p t t paths of collisional orogens pressure temperature time p t t paths summarize the changes in pressure and temperature imposed on a metamorphic rock during orogenesis they provide a convenient framework for the interpretation of complex metamorphic histories and also offer insight into the thermal and tectonic factors controlling metamorphism in collisional orogens p t t data are acquired through a combination of textural observations thermobarometry and thermochronometry and assembled into a p t t path using geological constraints one dimensional p t t models assuming instantaneous deformation and thermal relaxation by conduction are flexible and useful for testing tectonic models particularly where geochronological constraints are available two dimensional models allow more sophisticated deformation geometries and allow the effects of advection to be incorporated analysis of collisional orogens in terms of critical wedge theory can yield p t t paths that reflect coupling between thickening uplift exhumation erosion and convergence where rates of erosion approach rates of tectonic uplift as is currently happening in the southern alps of new zealand high grade metamorphic rocks can be exhumed rapidly from considerable depth alternatively rapid exhumation may reflect gravity driven extension in an over steepened or thermally weakened orogen

metamorphic reaction rates at 650 800 c from diffusion of niobium in rutile abstract the ability to quantify the rates at which metamorphic reactions occur is critical to assessing the extent to which equilibrium is achieved and maintained in a variety of dynamic settings here we investigate the kinetics of rutile replacement by titanite during amphibolite facies overprinting of eclogite garnet amphibolite and anorthosite from catalina island ca the tromso nappe norway the north qaidam terrane china and the guichicovi complex mexico trace element concentration profiles across rutile rimmed by titanite as determined by laser ablation inductively coupled plasma mass spectrometry la icp ms reveal nb zoning in rutile that we interpret as the result of nb back diffusion from the rutile titanite boundary we present new field based reaction rates calculated from grain boundary velocities which in turn were calculated using a 1 d diffusion model for nb back diffusion into rutile during titanite replacement over the temperature range 670 770 c our data are consistent with or slightly faster than previous estimates of field based reaction rates for regional metamorphism and extend the temperature and compositional range over which regional metamorphic reaction rates are known

timing and tectonic setting of grenvillian metamorphism constraints from a transect along georgian bay ontario systematic mapping of a transect along the well exposed shores of georgian bay ontario combined with the preliminary results of structural analysis geochronology and metamorphic petrology places some constraints on the geological setting of high grade metamorphism in this part of the central gneiss belt correlations within and between map units gneiss associations have allowed us to recognize five tectonic units that differ in various aspects of their lithology metamorphic and plutonic history and structural style the lowest unit which forms the footwall to a regional decollement locally preserves relic pre grenvillian granulite facies assemblages reworked under amphibolite facies conditions during the grenvillian orogeny tectonic units above the decollement apparently lack the early granulite facies metamorphism out of sequence thrusting in the south produced a duplex like structure two distinct stages of grenvillian metamorphism are apparent the earlier stage c 1160 1120 ma produced granulite facies assemblages in the parry sound domain and upper amphibolite facies assemblages in the parry island thrust sheet the later stage c 1040 1020 ma involved widespread dominantly upper amphibolite facies metamorphism within and beneath the duplex deformation and metamorphism recently reported from south and east of the parry sound domain at c 1100 1040 ma have not yet been documented along the georgian bay transect the data suggest that early convergence was followed by a period of crustal thickening in the orogenic core south east of the transect area with further advance to the north west during and after the waning stages of this deformation

palaeoenvironment of the eocene eckfeld maar lake germany implications from geochemical analysis of the oil shale sequence abstract drill core samples from the depth interval between 19 4 and 32 0 m of the laminated central lake facies of the eocene eckfeld maar were investigated for biomarker and stable isotope composition bulk organic geochemical parameters c n hi and the molecular composition of the soluble organic matter indicate a dominance of particulate organic matter from land plants and microbially derived lipids in the lower part of the sedimentary succession an angiosperm dominated vegetation is indicated from the terpenoid biomarker composition abundant 4 methylsteroids in the 25 6 30 8 m section of the oil shale sequence reflect a contribution of algal derived biomass samples with high concentrations of methylsteroids are characterized by low amounts of triterpenoids related to the arborane skeleton and vice versa this pattern is interpreted as reflecting differences in autochthonous organic matter production vs microbial activity in the lowermost section 32 0 30 6 m a trend towards heavier 18 o and 13 c values indicates the evolution of permanently meromictic conditions in the lake and an increase in methanogenesis high 13 c values of siderites 10 throughout most of the sequence are consistent with permanently anoxic conditions at the sediment water interface the lighter 18 o values of siderites from turbidites relative to siderites from biogenic laminites are postulated to have been caused by temporary phases of increased precipitation followed by landslides and improved circulation within the lake depletion of the organic matter in 13 c average 13 c 29 4 in comparison with the fossil wood ranging from 23 1 to 26 6 is explained by the dominance of waxy lipid rich land plant material e g leaf waxes resins bark over wood supplied to the lake carbon cycling during anoxic decomposition of organic matter is assumed to further affect the 13 c values through the activity of anaerobic e g methanogenic bacteria resulting in a depletion of the biomass in 13 c the overall trend in the isotopic composition of organic carbon towards heavier values in the depth interval between 26 0 and 3 2 m is accompanied by decreasing c n ratios indicating an increase in aquatic organic matter production the geochemistry of the oil shale succession points towards a highly productive eutrophic ecosystem with intense microbial activity under meromictic conditions in the maar lake beside the high input of land plants to the biomass major contributions from bacteria and phytoplankton are indicated by the biomarker composition

metamorphic interpretation of high pressure temperature metapelites with preserved growth zoning in garnet eastern grenville province canadian shield high pressure temperature metapelites that occur in close proximity to eclogitized mafic rocks in the southern part of the gagnon terrane parautochthonous belt eastern grenville province were investigated in order to constrain depths of burial and p t paths mineral assemblages and partial melting relationships in these metapelites are consistent with peak temperatures in the range between 700 and 800 c however growth zoning is apparently well preserved in garnets and only narrow rims width 100 500 m are obviously affected by diffusional retrograde resetting despite uncertainties regarding mineral assemblages and compositions of matrix minerals at early stages of garnet growth it can be shown that the observed growth zoning profiles of garnets imply increase of both pressure and temperature up to a common maximum at pressures between 1300 and 1600 mpa and that thermal relaxation did not occur during the initial stages of unloading on the other hand calculated retrograde p t conditions are consistent with steep decompression paths the inferred hair pin shaped p t path is consistent with independent evidence of rapid tectonically driven exhumation resulting in the preservation of growth zoning in garnets from such a high temperature regime

metamorphic response to collision in the central himalayan orogen abstract closure of the neotethys ocean and high angle continent continent collision between india and asia after about 55 ma resulted in low angle subduction of the indian plate below the tibetan plateau and by 30 ma established an arcuate 2300 km long shallow north dipping metamorphic fold thrust belt in the foreland this himalayan metamorphic front quickly established an upper plate lower plate paired metamorphic architecture centred on the median high himal thrust that largely controlled subsequent evolution the upper plate is a thick slab of high t moderate p high grade migmatized metamorphic rocks whereas the lower plate is an inverted series of moderate t high p schists in two crustal wedges the broad main central thrust zone and at lowest structural levels the footwall below the basal main central thrust spatial and temporal patterns of metamorphic response in the evolving himalayan metamorphic front has been characterized in a large scale integrated structural metamorphic study based on 8 profiles across eastern nepal metamorphic response at all structural levels is established using a large dataset n 160 of internally consistent quantitative pt determinations petrology of metapelite samples semi quantitative p t paths metamorphic mapping and metamorphic field gradients these results are integrated with previously published metamorphic studies structural profiles and metamorphic chronology from these datasets the architecture and evolution of the himalayan metamorphic front is constrained by rock kinematics metamorphic field gradients showing discontinuities and diachronous metamorphism with contrasting p t evolutions at different structural levels each of the three panels constituting the himalayan metamorphic front upper plate main central thrust zone and footwall experienced distinctly different tectono metamorphic histories crustal processes operating during metamorphism and exhumation differ between the upper and lower plates the upper plate experienced long lived metamorphism starting from at least 28 38 ma and tracking low p t clockwise p t paths that culminated at 19 27 ma in peak high grade condition with 27 31 c km thermal regimes protracted high grade conditions produced significant partial melt which facilitated gravity driven southward extrusion involving internal ductile flow processes southward extrusion of the upper plate was accommodated by coeval reverse movement on the high himal thrust and top down to the north normal reactivation of the south tibet detachment system between 22 10 ma transport of this thick slab to the south resulted in further prograde burial of the lower plate below culminating in peak metamorphism at the highest pressures attained in the lower plate rocks the lower plate consists of at least two deeply buried 7 5 9 4 kb crustal wedges both of which experienced steep p t hairpin clockwise p t paths with isothermal decompression the main central thrust zone experienced 20 26 c km metamorphism at 12 22 ma and was exhumed along the basal main central thrust after 11 ma whereas loading by the main central thrust zone gave rise to further prograde burial of the footwall which experienced 16 21 c km metamorphism at 4 10 ma and was exhumed along the main boundary thrust at 3 9 ma in contrast to the upper plate both crustal wedges were exhumed by a process of out wedging which involved upthrusting along basal and internal thrusts with coeval extensional slip in the hanging walls this three stage foreland propagating lateral exhumation history resulted in telescoping of the himalayan metamorphic front in concert with peak metamorphic events at different structural levels during main phase orogenesis and is not the result of superimposed retrograde reactivation of the belt

