mapping the distribution of melt during anatexis at the source area of crustal granites by synchrotron μ xrf proyecto fapa universidad de los andes bogota colombia centro nacional de pesquisa em energia e materiais brazilian synchrotron light laboratory lnls proposal n xafs1 17105 cariparo cassa di risparmio di padova e rovigo project makearth european union s horizon 2020 research and innovation programme under the marie sklodowska curie grant agreement no 654606

stationary wave reflection as a mechanism for zonalizing the atlantic winter jet at the lgm abstractcurrent estimates of the height of the laurentide ice sheet lis at the last glacial maximum lgm range from around 3000 to 4500 m modeling studies of the lgm using low end estimates of the lis height show a relatively weak and northeastward tilted winter jet in the north atlantic similar to the modern jet while simulations with high end lis elevations show a much more intense and zonally oriented jet here an explanation for this response of the atlantic circulation is sought using a sequence of lgm simulations spanning a broad range of lis elevations it is found that increasing lis height favors planetary wave breaking and nonlinear reflection in the subtropical north atlantic for high lis elevations planetary wave reflection becomes sufficiently prevalent that a poleward directed flux of wave activity appears in the climatology over the midlatitude north atlantic this entails a zonalization of the stationary wave phase lines and thus of the midlatitude jet

magnetic susceptibility anisotropy a new petrofabric tool in migmatites 1 the rheological behavior of the lower to middle continental crust during orogenic deformation is poorly understood migmatite common at this crustal level remains difficult to analyze from a structural viewpoint because of pervasive recrystallization we present new anisotropy of magnetic susceptibility ams data from 217 specimens of migmatites of the superior province in minnesota with the aim of investigating its potential as a petrofabric tool quarry exposures provide the ideal sampling playground for such a study the migmatites are coarse grained are granitic to tonalitic in composition and display a centimeter scale compositional layering the layering and the regional foliation are subhorizontal to shallowly dipping to the ne mineral lineations are difficult to observe due to recrystallization but trend around 70 n with gentle plunges magnetic properties are carried mainly by multidomain md primary magnetite grains ranging in size from 20 to 200 m the magnetic susceptibilities are generally high around 5 10 10 3 si the degree of magnetic anisotropy is large between 1 2 and 1 3 the principal axes of the ams ellipsoids coincide with those of the finite strain and the degree of anisotropy broadly correlates with the mineral fabric intensity this study is the first detailed investigation of magnetic fabrics in migmatites these preliminary results suggest that the ams technique is an easy and powerful tool for the petrofabric analysis of migmatites

the subtropical subpolar gyre exchange in the presence of annually migrating wind and a meandering jet water mass exchange abstract a simple barotropic double gyre jet ocean circulation model is developed driven by surface wind the model consists of a subtropical gyre in the south and a subpolar gyre in the north and a meandering jet between them using this ocean model the water mass exchange between two gyres is investigated by calculating the lagrangian trajectories of the water column the results show that the meandering jet will cause strong intergyre exchange and the exchange will be substantially enchanced when the wind is allowed to migrate north and south for example in the standard case adapted after the gulf stream it is found that about 10 subtropical water mass has been transferred into the subpolar gyre in 25 years when the wind is steady whereas it is increased to about 18 in the same period of time when the wind is migrating annually with a distance 800 km when the wind is steady the subtropical water mass enters the subpolar gyre mainly through the western boundary it flows eastward and then pen

material transport in oceanic gyres part i phenomenology abstract material spreading and mixing by oceanic mesoscale eddies are analyzed in an idealized numerical model of the wind driven midlatitude oceanic circulation the main focus is on the regime with large reynolds number re and vigorous mesoscale eddies although brief comparisons are made with less turbulent solutions at smaller re the analyses are based on ensembles of lagrangian particle trajectories the authors find that tracer transport by mesoscale eddies differs in many ways from the commonly used model of homogeneous isotropic eddy diffusion the single particle dispersion which describes the spreading process is generally anisotropic and inhomogeneous and in most places it is not diffusive i e not linear in time during intermediate time intervals after tracer release in most of the basin and especially in the deep layers subdiffusive single particle dispersion occurs due to long time trapping of material by coherent structures such as vortices near the strong currents and planeta

interannual to interdecadal variability of sea surface salinity in the atlantic and its link to the atmosphere in a coupled model 1 the interannual to interdecadal variability of sea surface salinity sss in the atlantic is investigated using 200 years of a control simulation of the bergen climate model after verifying that the model behaves realistically we show that most centers of sss variability are located near the mouths of the main rivers of the basin this variability is due primarily to anomalous runoff except in the st lawrence area and to anomalous ekman and geostrophic currents while fluctuations in the freshwater flux play a somewhat lesser role away from the coast sss variability is strong in the northern tropics due largely to anomalous advection and freshwater exchanges regression analysis and a lagrangian technique show that the sss anomalies are advected by the mean oceanic circulation and can be followed along the gyres for several years the link between sss anomalies and the dominant modes of variability of the atmosphere is also investigated the sss response to the north atlantic oscillation nao is dominated by relatively small scales that are forced by anomalous ekman currents but the relative influence of the large scale freshwater fluxes increases at long timescales the nao induced sss anomalies are also strongly advected and distorted by the mean currents so that their pattern at the interannual timescale only reflects in part that of the atmospheric forcing the link between sss anomalies and the east atlantic pattern is similar

