geochronology of very low grade mesozoic andean metabasites an approach through the k ar 40ar 39ar and u pb la mc icp ms methods multiple geochronological methods using different metamorphic minerals were combined to date the regional very low grade metamorphism affecting upper jurassic lower cretaceous volcano sedimentary successions in the andes of central chile early late cretaceous metamorphic ages between 82 and 108 ma were obtained by the k ar and u pb methods for celadonite and titanite a much younger thermal event is responsible for actinolite formation at 8 ma most probably related to the intrusion of proximal miocene granitoids previous models for the metamorphism should be reinterpreted taking into account the absence of a greenschist facies event the combination of different metamorphic minerals and chronometers is regarded as a powerful analytical tool to date the very low grade metamorphism associated with the mesozoic extensional regime developed within the andes

facies analysis of the lo valdes formation tithonian hauterivian of the high cordillera of central chile and the palaeogeographic evolution of the andean basin

anthropogenic pb in recent hydrothermal sediments from the tyrrhenian sea implications for seawater pb control on low temperature hydrothermal systems during a 1977 cruise of the r v bannock a core was taken from an area of extensive hydrothermal mineralization located on the slope of eolo seamount aeolian arc tyrrhenian sea the eolo hydrothermal sediments exhibit unusual pb isotopic compositions that cannot be solely derived from the plausible natural sources in the area mixing considerations indicate that a significant part of the pb in these sediments is anthropogenic in origin the anthropogenic pb was most probably scavenged from the mediterranean seawater by sinking hydrothermal plume particles apparently the hydrothermal products entering the seawater column did not carry significant amounts of pb extracted from the underlying rocks so their pb isotopic compositions were swamped by the seawater pb this indicates that pb in low temperature hydrothermal products is controlled by the sea water pb not by hydrothermal leaching from underlying rocks

a model of sea level rise caused by ocean thermal expansion abstract warming of the atmosphere as a result of an increased concentration of greenhouse gases is expected to lead to a significant rise is global sea level we present estimates of the component of this sea level rise caused by thermal expansion of the ocean these estimates are based on the idea that the upper layers of the main gyres of the ocean are ventilated by the subduction of water at higher latitudes and its subsequent equatorward and downward flow into the main thermocline along surfaces of constant density in this mechanism heat enters the ocean by an advection process rather than by vertical diffusion as in previous estimates of the component of sea level rise that is caused by thermal expansion after the heat initially enters the subtropical gyres by subduction it is then redistributed to preserve gradients of the depth integrated pressure field by an adjustment involving low vertical mode baroclinic waves estimates of historical sea level rise based on this simple ventilation sch

relative roles of source composition fractional crystallization and crustal contamination in the petrogenesis of andean volcanic rocks there are well established differences in the chemical and isotopic characteristics of the calc alkaline basalt andesite dacite rhyolite association of the northern n v z central c v z and southern volcanic zones s v z of the south american andes volcanic rocks of the alkaline basalt trachyte association occur within and to the east of these active volcanic zones the chemical and isotopic characteristics of the n v z basaltic andesites and andesites and the s v z basalts basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere conversely the alkaline lavas are derived from basaltic parent magmas formed from mantle of within plate character recent basaltic andesites from the cerro galan volcanic centre to the se of the c v z are derived from mantle containing both subduction zone and within plate components and have experienced assimilation and fractional crystallization a f c during uprise through the continental crust the c v z basaltic andesites are derived from mantle containing subduction zone components probably accompanied by a f c within the continental crust some c v z lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing the petrogenesis of the c v z lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation fractional crystallization and magma mixing during uprise through the continental crust

mantle and crustal processes in the magmatism of the campania region inferences from mineralogy geochemistry and sr nd o isotopes of young hybrid volcanics of the ischia island south italy ischia one active volcano of the phlegraean volcanic district prone to very high risk is dominated by a caldera formed 55 ka bp followed by resurgence of the collapsed area over the past 3 ka the activity extruded evolved potassic magmas only a few low energy explosive events were fed by less evolved magmas a geochemical and sr nd o isotope investigation has been performed on minerals and glass from products of three of such eruptions molara vateliero and cava nocelle 2 6 ka bp data document strong mineralogical geochemical and isotopic heterogeneities likely resulting from mingling mixing processes among mafic and felsic magmas that already fed the ischia volcanism in the past detailed study on the most mafic magma has permitted to investigate its origin the mantle sector below ischia underwent subduction processes that modified its pristine chemical isotopic and redox conditions by addition of 1 of sediment fluids melts similar processes occurred from southeast to northwest along the apennine compressive margin with addition of up to 2 5 of sediment derived material this is shown by volcanics with poorly variable typical 18o mantle values and 87sr 86sr progressively increasing toward typical continental crust values multiple partial melting of this modified mantle generated distinct primary magmas that occasionally assimilated continental crust acquiring more 18o than 87sr at ischia 7 of hercynian granodiorite assimilation produced isotopically distinct k basaltic to latitic magmas a sw ne regional tectonic structure gave these magmas coming from large depth the opportunity to mingle mix with felsic magmas stagnating in shallower reservoirs eventually triggering explosive eruptions

sea level variations induced by heating and cooling an evaluation of the boussinesq approximation in ocean models in this paper a sigma coordinate ocean model is modified to remove the commonly used boussinesq approximation so that the effect of thermal expansion is exactly included in the basic equations in order to cope with the seasonal heating cycle and the detection of climate change through variation in sea level height tests are performed to evaluate the differences between boussinesq and non boussinesq calculations under different heating and cooling conditions and different model domains for an idealized case of a flat bottom shallow ocean basin without wind forcing simulations of a warm eddy show that the non boussinesq dynamics have only a minor effect on the baroclinic current field however vertically averaged velocities though small compared with the baroclinic velocities are cyclonic for the boussinesq calculation and anticyclonic for the non boussinesq calculation the results indicate that global or closed basin boussinesq models should be able to simulate most of the observed steric sea level changes on seasonal or climate timescales when corrected by a spatially uniform time dependent factor calculated from the volume averaged density change the seasonal variation of the globally averaged sea level calculated from climatological data is small about 1 cm variations in steric sea level in regional models both boussinesq and non boussinesq may differ from those of global models owing to the unknown transport across their boundaries associated with the local heating and cooling a spatially uniform time dependent correction similar to that associated with thermal expansion is proposed to account for transport across open boundaries of regional models variations of sea level obtained from a boussinesq model of the atlantic ocean approximate the seasonal signal due to the heating cooling cycle of each hemisphere as observed by satellite altimeter data