peak metamorphic temperatures from cation diffusion zoning in garnet a model that relates the characteristic diffusion length and average cooling rate to peak temperature was developed for chemical diffusion in spherical geometries on the basis of geospeedometry principles and diffusion theory the model is quantitatively evaluated for cation diffusion profiles in garnet important model parameters were calibrated empirically using diffusion zoning of ca in garnet from the pikwitonei granulite domain a terrane for which the thermal history has been well characterized the results are used i to empirically test diffusion parameters for mg and fe ii and ii to develop a tool that uses the diffusion zoning of these cations in garnet to constrain peak temperature conditions for garnet bearing rocks the thermometric approach was externally tested by applying it to garnet crystals from various metamorphic terranes worldwide and comparing the results to published peak temperature estimates the results overlap within uncertainties in all cases but result that are based on fe ii and mg chemical diffusion profiles are up to three times more precise than those acquired by conventional methods the remarkable consistency of the results implies that the model is robust and provides a reliable means of estimating peak temperatures for different types of high grade metamorphic rock the tool could be of particular advantage in rocks where critical assemblages for conventional thermometry do not occur or have been replaced during retrogression

contrasting zoning profiles in high grade garnets evidence for the allochthonous nature of a grenville province terrane in the central part of the grenville province proterozoic metasediments of the reservoir cabonga terrane arc underlain by gently dipping archean migmatites a major mylonite zone located within the migmatites is the base of a large thrust sheet made up of the reservoir cabonga terrane and a migmatitic sole garnets from meta aluminous assemblages in proterozoic metasediments mylonites and migmatites display contrasting types of ca zoning patterns garnets with ca rich cores are found along the western edge of the reservoir cabonga terrane whereas garnets with flat ca profiles are found in the remaining proterozoic metapelites in the mylonites and in the archean migmatites considering samples in which an infinite reservoir of ca ions is warranted by abundant plagioclase in the matrix pressures well in excess of 1200 mpa at temperatures between 700 and 800 c are indicated for a metamorphic event recorded in the cores of garnets from the western edge of the reservoir cabonga terrane the inner rim of garnet records pressures of around 1000 mpa for the same temperature range in homogeneous garnets a single p t set around 800 mpa and 750 c is recorded in the migmatites some of the mylonites initiate their recrystallization under relatively high pressures which is continued during decompression and record the lowest p t values these metamorphic signatures suggest that the proterozoic metapelites were already metamorphosed under relatively high pressure when emplaced on to archean migmatites and that the entire area was subsequently subjected to metamorphism at a lower pressure

retrograde deformation within the carthage colton zone as recorded by fluid inclusions and feldspar compositions tectonic implications for the southern grenville province the carthage colton zone ccz located in the northwestern portion of the proterozoic adirondack terrane forms the boundary between the adirondack lowlands and highlands and is characterized by textures indicative of ductile deformation samples from three rock types have been collected from this zone 1 pyroxene bearing syenite gneisses of the diana igneous complex 2 paragneiss samples from near the northwestern boundary of the diana complex 3 a quartz rich metasediment feldspar geothermometry performed on the diana metasyenites shows that porphyroclasts are relict igneous grains that formed att 900 c while dynamic recrystallization occurred at temperatures as low as 470 to 550 c as shown by the compositions of feldspar neoblasts all samples examined in this study from the ccz contain a suite of co2 rich fluid inclusions that are distinctive both texturally and in their microthermometric behavior th 27 7 to 7 1 c as compared to co2 rich adirondack fluid inclusions that do not lie within this zone th 45 9 to 31 0 c the results from fluid inclusion microthermometry and feldspar geothermometry restrict the conditions of dynamic recrystallization to temperatures and pressures of 400 to 550 c and 3 to 5 kbar the retrograde pressure temperature path must pass through these conditions similar fluid inclusion results have been obtained from the parry sound shear zone pssz which is a grenvillian shear zone that is located in southern ontario lamb and moecher 1992 however the inferred retrogradep t paths for these two areas the ccz and the pssz are different and this difference may be a result of late deformation along shear zones that are located between the two areas

chemical and textural equilibration of garnet during amphibolite facies metamorphism the influence of coupled dissolution reprecipitation metamorphic equilibration requires chemical communication between minerals and may be inhibited through sluggish volume diffusion and or slow rates of dissolution in a fluid phase relatively slow diffusion and the perceived robust nature of chemical growth zoning may preclude garnet porphyroblasts from readily participating in low temperature amphibolite facies metamorphic reactions garnet is widely assumed to be a reactant in staurolite isograd reactions and the evidence for this has been assessed in the late proterozoic dalradian pelitic schists of the scottish highlands the 3d imaging of garnet porphyroblasts in staurolite bearing schists reveals a good crystal shape and little evidence of marginal dissolution however there is also lack of evidence for the involvement of either chlorite or chloritoid in the reaction staurolite forms directly adjacent to the garnet and its nucleation is strongly associated with deformation of the muscovite rich fabrics around the porphyroblasts cloudy fluid inclusion rich garnet forms in both marginal and internal parts of the garnet porphyroblast and is linked both to the production of staurolite and to the introduction of abundant quartz inclusions within the garnet such cloudy garnet typically has a mg rich mn poor composition and is interpreted to have formed during a coupled dissolution reprecipitation process triggered by a local influx of fluid all garnet in the muscovite bearing schists present in this area is potentially reactive irrespective of the garnet composition but very few of the schists contain staurolite the staurolite producing reaction appears to be substantially overstepped during the relatively high pressure barrovian regional metamorphism reflecting the limited permeability of the schists in peak metamorphic conditions fluid influx and hence reaction progress appear to be strongly controlled by subtle differences in deformation history the remaining garnet fails to achieve chemical equilibrium during the reaction creating distinctive patchy compositional zoning such zoning in metamorphic garnet created during coupled dissolution reprecipitation reactions may be difficult to recognize in higher grade pelites due to subsequent diffusive re equilibration fundamental assumptions about metamorphic processes are questioned by the lack of chemical equilibrium during this reaction and the restricted permeability of the regional metamorphic pelitic schists in addition the partial loss of prograde chemical and textural information from the garnet porphyroblasts cautions against their routine use as a reliable monitor of metamorphic history however the partial re equilibration of the porphyroblasts during coupled dissolution reprecipitation opens possibilities of mapping reaction progress in garnet as a means of assessing fluid access during peak metamorphic conditions

lipid geochemistry of sediments from upton broad a small productive lake major lipid classes isolated from 3 sections of the sediment profile of upton broad a shallow lake formed about 500 yr ago were correlated with input and with changes attributable to early diagenesis surficial sediment contains lipids characteristics of the known recent algal and microbial input preservation of chlorophyll pigments and absence of appropriate markers suggest that diagenesis is minimal older deposits from the eutrophic phase of the lake s history contain higher levels of bacterial lipids and diagenetic products the earliest sediment contains lipids characteristic of terrigenous input subjected to more extensive diagenesis than the younger sediment recognition of early diagenesis in anoxic sediment suggests that distributions of the shorter chain homologous free n alkanes alkanols and alkanoic acids result from microbial synthesis using material initially deposited at the sediment surface rather than partial preservation of the lipids of primary source organisms

response to increasing southern hemisphere winds in ccsm4 abstractresults from two perturbation experiments using the community climate system model version 4 where the southern hemisphere zonal wind stress is increased are described it is shown that the ocean response is in accord with experiments using much higher resolution ocean models that do not use an eddy parameterization the key to obtaining an appropriate response in the coarse resolution climate model is to specify a variable coefficient in the gent and mcwilliams eddy parameterization rather than a constant value this result contrasts with several recent papers that have suggested that coarse resolution climate models cannot obtain an appropriate response

the partial equilibration of garnet porphyroblasts in pelitic schists and its control on prograde metamorphism glen roy scotland garnet porphyroblasts in sillimanite bearing pelitic schists contain complex textural and compositional zoning with considerable variation both within and between adjacent samples the sillimanite bearing schists locally occur in regional barrovian garnet zone assemblages and are indicative of a persistent lack of equilibrium during prograde metamorphism garnet in these dalradian rocks from the scottish highlands preserves evidence of a range of metamorphic responses including initial growth and patchy coupled dissolution reprecipitation followed by partial dissolution individual porphyroblasts each have a unique and variable response to prograde metamorphism and garnet with mainly flat compositional profiles co exists with those containing largely unmodified characteristic bell shaped mn profiles this highlights the need for caution in applying traditional interpretations of effective volume diffusion eliminating compositional variation cloudy garnet with abundant fluid inclusions is produced during incomplete modification of the initial porphyroblasts and these porous garnet are then particularly prone to partial replacement in sillimanite producing reactions the modification of garnet via a dissolution reprecipitation process releases ca into the effective whole rock composition displacing the pressure temperature positions of subsequent isograd reactions this represents the first report of internal metasomatism controlling reaction pathways the behaviour of garnet highlights the importance of kinetic factors especially deformation and fluids in controlling reaction progress and how the resulting variability influences subsequent prograde history the lack of a consistent metamorphic response within and between adjacent schists suggests that on both local and regional scales these rocks have largely not equilibrated at peak metamorphic conditions

fatty acid geochemistry of a 200 m sediment core from lake biwa japan early diagenesis and paleoenvironmental information abstract fatty acids fas and hydroxy acids dicarboxylic acids and n alkanes were studied in a 200 m sediment core taken from lake biwa japan fas showed bimodal distribution with peaks at c 16 and c 22 c 28 their distribution patterns clearly changed with depth from lower molecular weight c 12 c 19 predominance to higher molecular weight c 20 c 32 predominance in the upper 20 m interval analyses of related compounds and hydroxy acids and dicarboxylic acids suggest that and oxidative degradation of c 12 c 19 fas has occurred in the sediments the ratio of bound c 12 c 19 to unbound fas increases with depth in the upper 0 1 m sediments suggesting that unbound fas are more labile however the ratio varies significantly in deeper sections and may be associated with water temperature in the sediments deeper than 20 m in depth c 12 c 19 fas gradually decrease on the other hand higher molecular weight fas hfas c 20 c 32 which were probably derived from terrestrial plants increase in concentration from 20 m to 100 m suddenly decrease at 100 m and show progressively lower concentration in deeper sediments these fluctuations are interpreted in relation to paleolimnological changes of the lake and the drainage basin hydroxy c 20 c 30 acids and c 20 c 30 dicarboxylic acids show a distribution pattern similar to hfas branched chain fas hydroxy acids and c 9 c 19 dicarboxylic acids show a major peak around 3 15 m in depth this peak is probably caused by increased bacterial activity in the water column and surface sediments in the past which may be associated with an increase in primary production of the lake