grain scale melt distribution in two contact aureole rocks implications for controls on melt localization and deformation the grain scale spatial arrangement of melt in layer parallel leucosomes in two anatectic rocks from two different contact aureoles located in central maine usa is documented and used to constrain the controls on grain scale melt localization the spatial distribution of grain scale melt is inferred from microstructural criteria for recognition of mineral pseudomorphs after melt and mineral grains of the solid matrix that hosted the melt in both rocks feldspar mimics the grain scale distribution of melt and quartz is the major constituent of the solid matrix the feldspar pockets consist of individual feldspar grains or aggregates of feldspar grains that show cuspate outlines they have low average width length ratios 0 54 and 0 55 respectively and are interstitial between more rounded and equant width length ratios 0 65 for both samples quartz grains in two dimensions the feldspar pockets extend over distances equivalent to multiple quartz grain diameters possibly forming a connected three dimensional intergranular network both samples show similar mesoscopic structural elements and in both samples the feldspar pockets have a shape preferred orientation in one sample feldspar inferred to replace melt is aligned subparallel to the shape preferred orientation of quartz indicating that pre or syn anatectic strain controlled the grain scale distribution of melt in the other sample the preferred orientation of feldspar inferred to replace melt is different from the orientations of all other mesoscopic or microscopic structures in the rock indicating that differential stress controlled grain scale melt localization this is probably facilitated by conditions of higher differential stress which may have promoted microfracturing grain scale melt distribution and inferred melt localization controls give insight into possible grain scale deformation mechanisms in melt bearing rocks application of these results to the interpretation of deep crustal anatectic rocks suggests that grain scale melt distribution should be controlled primarily by pre or syn anatectic deformation feedback relations between melt localization and deformation are to be expected with important implications for deformation and tectonic evolution of melt bearing rocks

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

the marine ostracod genus tasmanocypris from the neogene of southeastern australia systematic and palaeoceanographical relationships palaeoecology and palaeobiogeography abstract a new fossil paracypridine ostracod tasmanocypris lochardi sp nov is described from late miocene shallow marine strata of southeastern australia it has morphological features similar to a number of modern southern australian and southwest african tasmanocypris species here termed the dartnalli group this species group was likely present in early cenozoic temperate shallow seas around antarctica the first appearance of tasmanocypris lochardi in late miocene marine strata of the bass strait hinterland of se australia equates to a late miocene 9 7 ma intensification and northward latitudinal shift of the antarctic circumpolar current acc late miocene occurrences of tasmanocypris lochardi in southeast australia were likely associated with temperate eastward flows of the acc north of the subantarctic front during the early pliocene the warm zeehan current aka leeuwin current replaced the acc as the dominant easterly flowing current across bass strait and this 4 4 ma palaeoceanographical event correlates with the temporary but widespread disappearance of t lochardi from southeast australian marine waters however the presence of refugia populations of t lochardi along the east australian continental shelf between 4 4 and 3 4 ma likely enabled the brief re establishment of t lochardi in the east of bass strait during the late pliocene 3 2 3 0 ma tasmanocypris lochardi became permanently extinct in this region during the latest pliocene to early pleistocene

migmatites granites and orogeny flow modes of partially molten rocks and magmas associated with melt solid segregation in orogenic belts abstract this paper presents a model for the genesis of migmatites and granites during orogenic evolution based on the analysis of several phanerozoic crustal segments and a review of the physical properties of partially molten rocks and magmas this model inventories the modes of bulk flow of partially molten rocks and magmas and the mechanisms of melt solid segregation for each mode partial melting of rocks is associated with a strength decrease of two to three orders of magnitude leading to strain partitioning expressed by channel flow driven either by forces related to plate tectonics vertical channel flow or by the gravity force associated with lateral variations of crustal thicknesses horizontal channel flow although the structural characteristics of migmatites indicate that deformation plays a role in melt migration the emplacement of laccoliths of leucogranites above migmatites attests to the efficiency of the buoyancy force another decrease in apparent strength of about ten orders of magnitude is associated with the loss of continuity of the solid framework marking the transition from partially molten rocks to magmas the breakdown of the solid framework also allows for settling of the solid in suspension increasing the buoyancy of the remaining magma accordingly domes cored by diatexites former heterogeneous magmas and mantled by metatexites former partially molten rocks are interpreted as gravitational instabilities driven by the relative buoyancy of the magma and permitted by the weakness of the partially molten rocks this model provides a first order framework to elucidate the development of a crustal scale horizontal layering during the evolution of orogenic belts that are affected by partial melting in this case the middle crust is dominated by migmatites with domes cored by diatexites and mantled by metatexites that correspond to a partially molten and magmatic zone respectively the granitic dikes and sills and the associated laccoliths of leucogranites correspond to an intrusive zone overlying the partially molten zone the refractory lower crust is potentially in part formed by accumulation of solids segregated from the overlying heterogeneous magmas

a study of the interaction of the north atlantic oscillation with ocean circulation observed patterns of wind stress curl and air sea heat flux associated with the north atlantic oscillation nao are used to discuss the response of ocean gyres and thermohaline circulation to nao forcing and their possible feedback on the nao the observations motivate and are interpreted in the framework of a simple mathematical model that couples ekman layers ocean gyres and thermohaline circulation to the atmospheric jet stream meridional shifts in the zero wind stress curl line are invoked to drive anomalies in ocean gyres and north south dipoles in air sea flux drive anomalous thermohaline circulation both gyres and thermohaline circulation play a role in modulating sea surface temperature anomalies and hence through air sea interaction the overlying jet stream the model which can be expressed in the form of a delayed oscillator with ocean gyres and or thermohaline circulation providing the delay identifies key nondimensional parameters that control whether the ocean responds passively to nao forcing or actively couples it suggests that both thermohaline circulation and ocean gyres can play a role in coupled interactions on decadal timescales