seismic velocity structures of southern italy from tomographic imaging of the ionian slab and petrological inferences summary in this study we have determined detailed vp and vs seismic velocity models of the ionian lithosphere subducting beneath the tyrrhenian basin and of the surrounding mantle by applying a post processing technique to a large sample of local earthquake tomography studies our seismic velocity models permit us to infer the presence of low velocity anomalies within the slab which we interpret as regions that are partially hydrated by fluids released during the subduction process a petrological interpretation of the velocity anomalies gives new details on the magmatism of the volcanic aeolian arc furthermore our velocity models provideamoredetaileddescriptionoftheboundaryoftheslabanditsconnectionwiththelarge seismically active tindari letojanni strike slip system finally these results allow describing in detail some features of the slab as the presence of lateral and vertical tears in conclusion the obtained models provide some constraints for inferences on mantle circulation and on the geodynamical evolution of the central western mediterranean

transition from calc alkaline to potassium rich magmatism in subduction environments geochemical and sr nd pb isotopic constraints from the island of vulcano aeolian arc the problem of mantle metasomatism vs crustal contamination in the genesis of arc magmas with different potassium contents has been investigated using new trace element and sr nd pb isotopic data on the island of vulcano aeolian arc the analysed rocks range in age from 120 ka to the present day and cover a compositional range from basalt to rhyolite of the high k calc alkaline hkca to shoshonitic sho and potassic ks series older vulcano products 30 ka consist of hkca sho rocks with sio2 48 56 they show lower contents of k2o rb and of several other incompatible trace element abundances and ratios than younger rocks with comparable degree of evolution 87sr 86sr ranges from 0 70417 to 0 70504 and increases with decreasing mgo and compatible element contents 206pb 204pb ratios display significant variations 19 31 to 19 76 and are positively correlated with mgo 143nd 144nd 0 512532 0 512768 207pb 204pb 15 66 15 71 and 208pb 204pb 39 21 39 49 overall geochemical and isotopic data suggest that the evolution of the older series was dominated by assimilation fractional crystallisation afc with an important role for continuous mixing with mafic liquids magmas erupted within the last 30 ka consist mostly of sho and ks intermediate and acid rocks with minor mafic products except for a few acid rocks they display moderate isotopic variations e g 87sr 86sr 0 70457 0 70484 206pb 204pb 19 28 19 55 but 207pb 204pb 15 66 15 82 which suggest an evolution by fractional crystallisation or in some cases by mixing with little interaction with crustal material the higher sr isotopic ratios 87sr 86sr 0 70494 0 70587 of a few low volume intermediate to acid rocks support differentiation by afc at shallow depths for some magma batches new radiogenic isotope data on the aeolian islands of alicudi and stromboli as well as new data for lamproites from central italy are also reported in order to discuss along arc compositional variations and to evaluate the role of mantle metasomatism geochemical and petrological data demonstrate that the younger k rich mafic magmas from vulcano cannot be related to the older hkca and sho ones by intra crustal evolutionary processes and point to a derivation from different mantle sources the data from alicudi and stromboli suggest that even though interaction between magma and wall rocks of the calabrian basement during shallow level magma evolution was an important process locally a similar interpretation can be extended to the entire aeolian arc

crustal assimilation during turbulent magma ascent ata new isotopic evidence from the mull tertiary lava succession n w scotland assimilation of crustal rocks with concomitant fractional crystallisation afc is a well documented phenomenon in many igneous suites but geochemical evidence from the tertiary mull lava succession suggests that in these magmas crustal contamination occurred by a distinctly different mechanism lavas from the lower half of the mull plateau group mpg can be divided into two broad sub types high 8 mgo basalts with elevated ba and k and lower mgo 8 basaltic hawaiites with lower ba and k the lower crust and most of the upper crust beneath mull is probably of lewisian age the sr nd and pb isotope compositions of local lewisian crustal samples yield the following ranges 87sr 86sr 0 71002 0 72348 143nd 144nd 0 51045 0 51058 and 206pb 204pb 14 0 14 6 ten lavas have also been analysed and yield the following ranges 87sr 86sr 0 7028 0 7042 143nd 144nd 0 51214 0 51230 and 206pb 204pb 15 1 17 9 however within this range it is predominantly the more primitive mafic compositions with elevated mg ba and k that show the lowest nd and pb and the highest sr isotope values modelling of these isotopic results in conjunction with major and trace element data show that 1 contamination by lewisian lower crustal material does occur 2 that the process involved was not one of assimilation with concomitant fractional crystallisation afc the proposed contamination process is one whereby the hottest most mgo rich magmas have assimilated acidic partial melts of lewisian lower crust during turbulent ascent ata through thin poorly connected dyke and sill like magma chambers the chemical composition of the contaminated lavas can be modelled successfully through addition of 5 acidic lewisian crust to an uncontaminated lava in contrast the more evolved magmas which probably fractionated at sub crustal levels were either not hot enough to molt significant amounts of crust or did not ascend turbulently because of their higher viscosity and so are less contaminated with crust

the goldsbrough stommel circulation of the world oceans abstract goldsbrough first showed how the mass flux at the ocean surface due to the difference between evaporation and precipitation could induce barotropic flow in the ocean interior through the requirement of vorticity conservation stommel proposed to close this circulation by adding the western boundary currents here a first otder description of the goldsbrough stommel circulation for the world oceans is presented using available climatologies while such flows are an order of magnitude smaller than the wind driven circulation the interaction between the goldsbrough stommel gyres and the wind driven and thermally driven circulation determines the salinity distribution of the world oceans therefore it is important to study the goldsbrough stommel circulation and its interaction with motions driven by other forcings in addition the western boundary currents required to close the goldsbrough interior and to satisfy interbasin mass transport can be substantial in the atlantic the southward wester

the role of the crust in the magmatic evolution of the island of lipari aeolian islands italy volcanic rocks on the island of lipari show the entire range of sr nd pb isotopic compositions displayed by other islands in the aeolian archipelago the rapid isotopic evolution of subaerial volcanic rocks on lipari towards crustal values together with the appropriate isotopic composition of the neighbouring calabrian crust serre indicate that many geochemical characteristics observed in the lavas can be attributed to contamination and mixing with crustal materials and melts interpretation of the data is complicated by the fact that underplating onto the crust mantle boundary and the specific lithologies present in the crustal section differ underneath each individual sector of the island in the central and northern parts of the island metapelitic rocks were incorporated to provide the more radiogenic sr isotopic compositions of some lavas the products from m guardia in the southern part of lipari where activity is restricted to the last 30 40 ka bear geochemical similarities to the island of vulcano where it is proposed that considerable remobilization of the crust took place in the presence of mafic mantle derived melts on lipari the petrogenetic processes of magma mixing and assimilation dominate over fractional crystallization and the observed increase of k2o over na2o can be correlated with contributions from metapelitic crustal lithologies it is suggested that the variability in isotopic composition and the budget of alkalis na2o versus k2o in the lavas can be explained by invoking a heat source from an intruding asthenospheric morb type mantle into a cooler lithospheric crust mantle during the opening of the tyrrhenian basin