well preserved garnet growth zoning in granulite from the dabie mountains central china ultra high pressure eclogites and granulites both occur in the dabie mountains central china a garnet porphyroblast from felsic granulite in the dabie mountains has been analysed for compositional zoning by electron microprobe two segments of the porphyroblast have opposite compositional variations segment i from centre outward 9 mm to analytical point 18 has decreasing xsps and increasing xpyr while segment ii from analytical point 18 1 mm outward to the rim has increasing xsps and xalm and decreasing xpyr and xgrs the compositional zoning in segment i is considered as growth zoning and that in segment ii as diffusive retrograde zoning garnet growth zoning records a p t path prior to the peak granulite metamorphism the minimum p t conditions are estimated to be 1 35 gpa and 850 c for peak metamorphism based on the highest mg fe mg composition in the garnet analytical point 18 and matrix hypersthene biotite and plagioclase a symplectitic corona surrounds the porphyroblast and appears to have formed at 0 6 gpa and 700 c the well preserved growth zoning in garnet suggests a short residence time for the granulite at peak metamorphism and thus rapid tectonic uplift history the p t path is consistent with that of ultra high pressure eclogite in the area tectonic movements during a collisional event could have brought both the granulite and the eclogite to their present positions

diagenesis of biomarkers in biwa lake sediments over 1 million years abstract lipid biomarker compounds n alkanoic acids n alkanols sterols n alkanes chlorophyll derivatives and total lipid carbon in a chloroform extractable fraction isolated from sedimentary deposits up to 2 ma old of a 1400 m core sample of lake biwa were analyzed by gas chromatography gas chromatography mass spectrometry and a thin layer chromatography flame ionization detection analyzer tlc fid to investigate their diagenesis and their utilities as biomarkers the samples are divided into two parts at a depth of 911 4 m the samples below 911 4 m are basement rock the upper core is composed of clay from the surface to 249 5 m in depth and alternated with slit clay and gravels from 249 5 to 911 4 m the organic compound carbon obtained by hydrolysis of the lipid fraction by alkali solution comprised from 11 to 35 of the total lipid carbon tlc fid analysis indicated that significant amounts about 70 80 of the total lipid carbon were present in the polar fraction and small proportions were simple lipids the amounts of n alkanols were comparable to those of n alkanoic acids and sterols while contemporary lacustrine sediments usually contain a larger amount of n alkanoic acids than of n alkanols normal alkanes maximizing in abundance at c 27 or c 29 were most abundant among the lipid compounds variation in the distributions of sterols and stanols seemed to preserve the information of input sources and the c 27 c 29 ratios were correlated to the c n of the sediments the composition of n alkanols maximizing at c 24 or c 18 appeared to indicate an aquatic paleoenvironment a paleowater depth at least in the upper 250 m ratios of shorter to longer chain n alkanoic acids which had been believed to be an indicator of autochthonous to allochthonous origins clearly increased with time a marked correlation between chlorophyll derivatives ratio of chlorophyll derivatives to total lipid carbon and paleotemperature was found

juxtaposition of diverse subduction related tectonic blocks with contrasting metamorphic features and ages in the paleoproterozoic aketashitage orogen nw china implications for precambrian orogeny

temporal variability of the meridional overturning circulation at 34 5 s results from two pilot boundary arrays in the south atlantic data from two boundary arrays deployed along 34 5 s are combined to produce the first continuous in situ time series observations of the basin wide meridional overturning circulation moc in the south atlantic daily estimates of the moc between march 2009 and december 2010 range between 3 sv and 39 sv 1 sv 106 m3 s 1 after a 10 day low pass filter is applied much of the variability in this 20 month record occurs at periods shorter than 100 days approximately two thirds of the moc variability is due to changes in the geostrophic baroclinic plus barotropic volume transport with the remainder associated with the direct wind forced ekman transport when low pass filtered to match previously published analyses in the north atlantic the observed temporal standard deviation at 34 5 s matches or somewhat exceeds that observed by time series observations at 16 n 26 5 n and 41 n for periods shorter than 20 days the basin wide moc variations are most strongly influenced by ekman flows while at periods between 20 and 90 days the geostrophic flows tend to exert slightly more control over the total transport variability of the moc the geostrophic shear variations are roughly equally controlled by density variations on the western and eastern boundaries at all time scales captured in the record the observed time mean moc vertical structure and temporal variability agree well with the limited independent observations available for confirmation

fluid inclusions in adirondack granulites implications for the retrograde p t path investigation of fluid inclusions in granitic and calc silicate gneisses from the adirondack mountains new york has revealed the presence of various types including 1 co2 rich 2 mixed h20 c02 salt and 3 aqueous inclusions with no visible co2 many if not all of these inclusions were trapped or modified after the peak of granulite facies metamorphism as shown by textural relations or by the lack of agreement between the composition of the fluids found in some inclusions and the composition of the peak metamorphic fluid as estimated from mineral equilibria many fluid inclusions record conditions attained during retrograde cooling and uplift with minimum pressures and temper atures of 2 to 3 kbar and 200 to 300 c the tempera tures and pressures derived from the investigation of these inclusions constrain the retrograde p t path and the results indicate that a period of cooling with little or no decompression

extracting the buoyancy driven atlantic meridional overturning circulation abstractvariations in the atlantic meridional overturning circulation amoc driven by buoyancy forcing are typically characterized as having a low frequency time scale interhemispheric structure

two decades of the atlantic meridional overturning circulation anatomy variations extremes prediction and overcoming its limitations the zonally integratedmeridional volumetransport in the north atlantic atlantic meridionaloverturning circulation amoc is described in a 19 yr long ocean state estimate one consistent with a diverse global dataset apart from a weak increasing trend at high northern latitudes the amoc appears statistically stable over the last 19yr with fluctuations indistinguishable from those of a stationary gaussian stochastic process this characterization makes it possible to study using highly developed tools extreme values predictability and the statistical significance ofapparenttrends gaussianbehaviorisconsistentwith the central limittheorem for a process arising from numerous independent disturbances in this case generators include internal instabilities changes in wind and buoyancy forcing fields boundary waves the gulf stream and deep western boundary current transports the interior fraction in sverdrup balance and all similar phenomena arriving as summation effects from long distances and times as a zonal integral through the sum of the large variety of physical processes in the three dimensional ocean circulation understanding of the amoc if it is of central climate importance requires breaking it down into its unintegrated components over the entire basin

contrasting p t paths in the eastern himalaya nepal inverted isograds in a paired metamorphic mountain belt petrology and phase equilibria of rocks from two profiles in eastern d f matrix assemblages are overprinted by decompression reaction textures and in zones f and g progress into the sillimanite field nepal from the lesser himalayan sequences across the main central thrust zone and into the greater himalayan sequences the two terranes were brought into juxtaposition during formation of sillimanite biotite gedrite foliation seams s3 formed at reveal a paired metamorphic mountain belt pmmb composed of two thrust bound metamorphic terranes of contrasting metamorphic conditions of 674 33 c and 5 7 1 1 kbar the contrasting average geothermal gradients and p t paths of these two metastyle at the higher structural level the greater himalayan sequences experienced high t moderate p metamorphism with an anmorphic terranes suggest they make up a pmmb the upperplate position of the greater himalayan sequences produced an ticlockwise p t path low p inclusion assemblages of quartz hercynitic spinel sillimanite have been overgrown by peak anticlockwise p t path with the high average geothermal gradient being possibly due to high radiogenic element content in this terrane metamorphic garnet cordierite sillimanite assemblages that equilibrated at 837 59 c and 6 7 1 0 kbar matrix in contrast the lower plate lesser himalayan sequences were deeply buried metamorphosed in a clockwise p t path and display minerals are overprinted by numerous metamorphic reaction textures that document isobaric cooling and re equilibrated samples preserve inverted isograds as a result of progressive ductile overthrusting of the hot greater himalayan sequences during prograde metamorphism evidence of cooling to 600 45 c at 5 7 1 1 kbar below the main central thrust the lesser himalayan sequences are a continuous though inverted barrovian sequence of high p moderate t metamorphic rocks metamorphic zones upwards from the

neoarchaean metamorphic evolution of the yilgarn craton a record of subduction accretion extension and lithospheric delamination abstract the greater part of the metamorphic record of the yilgarn craton formed during a protracted middle neoarchaean orogenic cycle spanning from about 2750 to 2620 ma at least six distinct metamorphic events are defined by parageneses in different tectono stratigraphic settings this review characterizes the middle neoarchaean metamorphic response of the entire craton using large databases rock descriptions from 60 000 sites in government databases and 1040 pt determinations from all sources are used to construct metamorphic map patterns for each of these metamorphic events p t paths and timing of each metamorphic event are characterized using petrology and the well constrained pt determinations from this study n 287 combined with metamorphic age determinations from all sources n 114 the spatial patterns and metamorphic conditions of each event provides critical constraints on tectonic settings and changes in tectonics over 130 million years the record of metamorphism in conjunction with stratigraphic kinematic and magmatic constraints shows that the neoarchaean craton evolved from an accretionary crustal growth phase ma and m1 to thermal reworking of the crust during massive influx of granitic intrusions m2 and lithospheric extension after the termination of subduction m3 these events were followed by lithospheric delamination resulting in a craton wide diffusion delayed thermal pulse that coincided with renewed contraction m4 m1 metamorphism at 2748 19 2727 8 and 2706 10 ma experienced high p moderate t hairpin clockwise p t paths during burial of magmatic arc margins during terrane accretion events m2 regional contact type metamorphism at 2671 6 ma tracked low p moderate t clockwise p t paths in back arc settings during voluminous felsic magmatism related to shallow subduction m3 metamorphism at 2656 5 ma experienced low p moderate t anticlockwise p t paths in post volcanic rift basins formed during lithospheric extension m4 metamorphic peaks at 2644 4 and 2629 7 ma experienced low p high t clockwise p t paths during regional scale thermal pulses resulting from lower crust and mantle lithosphere delamination at 2665 2668 ma