the thermodynamics of deformed metamorphic rocks a review abstract the deformation of rocks is a disequilibrium and strongly non linear phenomenon with a number of interacting chemical thermal and microstructural processes operating simultaneously we review progress in this area over the past 30 years deforming chemically reacting systems are dissipative systems and hence are characterised by highly ordered structures that develop through cooperative processes once parameters such as critical strains strain rates fluid infiltration rates damage densities or temperatures are attained such criticality is the hallmark of deformed rocks at all length scales and is the basis for a diverse range of structures such as foliations and lineations produced by metamorphic differentiation rotation recrystallisation folding boudinage and micro to regional scale fracture systems criticality is identified with classical criticality and not self organised criticality the first and second laws of thermodynamics are used to show that such structural diversity arises from reaction diffusion deformation equations criticality of the system is associated with the stored energy becoming non convex and structures arise in order to minimise this non convex energy these structures are scale invariant and hence are characterised by fractal and minimal surface geometries thermodynamics is a powerful discipline to integrate seemingly unrelated processes in structural geology and produce an integrated approach to the subject that crosses all length scales

mechanisms and orientation of melt segregation paths during pure shearing of a partially molten rock analog norcamphor benzamide abstract in situ deformation experiments were performed on partially molten analog materials norcamphor in the presence of a benzamide norcamphor melt undergoing pure shearing at a constant melt fraction of 0 13 melt in the samples induces a strain dependent transition from purely dislocation creep to dislocation creep associated with minor intergranular fracturing and grain boundary sliding gbs intergranular fractures drain the melt from initially isotropic melt pockets to grain boundaries along such boundaries grain boundary migration recrystallization is inhibited while gbs occurs intergranular melt pockets occur along grain boundaries oriented subparallel to the shortening direction but melt must have migrated parallel to the elongation direction of the samples as indicated by melt accumulations at both extruding ends of the sample intergranular melt pockets parallel to the elongation direction were only rarely observed because melt was rapidly expelled from these sites nevertheless these grain boundaries are the pathways of melt segregation in the samples

decoupled ca and fe mg content of s type granites an investigation on the factors that control the ca budget of s type granites abstract the compositional variation of s type granites is thought to derive from source controlled processes whereby magmas acquire their composition as a result of entrainment of variable proportions of a peritectic rich residual mineral assemblage into the melt a corollary of this model is that the entrained phases keep the stoichiometric proportions they have in the partially melted source these proportions are controlled by the composition of the subsolidus minerals consequently it is expected that the ratio between maficity feot mgo and other compatible major elements in granites would be the same as those of the source this is true for ti but not for ca which shows systematically higher ca maficity ratios in order to explore the factors that cause this discrepancy thermodynamic calculations were used to study the partial melting of a representative metapelite and a metagreywacke under a range of crustal pressure and temperature conditions the modelling included segregation of melt or magma in pulses disequilibrium melting of plagioclase in which only a fraction of this phase participates in the melting system and produces two populations of plagioclase the unreacted cores with the original na rich composition and a second one with a ca rich composition and the entrainment of up to 40 wt minerals into the melt this entrained assemblage consists of two fractions one containing the minerals that are most likely to be surrounded by melt in the source and representing 80 wt of the total assemblage and another one consisting of the phases that are most likely to make up the solid framework with the minerals within each fraction keeping stoichiometric proportions the modelled magmas failed to reproduce the observed high ca maficity ratios this indicates that there are other processes that increase the ca content of granites several processes were evaluated including the presence of apatite enhanced availability of subsolidus plagioclase in the melting system disequilibrium ca rich melts and enhanced entrainment of ca rich plagioclase the last three processes were found to increase the ca content but only enhanced entrainment of ca rich plagioclase increases the ca maficity ratio to values similar to those of the granites a possible explanation for the preferential entrainment of ca rich plagioclase is that the density of this phase is different to that of garnet and ilmenite and similar to the density of the melt consequently a significant fraction of the plagioclase in granites may actually be of residual origin other relevant findings of this study are that metagreywackes seem to be the main source of s type granites as previous investigations suggested and that cordierite rich granitoids represent mineral rich magmas that are formed only from metapelites at pressures below 0 75 gpa this investigation emphasizes the importance of source controlled processes in the composition of s type granites and indicates that entrainment of a mineral assemblage into the melt is not a simple and straightforward process as previously thought

does net e p set a preference for north atlantic sinking abstractthe present day global meridional overturning circulation moc with formation of north atlantic deep water nadw and the absence of a deep water formation in the north pacific is often considered to be caused by the fact that the north pacific basin is a net precipitative while the north atlantic is a net evaporative basin in this paper the authors study the effect of asymmetries in continent geometry and freshwater fluxes on the moc both in an idealized two dimensional model and in a global ocean model this study approaches the problem from a multiple equilibria perspective where asymmetries in external factors constrain the existence of steady moc patterns both this multiple equilibria perspective and the fact that a realistic global geometry is used add new aspects to the problem in the global model it is shown that the atlantic forced by net precipitation can have a meridional overturning circulation with northern sinking and a sea surface salinity that resembles the present day sali

