sv the lifespan of each ite ranged from a few months to 1 year model results indicate that ites become detached from the pcuc under summer upwelling conditions in the coastal zone

evolution of the northward subduction of the neo tethys implications of geochemistry of cretaceous arc volcanics in qinghai tibetan plateau abstract the subduction history of the neo tethys is critical for understanding the early stage tectonic evolution of the qinghai tibetan plateau arc volcanics which usually record the subduction process thus can help trace the evolution of the neo tethys in this paper we report for the first time zircon la icp ms u pb ages whole rock major and trace element geochemistry as well as sr nd hf isotopic data for the volcanic rocks from the danshiting formation at the southern edge of the lhasa terrane two samples collected from the danshiting formation volcanic rocks yield zircon u pb ages of 97 1 0 8 ma and 90 1 0 7 ma respectively the volcanic rocks of the danshiting formation are composed dominantly of basalts and andesites characterized by depletion of high field strength elements low 87sr 86sr i ratios 0 7042 0 7045 high end t 2 1 to 2 7 and high ehf t values mean 11 6 these rocks show geochemical affinity of arc volcanic rocks the volcanic rocks of the danshiting formation may have formed during the northward subduction of the neo tethys this paper combined with the previous data briefly divide the northward subduction of the neo tethys into four periods the jurassic 195 150 ma when the magmatic activity was controlled by the northward high angle subduction of the neo tethys that produced volcanics of the yeba and bima formations the late jurassic to early cretaceous 150 110 ma when the neo tethys subducted at low angles the late cretaceous 110 80 ma when subduction was of the andean type and produced volcanic rocks of the danshiting formation the paleogene 70 40 ma when there was transition from ocean to continent subduction to continent continent collision that produced volcanic rocks of the linzizong group

tectonic evolution of the east junggar terrane evidence from the taheir tectonic window xinjiang china abstract the taheir tectonic window is located at the southern part of the yemaquan magmatic arc in east junggar this paper reports detailed petrology mineral chemistry whole rock and sr nd isotope geochemistry hornblende 40ar 39ar dating in situ zircon u pb dating and hf isotope analyses from igneous and meta igneous rocks from this region our new results show that the taheir tectonic window consists of metamorphic and deformed ordovician volcanic rocks and granitic porphyries ordovician silurian granites and undeformed silurian devonian granitic diorite diorites and rhyolitic porphyries the ordovician volcanic rocks and granitic porphyries and ordovician silurian granites in the taheir tectonic window exhibit distinct features of andean type continental arc such as enrichment in pb k and u depletion in nb p and ti negative eu anomalies high la yb th yb and ta yb values a high proportion of dacite rhyolite and andesite of the calc alkaline series massive contemporary granitic intrusions mixtures of the juvenile material and 2 5 ga crust and extensive crystallization differentiation these ordovician volcanic rocks witnessed a series of tectonic events including burial associated with the intrusion of 454 449 ma granitic porphyries underthrusting and subsidence to a depth in the middle crust associated with the intrusion of 443 432 ma granites the formation of albite hornblende schists hornblende albite quartz leptynites and amphibolites the transformation from continental to continental island arc at approximately 432 ma the exhumation associated with the intrusion of 416 406 ma diorites with geochemical signatures of continental island arc and exhumation and erosion between 398 ma and 390 ma are also identified the arc types that are associated with the taheir tectonic window and its host the yemaquan magmatic arc changed from andean type continental arc to continental island arc after the intra arc rifting that began at 432 ma on the basis of the new evidence the tectonic regime of the east junggar terrane is redefined and a new model is proposed it is suggested that the east junggar terrane is related to the southward subduction of the paleo asian ocean plate beneath the junggar continent in the early paleozoic and later shift to intra oceanic subduction

the geochemistry and petrogenesis of the lavas of the vulsinian district roman province central italy the vulsinian lavas are dominated by a suite of undersaturated leucite bearing basic to intermediate compositions the remaining lavas are mainly oversaturated and have shoshonitic affinities one hundred and thirty five samples have been analysed for major elements and most for 20 trace elements twenty seven lavas have been analysed for ree they are all perpotassic for the undersaturated lavas k2o na2o 2 8 and have very high lil element concentrations e g rb 400 800 ppm th 25 150 ppm ree reecho c 200 lree hree cho c 20 even in the most basic rocks