coupling of p t t d histories of eclogite and metagreywacke insights to late ordovician silurian crustal folding events recorded in the beishan orogen nw china

bathymetric influences on antarctic ice shelf melt rates ocean bathymetry exerts a strong control on ice sheet ocean interactions within antarctic ice shelf cavities where it can limit the access of warm dense water at depth to the underside of floatin

transect across the northwestern grenville orogen georgian bay ontario polystage convergence and extension in the lower orogenic crust the grenville orogenic cycle between 1190 and 980 ma involved accretion of magmatic arcs and or continental terranes to the laurentian craton a transect across the western central gneiss belt georgian bay ontario which crosses the boundary between parautochthonous and allochthonous units at an inferred orogenic depth of 20 30 km offers some insights on the thermal and mechanical behavior of the lower crust during the development of the grenville orogen prior to grenvillian metamorphism this part of laurentia consisted largely of meso proterozoic 1450 ma granitoid orthogneisses granulites and subordinate mafic and supracrustal rocks grenvillian convergence along the transect began with transport of the previously deformed and metamorphosed 1160 ma parry sound domain over the craton sometime between 1120 ma and 1080 ma this stage of transport was followed by out of sequence thrusting and further convergence along successively deeper foreland propagating ductile thrust zones a major episode of extension at 1020 ma resulted in southeast directed transport of allochthonous rocks along the midcrustal shawanaga shear zone the final stage of convergence involved deformation and metamorphism in the grenville front tectonic zone at 1000 980 ma peak metamorphism along most of the transect at 1065 1045 ma followed initial transport of allochthonous rocks over the craton by 15 35 m y regional cooling which postdated peak metamorphism by 70 m y was probably delayed by the combined effects of late stage extension and convergence transport of allochthons at least 100 km over the craton was accomplished along a weak migmatitic decollement further propagation of the orogen into the craton followed partial melting and weakening of parautochthonous rocks below this decollement extensional deformation was associated with distributed ductile flow the formation of regional transverse folds with axes parallel to the stretching direction and reactivation of the allochthon parautochthon thrust boundary as an extensional decollement the extensional lower crustal flow was likely the primary cause of the subhorizontal attitude of many structures and seismic reflectors in this part of the central gneiss belt

sedimentary processes in the great lakes sediments in the great lakes are subject to four general categories of processes input transport deposition and postdepositional alteration sedimentary input is from coastal erosion 64 riverine input 26 atmospheric transport 3 and several lesser sources 7 once in the lake sediments are transported to their place of deposition along the bottom and or in suspension depending upon grain size and density the rate of deposition in the great lakes is variable and ranges from zero in some areas to over 6000 g m sup 2 yr sup 1 in the eastern basin of lake erie after deposition sediments undergo bioturbation dissolution of carbonate and opal remobilization of many metals followed by reprecipitation within the surficial oxidized layer and degradation of organic compounds

organic geochemistry of deep sea drilling project sediments from the gulf of calofornia hydrothermal effects on unconsolidated diatom ooze abstract the effects of intrusive thermal stress have been studied on a number of pleistocene sediment samples obtained from leg 64 of the dsdp ipod program in the gulf of california samples were selected from sites 477 478 and 481 where the organic matter was subjected to thermal stress from sill intrusions for comparison purposes samples from sites 474 and 479 were selected as representative of unaltered material the gc and gc ms data show that lipids of the thermally unaltered samples were derived from microbial and terrestrial higher plant detritus samples from sill proximities were found to contain thermally derived distillates and those adjacent to sills contained essentially no lipids curie point pyrolysis combined with gc and gc ms was used to show that kerogens from the unaltered samples reflected their predominantly autochthonous microbial origin pyrograms of the altered kerogens were much less complex than the unaltered samples reflecting the thermal effects the kerogens adjacent to the sills produce little or no pyrolysis products since these intrusions into unconsolidated wet sediments resulted in in situ pyrolysis of the organic matter examination of the kerogens by esr showed that spin density and line width pass through a maximum during the course of alteration but esr g values show no correlation with maturity stable carbon isotope 13 c values of kerogens decrease by 1 1 5 near the sills at sites 477 and 481 and the atomic n c decreases slightly with proximity to a smaller sill at site 478 differences in maturation behavior between site 477 and 481 and site 478 are attributed to dissimilarities in thermal stress and to chemical and isotopic heterogeneity of guaymas basin protokerogen

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

construction of the adjoint mit ocean general circulation model and application to atlantic heat transport sensitivity we first describe the principles and practical considerations behind the computer generation of the adjoint to the massachusetts institute of technology ocean general circulation model gcm using r giering s software tool tangent linear and adjoint model compiler tamc the tamc s recipe for fortran line by line generation of adjoint code is explained by interpreting an adjoint model strictly as the operator that gives the sensitivity of the output of a model to its input then the sensitivity of 1993 annual mean heat transport across 29on in the atlantic to the hydrography on january 1 1993 is calculated from a global solution of the gcm the kinematic sensitivity to initial temperature variations is isolated showing how the latter would influence heat transport if they did not affect the density and hence the flow over 1 year the heat transport at 29on is influenced kinematically from regions up to 20 o upstream in the western boundary current and up to 5 o upstream in the interior in contrast the dynamical influences of initial temperature and salinity perturbations spread from as far as the rim of the labrador sea to the 29on section along the western boundary the sensitivities calculated with the adjoint compare excellently to those from a perturbation calculation with the dynamical model perturbations in initial interior salinity influence meridional overturning and heat transport when they have propagated to the western boundary and can thus influence the integrated east west density difference our results support the notion that boundary monitoring of meridional mass and heat transports is feasible

the role of mesoscale eddies in the remote oceanic response to altered southern hemisphere winds abstract it has been suggested that a strengthening of the southern hemisphere winds would induce a more vigorous overturning through an increased northward ekman flux bringing more light waters into the oceanic basins and enhancing the upwelling of north atlantic deep water in the southern ocean thereby increasing ocean ventilation simulations from a coarse and a fine resolution version of a coupled model subject to idealized wind stress changes in the southern ocean are presented in the fine resolution eddy permitting model changes in poleward eddy fluxes largely compensate for the enhanced equatorward ekman transport in the southern ocean as a consequence northward transport of light waters pycnocline depth northern hemisphere overturning and southern ocean upwelling anomalies are much reduced compared with simulations in the coarse resolution model with parameterized eddies these results suggest a relatively weak sensitivity of present day global ocean overturning circulation to the proj

seasonal variations in the south atlantic meridional overturning circulation from observations and numerical models monthly climatologies of temperature and salinity from observations and numerical models are used to estimate the atlantic meridional overturning circulation amoc at 34 s observational estimates suggest that the geostrophic transport plays an equal role to the ekman transport in the amoc seasonal variations at this latitude whereas in the models the ekman transport controls the amoc seasonality the seasonality of the geostrophic transport from observations is largely controlled by the seasonal density variations at the western boundary but in the models the eastern boundary dominates the observed density seasonality at the western boundary is linked to the intensity of the malvinas current which is poorly reproduced in the models the results indicate that the weak seasonal cycle in the model geostrophic transport can primarily be attributed to excessively strong baroclinicity below the surface mixed layer whereas the observations show a strong vertical coherence in the velocity down to 1200 m

linking organic matter deposition and iron mineral transformations to groundwater arsenic levels in the mekong delta cambodia enriched as in drinking water wells in south and southeast asia has increased the risk of cancer for nearly 100 million people this enrichment is generally attributed to the reductive dissolution of fe oxides however the complex expression of as enrichment in these areas is not yet well understood here the coupled sedimentological and geochemical factors that contribute to the extent and spatial distribution of groundwater as concentrations in the mekong river delta cambodia in an avulsed scroll bar sequence are examined x ray absorption spectroscopy xas was used to determine fe and as speciation in redox preserved sediment collected from drilled cores dissolved as fe and s solution concentrations in existing and newly drilled wells cores differed considerably depending on their source sedimentology the rapid burial of organic matter in the scroll bar sequence facilitated the development of extensive fe reducing conditions and as release into the aquifer in older features organic c levels are high enough to sustain extensive fe reduction and provide ample so4 which is reduced to sulfide this s reduction impacts as levels as is sequestered in sulfide minerals outside of the scrollbar sequence decreasing pore water concentrations in contrast as is depleted in sediments from the scroll sequence and associated with elevated pore water aqueous concentrations the concentration and form of organic c in the scrollbar sequence is related to depositional environment and can facilitate fe and s mineral transformations distinct sedimentary environments explain a portion of the inherent heterogeneity of aquifer as concentrations

atmospheric origins of variability in the south atlantic meridional overturning circulation abstractinsights from the rapid mocha observation network in the north atlantic have motivated a recent focus on the south atlantic where water masses are exchanged with neighboring ocean basins