melt segregation in the continental crust distribution and movement of melt in anatectic rocks the grain and outcrop scale distribution of melt has been mapped in anatectic rocks from regional and contact metamorphic environments and used to infer melt movement paths at the grain scale anatectic melt is pervasively distributed in the grain boundaries and in small pools consequently most melt is located parallel to the principal fabric in the rock typically a foliation short branched arrays of linked melt bearing grain boundaries connect melt depleted parts of the matrix to diffuse zones of melt accumulation protoleucosomes where magmatic flow and alignment of euhedral crystals grown from the melt developed the distribution of melt leucosome and residual rocks normally melanocratic in outcrop provides different but complementary information the residual rocks show where the melt came from and the leucosomes preserve some of the channels through which the melt moved or sites where it pooled different stages of the melt segregation process are recorded in the leucosome melanosome arrays regions where melting and segregation had just begun when crystallization occurred are characterized by short arrays of thin branching leucosomes with little melanosome a more advanced stage of melting and segregation is marked by the development of residual rocks around extensive branched leucosome arrays generally oriented along the foliation or melting layer places where melting had stopped or slowed down before crystallization began are marked by a high ratio of melanosome to leucosome because most of the melt has drained away very few leucosomes remain to mark the melt escape path this is common in melt depleted granulite terranes many migmatites contain abundant leucosomes oriented parallel to the foliation mostly these represent places where foliation planes dilated and melt drained from the matrix via the branched grain boundary and larger branched melt channel leucosome arrays collected melt collected in the foliation planes was partially or fully expelled later when discordant leucosomes formed leucosomes or veins oriented at high angles to the foliation layering formed last and commonly lack melanocratic borders hence they were not involved in draining the matrix of the melting layer discordant leucosomes represent the channels through which melt flowed out of the melting layer

large scale melt depletion in granulite terranes an example from the archean ashuanipi subprovince of quebec this study uses field petrographic and geochemical methods to estimate how much granitic melt was formed and extracted from a granulite facies terrane and to determine what the grain and outcrop scale melt flow paths were during the melt segregation process the ashuanipi subprovince located in the north eastern superior province of quebec is a large 90 000 km2 metasedimentary terrane in which 85 of the metasediments are of metagreywacke composition that was metamorphosed at mid crustal conditions 820 900 c and 6 7 kbar in a late archean dextral transpressive orogen decrease in modal biotite and quartz as orthopyroxene and plagioclase contents increase together with preserved former melt textures indicate that anatexis was by the biotite dehydration reaction biotite quartz plagioclase melt orthopyroxene oxides using melt orthopyroxene ratios for this reaction derived from experimental studies the modal orthopyroxene contents indicate that the metagreywacke rocks underwent an average of 31 vol partial melting the metagreywackes are enriched in mgo cao and feot and depleted in sio2 k2o rb cs and u have lower rb sr higher rb cs and th u ratios and positive eu anomalies compared to their likely protolith these compositions are modelled by the extraction of between 20 and 40 wt granitic melt from typical archean low grade metagreywackes a simple mass balance indicates that about 640 000 km3 of granitic melt was extracted from the depleted granulites the distribution of relict melt at thin section and outcrop scales indicates that in layers without leucosomes melt extraction occurred by a pervasive grain boundary porous flow from the site of melting across the layers and into bedding planes between adjacent layers in other rocks pervasive grain boundary flow of melt occurred along the layers for a few to tens of centimetres followed by channelled flow of melt in a network of short interconnected and structurally controlled conduits visible as the net like array of leucosomes in some outcrops the leucosomes contain very little residual material 5 biotite orthopyroxene indicating that the melt fraction was well separated from the residuum left in situ as melt depleted granulite only 1 3 vol percentage melt remained in the melt depleted granulites hence the extraction of melt generated by biotite dehydration melting in these granulites was virtually complete under conditions of natural melting and strain rates in a contractional orogen

an experimental study of grain scale melt segregation mechanisms in two common crustal rock types creation of pathways for melt to migrate from its source is the necessary first step for transport of magma to the upper crust to test the role of different dehydration melting reactions in the development of permeability during partial melting and deformation in the crust we experimentally deformed two common crustal rock types a muscovite biotite metapelite and a biotite gneiss were deformed at conditions below at and above their fluid absent solidus for the metapelite temperatures ranged between 650 and 800 c at pc 700 mpa to investigate the muscovite dehydration melting reaction for the biotite gneiss temperatures ranged between 850 and 950 c at pc 1000 mpa to explore biotite dehydration melting under lower crustal conditions deformation for both sets of experiments was performed at the same strain rate e 1 37 10 5 s 1 in the presence of deformation the positive v and associated high dilational strain of the muscovite dehydration melting reaction produces an increase in melt pore pressure with partial melting of the metapelite in contrast the biotite dehydration melting reaction is not associated with a large dilational strain and during deformation and partial melting of the biotite gneiss melt pore pressure builds more gradually due to the different rates in pore pressure increase melt enhanced deformation microstructures reflect the different dehydration melting reactions themselves permeability development in the two rocks differs because grain boundaries control melt distribution to a greater extent in the gneiss muscovite dehydration melting may develop melt pathways at low melt fractions due to a larger volume of melt in comparison with biotite dehydration melting generated at the solidus this may be a viable physical mechanism in which rapid melt segregation from a metapelitic source rock can occur alternatively the results from the gneiss experiments suggest continual draining of biotite derived magma from the lower crust with melt migration paths controlled by structural anisotropies in the protolith