early jurassic volcanic rocks in the xiongcun district southern lhasa subterrane tibet implications for the tectono magmatic events associated with the early evolution of the neo tethys ocean abstract early mesozoic late triassic to middle jurassic igneous rocks in the southern lhasa subterrane tibet record important information on the early tectono magmatic evolution of the neo tethys ocean this paper presents petrological geochronological and geochemical data for the xiongcun formation ignimbrites to constrain the petrogenesis and tectonic setting of these rocks in the southern lhasa subterrane the xiongcun formation is dominated by andesitic and dacitic rocks these rocks yield early jurassic 195 176 ma zircon u pb ages and display typical arc like geochemical signatures being enriched in large ion lithophile elements e g rb ba and u and depleted in high field strength elements e g nb ta and ti sr nd pb hf isotopic compositions are highly depleted these chemical and isotopic data suggest that the xiongcun formation ignimbrites probably formed in an intra oceanic island arc setting related to the northward subduction of the neo tethys oceanic slab the parental magmas were derived from a depleted mantle source modified by fluids released from the neo tethys oceanic slab combined with previously reported data we suggest that the volcanic rocks in the early jurassic xiongcun and yeba formations of the southern lhasa subterrane were generated by a single subduction system but developed on oceanic and continental crust respectively

seasonal and interannual variability of currents and temperature off central chile results are reported for continuous 6 year records of current and temperature from a continental slope station at 308s off chile these observations for november 1991 to november 1997 span the moderate weak and strong el nino events of 1991 1992 1994 and 1997 and the la nina event of 1995 1996 results for current and temperature are analyzed together with observations of wind along the south american coast from the ers 1 and 2 satellite scatterometers wind from a local coastal site sea level from northern and central chile sea surface temperature anomalies from the south pacific region and traditional el nino indices mean poleward flow of 12 8 cm s 21 was observed for the 6 year period in the core of the peru chile undercurrent 220 m mean flow in the depth range of antarctic intermediate water 750 m was equatorward at 1 1 cm s 21 intraseasonal scale variability associated with coastal trapped waves was weaker during the austral winter greatest during el nino events and weakest during the la nina event winds adjacent to the coast showed a strong annual cycle with a southward progression of maximum equatorward upwelling favorable winds alongshore flow over the slope exhibited strong semiannual and weaker annual variations poleward flow in the undercurrent was strongest in the austral spring and fall and weakest in the winter near the bottom 750 m seasonal scale variability was less intense but led that higher up in the water column 220 m by 1 month strong interannual variability of alongshore current and temperature was found at all depths over the slope whereby changes at depth led changes higher up a rapid warming event was observed at the end of 1996 beginning of 1997 over the slope this event also seen in sea level and sea surface temperature off chile led el nino indices by several months and may be best explained by local wind anomalies coupled to atmospheric teleconnections from the western tropical pacific at the onset of el nino some aspects of our current and temperature observations are consistent with results from eastern boundary current models our results indicate that both ocean and atmosphere pathways from the equatorial pacific contribute significantly to interannual scale variability of alongshore flow and thermocline depth off chile