redistribution of hfse elements during rutile replacement by titanite titanite growth at the expense of rutile during retrograde hydration of eclogite into amphibolite is a common phenomenon we investigated an amphibolite sample from the tromso eclogite facies terrain in northern norway to gain insight into the trace element distribution between rutile and titanite during incomplete resorption of the rutile by titanite patchy compositional zoning of al ti and f in titanite relates to the presence of a fluid with variable ti al and or f during its growth laser ablation icp ms and electron microprobe data for high field strength elements hfse nb zr ta and hf of rutile resorbed by titanite indicate a pronounced enrichment of these elements in the rim of a large single rutile crystal 8 mm and a systematic decrease towards uniform hfse contents in the large core hfse contents of smaller rutile grains 0 5 mm and rutile inclusions 100 m in the titanite overgrowth are similar or higher than in the rims of large rutile crystals element profiles from the rim inward demonstrate that hfse enrichment in rutile is controlled by diffusion hfse ratios in diffusion altered rutile show systematic variations compared with the uniform core composition of the large rutile modelling of zr and nb diffusion in rutile indicates that diffusion coefficients in rutile in fluid dominated natural systems must be considerably higher than those determined experimentally at 1 bar in dry systems variations of hfse contents in the newly formed titanite show no systematic spatial distribution hfse ratios in titanite and the rims of rutile are different indicating different solid fluid distribution coefficients in these minerals element fractionation by diffusion into the relict rutile and during fluid mediated growth of new titanite could substantially change the hfse budget of these minerals and could affect their use for geochemical tracing and other applications such as zr based geothermobarometry

localization of abrupt change in the north atlantic thermohaline circulation 1 recent climate model experiments as well as paleoclimate records suggest that the meridional overturning circulation or thermohaline circulation in the atlantic ocean could change abruptly as a result of global warming and that this could have a significant impact on european climate we use a reduced gravity model to investigate the response of the atlantic overturning circulation to changes in forcing we find that variability at decadal and higher frequencies is confined to a single hemisphere this implies that a overturning variability resulting from high frequency changes in buoyancy forcing in the labrador and greenland seas will be limited to the north atlantic and b any observed decadal and higher frequency fluctuations in north atlantic overturning can only result from changes in the surface fluxes within the north atlantic basin itself these results suggest that southern ocean wind forcing is not important for north atlantic overturning on decadal and shorter timescales

diagenesis of free and bound lipids in terrestrial detritus deposited in a lacustrine sediment recent sediments from an oligotrophic lake loch clair having uniform organic input for 2000 yr show changes in lipid abundance and composition with increasing depth attributed to diagenesis stability of free lipids decreases in the order n alkanes alkan 2 ones sterols n alkanoic acids n alkanols n alkenoic acids diagenetic loss of shorter chain homologues is complete within 400 yr stabilisation of bound relative to free lipids increases the proportion of the former with sediment age and reduces loss of shorter chain bound homologues in an eutrophic lake cross mere shorter chain free and bound sedimentary lipids show increased abundance compared with loch clair the relative importance of higher input of shorter chain lipids derived from aquatic detritus and slower initial diagenesis due to the anoxic hypolimnion as causative factors for this difference between lake types cannot yet be assessed

neoarchean greenstone metamorphism in the eastern dharwar craton india constraints from monazite u th pbtotalages andptpseudosection calculations abstractthe archean hutti maski greenstone belt hmgb and the south kolar greenstone belt skgb are the two richest gold provinces in india here we present results of texturally constrained u th pbtotal chime dating of monazites and pt pseudosection analyses to understand the geochronological and metamorphic evolution of the two greenstone terrains the ages of felsic volcanism are constrained at ca 2669 22 ma in the hmgb and 2661 32 ma in the skgb the hmgb rocks underwent midamphibolite facies metamorphism at ca 2564 12 ma the inferred pt path indicates a contemporaneous pt increase of up to 6 kbar and 620 c followed by postpeak near isothermal decompression for the hmgb rocks the skgb rocks underwent a lower amphibolite facies metamorphism at ca 2546 12 ma and are characterized by a synchronous pt increase of up to 4 6 kbar and 600 c followed by decompressional cooling these results indicate a mixed arc plume setting for the evolution of both the greenstone belts as suggested by

zoning patterns in orthopyroxene and garnet in granulites implications for geothermometry compositional maps of orthopyroxene and garnet of contrasting grain size and in contact with different minerals were made from two paragneiss granulites from the minto terrane of northern quebec the compositional maps provide clear evidence of late exchange of fe fe mg after ca in garnet and al in orthopyroxene had been quenched in the extent of late fe mg exchange was controlled by neighbouring minerals with negligible fe mg gradients against plagioclase and quartz and substantial gradients against exchangeable fe mg minerals cores of grains in contact with exchangeable fe mg neighbours are progressively more reset in fe fe mg as grain size decreases whereas cores of even small grains surrounded by only plagioclase and quartz are not significantly different in fe fe mg than cores of the largest grains gradients of ca in garnet and of al in orthopyroxene in grains of uniform fe fe mg preserve a high temperature retrograde history during which intergranular exchange effected compositional uniformity of mineral rims and intragranular fe mg diffusion in garnet and orthopyroxene was rapid enough to homogenize fe fe mg the transition from efficient intergranular exchange at relatively high temperatures to local fe mg exchange at lower temperatures may have been controlled by loss of an intergranular exchange medium in the rock possibly an internally generated dehydration melt phase implications for geothermometry of granulites include the following numerical values are particular to this study 1 core compositions of garnet and orthopyroxene grains in contact with exchangeable neighbours may be reset in fe fe mg relative to the most refractory compositions by an amount equivalent to 120d c 2 fe mg exchange thermometry using even the most refractory fe fe mg compositions may not record peak granulite conditions possibly recording instead the temperature at which an intergranular exchange medium was lost from the rock and 3 temperature sensitive net transfer equilibria involving al solubility in orthopyroxene yield temperatures up to 150d c higher than maximum fe mg exchange temperatures even in grains with flat fe fe mg compositional profiles making them a better means of estimating peak granulite temperatures than fe mg exchange thermometry

the origins of late twentieth century variations in the large scale north atlantic circulation abstractsurface forcing perturbation experiments are examined to identify the key forcing elements associated with late twentieth century interannual to decadal atlantic circulation variability as simulated in an ocean sea ice hindcast configuration of the community earth system model version 1 cesm1 buoyancy forcing accounts for most of the decadal variability in both the atlantic meridional overturning circulation amoc and the subpolar gyre circulation and the key drivers of these basin scale circulation changes are found to be the turbulent buoyancy fluxes evaporation as well as the latent and sensible heat fluxes these three fluxes account for almost all of the decadal amoc variability in the north atlantic even when applied only over the labrador sea region year to year changes in surface momentum forcing explain most of the interannual amoc variability at all latitudes as well as most of the decadal variability south of the equator the observed strengthening of southern ocean westerly wi

the shear zone related gold mineralization at the turmalina deposit quadrilatero ferrifero brazil structural evolution and the two stages of mineralization turmalina is an important orogenic gold deposit located in the nw region of the quadrilatero ferrifero the deposit is hosted in an archean greenstone belt composed of ortho amphibolites and pelites with interleaved tuffs metamorphosed under amphibolite facies conditions and intruded by a granite stock the orebodies are controlled by wnw ese trending shear zones associated with hydrothermal alteration three deformation events are recognized in the turmalina gold deposit d1 and d2 are the result of a progressive archean deformation under ductile conditions between 2749 7 and 2664 35 ma d3 is characterized by a transpressional event under ductile brittle conditions with the age still unclear the three generations of garnet observed show that grt1 blastesis is pre to syn d1 and grt2 growth during the late to post deformation stages of the d2 event the initial temperature grt1 core is around 548 600 c whereas during late d2 the temperatures reached 633 c metamorphic peak grt2 rim likely as a result of granite intrusion the grt3 resulted from re equilibration under retrograde conditions two gold bearing sulfide stages were identified pyrrhotite arsenopyrite lollingite chalcopyrite gold stage i precipitated below a metamorphic peak temperature of 598 19 c associated with s1 foliation d1 and pyrrhotite pyrite arsenopyrite chalcopyrite gold stage ii is located commonly along v3 quartz carbonate veinlets with a temperature range between 442 9 and 510 30 c we suggest that the granite intrusion imposed an additional thermal effect that promoted further dehydration of country rocks the au derived mainly from a metamorphic fluid source but potentially mixed with magmatic fluids from the granite

the effect of interbedding on shale reservoir properties north sea oil is overwhelmingly generated in shales of the upper jurassic basal cretaceous kimmeridge clay formation once generated the oil is expelled and ultimately migrates to accumulate in sandstone or carbonate reservoirs the source rock shales however still contain the portion of the oil that was not expelled as a consequence such shales and juxtaposed non source lithofacies can form the targets for the exploration of unconventional oil in this paper we examine part of the kimmeridge clay formation as a hybrid shale resource system within which hot shale and organic lean sandstone and siltstone intervals are intimately interbedded this hybrid system can contain a greater volume of oil because of the increased storage capacity due to larger matrix porosities of the sand silt interbeds together with a lower adsorptive affinity in the interbedded sandstone the relationship between the estimated volume percentages of sand and mudstone and free oil determined from rock eval s1 yields is used to place limits on the drainage of oil from source mudstone to reservoir sand at the decimeter scale these data are used to determine oil saturations in interbedded sand mudstone sequences at peak oil maturity higher values of free hydrocarbon as evidenced by the s1 value in mudstone suggest that more oil is being retained in the mudstone while higher s1 values in the interbedded sands suggest the oil is being drained to saturate the larger pore spaces high silica content in the interbeds confirms the brittleness in this mudstone sandstone lithofacies an important factor to be considered for fracture stimulation to successfully work in a hybrid system the key points of this hybrid unconventional system are the thickness storage capacity and the possibility to capture a portion of the expelled as well as retained oil

on the origins of the variability of the malvinas current in a global eddy permitting numerical simulation 1 this article investigates the origins of the variability of the malvinas current mc transport using the results of an eddy permitting ocean general circulation model first the dynamical links between the variabilities of the mc and the antarctic circumpolar current acc transports at the drake passage are established time series analyses indicate that the connection between the transport variations of the acc and the mc is masked by high frequency oscillations although a substantial portion of this highfrequency variability is produced and dissipated locally there are also anomalies that propagate between those regions the most conspicuous of these signals has an average speed of 6 7 cm s 1 and a period of 150 days second the contribution of the wind forcing to the variability of the acc and the mc is determined from principal estimator patterns analysis the analysis indicates that the variance of the transport of both currents is more directly related to the variability of the wind stress than to the wind stress curl the transport variability is particularly sensitive to zonal wind stress anomalies in the latitudinal range of the drake passage that extends farther north over the south indian ocean a rather counterintuitive result of our analysis is that the wind stress forcing over the south atlantic ocean is unimportant to the variability of the mc transport