andean tectonics as a consequence of sea floor spreading abstract the evolution of sea floor spreading directions and rates in the southeast pacific shows a close relationship with the andean structural directions and the plutonic episodicity as well as the succession of short compressive orogenic phases alternating with relatively longer periods of extension the orogenic periods coincided with the beginning of periods of relatively higher rates of plate convergence immediately after periods of relative quiescence with the following periodicity 110 85 76 70 63 60 49 45 35 33 16 13 7 m y the presence of oceanic structures as aseismic ridges or fracture zones produces weak benioff zones shallow and poorly defined without a corresponding active volcanism on the other hand ancient continental structures such as the precambrian paleozoic orogenic belts have active volcanism and neat deep and well developed benioff zones

sr nd pb o isotopic evidence for decreasing crustal contamination with ongoing magma evolution at alicudi volcano aeolian arc italy implications for style of magma crust interaction and for mantle source compositions abstract new isotopic sr nd pb o data are reported for a suite of basalts mgo up to 10 wt to andesites and associated mineral separates from the island of alicudi aeolian arc southern tyrrhenian sea with the aim of investigating the effects of magma wall rock interaction in continental magmatic systems major and trace elements at alicudi exhibit smooth variations suggesting derivation of the entire suite from a single type of parental magma that underwent fractional crystallisation however 87sr 86sr and 18o values decrease while 143nd 144nd increases with increasing sio2 and decreasing mgo moreover phenocryst phases show isotopic disequilibrium relative to whole rocks and groundmass such an unusual isotope vs major and trace element variation and isotopic disequilibria suggest interaction between magmas and crustal wall rocks but the decrease of 87sr 86sr with increasing differentiation excludes assimilation fractional crystallisation processes we suggest that mafic calcalkaline magmas with primitive sr nd o isotopic signatures were intruded into a deep reservoir where they underwent fractional crystallisation contamination occurred shortly before eruption as the magmas ascended to the surface interactions between magmas and wall rocks were more extensive for the basalts than basaltic andesites and andesites generating a positive correlation between mgo and 87sr 86sr ratios the variable degrees of magma wall rock interaction are suggested to depend on the differing capabilities of magmas to dissolve crustal rocks due to variable temperature and viscosity the present study therefore provides sr nd pb o isotopic evidence on an uncommon modality of magma contamination by upper crust the alicudi andesites have the most primitive isotope signatures over the entire aeolian arc in plots of 206pb 204pb vs 87sr 86sr or 143nd 144nd isotopes the bulk of the aeolian volcanoes fall along a curved trend that connects himu mantle reservoir and the upper crust in contrast the alicudi andesites fall outside this trend and plot on a binary trend connecting himu and em1 mantle reservoirs it is suggested that the alicudi source consisted of a hybrid himu em1 mantle that was modified by fluids or melts coming from an oceanic slab these fluids did not change significantly the isotopic signatures of the wedge but generated high lile hfse ratios which were inherited by the alicudi magma in contrast the compositions of other aeolian volcanoes and of central italian magmatism reflect addition of upper crust to a himu or fozo mantle collectively the data record the complex interplay between different mantle reservoirs and the addition of various amounts and types of subduction related components in the southern tyrrhenian sea

upper triassic to lower cretaceous continental and coastal saline lake evaporites inthe atacama region of northern chile evaporites within upper triassic to lower cretaceous sequences in the atacama region of northern chile are interpreted as the deposits of continental and coastal saline lakes halite casts and finely laminated calcareous evaporites intercalated with alluvial and fluvial sediments are probably playa lake deposits these continental evaporites have been recognized in upper triassic alluvial sediments cifuncho formation in upper triassic lower jurassic braided river deposits basal unit of the pan de azucar formation and within a sequence of lower cretaceous aeolian alluvial and playa lake mudflat sediments quebrada monardes formation lower cretaceous evaporites between marine limestones lautaro formation and continental redbeds quebrada monardes formation were probably deposited in coastal saline lagoons produced during a regionally extensive marine regression these sequences and other similar successions in northern chile provide a record of almost continuous evaporite deposition and hence of arid to semi arid conditions since upper triassic times these conditions were primarily the result of a constant latitudinal position within the subtropical zone a contributary factor was the geographical position of the area initially on the west coast of gondwanaland and subsequently on the coast of south america with cold northward flowing ocean currents and offshore winds

petrology and geochemistry of submarine volcanism in the sicily channel rift abstract submarine magmatism in the sicily channel rift began in the early pliocene and lasted until almost 200 yr ago we present here petrological and geochemical data on volcanic rocks dredged from graham and nameless banks and pantelleria seamounts in the pelagian sector of the sicily channel rift petrological evidence suggests that the ascent of magmas to the surface was relatively rapid probably through channels superimposed over the major tectonic discontinuities of the rift major and trace element data indicate an ocean island basalt affinity for graham and nameless bank alkaline lavas and a depleted tholeiitic signature for one pantelleria seamount which had a shallower mantle source sr nd pb isotopic compositions suggest a heterogeneous mantle source involving both focus zone fozo and high himu components lead isotopic compositions are slightly less radiogenic in the tholeiitic basalt and more radiogenic closer to himu in the alkaline lavas we hypothesize that a decompressional me

metalliferous sediments from eolo seamount tyrrhenian sea hydrothermal deposition and re deposition in a zone of oxygen depletion a sediment core taken from the south east slope of the eolo seamount is composed of alternating red brown and light brown to bluish grey layers with signs of re deposition in the middle upper section the red brown layers are fe rich metalliferous sediments formed as a result of low temperature 77 c hydrothermal discharge whereas the bluish grey layers most probably originated from background sedimentation of al rich detrital material the metalliferous layers are composed mainly of si rich goethite containing some al co precipitation of hydrothermally released sio44 and fe2 as amorphous or poorly crystalline fe si oxyhydroxides explains the high si concentration in goethite the elevated al content of the goethite is fairly unusual but reflects the extremely high background al content of the tyrrhenian seawater due to the high eolian terrigenous flux from the sahara desert the sr and nd isotope data suggest that the eolo metalliferous sediments are the product of a 3 component mixture hydrothermal fluid seawater and detrital material saharan dust and aeolian arc material the enrichment in fe p as mo cd be sb w y v depletion in ree and transition elements cu co ni zn and the ree distribution patterns support the low temperature hydrothermal deposition of the metalliferous layers the hydrothermal field is located in a seawater layer of relative o2 depletion which led to a significant fractionation of the hydrothermally emitted fe and mn fe oxyhydroxides precipitated immediately around the vents whereas mn stayed in solution longer and the mn oxides precipitated higher up on the seamount slope in seawater with relatively higher o2 levels high seismic activity led to sediment re deposition and slumping of the mn rich layers down slope and mixing with the fe rich layers

imaging b value variation beneath the pamir hindu kush region the frequency magnitude distribution b value for the seismicity of the pamir hindu kush region from august 2008 to june 2010 is analyzed we used a very precisely located earthquake dataset containing 9532 events with a magnitude of completeness of 2 9 we attempted both 1d and 2d approaches to resolve the b value variation as a function of depth several pockets of high b value were detected during the cross sectional analysis that may reflect the changes in the physical properties of the subducting slab with depth under the hindu kush sector a high b value 1 2 is identified at the depth of 150 km but under pamir this zone b 0 9 is apparent at shallower depth an earlier detailed seismic tomography study revealed a low velocity zone beneath hindu kush where the high b value is imaged in the present study this observation is corroborated by the existence of fluid due to the dehydration and increase in pore pressure within the lower portion of the indian lithosphere the relatively high b value at shallower depth could be associated with the higher slab temperature as caused by the slower subduction under pamir