topology of syntectonic melt flow networks in the deep crust inferences from three dimensional images of leucosome geometry in migmatites we have determined the three dimensional form of leucosome in two migmatites produced by syntectonic anatexis of different protoliths 1 stromatic migmatite derived from pelite which comprises sheets of leucosome quartzofeldspathic layers with grt with walls of melanosome bt rich selvages in mesosome schistose layers of bt pl qtz or grt or crd and 2 a migmatitic garnet amphibolite derived from basalt which is composed of spindle shaped leucosomes qtz pl spatially associated with peritectic grt in melanosome hbl qtz or cpx three dimensional images were generated from two dimensional representations of spatial data obtained by two methods 1 serial grinding and 2 high resolution x ray computed tomography hr x ray ct projections of three dimensional images of stromatic migmatite derived using data from either method show the planar nature of leucosome throughout the sample melt transport through this rock when it was partially molten could be modeled as flow in parallel conduits in the image derived from hr x ray ct data garnet in leucosome is only rarely in contact with melanosome which suggests these garnet grains were suspended in melt during flow projections of three dimensional images of the migmatitic garnet amphibolite do not reveal the full extent of leucosome connectivity due to the irregular geometry of leucosome connectivity in this sample can be shown however by virtual slicing of the three dimensional images perpendicular to the plane of the two dimensional representations approximately parallel to the lineation defined by the leucosome and by using three dimensional projections of a single leucosome connectivity tree constructed by projecting leucosome patches from slice to slice and noting the overlap based on leucosome geometry and volume we estimate effective porosity for flow in this rock to have been 20 vol at stagnation leucosome in the migmatitic garnet amphibolite occurs in strain shadows around garnet which are inferred to have been obstacles to flow along linear paths blocking of inferred flow channels by garnet contributes to the high degree of path length tortuosity in this sample tau 2 6 which is expressed visually by the complex form of the leucosome in three dimensions cross sectional areas for individual inferred melt flow paths are highly variable over 2 3 orders of magnitude and minimum channel radius is changeable by approximately 1 order of magnitude meaning there was large variability along the channels and implying strong local flow divergences based on these data unusually straight and uniform channels would have dominated the mesoscopic melt flux through this rock when it was partially molten

a simple model of the decadal response of the ocean to stochastic wind forcing abstract a simple linear model is used to estimate the decadal response of the extratropical ocean to wind stress forcing assuming a flat bottom a mean state at rest and no dissipation the barotropic fields are governed by a time dependent sverdrup balance the baroclinic ones by the long rossby wave equation the ocean is bounded by a coast in the east and a radiation condition is used in the west at each frequency the baroclinic response consists of a forced response plus a rossby wave generated at the eastern boundary for zonally independent forcing the response propagates westward at twice the rossby phase speed the wind stress is assumed to be stochastic with a white frequency spectrum so the model represents the continuous excitation of the ocean interior by the weather fluctuations the model predicts the shape and level of the frequency spectra of the oceanic pressure field and their variation with longitude and latitude the baroclinic response is spread over a continuum of frequencies

three dimensional imaging of earth and planetary materials x ray computed tomography neutron computed tomography and magnetic resonance imaging are driving novel scientific advances by enabling rapid non destructive three dimensional examination and analysis of earth and planetary materials discoveries catalyzed by these approaches range across fields from environmental geology to petroleum geology hydrology to soil science paleontology to petrology and geodynamics to meteoritics they have impacted our understanding of hydrocarbon reservoirs contaminant transport climate change co2 sequestration the evolution of life crustal uplift mantle metasomatism planetary differentiation and more three dimensional imaging is likely soon to become an essential component of every investigator s toolkit especially as instruments and facilities emerge that are optimized for increasingly sophisticated geological applications of these techniques and as access to them expands

on the interannual variability of surface salinity in the atlantic the mechanisms controlling the interannual variability of sea surface salinity sss in the atlantic are investigated using a simulation with the echam4 opa8 coupled model and for comparison the ncep reanalysis and an observed sss climatology anomalous ekman advection is found to be as important as the freshwater flux in generating sss anomalies in contrast to sea surface temperature sst anomalies which are primarily caused by surface heat flux fluctuations since the surface heat flux feedback does not damp the sss anomalies but generally damps existing sst anomalies sss anomalies have a larger characteristic time scale as a result they are more influenced by the mean currents and the geostrophic variability which dominate the sss changes at low frequency over much of the basin the link between sss anomalies and the dominant patterns of atmospheric variability in the north atlantic sector is also discussed it is shown that the north atlantic oscillation generates sss anomalies much more by ekman advection than by freshwater exchanges at least in the coupled model there is little one to one correspondence between the main atmospheric and sss anomaly patterns unlike what is found for sst anomalies

the wind driven circulation quasi geostrophic simulations and theory for nonsymmetric winds abstract simulations of the wind driven ocean circulation carded out with an eddy resolving quasi geostrophic numerical model and symmetric idealized wind forcing have a large scale structure that is predicted wen by the steady nonlinear theory of rhines and young the sharp jet and inertial recirculation am often confined weft inside the region of closed hyperbolic characteristics defined by that theory and hence do not affect the sverdrup dynamics part of the gyre the characteristics make possible simple predictions about the development of the circulation including time dependence and eddy stirring by tilting the line of vanishing ekman pumping away from the east west orientation as it is tilted in the north atlantic and less so the north pacific we explore a family of circulations as the tilt of the wind held is increased characteristics originating at the eastern boundary begin to thread through the energetic region occupied by the free jet then extensive new branches of eddy driven f

a closer look at particle exchange in the gulf stream abstract the trajectories of 95 isopycnal floats deployed in the gulf stream in the last decade have shown that a substantial amount of particle exchange takes place between the gulf stream and the surrounding fluid at the level of the main thermocline this exchange is suggestive of significant cross stream eddy mixing but in order to accurately interpret the float exchange in terms of property exchange the location of float deployment was assessed relative to the strong potential vorticity front associated with the gulf stream the basic result of this analysis is that most of the observed float exchange is not representative of cross frontal exchange at the level where a strong potential vorticity front is present some fluid particles escape from the jet but most of them stay on the same side of the front in the deep main thermocline significant particle exchange is observed between the gulf stream and fluid on both sides of the jet but this exchange is indicative of particles circulating in a r

robustness of multiple equilibria in the global ocean circulation 1 in an idealized atlantic pacific ocean model we study the steady state solutions versus freshwater input in the northern north atlantic we find that four different states the conveyor c the southern sinking ss the northern sinking ns and the inverse conveyor ic appear as two disconnected branches of solutions where the c is connected with the ss and the ns with the ic we argue that the latter has the intriguing consequence that the parameter volume for which multiple steady states exist is greatly increased