amphibolites of the shawanaga domain central gneiss belt grenville province ontario tectonic setting and implications for relations between the central gneiss belt and midcontinental usa abstract the lighthouse gneiss association is an amphibolite dominated assemblage situated in the allochthonous shawanaga domain of the central gneiss belt cgb grenville province it consists of two units in which the amphibolites differ in chemical composition and associated lithologies the upper unit consists of i thick intervals of amphibolite interpreted as mafic flows and which form about half of the unit ii a varied assemblage of thinly interlayered and laminated amphibolite and metasediment interpreted to have originated as mafic tuffs interlayered with sediment with a quartzofeldspathic source and iii thick horizons of semipelite or regularly interlayered psammites and pelites interpreted to be metamorphosed greywacke shale turbidites shed from a quartzofeldspathic source the lower unit has a much higher proportion of thick amphibolite interpreted as mafic flows and the metasediments are semipelitic geochemically both upper and lower amphibolites are olivine normative tholeiites but have distinct trace element characteristics the mantle normalized trace element pattern of amphibolite in the upper unit lacks a subduction imprint and suggests an asthenospheric source but that of the lower amphibolite has a subduction imprint or an indication of eruption through attenuated continental crust a back arc environment is most consistent with the chemistry of the amphibolites and the nature of the associated metasediments the recognition of the rocks of the lighthouse gneiss association as juvenile material and their juxtaposition with another juvenile member of the shawanaga domain the metarhyolite rich sand bay gneiss association leads to a refinement of current models for the tectonic evolution of the cgb before the 1200 1000 ma grenville orogenic cycle we also suggest that all elements of the proterozoic geology of midcontinental usa are present although jumbled by grenvillian tectonism in the cgb these elements include units interpreted as oceanward younging juvenile arcs that are overlain by a granite rhyolite layer and pierced by coeval plutons

anomalies of meridional overturning mechanisms in the north atlantic abstract optimal observations are used to investigate the overturning streamfunction in the north atlantic at 30 n and 900 m depth those observations are designed to impact the meridional overturning circulation moc in numerical models maximally when assimilated and therefore establish the most efficient observation network for studying changes in the moc they are also ideally suited for studying the related physical mechanisms in a general circulation model optimal observations are evaluated here in the framework of a global 1 model over a 10 yr period hydrographic observations useful to monitor the moc are primarily located along the western boundary north of 30 n and along the eastern boundary south of 30 n additional locations are in the labrador irminger and iberian seas on time scales of less than a year variations in moc are mainly wind driven and are made up through changes in ekman transport and coastal up and downwelling only a small fraction is buoyancy driven and constitutes a sl

monitoring the atlantic meridional overturning circulation the rapid climate change programme rapid has established a prototype system to continuously observe the strength and structure of the atlantic meridional overturning circulation moc at 26 5 n here we provide a detailed description of the rapid moc monitoring array and how it has evolved during the first four deployment years as well as an overview of the main findings so far the rapid moc monitoring array measures 1 gulf stream transport through florida strait by cable and repeat direct velocity measurements 2 ekman transports by satellite scatterometer measurements 3 deep western boundary currents by direct velocity measurements 4 the basin wide interior baroclinic circulation from moorings measuring vertical profiles of density at the boundaries and on either side of the mid atlantic ridge and 5 barotropic fluctuations using bottom pressure recorders the array became operational in late march 2004 and is expected to continue until at least 2014 the first 4 years of observations april 2004 april 2008 have provided an unprecedented insight into the moc structure and variability we show that the zonally integrated meridional flow tends to conserve mass with the fluctuations of the different transport components largely compensating at periods longer than 10 days we take this as experimental confirmation of the monitoring strategy which was initially tested in numerical models the moc at 26 5 n is characterised by a large variability even on timescales as short as weeks to months the mean maximum moc transport for the first 4 years of observations is 18 7 sv with a standard deviation of 4 8 sv the mechanisms causing the moc variability are not yet fully understood part of the observed moc variability consists of a seasonal cycle which can be linked to the seasonal variability of the wind stress curl close to the african coast close to the western boundary fluctuations in the gulf stream and in the north atlantic deep water nadw coincide with bottom pressure variations at the western margin thus suggesting a barotropic compensation ongoing and future research will put these local transport variations into a wider spatial and climatic context

north west propagation of the grenville orogen grenvillian structure and metamorphism near key harbour georgian bay ontario canada abstract we report structural and metamorphic data from a c 25 km transect across the eastern grenville front tectonic zone gftz to the britt domain at the northern end of georgian bay near key harbour ontario constrasting grenvillian structural and fabric elements characterize the eastern gftz northern britt domain and a narrow transition zone between them moderately to steeply dipping foliations with strong down dip lineations in all three divisions appear to be associated with nw directed thrusting in the transition zone and northern britt domain early s l fabrics with steep lineations are overprinted by younger structures s l with shallow se sse plunging lineations in which sparse dominantly but not exclusively normal sense kinematic indicators are recognized pressure and temperature estimates from grenvillian metamorphic assemblages in metadi abase indicate that conditions of p 12 kbar and t c 800 c were achieved before or during the thrust related deformation with p t t paths that indicate near isothermal decompression to p c 4 kbar and t c 700 c correlation of fabric elements with points on the p t t paths suggests that exhumation occurred during two stages the first associated with thrusting 1035 ma and the second with extension and thrusting pre 1003 ma the gftz contains steeply to moderately dipping thrust related fabrics and lacks shallow extensional structures the latest episode of thrusting in the gftz is inferred to have taken place at 990 980 ma the data are interpreted in terms of a tectonic model involving two stages of propagation of the grenville orogen towards its foreland 1035 ma and 980 ma with an intervening period of extension although the tectonic regime probably remained compressional on the scale of the orogen

sedimentary biomarker and isotopic indicators of the paleoclimatic history of the walker lake basin western nevada walker lake a terminal saline lake in western nevada has experienced major fluctuations in its water level due to changes in the regional climate during quaternary times as part of a paleo climatological study of western nevada we have investigated organic matter 6 3c and c n values and lipid biomarker contents of sediments deposited at various periods over the past 150 thousand years of lake history surficial sediments from two cross lake transects contain mostly lake derived organic matter diagenetic losses of organic matter are evident in deeper sediments and the proportion of aquatic and terrigenous organic materials changes in response to variations in preservational factors source identification of organic matter is complicated by the probability that walker lake has experienced desiccation at various times in its history which impacts the degree of preservation of organic substances

growth and retrograde zoning in garnets from high grade metapelites implications for pressure temperature paths a previously unrecognized pattern of garnet zoning has been preserved in garnets from the upper amphibolite facies britt domain ontario grenville province some large garnets contain discrete regions of high grossular content as well as variations in the mg mg fe and mn nearly parallel to grain boundaries the latter are superimposed on and cut across regions of high grossular content such crosscutting zoning patterns have not been previously recognized in garnets the ca zoning involves changes of 4 to 10 mol grossular and is interpreted to represent growth zoning whereas the decreasing mg mg fe and increasing mn from core to rim are believed to be a diffusional retrograde effect the ca zoning indicates a pressure drop of ca 5 kbar at 700 50 c

geolipid pollen and diaton stratigraphy in postglacial lacustrine sediments as part of our continuing investigation of specific compounds as organic matter indicators in lake bottoms we have examined geolipids pollen and diatoms in sediments from different periods in the postglacial history of heart lake new york sediment core sections representing the major watershed vegetation periods were extracted for unbound and bound fatty acids hydrocarbons and alcohols fatty acids constitute most of the extracted material minor decreases in unsaturated acids with depth indicate little degradation of organic matter in these sediments the dominant unbound n alkanoic acid in the core sections is either cz2 or c24 but bound fractions contain few long chain acids and are dominated by n cry nearly all the hydrocarbons are found in the unbound fraction the ratio of c2 c 7 n alkanes increases from the bottom of the core to near the top as watershed forests have matured and lake productivity has diminished but drops since european settlement of the region organic degradation in this lake bottom is mild and input indicators appear to be well preserved

melt segregation in migmatites anatectic stromatic migmatites have a symmetrical layered structure with a low ratio of thickness to length and a periodicity features that have not been explained satisfactorily but which are related to physical processes of melt segregation we evaluate the compaction model for segregation as it applies to migmatites and develop models for melt segregation based upon convection driven by volume change and upon advection down pressure gradients that result from applied differential stress acting on an anisotropic multilayer protolith compaction by gravity driven two phase flow results in asymmetric separation yields calculated segregation times that are slow or geologically unreasonable and yields relative volumes that are not consistent with the abundance of leucosome seen in natural migmatites although calculated segregation times for very wet granite might allow segregation by compaction some driving force in addition to gravity is needed to cause widespread melt segregation in the crust for segregation at low volume fraction of melt we develop a two dimensional two phase matrix and fluid viscous flow cell model length much greater than thickness with phase changes which predicts either expansion or contraction convection depending on whether volume change vr is positive or negative convection leads to melt segregation to form a stromatic structure in a geologically reasonable timescale at moderate volume fraction of melt segregation may occur by filter pressing in compositionally layered rocks in response to applied differential stress melt migration is by porous medium flow driven by differences in mean normal stress between the layers as a consequence of differences in rheology and shear enhanced matrix collapse calculated segregation rates are fast and the model yields adequate volume of leucosome the positive vr for volatile phase absent melting reactions under crustal pressures promotes melt escape unless extensional deformation facilitates melt accumulation if the rate of melt production exceeds the rate of melt escape then the increase in melt pressure may lead to melt enhanced embrittlement and fracture and melt may migrate out of the system in contrast water rich volatile phase present melt producing reactions have a negative vr which promotes melt retention after segregation unless deformation generates melt escape pathways evolution of stromatic structure through anatectic erosion of mesosome by increasing the melt fraction in situ may lead to breakdown of the solid matrix and will lead to instability due to buoyancy and magma may become mobile and entrain residual material restite