a note on the representation of steric sea level in models that conserve volume rather than mass this note discusses the representation of steric sea level in ocean circulation models changes in steric sea level are caused when changes in the density of the water column imply an expansion or contraction of the column models usually make the boussinesq approximation and conserve volume rather than mass and so do not properly represent expansion or contraction this means that although expansion contraction is included in the equation of state it is not accounted for by the model dynamics in this note we examine the equation governing the time evolution of the sea level displacement it is shown that requiring conservation of mass rather than volume introduces a new term to this equation a simple example is used to show the relationship of the new term to the surface buoyancy flux the equilibrium response to the new term has two parts one part consists of the goldsbrough and stommel gyres for which in the ocean interior vortex stretching due to the local expansion contraction of the water column is balanced by changes in planetary vorticity the other part corresponds to the inverse barometer the effect is to adjust sea level by a globally uniform but timevarying factor determined by the net expansion contraction of the global ocean since this correction is globally uniform it has no dynamical significance both the goldsbrough stommel gyres and the inverse barometer solution are missing from models as currently formulated this does not represent a serious error however if comparison is made with observations of sea level model calculated sea level should be adjusted by a globally uniform time varying factor determined by the net expansion contraction of the global ocean this would be important for assessing the likely rise in sea level in response to global warming

magmatic differentiation at la poruna scoria cone central andes northern chile evidence for assimilation during turbulent ascent processes and genetic links with mafic eruptions at adjacent san pedro volcano abstract la poruna 21 53 s 68 30 w is a 140 m high scoria cone composed of pyroclastic material and an extensive basaltic andesite to andesite lava flow that is up to 8 km in length automated mineralogical analysis describes a suite of porphyritic mafic samples comprising olivine and pyroxene bearing rocks well defined major element compositional trends as well as trace and rare earth element characteristics e g sr y 96 ka from san pedro volcano exhibit similar isotopic characteristics therefore evidence of similar magmatic processes this new dataset clearly defines magma compositional changes during the la poruna eruption ca 100 ka revealing an increase in crustal contamination at shallow crustal levels for the younger san pedro lavas

geophysical interpretation of observed geocenter variations geocenter variations are caused by mass redistribution within the earth system especially the atmosphere oceans and continental water using surface pressure fields and soil moisture and snow depth fields of the ncep ncar climate data assimilation system i cdas i 1 we estimate contributions from variations in atmospheric surface pressure and continental water storage to the earth s geocenter center of mass variation in addition sea surface anomalies determined by the topex poseidon altimeter are used to investigate geocenter variations resulting from ocean mass redistribution these sea surface height data were corrected using a simplified steric model a comparison with observed geocenter variations derived from lageos 1 and 2 satellite laser ranging data indicates that the atmosphere oceans and continental hydrological cycle all provide significant contributions at different frequencies geocenter variations estimated in this paper are in reasonably good agreement with results given by dong et al 1997 for atmospheric and ocean contributions but not for the estimates of continental hydrological contributions

the pliensbachian and tithonian extinction events the claim by raup and sepkoski1 that an approximately 26 myr mass extinction periodicity can be recognized on a global scale at family level over the past 250 myr has excited much attention and provoked speculation about an ultimate extraterrestrial cause2 10 while the purported periodicity can be challenged on grounds of both the inaccuracy of the geological timescale11 and the method of extinction analysis12 there can be no doubting the reality of at least some of the 12 proposed extinction events such as those at or near the end of the permian triassic and cretaceous others are less widely acknowledged further analysis by raup and sepkoski13 confirms the importance of two of these events within the jurassic at the end of the pliensbachian and tithonian stages i demonstrate here that marine invertebrate mass extinctions at approximately these times occurred on a regional not a global scale they can be related to severe reductions in habitat area provoked either by regression of epicontinental sea or by widespread anoxia

sequence stratigraphy of a tidally dominated carbonate siliciclastic ramp the tithonian early berriasian of the southern neuquen basin argentina the tithonian berriasian vaca muerta carrin cura and picun leufu formations in the southern neuquen basin were deposited on a tidally dominated mixed carbonate siliciclastic ramp basinal outer middle shallow and back ramp facies associations are recognized and a sequence stratigraphic analysis reveals that the ramp record consists of three shallowing upwards sequences ti1 ti2 and ti3 set within a lower order progradational cycle a higher order of cyclicity is superimposed on to the middle ti2 sequence the majority of the ramp facies belong to the transgressive and highstand systems tracts however at the base of ti2 a lowstand systems tract is identified characterized by a basal unconformity and an abrupt basinward shift of the shallow marine lithofacies transgressive systems tracts were characterized by slow sedimentation rates and rapid sea level rises that affected carbonate productivity highstand systems tracts show the greatest carbonate productivity and an increased progradation rate on account of a reduction in accommodation space generation palaeogeography played a major role in the development of the depositional systems partial isolation from the pacific ocean reflecting the growth of the andean magmatic arc and geographic restriction due to tectonic inversion in the central part of the basin resulted in a meso macrotidal regime that produced a tidally dominated sedimentary record in the shallow and back ramp environments coeval anoxic conditions in the central part of the neuquen basin favoured distal ramp and basinal black shale deposition during episodes of relative sea level rise

including non boussinesq effects in boussinesq ocean circulation models abstract a set of equations is derived to modify z level boussinesq ocean circulation models to account for non boussinesq effects these equations take the same form as those of the boussinesq models except for the addition of a few correction terms that require the calculation of integral density sources these corrections are estimated to be significant based on a scale analysis

sea surface elevation and bottom pressure anomalies due to thermohaline forcing part i isolated perturbations sea surface elevation and bottom pressure anomalies due to thermohaline forcing are examined through analytical and numerical models including boussinesq and non boussinesq models it is shown that boussinesq approximations can introduce noticeable errors depending on the spatial and temporal scales of the perturbations according to the theory of geostrophic adjustment when the initial perturbations have horizontal scales comparable to the barotropic radius of deformation the initial pressure perturbations will be basically retained through the adjustment on the other hand if the initial perturbations have horizontal scales much smaller than the barotropic radius of deformation the initial pressure perturbations will be largely lost precipitation has horizontal scales on the order of 10 100 km much smaller than the barotropic radius of deformation thus for timescales longer than days the contribution from individual precipitation events to the local free surface elevation and bottom pressure is small and is difficult to identify from satellite data on the other hand thermal forcing has horizontal scales comparable to the barotropic radius of deformation so its long term contribution to sea surface height anomaly is noticeable and is easily identified from satellite data because boussinesq models induce faulty sea surface height and bottom pressure signals the errors introduced by these models are noticeable for anomalies in large scale o 1000 km thermohaline forcing