structural control on volcanoes and magma paths from local to orogen scale the central andes case abstract assessing the parameters that control the location and geometry of magma paths is of paramount importance for the comprehension of volcanic plumbing systems and geo hazards we analyse the distribution of 1518 monogenic and polygenic volcanoes of miocene quaternary age of the central volcanic zone of the andes chile bolivia argentina and reconstruct the magma paths at 315 edifices by analysing the morphostructural characteristics of craters and cones then we compare these data with outcropping dykes tectonic structures and state of stress most magma paths trend n s nw se and ne sw in decreasing order of frequency the n s and nw se paths coexist in the northern and southern part of the study area whereas n s paths dominate east of the salar de atacama outcropping dykes show the same trends the regional holocene stress state is given by an e w greatest horizontal principal stress n s and nne ssw reverse faults and folds affect deposits of 4 8 3 2 and 1 3 ma bp especially in the central and southern study areas a few nw se left lateral strike slip faults are present in the interior of the volcanic arc part of which belong to the calama olacapato el toro fault the volcanic chain is also affected by several n s and nw se striking normal faults that offset pliocene and quaternary deposits the results indicate different scenarios of magma tectonic interaction given by n s normal and reverse faults and n s fold hinges that guide volcano emplacement and magma paths magma paths are also guided by strike slip and normal nw se faults especially in the northern part of the study area zones with verticalized strata with bedding striking ne sw also acted as preferential magma paths these data suggest that at convergence zones with continental crust shallow magma paths can be more sensitive to the presence and geometry of upper crustal weakness zones than to the regional state of stress

gulf stream variability and ocean atmosphere interactions abstract time series of gulf stream position derived from the topex poseidon altimeter from october 1992 to november 1998 are used to investigate the lead and lag relation between the gulf stream path as it leaves the continental shelf and the changes in sea level pressure surface wind stress and sea surface temperature sst as given by the ncep reanalysis the dominant signal is a northward southward displacement of gulf stream axis 11 to 18 months after the north atlantic oscillation nao reaches positive negative extrema a sst warming cooling peaking north of the gulf stream is also seen to precede the latitudinal shifts but it is a part of the large scale sst anomaly tripole that is generated by the nao fluctuations there is no evidence that the gulf stream shifts have a direct impact onto the large scale atmospheric circulation a fast passive response of the gulf stream to nao forcing is also suggested by a corresponding analysis of the yearly mean gulf stream position estimated from

non linear feedback loops in the rheology of cooling crystallizing felsic magma and heating melting felsic rock at least six major parameters control the rheology of partially molten systems melt content rate of melt production reaction to strain of the solid component reaction to strain of the molten component temperature and chemical composition of the source rocks we examine their interactions to understand the rheology of partially molten rocks and partly crystallised magmas this paper especially focuses on the rheology in the transitional domains between two pairs of thresholds that bracket a transitional regime between a solid state and a fluid behaviour during melting and crystallisation respectively we review related information and point out non linear effects that develop during heating of melting rocks and cooling of crystallising magmas owing to the non linear interactions positive or negative feedback loops accelerate or damp the system melt in migmatite experiences shear softening which along with strain partitioning facilitates melt segregation conversely the augmenting number of rigid crystals during cooling increases the suspension viscosity shear hardening which soon inhibits magma movement those effects reinforce the asymmetry between solid to melt and melt to solid transitions they severely contradict the concept of one rheological critical melt percentage valid for both melting and crystallisation transitions fabric acquisition competes with nucleation and crystal growth thus leading to hysteresis of the stress stain rate curves implications to field observations include horizontal magma segregation magma extraction and successive magma intrusions

origin of migmatites by deformation enhanced melt infiltration of orthogneiss a new model based on quantitative microstructural analysis a detailed field study reveals a gradual transition from high grade solid state banded orthogneiss via stromatic migmatite and schlieren migmatite to irregular foliation parallel bodies of nebulitic migmatite within the eastern part of the gfohl unit moldanubian domain bohemian massif the orthogneiss to nebulitic migmatite sequence is characterized by progressive destruction of well equilibrated banded microstructure by crystallization of new interstitial phases kfs pl and qtz along feldspar boundaries and by resorption of relict feldspar and biotite the grain size of all felsic phases decreases continuously whereas the population density of new phases increases the new phases preferentially nucleate along high energy like like boundaries causing the development of a regular distribution of individual phases this evolutionary trend is accompanied by a decrease in grain shape preferred orientation of all felsic phases to explain these data a new petrogenetic model is proposed for the origin of felsic migmatites by melt infiltration from an external source into banded orthogneiss during deformation in this model infiltrating melt passes pervasively along grain boundaries through the whole rock volume and changes completely its macro and microscopic appearance it is suggested that the individual migmatite types represent different degrees of equilibration between the host rock and migrating melt during exhumation the melt topology mimicked by feldspar in banded orthogneiss forms elongate pockets oriented at a high angle to the compositional banding indicating that the melt distribution was controlled by the deformation of the solid framework the microstructure exhibits features compatible with a combination of dislocation creep and grain boundary sliding deformation mechanisms the migmatite microstructures developed by granular flow accompanied by melt enhanced diffusion and or melt flow however an ams study and quartz microfabrics suggest that the amount of melt present did not exceed a critical threshold during the deformation to allow free movements of grains