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

metamorphic response and crustal architecture in a classic collisional orogen the damara belt namibia abstract the damara belt is a well exposed mid crustal section through a collisional orogen of cambrian age that closed the khomas ocean basin between passive margins on the congo and kalahari cratons collision resulted in a bi vergent orogen with a distinct paired metamorphic pattern of foreland vergent high p low t orogenic margins and a broad high grade low p high t orogen core spatial and temporal patterns of the metamorphic response to collision have been characterized for all parts of the belt using a large dataset n 240 of internally consistent quantitative pt determinations evolution of mineral parageneses and semi quantitative p t paths metamorphic mapping and quantitative metamorphic field gradients integration with deformation history structural profiles metamorphic chronology magmatic history and stratigraphy constrains a dynamic model of crustal architecture during peak metamorphic events the pattern of zonal metamorphic response is demarcated by three major metamorphic discontinuities md with steep pressure gradients inferring crustal scale structures that accommodated lateral exhumation of crustal wedges discontinuities are confirmed by deformation features in the field and metamorphic mineral growth indicates that vertical flattening at the peak of metamorphism progressing through ductile to brittle extensional structures crustal wedges along the orogenic margins experienced steep clockwise p t paths with peak pt conditions terminated by isothermal decompression during rapid exhumation in isostatic response to deep burial metamorphic chronology and over printing metamorphic fabrics constrain a sequence of foreland propagating out wedging of crustal thrust wedges that resulted in telescoping of the orogenic margins peak metamorphism at a geothermal gradient of 20 25 c km and 8 9 kb in the southern zone wedge i was attained between 517 530 ma followed by south directed out wedging at the uis pass suture accommodated by relative extension md1 at high structural levels near the boundary with the high grade orogen core out wedging of the southern zone further buried the southern margin zone wedge ii in the footwall below the uis pass suture peak metamorphism at 17 c km and 9 5 11 5 kb in the southern margin zone was attained at 517 4 ma and followed by out wedging on basal thrusts accommodated by vertical flattening and extensional reactivation of the uis pass suture md2 peak metamorphism at 17 c km and 10 5 kb in a high p low t crustal wedge in the northern margin wedge iii occurred at 510 4 ma peak metamorphism in this wedge was terminated by isothermal decompression during north directed thrusting accommodated by extension at higher structural levels near the high grade orogen core md3 granulite facies metamorphism in the high grade orogen core which formed the upper plate to the deeper thrust wedges occurred at significantly lower pressures 4 3 6 0 kb higher t depth ratios 38 47 c km and low p t clockwise p t paths indicating only moderate burial and protracted high grade conditions metamorphic chronology confirms high grade conditions 540 505 ma persisted beyond isostatic adjustment of the high p low t orogenic margins high heat flow conditions and long thermal lag are best explained by lithospheric breakoff during collision in contrast to the high p low t margins that experienced lateral exhumation in a convergent system the high grade orogen core was exhumed vertically as a broad core complex during extensional collapse of the orogen peak metamorphic conditions in the central part of the orogen core record higher pressures than marginal lower grade zones to both the north and south indicating vertical exhumation as a broad massif this post peak vertical exhumation of the central core occurred after 505 ma was accommodated by brittle extensional detachments at high stratigraphic levels with km scale omission of crustal section

global teleconnections of meridional overturning circulation anomalies there is a wide range of evidence from both models and palaeoclimatic data that indicates the possibility of abrupt changes in the oceanic meridional overturning circulation moc however much of our dynamical understanding of the moc comes from steady state models that rely upon the assumption of thermodynamic equilibrium and are therefore only valid on millennial time scales here a dynamical model for the global teleconnections of moc anomalies on annual to multidecadal time scales is developed it is based on a linear theory for the propagation of zonally integrated meridional transport anomalies in a reduced gravity ocean and allows for multiple ocean basins connected by a circumpolar channel to the south the theory demonstrates that the equator acts as a low pass filter to moc anomalies as a consequence moc anomalies on decadal and shorter time scales are confined to the hemispheric basin in which they are generated and have little impact on the remainder of the global ocean the linear theory is compared with the results of a global nonlinear numerical integration which it reproduces to a good approximation

the metamorphic architecture of a transpressional orogen the kaoko belt namibia s 64 61 goscombe b hand m 2001b metamorphic model for the inland branch of the damara orogen a paired metamorphic mountain belt pmmb geological society of australia specialist group in tectonics and structural geology conference ulverstone

change in the size of walker lake during the past 5000 years benson l v meyers p a and spencer r j 1991 change in the size of walker lake during the past 5000 years palaeogeogr palaeoclimatol palaeoecol 81 189 214 in 1984 a 12 m sediment core wlc84 8 was taken from the deepest part of walker lake samples of the core were analysed for diatoms pollen carbonate mineralogy magnesium content 6180 and 613c values of the total inorganic fraction 6180 and 613c values of limnocythere ceriotuberosa 613c values of the total organic fraction grain size and magnetic susceptibility the data indicate that walker lake became shallow and probably desiccated between i 5300 4800 and 27002100 yr b p each of the organic and inorganic proxy indicators of lake size discussed in this paper was useful in determining the presence of the shallow lake intervals however none of the indicators was useful in determining the cause of the shallowlake intervals instead the types of fish living in walker lake prior to 1940 were used to demonstrate that shallow lake intervals resulted from diversion of the walker river and not from climatic aridity major changes in mineralogy and magnesium content of carbonates and major changes in diatom populations with time were found to be a function of the chemical evolution of walker lake combined with changing lake size the stable isotopes of oxygen and carbon were found to be good indicators of lake volume changes a lake level record for walker lake constructed from stable isotope data was found to be similar to a lake level record constructed using tufa and tree stump data both records indicate relatively high lake levels between 4800 2700 yr b p at 1250 yr b p and within the last 300 yr substantial declines in lake level occurred 2000 and 1000 yr b p

an adjoint analysis of the meridional overturning circulation in an ocean model abstract using the adjoint of a fully three dimensional primitive equation ocean model in an idealized geometry spatial variations in the sensitivity to surface boundary forcing of the meridional overturning circulation s strength are studied steady state sensitivities to diapycnal mixing wind stress freshwater and heat forcing are examined three different commonly used boundary forcing scenarios are studied both with and without wind forcing almost identical circulation is achieved in each scenario but the sensitivity patterns show major quantitative and qualitative differences sensitivities to surface forcing and diapycnal mixing are substantially larger under mixed boundary conditions in which fluxes of freshwater and heat are supplemented by a temperature relaxation term or under flux boundary conditions in which climatological fluxes alone drive the circulation than under restoring boundary conditions the sensitivity pattern to diapycnal mixing which peaks in the tropics is similar

a40ar 39ar study of post tectonic cooling in the britt domain of the grenville province ontario abstract we report the results of a 40 ar 39 ar study of rocks from the britt domain northwestern grenville province most of the age spectra obtained for micas and amphiboles have well defined age plateaus typically k feldspars yielded spectra with age gradients and arrhenius plots with kinks or offsets hence some of the data were interpreted in terms of a multi diffusion domain size model this 40 ar 39 ar data base 5 amphiboles 9 micas 4 k feldspar along with some recently acquired uzpb data provide reasonable constraints on the post peak metamorphic cooling history which began at depth in the upper amphibolite facies comparison of the data with exhumation paths generated by thermal models suggest that cooling taking place over 400 ma was for the most part due to erosionally controlled exhumation although the decompression may have initiated with a short period of rapid extensional uplift the entire cooling history may have been erosionally controlled there is an apparent difference in cooling ages between north and south in the 40 ar 39 ar mica and k feldspar data for the britt domain which may be due to somewhat higher exhumation rates in the north and or an elevated geotherm in the south

temporal variability of the south atlantic meridional overturning circulation between 20 s and 35 s altimetry derived synthetic temperature and salinity profiles between 20 s and 34 5 s are used to estimate the meridional overturning circulation moc and meridional heat transport mht which are assessed against estimates obtained from expendable bathythermograph xbt measurements consistent with studies from xbts and argo data both the geostrophic and ekman contributions to the moc exhibit annual cycles and play an equal role in the moc seasonal variations the strongest variations on seasonal and interannual time scales in our study region are found at 34 5 s the dominance of the geostrophic and ekman components on the interannual variations in the moc and mht varies with time and latitude with the geostrophic component being dominant during 1993 2006 and the ekman component dominant between 2006 and 2011 at 34 5 s

decadal modulations of interhemispheric global atmospheric circulations and monsoons by the south atlantic meridional overturning circulation this study presents a physical mechanism on how low frequency variability of the south atlantic meridional heat transport samht may influence decadal variability of atmospheric circulation a multicentury simulationofacoupledgeneralcirculationmodelisusedasbasisfor theanalysis thehighlightofthefindings herein is that multidecadal variability of samht plays a key role in modulating global atmospheric circulation via its influence on interhemispheric redistributions of momentum heat and moisture weaker samht at 308s produces anomalous ocean heat divergence over the south atlantic resulting in negative ocean heat content anomalies about 15 20 years later this forces a thermally direct anomalous interhemispheric hadley circulation transporting anomalous atmospheric heat from the northern hemisphere nh to the southern hemisphere sh and moisture from the sh to the nh thereby modulating global monsoons further analysis shows that anomalous atmospheric eddies transport heat northward in both hemispheres producing eddy heat flux convergence divergence in the nh sh around 158 308 reinforcing the anomalous hadley circulation the effectofeddies onthe nh sh polewardof308 depicts heat flux divergence convergence whichmust be balanced by sinking rising motion consistent with a poleward equatorward displacement of the jet stream this study illustrates that decadal variations of samht could modulate the strength of global monsoons with 15 20 years of lead time suggesting that samht is a potential predictor of global monsoon variability a similar mechanistic link exists between the north atlantic meridional heat transport namht at 308 na nd global monsoons