continental rift to back arc basin jurassic cretaceous stratigraphical and structural evolution of the larsen basin antarctic peninsula the larsen basin developed in jurassic times as a result of continental rifting during the early stages of gondwana break up lower upper jurassic non marine sedimentary and volcanic rocks constitute a syn rift megasequence recording initial largely amagmatic extension and subsequent widespread extension related silicic volcanism a succeeding kimmeridgian early berriasian transgressive megasequence consisting largely of anoxic dysoxic hemipelagic mudstones is thought to have been deposited during a thermal subsidence phase when relative magmatic quiescence and peak jurassic eustatic sea levels served to maximize sediment starvation the fragmentary record for late berriasian barremian times suggests that a regressive megasequence may have developed in the earlier part of this period recording increased sediment yield to the larsen basin from the increasingly emergent antarctic peninsula arc subsequently strata in the southern but not the northern part of the basin underwent relatively intense eastward verging deformation possibly during the formation of a retro arc fold thrust belt where exposed the lower part of the succeeding aptian eocene megasequence consists of a deep marine clastic wedge deposited along the fault bounded western basin margin during a phase of arc uplift and related differential subsidence following partial basin inversion in late cretaceous times regression took place as reduced basinal subsidence rates allowed shallow marine facies to prograde basinward

decadal variabilities of the upper layers of the subtropical north atlantic an ocean model study numerical simulations of the atlantic ocean during the period 1950 to 1989 using a sigma coordinate free surface numerical model show long term variabilities in the upper ocean subtropical gyre similar to those obtained from observations the simulations show how westward propagating planetary waves originated in the eastern north atlantic affect interdecadal variabilities of ocean properties such as the bermuda sea level the gulf stream position and strength and subsurface temperature anomalies in the western north atlantic special attention is given to the dramatic sea level drop at bermuda in the early 1970s which is accompanied by cooling of subsurface layers in the western north atlantic and a northward shift and weakening of the gulf stream following these events between 1970 and 1980 the cold temperature anomalies in the upper layers of the western north atlantic slowly propagated eastward and downward the strongest propagating signal in the model is found at 200 m depth suggesting that advection of anomalies downstream by the gulf stream current and changes in winter mixing are involved significant correlations were found between the sea level anomalies at bermuda and sea level anomalies in the eastern north atlantic up to eight years earlier sensitivity experiments with different atmospheric forcing fields are used to study the ocean response to observed sea surface temperature and wind stress anomalies it is shown that on decadal timescales the ocean model responds in a linear fashion to the combined effect of sst and wind stress anomalies a fact that might be exploited in future climate prediction studies

relationships between crustal contamination and crystallisation in continental flood basalt magmas with special reference to the deccan traps of the western ghats india the upper part of the deccan traps sequence bushe to mahabaleshwar formations shows a statistically significant tendency for the most mafic lavas to be the most contaminated by crustal materials this is the reverse of the relationship shown by suites evolving by contamination accompanied by fractional crystallisation afc the observed correlations e g between mg number and sr isotope initial ratios are partly an accidental consequence of the fact that the most mafic lavas are more abundant in the lower part of the sequence while contaminant availability declines in the upper part it is probable however that the correlations are augmented by increased contamination of hotter magma batches during ascent through dykes a process during which fractional crystallisation is suppressed by magmatic turbulence the absence of afc relationships suggests that most of the contamination took place during the ascent stage rather than in a magma chamber other continental flood basalt provinces such as the parana and etendeka do show afc relationships and it is speculated that this may be a result of magma chamber contamination coupled with flow rates which prevent contamination during ascent

phenomena of pulsation tectonics related to the breakup of the eastern north american continental margin abstract new data from the recent ipod drilling of dsdp site 534 in the blake bahama basin give a definite age for the spreading center shift involved in the breakup of the north american atlantic margin a basal callovian age 155 m y is determined for the blake spur magnetic anomaly marking this spreadingcenter shift that signals the birth of the modern north atlantic ocean this is some 20 m y younger than previously thought an implication of this younger age for the blake spur event is that very high spreading rates are now required for the jurassic outer magnetic quiet zone along the north american margin this association of a relatively high spreading rate with a magnetic quiet zone is similar to that for the mid cretaceous and implies a link between the processes controlling plate spreading which are in the upper mantle and the processes controlling the magnetic field which are in the outer core a theory of pulsation tectonics involving the cyclic eruption of plumes of hot mantle material from the lowermost mantle could explain the correlation plumes carry heat away from the core mantle boundary and later reach the asthenosphere and lithosphere to induce faster spreading the pulse of fast spreading in the jurassic apparently followed the breakup of continents bordering the north atlantic ocean other pulses of fast spreading appear to correlate with major ocean openings on various parts of the globe implying that this might be a prevalent process rifting of passive margins may be controlled by the more fundamental global processes described by the theory of pulsation tectonics

geochemistry and petrology of a middle tithonian limestone marl rhythmite in the neuquen basin argentina depositional and burial history

orogens and slabs vs their direction of subduction abstract subduction zones appear primarily controlled by the polarity of their direction i e w directed or e to nne directed probably due to the westward drift of the lithosphere relative to the asthenosphere the decollement planes behave differently in the two end members in the w directed subduction zone the decollement of the plate to the east is warped and subducted whereas in the e to nne directed it is ramping upward at the surface there are w directed subduction zones that work also in absence of active convergence like the carpathians or the apennines w directed subduction zones have shorter life 30 40 ma than e or ne directed subduction zones even longer than 100 ma the different decollements in the two end members of subduction should control different ptt paths and therefore generate variable metamorphic assemblages in the associated accretionary wedges and orogens these asymmetries also determine different topographic and structural evolutions that are marked by low topography and a fast eastward migrating structural wave along w directed subduction zones whereas the topography and the structure are rapidly growing upward and expanding laterally along the opposite subduction zones the magmatic pair calc alkaline and alkaline tholeiitic volcanic products of the island arc and the back arc basin characterise the w directed subduction zones magmatic rocks associated with e or ne directed subduction zones have higher abundances of incompatible elements and mainly consist of calc alkaline shoshonitic suites with large volumes of batholithic intrusions and porphyry copper ore deposits the subduction zones surrounding the adriatic plate in the central mediterranean confirm the differences among subduction zones as primarily controlled by the geographic polarity of the main direction of the slab the western margin of the adriatic plate contemporaneously overridden and underthrust europe toward the west to generate respectively the alps and the apennines while the eastern margin subducted under the dinarides hellenides these belts confirm the characters of the end members of subduction zones as a function of their geographic polarity similarly to the pacific subduction zones