three dimensional grain fabric measurements using high resolution x ray computed tomography abstract high resolution x ray computed tomography hrxct provides detailed imagery of the interiors of rocks up to hand sample size non destructively and in three dimensions new tools described here allow these data to be used for analysis of grain fabrics two separate sets of measurement techniques have been developed the first concentrates on quantifying individual crystals phenocrysts porphyroblasts or other discrete objects or void spaces within a sample quantifiable properties include location size shape orientation and contact relationships with adjacent objects the second set of techniques performs a more general fabric analysis on any distinguishable component in a sample a fabric tensor can be computed based on a number of metrics including the star volume distribution svd star length distribution sld and mean intercept length mil methods the fabric tensors provide principal component directions and magnitudes which in turn provide a measure of degree of anisotropy and shape indices because the svd and sld measure only the material of interest whereas the mil is also influenced by spatial distribution results can be divergent for sparse phases also introduced is a three dimensional rose diagram that can be viewed interactively and inspected to reveal further details about non orthogonal directional components these techniques are demonstrated through analysis of a garnet kyanite schist from mica dam british columbia

nonlinear midlatitude ocean adjustment abstract ocean adjustment on annual to interdecadal scales to variable forcing is considered for a more nonlinear general circulation than has previously been studied the nature of the response is a strong function of forcing frequency and importantly involves the inertial recirculations rather than linear baroclinic waves the spatial expression of this variability is concentrated near the separation latitudes of the gulf stream extension a model region corresponding to an area in the real ocean of well known strong ocean atmosphere buoyancy exchange turn on cases periodically forced cases and stochastically forced cases are considered the first set of experiments clarifies the adjustment timescales and dynamics of a nonlinear circulation the second set examines modifications to that adjustment rendered by time dependent forcing the last set is perhaps the most realistic in terms of the atmospheric forcing of the ocean because wind spectra are not strongly peaked beyond a few weeks multidecad

scale invariance and self organized criticality in migmatites of the southern hualapai mountains arizona whether or not melt flow networks are scale invariant may have broad implications for the understanding of the development of magmatic systems leucosome distributions in natural migmatite samples from the hualapai mountains arizona are used to investigate the scaling characteristics of an inferred syndeformational melt flow network one dimensional line and two dimensional box counting analyses yield distributions that are consistent with a scale invariant relationship between the leucosome size and leucosome frequency we infer from these results that the interactions of anatexis and deformation gave rise to a self organized critical system in which melt distribution and melt movement were linked over a range of scales at least millimeter to meter scale we conclude that even in metatexite migmatites volumetrically dominated by solid phases melts can play an active role in determining the architecture of the melt flow network one implication of the envisioned self organized critical system is the potential for rapid large scale melt coalescence and escape without long term maintenance of a fully interconnected melt flow network

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

atmospheric control on the thermohaline circulation abstract in an attempt to elucidate the role of atmospheric and oceanic processes in setting a vigorous ocean overturning circulation in the north atlantic but not in the north pacific a comparison of the observed atmospheric circulation and net surface freshwater fluxes over the north atlantic and pacific basins is conducted it is proposed that the more erratic meridional displacements of the atmospheric jet stream over the north atlantic sector is instrumental in maintaining high surface salinities in its subpolar gyre in addition it is suggested that the spatial pattern of the net freshwater flux at the sea surface favors higher subpolar atlantic salinity because the geographical line separating net precipitation from net evaporation is found well south of the time mean gyre separation in the north pacific whereas the two lines tend to coincide in the north atlantic numerical experiments with an idealized two gyre system confirm that these differences impact the salinity budget of the subpolar g

twentieth century north atlantic jet variability long records of the latitude and speed of the north atlantic eddy driven jet stream since 1871 are presented from the newly available twentieth century reanalysis these jet variations underlie the variability associated with patterns such as the north atlantic oscillation nao and have considerable societal impact through variations in the prevailing westerly winds while the nao combines variations in the latitude and speed of the jet these two characteristics are shown to have quite different seasonal cycles and interannual variability suggesting that they may have different dynamical influences in general the features exhibited in shorter records are shown to be robust for example the strong skewness of the nao distribution related to this is a clear multimodality of the jet latitude distribution which suggests the existence of preferred positions of the jet decadal variations in jet latitude are shown to correspond to changes in the occurrence of these preferred positions however it is the speed rather than the latitude of the jet that exhibits the strongest decadal variability and in most seasons this is clearly distinct from a white noise representation of the seasonal means when viewed in this longer term context the variations of recent decades do not appear unusual and recent values of jet latitude and speed are not unprecedented in the historical record

observations of entry and exit of potential vorticity at the sea surface abstract although potential vorticity pv is central to many theories of the oceanic circulation the entry exit of pv at the sea surface has not been thoroughly discussed from an observational perspective after clarifying the notion of pv entry and exit and the mechanisms responsible for it a climatology of this quantity for the northern hemisphere is presented it is found that surface pv loss over western boundary current regions and their interior extension is a robust feature over the north pacific and atlantic basins at high latitudes mechanical and diabatic effects act in concert in the north atlantic to drive the net pv exit in the pacific however these effects oppose each other and the net entry exit of pv is more uncertain at low latitudes surface winds are found to be particularly important in setting the surface pv exit in the pacific equatorward of the intertropical convergence zone

observations of atmosphere ocean coupling in the north atlantic summary an index of sea surface temperature sst variability at is introduced that measures the difference in sst across the separated gulf stream in late winter by analysing a long observational record of sst and sea level pressure slp it is shown that at exhibits damped oscillations of decadal period and covaries with the strength of a dipolar slp anomaly reminiscent of the north atlantic oscillation nao analysis in the frequency domain shows a broad band peak at 10 20 years in at with a continuous decrease of power on longer time scales similar spectral signatures are found in the northern part of the slp dipole the greenland icelandic low region but not in its southern part the subtropical high region whose power increases on long time scales the observations are interpreted in the framework of a delayed oscillator model in which the ocean circulation introduces the delay and modulates at on decadal time scales the decrease of power seen on long time scales 25 years in the at index is captured by a model including wind driven ocean circulation and arises primarily as a passive response of the latter to the nao forcing variability of the ocean s meridional overturning circulation could also play a role in modulating at on decadal time scales if a small feedback of at on the nao pattern is introduced the simple model can also reproduce the spectral stmctures seen in the slp anomaly in the greenland iceland region