composite lava flows of ordovician age in the english lake district three composite andesitic lava flows within the ordovician borrowdale volcanic group are described they are 35 250 m thick and in their simplest form consist of a massive flow jointed andesite lower part and a flow laminated to blocky basaltic andesite upper part with a zone of interlayering between them one flow has a very thin discontinuous basal unit of xenolithic flow laminated basaltic andesite the interlayered zone comprises layers and lenses of andesite basaltic andesite and mixed rocks consisting of closely packed inclusions of pale coloured andesite in a chlorite rich matrix the rocks have undergone several stages of alteration a deuteric alteration including silicification associated with autobrecciation of the upper component and inter magma reactions in the interlayered zone b soda metasomatism preferentially of basaltic andesite c metamorphism attributed to the lake district granite batholith giving an actinolite sericite assemblage d regional metamorphism to give a chlorite epidote actinolite sphene assemblage with rare prehnite and pumpellyite e calcite veining these alterations have modified the bulk chemistry of the rocks but the concentrations of al p ti v cr co ni ga y zr nb la ce and th are largely unaffected on the scale of a 2 kg sample using these elements the composition of the lavas compares with high k orogenic andesites emplaced through continental crust each of the flows shows distinct chemical characteristics which may be explained by variations of phenocryst content or the assimilation of cognate xenoliths variations within flows can be explained by magma mixing and fractional crystallization of plagioclase minor pyroxene ilmenite and zircon a mechanism for eruption is proposed in which a volatile rich basic magma intruded de gassed cooler less dense andesite magma in a high level sub volcanic chamber the basic magma formed the lower layer in the chamber on cooling and crystallization of plagioclase near the interface the volatile content of the residual basic liquid rose and the density decreased allowing the liquids to form an emulsion like layer at the interface this separated and rose into the andesite magma and the process was repeated to form an interlayered zone at the junction before mixing was complete the magma was erupted as a series of composite flows

relationships between intermediate and acidic rocks in orogenic granitoid suites petrological geochemical and isotopic sr nd pb data from capo vaticano southern calabria italy abstract major trace element and isotopic data are reported for hercynian granodiorites and tonalites from capo vaticano calabria with the aim of clarifying the relationships between acidic and intermediate lithologies in orogenic intrusive suites these granodiorites sio 2 70 5 73 5 are peraluminous relatively depleted in rb u th and pb and display a large variation in many geochemical and isotopic parameters ree show fractionated cross cutting chondrite normalized patterns with small but significant negative eu anomalies initial 290 ma sr and nd and present day pb isotope ratios are 87 sr 86 sr 290 0 7105 0 7110 143 nd 144 nd 290 0 51175 0 51221 206 pb 204 pb 18 35 18 50 207 pb 204 pb 15 64 15 76 208 pb 204 pb 38 51 39 03 pb isotope ratios determined for separated feldspars show similar 207 pb 204 pb and 208 pb 204 pb and higher 207 pb 204 pb ratios compared to the present day values for the whole rock the tonalites sio 2 57 6 67 3 are typically calc alkaline in composition and most of them are weakly peraluminous they display large heterogeneities in trace element abundances ree patterns and nd and pb isotope ratios both between and within individual intrusive units sr nd and pb isotopic compositions display a range of values close to that of the associated granodiorites 87 sr 86 sr 290 0 7099 0 7111 143 nd 144 nd 290 0 51185 0 51224 206 pb 204 pb 18 31 18 56 207 pb 204 pb 15 65 15 72 208 pb 204 pb 38 41 39 59 the obtained data indicate that the tonalites and granodiorites share many compositional features which point to a genetic linkage likewise many petrological geochemical and field data exclude the possibility that all the granodiorites derive from intermediate magmas by any common evolutionary process such as crystal liquid fractionation or assimilation fractional crystallization afc and point to a different genesis for the two rock types an origin of the granodiorites by the mixing of two separate acidic melts one of crustal anatectic origin and one probably derived from an intermediate magma by crystal liquid fractionation or afc is suggested by the data presented the tonalites appear to have been generated by interaction of a mafic magma with crustal end member s with isotopic and geochemical signatures similar to those of the granodiorites the large involvement of crustal material in the genesis of the capo vaticano granitoids is responsible for the many common compositional characteristics observed in the intermediate and acidic rocks however a contribution from mantle components is also indicated by petrological and geochemical data as well as by the occurrence of mafic enclaves commonly present in the tonalites nevertheless the geochemical and isotopic features of such a mantle component appear to be greatly diluted by a large quantity of crustal material involved in the genesis of the studied granitoids