circulation and multiple scale variability in the southern california bight abstract the oceanic circulation in the southern california bight scb is influenced by the large scale california current offshore tropical remote forcing through the coastal wave guide alongshore and local atmospheric forcing the region is characterized by local complexity in the topography and coastline all these factors engender variability in the circulation on interannual seasonal and intraseasonal time scales this study applies the regional oceanic modeling system roms to the scb circulation and its multiple scale variability the model is configured in three levels of nested grids with the parent grid covering the whole us west coast the first child grid covers a large southern domain and the third grid zooms in on the scb region the three horizontal grid resolutions are 20 km 6 7 km and 1 km respectively the external forcings are momentum heat and freshwater flux at the surface and adaptive nudging to gyre scale soda reanalysis fields at the boundaries the momentum flux is from a three hourly reanalysis mesoscale mm5 wind with a 6 km resolution for the finest grid in the scb the oceanic model starts in an equilibrium state from a multiple year cyclical climatology run and then it is integrated from years 1996 through 2003 in this paper the 8 year simulation at the 1 km resolution is analyzed and assessed against extensive observational data high frequency hf radar data current meters acoustic doppler current profilers adcp data hydrographic measurements tide gauges drifters altimeters and radiometers the simulation shows that the domain scale surface circulation in the scb is characterized by the southern california cyclonic gyre comprised of the offshore equatorward california current system and the onshore poleward southern california countercurrent the simulation also exhibits three subdomain scale persistent i e standing cyclonic eddies related to the local topography and wind forcing the santa barbara channel eddy the central scb eddy and the catalina clemente eddy comparisons with observational data reveal that roms reproduces a realistic mean state of the scb oceanic circulation as well as its interannual mainly as a local manifestation of an enso event seasonal and intraseasonal eddy scale variations we find high correlations of the wind curl with both the alongshore pressure gradient apg and the eddy kinetic energy level in their variations on time scales of seasons and longer the geostrophic currents are much stronger than the wind driven ekman flows at the surface the model exhibits intrinsic eddy variability with strong topographically related heterogeneity westward propagating rossby waves and poleward propagating coastally trapped waves albeit with smaller amplitude than observed due to missing high frequency variations in the southern boundary conditions

sea level variability around japan during the twentieth century simulated by a regional ocean model abstractsea level variability around japan from 1906 to 2010 is examined using a regional ocean model along with observational data and the cmip5 historical simulations the regional model reproduces observed interdecadal sea level variability for example high sea level around 1950 low sea level in the 1970s and sea level rise during the most recent three decades along the japanese coast sensitivity runs reveal that the high sea level around 1950 was induced by the wind stress curl changes over the north pacific characterized by a weakening of the aleutian low in contrast the recent sea level rise is primarily caused by heat and freshwater flux forcings that the wind induced sea level rise along the japanese coast around 1950 is as large as the recent sea level rise highlights the importance of natural variability in understanding regional sea level change on interdecadal time scales

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

aspects of middle late jurassic cretaceous tethyan brachiopod biogeography in relation to tectonic and paleoceanographic developments abstract important tectonic and paleoceanographic events during the middle to late jurassic and cretaceous resulted in modifications to the biogeographic distributions of tethyan brachiopod genera from europe the development of the central atlantic ocean during the jurassic early cretaceous led to an increase in the number of brachiopod genera common to both the mexico eastern pacific and northwestern europe tethyan regions brachiopod genera recorded from tethys in europe show evidence of migration via at least four major routes as a consequence of tectonic developments dates in parentheses indicate stages where evidence exists for generic links 1 northwestern europe via mexico caribbean region oxfordian to south america valanginian hauterivian cenomanian 2 eastern tethys via eastern africa east african seaway to the south atlantic ocean late turonian early coniacian santonian campanian 3 northwestern europe via the central atlantic to the opening south atlantic reaching the antarctic peninsula region late albian santonian campanian 4 europe northward to higher latitudes russian platform to barents sea berriasian valanginian europe to east greenland valanginian europe canadian arctic islands albian and also earlier during the jurassic for routes 1 3 direction of dispersal may prove to have been in either direction at times it appears to have been in a southerly direction for route 3 stratigraphic age relationships suggest a south to north dispersal for routes considered under 4 except for the link to the canadian arctic islands which is inconclusive by the late cretaceous the low latitude faunas of europe and america had become isolated by the increasing width of the central atlantic ocean although some genera appear to be cosmopolitan

seasonal circulation on the western shelf of the gulf of mexico using a high resolution numerical model 1 the seasonal circulation on the western shelf of the gulf of mexico is studied using a high resolution numerical simulation historical hydrographic data sea level data and satellite images three regions are distinguished the tamaulipas veracruz tave shelf the louisiana texas latex shelf and the western campeche bank on the tave shelf there is a swift reversal of the along shelf current downcoast from september to march and upcoast from may to august when there is upwelling due to offshore ekman transport circulation on the western campeche bank is upcoast throughout the year the latex shelf has a cyclonic circulation except during summer months when the flow is eastward during spring summer the upcoast current on the tave shelf reaches the southern texas shelf where it encounters a downcoast coastal current favoring offshore transports in the fall winter the downcoast current reaches the southern bay of campeche where it meets an opposing along shelf current generating seasonal offshore transports during fall and winter cool low salinity water from the mississippi and atchafalaya rivers is advected westward along the latex shelf onto the tave shelf developing along shelf fronts and temperature inversions commonly observed over the outer shelf and shelf break the main forcing over the western shelf of the gulf is the along coast wind stress component the existence of the cross shelf transports in the confluence regions is supported by chlorophyll a data up to 80 of the seasonal sea level variability is explained by the along shelf currents and the low frequency variability of the atmospheric sea level pressure

temporal evolution of a three component system the island of lipari aeolian arc southern italy the volcanic products from lipari define an evolutionary trend with a high gradient of k enrichment similar to the calc alkaline to potassic volcanism of other islands in the aeolian arc stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages the first stage from 223 to 42 ka consists of six eruptive cycles and is characterized by basalts and basalt andesites showing progressive increase in both sio2 and k2o contents with time the second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products fractional crystallization assimilation and mixing models suggest that the geochemistry of lipari volcanism evolved with time by a complex interplay between two mantle derived components one sub alkaline and the other alkaline in addition to crustal melts and or crustally derived materials a petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro and microscopic features melts from the crustal and mantle end members are almost always present in the system but the relative proportions appear to vary with time the sub alkaline mantle component source of tyrrhenian tholeiites is an important contributor to the early evolution of the volcanism in lipari input from the alkaline mantle component source of the roman comagmatic province increases with time and the crustal component becomes dominant in the later activity the preferred petrogenetic model for the temporal evolution of the volcanic system in lipari involves melting initially caused by an increase in the thermal input related to the opening of the tyrrhenian sea and or to subduction processes the quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts