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

variation in metamorphic style along the northern margin of the damara orogen namibia the northern margin of the inland branch of the pan african damara orogen in namibia shows dramatic along strike variation in metamorphic character during convergence between the congo and kalahari cratons m3 metamorphic cycle low p contact metamorphism with anticlockwise p t paths dominates in the western domains ugab zone and western northern zone and high p barrovian metamorphism with a clockwise p t path is documented from the easternmost domain eastern northern zone the sequence of m3 mineral growth in contact aureoles shows early growth of cordierite porphyroblasts that were pseudomorphed to biotite chlorite muscovite at the same time as an andalusite biotite muscovite transposed foliation was developed in the matrix the peak t metamorphic assemblages and fabrics were overprinted by crenulations and retrograde chlorite muscovite the kfmash p t pseudosection for metapelites in the ugab zone and western northern zone contact aureoles indicates tight anticlockwise p t loops through peak metamorphic conditions of 540 570 c and 2 5 3 2 kbar these semi quantitative p t loops are consistent with average p t calculations using thermocalc which give a pooled mean of 556 26 c and 3 2 0 6 kbar indicating a high average thermal gradient of 50 c km in contrast the eastern northern zone experienced deep burial high p moderate t barrovian m3 metamorphism with an average thermal gradient of 21 c km and peak metamorphic conditions of c 635 c and 8 7 kbar the calculated p t pseudosection and garnet compositional isopleths in kfmash appropriate for the metapelite sample from this region document a clockwisep t path early plagioclase kyanite biotite parageneses evolved by plagioclase consumption and the growth of garnet to increasing xfe xmg and xca and decreasing xmn compositions indicating steep burial with heating the developed kyanite garnet biotite peak metamorphic parageneses were followed by the resorption of garnet and formation of plagioclase moats indicating decompression which was followed by retrogressive cooling and chlorite muscovite growth the clockwise p t loop is consistent with the foreland vergent fold thrust belt geometry in this part of the northern margin earlier formed 580 570ma pervasive matrix foliations m2 were overprinted by contact metamorphic parageneses m3 in the aureoles of 530 3ma granites in the ugab zone and 553 514ma granites in the western northern zone available geochronological data suggest that convergence between the congo and kalahari cratons was essentially coeval in all parts of the northern margin with similar ages of 535 530ma for the main phase of deformation in the eastern northern zone and northern platform and 538 505ma highgrade metamorphism of the central zone immediately to the south consequently nne ssw directed convergent deformation and associated m3 metamorphism of contrasting styles are interpreted to be broadly contemporaneous along the length of the northern margin of the inland branch in the west heat transfer was dominated by conduction and externally driven by granites whereas in the east heat transfer was dominated by advection and internally driven radiogenic heat production the ultimate cause was along orogen variation in crustal architecture including thickness of the passive margin lithosphere and thickness of the overlying sedimentary succession

buckle folding and deep crustal shearing of high grade gneisses at the junction of two major high strain zones central gneiss belt grenville province ontario low plunging transport parallel f3 folds are common at all scales in the central gneiss belt of the grenville province but few of these folds are sheath folds where the d1 d2 parry sound shear zone intersects the d3 shawanaga shear zone ssz at a high angle f3 folds formed at several scales centimetre to greater than outcrop scale in layered d1 d2 straight gneisses at the start of their evolution the f3 folds formed just beyond the ssz with hinges near orthogonal to the d3 shear direction and with typical buckle features e g wavelengths vary with layer thickness and hinges are discontinuous and bifurcate the buckle folds evolved within the ssz by rotation of hinges towards the shear direction even though hinges initiated at a high angle to the shear direction sheath folds were not produced in addition to tightening the buckles the ductile reorientation produced thin thick extended shortened limb pairs and very straight ridge like fold hinges and removed small folds from the extended

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

hydrocarbon and fatty acid distributions in rostherne lake sediment england abstract hydrocarbon and carboxylic acid distributions in the top 30 cm section of a contemporary lacustrine sediment rostherne mere cheshire england of age 0 150 yr present variations which can be correlated with changes in input of organic material as well as the effects of early diagenesis thus the higher proportions of short chain and branched lipids in the top 0 7 cm sediment section are as expected on the basis of the relatively greater contribution of algal and other microbial matter to the surface sediment layer similarly the increase in the ratio of saturated to unsaturated straight chain acids with depth is in accord with the more facile diagenesis of the unsaturated components acid hydrolysis of solvent extracted sediment afforded lipid fractions featuring a more significant microbial contribution than pre hydrolysis extracts as denoted by the greater abundance of c15 and c17iso and anteiso branched acids also no trend with depth in the ratio of saturated to unsaturated acids was observed for post hydrolysis extracts indicating that bound compounds may be somewhat protected relative to soluble lipids a contribution from petroleum derived hydrocarbons to the sediment apparent from the complex branched cyclic b c alkane distributions decreases with depth and is virtually absent from the 18 30 cm sediment section

interannual variations in the atlantic meridional overturning circulation and its relationship with the net northward heat transport in the south atlantic 1 variability of the atlantic meridional overturning circulation amoc and its effect on the net northward heat transport nht in the south atlantic are examined using a trans basin expendable bathythermograph xbt high density line at 35s ax18 the time mean amoc is 17 9 2 2 sv during 2002 2007 although the geostrophic transport dominates the time mean amoc both geostrophic and ekman transports are important in explaining the amoc variability the contributions of geostrophic and ekman transports to the amoc show annual cycles but they are out ofphase resultinginweakseasonalvariabilityoftheamoc the nht variability is significantly correlated with the amoc where a 1 sv increase in the amoc would yield a 0 05 0 01 pw increase in the nht partition of transport into the western and eastern boundaries and interior suggests that to quantify changes in the amoc and nht it is critical to monitor all three regions citation dong s s garzoli m baringer c meinen andg goni 2009 interannualvariations intheatlanticmeridionaloverturningcirculationanditsrelationship with the net northward heat transport in the south atlantic geophys res lett 36 l20606 doi 10 1029 2009gl039356

anticlockwise p t path of granulites from the monte castelo gabbro ordenes complex nw spain the study of mafic and aluminous granulites from the monte castelo gabbro ordenes complex nw spain reveals an anticlockwise p t path that we interpret as related to the tectonothermal activity in a magmatic arc probably an island arc the p t path was obtained after a detailed study of the textural relationships and mineral assemblage succession in the aluminous granulites and comparing these with an appropriate petrogenetic grid additional thermobarometry was also performed the granulites are highly heterogeneous with distinct compositional domains that may alternate even at thin section scale garnets are generally idiomorphic to subidiomorphic and in certain domains of the aluminous granulites they show overgrowths forming xenomorphic coronas around a more or less idiomorphic core both types of garnets show significant ca enrichment at the crystal rims which together with the other mineralogical and textural characteristics is compatible with a pressure increase with low t variation p t estimations indicate a peak of t 800 c and p 9 5 kbar attained after a significant increase in pressure that took place at high temperatures in the sillimanite field we suggest that this kind of trajectory probably anticlockwise is compatible only with a terrane heated by an intense magmatic activity after or during tectonic crustal thickening magmatic injection at the base and or into the crust which is characteristic of magmatic arcs

extrusional tectonics in the core of a transpressional orogen the kaoko belt namibia the pan african kaoko belt of nw namibia provides a wellexposed example of material flow in the evolving middle and lower crust during sinistral transpressional orogenesis the kaoko belt is a composite metamorphic belt with shear zone bounded zones of contrasting metamorphic style that were metamorphosed at approximately the same time 575 550ma it is divided into a barrovian style escape zone with inclined nappes and thrusts that verge outward towards the foreland a steep high grade orogen core that experienced intense wrench style deformation and in the hinterland an older 650ma exotic coastal terrane that was reworked at moderate t low p conditions during transpressional orogenesis the kinematic lineation array defined by stretching lineations and shear sense indicators shows variation in degree and polarity of lineation obliquity to the grain of the belt lineation plunge and different polarity of vergence along the plunge with respect to the overall sinistral shear sense the gross regional lineation pattern defines an arcuate array from near orogen parallel in the orogen core to higher angle obliquity across the escape zone reflecting lateral escape towards the orogen margin two highgrade lobes within the orogen core are coincident with obliqueinclined upward flow trajectories based on the kinematic lineation array and represent oblique extrusion of lower crustal material into middle crustal levels an intervening low grade metamorphic trough within the orogen core and the coastal terrane coincides with acute oblique downward and outboard directed apparent flow trajectories these kinematic patterns are consistent with barometric constraints for peak metamorphism of 5 2kbar and 4 5kbar in the low grade trough and coastal terrane and 8 0kbar in the two high grade lobes integration of the kinematic and metamorphic datasets shows that oblique shallowly inclined extrusion trajectories occurred within the orogen core of this classic transpressional orogen and that stretching lineations approximately reflect the particle paths experienced across orogen metamorphic gradients indicate a marked contrast between the escape zone and orogen core the escape zone experienced an inverted barrovian style high p moderate t metamorphism and low thermal gradients of 20 c km the orogen core experienced moderate p high t metamorphism and high thermal gradients of 30 40 c km clockwise p t paths were experienced in all parts of the kaoko belt tight and shallow conduction dominated p t paths were experienced in all orogen core domains involving heating dominated prograde paths followed by decompression consistent with extrusional tectonics steeper and more open advection dominated p t paths were experienced in the crustal over thrust escape zone which experienced low thermal gradients