geochemistry and geodynamic setting of volcanic and plutonic rocks associated with early archaean volcanogenic massive sulphide mineralization pilbara craton abstract early archaean volcanic rocks and syn volcanic granites at strelley east pilbara craton western australia were formed during an extensional tectonic phase associated with an active convergent continental margin the volcanic sequence comprises a bimodal suite of fractionated sub alkalic tholeiitic basalts andesites and dacites siliceous laminites and volcanogenic massive sulphide vms deposits in the footwall and hangingwall calc alkaline dacites the footwall rocks are characterized by th lapm 1 variably fractionated lree and relatively high y and yb 33 and 3 ppm respectively negative normalized anomalies of nb p ti are consistent with derivation via slab dehydration fusing the mantle wedge the co magmatic and syn volcanic strelley granite is enriched in lile relative to hfse and has distinctively low al2o3 11 14 and la yb n 4 10 suggesting a relatively mature and cool subducted oceanic lithosphere as for the majority of phanerozoic arc granitoids and convergent margin magma compositions the chemical composition of the footwall basaltic to dacitic rocks and the sub volcanic strelley granite display signatures highly prospective for vms mineralization large ve eu anomalies low zr y ratios high level magmatic fractionation comparable with the noranda fiiia type suite the hangingwall dacites have more pronounced hree fractionation than footwall counterparts and lower y and yb the chemistry of the footwall volcanic rocks and granite reflect typical phanerozoic conditions of steep subduction hydrous metasomatism in the mantle wedge and fractionation similar characteristics are also evident in plutonic volcanic suites associated with vms deposits in the late archaean as at noranda canada early extension with nascent back arc development coupled with steep subduction is considered critical to the development of vms deposits

the geology and geochemistry of an early proterozoic volcanic arc association at cartwright lake lynn lake greenstone belt northwestern manitoba the geology of the cartwright lake area consists of a 2 km thick conformable sequence of early proterozoic supracrustal rocks intruded by calc alkaline granitoid plutons the supracrustal successi

the geochemistry and tectonic significance of pre metamorphic minor intrusions of the central metasedimentary belt grenville province canada abstract more than 250 samples collected from dykes and sills intruded into the grenville supergroup have been analysed by xrf techniques for their major and trace element contents the ree contents of 43 of the samples have been determined by inaa using these data the rocks have been identified and placed in seven suites each characterized by its own trace element signature there are four tholeiitic suites the low zirconium suite which comprises a bimodal series of basalts and minor dacites the intermediate zirconium suite which is made up of basalts andesites dacites and rhyolites the high zirconium suite consisting of high iron basalts and rare highly fractionated tholeiites which comprise basalts characterized by high mg number high ni and cr contents and with strongly fractionated trace element patterns in addition a calc alkaline suite made up of basalts and andesites a transitional suite of andesites and trachyandesites and an ultra potassic suite of leucitites have been identified on chondrite normalized multi element plots all of the suites show negative nb and ti anomalies similar ranges of rock types with similar anomalies occur within volcanic arcs and back arc basins formed at collisional plate margins where the nb and ti anomalies are interpreted as subduction signatures and also in some continental flood basalt sequences in which the anomalies are commonly suggested to result from crustal contamination the geology of the central metasedimentary belt leads us to favour an interpretation in which the minor intrusions were emplaced in supracrustal rocks deposited upon attenuated continental crust in a back arc basin during a collisional orogeny

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

el nino variability in simple ocean data assimilation soda 1871 2008 1 a new ocean reanalysis that covers the period from 1871 to 2008 is used to explore the time evolving characteristics of el nino the new reanalysis assimilates all available hydrographic and sea surface temperature data into a model of the global ocean forced with surface boundary conditions from an atmospheric reanalysis that also covers the period from 1871 through 2008 using traditional measures of el nino our reanalysis shows that the timing of el nino events is in agreement with sea surface temperature reconstructions but el nino in the reanalysis is stronger particularly from 1871 to 1920 a new index based on the first moment of the temperature anomaly is introduced the new index is used to characterize the strength and location of el nino events and has the advantage that it is independent of the location of el nino using the new index el nino in the reanalysis shows prominent decadal variability of strength but relatively little long term trend el nino events were strong in the last part of the 19th century and first part of the 20th century and again in the latter part of the 20th century with weak el nino events in the middle of the 20th century the location of el nino also varies considerably ranging from the western to the eastern pacific near the coast of south america however the null hypothesis that the location of el nino can be represented as a random distribution about a central longitude of about 140 w cannot be rejected