the jurassic succession in west central argentina stratal patterns sequences and paleogeographic evolution abstract jurassic rocks in west central argentina are predominantly marine and marginal marine siliciclastics associated with prominent but volumetrically subordinate carbonates and evaporites facies developments were ruled by paleogeographic persistence within the southern infratropical latitude belt within 40 50 s and by siliciclastic derivation from the patagonian hinterland to the southwest minor volcanic and volcaniclastic supply arrived from the west out of a magmatic belt related to circum pacific convergence timing of the main marine flooding events and general correspondence with the high rank stratal packaging recorded in western north america suggest that global eustasy was also a factor in controlling the local stratigraphic record early jurassic sedimentation occurred within a series of semi isolated depocentres linked to fault bounded triassic troughs the sinemurian toarcian deposits record depocentre expansion and coalescence these trends were coeval with progressively more widespread marine invasions from the northwest and west leading to an elongate marine seaway which connected central patagonia with the pacific domain during the aalenian bajocian the region was subject to a more subdued tectonism and the foreland side of the basin became fringed by an extensive clastic embankment bathonian and early callovian were times when coarse clastics prograded into the basin while the marine embayment shrank as a result of stepwise forced regressions during late callovian to oxfordian globally rising sea level the depocentre witnessed the appearance of cosmopolitan invertebrates and a stratal pattern of basin widening and depositional underbalance that promoted cratonward onlap and inception of widespread carbonate deposition ooidal coralline carbonate development was terminated after a relatively sudden messinian style event that desiccated a large tract of the andean basin and favored massive precipitation of anhydrite in the course of the kimmeridgian the evaporite basin was largely flooded by siliciclastics and turned into a broad and featureless mudflat salina complex linked to a widespread erg and to an ephemeral drainage system by the tithonian at a period of peak oceanic stand marine connection was reinstated and recorded as the most widespread jurassic transgression across the neuquen aconcagua embayment shelfal deposition consisted of molluscs and ooid dominated carbonate terraces that grew in pulses tuned to eustatic fluctuations like in other prolific petroleum provinces around the world the tithonian basinal strata involve widespread euxinic deposits featuring unusually high organic content

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

regional stress field in the area of stromboli italy insights into structural data and crustal tectonic earthquakes abstract crustal tectonic seismicity on stromboli is here discussed along with the regional tectonic and geodynamic context of the aeolian archipelago italy the aim of this paper is to contribute to the reduction of the crucial gap in information concerning the tectonic activity originating at the volcano stromboli in the last decade it is indeed well known that strombolian eruptions related to the persistent state of activity on this volcano allow a fast collection of seismic data which are mainly represented by explosion quakes and tremor however only some sporadic information concerns tectonic earthquakes due to their low occurrence rate a catalog of 150 crustal tectonic earthquakes recorded at stromboli from 1985 to 1996 is presented here the analyses of the seismograms were carried out on the basis of the records of the station str located in the southwestern part of the island the magnitude considered ranged from 1 5 to 3 7 hypocentral location indicates foci at less than 12 km although for the majority of the earthquakes which are not recorded at the seismic stations deployed on the other islands of the aeolian archipelago a shallower within a few kilometers depth can be hypothesized the strain release associated with the 150 tectonic earthquakes of our catalog was also evaluated the low levels of occurrence and seismic energy release reached throughout the ca twelve years analyzed here confirm the minor role played by processes of brittle failure of rocks this aspect of seismic activity is nevertheless important as it can provide a contribution to the knowledge of the dynamics of this volcano the focal mechanisms available integrated with data from the literature show the t axes oriented about ne sw and nw se these findings are consistent with the deformative and tectonic characteristics of this volcanic edifice and of the aeolian archipelago which shows the same two directions of extension this is in agreement with subduction which is very old or which passively evolves towards the final stages and is controlled by the transform activity of the aeolian tindari giardini fault system

the elatina glaciation late cryogenian marinoan epoch south australia sedimentary facies and palaeoenvironments abstract the late cryogenian elatina glaciation in south australia of marinoan age is named after the elatina formation of the glaciogenic yerelina subgroup which covers 200 000 km2 in the adelaide geosyncline and on the cratonic stuart shelf and is up to 1500 m thick the elatina glaciation is marked by numerous facies that are like those of phanerozoic glaciations basal diamictite displaying glacitectonites with penetrative deformation of preglacial beds indicating grounded ice or scouring by icebergs glaciomarine diamictites containing numerous faceted and striated clasts up to several metres across of intrabasinal and extrabasinal origin laminated siltstone and mudstone containing scattered ice rafted dropstones in outer marine shelf environments sandstones deposited in fluvial deltaic and inner marine shelf settings tidalites deposited in estuaries and on tidal deltas during interstadial rise of sea level with cyclic tidal rhythmites recording the annual oscillation of sea level and displaying wave generated ripple marks which together indicate long lived and extensive open seas siltstone containing acicular crystal pseudomorphs implying the formation of evaporite minerals in littoral deposits permafrost regolith of frost shattered quartzite breccia 20 m deep displaying large scale periglacial structures including primary sand wedges 3 m deep that indicate a frigid strongly seasonal climate near sea level periglacial aeolian sandstone covering 25 000 km2 and containing primary sand wedges near its base these deposits record a spectrum of settings ranging from permafrost regolith and periglacial sand sheet on the stuart shelf in the west through fluvial deltaic and inner marine shelf in the western and central parts of the adelaide geosyncline to outer marine shelf in the north and southeast the widespread and persistent rainout of fine grained sediment and ice rafted debris indicates that the sea was not frozen over during the elatina glaciation no direct age determination is available for the elatina glaciation and only maximum and minimum age limits of 640 and 580 ma respectively can at present be applied high quality palaeomagnetic data for red beds from the elatina formation supported by positive fold tests on soft sediment slump folds that demonstrate the early acquisition of magnetic remanence indicate deposition within 10 of the palaeoequator the yerelina subgroup in the adelaide geosyncline and on the stuart shelf is disconformably to unconformably overlain by the nuccaleena formation cap carbonate that marks the early ediacaran post glacial marine transgression the presence in near equatorial palaeolatitudes of glaciomarine deposition grounded ice and permafrost near sea level a strongly seasonal periglacial climate and widespread open seas implies a paradoxical palaeoclimate and palaeogeographic setting for the elatina glaciation the strong evidence for a non actualistic late cryogenian glacial climate in south australia has been a stimulus to worldwide multidisciplinary research on cryogenian glaciogenic successions

paleoclimate of the kimmeridgian tithonian late jurassic world i results using a general circulation model abstract the kimmeridgian tithonian 154 7 145 6 ma middle and late late jurassic was a time of expanded continental rifting increased sea floor spreading and a relatively high eustatic sea level stand these processes collectively caused the fragmentation and flooding of the megacontinent pangea as well as the alteration of the global paleoclimate using a version of the community climate model ccm from the national center for atmospheric research we report two kimmeridgian tithonian paleoclimate seasonal simulations with geologically inferred paleotopography one using a co 2 concentration of 280 ppm pre industrial level and the other 1120 ppm increasing the co 2 four fold warms virtually the entire planet the greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas floras and sedimentary rocks model results indicate that sea ice was restricted to the high latitudes of the boreal and austral seas making landfall only in restricted areas the trade winds bring heavy rainfall in december january february to eastern gondwana and in june july august to the tethys sea margins a strong june july august monsoon occurs over southeast asia the distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level evaporites are localized to areas of negative precipitation evaporation runoff is restricted to regions of intense precipitation overall the 1120 ppm co 2 simulation provides a reasonable paleoclimate for the kimmeridgian tithonian and provides a standard until a ccm with oceanic heat transport a coupled atmospheric oceanic model or one with a finer grid cell configuration is available the results need further scrutiny in areas with more detailed geologic information