an introduction to the application of x ray microtomography to the three dimensional study of igneous rocks imaging rocks in three dimensions through x ray microtomography enables routine visualization of structures in samples which can be spatially resolved down to the sub micron scale although x ray tomography has been applied in biomedical research and clinical settings for decades it has only recently been applied to studies of rocks and few geoscientists realize its value and potential this contribution provides an introduction to the principles and techniques of x ray microtomography to the study of igneous rock textures as well as reviewing the current state of the art we hope that this short review will encourage more geoscientists to apply x ray microtomography in their research and that this will lead to new insights into the processes that occur in magmatic as well as other geological systems

shear zones and magma ascent a model based on a review of the tertiary magmatism in the alps 1 the alpine oligocene plutons are spatially and temporally associated with the activity of the periadriatic fault system pfs an orogen parallel crustal scale transpressive mylonitic belt excellent three dimensional exposure combined with a wealth of structural seismic petrological geochronological geochemical and paleomagnetic data collected over the last decades help to constrain the relationships between deformation ascent and emplacement of the plutons magmas were channeled from the base of the thickened continental crust into the narrow mylonitic belt of the periadriatic fault system which was used as ascent pathway to cover vertical lengths of 20 to 40 km therefore the linear alignment of the plutons at the surface is not the expression of a linear source region at depth ascent of the melts is controlled by the mylonitic foliation of the pfs which forms the only steep anisotropy continuously traversing the entire alpine crust in contrast the flow direction is not influenced by the specific kinematics of the faults final emplacement of the plutons occurred by extrusion from the periadriatic fault system into the adjacent country rocks the transition from ascent to final emplacement is favored by partitioning of transpressive deformation

processes governing the recovery of a perturbed thermohaline circulation in hadcm3 abstract in an experiment with the latest version of the hadley centre climate model the model response has been analyzed after the thermohaline circulation thc in the atlantic ocean has been suppressed the suppression is induced by a strong initial perturbation to the salinity distribution in the upper layer of the northern north atlantic the model is then allowed to adjust freely salinity gradually increases and deep water formation in the greenland and norwegian seas restarts later also in the labrador sea the meridional overturning recovers after about 120 yr in the first few decades when the overturning is very weak surface air temperature is dominated by cooling of much of the northern hemisphere and weak warming of the southern hemisphere leading to maximum global cooling of 0 9 c the disruption to the atmosphere s radiation balance results in a downward flux anomaly at the top of the atmosphere maximally 0 55 w m 2 in the first decade then decreasing with the thc recovery the processes

from migmatites to plutons power law relationships in the evolution of magmatic bodies magma is generated by partial melting from micrometre scale droplets at the source and may accumulate to form 100 km scale plutons magma accumulation thus spans well over ten orders of magnitude in scale here we provide measurements of migmatitic leucosomes and granitic veins in drill cores from the estonian proterozoic basement and outcrops at masku in sw finland and montemor o novo central portugal despite the differences in size and number of measured leucosomes and magmatic veins differences in host rock types and metamorphic grades the cumulative width distribution of the studied magmatic leucosomes veins follows a power law with exponents usually between 0 7 and 1 8 published maps of the se australian lachlan fold belt were used to investigate the distribution of granitoid pluton sizes the granites occupy ca 22 of the 2 6 105 km2 area the cumulative pluton area distributions show good power law distributions with exponents between 0 6 and 0 8 depending on pluton area group using the self affine nature of pluton shapes it is possible to estimate the total volume of magma that was expelled from the source in the 2 6 105 km2 map area giving an estimated 0 8 km3 of magma per km2 it has been suggested in the literature that magma batches in the source merge to form ever bigger batches in a self organized way this leads to a power law for the cumulative distribution of magma volumes with an exponent m v between 1 for inefficient melt extraction and 2 3 for maximum accumulation efficiency as most of the volume resides in the largest batches that can escape from the source if m v 1 the mass of the magma is dominated by small batches in case m 2 3 about 50 of all magma in the system is placed in a single largest batch our observations support the model that the crust develops a self organized critical state during magma generation in this state magma batches accumulate in a non continuous step wise manner to form ever larger accumulations there is no characteristic length or time scale in the partial melting process or its products smallest melt segregations and km scale plotuns form the end members of a continuous chain of mergers of magma batches

quantifying the three dimensional shapes of spheroidal objects in rocks imaged by tomography abstract the shapes of objects in rocks are sometimes measured through tomographic sections either physical sections or virtual x ray computed tomography approximation of these objects as ellipsoids is often sufficient in these analyses here we present an easily implemented algorithm to best fit an ellipsoid to a set of n points n 9 distributed on the surface of a spheroidal object observed in tomographic sections the method is demonstrated on x ray computed tomography data of 90 chondrules in a cr2 chondrite by averaging the ellipsoids for all the objects measured in a rock one can then readily describe its fabric by an average ellipsoid and if that average ellipsoid is interpreted as a strain ellipsoid and assuming all objects have undergone the same strain each object can be retro deformed and the inferred initial population of objects studied

petrogenesis of migmatites in maine usa possible source of peraluminous leucogranite in plutons high t low p facies series conditions during deformation within a devonian crustal scale shear zone system defined by kilometer scale straight belts of apparent flattening strain that anastomose around lozenges of apparent constrictional strain at upper amphibolite facies grade metapelites are partially melted the onset of which is introduction