geochemical evolution of the quaternary chachimbiro volcanic complex frontal volcanic arc of ecuador abstract the chachimbiro volcanic complex cvc is a composite volcano located in the frontal part of the ecuadorian quaternary arc four periods of activity can be differentiated in chachimbiro 400 ka long volcanic history named ch1 405 7 20 0 298 6 32 9 ka ch2 121 75 23 2 36 08 2 8 ka ch3 36080 280 22730 120 ybp and ch4 5 760 30 ybp respectively the magmatic suite ranges in composition from andesites to rhyodacites and displays systematic increases of sio2 sr y la yb incompatible elements e g lree mree lile and depletion of hree with time these geochemical features coupled with radiogenic isotope data and textural observations e g several resorption and overgrowth cycles in plagioclase phenocrysts suggest an open system evolution for cvc including typical crustal magmatic processes such as recharge assimilation and fractional crystallisation to better constrain the magmatic crustal processes of the cvc we use a multi model approach including three open system models rfc recharge fractional crystallisation afc assimilation fractional crystallisation and ec rafc energy constrained recharge assimilation fractional crystallisation different simulations have been developed to best fit cvc s geochemistry including trace elements sr y ratios and sr isotopes which suggest predominant fractional crystallisation and variable assimilation as the main processes explaining the bulk of the geochemical data of cvc this is consistent with an overall thermal decline of the magmatic system through time the genetic model here presented involves the input of a magmatic recharge component matured in the low mid crust through dominant fractionation of amphibole garnet into intermediate crustal reservoir s where magma undergoes extensive fc

isotopic evolution of the middle to late proterozoic awasib mountain terrain in southern namibia abstract the middle to late proterozoic awasib mountain terrain amt is situated at the approximate contact between the supracrustal sinclair sequence and the namaqualand metamorphic complex in southern namibia tholeiitic to alkaline metabasalts from the kairab metamorphic complex which forms part of the basement to the sinclair sequence in the amt yield an rb sr isochron age of 1461 169 ma with an initial 87sr 86sr r0 of 0 70269 12 a preliminary pb pb isochron age of 1467 215 201 ma for these metabasalts appears to confirm the rb sr age these metabasalts have been intruded by the calc alkaline aunis tonalite gneiss which yields an rb sr isochron age of 1271 62 ma and r0 of 0 7029 3 the low r0 obtained for both of these basement units implies that the ages are primary and hence that the isotope systematics have not been disturbed by subsequent deformation and metamorphism andesitic and rhyolitic volcanics of the haiber flats formation hff are correlated with the sinclair sequence basaltic andesites from the hff have shoshonitic affinities and may be classified as medium to high k and orogenic in character one basaltic andesite unit yields an age of 1086 44 ma and r0 of 0 70305 17 the low r0 indicating derivation from a mantle source region that is slightly depleted relative to a bulk earth or uniform reservoir composition the errorchron age estimate of 1038 74 ma and r0 of 0 718 15 obtained for a rhyolite porphyry from the hff is within error of that deduced for the basaltic andesite however the high r0 of this largely ignimbritic unit is probably due to a significant component of melted crust the younger possibly subvolcanic awasib granite yields an errorchron with an apparent age of 934 70 ma and r0 of 0 719 12 scatter of these data may be attributed to compositional variation in a postulated crustal source the a type characteristics exhibited by both the hff rhyolite and awasib granite are compatible with their derivation by crustal anatexis available isotopic and geochemical data together with field evidence suggest an extensional palaeoenvironment for much of the amt and sinclair sequence while isotopic data alone are insufficient to establish the nature of the rifting the broadly contemporaneous namaqua orogeny suggests that rifting may be collision induced furthermore the mantle source of abundant orogenic lavas in the amt and sinclair sequence appears to owe its imprint of subduction related metasomatism to a more ancient event