late mesozoic bivalve biostratigraphy of the antarctic peninsula region two groups of bivalves the inoceramids and buchiids are particularly useful zone fossils in the mesozoic sedimentary formations of the antarctic peninsula region in the upper jurassic species of the genera retroceramus malayomaorica buchia and anopaea can be traced considerable distances around the margins of gondwana and as such are especially valuable for regional correlations some of them such as the r haasti subhaasti group can also be employed in detailed local correlations in the lower cretaceous the presence of cosmopolitan inoceramus species such as members of the neocomiensis concentricus and anglicus groups permits correlation with northern hemisphere faunas for the first time other stratigraphically important inoceramids are the i ovatus group in the lower neocomian the i heteropterus group and anopaea trapezoidalis in the upper neocomian and an cf mandibula in the albian the only buchiids present in the lower cretaceous of antarctica belong to the extensive aucellina andina radiatostriata group two types of antarctic upper cretaceous inoceramids that are particularly important for regional correlations are the upper cenomanian i pictus group and the turonian coniacian i madagascariensis ernsti group senonian inoceramids are still poorly known but would seem to offer considerable scope for further studies

tectono stratigraphic evolution of the andean orogen between 31 and 37 s chile and western argentina fil charrier reynaldo universidad de chile facultad de ciencias fisicas y matematicas departamento de geologia chile universidad andres bello chile

magma storage conditions and differentiation of the mafic lower pollara volcanics salina island aeolian islands italy implications for the formation conditions of shoshonites and potassic rocks crystallization experiments of basaltic andesite mafic endmember from the 24 ka lower pollara eruption salina aeolian islands italy were investigated at 200 mpa 950 1100 c in the h2o activity ah2o range 0 3 to 1 and at two ranges of oxygen fugacity fo2 between fmq to fmq 1 and fmq 2 to fmq 3 3 log bars fmq is fayalite magnetite quartz comparison of the produced phase assemblages and phase compositions with the natural sample reveals that the storage conditions were 1050 c 2 8 wt h2o in the melt ah2o 0 5 and relatively oxidizing fmq 2 5 the composition of plagioclase in the groundmass indicates a period of cooling to 950 c the overall differentiation trends of the salina volcanics can be explained by fractional crystallization close to h2o saturated conditions 5 wt h2o in the melt at 200 mpa and most likely by accumulation of plagioclase i e in basaltic andesites and by various degree of mixing mingling between the corresponding differentiates the slightly elevated k2o contents of the most mafic basaltic andesites that can be found in the lowermost unit of the lower pollara pyroclastics reveal earlier processes of moderately hydrous fractional crystallization at higher temperature 1050 c fractional crystallization with decreasing influence of h2o causes a moderate decrease of mgo and a significant increase of k2o relative to sio2 in the residual liquids it is exemplarily shown that the crystallization of sio2 rich phases at high temperature and low ah2o of only moderately k2o rich calc alkaline basalts can produce shoshonitic and high potassic rocks similar to those of stromboli and volcano this suggests that the observed transition from calc alkaline to shoshonitic and high potassic volcanism at the aeolian arc over time can be initiated by a general increase of magmatic temperatures and a decrease of ah2o in response to the extensional tectonics and related increase of heat flow and declining influence of slab derived fluids

pre quaternary sea level changes while the paramount importance of global sea level changes has been widely accepted by quaternary geologists throughout this century it is only within the last decade that such changes in the rest of the phanerozoic have received much attention there are two principal reasons for this arousal of interest first increased exploration of the stratigraphic record across the earth both on land and under the sea and significant improvement in biostratigraphic correlation have drawn attention to what appear to have been globally synchronous events second oceanographic research has demonstrated the importance of tectonically controlled changes in the cubic capacity of the ocean basins notably variations in ridge volume which provide a ready mechanism for sea level changes even at nonglacial times the adjective eustatic was first proposed for global changes of sea level by suess 1906 in his great treatise the face of the earth the corresponding noun is eustasy not eustacy as it is commonly misspelt the unconvinced reader need only think of ecstasy eustatic sea level changes can be inferred as suess recognized by a plotting the temporal spread of marine sediments over the continents and b estimating the depositional depth variations in marine stratal sequences which can be correlated across and between continents to these methods can be added seismic stratigraphy in which biostratigraphically age determined seismic sequences on the con tinental margins are analyzed in terms of cycles of coastal onlap and offiap when the results of these methods are broadly in accord confidence in a eustatic interpretation is increased but the range of confidence can vary considerably it is widely accepted that there was an exceptionally high sea

magmatic intervals transgression regression cycles and oceanic events in the cretaceous and tertiary of southern south america abstract the southern part of south america provides an excellent test area to analyse relationships between transgression regression cycles along a passive continental margin with magmatic activity and tectonic movements of the andean orogen most of the tectono eustatic sea level changes recognized are related to magmatic activity whether calc alkaline or alkaline the magmatic activity depends on whether tectonic convergence or extension forces are dominant

volcanological and petrological evolution of vulcano island aeolian arc southern tyrrhenian sea petrological and geochemical data are reported for volcanic rocks from vulcano island the subaerial volcanism 120 ka to present built up a nw se elongated composite structure affected by two intersecting multistage calderas volcanics older than 20 ka consist mostly of high k calc alkaline hkca to shoshonitic sho mafic rocks these magmas interacted significantly with the continental crust which generated variable sr isotopic ratios 0 70412 0 70520 however a major role was also played by input of parental liquids into the magma chamber which prevented further evolution of the magmas hkca sho and potassic ks rocks formed from 20 to 8 ka display a much larger range of sio2 from shoshonites to rhyolites and higher concentrations of incompatible elements with respect to the previous stage sr isotopic ratios show small variations 0 70448 0 70486 mixing of silicic and mafic liquids and fractional crystallization processes fc were the main evolutionary processes during this stage volcanics younger than 8 ka consist of sho and leucite bearing ks mafic rocks with abundant intermediate and silicic products mafic and intermediate rocks display similar incompatible element abundances and sr isotopic ratios as the previous stage volcanics whereas higher 87sr 86sr 0 70494 0 70583 are observed in some rhyolites these products originated from a complex interplay of fc crustal assimilation and magma mixing processes the most mafic rocks show increasing incompatible element abundances rb sr rb ba mg al mg ca and a decrease in large ion lithophile to high field strength element ratios passing from older hkca sho to the younger sho ks volcanics these variations suggest a shifting of magma sources from a slightly metasomatized asthenosphere fertile peridotite to a more strongly metasomatized lithospheric mantle residual peridotite time related petrological and geochemical variations have been used to develop a model for the evolution of the vulcano plumbing system