geochronology and geochemistry of volcanic rocks of the bima formation southern lhasa subterrane tibet implications for early neo tethyan subduction abstract bima formation volcanic rocks which record the history of neo tethyan subduction are found within the central and eastern segments of the southern lhasa subterrane tibetan plateau zircon u pb dating whole rock major and trace element analysis and sr nd pb hf isotopic compositions of bima formation volcanic rocks from the central segment of the southern lhasa subterrane were used to constrain the magmatic and tectonic evolution of the lhasa terrane during the early mesozoic zircon u pb dating of five samples yielded consistent ages of 184 3 2 4 to 176 8 3 5 ma the dominant volcanic rock types within the bima formation are basalts basaltic andesites andesites and dacites which are enriched in the large ion lithophile elements e g rb sr and ba and depleted in high field strength elements e g nb ta and ti 87sr 86sr t ratios are low 0 702900 0 704146 end t and ehf t values are high and positive 4 4 to 6 9 and 9 6 to 15 7 respectively and pb isotope ratios are homogeneous initial 206pb 204pb 18 28 18 40 207pb 204pb 15 53 15 56 208pb 204pb 38 21 38 38 combining the new data with those from a previous study of bima formation volcanic rocks from the eastern segment of the southern lhasa subterrane indicates that the bima formation formed between the middle triassic and early jurassic it suggests that more widespread early mesozoic volcanic rocks in the southern margin of the lhasa terrane the basaltic rocks of the bima formation were generated by partial melting of a depleted mantle wedge metasomatized by slab derived fluids and subsequently experienced fractional crystallization without significant crustal contamination the andesitic and dacitic rocks were formed by fractional crystallization of the basaltic magma our study indicates that the bima formation volcanic rocks were generated within a continental island arc setting related to northward subduction of the neo tethyan oceanic slab during the early mesozoic

divergent pathways of cyclonic and anti cyclonic ocean eddies satellite altimetry is used to study the propagation pathways of warm and cold ocean eddies in different ocean basins we consider eddies that have a life span longer than 3 months and we present three regional studies in the southeast indian the southeast atlantic and the northeast pacific oceans the case studies show that simple theories for vortex propagation on a plane work in regions where energetic eddies propagate though a weak background flow under these conditions anticyclonic cyclonic eddies propagate westward and equatorward poleward this divergence in the eddy pathways implies a net equatorward eddy heat flux and has implications for the meridional transport of freshwater carbon nutrients etc

integrated diagenetic and sequence stratigraphy of a late oligocene early miocene mixed sediment platform austral basin southern patagonia resolving base level and paleoceanographic changes and paleoaquifer characteristics abstract a condensed 20 m thick marine transgressive highstand succession comprises the upper san julian formation upper oligocene lower miocene of the northern retroarc austral basin southern patagonia mixed sediment facies identify a shelf interior setting part of an overall warm temperate regional platform of moderate energy giant oyster dominated skeletal hiatal accumulations along the maximum flooding surface and forming high energy event beds in the highstand succession preserve relict micrite in protected shelter porosity and identify periods of reduced sediment accumulation the stratigraphic distribution of marine derived glaucony and diagenetic carbonates is spatially related to sequence development depositional siderite coincides with prominent marine transgression defining transient mixing of marine and meteoric waters across coastal plain deposits chemically evolved autochthonous glaucony coincides with periods of extended seafloor exposure and transgressions that bracket the marine succession and within the oyster dominated skeletal accumulations seafloor cement likely once magnesian calcite formed in association with an encrusting boring biota along the maximum flooding surface in concert with incursion of cool 11 13 c water the cement is present locally in skeletal event beds in the highstand succession suggesting a possible association with high order base level change and cooler water as the highstand succession coincides with elevated global sea level in the late oligocene early miocene the locally marine cemented glauconitic skeletal event beds in the highstand succession may identify higher order glacio eustatic control local stratal condensation however is best explained by regional differences in basement subsidence in the burial realm carbonate diagenesis produced layers of phreatic calcrete coincident with skeletal rich deposits zeolite clinoptilolite k cement is restricted to the lowermost marine transgressive interval probably due to initial elevated metastability of reworked weathered silicates clay illite cement is restricted to siliciclastic rich intervals wherein skeletal carbonate did not buffer pore water ph diagenetic carbonate geochemistry sr na and 18o and 13c shows that with burial the transgressive and highstand system tracts developed as distinct paleoaquifers resulting from different proximities to meteoric recharge zones